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Sample records for silica dissolution rates

  1. Constraining biogenic silica dissolution in marine sediments: a comparison between diagenetic models and experimental dissolution rates

    NARCIS (Netherlands)

    Khalil, K.; Rabouille, C.; Gallinari, M.; Soetaert, K.E.R.; DeMaster, D.J.; Ragueneau, O.

    2007-01-01

    The processes controlling preservation and recycling of particulate biogenic silica in sediments must be understood in order to calculate oceanic silica mass balances. The new contribution of this work is the coupled use of advanced models including reprecipitation and different phases of biogenic

  2. Deep-UV Raman spectroscopic analysis of structure and dissolution rates of silica-rich sodium borosilicate glasses

    Energy Technology Data Exchange (ETDEWEB)

    Windisch, Charles F.; Pierce, Eric M.; Burton, Sarah D.; Bovaird, Chase C.

    2011-03-24

    As part of ongoing studies to evaluate the relationships between structural variations in silicate glasses and rates of glass dissolution in aqueous media, molecular structures present in sodium borosilicate glasses of composition Na2O.xB2O3.(3-x)SiO2, with x 1 (Na2O/B2O3 ratio 1), were analyzed using deep-UV Raman spectroscopy. The results were quantified in terms of the fraction of SiO4 tetrahedra with one non-bridging oxygen (Q3) and then correlated with Na2O and B2O3 content. Increasing Na2O was found to raise the fraction of Q3 units in the glasses systematically, in agreement with studies on related glasses, and, as long as the value of x was not too high, contribute to higher rates of dissolution in single pass flow-through testing. The finding was obtained across more than one series of silica-rich glasses prepared for independent dissolution studies. In contrast, dissolution rates were less strongly determined by the Q3 fraction when the value of x was near unity and appeared to grow larger upon further reduction of the Q3 fraction. The results were interpreted to indicate the increasingly important role of network hydrolysis in the glass dissolution mechanism as the BO4 tetrahedron replaces the Q3 unit as the charge-compensating structure for Na+ ions. Finally, the use of deep-UV Raman spectroscopy was found to be advantageous in studying finely powdered glasses in cases where visible Raman spectroscopy suffered from weak Raman scattering and fluorescence interference.

  3. Deep-UV Raman spectroscopic analysis of structure and dissolution rates of silica-rich sodium borosilicate glasses

    Energy Technology Data Exchange (ETDEWEB)

    Pierce, Eric M [ORNL; WindischJr., Charles F. [Pacific Northwest National Laboratory (PNNL); Burton, Sarah D. [Pacific Northwest National Laboratory (PNNL); Bovaird, Chase C. [Pacific Northwest National Laboratory (PNNL)

    2010-01-01

    As part of ongoing studies to evaluate relationships between structure and rates of dissolution of silicate glasses in aqueous media, sodium borosilicate glasses of composition Na2O xB2O3 (3 x)SiO2, with x 1 (Na2O/B2O3 ratio 1), were analyzed using deep-UV Raman spectroscopy. Results were quantified in terms of the fraction of SiO4 tetrahedra with one non-bridging oxygen (Q3) and then correlated with Na2O and B2O3 content. The Q3 fractionwas found to increase with increasing Na2O content, in agreement with studies on related glasses, and, as long as the value of x was not too high, this contributed to higher rates of dissolution in single pass flow-through testing. In contrast, dissolution rates were less strongly determined by the Q3 fraction when the value of x was near unity, and appeared to grow larger upon further reduction of the Q3 fraction. Results were interpreted to indicate the increasingly important role of network hydrolysis in the glass dissolution mechanism as the BO4 tetrahedron replaces the Q3 unit as the charge-compensating structure for Na+ ions. Finally, the use of deep-UV Raman spectroscopy was found to be advantageous in studying finely powdered glasses in cases where visible Raman spectroscopy suffered from weak Raman scattering and fluorescence interference.

  4. Synthesis of novel core-shell structured dual-mesoporous silica nanospheres and their application for enhancing the dissolution rate of poorly water-soluble drugs

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Chao, E-mail: wuchao27@126.com [Department of Pharmaceutics, Liaoning Medical University, 40 Songpo Road, Linghe District, Jinzhou, Liaoning Province 121001 (China); Sun, Xiaohu [Management Center for Experiments, Bohai University, 19 Keji Road, Songshan District, Jinzhou, Liaoning Province 121000 (China); Zhao, Zongzhe; Zhao, Ying; Hao, Yanna; Liu, Ying [Department of Pharmaceutics, Liaoning Medical University, 40 Songpo Road, Linghe District, Jinzhou, Liaoning Province 121001 (China); Gao, Yu, E-mail: gaoyu_1116@163.com [Department of Medical Oncology, First Affiliated Hospital of Liaoning Medical University, 40 Songpo Road, Linghe District, Jinzhou, Liaoning Province 121001 (China)

    2014-11-01

    Novel core-shell dual-mesoporous silica nanospheres (DMSS) with a tunable pore size were synthesized successfully using a styrene monomer as a channel template for the core and cetyltrimethyl ammonium bromide (CTAB) as a channel template for the shell in order to improve the dissolution rate of poorly water-soluble drugs. Simvastatin was used as a model drug and loaded into DMSS and the mesoporous core without the shell (MSC) by the solvent evaporation method. The drug loading efficiency of DMSS and MSC were determined by thermogravimetric analysis (TGA) and ultraviolet spectroscopy (UV). Characterization, using scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) showed that simvastatin adsorbed in DMSS and MSC was in an amorphous state, and in vitro release test results demonstrated that both DMSS and MSC increased the water solubility and dissolution rate of simvastatin. The shell structure of DMSS was able to regulate the release of simvastatin compared with MSC. It is worth noting that DMSS has significant potential as a carrier for improving the dissolution of poorly water-soluble drugs and reducing the rapid release. - Highlights: • A novel core-shell DMSS is prepared for improving the dissolution rate of simvastatin. • The diffusional resistance of the mesoporous shell can delay and regulate drug release. • Simvastatin absorbed in DMSS exists in amorphous form due to spatial confinement.

  5. Synthesis of novel core-shell structured dual-mesoporous silica nanospheres and their application for enhancing the dissolution rate of poorly water-soluble drugs

    International Nuclear Information System (INIS)

    Wu, Chao; Sun, Xiaohu; Zhao, Zongzhe; Zhao, Ying; Hao, Yanna; Liu, Ying; Gao, Yu

    2014-01-01

    Novel core-shell dual-mesoporous silica nanospheres (DMSS) with a tunable pore size were synthesized successfully using a styrene monomer as a channel template for the core and cetyltrimethyl ammonium bromide (CTAB) as a channel template for the shell in order to improve the dissolution rate of poorly water-soluble drugs. Simvastatin was used as a model drug and loaded into DMSS and the mesoporous core without the shell (MSC) by the solvent evaporation method. The drug loading efficiency of DMSS and MSC were determined by thermogravimetric analysis (TGA) and ultraviolet spectroscopy (UV). Characterization, using scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) showed that simvastatin adsorbed in DMSS and MSC was in an amorphous state, and in vitro release test results demonstrated that both DMSS and MSC increased the water solubility and dissolution rate of simvastatin. The shell structure of DMSS was able to regulate the release of simvastatin compared with MSC. It is worth noting that DMSS has significant potential as a carrier for improving the dissolution of poorly water-soluble drugs and reducing the rapid release. - Highlights: • A novel core-shell DMSS is prepared for improving the dissolution rate of simvastatin. • The diffusional resistance of the mesoporous shell can delay and regulate drug release. • Simvastatin absorbed in DMSS exists in amorphous form due to spatial confinement

  6. Mesoporous silica formulation strategies for drug dissolution enhancement: a review.

    Science.gov (United States)

    McCarthy, Carol A; Ahern, Robert J; Dontireddy, Rakesh; Ryan, Katie B; Crean, Abina M

    2016-01-01

    Silica materials, in particular mesoporous silicas, have demonstrated excellent properties to enhance the oral bioavailability of poorly water-soluble drugs. Current research in this area is focused on investigating the kinetic profile of drug release from these carriers and manufacturing approaches to scale-up production for commercial manufacture. This review provides an overview of different methods utilized to load drugs onto mesoporous silica carriers. The influence of silica properties and silica pore architecture on drug loading and release are discussed. The kinetics of drug release from mesoporous silica systems is examined and the manufacturability and stability of these formulations are reviewed. Finally, the future prospects of mesoporous silica drug delivery systems are considered. Substantial progress has been made in the characterization and development of mesoporous drug delivery systems for drug dissolution enhancement. However, more research is required to fully understand the drug release kinetic profile from mesoporous silica materials. Incomplete drug release from the carrier and the possibility of drug re-adsorption onto the silica surface need to be investigated. Issues to be addressed include the manufacturability and regulation status of formulation approaches employing mesoporous silica to enhance drug dissolution. While more research is needed to support the move of this technology from the bench to a commercial medicinal product, it is a realistic prospect for the near future.

  7. Mesoporous Silica Molecular Sieve based Nanocarriers: Transpiring Drug Dissolution Research.

    Science.gov (United States)

    Pattnaik, Satyanarayan; Pathak, Kamla

    2017-01-01

    Improvement of oral bioavailability through enhancement of dissolution for poorly soluble drugs has been a very promising approach. Recently, mesoporous silica based molecular sieves have demonstrated excellent properties to enhance the dissolution velocity of poorly water-soluble drugs. Current research in this area is focused on investigating the factors influencing the drug release from these carriers, the kinetics of drug release and manufacturing approaches to scale-up production for commercial manufacture. This comprehensive review provides an overview of different methods adopted for synthesis of mesoporous materials, influence of processing factors on properties of these materials and drug loading methods. The drug release kinetics from mesoporous silica systems, the manufacturability and stability of these formulations are reviewed. Finally, the safety and biocompatibility issues related to these silica based materials are discussed. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

  8. Quartz dissolution and silica deposition in hot-dry-rock geothermal systems

    Energy Technology Data Exchange (ETDEWEB)

    Robinson, B.A.

    1982-07-01

    The kinetics of quartz dissolution control the produced fluid dissolved silica concentration in geothermal systems in which the downhole residence time is finite. The produced fluid of the Phase I, Run Segment 5 experimental Hot Dry Rock (HDR) geothermal system at Fenton Hill, NM, was undersaturated with respect to quartz in one pass through the reservoir, suggesting that the rate of granite dissolution governed the outlet dissolved silica concentration in this system. The literature data for the rate of quartz dissolution in water from 65 to 625/sup 0/C is correlated using an empirical rate law which is first order in quartz surface area and degree of undersaturation of the fluid. The Arrhenius plot (ln k vs T/sup -1/) is linear over eight orders of magnitude of the rate constant, verifying the validity of the proposed rate expression. Carefully performed quartz dissolution experiments in the present study duplicated the literature data and completed the data base in the temperature range from 150 to 250/sup 0/C. Identical experiments using crushed granite indicate that the rate of quartz dissolution in the presence of granite could be as much as 1 to 2 orders of magnitude faster than the rates observed in the pure quartz experiments. A temperature dependent HDR reservoir model incorporates the quartz dissolution rate law to simulate the dissolved silica behavior during the Fenton Hill Run Segment 5 experiment. For this low-permeability, fracture-dominated reservoir, the assumptions of one-dimensional plug flow through a vertically-inclined rectangular fracture and one-dimensional rock heat conduction perpendicular to the direction of flow are employed. These simplifications lead to an analytical solution for the temperature field in the reservoir.

  9. Affinity functions for modeling glass dissolution rates

    Energy Technology Data Exchange (ETDEWEB)

    Bourcier, W.L. [Lawrence Livermore National Lab., CA (United States)

    1997-07-01

    Glass dissolution rates decrease dramatically as glass approach ''saturation'' with respect to the leachate solution. Most repository sites are chosen where water fluxes are minimal, and therefore the waste glass is most likely to dissolve under conditions close to ''saturation''. The key term in the rate expression used to predict glass dissolution rates close to ''saturation'' is the affinity term, which accounts for saturation effects on dissolution rates. Interpretations of recent experimental data on the dissolution behaviour of silicate glasses and silicate minerals indicate the following: 1) simple affinity control does not explain the observed dissolution rate for silicate minerals or glasses; 2) dissolution rates can be significantly modified by dissolved cations even under conditions far from saturation where the affinity term is near unity; 3) the effects of dissolved species such as Al and Si on the dissolution rate vary with pH, temperature, and saturation state; and 4) as temperature is increased, the effect of both pH and temperature on glass and mineral dissolution rates decrease, which strongly suggests a switch in rate control from surface reaction-based to diffusion control. Borosilicate glass dissolution models need to be upgraded to account for these recent experimental observations. (A.C.)

  10. CALCIUM CARBONATE DISSOLUTION RATE IN LIMESTONE CONTACTORS

    Science.gov (United States)

    The rate of carbonate mineral dissolution from limestone was studied using a rotating disk apparatus and samples of limestone of varied composition. The purpose of this study was to determine the effect of limestone composition on the kinetics of carbonate mineral dissolution. Th...

  11. Biogenic silica dissolution in diatom aggregates: insights from reactive transport modelling

    KAUST Repository

    Moriceau, B

    2014-12-15

    © Inter-Research 2014. Diatom aggregates contribute significantly to the vertical sinking flux of particulate matter in the ocean. These fragile structures form a specific microhabitat for the aggregated cells, but their internal chemical and physical characteristics remain largely unknown. Studies on the impact of aggregation on the Si cycle led to apparent inconsistency. Despite a lower biogenic silica (bSiO2) dissolution rate and diffusion of the silicic acid (dSi) being similar in aggregates and in sea-water, dSi surprisingly accumulates in aggregates. A reaction-diffusion model helps to clarify this incoherence by reconstructing dSi accumulation measured during batch experiments with aggregated and non-aggregated Skeletonema marinoi and Chaetoceros decipiens. The model calculates the effective bSiO2 dissolution rate as opposed to the experimental apparent bSiO2 dissolution rate, which is the results of the effective dissolution of bSiO2 and transport of dSi out of the aggregate. In the model, dSi transport out of the aggregate is modulated by alternatively considering retention (decrease of the dSi diffusion constant) and adsorption (reversible chemical bonds between dSi and the aggregate matrix) processes. Modelled bSiO2 dissolution is modulated by the impact of dSi concentration inside aggregates and diatom viability, as enhanced persistence of metabolically active diatoms has been observed in aggregates. Adsorption better explains dSi accumulation within and outside aggregates, raising the possible importance of dSi travelling within aggregates to the deep sea (potentially representing 20% of the total silica flux). The model indicates that bSiO2 dissolution is effectively decreased in aggregates mainly due to higher diatom viability but also to other parameters discussed herein.

  12. Dissolution rate of BTEX contaminants in water

    International Nuclear Information System (INIS)

    Njobuenwu, D.O.; Amadi, S.A.; Ukpaka, P.C.

    2005-01-01

    Benzene, toluene, ethylbenzene and xylenes (BTEX) and substituted benzenes are the most common aromatic compounds in petroleum. BTEX components are the most soluble and mobile fraction of crude oil and many petroleum products, and frequently enter soil, sediments and aquatic environments because of accidental spills, leaks and improper oil waste disposal practices. The mass transfer process of hydrocarbons in aquatic mediums has received considerable attention in the literature. This paper focused on the molecular mass transfer rate of BTEX in water, with the aim of understanding and predicting contaminant fate and transport. A comprehensive model was developed to simulate the molecular dissolution rate of BTEX in a natural water stream. The model considered the physicochemical properties of the BTEX compounds and physical processes relevant to the spreading of contaminants in the sea. The dissolution rate was a function of oil slick area, dissolution mass transferability and oil solubility in water. The total dissolution rate N was calculated and the dissolution mass transfer coefficient K was given as the point value of mass transfer coefficient. Results for the dissolution rate based on the solubility of the components in the water were compared with analytical solutions from previous studies and showed good agreement. The model showed that benzene had the largest dissolution rate, while o-xylene had the lowest rate because of its lower fraction. Benzene dissolution rate was approximately 2.6, which was 20.6 times that of toluene and ethylbenzene. It was concluded that the model is useful in predicting and monitoring the dissolution rate of BTEX contaminants in soil and water systems. 22 refs., 2 tabs., 3 figs

  13. UO2 dissolution rates: A review

    International Nuclear Information System (INIS)

    McKenzie, W.F.

    1992-09-01

    This report reviews literature data on UO 2 dissolution kinetics and provides a framework for guiding future experimental studies as well as theoretical modeling studies. Under oxidizing conditions, UO 2 dissolution involves formation of an oxidized surface layer which is then dissolved by formation of aqueous complexes. Higher oxygen pressures or other oxidants are required at higher temperatures to have dissolution rates independent of oxygen pressure. At high oxygen pressures (1-5 atm, 25-70 C), the dissolution rate has a one-half order dependence on oxygen pressure, whereas at oxygen pressures below 0.2 atm, Grandstaff (1976), but nobody else, observed a first-order dependence on dissolution rate. Most people found a first-order dependence on carbonate concentration; Posey-Dowty (1987) found independence of carbonate at pH 7 to 8.2. Dissolution rates increase with temperature except in experiments involving granitic groundwater. Dissolution rates were generally greater under acid or basic conditions than near neutral pH

  14. Thermodynamics of Silica Dissolution From In-situ Raman +Spectroscopy

    Science.gov (United States)

    Davis, M. K.; Fumagalli, P.; Stixrude, L. P.

    2001-12-01

    Solubilities of cations, such as silicon, in water strongly effect both the physical and thermodynamical properties of supercritical metamorphic fluids. Modeling the thermodynamics of fluid-rock interactions requires therefore a profound understanding of cation dissolution and aqueous speciation. In-situ Raman experiments of the silica-water system were performed in an externally heated Bassett-type diamond-anvil cell at the Department of Geological Sciences, University of Michigan. Natural quartz samples (from Owl Creek Mountains, Wyoming) were loaded in the sample chamber with de-ionized or spectrographic water. All experiments used doubly polished rhenium gaskets with a thickness of 200 μ m, diameter of 1.0 mm, and a 500 μ m drillhole for the sample chamber. Temperature was measured using K-type thermocouples wrapped around both the upper and lower diamond anvils. Pressures are obtained on the basis of the shift of the 464 cm-1 Raman mode of quartz. In-situ Raman spectra were collected from 250-1200 cm-1, focusing on the vibrational modes of aqueous silica species at temperatures up to 700 ° C and pressures up to 14 kbar. We observed Si-O stretching modes attributable to dimer (H6Si2O7, 965 cm-1) and monomer (H4SiO4, 771 cm-1) aqueous silica species. The relative intensities of these two bands as a function of isochoric heating place constraints on the energetics of the polymerization reaction, if we assume that the intensity ratio is linearly related to concentration ratio. We have been able to perform experiments along two different isochores (0.9 and 0.75 g/cm3, respectively) from which we are able to derive the enthalpy of reaction.

  15. Tadalafil inclusion in microporous silica as effective dissolution enhancer: optimization of loading procedure and molecular state characterization.

    Science.gov (United States)

    Mehanna, Mohammed M; Motawaa, Adel M; Samaha, Magda W

    2011-05-01

    Tadalafil is an efficient drug used to treat erectile dysfunction characterized by poor water solubility, which has a negative influence on its bioavailability. Utilization of microporous silica represents an effective and facile technology to increase the dissolution rate of poorly soluble drugs. Our strategy involved directly introducing tadalafil as guest molecule into microporous silica as host material by incipient wetness impregnation method. To optimize tadalafil inclusion, response surface methodology (RSM) using 3(3) factorial design was utilized. Furthermore, to investigate the molecular state of tadalafil, Fourier-transform infrared spectroscopy, differential scanning calorimetery, thermal gravimetrical analysis, nitrogen adsorption, and powder X-ray diffraction (PXRD) were carried out. The results obtained pointed out that the quantity of microporous silica was the predominant factor that increased the loading efficiency. For the optimized formula, the loading efficiency was 42.50 wt %. Adsorption-desorption experiments indicated that tadalafil has been introduced into the micropores. Powder XRD and differential scanning calorimetry analyses revealed that tadalafil is arranged in amorphous form. In addition, the dissolution rate of tadalafil from the microporous silica was faster than that of free drug. Amorphous tadalafil occluded in microporous silica did not crystallize over 3 months. These findings contributed in opening a new strategy concerning the utilization of porous silica for the dissolution rate enhancement. Copyright © 2010 Wiley-Liss, Inc.

  16. Jarosite dissolution rates in perchlorate brine

    Science.gov (United States)

    Legett, Carey; Pritchett, Brittany N.; Elwood Madden, Andrew S.; Phillips-Lander, Charity M.; Elwood Madden, Megan E.

    2018-02-01

    Perchlorate salts and the ferric sulfate mineral jarosite have been detected at multiple locations on Mars by both landed instruments and orbiting spectrometers. Many perchlorate brines have eutectic temperatures bearing rocks and sediments may have been altered by perchlorate brines. Here we measured jarosite dissolution rates in 2 M sodium perchlorate brine as well as dilute water at 298 K to determine the effects of perchlorate anions on jarosite dissolution rates and potential reaction products. We developed a simple method for determining aqueous iron concentrations in high salinity perchlorate solutions using ultraviolet-visible spectrophotometry that eliminates the risk of rapid oxidation reactions during analyses. Jarosite dissolution rates in 2 M perchlorate brine determined by iron release rate (2.87 × 10-12 ±0.85 × 10-12 mol m-2 s-1) were slightly slower than the jarosite dissolution rate measured in ultrapure (18.2 MΩ cm-1) water (5.06 × 10-12 mol m-2 s-1) using identical methods. No additional secondary phases were observed in XRD analyses of the reaction products. The observed decrease in dissolution rate may be due to lower activity of water (ɑH2O = 0.9) in the 2 M NaClO4 brine compared with ultrapure water (ɑH2O = 1). This suggests that the perchlorate anion does not facilitate iron release, unlike chloride anions which accelerated Fe release rates in previously reported jarosite and hematite dissolution experiments. Since dissolution rates are slower in perchlorate-rich solutions, jarosite is expected to persist longer in perchlorate brines than in dilute waters or chloride-rich brines. Therefore, if perchlorate brines dominate aqueous fluids on the surface of Mars, jarosite may remain preserved over extended periods of time, despite active aqueous processes.

  17. Formation of quartz veins by local dissolution and transport of silica

    Energy Technology Data Exchange (ETDEWEB)

    Wangen, Magnus; Munz, Ingrid Anne

    2004-08-01

    A simple model is proposed for the (often) thick quartz veins observed in the Modum Complex in Southern Norway. The formation of these veins cannot easily be explained by silica imported by hot ascending fluids. The proposed model has dissolution in the host rock adjacent to the veins as the source for silica. The suggested process for vein formation is represented by a reaction-diffusion equation, and the process is studied in terms of a Damkoehler number. Estimates for the growth rate of quartz cement are derived. The estimates for the growth rate can be used to constrain poorly known parameters of the vein formation process, like for instance, the degree of supersaturation in the host rock. (Author)

  18. Chrysotile dissolution rates: Implications for carbon sequestration

    International Nuclear Information System (INIS)

    Thom, James G.M.; Dipple, Gregory M.; Power, Ian M.; Harrison, Anna L.

    2013-01-01

    Highlights: • Uncertainties in serpentine dissolution kinetics hinder carbon sequestration models. • A pH dependent, far from equilibrium dissolution rate law for chrysotile. • F chrysotile (mol/m 2 /s) = 10 −0.21pH−10.57 at 22 °C over pH 2–10. • Laboratory dissolution rates consistent with mine waste weathering observations. • Potential for carbon sequestration in mine tailings and aquifers is assessed. - Abstract: Serpentine minerals (e.g., chrysotile) are a potentially important medium for sequestration of CO 2 via carbonation reactions. The goals of this study are to report a steady-state, far from equilibrium chrysotile dissolution rate law and to better define what role serpentine dissolution kinetics will have in constraining rates of carbon sequestration via serpentine carbonation. The steady-state dissolution rate of chrysotile in 0.1 m NaCl solutions was measured at 22 °C and pH ranging from 2 to 8. Dissolution experiments were performed in a continuously stirred flow-through reactor with the input solutions pre-equilibrated with atmospheric CO 2 . Both Mg and Si steady-state fluxes from the chrysotile surface, and the overall chrysotile flux were regressed and the following empirical relationships were obtained: F Mg =-0.22pH-10.02;F Si =-0.19pH-10.37;F chrysotile =-0.21pH-10.57 where F Mg , F Si , and F chrysotile are the log 10 Mg, Si, and molar chrysotile fluxes in mol/m 2 /s, respectively. Element fluxes were used in reaction-path calculations to constrain the rate of CO 2 sequestration in two geological environments that have been proposed as potential sinks for anthropogenic CO 2 . Carbon sequestration in chrysotile tailings at 10 °C is approximately an order of magnitude faster than carbon sequestration in a serpentinite-hosted aquifer at 60 °C on a per kilogram of water basis. A serpentinite-hosted aquifer, however, provides a larger sequestration capacity. The chrysotile dissolution rate law determined in this study has

  19. Aqueous dissolution rates of uranium oxides

    International Nuclear Information System (INIS)

    Steward, S.A.; Mones, E.T.

    1994-10-01

    An understanding of the long-term dissolution of waste forms in groundwater is required for the safe disposal of high level nuclear waste in an underground repository. The main routes by which radionuclides could be released from a geological repository are the dissolution and transport processes in groundwater flow. Because uranium dioxide is the primary constituent of spent nuclear fuel, the dissolution of its matrix in spent fuel is considered the rate-limiting step for release of radioactive fission products. The purpose of our work has been to measure the intrinsic dissolution rates of uranium oxides under a variety of well-controlled conditions that are relevant to a repository and allow for modeling. The intermediate oxide phase U 3 O 8 , triuranium octaoxide, is quite stable and known to be present in oxidized spent fuel. The trioxide, UO 3 , has been shown to exist in drip tests on spent fuel. Here we compare the results of essentially identical dissolution experiments performed on depleted U 3 O 8 and dehyrated schoepite or uranium trioxide monohydrate (UO 3 ·H 2 O). These are compared with earlier work on spent fuel and UO 2 under similar conditions

  20. Sodium tetraphenylborate solubility and dissolution rates

    International Nuclear Information System (INIS)

    Barnes, M.J.; Peterson, R.A.; Swingle, R.F.; Reeves, C.T.

    1995-01-01

    The rate of solid sodium tetraphenylborate (NaTPB) dissolution in In-Tank Precipitation salt solutions has been experimentally determined. The data indicates that the dissolution rate of solid NaTPB is a minor contributor the lag time experienced in the 1983 Salt Decontamination Demonstration Test and should not be considered as the rate determining step. Current analytical models for predicting the time to reach the composite lower flammability limit assume that the lag time is not more than 6 hours, and the data supports this assumption (i.e., dissolution by itself requires much less than 6 hours). The data suggests that another step--such as mass transport, the reaction of a benzene precursor or the mixing behavior--is the rate determining factor for benzene release to the vapor space in Tank 48H. In addition, preliminary results from this program show that the degree of agitation employed is not a significant parameter in determining the rate of NaTPB dissolution. As a result of this study, an improved equation for predicting equilibrium tetraphenylborate solubility with respect to temperature and sodium ion concentration has been determined

  1. Crystal modifications and dissolution rate of piroxicam.

    Science.gov (United States)

    Lyn, Lim Yee; Sze, Huan Wen; Rajendran, Adhiyaman; Adinarayana, Gorajana; Dua, Kamal; Garg, Sanjay

    2011-12-01

    Piroxicam is a nonsteroidal anti-inflammatory drug with low aqueous solubility which exhibits polymorphism. The present study was carried out to develop polymorphs of piroxicam with enhanced solubility and dissolution rate by the crystal modification technique using different solvent mixtures prepared with PEG 4000 and PVP K30. Physicochemical characteristics of the modified crystal forms of piroxicam were investigated by X-ray powder diffractometry, FT-IR spectrophotometry and differential scanning calorimetry. Dissolution and solubility profiles of each modified crystal form were studied and compared with pure piroxicam. Solvent evaporation method (method I) produced both needle and cubic shaped crystals. Slow crystallization from ethanol with addition of PEG 4000 or PVP K30 at room temperature (method II) produced cubic crystal forms. Needle forms produced by method I improved dissolution but not solubility. Cubic crystals produced by method I had a dissolution profile similar to that of untreated piroxicam but showed better solubility than untreated piroxicam. Cubic shaped crystals produced by method II showed improved dissolution, without a significant change in solubility. Based on the XRPD results, modified piroxicam crystals obtained by method I from acetone/benzene were cube shaped, which correlates well with the FTIR spectrum; modified needle forms obtained from ethanol/methanol and ethanol/acetone showed a slight shift of FTIR peak that may be attributed to differences in the internal structure or conformation.

  2. Different effects of silica added internal or external on in vitro dissolution of indomethacin hot-melt extrudates.

    Science.gov (United States)

    Xia, Yulong; Yuan, Meng; Deng, Yueyang; Ke, Xue; Ci, Tianyuan

    2017-12-20

    The purpose of this work was to investigate the effect on the dissolution behavior when silica was added in different ways. The solid dispersion was prepared by hot-melt extrusion (HME) using indomethacin (IND) as a model drug and Kollidon VA64 as a carrier. In order to change the dissolution behavior, the silica was added during or after the HME respectively, to obtain the corresponding silica internal-added solid dispersion (InSD) and silica external-added solid dispersion (ExSD). According to the results, the internal-added silicon dioxide could reduce the dissolution rate from 66.91%/h to 24.12%/h and the water infiltration rate from 0.37mm/h to 0.16mm/h in the phosphate buffer solution (PBS) of pH 6.8, so the formulation of InSD had a significant sustained release effect. But the infiltration rate of the ExSD was increased to 13.22mm/h when silica was added external, and the density of VA64 in the powder was decreased from 541.87mg/cm3 to 141.87mg/cm3, leading to a weak resistance to the external force, and the powder was easy to be dispersed after wetted by water so that the formulation of ExSD had a relatively higher dissolution rate. This phenomenon was more visible when the phosphate buffer solution was changed to pH 5.6 in which the API was more difficult to be dissolved. Accordingly, different addition ways of aerosil would change release behavior of the HME preparation. Copyright © 2017. Published by Elsevier B.V.

  3. Feldspar dissolution rates in the Topopah Spring Tuff, Yucca Mountain, Nevada

    Science.gov (United States)

    Bryan, C.R.; Helean, K.B.; Marshall, B.D.; Brady, P.V.

    2009-01-01

    Two different field-based methods are used here to calculate feldspar dissolution rates in the Topopah Spring Tuff, the host rock for the proposed nuclear waste repository at Yucca Mountain, Nevada. The center of the tuff is a high silica rhyolite, consisting largely of alkali feldspar (???60 wt%) and quartz polymorphs (???35 wt%) that formed by devitrification of rhyolitic glass as the tuff cooled. First, the abundance of secondary aluminosilicates is used to estimate the cumulative amount of feldspar dissolution over the history of the tuff, and an ambient dissolution rate is calculated by using the estimated thermal history. Second, the feldspar dissolution rate is calculated by using measured Sr isotope compositions for the pore water and rock. Pore waters display systematic changes in Sr isotopic composition with depth that are caused by feldspar dissolution. The range in dissolution rates determined from secondary mineral abundances varies from 10-16 to 10-17 mol s-1 kg tuff-1 with the largest uncertainty being the effect of the early thermal history of the tuff. Dissolution rates based on pore water Sr isotopic data were calculated by treating percolation flux parametrically, and vary from 10-15 to 10-16 mol s-1 kg tuff-1 for percolation fluxes of 15 mm a-1 and 1 mm a-1, respectively. Reconciling the rates from the two methods requires that percolation fluxes at the sampled locations be a few mm a-1 or less. The calculated feldspar dissolution rates are low relative to other measured field-based feldspar dissolution rates, possibly due to the age (12.8 Ma) of the unsaturated system at Yucca Mountain; because oxidizing and organic-poor conditions limit biological activity; and/or because elevated silica concentrations in the pore waters (???50 mg L-1) may inhibit feldspar dissolution. ?? 2009 Elsevier Ltd. All rights reserved.

  4. Glass dissolution rate measurement and calculation revisited

    Energy Technology Data Exchange (ETDEWEB)

    Fournier, Maxime, E-mail: maxime.fournier@cea.fr [CEA, DEN, DTCD, SECM, F-30207, Bagnols sur Cèze (France); Ull, Aurélien; Nicoleau, Elodie [CEA, DEN, DTCD, SECM, F-30207, Bagnols sur Cèze (France); Inagaki, Yaohiro [Department of Applied Quantum Physics & Nuclear Engineering, Kyushu University, Fukuoka, 819-0395 (Japan); Odorico, Michaël [ICSM-UMR5257 CEA/CNRS/UM2/ENSCM, Site de Marcoule, BP17171, F-30207, Bagnols sur Cèze (France); Frugier, Pierre; Gin, Stéphane [CEA, DEN, DTCD, SECM, F-30207, Bagnols sur Cèze (France)

    2016-08-01

    Aqueous dissolution rate measurements of nuclear glasses are a key step in the long-term behavior study of such waste forms. These rates are routinely normalized to the glass surface area in contact with solution, and experiments are very often carried out using crushed materials. Various methods have been implemented to determine the surface area of such glass powders, leading to differing values, with the notion of the reactive surface area of crushed glass remaining vague. In this study, around forty initial dissolution rate measurements were conducted following static and flow rate (SPFT, MCFT) measurement protocols at 90 °C, pH 10. The international reference glass (ISG), in the forms of powders with different particle sizes and polished monoliths, and soda-lime glass beads were examined. Although crushed glass grains clearly cannot be assimilated with spheres, it is when using the samples geometric surface (S{sub geo}) that the rates measured on powders are closest to those found for monoliths. Overestimation of the reactive surface when using the BET model (S{sub BET}) may be due to small physical features at the atomic scale—contributing to BET surface area but not to AFM surface area. Such features are very small compared with the thickness of water ingress in glass (a few hundred nanometers) and should not be considered in rate calculations. With a S{sub BET}/S{sub geo} ratio of 2.5 ± 0.2 for ISG powders, it is shown here that rates measured on powders and normalized to S{sub geo} should be divided by 1.3 and rates normalized to S{sub BET} should be multiplied by 1.9 in order to be compared with rates measured on a monolith. The use of glass beads indicates that the geometric surface gives a good estimation of glass reactive surface if sample geometry can be precisely described. Although data clearly shows the repeatability of measurements, results must be given with a high uncertainty of approximately ±25%. - Highlights: • Initial dissolution

  5. Dissolution rates of DWPF glasses from long-term PCT

    International Nuclear Information System (INIS)

    Ebert, W.L.; Tam, S.W.

    1996-01-01

    We have characterized the corrosion behavior of several Defense Waste Processing Facility (DWPF) reference waste glasses by conducting static dissolution tests with crushed glasses. Glass dissolution rates were calculated from measured B concentrations in tests conducted for up to five years. The dissolution rates of all glasses increased significantly after certain alteration phases precipitated. Calculation of the dissolution rates was complicated by the decrease in the available surface area as the glass dissolves. We took the loss of surface area into account by modeling the particles to be spheres, then extracting from the short-term test results the dissolution rate corresponding to a linear decrease in the radius of spherical particles. The measured extent of dissolution in tests conducted for longer times was less than predicted with this linear dissolution model. This indicates that advanced stages of corrosion are affected by another process besides dissolution, which we believe to be associated with a decrease in the precipitation rate of the alteration phases. These results show that the dissolution rate measured soon after the formation of certain alteration phases provides an upper limit for the long-term dissolution rate, and can be used to determine a bounding value for the source term for radionuclide release from waste glasses. The long-term dissolution rates measured in tests at 20,000 per m at 90 degrees C in tuff groundwater at pH values near 12 for the Environmental Assessment glass and glasses made with SRL 131 and SRL 202 frits, respectively

  6. Dissolution enhancement of a model poorly water-soluble drug, atorvastatin, with ordered mesoporous silica: comparison of MSF with SBA-15 as drug carriers.

    Science.gov (United States)

    Maleki, Aziz; Hamidi, Mehrdad

    2016-01-01

    The purpose of this study was to develop mesoporous silica materials incorporated with poorly water-soluble drug atorvastatin calcium (AC) in order to improve drug dissolution, and intended to be orally administrated. A comparison between 2D-hexagonal silica nanostructured SBA-15 and mesocellular siliceous foam (MSF) with continuous 3D pore system on drug release rate was investigated. AC-loaded mesoporous silicas were characterized thorough N2 adsorption-desorption analysis, Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and dynamic light scattering (DLS). Results demonstrated a successful incorporation of AC into the silica-based hosts. The results taken from the drug release tests were also analyzed using different parameters, namely similarity factor (f2), difference factor (f1), dissolution efficiency (DE%), mean dissolution rate (MDR) and dissolution time (tm%). It confirmed a significant enhancement in the release profile of atorvastatin calcium with SBA-15, and MSF as drug carrier. Moreover, in comparison with SBA-15, MSF showed faster release rate of AC in enzyme-free simulated gastric fluid (pH 1.2). We believed that our findings can help the use of mesoporous silica materials in improving bioavailability of poorly water-soluble drugs.

  7. Transparent Exopolymeric Particles (TEP Selectively Increase Biogenic Silica Dissolution From Fossil Diatoms as Compared to Fresh Diatoms

    Directory of Open Access Journals (Sweden)

    Jordan Toullec

    2018-03-01

    Full Text Available Diatom production is mainly supported by the dissolution of biogenic silica (bSiO2 within the first 200 m of the water column. The upper oceanic layer is enriched in dissolved and/or colloidal organic matter, such as exopolymeric polysaccharides (EPS and transparent exopolymeric particles (TEP excreted by phytoplankton in large amounts, especially at the end of a bloom. In this study we explored for the first time the direct influence of TEP-enriched diatom excretions on bSiO2 dissolution. Twelve dissolution experiments on fresh and fossil diatom frustules were carried out on seawater containing different concentrations of TEP extracted from diatom cultures. Fresh diatom frustules were cleaned from the organic matter by low ash temperature, and fossil diatoms were made from diatomite powder. Results confirm that newly formed bSiO2 dissolved at a faster rate than fossil diatoms due to a lower aluminum (Al content. Diatom excretions have no effect on the dissolution of the newly formed bSiO2 from Chaetoceros muelleri. Reversely, the diatomite specific dissolution rate constant and solubility of the bSiO2 were positively correlated to TEP concentrations, suggesting that diatom excretion may provide an alternative source of dSi when limitations arise.

  8. Dissolution rate enhancement of piroxicam by ordered mixing.

    Science.gov (United States)

    Saharan, Vikas Anand; Choudhury, Pratim Kumar

    2012-07-01

    Micronized piroxicam was mixed with lactose, mannitol, sorbitol, maltitol and sodium chloride to produce ordered mixture in a glass vial by manual hand shaking method. The effect of excipients, surfactant, superdisintegrant, drug concentration and carrier particle size on dissolution rate was investigated. Dissolution rate studies of the prepared ordered mixtures revealed that all water soluble excipients increased the dissolution rate of piroxicam when compared to the dissolution rate of piroxicam or its suspension. Ordered mixture formulation PLF4, consisting of lactose as water soluble excipient, SSG (8% w/s) and SLS (1% w/w), released piroxcam at a very fast rate so much so that about 90% of the composition had passed into solution within 2 min. The order of the dissolution rate enhancement for ordered mixtures of various water soluble excipients was: lactose > mannitol > maltitol > sorbitol > sodium chloride. Carrier granules of size 355-710 µm were most effective in increasing the dissolution rate of drug from ordered mixtures. Decreasing the carrier particle size reduced drug dissolution from ordered mixtures. The dissolution rate of ordered mixtures consisting of 1-5% w/w piroxicam was superior to dissolution rate of piroxicam suspension. The dissolution data fitting and the resulting regression parameters indicated Hixson Crowell, cube root law, as the best fit to drug release data of ordered mixtures.

  9. Assessing the effect of dissolved organic ligands on mineral dissolution rates: An example from calcite dissolution

    International Nuclear Information System (INIS)

    DeMaio, T.; Grandstaff, D.E.

    1997-01-01

    Experiments suggest that dissolved organic ligands may primarily modify mineral dissolution rates by three mechanisms: (1) metal-ligand (M-L) complex formation in solution, which increases the degree of undersaturation, (2) formation of surface M-L complexes that attack the surface, and (3) formation of surface complexes which passivate or protect the surface. Mechanisms (1) and (2) increase the dissolution rate and the third decreases it compared with organic-free solutions. The types and importance of these mechanisms may be assessed from plots of dissolution rate versus degree of undersaturation. To illustrate this technique, calcite, a common repository cementing and vein-filling mineral, was dissolved at pH 7.8 and 22 C in Na-Ca-HCO 3 -Cl solutions with low concentrations of three organic ligands. Low citrate concentrations (50 microM) increased the dissolution rate consistent with mechanism (1). Oxalate decreased the rate, consistent with mechanism (3). Low phthalate concentration (<50 microM) decreased calcite dissolution rates; however, higher concentrations increased the dissolution rates, which became faster than in inorganic solutions. Thus, phthalate exhibits both mechanisms (2) and (3) at different concentrations. In such cases linear extrapolations of dissolution rates from high organic ligand concentrations may not be valid

  10. Effect of alteration phase formation on the glass dissolution rate

    International Nuclear Information System (INIS)

    Ebert, W.L.

    1997-01-01

    The dissolution rates of many glasses have been observed to increase upon the formation of certain alteration phases. While simulations have predicted the accelerating effect of formation of certain phases, the phases predicted to form in computer simulations are usually different than those observed to form in experiments. This is because kinetically favored phases form first in experiments, while simulations predict the thermodynamically favored phases. Static dissolution tests with crushed glass have been used to measure the glass dissolution rate after alteration phases form. Because glass dissolution rates are calculated on a per area basis, an important effect in tests conducted with crushed glass is the decrease in the surface area of glass that is available for reaction as the glass dissolves. This loss of surface area must be taken into account when calculating the dissolution rate. The phases that form and their effect on the dissolution rate are probably related to the glass composition. The impact of phase formation on the glass dissolution rate also varies according to the solubility products of the alteration phases and how the orthocilicic acid activity is affected. Insight into the relationship between the glass dissolution rate, solution chemistry and alteration phase formation is provided by the results of accelerated dissolution tests

  11. Effect of alteration phase formation on the glass dissolution rate

    Energy Technology Data Exchange (ETDEWEB)

    Ebert, W L [Argonne National Laboratory, Chemical Technology Div. (United States)

    1997-07-01

    The dissolution rates of many glasses have been observed to increase upon the formation of certain alteration phases. While simulations have predicted the accelerating effect of formation of certain phases, the phases predicted to form in computer simulations are usually different than those observed to form in experiments. This is because kinetically favored phases form first in experiments, while simulations predict the thermodynamically favored phases. Static dissolution tests with crushed glass have been used to measure the glass dissolution rate after alteration phases form. Because glass dissolution rates are calculated on a per area basis, an important effect in tests conducted with crushed glass is the decrease in the surface area of glass that is available for reaction as the glass dissolves. This loss of surface area must be taken into account when calculating the dissolution rate. The phases that form and their effect on the dissolution rate are probably related to the glass composition. The impact of phase formation on the glass dissolution rate also varies according to the solubility products of the alteration phases and how the orthocilicic acid activity is affected. Insight into the relationship between the glass dissolution rate, solution chemistry and alteration phase formation is provided by the results of accelerated dissolution tests.

  12. Physical heterogeneity control on effective mineral dissolution rates

    Science.gov (United States)

    Jung, Heewon; Navarre-Sitchler, Alexis

    2018-04-01

    Hydrologic heterogeneity may be an important factor contributing to the discrepancy in laboratory and field measured dissolution rates, but the governing factors influencing mineral dissolution rates among various representations of physical heterogeneity remain poorly understood. Here, we present multiple reactive transport simulations of anorthite dissolution in 2D latticed random permeability fields and link the information from local grid scale (1 cm or 4 m) dissolution rates to domain-scale (1m or 400 m) effective dissolution rates measured by the flux-weighted average of an ensemble of flow paths. We compare results of homogeneous models to heterogeneous models with different structure and layered permeability distributions within the model domain. Chemistry is simplified to a single dissolving primary mineral (anorthite) distributed homogeneously throughout the domain and a single secondary mineral (kaolinite) that is allowed to dissolve or precipitate. Results show that increasing size in correlation structure (i.e. long integral scales) and high variance in permeability distribution are two important factors inducing a reduction in effective mineral dissolution rates compared to homogeneous permeability domains. Larger correlation structures produce larger zones of low permeability where diffusion is an important transport mechanism. Due to the increased residence time under slow diffusive transport, the saturation state of a solute with respect to a reacting mineral approaches equilibrium and reduces the reaction rate. High variance in permeability distribution favorably develops large low permeability zones that intensifies the reduction in mixing and effective dissolution rate. However, the degree of reduction in effective dissolution rate observed in 1 m × 1 m domains is too small (equilibrium conditions reduce the effective dissolution rate by increasing the saturation state. However, in large domains where less- or non-reactive zones develop, higher

  13. Dissolution of basaltic glass in seawater: Mechanism and rate

    International Nuclear Information System (INIS)

    Crovisier, J.L.; Honnorez, J.; Eberhart, J.P.

    1987-01-01

    Basaltic glasses are considered as natural analogues for nuclear waste glasses. Thermodynamic computer codes used to evaluate long term behavior of both nuclear waste and basaltic glasses require the knowledge of the dissolution mechanism of the glass network. The paper presents the results of a series of experiments designed to study the structure and chemical composition of alteration layers formed on the surface of artificial tholeiitic glass altered in artificial seawater. Experiments were performed at 60 degree C, 1 bar and 350 bars in non-renewed conditions. A natural sample from Palagonia (Sicily) has been studied by electron microscopy and comparison between natural and experimental palagonitic layers is made. The behavior of dissolved silica during experiments, and both the structure and the chemical composition of the palagonitic layers, indicate that they form by precipitation of secondary minerals from solution after a total breakdown of the glassy network, i.e., congruent dissolution of the glass. Hence the dissolution equation necessary for thermodynamic modelling of basaltic glass dissolution in seawater at low temperature must be written as a simple stoichiometric process. These experiments indicate that the transformation of glass to palagonitic material is not isovolumetric. Hence it is preferable to use Fe or Ti as conservative elements for chemical budget calculations

  14. Surface controlled dissolution rates of gypsum in aqueous solutions exhibit nonlinear dissolution kinetics

    Science.gov (United States)

    Jeschke, Alexander A.; Vosbeck, Katrin; Dreybrodt, Wolfgang

    2001-01-01

    The effective dissolution rates of gypsum are determined by mixed kinetics, where the rate constants of dissolution at the surface and the transport constant of molecular diffusion of dissolved material are similar. To obtain the surface reaction rate law it is necessary to know the transport constant. We have determined the surface rate law for monocrystalline selenite by using a rotating disc set-up, where the transport coefficients are well known. As a result, up to a calcium concentration of 0.6 · ceq, we find a nearly linear rate law Rs = ksl (1- cs/ ceq) n1, where cs is the total calcium concentration at the surface and ceq the equilibrium concentration with respect to gypsum, n1 = 1.2 ± 0.2, and ksl = 1.1 · 10 -4 mmol cm -2 s -1 ± 15%. We also employed batch-experiments for selenite, alabaster and gypsum rock samples. The result of these experiments were interpreted by using a transport constant determined by NaCl dissolution experiments under similar physical conditions. The batch experiments reveal a dissolution rate law Rs = ksl (1- cs/ ceq) n1, ksl = 1.3 · 10 -4 mmol · cm -2 s -1, n1 = 1.2 ± 0.2 for c ≤ 0.94 · ceq. Close to equilibrium a nonlinear rate law, Rs = ks2 (1- cs/ ceq) n2, is observed, where ks2 is in the order of 10 mmol · cm -2 s -1 and n2 ≈ 4.5. The experimentally observed gypsum dissolution rates from the batch experiments could be accurately fitted, with only minor variations of the surface reaction constant obtained from the rotating disk experiment and the transport coefficient from the NaCl dissolution batch experiment. Batch experiments on pure synthetic gypsum, reveal a linear rate law up to equilibrium. This indicates inhibition of dissolution in natural samples close to equilibrium, as is known also for calcite minerals.

  15. Characterization of a silica-PVA hybrid for high density and stable silver dissolution

    Energy Technology Data Exchange (ETDEWEB)

    Dorin, Bryce, E-mail: bryce.dorin@postgrad.manchester.ac.uk [The Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); School of Chemical Engineering and Analytical Science, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); Zhu, Guangyu, E-mail: g.zhu@liverpool.ac.uk [Lairdside Laser Engineering Centre, The University of Liverpool, Campbeltown Road, Merseyside, CH41 9HP (United Kingdom); Parkinson, Patrick, E-mail: patrick.parkinson@manchester.ac.uk [The Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); Perrie, Walter, E-mail: wpfemto1@liverpool.ac.uk [Lairdside Laser Engineering Centre, The University of Liverpool, Campbeltown Road, Merseyside, CH41 9HP (United Kingdom); Benyezzar, Med, E-mail: med.benyezzar@manchester.ac.uk [The Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); Scully, Patricia, E-mail: patricia.scully@manchester.ac.uk [The Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); School of Chemical Engineering and Analytical Science, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)

    2016-07-01

    A silica and polyvinyl alcohol (PVA) hybrid material mixed with a high density of silver ions is synthesised and characterized in this work. The hybrid material can be cast into thick films, which we determined to be homogeneous using Raman spectroscopy. We observed that the silver ions remain stable in the material over time and at temperatures of 100 °C, which represents a marked improvement over previous solid solutions of silver. Differential scanning calorimetry and thermogravimetric analysis indicate the rapid activation of silver at 173 °C, resulting in a dense formation of silver nanoparticles within the hybrid. The activation of silver was also demonstrated in 3-dimensional geometries using femtosecond duration laser pulses. These results illustrate the silica-PVA hybrid is an attractive material for developing silver-insulator composites. - Highlights: • A novel PVA-silica hybrid is developed for silver ion dissolution. • The hybrid exhibits a high silver saturation point and good silver stability. • Heating and laser irradiation are capable of converting the silver ions to metal. • The hybrid material enables the fabrication of 3D metal-insulator composites.

  16. Effect of alumina on the dissolution rate of glasses

    International Nuclear Information System (INIS)

    Palavit, G.; Montagne, L.

    1997-01-01

    Small alumina addition to silicate glasses improves their chemical durability, but a large amount of alumina can also be beneficial to obtain a high dissolution rate. This paper describes the effect of Al 3+ on the early stage of glass alteration, in relation with its coordination in the glass and also with the reactions involved (hydrolysis and ionic exchange). We describe briefly nuclear magnetic resonance tools available to characterize the aluminum environments in the glasses. The rote of alumina on the dissolution rate of phosphate glasses is also discussed in order to show that the effect of Al 3+ is dependant upon the nature of the glass matrix. (author)

  17. Dissolution rate effect upon lyolumenescence of irradiated potassium chloride

    International Nuclear Information System (INIS)

    Leshchinskij, B.L.; Dzelme, Yu.R.; Tiliks, Yu.E.; Bugaenko, L.T.

    1985-01-01

    The paper is aimed at studying dissolution rate effect and concentration of electron acceptor upon lyoluminescence (LL) that occurs during dissolution of solids with radiation defects. For investigation gamma-irradiated potassium chloride monocrystalline disks were used. As a solvent 3x10sup(-6) M solution of C(RH) hodamine in 2.7 KCl aqueous solution is used. It is shown that LL occurs as a result of recombination of radiation defects with the solution and between themselves in two different regions of subsurface layer of the solid. Investigated dependences of LL intensty on dissolution rate are the efficient method of studying the structure of solids-aqueous solution interface and LL mechanism

  18. Quantifying Silica Reactivity in Subsurface Environments: Reaction Affinity and Solute Matrix Controls on Quartz and SiO2 Glass Dissolution Kinetics

    International Nuclear Information System (INIS)

    Dove, Patricia M.

    1999-01-01

    Our goal is to develop a quantitative and mechanistic understanding of amorphous silica, SiO2(am), dissolution kinetics in aqueous solutions. A knowledge of fundamental controls on the reactivity of simple Si-O bonded phases is the baseline of behavior for understanding highly complex silica phases. In the Earth, silicate minerals comprise >70% of the crust and dominate virtually every subsurface system. More importantly for the objectives of this EMSP project, the silicates are important because compositionally complex glasses will become the front line of defense in containing radioactive wastes in the nation's long term and interim storage strategies. To date, the behavior of SiO2(am) is largely inferred from studies of the better known crystalline polymorphs (e.g. alpha-quartz). In the first step towards constructing a general model for amorphous silica reactivity in the complex fluid compositions of natural waters, we are determining the dissolution behavior as a function of temperature, solution pH and cation concentration. With these data we are determining relationships between SiO2 glass structure and dissolution rates in aqueous solutions, as described below

  19. Enhancement of solubility and dissolution rate of atorvastatin ...

    African Journals Online (AJOL)

    Purpose: To investigate the formation of atorvastatin calcium (AC) co-crystal to improve its solubility and dissolution rate. Method: Co-crystallization of AC in equimolar ratio with isonicotinamide (INA) was carried out by slow solvent evaporation method using methanol. The solid obtained was characterized by powder x-ray ...

  20. Enhancement of solubility and dissolution rate of atorvastatin ...

    African Journals Online (AJOL)

    solvent evaporation method using methanol. ... crystal significantly increases in solubility with a dissolution rate 2 - 3 times faster than that of ... considered one of the most effective synthetic .... temperature of 37 ± 0.5 °C. The test was carried.

  1. Measurement of soluble nuclide dissolution rates from spent fuel

    International Nuclear Information System (INIS)

    Wilson, C.N.; Gray, W.J.

    1990-01-01

    Gaining a better understanding of the potential release behavior of water-soluble radionuclides is the focus of new laboratory spent fuel dissolution studies being planned in support of the Yucca Mountain Project. Previous studies have suggested that maximum release rates for actinide nuclides, which account for most of the long-term radioactivity in spent fuel, should be solubility-limited and should not depend on the characteristics or durability of the spent fuel waste form. Maximum actinide concentrations should be sufficiently low to meet the NRC (Nuclear Regulatory Commission) annual release limits. Potential release rates for soluble nuclides such as 99 Tc, 135 Cs, 14 C and 129 I, which account for about 1-2% of the activity in spent fuel at 1,000 years, are less certain and may depend on processes such as oxidation of the fuel in the repository air environment. Dissolution rates for several soluble nuclides have been measured from spent fuel specimens using static and semi-static methods. However, such tests do not provide a direct measurement of fuel matrix dissolution rates that may ultimately control soluble-nuclide release rates. Flow-through tests are being developed as a potential supplemental method for determining the matrix component of soluble-nuclide dissolution. Advantages and disadvantages of both semi-static and flow-through methods are discussed. Tests with fuel specimens representing a range of potential fuel states that may occur in the repository, including oxidized fuel, are proposed. Preliminary results from flow-through tests with unirradiated UO 2 suggesting that matrix dissolution rates are very sensitive to water composition are also presented

  2. Revisiting classical silicate dissolution rate laws under hydrothermal conditions

    Science.gov (United States)

    Pollet-Villard, Marion; Daval, Damien; Saldi, Giuseppe; Knauss, Kevin; Wild, Bastien; Fritz, Bertrand

    2015-04-01

    In the context of geothermal energy, the relative intensities of primary mineral leaching and secondary mineral precipitation can affect porosity and permeability of the reservoir, thereby influencing its hydraulic performance and the efficiency of the geothermal power station. That is why the prediction of reaction kinetics of fluid/rock interactions represents a critical issue in this context. Moreover, in several geothermal systems such as the one of Soultz-sous-Forêts (Alsace, France), the circulation of aqueous fluids induces only modest modifications of their chemical composition. Therefore, fluid-rock interactions take place at close-to-equilibrium conditions, where the rate-affinity relations are poorly known and intensively debated [1]. To describe more precisely the dissolution processes, our strategy consists in investigating the dissolution of the main cleavages of K-spar minerals (one of the prevalent primary minerals in the reservoir of Soultz-sous-Forêts geothermal system) over a wide range of Gibbs free energy (ΔG) conditions. The aims are to decipher the impact of crystallographic orientation and microstructural surface modifications on the dissolution kinetics and to propose a relation between K-spar dissolution rate and ΔG. Our experimental work relies on a coupled approach which combines classical experiments of K-spar dissolution monitored by aqueous chemical analyses (ICP-AES) and innovative techniques of nm- to μm-scale characterization of solid surface (SEM, AFM, VSI) [2]. Our results confirm that K-spar dissolution is an anisotropic process: we measure a tenfold factor between the slowest and the fastest-dissolving surfaces. Moreover, the formation of etch pits on surfaces during their alteration has been evidenced on all of the different faces that have been studied. This complex evolution of the surface topography casts doubt of the relevance of a surface model based on shrinking particles and represents a possible cause of an

  3. First-order dissolution rate law and the role of surface layers in glass performance assessment

    Science.gov (United States)

    Grambow, B.; Müller, R.

    2001-09-01

    The first-order dissolution rate law is used for nuclear waste glass performance predictions since 1984. A first discussion of the role of saturation effects was initiated at the MRS conference that year. In paper (1) it was stated that "For glass dissolution A* (the reaction affinity) cannot become zero since saturation only involves the reacting surface while soluble elements still might be extracted from the glass" [B. Grambow, J. Mater. Res. Soc. Symp. Proc. 44 (1985) 15]. Saturation of silica at the surface and condensation of surface silanol groups was considered as being responsible for the slow down of reaction rates by as much as a factor of 1000. Precipitation of Si containing secondary phases such as quartz was invoked as a mechanism for keeping final dissolution affinities higher than zero. Another (2) paper [A.B. Barkatt, P.B. Macedo, B.C. Gibson, C.J. Montrose, J. Mater. Res. Soc. Symp. Proc. 44 (1985) 3] stated that "… under repository conditions the extent of glass dissolution will be moderate due to saturation with respect to certain major elements (in particular, Si, Al and Ca). Consequently, the concentration levels of the more soluble glass constituents in the aqueous medium are expected to fall appreciable below their solubility limit." The formation of dense surface layers was considered responsible for explaining the saturation effect. The mathematical model assumed stop of reaction in closed systems, once solubility limits were achieved. For more than 15 years the question of the correctness of one or the other concept has seldom been posed and has not yet been resolved. The need of repository performance assessment for validated rate laws demands a solution, particularly since the consequences of the two concepts and research requirements for the long-term glass behavior are quite different. In concept (1) the stability of the `equilibrium surface region' is not relevant because, by definition, this region is stable chemically and after a

  4. Magnesite dissolution and precipitation rates at hydrothermal conditions

    International Nuclear Information System (INIS)

    Saldi, Giuseppe

    2009-01-01

    Magnesite (MgCO 3 ) is the stable anhydrous member of a series of Mg-carbonates with different degrees of hydration. Despite its relative scarcity in the natural environments, it constitutes an important mineral phase for the permanent sequestration of CO 2 as carbonate minerals. Experimental determination of magnesite precipitation and dissolution rates at conditions representative of the storage sites is therefore fundamental for the assessment of magnesite sequestration potential in basaltic and ultramafic rocks and the optimization of the techniques of CO 2 storage. Magnesite precipitation rates have been measured using mixed-flow and batch reactors as a function of temperature (100 ≤ T ≤ 200 deg. C), solution composition and CO 2 partial pressure (up to 30 bar). Rates were found to be independent of aqueous solution ionic strength at 0.1 M 3 2- activity at pH > 8. All rates obtained from mixed flow reactor experiments were found to be consistent with the model of Pokrovsky et al. (1999) where magnesite precipitation rates are proportional to the concentration of the >MgOH 2 + surface species. The study of magnesite crystallization using hydrothermal atomic force microscopy (HAFM) demonstrated the consistency of the rates derived from microscopic measurements with those obtained from bulk experiments and showed that these rates are also consistent with a spiral growth mechanism. According to AFM observations this mechanism controls magnesite growth over a wide range of temperatures and saturation states (15≤ Ω ≤200 for 80 ≤T 2 to accelerate the rate of the overall carbonation process, avoiding the inhibiting effect of carbonate ions on magnesite precipitation and increasing the rates of Mg-silicate dissolution via acidification of reacting solutions. Determination of magnesite dissolution rates by mixed flow reactor at 150 and 200 deg. C and at neutral to alkaline conditions allowed us to improve and extend to high temperatures the surface

  5. Improvement of dissolution rate of indomethacin by inkjet printing

    DEFF Research Database (Denmark)

    Wickström, Henrika; Palo, Mirja; Rijckaert, Karen

    2015-01-01

    The aim of this study was to prepare printable inks of the poorly water soluble drug indomethacin (IMC), fabricate printed systems with flexible doses and investigate the effect of ink excipients on the printability, dissolution rate and the solid state properties of the drug. A piezoelectric...... the spectra of the carrier substrate. Yet, the samples retained their yellow color after 6months of storage at room temperature and after drying at elevated temperature in a vacuum oven. This suggests that the samples remained either in a dissolved or an amorphous form. Based on the results from this study...... a formulation guidance for inkjet printing of poorly soluble drugs is also proposed....

  6. Enhancement of dissolution rate of piroxicam by electrospinning technique

    International Nuclear Information System (INIS)

    Begum, S K Raziya; Varma, M Mohan; Raju, D B; Prasad, R G S V; Phani, A R; Jacob, Biju; Salins, Paul C

    2012-01-01

    The use of electrospun nanofibers to enhance dissolution of poorly soluble drugs could be a novel strategy in future for pharmaceutical applications. In the present work electrospun nanofibers were prepared as a novel system for enhancing the delivery of piroxicam, a non-steroidal anti-inflammatory drug (NSAID). These nanofibers were prepared from polyvinyl pyrrolidone (PVP) (pharmaceutical grade), a biodegradable polymer, to obtain a solution with drug:polymer ratio of 1:4. The release rate of the piroxicam nanofibers was studied in simulated gastric fluid. Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) are used to evaluate the chemical and physical nature. The results showed that the release rates were twice increased in comparison with the pure drug. However, the blend of drug and polymer could be varied to optimize the release rates depending upon the need and formulation (paper)

  7. Enhancement of dissolution rate of piroxicam by electrospinning technique

    Science.gov (United States)

    Raziya Begum, S. K.; Mohan Varma, M.; Raju, D. B.; Prasad, R. G. S. V.; Phani, A. R.; Jacob, Biju; Salins, Paul C.

    2012-12-01

    The use of electrospun nanofibers to enhance dissolution of poorly soluble drugs could be a novel strategy in future for pharmaceutical applications. In the present work electrospun nanofibers were prepared as a novel system for enhancing the delivery of piroxicam, a non-steroidal anti-inflammatory drug (NSAID). These nanofibers were prepared from polyvinyl pyrrolidone (PVP) (pharmaceutical grade), a biodegradable polymer, to obtain a solution with drug:polymer ratio of 1:4. The release rate of the piroxicam nanofibers was studied in simulated gastric fluid. Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) are used to evaluate the chemical and physical nature. The results showed that the release rates were twice increased in comparison with the pure drug. However, the blend of drug and polymer could be varied to optimize the release rates depending upon the need and formulation

  8. A porous silica rock ("tripoli") in the footwall of the Jurassic Úrkút manganese deposit, Hungary: composition, and origin through carbonate dissolution

    Science.gov (United States)

    Polgari, Marta; Szabo, Zoltan; Szabo-Drubina, Magda; Hein, James R.; Yeh, Hsueh-Wen

    2005-01-01

    The mineralogical, chemical, and isotopic compositions were determined for a white tripoli from the footwall of the Jurassic Úrkút Mn-oxide ore deposit in the Bakony Mountains, Hungary. The tripoli consists of quartz and chalcedony, with SiO2 contents up to 100 wt.%; consequently, trace-element contents are very low. Oxygen isotopes and quartz crystallinity indicate a low-temperature diagenetic origin for this deposit. The tripoli was formed by dissolution of the carbonate portion of the siliceous (sponge spicules) Isztimér Limestone. Dissolution of the carbonate was promoted by inorganic and organic acids generated during diagensis and left a framework composed of diagenetic silica that preserved the original volume of the limestone layer. The relative enrichment of silica and high porosity is the result of that carbonate dissolution. The silty texture of this highly friable rock is due to the structurally weak silica framework.

  9. Dissolution rate enhancement of repaglinide by solid dispersion

    African Journals Online (AJOL)

    Keywords: Diabetes, Solid dispersion, Repaglinide, Solubility, Dissolution, Burst release. Tropical Journal of ... high lipophilicity (logP = 3.97) and relatively low oral bioavailability (56 .... II drug, i.e., low soluble and high permeable in nature. As.

  10. Permeability change with dissolution and precipitation reaction induced by highly alkaline plume in packed bed with amorphous silica particles

    International Nuclear Information System (INIS)

    Komatsu, Kyo; Kadowaki, Junichi; Niibori, Yuichi; Mimura, Hitoshi; Usui, Hideo

    2008-01-01

    A large amount of cement is used to construct of the geological disposal system. Such a material alters the pH of groundwater to highly alkaline region. The highly alkaline plume contains rich Ca ion compared to the surrounding environment, and the Ca ion reacts with soluble silicic acid. Its product would deposit on the surface of flow-paths in the natural barrier and decrease the permeability. In this study, the influence of Ca ions in highly alkaline plume on flow-paths has been examined by using packed bed column. The column was packed with the amorphous silica particles of 75-150 μm in diameter. The Ca(OH) 2 solution (0.78 mM, 2.58 mM, 4.37 mM, and 8.48 mM, pH: 12.2-12.4) was continuously injected into the column at a constant flow rate (5 ml/min, and 2 ml/min), and the change of permeability was monitored. At the same time, the concentrations of [Ca] total and [Si] in the eluted solution were measured by the inductively coupled plasma atomic emission spectrometry (ICP-AES). The Ca(OH) 2 solutions were prepared with CO 2 -free pure water, and filtrated through 0.45 μm filter. The permeability was normalized by the initial permeability value. In the experiment results, the permeability dramatically changed with increasing Ca concentration, because Ca ions and H 4 SiO 4 (due to the dissolution of SiO 2 ) produce C-S-H gel between the packed particles in the column. The SEM images and XRD analyses showed that the surface of SiO 2 particles was covered with the C-S-H gel precipitation. On the other hand, when the Ca concentration was relatively low, the permeability did not show remarkable change. For the cross section of SiO 2 particles, EPMA analysis suggested the consumption of Ca in the inner pore of the SiO 2 particles. However, the time-change in the concentrations of Si and Ca was not always simple. Such time-change strongly depended not only on pH or Ca concentration, but also on the flow rates. This suggested that mass transport controls the chemical

  11. A Study of Analytical Solution for the Special Dissolution Rate Model of Rock Salt

    Directory of Open Access Journals (Sweden)

    Xin Yang

    2017-01-01

    Full Text Available By calculating the concentration distributions of rock salt solutions at the boundary layer, an ordinary differential equation for describing a special dissolution rate model of rock salt under the assumption of an instantaneous diffusion process was established to investigate the dissolution mechanism of rock salt under transient but stable conditions. The ordinary differential equation was then solved mathematically to give an analytical solution and related expressions for the dissolved radius and solution concentration. Thereafter, the analytical solution was fitted with transient dissolution test data of rock salt to provide the dissolution parameters at different flow rates, and the physical meaning of the analytical formula was also discussed. Finally, the influential factors of the analytical formula were investigated. There was approximately a linear relationship between the dissolution parameters and the flow rate. The effects of the dissolution area and initial volume of the solution on the dissolution rate equation of rock salt were computationally investigated. The results showed that the present analytical solution gives a good description of the dissolution mechanism of rock salt under some special conditions, which may provide a primary theoretical basis and an analytical way to investigate the dissolution characteristics of rock salt.

  12. Biogenic silica dissolution in diatom aggregates: insights from reactive transport modelling

    KAUST Repository

    Moriceau, B; Laruelle, GG; Passow, U; Van Cappellen, P; Ragueneau, O

    2014-01-01

    , dSi transport out of the aggregate is modulated by alternatively considering retention (decrease of the dSi diffusion constant) and adsorption (reversible chemical bonds between dSi and the aggregate matrix) processes. Modelled bSiO2 dissolution

  13. Factors affecting the differences in reactivity and dissolution rates between UO2 and spent nuclear fuel

    International Nuclear Information System (INIS)

    Shoesmith, D.W.; Tait, J.C.; Sunder, S.; Steward, S.; Russo, R.E.; Rudnicki, J.D.

    1996-08-01

    Strategies for the permanent disposal of spent nuclear fuel are being investigated by the U.S. Department of Energy at the Yucca Mountain site and by Atomic Energy of Canada Limited (AECL) in plutonic rock formations in the Canadian Shield. Uranium dioxide is the primary constituent of spent nuclear fuel and dissolution of the matrix is regarded as a necessary step for the release of radionuclides to repository groundwaters. In order to develop models to describe the dissolution of the U0 2 fuel matrix and subsequent release of radionuclides, it is necessary to understand both chemical and oxidative dissolution processes and how they can be affected by parameters such as groundwater composition, pH, temperature, surface area, radiolysis and redox potential. This report summarizes both published and on-going dissolution studies of U0 2 and both LWR and CANDU spent fuels being conducted at the Pacific Northwest Laboratory, Lawrence Livermore National Laboratory and Lawrence Berkeley Laboratory in the U.S. and at AECL's Whiteshell Laboratories in Canada. The studies include both dissolution tests and electrochemical experiments to measure uranium dissolution rates. The report focuses on identifying differences in reactivity towards aqueous dissolution between U0 2 and spent fuel samples as well as estimating bounding values for uranium dissolution rates. This review also outlines the basic tenets for the development of a dissolution model that is based on electrochemical principles. (author). 49 refs., 2 tabs., 11 figs

  14. Development of a novel starch with a three-dimensional ordered macroporous structure for improving the dissolution rate of felodipine

    Energy Technology Data Exchange (ETDEWEB)

    Hao, Yanna; Wu, Chao, E-mail: wuchao27@126.com; Zhao, Zongzhe; Zhao, Ying; Xu, Jie; Qiu, Yang; Jiang, Jie; Yu, Tong; Ma, Chunyu; Zhou, Buyun

    2016-01-01

    In this study, silica nanospheres with different particle sizes were used as hard template for synthesis of a starch with a novel three-dimensional ordered macroporous structure (3DOMTS). As a pharmaceutical adjuvant, 3DOMTS was used to improve the dissolution rate and oral relative bioavailability of water-insoluble drugs. Felodipine (FDP) was chosen as a model drug and was loaded into the 3DOMTS by solvent evaporation. FDP loading into 3DOMTS with different pore sizes was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimeter (DSC), powder X-ray diffractometer (PXRD) and Fourier-Transform Infrared (FTIR). The results obtained showed that FDP was present in the pores in an amorphic or microcrystalline state. The in vitro dissolution results showed that 3DOMTS could effectively improve the dissolution rate of FDP in comparison with commercial common tablets. Pharmacokinetic results indicated that the oral relative bioavailability of self-made FDP–3DOMTS tablets were 184%, showing that 3DOMTS produced a significantly increased oral absorption of FDP. In conclusion, 3DOMTS exhibits the dual potential of improving the dissolution rate of poorly water soluble drugs and the novel filler produced by direct compression technology confirming that 3DOMTS will be useful for many applications in the field of pharmaceutics. - Highlights: • We successfully prepared a starch with a novel three-dimensional ordered macroporous structure (3DOMTS). • 3DOMTS can suppress the crystallinity of the drug to maintain it at amorphous state. • In vivo and in vitro experiments proved that 3DOMTS can improve the solubility and bioavailability of felodipine.

  15. Dissolution rates of airborne uranium in simulated lung fluid

    International Nuclear Information System (INIS)

    Thein, M.; Maitz, A.H.; Austin, M.A.; Rao, G.R.; Gur, D.

    1982-01-01

    The airborne uranium, collected on three sets of air filter samples at different times, near a uranium fuel fabrication plant, was classified to assess the potential radiological and toxicological hazards of respirable particles with aerodynamic equivalent diameters of less than 15 μm. A model was developed to calculate radiation dose from radionuclides deposited in the lung by inhalation. Knowing the solubility category and dissolution half-time, the likely doses to residents near such plants can be assessed. (U.K.)

  16. On the estimate of the rate constant in the homogeneous dissolution model

    Czech Academy of Sciences Publication Activity Database

    Čupera, Jakub; Lánský, Petr

    2013-01-01

    Roč. 39, č. 10 (2013), s. 1555-1561 ISSN 0363-9045 Institutional support: RVO:67985823 Keywords : dissolution * estimation * rate constant Subject RIV: FR - Pharmacology ; Medidal Chemistry Impact factor: 2.006, year: 2013

  17. Dissolution rates of over-the-counter painkillers: a comparison among formulations.

    Science.gov (United States)

    Alemanni, Matteo; Gatoulis, Sergio C; Voelker, Michael

    2016-06-01

    We wanted to compare the dissolution profile of several over-the-counter analgesics to understand whether the different formulation techniques employed to enhance absorption were associated with variations in the dissolution rate, a parameter known to affect drug absorption. We considered 5 formulations currently marketed in Italy: aspirin tablets (Aspirina Dolore e Infiammazione®), ibuprofen tablets and liquid capsules (Moment®), ibuprofen lysine tablets (Nurofenimmedia®) and dexketoprofen trometamol tablets (Enantyum®). Dissolution tests were performed according to the current USP/NF monograph dissolution procedure. Drug dissolution was evaluated at 1, 3, 6, 15, and 30 minutes since the start of the test. Dissolution was evaluated at three different pH: 1.2, 4.5 and 6.8. Every test was repeated 12 times. The aspirin formulation was by far the most rapid dissolving formulation, among those tested, with more than 80% of the tablet dissolved at 6 minutes for every pH considered. At pH 1.2 and 4.5, only the dexketoprofen formulation was able to reach the dissolution level of aspirin at 30 minutes, but had lower levels of dissolution at the previous time points. Instead, at pH 6.8, most of the formulations approached aspirin dissolution level, but only after 15 minutes. Ibuprofen capsules had the slowest kinetics, with a lag phase the first 6 minutes. Different formulation strategies can lead to great differences in the dissolution rates even among drugs of the same class, suggesting that enhancements in the formulation of painkillers can lead to improvements in drug absorption, and thus in the onset of analgesia.

  18. Calculation methods for dissolution rate of multicomponent alloys during electrochemical machining

    International Nuclear Information System (INIS)

    Dikusar, A.I.; Petrenko, V.I.; Dikusar, G.K.; Ehngel'gardt, G.R.; Michukova, N.Yu.

    1981-01-01

    The possibility of theoretical calculation of metal dissolution rate during electrochemical mashining is considered. Two calculation techniques are compared at the example of two-component W-Re, Ni-W, Mo-Re alloys, namely: ''charge superposition'' and ''weight percents''. It is concluded that the technique of ''charge superposition'' is the only grounded calculation technique of specific rates of dissolution for alloys [ru

  19. Reexamining the Dissolution of Spent Fuel: A Comparison of Different Methods for Calculating Rates

    International Nuclear Information System (INIS)

    Hanson, Brady D.; Stout, Ray B.

    2004-01-01

    Dissolution rates for spent fuel have typically been reported in terms of a rate normalized to the surface area of the specimen. Recent evidence has shown that neither the geometric surface area nor that measured with BET accurately predicts the effective surface area of spent fuel. Dissolution rates calculated from results obtained by flowthrough tests were reexamined comparing the cumulative releases and surface area normalized rates. While initial surface area is important for comparison of different rates, it appears that normalizing to the surface area introduces unnecessary uncertainty compared to using cumulative or fractional release rates. Discrepancies in past data analyses are mitigated using this alternative method

  20. Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore.

    Science.gov (United States)

    Fischer, Cornelius; Finkeldei, Sarah; Brandt, Felix; Bosbach, Dirk; Luttge, Andreas

    2015-08-19

    The long-term stability of ceramic materials that are considered as potential nuclear waste forms is governed by heterogeneous surface reactivity. Thus, instead of a mean rate, the identification of one or more dominant contributors to the overall dissolution rate is the key to predict the stability of waste forms quantitatively. Direct surface measurements by vertical scanning interferometry (VSI) and their analysis via material flux maps and resulting dissolution rate spectra provide data about dominant rate contributors and their variability over time. Using pyrochlore (Nd2Zr2O7) pellet dissolution under acidic conditions as an example, we demonstrate the identification and quantification of dissolution rate contributors, based on VSI data and rate spectrum analysis. Heterogeneous surface alteration of pyrochlore varies by a factor of about 5 and additional material loss by chemo-mechanical grain pull-out within the uppermost grain layer. We identified four different rate contributors that are responsible for the observed dissolution rate range of single grains. Our new concept offers the opportunity to increase our mechanistic understanding and to predict quantitatively the alteration of ceramic waste forms.

  1. Controlled precipitation for enhanced dissolution rate of flurbiprofen: development of rapidly disintegrating tablets.

    Science.gov (United States)

    Essa, Ebtessam A; Elmarakby, Amira O; Donia, Ahmed M A; El Maghraby, Gamal M

    2017-09-01

    The aim of this work was to investigate the potential of controlled precipitation of flurbiprofen on solid surface, in the presence or absence of hydrophilic polymers, as a tool for enhanced dissolution rate of the drug. The work was extended to develop rapidly disintegrated tablets. This strategy provides simple technique for dissolution enhancement of slowly dissolving drugs with high scaling up potential. Aerosil was dispersed in ethanolic solution of flurbiprofen in the presence and absence of hydrophilic polymers. Acidified water was added as antisolvent to produce controlled precipitation. The resultant particles were centrifuged and dried at ambient temperature before monitoring the dissolution pattern. The particles were also subjected to FTIR spectroscopic, X-ray diffraction and thermal analyses. The FTIR spectroscopy excluded any interaction between flurbiprofen and excipients. The thermal analysis reflected possible change in the crystalline structure and or crystal size of the drug after controlled precipitation in the presence of hydrophilic polymers. This was further confirmed by X-ray diffraction. The modulation in the crystalline structure and size was associated with a significant enhancement in the dissolution rate of flurbiprofen. Optimum formulations were successfully formulated as rapidly disintegrating tablet with subsequent fast dissolution. Precipitation on a large solid surface area is a promising strategy for enhanced dissolution rate with the presence of hydrophilic polymers during precipitation process improving the efficiency.

  2. Development and characterization of solid dispersion of piroxicam for improvement of dissolution rate using hydrophilic carriers

    Directory of Open Access Journals (Sweden)

    Mohammad Barzegar-jalali

    2014-09-01

    Full Text Available Introduction: The main objective of this study was preparation and characterization of solid dispersion of piroxicam to enhance its dissolution rate. Methods: Solid dispersion formulations with different carriers including crospovidone, microcrystalline cellulose and Elaeagnus angustifolia fruit powder and with different drug: carrier ratios were prepared employing cogrinding method. Dissolution study of the piroxicam powders, physical mixtures and solid dispersions was performed in simulated gastric fluid and simulated intestinal fluid using USP Apparatus type II. The physical characterization of formulations were analyzed using powder X ray diffraction (PXRD, particle size analyzer and differential scanning calorimetry (DSC. Interactions between the drug and carriers were evaluated by Fourier transform infrared (FT-IR spectroscopic method. Results: It was revealed that all of three carriers increase the dissolution rate of piroxicam from physical mixtures and especially in solid dispersions compared to piroxicam pure and treated powders. PXRD and DSC results were confirmed the reduction of crystalline form of piroxicam. FT-IR analysis did not show any physicochemical interaction between drug and carriers in the solid dispersion formulations. Conclusion: Dissolution rate was dependent on the type and ratio of drug: carrier as well as pH of dissolution medium. Dissolution data of formulations were fitted well in to the linear Weibull as well as non-linear logistic and a suggested models.

  3. Carbonate dissolution rates in high salinity brines: Implications for post-Noachian chemical weathering on Mars

    Science.gov (United States)

    Phillips-Lander, Charity M.; Parnell, S. R.; McGraw, L. E.; Elwood Madden, M. E.

    2018-06-01

    A diverse suite of carbonate minerals including calcite (CaCO3) and magnesite (MgCO3) have been observed on the martian surface and in meteorites. Terrestrial carbonates usually form via aqueous processes and often record information about the environment in which they formed, including chemical and textural biosignatures. In addition, terrestrial carbonates are often found in association with evaporite deposits on Earth. Similar high salinity environments and processes were likely active on Mars and some areas may contain active high salinity brines today. In this study, we directly compare calcite and magnesite dissolution in ultrapure water, dilute sulfate and chloride solutions, as well as near-saturated sulfate and chloride brines with known activity of water (aH2O) to determine how dissolution rates vary with mineralogy and aH2O, as well as aqueous cation and anion chemistry to better understand how high salinity fluids may have altered carbonate deposits on Mars. We measured both calcite and magnesite initial dissolution rates at 298 K and near neutral pH (6-8) in unbuffered solutions containing ultrapure water (18 MΩ cm-1 UPW; aH2O = 1), dilute (0.1 mol kg-1; aH2O = 1) and near-saturated Na2SO4 (2.5 mol kg-1, aH2O = 0.92), dilute (0.1 mol kg-1, aH2O = 1) and near-saturated NaCl (5.7 mol kg-1, aH2O = 0.75). Calcite dissolution rates were also measured in dilute and near-saturated MgSO4 (0.1 mol kg-1, aH2O = 1 and 2.7 mol kg-1, aH2O = 0.92, respectively) and MgCl2 (0.1 mol kg-1, aH2O = 1 and 3 mol kg-1, aH2O = 0.73, respectively), while magnesite dissolution rates were measured in dilute and near-saturated CaCl2 (0.1 mol kg-1, aH2O = 1 and 9 mol kg-1, aH2O = 0.35). Initial calcite dissolution rates were fastest in near-saturated MgCl2 brine, while magnesite dissolution rates were fastest in dilute (0.1 mol kg-1) NaCl and CaCl2 solutions. Calcite dissolution rates in near-saturated Na2SO4 were similar to those observed in the dilute solutions (-8.00 ± 0

  4. Dissolution rate and radiation dosimetry of metal tritides

    International Nuclear Information System (INIS)

    Jow, Hong-Nian; Cheng, Yung-Sung

    1993-01-01

    Metal tritides including titanium tritide (Ti 3 H x ) and erbium tritide (Er 3 H x ) have been used as components of neutron generators. These compounds can be released to the air as aerosols during fabrication, assembling and testing of components or in accidental or fugitive releases. As a result, workers could be exposed to these compounds by inhalation. A joint research project between SNL and ITRI (Inhalation Toxicology Research Institute) was initiated last fall to investigate the solubility of metal tritides, retention and translocation of inhaled particles and internal dosimetry of metal tritides. The current understanding of metal tritides and their radiation dosimetry for internal exposure are very limited. There is no provision in the ICRP-30 for tritium dosimetry in metal tritide form. However, a few papers in the literature suggested that the solubility of metal tritide could be low. The current radiation protection guidelines for metal tritide particles are based on the assumption that the biological behavior is similar to tritiated water which behaves like body fluid with a relative short biological half life (10 days). If the solubility of metal tritide is low, the biological half life of metal tritide particles and the dosimetry of inhalation exposure to these particles could be quite different from tritiated water. This would have major implications in current radiation protection guidelines for metal tritides Including annual limits of intakes and derived air concentrations. The preliminary results of metal tritide dissolution study at ITRI indicate that the solubility of titanium tritide is low. The outlines of the project, the preliminary results and future work will be discussed in presentation

  5. From laboratory experiments to a geological disposal vault: calculation of used nuclear fuel dissolution rates

    International Nuclear Information System (INIS)

    Sunder, S.; Shoesmith, D.W.; Kolar, M.; Leneveu, D.M.

    1998-01-01

    Calculation of used nuclear fuel dissolution rates in a geological disposal vault requires a knowledge of the redox conditions in the vault. For redox conditions less oxidizing than those causing UO 2 oxidation to the U 3 O 7 , stage, a thermodynamically-based model is appropriate. For more oxidizing redox conditions a kinetic or an electrochemical model is needed to calculate these rates. The redox conditions in a disposal vault will be affected by the radiolysis of groundwater by the ionizing radiation associated with the fuel. Therefore, we have calculated the alpha-, beta- and gamma-dose rates in water in contact with the reference used fuel in the Canadian Nuclear Fuel Waste Management Program (CNFWMP) as a function of cooling time. Also, we have determined dissolution rates of UO 2 fuel as a function of alpha and gamma dose rates from our electrochemical measurements. These room-temperature rates are used to calculate the dissolution rates of used fuel at 100 o C, the highest temperature expected in a container in the CNFWMP, as a function of time since emplacement. It is shown that beta radiolysis of water will be the main cause of oxidation of used CANDU fuel in a failed container. The use of a kinetic or an electrochemical corrosion model, to calculate fuel dissolution rates, is required for a period of ∼1000 a following emplacement of copper containers in the geologic disposal vault envisaged in the CNFWMP. Beyond this time period a thermodynamically-based model adequately predicts the fuel dissolution rates. The results presented in this paper can be adopted to calculate used fuel dissolution rates for other used UO 2 fuels in other waste management programs. (author)

  6. Comparison of uranium dissolution rates from spent fuel and uranium dioxide

    International Nuclear Information System (INIS)

    Steward, S.A.; Gray, W.J.

    1994-01-01

    Two similar sets of dissolution experiments, resulting from a statistical experimental design were performed in order to examine systematically the effects of temperature (25--75 degree C), dissolved oxygen (0.002-0.2 atm overpressure), pH (8--10) and carbonate concentrations (2--200 x 10 -4 molar) on aqueous dissolution of UO 2 and spent fuel. The average dissolution rate was 8.6 mg/m 2 ·day for UO 2 and 3.1 mg/m 2 ·day for spent fuel. This is considered to be an insignificant difference; thus, unirradiated UO 2 and irradiated spent fuel dissolved at about the same rate. Moreover, regression analyses indicated that the dissolution rates of UO 2 and spent fuel responded similarly to changes in pH, temperature, and carbonate concentration. However, the two materials responded very differently to dissolved oxygen concentration. Approximately half-order reaction rates with respect to oxygen concentration were found for UO 2 at all conditions tested. At room temperature, spent fuel dissolution (reaction) rates were nearly independent of oxygen concentration. At 75 degree C, reaction orders of 0.35 and 0.73 were observed for spent fuel, and there was some indication that the reaction order with respect to oxygen concentration might be dependent on pH and/or carbonate concentration as well as on temperature

  7. Constraints on the affinity term for modeling long-term glass dissolution rates

    International Nuclear Information System (INIS)

    Bourcier, W.L.; Carroll, S.A.; Phillips, B.L.

    1993-11-01

    Predictions of long-term glass dissolution rates are highly dependent on the form of the affinity term in the rate expression. Analysis of the quantitative effect of saturation state on glass dissolution rate for CSG glass (a simple analog of SRL-165 glass), shows that a simple (1-Q/K) affinity term does not match experimental results. Our data at 100 degree C show that the data is better fit by an affinity term having the form (1 - (Q/K) 1 /σ) where σ = 10

  8. Chitosan and chitosan chlorhydrate based various approaches for enhancement of dissolution rate of carvedilol

    Directory of Open Access Journals (Sweden)

    Shete Amol S

    2012-12-01

    Full Text Available Abstract Background and the purpose of the study Carvedilol nonselective β-adrenoreceptor blocker, chemically (±-1-(Carbazol-4-yloxy-3-[[2-(o-methoxypHenoxy ethyl] amino]-2-propanol, slightly soluble in ethyl ether; and practically insoluble in water, gastric fluid (simulated, TS, pH 1.1, and intestinal fluid (simulated, TS without pancreatin, pH 7.5 Compounds with aqueous solubility less than 1% W/V often represents dissolution rate limited absorption. There is need to enhance the dissolution rate of carvedilol. The objective of our present investigation was to compare chitosan and chitosan chlorhydrate based various approaches for enhancement of dissolution rate of carvedilol. Methods The different formulations were prepared by different methods like solvent change approach to prepare hydrosols, solvent evaporation technique to form solid dispersions and cogrind mixtures. The prepared formulations were characterized in terms of saturation solubility, drug content, infrared spectroscopy (FTIR, differential scanning calorimetry (DSC, powder X-ray diffraction (PXRD, electron microscopy, in vitro dissolution studies and stability studies. Results The practical yield in case of hydrosols was ranged from 59.76 to 92.32%. The drug content was found to uniform among the different batches of hydrosols, cogrind mixture and solid dispersions ranged from 98.24 to 99.89%. There was significant improvement in dissolution rate of carvedilol with chitosan chlorhdyrate as compare to chitosan and explanation to this behavior was found in the differences in the wetting, solubilities and swelling capacity of the chitosan and chitosan salts, chitosan chlorhydrate rapidly wet and dissolve upon its incorporation into the dissolution medium, whereas the chitosan base, less water soluble, would take more time to dissolve. Conclusion This technique is scalable and valuable in manufacturing process in future for enhancement of dissolution of poorly water soluble

  9. Mechanisms and kinetics laws of inactive R7T7 reference glass dissolution in water at 90 deg C: initial dissolution rate measurements

    International Nuclear Information System (INIS)

    Advocat, T.; Ghaleb, D.; Vernaz, E.

    1993-02-01

    The initial dissolution rate of inactive R7T7 reference glass was measured at 90 deg C in dilute aqueous solutions first at unspecified pH, then with imposed pH values. In distilled water, R7T7 glass corrosion initially involved preferential extraction of boron and network modifier elements (Li, Na, Ca) as long as the solution pH remained acid. When the solution pH became alkaline, glass dissolution was stoichiometric. These two mechanisms were confirmed by dissolution tests in aqueous solutions at imposed pH values under acid and alkaline conditions. The initial dissolution rate r 0 in mole.cm -3 .s -1 also increased significantly in alkaline media when the pH of the aqueous phase increased: in slightly acid media, selective glass dissolution formed a residual, de-alkalinized, hydrated glass that was characterized by transmission electron microscopy and secondary ion mass spectrometry. Under steady-state dissolution conditions, the initial glass corrosion rate (in mole.cm -3 .s -1 ) was: in acid and alkaline media, amorphous and crystallized alteration products formed after complete dissolution of the silicated glass network. The first products formed consisted mainly of Zr, Rare Earths, Fe and Al. (author). 67 refs., 29 figs., 26 tabs., 21 plates

  10. Silica coatings on clarithromycin.

    Science.gov (United States)

    Bele, Marjan; Dmitrasinovic, Dorde; Planinsek, Odon; Salobir, Mateja; Srcic, Stane; Gaberscek, Miran; Jamnik, Janko

    2005-03-03

    Pre-crystallized clarithromycin (6-O-methylerythromycin A) particles were coated with silica from the tetraethyl orthosilicate (TEOS)-ethanol-aqueous ammonia system. The coatings had a typical thickness of 100-150 nm and presented about 15 wt.% of the silica-drug composite material. The properties of the coatings depended on reactant concentration, temperature and mixing rate and, in particular, on the presence of a cationic surfactant (cetylpyridinium chloride). In the presence of cetylpyridinium chloride the silica coatings slightly decreased the rate of pure clarithromycin dissolution.

  11. Diurnal variation in rates of calcification and carbonate sediment dissolution in Florida Bay

    Science.gov (United States)

    Yates, K.K.; Halley, R.B.

    2006-01-01

    Water quality and circulation in Florida Bay (a shallow, subtropical estuary in south Florida) are highly dependent upon the development and evolution of carbonate mud banks distributed throughout the Bay. Predicting the effect of natural and anthropogenic perturbations on carbonate sedimentation requires an understanding of annual, seasonal, and daily variations in the biogenic and inorganic processes affecting carbonate sediment precipitation and dissolution. In this study, net calcification rates were measured over diurnal cycles on 27 d during summer and winter from 1999 to 2003 on mud banks and four representative substrate types located within basins between mud banks. Substrate types that were measured in basins include seagrass beds of sparse and intermediate density Thalassia sp., mud bottom, and hard bottom communities. Changes in total alkalinity were used as a proxy for calcification and dissolution. On 22 d (81%), diurnal variation in rates of net calcification was observed. The highest rates of net carbonate sediment production (or lowest rates of net dissolution) generally occurred during daylight hours and ranged from 2.900 to -0.410 g CaCO3 m-2 d-1. The lowest rates of carbonate sediment production (or net sediment dissolution) occurred at night and ranged from 0.210 to -1.900 g CaCO3 m -2 night-1. During typical diurnal cycles, dissolution during the night consumed an average of 29% of sediment produced during the day on banks and 68% of sediment produced during the day in basins. Net sediment dissolution also occurred during daylight, but only when there was total cloud cover, high turbidity, or hypersalinity. Diurnal variation in calcification and dissolution in surface waters and surface sediments of Florida Bay is linked to cycling of carbon dioxide through photosynthesis and respiration. Estimation of long-term sediment accumulation rates from diurnal rates of carbonate sediment production measured in this study indicates an overall average

  12. Dissolution rate of alpha-doped UO2 in natural groundwater

    International Nuclear Information System (INIS)

    Ollila, Kaija; Myllykylä, Emmi; Tanhua-Tyrkkö, Merja; Lavonen, Tiina

    2013-01-01

    The objective of this work is to determine whether the presence of trace elements in natural groundwaters affects the dissolution rate of uranium dioxide in the presence of alpha radiation that causes radiolysis of water. The study is a part of the project Reducing Uncertainty in Performance Prediction (REDUPP) under the Seventh Framework Programme of the European Atomic Energy Community (EURATOM). The project aims to reduce uncertainties related to the extrapolation of the results of laboratory experiments to the conditions expected under geologic disposal. Thus far, synthetic groundwater has been normally used in the experiments. The synthetic groundwaters used do not contain all of the chemical elements that occur in natural groundwaters. Three natural groundwaters were chosen for the dissolution experiments with 0%, 5%, and 10% 233 U-doped UO 2 samples. These include a brackish groundwater, a saline groundwater and a low ionic strength groundwater. At the time of writing this paper, the dissolution experiments have been finished in the first groundwater, which was a moderately saline, brackish groundwater. The groundwater samples for the experiments were taken from a borehole in the Olkiluoto site in Finland. The measurements for dissolution rates were conducted under reducing conditions established using metallic iron in solution and an argon atmosphere in the glove box. The isotope dilution method was used to decrease uncertainties due to precipitation and sorption effects. The resulting dissolution rates in OL-KR6 natural groundwater were generally somewhat higher than the rates measured previously in synthetic groundwaters under similar redox conditions. No clear effect of alpha radiolysis could be seen for tests with lower SA/V, while those for higher SA/V indicated that the dissolution rate was higher for the 10% 233 U-doped UO 2 , suggesting the effect of alpha radiolysis under these conditions

  13. Comparison of two lung clearance models based on the dissolution rates of oxidized depleted uranium

    International Nuclear Information System (INIS)

    Crist, K.C.

    1984-10-01

    An in-vitro dissolution study was conducted on two respirable oxidized depleted uranium samples. The dissolution rates generated from this study were then utilized in the International Commission on Radiological Protection Task Group lung clearance model and a lung clearance model proposed by Cuddihy. Predictions from both models based on the dissolution rates of the amount of oxidized depleted uranium that would be cleared to blood from the pulmonary region following an inhalation exposure were compared. It was found that the predictions made by both models differed considerably. The difference between the predictions was attributed to the differences in the way each model perceives the clearance from the pulmonary region. 33 references, 11 figures, 9 tables

  14. Comparison of two lung clearance models based on the dissolution rates of oxidized depleted uranium

    Energy Technology Data Exchange (ETDEWEB)

    Crist, K.C.

    1984-10-01

    An in-vitro dissolution study was conducted on two respirable oxidized depleted uranium samples. The dissolution rates generated from this study were then utilized in the International Commission on Radiological Protection Task Group lung clearance model and a lung clearance model proposed by Cuddihy. Predictions from both models based on the dissolution rates of the amount of oxidized depleted uranium that would be cleared to blood from the pulmonary region following an inhalation exposure were compared. It was found that the predictions made by both models differed considerably. The difference between the predictions was attributed to the differences in the way each model perceives the clearance from the pulmonary region. 33 references, 11 figures, 9 tables.

  15. The dissolution rate of silicate glasses and minerals: an alternative model based on several activated complexes

    International Nuclear Information System (INIS)

    Berger, G.

    1997-01-01

    Most of the mineral reactions in natural water-rock systems progress at conditions close to the chemical equilibrium. The kinetics of these reactions, in particular the dissolution rate of the primary minerals, is a major constrain for the numerical modelling of diagenetic and hydrothermal processes. In the case of silicates, recent experimental studies have pointed out the necessity to better understand the elementary reactions which control the dissolution process. This article presents several models that have been proposed to account for the observed dissolution rate/chemical affinity relationships. The case of glasses (R7T7), feldspars and clays, in water, in near neutral pH aqueous solutions and in acid/basic media, are reviewed. (A.C.)

  16. Differing disintegration and dissolution rates, pharmacokinetic profiles and gastrointestinal tolerability of over the counter ibuprofen formulations.

    Science.gov (United States)

    Bjarnason, Ingvar; Sancak, Ozgur; Crossley, Anne; Penrose, Andrew; Lanas, Angel

    2018-02-01

    Formulations of over the counter (OTC) NSAIDs differ substantially, but information is lacking on whether this alters their gastrointestinal profiles. To assess disintegration and dissolution rates and pharmacokinetics of four preparations of OTC ibuprofen and relate these with spontaneously reported gastrointestinal adverse events. Disintegration and dissolution rates of ibuprofen tablets as (a) acid, (b) sodium salt, (c) lysine salt, and (d) as a liquid gelatine capsule were assessed. Pharmacokinetic data gastrointestinal and spontaneously reported adverse events arising from global sales were obtained from files from Reckitt Benckiser. Disintegration at low pH was progressively shorter for the preparations from a-to-d with formation of correspondingly smaller ibuprofen crystals, while dissolution was consistently poor. Dissolution at a neutral pH was least rapid for the liquid gelatine capsule. Pharmacokinetic data showed a shorter t max and a higher C max for preparations b-d as compared with ibuprofen acid. Spontaneously reported abdominal symptoms were rare with the liquid gelatine preparation. The formulations of OTC ibuprofen differ in their disintegration and dissolution properties, pharmacokinetic profiles and apparent gastrointestinal tolerability. Spontaneously reported abdominal symptoms were five times lower with the liquid gelatine capsule as compared with ibuprofen acid despite a 30% increase in C max . © 2017 Royal Pharmaceutical Society.

  17. Use of the liquisolid compact technique for improvement of the dissolution rate of valsartan

    Directory of Open Access Journals (Sweden)

    Naveen Chella

    2012-10-01

    Full Text Available The aim of this study was to improve the dissolution rate of the poorly soluble drug valsartan by delivering the drug as a liquisolid compact. Liquisolid compacts were prepared using propylene glycol as solvent, Avicel PH102 as carrier, and Aerosil 200 as the coating material. The crystallinity of the newly formulated drug and the interaction between excipients was examined by X-ray powder diffraction and Fourier-transform infrared spectroscopy, respectively. The dissolution studies for the liquisolid formulation and the marketed product were carried out at different pH values. The results showed no change in the crystallinity of the drug and no interaction between excipients. The dissolution efficiency of valsartan at 15 min was increased from 4.02% for plain drug and 13.58% for marketed product to 29.47% for the liquisolid formulation. The increase in the dissolution rate was also found to be significant compared to the marketed product at lower pH values, simulating the gastric environment where valsartan is largely absorbed. The liquisolid technique appears to be a promising approach for improving the dissolution of poorly soluble drugs like valsartan.

  18. Low dose rate gamma ray induced loss and data error rate of multimode silica fibre links

    International Nuclear Information System (INIS)

    Breuze, G.; Fanet, H.; Serre, J.

    1993-01-01

    Fiber optics data transmission from numerous multiplexed sensors, is potentially attractive for nuclear plant applications. Multimode silica fiber behaviour during steady state gamma ray exposure is studied as a joint programme between LETI CE/SACLAY and EDF Renardieres: transmitted optical power and bit error rate have been measured on a 100 m optical fiber

  19. Humid storage conditions increase the dissolution rate of diazepam from solid dispersions prepared by melt agglomeration

    DEFF Research Database (Denmark)

    Jørgensen, Anna Cecilia; Torstenson, Anette Seo

    2008-01-01

    The purpose of this study is to investigate the effect of cooling mode and storage conditions on the dissolution rate of a solid dispersion prepared by melt agglomeration. The aim has been to relate this effect to the solid state properties of the agglomerates. The cooling mode had an effect on t...

  20. Dissolution rate measurements of sea water soluble pigments for antifouling paints

    DEFF Research Database (Denmark)

    Yebra, Diego Meseguer; Kiil, Søren; Erik Weinell, Claus

    2006-01-01

    The dissolution of soluble pigments from both tin-based and tin-free chemically active antifouling (AF) paints is a key process influencing their polishing and biocide leaching rates. In this context, a low time- and resources-consuming method capable of screening the pigment behaviour in the sea...

  1. Influence of pH and temperature on alunite dissolution rates and products

    Science.gov (United States)

    Acero, Patricia; Hudson-Edwards, Karen

    2015-04-01

    Aluminium is one of the main elements in most mining-affected environments, where it may influence the mobility of other elements and play a key role on pH buffering. Moreover, high concentrations of Al can have severe effects on ecosystems and humans; Al intake, for example, has been implicated in neurological pathologies (e.g., Alzheimer's disease; Flaten, 2001). The behaviour of Al in mining-affected environments is commonly determined, at least partially, by the dissolution of Al sulphate minerals and particularly by the dissolution of alunite (KAl3(SO4)2(OH)6), which is one of the most important and ubiquitous Al sulphates in mining-affected environments (Nordstrom, 2011). The presence of alunite has been described in other acid sulphate environments, including some soils (Prietzel & Hirsch, 1998) and on the surface of Mars (Swayze et al., 2008). Despite the important role of alunite, its dissolution rates and products, and their controlling factors under conditions similar to those found in these environments, remain largely unknown. In this work, batch dissolution experiments have been carried out in order to shed light on the rates, products and controlling factors of alunite dissolution under different pH conditions (between 3 and 8) and temperatures (between 279 and 313K) similar to those encountered in natural systems. The obtained initial dissolution rates using synthetic alunite, based on the evolution of K concentrations, are between 10-9.7 and 10-10.9 mol-m-2-s-1, with the lowest rates obtained at around pH 4.8, and increases in the rates recorded with both increases and decreases in pH. Increases of temperature in the studied range also cause increases in the dissolution rates. The dissolution of alunite dissolution is incongruent, as has been reported for jarosite (isostructural with alunite) by Welch et al. (2008). Compared with the stoichiometric ratio in the bulk alunite (Al/K=3), K tends to be released to the solution preferentially over Al

  2. Effects of ocean acidification on the dissolution rates of reef-coral skeletons

    Directory of Open Access Journals (Sweden)

    Robert van Woesik

    2013-11-01

    Full Text Available Ocean acidification threatens the foundation of tropical coral reefs. This study investigated three aspects of ocean acidification: (i the rates at which perforate and imperforate coral-colony skeletons passively dissolve when pH is 7.8, which is predicted to occur globally by 2100, (ii the rates of passive dissolution of corals with respect to coral-colony surface areas, and (iii the comparative rates of a vertical reef-growth model, incorporating passive dissolution rates, and predicted sea-level rise. By 2100, when the ocean pH is expected to be 7.8, perforate Montipora coral skeletons will lose on average 15 kg CaCO3 m−2 y−1, which is approximately −10.5 mm of vertical reduction of reef framework per year. This rate of passive dissolution is higher than the average rate of reef growth over the last several millennia and suggests that reefs composed of perforate Montipora coral skeletons will have trouble keeping up with sea-level rise under ocean acidification. Reefs composed of primarily imperforate coral skeletons will not likely dissolve as rapidly, but our model shows they will also have trouble keeping up with sea-level rise by 2050.

  3. The dissolution rate constant of magnetite in water at different temperatures and pH conditions

    International Nuclear Information System (INIS)

    Mohajery, Khatereh; Deydier de Pierrefeu, Laurent; Lister, Derek H.

    2012-09-01

    Under the nominal conditions of power system coolants, the corrosion of components made of carbon steel is limited by the magnetite films that develop on surfaces. In some situations, the magnetite film loses much of its protective ability and corrosion and loss of iron to the system are exacerbated. Common examples of such situations occur when the system is non-isothermal so that temperature gradients cause differences in magnetite solubility around the circuit; the resulting areas of under-saturation in iron give rise to dissolution of normally protective films. Condensing steam in two-phase systems may also promote oxide dissolution. When the turbulence in the system is high, oxide degradation is aggravated and flow-accelerated corrosion (FAC) results. The subsequent increased loading of systems with iron leads to fouling of flow passages and heat transfer surfaces and in reactor primary coolants to rising radiation fields, while FAC can have disastrous results in terms of pipe wall thinning and eventual rupture. Magnetite dissolution is clearly a key contributor to these processes. Thus, the conventional mechanistic description of FAC postulates magnetite dissolution in series with mass transfer of iron from the film to the bulk coolant. In the resulting equations, if the dissolution rate constant is considerably less than the mass transfer coefficient for a particular situation, dissolution will control and flow should have no effect. This is clearly untenable for FAC, so it is often assumed that mass transfer controls and the contribution from oxide dissolution is ignored - on occasion when data on dissolution kinetics are available and sometimes when those data show that dissolution should control. In most cases, however, dissolution rate constants for magnetite are not available. At UNB Nuclear we have a research program using a high-temperature loop to measure dissolution rates of magnetite in water under various conditions of flow, temperature and

  4. Effect of Callovo-Oxfordian clay rock on the dissolution rate of the SON68 simulated nuclear waste glass

    Energy Technology Data Exchange (ETDEWEB)

    Neeway, James J., E-mail: James.Neeway@pnnl.gov [SUBATECH, Unité Mixte de Recherche 6457, École des Mines de Nantes, CNRS/IN2P3, Université de Nantes, BP 20722, 44307 Nantes cedex 3 (France); Abdelouas, Abdesselam; Ribet, Solange; El Mendili, Yassine [SUBATECH, Unité Mixte de Recherche 6457, École des Mines de Nantes, CNRS/IN2P3, Université de Nantes, BP 20722, 44307 Nantes cedex 3 (France); Schumacher, Stéphan [ANDRA, Parc de la Croix Blanche, 1/7 rue Jean Monnet, 92298 Châtenay-Malabry (France); Grambow, Bernd [SUBATECH, Unité Mixte de Recherche 6457, École des Mines de Nantes, CNRS/IN2P3, Université de Nantes, BP 20722, 44307 Nantes cedex 3 (France)

    2015-04-15

    Long-term storage of high-level nuclear waste glass in France is expected to occur in an engineered barrier system (EBS) located in a subsurface Callovo-Oxfordian (COx) clay rock formation in the Paris Basin in northeastern France. Understanding the behavior of glass dissolution in the complex system is critical to be able to reliably model the performance of the glass in this complex environment. To simulate this multi-barrier repository scenario in the laboratory, several tests have been performed to measure glass dissolution rates of the simulated high-level nuclear waste glass, SON68, in the presence of COx claystone at 90 °C. Experiments utilized a High-Performance Liquid Chromatography (HPLC) pump to pass simulated Bure site COx pore water through a reaction cell containing SON68 placed between two COx claystone cores for durations up to 200 days. Silicon concentrations at the outlet were similar in all experiments, even the blank experiment with only the COx claystone (∼4 mg/L at 25 °C and ∼15 mg/L at 90 °C). The steady-state pH of the effluent, measured at room temperature, was roughly 7.1 for the blank and 7.3–7.6 for the glass-containing experiments demonstrating the pH buffering capacity of the COx claystone. Dissolution rates for SON68 in the presence of the claystone were elevated compared to those obtained from flow-through experiments conducted with SON68 without claystone in silica-saturated solutions at the same temperature and similar pH values. Additionally, through surface examination of the monoliths, the side of the monolith in direct contact with the claystone was seen to have a corrosion thickness 2.5× greater than the side in contact with the bulk glass powder. Results from one experiment containing {sup 32}Si-doped SON68 also suggest that the movement of Si through the claystone is controlled by a chemically coupled transport with a Si retention factor, K{sub d}, of 900 mL/g.

  5. Spent fuel dissolution rates as a function of burnup and water chemistry

    International Nuclear Information System (INIS)

    Gray, W.J.

    1998-06-01

    To help provide a source term for performance-assessment calculations, dissolution studies on light-water-reactor (LWR) spent fuel have been conducted over the past few years at Pacific Northwest National Laboratory in support of the Yucca Mountain Site Characterization Project. This report describes that work for fiscal years 1996 through mid-1998 and includes summaries of some results from previous years for completeness. The following conclusions were based on the results of various flowthrough dissolution rate tests and on tests designed to measure the inventories of 129 I located within the fuel/cladding gap region of different spent fuels: (1) Spent fuels with burnups in the range 30 to 50 MWd/kgM all dissolved at about the same rate over the conditions tested. To help determine whether the lack of burnup dependence extends to higher and lower values, tests are in progress or planned for spent fuels with burnups of 13 and ∼ 65 MWd/kgM. (2) Oxidation of spent fuel up to the U 4 O 9+x stage does not have a large effect on intrinsic dissolution rates. However, this degree of oxidation could increase the dissolution rates of relatively intact fuel by opening the grain boundaries, thereby increasing the effective surface area that is available for contact by water. From a disposal viewpoint, this is a potentially more important consideration than the effect on intrinsic rates. (3) The gap inventories of 129 I were found to be smaller than the fission gas release (FGR) for the same fuel rod with the exception of the rod with the highest FGR. Several additional fuels would have to be tested to determine whether a generalized relationship exists between FGR and 129 I gap inventory for US LWR fuels

  6. Aqueous corrosion of french R7T7 nuclear waste glass: selective then congruent dissolution by pH increase

    International Nuclear Information System (INIS)

    Advocat, T.; Vernaz, E.; Crovisier, J.L.

    1991-01-01

    A study of the corrosion of a borosilicate nuclear glass shows the strong effect of the pH on the dissolution mechanism. Acidic media lead to selective extraction of the glass modifier elements (Li, Na, Ca) as well as B, while dissolution is congruent under alkaline conditions. The silica dissolution rate significantly increases with increasing pH [fr

  7. The Influence of Pressure on the Intrinsic Dissolution Rate of Amorphous Indomethacin

    Directory of Open Access Journals (Sweden)

    Korbinian Löbmann

    2014-08-01

    Full Text Available New drug candidates increasingly tend to be poorly water soluble. One approach to increase their solubility is to convert the crystalline form of a drug into the amorphous form. Intrinsic dissolution testing is an efficient standard method to determine the intrinsic dissolution rate (IDR of a drug and to test the potential dissolution advantage of the amorphous form. However, neither the United States Pharmacopeia (USP nor the European Pharmacopeia (Ph.Eur state specific limitations for the compression pressure in order to obtain compacts for the IDR determination. In this study, the influence of different compression pressures on the IDR was determined from powder compacts of amorphous (ball-milling indomethacin (IND, a glass solution of IND and poly(vinylpyrrolidone (PVP and crystalline IND. Solid state properties were analyzed with X-ray powder diffraction (XRPD and the final compacts were visually observed to study the effects of compaction pressure on their surface properties. It was found that there is no significant correlation between IDR and compression pressure for crystalline IND and IND–PVP. This was in line with the observation of similar surface properties of the compacts. However, compression pressure had an impact on the IDR of pure amorphous IND compacts. Above a critical compression pressure, amorphous particles sintered to form a single compact with dissolution properties similar to quench-cooled disc and crystalline IND compacts. In such a case, the apparent dissolution advantage of the amorphous form might be underestimated. It is thus suggested that for a reasonable interpretation of the IDR, surface properties of the different analyzed samples should be investigated and for amorphous samples the IDR should be measured also as a function of the compression pressure used to prepare the solid sample for IDR testing.

  8. Examining the Conservatisms in Dissolution Rates of Commercial Spent Nuclear Fuel

    International Nuclear Information System (INIS)

    Hanson, Brady D.

    2008-01-01

    Most models for commercial spent nuclear fuel dissolution are based on data obtained from single-pass flow-through tests. These tests are designed to have a high water volume to fuel surface area ratio so that the concentration of radionuclides in solution are below solubility limits and thus back reactions and the formation of alteration products are minimized. While this method is ideal for determining the dependence of the dissolution rate on various parameters, it is important to examine the differences between these tests and the realistic scenarios that will exist in a geologic repository. Many of the inherent conservatisms that are part of the models are examined. These conservatisms include: limited water, short-term vs. long-term rates, groundwater effects, non-congruent release, radiolysis, and fuel chemistry effects. Each of these conservatisms has the potential to decrease the currently modeled dissolution rates by between a factor of 2 and 200. The combined effects are unknown, but, if quantified, could significantly improve the waste form performance relative to current models.

  9. Effect of Phosphate, Fluoride, and Nitrate on Gibbsite Dissolution Rate and Solubility

    International Nuclear Information System (INIS)

    Herting, Daniel L.

    2014-01-01

    Laboratory tests have been completed with simulated tank waste samples to investigate the effects of phosphate, fluoride, and nitrate on the dissolution rate and equilibrium solubility of gibbsite in sodium hydroxide solution at 22 and 40 deg C. Results are compared to relevant literature data and to computer model predictions. The presence of sodium nitrate (3 M) caused a reduction in the rate of gibbsite dissolution in NaOH, but a modest increase in the equilibrium solubility of aluminum. The increase in solubility was not as large, though, as the increase predicted by the computer model. The presence of phosphate, either as sodium phosphate or sodium fluoride phosphate, had a negligible effect on the rate of gibbsite dissolution, but caused a slight increase in aluminum solubility. The magnitude of the increased solubility, relative to the increase caused by sodium nitrate, suggests that the increase is due to ionic strength (or water activity) effects, rather than being associated with the specific ion involved. The computer model predicted that phosphate would cause a slight decrease in aluminum solubility, suggesting some Al-PO4 interaction. No evidence was found of such an interaction

  10. Exploitation of 3D face-centered cubic mesoporous silica as a carrier for a poorly water soluble drug: influence of pore size on release rate.

    Science.gov (United States)

    Zhu, Wenquan; Wan, Long; Zhang, Chen; Gao, Yikun; Zheng, Xin; Jiang, Tongying; Wang, Siling

    2014-01-01

    The purposes of the present work were to explore the potential application of 3D face-centered cubic mesoporous silica (FMS) with pore size of 16.0nm as a delivery system for poorly soluble drugs and investigate the effect of pore size on the dissolution rate. FMS with different pore sizes (16.0, 6.9 and 3.7nm) was successfully synthesized by using Pluronic block co-polymer F127 as a template and adjusting the reaction temperatures. Celecoxib (CEL), which is a BCS class II drug, was used as a model drug and loaded into FMS with different pore sizes by the solvent deposition method at a drug-silica ratio of 1:4. Characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformation infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), nitrogen adsorption, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) was used to systematically investigate the drug loading process. The results obtained showed that CEL was in a non-crystalline state after incorporation of CEL into the pores of FMS-15 with pore size of 16.0nm. In vitro dissolution was carried out to demonstrate the effects of FMS with different pore sizes on the release of CEL. The results obtained indicated that the dissolution rate of CEL from FMS-15 was significantly enhanced compared with pure CEL. This could be explained by supposing that CEL encountered less diffusion resistance and its crystallinity decreased due to the large pore size of 16.0nm and the nanopore channels of FMS-15. Moreover, drug loading and pore size both play an important role in enhancing the dissolution properties for the poorly water-soluble drugs. As the pore size between 3.7 and 16.0nm increased, the dissolution rate of CEL from FMS gradually increased. © 2013.

  11. Determining the dissolution rates of actinide glasses: A time and temperature Product Consistency Test study

    International Nuclear Information System (INIS)

    Daniel, W.E.; Best, D.R.

    1995-01-01

    Vitrification has been identified as one potential option for the e materials such as Americium (Am), Curium (Cm), Neptunium (Np), and Plutonium (Pu). A process is being developed at the Savannah River Site to safely vitrify all of the highly radioactive Am/Cm material and a portion of the fissile (Pu) actinide materials stored on site. Vitrification of the Am/Cm will allow the material to be transported and easily stored at the Oak Ridge National Laboratory. The Am/Cm glass has been specifically designed to be (1) highly durable in aqueous environments and (2) selectively attacked by nitric acid to allow recovery of the valuable Am and Cm isotopes. A similar glass composition will allow for safe storage of surplus plutonium. This paper will address the composition, relative durability, and dissolution rate characteristics of the actinide glass, Loeffler Target, that will be used in the Americium/Curium Vitrification Project at Westinghouse Savannah River Company near Aiken, South Carolina. The first part discusses the tests performed on the Loeffler Target Glass concerning instantaneous dissolution rates. The second part presents information concerning pseudo-activation energy for the one week glass dissolution process

  12. Exploitation of 3D face-centered cubic mesoporous silica as a carrier for a poorly water soluble drug: Influence of pore size on release rate

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Wenquan; Wan, Long; Zhang, Chen; Gao, Yikun; Zheng, Xin; Jiang, Tongying; Wang, Siling, E-mail: silingwang@syphu.edu.cn

    2014-01-01

    The purposes of the present work were to explore the potential application of 3D face-centered cubic mesoporous silica (FMS) with pore size of 16.0 nm as a delivery system for poorly soluble drugs and investigate the effect of pore size on the dissolution rate. FMS with different pore sizes (16.0, 6.9 and 3.7 nm) was successfully synthesized by using Pluronic block co-polymer F127 as a template and adjusting the reaction temperatures. Celecoxib (CEL), which is a BCS class II drug, was used as a model drug and loaded into FMS with different pore sizes by the solvent deposition method at a drug–silica ratio of 1:4. Characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformation infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), nitrogen adsorption, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) was used to systematically investigate the drug loading process. The results obtained showed that CEL was in a non-crystalline state after incorporation of CEL into the pores of FMS-15 with pore size of 16.0 nm. In vitro dissolution was carried out to demonstrate the effects of FMS with different pore sizes on the release of CEL. The results obtained indicated that the dissolution rate of CEL from FMS-15 was significantly enhanced compared with pure CEL. This could be explained by supposing that CEL encountered less diffusion resistance and its crystallinity decreased due to the large pore size of 16.0 nm and the nanopore channels of FMS-15. Moreover, drug loading and pore size both play an important role in enhancing the dissolution properties for the poorly water-soluble drugs. As the pore size between 3.7 and 16.0 nm increased, the dissolution rate of CEL from FMS gradually increased. - Highlights: • Exploitation of 3D cubic mesoporous silica (16 nm) as a carrier was completed. • The release rate of CEL increased on increasing the pore size of carriers. • The crystallinity

  13. Determination of dissolution rates of spent fuel in carbonate solutions under different redox conditions with a flow-through experiment

    International Nuclear Information System (INIS)

    Roellin, S.; Spahiu, K.; Eklund, U.-B.

    2001-01-01

    Dissolution rates of spent UO 2 fuel have been investigated using flow-through experiments under oxidizing, anoxic and reducing conditions. For oxidizing conditions, approximately congruent dissolution rates were obtained in the pH range 3-9.3 for U, Np, Ba, Tc, Cs, Sr and Rb. For these elements, steady-state conditions were obtained in the flow rate range 0.02-0.3 ml min -1 . The dissolution rates were about 3 mg d -1 m -2 for pH>6. For pH 2 (g) saturated solutions dropped by up to four orders of magnitude as compared to oxidizing conditions. Because of the very low concentrations, only U, Pu, Am, Mo, Tc and Cs could be measured. For anoxic conditions, both the redox potential and dissolution rates increased approaching the same values as under oxidizing conditions

  14. Lyoluminescence of irradiated carbohydrates - the role of dissolution rate and oxygen

    International Nuclear Information System (INIS)

    Baugh, P.J.; Laflin, P.

    1980-01-01

    The lyoluminescent emission from γ-irradiated carbohydrates is shown to be strictly controlled by the rate of dissolution of the solid and the availability of oxygen for reaction during dissolution. These effects are explained in terms of oxidation of trapped radicals diffusing from the dissolving carbohydrate which react in an 'active volume' set up at the onset of dissolution at the crystal-water interface. At irradiation doses greater than 82.5 krad for mannose there is a suppression of the emission which results from an incomplete oxidation of the diffusing radicals due to insufficient O 2 in the active volume leading to a reaction involving unoxidised radicals and peroxyl radicals which are believed to be the precursors of the emission. This reaction is suppressed when the oxygen supply to the 'active volume' is increased. This can be achieved by increasing the oxygen content of the injector gas and indirectly by decreasing the solubility of the carbohydrate. Under these conditions the linear dose range of the lyoluminescence response is extended to ca. 330 krad close to the dose at which trapped radicals saturate in the irradiated solid carbohydrate. Although lyoluminescence is a liquid surface-layer effect as expected the generation of the emission is greatly influenced by oxygen present in the injection atmosphere. Quenching of lyoluminescence by adding peroxyl radical quenchers Cu(II) ions and hydroquinone, suggests that the reaction involving these quenchers also occurs in the 'active volume'. The results generally can be interpreted in terms of a diffusion model. (author)

  15. In-vitro dissolution rate and molecular docking studies of cabergoline drug with β-cyclodextrin

    Science.gov (United States)

    Shanmuga priya, Arumugam; Balakrishnan, Suganya bharathi; Veerakanellore, Giri Babu; Stalin, Thambusamy

    2018-05-01

    The physicochemical properties and dissolution profile of cabergoline drug (CAB) with β-cyclodextrin (β-CD) inclusion complex were investigated by the UV spectroscopy. The inclusion complex has used to calculate the stability constant and gives the stoichiometry molar ratio is 1:1 between CAB and β-CD. The phase solubility diagram and the aqueous solubility of CAB (60%) was found to be enhanced by β-CD. In addition, the phase solubility profile of CAB with β-CD was classified as AL-type. Binary systems of CAB with β-CD were prepared by Physical mixture, Kneading and solvent evaporation methods. The solid-state properties of the inclusion complex were characterized by Fourier transformation-infrared spectroscopy, Differential scanning calorimetry, Powder X-ray diffractometric patterns and Scanning electron microscopic techniques. Theoretically, β-CD and CAB inclusion complex obtained by molecular docking studies, it is in good correlation with the results obtained through experimental methods using the Schrödinger software program. In-vitro dissolution profiles of the inclusion complexes were carried out and obvious increase in dissolution rate was observed when compared with pure CAB drug and the complexes.

  16. Dissolution of biogenic silica: Roles of pH, salinity, pressure, electrical charging and reverse weathering. Geologica Ultraiectina (302)

    NARCIS (Netherlands)

    Loucaides, S.

    2009-01-01

    The recycling of biogenic silica (bSiO2) produced by diatoms is a vital process sustaining a significant fraction of primary production in the oceans. The efficiency with which bSiO2 dissolves controls the availability of nutrient silicon in the water column, and modulates the export of organic

  17. Knowledge gaps in risk assessment of nanosilica in food: evaluation of the dissolution and toxicity of different forms of silica

    NARCIS (Netherlands)

    Dekkers, S.; Bouwmeester, H.; Bos, P.M.J.; Peters, R.J.B.; Rietveld, A.; Oomen, A.G.

    2013-01-01

    This manuscript describes the follow-up study of our previous publication on the presence and risks of nanosilica in food. New information on the presence of nanosilica in the gastrointestinal tract is evaluated and information on nanosilica and synthetic amorphous silica (SAS) is compared to assess

  18. Influence of Type and Neutralisation Capacity of Antacids on Dissolution Rate of Ciprofloxacin and Moxifloxacin from Tablets

    Directory of Open Access Journals (Sweden)

    Alija Uzunović

    2009-02-01

    Full Text Available Dissolution rate of two fluoroquinolone antibiotics (ciprofloxacin and moxifloxacin was analysed in presence/absence of three antacid formulations. Disintegration time and neutralisation capacity of antacid tablets were also checked. Variation in disintegration time indicated the importance of this parameter, and allowed evaluation of the influence of postponed antacid-fluoroquinolone contact. The results obtained in this study showed decreased dissolution rate of fluoroquinolone antibiotics from tablets in simultaneous presence of antacids, regardless of their type and neutralisation capacity.

  19. Enhancement of Solubility, Dissolution rate and Bioavailability of Efavirenz by Cyclodextrins and Solutol HS15 - A Factorial Study

    OpenAIRE

    R. Yogananda; K. P. R. Chowdary

    2013-01-01

    Efavirenz widely prescribed anti-retroviral drug belongs to class II BCS and exhibit low and variable oral bioavailability due to its poor aqueous solubility and it requires enhancement in solubility and dissolution rate for increasing its oral bioavailability. The objective of the present investigation is to enhance the solubility, dissolution rate and bioavailability of efavirenz by the use of cyclodextrins (%CD and HP%CD) and surfactant, Solutol HS15. The individual main effects and combin...

  20. Agitation Rate and Time for Complete Dissolution in BCS Biowaivers Based on Investigation of a BCS Biowaiver for Dexketoprofen Tablets.

    Science.gov (United States)

    Garcia-Arieta, Alfredo; Gordon, John; Gwaza, Luther; Mangas-Sanjuan, V; Álvarez, Covadonga; Torrado, Juan J

    2015-09-08

    The objective of the present work is to investigate the validity of the existing requirements for BCS biowaivers of immediate release products containing a class I drug in relation to the agitation rate (50 or 75 rpm in the paddle apparatus) and the time limit for complete dissolution (30 min) in the current biowaivers in vitro dissolution tests. Further, the possibility of extensions will be examined since it has been proposed that the time limit for complete dissolution should be revised to 60 min, and also, if cone formation occurs with apparatus 2 at 50 rpm, then a higher agitation rate is acceptable to eliminate it. The development of four generic dexketoprofen immediate release tablets is described. Dexketoprofen is the eutomer of ketoprofen. According to the BCS, dexketoprofen is a class I drug. Three out of the four products failed to show bioequivalence for Cmax in the initial bioequivalence study conducted with the product despite similar but nonrapid dissolution profiles at 50 rpm in the paddle apparatus, or similar and very rapid dissolution profiles at 75 rpm. In conclusion, these data indicate that BCS biowaivers for class I drugs should be granted only when dissolution with the paddle apparatus is complete in 30 min at 50 rpm. The time limit for complete dissolution should not be extended to 60 min. Furthermore, the agitation rate should not be increased to 75 rpm, even in the case of a coning effect.

  1. Improving the API dissolution rate during pharmaceutical hot-melt extrusion I: Effect of the API particle size, and the co-rotating, twin-screw extruder screw configuration on the API dissolution rate.

    Science.gov (United States)

    Li, Meng; Gogos, Costas G; Ioannidis, Nicolas

    2015-01-15

    The dissolution rate of the active pharmaceutical ingredients in pharmaceutical hot-melt extrusion is the most critical elementary step during the extrusion of amorphous solid solutions - total dissolution has to be achieved within the short residence time in the extruder. Dissolution and dissolution rates are affected by process, material and equipment variables. In this work, we examine the effect of one of the material variables and one of the equipment variables, namely, the API particle size and extruder screw configuration on the API dissolution rate, in a co-rotating, twin-screw extruder. By rapidly removing the extruder screws from the barrel after achieving a steady state, we collected samples along the length of the extruder screws that were characterized by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) to determine the amount of undissolved API. Analyses of samples indicate that reduction of particle size of the API and appropriate selection of screw design can markedly improve the dissolution rate of the API during extrusion. In addition, angle of repose measurements and light microscopy images show that the reduction of particle size of the API can improve the flowability of the physical mixture feed and the adhesiveness between its components, respectively, through dry coating of the polymer particles by the API particles. Copyright © 2014. Published by Elsevier B.V.

  2. Thermodynamic and structural models compared with the initial dissolution rates of SON glass samples

    International Nuclear Information System (INIS)

    Tovena, I.; Advocat, T.; Ghaleb, D.; Vernaz, E.

    1993-01-01

    The experimentally determined initial dissolution rate R 0 of nuclear glass was correlated with thermodynamic parameters and structural parameters. The initial corrosion rates of six ''R7T7'' glass samples measured at 100 deg C in a Soxhlet device were correlated with the glass free hydration energy and the glass formation enthalpy. These correlations were then tested with a group of 26 SON glasses selected for their wide diversity of compositions. The thermodynamic models provided a satisfactory approximation of the initial dissolution rate determined under Soxhlet conditions for SON glass samples that include up to 15 wt% of boron and some alumina. Conversely, these models are inaccurate if the boron concentration exceeds 15 wt% and the glass contains no alumina. Possible correlations between R 0 and structural parameters, such as the boron coordination number and the number of nonbridging oxygen atoms, were also investigated. The authors show that R 0 varies inversely with the number of 4-coordinate boron atoms; conversely, the results do not substantiate published reports of a correlation between R 0 and the number of nonbridging oxygen atoms. (authors). 13 refs., 2 figs., 4 tabs

  3. Radon exhalation rates of concrete modified with fly ash and silica fumes

    International Nuclear Information System (INIS)

    Amit Kumar; Chauhan, R.P.; Mehta, Vimal; Kant, K.

    2013-01-01

    The radiological impact of the environmental gas radon to the health of general public is of concern since many decades. Cement used for the construction blended with fly ash and silica fumes is recommended by Government in order to avoid the soil and environmental pollution. But these addition step-up the Indoor radon level in the dwelling due to radioactivity contents. The exhalation of radon from concrete blended with silica fumes and fly ash depends upon addition level, porosity, moisture and radioactivity content. In order to optimize the level of substitution of silica fumes and fly ash, measurements of radon exhalation rates from the concrete blended with different proportions of fly ash and silica fumes was carried out using active scintillation radon monitor. The effect of porosity, moisture, back diffusion and radioactivity content of the concrete on exhalation rates is studied. The measured exhalation rates were extrapolated for indoor radon concentration and effective dose equivalent using ICRP, 1987 recommendations. (author)

  4. On the Impact of the Fuel Dissolution Rate Upon Near-Field Releases From Nuclear Waste Disposal

    Directory of Open Access Journals (Sweden)

    A Pereira

    2016-09-01

    Full Text Available Calculations of the impact of the dissolution of spent nuclear fuel on the release from a damaged canister in a KBS-3 repository are presented. The dissolution of the fuel matrix is a complex process and the dissolution rate is known to be one of the most important parameters in performance assessment models of the near-field of a geological repository. A variability study has been made to estimate the uncertainties associated with the process of fuel dissolution. The model considered in this work is a 3D model of a KBS-3 copper canister. The nuclide used in the calculations is Cs-135. Our results confirm that the fuel degradation rate is an important parameter, however there are considerable uncertainties associated with the data and the conceptual models. Consequently, in the interests of safety one should reduce, as far as possible, the uncertainties coupled to fuel degradation.

  5. Quantifying Silica Reactivity in Subsurface Environments: Reaction Affinity and Solute Matrix Controls on Quartz and SiO2 Glass Dissolution Kinetics

    International Nuclear Information System (INIS)

    Dove, Patricia M.

    2000-01-01

    During the three years of this project, Professor Dove's laboratory made tremendous progress in understanding controls on amorphous silica dissolution kinetics in aqueous solutions. Our findings have already received considerable attention. In hydrothermal and low temperature studies, the work focused on determining quantitative and mechanistic controls on the most abundant silica polymorphs in Earth environments--quartz and amorphous silica. Our studies achieved goals set forth in the original proposal to establish a new quantitative understanding of amorphous silica dissolution. This support has resulted in 10 journal, 12 abstracts and 2 thesis publications. The PI and students were also recognized with 6 awards during this period. The 1998 EMSP conference in Chicago was an important meeting for our project. The symposium, enabled P.I. Dove to establish valuable contacts with ''users'' having specific needs for the findings of our EMSP project related to the urgency of problems in the Tanks Focus Area (TFA). Since that time, our working relations developed as Dove interacted with TFA scientists and engineers on the problems of waste glass properties. These interactions refined our experimental objectives to better meet their needs. Dove presented the results of EMSP research findings to a TFA subgroup at a Product Acceptance Workshop held in Salt Lake City during December 1998. The travel costs to attend this unanticipated opportunity were paid from EMSP project funds. In January 2000, Dove also attended a similar meeting in Atlanta with PNNL, SRL and BNF scientists/engineers to discuss new issues and make another level of decisions on the Product Acceptance goals. Our EMSP-funded research interfaced very well with the ongoing studies of Dr. Pete McGrail and colleagues in the Applied Geochemistry Group at PNNL. The value of our work to ''users'' was further demonstrated when Dove's EMSP-funded Postdoc, Dr. Jonathan Icenhower was hired by the same PNNL group. With

  6. Standard practice for measurement of the glass dissolution rate using the single-pass flow-through test method

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2010-01-01

    1.1 This practice describes a single-pass flow-through (SPFT) test method that can be used to measure the dissolution rate of a homogeneous silicate glass, including nuclear waste glasses, in various test solutions at temperatures less than 100°C. Tests may be conducted under conditions in which the effects from dissolved species on the dissolution rate are minimized to measure the forward dissolution rate at specific values of temperature and pH, or to measure the dependence of the dissolution rate on the concentrations of various solute species. 1.2 Tests are conducted by pumping solutions in either a continuous or pulsed flow mode through a reaction cell that contains the test specimen. Tests must be conducted at several solution flow rates to evaluate the effect of the flow rate on the glass dissolution rate. 1.3 This practice excludes static test methods in which flow is simulated by manually removing solution from the reaction cell and replacing it with fresh solution. 1.4 Tests may be conducted wit...

  7. Dissolution rates of aluminum-based spent fuels relevant to geological disposal

    International Nuclear Information System (INIS)

    Mickalonis, J.I.

    2000-01-01

    The Department of Energy is pursuing the option of direct disposal of a wide variety of spent nuclear fuels under its jurisdiction. Characterization of the various types of spent fuel is required prior to licensing by the Nuclear Regulatory Commission and acceptance of the fuel at a repository site. One category of required data is the expected rate of radionuclide and fissile release to the environment as a result of exposure to groundwater after closure of the repository. To provide this type of data for four different aluminum-based spent fuels, tests were conducted using a flow through method that allows the dissolution rate of the spent fuel matrix to be measured without interference by secondary precipitation reactions that would muddle interpretation of the results. Similar tests had been conducted earlier with light water reactor spent fuel, thereby allowing direct comparisons

  8. Nanosized particles of orlistat with enhanced in vitro dissolution rate and lipase inhibition.

    Science.gov (United States)

    Dolenc, Andrej; Govedarica, Biljana; Dreu, Rok; Kocbek, Petra; Srcic, Stane; Kristl, Julijana

    2010-08-30

    Orlistat is locally acting inhibitor of gastrointestinal lipases which has been developed for the treatment of obesity. The present study was designed with the intent to formulate orlistat in a different way compared to the current practice and investigate its inhibition of gastrointestinal lipases. Orlistat is considered as a technologically problematic and unmanageable substance because of waxy nature, low melting point and low chemical stability. The manuscript presents the critical issues regarding engineering of its nanosuspension with controlled particle size by melt emulsification and high pressure homogenization. In order to formulate dry product, lactose was dissolved in nanosuspension as filler and spray drying has been performed for obtaining the final powder product. Laser diffraction, scanning electron microscopy and atomic force microscopy have been used for orlistat nanosuspension characterization, dissolution studies and lipase inhibition studies were performed to characterize the in vitro efficacy of formulated orlistat. The advantage of selected technological procedures is nanosized orlistat with elevated in vitro dissolution rate in comparison to raw drug, physical mixture and marketed product. Furthermore, nanosuspension demonstrated significantly higher in vitro lipase inhibition in comparison to references. To conclude, the results show new technological solution and remarkable increase of pharmacological effect which could potentially lead to decreasing the dose and consequently dose dependent side effects. Copyright 2010 Elsevier B.V. All rights reserved.

  9. Strong strain rate effect on the plasticity of amorphous silica nanowires

    International Nuclear Information System (INIS)

    Yue, Yonghai; Zheng, Kun

    2014-01-01

    With electron-beam (e-beam) off, in-situ tensile experiments on amorphous silica nanowires (NWs) were performed inside a transmission electron microscope (TEM). By controlling the loading rates, the strain rate can be adjusted accurately in a wide range. The result shows a strong strain rate effect on the plasticity of amorphous silica NWs. At lower strain rate, the intrinsic brittle materials exhibit a pronounced elongation higher than 100% to failure with obvious necking near ambient temperature. At the strain rate higher than 5.23 × 10 −3 /s, the elongation of the NW decreased dramatically, and a brittle fracture feature behavior was revealed. This ductile feature of the amorphous silica NWs has been further confirmed with the in-situ experiments under optical microscopy while the effect of e-beam irradiation could be eliminated.

  10. Accurate rates of the complex mechanisms for growth and dissolution of minerals using a combination of rare event theories

    International Nuclear Information System (INIS)

    Stack, Andrew G.; Raiten, Paolo; Gale, Julian D.

    2012-01-01

    Mineral growth and dissolution are often treated as occurring via a single, reversible process that governs the rate of reaction. We show that multiple, distinct intermediate states can occur during both growth and dissolution. Specifically, we have used metadynamics, a method to efficiently explore the free energy landscape of a system, coupled to umbrella sampling and reactive flux calculations, to examine the mechanism and rates of attachment and detachment of a barium ion onto a stepped, barite (BaSO4) surface. The activation energies calculated for the rate limiting reactions, which are different for attachment and detachment, precisely match those measured experimentally during both growth and dissolution. These results can potentially explain anomalous, non-steady state mineral reaction rates observed experimentally, and will enable the design of more efficient growth inhibitors and facilitate an understanding of the effect of impurities.

  11. Inclusion complex of amiodarone hydrochloride with cyclodextrins: preparation, characterization and dissolution rate evaluation

    Directory of Open Access Journals (Sweden)

    Alexandre Machado Rubim

    2017-06-01

    Full Text Available ABSTRACT This study aimed to improve the water solubility of amiodarone hydrochloride (AMH via inclusion complexes with β-cyclodextrin, methyl-β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin. Inclusion complexes were developed by physical mixture, coevaporation, spray-drying and freeze-drying. Solid state analysis was performed using X-ray powder diffraction, differential scanning calorimetry and scanning electronic microscopy. Thermodynamic studies demonstrate that the inclusion complexes of drug into different cyclodextrins were an exothermic process that occurred spontaneously. Water solubility and drug dissolution rates were significantly increased after the formation of inclusion complexes with the cyclodextrins evaluated in relation to the physical mixture and pure drug. The present study provides useful information for the potential application of complexation with amiodarone HCl. This may be a good strategy for the development of solid pharmaceutical dosage forms.

  12. Overview of chemical modeling of nuclear waste glass dissolution

    International Nuclear Information System (INIS)

    Bourcier, W.L.

    1991-02-01

    Glass dissolution takes place through metal leaching and hydration of the glass surface accompanied by development of alternation layers of varying crystallinity. The reaction which controls the long-term glass dissolution rate appears to be surface layer dissolution. This reaction is reversible because the buildup of dissolved species in solution slows the dissolution rate due to a decreased dissolution affinity. Glass dissolution rates are therefore highly dependent on silica concentrations in solution because silica is the major component of the alteration layer. Chemical modeling of glass dissolution using reaction path computer codes has successfully been applied to short term experimental tests and used to predict long-term repository performance. Current problems and limitations of the models include a poorly defined long-term glass dissolution mechanism, the use of model parameters determined from the same experiments that the model is used to predict, and the lack of sufficient validation of key assumptions in the modeling approach. Work is in progress that addresses these issues. 41 refs., 7 figs., 2 tabs

  13. Liquigroud technique: a new concept for enhancing dissolution rate of glibenclamide by combination of liquisolid and co-grinding technologies.

    Science.gov (United States)

    Azharshekoufeh, Leila; Shokri, Javad; Barzegar-Jalali, Mohammad; Javadzadeh, Yousef

    2017-01-01

    Introduction: The potential of combining liquisolid and co-grinding technologies (liquiground technique) was investigated to improve the dissolution rate of a water-insoluble agent (glibenclamide) with formulation-dependent bioavailability. Methods: To this end, different formulations of liquisolid tablets with a wide variety of non-volatile solvents contained varied ratios of drug: solvent and dissimilar carriers were prepared, and then their release profiles were evaluated. Furthermore, the effect of size reduction by ball milling on the dissolution behavior of glibenclamide from liquisolid tablets was investigated. Any interaction between the drug and the excipient or crystallinity changes during formulation procedure was also examined using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Results: The present study revealed that classic liquisolid technique did not significantly affect the drug dissolution profile as compared to the conventional tablets. Size reduction obtained by co-grinding of liquid medication was more effective than the implementation of liquisolid technique in enhancing the dissolution rate of glibenclamide. The XRD and DSC data displayed no formation of complex or any crystallinity changes in both formulations. Conclusion: An enhanced dissolution rate of glibenclamide is achievable through the combination of liquisolid and co-grinding technologies.

  14. Dissolution and Precipitation Behaviour during Continuous Heating of Al–Mg–Si Alloys in a Wide Range of Heating Rates

    Science.gov (United States)

    Osten, Julia; Milkereit, Benjamin; Schick, Christoph; Kessler, Olaf

    2015-01-01

    In the present study, the dissolution and precipitation behaviour of four different aluminium alloys (EN AW-6005A, EN AW-6082, EN AW-6016, and EN AW-6181) in four different initial heat treatment conditions (T4, T6, overaged, and soft annealed) was investigated during heating in a wide dynamic range. Differential scanning calorimetry (DSC) was used to record heating curves between 20 and 600 °C. Heating rates were studied from 0.01 K/s to 5 K/s. We paid particular attention to control baseline stability, generating flat baselines and allowing accurate quantitative evaluation of the resulting DSC curves. As the heating rate increases, the individual dissolution and precipitation reactions shift to higher temperatures. The reactions during heating are significantly superimposed and partially run simultaneously. In addition, precipitation and dissolution reactions are increasingly suppressed as the heating rate increases, whereby exothermic precipitation reactions are suppressed earlier than endothermic dissolution reactions. Integrating the heating curves allowed the enthalpy levels of the different initial microstructural conditions to be quantified. Referring to time–temperature–austenitisation diagrams for steels, continuous heating dissolution diagrams for aluminium alloys were constructed to summarise the results in graphical form. These diagrams may support process optimisation in heat treatment shops.

  15. Dissolution and Precipitation Behaviour during Continuous Heating of Al–Mg–Si Alloys in a Wide Range of Heating Rates

    Directory of Open Access Journals (Sweden)

    Julia Osten

    2015-05-01

    Full Text Available In the present study, the dissolution and precipitation behaviour of four different aluminium alloys (EN AW-6005A, EN AW-6082, EN AW-6016, and EN AW-6181 in four different initial heat treatment conditions (T4, T6, overaged, and soft annealed was investigated during heating in a wide dynamic range. Differential scanning calorimetry (DSC was used to record heating curves between 20 and 600 °C. Heating rates were studied from 0.01 K/s to 5 K/s. We paid particular attention to control baseline stability, generating flat baselines and allowing accurate quantitative evaluation of the resulting DSC curves. As the heating rate increases, the individual dissolution and precipitation reactions shift to higher temperatures. The reactions during heating are significantly superimposed and partially run simultaneously. In addition, precipitation and dissolution reactions are increasingly suppressed as the heating rate increases, whereby exothermic precipitation reactions are suppressed earlier than endothermic dissolution reactions. Integrating the heating curves allowed the enthalpy levels of the different initial microstructural conditions to be quantified. Referring to time–temperature–austenitisation diagrams for steels, continuous heating dissolution diagrams for aluminium alloys were constructed to summarise the results in graphical form. These diagrams may support process optimisation in heat treatment shops.

  16. Effects of alteration product precipitation on glass dissolution

    Energy Technology Data Exchange (ETDEWEB)

    Strachan, Denis M.; Neeway, James J.

    2014-06-01

    Understanding the mechanisms that control the durability of nuclear waste glass is paramount if reliable models are to be constructed so that the glass dissolution rate in a given geological repository can be calculated. Presently, it is agreed that (boro)silicate glasses dissolve in water at a rate dependent on the solution concentration of orthosilicic acid (H4SiO4) with higher [H4SiO4] leading to lower dissolution rates. Once the reaction has slowed as a result of the buildup of H4SiO4, another increase in the rate has been observed that corresponds to the precipitation of certain silica-bearing alteration products. However, it has also been observed that the concentration of silica-bearing solution species does not significantly decrease, indicating saturation, while other glass tracer elements concentrations continue to increase, indicating that the glass is still dissolving. In this study, we have used the Geochemist’s Workbench code to investigate the relationship between glass dissolution rates and the precipitation rate of a representative zeolitic silica-bearing alteration product, analcime [Na(AlSi2O6)∙H2O]. To simplify the calculations, we suppressed all alteration products except analcime, gibbsite (Al(OH)3), and amorphous silica. The pseudo-equilibrium-constant matrix for amorphous silica was substituted for the glass pseudo-equilibrium-constant matrix because it has been shown that silicate glasses act as a silica-only solid with respect to kinetic considerations. In this article, we present the results of our calculations of the glass dissolution rate at different values for the analcime precipitation rate constant and the effects of varying the glass dissolution rate constant at a constant analcime precipitation rate constant. From the simulations we conclude, firstly, that the rate of glass dissolution is dependent on the kinetics of

  17. Dissolution of aluminium

    International Nuclear Information System (INIS)

    Uriarte Hueda, A.; Berberana Eizmendi, M.; Pereira Sanchez, G.

    1968-01-01

    The dissolution of aluminum with acid solutions ( nitric acid-mercuric nitrate) and alkaline solutions (sodium hydroxide-sodium nitrate) has been studied. The instantaneous dissolution rate (IDR) has been studied in function of the concentration of the used reagents and the dissolution temperature. The complete dissolution has been included in the second part of this report, to know the total dissolution time, the consume of reagents and the stability of the resultant solutions. (Author)

  18. Synthesis of Cefixime and Azithromycin Nanoparticles: An Attempt to Enhance Their Antimicrobial Activity and Dissolution Rate

    Directory of Open Access Journals (Sweden)

    Farhat Ali Khan

    2016-01-01

    Full Text Available In this study cefixime and azithromycin nanoparticles were prepared by antisolvent precipitation with syringe pump (APSP and evaporator precipitation nanosuspension (EPN methods. The nanoparticles were characterized by XRD, FTIR, SEM, and TGA. X-ray diffraction pattern of cefixime samples showed the amorphous form, while azithromycin samples showed crystalline form. The FTIR spectra of parental drugs and synthesized nanoparticles have no major structural changes detected. The SEM images showed that nanoparticles of both drugs have submicron sized and nanosized particles. TGA analyses showed that above 30°C the decomposition of cefixime samples starts and their weight gradually decreases up to 600°C, while, in case of azithromycin, 30°C to 250°C, very small changes occur in weight; from above 250°C decomposition of the sample took place to a greater extent. The antibacterial activities of raw drugs and prepared samples of nanoparticles were determined against Staphylococcus aureus, Shigella, E. coli, and Salmonella typhi by agar well diffusion method. Every time the nanoparticles samples showed better results than parental drugs. The dissolution rates of raw drugs and prepared nanoparticles were also determined. The results were always better for the synthesized nanoparticles than parental drug.

  19. The dissolution rate of UO2 in the alkaline regime under oxidizing conditions using a simplified ground water analog

    International Nuclear Information System (INIS)

    Leider, H.R.; Nguyen, S.N.; Weed, H.C.; Steward, S.A.

    1992-01-01

    The major factor controlling the long term release of radionuclides from spent fuel in a geologic repository is the leaching/dissolution by groundwater of the UO 2 matrix, since more than 90% of the radionuclide waste is contained in the fuel matrix. The objective of this investigation is to provide experimental dissolution rates for UO 2 samples which can be used to develop a mechanistic release model (or models) for UO 2+x (x≥0) under repository conditions. Several types of data will be obtained from this study: (1) the dissolution rates of UO 2 as a function of pI-L temperature, carbonate and oxygen fugacity; (2) the comparison of the steady state dissolution rates of ''not-reduced'' versus ''reduced'' UO 2 samples and of single crystal versus polycrystalline UO 2 under identical experimental conditions; (3) the pre- and post-test surface analyses of the samples to provide information on the surface phases that may be formed under experimental conditions

  20. Increasing the dissolution rate and oral bioavailability of the poorly water-soluble drug valsartan using novel hierarchical porous carbon monoliths.

    Science.gov (United States)

    Zhang, Yanzhuo; Che, Erxi; Zhang, Miao; Sun, Baoxiang; Gao, Jian; Han, Jin; Song, Yaling

    2014-10-01

    In the present study, a novel hierarchical porous carbon monolith (HPCM) with three-dimensionally (3D) ordered macropores (∼ 400 nm) and uniform accessible mesopores (∼ 5.2 nm) was synthesized via a facile dual-templating technique using colloidal silica nanospheres and Poloxamer 407 as templates. The feasibility of the prepared HPCM for oral drug delivery was studied. Valsartan (VAL) was chosen as a poorly water-soluble model drug and loaded into the HPCM matrix using the solvent evaporation method. Scanning electron microscopy (SEM) and specific surface area analysis were employed to characterize the drug-loaded HPCM-based formulation, confirming the successful inclusion of VAL into the nanopores of HPCM. Powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) demonstrated that the incorporated drug in the HPCM matrix was in an amorphous state and the VAL formulation exhibited good physical stability for up to 6 months. In vitro tests showed that the dissolution rate of HPCM-based formulation was increased significantly compared with that of crystalline VAL or VAL-loaded 3D ordered macroporous carbon monoliths (OMCMs). Furthermore, a pharmacokinetic study in rats demonstrated about 2.4-fold increase in oral bioavailability of VAL in the case of HPCM-based formulation compared with the commercially available VAL preparation (Valzaar(®)). These results therefore suggest that HPCM is a promising carrier able to improve the dissolution rate and oral bioavailability of the poorly water-soluble drug VAL. Copyright © 2014. Published by Elsevier B.V.

  1. Solid dispersions, part II: new strategies in manufacturing methods for dissolution rate enhancement of poorly water-soluble drugs.

    Science.gov (United States)

    Bikiaris, Dimitrios N

    2011-12-01

    The absorption of poorly water-soluble drugs, when presented in the crystalline state to the gastrointestinal tract, is typically dissolution rate-limited, and according to BCS these drugs belong mainly to class II. Both dissolution kinetics and solubility are particle size dependent. Nowadays, various techniques are available to the pharmaceutical industry for dissolution rate enhancement of such drugs. Among such techniques, nanosuspensions and drug formulation in solid dispersions are those with the highest interest. This review discusses strategies undertaken over the last 10 years, which have been applied for the dissolution enhancement of poorly water-soluble drugs; such processes include melt mixing, electrospinning, microwave irradiation and the use of inorganic nanoparticles. Many problems in this field still need to be solved, mainly the use of toxic solvents, and for this reason the use of innovative new procedures and materials will increase over the coming years. Melt mixing remains extremely promising for the preparation of SDs and will probably become the most used method in the future for the preparation of solid drug dispersions.

  2. Enhancement of the glass corrosion in the presence of clay minerals: testing experimental results with an integrated glass dissolution model

    International Nuclear Information System (INIS)

    Godon, N.; Vernaz, E.Y.

    1992-01-01

    Recent glass dissolution experiments, conducted at 90 deg C in the presence of potential backfill materials, indicate remarkably faster glass corrosion in the presence of clay, compared to tests where the glass is leached either alone or with alternative backfill materials. This effect correlates with the clay content in the backfill, and may be attributed to the removal of silica from solution. Scorpion, or dissolution with reprecipitation of a silica-rich clay, have been proposed as possible mechanisms for the silica consumption. The results of some experiments have been tested against a glass dissolution model, in which a widely used kinetic equation for glass corrosion is coupled with diffusive silica transport through a single porosity, linearly sorbing medium, which represents the backfilling. Because the glass corrosion rates imposed by the kinetic equation are inversely proportional to the silicic acid concentration of the leachant contacting the glass, the model predicts enhanced glass dissolution if silica is sorbed by the porous medium. The experimental data proved to be consistent with the predicted enhancement of the glass dissolution. Moreover, the model-estimated distribution coefficients for silica sorption (K d ) fall within the range of values extracted from available literature data, thus supporting the hypothesis that the observed high corrosion rates are due to sorption of silica on the clay mineral surfaces. (author)

  3. Coamorphous drug systems: enhanced physical stability and dissolution rate of indomethacin and naproxen

    DEFF Research Database (Denmark)

    Löbmann, Korbinian; Laitinen, Riikka; Grohganz, Holger

    2011-01-01

    . In this study, a coamorphous drug/drug combination between the two nonsteroidal anti-inflammatory drugs, naproxen and ¿-indomethacin, was prepared and investigated. At molar ratios of 2:1, 1:1 and 1:2, the drugs were quench cooled in order to obtain a coamorphous binary phase. Physical stability was examined...... at 277.15 and 298.15 K under dry conditions (phosphorus pentoxide) and analyzed with X-ray powder diffraction (XRPD). Intrinsic dissolution testing was carried out to identify dissolution advantages of the coamorphous form over its crystalline counterparts or amorphous indomethacin. Fourier transform...

  4. Kinetic and thermodynamic controls on silica reactivity: an analog for waste disposal media

    International Nuclear Information System (INIS)

    Dove, P.M.; Icenhower, J.

    1997-01-01

    Silicate glasses are currently being proposed as the disposal media for radioactive and other toxic wastes. The dissolution behaviour of borosilicate glass is incompletely understood. One approach is to simplify the chemistry and first develop a better understanding of vitreous silica (v-SiO 2 ) as a simple analog of waste glass. This article reviews all the knowledge that is known about the dissolution of silica. Studies quantifying the effects of temperature, solution pH, and single salts on dissolution rates of quartz suggest that pH and cation-dependent dissolution trends hold for all of the silica polymorphs. The purpose of this review is to develop a consistent picture of glass reactivity by understanding how the molecular arrangement of constituents within glass, beginning with the Si-O bond, affects the dissolution processes. (A.C.)

  5. Kinetic and thermodynamic controls on silica reactivity: an analog for waste disposal media

    Energy Technology Data Exchange (ETDEWEB)

    Dove, P.M.; Icenhower, J. [Georgia Inst. of Tech., School of Earth and Atmospheric Sciences, Atlanta, GA (United States)

    1997-07-01

    Silicate glasses are currently being proposed as the disposal media for radioactive and other toxic wastes. The dissolution behaviour of borosilicate glass is incompletely understood. One approach is to simplify the chemistry and first develop a better understanding of vitreous silica (v-SiO{sub 2}) as a simple analog of waste glass. This article reviews all the knowledge that is known about the dissolution of silica. Studies quantifying the effects of temperature, solution pH, and single salts on dissolution rates of quartz suggest that pH and cation-dependent dissolution trends hold for all of the silica polymorphs. The purpose of this review is to develop a consistent picture of glass reactivity by understanding how the molecular arrangement of constituents within glass, beginning with the Si-O bond, affects the dissolution processes. (A.C.)

  6. Setting accelerated dissolution test for PLGA microspheres containing peptide, investigation of critical parameters affecting drug release rate and mechanism.

    Science.gov (United States)

    Tomic, I; Vidis-Millward, A; Mueller-Zsigmondy, M; Cardot, J-M

    2016-05-30

    The objective of this study was development of accelerated in vitro release method for peptide loaded PLGA microspheres using flow-through apparatus and assessment of the effect of dissolution parameters (pH, temperature, medium composition) on drug release rate and mechanism. Accelerated release conditions were set as pH 2 and 45°C, in phosphate buffer saline (PBS) 0.02M. When the pH was changed from 2 to 4, diffusion controlled phases (burst and lag) were not affected, while release rate during erosion phase decreased two-fold due to slower ester bonds hydrolyses. Decreasing temperature from 45°C to 40°C, release rate showed three-fold deceleration without significant change in release mechanism. Effect of medium composition on drug release was tested in PBS 0.01M (200 mOsm/kg) and PBS 0.01M with glucose (380 mOsm/kg). Buffer concentration significantly affected drug release rate and mechanism due to the change in osmotic pressure, while ionic strength did not have any effect on peptide release. Furthermore, dialysis sac and sample-and-separate techniques were used, in order to evaluate significance of dissolution technique choice on the release process. After fitting obtained data to different mathematical models, flow-through method was confirmed as the most appropriate for accelerated in vitro dissolution testing for a given formulation. Copyright © 2016 Elsevier B.V. All rights reserved.

  7. Mesoporous carbon with spherical pores as a carrier for celecoxib with needle-like crystallinity: Improve dissolution rate and bioavailability

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Wenquan; Zhao, Qinfu; Sun, Changshan [Department of Pharmaceutics, Shenyang Pharmaceutical University, Shenyang (China); Zhang, Zhiwen [Center of Pharmaceutics, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 501 Haike Road, Shanghai 201203 (China); Jiang, Tongying; Sun, Jin [Department of Pharmaceutics, Shenyang Pharmaceutical University, Shenyang (China); Li, Yaping [Center of Pharmaceutics, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 501 Haike Road, Shanghai 201203 (China); Wang, Siling, E-mail: silingwang@syphu.edu.cn [Department of Pharmaceutics, Shenyang Pharmaceutical University, Shenyang (China)

    2014-06-01

    The purposes of this investigation are to design mesoporous carbon (MC) with spherical pore channels and incorporate CEL to it for changing its needlelike crystal form and improving its dissolution and bioavailability. A series of solid-state characterization methods, such as SEM, TEM, DSC and XRD, were employed to systematically investigate the existing status of celecoxib (CEL) within the pore channels of MC. The pore size, pore volume and surface area of samples were characterized by nitrogen physical absorption. Gastric mucosa irritation test was carried out to evaluate the safety of mesoporous carbon as a drug carrier. Dissolution tests and in vivo pharmacokinetic studies were conducted to confirm the improvement in drug dissolution kinetics and oral bioavailability. Uptake experiments were conducted to investigate the mechanism of the improved oral bioavailability. The results of solid state characterization showed that MC was prepared successfully and CEL was incorporated into the mesoporous channels of the MC. The crystallinity of CEL in MC was affected by different loading methods, which involve evaporation method and melting method. The dissolution rate of CEL from MC was found to be significantly higher than that of pure CEL, which attributed to reduced crystallinity of CEL. The gastric mucosa irritation test indicated that the MC caused no harm to the stomach and produced a protective effect on the gastric mucosa. Uptake experiments indicated that MC enhanced the amount of CEL absorbed by Caco-2 cells. Moreover, oral bioavailability of CEL loaded within the MC was approximately 1.59-fold greater than that of commercial CEL. In conclusion, MC was a safe carrier to load water insoluble drug by controlling the crystallinity or crystal form with improvement in drug dissolution kinetics and oral bioavailability. - Highlights: • Mesoporous carbon with spherical pore structure was prepared according to the needlelike crystalline of celecoxib. • The

  8. Mesoporous carbon with spherical pores as a carrier for celecoxib with needle-like crystallinity: Improve dissolution rate and bioavailability

    International Nuclear Information System (INIS)

    Zhu, Wenquan; Zhao, Qinfu; Sun, Changshan; Zhang, Zhiwen; Jiang, Tongying; Sun, Jin; Li, Yaping; Wang, Siling

    2014-01-01

    The purposes of this investigation are to design mesoporous carbon (MC) with spherical pore channels and incorporate CEL to it for changing its needlelike crystal form and improving its dissolution and bioavailability. A series of solid-state characterization methods, such as SEM, TEM, DSC and XRD, were employed to systematically investigate the existing status of celecoxib (CEL) within the pore channels of MC. The pore size, pore volume and surface area of samples were characterized by nitrogen physical absorption. Gastric mucosa irritation test was carried out to evaluate the safety of mesoporous carbon as a drug carrier. Dissolution tests and in vivo pharmacokinetic studies were conducted to confirm the improvement in drug dissolution kinetics and oral bioavailability. Uptake experiments were conducted to investigate the mechanism of the improved oral bioavailability. The results of solid state characterization showed that MC was prepared successfully and CEL was incorporated into the mesoporous channels of the MC. The crystallinity of CEL in MC was affected by different loading methods, which involve evaporation method and melting method. The dissolution rate of CEL from MC was found to be significantly higher than that of pure CEL, which attributed to reduced crystallinity of CEL. The gastric mucosa irritation test indicated that the MC caused no harm to the stomach and produced a protective effect on the gastric mucosa. Uptake experiments indicated that MC enhanced the amount of CEL absorbed by Caco-2 cells. Moreover, oral bioavailability of CEL loaded within the MC was approximately 1.59-fold greater than that of commercial CEL. In conclusion, MC was a safe carrier to load water insoluble drug by controlling the crystallinity or crystal form with improvement in drug dissolution kinetics and oral bioavailability. - Highlights: • Mesoporous carbon with spherical pore structure was prepared according to the needlelike crystalline of celecoxib. • The

  9. Estimate of long-term dissolution rate of basaltic glass. A case study on Mt. Fuji area

    Energy Technology Data Exchange (ETDEWEB)

    Shikazono, Naotatsu; Takino, Akitsugu [Keio Univ., Environmental Geochemistry, Tokyo (Japan)

    2002-03-01

    Bulk compositional, mineralogical and physical properties of weathered basaltic ash soil ('Andisol') derived mainly from Mt. Fuji were studied. Mineralogical studies revealed that the dominant primary material and weathering products are volcanic glass, allophane and halloysite and the sequence of weathering is volcanic glass {yields} allophane {yields} 10A halloysite {yields} 7A halloysite. X-ray fluorescence analysis indicates that the relative elemental mobilities during the weathering is Na, Ca>K>Mg>P>Si>Ti, Fe>Al>Mn. The trends of soilwater chemistry (H{sub 4}SiO{sub 4} concentration) with depth were calculated based on dissolution - precipitation kinetics - fluid flow coupling model. In order to calculate the trends, the data on present-day annual rainfall, solubility of basalt glass, porosity and specific weight of soil, deposition rate of volcanic ash and grain size of volcanic glass were used. The calculated results were compared with analytical trends of soilwater chemistry. From this comparison the dissolution rate constant of basalt glass was estimated to be 10{sup -9.4} - 10{sup -9.2} (mole Si m{sup -2} s{sup -1}). This value is consistent with previous experimental dissolution rate constant of basalt glass reported in the literature. (author)

  10. Estimate of long-term dissolution rate of basaltic glass. A case study on Mt. Fuji area

    International Nuclear Information System (INIS)

    Shikazono, Naotatsu; Takino, Akitsugu

    2002-01-01

    Bulk compositional, mineralogical and physical properties of weathered basaltic ash soil ('Andisol') derived mainly from Mt. Fuji were studied. Mineralogical studies revealed that the dominant primary material and weathering products are volcanic glass, allophane and halloysite and the sequence of weathering is volcanic glass → allophane → 10A halloysite → 7A halloysite. X-ray fluorescence analysis indicates that the relative elemental mobilities during the weathering is Na, Ca>K>Mg>P>Si>Ti, Fe>Al>Mn. The trends of soilwater chemistry (H 4 SiO 4 concentration) with depth were calculated based on dissolution - precipitation kinetics - fluid flow coupling model. In order to calculate the trends, the data on present-day annual rainfall, solubility of basalt glass, porosity and specific weight of soil, deposition rate of volcanic ash and grain size of volcanic glass were used. The calculated results were compared with analytical trends of soilwater chemistry. From this comparison the dissolution rate constant of basalt glass was estimated to be 10 -9.4 - 10 -9.2 (mole Si m -2 s -1 ). This value is consistent with previous experimental dissolution rate constant of basalt glass reported in the literature. (author)

  11. The dissolution rate constant of magnetite in water at different temperatures and neutral or ammoniated chemistry conditions

    International Nuclear Information System (INIS)

    Mohajery, K.; Lister, D.H.

    2012-01-01

    In this study, the dissolution rate constants of magnetite were measured at various water chemistry conditions and different temperatures, corresponding to several feedwater conditions of water-cooled reactors. Sintered magnetite pellets were used as the dissolving material and these were mounted in a jet-impingement apparatus in a recirculating water loop. Exposures were carried out at temperatures of 25, 55 and 140 o C and pHs of neutral and 9.2 in which many FAC (Flow Accelerated Corrosion) studies have been conducted. Average dissolution rate constants were estimated by measuring the volume of lost material with a profilometry technique. The excellent correspondent between the calculated value of dissolution rate constant of 2.20 mm/s for the synthesized magnetite and 2.05 mm/s for the single crystal of magnetite at neutral condition shows that the particle removal from the synthesized pellets is not an obstruction in this technique. Also, good agreement between the values calculated in duplicated runs at neutral condition at room temperature supports the accuracy of the method. (author)

  12. Rate of formation and dissolution of mercury sulfide nanoparticles: The dual role of natural organic matter

    Science.gov (United States)

    Slowey, Aaron J.

    2010-01-01

    Mercury is a global contaminant of concern due to its transformation by microorganisms to form methylmercury, a toxic species that accumulates in biological tissues. The effect of dissolved organic matter (DOM) isolated from natural waters on reactions between mercury(II) (Hg) and sulfide (S(-II)) to form HgS(s) nanoparticles across a range of Hg and S(-II) concentrations was investigated. Hg was equilibrated with DOM, after which S(-II) was added. Dissolved Hg (Hgaq) was periodically quantified using ultracentrifugation and chemical analysis following the addition of S(-II). Particle size and identity were determined using dynamic light scattering and X-ray absorption spectroscopy. S(-II) reacts with Hg to form 20 to 200nm aggregates consisting of 1-2 nm HgS(s) subunits that are more structurally disordered than metacinnabar in the presence of 2 x 10-9 to 8 x 10-6M Hg and 10 (mg C)L-1 DOM. Some of the HgS(s) nanoparticle aggregates are subsequently dissolved by DOM and (re)precipitated by S(-II) over periods of hours to days. At least three fractions of Hg-DOM species were observed with respect to reactivity toward S(-II): 0.3 μmol reactive Hg per mmol C (60 percent), 0.1 μmol per mmol C (20 percent) that are kinetically hindered, and another 0.1 μmol Hg per mmol C (20 percent) that are inert to reaction with S(-II). Following an initial S(-II)-driven precipitation of HgS(s), HgS(s) was dissolved by DOM or organic sulfur compounds. HgS(s) formation during this second phase was counterintuitively favored by lower S(-II) concentrations, suggesting surface association of DOM moieties that are less capable of dissolving HgS(s). DOM partially inhibits HgS(s) formation and mediates reactions between Hg and S(-II) such that HgS(s) is susceptible to dissolution. These findings indicate that Hg accessibility to microorganisms could be controlled by kinetic (intermediate) species in the presence of S(-II) and DOM, undermining the premise that equilibrium Hg species

  13. Dissolution rates and solubility of some metals in liquid gallium and aluminum

    International Nuclear Information System (INIS)

    Yatsenko, S P; Sabirzyanov, N A; Yatsenko, A S

    2008-01-01

    The effect of liquid gallium and aluminum on some hard metals leading to dissolution and formation of intermetallic compounds (IMC) under static conditions and rotation of a specimen is studied. The solubility parameters from the Clapeyron-Clausius equation were considered to estimate the stability of still not studied metals. The presented experimental data on solubility and corrosion in a wide temperature range allow to calculate a number of parameters useful in manufacturing and application of master-alloys

  14. Effect of taste masking technology on fast dissolving oral film: dissolution rate and bioavailability

    Science.gov (United States)

    Zhu, Ying; You, Xinru; Huang, Keqing; Raza, Faisal; Lu, Xin; Chen, Yuejian; Dhinakar, Arvind; Zhang, Yuan; Kang, Yang; Wu, Jun; Ge, Liang

    2018-07-01

    Fast dissolving oral film is a stamp-style, drug-loaded polymer film with rapid disintegration and dissolution. This new kind of drug delivery system requires effective taste masking technology. Suspension intermediate and liposome intermediate were prepared, respectively, for the formulation of two kinds of fast dissolving oral films with the aim of studying the effect of taste masking technology on the bioavailability of oral films. Loratadine was selected as the model drug. The surface pH of the films was close to neutral, avoiding oral mucosal irritation or side effects. The thickness of a 2 cm × 2 cm suspension oral film containing 10 mg of loratadine was 100 μm. Electron microscope analysis showed that liposomes were spherical before and after re-dissolution, and drugs with obvious bitterness could be masked by the encapsulation of liposomes. Dissolution of the two films was superior to that of the commercial tablets. Rat pharmacokinetic experiments showed that the oral bioavailability of the suspension film was significantly higher than that of the commercial tablets, and the relative bioavailability of the suspension film was 175%. Liposomal film produced a certain amount of improvement in bioavailability, but lower than that of the suspension film.

  15. Effect of taste masking technology on fast dissolving oral film: dissolution rate and bioavailability.

    Science.gov (United States)

    Zhu, Ying; You, Xinru; Huang, Keqing; Raza, Faisal; Lu, Xin; Chen, Yuejian; Dhinakar, Arvind; Zhang, Yuan; Kang, Yang; Wu, Jun; Ge, Liang

    2018-07-27

    Fast dissolving oral film is a stamp-style, drug-loaded polymer film with rapid disintegration and dissolution. This new kind of drug delivery system requires effective taste masking technology. Suspension intermediate and liposome intermediate were prepared, respectively, for the formulation of two kinds of fast dissolving oral films with the aim of studying the effect of taste masking technology on the bioavailability of oral films. Loratadine was selected as the model drug. The surface pH of the films was close to neutral, avoiding oral mucosal irritation or side effects. The thickness of a 2 cm × 2 cm suspension oral film containing 10 mg of loratadine was 100 μm. Electron microscope analysis showed that liposomes were spherical before and after re-dissolution, and drugs with obvious bitterness could be masked by the encapsulation of liposomes. Dissolution of the two films was superior to that of the commercial tablets. Rat pharmacokinetic experiments showed that the oral bioavailability of the suspension film was significantly higher than that of the commercial tablets, and the relative bioavailability of the suspension film was 175%. Liposomal film produced a certain amount of improvement in bioavailability, but lower than that of the suspension film.

  16. Dissolution processes

    International Nuclear Information System (INIS)

    Silver, G.L.

    1976-01-01

    This review contains more than 100 observations and 224 references on the dissolution phenomenon. The dissolution processes are grouped into three categories: methods of aqueous attack, fusion methods, and miscellaneous observations on phenomena related to dissolution problems

  17. Effect of low dose rate irradiation on doped silica core optical fibers

    International Nuclear Information System (INIS)

    Friebele, E.J.; Askins, C.G.; Gingerich, M.E.

    1984-01-01

    The optical attenuation induced in multimode doped silica core optical fiber waveguides by a year's exposure to low dose rate (1 rad/day) ionizing radiation was studied, allowing a characterization of fibers deployed in these environments and a determination of the permanent induced loss in the waveguides. Variations in the induced attenuation at 0.85 μm have been observed with changes in the dose rate between 1 rad/day and 9000 rads/min. These dose rate dependences have been found to derive directly from the recovery that occurs during the exposure; the recovery data predict little or no dose rate dependence of the damage at 1.3 μm. The low dose rate exposure has been found to induce significant permanent attenuation in the 0.7-1.7-μm spectral region in all fibers containing P in the core, whether doped uniformly across the diameter or constrained to a narrow spike on the centerline. Whereas permanent loss was induced at 0.85 μm in a P-free binary Ge-doped silica core fiber by the year's exposure, virtually no damage was observed at 1.3 μm

  18. Dissolution Rate And Mechanism Of Metals In Molten Aluminum Alloy A380

    OpenAIRE

    Zhu, Hengyu

    2014-01-01

    Shot sleeve is a very easily worn out part in a high-pressure die-casting machine due to serious dissolution of the area underneath the pouring hole. It is because during a normal pouring process, the high temperature molten aluminum will impact and dissolve that area of the shot sleeve by complex chemical and physical process. Rotation experiment was carried out to H13 and four kinds of refractory metal samples. SEM and EDS pictures were taken in order to investigate the microstructure and t...

  19. Alloying effects on dissolution rate of crevice corrosion for austenitic stainless steels in 3% NaCl solution at 80 C

    International Nuclear Information System (INIS)

    Chen, P.; Shinohara, Tadashi; Tsujikawa, Shigeo

    1996-01-01

    Chloride stress corrosion cracking (SCC) has been a problem for austenitic stainless steel in aqueous environments containing chlorides. Studies have found that SCC initiates only from a dissolving surface and under the condition that the crack growth rate is higher than the dissolution rate of the dissolving surface. Research conducted to improve the resistance to SCC for Type 304 steels (UNS S30400) have revealed that while molybdenum and phosphorus are unfavored, the combined alloying of 3% aluminum with 2% copper can almost nullify their detrimental effect. Based on the mentioned criteria, this study was dedicated to clarify the mechanism behind these alloying effects by examining the relationship between the measured enhancements on SCC resistance and the dissolution rate observed via the moire technique. It was found that the addition of both molybdenum and phosphorus reduces the dissolution rate and therefore impaired SCC resistance; the addition of copper increases the dissolution rate of steady growth stage where crevice corrosion proceeds at a constant rate. Moreover this dissolution rate could further be increased when combined with the alloying of aluminum. These observed results correspond well to that of the measured behavior of the SCC critical temperature, T c , suggesting that the SCC susceptibility is influenced by anodic dissolution

  20. Modeling the dissolution behavior of defense waste glass in a salt repository environment

    International Nuclear Information System (INIS)

    McGrain, B.P.

    1988-02-01

    A mechanistic model describing a dynamic mass balance between the production and consumption of dissolved silica was found to describe the dissolution behavior of SRL-165 defense waste glass in a high-magnesium brine (PBB3) at a temperature of 90 0 C. The synergistic effect of the waste package container on the glass dissolution rate was found to depend on a precipitation reaction for a ferrous silicate mineral. The model predicted that the ferrous silicate precipitate should be variable in composition where the iron/silica stoichiometry depended on the metal/glass surface area ratio used in the experiment. This prediction was confirmed experimentally by the variable iron/silica ratios observed in filtered leachates. However, the interaction between dissolved silica and iron corrosion products needs to be much better understood before the model can be used with confidence in predicting radionuclide release rates for a salt repository. 25 refs., 4 figs., 1 tab

  1. Preparation and evaluation of azithromycin binary solid dispersions using various polyethylene glycols for the improvement of the drug solubility and dissolution rate

    Directory of Open Access Journals (Sweden)

    Ehsan Adeli

    Full Text Available ABSTRACT Azithromycin is a water-insoluble drug, with a very low bioavailability. In order to increase the solubility and dissolution rate, and consequently increase the bioavailability of poorly-soluble drugs (such as azithromycin, various techniques can be applied. One of such techniques is "solid dispersion". This technique is frequently used to improve the dissolution rate of poorly water-soluble compounds. Owing to its low solubility and dissolution rate, azithromycin does not have a suitable bioavailability. Therefore, the main purpose of this investigation was to increase the solubility and dissolution rate of azithromycin by preparing its solid dispersion, using different Polyethylene glycols (PEG. Preparations of solid dispersions and physical mixtures of azithromycin were made using PEG 4000, 6000, 8000, 12000 and 20000 in various ratios, based on the solvent evaporation method. From the studied drug release profile, it was discovered that the dissolution rate of the physical mixture, as the well as the solid dispersions, were higher than those of the drug alone. There was no chemical incompatibility between the drug and polymer from the observed Infrared (IR spectra. Drug-polymer interactions were also investigated using Differential Scanning Calorimetry (DSC, Powder X-Ray Diffraction (PXRD and Scanning Election Microscopy (SEM. In conclusion, the dissolution rate and solubility of azithromycin were found to improve significantly, using hydrophilic carriers, especially PEG 6000.

  2. Thermodynamic and structural models compared with the initial dissolution rates of open-quotes SONclose quotes glass samples

    International Nuclear Information System (INIS)

    Tovena, I.; Advocat, T.; Ghaleb, D.; Vernaz, E.; Larche, F.

    1994-01-01

    The experimentally determined initial dissolution rate R 0 of nuclear glass was correlated with thermodynamic parameters and structural parameters. The initial corrosion rates of six open-quotes R7T7close quotes glass samples measured at 100 degrees C in a Soxhlet device were correlated with the glass free hydration energy and the glass formation enthalpy. These correlations were then tested with a group of 26 SON glasses selected for their wide diversity of compositions. The thermodynamic models provided a satisfactory approximation of the initial dissolution rate determined under Soxhlet conditions for SON glass samples that include up to 15 wt% of boron and some alumina. Conversely, these models are inaccurate if the boron concentration exceeds 15 wt% and the glass contains no alumina. Possible correlations between R 0 and structural parameters, such as the boron coordination number and the number of nonbridging oxygen atoms, were also investigated. The authors show that R 0 varies inversely with the number of 4-coordinate boron atoms; conversely, the results do not substantiate published reports of a correlation between R 0 and the number of nonbridging oxygen atoms

  3. Age- and gender-specific estimates of partnership formation and dissolution rates in the Seattle sex survey.

    Science.gov (United States)

    Nelson, Sara J; Hughes, James P; Foxman, Betsy; Aral, Sevgi O; Holmes, King K; White, Peter J; Golden, Matthew R

    2010-04-01

    Partnership formation and dissolution rates are primary determinants of sexually transmitted infection (STI) transmission dynamics. The authors used data on persons' lifetime sexual experiences from a 2003-2004 random digit dialing survey of Seattle residents aged 18-39 years (N=1,194) to estimate age- and gender-specific partnership formation and dissolution rates. Partnership start and end dates were used to estimate participants' ages at the start of each partnership and partnership durations, and partnerships not enumerated in the survey were imputed. Partnership formation peaked at age 19 at 0.9 (95% confidence interval [CI]: 0.76-1.04) partnerships per year and decreased to 0.1 to 0.2 after age 30 for women and peaked at age 20 at 1.4 (95% CI: 1.08-1.64) and declined to 0.5 after age 30 for men. Nearly one fourth (23.7%) of partnerships ended within 1 week and more than one half (51.2%) ended within 12 weeks. Most (63.5%) individuals 30 to 39 years of age had not formed a new sexual partnership in the past 3 years. A large proportion of the heterosexual population is no longer at substantial STI risk by their early 30s, but similar analyses among high-risk populations may give insight into reasons for the profound disparities in STI rates across populations. Copyright (c) 2010 Elsevier Inc. All rights reserved.

  4. The influence of pressure on the intrinsic dissolution rate of amorphous indomethacin

    DEFF Research Database (Denmark)

    Löbmann, Korbinian; Flouda, Konstantina; Qiu, Danwen

    2014-01-01

    of different compression pressures on the IDR was determined from powder compacts of amorphous (ball-milling) indomethacin (IND), a glass solution of IND and poly(vinylpyrrolidone) (PVP) and crystalline IND. Solid state properties were analyzed with X-ray powder diffraction (XRPD) and the final compacts were...... and to test the potential dissolution advantage of the amorphous form. However, neither the United States Pharmacopeia (USP) nor the European Pharmacopeia (Ph.Eur) state specific limitations for the compression pressure in order to obtain compacts for the IDR determination. In this study, the influence...... visually observed to study the effects of compaction pressure on their surface properties. It was found that there is no significant correlation between IDR and compression pressure for crystalline IND and IND-PVP. This was in line with the observation of similar surface properties of the compacts. However...

  5. Effect of chemical composition of man-made vitreous fibers on the rate of dissolution in vitro at different pHs.

    Science.gov (United States)

    Christensen, V R; Jensen, S L; Guldberg, M; Kamstrup, O

    1994-10-01

    Measurements of rates of dissolution of typical insulation wool fibers (glasswool and basalt based stonewool) and an experimental fiber were made using a flow-through equipment. The liquids used were a modified Gamble's solution, adjusted to pH 4.8 and 7.7 +/- 0.2, respectively. The dissolution of SiO2 and CaO was determined over periods of up to three months. The rate of dissolution of stonewool fibers was lower than that of glasswool fibers at pH 7.7, whereas the opposite was true at pH 4.8. The stonewool fibers dissolve congruently, but glasswool fibers tend to dissolve with leaching. The rates of dissolution of fibers of different compositions, including insulation wool (glasswool, basalt-based stonewool, slagwool) and experimental fibers were screened using a stationary set-up. Both the chemical composition and pH influenced the rates of dissolution. At pH 7.7 alumina was a determining component and at pH 4.8 the content of SiO2 and CaO was determinant. One experimental fiber with a high content of alumina was an exception having a fairly high rate of dissolution both at pH 4.8 and 7.7.

  6. Dissolution kinetics of heulandite at pH 2--12 and 25 degrees C

    International Nuclear Information System (INIS)

    Ragnarsdottir, K.V.

    1993-01-01

    Because of their favourable cation exchange reactions, heulandite and clinoptilolite have been suggested as being capable of immobilizing radionuclides and therefore could possibly act as an important barrier for nuclear waste. Recent studies of laboratory-reacted minerals indicate, however, that hydrated surface layers tend to accumulate highly hydrolyzable heavy elements. These hydrated layers may therefore be the most important retardants for radionuclides. The dissolution rate of heulandite depends strongly on pH. Based on silica release, the logarithm of the steady-state dissolution rate at pH 2 is -13.1 mol cm -2 s -1 . The logarithm of the rate decreases to -15.8 mol cm -2 s -1 at pH 7.2 and increases again to -14.6 mol cm -2 s -1 at pH 12.2. At low pH, Al is released preferentially to silica; but at intermediate and high pH, the release of silica appears to be congruent relative to Al. The change in dissolution rate with pH indicates that at low pH, the dissolution mechanism is controlled by the detachment of a positively charged Al species, >Al-OH 2 + . Below pH 5, however, a silica-rich surface layer is formed requiring diffusion through the layer. At intermediate and high pH, it is likely that the dissolution rate is controlled by the detachment of a negatively charged silica species, >Si - O - . The reaction order of the hydrogen ion under low pH conditions is 0.7, and the reaction order of the OH - ion is 0.3 at high pH. The measured dissolution rates indicate that a 1 mm heulandite crystal would dissolve in 300,000 yrs if the solution composition is maintained undersaturated. 75 refs., 11 figs., 3 tabs

  7. Selection of effective cocrystals former for dissolution rate improvement of active pharmaceutical ingredients based on lipoaffinity index.

    Science.gov (United States)

    Cysewski, Piotr; Przybyłek, Maciej

    2017-09-30

    New theoretical screening procedure was proposed for appropriate selection of potential cocrystal formers possessing the ability of enhancing dissolution rates of drugs. The procedure relies on the training set comprising 102 positive and 17 negative cases of cocrystals found in the literature. Despite the fact that the only available data were of qualitative character, performed statistical analysis using binary classification allowed to formulate quantitative criterions. Among considered 3679 molecular descriptors the relative value of lipoaffinity index, expressed as the difference between values calculated for active compound and excipient, has been found as the most appropriate measure suited for discrimination of positive and negative cases. Assuming 5% precision, the applied classification criterion led to inclusion of 70% positive cases in the final prediction. Since lipoaffinity index is a molecular descriptor computed using only 2D information about a chemical structure, its estimation is straightforward and computationally inexpensive. The inclusion of an additional criterion quantifying the cocrystallization probability leads to the following conjunction criterions H mix 3.61, allowing for identification of dissolution rate enhancers. The screening procedure was applied for finding the most promising coformers of such drugs as Iloperidone, Ritonavir, Carbamazepine and Enthenzamide. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Enhanced dissolution rate of dronedarone hydrochloride via preparation of solid dispersion using vinylpyrrolidone-vinyl acetate copolymer (Kollidone® VA 64)

    Energy Technology Data Exchange (ETDEWEB)

    Jung, Hyuck Jun; Kang, Myung Joo [College of Pharmacy, Dankook University, Cheonan (Korea, Republic of); Han, Sang Duk [Dong-A ST Rese arch Institute, Pharmaceutical Product Research Laboratories, Yongin (Korea, Republic of)

    2015-09-15

    Solid dispersion (SD) systems have been widely used to increase the dissolution rate and oral absorption of poorly water-soluble compounds. In order to enhance the dissolution rate of dronedarone hydrochloride (DRN), a recent antiarrhythmic agent, SDs of DRN were formulated using conventional solvent evaporation method with amorphous polymers including hydroxypropyl methyl cellulose (HPMC), poly(vinyl pyrrolidone) (PVP), and vinylpyrrolidone-vinyl acetate copolymer (VA64). The prepared SDs were characterized in terms of drug crystallinity, morphology, and in vitro dissolution profile in aqueous medium. The physical characterization using differential scanning calorimetry and X-ray powder diffraction revealed that the active compound was molecularly dispersed in all polymeric carriers tested, in a stable amorphous form in drug to polymer ratios ranging from 1:0.5 to 1:2. The dissolution rates of DRN in all SDs were much higher than those from the corresponding physical mixture and drug powder alone. In particular, the greatest dissolution enhancement was obtained from the VA64-based SD in a drug to polymer weight ratio of 1:1, achieving almost complete drug release after 120 min at pH 1.2. Thus, VA64-based SD with higher drug dissolution rate along with a simple preparation process is suggested as an alternative for the oral formulation of the benzofuran derivative.

  9. The Influence of Polyethylene Glycol Solution on the Dissolution Rate of Sustained Release Morphine.

    Science.gov (United States)

    Hodgman, Michael; Holland, Michael G; Englich, Ulrich; Wojcik, Susan M; Grant, William D; Leitner, Erich

    2016-12-01

    Whole bowel irrigation (WBI) is a management option for overdose of medications poorly adsorbed to activated charcoal, with modified release properties, or for body packers. Polyethylene glycol (PEG) is a mixture of ethylene oxide polymers of varying molecular weight. PEG with an average molecular weight of 3350 g/mol is used for WBI. PEG electrolyte lavage solution has been shown in vitro to hasten the dissolution of acetaminophen. The impact of PEG on the pharmacokinetics of extended release pharmaceuticals is unknown. Lower average molecular weight PEG mixtures are used as solvents and excipients. We sought to investigate the impact of PEG on the release of morphine from several extended release morphine formulations. An in vitro gastric model was developed. To test the validity of our model, we first investigated the previously described interaction of ethanol and Avinza®. Once demonstrated, we then investigated the effect of PEG with several extended release morphine formulations. In the validation portion of our study, we confirmed an ethanol Avinza® interaction. Subsequently, we did not observe accelerated release of morphine from Avinza® or generic extended release morphine in the presence of PEG. The use of PEG for gastric decontamination following ingestion of these extended release morphine formulations is unlikely to accelerate morphine release and aggravate intoxication.

  10. Glacial--interglacial stability of ocean pH inferred from foraminifer dissolution rates.

    Science.gov (United States)

    Anderson, David M; Archer, David

    2002-03-07

    The pH of the ocean is controlled by the chemistry of calcium carbonate. This system in turn plays a large role in regulating the CO2 concentration of the atmosphere on timescales of thousands of years and longer. Reconstructions of ocean pH and carbonate-ion concentration are therefore needed to understand the ocean's role in the global carbon cycle. During the Last Glacial Maximum (LGM), the pH of the whole ocean is thought to have been significantly more basic, as inferred from the isotopic composition of boron incorporated into calcium carbonate shells, which would partially explain the lower atmospheric CO2 concentration at that time. Here we reconstruct carbonate-ion concentration--and hence pH--of the glacial oceans, using the extent of calcium carbonate dissolution observed in foraminifer faunal assemblages as compiled in the extensive global CLIMAP data set. We observe decreased carbonate-ion concentrations in the glacial Atlantic Ocean, by roughly 20 micromolkg-1, while little change occurred in the Indian and Pacific oceans relative to today. In the Pacific Ocean, a small (5 micromolkg-1) increase occurred below 3,000m. This rearrangement of ocean pH may be due to changing ocean circulation from glacial to present times, but overall we see no evidence for a shift in the whole-ocean pH as previously inferred from boron isotopes.

  11. pH dependence of the aqueous dissolution rates of perovskite and zirconolite at 90 C

    International Nuclear Information System (INIS)

    McGlinn, P.J.; Hart, K.P.; Loi, E.H.; Vance, E.R.

    1995-01-01

    Perovskite and zirconolite are two of the major phases of the Synroc titanate mineral assemblage. Their aqueous durability under a range of pH conditions at 90 C has been examined. Solution analysis, electron microscopy and X-ray diffraction have been used to investigate the dissolution behavior of these phases, and a perovskite phase doped with Nd, Sr and Al, using buffered solutions at pH levels of 2.1, 3.7, 6.1, 7.9 and 12.9. After 43 days of leaching, Ca and Ti extractions from perovskite and zirconolite show only a weak pH-dependence. SEM investigation of the samples leached at pH 2.1, 6.1 and 12.9 showed that a titanaceous surface layer formed on the perovskite specimens. XRD analysis of the perovskite samples showed that anatase formed on the leached surface at acidic and neutral pHs, but not under alkaline conditions, and that minor amounts of rutile also formed. In the leached perovskite specimens doped with Nd, Sr and Al, no rule was found by XRD and anatase was only detected in the sample leached at pH 2.1. There were no detectable changes in the leached zirconolite samples examined by SEM and XRD

  12. Disintegration rate and properties of active pharmaceutical ingredient particles as determined from the dissolution time profile of a pharmaceutical formulation: an inverse problem.

    Science.gov (United States)

    Horkovics-Kovats, Stefan

    2014-02-01

    Dissolution profile of a finished dosage form (FDF) contains hidden information regarding the disintegration of the form and the particle properties of the active pharmaceutical ingredient. Here, an extraction of this information from the dissolution profile without limitation to sink conditions is provided. In the article, mathematical relationships between the continuously measured dissolution profile of an FDF containing uniform or heterogeneous particles and its disintegration rate are developed. Further, the determinability of the disintegration kinetics and particle properties released from an FDF using the derived recurrent procedure was analyzed. On the basis of the theoretical data sets, it was demonstrated that the introduced analysis of dissolution profiles correctly identifies the disintegration rate of FDF containing multiple particle types. Furthermore, for known disintegration rates, the intrinsic lifetime of particles (time needed for total particle dissolution in infinite volume) released from the FDF and their relative amount can be determined. The extractable information from FDF dissolution time profiles can be utilized in designing of the formulation process, resulting in improved understanding of FDF properties, contributing thus to the implementation of quality by design in the FDF development. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association.

  13. Method of simultaneous continuous determination of transfer rates of iron and chromium into solution during Fe-Cr alloys dissolution

    International Nuclear Information System (INIS)

    Shirinov, T.I.; Florianovich, G.M.; Skuratnik, Ya.B.

    1978-01-01

    Radiometry method of simultaneous continuous registration of transfer rates of iron and chromium into solution from Fe-Cr alloys with various composition has been developed. Using gamma-spectrometer components of Fe-Cr alloys can be determined with high sensitivity in separate samples according to Fe 59 and Cr 51 radioactive labels, obtained by neutron activation. The above method is applied to estimate Fe and Cr transfer rates into H 2 SO 4 solution at the temperature of 50 deg from Fe - 28% Cr alloy during its active dissolution. It is established, that beginning with some seconds of alloy and solution contact, its components transfer into the solution in the same composition, as in the alloy. The method enables to determine Fe with the accuracy of up to 5% and Cr with that of up to 10%

  14. Enhanced Solubility and Dissolution Rate of Lacidipine Nanosuspension: Formulation Via Antisolvent Sonoprecipitation Technique and Optimization Using Box-Behnken Design.

    Science.gov (United States)

    Kassem, Mohamed A A; ElMeshad, Aliaa N; Fares, Ahmed R

    2017-05-01

    Lacidipine (LCDP) is a highly lipophilic calcium channel blocker of poor aqueous solubility leading to poor oral absorption. This study aims to prepare and optimize LCDP nanosuspensions using antisolvent sonoprecipitation technique to enhance the solubility and dissolution of LCDP. A three-factor, three-level Box-Behnken design was employed to optimize the formulation variables to obtain LCDP nanosuspension of small and uniform particle size. Formulation variables were as follows: stabilizer to drug ratio (A), sodium deoxycholate percentage (B), and sonication time (C). LCDP nanosuspensions were assessed for particle size, zeta potential, and polydispersity index. The formula with the highest desirability (0.969) was chosen as the optimized formula. The values of the formulation variables (A, B, and C) in the optimized nanosuspension were 1.5, 100%, and 8 min, respectively. Optimal LCDP nanosuspension had particle size (PS) of 273.21 nm, zeta potential (ZP) of -32.68 mV and polydispersity index (PDI) of 0.098. LCDP nanosuspension was characterized using x-ray powder diffraction, differential scanning calorimetry, and transmission electron microscopy. LCDP nanosuspension showed saturation solubility 70 times that of raw LCDP in addition to significantly enhanced dissolution rate due to particle size reduction and decreased crystallinity. These results suggest that the optimized LCDP nanosuspension could be promising to improve oral absorption of LCDP.

  15. Porous calcium carbonate as a carrier material to increase the dissolution rate of poorly soluble flavouring compounds.

    Science.gov (United States)

    Lundin Johnson, Maria; Noreland, David; Gane, Patrick; Schoelkopf, Joachim; Ridgway, Cathy; Millqvist Fureby, Anna

    2017-04-19

    Two different food grade functionalised porous calcium carbonates (FCC), with different pore size and pore size distributions, were characterised and used as carrier materials to increase the dissolution rate of poorly soluble flavouring compounds in aqueous solution. The loading level was varied between 1.3% by weight (wt%) and 35 wt%, where the upper limit of 35 wt% was the total maximum loading capacity of flavouring compound in FCC based on the fraction of the total weight of FCC plus flavouring compound. Flavouring compounds (l-carvone, vanillin, and curcumin) were selected based on their difference in hydrophilicity and capacity to crystallise. Release kinetic studies revealed that all flavouring compounds showed an accelerated release when loaded in FCC compared to dissolution of the flavouring compound itself in aqueous medium. The amorphous state and/or surface enlargement of the flavouring compound inside or on FCC explains the faster release. The flavouring compounds capable of crystallising (vanillin and curcumin) were almost exclusively amorphous within the porous FCC material as determined by X-ray powder diffraction one week after loading and after storing the loaded FCC material for up to 9 months at room temperature. A small amount of crystalline vanillin and curcumin was detected in the FCC material with large pores and high flavouring compound loading (≥30 wt%). Additionally, two different loading strategies were evaluated, loading by dissolving the flavouring compound in acetone or loading by a hot melt method. Porosimetry data showed that the melt method was more efficient in filling the smallest pores (<100 nm). The main factor influencing the release rate appears to be the amorphous state of the flavouring compound and the increase in exposed surface area. The confinement in small pores prevents crystallisation of the flavouring compounds during storage, providing a stable amorphous form retaining high release rate also after storage.

  16. The effects of disordered structure on the solubility and dissolution rates of some hydrophilic, sparingly soluble drugs.

    Science.gov (United States)

    Mosharraf, M; Sebhatu, T; Nyström, C

    1999-01-15

    The effects of experimental design on the apparent solubility of two sparingly soluble hydrophilic compounds (barium sulphate and calcium carbonate) were studied in this paper. The apparent solubility appeared to be primarily dependent on the amount of solute added to the solvent in each experiment, increasing with increased amounts. This effect seems to be due to the existence of a peripheral disordered layer. However physico-chemical methods used in the present study were not able to unambiguously verify the existence of any disorder in the solid state structure of the drugs. At higher proportions of solute to solvent, the solubility reached a plateau corresponding to the solubility of the disordered or amorphous molecular form of the material. Milling the powders caused the plateau to be reached at lower proportions of solute to solvent, since this further disordered the surface of the drug particles. It was also found that the apparent solubility of the drugs tested decreased after storage at high relative humidities. A model for describing the effects of a disordered surface layer of varying thickness and continuity on the solubility of a substance is presented. This model may be used as a method for detection of minute amount of disorder, where no other technique is capable of detecting the disordered structure. It is suggested that recrystallisation of the material occurs via slow solid-state transition at the surface of the drug particle; this would slowly reduce the apparent solubility of the substance at the plateau level to the thermodynamically stable value. A biphasic dissolution rate profile was obtained. The solubility of the disordered surface of the particles appeared to be the rate-determining factor during the initial dissolution phase, while the solubility of the crystalline core was the rate-determining factor during the final slower phase.

  17. In vitro acellular dissolution of mineral fibres: A comparative study.

    Science.gov (United States)

    Gualtieri, Alessandro F; Pollastri, Simone; Bursi Gandolfi, Nicola; Gualtieri, Magdalena Lassinantti

    2018-05-04

    The study of the mechanisms by which mineral fibres promote adverse effects in both animals and humans is a hot topic of multidisciplinary research with many aspects that still need to be elucidated. Besides length and diameter, a key parameter that determines the toxicity/pathogenicity of a fibre is biopersistence, one component of which is biodurability. In this paper, biodurability of mineral fibres of social and economic importance (chrysotile, amphibole asbestos and fibrous erionite) has been determined for the first time in a systematic comparative way from in vitro acellular dissolution experiments. Dissolution was possible using the Gamble solution as simulated lung fluid (pH = 4 and at body temperature) so to reproduce the macrophage phagolysosome environment. The investigated mineral fibres display very different dissolution rates. For a 0.25 μm thick fibre, the calculated dissolution time of chrysotile is in the range 94-177 days, very short if compared to that of amphibole fibres (49-245 years), and fibrous erionite (181 years). Diffraction and SEM data on the dissolution products evidence that chrysotile rapidly undergoes amorphization with the formation of a nanophasic silica-rich fibrous metastable pseudomorph as first dissolution step whereas amphibole asbestos and fibrous erionite show minor signs of dissolution even after 9-12 months.

  18. Theoretical consideration on the application of the Aagaard-Helgeson rate law to the dissolution of silicate minerals and glasses

    International Nuclear Information System (INIS)

    Gin, S.; Jegou, C.; Frugier, P.; Minet, Y.

    2008-01-01

    The kinetic laws derived from the work of Aagaard and Helgeson are discussed, notably those applied to aluminosilicate or borosilicate glasses. Aagaard and Helgeson extended the kinetic formalism of an elementary reaction in a homogeneous medium to overall alteration processes in heterogeneous media by assuming they consist of a series of elementary steps. The dissolution rate of a mineral phase can thus be expressed as follows: r φ = k φ Π(i)a i -n ij (1-exp(-A/σRT)) (1) where k φ is the kinetic constant of hydrolysis of the mineral φ, a i the activity of the reactants i in the limiting elementary step j, n ij the stoichiometric coefficient for reactant i in the limiting reaction j, A the chemical affinity of the overall dissolution reaction, σ the average stoichiometric number of the overall reaction, R the ideal gas constant and T the temperature. We first illustrate the relation between transition state theory and a kinetic law such as Eq. (1) initially associated with an elementary reaction, using the simple example of hydriodic acid synthesis. We then discuss the extension of Eq. (1) to overall processes, showing that there is no obvious relation between the elementary limiting step and the contents of the affinity function and that this reflects a problem of scale in the Aagaard-Helgeson law between the kinetic constant (based on microscopic theories) and the affinity term (a macroscopic entity derived from classical thermodynamics). The discussion shows the difficulties encountered in attempting to determine the activity of the reactants in the elementary limiting step, particularly in the case of surface groups, and highlights the limited validity of extending a chemical affinity law of the type (1-exp(-ΔG/RT))- which is theoretically valid for an elementary reaction near equilibrium for an overall process. Our article then reviews Grambow's reasoning and the difficulties he encountered in applying the Aagaard-Helgeson law to the dissolution of

  19. The effect of clay on the dissolution of nuclear waste glass

    Science.gov (United States)

    Lemmens, K.

    2001-09-01

    In a nuclear waste repository, the waste glass can interact with metals, backfill materials (if present) and natural host rock. Of the various host rocks considered, clays are often reported to delay the onset of the apparent glass saturation, where the glass dissolution rate becomes very small. This effect is ascribed to the sorption of silica or other glass components on the clay. This can have two consequences: (1) the decrease of the silica concentration in solution increases the driving force for further dissolution of glass silica, and (2) the transfer of relatively insoluble glass components (mainly silica) from the glass surface to the clay makes the alteration layer less protective. In recent literature, the latter explanation has gained credibility. The impact of the environmental materials on the glass surface layers is however not well understood. Although the glass dissolution can initially be enhanced by clay, there are arguments to assume that it will decrease to very low values after a long time. Whether this will indeed be the case, depends on the fate of the released glass components in the clay. If they are sorbed on specific sites, it is likely that saturation of the clay will occur. If however the released glass components are removed by precipitation (growth of pre-existing or new secondary phases), saturation of the clay is less likely, and the process can continue until exhaustion of one of the system components. There are indications that the latter mechanism can occur for varying glass compositions in Boom Clay and FoCa clay. If sorption or precipitation prevents the formation of protective surface layers, the glass dissolution can in principle proceed at a high rate. High silica concentrations are assumed to decrease the dissolution rate (by a solution saturation effect or by the impact on the properties of the glass alteration layer). In glass corrosion tests at high clay concentrations, silica concentrations are, however, often higher

  20. The effect of clay on the dissolution of nuclear waste glass

    International Nuclear Information System (INIS)

    Lemmens, K.

    2001-01-01

    In a nuclear waste repository, the waste glass can interact with metals, backfill materials (if present) and natural host rock. Of the various host rocks considered, clays are often reported to delay the onset of the apparent glass saturation, where the glass dissolution rate becomes very small. This effect is ascribed to the sorption of silica or other glass components on the clay. This can have two consequences: (1) the decrease of the silica concentration in solution increases the driving force for further dissolution of glass silica, and (2) the transfer of relatively insoluble glass components (mainly silica) from the glass surface to the clay makes the alteration layer less protective. In recent literature, the latter explanation has gained credibility. The impact of the environmental materials on the glass surface layers is however not well understood. Although the glass dissolution can initially be enhanced by clay, there are arguments to assume that it will decrease to very low values after a long time. Whether this will indeed be the case, depends on the fate of the released glass components in the clay. If they are sorbed on specific sites, it is likely that saturation of the clay will occur. If however the released glass components are removed by precipitation (growth of pre-existing or new secondary phases), saturation of the clay is less likely, and the process can continue until exhaustion of one of the system components. There are indications that the latter mechanism can occur for varying glass compositions in Boom Clay and FoCa clay. If sorption or precipitation prevents the formation of protective surface layers, the glass dissolution can in principle proceed at a high rate. High silica concentrations are assumed to decrease the dissolution rate (by a solution saturation effect or by the impact on the properties of the glass alteration layer). In glass corrosion tests at high clay concentrations, silica concentrations are, however, often higher

  1. Morphological evolution of dissolving feldspar particles with anisotropic surface kinetics and implications for dissolution rate normalization and grain size dependence: A kinetic modeling study

    Science.gov (United States)

    Zhang, Li; Lüttge, Andreas

    2009-11-01

    With previous two-dimensional (2D) simulations based on surface-specific feldspar dissolution succeeding in relating the macroscopic feldspar kinetics to the molecular-scale surface reactions of Si and Al atoms ( Zhang and Lüttge, 2008, 2009), we extended our modeling effort to three-dimensional (3D) feldspar particle dissolution simulations. Bearing on the same theoretical basis, the 3D feldspar particle dissolution simulations have verified the anisotropic surface kinetics observed in the 2D surface-specific simulations. The combined effect of saturation state, pH, and temperature on the surface kinetics anisotropy has been subsequently evaluated, found offering diverse options for morphological evolution of dissolving feldspar nanoparticles with varying grain sizes and starting shapes. Among the three primary faces on the simulated feldspar surface, the (1 0 0) face has the biggest dissolution rate across an extensively wide saturation state range and thus acquires a higher percentage of the surface area upon dissolution. The slowest dissolution occurs to either (0 0 1) or (0 1 0) faces depending on the bond energies of Si-(O)-Si ( ΦSi-O-Si/ kT) and Al-(O)-Si ( ΦAl-O-Si/ kT). When the ratio of ΦSi-O-Si/ kT to ΦAl-O-Si/ kT changes from 6:3 to 7:5, the dissolution rates of three primary faces change from the trend of (1 0 0) > (0 1 0) > (0 0 1) to the trend of (1 0 0) > (0 0 1) > (0 1 0). The rate difference between faces becomes more distinct and accordingly edge rounding becomes more significant. Feldspar nanoparticles also experience an increasing degree of edge rounding from far-from-equilibrium to close-to-equilibrium. Furthermore, we assessed the connection between the continuous morphological modification and the variation in the bulk dissolution rate during the dissolution of a single feldspar particle. Different normalization treatments equivalent to the commonly used mass, cube assumption, sphere assumption, geometric surface area, and reactive

  2. Impact of pore characteristics of silica materials on loading capacity and release behavior of ibuprofen

    Energy Technology Data Exchange (ETDEWEB)

    Numpilai, Thanapha [Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900 (Thailand); Muenmee, Suthaporn [Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900 (Thailand); Center for Advanced Studies in Nanotechnology and Its Applications in Chemical Food and Agricultural Industries, Kasetsart University, Bangkok 10900 (Thailand); Witoon, Thongthai, E-mail: fengttwi@ku.ac.th [Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900 (Thailand); Center for Advanced Studies in Nanotechnology and Its Applications in Chemical Food and Agricultural Industries, Kasetsart University, Bangkok 10900 (Thailand); NANOTEC-KU-Center of Excellence on Nanoscale Materials Design for Green Nanotechnology, Kasetsart University, Bangkok 10900 (Thailand)

    2016-02-01

    Impact of pore characteristics of porous silica supports on loading capacity and release behavior of ibuprofen was investigated. The porous silica materials and ibuprofen-loaded porous silica materials were thoroughly characterized by N{sub 2}-sorption, thermal gravimetric and derivative weight analyses (TG-DTW), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM) to determine the physical properties of materials, amount of ibuprofen adsorbed and position of ibuprofen. The detailed characterization reveals that the ibuprofen molecules adsorbed inside the mesopores. Increasing the mesopore size from 5 nm to 10 nm increased the ibuprofen loading from 0.74 to 0.85 mmol/g, respectively. Incorporation of macropore into the structure of porous silica materials enhanced the ibuprofen loading capacity of 11.8–20.3%. The ibuprofen-loaded bimodal meso-macroporous silica materials exhibited the highest dissolution of 92 wt.% within an hour. The ibuprofen particles deposited on the external surface of the porous silica materials showed a lower dissolution rate than the ibuprofen adsorbed inside the mesopores due to the formation of ibuprofen crystalline. - Highlights: • Impacts of pore characteristics of supports on adsorption and release of ibuprofen • Increasing mesopore size increased the ibuprofen loading and dissolution rate. • Macropores reduced the diffusion pathway of ibuprofen and dissolution medium.

  3. Impact of pore characteristics of silica materials on loading capacity and release behavior of ibuprofen

    International Nuclear Information System (INIS)

    Numpilai, Thanapha; Muenmee, Suthaporn; Witoon, Thongthai

    2016-01-01

    Impact of pore characteristics of porous silica supports on loading capacity and release behavior of ibuprofen was investigated. The porous silica materials and ibuprofen-loaded porous silica materials were thoroughly characterized by N 2 -sorption, thermal gravimetric and derivative weight analyses (TG-DTW), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM) to determine the physical properties of materials, amount of ibuprofen adsorbed and position of ibuprofen. The detailed characterization reveals that the ibuprofen molecules adsorbed inside the mesopores. Increasing the mesopore size from 5 nm to 10 nm increased the ibuprofen loading from 0.74 to 0.85 mmol/g, respectively. Incorporation of macropore into the structure of porous silica materials enhanced the ibuprofen loading capacity of 11.8–20.3%. The ibuprofen-loaded bimodal meso-macroporous silica materials exhibited the highest dissolution of 92 wt.% within an hour. The ibuprofen particles deposited on the external surface of the porous silica materials showed a lower dissolution rate than the ibuprofen adsorbed inside the mesopores due to the formation of ibuprofen crystalline. - Highlights: • Impacts of pore characteristics of supports on adsorption and release of ibuprofen • Increasing mesopore size increased the ibuprofen loading and dissolution rate. • Macropores reduced the diffusion pathway of ibuprofen and dissolution medium.

  4. Non-destructive prediction of enteric coating layer thickness and drug dissolution rate by near-infrared spectroscopy and X-ray computed tomography.

    Science.gov (United States)

    Ariyasu, Aoi; Hattori, Yusuke; Otsuka, Makoto

    2017-06-15

    The coating layer thickness of enteric-coated tablets is a key factor that determines the drug dissolution rate from the tablet. Near-infrared spectroscopy (NIRS) enables non-destructive and quick measurement of the coating layer thickness, and thus allows the investigation of the relation between enteric coating layer thickness and drug dissolution rate. Two marketed products of aspirin enteric-coated tablets were used in this study, and the correlation between the predicted coating layer thickness and the obtained drug dissolution rate was investigated. Our results showed correlation for one product; the drug dissolution rate decreased with the increase in enteric coating layer thickness, whereas, there was no correlation for the other product. Additional examination of the distribution of coating layer thickness by X-ray computed tomography (CT) showed homogenous distribution of coating layer thickness for the former product, whereas the latter product exhibited heterogeneous distribution within the tablet, as well as inconsistent trend in the thickness distribution between the tablets. It was suggested that this heterogeneity and inconsistent trend in layer thickness distribution contributed to the absence of correlation between the layer thickness of the face and side regions of the tablets, which resulted in the loss of correlation between the coating layer thickness and drug dissolution rate. Therefore, the predictability of drug dissolution rate from enteric-coated tablets depended on the homogeneity of the coating layer thickness. In addition, the importance of micro analysis, X-ray CT in this study, was suggested even if the macro analysis, NIRS in this study, are finally applied for the measurement. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Hindered disulfide bonds to regulate release rate of model drug from mesoporous silica.

    Science.gov (United States)

    Nadrah, Peter; Maver, Uroš; Jemec, Anita; Tišler, Tatjana; Bele, Marjan; Dražić, Goran; Benčina, Mojca; Pintar, Albin; Planinšek, Odon; Gaberšček, Miran

    2013-05-01

    With the advancement of drug delivery systems based on mesoporous silica nanoparticles (MSNs), a simple and efficient method regulating the drug release kinetics is needed. We developed redox-responsive release systems with three levels of hindrance around the disulfide bond. A model drug (rhodamine B dye) was loaded into MSNs' mesoporous voids. The pore opening was capped with β-cyclodextrin in order to prevent leakage of drug. Indeed, in absence of a reducing agent the systems exhibited little leakage, while the addition of dithiothreitol cleaved the disulfide bonds and enabled the release of cargo. The release rate and the amount of released dye were tuned by the level of hindrance around disulfide bonds, with the increased hindrance causing a decrease in the release rate as well as in the amount of released drug. Thus, we demonstrated the ability of the present mesoporous systems to intrinsically control the release rate and the amount of the released cargo by only minor structural variations. Furthermore, an in vivo experiment on zebrafish confirmed that the present model delivery system is nonteratogenic.

  6. Dissolution kinetics of smectite in geological repository system of TRU waste

    International Nuclear Information System (INIS)

    Sato, Tsutomu

    2005-02-01

    Extensive use of cement for encapsulation, mine timbering, and grouting purposes is envisaged in geological repositories of TRU waste. Degradation of cement materials in the repositories can produce a high pH pore fluid initially ranging from pH 13.0 to 13.5. The high pH pore fluids can migrate and react chemically with the host rock and bentonites which were employed to enhance repository's integrity. These chemical reactions can effect the capacity of the rocks and bentonites in retarding the migration of radionuclides. Smectite, main component of bentonite, can lose some of their desirable properties at the early stages of bentonite-cement fluid interaction. This has been a key research issue in performance assessment of TRU waste disposal. In this study, firstly, the factors affected on dissolution rate of smectite and equations describing dissolution rate were reviewed. Secondly, the effect of dissolved silica on the dissolution behavior of Na-montmorillonite was investigated. Bulk sample flow-through dissolution experiments at alkaline condition (pH 13.3) with different dissolved silica concentrations at different temperatures were performed. Titration experiments were also carried out at similar conditions. Atomic Force Microscopy (AFM) ex situ observations (i.e. on samples from flow-through experiments) was also performed to obtain the dissolution rate. Current results from bulk sample surface titration experiments indicate that dissolved silica has no pronounced effect on the surface titration behavior of Na-montmorillonite at any temperature. However, the trends for the surface titration behavior represent the averaged behavior of all particle sizes (i.e. including colloids) such that within an order of magnitude change cannot be quantified appreciably. Bulk flow-through dissolution experiments coupled with ex situ AFM observations indicate that there is also no effect of dissolved silica with comparatively low concentration of the reacting solution on

  7. Dissolution rates of unirradiated UO2, UO2 doped with 233U, and spent fuel under normal atmospheric conditions and under reducing conditions using an isotope dilution method

    International Nuclear Information System (INIS)

    Ollila, Kaija; Albinsson, Yngve; Oversby, Virginia; Cowper, Mark

    2003-10-01

    The experimental results given in this report allow us to draw the following conclusions. 1) Tests using unirradiated fuel pellet materials from two different manufacturers gave very different dissolution rates under air atmosphere testing. Tests for fragments of pellets from different pellets made by the same manufacturer gave good agreement. This indicates that details of the manufacturing process have a large effect on the behavior of unirradiated UO 2 in dissolution experiments. Care must be taken in interpreting differences in results obtained in different laboratories because the results may be affected by manufacturing effects. 2) Long-term tests under air atmosphere have begun to show the effects of precipitation. Further testing will be needed before the samples reach steady state. 3) Testing of unirradiated UO 2 in systems containing an iron strip to produce reducing conditions gave [U] less than detection limits ( 235 U added as spike was recovered, indicating that 90% of the spike had precipitated onto the solid sample or the iron strip. 9) Tests of UO 2 pellet materials containing 233 U to provide an alpha decay activity similar to that expected for spent fuel 3000 and 10,000 years after disposal showed that the pellet materials behaved as expected under air atmosphere conditions, showing that the manufacturing method was successful. 10) Early testing of the 233 U-doped materials under reducing conditions showed relatively rapid (30 minute) dissolution of small amounts of U at the start of the puff test procedure. Results of analyses of an acidified fraction of the same solutions after 1 or 2 weeks holding indicate that the solutions were inhomogeneous, indicating the presence of colloidal material or small grains of solid. 11) Samples from the 233 U-doped tests initially indicated dissolution of solid during the first week of testing, with some indication of more rapid dissolution of the material with the higher doping. 12) The second cycle of testing

  8. Calcite Dissolution Kinetics

    Science.gov (United States)

    Berelson, W.; Subhas, A.; Dong, S.; Naviaux, J.; Adkins, J. F.

    2016-12-01

    A geological buffer for high atmospheric CO2 concentrations is neutralization via reaction with CaCO3. We have been studying the dissolution kinetics of carbonate minerals using labeled 13C calcite and Picarro-based measurements of 13C enrichments in solution DIC. This methodology has greatly facilitated our investigation of dissolution kinetics as a function of water carbonate chemistry, temperature and pressure. One can adjust the saturation state Omega by changing the ion activity product (e.g. adjusting carbonate ion concentration), or by changing the solubility product (e.g. adjusting temperature or pressure). The canonical formulation of dissolution rate vs. omega has been refined (Subhas et al. 2015) and shows distinct non-linear behavior near equilibrium and rates in sea water of 1-3 e-6 g/cm2day at omega = 0.8. Carbonic anhydrase (CA), an enzyme that catalyzes the hydration of dissolved CO2 to carbonic acid, was shown (in concentrations 500x. This result points to the importance of carbonic acid in enhancing dissolution at low degrees of undersaturation. CA activity and abundance in nature must be considered regarding the role it plays in catalyzing dissolution. We also have been investigating the role of temperature on dissolution kinetics. An increase of 16C yields an order of magnitude increase in dissolution rate. Temperature (and P) also change Omega critical, the saturation state where dissolution rates change substantially. Increasing pressure (achieved in a pressure reaction chamber we built) also shifts Omega critical closer to equilibrium and small pressure increases have large impact on dissolution kinetics. Dissolution rates are enhanced by an order of magnitude for a change in pressure of 1500 psi relative to the dissolution rate achieved by water chemistry effects alone for an omega of 0.8. We've shown that the thermodynamic determination of saturation state does not adequately describe the kinetics of dissolution. The interplay of mineral

  9. Effects of network dissolution changes on pore-to-core upscaled reaction rates for kaolinite and anorthite reactions under acidic conditions

    KAUST Repository

    Kim, Daesang

    2013-11-01

    We have extended reactive flow simulation in pore-network models to include geometric changes in the medium from dissolution effects. These effects include changes in pore volume and reactive surface area, as well as topological changes that open new connections. The computed changes were based upon a mineral map from an X-ray computed tomography image of a sandstone core. We studied the effect of these changes on upscaled (pore-scale to core-scale) reaction rates and compared against the predictions of a continuum model. Specifically, we modeled anorthite and kaolinite reactions under acidic flow conditions during which the anorthite reactions remain far from equilibrium (dissolution only), while the kaolinite reactions can be near-equilibrium. Under dissolution changes, core-scale reaction rates continuously and nonlinearly evolved in time. At higher injection rates, agreement with predictions of the continuum model degraded significantly. For the far-from-equilibrium reaction, our results indicate that the ability to correctly capture the heterogeneity in dissolution changes in the reactive mineral surface area is critical to accurately predict upscaled reaction rates. For the near-equilibrium reaction, the ability to correctly capture the heterogeneity in the saturation state remains critical. Inclusion of a Nernst-Planck term to ensure neutral ionic currents under differential diffusion resulted in at most a 9% correction in upscaled rates.

  10. Bubbles and Dust: Dissolution Rates of Unhydrated Volcanic Ash as a Function of Morphology, Composition, and Particle Size

    Science.gov (United States)

    Wygel, C. M.; Sahagian, D. L.

    2017-12-01

    Volcanic eruptions are natural hazards due to their explosive nature and widespread transportation and deposition of ash particles. After deposition and subsequent leaching in soils or water bodies, ash deposition positively (nutrients) and negatively (contaminants) impacts the health of flora and fauna, including humans. The effects of ash leachates have been difficult to replicate in field and laboratory studies due to the many complexities and differences between ash particles. Ash morphology is characteristic for each eruption, dependent upon eruption energy, and should play a critical role in determining leaching rates. Morphology reflects overall particle surface area, which is strongly influenced by the presence of surface dust. In addition, ash composition, which in part controls morphology and particle size, may also affect leaching rates. This study determines the extent to which ash morphology, surface area, composition, and particle size control ash dissolution rates. Further, it is necessary to determine whether compound vesicular ash particles permit water into their interior structures to understand if both the internal and external surface areas are available for leaching. To address this, six fresh, unhydrated ash samples from diverse volcanic environments and a large range in morphology, from Pele's spheres to vesicular compound ash, are tested in the laboratory. Ash morphology was characterized on the Scanning Electron Microscope (SEM) before and after leaching and surface area was quantified by Brunauer Emmett Teller (BET) analysis and with geometric calculations. Column Leachate Tests (CLT) were conducted to compare leaching rates over a range of basaltic to silicic ashes as a function of time and surface area, to recreate the effects of ash deposition in diverse volcanic environments. After the CLT, post-leaching water analyses were conducted by Ion Coupled Plasma-Mass Spectrometry (ICP-MS) and Ion Chromatography (IC). We find that leaching

  11. Surface properties, solubility and dissolution kinetics of bamboo phytoliths

    Science.gov (United States)

    Fraysse, Fabrice; Pokrovsky, Oleg S.; Schott, Jacques; Meunier, Jean-Dominique

    2006-04-01

    Although phytoliths, constituted mainly by micrometric opal, exhibit an important control on silicon cycle in superficial continental environments, their thermodynamic properties and reactivity in aqueous solution are still poorly known. In this work, we determined the solubility and dissolution rates of bamboo phytoliths collected in the Réunion Island and characterized their surface properties via electrophoretic measurements and potentiometric titrations in a wide range of pH. The solubility product of "soil" phytoliths ( pKsp0=2.74 at 25 °C) is equal to that of vitreous silica and is 17 times higher than that of quartz. Similarly, the enthalpy of phytoliths dissolution reaction (ΔHr25-80°C=10.85kJ/mol) is close to that of amorphous silica but is significantly lower than the enthalpy of quartz dissolution. Electrophoretic measurements yield isoelectric point pH IEP = 1.2 ± 0.1 and 2.5 ± 0.2 for "soil" (native) and "heated" (450 °C heating to remove organic matter) phytoliths, respectively. Surface acid-base titrations allowed generation of a 2-p K surface complexation model. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 2 ⩽ pH ⩽ 12, were found to be intermediate between those of quartz and vitreous silica. The dissolution rate dependence on pH was modeled within the concept of surface coordination theory using the equation: R=k1·{>SiOH2+}n+k2·{>SiOH0}+k3·{>SiO-}m, where {> i} stands for the concentration of the surface species present at the SiO 2-H 2O interface, ki are the rate constants of the three parallel reactions and n and m represent the order of the proton- and hydroxy-promoted reactions, respectively. It follows from the results of this study that phytoliths dissolution rates exhibit a minimum at pH ˜ 3. This can explain their good preservation in the acidic soil horizons of Réunion Island. In terms of silicon biogeochemical cycle, phytoliths represent a large buffering reservoir

  12. Application of experimental design in examination of the dissolution rate of carbamazepine from formulations: Characterization of the optimal formulation by DSC, TGA, FT-IR and PXRD analysis

    Directory of Open Access Journals (Sweden)

    Krstić Marko

    2015-01-01

    Full Text Available Poor solubility is one of the key reasons for the poor bioavailability of these drugs. This paper displays a formulation of a solid surfactant system with carbamazepine, in order to increase its dissolution rate. Solid state surfactant systems are formed by application of fractal experimental design. Poloxamer 237 and Poloxamer 338 were used as surfactants and Brij® 35 was used as the co-surfactant. The ratios of the excipients and carbamazepine were varied and their effects on the dissolution rate of carbamazepine were examined. Moreover, the effects of the addition of natural (diatomite and a synthetic adsorbent carrier (Neusiline UFL2 on the dissolution rate of carbamazepine were also tested. The prepared surfactant systems were characterized and the influence of the excipients on possible changes of the polymorphous form of carbamazepine examined by application of analytical techniques (DSC, TGA, FT-IR, PXRD. It was determined that an appropriate selection of the excipient type and ratio could provide a significant increase in the carbamazepine dissolution rate. By application of analytical techniques, it was found that that the employed excipients induce a transition of carbamazepine into the amorphous form and that the selected sample was stable for three months, when kept under ambient conditions. [Projekat Ministarstva nauke Republike Srbije, br. TR34007

  13. Effect of particle size on solubility, dissolution rate, and oral bioavailability: evaluation using coenzyme Q10 as naked nanocrystals

    Directory of Open Access Journals (Sweden)

    Sun J

    2012-11-01

    Full Text Available Jiao Sun,1 Fan Wang,1,2 Yue Sui,1 Zhennan She,1 Wenjun Zhai,1 Chunling Wang,1 Yihui Deng11College of Pharmacy, Shenyang Pharmaceutical University, Shenyang, China; 2Beijing Zhijianjinrui Applied Pharmaceutical Science Inc, Beijing, ChinaAbstract: In this paper work, four naked nanocrystals (size range 80–700 nm were prepared without any surfactant or polymer using the solvent/nonsolvent method. The effects of particle size on their solubility, dissolution, and oral bioavailability were investigated. Solubility and dissolution testing were performed in three types of dissolution medium, and the studies demonstrated that the equilibrium solubilities of coenzyme Q10 nanocrystals and bulk drugs were not affected by the dissolution media but the kinetic solubilities were. Kinetic solubility curves and changes in particle size distribution were determined and well explained by the proposed solubilization model for the nanocrystals and bulk drugs. The particle size effect on dissolution was clearly influenced by the diffusion coefficients of the various dissolution media, and the dissolution velocity of coenzyme Q10 increased as particle size decreased. The bioavailability of coenzyme Q10 after oral administration in beagle dogs was improved by reducing the particle size. For 700 nm nanocrystals, the AUC0–48 was 4.4-fold greater than that for the coarse suspensions, but a further decrease in particle size from 700 nm to 120 nm did not contribute to improvement in bioavailability until the particle size was reduced to 80 nm, when bioavailability was increased by 7.3-fold.Keywords: particle size, solubility, dissolution, nanocrystal, bioavailability, coenzyme Q10

  14. Enhancement of the dissolution rate and bioavailability of fenofibrate by a melt-adsorption method using supercritical carbon dioxide

    Directory of Open Access Journals (Sweden)

    Cha KH

    2012-10-01

    Full Text Available Kwang-Ho Cha,1,3 Kyung-Jin Cho,3 Min-Soo Kim,4 Jeong-Soo Kim,3 Hee Jun Park,1,3 Junsung Park,1,3 Wonkyung Cho,1,3 Jeong-Sook Park,3 Sung-Joo Hwang1,21Yonsei Institute of Pharmaceutical Sciences, 2College of Pharmacy, Yonsei University, Incheon, Republic of Korea; 3College of Pharmacy, Chungnam National University, Daejeon, Republic of Korea; 4Department of Pharmaceutical Engineering, Inje University, Gimhae, Republic of KoreaBackground: The aim of this study was to enhance the bioavailability of fenofibrate, a poorly water-soluble drug, using a melt-adsorption method with supercritical CO2.Methods: Fenofibrate was loaded onto Neusilin® UFL2 at different weight ratios of fenofibrate to Neusilin UFL2 by melt-adsorption using supercritical CO2. For comparison, fenofibrate-loaded Neusilin UFL2 was prepared by solvent evaporation and hot melt-adsorption methods. The fenofibrate formulations prepared were characterized by differential scanning calorimetry, powder x-ray diffractometry, specific surface area, pore size distribution, scanning electron microscopy, and energy-dispersive x-ray spectrometry. In vitro dissolution and in vivo bioavailability were also investigated.Results: Fenofibrate was distributed into the pores of Neusilin UFL2 and showed reduced crystal formation following adsorption. Supercritical CO2 facilitated the introduction of fenofibrate into the pores of Neusilin UFL2. Compared with raw fenofibrate, fenofibrate from the prepared powders showed a significantly increased dissolution rate and better bioavailability. In particular, the area under the drug concentration-time curve and maximal serum concentration of the powders prepared using supercritical CO2 were 4.62-fold and 4.52-fold greater than the corresponding values for raw fenofibrate.Conclusion: The results of this study highlight the usefulness of the melt-adsorption method using supercritical CO2 for improving the bioavailability of fenofibrate.Keywords: fenofibrate

  15. Effect of clayey groundwater on the dissolution rate of SON68 simulated nuclear waste glass at 70 °C

    Science.gov (United States)

    De Echave, T.; Tribet, M.; Jollivet, P.; Marques, C.; Gin, S.; Jégou, C.

    2018-05-01

    To predict the long-term behavior of high-level radioactive waste glass, it is necessary to study aqueous dissolution of the glass matrix under geological repository conditions. The present article focuses on SON68 (an inactive surrogate of the R7T7 glass) glass alteration in synthetic clayey groundwater at 70 °C. Experiments in deionized water as reference were also performed in the same conditions. Results are in agreement with those of previous studies showing that magnesium present in the solution is responsible for higher glass alteration. This effect is transient and pH-dependent: Once all the magnesium is consumed, the glass alteration rate diminishes. Precipitation of magnesium silicate of the smectite group seems to be the main factor for the increased glass alteration. A pH threshold of 7.5-7.8 was found, above which precipitation of these magnesium silicates at 70 °C is possible. TEM observations reveal that magnesium silicates grow at the expense of the passivating gel, which partly dissolves, forming large pores which increase mass transfer between the reacting glass surface and the bulk solution.

  16. Preparation of Vitexin Nanoparticles by Combining the Antisolvent Precipitation and High Pressure Homogenization Approaches Followed by Lyophilization for Dissolution Rate Enhancement.

    Science.gov (United States)

    Gu, Chengbo; Liu, Ziwei; Yuan, Xiaohan; Li, Wang; Zu, Yuangang; Fu, Yujie

    2017-11-22

    Vitexin, a natural flavonoid found in many medicinal plants, is well known for its rich pharmacological activities. However, the poor water solubility of vitexin has limited its therapeutic application. The aim of this study was to prepare the nanoparticles of vitexin by combining the antisolvent precipitation (ASP) and high pressure homogenization (HPH) approaches followed by lyophilization for improving the dissolution rate of this poorly water-soluble drug. The effects of main factors influencing the mean particle size (MPS) of vitexin were investigated and optimized. Under optimum conditions, vitexin nanosuspensions with an MPS of 80.5 nm were obtained and then lyophilized to form nanoparticles. The obtained vitexin nanoparticles were further characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), mass spectrometry (MS), X-ray powder diffraction (XRPD), gas chromatography (GC) and dissolution testing. The results showed that the nanoparticles of vitexin were converted into an amorphous form, with its chemical structure unchanged. Additionally, the residual dimethyl sulfoxide (DMSO) is lower than the International Conference on Harmonization (ICH) limit for class 3 solvents. The dissolution rate of processed vitexin was significantly higher (5.58-fold) than that of raw drug. Overall, the combinative process we developed is an effective way to produce vitexin nanoparticles with markedly enhanced dissolution rate.

  17. Solid dispersions, part I: recent evolutions and future opportunities in manufacturing methods for dissolution rate enhancement of poorly water-soluble drugs.

    Science.gov (United States)

    Bikiaris, Dimitrios N

    2011-11-01

    In recent years, the number of active pharmaceutical ingredients with high therapeutic impact, but very low water solubility, has increased significantly. Thus, a great challenge for pharmaceutical technology is to create new formulations and efficient drug-delivery systems to overcome these dissolution problems. Drug formulation in solid dispersions (SDs) is one of the most commonly used techniques for the dissolution rate enhancement of poorly water-soluble drugs. Generally, SDs can be defined as a dispersion of active ingredients in molecular, amorphous and/or microcrystalline forms into an inert carrier. This review covers literature which states that the dissolution enhancement of SDs is based on the fact that drugs in the nanoscale range, or in amorphous phase, dissolve faster and to a greater extent than micronized drug particles. This is in accordance to the Noyes-Whitney equation, while the wetting properties of the used polymer may also play an important role. The main factors why SD-based pharmaceutical products on the market are steadily increasing over the last few years are: the recent progress in various methods used for the preparation of SDs, the effect of evolved interactions in physical state of the drug and formulation stability during storage, the characterization of the physical state of the drug and the mechanism of dissolution rate enhancement.

  18. Dissolution of nuclear fuels

    International Nuclear Information System (INIS)

    Uriarte Hueda, A.; Berberana Eizmendi, M.; Rainey, R.

    1968-01-01

    A laboratory study was made of the instantaneous dissolution rate (IDR) for unirradiated uranium metal rods and UO 2 , PuO 2 and PuO 2 -UO 2 pellets in boiling nitric acid alone and with additives. The uranium metal and UO 2 dissolved readily in nitric acid alone; PuO 2 dissolved slowly even with the addition of fluoride; PuO 2 -UO 2 pellets containing as much as 35% PuO 2 in UO 2 gave values of the instantaneous dissolution rate to indicate can be dissolved with nitric acid alone. An equation to calculate the time for complete dissolution has been determinate in function of the instantaneous dissolution rates. The calculated values agree with the experimental. Uranium dioxide pellets from various sources but all having a same density varied in instantaneous dissolution rate. All the pellets, however, have dissolved ved in the same time. The time for complete dissolution of PuO 2 -UO 2 pellets, having the same composition, and the concentration of the used reagents are function of the used reagents are function of the fabrication method. (Author) 8 refs

  19. Effect of Microenvironmental pH Modulation on the Dissolution Rate and Oral Absorption of the Salt of a Weak Acid - Case Study of GDC-0810.

    Science.gov (United States)

    Hou, Hao Helen; Jia, Wei; Liu, Lichuan; Cheeti, Sravanthi; Li, Jane; Nauka, Ewa; Nagapudi, Karthik

    2018-01-29

    The purpose of this work is to investigate the effect of microenvironmental pH modulation on the in vitro dissolution rate and oral absorption of GDC-0810, an oral anti-cancer drug, in human. The pH-solubility profile of GDC-0810 free acid and pH max of its N-Methyl-D-glucamine (NMG) salt were determined. Precipitation studies were conducted for GDC-0810 NMG salt at different pH values. GDC-0810 200-mg dose NMG salt tablet formulations containing different levels of sodium bicarbonate as the pH modifier were tested for dissolution under the dual pH-dilution scheme. Three tablet formulations were evaluated in human as a part of a relative bioavailability study. A 200-mg dose of GDC-0810 was administered QD with low fat food. Intrinsic solubility of GDC-0810 free acid was found to be extremely low. The pH max of the NMG salt suggested a strong tendency for form conversion to the free acid under GI conditions. In vitro dissolution profiles showed that the dissolution rate and extent of GDC-0810 increased with increasing the level of sodium bicarbonate in the formulation. The human PK data showed a similar trend for the geometric mean of C max and AUC 0-t for formulations containing 5%, 10%, and 15% sodium bicarbonate, but the difference is not statistically significant. Incorporation of a basic pH modifier, sodium bicarbonate, in GDC-0810 NMG salt tablet formulations enhanced in vitro dissolution rate of GDC-0810 via microenvironmental pH modulation. The human PK data showed no statistically significant difference in drug exposure from tablets containing 5%, 10%, and 15% sodium bicarbonate.

  20. Solubility limits on radionuclide dissolution

    Energy Technology Data Exchange (ETDEWEB)

    Kerrisk, J.F.

    1984-12-31

    This paper examines the effects of solubility in limiting dissolution rates of a number of important radionuclides from spent fuel and high-level waste. Two simple dissolution models were used for calculations that would be characteristics of a Yucca Mountain repository. A saturation-limited dissolution model, in which the water flowing through the repository is assumed to be saturated with each waste element, is very conservative in that it overestimates dissolution rates. A diffusion-limited dissolution model, in which element-dissolution rates are limited by diffusion of waste elements into water flowing past the waste, is more realistic, but it is subject to some uncertainty at this time. Dissolution rates of some elements (Pu, Am, Sn, Th, Zr, Sm) are always limited by solubility. Dissolution rates of other elements (Cs, Tc, Np, Sr, C, I) are never solubility limited; their release would be limited by dissolution of the bulk waste form. Still other elements (U, Cm, Ni, Ra) show solubility-limited dissolution under some conditions. 9 references, 3 tables.

  1. Influence of the oral dissolution time on the absorption rate of locally administered solid formulations for oromucosal use: the flurbiprofen lozenges paradigm.

    Science.gov (United States)

    Imberti, Roberto; De Gregori, Simona; Lisi, Lucia; Navarra, Pierluigi

    2014-01-01

    Flurbiprofen is a nonsteroidal anti-inflammatory agent preferentially used for local oromucosal treatment of painful and/or inflammatory conditions of the oropharynx such as gingivitis, stomatitis, periodontitis, pharyngitis and laryngitis. In this study, we have investigated the bioavailability of a new generic formulation of flurbiprofen lozenges developed by Epifarma Srl, compared to the originator Benactiv Gola® taken as reference. Within the framework of a formal bioequivalence study, we investigated in particular the putative influence of oral dissolution time (i.e. the time spent suckling the lozenge from its intake to complete dissolution) on the absorption rate, and the contribution of this factor to the total variability of plasma flurbiprofen during absorption. We found that the amount of flurbiprofen absorbed into the systemic circulation is not significantly higher for the test drug compared to that of the reference product. We observed that the length of oral dissolution time is inversely correlated to 10-min flurbiprofen plasma levels in the test but not in the reference formulation. We estimated that oral dissolution time accounts for about 14% of overall variability in flurbiprofen plasma 10 min after test drug administration. © 2014 S. Karger AG, Basel.

  2. GLAMOR - Or How We Achieved A Common Understanding On The Decrease Of Glass Dissolution Kinetics Through International Cooperation

    International Nuclear Information System (INIS)

    Van Iseghem, Pierre; Aerstens, Marc; Gin, Stephane; Grambow, Bernd; Strachan, Denis M.; McGrail, B. Peter; Wicks, George G.; McMenamin, Thomas

    2011-01-01

    The objective of the EC funded GLAMOR project was to achieve a common understanding of the processes that control the decrease of the dissolution rate of high-level waste glass in water when silica becomes saturated. Is affinity control or a protective layer dominating? The following steps were taken: (1) review of the literature, (2) selection ofselect an experimental dataset, and selection of the models r(t) and GM2003, and (3) application apply by the GLAMOR partners of the models to the datasets. The main focus has beenwas on dissolution tests in pure water at different values of surface-to-volume and pH. Some of the main conclusions were: (1) both affinity and protective layer concepts must be considered in the interpretation of the rate decreasing stage, (2) the residual dissolution rate observed beyond the silica saturation stage is far more important in view of the long-term performance of the glass, and deserves more attention in future R and D. In the GLAMOR final report, we also discussed in detail the modeling parameters, such as the silica saturation concentration, the silica diffusion coefficient, the silica retention factor in the reaction layer, and the water diffusion coefficient.

  3. Ordered nanoporous silica as carriers for improved delivery of water insoluble drugs: a comparative study between three dimensional and two dimensional macroporous silica

    Directory of Open Access Journals (Sweden)

    Wang Y

    2013-10-01

    Full Text Available Ying Wang, Qinfu Zhao, Yanchen Hu, Lizhang Sun, Ling Bai, Tongying Jiang, Siling WangDepartment of Pharmaceutics, Shenyang Pharmaceutical University, Liaoning Province, People’s Republic of ChinaAbstract: The goal of the present study was to compare the drug release properties and stability of the nanoporous silica with different pore architectures as a matrix for improved delivery of poorly soluble drugs. For this purpose, three dimensional ordered macroporous (3DOM silica with 3D continuous and interconnected macropores of different sizes (200 nm and 500 nm and classic mesoporous silica (ie, Mobil Composition of Matter [MCM]-41 and Santa Barbara Amorphous [SBA]-15 with well-ordered two dimensional (2D cylindrical mesopores were successfully fabricated and then loaded with the model drug indomethacin (IMC via the solvent deposition method. Scanning electron microscopy (SEM, N2 adsorption, differential scanning calorimetry (DSC, and X-ray diffraction (XRD were applied to systematically characterize all IMC-loaded nanoporous silica formulations, evidencing the successful inclusion of IMC into nanopores, the reduced crystallinity, and finally accelerated dissolution of IMC. It was worth mentioning that, in comparison to 2D mesoporous silica, 3DOM silica displayed a more rapid release profile, which may be ascribed to the 3D interconnected pore networks and the highly accessible surface areas. The results obtained from the stability test indicated that the amorphous state of IMC entrapped in the 2D mesoporous silica (SBA-15 and MCM-41 has a better physical stability than in that of 3DOM silica. Moreover, the dissolution rate and stability of IMC loaded in 3DOM silica was closely related to the pore size of macroporous silica. The colorimetric 3-(4,5-Dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide (MTT and Cell Counting Kit (CCK-8 assays in combination with direct morphology observations demonstrated the good biocompatibility of nanoporous

  4. The biowaiver extension for BCS class III drugs: the effect of dissolution rate on the bioequivalence of BCS class III immediate-release drugs predicted by computer simulation.

    Science.gov (United States)

    Tsume, Yasuhiro; Amidon, Gordon L

    2010-08-02

    The Biopharmaceutical Classification System (BCS) guidance issued by the FDA allows waivers for in vivo bioavailability and bioequivalence studies for immediate-release (IR) solid oral dosage forms only for BCS class I drugs. However, a number of drugs within BCS class III have been proposed to be eligible for biowaivers. The World Health Organization (WHO) has shortened the requisite dissolution time of BCS class III drugs on their Essential Medicine List (EML) from 30 to 15 min for extended biowaivers; however, the impact of the shorter dissolution time on AUC(0-inf) and C(max) is unknown. The objectives of this investigation were to assess the ability of gastrointestinal simulation software to predict the oral absorption of the BCS class I drugs propranolol and metoprolol and the BCS class III drugs cimetidine, atenolol, and amoxicillin, and to perform in silico bioequivalence studies to assess the feasibility of extending biowaivers to BCS class III drugs. The drug absorption from the gastrointestinal tract was predicted using physicochemical and pharmacokinetic properties of test drugs provided by GastroPlus (version 6.0). Virtual trials with a 200 mL dose volume at different drug release rates (T(85%) = 15 to 180 min) were performed to predict the oral absorption (C(max) and AUC(0-inf)) of the above drugs. Both BCS class I drugs satisfied bioequivalence with regard to the release rates up to 120 min. The results with BCS class III drugs demonstrated bioequivalence using the prolonged release rate, T(85%) = 45 or 60 min, indicating that the dissolution standard for bioequivalence is dependent on the intestinal membrane permeability and permeability profile throughout the gastrointestinal tract. The results of GastroPlus simulations indicate that the dissolution rate of BCS class III drugs could be prolonged to the point where dissolution, rather than permeability, would control the overall absorption. For BCS class III drugs with intestinal absorption patterns

  5. The influence of co-formers on the dissolution rates of co-amorphous sulfamerazine/excipient systems

    DEFF Research Database (Denmark)

    Gniado, Katarzyna; Löbmann, Korbinian; Rades, Thomas

    2016-01-01

    A comprehensive study on the dissolution properties of three co-amorphous sulfamerazine/excipient systems, namely sulfamerazine/deoxycholic acid, sulfamerazine/citric acid and sulfamerazine/sodium taurocholate (SMZ/DA, SMZ/CA and SMZ/NaTC; 1:1 molar ratio), is reported. While all three co...

  6. Increase of apatite dissolution rate by Scots pine roots associated or not with Burkholderia glathei PML1(12)Rp in open-system flow microcosms

    Science.gov (United States)

    Calvaruso, Christophe; Turpault, Marie-Pierre; Frey-Klett, Pascale; Uroz, Stéphane; Pierret, Marie-Claire; Tosheva, Zornitza; Kies, Antoine

    2013-04-01

    The release of nutritive elements through apatite dissolution represents the main source of phosphorus, calcium, and several micronutrients (e.g., Zn, Cu) for organisms in non-fertilized forest ecosystems. The aim of this study was to quantify, for the first time, the dissolution rate of apatite grains by tree roots that were or were not associated with a mineral weathering bacterial strain, and by various acids known to be produced by tree roots and soil bacterial strains in open-system flow microcosms. In addition, we explored whether the mobilization of trace elements (including rare earth elements) upon apatite dissolution was affected by the presence of trees and associated microorganisms. The dissolution rate of apatite by Scots pine plants that were or were not inoculated with the strain Burkholderia glathei PML1(12)Rp, and by inorganic (nitric) and organic (citric, oxalic and gluconic) acids at pH 5.5, 4.8, 3.8, 3.5, 3.0, and 2.0 was monitored in two controlled experiments: "plant-bacteria interaction" and "inorganic and organic acids". Analyses of the outlet solutions in the "plant-bacteria interaction" experiment showed that Scots pine roots and B. glathei PML1(12)Rp produced protons and organic acids such as gluconate, oxalate, acetate, and lactate. The weathering budget calculation revealed that Scots pines (with or without PML1(12)Rp) significantly increased (factor > 10) the release of Ca, P, As, Sr, Zn, U, Y, and rare earth elements such as Ce, La, Nd from apatite, compared to control abiotic treatment. Scanning electron microscopy observation confirmed traces of apatite dissolution in contact of roots. Most dissolved elements were taken up by Scots pine roots, i.e., approximately 50% of Ca, 70% of P, 30% of As, 70% of Sr, 90% of Zn, and 100% of U, Y, and rare earth elements. Interestingly, no significant additional effect due to the bacterial strain PML1(12)Rp on apatite dissolution and Scots pine nutrition and growth was observed. The "inorganic

  7. Application of experimental design in examination of the dissolution rate of carbamazepine from formulations: Characterization of the optimal formulation by DSC, TGA, FT-IR and PXRD analysis

    OpenAIRE

    Krstić Marko; Ražić Slavica; Vasiljević Dragana; Spasojević Đurđija; Ibrić Svetlana

    2015-01-01

    Poor solubility is one of the key reasons for the poor bioavailability of these drugs. This paper displays a formulation of a solid surfactant system with carbamazepine, in order to increase its dissolution rate. Solid state surfactant systems are formed by application of fractal experimental design. Poloxamer 237 and Poloxamer 338 were used as surfactants and Brij® 35 was used as the co-surfactant. The ratios of the excipients and carbamazepine were varied...

  8. Solid dispersion of dutasteride using the solvent evaporation method: Approaches to improve dissolution rate and oral bioavailability in rats.

    Science.gov (United States)

    Choi, Jin-Seok; Lee, Sang-Eun; Jang, Woo Suk; Byeon, Jong Chan; Park, Jeong-Sook

    2018-09-01

    The aim of this study was to develop a dutasteride (DUT) solid dispersion (SD) using hydrophilic substances to enhance its dissolution (%) and oral bioavailability in rats. DUT-SD formulations were prepared with various co-polymers using a solvent evaporation method. The physical properties of DUT-SD formulations were confirmed using field emission scanning electron microscopy (FE-SEM), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopy. The toxicity and oral bioavailability of DUT-SD formulations were evaluated. Tocopheryl polyethylene glycol-1000-succinate (TPGS) was chosen as the solubilizer; and methylene chloride, and Aerosil® 200 or microcrystalline cellulose (MCC) were chosen as the solvent and carrier, respectively, based on a solubility test and pre-dissolution study. The dissolution levels of DUT-SD formulations were 86.3 ± 2.3% (F15) and 95.1 ± 1.9% (F16) after 1 h, which were higher than those of the commercial product, i.e., Avodart® (75.8 ± 1.5%) in 0.1 N HCl containing 1% (w/v) sodium lauryl sulfate (SLS). The F16 formulation was found to be stable, after assessing its dissolution (%) and drug content (%) for 6 months. The DUT-SD formulations resulted in relative bioavailability (BA) values of 126.4% (F15) and 132.1% (F16), which were enhanced compared to that of Avodart®. Dissolution (%) and relative BA values were both increased by hydrogen interaction between TPGS and DUT. This study might contribute to a new formulation (powder) whose oral bioavailability is greater than that of Avodart® (soft capsule), which could facilitate to the use of the SD system during the production process. Copyright © 2018 Elsevier B.V. All rights reserved.

  9. Dissolution of aluminium; Disolucion de aluminio

    Energy Technology Data Exchange (ETDEWEB)

    Uriarte Hueda, A; Berberana Eizmendi, M; Pereira Sanchez, G

    1968-07-01

    The dissolution of aluminum with acid solutions ( nitric acid-mercuric nitrate) and alkaline solutions (sodium hydroxide-sodium nitrate) has been studied. The instantaneous dissolution rate (IDR) has been studied in function of the concentration of the used reagents and the dissolution temperature. The complete dissolution has been included in the second part of this report, to know the total dissolution time, the consume of reagents and the stability of the resultant solutions. (Author)

  10. Development of surface stabilized candesartan cilexetil nanocrystals with enhanced dissolution rate, permeation rate across CaCo-2, and oral bioavailability.

    Science.gov (United States)

    Jain, Sanyog; Reddy, Venkata Appa; Arora, Sumit; Patel, Kamlesh

    2016-10-01

    Candesartan cilexetil (CC), an ester prodrug of candesartan, is BCS class II drug with extremely low aqueous solubility limiting its oral bioavailability. The present research aimed to develop a nanocrystalline formulation of CC with improved saturation solubility in gastrointestinal fluids and thereby, exhibiting enhanced oral bioavailability. CC nanocrystals were prepared using a low energy antisolvent precipitation methodology. A combination of hydroxypropyl methylcellulose (HPMC) and Pluronic® F 127 (50:50 w/w) was found to be optimum for the preparation of CC nanocrystals. The particle size, polydispersity index (PDI), and zeta potential of optimized formulation was found to be 159 ± 8.1 nm, 0.177 ± 0.043, and -23.7 ± 1.02 mV, respectively. Optimized formulation was found to possess irregular, plate-like morphology as evaluated by scanning electron microscopy and crystalline as evaluated by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD). A significant increase in saturation solubility and dissolution rate of the optimized nanosuspension was observed at all the tested pH conditions. Optimized CC nanocrystals exhibited a storage stability of more than 3 months when stored under cold and room temperature conditions. In vitro Caco-2 permeability further revealed that CC nanocrystals exhibited nearly 4-fold increase in permeation rate compared to the free CC. In vivo oral bioavailability studies of optimized CC nanocrystals in murine model revealed 3.8-fold increase in the oral bioavailability and twice the C max as compared with the free CC when administered orally. In conclusion, this study has established a crystalline nanosuspension formulation of CC with improved oral bioavailability in murine model. Graphical Abstract Antisolvent precipitation methodology for the preparation of Candesartan Cilexetil nanocrystals for enhanced solubility and oral bioavailability.

  11. 8 Dissolution Kinetics

    African Journals Online (AJOL)

    user

    Experiments measuring the dissolution rates of stilbite (NaCa [Al Si O ].14H O) in pH-buffered ... The rate law was established as R = k (a ) , where k is ... crystalline hydrated aluminosilicate minerals ..... from the crushing process, thin edges or.

  12. Glass properties in the yttria-alumina-silica system

    Science.gov (United States)

    Hyatt, M. J.; Day, D. E.

    1987-01-01

    The glass formation region in the yttria-alumina-silica system was investigated. Properties of glasses containing 25 to 55 wt pct yttria were measured and the effect of the composition was determined. The density, refractive index, thermal-expansion coefficient, and microhardness increased with increasing yttria content. The dissolution rate in 1N HCl increased with increasing yttria content and temperature. These glasses were also found to have high electrical resistivity.

  13. Dissolution characteristics of chalcedony under alkaline condition. Study for changes in mineral composition of engineered barrier composed by bentonite

    International Nuclear Information System (INIS)

    Watanabe, Yasutaka; Yokoyama, Shingo

    2016-01-01

    In the engineered barrier of radioactive waste disposal facilities, it is expected that bentonite is exposed to alkaline groundwater which arise from leaching of cementations materials. Minerals contained in the bentonite will be dissolved by reactions of the alkaline groundwater. Some bentonite contains silica such as quartz and chalcedony. Chalcedony is categorized in intermediate silica which is microcrystalline. It is known that dissolution of silica influences to the dissolution of smectite by means of solubility. However, dissolution kinetics of chalcedony in the alkaline condition has not been investigated, which is an uncertainty in geochemical simulations to evaluate a long-term stability of the engineered barrier. Therefore, this study performed flow-through experiments in alkaline conditions using chalcedony in order to obtain the dissolution rate of the chalcedony. The flow-through experiments was performed using NaOH-NaCl solution adjusted to 0.3 mol/L of ionic strength. Initial pH of the solution was from 8.9 to 13.5. As a result, higher pH and higher temperature showed higher Si ion concentrations of reacted solutions. The dissolution rate of the samples was calculated using Si ion concentrations at steady state of the experiment. Note that, the dissolution rate of the chalcedony was almost same as that of quartz at same temperature. After the experiments, SEM observation showed that rough surface of the chalcedony partly changed to smooth surface like quartz. It is supposed that rough surface of chalcedony was rapidly dissolved because of low degree of crystallization. The dissolution rate obtained is supposedly applicable to highly crystalline SiO 2 of chalcedony. (author)

  14. A general model for the dissolution of nuclear waste glasses in salt brine

    International Nuclear Information System (INIS)

    McGrail, B.P.; Strachan, D.M.

    1988-07-01

    A mechanistic model describing a dynamic mass balance between the production and consumption of dissolved silica was found to describe the dissolution of SRL-165 defense waste glass in a high-magnesium (PBB3) brine at a temperature of 90/degree/C. The synergetic effect of the waste package container on the glass dissolution rate was found to depend on a precipitation reaction for a ferrous silicate mineral. The model predicted that the ferrous silicate precipitate should be variable in composition where the iron-silica ratio depended on the metal-to-glass surface area ratio used in the experiment. This prediction was confirmed experimentally by the variable iron-silica ratios observed in filtered leachates. However, the interaction between dissolved silica and iron corrosion products needs to be much better understood before the model could be used with confidence in predicting radionuclide release rates for a salt repository. If the deleterious effects of the iron corrosion products can be shown to be transient, and the fracturing of the glass can be minimized, it appears that the performance of SRL-165 defense waste glass will be near the NRC regulatory criterion for fraction release of one part in 100,000 in PBB3 brine at 90/degree/C under silica-saturated conditions. 47 refs., 6 figs., 1 tab

  15. Initial results from dissolution rate testing of N-Reactor spent fuel over a range of potential geologic repository aqueous conditions

    International Nuclear Information System (INIS)

    Gray, W.J.; Einziger, R.E.

    1998-04-01

    Hanford N-Reactor spent nuclear fuel (HSNF) may ultimately be placed in a geologic repository for permanent disposal. To determine whether the engineered barrier system that will be designed for emplacement of light-water-reactor (LWR) spent fuel will also suffice for HSNF, aqueous dissolution rate measurements were conducted on the HSNF. The purpose of these tests was to determine whether HSNF dissolves faster or slower than LWR spent fuel under some limited repository-relevant water chemistry conditions. The tests were conducted using a flowthrough method that allows the dissolution rate of the uranium matrix to be measured without interference by secondary precipitation reactions that would confuse interpretation of the results. Similar tests had been conducted earlier with LWR spent fuel, thereby allowing direct comparisons. Two distinct corrosion modes were observed during the course of these 12 tests. The first, Stage 1, involved no visible corrosion of the test specimen and produced no undissolved corrosion products. The second, Stage 2, resulted in both visible corrosion of the test specimen and left behind undissolved corrosion products. During Stage 1, the rate of dissolution could be readily determined because the dissolved uranium and associated fission products remained in solution where they could be quantitatively analyzed. The measured rates were much faster than has been observed for LWR spent fuel under all conditions tested to date when normalized to the exposed test specimen surface areas. Application of these results to repository conditions, however, requires some comparison of the physical conditions of the different fuels. The surface area of LWR fuel that could potentially be exposed to repository groundwater is estimated to be approximately 100 times greater than HSNF. Therefore, when compared on the basis of mass, which is more relevant to repository conditions, the HSNF and LWR spent fuel dissolve at similar rates

  16. Kinetics of silica-phase transitions

    International Nuclear Information System (INIS)

    Duffy, C.J.

    1993-07-01

    In addition to the stable silica polymorph quartz, several metastable silica phases are present in Yucca Mountain. The conversion of these phases to quartz is accompanied by volume reduction and a decrease in the aqueous silica activity, which may destabilize clinoptilolite and mordenite. The primary reaction sequence for the silica phases is from opal or glass to disordered opal-CT, followed by ordering of the opal-CT and finally by the crystallization of quartz. The ordering of opal-CT takes place in the solid state, whereas the conversion of opal-CT takes place through dissolution-reprecipitation involving the aqueous phase. It is proposed that the rate of conversion of opal-CT to quartz is controlled by diffusion of defects out of a disordered surface layer formed on the crystallizing quartz. The reaction rates are observed to be dependent on temperature, pressure, degree of supersaturation, and pH. Rate equations selected from the literature appear to be consistent with observations at Yucca Mountain

  17. Spent fuel dissolution mechanisms

    International Nuclear Information System (INIS)

    Ollila, K.

    1993-11-01

    This study is a literature survey on the dissolution mechanisms of spent fuel under disposal conditions. First, the effects of radiolysis products on the oxidative dissolution mechanisms and rates of UO 2 are discussed. These effects have mainly been investigated by using electrochemical methods. Then the release mechanisms of soluble radionuclides and the dissolution of the UO 2 matrix including the actinides, are treated. Experimental methods have been developed for measuring the grain-boundary inventories of radionuclides. The behaviour of cesium, strontium and technetium in leaching tests shows different trends. Comparison of spent fuel leaching data strongly suggests that the release of 90 Sr into the leachant can be used as a measure of the oxidation/dissolution of the fuel matrix. Approaches to the modelling UO 2 , dissolution are briefly discussed in the next chapter. Lastly, the use of natural material, uraninite, in the evaluation of the long-term performance of spent fuel is discussed. (orig.). (81 ref., 37 figs., 8 tabs.)

  18. Dissolution rate enhancement of the poorly water-soluble drug Tibolone using PVP, SiO2, and their nanocomposites as appropriate drug carriers.

    Science.gov (United States)

    Papadimitriou, Sofia; Bikiaris, Dimitrios

    2009-09-01

    Creation of immediate release formulations for the poorly water-soluble drug Tibolone through the use of solid dispersions (SDs). SD systems of Tibolone (Tibo) with poly(vinylpyrrolidone) (PVP), fumed SiO(2) nanoparticles, and their corresponding ternary systems (PVP/SiO(2)/Tibo) were prepared and studied in order to produce formulations with enhanced drug dissolution rates. The prepared SDs were characterized by the use of differential scanning calorimetry and wide-angle X-ray diffractometry techniques. Also dissolution experiments were performed. From the results it was concluded that PVP as well as SiO(2) can be used as appropriate carriers for the amorphization of Tibo, even when the drug is used at high concentrations (20-30%, w/w). This is due to the evolved interactions taking place between the drug and the used carriers, as was verified by Fourier transform infrared spectroscopy. At higher concentrations the drug was recrystallized. Similar are the observations on the ternary PVP/SiO(2)/Tibo SDs. The dissolution profiles of the drug in PVP/Tibo and SiO(2)/Tibo SDs are directly dependent on the physical state of the drug. Immediately release rates are observed in SD with low drug concentrations, in which Tibo was in amorphous state. However, these release profiles are drastically changed in the ternary PVP/SiO(2)/Tibo SDs. An immediate release profile is observed for low drug concentrations and an almost sustained release as the concentration of Tibo increases. This is due to the weak interactions that take place between PVP and SiO(2), which result in alterations of the characteristics of the carrier (PVP/SiO(2) nanocomposites). Immediate release formulation was created for Tibolone as well as new nanocomposite matrices of PVP/SiO((2)), which drastically change the release profile of the drug to a sustained delivery.

  19. Thermokinetic model of borosilicate glass dissolution: Contextual affinity

    International Nuclear Information System (INIS)

    Advocat, T.; Vernaz, E.; Crovisier, J.L.; Fritz, B.

    1990-01-01

    Short and long-term geochemical interactions of R7T7 nuclear glass with water at 100C were simulated with the DISSOL thermokinetic computer code. Both the dissolved glass quantity and the resulting water composition, saturation states and mineral quantities produced were calculated as a function of time. The rate equation used in the simulation was first proposed by Aagaard and Hegelson: v = k + · S · a( H + ) -n · (1 - e -(A/RT) ). It simulates a gradually diminishing dissolution rate as the reaction affinity diminishes. The best agreement with 1-year experimental data was obtained with a reaction affinity calculated from silica activity (Grambow's hypothesis) rather than taking into account the activity of all the glass components as proposed by Jantzen and Plodinec. The concept of residual affinity was introduced by Grambow to express the fact that the glass dissolution rate does not cease. The authors prefer to replace the term residual affinity by contextual affinity, which expresses the influence on the dissolution rate of three factors: the solution chemistry, the metastability of SiO 2 (m), and the possible precipitation of certain aluminosilicates such as zeolites

  20. Thermokinetic model of borosilicate glass dissolution: contextual affinity

    International Nuclear Information System (INIS)

    Advocat, T.; Vernaz, E.; Crovisier, J.L.; Fritz, B.

    1989-01-01

    Short and long-term geochemical interactions of R7T7 nuclear glass with water at 100 0 C were simulated with the DISSOL thermokinetic computer code. Both the dissolved glass quantity and the resulting water composition, saturation states and mineral quantities produced were calculated as a function of time. The rate equation used in the simulation was first proposed by Aagaard and Helgeson. It simulates a gradually diminishing dissolution rate as the reaction affinity diminishes. The best agreement with 1-year experimental data was obtained with a reaction affinity calculated from silica activity (Grambow's hypothesis) rather than taking into account the activity of all the glass components as proposed by Jantzen and Plodinec. The concept of residual affinity was introduced by Grambow to express the fact that the glass dissolution rate does not cease. We prefer to replace the term residual affinity by contextual affinity, which expresses the influence on the dissolution rate of three factors: the solution chemistry, the metastability of SiO 2 (m), and the possible precipitation of certain aluminosilicates such as zeolites. 19 refs

  1. Effect of Initial Iron Content in a Zinc Bath on the Dissolution Rate of Iron During a Hot Dip Galvanizing Process

    Science.gov (United States)

    Lee, Sang Myung; Lee, Suk Kyu; Paik, Doo-Jin; Park, Joo Hyun

    2017-04-01

    The mechanism of iron dissolution and the effect of initial Fe content in a Zn bath on the dissolution rate of iron were investigated using a finger rotating method (FRM). When the initial iron content, [Fe]°, in the zinc bath was less than the solubility limit, the iron content in the zinc bath showed a rapid increase, whereas a moderate increase was observed when [Fe]° was close to the solubility limit. Based on Eisenberg's kinetic model, the mass transfer coefficient of iron in the present experimental condition was calculated to be k M = 1.2 × 10-5 m/s, which was similar to the results derived by Giorgi et al. under industrial practice conditions. A dissolution of iron occurred even when the initial iron content in the zinc bath was greater than the solubility limit, which was explained by the interfacial thermodynamics in conjunction with the morphology of the surface coating layer. By analyzing the diffraction patterns using TEM, the outermost dendritic-structured coating layer was confirmed as FeZn13 ( ζ). In order to satisfy the local equilibrium based on the Gibbs-Thomson equation, iron in the dendrite-structured phase spontaneously dissolved into the zinc bath, resulting in the enrichment of iron in front of the dendrite tip. Through the diffusion boundary layer in front of the dendritic-structured layer, dissolved Fe atoms diffused out and reacted with Zn and small amounts of Al, resulting in the formation of dross particles such as FeZn10Al x ( δ). It was experimentally confirmed that the smaller the difference between the initial iron content in the zinc bath and the iron solubility limit at a given temperature, the lower the number of formed dross particles.

  2. Uranothorite solid solutions: From synthesis to dissolution

    International Nuclear Information System (INIS)

    Costin, Dan-Tiberiu

    2012-01-01

    USiO 4 coffinite appears as one of the potential phases formed in the back-end of the alteration of spent fuel, in reducing storage conditions. A study aiming to assess the thermodynamic data associated with coffinite through an approach based on the preparation of Th 1-x U x SiO 4 uranothorite solid solutions was then developed during this work. First, the preparation of uranothorite samples was successfully undertaken in hydrothermal conditions. However, the poly-phased samples systematically formed for x ≥ 0,2 underlined the kinetic hindering linked with the preparation of uranium-enriched samples, including coffinite end-member. Nevertheless, the characterization of the various samples led to confirm the formation of an ideal solid solution and allowed the constitution of a spectroscopic database. The purification of the samples was then performed by the means of different protocols based on physical (dispersion-centrifugation) or chemical (selective dissolution of secondary phases) methods. This latter led to a complete of the impurities (Th 1-y U y O 2 mixed oxide and amorphous silica) through successive washing steps in acid then basic media. Finally, dissolution experiments were undertaken on uranothorite samples (0 ≤ xexp. ≤ 0,5) and allowed pointing out the influence of composition, pH and temperature on the normalized dissolution rate of the compounds. Also, the associated thermodynamic data, such as activation energy, indicate that the reaction is controlled by surface reactions. Once the equilibrium is reached, the analogous solubility constants were determined for each composition studied, then allowing the extrapolation to coffinite value. It was then finally possible to conclude on the inversion of coffinitisation reaction with temperature. (author) [fr

  3. Impact of pore characteristics of silica materials on loading capacity and release behavior of ibuprofen.

    Science.gov (United States)

    Numpilai, Thanapha; Muenmee, Suthaporn; Witoon, Thongthai

    2016-02-01

    Impact of pore characteristics of porous silica supports on loading capacity and release behavior of ibuprofen was investigated. The porous silica materials and ibuprofen-loaded porous silica materials were thoroughly characterized by N2-sorption, thermal gravimetric and derivative weight analyses (TG-DTW), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM) to determine the physical properties of materials, amount of ibuprofen adsorbed and position of ibuprofen. The detailed characterization reveals that the ibuprofen molecules adsorbed inside the mesopores. Increasing the mesopore size from 5nm to 10nm increased the ibuprofen loading from 0.74 to 0.85mmol/g, respectively. Incorporation of macropore into the structure of porous silica materials enhanced the ibuprofen loading capacity of 11.8-20.3%. The ibuprofen-loaded bimodal meso-macroporous silica materials exhibited the highest dissolution of 92wt.% within an hour. The ibuprofen particles deposited on the external surface of the porous silica materials showed a lower dissolution rate than the ibuprofen adsorbed inside the mesopores due to the formation of ibuprofen crystalline. Copyright © 2015 Elsevier B.V. All rights reserved.

  4. Comparison of the Kinetic Rate Law Parameters for the Dissolution of Natural and Synthetic Autunite in the Presence of Aqueous Bicarbonate Ions

    Energy Technology Data Exchange (ETDEWEB)

    Gudavalli, Ravi; Katsenovich, Yelena; Wellman, Dawn M.; Idarraga, Melina; Lagos, Leonel; Tansel, Berrin

    2013-08-02

    Bicarbonate is one of the most significant components within the uranium geochemical cycle. In aqueous solutions, bicarbonate forms strong complexes with uranium. As such, aqueous bicarbonate may significantly increase the rate of uranium release from uranium minerals. Quantifying the relationship of aqueous bicarbonate concentration to the rate of uranium release during dissolution is critical to understanding the long-term fate of uranium within the environment. Single-pass flow-through (SPTF) experiments were conducted to estimate the rate of uranium release from Na meta-autunite as a function of bicarbonate (0.0005-0.003 M) under the pH range of 6-11 and a temperature range of 5-60oC. Consistent with the results of previous investigation, the rate of uranium release exhibited minimal dependency on temperature; but were strongly dependent on pH. Increasing aqueous bicarbonate concentrations afforded comparable increases in the rate of release of uranium. Most notably under low pH conditions the aqueous bicarbonate resulted in up to 370 fold increases in the rate of uranium release in relative to the rate of uranium release in the absence of bicarbonate. However, the effect of aqueous bicarbonate on the release of uranium was significantly less under higher pH conditions. It is postulated that at high pH values, surface sites are saturated with carbonate, thus the addition of more bicarbonate would have less effect on uranium release.

  5. Feasibility study of the dissolution rates of uranium ore dust, uranium concentrates and uranium compounds in simulated lung fluid

    International Nuclear Information System (INIS)

    Robertson, R.

    1986-01-01

    A flow-through apparatus has been devised to study the dissolution in simulated lung fluid of aerosol materials associated with the Canadian uranium industry. The apparatus has been experimentally applied over 16 day extraction periods to approximately 2g samples of < 38um and 53-75um particle-size fractions of both Elliot Lake and Mid-Western uranium ores. The extraction of uranium-238 was in the range 24-60% for these samples. The corresponding range for radium-226 was 8-26%. Thorium-230, lead-210, polonium-210, and thorium-232 were not significantly extracted. It was incidentally found that the elemental composition of the ores studied varies significantly with particle size, the radionuclide-containing minerals and several extractable stable elements being concentrated in the smaller size fraction. Samples of the refined compounds uranium dioxide and uranium trioxide were submitted to similar 16 day extraction experiments. Approximately 0.5% of the uranium was extracted from a 0.258g sample of unsintered (fluid bed) uranium dioxide of particle size < 38um. The corresponding figure for a 0.292g sample of uranium trioxide was 97%. Two aerosol samples on filters were also studied. Of the 88ug uranium initially measured on stage 2 of a cascade impactor sample collected from the yellow cake packing area of an Elliot Lake mill, essentially 100% was extracted over a 16 day period. The corresponding figure for an open face filter sample collected in a fuel fabrication plant and initially measured at 288ug uranium was approximately 3%. Recommendations are made with regard to further work of a research nature which would be useful in this area. Recommendations are also made on sampling methods, analytical methods and extraction conditions for various aerosols of interest which are to be studied in a work of broader scope designed to yield meaningful data in connection with lung dosimetry calculations

  6. The dissolution of chalcopyrite in chloride media

    International Nuclear Information System (INIS)

    Ibanez, T.; Velasquez, L.

    2013-01-01

    The aim of this investigation is to determinate the effects of parameters and additives on the kinetics of dissolution of chalcopyrite on moderated conditions by means of dissolutions test with chalcopyrite concentrate and pure chalcopyrite in shake flasks and instrumented stirred reactors. A study of the dissolution of chalcopyrite in chloride solutions has demonstrated that the rate of dissolution of chalcopyrite is strongly dependent on the potential of the solution within a range of 540 to 630 mV (versus SHE). Leaching at pH around 2.5 results in increased rates of copper dissolution suggesting the possibility to keep the solution potential within the range. Both pyrite and silver ions enhance the dissolution of chalcopyrite and this effect increases when both species are present. The MnO 2 has a negative effect on the dissolution increasing the solution potential to values where the rate decreases considerably. (Author)

  7. Fumed silica. Fumed silica

    Energy Technology Data Exchange (ETDEWEB)

    Sukawa, T.; Shirono, H. (Nippon Aerosil Co. Ltd., Tokyo (Japan))

    1991-10-18

    The fumed silica is explained in particulate superfineness, high purity, high dispersiveness and other remarkable characteristics, and wide application. The fumed silica, being presently produced, is 7 to 40nm in average primary particulate diameter and 50 to 380m{sup 2}/g in specific surface area. On the surface, there coexist hydrophilic silanol group (Si-OH) and hydrophobic siloxane group (Si-O-Si). There are many characteristics, mutually different between the fumed silica, made hydrophobic by the surface treatment, and untreated hydrophilic silica. The treated silica, if added to the liquid product, serves as agent to heighten the viscosity, prevent the sedimentation and disperse the particles. The highest effect is given to heighten the viscosity in a region of 4 to 9 in pH in water and alcohol. As filling agent to strengthen the elastomer and polymer, and powder product, it gives an effect to prevent the consolidation and improve the fluidity. As for its other applications, utilization is made of particulate superfineness, high purity, thermal insulation properties and adsorption characteristics. 2 to 3 patents are published for it as raw material of quartz glass. 38 refs., 16 figs., 4 tabs.

  8. MECHANISMS CONTROLLING Ca ION RELEASE FROM SOL-GEL DERIVED IN SITU APATITE-SILICA NANOCOMPOSITE POWDER

    Directory of Open Access Journals (Sweden)

    Seyed Mohsen Latifi

    2015-03-01

    Full Text Available Ca ion release from bioactive biomaterials could play an important role in their bioactivity and osteoconductivity properties. In order to improve hydroxyapatite (HA dissolution rate, in situ apatite-silica nanocomposite powders with various silica contents were synthesized via sol-gel method and mechanisms controlling the Ca ion release from them were investigated. Obtained powders were characterized by X-ray diffraction (XRD and transmission electron spectroscopy (TEM techniques, acid dissolution test, and spectroscopy by atomic absorption spectrometer (AAS. Results indicated the possible incorporation of (SiO44- into the HA structure and tendency of amorphous silica to cover the surface of HA particles. However, 20 wt. % silica was the lowest amount that fully covered HA particles. All of the nanocomposite powders showed more Ca ion release compared with pure HA, and HA - 10 wt. % silica had the highest Ca ion release. The crystallinity, the crystallite size, and the content of HA, along with the integrity, thickness, and ion diffusion possibility through the amorphous silica layer on the surface of HA, were factors that varied due to changes in the silica content and were affected the Ca ion release from nanocomposite powders.

  9. Effect of the size of nanoparticles on their dissolution within metal-glass nanocomposites under sustained irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Vu, T. H. Y., E-mail: thi-hai-yen.vu@polytechnique.edu; Ramjauny, Y.; Rizza, G.; Hayoun, M. [Laboratoire des Solides Irradiés, École Polytechnique, CNRS, CEA, Université Paris-Saclay, F-91128 Palaiseau (France)

    2016-01-21

    We investigate the dissolution law of metallic nanoparticles (NPs) under sustained irradiation. The system is composed of isolated spherical gold NPs (4–100 nm) embedded in an amorphous silica host matrix. Samples are irradiated at room temperature in the nuclear stopping power regime with 4 MeV Au ions for fluences up to 8 × 10{sup 16 }cm{sup −2}. Experimentally, the dependence of the dissolution kinetics on the irradiation fluence is linear for large NPs (45–100 nm) and exponential for small NPs (4–25 nm). A lattice-based kinetic Monte Carlo (KMC) code, which includes atomic diffusion and ballistic displacement events, is used to simulate the dynamical competition between irradiation effects and thermal healing. The KMC simulations allow for a qualitative description of the NP dissolution in two main stages, in good agreement with the experiment. Moreover, the perfect correlation obtained between the evolution of the simulated flux of ejected atoms and the dissolution rate in two stages implies that there exists an effect of the size of NPs on their dissolution and a critical size for the transition between the two stages. The Frost-Russell model providing an analytical solution for the dissolution rate, accounts well for the first dissolution stage but fails in reproducing the data for the second stage. An improved model obtained by including a size-dependent recoil generation rate permits fully describing the dissolution for any NP size. This proves, in particular, that the size effect on the generation rate is the principal reason for the existence of two regimes. Finally, our results also demonstrate that it is justified to use a unidirectional approximation to describe the dissolution of the NP under irradiation, because the solute concentration is particularly low in metal-glass nanocomposites.

  10. Investigation of gamma ray shielding, structural and dissolution rate properties of Bi2O3-BaO-B2O3-Na2O glass system

    Science.gov (United States)

    Dogra, Mridula; Singh, K. J.; Kaur, Kulwinder; Anand, Vikas; Kaur, Parminder; Singh, Prabhjot; Bajwa, B. S.

    2018-03-01

    In the present study, quaternary system of the composition (0.45 + x) Bi2O3-(0.25 - x) BaO-0.15 B2O3-0.15 Na2O (where 0 ≤ x ≤ 0.2 mol fraction) has been prepared by using melt-quenching technique for investigation of gamma ray shielding properties. Mass attenuation coefficients and half value layer parameters have been determined experimentally at 662 keV by using 137Cs source. It has been found that experimental results of these parameters hold good agreement with theoretical values. The density, molar volume, XRD, FTIR, Raman and UV-visible studies have been used to determine structural properties of the prepared glass samples. Dissolution rate of the samples has also been measured to check their utility as long term durable glasses.

  11. Evaluation of source term parameters for spent fuel disposal in foreign countries. (2) Dissolution rates of spent fuel matrices and construction materials for fuel assemblies

    International Nuclear Information System (INIS)

    Kitamura, Akira; Chikazawa, Takahiro; Tachi, Yukio; Akahori, Kuniaki

    2016-01-01

    The Japanese geological disposal program has started researching disposal of spent nuclear fuel (SF) in deep geological strata (hereafter 'direct disposal of SF') as an alternative management option other reprocessing followed by vitrification and geological disposal of high-level radioactive waste. We conducted literature survey of dissolution rate of SF matrix and constructing materials (e.g. zircaloy cladding and control rods) selected in safety assessment reports for direct disposal of SF in Europe and United States. We also investigated basis of release rate determination and assignment of uncertainties in the safety assessment reports. Furthermore, we summarized major conclusions proposed by some European projects governed by European Commission. It was found that determined release rates are fairly similar to each other due to use of similar literature data in all countries of interest. It was also found that the determined release rates were including conservativeness because it was difficult to assign uncertainties quantitatively. It is expected that these findings are useful as fundamental information for determination of the release rates for the safety assessment of Japanese SF disposal system. (author)

  12. A kinetic model for borosilicate glass dissolution based on the dissolution affinity of a surface alteration layer

    International Nuclear Information System (INIS)

    Bourcier, W.L.; Peiffer, D.W.; Knauss, K.G.; McKeegan, K.D.; Smith, D.K.

    1989-11-01

    A kinetic model for the dissolution of borosilicate glass is used to predict the dissolution rate of a nuclear waste glass. In the model, the glass dissolution rate is controlled by the rate of dissolution of an alkali-depleted amorphous surface (gel) layer. Our model predicts that all components concentrated in the surface layer, affect glass dissolution rates. The good agreement between predicted and observed elemental dissolution rates suggests that the dissolution rate of the gel layer limits the overall rate of glass dissolution. The model predicts that the long-term rate of glass dissolution will depend mainly on ion concentrations in solution, and therefore on the secondary phases which precipitate and control ion concentrations. 10 refs., 5 figs., 1 tab

  13. Mathematical modeling of drug dissolution.

    Science.gov (United States)

    Siepmann, J; Siepmann, F

    2013-08-30

    The dissolution of a drug administered in the solid state is a pre-requisite for efficient subsequent transport within the human body. This is because only dissolved drug molecules/ions/atoms are able to diffuse, e.g. through living tissue. Thus, generally major barriers, including the mucosa of the gastro intestinal tract, can only be crossed after dissolution. Consequently, the process of dissolution is of fundamental importance for the bioavailability and, hence, therapeutic efficacy of various pharmaco-treatments. Poor aqueous solubility and/or very low dissolution rates potentially lead to insufficient availability at the site of action and, hence, failure of the treatment in vivo, despite a potentially ideal chemical structure of the drug to interact with its target site. Different physical phenomena are involved in the process of drug dissolution in an aqueous body fluid, namely the wetting of the particle's surface, breakdown of solid state bonds, solvation, diffusion through the liquid unstirred boundary layer surrounding the particle as well as convection in the surrounding bulk fluid. Appropriate mathematical equations can be used to quantify these mass transport steps, and more or less complex theories can be developed to describe the resulting drug dissolution kinetics. This article gives an overview on the current state of the art of modeling drug dissolution and points out the assumptions the different theories are based on. Various practical examples are given in order to illustrate the benefits of such models. This review is not restricted to mathematical theories considering drugs exhibiting poor aqueous solubility and/or low dissolution rates, but also addresses models quantifying drug release from controlled release dosage forms, in which the process of drug dissolution plays a major role. Copyright © 2013 Elsevier B.V. All rights reserved.

  14. Experimental Evaluation of Turbidity Impact on the Fluence Rate Distribution in a UV Reactor Using a Microfluorescent Silica Detector.

    Science.gov (United States)

    Li, Mengkai; Li, Wentao; Wen, Dong; Qiang, Zhimin; Blatchley, Ernest R

    2017-11-21

    Turbidity is a common parameter used to assess particle concentration in water using visible light. However, the fact that particles play multiple roles (e.g., scattering, refraction, and reflection) in influencing the optical properties of aqueous suspensions complicates examinations of their effects on ultraviolet (UV) photoreactor performance. To address this issue, UV fluence rate (FR) distributions in a photoreactor containing various particle suspensions (SiO 2 , MgO, and TiO 2 ) were measured using a microfluorescent silica detector (MFSD). Reflectance of solid particles, as well as transmittance and scattering properties of the suspensions were characterized at UV, visible, and infrared (IR) wavelengths. The results of these measurements indicated that the optical properties of all three particle types were similar at visible and IR wavelengths, but obvious differences were evident in the UV range. The FR results indicated that for turbidity associated with SiO 2 and MgO suspensions, the weighted average FR (WAFR) increased relative to deionized water. These increases were attributed to low particle photon absorption and strong scattering. In contrast, the WAFR values decreased with increasing turbidity for TiO 2 suspensions because of their high particle photon absorption and low scattering potential. The findings also indicate that measurements of scattering and transmittance at UV wavelengths can be used to quantify the effects of turbidity on UV FR distributions.

  15. Dissolution of crystalline ceramics

    International Nuclear Information System (INIS)

    White, W.B.

    1982-01-01

    The present program objectives are to lay out the fundamentals of crystalline waste form dissolution. Nuclear waste ceramics are polycrystalline. An assumption of the work is that to the first order, the release rate of a particular radionuclide is the surface-weighted sum of the release rates of the radionuclide from each crystalline form that contains it. In the second order, of course, there will be synergistic effects. There will be also grain boundary and other microstructural influences. As a first approximation, we have selected crystalline phases one at a time. The sequence of investigations and measurements is: (i) Identification of the actual chemical reactions of dissolution including identification of the solid reaction products if such occur. (ii) The rates of these reactions are then determined empirically to give what may be called macroscopic kinetics. (iii) Determination of the rate-controlling mechanisms. (iv) If the rate is controlled by surface reactions, the final step would be to determine the atomic kinetics, that is the specific atomic reactions that occur at the dissolving interface. Our concern with the crystalline forms are in two areas: The crystalline components of the reference ceramic waste form and related ceramics and the alumino-silicate phases that appear in some experimental waste forms and as waste-rock interaction products. Specific compounds are: (1) Reference Ceramic Phases (zirconolite, magnetoplumbite, spinel, Tc-bearing spinel and perovskite); (2) Aluminosilicate phases (nepheline, pollucite, CsAlSi 5 O 12 , Sr-feldspar). 5 figures, 1 table

  16. Optimization of Dissolution Compartments in a Biorelevant Dissolution Apparatus Golem v2, Supported by Multivariate Analysis

    Directory of Open Access Journals (Sweden)

    Ivan Stupák

    2017-11-01

    Full Text Available Biorelevant dissolution instruments represent an important tool for pharmaceutical research and development. These instruments are designed to simulate the dissolution of drug formulations in conditions most closely mimicking the gastrointestinal tract. In this work, we focused on the optimization of dissolution compartments/vessels for an updated version of the biorelevant dissolution apparatus—Golem v2. We designed eight compartments of uniform size but different inner geometry. The dissolution performance of the compartments was tested using immediate release caffeine tablets and evaluated by standard statistical methods and principal component analysis. Based on two phases of dissolution testing (using 250 and 100 mL of dissolution medium, we selected two compartment types yielding the highest measurement reproducibility. We also confirmed a statistically ssignificant effect of agitation rate and dissolution volume on the extent of drug dissolved and measurement reproducibility.

  17. In vitro Dissolution Studies on Solid Dispersions of Mefenamic Acid.

    Science.gov (United States)

    Rao, K R S Sambasiva; Nagabhushanam, M V; Chowdary, K P R

    2011-03-01

    Solid dispersions of mefanamic acid with a water-soluble polymer polyvinyl pyrrolidine and a super disintegrant, primojel were prepared by common solvent and solvent evaporation methods employing methanol as the solvent. The dissolution rate and dissolution efficiency of the prepared solid dispersions were evaluated in comparison to the corresponding pure drug. Solid dispersions of mefenamic acid showed a marked enhancement in dissolution rate and dissolution efficiency. At 1:4 ratio of mefenamic acid-primojel a 2.61 fold increase in the dissolution rate of mefenamic acid was observed with solid dispersion. The solid dispersions in combined carriers gave much higher rates of dissolution than super disintegrants alone. Mefanamic acid-primojel-polyvinyl pyrrolidine (1:3.2:0.8) solid dispersion gave a 4.11 fold increase in the dissolution rate of mefenamic acid. Super disintegrants alone or in combination with polyvinyl pyrrolidine could be used to enhance the dissolution rate of mefenamic acid.

  18. Dissolution Methods Database

    Data.gov (United States)

    U.S. Department of Health & Human Services — For a drug product that does not have a dissolution test method in the United States Pharmacopeia (USP), the FDA Dissolution Methods Database provides information on...

  19. Marital dissolution and blood pressure reactivity: evidence for the specificity of emotional intrusion-hyperarousal and task-rated emotional difficulty.

    Science.gov (United States)

    Sbarra, David A; Law, Rita W; Lee, Lauren A; Mason, Ashley E

    2009-06-01

    To assess blood pressure (BP) reactivity as recently separated adults completed a laboratory task asking to mentally reflect on their relationship experiences. Marital separations and the experience of divorce are associated with increased risk for early mortality and poor health outcomes. Few studies, however, have investigated the potential psychophysiological mechanisms that may account for these broad-based associations. Seventy recently separated or divorced community-dwelling adults (26 men) completed self-report measures of divorce-related psychological adjustment. During a laboratory visit, quasi-continuous BP was assessed across four task periods, including a divorce-specific mental activation task (DMAT). A task-rated emotional difficulty (TRED) index was computed based on participants' immediate appraisals of the task demands. After accounting for relevant health-related covariates and depressed mood, participants who reported higher degrees of divorce-related emotional intrusion and physical hyperarousal demonstrated significantly elevated resting BP at entry into the study. When assessing change from a within-person control task to the DMAT, a three-way interaction indicated that men reporting high TRED scores evidenced significant increases in BP, whereas men reporting low TRED scores evidenced significant decreases in BP. Women evidenced no significant changes in BP across study periods. Results suggest that divorce-related emotional intrusion-hyperarousal and real-time ratings of emotional difficulty (when people think about their separation experience) may play a specific role in BP reactivity, especially for men. These data shed new light on the potential mechanisms that may link marital dissolution and poor health.

  20. Experimental and numerical simulation of dissolution and precipitation: implications for fracture sealing at Yucca Mountain, Nevada

    Science.gov (United States)

    Dobson, Patrick F.; Kneafsey, Timothy J.; Sonnenthal, Eric L.; Spycher, Nicolas; Apps, John A.

    2003-05-01

    Plugging of flow paths caused by mineral precipitation in fractures above the potential repository at Yucca Mountain, Nevada could reduce the probability of water seeping into the repository. As part of an ongoing effort to evaluate thermal-hydrological-chemical (THC) effects on flow in fractured media, we performed a laboratory experiment and numerical simulations to investigate mineral dissolution and precipitation under anticipated temperature and pressure conditions in the repository. To replicate mineral dissolution by vapor condensate in fractured tuff, water was flowed through crushed Yucca Mountain tuff at 94 °C. The resulting steady-state fluid composition had a total dissolved solids content of about 140 mg/l; silica was the dominant dissolved constituent. A portion of the steady-state mineralized water was flowed into a vertically oriented planar fracture in a block of welded Topopah Spring Tuff that was maintained at 80 °C at the top and 130 °C at the bottom. The fracture began to seal with amorphous silica within 5 days. A 1-D plug-flow numerical model was used to simulate mineral dissolution, and a similar model was developed to simulate the flow of mineralized water through a planar fracture, where boiling conditions led to mineral precipitation. Predicted concentrations of the major dissolved constituents for the tuff dissolution were within a factor of 2 of the measured average steady-state compositions. The mineral precipitation simulations predicted the precipitation of amorphous silica at the base of the boiling front, leading to a greater than 50-fold decrease in fracture permeability in 5 days, consistent with the laboratory experiment. These results help validate the use of a numerical model to simulate THC processes at Yucca Mountain. The experiment and simulations indicated that boiling and concomitant precipitation of amorphous silica could cause significant reductions in fracture porosity and permeability on a local scale. However

  1. Evolution of permeability in siliceous rocks induced by mineral dissolution and precipitation

    International Nuclear Information System (INIS)

    Yasuhara, Hideaki; Kinoshita, Naoki; Kurikami, Hiroshi; Nakashima, Shinichiro; Kishida, Kiyoshi

    2007-01-01

    A conceptual model is presented to follow the evolution of permeability in siliceous rocks mediated by pressure solution. Specifically, the main minerals of siliceous rocks that are quartz, cristobalite, and amorphous silica, are focused to examine differences of the permeability evolutions among them at effective pressures of 1, 5, and 10 MPa, and temperatures of 20 and 90degC. The rates and magnitudes of permeability reduction increase with increases of the pressures and temperatures applied. Ultimate permeabilities reduced by the order of 90 % at the completion of dissolution-mediated compaction at 10 MPa and 90degC. Precipitation may augment more degradation of flow transport in time. (author)

  2. Initial dissolution rate of a Japanese simulated high-level waste glass P0798 as a function of pH and temperature measured by using micro-channel flow-through test method

    International Nuclear Information System (INIS)

    Inagaki, Yaohiro; Makigaki, Hikaru; Idemitsu, Kazuya; Arima, Tatsumi; Mitsui, Sei-ichiro; Noshita, Kenji

    2012-01-01

    Aqueous dissolution tests were performed for a Japanese type of simulated high-level waste (HLW) glass P0798 by using a newly developed test method of micro-channel flow-through (MCFT) method, and the initial dissolution rate of glass matrix, r 0 , was measured as a function of solution pH (3-11) and temperature (25-90degC) precisely and consistently for systematic evaluation of the dissolution kinetics. The MCFT method using a micro-channel reactor with a coupon shaped glass specimen has the following features to provide precise and consistent data on the glass dissolution rate: (1) any controlled constant solution condition can be provided over the test duration; (2) the glass surface area actually reacting with solution can be determined accurately; and (3) direct and totally quantitative analyses of the reacted glass surface can be performed for confirming consistency of the test results. The present test results indicated that the r 0 shows a 'V-shaped' pH dependence with a minimum at around pH 6 at 25degC, but it changes to a 'U-shaped' one with a flat bottom at neutral pH at elevated temperatures of up to 90degC. The present results also indicated that the r 0 increases with temperature according to an Arrhenius law at any pH, and the apparent activation energy evaluated from Arrhenius relation increases with pH from 54 kJ/mol at pH 3 to 76 kJ/mol at pH 10, which suggests that the dissolution mechanism changes depending on pH. (author)

  3. Silica aerogel Cerenkov counter

    International Nuclear Information System (INIS)

    Yasumi, S.; Masaike, A.; Yamamoto, A.; Yoshimura, Y.; Kawai, H.

    1984-03-01

    In order to obtain silica aerogel radiators of good quality, the prescription used by Saclay group has been developed. We have done several experiments using beams from KEK.PS to test the performance of a Cerenkov counter with aerogel modules produced in KEK. It turned out that these modules had excellent quality. The production rate of silica aerogel in KEK is 15 -- 20 litres a week. Silica aerogel modules of 20 x 10 x 3 cm 3 having the refractive index of 1.058 are successfully being used by Kyoto University group in the KEK experiment E92 (Σ). Methodes to produce silica aerogel with higher refractive index than 1.06 has been investigated both by heating an module with the refractive index of 1.06 and by hydrolyzing tetraethyl silicate. (author)

  4. Kinetics of oxidic phase dissolution in acids

    International Nuclear Information System (INIS)

    Gorichev, I.G.; Kipriyanov, N.A.

    1981-01-01

    The critical analysis of the experimental data on dissolution kinetics of metal oxides (BeO, V 2 O 5 , UO 2 , Nb 2 O 5 , Ta 2 O 5 etc.) in acid media is carried out. Kinetic peculiarities of oxide dissolution are explained on the basis of the notions of electron- proton theory. It is established that the surface nonstoichiometric ccomposition of oxide phase and potential jump, appearing on the interface of the oxide-electrolyte phase are the important factors, determining the dissolution rate of a solid phase. The dissolution rate of metal oxides is limited by the transition of protons into the solid oxide phase. Morphological models of heterogeneous kinetics are used when explaining kinetic regularities of oxide dissolution process [ru

  5. Fast dissolving cyclodextrin complex of piroxicam in solid dispersion part I: influence of β-CD and HPβ-CD on the dissolution rate of piroxicam.

    Science.gov (United States)

    Bouchal, F; Skiba, M; Chaffai, N; Hallouard, F; Fatmi, S; Lahiani-Skiba, M

    2015-01-30

    Sublingual drug delivery is an interesting route for drug having significant hepatic first-pass metabolism or requiring rapid pharmacological effect as for patients suffering from swallowing difficulties, nausea or vomiting. Sublingual absorption could however be limited by the kinetic of drug dissolution. This study evaluated influences of cyclodextrins (β-CD or HP-β-CD) and their different inclusion process (spray-drying or freeze-drying) on the drug dissolution kinetic of solid dispersions in poly(ethylene glycol) (PEG, Mw 6000Da) of piroxicam, used as poor hydrosoluble drug model. A secondary objective was to determine influences of drug dispersion process in PEG (evaporation or melting methods) on the drug dissolution kinetic of piroxicam. Piroxicam solid dispersions containing or not cyclodextrins were characterized by different scanning calorimetry (DSC), Thermogravometry analyser (TGA) and Fourier transform-infrared spectroscopy (FT-IR) spectroscopy. In vitro drug dissolution study of these solid dispersions was then performed. The results demonstrated the high potential and interest of solid dispersions of drug previously included in cyclodextrins for sublingual delivery of hydrophobic drugs. This study also showed the advantages of evaporation method on the melting ones during drug dispersion in PEG. Indeed, drug complexation with cyclodextrins as dispersion by melting prevented the presence in solid dispersions of drug in crystalline form which can represent up to 63%. Moreover, dispersion in PEG by evaporation method gave more porous drug delivery system than with melting methods. This allowed complete (limited at most at 80-90% with melting methods) and quick drug dissolution without rebound effect like with melting ones. Copyright © 2014 Elsevier B.V. All rights reserved.

  6. Viability for controlling long-term leaching of radionuclides from HLW glass by amorphous silica additives

    International Nuclear Information System (INIS)

    Inagaki, Y.; Uehara, S.

    2004-01-01

    Dissolution and deterioration experiments in coexistence system of amorphous silica and vitrified wastes have been executed in order to evaluating the effects of amorphous silica addition to high level radioactive vitrified waste (HLW glass) on suppression of nuclide leaching. Geo-chemical reaction mechanism among the vitrified waste, the amorphous silica and water was also evaluated. Dissolution of the silica network was suppressed by addition of the amorphous silica. However, the leaching of soluble nuclides like B proceeded depending on the hydration deterioration reaction. (A. Hishinuma)

  7. Dissolution of minerals with rough surfaces

    Science.gov (United States)

    de Assis, Thiago A.; Aarão Reis, Fábio D. A.

    2018-05-01

    We study dissolution of minerals with initial rough surfaces using kinetic Monte Carlo simulations and a scaling approach. We consider a simple cubic lattice structure, a thermally activated rate of detachment of a molecule (site), and rough surface configurations produced by fractional Brownian motion algorithm. First we revisit the problem of dissolution of initial flat surfaces, in which the dissolution rate rF reaches an approximately constant value at short times and is controlled by detachment of step edge sites. For initial rough surfaces, the dissolution rate r at short times is much larger than rF ; after dissolution of some hundreds of molecular layers, r decreases by some orders of magnitude across several time decades. Meanwhile, the surface evolves through configurations of decreasing energy, beginning with dissolution of isolated sites, then formation of terraces with disordered boundaries, their growth, and final smoothing. A crossover time to a smooth configuration is defined when r = 1.5rF ; the surface retreat at the crossover is approximately 3 times the initial roughness and is temperature-independent, while the crossover time is proportional to the initial roughness and is controlled by step-edge site detachment. The initial dissolution process is described by the so-called rough rates, which are measured for fixed ratios between the surface retreat and the initial roughness. The temperature dependence of the rough rates indicates control by kink site detachment; in general, it suggests that rough rates are controlled by the weakest microscopic bonds during the nucleation and formation of the lowest energy configurations of the crystalline surface. Our results are related to recent laboratory studies which show enhanced dissolution in polished calcite surfaces. In the application to calcite dissolution in alkaline environment, the minimal values of recently measured dissolution rate spectra give rF ∼10-9 mol/(m2 s), and the calculated rate

  8. Evaluation of a three compartment in vitro gastrointestinal simulator dissolution apparatus to predict in vivo dissolution.

    Science.gov (United States)

    Takeuchi, Susumu; Tsume, Yasuhiro; Amidon, Gregory E; Amidon, Gordon L

    2014-11-01

    In vitro dissolution tests are performed for new formulations to evaluate in vivo performance, which is affected by the change of gastrointestinal (GI) physiology, in the GI tract. Thus, those environmental changes should be introduced to an in vitro dissolution test. Many studies have successfully shown the improvement of in vitro-in vivo correlations (IVIVC) by introducing those physiological changes into dissolution tests. The gastrointestinal simulator (GIS), a multicompartment in vitro dissolution apparatus, was developed to evaluate in vivo drug dissolution. A gastric-emptying rate along with transit rate are key factors to evaluate in vivo drug dissolution and, hence, drug absorption. Dissolution tests with the GIS were performed with Biopharmaceutical Classification System class I drugs at five different gastric-emptying rates in the fasted state. Computational models were used to determine in vivo gastric-emptying time for propranolol and metoprolol based on the GIS dissolution results. Those were compared with published clinical data to determine the gastric half-emptying time. In conclusion, the GIS is a practical tool to assess dissolution properties and can improve IVIVC. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

  9. Investigation of dissolution kinetics of a Nigerian columbite in ...

    African Journals Online (AJOL)

    Investigation of dissolution kinetics of a Nigerian columbite in hydrofluoric acid using the shrinking core model. ... Experimental results indicate that the dissolution rate is chemical reaction controlled, with reaction order of 0.57. Dissolution of over 90 % of the columbite was achieved in 5 h, using 20 M HF at 90 oC with 100 ...

  10. Silica Nephropathy

    Directory of Open Access Journals (Sweden)

    N Ghahramani

    2010-06-01

    Full Text Available Occupational exposure to heavy metals, organic solvents and silica is associated with a variety of renal manifestations. Improved understanding of occupational renal disease provides insight into environmental renal disease, improving knowledge of disease pathogenesis. Silica (SiO2 is an abundant mineral found in sand, rock, and soil. Workers exposed to silica include sandblasters, miners, quarry workers, masons, ceramic workers and glass manufacturers. New cases of silicosis per year have been estimated in the US to be 3600–7300. Exposure to silica has been associated with tubulointerstitial disease, immune-mediated multisystem disease, chronic kidney disease and end-stage renal disease. A rare syndrome of painful, nodular skin lesions has been described in dialysis patients with excessive levels of silicon. Balkan endemic nephropathy is postulated to be due to chronic intoxication with drinking water polluted by silicates released during soil erosion. The mechanism of silica nephrotoxicity is thought to be through direct nephrotoxicity, as well as silica-induced autoimmune diseases such as scleroderma and systemic lupus erythematosus. The renal histopathology varies from focal to crescentic and necrotizing glomerulonephritis with aneurysm formation suggestive of polyarteritis nodosa. The treatment for silica nephrotoxicity is non-specific and depends on the mechanism and stage of the disease. It is quite clear that further research is needed, particularly to elucidate the pathogenesis of silica nephropathy. Considering the importance of diagnosing exposure-related renal disease at early stages, it is imperative to obtain a thorough occupational history in all patients with renal disease, with particular emphasis on exposure to silica, heavy metals, and solvents.

  11. Effect of radiation-induced amorphization on smectite dissolution.

    Science.gov (United States)

    Fourdrin, C; Allard, T; Monnet, I; Menguy, N; Benedetti, M; Calas, G

    2010-04-01

    Effects of radiation-induced amorphization of smectite were investigated using artificial irradiation. Beams of 925 MeV Xenon ions with radiation dose reaching 73 MGy were used to simulate the effects generated by alpha recoil nuclei or fission products in the context of high level nuclear waste repository. Amorphization was controlled by X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. An important coalescence of the smectite sheets was observed which lead to a loss of interparticle porosity. The amorphization is revealed by a loss of long-range structure and accompanied by dehydroxylation. The dissolution rate far-from-equilibrium shows that the amount of silica in solution is two times larger in the amorphous sample than in the reference clay, a value which may be enhanced by orders of magnitude when considering the relative surface area of the samples. Irradiation-induced amorphization thus facilitates dissolution of the clay-derived material. This has to be taken into account for the safety assessment of high level nuclear waste repository, particularly in a scenario of leakage of the waste package which would deliver alpha emitters able to amorphize smectite after a limited period of time.

  12. Silica-Based and Borate-Based, Titania-Containing Bioactive Coatings Characterization: Critical Strain Energy Release Rate, Residual Stresses, Hardness, and Thermal Expansion

    Directory of Open Access Journals (Sweden)

    Omar Rodriguez

    2016-12-01

    Full Text Available Silica-based and borate-based glass series, with increasing amounts of TiO2 incorporated, are characterized in terms of their mechanical properties relevant to their use as metallic coating materials. It is observed that borate-based glasses exhibit CTE (Coefficient of Thermal Expansion closer to the substrate’s (Ti6Al4V CTE, translating into higher mode I critical strain energy release rates of glasses and compressive residual stresses and strains at the coating/substrate interface, outperforming the silica-based glasses counterparts. An increase in the content of TiO2 in the glasses results in an increase in the mode I critical strain energy release rate for both the bulk glass and for the coating/substrate system, proving that the addition of TiO2 to the glass structure enhances its toughness, while decreasing its bulk hardness. Borate-based glass BRT3, with 15 mol % TiO2 incorporated, exhibits superior properties overall compared to the other proposed glasses in this work, as well as 45S5 Bioglass® and Pyrex.

  13. Numerical modelling of glass dissolution: gel layer morphology

    Energy Technology Data Exchange (ETDEWEB)

    Devreux, F. E-mail: fd@pmc.polytechnique.fr; Barboux, P

    2001-09-01

    Numerical simulations of glass dissolution are presented. The glass is modelized as a random binary mixture composed of two species representing silica and soluble oxides, such as boron and alkali oxides. The soluble species are dissolved immediately when they are in contact with the solution. For the species which represents silica, one introduces dissolution and condensation probabilities. It is shown that the morphology and the thickness of the surface hydration layer (the gel) are highly dependent on the dissolution model, especially on the parameter which controls the surface tension. Simulations with different glass surface area to solution volume ratio (S/V) show that this experimental parameter has important effects on both the shrinkage and the gel layer thickness.

  14. Status report on dissolution model development

    International Nuclear Information System (INIS)

    Jackson, D.D.

    1983-07-01

    The computer program PROTOCOL models the dissolution reactions of chemical species in water. It is being developed particularly to study the dissolution of proposed nuclear waste forms and related phases. Experimentally derived leaching rate functions are coupled to thermochemical equilibrium calculations and water flow rates. The program has been developed over a period of years. This report describes improvements that have been done in the past year

  15. Impact of physicochemical properties of porous silica materials conjugated with dexamethasone via pH-responsive hydrazone bond on drug loading and release behavior

    Science.gov (United States)

    Numpilai, Thanapha; Witoon, Thongthai; Chareonpanich, Metta; Limtrakul, Jumras

    2017-02-01

    The conjugation of dexamethasone (DEX) onto modified-porous silica materials via a pH-responsive hydrazone bond has been reported to be highly efficient method to specifically deliver the DEX to diseased sites. However, the influence of physicochemical properties of porous silica materials has not yet been fully understood. In this paper, the impact of pore sizes, particle sizes and silanol contents on surface functionalization, drug loading and release behavior of porous silica materials conjugated with dexamethasone via pH-responsive hydrazone bond was investigated. The grafting density was found to relate to the number of silanol groups on the surface of porous silica materials. The particle size and macropores of the porous silica materials played an vital role on the drug loading and release behavior. Although the porous silica materials with larger particle sizes possessed a lower grafting density, a larger amount of drug loading could be achieved. Moreover, the porous silica materials with larger particle sizes showed a slower release rate of DEX due to a longer distance for cleaved DEX diffusion out of pores. DEX release rate exhibited pH-dependent, sustained release. At pH 4.5, the amount of DEX release within 10 days could be controlled in the range of 12.74-36.41%, depending on the host material. Meanwhile, less than 1.5% of DEX was released from each of type of the porous silica materials at pH 7.4. The results of silica dissolution suggested that the degradation of silica matrix did not significantly affect the release rate of DEX. In addition, the kinetic modeling studies revealed that the DEX releases followed Korsmeyer-Peppas model with a release exponent (n) ranged from 0.3 to 0.47, indicating a diffusion-controlled release mechanism.

  16. Functionalized bimodal mesoporous silicas as carriers for controlled aspirin delivery

    International Nuclear Information System (INIS)

    Gao Lin; Sun Jihong; Li Yuzhen

    2011-01-01

    The bimodal mesoporous silica modified with 3-aminopropyltriethoxysilane was performed as the aspirin carrier. The samples' structure, drug loading and release profiles were characterized with X-ray diffraction, scanning electron microscopy, N 2 adsorption and desorption, Fourier transform infrared spectroscopy, TG analysis, elemental analysis and UV-spectrophotometer. For further exploring the effects of the bimodal mesopores on the drug delivery behavior, the unimodal mesoporous material MCM-41 was also modified as the aspirin carrier. Meantime, Korsmeyer-Peppas equation f t =kt n was employed to analyze the dissolution data in details. It is indicated that the bimodal mesopores are beneficial for unrestricted drug molecules diffusing and therefore lead to a higher loading and faster releasing than that of MCM-41. The results show that the aspirin delivery properties are influenced considerably by the mesoporous matrix, whereas the large pore of bimodal mesoporous silica is the key point for the improved controlled-release properties. - Graphical abstract: Loading (A) and release profiles (B) of aspirin in N-BMMs and N-MCM-41 indicated that BMMs have more drug loading capacity and faster release rate than that MCM-41. Highlights: → Bimodal mesoporous silicas (BMMs) and MCM-41 modified with amino group via post-treatment procedure. → Loading and release profiles of aspirin in modified BMMs and MCM-41. → Modified BMMs have more drug loading capacity and faster release rate than that modified MCM-41.

  17. Particulate silica and Si recycling in the surface waters of the Eastern Equatorial Pacific

    DEFF Research Database (Denmark)

    Adjou, Mohamed; Tréguer, Paul; Dumousseaud, Cynthia

    2011-01-01

    SiO2) was generally waters. These low concentrations confirm low atmospheric inputs of particulate Si, consistent with reported low inputs of wind-borne material in the EEP. In spite of active upwelling of silicic acid......-rich waters the biogenic silica (bSiO2) concentrations were generally low, falling between 100 and 180 nmol Si l-1 in the upper 50 m and decreasing to less than 50 nmol Si l-1 below ~90 m. Estimates of net bSiO2 production rates revealed that the rate of production exceeded that of dissolution in the upper...

  18. Serpentinization processes: Influence of silica

    Science.gov (United States)

    Huang, R.; Sun, W.; Ding, X.; Song, M.; Zhan, W.

    2016-12-01

    Serpentinization systems are highly enriched in molecular hydrogen (H2) and hydrocarbons (e.g. methane, ethane and propane). The production of hydrocarbons results from reactions between H2 and oxidized carbon (carbon dioxide and carbon monoxide), which possibly contribute to climate changes during early history of the Earth. However, the influence of silica on the production of H2 and hydrocarbons was poorly constrained. We performed experiments at 311-500 °C and 3.0 kbar using mechanical mixtures of silica and olivine in ratios ranging from 0 to 40%. Molecular hydrogen (H2), methane, ethane and propane were formed, which were analyzed by gas chromatography. It was found that silica largely decreased H2 production. Without any silica, olivine serpentinization produced 94.5 mmol/kg H2 after 20 days of reaction time. By contrast, with the presence of 20% silica, H2 concentrations decreased largely, 8.5 mmol/kg. However, the influence of silica on the production of hydrocarbons is negligible. Moreover, with the addition of 20%-40% silica, the major hydrous minerals are talc, which was quantified according to an established standard curve calibrated by infrared spectroscopy analyses. It shows that silica greatly enhances olivine hydration, especially at 500 °C. Without any addition of silica, reaction extents were serpentinization at 500 °C and 3.0 kbar. By contrast, with the presence of 50% silica, olivine was completely transformed to talc within 9 days. This study indicates that silica impedes the oxidation of ferrous iron into ferric iron, and that rates of olivine hydration in natural geological settings are much faster with silica supply.

  19. Kinetics of dissolution of sapphire in melts in the CaO-Al2O3-SiO2 system

    Science.gov (United States)

    Shaw, Cliff S. J.; Klausen, Kim B.; Mao, Huahai

    2018-05-01

    The dissolution rate of sapphire in melts in the CAS system of varying silica activity, viscosity and degree of alumina saturation has been determined at 1600 °C and 1.5 GPa. After an initiation period of up to 1800 s, dissolution is controlled by diffusion of cations through the boundary layer adjacent to the dissolving sapphire. The dissolution rate decreases with increasing silica activity, viscosity and molar Al2O3/CaO. The calculated diffusion matrix for each solvent melt shows that CAS 1 and 9 which have molar Al2O3/CaO of 0.33 and 0.6 and dissolution rate constants of 0.65 × 10-6 and 0.59 × 10-6 m/s0.5 have similar directions and magnitudes of diffusive coupling: DCaO-Al2O3 and DAl2O3-CaO are both negative are approximately equal. The solvent with the fastest dissolution rate: CAS 4, which has a rate constant of 1.5 × 10-6 m/s0.5 and Al2O3/CaO of 0.31 has positive DCaO-Al2O3 and negative DAl2O3-CaO and the absolute values vary by a factor of 4. Although many studies show that aluminium is added to the melts via the reaction: Si4+ =Al3+ + 0.5Ca2+ the compositional profiles show that this reaction is not the only one involved in accommodating the aluminium added during sapphire dissolution. Rather, aluminium is incorporated as both tetrahedrally coordinated Al charge balanced by Ca and as aluminium not charge balanced by Ca (termed Alxs). This reaction: AlIV -Ca =Alxs +CaNBO where CaNBO is a non-bridging oxygen associated with calcium, may involve the formation of aluminium triclusters. The shape of the compositional profiles and oxide-oxide composition paths is controlled by the aluminium addition reaction. When Alxs exceeds 2%, CaO diffusion becomes increasingly anomalous and since the bond strength of Alxs correlates with CaO/CaO + Al2O3, the presence of more than 2% Alxs leads to significantly slower dissolution than when Alxs is absent or at low concentration. Thus, dissolution is controlled by diffusion of cations through the boundary layer, but this

  20. Production and Application of Olivine Nano-Silica in Concrete

    Science.gov (United States)

    Mardiana, Oesman; Haryadi

    2017-05-01

    The aim of this research was to produce nano silica by synthesis of nano silica through extraction and dissolution of ground olivine rock, and applied the nano silica in the design concrete mix. The producing process of amorphous silica used sulfuric acid as the dissolution reagent. The separation of ground olivine rock occurred when the rock was heated in a batch reactor containing sulfuric acid. The results showed that the optimum mole ratio of olivine- acid was 1: 8 wherein the weight ratio of the highest nano silica generated. The heating temperature and acid concentration influenced the mass of silica produced, that was at temperature of 90 °C and 3 M acid giving the highest yield of 44.90%. Characterization using Fourier Transform Infrared (FTIR ) concluded that amorphous silica at a wavenumber of 1089 cm-1 indicated the presence of siloxane, Si-O-Si, stretching bond. Characterization using Scanning Electron Microscope - Energy Dispersive Spectroscopy (SEM-EDS) showed the surface and the size of the silica particles. The average size of silica particles was between 1-10 μm due to the rapid aggregation of the growing particles of nano silica into microparticles, caused of the pH control was not fully achieved.

  1. Modelling of the UO2 dissolution mechanisms in synthetic groundwater solutions. Dissolution experiments carried out under oxic conditions

    International Nuclear Information System (INIS)

    Cera, E.; Grive, M.; Bruno, J.; Ollila, K.

    2001-02-01

    The analytical data generated during the last three years within the 4th framework program of the European Community at VTT Chemical Technology concerning UO 2 dissolution under oxidising conditions have been modelled in the present work. The modelling work has been addressed to perform a kinetic study of the dissolution data generated by Ollila (1999) under oxidising conditions by using unirradiated uranium dioxide as solid sample. The average of the normalised UO 2 dissolution rates determined by using the initial dissolution data generated in all the experimental tests is (6.06 ± 3.64)* 10 -7 mol m -2 d -1 . This dissolution rate agrees with most of the dissolution rates reported in the literature under similar experimental conditions. The results obtained in this modelling exercise show that the same bicarbonate promoted oxidative dissolution processes operate for uranium dioxide, as a chemical analogue of the spent fuel matrix, independently of the composition of the aqueous solution used. (orig.)

  2. Biomimetic synthesis of proline-derivative templated mesoporous silica for increasing the brain distribution of diazepam and improving the pharmacodynamics of nimesulide

    DEFF Research Database (Denmark)

    Li, Heran; Wang, Jianxin; Cong, Jialiang

    2017-01-01

    Herein a new kind of proline-derivative templated mesoporous silica with curved channels (CMS) was biomimetically synthesized and applied as carrier to improve the drug dissolution and bioavailability of hydrophobic diazepam (DZP) and nimesulide (NMS). Drugs can be incorporated into CMS with high...... improved, and the inhibition rates of 1:3 NMS/CMS in all pharmacodynamics tests varied from 102.2% to 904.3%....

  3. Template occluded SBA-15: An effective dissolution enhancer for poorly water-soluble drug

    Energy Technology Data Exchange (ETDEWEB)

    Fu Tingming, E-mail: futingming@gmail.com [College of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210029 (China); Guo Liwei; Le Kang; Wang Tianyao; Lu Jin [College of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210029 (China)

    2010-09-15

    The aim of the present work was to improve the dissolution rate of piroxicam by inclusion into template occluded SBA-15. Our strategy involves directly introducing piroxicam into as-prepared SBA-15 occluded with P123 (EO{sub 20}PO{sub 70}EO{sub 20}) by self assembling method in acetonitrile/methylene chloride mixture solution. Ultraviolet spectrometry experiment and thermogravimetric analysis-differential scanning calorimetry (TG-DSC) profiles show that the piroxicam and P123 contents in the inclusion compound are 12 wt% and 28 wt%, respectively. X-ray powder diffraction and DSC analysis reveal that the included piroxicam is arranged in amorphous form. N{sub 2} adsorption-desorption experiment indicates that the piroxicam has been introduced to the mesopores instead of precipitating at the outside of the silica material. The inclusion compound was submitted to in vitro dissolution tests, the results show that the piroxicam dissolve from template occluded inclusion compound more rapidly, than these from the piroxicam crystalline and template removed samples in all tested conditions. Thus a facile method to improve the dissolution rate of poorly water-soluble drug was established, and this discovery opens a new avenue for the utilization of templates used for the synthesis of mesoporous materials.

  4. Template occluded SBA-15: An effective dissolution enhancer for poorly water-soluble drug

    International Nuclear Information System (INIS)

    Fu Tingming; Guo Liwei; Le Kang; Wang Tianyao; Lu Jin

    2010-01-01

    The aim of the present work was to improve the dissolution rate of piroxicam by inclusion into template occluded SBA-15. Our strategy involves directly introducing piroxicam into as-prepared SBA-15 occluded with P123 (EO 20 PO 70 EO 20 ) by self assembling method in acetonitrile/methylene chloride mixture solution. Ultraviolet spectrometry experiment and thermogravimetric analysis-differential scanning calorimetry (TG-DSC) profiles show that the piroxicam and P123 contents in the inclusion compound are 12 wt% and 28 wt%, respectively. X-ray powder diffraction and DSC analysis reveal that the included piroxicam is arranged in amorphous form. N 2 adsorption-desorption experiment indicates that the piroxicam has been introduced to the mesopores instead of precipitating at the outside of the silica material. The inclusion compound was submitted to in vitro dissolution tests, the results show that the piroxicam dissolve from template occluded inclusion compound more rapidly, than these from the piroxicam crystalline and template removed samples in all tested conditions. Thus a facile method to improve the dissolution rate of poorly water-soluble drug was established, and this discovery opens a new avenue for the utilization of templates used for the synthesis of mesoporous materials.

  5. Dissolution studies of synthetic soddyite and uranophane

    International Nuclear Information System (INIS)

    Casas, I.; Perez, I.; Torrero, E.; Bruno, J.; Cera, E.; Duro, L.

    1997-09-01

    The dissolution of synthetically obtained soddyite and uranophane has been studied in solutions of low ionic strength. These are the likely final phases of the oxidative alternation pathway of uranium dioxide. The thermodynamic and kinetic dissolution properties of these phases have been determined at different bicarbonate concentrations. The solubilities determined in the experiments with soddyite correspond fairly well to the theoretical model calculated with a log K 0 s0 =3.9±0.7. For uranophane, the best fitting was obtained for a log K 0 s0 =11.7±0.6. The dissolution rate in the presence of bicarbonate gave for soddyite an average value of 6.8(±4.4) 10 -10 mol m -2 s -1 . For uranophane, under the same experimental conditions, the following dissolution rate equation has been derived: r 0 (mol m -2 s -1 )=10 -9±2. [HCO 3 - ] 0.69±0.09 2

  6. Low temperature dissolution flowsheet for plutonium metal

    Energy Technology Data Exchange (ETDEWEB)

    Daniel, W. E. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Almond, P. M. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Rudisill, T. S. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2016-05-01

    The H-Canyon flowsheet used to dissolve Pu metal for PuO2 production utilizes boiling HNO3. SRNL was requested to develop a complementary dissolution flowsheet at two reduced temperature ranges. The dissolution and H2 generation rates of Pu metal were investigated using a dissolving solution at ambient temperature (20-30 °C) and for an intermediate temperature of 50-60 °C. Additionally, the testing included an investigation of the dissolution rates and characterization of the off-gas generated from the ambient temperature dissolution of carbon steel cans and the nylon bags that contain the Pu metal when charged to the dissolver.

  7. Dissolution of the Mors salt dome

    International Nuclear Information System (INIS)

    Lindstroem Jensen, K.E.

    1982-01-01

    Regardless of the interpretation of the measured salinity profiles above the Mors salt dome, they can at most be the result of dissolution rates of about 0.004 mm per year. This means that it would take more than 2.5 mill. years to dissolve 10 m of salt. Variations in groun water velocity and cap rock porosity will not significantly change this condition. The stability of the Mors salt dome is therefore not affected by dissolution of the dome. (EG)

  8. Preparation of an amorphous sodium furosemide salt improves solubility and dissolution rate and leads to a faster Tmax after oral dosing to rats

    DEFF Research Database (Denmark)

    Nielsen, Line Hagner; Gordon, Sarah; Holm, René

    2013-01-01

    Amorphous forms of furosemide sodium salt and furosemide free acid were prepared by spray drying. For the preparation of the amorphous free acid, methanol was utilised as the solvent, whereas the amorphous sodium salt was formed from a sodium hydroxide-containing aqueous solvent in equimolar...... amounts of NaOH and furosemide. Information about the structural differences between the two amorphous forms was obtained by Fourier Transform Infrared Spectroscopy (FTIR), and glass transition temperature (Tg) was determined using Differential Scanning Calorimetry (DSC). The stability and devitrification...... tendency of the two amorphous forms were investigated by X-ray Powder Diffraction (XRPD). The apparent solubility of the two amorphous forms and the crystalline free acid form of furosemide in various gastric and intestinal stimulated media was determined. Moreover, the dissolution characteristics...

  9. The synthesis and application involving regulation of the insoluble drug release from mesoporous silica nanotubes

    International Nuclear Information System (INIS)

    Li, Jia; Wang, Yan; Zheng, Xin; Zhang, Ying; Sun, Changshan; Gao, Yikun; Jiang, Tongying; Wang, Siling

    2015-01-01

    Highlights: • Mesoporous silica nanotubes (SNT) were synthesized by using CNT as hard template, and the formation of the SNT shows that CTAB played a significant effect on the coating process. • The tube mesoporous silica materials which were seldom reported were applied in the drug delivery system to improve the loading amount and the drug dissolution. • The release rate could be controlled by the gelatin layer on the silica surface and the mechanism was illustrated. - Abstract: Mesoporous silica nanotubes (SNT) were synthesized using hard template carbon nanotubes (CNT) with the aid of cetyltrimethyl ammonium bromide (CTAB) in a method, which was simple and inexpensive. Scanning electron microscopy, transmission electron microscopy and specific surface area analysis were employed to characterize the morphology and structure of SNT, and the formation mechanism of SNT was also examined by Fourier transform infrared spectroscopy. There are few published reports of the mesoporous SNT with large specific surface area applied in the drug delivery systems to improve the amount of drug loading. In addition, the structure of SNT allows investigators to control the drug particle size in the pore channels and significantly increase the drug dissolution rate. The insoluble drug, cilostazol, was chosen as a model drug to be loaded into SNT and we developed a simple and efficient method for regulating the drug release by using a gelatin coating with different thicknesses around the SNT. The release rate was adjusted by the amount of gelatin surrounding the SNT, with an increased barrier leading to a reduction in the release rate. A model developed on the basis of the Weibull modulus was established to fit the release results

  10. Dissolution rates of unirradiated UO{sub 2}, UO{sub 2} doped with {sup 233}U, and spent fuel under normal atmospheric conditions and under reducing conditions using an isotope dilution method

    Energy Technology Data Exchange (ETDEWEB)

    Ollila, Kaija [VTT Processes, Helsinki (Finland); Albinsson, Yngve [Chalmers Univ. of Technology, Goeteborg (Sweden); Oversby, Virginia [VMO Konsult, Stockholm (Sweden); Cowper, Mark [AEA Technology, Harwell (United Kingdom)

    2003-10-01

    The experimental results given in this report allow us to draw the following conclusions. 1) Tests using unirradiated fuel pellet materials from two different manufacturers gave very different dissolution rates under air atmosphere testing. Tests for fragments of pellets from different pellets made by the same manufacturer gave good agreement. This indicates that details of the manufacturing process have a large effect on the behavior of unirradiated UO{sub 2} in dissolution experiments. Care must be taken in interpreting differences in results obtained in different laboratories because the results may be affected by manufacturing effects. 2) Long-term tests under air atmosphere have begun to show the effects of precipitation. Further testing will be needed before the samples reach steady state. 3) Testing of unirradiated UO{sub 2} in systems containing an iron strip to produce reducing conditions gave [U] less than detection limits (<0.02 ppb) after a few days to a few weeks of testing. Uranium recovered from the rinsing of reaction vessels and from acid stripping of vessels was shown to be from dissolution of grains of solid dislodged when the samples were handled after the tests were terminated. 4) Batch tests conducted under reducing conditions showed evidence of colloidal material in the early solution samples. 5) In the batch tests, measurements taken at day 3 and day 5 show that precipitation occurs from day 3 to day 5 without any further dissolution of the solid. 6) At termination of the batch tests, all but one sample had [U] in solution less than detection limits (< 0.02 ppb). Materials recovered in test termination samples showed evidence for recovery of small amounts - amounts corresponding to that expected from a few grains of 5 to 10 {mu}m size - in the acidified solution samples. These are interpreted to have been dislodged during sample handling operations. 7) Batch test data show that increasing test duration beyond 2 weeks does not provide

  11. Simfuel dissolution studies in granitic groundwater

    International Nuclear Information System (INIS)

    Casas, I.; Caceci, M.S.; Bruno, J.; Sandino, A.; Ollila, K.

    1991-09-01

    The dissolution behavior of an unirradiated chemical analogue of spent nuclear fuel (SIMFUEL) has been studied in the presence of two different synthetic groundwater at 25 deg C and under both oxic and anoxic conditions. The release of U, Mo, Ba, Y and Sr was monitored during static (batch) leaching experiments of long duration (about 250 days). Preliminary results from continuous flow-through reactor experiments are also reported. The results obtained indicate the usefulness and limitations of SIMFUEL in the study of the kinetics and mechanism of dissolution of the minor components of spent nuclear fuel. Molybdenum, barium and strontium have shown a trend to congruent dissolution with the SIMFUEL matrix after a higher initial fractional release. Yttrium release has been found to be solubility controlled under the experimental conditions. A clear dependence on the partial pressure of O 2 of the rates of dissolution of uranium has been observed

  12. SIMFUEL dissolution studies in granitic groundwater

    International Nuclear Information System (INIS)

    Casas, I.; Caceci, M.S.; Bruno, J; Sandino, A.

    1991-09-01

    The dissolution behavior of an unirradiated chemical analogue of spent nuclear fuel (SIMFUEL) has been studied in the presence of two different synthetic groundwaters at 25 degrees C and under both oxic and anoxic conditions. The release of U, Mo, Ba, Y and Sr was monitored during static (batch) leaching experiments of long duration (about 250 days). Preliminary results from continuous flow-through reactor experiments are also reported. The results obtained indicate the usefulness and limitations of SIMFUEL in the study of the kinetics and mechanism of dissolution of the minor components of spent nuclear fuel. Molybdenum, barium and strontium have shown a trend of congruent dissolution with the SIMFUEL matrix after a higher initial fractional release has been found to be solubility controlled under the experimental conditions. A clear dependence on the partial pressure of O 2 of the rate of dissolution of uranium has been observed. (au)

  13. Fast dissolution of poorly water soluble drugs from fluidized bed coated nanocomposites: Impact of carrier size.

    Science.gov (United States)

    Azad, Mohammad; Moreno, Jacqueline; Bilgili, Ecevit; Davé, Rajesh

    2016-11-20

    Formation of core-shell nanocomposites of Fenofibrate and Itraconazole, model poorly water soluble drugs, via fluidized bed (FB) coating of their well-stabilized high drug loaded nanosuspensions is investigated. Specifically, the extent of dissolution enhancement, when fine carrier particles (sub-50μm) as opposed to the traditional large carrier particles (>300μm) are used, is examined. This allows testing the hypothesis that greatly increased carrier surface area and more importantly, thinner shell for finer carriers at the same drug loading can significantly increase the dissolution rate when spray-coated nanosuspensions are well-stabilized. Fine sub-50μm lactose (GranuLac ® 200) carrier particles were made fluidizable via dry coating with nano-silica, enabling decreased cohesion, fluidization and subsequent nanosuspension coating. For both drugs, 30% drug loaded suspensions were prepared via wet-stirred media milling using hydroxypropyl methyl cellulose and sodium dodecyl sulfate as stabilizers. The stabilizer concentrations were varied to affect the milled particle size and prepare a stable nanosuspension. The suspensions were FB coated onto hydrophilic nano-silica (M-5P) dry coated sub-50μm lactose (GranuLac ® 200) carrier particles or larger carrier particles of median size >300μm (PrismaLac ® 40). The resulting finer composite powders (sub-100μm) based on GranuLac ® 200 were freely flowing, had high bulk density, and had much faster, immediate dissolution of the poorly water-soluble drugs, in particular for Itraconazole. This is attributed to a much higher specific surface area of the carrier and corresponding thinner coating layer for fine carriers as opposed to those for large carrier particles. Copyright © 2016 Elsevier B.V. All rights reserved.

  14. Graft shrinkage and survival rate of implants after sinus floor elevation using a nanocrystalline hydroxyapatite embedded in silica gel matrix: a 1-year prospective study.

    Science.gov (United States)

    El Hage, Marc; Abi Najm, Semaan; Bischof, Mvark; Nedir, Rabah; Carrel, Jean-Pierre; Bernard, Jean-Pierre

    2012-06-01

    The aims of this study were (1) to evaluate the vertical shrinkage percentage of nanocrystalline hydroxyapatite embedded in silica gel used for maxillary sinus floor elevation (SFE) and (2) to determine the survival rate of the implants 1 year after placement in the healed grafted sinuses. Eleven maxillary sinuses were augmented in eight patients with NanoBone. After a healing period averaging 14.42 months, 19 implants were placed and followed up with clinical and radiographic evaluation. Panoramic radiographs were taken immediately after SFE and at 12 months after grafting. Measurements of changes in height were made by a computerized measuring technique using an image editing software. The mean graft height shrinkage percentage at 12 months after surgery was 8.84% (±5.32). One implant was lost before loading. All the 18 remaining osseointegrated implants received the prosthetic rehabilitation and were controlled after 3 months of functional loading. The implant survival rate at the 1-year interval was 94.74%. A 100% NanoBone alloplastic graft used in lateral SFE procedures presented limited height shrinkage. Implants placed in these grafted sinuses showed survival rates similar to those found in published data. These results should be interpreted cautiously considering the study's reduced sample size.

  15. Dissolution experiments of unirradiated uranium dioxide pellets

    International Nuclear Information System (INIS)

    Ollila, K.

    1985-01-01

    The purpose of this study was to measure the dissolution rate of uranium from unirradiated uranium dioxide pellets in deionized water and natural groundwater. Moreover, the solubility limit of uranium in natural groundwater was measured. Two different temperatures, 25 and 60 deg C were used. The low oxygen content of deep groundwater was simulated. The dissolution rate of uranium varied from 10 -7 to 10 -8 g cm -2 d -1 . The rate in reionized water was one order of magnitude lower than in groundwater. No great difference was observed between the natural groundwaters with different composition. Temperature seems to have effect on the dissolution rate. The solubility limit of uranium in natural groundwater in reducing conditions, at 25 deg C, varied from 20 to 600 μg/l and in oxidizing conditions, at 60 deg C, from 4 to 17 mg/l

  16. Waste form dissolution in bedded salt

    International Nuclear Information System (INIS)

    Kaufman, A.M.

    1980-01-01

    A model was devised for waste dissolution in bedded salt, a hydrologically tight medium. For a typical Spent UnReprocessed Fuel (SURF) emplacement, the dissolution rate wll be diffusion limited and will rise to a steady state value after t/sub eq/ approx. = 250 (1+(1-epsilon 0 ) K/sub D//epsilon 0 ) (years) epsilon 0 is the overpack porosity and K/sub d/ is the overpack sorption coefficient. The steady state dissolution rate itself is dominated by the solubility of UO 2 . Steady state rates between 5 x 10 -5 and .5 (g/year) are achievable by SURF emplacements in bedded salt without overpack, and rates between 5 x 10 -7 and 5 x 10 -3 (g/year) with an overpack having porosity of 10 -2

  17. Importance of surface structure on dissolution of fluorite

    DEFF Research Database (Denmark)

    Godinho, Jose; Piazolo, Sandra; Balic Zunic, Tonci

    2014-01-01

    forming the initial surface and its inclination to the closest stable planes, which are specific for each surface orientation. During an initial dissolution regime dissolution rates decrease significantly, even though the total surface area increases. During a second dissolution regime, some surfaces...... by the relative stability of the planes and type of edges that constitute a surface needs to be considered. Significant differences between dissolution rates calculated based on surface area alone, and based on surface reactivity are expected for materials with the fluorite structure....

  18. Dissolution of UO2 in redox conditions

    International Nuclear Information System (INIS)

    Casas, I.; Pablo de, J.; Rovira, M.

    1998-01-01

    The performance assessment of the final disposal of the spent nuclear fuel in geological formations is strongly dependent on the spent fuel matrix dissolution. Unirradiated uranium (IV) dioxide has shown to be very useful for such purposes. The stability of UO 2 is very dependent on vault redox conditions. At reducing conditions, which are expected in deep groundwaters, the dissolution of the UO 2 -matrix can be explained in terms of solubility, while under oxidizing conditions, the UO 2 is thermodynamically unstable and the dissolution is kinetically controlled. In this report the parameters which affect the uranium solubility under reducing conditions, basically pH and redox potential are discussed. Under oxidizing conditions, UO 2 dissolution rate equations as a function of pH, carbonate concentration and oxidant concentration are reported. Dissolution experiments performed with spent fuel are also reviewed. The experimental equations presented in this work, have been used to model independent dissolution experiments performed with both unirradiated and irradiated UO 2 . (Author)

  19. Dissolution of uranium oxide TBP-HNO3 complex

    International Nuclear Information System (INIS)

    Mizuno, Mineo; Kosaka, Yuji; Mori, Yukihide; Shimada, Takashi

    2002-12-01

    As a head end process for the pulverization of the spent fuel, the mechanical method (the shredder method) and the pyro-chemical method (oxidisation heat-treatment) have been examined. UO 2 is a main ingredient of Uranium oxide powder by the mechanical method, and U 3 O 8 is that by the pyro-chemical method. Moreover, the particle size of the pulverized powder depend on the conditions of the pulverizing process. As it was considered that the difference of dissolution rates of samples was caused by the difference of sample chemical forms and dissolution temperature, parametric surveys on chemical form and particle size of powder and dissolution temperature were carried out, and the following results were obtained. 1) The remarkable difference of dissolution rate between U 3 O 8 powder (average particle size 3.7 μm) and UO 2 powder (average particle size 2.4 μm) which have comparatively similar particle size was not observed. 2) It was confirmed that the dissolution rate became lower according to the particle size increase (average particle size 2.4 μm-1 mm). And it was considered that dissolution rate had strong dependency on particle size, according to the results that the powder with 1 mm particle size did not dissolute completely after 5 hours test. 3) The temperature dependency of the dissolution rate was confirmed by dissolution test with UO 2 powder (average particle size 2.4 μm-1 mm). The higher dissolution rate was obtained in the higher dissolution temperature, and 11 kcal/mol was obtained as activation energy of dissolution. 4) In the dissolution test of UO 2 powder, the nitric acid concentration started to change earlier than that of U 3 O 8 powder and concentration change range became larger compared with that in the dissolution test of U 3 O 8 powder. It was considered that those differences were caused by difference in mole ratio of Uranium and nitric acid which are consumed in the dissolution reaction (3:7 for U 3 O 8 , 3:8 for UO 2 ). 5) In case

  20. Does the dose-solubility ratio affect the mean dissolution time of drugs?

    Science.gov (United States)

    Lánský, P; Weiss, M

    1999-09-01

    To present a new model for describing drug dissolution. On the basis of the new model to characterize the dissolution profile by the distribution function of the random dissolution time of a drug molecule, which generalizes the classical first order model. Instead of assuming a constant fractional dissolution rate, as in the classical model, it is considered that the fractional dissolution rate is a decreasing function of the dissolved amount controlled by the dose-solubility ratio. The differential equation derived from this assumption is solved and the distribution measures (half-dissolution time, mean dissolution time, relative dispersion of the dissolution time, dissolution time density, and fractional dissolution rate) are calculated. Finally, instead of monotonically decreasing the fractional dissolution rate, a generalization resulting in zero dissolution rate at time origin is introduced. The behavior of the model is divided into two regions defined by q, the ratio of the dose to the solubility level: q 1 (saturation of the solution, saturation time). The singular case q = 1 is also treated and in this situation the mean as well as the relative dispersion of the dissolution time increase to infinity. The model was successfully fitted to data (1). This empirical model is descriptive without detailed physical reasoning behind its derivation. According to the model, the mean dissolution time is affected by the dose-solubility ratio. Although this prediction appears to be in accordance with preliminary application, further validation based on more suitable experimental data is required.

  1. Iron oxides photochemical dissolution

    International Nuclear Information System (INIS)

    Blesa, M.A.; Litter, M.I.

    1987-01-01

    This work was intended to study the light irradiation influence of diverse wave-lengths on iron oxides dissolution in aqueous solutions. The objectives of this work were: the exploration of photochemical processes with the aim of its eventual application in: a) decontamination and chemical cleaning under special conditions; b) materials for solar energy conversion. (Author)

  2. Plutonium oxide dissolution

    International Nuclear Information System (INIS)

    Gray, J.H.

    1992-01-01

    Several processing options for dissolving plutonium oxide (PuO 2 ) from high-fired materials have been studied. The scoping studies performed on these options were focused on PuO 2 typically generated by burning plutonium metal and PuO 2 produced during incineration of alpha contaminated waste. At least two processing options remain applicable for dissolving high-fired PuO 2 in canyon dissolvers. The options involve solid solution formation of PuO 2 With uranium oxide (UO 2 ) and alloying incinerator ash with aluminum. An oxidative dissolution process involving nitric acid solutions containing a strong oxidizing agent, such as cerium (IV), was neither proven nor rejected. This uncertainty was due to difficulty in regenerating cerium (IV) ions during dissolution. However, recent work on silver-catalyzed dissolution of PuO 2 with persulfate has demonstrated that persulfate ions regenerate silver (II). Use of persulfate to regenerate cerium (IV) or bismuth (V) ions during dissolution of PuO 2 materials may warrant further study

  3. Evolution of Morphology and Crystallinity of Silica Minerals Under Hydrothermal Conditions

    Science.gov (United States)

    Isobe, H.

    2011-12-01

    granules with various surface structures. At the very initial stage of cristobalite crystallization within 2 days run duration, cristobalite shows lepispheres a few micron meters in diameter with irregular, submicron scale ridges and grooves on the surface. With the run duration up to 7 days, lepispheres change to granules with smooth surface remaining a few micron meters in diameter. Crystallinity of cristobalite lepispheres and granules corresponds to opal-CT. Euhedral quartz crystals grow with dissolution of cristobalite grains. Growth rate of cristobalite and quartz is controlled by crystallization kinetics with induction period strongly depending on temperature. Induction period of cristobalite crystallization from amorphous silica may exceed several million years at temperature below 100 °C. Crystallinity, morphology and growth rate of silica minerals occurred in various terrestrial and planetary processes are controlled by temperature and acidity of hydrothermal fluid and nucleation and growth kinetics of silica minerals.

  4. Enhancing the performance of green solid-state electric double-layer capacitor incorporated with fumed silica nanoparticles

    Science.gov (United States)

    Chong, Mee Yoke; Numan, Arshid; Liew, Chiam-Wen; Ng, H. M.; Ramesh, K.; Ramesh, S.

    2018-06-01

    Solid polymer electrolyte (SPE) based on fumed silica nanoparticles as nanofillers, hydroxylethyl cellulose (HEC) as host polymer, magnesium trifluoromethanesulfonate salt and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid is prepared by solution casting technique. The ionic conductivity, interactions of adsorbed ions on the host polymer, structural crystallinity and thermal stability are evaluated by electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), respectively. Ionic conductivity studies at room temperature reveals that the SPE with 2 wt. % of fumed silica nanoparticles gives the highest conductivity compared to its counterpart. The XRD and FTIR studies confirm the dissolution of salt, ionic liquid and successful incorporation of fumed silica nanoparticles with host polymer. In order to examine the performance of SPEs, electric double-layer capacitor (EDLC) are fabricated by using activated carbon electrodes. EDLC studies demonstrate that SPE incorporated with 2 wt. % fumed silica nanoparticles gives high specific capacitance (25.0 F/g) at a scan rate of 5 mV/s compared to SPE without fumed silica. Additionally, it is able to withstand 71.3% of capacitance from its initial capacitance value over 1600 cycles at a current density of 0.4 A/g.

  5. Impact of dissolution and carbonate precipitation on carbon storage in basalt

    Science.gov (United States)

    Wells, R. K.; Xiong, W.; Tadeoye, J.; Menefee, A.; Ellis, B. R.; Skemer, P. A.; Giammar, D.

    2016-12-01

    The spatial evolution of silicate mineral dissolution, carbonate precipitation, and the transport of fluids influence the viability of carbon storage in basalt reservoirs. Dissolution of natural basalt and subsequent carbonate precipitation in systems with different transport processes operating were characterized using static and flow-through (5 mL/hr) experiments at 50, 100, and 150 °C, and 100 bar CO2. Intact samples and cores with milled pathways that simulate fractures were tested. Spatial and mineralogical patterns in dissolution and precipitation were analyzed using optical and electron microscopy, microCT scanning, and surface roughness data. Precipitates and fluid chemistry were analyzed using Raman spectroscopy, SEM-EDS, and ICP-MS. Analysis of the bulk solution and surface topography suggests dissolution of olivine and pyroxene grains begins within hours of the start of the experiments. In flow-through experiments, total effluent cation concentrations reach a peak concentration within a few hours then drop towards a steady state within a few days. In static experiments, the initial rate of cation release is faster than it is after several weeks. In both cases Ca2+, Mg2+, and Fe2+ are the dominant cations in solution in the initial stages of reaction. Lower concentrations of Na2+, K+, and Al3+, and the preservation of feldspar and matrix grains after several weeks of reaction indicate the slow reactivity of these minerals. As the reaction progresses, the surface roughness increases steadily with cavities developing at the sites of olivine and pyroxene grains. Post-reaction analysis of basalt samples reacted at static conditions with milled pathways reveals that both siderite and amorphous silica precipitated within diffusion-limited zones as early as 4-6 weeks. Siderite abundance varies with distance along the pathway with the highest concentration of carbonates 1-2 cm below the fracture opening. Siderite precipitates are large enough to fill fracture

  6. Rate and Selectivity Control in Thioether and Alkene Oxidation with H 2 O 2 over Phosphonate-Modified Niobium(V)-Silica Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Thornburg, Nicholas E.; Notestein, Justin M. (NWU)

    2017-09-05

    Supported metal oxide catalysts are versatile materials for liquid-phase oxidations, including alkene epoxidation and thioether sulfoxidation with H2O2. Periodic trends in H2O2 activation was recently demonstrated for alkene epoxidation, highlighting Nb-SiO2 as a more active and selective catalyst than Ti-SiO2. Three representative catalysts are studied consisting of NbV, TiIV, and ZrIV on silica, each made through a molecular precursor approach that yields highly dispersed oxide sites, for thioanisole oxidation by H2O2. Initial rates trend Nb>Ti>>Zr, as for epoxidation, and Nb outperforms Ti for a number of other thioethers. In contrast, selectivity to sulfoxide vs. sulfone trends Ti>Nb>>Zr at all conversions. Modifying the Nb-SiO2 catalyst with phenylphosphonic acid does not completely remove sulfoxidation reactivity, as it did for photooxidation and epoxidation, and results in an unusual material active for sulfoxidation but neither epoxidation nor overoxidation to the sulfone.

  7. Comparison of the in vitro and in vivo dissolution rates of two diuranates and research on an early urinary indicator of renal failure in humans and animals poisoned with uranium

    International Nuclear Information System (INIS)

    Henge-Napoli, M.H.; Rongier, E.; Ansoborlo, E.; Chalabreysse, J.

    1989-01-01

    The objective of this study was to investigate the solubility of industrial calcined diuranate in various in vitro systems and to test the sensitivity of biological parameters in detecting renal alterations after intoxication in animals and in human subjects. The dissolution rates in in vitro static and dynamic tests are consistent for each solution for both types of test. The in vivo results are comparable to the in vitro results obtained with Gamble solution for both compounds. The excretion kinetics observed are compared with the values calculated from ICRP standards. Urinary GGT excretion measurements are found to be a satisfactory indicator of uranium-induced kidney alterations. GGT excretion increases for injected doses exceeding 50 μg.kg -1 . Initial results in human subjects suggest that following accidental exposure to uranium, GGT is a more sensitive indicator of kidney damage than glycosuria. (author)

  8. The relationship between Al and Si in biogenic silica as determined by PIXE and XAS

    International Nuclear Information System (INIS)

    Beck, L.; Gehlen, M.; Flank, A.-M.; Bennekom, A.J. van; Beusekom, J.E.E. van

    2002-01-01

    Biogenic silica, one of the major constituents of marine sediments, is a potentially powerful paleoceanographic tool, revealing information on past productivity. Interpreting the sedimentary records of the biogenic silica requires, however, an understanding of its preservation. Dissolution of biogenic silica is controlled by the presence of trace elements such as Al. The work in this paper focuses on the association of Al and Si in biogenic silica. The composition and the atomic structure of cultured and natural diatoms were determined by using PIXE and XAS techniques. This study provides the first evidence for a structural association of Al and Si in biogenic silica

  9. Effects of nano-silica (NS) additions on durability of SCC mixtures

    NARCIS (Netherlands)

    Quercia Bianchi, G.; Spiesz, P.R.; Brouwers, H.J.H.; Andrade, C; Gulikers, JJW; Polder, R

    2015-01-01

    In this study, three different types of nano-silica were applied in self-compacting concrete (SCC), one produced by the controlled dissolution of the olivine mineral and two having similar particle size distributions (PSD), but produced through two different processes: fumed powder nano-silica and

  10. Dissolution studies with pilot plant and actual INTEC calcines

    International Nuclear Information System (INIS)

    Herbst, R.S.; Garn, T.G.

    1999-01-01

    The dissolution of Idaho Nuclear Technology and Engineering Center (INTEC) pilot plant calcines was examined to determine solubility of calcine matrix components in acidic media. Two representatives pilot plant calcine types were studied: Zirconia calcine and Zirconia/Sodium calcine. Dissolution of these calcines was evaluated using lower initial concentrations of nitric acid than used in previous tests to decrease the [H+] concentration in the final solutions. Lower [H+] concentrations contribute to more favorable TRUEX/SREX solvent extraction flowsheet performance. Dissolution and analytical results were also obtained for radioactive calcines produced using high sodium feeds blended with non-radioactive Al(NO 3 ) 3 solutions to dilute the sodium concentration and prevent bed agglomeration during the calcination process. Dissolution tests indicated >95 wt.% of the initial calcine mass can be dissolved using the baseline dissolution procedure, with the exception that higher initial nitric acid concentrations are required. The higher initial acid concentration is required for stoichiometric dissolution of the oxides, primarily aluminum oxide. Statistically designed experiments using pilot plant calcine were performed to determine the effect of mixing rate on dissolution efficiency. Mixing rate was determined to provide minimal effects on wt.% dissolution. The acid/calcine ratio and temperature were the predominate variables affecting the wt.% dissolution, a result consistent with previous studies using other similar types of pilot plant calcines

  11. In vivo in vitro correlations for a poorly soluble drug, danazol, using the flow-through dissolution method with biorelevant dissolution media

    DEFF Research Database (Denmark)

    Sunesen, Vibeke Hougaard; Pedersen, Betty Lomstein; Kristensen, Henning Gjelstrup

    2005-01-01

    The purpose of the study was to design dissolution tests that were able to distinguish between the behaviour of danazol under fasted and fed conditions, by using biorelevant media. In vitro dissolution of 100mg danazol capsules was performed using the flow-through dissolution method. Flow rates w...

  12. Biomimetic synthesized chiral mesoporous silica: Structures and controlled release functions as drug carrier

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jing; Xu, Lu, E-mail: xl2013109@163.com; Yang, Baixue; Bao, Zhihong; Pan, Weisan; Li, Sanming, E-mail: li_sanming2013@163.com

    2015-10-01

    This work initially illustrated the formation mechanism of chiral mesoporous silica (CMS) in a brand new insight named biomimetic synthesis. Three kinds of biomimetic synthesized CMS (B-CMS, including B-CMS1, B-CMS2 and B-CMS3) were prepared using different pH or stirring rate condition, and their characteristics were tested with transmission electron microscope and small angle X-ray diffraction. The model drug indomethacin was loaded into B-CMS and drug loading content was measured using ultraviolet spectroscopy. The result suggested that pH condition influenced energetics of self-assembly process, mainly packing energetics of the surfactant, while stirring rate was the more dominant factor to determine particle length. In application, indomethacin loading content was measured to be 35.3%, 34.8% and 35.1% for indomethacin loaded B-CMS1, indomethacin loaded B-CMS2 and indomethacin loaded B-CMS3. After loading indomethacin into B-CMS carriers, surface area, pore volume and pore diameter of B-CMS carriers were reduced. B-CMS converted crystalline state of indomethacin to amorphous state, leading to the improved indomethacin dissolution. B-CMS1 controlled drug release without burst-release, while B-CMS2 and B-CMS3 released indomethacin faster than B-CMS1, demonstrating that the particle length, the ordered lever of multiple helixes, the curvature degree of helical channels and pore diameter greatly contributed to the release behavior of indomethacin loaded B-CMS. - Highlights: • Chiral mesoporous silica was synthesized using biomimetic method. • pH influenced energetics of self-assembly process of chiral mesoporous silica. • Stirring rate determined the particle length of chiral mesoporous silica. • Controlled release behaviors of chiral mesoporous silica varied based on structures.

  13. Biomimetic synthesized chiral mesoporous silica: Structures and controlled release functions as drug carrier

    International Nuclear Information System (INIS)

    Li, Jing; Xu, Lu; Yang, Baixue; Bao, Zhihong; Pan, Weisan; Li, Sanming

    2015-01-01

    This work initially illustrated the formation mechanism of chiral mesoporous silica (CMS) in a brand new insight named biomimetic synthesis. Three kinds of biomimetic synthesized CMS (B-CMS, including B-CMS1, B-CMS2 and B-CMS3) were prepared using different pH or stirring rate condition, and their characteristics were tested with transmission electron microscope and small angle X-ray diffraction. The model drug indomethacin was loaded into B-CMS and drug loading content was measured using ultraviolet spectroscopy. The result suggested that pH condition influenced energetics of self-assembly process, mainly packing energetics of the surfactant, while stirring rate was the more dominant factor to determine particle length. In application, indomethacin loading content was measured to be 35.3%, 34.8% and 35.1% for indomethacin loaded B-CMS1, indomethacin loaded B-CMS2 and indomethacin loaded B-CMS3. After loading indomethacin into B-CMS carriers, surface area, pore volume and pore diameter of B-CMS carriers were reduced. B-CMS converted crystalline state of indomethacin to amorphous state, leading to the improved indomethacin dissolution. B-CMS1 controlled drug release without burst-release, while B-CMS2 and B-CMS3 released indomethacin faster than B-CMS1, demonstrating that the particle length, the ordered lever of multiple helixes, the curvature degree of helical channels and pore diameter greatly contributed to the release behavior of indomethacin loaded B-CMS. - Highlights: • Chiral mesoporous silica was synthesized using biomimetic method. • pH influenced energetics of self-assembly process of chiral mesoporous silica. • Stirring rate determined the particle length of chiral mesoporous silica. • Controlled release behaviors of chiral mesoporous silica varied based on structures

  14. Determinants of marriage dissolution

    Science.gov (United States)

    Rahim, Mohd Amirul Rafiq Abu; Shafie, Siti Aishah Mohd; Hadi, Az'lina Abdul; Razali, Nornadiah Mohd; Azid @ Maarof, Nur Niswah Naslina

    2015-10-01

    Nowadays, the number of divorce cases among Muslim couples is very worrisome whereby the total cases reported in 2013 increased by half of the total cases reported in the previous year. The questions on the true key factors of dissolution of marriage continue to arise. Thus, the objective of this study is to reveal the factors that contribute to the dissolution of marriage. A total of 181 cases and ten potential determinants were included in this study. The potential determinants considered were age at marriage of husband and wife, educational level of husband and wife, employment status of husband and wife, income of husband and wife, the number of children and the presence at a counseling session. Logistic regression analysis was used to analyze the data. The findings revealed that four determinants, namely the income of husband and wife, number of children and the presence at a counselling session were significant in predicting the likelihood of divorce among Muslim couples.

  15. Collective dissolution of microbubbles

    Science.gov (United States)

    Michelin, Sébastien; Guérin, Etienne; Lauga, Eric

    2018-04-01

    A microscopic bubble of soluble gas always dissolves in finite time in an undersaturated fluid. This diffusive process is driven by the difference between the gas concentration near the bubble, whose value is governed by the internal pressure through Henry's law, and the concentration in the far field. The presence of neighboring bubbles can significantly slow down this process by increasing the effective background concentration and reducing the diffusing flux of dissolved gas experienced by each bubble. We develop theoretical modeling of such diffusive shielding process in the case of small microbubbles whose internal pressure is dominated by Laplace pressure. We first use an exact semianalytical solution to capture the case of two bubbles and analyze in detail the shielding effect as a function of the distance between the bubbles and their size ratio. While we also solve exactly for the Stokes flow around the bubble, we show that hydrodynamic effects are mostly negligible except in the case of almost-touching bubbles. In order to tackle the case of multiple bubbles, we then derive and validate two analytical approximate yet generic frameworks, first using the method of reflections and then by proposing a self-consistent continuum description. Using both modeling frameworks, we examine the dissolution of regular one-, two-, and three-dimensional bubble lattices. Bubbles located at the edge of the lattices dissolve first, while innermost bubbles benefit from the diffusive shielding effect, leading to the inward propagation of a dissolution front within the lattice. We show that diffusive shielding leads to severalfold increases in the dissolution time, which grows logarithmically with the number of bubbles in one-dimensional lattices and algebraically in two and three dimensions, scaling respectively as its square root and 2 /3 power. We further illustrate the sensitivity of the dissolution patterns to initial fluctuations in bubble size or arrangement in the case

  16. Dissolution enhancement of drugs. part i: technologies and effect of ...

    African Journals Online (AJOL)

    and steam aided granulation. In these techniques carrier plays an important role in improving solubility and dissolution rate. Polymers, superdisintegrants, surfactants are extensively studied in recent years for dissolution enhancement in drugs. This part of this review discusses technological overview and effect of polymers,

  17. Catalysed electrolytic metal oxide dissolution processes

    International Nuclear Information System (INIS)

    Machuron-Mandard, X.

    1994-01-01

    The hydrometallurgical processes designed for recovering valuable metals from mineral ores as well as industrial wastes usually require preliminary dissolution of inorganic compounds in aqueous media before extraction and purification steps. Unfortunately, most of the minerals concerned hardly or slowly dissolve in acidic or basic solutions. Metallic oxides, sulfides and silicates are among the materials most difficult to dissolve in aqueous solutions. They are also among the main minerals containing valuable metals. The redox properties of such materials sometimes permit to improve their dissolution by adding oxidizing or reducing species to the leaching solution, which leads to an increase in the dissolution rate. Moreover, limited amounts of redox promoters are required if the redox agent is regenerated continuously thanks to an electrochemical device. Nuclear applications of such concepts have been suggested since the dissolution of many actinide compounds (e.g., UO 2 , AmO 2 , PuC, PuN,...) is mainly based on redox reactions. In the 1980s, improvements of the plutonium dioxide dissolution process have been proposed on the basis of oxidation-reduction principles, which led a few years later to the design of industrial facilities (e.g., at Marcoule or at the french reprocessing plant of La Hague). General concepts and well-established results obtained in France at the Atomic Energy Commission (''Commissariat a l'Energie Atomique'') will be presented and will illustrate applications to industrial as well as analytical problems. (author)

  18. Physicochemical characterization and dissolution properties of ...

    African Journals Online (AJOL)

    calorimetry (DSC), powder x-ray diffractometry (PXRD) and Fourier transform infrared (FT-IR) spectroscopy. Phase solubility studies revealed an AL-type diagram indicating a 1:1 stoichiometric inclusion complex and a stability constant value of 914 M-1. Solubility and dissolution rates of PYR and the binary systems were ...

  19. Modeling of Dissolution Effects on Waterflooding

    DEFF Research Database (Denmark)

    Alexeev, Artem; Shapiro, Alexander; Thomsen, Kaj

    2015-01-01

    reaction rates) may exhibit rapid increase of porosity and permeability near the inlet probably indicating a formation of high permeable channels (wormholes). Water saturation in the zone of dissolution increases due to an increase in the bulk volume accessible for the injected fluid. Volumetric non...

  20. Physicochemical characterization and dissolution properties of ...

    African Journals Online (AJOL)

    STORAGESEVER

    2009-04-20

    Apr 20, 2009 ... 1Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Obafemi Awolowo University, Ile-Ife, Nigeria. .... were carefully and homogenously blended in a mortar, to prepare ... different binary systems with HP-β-CD were carried out by adding an excess ..... Overall, the rank order of dissolution rates of.

  1. Pumping Iron and Silica Bodybuilding

    Science.gov (United States)

    Mcnair, H.; Brzezinski, M. A.; Krause, J. W.; Parker, C.; Brown, M.; Coale, T.; Bruland, K. W.

    2016-02-01

    The availability of dissolved iron influences the stoichiometry of nutrient uptake by diatoms. Under nutrient replete conditions diatoms consume silicic acid and nitrate in a 1:1 ratio, this ratio increases under iron stress. Using the tracers 32Si and PDMPO, the total community and group-specific silica production rates were measured along a gradient of dissolved iron in an upwelling plume off the California coast. At each station, a control (ambient silicic acid) and +20 µM silicic acid treatment were conducted with each tracer to determine whether silicic acid limitation controlled the rate of silica production. Dissolved iron was 1.3 nmol kg-1 nearshore and decreased to 0.15 nmol kg-1 offshore. Silicic acid decreased more rapidly than nitrate, it was nearly 9 µM higher in the nearshore and 7 µM lower than nitrate in the middle of the transect where the iron concentration had decreased. The rate of diatom silica production decreased in tandem with silicic acid concentration, and silica production limitation by low silicic acid was most pronounced when iron concentrations were >0.4 nmol kg-1. The composition of the diatom assemblage shifted from Chaetoceros spp. dominated nearshore to a more sparse pennate-dominated assemblage offshore. Changes in taxa-specific silica production rates will be reported based on examination of PDMPO labeled cells using confocal microscopy.

  2. Plutonium dioxide dissolution in glass

    Energy Technology Data Exchange (ETDEWEB)

    Vienna, J.D.; Alexander, D.L.; Li, Hong [and others

    1996-09-01

    In the aftermath of the Cold War, the U.S. Department of Energy`s (DOE) Office of Fissile Materials Disposition (OFMD) is charged with providing technical support for evaluation of disposition options for excess fissile materials manufactured for the nation`s defense. One option being considered for the disposition of excess plutonium (Pu) is immobilization by vitrification. The vitrification option entails immobilizing Pu in a host glass and waste package that are criticality-safe (immune to nuclear criticality), proliferation-resistant, and environmentally acceptable for long-term storage or disposal. To prove the technical and economic feasibility of candidate vitrification options it is necessary to demonstrate that PuO{sub 2} feedstock can be dissolved in glass in sufficient quantity. The OFMD immobilization program has set a Pu solubility goal of 10 wt% in glass. The life cycle cost of the vitrification options are strongly influenced by the rate at which PUO{sub 2} dissolves in glass. The total number of process lines needed for vitrification of 50 t of Pu in 10 years is directly dependent upon the time required for Pu dissolution in glass. The objective of this joint Pacific Northwest National Laboratory (PNNL) - Savannah River Technology Center (SRTC) study was to demonstrate a high Pu solubility in glass and to identify on a rough scale the time required for Pu dissolution in the glass. This study was conducted using a lanthanide borosilicate (LaBS) glass composition designed at the SRTC for the vitrification of actinides.

  3. Plutonium dioxide dissolution in glass

    International Nuclear Information System (INIS)

    Vienna, J.D.; Alexander, D.L.; Li, Hong

    1996-09-01

    In the aftermath of the Cold War, the U.S. Department of Energy's (DOE) Office of Fissile Materials Disposition (OFMD) is charged with providing technical support for evaluation of disposition options for excess fissile materials manufactured for the nation's defense. One option being considered for the disposition of excess plutonium (Pu) is immobilization by vitrification. The vitrification option entails immobilizing Pu in a host glass and waste package that are criticality-safe (immune to nuclear criticality), proliferation-resistant, and environmentally acceptable for long-term storage or disposal. To prove the technical and economic feasibility of candidate vitrification options it is necessary to demonstrate that PuO 2 feedstock can be dissolved in glass in sufficient quantity. The OFMD immobilization program has set a Pu solubility goal of 10 wt% in glass. The life cycle cost of the vitrification options are strongly influenced by the rate at which PUO 2 dissolves in glass. The total number of process lines needed for vitrification of 50 t of Pu in 10 years is directly dependent upon the time required for Pu dissolution in glass. The objective of this joint Pacific Northwest National Laboratory (PNNL) - Savannah River Technology Center (SRTC) study was to demonstrate a high Pu solubility in glass and to identify on a rough scale the time required for Pu dissolution in the glass. This study was conducted using a lanthanide borosilicate (LaBS) glass composition designed at the SRTC for the vitrification of actinides

  4. Controlling the synthesis conditions for silica nanosphere from semi-burned rice straw

    International Nuclear Information System (INIS)

    Hessien, M.M.; Rashad, M.M.; Zaky, R.R.; Abdel-Aal, E.A.; El-Barawy, K.A.

    2009-01-01

    Silica nanoparticles have been prepared through dissolution-precipitation process from rice straw ash (RSA) for different electronic applications. The dissolution of silica from RSA was carried out using alkali leaching process by sodium hydroxide. The precipitation of silica from the produced sodium silicate solution was carried out using sulphuric acid at pH 7. The factors affecting the precipitation process of the sodium silicate solution of dissociated RSA; such as; sodium silicate concentration, sulfuric acid concentration and addition of anionic surfactant (sodium dodecyl sulfate, SDS) on the particle size of the precipitated silica were studied. X-ray diffraction (XRD), X-ray fluorescence (XRF), specific surface area S BET and transmission electron microscope (TEM) have been used for the characterization of the produced nano-silica. The results showed that the optimum conditions of the dissolution efficiency of the silica of about 99% was achieved at 100 deg. C for 4 h, and NaOH/SiO 2 molar ratio three. The particle size of the precipitated silica gel was decreased with increasing Na 2 SiO 3 and SDS concentrations, while H 2 SO 4 concentration had insignificant effect. Particle size of about 16 nm can be achieved at 30% Na 2 SiO 3 , 4% H 2 SO 4 and 200 ppm SDS. The produced silica had 99.93% purity, amorphous and nanosphere particles with narrow size distribution. The produced silica can be used in many applications especially for chemical mechanical polishing (CMP) slurries for semiconductors industries.

  5. Effects of network dissolution changes on pore-to-core upscaled reaction rates for kaolinite and anorthite reactions under acidic conditions

    KAUST Repository

    Kim, Daesang; Lindquist, W. Brent

    2013-01-01

    new connections. The computed changes were based upon a mineral map from an X-ray computed tomography image of a sandstone core. We studied the effect of these changes on upscaled (pore-scale to core-scale) reaction rates and compared against

  6. DISSOLUTION OF IRRADIATED MURR FUEL ASSEMBLIES

    Energy Technology Data Exchange (ETDEWEB)

    Kyser, E.

    2010-06-17

    A literature survey on the dissolution of spent nuclear fuel from the University of Missouri Research Reactor (MURR) has been performed. This survey encompassed both internal and external literature sources for the dissolution of aluminum-clad uranium alloy fuels. The most limiting aspect of dissolution in the current facility configuration involves issues related to the control of the flammability of the off-gas from this process. The primary conclusion of this work is that based on past dissolution of this fuel in H-Canyon, four bundles of this fuel (initial charge) may be safely dissolved in a nitric acid flowsheet catalyzed with 0.002 M mercuric nitrate using a 40 scfm purge to control off-gas flammability. The initial charge may be followed by a second charge of up to five bundles to the same dissolver batch depending on volume and concentration constraints. The safety of this flowsheet relies on composite lower flammability limits (LFL) estimated from prior literature, pilot-scale work on the dissolution of site fuels, and the proposed processing flowsheet. Equipment modifications or improved LFL data offer the potential for improved processing rates. The fuel charging sequence, as well as the acid and catalyst concentrations, will control the dissolution rate during the initial portion of the cycle. These parameters directly impact the hydrogen and off-gas generation and, along with the purge flowrate determine the number of bundles that may be charged. The calculation approach within provides Engineering a means to determine optimal charging patterns. Downstream processing of this material should be similar to that of recent processing of site fuels requiring only minor adjustments of the existing flowsheet parameters.

  7. Microbially mediated barite dissolution in anoxic brines

    International Nuclear Information System (INIS)

    Ouyang, Bingjie; Akob, Denise M.; Dunlap, Darren; Renock, Devon

    2017-01-01

    Fluids injected into shale formations during hydraulic fracturing of black shale return with extraordinarily high total-dissolved-solids (TDS) and high concentrations of barium (Ba) and radium (Ra). Barite, BaSO_4, has been implicated as a possible source of Ba as well as a problematic mineral scale that forms on internal well surfaces, often in close association with radiobarite, (Ba,Ra)SO_4. The dissolution of barite by abiotic processes is well quantified. However, the identification of microbial communities in flowback and produced water necessitates the need to understand barite dissolution in the presence of bacteria. Therefore, we evaluated the rates and mechanisms of abiotic and microbially-mediated barite dissolution under anoxic and hypersaline conditions in the laboratory. Barite dissolution experiments were conducted with bacterial enrichment cultures established from produced water from Marcellus Shale wells located in northcentral Pennsylvania. These cultures were dominated by anaerobic halophilic bacteria from the genus Halanaerobium. Dissolved Ba was determined by ICP-OES and barite surfaces were investigated by SEM and AFM. Our results reveal that: 1) higher amounts of barium (up to ∼5 × ) are released from barite in the presence of Halanaerobium cultures compared to brine controls after 30 days of reaction, 2) etch pits that develop on the barite (001) surface in the presence of Halanaerobium exhibit a morphology that is distinct from those that form during control experiments without bacteria, 3) etch pits that develop in the presence of Halanaerobium exhibit a morphology that is similar to the morphology of etch pits formed in the presence of strong organic chelators, EDTA and DTPA, and 4) experiments using dialysis membranes to separate barite from bacteria suggest that direct contact between the two is not required in order to promote dissolution. These results suggest that Halanaerobium increase the rate of barite dissolution in anoxic

  8. Biorelevant characterisation of amorphous furosemide salt exhibits conversion to a furosemide hydrate during dissolution

    DEFF Research Database (Denmark)

    Nielsen, Line Hagner; Gordon, Sarah; Pajander, Jari Pekka

    2013-01-01

    , as well as of crystalline furosemide salt and acid showed a higher rate of dissolution of the salt forms in comparison with the two acid forms. The measured dissolution rates of the four furosemide forms from the UV imaging system and from eluted effluent samples were consistent with dissolution rates...... obtained from micro dissolution experiments. Partial least squares-discriminant analysis of Raman spectra of the amorphous acid form during flow through dissolution showed that the amorphous acid exhibited a fast conversion to the crystalline acid. Flow through dissolution coupled with Raman spectroscopy...... showed a conversion of the amorphous furosemide salt to a more stable polymorph. It was found by thermogravimetric analysis and hot stage microscopy that the salt forms of furosemide converted to a trihydrate during dissolution. It can be concluded that during biorelevant dissolution, the amorphous...

  9. Chemical Dissolution of Simulant FCA Cladding and Plates

    Energy Technology Data Exchange (ETDEWEB)

    Daniel, G. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Pierce, R. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); O' Rourke, P. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2017-11-08

    The Savannah River Site (SRS) has received some fast critical assembly (FCA) fuel from the Japan Atomic Energy Agency (JAEA) for disposition. Among the JAEA FCA fuel are approximately 7090 rectangular Stainless Steel clad fuel elements. Each element has an internal Pu-10.6Al alloy metal wafer. The thickness of each element is either 1/16 inch or 1/32 inch. The dimensions of each element ranges from 2 inches x 1 inch to 2 inches x 4 inches. This report discusses the potential chemical dissolution of the FCA clad material or stainless steel. This technology uses nitric acid-potassium fluoride (HNO3-KF) flowsheets of H-Canyon to dissolve the FCA elements from a rack of materials. Historically, dissolution flowsheets have aimed to maximize Pu dissolution rates while minimizing stainless steel dissolution (corrosion) rates. Because the FCA cladding is made of stainless steel, this work sought to accelerate stainless steel dissolution.

  10. Biorelevant dissolution media

    DEFF Research Database (Denmark)

    Ilardia-Arana, David; Kristensen, Henning G; Müllertz, Anette

    2006-01-01

    Biorelevant dissolution media containing bile salt and lecithin at concentrations appropriate for fed and fasted state are useful when testing oral solid formulations of poorly water-soluble drugs. Dilution of amphiphile solutions affects the aggregation state of the amphiphiles because bile salt...... is partitioned between the aqueous phase and the aggregates. The aim of the investigation was to study the effect of dilution on the size distribution of aggregates and its effect on the solubilization capacity. Clear buffered solutions of four intestinal amphiphiles (sodium glycocholate, lecithin, monoolein...

  11. Dissolution kinetics of lead telluride in alkali solutions of hydrogen peroxide

    International Nuclear Information System (INIS)

    Danilova, M.G.; Sveshnikova, L.L.; Stavitskaya, T.A.; Repinskij, S.M.

    1991-01-01

    Dissolution kinetics of lead telluride in alkali solutions of hydrogen peroxide was investigated. Dependences of change of PbTe dissolution rate on concentration of hydrogen peroxide and alkali in the solution were obtained. It is shown that dissolution rate of lead telluride is affected by dissolution rate of lead oxide, representing the product of ReTe dissolution. The obtained regularities can be explained by change of solution structure with increase of KOH concentration and by the state of hydrogen peroxide in the solution

  12. Dissolution behaviour of silicon nitride coatings for joint replacements

    Energy Technology Data Exchange (ETDEWEB)

    Pettersson, Maria [Materials in Medicine Group, Div. of Applied Materials Science, Dept. of Engineering Sciences, Uppsala University, Uppsala (Sweden); Bryant, Michael [Institute of Functional Surfaces (iFS), School of Mechanical Engineering, University of Leeds, Leeds (United Kingdom); Schmidt, Susann [Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping (Sweden); Engqvist, Håkan [Materials in Medicine Group, Div. of Applied Materials Science, Dept. of Engineering Sciences, Uppsala University, Uppsala (Sweden); Hall, Richard M. [Institute of Medical and Biological Engineering (iMBE), School of Mechanical Engineering, University of Leeds, Leeds (United Kingdom); Neville, Anne [Institute of Functional Surfaces (iFS), School of Mechanical Engineering, University of Leeds, Leeds (United Kingdom); Persson, Cecilia, E-mail: cecilia.persson@angstrom.uu.se [Materials in Medicine Group, Div. of Applied Materials Science, Dept. of Engineering Sciences, Uppsala University, Uppsala (Sweden)

    2016-05-01

    In this study, the dissolution rate of SiN{sub x} coatings was investigated as a function of coating composition, in comparison to a cobalt chromium molybdenum alloy (CoCrMo) reference. SiN{sub x} coatings with N/Si ratios of 0.3, 0.8 and 1.1 were investigated. Electrochemical measurements were complemented with solution (inductively coupled plasma techniques) and surface analysis (vertical scanning interferometry and x-ray photoelectron spectroscopy). The dissolution rate of the SiN{sub x} coatings was evaluated to 0.2–1.4 nm/day, with a trend of lower dissolution rate with higher N/Si atomic ratio in the coating. The dissolution rates of the coatings were similar to or lower than that of CoCrMo (0.7–1.2 nm/day). The highest nitrogen containing coating showed mainly Si–N bonds in the bulk as well as at the surface and in the dissolution area. The lower nitrogen containing coatings showed Si–N and/or Si–Si bonds in the bulk and an increased formation of Si–O bonds at the surface as well as in the dissolution area. The SiN{sub x} coatings reduced the metal ion release from the substrate. The possibility to tune the dissolution rate and the ability to prevent release of metal ions encourage further studies on SiN{sub x} coatings for joint replacements. - Graphical abstract: Dissolution rates of SiN{sub 0.3}, SiN{sub 0.8}, and SiN{sub 1.1} coatings on CoCrMo compared to uncoated CoCrMo. Dissolution rates were obtained from i) electrochemical measurements of I{sub corr}, ii) the step height between covered and solution-exposed surfaces, measured using VSI, and iii) the ion concentration in the solution, measured with ICP. - Highlights: • The dissolution of SiN{sub x} coatings was investigated in comparison to (bulk) CoCrMo. • The coatings gave a lower or similar dissolution rate to CoCrMo, of 0.2–1.2 nm/day. • An increased nitrogen content in the coatings gave lower dissolution rates. • SiN{sub x} coatings on CoCrMo reduced the metal ion release

  13. Quantifying silica reactivity in subsurface environments: Reaction affinity and solute matrix controls on quartz and SiO2 glass. 1997 annual progress report

    International Nuclear Information System (INIS)

    Dove, P.M.

    1997-01-01

    'The author reports the preliminary results of the experiments on the dissolution behavior of vitreous silica (v-SiO 2 ) into aqueous solutions of variable pH and ionic strength. The experiments are being conducted in mixed flow reactors with a high circulation rate that simulates constant-stirred conditions, the efficacy of which the authors discuss below. The preliminary results indicate that v-SiO 2 dissolves into aqueous solutions approximately two orders of magnitude more quickly than crystalline silica (e.g., quartz). With additional experiments, they will utilize the dissolution rate data as a framework for understanding the behavior of waste glass compositions in the subsurface. In other work related to the studies of glass reactivity, the author has written one book chapter that will be published as part of a proceedings for the CEA/VALRHO international nuclear waste disposal conference held in Mejannes le Clap, France. In separate work, she is presently writing a second book chapter for the volume entitled Adsorption on Silica Surfaces.'

  14. Aluminum Target Dissolution in Support of the Pu-238 Program

    Energy Technology Data Exchange (ETDEWEB)

    McFarlane, Joanna [ORNL; Benker, Dennis [ORNL; DePaoli, David W [ORNL; Felker, Leslie Kevin [ORNL; Mattus, Catherine H [ORNL

    2014-09-01

    Selection of an aluminum alloy for target cladding affects post-irradiation target dissolution and separations. Recent tests with aluminum alloy 6061 yielded greater than expected precipitation in the caustic dissolution step, forming up to 10 wt.% solids of aluminum hydroxides and aluminosilicates. We present a study to maximize dissolution of aluminum metal alloy, along with silicon, magnesium, and copper impurities, through control of temperature, the rate of reagent addition, and incubation time. Aluminum phase transformations have been identified as a function of time and temperature, using X-ray diffraction. Solutions have been analyzed using wet chemical methods and X-ray fluorescence. These data have been compared with published calculations of aluminum phase diagrams. Temperature logging during the transients has been investigated as a means to generate kinetic and mass transport data on the dissolution process. Approaches are given to enhance the dissolution of aluminum and aluminosilicate phases in caustic solution.

  15. investigation of dissolution kinetics of a nigerian columbite

    African Journals Online (AJOL)

    user

    1,2 DEPARTMENT OF CHEMICAL ENGINEERING, OBAFEMI AWOLOWO UNIVERSITY, ILE-IFE, OSUN STATE NIGERIA. E-mail addresses: ... Experimental results indicate that the dissolution rate is chemical reaction ..... Nuclear Instruments.

  16. Kinetics of Inorganic Calcite Dissolution in Seawater under Pressure

    Science.gov (United States)

    Dong, S.; Subhas, A.; Rollins, N.; Berelson, W.; Adkins, J. F.

    2016-02-01

    While understanding calcium carbonate dissolution is vital in constructing global carbon cycles and predicting the effect of seawater acidification as a result of increasing atmospheric CO2, there is still a major debate over the basic formulation of a dissolution rate law. The kinetics of calcium carbonate dissolution are typically described by the equation: Rate=k(1-Ω)n, while Ω=[Ca2+][CO32-]/Ksp. In this study, 13C-labeled calcite is dissolved in unlabeled seawater and the evolving d13C composition of the fluid is traced over time to establish dissolution rate. Instead of changing ion concentration to obtain varying Ω (as in our previous study; Subhas et al. 2015), we changed Ksp by conducting experiments under different pressures (described in theory as ∂lnKsp/∂P=-ΔV/RT, where ΔV is partial molal volume). This involved the construction of a pressure vessel that could hold our sample bag and provide aliquots while remaining pressurized. Pressure experiments were conducted between 0-2000PSI. Results support the conclusion in our previous study that near-equilibrium dissolution rates are highly nonlinear, but give a disparate relationship between undersaturation and dissolution rate if Ω is calculated assuming the specific ΔV embedded in CO2SYS. A revised ΔV from -37cm3 to -65cm3 would make the dissolution formulation equation agree, but clearly appears unreasonable. Our results are explained by a pressure effect on carbonate dissolution kinetics over and above the influence of pressure on Ω. If this is a phenomenon that occurs in nature, then we would predict that dissolution should be occurring shallower in the water column (as sometimes observed) than indicated by standard Ω calculations.

  17. Cellular membrane trafficking of mesoporous silica nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Fang, I-Ju [Iowa State Univ., Ames, IA (United States)

    2012-01-01

    the specific organelle that mesoporous silica nanoparticles could approach via the identification of harvested proteins from exocytosis process. Based on the study of endo- and exocytosis behavior of mesoporous silica nanoparticle materials, we can design smarter drug delivery vehicles for cancer therapy that can be effectively controlled. The destination, uptake efficiency and the cellular distribution of mesoporous silica nanoparticle materials can be programmable. As a result, release mechanism and release rate of drug delivery systems can be a well-controlled process. The deep investigation of an endo- and exocytosis study of mesoporous silica nanoparticle materials promotes the development of drug delivery applications.

  18. Dissolution of covalent adaptable network polymers in organic solvent

    Science.gov (United States)

    Yu, Kai; Yang, Hua; Dao, Binh H.; Shi, Qian; Yakacki, Christopher M.

    2017-12-01

    It was recently reported that thermosetting polymers can be fully dissolved in a proper organic solvent utilizing a bond-exchange reaction (BER), where small molecules diffuse into the polymer, break the long polymer chains into short segments, and eventually dissolve the network when sufficient solvent is provided. The solvent-assisted dissolution approach was applied to fully recycle thermosets and their fiber composites. This paper presents the first multi-scale modeling framework to predict the dissolution kinetics and mechanics of thermosets in organic solvent. The model connects the micro-scale network dynamics with macro-scale material properties: in the micro-scale, a model is developed based on the kinetics of BERs to describe the cleavage rate of polymer chains and evolution of chain segment length during the dissolution. The micro-scale model is then fed into a continuum-level model with considerations of the transportation of solvent molecules and chain segments in the system. The model shows good prediction on conversion rate of functional groups, degradation of network mechanical properties, and dissolution rate of thermosets during the dissolution. It identifies the underlying kinetic factors governing the dissolution process, and reveals the influence of different material and processing variables on the dissolution process, such as time, temperature, catalyst concentration, and chain length between cross-links.

  19. Electrochemical and CMT measurements of the anomalous dissolution of nickel in solutions containing oxygen

    DEFF Research Database (Denmark)

    Bech-Nielsen, Gregers; de Fontenay, Frank; Poulsen, Henning

    1997-01-01

    In addition to single nickel crystals also nickel samples produced by dc and pr (pulse-reversal) plating were examined. As previously reported the true rate of dissolution of nickel in solutions containing oxygen was found to be as much as three times the electrochemical rate at the corrosion...... potential. When passivation was approached (spontaneously or by anodic polarization) the true rate of dissolution approached the rate of anodic reaction. During cathodic polarization there was still a significant rate of dissolution. The true rate of dissolution was determined by CMT measurements (Corrosion...

  20. The dissolution of chalcopyrite in chloride media; Lixiviacion de la calcopirita en medios clorurados

    Energy Technology Data Exchange (ETDEWEB)

    Ibanez, T.; Velasquez, L.

    2013-06-01

    The aim of this investigation is to determinate the effects of parameters and additives on the kinetics of dissolution of chalcopyrite on moderated conditions by means of dissolutions test with chalcopyrite concentrate and pure chalcopyrite in shake flasks and instrumented stirred reactors. A study of the dissolution of chalcopyrite in chloride solutions has demonstrated that the rate of dissolution of chalcopyrite is strongly dependent on the potential of the solution within a range of 540 to 630 mV (versus SHE). Leaching at pH around 2.5 results in increased rates of copper dissolution suggesting the possibility to keep the solution potential within the range. Both pyrite and silver ions enhance the dissolution of chalcopyrite and this effect increases when both species are present. The MnO{sub 2} has a negative effect on the dissolution increasing the solution potential to values where the rate decreases considerably. (Author)

  1. Reactive silica transport in fractured porous media: Analytical solutions for a system of parallel fractures

    Science.gov (United States)

    Yang, Jianwen

    2012-04-01

    A general analytical solution is derived by using the Laplace transformation to describe transient reactive silica transport in a conceptualized 2-D system involving a set of parallel fractures embedded in an impermeable host rock matrix, taking into account of hydrodynamic dispersion and advection of silica transport along the fractures, molecular diffusion from each fracture to the intervening rock matrix, and dissolution of quartz. A special analytical solution is also developed by ignoring the longitudinal hydrodynamic dispersion term but remaining other conditions the same. The general and special solutions are in the form of a double infinite integral and a single infinite integral, respectively, and can be evaluated using Gauss-Legendre quadrature technique. A simple criterion is developed to determine under what conditions the general analytical solution can be approximated by the special analytical solution. It is proved analytically that the general solution always lags behind the special solution, unless a dimensionless parameter is less than a critical value. Several illustrative calculations are undertaken to demonstrate the effect of fracture spacing, fracture aperture and fluid flow rate on silica transport. The analytical solutions developed here can serve as a benchmark to validate numerical models that simulate reactive mass transport in fractured porous media.

  2. Development of Dissolution Test Method for Drotaverine ...

    African Journals Online (AJOL)

    Development of Dissolution Test Method for Drotaverine ... Methods: Sink conditions, drug stability and specificity in different dissolution media were tested to optimize a dissolution test .... test by Prism 4.0 software, and differences between ...

  3. High drug load, stable, manufacturable and bioavailable fenofibrate formulations in mesoporous silica: a comparison of spray drying versus solvent impregnation methods.

    Science.gov (United States)

    Hong, Shiqi; Shen, Shoucang; Tan, David Cheng Thiam; Ng, Wai Kiong; Liu, Xueming; Chia, Leonard S O; Irwan, Anastasia W; Tan, Reginald; Nowak, Steven A; Marsh, Kennan; Gokhale, Rajeev

    2016-01-01

    Encapsulation of drugs in mesoporous silica using co-spray drying process has been recently explored as potential industrial method. However, the impact of spray drying on manufacturability, physiochemical stability and bioavailability in relation to conventional drug load processes are yet to be fully investigated. Using a 2(3) factorial design, this study aims to investigate the effect of drug-loading process (co-spray drying and solvent impregnation), mesoporous silica pore size (SBA-15, 6.5 nm and MCM-41, 2.5 nm) and percentage drug load (30% w/w and 50% w/w) on material properties, crystallinity, physicochemical stability, release profiles and bioavailability of fenofibrate (FEN) loaded into mesoporous silica. From the scanning electronic microscopy (SEM) images, powder X-ray diffraction and Differential scanning calorimetry measurements, it is indicated that the co-spray drying process was able to load up to 50% (w/w) FEN in amorphous form onto the mesoporous silica as compared to the 30% (w/w) for solvent impregnation. The in vitro dissolution rate of the co-spray dried formulations was also significantly (p = 0.044) better than solvent impregnated formulations at the same drug loading. Six-month accelerated stability test at 40 °C/75 RH in open dish indicated excellent physical and chemical stability of formulations prepared by both methods. The amorphous state of FEN and the enhanced dissolution profiles were well preserved, and very low levels of degradation were detected after storage. The dog data for the three selected co-spray-dried formulations revealed multiple fold increment in FEN bioavailability compared to the reference crystalline FEN. These results validate the viability of co-spray-dried mesoporous silica formulations with high amorphous drug load as potential drug delivery systems for poorly water soluble drugs.

  4. Dissolution of nuclear fuels; Disolucion de combustibles Nucleares

    Energy Technology Data Exchange (ETDEWEB)

    Uriarte Hueda, A; Berberana Eizmendi, M; Rainey, R

    1968-07-01

    A laboratory study was made of the instantaneous dissolution rate (IDR) for unirradiated uranium metal rods and UO{sub 2}, PuO{sub 2} and PuO{sub 2}-UO{sub 2} pellets in boiling nitric acid alone and with additives. The uranium metal and UO{sub 2} dissolved readily in nitric acid alone; PuO{sub 2} dissolved slowly even with the addition of fluoride; PuO{sub 2}-UO{sub 2} pellets containing as much as 35% PuO{sub 2} in UO{sub 2} gave values of the instantaneous dissolution rate to indicate can be dissolved with nitric acid alone. An equation to calculate the time for complete dissolution has been determinate in function of the instantaneous dissolution rates. The calculated values agree with the experimental. Uranium dioxide pellets from various sources but all having a same density varied in instantaneous dissolution rate. All the pellets, however, have dissolved ved in the same time. The time for complete dissolution of PuO{sub 2}-UO{sub 2} pellets, having the same composition, and the concentration of the used reagents are function of the used reagents are function of the fabrication method. (Author) 8 refs.

  5. Predicting the dissolution kinetics of silicate glasses using machine learning

    Science.gov (United States)

    Anoop Krishnan, N. M.; Mangalathu, Sujith; Smedskjaer, Morten M.; Tandia, Adama; Burton, Henry; Bauchy, Mathieu

    2018-05-01

    Predicting the dissolution rates of silicate glasses in aqueous conditions is a complex task as the underlying mechanism(s) remain poorly understood and the dissolution kinetics can depend on a large number of intrinsic and extrinsic factors. Here, we assess the potential of data-driven models based on machine learning to predict the dissolution rates of various aluminosilicate glasses exposed to a wide range of solution pH values, from acidic to caustic conditions. Four classes of machine learning methods are investigated, namely, linear regression, support vector machine regression, random forest, and artificial neural network. We observe that, although linear methods all fail to describe the dissolution kinetics, the artificial neural network approach offers excellent predictions, thanks to its inherent ability to handle non-linear data. Overall, we suggest that a more extensive use of machine learning approaches could significantly accelerate the design of novel glasses with tailored properties.

  6. In vivo dissolution measurement with indium-111 summation peak ratios

    International Nuclear Information System (INIS)

    Jay, M.; Woodward, M.A.; Brouwer, K.R.

    1985-01-01

    Dissolution of [ 111 In]labeled tablets was measured in vivo in a totally noninvasive manner by using a modification of the perturbed angular correlation technique known as the summation peak ratio method. This method, which requires the incorporation of only 10-12 microCi into the dosage form, provided reliable dissolution data after oral administration of [ 111 In]lactose tablets. These results were supported by in vitro experiments which demonstrated that the dissolution rate as measured by the summation peak ratio method was in close agreement with the dissolution rate of salicylic acid in a [ 111 In]salicylic acid tablet. The method has the advantages of using only one detector, thereby avoiding the need for complex coincidence counting systems, requiring less radioactivity, and being potentially applicable to a gamma camera imaging system

  7. Montmorillonite dissolution kinetics: Experimental and reactive transport modeling interpretation

    Science.gov (United States)

    Cappelli, Chiara; Yokoyama, Shingo; Cama, Jordi; Huertas, F. Javier

    2018-04-01

    The dissolution kinetics of K-montmorillonite was studied at 25 °C, acidic pH (2-4) and 0.01 M ionic strength by means of well-mixed flow-through experiments. The variations of Si, Al and Mg over time resulted in high releases of Si and Mg and Al deficit, which yielded long periods of incongruent dissolution before reaching stoichiometric steady state. This behavior was caused by simultaneous dissolution of nanoparticles and cation exchange between the interlayer K and released Ca, Mg and Al and H. Since Si was only involved in the dissolution reaction, it was used to calculate steady-state dissolution rates, RSi, over a wide solution saturation state (ΔGr ranged from -5 to -40 kcal mol-1). The effects of pH and the degree of undersaturation (ΔGr) on the K-montmorillonite dissolution rate were determined using RSi. Employing dissolution rates farthest from equilibrium, the catalytic pH effect on the K-montmorillonite dissolution rate was expressed as Rdiss = k·aH0.56±0.05 whereas using all dissolution rates, the ΔGr effect was expressed as a non-linear f(ΔGr) function Rdiss = k · [1 - exp(-3.8 × 10-4 · (|ΔGr|/RT)2.13)] The functionality of this expression is similar to the equations reported for dissolution of Na-montmorillonite at pH 3 and 50 °C (Metz, 2001) and Na-K-Ca-montmorillonite at pH 9 and 80 °C (Cama et al., 2000; Marty et al., 2011), which lends support to the use of a single f(ΔGr) term to calculate the rate over the pH range 0-14. Thus, we propose a rate law that also accounts for the effect of pOH and temperature by using the pOH-rate dependence and the apparent activation energy proposed by Rozalén et al. (2008) and Amram and Ganor (2005), respectively, and normalizing the dissolution rate constant with the edge surface area of the K-montmorillonite. 1D reactive transport simulations of the experimental data were performed using the Crunchflow code (Steefel et al., 2015) to quantitatively interpret the evolution of the released cations

  8. Development of silica RO membranes

    International Nuclear Information System (INIS)

    Ikeda, Ayumi; Kawamoto, Takashi; Matsuyama, Emi; Utsumi, Keisuke; Nomura, Mikihiro; Sugimoto, Masaki; Yoshikawa, Masato

    2012-01-01

    Silica based membranes have been developed by using a counter diffusion CVD method. Effects of alkyl groups in the silica precursors and deposition temperatures had investigated in order to control pore sizes of the silica membranes. In this study, this type of a silica membrane was applied for RO separation. Effects of silica sources, deposition temperatures and post treatments had been investigated. Tetramethoxysilane (TMOS), Ethyltrimethoxysilane (ETMOS) and Phenyltrimethoxysilane (PhTMOS) were used as silica precursors. A counter diffusion CVD method was carried out for 90 min at 270 - 600degC on γ-alumina capillary substrates (effective length: 50 mm, φ: 4 nm: NOK Co.). O 3 or O 2 was introduced into the inside of the substrate at the O 2 rate of 0.2 L min -1 . Ion beam irradiation was carried out for a post treatment using Os at 490 MeV for 1.0 x 10 10 ions cm -2 or 3.0 x 10 10 ions cm -2 . Single gas permeance was measured by using H 2 , N 2 and SF 6 . RO tests were employed at 3.0 or 5.4 MPa for 100 mg L -1 of feed NaCl solution. First, effects of the silica sources were investigated. The total fluxes increased by increasing N 2 permeance through the silica membrane deposited by ETMOS. The maximum NaCl rejection was 28.2% at 12.2 kg m -2 h -1 of the total flux through the membrane deposited at 270degC. N 2 permeance was 9.6 x 10 -9 mol m -2 s -1 Pa -1 . While, total fluxes through the membrane deposited by using PhTMOS were smaller than those through the ETMOS membranes. The phenyl groups for the PhTMOS membrane must be important for the hydrophobic properties through the membrane. Next, effects of ion beam irradiation were tested for the TMOS membranes. Water is difficult to permeate through the TMOS membranes due to the low N 2 permeance through the membrane (3.1 x 10 -11 mol m -2 s -1 Pa -1 ). N 2 permeance increased to 7.3 x 10 -9 mol m -2 s -1 Pa -1 by the irradiation. Irradiation amounts had little effects on N 2 permeance. However, NaCl rejections

  9. Dissolution and carbonation of a serpentinite: Inferences from acid attack and high P-T experiments performed in aqueous solutions at variable salinity

    International Nuclear Information System (INIS)

    Orlando, Andrea; Borrini, Daniele; Marini, Luigi

    2011-01-01

    ) the log rate [mole m -2 s -1 ] value of -12.08 ± 0.16 (1σ), as representative of the neutral dissolution mechanism at 25 deg. C and (ii) the following relationship for the acidic dissolution mechanism at 25 deg. C: log rate=-0.45(±0.09)xpH-10.01(±0.30). The initial dissolution rate (for 25 deg. C) by acid attack obtained in this work is consistent with this relationship. In contrast, the average dissolution rate (for 25 deg. C) determined in this study through the pressure-vessel experiments is ∼4.5 orders of magnitude lower than that computed through this equation, suggesting that silica armoring of serpentinite grains played a significant role in these experiments. Overall, the obtained data may improve both the planning of ex-situ mineral carbonation using the CO 2 separated from biogas and the modeling of in-situ mineral carbonation.

  10. Dissolution and carbonation of a serpentinite: Inferences from acid attack and high P-T experiments performed in aqueous solutions at variable salinity

    Energy Technology Data Exchange (ETDEWEB)

    Orlando, Andrea, E-mail: orlando@igg.cnr.it [C.N.R., Istituto di Geoscienze e Georisorse, U.O.S. di Firenze, Via G. La Pira, 4, I-50121 Firenze (Italy); Borrini, Daniele [Dipartimento di Scienze della Terra, Universita degli Studi di Firenze, Via G. La Pira, 4, I-50121 Firenze (Italy); Marini, Luigi [Consultant in Applied Geochemistry, Via A. Fratti 253, I-55049 Viareggio (Italy)

    2011-08-15

    investigations on the dissolution kinetics of serpentine minerals the authors propose adopting: (i) the log rate [mole m{sup -2} s{sup -1}] value of -12.08 {+-} 0.16 (1{sigma}), as representative of the neutral dissolution mechanism at 25 deg. C and (ii) the following relationship for the acidic dissolution mechanism at 25 deg. C: log rate=-0.45({+-}0.09)xpH-10.01({+-}0.30). The initial dissolution rate (for 25 deg. C) by acid attack obtained in this work is consistent with this relationship. In contrast, the average dissolution rate (for 25 deg. C) determined in this study through the pressure-vessel experiments is {approx}4.5 orders of magnitude lower than that computed through this equation, suggesting that silica armoring of serpentinite grains played a significant role in these experiments. Overall, the obtained data may improve both the planning of ex-situ mineral carbonation using the CO{sub 2} separated from biogas and the modeling of in-situ mineral carbonation.

  11. Study of dissolution process and its modelling

    Directory of Open Access Journals (Sweden)

    Juan Carlos Beltran-Prieto

    2017-01-01

    Full Text Available The use of mathematical concepts and language aiming to describe and represent the interactions and dynamics of a system is known as a mathematical model. Mathematical modelling finds a huge number of successful applications in a vast amount of science, social and engineering fields, including biology, chemistry, physics, computer sciences, artificial intelligence, bioengineering, finance, economy and others. In this research, we aim to propose a mathematical model that predicts the dissolution of a solid material immersed in a fluid. The developed model can be used to evaluate the rate of mass transfer and the mass transfer coefficient. Further research is expected to be carried out to use the model as a base to develop useful models for the pharmaceutical industry to gain information about the dissolution of medicaments in the body stream and this could play a key role in formulation of medicaments.

  12. Dissolution of FFTF vendor fuel

    International Nuclear Information System (INIS)

    Lerch, R.E.

    1979-08-01

    Dissolution experiments were performed on FFTF vendor fuel (both mechanically mixed and coprecipitated) during 1974, 1975, and 1976. A marked improvement was noted in the completeness of fuel dissolution from 1974 to 1976. The reason for this is unknown but may have been attributable to slight changes in fuel fabrication conditions. In general, the bulk of the fuel pellets tested dissolved to greater than 99.9% in nitric acid alone

  13. Dissolution of FFTF vendor fuel

    Energy Technology Data Exchange (ETDEWEB)

    Lerch, R.E.

    1979-08-01

    Dissolution experiments were performed on FFTF vendor fuel (both mechanically mixed and coprecipitated) during 1974, 1975, and 1976. A marked improvement was noted in the completeness of fuel dissolution from 1974 to 1976. The reason for this is unknown but may have been attributable to slight changes in fuel fabrication conditions. In general, the bulk of the fuel pellets tested dissolved to greater than 99.9% in nitric acid alone.

  14. Dissolution of ion exchange resin by hydrogen peroxide

    International Nuclear Information System (INIS)

    Lee, S.C.

    1981-08-01

    The resin dissolution process was conducted successfully in full-scale equipment at the SRL Semiworks. A solution containing 0.001M Fe 2+ , or Fe 3+ , and 3 vol % H 2 O 2 in 0.1M HNO 3 is sufficient to dissolve up to 40 vol % resin slurry (Dowex 50W-X8). Foaming and pressurization can be eliminated by maintaining the dissolution temperature below 99 0 C. The recommended dissolution temperature range is 85 to 90 0 C. Premixing hydrogen peroxide with all reactants will not create a safety hazard, but operating with a continual feed of hydrogen peroxide is recommended to control the dissolution rate. An air sparging rate of 1.0 to 1.5 scfm will provide sufficient mixing. Spent resin from chemical separation contains DTPA (diethylenetriaminepentaacetic acid) residue, and the resin must be washed with 0.1M NH 4 OH to remove excess DTPA before dissolution. Gamma irradiation of resin up to 4 kW-hr/L did not change the dissolution rate significantly

  15. Dissolution of mixed oxide spent fuel from FBR

    International Nuclear Information System (INIS)

    Sanyoshi, H.; Nishina, H.; Toyota, O.; Yamamoto, R.; Nemoto, S.; Okamoto, F.; Togashi, A.; Kawata, T.; Hayashi, S.

    1991-01-01

    At the Tokai Works of the Power Reactor and Nuclear Fuel Development Corporation (PNC), the Chemical Processing Facility (CPF) has been continuing operation since 1982 for laboratory scale hot experiments on reprocessing of FBR mixed oxide fuel. As a part of these experiments, dissolution experiments have been performed to define the key parameters affecting dissolution rates such as concentration of nitric acid, temperature and burnup and also to confirm the amount of insoluble residue. The dissolution rate of the irradiated fuel was determined to be in proportion to the 1.7 power of the nitric acid concentration. The activation energy determined from the experiments varied from 6 to 11 kcal/mol depending on the method of dissolution. The dissolution rate decreased as the fuel burnup increased in low nitric acid media below 5 mol/l. However, it was found that the effect of the burnup became negligible in a high concentration of nitric acid media. The amount of insoluble residue and its constituents were evaluated by changing the dissolution condition. (author)

  16. Formalization of the kinetics for autocatalytic dissolutions. Focus on the dissolution of uranium dioxide in nitric medium

    International Nuclear Information System (INIS)

    Charlier, F.; Canion, D.; Gravinese, A.; Magnaldo, A.; Lalleman, S.; Borda, G.; Schaer, E.

    2017-01-01

    Uranium dioxide dissolution in nitric acid is a complex reaction. On the one hand, the dissolution produces nitrous oxides (NOX), which makes it a triphasic reaction. On the other hand, one of the products accelerates the kinetic rate; the reaction is hence called autocatalytic.The kinetics for these kinds of reactions need to be formalized in order to optimize and design innovative dissolution reactors. In this work, the kinetics rates have been measured by optical microscopy using a single particle approach. The advantages of this analytical technique are an easier management of species transport in solution and a precise following of the dissolution rate. The global rate is well described by a mechanism considering two steps: a non-catalyzed reaction, where the catalyst concentration has no influence on the dissolution rate, and a catalyzed reaction. The mass transfer rate of the catalyst was quantified in order to discriminate when the reaction was influenced by catalyst accumulated in the boundary layer or uncatalyzed. This first approximation described well the sigmoid dissolution curve profile. Moreover, experiments showed that solutions filled with catalyst proved to lose reactivity over time. Results pointed out that the higher the liquid-gas exchanges, the faster the kinetic rate decreases with time. Thus, it was demonstrated, for the first time, that there is a link between catalyst and nitrous oxides. The outcome of this study leads to new ways for improving the design of dissolvers. Gas-liquid exchanges are indeed a lever to impact dissolution rates. Temperature and catalyst concentration can be optimized to reduce residence times in dissolvers. (authors)

  17. Results from NNWSI [Nevada Nuclear Waste Storage Investigations] Series 2 bare fuel dissolution tests

    International Nuclear Information System (INIS)

    Wilson, C.N.

    1990-09-01

    The dissolution and radionuclide release behavior of spent fuel in groundwater is being studied by the Nevada Nuclear Waste Storage Investigations (NNWSI) Project. Two bare spent fuel specimens plus the empty cladding hulls were tested in NNWSI J-13 well water in unsealed fused silica vessels under ambient hot cell air conditions (25 degree C) in the currently reported tests. One of the specimens was prepared from a rod irradiated in the H. B. Robinson Unit 2 reactor and the other from a rod irradiated in the Turkey Point Unit 3 reactor. Results indicate that most radionuclides of interest fall into three groups for release modeling. The first group principally includes the actinides (U, Np, Pu, Am, and Cm), all of which reached solubility-limited concentrations that were orders of magnitude below those necessary to meet the NRC 10 CFR 60.113 release limits for any realistic water flux predicted for the Yucca Mountain repository site. The second group is nuclides of soluble elements such as Cs, Tc, and I, for which release rates do not appear to be solubility-limited and may depend on the dissolution rate of fuel. In later test cycles, 137 Cs, 90 Sr, 99 Tc, and 129 I were continuously released at rates between about 5 x 10 -5 and 1 x 10 -4 of inventory per year. The third group is radionuclides that may be transported in the vapor phase, of which 14 C is of primary concern. Detailed test results are presented and discussed. 17 refs., 15 figs., 21 tabs

  18. Dissolution glow curve in LLD

    International Nuclear Information System (INIS)

    Haverkamp, U.; Wiezorek, C.; Poetter, R.

    1990-01-01

    Lyoluminescence dosimetry is based upon light emission during dissolution of previously irradiated dosimetric materials. The lyoluminescence signal is expressed in the dissolution glow curve. These curves begin, depending on the dissolution system, with a high peak followed by an exponentially decreasing intensity. System parameters that influence the graph of the dissolution glow curve, are, for example, injection speed, temperature and pH value of the solution and the design of the dissolution cell. The initial peak does not significantly correlate with the absorbed dose, it is mainly an effect of the injection. The decay of the curve consists of two exponential components: one fast and one slow. The components depend on the absorbed dose and the dosimetric materials used. In particular, the slow component correlates with the absorbed dose. In contrast to the fast component the argument of the exponential function of the slow component is independent of the dosimetric materials investigated: trehalose, glucose and mannitol. The maximum value, following the peak of the curve, and the integral light output are a measure of the absorbed dose. The reason for the different light outputs of various dosimetric materials after irradiation with the same dose is the differing solubility. The character of the dissolution glow curves is the same following irradiation with photons, electrons or neutrons. (author)

  19. Real-time dissolution behavior of furosemide in biorelevant media as determined by UV imaging

    DEFF Research Database (Denmark)

    Gordon, Sarah; Naelapää, Kaisa; Rantanen, Jukka

    2013-01-01

    M bile salt/phospholipid, pH 6.5) together with corresponding blank buffer were employed. Dissolution rates as a function of flow rate (0.2-1.0 mL/min) were determined directly from UV images, and by analysis of collected effluent using UV spectrophotometry. A good agreement in dissolution rates...

  20. Waste dissolution with chemical reaction, diffusion and advection

    International Nuclear Information System (INIS)

    Chambre, P.L.; Kang, C.H.; Lee, W.W.L.; Pigford, T.H.

    1987-06-01

    This paper extends the mass-transfer analysis to include the effect of advective transport in predicting the steady-state dissolution rate, with a chemical-reaction-rate boundary condition at the surface of a waste form of arbitrary shape. This new theory provides an analytic means of predicting the ground-water velocities at which dissolution rate in a geologic environment will be governed entirely to the chemical reaction rate. As an illustration, we consider the steady-state potential flow of ground water in porous rock surrounding a spherical waste solid. 3 refs., 2 figs

  1. High temperature dissolution of chromium substituted nickel ferrite in nitrilotriacetic acid medium

    Energy Technology Data Exchange (ETDEWEB)

    Sathyaseelan, V.S.; Chandramohan, P.; Velmurugan, S., E-mail: svelu@igcar.gov.in

    2016-12-01

    High temperature (HT) dissolution of chromium substituted nickel ferrite was carried out with relevance to the decontamination of nuclear reactors by way of chemical dissolution of contaminated corrosion product oxides present on stainless steel coolant circuit surfaces. Chromium substituted nickel ferrites of composition, NiFe{sub (2−x)}Cr{sub x}O{sub 4} (x ≤ 1), was synthetically prepared and characterized. HT dissolution of these oxides was carried out in nitrilotriacetic acid medium at 160 °C. Dissolution was remarkably increased at 160 °C when compared to at 85 °C in a reducing decontamination formulation. Complete dissolution could be achieved for the oxides with chromium content 0 and 0.2. Increasing the chromium content brought about a marked reduction in the dissolution rate. About 40 fold decrease in rate of dissolution was observed when chromium was increased from 0 to 1. The rate of dissolution was not very significantly reduced in the presence of N{sub 2}H{sub 4}. Dissolution of oxide was found to be stoichiometric. - Highlights: • Dissolution of NiFe{sub (2−x)}Cr{sub x}O{sub 4} was remarkably increased at 160 °C in NTA medium. • The dissolution was significantly decreasing with the increase in Cr content in the oxide. • Dissolution rate is dependent on the lability of metal-oxo bonds. • The rate of dissolution was not significantly reduced in the presence of N{sub 2}H{sub 4.} • NTA at high temperature is effective for decontamination of stainless steel surfaces.

  2. Microporous silica membranes

    DEFF Research Database (Denmark)

    Boffa, Vittorio; Yue, Yuanzheng

    2012-01-01

    Hydrothermal stability is a crucial factor for the application of microporous silica-based membranes in industrial processes. Indeed, it is well established that steam exposure may cause densification and defect formation in microporous silica membranes, which are detrimental to both membrane...... permeability and selectivity. Numerous previous studies show that microporous transition metal doped-silica membranes are hydrothermally more stable than pure silica membranes, but less permeable. Here we present a quantitative study on the impact of type and concentration of transition metal ions...... on the microporous structure, stability and permeability of amorphous silica-based membranes, providing information on how to design chemical compositions and synthetic paths for the fabrication of silica-based membranes with a well accessible and highly stabile microporous structure....

  3. TANK 12 SLUDGE CHARACTERIZATION AND ALUMINUM DISSOLUTION DEMONSTRATION

    International Nuclear Information System (INIS)

    Reboul, S.; Hay, Michael; Zeigler, Kristine; Stone, Michael

    2009-01-01

    A 3-L sludge slurry sample from Tank 12 was characterized and then processed through an aluminum dissolution demonstration. The dominant constituent of the sludge was found to be aluminum in the form of boehmite. The iron content was minor, about one-tenth that of the aluminum. The salt content of the supernatant was relatively high, with a sodium concentration of ∼7 M. Due to these characteristics, the yield stress and plastic viscosity of the unprocessed slurry were relatively high (19 Pa and 27 cP), and the settling rate of the sludge was relatively low (∼20% settling over a two and a half week period). Prior to performing aluminum dissolution, plutonium and gadolinium were added to the slurry to simulate receipt of plutonium waste from H-Canyon. Aluminum dissolution was performed over a 26 day period at a temperature of 65 C. Approximately 60% of the insoluble aluminum dissolved during the demonstration, with the rate of dissolution slowing significantly by the end of the demonstration period. In contrast, approximately 20% of the plutonium and less than 1% of the gadolinium partitioned to the liquid phase. However, about a third of the liquid phase plutonium became solubilized prior to the dissolution period, when the H-Canyon plutonium/gadolinium simulant was added to the Tank 12 slurry. Quantification of iron dissolution was less clear, but appeared to be on the order of 1% based on the majority of data (a minor portion of the data suggested iron dissolution could be as high as 10%). The yield stress of the post-dissolution slurry (2.5 Pa) was an order of magnitude lower than the initial slurry, due most likely to the reduced insoluble solids content caused by aluminum dissolution. In contrast, the plastic viscosity remained unchanged (27 cP). The settling rate of the post-dissolution slurry was higher than the initial slurry, but still relatively low compared to settling of typical high iron content/low salt content sludges. Approximately 40% of the

  4. On-line monitoring of lithium carbonate dissolution

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Yuzhu; Song, Xingfu; Wang, Jin; Luo, Yan; Yu, Jianguo [National Engineering Research Center for Integrated Utilization Salt Lake Resources, East China University of Science and Technology, Shanghai (China)

    2009-11-15

    Dissolution of lithium carbonate (Li{sub 2}CO{sub 3}) in aqueous solution was investigated using three on-line apparatuses: the concentration of Li{sub 2}CO{sub 3} was measured by electrical conductivity equipment; CLD (Chord Length Distribution) was monitored by FBRM (Focused Beam Reflectance Measurement); crystal image was observed by PVM (Particle Video Microscope). Results show dissolution rate goes up with a decrease of particle size, and with an increase in temperature; stirring speed causes little impact on dissolution; ultrasound facilitates dissolution obviously. The CLD evolution and crystal images of Li{sub 2}CO{sub 3}powders in stirred fluid were observed detailedly by FBRM and PVM during dissolution. Experimental data were fitted to Avrami model, through which the activation energy was found to be 34.35 kJ/mol. PBE (Population Balance Equation) and moment transform were introduced to calculate dissolution kinetics, obtaining correlation equations of particle size decreasing rate as a function of temperature and undersaturation. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Phosphorous availability influences the dissolution of apatite by soil fungi

    Science.gov (United States)

    Rosling, A.; Suttle, K. B.; Johansson, E.; van Hees, P. W.; Banfield, J. F.

    2007-12-01

    We conducted mineral dissolution experiments using fungi isolated from a grassland soil in northern California to determine the response of fungi to different levels of phosphorus availability and to identify pathways of apatite dissolution by fungal exudates. Fluorapatite dissolution experiments were performed either with fungi present or under abiotic conditions using cell-free liquid media conditioned by fungal growth at different phosphorus and calcium availabilities. Among biogeochemically active soil fungal isolates apatite dissolution was either active in response to phosphorus limiting growth conditions or passive as a result of mycelial growth. Zygomycete isolates in the order of Mucorales acidify their growth media substrate in the presence of phosphorus, mainly through production of oxalic acid. Cell-free exudates induced fluorapatite dissolution at a rate of 10 -0.9 ± 0.14 and 10 -1.2 ± 0.22 mmol P/m2/s. The Ascomycete isolate, in the family Trichocomaceae, induced fluorapatite dissolution at a rate of 10 - 1.1 ± 0.05 mmol P/m2/s by lowering the pH of the media under phosphorus-limited conditions, without producing significant amounts of low molecular weight organic acids (LMWOAs). Oxalate strongly etches fluorapatite along channels parallel to [001], forming needle like features, while exudates from Trichocomaceae induced surface rounding. We conclude that while LMWOAs are well-studied weathering agents these does not appear to be produced by fungi in response to phosphorus limiting growth conditions.

  6. Mineralogical characteristics of the silica polymorphs in relation to their biological activities

    Energy Technology Data Exchange (ETDEWEB)

    Guthrie, G.D. Jr. [Los Alamos National Lab., NM (United States); Heaney, P.J. [Princeton Univ., NJ (United States). Dept. of Geological and Geophysical Sciences

    1993-10-01

    Numerous aspects of minerals (including the silica polymorphs) can effect their biological activities. These include periodic structures, compositional variations, dissolution characteristics, surface properties, and particle size/shape. In order to understand mineral-induced pathogenesis in a mechanistic way, the links between these properties and biochemical processes must be elucidated. This paper presents some of the basic properties of the silica polymorphs that may relate to pathogenicity and mineralogical strategies for designing biological assays to evaluate these properties.

  7. What Is Crystalline Silica?

    Science.gov (United States)

    ... and ceramic manufacturing and the tool and die, steel and foundry industries. Crystalline silica is used in manufacturing, household abrasives, adhesives, paints, soaps, and glass. Additionally, ...

  8. Aggregation, sedimentation, dissolution and bioavailability of ...

    Science.gov (United States)

    To understand their fate and transport in estuarine systems, the aggregation, sedimentation, and dissolution of CdSe quantum dots (QDs) in seawater were investigated. Hydrodynamic size increased from 40 to 60 nm to >1 mm within 1 h in seawater, and the aggregates were highly polydispersed. Their sedimentation rates in seawater were measured to be 4–10 mm/day. Humic acid (HA), further increased their size and polydispersity, and slowed sedimentation. Light increased their dissolution and release of dissolved Cd. The ZnS shell also slowed release of Cd ions. With sufficient light, HA increased the dissolution of QDs, while with low light, HA alone did not change their dissolution. The benthic zone in estuarine systems is the most probable long-term destination of QDs due to aggregation and sedimentation. The bioavailability of was evaluated using the mysid Americamysis bahia. The 7-day LC50s of particulate and dissolved QDs were 290 and 23 μg (total Cd)/L, respectively. For mysids, the acute toxicity appears to be from Cd ions; however, research on the effects of QDs should be conducted with other organisms where QDs may be lodged in critical tissues such as gills or filtering apparatus and Cd ions may be released and delivered directly to those tissues. Because of their increasing use and value to society, cadmium-based quantum dots (QDs) will inevitably find their way into marine systems. In an effort to understand the fate and transport of CdSe QDs in estuar

  9. Characterization and Comparison of Mesoporous Silica Particles for Optimized Drug Delivery

    Directory of Open Access Journals (Sweden)

    Xinyue Huang

    2014-01-01

    Full Text Available In this study we have investigated the suitability of a number of different mesoporous silica nanoparticle structures for carrying a drug cargo. We have fully characterized the nanoparticles in terms of their physical parameters; size, surface area, internal pore size and structure. These data are all required if we are to make an informed judgement on the suitability of the structure for drug delivery in vivo. With these parameters in mind, we investigated the loading/ unloading profile of a model therapeutic into the pore structure of the nanoparticles. We demonstrate that the release can be controlled by capping the pores on the nanoparticles to achieve temporal control of the unloading. We have also examined the rate and mechanism of the degradation of the nanoparticles over an extended period of time. The eventual dissolution of the nanoparticles after cargo release is a desirable property for a drug delivery system.

  10. Enhanced diffusion of solute metals forming complexes with radiation defects in silica

    International Nuclear Information System (INIS)

    Pivin, J.C.; Garrido, E.; Rizza, G.; Thome, L.

    1998-01-01

    The mixing kinetics of Cu, Ag, W, Pt, and Au single layers embedded in silica when irradiated with heavy ions at temperatures (T) of 110 and 300 K was investigated by means of in situ RBS analyses in alternation with irradiations. The spreading of peaks related to the metallic species is generally anisotropic and obeys either a quadratic or a linear dependence on the ion dose according to the increasing T. The quadratic law is attributed to a control of the diffusion by the coupling of the large impurity atoms M with matrix defects, and a classical regime of radiation enhanced diffusion is observed when this coupling is made easier (higher T or mass of M). Other factors such as internal stresses affect the rates of M dissolution and diffusion. (orig.)

  11. Chemical dissolution of spent fuel and cladding using complexed fluoride species

    International Nuclear Information System (INIS)

    Rance, P.J.W.; Freeman, G.A.; Mishin, V.; Issoupov, V.

    2001-01-01

    The dissolution of LWR fuel cladding using two fluoride ion donors, HBF 4 and K 2 ZrF 6 , in combination with nitric acid has been investigated as a potential reprocessing head-end process suitable for chemical decladding and fuel dissolution in a single process step. Maximum zirconium concentrations in the order of 0,75 to 1 molar have been achieved and dissolution found to continue to low F:Zr ratios albeit at ever decreasing rates. Dissolution rates of un-oxidised zirconium based fuel claddings are fast, whereas oxidised materials exhibit an induction period prior to dissolution. Data is presented relating to the rates of dissolution of cladding and UO 2 fuels under various conditions. (author)

  12. Formation and dissolution of the anodic oxide film on zirconium in alcoholic aqueous solutions

    International Nuclear Information System (INIS)

    Mogoda, A.S.

    1995-01-01

    The dissolution behavior of the anodic oxide film formed in alcoholic aqueous solutions was studied. Results indicated the dissolution mechanism of the duplex oxide film followed a zero-order rate equation. The increase in methanol concentration in the formation medium (phosphoric acid [H 3 PO 4 ]) resulted in formation of an oxide film that incorporated little phosphate ion and that dissolved at a low rate. The dissolution rate of the oxide film decreased with increasing methanol concentration in the dissolution medium. This was attributed to the increase in the viscosity of the medium, which led to a decrease in the diffusion coefficient of the dissolution product of the zirconium oxide film. Dissolution of the anodic oxide film also was investigated as a function of the chain length of alcohols

  13. Dissolution of artemisinin/polymer composite nanoparticles fabricated by evaporative precipitation of nanosuspension.

    Science.gov (United States)

    Kakran, Mitali; Sahoo, Nanda Gopal; Li, Lin; Judeh, Zaher

    2010-04-01

    An evaporative precipitation of nanosuspension (EPN) method was used to fabricate composite particles of a poorly water-soluble antimalarial drug, artemisinin, with a hydrophilic polymer, polyethylene glycol (PEG), with the aim of enhancing the dissolution rate of artemisinin. We investigated the effect of polymer concentration on the physical, morphological and dissolution properties of the EPN-prepared artemisinin/PEG composites. The original artemisinin powder, EPN-prepared artemisinin nanoparticles and artemisinin/PEG composites were characterised by scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), dissolution testing and HPLC. The percentage dissolution efficiency, relative dissolution, time to 75% dissolution and mean dissolution time were calculated. The experimental drug dissolution data were fitted to various mathematical models (Weibull, first-order, Korsemeyer-Peppas, Hixson-Crowell cube root and Higuchi models) in order to analyse the release mechanism. The DSC and XRD studies suggest that the crystallinity of the EPN-prepared artemisinin decreased with increasing polymer concentration. The phase-solubility studies revealed an A(L)-type curve, indicating a linear increase in drug solubility with PEG concentration. The dissolution rate of the EPN-prepared artemisinin and artemisinin/PEG composites increased markedly compared with the original artemisinin powder. EPN can be used to prepare artemisinin nanoparticles and artemisinin/PEG composite particles that have a significantly enhanced dissolution rate. The mechanism of drug release involved diffusion and erosion.

  14. Effect of the Silica Content of Diatoms on Protozoan Grazing

    Directory of Open Access Journals (Sweden)

    Shuwen Zhang

    2017-06-01

    Full Text Available This study examined the effect that silica content in diatom cells has on the behavior of protists. The diatoms Thalassiosira weissflogii and T. pseudonana were cultured in high or low light conditions to achieve low and high silica contents, respectively. These cells were then fed to a heterotrophic dinoflagellate Noctiluca scintillans and a ciliate Euplotes sp. in single and mixed diet experiments. Our results showed that in general, N. scintillans and Euplotes sp. both preferentially ingested the diatoms with a low silica content rather than those with a high silica content. However, Euplotes sp. seemed to be less influenced by the silica content than was N. scintillans. In the latter case, the clearance and ingestion rate of the low silica diatoms were significantly higher, both in the short (6-h and long (1-d duration grazing experiments. Our results also showed that N. scintillans required more time to digest the high silica-containing cells. As the high silica diatoms are harder to digest, this might explain why N. scintillans exhibits a strong preference for the low silica prey. Thus, the presence of high silica diatoms might limit the ability of the dinoflagellate to feed. Our findings suggest that the silica content of diatoms affects their palatability and digestibility and, consequently, the grazing activity and selectivity of protozoan grazers.

  15. Kinetics of dissolution of magnetite in PDCA based formulations

    International Nuclear Information System (INIS)

    Ranganathan, S.; Prince, A.A.M.; Raghavan, P.S.; Gopalan, R.; Srinivasan, M.P.; Narasimhan, S.V.

    1997-01-01

    Magnetite is one of the important corrosion products of pressurized heavy water reactors (PHWRs) where carbon steel is the dominant surface in the primary heat transport system. Designing of formulations capable of dissolving magnetite is important for effective decontamination of such surfaces. The rate of dissolution of synthetically prepared magnetite was studied in low concentrations of PDCA containing acidic formulations. The effect of addition of ascorbic acid, citric acid, Fe 2+ -PDCA complex on the rate was also studied. The effects of pH and the temperature on the dissolution rate were determined. The PDCA as a complexant has some positive factors like low protonation constant and enhanced stability to radiation. (author)

  16. Grafting of polymer onto silica surface in the presence of γ-ray irradiated silica

    International Nuclear Information System (INIS)

    Tsuchida, A.; Yokoyama, R.; Takami, M.; Chen, J.; Ohta, M.; Tsubokawa, N.

    2002-01-01

    Complete text of publication follows. We have reported the graft polymerization of vinyl monomers initiated by surface radicals formed by the decomposition of azo and peroxide groups previously introduced onto the surface. In addition, the grafting of polymers onto carbon black has been reported by the reaction of polymer radicals with the surface. On the other hand, it is well known that the relatively stable radicals are generated on the surface by the γ-ray irradiation. In this paper, the grafting of polystyrene onto silica surface during the thermal polymerization of styrene in the presence of γ-ray irradiated silica, grafting mechanism and thermal stability of grafted polymer will be discussed. The grafting of polymers onto silica surface by irradiation of polymer-adsorbed silica was also investigated. Silica obtained from Mitsubishi Chemical Co., Japan was used after pulverization: the particle size was 0.037-0.088 mm. Irradiation was performed in Cs-137 source at room temperature. The silica was irradiated at 50 Gy with dose rate of 3.463 Gy/min. Into a polymerization tube, styrene and irradiated silica was charged and the polymerization was carried out under argon under stirring. The percentage of polystyrene grafting was determined from weight loss when polystyrene-grafted silica was heated at 600 deg C by a thermal analyzer. Untreated silica did not affect the thermal polymerization of styrene. On the contrary, the thermal polymerization of styrene was remarkably retarded in the presence of the irradiated silica at 60 deg C. Similar tendency was reported during the polymerization of vinyl monomers in the presence of carbon black. In the initial stage of the polymerization in the presence of the irradiated silica below 50 deg C, the polymerization was accelerated. During the polymerization in the presence of irradiated silica, polystyrene was grafted onto the surface: the percentage of grafting was 5-11%. The amount of polystyrene grafted onto silica

  17. Examining the role of shrub expansion and fire in Arctic plant silica cycling

    Science.gov (United States)

    Carey, J.; Fetcher, N.; Parker, T.; Rocha, A. V.; Tang, J.

    2017-12-01

    All terrestrial plants accumulate silica (SiO2) to some degree, although the amount varies by species type, functional group, and environmental conditions. Silica improves overall plant fitness, providing protection from a variety of biotic and abiotic stressors. Plant silica uptake serves to retain silica in terrestrial landscapes, influencing silica export rates from terrestrial to marine systems. These export rates are important because silica is often the limiting nutrient for primary production by phytoplankton in coastal waters. Understanding how terrestrial plant processes influence silica export rates to oceanic systems is of interest on the global scale, but nowhere is this issue more important than in the Arctic, where marine diatoms rely on silica for production in large numbers and terrestrial runoff largely influences marine biogeochemistry. Moreover, the rapid rate of change occurring in the Arctic makes understanding plant silica dynamics timely, although knowledge of plant silica cycling in the region is in its infancy. This work specifically examines how shrub expansion, permafrost thaw, and fire regimes influence plant silica behavior in the Alaskan Arctic. We quantified silica accumulation in above and belowground portions of three main tundra types found in the Arctic (wet sedge, moist acidic, moist non-acidic tundra) and scaled these values to estimate how shrub expansion alters plant silica accumulation rates. Results indicate that shrub expansion via warming will increase silica storage in Arctic land plants due to the higher biomass associated with shrub tundra, whereas conversion of tussock to wet sedge tundra via permafrost thaw would produce the opposite effect in the terrestrial plant BSi pool. We also examined silica behavior in plants exposed to fire, finding that post-fire growth results in elevated plant silica uptake. Such changes in the size of the terrestrial vegetation silica reservoir could have direct consequences for the rates

  18. Oxidation and dissolution of UO{sub 2} in bicarbonate media: Implications for the spent nuclear fuel oxidative dissolution mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Gimenez, J. [Department of Chemical Engineering, Universitat Politecnica de Catalunya, Diagonal 647, 08028 Barcelona (Spain)]. E-mail: francisco.javier.gimenez@upc.edu; Clarens, F. [Department of Chemical Engineering, Universitat Politecnica de Catalunya, Diagonal 647, 08028 Barcelona (Spain); Casas, I. [Department of Chemical Engineering, Universitat Politecnica de Catalunya, Diagonal 647, 08028 Barcelona (Spain); Rovira, M. [CTM Centre Tecnologic, Avda. Bases de Manresa 1. 08240 Manresa (Spain); Pablo, J. de [Department of Chemical Engineering, Universitat Politecnica de Catalunya, Diagonal 647, 08028 Barcelona (Spain); Bruno, J. [Enresa-Enviros Environmental Science and Waste Management Chair, UPC, Jordi Girona 1-3 B2, 08034 Barcelona (Spain)

    2005-10-15

    The objective of this work is to study the UO{sub 2} oxidation by O{sub 2} and dissolution in bicarbonate media and to extrapolate the results obtained to improve the knowledge of the oxidative dissolution of spent nuclear fuel. The results obtained show that in the studied range the oxygen consumption rate is independent on the bicarbonate concentration while the UO{sub 2} dissolution rate does depend on. Besides, at 10{sup -4} mol dm{sup -3} bicarbonate concentration, the oxygen consumption rate is almost two orders of magnitude higher than the UO{sub 2} dissolution rate. These results suggest that at low bicarbonate concentration (<10{sup -2} mol dm{sup -3}) the alteration of the spent nuclear fuel cannot be directly derived from the measured uranium concentrations in solution. On the other hand, the study at low bicarbonate concentrations of the evolution of the UO{sub 2} surface at nanometric scale by means of the SFM technique shows that the difference between oxidation and dissolution rates is not due to the precipitation of a secondary solid phase on UO{sub 2}.

  19. Accelerated dissolution testing for controlled release microspheres using the flow-through dissolution apparatus.

    Science.gov (United States)

    Collier, Jarrod W; Thakare, Mohan; Garner, Solomon T; Israel, Bridg'ette; Ahmed, Hisham; Granade, Saundra; Strong, Deborah L; Price, James C; Capomacchia, A C

    2009-01-01

    Theophylline controlled release capsules (THEO-24 CR) were used as a model system to evaluate accelerated dissolution tests for process and quality control and formulation development of controlled release formulations. Dissolution test acceleration was provided by increasing temperature, pH, flow rate, or adding surfactant. Electron microscope studies on the theophylline microspheres subsequent to each experiment showed that at pH values of 6.6 and 7.6 the microspheres remained intact, but at pH 8.6 they showed deterioration. As temperature was increased from 37-57 degrees C, no change in microsphere integrity was noted. Increased flow rate also showed no detrimental effect on integrity. The effect of increased temperature was determined to be the statistically significant variable.

  20. Active silica sources in the Sele formation and quartz cementation in mudstone-Examples from the Siri Canyon, Danish North Sea

    DEFF Research Database (Denmark)

    Kazerouni, Afsoon Moatari; Friis, Henrik; Svendsen, Johan B.

    shale to document the diagenetic steps which releases silica and to evaluate the possible timing of the silica export from the shale into neighbouring sandstones. The major silica mobilization occur at shallow depths, related to the transformation of biogenic opal and volcanic ash, and at intermediate...... depths, related to the dissolution of opal-CT and zeolite.  At these processes, the shale may have been active silica exported.  Reported sandstone cementation patterns indicate the earlier phase is related to major export of silica, whereas the shale itself was the major consumer during the intermediate...

  1. Dissolution of coccolithophorid calcite by microzooplankton and copepod grazing

    Science.gov (United States)

    Antia, A. N.; Suffrian, K.; Holste, L.; Müller, M. N.; Nejstgaard, J. C.; Simonelli, P.; Carotenuto, Y.; Putzeys, S.

    2008-01-01

    Independent of the ongoing acidification of surface seawater, the majority of the calcium carbonate produced in the pelagial is dissolved by natural processes above the lysocline. We investigate to what extent grazing and passage of coccolithophorids through the guts of copepods and the food vacuoles of microzooplankton contribute to calcite dissolution. In laboratory experiments where the coccolithophorid Emiliania huxleyi was fed to the rotifer Brachionus plicatilis, the heterotrophic flagellate Oxyrrhis marina and the copepod Acartia tonsa, calcite dissolution rates of 45-55%, 37-53% and 5-22% of ingested calcite were found. We ascribe higher loss rates in microzooplankton food vacuoles as compared to copepod guts to the strongly acidic digestion and the individual packaging of algal cells. In further experiments, specific rates of calcification and calcite dissolution were also measured in natural populations during the PeECE III mesocosm study under differing ambient pCO2 concentrations. Microzooplankton grazing accounted for between 27 and 70% of the dynamic calcite stock being lost per day, with no measurable effect of CO2 treatment. These measured calcite dissolution rates indicate that dissolution of calcite in the guts of microzooplankton and copepods can account for the calcite losses calculated for the global ocean using budget and model estimates.

  2. Silica based gel as a potential waste form for high level waste from fuel reprocessing

    International Nuclear Information System (INIS)

    Ford, C.E.; Dempster, T.J.; Melling, P.J.

    1983-10-01

    To assess the feasibility of safe disposal of high-level radioactive waste as synthetic clay, or material that would react with ground water to form clay, experiments have been carried out to determine the hydrothermal crystallisation and leaching behaviour of silica based gels fired at 900 deg C. Crystallisation rates at a pressure of 500 bars and at temperatures below 400 deg C are negligible and this more or less precludes pre-disposal production of synthetic clay on the scale required. Leaching experiments suggest that the leach rates of Cs from gels by distilled water are higher than those of boro-silicate glasses and SYNROC at the lower temperatures that would be preferred for geological storage. However, amounts of bulk dissolution of gels may be lower than those of boro-silicate glasses. The initial leaching behaviour of gels might be considerably improved by hot compaction at 900 to 1000 deg C. Consideration of likely waste form dissolution behaviour in a repository environment suggests that gels of appropriate composition might perform as well as, or better than, boro-silicate glasses. A novel hypothetical plant is described that could produce the gel waste form on the scale required on a more or less continuous basis. (author)

  3. Stimulated resonant scattering at stressed fused silica surface

    International Nuclear Information System (INIS)

    Bouchut, Philippe; Reymermier, Maryse

    2015-01-01

    The radiative emission in CO 2 laser heated stressed fused silica is radically modified when gold microspheres are on the surface. At high heating rates, the emission dynamics changes from thermoluminescence to stimulated resonant scattering with an emission rate that is increased tenfold and the near infrared (NIR) spectrum is red-shifted. We show that the dynamic tensile stress that rises in heated silica is coupled with a fluctuating electromagnetic field that enables electromagnetic friction between moving OH emitters from silica bulk and NIR resonant scatterers at the silica surface. (paper)

  4. Influence of Sodium Lauryl Sulfate and Tween 80 on Carbamazepine–Nicotinamide Cocrystal Solubility and Dissolution Behaviour

    OpenAIRE

    Ke Wang; Ning Qiao; Mingzhong Li

    2013-01-01

    The influence of the surfactants of sodium lauryl sulfate (SLS) and Tween 80 on carbamazepine–nicotinamide (CBZ–NIC) cocrystal solubility and dissolution behaviour has been studied in this work. The solubility of the CBZ–NIC cocrystal was determined by measuring the eutectic concentrations of the drug and the coformer. Evolution of the intrinsic dissolution rate (IDR) of the CBZ–NIC cocrystal was monitored by the UV imaging dissolution system during dissolution. Experimental results indicated...

  5. Crystalline Silica Primer

    Science.gov (United States)

    ,

    1992-01-01

    Crystalline silica is the scientific name for a group of minerals composed of silicon and oxygen. The term crystalline refers to the fact that the oxygen and silicon atoms are arranged in a threedimensional repeating pattern. This group of minerals has shaped human history since the beginning of civilization. From the sand used for making glass to the piezoelectric quartz crystals used in advanced communication systems, crystalline silica has been a part of our technological development. Crystalline silica's pervasiveness in our technology is matched only by its abundance in nature. It's found in samples from every geologic era and from every location around the globe. Scientists have known for decades that prolonged and excessive exposure to crystalline silica dust in mining environments can cause silicosis, a noncancerous lung disease. During the 1980's, studies were conducted that suggested that crystalline silica also was a carcinogen. As a result of these findings, crystalline silica has been regulated under the Occupational Safety and Health Administration's (OSHA) Hazard Communication Standard (HCS). Under HCS, OSHAregulated businesses that use materials containing 0.1% or more crystalline silica must follow Federal guidelines concerning hazard communication and worker training. Although the HCS does not require that samples be analyzed for crystalline silica, mineral suppliers or OSHAregulated

  6. Dissolution Threats and Legislative Bargaining

    DEFF Research Database (Denmark)

    Becher, Michael; Christiansen, Flemming Juul

    2015-01-01

    Chief executives in many parliamentary democracies have the power to dissolve the legislature. Despite a well-developed literature on the endogenous timing of parliamentary elections, political scientists know remarkably little about the strategic use of dissolution power to influence policymaking....... To address this gap, we propose and empirically evaluate a theoretical model of legislative bargaining in the shadow of executive dissolution power. The model implies that the chief executive's public support and legislative strength, as well as the time until the next constitutionally mandated election...

  7. Actor bonds after relationship dissolution

    DEFF Research Database (Denmark)

    Skaates, Maria Anne

    2000-01-01

    Most of the presented papers at the 1st NoRD Workshop can be classified as belonging to the business marketing approach to relationship dissolution. Two papers were conceptual, and the remaining six were empirical studies. The first conceptual study by Skaates (2000) focuses on the nature...... of the actor bonds that remain after a business relationship has ended. The study suggests that an interdisciplinary approach would provide a richer understanding of the phenomenon; this could be achieved by using e.g. Bourdieu's sociological concepts in dissolution research....

  8. The velocity dependent dissolution of spent nuclear fuel in a geologic repository

    International Nuclear Information System (INIS)

    Nutt, W.M.

    1990-02-01

    A model describing the dissolution of fission products and transuranic isotopes from spent nuclear fuel into flowing ground water has been developed. This model is divided into two parts. The first part of the model calculates the temperature within a consolidated spent fuel waste form at a given time and ground water velocity. This model was used to investigate whether water flowing at rates representative of a geological repository located at Yucca Mountain, Nevada, will cool a wasteform consisting of consolidated spent nuclear fuel pins. Time and velocity dependent temperature profiles were generated. These profiles were input into the second model, which calculates the dissolution rate of waste isotopes from a spent fuel pin. Two dissolution limiting processes were modeled; the processes are dissolution limited by the solubility limit of an isotopes in the ground water, and dissolution limited by the diffusion of waste isotopes from the interior of a spent fuel pin to the surface where dissolution can occur

  9. Petrography, mineralogy, and chemistry of calcite-silica deposits at Exile Hill, Nevada, compared with local spring deposits

    International Nuclear Information System (INIS)

    Vaniman, D.T.; Chipera, S.J.; Bish, D.L.

    1995-12-01

    Chemical, mineralogic, and petrographic analyses of siliceous calcretes from Exile Hill east of Yucca Mountain, Nevada, indicate that pedogenic processes alone account for the formation of the calcretes. These calcretes have been interpreted by some observers as evidence of seismically triggered eruptions of deep water. Such an origin could have important consequences if Yucca Mountain is developed as an unsaturated site for the disposal of high-level nuclear waste. At odds with this hypothesis are the absence of features that should be present at fault-fed springs (e.g., fissure-ridge mounds with microterraces) and the preservation within root casts of delicate pedogenic microfossils, such as calcified filaments and needle-fiber calcites. Mineral-chemical evidence of pedogenic origin is found in heavy-mineral concentrations, reflected in Fe and Sc enrichments. These concentrations, which occur in the most massive of the vein calcretes, require derivation of detritus from a mixture of weathered and eolian materials that occur in the overlying B soil horizons, as opposed to direct incorporation of adjacent unweathered bedrock. Carbonate and silica abundances and accumulation rates are well within the scope of pedogenic processes. Calcium is derived from rainwater or eolian sources, whereas silica is derived in part by dissolution of local volcanic glasses or from dissolution of unstable silica minerals that are abundant in the local tuffs. In contrast with local deposits that are of spring or seep origin, the siliceous calcretes at Yucca Mountain are pedogenic in origin as well as evolution and provide no evidence in support of conjectured spring activity

  10. Dissolution of intact UO2 pellet in batch and rotary dissolver conditions

    International Nuclear Information System (INIS)

    Jayendra Kumar Gelatar; Bijendra Kumar; Sampath, M.; Shekhar Kumar; Kamachi Mudali, U.; Natarajan, R.

    2015-01-01

    Comparative dissolution of intact un-irradiated UO 2 pellet of PHWR fuel dimensions was performed in batch and dynamic rotary dissolver conditions in aqueous nitric acid solutions at elevated temperatures. The extent of dissolution was estimated by determining the uranium concentration of the resulting aqueous solution. It was observed that rate of dissolution was much faster in dynamic conditions as compared to static batch conditions. (author)

  11. Antiproliferative effect of Antrodia camphorata polysaccharides encapsulated in chitosan-silica nanoparticles strongly depends on the metabolic activity type of the cell line

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Zwe-Ling, E-mail: kongzl@mail.ntou.edu.tw; Chang, Jenq-Sheng; Chang, Ke Liang B. [National Taiwan Ocean University, Department of Food Science (China)

    2013-09-15

    Chitosan molecules interact with silica and encapsulate the Antrodia camphorata extract (ACE) polysaccharides to form composite nanoparticles. The nanoparticle suspensions of ACE polysaccharides encapsulated in silica-chitosan and silica nanoparticles approach an average particle size of 210 and 294 nm in solution, respectively. The encapsulation efficiencies of ACE polysaccharides are 66 and 63.5 %, respectively. Scanning electron micrographs confirm the formation of near-spherical nanoparticles. ACE polysaccharides solution had better antioxidative capability than ACE polysaccharides encapsulated in silica or silica-chitosan nanoparticles suspensions. The antioxidant capacity of nanoparticles increases with increasing dissolution time. The antitumor effects of ACE polysaccharides, ACE polysaccharides encapsulated in silica, or silica-chitosan nanoparticles increased with increasing concentration of nanoparticles. This is the first report demonstrating the potential of ACE polysaccharides encapsulated in chitosan-silica nanoparticles for cancer chemoprevention. Furthermore, this study suggests that antiproliferative effect of nanoparticle-encapsulated bioactive could significantly depend on the metabolic activity type of the cell line.

  12. Antiproliferative effect of Antrodia camphorata polysaccharides encapsulated in chitosan-silica nanoparticles strongly depends on the metabolic activity type of the cell line

    Science.gov (United States)

    Kong, Zwe-Ling; Chang, Jenq-Sheng; Chang, Ke Liang B.

    2013-09-01

    Chitosan molecules interact with silica and encapsulate the Antrodia camphorata extract (ACE) polysaccharides to form composite nanoparticles. The nanoparticle suspensions of ACE polysaccharides encapsulated in silica-chitosan and silica nanoparticles approach an average particle size of 210 and 294 nm in solution, respectively. The encapsulation efficiencies of ACE polysaccharides are 66 and 63.5 %, respectively. Scanning electron micrographs confirm the formation of near-spherical nanoparticles. ACE polysaccharides solution had better antioxidative capability than ACE polysaccharides encapsulated in silica or silica-chitosan nanoparticles suspensions. The antioxidant capacity of nanoparticles increases with increasing dissolution time. The antitumor effects of ACE polysaccharides, ACE polysaccharides encapsulated in silica, or silica-chitosan nanoparticles increased with increasing concentration of nanoparticles. This is the first report demonstrating the potential of ACE polysaccharides encapsulated in chitosan-silica nanoparticles for cancer chemoprevention. Furthermore, this study suggests that antiproliferative effect of nanoparticle-encapsulated bioactive could significantly depend on the metabolic activity type of the cell line.

  13. Glass Dissolution Parameters: Update for Entsorgungsnachweis

    International Nuclear Information System (INIS)

    Curti, E.

    2003-11-01

    This document provides updated long-term corrosion rates for borosilicate glasses used in Switzerland as a matrix for high-level radioactive waste. The new rates are based on long-term leaching experiments conducted at PSI and are corroborated by recent investigations. The asymptotic rates have been determined through weighted linear regressions of the normalised mass losses, directly calculated from B and Li concentrations in the leaching solutions. Special attention was given to the determination of the analytical uncertainty of the mass losses. The sensitivity of the corrosion rates to analytical uncertainties and to other criteria (e.g. the choice of data points for the regressions) was also studied. A major finding was that the uncertainty of the corrosion rate mainly depends on the uncertainty of the specific glass surface area. The reference rates proposed for safety assessment calculations are 1.5 mg m -2 d -1 for BNFL glasses and 0.2 mg m -2 d -1 for Cogema glasses. The relevance of the proposed corrosion rates for repository conditions is shown based on the analysis of processes and parameters currently known to affect the long-term kinetics of silicate glasses. Specifically, recent studies indicate that potentially detrimental effects, notably the removal of silica from solution through adsorption on clay minerals, are transitory and will not affect the long-term corrosion rate of the Swiss reference glasses. Iron corrosion products are also known to bind silica, but present data are not sufficient to quantify their influence on the long-term rate. (author)

  14. Marital dissolution: an economic analysis.

    Science.gov (United States)

    Hunter, K A

    1984-01-01

    A longitudinal analysis of factors affecting marital dissolution in the United States is presented using data from the Coleman-Rossi Retrospective Life History. Factors considered include labor force participation of both spouses, wage growth, size of family unit, age at marriage, and educational status. The study is based on the economic analysis approach developed by Gary S. Becker and others.

  15. Evaluation of a dynamic dissolution/permeation model

    DEFF Research Database (Denmark)

    Sironi, Daniel; Christensen, Mette; Rosenberg, Jörg

    2017-01-01

    -steady state). To this end, a model case was construed: compacts of pure crystalline hydrocortisone methanolate (HC·MeOH) of slow release rates were prepared, and their dissolution and permeation determined simultaneously in a side-by-side setup, separated by a biomimetic barrier (Permeapad...... dissolution rate and flux influenced each other. Interestingly, for all the dynamic scenarios, the incremental flux values obtained correlated nicely with the corresponding actual donor concentrations. Furthermore, donor depletion was tested using a HC solution. The dynamic interplay between decrease in donor...

  16. Glass composition and solution speciation effects on stage III dissolution

    Energy Technology Data Exchange (ETDEWEB)

    Trivelpiece, Cory L. [Pennsylvania State Univ., University Park, PA (United States); Rice, Jarret A. [Pennsylvania State Univ., University Park, PA (United States); Pantano, Carlo G. [Pennsylvania State Univ., University Park, PA (United States)

    2017-10-03

    To understand and mitigate the onset of Stage III corrosion of multicomponent oxides waste glasses. Stage III refers to a resumption of the high initial rate of glass dissolution in some glass samples that have otherwise exhibited dissolution at the much lower residual rate for a long time (Stage II). Although the onset of Stage III is known to occur concurrently with the precipitation of particular alteration products, the root cause of the transition is still unknown. Certain glass compositions (notably AFCI) and high pH environmental conditions are also associated with this observed transition.

  17. Glass composition and solution speciation effects on stage III dissolution

    International Nuclear Information System (INIS)

    Trivelpiece, Cory L.; Rice, Jarret A.; Pantano, Carlo G.

    2017-01-01

    To understand and mitigate the onset of Stage III corrosion of multicomponent oxides waste glasses. Stage III refers to a resumption of the high initial rate of glass dissolution in some glass samples that have otherwise exhibited dissolution at the much lower residual rate for a long time (Stage II). Although the onset of Stage III is known to occur concurrently with the precipitation of particular alteration products, the root cause of the transition is still unknown. Certain glass compositions (notably AFCI) and high pH environmental conditions are also associated with this observed transition.

  18. Study of dissolution factors of U, Th and Ta

    International Nuclear Information System (INIS)

    Santos, Maristela; Medeiros, Geiza; Zouain, Felipe; Cunha, Kenya Dias da; Pitassi, Gabriel; Lima, Cintia; Leite, Carlos Vieira Barros; Nascimento, Jose Eduardo; Dalia, Kely Cristina

    2009-01-01

    Air pollution can be a problem in industrial processes, but monitoring and controlling the aerosols in the work place is not enough to estimate the occupational risk due to dust particle inhalation. The solubility in lung fluid is considered to estimate this risk. The aim of this study is to determine in vitro specific dissolution parameters for thorium (Th), uranium (U) and tantalum (Ta) associated to crystal lattice of a niobium mineral (pyrochlore). Th, U and Ta dissolution factors in vitro were obtained using the Gamble solution (Simulant Lung Fluid, SLF), PIXE (Particle Induced X ray Emission) and alpha spectrometry as analytical techniques. Ta, Th and U are present in the pyrochlore crystal lattice as oxide; however they have shown different dissolution parameters. The rapid dissolution fraction (fr), rapid dissolution rate (λr); slow dissolution rate (fs) and slow dissolution fraction ((λs) measured for tantalum oxide were equal to 0.1, 0.45 d -1 and 0.00007 d -1 , respectively; for uranium oxide fr was equal to 0.05, (λr equal to 1.1 d -1 ; (λs equal to 0.000068 d -1 ; for thorium oxide fr was 0.025, (λr was 1.5 d -1 and (λs: 0.000065 d -1 . These results show that chemical behavior of these 3 compounds in the SLF could not be represented by the same parameter. The ratio of uranium concentration in urine and feces samples from workers exposed to pyrochlore dust particle was determined. These values agree with the theoretical values of estimated uranium concentration using specific parameters for uranium oxide present in pyrochlore. (author)

  19. Controlled evaluation of silver nanoparticle dissolution using atomic force microscopy.

    Science.gov (United States)

    Kent, Ronald D; Vikesland, Peter J

    2012-07-03

    Incorporation of silver nanoparticles (AgNPs) into an increasing number of consumer products has led to concern over the potential ecological impacts of their unintended release to the environment. Dissolution is an important environmental transformation that affects the form and concentration of AgNPs in natural waters; however, studies on AgNP dissolution kinetics are complicated by nanoparticle aggregation. Herein, nanosphere lithography (NSL) was used to fabricate uniform arrays of AgNPs immobilized on glass substrates. Nanoparticle immobilization enabled controlled evaluation of AgNP dissolution in an air-saturated phosphate buffer (pH 7.0, 25 °C) under variable NaCl concentrations in the absence of aggregation. Atomic force microscopy (AFM) was used to monitor changes in particle morphology and dissolution. Over the first day of exposure to ≥10 mM NaCl, the in-plane AgNP shape changed from triangular to circular, the sidewalls steepened, the in-plane radius decreased by 5-11 nm, and the height increased by 6-12 nm. Subsequently, particle height and in-plane radius decreased at a constant rate over a 2-week period. Dissolution rates varied linearly from 0.4 to 2.2 nm/d over the 10-550 mM NaCl concentration range tested. NaCl-catalyzed dissolution of AgNPs may play an important role in AgNP fate in saline waters and biological media. This study demonstrates the utility of NSL and AFM for the direct investigation of unaggregated AgNP dissolution.

  20. Interactions between a poorly soluble cationic drug and sodium dodecyl sulfate in dissolution medium and their impact on in vitro dissolution behavior.

    Science.gov (United States)

    Huang, Zongyun; Parikh, Shuchi; Fish, William P

    2018-01-15

    In the pharmaceutical industry, in vitro dissolution testing ofsolid oral dosage forms is a very important tool for drug development and quality control. However, ion-pairing interaction between the ionic drugand surfactants in dissolution medium often occurs, resulting in inconsistent and incomplete drug release. The aim of this study is toevaluate the effects ofsodium dodecyl sulfate (SDS) mediated medium onthe dissolution behaviors of a poorly soluble cationic drug (Drug B). The study was carried out by measuring solubility of Drug B substance and dissolution rate of Drug B product in media containing SDS.Desolubilization of Drug B substance was observed at pH 4.5 in the presence of SDS at concentrations below critical micelle concentration (CMC) which is attributed to the formation of an insoluble di-dodecyl sulfate salt between SDS and Drug B. This ion-pairing effect is less significant with increasing medium pH where Drug B is less ionized and CMC of SDS is lower. In medium at pH 4.5, dissolution of Drug B product was found incomplete with SDS concentration below CMC due to the desolubilization of Drug B substance. In media with SDS level above CMC, the dissolution rate is rather slower with higher inter-vessel variations compared to that obtained in pH 4.5 medium without SDS. The dissolution results demonstrate that the presence of SDS in medium generates unexpected irregular dissolution profiles for Drug B which are attributed to incompatible dissolution medium for this particular drug. Therefore, non-ionic surfactant was selected for Drug B product dissolution method and ion-pairing effect in SDS mediated medium should be evaluated when developing a dissolution method for any poorly soluble cationic drugs. Copyright © 2017 Elsevier B.V. All rights reserved.

  1. Oxygen configurations in silica

    International Nuclear Information System (INIS)

    Chelikowsky, James R.; Chadi, D. J.; Binggeli, N.

    2000-01-01

    We propose a transition state for oxygen in silica. This state is produced by the insertion of an oxygen molecule into the Si-O-Si bond, i.e., it consists of producing a Si-O-O-O-Si bond. This state allows molecular oxygen diffusion in silica without breaking the molecular O 2 bond and it is energetically more stable than a peroxy configuration. This configuration may allow for exchange of molecular oxygen with the oxygen in the silica framework. (c) 2000 The American Physical Society

  2. Evidence of intensified biogenic silica recycling in the Black Sea after 1970

    DEFF Research Database (Denmark)

    Mousing, Erik Askov; Adjou, Mohamed; Ellegaard, Marianne

    2015-01-01

    140 years and show that siliceous protists became significantly more dissolved after the late 1960s indicating a reduction of the silicate pool preserved in the deep sea sediment. We hypothesize that the decline in the dissolution state is caused by increased recycling of biogenic silica in the water...

  3. Impact of Micro Silica Surface Hydroxyl Groups on the Properties of Calcium Silicate Products

    DEFF Research Database (Denmark)

    Haastrup, Sonja; Jørgensen, Bianca; Yu, Donghong

    2017-01-01

    Porous calcium silicates are widely used in insulating systems for high temperature applications. In the production of porous calcium silicates, quicklime and micro silica have been utilized as key raw materials. In the reaction between SiO2 and CaO, the dissolution of SiO2 has been proven...

  4. Experimental hydrothermal dissolution of forsterite, enstatite, diopside, and labradorite

    Energy Technology Data Exchange (ETDEWEB)

    Ponader, H.B.

    1989-01-01

    Natural hydrothermal water/rock interactions such as those which occur during mineral dissolution and serpentinization were experimentally duplicated using a flow-through apparatus. Labradorite, forsterite, enstatite, diopside, and lherzolite powders were reached with flowing aqueous fluids ({approximately} 10 ml/day) at 300 C and 300 bars for up to 58 days in order to quantify mineral stabilities and dissolution rates, and to characterize dissolution textures and mechanisms. The principal methods for characterization of the solids included surface sensitive spectroscopies (SAM and SPS), SEM, and XRD; reacted fluids were analyzed for major element chemistry and pH. Chapters 1 and 2 investigate labradorite dissolution by deionized water. The labradorite powder dissolved extensively while boehmite and halloysite precipitated. The SAM results show that, in general, the reacted surfaces are enriched in Al and depleted in Si, Na, and Ca. Chapter 3 describes the experiments that reacted deionized water with diopside, enstatite, forsterite, and lherzolite, from which lizardite {plus minus} chrysotile {plus minus} Fe-oxides precipitated. The reacted diopside and enstatite surfaces appeared highly corroded; their crystal structures, in part, control the mechanisms by which they dissolve. The stabilities of the minerals decrease in the order: lherzolite > diopside > enstatite > forsterite. At near neutral pH, the degree to which total surface areas influence dissolution rates appears greater that the effect of mineral composition and interaction of the primary minerals within the lherzolite.

  5. Kinetics of dissolution of calcium phosphate (Ca-P bioceramics

    Directory of Open Access Journals (Sweden)

    Lukas Brazda

    2008-06-01

    Full Text Available Hydroxyapatite (HAp and β-tricalcium phosphate (β-TCP are widely used bioceramics for surgical or dental applications. This paper is dealing with dissolution kinetics of synthetically prepared β-TCP and four types of HAp granules. Two groups of HAp, treated at different temperatures, each of them with two different granule sizes, were tested. Three corrosive solutions with different pH and simulated body fluid (SBF were used for immersing of the samples. Changes in concentrations of calcium and phosphate ions, pH level and weight changes of the samples were observed. It was found that presence of TRIS buffer enhanced dissolution rate of the β-TCP approximately two times. When exposed to SBF solution, calcium phosphate (most probably hydroxyapatite precipitation predominates over β-TCP dissolution. Results from HAp samples dissolution showed some unexpected findings. Neither heat treatment nor HAp particle size made any major differences in dissolution rate of the same mass of each HAp sample.

  6. Optimization of dissolution process parameters for uranium ore concentrate powders

    Energy Technology Data Exchange (ETDEWEB)

    Misra, M.; Reddy, D.M.; Reddy, A.L.V.; Tiwari, S.K.; Venkataswamy, J.; Setty, D.S.; Sheela, S.; Saibaba, N. [Nuclear Fuel Complex, Hyderabad (India)

    2013-07-01

    Nuclear fuel complex processes Uranium Ore Concentrate (UOC) for producing uranium dioxide powder required for the fabrication of fuel assemblies for Pressurized Heavy Water Reactor (PHWR)s in India. UOC is dissolved in nitric acid and further purified by solvent extraction process for producing nuclear grade UO{sub 2} powder. Dissolution of UOC in nitric acid involves complex nitric oxide based reactions, since it is in the form of Uranium octa oxide (U{sub 3}O{sub 8}) or Uranium Dioxide (UO{sub 2}). The process kinetics of UOC dissolution is largely influenced by parameters like concentration and flow rate of nitric acid, temperature and air flow rate and found to have effect on recovery of nitric oxide as nitric acid. The plant scale dissolution of 2 MT batch in a single reactor is studied and observed excellent recovery of oxides of nitrogen (NO{sub x}) as nitric acid. The dissolution process is automated by PLC based Supervisory Control and Data Acquisition (SCADA) system for accurate control of process parameters and successfully dissolved around 200 Metric Tons of UOC. The paper covers complex chemistry involved in UOC dissolution process and also SCADA system. The solid and liquid reactions were studied along with multiple stoichiometry of nitrous oxide generated. (author)

  7. Computational fluid dynamics (CFD) studies of a miniaturized dissolution system.

    Science.gov (United States)

    Frenning, G; Ahnfelt, E; Sjögren, E; Lennernäs, H

    2017-04-15

    Dissolution testing is an important tool that has applications ranging from fundamental studies of drug-release mechanisms to quality control of the final product. The rate of release of the drug from the delivery system is known to be affected by hydrodynamics. In this study we used computational fluid dynamics to simulate and investigate the hydrodynamics in a novel miniaturized dissolution method for parenteral formulations. The dissolution method is based on a rotating disc system and uses a rotating sample reservoir which is separated from the remaining dissolution medium by a nylon screen. Sample reservoirs of two sizes were investigated (SR6 and SR8) and the hydrodynamic studies were performed at rotation rates of 100, 200 and 400rpm. The overall fluid flow was similar for all investigated cases, with a lateral upward spiraling motion and central downward motion in the form of a vortex to and through the screen. The simulations indicated that the exchange of dissolution medium between the sample reservoir and the remaining release medium was rapid for typical screens, for which almost complete mixing would be expected to occur within less than one minute at 400rpm. The local hydrodynamic conditions in the sample reservoirs depended on their size; SR8 appeared to be relatively more affected than SR6 by the resistance to liquid flow resulting from the screen. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Dissolution Enhancement of Rosuvastatin Calcium by Liquisolid Compact Technique

    Directory of Open Access Journals (Sweden)

    V. J. Kapure

    2013-01-01

    Full Text Available In present investigation liquisolid compact technique is investigated as a tool for enhanced dissolution of poorly water-soluble drug Rosuvastatin calcium (RVT. The model drug RVT, a HMG-Co A reductase inhibitor was formulated in form of directly compressed tablets and liquisolid compacts; and studied for in-vitro release characteristics at different dissolution conditions. In this technique, liquid medications of water insoluble drugs in non-volatile liquid vehicles can be converted into acceptably flowing and compressible powders. Formulated systems were assessed for precompression parameters like flow properties of liquisolid system, Fourior transform infra red spectra (FTIR analysis, X-ray powder diffraction (XRPD, differential scanning calorimetry (DSC, and post compression parameters like content uniformity, weight variation, hardness and friability, disintegration test, wetting time, in vitro dissolution studies, effect of dissolution volume on drug release rate, and estimation of fraction of molecularly dispersed drug in liquid medication. As liquisolid compacts demonstrated significantly higher drug release rates, we lead to conclusion that it could be a promising strategy in improving the dissolution of poor water soluble drugs and formulating immediate release solid dosage forms.

  9. Thoria/thoria-urania dissolution studies for reprocessing application

    International Nuclear Information System (INIS)

    Srinivas, C.; Yalmali, Vrunda; Pente, A.S.; Wattal, P.K.; Misra, S.D.

    2012-06-01

    Thoria dissolution is normally conducted in 13M nitric acid in the presence of 0.03M sodium fluoride or HF as catalyst and 0.1M aluminium nitrate for mitigation of fluoride related corrosion of SS 304L dissolver vessel. Addition of aluminium nitrate in such high concentrations has undesirable consequences in the downstream high level radioactive liquid waste vitrification process at 900-1000 degC. Besides, because of the highly corrosive nature of fluoride ion, lowering its concentration in the dissolution reaction is advantageous in reducing the corrosion of dissolver and other downstream equipments. The present work was done with twin objectives of avoiding aluminium nitrate addition and lowering the fluoride ion concentration during dissolution reaction. High temperature sintered thoria and thoria-4 weight% urania dissolution reactions were investigated in the absence of aluminium nitrate and at reduced fluoride concentrations. Corrosion rates of SS 304L zircaloy in various dissolvent mixtures were studied by weight loss method. These studies clearly showed that aluminium nitrate addition for control of fluoride related corrosion of SS 304L can be avoided when zircaloy-clad thoria/thoria-urania pellets are dissolved. Dissolved zirconium ion was observed to be as effective as aluminium ion. Moreover, dissolution could be achieved with reasonable reaction rates at reduced fluoride concentration of 0.005-0.01M instead of 0.03M by changing the method of addition of the fluoride catalyst. (author)

  10. Photooxidation of ethylene over Cu-modified and unmodified silica

    OpenAIRE

    Ichihashi, Yuichi; Matsumura, Yasuyuki

    2003-01-01

    Silica catalyzes photooxidation of ethylene to carbon dioxide and modification of copper on silica results in the lower reaction rate and partial production of ethylene oxide. The reaction does not proceed by the light irradiation through a color filter (λ>280 nm). ESR measurement indicates that radical oxygen species assignable T-shape Si − O3− can be produced on silica by UV irradiation at 77 K. The same species are also found on silica modified with copper by UV irradiation whi...

  11. Dissolution test for glibenclamide tablets

    Directory of Open Access Journals (Sweden)

    Elisabeth Aparecida dos Santos Gianotto

    2007-10-01

    Full Text Available The aim of this work is to develop and validate a dissolution test for glibenclamide tablets. Optimal conditions to carry out the dissolution test are 500 mL of phosphate buffer at pH 8.0, paddles at 75 rpm stirring speed, time test set to 60 min and using equipment with six vessels. The derivative UV spectrophotometric method for determination of glibenclamide released was developed, validated and compared with the HPLC method. The UVDS method presents linearity (r² = 0.9999 in the concentration range of 5-14 µg/mL. Precision and recoveries were 0.42% and 100.25%, respectively. The method was applied to three products commercially available on the Brazilian market.

  12. Melt flow and mechanical properties of silica/perfluoropolymer nanocomposites Fabricated by direct melt-compounding without surface modification on nano-silica.

    Science.gov (United States)

    Tanahashi, Mitsuru; Watanabe, Yusuke; Lee, Jeong-Chang; Takeda, Kunihiko; Fujisawa, Toshiharu

    2009-01-01

    The authors have previously developed a novel method for the fabrication of silica/perfluoropolymer nanocomposites, wherein nano-sized silica particles without surface modification were dispersed uniformly through breakdown of loosely packed agglomerates of silica nanoparticles with low fracture strength in a polymer melt during direct melt-compounding. The method consists of two stages; the first stage involves preparation of the loose silica agglomerate, and the second stage involves melt-compounding of a completely hydrophobic perfluoropolymer, PFA (poly(tetrafluoroethylene-co-perfluoropropylvinylether)), with the loose silica agglomerates. By using this simple method without any lipophilic treatment of the silica surfaces, silica nanoparticles with a primary diameter of 190 nm could be dispersed uniformly into the PFA matrix. The main purpose of the present study is to evaluate the melt flow and tensile properties of silica/PFA nanocomposites fabricated by the above method. In order to elucidate the effects of the size of the dispersed silica in the PFA matrix on the properties of the composites, silica/PFA composite samples exhibiting the dispersion of larger-sized silica particle-clusters were fabricated as negative controls of the silica dispersion state. The results obtained under the present experimental conditions showed that the size of the dispersed silica in the PFA matrix exerts a strong influence on the ultimate tensile properties, such as tensile strength and elongation at break, and the melt flow rate (MFR) of the composite materials. The MFR of the silica/PFA nanocomposite became higher than that of the pure PFA without silica addition, although the MFR of the PFA composites containing larger silica particle-clusters became much lower than that of the pure PFA. Furthermore, uniform dispersion of isolated silica nanoparticles was found to improve not only the Young's modulus but also the ultimate tensile properties of the composite.

  13. Study of the pluronic-silica interaction in synthesis of mesoporous silica under mild acidic conditions.

    Science.gov (United States)

    Sundblom, Andreas; Palmqvist, Anders E C; Holmberg, Krister

    2010-02-02

    The interaction between silica and poly(ethylene oxide) (PEO) in water may appear trivial and it is generally stated that hydrogen bonding is responsible for the attraction. However, a literature search shows that there is not a consensus with respect to the mechanism behind the attractive interaction. Several papers claim that only hydrogen bonding is not sufficient to explain the binding. The silica-PEO interaction is interesting from an academic perspective and it is also exploited in the preparation of mesoporous silica, a material of considerable current interest. This study concerns the very early stage of synthesis of mesoporous silica under mild acidic conditions, pH 2-5, and the aim is to shed light on the interaction between silica and the PEO-containing structure directing agent. The synthesis comprises two steps. An organic silica source, tetraethylorthosilicate (TEOS), is first hydrolyzed and Pluronic P123, a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer, is subsequently added at different time periods following the hydrolysis of TEOS. It is shown that the interaction between the silica and the Pluronic is dependent both on the temperature and on the time between onset of TEOS hydrolysis and addition of the copolymer. The results show that the interaction is mainly driven by entropy. The effect of the synthesis temperature and of the time between hydrolysis and addition of the copolymer on the final material is also studied. The material with the highest degree of mesoorder was obtained when the reaction was performed at 20 degrees C and the copolymer was added 40 h after the start of TEOS hydrolysis. It is claimed that the reason for the good ordering of the silica is that whereas particle formation under these conditions is fast, the rate of silica condensation is relatively low.

  14. Interlaboratory validation of small-scale solubility and dissolution measurements of poorly water-soluble drugs

    DEFF Research Database (Denmark)

    Andersson, Sara B. E.; Alvebratt, Caroline; Bevernage, Jan

    2016-01-01

    The purpose of this study was to investigate the interlaboratory variability in determination of apparent solubility (Sapp) and intrinsic dissolution rate (IDR) using a miniaturized dissolution instrument. Three poorly water-soluble compounds were selected as reference compounds and measured at m...

  15. Working Late: Do Workplace Sex Ratios Affect Partnership Formation and Dissolution?

    Science.gov (United States)

    Svarer, Michael

    2007-01-01

    In this paper, I analyze the association between workplace sex ratios and partnership formation and dissolution. I find that the risk of dissolution increases with the fraction of coworkers of the opposite sex at both the female and male workplace. On the other hand, workplace sex ratios are not important for the overall transition rate from…

  16. Monitoring the hydrolyzation of aspirin during the dissolution testing for aspirin delayed-release tablets with a fiber-optic dissolution system

    Directory of Open Access Journals (Sweden)

    Yan Wang

    2012-10-01

    Full Text Available The purpose of this study was to investigate the hydrolyzation of aspirin during the process of dissolution testing for aspirin delayed-release tablets. Hydrolysis product of salicylic acid can result in adverse effects and affect the determination of dissolution rate assaying. In this study, the technique of differential spectra was employed, which made it possible to monitor the dissolution testing in situ. The results showed that the hydrolyzation of aspirin made the percentage of salicylic acid exceed the limit of free salicylic acid (4.0, and the hydrolyzation may affect the quality detection of aspirin delayed-release tablets. Keywords: Aspirin delayed-release tablets, Drug dissolution test, Fiber-optic dissolution system, UV–vis spectrum

  17. Laboratory simulation of salt dissolution during waste removal

    International Nuclear Information System (INIS)

    Wiersma, B.J.; Parish, W.R.

    1997-01-01

    Laboratory experiments were performed to support the field demonstration of improved techniques for salt dissolution in waste tanks at the Savannah River Site. The tests were designed to investigate three density driven techniques for salt dissolution: (1) Drain-Add-Sit-Remove, (2) Modified Density Gradient, and (3) Continuous Salt Mining. Salt dissolution was observed to be a very rapid process as salt solutions with densities between 1.38-1.4 were frequently removed. Slower addition and removal rates and locating the outlet line at deeper levels below the top of the saltcake provided the best contact between the dissolution water and the saltcake. It was observed that dissolution with 1 M sodium hydroxide solution resulted in salt solutions that were within the current inhibitor requirements for the prevention of stress corrosion cracking. This result was independent of the density driven technique. However, if inhibited water (0.01 M sodium hydroxide and 0.011 M sodium nitrite) was utilized, the salt solutions were frequently outside the inhibitor requirements. Corrosion testing at conditions similar to the environments expected during waste removal was recommended

  18. Dissolution mechanism of UO2 at various parametric conditions

    International Nuclear Information System (INIS)

    Ollila, K.

    1988-04-01

    The aim of this experimental study is to investigate the solubility and dissolution mechanism of uranium dioxide under simulated disposal conditions of spent fuel. Unirradiated UO 2 is used as a surrogate for spent fuel. Two types of synthetic groundwaters were used in these experiments, on simulating the natural conditions deep in granitic bedrock (synthetic groundwater I) and the other simulating the effects of bentonite on groundwater (synthetic groundwater II). The effect of carbonate concentration was investigated by following dissolution in sodium bicarbonate solution as a function of bicarbonate concentration. Deionized wate was used as a reference water. All the experiments were carried out under both air-saturated, oxidizing and anoxic, reducing conditions. A separate test series under anoxic conditions was initiated in order to study the oxidation state of uranium. The experimental uranium solubilities are compared with the solubilities obtained from theoetical calculations by applying the geochemical code PHREEQ. The theoretical solubility values of uranium under oxidizing conditions calculated by PHREEQE are higher when compared to the corresponding experimental solubility values. The reason for the lower solubility values may be the mechanism of dissolution leading for example either to a situation where low dissolution rate is a limiting factor or to formation of some solid phase of uranium with lower solubility. Formation of a surface layer was observed on the pellet after dissolution in synthetic groundwater II. The theoretical solubility values under educing conditions calculated for uranium by PHREEQE appear to be in good agreement with the experimental solubility values

  19. Bench Scale Saltcake Dissolution Test Report

    International Nuclear Information System (INIS)

    BECHTOLD, D.B.; PACQUET, E.A.

    2000-01-01

    A potential scenario for retrieving saltcake from single shell tanks is the ''Rainbird(reg s ign) sprinkler'' method. Water is distributed evenly across the surface of the saltcake and allowed to percolate by gravity through the waste. The salt dissolves in the water, forming a saturated solution. The saturated liquid is removed by a saltwell pump situated near the bottom of the tank. By this method, there is never a large inventory of liquid in the tank that could pose a threat of leakage. There are many variables or factors that can influence the hydrodynamics of this retrieval process. They include saltcake porosity; saltwell pumping rate; salt dissolution chemistry; factors that could promote flow channeling (e.g. tank walls, dry wells, inclusions or discontinuities in the saltcake); method of water distribution; plug formation due to crystal formations or accumulation of insoluble solids. A brief literature search indicates that very little experimental data exist on these aspects of saltcake dissolution (Wiersma 1996, 1997). The tests reported here were planned (Herting, 2000) to provide preliminary data and information for planning future, scaled-up tests of the sprinkler method

  20. Turbulent solutal convection and surface patterning in solid dissolution

    International Nuclear Information System (INIS)

    Sullivan, T.S.; Liu, Y.; Ecke, R.E.

    1996-01-01

    We describe experiments in which crystals of NaCl, KBr, and KCl are dissolved from below by aqueous solutions containing concentrations of the respective salts from zero concentration to near saturation. The solution near the solid-liquid interface is gravitationally unstable, producing turbulent hydrodynamic motion similar to thermal convection from a single surface cooled from above. The coupling of the fluid flow with the solid dissolution produces irregular patterns at the solid-liquid interface with a distribution of horizontal length scales. The dissolution mass flux and the pattern length scales are compared with a turbulent boundary layer model. Remarkable agreement is found, showing that the fluid motion controls both the dissolution rate and the interface patterning. copyright 1996 The American Physical Society

  1. Peroxide formation and kinetics of sodium dissolution in alcohols

    International Nuclear Information System (INIS)

    Muralidaran, P.; Chandran, K.; Ganesan, V.; Periaswami, G.

    1997-01-01

    Suitable techniques for sodium removal and decontamination of sodium wetted components of Liquid Metal Fast Reactors (LMFRs) are necessary both for repair, reuse and decommissioning of such components. Among the methods followed for sodium removal, alcohol dissolution is usually employed for small components like bellow sealed valves, gripping tools to handle core components and sodium sampling devices (primary and secondary). One of the concerns in the alcohol dissolution method is the possible role of peroxide formation in the ethoxy group during storage and handling leading to explosion. This paper describes the study of peroxide formation in ethyl carbitol and butyl cellosolve as well as some of the results of dissolution kinetic studies carried out in our laboratory using different alcohols. The peroxide formation of ethyl carbitol and butyl cellosolve were studied by iodometric technique. It has been found that the peroxide formation is less in sodium containing alcohol than in pure one. Ethyl carbitol, butyl cellosolve and Jaysol-SS (mixture of ethyl alcohol, methyl alcohol, isopropyl alcohol and methyl isobutyl ketone) were used in dissolution kinetics studies. The effects due to area and orientation of the fresh sodium surface have also been investigated. The reaction rates were studied in the temperature range of 303-343 K. The rate of dissolution was estimated by measuring the sodium content of alcohol at periodic intervals. It is found that the reaction rate varies in the order of ethyl alcohol-water mixture > Jaysol-SS > butyl cellosolve > ethyl carbitol. While cleaning sodium using alcohol, the concentration of alcohol is held essentially constant throughout the process. The rate of reaction depends only on the amount of sodium and follows pseudo-first order kinetics. Increase in surface area has a marked impact on the dissolution rate at lower temperatures while at higher temperatures, the temperature factor overrides the effect due to surface area

  2. Contact Angle Measurements: an Alternative Approach Towards Understanding the Mechanism of Increased Drug Dissolution from Ethylcellulose Tablets Containing Surfactant and Exploring the Relationship Between Their Contact Angles and Dissolution Behaviors.

    Science.gov (United States)

    Liu, Tiaotiao; Hao, Jingqiang; Yang, Baixue; Hu, Beibei; Cui, Zhixiang; Li, Sanming

    2018-05-01

    The addition of surfactant in tablet was a well-defined approach to improve drug dissolution rate. While the selected surfactant played a vital role in improving the wettability of tablet by medium, it was equally important to improve the dissolution rate by permeation effect due to production of pores or the reduced inter-particle adhesion. Furthermore, understanding the mechanism of dissolution rate increased was significant. In this work, contact angle measurement was taken up as an alternative approach for understanding the dissolution rate enhancement for tablet containing surfactant. Ethylcellulose, as a substrate, was used to prepare tablet. Four surfactants, sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), dodecyltrimethylammonium bromide (DTAB), and sodium lauryl sulfonate (SLS), were used. Berberine hydrochloride, metformin hydrochloride, and rutin were selected as model drugs. The contact angle of tablet in the absence and presence of surfactant was measured to explore the mechanism. The dissolution test was investigated to verify the mechanism and to establish a correlation with the contact angle. The result showed that the mechanism was the penetration effect rather than the wetting effect. The dissolution increased with a reduction in the contact angle. DTAB was found to obtain the highest level of dissolution enhancement and the lowest contact angle, while SDS, SDBS, and SLS were found to be the less effective in both dissolution enhancement and contact angle decrease. Therefore, contact angle was a good indicator for dissolution behavior besides exploring the mechanism of increased dissolution, which shows great potential in formula screening.

  3. Hot Melt Extrusion as Solvent-Free Technique for a Continuous Manufacturing of Drug-Loaded Mesoporous Silica

    DEFF Research Database (Denmark)

    Genina, Natalja; Hadi, Batol; Löbmann, Korbinian

    2018-01-01

    The aim of this study is to explore hot melt extrusion (HME) as a solvent-free drug loading technique for preparation of stable amorphous solid dispersions using mesoporous silica (PSi). Ibuprofen and carvedilol were used as poorly soluble active pharmaceutical ingredients (APIs). Due to the high...... friction of an API:PSi mixture below the loading limit of the API, it was necessary to add the polymer Soluplus(®) (SOL) in order to enable the extrusion process. As a result, the APIs were distributed between the PSi and SOL phase after HME. Due to its higher affinity to PSi, ibuprofen was mainly adsorbed...... into the PSi, whereas carvedilol was mainly found in the SOL phase. Intrinsic dissolution rate was highest for HME formulations, containing PSi, compared to pure crystalline (amorphous) APIs and HME formulations without PSi. HME is a feasible solvent-free drug loading technique for preparation of PSi...

  4. Initial Drug Dissolution from Amorphous Solid Dispersions Controlled by Polymer Dissolution and Drug-Polymer Interaction.

    Science.gov (United States)

    Chen, Yuejie; Wang, Shujing; Wang, Shan; Liu, Chengyu; Su, Ching; Hageman, Michael; Hussain, Munir; Haskell, Roy; Stefanski, Kevin; Qian, Feng

    2016-10-01

    To identify the key formulation factors controlling the initial drug and polymer dissolution rates from an amorphous solid dispersion (ASD). Ketoconazole (KTZ) ASDs using PVP, PVP-VA, HMPC, or HPMC-AS as polymeric matrix were prepared. For each drug-polymer system, two types of formulations with the same composition were prepared: 1. Spray dried dispersion (SDD) that is homogenous at molecular level, 2. Physical blend of SDD (80% drug loading) and pure polymer (SDD-PB) that is homogenous only at powder level. Flory-Huggins interaction parameters (χ) between KTZ and the four polymers were obtained by Flory-Huggins model fitting. Solution (13)C NMR and FT-IR were conducted to investigate the specific drug-polymer interaction in the solution and solid state, respectively. Intrinsic dissolution of both the drug and the polymer from ASDs were studied using a Higuchi style intrinsic dissolution apparatus. PXRD and confocal Raman microscopy were used to confirm the absence of drug crystallinity on the tablet surface before and after dissolution study. In solid state, KTZ is completely miscible with PVP, PVP-VA, or HPMC-AS, demonstrated by the negative χ values of -0.36, -0.46, -1.68, respectively; while is poorly miscible with HPMC shown by a positive χ value of 0.23. According to solution (13)C NMR and FT-IR studies, KTZ interacts with HPMC-AS strongly through H-bonding and dipole induced interaction; with PVPs and PVP-VA moderately through dipole-induced interactions; and with HPMC weakly without detectable attractive interaction. Furthermore, the "apparent" strength of drug-polymer interaction, measured by the extent of peak shift on NMR or FT-IR spectra, increases with the increasing number of interacting drug-polymer pairs. For ASDs with the presence of considerable drug-polymer interactions, such as KTZ/PVPs, KTZ/PVP-VA, or KTZ /HPMC-AS systems, drug released at the same rate as the polymer when intimate drug-polymer mixing was ensured (i.e., the SDD systems

  5. Furosemide Loaded Silica-Lipid Hybrid Microparticles: Formulation Development, in vitro and ex vivo Evaluation.

    Science.gov (United States)

    Sambaraj, Swapna; Ammula, Divya; Nagabandi, Vijaykumar

    2015-09-01

    The main objective of the current research work was to formulate and evaluate furosemide loaded silica lipid hybrid microparticles for improved oral delivery. A novel silica-lipid hybrid microparticulate system is used for enhancing the oral absorption of low solubility and low permeability of (BCS Class IV) drugs. Silica-lipid hybrid microparticles include the drug solubilising effect of dispersed lipids and stabilizing effect of hydrophilic silica particles to increase drug solubilisation, which leads to enhanced oral bioavailability. The slica lipid hybrid (SLH) microparticles were composed of poorly soluble drug (furosemide), dispersion of oil phase (Soya bean oil and miglyol) in lecithin (Phospholipoid 90H), non-ionic surfactant (Polysorbate 80) and adsorbent (Aerosol 380). Saturation solubility studies were performed in different oils and surfactants with increased concentration of drug revealed increased solubility of furosemide. In vitro dissolution studies conducted under simulated gastric medium revealed 2-4 fold increase in dissolution efficiencies for SLH microparticles compared to that of pure drug (furosemide) and marketed formulation Lasix®. Ex vivo studies showed enhanced lipid digestibility, which improved drug permeability. Solid-state characterization of SLH microparticles by X-ray powder diffraction and Fourier transform infrared spectroscopic analysis confirmed non-crystalline nature and more compatibility of furosemide in silica-lipid hybrid microparticles. It can be concluded that the role of lipids and hydrophilic silica based carrier highlighted in enhancing solubility and permeability, and hence the oral bioavailability of poorly soluble drugs.

  6. The effect of Ti and Nb on nitrogen dissolution reaction in stainless steel melt

    International Nuclear Information System (INIS)

    Jang, Min Whan; Hong, In Kook; Pak, Jong Jin; Song, Hyo Seok; Lee, Yong Deuk

    2002-01-01

    A kinetic study of nitrogen dissolution in STS304 stainless steel melt containing Ti and Nb has been carried out at 1500 degree C using an induction furnace and a levitation melting furnace. At low O and S levels, the nitrogen dissolution rate showed the first-order kinetics being controlled by the mass transfer of nitrogen in the melt. Ti addition to STS304 stainless melt significantly retarded the nitrogen dissolution rate by the formation of solid Ti oxide layer adhered on the melt surface. Nb did not affect the rate of nitrogen dissolution. In the levitation melting experiment where the oxide layer was removed from the melt surface, Ti did not retard the nitrogen dissolution rate. Simultaneous addition of Ti and Al increased the dissolution rate by the formation of non-wetting Al 2 O 3 on the melt surface. A small addition of CaO-Al 2 O 3 synthetic flux to Ti containing melt was very effective to remove the oxide layer, hence to increase the nitrogen dissolution rate

  7. The effect of Ti and Nb on nitrogen dissolution reaction in stainless steel melt

    Energy Technology Data Exchange (ETDEWEB)

    Jang, Min Whan; Hong, In Kook; Pak, Jong Jin [Hanyang Univ., Ansan (Korea, Republic of); Song, Hyo Seok; Lee, Yong Deuk [POSCO, Pohang (Korea, Republic of)

    2002-03-01

    A kinetic study of nitrogen dissolution in STS304 stainless steel melt containing Ti and Nb has been carried out at 1500 degree C using an induction furnace and a levitation melting furnace. At low O and S levels, the nitrogen dissolution rate showed the first-order kinetics being controlled by the mass transfer of nitrogen in the melt. Ti addition to STS304 stainless melt significantly retarded the nitrogen dissolution rate by the formation of solid Ti oxide layer adhered on the melt surface. Nb did not affect the rate of nitrogen dissolution. In the levitation melting experiment where the oxide layer was removed from the melt surface, Ti did not retard the nitrogen dissolution rate. Simultaneous addition of Ti and Al increased the dissolution rate by the formation of non-wetting Al{sub 2}O{sub 3} on the melt surface. A small addition of CaO-Al{sub 2}O{sub 3} synthetic flux to Ti containing melt was very effective to remove the oxide layer, hence to increase the nitrogen dissolution rate.

  8. Dissolution of organic solvents from painted surfaces into water

    International Nuclear Information System (INIS)

    Wren, J.C.; Jobe, D.J.; Sanipelli, G.G.; Ball, J.M.

    2000-01-01

    The presence of volatile iodine in containment buildings is one of the major safety concerns in the potential event of nuclear reactor accidents. Organic impurities in containment water, originating from various painted structural surfaces and organic materials, could have a significant impact on iodine volatility following an accident. To determine the source and magnitude of organic impurities and their effects on time-dependent iodine volatility, the dissolution for organic constituents from paints used in reactor buildings has been studied under postulated accident conditions. The studies of the organic dissolution from carbon steel coupons coated with zinc-primed vinyl, epoxy-primed polyurethane or epoxy paints over the temperature range 25-90 deg C are reported. Relatively large activation energies were measured for the release of the principal organic compounds from painted surfaces, suggesting it is the release of the solvents from the paint matrix rather than their diffusion through the solution that is the rate determining step for the dissolution mechanism. The similarities in the values of activation energies for the dissolution of different organic compounds from the paints suggest the release rate is independent of the nature of the painted surface or the type of organic being released from the surface. These two observations indicate that it may be possible to write a generalized rate expression for the release of organic compounds from painted surfaces in containment following an accident. The possible implications of these results for predicting iodine volatility in containment are also discussed. (author)

  9. The Use of Artificial Neural Network for Prediction of Dissolution Kinetics

    Directory of Open Access Journals (Sweden)

    H. Elçiçek

    2014-01-01

    Full Text Available Colemanite is a preferred boron mineral in industry, such as boric acid production, fabrication of heat resistant glass, and cleaning agents. Dissolution of the mineral is one of the most important processes for these industries. In this study, dissolution of colemanite was examined in water saturated with carbon dioxide solutions. Also, prediction of dissolution rate was determined using artificial neural networks (ANNs which are based on the multilayered perceptron. Reaction temperature, total pressure, stirring speed, solid/liquid ratio, particle size, and reaction time were selected as input parameters to predict the dissolution rate. Experimental dataset was used to train multilayer perceptron (MLP networks to allow for prediction of dissolution kinetics. Developing ANNs has provided highly accurate predictions in comparison with an obtained mathematical model used through regression method. We conclude that ANNs may be a preferred alternative approach instead of conventional statistical methods for prediction of boron minerals.

  10. A Novel Approach to Experimental Studies of Mineral Dissolution Kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Chen Zhu

    2006-08-31

    Currently, DOE is conducting pilot CO{sub 2} injection tests to evaluate the concept of geological sequestration. One strategy that potentially enhances CO{sub 2} solubility and reduces the risk of CO{sub 2} leak back to the surface is dissolution of indigenous minerals in the geological formation and precipitation of secondary carbonate phases, which increases the brine pH and immobilizes CO{sub 2}. Clearly, the rates at which these dissolution and precipitation reactions occur directly determine the efficiency of this strategy. However, one of the fundamental problems in modern geochemistry is the persistent two to five orders of magnitude discrepancy between laboratory measured and field derived feldspar dissolution rates. To date, there is no real guidance as to how to predict silicate reaction rates for use in quantitative models. Current models for assessment of geological carbon sequestration have generally opted to use laboratory rates, in spite of the dearth of such data for compositionally complex systems, and the persistent disconnect between laboratory and field applications. Therefore, a firm scientific basis for predicting silicate reaction kinetics in CO2 injected geological formations is urgently needed to assure the reliability of the geochemical models used for the assessments of carbon sequestration strategies. The funded experimental and theoretical study attempts to resolve this outstanding scientific issue by novel experimental design and theoretical interpretation to measure silicate dissolution rates and iron carbonate precipitation rates at conditions pertinent to geological carbon sequestration. In the second year of the project, we completed CO{sub 2}-Navajo sandstone interaction batch and flow-through experiments and a Navajo sandstone dissolution experiment without the presence of CO{sub 2} at 200 C and 250-300 bars, and initiated dawsonite dissolution and solubility experiments. We also performed additional 5-day experiments at the

  11. In vitro release of ketoprofen suppositories using the USP basket and the flow-through cell dissolution methods.

    Science.gov (United States)

    Medina, José Raúl; Padilla, Adrián Roberto; Hurtado, Marcela; Cortés, Alma Rosa; Domínguez-Ramírez, Adriana Miriam

    2014-05-01

    In order to study the release characteristics of ketoprofen suppositories under the hydrodynamic environment generated by USP Apparatus 1 and 4, the dissolution profiles of the Mexican reference product (100 mg) were determined. Phosphate buffer pH 8 and 1% sodium lauryl sulfate (SLS) aqueous solutions were proved as dissolution mediums. Baskets were rotated at 100 rpm with USP Apparatus 1 and different flow rates from 16-32 mL/min with USP Apparatus 4 were used. Drug samples were taken and quantified during 60 min by UV analysis at 260 nm. Mean dissolution time (MDT) and dissolution efficiency (DE) were calculated by model-independent methods. Data were also fitted to several kinetic models. Poor dissolution was found in both dissolution mediums when USP basket method was used ( 0.99). The results suggest the need to establish an adequate dissolution method to evaluate the release kinetics of ketoprofen from suppositories.

  12. Synthesis of silica nanosphere from homogeneous and ...

    Indian Academy of Sciences (India)

    WINTEC

    avoid it, reaction in heterogeneous system using CTABr was carried out. Nanosized silica sphere with ... Homogeneous system contains a mixture of ethanol, water, aqueous ammonia and ... heated to 823 K (rate, 1 K/min) in air and kept at this.

  13. The Influence of Milling on the Dissolution Performance of Simvastatin

    Directory of Open Access Journals (Sweden)

    Thomas Rades

    2010-12-01

    Full Text Available Particle size reduction is a simple means to enhance the dissolution rate of poorly water soluble BCS-class II and IV drugs. However, the major drawback of this process is the possible introduction of process induced disorder. Drugs with different molecular arrangements may exhibit altered properties such as solubility and dissolution rate and, therefore, process induced solid state modifications need to be monitored. The aim of this study was two-fold: firstly, to investigate the dissolution rates of milled and unmilled simvastatin; and secondly, to screen for the main milling factors, as well as factor interactions in a dry ball milling process using simvastatin as model drug, and to optimize the milling procedure with regard to the opposing responses particle size and process induced disorder by application of a central composite face centered design. Particle size was assessed by scanning electron microscopy (SEM and image analysis. Process induced disorder was determined by partial least squares (PLS regression modeling of respective X-ray powder diffractograms (XRPD and Raman spectra. Valid and significant quadratic models were built. The investigated milling factors were milling frequency, milling time and ball quantity at a set drug load, out of which milling frequency was found to be the most important factor for particle size as well as process induced disorder. Milling frequency and milling time exhibited an interaction effect on the responses. The optimum milling settings using the maximum number of milling balls (60 balls with 4 mm diameter was determined to be at a milling frequency of 21 Hz and a milling time of 36 min with a resulting primary particle size of 1.4 μm and a process induced disorder of 6.1% (assessed by Raman spectroscopy and 8.4% (assessed by XRPD, at a set optimization limit of < 2 μm for particle size and < 10% for process induced disorder. This optimum was tested experimentally and the process induced disorder

  14. Calcination/dissolution residue treatment

    International Nuclear Information System (INIS)

    Knight, R.C.; Creed, R.F.; Patello, G.K.; Hollenberg, G.W.; Buehler, M.F.; O'Rourke, S.M.; Visnapuu, A.; McLaughlin, D.F.

    1994-09-01

    Currently, high-level wastes are stored underground in steel-lined tanks at the Hanford site. Current plans call for the chemical pretreatment of these wastes before their immobilization in stable glass waste forms. One candidate pretreatment approach, calcination/dissolution, performs an alkaline fusion of the waste and creates a high-level/low-level partition based on the aqueous solubilities of the components of the product calcine. Literature and laboratory studies were conducted with the goal of finding a residue treatment technology that would decrease the quantity of high-level waste glass required following calcination/dissolution waste processing. Four elements, Fe, Ni, Bi, and U, postulated to be present in the high-level residue fraction were identified as being key to the quantity of high-level glass formed. Laboratory tests of the candidate technologies with simulant high-level residues showed reductive roasting followed by carbonyl volatilization to be successful in removing Fe, Ni, and Bi. Subsequent bench-scale tests on residues from calcination/dissolution processing of genuine Hanford Site tank waste showed Fe was separated with radioelement decontamination factors of 70 to 1,000 times with respect to total alpha activity. Thermodynamic analyses of the calcination of five typical Hanford Site tank waste compositions also were performed. The analyses showed sodium hydroxide to be the sole molten component in the waste calcine and emphasized the requirement for waste blending if fluid calcines are to be achieved. Other calcine phases identified in the thermodynamic analysis indicate the significant thermal reconstitution accomplished in calcination

  15. Study of radon transport through concrete modified with silica fume

    International Nuclear Information System (INIS)

    Chauhan, R.P.; Kumar, Amit

    2013-01-01

    The concentration of radon in soil usually varies between a few kBq/m 3 and tens or hundreds of kBq/m 3 depending upon the geographical region. This causes the transport of radon from the soil to indoor environments by diffusion and advection through the pore space of concrete. To reduce indoor radon levels, the use of concrete with low porosity and a low radon diffusion coefficient is recommended. A method of reducing the radon diffusion coefficient through concrete and hence the indoor radon concentration by using silica fume to replace an optimum level of cement was studied. The diffusion coefficient of the concrete was reduced from (1.63 ± 0.3) × 10 −7 to (0.65 ± 0.01) × 10 −8 m 2 /s using 30% substitution of cement with silica fume. The compressive strength of the concrete increased as the silica-fume content increased, while radon exhalation rate and porosity of the concrete decreased. This study suggests a cost-effective method of reducing indoor radon levels. -- Highlights: • Radon diffusion study through silica fume modified concrete was carried out. • Radon diffusion coefficient of concrete decreased with increase of silica fume contents. • Compressive strength increased with increase of silica fume. • Radon exhalation rates and porosity of samples decreased with addition of silica fume. • Radon diffusion coefficient decreased to 2.6% by 30% silica fume substitution

  16. Organic ligand-induced dissolution kinetics of antimony trioxide

    Institute of Scientific and Technical Information of China (English)

    Xingyun Hu; Mengchang He

    2017-01-01

    The influence of low-molecular-weight dissolved organic matter (LMWDOM) on the dissolution rate of Sb2O3 was investigated.Some representative LMWDOMs with carboxyl,hydroxyl,hydrosulfuryl and amidogen groups occurring naturally in the solution were chosen,namely oxalic acid,citric acid,tartaric acid,EDTA,salicylic acid,phthalandione,glycine,thiolactic acid,xylitol,glucose and catechol.These LMWDOMs were dissolved in inert buffers at pH =3.7,6.6 and 8.6 and added to powdered Sb2O3 in a stirred,thermostatted reactor (25℃).The addition of EDTA,tartaric acid,thiolactic acid,citric acid and oxalic acid solutions at pH 3.7 and catechol at pH 8.6 increased the rate of release of antimony.In the 10 mmol/L thiolactic acid solution,up to 97% by mass of the antimony was released after 120 min reaction.There was no effect on the dissolution of Sb2O3 for the other ligands.A weak correlation between dissolution rate with the dissociation constant of ligands and the stability of the dissolved complex was also found.All the results showed that the extent of the promoting effect of ligands on the dissolution of Sb2O3 was not determined by the stability of the dissolved complex,but by the dissociation constant of ligands and detachment rate of surface chelates from the mineral surface.This study can not only help in further understanding the effect of individual low-molecular-weight organic ligands,but also provides a reference to deduce the effect of natural organic matters with oxygen-bearing functional groups on the dissolution of antimony oxide minerals.

  17. Organic ligand-induced dissolution kinetics of antimony trioxide.

    Science.gov (United States)

    Hu, Xingyun; He, Mengchang

    2017-06-01

    The influence of low-molecular-weight dissolved organic matter (LMWDOM) on the dissolution rate of Sb 2 O 3 was investigated. Some representative LMWDOMs with carboxyl, hydroxyl, hydrosulfuryl and amidogen groups occurring naturally in the solution were chosen, namely oxalic acid, citric acid, tartaric acid, EDTA, salicylic acid, phthalandione, glycine, thiolactic acid, xylitol, glucose and catechol. These LMWDOMs were dissolved in inert buffers at pH=3.7, 6.6 and 8.6 and added to powdered Sb 2 O 3 in a stirred, thermostatted reactor (25°C). The addition of EDTA, tartaric acid, thiolactic acid, citric acid and oxalic acid solutions at pH3.7 and catechol at pH8.6 increased the rate of release of antimony. In the 10mmol/L thiolactic acid solution, up to 97% by mass of the antimony was released after 120min reaction. There was no effect on the dissolution of Sb 2 O 3 for the other ligands. A weak correlation between dissolution rate with the dissociation constant of ligands and the stability of the dissolved complex was also found. All the results showed that the extent of the promoting effect of ligands on the dissolution of Sb 2 O 3 was not determined by the stability of the dissolved complex, but by the dissociation constant of ligands and detachment rate of surface chelates from the mineral surface. This study can not only help in further understanding the effect of individual low-molecular-weight organic ligands, but also provides a reference to deduce the effect of natural organic matters with oxygen-bearing functional groups on the dissolution of antimony oxide minerals. Copyright © 2016. Published by Elsevier B.V.

  18. Effects of natural organic matter properties on the dissolution kinetics of zinc oxide nanoparticles

    Science.gov (United States)

    Jiang, Chuanjia; Aiken, George R.; Hsu-Kim, Heileen

    2015-01-01

    The dissolution of zinc oxide (ZnO) nanoparticles (NPs) is a key step of controlling their environmental fate, bioavailability, and toxicity. Rates of dissolution often depend upon factors such as interactions of NPs with natural organic matter (NOM). We examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs in buffered potassium chloride solution using anodic stripping voltammetry to directly measure dissolved zinc concentrations. The observed dissolution rate constants (kobs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg C L–1) for Suwannee River humic and fulvic acids and Pony Lake fulvic acid. When dissolution rates were compared for the 16 NOM isolates, kobs was positively correlated with certain properties of NOM, including specific ultraviolet absorbance (SUVA), aromatic and carbonyl carbon contents, and molecular weight. Dissolution rate constants were negatively correlated to hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. The findings of this study facilitate a better understanding of the fate of ZnO NPs in organic-rich aquatic environments and highlight SUVA as a facile and useful indicator of NOM interactions with metal-based nanoparticles.

  19. Dissolution Flowsheet for High Flux Isotope Reactor Fuel

    Energy Technology Data Exchange (ETDEWEB)

    Daniel, W. E. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Rudisill, T. S. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); O' Rourke, P. E. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Karay, N. S [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2016-09-27

    As part of the Spent Nuclear Fuel (SNF) processing campaign, H-Canyon is planning to begin dissolving High Flux Isotope Reactor (HFIR) fuel in late FY17 or early FY18. Each HFIR fuel core contains inner and outer fuel elements which were fabricated from uranium oxide (U3O8) dispersed in a continuous Al phase using traditional powder metallurgy techniques. Fuels fabricated in this manner, like other SNF’s processed in H-Canyon, dissolve by the same general mechanisms with similar gas generation rates and the production of H2. The HFIR fuel cores will be dissolved and the recovered U will be down-blended into low-enriched U. HFIR fuel was previously processed in H-Canyon using a unique insert in both the 6.1D and 6.4D dissolvers. Multiple cores will be charged to the same dissolver solution maximizing the concentration of dissolved Al. The objective of this study was to identify flowsheet conditions through literature review and laboratory experimentation to safely and efficiently dissolve the HFIR fuel in H-Canyon. Laboratory-scale experiments were performed to evaluate the dissolution of HFIR fuel using both Al 1100 and Al 6061 T6 alloy coupons. The Al 1100 alloy was considered a representative surrogate which provided an upper bound on the generation of flammable (i.e., H2) gas during the dissolution process. The dissolution of the Al 6061 T6 alloy proceeded at a slower rate than the Al 1100 alloy, and was used to verify that the target Al concentration in solution could be achieved for the selected Hg concentration. Mass spectrometry and Raman spectroscopy were used to provide continuous monitoring of the concentration of H2 and other permanent gases in the dissolution offgas, allowing the development of H2 generation rate profiles. The H2 generation rates were subsequently used to evaluate if a full HFIR core could be dissolved in an H-Canyon dissolver without exceeding 60% of the

  20. The dissolution phenomenon of lysozyme crystals

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, C.; Ulrich, J. [Martin Luther University Halle-Wittenberg, Department of Thermal Separation Processes, Centre of Engineering Science, Halle/Saale (Germany)

    2012-02-15

    Dissolution studies on lysozyme crystals were carried out since the observed dissolution pattern look different from non-protein dissolved crystals. The Tetragonal, High Temperature and Low Temperature Orthorhombic morphologies, crystallized using sodium chloride, were chosen and the influence of different pH, salt and protein concentration on their dissolution was investigated. An increase in pH and/or salt concentration can modify the dissolution behaviour. The pattern of the crystals during the dissolution process will, therefore, develop differently. Frequently a skeleton like crystal pattern followed by a falling apart of the crystals is observed. The multi-component character of the lysozyme crystal (protein, water, buffer, salt) as well as ''solvatomorphism'' gives first insights in the phenomena happening in the dissolution process. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Silica-Immobilized Enzyme Reactors

    Science.gov (United States)

    2007-08-01

    Silica-IMERs 14 implicated in neurological disorders such as Schizophrenia and Parkinson’s disease.[86] Drug discovery for targets that can alter the...primarily the activation of prodrugs and proantibiotics for cancer treatments or antibiotic therapy , respectively.[87] Nitrobenzene nitroreductase was...BuChE) Monolith disks* Packed Silica Biosilica Epoxide- Silica Silica-gel Enzyme Human AChE Human AChE Human AChE Equine BuChE Human

  2. Oxidative dissolution of ADOPT compared to standard UO2 fuel

    International Nuclear Information System (INIS)

    Nilsson, Kristina; Roth, Olivia; Jonsson, Mats

    2017-01-01

    In this work we have studied oxidative dissolution of pure UO 2 and ADOPT (UO 2 doped with Al and Cr) pellets using H 2 O 2 and gammaradiolysis to induce the process. There is a small but significant difference in the oxidative dissolution rate of UO 2 and ADOPT pellets, respectively. However, the difference in oxidative dissolution yield is insignificant. Leaching experiments were also performed on in-reactor irradiated ADOPT and UO 2 pellets under oxidizing conditions. The results indicate that the U(VI) release is slightly slower from the ADOPT pellet compared to the UO 2. This could be attributed to differences in exposed surface area. However, fission products with low UO 2 solubility display a higher relative release from ADOPT fuel compared to standard UO 2 -fuel. This is attributed to a lower matrix solubility imposed by the dopants in ADOPT fuel. The release of Cs is higher from UO 2 which is attributed to the larger grain size of ADOPT. - Highlights: •Oxidative dissolution of ADOPT fuel is compared to standard UO 2 fuel. •Only marginal differences are observed. •The main difference observed is in the relative release rate of fission products. •Differences are claimed to be attributed to a lower matrix solubility imposed by the dopants in ADOPT fuel.

  3. Silica reinforced triblock copolymer gels

    DEFF Research Database (Denmark)

    Theunissen, E.; Overbergh, N.; Reynaers, H.

    2004-01-01

    The effect of silica and polymer coated silica particles as reinforcing agents on the structural and mechanical properties of polystyrene-poly(ethylene/butylene)-polystyrene (PS-PEB-PS) triblock gel has been investigated. Different types of chemically modified silica have been compared in order...

  4. Linking dissolution to disintegration in immediate release tablets using image analysis and a population balance modelling approach.

    Science.gov (United States)

    Wilson, David; Wren, Stephen; Reynolds, Gavin

    2012-01-01

    In order to achieve an improved understanding of disintegration and dissolution phenomena for an immediate release tablet formulation, a technique to monitor the number and size of particles entrained within the dissolution media was developed in combination with a population balancing model. Tablets were first characterized for crushing force, disintegration time and dissolution performance using standard USP methodologies. The performance of the tablets was then assessed using a new measurement system which links a "QicPic" particle imaging device to a USP dissolution vessel. This system enables us to measure the number and size of particles generated during tablet dissolution. The population balance mathematical model allowed a tablet erosion rate to be manipulated to fit the experimental data. Results showed that tablets with differing crushing forces showed different dissolution behaviors that could be explained by differing rates of particle release into the dissolution media. These behaviors were then successfully modeled to provide a description of the dissolution and disintegration behavior of the tablets in terms of a tablet erosion rate. A new approach was developed that allowed the description of the dissolution behaviors of the tablets in terms of the rate that they release particles into solution. This was then successfully modeled in terms of a tablet erosion rate.

  5. Evaluation of the coat quality of sustained release pellets by individual pellet dissolution methodology.

    Science.gov (United States)

    Xu, Min; Liew, Celine Valeria; Heng, Paul Wan Sia

    2015-01-15

    This study explored the application of 400-DS dissolution apparatus 7 for individual pellet dissolution methodology by a design of experiment approach and compared its capability with that of the USP dissolution apparatus 1 and 2 for differentiating the coat quality of sustained release pellets. Drug loaded pellets were prepared by extrusion-spheronization from powder blends comprising 50%, w/w metformin, 25%, w/w microcrystalline cellulose and 25%, w/w lactose, and then coated with ethyl cellulose to produce sustained release pellets with 8% and 10%, w/w coat weight gains. Various pellet properties were investigated, including cumulative drug release behaviours of ensemble and individual pellets. When USP dissolution apparatus 1 and 2 were used for drug release study of the sustained release pellets prepared, floating and clumping of pellets were observed and confounded the release profiles of the ensemble pellets. Hence, the release profiles obtained did not characterize the actual drug release from individual pellet and the applicability of USP dissolution apparatus 1 and 2 to evaluate the coat quality of sustained release pellets was limited. The cumulative release profile of individual pellet using the 400-DS dissolution apparatus 7 was found to be more precise at distinguishing differences in the applied coat quality. The dip speed and dip interval of the reciprocating holder were critical operational parameters of 400-DS dissolution apparatus 7 that affected the drug release rate of a sustained release pellet during the individual dissolution study. The individual dissolution methodology using the 400-DS dissolution apparatus 7 is a promising technique to evaluate the individual pellet coat quality without the influence of confounding factors such as pellet floating and clumping observed during drug release test with dissolution apparatus 1 and 2, as well as to facilitate the elucidation of the actual drug release mechanism conferred by the applied sustained

  6. Dissolution of Si in Molten Al with Gas Injection

    Science.gov (United States)

    Seyed Ahmadi, Mehran

    Silicon is an essential component of many aluminum alloys, as it imparts a range of desirable characteristics. However, there are considerable practical difficulties in dissolving solid Si in molten Al, because the dissolution process is slow, resulting in material and energy losses. It is thus essential to examine Si dissolution in molten Al, to identify means of accelerating the process. This thesis presents an experimental study of the effect of Si purity, bath temperature, fluid flow conditions, and gas stirring on the dissolution of Si in molten Al, plus the results of physical and numerical modeling of the flow to corroborate the experimental results. The dissolution experiments were conducted in a revolving liquid metal tank to generate a bulk velocity, and gas was introduced into the melt using top lance injection. Cylindrical Si specimens were immersed into molten Al for fixed durations, and upon removal the dissolved Si was measured. The shape and trajectory of injected bubbles were examined by means of auxiliary water experiments and video recordings of the molten Al free surface. The gas-agitated liquid was simulated using the commercial software FLOW-3D. The simulation results provide insights into bubble dynamics and offer estimates of the fluctuating velocities within the Al bath. The experimental results indicate that the dissolution rate of Si increases in tandem with the melt temperature and bulk velocity. A higher bath temperature increases the solubility of Si at the solid/liquid interface, resulting in a greater driving force for mass transfer, and a higher liquid velocity decreases the resistance to mass transfer via a thinner mass boundary layer. Impurities (with lower diffusion coefficients) in the form of inclusions obstruct the dissolution of the Si main matrix. Finally, dissolution rate enhancement was observed by gas agitation. It is postulated that the bubble-induced fluctuating velocities disturb the mass boundary layer, which

  7. Correlation of dissolution and disintegration results for an immediate-release tablet.

    Science.gov (United States)

    Nickerson, Beverly; Kong, Angela; Gerst, Paul; Kao, Shangming

    2018-02-20

    The drug release rate of a rapidly dissolving immediate-release tablet formulation with a highly soluble drug is proposed to be controlled by the disintegration rate of the tablet. Disintegration and dissolution test methods used to evaluate the tablets were shown to discriminate manufacturing process differences and compositionally variant tablets. In addition, a correlation was established between disintegration and dissolution. In accordance with ICH Q6A, this work demonstrates that disintegration in lieu of dissolution is suitable as the drug product quality control method for evaluating this drug product. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Silica from Ash

    Indian Academy of Sciences (India)

    management, polymer composites and chemical process design. Figure 1 Difference in color of the ash ... The selection of ash is important as the quality of ash determines the total amount as well as quality of silica recoverable Ash which has undergone maximum extent of combustion is highly desirable as it contains ...

  9. Dissolution and compaction instabilities in geomaterials

    Science.gov (United States)

    Stefanou, I.; Sulem, J.; de Sauvage, J.

    2014-12-01

    Compaction bands play an important role in reservoir engineering and geological storage. Their presence in geological formations may also provide useful information on various geological processes. Several mechanisms can be involved at different scales and may be responsible for compaction band instabilities [1]. Compaction bands can be seen as a particular instability of the governing mathematical system leading to localization of deformation [2-4]. In a saturated porous rock, the progressive mechanical damage of the solid skeleton during compaction, results in the increase of the interface area of the reactants and consequently in the acceleration of the dissolution rate of the solid phase [2,5]. Thus, the solid skeleton is degraded more rapidly (mass removal because of dissolution), the overall mechanical properties of the system diminish (contraction of the elastic domain - chemical softening), deformations increase and the solid skeleton is further damaged (intergranular fractures, debonding, breakage of the porous network etc.). The stability of this positive feedback process is investigated analytically through linear stability analysis by considering the strong chemo-poro-mechanical coupling due to chemical dissolution. The post bifurcation behavior is then studied analytically and numerically revealing the compaction band thickness and periodicity. The effect of various parameters is studied as for instance the influence of the hydraulic diffusivity on the compaction band thickness. [1] P. Baud, S. Vinciguerra, C. David, A. Cavallo, E. Walker and T. Reuschlé (2009), Pure Appl. Geophys., 166(5-7), 869-898 [2] I. Stefanou and J. Sulem (2014), JGR: Solid Earth, 119(2), 880-899. doi:10.1002/2013JB010342I [3] J.W. Rudnicki and J.R. Rice (1975), Journal of the Mechanics and Physics of Solids 23(6),: 371-394 [4] K.A. Issen and J.W. Rudnicki (2000), JGR, 105(B9), 21529. doi:10.1029/2000JB900185 [5] R. Nova, R. Castellanza and C. Tamagnini (2003), International

  10. Etude cinetique et thermodynamique de la dissolution de la fluorapatite dans l'acide phosphorique

    International Nuclear Information System (INIS)

    Brahim, K.; Khattech, I.; Dubes, J.P.; Jemal, M.

    2005-01-01

    A modification on the reversal cells of a C-80 SETARAM calorimeter allows a Joule effect in the reaction cells to determine a transfer function in experimental conditions close to those of dissolution of a solid in a liquid. The calorimeter was then used to determine in isothermal conditions both thermodynamic and kinetic parameters associated with dissolution of synthetic fluorapatite in phosphoric acid solutions. Due to the rapidity of reaction, the heat flow recordings were deconvoluted and the resulting curves were analyzed iteratively to obtain the rates of digestion and the enthalpy of dissolution at 298 K of fluorapatite in phosphoric acid solution containing 10, 18 or 30 wt% P 2 O 5 . The results agree with a two-step dissolution mechanism. The first step is the dissolution of the solid in phosphoric acid, and the second is the formation of the complex Ca(H 2 PO 4 ) +

  11. Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters.

    Science.gov (United States)

    Becková, Vera; Malátová, Irena

    2008-01-01

    Kinetics of dissolution of (238)U, (234)U and (230)Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultrafiltrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolní Rozínka' at Rozná, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h(-1) and the sampling period is typically 1 month. Studied filters contained 125 +/- 6 mBq (238)U in equilibrium with (234)U and (230)Th; no (232)Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for (238)U and (234)U and slow dissolution half-times of 173 and 116 d were found for (238)U and (234)U, respectively. No detectable dissolution of (230)Th was found.

  12. Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters

    International Nuclear Information System (INIS)

    Beckova, V.; Malatova, I.

    2008-01-01

    Kinetics of dissolution of 238 U, 234 U and 230 Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultra-filtrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolni Rozinka' at Rozna, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h -1 and the sampling period is typically 1 month. Studied filters contained 125 ± 6 mBq 238 U in equilibrium with 234 U and 230 Th; no 232 Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for 238 U and 234 U and slow dissolution half-times of 173 and 116 d were found for 238 U and 234 U, respectively. No detectable dissolution of 230 Th was found. (authors)

  13. Characterisation of human saliva as a platform for oral dissolution medium development.

    Science.gov (United States)

    Gittings, Sally; Turnbull, Neil; Henry, Brian; Roberts, Clive J; Gershkovich, Pavel

    2015-04-01

    Human saliva is a biological fluid of great importance in the field of dissolution testing. However, until now, no consensus has been reached on its key characteristics relevant to dissolution testing. As a result, it is difficult to select or develop an in vitro dissolution medium to best represent human saliva. In this study, the pH, buffer capacity, surface tension, viscosity and flow rate of both unstimulated (US) and stimulated (SS) human saliva were investigated in order to provide a platform of reference for future dissolution studies using simulated salivary fluids. Age and gender related differences in a sample size of 30 participants for each parameter were investigated. Significant differences were established between US and SS for all characteristics except surface tension. Therefore, the requirement for using two simulated salivary fluids should be considered when developing an oral dissolution model. Copyright © 2015 Elsevier B.V. All rights reserved.

  14. Better understanding of dissolution behaviour of amorphous drugs by in situ solid-state analysis using Raman spectroscopy

    DEFF Research Database (Denmark)

    Savolainen, M; Kogermann, K; Heinz, A

    2009-01-01

    of two amorphous drugs, indomethacin (IMC) and carbamazepine (CBZ). The dissolution rate was higher from amorphous IMC compared to the crystalline alpha- and gamma-forms. However, the dissolution rate started to slow down during the experiment. In situ Raman analysis verified that at that time point...

  15. Sampling times influence the estimate of parameters in the Weibull dissolution model

    Czech Academy of Sciences Publication Activity Database

    Čupera, J.; Lánský, Petr; Šklubalová, Z.

    2015-01-01

    Roč. 78, Oct 12 (2015), s. 171-176 ISSN 0928-0987 Institutional support: RVO:67985823 Keywords : dissolution * Fisher information * rate constant * optimal sampling times Subject RIV: BA - General Mathematics Impact factor: 3.773, year: 2015

  16. Kinetics of dissolution of magnetite in PDCA based formulations

    Energy Technology Data Exchange (ETDEWEB)

    Ranganathan, S.; Prince, A.A.M.; Raghavan, P.S.; Gopalan, R. [Madras Christian Coll., Tambaram (India); Srinivasan, M.P.; Narasimhan, S.V.

    1997-08-01

    Magnetite is one of the important corrosion products of pressurized heavy water reactors (PHWRs) where carbon steel is the dominant surface in the primary heat transport system. Designing of formulations capable of dissolving magnetite is important for effective decontamination of such surfaces. The rate of dissolution of synthetically prepared magnetite was studied in low concentrations of PDCA containing acidic formulations. The effect of addition of ascorbic acid, citric acid, Fe{sup 2+}-PDCA complex on the rate was also studied. The effects of pH and the temperature on the dissolution rate were determined. The PDCA as a complexant has some positive factors like low protonation constant and enhanced stability to radiation. (author)

  17. Sonochemical synthesis of silica particles and their size control

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hwa-Min [Advanced Materials and Chemical Engineering, Catholic University of Daegu, Gyeongbuk 38430 (Korea, Republic of); Lee, Chang-Hyun [Electronic and Electrical Engineering, Catholic University of Daegu, Gyeongbuk 38430 (Korea, Republic of); Kim, Bonghwan, E-mail: bhkim@cu.ac.kr [Electronic and Electrical Engineering, Catholic University of Daegu, Gyeongbuk 38430 (Korea, Republic of)

    2016-09-01

    Graphical abstract: - Highlights: • Silica particles were easily prepared by an ultrasound-assisted sol–gel method. • The particle size was controlled by the ammonium hydroxide/water molar ratio. • The size-controlled diameter of silica particles ranged from 40 to 400 nm. • The particles were formed in a relatively short reaction time. - Abstract: Using an ultrasound-assisted sol–gel method, we successfully synthesized very uniformly shaped, monodisperse, and size-controlled spherical silica particles from a mixture of ethanol, water, and tetraethyl orthosilicate in the presence of ammonia as catalyst, at room temperature. The diameters of the silica particles were distributed in the range from 40 to 400 nm; their morphology was well characterized by scanning electron microscopy. The silica particle size could be adjusted by choosing suitable concentrations of ammonium hydroxide and water, which in turn determined the nucleation and growth rates of the particles during the reaction. This sonochemical-based silica synthesis offers an alternative way to produce spherical silica particles in a relatively short reaction time. Thus, we suggest that this simple, low-cost, and efficient method of preparing uniform silica particles of various sizes will have practical and wide-ranging industrial applicability.

  18. Hydrothermal stability of silica, hybrid silica and Zr-doped hybrid silica membranes

    NARCIS (Netherlands)

    ten Hove, Marcel; Luiten-Olieman, Mieke W.J.; Huiskes, Cindy; Nijmeijer, Arian; Winnubst, Louis

    2017-01-01

    Hybrid silica membranes have demonstrated to possess a remarkable hydrothermal stability in pervaporation and gas separation processes allowing them to be used in industrial applications. In several publications the hydrothermal stability of pure silica or that of hybrid silica membranes are

  19. Aluminosilicate Dissolution and Silicate Carbonation during Geologic CO2 Sequestration

    Science.gov (United States)

    Min, Yujia

    silicates dissolution to the high salinity conditions in subsurface environments. In addition to cations, the role of anions in geochemical reactions in subsurfaces are important. This study investigated the anion effects by studying sulfate and oxalate. Sulfate formed monodentate surface complexes with the Al sites on plagioclase surface and enhanced the dissolution. Oxalate was also found to enhance the plagioclase dissolution. Co-existing oxalate and sulfate suppressed the effects of sulfate on plagioclase dissolution. This information provides useful insights for understanding the roles of sulfate and organic compounds on the CO2 water-mineral interactions during scCO2 enhanced oil recovery. The results also aid in formulating a scientific guideline of the proper amount of SO2 co-injection with CO2. Water in GCS sites can exist in water-bearing scCO2 in addition to the aqueous phase in brine. Thus, it is important to understand the effects of water-bearing scCO2 on the carbonation of silicates. To address the gap between the nano- and micro-sized particles used in the laboratory to the large grains in field sites, we utilized wollastonite and investigated the effects of particle sizes on the wollastonite carbonation in water-bearing scCO2. The thickness of the reacted layer on the particle surfaces was found to be constant for different sized particles. The amorphous silica layer formed act as a diffusion barrier for water-bearing scCO2. In addition, the reaction extent was higher with more water, lower temperature, and higher pressure. Further, higher water saturation percentage and lower temperature can lead to the formation of more permeable amorphous silica layers. This thesis included the investigations of both liquid phase and vapor phase water that contacted with scCO2, and the effects of cations and anions on both formation and caprock minerals. The findings from this work improve our knowledge of the geochemical reactions at CO2-water-mineral interfaces, which

  20. Functionalized bimodal mesoporous silicas as carriers for controlled aspirin delivery

    Science.gov (United States)

    Gao, Lin; Sun, Jihong; Li, Yuzhen

    2011-08-01

    The bimodal mesoporous silica modified with 3-aminopropyltriethoxysilane was performed as the aspirin carrier. The samples' structure, drug loading and release profiles were characterized with X-ray diffraction, scanning electron microscopy, N 2 adsorption and desorption, Fourier transform infrared spectroscopy, TG analysis, elemental analysis and UV-spectrophotometer. For further exploring the effects of the bimodal mesopores on the drug delivery behavior, the unimodal mesoporous material MCM-41 was also modified as the aspirin carrier. Meantime, Korsmeyer-Peppas equation ft= ktn was employed to analyze the dissolution data in details. It is indicated that the bimodal mesopores are beneficial for unrestricted drug molecules diffusing and therefore lead to a higher loading and faster releasing than that of MCM-41. The results show that the aspirin delivery properties are influenced considerably by the mesoporous matrix, whereas the large pore of bimodal mesoporous silica is the key point for the improved controlled-release properties.

  1. Carbonate mineral dissolution kinetics in high pressure experiments

    Science.gov (United States)

    Dethlefsen, F.; Dörr, C.; Schäfer, D.; Ebert, M.

    2012-04-01

    The potential CO2 reservoirs in the North German Basin are overlain by a series of Mesozoic barrier rocks and aquifers and finally mostly by Tertiary and Quaternary close-to-surface aquifers. The unexpected rise of stored CO2 from its reservoir into close-to-surface aquifer systems, perhaps through a broken well casing, may pose a threat to groundwater quality because of the acidifying effect of CO2 dissolution in water. The consequences may be further worsening of the groundwater quality due to the mobilization of heavy metals. Buffer mechanisms counteracting the acidification are for instance the dissolution of carbonates. Carbonate dissolution kinetics is comparably fast and carbonates can be abundant in close-to-surface aquifers. The disadvantages of batch experiments compared to column experiments in order to determine rate constants are well known and have for instance been described by v. GRINSVEN and RIEMSDIJK (1992). Therefore, we have designed, developed, tested, and used a high-pressure laboratory column system to simulate aquifer conditions in a flow through setup within the CO2-MoPa project. The calcite dissolution kinetics was determined for CO2-pressures of 6, 10, and 50 bars. The results were evaluated by using the PHREEQC code with a 1-D reactive transport model, applying a LASAGA (1984) -type kinetic dissolution equation (PALANDRI and KHARAKA, 2004; eq. 7). While PALANDRI and KHARAKA (2004) gave calcite dissolution rate constants originating from batch experiments of log kacid = -0.3 and log kneutral = -5.81, the data of the column experiment were best fitted using log kacid = -2.3 and log kneutral = -7.81, so that the rate constants fitted using the lab experiment applying 50 bars pCO2 were approximately 100 times lower than according to the literature data. Rate constants of experiments performed at less CO2 pressure (pCO2 = 6 bars: log kacid = -1.78; log kneutral = -7.29) were only 30 times lower than literature data. These discrepancies in the

  2. Investigating dissolution of mechanically activated olivine for carbonation purposes

    International Nuclear Information System (INIS)

    Haug, Tove Anette; Kleiv, Rolf Arne; Munz, Ingrid Anne

    2010-01-01

    Research highlights: → Dissolution of mechanically activated olivine increased with 3 orders of magnitude. → Crystallinity changes of olivine is important for the observed dissolution rates. → Activation probably decreases with the degree of dissolution of each particle. - Abstract: Mineral carbonation is one of several alternatives for CO 2 sequestration and storage. The reaction rates of appropriate minerals with CO 2 , for instance olivine and serpentine with vast resources, are relatively slow in a CO 2 sequestration context and the rates have to be increased to make mineral carbonation a good storage alternative. Increasing the dissolution rate of olivine has been the focus of this paper. Olivine was milled with very high energy intensity using a laboratory planetary mill to investigate the effect of mechanical activation on the Mg extraction potential of olivine in 0.01 M HCl solution at room temperature and pressure. Approximately 30-40% of each sample was dissolved and water samples were taken at the end of each experiment. The pH change was used to calculate time series of the Mg concentrations, which also were compared to the final Mg concentrations in the water samples. Percentage dissolved and the specific reaction rates were estimated from the Mg concentration time series. The measured particle size distributions could not explain the rate constants found, but the specific surface area gave a good trend versus dissolution for samples milled wet and the samples milled with a small addition of water. The samples milled dry had the lowest measured specific surface areas ( 2 /g), but had the highest rate constants. The crystallinity calculated from X-ray diffractograms, was the material parameter with the best fit for the observed differences in the rate constants. Geochemical modelling of mechanically activated materials indicated that factors describing the changes in the material properties related to the activation must be included. The

  3. Kinetics of reductive bulk dissolution of lepidocrocite, ferrihydrite, and geothite

    DEFF Research Database (Denmark)

    Larsen, O.; Postma, Diederik Jan

    2001-01-01

    of the reduction experiments, lepidocrocite crystals were subsampled and the change in crystal habit and size distribution was studied by transmission electron microscopy. The rate of complete dissolution was described by the function J/m0 5 k9(m/m0)g where J is the overall rate of dissolution (mol/s), m0...... for lepidocrocite showed strong etch-pitting of the crystals parallel to the c-axis resulting ultimately in disintegration of the crystals. For the different iron oxides, the initial rate was independent of the specific surface area, emphasizing the importance of the crystal structure for the dissolution rate....... However, among the lepidocrocites the initial rate was proportional to the specific surface area. The exponent, g was found to vary from a value near 1.0 for one of the 2-line ferrihydrites, two of the lepidocrocites and the goethite, to values close to 2.3 for the other 2-line ferrihydrite and the 6-line...

  4. Dissolution properties of co-amorphous drug-amino acid formulations in buffer and biorelevant media.

    Science.gov (United States)

    Heikkinen, A T; DeClerck, L; Löbmann, K; Grohganz, H; Rades, T; Laitinen, R

    2015-07-01

    Co-amorphous formulations, particularly binary drug-amino acid mixtures, have been shown to provide enhanced dissolution for poorly-soluble drugs and improved physical stability of the amorphous state. However, to date the dissolution properties (mainly intrinsic dissolution rate) of the co-amorphous formulations have been tested only in buffers and their supersaturation ability remain unexplored. Consequently, dissolution studies in simulated intestinal fluids need to be conducted in order to better evaluate the potential of these systems in increasing the oral bioavailability of biopharmaceutics classification system class II drugs. In this study, solubility and dissolution properties of the co-amorphous simvastatin-lysine, gibenclamide-serine, glibenclamide-threonine and glibenclamide-serine-threonine were studied in phosphate buffer pH 7.2 and biorelevant media (fasted and fed state simulated intestinal fluids (FaSSIF and FeSSIF, respectively)). The co-amorphous formulations were found to provide a long-lasting supersaturation and improve the dissolution of the drugs compared to the crystalline and amorphous drugs alone in buffer. Similar improvement, but in lesser extent, was observed in biorelevant media suggesting that a dissolution advantage observed in aqueous buffers may overestimate the advantage in vivo. However, the results show that, in addition to stability advantage shown earlier, co-amorphous drug-amino acid formulations provide dissolution advantage over crystalline drugs in both aqueous and biorelevant conditions.

  5. Impact of dissolution on the sedimentary record of the Paleocene-Eocene thermal maximum

    Science.gov (United States)

    Bralower, Timothy J.; Kelly, D. Clay; Gibbs, Samantha; Farley, Kenneth; Eccles, Laurie; Lindemann, T. Logan; Smith, Gregory J.

    2014-09-01

    The input of massive amounts of carbon to the atmosphere and ocean at the Paleocene-Eocene Thermal Maximum (PETM; ˜55.53 Ma) resulted in pervasive carbonate dissolution at the seafloor. At many sites this dissolution also penetrated into the underlying sediment column. The magnitude of dissolution at and below the seafloor, a process known as chemical erosion, and its effect on the stratigraphy of the PETM, are notoriously difficult to constrain. Here, we illuminate the impact of dissolution by analyzing the complete spectrum of sedimentological grain sizes across the PETM at three deep-sea sites characterized by a range of bottom water dissolution intensity. We show that the grain size spectrum provides a measure of the sediment fraction lost during dissolution. We compare these data with dissolution and other proxy records, electron micrograph observations of samples and lithology. The complete data set indicates that the two sites with slower carbonate accumulation, and less active bioturbation, are characterized by significant chemical erosion. At the third site, higher carbonate accumulation rates, more active bioturbation, and possibly winnowing have limited the impacts of dissolution. However, grain size data suggest that bioturbation and winnowing were not sufficiently intense to diminish the fidelity of isotopic and microfossil assemblage records.

  6. Effect of alkali metal cations on anodic dissolution of gold in cyanide solutions. Potentiodynamic measurement

    International Nuclear Information System (INIS)

    Bek, R.Yu.; Rogozhnikov, N.A.; Kosolapov, G.V.

    1998-01-01

    It is shown that gold dissolution rate in cyanic solutions in Li + , Na + , K + , Cs + cation series increases basically and decreases under cation concentration increasing. Cation effect on current value is caused by cations drawing in dense layer. A model of dense part of double layer with two Helmholtz planes (anion and cation) is suggested. Effect of nature and concentration of alkali metal cations on gold dissolution rate is explained on the base of the model [ru

  7. DISSOLUTION OF LANTHANUM FLUORIDE PRECIPITATES

    Science.gov (United States)

    Fries, B.A.

    1959-11-10

    A plutonium separatory ore concentration procedure involving the use of a fluoride type of carrier is presented. An improvement is given in the derivation step in the process for plutonium recovery by carrier precipitation of plutonium values from solution with a lanthanum fluoride carrier precipitate and subsequent derivation from the resulting plutonium bearing carrier precipitate of an aqueous acidic plutonium-containing solution. The carrier precipitate is contacted with a concentrated aqueous solution of potassium carbonate to effect dissolution therein of at least a part of the precipitate, including the plutonium values. Any remaining precipitate is separated from the resulting solution and dissolves in an aqueous solution containing at least 20% by weight of potassium carbonate. The reacting solutions are combined, and an alkali metal hydroxide added to a concentration of at least 2N to precipitate lanthanum hydroxide concomitantly carrying plutonium values.

  8. Modeling of solution renewal with the Kindis code: example of R7T7 glass dissolution at 90 deg C

    International Nuclear Information System (INIS)

    Advocat, T.; Vernaz, E.; Crovisier, J.L.; Clement, A.; Gerard, F.

    1994-01-01

    The deep underground environment that would correspond to a geological repository is a system open to fluid flow. It is therefore necessary to investigate the effects of solution renewal on the long-term behavior of glass in contact with water. These effects can now be simulated using the new version of the geochemical KINDIS model (thermodynamic and kinetic model). We tested the model at 90 deg C with an SA/V ratio of 400 m -1 at twelve renewal rates of pure water ranging from 200 to 0 vol% per day. With renewal rates between 200 and 0.065 vol% per day, steady-state conditions were obtained in the reaction system: i.e. the glass corrosion rate remained constant as did the concentrations of the dissolved species in solution (although at different values depending on the renewal rate). The ionic strength never exceeded 1 (the validity limit for the DEBYE-HUCKEL law) and long term predictions of the dissolved glass mass, the solution composition and the potential secondary mineral sequence are possible. For simulated renewal rates of less than 0.065 vol% per day (27% per year), the ionic strength rose above 1 (as in a closed system) before steady-state conditions were reached, making it critical to calculate long-term rates; A constant and empirical long-term rate, derived from laboratory measurement, have to be extrapolated. These calculations were based on a first order equation to describe the glass dissolution kinetic. The results obtained with the KINDIS code show discrepancies with some major experimental kinetic data (the long term rate must decrease with the ''glass-water'' reaction progress, under silica saturation conditions). This clearly indicates that a more refine kinetic relation is needed for the glass matrix. (authors). 16 refs., 4 figs., 4 tabs

  9. An autoclave system for uranium oxide dissolution experiments

    International Nuclear Information System (INIS)

    Nykyri, Mikko

    1985-05-01

    According to the decision in principle of the Council of State of Finland the nuclear energy producers must provide preparedness for carrying out the final disposal of spent nuclear fuel in Finland. By the present principal concept the spent fuel will be disposed deep into the granitic bedrock. A parameter needed by risk analysis models is the dissolution rate of the uranium oxide matrix in the fuel pellets. In order to approach conditions prevailing deep in the groundwater, and autoclave system for dissolution experiments was developed at the Technical Research Centre of Finland. The low oxygen content and high pressure at elevated temperatures are simulated in the system. 20 MPa and 100 deg C are the upper operation limits of pressure and temperature. Water can be changed in the experiment autoclave without remarkable pressure and temperature variations. This has been arranged by using three pressure vessels: a supply vessel, a dissolution vessel and a depletion vessel. The extreme vessels serve pressure balancing purposes during water exchange. The water is deoxygenated during a preparation phase in the supply vessel by flushing it with nitrogen gas. Polytetrafluoroethylene is the principal material in contact with the water. A redox electrode couple was developed for potential measurements inside the dissolution vessel. The reference electrode is of Ag/AgCl-type with saturated KC1 electrolyte. A platinum wire operates as a measuring electrode

  10. Emotional and Cognitive Coping in Relationship Dissolution

    Science.gov (United States)

    Wrape, Elizabeth R.; Jenkins, Sharon Rae; Callahan, Jennifer L.; Nowlin, Rachel B.

    2016-01-01

    Dissolution of a romantic relationship can adversely affect functioning among college students and represents one primary reason for seeking campus counseling. This study examined the associations among common coping strategies and distress following relationship dissolution. Avoidance and repetitive negative thinking (RNT) were significantly…

  11. Colloid-facilitated effects on migration of radionuclides in fractured rock with a kinetic solubility-limited dissolution model

    International Nuclear Information System (INIS)

    Jen Chunping; Tien Nengchuan

    2010-01-01

    Nuclides can move with groundwater either as solutes or colloids, where the latter mechanism generally results in much shorter traveling time as the nuclides interact strongly with solid phases, such as actinides. In the performance assessment, it is therefore essential to assess the relative importance of these two transport mechanisms for different nuclides. The relative importance of colloids depends on the nature and concentration of the colloids in groundwater. Plutonium (Pu), neptunium (Np), uranium (U) and americium (Am) are four nuclides of concern for the long-term emplacement of nuclear wastes at potential repository sites. These four actinides have a high potential for migrating if attached to iron oxide, clay or silica colloids in the groundwater.Strong sorption of the actinides by colloids in the groundwater may facilitate the transport of these nuclides along potential flow paths. The solubility-limited dissolution model can be used to assess the safety of the release of nuclear waste in geological disposal sites. Usually, it has been assumed that the solubility of the waste form is constant. If a nuclide reaches its solubility limit at an inner location near the waste form, it is unlikely that the same nuclide will reach its solubility limit at an outer location unless this nuclide has a parent nuclide. It is unlikely that the daughter nuclides will exceed their solubility limit due to decay of their parent nuclide. The present study investigates the effect of colloids on the transport of solubility-limited nuclides under the kinetic solubility-limited dissolution (KSLD) boundary condition in fractured media. The release rate of the nuclides is proportional to the difference between the saturation concentration and the inlet aqueous concentration of the nuclides. The presence of colloids decreases the aqueous concentration of nuclides and, thus, increases the release flux of nuclides from the waste form. (authors)

  12. An oral delivery system for indomethicin engineered from cationic lipid emulsions and silica nanoparticles

    DEFF Research Database (Denmark)

    Simovic, Spomenka; Hui, He; Song, Yunmei

    2010-01-01

    We report on a porous silica-lipid hybrid microcapsule (SLH) oral delivery system for indomethacin fabricated from Pickering emulsion templates, where the drug forms an electrostatic complex with cationic lipid present in the oil phase. Dry SLH microcapsules prepared either by spray drying...... (approximately 1-5 microm) or phase coacervation (20-50 microm) exhibit a specific internal porous matrix structure with pore diameters in the range of 20 to 100 nm. Dissolution studies under sink conditions and in the presence of electrolytes revealed a decreased extent of dissolution; this confirms...

  13. Determination of respirable-sized crystalline silica in different ambient environments in the United Kingdom with a mobile high flow rate sampler utilising porous foams to achieve the required particle size selection

    Science.gov (United States)

    Stacey, Peter; Thorpe, Andrew; Roberts, Paul; Butler, Owen

    2018-06-01

    Inhalation of respirable crystalline silica (RCS) can cause diseases including silicosis and cancer. Levels of RCS close to an emission source are measured but little is known about the wider ambient exposure from industry emissions or natural sources. The aim of this work is to report the RCS concentrations obtained from a variety of ambient environments using a new mobile respirable (PM4) sampler. A mobile battery powered high flow rate (52 L min-1) sampler was developed and evaluated for particulate aerosol sampling employing foams to select the respirable particle size fraction. Sampling was conducted in the United Kingdom at site boundaries surrounding seven urban construction and demolition and five sand quarry sites. These are compared with data from twelve urban aerosol samples and from repeat measurements from a base line study at a single rural site. The 50% particle size penetration (d50) through the foam was 4.3 μm. Over 85% of predict bias values were with ±10% of the respirable convention, which is based on a log normal curve. Results for RCS from all construction and quarry activities are generally low with a 95 th percentile of 11 μg m-3. Eighty percent of results were less than the health benchmark value of 3 μg m-3 used in some states in America for ambient concentrations. The power cutting of brick and the largest demolition activities gave the highest construction levels. Measured urban background RCS levels were typically below 0.3 μg m-3 and the median RCS level, at a rural background location, was 0.02 μg m-3. These reported ambient RCS concentrations may provide useful baseline values to assess the wider impact of fugitive, RCS containing, dust emissions into the wider environment.

  14. Dissolution of B-doped S1(100) layers in NaOH aqueous solutions

    International Nuclear Information System (INIS)

    Akhter, P.; Baig, A.; Mufti, A.

    1988-12-01

    NaOH solution has been used to study the dissolution rates of boron doped Sl(100) wafers as a function of solution normality (0.02 N to 15 N) and temperature in the range of 30 deg. C to boiling point. For a dissolution at boiling point, two distinctive ranges of solution normalities have been observed. For N ≤ 4.5, the dissolution rate increases logarithmically and is defect dependent. For higher values of N ≥ 4.5 normal, the dissolution rate becomes a linear function of normality and reaction is defect dependent. The reaction activation energy has been measured equal to 0.65 +- 0.03 eV. (author). 7 refs, 5 figs

  15. Accelerated dissolution of iron oxides in ice

    Directory of Open Access Journals (Sweden)

    D. Jeong

    2012-11-01

    Full Text Available Iron dissolution from mineral dusts and soil particles is vital as a source of bioavailable iron in various environmental media. In this work, the dissolution of iron oxide particles trapped in ice was investigated as a new pathway of iron supply. The dissolution experiments were carried out in the absence and presence of various organic complexing ligands under dark condition. In acidic pH conditions (pH 2, 3, and 4, the dissolution of iron oxides was greatly enhanced in the ice phase compared to that in water. The dissolved iron was mainly in the ferric form, which indicates that the dissolution is not a reductive process. The extent of dissolved iron was greatly affected by the kind of organic complexing ligands and the surface area of iron oxides. The iron dissolution was most pronounced with high surface area iron oxides and in the presence of strong iron binding ligands. The enhanced dissolution of iron oxides in ice is mainly ascribed to the "freeze concentration effect", which concentrates iron oxide particles, organic ligands, and protons in the liquid like ice grain boundary region and accelerates the dissolution of iron oxides. The ice-enhanced dissolution effect gradually decreased when decreasing the freezing temperature from −10 to −196 °C, which implies that the presence and formation of the liquid-like ice grain boundary region play a critical role. The proposed phenomenon of enhanced dissolution of iron oxides in ice may provide a new pathway of bioavailable iron production. The frozen atmospheric ice with iron-containing dust particles in the upper atmosphere thaws upon descending and may provide bioavailable iron upon deposition onto the ocean surface.

  16. In vitro effects of cisplatin-functionalized silica nanoparticles on chondrocytes

    Energy Technology Data Exchange (ETDEWEB)

    Bhowmick, Tridib Kumar; Yoon, Diana [University of Maryland, Department of Chemical and Biomolecular Engineering (United States); Patel, Minal; Fisher, John [University of Maryland, Fischell Department of Bioengineering (United States); Ehrman, Sheryl, E-mail: sehrman@umd.ed [University of Maryland, Department of Chemical and Biomolecular Engineering (United States)

    2010-10-15

    In this study, we evaluated the combined effect of a known toxic molecule, cisplatin, in combination with relatively nontoxic nanoparticles, amorphous fumed silica, on chondrocyte cells. Cisplatin was attached to silica nanoparticles using aminopropyltriethoxy silane as a linker molecule, and characterized in terms of size, shape, specific surface area, as well as the dissolution of cisplatin from the silica surface. The primary particle diameter of the as-received silica nanoparticles ranged from 7.1 to 61 nm, estimated from measurements of specific surface area, and the primary particles were aggregated. The effects of cisplatin-functionalized silica particles with different specific surface areas (41, 85, 202, 237, and 297 m{sup 2}/g) were compared in vitro on chondrocytes, the parenchymal cell of hyaline cartilage. The results show that adverse effects on cell function, as evidenced by reduced metabolic activity measured by the MTT assay and increased membrane permeability observed using the Live/Dead stain, can be correlated with specific surface area of the silica. Cisplatin-functionalized silica nanoparticles with the highest specific surface area incited the greatest response, which was almost equivalent to that induced by free cisplatin. This result suggests the importance of particle specific surface area in interactions between cells and surface-functionalized nanomaterials.

  17. In vitro effects of cisplatin-functionalized silica nanoparticles on chondrocytes

    Science.gov (United States)

    Bhowmick, Tridib Kumar; Yoon, Diana; Patel, Minal; Fisher, John; Ehrman, Sheryl

    2010-10-01

    In this study, we evaluated the combined effect of a known toxic molecule, cisplatin, in combination with relatively nontoxic nanoparticles, amorphous fumed silica, on chondrocyte cells. Cisplatin was attached to silica nanoparticles using aminopropyltriethoxy silane as a linker molecule, and characterized in terms of size, shape, specific surface area, as well as the dissolution of cisplatin from the silica surface. The primary particle diameter of the as-received silica nanoparticles ranged from 7.1 to 61 nm, estimated from measurements of specific surface area, and the primary particles were aggregated. The effects of cisplatin-functionalized silica particles with different specific surface areas (41, 85, 202, 237, and 297 m2/g) were compared in vitro on chondrocytes, the parenchymal cell of hyaline cartilage. The results show that adverse effects on cell function, as evidenced by reduced metabolic activity measured by the MTT assay and increased membrane permeability observed using the Live/Dead stain, can be correlated with specific surface area of the silica. Cisplatin-functionalized silica nanoparticles with the highest specific surface area incited the greatest response, which was almost equivalent to that induced by free cisplatin. This result suggests the importance of particle specific surface area in interactions between cells and surface-functionalized nanomaterials.

  18. The influence of milling on the dissolution performance of simvastatin

    DEFF Research Database (Denmark)

    Zimper, Ulrike; Aaltonen, Jaakko; Krauel-Goellner, Karen

    2012-01-01

    properties such as solubility and dissolution rate and, therefore, process induced solid state modifications need to be monitored. The aim of this study was two-fold: firstly, to investigate the dissolution rates of milled and unmilled simvastatin; and secondly, to screen for the main milling factors......, as well as factor interactions in a dry ball milling process using simvastatin as model drug, and to optimize the milling procedure with regard to the opposing responses particle size and process induced disorder by application of a central composite face centered design. Particle size was assessed...... by scanning electron microscopy (SEM) and image analysis. Process induced disorder was determined by partial least squares (PLS) regression modeling of respective X-ray powder diffractograms (XRPD) and Raman spectra. Valid and significant quadratic models were built. The investigated milling factors were...

  19. Development of simulation code for MOX dissolution using silver-mediated electrochemical method (Contract research)

    Energy Technology Data Exchange (ETDEWEB)

    Kida, Takashi; Umeda, Miki; Sugikawa, Susumu [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    2003-03-01

    MOX dissolution using silver-mediated electrochemical method will be employed for the preparation of plutonium nitrate solution in the criticality safety experiments in the Nuclear Fuel Cycle Safety Engineering Research Facility (NUCEF). A simulation code for the MOX dissolution has been developed for the operating support. The present report describes the outline of the simulation code, a comparison with the experimental data and a parameter study on the MOX dissolution. The principle of this code is based on the Zundelevich's model for PuO{sub 2} dissolution using Ag(II). The influence of nitrous acid on the material balance of Ag(II) is taken into consideration and the surface area of MOX powder is evaluated by particle size distribution in this model. The comparison with experimental data was carried out to confirm the validity of this model. It was confirmed that the behavior of MOX dissolution could adequately be simulated using an appropriate MOX dissolution rate constant. It was found from the result of parameter studies that MOX particle size was major governing factor on the dissolution rate. (author)

  20. Rapid and gradual modes of aerosol trace metal dissolution in seawater

    Directory of Open Access Journals (Sweden)

    Katherine Rose Marie Mackey

    2015-01-01

    Full Text Available Atmospheric deposition is a major source of trace metals in marine surface waters and supplies vital micronutrients to phytoplankton, yet measured aerosol trace metal solubility values are operationally defined and there are relatively few multi-element studies on aerosol-metal solubility in seawater. Here we measure the solubility of aluminum (Al, cadmium (Cd, cobalt (Co, copper (Cu, iron (Fe, manganese (Mn, nickel (Ni, lead (Pb, and zinc (Zn from natural aerosol samples in seawater over a 7 day period to (1 evaluate the role of extraction time in trace metal dissolution behavior and (2 explore how the individual dissolution patterns could influence biota. Dissolution behavior occurs over a continuum ranging from rapid dissolution, in which the majority of soluble metal dissolved immediately upon seawater exposure (Cd and Co in our samples, to gradual dissolution, where metals dissolved slowly over time (Zn, Mn, Cu, and Al in our samples. Additionally, dissolution affected by interactions with particles was observed in which a decline in soluble metal concentration over time occurred (Fe and Pb in our samples. Natural variability in aerosol chemistry between samples can cause metals to display different dissolution kinetics in different samples, and this was particularly evident for Ni, for which samples showed a broad range of dissolution rates. The elemental molar ratio of metals in the bulk aerosols was 23,189Fe: 22,651Al: 445Mn: 348Zn: 71Cu: 48Ni: 23Pb: 9Co: 1Cd, whereas the seawater soluble molar ratio after 7 days of leaching was 11Fe: 620Al: 205Mn: 240Zn: 20Cu: 14Ni: 9Pb: 2Co: 1Cd. The different kinetics and ratios of aerosol metal dissolution have implications for phytoplankton nutrition, and highlight the need for unified extraction protocols that simulate aerosol metal dissolution in the surface ocean.

  1. Diatom species abundance and morphologically-based dissolution proxies in coastal Southern Ocean assemblages

    Science.gov (United States)

    Warnock, Jonathan P.; Scherer, Reed P.

    2015-07-01

    Taphonomic processes alter diatom assemblages in sediments, thus potentially negatively impacting paleoclimate records at various rates across space, time, and taxa. However, quantitative taphonomic data is rarely included in diatom-based paleoenvironmental reconstructions and no objective standard exists for comparing diatom dissolution in sediments recovered from marine depositional settings, including the Southern Ocean's opal belt. Furthermore, identifying changes to diatom dissolution through time can provide insight into the efficiency of both upper water column nutrient recycling and the biological pump. This is significant in that reactive metal proxies (e.g. Al, Ti) in the sediments only account for post-depositional dissolution, not the water column where the majority of dissolution occurs. In order to assess the range of variability of responses to dissolution in a typical Southern Ocean diatom community and provide a quantitative guideline for assessing taphonomic variability in diatoms recovered from core material, a sediment trap sample was subjected to controlled, serial dissolution. By evaluating dissolution-induced changes to diatom species' relative abundance, three preservational categories of diatoms have been identified: gracile, intermediate, and robust. The relative abundances of these categories can be used to establish a preservation grade for diatom assemblages. However, changes to the relative abundances of diatom species in sediment samples may reflect taphonomic or ecological factors. In order to address this complication, relative abundance changes have been tied to dissolution-induced morphological change to the areolae of Fragilariopsis curta, a significant sea-ice indicator in Southern Ocean sediments. This correlation allows differentiation between gracile species loss to dissolution versus ecological factors or sediment winnowing. These results mirror a similar morphological dissolution index from a parallel study utilizing

  2. Sex Preferences, Marital Dissolution and the Economic Status of Women

    OpenAIRE

    Bedard, Kelly; Deschenes, Olivier

    2003-01-01

    The rise in the divorce rate over the past 40 years is one of the fundamental changes in American society. A seemingly ever-increasing number of women and children spend some fraction of their life in single female-headed households, leading many to be concerned about the economic circumstances of these women their and children. Estimating the cause-to-effect relationship between marital dissolution and female economic status is complicated because the same factors that increase marital insta...

  3. The effect of fuel chemistry on UO{sub 2} dissolution

    Energy Technology Data Exchange (ETDEWEB)

    Casella, Amanda, E-mail: amanda.casella@pnnl.gov [Pacific Northwest National Laboratory, PO Box 999, MSIN P7-25, Richland, WA 99352 (United States); Hanson, Brady, E-mail: brady.hanson@pnnl.gov [Pacific Northwest National Laboratory, PO Box 999, MSIN P7-27, Richland, WA 99352 (United States); Miller, William [University of Missouri Research Reactor, 1513 Research Park Drive, Columbia, MO 65211 (United States)

    2016-08-01

    The dissolution rate of both unirradiated UO{sub 2} and used nuclear fuel has been studied by numerous countries as part of the performance assessment of proposed geologic repositories. In the scenario of waste package failure and groundwater contact with the fuel, the effects of variables such as temperature, dissolved oxygen, and water and fuel chemistry on the dissolution rates of the fuel are necessary to provide a quantitative estimate of the potential release over geologic time frames. The primary objective of this research was to determine the influence these parameters, with primary focus on the fuel chemistry, have on the dissolution rate of unirradiated UO{sub 2} under oxidizing repository conditions and compare them to the rates predicted by current dissolution models. Both unirradiated UO{sub 2} and UO{sub 2} doped with varying concentrations of Gd{sub 2}O{sub 3}, to simulate used fuel composition after long time periods when radiolysis has minor contributions to dissolution, were examined. In general, a rise in temperature increased the dissolution rate of UO{sub 2} and had a larger effect on pure UO{sub 2} than on those doped with Gd{sub 2}O{sub 3}. Oxygen dependence was observed in the UO{sub 2} samples with no dopant and increased as the temperature rose; in the doped fuels less dependence was observed. The addition of gadolinia into the UO{sub 2} matrix resulted in a significant decrease in the dissolution rate. The matrix stabilization effect resulting from the dopant proved even more beneficial in lowering the dissolution rate at higher temperatures and dissolved O{sub 2} concentrations in the leachate where the rates would typically be elevated. - Highlights: • UO{sub 2} dissolution rates were measured for a matrix of repository relevant conditions. • Dopants in the UO{sub 2} matrix lowered the dissolution rate. • Reduction in rates by dopants were increased at elevated temperature and O{sub 2} levels. • UO{sub 2} may be overly

  4. Silica removal in industrial effluents with high silica content and low hardness.

    Science.gov (United States)

    Latour, Isabel; Miranda, Ruben; Blanco, Angeles

    2014-01-01

    High silica content of de-inked paper mill effluents is limiting their regeneration and reuse after membrane treatments such as reverse osmosis (RO). Silica removal during softening processes is a common treatment; however, the effluent from the paper mill studied has a low hardness content, which makes the addition of magnesium compounds necessary to increase silica removal. Two soluble magnesium compounds (MgCl₂∙6H₂O and MgSO₄∙7H₂O) were tested at five dosages (250-1,500 mg/L) and different initial pH values. High removal rates (80-90%) were obtained with both products at the highest pH tested (11.5). With these removal efficiencies, it is possible to work at high RO recoveries (75-85%) without silica scaling. Although pH regulation significantly increased the conductivity of the waters (at pH 11.5 from 2.1 to 3.7-4.0 mS/cm), this could be partially solved by using Ca(OH)₂ instead of NaOH as pH regulator (final conductivity around 3.0 mS/cm). Maximum chemical oxygen demand (COD) removal obtained with caustic soda was lower than with lime (15 vs. 30%). Additionally, the combined use of a polyaluminum coagulant during the softening process was studied; the coagulant, however, did not significantly improve silica removal, obtaining a maximum increase of only 10%.

  5. Enhancement of carbon dioxide reduction and methane production by an obligate anaerobe and gas dissolution device.

    Science.gov (United States)

    Kim, Seungjin; Choi, Kwangkeun; Kim, Jong-Oh; Chung, Jinwook

    2016-01-25

    The use of gas dissolution devices to improve the efficiency of H2 dissolution has enhanced CO2 reduction and CH4 production. In addition, the nutrients that initially existed in anaerobic sludge were exhausted over time, and the activities of anaerobic microorganisms declined. When nutrients were artificially injected, CO2 reduction and CH4 production rates climbed. Thus, assuming that the activity of the obligatory anaerobic microorganisms is maintained, a gas dissolution device will further enhance the efficiency of CO2 reduction and CH4 production. Copyright © 2015 Elsevier B.V. All rights reserved.

  6. Attenuation of glass dissolution in the presence of natural additives

    Energy Technology Data Exchange (ETDEWEB)

    Sang, Jing C.; Barkatt, Aaron [Department of Chemistry, The Catholic University of America, Washington, DC (United States); O`Keefe, John A. [National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, MD (United States)

    1996-11-01

    The dissolution kinetics of silicate glasses in aqueous environments in systems which included a variety of natural crystalline solids in addition to the glass itself and the aqueous phase are reported. The results demonstrate the possibility of a dramatic decrease in the rate of dissolution of silicate glass in the presence of certain varieties of olivine-based materials. This decrease in dissolution rate was shown to be due to the fact that these additives consist mostly of Mg-based material but also contain minor amounts of Al and Ca. The combined presence of Mg with these minor species affected the corrosion rate of the glass as a whole, including its most soluble components such as boron. This study has potentially important implications to the durability of glasses exposed to natural environments. The results may be relevant to the use of active backfill materials in burial sites for nuclear waste glasses, as well as to better understanding of the environmental degradation of natural and ancient glasses.

  7. Silica particles and method of preparation thereof

    NARCIS (Netherlands)

    2015-01-01

    The invention is in the field of silica products. More in particular, the invention is in the field of amorphous silica particles. The invention is directed to amorphous silica particles and related products including clusters of said silica particles, a suspension of said silica particles, and an

  8. Mechanistic Basis of Cocrystal Dissolution Advantage.

    Science.gov (United States)

    Cao, Fengjuan; Amidon, Gordon L; Rodríguez-Hornedo, Naír; Amidon, Gregory E

    2018-01-01

    Current interest in cocrystal development resides in the advantages that the cocrystal may have in solubility and dissolution compared with the parent drug. This work provides a mechanistic analysis and comparison of the dissolution behavior of carbamazepine (CBZ) and its 2 cocrystals, carbamazepine-saccharin (CBZ-SAC) and carbamazepine-salicylic acid (CBZ-SLC) under the influence of pH and micellar solubilization. A simple mathematical equation is derived based on the mass transport analyses to describe the dissolution advantage of cocrystals. The dissolution advantage is the ratio of the cocrystal flux to drug flux and is defined as the solubility advantage (cocrystal to drug solubility ratio) times the diffusivity advantage (cocrystal to drug diffusivity ratio). In this work, the effective diffusivity of CBZ in the presence of surfactant was determined to be different and less than those of the cocrystals. The higher effective diffusivity of drug from the dissolved cocrystals, the diffusivity advantage, can impart a dissolution advantage to cocrystals with lower solubility than the parent drug while still maintaining thermodynamic stability. Dissolution conditions where cocrystals can display both thermodynamic stability and a dissolution advantage can be obtained from the mass transport models, and this information is useful for both cocrystal selection and formulation development. Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  9. Dissolution Dominating Calcification Process in Polar Pteropods Close to the Point of Aragonite Undersaturation

    Science.gov (United States)

    Bednaršek, Nina; Tarling, Geraint A.; Bakker, Dorothee C. E.; Fielding, Sophie; Feely, Richard A.

    2014-01-01

    Thecosome pteropods are abundant upper-ocean zooplankton that build aragonite shells. Ocean acidification results in the lowering of aragonite saturation levels in the surface layers, and several incubation studies have shown that rates of calcification in these organisms decrease as a result. This study provides a weight-specific net calcification rate function for thecosome pteropods that includes both rates of dissolution and calcification over a range of plausible future aragonite saturation states (Ωar). We measured gross dissolution in the pteropod Limacina helicina antarctica in the Scotia Sea (Southern Ocean) by incubating living specimens across a range of aragonite saturation states for a maximum of 14 days. Specimens started dissolving almost immediately upon exposure to undersaturated conditions (Ωar∼0.8), losing 1.4% of shell mass per day. The observed rate of gross dissolution was different from that predicted by rate law kinetics of aragonite dissolution, in being higher at Ωar levels slightly above 1 and lower at Ωar levels of between 1 and 0.8. This indicates that shell mass is affected by even transitional levels of saturation, but there is, nevertheless, some partial means of protection for shells when in undersaturated conditions. A function for gross dissolution against Ωar derived from the present observations was compared to a function for gross calcification derived by a different study, and showed that dissolution became the dominating process even at Ωar levels close to 1, with net shell growth ceasing at an Ωar of 1.03. Gross dissolution increasingly dominated net change in shell mass as saturation levels decreased below 1. As well as influencing their viability, such dissolution of pteropod shells in the surface layers will result in slower sinking velocities and decreased carbon and carbonate fluxes to the deep ocean. PMID:25285916

  10. Chemical dissolution of sulfide minerals

    Science.gov (United States)

    Chao, T.T.; Sanzolone, R.F.

    1977-01-01

    Chemical dissolution treatments involving the use of aqua regia, 4 N HNO3, H2O2-ascorbic acid, oxalic acid, KClO3+HCl, and KClO3+HCl followed by 4 N HNO3 were applied to specimens of nine common sulfide minerals (galena, chalcopyrite, cinnabar, molybdenite, orpiment, pyrite, stibnite, sphalerite, and tetrahedrite) mixed individually with a clay loam soil. The resultant decrease in the total sulfur content of the mixture, as determined by using the Leco induction furnace, was used to evaluate the effectiveness of each chemical treatment. A combination of KClO3+HCl followed by 4 N HNO3 boiling gently for 20 min has been shown to be very effective in dissolving all the sulfide minerals. This treatment is recommended to dissolve metals residing in sulfide minerals admixed with secondary weathering products, as one step in a fractionation scheme whereby metals in soluble and adsorbed forms, and those associated with organic materials and secondary oxides, are first removed by other chemical extractants.

  11. Dissolution kinetics of purified and synthetic smectites at 25°C and PH∼9

    International Nuclear Information System (INIS)

    Marty, Nicolas C.M.; Tournassat, Christophe; Gaucher, Eric C.; Chino, Daisuke; Sato, Tsutomu; Villieras, Frederic; Giffaut, Eric; Cama, Jordi; Soler, J.M.

    2010-01-01

    Document available in extended abstract form only. Mineral rate laws that account for the kinetics of dissolution/precipitation of clays and other minerals are used in reactive transport codes to simulate and evaluate the evolution of geochemical conditions in the near-field of high level radioactive waste (HLW) in deep geological repositories. Smectite is the main component in the compacted bentonite used in the Multi-barrier system to lower permeability. As a consequence, molecular diffusion becomes the main mechanism of mass transport, and dissolution and precipitation reactions take place in close-to-equilibrium conditions. Nonetheless, in the reactive transport codes, databases utilized mainly incorporate rate laws derived at far-from- equilibrium conditions, which are not representative of near-field and far-field conditions of concrete-clay or iron-clay interfaces. Hence, there is an important need to derive kinetic rate laws that allow extrapolation of mineral dissolution/precipitation as a function of the solution saturation state (i.e., Gibbs free energy, ΔG r ). Once the effect of the environmental variables, such as pH, T and ΔG r , etc. exert on smectite dissolution is discerned, evaluation of the evolution of geochemical conditions in the HLW repository is carried out using reactive transport codes that couple the rate laws with transport equations. Several studies related dissolution of natural smectites with pH, and just a few dealt with the rate dependency on Gibbs free energy. The present study aims at estimating dissolution rates of montmorillonite in conditions as close as possible to those expected in the Callovo-Oxfordian formation, i.e. pH∼7.2 and 25 deg. C. Dissolution kinetics of two montmorillonites (natural Na-montmorillonite purified from MX80 and synthetic smectite) were investigated by means of flow-through experiments and solution-chemistry data obtained. The calculated rates were based on release of Si, Al and Mg and normalized

  12. Dissolution of metallic uranium in alkalis

    International Nuclear Information System (INIS)

    Mondino, Angel V.; Wilkinson, Maria V.; Manzini, Alberto C.

    1999-01-01

    The dissolution of U metallic foils has been studied in the framework of the development of an improved 99 Mo-production process. The best conditions for the dissolution of uranium foils of approximately 150 μm are the following: a) NaClO concentrations of 0.20 and 0.23 M with NaOH of 0.27 and 0.31 M respectively; b) temperature of the solution, 70 C degrees; c) volume of the solution, 15 ml / cm 2 of uranium foil; d) dissolution time, 30 minutes. (author)

  13. Dissolution studies of spent nuclear fuels

    International Nuclear Information System (INIS)

    1991-02-01

    To obtain quantitative data on the dissolution of high burnup spent nuclear fuel, dissolution study have been carried out at the Department of Chemistry, JAERI, from 1984 under the contract with STA entitled 'Reprocessing Test Study of High Burnup Fuel'. In this study PWR spent fuels of 8,400 to 36,100 MWd/t in averaged burnup were dissolved and the chemical composition and distribution of radioactive nuclides were measured for insoluble residue, cladding material (hull), off-gas and dissolved solution. With these analyses basic data concerning the dissolution and clarification process in the reprocessing plant were accumulated. (author)

  14. Preparation of chromous complexes and their effect on the dissolution of ferrites and chromites

    International Nuclear Information System (INIS)

    Sathyaseelan, V.S.; Rufus, A.L.; Velmurugan, S.; Pavithra, E.

    2012-09-01

    Decontamination of reactor coolant circuits is inevitable in minimising radiation exposure hazard especially during maintenance. Dilute chemical decontamination processes involving organic complexing agents viz., EDTA or NTA along with reducing agents such as ascorbic acid or oxalic acid are quite effective in dissolving magnetite, the predominant corrosion product oxide in carbon steel systems viz., PHWRs. However, dissolution of hematite, mixed ferrites and chromites found in stainless steel systems of BWRs and PWRs are not that easy to dissolve. A two-step process involving oxidation and reduction processes is required to dissolve these oxides. Studies were carried out to develop a single step process. Our earlier studies on high temperature decontamination at 160 deg. C have showed improved dissolution of magnetite, nickel ferrite and other oxides. In the present study, attempt has been made to carry out the oxide dissolution in formulations containing strong reducing agents such as chromous complexes. Dissolution of hematite is very effective under reducing conditions. Addition of ascorbic acid to the formulation containing EDTA and citric acid (EC) enhanced the kinetics 20 folds, while the addition of Cr (II)-EDTA to EC formulation increased the rate 100 folds. In the case of formulation containing NTA and citric acid (NC), the addition of chromous-NTA increased the rate 14 folds. NiFe 2 O 4 showed hardly any dissolution in EC formulation. However, in EAC (formulation containing EDTA, citric acid and ascorbic acid), the rate constant for the dissolution was 1.2x10 -3 min -1 , while it was 8.5x10 -3 min -1 in the case of ECCr (EDTA, citric acid containing chromous ions) formulation. In NTA based formulations also, dissolution rate was found to be enhanced in the presence of chromous ions. Further, there was no preferential dissolution of either Fe or Ni by both EDTA and NTA based formulations and also the rate of dissolution was found to depend linearly on the

  15. CHARACTERIZATION AND ALUMINUM DISSOLUTION DEMONSTRATION WITH A 3 LITER TANK 51H SAMPLE

    International Nuclear Information System (INIS)

    Hay, M; John Pareizs, J; Cj Bannochie, C; Michael Stone, M; Damon Click, D; Daniel McCabe, D

    2008-01-01

    A 3-liter sludge slurry sample was sent to SRNL for demonstration of a low temperature aluminum dissolution process. The sludge was characterized before and after the aluminum dissolution. Post aluminum dissolution sludge settling and the stability of the decanted supernate were also observed. The characterization of the as-received 3-liter sample of Tank 51H sludge slurry shows a typical high aluminum HM sludge. The XRD analysis of the dried solids indicates Boehmite is the predominant crystalline form of aluminum in the sludge solids. However, amorphous phases of aluminum present in the sludge would not be identified using this analytical technique. The low temperature (55 C) aluminum dissolution process was effective at dissolving aluminum from the sludge. Over the three week test, ∼42% of the aluminum was dissolved out of the sludge solids. The process appears to be selective for aluminum with no other metals dissolving to any appreciable extent. At the termination of the three week test, the aluminum concentration in the supernate had not leveled off indicating more aluminum could be dissolved from the sludge with longer contact times or higher temperatures. The slow aluminum dissolution rate in the test may indicate the dissolution of the Boehmite form of aluminum however; insufficient kinetic data exists to confirm this hypothesis. The aluminum dissolution process appears to have minimal impact on the settling rate of the post aluminum dissolution sludge. However, limited settling data were generated during the test to quantify the effects. The sludge settling was complete after approximately twelve days. The supernate decanted from the settled sludge after aluminum dissolution appears stable and did not precipitate aluminum over the course of several months. A mixture of the decanted supernate with Tank 11 simulated supernate was also stable with respect to precipitation

  16. In situ measurement of solvent-mediated phase transformations during dissolution testing

    DEFF Research Database (Denmark)

    Aaltonen, Jaakko; Heinänen, Paula; Peltonen, Leena

    2006-01-01

    In this study, solvent-mediated phase transformations of theophylline (TP) and nitrofurantoin (NF) were measured in a channel flow intrinsic dissolution test system. The test set-up comprised simultaneous measurement of drug concentration in the dissolution medium (with UV-Vis spectrophotometry......) and measurement of the solid-state form of the dissolving solid (in situ with Raman spectroscopy). The solid phase transformations were also investigated off-line with scanning electron microscopy. TP anhydrate underwent a transformation to TP monohydrate, and NF anhydrate (form beta) to NF monohydrate (form II......). Transformation of TP anhydrate to TP monohydrate resulted in a clear decrease in the dissolution rate, while the transformation of NF anhydrate (form beta) to NF monohydrate (form II) could not be linked as clearly to changes in the dissolution rate. The transformation of TP was an order of magnitude faster than...

  17. Modeling of UO2 aqueous dissolution over a wide range of conditions

    International Nuclear Information System (INIS)

    Steward, S.A.; Weed, H.C.

    1993-11-01

    Previously it was not possible to predict reliably the rate at which spent fuel would react with groundwater because of conflicting data in the literature. The dissolution of the UO 2 spent fuel matrix is a necessary step for aqueous release of radioactive fission products. Statistical experimental design was used to plan a set of UO 2 dissolution experiments to examine systematically the effects of temperature (25--75C), dissolved oxygen (0.002--0.2 atm overpressure), pH (8--10) and carbonate (2-200x10 -4 molar) concentrations on UO 2 dissolution. The average uranium dissolution rate was 4.3 mg/m 2 /day. The regression fit of the data indicate an Arrhenius type activation energy of 8750 cal/mol and a half-power dependence on dissolved oxygen in the simulated groundwater

  18. Surface studies of feldspar dissolution using surface replication combined with electron microscopic and spectroscopic techniques

    Energy Technology Data Exchange (ETDEWEB)

    Fung, P C [Petro-Canada, Calgary, Alberta; Sanipelli, G G

    1982-04-01

    The replica of a microcline cleavage surface was examined before and at various stages of interaction with water and acid solutions at 70/sup 0/C, as part of basic geochemical research for the Canadian Nuclear Fuel Waste Management Program to investigate the feasibility of disposal of these wastes in repositories mined in crystalline rocks. The objective of the report presented was to investigate the mechanism for Al and Si removal during incongruent dissolution of feldspars and its effect on dissolution rate. It was found that phase transformation, like dissolution occured preferentially along crystal defects on the surfaces of the feldspars. Secondary minerals always occured as discrete particles occupying only a very small fraction of the total parent surface, and hence, their presence would not affect the bulk composition or, in this regard, the overall dissolution rate of the feldspars by the formation of diffusion barriers.

  19. Short-term dissolution experiments on various cement formulations in standard Canadian shield saline solution in the presence of clay

    International Nuclear Information System (INIS)

    Heimann, R.B.; Stanchell, M.A.T.

    1986-12-01

    A commercially available sulphate-resisting portland cement (SRPC) and three cement formulations derived from it by adding 10 and 20 vol% silica fume or 35 vol% fly-ash have been leached in Standard Canadian Shield Saline Solution (SCSSS) with added calcium-montmorillonite or sodium-montmorillonite at 150 degrees C for 14 days. The leach solutions have been analyzed by atomic absorption spectroscopy for silicon, magensium, iron and potassium, and by inductively coupled plasma spectrometry for aluminum and phosphorous. The surfaces of the leached samples have been investigated by scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy, and by X-ray powder diffraction methods. Cumulative pore size distrubtion curves have been recorded for as-cured and leached cement samples. It has been shown that the presence of clay accelerates the rate of dissolution of the various cements, and that the pH of the leaching solutions plays a dominant role in the elemental release kinetics

  20. Unexpected differences in dissolution behavior of tablets prepared from solid dispersions with a surfactant physically mixed or incorporated

    NARCIS (Netherlands)

    de Waard, H.; Hinrichs, W.L.J.; Visser, M.R.; Bologna, C.; Frijlink, H.W.

    2008-01-01

    In a previous study, it was shown that the incorporation of poorly soluble drugs (BCS class II) in sugar glasses could largely increase the drug's dissolution rate [van Drooge, D.J., Hinrichs, W.L.J., Frijlink, H.W., 20041). Anomalous dissolution behaviour of tablets prepared from sugar glass-based

  1. Influence of processing-induced phase transformations on the dissolution of theophylline tablets

    OpenAIRE

    Debnath, Smita; Suryanarayanan, Raj

    2004-01-01

    The object of this investigation was to evaluate the influence of (1) processing-induced decrease in drug crystallinity and (2) phase transformations during dissolution, on the per-formance of theophylline tablet formulations. Anhydrous theophylline underwent multiple transformations (anhydrate »hydrate»anhydrate) during processing. Although the crystallinity of the anhydrate obtained finally was lower than that of the unprocessed drug, it dissolved at a slower rate. This decrease in dissolut...

  2. A mathematical analysis of drug dissolution in the USP flow through apparatus

    Science.gov (United States)

    McDonnell, David; D'Arcy, D. M.; Crane, L. J.; Redmond, Brendan

    2018-03-01

    This paper applies boundary layer theory to the process of drug dissolution in the USP (United States Pharmacopeia) Flow Through Apparatus. The mass transfer rate from the vertical planar surface of a compact within the device is examined. The theoretical results obtained are then compared with those of experiment. The paper also examines the effect on the dissolution process caused by the interaction between natural and forced convection within the apparatus and the introduction of additional boundaries.

  3. Dissolution study of tremolite and anthophyllite: pH effect on the reaction kinetics

    International Nuclear Information System (INIS)

    Rozalen, M.; Ramos, M.E.; Gervilla, F.; Kerestedjian, T.; Fiore, S.; Huertas, F.J.

    2014-01-01

    Highlights: • Dissolution rates strongly depend on pH and it is different for each mineral. • Anthophyllite dissolves up to 8 times faster than tremolite in similar conditions. • SEM images show different particle breakage and carbonation effects at basic pHs. • Our results are a good background to develop remediation processes of contaminated sites. - Abstract: The effect of pH on the kinetics of tremolite and anthophyllite dissolution was investigated at 25 °C in batch reactors over the pH range of 1–13.5, in inorganic buffered solutions. Dissolution rates were obtained based on the release of Si and Mg. Results obtained in this study show different behaviors for both minerals. For tremolite, dissolution rates show a noticeable dependence on pH between 1 and 8, decreasing as pH increases and reaching a minimum around neutral conditions. At basic pH this dependence becomes even stronger, but dissolution takes place together with collateral effects of saturation and carbonation. A preferential release of Ca and Mg is observed in acid media, lowering the Mg/Si ratio to the extent that Mg solubility decreases with pH. For anthophyllite, dissolution rates also show a strong dependence on pH, between 1 and 9.5. At the same pH, anthophyllite dissolves up to 8 times faster than tremolite. For pH > 9.5 this dependence is smooth, and it is probably associated with effects of saturation and carbonation. Dissolution is also non-stoichiometric with a faster release of Mg with respect to Si in acid media. SEM observations show differences in the breakage mechanism of the fibers. The anthophyllite particle breakage during dissolution consists of the splitting of bundle fibers parallel to the fiber longitudinal direction. However, for tremolite, other than fiber splitting, particles shorten induced by coalescence of etch pits developed perpendicular to c axe

  4. Dissolution enhancement of Deflazacort using hollow crystals prepared by antisolvent crystallization process.

    Science.gov (United States)

    Paulino, A S; Rauber, G; Campos, C E M; Maurício, M H P; de Avillez, R R; Capobianco, G; Cardoso, S G; Cuffini, S L

    2013-05-13

    Deflazacort (DFZ), a derivate of prednisolone, is a poorly soluble drug which has been proposed to have major advantages over other corticosteroids. Poorly soluble drugs present limited bioavailability due to their low solubility and dissolution rate and several strategies have been developed in order to find ways to improve them. In general, pharmaceutical laboratories use a micronized process to reduce the particle size in order to increase the dissolution of the drugs. However, this process causes changes such as polymorphic transitions, particle agglomeration and a reduction in fluidity and wettability. These solid-state properties affect the dissolution behavior and stability performance of drugs. Crystallization techniques are widely used in the pharmaceutical industry and antisolvent crystallization has been used to obtain ultrafine particles. In this study, DFZ was investigated in terms of its antisolvent crystallization in different solvents and under various preparation conditions (methanol/water ratio, stirring and evaporation rate, etc.), in order to compare the physicochemical properties between crystallized samples and raw materials available on the Brazilian market with and without micronization. Crystalline structure, morphology, and particle size, and their correlation with the Intrinsic Dissolution Rate (IDR) and dissolution profile as relevant biopharmaceutical properties were studied. Crystallization conditions were achieved which provided crystalline samples of hollow-shaped crystals with internal channels, which increased the dissolution rate of DFZ. The antisolvent crystallization process allowed the formation of hollow crystals, which demonstrated a better dissolution profile than the raw material (crystalline and micronized), making this a promising technique as a crystallization strategy for improving the dissolution and thus the bioavailability of poorly soluble drugs. Copyright © 2013 Elsevier B.V. All rights reserved.

  5. Reducing ZnO nanoparticles toxicity through silica coating

    Directory of Open Access Journals (Sweden)

    Sing Ling Chia

    2016-10-01

    Full Text Available ZnO NPs have good antimicrobial activity that can be utilized as agents to prevent harmful microorganism growth in food. However, the use of ZnO NPs as food additive is limited by the perceived high toxicity of ZnO NPs in many earlier toxicity studies. In this study, surface modification by silica coating was used to reduce the toxicity of ZnO NPs by significantly reducing the dissolution of the core ZnO NPs. To more accurately recapitulate the scenario of ingested ZnO NPs, we tested our as synthesized ZnO NPs in ingestion fluids (synthetic saliva and synthetic gastric juice to determine the possible forms of ZnO NPs in digestive system before exposing the products to colorectal cell lines. The results showed that silica coating is highly effective in reducing toxicity of ZnO NPs through prevention of the dissociation of ZnO NPs to zinc ions in both neutral and acidic condition. The silica coating however did not alter the desired antimicrobial activity of ZnO NPs to E. coli and S. aureus. Thus, silica coating offered a potential solution to improve the biocompatibility of ZnO NPs for applications such as antimicrobial agent in foods or food related products like food packaging. Nevertheless, caution remains that high concentration of silica coated ZnO NPs can still induce undesirable cytotoxicity to mammalian gut cells. This study indicated that upstream safer-by-design philosophy in nanotechnology can be very helpful in a product development.

  6. In Vivo Predictive Dissolution: Comparing the Effect of Bicarbonate and Phosphate Buffer on the Dissolution of Weak Acids and Weak Bases.

    Science.gov (United States)

    Krieg, Brian J; Taghavi, Seyed Mohammad; Amidon, Gordon L; Amidon, Gregory E

    2015-09-01

    Bicarbonate is the main buffer in the small intestine and it is well known that buffer properties such as pKa can affect the dissolution rate of ionizable drugs. However, bicarbonate buffer is complicated to work with experimentally. Finding a suitable substitute for bicarbonate buffer may provide a way to perform more physiologically relevant dissolution tests. The dissolution of weak acid and weak base drugs was conducted in bicarbonate and phosphate buffer using rotating disk dissolution methodology. Experimental results were compared with the predicted results using the film model approach of (Mooney K, Mintun M, Himmelstein K, Stella V. 1981. J Pharm Sci 70(1):22-32) based on equilibrium assumptions as well as a model accounting for the slow hydration reaction, CO2 + H2 O → H2 CO3 . Assuming carbonic acid is irreversible in the dehydration direction: CO2 + H2 O ← H2 CO3 , the transport analysis can accurately predict rotating disk dissolution of weak acid and weak base drugs in bicarbonate buffer. The predictions show that matching the dissolution of weak acid and weak base drugs in phosphate and bicarbonate buffer is possible. The phosphate buffer concentration necessary to match physiologically relevant bicarbonate buffer [e.g., 10.5 mM (HCO3 (-) ), pH = 6.5] is typically in the range of 1-25 mM and is very dependent upon drug solubility and pKa . © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

  7. Calcium Carbonate Dissolution Above the Lysocline: Implications of Copepod Grazing on Coccolithophores

    Science.gov (United States)

    White, M. M.; Waller, J. D.; Lubelczyk, L.; Drapeau, D.; Bowler, B.; Wyeth, A.; Fields, D.; Balch, W. M.

    2016-02-01

    Copepod-coccolithophore predator-prey interactions are of great importance because they facilitate the export of particulate inorganic and organic carbon (PIC and POC) from the surface ocean. Coccolith dissolution in acidic copepod guts has been proposed as a possible explanation for the paradox of PIC dissolution above the lysocline, but warrants further investigation. Using a new application of the 14C-microdiffusion technique, we investigated the dissolution of coccoliths in copepod guts. We considered both an estuarine predator-prey model (Acartia tonsa and Pleurochrysis carterae) and an open ocean predator-prey model (Calanus finmarchicus and Emiliania huxleyi). Additionally, we considered the impacts of pCO2 on this process to advance our understanding of the effects of ocean acidification on trophic interactions. In the estuarine predator-prey model, fecal pellets produced immediately after previously-starved copepods grazed on P. carterae had PIC/POC ratios 27-40 % lower than that of the algae, indicating PIC dissolution within the copepod gut, with no impact of pCO2 on this dissolution. Subsequent fecal pellets showed increasing PIC/POC, suggesting that calcite dissolution decreases as the gut fills. The open ocean predator-prey model showed equivocal results, indicating high variability among individual grazing behavior, and therefore no consistent impact of copepod grazing on coccolith dissolution above the lysocline in the open ocean. We will further discuss the effects of fecal pellet PIC/POC ratios on sinking rate.

  8. Role of nitrous acid during the dissolution of UO2 in nitric acid

    International Nuclear Information System (INIS)

    Deigan, N.; Pandey, N.K.; Kamachi Mudali, U.; Joshi, J.B.

    2016-01-01

    Understanding the dissolution behaviour of sintered UO 2 pellet in nitric acid is very important in designing an industrial scale dissolution system for the plutonium rich fast reactor MOX fuel. In the current article we have established the role of nitrous acid on the dissolution kinetics of UO 2 pellets in nitric acid. Under the chemical conditions that prevail in a typical Purex process, NO and NO 2 gases gets generated in the process streams. These gases produce nitrous acid in nitric acid medium. In addition, during the dissolution of UO 2 in nitric acid medium, nitrous acid is further produced in-situ at the pellet solution interface. As uranium dissolves oxidatively in nitric acid medium wherein it goes from U(IV) in solid to U(VI) in liquid, presence of nitrous acid (a good oxidizing agent) accelerates the reaction rate. Hence for determining the reaction mechanism of UO 2 dissolution in nitric acid medium, knowing the nitrous acid concentration profile during the course of dissolution is important. The current work involves the measurement of nitrous acid concentration during the course of dissolution of sintered UO 2 pellets in 8M starting nitric acid concentration as a function of mixing intensity from unstirred condition to 1500 RPM

  9. Evaporite dissolution relevant to the WIPP site, northern Delaware Basin, southeastern New Mexico

    International Nuclear Information System (INIS)

    Lambert, S.J.

    1982-01-01

    Evaluation of the threat of natural dissolution of host evaporites to the integrity of the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico has taken into consideration (1) the volume of missing rock salt, (2) the occurrence (or not) of characteristic dissolution brines, (3) geomorphic features, some of which are unrelated to dissolution, and (4) the time intervals over which dissolution may have been active. Even under the assumption that all missing halite was originally present and has been removed by dissolution, there is no evidence of active preferential removal of the lower Salado Formation halite by any geologically reasonable process. The geologic record contains evidence of dissolution in the Triassic and Jurassic; to constrain all removal of basinal halite to the late Cenozoic yields an unrealistically high rate of removal. Application to the lower Salado of a stratabound mechanism known to be active in Nash Draw, a near-surface feature within the Basin, allows a minimum survival time of 2,500,000 years to be predicted for the subsurface facility for storage of radioactive waste at WIPP. This calculation is based on an analysis of all known dissolution features in the Delaware Basin, and takes into account the wetter (pluvial) climate during the past 600,000 years. 2 figures, 1 table

  10. Chitosan-silica complex membranes from sulfonic acid functionalized silica nanoparticles for pervaporation dehydration of ethanol-water solutions.

    Science.gov (United States)

    Liu, Ying-Ling; Hsu, Chih-Yuan; Su, Yu-Huei; Lai, Juin-Yih

    2005-01-01

    Nanosized silica particles with sulfonic acid groups (ST-GPE-S) were utilized as a cross-linker for chitosan to form a chitosan-silica complex membranes, which were applied to pervaporation dehydration of ethanol-water solutions. ST-GPE-S was obtained from reacting nanoscale silica particles with glycidyl phenyl ether, and subsequent sulfonation onto the attached phenyl groups. The chemical structure of the functionalized silica was characterized with FTIR, (1)H NMR, and energy-dispersive X-ray. Homogeneous dispersion of the silica parti