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

chemistry. For most determinations, a jet of water conditioned to the required chemistry but stripped of dissolved iron with ion-exchange is directed onto a pellet of magnetite and the dissolution monitored; the high velocity of the jet ensures that mass transfer effects are minimised. The magnetite is synthesised by a solid-state method involving heating a mixture of haematite and iron under vacuum at 600 deg. C, compacting under pressure and sintering into a pellet under argon at 1,100 deg. C. The product has an appropriate consistency and resistance to erosion. Most experiments have measured the average dissolution rate by estimating the amount of magnetite lost from the pellet by surface analysis and profilometry after exposure for a given time. Concomitant electrochemical information is obtained by electrically isolating the pellet from the loop and connecting it to a potentiostat, along with a counter-electrode and reference electrode strategically mounted in the loop test section. Detailed kinetic data are obtained by irradiating the magnetite before installation in the loop and monitoring on-line with gamma spectrometry the transport of dissolved, radioactive 59 Fe. Preliminary determinations had used radioactive magnetite precipitated under galvanostatic conditions from a solution of irradiated FeSO 4 in EDTA onto a platinum coupon. The coupon was then mounted axially in the loop test section and subjected to a range of imposed potentials during exposure; however, this coupon technique gave dissolution results confounded by the release of magnetite crystallites, so we concentrated on the pellet technique. The paper presents the results of exposures carried out over a range of temperatures and alkalinities at oxygen concentrations between 0 and 20 ppb. It shows how dissolution rate constants obtained under CANDU primary coolant conditions of 310 deg. C and pH 25C 10.5 (with LiOH) fall between published values, which were obtained with a different technique under

In silico prediction of drug dissolution and absorption with variation in intestinal pH for BCS class II weak acid drugs: ibuprofen and ketoprofen.

Science.gov (United States)

Tsume, Yasuhiro; Langguth, Peter; Garcia-Arieta, Alfredo; Amidon, Gordon L

2012-10-01

The FDA Biopharmaceutical Classification System guidance allows waivers for in vivo bioavailability and bioequivalence studies for immediate-release solid oral dosage forms only for BCS class I. Extensions of the in vivo biowaiver for a number of drugs in BCS class III and BCS class II have been proposed, in particular, BCS class II weak acids. However, a discrepancy between the in vivo BE results and in vitro dissolution results for BCS class II acids was recently observed. The objectives of this study were to determine the oral absorption of BCS class II weak acids via simulation software and to determine if the in vitro dissolution test with various dissolution media could be sufficient for in vitro bioequivalence studies of ibuprofen and ketoprofen as models of carboxylic acid drugs. The oral absorption of these BCS class II acids from the gastrointestinal tract was predicted by GastroPlus™. Ibuprofen did not satisfy the bioequivalence criteria at lower settings of intestinal pH of 6.0. Further the experimental dissolution of ibuprofen tablets in a low concentration phosphate buffer at pH 6.0 (the average buffer capacity 2.2 mmol l (-1) /pH) was dramatically reduced compared with the dissolution in SIF (the average buffer capacity 12.6 mmol l (-1) /pH). Thus these predictions for the oral absorption of BCS class II acids indicate that the absorption patterns depend largely on the intestinal pH and buffer strength and must be considered carefully for a bioequivalence test. Simulation software may be a very useful tool to aid the selection of dissolution media that may be useful in setting an in vitro bioequivalence dissolution standard. Copyright © 2012 John Wiley & Sons, Ltd.

In Silico Prediction of Drug Dissolution and Absorption with variation in Intestinal pH for BCS Class II Weak Acid Drugs: Ibuprofen and Ketoprofen§

Science.gov (United States)

Tsume, Yasuhiro; Langguth, Peter; Garcia-Arieta, Alfredo; Amidon, Gordon L.

2012-01-01

The FDA Biopharmaceutical Classification System guidance allows waivers for in vivo bioavailability and bioequivalence studies for immediate-release solid oral dosage forms only for BCS class I. Extensions of the in vivo biowaiver for a number of drugs in BCS Class III and BCS class II have been proposed, particularly, BCS class II weak acids. However, a discrepancy between the in vivo- BE results and in vitro- dissolution results for a BCS class II acids was recently observed. The objectives of this study were to determine the oral absorption of BCS class II weak acids via simulation software and to determine if the in vitro dissolution test with various dissolution media could be sufficient for in vitro bioequivalence studies of ibuprofen and ketoprofen as models of carboxylic acid drugs. The oral absorption of these BCS class II acids from the gastrointestinal tract was predicted by GastroPlus™. Ibuprofen did not satisfy the bioequivalence criteria at lower settings of intestinal pH=6.0. Further the experimental dissolution of ibuprofen tablets in the low concentration phosphate buffer at pH 6.0 (the average buffer capacity 2.2 mmol L-1/pH) was dramatically reduced compared to the dissolution in SIF (the average buffer capacity 12.6 mmol L -1/pH). Thus these predictions for oral absorption of BCS class II acids indicate that the absorption patterns largely depend on the intestinal pH and buffer strength and must be carefully considered for a bioequivalence test. Simulation software may be very useful tool to aid the selection of dissolution media that may be useful in setting an in vitro bioequivalence dissolution standard. PMID:22815122

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.

Effect of sodium lauryl sulfate in dissolution media on dissolution of hard gelatin capsule shells.

Science.gov (United States)

Zhao, Fang; Malayev, Vyacheslav; Rao, Venkatramana; Hussain, Munir

2004-01-01

Sodium lauryl sulfate (SLS) is a commonly used surfactant in dissolution media for poorly water soluble drugs. However, it has occasionally been observed that SLS negatively impacts the dissolution of drug products formulated in gelatin capsules. This study investigated the effect of SLS on the dissolution of hard gelatin capsule shells. The USP paddle method was used with online UV monitoring at 214 nm (peptide bond). Empty size #0 capsule shells were held to the bottom of the dissolution vessel by magnetic three-prong sinkers. SLS significantly slowed down the dissolution of gelatin shells at pH < 5. Visually, the gelatin shells transformed into some less-soluble precipitate under these conditions. This precipitate was found to contain a higher sulfur content than the gelatin control sample by elemental analysis, indicating that SLS is part of the precipitate. Additionally, the slowdown of capsule shell dissolution was shown to be dependent on the SLS concentration and the ionic strength of the media. SLS interacts with gelatin to form a less-soluble precipitate at pH < 5. The use of SLS in dissolution media at acidic pH should be carefully evaluated for gelatin capsule products.

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.

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

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)

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

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.)

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

Chlorite, Biotite, Illite, Muscovite, and Feldspar Dissolution Kinetics at Variable pH and Temperatures up to 280 C

Energy Technology Data Exchange (ETDEWEB)

Carroll, S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Smith, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Lammers, K. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2016-10-05

Summary Sheet silicates and clays are ubiquitous in geothermal environments. Their dissolution is of interest because this process contributes to scaling reactions along fluid pathways and alteration of fracture surfaces, which could affect reservoir permeability. In order to better predict the geochemical impacts on long-term performance of engineered geothermal systems, we have measured chlorite, biotite, illite, and muscovite dissolution and developed generalized kinetic rate laws that are applicable over an expanded range of solution pH and temperature for each mineral. This report summarizes the rate equations for layered silicates where data were lacking for geothermal systems.

Effect of pH on the dissolution kinetics of zero-valent iron in the presence of EDDHA and EDTA

International Nuclear Information System (INIS)

Lodge, Alexander M.; Pierce, Eric M.; Wellman, Dawn M.; Rodriguez, Elsa A.

2007-01-01

The effect of environmental factors (e.g., pH, solution composition, and temperature) that affect the longevity of Fe(0) barriers in the subsurface are difficult to quantify independently from changes that occur to the passivating layer. Therefore, to quantify the rate of Fe(0) dissolution under conditions which maintain the pO2 at a relatively constant level and minimize the formation of a passivating layer on the metal surface, a series of experiments have been conducted with the single-pass flow-through (SPFT) apparatus. These experiments were conducted over the pH range from 7.0 to 12.0 at 90 C in the presence of 5 mM EDDHA or 5 mM EDTA. The organic acids, EDDHA and EDTA, helped to maintain the aqueous Fe concentration below saturation with respect to Fe-bearing alteration phases and minimize the formation of a partially oxidized surface film. Results suggest the corrosion of Fe(0) is relatively insensitive to pH and the forward or maximum dissolution rate is 3 to 4 orders of magnitude higher than when a passive film and corrosion products are present

In vitro dissolution methodology, mini-Gastrointestinal Simulator (mGIS), predicts better in vivo dissolution of a weak base drug, dasatinib.

Science.gov (United States)

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

2015-08-30

USP apparatus I and II are gold standard methodologies for determining the in vitro dissolution profiles of test drugs. However, it is difficult to use in vitro dissolution results to predict in vivo dissolution, particularly the pH-dependent solubility of weak acid and base drugs, because the USP apparatus contains one vessel with a fixed pH for the test drug, limiting insight into in vivo drug dissolution of weak acid and weak base drugs. This discrepancy underscores the need to develop new in vitro dissolution methodology that better predicts in vivo response to assure the therapeutic efficacy and safety of oral drug products. Thus, the development of the in vivo predictive dissolution (IPD) methodology is necessitated. The major goals of in vitro dissolution are to ensure the performance of oral drug products and the support of drug formulation design, including bioequivalence (BE). Orally administered anticancer drugs, such as dasatinib and erlotinib (tyrosine kinase inhibitors), are used to treat various types of cancer. These drugs are weak bases that exhibit pH-dependent and high solubility in the acidic stomach and low solubility in the small intestine (>pH 6.0). Therefore, these drugs supersaturate and/or precipitate when they move from the stomach to the small intestine. Also of importance, gastric acidity for cancer patients may be altered with aging (reduction of gastric fluid secretion) and/or co-administration of acid-reducing agents. These may result in changes to the dissolution profiles of weak base and the reduction of drug absorption and efficacy. In vitro dissolution methodologies that assess the impact of these physiological changes in the GI condition are expected to better predict in vivo dissolution of oral medications for patients and, hence, better assess efficacy, toxicity and safety concerns. The objective of this present study is to determine the initial conditions for a mini-Gastrointestinal Simulator (mGIS) to assess in vivo

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

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.

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.

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)

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.)

Solubility and dissolution improvement of ketoprofen by emulsification ionic gelation

Science.gov (United States)

Rachmaniar, Revika; Tristiyanti, Deby; Hamdani, Syarif; Afifah

2018-02-01

Ketoprofen or [2-(3-benzoylphenyl) propionic acid] is non-steroidal anti-inflammatory (NSAID) and an analgesic which has high permeability and low solubility. The purpose of this work was to improve the solubility and dissolution of poorly water-soluble ketoprofen prepared by emulsification ionic gelation method and utilizing polymer (chitosan) and cross linker (tripolyphosphate, TPP) for particles formulation. The results show that increasing pH value of TPP, higher solubility and dissolution of as-prepared ketoprofen-chitosan was obtained. The solubility in water of ketoprofen-chitosan with pH 6 for TPP increased 2.71-fold compared to untreated ketoprofen. While the dissolution of ketoprofen-chitosan with pH 6 of TPP in simulated gastric fluid without enzyme (0.1 N HCl), pH 4.5 buffer and simulated intestinal fluid without enzyme (phosphate buffer pH 6.8) was increased 1.9-fold, 1.6-fold and 1.2-fold compared to untreated ketoprofen for dissolution time of 30 minutes, respectively. It could be concluded that chitosan and TPP in the emulsification ionic gelation method for ketoprofen preparation effectively increases solubility and dissolution of poorly water-soluble ketoprofen.

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

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

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.

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

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.

Mathematical methods for quantification and comparison of dissolution testing data.

Science.gov (United States)

Vranić, Edina; Mehmedagić, Aida; Hadzović, Sabira

2002-12-01

In recent years, drug release/dissolution from solid dosage forms has been the subject of intense and profitable scientific developments. Whenever a new solid dosage form is developed or produced, it is necessary to ensure that drug dissolution occurs in an appropriate manner. The pharmaceutical industry and the registration authorities do focus, nowadays, on drug dissolution studies. The quantitative analysis of the values obtained in dissolution/release tests is easier when mathematical formulas that express the dissolution results as a function of some of the dosage forms characteristics are used. This work discusses the analysis of data obtained for dissolution profiles under different media pH conditions using mathematical methods of analysis described by Moore and Flanner. These authors have described difference factor (f1) and similarity factor (f2), which can be used to characterise drug dissolution/release profiles. In this work we have used these formulas for evaluation of dissolution profiles of the conventional tablets in different pH of dissolution medium (range of physiological variations).

Effect of dissolution kinetics on flotation response of calcite with oleate

Directory of Open Access Journals (Sweden)

D. G. Horta

Full Text Available Abstract Phosphate flotation performance can be influenced by the dissolution kinetics of the minerals that compose the ore. The purpose of this work was to investigate the effect of dissolution kinetics on flotation response with oleate (collector of calcites from different origins and genesis. The calcite samples were first purified and characterized by x-ray Fluorescence (XRF and the Rietveld method applied to x-ray Diffractometry data (RXD. Experiments of calcite dissolution and microflotationwere performed at pH 8 and pH 10.The pH effect on the calcite dissolution and flotation indicates the possible influence of the carbonate/bicarbonate ions provided by the CO2 present in the air. In addition, the flotation response is greater as the dissolution increases, making more Ca2+ ions available to interact with collector molecules. This result corroborates the surface precipitation mechanism proposed foroleate adsorption on the calcite surface.

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.

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.

Mathematical methods for quantification and comparison of dissolution testing data

Directory of Open Access Journals (Sweden)

Edina Vranić

2002-02-01

Full Text Available In recent years, drug release/dissolution from solid dosage forms has been the subject of intense and profitable scientific developments. Whenever a new solid dosage form is developed or produced, it is necessary to ensure that drug dissolutionoccurs in an appropriate manner. The pharmaceutical industry and the registration authorities do focus, nowadays, on drug dissolution studies. The quantitative analysis of the values obtained in dissolution/release tests is easier when mathematicalformulas that express the dissolution results as a function of some of the dosage forms characteristics are used. This work discusses the analysis of data obtained for dissolution profiles under different media pH conditions using mathematical methodsof analysis described by Moore and Flanner. These authors have described difference factor (f1 and similarity factor (f2, which can be used to characterise drug dissolution/release profiles. In this work we have used these formulas for evaluation of dissolution profiles of the conventional tablets in different pH of dissolution medium (range of physiological variations.

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)

Free Energy Landscape of the Dissolution of Gibbsite at High pH

Energy Technology Data Exchange (ETDEWEB)

Shen, Zhizhang; Kerisit, Sebastien N.; Stack, Andrew G.; Rosso, Kevin M.

2018-03-26

The individual elementary reactions involved in the dissolution of a solid into solution remain mostly speculative due to a lack of suitable, direct experimental probes. In this regard, we have applied atomistic simulations to map the free energy landscape of the dissolution of gibbsite from a step edge, as a model of metal hydroxide dissolution. The overall reaction combines kink site formation and kink site propagation. Two individual reactions were found to be rate-limiting for kink site formation, that is, the displacement of Al from a step site to a ledge adatom site and its detachment from ledge/terrace adatom sites into the solution. As a result, a pool of mobile and labile Al adsorbed species, or adatoms, exists before the release of Al into solution. Because of the quasi-hexagonal symmetry of gibbsite, kink site propagation can occur in multiple directions. Overall, the simulation results will enable the development of microscopic mechanistic models of metal oxide dissolution.

Examination of Uranium(VI) Leaching During Ligand Promoted Dissolution of Waste Tank Sludge Surrogates

Energy Technology Data Exchange (ETDEWEB)

Powell, Brian; Powell, Brian A.; Rao, Linfeng; Nash, Kenneth. L.

2008-06-10

The dissolution of synthetic boehmite (?-AlOOH) by 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) was examined in a series of batch adsorption/dissolution experiments. Additionally, the leaching behavior of {sup 233}U(VI) from boehmite was examined as a function of pH and HEDPA concentration. The results are discussed in terms of sludge washing procedures that may be utilized during underground tank waste remediation. In the pH range 4 to 10, complexation of Al(III) by HEDPA significantly enhanced dissolution of boehmite. This phenomenon was especially pronounced in the neutral pH region where the solubility of aluminum, in the absence of complexants, is limited by the formation of sparsely soluble aluminum hydroxides. At pH higher than 10, dissolution of synthetic boehmite was inhibited by HEDPA, likely due to sorption of Al(III):HEDPA complexes. Addition of HEDPA to equilibrated U(VI)-synthetic boehmite suspensions yielded an increase in the aqueous phase uranium concentration. Partitioning of uranium between the solid and aqueous phase is described in terms of U(VI):HEDPA speciation and dissolution of the boehmite solid phase.

Development of a μDissolution-Permeation model with in situ drug concentration monitoring

DEFF Research Database (Denmark)

Berthelsen, Ragna; Byrialsen, Julie Pelle; Holm, René

2016-01-01

state biorelevant medium consisting of HBSS pH 6.5 supplemented with bile salts and lecithin was used as the apical dissolution media, while HBSS pH 7.4 was used as the basolateral medium. The apparent permeability (Papp) and dissolution-time profiles for albendazole, felodipine and fenofibrate were...

Accelerating the dissolution of enteric coatings in the upper small intestine: evolution of a novel pH 5.6 bicarbonate buffer system to assess drug release.

Science.gov (United States)

Varum, Felipe J O; Merchant, Hamid A; Goyanes, Alvaro; Assi, Pardis; Zboranová, Veronika; Basit, Abdul W

2014-07-01

Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) products can take up to 2 h to disintegrate in the human small intestine, which clearly highlights the inadequacy of the in vitro test method to predict in vivo behaviour of these formulations. The aim of this study was to establish the utility of a novel pH 5.6 bicarbonate buffer, stabilized by an Auto pH™ System, as a better surrogate of the conditions of the proximal small intestine to investigate the dissolution behaviour of standard and accelerated release enteric double coating formulations. Prednisolone tablets were coated with 3 or 5 mg/cm(2) of partially neutralized EUDRAGIT(®) L 30 D-55, HP-55 or HPMC adjusted to pH 6 or 8. An outer layer of EUDRAGIT(®) L 30 D-55 was applied at 5mg/cm(2). For comparison purposes, a standard single layer of EUDRAGIT(®) L 30 D-55 was applied to the tablets. Dissolution was carried out using USP II apparatus in 0.1 M HCl for 2 h, followed by pH 5.6 bicarbonate buffer. EUDRAGIT(®) L 30 D-55 single-coated tablets showed a slow drug release with a lag time of 75 min in buffer, whereas release from the EUDRAGIT(®) L 30 D-55 double-coated tablets was accelerated. These in vitro lag times closely match the in vivo disintegration times for these coated tablets reported previously. Drug release was further accelerated from modified double coatings, particularly in the case of coatings with a thinner inner layer of HP-55 or HPMC (pH 8 and KH2PO4). This study confirms that the pH 5.6 bicarbonate buffer system offers significant advantages during the development of dosage forms designed to release the drug in the upper small intestine. Copyright © 2014. Published by Elsevier B.V.

Dissolution enhancement of curcumin via curcumin-prebiotic inulin nanoparticles.

Science.gov (United States)

Fares, Mohammad M; Salem, Mu'taz Sheikh

2015-01-01

Dissolution enhancement of curcumin via prebiotic inulin designed to orally deliver poorly water-soluble curcumin at duodenum low acidity (pH 5.5) was investigated. Different prebiotic inulin-curcumin nanoparticles were synthesized in ethanol-water binary system at different pre-adjusted pH values. Characterization via FTIR, XRD and TGA revealed the formation of curcumin-inulin conjugates, whereas surface morphology via SEM and TEM techniques implied the formation of nanoparticle beads and nanoclusters. Prebiotic inulin-curcumin nanoparticles prepared at pH 7.0 demonstrated a maximum curcumin dissolution enhancement of ≈90% with respect to 30% for curcumin alone at pH 5.5. Power law constant values were in accordance with dissolution enhancement investigations. All samples show Fickian diffusion mechanism. XRD investigations confirm that inulin maintain its crystalline structure in curcumin-inulin conjugate structure, which confirms that it can exert successfully its prebiotic role in the gastrointestinal (GI) tract. Therefore, the use of curcumin-inulin nanoparticles can perform dual-mission in the GI tract at the duodenum environment; release of 90% of curcumin followed by prebiotic activity of inulin, which will probably play a significant role in cancer therapeutics for the coming generations.

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

Use of micro-reactors to obtain new insights into the factors influencing tricalcium silicate dissolution

International Nuclear Information System (INIS)

Suraneni, Prannoy; Flatt, Robert J.

2015-01-01

A micro-reactor approach, developed previously, is used to study the early dissolution of tricalcium silicate. This approach uses micron-sized gaps mimicking particles in close contact to understand dissolution, nucleation, and growth processes. The main factors influencing the dissolution kinetics of tricalcium silicate are presented. We show that the presence of defects caused by polishing does not affect the extent of dissolution. A strong effect of aluminum in solution reducing the extent of dissolution is however identified. This effect is highly dependent on the pH, and is much lower above pH 13. We show also that superplasticizers reduce the extent of dissolution; however, the exact reason for this effect is not clear.

The dissolution kinetics and apparent solubility of natural apatite in closed reactors at temperatures from 5 to 50 degrees C and pH from 1 to 6

Energy Technology Data Exchange (ETDEWEB)

Harouiya, N.; Chairat, C.; Kohler, S.J.; Gout, R.; Oelkers, E.H. [Univ Toulouse 3, CNRS, UMR 5563, F-31400 Toulouse (France); Chairat, C. [CEA, LCLT SECM DTCD, Lab Etud Comportement Long Terme, F-30207 Bagnols Sur Ceze, (France)

2007-07-01

The apparent solubility and dissolution rates of natural apatite were measured in closed-system reactors as a function of temperature from 5 to 50 degrees C and pH from 1 to 6. The temporal release rates of Ca, P, and F during the experiments are approximately consistent with stoichiometric dissolution in all experiments. One advantage of closed-system experiments is that they allow determination of reactive fluid evolution and dissolution rates at far-from to near-to equilibrium conditions. Surface area normalized apatite dissolution rates, r, obtained in all experiments are consistent with r = A{sub A}a{sub H{sup +}}{sup n}exp(E{sub A}/RT)(1 -exp(-A/{sigma} RT)) where A{sub A} stands for a rate constant equal to 4 * 10{sup -3} mol/cm{sup 2}/s, a{sub H{sup +}}) denotes the activity of the aqueous H{sup +}, n designates a reaction order equal to 0.6, E{sub A} symbolizes an activation energy equal to 11.0 kcal/mol, A refers to the chemical affinity of the dissolving apatite, {sigma} stands for Temkin's average stoichiometric number equal to 5; R designates the gas constant, and T represents absolute temperature. Logarithms of apparent equilibrium constants obtained from experiments performed at 3 {<=} pH {<=} 5.6 for the apatite dissolution reaction: Ca{sub 5}(PO{sub 4}){sub 3}F + 3H{sup +} = 5Ca{sup 2+} + 3HPO{sub 4}{sup 2-} + F{sup -} are found to be - 29.5 {+-} 0.6, - 29.4 {+-} 0.9 and - 29.9 {+-} 1.3 at 5, 25, and 50 degrees C, respectively. (authors)

Inhibition of cobalt active dissolution by benzotriazole in slightly alkaline bicarbonate aqueous media

Energy Technology Data Exchange (ETDEWEB)

Gallant, Danick [Departement de Chimie, Universite Laval, Quebec (Canada); Departement de Biologie, Chimie et Geographie, Universite du Quebec a Rimouski, 300, Allee des Ursulines, Rimouski, Quebec (Canada); E-mail: danick.gallant.1@ulaval.ca; Pezolet, Michel [Departement de Chimie, Universite Laval, Quebec (Canada)]. E-mail: michel.pezolet@chm.ulaval.ca; Simard, Stephan [Departement de Chimie, Universite Laval, Quebec (Canada); Departement de Biologie, Chimie et Geographie, Universite du Quebec a Rimouski, 300, Allee des Ursulines, Rimouski, Quebec (Canada); E-mail: stephan_simard@uqar.qc.ca

2007-04-20

The efficiency of benzotriazole as inhibiting agent for the corrosion of cobalt was probed at pH ranging from 8.3 to 10.2 in a sodium bicarbonate solution, chosen to simulate mild natural environments. From electrochemical, Raman spectroscopy, atomic force microscopy and ellipsometry experiments, we have demonstrated that benzotriazole markedly affects the electrodissolution reactions, which become modeled by the formation of a [Co(II)(BTA){sub 2}.H{sub 2}O] {sub n} film according to two different mechanisms. Surface-enhanced Raman spectroscopy has shown that the polarization of a cobalt electrode at cathodic potentials with respect to its potential of zero charge allows a mechanism of specific adsorption of the neutral form of benzotriazole to take place through a suspected metal-to-molecule electron transfer and which follows Frumkin's adsorption isotherms. At the onset of the anodic dissolution, some experimental evidence suggests that these adsorbed neutral benzotriazole molecules deprotonate to yield a very thin [Co(II)(BTA){sub 2}.H{sub 2}O] {sub n} polymer-like and water-insoluble protective film, responsible for the inhibition of active dissolution processes occurring at slightly more anodic potentials. In the anodic dissolution region, deprotonated benzotriazole species present in the bulk solution favors the formation of a multilayered [Co(II)(BTA){sub 2}.H{sub 2}O] {sub n} film, which also contributes to the inhibition of any further cobalt dissolution usually observed at higher electrode potentials.

Preparation and Characterization of Liquisolid Compacts for Improved Dissolution of Telmisartan

Directory of Open Access Journals (Sweden)

Naveen Chella

2014-01-01

Full Text Available The objective of the present work was to obtain pH independent and improved dissolution profile for a poorly soluble drug, telmisartan using liquisolid compacts. Liquisolid compacts were prepared using Transcutol HP as vehicle, Avicel PH102 as carrier, and Aerosil 200 as a coating material. The formulations were evaluated for drug excipient interactions, change in crystallinity of drug, flow properties, and general quality control tests of tablets using Fourier transform infrared (FTIR spectroscopy, differential scanning calorimetry (DSC, X-ray diffraction (XRD, angle of repose, and various pharmacopoeial tests. In vitro dissolution studies were performed at three pH conditions (1.2, 4.5 and 7.4. Stability studies were performed at 40°C and 75% RH for three months. The formulation was found to comply with Indian pharmacopoeial limits for tablets. FTIR studies confirmed no interaction between drug and excipients. XRD and DSC studies indicate change/reduction in crystallinity of drug. Dissolution media were selected based on the solubility studies. The optimized formulation showed pH independent release profile with significant improvement P<0.005 in dissolution compared to plain drug and conventional marketed formulation. No significant difference was seen in the tablet properties, and drug release profile after storage for 3 months.

Design and optimization of self-nanoemulsifying drug delivery systems (SNEDDS) for enhanced dissolution of gemfibrozil.

Science.gov (United States)

Villar, Ana Maria Sierra; Naveros, Beatriz Clares; Campmany, Ana Cristina Calpena; Trenchs, Monserrat Aróztegui; Rocabert, Coloma Barbé; Bellowa, Lyda Halbaut

2012-07-15

Self-nanoemulsifying drug delivery systems of gemfibrozil were developed under Quality by Design approach for improvement of dissolution and oral absorption. Preliminary screening was performed to select proper components combination. Box-Behnken experimental design was employed as statistical tool to optimize the formulation variables, X(1) (Cremophor(®) EL), X(2) (Capmul(®) MCM-C8), and X(3) (lemon essential oil). Systems were assessed for visual characteristics (emulsification efficacy), turbidity, droplet size, polydispersity index and drug release. Different pH media were also assayed for optimization. Following optimization, the values of formulation components (X(1), X(2), and X(3)) were 32.43%, 29.73% and 21.62%, respectively (16.22% of gemfibrozil). Transmission electron microscopy demonstrated spherical droplet morphology. SNEEDS release study was compared to commercial tablets. Optimized SNEDDS formulation of gemfibrozil showed a significant increase in dissolution rate compared to conventional tablets. Both formulations followed Weibull mathematical model release with a significant difference in t(d) parameter in favor of the SNEDDS. Equally amodelistic parameters were calculated being the dissolution efficiency significantly higher for SNEDDS, confirming that the developed SNEDDS formulation was superior to commercial formulation with respect to in vitro dissolution profile. This paper provides an overview of the SNEDDS of the gemfibrozil as a promising alternative to improve oral absorption. Copyright © 2012 Elsevier B.V. All rights reserved.

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

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.

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.

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

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

[Comparison in dissolution behavior of ethical and over-the counter scopolamine butylbromide].

Science.gov (United States)

Suzuki, Ichie; Miyazaki, Yasunori; Uchino, Tomonobu; Kagawa, Yoshiyuki

2011-01-01

Marketing authorization holders do not disclose any information on the pharmaceutical properties of over-the-counter drugs (OTC). When a drug is switched from a prescription drug to OTC, pharmacists can acquire that information from the corresponding ethical drug (ED) through the package insert, interview form, and so on. However, the pharmaceutical equivalence between ED and OTC is unclear. In this study, we examined the drug dissolution behavior of both ED and OTCs containing scopolamine butylbromide. Dissolution tests were performed by the paddle method using Japanese Pharmacopeia (JP) XV test fluids at pH 1.2, 4.0 and 6.8 and water based on the guidelines for bioequivalence studies of generic products. The dissolution profiles of OTCs differed significantly from ED showing a similarity factor (f2) value ranging from 8.9 to 42.9. Time until 85% dissolution ranged from 23 to 95 min and from 17 to 174 min at pH 1.2 and pH 6.8, respectively. Then JP XV disintegration tests were conducted to investigate differences in the disintegration process. The disintegration time of preparations showing delayed dissolution was prolonged compared to that of others, suggesting that the disintegration of the tablet or capsule is one of the important factors affecting the drug dissolution. These differences in the disintegration and drug dissolution might cause differences in the bioavailability of the drug. For patient safety, more detailed product information of OTCs should be supplied by the manufacturer, and not be assumed from that of corresponding ED.

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.

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)

Equilibrium solubility versus intrinsic dissolution: characterization of lamivudine, stavudine and zidovudine for BCS classification

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André Bersani Dezani

2013-12-01

Full Text Available Solubility and dissolution rate of drugs are of major importance in pre-formulation studies of pharmaceutical dosage forms. The solubility improvement allows the drugs to be potential biowaiver candidates and may be a good way to develop more dose-efficient formulations. Solubility behaviour of lamivudine, stavudine and zidovudine in individual solvents (under pH range of 1.2 to 7.5 was studied by equilibrium solubility and intrinsic dissolution methods. In solubility study by equilibrium method (shake-flask technique, known amounts of drug were added in each media until to reach saturation and the mixture was subjected to agitation of 150 rpm for 72 hours at 37 ºC. In intrinsic dissolution test, known amount of each drug was compressed in the matrix of Wood's apparatus and subjected to dissolution in each media with agitation of 50 rpm at 37 ºC. In solubility by equilibrium method, lamivudine and zidovudine can be considered as highly soluble drugs. Although stavudine present high solubility in pH 4.5, 6.8, 7.5 and water, the solubility determination in pH 1.2 was not possible due stability problems. Regarding to intrinsic dissolution, lamivudine and stavudine present high speed of dissolution. Considering a boundary value presented by Yu and colleagues (2004, all drugs studied present high solubility characteristics in intrinsic dissolution method. Based on the obtained results, intrinsic dissolution seems to be superior for solubility studies as an alternative method for biopharmaceutical classification purposes.

pH-Dependent Solubility and Dissolution Behavior of Carvedilol--Case Example of a Weakly Basic BCS Class II Drug.

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Hamed, Rania; Awadallah, Areeg; Sunoqrot, Suhair; Tarawneh, Ola; Nazzal, Sami; AlBaraghthi, Tamadur; Al Sayyad, Jihan; Abbas, Aiman

2016-04-01

The objective of this study was to investigate the pH-dependent solubility and dissolution of weakly basic Biopharmaceutical Classification Systems (BCS) class II drugs, characterized by low solubility and high permeability, using carvedilol, a weak base with a pK a value of 7.8, as a model drug. A series of solubility and in vitro dissolution studies was carried out using media that simulate the gastric and intestinal fluids and cover the physiological pH range of the GI from 1.2 to 7.8. The effect of ionic strength, buffer capacity, and buffer species of the dissolution media on the solubility and dissolution behavior of carvedilol was also investigated. The study revealed that carvedilol exhibited a typical weak base pH-dependent solubility profile with a high solubility at low pH (545.1-2591.4 μg/mL within the pH range 1.2-5.0) and low solubility at high pH (5.8-51.9 μg/mL within the pH range 6.5-7.8). The dissolution behavior of carvedilol was consistent with the solubility results, where carvedilol release was complete (95.8-98.2% released within 60 min) in media simulating the gastric fluid (pH 1.2-5.0) and relatively low (15.9-86.2% released within 240 min) in media simulating the intestinal fluid (pH 6.5-7.8). It was found that the buffer species of the dissolution media may influence the solubility and consequently the percentage of carvedilol released by forming carvedilol salts of varying solubilities. Carvedilol solubility and dissolution decreased with increasing ionic strength, while lowering the buffer capacity resulted in a decrease in carvedilol solubility and dissolution rate.

In Vitro Dissolution of Fluconazole and Dipyridamole in Gastrointestinal Simulator (GIS), Predicting in Vivo Dissolution and Drug-Drug Interaction Caused by Acid-Reducing Agents.

Science.gov (United States)

Matsui, Kazuki; Tsume, Yasuhiro; Amidon, Gregory E; Amidon, Gordon L

2015-07-06

Weakly basic drugs typically exhibit pH-dependent solubility in the physiological pH range, displaying supersaturation or precipitation along the gastrointestinal tract. Additionally, their oral bioavailabilities may be affected by coadministration of acid-reducing agents that elevate gastric pH. The purpose of this study was to assess the feasibility of a multicompartmental in vitro dissolution apparatus, Gastrointestinal Simulator (GIS), in predicting in vivo dissolution of certain oral medications. In vitro dissolution studies of fluconazole, a BCS class I, and dipyridamole, a BCS class II weak bases (class IIb), were performed in the GIS as well as United States Pharmacopeia (USP) apparatus II and compared with the results of clinical drug-drug interaction (DDI) studies. In both USP apparatus II and GIS, fluconazole completely dissolved within 60 min regardless of pH, reflecting no DDI between fluconazole and acid-reducing agents in a clinical study. On the other hand, seven-fold and 15-fold higher concentrations of dipyridamole than saturation solubility were observed in the intestinal compartments in GIS with gastric pH 2.0. Precipitation of dipyridamole was also observed in the GIS, and the percentage of dipyridamole in solution was 45.2 ± 7.0%. In GIS with gastric pH 6.0, mimicking the coadministration of acid-reducing agents, the concentration of dipyridamole was equal to its saturation solubility, and the percentage of drug in solution was 9.3 ± 2.7%. These results are consistent with the clinical DDI study of dipyridamole with famotidine, which significantly reduced the Cmax and area under the curve. An In situ mouse infusion study combined with GIS revealed that high concentration of dipyridamole in the GIS enhanced oral drug absorption, which confirmed the supersaturation of dipyridamole. In conclusion, GIS was shown to be a useful apparatus to predict in vivo dissolution for BCS class IIb drugs.

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.

Vulnerability of the paper Nautilus (Argonauta nodosa) shell to a climate-change ocean: potential for extinction by dissolution.

Science.gov (United States)

Wolfe, Kennedy; Smith, Abigail M; Trimby, Patrick; Byrne, Maria

2012-10-01

Shell calcification in argonauts is unique. Only females of these cephalopods construct the paper nautilus shell, which is used as a brood chamber for developing embryos in the pelagic realm. As one of the thinnest (225 μm) known adult mollusc shells, and lacking an outer protective periostracum-like cover, this shell may be susceptible to dissolution as the ocean warms and decreases in pH. Vulnerability of the A. nodosa shell was investigated through immersion of shell fragments in multifactorial experiments of control (19 °C/pH 8.1; pCO(2) 419; Ω(Ca) = 4.23) and near-future conditions (24 °C/pH 7.8-7.6; pCO(2) 932-1525; Ω(Ca) = 2.72-1.55) for 14 days. More extreme pH treatments (pH 7.4-7.2; pCO(2) 2454-3882; Ω(Ca) = 1.20-0.67) were used to assess tipping points in shell dissolution. X-ray diffractometry revealed no change in mineralogy between untreated and treated shells. Reduced shell weight due to dissolution was evident in shells incubated at pH 7.8 (projected for 2070) after 14 days at control temperature, with increased dissolution in warmer and lower pH treatments. The greatest dissolution was recorded at 24 °C (projected for local waters by 2100) compared to control temperature across all low-pH treatments. Scanning electron microscopy revealed dissolution and etching of shell mineral in experimental treatments. In the absence of compensatory mineralization, the uncovered female brood chamber will be susceptible to dissolution as ocean pH decreases. Since the shell was a crucial adaptation for the evolution of the argonauts' holopelagic existence, persistence of A. nodosa may be compromised by shell dissolution in an ocean-change world.

Corrosion of glass-bonded sodalite as a function of pH and temperature

International Nuclear Information System (INIS)

Morss, L. R.; Stanley, M.; Tatko, C.; Ebert, W. L.

1999-01-01

This paper reports the results of corrosion tests with monoliths of sodalite, binder glass, and glass-bonded sodalite, a ceramic waste form (CWF) that is being developed to immobilize radioactive electrorefiner salt used to condition spent sodium-bonded nuclear fuel. These tests were performed with dilute pH-buffered solutions in the pH range of 5-10 at temperatures of 70 and 90 C. The pH dependence of the forward dissolution rates of the CWF and its components have been determined. The pH dependence of the dissolution rates of sodalite, binder glass, and glass-bonded sodalite are similar to the pH dependence of dissolution rate of borosilicate nuclear waste glasses, with a negative pH dependence in the acidic region and a positive pH dependence in the basic region. Our results on the forward dissolution rates and their temperature and pH dependence will be used as components of a waste form degradation model to predict the long-term behavior of the CWF in a nuclear waste repository

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

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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.

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.

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

Antibacterial effects and dissolution behavior of six bioactive glasses.

Science.gov (United States)

Zhang, Di; Leppäranta, Outi; Munukka, Eveliina; Ylänen, Heimo; Viljanen, Matti K; Eerola, Erkki; Hupa, Mikko; Hupa, Leena

2010-05-01

Dissolution behavior of six bioactive glasses was correlated with the antibacterial effects of the same glasses against sixteen clinically important bacterial species. Powdered glasses (<45 microm) were immersed in simulated body fluid (SBF) for 48 h. The pH in the solution inside the glass powder was measured in situ with a microelectrode. After 2, 4, 27, and 48 h, the pH and concentration of ions after removing the particles and mixing the SBF were measured with a normal glass pH electrode and ICP-OES. The bacteria were cultured in broth with the glass powder for up to 4 days, after which the viability of the bacteria was determined. The antibacterial effect of the glasses increased with increasing pH and concentration of alkali ions and thus with increased dissolution tendency of the glasses, but it also depended on the bacterium type. The changes in the concentrations of Si, Ca, Mg, P, and B ions in SBF did not show statistically significant influence on the antibacterial property. Bioactive glasses showed strong antibacterial effects for a wide selection of aerobic bacteria at a high sample concentration (100 mg/mL). The antibacterial effects increased with glass concentration and a concentration of 50 mg/mL (SA/V 185 cm(-1)) was required to generate the bactericidal effects. Understanding the dissolution mechanisms of bioactive glasses is essential when assessing their antibacterial effects. Copyright 2009 Wiley Periodicals, Inc.

Dissolution test for glibenclamide tablets

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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.

The dissolution behavior of borosilicate glasses in far-from equilibrium conditions

Science.gov (United States)

Neeway, James J.; Rieke, Peter C.; Parruzot, Benjamin P.; Ryan, Joseph V.; Asmussen, R. Matthew

2018-04-01

An area of agreement in the waste glass corrosion community is that, at far-from-equilibrium conditions, the dissolution of borosilicate glasses used to immobilize nuclear waste is known to be a function of both temperature and pH. The aim of this work is to study the effects of temperature and pH on the dissolution rate of three model nuclear waste glasses (SON68, ISG, AFCI). The dissolution rate data are then used to parameterize a kinetic rate model based on Transition State Theory that has been developed to model glass corrosion behavior in dilute conditions. To do this, experiments were conducted at temperatures of 23, 40, 70, and 90 °C and pH (22 °C) values of 9, 10, 11, and 12 with the single-pass flow-through (SPFT) test method. Both the absolute dissolution rates and the rate model parameters are compared with previous results. Rate model parameters for the three glasses studied here are nearly equivalent within error and in relative agreement with previous studies though quantifiable differences exist. The glass dissolution rates were analyzed with a linear multivariate regression (LMR) and a nonlinear multivariate regression performed with the use of the Glass Corrosion Modeling Tool (GCMT), with which a robust uncertainty analysis is performed. This robust analysis highlights the high degree of correlation of various parameters in the kinetic rate model. As more data are obtained on borosilicate glasses with varying compositions, a mathematical description of the effect of glass composition on the rate parameter values should be possible. This would allow for the possibility of calculating the forward dissolution rate of glass based solely on composition. In addition, the method of determination of parameter uncertainty and correlation provides a framework for other rate models that describe the dissolution rates of other amorphous and crystalline materials in a wide range of chemical conditions. The higher level of uncertainty analysis would provide

The dissolution of high-FeO olivine rock from the Lovasjaervi intrusion (SE-Finland) at 25 deg. C as a function of pH

International Nuclear Information System (INIS)

Duro, Lara; El Aamrani, Fatima; Rovira, Miquel; Gimenez, Javier; Casas, Ignasi; Pablo, Joan de; Bruno, Jordi

2005-01-01

The high-FeO olivine-rich rock from the Lovasjaervi intrusion (65% olivine, 20% plagioclase, 8% magnetite, 4% pyroxene and 3% serpentine) has been proposed as a potential redox-active backfill-additive in deep high level nuclear waste repositories. In this work, the authors report on kinetic dissolution studies of this solid under different pH and redox conditions performed by using a flow-through methodology. Assuming that silicon is mainly released to solution from the olivine contained in the solid, the experimental results have been adjusted to an empirical rate law as a function of proton concentration. The proton concentration reaction orders agree with results found in the literature for both acidic and alkaline pH ranges. The calculations conducted with the reactive transport code RETRASO show that at alkaline pH, the olivine rock might have a lower redox buffer capacity than expected

Effect of gastric pH on the pharmacokinetics of a BCS class II compound in dogs: utilization of an artificial stomach and duodenum dissolution model and GastroPlus,™ simulations to predict absorption.

Science.gov (United States)

Bhattachar, Shobha N; Perkins, Everett J; Tan, Jeffrey S; Burns, Lee J

2011-11-01

Dogs are one of the most commonly used non-rodent species in toxicology studies and are known to have basal stomach pH ranging from 2 to 7 in the fasted state. Thus absorption and resulting plasma exposure of weakly basic compounds administered as crystalline suspensions to dogs are often variable. LY2157299 is a potent and selective transforming growth factor (TGF)-beta receptor type 1 kinase (TGF-βRI) inhibitor that displayed variable absorption in early dog studies. This molecule is a weakly basic Biopharmaceutics Classification System (BCS)Class II compound, and depends on the rate and extent of dissolution to drive oral absorption. An artificial stomach and duodenum (ASD) dissolution model was utilized to evaluate potential effect of gastric pH on the absorption of suspension and buffered solution formulations. GastroPlus™ was also employed to predict the magnitude of gastric pH changes on LY2157299 absorption. The ASD experiments demonstrated that administration of a buffered acidic solution could improve the potential for absorption by normalizing gastric pH and enabling supersaturation in the duodenum. GastroPlus™ modeling suggested that direct modulation of gastric pH could lead to marked changes in bioavailability. Pharmacokinetic experiments were conducted in dogs to evaluate the effect of gastric pH modification on plasma exposure. The data were qualitatively consistent with the predictions. Copyright © 2011 Wiley-Liss, Inc.

In vitro dissolution of proton-pump inhibitor products intended for paediatric and geriatric use in physiological bicarbonate buffer.

Science.gov (United States)

Liu, Fang; Shokrollahi, Honaz

2015-05-15

Proton-pump inhibitor (PPI) products based on enteric coated multiparticulates are design to meet the needs of patients who cannot swallow tablets such as children and older adults. Enteric coated PPI preparations exhibit delays in in vivo absorption and onset of antisecretory effects, which is not reflected by the rapid in vitro dissolution in compendial pH 6.8 phosphate buffer commonly used for assessment of these products. A more representative and physiological medium, pH 6.8 mHanks bicarbonate buffer, was used in this study to evaluate the in vitro dissolution of enteric coated multiparticulate-based PPI products. Commercially available omeprazole, lansoprazole and esomeprazole products were subject to dissolution tests using USP-II apparatus in pH 4.5 phosphate buffer saline for 45 min (acid stage) followed by pH 6.8 phosphate buffer or pH 6.8 mHanks bicarbonate buffer. In pH 6.8 phosphate buffer, all nine tested products displayed rapid and comparable dissolution profiles meeting the pharmacopeia requirements for delayed release preparations. In pH 6.8 mHanks buffer, drug release was delayed and failed the pharmacopeia requirements from most enteric coated preparations. Despite that the same enteric polymer, methacrylic acid-ethyl acrylate copolymer (1:1), was applied to all commercial multiparticulate-based products, marked differences were observed between dissolution profiles of these preparations. The use of pH 6.8 physiological bicarbonate (mHanks) buffer can serve as a useful tool to provide realistic and discriminative in vitro release assessment of enteric coated PPI preparations and to assist rational formulation development of these products. Copyright © 2015 Elsevier B.V. All rights reserved.

Dissolution of anodic zirconium dioxide films in aqueous media

International Nuclear Information System (INIS)

Merati, A.; Cox, B.

1999-01-01

Zirconium with a low thermal neutron cross section, good corrosion resistance in high-temperature water, and high thermal conductivity is an ideal material for nuclear reactors. Its good resistance to water and steam at reactor temperatures is of the greatest interest to nuclear fuel designers. Dissolution of zirconium dioxide (ZrO 2 ) films in aggressive media was investigated. The extent of uniform and localized dissolution was measured by ultraviolet-visible (UV-VIS) spectrometry and an alternating current (AC) impedance test, respectively. Scanning electron microscopy (SEM) showed the extent of dissolution of ZrO 2 was a function only of the fluoride ion content and pH of the medium. Cathodic polarization was used to identify the preferred sites for localized dissolution of the oxide film. In 0.1 M potassium bifluoride (KHF 2 ), both uniform thinning and local breakdown of the oxide were observed. Within the limits of the investigating techniques, no evidence of dissolution was observed in the other solutions tested: 0.5 M sulfuric acid (H 2 SO 4 ). 1.0 M nitric acid (HNO 3 ), 5 M hydrochloric acid (HCl), or 0.1 M potassium fluoride (KF). In areas around iron-containing particles, fine cracks in the anodic oxide at prior metal grain boundaries and arrays of cracks in the oxide associated with residual scratches from the initial specimen preparation were the preferred spots for localized dissolution of the oxide film. Iron precipitates immediately below the surface of the oxide layer increased the local electrical conductivity. Enrichment of iron in the oxide matrix around these precipitates during the anodization process appeared to cause prospective spots, acting as anodic sites for pH formation

Freezing-Enhanced Dissolution of Iron Oxides: Effects of Inorganic Acid Anions.

Science.gov (United States)

Jeong, Daun; Kim, Kitae; Min, Dae Wi; Choi, Wonyong

2015-11-03

Dissolution of iron from mineral dust particles greatly depends upon the type and amount of copresent inorganic anions. In this study, we investigated the roles of sulfate, chloride, nitrate, and perchlorate on the dissolution of maghemite and lepidocrocite in ice under both dark and UV irradiation and compared the results with those of their aqueous counterparts. After 96 h of reaction, the total dissolved iron in ice (pH 3 before freezing) was higher than that in the aqueous phase (pH 3) by 6-28 times and 10-20 times under dark and UV irradiation, respectively. Sulfuric acid was the most efficient in producing labile iron under dark condition, whereas hydrochloric acid induced the most dissolution of the total and ferrous iron in the presence of light. This ice-induced dissolution result was also confirmed with Arizona Test Dust (AZTD). In the freeze-thaw cycling test, the iron oxide samples containing chloride, nitrate, or perchlorate showed a similar extent of total dissolved iron after each cycling while the sulfate-containing sample rapidly lost its dissolution activity with repeating the cycle. This unique phenomenon observed in ice might be related to the freeze concentration of protons, iron oxides, and inorganic anions in the liquid-like ice grain boundary region. These results suggest that the ice-enhanced dissolution of iron oxides can be a potential source of bioavailable iron, and the acid anions critically influence this process.

Characterization, Dissolution, and Solubility of Lead Hydroxypyromorphite [Pb5(PO43OH] at 25–45°C

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Yinian Zhu

2015-01-01

Full Text Available Dissolution of the hydroxypyromorphite [lead hydroxyapatite, Pb5(PO43OH] in HNO3 solution (pH = 2.00, ultrapure water (pH = 5.60, and NaOH solution (pH = 9.00 was experimentally studied at 25°C, 35°C, and 45°C. The XRD, FT-IR, and FE-SEM analyses indicated that the hydroxypyromorphite solids were observed to have indistinguishable change during dissolution. For the hydroxypyromorphite dissolution in aqueous acidic media at initial pH 2.00 and 25°C, the aqueous phosphate concentrations rose quickly and reached the peak values after 1 h dissolution, while the aqueous lead concentrations rose slowly and reached the peak values after 1440 h. The solution Pb/P molar ratio increased constantly from 1.10 to 1.65 near the stoichiometric ratio of 1.67 to 209.85~597.72 and then decreased to 74.76~237.26 for the dissolution at initial pH 2.00 and 25°C~45°C. The average Ksp values for Pb5(PO43OH were determined to be 10−80.77 (10−80.57−10−80.96 at 25°C, 10−80.65 (10−80.38−10−80.99 at 35°C, and 10−79.96 (10−79.38−10−80.71 at 45°C. From the obtained solubility data for the dissolution at initial pH 2.00 and 25°C, the Gibbs free energy of formation [ΔGfo] for Pb5(PO43OH was calculated to be −3796.71 kJ/mol (−3795.55~−3797.78 kJ/mol.

Comparative Studies on the Dissolution Profiles of Oral Ibuprofen Suspension and Commercial Tablets using Biopharmaceutical Classification System Criteria

Science.gov (United States)

Rivera-Leyva, J. C.; García-Flores, M.; Valladares-Méndez, A.; Orozco-Castellanos, L. M.; Martínez-Alfaro, M.

2012-01-01

In vitro dissolution studies for solid oral dosage forms have recently widened the scope to a variety of special dosage forms such as suspensions. For class II drugs, like Ibuprofen, it is very important to have discriminative methods for different formulations in physiological conditions of the gastrointestinal tract, which will identify different problems that compromise the drug bioavailability. In the present work, two agitation speeds have been performed in order to study ibuprofen suspension dissolution. The suspensions have been characterised relatively to particle size, density and solubility. The dissolution study was conducted using the following media: buffer pH 7.2, pH 6.8, 4.5 and 0.1 M HCl. For quantitative analysis, the UV/Vis spectrophotometry was used because this methodology had been adequately validated. The results show that 50 rpm was the adequate condition to discriminate the dissolution profile. The suspension kinetic release was found to be dependent on pH and was different compared to tablet release profile at the same experimental conditions. The ibuprofen release at pH 1.0 was the slowest. PMID:23626386

Development of pH sensitive polymeric nanoparticles of erythromycin stearate

Directory of Open Access Journals (Sweden)

Sulekha Bhadra

2016-01-01

Full Text Available Context: Bioavailability of conventional tablet of erythromycin stearate is low as it is unstable at acidic pH and also shows a low dissolution rate. Objective: It was proposed to protect it from the acidic condition of the stomach along with an increase in dissolution rate by formulating pH sensitive nanoparticles. Materials and Methods: The nanoparticles were prepared by the solvent evaporation technique using different quantities of Eudragit L100-55 and polyvinyl alcohol (PVA. Size reduction was achieved by high speed homogenization technique using Digital Ultra Turrax homogenizer. The formulation was optimized using 32 factorial design, keeping drug polymer ratio and surfactant concentration as independent variables. Particle size, entrapment efficiency, and drug-release (DR were studied as dependent variables. Results: Optimized batch containing 1:0.3 erythromycin stearate: Eudragit L100-55 ratio and 1.0% PVA showed 8.24 ± 0.71% DR in pH 1.2 in 1-h and 90.38 ± 5.97% in pH 5.5 and pH 6.8 within 2-h, respectively. Discussion: The optimized batch exhibited lower release in acidic pH and faster release in higher pH compared to the marketed preparation. Conclusion: Thus the present study concludes that pH sensitive nanoparticles of erythromycin stearate increases the dissolution of the drug in intestinal pH and also protect it from acidic pH, which may help in improving the bioavailability of erythromycin.

Principles of calcite dissolution in human and artificial otoconia.

Directory of Open Access Journals (Sweden)

Leif Erik Walther

Full Text Available Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV. The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic otoconia (calcite gelatin nanocomposits and natural calcite were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM. Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of calcite dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV.

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

Agglomeration, isolation and dissolution of commercially manufactured silver nanoparticles in aqueous environments

International Nuclear Information System (INIS)

Elzey, Sherrie; Grassian, Vicki H.

2010-01-01

The increasing use of manufactured nanoparticles ensures these materials will make their way into the environment. Silver nanoparticles in particular, due to use in a wide range of applications, have the potential to get into water systems, e.g., drinking water systems, ground water systems, estuaries, and/or lakes. One important question is what is the chemical and physical state of these nanoparticles in water? Are they present as isolated particles, agglomerates or dissolved ions, as this will dictate their fate and transport. Furthermore, does the chemical and physical state of the nanoparticles change as a function of size or differ from micron-sized particles of similar composition? In this study, an electrospray atomizer coupled to a scanning mobility particle sizer (ES-SMPS) is used to investigate the state of silver nanoparticles in water and aqueous nitric acid environments. Over the range of pH values investigated, 0.5-6.5, silver nanoparticles with a bimodal primary particle size distribution with the most intense peak at 5.0 ± 7.4 nm, as determined from transmission electron microscopy (TEM), show distinct size distributions indicating agglomeration between pH 6.5 and 3 and isolated nanoparticles at pH values from 2.5 to 1. At the lowest pH investigated, pH 0.5, there are no peaks detected by the SMPS, indicating complete nanoparticle dissolution. Further analysis of the solution shows dissolved Ag ions at a pH of 0.5. Interestingly, silver nanoparticle dissolution shows size dependent behavior as larger, micron-sized silver particles show no dissolution at this pH. Environmental implications of these results are discussed.

Agglomeration, isolation and dissolution of commercially manufactured silver nanoparticles in aqueous environments

Energy Technology Data Exchange (ETDEWEB)

Elzey, Sherrie; Grassian, Vicki H., E-mail: vicki-grassian@uiowa.ed [University of Iowa, Department of Chemical and Biochemical Engineering (United States)

2010-06-15

The increasing use of manufactured nanoparticles ensures these materials will make their way into the environment. Silver nanoparticles in particular, due to use in a wide range of applications, have the potential to get into water systems, e.g., drinking water systems, ground water systems, estuaries, and/or lakes. One important question is what is the chemical and physical state of these nanoparticles in water? Are they present as isolated particles, agglomerates or dissolved ions, as this will dictate their fate and transport. Furthermore, does the chemical and physical state of the nanoparticles change as a function of size or differ from micron-sized particles of similar composition? In this study, an electrospray atomizer coupled to a scanning mobility particle sizer (ES-SMPS) is used to investigate the state of silver nanoparticles in water and aqueous nitric acid environments. Over the range of pH values investigated, 0.5-6.5, silver nanoparticles with a bimodal primary particle size distribution with the most intense peak at 5.0 {+-} 7.4 nm, as determined from transmission electron microscopy (TEM), show distinct size distributions indicating agglomeration between pH 6.5 and 3 and isolated nanoparticles at pH values from 2.5 to 1. At the lowest pH investigated, pH 0.5, there are no peaks detected by the SMPS, indicating complete nanoparticle dissolution. Further analysis of the solution shows dissolved Ag ions at a pH of 0.5. Interestingly, silver nanoparticle dissolution shows size dependent behavior as larger, micron-sized silver particles show no dissolution at this pH. Environmental implications of these results are discussed.

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

Improved dissolution and absorption of ketoconazole in the presence of organic acids as pH-modifiers.

Science.gov (United States)

Adachi, Masashi; Hinatsu, Yuta; Kusamori, Kosuke; Katsumi, Hidemasa; Sakane, Toshiyasu; Nakatani, Manabu; Wada, Koichi; Yamamoto, Akira

2015-08-30

Formulation development of poorly water-soluble compounds can be challenging because of incomplete dissolution that causes low and variable bioavailability. Enhancing compound solubility is important and many techniques have been investigated to that end, but they require specific materials and machinery. This study investigates the incorporation of a pH-modifier as a method to increase compound solubility and uses ketoconazole (KZ), which is weakly basic (pKa: 6.5), as a model compound. Organic acids are effective pH-modifiers and are generally used in pharmaceutical industries. We successfully obtained granules containing variable organic acids (KZ/acid granule) using a high-shear mixer. Dissolution tests of the KZ/acid granule resulted in highly enhanced solubility under non-sink conditions. Adding water-soluble acids, such as citric acid (CA) and tartaric acid, resulted in more than 8-fold higher dissolution at pH 6.0 compared to that of KZ only. The granules containing citric acid (KZ/CA granule) improved the dissolution of KZ after oral administration to rats under low gastric acid conditions, where the bioavailability of the KZ/CA granules at elevated gastric pH was comparable with that of KZ only at gastric acidic pH. The incorporation of organic acids would result in effective therapeutic outcomes independent of gastric pH in patients. In addition, higher bioavailability of KZ was observed after oral administration of KZ/CA granules under gastric acidic pH conditions than that of KZ alone. Thus, CA improved the dissolution and absorption rate of KZ after oral administration. Copyright © 2015 Elsevier B.V. All rights reserved.

A Study on the Oxidative-dissolution Leaching of Fission Product Oxides in the carbonate solution

International Nuclear Information System (INIS)

Lee, Eil Hee; Kim, Kwang Wook; Lim, Jae Gwan; Chung, Dong Yong; Yang, Han Beom; Joe, Kih Soo; Seo, Heui Seung; Kim, Yeon Hwa; Lee, Se Yoon

2009-07-01

This study was carried out to investigate the characteristics of an oxidativedissolution leaching of FP co-dissolved with U in a carbonate solution of Na 2 CO 3 - H 2 O 2 and (NH 4 ) 2 CO 3 -H 2 O 2 , respectively. Simulated FP-oxides which contained 12 components have been added to the solution to examine their oxidative dissolution characteristics. It was found that H 2 O 2 was an effective oxidant to minimize the dissolution of FP in a carbonate solution. In 0.5M Na 2 CO 3 -0.5M H 2 O 2 and 0.5M (NH 4 ) 2 CO 3 -0.5M H 2 O 2 solution, some elements such as Re, Te, Cs and Mo seem to be dissolved together with U. It is revealed that dissolution rates of Re, Te and Cs are high (completely dissolved within 10∼20 minutes) due to their high solubility in Na 2 CO 3 and (NH 4 ) 2 CO 3 solution regardless of the addition of H 2 O 2 , and independent of the concentrations of Na 2 CO 3 and H 2 O 2 . However, Mo was slowly dissolved by an oxidative dissolution with H 2 O 2 . It is found that the most important factor for the oxidative dissolution of FP is the pH of the solution and an effective oxidative dissolution is achieved at a pH between 10∼12 for Na 2 CO 3 and a pH between 9∼10 for (NH 4 ) 2 CO 3 , respectively, in order to minimize the dissolution of FP

Role of Adsorption Phenomena in Cubic Tricalcium Aluminate Dissolution.

Science.gov (United States)

Myers, Rupert J; Geng, Guoqing; Li, Jiaqi; Rodríguez, Erich D; Ha, Juyoung; Kidkhunthod, Pinit; Sposito, Garrison; Lammers, Laura N; Kirchheim, Ana Paula; Monteiro, Paulo J M

2017-01-10

The workability of fresh Portland cement (PC) concrete critically depends on the reaction of the cubic tricalcium aluminate (C 3 A) phase in Ca- and S-rich pH >12 aqueous solution, yet its rate-controlling mechanism is poorly understood. In this article, the role of adsorption phenomena in C 3 A dissolution in aqueous Ca-, S-, and polynaphthalene sulfonate (PNS)-containing solutions is analyzed. The zeta potential and pH results are consistent with the isoelectric point of C 3 A occurring at pH ∼12 and do not show an inversion of its electric double layer potential as a function of S or Ca concentration, and PNS adsorbs onto C 3 A, reducing its zeta potential to negative values at pH >12. The S and Ca K-edge X-ray absorption spectroscopy (XAS) data obtained do not indicate the structural incorporation or specific adsorption of SO 4 2- on the partially dissolved C 3 A solids analyzed. Together with supporting X-ray ptychography and scanning electron microscopy results, a model for C 3 A dissolution inhibition in hydrated PC systems is proposed whereby the formation of an Al-rich leached layer and the complexation of Ca-S ion pairs onto this leached layer provide the key inhibiting effect(s). This model reconciles the results obtained here with the existing literature, including the inhibiting action of macromolecules such as PNS and polyphosphonic acids upon C 3 A dissolution. Therefore, this article advances the understanding of the rate-controlling mechanism in hydrated C 3 A and thus PC systems, which is important to better controlling the workability of fresh PC concrete.

The dissolution kinetics of magnetite under regenerative conditions

International Nuclear Information System (INIS)

Ranganathan, S.

2004-01-01

Dissolution studies of magnetite were carried out under regenerative conditions in dilute chemical decontamination formulations. During regeneration of the formulation, the H + from the strong acid cation exchange resin gets released and the metal is absorbed on the resin. The efficiency of the regenerative process depends on the stability constants of the complexes involved and the selectivity on the ion exchange column. The regenerative condition helps to maintain a constant chelating agent concentration and pH during the dissolution experiment. Such a condition is ideal for obtaining data on the dissolution behaviour of the corrosion products with special application to actual reactor decontamination. The ethylenediaminetetraacetic acid (EDTA) based formulation used was found to be ineffective due to the high stability constant of Fe(III)-EDTA complex, which is not easily cleaved by the cation exchange resin. Hence, knowledge of the kinetics of magnetite dissolution under regenerative condition is of primary importance. The 2,6-pyridinedicarboxylic acid formulation is found to be better for the dissolution of Fe 3 O 4 in both static and regenerative modes in the presence of reductants than nitrilotriacetic acid and EDTA. (orig.)

The dissolution kinetics of magnetite under regenerative conditions

Energy Technology Data Exchange (ETDEWEB)

Ranganathan, S. [New Brunswick Univ., Frederiction (Canada). Dept. of Chemical Engineering; Raghavan, P.S.; Gopalan, R.; Srinivasan, M.P.; Narasimhan, S.V. [Water and Steam Chemistry Lab. of Bhabha Atomic Research Centre (BARC) (India)

2004-07-01

Dissolution studies of magnetite were carried out under regenerative conditions in dilute chemical decontamination formulations. During regeneration of the formulation, the H{sup +} from the strong acid cation exchange resin gets released and the metal is absorbed on the resin. The efficiency of the regenerative process depends on the stability constants of the complexes involved and the selectivity on the ion exchange column. The regenerative condition helps to maintain a constant chelating agent concentration and pH during the dissolution experiment. Such a condition is ideal for obtaining data on the dissolution behaviour of the corrosion products with special application to actual reactor decontamination. The ethylenediaminetetraacetic acid (EDTA) based formulation used was found to be ineffective due to the high stability constant of Fe(III)-EDTA complex, which is not easily cleaved by the cation exchange resin. Hence, knowledge of the kinetics of magnetite dissolution under regenerative condition is of primary importance. The 2,6-pyridinedicarboxylic acid formulation is found to be better for the dissolution of Fe{sub 3}O{sub 4} in both static and regenerative modes in the presence of reductants than nitrilotriacetic acid and EDTA. (orig.)

Dissolution behavior of 137Cs absorbed on the green tea leaves

International Nuclear Information System (INIS)

Oya, Yasuhisa; Uchimura, Hiromichi; Toda, Kensuke; Okuno, Kenji; Ikka, Takashi; Morita, Akio

2013-01-01

The green tea leaves was dipped in the 137 CsCl solution to elucidate the dissolution behavior of 137 Cs contaminated on the green tea leaves. It was found that the amount of 137 Cs dissolved into tea water was controlled by the temperature of water, and the activation energy of 137 Cs dissolution was estimated to be 0.045 eV, indicating that most of 137 Cs would exist as the adsorbed state. In addition, the dissolution behavior was controlled by the concentration of stable Cs dissolved in water, although no large correlation with pH was observed. (author)

Development and validation of a dissolution test for diltiazem hydrochloride in immediate release capsules

Directory of Open Access Journals (Sweden)

Taciane Ferreira Mendonça

2011-01-01

Full Text Available This work describes the development and validation of a dissolution test for 60 mg of diltiazem hydrochloride in immediate release capsules. The best dissolution in vitro profile was achieved using potassium phosphate buffer at pH 6.8 as the dissolution medium and paddle as the apparatus at 50 rpm. The drug concentrations in the dissolution media were determined by UV spectrophotometry and HPLC and a statistical analysis revealed that there were significant differences between HPLC and spectrophotometry. This study illustrates the importance of an official method for the dissolution test, since there is no official monograph for diltiazem hydrochloride in capsules.

Electrochemical characteristics of bioresorbable binary MgCa alloys in Ringer's solution: Revealing the impact of local pH distributions during in-vitro dissolution

Energy Technology Data Exchange (ETDEWEB)

Mareci, D., E-mail: danmareci@yahoo.com [Faculty of Chemical Engineering and Environmental Protection, The “Gheorghe Asachi” Technical University of Iasi, 700050, Iasi (Romania); Bolat, G. [Faculty of Chemical Engineering and Environmental Protection, The “Gheorghe Asachi” Technical University of Iasi, 700050, Iasi (Romania); Izquierdo, J. [Department of Chemistry, University of La Laguna, P.O. Box 456, E-38200 La Laguna (Tenerife) (Spain); Crimu, C.; Munteanu, C. [Faculty of Mechanical Engineering, The “Gheorghe Asachi” Technical University of Iasi, 700050, Iasi (Romania); Antoniac, I. [Faculty of Materials Science and Engineering, Politehnica of Bucharest, 060042 Bucharest (Romania); Souto, R.M., E-mail: rsouto@ull.es [Department of Chemistry, University of La Laguna, P.O. Box 456, E-38200 La Laguna (Tenerife) (Spain); Faculty of Materials Science and Engineering, Politehnica of Bucharest, 060042 Bucharest (Romania)

2016-03-01

Biodegradable magnesium–calcium (MgCa) alloy is a very attractive biomaterial. Two MgCa alloys below the solid solubility of Ca were considered, as to solely investigate the effect of Ca content on the behavior of magnesium and the pH changes associated to metal dissolution. X-ray diffraction analysis and optical microscopy showed that both Mg–0.63Ca and Mg–0.89Ca alloys were solely composed of α(Mg) phase. Degradation characteristics and electrochemical characterization of MgCa alloys were investigated during exposure to Ringer's solution at 37 °C by electrochemical impedance spectroscopy and scanning electrochemical microscopy. The impedance behavior showed both capacitive and inductive features that are related to the alloy charge transfer reaction and the relaxation of the absorbed corrosion compounds, and can be described in terms of an equivalent circuit. Scanning electron microscopy (SEM) was employed to view the surface morphology of the MgCa samples after 1 week immersion in Ringer's solution showing extensive precipitation of corrosion products, whereas the substrate shows evidence of a non-uniform corrosion process. Energy dispersive analysis showed that the precipitates contained oxygen, calcium, magnesium and chlorine, and the Mg:Ca ratios were smaller than in the alloys. Scanning electrochemical microscopy (SECM) was used to visualize local pH changes associated to these physicochemical processes with high spatial resolution. The occurrence of pH variations in excess of 3 units between anodic and cathodic half-cell reactions was monitored in situ. - Highlights: • Spontaneous degradation of MgCa alloys in Ringer's solution characterized at 37 °C • Reactivity differences between Mg0.63Ca and Mg0.89Ca are evidenced using multiscale electrochemical characterization. • Electrochemical activation occurs heterogeneously on the alloy surface. • Metal dissolution is accompanied by local pH changes. • Mg0.63Ca degrades faster

Dissolution and solubility behavior of fenofibrate in sodium lauryl sulfate solutions.

Science.gov (United States)

Granero, Gladys E; Ramachandran, Chandrasekharan; Amidon, Gordon L

2005-10-01

The solubility of fenofibrate in pH 6.8 McIlvaine buffers containing varying concentrations of sodium lauryl sulfate was determined. The dissolution behavior of fenofibrate was also examined in the same solutions with rotating disk experiments. It was observed that the enhancement in intrinsic dissolution rate was approximately 500-fold and the enhancement in solubility was approximately 2000-fold in a pH 6.8 buffer containing 2% (w/v) sodium lauryl sulfate compared to that in buffer alone. The micellar solubilization equilibrium coefficient (k*) was estimated from the solubility data and found to be 30884+/-213 L/mol. The diffusivity for the free solute, 7.15x10(-6) cm2/s, was calculated using Schroeder's additive molal volume estimates and Hayduk-Laurie correlation. The diffusivity of the drug-loaded micelle, estimated from the experimental solubility and dissolution data and the calculated value for free solute diffusivity, was 0.86x10(-6) cm2/s. Thus, the much lower enhancement in dissolution of fenofibrate compared to its enhancement in solubility in surfactant solutions appears to be consistent with the contribution to the total transport due to enhanced micellar solubilization as well as a large decrease (approximately 8-fold) in the diffusivity of the drug-loaded micelle.

Development and validation of dissolution method for carvedilol compression-coated tablets

Directory of Open Access Journals (Sweden)

Ritesh Shah

2011-12-01

Full Text Available The present study describes the development and validation of a dissolution method for carvedilol compression-coated tablets. Dissolution test was performed using a TDT-06T dissolution apparatus. Based on the physiological conditions of the body, 0.1N hydrochloric acid was used as dissolution medium and release was monitored for 2 hours to verify the immediate release pattern of the drug in acidic pH, followed by pH 6.8 in citric-phosphate buffer for 22 hours, to simulate a sustained release pattern in the intestine. Influences of rotation speed and surfactant concentration in medium were evaluated. Samples were analysed by validated UV visible spectrophotometric method at 286 nm. 1% sodium lauryl sulphate (SLS was found to be optimum for improving carvedilol solubility in pH 6.8 citric-phosphate buffer. Analysis of variance showed no significant difference between the results obtained at 50 and 100 rpm. The discriminating dissolution method was successfully developed for carvedilol compression-coated tablets. The conditions that allowed dissolution determination were USP type I apparatus at 100 rpm, containing 1000 ml of 0.1N HCl for 2 hours, followed by pH 6.8 citric-phosphate buffer with 1% SLS for 22 hours at 37.0 ± 0.5 ºC. Samples were analysed by UV spectrophotometric method and validated as per ICH guidelines.O presente estudo descreve o desenvolvimento e a validação de método de dissolução para comprimidos revestidos de carvedilol. O teste de dissolução foi efetuado utilizando-se o aparelho para dissolução TDT-06T. Com base nas condições fisiológicas do organismo, utilizou-se ácido clorídrico 0,1 N como meio de dissolução e a liberação foi monitorada por 2 horas para se verificar o padrão de liberação imediata do fármaco em condições de pH baixo, seguidas por pH 6,8 em tampão cítrico-fosfato por 22 horas, para simular o padrão de liberação controlada no intestino. Avaliou-se a influência da velocidade de

Effects of acid deposition on dissolution of carbonate stone during summer storms in the Adirondack Mountains, New York, 1987-89

Science.gov (United States)

Schuster, Paul F.; Reddy, Michael M.; Sherwood, S.I.

1994-01-01

This study is part of a long-term research program designed to identify and quantify acid rain damage to carbonate stone. Acidic deposition accelerates the dissolution of carbonate-stone monuments and building materials. Sequential sampling of runoff from carbonate-stone (marble) and glass (reference) microcatchments in the Adirondack Mountains in New York State provided a detailed record of the episodic fluctuations in rain rate and runoff chemistry during individual summer storms. Rain rate and chemical concentrations from carbonate-stone and glass runoff fluctuated three to tenfold during storms. Net calcium-ion concentrations from the carbonatestone runoff, a measure of stone dissolution, typically fluctuated twofold during these storms. High net sulfate and net calcium concentrations in the first effective runoff at the start of a storm indicated that atmospheric pollutants deposited on the stone surface during dry periods formed calcium sulfate minerals, an important process in carbonate stone dissolution. Dissolution of the carbonate stone generally increased up to twofold during coincident episodes of low rain rate (less than 5 millimeters per hour) and decreased rainfall (glass runoff) pH (less than 4.0); episodes of high rain rate (cloudbursts) were coincident with a rapid increase in rainfall pH and also a rapid decrease in the dissolution of carbonate-stone. During a storm, it seems the most important factors causing increased dissolution of carbonate stone are coincident periods of low rain rate and decreased rainfall pH. Dissolution of the carbonate stone decreased slightly as the rain rate exceeded about 5 millimeters per hour, probably in response to rapidly increasing rainfall pH during episodes of high rain rate and shorter contact time between the runoff and the stone surface. High runoff rates resulting from cloudbursts remove calcium sulfate minerals formed during dry periods prior to storms and also remove dissolution products formed in large

Chemical alteration of cement hydrates by dissolution

International Nuclear Information System (INIS)

Sugiyama, Daisuke; Fujita, Tomonari; Nakanishi, Kiyoshi

2000-01-01

Cementitious material is a potential waste packaging and backfilling material for the radioactive waste disposal, and is expected to provide both physical and chemical containment. In particular, the sorption of radionuclides onto cementitious material and the ability to provide a high pH condition are very important parameters when considering the release of radionuclides from radioactive wastes. For the long term, in the geological disposal environment, cement hydrates will be altered by, for example, dissolution, chemical reaction with ions in the groundwater, and hydrothermal reaction. Once the composition or crystallinity of the constituent minerals of a cement hydrate is changed by these processes, the pH of the repository buffered by cementitious material and its sorption ability might be affected. However, the mechanism of cement alteration is not yet fully understood. In this study, leaching experiments of some candidate cements for radioactive waste disposal were carried out. Hydrated Ordinary Portland Cement (OPC), Blast Furnace Slag blended cement (OPC/BFS) and Highly containing Flyash and Silicafume Cement (HFSC) samples were contacted with distilled water at liquid:solid ratios of 10:1, 100:1 and 1000:1 at room temperature for 200 days. In the case of OPC, Ca(OH) 2 dissolved at high liquid:solid ratios. The specific surface area of all cement samples increased by leaching process. This might be caused by further hydration and change of composition of constituent minerals. A model is presented which predicts the leaching of cement hydrates and the mineral composition in the hydrated cement solid phase, including the incongruent dissolution of CSH gel phases and congruent dissolution of Ca(OH) 2 , Ettringite and Hydrotalcite. Experimental results of dissolution of Ca-O-H and Ca-Si-O-H phases were well predicted by this model. (author)

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...

A comparison of sports and energy drinks--Physiochemical properties and enamel dissolution.

Science.gov (United States)

Jain, Poonam; Hall-May, Emily; Golabek, Kristi; Agustin, Ma Zenia

2012-01-01

The consumption of sports and energy drinks by children and adolescents has increased at an alarming rate in recent years. It is essential for dental professionals to be informed about the physiochemical properties of these drinks and their effects on enamel. The present study measured the fluoride levels, pH, and titratable acidity of multiple popular, commercially available brands of sports and energy drinks. Enamel dissolution was measured as weight loss using an in vitro multiple exposure model consisting of repeated short exposures to these drinks, alternating with exposure to artificial saliva. The relationship between enamel dissolution and fluoride levels, pH, and titratable acidity was also examined. There was a statistically significant difference between the fluoride levels (p = 0.034) and pH (p = 0.04) of the sports and energy drinks studied. The titratable acidity of energy drinks (11.78) was found to be significantly higher than that of sports drinks (3.58) (p energy drinks (Red Bull Sugar Free, Monster Assault, Von Dutch, Rockstar, and 5-Hour Energy) were found to have the highest titratable acidity values among the brands studied. Enamel weight loss after exposure to energy drinks was significantly higher than it was after exposure to sports drinks. The effect of titratable acidity on enamel weight loss was found to vary inversely with the pH of the drinks. The findings indicated that energy drinks have significantly higher titratable acidity and enamel dissolution associated with them than sports drinks. Enamel weight loss after exposure to energy drinks was more than two times higher than it was after exposure to sports drinks. Titratable acidity is a significant predictor of enamel dissolution, and its effect on enamel weight loss varies inversely with the pH of the drink. The data from the current study can be used to educate patients about the differences between sports and energy drinks and the effects of these drinks on tooth enamel.

Thorium oxide dissolution kinetics for hydroxide and carbonate complexation

International Nuclear Information System (INIS)

Jardin, R.; Curran, V.; Czerwinski, K.R.

2002-01-01

The purpose of this project was to determine the kinetics and thermodynamics of thorium oxide dissolution in the environment. Solubility is important because it establishes an upper concentration limit on the concentration of a dissolved radionuclide in solution L1. While understanding the behavior of thorium fuels in the proposed repository at Yucca Mountain is most applicable, a more rigorous study of thorium solubility over a wide pH range was performed so that the data could also be used to model the behavior of thorium fuels in any environmental system. To achieve this, the kinetics and thermodynamics of thorium oxide dissolution under both pure argon and argon with P CO2 of 0. 1 were studied under the full pH range available in each atmosphere. In addition, thorium oxide powder remnants were studied after each experiment to examine structural changes that may affect kinetics

The kinetics of anodic dissolution of rhenium in aqueous electrolyte solutions

International Nuclear Information System (INIS)

Atanasyants, A.G.; Kornienko, V.A.

1986-01-01

The kinetics of anodic rhenium dissolution was investigated by means of potentiodynamic and potentiostatic polarization curves recorded at temperature from 293 to 333 K in different media (NaOH, KOH, NaCl, NaBr, HCl, H 2 SO 4 ) using the rotating disc technique. It is shown that the kinetics of anodic rhenium dissolution and effective activation energy depend not only on the composition and pH value of the solutions but also on the structure of the dissolving rhenium surface. The investigation of the anodic behaviour of the rhenium monocrystal revealed the existence of anisotropy of the monocrystal electrochemical properties. The experimental results point to an important role of adsorption processes in anodic rhenium dissolution. Rhenium dissolution proceeds with formation of intermediate surface adsorption complexes between the metal and the components of the solution

Uranium dissolution in hyper-alkaline TMA-OH solutions: Preliminary results

Energy Technology Data Exchange (ETDEWEB)

Cachoir, C.; Salah, S.; Mennecart, T.; Lemmens, K. [Belgian Research Nuclear Centre - SCK-CEN, Boeretang 200, 2400 Mol (Belgium)

2016-07-01

Leaching experiments were performed with depleted UO{sub 2} powders in tetramethylammonium solutions (TMA-OH) at pH 13.5 and 12.5, and at different UO{sub 2} surface area to volume of solution (SA/V) ratio's to determine the solubility and the dissolution kinetics of UO{sub 2} at high pH in absence of cations dominating cementitious waters (Ca, Na, K). The solubility of UO{sub 2} increased from pH 12.5 to 13.5 and by increasing the SA/V ratio up to 100 m{sup -1}. However, no known U secondary-phases were predicted by geochemical calculations to control the measured U-concentrations. We interpreted the UO{sub 2} dissolution process as a 2-step process. For all experiments, we observe a fast initial rate, hydroxo promoted and likely surface controlled. Afterwards the rate is apparently negative at low SA/V over time while it is positive at higher SA/V ratio's. The former is interpreted to be related to a sorption process, while the latter reveals a continuous residual dissolution process. No solubility enhancing effect of U-colloids was observed in the TMA-OH media. However, there is much less uranium colloid formation in TMA-OH tests with low Ca (Na, K) concentration than in previous tests with higher Ca (Na, K) concentrations. This suggests that the colloid formation is promoted by alkali and/or alkali-earth elements.

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.

Dissolution of oxide films on iron in aqueous solutions containing complexing anions

International Nuclear Information System (INIS)

Shoesmith, D.W.; Lee, W.; Owen, D.G.

1981-01-01

The dissolution, in oxalic acid and oxalic acid plus ethylenediaminetetraacetate, of magnetite films grown at high temperature on iron has been studied under varying conditions of pH and temperature. For oxalate concentrations greater than about 2 x 10 -3 mol dm -3 , magnetite dissolves by direct chemical dissolution. The mechanism appears to involve adsorption of oxalate ions at ferric ion sites in the oxide lattice, followed by proton attack and desorption of cationic species. Once metal dissolution starts, β-ferrous oxalate dihydrate is precipitated on the electrode, leading to erratic fluctuations in the electrode potential and eventually to inhibition of metal dissolution. For oxalate concentrations -3 mol dm -3 , the predominant dissolution mechanism appears to involve reduction by the metal. Also, once solution penetration to the underlying metal has occurred, and the electrode has returned to the active state, autoreductive dissolution appears to predominate even at higher oxalate concentrations. This change in mechanism from predominantly chemical dissolution to predominantly autoreductive dissolution may be due, at least in part, to the desorption of oxalate ions at the more negative potentials achieved in the active state. (author)

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)

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

Anodic dissolution of UO2 in slightly alkaline sodium perchlorate solutions

International Nuclear Information System (INIS)

Sunder, S.; Strandlund, L.K.; Shoesmith, D.W.

1996-04-01

The anodic dissolution of UO 2 has been studied in aqueous sodium perchlorate solutions at pH ∼ 9.5. Under potentiostatic conditions two distinct regions of oxidation/dissolution behaviour were observed. In the potential (E) range 0.100 V A , Q C respectively) obtained by integration of the anodic current-time plots (Q A ) and cathodic potential scans to reduce accumulated oxidized surface films (Q C ), it was shown that > ∼ 90% of the anodic oxidation current went to produce these films. For E > ∼ 0.350 V, steady-state currents were obtained and measurements of Q A and Q C showed the majority of the current went to produce soluble species. The film blocking anodic dissolution appeared to be either UO 2.27 or, more probably, UO 3 .2H 2 O located primarily at grain boundaries. It is proposed that, at the higher potentials, rapid oxidation and dissolution followed by the hydrolysis of dissolved uranyl species leads to the development of acidic conditions in the grain boundaries. At these lower pH values the UO 3 .2H 2 O is soluble and therefore does not accumulate. Alternatively, if this oxide has been formed by prior oxidation at a lower potential, the formation of protons on oxidizing at E > ∼ 0.350V causes its redissolution, allowing the current to rise to a steady-state value. On the basis of Tafel slopes, an attempt was made to demonstrate that the observed behaviour was consistent with dissolution under acidic conditions. This analysis was only partially successful. (author) 34 refs. 11 figs

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.

Chemometrics-assisted spectrophotometric green method for correcting interferences in biowaiver studies: Application to assay and dissolution profiling study of donepezil hydrochloride tablets

Science.gov (United States)

Korany, Mohamed A.; Mahgoub, Hoda; Haggag, Rim S.; Ragab, Marwa A. A.; Elmallah, Osama A.

2018-06-01

A green, simple and cost effective chemometric UV-Vis spectrophotometric method has been developed and validated for correcting interferences that arise during conducting biowaiver studies. Chemometric manipulation has been done for enhancing the results of direct absorbance, resulting from very low concentrations (high incidence of background noise interference) of earlier points in the dissolution timing in case of dissolution profile using first and second derivative (D1 & D2) methods and their corresponding Fourier function convoluted methods (D1/FF& D2/FF). The method applied for biowaiver study of Donepezil Hydrochloride (DH) as a representative model was done by comparing two different dosage forms containing 5 mg DH per tablet as an application of a developed chemometric method for correcting interferences as well as for the assay and dissolution testing in its tablet dosage form. The results showed that first derivative technique can be used for enhancement of the data in case of low concentration range of DH (1-8 μg mL-1) in the three different pH dissolution media which were used to estimate the low drug concentrations dissolved at the early points in the biowaiver study. Furthermore, the results showed similarity in phosphate buffer pH 6.8 and dissimilarity in the other 2 pH media. The method was validated according to ICH guidelines and USP monograph for both assays (HCl of pH 1.2) and dissolution study in 3 pH media (HCl of pH 1.2, acetate buffer of pH 4.5 and phosphate buffer of pH 6.8). Finally, the assessment of the method greenness was done using two different assessment techniques: National Environmental Method Index label and Eco scale methods. Both techniques ascertained the greenness of the proposed method.

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.

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.

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.

In vitro dissolution of curium oxide using a phagolysosomal simulant solvent system

International Nuclear Information System (INIS)

Helfinstine, S.Y.; Guilmette, R.A.; Schlapper, G.A.

1992-01-01

Detailed study of actinide oxide behavior in alveolar macrophages (AM) in vitro is limited because of the short life span of these cells in culture. We created an in vitro dissolution system that could mimic the acidic phagolysosomal environment for the actinide and be maintained for an indefinite period so that dissolution of more insoluble materials could be measured. The dissolution system for this investigation, consisting of nine different solutions of HCl and the chelating agent diethylenetriamine pentaacetate (DTPA) in distilled water, is called the phagolysosomal simulant solvent (PSS). In this system, both the pH and the amount of DTPA were varied. We could observe the effect of altering pH within a range of 4.0-6.0 (similar to that of the phagolysosome) and the effect of the molar ratio of DTPA to curium at 1000: 1, 100;1, or 10:1. We chose curium sesquioxide ( 244 Cm 2 O 3 ) to validate the PSS for actinide dissolution versus that occurring in AM in vitro because it dissolves significantly in less than 1 week. The polydisperse 244 Cm 2 O 3 aerosol was generated, collected on filters, resuspended, and added to the PSS solutions and to cultured canine AM. By comparing dissolution in the two systems directly, we hoped to arrive at an optimum PSS for future dissolution studies. PSS and cell culture samples were taken daily for 7 days after exposure and tested for the solubilized curium. The amount of soluble material was determined by ultracentrifugation to separate the insoluble CM 2 O 3 from the soluble curium in the PSS solutions and filtration for the cell-containing material. After separating the soluble and insoluble fractions, the samples were analyzed using alpha liquid scintillation counting. Time-dependent dissolution measurements from the PSS/AM showed that the CM 2 O 3 dissolution was similar for both the PSS solutions and the cultured AM. 13 refs., 4 tabs

Development and Validation of Discriminating and Biorelevant Dissolution Test for Lornoxicam Tablets.

Science.gov (United States)

Anumolu, P D; Sunitha, G; Bindu, S Hima; Satheshbabu, P R; Subrahmanyam, C V S

2015-01-01

The establishment of biorelevant and discriminating dissolution procedure for drug products with limited water solubility is a useful technique for qualitative forecasting of the in vivo behavior of formulations. It also characterizes the drug product performance in pharmaceutical development. Lornoxicam, a BCS class-II drug is a nonsteroidal antiinflammatory drug of the oxicam class, has no official dissolution media available in the literature. The objective of present work was to develop and validate a discriminating and biorelevant dissolution test for lornoxicam tablet dosage forms. To quantify the lornoxicam in dissolution samples, UV spectrophotometric method was developed using 0.01M sodium hydroxide solution as solvent at λma×376 nm. After evaluation of saturation solubility, dissolution, sink conditions and stability of lornoxicam bulk drug in different pH solutions and biorelevant media, the dissolution method was optimized using USP paddle type apparatus at 50 rpm rotation speed and 500 ml simulated intestinal fluid as discriminating and biorelevant dissolution medium. The similarity factor (f2) were investigated for formulations with changes in composition and manufacturing variations, values revealed that dissolution method having discriminating power and method was validated as per standard guidelines. The proposed dissolution method can be effectively applied for routine quality control in vitro dissolution studies of lornoxicam in tablets and helpful to pharmacopoeias.

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

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

Kinetic Rate Law Parameter Measurements on a Borosilicate Waste Glass: Effect of Temperature, pH, and Solution Composition on Alkali Ion Exchange

International Nuclear Information System (INIS)

Pierce, Eric M.; McGrail, B PETER.; Icenhower, J P.; Rodriguez, Elsa A.; Steele, Jackie L.; Baum, Steven R.

2004-01-01

The reaction kinetics of glass is controlled by matrix dissolution and ion exchange (IEX). Dissolution of an alkali-rich simulated borosilicate waste glass was investigated using single-pass flow-through (SPFT) experiments. Experiments were conducted as a function of temperature, pH, and solution composition by varying the SiO 2 (aq) activity in the influent solution. Results showed that under dilute conditions matrix dissolution increased with increasing pH and temperature, and decreased with increasing SiO 2 (aq) activity. IEX rates decreased with increasing pH and temperature, and increased with increasing SiO 2 (aq) activity. Over the solution composition range interrogated in this study the dominant dissolution mechanism changed from matrix dissolution to IEX. These results suggest that ''secondary'' reactions may become dominant under certain environmental conditions and emphasize the need to incorporate these reactions into dissolution rate models

Kinetics and thermodynamics of the dissolution of Th1-xMxO2 solid solutions (M = U, Pu)

International Nuclear Information System (INIS)

Hubert, S.; Heisbourg, G.; Dacheux, N.; Moisy, Ph.; Purans, J.

2004-01-01

Kinetics of the dissolution of Th 1-x M x O 2 (M = U, Pu) solid solutions was investigated as a function of several chemical parameters such as pH, substitution ratio, temperature, ionic strength, and electrolyte. Several compositions of Th 1-x U x O 2 and Th 1-x Pu x O 2 were synthesized and characterized before and after leaching by using several methods such as XRD, EXAFS, BET, PIXE, SEM, and XPS. Leaching tests were performed in nitric, hydrochloric or sulfuric media and groundwater. The normalized dissolution rates were evaluated for Th 1-x U x O 2 , and Th 0.88 Pu 0.12 O 2 leading to the determination of the partial order related to the proton concentration, n, and to the corresponding normalized dissolution rate constant at pH = 0, k'T. While for Th enriched solids, the solid solutions Th 1-x U x O 2 have the same dissolution behaviour than ThO 2 with a partial order n ∼ 0.3, in the case of uranium enriched solids, Th 1-x U x O 2 has the same dissolution behaviour than UO 2 with a partial order of n = 1, indicating that uranium oxidation rate becomes the limiting step of the dissolution process. The stoichiometry of the release of both actinides (U or Pu, Th) was verified until the precipitation of thorium occurred in the leachate for pH > 2, while uranium was released in the solution as an uranyl form. For uranium enriched solid solutions, thermodynamic equilibrium was reached after 100 days, and solubility constant of secondary phase was determined. In the case of Th 1-x Pu x O 2 , the dissolution behaviour is similar to that of ThO 2 , but only kinetic aspect of the dissolution can be studied. From the analysis of XPS and EXAFS data on leached and un-leached Th 1-x U x O 2 samples, the dissolution mechanism of solid solutions was explained and will be discussed. The role of the electrolytes on the dissolution of the solid solutions is discussed. Kinetics parameters of dissolution are also given in groundwater and in neutral media

Aqueous dissolution of sodium aluminosilicate geopolymers derived from metakaolin

Energy Technology Data Exchange (ETDEWEB)

Aly, Z., E-mail: zaynab.aly@ansto.gov.au [Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232 (Australia); Vance, E.R. [Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232 (Australia); Perera, D.S. [School of Materials Science, University of NSW, Kensington, NSW 2052 (Australia)

2012-05-15

Highlights: Black-Right-Pointing-Pointer In dilute solutions, Na, Al and Si releases were not sensitive to pH in range 4-10. Black-Right-Pointing-Pointer On heating from 18 to 90 Degree-Sign C in DIW, Na dissolution rate increased by a factor of {approx}4. Black-Right-Pointing-Pointer Elemental extractions in DIW at 18 Degree-Sign C increased linearly with time over 1-7 days. Black-Right-Pointing-Pointer Na release kinetics in DIW followed a pseudo-second-order kinetic model. Black-Right-Pointing-Pointer Contact with KCl, KHCO{sub 3} and phthalate buffers (pH6 and 10) resulted in Na{sup +} {r_reversible} K{sup +} exchange. - Abstract: In dilute aqueous solutions, the elemental releases of Na, Al and Si from a metakaolin-based sodium aluminosilicate geopolymer were not very sensitive to pH in the range of 4-10 but increased outside this range, particularly on the acidic side. To minimise pH drifts, experiments were carried out using small amounts of graded powders in relatively large volumes of water. In deionised water, the Na dissolution rate in 7 days was dominant and increased by at least a factor of {approx}4 on heating from 18 to 90 Degree-Sign C, with greater increases in the extractions of Al and Si. At 18 Degree-Sign C the elemental extractions in deionised water increased approximately linearly with time over the 1-7 days period. Further exposure led to a slower extraction into solution for Na and Si, with a decrease in extraction of Al. It was deduced that framework dissolution was important in significantly acidic or alkaline solutions, but that contributions from water transfer from pores to elemental extractions were present, even at low temperatures in neutral solutions. It was also deduced from the Na release data that the Na leaching kinetics of geopolymer in deionised water (dilute solutions) followed the pseudo-second-order kinetic model and the pseudo-second-order rate constant evaluated. Contact with KCl, KHCO{sub 3}, and pH {approx}6 and 10

Biotite and chlorite weathering at 25 degrees C: the dependence of pH and (bi)carbonate on weathering kinetics, dissolution stoichiometry, and solubility; and the relation to redox conditions in granitic aquifers

Energy Technology Data Exchange (ETDEWEB)

Malmstroem, M.; Banwart, S. [Royal Inst. of Technology, Stockholm (Sweden). Dept. of Inorganic Chemistry; Duro, L. [Universidad Politecnica de Cataluna, Barcelona (Spain). Dept. de Ingneria Quimica; Wersin, P.; Bruno, J. [MBT Technologia Ambiental, Cerdanyola (Spain)

1995-01-01

We have studied the kinetics and thermodynamics of biotite and chlorite weathering in the pH range 2<pH<10 at 25 degrees C. The dissolution is highly non-stoichiometric and pH dependent in the whole pH region. By XPD we have identified a clay mineral to be the main weathering product formed. A model of biotite dissolution and the formation of secondary solubility controlling minerals, such as Fe(III)-hydroxide, Na-clay, quartz and gibbsite is used to explain experimental equilibrium concentrations of silicon, iron, aluminium and magnesium. The model predict redox potentials in the range of -200-400 mV at neutral pH and qualitatively agrees with field data reported in the literature. We use observed iron release rate to make conservative estimates of timescales of 1. the depletion of molecular oxygen from deep aquifers (810{sup 2}-10{sup 2} year); and 2. the development of characteristic Fe(III) concentrations (10{sup -5} M in 10{sup -}1 years). The Fe(III)-bearing clay minerals formed during these experiments are similar to the fracture-filling-material observed at the Aespoe Hard Rock Laboratory. Such clays can provide reducing capacity to a repository. They can help maintain anoxic conditions by consuming oxygen that enters the repository during the construction and operation phases thereby helping maintain the redox stability of the repository regarding canister corrosion. The half-life of oxygen trapped in the repository at the time of closure depends on the rate of oxygen uptake by Fe(II) minerals, sulfide minerals and organic carbon. Fe(II)-clay minerals are important to the redox stability of a repository, as well as providing a sorption barrier to radionuclide migration. 107 refs, 52 figs, 35 tabs.

Dissolution of Fe(III)(hydr)oxides by an Aerobic Bacterium

International Nuclear Information System (INIS)

Maurice, P.

2004-01-01

This project investigated the effects of an aerobic Pseudomonas mendocina bacterium on the dissolution of Fe(III)(hydr)oxides. The research is important because metals and radionuclides that adsorb to Fe(III)(hydr)oxides could potentially be remobilized by dissolving bacteria. We showed that P. mendocina is capable of dissolving Fe-bearing minerals by a variety of mechanisms, including production of siderophores, pH changes, and formation of reductants. The production of siderophores by P. mendocina was quantified under a variety of growth conditions. Finally, we demonstrated that microbial siderophores may adsorb to and enhance dissolution of clay minerals

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.

Reductive Dissolution of Goethite and Hematite by Reduced Flavins

Energy Technology Data Exchange (ETDEWEB)

Shi, Zhi; Zachara, John M.; Wang, Zheming; Shi, Liang; Fredrickson, Jim K.

2013-10-02

The abiotic reductive dissolution of goethite and hematite by the reduced forms of flavin mononucleotide (FMNH2) and riboflavin (RBFH2), electron transfer mediators (ETM) secreted by the dissimilatory iron-reducing bacterium Shewanella, was investigated under stringent anaerobic conditions. In contrast to the rapid redox reaction rate observed for ferrihydrite and lepidocrocite (Shi et al., 2012), the reductive dissolution of crystalline goethite and hematite was slower, with the extent of reaction limited by the thermodynamic driving force at circumneutral pH. Both the initial reaction rate and reaction extent increased with decreasing pH. On a unit surface area basis, goethite was less reactive than hematite between pH 4.0 and 7.0. AH2DS, the reduced form of the well-studied synthetic ETM anthraquinone-2,6-disulfonate (AQDS), yielded higher rates than FMNH2 under most reaction conditions, despite the fact that FMNH2 was a more effective reductant than AH2DS for ferryhydrite and lepidocrocite. Two additional model compounds, methyl viologen and benzyl viologen, were investigated under similar reaction conditions to explore the relationship between reaction rate and thermodynamic properties. Relevant kinetic data from the literature were also included in the analysis to span a broad range of half-cell potentials. Other conditions being equal, the surface area normalized initial reaction rate (ra) increased as the redox potential of the reductant became more negative. A non-linear, parabolic relationship was observed between log ra and the redox potential for eight reducants at pH 7.0, as predicted by Marcus theory for electron transfer. When pH and reductant concentration were fixed, log ra was positively correlated to the redox potential of four Fe(III) oxides over a wide pH range, following a non-linear parabolic relationship as well.

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

Influence of cell culture medium composition on in vitro dissolution behavior of a fluoride-containing bioactive glass.

Science.gov (United States)

Shah, Furqan A; Brauer, Delia S; Wilson, Rory M; Hill, Robert G; Hing, Karin A

2014-03-01

Bioactive glasses are used clinically for bone regeneration, and their bioactivity and cell compatibility are often characterized in vitro, using physiologically relevant test solutions. The aim of this study was to show the influence of varying medium characteristics (pH, composition, presence of proteins) on glass dissolution and apatite formation. The dissolution behavior of a fluoride-containing bioactive glass (BG) was investigated over a period of one week in Eagle's Minimal Essential Medium with Earle's Salts (MEM), supplemented with either, (a) acetate buffer, (b) 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer, (c) HEPES + carbonate, or (d) HEPES + carbonate + fetal bovine serum. Results show pronounced differences in pH, ion release, and apatite formation over 1 week: Despite its acidic pH (pH 5.8 after BG immersion, as compared to pH 7.4-8.3 for HEPES-containing media), apatite formation was fastest in acetate buffered (HEPES-free) MEM. Presence of carbonate resulted in formation of calcite (calcium carbonate). Presence of serum proteins, on the other hand, delayed apatite formation significantly. These results confirm that the composition and properties of a tissue culture medium are important factors during in vitro experiments and need to be taken into consideration when interpreting results from dissolution or cell culture studies. Copyright © 2013 Wiley Periodicals, Inc.

Dissolution kinetics of magnesium hydroxide for CO{sub 2} separation from coal-fired power plants

Energy Technology Data Exchange (ETDEWEB)

Bharadwaj, Hari Krishna [Chemical Engineering Program, School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH 45221-0012 (United States); Lee, Joo-Youp, E-mail: joo.lee@uc.edu [Chemical Engineering Program, School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH 45221-0012 (United States); Li, Xin; Liu, Zhouyang [Chemical Engineering Program, School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH 45221-0012 (United States); Keener, Tim C. [Environmental Engineering Program, School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH 45221-0012 (United States)

2013-04-15

Highlights: ► Magnesium hydroxide dissolution was found to be controlled by chemical reaction. ► The intrinsic kinetics has a fractional order between 0.20 and 0.31. ► The true activation energy value was found to have 76 ± 11 kJ/gmol. ► A shrinking-core model predicted experimental data with good accuracy. -- Abstract: The dissolution of magnesium hydroxide in water for the release of magnesium and hydroxyl ions into the solution to maintain suitable alkalinity is a crucial step in the Mg(OH){sub 2}-based CO{sub 2} absorption process. In this study, the rate of dissolution of Mg(OH){sub 2} was investigated under different operating conditions using a pH stat apparatus. The dissolution process was modeled using a shrinking core model and the overall Mg(OH){sub 2} dissolution process was found to be controlled by the surface chemical reaction of Mg(OH){sub 2} with H{sup +} ions. Under the chemical reaction control regime, the dissolution of Mg(OH){sub 2} in alkaline conditions was found not to follow a first-order reaction, and the fractional order of reaction was estimated to lie between 0.20 and 0.31. This suggests that the dissolution reaction is a non-elementary reaction, consisting of a sequence of elementary reactions, via most likely forming a surface magnesium complex. The true activation energy value of 76 ± 11 kJ/gmol was found to be almost twice as much as the observed activation energy value of 42 ± 6 kJ/gmol determined at pH 8.6, and was comparable with the previously reported values. The particle sizes predicted from the intrinsic kinetics determined from the model were in good agreement with the experimentally measured particle sizes during the dissolution process.

Effect of micro-environment modification and polymer type on the in-vitro dissolution behavior and in-vivo performance of amorphous solid dispersions.

Science.gov (United States)

Sun, Weiwei; Pan, Baoliang

2017-06-15

This study investigates the effects of micro-environment modification and polymer type on the in-vitro dissolution behavior and in-vivo performance of micro-environment pH modifying solid dispersions (pH M -SD) for the poorly water-soluble model drug Toltrazuril (TOL). Various pH M -SDs were prepared using Ca(OH) 2 as a pH-modifier in hydrophilic polymers, including polyethylene glycol 6000 (PEG6000), polyvinylpyrrolidone k30 (PVPk30) and hydroxypropyl methylcellulose (HPMC). Based on the results of physicochemical characterizations and in-vitro dissolution testing, the representative ternary (Ca(OH) 2 :TOL:PEG6000/HPMC/PVPk30=1:8:24, w/w/w) and binary (TOL:PVPk30=1:3, w/w) solid dispersions were selected and optimized to perform in-vivo pharmacokinetic study. The micro-environment pH modification improved the in-vitro water-solubility and in-vivo bioavailability of parent drug TOL. Furthermore, the addition of alkalizers not only enhanced the release and absorption of prototype drug, but also promoted the generation of active metabolites, including toltrazuril sulfoxide (TOLSO) and toltrazuril sulfone (TOLSO 2 ). The in-vitro dissolution profiles and in-vivo absorption, distribution and metabolism behaviors of the pH M -SDs varied with polymer type. Moreover, in-vivo bioavailability of three active pharmaceutical ingredients increased with an increase in in-vitro dissolution rates of the drug from the pH M -SDs prepared with various polymers. Therefore, a non-sink in-vitro dissolution method can be used to predict the in-vivo performance of pH M -SDs formulated with various polymers with trend consistency. In-vitro and in-vivo screening procedures revealed that the pH M -SD composed of Ca(OH) 2 , TOL and PVPk30 at a weight ratio of 1:8:24, of which the safety was adequately proved via histopathological examination, may be a promising candidate for providing better clinical outcomes. Copyright © 2017. Published by Elsevier B.V.

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.

Dissolution of metal and metal oxide nanoparticles in aqueous media

International Nuclear Information System (INIS)

Odzak, Niksa; Kistler, David; Behra, Renata; Sigg, Laura

2014-01-01

The dissolution of Ag (citrate, gelatin, polyvinylpyrrolidone and chitosan coated), ZnO, CuO and carbon coated Cu nanoparticles (with two nominal sizes each) has been studied in artificial aqueous media, similar in chemistry to environmental waters, for up to 19 days. The dissolved fraction was determined using DGT (Diffusion Gradients in Thin films), dialysis membrane (DM) and ultrafiltration (UF). Relatively small fractions of Ag nanoparticles dissolved, whereas ZnO dissolved nearly completely within few hours. Cu and CuO dissolved as a function of pH. Using DGT, less dissolved Ag was measured compared to UF and DM, likely due to differences in diffusion of organic complexes. Similar dissolved metal concentrations of ZnO, Cu and CuO nanoparticles were determined using DGT and UF, but lower using DM. The results indicate that there is a need to apply complementary techniques to precisely determine dissolution of nanoparticles in aqueous media. - Highlights: • Three different techniques used simultaneously to measure NPs dissolution. • ZnO-NPs are the most soluble, followed by CuO-NPs, carbon coated Cu-NPs and Ag-NPs. • Dissolution is an important process affecting the fate of nanoparticles. • Complementary techniques are needed to precisely determine dissolution of NPs. - Dissolution of several types of nanoparticles was examined in aqueous media using three complementary techniques

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.

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

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

Development of a microprocessor-controlled coulometric system for stable ph control

NARCIS (Netherlands)

Bergveld, Piet; van der Schoot, B.H.

1983-01-01

The coulometric pH control system utilizes a programmable coulostat for controlling the pH of a certain volume of unbuffered solution. Based on theoretical considerations, conditions are established which guarantee stable operation with maximum suppression of disturbances from the dissolution of

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)

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)

Dissolution process of atmospheric aerosol particles into cloud droplets; Processus de dissolution des aerosols atmospheriques au sein des gouttes d'eau nuageuses

Energy Technology Data Exchange (ETDEWEB)

Desboeufs, K

2001-01-15

Clouds affect both climate via the role they play in the Earth's radiation balance and tropospheric chemistry since they are efficient reaction media for chemical transformation of soluble species. Cloud droplets are formed in the atmosphere by condensation of water vapour onto aerosol particles, the cloud condensation nuclei (CCN). The water soluble fraction of these CCN governs the cloud micro-physics, which is the paramount factor playing on the radiative properties of clouds. Moreover, this soluble fraction is the source of species imply in the oxidation/reduction reactions in the aqueous phase. Thus, it is of particular importance to understand the process controlling the solubilization of aerosols in the cloud droplets. The main purpose of this work is to investigate experimentally and theoretically the dissolution of particles incorporated in the aqueous phase. From the studies conducted up to now, we have identify several factors playing on the dissolution reaction of aerosols. However, the quantification of the effects of these factors is difficult since the current means of study are not adapted to the complexity of cloud systems. First, this work consisted to perform a experimental system, compound by an open flow reactor, enabling to follow the kinetic of dissolution in conditions representative of cloud. This experimental device is used to a systematic characterisation of the known factors playing on the dissolution, i.e. pH, aerosol nature, aerosol weathering... and also for the identification and the quantification of the effects of other factors: ionic strength, acid nature, clouds processes. These experiments gave quantitative results, which are used to elaborate a simple model of aerosol dissolution in the aqueous phase. This model considers the main factors playing on the dissolution and results in a general mechanism of aerosol dissolution extrapolated to the cloud droplets. (author)

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.

Disintegration and dissolution of spent radioactive cationic exchange resins using Fenton-like oxidation process

International Nuclear Information System (INIS)

Wan, Zhong; Xu, Lejin; Wang, Jianlong

2015-01-01

Highlights: • The spent radioactive resins could be oxidized by Fenton-like process. • The influencing factors on resin oxidation were evaluated. • Chemical oxygen demand (COD) reduction rate was more than 99%. • SEM and Raman spectrum were used to analyze the resins morphological change. - Abstract: The treatment and disposal of the spent radioactive resins is essential for the sustainable development of the nuclear industry. In this paper, the disintegration and dissolution of spent cationic resins were studied by Fenton-like process. The influencing factors on resin dissolution, such as pH, temperature, type and concentration of catalysts were evaluated. The results showed that the spent resins could be effectively dissolved at pH < 1, [Fe 2+ ] = 0.2 M and T = 97 ± 2 °C. Chemical oxygen demand (COD) reduction rate was more than 99%. The scanning electron microscopy and the Raman spectrum were used to observe the morphological changes of the spent resins during the dissolution process. Fenton-like oxidation is an efficient method for the volume reduction and stabilization of the spent resins before further immobilization

Disintegration and dissolution of spent radioactive cationic exchange resins using Fenton-like oxidation process

Energy Technology Data Exchange (ETDEWEB)

Wan, Zhong; Xu, Lejin [Collaborative Innovation Center for Advanced Nuclear Energy Technology, INET, Tsinghua University, Beijing 100084 (China); Wang, Jianlong, E-mail: wangjl@tsinghua.edu.cn [Collaborative Innovation Center for Advanced Nuclear Energy Technology, INET, Tsinghua University, Beijing 100084 (China); Beijing Key Laboratory of Radioactive Wastes Treatment, Tsinghua University, Beijing 100084 (China)

2015-09-15

Highlights: • The spent radioactive resins could be oxidized by Fenton-like process. • The influencing factors on resin oxidation were evaluated. • Chemical oxygen demand (COD) reduction rate was more than 99%. • SEM and Raman spectrum were used to analyze the resins morphological change. - Abstract: The treatment and disposal of the spent radioactive resins is essential for the sustainable development of the nuclear industry. In this paper, the disintegration and dissolution of spent cationic resins were studied by Fenton-like process. The influencing factors on resin dissolution, such as pH, temperature, type and concentration of catalysts were evaluated. The results showed that the spent resins could be effectively dissolved at pH < 1, [Fe{sup 2+}] = 0.2 M and T = 97 ± 2 °C. Chemical oxygen demand (COD) reduction rate was more than 99%. The scanning electron microscopy and the Raman spectrum were used to observe the morphological changes of the spent resins during the dissolution process. Fenton-like oxidation is an efficient method for the volume reduction and stabilization of the spent resins before further immobilization.

Possible factors that control calcite dissolution in the western tropical Indian Ocean

Digital Repository Service at National Institute of Oceanography (India)

Naik, S.S.; Naidu, P.D.

and preservation of calcium carbonate in deep-sea sedi- ments 1 . Carbon dioxide dissolved in sea water is present as CO 2 gas, H 2 CO 3 , HCO – 3 and CO = 3 . All these species together con- stitute the Dissolved Inorganic Carbon (DIC) 2 which controls... the sea water pH, which in turn controls preservation/ dissolution of CaCO 3 . Precipitation of carbonate carbon results in an increase in ocean pCO 2 , and with it an increase in atmospheric CO 2 concentration. Con- versely, dissolution of CaCO 3...

Hydrolysis of R7T7 nuclear waste glass in dilute media: mechanisms and rate as a function of pH

International Nuclear Information System (INIS)

Advocat, T.; Vernaz, E.; Charpentier, H.; Crovisier, J.L.; Ehret, G.

1990-01-01

R7T7 nuclear waste glass dissolution in highly dilute aqueous media under static conditions at 90 0 C occurs according to two different mechanisms depending on the solution acidity. In acid media (pH 4.8 and 5.5), preferential extraction of glass network modifiers results in the formation of an alkali metal-depleted surface region on which amorphous and crystallized (phosphate) compounds rich in transition elements precipitate. Steady-state dissolution conditions are not reached, as attested by variable normalized Si, B and Na mass losses. Glass dissolution is stoichiometric in basic media (pH 7 to 10): the strong bonds of the silicated network are broken at a rate that increases with the pH: the glass dissolution rate increases by a factor of 15 between pH 7 and 10. Under these conditions, alteration products at the glass/solution interface do not constitute a short-term kinetic barrier against the release of the major glass components

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.

PRINCIPAL COMPONENT ANALYSIS OF FACTORS DETERMINING PHOSPHATE ROCK DISSOLUTION ON ACID SOILS

Directory of Open Access Journals (Sweden)

Yusdar Hilman

2016-10-01

Full Text Available Many of the agricultural soils in Indonesia are acidic and low in both total and available phosphorus which severely limits their potential for crops production. These problems can be corrected by application of chemical fertilizers. However, these fertilizers are expensive, and cheaper alternatives such as phosphate rock (PR have been considered. Several soil factors may influence the dissolution of PR in soils, including both chemical and physical properties. The study aimed to identify PR dissolution factors and evaluate their relative magnitude. The experiment was conducted in Soil Chemical Laboratory, Universiti Putra Malaysia and Indonesian Center for Agricultural Land Resources Research and Development from January to April 2002. The principal component analysis (PCA was used to characterize acid soils in an incubation system into a number of factors that may affect PR dissolution. Three major factors selected were soil texture, soil acidity, and fertilization. Using the scores of individual factors as independent variables, stepwise regression analysis was performed to derive a PR dissolution function. The factors influencing PR dissolution in order of importance were soil texture, soil acidity, then fertilization. Soil texture factors including clay content and organic C, and soil acidity factor such as P retention capacity interacted positively with P dissolution and promoted PR dissolution effectively. Soil texture factors, such as sand and silt content, soil acidity factors such as pH, and exchangeable Ca decreased PR dissolution.

In Silico Modeling Approach for the Evaluation of Gastrointestinal Dissolution, Supersaturation, and Precipitation of Posaconazole.

Science.gov (United States)

Hens, Bart; Pathak, Shriram M; Mitra, Amitava; Patel, Nikunjkumar; Liu, Bo; Patel, Sanjaykumar; Jamei, Masoud; Brouwers, Joachim; Augustijns, Patrick; Turner, David B

2017-12-04

The aim of this study was to evaluate gastrointestinal (GI) dissolution, supersaturation, and precipitation of posaconazole, formulated as an acidified (pH 1.6) and neutral (pH 7.1) suspension. A physiologically based pharmacokinetic (PBPK) modeling and simulation tool was applied to simulate GI and systemic concentration-time profiles of posaconazole, which were directly compared with intraluminal and systemic data measured in humans. The Advanced Dissolution Absorption and Metabolism (ADAM) model of the Simcyp Simulator correctly simulated incomplete gastric dissolution and saturated duodenal concentrations of posaconazole in the duodenal fluids following administration of the neutral suspension. In contrast, gastric dissolution was approximately 2-fold higher after administration of the acidified suspension, which resulted in supersaturated concentrations of posaconazole upon transfer to the upper small intestine. The precipitation kinetics of posaconazole were described by two precipitation rate constants, extracted by semimechanistic modeling of a two-stage medium change in vitro dissolution test. The 2-fold difference in exposure in the duodenal compartment for the two formulations corresponded with a 2-fold difference in systemic exposure. This study demonstrated for the first time predictive in silico simulations of GI dissolution, supersaturation, and precipitation for a weakly basic compound in part informed by modeling of in vitro dissolution experiments and validated via clinical measurements in both GI fluids and plasma. Sensitivity analysis with the PBPK model indicated that the critical supersaturation ratio (CSR) and second precipitation rate constant (sPRC) are important parameters of the model. Due to the limitations of the two-stage medium change experiment the CSR was extracted directly from the clinical data. However, in vitro experiments with the BioGIT transfer system performed after completion of the in silico modeling provided an almost

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)

Dissolution process of atmospheric aerosol particles into cloud droplets; Processus de dissolution des aerosols atmospheriques au sein des gouttes d'eau nuageuses

Energy Technology Data Exchange (ETDEWEB)

Desboeufs, K.

2001-01-15

Clouds affect both climate via the role they play in the Earth's radiation balance and tropospheric chemistry since they are efficient reaction media for chemical transformation of soluble species. Cloud droplets are formed in the atmosphere by condensation of water vapour onto aerosol particles, the cloud condensation nuclei (CCN). The water soluble fraction of these CCN governs the cloud micro-physics, which is the paramount factor playing on the radiative properties of clouds. Moreover, this soluble fraction is the source of species imply in the oxidation/reduction reactions in the aqueous phase. Thus, it is of particular importance to understand the process controlling the solubilization of aerosols in the cloud droplets. The main purpose of this work is to investigate experimentally and theoretically the dissolution of particles incorporated in the aqueous phase. From the studies conducted up to now, we have identify several factors playing on the dissolution reaction of aerosols. However, the quantification of the effects of these factors is difficult since the current means of study are not adapted to the complexity of cloud systems. First, this work consisted to perform a experimental system, compound by an open flow reactor, enabling to follow the kinetic of dissolution in conditions representative of cloud. This experimental device is used to a systematic characterisation of the known factors playing on the dissolution, i.e. pH, aerosol nature, aerosol weathering... and also for the identification and the quantification of the effects of other factors: ionic strength, acid nature, clouds processes. These experiments gave quantitative results, which are used to elaborate a simple model of aerosol dissolution in the aqueous phase. This model considers the main factors playing on the dissolution and results in a general mechanism of aerosol dissolution extrapolated to the cloud droplets. (author)

Geoengineering impact of open ocean dissolution of olivine on atmospheric CO2, surface ocean pH and marine biology

International Nuclear Information System (INIS)

Köhler, Peter; Abrams, Jesse F; Völker, Christoph; Hauck, Judith; Wolf-Gladrow, Dieter A

2013-01-01

Ongoing global warming induced by anthropogenic emissions has opened the debate as to whether geoengineering is a ‘quick fix’ option. Here we analyse the intended and unintended effects of one specific geoengineering approach, which is enhanced weathering via the open ocean dissolution of the silicate-containing mineral olivine. This approach would not only reduce atmospheric CO 2 and oppose surface ocean acidification, but would also impact on marine biology. If dissolved in the surface ocean, olivine sequesters 0.28 g carbon per g of olivine dissolved, similar to land-based enhanced weathering. Silicic acid input, a byproduct of the olivine dissolution, alters marine biology because silicate is in certain areas the limiting nutrient for diatoms. As a consequence, our model predicts a shift in phytoplankton species composition towards diatoms, altering the biological carbon pumps. Enhanced olivine dissolution, both on land and in the ocean, therefore needs to be considered as ocean fertilization. From dissolution kinetics we calculate that only olivine particles with a grain size of the order of 1 μm sink slowly enough to enable a nearly complete dissolution. The energy consumption for grinding to this small size might reduce the carbon sequestration efficiency by ∼30%. (letter)

Photoreductive dissolution of iron oxides trapped in ice and its environmental implications.

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Kim, Kitae; Choi, Wonyong; Hoffmann, Michael R; Yoon, Ho-Il; Park, Byong-Kwon

2010-06-01

The availability of iron has been thought to be a main limiting factor for the productivity of phytoplankton and related with the uptake of atmospheric CO(2) and algal blooms in fresh and sea waters. In this work, the formation of bioavailable iron (Fe(II)(aq)) from the dissolution of iron oxide particles was investigated in the ice phase under both UV and visible light irradiation. The photoreductive dissolution of iron oxides proceeded slowly in aqueous solution (pH 3.5) but was significantly accelerated in polycrystalline ice, subsequently releasing more bioavailable ferrous iron upon thawing. The enhanced photogeneration of Fe(II)(aq) in ice was confirmed regardless of the type of iron oxides [hematite, maghemite (gamma-Fe(2)O(3)), goethite (alpha-FeOOH)] and the kind of electron donors. The ice-enhanced dissolution of iron oxides was also observed under visible light irradiation, although the dissolution rate was much slower compared with the case of UV radiation. The iron oxide particles and organic electron donors (if any) in ice are concentrated and aggregated in the liquid-like grain boundary region (freeze concentration effect) where protons are also highly concentrated (lower pH). The enhanced photodissolution of iron oxides should occur in this confined boundary region. We hypothesized that electron hopping through the interconnected grain boundaries of iron oxide particles facilitates the separation of photoinduced charge pairs. The outdoor experiments carried out under ambient solar radiation of Ny-Alesund (Svalbard, 78 degrees 55'N) also showed that the generation of dissolved Fe(II)(aq) via photoreductive dissolution is enhanced when iron oxides are trapped in ice. Our results imply that the ice(snow)-covered surfaces and ice-cloud particles containing iron-rich mineral dusts in the polar and cold environments provide a source of bioavailable iron when they thaw.

The initial stages of NaCl dissolution: Ion or ion pair solvation?

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Klimes, Jiri; Michaelides, Angelos

2009-03-01

The interaction of water with rock salt (NaCl) is important in a wide variety of natural processes and human activities. A lot is known about NaCl dissolution at the macroscopic level but we do not yet have a detailed atomic scale picture of how salt crystals dissolve. Here we report an extensive series of density functional theory, forcefield and molecular dynamics studies of water clusters at flat and defective NaCl surfaces and NaCl clusters. The focus is on answering seemingly elementary questions such as how many water molecules are needed before it becomes favorable to extract an ion or a pair of ions from the crystal or the cluster. It turns out, however, that the answers to these questions are not so straightforward: below a certain number of water molecules (˜ 12) solvation of individual ions is less costly and above this number solvation of ion pairs is favored. These results reveal a hitherto unknown complexity in the NaCl dissolution process born out of a subtle interplay between water-water and water-ion interactions.

Structure and reactivity of oxalate surface complexes on lepidocrocite derived from infrared spectroscopy, DFT-calculations, adsorption, dissolution and photochemical experiments

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Borowski, Susan C.; Biswakarma, Jagannath; Kang, Kyounglim; Schenkeveld, Walter D. C.; Hering, Janet G.; Kubicki, James D.; Kraemer, Stephan M.; Hug, Stephan J.

2018-04-01

Oxalate, together with other ligands, plays an important role in the dissolution of iron(hdyr)oxides and the bio-availability of iron. The formation and properties of oxalate surface complexes on lepidocrocite were studied with a combination of infrared spectroscopy (IR), density functional theory (DFT) calculations, dissolution, and photochemical experiments. IR spectra measured as a function of time, concentration, and pH (50-200 μM oxalate, pH 3-7) showed that several surface complexes are formed at different rates and in different proportions. Measured spectra could be separated into three contributions described by Gaussian line shapes, with frequencies that agreed well with the theoretical frequencies of three different surface complexes: an outer-sphere complex (OS), an inner-sphere monodentate mononuclear complex (MM), and a bidentate mononuclear complex (BM) involving one O atom from each carboxylate group. At pH 6, OS was formed at the highest rate. The contribution of BM increased with decreasing pH. In dissolution experiments, lepidocrocite was dissolved at rates proportional to the surface concentration of BM, rather than to the total adsorbed concentration. Under UV-light (365 nm), BM was photolyzed at a higher rate than MM and OS. Although the comparison of measured spectra with calculated frequencies cannot exclude additional possible structures, the combined results allowed the assignment of three main structures with different reactivities consistent with experiments. The results illustrate the importance of the surface speciation of adsorbed ligands in dissolution and photochemical reactions.

Anomalous dissolution of metals and chemical corrosion

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DRAGUTIN M. DRAZIC

2005-03-01

Full Text Available An overview is given of the anomalous behavior of some metals, in particular Fe and Cr, in acidic aqueous solutions during anodic dissolution. The anomaly is recognizable by the fact that during anodic dissolutionmore material dissolves than would be expected from the Faraday law with the use of the expected valence of the formed ions. Mechanical disintegration, gas bubble blocking, hydrogen embrittlement, passive layer cracking and other possible reasons for such behavior have been discussed. It was shown, as suggested by Kolotyrkin and coworkers, that the reason can be, also, the chemical reaction in which H2O molecules with the metal form metal ions and gaseous H2 in a potential independent process. It occurs simultaneously with the electrochemical corrosion process, but the electrochemical process controls the corrosion potential. On the example of Cr in acid solution itwas shown that the reason for the anomalous behavior is dominantly chemical dissolution, which is considerably faster than the electrochemical corrosion, and that the increasing temperature favors chemical reaction, while the other possible reasons for the anomalous behavior are of negligible effect. This effect is much smaller in the case of Fe, but exists. The possible role of the chemical dissolution reacton and hydrogen evolution during pitting of steels and Al and stress corrosion cracking or corrosion fatigue are discussed.

In vitro dissolution profile study of mucolytic drug ambroxol hydrochloride from solid oral dosage form by UHPLC-MS/MS

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Vujović Maja M.

2017-01-01

Full Text Available In this paper a simplified dissolution test was performed for the release of ambroxol from tablets according to the European Pharmacopoeia. In vitro, three different dissolution media; 0.1 M HCl pH 1.2, acetate buffer (ABS pH 4.5 and phosphate buffer (PBS pH 6.8 were used for the simulation of the gastrointestinal conditions at temperature of 37.0±0.5°C. The drug release was evaluated by a new ultra - high performance liquid chromatography (UHPLC - tandem mass spectrometry (MS/MS method. The method was validated to meet requirements as per ICH guidelines which include linearity, specificity, precision, accuracy and robustness. The corresponding dissolution profiles showed more than 80% drug release within 30 minutes without significant differences. Further, the developed and validated UHPLC-MS/MS method could find a useful application in the process of production, quality control and bioavailability/bioequivalence studies of new pharmaceutical formulations of drugs in order to achieve a safe therapeutic efficacy. [Projekat Ministarstva nauke Republike Srbije, br. 175045

Dissolution kinetics of schwertmannite and ferrihydrite in oxidized mine samples and their detection by differential X-ray diffraction (DXRD)

International Nuclear Information System (INIS)

Dold, Bernhard

2003-01-01

A dissolution test with 9 natural and synthetic schwertmannite and ferrihydrite samples was performed by reaction with 0.2 M ammonium oxalate at pH 3.0 in the dark. The method was coupled with differential X-ray diffraction (DXRD) to successfully detect schwertmannite at low concentrations in oxidized mine tailings. Rapid dissolution was observed for all schwertmannites (> 94% in 60 min) and natural 2-line ferrihydrites (> 85% in 60 min); however, synthetic 2-line and 6-line ferrihydrite dissolved slower (42 and 16% after 60 min, respectively). The results showed that it was not possible to distinguish between natural schwertmannites and ferrihydrites on the basis of their dissolution kinetics. Modeling of the schwertmannite dissolution curves, examinations of mineral shape by scanning electron microscopy, and Fe/S mole ratios of the dissolved fractions indicated that two different schwertmannite particle morphologies (spherical and web-like) occurred. Collapse of spherical (sea-urchin) schwertmannite aggregates seemed to control the dissolution kinetics according to a shrinking core model. In the case of web-like schwertmannite, dissolution could be modeled with a simple first order equation, and structural SO 4 2- may have affected the dissolution kinetics. No relationship was found between ferrihydrite particle shape and dissolution behavior in acid NH 4 -oxalate. A 1-h extraction with 0.2 M NH 4 -oxalate at pH 3.0 in the dark should be adequate to dissolve schwertmannite and natural 2-line ferrihydrite in most samples. In some cases, a fraction of secondary jarosite or goethite may also be dissolved, although at a slower rate. If only schwertmannite is of interest (e.g., determination by DXRD), a 15 min attack should be used to increase selectivity. A truly selective leach of schwertmannite and ferrihydrite should be based on dissolution tests, as a broad variety of dissolution kinetics can be observed in this mineral group

Dissolution of targets for the production of Mo-99: Part 2. Influence of excess of reagent and aluminium mass on dissolution time

International Nuclear Information System (INIS)

Araujo, Izilda da C.; Camilo, Ruth L.; Mindrisz, Ana C.; Forbicini, Christina A.L.G. de O.

2011-01-01

Radioisotopes play an important role in the peaceful uses of nuclear energy. Radionuclides in nuclear medicine can be used for diagnosis and therapy. The 9T c, daughter of 99 Mo is most often used in nuclear medicine as tracer element because of its favorable nuclear properties, accounting for about 80% of all diagnostic procedures in vivo. Nowadays, the supply of this important isotope is deficient, due to the shutdown of the reactors in Canada and Belgium, the world's largest producers. Aiming to resolve the dependency of Brazil with respect to the supply of 99 Mo was created the Brazilian Multipurpose Reactor project (RMB), started in 2008, having as main objective to produce about 1000 Ci/week of 99 Mo. This study is part of the project to obtain 99 Mo by alkaline dissolution of UA1 x -A1 targets. Al, which corresponds to 79% of the total mass, was used to simulate the targets. The reagent used in the dissolution was a 3 mol.L -1 NaOH/NaNO 3 solution and initial temperature of 88 degree influence of the reagent on the dissolution time, related to the molar ratio 1Al:1.66NaOH:1.66NaNO 3 , for a range of over 5 to 50%, and the influence of the amount of mass in a range from 16 to 48 g of Al were studied. It was observed that the dissolution time. (author)

Dissolution characteristics of sericite in chalcopyrite bioleaching and its effect on copper extraction

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Dong, Ying-bo; Li, Hao; Lin, Hai; Zhang, Yuan

2017-04-01

The effects of sericite particle size, rotation speed, and leaching temperature on sericite dissolution and copper extraction in a chalcopyrite bioleaching system were examined. Finer particles, appropriate temperature and rotation speed for Acidithiobacillus ferrooxidans resulted in a higher Al3+ dissolution concentration. The Al3+ dissolution concentration reached its highest concentration of 38.66 mg/L after 48-d leaching when the sericite particle size, temperature, and rotation speed were -43 μm, 30°C, and 160 r/min, respectively. Meanwhile, the sericite particle size, rotation speed, and temperature can affect copper extraction. The copper extraction rate is higher when the sericite particle size is finer. An appropriately high temperature is favorable for copper leaching. The dissolution of sericite fitted the shrinking core model, 1-(2/3) α-(1- α)2/3 = k 1 t, which indicates that internal diffusion is the decision step controlling the overall reaction rate in the leaching process. Scanning electron microscopy analysis showed small precipitates covered on the surface of sericite after leaching, which increased the diffusion resistance of the leaching solution and dissolved ions.

Combinational approach using solid dispersion and semi-solid matrix technology to enhance in vitro dissolution of telmisartan

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Syed Faisal Ali

2016-02-01

Full Text Available The present investigation was focused to formulate semi-solid capsules (SSCs of hydrophobic drug telmisartan (TLMS by encapsulating semi-solid matrix of its solid dispersion (SD in HPMC capsules. The combinational approach was used to reduce the lag time in drug release and improvise its dissolution. SDs of TLMS was prepared using hot fusion method by varying the combinations of Pluronic-F68, Gelucire 50/13 and Plasdone S630. A total of nine batches (SD1-SD9 were characterized for micromeritic properties, in vitro dissolution behavior and surface characterization. SD4 with 52.43% cumulative drug release (CDR in phosphate buffer, pH 7.4, in 120 min, t50% 44.2 min and DE30min 96.76% was selected for the development of semi-solid capsules. Differential scanning calorimetry of SD4 revealed molecular dispersion of TLMS in Pluronic-F68. SD4 was formulated into SSCs using Gelucire 44/14 and PEG 400 as semi-solid components and PEG 6000 as a suspending agent to achieve reduction in lag time for effective drug dissolution. SSC6 showed maximum in vitro drug dissolution 97.49 % in phosphate buffer, pH 7.4 with in 20 min that was almost a three folds reduction in the time required to achieve similar dissolution by SD. Thus, SSCs present an excellent approach to enhance in vitro dissolution as well as to reduce the lag time of dissolution for poorly water soluble drugs especially to those therapeutic classes that are intended for faster onset of action. Developed approach based on HPMC capsules provided a better alternative to target delivery of telmisartan to the vegetarian population.

Effect of pH on corrosion behavior of CuCrZr in solution without and with NaCl

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Kwok, C.T.; Wong, P.K. [Department of Electromechanical Engineering, University of Macau (China); Man, H.C. [Department of Industrial and Systems Engineering, Hong Kong Polytechnic University (Hong Kong); Cheng, F.T., E-mail: apaftche@polyu.edu.h [Department of Applied Physics, Hong Kong Polytechnic University (Hong Kong)

2009-10-01

CuCrZr is a high copper alloy widely used as electrical and thermal conducting material, especially in heat exchangers in nuclear reactors. In this respect, the physical and fatigue properties of CuCrZr have been extensively studied. The electrochemical behavior of CuCrZr, on the other hand, has not been adequately investigated. In the present study, the effect of pH on the corrosion behavior of CuCrZr in aqueous solutions without and with chloride (0.6 M NaCl) was studied. The pH of the solutions is found to exert significant influence on the corrosion behavior of CuCrZr. In acidic solutions without chloride, the corrosion of CuCrZr is ascribed to active dissolution with soluble products. In neutral and alkaline solutions without NaCl, the presence of oxides on the surface of CuCrZr leads to a noble shift in corrosion potential and passivation results in increased corrosion resistance. In chloride solutions at various pH values, the chloride ions influence the formation of the surface layers and the anodic dissolution process during polarization. At high pH, CuCrZr shows significant passivity and high corrosion resistance due to the growth of Cu{sub 2}O/Cu(OH) film which hinders further dissolution whereas at low pH the corrosion resistance is lowered due to active dissolution of Cu.

Effect of pH on corrosion behavior of CuCrZr in solution without and with NaCl

International Nuclear Information System (INIS)

Kwok, C.T.; Wong, P.K.; Man, H.C.; Cheng, F.T.

2009-01-01

CuCrZr is a high copper alloy widely used as electrical and thermal conducting material, especially in heat exchangers in nuclear reactors. In this respect, the physical and fatigue properties of CuCrZr have been extensively studied. The electrochemical behavior of CuCrZr, on the other hand, has not been adequately investigated. In the present study, the effect of pH on the corrosion behavior of CuCrZr in aqueous solutions without and with chloride (0.6 M NaCl) was studied. The pH of the solutions is found to exert significant influence on the corrosion behavior of CuCrZr. In acidic solutions without chloride, the corrosion of CuCrZr is ascribed to active dissolution with soluble products. In neutral and alkaline solutions without NaCl, the presence of oxides on the surface of CuCrZr leads to a noble shift in corrosion potential and passivation results in increased corrosion resistance. In chloride solutions at various pH values, the chloride ions influence the formation of the surface layers and the anodic dissolution process during polarization. At high pH, CuCrZr shows significant passivity and high corrosion resistance due to the growth of Cu 2 O/Cu(OH) film which hinders further dissolution whereas at low pH the corrosion resistance is lowered due to active dissolution of Cu.

Mechanism and Kinetics for the Dissolution of Apatitic Materials in Acid Solutions

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Calmanovici C.E.

1997-01-01

Full Text Available Abstract - This work concerns the study of the digestion step in the production process of phosphoric acid. Some qualitative experiments indicate that the difference between the pH at the surface of the phosphate and that in the bulk of the solution is negligible and that the dissolution is controlled by diffusion of products away from the phosphate particle. In further experiments, to isolate the dissolution phenomenon from the formation of calcium sulfate, the sulfuric acid normally used industrially is replaced by hydrochloric acid. The phosphate material used in our experiments is a model apatitic material: synthetic hydroxyapatite (HAP. The dissolution of calcium hydroxyapatite was studied with increasing amounts of calcium and phosphate at different temperatures. A simple method was developed for this observation based on the time required for complete dissolution of the HAP powder. The results confirm that the dissolution is controlled by a diffusional process through an interface of calcium and phosphate ions released from the solid surface. A kinetic model for the dissolution of apatitic materials is proposed which assumes a shrinking particle behaviour controlled by diffusion of calcium ions. The experimental results are fitted to this model to determine the mass transfer constant for HAP dissolution in acid solutions. The activation energy of the reaction is about 14kJ/mol. This study was carried on in conditions similar to the industrial ones for the production of phosphoric acid by the dihydrate-process

Influence of Dissolution Media and Presence of Alcohol on the In Vitro Performance of Pharmaceutical Products Containing an Insoluble Drug.

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Friuli, Valeria; Bruni, Giovanna; Musitelli, Giorgio; Conte, Ubaldo; Maggi, Lauretta

2018-01-01

The purpose of this investigation is to determine how the dissolution media may influence the release rate of an insoluble drug in in vitro conditions. Some oral dosage forms containing ibuprofen, a molecule that shows pH-dependent solubility, are tested. They are evaluated in different media to simulate the gastrointestinal transit at paddle rotation speeds of 50 and 100 rpm. Moreover, the potential effect of different ethanol concentrations on drug release is tested. The dissolution profiles of the tablets show a similar behavior in water (pH 1.0) and phosphate buffer (pH 4.5) where the 2 doses are not completely dissolved. The soft capsules show a different behavior: a certain amount of ibuprofen, which is in solution inside the capsule, reprecipitates in water and in the pH 4.5 buffer. Instead, ibuprofen dissolves rapidly in the pH 6.8 buffer from all the formulations. In the water-ethanol solutions, the dissolution curves show a valuable increase in the drug dissolved at higher ethanol concentrations. Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Dissolution properties of co-amorphous drug-amino acid formulations in buffer and biorelevant media.

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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.

Measurement uncertainty of dissolution test of acetaminophen immediate release tablets using Monte Carlo simulations

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Daniel Cancelli Romero

2017-10-01

Full Text Available ABSTRACT Analytical results are widely used to assess batch-by-batch conformity, pharmaceutical equivalence, as well as in the development of drug products. Despite this, few papers describing the measurement uncertainty estimation associated with these results were found in the literature. Here, we described a simple procedure used for estimating measurement uncertainty associated with the dissolution test of acetaminophen tablets. A fractionate factorial design was used to define a mathematical model that explains the amount of acetaminophen dissolved (% as a function of time of dissolution (from 20 to 40 minutes, volume of dissolution media (from 800 to 1000 mL, pH of dissolution media (from 2.0 to 6.8, and rotation speed (from 40 to 60 rpm. Using Monte Carlo simulations, we estimated measurement uncertainty for dissolution test of acetaminophen tablets (95.2 ± 1.0%, with a 95% confidence level. Rotation speed was the most important source of uncertainty, contributing about 96.2% of overall uncertainty. Finally, it is important to note that the uncertainty calculated in this paper reflects the expected uncertainty to the dissolution test, and does not consider variations in the content of acetaminophen.

Calcite Dissolution Kinetics

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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

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

Effect of Acid Dissolution Conditions on Recovery of Valuable Metals from Used Plasma Display Panel Scrap

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Kim Chan-Mi

2017-06-01

Full Text Available The objective of this particular study was to recover valuable metals from waste plasma display panels using high energy ball milling with subsequent acid dissolution. Dissolution of milled (PDP powder was studied in HCl, HNO3, and H2SO4 acidic solutions. The effects of dissolution acid, temperature, time, and PDP scrap powder to acid ratio on the leaching process were investigated and the most favorable conditions were found: (1 valuable metals (In, Ag, Mg were recovered from PDP powder in a mixture of concentrated hydrochloric acid (HCl:H2O = 50:50; (2 the optimal dissolution temperature and time for the valuable metals were found to be 60°C and 30 min, respectively; (3 the ideal PDP scrap powder to acid solution ratio was found to be 1:10. The proposed method was applied to the recovery of magnesium, silver, and indium with satisfactory results.

Utilization of spray drying technique for improvement of dissolution and anti-inflammatory effect of Meloxicam.

Science.gov (United States)

Shazly, Gamal; Badran, Mohamed; Zoheir, Khairy; Alomrani, Abdullah

2015-01-01

Meloxicam (MLX) is a poorly water-soluble non steroidal anti-inflammatory drug (NSAID). The main objective of the present work was to enhance the dissolution of MLX and thus its bioavailability by the aid of additives. The novelty of this work rises from the utilization of spray drying technology to produce micro particulates solid dispersion systems containing MLX in the presence of small amount of additives. Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and Scan Electron Microscope (SEM) were used for studying the physico-chemical and morphological properties of MLX samples. The dissolution of MLX samples was investigated in two different pH media. The morphology of MLX solid dispersion micro-particles was spherical in shape according to SEM. FT-IR profiles indicated that a complex was formed between MLX and the additives. DSC patterns of the MLX micro-particles suggested a reduction in the crystallinity of MLX and probability of presence of an interaction between MLX and the additives. The rate of dissolution of the spray-dried MLX enhanced as compared with the unprocessed MLX in both acidic and neutral media. It was found that 100% of the added MLX released within 5 min in phosphate buffer dissolution medium (pH 7.4) compared to that of the unprocessed MLX (15% in 60 min). Such increase rate in the dissolution of the spray dried MLX could be attributed to the increase in wettability of MLX particles and the hydrophilic nature of the additives. The anti-inflammatory effect of the spray dried MLX was explored using formalin induced rat paw edema model. The spray-dried samples showed an increase in the anti-inflammatory activity of MLX as compared to the unprocessed MLX. This work reveals that the spray drying technique is suitable for preparation of micro-particles with improved dissolution and anti-inflammatory effect of MLX.

Validation of a dissolution method with RP-HPLC analysis for Perindopril erbumine and Indapamide combination tablet

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Jain P.S.

2012-01-01

Full Text Available A Dissolution method with high performance liquid chromatography (HPLC analysis was validated for perindopril erbumine and indapamide in combination tablet formulation. The method was validated to meet requirements for a global regulatory filing and this validation included specificity, linearity, accuracy, precision, range, robustness and solution stability studies. The dissolution method, which uses USP apparatus 1 with basket rotating at 100 rpm, 1000 ml of phosphate buffer pH 6.8 as the dissolution medium, and reversed-phased HPLC was carried out at 50⁰C on a 4.6mm×250mm 5μm cyano column that contained USP packing L1 with acetonitrile: buffer pH 2.8::40:60 (v/v, as mobile phase. UV detector was set at 225 nm. A method was found to be selective, linear, accurate and precise in the specified ranges. Intra-day and inter-day variability for method was <2% RSD. This method was successfully used for quantification of perindopril erbumine and indapamide combination tablet formulations.

High temperature dissolution of ferrites, chromites and bonaccordite in chelating media

Energy Technology Data Exchange (ETDEWEB)

Sathyaseelan, V.S.; Subramanian, H.; Anupkumar, B.; Rufus, A.L.; Velmurugan, S.; Narasimhan, S.V., E-mail: snv@igcar.gov.in [BARC Facilities, Water and Steam Chemistry Div., Tamilnadu (India)

2010-07-01

by the reagents used in chemical decontamination processes. Sample of bonaccordite was prepared by solid state route by heating stoichiometric mixtures of Hematite, Nickel Oxide and Boric acid at 900{sub o}C for 24 Hours. The phase purity of Bonaccordite formed was confirmed by XRD and Laser Raman Spectroscopy. Studies carried out in the Teflon lined autoclave indicated that boron and zinc containing oxides/ ferrites can be dissolved more easily at elevated temperatures (>140{sub o}C) as compared to normal temperatures (80 - 100{sub o}C). The effect of variation of temperature, concentration of chelating agent, presence of reducing agents has also been studied. High temperature corrosion study of carbon steel (CS) and stainless steel in all the above chelating medium in the presence and the absence of reductants has been carried out. About 60% reduction in corrosion rate was observed for CS in NTA medium in the presence of N{sub 2}H{sub 4} at 160{sup o}C and at pH 6.5. However, at the same temperature and pH, in the absence of N{sub 2}H{sub 4}, corrosion rate of CS was decreased drastically. With increase in temperature, dissolution rate of chromium oxide also increased considerably. The effectiveness of high temperature process was substantiated by using oxide covered specimen prepared under simulated BWR water chemistry conditions. (author)

Electrochemical characteristics of bioresorbable binary MgCa alloys in Ringer's solution: Revealing the impact of local pH distributions during in-vitro dissolution.

Science.gov (United States)

Mareci, D; Bolat, G; Izquierdo, J; Crimu, C; Munteanu, C; Antoniac, I; Souto, R M

2016-03-01

Biodegradable magnesium-calcium (MgCa) alloy is a very attractive biomaterial. Two MgCa alloys below the solid solubility of Ca were considered, as to solely investigate the effect of Ca content on the behavior of magnesium and the pH changes associated to metal dissolution. X-ray diffraction analysis and optical microscopy showed that both Mg-0.63Ca and Mg-0.89Ca alloys were solely composed of α(Mg) phase. Degradation characteristics and electrochemical characterization of MgCa alloys were investigated during exposure to Ringer's solution at 37 °C by electrochemical impedance spectroscopy and scanning electrochemical microscopy. The impedance behavior showed both capacitive and inductive features that are related to the alloy charge transfer reaction and the relaxation of the absorbed corrosion compounds, and can be described in terms of an equivalent circuit. Scanning electron microscopy (SEM) was employed to view the surface morphology of the MgCa samples after 1 week immersion in Ringer's solution showing extensive precipitation of corrosion products, whereas the substrate shows evidence of a non-uniform corrosion process. Energy dispersive analysis showed that the precipitates contained oxygen, calcium, magnesium and chlorine, and the Mg:Ca ratios were smaller than in the alloys. Scanning electrochemical microscopy (SECM) was used to visualize local pH changes associated to these physicochemical processes with high spatial resolution. The occurrence of pH variations in excess of 3 units between anodic and cathodic half-cell reactions was monitored in situ. Copyright © 2015 Elsevier B.V. All rights reserved.

Modeling surface area to volume effects on borosilicate glass dissolution

International Nuclear Information System (INIS)

Bourcier, W.L.; Ebert, W.L.; Feng, X.

1992-11-01

We simulated the reaction of SRL-131 glass with equilibrated J-13 water in order to investigate the effects of surface area to volume ratio (SA/V) on glass dissolution. We show that glass-fluid ion exchange causes solution pH to rise to progressively higher values as SA/V increases. Because the ion exchange is rapid relative to the duration of the glass dissolution experiment, the pH effect does not scale with (SA/V)*time. Experiments compared at the same (SA/V)*time value therefore have different pHs, with higher pHs at higher SA/V ratios. Both experimental data and our simulation results show similar trends of increasing reaction rate as a function of SA/V ratio when scaled to (SA/V)*time. Glasses which react in systems of differing SA/V ratio therefore follow different reaction paths and high SA/V ratios cannot be used to generate data which accurately scales to long time periods unless the ion exchange effect is taken into account. We suggest some simple test designs which enable more reliable high. SA/V accelerated tests

Dissolution of various metal oxides in different forms in dilute organic complexants

Energy Technology Data Exchange (ETDEWEB)

Srinivasan, M.P.; Chandramohan, P.; Velmurugan, S.; Narasimhan, S.V. [Water and Steam Chemistry Lab., BARC Facilities, Tamilnadu (India); Ranganathan, S. [Madras Univ. (India). Research Scholar

2002-07-01

The dissolution of iron containing metal oxides is of importance in various power plant industries from the point of crud and scale removal for efficient operation and better performance of plant. The removal of these oxides has to be accomplished with minimum corrosion to the structural material, with minimum cost and removal duration and also with minimum waste generation for easy disposal. Activity build-up due to pick up of {sup 60}Co and fission products occurs on PHT system surfaces of nuclear power plants. The dissolution kinetics of these oxides are influenced by pH, redox potential, chelating strength, concentration and temperature of the solution, constitution of oxides, and the physical form of existence of oxides. In this paper the influence of the existence of different forms of iron oxides on the ability of the dissolution characteristics of the different formulations have been brought out. How the change in dissolution characteristics can be ingenuously used to characterize both qualitatively and quantitatively the mixtures of oxides have been brought out. How the magnetite dissolution behaviour varies for base metal unaided condition in different formulation in static condition, in regenerative mode is also brought out. The OCP values and iron release behaviour for magnetite coated CS surface and magnetite pellet were also described. (authors)

Dissolution of various metal oxides in different forms in dilute organic complexants

International Nuclear Information System (INIS)

Srinivasan, M.P.; Chandramohan, P.; Velmurugan, S.; Narasimhan, S.V.; Ranganathan, S.

2002-01-01

The dissolution of iron containing metal oxides is of importance in various power plant industries from the point of crud and scale removal for efficient operation and better performance of plant. The removal of these oxides has to be accomplished with minimum corrosion to the structural material, with minimum cost and removal duration and also with minimum waste generation for easy disposal. Activity build-up due to pick up of 60 Co and fission products occurs on PHT system surfaces of nuclear power plants. The dissolution kinetics of these oxides are influenced by pH, redox potential, chelating strength, concentration and temperature of the solution, constitution of oxides, and the physical form of existence of oxides. In this paper the influence of the existence of different forms of iron oxides on the ability of the dissolution characteristics of the different formulations have been brought out. How the change in dissolution characteristics can be ingenuously used to characterize both qualitatively and quantitatively the mixtures of oxides have been brought out. How the magnetite dissolution behaviour varies for base metal unaided condition in different formulation in static condition, in regenerative mode is also brought out. The OCP values and iron release behaviour for magnetite coated CS surface and magnetite pellet were also described. (authors)

Development and validation of dissolution study of sustained release dextromethorphan hydrobromide tablets.

Science.gov (United States)

Rajan, Sekar; Colaco, Socorrina; Ramesh, N; Meyyanathan, Subramania Nainar; Elango, K

2014-02-01

This study describes the development and validation of dissolution tests for sustained release Dextromethorphan hydrobromide tablets using an HPLC method. Chromatographic separation was achieved on a C18 column utilizing 0.5% triethylamine (pH 7.5) and acetonitrile in the ratio of 50:50. The detection wavelength was 280 nm. The method was validated and response was found to be linear in the drug concentration range of 10-80 microg mL(-1). The suitable conditions were clearly decided after testing sink conditions, dissolution medium and agitation intensity. The most excellent dissolution conditions tested, for the Dextromethorphan hydrobromide was applied to appraise the dissolution profiles. The method was validated and response was found to be linear in the drug concentration range of 10-80 microg mL(-1). The method was established to have sufficient intermediate precision as similar separation was achieved on another instrument handled by different operators. Mean Recovery was 101.82%. Intra precisions for three different concentrations were 1.23, 1.10 0.72 and 1.57, 1.69, 0.95 and inter run precisions were % RSD 0.83, 1.36 and 1.57%, respectively. The method was successfully applied for dissolution study of the developed Dextromethorphan hydrobromide tablets.

Chalcopyrite Dissolution at 650 mV and 750 mV in the Presence of Pyrite

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Yubiao Li

2015-08-01

Full Text Available The dissolution of chalcopyrite in association with pyrite in mine waste results in the severe environmental issue of acid and metalliferous drainage (AMD. To better understand chalcopyrite dissolution, and the impact of chalcopyrite’s galvanic interaction with pyrite, chalcopyrite dissolution has been examined at 75 °C, pH 1.0, in the presence of quartz (as an inert mineral and pyrite. The presence of pyrite increased the chalcopyrite dissolution rate by more than five times at Eh of 650 mV (SHE (Cu recovery 2.5 cf. 12% over 132 days due to galvanic interaction between chalcopyrite and pyrite. Dissolution of Cu and Fe was stoichiometric and no pyrite dissolved. Although the chalcopyrite dissolution rate at 750 mV (SHE was approximately four-fold greater (Cu recovery of 45% within 132 days as compared to at 650 mV in the presence of pyrite, the galvanic interaction between chalcopyrite and pyrite was negligible. Approximately all of the sulfur from the leached chalcopyrite was converted to S0 at 750 mV, regardless of the presence of pyrite. At this Eh approximately 60% of the sulfur associated with pyrite dissolution was oxidised to S0 and the remaining 40% was released in soluble forms, e.g., SO42−.

The study on the pH behavior of the HFSC leached solution. The development of model considering the pozzolanic reaction

International Nuclear Information System (INIS)

Yoshida, Yasushi; Mihara, Morihiro

2005-09-01

The development of low alkalinity cement (high fly-ash contained silica-fume cement, HFSC) has been carried out in JNC. Low alkalinity for this cement is achieved by adding pozzolan materials to ordinary portland cement and Ca ion attributed to high alkalinity is consumed by forming CHS gel. This report shows the calculation model to predict the composition for HFSC reacted solution which considers cement mineral dissolution/precipitation as equilibrium reactions and dissolution for pozzolan material as a kinetic reaction. The dissolution kinetic equation for pozzolan material is also derived from leaching experiment. This calculation model is applied to the leaching experiment where powdered HFSC was reacted with distilled water. As a result of comparison between calculation and experimental measurement at the early stage for leaching the tendency for pH, pH decrease from 12.5 to 11.5 drastically, could be interpreted by this calculation model, however, after this drastic pH decreasing pH predicted by calculation model also shows drastic decrease whereas pH for experiment decreased mildly around pH 11.5. It could be thought that this difference between experiment and calculation is caused by inappropriate modelling for CSH gel dissolution/precipitation of C/S value lower than 1.0. For this C/S range thermodynamic data for intermediate and end member for solid solution for CSH gel and in addition the reaction kinetic for CSH gel should be examined in detail. (author)

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)

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.)

Kinetics of UO2(s) dissolution under reducing conditions: Numerical modelling

International Nuclear Information System (INIS)

Puigdomenech, I.; Casas, I.; Bruno, J.

1990-05-01

A numerical model is presented that describes the dissolution and precipitation of UO 2 (s) under reducing conditions. For aqueous solutions with pH>4, main reaction is: UO 2 (s)+2H 2 O↔U(OH) 4 (aq). The rate constant for the precipitation reaction is found to be log(k p )=-1.2±0.2 h -1 m -2 , while the value for the rate constant of the dissolution reaction is log(k d )=-9.0±0.2 mol/(1 h m 2 ). Most of the experiments reported in the literature show a fast initial dissolution of a surface film of hexavalent uranium oxide. Making the assumption that the chemical composition of the surface coating is U 3 O 7 (s), we have derived a mechanism for this process, and its rate constants have been obtained. The influence of HCO 3 - and CO 3 2- on the mechanism of dissolution and precipitation of UO 2 (s) is still unclear. From the solubility measurements reported, one may conclude that the identity of the aqueous complexes in solution is not well known. Therefore it is not possible to make a mechanistic interpretation of the kinetic data in carbonate medium. (orig.)

Solubility and dissolution enhancement of flurbiprofen by solid dispersion using hydrophilic carriers

Directory of Open Access Journals (Sweden)

Bhaskar Daravath

2018-05-01

Full Text Available ABSTRACT The intent of the current work is to study the effect of polyethylene glycol 8000 and polyethylene glycol 10000 as hydrophilic carriers on dissolution behaviour of flurbiprofen. In the present study, solvent evaporation method was used to prepare flurbiprofen solid dispersions and evaluated for physico-chemical properties, drug-carrier compatibility studies and dissolution behaviour of drug. Solubility studies showed more solubility in higher pH values and formulations SD4 and SD8 were selected to prepare the fast dissolving tablets. FTIR and DSC study showed no interaction and drug was dispersed molecularly in hydrophilic carrier. XRD studies revealed that there was change in the crystallinity of the drug. The results of In vitro studies showed SD8 formulation confer significant improvement (p<0.05 in drug release, Q20 was 99.08±1.35% compared to conventional and marketed tablets (47.31±0.74% and 56.86±1.91%. The mean dissolution time (MDT was reduced to 8.79 min compared to conventional and marketed tablets (25.76 and 22.22 min. indicating faster drug release. The DE (% dissolution efficiency was increased by 2.5 folds (61.63% compared to conventional tablets (23.71%. From the results, it is evident that polyethylene glycol solid dispersions in less carrier ratio may enhance the solubility and there by improve the dissolution rate of flurbiprofen.

Dissolution chemistry and biocompatibility of silicon- and germanium-based semiconductors for transient electronics.

Science.gov (United States)

Kang, Seung-Kyun; Park, Gayoung; Kim, Kyungmin; Hwang, Suk-Won; Cheng, Huanyu; Shin, Jiho; Chung, Sangjin; Kim, Minjin; Yin, Lan; Lee, Jeong Chul; Lee, Kyung-Mi; Rogers, John A

2015-05-06

Semiconducting materials are central to the development of high-performance electronics that are capable of dissolving completely when immersed in aqueous solutions, groundwater, or biofluids, for applications in temporary biomedical implants, environmentally degradable sensors, and other systems. The results reported here include comprehensive studies of the dissolution by hydrolysis of polycrystalline silicon, amorphous silicon, silicon-germanium, and germanium in aqueous solutions of various pH values and temperatures. In vitro cellular toxicity evaluations demonstrate the biocompatibility of the materials and end products of dissolution, thereby supporting their potential for use in biodegradable electronics. A fully dissolvable thin-film solar cell illustrates the ability to integrate these semiconductors into functional systems.

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

Improvement of dissolution and hypoglycemic efficacy of glimepiride by different carriers.

Science.gov (United States)

Mohamed, Elham A; Meshali, Mahasen M; Foda, Abdel Monem M; Borg, Thanaa M

2012-09-01

Effects of tromethamine (Tris), polyvinylpyrrolidone (PVP-K25), and low molecular weight chitosan (LM-CH) on dissolution and therapeutic efficacy of glimepiride (Gmp) were investigated using physical mixtures (PMs), coground mixtures, coprecipitates (Coppts) or kneaded mixtures (KMs), and compared with drug alone. Fourier transform infrared spectroscopy, differential scanning colorimetry, and X-ray diffractometry were performed to identify any physicochemical interaction with Gmp. Surface morphology was examined via scanning electron microscopy. The results of Gmp in vitro dissolution revealed that it was greatly enhanced by Coppt with Tris or PVP-K25 and KM with LM-CH at a drug to carrier ratio of 1:8. Gmp amorphization by PVP-K25 and LM-CH was a major factor in increasing Gmp dissolution. Being basic, Tris might increase the pH of the microdiffusion layer around Gmp particles improving its dissolution. Formation of water-soluble complexes suggested by solubility study may also explain the enhanced dissolution. Capsules were prepared from Coppts and KM 1:8 drug to carrier binary systems and also with Tris PMs. In vivo, the hypoglycemic efficacy of Gmp capsules in rabbits increased by 1.63-, 1.50-, and 1.46-fold for 1:8 Coppts with Tris or PVP-K25 and KM with LM-CH respectively, compared with Gmp alone. Surprisingly, the response to Tris PM 1:20 capsules was 1.52-fold revealing statistically insignificant difference to that of Tris Coppt 1:8 (1.63 fold). As a conclusion, dissolution enhancement and hypoglycemic potentiation by 1:20 PM of Gmp/Tris, being simple and easy to prepare, may enable development of a reduced-dose and fast-release oral dosage form of Gmp.

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.

Double porosity model to describe both permeability change and dissolution processes

International Nuclear Information System (INIS)

Niibori, Yuichi; Usui, Hideo; Chida, Taiji

2015-01-01

Cement is a practical material for constructing the geological disposal system of radioactive wastes. The dynamic behavior of both permeability change and dissolution process caused by a high pH groundwater was explained using a double porosity model assuming that each packed particle consists of the sphere-shaped aggregation of smaller particles. This model assumes two kinds of porosities between the particle clusters and between the particles, where the former porosity change mainly controls the permeability change of the bed, and the latter porosity change controls the diffusion of OH"- ions inducing the dissolution of silica. The fundamental equations consist of a diffusion equation of spherical coordinates of OH"- ions including the first-order reaction term and some equations describing the size changes of both the particles and the particle clusters with time. The change of over-all permeability of the packed bed is evaluated by Kozeny-Carman equation and the calculated radii of particle clusters. The calculated result well describes the experimental result of both permeability change and dissolution processes. (author)

Designing a dynamic dissolution method: a review of instrumental options and corresponding physiology of stomach and small intestine.

Science.gov (United States)

Culen, Martin; Rezacova, Anna; Jampilek, Josef; Dohnal, Jiri

2013-09-01

Development of new pharmaceutical compounds and dosage forms often requires in vitro dissolution testing with the closest similarity to the human gastrointestinal (GI) tract. To create such conditions, one needs a suitable dissolution apparatus and the appropriate data on the human GI physiology. This review discusses technological approaches applicable in biorelevant dissolutions as well as the physiology of stomach and small intestine in both fasted and fed state, that is, volumes of contents, transit times for water/food and various solid oral dosage forms, pH, osmolality, surface tension, buffer capacity, and concentrations of bile salts, phospholipids, enzymes, and Ca(2+) ions. The information is aimed to provide clear suggestions on how these conditions should be set in a dynamic biorelevant dissolution test. Copyright © 2013 Wiley Periodicals, Inc.

Growth of rhombohedral insulin crystals and in vitro modeling of their dissolution in the blood stream

Energy Technology Data Exchange (ETDEWEB)

Nanev, C.N.; Dimitrov, I.L.; Hodzhaoglu, F.V. [Rostislaw Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia (Bulgaria)

2011-02-15

Insulin is the only protein that is secreted in a crystalline form in a human healthy body. To mimic the secretion process we used NaCl salting-out to growing tiny rhombohedral Zn-insulin crystals. The dissolution of the insulin crystals is of special interest for the therapeutical praxis, because the human body is supplied with the physiologically active monomers of the insulin through dissolution of the crystalline granules secreted in the pancreatic {beta}-cells. Sets of tiny rhombohedral Zn-insulin crystals, which resembled the granules secreted in the {beta}-cells, were subjected to dissolution in blood plasma and model solutions. The impacts of the solution composition, flow rate, pH and ionic strength on the insulin crystal dissolution were investigated. The effect of the blood plasma was determinant because it dissolved the rhombohedral Zn-insulin crystals almost instantly, while the effects of solution's physicochemical characteristics were of minor importance. In addition, we found that the presence of abundant zinc ions suppressed the dissolution of the insulin crystals. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Enhanced dissolution and bioavailability of Nateglinide by microenvironmental pH-regulated ternary solid dispersion: in-vitro and in-vivo evaluation.

Science.gov (United States)

Wairkar, Sarika; Gaud, Ram; Jadhav, Namdeo

2017-09-01

Nateglinide, an Antidiabetic drug (BCS II), shows pH-dependent solubility and variable bioavailability. The purpose of study was to increase dissolution and bioavailability of Nateglinide by development of its microenvironmental pH-regulated ternary solid dispersion (MeSD). MeSD formulation of Nateglinide, poloxamer-188 and Na 2 CO 3 was prepared by melt dispersion in 1 : 2 : 0.2 w/w ratio and further characterised for solubility, In-vitro dissolution, microenvironmental pH, crystallinity/amorphism, physicochemical interactions, bioavailability in Wistar rats. Solubility of Nateglinide was increased notably in MeSD, and its in-vitro dissolution study showed fourfold increase in the dissolution, particularly in 1.2 pH buffer. Prominent reduction in the peak intensity of X-ray powder diffraction (XRPD) and absence of endotherm in DSC thermogram confirmed the amorphism of Nateglinide in MeSD. Attenuated total reflectance Fourier transform infrared spectra revealed the hydrogen bond interactions between Nateglinide and poloxamer-188. In-vivo study indicated that MeSD exhibited fourfold increase in area under curve over Nateglinide. Tmax of MeSD was observed at 0.25 h, which is beneficial for efficient management of postprandial sugar. Instead of mere transformation of the Nateglinide to its amorphous form as evidenced by DSC and XRPD, formation of a soluble carboxylate compound of Nateglinide in MeSD was predominantly responsible for dissolution and bioavailability enhancement. The study demonstrates the utility of MeSD in achieving pH-independent dissolution, reduced T max and enhanced bioavailability of Nateglinide. © 2017 Royal Pharmaceutical Society.

Theoretical study of the dissolution kinetics of galena and cerussite in an abandoned mining area (Zaida mine, Morocco)

Science.gov (United States)

El Alaoui, Lamiae; Dekayir, Abdelilah

2018-05-01

In the abandoned mine in Zaida, the pit lakes filled with water constitute significant water reserves. In these lakes, the waters are permanently in contact with ore deposit (cerussite and galena). The modelling of the interaction of waters with this mineralization shows that cerussite dissolves more rapidly than galena. This dissolution is controlled by the pH and dissolved oxygen concentration in solution. The lead concentrations recorded in these lakes come largely from the dissolution of cerussite.

Dissolution profiles of perindopril and indapamide in their fixed-dose formulations by a new HPLC method and different mathematical approaches

Directory of Open Access Journals (Sweden)

Gumieniczek Anna

2015-09-01

Full Text Available A new HPLC method was introduced and validated for simultaneous determination of perindopril and indapamide. Validation procedure included specificity, sensitivity, robustness, stability, linearity, precision and accuracy. The method was used for the dissolution test of perindopril and indapamide in three fixed-dose formulations. The dissolution procedure was optimized using different media, different pH of the buffer, surfactants, paddle speed and temperature. Similarity of dissolution profiles was estimated using different model-independent and model-dependent methods and, additionally, by principal component analysis (PCA. Also, some kinetic models were checked for dissolved amounts of drugs as a function of time.

Recovery of uranium from (U,Gd)O{sub 2} nuclear fuel scrap using dissolution and precipitation in carbonate media

Energy Technology Data Exchange (ETDEWEB)

Kim, Kwang-Wook, E-mail: nkwkim@kaeri.re.kr [Korea Atomic Energy Research Institute, 1045 Daedeok daero, Yuseong, Daejeon 305-353 (Korea, Republic of); KEPCO NF 1047 Daedeok daero, Yuseong, Daejeon 305-353 (Korea, Republic of); Hyun, Jun-Taek; Lee, Eil-Hee; Park, Geun-Il; Lee, Kune-Woo [Korea Atomic Energy Research Institute, 1045 Daedeok daero, Yuseong, Daejeon 305-353 (Korea, Republic of); Yoo, Myung-June [KEPCO NF 1047 Daedeok daero, Yuseong, Daejeon 305-353 (Korea, Republic of); Song, Kee-Chan; Moon, Jei-Kwon [Korea Atomic Energy Research Institute, 1045 Daedeok daero, Yuseong, Daejeon 305-353 (Korea, Republic of)

2011-11-15

Highlights: > A treatment of (U,Gd)O{sub 2} scrap with a dissolution in carbonate solution with H{sub 2}O{sub 2}. > Partial dissolution of Gd together with uranium in carbonate solution. > Solubilities of Gd in solutions with and without carbonate at several pHs. > Purification of Gd-contaminated UO{sub 4} by dissolution and precipitation of UO{sub 4}. - Abstract: This work studied a process to recover uranium from contaminated (U,Gd)O{sub 2} scraps generated from nuclear fuel fabrication processes by using the dissolution of (U,Gd)O{sub 2} scraps in a carbonate with H{sub 2}O{sub 2} and the precipitation of the dissolved uranium as UO{sub 4}. The dissolution characteristics of uranium, Gd, and impurity metal oxides were tested, and the behaviors of UO{sub 4} precipitation and Gd solubility were evaluated with changes of the pH of the solution. A little Gd was entrained in the UO{sub 4} precipitate to contaminate the uranium precipitate. Below a pH of 3, the uranium dissolved in the form of uranyl peroxo-carbonato complex ions in the carbonate solution was precipitated as UO{sub 4} with a high precipitation yield, and the Gd had a very high solubility. Using these characteristics, the Gd-contaminated UO{sub 4} could be purified using dissolution in a 1-M HNO{sub 3} solution with heating and re-precipitation upon addition of H{sub 2}O{sub 2} to the solution. Finally, an environmentally friendly and economical process to recover pure uranium from contaminated (U,Gd)O{sub 2} scraps was suggested.

Neutralization of sulfuric acid solutions by calcite dissolution and the application to anoxic limestone drain design

International Nuclear Information System (INIS)

Huminicki, Danielle M.C.; Rimstidt, J. Donald

2008-01-01

Batch reactor (BR) experiments were conducted to measure the effect of hydrodynamics and gypsum coatings on calcite neutralization rates. A factorial array of BR experiments measured the H + concentration change by calcite dissolution over a pH range of 1.5-3.5 and Na 2 SO 4 concentrations of 0-1 M. The rate of H + concentration change with time was determined by numerical differentiation of H + concentration versus time. Regression modeling showed that for uncoated calcite, rates are only significantly affected by pH, r=-10 -2.32 a H + 0.76 . Whereas, for calcite coated with gypsum only time had a significant effect on calcite dissolution rates, r = -10 -1.96 t -0.53 . Because transport-limited dissolution rates for uncoated calcite are a function of the pH and Reynolds number, a model was developed to express the effects of these two variables on the rate of H + consumption for a solution with a Darcy velocity, q, through a porous medium with a particle radius, r p , such that r ' =1.08x10 -3 q 0.31 r p -0.69 m H + 0.87 . This equation was integrated via a numerical model to simulate the performance of an idealized anoxic limestone drain (ALD). This model predicts the pH and alkalinity change along the length of an ALD. The model shows that the efficiency of an ALD is greater when the Darcy velocity is low and the particle radius is small. In addition, the growth of gypsum coatings causes the rate of H + neutralization to decline as the square root of time as they form and block the H + transport to the calcite surface. Supersaturation with respect to gypsum, leading to coating formation, can be avoided by diluting the ALD feed solution or by replacing limestone with dolomite

Enhanced dissolution and oral bioavailability of valsartan solid dispersions prepared by a freeze-drying technique using hydrophilic polymers.

Science.gov (United States)

Xu, Wei-Juan; Xie, Hong-Juan; Cao, Qing-Ri; Shi, Li-Li; Cao, Yue; Zhu, Xiao-Yin; Cui, Jing-Hao

2016-01-01

This study aimed to improve the dissolution rate and oral bioavailability of valsartan (VAL), a poorly soluble drug using solid dispersions (SDs). The SDs were prepared by a freeze-drying technique with polyethylene glycol 6000 (PEG6000) and hydroxypropylmethylcellulose (HPMC 100KV) as hydrophilic polymers, sodium hydroxide (NaOH) as an alkalizer, and poloxamer 188 as a surfactant without using any organic solvents. In vitro dissolution rate and physicochemical properties of the SDs were characterized using the USP paddle method, differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and Fourier transform-infrared (FT-IR) spectroscopy, respectively. In addition, the oral bioavailability of SDs in rats was evaluated by using VAL (pure drug) as a reference. The dissolution rates of the SDs were significantly improved at pH 1.2 and pH 6.8 compared to those of the pure drug. The results from DSC, XRD showed that VAL was molecularly dispersed in the SDs as an amorphous form. The FT-IR results suggested that intermolecular hydrogen bonding had formed between VAL and its carriers. The SDs exhibited significantly higher values of AUC 0-24 h and Cmax in comparison with the pure drug. In conclusion, hydrophilic polymer-based SDs prepared by a freeze-drying technique can be a promising method to enhance dissolution rate and oral bioavailability of VAL.

Approaches for Establishing Clinically Relevant Dissolution Specifications for Immediate Release Solid Oral Dosage Forms.

Science.gov (United States)

Hermans, Andre; Abend, Andreas M; Kesisoglou, Filippos; Flanagan, Talia; Cohen, Michael J; Diaz, Dorys A; Mao, Y; Zhang, Limin; Webster, Gregory K; Lin, Yiqing; Hahn, David A; Coutant, Carrie A; Grady, Haiyan

2017-11-01

This manuscript represents the perspective of the Dissolution Analytical Working Group of the IQ Consortium. The intent of this manuscript is to highlight the challenges of, and to provide a recommendation on, the development of clinically relevant dissolution specifications (CRS) for immediate release (IR) solid oral dosage forms. A roadmap toward the development of CRS for IR products containing active ingredients with a non-narrow therapeutic window is discussed, within the context of mechanistic dissolution understanding, supported by in-human pharmacokinetic (PK) data. Two case studies present potential outcomes of following the CRS roadmap and setting dissolution specifications. These cases reveal some benefits and challenges of pursuing CRS with additional PK data, in light of current regulatory positions, including that of the US Food and Drug Administration (FDA), who generally favor this approach, but with the understanding that both industry and regulatory agency perspectives are still evolving in this relatively new field. The CRS roadmap discussed in this manuscript also describes a way to develop clinically relevant dissolution specifications based primarily on dissolution data for batches used in pivotal clinical studies, acknowledging that not all IR product development efforts need to be supported by additional PK studies, albeit with the associated risk of potentially unnecessarily tight manufacturing controls. Recommendations are provided on what stages during the life cycle investment into in vivo studies may be valuable. Finally, the opportunities for CRS within the context of post-approval changes, Modeling and Simulation (M&S), and the application of biowaivers, are briefly discussed.

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...

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...

In vivo predictive dissolution: transport analysis of the CO2 , bicarbonate in vivo buffer system.

Science.gov (United States)

Krieg, Brian J; Taghavi, Seyed Mohammad; Amidon, Gordon L; Amidon, Gregory E

2014-11-01

Development of an oral in vivo predictive dissolution medium for acid drugs with a pKa in the physiological range (e.g., Biopharmaceutics Classification System Class IIa) requires transport analysis of the complex in vivo CO2 /bicarbonate buffering system. In this report, we analyze this buffer system using hydrodynamically defined rotating disk dissolution. Transport analysis of drug flux was predicted using the film model approach of Mooney et al based on equilibrium assumptions as well as accounting for the slow hydration reaction, CO2 + H2 O → H2 CO3 . The accuracy of the models was compared with experimentally determined results using the rotating disk dissolution of ibuprofen, indomethacin, and ketoprofen. The equilibrium and slow hydration reaction rate models predict significantly different dissolution rates. The experimental results are more accurately predicted by accounting for the slow hydration reaction under a variety of pH and hydrodynamic conditions. Although the complex bicarbonate buffering system requires further consideration given its dynamic nature in vivo, a simplifying irreversible reaction (IRR) transport analysis accurately predicts in vitro rotating disk dissolution rates of several carboxylic acid drugs. This IRR transport model provides further insight into bicarbonate buffer and can be useful in developing more physiologically relevant buffer systems for dissolution testing. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

Effect of pH Value on the Electrochemical and Stress Corrosion Cracking Behavior of X70 Pipeline Steel in the Dilute Bicarbonate Solutions

Science.gov (United States)

Cui, Z. Y.; Liu, Z. Y.; Wang, L. W.; Ma, H. C.; Du, C. W.; Li, X. G.; Wang, X.

2015-11-01

In this work, effects of pH value on the electrochemical and stress corrosion cracking (SCC) behavior of X70 pipeline steel in the dilute bicarbonate solutions were investigated using electrochemical measurements, slow strain rate tensile tests and surface analysis techniques. Decrease of the solution pH from 6.8 to 6.0 promotes the anodic dissolution and cathodic reduction simultaneously. Further decrease of the pH value mainly accelerates the cathodic reduction of X70 pipeline steel. As a result, when the solution pH decreases form 6.8 to 5.5, SCC susceptibility decreases because of the enhancement of the anodic dissolution. When the solution pH decreases from 5.5 to 4.0, SCC susceptibility increases gradually because of the acceleration of cathodic reactions.

Sorption, dissolution and pH determine the long-term equilibration and toxicity of coated and uncoated ZnO nanoparticles in soil.

Science.gov (United States)

Waalewijn-Kool, Pauline L; Diez Ortiz, Maria; van Straalen, Nico M; van Gestel, Cornelis A M

2013-07-01

To assess the effect of long-term dissolution on bioavailability and toxicity, triethoxyoctylsilane coated and uncoated zinc oxide nanoparticles (ZnO-NP), non-nano ZnO and ZnCl2 were equilibrated in natural soil for up to twelve months. Zn concentrations in pore water increased with time for all ZnO forms but peaked at intermediate concentrations of ZnO-NP and non-nano ZnO, while for coated ZnO-NP such a clear peak only was seen after 12 months. Dose-related increases in soil pH may explain decreased soluble Zn levels due to fixation of Zn released from ZnO at higher soil concentrations. At T = 0 uncoated ZnO-NP and non-nano ZnO were equally toxic to the springtail Folsomia candida, but not as toxic as coated ZnO-NP, and ZnCl2 being most toxic. After three months equilibration toxicity to F. candida was already reduced for all Zn forms, except for coated ZnO-NP which showed reduced toxicity only after 12 months equilibration. Copyright © 2013 Elsevier Ltd. All rights reserved.

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

Effects of ions traces on the dissolution of bioceramics composed of hydroxyapatite and β-tricalcium phosphate

Directory of Open Access Journals (Sweden)

Mohamed Jamil

2015-02-01

Full Text Available The aim of this work is to study the effect of trace ions as Mg2+, Sr2+, (SiO44- and Al3+, brought by the raw material, on the dissolution of the calcium-phosphate bioceramics.  The precursor powders prepared by aqueous precipitation with molar ratio Ca / P = 1.630 ± 0.002, were calcined at 1100°C resulting in the formation of a mixture of hydroxyapatite (Ca10(PO46(OH2 and β-tricalcium phosphate (β-Ca3(PO42.  Two mixtures which differ by the content of trace ions were characterized for phase purity, chemical composition and morphology.  The dissolution tests were performed at 37 °C in acidic buffers solution at pH 4.8.  The results showed that the dissolution of calcium ions is more important in the presence of ions trace while the phosphor ions were not affected.  The dissolution and dissolution-reprecipitation observed of various ions trace can modify the surface properties of calcium phosphate bioceramics and therefore the properties of biological products, such as resorbtion and reactivity can be affected.

Validated, Ultra Violet Spectroscopy method for the Dissolution study of Mycophenolate mofetil immediate release 500mg tablets

OpenAIRE

Surajpal P. Verma; Ozair Alam; Pooja Mullick; Nadeem Siddiqui; Suroor A. Khan

2008-01-01

A simple, selective and precise dissolution method was developed and validated for the Mycophenolate mofetil immediate release tablets. The method employed dissolution medium 0.1N HCl (pH1.2) and volume 900ml with USP-II apparatus (Paddle). Detection was made by measuring the absorbance on UV at the [lambda]~max~ 250nm. The method show the linearity in the range of conc. 5[micro]g/ml to 40[micro]g/ml with r^2^=0.999. The method is also validated as per International Conference of Harmonizatio...

Influence of pH and media composition on suspension stability of silver, zinc oxide, and titanium dioxide nanoparticles and immobilization of Daphnia magna under guideline testing conditions.

Science.gov (United States)

Cupi, Denisa; Hartmann, Nanna B; Baun, Anders

2016-05-01

In aquatic toxicity testing of engineered nanoparticles (ENPs) the process of agglomeration is very important as it may alter bioavailability and toxicity. In the present study, we aimed to identify test conditions that are favorable for maintaining stable ENP suspensions. We evaluated the influence of key environmental parameters: pH (2-12) and ionic strength using M7, Soft EPA (S EPA) medium, and Very Soft EPA (VS EPA) medium; and observed the influence of these parameters on zeta potential, zeta average, and acute immobilization of Daphnia magna for three different ENPs. Despite being sterically stabilized, test suspensions of silver (Ag) ENPs formed large agglomerates in both VS EPA and M7 media; and toxicity was found to be higher in VS EPA medium due to increased dissolution. Low-agglomerate suspensions for zinc oxide (ZnO) could be obtained at pH 7 in VS EPA medium, but the increase in dissolution caused higher toxicity than in M7 medium. Titanium dioxide (TiO2) ENPs had a point of zero charge in the range of pH 7-8. At pH 7 in VS EPA, agglomerates with smaller hydrodynamic diameters (~200nm) were present compared to the high ionic strength M7 medium where hydrodynamic diameters reached micrometer range. The stable suspensions of TiO2 ENPs caused immobilization of D. magna, 48-h EC50 value of 13.7mgL(-1) (95% CI, 2.4mg-79.1mgL(-1)); whereas no toxicity was seen in the unstable, highly agglomerated M7 medium suspensions, 48-h EC50 >100mgL(-1). The current study provides a preliminary approach for methodology in testing and assessing stability and toxicity of ENPs in aquatic toxicity tests of regulatory relevance. Copyright © 2016 Elsevier Inc. All rights reserved.

Low pH Cements

International Nuclear Information System (INIS)

Savage, David; Benbow, Steven

2007-05-01

speciation of silicon at pH 10 has a significant impact upon the solubility of montmorillonite and would thus constitute a logical choice of pH limit for cement-derived pore fluids, but it is unlikely that cement-based grouts could be developed to meet this limit. Control of mass transport by diffusion processes serves as a significant constraint over the amount of bentonite that can be degraded. Computer simulations indicate that porosity reduction is likely at the interface between cement and bentonite. However, it is not clear how the transport properties of bentonite may be modified due to mineral alteration processes. There are considerable uncertainties concerning the precise mechanism of the rate of montmorillonite dissolution at elevated pH. The rate of dissolution may be inhibited by the presence of dissolved Si (and perhaps Al), but this mechanism has yet to be confirmed at high pH. The type of secondary minerals assumed to form from cement-bentonite interaction will also have a significant impact upon the rate of montmorillonite dissolution. Low-pH cement systems have received little attention thus far regarding the development of models for the chemical evolution of pore fluids. Low Ca/Si CSH gels show preferential leaching of Si, which is in marked contrast with gels of greater Ca/Si ratio. Models apparently capable of predicting pore fluid composition coexisting with low Ca/Si CSH gels are a modified Berner model and a solid-solution model proposed by Sugiyama and Fujita. The solubility of silica in pore fluids coexisting with low Ca/Si gels may exceed that of amorphous silica, and may pose problems regarding the stability of montmorillonite in relation to framework silicates such as feldspars. However, the potential rate of conversion of montmorillonite to feldspar under repository conditions is uncertain. It is necessary to use additives such as super plasticiser to improve the workability of low-pH cements. These organic additives have the potential to

Low pH Cements

Energy Technology Data Exchange (ETDEWEB)

Savage, David; Benbow, Steven [Quintessa Ltd., Henley-on-Thames (United Kingdom)

2007-05-15

speciation of silicon at pH 10 has a significant impact upon the solubility of montmorillonite and would thus constitute a logical choice of pH limit for cement-derived pore fluids, but it is unlikely that cement-based grouts could be developed to meet this limit. Control of mass transport by diffusion processes serves as a significant constraint over the amount of bentonite that can be degraded. Computer simulations indicate that porosity reduction is likely at the interface between cement and bentonite. However, it is not clear how the transport properties of bentonite may be modified due to mineral alteration processes. There are considerable uncertainties concerning the precise mechanism of the rate of montmorillonite dissolution at elevated pH. The rate of dissolution may be inhibited by the presence of dissolved Si (and perhaps Al), but this mechanism has yet to be confirmed at high pH. The type of secondary minerals assumed to form from cement-bentonite interaction will also have a significant impact upon the rate of montmorillonite dissolution. Low-pH cement systems have received little attention thus far regarding the development of models for the chemical evolution of pore fluids. Low Ca/Si CSH gels show preferential leaching of Si, which is in marked contrast with gels of greater Ca/Si ratio. Models apparently capable of predicting pore fluid composition coexisting with low Ca/Si CSH gels are a modified Berner model and a solid-solution model proposed by Sugiyama and Fujita. The solubility of silica in pore fluids coexisting with low Ca/Si gels may exceed that of amorphous silica, and may pose problems regarding the stability of montmorillonite in relation to framework silicates such as feldspars. However, the potential rate of conversion of montmorillonite to feldspar under repository conditions is uncertain. It is necessary to use additives such as super plasticiser to improve the workability of low-pH cements. These organic additives have the potential to

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.

Dissolution kinetics of UO2: Flow-through tests on UO2.00 pellets and polycrystalline schoepite samples in oxygenated, carbonate/bicarbonate buffer solutions at 25 degree C

International Nuclear Information System (INIS)

Nguyen, S.N.; Weed, H.C.; Leider, H.R.; Stout, R.B.

1991-10-01

The modelling of radionuclide release from waste forms is an important part of the performance assessment of a potential, high-level radioactive waste repository. Since spent fuel consists of UO 2 containing actinide elements and other fission products, it is necessary to determine the principal parameters affecting UO 2 dissolution and quantify their effects on the dissolution rate before any prediction of long term release rates of radionuclides from the spent fuel can be made. As part of a complex matrix to determine the dissolution kinetics of UO 2 as a function of time, pH, carbonate/bicarbonate concentration and oxygen activity, we have measured the dissolution rates at 25 degrees C of: (1) UO 2 pellets; (2) UO 2.00 powder and (3) synthetic dehydrated schoepite, UO 3 .H 2 O using a single-pass flow through system in an argon-atmosphere glove box. Carbonate, carbonate/bicarbonate, and bicarbonate buffers with concentrations ranging from 0.0002 M to 0.02 M and pH values form 8 to 11 have been used. Argon gas mixtures containing oxygen (from 0.002 to 0.2 atm) and carbon dioxide (from 0 to 0.011 atm) were bubbled through the buffers to stabilize their pH values. 12 refs., 2 tabs

DNAPL remediation with in situ chemical oxidation using potassium permanganate - Part I. Mineralogy of Mn oxide and its dissolution in organic acids

Science.gov (United States)

Li, X. David; Schwartz, Franklin W.

2004-01-01

Previous studies on in situ chemical oxidation of trichloroethylene (TCE) with potassium permanganate indicated that the solid reaction product, Mn oxide, could reduce the permeability of the porous medium and impact the success of dense non-aqueous phase liquid (DNAPL) removal. In order to address the issue of permeability reduction caused by precipitation, this study investigated the mineralogy of Mn oxides and the possibilities of removing the solid precipitates by dissolution. The solid reaction product from the oxidation of TCE by permanganate is semi-amorphous potassium-rich birnessite, which has a layered mineral structure with an interlayer spacing of 7.3 Å. The chemical formula is K 0.854Mn 1.786O 4·1.55H 2O. It has a relatively small specific surface area at 23.6±0.82 m 2/g. Its point of zero charge (pzc) was measured as 3.7±0.4. This birnessite is a relatively active species and could participate in various reactions with existing organic and inorganic matter. The dissolution kinetics of Mn oxide was evaluated in batch experiments using solutions of citric acid, oxalic acid, and ethylenediaminetetraacetic acid (EDTA). Initial dissolution rates were determined to be 0.126 mM/m 2/h for citric acid, 1.35 mM/m 2/h for oxalic acid, and 5.176 mM/m 2/h for EDTA. These rates compare with 0.0025 mM/m 2/h for nitric acid at pH=2. Organic acids dissolve Mn oxide quickly. Reaction rates increase with acid concentration, as tested with citric acid. The dissolution mechanism likely involves proton and ligand-promoted dissolution and reductive dissolution. Citric and oxalic acid can induce ligand-promoted dissolution, while EDTA can induce ligand-promoted and reductive dissolutions. At low pH, proton-promoted dissolution seems to occur with all the acids tested, but this process is not dominant. Reductive dissolution appears to be the most effective process in dissolving the solid, followed by ligand-promoted dissolution. These experiments indicate the significant

The anodic dissolution of SIMFUEL (UO2) in slightly alkaline sodium carbonate/bicarbonate solutions

International Nuclear Information System (INIS)

Keech, P.G.; Goldik, J.S.; Qin, Z.; Shoesmith, D.W.

2011-01-01

The corrosion of nuclear fuel under waste disposal conditions is likely to be influenced by the bicarbonate/carbonate content of the groundwater since it increases the solubility of the U VI corrosion product, [UO 2 ] 2+ . As one of the half reactions involved in the corrosion process, the anodic dissolution of SIMFUEL (UO 2 ) has been studied in bicarbonate/carbonate solutions (pH 9.8) using voltammetric and potentiostatic techniques and electrochemical impedance spectroscopy. The reaction proceeds by two consecutive one electron transfer reactions (U IV → U V → U VI ). At low potentials (≤250 mV (vs. SCE) the rate of the first electron transfer reaction is rate determining irrespective of the total carbonate concentration. At potentials >250 mV (vs. SCE) the formation of a U VI O 2 CO 3 surface layer begins to inhibit the dissolution rate and the current becomes independent of potential indicating rate control by the chemical dissolution of this layer.

Kinetics of dissolution of thorium and uranium doped britholite ceramics

Energy Technology Data Exchange (ETDEWEB)

Dacheux, N., E-mail: nicolas.dacheux@univ-montp2.f [Groupe de Radiochimie, Institut de Physique Nucleaire d' Orsay, Bat. 100, Universite Paris-Sud-11, 91406 Orsay (France); Institut de Chimie Separative de Marcoule, UMR 5257 (Universite Montpellier 2/CNRS/CEA/ENSCM), Bat. 426, Centre de Marcoule, BP 17171, 30207 Bagnols sur ceze cedex (France); Du Fou de Kerdaniel, E. [Groupe de Radiochimie, Institut de Physique Nucleaire d' Orsay, Bat. 100, Universite Paris-Sud-11, 91406 Orsay (France); Clavier, N. [Groupe de Radiochimie, Institut de Physique Nucleaire d' Orsay, Bat. 100, Universite Paris-Sud-11, 91406 Orsay (France); Institut de Chimie Separative de Marcoule, UMR 5257 (Universite Montpellier 2/CNRS/CEA/ENSCM), Bat. 426, Centre de Marcoule, BP 17171, 30207 Bagnols sur ceze cedex (France); Podor, R. [Institut de Chimie Separative de Marcoule, UMR 5257 (Universite Montpellier 2/CNRS/CEA/ENSCM), Bat. 426, Centre de Marcoule, BP 17171, 30207 Bagnols sur ceze cedex (France); Institut Jean Lamour - Departement CP2S - Equipe 206, Faculte des Sciences et Techniques - Nancy Universite, BP 70239, 54506 Vandoeuvre les Nancy cedex (France); Aupiais, J. [CEA DAM DIF, 91297 Arpajon (France); Szenknect, S. [Institut de Chimie Separative de Marcoule, UMR 5257 (Universite Montpellier 2/CNRS/CEA/ENSCM), Bat. 426, Centre de Marcoule, BP 17171, 30207 Bagnols sur ceze cedex (France)

2010-09-01

In the field of immobilization of actinides in phosphate-based ceramics, several thorium and uranium doped britholite samples were submitted to leaching tests. The normalized dissolution rates determined for several pH values, temperatures and acidic media from the calcium release range from 4.7 x 10{sup -2} g m{sup -2} d{sup -1} to 21.6 g m{sup -2} d{sup -1}. Their comparison with that determined for phosphorus, thorium and uranium revealed that the dissolution is clearly incongruent for all the conditions examined. Whatever the leaching solution considered, calcium and phosphorus elements were always released with higher R{sub L} values than the other elements (Nd, Th, U). Simultaneously, thorium was found to quickly precipitate as alteration product, leading to diffusion phenomena for uranium. For all the media considered, the uranium release is higher than that of thorium, probably due to its oxidation from tetravalent oxidation state to uranyl. Moreover, the evaluation of the partial order related to proton concentration and the apparent energy of activation suggest that the reaction of dissolution is probably controlled by surface chemical reactions occurring at the solid/liquid interface. Finally, comparative leaching tests performed in sulphuric acid solutions revealed a significant influence of such media on the chemical durability of the leached pellets, leading to higher normalized dissolution rates for all the elements considered. On the basis of the results of chemical speciation, this difference was mainly explained in the light of higher complexion constants by sulfate ions compared to nitrate, chloride and phosphate.

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

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.

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.

HB-Line Dissolution of Glovebox Floor Sweepings

International Nuclear Information System (INIS)

Gray, J.H.

1998-02-01

Two candidate flowsheets for dissolving glovebox floor sweepings in the HB-Line Phase I geometrically favorable dissolver have been developed.Dissolving conditions tested and modified during the laboratory program were based on the current processing scheme for dissolving high-fired Pu-238 oxide in HB-Line. Subsequent adjustments made to the HB-Line flowsheet reflected differences in the dissolution behavior between high-fired Pu-238 oxide and the MgO sand/PuF 4 /PuO 2 mixture in glovebox floor sweepings. Although both candidate flowsheets involved two separate dissolving steps and resulted incomplete dissolution of all solids, the one selected for use in HB-Line will require fewer processing operations and resembles the initial flowsheet proposed for dissolving sand, slag, and crucible material in F-Canyon dissolvers. Complete dissolution of glovebox floor sweepings was accomplished in the laboratory by initially dissolving between 55 and 65 degree in a 14 molar nitric acid solution. Under these conditions, partial dissolution of PuF 4 and complete dissolution of PuO 2 and MgO sand were achieved in less than one hour. The presence of free fluoride in solution,uncomplexed by aluminum, was necessary for complete dissolution of the PuO 2 .The remaining PuF 4 dissolved following addition of aluminum nitrate nonahydrate (ANN) to complex the fluoride and heating between 75 and 85 degree C for an additional hour. Precipitation of magnesium and/or aluminum nitrates could occur before, during, and after transfer of product solutions. Both dilution and/or product solution temperature controls may be necessary to prevent precipitation of these salts. Corrosion of the dissolver should not be an issue during these dissolving operations. Corrosion is minimized when dissolving at 55-65 degree C for one to three hours at a maximum uncomplexed free fluoride concentration of 0.07 molar and by dissolving at 75-85 degree C at a one to one aluminum to fluoride mole ratio for another

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

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.)

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

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.

Production of monodisperse respirable aerosols of 241AmO2 and evaluation of in vitro dissolution

International Nuclear Information System (INIS)

Boyd, H.A.; Raabe, O.G.; Peterson, P.K.

1974-01-01

A method is described for production of monodisperse (sigma//sub g/ less than 1.2) particles of 241 AmO 2 for use in inhalation experiments with dogs and rodents. The effects of physical and chemical factors on the production of polydisperse aerosols of 241 AmO 2 were studied and evaluated. The best aerosol was achieved when a suspension of americium hydroxide with 2.5 mg Am/ml at pH = 7.3 was aerosolized and passed through two heating columns in succession, the first at 300 0 C and the second at 1050 0 C. The particles were roughly spherical and had densities near 8 gm/cm 3 ; the aerosol AMAD and sigma/sub g/ were about 1.5 μm and 1.7, respectively. Monodisperse particles were separated and collected with the Lovelace Aerosol Particle Separator (LAPS) and subsequently suspended in deionized water with pH adjusted to 10.2 with NH 3 for nebulization to produce monodisperse aerosols for inhalation exposures. Particles collected on filters during inhalation experiments were used for evaluation of in vitro dissolution rates with two systems and various forms of a lung fluid simulant. The important role of phosphate ions in such dissolution systems was demonstrated, suggesting the potential for the equally important role of free phosphate in retarding dissolution of AmO 2 particles in the lung. (U.S.)

Effect of a cement buffer on spent fuel dissolution

International Nuclear Information System (INIS)

Mennecart, Thierry; Cachoir, Christelle; Lemmens, Karel; Gielen, Ben; Vercauter, Regina

2012-01-01

The Belgian agency for radioactive waste has selected the super-container design with an Ordinary Portland Cement (OPC) buffer as the reference design for geological disposal of High-Level Waste (HLW) and Spent Fuel (SF) in the Boom Clay formation. In the super-container design, the canisters of HLW or SF will be enclosed by a 30 mm thick carbon steel overpack and a 700 mm thick concrete buffer. The overpack will prevent contact with the (cementitious) pore water during the thermal phase. On the other hand, once the overpack will be locally perforated, the high pH of the incoming water may have an impact on the lifetime of the waste. Most published data and national programs are related to clayey backfill materials, and few studies are reported in alkaline media. Hence, a set of experiments was conducted to evaluate the behavior of spent fuel (UO 2 dissolution rate and UO 2 solubility) in such an environment. The objective was to estimate the spent fuel dissolution rate in super-container conditions for use in preliminary performance assessment calculations

Capsule shell material impacts the in vitro disintegration and dissolution behaviour of a green tea extract☆

Science.gov (United States)

Glube, Natalie; Moos, Lea von; Duchateau, Guus

2013-01-01

Purpose In vitro disintegration and dissolution are routine methods used to assess the performance and quality of oral dosage forms. The purpose of the current work was to determine the potential for interaction between capsule shell material and a green tea extract and the impact it can have on the release. Methods A green tea extract was formulated into simple powder-in-capsule formulations of which the capsule shell material was either of gelatin or HPMC origin. The disintegration times were determined together with the dissolution profiles in compendial and biorelevant media. Results All formulations disintegrated within 30 min, meeting the USP criteria for botanical formulations. An immediate release dissolution profile was achieved for gelatin capsules in all media but not for the specified HPMC formulations. Dissolution release was especially impaired for HPMCgell at pH 1.2 and for both HPMC formulations in FeSSIF media suggesting the potential for food interactions. Conclusions The delayed release from studied HPMC capsule materials is likely attributed to an interaction between the catechins, the major constituents of the green tea extract, and the capsule shell material. An assessment of in vitro dissolution is recommended prior to the release of a dietary supplement or clinical trial investigational product to ensure efficacy. PMID:25755998

Capsule shell material impacts the in vitro disintegration and dissolution behaviour of a green tea extract.

Science.gov (United States)

Glube, Natalie; Moos, Lea von; Duchateau, Guus

2013-01-01

In vitro disintegration and dissolution are routine methods used to assess the performance and quality of oral dosage forms. The purpose of the current work was to determine the potential for interaction between capsule shell material and a green tea extract and the impact it can have on the release. A green tea extract was formulated into simple powder-in-capsule formulations of which the capsule shell material was either of gelatin or HPMC origin. The disintegration times were determined together with the dissolution profiles in compendial and biorelevant media. All formulations disintegrated within 30 min, meeting the USP criteria for botanical formulations. An immediate release dissolution profile was achieved for gelatin capsules in all media but not for the specified HPMC formulations. Dissolution release was especially impaired for HPMCgell at pH 1.2 and for both HPMC formulations in FeSSIF media suggesting the potential for food interactions. The delayed release from studied HPMC capsule materials is likely attributed to an interaction between the catechins, the major constituents of the green tea extract, and the capsule shell material. An assessment of in vitro dissolution is recommended prior to the release of a dietary supplement or clinical trial investigational product to ensure efficacy.

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)

Effect of pH and chloride concentration on the removal of hexavalent chromium in a batch electrocoagulation reactor

International Nuclear Information System (INIS)

Arroyo, M.G.; Perez-Herranz, V.; Montanes, M.T.; Garcia-Anton, J.; Guinon, J.L.

2009-01-01

In this work, the effect of pH and chloride ions concentration on the removal of Cr(VI) from wastewater by batch electrocoagulation using iron plate electrodes has been investigated. The initial solution pH was adjusted with different concentrations of H 2 SO 4 . The presence of chloride ions enhances the anode dissolution due to pitting corrosion. Fe 2+ ions formed during the anode dissolution cause the reduction of Cr(VI) to form Cr(III), which are co-precipitated with Fe 3+ ions at relatively low pH. The reduction degree of Cr(VI) to Cr(III) and the solubility of metal hydroxide species (both chromic and iron hydroxides) depend on pH. At higher concentrations of H 2 SO 4 , the reduction of Cr(VI) to Cr(III) by Fe 2+ ions is preferred, but the coagulation of Fe 3+ and Cr(III) is favoured at the lower H 2 SO 4 concentrations.

Effect of pH and chloride concentration on the removal of hexavalent chromium in a batch electrocoagulation reactor

Energy Technology Data Exchange (ETDEWEB)

Arroyo, M.G. [Departamento de Ingenieria Quimica y Nuclear, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia (Spain); Perez-Herranz, V., E-mail: vperez@iqn.upv.es [Departamento de Ingenieria Quimica y Nuclear, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia (Spain); Montanes, M.T.; Garcia-Anton, J.; Guinon, J.L. [Departamento de Ingenieria Quimica y Nuclear, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia (Spain)

2009-09-30

In this work, the effect of pH and chloride ions concentration on the removal of Cr(VI) from wastewater by batch electrocoagulation using iron plate electrodes has been investigated. The initial solution pH was adjusted with different concentrations of H{sub 2}SO{sub 4}. The presence of chloride ions enhances the anode dissolution due to pitting corrosion. Fe{sup 2+} ions formed during the anode dissolution cause the reduction of Cr(VI) to form Cr(III), which are co-precipitated with Fe{sup 3+} ions at relatively low pH. The reduction degree of Cr(VI) to Cr(III) and the solubility of metal hydroxide species (both chromic and iron hydroxides) depend on pH. At higher concentrations of H{sub 2}SO{sub 4}, the reduction of Cr(VI) to Cr(III) by Fe{sup 2+} ions is preferred, but the coagulation of Fe{sup 3+} and Cr(III) is favoured at the lower H{sub 2}SO{sub 4} concentrations.

In vitro solubility, dissolution and permeability studies combined with semi-mechanistic modeling to investigate the intestinal absorption of desvenlafaxine from an immediate- and extended release formulation.

Science.gov (United States)

Franek, F; Jarlfors, A; Larsen, F; Holm, P; Steffansen, B

2015-09-18

Desvenlafaxine is a biopharmaceutics classification system (BCS) class 1 (high solubility, high permeability) and biopharmaceutical drug disposition classification system (BDDCS) class 3, (high solubility, poor metabolism; implying low permeability) compound. Thus the rate-limiting step for desvenlafaxine absorption (i.e. intestinal dissolution or permeation) is not fully clarified. The aim of this study was to investigate whether dissolution and/or intestinal permeability rate-limit desvenlafaxine absorption from an immediate-release formulation (IRF) and Pristiq(®), an extended release formulation (ERF). Semi-mechanistic models of desvenlafaxine were built (using SimCyp(®)) by combining in vitro data on dissolution and permeation (mechanistic part of model) with clinical data (obtained from literature) on distribution and clearance (non-mechanistic part of model). The model predictions of desvenlafaxine pharmacokinetics after IRF and ERF administration were compared with published clinical data from 14 trials. Desvenlafaxine in vivo dissolution from the IRF and ERF was predicted from in vitro solubility studies and biorelevant dissolution studies (using the USP3 dissolution apparatus), respectively. Desvenlafaxine apparent permeability (Papp) at varying apical pH was investigated using the Caco-2 cell line and extrapolated to effective intestinal permeability (Peff) in human duodenum, jejunum, ileum and colon. Desvenlafaxine pKa-values and octanol-water partition coefficients (Do:w) were determined experimentally. Due to predicted rapid dissolution after IRF administration, desvenlafaxine was predicted to be available for permeation in the duodenum. Desvenlafaxine Do:w and Papp increased approximately 13-fold when increasing apical pH from 5.5 to 7.4. Desvenlafaxine Peff thus increased with pH down the small intestine. Consequently, desvenlafaxine absorption from an IRF appears rate-limited by low Peff in the upper small intestine, which "delays" the predicted

Antagonistic Effects of Ocean Acidification and Rising Sea Surface Temperature on the Dissolution of Coral Reef Carbonate Sediments

Directory of Open Access Journals (Sweden)

Daniel Trnovsky

2016-11-01

Full Text Available Increasing atmospheric CO2 is raising sea surface temperature (SST and increasing seawater CO2 concentrations, resulting in a lower oceanic pH (ocean acidification; OA, which is expected to reduce the accretion of coral reef ecosystems. Although sediments comprise most of the calcium carbonate (CaCO3 within coral reefs, no in situ studies have looked at the combined effects of increased SST and OA on the dissolution of coral reef CaCO3 sediments. In situ benthic chamber incubations were used to measure dissolution rates in permeable CaCO3 sands under future OA and SST scenarios in a coral reef lagoon on Australia’s Great Barrier Reef (Heron Island. End of century (2100 simulations (temperature +2.7°C and pH -0.3 shifted carbonate sediments from net precipitating to net dissolving. Warming increased the rate of benthic respiration (R by 29% per 1°C and lowered the ratio of productivity to respiration (P/R; ΔP/R = -0.23, which increased the rate of CaCO3 sediment dissolution (average net increase of 18.9 mmol CaCO3 m-2 d-1 for business as usual scenarios. This is most likely due to the influence of warming on benthic P/R which, in turn, was an important control on sediment dissolution through the respiratory production of CO2. The effect of increasing CO2 on CaCO3 sediment dissolution (average net increase of 6.5 mmol CaCO3 m-2 d-1 for business as usual scenarios was significantly less than the effect of warming. However, the combined effect of increasing both SST and pCO2 on CaCO3 sediment dissolution was non-additive (average net increase of 5.6 mmol CaCO3 m-2 d-1 due to the different responses of the benthic community. This study highlights that benthic biogeochemical processes such as metabolism and associated CaCO3 sediment dissolution respond rapidly to changes in SST and OA, and that the response to multiple environmental changes are not necessarily additive.

Study of the H+, F- and C2O42- ions effect on the Columbo-Tantalites dissolution

International Nuclear Information System (INIS)

Rodriguez, Mario; Ruiz, Maria del Carmen

2003-01-01

The dissolution reaction of Nb, Ta, Fe and Mn in aqueous solutions of HF, HF-H 2 C 2 O 4 , HF-Na 2 C 2 O 4 and H 2 C 2 O 4 -NaF mixtures, using columbo-tantalites of the San Luis Province, has been studied using a Parr autoclave.The temperature range investigated in this work is between 340 and 396 K.At the moment, the experimental data show that the presence of H + and F - ions in the leaching solution is necessary to produce an appreciable dissolution of columbo-tantalite.Also, the presence of C 2 O 4 2- ions favors the mineral dissolution.On the other hand, both the rise of the H + , F - and C 2 O 4 2- ions concentrations and the increase temperature lead to higher Nb and Ta extractions.Moreover, the presence of the Na + of ion in the leaching media induce the formation of Nb and/or Ta insoluble complexes that settle on the residue

Use of acidifier and solubilizer in tadalafil solid dispersion to enhance the in vitro dissolution and oral bioavailability in rats.

Science.gov (United States)

Choi, Jin-Seok; Kwon, Soon-Hyung; Lee, Sang-Eun; Jang, Woo Suk; Byeon, Jong Chan; Jeong, Hyeong Mo; Park, Jeong-Sook

2017-06-30

The purpose of this study is to improve the solubility, in vitro dissolution, and oral bioavailability in rats of tadalafil (TDF) by using SD technique with a weak acid and a copolymer. TDF-SD was prepared via solvent evaporation, coupled with the incorporation of an acidifier and solubilizer. Tartaric acid enhanced the solubility of TDF over 5-fold in DW, and Soluplus ® enhanced the solubility of TDF over 8.7-fold and 19.2-fold compared to that of TDF (pure) in DW and pH 1.2 for 1h, respectively. The optimal formulation of TDF-SD3 was composed of TDF vs Tartaric acid vs Soluplus ® vs Aerosil=1:1:3:3. The in vitro dissolution rate of TDF-SD3 in DW, pH 1.2 and pH 6.8 buffer (51.5%, 53.3%, and 33.2%, respectively) was significantly higher than that of the commercial product (Cialis ® ) powder (16.5%, 15.2%, and 14.8%, respectively). TDF was completely transformed to an amorphous form as shown in SEM, DSC and PXRD data. The stability of TDF-SD3 included drug contents and in vitro dissolution for 1 month were similar to those of Cialis ® , and the amorphous form of TDF-SD3 was well maintained for 6 months. The TDF-SD3 formulation improved the relative bioavailability (BA) and peak plasma concentration (C max ) compared to that of Cialis ® powder after oral administration in rats as 117.3% and 135.7%, respectively. From the results, we found that the acidifier increased the wettability of TDF, and the solubilizer improved solubility through hydrogen bonding with TDF, thereby increasing the solubility, dissolution and oral bioavailability of TDF in TDF-SD3. Copyright © 2017 Elsevier B.V. All rights reserved.

Dissolution of granulated wood ash examined by in situ incubation: Effects of tree species and soil type

DEFF Research Database (Denmark)

Callesen, Ingeborg; Ingerslev, M.; Raulund-Rasmussen, K.

2007-01-01

handling and to avoid undesired effects on vegetation and leaching of nutrients. Forest ecosystems with different tree species and soils provide variable conditions for mineral dissolution with respect to pH, amount of organic ligands and humidity in the forest floor and the top soil. To study the effects...

The Dissolution Behavior of Borosilicate Glasses in Far-From Equilibrium Conditions

Energy Technology Data Exchange (ETDEWEB)

Neeway, James J.; Rieke, Peter C.; Parruzot, Benjamin PG; Ryan, Joseph V.; Asmussen, Robert M.

2018-02-10

In far-from-equilibrium conditions, the dissolution of borosilicate glasses used to immobilize nuclear waste is known to be a function of both temperature and pH. The aim of this paper is to study effects of these variables on three model waste glasses (SON68, ISG, AFCI). To do this, experiments were conducted at temperatures of 23, 40, 70, and 90 °C and pH(RT) values of 9, 10, 11, and 12 with the single-pass flow-through (SPFT) test method. The results from these tests were then used to parameterize a kinetic rate model based on transition state theory. Both the absolute dissolution rates and the rate model parameters are compared with previous results. Discrepancies in the absolute dissolution rates as compared to those obtained using other test methods are discussed. Rate model parameters for the three glasses studied here are nearly equivalent within error and in relative agreement with previous studies. The results were analyzed with a linear multivariate regression (LMR) and a nonlinear multivariate regression performed with the use of the Glass Corrosion Modeling Tool (GCMT), which is capable of providing a robust uncertainty analysis. This robust analysis highlights the high degree of correlation of various parameters in the kinetic rate model. As more data are obtained on borosilicate glasses with varying compositions, the effect of glass composition on the rate parameter values could possibly be obtained. This would allow for the possibility of predicting the forward dissolution rate of glass based solely on composition

Novel pH control strategy for glutathione overproduction in batch ...

African Journals Online (AJOL)

The effects of pH values on cell growth and glutathione (GSH) production were studied in batch cultivation of Candida utilis. According to the fact that lower pH value favors cells growth but retards GSH production and higher pH value promotes GSH production while inhibits cells growth, a pH-shift strategy, optimized via ...

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

concentration of chromous ions. Of all the formulations studied, ECCr formulation was found to be efficient in dissolving FeCr 2 O 4 . In the case of EAC and NCCr, there was an induction period for the dissolution to commence. Further, the rate of dissolution was found to decrease with the increase in pH and increase with the increase in the amount of chromous ions in the formulation. (authors)

Studies on the dissolution of antimony doped ferrites

International Nuclear Information System (INIS)

Keny, S.J.; Kumbhar, A.G.; Sanjukta, A.; Pandey, S.; Venkateswaran, G.; Ramanathan, S.

2008-01-01

Antimony (Sb) present in the PHT (primary heat transport) pump seals and bearings of PHWRs (Pressurized Heavy Water Reactor) is released during operation of the reactor and gets deposited on the in-core zircaloy surfaces. Neutron flux in the reactor core activates this Sb to 122 Sb (t 1/2 2.6 days) and 124 Sb (t 1/2 60 days). Release of this Sb (radioactive antimony) and its deposition on out of core surfaces occurs due to oxygen ingress in the system during shutdown periods and off normal conditions. Sb deposition on the magnetite bearing carbon steel surface of the PHT system results in increase of radiation fields. The consequence of this is low apparent decontamination factors observed after system decontamination. Once Sb is deposited on bare carbon steel (CS) surface or magnetite bearing carbon steel surface it is not amenable for removal by normal reductive decontamination process. It has to decay by its own half-life or has to be removed by oxidative dissolution. To understand the role of antimony and its removal on the ion exchange column, antimony doped ferrites were prepared and their dissolution in CNA (citric acid, NTA, Ascorbic acid; 1.4+1.4+1.7 mM) formulation was studied. The time taken for the dissolution of antimony-doped ferrites was found to increase with increasing Sb content in the ferrite. The point of zero charge (pzc) value of Sb substituted magnetite was determined to understand its adsorption on carbon steel surfaces of the PHT system. The pzc values for Fe 3 O 4 and Sb 2 O 3 , with H + / OH - as only potential determining ions in the aqueous medium, were 6.5 and 1.7 respectively. While, pzc of magnetite in typical decontamination formulations was below 3. The pzc for aqueous suspension of antimony-substituted magnetite (sintered at 1173 K) was 4.4. On the other hand, in CEA (citric acid, EDTA, Ascorbic acid) formulation up to a pH of 1.5, surface charge on the antimony-substituted magnetite was negative. Hence, even at this low pH, pzc

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.

Preparation, characterization, and dissolution studies of naproxen solid dispersions using polyethylene glycol 6000 and labrafil M2130

Directory of Open Access Journals (Sweden)

Jafar Akbari

2015-06-01

Full Text Available Naproxen is a poor water soluble, non-steroidal analgesic and anti-inflammatory drug. The enhancement of oral bioavailability of poor water soluble drugs remains one of the most challenging aspects of drug development. Although salt formation, solubilization and particle size reduction have commonly been used to increase dissolution rate and thereby oral absorption and bioavailability of low water soluble drugs, there are practical limitation of these techniques. However, the most attractive option for increasing the release rate is improvement of solubility through formulation approaches. In this study, solid dispersions (SD of naproxen were prepared by hot melt method using various ratios of drug to polymers (PEG6000 separately and characterized for physical appearance, FTIR, DSC, X-Ray crystallography, and in-vitro dissolution studies. The influence of several amounts of Labrafil M2130 was also studied. FTIR study revealed that drug was stable in SDs, and great state of amorphous formed particles was proofed by DSC analysis. The in vitro dissolution studies were carried using USP type II (paddle dissolution apparatus at medium (pH 1.5. Solubility of naproxen from SDs was increased in dissolution media. The prepared dispersion showed increase in the dissolution rate of naproxen comparing to that of physical mixtures of drug and polymers and pure drug. Percent of drug released in 60 minutes was 23.92% for pure naproxen witch is increased in SDs and reached to100% for best formulations of PEG6000 and labrafil based SDs respectively, considering ratio of drug to polymers.It is concluded that dissolution of the naproxen could be improved by the solid dispersion. Although physical mixtures have increased the rate of dissolution, dissolution shows faster release from SDs which would therefore be due to formation of amorphous particles through the hot melt process which was also revealed by DSC analysis and XRD.

Dissolution of two NWCF calcines: Extent of dissolution and characterization of undissolved solids

International Nuclear Information System (INIS)

Brewer, K.N.; Herbst, R.S.; Tranter, T.J.

1995-01-01

A study was undertaken to determine the dissolution characteristics of two NWCF calcine types. A two-way blended calcine made from 4 parts nonradioactive aluminum nitrate and one part WM-102 was studied to determine the extent of dissolution for aluminum-type calcines. A two-way blend of 3.5 parts fluorinel waste from WM-187 and 1 part sodium waste from WM-185 was used to determine the extent of dissolution for zirconium-type calcines. This study was necessary to develop suitable aqueous separation flowsheets for the partitioning of actinides and fission products from ICPP calcines and to determine the disposition of the resulting undissolved solids (UDS). The dissolution flowsheet developed by Herbst was used to dissolve these two NWCF calcine types. Results show that greater than 95 wt% of aluminum and zirconium calcine types were dissolved after a single batch contact with 5 M HNO 3 . A characterization of the UDS indicates that the weight percent of TRU elements in the UDS resulting from both calcine type dissolutions increases by approximately an order of magnitude from their concentrations prior to dissolution. Substantial activities of cesium and strontium are also present in the UDS resulting from the dissolution of both calcine types. Multiple TRU, Cs, and Sr analyses of both UDS types show that these solids are relatively homogeneous. From this study, it is estimated that between 63.5 and 635 cubic meters of UDS will be generated from the dissolution of 3800 M 3 of calcine. The significant actinide and fission product activities in these UDS will preclude their disposal as low-level waste. If the actinide and fission activity resulting from the UDS is the only considered source in the dissolved calcine solutions, an estimated 99.9 to 99.99 percent of the solids must be removed from this solution for it to meet non-TRU Class A low-level waste

A study on dissolution and leaching behaviour of spent nuclear fuels

International Nuclear Information System (INIS)

Lee, Chang Heon; Im, Hee Jung; Kim, Jong Gu; Park, Yang Soon; Ha, Yeong Keong

2010-12-01

This state of the art report describes a leaching behaviour of spent nuclear fuels which should be considered for safety assessment of spent nuclear fuel disposal in a deep geological repository. A decisive factor of a dissolution of UO 2 , a matrix of the fuel, is chemical characters (redox potential, pH, concentration of inorganic anions, water radiolysis subsequent by radiation field of the fuels) of ground water expected to be in contact with the fuels after the container has failed due to corrosion as well as atmosphere condition of a deep geological repository, which can change the oxidation state of UO 2 . The release rates of radionuclides from UO 2 matrix depend largely on their location within the fuels, that is, the radionuclides fixed in the fuel/cladding gap and grain boundaries are rapidly released. However, the radionuclides within the grains of the fuel are slowly released, and then their release rate is governed by a dissolution behaviour of UO 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.

On the Sensitivity of Peptide Nucleic Acid Duplex Formation and Crystal Dissolution to a Variation of Force-Field Parameters.

Science.gov (United States)

Bachmann, Stephan J; Lin, Zhixiong; Stafforst, Thorsten; van Gunsteren, Wilfred F; Dolenc, Jožica

2014-01-14

The technique of one-step perturbation to explore the relation between particular force-field parameters on the one hand and particular properties of a biomolecular system on the other hand from one or a few molecular dynamics simulations is applied to investigate the dependence of the free enthalpy of dimer formation and of crystal dissolution of a self-complementary fragment (H-CGTACG-NH2) of peptide nucleic acid, PNA, a mimic of DNA. The simulations show that PNA dimer formation in aqueous solution is favored by a decrease in the base charges with respect to values of the GROMOS 45A4 force field, while it is disfavored by a decrease in the backbone charges. In contrast, crystal dissolution of the PNA dimer is favored by a decrease in base charges, while a variation of backbone charges has a minor effect on this free enthalpy change. These opposite effects in a crystalline versus aqueous solution environment can be understood from the different water contents for these systems and have consequences for biomolecular force-field development.

The effect of pH and ionic strength of dissolution media on in-vitro release of two model drugs of different solubilities from HPMC matrices.

Science.gov (United States)

Asare-Addo, Kofi; Conway, Barbara R; Larhrib, Hassan; Levina, Marina; Rajabi-Siahboomi, Ali R; Tetteh, John; Boateng, Joshua; Nokhodchi, Ali

2013-11-01

The evaluation of the effects of different media ionic strengths and pH on the release of hydrochlorothiazide, a poorly soluble drug, and diltiazem hydrochloride, a cationic and soluble drug, from a gel forming hydrophilic polymeric matrix was the objective of this study. The drug to polymer ratio of formulated tablets was 4:1. Hydrochlorothiazide or diltiazem HCl extended release (ER) matrices containing hypromellose (hydroxypropyl methylcellulose (HPMC)) were evaluated in media with a pH range of 1.2-7.5, using an automated USP type III, Bio-Dis dissolution apparatus. The ionic strength of the media was varied over a range of 0-0.4M to simulate the gastrointestinal fed and fasted states and various physiological pH conditions. Sodium chloride was used for ionic regulation due to its ability to salt out polymers in the midrange of the lyotropic series. The results showed that the ionic strength had a profound effect on the drug release from the diltiazem HCl K100LV matrices. The K4M, K15M and K100M tablets however withstood the effects of media ionic strength and showed a decrease in drug release to occur with an increase in ionic strength. For example, drug release after the 1h mark for the K100M matrices in water was 36%. Drug release in pH 1.2 after 1h was 30%. An increase of the pH 1.2 ionic strength to 0.4M saw a reduction of drug release to 26%. This was the general trend for the K4M and K15M matrices as well. The similarity factor f2 was calculated using drug release in water as a reference. Despite similarity occurring for all the diltiazem HCl matrices in the pH 1.2 media (f2=64-72), increases of ionic strength at 0.2M and 0.4M brought about dissimilarity. The hydrochlorothiazide tablet matrices showed similarity at all the ionic strength tested for all polymers (f2=56-81). The values of f2 however reduced with increasing ionic strengths. DSC hydration results explained the hydrochlorothiazide release from their HPMC matrices. There was an increase in

Modelling the Interaction of Low pH Cements and Bentonite. Issues Affecting the Geochemical Evolution of Repositories for Radioactive Waste

International Nuclear Information System (INIS)

Watson, Claire; Benbow, Steven; Savage, David

2007-05-01

It is well known that in the hyperalkaline conditions (pH > 12) of standard cement pore fluids, there is potential for deleterious effects upon the host rock and other EBS materials, notably bentonite, in geological repositories for radioactive waste. Low pH cements are beginning to be considered as a potential alternative material that may address some of these concerns. Low pH cement (also known as low heat cement) was developed by the cement industry for use where large masses of cement (e.g. dams) could cause problems regarding heat generated during curing. In low pH cements, the amount of cement is reduced by substitution of materials such as fly ash, blast furnace slag, silica fume, and/or non pozzolanic silica flour. NUMO, Posiva and SKB have defined a pH limit ≤ 11 for cement grout leachates. To attain this pH, blending agents must comprise at least 50 wt % of dry materials. Because low pH cement has little, or no free portlandite, the cement consists predominantly of calcium silicate hydrate (CSH) gel with a Ca/Si ratio ≤ 0.8. In this report we give the results of a preliminary modelling study to investigate the potential impacts of low pH cement water. We compare the evolution of a bentonite sample under the influence of several invading cement porewaters over a pH range from 10 to 13.2. The porewater compositions are taken from published CSH gel leaching experiments and published cement-bentonite modelling studies. The models suggest that the amount of degradation that is likely to be observed when low pH cement water interacts with bentonite is likely to be much less than when OPC water is the invading fluid. Below pH 11 there was not an observable Na montmorillonite dissolution front which would tend to support the pH ≤ 11 target suggested by NUMO, Posiva and SKB. The models used in this study could be improved upon by including a cement component to the model (rather than representing cement as a fixed boundary condition). Solid-solution models

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

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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.

Molecular-level elucidation of saccharin-assisted rapid dissolution and high supersaturation level of drug from Eudragit® E solid dispersion.

Science.gov (United States)

Ueda, Keisuke; Kanaya, Harunobu; Higashi, Kenjirou; Yamamoto, Keiji; Moribe, Kunikazu

2018-03-01

In this work, the effect of saccharin (SAC) addition on the dissolution and supersaturation level of phenytoin (PHT)/Eudragit® E (EUD-E) solid dispersion (SD) at neutral pH was examined. The PHT/EUD-E SD showed a much slower dissolution of PHT compared to the PHT/EUD-E/SAC SD. EUD-E formed a gel layer after the dispersion of the PHT/EUD-E SD into an aqueous medium, resulting in a slow dissolution of PHT. Pre-dissolving SAC in the aqueous medium significantly improved the dissolution of the PHT/EUD-E SD. Solid-state 13 C NMR measurements showed an ionic interaction between the tertiary amino group of EUD-E and the amide group of SAC in the EUD-E gel layer. Consequently, the ionized EUD-E could easily dissolve from the gel layer, promoting PHT dissolution. Solution-state 1 H NMR measurements revealed the presence of ionic interactions between SAC and the amino group of EUD-E in the PHT/EUD-E/SAC solution. In contrast, interactions between PHT and the hydrophobic group of EUD-E strongly inhibited the crystallization of the former from its supersaturated solution. The PHT supersaturated solution was formed from the PHT/EUD-E/SAC SD by the fast dissolution of PHT and the strong crystallization inhibition effect of EUD-E after aqueous dissolution. Copyright © 2018 Elsevier B.V. All rights reserved.

The kinetics of Dissolution of Biologically Formed Calcific Deposits.

Science.gov (United States)

Rokidi, Stamatia; Koutsoukos, Petros

2015-04-01

The calcification of aortic valves results in the formation of non stoichiometric apatitic deposits which may have serious health implications because of the fact that these minerals adhere tenaciously on tissues like heart valves and arteries causing permanent damage which is partly due to their low solubility. In the present work, calcium phosphate biominerals were extracted from clinically removed tissues and were characterized with respect to their mineralogical constituents and other properties including morphology, specific surface area analyses and thermogravimetric analysis. In all cases, the biominerals may be described as non stoichiometric apatitic materials, although traces of the precursor phase of octacalcium phosphate (Ca8H2(PO4)6•5H2O, OCP) were identified on the basis of their morphological examination. The kinetics of dissolution of the biomineral deposits was investigated in solutions undersaturated with respect to hydroxyapatite (Ca5(PO4)3OH, HAP) at conditions of constant undersaturation at pH 7.40, 37°C, 0.15M NaCl. Synthetic stoichiometric HAP was used as the control mineral. The experiments in the present work used solutions prepared from calcium chloride and sodium hydrogen phosphate and the relative undersaturation, σ, was in the range 0.38-0.74 with respect to HAP and 0.49-0.85 with respect to OCP (σ=1 in water). The dissolution process started immediately upon the introduction of an accurately weighted amount of powdered biomineral in the undersaturated solutions homogenized by magnetic stirring. Inert atmosphere was ensured with the bubbling of water vapor saturated nitrogen through the demineralizing solutions. A glass/Ag/AgCl combination electrode was used as a probe to monitor the process and to control the addition of diluent solutions with the stoichiometry of the dissolving mineral. The measurements of the rates of crystal dissolution, showed a parabolic dependence on the relative solution undersaturation for HAP and higher

Determining pH at elevated pressure and temperature using in situ ¹³C NMR.

Science.gov (United States)

Surface, J Andrew; Wang, Fei; Zhu, Yanzhe; Hayes, Sophia E; Giammar, Daniel E; Conradi, Mark S

2015-02-03

We have developed an approach for determining pH at elevated pressures and temperatures by using (13)C NMR measurements of inorganic carbon species together with a geochemical equilibrium model. The approach can determine in situ pH with precision better than 0.1 pH units at pressures, temperatures, and ionic strengths typical of geologic carbon sequestration systems. A custom-built high pressure NMR probe was used to collect (13)C NMR spectra of (13)C-labeled CO2 reactions with NaOH solutions and Mg(OH)2 suspensions at pressures up to 107 bar and temperatures of 80 °C. The quantitative nature of NMR spectroscopy allows the concentration ratio [CO2]/[HCO3(-)] to be experimentally determined. This ratio is then used with equilibrium constants calculated for the specific pressure and temperature conditions and appropriate activity coefficients for the solutes to calculate the in situ pH. The experimentally determined [CO2]/[HCO3(-)] ratios agree well with the predicted values for experiments performed with three different concentrations of NaOH and equilibration with multiple pressures of CO2. The approach was then applied to experiments with Mg(OH)2 slurries in which the change in pH could track the dissolution of CO2 into solution, rapid initial Mg(OH)2 dissolution, and onset of magnesium carbonate precipitation.

Preparation and physicochemical characterization of acyclovir cocrystals with improved dissolution properties.

Science.gov (United States)

Bruni, Giovanna; Maietta, Mariarosa; Maggi, Lauretta; Mustarelli, Piercarlo; Ferrara, Chiara; Berbenni, Vittorio; Milanese, Chiara; Girella, Alessandro; Marini, Amedeo

2013-11-01

Acyclovir is a well-known antiviral agent. It can be administered in very high doses (from 200 to 1000 mg even three-four times daily). It has absorption problems mainly due to its poor solubility in water (about 0.2 g/100 mL at 25°C) and its oral bioavailability is approximately 15%-20% with a half-life of about 3 h. To improve acyclovir solubility and/or its dissolution properties, two cocrystals of this drug were successfully produced with glutaric acid (AGA1:1) and fumaric acid (AFA1:1) as conformers, using a cogrinding method. Their effective formation was investigated by a broad range of techniques: thermal analysis, Fourier transform infrared spectroscopy, X-ray powder diffraction, solid state nuclear magnetic resonance, and scanning electron microscopy coupled with energy dispersive X-ray spectrometry. The water solubility of the AGA1:1 cocrystal was not improved in comparison to acyclovir, while AFA1:1 showed a slight increased solubility at equilibrium. The main difference was detected in terms of intrinsic dissolution rates (IDR). The IDR of the new phases were much faster compared with acyclovir, particularly at neutral pH. AFA1:1 showed the most rapid dissolution behavior in water; within 10 min, the drug was released completely, while just 60% of acyclovir was dissolved in 1 h. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association.

Effects of acid rain and sulfur dioxide on marble dissolution

Science.gov (United States)

Schuster, Paul F.; Reddy, Michael M.; Sherwood, Susan I.

1994-01-01

Acid precipitation and the dry deposition of sulfur dioxide (SO2) accelerate damage to carbonate-stone monuments and building materials. This study identified and quantified environmental damage to a sample of Vermont marble during storms and their preceding dry periods. Results from field experiments indicated the deposition of SO2 gas to the stone surface during dry periods and a twofold increase in marble dissolution during coincident episodes of low rain rate and decreased rainfall pH. The study is widely applicable to the analysis of carbonate-stone damage at locations affected by acid rain and air pollution.

The anodic dissolution of SIMFUEL (UO{sub 2}) in slightly alkaline sodium carbonate/bicarbonate solutions

Energy Technology Data Exchange (ETDEWEB)

Keech, P.G.; Goldik, J.S.; Qin, Z. [Department of Chemistry, University of Western Ontario, 1151 Richmond St, London ON, N6A 5B7 (Canada); Shoesmith, D.W., E-mail: dwshoesm@uwo.ca [Department of Chemistry, University of Western Ontario, 1151 Richmond St, London ON, N6A 5B7 (Canada)

2011-09-30

The corrosion of nuclear fuel under waste disposal conditions is likely to be influenced by the bicarbonate/carbonate content of the groundwater since it increases the solubility of the U{sup VI} corrosion product, [UO{sub 2}]{sup 2+}. As one of the half reactions involved in the corrosion process, the anodic dissolution of SIMFUEL (UO{sub 2}) has been studied in bicarbonate/carbonate solutions (pH 9.8) using voltammetric and potentiostatic techniques and electrochemical impedance spectroscopy. The reaction proceeds by two consecutive one electron transfer reactions (U{sup IV} {yields} U{sup V} {yields} U{sup VI}). At low potentials ({<=}250 mV (vs. SCE) the rate of the first electron transfer reaction is rate determining irrespective of the total carbonate concentration. At potentials >250 mV (vs. SCE) the formation of a U{sup VI}O{sub 2}CO{sub 3} surface layer begins to inhibit the dissolution rate and the current becomes independent of potential indicating rate control by the chemical dissolution of this layer.

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

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.)

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.

Thermodynamic and Kinetic Aspects of the Dissolution of Quartz-Kaolinite Mixtures by Alkalis Aspects thermodynamiques et cinétiques de la dissolution des mélanges quartz-kaolinite par les alcalis

Directory of Open Access Journals (Sweden)

Labrid J.

2006-11-01

Full Text Available Mineral-alkali interactions have received considerable attention in the recent literature dealing with enhanced oil recovery techniques and clay stabilization treatments. One of the critical factors to be considered is alkali consumption. Alkalinity decrease occurs through several mechanisms, which are ion exchange, precipitation, reaction with crude oil components, and dissolution of minerals. This paper describes the dissolution process. An original kinetic model is proposed to describe the alkaline dissolution of a clayey sandstone. This model is based first on results concerning quartz dissolution/condensation processes. It is also based on new experimental data, which demonstrate the inhibiting effect of aluminum and, as the reaction proceeds, the precipitation of an aluminosilicate whose the chemical composition has been determined. From these data, a kinetic scheme has been conceived in which adsorption of different chemical species is assumed to occur onto solid surfaces. These species play a more or less important role according to the extent of the reaction. In the mechanisms considered, the argillaceous fraction of the rock provides silicon and aluminum which inhibit the dissolution of the matrix while silicon coming from quartz interferes with clay attack. The kinetic model depicts the coupling of elementary dissolution processes and calculates dissolved silicon and aluminum. It has been tested for various operating conditions, providing initial reaction rates for quartz and clay. Results emphasize the definitive advantage of carbonate compared to other alkaline chemicals owing to the relative low pH of solutions, which is particularly favorable for promoting inhibition by aluminum and, as a general rule, for reducing mineral dissolution. Ce résumé contient des formules (*** qui ne peuvent s'afficher à l'écran L'emploi des agents alcalins pour améliorer la récupération du pétrole a été préconisé à l'origine dans le but

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

Dissolution process for advanced-PWR-type fuels

International Nuclear Information System (INIS)

Black, D.E.; Decker, L.A.; Pearson, L.G.

1979-01-01

The new Fluorinel Dissolution Process and Fuel Storage (FAST) Facility at ICPP will provide underwater storage of spent PWR fuel and a new head-end process for fuel dissolution. The dissolution will be two-stage, using HF and HNO 3 , with an intermittent H 2 SO 4 dissolution for removing stainless steel components. Equipment operation is described

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.

Improving dissolution and oral bioavailability of pranlukast hemihydrate by particle surface modification with surfactants and homogenization

Directory of Open Access Journals (Sweden)

Ha ES

2015-06-01

Full Text Available Eun-Sol Ha,1 In-hwan Baek,2 Jin-Wook Yoo,1 Yunjin Jung,1 Min-Soo Kim1 1College of Pharmacy, Pusan National University, 2College of Pharmacy, Kyungsung University, Busan, Republic of Korea Abstract: The present study was carried out to develop an oral formulation of pranlukast hemihydrate with improved dissolution and oral bioavailability using a surface-modified microparticle. Based on solubility measurements, surface-modified pranlukast hemihydrate microparticles were manufactured using the spray-drying method with hydroxypropylmethyl cellulose, sucrose laurate, and water and without the use of an organic solvent. The hydrophilicity of the surface-modified pranlukast hemihydrate microparticle increased, leading to enhanced dissolution and oral bioavailability of pranlukast hemihydrate without a change in crystallinity. The surface-modified microparticles with an hydroxypropylmethyl cellulose/sucrose laurate ratio of 1:2 showed rapid dissolution of up to 85% within 30 minutes in dissolution medium (pH 6.8 and oral bioavailability higher than that of the commercial product, with approximately 2.5-fold and 3.9-fold increases in area under the curve (AUC0→12 h and peak plasma concentration, respectively. Therefore, the surface-modified microparticle is an effective oral drug delivery system for the poorly water-soluble therapeutic pranlukast hemihydrate. Keywords: solubility, wettability, sucrose laurate, cellulose

Stabilizing sodium hypochlorite at high pH: effects on soft tissue and dentin.

Science.gov (United States)

Jungbluth, Holger; Marending, Monika; De-Deus, Gustavo; Sener, Beatrice; Zehnder, Matthias

2011-05-01

When sodium hypochlorite solutions react with tissue, their pH drops and tissue sorption decreases. We studied whether stabilizing a NaOCl solution at a high pH would increase its soft-tissue dissolution capacity and effects on the dentin matrix compared with a standard NaOCl solution of the same concentration and similar initial pH. NaOCl solutions were prepared by mixing (1:1) a 10% stock solution with water (standard) or 2 mol/L NaOH (stabilized). Physiological saline and 1 mol/L NaOH served as the controls. Chlorine content and alkaline capacity of NaOCl solutions were determined. Standardized porcine palatal soft-tissue specimens and human root dentin bars were exposed to test and control solutions. Weight loss percentage was assessed in the soft-tissue dissolution assay. Three-point bending tests were performed on the root dentin bars to determine the modulus of elasticity and flexural strength. Values between groups were compared using one-way analysis of variance with the Bonferroni correction for multiple testing (α pH level of 7.5, respectively. The stabilized NaOCl dissolved significantly more soft tissue than the standard solution, and the pH remained high. It also caused a higher loss in elastic modulus and flexure strength (P < .05) than the control solutions, whereas the standard solution did not. NaOH-stabilized NaOCl solutions have a higher alkaline capacity and are thus more proteolytic than standard counterparts. Copyright © 2011 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Dissolution of magnetite in a dilute chemical decontaminant formulation containing gallic acid as a reductant

International Nuclear Information System (INIS)

Kishore, Kamal; Rajesh, Puspalata; Dey, G.R.

2000-01-01

Gallic acid (GA) was tried as a reductant in place of ascorbic acid in dilute chemical decontaminant (DCD) formulations. Dissolution of magnetite in GA based DCD formulations was studied at 50 deg as well as 80 degC. It was found to be a good substitute for ascorbic acid in EDTA/ascorbic acid/citric acid i.e. EAC formulation. The efficiency of EDTA/GA/CA formulation was as good as that of EAC formulation. 2.8 was found to be the optimum pH for this formulation and dissolution decreased at lower as well as higher pHs. The ion-exchange behaviour of GA is also appropriate for using it in a regenerating type of formulation. Being an aromatic compound, gallic acid has inherent stability against radiation degradation. (author)

An iridium oxide microelectrode for monitoring acute local pH changes of endothelial cells.

Science.gov (United States)

Ng, Shu Rui; O'Hare, Danny

2015-06-21

pH sensors were fabricated by anodically electrodepositing iridium oxide films (AEIROFs) onto microelectrodes on chips and coated with poly(ethyleneimine) (PEI) for mechanical stability. These demonstrate super-Nernstian response to pH from pH 4.0 to 7.7 in chloride-free phosphate buffer. The surface of the chip was coated with fibronectin for the attachment of porcine aortic endothelial cells (PAECs). The working capability of the pH sensor for monitoring acute local pH changes was investigated by stimulating the PAECs with thrombin. Our results show that thrombin induced acute extracellular acidification of PAECs and dissolution of fibronectin, causing the local pH to decrease. The use of PD98059, a mitogen-activated protein kinase (MAPK) inhibitor, reduced extracellular acidification and an increase in local pH was observed. This study shows that our pH sensors can facilitate the investigation of acute cellular responses to stimulation by monitoring the real-time, local pH changes of cells attached to the sensors.

Effect of pH on paste properties of irradiated corn starch by gamma-rays

International Nuclear Information System (INIS)

Kume, Tamikazu; Aoki, Shohei; Kobayashi, Nobuo; Okuaki, Akira.

1979-01-01

The degradation of starch by γ-irradiation and the effect of pH on gelatinization of starch after irradiation were investigated. Paste viscosities were markedly affected by pH on gelatinization and a decrease in the viscosity of irradiated starch was stimulated by increasing pH. On the other hand, the solubility of irradiated starch increased significantly at the high pH. The granule structure of irradiated starch easily disintegrated at alkaline pH. Remarkable dissolution from the surface of the irradiated starch granules was observed after heating at high pH only a filamentous network frame remained, but the unirradiated one collapsed and folded. It was seen that alkali treatment after irradiation reduces the required dose to obtain low viscosity starch. The required dose to produce a low viscosity starch, for example Ajinomoto Essan Sizer 600 grade, was ca. 3 Mrad at pH 11.0 and ca. 5 Mrad at pH 7.0, whereas it was ca. 7 Mrad without pH adjustment. (author)

Spent-fuel special-studies progress report: probable mechanisms for oxidation and dissolution of single-crystal UO2 surfaces

International Nuclear Information System (INIS)

Wang, R.

1981-03-01

Due to the complexity of the structural, microstructural and compositional characteristics of spent fuel, basic leaching and dissolution mechanisms were studied with UO 2 matrix material, specifically with single-crystal UO 2 , to isolate individual contributory factors. The effects of oxidation and oxidation-dissolution were investigated in different oxidation conditions, such as in air, oxygenated solutions and deionized water containing H 2 O 2 . In addition, the effects of temperature on dissolution of UO 2 were studied in autoclaves at 75 and 150 0 C. Also, oxidation and dissolution measurements were investigated via electrochemical methods to determine if those techniques could be applied to the characterization of leaching and dissolution of spent fuel in a hot cell. Finally, the effects of radiation were explored since the radiolysis of water may create a localized oxidizing condition at or near the spent fuel-solution interface, even in neutral or reducing conditions as commonly found in deep geological environments. The oxidation and oxidation-dissolution mechanisms for UO 2 are proposed as follows: The UO 2 surface is first oxidized in solution to form a UO/sub 2+x/ surface layer several angstroms thick. This oxidized surface has a high dissolution rate since the UO/sub 2+x/ reacts with the dissolved O 2 , or H 2 O 2 , to form uranyl complex ions in a U(VI) state. As the uranyl ions exceed the solubility limits in solution, they become hydrolyzed to form solid deposits and suspended particles of UO 3 hydrates. The thickness and porosity of the deposited UO 3 hydrate surface-film is dependent on temperature, pH and deposition time. A long-term dissolution rate is then determined by the nature of the surface film, such as porosity, solubility and mechanical properties

The use of commercial microwave dissolution equipment for the fast and reliable dissolution of high-fired POX and MOX samples

International Nuclear Information System (INIS)

Tushingham, J.; McInnes, C.; Firkin, S.

1998-09-01

The use of commercially available microwave dissolution equipment for the fast and reliable dissolution of high-fired plutonium dioxide (POX) and mixed oxide (MOX) samples has been evaluated for application to Safeguards Analysis. Under the auspices of the UK R and D Support Programme to the IAEA, equipment has been purchased and tested for the high-pressure microwave dissolution of POX samples fired to 1250 deg. C and MOX samples fired to 1600 deg. C, in concentrated nitric acid and hydrofluoric acid mixture. Considerable problems were encountered during development of procedures for microwave dissolution, resulting largely from sudden changes in pressure within dissolution vessels, which resulted in actuation of safety interlocks designed to prevent overpressurisation. These difficulties were alleviated by controlling the microwave power to reduce the reaction temperature and pressure, and also by introducing additional safety valves into the digestion vessels. Using microwave digestion, dissolution times for high fired POX and MOX samples were substantially reduced. Samples which required ca. 10 hours to dissolve by conventional means could be dissolved in ca. 80 minutes by microwave digestion. Whilst a similar performance in terms of plutonium recovery was achieved for some materials by microwave and conventional dissolution, for other materials microwave dissolution gave higher plutonium recoveries but with poorer precision. This suggests the possible presence of some plutonium oxide within high-fired materials which is more difficult to dissolve than the bulk, and which is perhaps dissolved to an additional but variable degree by the current microwave dissolution procedure. Microwave dissolution has been demonstrated to increase the speed of dissolution of high-fired POX and MOX materials, compared with conventional dissolution. However, the technique has not yet proved satisfactory for the complete dissolution of all high-fired materials tested because of

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.

Microscopic Mechanisms of Dissolution-Precipitation at the Water-Manganese Mineral Interfaces

Science.gov (United States)

Jun, Y.; Martin, S. T.

2006-12-01

The fate and transport of metal contaminants in water are often affected by the manganese redox cycling and the accompanying dissolution and precipitation reactions. Direct microscopic observations of such dynamic reactions, however, are sparse. In this work, microscopic mechanisms of simultaneous dissolution and precipitation of manganese minerals is studied by atomic force microscope (AFM) at circumneutral pH. The effects of the substrate surface morphology, the substrate atomic structure, and the aqueous concentration of Mn2+ on the formation of Mn oxide islands are investigated. Under oxic conditions, Mn2+(aq) dissolved from MnCO3 surface is reacted with O2(aq) at circumneutral pH to form Mn oxide islands on the (10-14) surface of MnCO3. The Mn oxide islands grow heteroepitaxially. On terraces, rhombohedral islands form with 90° rotation relative to crystallographic axis of the underlying substrate, and with z-directional self-limitation. Comparison studies done with MgCO3 and CaCO3 show that the former also promotes heteroepitaxial growth whereas the latter does not. This difference is explained by the relative bond length mismatch between the structures of the carbonate substrates and the atomic structures of Mn oxide islands. A free energy model is also employed to explain why the heights of the Mn oxide islands self limit. Our results provide an improved understanding for the development of predictive models both of exchange across the sediment-water interfaces and the fate and transport of contaminants in aqueous environments.

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 ...

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

Development and validation of spectrophotometric method for assay determination and in vitro dissolution studies of sofosbuvir tablets

International Nuclear Information System (INIS)

Zaman, B.; Hassan, W.; Noreen, H.

2017-01-01

In vitro dissolution of sofosbuvir 400 mg tablets dosage form was performed, using USP dissolution apparatus type-II (paddle type), at 75rpm ± 4 %, and 900mL ± 1%, 0.05 M phosphate buffer pH 6.8 ± 0.05 equilibrated at 37.0 ± 0.5ºC as dissolution medium. Percentage of dissolved sofosbuvir as a function of time was determined using the straight line equation and linear regression using zero order and first order ANOVA based kinetics model. Comparative dissolution studies on two different generic brands A and B was performed comparing the drug release profile with innovator brand Sovaldi 400 mg tablets. The comparison of dissolution profiles was evaluated using model independent approach. The values of similarity factor f2 were (4 and 3) and the difference factor f1 were (64 and 50) for both generic products A and B respectively. A simple and precise spectrophotometric method was developed for estimation of sofosbuvir in dissolution medium based on spectrophotometric detection at wavelength 262 nm. The specific absorbance (A = 1%) of sofosbuvir was 178.5 ± 4% and Beer’s law was obeyed in the concentration ranges 4µg mL−1 to 48µg mL−1. The method was validated appropriately for accuracy, precision, linearity, and specificity, according the guidelines of United State Pharmacopoeia and International Conference on Harmonization. The calibration curve was linear with correlation coefficient (r > 0.9999) and there was no spectral interference from excipients present in the tablets dosage form. This method is precise, rapid and specific for determination of sofosbuvir in tablets dosage form and successfully applied for assay determination and in vitro dissolution studies. (author)

Application of an Artificial Stomach-Duodenum Reduced Gastric pH Dog Model for Formulation Principle Assessment and Mechanistic Performance Understanding.

Science.gov (United States)

Lee, Chen-Ming; Luner, Paul E; Locke, Karen; Briggs, Katherine

2017-08-01

The objective of this study was to develop an artificial stomach-duodenum (ASD) dissolution model as an in vitro evaluation tool that would simulate the gastrointestinal physiology of gastric pH-reduced dogs as a method to assess formulations for a poorly soluble free acid compound with ng/mL solubility. After establishing the ASD model with well-controlled duodenum pH, 5 formulations each applying different solubilization principles were developed and their performance in the ASD model and in vivo in dogs was evaluated. Excellent correlations were obtained between dog area under the curve (AUC) and ASD AUC of 5 formulations evaluated with simulated intestinal fluid (r 2  = 0.987) and fasted-state simulated intestinal fluid (r 2  = 0.989) as the duodenum dissolution medium, indicating that the approach of infusing NaOH into duodenum compartment to maintain duodenum pH of an ASD worked properly in simulating gastric pH-reduced dog. Raman spectroscopy was used to study drug dissolution kinetics associated with different solubilization principles and the results suggested that the solubilization principles performed as designed. Spectroscopic results also identified that the compound formed a gel during dissolution and hypromellose maintained the drug-gelled state to avoid further solid form conversion. The implication of the compound physical gelation to drug dissolution kinetics and in vivo exposure are discussed. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Reductive reactivity of iron(III) oxides in the east china sea sediments: characterization by selective extraction and kinetic dissolution.

Science.gov (United States)

Chen, Liang-Jin; Zhu, Mao-Xu; Yang, Gui-Peng; Huang, Xiang-Li

2013-01-01

Reactive Fe(III) oxides in gravity-core sediments collected from the East China Sea inner shelf were quantified by using three selective extractions (acidic hydroxylamine, acidic oxalate, bicarbonate-citrate buffered sodium dithionite). Also the reactivity of Fe(III) oxides in the sediments was characterized by kinetic dissolution using ascorbic acid as reductant at pH 3.0 and 7.5 in combination with the reactive continuum model. Three parameters derived from the kinetic method: m 0 (theoretical initial amount of ascorbate-reducible Fe(III) oxides), k' (rate constant) and γ (heterogeneity of reactivity), enable a quantitative characterization of Fe(III) oxide reactivity in a standardized way. Amorphous Fe(III) oxides quantified by acidic hydroxylamine extraction were quickly consumed in the uppermost layer during early diagenesis but were not depleted over the upper 100 cm depth. The total amounts of amorphous and poorly crystalline Fe(III) oxides are highly available for efficient buffering of dissolved sulfide. As indicated by the m 0, k' and γ, the surface sediments always have the maximum content, reactivity and heterogeneity of reactive Fe(III) oxides, while the three parameters simultaneously downcore decrease, much more quickly in the upper layer than at depth. Albeit being within a small range (within one order of magnitude) of the initial rates among sediments at different depths, incongruent dissolution could result in huge discrepancies of the later dissolution rates due to differentiating heterogeneity, which cannot be revealed by selective extraction. A strong linear correlation of the m 0 at pH 3.0 with the dithionite-extractable Fe(III) suggests that the m 0 may represent Fe(III) oxide assemblages spanning amorphous and crystalline Fe(III) oxides. Maximum microbially available Fe(III) predicted by the m 0 at pH 7.5 may include both amorphous and a fraction of other less reactive Fe(III) phases.

The temporal evolution of magnesium isotope fractionation during hydromagnesite dissolution, precipitation, and at equilibrium

Science.gov (United States)

Oelkers, Eric H.; Berninger, Ulf-Niklas; Pérez-Fernàndez, Andrea; Chmeleff, Jérôme; Mavromatis, Vasileios

2018-04-01

This study provides experimental evidence of the resetting of the magnesium (Mg) isotope signatures of hydromagnesite in the presence of an aqueous fluid during its congruent dissolution, precipitation, and at equilibrium at ambient temperatures over month-long timescales. All experiments were performed in batch reactors in aqueous sodium carbonate buffer solutions having a pH from 7.8 to 9.2. The fluid phase in all experiments attained bulk chemical equilibrium within analytical uncertainty with hydromagnesite within several days, but the experiments were allowed to continue for up to 575 days. During congruent hydromagnesite dissolution, the fluid first became enriched in isotopically light Mg compared to the dissolving hydromagnesite, but this Mg isotope composition became heavier after the fluid attained chemical equilibrium with the mineral. The δ26Mg composition of the fluid was up to ∼0.35‰ heavier than the initial dissolving hydromagnesite at the end of the dissolution experiments. Hydromagnesite precipitation was provoked during one experiment by increasing the reaction temperature from 4 to 50 °C. The δ26Mg composition of the fluid increased as hydromagnesite precipitated and continued to increase after the fluid attained bulk equilibrium with this phase. These observations are consistent with the hypothesis that mineral-fluid equilibrium is dynamic (i.e. dissolution and precipitation occur at equal, non-zero rates at equilibrium). Moreover the results presented in this study confirm (1) that the transfer of material from the solid to the fluid phase may not be conservative during stoichiometric dissolution, and (2) that the isotopic compositions of carbonate minerals can evolve even when the mineral is in bulk chemical equilibrium with its coexisting fluid. This latter observation suggests that the preservation of isotopic signatures of carbonate minerals in the geological record may require a combination of the isolation of fluid-mineral system

Dissolution of metallic uranium and its alloys. Part 1. Review of analytical and process-scale metallic uranium dissolution

International Nuclear Information System (INIS)

Laue, C.A.; Gates-Anderson, D.; Fitch, T.E.

2004-01-01

This review focuses on dissolution/reaction systems capable of treating uranium metal waste to remove its pyrophoric properties. The primary emphasis is the review of literature describing analytical and production-scale dissolution methods applied to either uranium metal or uranium alloys. A brief summary of uranium's corrosion behavior is included since the corrosion resistance of metals and alloys affects their dissolution behavior. Based on this review, dissolution systems were recommended for subsequent screening studies designed to identify the best system to treat depleted uranium metal wastes at Lawrence Livermore National Laboratory (LLNL). (author)

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

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.

Improvement of database on glass dissolution

International Nuclear Information System (INIS)

Hayashi, Maki; Sasamoto, Hiroshi; Yoshikawa, Hideki

2008-03-01

In geological disposal system, high-level radioactive waste (HLW) glass is expected to retain radionuclide for the long term as the first barrier to prevent radionuclide release. The advancement of its performance assessment technology leads to the reliability improvement of the safety assessment of entire geological disposal system. For this purpose, phenomenological studies for improvement of scientific understanding of dissolution/alteration mechanisms, and development of robust dissolution/alteration model based on the study outcomes are indispensable. The database on glass dissolution has been developed for supporting these studies. This report describes improvement of the prototype glass database. Also, this report gives an example of the application of the database for reliability assessment of glass dissolution model. (author)

Formation, transformation and dissolution of phases formed on surfaces

International Nuclear Information System (INIS)

Shoesmith, D.W.

1983-03-01

The basic mechanisms of film growth, transformation, and dissolution of phases formed on surfaces are discussed. Film growth can occur via solid-state processes or via substrate (usally metal or alloy) dissolution, followed by local supersaturation and precipitation of an insoluble phase. The phase(s) formed may be metastable and transform to a more stable phase, via either solid-state or dissolution-reprecipitation processes. Film dissolution reactions can also occur via a variety of mechanisms, including: (i) direct chemical dissolution when no oxidation state change occurs; (ii) redox dissolution when the film dissolves via a redox reaction involving a reducing or oxidizing agent in solution; and (iii) autoreduction, where film dissolution is coupled to metal dissolution. Such film-growth and dissolution processes, which often produce complex multilayer films, are common in the nuclear industry. A number of examples are discussed

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.

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

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

Diblock Terpolymers Are Tunable and pH Responsive Vehicles To Increase Hydrophobic Drug Solubility for Oral Administration.

Science.gov (United States)

Tale, Swapnil; Purchel, Anatolii A; Dalsin, Molly C; Reineke, Theresa M

2017-11-06

Synthetic polymers offer tunable platforms to create new oral drug delivery vehicles (excipients) to increase solubility, supersaturation maintenance, and bioavailability of poorly aqueous soluble pharmaceutical candidates. Five well-defined diblock terpolymers were synthesized via reversible addition-fragmentation chain transfer polymerization (RAFT) and consist of a first block of either poly(ethylene-alt-propylene) (PEP), poly(N-isopropylacrylamide) (PNIPAm), or poly(N,N-diethylaminoethyl methacrylate) (PDEAEMA) and a second hydrophilic block consisting of a gradient copolymer of N,N-dimethylacrylamide (DMA) and 2-methacrylamidotrehalose (MAT). This family of diblock terpolymers offers hydrophobic, hydrophilic, or H-bonding functionalities to serve as noncovalent sites of drug binding. Drug-polymer spray dried dispersions (SDDs) were created with a model drug, probucol, and characterized by differential scanning calorimetry (DSC). These studies revealed that probucol crystallinity decreased with increasing H-bonding sites available in the polymer. The PNIPAm-b-P(DMA-grad-MAT) systems revealed the best performance at pH 6.5, where immediate probucol release and effective maintenance of 100% supersaturation was found, which is important for facilitating drug solubility in more neutral conditions (intestinal environment). However, the PDEAEMA-b-P(DMA-grad-MAT) system revealed poor probucol dissolution at pH 6.5 and 5.1. Alternatively, at an acidic pH of 3.1, a rapid and high dissolution profile and effective supersaturation maintenance of up to 90% of the drug was found, which could be useful for triggering drug release in acidic environments (stomach). The PEP-b-P(DMA-grad-MAT) system showed poor performance (only ∼20% of drug solubility at pH 6.5), which was attributed to the low solubility of the polymers in the dissolution media. This work demonstrates the utility of diblock terpolymers as a potential new excipient platform to optimize design parameters for

Final Report of Tank 241-C-105 Dissolution, the Phase 2 Study

International Nuclear Information System (INIS)

Meznarich, Huei K.; Bolling, Stacey D.; Cooke, Gary A.; Ely, Thomas M.; Herting, Daniel L.; Lachut, James S.; LaMothe, Margaret E.

2016-01-01

Three clamshell grab samples were taken from Tank 241-C-105 in October 2015 in accordance with RPP-PLAN-60011. Analytical results of those samples were issued in the report RPP-RPT-59115 by Wastren Advantage, Inc., Hanford Laboratory. Solid phase characterization results were reported separately in LAB-RPT-15-00011 and in RPP-RPT-59147. The major solid phases reported to be present were dawsonite [NaAlCO 3 (OH) 2 ], trona [Na 3 (HCO 3 )(CO 3 )⋅2H 2 O], cejkaite [Na 4 (UO 2 )(CO 3 ) 3 ], and an unidentified organic solid, with minor amounts of gibbsite [Al(OH) 3 ], natrophosphate [Na 7 F(PO 4 ) 2 ⋅19H 2 O], and traces of unidentified iron-rich and manganese-rich phases. Note that the presence of dawsonite, trona, and cejkaite requires a relatively low pH, likely around pH 9 to 10. One aliquot of each grab sample was provided to 222-S Laboratory Process Chemistry for dissolution studies. Phase 1 of the dissolution testing followed the approved test plan, WRPS-1404813, Rev. 3, and examined the behavior of the Tank 241-C-105 solids treated with water, 19M sodium hydroxide, 2M nitric acid, and 0.5M oxalic acid/2M nitric acid. Phase 2 of the testing was conducted in accordance with instructions from the client and emphasized treatment with 19M sodium hydroxide followed by water washing. This is the report of the Phase 2 testing.

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)

Andrographis paniculata: Dissolution investigation and pharmacokinetic studies of four major active diterpenoids after multiple oral dose administration in healthy Thai volunteers.

Science.gov (United States)

Pholphana, Nanthanit; Panomvana, Duangchit; Rangkadilok, Nuchanart; Suriyo, Tawit; Puranajoti, Porranee; Ungtrakul, Teerapat; Pongpun, Wanwisa; Thaeopattha, Saichit; Songvut, Phanit; Satayavivad, Jutamaad

2016-12-24

Andrographis paniculata is included in 'The National List of Essential Herbal Drugs A.D. 1999' of Thailand as an herbal drug for the treatment of common cold symptoms and non-infectious diarrhea. The therapeutic activities of A. paniculata are attributed to four major active diterpenoids: andrographolide (1), 14-deoxy-11, 12-didehydroandrographolide (2), neoandrographolide (3), and 14-deoxyandrographolide (4). However, the pharmacokinetic studies in humans of this plant were performed after a single oral dose administration and reported the parameters related to be of only 1. This study aims to determine the pharmacokinetic parameters of four major active diterpenoids after multiple oral dose administration of A. paniculata capsules in healthy volunteers. The dissolution testing of these four diterpenoids was also performed. The dissolution testing of four major active diterpenoids was conducted in pH 1.2, pH 4.5, and pH 6.8 for 10-100min. The pharmacokinetic study of these active diterpenoids was designed as an open-label, multiple oral dose administration of A. paniculata capsules in 20 healthy Thai volunteers at 1:1 ratio of female and male. Each volunteer was given four A. paniculata capsules each time which contained 1, 2, 3, and 4 in the quantities of 32.64, 5.40, 3.60, and 3.84mg, respectively, three times a day for three consecutive days. On the fourth day, after the first dose of the day was administered, blood samples were collected at the predefined time points. The validated LC-MS/MS method was used to simultaneously determine the concentrations of these diterpenoids in the human plasma samples. The pharmacokinetic parameters of each active diterpenoid were determined. All four major active diterpenoids have been completely dissolved in the simulated pH of gastrointestinal tract within 60min of dissolution. The dissolution profiles were found to be highest in pH 6.8 and lowest in pH 1.2, especially for 3. In the pharmacokinetic study, although 1 was

In situ spectroscopic and solution analyses of the reductive dissolution of Mn02 by Fe(II)

Science.gov (United States)

Villinski, John E.; O'Day, Peggy A.; Corley, Timothy L.; Conklin, Martha H.

2001-01-01

The reductive dissolution of MnO2 by Fe(II) under conditions simulating acid mine drainage (pH 3, 100 mM SO42-) was investigated by utilizing a flow-through reaction cell and synchrotron X-ray absorption spectroscopy. This configuration allows collection of in situ, real-time X-ray absorption near-edge structure (XANES) spectra and bulk solution samples. Analysis of the solution chemistry suggests that the reaction mechanism changed (decreased reaction rate) as MnO2 was reduced and Fe(III) precipitated, primarily as ferrihydrite. Simultaneously, we observed an additional phase, with the local structure of jacobsite (MnFe2O4), in the Mn XANES spectra of reactants and products. The X-ray absorbance of this intermediate phase increased during the experiment, implying an increase in concentration. The presence of this phase, which probably formed as a surface coating, helps to explain the reduced rate of dissolution of manganese(IV) oxide. In natural environments affected by acid mine drainage, the formation of complex intermediate solid phases on mineral surfaces undergoing reductive dissolution may likewise influence the rate of release of metals to solution.

PhAST: pharmacophore alignment search tool.

Science.gov (United States)

Hähnke, Volker; Hofmann, Bettina; Grgat, Tomislav; Proschak, Ewgenij; Steinhilber, Dieter; Schneider, Gisbert

2009-04-15

We present a ligand-based virtual screening technique (PhAST) for rapid hit and lead structure searching in large compound databases. Molecules are represented as strings encoding the distribution of pharmacophoric features on the molecular graph. In contrast to other text-based methods using SMILES strings, we introduce a new form of text representation that describes the pharmacophore of molecules. This string representation opens the opportunity for revealing functional similarity between molecules by sequence alignment techniques in analogy to homology searching in protein or nucleic acid sequence databases. We favorably compared PhAST with other current ligand-based virtual screening methods in a retrospective analysis using the BEDROC metric. In a prospective application, PhAST identified two novel inhibitors of 5-lipoxygenase product formation with minimal experimental effort. This outcome demonstrates the applicability of PhAST to drug discovery projects and provides an innovative concept of sequence-based compound screening with substantial scaffold hopping potential. 2008 Wiley Periodicals, Inc.

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.)

In situ amorphisation of indomethacin with Eudragit® E during dissolution

DEFF Research Database (Denmark)

Priemel, Petra A; Laitinen, Riikka; Grohganz, Holger

2013-01-01

at pH 6.8 at which IMC but not the polymer is soluble. Compacts changed their colour from white to yellow indicating amorphisation of IMC. X-ray powder diffractometry (XRPD) confirmed the amorphisation and only one glass transition temperature was observed (58.1 °C, 54.4 °C, and 50.1 °C for the 3:1, 1......In this study, the possibility of utilising in situ crystalline-to-amorphous transformation for the delivery of poorly water soluble drugs was investigated. Compacts of physical mixtures of γ-indomethacin (IMC) and Eudragit® E in 3:1, 1:1 and 1:3 (w/w) ratios were subjected to dissolution testing...

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

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

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.

Fe(II)-induced transformation from ferrihydrite to lepidocrocite and goethite

International Nuclear Information System (INIS)

Liu Hui; Li Ping; Zhu Meiying; Wei Yu; Sun Yuhan

2007-01-01

The transformation of Fe(II)-adsorbed ferrihydrite was studied. Data tracking the formation of products as a function of pH, temperature and time is presented. The results indicate that trace of Fe(II) adsorbed on ferrihydrite can accelerate its transformation obviously. The products are lepidocrocite and/or goethite and/or hematite, which is different from those without Fe(II). That is, Fe(II) not only accelerates the transformation of ferrihydrite but also leads to the formation of lepidocrocite by a new path. The behavior of Fe(II) is shown in two aspects-catalytic dissolution-reprecipitation and catalytic solid-state transformation. The results indicate that a high temperature and a high pH(in the range from 5 to 9) are favorable to solid-state transformation and the formation of hematite, while a low temperature and a low pH are favorable to dissolution-reprecipitation mechanism and the formation of lepidocrocite. Special attentions were given to the formation mechanism of lepidocrocite and goethite. - Graphical abstract: Fe(II)-adsorbed ferrihydrite can rapidly transform into lepidocrocite or/and goethite or/and hematite. Which product dominates depends on the transformation conditions of ferrihydrite such as temperature, pH, reaction time, etc. In the current system, there exist two transformation mechanisms. One is dissolution/reprecipitation and the other is solid-state transformation. The transformation mechanisms from Fe(II)-adsorbed ferrihydrite to lepidocrocite and goethite were investigated

Use of partial dissolution techniques in geochemical exploration

Science.gov (United States)

Chao, T.T.

1984-01-01

Application of partial dissolution techniques to geochemical exploration has advanced from an early empirical approach to an approach based on sound geochemical principles. This advance assures a prominent future position for the use of these techniques in geochemical exploration for concealed mineral deposits. Partial dissolution techniques are classified as single dissolution or sequential multiple dissolution depending on the number of steps taken in the procedure, or as "nonselective" extraction and as "selective" extraction in terms of the relative specificity of the extraction. The choice of dissolution techniques for use in geochemical exploration is dictated by the geology of the area, the type and degree of weathering, and the expected chemical forms of the ore and of the pathfinding elements. Case histories have illustrated many instances where partial dissolution techniques exhibit advantages over conventional methods of chemical analysis used in geochemical exploration. ?? 1984.

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.

Robustness testing, using experimental design, of a flow-through dissolution method for a product where the actives have markedly differing solubility properties.

Science.gov (United States)

Bloomfield, M S; Butler, W C

2000-09-25

The use of experimental design for the robustness testing of a flow-through dissolution method (Ph Eur/USP Apparatus 4) for atovaquone, one of the drug substances in a dual-active anti-malarial tablet formulation, Malarone tablets, is described. This procedure was developed to overcome the suppression of the atovaquone solubility, caused by the presence of the co-drug proguanil hydrochloride and potential imprecision due to the poor solubility of the coating material in the basic dissolution media employed. For this testing a quarter fractional two-level factorial design was applied, assessing six factors in sixteen experiments, with a further six centre points to assess natural experimental variation. Results demonstrate that the method is robust to small changes in all the main factors evaluated at sample times of 30 min or greater. At 15 min, variations in the concentration of sodium hydroxide in the dissolution media, peristaltic pump speed and flow rate were assessed as statistically significant. This observation is a result of the initial steepness of the dissolution release curve and hence these factors are now controlled routinely in the method. Release of this poorly soluble drug is limited at the 45 min time point (Q=75%) according to pharmacopoeial guidelines. The approach may be applied for other dissolution procedures.

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

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)

Microbial- and Thiosulfate-Mediated Dissolution of Mercury Sulfide Minerals and Transformation to Gaseous Mercury

Directory of Open Access Journals (Sweden)

Adiari eVázquez-Rodríguez

2015-06-01

Full Text Available Mercury (Hg is a toxic heavy metal that poses significant human and environmental health risks. Soils and sediments, where Hg can exist as the Hg sulfide mineral metacinnabar (β-HgS, represent major Hg reservoirs in aquatic environments. Metacinnabar has historically been considered a sink for Hg in all but severely acidic environments, and thus disregarded as a potential source of Hg back to aqueous or gaseous pools. Here, we conducted a combination of field and laboratory incubations to identify the potential for metacinnabar as a source of dissolved Hg within near neutral pH environments and the underpinning (abiotic mechanisms at play. We show that the abundant and widespread sulfur-oxidizing bacterium Thiobacillus extensively colonized metacinnabar chips incubated within aerobic, near neutral pH creek sediments. Laboratory incubations of axenic Thiobacillus cultures lead to the release of metacinnabar-hosted Hg(II and subsequent volatilization to Hg(0. This dissolution and volatilization was greatly enhanced in the presence of the sulfur intermediate, thiosulfate, which served a dual role by enhancing HgS dissolution and providing an additional metabolic substrate for Thiobacillus. These findings reveal a new coupled abiotic-biotic pathway for the transformation of metacinnabar-bound Hg(II to Hg(0, while expanding the sulfide substrates available for neutrophilic chemosynthetic bacteria to Hg-laden sulfides. They also point to mineral-hosted Hg as an underappreciated source of gaseous elemental Hg to the environment.

Development and Validation of a Dissolution Test Method for ...

African Journals Online (AJOL)

Purpose: To develop and validate a dissolution test method for dissolution release of artemether and lumefantrine from tablets. Methods: A single dissolution method for evaluating the in vitro release of artemether and lumefantrine from tablets was developed and validated. The method comprised of a dissolution medium of ...

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.

The Biopharmaceutics Classification System: subclasses for in vivo predictive dissolution (IPD) methodology and IVIVC.

Science.gov (United States)

Tsume, Yasuhiro; Mudie, Deanna M; Langguth, Peter; Amidon, Greg E; Amidon, Gordon L

2014-06-16

The Biopharmaceutics Classification System (BCS) has found widespread utility in drug discovery, product development and drug product regulatory sciences. The classification scheme captures the two most significant factors influencing oral drug absorption; solubility and intestinal permeability and it has proven to be a very useful and a widely accepted starting point for drug product development and drug product regulation. The mechanistic base of the BCS approach has, no doubt, contributed to its wide spread acceptance and utility. Nevertheless, underneath the simplicity of BCS are many detailed complexities, both in vitro and in vivo which must be evaluated and investigated for any given drug and drug product. In this manuscript we propose a simple extension of the BCS classes to include sub-specification of acid (a), base (b) and neutral (c) for classes II and IV. Sub-classification for Classes I and III (high solubility drugs as currently defined) is generally not needed except perhaps in border line solubility cases. It is well known that the , pKa physical property of a drug (API) has a significant impact on the aqueous solubility dissolution of drug from the drug product both in vitro and in vivo for BCS Class II and IV acids and bases, and is the basis, we propose for a sub-classification extension of the original BCS classification. This BCS sub-classification is particularly important for in vivo predictive dissolution methodology development due to the complex and variable in vivo environment in the gastrointestinal tract, with its changing pH, buffer capacity, luminal volume, surfactant luminal conditions, permeability profile along the gastrointestinal tract and variable transit and fasted and fed states. We believe this sub-classification is a step toward developing a more science-based mechanistic in vivo predictive dissolution (IPD) methodology. Such a dissolution methodology can be used by development scientists to assess the likelihood of a

UV-vis Imaging of Piroxicam Supersaturation, Precipitation, and Dissolution in a Flow-Through Setup.

Science.gov (United States)

Sun, Yu; Chapman, Alex; Larsen, Susan W; Jensen, Henrik; Petersen, Nickolaj J; Goodall, David M; Østergaard, Jesper

2018-06-05

Evaluation of drug precipitation is important in order to address challenges regarding low and variable bioavailability of poorly water-soluble drugs, to assess potential risk of patient safety with infusion therapy, and to explore injectable in situ suspension-forming drug delivery systems. Generally, drug precipitation is assessed in vitro through solution concentration analysis methods. Dual-wavelength UV-vis imaging is a novel imaging technique that may provide an opportunity for simultaneously monitoring changes in both solution and solid phases during precipitation. In the present study, a multimodal approach integrating UV-vis imaging, light microscopy, and Raman spectroscopy was developed for characterization of piroxicam supersaturation, precipitation, and dissolution in a flow-through setup. A solution of piroxicam dissolved in 1-methyl-2-pyrrolidinone was injected into a flowing aqueous environment (pH 7.4), causing piroxicam to precipitate. Imaging at 405 and 280 nm monitored piroxicam concentration distributions during precipitation and revealed different supersaturation levels dependent on the initial concentration of the piroxicam solution. The combination with imaging at 525 nm, light microscopy, and Raman spectroscopy measurements demonstrated concentration-dependent precipitation and the formation, growth, and dissolution of individual particles. Results emphasize the importance of the specific hydrodynamic conditions on the piroxicam precipitation. The approach used may facilitate comprehensive understanding of drug precipitation and dissolution processes and may be developed further into a basic tool for formulation screening and development.

In Vitro Dissolution Profile of Dapagliflozin: Development, Method Validation, and Analysis of Commercial Tablets

Directory of Open Access Journals (Sweden)

Rafaela Zielinski Cavalheiro de Meira

2017-01-01

Full Text Available Dapagliflozin was the first of its class (inhibitors of sodium-glucose cotransporter to be approved in Europe, USA, and Brazil. As the drug was recently approved, there is the need for research on analytical methods, including dissolution studies for the quality evaluation and assurance of tablets. The dissolution methodology was developed with apparatus II (paddle in 900 mL of medium (simulated gastric fluid, pH 1.2, temperature set at 37±0.5°C, and stirring speed of 50 rpm. For the quantification, a spectrophotometric (λ=224 nm method was developed and validated. In validation studies, the method proved to be specific and linear in the range from 0.5 to 15 μg·mL−1 (r2=0.998. The precision showed results with RSD values lower than 2%. The recovery of 80.72, 98.47, and 119.41% proved the accuracy of the method. Through a systematic approach by applying Factorial 23, the robustness of the method was confirmed (p>0.05. The studies of commercial tablets containing 5 or 10 mg demonstrated that they could be considered similar through f1, f2, and dissolution efficiency analyses. Also, the developed method can be used for the quality evaluation of dapagliflozin tablets and can be considered as a scientific basis for future official pharmacopoeial methods.

The pH of beverages in the United States.

Science.gov (United States)

Reddy, Avanija; Norris, Don F; Momeni, Stephanie S; Waldo, Belinda; Ruby, John D

2016-04-01

Dental erosion is the chemical dissolution of tooth structure in the absence of bacteria when the environment is acidic (pH beverage's erosive potential. In addition, citrate chelation of calcium ions may contribute to erosion at higher pH. The authors of this study determined the erosive potential measured by the pH of commercially available beverages in the United States. The authors purchased 379 beverages from stores in Birmingham, Alabama, and categorized them (for example, juices, sodas, flavored waters, teas, and energy drinks) and assessed their pH. They used a pH meter to measure the pH of each beverage in triplicate immediately after it was opened at a temperature of 25°C. The authors recorded the pH data as mean (standard deviation). Most (93%, 354 of 379) beverages had a pH of less than 4.0, and 7% (25 of 379) had a pH of 4.0 or more. Relative beverage erosivity zones based on studies of apatite solubility in acid indicated that 39% (149 of 379) of the beverages tested in this study were considered extremely erosive (pH beverages in the United States found that most are potentially erosive to the dentition. This study's findings provide dental clinicians and auxiliaries with information regarding the erosive potential of commercially available beverages. Specific dietary recommendations for the prevention of dental erosion may now be developed based on the patient's history of beverage consumption. Copyright © 2016 American Dental Association. Published by Elsevier Inc. All rights reserved.

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

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)

Preparation, characterization and in vitro dissolution study of Nitrazepam: Cyclodextrin inclusion complex

Directory of Open Access Journals (Sweden)

J S Patel

2012-01-01

Full Text Available The objectives of this research were to prepare and characterize inclusion complexes of Nitrazepam with Hydroxypropyl-β-cyclodextrin (HPβCD and Sulfobutyl ether β-cyclodextrin (SBEβCD to study the effect of complexation on the dissolution rate of Nitrazepam, a water-insoluble drug. The phase solubility profile of Nitrazepam with Hydroxypropyl- β-cyclodextrin and Sulfobutyl ether β-cyclodextrin was an AP-type, indicating the formation of 2:1 stoichiometric inclusion complexes. Gibbs free energy values were all negative, indicating the spontaneous nature Nitrazepam solubilization and their value decreased with increase in the cyclodextrin concentration, demonstrating that the reaction conditions became more favorable as the concentration of cyclodextrins increased. Complexes of Nitrazepam were prepared with cyclodextrin using various methods such as physical mixing, kneading, spray-drying and lyophilization. The complexes were characterized by Differential scanning calorimetry, Fourier-transform infrared, scanning electron microscopy and powder X-ray diffraction studies. These studies indicated that a complex prepared by lyophilization had successful inclusion of the Nitrazepam molecule into the cyclodextrin cavity. Complexation resulted in a marked improvement in the solubility and wettability of Nitrazepam. Among all the samples, a complex prepared with Sulfobutyl ether β-cyclodextrin by lyophilization had the greatest improvement in the in vitro rate of Nitrazepam dissolution. The mean dissolution time for Nitrazepam decreased significantly after preparing complexes. The similarity factor indicated a significant difference between the release profiles of Nitrazepam from complexes, physical mixtures and plain Nitrazepam. To conclude that, the tablets containing complexes prepared with Cyclodextrins had significant improvement in the release profile of Nitrazepam as compared to tablets containing Nitrazepam without cyclodextrin.

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

JSS project phase 4: Experimental and modelling studies of HLW glass dissolution in repository environments

International Nuclear Information System (INIS)

1987-10-01

A goal of the JSS project was to develop a scientific basis for understanding the effects of waste package components, groundwater chemistry, and other repository conditions on glass dissolution behaviour, and to develop and refine a model for the processes governing glass dissolution. The fourth phase of the project, which was performed by the Hahn-Meitner-Institut, Berlin, FRG, dealt specifically with model development and application. Phase 4 also adressed whether basaltic glasses could serve as natural analogues for nuclear waste glasses, thus providing a means to test the capability of the model for long-term predictions. Additional experiments were performed in order to complete the data base necessary to model interactions between the glass and bentonite and between glass and steel corrosion products. More data on temperature, S/V, and pH dependence of the glass/water reaction were also collected. In this report, the data acquired during phase 4 are presented and discussed. (orig./DG)

Positively Charged Nanostructured Lipid Carriers and Their Effect on the Dissolution of Poorly Soluble Drugs

Directory of Open Access Journals (Sweden)

Kyeong-Ok Choi

2016-05-01

Full Text Available The objective of this study is to develop suitable formulations to improve the dissolution rate of poorly water soluble drugs. We selected lipid-based formulation as a drug carrier and modified the surface using positively charged chitosan derivative (HTCC to increase its water solubility and bioavailability. Chitosan and HTCC-coated lipid particles had higher zeta-potential values than uncoated one over the whole pH ranges and improved encapsulation efficiency. In vitro drug release showed that all NLC formulations showed higher in vitro release efficiency than drug particle at pH 7.4. Furthermore, NLC formulation prepared with chitosan or HTCC represented good sustained release property. The results indicate that chitosan and HTCC can be excellent formulating excipients of lipid-based delivery carrier for improving poorly water soluble drug delivery.

Positively Charged Nanostructured Lipid Carriers and Their Effect on the Dissolution of Poorly Soluble Drugs.

Science.gov (United States)

Choi, Kyeong-Ok; Choe, Jaehyeog; Suh, Seokjin; Ko, Sanghoon

2016-05-20

The objective of this study is to develop suitable formulations to improve the dissolution rate of poorly water soluble drugs. We selected lipid-based formulation as a drug carrier and modified the surface using positively charged chitosan derivative (HTCC) to increase its water solubility and bioavailability. Chitosan and HTCC-coated lipid particles had higher zeta-potential values than uncoated one over the whole pH ranges and improved encapsulation efficiency. In vitro drug release showed that all NLC formulations showed higher in vitro release efficiency than drug particle at pH 7.4. Furthermore, NLC formulation prepared with chitosan or HTCC represented good sustained release property. The results indicate that chitosan and HTCC can be excellent formulating excipients of lipid-based delivery carrier for improving poorly water soluble drug delivery.

Development and validation of dissolution test for Metoprolol ...

African Journals Online (AJOL)

The dissolution method which uses USP apparatus I (Basket) with rotating at 100 rpm, 900 ml of different dissolution medium, ultra violet spectroscopy for quantification was demonstrated to be robust, discriminating and transferable. Dissolution tests conditions were selected after it was demonstrated that the Metoprolol ...

Final Report of Tank 241-C-105 Dissolution, the Phase 2 Study

Energy Technology Data Exchange (ETDEWEB)

Meznarich, Huei K. [Washington River Protection Solutions LLC., Richland, WA (United States); bolling, Stacey D. [Washington River Protection Solutions LLC., Richland, WA (United States); Cooke, Gary A. [Washington River Protection Solutions LLC., Richland, WA (United States); Ely, Thomas M. [Washington River Protection Solutions LLC., Richland, WA (United States); Herting, Daniel L. [Washington River Protection Solutions LLC., Richland, WA (United States); Lachut, James S. [Washington River Protection Solutions LLC., Richland, WA (United States); LaMothe, Margaret E. [Washington River Protection Solutions LLC., Richland, WA (United States)

2016-10-01

Three clamshell grab samples were taken from Tank 241-C-105 in October 2015 in accordance with RPP-PLAN-60011. Analytical results of those samples were issued in the report RPP-RPT-59115 by Wastren Advantage, Inc., Hanford Laboratory. Solid phase characterization results were reported separately in LAB-RPT-15-00011 and in RPP-RPT-59147. The major solid phases reported to be present were dawsonite [NaAlCO₃(OH)₂], trona [Na₃(HCO₃)(CO₃)·2H₂O], cejkaite [Na₄(UO₂)(CO₃)₃], and an unidentified organic solid, with minor amounts of gibbsite [Al(OH)₃], natrophosphate [Na₇F(PO₄)₂·19H₂O], and traces of unidentified iron-rich and manganese-rich phases. Note that the presence of dawsonite, trona, and cejkaite requires a relatively low pH, likely around pH 9 to 10. One aliquot of each grab sample was provided to 222-S Laboratory Process Chemistry for dissolution studies. Phase 1 of the dissolution testing followed the approved test plan, WRPS-1404813, Rev. 3, and examined the behavior of the Tank 241-C-105 solids treated with water, 19M sodium hydroxide, 2M nitric acid, and 0.5M oxalic acid/2M nitric acid. Phase 2 of the testing was conducted in accordance with instructions from the client and emphasized treatment with 19M sodium hydroxide followed by water washing. This is the report of the Phase 2 testing.

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)

Dissolution testing of orally disintegrating tablets.

Science.gov (United States)

Kraemer, Johannes; Gajendran, Jayachandar; Guillot, Alexis; Schichtel, Julian; Tuereli, Akif

2012-07-01

For industrially manufactured pharmaceutical dosage forms, product quality tests and performance tests are required to ascertain the quality of the final product. Current compendial requirements specify a disintegration and/or a dissolution test to check the quality of oral solid dosage forms. These requirements led to a number of compendial monographs for individual products and, at times, the results obtained may not be reflective of the dosage form performance. Although a general product performance test is desirable for orally disintegrating tablets (ODTs), the complexity of the release controlling mechanisms and short time-frame of release make such tests difficult to establish. For conventional oral solid dosage forms (COSDFs), disintegration is often considered to be the prerequisite for subsequent dissolution. Hence, disintegration testing is usually insufficient to judge product performance of COSDFs. Given the very fast disintegration of ODTs, the relationship between disintegration and dissolution is worthy of closer scrutiny. This article reviews the current status of dissolution testing of ODTs to establish the product quality standards. Based on experimental results, it appears that it may be feasible to rely on the dissolution test without a need for disintegration studies for selected ODTs on the market. © 2012 The Authors. JPP © 2012 Royal Pharmaceutical Society.

Influence of spray drying and dispersing agent on surface and dissolution properties of griseofulvin micro and nanocrystals.

Science.gov (United States)

Shah, Dhaval A; Patel, Manan; Murdande, Sharad B; Dave, Rutesh H

2016-11-01

The purpose for the current research is to compare and evaluate physiochemical properties of spray-dried (SD) microcrystals (MCs), nanocrystals (NCs), and nanocrystals with a dispersion agent (NCm) from a poorly soluble compound. The characterization was carried out by performing size and surface analysis, interfacial tension (at particle moisture interface), and in-vitro drug dissolution rate experiments. Nanosuspensions were prepared by media milling and were spray-dried. The SD powders that were obtained were characterized morphologically using scanning electron microscopy (SEM), polarized light microscopy (PLM), and Flowchem. Solid-state characterization was performed using X-ray powder diffraction (XRPD), Fourier transfer infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC) for the identification of the crystalline nature of all the SD powders. The powders were characterized for their redispersion tendency in the water and in pH 1.2. Significant differences in redispersion were noted for both the NCs in both dissolution media. The interfacial tension for particle moisture interface was determined by applying the BET (Braunauer-Emmett-Teller) equation to the vapor sorption data. No significant reduction in the interfacial tension was observed between MCs and NCs; however, a significant reduction in the interfacial tension was observed for NCm at both 25 °C and 35 °C temperatures. The difference in interfacial tension and redispersion behavior can be attributed to a difference in the wetting tendency for all the SD powders. The dissolution studies were carried out under sink and under non-sink conditions. The non-sink dissolution approach was found suitable for quantification of the dissolution rate enhancement, and also for providing the rank order to the SD formulations.

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....

Chapter 9: Model Systems for Formation and Dissolution of Calcium Phosphate Minerals

Energy Technology Data Exchange (ETDEWEB)

Orme, C A; Giocondi, J L

2006-07-29

Calcium phosphates are the mineral component of bones and teeth. As such there is great interest in understanding the physical mechanisms that underlie their growth, dissolution, and phase stability. Control is often achieved at the cellular level by the manipulation of solution states and the use of crystal growth modulators such as peptides or other organic molecules. This chapter begins with a discussion of solution speciation in body fluids and relates this to important crystal growth parameters such as the supersaturation, pH, ionic strength and the ratio of calcium to phosphate activities. We then discuss the use of scanning probe microscopy as a tool to measure surface kinetics of mineral surfaces evolving in simplified solutions. The two primary themes that we will touch on are the use of microenvironments that temporally evolve the solution state to control growth and dissolution; and the use of various growth modifiers that interact with the solution species or with mineral surfaces to shift growth away from the lowest energy facetted forms. The study of synthetic minerals in simplified solution lays the foundation for understand mineralization process in more complex environments found in the body.

Mineral dissolution and precipitation in carbonate dominated terranes assessed using Mg isotopes

Science.gov (United States)

Tipper, E.; Calmels, D.; Gaillardet, J.; Galy, A.

2013-12-01

Carbonate weathering by carbonic acid consumes atmospheric CO2 during mineral dissolution, fixing it as aqueous bicarbonate over millennial time-scales. Ocean acidification has increased the solubility of CO2 in seawater by changing the balance of pH to alkalinity (the oceanic reservoir of carbon). This has lengthened the time-scale for CO2 sequestration by carbonate weathering to tens of thousands of years. At a global scale, the net consumption of CO2 is at least equal to that from silicate weathering, but there is far less work on carbonate weathering compared to silicate weathering because it has generally been assumed to be CO2 neutral on geological time-scales. Carbonate rocks are more readily dissolved than silicate rocks, meaning that their dissolution will likely respond much more rapidly to global environmental change when compared with the dissolution of silicate minerals. Although far less concentrated than Ca in many carbonates, Mg substitutes for Ca and is more concentrated than any other metal ion. Tracing the behavior of Mg in river waters, using Mg stable isotopes (26Mg/24Mg ratio expressed as delta26Mg in per mil units) is therefore a novel way to understand the complex series of dissolution/precipitation reactions that govern solute concentrations of Ca and Mg, and hence CO2 transfer by carbonate weathering. We present new Mg isotope data on a series of river and spring waters from the Jura mountains in North-East France. The stratigraphic column is relatively uniform throughout the Jura mountains and is dominated by limestones. As the limestone of the Jura Mountains were deposited in high-energy shallow water environments (shore line, lagoon and coral reefs), they are usually clay and organic poor. The delta26Mg of the local rocks is very constant at circa -4permil. The delta26Mg of the river waters is also fairly constant, but offset from the rock at -2.5permil. This is an intriguing observation because the dissolution of limestones is expected

pH- and temperature-sensitive polymeric microspheres for drug delivery: the dissolution of copolymers modulates drug release.

Science.gov (United States)

Fundueanu, Gheorghe; Constantin, Marieta; Stanciu, Cristina; Theodoridis, Georgios; Ascenzi, Paolo

2009-12-01

Most pH-/temperature-responsive polymers for controlled release of drugs are used as cross-linked hydrogels. However, the solubility properties of the linear polymers below and above the lower critical solution temperature (LCST) are not exploited. Here, the preparation and characterization of poly (N-isopropylacrylamide-co-methacrylic acid-co-methyl methacrylate) (poly (NIPAAm-co-MA-co-MM)) and poly (N-isopropylacrylamide-co-acrylamide) (poly (NIPAAm-co-AAm)), known as "smart" polymers (SP), is reported. Both poly (NIPAAm-co-MA-co-MM) and poly (NIPAAm-co-AAm) display pH- and temperature-responsive properties. Poly (NIPAAm-co-MA-co-MM) was designed to be insoluble in the gastric fluid (pH = 1.2), but soluble in the intestinal fluid (pH = 6.8 and 7.4), at the body temperature (37 degrees C). Poly (NIPAAm-co-AAm) was designed to have a lower critical solution temperature (LCST) corresponding to 37 degrees C at pH = 7.4, therefore it is not soluble above the LCST. The solubility characteristics of these copolymers were exploited to modulate the rate of release of drugs by changing pH and/or temperature. These copolymers were solubilized with hydrophobic cellulose acetate butyrate (CAB) and vitamin B(12) (taken as a water soluble drug model system) in an acetone/methanol mixture and dispersed in mineral oil. By a progressive evaporation of the solvent, the liquid droplets were transformed into loaded CAB/SP microspheres. Differential scanning calorimetric studies and scanning electron microscopy analysis demonstrated that the polymeric components of the microspheres precipitated separately during solvent evaporation forming small microdomains. Moreover, vitamin B(12) was found to be molecularly dispersed in both microdomains with no specific affinity for any polymeric component of microspheres. The release of vitamin B(12) was investigated as a function of temperature, pH, and the CAB/SP ratio.

A comparative study of dissolution of {alpha}-Fe{sub 2}O{sub 3} and {gamma}-Fe{sub 2}O{sub 3} in DCD formulations

Energy Technology Data Exchange (ETDEWEB)

Ranganathan, S.; Raghavan, P.S.; Gopalan, R. [Madras Christian Coll. (India). Dept. of Chemistry; Srinivasan, M.P.; Narasimhan, S.V.

1998-12-31

The important corrosion products deposited on the surfaces of structural materials such as stainless steel in the primary coolant system of BWRs are haematite in the outer layers and ferrites such as magnetite, nickel ferrite, cobalt ferrite, etc., in the inner layers. Magnetite dissolution by 2, 6 Pyridinedicarboxylic acid (PDCA), Ethylenediaminetetraacetic acid (EDTA) and Nitrolotriacetic acid (NTA) showed that there is an optimum pH of dissolution for each ligand. The leaching of the metal ions from the oxides is controlled in part by reductive dissolution; this is due to the presence of Fe(II)-L complexes generated from the released Fe{sup 2+} ions. The addition of Fe(II)-L with the formulation greatly increases the rate of dissolution. In order to understand the role of Fe{sup 2+} arising from the spinel lattice of Fe{sub 3}O{sub 4} in aiding the dissolution of magnetite, it is appropriate to study the dissolution behaviour of the system like Fe{sub 2}O{sub 3} which is not containing any Fe{sup 2+} in the crystal lattice. The present study has been carried out with {alpha}-Fe{sub 2}O{sub 3} and {gamma}-Fe{sub 2}O{sub 3} in DCD formulation in the presence of ascorbic acid and with the addition of Fe(II)-L as a reductant. (author)

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...

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

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.

Investigation of the Dissolution-Reformation Cycle of the Passive Oxide Layer on NiTi Orthodontic Archwires

Science.gov (United States)

Uzer, B.; Birer, O.; Canadinc, D.

2017-09-01

Dissolution-reformation cycle of the passive oxide layer on the nickel-titanium (NiTi) orthodontic archwires was investigated, which has recently been recognized as one of the key parameters dictating the biocompatibility of archwires. Specifically, commercially available NiTi orthodontic archwires were immersed in artificial saliva solutions of different pH values (2.3, 3.3, and 4.3) for four different immersion periods: 1, 7, 14, and 30 days. Characterization of the virgin and tested samples revealed that the titanium oxide layer on the NiTi archwire surfaces exhibit a dissolution-reformation cycle within the first 14 days of the immersion period: the largest amount of Ni ion release occurred within the first week of immersion, while it significantly decreased during the reformation period from day 7 to day 14. Furthermore, the oxide layer reformation was catalyzed on the grooves within the peaks and valleys due to relatively larger surface energy of these regions, which eventually decreased the surface roughness significantly within the reformation period. Overall, the current results clearly demonstrate that the analyses of dissolution-reformation cycle of the oxide layer in orthodontic archwires, surface roughness, and ion release behavior constitute utmost importance in order to ensure both the highest degree of biocompatibility and an efficient medical treatment.

Release of copper from sintered tungsten-bronze shot under different pH conditions and its potential toxicity to aquatic organisms

International Nuclear Information System (INIS)

Thomas, Vernon G.; Santore, Robert C.; McGill, Ian

2007-01-01

Sintered tungsten-bronze is a new substitute for lead shot, and is about to be deposited in and around the wetlands of North America. This material contains copper in the alloyed form of bronze. This in vitro study was performed according to U.S. Fish and Wildlife Service criteria to determine the dissolution rate of copper from the shot, and to assess the toxic risk that it may present to aquatic organisms. The dissolution of copper from tungsten-bronze shot, pure copper shot, and glass beads was measured in a buffered, moderately hard, synthetic water of pH 5.5, 6.6, and 7.8 over a 28-day period. The dissolution of copper from both the control copper shot and the tungsten-bronze shot was affected significantly by the pH of the water and the duration of dissolution (all p values < 0.000). The rate of copper release from tungsten bronze shot was 30 to 50 times lower than that from the copper shot, depending on pH (p < 0.0000). The observed expected environmental concentration of copper released from tungsten-bronze shot after 28 days was 0.02 μg/L at pH 7.8, and 0.4 μg/L at pH 5.6, using a loading and exposure scenario specific in a U.S. Fish and Wildlife Service protocol. Ratio Quotient values derived from the highest EEC observed in this study (0.4 μg/L), and the copper toxic effect levels for all aquatic species listed in the U.S. Environmental Protection Agency ambient water quality criteria database, were all far less than the 0.1 criterion value. Given the conditions stipulated by the U.S. Fish and Wildlife Service and the U.S. Environmental Protection Agency, heavy loading from discharged tungsten-bronze shot would not pose a toxic risk to potable water, or to soil. Consequently, it would appear that no toxic risks to aquatic organisms will attend the use of tungsten-bronze shot of the approved composition. Given the likelihood that sintered tungsten-bronze of the same formula will be used for fishing weights, bullets, and wheel balance weights, it is

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.

Comparison of bio-dissolution of spent Ni-Cd batteries by sewage sludge using ferrous ions and elemental sulfur as substrate.

Science.gov (United States)

Zhao, Ling; Zhu, Nan-Wen; Wang, Xiao-Hui

2008-01-01

Bioleaching of spent Ni-Cd batteries using acidified sewage sludge was carried out in a continuous flow two-step leaching system including an acidifying reactor and a leaching reactor. Two systems operated about 30d to achieve almost complete dissolution of heavy metals Ni, Cd and Co in four Ni-Cd batteries. Ferrous sulphate and elemental sulfur were used as two different substrates to culture indigenous thiobacilli in sewage sludge. pH and ORP of the acidifying reactor was stabilized around 2.3 and 334mV for the iron-oxidizing system and 1.2 and 390mV for the sulfur-oxidizing system. It was opposite to the acidifying reactor, the pH/ORP in the leaching reactor of the iron-oxidizing system was relatively lower/higher than that of the sulphur-oxidizing system in the first 17d. The metal dissolution, in the first 12-16d, was faster in the iron-oxidizing system than in the sulphur-oxidizing system due to the lower pH. In the iron-oxidizing system, the maximum solubilization of cadmium (2500mg l(-1)) and cobalt (260mg l(-1)) can be reached at day 6-8 and the most of metal nickel was leached in the first 16d. But in the sulphur-oxidizing system there was a lag period of 4-8d to reach the maximum solubilization of cadmium and cobalt. The maximum dissolution of nickel hydroxide (1400mg l(-1)) and metallic nickel (2300mg l(-1)) occurred at about day 12 and day 20, respectively.

Application of Liquisolid Technology for Enhancing Solubility and Dissolution of Rosuvastatin

Directory of Open Access Journals (Sweden)

Pavan Ram Kamble

2014-03-01

Full Text Available Purpose: Rosuvastatin is a poorly water soluble drug and the rate of its oral absorption is often controlled by the dissolution rate in the gastrointestinal tract. Hence it is necessary to increase the solubility of the Rosuvastatin. Methods: Several liquisolid tablets formulations containing various drug concentrations in liquid medication (ranging from 15% to 25% w/w were prepared. The ratio of Avicel PH 102 (carrier to Aerosil 200 (coating powder material was kept 10, 20, 30. The prepared liquisolid systems were evaluated for their flow properties and possible drug-excipient interactions by Infrared spectra (IR analysis, differential scanning calorimetry (DSC and X- ray powder diffraction (XRPD. Results: The liquisolid system showed acceptable flow properties. The IR and DSC studies demonstrated that there is no significant interaction between the drug and excipients. The XRPD analysis confirmed formation of a solid solution inside the compact matrix. The tabletting properties of the liquisolid compacts were within the acceptable limits. Liquisolid compacts demonstrated significantly higher drug release rates than those of conventional and marketed tablet due to increasing wetting properties and surface area of the drug. Conclusion: This study shows that liquisolid technique is a promising alternative for improvement of the dissolution rate of water insoluble drug.

Dissolution behaviour of ferric pyrophosphate and its mixtures with soluble pyrophosphates: Potential strategy for increasing iron bioavailability.

Science.gov (United States)

Tian, Tian; Blanco, Elena; Smoukov, Stoyan K; Velev, Orlin D; Velikov, Krassimir P

2016-10-01

Ferric pyrophosphate (FePP) is a widely used iron source in food fortification and in nutritional supplements, due to its white colour, that is very uncommon for insoluble Fe salts. Although its dissolution is an important determinant of Fe adsorption in human body, the solubility characteristics of FePP are complex and not well understood. This report is a study on the solubility of FePP as a function of pH and excess of pyrophosphate ions. FePP powder is sparingly soluble in the pH range of 3-6 but slightly soluble at pH8. In the presence of pyrophosphate ions the solubility of FePP strongly increases at pH 5-8.5 due to formation a soluble complex between Fe(III) and pyrophosphate ions, which leads to an 8-10-fold increase in the total ionic iron concentration. This finding is beneficial for enhancing iron bioavailability, which important for the design of fortified food, beverages, and nutraceutical products. Copyright © 2016 Elsevier Ltd. All rights reserved.

Mixed Micelle System Produced by Interaction Between Transglycosylated Stevia and an Ionic Surfactant Improves Dissolution Profile of Mefenamic Acid.

Science.gov (United States)

Fujimori, Miki; Kadota, Kazunori; Tozuka, Yuichi

2017-04-01

Transglycosylated stevia (stevia-G) can effectively improve the dissolution and bioavailability of poorly water-soluble drugs. Furthermore, addition of an ionic surfactant to stevia-G solution has been shown to enhance the dissolution effect of stevia-G on flurbiprofen. Herein, 4 surfactants, namely sodium dodecyl sulfate, sodium N-dodecanoylsarcosinate, sodium monododecyl phosphate, and lauryltrimethylammonium chloride (LTAC) were screened to investigate their synergistic effect with stevia-G in enhancing the solubility of mefenamic acid (MFA). The ternary formulation containing LTAC produced the highest increase in solubility, whereas the binary MFA/LTAC formulation did not increase the solubility of MFA. Surface tension was evaluated to analyze the interaction between stevia-G and each ionic surfactant, wherein the Rubingh model was applied to predict mixed micelle formation between stevia-G and LTAC. Interaction parameters calculated by the Rubingh model reflected mixed micelle formation between stevia-G and LTAC relative to the self-interactions of the 2 individual surfactants. All interaction parameters in this system showed negative values, indicating a favorable interaction (e.g., hydrogen bond or electrostatic and dipole) between binary components in the mixed micelles. Spray-dried particles of ternary formulations (MFA/stevia-G/LTAC) were prepared to evaluate the dissolution profile and physicochemical properties. Dissolution profiling showed that the concentration of MFA released from spray-dried particles was significantly higher than untreated MFA. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

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

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)

Development and validation of a dissolution test with reversed-phase high performance liquid chromatographic analysis for Candesartan cilexetil in tablet dosage forms

Directory of Open Access Journals (Sweden)

Vairappan Kamalakkannan

2016-09-01

Full Text Available A simple, rapid, selective and reproducible reversed-phase high performance liquid chromatographic (RP-HPLC method has been developed and validated for the estimation of release of Candesartan cilexetil (CC in tablets. Analysis was performed on an Agilent, Zorbax C8 column (150mm × 4.6mm, 5μm with the mobile phase consisting of phosphate buffer (pH2.5–acetonitrile (15:85, v/v at a flow rate of 1.0mL/min. UV detection was performed at 215nm and the retention time for CC was 2.2. The calibration curve was linear (correlation coefficient = 1.000 in the selected range of analyte. The optimized dissolution conditions include the USP apparatus 2 at a paddle rotation rate of 50rpm and 900mL of phosphate buffer (pH7.2 with 0.03% of polysorbate 80 as dissolution medium, at 37.0 ± 0.5°C. The method was validated for precision, linearity, specificity, accuracy, limit of quantitation and ruggedness. The system suitability parameters, such as theoretical plate, tailing factor and relative standard deviation (RSD between six standard replicates were well within the limits. The stability result shows that the drug is stable in the prescribed dissolution medium. Three different batches (A, B and C of the formulation containing 8mg of Candesartan cilexetil was performed with the developed method and the results showed no significant differences among the batches.

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.

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}.

Frogging It: A poetic Analysis of Relationship Dissolution

Directory of Open Access Journals (Sweden)

Sandra L. Faulkner

2012-10-01

Full Text Available Often, themes in work and life intertwine; the author recognized that a cadre of poems she had written during the past several years were about relationship dissolution. The poems concerned romantic and friendship dissolution and the aspects of identity creation and loss this entails. The author presents the poems and makes an explicit connection to interpersonal relationship dissolution literature through the technique of poetic analysis. This analysis serves as an exemplar for how poetry as performative writing offers a valuable addition to interpersonal communication research through the poeticizing of relational dissolution as an everyday relational challenge.

Uranium carbide dissolution in nitric solution: Sonication vs. silent conditions

International Nuclear Information System (INIS)

Virot, Matthieu; Szenknect, Stéphanie; Chave, Tony; Dacheux, Nicolas; Moisy, Philippe; Nikitenko, Sergey I.

2013-01-01

The dissolution of uranium carbide (UC) in nitric acid media is considered by means of power ultrasound (sonication) or magnetic stirring. The induction period required to initiate UC dissolution was found to be dramatically shortened when sonicating a 3 M nitric solution (Ar, 20 kHz, 18 W cm −2 , 20 °C). At higher acidity, magnetic stirring offers faster dissolution kinetics compared to sonication. Ultrasound-assisted UC dissolution is found to be passivated after ∼60% dissolution and remains incomplete whatever the acidity which is confirmed by ICP–AES, LECO and SEM–EDX analyses. In general, the kinetics of UC dissolution is linked to the in situ generation of nitrous acid in agreement with the general mechanism of UC dissolution; the nitrous acid formation is reported to be faster under ultrasound at low acidity due to the nitric acid sonolysis. The carbon balance shared between the gaseous, liquid, and solid phases is strongly influenced by the applied dissolution procedure and HNO 3 concentration

Uranium carbide dissolution in nitric solution: Sonication vs. silent conditions

Science.gov (United States)

Virot, Matthieu; Szenknect, Stéphanie; Chave, Tony; Dacheux, Nicolas; Moisy, Philippe; Nikitenko, Sergey I.

2013-10-01

The dissolution of uranium carbide (UC) in nitric acid media is considered by means of power ultrasound (sonication) or magnetic stirring. The induction period required to initiate UC dissolution was found to be dramatically shortened when sonicating a 3 M nitric solution (Ar, 20 kHz, 18 W cm-2, 20 °C). At higher acidity, magnetic stirring offers faster dissolution kinetics compared to sonication. Ultrasound-assisted UC dissolution is found to be passivated after ∼60% dissolution and remains incomplete whatever the acidity which is confirmed by ICP-AES, LECO and SEM-EDX analyses. In general, the kinetics of UC dissolution is linked to the in situ generation of nitrous acid in agreement with the general mechanism of UC dissolution; the nitrous acid formation is reported to be faster under ultrasound at low acidity due to the nitric acid sonolysis. The carbon balance shared between the gaseous, liquid, and solid phases is strongly influenced by the applied dissolution procedure and HNO3 concentration.

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.

The effect of high pH alkaline solutions on the mineral stability of the Boom Clay - Batch experiments at 60 deg. C

International Nuclear Information System (INIS)

Honty, M.; De Craen, M.; Wang, L.; Madejova, J.; Czimerova, A.; Pentrak, M.; Stricek, I.; Van Geet, M.

2010-01-01

Boom Clay is currently viewed as a reference host formation for studies on deep geological disposal of radioactive waste in Belgium. The interactions between bulk rock Boom Clay and 0.1 M KOH, 0.1 M NaOH, 0.1 M Ca(OH) 2 , young cement water and evolved cement water solutions, ranging in pH from 12.5 to 13.2, were examined as static batch experiments at 60 deg. C to simulate alkaline plume perturbations, which are expected to occur in the repository due to the presence of concrete. Both liquids and solids were investigated at specific times between 90 and 510 days in order to control the elemental budget and to search for potential mineralogical alterations. Also, the clay fraction was separated from the whole-rock Boom Clay at the end of each run and characterized for its mineralogical composition. Thereby, the importance of the mineral matrix to buffer the alkaline attack and the role of organic matter to protect clay minerals were also addressed. The results indicate that the degree of geochemical perturbation in Boom Clay is dependent on the initial pH of the applied solution together with the nature of the major cation in the reactant fluids. The higher the initial pH of the media, the stronger its interaction with Boom Clay. No major non-clay mineralogical alteration of the Boom Clay was detected, but dissolution of kaolinite, smectite and illite occurred within the studied experimental conditions. The dissolution of clays is accompanied by the decrease in the layer charge, followed by a decrease in the cation-exchange capacity. The highest TOC values coincide with the highest total elemental concentrations in the leachates, and correspondingly, the highest dissolution degree. However, no quantitative link could be established between the degree of organic matter decomposition and clay dissolution.

A combined experimental study of vivianite and As (V) reactivity in the pH range 2-11

International Nuclear Information System (INIS)

Thinnappan, V.; Merrifield, C.M.; Islam, F.S.; Polya, D.A.; Wincott, P.; Wogelius, R.A.

2008-01-01

Four different sets of experiments were completed in order to constrain vivianite [Fe 3 (PO 4 ) 2 . 8H 2 O] reactivity under conditions pertinent to As(V)-bearing groundwater systems. Firstly, titration experiments were undertaken in the pH range 4-9 to determine the zero point of charge (ZPC) of vivianite; showing that the ZPC lies at a pH of approximately 5.3. Secondly, the steady state dissolution rates of vivianite far from equilibrium were measured in aqueous solutions in the pH range 2-10 at 18.5 d eg. C (±3 deg. C) using a fluidized bed reactor. The rate of vivianite dissolution, R, is given by (1)R(moless -1 cm -2 )=1.18x10 -10 a H+ 0.77 +1x10 -15 +6.92x10 -24 a H+ -1 The dissolution rate exhibits an exponential increase with increase in the activity of the H + ion (a H+ ) in solution at 2 8. Thirdly, the sorption of arsenate [As(V)] onto natural well-crystallized vivianite in the pH range 3-11 under static flow conditions was determined. 25-40% of As(V) from a starting concentration (C 0 ) of 100 μM was adsorbed onto vivianite. Static adsorption experiments were also completed at two lower As(V) concentrations (C 0 = 10 and 1 μM). Sorption was determined to be only weakly dependent on pH. Fourthly, the final part of this study investigated the sorption of As(V) onto vivianite at pH 9 under dynamic flow conditions. An input solution of 4 mM As(V) was applied to water saturated columns, followed by leaching with deionised water (DIW). Breakthrough curves show that the retention and exchangeability of As within the column is enhanced with vivianite present, consistent with solid phase analysis of unreacted and reacted solid materials. A simple calculation based on a model shallow Bengal sediment having about 0.2 wt% of vivianite and total initial dissolved As concentrations of 100 μM showed that under such conditions 88% of dissolved As(V) could potentially be adsorbed onto vivianite. These results will help to better understand As mobility in the

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

Hyperpolarized Amino Acid Derivatives as Multivalent Magnetic Resonance pH Sensor Molecules

Directory of Open Access Journals (Sweden)

Christian Hundshammer

2018-02-01

Full Text Available pH is a tightly regulated physiological parameter that is often altered in diseased states like cancer. The development of biosensors that can be used to non-invasively image pH with hyperpolarized (HP magnetic resonance spectroscopic imaging has therefore recently gained tremendous interest. However, most of the known HP-sensors have only individually and not comprehensively been analyzed for their biocompatibility, their pH sensitivity under physiological conditions, and the effects of chemical derivatization on their logarithmic acid dissociation constant (pKa. Proteinogenic amino acids are biocompatible, can be hyperpolarized and have at least two pH sensitive moieties. However, they do not exhibit a pH sensitivity in the physiologically relevant pH range. Here, we developed a systematic approach to tailor the pKa of molecules using modifications of carbon chain length and derivatization rendering these molecules interesting for pH biosensing. Notably, we identified several derivatives such as [1-13C]serine amide and [1-13C]-2,3-diaminopropionic acid as novel pH sensors. They bear several spin-1/2 nuclei (13C, 15N, 31P with high sensitivity up to 4.8 ppm/pH and we show that 13C spins can be hyperpolarized with dissolution dynamic polarization (DNP. Our findings elucidate the molecular mechanisms of chemical shift pH sensors that might help to design tailored probes for specific pH in vivo imaging applications.

Hyperpolarized Amino Acid Derivatives as Multivalent Magnetic Resonance pH Sensor Molecules.

Science.gov (United States)

Hundshammer, Christian; Düwel, Stephan; Ruseckas, David; Topping, Geoffrey; Dzien, Piotr; Müller, Christoph; Feuerecker, Benedikt; Hövener, Jan B; Haase, Axel; Schwaiger, Markus; Glaser, Steffen J; Schilling, Franz

2018-02-15

pH is a tightly regulated physiological parameter that is often altered in diseased states like cancer. The development of biosensors that can be used to non-invasively image pH with hyperpolarized (HP) magnetic resonance spectroscopic imaging has therefore recently gained tremendous interest. However, most of the known HP-sensors have only individually and not comprehensively been analyzed for their biocompatibility, their pH sensitivity under physiological conditions, and the effects of chemical derivatization on their logarithmic acid dissociation constant (p K a ). Proteinogenic amino acids are biocompatible, can be hyperpolarized and have at least two pH sensitive moieties. However, they do not exhibit a pH sensitivity in the physiologically relevant pH range. Here, we developed a systematic approach to tailor the p K a of molecules using modifications of carbon chain length and derivatization rendering these molecules interesting for pH biosensing. Notably, we identified several derivatives such as [1- 13 C]serine amide and [1- 13 C]-2,3-diaminopropionic acid as novel pH sensors. They bear several spin-1/2 nuclei ( 13 C, 15 N, 31 P) with high sensitivity up to 4.8 ppm/pH and we show that 13 C spins can be hyperpolarized with dissolution dynamic polarization (DNP). Our findings elucidate the molecular mechanisms of chemical shift pH sensors that might help to design tailored probes for specific pH in vivo imaging applications.

A novel dissolution media for testing drug release from a nanostructured polysaccharide-based colon specific drug delivery system: an approach to alternative colon media.

Science.gov (United States)

Kotla, Niranjan G; Singh, Sima; Maddiboyina, Balaji; Sunnapu, Omprakash; Webster, Thomas J

2016-01-01

The aim of this study was to develop a novel microbially triggered and animal-sparing dissolution method for testing of nanorough polysaccharide-based micron granules for colonic drug delivery. In this method, probiotic cultures of bacteria present in the colonic region were prepared and added to the dissolution media and compared with the performance of conventional dissolution methodologies (such as media with rat cecal and human fecal media). In this study, the predominant species (such as Bacteroides, Bifidobacterium, Lactobacillus species, Eubacterium and Streptococcus) were cultured in 12% w/v skimmed milk powder and 5% w/v grade "A" honey. Approximately 10(10)-10(11) colony forming units m/L of probiotic culture was added to the dissolution media to test the drug release of polysaccharide-based formulations. A USP dissolution apparatus I/II using a gradient pH dissolution method was used to evaluate drug release from formulations meant for colonic drug delivery. Drug release of guar gum/Eudragit FS30D coated 5-fluorouracil granules was assessed under gastric and small intestine conditions within a simulated colonic environment involving fermentation testing with the probiotic culture. The results with the probiotic system were comparable to those obtained from the rat cecal and human fecal-based fermentation model, thereby suggesting that a probiotic dissolution method can be successfully applied for drug release testing of any polysaccharide-based oral formulation meant for colonic delivery. As such, this study significantly adds to the nanostructured biomaterials' community by elucidating an easier assay for colonic drug delivery.

Effects of water chemistry on the dissolution of ZnO nanoparticles and their toxicity to Escherichia coli

International Nuclear Information System (INIS)

Li Mei; Lin Daohui; Zhu Lizhong

2013-01-01

The dissolution of ZnO nanoparticles (nano-ZnO) plays an important role in the toxicity of nano-ZnO to the aquatic organisms. The effects of water chemistry such as pH, ionic components, and dissolved organic matter (DOM) on the dissolution of nano-ZnO and its toxicity to Escherichia coli (E. coli) were investigated in synthetic and natural water samples. The results showed that the toxicity of nano-ZnO to E. coli depended on not only free Zn 2+ but also the coexisting cations which could reduce the toxicity of Zn 2+ . Increasing solution pH, HPO 4 2− , and DOM reduced the concentration of free Zn 2+ released from nano-ZnO, and thus lowered the toxicity of nano-ZnO. In addition, both Ca 2+ and Mg 2+ dramatically reduced the toxicity of Zn 2+ to E. coli. These results highlight the importance of water chemistry on the toxicity evaluation of nano-ZnO in natural waters. - Highlights: ► The effects of water chemistry on the toxicity of nano-ZnO were investigated. ► Increasing solution pH, HPO 4 2− , and DOM reduced nano-ZnO toxicity to E. coli. ► Ca 2+ and Mg 2+ could dramatically reduce the toxicity of nano-ZnO to E. coli. ► Free Zn 2+ ions and water hardness together controlled nano-ZnO toxicity in waters. - The toxicity of nano-ZnO to E. coli depended on not only free Zn 2+ but also Ca 2+ and Mg 2+ which could reduce the toxicity of Zn 2+ .

Kinetics of carbonate dissolution in CO2-saturated aqueous system at reservoir conditions

Science.gov (United States)

Peng, Cheng; Crawshaw, John P.; Maitland, Geoffrey; Trusler, J. P. Martin

2014-05-01

results of the study indicate that the rotating disc technique can allow accurate measurement of the carbonate dissolution rate under surface-reaction-controlled conditions, and that the carbonate dissolution rate typically increases with the increase of temperature, CO2 partial pressure and solution acidity. The study shows that the dissolution of carbonate in CO2-free acidic solutions can be described as a first order heterogeneous reaction; however, this model is not sufficient to describe the reaction kinetics of carbonate minerals in the (CO2 + H2O) system, particularly for high reactivity carbonates, such as calcite, at reservoir conditions. For these systems, both pH and the activity of CO2(aq) influence the dissolution rate. Based on the experimental results, kinetic models have been developed and parameterised to describe the dissolution of different carbonate minerals. The results of this study should facilitate more rigorous modelling of mineral dissolution in deep saline aquifers used for CO2 storage. We gratefully acknowledge the funding of QCCSRC provided jointly by Qatar Petroleum, Shell, and the Qatar Science & Technology Park. Keywords: Carbon Dioxide, Carbonate, High Pressure, High Temperature, Reaction Kinetics.

Stress corrosion cracking in 17-4PH and 17-7PH stainless steels in NaCl and NaOH (20%) a 90 deg C

International Nuclear Information System (INIS)

Gaona-Tiburcio, C.; Almeraya-Calderon, F.; Martinez-Villafane, A.

2000-01-01

One of the problems that affects to the electric industry is the not programmed stoppages in the power plants, due to the failure of any main component: boiler, turbine and generator. In the turbine, the combined action of a corrosive agent (humid polluted vapor) and a mechanical effort, generally will result in Stress Corrosion Cracking (SCC). In this work the SCC susceptibility of the precipitation hardening stainless steels 17-4PH and 17-17PH, thoroughly used in steam turbine blades of power stations is analyzed. The specimens were tested in the presence of NaCl and NaOH(20%) to 90 deg C and different pH. The CERT test (Constant Extension Rate Test) was used, at 10''-6 s''-1, supplementing it with electrochemical noise, the aim was to identify the conditions of maximum susceptibility and the performance of the studied materials. The fractographic analysis revealed ductile and brittle fracture. Intergranular cracking, characteristic of the anodic dissolution mechanisms of the materials was observed. Nevertheless, the main mechanism responsible the failure was hydrogen embrittlement. (Author) 6 refs

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

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.

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

Highlights: → In order to perform geological sequestration of CO 2 , serpentinite should be dissolved by acids or by aqueous solutions. → At atmospheric pressure serpentinite is efficaciously dissolved at 70 deg. C using acid attacks. → At higher P-T conditions, significant carbonation occurs at 30 MPa and 300 deg. C using CO 2 saturated aqueous solutions. - Abstract: Dissolution experiments on a serpentinite were performed at 70 deg. C, 0.1 MPa, in H 2 SO 4 solution, in open and closed systems, in order to evaluate the overall dissolution rate of mineral components over different times (4, 9 and 24 h). In addition, the serpentinite powder was reacted with a NaCl-bearing aqueous solution and supercritical CO 2 for 24 h at higher pressures (9-30 MPa) and temperatures (250-300 deg. C) either in a stirred reactor or in an externally-heated pressure vessel to assess both the dissolution rate of serpentinite minerals and the progress of the carbonation reaction. Results show that, at 0.1 MPa, MgO extraction from serpentinite ranges from 82% to 98% and dissolution rate varies from 8.5 x 10 -10 mole m -2 s -1 to 4.2 x 10 -9 mole m -2 s -1 . Attempts to obtain carbonates from the Mg-rich solutions by increasing their pH failed since Mg- and NH 4 - bearing sulfates promptly precipitated. On the other hand, at higher pressures, significant crystallization (5.0-10.4 wt%) of Ca- and Fe-bearing magnesite was accomplished at 30 MPa and 300 deg. C using 100 g L -1 NaCl aqueous solutions. The corresponding amount of CO 2 sequestered by crystallization of carbonates is 9.4-15.9 mole%. Dissolution rate (from 6.3 x 10 -11 mole m -2 s -1 to 1.3 x 10 -10 mole m -2 s -1 ) is lower than that obtained at 0.1 MPa and 70 deg. C but it is related to pH values much higher (3.3-4.4) than that (-0.65) calculated for the H 2 SO 4 solution. Through a thorough review of previous experimental investigations on the dissolution kinetics of serpentine minerals the authors propose adopting: (i

Semisolid matrix-filled hard gelatin capsules for rapid dissolution of amlodipine besilate: Development and assessment

Directory of Open Access Journals (Sweden)

Vijay K Tyagi

2013-01-01

Full Text Available The objective of the study was to prepare semisolid capsules (SSCs of poorly water-soluble drug amlodipine besilate (AB using a combination of technologies involving solid dispersion (SD preparation and converting it into semisolid matrix filled in hard gelatin capsules (termed as SSCs with the aim of reducing lag time in drug release and to improve the dissolution rate. AB is used for its anti-arrhythmic, anti-anginal, and anti-hypertensive activity. These are the emergency activities which should be treated as fast as possible like in the case of angina attack (heart attack. Any lag time that is generated due to its poor dissolution can add on in this emergency and that can be avoided by developing a readily dissolvable formulation: SDs of AB. SD of AB was prepared by fusion method using varying combinations of Poloxamer 407 and Plasdone S630. A total of nine batches (SD1−SD9 were characterized for the in vitro dissolution behavior in phosphate buffer pH7.4. SD8 with 95.8% cumulative drug release in 60 min, t50% = 4.1 min and DE 30 Min = 84.2% were selected for the development of the semisolid matrix. Differential scanning calorimetry of SD8 revealed molecular dispersion of AB and Plasdone S630 in Poloxamer 407. SD8 was then formulated as SSCs using gelucire 44/14 and PEG 400 as semisolid components and PEG 6000 as a suspending agent to achieve the reduction in lag time for drug release. A total of seven SSC formulations were prepared and evaluated for drug release. Formulation of SSC4 showed maximum cumulative drug release (CDR of 98.9% within 20 min that was almost a threefold reduction in the time required to achieve similar CDR by SD of AB. Thus, SSCs present an excellent approach to enhance the dissolution as well as to reduce the lag time of dissolution for poor water-soluble drugs especially to those therapeutic classes that are intended for faster onset of action.

Double-Track Electrochemical Green Approach for Simultaneous Dissolution Profiling of Naproxen Sodium and Diphenhydramine Hydrochloride.

Science.gov (United States)

Shehata, Mostafa A; Fawaz, Esraa M; El-Rahman, Mohamed K Abd; Abdel-Moety, Ezzat M

2017-11-30

Acquisition of the dissolution profiles of more than single active ingredient in a multi-analyte pharmaceutical formulation is a mandatory manufacturing practice that is dominated by utilization of the off-line separation-based chromatographic methods. This contribution adopts a new "Double-Track" approach with the ultimate goal of advancing the in-line potentiometric sensors to their most effective applicability for simultaneous acquisition of the dissolution profiles of two active ingredients in a binary pharmaceutical formulation. The unique abilities of these sensors for real-time measurements is the key driver for adoption of "green analytical chemistry" (GAC) principles aiming to expand the application of eco-friendly analytical methods With the aim of performing a side-by-side comparison, this work investigates the degree of adherence of ISEs to the 12 principles of GAC in multicomponent dissolution profiling with respect to the HPLC. For the proof of concept, a binary mixture of naproxen sodium (NAPR) and diphenhydramine hydrochloride (DIPH) marketed as Aleve pm ® tablets was selected as a model for which dissolution profiles were attained by two techniques. The first "Double-Track" in-line strategy depends on dipping two highly integrated membrane sensors for continuous monitoring of the dissolution of each active pharmaceutical ingredient (API) by tracing the e.m.f change over the time scale. For the determination of NAPR, sensor I was developed using tridodecyl methyl ammonium chloride as an anion exchanger, while sensor II was developed for the determination of DIPH using potassium tetrakis (4-chlorophenyl) borate as a cation exchanger. The second off-line strategy utilizes a separation-based HPLC method via off-line tracking the increase of peak area by UV detection at 220nm over time using a mobile phase of acetonitrile: water (90:10) pH 3. The advantages of the newly introduced "Double-Track" approach regarding GAC principles are highlighted, and

Influence of initial temperature and heating method in the temperature profile during alkaline dissolution of Al for the production of Mo-99

Energy Technology Data Exchange (ETDEWEB)

Camilo, Ruth L.; Araujo, Izilda C.; Mindrisz, Ana C.; Forbicini, Christina A.L.G. de O., E-mail: rcamilo@ipen.br, E-mail: cruzaraujo22@gmail.com, E-mail: acmindri@ipen.br, E-mail: cforbici@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

2013-07-01

Radionuclides in nuclear medicine can be used for diagnosis and therapy. The {sup 99m}Tc, son of {sup 99}Mo, is most often used in nuclear medicine as tracer element because of its favorable nuclear properties, accounting for about 80% of all diagnostic procedures in vivo. Aiming to resolve the dependency of Brazil with respect to the supply of {sup 99}Mo was created the Brazilian Multipurpose Reactor project (BMR), started in 2008, having as main objective to produce about 1000 Ci/week of {sup 99}Mo. This study is part of the project to obtain {sup 9}'9Mo by alkaline dissolution of UAl{sub x}-Al targets. The initial reaction temperature is an important parameter, since it has great influence on the value of the maximum temperature and dissolution time. According to literature, for security reasons the dissolution process must have its temperature controlled so that the maximum temperature has to be around 90 deg C. The behavior of the temperature during dissolution using three different methods of heating in order to minimize the fluctuation of temperature during dissolution, keeping its maximum value at around 90 deg C was studied. The three methods of heating chosen were: a) initial temperature of 85 deg C with continuous heating, b) heating water bath until it reaches the initial temperature (70 to 95 deg C), turning off after that, and c) external heating until it reached the starting temperature (60-95 deg C). The alkaline solution used was 3 mol.L{sup -1} NaOH{sub 3} and 2 mol.L{sup -1} NaNO{sub 3}. In the first study it was observed that after 1 minute of dissolution the solution temperature reached 100 deg C on average, up to a maximum of 109 deg C, ending with values around 95 deg C. In the second study after 3 minutes of dissolution the maximum temperature was 106 deg C and the minimum 100 deg C. In the third study the temperature rise during dissolution increased with increasing initial temperature which practically remains constant until the end

Low Buffer Capacity and Alternating Motility along the Human Gastrointestinal Tract: Implications for in Vivo Dissolution and Absorption of Ionizable Drugs.

Science.gov (United States)

Hens, Bart; Tsume, Yasuhiro; Bermejo, Marival; Paixao, Paulo; Koenigsknecht, Mark J; Baker, Jason R; Hasler, William L; Lionberger, Robert; Fan, Jianghong; Dickens, Joseph; Shedden, Kerby; Wen, Bo; Wysocki, Jeffrey; Loebenberg, Raimar; Lee, Allen; Frances, Ann; Amidon, Greg; Yu, Alex; Benninghoff, Gail; Salehi, Niloufar; Talattof, Arjang; Sun, Duxin; Amidon, Gordon L

2017-12-04

In this study, we determined the pH and buffer capacity of human gastrointestinal (GI) fluids (aspirated from the stomach, duodenum, proximal jejunum, and mid/distal jejunum) as a function of time, from 37 healthy subjects after oral administration of an 800 mg immediate-release tablet of ibuprofen (reference listed drug; RLD) under typical prescribed bioequivalence (BE) study protocol conditions in both fasted and fed states (simulated by ingestion of a liquid meal). Simultaneously, motility was continuously monitored using water-perfused manometry. The time to appearance of phase III contractions (i.e., housekeeper wave) was monitored following administration of the ibuprofen tablet. Our results clearly demonstrated the dynamic change in pH as a function of time and, most significantly, the extremely low buffer capacity along the GI tract. The buffer capacity on average was 2.26 μmol/mL/ΔpH in fasted state (range: 0.26 and 6.32 μmol/mL/ΔpH) and 2.66 μmol/mL/ΔpH in fed state (range: 0.78 and 5.98 μmol/mL/ΔpH) throughout the entire upper GI tract (stomach, duodenum, and proximal and mid/distal jejunum). The implication of this very low buffer capacity of the human GI tract is profound for the oral delivery of both acidic and basic active pharmaceutical ingredients (APIs). An in vivo predictive dissolution method would require not only a bicarbonate buffer but also, more significantly, a low buffer capacity of dissolution media to reflect in vivo dissolution conditions.

Dissolution Model Development: Formulation Effects and Filter Complications

DEFF Research Database (Denmark)

Berthelsen, Ragna; Holm, Rene; Jacobsen, Jette

2016-01-01

This study describes various complications related to sample preparation (filtration) during development of a dissolution method intended to discriminate among different fenofibrate immediate-release formulations. Several dissolution apparatus and sample preparation techniques were tested. The fl....... With the tested drug–formulation combination, the best in vivo–in vitro correlation was found after filtration of the dissolution samples through 0.45-μm hydrophobic PTFE membrane filters....

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)

Dissolution of ibuprofen enantiomers from coprecipitates and suspensions containing chiral excipients.

Science.gov (United States)

Janjikhel, R K; Adeyeye, C M

1999-01-01

The purpose of this research was to evaluate the stereospecific interaction of ibuprofen with chiral excipients such as hydroxypropyl-beta-cyclodextrin (HPCD), tartaric acid, sucrose, hydroxypropylmethylcellulose (HPMC), methylcellulose (MC), and a nonchiral excipient, citric acid. Coprecipitates of ibuprofen were prepared in molar ratios ranging between 1:0.5 and 1:10 by a solvent evaporation method and characterized using x-ray diffraction, Fourier-transform infrared (FTIR) spectroscopy, and dissolution testing. Phase solubility studies of ibuprofen were carried out by adding excess amount of ibuprofen to aqueous excipient solutions of varying concentrations. Interaction was studied in suspensions of ibuprofen with HPMC, MC, and sucrose stored at room temperature and 60 degrees C for 12 weeks. Solubility of ibuprofen in HPCD solutions increased 10-fold, whereas solubility decreased in the tartaric and citric acid solutions, a result of decreased pH with increased amount of the acids in which ibuprofen (pKa 4.8) is less soluble. Phase solubility diagrams of ibuprofen in aqueous HPCD, citric acid, and tartaric acid solutions showed no stereospecific differences in solubility of the two enantiomers. X-ray diffraction studies showed that ibuprofen exists in a crystalline form at low ibuprofen-to-excipient ratios, whereas at the higher ratios, it exists in an amorphous form. FTIR spectroscopy for HPCD coprecipitates showed a shift of the carbonyl stretching band of ibuprofen to a higher wavelength with a markedly decreased intensity, probably because of a breakdown in the intermolecular hydrogen bonding with ibuprofen and restriction of the drug molecule in the HPCD cavity, respectively. Dissolution profiles of the coprecipitates demonstrated higher dissolution rates than those of pure ibuprofen. The presence of chiral excipients did not appear to cause stereoselective release of the drug from the coprecipitates and the suspensions.

Impact of iron chelators on short-term dissolution of basaltic glass

Science.gov (United States)

Perez, Anne; Rossano, Stéphanie; Trcera, Nicolas; Verney-Carron, Aurélie; Huguenot, David; van Hullebusch, Eric D.; Catillon, Gilles; Razafitianamaharavo, Angelina; Guyot, François

2015-08-01

Although microorganisms seem to play an important role in the alteration processes of basaltic glasses in solution, the elementary mechanisms involved remain unclear in particular with regard to the role of organic ligands excreted by the cells. Two glasses, one with Fe and one without Fe were synthesized to model basaltic glass compositions. Fe in the glass was mostly Fe(III) for enhancing interaction with siderophores, yet with small but significant amounts of Fe(II) (between 10% and 30% of iron). The prepared samples were submitted to abiotic alteration experiments in buffered (pH 6.4) diluted solutions of metal-specific ligands, namely oxalic acid (OA, 10 mM), desferrioxamine (DFA, 1 mM) or 2,2‧-bipyridyl (BPI, 1 mM). Element release from the glass into the solution after short term alteration (maximum 1 week) was measured by ICP-OES, and normalized mass losses and relative release ratios (with respect to Si) were evaluated for each element in each experimental condition. The presence of organic ligands had a significant effect on the dissolution of both glasses. Trivalent metals chelators (OA, DFA) impacted on the release of Fe3+ and Al3+, and thus on the global dissolution of both glasses, enhancing all release rates and dissolution stoichiometry (release rates were increased up to 7 times for Al or Fe). As expected, the mostly divalent metal chelator BPI interacted preferentially with Ca2+, Mg2+ and Fe2+. This study thus allows to highlight the central roles of iron and aluminium in interaction with some organic ligands in the alteration processes of basaltic glasses. It thus provides a step toward understanding the biological contribution of this fundamental geological process.

Application of Soluplus to Improve the Flowability and Dissolution of Baicalein Phospholipid Complex

Directory of Open Access Journals (Sweden)

Junting Fan

2017-05-01

Full Text Available In this study, a novel ternary complex system (TCS composed of baicalein, phospholipids, and Soluplus was prepared to improve the flowability and dissolution for baicalein phospholipid complex (BPC. TCS was characterized using differential scanning calorimetry (DSC, infrared spectroscopy (IR, powder X-ray diffraction (PXRD, and scanning electron microscopy (SEM. The flowability, solubility, oil–water partition coefficient, in vitro dissolution, and in vivo pharmacokinetics of the system were also evaluated. DSC, IR, PXRD, and SEM data confirmed that the crystal form of baicalein disappeared in BPC and TCS. Furthermore, the angle of repose of TCS of 35° indicated an improvement in flowability, and solubility increased by approximately eight-fold in distilled water when TCS was compared with BPC (41.00 ± 4.89 μg/mL vs. 5.00 ± 0.16 μg/mL. Approximately 91.24% of TCS was released at the end of 60 min in 0.5% SDS (pH = 6.8, which suggested that TCS could improve the dissolution velocity and extent. Moreover, TCS exhibited a considerable enhancement in bioavailability with higher peak plasma concentration (25.55 μg/mL vs. 6.05 μg/mL and increased AUC0–∞ (62.47 μg·h/mL vs. 50.48 μg·h/mL with 123.75% relative bioavailability compared with BPC. Thus, Soluplus achieved the purpose of improving the flowability and solubility of baicalein phospholipid complexes. The application of Soluplus to phospholipid complexes has great potential.

The impact of changing surface ocean conditions on the dissolution of aerosol iron

Science.gov (United States)

Fishwick, Matthew P.; Sedwick, Peter N.; Lohan, Maeve C.; Worsfold, Paul J.; Buck, Kristen N.; Church, Thomas M.; Ussher, Simon J.

2014-11-01

The proportion of aerosol iron (Fe) that dissolves in seawater varies greatly and is dependent on aerosol composition and the physicochemical conditions of seawater, which may change depending on location or be altered by global environmental change. Aerosol and surface seawater samples were collected in the Sargasso Sea and used to investigate the impact of these changing conditions on aerosol Fe dissolution in seawater. Our data show that seawater temperature, pH, and oxygen concentration, within the range of current and projected future values, had no significant effect on the dissolution of aerosol Fe. However, the source and composition of aerosols had the most significant effect on the aerosol Fe solubility, with the most anthropogenically influenced samples having the highest fractional solubility (up to 3.2%). The impact of ocean warming and acidification on aerosol Fe dissolution is therefore unlikely to be as important as changes in land usage and fossil fuel combustion. Our experimental results also reveal important changes in the size distribution of soluble aerosol Fe in solution, depending on the chemical conditions of seawater. Under typical conditions, the majority (77-100%) of Fe released from aerosols into ambient seawater existed in the colloidal (0.02-0.4 µm) size fraction. However, in the presence of a sufficient concentration of strong Fe-binding organic ligands (10 nM) most of the aerosol-derived colloidal Fe was converted to soluble Fe (<0.02 µm). This finding highlights the potential importance of organic ligands in retaining aerosol Fe in a biologically available form in the surface ocean.

Investigations on the passivity of iron in borate and phosphate buffers, pH 8.4

International Nuclear Information System (INIS)

Sieber, I.V.; Hildebrand, H.; Virtanen, S.; Schmuki, P.

2006-01-01

In the present work surface analytical experiments (XPS and AES) on the passive film on iron formed in borate and phosphate buffers (pH 8.4) have been carried out. In the passive film formed in phosphate buffer a significant amount of phosphates is found in the outer part of the film. Boron species are not significantly incorporated in the passive film formed in borate buffer. The mechanism of the reduction of the passive film depends strongly on the electrolyte composition. In borate buffer, cathodic polarization leads to reductive dissolution of the passive film whereas in phosphate buffer the passive film is converted into metallic iron without dissolution but via laterally inhomogeneously formation of an intermediate Fe(II) phosphate layer

Etching of semiconductor cubic crystals: Determination of the dissolution slowness surfaces

Science.gov (United States)

Tellier, C. R.

1990-03-01

Equations of the representative surface of dissolution slowness for cubic crystals are determined in the framework of a tensorial approach of the orientation-dependent etching process. The independent dissolution constants are deduced from symmetry considerations. Using previous data on the chemical etching of germanium and gallium arsenide crystals, some possible polar diagrams of the dissolution slowness are proposed. A numerical and graphical simulation method is used to obtain the derived dissolution shapes. The influence of extrema in the dissolution slowness on the successive dissolution shapes is also examined. A graphical construction of limiting shapes of etched crystals appears possible using the tensorial representation of the dissolution slowness.

Dissolution studies on Nickel ferrite in dilute chemical decontamination formulations

Energy Technology Data Exchange (ETDEWEB)

Ranganathan, S. [New Brunswick Univ., Fredericton, NB (Canada). Dept. of Chemical Engineering; Srinivasan, M.P. [Bhabha Atomic Research Centre (BARC) (India). Water and Steam Chemistry Laboratory; Raghavan, P.S. [Madras Christian College, Chennai (India); Narasimhan, S.V. [Bhabha Atomic Research Centre, Bombay (India); Gopalan, R. [Madras Christian College, Chennai (India). Department of Chemistry

2004-09-01

Nickel ferrite is one of the important corrosion products in the pipeline surfaces of water-cooled nuclear reactors. The dissolution of the nickel ferrite by chelating agents is very sensitive to the nature of the chelant, the nature of the reductant used in the formulation and the temperature at which the dissolution studies are performed. The dissolution is mainly controlled by the reductive dissolution of the ferrite particles, but complexing agents also play a significant role in the dissolution process. This study deals with the leaching of iron and nickel from nickel ferrite prepared by the solid-state method. The dissolution studies are performed in pyridine-2,6-dicarboxylic acid (PDCA), nitrilotriacetic acid (NTA), and ethylenediaminetetraacetic acid (EDTA) formulations containing organic reductants like ascorbic acid and low oxidation state transition metal ion reductants like Fe(II)-L (where L = PDCA, NTA, EDTA) at 85 C. The dissolution of nickel ferrite in PDCA, NTA and EDTA formulations is influenced by the presence of reductants in the formulations. The addition of Fe(II)-L in the formulation greatly enhances the dissolution of nickel ferrite. The preferential leaching of nickel over iron during the dissolution of nickel ferrite was observed in all the formulations. (orig.)

Dissolution studies on Nickel ferrite in dilute chemical decontamination formulations

International Nuclear Information System (INIS)

Ranganathan, S.; Narasimhan, S.V.; Gopalan, R.

2004-01-01

Nickel ferrite is one of the important corrosion products in the pipeline surfaces of water-cooled nuclear reactors. The dissolution of the nickel ferrite by chelating agents is very sensitive to the nature of the chelant, the nature of the reductant used in the formulation and the temperature at which the dissolution studies are performed. The dissolution is mainly controlled by the reductive dissolution of the ferrite particles, but complexing agents also play a significant role in the dissolution process. This study deals with the leaching of iron and nickel from nickel ferrite prepared by the solid-state method. The dissolution studies are performed in pyridine-2,6-dicarboxylic acid (PDCA), nitrilotriacetic acid (NTA), and ethylenediaminetetraacetic acid (EDTA) formulations containing organic reductants like ascorbic acid and low oxidation state transition metal ion reductants like Fe(II)-L (where L = PDCA, NTA, EDTA) at 85 C. The dissolution of nickel ferrite in PDCA, NTA and EDTA formulations is influenced by the presence of reductants in the formulations. The addition of Fe(II)-L in the formulation greatly enhances the dissolution of nickel ferrite. The preferential leaching of nickel over iron during the dissolution of nickel ferrite was observed in all the formulations. (orig.)

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.

Performance of denitrifying microbial fuel cell subjected to variation in pH, COD concentration and external resistance.

Science.gov (United States)

Li, Jin-Tao; Zhang, Shao-Hui; Hua, Yu-Mei

2013-01-01

The effects of pH, chemical oxygen demand (COD) concentration and external resistance on denitrifying microbial fuel cell were evaluated in terms of electricity generation characteristics and pollutant removal performance. The results showed that anodic influent with weakly alkaline or neutral pH and cathodic influent with weakly acidic pH favored pollutant removal and electricity generation. The suitable influent pH of the anode and cathode were found to be 7.5-8.0 and 6.0-6.5, respectively. In the presence of sufficient nitrate in the cathode, higher influent COD concentration led to more electricity generation and greater pollutant removal rates. With an anodic influent pH of 8.0 and a cathodic influent pH of 6.0, an influent COD concentration of 400 mg/L was deemed to be appropriate. Low external resistance favored nitrate and COD removal. The results suggest that operation of denitrifying microbial fuel cell at a lower external resistance would be desirable for pollutant removal but not electricity generation.

Criticality safety in high explosives dissolution

International Nuclear Information System (INIS)

Troyer, S.D.

1997-01-01

In 1992, an incident occurred at the Pantex Plant in which the cladding around a fissile material component (pit) cracked during dismantlement of the high explosives portion of a nuclear weapon. Although the event did not result in any significant contamination or personnel exposures, concerns about the incident led to the conclusion that the current dismantlement process was unacceptable. Options considered for redesign, dissolution tooling design considerations, dissolution tooling design features, and the analysis of the new dissolution tooling are summarized. The final tooling design developed incorporated a number of safety features and provides a simple, self-contained, low-maintenance method of high explosives removal for nuclear explosive dismantlement. Analyses demonstrate that the tooling design will remain subcritical under normal, abnormal, and credible accident scenarios. 1 fig

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

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…

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...

Meios para dissolução de comprimidos de nimesulida: ação dos tensoativos Media for nimesulide tablet dissolution: surfactant action

Directory of Open Access Journals (Sweden)

Regina Lengruber da Silva

2002-06-01

Full Text Available A nimesulida é um antiinflamatório não-esteróide com baixa solubilidade em água e caráter fracamente ácido. O desenvolvimento dos ensaios de dissolução para fármacos de baixa hidrossolubilidade pode ser problemático e tensoativos são freqüentemente requeridos para aumentar a solubilização dos mesmos. No presente trabalho avaliou-se o efeito dos tensoativos lauril sulfato de sódio e polissorbato 80, na promoção da solubilidade da nimesulida em meio aquoso, determinando-se também o pH, a tensão superficial e a concentração micelar crítica dos meios testados. A nimesulida apresentou baixa solubilidade nos meios sem tensoativos (300 mg/mL foram observadas em tampão fosfato pH 7,4 com polissorbato 80. A concentração de saturação do fármaco aumentou proporcionalmente com a concentração dos tensoativos, os quais atuam pelo mecanismo de solubilização micelar. Obtiveram-se perfis de dissolução de três formulações de comprimidos de nimesulida, em meios com diversas concentrações de tensoativo, empregando-se o aparelho de dissolução com agitador de pá. Os resultados mostraram que a escolha do meio de dissolução para nimesulida deve ser criteriosa, de modo a evitar condições de baixo poder discriminante das formulações.Nimesulide is a non-steroidal anti-inflammatory drug, which presents low water-solubility and weak-acid properties. The intrinsic solubility of a drug plays an important role on drug dissolution from a solid dosage form. The development of a dissolution test for poorly hydrophilic drugs can exhibit some difficulties and surfactants are often used to promote drug solubilization. In this work the influences of both sodium laurylsulfate and polysorbate 80 on promotion of nimesulide aqueous solubility were studied. The media were also evaluated regarding their pH, surface tension and critical micelle concentration. All media without surfactant gave very low nimesulide solubility (300 mg/mL were got

α-MnO2 nanowires transformed from precursor δ-MnO2 by refluxing under ambient pressure: The key role of pH and growth mechanism

International Nuclear Information System (INIS)

Zhang Qin; Xiao Zhidong; Feng Xionghan; Tan Wenfeng; Qiu Guohong; Liu Fan

2011-01-01

α-MnO 2 nanowires were obtained by reflux treatment of precursor δ-MnO 2 in acidic medium under ambient pressure. The great effects of pH on the transformation of δ-MnO 2 to α-MnO 2 and the concentration of coexistent cations (K + , Mn 2+ ) was investigated in systematically designed experiments by using powder X-ray diffraction and atomic absorption spectrometry analysis. The specific surface area of the products could be simply controlled by adjusting the initial pH value of the suspension. The micro-morphologies during the transition process from the precursors to final products were characterized by SEM and TEM. A dissolution-recrystallization mechanism was proposed to describe the growth process of the one-dimensional nanowire. MnO x units or MnO 6 octahedra was formed firstly from the dissolution of outmost surfaces of δ-MnO 2 , followed by a rearrangement/crystallization to form one-dimensional α-MnO 2 nanowire. In addition, the time-dependent process of dissolution would take place gradually from the external to internal of the precursor.

Dissolution mechanisms of CO2 hydrate droplets in deep seawaters

International Nuclear Information System (INIS)

Gabitto, Jorge; Tsouris, Costas

2006-01-01

Carbon dioxide dissolution at intermediate ocean depths was studied using physical and mass transfer models. Particle density and hydrate layer thickness were determined using existing field data. Pseudo-homogeneous and heterogeneous mass transfer models were proposed to study the dissolution process. Pseudo-homogeneous models do not seem to represent the dissolution process well. Although heterogeneous models interpret the physical behavior better, unresolved issues related to hydrate dissolution still remain. For example, solid hydrate forms on one side of the hydrate film while it dissolves on the other. Dissolution is a complex process that comprises at least two sequential steps. The global process is controlled by mass transfer inside the hydrate layer or by a dissolution reaction at the hydrate-water interface

Hydro-chemo-mechanical coupling in sediments: Localized mineral dissolution

KAUST Repository

Cha, Minsu; Santamarina, Carlos

2016-01-01

Mineral dissolution is inherently a chemo-hydro-mechanical coupled process. Field evidence and laboratory results show that dissolution may localize and form open conduits in cohesive media such as carbonate rocks. This study focuses on the evolution of localized dissolution in soils (i.e., frictional and non-cohesive granular materials) under effective confining stresses. Experimental results show the development of localized dissolution (“pipe”) when a carbonate-quartz sand is subjected to reactive fluid flow: only loosely packed quartz grains remain within pipes, and the number of pipes decreases away from the inlet port. Concurrent shear wave velocity measurements show a decrease in stiffness during dissolution due to stress and fabric changes, and more complex signal codas anticipate the development of internal heterogeneity. The discrete element method is used to simulate localized vertical dissolution features in granular materials, under constant vertical stress and zero lateral strain far-field boundaries. As porosity increases along dissolution pipes, vertical load is transferred to the surrounding soils and marked force chains develop. In terms of equivalent stress, principal stress rotation takes place within pipes and the sediment reaches the Coulomb failure condition inside pipes and in the surrounding medium. Dissolution pipes alter the geo-plumbing of the subsurface, enhance fluid transport but limit the long term performance of storage systems, alter the fluid pressure and effective stress fields, soften the sediment and may trigger shear failures.

Hydro-chemo-mechanical coupling in sediments: Localized mineral dissolution

KAUST Repository

Cha, Minsu

2016-06-11

Mineral dissolution is inherently a chemo-hydro-mechanical coupled process. Field evidence and laboratory results show that dissolution may localize and form open conduits in cohesive media such as carbonate rocks. This study focuses on the evolution of localized dissolution in soils (i.e., frictional and non-cohesive granular materials) under effective confining stresses. Experimental results show the development of localized dissolution (“pipe”) when a carbonate-quartz sand is subjected to reactive fluid flow: only loosely packed quartz grains remain within pipes, and the number of pipes decreases away from the inlet port. Concurrent shear wave velocity measurements show a decrease in stiffness during dissolution due to stress and fabric changes, and more complex signal codas anticipate the development of internal heterogeneity. The discrete element method is used to simulate localized vertical dissolution features in granular materials, under constant vertical stress and zero lateral strain far-field boundaries. As porosity increases along dissolution pipes, vertical load is transferred to the surrounding soils and marked force chains develop. In terms of equivalent stress, principal stress rotation takes place within pipes and the sediment reaches the Coulomb failure condition inside pipes and in the surrounding medium. Dissolution pipes alter the geo-plumbing of the subsurface, enhance fluid transport but limit the long term performance of storage systems, alter the fluid pressure and effective stress fields, soften the sediment and may trigger shear failures.

Simulated nutrient dissolution of Asian aerosols in various atmospheric waters: Potential links to marine primary productivity

Science.gov (United States)

Wang, Lingyan; Bi, Yanfeng; Zhang, Guosen; Liu, Sumei; Zhang, Jing; Xu, Zhaomeng; Ren, Jingling; Zhang, Guiling

2017-09-01

To probe the bioavailability and environmental mobility of aerosol nutrient elements (N, P, Si) in atmospheric water (rainwater, cloud and fog droplets), ten total suspended particulate (TSP) samples were collected at Fulong Mountain, Qingdao from prevailing air mass trajectory sources during four seasons. Then, a high time-resolution leaching experiment with simulated non-acidic atmospheric water (non-AAW, Milli-Q water, pH 5.5) and subsequently acidic atmospheric water (AAW, hydrochloric acid solution, pH 2) was performed. We found that regardless of the season or source, a monotonous decreasing pattern was observed in the dissolution of N, P and Si compounds in aerosols reacted with non-AAW, and the accumulated dissolved curves of P and Si fit a first-order kinetic model. No additional NO3- + NO2- dissolved out, while a small amount of NH4+ in Asian dust (AD) samples was released in AAW. The similar dissolution behaviour of P and Si from non-AAW to AAW can be explained by the Transition State Theory. The sources of aerosols related to various minerals were the natural reasons that affected the amounts of bioavailable phosphorus and silicon in aerosols (i.e., solubility), which can be explained by the dissolution rate constant of P and Si in non-AAW with lower values in mineral aerosols. The acid/particle ratio and particle/liquid ratio also have a large effect on the solubility of P and Si, which was implied by Pearson correlation analysis. Acid processing of aerosols may have great significance for marine areas with limited P and Si and post-acidification release increases of 1.1-10-fold for phosphorus and 1.2-29-fold for silicon. The decreasing mole ratio of P and Si in AAW indicates the possibility of shifting from a Si-limit to a P-limit in aerosols in the ocean, which promotes the growth of diatoms prior to other algal species.

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...

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

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.

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

Effect of iron II on hydroxyapatite dissolution and precipitation in vitro.

Science.gov (United States)

Delbem, A C B; Alves, K M R P; Sassaki, K T; Moraes, J C S

2012-01-01

The aim of this study was to evaluate the effect of iron II on the dissolution and precipitation of synthetic hydroxyapatite (HA). HA powder was suspended in solutions of iron (0.84 µg/ml, Fe0.84; 18.0 µg/ml, Fe18; 70.0 µg/ml, Fe70), fluoride (1,100 µg/ml, F1,100), and deionized water and submitted to pH cycling. After pH cycling, the samples were analyzed by infrared spectroscopy and X-ray diffraction. The concentrations of fluoride, calcium, phosphorus, and iron were also analyzed. The data were submitted to ANOVA, and analyzed by Tukey's test (p iron. The intensity of the phosphate bands increased and that of the hydroxyl bands decreased in the group F1,100. It was observed that there was a higher concentration of Ca in the group F1,100, with no significant difference between the groups Fe18 and Fe70 (p > 0.05). There was an increase in Fe concentration in the HA directly related to the Fe concentration of the treatment solutions. Results show that the presence of Fe causes the precipitation of apatite with high solubility. Copyright © 2012 S. Karger AG, Basel.

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.

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

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.

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.

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....

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

pH-Dependent Toxicity of High Aspect Ratio ZnO Nanowires in Macrophages Due to Intracellular Dissolution

KAUST Repository

H. Müller, Karin

2010-11-23

High-aspect ratio ZnO nanowires have become one of the most promising products in the nanosciences within the past few years with a multitude of applications at the interface of optics and electronics. The interaction of zinc with cells and organisms is complex, with both deficiency and excess causing severe effects. The emerging significance of zinc for many cellular processes makes it imperative to investigate the biological safety of ZnO nanowires in order to guarantee their safe economic exploitation. In this study, ZnO nanowires were found to be toxic to human monocyte macrophages (HMMs) at similar concentrations as ZnCl2. Confocal microscopy on live cells confirmed a rise in intracellular Zn2+ concentrations prior to cell death. In vitro, ZnO nanowires dissolved very rapidly in a simulated body fluid of lysosomal pH, whereas they were comparatively stable at extracellular pH. Bright-field transmission electron microscopy (TEM) showed a rapid macrophage uptake of ZnO nanowire aggregates by phagocytosis. Nanowire dissolution occurred within membrane-bound compartments, triggered by the acidic pH of the lysosomes. ZnO nanowire dissolution was confirmed by scanning electron microscopy/energy-dispersive X-ray spectrometry. Deposition of electron-dense material throughout the ZnO nanowire structures observed by TEM could indicate adsorption of cellular components onto the wires or localized zinc-induced protein precipitation. Our study demonstrates that ZnO nanowire toxicity in HMMs is due to pH-triggered, intracellular release of ionic Zn2+ rather than the high-aspect nature of the wires. Cell death had features of necrosis as well as apoptosis, with mitochondria displaying severe structural changes. The implications of these findings for the application of ZnO nanowires are discussed. © 2010 American Chemical Society.

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 ...

Dissolution behavior of PFBR MOX fuel in nitric acid

International Nuclear Information System (INIS)

Kelkar, Anoop; Kapoor, Y.S.; Singh, Mamta; Meena, D.L.; Pandey, Ashish; Bhatt, R.B.; Behere, P.G.

2017-01-01

Present paper describes the dissolution characteristics of PFBR MOX fuel (U,Pu)O 2 in nitric acid. An overview of batch dissolution experiments, studying the percentage dissolution of uranium and plutonium in (U, Pu)O 2 MOX sintered pellets with different percentage of PuO 2 with reference to time and nitric acid concentration are described. 90% of uranium and plutonium of PFBR MOX gets dissolves in 2 hrs and amount of residue increases with the decrease in nitric acid concentration. Overall variation in percentage residue in PFBR MOX fuel after dissolution test also described. (author)

Do Workplace Sex Ratios Affect Partnership Formation and Dissolution?

DEFF Research Database (Denmark)

Svarer, Michael

In this paper, I analyse 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 ......In this paper, I analyse 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...

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

Highlights: > In order to perform geological sequestration of CO{sub 2}, serpentinite should be dissolved by acids or by aqueous solutions. > At atmospheric pressure serpentinite is efficaciously dissolved at 70 deg. C using acid attacks. > At higher P-T conditions, significant carbonation occurs at 30 MPa and 300 deg. C using CO{sub 2} saturated aqueous solutions. - Abstract: Dissolution experiments on a serpentinite were performed at 70 deg. C, 0.1 MPa, in H{sub 2}SO{sub 4} solution, in open and closed systems, in order to evaluate the overall dissolution rate of mineral components over different times (4, 9 and 24 h). In addition, the serpentinite powder was reacted with a NaCl-bearing aqueous solution and supercritical CO{sub 2} for 24 h at higher pressures (9-30 MPa) and temperatures (250-300 deg. C) either in a stirred reactor or in an externally-heated pressure vessel to assess both the dissolution rate of serpentinite minerals and the progress of the carbonation reaction. Results show that, at 0.1 MPa, MgO extraction from serpentinite ranges from 82% to 98% and dissolution rate varies from 8.5 x 10{sup -10} mole m{sup -2} s{sup -1} to 4.2 x 10{sup -9} mole m{sup -2} s{sup -1}. Attempts to obtain carbonates from the Mg-rich solutions by increasing their pH failed since Mg- and NH{sub 4}- bearing sulfates promptly precipitated. On the other hand, at higher pressures, significant crystallization (5.0-10.4 wt%) of Ca- and Fe-bearing magnesite was accomplished at 30 MPa and 300 deg. C using 100 g L{sup -1} NaCl aqueous solutions. The corresponding amount of CO{sub 2} sequestered by crystallization of carbonates is 9.4-15.9 mole%. Dissolution rate (from 6.3 x 10{sup -11} mole m{sup -2} s{sup -1} to 1.3 x 10{sup -10} mole m{sup -2} s{sup -1}) is lower than that obtained at 0.1 MPa and 70 deg. C but it is related to pH values much higher (3.3-4.4) than that (-0.65) calculated for the H{sub 2}SO{sub 4} solution. Through a thorough review of previous experimental

The complexity of nanoparticle dissolution and its importance in nanotoxicological studies

International Nuclear Information System (INIS)

Misra, Superb K.; Dybowska, Agnieszka; Berhanu, Deborah; Luoma, Samuel N.; Valsami-Jones, Eugenia

2012-01-01

Dissolution of nanoparticles (NPs) is an important property that alters their abundance and is often a critical step in determining safety of nanoparticles. The dissolution status of the NPs in exposure media (i.e. whether they remain in particulate form or dissolve — and to what extent), strongly affects the uptake pathway, toxicity mechanisms and the environmental compartment in which NPs will have the highest potential impact. A review of available dissolution data on NPs demonstrates there is a range of potential outcomes depending on the NPs and the exposure media. For example two nominally identical nanoparticles, in terms of size and composition, could have totally different dissolution behaviours, subject to different surface modifications. Therefore, it is imperative that toxicological studies are conducted in conjunction with dissolution of NPs to establish the true biological effect of NPs and hence, assist in their regulation. -- Graphical abstract: Various physicochemical factors affecting dissolution of nanoparticles. Highlights: ► In this study we discuss dissolution of nanoparticles. ► Physicochemical properties of nanoparticles influence dissolution. ► Measuring dissolution of nanoparticles can help to understand their biological response.

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

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.

Dissolution of cellulose in ionic liquid: A review

Science.gov (United States)

Mohd, N.; Draman, S. F. S.; Salleh, M. S. N.; Yusof, N. B.

2017-02-01

Dissolution of cellulose with ionic liquids (IL) and deep eutectic solvent (DES) lets the comprehensive dissolution of cellulose. Basically, cellulose can be dissolved, in some hydrophilic ionic liquids, such as 1-butyl-3-methylimidazolium chloride (BMIMCl) and 1-allyl-3-methylimidazolium chloride (AMIMCl). Chloride based ionic liquids are suitable solvents for cellulose dissolution. Although the ILs is very useful in fine chemical industry, its application in the pharmaceutical and food industry have been very limited due to issues with toxicity, purity, and high cost. Seeing to these limitations, new green alternative solvent which is DES was used. This green solvents, may be definitely treated as the next-generation reagents for more sustainable industrial development. Thus, this review aims to discuss the dissolution of cellulose either with ionic liquids or DES and its application.

The anodic dissolution of zinc and zinc alloys in alkaline solution. II. Al and Zn partial dissolution from 5% Al–Zn coatings

International Nuclear Information System (INIS)

Vu, T.N.; Mokaddem, M.; Volovitch, P.; Ogle, K.

2012-01-01

Graphical abstract: - Abstract: The polarization behavior of a 5 wt% Al–Zn steel coating (Galfan™) has been investigated in alkaline solution using atomic emission spectroelectrochemistry (AESEC). The instantaneous Zn and Al dissolution rates were measured as a function of time during a linear scan and potential step transients. The formation rate of insoluble oxides was determined from the difference between the convoluted total current and the sum of the elemental dissolution currents. It was found that, over a wide potential range, the zinc and aluminum partial currents behaved in a similar way to pure zinc and pure aluminum independently. However, during the period in which zinc was active, aluminum dissolution was inhibited. This is attributed to the inhibitive effect of the first and/or the second states of zinc oxide that are formed during the active potential domain. The third form of zinc oxide, observed at higher potential and responsible for the passivation of zinc dissolution, does not have a measurable effect on the Al dissolution rate.

Dilution physics modeling: Dissolution/precipitation chemistry

International Nuclear Information System (INIS)

Onishi, Y.; Reid, H.C.; Trent, D.S.

1995-09-01

This report documents progress made to date on integrating dilution/precipitation chemistry and new physical models into the TEMPEST thermal-hydraulics computer code. Implementation of dissolution/precipitation chemistry models is necessary for predicting nonhomogeneous, time-dependent, physical/chemical behavior of tank wastes with and without a variety of possible engineered remediation and mitigation activities. Such behavior includes chemical reactions, gas retention, solids resuspension, solids dissolution and generation, solids settling/rising, and convective motion of physical and chemical species. Thus this model development is important from the standpoint of predicting the consequences of various engineered activities, such as mitigation by dilution, retrieval, or pretreatment, that can affect safe operations. The integration of a dissolution/precipitation chemistry module allows the various phase species concentrations to enter into the physical calculations that affect the TEMPEST hydrodynamic flow calculations. The yield strength model of non-Newtonian sludge correlates yield to a power function of solids concentration. Likewise, shear stress is concentration-dependent, and the dissolution/precipitation chemistry calculations develop the species concentration evolution that produces fluid flow resistance changes. Dilution of waste with pure water, molar concentrations of sodium hydroxide, and other chemical streams can be analyzed for the reactive species changes and hydrodynamic flow characteristics

Determination of the dissolution slowness surface by study of etched shapes I. Morphology of the dissolution slowness surface and theoretical etched shapes

Science.gov (United States)

Leblois, T.; Tellier, C. R.

1992-07-01

We propose a theoretical model for the anisotropic etching of crystals, in order to be applied in the micromachining. The originality of the model is due to the introduction of dissolution tensors to express the representative surface of the dissolution slowness. The knowledge of the equation of the slowness surface allows us to determine the trajectories of all the elements which compose the starting surface. It is then possible to construct the final etched shape by numerical simulation. Several examples are given in this paper which show that the final etched shapes are correlated to the extrema of the dissolution slowness. Since the slowness surface must be determined from experiments, emphasis is placed on difficulties encountered when we correlate theory to experiments. Nous avons modélisé le processus de dissolution anisotrope des cristaux en vue d'une application à la simulation des formes obtenues par photolithogravure chimique. La principale originalité de ce modèle tient à l'introduction de tenseurs de dissolution pour exprimer la surface représentative de la lenteur de dissolution. La connaissance de l'équation de la lenteur de dissolution permet de calculer les trajectoires des différents éléments constituant la surface de départ puis de reconstituer par simulation la forme dissoute. Les simulations démontrent que les formes limites des cristaux dissous sont corrélées aux extrema de la lenteur de dissolution. La détermination de la surface de la lenteur se faisant à partir de mesures expérimetales, nous nous sommes efforcés de montrer toutes les difficultés attachées à cette analyse.

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.

Magnetic resonance imaging of tablet dissolution.

Science.gov (United States)

Nott, Kevin P

2010-01-01

Magnetic resonance imaging (MRI) is the technique of choice for measuring hydration, and its effects, during dissolution of tablets since it non-invasively maps (1)H nuclei associated with 'mobile' water. Although most studies have used MRI systems with high-field superconducting magnets, low-field laboratory-based instruments based on permanent magnet technology are being developed that provide key data for the formulation scientist. Incorporation of dissolution hardware, in particular the United States Pharmacopeia (USP) apparatus 4 flow-through cell, allows measurements under controlled conditions for comparison against other dissolution methods. Furthermore, simultaneous image acquisition and measurement of drug concentration allow direct comparison of the drug release throughout the hydration process. The combination of low-field MRI with USP-4 apparatus provides another tool to aid tablet formulation. Copyright 2009 Elsevier B.V. All rights reserved.

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

Effect of dissolution on the load–settlement behavior of shallow foundations

KAUST Repository

Cha, Minsu

2016-03-10

Mineral dissolution and solid-liquid phase change may cause settlement or affect the bearing capacity of shallow foundations. The effect of gradual grain dissolution on small-scale shallow foundation behavior is investigated using the discrete element method. Results show that dissolution is most detrimental during early stages, as initially contacting particles shrink and force chains must reform throughout the medium. Porosity tends to increase during dissolution and force chains evolve into strong localized forces with a honeycomb topology. Higher settlements are required to mobilize bearing resistance in postdissolution sediments than in pre-dissolution ones. Subsurface mineral dissolution beneath a footing under load is the worst condition; in fact, settlements in such cases are higher than when a foundation load is applied on a sediment that has already experienced dissolution. © the author(s) or their institution(s).

Effect of dissolution on the load–settlement behavior of shallow foundations

KAUST Repository

Cha, Minsu; Santamarina, Carlos

2016-01-01

Mineral dissolution and solid-liquid phase change may cause settlement or affect the bearing capacity of shallow foundations. The effect of gradual grain dissolution on small-scale shallow foundation behavior is investigated using the discrete element method. Results show that dissolution is most detrimental during early stages, as initially contacting particles shrink and force chains must reform throughout the medium. Porosity tends to increase during dissolution and force chains evolve into strong localized forces with a honeycomb topology. Higher settlements are required to mobilize bearing resistance in postdissolution sediments than in pre-dissolution ones. Subsurface mineral dissolution beneath a footing under load is the worst condition; in fact, settlements in such cases are higher than when a foundation load is applied on a sediment that has already experienced dissolution. © the author(s) or their institution(s).

The effect of sodium chloride on the dissolution of calcium silicate hydrate gels

International Nuclear Information System (INIS)

Hill, J.; Harris, A.W.; Manning, M.; Chambers, A.; Swanton, S.W.

2006-01-01

The use of cement based materials will be widespread in the long-term management of radioactive materials in the United Kingdom. One of the applications could be the Nirex reference vault backfill (NRVB) as an engineered barrier within a deep geological repository. NRVB confers alkaline conditions, which would provide a robust chemical barrier through the control of the solubility of some key radionuclides, enhanced sorption and minimised corrosion of steel containers. An understanding of the dissolution of C-S-H gels in cement under the appropriate conditions (e.g., saline groundwaters) is necessary to demonstrate the expected evolution of the chemistry over time and to provide sufficient cement to buffer the porewater conditions for the required time. A programme of experimental work has been undertaken to investigate C-S-H gel dissolution behaviour in sodium chloride solutions and the effect of calcium/silicon ratio (C/S), temperature and cation type on this behaviour. Reductions in calcium concentration and pH values were observed with samples equilibrated at 45 deg. C compared to those prepared at 25 deg. C. The effect of salt cation type on salt-concentration dependence of the dissolution of C-S-H gels was investigated by the addition of lithium or potassium chloride in place of sodium chloride for gels with a C/S of 1.0 and 1.8. With a C/S of 1.0, similar increases in dissolved calcium concentration with increasing ionic strength were recorded for the different salts. However, at a C/S of 1.8, anomalously high calcium concentrations were observed in the presence of lithium

Use of carbon paste electrodes for the voltammetric detection of silver leached from the oxidative dissolution of silver nanoparticles

Science.gov (United States)

Mullaugh, Katherine M.; Pearce, Olivia M.

2017-04-01

The widespread use of silver nanoparticles (Ag NPs) in consumer goods has raised concerns about the release of silver in environmental waters. Of particular concern is the oxidative dissolution of Ag NPs to release Ag+ ions, which are highly toxic to many aquatic organisms. Here, we have investigated the application of differential pulse stripping voltammetry (DPSV) with carbon paste electrodes (CPEs) in monitoring the oxidation of Ag NPs. Using a commercially available, unmodified carbon paste and 60-s deposition times, a detection limit of 3 nM Ag+ could be achieved. We demonstrate its selectivity for free Ag+ ions over Ag nanoparticles, allowing for analysis of the oxidation of Ag NPs without the need for separation of ions and nanoparticles prior to analysis. We applied this approach to investigate the effect of pH in the oxidative dissolution of Ag NPs, demonstrating the usefulness of CPEs in studies of this type.

Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS): A rapid test for enteric coating thickness and integrity of controlled release pellet formulations.

Science.gov (United States)

Alfarsi, Anas; Dillon, Amy; McSweeney, Seán; Krüse, Jacob; Griffin, Brendan; Devine, Ken; Sherry, Patricia; Henken, Stephan; Fitzpatrick, Stephen; Fitzpatrick, Dara

2018-04-12

There are no rapid dissolution based tests for determining coating thickness, integrity and drug concentration in controlled release pellets either during production or post-production. The manufacture of pellets requires several coating steps depending on the formulation. The sub-coating and enteric coating steps typically take up to six hours each followed by additional drying steps. Post production regulatory dissolution testing also takes up to six hours to determine if the batch can be released for commercial sale. The thickness of the enteric coating is a key factor that determines the release rate of the drug in the gastro-intestinal tract. Also, the amount of drug per unit mass decreases with increasing thickness of the enteric coating. In this study, the coating process is tracked from start to finish on an hourly basis by taking samples of pellets during production and testing those using BARDS (Broadband Acoustic Resonance Dissolution Spectroscopy). BARDS offers a rapid approach to characterising enteric coatings with measurements based on reproducible changes in the compressibility of a solvent due to the evolution of air during dissolution. This is monitored acoustically via associated changes in the frequency of induced acoustic resonances. A steady state acoustic lag time is associated with the disintegration of the enteric coatings in basic solution. This lag time is pH dependent and is indicative of the rate at which the coating layer dissolves. BARDS represents a possible future surrogate test for conventional USP dissolution testing as its data correlates directly with the thickness of the enteric coating, its integrity and also with the drug loading as validated by HPLC. Copyright © 2018 Elsevier B.V. All rights reserved.

Investigation of the gas formation in dissolution process of nuclear reactor fuel

International Nuclear Information System (INIS)

Zhang Qinfen; Liao Yuanzhong; Chen Yongqing; Sun Shuyun; Fan Yincheng

1987-12-01

The gas formation in dissolution process of two kinds of nuclear fuels was studied. The results shows that the maximum volume flow released from dissolution system is composed of two parts. One of them is air remained in dissolver and pushed out by acid vapor. The other is produced in dissolution reaction. The procedure of calculating the gas amount produced in dissolution process has been given. It is based on variation of components of dissolution solution. The gas amount produced in dissolution process of spent UO 2 fuel elements was calculated. The condenser system and loading volume of disposal system of tail gas of dissolution of spent fuel were discussed

Ph3CCOOSnPh3.Ph3PO AND Ph3CCOOSnPh3.Ph3AsO: SYNTHESIS AND INFRARED STUDY

Directory of Open Access Journals (Sweden)

ABDOU MBAYE

2014-08-01

Full Text Available The mixture of ethanolic solutions of Ph3CCOOSnPh3 and Ph3PO or Ph3AsO gives Ph3CCOOSnPh3.Ph3PO and Ph3CCOOSnPh3.Ph3AsO adducts which have been characterized by infrared spectroscopy. A discrete structure is suggested for both, the environment around the tin centre being trigonal bipyramidal, the triphenylacetate anion behaving as a mondentate ligand.

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)