WorldWideScience

Sample records for b4c oxidation modelling

  1. Oxidation of B4C by steam at high temperatures: New experiments and modelling

    International Nuclear Information System (INIS)

    The oxidation kinetics of various types of boron carbides (pellets, powder) were investigated in the temperature range between 1073 and 1873 K. Oxidation rates were measured in transient and isothermal tests by means of mass spectrometric gas analysis. It was found that oxidation is strongly influenced by the thermohydraulic boundary conditions and in particular by the steam partial pressure and flow rate. On the other hand, the microstructure of the B4C samples has a limited influence on oxidation. Very low amounts of methane were produced in these tests. On the basis of the experimental data obtained in the isothermal tests, a new model on boron carbide oxidation was developed. The model self-consistently simulates surface reaction kinetics and mass transport of various species in the multi-component gas phase as rate determining steps of the oxidation process. The model was implemented in the SVECHA/QUENCH code and verified against the transient tests

  2. Heat release from B4C oxidation in steam and air

    International Nuclear Information System (INIS)

    BWR and some PWR cores contain boron carbide (B4C) as neutron absorber. During a severe accident, the B4C can potentially react with steam under release of heat and hydrogen. Although models for B4C oxidation already exist in MELCOR and SCDAP/RELAP5, a development of a new model for another computer code seems to be difficult due to a missing comprehensive description of the current modelling methodology and scarce experimental data. The aim of this paper is to highlight the key points of the B4C oxidation using the existing available experimental data and to perform a simple heat balance analysis of the B4C/steam and B4C/air chemical reactions. The analysis of literature data shows that the B4C oxidation phenomenon is qualitatively well described below 1000 deg. C. However, no reliable data exist for the reaction kinetics especially above this temperature. It was found that the experimental results strongly depend on the experimental arrangement. The reaction heats, calculated in this study, indicate that the B4C oxidation is an exothermic reaction, releasing more heat in air than in steam. The formation of boric acids from the boron oxide increases the heat release from B4C by ∼ 10%, in the worst case. Although the total heat, released in a PWR core from the B4C oxidation, is probably much smaller than the heat released from the Zr/steam reaction, it is not excluded that the B4C oxidation can locally contribute to the damage of the control elements due to local overheating. Modelling of these phenomena is, however, very difficult due to the complex geometry of the liquefied control elements and due to absence of suitable data on the reaction kinetics. (author). 25 refs, 2 figs, 3 tabs

  3. Surface quality improvement of B4C particles for electroless copper coating by Cu activation and oxidation roughening methods

    International Nuclear Information System (INIS)

    Highlights: • Cu activation increases surface activity by depositing Cu nano-crystals on B4C. • The best result of Cu activation comes out at pH 12. • Oxidation roughening improves wettability of B4C by aqueous solution. • Oxidation roughening promotes Cu nucleation on B4C surface. - Abstract: Surface quality improvement by Cu activation and oxidation roughening process was studied during electroless coating Cu on boron carbide (B4C) particles. The surface morphology was characterized by scanning electron microscope (SEM) and the phase identification was determined by X-ray diffraction (XRD) analysis. Two aspects concluding surface activation and surface roughening were investigated to understand the effect of each on Cu coating. Cu activation process increased surface activity of B4C by pre-deposition Cu nano-crystals, which was effective and cost-saving when compared with conventional Pd activation method. The influence of activation pH on electroless Cu coating was discussed and a moderate pH 12 is suitable for Cu deposition. Surface roughening process availably promoted wettability of B4C particles with aqueous solution. Etched pits were formed on B4C surface and resulted in fresh surface exposed after oxidization roughening process, which was beneficial for Cu bonding and coating on B4C surface

  4. Model of deformation and fracture of TiB2+B4C based cermet under dynamic loading

    International Nuclear Information System (INIS)

    One introduces a mathematical model describing deformation and fracture of titanium diboride and boron carbide base (TiB2+B4C) cermet with a metal binder under impact loading. TiB2+B4C base cermet with a metal binder was prepared by means of self-propagating high-temperature synthesis. In terms of the mentioned model one solved the problem dealing with penetration of TiB2+B4C base cermet into aluminium semi-infinite barrier

  5. Validierung und Verbesserung des Programmsystems ATHLET-CD hinsichtlich der B4C-Oxidation in Dampfatmosphäre

    OpenAIRE

    Drath, Tilman

    2007-01-01

    In Leichtwasserreaktoren kann es während eines postulierten Kühlmittelverluststörfalls bei gleichzeitigem Ausfall aller Sicherheitssysteme zum Ausdampfen des Primärsystems und damit zur Kernaufheizung und -zerstörung kommen. Dabei stellen exotherme Oxidationsvorgänge in Dampf ein wesentliches Phänomen dar, da sie die Aufheizung zusätzlich beschleunigen und zum H2-Quellterm beitragen. Im Gegensatz zur Oxidation des Hüllrohrwerkstoffs Zirkon werden bei der Oxidation des Absorbermate...

  6. Chemical modification of B4C cap layers on Pd/B4C multilayers

    Science.gov (United States)

    Supruangnet, Ratchadaporn; Morawe, Christian; Peffen, Jean-Christophe; Nakajima, Hideki; Rattanasuporn, Surachet; Photongkam, Pat; Jearanaikoon, Nichada; Busayaporn, Wutthikri

    2016-03-01

    Chemical modifications of B4C cap layers on sputtered Pd/B4C multilayer coatings for X-ray optical applications were investigated using X-ray reflectivity, photoemission electron spectroscopy, photoemission electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and infrared spectroscopy. The results indicate oxidation down to probing depths of about 10 nm and strong evidence for the formation of B2O3 crystals at the sample surface, while B4C like compounds are absent.

  7. Sintering of boron carbide (B4C)

    International Nuclear Information System (INIS)

    Boron carbide (B4C) is used as a control element in different types of reactors due to the high fast and thermal neutron absorption cross-section of B-10. Requirements of the Advanced Reactor Division of the Bariloche Atomic Center triggered the study of the possibilities of fabricating B4C pellets by cold-pressing and sintering. The results of essays of sinterability of two different commercial boron carbide powders, sintered at temperatures between 1200 and 2200 deg C, are given. Characterizations of the samples were made to determine the evolution of density, porosity, microstructure and boron content as a function of sintering temperature. (Author)

  8. Experimental investigation on mechanical behaviour, modelling and optimization of wear parameters of B4C and graphite reinforced aluminium hybrid composites

    International Nuclear Information System (INIS)

    Highlights: • Aluminium alloy reinforced with boron carbide and graphite through liquid casting. • The high hardness and elongation obtained in the AA 7075 hybrid composite. • SEM, EDS observations were used to evaluate the worn surface. • MINITAB software was used to analyse the wear rate and develop the map. - Abstract: Aluminium alloy (AA) 6061 and 7075 were reinforced with 10 wt.% of boron carbide (B4C) and 5 wt.% of graphite through liquid casting technique. The Scanning Electron Microscope (SEM) and Energy Dispersive Spectrum (EDS) were used for the characterization of composites. The wear experiment was carried out by using a pin-on-disc apparatus with various input parameters like applied load (10, 20, and 30 N), sliding speed (0.6, 0.8, and 1.0 m/s) and sliding distance (1000, 1500, and 2000 m). Response Surface Methodology (RSM) using MINITAB 14 software was used to analyse the wear rate of hybrid composites and aluminium alloys. The worn surfaces of hybrid composites and base alloys were studied through SEM and EDS systems and some useful conclusions were made

  9. Pressure effect on structural, elastic, and thermodynamic properties of tetragonal B4C4

    International Nuclear Information System (INIS)

    The compressibility, elastic anisotropy, and thermodynamic properties of the recently proposed tetragonal B4C4 (t-B4C4) are investigated under high temperature and high pressure by using of first-principles calculations method. The elastic constants, bulk modulus, shear modulus, Young’s modulus, Vickers hardness, Pugh’s modulus ratio, and Poisson’s ratio for t-B4C4 under various pressures are systematically explored, the obtained results indicate that t-B4C4 is a stiffer material. The elastic anisotropies of t-B4C4 are discussed in detail under pressure from 0 GPa to 100 GPa. The thermodynamic properties of t-B4C4, such as Debye temperature, heat capacity, and thermal expansion coefficient are investigated by the quasi-harmonic Debye model

  10. Pressure effect on structural, elastic, and thermodynamic properties of tetragonal B4C4

    Directory of Open Access Journals (Sweden)

    Baobing Zheng

    2015-03-01

    Full Text Available The compressibility, elastic anisotropy, and thermodynamic properties of the recently proposed tetragonal B4C4 (t-B4C4 are investigated under high temperature and high pressure by using of first-principles calculations method. The elastic constants, bulk modulus, shear modulus, Young’s modulus, Vickers hardness, Pugh’s modulus ratio, and Poisson’s ratio for t-B4C4 under various pressures are systematically explored, the obtained results indicate that t-B4C4 is a stiffer material. The elastic anisotropies of t-B4C4 are discussed in detail under pressure from 0 GPa to 100 GPa. The thermodynamic properties of t-B4C4, such as Debye temperature, heat capacity, and thermal expansion coefficient are investigated by the quasi-harmonic Debye model.

  11. B4C thin films for neutron detection

    OpenAIRE

    Höglund, Carina; Birch, Jens; Andersen, Ken; Bigault, Thierry; Buffet, Jean-Claude; Correa, Jonathan; Van Esch, Patrick; Guerard, Bruno; Hall-Wilton, Richard; Jensen, Jens; Khaplanov, Anton; Piscitelli, Francesco; Vettier, Christian; Vollenberg, Wilhelmus; Hultman, Lars

    2012-01-01

    Due to the very limited availability of He-3, new kinds of neutron detectors, not based on 3He, are urgently needed. Here, we present a method to produce thin films of (B4C)-B-10, with maximized detection efficiency, intended to be part of a new generation of large area neutron detectors. B4C thin Films have been deposited onto Al-blade and Si wafer substrates by dc magnetron sputtering from (B4C)-B-nat and (B4C)-B-10 targets in an Ar discharge, using an industrial deposition system. The film...

  12. Retention of deuterium implanted into B4C-overlaid isotropic graphites and hot-pressed B4C

    International Nuclear Information System (INIS)

    Retention characteristics of two kinds of B4C-overlaid graphites and hot-pressed B4C were investigated. An ion beam of 3 keV D2+ was implanted into the specimens at room temperature. The amount of retained deuteriums was measured as function of the implantation fluence and temperature by elastic recoil detection analysis. Thermal release behavior of implanted deuteriums was also measured by isochronal annealing. The concentration of retained deuterium reaches saturation similarly in three kinds of B4C-overlaid specimens at the fluences over 1018 D+/cm2 as in isotropic graphite. The release temperature, at which the number of retained deuterium decreases to one half in isochronal annealing are about 250 K lower for three kinds of B4C specimens than for graphite. The release temperature of deuterium from unsaturated hot-pressed B4C isochronal annealing is about 500 K higher than that from saturated one. (orig.)

  13. Boron carbide (B4C) coating. Deposition and testing

    International Nuclear Information System (INIS)

    Boron carbide was proposed as a material of in-situ protecting coating for tungsten tiles of ITER divertor. To prove this concept the project including investigation of regimes of plasma deposition of B4C coating on tungsten and tests of boron carbide layer in ITER-like is started recently. The paper contends the first results of the project. The results of B4C coating irradiation by the plasma pulses of QSPU-T plasma accelerator are presented. The new device capable of B4C film deposition on tungsten and testing of the films and materials with ITER-like heat loads and ion- and electron irradiation is described. The results of B4C coating deposition and testing of both tungsten substrate and coating are shown and discussed

  14. Boron carbide (B4C) coating. Deposition and testing

    Science.gov (United States)

    Azizov, E.; Barsuk, V.; Begrambekov, L.; Buzhinsky, O.; Evsin, A.; Gordeev, A.; Grunin, A.; Klimov, N.; Kurnaev, V.; Mazul, I.; Otroshchenko, V.; Putric, A.; Sadovskiy, Ya.; Shigin, P.; Vergazov, S.; Zakharov, A.

    2015-08-01

    Boron carbide was proposed as a material of in-situ protecting coating for tungsten tiles of ITER divertor. To prove this concept the project including investigation of regimes of plasma deposition of B4C coating on tungsten and tests of boron carbide layer in ITER-like is started recently. The paper contends the first results of the project. The results of B4C coating irradiation by the plasma pulses of QSPU-T plasma accelerator are presented. The new device capable of B4C film deposition on tungsten and testing of the films and materials with ITER-like heat loads and ion- and electron irradiation is described. The results of B4C coating deposition and testing of both tungsten substrate and coating are shown and discussed.

  15. Interfacial reaction mechanism between matrix and reinforcement in B4C/6061Al composites

    International Nuclear Information System (INIS)

    The interfacial reaction mechanism in B4C/6061Al composites, fabricated by the powder metallurgy technique at 560 and 620 °C with various holding times, was subjected to detailed investigations using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and hardness tests. Results showed that complicated interfacial reactions occurred in the B4C/6061Al composites, forming Al3BC, MgAl2O4, MgB7, Mg0.78Al0.75B14, AlB12C2 and Al4SiC4 as the main products, which clearly deteriorated the age-hardening ability of the composites. The interfacial reactions involving Mg and Si could be divided into two series. The oxidation of Mg occurred at both 560 and 620 °C, whereas other reactions only occurred at 620 °C. The existence of the liquid phase at 620 °C activated the reaction between Al and B4C, leading to the generation of free B, and subsequent reactions involving B and Mg occurred. After the reactions involving B and Mg was completed, the reaction involving Al, Si and C took place. It was determined that the reactions involving B and Mg rather than the oxidation of Mg or the reaction involving Si were the main reasons for the consumption of Mg and the deterioration of age-hardening ability of the B4C/6061Al composites at 620 °C. - Highlights: • Complicated interfacial reactions occurred in B4C/6061Al composites. • Reactions involving Mg and Si were divided into oxidation of Mg and other reactions. • Al/B4C reaction produced free B and then activated B/Mg reactions. • B/Mg reactions rather than Mg oxidation were main reasons for Mg consumption. • Interfacial reactions definitely deteriorate age-hardening ability of composites

  16. Hot pressing of B4C/SiC composites

    International Nuclear Information System (INIS)

    B4C/SiC ceramic composites containing 10-20-30 vol % SiC were prepared by hot pressing method. The effect of SiC addition and hot pressing temperature on sintering behaviour and mechanical properties of hot pressed composites were investigated. Microstructures of hot pressed samples were examined by SEM technique. Three different temperatures (2100 deg. C, 2200 deg. C and 2250 deg. C) were used to optimize hot pressing temperature applying 100 MPa pressure under argon atmosphere during the sintering procedure. The highest relative density of 98.44 % was obtained by hot pressing at 2250 deg. C. However, bending strengths of B4C/SiC composite samples were lower than monolithic B4C in all experimental conditions. (authors)

  17. B4C thin films for neutron detection

    International Nuclear Information System (INIS)

    Due to the very limited availability of 3He, new kinds of neutron detectors, not based on 3He, are urgently needed. Here, we present a method to produce thin films of 10B4C, with maximized detection efficiency, intended to be part of a new generation of large area neutron detectors. B4C thin films have been deposited onto Al-blade and Si wafer substrates by dc magnetron sputtering from natB4C and 10B4C targets in an Ar discharge, using an industrial deposition system. The films were characterized with scanning electron microscopy, elastic recoil detection analysis, x-ray reflectivity, and neutron radiography. We show that the film-substrate adhesion and film purity are improved by increased substrate temperature and deposition rate. A deposition rate of 3.8 A/s and substrate temperature of 400 deg. C result in films with a density close to bulk values and good adhesion to film thickness above 3 μm. Boron-10 contents of almost 80 at. % are obtained in 6.3 m2 of 1 μm thick 10B4C thin films coated on Al-blades. Initial neutron absorption measurements agree with Monte Carlo simulations and show that the layer thickness, number of layers, neutron wavelength, and amount of impurities are determining factors. The study also shows the importance of having uniform layer thicknesses over large areas, which for a full-scale detector could be in total ∼1000 m2 of two-side coated Al-blades with ∼1 μm thick 10B4C films.

  18. Directional crystallization of B4C-NbB2 and B4C-MoB2 eutectic compositions

    International Nuclear Information System (INIS)

    We studied the directional crystallization of different compositions in B4C-NbB2 and B4C-MoB2 systems. The eutectic compositions for both systems are evaluated. It is shown that in the first system the rod-like eutectic structure is formed, in second, the 'Chinese hieroglyphics'. In both cases high hardness and high microplasticity are observed, which are much more than for individual component phases. These compositions may be considered as a new kind of self-strengthening composite materials

  19. Reaction behavior between B4C, 304 grade of stainless steel and Zircaloy at 1473 K

    Science.gov (United States)

    Sasaki, Ryosuke; Ueda, Shigeru; Kim, Sun-Joong; Gao, Xu; Kitamura, Shin-ya

    2016-08-01

    For a better understanding of the decommissioning of the Fukushima-daiichi nuclear power plant, the melting behavior of the control blade and the channel box should be clarified. In Fukushima nuclear reactor, the channel box was made of Zircaloy-4, and the control rode is made of B4C together with stainless steel cladding and sheath. In the study, the interaction among B4C, stainless steel (SUS), and Zircaloy-4 was investigated at 1473 K in either argon or air atmosphere. In argon, Zircaloy is melted by the diffusion of elements from SUS, and SUS was melted at 1473 K by the diffusion of C and B. In air, SUS reacted with B2O3 and formed an oxides melt firstly. Then, the oxidized Zircaloy contacted with this melt and fused. Moreover, the progress of core melting process during severe accident under different atmospheres was firstly discussed.

  20. Gaseous swelling of B4C and UO2 fuel: similarities and differences

    International Nuclear Information System (INIS)

    A major factor limiting the resource of control rods (CRs) for WWER-1000 reactors is their radiation damage. Radiation induced embrittlement of the CRs cladding, core swelling and gaseous internal pressure in CRs result in mechanical core-cladding interaction. This work is devoted to the physical analysis of processes that control the structural changes in neutron absorber elements with B4C under irradiation in water reactors. Particularly, the analysis of mechanisms of the helium porosity formation in B4C is undertaken. In view of the deficiency of experimental data on the subject, a fruitful approach to the problem is a comparative analysis of the swelling mechanisms in B4C absorber and UO2 fuel. Using this similarity a phenomenological model of fission gas behavior in boron carbide is proposed. The model predictions for radial profile of 10B burnup under influence of thermal and epithermal neutrons are compared with experimental results. The main results show that despite the external similarity of the process of fission gas accumulation in UO2 and in B4C, phenomenology of gaseous swelling is much different for the fuel and the CR core. The reason for that difference is the distinction of physical conditions in irradiated fuel and CR core

  1. Microstructure and mechanical properties of pulsed electric current sintered B4C-TiB2 composites

    International Nuclear Information System (INIS)

    Research highlights: → Fast densification of B4C-TiB2 particulate composites. → Oxide impurity removal by evaporation. → Judiciously controlled loading cycle during pulsed electric current sintering. → High strength micrometer sized B4C-TiB2 composites. - Abstract: Monolithic B4C, TiB2 and B4C-TiB2 particulate composites were consolidated without sintering additives by means of pulsed electric current sintering in vacuum. Sintering studies on B4C-TiB2 composites were carried out to reveal the influence of the pressure loading cycle during pulsed electrical current sintering (PECS) on the removal of oxide impurities, i.e. boron oxide and titanium oxide, hereby influencing the densification behavior as well as microstructure evolvement. The critical temperature to evaporate the boron oxide impurities was determined to be 2000 deg. C. Fully dense B4C-TiB2 composites were achieved by PECS for 4 min at 2000 deg. C when applying the maximum external pressure of 60 MPa after volatilization of the oxide impurities, whereas a relative density of 95-97% was obtained when applying the external pressure below 2000 deg. C. Microstructural analysis showed that B4C and TiB2 grain growth was substantially suppressed due to the pinning effect of the secondary phase and the rapid sintering cycle, resulting in micrometer sized and homogeneous microstructures. Excellent properties were obtained for the 60 vol% TiB2 composite, combining a Vickers hardness of 29 GPa, a fracture toughness of 4.5 MPa m1/2 and a flexural strength of 867 MPa, as well as electrical conductivity of 3.39E+6 S/m.

  2. Characteristics of electrodeposited RE-Ni-W-B-B4C-MoS2 composite coating

    Institute of Scientific and Technical Information of China (English)

    马克毅; 郭忠诚; 朱晓云; 徐瑞东

    2003-01-01

    The high temperature oxidation resistance of RE-Ni-W-B-B4C-MoS2 composite coating, the effects of electrodeposition conditions on the morphologies of the coating and the effect of heat treatment temperature on its hardness, abrasion resistance and phase structure were investigated by using scanning electron microscope(SEM), X-ray diffractometer, microhardness tester and abrasion machine. The results show that the oxidation degree of RE-Ni-W-B-B4C-MoS2 composite coating is small when the temperature is lower than 700 ℃, but it increases sharply when the temperature is higher than 700 ℃. The hardness of RE-Ni-W-B-B4C-MoS2 composite coating increases with increasing heat treatment temperature, it comes up to the maximum value at 400 ℃,but it decreases gradually if the temperature rises continuously. The most favourable abrasion resistance was attained after RE-Ni-W-B-B4C-MoS2 composite coating being heat treated at 400 ℃. Without heat treating, it is mainly amorphous and partially crystallized, but wholly crystallized after being heat treated at 500 ℃. RE in the composite coating is in the form of CeO2 and additions of CeO2 and B4C can enhance the thermostability of RE-Ni-W-B-B4C-MoS2 composite coating.

  3. Separation of B4C powder by air classification

    International Nuclear Information System (INIS)

    Large quantities of bulk powder can be separated according to particle size and density by air classifiers. Classifiers disperse the powder and usually achieve size differentiation by drag and centrifugal forces acting on individual particles in the gas stream. A Donaldson ''acucut'' Classifier for the separation of B4C powder is evaluated. Experimental tests were conducted to determine the particle cut sizes and powder yields obtained by variation of operating parameters. To assess the classifier's performance further results of the sharpness of the powder cuts were evaluated and compared with the vendor's prediction. 7 figures, 3 tables

  4. CODEX-B4C experiment. Core degradation test with boron carbide control rod

    International Nuclear Information System (INIS)

    The CODEX-B4C bundle test has been successfully performed on 25th May 2001 in the framework of the COLOSS project of the EU 5th FWP. The high temperature degradation of a VVER-1000 type bundle with B4C control rod was investigated with electrically heated fuel rods. The experiment was carried out according to a scenario selected in favour of methane formation. Degradation of control rod and fuel bundle took place at temperatures ∼2000 deg C, cooling down of the bundle was performed in steam atmosphere. The gas composition measurement indicated no methane production during the experiment. High release of aerosols was detected in the high temperature oxidation phase. The on-line measured data are collected into a database and are available for code validation and development. (author)

  5. Chemical State Mapping of Degraded B4C Control Rod Investigated with Soft X-ray Emission Spectrometer in Electron Probe Micro-analysis

    Science.gov (United States)

    Kasada, R.; Ha, Y.; Higuchi, T.; Sakamoto, K.

    2016-05-01

    B4C is widely used as control rods in light water reactors, such as the Fukushima Daiichi nuclear power plant, because it shows excellent neutron absorption and has a high melting point. However, B4C can melt at lower temperatures owing to eutectic interactions with stainless steel and can even evaporate by reacting with high-temperature steam under severe accident conditions. To reduce the risk of recriticality, a precise understanding of the location and chemical state of B in the melt core is necessary. Here we show that a novel soft X-ray emission spectrometer in electron probe microanalysis can help to obtain a chemical state map of B in a modeled control rod after a high-temperature steam oxidation test.

  6. Chemical State Mapping of Degraded B4C Control Rod Investigated with Soft X-ray Emission Spectrometer in Electron Probe Micro-analysis.

    Science.gov (United States)

    Kasada, R; Ha, Y; Higuchi, T; Sakamoto, K

    2016-01-01

    B4C is widely used as control rods in light water reactors, such as the Fukushima Daiichi nuclear power plant, because it shows excellent neutron absorption and has a high melting point. However, B4C can melt at lower temperatures owing to eutectic interactions with stainless steel and can even evaporate by reacting with high-temperature steam under severe accident conditions. To reduce the risk of recriticality, a precise understanding of the location and chemical state of B in the melt core is necessary. Here we show that a novel soft X-ray emission spectrometer in electron probe microanalysis can help to obtain a chemical state map of B in a modeled control rod after a high-temperature steam oxidation test. PMID:27161666

  7. Cr/B4C multilayer mirrors: Study of interfaces and X-ray reflectance

    Science.gov (United States)

    Burcklen, C.; Soufli, R.; Dennetiere, D.; Polack, F.; Capitanio, B.; Gullikson, E.; Meltchakov, E.; Thomasset, M.; Jérome, A.; de Rossi, S.; Delmotte, F.

    2016-03-01

    We present an experimental study of the effect of layer interfaces on the x-ray reflectance in Cr/B4C multilayer interference coatings with layer thicknesses ranging from 0.7 nm to 5.4 nm. The multilayers were deposited by magnetron sputtering and by ion beam sputtering. Grazing incidence x-ray reflectometry, soft x-ray reflectometry, and transmission electron microscopy reveal asymmetric multilayer structures with a larger B4C-on-Cr interface, which we modeled with a 1-1.5 nm thick interfacial layer. Reflectance measurements in the vicinity of the Cr L2,3 absorption edge demonstrate fine structure that is not predicted by simulations using the currently tabulated refractive index (optical constants) values for Cr.

  8. Stress evolution in B4C and Cr mono-layer and B4C/Cr multilayer films with variable layer thickness for neutron detectors

    International Nuclear Information System (INIS)

    A serial of Cr-, B4C-monolayer and B4C/Cr multilayer films with variable layer thickness were deposited on BK-7 glass substrates using magnetron sputtering to study the stress evolution by detecting the changes of the substrate curvature with the optical interferometry technique. The stress of Cr-monolayer is tensile and decreases as its thickness increases, while the stress of B4C-monolayer is compressive and almost independent on its thickness. The residual stresses of B4C/Cr multilayer films are dependent not only on the stresses of B4C and Cr layers, but also on the interface stress between two neighboring layers. If the B4C layer thickness is kept constant, the stresses of B4C/Cr multilayer films change from compressive to tensile with the increasing of Cr layer thickness. Based on the theoretical analysis, the interface stress is mostly affected by the thickness of B4C layer and nearly negligible on the thickness of Cr layer. When the thicknesses of B4C and Cr layers are both 60 nm, the multilayer has very low residual stress, even with the period up to 17. - Highlights: ► The low residual stress of thick B4C film is achieved by inserting the Cr layers. ► The residual stresses of B4C/Cr multilayer films depend on their interface stress. ► The interface stress is dependent on the B4C layer thickness in multilayer. ► The interface stress is independent on the Cr layer thickness in multilayer

  9. Effect of the Ti/B4C mole ratio on the reaction products and reaction mechanism in an Al–Ti–B4C powder mixture

    International Nuclear Information System (INIS)

    The effect of the Ti/B4C mole ratio on the fabrication behavior of Al composites is investigated using Al–Ti–B4C powder mixtures as reactants. The quick spontaneous infiltration (QSI) process combined with the combustion reaction and DTA analysis were used. According to the thermodynamic predictions, which are verified in the experimental results, TiB2 is formed in all the samples whereas TiC is only formed in reactants with a Ti/B4C mole ratio of more than two. The C atoms from the reacted B4C do not move into TiC but instead they move into Al3BC or Al4C3 when the Ti/B4C mole ratio is less than two. In addition, the reaction mechanism with a Ti/B4C mole ratio of 0.75 is investigated extensively. - Highlights: • The critical role of the Ti/B4C mole ratio on the reaction products of Al–Ti–B4C was studied using experiments. • The experimental results are also supported by thermodynamic calculations presented in this paper. • The reaction mechanism with a Ti/B4C mole ratio of 0.75 is investigated extensively

  10. Fabrication and evaluation of B4C/Cu FGM as plasma facing materials

    International Nuclear Information System (INIS)

    B4C is a promising candidate for using as plasma-facing material in fusion devices. In this paper, both B4C/Cu coating FGM (Functionally graded material) and B4C/Cu bulk FGM containing a spectrum of 0-100% compositional distributions of B4C were fabricated by atmosphere plasma spray and ultra-high pressure consolidation respectively. The microstructure of B4C/Cu FGM showed good graded composition distribution. Water quenching and high heat loading experiments using an electron beam were carried out to evaluate the high heat load resistance of B4C/Cu FGMs. The in situ plasma irradiation in a Tokamak facility showed that the B4C/Cu bulk FGM has higher physical sputtering performance than that of B4C/Cu coating FGM. (orig.)

  11. Grazing incidence Fe-line telescopes using W/B4C multilayers

    DEFF Research Database (Denmark)

    Joensen, Karsten D.; Gorenstein, Paul; Christensen, Finn Erland; Gutman, George

    1994-01-01

    Traditional high-Z coated X-ray telescopes for the >= 1 keV range all have a loss of throughput with higher energies, owing to the inverse proportionality between the critical angle and energy. We have shown that this can, to some degree, be countered by employing multilayers on the outermost...... reflectors. A W/B4C multilayer has been fabricated and its 8 keV X-ray reflectivity measured and modeled, yielding an interface-roughness of 3.6 angstroms. This measurement and the resulting model-fit form the basis for computing the performance of `AXAF-S'-sized conical and Kirkpatrick-Baez telescopes...

  12. Comparison of nanostructured Al/B4C composite produced by ARB and Al/B4C composite produced by RRB process

    International Nuclear Information System (INIS)

    Research highlights: → The SEM microstructures revealed the well distributed B4C particles in the aluminum matrix for both the composites. → The TEM analysis showed the nanostructured Al/B4C composite was produced by the ARB process successfully. → The ductility (elongation) of the RRB processed composite is higher than that of the ARB processed composite. → The microhardness of the ARB processed composite is higher than that of the RRB processed composite. - Abstract: In the present study, Al/B4C composites were produced and compared in the form of sheets, through accumulative roll bonding (ARB) and repeated roll bonding (RRB) processes. The microstructure of the composites fabricated by both the methods, revealed by scanning electron microscopy (SEM), showed the B4C particles properly distributed in the aluminum matrix. The average grain size of the ARB processed composite was about 186 nm by linear intercept method, based on transmission electron microscopy (TEM) observations. Mechanical properties of the Al/B4C composites produced by two methods were investigated by tensile and hardness tests. The results showed that the tensile strength and hardness of the ARB and RRB processed composites increase with the number of cycles. However, the tensile strength and hardness of the ARB processed composite are much higher than those of the RRB processed composite. The tensile test results revealed that the elongation of the ARB processed composite is lower than that of the RRB processed composite.

  13. Effect of sintering temperature on structure of C-B4C-SiC composites with silicon additive

    International Nuclear Information System (INIS)

    Carbon materials possess good electric conductivity, heat conductivity, corrosion-resistance, self-lubrication and hot-shocking resistance, and are easily machined. However, they have low mechanical strength, and are easily oxidized in air at high temperature. On the contrary, ceramic materials have high mechanical strength and hardness, and have good wear-resistance and oxidation-resistance. However, they have the shortages of poor thermal-shock resistance lubrication, and are difficult to machine. Therefore, carbon/ceramic composites with the advantages of both carbon and ceramic materials have been widely studied in the recent years. Huang prepared C-B4C-SiC composites with the free sintering method and the hot pressing method, and studied the effects of Si, Al, Al2O3, Ni and Ti additives on the properties of the composites. The results showed that these additives could improve the properties of the composites. Zhao et al. studies the structure of C-B4C-SiC composites with Si additive sintered at 2,000 C and found two c-center monoclinic phases. In this paper, the authors discussed the effect of the sintering temperature on the structure of C-B4C-SiC composites with Si additive by means of transmission electron microscope (TEM) and x-ray diffractometer (XRD)

  14. Al/ B4C Composites with 5 and 10 wt% Reinforcement Content Prepared by Powder Metallurgy

    International Nuclear Information System (INIS)

    The preparation, physical and mechanical properties of Al/ B4C composites with 5 and 10 wt.% reinforcement content were investigated. In order to obtain the feedstock with a low powder loading, B4C mixtures containing fine powders were investigated to obtain the optimal particle packing. The experimental results indicated that the fine containing 5 and 10 wt.% particles are able to prepare the feedstock with a good flowability. The composites fabricated by powder metallurgy have low densities and homogeneous microstructures. Additionally there is no interface reaction observed between the reinforcement and matrix by XRD analysis. The hardness of Al/ B4C composites prepared by powder metallurgy was high. (Author)

  15. Sintering of B4C powder obtained by a modified carbo-thermal reaction

    International Nuclear Information System (INIS)

    Boron carbide is one of the hardest materials and a highly refractory material that is of great interest for structural, electronic and nuclear applications. B4C is commercially manufactured by the carbo-thermal reduction of a mixture of boron oxide (B2O3) in an batch electric arc furnace process. However the carbo-thermal reaction on the stoichiometric starting composition results an excess carbon residue because of the boron loss in the form of B2O2. Thus, a modified carbo-thermal reaction is applied with an excess B2O3 to compensate the loss and to obtain stoichiometric powders. The aim of this work is to study the sinterability of this powder with the lower carbon residue acting as sintering additive. Pressureless sintering in the temperatures of 1900 deg. C/30 min and 2100 deg. C/30 min in argon atmosphere were applied. The synthesized powders were analysed by XRD and SEM. Density of 94% of theoretical density was achieved for sample prepared with the powder obtained with 50% B2O3 excess synthesized at 1700 deg. C/15 min. (authors)

  16. Study of influence content of TiB2 by reaction in situ B4C and TiC in mechanical properties on B4C ceramics

    International Nuclear Information System (INIS)

    The low density of ceramic materials promoted a change in research lines in the defense field. Research efforts and development directed to obtaining products of high density sintered of Al2O3, SiC and B4C, using different routes, both traditional as innovative, led to promising initial results, which justify the convergence of skills for the consolidation of research lines and the nationalization that sintered components of B4C with characteristics and properties compatible with the technical requirements established for the ballistic application. The low density of boron carbide (2.52 g/cm3) gives in the final product a weight approximately 30% lower than armor made of alumina (3.96 g/cm3). (author)

  17. Enhancement of thermal neutron attenuation of nano-B4C, -BN dispersed neutron shielding polymer nanocomposites

    International Nuclear Information System (INIS)

    Highlights: • Preparation of B4C and BN nanopowders using a simple ball milling process. • Homogeneous dispersion and strong adhesion of nano-B4C and -BN with polymer matrix. • Enhancement of mechanical properties of the nanocomposites compared to their micro counterparts. • Enhancement of thermal neutron attenuation of the nanocomposites. - Abstract: Nano-sized boron carbide (B4C) and boron nitride (BN) powder were prepared using ball milling. Micro- and milled nano-powders were melt blended with high density polyethylene (HDPE) using a polymer mixer followed by hot pressing to fabricate sheet composites. The tensile and flexural strengths of HDPE nanocomposites were ∼20% higher than their micro counterparts, while those for latter decreased compared to neat HDPE. Thermal neutrons attenuation of the prepared HDPE nanocomposites was evaluated using a monochromatic ∼0.025 eV neutron beam. Thermal neutron attenuation of the HDPE nanocomposites was greatly enhanced compared to their micro counterparts at the same B-10 areal densities. Monte Carlo n-Particles (MCNP) simulations based on the lattice structure modeling also shows the similar filler size dependent thermal neutron absorption

  18. Interlayer growth in Mo/B4C multilayered structures upon thermal annealing

    International Nuclear Information System (INIS)

    Both multilayer period thickness expansion and compaction were observed in Mo/B4C multilayers upon annealing, and the physical causes for this were explored in detail. Using in situ time-dependent grazing incidence X-ray reflectometry, period changes down to picometer-scale were resolved. It was shown that the changes depend on the thickness of the B4C layers, annealing temperature, and annealing time. Although strong stress relaxation during annealing was observed, it was excluded as a cause for period expansion. Auger electron spectroscopy and wide angle X-ray diffraction measurements revealed the growth of interlayers, with associated period changes influenced by the supply of B and C atoms to the growing compound interlayers. For multilayers with a Mo thickness of 3 nm, two regimes were recognized, depending on the deposited B4C thickness: in multilayers with B4C ≤ 1.5 nm, the supply of additional Mo into the already formed MoBxCy interlayer was dominant and led to densification, resulting in period compaction. For multilayers with B4C ≥ 2 nm, the B and C enrichment of interlayers formed low density compounds and yielded period expansion.

  19. Wetting of B4C, TiC and graphite substrates by molten Mg

    International Nuclear Information System (INIS)

    Highlights: → The wettability of TiC, B4C and C by molten Mg was determined using an improved sessile drop method. → A new method to evaluate the wetting behavior coupled with evaporation and reaction was proposed. → The bonding characteristics in the Mg/B4C, Mg/TiC and Mg/graphite systems were evaluated. - Abstract: The isotherm wetting of B4C, TiC and graphite substrates by molten Mg was studied in a flowing Ar atmosphere at 973-1173 K using an improved sessile drop method. The initial contact angles are in the ranges of 95-87 deg., 74-60 deg. and 142-124 deg., respectively, moderately depending on the temperature. All the systems are non-reactive in nature; however, the presence of impurity of free boron at the B4C surface gave rise to the chemical reaction with molten Mg and thus promoted the wettability to a certain degree. A new method was proposed to evaluate the wetting behavior coupled with evaporation and chemical reaction. Furthermore, based on the comparison of the work of adhesion and cohesion, the bonding in the Mg/B4C and Mg/TiC systems is presumably mainly chemical while that in the Mg/graphite system is physical.

  20. The design, fabrication and properties of B4C/Al neutron absorbers

    International Nuclear Information System (INIS)

    Neutron absorber is used for the criticality safety during the storage or transportation of spent nuclear fuel. In this work, the metal matrix composite with good mechanical property and thermal neutron absorbing ability was investigated based on B4C/Al neutron radiation shielding material. The composition ratio for B4C/Al composite was firstly designed and the dependence of the neutron transmission on the thickness of the material was calculated. By vacuum hot-pressing technique at a low temperature, the neutron absorbers with high concentration of B4C were fabricated. Furthermore, the corresponding microstructure, physical, mechanical and corrosion properties as well as fracture surface were analyzed, proving that the developed composites can shield the neutron radiation as effectively as cadmium materials

  1. Neutron absorption of Al-Si-Mg-B4C composite

    International Nuclear Information System (INIS)

    Al-Si-Mg-B4C composites containing 2-8 wt% of B4C were prepared by stir casting technique. Homogenization treatment was carried out at temperatures of 540°C for 4 houra and followed by ageing at 180°C for 2 houra. Microstructure and phase identification were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Neutron absorption study was investigated using neutron source Am/Be241. The result indicated that higher B4C content improved the neutron absorption property. Meanwhile homogeneity of the composite was increased by ageing processes. This composite is potential to be used as neutron shielding material especially for nuclear reactor application

  2. Stability of 10B4C thin films under neutron radiation

    International Nuclear Information System (INIS)

    Thin films of 10B4C have shown to be very suitable as neutron-converting material in the next generation of neutron detectors, replacing the previous predominantly used 3He. In this contribution we show under realistic conditions that 10B4C films are not damaged by the neutron irradiation and interactions, which they will be exposed to under many years in a neutron detector. 1 μm thick 10B4C thin films were deposited onto Al or Si substrates using dc magnetron sputtering. As-deposited films were exposed to a cold neutron beam with fluences of up to 1.1×1014 cm−2 and a mean wavelength of 6.9 Å. Both irradiated and as-deposited reference samples were characterized with time-of-flight elastic recoil detection analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoemission spectroscopy, and X-ray diffraction. We show that only 1.8 ppm of the 10B atoms were consumed and that the film composition does not change by the neutron interaction within the measurement accuracy. The irradiation does not deteriorate the film adhesion and there is no indication that it results in increased residual stress values of the as-deposited films of 0.095 GPa. From what is visible with the naked eye and down to atomic level studies, no change from the irradiation could be found using the above-mentioned characterization techniques. - Highlights: • 10B4C films are not damaged by radiation during many years in a neutron detector. • 1 μm 10B4C thin films were exposed to a 1.1×1014 cm−2 cold neutron beam. • Only 1.8 ppm of the 10B atoms were consumed. • No change in film composition, adhesion or residual stress. • 10B4C based neutron detectors are very suitable replacements for 3He detectors

  3. Chemical interactions of B4C pellets with Zr1%Nb and stainless steels

    International Nuclear Information System (INIS)

    Chemical interactions between B4C absorber material and X18H10T stainless steel absorber cladding of WWER type nuclear reactor, together with those between B4C and Zr1%Nb guide tube were investigated in the temperature range of 800-1200 and 1200-1600 deg C, respectively. After annealing, the specimens where exposed to metallograhical testing. The results show that the reaction obeys parabolic law, and the growth rate of the reaction layers can be described by an Arrhenius correlation. (author). 5 refs., 20 figs., 3 tabs

  4. Hardness and wear resistance of reaction bonded SiC-B4C composite

    International Nuclear Information System (INIS)

    Hardness and wear resistant characteristics of reaction-bonded silicon carbides with boron carbide additions are evaluated relative to those of reaction bonded silicon carbide (RBSC). The reaction-bonded SiC-B4C composites exhibit a distinctive improvement of hardness and wear resistance, indicative of high resistance against wear environment. Removal rates for the wear tests are decisively reduced by the addition of boron carbide in the composites. Controlling the amount of carbon content in the starting composition more enhances the hardness of the reaction-bonded composites. Implications concerning the partial decomposition of B4C during reaction process are considered. (orig.)

  5. Preparation of homogeneous B4C ceramics with high toughness by tape casting

    International Nuclear Information System (INIS)

    Highlights: ► The homogeneous B4C ceramics are prepared by tape casting and hot pressing. ► Phase, microstructure and mechanical properties of samples were investigated. ► The reasons for the improvement in mechanical properties were discussed. - Abstract: The homogeneous B4C ceramics are successfully prepared through tape casting, laminating and hot pressing. The obtained B4C slurry exhibited a shear thinning behavior. After tape casting, both sides of the green sheets were smooth and homogeneous. After lamination and decomposition treatment developed in argon, hot press sintering of laminated boron carbide was proceed at 2000 °C. The results indicate that the strength and fracture toughness of B4C specimens are 585 MPa and 4.9 MPa m1/2, respectively. The primary fracture mode is an intergranular type. The reasons for the improvement in mechanical properties should lie in the tape casting processing technique and the presence of carbonaceous residues in specimen.

  6. Tribological behavior of liquid metallurgy-processed AA 6061-B4C composites

    International Nuclear Information System (INIS)

    Aluminum metal matrix composites (AMMCs) possess improved properties compared to their monolithic counterparts and serve as a reliable alternative to replace them for applications that are considered as their niche. In the present investigation, 6061 Al alloy-10 wt% B4C composite is fabricated through liquid metallurgy stir casting technique and analyzed for its tribological characteristics. The uniform distribution of B4C reinforcement particles in the composite is achieved by the above route and is characterized using microstructure analysis and x-ray diffraction spectrum. The dry wear tests have been conducted under ambient conditions using a pin-on-disc tribometer. The worn surface and debris of the composite are also characterized using a scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS). It is found that the combination of adhesion, delamination and abrasion constitute the predominant wear mechanism and this is influenced by the B4C particles, applied load, sliding distance and speed. The wear and friction coefficient increase with increase in applied load for all the load conditions studied. While the sliding speed fosters the engendering of a mechanically mixed layer (MML) to reduce the wear and friction coefficient, in contrast, the increase in sliding distance scuttles the MML formation owing to abrasion induced by the hard B4C particles. (paper)

  7. Tribological behavior of liquid metallurgy-processed AA 6061-B4C composites

    Science.gov (United States)

    Monikandan, V. V.; Joseph, M. A.; Rajendrakumar, P. K.; Sreejith, M.

    2015-01-01

    Aluminum metal matrix composites (AMMCs) possess improved properties compared to their monolithic counterparts and serve as a reliable alternative to replace them for applications that are considered as their niche. In the present investigation, 6061 Al alloy-10 wt% B4C composite is fabricated through liquid metallurgy stir casting technique and analyzed for its tribological characteristics. The uniform distribution of B4C reinforcement particles in the composite is achieved by the above route and is characterized using microstructure analysis and x-ray diffraction spectrum. The dry wear tests have been conducted under ambient conditions using a pin-on-disc tribometer. The worn surface and debris of the composite are also characterized using a scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS). It is found that the combination of adhesion, delamination and abrasion constitute the predominant wear mechanism and this is influenced by the B4C particles, applied load, sliding distance and speed. The wear and friction coefficient increase with increase in applied load for all the load conditions studied. While the sliding speed fosters the engendering of a mechanically mixed layer (MML) to reduce the wear and friction coefficient, in contrast, the increase in sliding distance scuttles the MML formation owing to abrasion induced by the hard B4C particles.

  8. New neutron-shielding material SBR admixed with B4C

    International Nuclear Information System (INIS)

    Styrene-Butadiene-Rubber (SBR) admixed with similar quantity of B4C powder has been developed for shielding of thermal neutrons. The material has both high flexibility and good workability. It is successfully used as part of the shielding for a neutron spectrometer. (auth.)

  9. Mechanism for amorphization of boron carbide B4C under uniaxial compression

    Science.gov (United States)

    Aryal, Sitaram; Rulis, Paul; Ching, W. Y.

    2011-11-01

    Boron carbide undergoes an amorphization transition under high-velocity impacts, causing it to suffer a catastrophic loss in strength. The failure mechanism is not clear and this limits the ways to improve its resistance to impact. To help uncover the failure mechanism, we used ab initio methods to carry out large-scale uniaxial compression simulations on two polytypes of stoichiometric boron carbide (B4C), B11C-CBC, and B12-CCC, where B11C or B12 is the 12-atom icosahedron and CBC or CCC is the three-atom chain. The simulations were performed on large supercells of 180 atoms. Our results indicate that the B11C-CBC (B12-CCC) polytype becomes amorphous at a uniaxial strain s = 0.23 (0.22) and with a maximum stress of 168 (151) GPa. In both cases, the amorphous state is the consequence of structural collapse associated with the bending of the three-atom chain. Careful analysis of the structures after amorphization shows that the B11C and B12 icosahedra are highly distorted but still identifiable. Calculations of the elastic coefficients (Cij) at different uniaxial strains indicate that both polytypes may collapse under a much smaller shear strain (stress) than the uniaxial strain (stress). On the other hand, separate simulations of both models under hydrostatic compression up to a pressure of 180 GPa show no signs of amorphization, in agreement with experimental observation. The amorphized nature of both models is confirmed by detailed analysis of the evolution of the radial pair distribution function, total density of states, and distribution of effective charges on atoms. The electronic structure and bonding of the boron carbide structures before and after amorphization are calculated to further elucidate the mechanism of amorphization and to help form the proper rationalization of experimental observations.

  10. Mechanical Properties and Strengthening Mechanisms of Al-15 Pct B4C Composites with Sc and Zr at Elevated Temperatures

    Science.gov (United States)

    Qin, Jian; Zhang, Zhan; Chen, X.-Grant

    2016-09-01

    The mechanical properties at ambient and elevated temperatures of two Al-15 vol pct B4C composites, S40 with 0.4 wt pct Sc and SZ40 with 0.4 wt pct Sc and 0.24 wt pct Zr, are investigated during long-term thermal annealing. The presence of large B4C particles in the microscale has a moderate but stable strengthening effect on Al-B4C composites at ambient and elevated temperatures, while the precipitation of nanoscale Al3Sc and Al3(Sc, Zr) in the composite matrix provides a predominate contribution to the composite strength, which is varied by tested temperatures. The Al3Sc precipitates in S40 remain coarsening resistant at 523 K (250 °C), whereas the Al3(Sc, Zr) precipitates in SZ40 are thermally stable at 573 K (300 °C) over 2000 hours of annealing. At higher annealing temperatures (573 K (300 °C) for S40 and 623 K (350 °C) for SZ40), both Al3Sc and Al3(Sc, Zr) precipitates become coarsening with prolonged annealing time. The yield strength of S40 and SZ40 at ambient temperature decreases with the increasing precipitate size, which can be explained by the classical precipitate shearing and Orowan bypass mechanisms. At elevated temperatures [523 K to 623 K (250 °C to 350 °C)], considerably lower yield stresses are observed compared to those at ambient temperature, which invokes a dislocation climb mechanism. The predicted yield strengths at elevated temperatures by the combination of dislocation climb and Orowan models are in good agreement with the experimental data.

  11. Study on the influence of the B4C layer thickness on the neutron flux and energy distribution shape in multi-electrode ionisation chamber

    International Nuclear Information System (INIS)

    A model of a multi-electrode ionisation chamber, with polypropylene electrodes coated with a thin layer of B4C was created within Monte Carlo N-Particle Transport Code (MCNPX) and Fluktuierende Kaskade (FLUKA) codes. The influence of the layer thickness on neutron absorption in B4C and on the neutron spectra in the consecutive intra-electrode gas volumes has been studied using the MCNPX and FLUKA codes. The results will be used for designing the new type of the ionisation chamber. Presented results of calculations provide quantitative information on attenuation and absorption of neutrons in simulated multi-electrode ionisation chamber with electrodes coated with B4C. The main interest was to compare the neutron spectra at consecutive collecting electrodes for different thicknesses of the B4C layer. The calculations were performed for neutrons from 252Cf radiation source. The results indicated that obviously, the largest effect on the spectrum shape will be observed at the thickest B4C layer; however, the layer of ∼100-300 mg cm-2 becomes of interest when one wants to combine considerable modification of the spectrum with limited attenuation of the total flux. Maximum sensitivity of the chamber can be obtained when very thin B4C layers of ∼1 mg cm-2 are used. Such layers can be considered as the optimum ones, when the chamber is used as a moderating device with detection of thermal neutrons flux in each of the intra-electrode volumes. The results of calculations performed with MCNPX and FLUKA codes are qualitatively consistent with each other; however, differs in quantitative estimations. In the low-energy range a discrepancy can be observed probably due to differences in the cross section libraries of both codes. (authors)

  12. Analysis of B4C influences on thermodynamic properties and phase separation of molten corium with ionic liquid U-Zr-Fe-O-B-C-FPs database

    International Nuclear Information System (INIS)

    Boron carbide influences on thermodynamic properties and phase separation of molten corium such as liquidus temperature were estimated with our U-Zr-Fe-O-B-C-FPs thermodynamic database. The liquidus temperature of the oxide for the typical corium was estimated to increase by a hundred degrees with B4C addition when the corium included up to 10 wt% Fe. On the other hand, the liquidus temperature was hardly changed when the corium included 50 wt% Fe. The interaction temperature between the steel and the corium with B4C was estimated at 1130 K. We define the interaction temperature as the lowest temperature where the solid Fe and the liquid phase of a corium are in equilibrium, at which interactions such as microstructure change of the vessel were observed in test studies. Although it is 180 K lower than that without B4C, the estimated temperature is still over 200 K higher than the criterion temperature where the vessel loses its structural strength, which has been used in the feasibility evaluation of the in-vessel retention. Other thermodynamic influences of B4C were also estimated as not having a negative impact on the in-vessel retention. (author)

  13. Chemical compatibility of sodium exposed alloy D9 with B4C

    International Nuclear Information System (INIS)

    The control rods in India's first prototype fast breeder reactor (PFBR) would consist of high-density B4C (containing 67% 10B isotope) pellets enclosed in alloy D9 clad tubes. Enriched boron carbide required for control rod applications in PFBR is being produced indigenously by reacting elemental boron with graphite at high temperatures. The gap between the control rod material and the clad is filled with liquid sodium as the pins are of vented type. At the reactor operating temperatures of 773-873 K, the chemical interaction between B4C and D9 clad material surface modified by liquid sodium needs to be investigated and understood. Towards this, out-of-pile accelerated chemical compatibility experiments were carried out and the SEM/EDS, XRD and XPS results of the studies carried out at 973 K for 5000 h are presented in this paper

  14. Corrosion and tribocorrosion behavior of Ti-B4C composite intended for orthopaedic implants.

    Science.gov (United States)

    Toptan, F; Rego, A; Alves, A C; Guedes, A

    2016-08-01

    Poor wear resistance of titanium is a major concern since relative movements due to the cyclic loads in body environment cause wear between the bone and the implant material leading to detachment of the wear debris and release of metal ions due to the simultaneous action of corrosion and wear, defined as tribocorrosion. In order to increase the tribocorrosion resistance, Grade 2 Ti matrix 24vol% B4C particle reinforced composites were processed by hot pressing. Corrosion behaviour was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization in 9g/L NaCl solution at body temperature. Tribocorrosion tests were performed under open circuit potential, as well as under potentiodynamic polarization using a reciprocating ball-on-plate tribometer. Results suggested that the addition of B4C particles provided lower tendency to corrosion and lower corrosion kinetics under sliding, along with significantly reduced wear loss, mainly due to the load carrying effect given by the reinforcement particles. PMID:26866451

  15. Consolidation of B4C-TaB2 eutectic composites by spark plasma sintering

    OpenAIRE

    Dmytro Demirskyi

    2015-01-01

    The in situ synthesis/consolidation of B4C-TaB2 eutectic composites by spark plasma sintering (SPS) is reported. The microstructure–property relations were determined for composites with the B4C-TaB2 eutectic composition as functions of TaB2 content, and TaB2-TaB2 interlamellar spacing. A clear maximum in fracture toughness was identified (∼4.5 MPa m1/2) for eutectic composites with interlamellar spacing between 0.9 and 1.1 μm. The composites with the hypereutectic composition of 40 mol.% TaB...

  16. Thermal safety analysis of aluminum matrix B4C irradiation in-pile

    International Nuclear Information System (INIS)

    Aluminum matrix B4C is a new structural material for spent fuel storage and related performances need in-depth research, especially the irradiation-resistance capability. The thermal calculations were completed by using the CFD software to ensure the safety of the in-pile irradiation test. Considering the characteristic of the irradiation project, the thermal safety feature of the in-pile test was analyzed, and the irradiation project was optimized. (authors)

  17. Structural modifications induced by ion irradiation and temperature in boron carbide B4C

    Science.gov (United States)

    Victor, G.; Pipon, Y.; Bérerd, N.; Toulhoat, N.; Moncoffre, N.; Djourelov, N.; Miro, S.; Baillet, J.; Pradeilles, N.; Rapaud, O.; Maître, A.; Gosset, D.

    2015-12-01

    Already used as neutron absorber in the current French nuclear reactors, boron carbide (B4C) is also considered in the future Sodium Fast Reactors of the next generation (Gen IV). Due to severe irradiation conditions occurring in these reactors, it is of primary importance that this material presents a high structural resistance under irradiation, both in the ballistic and electronic damage regimes. Previous works have shown an important structural resistance of boron carbide even at high neutron fluences. Nevertheless, the structural modification mechanisms due to irradiation are not well understood. Therefore the aim of this paper is to study structural modifications induced in B4C samples in different damage regimes. The boron carbide pellets were shaped and sintered by using spark plasma sintering method. They were then irradiated in several conditions at room temperature or 800 °C, either by favoring the creation of ballistic damage (between 1 and 3 dpa), or by favoring the electronic excitations using 100 MeV swift iodine ions (Se ≈ 15 keV/nm). Ex situ micro-Raman spectroscopy and Doppler broadening of annihilation radiation technique with variable energy slow positrons were coupled to follow the evolution of the B4C structure under irradiation.

  18. Experiment and analysis of B4C simulating control rod on FCA V-3 Assembly

    International Nuclear Information System (INIS)

    Reactivity worths of the B4C simulating control rods have been measured and analysed on FCA V-3 Assembly which was constructed as the engineering mock-up for Experimental Fast Reactor ''JOYO''. Assembly V-3 differs from JOYO in the blanket composition and the simulating control rod is 1/2 of that of JOYO in size. We have made efforts to check the adequacy of the nuclear design method and to improve the design accuracy for JOYO by determining the range of ratios of the theoretical to experimental values (C/E). The reactivity worth of the B4C control rod is obtained by the measurement of the sub-criticality of the system containing the control rod. In the present work the neutron source multiplication method was employed. In the calculation we employed the multigroup diffusion approximation for the core and blanket, and the collision probability method for the effective cross sections of the B4C simulating control rod region. The cross section set used in the calculation is JAERI-FAST Version II. The lowest limit of the sub-criticality of the system is -6% delta k/k and the C/E ranges from 1.00 to 1.03 in the present work. (author)

  19. Preparation and investigation of Al–4 wt% B4C nanocomposite powders using mechanical milling

    Indian Academy of Sciences (India)

    A Alizadeh; E Taheri-Nassaj; H R Baharvandi

    2011-08-01

    Boron carbide nanoparticles were produced using commercially available boron carbide powder (0.8 m).Mechanical milling was used to synthesize Al nanostructured powder in a planetary ball-mill under argon atmosphere up to 20 h. The same process was applied for Al–4 wt% B4C nanocomposite powders to explore the role of nanosize reinforcements on mechanical milling stages. Scanning electron microscopy (SEM) analysis as well as apparent density measurements were used to optimize the milling time needed for completion of the mechanical milling process. The results show that the addition of boron carbide particles accelerate the milling process, leading to a faster work hardening rate and fracture of aluminum matrix. FE-SEM images show that distribution of boron carbide particles in aluminum matrix reaches a full homogeneity when steady state takes place. The better distribution of reinforcement throughout the matrix would increase hardness of the powder. To study the compressibility of milled powder, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B4C particles. For better distribution of reinforcement throughout the matrix, , modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B4C particles.

  20. Laser controlled melting of HSLA steel surface with presence of B4C particles

    Science.gov (United States)

    Yilbas, B. S.; Patel, F.; Karatas, C.

    2013-10-01

    Laser gas assisted melting of high strength low alloy steel surface is carried out. The alloy surface is pre-prepared to contain 5% B4C particles in a 40 μm thick carbon film prior to laser treatment process. Metallurgical and morphological changes in the laser treated layer are examined by using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The residual stress developed and the microhardness of the resulting surface is measured. It is found that B4C particles remain in solid phase in the surface region due to their high melting temperature. The dense layer consisting of fine grains are formed at the surface and the feathery like structure is observed below the surface vicinity, which consists of martensite and nitride precipitations. The use of nitrogen at high pressure causes the formation of nitride compounds at the surface, which contributes to the volume shrinkage in the dense layer. Surface microhardness increases considerably because of attainment of high cooling rates, formation of nitride compounds, and presence of B4C particles at the surface.

  1. Evolution of reinforcement distribution in Al-B4C composites during accumulative roll bonding

    International Nuclear Information System (INIS)

    Highlights: → ARB developed a nanostructure in the matrix of the Al-B4C composite. → An improvement in the reinforcement distribution was found by increasing ARB passes. → By progression of ARB from one to seven passes, hardness increased from 60 to 82 HV. -- Abstract: The distribution of reinforcement particles in the matrix of a composite is one of the most important microstructural features affecting properties. In this study, nanostructured Al-B4C composite sheets were processed by accumulative roll bonding (ARB), and the effect of the number of ARB cycles on the distribution of the B4C particles in the Al matrix was evaluated. From optical microscopic studies accompanied by the radial distribution function analysis, it was realized that the microstructure uniformity is improved by increasing the number of ARB cycles. It was in good agreement with bulk hardness measurements in which the standard deviation of the hardness values was decreased by progression of the ARB process. In addition, the X-ray diffraction peak profile analysis revealed that the area weighted mean crystallite size of the Al matrix decreases to the nanometric scale (114 nm) after seven ARB cycles.

  2. Preparation and characterization of B4C coatings for advanced research light sources.

    Science.gov (United States)

    Störmer, Michael; Siewert, Frank; Sinn, Harald

    2016-01-01

    X-ray optical elements are required for beam transport at the current and upcoming free-electron lasers and synchrotron sources. An X-ray mirror is a combination of a substrate and a coating. The demand for large mirrors with single layers consisting of light or heavy elements has increased during the last few decades; surface finishing technology is currently able to process mirror lengths up to 1 m with microroughness at the sub-nanometre level. Additionally, thin-film fabrication is able to deposit a suitable single-layer material, such as boron carbide (B4C), some tens of nanometres thick. After deposition, the mirror should provide excellent X-ray optical properties with respect to coating thickness errors, microroughness values and slope errors; thereby enabling the mirror to transport the X-ray beam with high reflectivity, high beam flux and an undistorted wavefront to an experimental station. At the European XFEL, the technical specifications of the future mirrors are extraordinarily challenging. The acceptable shape error of the mirrors is below 2 nm along the whole length of 1 m. At the Helmholtz-Zentrum Geesthacht (HZG), amorphous layers of boron carbide with thicknesses in the range 30-60 nm were fabricated using the HZG sputtering facility, which is able to cover areas up to 1500 mm long by 120 mm wide in one step using rectangular B4C sputtering targets. The available deposition area is suitable for the specified X-ray mirror dimensions of upcoming advanced research light sources such as the European XFEL. The coatings produced were investigated by means of X-ray reflectometry and interference microscopy. The experimental results for the B4C layers are discussed according to thickness uniformity, density, microroughness and thermal stability. The variation of layer thickness in the tangential and sagittal directions was investigated in order to estimate the achieved level of uniformity over the whole deposition area, which is considerably

  3. Al-Si/B4C composite coatings on Al-Si substrate by plasma spray technique

    International Nuclear Information System (INIS)

    Plasma-sprayed coatings of Al-Si/B4C have been prepared on Al-Si piston alloys for diesel engine motors. The Al-Si/B4C composite powders including 5-25 wt% B4C were prepared by mixing and ball-milling processes. These powders were deposited on Al-Si substrate using an atmospheric plasma spray technique. The coatings have been characterised with respect to phase composition, microstructure, microhardness, bond strength and thermal expansion. It was found that Al, Si, B4C and Al2O3 phases were determined in the coatings with approximately 600 μm thick by using X-ray diffraction analysis. Scanning electron microscope observation revealed that boron carbide particles were uniformly distributed in composite coatings and B4C particles were fully wetted by Al-Si alloy. Also, no reaction products were observed in Al-Si/B4C composite coatings. It was found that surface roughness, porosity, bond strength and thermal expansion coefficient of composite coatings decreased with increasing fraction of the boron carbide particle. It was demonstrated that the higher the B4C content, the higher the hardness of coatings because the hardness of B4C is higher than that of Al-Si

  4. Optical properties of boron carbide near the boron K edge evaluated by soft-x-ray reflectometry from a Ru/B4C multilayer

    International Nuclear Information System (INIS)

    Soft-x-ray Bragg reflection from two Ru/B4C multilayers with 10 and 63 periods was used for independent determination of both real and imaginary parts of the refractive index n = 1 -δ + iβ close to the boron K edge (∼188 eV). Prior to soft x-ray measurements, the structural parameters of the multilayers were determined by x-ray reflectometry using hard x rays. For the 63-period sample, the optical properties based on the predictions made for elemental boron major deviations were found close to the K edge of boron for the 10-period sample explained by chemical bonding of boron to B4C and various boron oxides.

  5. Optical properties of boron carbide near the boron K edge evaluated by soft-x-ray reflectometry from a Ru/B(4)C multilayer.

    Science.gov (United States)

    Ksenzov, Dmitriy; Panzner, Tobias; Schlemper, Christoph; Morawe, Christian; Pietsch, Ullrich

    2009-12-10

    Soft-x-ray Bragg reflection from two Ru/B(4)C multilayers with 10 and 63 periods was used for independent determination of both real and imaginary parts of the refractive index n = 1 - delta + ibeta close to the boron K edge (approximately 188 eV). Prior to soft x-ray measurements, the structural parameters of the multilayers were determined by x-ray reflectometry using hard x rays. For the 63-period sample, the optical properties based on the predictions made for elemental boron major deviations were found close to the K edge of boron for the 10-period sample explained by chemical bonding of boron to B(4)C and various boron oxides. PMID:20011008

  6. Laser surface treatment of aluminum based composite mixed with B4C particles

    Science.gov (United States)

    Yilbas, B. S.; Karatas, C.; Karakoc, Halil; Abdul Aleem, B. J.; Khan, S.; Al-Aqeeli, N.

    2015-03-01

    Laser treatment of hot pressed mixture of aluminum (85 wt%) and B4C (15 wt%) is carried out. Metallurgical and morphological changes at the laser treated surface are examined using the analytical tools. Microhardness and fracture toughness of the workpiece surfaces are determined prior to and after the laser treatment process. Texture and hydrophobicity of the laser treated surface is assessed incorporating the atomic force microscopy and contact angle measurements. It is found that a dense layer consisting of fine grains of sub-micron sizes (0.8-0.4 μm) and B4C particles is formed at the laser treated surface. Microhardness increases at the laser treated surface because of the presence of the dense layer and the formation of AlN compounds at the surface. Fracture toughness of the laser treated surface reduces slightly because of the microhardness enhancement at the surface. The textures of the laser treated surface compose of micro/nano poles, which result in higher contact angles than that of the untreated surface, and formation of AlN compound adds to the surface hydrophobicity enhancements.

  7. Helium bubble evolution in ion irradiated Al/B4C metal matrix composite

    International Nuclear Information System (INIS)

    Graphical abstract: Scheme of combined irradiation includes a pre-implantation of 400 keV He+ to 1.0 × 1016 ions/cm2 followed by a 1.5 MeV proton irradiation to 2.2 × 1019 ions/cm2 on the perpendicular surface. TEM samples were prepared by FIB. The area suffered with both He+ pre-implantation and proton irradiation was marked as light blue. - Abstract: Helium behavior in Al/B4C metal matrix composite with two different sets of ion irradiation conditions has been investigated by transmission electron microscopy. Helium bubbles in Al were found to be much larger than those in B4C after a helium fluence of 1.5 × 1017 ions/cm2 at the room temperature. Also, bubbles at grain boundaries and their vicinity in aluminum are faceted. With additional proton irradiation, a bubble denuded zone along the aluminum grain boundary appears. The results are discussed in terms of the energetics of the material system

  8. Consolidation of B4C-TaB2 eutectic composites by spark plasma sintering

    Directory of Open Access Journals (Sweden)

    Dmytro Demirskyi

    2015-12-01

    Full Text Available The in situ synthesis/consolidation of B4C-TaB2 eutectic composites by spark plasma sintering (SPS is reported. The microstructure–property relations were determined for composites with the B4C-TaB2 eutectic composition as functions of TaB2 content, and TaB2-TaB2 interlamellar spacing. A clear maximum in fracture toughness was identified (∼4.5 MPa m1/2 for eutectic composites with interlamellar spacing between 0.9 and 1.1 μm. The composites with the hypereutectic composition of 40 mol.% TaB2 obtained by SPS exhibited lower Vickers hardness (25–26 GPa but higher indentation fracture toughness (up to 4.9 MPa m1/2 than eutectic composites with 30–35 mol.% of TaB2.

  9. Influence of graphite on the hardness and wear behavior of AA6061-B4C composite: Vpliv grafita na trdoto in vedenje kompozita AA6061-B4C pri obrabi:

    OpenAIRE

    Chandramohan, Govindarajulu; Prabagaran, Subramaniam; Shanmughasundaram, Palanisamy

    2014-01-01

    Dry-sliding-wear behavior of AA6061, AA6061-B4C composite and AA6061-B4C-Gr hybrid composite was investigated by employing a pin-on-disc wear-test rig. Hardness tests were also carried out. Graphite was used as a solid lubricant since it is a soft, slippery and greyish-black substance. Because of the cleavage (crystal) loose interlamellar coupling, graphite has good lubricating properties. A comparative analysis was made on the hardness and wear behavior of AA6061, AA6061-B4C composite and AA...

  10. Ballistic Impact Behavior of Nacre-Like Laminated Composites Consisting of B4C Tablets and Polyurea Matrix

    Science.gov (United States)

    Grujicic, M.; Snipes, J. S.; Ramaswami, S.

    2016-03-01

    A nacre-like composite armor consisting of B4C tablets and polyurea matrix is modeled, and its ballistic impact behavior and penetration resistance (under a normal and a 15°-oblique impact by a solid right circular cylindrical projectile) were analyzed using a series of transient, nonlinear dynamic, finite-element analyses. Nacre is a biological material constituting the innermost layer of the shells of gastropods and bivalves. It consists of polygonal tablets of aragonite, tessellated to form individual layers and having the adjacent layers as well as the tablets within a layer bonded by a biopolymer. Due to its highly complex hierarchical microstructure, nacre possesses an outstanding combination of mechanical properties, the properties which are far superior to the ones that are predicted using the homogenization techniques such as the rule of mixtures. The results of the transient nonlinear dynamic analysis pertaining to the ballistic impact response and the penetration resistance of the modeled nacre-like armor are compared with their counterparts for the B4C single-block armor having an identical areal density. Furthermore, the effect of various nacre microstructural features (e.g., surface profiling, micron-scale asperities, mineral bridges between the overlapping tablets lying in adjacent layers) on the ballistic penetration resistance of the nacre-like composite armor is investigated in order to identify an optimal nacre-like composite-armor architecture having the largest penetration resistance. The results obtained clearly show that a nacre-like armor possesses a superior penetration resistance relative to its monolithic counterpart, and that the nacre microstructural features considered play a critical role in the armor penetration resistance.

  11. B4C solid target boronization of the MST reversed-field pinch

    International Nuclear Information System (INIS)

    A solid rod of hot-pressed boron carbide is being used as the source of boron during boronization of MST. The most striking result of this procedure is the reduction in oxygen contamination of the plasma (O III radiation, characteristic of oxygen at the edge, falls by about a factor of 3 after boronization.). The radiated power fraction drops to about half its initial value. Particle reflux from the wall is also lowered, making density control simpler. The rod (12.7 mm diameter) is inserted into the edge plasma of normal high-power RFP discharges. B4C is ablated from the surface of the rod and deposited in a thin film (a-B/C:H) on the walls and limiters. The energy flux carried by ''superthermal'' (not ''runaway'') electrons at the edge of MST appears to enhance the efficient, non-destructive ablation of the boron carbide rod

  12. Processing and characterization of B4C-SiC-Si-TiB2 composites

    International Nuclear Information System (INIS)

    B4C-SiC-Si-TiB2 composites were synthesized by a two step process. TiB2 particles in the size range 2-5 μm were generated in situ in the first step and were distributed in the residual silicon present in the reaction bonded boron carbide, in the second step. The composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro analysis (EPMA) and micro-hardness testing. The density and average hardness of siliconized boron carbide samples with and without TiB2 particle reinforcement were found to be 2.67 g/cm3 and 25 GPa and 2.54 g/cm3 and 21 GPa, respectively.

  13. TEM characterization of La/B4C multilayer systems by the geometric phase method

    International Nuclear Information System (INIS)

    New La/B4C multilayer systems with layer thicknesses in the nanometer range have been deposited onto structured silicon (001) surfaces by magnetron sputtering and have been characterized by transmission electron microscopy (TEM). By applying a geometric phase method which has been originally developed for measuring displacement fields from high-resolution TEM images, we demonstrate that the structural perfection of multilayers, especially their local layer periods and local layer orientations, can be analyzed with high sensitivity from bright-field TEM images of cross-section specimens. The determination of these structure parameters is relevant for the assessment of the reflectivity properties of such multilayer systems in advanced X-ray optical components. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Comparison of microstructural and mechanical properties of Al–TiC, Al–B4C and Al–TiC–B4C composites prepared by casting techniques

    International Nuclear Information System (INIS)

    In the present work, production of Al–10%TiC, Al–10% B4C, Al–5%TiC–5%B4C (volume fraction) composites by casting techniques were studied. However, casting techniques suffers from poor incorporation and distribution of the reinforcement particles in the matrix. These problems become especially significant as the reinforcement size decreases due to greater agglomeration tendency and reduced wettability of the particles with the melt. Microstructure characterization of the composite samples was investigated by using scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD).The results showed heat treatment of B4C particles and addition of TiC particles with the flux improved the wettability and incorporation of reinforcement particles into melt. Mechanical characterization of samples showed that maximum hardness had belonged to Al–5%TiC–5%B4C composite, maximum yield and tensile strength had belonged to Al–10%B4C composite and maximum elongation had belonged to Al–10%TiC composite. Furthermore, wear properties of composites revealed the better behavior for Al–B4C composite.

  15. Processing and characterization of B4C/Cu graded composite as plasma facing component for fusion reactors

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    A new approach for fabricating B4C/Cu graded composite by rapid self-resistance sintering under ultra-high pressure was presented, by which a near dense B4C/Cu graded composite with a compositional spectrum of 0-100% was successfully fabricated. Plasma relevant performances ofsintered B4C/Cu composite were preliminarily characterized, it is found that its chemical sputtering yield is 70% lower than that of SMF800 nuclear graphite under 2.7 keV D+ irradiation, and almost no damages after 66 shots of in situ plasma discharge in HL-1 Tokamak facility, which indicates B4C/Cu plasma facing component has a good physical and chemical sputtering resistance performance compared with nuclear graphite.

  16. Fabrication of Al5083/B4C surface composite by friction stir processing and its tribological characterization

    OpenAIRE

    Narayana Yuvaraj; Sivanandam Aravindan; Vipin

    2015-01-01

    Improved surface properties with the retainment of bulk properties are necessary for a component for enhanced wear characteristics. Friction stir processing (FSP) is used to produce such surface composites. Fabrication of 5083 aluminum alloy with reinforced layers of boron carbide (B4C) through FSP was carried out. Micro and nano sized B4C particles were used as reinforcements. The friction processed surface composite layer was analyzed through optical and scanning electron microscopical stud...

  17. Thermal stability studies of ion beam sputter deposited C/B4C X-ray multilayer mirror

    International Nuclear Information System (INIS)

    We report the results of thermal stability study carried out on C/B4C multilayer structure. We have analyzed the structure of as-deposited and vacuum annealed C/B4C multilayer film by soft X-ray reflectivity measurements. We observed that multilayer period expansion continues till 600 °C and slight contraction at higher annealing temperature. The results show that the multilayer structure is stable even after 700 °C annealing. Raman spectroscopy indicates graphitization of carbon layer with increasing annealing temperature. Graphitization of carbon results in increases of layer thickness and decreases in density as also observed by soft X-ray reflectivity. We observed reduction in measured soft X-ray reflectivity at 6.56 and 4.39 nm wavelengths after 800 °C annealing. C/B4C multilayer structure has been tested over a period of one year to investigate its temporal stability. - Highlights: ► We reported the experimental results on thermal stability of C/B4C combination. ► Multilayer structure is stable even after 700 °C annealing. ► C/B4C can be used as a stable multilayer mirror both in soft and hard X-ray regions. ► C/B4C multilayer structure has shown good temporal stability

  18. Eu2O3 and B4C worth calculations in fast reactor spectra

    International Nuclear Information System (INIS)

    Work is now in progress to design and fabricate europia (Eu2O3) control rods for irradiation testing in one of the early operating cycles of the Fast Test Reactor (FTR). These tests will provide data for evaluating europia as a possible control rod absorber material in fast reactors. Prediction of the reactivity worth of the europia rods is a necessary part of the design process. To improve the accuracy of these predictions, an experiment was performed in the FTR Engineering Mockup Critical (EMC) to determine the relative reactivity worth of Eu2O3 and boron carbide (B4C) in control rod size quantities. Upon completion of the experiment, calculations were performed to obtain reactivity worths for comparison with the measured worths. From this comparison, calculation-vs.-experiment (C/E) bias factors were obtained for use in correcting the computed reactivity worth of europia in the FTR. A brief description of the experiment is presented together with the experimental results, a description of the analytical methods, the calculated results, and a comparison of the calculated and experimental results. Also included are discussions of the effects of resonance self-shielding and mesh spacing on computed absorber rod worths

  19. Fission products measured from highly-enriched uranium irradiated under 10B4C in a research reactor

    International Nuclear Information System (INIS)

    Prior work has demonstrated the use of a natural B4C capsule for spectral-tailoring in a mixed spectrum reactor as an alternate and complementary method to critical assemblies for performing nuclear data measurements at near 235U fission-energy neutron spectrum. Previous fission product measurements showed that the neutron spectrum achievable with natural B4C was not as hard as what can be achieved with critical assemblies. New measurements performed with the Washington State University TRIGA reactor using a B4C capsule 96 % enriched in 10B resulted in a neutron spectrum very similar to a critical assembly and a pure 235U fission spectrum. Fission product yields measured following an irradiation of a sample with this new method and subsequent radiochemical separations are presented here. (author)

  20. Structure and characteristics of electrodeposited RE-Ni-W-P-B4C-PTFE composite coatings

    Institute of Scientific and Technical Information of China (English)

    陈凌; 郭忠诚; 杨显万

    2001-01-01

    Hardness, friction and wear characteristics of electrodeposited RE-Ni-W-P-B4C-PTFE composite coatings were studied, and the reason for these fine characteristics was explained in respect of structure. The results show that 1)the structure of RE-Ni-W-P-B4C-PTFE composite coatings experiences a transformation process from amorphous to mixture then to crystal as the heat-treatment temperature rises; 2) incorporating of B4C greatly increases the hardness of the coating; 3) the wear resistance of the coating is best with heat-treatment for 1 h at 300 ℃, which is greatly superior to that of the other traditional coatings.

  1. A W:B4C multilayer phase retarder for broadband polarization analysis of soft x-ray radiation

    NARCIS (Netherlands)

    MacDonald, Michael A.; Schaefers, Franz; Pohl, R.; Poole, Ian B.; Gaupp, Andreas; Quinn, Frances M.

    2008-01-01

    A W:B4C multilayer phase retarder has been designed and characterized which shows a nearly constant phase retardance between 640 and 850 eV photon energies when operated near the Bragg condition. This freestanding transmission multilayer was used successfully to determine, for the first time, the fu

  2. High reflectance Cr/V multilayer with B(4)C barrier layer for water window wavelength region.

    Science.gov (United States)

    Huang, Qiushi; Fei, Jiani; Liu, Yang; Li, Pin; Wen, Mingwu; Xie, Chun; Jonnard, Philippe; Giglia, Angelo; Zhang, Zhong; Wang, Kun; Wang, Zhanshan

    2016-02-15

    To develop the high reflectance mirror for the short wavelength range of the water window region (λ=2.42-2.73  nm), Cr/V multilayers with B4C barrier layers are studied. The grazing incidence x-ray reflectometry results show that the multilayer interface widths are significantly reduced down to 0.21-0.31 nm, after the introduction of 0.1 nm B4C barrier layers at both interfaces. The [B4C/Cr/B4C/V] multilayer with a large number of bilayers of N=300 maintains the same small interface widths while the surface roughness is only 0.2 nm. According to the transmission electron microscope measurements, the layer structure improvement with barrier layers can be attributed to the suppression of the crystallization of vanadium inside the structure. Using the interface engineered multilayer, a maximum soft x-ray reflectance of 24.3% is achieved at λ=2.441  nm, under the grazing incidence of 42°. PMID:26872167

  3. Resonant soft x-ray reflectivity of Me/B(4)C multilayers near the boron K edge.

    Science.gov (United States)

    Ksenzov, Dmitriy; Schlemper, Christoph; Pietsch, Ullrich

    2010-09-01

    Energy dependence of the optical constants of boron carbide in the short period Ru/B(4)C and Mo/B(4)C multilayers (MLs) are evaluated from complete reflectivity scans across the boron K edge using the energy-resolved photon-in-photon-out method. Differences between the refractive indices of the B(4)Cmaterial inside and close to the surface are obtained from the peak profile of the first order ML Bragg peak and the reflection profile near the critical angle of total external reflection close to the surface. Where a Mo/B(4)C ML with narrow barrier layers appears as a homogeneous ML at all energies, a Ru/B(4)C ML exhibits another chemical nature of boron at the surface compared to the bulk. From evaluation of the critical angle of total external reflection in the energy range between 184 and 186eV, we found an enriched concentration of metallic boron inside the Ru-rich layer at the surface, which is not visible in other energy ranges. PMID:20820220

  4. Study of multi-carbide B4C-SiC/(Al, Si) reaction infiltrated composites by SEM with EBSD

    International Nuclear Information System (INIS)

    In the definition of conceptual developments and design of new materials with singular or unique properties, characterisation takes a key role in clarifying the relationships of composition, properties and processing that define the new material. B4C has a rare combination of properties that makes it suitable for a wide range of applications in engineering: high refractoriness, thermal stability, high hardness and abrasion resistance coupled to low density. However, the low self-diffusion coefficient of B4C limits full densification by sintering. A way to overturn this constraint is by using an alloy, for example Al-Si, forming composites with B4C. Multi-carbide B4C-SiC/(Al, Si) composites were produced by the reactive melt infiltration technique at 1200 – 1350 °C with up to 1 hour of isothermal temperature holds. Pressed preforms made from C-containing B4C were spontaneously infiltrated with Al-Si alloys of composition varying from 25 to 50 wt% Si. The present study involves the characterisation of the microstructure and crystalline phases in the alloys and in the composites by X-ray diffraction and SEM/EDS with EBSD. Electron backscatter diffraction is used in detail to look for segregation and spatial distribution of Si and Al containing phases during solidification of the metallic infiltrate inside the channels of the ceramic matrix when the composite cools down to the eutectic temperature (577 °C). It complements elemental maps of the SEM/EDS. The production of a flat surface by polishing is intrinsically difficult and the problems inherent to the preparation of EBSD qualified finishing in polished samples of such type of composites are further discussed

  5. Fabrication of steel matrix composites locally reinforced with different ratios of TiC/TiB2 particulates using SHS reactions of Ni-Ti-B4C and Ni-Ti-B4C-C systems during casting

    International Nuclear Information System (INIS)

    Steel matrix composites locally reinforced with different molar ratios of in situ TiC/TiB2 particulates (2:1, 1:1 and 1:2, respectively) have been fabricated successfully utilizing the self-propagating high-temperature synthesis (SHS) reactions of Ni-Ti-B4C and Ni-Ti-B4C-C systems during casting. Differential thermal analysis (DTA) and X-ray diffraction (XRD) results reveal that the exothermic reactions of the Ni-Ti-B4C and Ni-Ti-B4C-C systems proceed in such a way that Ni initially reacts with B4C and Ti to form Ni2B and Ti2Ni compounds, respectively, with heat evolution at 1037 deg. C; Subsequently, the external heat and the evolved heat from these exothermic reactions promote the reactions forming TiC and TiB2 at 1133 deg. C. In the composites reinforced with 1:2 molar ratio of TiC/TiB2, almost all TiB2 grains have clubbed structures, while TiC grains exhibit near-spherical morphologies. Furthermore, TiB2 grain sizes decrease, with the increase of TiC content. In particular, in the composites reinforced with 2:1 molar ratio of TiC/TiB2, it is difficult to find the clubbed TiB2 grains. Macro-pores and blowholes are absent in the local reinforcing region of the composites reinforced with 1:1 and 1:2 molar ratios of TiC/TiB2, while a few macro-pores can be observed in the composite reinforced with 2:1 molar ratio of TiC/TiB2. Moreover, the densities of the composites reinforced with 1:1 and 1:2 molar ratios of TiC/TiB2 are higher than that of the composite reinforced with 2:1 molar ratio of TiC/TiB2. The composite reinforced with 1:2 molar ratio of TiC/TiB2 has the highest hardness and the best wear resistance

  6. High temperature tribological behaviour of carbon based (B4C and DLC) coatings in sliding contact with aluminum

    International Nuclear Information System (INIS)

    Carbon based coatings, particularly diamond-like carbon (DLC) films are known to resist aluminum adhesion and reduce friction at room temperature. This attractive tribological behaviour is useful for applications such as tool coatings used for aluminum forming and machining. However, for those operations that are performed at elevated temperatures (e.g. hot forming) or that generate frictional heat during contact (e.g. dry machining) the suitable coatings are required to maintain their tribological properties at high temperatures. Candidates for these demanding applications include boron carbide (B4C) and DLC coatings. An understanding of the mechanisms of friction, wear and adhesion of carbon based coatings against aluminum alloys at high temperatures will help in designing coatings with improved high temperature tribological properties. With this goal in mind, this study focused on B4C and a hydrogenated DLC coatings sliding against a 319 grade cast aluminum alloy by performing pin-on-disk experiments at temperatures up to 400 oC. Experimental results have shown that the 319 Al/B4C tribosystem generated coefficient of friction (COF) values ranging between 0.42 and 0.65, in this temperature range. However, increased amounts of aluminum adhesion were detected in the B4C wear tracks at elevated temperatures. Focused ion beam (FIB) milled cross sections of the wear tracks revealed that the coating failed due to shearing along the columnar grain boundaries of the coating. The 319 Al/DLC tribosystem maintained a low COF (0.15-0.06) from room temperature up to 200 oC. This was followed by an abrupt increase to 0.6 at 400 oC. The deterioration of friction behaviour at T > 200 oC was attributed to the exhaustion of hydrogen and hydroxyl passivants on the carbon transfer layer formed on the Al pin.

  7. 10B4C Multi-Grid as an alternative to 3He for Large Area Neutron Detectors

    OpenAIRE

    Correa Magdalena, Jonathan

    2012-01-01

    Despite its present shortage, 3He continues to be the most common neutron converter for detectors in neutron scattering science. However, it is obvious that the development of large area neutron detectors based on alternative neutron converters is rapidly becoming a matter of urgency. In the technique presented, grids each comprising 30 10B4C layers (each 1 µm thick) are used to convert neutrons into ionising particles which are subsequently detected in proportional gas counters. Several pro...

  8. 10B4C Multi-Grid as an alternative to 3He for Large Area Neutron Detectors

    OpenAIRE

    Correa Magdalena, Jonathan; Guerard, Bruno; Campo Ruiz, Jesús Javier

    2013-01-01

    Despite its present shortage, 3He continues to be the most common neutron converter for detectors in neutron scattering science. However, it is obvious that the development of large area neutron detectors based on alternative neutron converters is rapidly becoming a matter of urgency. In the technique presented, grids each comprising 30 10B4C layers (each 1 µm thick) are used to convert neutrons into ionising particles which are subsequently detected in proportional gas counters. Several pro...

  9. Transmission electron microscope studies of the chromium cast iron modified at use of B4C addition

    Directory of Open Access Journals (Sweden)

    K. Labisz

    2010-10-01

    Full Text Available Results of studies of the high alloy chromium cast iron with boron addition in form of the B4C phase powder are presented in this paper.The main field of interest is the identification of phases based on the transmission electron microscope study, occurred in this alloy aftersolidification process. The structure mainly consists of the austenite matrix and M7C3 carbide identified as the Cr7C3 phase.

  10. Fabrication of dense B4C/CNF composites having extraordinary high strength and toughness at elevated temperatures

    International Nuclear Information System (INIS)

    Fully dense B4C/CNF composites have been fabricated from the mixture of amorphous fine powders of boron and carbon, and carbon nano-fiber (CNF) using pulsed electric-current pressure sintering (PECPS) at 2173 K (1900 °C) for 10 min under 30 MPa in a vacuum. They showed a moderate mechanical properties at room temperature: bending strength σb more than 450 MPa, Vickers hardness Hv of 29–36 GPa, and fracture toughness KIC ranging from 4.1 to 5.7 MPa m1/2. However, they revealed extraordinary high strength more than 600 MPa at 1673–1873 K (1400–1600 °C) in an inert gas atmosphere, especially, σb of 830 MPa at 1773 K (1500 °C) (12.5 vol% CNF added composite) and σb of 800 MPa at 1873 K (1600 °C) (10.0 vol% CNF added composite). In addition, these B4C/CNF composites also showed much improved high-temperature fracture toughness by a factor of around 20, in comparison with monolithic B4C ceramics at 1773 K (1500 °C). These extraordinary both high strength and toughness might be explained in terms of the suppression of grain growth by CNF at elevated temperatures, an inverse strength temperature-dependence for carbides, and anchor effect induced by CNF

  11. Mechanical performance optimization of neutron shielding material based on short carbon fiber reinforced B4C/epoxy resin

    International Nuclear Information System (INIS)

    To satisfy engineering requirements for mechanics performance of neutron shielding material, short carbon fiber was used to reinforce the traditional containing B4C neutron shielding material and effects of fiber content, length and surface treatment to mechanics performance of material was discussed. Based on Americium-Beryllium neutron source, material's neutron shielding performance was tested. The result of experiment prove that tensile strength of material which the quality ratio of resin and fiber is 5:1 is comparatively excellent for 10wt% B4C of carbon fiber reinforced epoxy resin. The tensile properties of material change little with the fiber length ranged from 3-10 mm The treatment of fiber surface with silane coupling agent KH-550 can increase the tensile properties of materials by 20% compared with the untreated of that. A result of shielding experiment that the novel neutron shielding material can satisfy the neutron shielding requirements can be obtained by comparing with B4C/polypropylene materials. The material has good mechanical properties and wide application prospect. (authors)

  12. Effects of B4C addition on the micro- structural and thermal properties of hot pressed SiC ceramic matrix composites

    OpenAIRE

    Z. Keçeli; H. Ögünç; T. Boyraz; H. Gökçe; O. Addemir; M. Lütfi Öveçoğlu

    2009-01-01

    Purpose: The purpose of paper is to evaluate effects of B4C addition on the microstructural and thermal properties of hot pressed SiC ceramic matrix composites.Design/methodology/approach: The effect of B4C addition on microstructural and thermal properties of the SiC-B4C powder composites were investigated after high energy milling and hot pressing. SiC powders containing 5wt%, 10wt%, 15wt% B4C were mechanically alloyed in a high energy ball mill for 8 h.Findings: Microstructural characteris...

  13. Electronic transport in boron carbides: temperature (4K-300K), frequency (0-1 GHz) and composition (B13C2-B4C) effects

    International Nuclear Information System (INIS)

    Boron carbide is a light ceramics of industrial interest. The equilibrium diagram reveals a large compositional range (B9C to B4C). The compositions close to the boundary B4C are obtained by pressing directly in graphite dies while the other compositions were obtained by using boron nitride lined graphite dies and boron additions to the commercial powders. The starting point of the present study was the idea to use the electrical transport properties as possible ways of characterising the industrial materials. We were thus led to measure at low temperatures dc and ac conductivity, dielectric constant and thermopower. The successful study of a measurement method for ac measurements between 10 KHz and 1 GHz and between 4 K and 300 K was one of the main experimental points of the present work. ac measurements have permitted a clear separation between bulk and grain boundary effects on the transport. The bulk results were analysed in terms of the usual conduction models in disordered solids (hopping, polarons...)

  14. Deposition and characterization of B4C/CeO2 multilayers at 6.x nm extreme ultraviolet wavelengths

    Science.gov (United States)

    Sertsu, M. G.; Giglia, A.; Brose, S.; Park, D.; Wang, Z. S.; Mayer, J.; Juschkin, L.; Nicolosi, P.

    2016-03-01

    New multilayers of boron carbide/cerium dioxide (B4C/CeO2) combination on silicon (Si) substrate are manufactured to represent reflective-optics candidates for future lithography at 6.x nm wavelength. This is one of only a few attempts to make multilayers of this kind. Combination of several innovative experiments enables detailed study of optical properties, structural properties, and interface profiles of the multilayers in order to open up a room for further optimization of the manufacturing process. The interface profile is visualized by high-angle annular dark-field imaging which provides highly sensitive contrast to atomic number. Synchrotron based at-wavelength extreme ultraviolet (EUV) reflectance measurements near the boron (B) absorption edge allow derivation of optical parameters with high sensitivity to local atom interactions. X-ray reflectivity measurements at Cu-Kalpha (8 keV ) determine the period of multilayers with high in-depth resolution. By combining these measurements and choosing robust nonlinear curve fitting algorithms, accuracy of the results has been significantly improved. It also enables a comprehensive characterization of multilayers. Interface diffusion is determined to be a major cause for the low reflectivity performance. Optical constants of B4C and CeO2 layers are derived in EUV wavelengths. Besides, optical properties and asymmetric thicknesses of inter-diffusion layers (interlayers) in EUV wavelengths near the boron edge are determined. Finally, ideal reflectivity of the B4C/CeO2 combination is calculated by using optical constants derived from the proposed measurements in order to evaluate the potentiality of the design.

  15. Recent results at the SIRa test bench: diffusion properties of carbon graphite and B4C targets

    International Nuclear Information System (INIS)

    The diffusion properties of graphite targets with 1, 4 and 15 microns microstructure has been measured for He and Ar isotopes. An important enhancement of the diffusion efficiency for the smaller microstructure is observed. A releasing efficiency of the order of 100% was obtained for 6He (T1/2 = 806 ms) at a temperature of 1600 K. The diffusion and production properties of He isotopes in a target of B4C (Boron Carbide) have also been studied. Yields of 1.5 108 pps and 106 pps for 6He and 8He has been obtained. (authors)

  16. A W:B4C multilayer phase retarder for broadband polarization analysis of soft x-ray radiation

    OpenAIRE

    MacDonald, Michael A.; Schaefers, Franz; Pohl, R.; Poole, Ian B.; Gaupp, Andreas; Quinn, Frances M.

    2008-01-01

    A W:B4C multilayer phase retarder has been designed and characterized which shows a nearly constant phase retardance between 640 and 850 eV photon energies when operated near the Bragg condition. This freestanding transmission multilayer was used successfully to determine, for the first time, the full polarization vector at soft x-ray energies above 600 eV, which was not possible before due to the lack of suitable optical elements. Thus, quantitative polarimetry is now possible at the 2p edge...

  17. Interface study and performance of large layer pair ultra-short period W/B4C X-ray multilayer

    International Nuclear Information System (INIS)

    The nature of interfaces in ultra short period W/B4C multilayers (MLs) is studied using hard x-ray reflectivity and cross sectional transmission electron microscope. W/B4C MLs are fabricated using magnetron sputtering system with systematic varying thickness of both W and B4C layers from ∼5 to 30 Å keeping number of layer pairs fixed at 10. It is observed that in low period W/B4C ML, as the layer thickness decreases, the interdiffusion plays a significant role because of the discontinuous nature of film. This gives variation of density and roughness of the layer as well as generates thickness errors in the ML structure due to volume changes which is originated by interdifusion process. Finally, W/B4C MLs with large number of layer pairs (300) are fabricated with periodicity d= 20 Å which gives ∼54 % of reflectivity at energy 8.047 keV

  18. Development and Characterization of B4C Reinforced Detonation-Sprayed Al Coatings

    Science.gov (United States)

    Tillmann, W.; Hollingsworth, P. S.; Fischer, G.; Nellesen, J.; Beckmann, F.

    2014-02-01

    Because of their excellent properties aluminum and its alloys cover a wide range of applications especially in the lightweight construction sector. In order to reach a higher strength and wear resistance metal matrix composites (MMCs) are used. Typically Al MMCs are manufactured by casting or extrusion processes. The disadvantage of these production routes is a cost-intensive and time-consuming finishing in terms of grinding and milling. The technique of thermal spraying provides the possibility to coat aluminum parts with MMCs close to their final shape. In addition to the shape accuracy the ductility and toughness of the coated parts are generally higher compared to extruded or casted parts. This study describes the development of detonation-sprayed boron carbide reinforced aluminum coatings on aluminum (EN AW 5754) substrates. The optimization of the coatings was focused on a homogeneous coating structure, a low coating porosity, a high deposition efficiency, a high number of embedded carbides, and a small percentage of oxides. In continuous tensile tests the influence of the MMC coating on the tensile strength was determined. Furthermore, the tensile strength was investigated in a discontinuous tensile test step by step. The different stages of deformation were analyzed by using micro computed tomography. This method enables the observation of tensile specimens in 3D, and consequently the site and moment of crack formation.

  19. Laser controlled melting of H12 hot-work tool steel with B4C particles at the surface

    Science.gov (United States)

    Yilbas, B. S.; Patel, F.; Karatas, C.

    2015-11-01

    Laser controlled melting of pre-prepared H12 hot-work tool steel surface is carried out. B4C particles in the carbon film are located at the workpiece surface prior to the laser treatment process. Nitrogen at high pressure is used as an assisting gas during the laser melting. Morphological and metallurgical changes in the treated layer are examined using scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. Microhardness of the treated surface is measured and the residual stress formed at the treated surface vicinity is obtained using the X-ray diffraction technique. It is found that a dense layer consisting of fine grains is formed at the treated surface. Microhardness of the treated surface improves significantly because of fine grains, nitride compounds formed at the surface and micro-stresses developed due to mismatched of thermal expansion coefficients of B4C and the base material. The residual stress formed at the surface is suppressed by the self annealing effect of the initially formed laser scans.

  20. Neutron reflectometry on highly absorbing films and its application to 10B4C-based neutron detectors

    Science.gov (United States)

    Piscitelli, F.; Khaplanov, A.; Devishvili, A.; Schmidt, S.; Höglund, C.; Birch, J.; Dennison, A. J. C.; Gutfreund, P.; Hall-Wilton, R.; Van Esch, P.

    2016-01-01

    Neutron reflectometry is a powerful tool used for studies of surfaces and interfaces. The absorption in the typical studied materials is neglected and this technique is limited only to the reflectivity measurement. For strongly absorbing nuclei, the absorption can be directly measured by using the neutron-induced fluorescence technique which exploits the prompt particle emission of absorbing isotopes. This technique is emerging from soft matter and biology where highly absorbing nuclei, in very small quantities, are used as a label for buried layers. Nowadays, the importance of absorbing layers is rapidly increasing, partially because of their application in neutron detection; a field that has become more active also due to the 3He-shortage. We extend the neutron-induced fluorescence technique to the study of layers of highly absorbing materials, in particular 10B4C. The theory of neutron reflectometry is a commonly studied topic; however, when a strong absorption is present the subtle relationship between the reflection and the absorption of neutrons is not widely known. The theory for a general stack of absorbing layers has been developed and compared to measurements. We also report on the requirements that a 10B4C layer must fulfil in order to be employed as a converter in neutron detection. PMID:26997902

  1. Fabrication of Al5083/B4C surface composite by friction stir processing and its tribological characterization

    Directory of Open Access Journals (Sweden)

    Narayana Yuvaraj

    2015-10-01

    Full Text Available Improved surface properties with the retainment of bulk properties are necessary for a component for enhanced wear characteristics. Friction stir processing (FSP is used to produce such surface composites. Fabrication of 5083 aluminum alloy with reinforced layers of boron carbide (B4C through FSP was carried out. Micro and nano sized B4C particles were used as reinforcements. The friction processed surface composite layer was analyzed through optical and scanning electron microscopical studies. The number of passes and the size of reinforcement play a vital role in the development of surface composites by FSP. Mechanical properties of the friction stir processed surface composites were evaluated through micro hardness and universal tensile tests. The results were compared with the properties of the base metal. The role of reinforcement and number of passes on properties were also evaluated. Tribological performance of the surface composites is tested through pin on disk test. The surface composite layer resulted in three passes with nano particle reinforcement exhibited better properties in hardness, tensile behavior and wear resistance compared to the behavior of the base metal.

  2. High frequency complex permeability of flake-shaped Fe74Cr2Mo2Sn2P10Si4B4C2 particle composite material

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A composite consisting of flake-shaped Fe74Cr2Mo2Sn2P10Si4B4C2 particles was prepared.The flake-shaped particles included in the composite were prepared by planetary ball milling.The complex permeability of the composite material was measured at frequency range from 10 MHz to 8.5 GHz.The permeability of the composite containing flake-shaped particles was much higher than that of the spherical particles.The permeability of particles was improved by means of heat-treatment.In contrast to the random-spatial-distributed flake-shaped particle composites,the oriented-distributed ones had a higher effective permeability.A model was proposed considering the orientation ratio,and our calculation agreed well with the experimental data.

  3. Investigation on the Behaviours of TiB2 Reinforced B4C-SiC Composites Against Co-60 Gamma Radioisotope Source

    OpenAIRE

    Bülent Büyük; Tuğrul, Beril A.

    2015-01-01

    In the present study, the gamma attenuation behaviours of the Titanium diboride (TiB2) reinforced boron carbide (B4C)-silicon carbide (SiC) composite materials were investigated against Co-60 gamma radioisotope source. In the experiments TiB2 unreinforced and 2% and 4% TiB2 (by volume) reinforced B4C-SiC composite materials were used. In the composite materials B4C/SiC ratio has been realized as 6/4 by volume. The linear and mass attenuation coefficients of the samples were carried out for Co...

  4. Effect of the content of B4C on microstructural evolution and wear behaviors of the laser-clad coatings fabricated on Ti6Al4V

    Science.gov (United States)

    Bai, L. L.; Li, J.; Chen, J. L.; Song, R.; Shao, J. Z.; Qu, C. C.

    2016-01-01

    TiNi/Ti2Ni-based composite coatings reinforced by TiC and TiB2 were produced on Ti6Al4V by laser cladding the mixture of a Ni-based alloy and different contents of B4C (0 wt%, 5 wt%, 15 wt%, and 25 wt%). The macromorphologies and microstructures of the coatings were examined through optical microscopy, X-ray diffractometry, scanning electron microscopy, and energy dispersive spectrometry. The microhardness, fracture toughness, and wear behaviors of the coatings were also investigated by using a microhardness tester and an ultra-functional wear testing machine. Results showed that the coatings were mainly composed of TiNi/Ti2Ni and TiC/TiB2 as the matrix and reinforcement particles, respectively. The phase constituents of the coatings were not influenced by addition of different contents of B4C. The microstructure of the reinforcements in the coatings presented the following evolution: hypereutectic consisting of blocky (TiC+TiB2)e eutectic and primary TiCp cellular dendrites (0 wt% B4C), mixture of hypereutectic and willow-shaped (TiB2+TiC)p pseudoeutectic (5 wt% B4C), and pseudoeutectic (15 and 25 wt% B4C). With increasing B4C content, the volume fraction and size of the pseudoeutectic structures as well as the average microhardness of the coatings (850, 889, 969, and 1002 HV0.2) were increased. By contrast, the average fracture toughness of the coatings was gradually decreased (4.47, 4.21, 4.06, and 3.85 Mpa m1/2) along with their wear volumes (0 wt%, 5 wt%, and 15 wt% B4C). The increase in B4C content to 25 wt% did not further reduce wear loss. The wear mechanism transformed from micro-cutting (0 wt% B4C) into a combination of micro-cutting and brittle debonding (5 wt% B4C) and finally led to brittle debonding (15 wt% and 25 wt% B4C). Coatings with suitable contents of B4C (less than 15 wt%) showed excellent comprehensive mechanical properties.

  5. Reactivity and neutron flux measurements in IPEN/MB-01 reactor with B4C burnable poison

    International Nuclear Information System (INIS)

    Burnable poison rods, made of B4C- Al2 O3 pellets with 5.01 mg/cm310 B concentration, have been manufactured for a set of experiments in the IPEN/MB-01 zero-power reactor. Several core parameters which are affected by the burnable poisons rods have been measured. The principal results, for the situation in which the burnable poison rods are located near the absorber rods of a control rod, are they cause a 29% rod worth shadowing, a reduction of 39% in the local void coefficient of reactivity, a reduction of 4.8% in the isothermal temperature coefficient of reactivity, and a reduction of 9% in the thermal neutron flux in the region where the burnable poison rods are located. These experimental results will be used for the validation of burnable poison calculation methods in the CTMSP. (author)

  6. Preparation and Its Properties of Vanadium Carbide Coating Through B4C Reducing V2O5

    Institute of Scientific and Technical Information of China (English)

    WangBiao; WangYudong; ZhangZihua

    2005-01-01

    A vanadium carbide coating on steel's substrates was prepared through B4C reducing V2O5 in molten salt bath. The thickness of VC-coating reached 14-18μm at 920℃ for 6h, and the hardness of VC-coating reached HV2200-HV2400. The sliding wear resistance of the VC-coating is not only 3350 times of that of SCN-coating, but also more excellent than that of other VC-coatings, prepared through aluminum reducing V2O5 or through TD processing. The experimental results indicate that the different VC-coating resistances to wear and corrosion increase with a raise of the free carbon contents in VC-coatings. The continuous service life of a tongue grooves of the high speed cigarette machines, with this VC-coating, reached good results of 140-150days.

  7. Fabrication and characterization of hybrid structured Al alloy matrix composites reinforced by high volume fraction of B4C particles

    International Nuclear Information System (INIS)

    In the present paper, hybrid structured B4C particles reinforced Al2024 matrix composites were prepared by the powder metallurgy method. The composites made from 100% mechanical milled composite powders have fracture strength of 670 MPa. With the addition of un-milled Al2024 powder increased from 10 vol% to 40 vol%, the room temperature compression strength decreased from 1115 MPa to 739 MPa, without any visible plastic deformation. However, when the fraction of un-milled Al2024 powder increased to 50 vol%, the compression strength was decreased to 580 MPa, while retaining a remarkable fracture strain up to 10%. The microstructures of the composites with different composition were examined by a scanning electron microscope and a transmission electron microscope. The contribution from different strengthening mechanisms was discussed. The hybrid structures are proved to account for the dramatic change of the fracture mechanism of the composites

  8. Synthesis of B4C-Nano TiB2 Composite Powder by Sol-Gel Method

    Science.gov (United States)

    Baharvandi, H. R.; Talebzadeh, N.; Ehsani, N.; Aghand, F.

    2009-04-01

    Production of (B4C-nano TiB2) composite powder by chemical method was evaluated in this study. Starting materials were boron carbide, carbon, and titanium (IV) iso propoxide (TTIP). Water was used as a hydrolyser agent. TTIP was hydrolyzed with water and, consequently, amorphous Ti(OH)4 was formed. Heat-treatment of Ti(OH)4 at 100 and 850 °C led to the production of TiO2 and TiB2 phases, respectively. The effect of heat-treatment time and temperature on the phase transformation and size of the produced nano powder were investigated. The produced nano powder was characterized by XRD, SEM, and DTA. It was found that heat-treatment time and temperature have significant effects on the amount and size of the produced TiB2 powder. The data also reveal that the minimum temperature for TiB2 formation is 650 °C.

  9. Porosity dependence of wear and other mechanical properties on fine-grain Al2O3 and B4C

    International Nuclear Information System (INIS)

    Macro (taber) wear tests and especially micro (pin-on-disk) tests performed on Al2O3 and B4C, as a function of varying porosity, show wear increasing exponentially with porosity. Al2O3, which was tested over a much more extensive range of porosity, showed a significant change in the porosity dependence of wear at approximately 20% porosity, which is attributed to densification. The same materials used for these wear tests were also used for measurement of Young's modulus, fexural strength, fracture toughness, and Vicker's hardness at room temperature, which all show an exponential dependence on porosity as expected. All but hardness show a lower porosity dependence of wear. Reasons for these differences are discussed

  10. Simulation response of B4C-coated PPAC for thermal neutrons using GEANT4 Monte Carlo approach

    Science.gov (United States)

    Jamil, M.; Rhee, J. T.; Jeon, Y. J.

    2013-08-01

    In this work we report a technique employed for the detection of thermal neutrons using the parallel plate avalanche counter (PPAC). In order to make the detector sensitive to thermal neutrons a thin layer of B4C has been coated on the forward electrode of the PPAC configuration. Upon falling on the converter coating, charged particles were generated via the 10B (n , α)7Li reaction. In this simulation study, thermal neutrons have been simulated using the GEANT4 MC code, and the response of the detector has been evaluated as a function of neutron energy. For a better understanding of the simulation response, the performance of the detector has been found using the two different physics list i.e., QGSP _ BIC _ HP and QGSP _ BERT _ HP. The obtained results predict that such boron-carbide based PPAC can be potentially utilized for thermal neutron detection. A complete description of the detector configuration and the simulation results is also presented.

  11. Influence of B4C to TTIP Molar Ratio on Synthesis of Nano Titanium Diboride Powders via Sol-Gel Method

    Science.gov (United States)

    Sinaei Pour Fard, Hamed; Baharvandi, Hamidreza; Abdizadeh, Hossein

    Titanium diboride (TiB2) has attracted great interests for its excellent mechanical properties, chemical resistance and good thermal and electrical conductivities. So it is widely applied as cutting tool composites, wear resistant parts, metal melting crucibles and electrode materials. This paper presents synthesis of nano titanium diboride powders via sol-gel method using a mixture of TTIP and B4C as precursors. In the hydrolysis step, B4C to TTIP molar ratio varied from 1.3 to 2.5. Solution samples stirred well and after aging and drying process, they were heat treated in an argon atmosphere. X-ray diffraction (XRD) patterns and Scanning electron microscopy (SEM) analysis showed that the percentage of synthesized TiB2 increased gradually as the molar ratio of B4C to TTIP reached to 2.3, afterward increasing the B4C to TTIP molar ratio caused decreasing of titanium diboride percentage.

  12. Effects of B4C addition on the micro- structural and thermal properties of hot pressed SiC ceramic matrix composites

    Directory of Open Access Journals (Sweden)

    Z. Keçeli

    2009-12-01

    Full Text Available Purpose: The purpose of paper is to evaluate effects of B4C addition on the microstructural and thermal properties of hot pressed SiC ceramic matrix composites.Design/methodology/approach: The effect of B4C addition on microstructural and thermal properties of the SiC-B4C powder composites were investigated after high energy milling and hot pressing. SiC powders containing 5wt%, 10wt%, 15wt% B4C were mechanically alloyed in a high energy ball mill for 8 h.Findings: Microstructural characterisation investigations (SEM, XRD were carried out on mechanically alloyed SiC powder composites containing 5 wt %, 10 wt %, 15 wt % B4C powders and on these powder composites sintered in vacuum at 50 MPa at 2100ºC. The thermal properties were characterised using DTA, TGA and dilatometer. The results were evaluated.Research limitations/implications: In this study, the effect of B4C addition on microstructural and mechanical properties of the SiC-B4C powder composites was investigated after high energy milling and hot pressing.Originality/value: Ceramic matrix composite (CMC material systems are stimulating a lot of interest to be used and provide unique properties for aircraft and land-based turbine engines, defence applications, rocket motors, aerospace hot structures and industrial applications. Boron carbide (B4C-silicon carbide (SiC ceramic composites are very promising armour materials because they are intrinsically very hard. Advanced SiC-based armour is desired so that the projectile is completely defeated without penetrating the ceramic armour.

  13. Chemical compatibility of B4C/Na/S.S.. Pt.1: The effects of temperature and B/C ratio

    International Nuclear Information System (INIS)

    B4C pellets with different B/C ratio and nuclear purity grade sodium were put into a stainless steel cladding tubes and the out-of-pile tests were carried out at 550, 650 and 750 degree C. The test period is 82 d. After compatibility test, the appearance of B4C pellets is integral, and crack or break are not found. However, the surfaces become rough and original metal luster is lost. The chemical reaction product NaB5O8 deposits and adheres to the surface of B4C pellets. This results in the volume increasing of B4C pellets. No considerable change in microstructure and grain size of B4C pellets are observed. There are B, Na and C penetrate into cladding inner surface. The amount of B and Na penetration increases with the temperature and B/C ratio increasing, but C penetration is opposite. The chemical reaction products among Na, impurities in sodium, B4C and cladding are NaBO2 , Cr2B, Fe2B and Ni3B. The formation of the borides made increasing considerably in microhardness at the cladding inner surface

  14. Photocatalytic CO2 reduction over B4C/C3N4 with internal electric field under visible light irradiation.

    Science.gov (United States)

    Zhang, Xiaojie; Wang, Lei; Du, Quanchao; Wang, Zhiyong; Ma, Shuguo; Yu, Miao

    2016-02-15

    Boron carbide/graphitic carbon nitride (B4C/g-C3N4) p-n hetero-junction photocatalyst with an internal electric field was synthesized by a facile solvent evaporation method and characterized by field emission scanning electron microscope (FESEM), UV-Vis diffuse reflectance spectra (UV-Vis DRS), photoluminescence spectra (PL), etc. Photocatalytic activity of the composite B4C/g-C3N4 loaded with Pt co-catalyst was evaluated using CO2 conversion to CH4 with H2 as the hydrogen source and reductant under visible light irradiation. The coupling of p-type B4C with n-type g-C3N4 significantly improved the performance of photocatalytic CO2 reduction; with the optimum B4C mass fraction of 1/6, the composite photocatalyst showed approximately 6 and 8 times higher CH4 generation rate than g-C3N4 and B4C, respectively. The enhancement was attributed to efficient photo-excited electron/hole separation due to the formation of internal electric field at the p-B4C/n-C3N4 interface. PMID:26609927

  15. Effects of B4C Addition on the Laser Beam Welding Characteristics of Al/SiC MMCs Produced By P/M

    Directory of Open Access Journals (Sweden)

    Serdar KARAOĞLU

    2011-01-01

    Full Text Available Fusion weldability characteristics of metal matrix composites (MMC produced by powder metallurgy (P/M are usually insufficient due to unwanted micro-structural changes that occur during welding. This study aims to investigate the effects of B4C addition as reinforcement on the weld quality of Al/SiC MMCs. After the production of Al/SiC MMCs by P/M with or without the addition of B4C, laser beam welding (LBW characteristics of the materials were investigated by focusing on the integrity of the welds. Optical microscopy (OM, scanning electron microscopy (SEM, and energy dispersive X-ray analysis (EDX were utilized for the characterization of the welds. Results show that Al/SiC MMCs produced by P/M can not be easily welded by LBW, but weldability characteristics of the material can be improved by the addition of B4C.

  16. High heat flux testing of B4C/Cu and SiC/Cu functionally graded materials simulated by laser and electron beam

    International Nuclear Information System (INIS)

    B4C, SiC and C, Cu functionally graded-materials (FGMs) have been developed by plasma spraying and hot pressing. Their high-heat flux properties have been investigated by high energy laser and electron beam for the simulation of plasma disruption process of the future fusion reactors. And a study on eroded products of B4C/Cu FGM under transient thermal load of electron beam was performed. In the experiment, SEM and EDS analysis indicated that B4C and SiC were decomposed, carbon was preferentially evaporated under high thermal load, and a part of Si and Cu were melted, in addition, the splash of melted metal and the particle emission of brittle destruction were also found. Different erosive behaviors of carbon-based materials (CBMs) caused by laser and electron beam were also discussed

  17. Investigation on the Behaviours of TiB2 Reinforced B4C-SiC Composites Against Co-60 Gamma Radioisotope Source

    Directory of Open Access Journals (Sweden)

    Bülent Büyük

    2015-02-01

    Full Text Available In the present study, the gamma attenuation behaviours of the Titanium diboride (TiB2 reinforced boron carbide (B4C-silicon carbide (SiC composite materials were investigated against Co-60 gamma radioisotope source. In the experiments TiB2 unreinforced and 2% and 4% TiB2 (by volume reinforced B4C-SiC composite materials were used. In the composite materials B4C/SiC ratio has been realized as 6/4 by volume. The linear and mass attenuation coefficients of the samples were carried out for Co60 gamma radioisotope source which has two energy peaks (1.17 and 1.33 MeV. Then mass attenuation coefficients and half-value thicknesses (HVT of the materials were calculated. Experimental mass attenuation coefficients were compared with the theoretical values which were calculated from XCOM computer code. Furthermore HVTs of the samples were evaluated and compared each other. It has been seen that the experimental and theoretical mass attenuation coefficients are closed to each other and differences are under 10 percent. In addition, TiB2 reinforced B4C-SiC composites have smaller HVTs than unreinforced one. Moreover 4% TiB2 reinforced B4C-SiC composite has smaller HVT than the 2% reinforced sample. Reinforcing TiB2 and increasing TiB2 ratio increase the gamma attenuation property of the B4C-SiC composites against Co-60 gamma radioisotope source.

  18. The effect of carbon on the synthesis of the carbon-free B4C powder by carbothermic reduction of B2O3

    International Nuclear Information System (INIS)

    Boron carbide(B4C) is the one of the hardest materials that has been interesting in ceramic industries and is now used as high abrasive materials in power form and as a neutron absorber due to the high cross section area for neutron. Generally, boric acid or B2O3 and carbon are used to form B4C (2B2O3+7C=B4C+6CO). However, the complete reaction of the carbon is difficult because the reaction by-product, carbon monoxide, takes volatile boric species away from the reaction site. In this present research, to minimize the amount of free carbon present in the product, a carbon deficiency composition is selected. Some parameters of the process in obtaining the B4C powder without free carbon in the carbothermal reduction have been studied. X-ray diffraction analysis was carried our for phase analysis, and the morphology and the particle size of synthesized powders were investigated by SEM

  19. Low pressure hot pressing of B4C matrix ceramic composites improved by Al2O3 and TiC additives

    International Nuclear Information System (INIS)

    B4C matrix ceramic composites toughened by Al2O3 and TiC were prepared by low pressure hot pressing. The relative density, Vickers hardness, fracture toughness and flexural strength of the new fabricated composites were measured. Microstructure observations of the fracture surfaces and the indentation cracks of the B4C matrix ceramic composites were analyzed, and an X-ray diffraction phase analysis was performed. The experiment results showed that chemical reactions took place during the low pressure hot pressing process and resulted in the B4C/Al2O3/TiB2 composite. The densification rate of the B4C matrix ceramic composites was enhanced and the mechanical properties were improved via the introduction of Al2O3 and TiC additives. The Vickers hardness, fracture toughness and flexural strength of the composite with the addition of 4.7 wt.% Al2O3 and 10 wt.% TiC were 24.8 GPa, 4.8 MPa m1/2 and 445 MPa, respectively.

  20. The effect of strontium on the microstructure, porosity and tensile properties of A356-10%B4C cast composite

    International Nuclear Information System (INIS)

    This study was undertaken to investigate the effect of different concentrations of strontium (0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 1%) on the microstructure, porosity content and tensile properties of A356-10%B4C particulate metal matrix composite. In this work, the matrix alloy and composite were characterized by optical microscope, scanning electron microscope equipped with EDS and XRD. The composite ingots were made by stir casting process. The results showed that the addition of 0.03%Sr strongly modified silicon eutectic phase in A356 monolithic alloy, but 0.5%Sr was needed to complete the modification of A356-10%B4C composite. Results also demonstrated that Sr addition increases shrinkage porosity and generates new intermetallics in the microstructure. Further investigations on tensile tests revealed optimum strontium levels for improving tensile properties. In the point of fracture behavior of the composite, modified specimens with 0.2%Sr showed broken B4C particles and acceptable cohesion between B4C and matrix.

  1. Impact of B4C capping layer for extreme ultraviolet mask on the sensitivity of patterned mask inspection using a projection electron microscope

    Science.gov (United States)

    Iida, Susumu; Hirano, Ryoichi; Amano, Tsuyoshi; Watanabe, Hidehiro

    2014-10-01

    The inspection sensitivity of a patterned extreme ultraviolet mask with B4C-capped multilayer (ML) was investigated using a simulated projection electron microscope (PEM) image. Extrusion and intrusion defects with 16-nm size were detected with their intensity of >10 times the standard deviation of the background level on a half-pitch 64-nm line-and-space pattern. The defect detection sensitivity in this case was higher than that of a Ru-capped ML sample and has a potential to meet the requirement for beyond 16-nm node generation from the standpoint of patterned mask inspection using the PEM technique. These results indicate that the B4C capping layer, besides its good durability, has an advantage for high sensitivity of patterned mask inspection. The optimal condition of the incident beam energy was found to be 500 and 1,000 eV for the samples of B4C-capped ML and B4C-buffered Ru-capped ML, respectively. The sensitivity of defect detection was strongly affected by the difference of secondary electron emission coefficients (SEECs) between the absorber layer and capping layer. However, the small incident beam energy was found to be preferable when the SEEC difference was relatively high.

  2. Impact of B4C capping layer for EUV mask on the sensitivity of patterned mask inspection using projection electron microscope

    Science.gov (United States)

    Iida, Susumu; Hirano, Ryoichi; Amano, Tsuyoshi; Watanabe, Hidehiro

    2014-10-01

    The inspection sensitivity of a patterned extreme ultraviolet (EUV) mask with B4C capped multilayer (ML) was investigated using a simulated projection electron microscope (PEM) image. Extrusion and intrusion defects with 16 nm in size were detected with their intensity of > 10 times the standard deviation of the background level on a half-pitch (hp) 64 nm line and space pattern. The defect detection sensitivity in this case was higher than that of Ru capped ML sample, and has a potential to meet the requirement for beyond 16 nm node generation from the standpoint of patterned mask inspection using the PEM technique. These results indicate that B4C capping layer besides its good durability has an advantage for high sensitivity of patterned mask inspection. The optimal condition of the incident beam energy was found to be 500 and 1000 eV for the samples of B4C capped ML and B4C buffered Ru capped ML, respectively. The sensitivity of defect detection was strongly affected by the difference of secondary electron emission coefficients (SEECs) between the absorber layer and capping layer. However, severely scattered electrons near the pattern edge become a source of noise and then they block the effect of large SEEC difference. Thus, the small incident beam energy was found to be preferable when the SEEC difference was relatively high.

  3. Friction and wear studies in N-implanted Al2O3, SiC, TiB2, and B4C ceramics

    International Nuclear Information System (INIS)

    Bulk polycrystalline samples of sintered Al2O3, and hot-pressed Al2 O3 , SiC, TiB2 , and B4 C ceramics were ion implanted at 77 K with 190 keV N+ to a dose of 3 x 1017 N/cm2. Nitrogen implantation resulted in reduced friction coefficients for SiC, TiB2 , and B4 C samples and a reduction in wear for TiB2. Both Al2 O3 samples showed a significant increase in friction coefficients after nitrogen implantation. Nitrogen-implantation-induced changes in these properties appear to be correlated with the thermodynamic tendency of the sample to form ''nitridelike'' bonds

  4. A Comparative Study on SiC-B4C-Si Cermet Prepared by Pressureless Sintering and Spark Plasma Sintering Methods

    Science.gov (United States)

    Sahani, P.; Karak, S. K.; Mishra, B.; Chakravarty, D.; Chaira, D.

    2016-06-01

    Silicon carbide (SiC)-boron carbide (B4C) based cermets were doped with 5, 10, and 20 wt pct Silicon (Si) and their sinterability and properties were investigated for conventional sintering at 2223 K (1950 °C) and spark plasma sintering (SPS) at 1623 K (1350 °C). An average particle size of ~3 µm was obtained after 10 hours of milling. There is an enhancement of Vickers microhardness in the 10 wt pct Si sample from 18.10 in conventional sintering to 27.80 GPa for SPS. The relative density, microhardness, and indentation fracture toughness of the composition SiC60(B4C)30Si10 fabricated by SPS are 98 pct, 27.80 GPa, and 3.8 MPa m1/2, respectively. The novelty of the present study is to tailor the wettability and ductility of the cermet by addition of Si into the SiC-B4C matrix. Better densification with improved properties is achieved for cermets consolidated by SPS at lower temperatures than conventional sintering.

  5. A Comparative Study on SiC-B4C-Si Cermet Prepared by Pressureless Sintering and Spark Plasma Sintering Methods

    Science.gov (United States)

    Sahani, P.; Karak, S. K.; Mishra, B.; Chakravarty, D.; Chaira, D.

    2016-03-01

    Silicon carbide (SiC)-boron carbide (B4C) based cermets were doped with 5, 10, and 20 wt pct Silicon (Si) and their sinterability and properties were investigated for conventional sintering at 2223 K (1950 °C) and spark plasma sintering (SPS) at 1623 K (1350 °C). An average particle size of ~3 µm was obtained after 10 hours of milling. There is an enhancement of Vickers microhardness in the 10 wt pct Si sample from 18.10 in conventional sintering to 27.80 GPa for SPS. The relative density, microhardness, and indentation fracture toughness of the composition SiC60(B4C)30Si10 fabricated by SPS are 98 pct, 27.80 GPa, and 3.8 MPa m1/2, respectively. The novelty of the present study is to tailor the wettability and ductility of the cermet by addition of Si into the SiC-B4C matrix. Better densification with improved properties is achieved for cermets consolidated by SPS at lower temperatures than conventional sintering.

  6. Development of electroless Ni-P-B4C composite coatings%镍-磷-碳化硼化学复合镀层的研制

    Institute of Scientific and Technical Information of China (English)

    KARTHIKEYAN S; VENKATACHALAM G; SRINIVASAN K N; VASUDEVAN T; NARAYANAN S

    2011-01-01

    Ni-P-B4C composite coatings were prepared on mild steel by electroless plating from a stable bath containing nickel carbonate 15 g/L, hypophosphorous acid 32 mL/L, sodium hypophosphite 15 g/L, lactic acid 32 mL/L, acetic acid 18 g/L, propionic acid 3 mL/L, dimethylamine 1.7 g/L, and boron carbide (B4C) particles 0-25 g/L. The microhardness of the composite coatings was examined by Vickers tester, the wear resistance by Taber abrasion tester, the microscopic morphology and structure by SEM and X-ray diffraction, and the corrosion resistance by potenfiodynamic polarization and electrochemical impedance spectroscopy. The incorporation of B4C increases the microhardness, wear resistance, and corrosion resistance of the Ni-P alloy matrix. The Ni-P-B4C composite coating features a popcorn-like structure with coarse-grained composite particles.%在由碳酸镍15 g/L、次磷酸32 mL/L、次磷酸钠15 g/L、乳酸32mL/L、乙酸189/L、丙酸3mL/L、二甲胺1.7g/L及碳化硼(即B4C)0~25 g/L组成的稳定镀液中,采用化学镀的方法在低碳钢上制备了Ni-P-B4C复合镀层.其显微硬度采用韦氏硬度法测量,耐磨性用Taber磨耗试验机测量,微观形貌和组织采用扫描电镜和X射线衍射进行分析,耐蚀性以动电位极化及电化学阻抗谱测定.碳化硼的掺入提高了镍-磷合金基体的显微硬度、耐磨性和耐蚀性.Ni-P-B4C复合镀层颗粒粗大,具有爆米花式组织结构.

  7. Carbon-rich icosahedral boron carbides beyond B4C and their thermodynamic stabilities at high temperature and pressure from first principles

    Science.gov (United States)

    Ektarawong, A.; Simak, S. I.; Alling, B.

    2016-08-01

    We investigate the thermodynamic stability of carbon-rich icosahedral boron carbide at different compositions, ranging from B4C to B2C , using first-principles calculations. Apart from B4C , generally addressed in the literature, B2.5C , represented by B10C2p (C-C), where Cp and (C-C) denote a carbon atom occupying the polar site of the icosahedral cluster and a diatomic carbon chain, respectively, is predicted to be thermodynamically stable under high pressures with respect to B4C as well as pure boron and carbon phases. The thermodynamic stability of B2.5C is determined by the Gibbs free energy G as a function of pressure p and temperature T , in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. The stability range of B2.5C is then illustrated through the p -T phase diagrams. Depending on the temperatures, the stability range of B2.5C is predicted to be within the range between 40 and 67 GPa. At T ≳ 500 K, the icosahedral Cp atoms in B2.5C configurationally disorder at the polar sites. By investigating the properties of B2.5C , e.g., elastic constants and phonon and electronic density of states, we demonstrate that B2.5C is both mechanically and dynamically stable at zero pressure, and is an electrical semiconductor. Furthermore, based on the sketched phase diagrams, a possible route for experimental synthesis of B2.5C as well as a fingerprint for its characterization from the simulations of x-ray powder diffraction pattern are suggested.

  8. Determination of gamma ray attenuation coefficients of Al–4% Cu/B4C metal matrix composites at 662, 1173 and 1332 keV

    Indian Academy of Sciences (India)

    I Akkurt; K Günoğlu; A Çalik; M S Karakas

    2014-08-01

    Gamma ray attenuation coefficients of metal matrix composites have been investigated. For this purpose, the linear attenuation coefficients of composites containing boron carbide (B4C) at different rates have been measured using a gamma spectrometer that contains a NaI(Tl) detector and MCA at 662, 1173 and 1332 keV, which are obtained from 137Cs and 60Co sources. The measured results were compared with the calculation obtained using computer code of XCOM for 1 keV–1 GeV gamma energies.

  9. Chemical compatibility of B-4C/Na/S.S. system. Pt.2: Effects of test period and oxygen content in sodium

    International Nuclear Information System (INIS)

    The simulation specimens of the fast breeder reactor' control rod were put into the thermal convection sodium loop, and the out of pile tests for B4C/Na/S.S. system chemical compatibility were performed at 550 degree C, and the effects of the test period and oxygen content in sodium on the compatibility characters were investigated. The appearance of B4C pellets is integral, and crack or break are not found after compatible test. There is B penetration in cladding inner surface, the amount of B penetration is proportional to the square root of the test period. The depth of B penetration is not changed with the add of the test period. The microhardness at the cladding inner surface increases clearly, its increment is increasing slightly with the add of the test period. The depth of the hardening layers is about 40 μm for different test periods. The reaction products Cr2B, Na4B10O17, B6Fe23, CrB, Nib and NiB12 are formed according to priority at the cladding inner surface for 80 to 400 d. The diffusion of B into the cladding relates to the temperature, test period and the oxygen content, and the oxygen promotes the B diffusion

  10. Degree of crystallinity and strain in B4C and SiC thin films as a function of processing conditions

    International Nuclear Information System (INIS)

    Amorphous and crystalline content in sputtered B4C and SiC thin films has been analyzed by synchrotron grazing incidence x-ray scattering (GIXS). GIXS provided quantitative information on the average structure while TEM was used to find inhomogeneities such as small volume fraction phases. GIXS results were compared to simulations to determine average particle size or bond length for crystalline or amorphous phases respectively. In this work, the authors compared results from films deposited with, and without, an RF bias applied to the substrate during deposition. Results indicated that SiC can be described as strained polycrystalline material with particle size of approximately 13 angstrom for biased samples and 9 angstrom for unbiased samples. Boron carbide deposited without bias was completely crystalline with a particle size of approximately 30 angstrom, while the data suggested that B4C deposited with bias is amorphous. The scattering from the biased materials was fourier transformed to yield radial distribution functions (RDF). This provided nearest neighbor distances, and it was demonstrated that the technique can be used to determine full three-dimensional strain tensors in amorphous thin films

  11. Characterization of ion-bombardment induced modifications of periodic La/B4C-multilayer-mirrors for the reflection of soft X-ray radiation

    International Nuclear Information System (INIS)

    The applicability of reflective optical components for the soft X-Ray region depends on the existence of multilayer-optics. Therefore stacks of alternating layers of two materials with different refractive index are applied. For the photon energy range of 100-190 eV Lanthanum (La) is favoured as the absorber material and Boroncarbide (B4C) as the spacer material. Thin periodic layer systems of those materials with double layer periods of 5.6 nm have been produced by UHV Electron Beam Evaporation. The layer thickness is controlled by in-situ X-Ray Reflectometry. The purity and the stoichiometry of the layers has been analyzed by electron beam induced in-situ Auger Spectroscopy. Ion Polishing of each interface should diminish the interface roughness and thus enhance the reflectivity. The modification of the La- and B4C-layers due to ion bombardment has been investigated by the in-situ Auger Spectroscopy, ex-situ X-Ray Diffraction and at-wavelength reflectivity measurements by use of Synchrotron radiation at the BESSY II facility. Effects of compaction, mixing, sputter-etching and smoothing have been found. The modifications can be influenced by varying the kinetic energy of the ions and/or the duration of the treatment.

  12. Proton-induced nanorod melting in a coating obtained from the pulsed laser ablation of W2B5/B4C

    International Nuclear Information System (INIS)

    Highlights: • Coatings from ablated B4C/W2B5 were irradiated with 900 keV protons. • Nanorod clusters were observed to melt and disperse. • Uniformly shaped nanorods were observed to grow. • Lateral diffusion of energy and lateral dispersion of matter were observed. - Abstract: Coatings obtained from pulsed laser ablated W2B5/B4C were irradiated with 900keV protons at fluences ranging from about 1×1015protons/cm2 to about 4×1015protons/cm2. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to study the resulting structural effects. Clusters of nanorods were observed to disperse and reduce in number with increase in proton fluence. The atomic percentage of constituent elements were observed to vary with proton fluence, both within the nanorods and the film floor. Our results show that the structural effect of proton irradiation on the coating is lateral dispersion of matter

  13. The mechanism of thermal explosion (TE) synthesis of TiC–TiB2 particulate locally reinforced steel matrix composites from an Al–Ti–B4C system via a TE-casting route

    International Nuclear Information System (INIS)

    Highlights: ► We successfully fabricated TiC–TiB2 locally reinforced steel matrix composites. ► We investigated the product microstructure and formation mechanism of TiC and TiB2. ► The formation mechanism during casting is dependent on B4C particle size. ► Fe melt promotes the full dissociation of remnant B4C particles during casting. ► The relationship between the mechanisms in the ERF and during casting was proposed. - Abstract: TiC–TiB2 particulate locally reinforced steel matrix composites were fabricated by a novel TE-casting route from an Al–Ti–B4C system with various B4C particle sizes. The formation mechanism of TiC and TiB2 in the locally reinforced regions was investigated. The results showed that TiC and TiB2 are formed and precipitated from Al–Ti–B–C melt resulting from the dissociation of B4C into Al–Ti melt when the concentrations of B and C atoms in the Al–Ti–B–C melt become saturated. However, in the case of coarse B4C powders (≥40 μm) used, the primary reaction in the Al–Ti–B–C melt is quite limited due to the poor dissociation of B4C. The poured steel melt infiltrates into the primary reaction product and thus leads to the formation of Al–Fe–Ti–B–C melt, thanks to the favorable reaction of molten Fe with remnant B4C, and then TiC and TiB2 are further formed and precipitated from the saturated Al–Fe–Ti–B–C melt. The relationship between the mechanisms of thermal explosion (TE) synthesis of TiC and TiB2 in the electric resistance furnace and during casting was proposed.

  14. Oxidative desulfurization: kinetic modelling.

    Science.gov (United States)

    Dhir, S; Uppaluri, R; Purkait, M K

    2009-01-30

    Increasing environmental legislations coupled with enhanced production of petroleum products demand, the deployment of novel technologies to remove organic sulfur efficiently. This work represents the kinetic modeling of ODS using H(2)O(2) over tungsten-containing layered double hydroxide (LDH) using the experimental data provided by Hulea et al. [V. Hulea, A.L. Maciuca, F. Fajula, E. Dumitriu, Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides, Appl. Catal. A: Gen. 313 (2) (2006) 200-207]. The kinetic modeling approach in this work initially targets the scope of the generation of a superstructure of micro-kinetic reaction schemes and models assuming Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Subsequently, the screening and selection of above models is initially based on profile-based elimination of incompetent schemes followed by non-linear regression search performed using the Levenberg-Marquardt algorithm (LMA) for the chosen models. The above analysis inferred that Eley-Rideal mechanism describes the kinetic behavior of ODS process using tungsten-containing LDH, with adsorption of reactant and intermediate product only taking place on the catalyst surface. Finally, an economic index is presented that scopes the economic aspects of the novel catalytic technology with the parameters obtained during regression analysis to conclude that the cost factor for the catalyst is 0.0062-0.04759 US $ per barrel. PMID:18541367

  15. Oxidative desulfurization: Kinetic modelling

    International Nuclear Information System (INIS)

    Increasing environmental legislations coupled with enhanced production of petroleum products demand, the deployment of novel technologies to remove organic sulfur efficiently. This work represents the kinetic modeling of ODS using H2O2 over tungsten-containing layered double hydroxide (LDH) using the experimental data provided by Hulea et al. [V. Hulea, A.L. Maciuca, F. Fajula, E. Dumitriu, Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides, Appl. Catal. A: Gen. 313 (2) (2006) 200-207]. The kinetic modeling approach in this work initially targets the scope of the generation of a superstructure of micro-kinetic reaction schemes and models assuming Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Subsequently, the screening and selection of above models is initially based on profile-based elimination of incompetent schemes followed by non-linear regression search performed using the Levenberg-Marquardt algorithm (LMA) for the chosen models. The above analysis inferred that Eley-Rideal mechanism describes the kinetic behavior of ODS process using tungsten-containing LDH, with adsorption of reactant and intermediate product only taking place on the catalyst surface. Finally, an economic index is presented that scopes the economic aspects of the novel catalytic technology with the parameters obtained during regression analysis to conclude that the cost factor for the catalyst is 0.0062-0.04759 US $ per barrel

  16. Reactivity determination of the Al2O3-B4C burnable poison as a function of its concentration in the IPEN/MB-01 reactor

    International Nuclear Information System (INIS)

    Burnable poison rods made of Al2O3-B4C pellets with different concentrations of 10B have been manufactured for a set of experiments in the IPEN/MB-01 zero-power reactor. The experiments evaluated the reactivity of the burnable poison rods as a function of the 10B concentration, and the shadowing effect on the control rod reactivity worth as a function of the distance between the burnable position rods and the control rod. The results showed that the burnable poison rods have a non-linear behavior as function of the 10 B concentration, starting to reach an asymptotic value for concentrations higher than 7 g/cm3 of 10B. The shadowing effect on the control rods was substantial. When the burnable poison rods were beside the control rod, its reactivity worth decreased as much as 30 %, and when they were 10,5 cm distant, the control rod worth decreased by 7 %. The MCNP results for the burnable poison reactivity effects agreed within experimental errors with the measured values. (author)

  17. Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics

    Science.gov (United States)

    Ektarawong, A.; Simak, S. I.; Hultman, L.; Birch, J.; Tasnádi, F.; Wang, F.; Alling, B.

    2016-04-01

    The elastic properties of alloys between boron suboxide (B6O) and boron carbide (B13C2), denoted by (B6O)1-x(B13C2)x, as well as boron carbide with variable carbon content, ranging from B13C2 to B4C are calculated from first-principles. Furthermore, the mixing thermodynamics of (B6O)1-x(B13C2)x is studied. A superatom-special quasirandom structure approach is used for modeling different atomic configurations, in which effects of configurational disorder between the carbide and suboxide structural units, as well as between boron and carbon atoms within the units, are taken into account. Elastic properties calculations demonstrate that configurational disorder in B13C2, where a part of the C atoms in the CBC chains substitute for B atoms in the B12 icosahedra, drastically increase the Young's and shear modulus, as compared to an atomically ordered state, B12(CBC). These calculated elastic moduli of the disordered state are in excellent agreement with experiments. Configurational disorder between boron and carbon can also explain the experimentally observed almost constant elastic moduli of boron carbide as the carbon content is changed from B4C to B13C2. The elastic moduli of the (B6O)1-x(B13C2)x system are also practically unchanged with composition if boron-carbon disorder is taken into account. By investigating the mixing thermodynamics of the alloys, in which the Gibbs free energy is determined within the mean-field approximation for the configurational entropy, we outline the pseudo-binary phase diagram of (B6O)1-x(B13C2)x. The phase diagram reveals the existence of a miscibility gap at all temperatures up to the melting point. Also, the coexistence of B6O-rich as well as ordered or disordered B13C2-rich domains in the material prepared through equilibrium routes is predicted.

  18. Helium release and physical property change of neutron-irradiated α-SiC containing B4C of different 10B concentrations

    International Nuclear Information System (INIS)

    Sintered α-SiC ceramics containing B4C with various 10B concentrations were neutron-irradiated, and the helium release rate during increasing annealing temperature was observed. The lattice parameter and the macroscopic length changes of the same specimens were also observed. The helium release rate from powdered specimens increased markedly above 650degC, and showed a sharp peak at ∼1,160degC independent of the 10B concentration, but the rate was higher for the specimen containing higher concentration of 10B. The macroscopic volume of the SiC specimen with higher 10B concentration was expanded larger than that of the lower one by the irradiation. The unit cell volume change was mostly independent of 10B concentration, whereas the each axis changed different manner. A-axis started to shrink around the irradiation temperature, and contracted mostly linearly with increasing annealing temperature. On the other hand, contraction of the c-axis was not parallel to that of a-axis, and was retarded between 500-1,100degC. It is supposed that helium will induce some lattice defects, which expands c-axis length of SiC. These defects retained up to 1,100degC with support of helium migration. During the annealing, the expansion of macroscopic length occurred at higher temperature than 1,300degC, where the higher 10B concentration specimen gave the larger expansion, indicating the formation of grain boundary helium bubbles. (author)

  19. Ternary rare earth metal boride carbides containing two-dimensional boron-carbon network: The crystal and electronic structure of R2B4C (R=Tb, Dy, Ho, Er)

    International Nuclear Information System (INIS)

    The ternary rare earth boride carbides R2B4C (R=Tb, Dy, Ho, Er) have been synthesized by reacting the elements at temperatures between 1800 and 2000K. The crystal structure of Dy2B4C has been determined from single-crystal X-ray diffraction data. It crystallizes in a new structure type in the orthorhombic space group Immm (a=3.2772(6) A, b=6.567(2) A, c=7.542(1) A, Z=2, R1=0.035 (wR2=0.10) for 224 reflections with Io>2σ(Io)). Boron atoms form infinite chains of fused B6 rings in [100] joined with carbon atoms into planar, two-dimensional networks which alternate with planar sheets of rare earth metal atoms. The electronic structure of Dy2B4C was also analyzed using the tight-binding extended Hueckel method. - Graphical abstract: Dy2B4C crystallizes a new structure type where planar 63-Dy metal atom layers alternate with planar non-metal layers consisting of ribbons of fused B6 hexagons bridged by carbon atoms. Isostructural analogues with Tb, Ho and Er have also been characterized

  20. 以聚碳硅烷包覆B4C为原料温压-烧结原位制备SiC/B4C复相陶瓷%SiC/B4C Multiphase Ceramics Using Polycarbosilane-Coating B4C as Raw Materials Prepared In-suit by Warm Pressing and Sintering

    Institute of Scientific and Technical Information of China (English)

    林文松; 何亮

    2011-01-01

    B4 C/SiC pellets were prepared by warm pressing of polycarbosilane-coating boron carbide powder at the temperature of 300 ℃ under the pressure of 50 Mpa, and cold isostatic pressing under the pressure of 800 Mpa, respectively. The samples were then kept warm at 1 200 ℃ for 2 h in flowing Ar, with subsequent sintering for 3 h between 1 800 and 2 000 ℃ in vacuum. Relative densities, phases and microstructures of the multiphase ceramics were investigated. The results show that the multiphase ceramics prepared by warm pressing (WP) had higher density than that by cold isostatic pressing (CIP). The multiphase ceramics with maximum relative density was achieved after the warm pressing green bodies containing 15% SiC sintered for 3 h, and its relative density was more than 93%. The multiphase ceramics consisted of B4C and SiC and SiC phases distributed uniformly on the B1C particles interface.%以聚碳硅烷(PCS)包覆B4C粉为原料,分别在300℃、50 MPa下温压成型和800MPa下冷等静压成型,而后将压坯置于氩气气氛保护下在1 200℃保温2 h,再在1 800~2 000℃下真空烧结3 h,原位反应制备出SiC/B4C复相陶瓷;研究了它的相对密度、物相组成和显微结构。结果表明:温压工艺比冷等静压工艺能得到更高密度的复相陶瓷;合15%SoC的温压压坯在烧结3 h后得到复相陶瓷的相对密度大于93%;复相陶瓷由B4C和SiC相组成,SiC相均匀分布在B4C颗粒界面上。

  1. Influence of LOTUS concrete structure, boron-loaded sheets, and B4C filter on the integral tritium production of a nature lithium graphite-reflected blanket and comparison with experiment

    International Nuclear Information System (INIS)

    Integral tritium production rate (TPR) measurements are important in comparisons of calculations to ascertain the suitability of computer codes and cross-section sets used in calculation. At the LOTUS facility, one of the objectives is to make measurements with different types of pure fusion and hybrid blankets and compare the results with calculations. Since the concrete cavity housing the blankets is small, it is of direct relevance to determine the influence of room-reflected neutrons on the integral TPR and, if possible, to reduce this effect by special absorbers. The effects on the TPR of a stainless steel-natural lithium-graphite-reflected blanket due to the concrete structure, B4C filter, and boron-loaded sheets covering the assembly are studied. Calculations are performed by the MCNP Monte Carlo code. Since the room-returned component depends strongly on the composition of the concrete and, more-over, does not correspond to a real blanket situation, it is advisable to compare measurements with calculations for the region where such interference is minimal. A central region is identified for the purpose of comparison. In addition to calculations for a fully homogenized blanket, the important central blanket region is considered in the form of rods, and the remaining blanket as a homogeneous region, to assess the effect of neutron streaming on the TPR of the assembly. An experiment is done by irradiating several Li2CO3 probes positioned in each tube so that the central region of interest is fully covered. The activity of the probes is measured by the standard liquid scintillation method, and the TPR for the entire region can be derived from the experimental reaction rate data. The complete details of the calculational model and the experimental procedure are provided. Good agreement is found between the calculated and experimental TPRs after accounting for various sources of errors. 14 refs., 6 figs., 4 tabs

  2. Chemical Compatibility of B4C/Na/S.S.Ⅰ.The Effects of Temperature and B/C Ratio%B4C/Na/S.S.三元体系的化学相容性Ⅰ.温度效应及B/C比的影响

    Institute of Scientific and Technical Information of China (English)

    许咏丽; 龙斌; 张道德

    2000-01-01

    在堆用不锈钢包壳管内分别填装不同B/C比的B4C芯块及核级钠,以模拟快堆控制棒内的B4C/Na/S.S.三元体系,在堆外550、650和750 ℃下相互作用82 d.试验后的B4C芯块外观完整,未见掉角、龟裂或破碎;表面变得粗糙,失去原有的金属光泽,化学反应产物NaB5O8等在表面沉积和粘附,并导致B4C芯块体积增大;芯块的微观结构和晶粒度试验前后无明显变化.包壳管内表面渗B、渗Na和渗C,渗B和渗Na量均随温度升高和B/C比增大而增加,渗C则反之.Na和Na中杂质以及B4C与包壳间的化学反应产物为NaBO2、Cr2B、Fe2B和Ni3B.B化物的形成使包壳管内表面显微硬度显著增大.

  3. Wet oxidation of a spacecraft model waste

    Science.gov (United States)

    Johnson, C. C.; Wydeven, T.

    1985-01-01

    Wet oxidation was used to oxidize a spacecraft model waste under different oxidation conditions. The variables studied were pressure, temperature, duration of oxidation, and the use of one homogeneous and three heterogeneous catalysts. Emphasis is placed on the final oxidation state of carbon and nitrogen since these are the two major components of the spacecraft model waste and two important plant nutrients.

  4. Creep behavior in interlaminar shear of a Hi-NicalonTM/ SiC-B4C composite at 1200∘C in air and in steam

    OpenAIRE

    Ruggles-Wrenn Marina; Pope Matthew

    2015-01-01

    Creep behavior in interlaminar shear of a non-oxide ceramic composite with a multilayered matrix was investigated at 1200∘C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-NicalonTM fibers woven in a five-harness-satin weave. Fiber preforms had pyrolytic carbon fiber coatin...

  5. In situ synthesis of TiB2-TiC particulates locally reinforced medium carbon steel-matrix composites via the SHS reaction of Ni-Ti-B4C system during casting

    International Nuclear Information System (INIS)

    The fabrication of medium carbon steel-matrix composites locally reinforced with in situ TiB2-TiC particulates using self-propagating high-temperature synthesis (SHS) reaction of Ni-Ti-B4C system during casting was investigated. X-ray diffraction (XRD) results reveal that the exotherm of 1042 deg. C initiated by heat release of the solid state reaction in the differential thermal analysis (DTA) curve is an incomplete reaction in Ni-Ti-B4C system. As-cast microstructures of the in situ processed composites reveal a relatively uniform distribution of TiB2-TiC particulates in the locally reinforced regions. Furthermore, the particulate size and micro-porosity in the locally reinforced regions are significantly decreased with the increasing of the Ni content in the preforms. For a Ni content of 30 and 40 wt.%, near fully dense composites locally reinforced with in situ TiB2 and TiC particulates can be fabricated. Although most of fine TiB2 and TiC particulates which form by the reaction-precipitation mechanism during SHS reaction are present in the locally reinforced region, some large particulates which form by the nucleation-growth mechanism during solidification are entrapped inside the Fe-rich region located in the reinforcing region or inside the matrix region nearby the interface between matrix and reinforcing region. The hardness of the reinforcing region in the composite is significantly higher than that of the unreinforced medium carbon steel. Furthermore, the hardness values of the composites synthesized from 30 to 40 wt.% Ni-Ti-B4C systems are higher than those of the composites synthesized from 10 to 20 wt.% Ni-Ti-B4C systems

  6. Chemical Compatibility of B4C/Na/S.S. System Ⅱ. Effects of Test Period and Oxygen Content in Sodium%B4C/Na/S.S.三元体系化学相容性研究Ⅱ.相容时间及钠中氧含量的影响

    Institute of Scientific and Technical Information of China (English)

    许咏丽; 龙斌; 张道德

    2000-01-01

    将快堆控制棒模拟样品置于高温热对流钠回路中,于550 ℃下进行B4C/Na/S.S.三元体系化学相容性试验,研究相容时间及钠中氧含量对相互作用特性的影响.结果表明:试验后的B4C芯块完整,无掉角、龟裂或破碎;包壳管内表面渗B,渗B量与相容时间的平方根成正比,渗B深度不随相容时间变化;包壳管内表面显微硬度明显升高,其升高幅度随相容时间增长略有增大,不同相容时间下的硬化层深度均约为40 μm;相容时间从80 d增加到400 d,包壳管内表面相继出现反应产物Cr2B,Na4B10O17,B6Fe23,CrB和NiB,NiB12;B向包壳管内表面的扩散与温度、相容时间及钠中氧含量有关,氧对B的扩散起促进作用.

  7. Creep behavior in interlaminar shear of a Hi-NicalonTM/ SiC-B4C composite at 1200∘C in air and in steam

    Directory of Open Access Journals (Sweden)

    Ruggles-Wrenn Marina

    2015-01-01

    Full Text Available Creep behavior in interlaminar shear of a non-oxide ceramic composite with a multilayered matrix was investigated at 1200∘C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI. The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-NicalonTM fibers woven in a five-harness-satin weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. The interlaminar shear properties were measured. The creep behavior was examined for interlaminar shear stresses in the 16–22 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. In air and in steam, creep run-out defined as 100 h at creep stress was achieved at 16 MPa. Similar creep strains were accumulated in air and in steam. Furthermore, creep strain rates and creep lifetimes were only moderately affected by the presence of steam. The retained properties of all specimens that achieved run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated. The tested specimens were also examined using electron probe microanalysis (EPMA with wavelength dispersive spectroscopy (WDS. Analysis of the fracture surfaces revealed significant surface oxidation, but only trace amounts of boron and carbon. Cross sectional analysis showed increasing boron concentration in the specimen interior.

  8. Creep behavior in interlaminar shear of a Hi-Nicalon™/SiC–B4C composite at 1200 °C in air and in steam

    International Nuclear Information System (INIS)

    Creep behavior in interlaminar shear of a non-oxide ceramic composite with a multilayered matrix was investigated at 1200 °C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon™ fibers woven in a five-harness-satin weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. The interlaminar shear properties were measured. The creep behavior was examined for interlaminar shear stresses in the 16–22 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. In air and in steam, creep run-out defined as 100 h at creep stress was achieved at 16 MPa. Similar creep strains were accumulated in air and in steam. Furthermore, creep strain rates and creep lifetimes were only moderately affected by the presence of steam. The retained properties of all specimens that achieved run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated. The tested specimens were also examined using electron probe microanalysis (EPMA) with wavelength dispersive spectroscopy (WDS). Analysis of the fracture surfaces revealed significant surface oxidation, but only trace amounts of boron and carbon. Cross sectional analysis showed increasing boron concentration in the specimen interior

  9. Effect of Mg/B2O3 molar ratio and furnace temperature on the phase evaluation and morphology of SiC–B4C nanocomposite prepared by MASHS method

    International Nuclear Information System (INIS)

    In this study, SiC–B4C nanocomposite has been synthesized in situ successfully by Mechanical activated combustion synthesis method (MASHS). Initially Si, C, B2O3 and Mg powders as raw materials were weighed according to different molar ratio of Mg to B2O3. In next step theses materials were milled in a planetary mill under Ar atmosphere. The synthesis step was performed in a tube furnace equipped with controlled atmosphere system. The different furnace temperature was investigated on the phase synthesis and morphology of the products. The specimens in the various steps were studied by XRD analysis for evaluation of the phase compositions and calculation of the average crystallite size of them. The morphology of synthesized products was investigated by scanning and transmission electron microscopes (SEM&TEM). The final product contains main phases MgO, B4C and SiC. Also, In this sample byproducts were characterized such as Mg3B2O6, Mg2B2O5 and remaining carbon. XRD pattern of synthesized sample showed the considerable effect of increasing Mg to B2O3 molar ratio on reducing the amount of Mg3B2O6, Mg2B2O5 and remaining carbon. SiC–B4C composite was synthesized with more homogenous morphology by reducing the furnace temperature from 1000 to 900 °C, but reduction of temperature up to 800 °C give rise to uncompleted reaction whereas some unreacted Si remains. Average crystallite sizes of optimal sample were calculated 10.5 and 8 nm for SiC and B4C respectively. These values are consisted of the TEM results somehow while grain size was less than 70 nm. Also SEM observation showed fine grains with sizes falling in the nanometer range. - Graphical abstract: Display Omitted - Highlights: • Composite prepared by combustion synthesis method in system of Si, C, B2O3 and Mg. • More than stoichiometric Mg/B2O3 molar ratio cause to more complete synthesis. • Lower than 900 °C furnace temperature cause to incomplete synthesis. • Nanocomposite with a high

  10. The human polynucleotide kinase/phosphatase (hPNKP) inhibitor A12B4C3 radiosensitizes human myeloid leukemia cells to Auger electron-emitting anti-CD123 111In-NLS-7G3 radioimmunoconjugates

    International Nuclear Information System (INIS)

    Introduction: Leukemia stem cells (LSCs) are believed to be responsible for initiating and propagating acute myeloid leukemia (AML) and for causing relapse after treatment. Radioimmunotherapy (RIT) targeting these cells may improve the treatment of AML, but is limited by the low density of target epitopes. Our objective was to study a human polynucleotide kinase/phosphatase (hPNKP) inhibitor that interferes with DNA repair as a radiosensitizer for the Auger electron RIT agent, 111In-NLS-7G3, which recognizes the CD123+/CD131- phenotype uniquely displayed by LSCs. Methods: The surviving fraction (SF) of CD123+/CD131- AML-5 cells exposed to 111In-NLS-7G3 (33–266 nmols/L; 0.74 MBq/μg) or to γ-radiation (0.25-5 Gy) was determined by clonogenic assays. The effect of A12B4C3 (25 μmols/L) combined with 111In-NLS-7G3 (16–66 nmols/L) or with γ-radiation (0.25–2 Gy) on the SF of AML-5 cells was assessed. The density of DNA double-strand breaks (DSBs) in the nucleus was measured using the γ-H2AX assay. Cellular dosimetry was estimated based on the subcellular distribution of 111In-NLS-7G3 measured by cell fractionation. Results: Binding of 111In-NLS-7G3 to AML-5 cells was reduced by 2.2-fold in the presence of an excess (1 μM) of unlabeled NLS-7G3, demonstrating specific binding to the CD123+/CD131- epitope. 111In-NLS-7G3 reduced the SF of AML-5 cells from 86.1 ± 11.0% at 33 nmols/L to 10.5 ± 3.6% at 266 nmols/L. Unlabeled NLS-7G3 had no significant effect on the SF. Treatment of AML-5 cells with γ-radiation reduced the SF from 98.9 ± 14.9% at 0.25 Gy to 0.03 ± 0.1% at 5 Gy. A12B4C3 combined with 111In-NLS-7G3 (16–66 nmols/L) enhanced the cytotoxicity up to 1.7-fold compared to treatment with radioimmunoconjugates alone and was associated with a 1.6-fold increase in DNA DSBs in the nucleus. A12B4C3 enhanced the cytotoxicity of γ-radiation (0.25–0.5 Gy) on AML-5 cells by up to 1.5-fold, and DNA DSBs were increased by 1.7-fold. Exposure to 111In-NLS-7G3

  11. Al-B4C复合材料在硼酸溶液中腐蚀机理研究%Corrosion Mechanism of Al-B4C Composite Materials in Boric Acid

    Institute of Scientific and Technical Information of China (English)

    石建敏; 沈春雷; 张玲; 雷家荣; 龙兴贵; 周晓松

    2012-01-01

    采用硼酸溶液模拟乏燃料贮存水池环境,研究A1-B4C复合材料在其中的腐蚀行为.用SEM、EDS观测腐蚀试样的微观形貌,用XRD测试腐蚀前后试样的物相,并测试腐蚀过程中试样的干重.结果表明:材料中的Al是引起腐蚀的主要因素;0~500 ppm硼酸溶液中,试样腐蚀增重,在表面生成斜晶结构的Al(OH)3氧化膜,对材料起一定保护作用;2500 ppm硼酸溶液中,试样腐蚀增重,在表面沉积非晶结构的Al(OH)3絮状腐蚀产物;10 000~25000 ppm硼酸溶液中,试样腐蚀失重,表面局部微小区域可观察到龟裂和腐蚀“坑”生成.材料抗腐蚀性能随溶液硼酸浓度的增加而降低,欲提高材料抗腐蚀性能,需对其进行表面保护处理.%A boric acid solution was used to simulate the environment of actual spent fuel storage. The corrosion behaviors of A1-B4C composite materials in boric acid solutions were investigated. The microscopic morphology was observed by SEM and EDS. The phases of samples before and after the corrosion tests were measured by XRD and the dry weight of the samples was also measured. The results show that the corrosion is caused by aluminum in the A1-B4C composite; a dense layer of A1(OH)3 is formed after corrosion test in boric acid solution at 0 to 500 ppm and the samples gain weight after corrosion test; an amorphous A1(OH)3 sediments with wadding structure are found after corrosion in boric acid solution at 2 500 ppm and the samples also gain weight; some local areas appeared chapped and the corroded pits can be observed after corrosion in boric solution at 10 000 to 25 000 ppm and the samples lost weight. The corrosion resistance decreases with the increasing of concentration of boric acid. In order to improve the corrosion resistance, it is necessary to make a surface protection on A1-B4C composite.

  12. COSP - A computer model of cyclic oxidation

    Science.gov (United States)

    Lowell, Carl E.; Barrett, Charles A.; Palmer, Raymond W.; Auping, Judith V.; Probst, Hubert B.

    1991-01-01

    A computer model useful in predicting the cyclic oxidation behavior of alloys is presented. The model considers the oxygen uptake due to scale formation during the heating cycle and the loss of oxide due to spalling during the cooling cycle. The balance between scale formation and scale loss is modeled and used to predict weight change and metal loss kinetics. A simple uniform spalling model is compared to a more complex random spall site model. In nearly all cases, the simpler uniform spall model gave predictions as accurate as the more complex model. The model has been applied to several nickel-base alloys which, depending upon composition, form Al2O3 or Cr2O3 during oxidation. The model has been validated by several experimental approaches. Versions of the model that run on a personal computer are available.

  13. SCALE UP OF Si/Si0.8Ge0.2 AND B4C/B9C SUPERLATTICES FOR HARVESTING OF WASTE HEAT IN DIESEL ENGINES

    Energy Technology Data Exchange (ETDEWEB)

    Martin, P; Olsen, L

    2003-08-24

    Thermoelectric devices show significant promise for harvesting and recovery of waste heat from diesel engines, exhaust systems and industrial heat sources. While these devices convert a heat flow directly into electrical energy, cooling can be accomplished by the same device with application of a direct current (Peltier effect). Conversion efficiencies of bulk thermoelectric systems, however, are still too low for economical power conversion in diesel powered vehicles and heavy vehicles. Thermoelectric superlattice devices have demonstrated the potential for increased efficiencies and utilization of waste heat. Although reported efficiencies are well above 15%, fabrication costs are still too high for use in diesel engine systems. To realize this efficiency goal of {approx} 20% and power generation in the kWMW range, large quantities of superlattice materials are required. Additionally, if the figure of merit (ZT) of these superlattices can be increased to > 2, even less superlattice material will be required to generate electric power from heat in diesel engines. We report on development of and recent progress in scale up of Si/Si0.8Ge0.2 and B4C/B9C superlattices for thermoelectric applications, and particularly for fabrication of large quantities of these materials. We have scaled up the magnetron sputtering process to produce large quantities of Si/Si0.8Ge0.2 and B4 C/B9C superlattices with high ZT at low cost. Quantum well films with up to 1000 layers were deposited onto substrate areas as large as 0.5 m2 by magnetron sputtering. Initial studies showed that the power factor of these SL's was high enough to produce a ZT significantly greater than 1. Both p- and n-type superlattices were fabricated to form a complete thermoelectric power generating device. ZT measurements will be reported, and based on measured power factor of these materials, should be significantly greater than 1. These results are encouraging for the use of quantum well materials in

  14. Graphite oxidation modeling for application in MELCOR.

    Energy Technology Data Exchange (ETDEWEB)

    Gelbard, Fred

    2009-01-01

    The Arrhenius parameters for graphite oxidation in air are reviewed and compared. One-dimensional models of graphite oxidation coupled with mass transfer of oxidant are presented in dimensionless form for rectangular and spherical geometries. A single dimensionless group is shown to encapsulate the coupled phenomena, and is used to determine the effective reaction rate when mass transfer can impede the oxidation process. For integer reaction order kinetics, analytical expressions are presented for the effective reaction rate. For noninteger reaction orders, a numerical solution is developed and compared to data for oxidation of a graphite sphere in air. Very good agreement is obtained with the data without any adjustable parameters. An analytical model for surface burn-off is also presented, and results from the model are within an order of magnitude of the measurements of burn-off in air and in steam.

  15. Thermal Safety Analysis of Aluminum Matrix B4C In-Pile Irradiation%铝基碳化硼堆内辐照热工安全分析

    Institute of Scientific and Technical Information of China (English)

    米向秒; 钱达志; 邓勇军; 张之华; 黄洪文; 郭海兵

    2012-01-01

    Aluminum matrix B4C is a new structural material for spent fuel storage and related performances need in-depth research, especially the irradiation resistance capability. The thermal calculations were completed by using the CFD software to ensure the safety of the in-pile irradiation test. Considering the characteristic of the irradiation project, the thermal safety feature of the in-pile test was analyzed, and the irradiation project was optimized.q%铝基碳化硼是一种新型的乏燃料贮存架结构材料,需对其各项性能进行研究,其中,铝基碳化硼材料的耐辐照性能是关键参数之一.为进行铝基碳化硼材料的堆内辐照考验,并保证其在堆内辐照的安全,针对铝基碳化硼辐照方案的特点,采用了CFD程序进行热工校核计算,分析了铝基碳化硼材料在堆内辐照的安全特性,优化了堆内辐照方案.

  16. Oxide behaviour modelling progress in COMETHE

    International Nuclear Information System (INIS)

    An attempt has been made to develop a global model which simultaneously describes many important aspects of uranium oxide under irradiation. The individual models describing fuel structural changes, swelling and gas release, which were earlier separate from one another, are now part of a more realistic integral fuel model. Fission gas release depends now on an explicitely calculated open porosity, which is generated by fuel swelling; the latter is in turn connected to fission gas release. The paper describes the individual oxide models and how they are linked together. (author)

  17. Modelling of UO2 oxidation in steam

    International Nuclear Information System (INIS)

    A computer model has been developed for calculating oxidation of UO2 at high temperatures in steam oxidising conditions. Several methods to calculate the partial pressure of oxygen in the fuel and in the environment surrounding the fuel are available. The various methodologies have been compared and the best models have been compiled into a computer model which will be implemented into fuel thermal/mechanical behaviour codes such as FACTAR 2.0 (LOECI) and ELESIM/ELOCA. Calculations from the computer model have been compared to experimental results. The calculated oxidation reaction kinetics are in good agreement with the experimental data. (author)

  18. 铝基碳化硼材料堆内辐照方案设计%Design of Aluminum Matrix B4C In-Core Irradiation Test Program

    Institute of Scientific and Technical Information of China (English)

    袁姝; 冯琦杰; 郭海兵; 刘晓; 邓勇军

    2012-01-01

    铝基碳化硼是一种新型的乏燃料贮存格架用材料,为检验其辐照性能,需进行堆内辐照实验.本文从样品成分及形状、辐照罐结构、辐照位置等方面,对铝基碳化硼材料堆内辐照方案进行设计.经初步中子物理学和热工计算表明:在所选择的两个辐照孔道内进行辐照考验,试件所接受的累积γ射线照射剂量和相应的快中子积分注量均满足技术要求,且辐照罐样品入堆后对功率峰值因子、反应性、发热率等与堆运行安全相关因子的影响均在安全范围内.%As a new candidate for spent fuel storage framework material, in-core irradiation test for aluminum matrix boron carbide (B4C) was performed to evaluate its irradiation behavior. The experiment was designed and analyzed according to sample's composition and shape, irradiation box characters, and core arrangement. The neutronic and thermal hydraulic simulations indicate that the scheme of the experiment chosen can meet the requirement of all parameters, such as y dose, integral fast neutron flux, power peaking factor, core reactivity, and sample heating rate.

  19. Nonequilibrium Thermodynamic Model of Manganese Carbonate Oxidation

    Institute of Scientific and Technical Information of China (English)

    郝瑞霞; 彭省临

    1999-01-01

    Manganese carbonate can be converted to many kinds of manganese oxides when it is aerated in air and oxygen.Pure manganese carbonate can be changed into Mn3O4 and γ-MnOOH,and manganese carbonate ore can be converted to MnO2 under the air-aerating and oxygen-aerating circumstances.The oxidation process of manganese carbonate is a changing process of mineral association,and is also a converting process of valence of manganese itself.Not only equilibrium stat,but also nonequilibrium state are involved in this whole process,This process is an irreversible heterogeneous complex reaction,and oberys the nonequilibrium thermodynamic model,The oxidation rate of manganese cabonate is controlled by many factors,especially nonmanganese metallic ions which play an important role in the oxidation process of manganese carbonate.

  20. Application of Substitutional Model in Oxide Systems

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The application of substitutional model in oxide systems, in comparison with that of sublattice model, is discussed.The results show that in the case of crystalline phases and liquid phases without molecular-like associates or theshortage of element in sublattice, these two models get consistent in the description of the formalism of Gibbs freeenergies of phases and obtain the same result of phase diagram calculation when the valence of the cations keep thesame.

  1. Advanced oxidation processes: overall models

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, M. [Univ. de los Andes, Escuela Basica de Ingenieria, La Hechicera, Merida (Venezuela); Curco, D.; Addardak, A.; Gimenez, J.; Esplugas, S. [Dept. de Ingenieria Quimica. Univ. de Barcelona, Barcelona (Spain)

    2003-07-01

    Modelling AOPs implies to consider all the steps included in the process, that means, mass transfer, kinetic (reaction) and luminic steps. In this way, recent works develop models which relate the global reaction rate to catalyst concentration and radiation absorption. However, the application of such models requires to know what is the controlling step for the overall process. In this paper, a simple method is explained which allows to determine the controlling step. Thus, it is assumed that reactor is divided in two hypothetical zones (dark and illuminated), and according to the experimental results, obtained by varying only the reaction volume, it can be decided if reaction occurs only in the illuminated zone or in the all reactor, including dark zone. The photocatalytic degradation of phenol, by using titania degussa P-25 as catalyst, is studied as reaction model. The preliminary results obtained are presented here, showing that it seems that, in this case, reaction only occurs in the illuminated zone of photoreactor. A model is developed to explain this behaviour. (orig.)

  2. A Self-Consistent Model for Thermal Oxidation of Silicon at Low Oxide Thickness

    OpenAIRE

    Gerlach, Gerald; Maser, Karl

    2016-01-01

    Thermal oxidation of silicon belongs to the most decisive steps in microelectronic fabrication because it allows creating electrically insulating areas which enclose electrically conductive devices and device areas, respectively. Deal and Grove developed the first model (DG-model) for the thermal oxidation of silicon describing the oxide thickness versus oxidation time relationship with very good agreement for oxide thicknesses of more than 23 nm. Their approach named as general relationship ...

  3. Modelling the oxidation of defected fuel elements

    International Nuclear Information System (INIS)

    Interim dry storage of used fuel is an economical alternative to storage in water pools. The fuel must remain intact during the dry-storage period, otherwise future handling of the fuel will be expensive. Oxidation of defected fuel elements can lead to fuel disintegration. Thus it is important to be able to predict the extent of oxidation of defected fuel elements in a dry-storage facility. In this report, a model is developed for predicting the extent or rate of oxidation of defected fuel elements stored at temperatures up to 170 C. The model employs equivalent porous medium representation of the fuel and described the oxygen concentration in the fuel element using a reaction-diffusion equation. The one- and two-dimensional reaction-diffusion equations are solved on the assumption that the oxygen-fuel reaction is either zeroth or first order in the oxygen concentration. Dimensional analysis of the model equations shows that the solution depends explicitly on a single parameter p. The value of p can be calculated using data from the literature, or it can be estimated from the results of the CEX-1 experiments being carried out at Whiteshell Laboratories. The value of p, estimated from the CEX-1 results, is more than two orders of magnitude larger than the value of p calculated from literature data. Although some reasons for this large difference are suggested, further work is needed to resolve this discrepancy. (author). 16 refs., 2 tabs., 11 figs

  4. A Self-Consistent Model for Thermal Oxidation of Silicon at Low Oxide Thickness

    Directory of Open Access Journals (Sweden)

    Gerald Gerlach

    2016-01-01

    Full Text Available Thermal oxidation of silicon belongs to the most decisive steps in microelectronic fabrication because it allows creating electrically insulating areas which enclose electrically conductive devices and device areas, respectively. Deal and Grove developed the first model (DG-model for the thermal oxidation of silicon describing the oxide thickness versus oxidation time relationship with very good agreement for oxide thicknesses of more than 23 nm. Their approach named as general relationship is the basis of many similar investigations. However, measurement results show that the DG-model does not apply to very thin oxides in the range of a few nm. Additionally, it is inherently not self-consistent. The aim of this paper is to develop a self-consistent model that is based on the continuity equation instead of Fick’s law as the DG-model is. As literature data show, the relationship between silicon oxide thickness and oxidation time is governed—down to oxide thicknesses of just a few nm—by a power-of-time law. Given by the time-independent surface concentration of oxidants at the oxide surface, Fickian diffusion seems to be neglectable for oxidant migration. The oxidant flux has been revealed to be carried by non-Fickian flux processes depending on sites being able to lodge dopants (oxidants, the so-called DOCC-sites, as well as on the dopant jump rate.

  5. Research Progress in Boron Carbide-Aluminum Composites with Applications to Storage and Transportation of Reactor Spent Fuel%用于反应堆乏燃料贮存和运输的B4C/Al复合材料研究进展

    Institute of Scientific and Technical Information of China (English)

    鲜亚疆; 庞晓轩; 王伟; 刘鹏闯; 张鹏程

    2015-01-01

    B4C/Al复合材料是一种集结构和功能于一体的中子吸收材料,在反应堆乏燃料贮存和运输领域有着广阔的应用前景.综述了B4C/Al复合材料的主要制备工艺及国内外研究现状,并展望了未来的发展方向,最后指出随着我国核电事业的发展,B4C颗粒增强铝基复合材料将作为研究重点并在辐射屏蔽领域广泛应用.

  6. Modeling Nitrogen Oxides in the Lower Stratosphere

    Science.gov (United States)

    Kawa, S. Randy; Einaudi, Franco (Technical Monitor)

    2001-01-01

    This talk will focus on the status of current understanding (not a historical review) as regards modeling nitrogen oxides (NOy) in the lower stratosphere (LS). The presentation will be organized around three major areas of process understanding: 1) NOy sources, sinks, and transport to the LS, 2) NOy species partitioning, and 3) polar multiphase processes. In each area, process topics will be identified with an estimate of the degree of confidence associated with their representation in numerical models. Several exotic and/or speculative processes will also be discussed. Those topics associated with low confidence or knowledge gaps, weighted by their prospective importance in stratospheric chemical modeling, will be collected into recommendations for further study. Suggested approaches to further study will be presented for discussion.

  7. Modeling of oxide fuel dissolution kinetics

    International Nuclear Information System (INIS)

    Since the 1970's, CEA [1] has carried on research on the head-end steps of PWR and FBR-Na spent fuel reprocessing and more specifically the fuel dissolution step. It consists to convert the irradiated solid oxide into a nitrate solution by a hot nitric acid attack. As complementary approach of the usual experiments performed in specific hot cells facilities, the issue of modeling the kinetics of the oxide fuel dissolution has been developed. In a first phase, numerous experimental results have allowed a simple kinetic law to be established (in which the oxide dissolution rate is normalized to the surface unit), based on the theoretical concepts of heterogeneous kinetics and on some chemical considerations in an extended temperature range (70 deg. C to boiling point), acidity (2-9 M), and uranyl concentration (0-250 g/L), defining the effects of these three main parameters as in the following equation: ν(mg.cm-2.h-1) = kapp ([HNO3] + 2[UO2(NO3)2])aexp(-Eapp/RT). The same corresponding significant factors kapp, a, Eapp of this law were determined for various tests involving either single or mixed oxide or irradiated or non-irradiated fuel. It appears that the kinetic control of the heterogeneous reactions recovers an important complexity: physical phenomena of transfer at the interface and autocatalytic chemical phenomena by nitrogen compounds. Therefore, the macrostructure of the fuel has to be taken into account like the cracks networks [2] caused by the irradiation of the fuel in its cladding either the dislodged fuel powder fraction resulting from the cladding shearing. Some mathematical development is expected to consider hydrodynamics effects in the model. Furthermore, different burn-up spent fuel kinetic behaviors have indicated that the microstructure is another influent factor and demonstrate how important is to understand irradiation effects on the oxide from the crystal to the grain scale. In the same topics, plutonium-uranium oxide fuels have been

  8. Kinetic Modelling of Macroscopic Properties Changes during Crosslinked Polybutadiene Oxidation

    Science.gov (United States)

    Audouin, Ludmila; Coquillat, Marie; Colin, Xavier; Verdu, Jacques; Nevière, Robert

    2008-08-01

    The thermal oxidation of additive free hydroxyl-terminated polybutadiene (HTPB) isocyanate crosslinked rubber bulk samples has been studied at 80, 100 and 120 °C in air. The oxidation kinetics has been monitored by gravimetry and thickness distribution of oxidation products was determined by FTIR mapping. Changes of elastic shear modulus G' during oxidation were followed during oxidation at the same temperatures. The kinetic model established previously for HTPB has been adapted for bulk sample oxidation using previously determined set of kinetic parameters. Oxygen diffusion control of oxidation has been introduced into the model. The mass changes kinetic curves and oxidation products profiles were simulated and adequate fit was obtained. Using the rubber elasticity theory the elastic modulus changes were simulated taking into account the elastically active chains concentration changes due to chain scission and crosslinking reactions. The reasonable fit of G' as a function of oxidation time experimental curves was obtained.

  9. Modeling Degradation in Solid Oxide Electrolysis Cells

    Energy Technology Data Exchange (ETDEWEB)

    Manohar S. Sohal; Anil V. Virkar; Sergey N. Rashkeev; Michael V. Glazoff

    2010-09-01

    Idaho National Laboratory has an ongoing project to generate hydrogen from steam using solid oxide electrolysis cells (SOECs). To accomplish this, technical and degradation issues associated with the SOECs will need to be addressed. This report covers various approaches being pursued to model degradation issues in SOECs. An electrochemical model for degradation of SOECs is presented. The model is based on concepts in local thermodynamic equilibrium in systems otherwise in global thermodynamic no equilibrium. It is shown that electronic conduction through the electrolyte, however small, must be taken into account for determining local oxygen chemical potential, , within the electrolyte. The within the electrolyte may lie out of bounds in relation to values at the electrodes in the electrolyzer mode. Under certain conditions, high pressures can develop in the electrolyte just near the oxygen electrode/electrolyte interface, leading to oxygen electrode delamination. These predictions are in accordance with the reported literature on the subject. Development of high pressures may be avoided by introducing some electronic conduction in the electrolyte. By combining equilibrium thermodynamics, no equilibrium (diffusion) modeling, and first-principles, atomic scale calculations were performed to understand the degradation mechanisms and provide practical recommendations on how to inhibit and/or completely mitigate them.

  10. A temperature dependent ENDF/B-VI.8 ACE library for UO2, ThO2, Zirc4, SS AISI-348, H2O, B4C and Ag-In-Cd alloy

    International Nuclear Information System (INIS)

    Most MCNP standard neutron ACE libraries are processed at room temperature, 293,6 deg K. The temperature enters into the processing of the evaluation of a data file through the Doppler broadening of cross-sections. The nuclear fuel burnup usually takes place at reactor core temperatures much higher than room temperature, consequently, Monte Carlo burnup calculations should not only use the best cross-sections evaluations available but also use evaluations that are at temperatures approximating the temperatures of the application. In order to face the scarcity of temperature dependent MCNP cross-sections data to most isotopes, CDTN is developing an in-house temperature dependent neutron library for those nuclides commonly necessary in the systems simulated for the ongoing projects demanding Monte Carlo burnup. This paper describes the data processing of the ENDF/B-VI, release 8, using the NJOY99 code, towards provides this temperature dependent ACE library. Up to now fifty one elements and isotopes of the materials uranium oxide, thorium oxide, zircaloy-4, stainless steel AISI-348, light water, boron carbide and the silver-indium-cadmium alloy were processed at temperatures range from 293,6 deg K to 1200 deg K. Some benchmarks for thorium cycle described in the 'OECD/NEA International Handbook of Evaluated Criticality Safety Benchmark Experiments' were simulated using MCNP5 and the data set of this in-house library and the results usually agree with those obtained for the .60c standard MCNP neutron library for room temperature. (author)

  11. Simplified Modeling of Oxidation of Hydrocarbons

    Science.gov (United States)

    Bellan, Josette; Harstad, Kenneth

    2008-01-01

    A method of simplified computational modeling of oxidation of hydrocarbons is undergoing development. This is one of several developments needed to enable accurate computational simulation of turbulent, chemically reacting flows. At present, accurate computational simulation of such flows is difficult or impossible in most cases because (1) the numbers of grid points needed for adequate spatial resolution of turbulent flows in realistically complex geometries are beyond the capabilities of typical supercomputers now in use and (2) the combustion of typical hydrocarbons proceeds through decomposition into hundreds of molecular species interacting through thousands of reactions. Hence, the combination of detailed reaction- rate models with the fundamental flow equations yields flow models that are computationally prohibitive. Hence, further, a reduction of at least an order of magnitude in the dimension of reaction kinetics is one of the prerequisites for feasibility of computational simulation of turbulent, chemically reacting flows. In the present method of simplified modeling, all molecular species involved in the oxidation of hydrocarbons are classified as either light or heavy; heavy molecules are those having 3 or more carbon atoms. The light molecules are not subject to meaningful decomposition, and the heavy molecules are considered to decompose into only 13 specified constituent radicals, a few of which are listed in the table. One constructs a reduced-order model, suitable for use in estimating the release of heat and the evolution of temperature in combustion, from a base comprising the 13 constituent radicals plus a total of 26 other species that include the light molecules and related light free radicals. Then rather than following all possible species through their reaction coordinates, one follows only the reduced set of reaction coordinates of the base. The behavior of the base was examined in test computational simulations of the combustion of

  12. Model for low temperature oxidation during long term interim storage

    International Nuclear Information System (INIS)

    Low-alloyed steels or carbon steels are considered as candidate materials for the fabrication of some nuclear waste package containers for long term interim storage. The containers are required to remain retrievable for centuries. One factor limiting their performance on this time scale is corrosion. The estimation of the metal thickness lost by dry oxidation over such long periods requires the construction of reliable models from short-time experimental data. In a first step, models based on simplified oxidation theories have been derived from experimental data on iron and a low-alloy steel oxidation. Their extrapolation to long oxidation periods confirms that the expected damage due to dry oxidation could be small. In order to improve the reliability of these predictions advanced models taking into account the elementary processes involved in the whole oxidation mechanism, are under development. (authors)

  13. Multiscale model of metal alloy oxidation at grain boundaries.

    Science.gov (United States)

    Sushko, Maria L; Alexandrov, Vitaly; Schreiber, Daniel K; Rosso, Kevin M; Bruemmer, Stephen M

    2015-06-01

    High temperature intergranular oxidation and corrosion of metal alloys is one of the primary causes of materials degradation in nuclear systems. In order to gain insights into grain boundary oxidation processes, a mesoscale metal alloy oxidation model is established by combining quantum Density Functional Theory (DFT) and mesoscopic Poisson-Nernst-Planck/classical DFT with predictions focused on Ni alloyed with either Cr or Al. Analysis of species and fluxes at steady-state conditions indicates that the oxidation process involves vacancy-mediated transport of Ni and the minor alloying element to the oxidation front and the formation of stable metal oxides. The simulations further demonstrate that the mechanism of oxidation for Ni-5Cr and Ni-4Al is qualitatively different. Intergranular oxidation of Ni-5Cr involves the selective oxidation of the minor element and not matrix Ni, due to slower diffusion of Ni relative to Cr in the alloy and due to the significantly smaller energy gain upon the formation of nickel oxide compared to that of Cr2O3. This essentially one-component oxidation process results in continuous oxide formation and a monotonic Cr vacancy distribution ahead of the oxidation front, peaking at alloy/oxide interface. In contrast, Ni and Al are both oxidized in Ni-4Al forming a mixed spinel NiAl2O4. Different diffusivities of Ni and Al give rise to a complex elemental distribution in the vicinity of the oxidation front. Slower diffusing Ni accumulates in the oxide and metal within 3 nm of the interface, while Al penetrates deeper into the oxide phase. Ni and Al are both depleted from the region 3-10 nm ahead of the oxidation front creating voids. The oxide microstructure is also different. Cr2O3 has a plate-like structure with 1.2-1.7 nm wide pores running along the grain boundary, while NiAl2O4 has 1.5 nm wide pores in the direction parallel to the grain boundary and 0.6 nm pores in the perpendicular direction providing an additional pathway for oxygen

  14. Multiscale model of metal alloy oxidation at grain boundaries

    International Nuclear Information System (INIS)

    High temperature intergranular oxidation and corrosion of metal alloys is one of the primary causes of materials degradation in nuclear systems. In order to gain insights into grain boundary oxidation processes, a mesoscale metal alloy oxidation model is established by combining quantum Density Functional Theory (DFT) and mesoscopic Poisson-Nernst-Planck/classical DFT with predictions focused on Ni alloyed with either Cr or Al. Analysis of species and fluxes at steady-state conditions indicates that the oxidation process involves vacancy-mediated transport of Ni and the minor alloying element to the oxidation front and the formation of stable metal oxides. The simulations further demonstrate that the mechanism of oxidation for Ni-5Cr and Ni-4Al is qualitatively different. Intergranular oxidation of Ni-5Cr involves the selective oxidation of the minor element and not matrix Ni, due to slower diffusion of Ni relative to Cr in the alloy and due to the significantly smaller energy gain upon the formation of nickel oxide compared to that of Cr2O3. This essentially one-component oxidation process results in continuous oxide formation and a monotonic Cr vacancy distribution ahead of the oxidation front, peaking at alloy/oxide interface. In contrast, Ni and Al are both oxidized in Ni-4Al forming a mixed spinel NiAl2O4. Different diffusivities of Ni and Al give rise to a complex elemental distribution in the vicinity of the oxidation front. Slower diffusing Ni accumulates in the oxide and metal within 3 nm of the interface, while Al penetrates deeper into the oxide phase. Ni and Al are both depleted from the region 3–10 nm ahead of the oxidation front creating voids. The oxide microstructure is also different. Cr2O3 has a plate-like structure with 1.2–1.7 nm wide pores running along the grain boundary, while NiAl2O4 has 1.5 nm wide pores in the direction parallel to the grain boundary and 0.6 nm pores in the perpendicular direction providing an additional pathway for

  15. Modeling for CVD of Solid Oxide Electrolyte

    Energy Technology Data Exchange (ETDEWEB)

    Starr, T.L.

    2002-09-18

    Because of its low thermal conductivity, high thermal expansion and high oxygen ion conductivity yttria-stabilized zirconia (YSZ) is the material of choice for high temperature electrolyte applications. Current coating fabrication methods have their drawbacks, however. Air plasma spray (APS) is a relatively low-cost process and is suitable for large and relatively complex shapes. it is difficult to produce uniform, relatively thin coatings with this process, however, and the coatings do not exhibit the columnar microstructure that is needed for reliable, long-term performance. The electron-beam physical vapor deposition (EB-PVD) process does produce the desirable microstructure, however, the capital cost of these systems is very high and the line-of-sight nature of the process limits coating uniformity and the ability to coat large and complex shapes. The chemical vapor deposition (CVD) process also produces the desirable columnar microstructure and--under proper conditions--can produce uniform coatings over complex shapes. CVD has been used for many materials but is relatively undeveloped for oxides, in general, and for zirconia, in particular. The overall goal of this project--a joint effort of the University of Louisville and Oak Ridge National Laboratory (ORNL)--is to develop the YSZ CVD process for high temperature electrolyte applications. This report describes the modeling effort at the University of Louisville, which supports the experimental work at ORNL. Early work on CVD of zirconia and yttria used metal chlorides, which react with water vapor to form solid oxide. Because of this rapid gas-phase reaction the water generally is formed in-situ using the reverse water-gas-shift reaction or a microwave plasma. Even with these arrangements gas-phase nucleation and powder formation are problems when using these precursors. Recent efforts on CVD of zirconia and YSZ have focused on use of metal-organic precursors (MOCVD). These are more stable in the gas

  16. Oxidative activation of methane over MgO model catalysts

    OpenAIRE

    Schwach, P.

    2014-01-01

    The role of surface structure and defects in the oxidative coupling of methane (OCM) was studied over magnesium oxide as a model catalyst. Pure MgO nano-particles with varying primary particle size, shape and specific surface area were prepared by sol-gel synthesis, oxidation of metallic magnesium and hydrothermal post treatments. Kinetic studies reveal the occurrence of two parallel reaction mechanisms and a change in the contribution of these pathways to the overall performance of the catal...

  17. Local scale plume model for nitrogen oxides. Model description

    Energy Technology Data Exchange (ETDEWEB)

    Persson, C.; Funkquist, L.

    1984-09-01

    A plume dispersion model on local scale (0 to approximately 20 km) including atmospheric chemistry for nitrogen is developed. The purpose of the study is to obtain a practical air quality model wich can be used in environmental planning for eg coal fired power plants. Problems concerning both high concentrations of NO/sub 2/ in the air and deposition of different nitrogen compounds to the ground is considered. The instantaneous plume dilution is described - assuming total mixing within the plume - as a function of emission parameters and meteorological conditions. The interplay of emissions, instantaneous plume dilution, entrainment of polluted ambient air, meteorological conditions and atmospheric chemistry processes determines production or loss of the different compounds. On a local scale only six chemical reactions need to be included. On a somewhat larger scale the number of reactions needed increases substantially. For the numerical solution we have used the method by Gear. In order to obtain hourly mean values of different nitrogen oxides and long-term deposition values conventional Gaussian respectively K-formulation procedures are used. Meteorological input data are obtained from climatological observations and also generated by a boundery layer model. From the results it is obvious that the meteorological conditions and the ambient ozone concentration are of great importance for the relative amount of NO/sub 2/ in the plume. On a local geographical scale the plume chemistry is diffusion controlled. (Author).

  18. Extension of silicon emission model to silicon pillar oxidation

    Science.gov (United States)

    Kageshima, Hiroyuki; Shiraishi, Kenji; Endoh, Tetsuo

    2016-08-01

    Missing Si in the oxidation of Si pillar structures is investigated by extending the Si emission model to the oxidation of planar structures. The original Si emission model [H. Kageshima et al., Jpn. J. Appl. Phys. 38, L971 (1999)] assumes the emission of excess Si from the interface into the oxide during the oxidation process, the diffusion of the excess Si through the oxide, and the control of the oxidation rate by the concentration of remaining excess Si around the interface. By assuming the sublimation of the excess Si from the oxide surface in addition to the assumptions of the original Si emission model, the origin of the missing Si is consistently explained. It is suggested that the amount of the missing Si is enhanced by the geometrical effect of the pillar structure because the concentration of excess Si is inversely proportional to the radial position. This also suggests that the missing Si is inevitable for the thin pillar structures. Careful approaches to the oxidation process are recommended for pillar structures.

  19. Implementation of model predictive control on a hydrothermal oxidation reactor

    Energy Technology Data Exchange (ETDEWEB)

    Muske, K.R. [Villanova Univ., PA (United States). Dept. of Chemical Engineering; Dell`Orco, P.C.; Le, L.A.; Flesner, R.L. [Los Alamos National Lab., NM (United States). High Explosives Science and Technology Group

    1998-12-31

    This paper describes the model-based control algorithm developed for a hydrothermal oxidation reactor at the Pantex Department of Energy facility in Amarillo, Texas. The combination of base hydrolysis and hydrothermal oxidation is used for the disposal of PBX 9404 high explosive at Pantex. The reactor oxidizes the organic compounds in the hydrolysate solutions obtained from the base hydrolysis process. The objective of the model predictive controller is to minimize the total aqueous nitrogen compounds in the effluent of the reactor. The controller also maintains a desired excess oxygen concentration in the reactor effluent to ensure the complete destruction of the organic carbon compounds in the hydrolysate.

  20. Model for low temperature oxidation during long term interim storage

    International Nuclear Information System (INIS)

    For high-level nuclear waste containers in long-term interim storage, dry oxidation will be the first and the main degradation mode during about one century. The metal lost by dry oxidation over such a long period must be evaluated with a good reliability. To achieve this goal, modelling of the oxide scale growth is necessary and this is the aim of the dry oxidation studies performed in the frame of the COCON program. An advanced model based on the description of elementary mechanisms involved in scale growth at low temperatures, like partial interfacial control of the oxidation kinetics and/or grain boundary diffusion, is developed in order to increase the reliability of the long term extrapolations deduced from basic models developed from short time experiments. Since only few experimental data on dry oxidation are available in the temperature range of interest, experiments have also been performed to evaluate the relevant input parameters for models like grain size of oxide scale, considering iron as simplified material. (authors)

  1. Effects of Oxidation on Oxidation-Resistant Graphite

    Energy Technology Data Exchange (ETDEWEB)

    Windes, William [Idaho National Lab. (INL), Idaho Falls, ID (United States); Smith, Rebecca [Idaho National Lab. (INL), Idaho Falls, ID (United States); Carroll, Mark [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-05-01

    The Advanced Reactor Technology (ART) Graphite Research and Development Program is investigating doped nuclear graphite grades that exhibit oxidation resistance through the formation of protective oxides on the surface of the graphite material. In the unlikely event of an oxygen ingress accident, graphite components within the VHTR core region are anticipated to oxidize so long as the oxygen continues to enter the hot core region and the core temperatures remain above 400°C. For the most serious air-ingress accident which persists over several hours or days the continued oxidation can result in significant structural damage to the core. Reducing the oxidation rate of the graphite core material during any air-ingress accident would mitigate the structural effects and keep the core intact. Previous air oxidation testing of nuclear-grade graphite doped with varying levels of boron-carbide (B4C) at a nominal 739°C was conducted for a limited number of doped specimens demonstrating a dramatic reduction in oxidation rate for the boronated graphite grade. This report summarizes the conclusions from this small scoping study by determining the effects of oxidation on the mechanical strength resulting from oxidation of boronated and unboronated graphite to a 10% mass loss level. While the B4C additive did reduce mechanical strength loss during oxidation, adding B4C dopants to a level of 3.5% or more reduced the as-fabricated compressive strength nearly 50%. This effectively minimized any benefits realized from the protective film formed on the boronated grades. Future work to infuse different graphite grades with silicon- and boron-doped material as a post-machining conditioning step for nuclear components is discussed as a potential solution for these challenges in this report.

  2. Modelling carbon for industry: radiolytic oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Leary, P.; Ewels, C.P.; Heggie, M.I. [Sussex Univ., Brighton (United Kingdom). Dept. of Chem., Phys. and Environ. Sci.; Jones, R. [Exeter Univ. (United Kingdom). Dept. of Physics; Briddon, P.R. [Newcastle upon Tyne Univ. (United Kingdom). Dept. of Physics

    2000-01-01

    An ab initio density functional technique (AIMPRO) has been employed to investigate the structure, vibrational properties, and dissociation mechanisms of CO{sub 3}{sup 0}, the important radical anion CO{sub 3}{sup -} and the interaction of this species with the graphite basal plane. The results are discussed in the context of the radiolytic oxidation of graphite: a process of relevance to the British nuclear industry, which relies for the most part on graphite-cored, CO{sub 2}-cooled reactors. The radiation field splits coolant molecules and produces, amongst other things, a very reactive radical anion CO{sub 3}{sup -}, which has been suggested as the main agent for the accelerated oxidation of graphite. This paper shows that CO{sub 3}{sup -} binds strongly to graphite after combining with an electronic hole and forming a long and strong ionic bond. It still remains mobile on the basal plane and can diffuse to a graphite edge and oxidize it. (orig.)

  3. A cladding oxidation model based on diffusion equations

    International Nuclear Information System (INIS)

    During severe accident in PWRs, the cladding oxidation with steam in the core is very important to the accident process. When oxidation time is long, or oxidation occurs in steam starvation conditions, the parabolic rate correlations based on experiments are restricted, which impacts the prediction of cladding failure, hydrogen production, and temperature. According to Fick's laws, a cladding oxidation model in a wide temperature range based on diffusion equations is developed. The developed oxidation model has a wider applicability than those parabolic rate correlations, and can simulate long-term experiments well. The restricted assumptions of short term oxidation time and enough steam environment in the core implemented by those parabolic rate correlations are removed in the model, therefore this model perfectly fit for long-term and steam starvation conditions which are more realistic during a severe accident. This model also can obtain detailed oxygen distribution in the cladding, which is helpful to simulate the cladding failure in detail and develop advanced cladding failure criteria. (authors)

  4. Advanced methods of solid oxide fuel cell modeling

    CERN Document Server

    Milewski, Jaroslaw; Santarelli, Massimo; Leone, Pierluigi

    2011-01-01

    Fuel cells are widely regarded as the future of the power and transportation industries. Intensive research in this area now requires new methods of fuel cell operation modeling and cell design. Typical mathematical models are based on the physical process description of fuel cells and require a detailed knowledge of the microscopic properties that govern both chemical and electrochemical reactions. ""Advanced Methods of Solid Oxide Fuel Cell Modeling"" proposes the alternative methodology of generalized artificial neural networks (ANN) solid oxide fuel cell (SOFC) modeling. ""Advanced Methods

  5. Modelling of fuel oxidation behaviour in operating defective fuel rods

    International Nuclear Information System (INIS)

    A fuel oxidation model is proposed for operating defective nuclear fuel rods. The present model is based on adsorption theory and accounts for high pressure effects. This model is in agreement with the fuel oxidation kinetics observed in high temperature annealing experiments conducted at 1 473 to 1 623 K in steam over a range of pressure from 0.001 to 0.1 MPa. Using a Freundlich adsorption isotherm, the current model is also consistent with recent experiments conducted at a higher pressure of 7 MPa. The model also considers radiolytic effects as a consequence of fission fragment bombardment in the fuel-to-clad gap. This treatment suggests that radiolysis-assisted oxidation is insignificant in operating defective rods (as compared to thermal effects), as supported by limited in-reactor data. The effects of diffusion of the interstitial oxygen ions in the solid in the operating rod is further discussed. (authors)

  6. Radiation induced oxidation of liquid alkanes as a polymer model

    International Nuclear Information System (INIS)

    Radiation induced oxidation of liquid n-hexadecane (n-C16H34) and squalane (C30H62) as a polymer model has been investigated by the measurements of the gas evolution and O2 uptake, and analyses of the oxidation products. Low O2 uptake, [G(-O2) ∼ 6.0] in liquid alkanes, indicates that the oxidation reaction does not exhibit chain kinetics, which is a big contrast to the process observed in solid, G(-O2) >> 10. H2 is the main gas product. More than 90% of the consumed O2 are converted into the oxidation products in liquid phase, mainly carboxylic acids, which is also a big contrast to the results of the radiolysis of liquid cyclohexane in the presence of O2 and thermal oxidation of hexadecane at elevated temperatures, where ketones and alcohols are major products at the initial stage. In the presence of aromatic additives, energy and charge transfer to the additives taking place despite the presence of O2 reduce the H2 evolution and the acid formation in parallel. Although hydroaromatic compounds act as an energy and charge scavenger, they are selectively oxidized through the donation of hydrogen in cyclic alkyl part attached to the phenyl ring, leading to large O2 uptake and corresponding ketone formation. From the comparison of the G-values of the O2 uptake, it was found that the oxidation reactions of liquid alkanes reflect well the oxidation of amorphous part in polymers. (author)

  7. Modeling SOA production from the oxidation of intermediate volatility alkanes

    Science.gov (United States)

    Aumont, B.; Mouchel-Vallon, C.; Camredon, M.; Lee-Taylor, J.; Madronich, S.

    2012-12-01

    Secondary Organic Aerosols (SOA) production and ageing is a multigenerational oxidation process involving the formation of successive organic compounds with higher oxidation degree and lower vapour pressure. This process was investigated using the explicit oxidation model GECKO-A (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere). Results for the C8-C24 n-alkane series show the expected trends, i.e. (i) SOA yield grows with the carbon backbone of the parent hydrocarbon, (ii) SOA yields decreases with the decreasing pre-existing organic aerosol concentration, (iii) the number of generations required to describe SOA production increases when the pre-existing organic aerosol concentration decreases. Most SOA contributors were found to be not oxidized enough to be categorized as highly oxygenated organic aerosols (OOA) but reduced enough to be categorized as hydrocarbon like organic aerosols (HOA). Branched alkanes are more prone to fragment in the early stage of the oxidation than their corresponding linear analogues. Fragmentation is expected to alter both the yield and the mean oxidation state of the SOA. Here, GECKO-A is applied to generate highly detailed oxidation schemes for various series of branched and cyclised alkanes. Branching and cyclisation effects on SOA yields and oxidation states will be examined.

  8. Modeling oxidation damage of continuous fiber reinforced ceramic matrix composites

    Institute of Scientific and Technical Information of China (English)

    Cheng-Peng Yang; Gui-Qiong Jiao; Bo Wang

    2011-01-01

    For fiber reinforced ceramic matrix composites (CMCs), oxidation of the constituents is a very important damage type for high temperature applications. During the oxidizing process, the pyrolytic carbon interphase gradually recesses from the crack site in the axial direction of the fiber into the interior of the material. Carbon fiber usually presents notch-like or local neck-shrink oxidation phenomenon, causing strength degradation. But, the reason for SiC fiber degradation is the flaw growth mechanism on its surface. A micromechanical model based on the above mechanisms was established to simulate the mechanical properties of CMCs after high temperature oxidation. The statistic and shearlag theory were applied and the calculation expressions for retained tensile modulus and strength were deduced, respectively. Meanwhile, the interphase recession and fiber strength degradation were considered. And then, the model was validated by application to a C/SiC composite.

  9. Simplified kinetic models of methanol oxidation on silver

    DEFF Research Database (Denmark)

    Andreasen, A.; Lynggaard, H.; Stegelmann, C.;

    2005-01-01

    Recently the authors developed a microkinetic model of methanol oxidation on silver [A. Andreasen, H. Lynggaard, C. Stegelmann, P. Stoltze, Surf. Sci. 544 (2003) 5-23]. The model successfully explains both surface science experiments and kinetic experiments at industrial conditions applying...

  10. Simplified kinetic models of methanol oxidation on silver

    DEFF Research Database (Denmark)

    Andreasen, Anders; Lynggaard, Hasse Harloff; Stegelmann, Carsten;

    2005-01-01

    Recently the authors developed a microkinetic model of methanol oxidation on silver [A. Andreasen, H. Lynggaard, C. Stegelmann, P. Stoltze, Surf. Sci. 544 (2003) 5–23]. The model successfully explains both surface science experiments and kinetic experiments at industrial conditions applying...

  11. Modeling of oxidation of aluminum nanoparticles by using Cabrera Mott Model

    Science.gov (United States)

    Ramazanova, Zamart; Zyskin, Maxim; Martirosyan, Karen

    2012-10-01

    Our research focuses on modeling new Nanoenergetic Gas-Generator (NGG) formulations that rapidly release a large amount of gaseous products and generates shock and pressure waves. Nanoenergetic thermite reagents include mixtures of Al and metal oxides such as bismuth trioxide and iodine pentoxide. The research problem is considered a spherically symmetric case and used the Cabrera Mott oxidation model to describe the kinetics of oxide growth on spherical Al nanoparticles for evaluating reaction time which a process of the reaction with oxidizer happens on the outer part of oxide layer of aluminum ions are getting in contact with an oxidizing agent and react. We assumed that a ball of Al of radius 20 to 50 nm is covered by a thin oxide layer 2-4 nm and is surrounded by abundant amount of oxygen stored by oxidizers. The ball is rapidly heated up to ignition temperature to initiate self-sustaining oxidation reaction. As a result highly exothermic reaction is generated. In the oxide layer of excess concentrations of electrons and ions are dependent on the electric field potential with the corresponding of the Gibbs factors and that it conducts to the solution of a nonlinear Poisson equation for the electric field potential in a moving boundary domain. Motion of the boundary is determined by the gradient of a solution on the boundary. We investigated oxidation model numerically, using the COMSOL software utilizing finite element analysis. The computing results demonstrate that oxidation rate increases with the decreasing particle radius.

  12. Modelling nitrous oxide emissions from organic soils in Europe

    Science.gov (United States)

    Leppelt, Thomas; Dechow, Rene; Gebbert, Sören; Freibauer, Annette

    2013-04-01

    The greenhouse gas emission potential of peatland ecosystems are mandatory for a complete annual emission budget in Europe. The GHG-Europe project aims to improve the modelling capabilities for greenhouse gases, e.g., nitrous oxide. The heterogeneous and event driven fluxes of nitrous oxide are challenging to model on European scale, especially regarding the upscaling purpose and certain parameter estimations. Due to these challenges adequate techniques are needed to create a robust empirical model. Therefore a literature study of nitrous oxide fluxes from organic soils has been carried out. This database contains flux data from boreal and temperate climate zones and covers the different land use categories: cropland, grassland, forest, natural and peat extraction sites. Especially managed crop- and grassland sites feature high emission potential. Generally nitrous oxide emissions increases significantly with deep drainage and intensive application of nitrogen fertilisation. Whereas natural peatland sites with a near surface groundwater table can act as nitrous oxide sink. An empirical fuzzy logic model has been applied to predict annual nitrous oxide emissions from organic soils. The calibration results in two separate models with best model performances for bogs and fens, respectively. The derived parameter combinations of these models contain mean groundwater table, nitrogen fertilisation, annual precipitation, air temperature, carbon content and pH value. Influences of the calibrated parameters on nitrous oxide fluxes are verified by several studies in literature. The extrapolation potential has been tested by an implemented cross validation. Furthermore the parameter ranges of the calibrated models are compared to occurring values on European scale. This avoid unknown systematic errors for the regionalisation purpose. Additionally a sensitivity analysis specify the model behaviour for each alternating parameter. The upscaling process for European peatland

  13. Modeling of thermal expansion coefficient of perovskite oxide for solid oxide fuel cell cathode

    Science.gov (United States)

    Heydari, F.; Maghsoudipour, A.; Alizadeh, M.; Khakpour, Z.; Javaheri, M.

    2015-09-01

    Artificial intelligence models have the capacity to eliminate the need for expensive experimental investigation in various areas of manufacturing processes, including the material science. This study investigates the applicability of adaptive neuro-fuzzy inference system (ANFIS) approach for modeling the performance parameters of thermal expansion coefficient (TEC) of perovskite oxide for solid oxide fuel cell cathode. Oxides (Ln = La, Nd, Sm and M = Fe, Ni, Mn) have been prepared and characterized to study the influence of the different cations on TEC. Experimental results have shown TEC decreases favorably with substitution of Nd3+ and Mn3+ ions in the lattice. Structural parameters of compounds have been determined by X-ray diffraction, and field emission scanning electron microscopy has been used for the morphological study. Comparison results indicated that the ANFIS technique could be employed successfully in modeling thermal expansion coefficient of perovskite oxide for solid oxide fuel cell cathode, and considerable savings in terms of cost and time could be obtained by using ANFIS technique.

  14. Developments in kinetic modelling of chalcocite particle oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Jaervi, J.; Ahokainen, T.; Jokilaakso, A. [Helsinki Univ. of Technology, Otaniemi (Finland). Lab. of Materials Processing and Powder Metallurgy

    1997-12-31

    A mathematical model for simulating chalcocite particle oxidation is presented. Combustion of pure chalcocite with oxygen is coded as a kinetic module which can be connected as a separate part of commercial CFD-package, PHOENICS. Heat transfer, fluid flow and combustion phenomena can be simulated using CFD-calculation together with the kinetic model. Interaction between gas phase and particles are taken into account by source terms. The aim of the kinetic model is to calculate the particle temperature, contents of species inside the particle, oxygen consumption and formation of sulphur dioxide. Four oxidation reactions are considered and the shrinking core model is used to describe the rate of the oxidation reactions. The model is verified by simulating the particle oxidation reactions in a laboratory scale laminar-flow furnace under different conditions and the model predicts the effects of charges correctly. In the future, the model validation will be done after experimental studies in the laminar flow-furnace. (author) 18 refs.

  15. Influence of the Radio-Oxidation Kinetic Model on the Critical Oxided Thickness

    International Nuclear Information System (INIS)

    The diffusion-controlled oxidation (also named physical effect of the dose rate) is an unavoidable phenomenon that occurs in polymers under ionising radiation in presence of oxygen. Indeed, oxygen is consumed inside the polymer consecutively to radio-oxidative processes. When oxygen molecules are consumed faster than they can diffuse inside the sample, oxidation is not homogeneous within the sample thickness. This leads to a heterogeneous oxidation profile with a minimum of oxidation at the centre of the sample. In this context, the concept of critical thickness Lc has been introduced. It corresponds to the thickness for which the cumulative oxygen consumption is equal to 90 % of the oxygen consumption which would occur if the oxidation was not limited by the oxygen diffusion. Gillen and Clough have determined a practical way to estimate the value of Lc from several parameters linked to the experimental conditions in the frame of the homogeneous steady?state kinetic model simplified by a relation giving the reaction constant for the recombination between the macroradicals, P degree and the peroxyl radicals, POO degree. This common assumption has the unique purpose of providing an analytical solution of the oxidation rate but is in fact unfounded. Consequently, we reconsidered the calculus, still in the frame of the homogeneous steady-state kinetic model, but without this unrealistic hypothesis on the reaction rate between P degree and POO degree. We compared the results obtained in both cases. And it appears that, exception made of the very low oxygen pressure region, Lc is not significantly affected by choosing the simplified kinetic model

  16. Modeling the Shock Ignition of a Copper Oxide Aluminum Thermite

    Science.gov (United States)

    Lee, Kibaek; Stewart, D. Scott; Clemenson, Michael; Glumac, Nick; Murzyn, Christopher

    2015-06-01

    An experimental ``striker confinement'' shock compression test was developed in the Glumac-group at the University of Illinois to study ignition and reaction in composite reactive materials. These include thermitic and intermetallic reactive powders. The test places a sample of materials such as a thermite mixture of copper oxide and aluminum powders that are initially compressed to about 80 percent full density. Two RP-80 detonators simultaneously push steel bars into reactive material and the resulting compression causes shock compaction of the material and rapid heating. At that point one observes significant reaction and propagation of fronts. But the fronts are peculiar in that they are comprised of reactive events that can be traced to the reaction/diffusion of the initially separated reactants of copper oxide and aluminum that react at their mutual interfaces that nominally make copper liquid and aluminum oxide products. We discuss our model of the shock ignition of the copper oxide aluminum thermite in the context of the striker experiment and how a Gibbs formulation model, that includes multi-components for liquid and solid phases of aluminum, copper oxide, copper and aluminum oxide can predict the events observed at the particle scale in the experiments. Supported by HDTRA1-10-1-0020 (DTRA), N000014-12-1-0555 (ONR).

  17. Detailed Chemical Kinetic Modeling of Cyclohexane Oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Silke, E J; Pitz, W J; Westbrook, C K; Ribaucour, M

    2006-11-10

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of cyclohexane at both low and high temperatures. Reaction rate constant rules are developed for the low temperature combustion of cyclohexane. These rules can be used for in chemical kinetic mechanisms for other cycloalkanes. Since cyclohexane produces only one type of cyclohexyl radical, much of the low temperature chemistry of cyclohexane is described in terms of one potential energy diagram showing the reaction of cyclohexyl radical + O{sub 2} through five, six and seven membered ring transition states. The direct elimination of cyclohexene and HO{sub 2} from RO{sub 2} is included in the treatment using a modified rate constant of Cavallotti et al. Published and unpublished data from the Lille rapid compression machine, as well as jet-stirred reactor data are used to validate the mechanism. The effect of heat loss is included in the simulations, an improvement on previous studies on cyclohexane. Calculations indicated that the production of 1,2-epoxycyclohexane observed in the experiments can not be simulated based on the current understanding of low temperature chemistry. Possible 'alternative' H-atom isomerizations leading to different products from the parent O{sub 2}QOOH radical were included in the low temperature chemical kinetic mechanism and were found to play a significant role.

  18. Modeling the viscosity of silicate melts containing manganese oxide

    Directory of Open Access Journals (Sweden)

    Kim Wan-Yi

    2013-01-01

    Full Text Available Our recently developed model for the viscosity of silicate melts is applied to describe and predict the viscosities of oxide melts containing manganese oxide. The model requires three pairs of adjustable parameters that describe the viscosities in three systems: pure MnO, MnO-SiO2 and MnO-Al2O3-SiO2. The viscosity of other ternary and multicomponent silicate melts containing MnO is then predicted by the model without any additional adjustable model parameters. Experimental viscosity data are reviewed for melts formed by MnO with SiO2, Al2O3, CaO, MgO, PbO, Na2O and K2O. The deviation of the available experimental data from the viscosities predicted by the model is shown to be within experimental error limits.

  19. Tribological behavior of hot-pressed boron carbide with oxidation

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The oxidation behavior at 973-1 273 K and the effect of oxidation on the room-temperature tribological properties of hot-pressed boron carbide ceramic were investigated. Oxidized samples were studied by X-ray diffractometer and scanning electron microscopy. It is demonstrated that the oxidation results in the formation of a thin transparent B2O3 film, and the oxide film is severely cracked during cooling due to the thermal expansion mismatch between the oxide film and B4C substrate. B2O3 reacts with moisture in air to form boric acid, which is a kind of solid lubricant. The sliding friction factors of oxidized B4C pair are about 0.05-0.08, compared to 0.25-0.35 of the as-received B4C pair. When the oxidation temperature is up to 1 273 K, severe unstability and increase of friction factor are observed. Visual inspection of the wear track reveals that the lubricant film is broken and some debris particles occur on and around the rubbing surfaces, because the friction interface is rough by the severe etching of grain boundaries.

  20. Modelling toluene oxidation : Incorporation of mass transfer phenomena

    NARCIS (Netherlands)

    Hoorn, J.A.A.; van Soolingen, J.; Versteeg, G. F.

    2005-01-01

    The kinetics of the oxidation of toluene have been studied in close interaction with the gas-liquid mass transfer occurring in the reactor. Kinetic parameters for a simple model have been estimated on basis of experimental observations performed under industrial conditions. The conclusions for the m

  1. Animation Model to Conceptualize ATP Generation: A Mitochondrial Oxidative Phosphorylation

    Science.gov (United States)

    Jena, Ananta Kumar

    2015-01-01

    Adenosine triphosphate (ATP) is the molecular unit of intracellular energy and it is the product of oxidative phosphorylation of cellular respiration uses in cellular processes. The study explores the growth of the misconception levels amongst the learners and evaluates the effectiveness of animation model over traditional methods. The data…

  2. Mathematical Modeling of Wastewater Oxidation under Microgravity Conditions

    Directory of Open Access Journals (Sweden)

    Boyun Guo

    2005-01-01

    Full Text Available Volatile removal assembly (VRA is a module installed in the International Space Station for removing contaminants (volatile organics in the wastewater produced by the crew. The VRA contains a slim pack bed reactor to perform catalyst oxidation of the wastewater at elevated pressure and temperature under microgravity conditions. Optimal design of the reactor requires a thorough understanding about how the reactor performs under microgravity conditions. The objective of this study was to theoretically investigate factors affecting the performance of the VRA reactor under microgravity conditions. The efficiency of catalyst oxidation is controlled by catalyst oxidation kinetics and oxygen gas distribution in the reactor. The process involves bubbly flow in porous media with chemical reactions in a microgravity environment, which has not been previously studied. We have developed and used a mathematical model in this study to simulate the organics oxidation process in the VRA reactor. On the basis of theoretical studies with the model, we conclude that 1 the remaining oxygen gas in the VRA reactor should decline exponentially with reactor length; 2 the decline rate is directly proportional to the rate of oxidation per unit area and bubble sphericity and inversely proportional to bubble size, oxygen density and bubble velocity; and 3 gravity affects oxygen utilization through changing several parameters including oxygen bubble size.

  3. Oxide-supported metal clusters: models for heterogeneous catalysts

    International Nuclear Information System (INIS)

    Understanding the size-dependent electronic, structural and chemical properties of metal clusters on oxide supports is an important aspect of heterogeneous catalysis. Recently model oxide-supported metal catalysts have been prepared by vapour deposition of catalytically relevant metals onto ultra-thin oxide films grown on a refractory metal substrate. Reactivity and spectroscopic/microscopic studies have shown that these ultra-thin oxide films are excellent models for the corresponding bulk oxides, yet are sufficiently electrically conductive for use with various modern surface probes including scanning tunnelling microscopy (STM). Measurements on metal clusters have revealed a metal to nonmetal transition as well as changes in the crystal and electronic structures (including lattice parameters, band width, band splitting and core-level binding energy shifts) as a function of cluster size. Size-dependent catalytic reactivity studies have been carried out for several important reactions, and time-dependent catalytic deactivation has been shown to arise from sintering of metal particles under elevated gas pressures and/or reactor temperatures. In situ STM methodologies have been developed to follow the growth and sintering kinetics on a cluster-by-cluster basis. Although several critical issues have been addressed by several groups worldwide, much more remains to be done. This article highlights some of these accomplishments and summarizes the challenges that lie ahead. (topical review)

  4. European scale modeling of sulfur, oxidized nitrogen and photochemical oxidants. Model development and evaluation for the 1994 growing season

    Energy Technology Data Exchange (ETDEWEB)

    Langner, J.; Bergstroem, R. [Swedish Meteorological and Hydrological Inst., Norrkoeping (Sweden); Pleijel, K. [Swedish Environmental Research Inst., Goeteborg (Sweden)

    1998-09-01

    A chemical mechanism, including the relevant reactions leading to the production of ozone and other photochemical oxidants, has been implemented in the MATCH regional tracer transport/chemistry/deposition model. The aim has been to develop a model platform that can be used as a basis for a range of regional scale studies involving atmospheric chemistry, including assessment of the importance of different sources of pollutants to the levels of photochemical oxidants and air pollutant forecasting. Meteorological input data to the model were taken from archived output from the operational version of HIRLAM at SMHI. Evaluation of model calculations over Europe for a six month period in 1994 for a range of chemical components show good results considering known sources of error and uncertainties in input data and model formulation. With limited further work the system is sufficiently good to be applied for scenario studies and for regional scale air pollutant forecasts 42 refs, 24 figs, 17 tabs

  5. A model for the degradation of polyimides due to oxidation

    OpenAIRE

    Karra, Satish; K.R. Rajagopal

    2010-01-01

    Polyimides, due to their superior mechanical behavior at high temperatures, are used in a variety of applications that include aerospace, automobile and electronic packaging industries, as matrices for composites, as adhesives etc. In this paper, we extend our previous model in [S. Karra, K. R. Rajagopal, Modeling the non-linear viscoelastic response of high temperature polyimides, Mechanics of Materials, In press, doi:10.1016/j.mechmat.2010.09.006], to include oxidative degradation of these ...

  6. Multi-component transparent conducting oxides: progress in materials modelling

    International Nuclear Information System (INIS)

    Transparent conducting oxides (TCOs) play an essential role in modern optoelectronic devices through their combination of electrical conductivity and optical transparency. We review recent progress in our understanding of multi-component TCOs formed from solid solutions of ZnO, In2O3, Ga2O3 and Al2O3, with a particular emphasis on the contributions of materials modelling, primarily based on density functional theory. In particular, we highlight three major results from our work: (i) the fundamental principles governing the crystal structures of multi-component oxide structures including (In2O3)(ZnO)n and (In2O3)m(Ga2O3)l(ZnO)n; (ii) the relationship between elemental composition and optical and electrical behaviour, including valence band alignments; (iii) the high performance of amorphous oxide semiconductors. On the basis of these advances, the challenge of the rational design of novel electroceramic materials is discussed. (topical review)

  7. Multi-component transparent conducting oxides: progress in materials modelling

    Science.gov (United States)

    Walsh, Aron; Da Silva, Juarez L. F.; Wei, Su-Huai

    2011-08-01

    Transparent conducting oxides (TCOs) play an essential role in modern optoelectronic devices through their combination of electrical conductivity and optical transparency. We review recent progress in our understanding of multi-component TCOs formed from solid solutions of ZnO, In2O3, Ga2O3 and Al2O3, with a particular emphasis on the contributions of materials modelling, primarily based on density functional theory. In particular, we highlight three major results from our work: (i) the fundamental principles governing the crystal structures of multi-component oxide structures including (In2O3)(ZnO)n and (In2O3)m(Ga2O3)l(ZnO)n; (ii) the relationship between elemental composition and optical and electrical behaviour, including valence band alignments; (iii) the high performance of amorphous oxide semiconductors. On the basis of these advances, the challenge of the rational design of novel electroceramic materials is discussed.

  8. [Neuroprotection strategies: effect of vinpocetine in vitro oxidative stress models].

    Science.gov (United States)

    Pereira, Cláudia; Agostinho, Paula; Moreira, Paula I; Duarte, Ana I; Santos, Maria S; Oliveira, Catarina R

    2003-01-01

    Reactive oxygen species (ROS) play an important role in neuronal damage and death that occurs in several neurodegenerative disorders, namely in Alzheimer's disease (AD). The observation that ROS neutralization may slow or reduce the neurodegenerative process associated with those pathologies stimulates the development of new drugs, more efficient and well tolerated, with antioxidant properties. Vinpocetine [14-etoxicarbonyl-3alpha,16alpha-ethyl)-14,15-eburnamine], a vincamine derivative, efficiently protects cells from ROS attack. Recently, the protective effect of vinpocetine was demonstrated using in vitro models of oxidative stress induced by the oxidant pair ascorbate/Fe2+ and by synthetic peptides of the AD-associated b-amyloid protein (Abeta). Results obtained from these in vitro experiences support that additional clinical trials should be carried out using vinpocetine, or vinpocetine derivatives, in order to test its therapeutical or preventive effects in diseases where oxidative stress plays a crucial role. PMID:15631851

  9. A model of pyritic oxidation in waste rock dumps

    International Nuclear Information System (INIS)

    The oxidation of pyrite can lead to high acid levels and high concentrations of trace metals in the water that runs off and percolates through pyritic material. This is the situation at the abandoned uranium mine at Rum Jungle in the Northern Territory of Australia, where pyritic oxidation in the waste rock dumps resulting from open cut mining of the uranium orebody has led to pollution of the nearby East Branch of the Finniss River, with trace metals such as copper, manganese and zinc. Mathematical equations are formulated which describe a model of pyritic oxidation within a waste rock dump, where it is assumed that oxygen transport is the rate limiting step in the oxidation process and that oxygen is transported by gaseous diffusion through the pore space of the dump, followed by diffusion into oxidation sites within the particles that comprise the dump. The equations have been solved numerically assuming values for such parameters as porosity, sulphur density and oxygen diffusion coefficients which are applicable to the waste rock dumps at Rum Jungle. An approximate solution to the equations is also presented. Calculations of the heat source distribution and the total SO4 production rate are presented for both single size particles and for a range of particle sizes in the dump. The usefulness of the approximate solution, and of calculations based on single size particles in the dump in assessing the effectiveness of strategies to reduce pollution from such waste rock dumps are discussed

  10. Global atmospheric model for mercury including oxidation by bromine atoms

    Directory of Open Access Journals (Sweden)

    C. D. Holmes

    2010-12-01

    Full Text Available Global models of atmospheric mercury generally assume that gas-phase OH and ozone are the main oxidants converting Hg0 to HgII and thus driving mercury deposition to ecosystems. However, thermodynamic considerations argue against the importance of these reactions. We demonstrate here the viability of atomic bromine (Br as an alternative Hg0 oxidant. We conduct a global 3-D simulation with the GEOS-Chem model assuming gas-phase Br to be the sole Hg0 oxidant (Hg + Br model and compare to the previous version of the model with OH and ozone as the sole oxidants (Hg + OH/O3 model. We specify global 3-D Br concentration fields based on our best understanding of tropospheric and stratospheric Br chemistry. In both the Hg + Br and Hg + OH/O3 models, we add an aqueous photochemical reduction of HgII in cloud to impose a tropospheric lifetime for mercury of 6.5 months against deposition, as needed to reconcile observed total gaseous mercury (TGM concentrations with current estimates of anthropogenic emissions. This added reduction would not be necessary in the Hg + Br model if we adjusted the Br oxidation kinetics downward within their range of uncertainty. We find that the Hg + Br and Hg + OH/O3 models are equally capable of reproducing the spatial distribution of TGM and its seasonal cycle at northern mid-latitudes. The Hg + Br model shows a steeper decline of TGM concentrations from the tropics to southern mid-latitudes. Only the Hg + Br model can reproduce the springtime depletion and summer rebound of TGM observed at polar sites; the snowpack component of GEOS-Chem suggests that 40% of HgII deposited to snow in the Arctic is transferred to the ocean and land reservoirs, amounting to a net deposition flux to the Arctic of 60 Mg a−1. Summertime events of depleted Hg0 at Antarctic sites due to subsidence are much better simulated by

  11. Oxide thinning percolation statistical model for soft breakdown in ultrathin gate oxides

    Science.gov (United States)

    Chen, Ming-Jer; Kang, Ting-Kuo; Liu, Chuan-Hsi; Chang, Yih J.; Fu, Kuan-Yu

    2000-07-01

    An existing cell-based percolation model with parameter correlation can find its potential applications in assessing soft-breakdown (BD) statistics as long as the oxide thinning due to the localized physical damage near the SiO2/Si interface is accounted for. The resulting model is expressed explicitly with the critical trap number per cell nBD and the remaining oxide thickness tox' both as parameters. Reproduction of time-to-bimodal (soft- and hard-) breakdown statistical data from 3.3-nm-thick gate-oxide samples yields nBD of 3 and 4 for soft and hard breakdown, respectively. The extracted tox' of 1.0 nm for soft breakdown, plus the transition layer thickness of 0.5 nm in the model, is fairly comparable with literature values from current-voltage fitting. The dimension and area of the localized physically damaged region or percolation path (cell) are quantified as well. Based on the work, the origins of soft and hard breakdown are clarified in the following: (i) soft breakdown behaves intrinsically as hard breakdown, that is, they share the same defect (neutral trap) generation process and follow Poisson random statistics; (ii) both are independent events corresponding to different tox' requirements; and (iii) hard breakdown takes place in a certain path located differently from that for the first soft breakdown.

  12. Controllably Inducing and Modeling Optical Response from Graphene Oxide

    Science.gov (United States)

    Lombardo, Nicholas; Naumov, Anton

    Graphene, a novel 2-dimensional sp2-hybridized allotrope of Carbon, has unique electrical and mechanical properties. While it is naturally a highly conductive zero band gap semiconductor, graphene does not exhibit optical emission. It has been shown that functionalization with oxygen-containing groups elicits an opening of band gap in graphene. In this work, we aim to induce an optical response in graphene via controlled oxidation, and then explore potential origins of its photoluminescence through mathematical modeling. We employ timed ozone treatment of initially non-fluorescent reduced graphene oxide (RGO) to produce graphene oxide (GO) with specific optical properties. Oxidized material exhibits substantial changes in the absorption spectra and a broad photoluminescence feature, centered at 532 nm, which suggests the appearance of a band gap. We then explore a number of possible mechanisms for the origin of GO photoluminescence via PM3 and ab initio calculations on a functionalized single sheet of graphene. By adjusting modeling parameters to fit experimentally obtained optical transition energies we estimate the size of the sp2 graphitic regions in GO and the arrangement of functional groups that could be responsible for the observed emission.

  13. Impedance Modeling of Solid Oxide Fuel Cell Cathodes

    DEFF Research Database (Denmark)

    Mortensen, Jakob Egeberg; Søgaard, Martin; Jacobsen, Torben

    2010-01-01

    partial pressure range 0.028-1.00 atm. The recorded impedance spectra were successfully analyzed using the developed impedance model in the investigated temperature and oxygen partial pressure range. It is also demonstrated that the model can be used to predict how impedance spectra evolve with different......A 1-dimensional impedance model for a solid oxide fuel cell cathode is formulated and applied to a cathode consisting of 50/50 wt% strontium doped lanthanum cobaltite and gadolinia doped ceria. A total of 42 impedance spectra were recorded in the temperature range: 555-852°C and in the oxygen...

  14. Ab initio and kinetic modeling studies of formic acid oxidation

    DEFF Research Database (Denmark)

    Marshall, Paul; Glarborg, Peter

    2015-01-01

    A detailed chemical kinetic model for oxidation of formic acid (HOCHO) in flames has been developed, based on theoretical work and data from literature. Ab initio calculations were used to obtain rate coefficients for reactions of HOCHO with H, O, and HO2. Modeling predictions with the mechanism...... on calculations with the kinetic model. Formic acid is consumed mainly by reaction with OH, yielding OCHO, which dissociates rapidly to CO2 + H, and HOCO, which may dissociate to CO + OH or CO2 + H, or react with H, OH, or O2 to form more stable products. The branching fraction of the HOCHO + OH...

  15. Growth Model for Pulsed-Laser Deposited Perovskite Oxide Films

    Institute of Scientific and Technical Information of China (English)

    WANG Xu; FEI Yi-Yan; ZHU Xiang-Dong; Lu Hui-Bin; YANG Guo-Zhen

    2008-01-01

    We present a multi-level growth model that yields some of the key features of perovskite oxide film growth as observed in the reflection high energy electron diffraction(RHEED)and ellipsometry studies.The model describes the effect of deposition,temperature,intra-layer transport,interlayer transport and Ostwald ripening on the morphology of a growth surface in terms of the distribution of terraces and step edges during and after deposition.The numerical results of the model coincide well with the experimental observation.

  16. Fundamental Studies of Butane Oxidation over Model-Supported Vanadium Oxide Catalysts: Molecular Structure-Reactivity Relationships

    OpenAIRE

    Wachs, I.E.; Jehng, J.M.; Deo, G.; Weckhuysen, B. M.; Guliants, V.V.; Benziger, J. B.; Sundaresan, S.

    1997-01-01

    The oxidation of n-butane to maleic anhydride was investigated over a series of model-supported vanadia catalysts where the vanadia phase was present as a two-dimensional metal oxide overlayer on the different oxide supports (TiO2, ZrO2, CeO2, Nb2O5, Al2O3, and SiO2). No correlation was found between the properties of the terminal V==O bond and the butane oxidation turnover frequency (TOF) during in situ Raman spectroscopy study. Furthermore, neither the n-butane oxidation TOF nor maleic anhy...

  17. A Cellular Model for Screening Neuronal Nitric Oxide Synthase Inhibitors

    OpenAIRE

    Fang, Jianguo; Silverman, Richard B.

    2009-01-01

    Nitric oxide synthase (NOS) inhibitors are potential drug candidates because it has been well demonstrated that excessive production of NO critically contributes to a range of diseases. Most inhibitors have been screened in vitro using recombinant enzymes, leading to the discovery of a variety of potent compounds. To make inhibition studies more physiologically relevant and bridge the gap between the in vitro assay and in vivo studies, we report here a cellular model for screening NOS inhibit...

  18. Modeling of nitric oxide emissions from temperate agricultural ecosystems.

    OpenAIRE

    Rolland, Marie-Noëlle; Gabrielle, Benoît; Laville, Patricia; Serça, Dominique; Cortinovis, Jérôme; Larmanou, Eric; Lehuger, Simon; Cellier, Pierre

    2006-01-01

    48 p. Arable soils are a significant source of nitric oxide (NO), most of which is derived from nitrogen fertilizers. Precise estimates of NO emissions from these soils are thus essential to devise strategies to mitigate the impact of agriculture on tropospheric ozone regulation. This paper presents the implementation of a soil NO emissions submodel within the environmentally-orientated soil crop model, CERES-EGC. The submodel simulates the NO production via nitrification pathway, as modul...

  19. Assessment of the basis for modeling releases from plutonium oxidation

    International Nuclear Information System (INIS)

    Ideally, a model of the release of plutonium aerosols from plutonium during oxidation or combustion should begin from a description of the plutonium material and its surroundings and proceed unequivocally to a situation-dependent estimate of the amount of oxide released and its size distribution. Such a model would need to provide a description of the heat- and mass-transfer processes involved and link them directly to the rate of aerosol production. The first step, the description of heat and mass transfer, is more easily achieved from current information than the second, the aerosol release. The sections of this report titled ''Physical Fundamentals'' and ''Available Theoretical Information'' describe the approach that would be required for theoretical modeling. The ''Experimental Results'' section describes the information on aerosol releases, size distributions, peak temperatures, oxidation rates, and experimental conditions that we have gleaned from the existing experimental literature. The data is summarized and the bibliography lists the relevant literature that has and has not been reviewed. 42 refs., 10 figs., 6 tabs

  20. Modeling of metal–oxide semiconductor: Analytical bond-order potential for cupric oxide

    International Nuclear Information System (INIS)

    Atomistic potentials for cupric element and cupric oxide are derived based on the analytical bond-order scheme that was presented by Brenner [Brenner D W, “Erratum: Empirical potential for hydrocarbons for use in simulating the chemical vapor deposition of diamond films”, Phys. Rev. B 1992, 46 1948]. In this paper, for the pure cupric element, the energy and structural parameters for several bulk phases as well as dimmer structure are well reproduced. The reference data are taken from our density functional theory calculations and the available experiments. The model potential also provides a good description of the bulk properties of various solid structures of cupric oxide compound structures, including cohesive energies, lattice parameters, and elastic constants. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  1. A microkinetic model of the methanol oxidation over silver

    DEFF Research Database (Denmark)

    Andreasen, A.; Lynggaard, H.; Stegelmann, C.;

    2003-01-01

    A simple microkinetic model for the oxidation of methanol on silver based on surface science studies at UHV and low temperatures has been formulated. The reaction mechanism is a simple Langmuir-Hinshelwood mechanism, with one type of active oxygen and one route to formaldehyde and carbon dioxide......, respectively. The model explains observed reaction orders, selectivity, apparent activation enthalpies and the choice of industrial reaction conditions. More interesting the model disproves the notion that the mechanism deduced from surface science in UHV cannot be responsible for formaldehyde synthesis at...... industrial steady-state conditions. The present work therefore seriously questions the prevailing models of formaldehyde synthesis in the literature. One of the reasons for this controversy is that many of the models in the literature are derived from transient experiments exhibiting dynamic effects that are...

  2. A model for the thermo-oxidative degradation of polyimides

    Science.gov (United States)

    Karra, Satish; Rajagopal, K. R.

    2012-08-01

    Polyimides, due to their superior mechanical behavior at high temperatures, are used in a variety of applications that include aerospace, automobile and electronic packaging industries, as matrices for composites, as adhesives etc. In this paper, we extend our previous model in S. Karra and K. Rajagopal (Mech. Mater. 43(1):54-61, 2011), to include thermo-oxidative degradation of these high temperature polyimides. Appropriate forms for the Helmholtz potential and the rate of dissipation are chosen to describe the degradation. The results for a specific boundary value problem, using our model, compares well with the experimental creep data for PMR-15 resin that is aged in air.

  3. The Lightning Nitrogen Oxides Model (LNOM): Status and Recent Applications

    Science.gov (United States)

    Koshak, William; Khan, Maudood; Peterson, Harold

    2011-01-01

    Improvements to the NASA Marshall Space Flight Center Lightning Nitrogen Oxides Model (LNOM) are discussed. Recent results from an August 2006 run of the Community Multiscale Air Quality (CMAQ) modeling system that employs LNOM lightning NOx (= NO + NO2) estimates are provided. The LNOM analyzes Lightning Mapping Array (LMA) data to estimate the raw (i.e., unmixed and otherwise environmentally unmodified) vertical profile of lightning NOx. The latest LNOM estimates of (a) lightning channel length distributions, (b) lightning 1-m segment altitude distributions, and (c) the vertical profile of NOx are presented. The impact of including LNOM-estimates of lightning NOx on CMAQ output is discussed.

  4. Discrete Event System Based Pyroprocessing Modeling and Simulation: Oxide Reduction

    International Nuclear Information System (INIS)

    Dynamic changes according to the batch operation cannot be predicted in an equilibrium material flow. This study began to build a dynamic material balance model based on the previously developed pyroprocessing flowsheet. As a mid- and long-term research, an integrated pyroprocessing simulator is being developed at the Korea Atomic Energy Research Institute (KAERI) to cope with a review on the technical feasibility, safeguards assessment, conceptual design of facility, and economic feasibility evaluation. The most fundamental thing in such a simulator development is to establish the dynamic material flow framework. This study focused on the operation modeling of pyroprocessing to implement a dynamic material flow. As a case study, oxide reduction was investigated in terms of a dynamic material flow. DES based modeling was applied to build a pyroprocessing operation model. A dynamic material flow as the basic framework for an integrated pyroprocessing was successfully implemented through ExtendSim's internal database and item blocks. Complex operation logic behavior was verified, for example, an oxide reduction process in terms of dynamic material flow. Compared to the equilibrium material flow, a model-based dynamic material flow provides such detailed information that a careful analysis of every batch is necessary to confirm the dynamic material balance results. With the default scenario of oxide reduction, the batch mass balance was verified in comparison with a one-year equilibrium mass balance. This study is still under progress with a mid-and long-term goal, the development of a multi-purpose pyroprocessing simulator that is able to cope with safeguards assessment, economic feasibility, technical evaluation, conceptual design, and support of licensing for a future pyroprocessing facility

  5. Fundamental Studies of Butane Oxidation over Model-Supported Vanadium Oxide Catalysts: Molecular Structure-Reactivity Relationships

    NARCIS (Netherlands)

    Wachs, I.E.; Jehng, J.M.; Deo, G.; Weckhuysen, B.M.; Guliants, V.V.; Benziger, J.B.; Sundaresan, S.

    1997-01-01

    The oxidation of n-butane to maleic anhydride was investigated over a series of model-supported vanadia catalysts where the vanadia phase was present as a two-dimensional metal oxide overlayer on the different oxide supports (TiO2, ZrO2, CeO2, Nb2O5, Al2O3, and SiO2). No correlation was found betwee

  6. Advanced impedance modeling of solid oxide electrochemical cells

    DEFF Research Database (Denmark)

    Graves, Christopher R.; Hjelm, Johan

    2014-01-01

    Impedance spectroscopy is a powerful technique for detailed study of the electrochemical and transport processes that take place in fuel cells and electrolysis cells, including solid oxide cells (SOCs). Meaningful analysis of impedance measurements is nontrivial, however, because a large number of...... modeling parameters are fit to the many processes which often overlap in the same frequency ranges. Also, commonly used equivalent circuit (EC) models only provide zero-dimensional (0-D) approximations of the processes of the two electrodes, electrolyte and gas transport. Employing improved analytical...... electrode and 2-D gas transport models which have fewer unknown parameters for the same number of processes, (ii) use of a new model fitting algorithm, “multi-fitting”, in which multiple impedance spectra are fit simultaneously with parameters linked based on the variation of measurement conditions, (iii...

  7. A Structural Molar Volume Model for Oxide Melts Part III: Fe Oxide-Containing Melts

    Science.gov (United States)

    Thibodeau, Eric; Gheribi, Aimen E.; Jung, In-Ho

    2016-04-01

    As part III of this series, the model is extended to iron oxide-containing melts. All available experimental data in the FeO-Fe2O3-Na2O-K2O-MgO-CaO-MnO-Al2O3-SiO2 system were critically evaluated based on the experimental condition. The variations of FeO and Fe2O3 in the melts were taken into account by using FactSage to calculate the Fe2+/Fe3+ distribution. The molar volume model with unary and binary model parameters can be used to predict the molar volume of the molten oxide of the Li2O-Na2O-K2O-MgO-CaO-MnO-PbO-FeO-Fe2O3-Al2O3-SiO2 system in the entire range of compositions, temperatures, and oxygen partial pressures from Fe saturation to 1 atm pressure.

  8. Density functional theory modeling of multilayer "epitaxial" graphene oxide.

    Science.gov (United States)

    Zhou, Si; Bongiorno, Angelo

    2014-11-18

    CONSPECTUS: Graphene oxide (GO) is a complex material of both fundamental and applied interest. Elucidating the structure of GO is crucial to achieve control over its properties and technological applications. GO is a nonstoichiometric and hygroscopic material with a lamellar structure, and its physical chemical properties depend critically on synthesis procedures and postsynthesis treatments. Numerous efforts are in place to both understand and exploit this versatile layered carbon material. This Account reports on recent density functional theory (DFT) studies of "epitaxial" graphene oxide (hereafter EGO), a type of GO obtained by oxidation of graphene films grown epitaxially on silicon carbide. Here, we rely on selected X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), and X-ray diffraction (XRD) measurements of EGO, and we discuss in great detail how we utilized DFT-based techniques to project out from the experimental data basic atomistic information about the chemistry and structure of these films. This Account provides an example as to how DFT modeling can be used to elucidate complex materials such as GO from a limited set of experimental information. EGO exhibits a uniform layered structure, consisting of a stack of graphene planes hosting predominantly epoxide and hydroxyl groups, and water molecules intercalated between the oxidized carbon layers. Here, we first focus on XPS measurements of EGO, and we use DFT to generate realistic model structures, calculate core-level chemical shifts, and through the comparison with experiment, gain insight on the chemical composition and metastability characteristics of EGO. DFT calculations are then used to devise a simplistic but accurate simulation scheme to study thermodynamic and kinetic stability and to predict the intralayer structure of EGO films aged at room temperature. Our simulations show that aged EGO encompasses layers with nanosized oxidized domains presenting a high concentration of

  9. Evidence of Oxidative Stress in Autism Derived from Animal Models

    Directory of Open Access Journals (Sweden)

    Xue Ming

    2008-01-01

    Full Text Available Autism is a pervasive neurodevelopmental disorder that leads to deficits in social interaction, communication and restricted, repetitive motor movements. Autism is a highly heritable disorder, however, there is mounting evidence to suggest that toxicant-induced oxidative stress may play a role. The focus of this article will be to review our animal model of autism and discuss our evidence that oxidative stress may be a common underlying mechanism of neurodevelopmental damage. We have shown that mice exposed to either methylmercury (MeHg or valproic acid (VPA in early postnatal life display aberrant social, cognitive and motor behavior. Interestingly, early exposure to both compounds has been clinically implicated in the development of autism. We recently found that Trolox, a water-soluble vitamin E derivative, is capable of attenuating a number of neurobehavioral alterations observed in mice postnatally exposed to MeHg. In addition, a number of other investigators have shown that oxidative stress plays a role in neural injury following MeHg exposure both in vitro and in vivo. New data presented here will show that VPA-induced neurobehavioral deficits are attenuated by vitamin E as well and that the level of glial fibrillary acidic protein (GFAP, a marker of astrocytic neural injury, is altered following VPA exposure. Collectively, these data indicate that vitamin E and its derivative are capable of protecting against neurobehavioral deficits induced by both MeHg and VPA. This antioxidant protection suggests that oxidative stress may be a common mechanism of injury leading to aberrant behavior in both our animal model as well as in the human disease state.

  10. LG Solid Oxide Fuel Cell (SOFC) Model Development

    Energy Technology Data Exchange (ETDEWEB)

    Haberman, Ben [LG Fuel Cell Systems Inc., North Canton, OH (United States); Martinez-Baca, Carlos [LG Fuel Cell Systems Inc., North Canton, OH (United States); Rush, Greg [LG Fuel Cell Systems Inc., North Canton, OH (United States)

    2013-05-31

    This report presents a summary of the work performed by LG Fuel Cell Systems Inc. during the project LG Solid Oxide Fuel Cell (SOFC) Model Development (DOE Award Number: DE-FE0000773) which commenced on October 1, 2009 and was completed on March 31, 2013. The aim of this project is for LG Fuel Cell Systems Inc. (formerly known as Rolls-Royce Fuel Cell Systems (US) Inc.) (LGFCS) to develop a multi-physics solid oxide fuel cell (SOFC) computer code (MPC) for performance calculations of the LGFCS fuel cell structure to support fuel cell product design and development. A summary of the initial stages of the project is provided which describes the MPC requirements that were developed and the selection of a candidate code, STAR-CCM+ (CD-adapco). This is followed by a detailed description of the subsequent work program including code enhancement and model verification and validation activities. Details of the code enhancements that were implemented to facilitate MPC SOFC simulations are provided along with a description of the models that were built using the MPC and validated against experimental data. The modeling work described in this report represents a level of calculation detail that has not been previously available within LGFCS.

  11. Modeling toxic compounds from nitric oxide emission measurements

    Science.gov (United States)

    Vallero, Daniel A.; Peirce, Jeffrey; Cho, Ki Don

    Determining the amount and rate of degradation of toxic pollutants in soil and groundwater is difficult and often requires invasive techniques, such as deploying extensive monitoring well networks. Even with these networks, degradation rates across entire systems cannot readily be extrapolated from the samples. When organic compounds are degraded by microbes, especially nitrifying bacteria, oxides or nitrogen (NO x) are released to the atmosphere. Thus, the flux of nitric oxide (NO) from the soil to the lower troposphere can be used to predict the rate at which organic compounds are degraded. By characterizing and applying biogenic and anthropogenic processes in soils the rates of degradation of organic compounds. Toluene was selected as a representative of toxic aromatic compounds, since it is inherently toxic, it is a substituted benzene compound and is listed as a hazardous air pollutant under Section 12 of the Clean Air Act Amendments of 1990. Measured toluene concentrations in soil, microbial population growth and NO fluxes in chamber studies were used to develop and parameterize a numerical model based on carbon and nitrogen cycling. These measurements, in turn, were used as indicators of bioremediation of air toxic (i.e. toluene) concentrations. The model found that chemical concentration, soil microbial abundance, and NO production can be directly related to the experimental results (significant at P < 0.01) for all toluene concentrations tested. This indicates that the model may prove useful in monitoring and predicting the fate of toxic aromatic contaminants in a complex soil system. It may also be useful in predicting the release of ozone precursors, such as changes in reservoirs of hydrocarbons and oxides of nitrogen. As such, the model may be a tool for decision makers in ozone non-attainment areas.

  12. Modeling of Yb(III) sorption on kaolinite by using single oxide surface complexation models

    International Nuclear Information System (INIS)

    The rare earth elements present strong chemical analogies with trivalent actinides, and may be used to develop methodologies and to quantify relevant processes. Nevertheless, their sorption behavior is poorly known. In this work, the authors study the sorption of ytterbium on kaolinite using surface complexation models. The aim is as a first step, to determine surface parameters of two single oxides, alumina and silica, by means of an experimental method tested on iron oxides, and in a second step to use these parameters to describe surface reactions on kaolinite surface. this application of single oxide surface parameters to aluminosilicates has been already tested and they extend this approach to study the ytterbium sorption

  13. Macro Level Modeling of a Tubular Solid Oxide Fuel Cell

    Directory of Open Access Journals (Sweden)

    Farshid Zabihian

    2010-11-01

    Full Text Available This paper presents a macro-level model of a solid oxide fuel cell (SOFC stack implemented in Aspen Plus® for the simulation of SOFC system. The model is 0-dimensional and accepts hydrocarbon fuels such as reformed natural gas, with user inputs of current density, fuel and air composition, flow rates, temperature, pressure, and fuel utilization factor. The model outputs the composition of the exhaust, work produced, heat available for the fuel reformer, and electrochemical properties of SOFC for model validation. It was developed considering the activation, concentration, and ohmic losses to be the main over-potentials within the SOFC, and mathematical expressions for these were chosen based on available studies in the literature. The model also considered the water shift reaction of CO and the methane reforming reaction. The model results were validated using experimental data from Siemens Westinghouse. The results showed that the model could capture the operating pressure and temperature dependency of the SOFC performance successfully in an operating range of 1–15 atm for pressure and 900 °C–1,000 °C for temperature. Furthermore, a sensitivity analysis was performed to identify the model constants and input parameters that impacted the over-potentials.

  14. Modeling the oxidation of phenolic compounds by hydrogen peroxide photolysis.

    Science.gov (United States)

    Zhang, Tianqi; Cheng, Long; Ma, Lin; Meng, Fanchao; Arnold, Robert G; Sáez, A Eduardo

    2016-10-01

    Hydrogen peroxide UV photolysis is among the most widely used advanced oxidation processes (AOPs) for the destruction of trace organics in waters destined for reuse. Previous kinetic models of hydrogen peroxide photolysis focus on the dynamics of hydroxyl radical production and consumption, as well as the reaction of the target organic with hydroxyl radicals. However, the rate of target destruction may also be affected by radical scavenging by reaction products. In this work, we build a predictive kinetic model for the destruction of p-cresol by hydrogen peroxide photolysis based on a complete reaction mechanism that includes reactions of intermediates with hydroxyl radicals. The results show that development of a predictive kinetic model to evaluate process performance requires consideration of the complete reaction mechanism, including reactions of intermediates with hydroxyl radicals. PMID:27448315

  15. Mechanical modeling of porous oxide fuel pellet A Test Problem

    International Nuclear Information System (INIS)

    A poro-elasto-plastic material model has been developed to capture the response of oxide fuels inside the nuclear reactors under operating conditions. Behavior of the oxide fuel and variation in void volume fraction under mechanical loading as predicted by the developed model has been reported in this article. The significant effect of void volume fraction on the overall stress distribution of the fuel pellet has also been described. An important oxide fuel issue that can have significant impact on the fuel performance is the mechanical response of oxide fuel pellet and clad system. Specifically, modeling the thermo-mechanical response of the fuel pellet in terms of its thermal expansion, mechanical deformation, swelling due to void formation and evolution, and the eventual contact of the fuel with the clad is of significant interest in understanding the fuel-clad mechanical interaction (FCMI). These phenomena are nonlinear and coupled since reduction in the fuel-clad gap affects thermal conductivity of the gap, which in turn affects temperature distribution within the fuel and the material properties of the fuel. Consequently, in order to accurately capture fuel-clad gap closure, we need to account for fuel swelling due to generation, retention, and evolution of fission gas in addition to the usual thermal expansion and mechanical deformation. Both fuel chemistry and microstructure also have a significant effect on the nucleation and growth of fission gas bubbles. Fuel-clad gap closure leading to eventual contact of the fuel with the clad introduces significant stresses in the clad, which makes thermo-mechanical response of the clad even more relevant. The overall aim of this test problem is to incorporate the above features in order to accurately capture fuel-clad mechanical interaction. Because of the complex nature of the problem, a series of test problems with increasing multi-physics coupling features, modeling accuracy, and complexity are defined with the

  16. Modelling of the partial oxidation of {alpha}, {beta}-unsaturated aldehydes on Mo-V-oxides based catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Boehnke, H.; Petzoldt, J.C.; Stein, B.; Weimer, C.; Gaube, J.W. [Technische Univ. Darmstadt (Germany). Inst. fuer Chemische Technologie

    1998-12-31

    A kinetic model based on the Mars-van Krevelen mechanism that allows to describe the microkinetics of the heterogeneously catalysed partial oxidation of {alpha}, {beta}-unsaturated aldehydes is presented. This conversion is represented by a network, composed of the oxidation of the {alpha}, {beta}-unsaturated aldehyde towards the {alpha}, {beta}-unsaturated carboxylic acid and the consecutive oxidation of the acid as well as the parallel reaction of the aldehyde to products of deeper oxidation. The reaction steps of aldehyde respectively acid oxidation and catalyst reoxidation have been investigated separately in transient experiments. The combination of steady state and transient experiments has led to an improved understanding of the interaction of the catalyst with the aldehyde and the carboxylic acids as well as to a support of the kinetic model assumptions. (orig.)

  17. MODEL-BASED STUDY OF OXIDATION PROCESSES IN A JET ENGINE FUEL LIQUID PHASE

    OpenAIRE

    Orlovskaya, N.; Shupranov, D.; Bezborodov, Yu; Nadeykin, I.

    2009-01-01

    The process of oxidation in hexadecane liquid phase as a conventional model of oil hydrocarbons is investigated. The oxidation product structure is defined by means of Chromatography/Mass Spectrometry.

  18. Oxidation Resistant Graphite Studies

    Energy Technology Data Exchange (ETDEWEB)

    W. Windes; R. Smith

    2014-07-01

    The Very High Temperature Reactor (VHTR) Graphite Research and Development Program is investigating doped nuclear graphite grades exhibiting oxidation resistance. During a oxygen ingress accident the oxidation rates of the high temperature graphite core region would be extremely high resulting in significant structural damage to the core. Reducing the oxidation rate of the graphite core material would reduce the structural effects and keep the core integrity intact during any air-ingress accident. Oxidation testing of graphite doped with oxidation resistant material is being conducted to determine the extent of oxidation rate reduction. Nuclear grade graphite doped with varying levels of Boron-Carbide (B4C) was oxidized in air at nominal 740°C at 10/90% (air/He) and 100% air. The oxidation rates of the boronated and unboronated graphite grade were compared. With increasing boron-carbide content (up to 6 vol%) the oxidation rate was observed to have a 20 fold reduction from unboronated graphite. Visual inspection and uniformity of oxidation across the surface of the specimens were conducted. Future work to determine the remaining mechanical strength as well as graphite grades with SiC doped material are discussed.

  19. Methanol Oxidation on Model Elemental and Bimetallic Transition Metal Surfaces

    DEFF Research Database (Denmark)

    Tritsaris, G. A.; Rossmeisl, J.

    2012-01-01

    Direct methanol fuel cells are a key enabling technology for clean energy conversion. Using density functional theory calculations, we study the methanol oxidation reaction on model electrodes. We discuss trends in reactivity for a set of monometallic and bimetallic transition metal surfaces, fla...... active sites on the surface and to screen for novel bimetallic surfaces of enhanced activity. We suggest platinum copper surfaces as promising anode catalysts for direct methanol fuel cells....... and stepped, which includes platinum-based alloys with ruthenium, tin, and copper, as well as nonprecious alloys, overlayer structures, and modified edges. A common lower bound on the overpotential is estimated (ca. 0.3 V). A model for bifunctional alloys is employed to investigate the nature of the...

  20. A Simple Hydraulic Analog Model of Oxidative Phosphorylation.

    Science.gov (United States)

    Willis, Wayne T; Jackman, Matthew R; Messer, Jeffrey I; Kuzmiak-Glancy, Sarah; Glancy, Brian

    2016-06-01

    Mitochondrial oxidative phosphorylation is the primary source of cellular energy transduction in mammals. This energy conversion involves dozens of enzymatic reactions, energetic intermediates, and the dynamic interactions among them. With the goal of providing greater insight into the complex thermodynamics and kinetics ("thermokinetics") of mitochondrial energy transduction, a simple hydraulic analog model of oxidative phosphorylation is presented. In the hydraulic model, water tanks represent the forward and back "pressures" exerted by thermodynamic driving forces: the matrix redox potential (ΔGredox), the electrochemical potential for protons across the mitochondrial inner membrane (ΔGH), and the free energy of adenosine 5'-triphosphate (ATP) (ΔGATP). Net water flow proceeds from tanks with higher water pressure to tanks with lower pressure through "enzyme pipes" whose diameters represent the conductances (effective activities) of the proteins that catalyze the energy transfer. These enzyme pipes include the reactions of dehydrogenase enzymes, the electron transport chain (ETC), and the combined action of ATP synthase plus the ATP-adenosine 5'-diphosphate exchanger that spans the inner membrane. In addition, reactive oxygen species production is included in the model as a leak that is driven out of the ETC pipe by high pressure (high ΔGredox) and a proton leak dependent on the ΔGH for both its driving force and the conductance of the leak pathway. Model water pressures and flows are shown to simulate thermodynamic forces and metabolic fluxes that have been experimentally observed in mammalian skeletal muscle in response to acute exercise, chronic endurance training, and reduced substrate availability, as well as account for the thermokinetic behavior of mitochondria from fast- and slow-twitch skeletal muscle and the metabolic capacitance of the creatine kinase reaction. PMID:26807634

  1. An experimental and modeling study of diethyl carbonate oxidation

    KAUST Repository

    Nakamura, Hisashi

    2015-04-01

    Diethyl carbonate (DEC) is an attractive biofuel that can be used to displace petroleum-derived diesel fuel, thereby reducing CO2 and particulate emissions from diesel engines. A better understanding of DEC combustion characteristics is needed to facilitate its use in internal combustion engines. Toward this goal, ignition delay times for DEC were measured at conditions relevant to internal combustion engines using a rapid compression machine (RCM) and a shock tube. The experimental conditions investigated covered a wide range of temperatures (660-1300K), a pressure of 30bar, and equivalence ratios of 0.5, 1.0 and 2.0 in air. To provide further understanding of the intermediates formed in DEC oxidation, species concentrations were measured in a jet-stirred reactor at 10atm over a temperature range of 500-1200K and at equivalence ratios of 0.5, 1.0 and 2.0. These experimental measurements were used to aid the development and validation of a chemical kinetic model for DEC.The experimental results for ignition in the RCM showed near negative temperature coefficient (NTC) behavior. Six-membered alkylperoxy radical (RO˙2) isomerizations are conventionally thought to initiate low-temperature branching reactions responsible for NTC behavior, but DEC has no such possible 6- and 7-membered ring isomerizations. However, its molecular structure allows for 5-, 8- and 9-membered ring RO˙2 isomerizations. To provide accurate rate constants for these ring structures, ab initio computations for RO˙2⇌Q˙OOH isomerization reactions were performed. These new RO˙2 isomerization rate constants have been implemented in a chemical kinetic model for DEC oxidation. The model simulations have been compared with ignition delay times measured in the RCM near the NTC region. Results of the simulation were also compared with experimental results for ignition in the high-temperature region and for species concentrations in the jet-stirred reactor. Chemical kinetic insights into the

  2. Photosynthetic water oxidation: insights from manganese model chemistry.

    Science.gov (United States)

    Young, Karin J; Brennan, Bradley J; Tagore, Ranitendranath; Brudvig, Gary W

    2015-03-17

    Catalysts for light-driven water oxidation are a critical component for development of solar fuels technology. The multielectron redox chemistry required for this process has been successfully deployed on a global scale in natural photosynthesis by green plants and cyanobacteria using photosystem II (PSII). PSII employs a conserved, cuboidal Mn4CaOX cluster called the O2-evolving complex (OEC) that offers inspiration for artificial O2-evolution catalysts. In this Account, we describe our work on manganese model chemistry relevant to PSII, particularly the functional model [Mn(III/IV)2(terpy)2(μ-O)2(OH2)2](NO3)3 complex (terpy = 2,2';6',2″-terpyridine), a mixed-valent di-μ-oxo Mn dimer with two terminal aqua ligands. In the presence of oxo-donor oxidants such as HSO5(-), this complex evolves O2 by two pathways, one of which incorporates solvent water in an O-O bond-forming reaction. Deactivation pathways of this catalyst include comproportionation to form an inactive Mn(IV)Mn(IV) dimer and also degradation to MnO2, a consequence of ligand loss when the oxidation state of the complex is reduced to labile Mn(II) upon release of O2. The catalyst's versatility has been shown by its continued catalytic activity after direct binding to the semiconductor titanium dioxide. In addition, after binding to the surface of TiO2 via a chromophoric linker, the catalyst can be oxidized by a photoinduced electron-transfer mechanism, mimicking the natural PSII process. Model oxomanganese complexes have also aided in interpreting biophysical and computational studies on PSII. In particular, the μ-oxo exchange rates of the Mn-terpy dimer have been instrumental in establishing that the time scale for μ-oxo exchange of high-valent oxomanganese complexes with terminal water ligands is slower than O2 evolution in the natural photosynthetic system. Furthermore, computational studies on the Mn-terpy dimer and the OEC point to similar Mn(IV)-oxyl intermediates in the O-O bond

  3. Modeling Degradation in Solid Oxide Electrolysis Cells - Volume II

    Energy Technology Data Exchange (ETDEWEB)

    Manohar Motwani

    2011-09-01

    Idaho National Laboratory has an ongoing project to generate hydrogen from steam using solid oxide electrolysis cells (SOECs). To accomplish this, technical and degradation issues associated with the SOECs will need to be addressed. This report covers various approaches being pursued to model degradation issues in SOECs. An electrochemical model for degradation of SOECs is presented. The model is based on concepts in local thermodynamic equilibrium in systems otherwise in global thermodynamic non-equilibrium. It is shown that electronic conduction through the electrolyte, however small, must be taken into account for determining local oxygen chemical potential,, within the electrolyte. The within the electrolyte may lie out of bounds in relation to values at the electrodes in the electrolyzer mode. Under certain conditions, high pressures can develop in the electrolyte just near the oxygen electrode/electrolyte interface, leading to oxygen electrode delamination. These predictions are in accordance with the reported literature on the subject. Development of high pressures may be avoided by introducing some electronic conduction in the electrolyte. By combining equilibrium thermodynamics, non-equilibrium (diffusion) modeling, and first-principles, atomic scale calculations were performed to understand the degradation mechanisms and provide practical recommendations on how to inhibit and/or completely mitigate them.

  4. Modelling nitrous oxide emissions from grazed grassland systems

    International Nuclear Information System (INIS)

    Grazed grassland systems are an important component of the global carbon cycle and also influence global climate change through their emissions of nitrous oxide and methane. However, there are huge uncertainties and challenges in the development and parameterisation of process-based models for grazed grassland systems because of the wide diversity of vegetation and impacts of grazing animals. A process-based biogeochemistry model, DeNitrification-DeComposition (DNDC), has been modified to describe N2O emissions for the UK from regional conditions. This paper reports a new development of UK-DNDC in which the animal grazing practices were modified to track their contributions to the soil nitrogen (N) biogeochemistry. The new version of UK-DNDC was tested against datasets of N2O fluxes measured at three contrasting field sites. The results showed that the responses of the model to changes in grazing parameters were generally in agreement with observations, showing that N2O emissions increased as the grazing intensity increased. - Highlights: ► Parameterisation of grazing system using grazing intensity. ► Modification of UKDNDC for the UK soil and weather conditions. ► Validation of the UKDNDC against measured data of N2O emissions in three UK sites. ► Estimating influence of animal grazing practises on N2O emissions. - Grazing system was parameterised using grazing intensity and UK-DNDC model was modified and validated against measured data of N2O emissions in three UK sites.

  5. The role of lager beer yeast in oxidative stability of model beer

    DEFF Research Database (Denmark)

    Berner, Torben Sune; Arneborg, Nils

    2012-01-01

    AIMS: In this study, we investigated the relationship between the ability of lager brewing yeast strains to tolerate oxidative stress and their ability to produce oxidative stable model beer. METHODS AND RESULTS: Screening of 21 lager brewing yeast strains against diamide and paraquat showed...... that the oxidative stress resistance was strain dependent. Fermentation of model wort in European Brewing Convention tubes using three yeast strains with varying oxidative stress resistances resulted in three model beers with different rates of radical formation as measured by electron spin resonance in forced...... in the model beers. CONCLUSIONS: A more oxidative stable beer is not obtained by a more-oxidative-stress-tolerant lager brewing yeast strain, exhibiting a higher secretion of thioredoxin, but rather by a less-oxidative-stress-tolerant strain, exhibiting a higher iron uptake. SIGNIFICANCE AND IMPACT...

  6. Experimental and modeling study of the oxidation of xylenes

    CERN Document Server

    Battin-Leclerc, F; Glaude, P A; Belmekki, N; Battin-Leclerc, Fr\\'{e}d\\'{e}rique; Bounaceur, Roda; Glaude, Pierre-Alexandre; Belmekki, Najib

    2006-01-01

    This paper describes an experimental and modeling study of the oxidation of the three isomers of xylene (ortho-, meta- and para-xylenes). For each compound, ignition delay times of hydrocarbon-oxygen-argon mixtures with fuel equivalence ratios from 0.5 to 2 were measured behind reflected shock waves for temperatures from 1330 to 1800 K and pressures from 6.7 to 9 bar. The results show a similar reactivity for the three isomers. A detailed kinetic mechanism has been proposed, which reproduces our experimental results, as well as some literature data obtained in a plug flow reactor at 1155 K showing a clear difference of reactivity between the three isomers of xylene. The main reaction paths have been determined by sensitivity and flux analyses and have allowed the differences of reactivity to be explained.

  7. Reactor modeling and process analysis for partial oxidation of natural gas

    NARCIS (Netherlands)

    Albrecht, Bogdan Alexandru

    2004-01-01

    This thesis analyses a novel process of partial oxidation of natural gas and develops a numerical tool for the partial oxidation reactor modeling. The proposed process generates syngas in an integrated plant of a partial oxidation reactor, a syngas turbine and an air separation unit. This is called

  8. Boolean modeling and fault diagnosis in oxidative stress response

    OpenAIRE

    Sridharan Sriram; Layek Ritwik; Datta Aniruddha; Venkatraj Jijayanagaram

    2012-01-01

    Abstract Background Oxidative stress is a consequence of normal and abnormal cellular metabolism and is linked to the development of human diseases. The effective functioning of the pathway responding to oxidative stress protects the cellular DNA against oxidative damage; conversely the failure of the oxidative stress response mechanism can induce aberrant cellular behavior leading to diseases such as neurodegenerative disorders and cancer. Thus, understanding the normal signaling present in ...

  9. An approach to modeling of silicon oxidation in a wet ultra-diluted ambient

    NARCIS (Netherlands)

    Kovalgin, A.Y.; Hof, A.J.; Schmitz, J.

    2005-01-01

    In this work, we make steps towards developing a new wet-oxidation model of silicon based on electron-stimulated dissociation of H2O molecules. The need for a new model arises from the fact that existing physical models are inadequate to describe the thin-oxide regime. Two regimes of silicon oxidati

  10. Ultrasound assisted synthesis of nanocrystalline zinc oxide: Experiments and modelling

    Energy Technology Data Exchange (ETDEWEB)

    Hosni, Mongia [Laboratoire des Sciences des Procédés et des Matériaux, LSPM-CNRS, Université Paris 13, 99 av. J.B. Clément, 93430 Villetaneuse (France); Farhat, Samir, E-mail: farhat@lspm.cnrs.fr [Laboratoire des Sciences des Procédés et des Matériaux, LSPM-CNRS, Université Paris 13, 99 av. J.B. Clément, 93430 Villetaneuse (France); Schoenstein, Frederic; Karmous, Farah; Jouini, Noureddine [Laboratoire des Sciences des Procédés et des Matériaux, LSPM-CNRS, Université Paris 13, 99 av. J.B. Clément, 93430 Villetaneuse (France); Viana, Bruno [LCMCP Chimie-Paristech, UPMC, Collège de France, 11 Rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); Mgaidi, Arbi [Laboratoire de chimie minérale industrielle université Tunis el Manar (Tunisia)

    2014-12-05

    Highlights: • ZnO nanospheres and nanowires were grown using ultrasound and thermal activation techniques. • The growth uses forced hydrolysis of zinc acetate in diethylene glycol (DEG). • A thermochemical model was developed based on thermodynamic equilibrium calculations. • We estimate species distribution in the bubble in temperature range from 5000 K to ambient. • We propose a new mechanism for ZnO growth assisted by ultrasound irradiation. - Abstract: A fast and green approach is proposed for the preparation of nanocrystalline zinc oxide (ZnO) via ultrasonic (US) irradiation in polyol medium. The process uses forced hydrolysis of zinc acetate in diethylene glycol (DEG). The protocol is compared to thermal activation under the same chemical environment. The activation method is found to be playing a critical role in the selective synthesis of morphologically distinct nanostructures. As compared to thermally activated conventional polyol process, (US) permits to considerably reduce reaction time as well as size of particles. In addition, the shape of these nanoparticles was changed from long nanowires to small nanospheres, indicating different reaction mechanisms. To explain this difference, a thermochemical model was developed based on thermodynamic equilibrium calculations. The model estimate species distribution in the bubble in temperature range from 5000 K to ambient simulating quenching process during bubble formation and collapse. Our results indicate the presence of high density of zinc atoms that could be responsible of a high density of nucleation as compared to thermal activation.

  11. A comprehensive experimental and modeling study of isobutene oxidation

    KAUST Repository

    Zhou, Chong-Wen

    2016-03-17

    Isobutene is an important intermediate in the pyrolysis and oxidation of higher-order branched alkanes, and it is also a component of commercial gasolines. To better understand its combustion characteristics, a series of ignition delay time (IDT) and laminar flame speed (LFS) measurements have been performed. In addition, flow reactor speciation data recorded for the pyrolysis and oxidation of isobutene is also reported. Predictions of an updated kinetic model described herein are compared with each of these data sets, as well as with existing jet-stirred reactor (JSR) species measurements. IDTs of isobutene oxidation were measured in four different shock tubes and in two rapid compression machines (RCMs) under conditions of relevance to practical combustors. The combination of shock tube and RCM data greatly expands the range of available validation data for isobutene oxidation models to pressures of 50 atm and temperatures in the range 666–1715 K. Isobutene flame speeds were measured experimentally at 1 atm and at unburned gas temperatures of 298–398 K over a wide range of equivalence ratios. For the flame speed results, there was good agreement between different facilities and the current model in the fuel-rich region. Ab initio chemical kinetics calculations were carried out to calculate rate constants for important reactions such as H-atom abstraction by hydroxyl and hydroperoxyl radicals and the decomposition of 2-methylallyl radicals. A comprehensive chemical kinetic mechanism has been developed to describe the combustion of isobutene and is validated by comparison to the presently considered experimental measurements. Important reactions, highlighted via flux and sensitivity analyses, include: (a) hydrogen atom abstraction from isobutene by hydroxyl and hydroperoxyl radicals, and molecular oxygen; (b) radical–radical recombination reactions, including 2-methylallyl radical self-recombination, the recombination of 2-methylallyl radicals with

  12. Chronic antioxidant therapy reduces oxidative stress in a mouse model of Alzheimer’s disease

    OpenAIRE

    Siedlak, Sandra L.; Casadesus, Gemma; Webber, Kate M; Pappolla, Miguel A.; Atwood, Craig S.; Smith, Mark A.; Perry, George

    2009-01-01

    Oxidative modifications are a hallmark of oxidative imbalance in the brains of individuals with Alzheimer’s, Parkinson’s and prion diseases and their respective animal models. While the causes of oxidative stress are relatively well-documented, the effects of chronically reducing oxidative stress on cognition, pathology and biochemistry require further clarification. To address this, young and aged control and amyloid-β protein precursor-over-expressing mice were fed a diet with added R-alpha...

  13. Protective Effect of Arginine on Oxidative Stress in Transgenic Sickle Mouse Models

    OpenAIRE

    Dasgupta, Trisha; Hebbel, Robert P.; Kaul, Dhananjay K.

    2006-01-01

    Sickle cell disease (SCD) is characterized by reperfusion injury and chronic oxidative stress. Oxidative stress and hemolysis in SCD result in inactivation of nitric oxide (NO) and depleted arginine levels. We hypothesized that augmenting NO production by arginine supplementation will reduce oxidative stress in SCD. To this end, we measured the effect of arginine (5% in mouse chow) on NO metabolites (NOx), lipid peroxidation (LPO) and selected antioxidants in transgenic sickle mouse models. U...

  14. Modeling the chemical evolution of nitrogen oxides near roadways

    Science.gov (United States)

    Wang, Yan Jason; DenBleyker, Allison; McDonald-Buller, Elena; Allen, David; Zhang, K. Max

    2011-01-01

    The chemical evolution of nitrogen dioxide (NO 2) and nitrogen monoxide (NO) in the vicinity of roadways is numerically investigated using a computational fluid dynamics model, CFD-VIT-RIT and a Gaussian-based model, CALINE4. CFD-VIT-RIT couples a standard k- ɛ turbulence model for turbulent mixing and the Finite-Rate model for chemical reactions. CALINE4 employs a discrete parcel method, assuming that chemical reactions are independent of the dilution process. The modeling results are compared to the field measurement data collected near two roadways in Austin, Texas, State Highway 71 (SH-71) and Farm to Market Road 973 (FM-973), under parallel and perpendicular wind conditions during the summer of 2007. In addition to ozone (O 3), other oxidants and reactive species including hydroperoxyl radical (HO 2), organic peroxyl radical (RO 2), formaldehyde (HCHO) and acetaldehyde (CH 3CHO) are considered in the transformation from NO to NO 2. CFD-VIT-RIT is shown to be capable of predicting both NO x and NO 2 profiles downwind. CALINE4 is able to capture the NO x profiles, but underpredicts NO 2 concentrations under high wind velocity. Our study suggests that the initial NO 2/NO x ratios have to be carefully selected based on traffic conditions in order to assess NO 2 concentrations near roadways. The commonly assumed NO 2/NO x ratio by volume of 5% may not be suitable for most roadways, especially those with a high fraction of heavy-duty truck traffic. In addition, high O 3 concentrations and high traffic volumes would lead to the peak NO 2 concentration occurring near roadways with elevated concentrations persistent over a long distance downwind.

  15. Modeling of structural effects in biomedical elements after titanium oxidation in fluidized bed

    Science.gov (United States)

    Jasiński, J.; Szota, M.; Mendzik, K.

    2010-06-01

    Oxidation is one of the most employed methods to improve titanium and its alloys properties especially due to medical application. This process like most of the thermochemical treatment processes substantially influences on the characteristic of surface layers and the same on its mechanical and useful properties. Oxide coatings produced during titanium oxidation were examined due to their composition identification. Titanium was oxidized in fluidized bed in temperature range between 500÷700°C. Microstructures of titanium with a visible oxide coating on its surface after thermochemical treatment and changes of grain size in core of titanium samples are described. Moreover Xray phase analysis of obtained oxides coatings was made as well as microhardness measurements of titanium surface layers after oxidation process. Finally, the surfaces of titanium after oxidation in fluidized bed were measured by Auger electron spectroscopy. All research results are used to built numerical model of oxidation process in fluidized. Titanium oxidation process in fluidized bed is very complicated, because changes of parameters are non linear characteristics. This fact and lack of mathematical algorithms describing this process makes modeling properties of titanium elements by traditional numerical methods difficult or even impossible. In this case it is possible to try using artificial neural network. Using neural networks for modeling oxidizing in fluidized bed is caused by several nets' features: non linear character, ability to generalize the results of calculations for data out of training set, no need for mathematical algorithms describing influence changes input parameters on modeling materials properties.

  16. Transgenic Mouse Model for Reducing Oxidative Damage in Bone

    Science.gov (United States)

    Schreurs, A.-S.; Torres, S.; Truong, T.; Kumar, A.; Alwood, J. S.; Limoli, C. L.; Globus, R. K.

    2014-01-01

    Exposure to musculoskeletal disuse and radiation result in bone loss; we hypothesized that these catabolic treatments cause excess reactive oxygen species (ROS), and thereby alter the tight balance between bone resorption by osteoclasts and bone formation by osteoblasts, culminating in bone loss. To test this, we used transgenic mice which over-express the human gene for catalase, targeted to mitochondria (MCAT). Catalase is an anti-oxidant that converts the ROS hydrogen peroxide into water and oxygen. MCAT mice were shown previously to display reduced mitochondrial oxidative stress and radiosensitivity of the CNS compared to wild type controls (WT). As expected, MCAT mice expressed the transgene in skeletal tissue, and in marrow-derived osteoblasts and osteoclast precursors cultured ex vivo, and also showed greater catalase activity compared to wildtype (WT) mice (3-6 fold). Colony expansion in marrow cells cultured under osteoblastogenic conditions was 2-fold greater in the MCAT mice compared to WT mice, while the extent of mineralization was unaffected. MCAT mice had slightly longer tibiae than WT mice (2%, P less than 0.01), although cortical bone area was slightly lower in MCAT mice than WT mice (10%, p=0.09). To challenge the skeletal system, mice were treated by exposure to combined disuse (2 wk Hindlimb Unloading) and total body irradiation Cs(137) (2 Gy, 0.8 Gy/min), then bone parameters were analyzed by 2-factor ANOVA to detect possible interaction effects. Treatment caused a 2-fold increase (p=0.015) in malondialdehyde levels of bone tissue (ELISA) in WT mice, but had no effect in MCAT mice. These findings indicate that the transgene conferred protection from oxidative damage caused by treatment. Unexpected differences between WT and MCAT mice emerged in skeletal responses to treatment.. In WT mice, treatment did not alter osteoblastogenesis, cortical bone area, moment of inertia, or bone perimeter, whereas in MCAT mice, treatment increased these

  17. Modeling of Alkane Oxidation Using Constituents and Species

    Science.gov (United States)

    Bellan, Jasette; Harstad, Kenneth G.

    2010-01-01

    It is currently not possible to perform simulations of turbulent reactive flows due in particular to complex chemistry, which may contain thousands of reactions and hundreds of species. This complex chemistry results in additional differential equations, making the numerical solution of the equation set computationally prohibitive. Reducing the chemical kinetics mathematical description is one of several important goals in turbulent reactive flow modeling. A chemical kinetics reduction model is proposed for alkane oxidation in air that is based on a parallel methodology to that used in turbulence modeling in the context of the Large Eddy Simulation. The objective of kinetic modeling is to predict the heat release and temperature evolution. This kinetic mechanism is valid over a pressure range from atmospheric to 60 bar, temperatures from 600 K to 2,500 K, and equivalence ratios from 0.125 to 8. This range encompasses diesel, HCCI, and gas-turbine engines, including cold ignition. A computationally efficient kinetic reduction has been proposed for alkanes that has been illustrated for n-heptane using the LLNL heptane mechanism. This model is consistent with turbulence modeling in that scales were first categorized into either those modeled or those computed as progress variables. Species were identified as being either light or heavy. The heavy species were decomposed into defined 13 constituents, and their total molar density was shown to evolve in a quasi-steady manner. The light species behave either in a quasi-steady or unsteady manner. The modeled scales are the total constituent molar density, Nc, and the molar density of the quasi-steady light species. The progress variables are the total constituent molar density rate evolution and the molar densities of the unsteady light species. The unsteady equations for the light species contain contributions of the type gain/loss rates from the heavy species that are modeled consistent with the developed mathematical

  18. Physical chemistry and modelling of the sintering of actinide oxides

    International Nuclear Information System (INIS)

    This report gives a synthesis of the work I have carried out or to which I have numerically contributed to from 1996 up to 2012 in the Department of Plutonium Uranium and minor Actinides in Cadarache CEA Center. Their main goal is the study and the modeling of the sintering process of nuclear fuels which is the unifying thread of this document. Both in order to take into account the physical and chemical features of the actinide bearing oxide material and in order to combine the different transport phenomena leading to sintering, a sub-granular scale model is under development. Extension to a varying chemical composition as well as exchanges with the gaseous phase are foreseen. A simulation on a larger scale (pellet scale) is ongoing in the framework of a PhD thesis. Validation means have been tested with (U,Pu)O2 material on the scale of the pellet (Small Angle Neutron Diffusion), on the scale of powder granules (X-Ray High Resolution Micro-Tomography) and with CeO2 at the 'Institut de Chimie Separative' in Marcoule on a single crystal scale (Environmental Scanning Electron Microscope). The required microstructure homogeneity for nuclear fuels has led to a campaign of experimental studies about the role of Cr2O3 as a sintering aid. Whole of these studies improve our understanding of fuel sintering and hence leads to an improved mastering of this process. (author)

  19. Qualitative model of stress distribution in Zr alloys oxidized under high temperatures

    International Nuclear Information System (INIS)

    The results are summed up of an experimental study of oxide layers and metal substrate for different types of zirconium alloys with Cu, Fe, Mo, V. and Cr additions oxidized at high temperatures. The state of stress in oxidized samples of different zirconium alloy samples was studied by determining the average stress in oxide layers of different thicknesses, the course of stress in an oxide layer of a certain thickness, and by determining the course of residual deformation in a metal layer adjacent to the oxide/metal interface. A qualitative model was proposed for stress distribution in both components of the metal/oxide system at oxidation and room temperatures. The hypothetical stress distribution qualitatively agrees with experimental results and literature data based on elastic-plastic behaviour of zirconium alloys. (Z.M.)

  20. Electro oxidation of Malachite Green and Modeling Using ANN

    OpenAIRE

    Antony Soloman, P.; Ahmed Basha, C.; Velan, M.; Balasubramanian, N.

    2010-01-01

    This study involves the electro-oxidation of malachite green, a triphenyl methane dye, extensively used in industries and aquaculture, and later banned in most developed countries because of its potential carcinogenicity, mutagenicity and teratogenicity in mammals. The study is conducted in a batch electro-chemical reactor using the catalytic anode (made of noble oxide coated, RuOx-TiOx, titanium expanded mesh) that mediates the oxidation of organic species by the formation of higher oxida...

  1. Spectroscopic studies of alpha tocopherol interaction with a model liposome and its influence on oxidation dynamics

    Science.gov (United States)

    Krilov, Dubravka; Kosović, Marin; Serec, Kristina

    2014-08-01

    The influence of α-tocopherol on the surface conformation of liposome, as a model component of lipoproteins, and its role in oxidation process were studied. FT-IR spectra from suspensions of neat liposome, mixtures of liposome and α-tocopherol and liposome with incorporated α-tocopherol were analyzed. When α-tocopherol was incorporated into liposome, intensities of some bands were decreased or increased in comparison with the spectra of liposome and α-tocopherol mixture. These changes reflect the different localization of α-tocopherol in two types of liposome suspensions. The oxidation of liposome suspensions was initiated by addition of cupric ions. After prolonged oxidation, the differences in FT-IR spectra of oxidized samples were recorded. Differences were observed in comparison with spectra of native and oxidized liposomes were analyzed. The rate of oxidation was measured by EPR oximetry. Oxidation was generally very slow, but faster in liposome without α-tocopherol, indicating the protective role of α-tocopherol against liposome oxidation. On the other hand, liposome suspensions with EDTA in the buffer were not oxidized at all, while those with α-tocopherol and liposome mixture were only slightly oxidized. In this case the consumption of oxygen was the result of liposome oxidation supported by α-tocopherol. These results reflect the ambivalent role of α-tocopherol in liposome oxidation, similarly to findings in studies of lipoprotein oxidation.

  2. Kinetic modeling of antimony(III) oxidation and sorption in soils.

    Science.gov (United States)

    Cai, Yongbing; Mi, Yuting; Zhang, Hua

    2016-10-01

    Kinetic batch and saturated column experiments were performed to study the oxidation, adsorption and transport of Sb(III) in two soils with contrasting properties. Kinetic and column experiment results clearly demonstrated the extensive oxidation of Sb(III) in soils, and this can in return influence the adsorption and transport of Sb. Both sorption capacity and kinetic oxidation rate were much higher in calcareous Huanjiang soil than in acid red Yingtan soil. The results indicate that soil serve as a catalyst in promoting oxidation of Sb(III) even under anaerobic conditions. A PHREEQC model with kinetic formulations was developed to simulate the oxidation, sorption and transport of Sb(III) in soils. The model successfully described Sb(III) oxidation and sorption data in kinetic batch experiment. It was less successful in simulating the reactive transport of Sb(III) in soil columns. Additional processes such as colloid facilitated transport need to be quantified and considered in the model. PMID:27214003

  3. Thermodynamic and kinetic modeling of oxide precipitation in nanostructured ferritic alloys

    International Nuclear Information System (INIS)

    The mechanical properties and radiation tolerance of nanostructured ferritic alloys rely on a dense population of nanometer-scale Y–Ti oxides. The stability of these nano-oxides during extended service is critical in high temperature applications. Here, a model framework is developed for the thermodynamics and kinetics of Y–Ti oxide nucleation, growth and coarsening. The model, which is based upon available thermodynamic and kinetic data as well as key density functional theory calculations, shows that nano-oxide nucleation and growth are highly driven and that pipe diffusion is the dominant mode of their coarsening, in agreement with previous analyses of experimental high temperature data. The model predicts that the nano-oxides are thermally stable for 80 or more years below 1175 K. This analysis also provides insights into the effect of O and Ti on nano-oxide sizes, and on optimization of alloy microstructure

  4. Photoelectrolysis at the oxide-electrolyte interface as interpreted through the 'transition' layer model

    Science.gov (United States)

    Kalia, R. K.; Weber, Michael F.; Schumacher, L.; Dignam, M. J.

    1980-12-01

    A transition layer model of the oxide-electrolyte interface, proposed earlier by one of us, is outlined and then examined in the light of experimental data relating primarily to photoelectrolysis of water at semiconducting oxide electrodes. The model provides useful insight into the behaviour of the system and allows a calculation of thc minimum bias potential needed for photoelectrolysis, thus illuminating the origin of the requirement for such an external bias. In order to electrolyse water without a bias, the model requires an n-type oxide to be sufficiently reduced so that it is thermodynamically capable of chemically reducing water to produce hydrogen at 1 atm pressure. Similarly, for bias-free operation, a p-type metal oxide must be thermodynamically unstable with respect to the release of oxygen at 1 atm pressure. In the face of these requirements it is apparent that oxide stability is bound to be in general a serious problem for nonstoichiometric single metal oxides.

  5. Copper Oxide Nanoparticles for Advanced Refrigerant Thermophysical Properties: Mathematical Modeling

    Directory of Open Access Journals (Sweden)

    S. A. Fadhilah

    2014-01-01

    Full Text Available In modern days, refrigeration systems are important for industrial and domestic applications. The systems consume more electricity as compared to other appliances. The refrigeration systems have been investigated thoroughly in many ways to reduce the energy consumption. Hence, nanorefrigerant which is one kind of nanofluids has been introduced as a superior properties refrigerant that increased the heat transfer rate in the refrigeration system. Many types of materials could be used as the nanoparticles to be suspended into the conventional refrigerants. In this study, the effect of the suspended copper oxide (CuO nanoparticles into the 1,1,1,2-tetrafluoroethane, R-134a is investigated by using mathematical modeling. The investigation includes the thermal conductivity, dynamic viscosity, and heat transfer rate of the nanorefrigerant in a tube of evaporator. The results show enhanced thermophysical properties of nanorefrigerant compared to the conventional refrigerant. These advanced thermophysical properties increased the heat transfer rate in the tube. The nanorefrigerant could be a potential working fluid to be used in the refrigeration system to increase the heat transfer characteristics and save the energy usage.

  6. Mass transfer model for two-layer TBP oxidation reactions

    International Nuclear Information System (INIS)

    To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. This report presents measurements of mass transfer rates for the mixing of water and butanol in two-layer, TBP-aqueous mixtures, where the top layer is primarily TBP and the bottom layer is comprised of water or aqueous salt solution. Mass transfer coefficients are derived for use in the modeling of two-layer TBP-nitric acid oxidation experiments. Three cases were investigated: (1) transfer of water into the TBP layer with sparging of both the aqueous and TBP layers, (2) transfer of water into the TBP layer with sparging of just the TBP layer, and (3) transfer of butanol into the aqueous layer with sparging of both layers. The TBP layer was comprised of 99% pure TBP (spiked with butanol for the butanol transfer experiments), and the aqueous layer was comprised of either water or an aluminum nitrate solution. The liquid layers were air sparged to simulate the mixing due to the evolution of gases generated by oxidation reactions. A plastic tube and a glass frit sparger were used to provide different size bubbles. Rates of mass transfer were measured using infrared spectrophotometers provided by SRTC/Analytical Development

  7. Influence of oxide microstructure on corrosion behavior of zirconium-based model alloys

    Science.gov (United States)

    Silva, Marcelo Jose Gomes Da

    The extensive utilization of zirconium-based alloys in fuel cladding and other reactor internal components in the nuclear power industry has led to the continuous improvement of these alloys. At the present moment, demands for better performing nuclear fuel cladding materials are increasing. Also, new reactor designs have been proposed that would require the materials to withstand even more rigorous conditions. One of the factors that limit s fuel cladding utilization in nuclear reactors is uniform corrosion and the consequent hydriding of the fuel. In an attempt to develop mechanistic understanding of the role of alloying elements in the growth of a stable protective oxide, a series of model zirconium-based alloys was prepared (Zr-xFe-yCr, Zr-xCu-yMo, Zr-xNb-ySn, for various x and y, pure Zr and Zircaloy-4) and examined with advanced characterization techniques. The alloys were corrosion tested in autoclaves under three different conditions: 360°C water, 500°C steam and 500°C supercritical water in excess of 400 days. These autoclave testing conditions simulate nuclear reactor environment for both current designs (360°C water) and the new supercritical water reactor (500°C steam and 500°C supercritical water) proposed by the generation-IV initiative. The oxide films formed were systematically examined at the Advanced Photon Source using microbeam synchrotron radiation diffraction and fluorescence of cross-sectional samples to determine the oxide phases present and their crystallographic texture as a function of distance from the metal/oxide interface. Also, the overall texture of the oxide layers was investigated using synchrotron radiation diffraction in frontal geometry. The corrosion kinetics is a function of the alloy system and showed a wide range of behaviors, from immediately unstable oxide growth to stable behavior. The corrosion weight gains from testing at high temperature are a factor of five higher than those measured at 360°C but the

  8. Observations and Model Analysis of Enhanced Oxidized Mercury in the Free Troposphere during NOMADSS

    Science.gov (United States)

    Gratz, L.; Shah, V.; Ambrose, J. L., II; Jaffe, D. A.; Jaegle, L.; Selin, N. E.; Song, S.; Festa, J.; Stutz, J.

    2014-12-01

    Mercury (Hg) is a hazardous neurotoxic pollutant with complex atmospheric speciation and chemistry. It exists in the atmosphere primarily as gaseous elemental Hg (GEM), with a lifetime on the order of months, while oxidized Hg is more water soluble and deposits readily. Thus, Hg is considered both a local and a global pollutant. There are significant limitations in our understanding of global Hg cycling, including the sources and chemical mechanisms producing enhanced oxidized Hg in the free troposphere. Ground-based and airborne studies have associated free tropospheric oxidized Hg with GEM oxidation and atmospheric subsidence. Chemical transport models suggest that free tropospheric GEM oxidation is largely attributable to bromine (Br) atoms. During the 2013 Nitrogen Oxidants Mercury and Aerosol Distributions Sources and Sinks (NOMADSS) campaign, we sought to quantify the distribution and chemical transformation of Hg species in the free troposphere over the southeastern US. Enhanced oxidized Hg over North Texas was associated with long-range transport and subsidence from the sub-tropical Pacific free troposphere, where GEOS-Chem predicts air enriched in oxidized Hg. Bromine oxide (BrO) concentrations were also elevated over North Texas, perhaps supporting halogen oxidation as a source of free tropospheric oxidized Hg. Over the Atlantic Ocean, oxidized Hg up to 680 pg m-3 was associated with GEM oxidation and subsidence within the Atlantic high pressure system. The standard GEOS-Chem model underestimates free tropospheric oxidized Hg in these locations by a factor of three to ten, possibly due to underestimation of Br concentrations and/or uncertainty in the Hg+Br rate constant. We investigate GEOS-Chem's improved ability to reproduce the observed concentrations by tripling free tropospheric Br in the tropics and implementing a faster Hg+Br oxidation mechanism. Results have important implications for our understanding of global-scale atmospheric Hg chemistry and

  9. Inhibition of oxidation in nuclear graphite

    International Nuclear Information System (INIS)

    Graphite is a fundamental material of high-temperature gas-cooled nuclear reactors, providing both structure and neutron moderation. Its high thermal conductivity, chemical inertness, thermal heat capacity, and high thermal structural stability under normal and off-normal conditions contribute to the inherent safety of these reactor designs. One of the primary safety issues for a high-temperature graphite reactor core is the possibility of rapid oxidation of the carbon structure during an off-normal design basis event where an oxidising atmosphere (air ingress) can be introduced to the hot core. Although the current Generation IV high-temperature reactor designs attempt to mitigate any damage caused by a postulated air ingress event, the use of graphite components that inhibit oxidation is a logical step to increase the safety of these reactors. Recent experimental studies of graphite containing between 5.5 and 7 wt% boron carbide (B4C) indicate that oxidation is dramatically reduced even at prolonged exposures at temperatures up to 900 deg. C. The proposed addition of B4C to graphite components in the nuclear core would necessarily be enriched in B-11 isotope in order to minimise B-10 neutron absorption and graphite swelling. The enriched boron can be added to the graphite during billet fabrication. Experimental oxidation rate results and potential applications for borated graphite in nuclear reactor components will be discussed. (authors)

  10. Model-based evaluation of the role of Anammox on nitric oxide and nitrous oxide productions in membrane aerated biofilm reactor

    DEFF Research Database (Denmark)

    Ni, Bing-Jie; Smets, Barth F.; Yuan, Zhiguo;

    2013-01-01

    A multispecies one-dimensional biofilm model considering nitric oxide (NO) and nitrous oxide (N2O) productions for membrane aerated biofilm reactor (MABR) that remove nitrogen autotrophically through aerobic ammonia oxidation followed by Anammox is used to study the role of Anammox activity on th...

  11. Geochemical modelling of arsenic adsorption to oxide surfaces

    OpenAIRE

    Gustafsson, Jon Petter; Bhattacharya, Prosun

    2007-01-01

    In natural environments, arsenic chemistry is dominated by the reactions of its two predominant soluble forms, arsenate and arsenite. To predict the fate of As in the environment, it is necessary to consider processes that act to restrict its mobility. The mobility of As is strongly influenced by adsorption reactions to particle surfaces. Arsenate and arsenite may form surface complexes with a number of different oxides, including Fe-, Al-, Mn- and Ti oxides. The focus of this chapter is on t...

  12. A kinetic model of municipal sludge degradation during non-catalytic wet oxidation.

    Science.gov (United States)

    Prince-Pike, Arrian; Wilson, David I; Baroutian, Saeid; Andrews, John; Gapes, Daniel J

    2015-12-15

    Wet oxidation is a successful process for the treatment of municipal sludge. In addition, the resulting effluent from wet oxidation is a useful carbon source for subsequent biological nutrient removal processes in wastewater treatment. Owing to limitations with current kinetic models, this study produced a kinetic model which predicts the concentrations of key intermediate components during wet oxidation. The model was regressed from lab-scale experiments and then subsequently validated using data from a wet oxidation pilot plant. The model was shown to be accurate in predicting the concentrations of each component, and produced good results when applied to a plant 500 times larger in size. A statistical study was undertaken to investigate the validity of the regressed model parameters. Finally the usefulness of the model was demonstrated by suggesting optimum operating conditions such that volatile fatty acids were maximised. PMID:26426294

  13. Quantitative Mapping of Reversible Mitochondrial Complex I Cysteine Oxidation in a Parkinson Disease Mouse Model*

    OpenAIRE

    Danielson, Steven R.; Held, Jason M.; Oo, May; Riley, Rebeccah; Bradford W Gibson; Julie K. Andersen

    2011-01-01

    Differential cysteine oxidation within mitochondrial Complex I has been quantified in an in vivo oxidative stress model of Parkinson disease. We developed a strategy that incorporates rapid and efficient immunoaffinity purification of Complex I followed by differential alkylation and quantitative detection using sensitive mass spectrometry techniques. This method allowed us to quantify the reversible cysteine oxidation status of 34 distinct cysteine residues out of a total 130 present in muri...

  14. Biogeochemical modelling of anaerobic vs. aerobic methane oxidation in a meromictic crater lake (Lake Pavin, France)

    International Nuclear Information System (INIS)

    Methane is a powerful greenhouse gas and its concentration in the atmosphere has increased over the past decades. Methane produced by methanogenic Archae can be consumed through aerobic and anaerobic oxidation pathways. In anoxic conditions found in freshwater environments such as meromictic lakes, CH4 oxidation pathways involving different terminal electron acceptors such as NO3-, SO42-, and oxides of Fe and Mn are thermodynamically possible. In this study, a reactive transport model was developed to assess the relative significance of the different pathways of CH4 consumption in the water column of Lake Pavin. In most cases, the model reproduced experimental data collected from the field from June 2006 to June 2007. Although the model and the field measurements suggest that anaerobic CH4 oxidation may contribute to CH4 consumption in the water column of Lake Pavin, aerobic oxidation remains the major sink of CH4 in this lake.

  15. Experimental kinetic study and modeling of calcium oxide carbonation

    International Nuclear Information System (INIS)

    Anthropogenic carbon dioxide (CO2) emissions, major contributors to the greenhouse effect, are considered as the main cause of global warming. So, decrease of CO2 emitted by large industrial combustion sources or power plants, is an important scientific goal. One of the approaches is based on CO2 separation and capture from flue gas, followed by sequestration in a wide range of geological formations. In this aim, CO2 is captured by sorbents like calcium oxide (CaO) in multi-cycle process of carbonation/de-carbonation. However, it was shown that the most important limitations of such process are related to the reversibility of reaction. CaO rapidly loses activity towards CO2, so the maximum extent of carbonation decreases as long as the number of cycles increases. In order to well understand the processes and parameters influencing the capture capacity of CaO-based sorbents, it appears important to get details on the kinetic law governing the reaction, which have not been really studied up to now. To investigate this reaction, CaO carbonation kinetics was followed by means of thermogravimetric analysis (TGA) on divided materials. Special care was given to the validation of the usual kinetic assumptions such as steady state and rate-determining step assumptions. The aim was to obtain a model describing the reaction in order to explain the influence of intensive variables such as carbonation temperature and CO2 partial pressure. TGA curves obtained under isothermal and isobaric conditions showed an induction period linked to the nucleation process and a strong slowing down of the reaction rate once a given fractional conversion was reached. Both phenomena were observed to depend on carbonation temperature and CO2 partial pressure. To explain these results, the evolution of texture and microstructure of the solid during the reaction was regarded as essential. Reaction at the grain scale induces a volume increase from CaO to CaCO3 which causes a change in the porosity

  16. Modeling of combined high-temperature oxidation and nitridation under isothermal and thermal-cycling conditions

    International Nuclear Information System (INIS)

    A computer model was developed to simulate the oxidation and nitridation behavior of nickel-base alloys at high temperatures. The numerical model combines a commercial thermochemical software (ChemApp) with a two-dimensional finite-difference diffusion calculation. The growth of the external oxide scale and the dependence of the internal corrosion behavior on cracking and spalling of the oxide layer have been incorporated into the simulation. The model has been applied to reveal the mechanisms of several corrosion processes which have been investigated in air and oxygen-free nitrogen atmosphere under isothermal and thermal-cycling conditions. (orig.)

  17. Global modelling of the ClNO2 production impact on tropospheric nitrogen oxides and main oxidants

    Science.gov (United States)

    Cuevas Rodríguez, Carlos Alberto; Brown, Steven S.; Lamarque, Jean-Francoise; Saiz-Lopez, Alfonso; Kinnison, Douglas E.; Lopez-Hilfiker, Felipe; Thornton, Joel A.; Jaegle, Lyatt; Fibiger, Dorothy; McDuffie, Erin E.; Sullivan, Amy P.; Weber, Rodney J.; Dibb, Jack

    2016-04-01

    Heterogeneous uptake of dinitrogen pentoxide, N2O5, to aerosol is one of the most important reactions controlling the global budget of nitrogen oxides, with subsequent impacts on oxidants such as ozone and hydroxyl radical. Most chemistry global models assume that this uptake proceeds through hydrolysis to produce nitric acid, effectively a terminal sink for nitrogen oxides. However, recent field studies have shown that the yield of nitryl chloride, ClNO2, from N2O5 uptake is significant in many locations. Because ClNO2 photolyzes subsequent to its nighttime production to recycle NO2 and produce atomic chlorine, a potent oxidant, the impact of heterogeneous N2O5 uptake and the role of ClNO2 on the scale distribution of oxidants need to be re-assessed. Here we present global simulations using the chemistry-climate model CAM-Chem, including a state of the art halogen chemistry scheme and different assumptions for the magnitude and spatial distribution of ClNO2 yields from N2O5. The model shows a significant effect of ClNO2 production on tropospheric ozone, hydroxyl radical and peroxyacyl nitrates (PAN) during northern hemisphere late winter and early spring. Simulations are compared to observations from recent field campaigns, including ClNO2 and N2O5 from the Wintertime INvestigation of Transport, Emissions and Reactivity (WINTER) study on the NSF / NCAR C-130 aircraft on the U.S. East Coast in February and March of 2015.

  18. Evaluation and Model of Performance of A Tubular Solid Oxide Fuel Cell

    Institute of Scientific and Technical Information of China (English)

    JIA Jun-xi; SHEN Sheng-qiang

    2005-01-01

    A simulation model was developed to analyze the steady state and transient operation of a tubular solid oxide fuel cell. The model covers both the electrochemical and the heat transfer models. The electrochemical model deals with the Nernst potential, ohmic polarization, activation polarization, and concentration polarization, while the heat transfer model concerns the heat transfer by conduction, convection and radiation. The numerical results show that the ohmic loss is the dominant one among the three polarizations in a cathode-supported solid oxide fuel cell and in the middle part of a solid oxide fuel cell the temperature is higher than those at both the ends. When the inlet temperature and the flow rates of the fuel and the oxidant are kept constantly, the temperature of the solid structure of the cell will increase due to the increase of power output of the cell from the initial state to the new one.

  19. Models and experiments on degradation of oxidized silicon

    Science.gov (United States)

    Sah, C. T.

    1990-02-01

    The concepts of electronic and protonic traps are introduced to delineate and classify the fundamental mechanisms of charging, generation, annealing and hydrogenation of electronic or electron and hole traps located in the interfacial (gate-conductor/oxide, oxide/nitride and oxide/silicon), insulator (oxide, nitride and oxynitride) and semiconductor surface layers of silicon MOS transistors and integrated circuits. Two matrix tables, one without tunneling (3 × 3) and one with tunneling (3 × 4) are used to classify the trap charging and electronic injection mechanisms according to the initial and final (band or bound) states of the electronic transition and the energy exchange mechanisms (thermal, optical and Auger-impact). The importance of tunneling to and from traps (TTT) as an oxide charge build-up mechanism is discussed. A theoretical tunneling rate to traps is given showing that traps shallower than about 2 eV from the oxide conduction band edge or 3 eV from the oxide valence band edge cannot be charged by the TTT transitions alone. Experimental examples illustrating the use of these mechanism tables as well as the importance of breaking hydrogen and strained intrinsic bonds by hot electron impact and by thermal hole capture are discussed, including: (i) annealing of the oxide/Si interface traps via hydrogenation during 380C chip bonding and during Fowler-Nordheim tunneling electron injection (FN-TEI) and avalanche electron injection (AEI) stresses, (ii) interface trap generation and positive oxide charge build-up during electron injection via FN-TEI or AEI, and (iii) electrical deactivation of boron and other group-III acceptors (Al, Ga, In) in the silicon surface layer during FNTEI or AEI stresses. Examples at three d.c. bias conditions to delineate the dominant degradation mechanisms in silicon MOS transistors are given showing that trap charging via tunneling (FNTEI, FNTHI and TTT) dominates below about 3.3 V in both n-MOS and p-MOS but trap generation

  20. Models for the Configuration and Integrity of Partially Oxidized Fuel Rod Cladding at High Temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Siefken, L.J.

    1999-01-01

    Models were designed to resolve deficiencies in the SCDAP/RELAP5/MOD3.2 calculations of the configuration and integrity of hot, partially oxidized cladding. These models are expected to improve the calculations of several important aspects of fuel rod behavior. First, an improved mapping was established from a compilation of PIE results from severe fuel damage tests of the configuration of melted metallic cladding that is retained by an oxide layer. The improved mapping accounts for the relocation of melted cladding in the circumferential direction. Then, rules based on PIE results were established for calculating the effect of cladding that has relocated from above on the oxidation and integrity of the lower intact cladding upon which it solidifies. Next, three different methods were identified for calculating the extent of dissolution of the oxidic part of the cladding due to its contact with the metallic part. The extent of dissolution effects the stress and thus the integrity of the oxidic part of the cladding. Then, an empirical equation was presented for calculating the stress in the oxidic part of the cladding and evaluating its integrity based on this calculated stress. This empirical equation replaces the current criterion for loss of integrity which is based on temperature and extent of oxidation. Finally, a new rule based on theoretical and experimental results was established for identifying the regions of a fuel rod with oxidation of both the inside and outside surfaces of the cladding. The implementation of these models is expected to eliminate the tendency of the SCDAP/RELAP5 code to overpredict the extent of oxidation of the upper part of fuel rods and to underpredict the extent of oxidation of the lower part of fuel rods and the part with a high concentration of relocated material. This report is a revision and reissue of the report entitled, Improvements in Modeling of Cladding Oxidation and Meltdown.

  1. A fully coupled model for water-gas-heat reactive transport with methane oxidation in landfill covers.

    Science.gov (United States)

    Ng, C W W; Feng, S; Liu, H W

    2015-03-01

    Methane oxidation in landfill covers is a complex process involving water, gas and heat transfer as well as microbial oxidation. The coupled phenomena of microbial oxidation, water, gas, and heat transfer are not fully understood. In this study, a new model is developed that incorporates water-gas-heat coupled reactive transport in unsaturated soil with methane oxidation. Effects of microbial oxidation-generated water and heat are included. The model is calibrated using published data from a laboratory soil column test. Moreover, a series of parametric studies are carried out to investigate the influence of microbial oxidation-generated water and heat, initial water content on methane oxidation efficiency. Computed and measured results of gas concentration and methane oxidation rate are consistent. It is found that the coupling effects between water-gas-heat transfer and methane oxidation are significant. Ignoring microbial oxidation-generated water and heat can result in a significant difference in methane oxidation efficiency by 100%. PMID:25489976

  2. Models for solid oxide fuel cell systems exploitation of models hierarchy for industrial design of control and diagnosis strategies

    CERN Document Server

    Marra, Dario; Polverino, Pierpaolo; Sorrentino, Marco

    2016-01-01

    This book presents methodologies for optimal design of control and diagnosis strategies for Solid Oxide Fuel Cell systems. A key feature of the methodologies presented is the exploitation of modelling tools that balance accuracy and computational burden.

  3. New experimental evidence and modeling study of the ethylbenzene oxidation

    OpenAIRE

    Husson, Benoit; Ferrari, Maude; Herbinet, Olivier; Sayeed Ahmed, Syed; Glaude, Pierre-Alexandre; Battin-Leclerc, Frédérique

    2013-01-01

    A study of the oxidation of ethylbenzene has been performed in a jet-stirred reactor (JSR) at quasi-atmospheric pressure (800 Torr), at temperatures ranging 750-1100 K, at a mean residence time of 2 s and at three equivalence ratios ϕ (0.25, 1, and 2). Reactants and 25 reaction products were analyzed online by gas chromatography after sampling in the outlet gas. A new mechanism for the oxidation of ethylbenzene was proposed whose predictions were in satisfactory agreement with the measured sp...

  4. Metal Oxide Nanomaterial QNAR Models: Available Structural Descriptors and Understanding of Toxicity Mechanisms

    Directory of Open Access Journals (Sweden)

    Jiali Ying

    2015-10-01

    Full Text Available Metal oxide nanomaterials are widely used in various areas; however, the divergent published toxicology data makes it difficult to determine whether there is a risk associated with exposure to metal oxide nanomaterials. The application of quantitative structure activity relationship (QSAR modeling in metal oxide nanomaterials toxicity studies can reduce the need for time-consuming and resource-intensive nanotoxicity tests. The nanostructure and inorganic composition of metal oxide nanomaterials makes this approach different from classical QSAR study; this review lists and classifies some structural descriptors, such as size, cation charge, and band gap energy, in recent metal oxide nanomaterials quantitative nanostructure activity relationship (QNAR studies and discusses the mechanism of metal oxide nanomaterials toxicity based on these descriptors and traditional nanotoxicity tests.

  5. Empirical Modeling of Iron Oxide Dissolution in Sulphuric and Hydrochloric Acid

    Science.gov (United States)

    Hemmelmann, Jan C.; Xu, Hao; Krumm, Wolfgang

    2013-10-01

    A new approach is presented to an empirical modeling of chemical pickling processes, based on the activation energy of oxide dissolution in hydrochloric acid (HCl) and sulfuric acid (H2SO4). The model allows us to calculate pickling times as a function of definite parameters. The main oxide layers on hot-rolled materials are magnetite (Fe3O4), hematite (Fe2O3), and wustite (FeO). On the laboratory scale, the activation energy of each oxide has been determined. FeO is a metastable oxide and has been produced based on magnetite powder in a H2/H2O atmosphere. The oxide powders used for the experimental procedure have been analyzed by X-ray powder diffraction to insure the proper stoichiometry and composition. The model allows us to calculate the time of oxide dissolution based on the parameters temperature, acid concentration, and the composition of the oxide layer. Calculated values are verified by surface potential measurement on industrial oxide layers. The hot-rolled material used for verification is low carbon steel. A comparison between calculated pickling times and experimental data will be presented.

  6. Modeling of autoignition and NO sensitization for the oxidation of IC engine surrogate fuels

    CERN Document Server

    Anderlohr, Jörg; Da Cruz, A Pires; Battin-Leclerc, Frédérique; 10.1016/j.combustflame.2008.09.009

    2009-01-01

    This paper presents an approch for modeling with one single kinetic mechanism the chemistry of the autoignition and combustion processes inside an internal combustion engine, as well as the chemical kinetics governing the post-oxidation of unburned hydrocarbons in engine exhaust gases. Therefore a new kinetic model was developed, valid over a wide range of temperatures including the negative temperature coefficient regime. The model simulates the autoignition and the oxidation of engine surrogate fuels composed of n-heptane, iso-octane and toluene, which are sensitized by the presence of nitric oxides. The new model was obtained from previously published mechanisms for the oxidation of alkanes and toluene where the coupling reactions describing interactions between hydrocarbons and NOx were added. The mechanism was validated against a wide range of experimental data obtained in jet-stirred reactors, rapid compression machines, shock tubes and homogenous charge compression ignition engines. Flow rate and sensi...

  7. Mathematical model for microbial oxidation of pure lead sulfide by Thiobacillus ferrooxidans.

    Science.gov (United States)

    Kargi, F

    1989-08-01

    A shrinking-core mathematical model describing bioleaching of lead sulfide is developed considering the deposition of insoluble bio-oxidation products on metal sulfide particle surfaces. Variations in particle size are considered as it affects diffusion limitations. PMID:18588129

  8. Pulmonary oxidative stress, inflammation and dysregulated iron homeostatis in rat models of cardiovascular disease

    Science.gov (United States)

    Underlying cardiovascular disease (CVD) is considered a risk factor for the exacerbation of air pollution health effects. Therefore, rodent models of CVD are increasingly used to examine mechanisms ofvariation in susceptibility. Pulmonary oxidative stress, inflammation and altere...

  9. The NASA Lightning Nitrogen Oxides Model (LNOM): Application to Air Quality Modeling

    Science.gov (United States)

    Koshak, William; Peterson, Harold; Khan, Maudood; Biazar, Arastoo; Wang, Lihua

    2011-01-01

    Recent improvements to the NASA Marshall Space Flight Center Lightning Nitrogen Oxides Model (LNOM) and its application to the Community Multiscale Air Quality (CMAQ) modeling system are discussed. The LNOM analyzes Lightning Mapping Array (LMA) and National Lightning Detection Network(TradeMark)(NLDN) data to estimate the raw (i.e., unmixed and otherwise environmentally unmodified) vertical profile of lightning NO(x) (= NO + NO2). The latest LNOM estimates of lightning channel length distributions, lightning 1-m segment altitude distributions, and the vertical profile of lightning NO(x) are presented. The primary improvement to the LNOM is the inclusion of non-return stroke lightning NOx production due to: (1) hot core stepped and dart leaders, (2) stepped leader corona sheath, K-changes, continuing currents, and M-components. The impact of including LNOM-estimates of lightning NO(x) for an August 2006 run of CMAQ is discussed.

  10. Mathematical Modelling to Predict Oxidative Behaviour of Conjugated Linoleic Acid in the Food Processing Industry

    Directory of Open Access Journals (Sweden)

    Aitziber Ojanguren

    2013-06-01

    Full Text Available Industrial processes that apply high temperatures in the presence of oxygen may compromise the stability of conjugated linoleic acid (CLA bioactive isomers. Statistical techniques are used in this study to model and predict, on a laboratory scale, the oxidative behaviour of oil with high CLA content, controlling the limiting factors of food processing. This modelling aims to estimate the impact of an industrial frying process (140 °C, 7 L/h air on the oxidation of CLA oil for use as frying oil instead of sunflower oil. A factorial design was constructed within a temperature (80–200 °C and air flow (7–20 L/h range. Oil stability index (Rancimat method was used as a measure of oxidation. Three-level full factorial design was used to obtain a quadratic model for CLA oil, enabling the oxidative behaviour to be predicted under predetermined process conditions (temperature and air flow. It is deduced that temperatures applied in food processes affect the oxidation of CLA to a greater extent than air flow. As a result, it is estimated that the oxidative stability of CLA oil is less resistant to industrial frying than sunflower oil. In conclusion, thanks to the mathematical model, a good choice of the appropriate industrial food process can be selected to avoid the oxidation of the bioactive isomers of CLA, ensuring its functionality in novel applications.

  11. Modelling of stable isotope fractionation by methane oxidation and diffusion in landfill cover soils

    International Nuclear Information System (INIS)

    A technique to measure biological methane oxidation in landfill cover soils that is gaining increased interest is the measurement of stable isotope fractionation in the methane. Usually to quantify methane oxidation, only fractionation by oxidation is taken into account. Recently it was shown that neglecting the isotope fractionation by diffusion results in underestimation of the methane oxidation. In this study a simulation model was developed that describes gas transport and methane oxidation in landfill cover soils. The model distinguishes between 12CH4, 13CH4, and 12CH3D explicitly, and includes isotope fractionation by diffusion and oxidation. To evaluate the model, the simulations were compared with column experiments from previous studies. The predicted concentration profiles and isotopic profiles match the measured ones very well, with a root mean square deviation (RMSD) of 1.7 vol% in the concentration and a RMSD of 0.8 per mille in the δ13C value, with δ13C the relative 13C abundance as compared to an international standard. Overall, the comparison shows that a model-based isotope approach for the determination of methane oxidation efficiencies is feasible and superior to existing isotope methods

  12. Modeling CO Oxidation on Silica-Supported Iron Oxide under Transient Conditions

    OpenAIRE

    Randall, Harvey; Doepper, Ralf; Renken, Albert

    1997-01-01

    The oxidn. of CO on silica-supported hematite (Fe2O3) was studied by the step-response method in a tubular fixed-bed reactor at temps. 270-350 Deg. The oxidn. process appeared to proceed in two stages. First, oxygen atoms adsorbed on the surface of hematite react with gas phase CO according to an Eley-Rideal mechanism. Once that adsorbed oxygen has been consumed to some extent, surface oxygen from the lattice of iron oxide is removed in a second stage involving CO adsorption and CO reactive d...

  13. Ab Initio Thermodynamic Modeling of Electrified Metal-Oxide Interfaces

    DEFF Research Database (Denmark)

    Zeng, Zhenhua; Hansen, Martin Hangaard; Greeley, Jeff; Rossmeisl, Jan; Björketun, Mårten

    Solid oxide fuel cells are attractive devices in a sustainable energy context because of their fuel flexibility and potentially highly efficient conversion of chemical to electrical energy. The performance of the device is to a large extent determined by the atomic structure of the electrode......-electrolyte interface. Lack of atomic-level information about the interface has limited the fundamental understanding, which further limits the opportunity for optimization. The atomic structure of the interface is affected by electrode potential, chemical potential of oxygen ions, temperature and gas pressures. Here...... we present a scheme to determine the metal-oxide interface structure at a given set of these environmental parameters based on quantum chemical calculations. As an illustration we determine the structure of a Ni-YSZ anode as a function of electrode potential at 0 and 1000 K. We further describe how...

  14. Molecular modeling studies of oleate adsorption on iron oxides

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Plane wave periodic DFT study of oleate-iron oxide interaction. • Magnetite-oleate complex is more stable than hematite and goethite. • Flotation recovery of magnetite is more compared to the other two oxides. - Abstract: Comparative studies of oleate interaction with hematite, magnetite and goethite using density functional calculations are presented. The approach is illustrated by carrying out geometric optimization of oleate on the stable and most exposed planes of hematite, magnetite, and goethite. Interaction energies for oleate-mineral surface have been determined, based on which, magnetite is found to be forming the most stable complex with oleate. Trend as obtained from the quantum chemical calculations has been validated by contact angle measurements and flotation studies on hematite, magnetite and goethite with sodium oleate at different pH and collector concentrations

  15. Molecular modeling studies of oleate adsorption on iron oxides

    Energy Technology Data Exchange (ETDEWEB)

    Rath, Swagat S. [CSIR-Institute of Minerals and Materials Technology, Bhubaneswar (India); Sinha, Nishant [Accelrys K.K, Bengaluru (India); Sahoo, Hrushikesh [CSIR-Institute of Minerals and Materials Technology, Bhubaneswar (India); Das, Bisweswar, E-mail: bdas@immt.res.in [CSIR-Institute of Minerals and Materials Technology, Bhubaneswar (India); Mishra, Barada Kanta [CSIR-Institute of Minerals and Materials Technology, Bhubaneswar (India)

    2014-03-01

    Graphical abstract: - Highlights: • Plane wave periodic DFT study of oleate-iron oxide interaction. • Magnetite-oleate complex is more stable than hematite and goethite. • Flotation recovery of magnetite is more compared to the other two oxides. - Abstract: Comparative studies of oleate interaction with hematite, magnetite and goethite using density functional calculations are presented. The approach is illustrated by carrying out geometric optimization of oleate on the stable and most exposed planes of hematite, magnetite, and goethite. Interaction energies for oleate-mineral surface have been determined, based on which, magnetite is found to be forming the most stable complex with oleate. Trend as obtained from the quantum chemical calculations has been validated by contact angle measurements and flotation studies on hematite, magnetite and goethite with sodium oleate at different pH and collector concentrations.

  16. Generalized molybdenum oxide surface chemical state XPS determination via informed amorphous sample model

    Energy Technology Data Exchange (ETDEWEB)

    Baltrusaitis, Jonas, E-mail: job314@lehigh.edu [Department of Chemical Engineering, Lehigh University, B336 Iacocca Hall, 111 Research Drive, Bethlehem, PA 18015 (United States); PhotoCatalytic Synthesis group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente, Meander 229, P.O. Box 217, 7500 AE Enschede (Netherlands); Mendoza-Sanchez, Beatriz [CRANN, Chemistry School, Trinity College Dublin, Dublin (Ireland); Fernandez, Vincent [Institut des Matériaux Jean Rouxel, 2 rue de la Houssinière, BP 32229, F-44322 Nantes Cedex 3 (France); Veenstra, Rick [PhotoCatalytic Synthesis group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente, Meander 229, P.O. Box 217, 7500 AE Enschede (Netherlands); Dukstiene, Nijole [Department of Physical and Inorganic Chemistry, Kaunas University of Technology, Radvilenu pl. 19, LT-50254 Kaunas (Lithuania); Roberts, Adam [Kratos Analytical Ltd, Trafford Wharf Road, Wharfside, Manchester, M17 1GP (United Kingdom); Fairley, Neal [Casa Software Ltd, Bay House, 5 Grosvenor Terrace, Teignmouth, Devon TQ14 8NE (United Kingdom)

    2015-01-30

    Highlights: • We analyzed and modeled spectral envelopes of complex molybdenum oxides. • Molybdenum oxide films of varying valence and crystallinity were synthesized. • MoO{sub 3} and MoO{sub 2} line shapes from experimental data were created. • Informed amorphous sample model (IASM) developed. • Amorphous molybdenum oxide XPS envelopes were interpreted. - Abstract: Accurate elemental oxidation state determination for the outer surface of a complex material is of crucial importance in many science and engineering disciplines, including chemistry, fundamental and applied surface science, catalysis, semiconductors and many others. X-ray photoelectron spectroscopy (XPS) is the primary tool used for this purpose. The spectral data obtained, however, is often very complex and can be subject to incorrect interpretation. Unlike traditional XPS spectra fitting procedures using purely synthetic spectral components, here we develop and present an XPS data processing method based on vector analysis that allows creating XPS spectral components by incorporating key information, obtained experimentally. XPS spectral data, obtained from series of molybdenum oxide samples with varying oxidation states and degree of crystallinity, were processed using this method and the corresponding oxidation states present, as well as their relative distribution was elucidated. It was shown that monitoring the evolution of the chemistry and crystal structure of a molybdenum oxide sample due to an invasive X-ray probe could be used to infer solutions to complex spectral envelopes.

  17. Mathematical Modeling of Wastewater Oxidation under Microgravity Conditions

    OpenAIRE

    Boyun Guo; Donald W. Holder; David S. Schechter

    2005-01-01

    Volatile removal assembly (VRA) is a module installed in the International Space Station for removing contaminants (volatile organics) in the wastewater produced by the crew. The VRA contains a slim pack bed reactor to perform catalyst oxidation of the wastewater at elevated pressure and temperature under microgravity conditions. Optimal design of the reactor requires a thorough understanding about how the reactor performs under microgravity conditions. The objective of this study was to theo...

  18. Pineapple Waste Extract for Preventing Oxidation in Model Food Systems.

    Science.gov (United States)

    Segovia Gómez, Francisco; Almajano Pablos, María Pilar

    2016-07-01

    Pineapple (Ananas comosus) is consumed in the form of chunks (canned), cubes, fruit salad, and also in juices, concentrates, and jams. In the processes to produce these products, the waste generated represents a high percentage of the total fruit. Some studies have shown that residues of certain fruits, such as pineapple, have the same antioxidant activity as the fruit pulp. So although these residues are discarded, they could be used as an alternative source of polyphenols, as natural antioxidants. This study is focused on the antioxidant activity of wastes obtained in the production of pineapple products and their application. The polyphenols' scavenging activity was determined by the oxygen radical antioxidant capacity assay. The antioxidant potential was determined in emulsions (o/w) and in muffins, where the primary oxidation products (by peroxide value, PV) and the secondary oxidation products (by thiobarbituric acid reactive substances) were analyzed. In addition the muffins were analyzed by means of a triangular sensory test. The PV method showed that pineapple waste extracts caused a reduction in oxidation products of 59% in emulsions and 91% in the muffins. The reduction in TBARs values for emulsions were 27% and for muffins were 51%. The triangular sensory test showed that the samples containing the extract were not distinguished from the control (α = 0.05). PMID:27384012

  19. Modeling SOA formation from the oxidation of intermediate volatility n-alkanes

    Directory of Open Access Journals (Sweden)

    J. Lee-Taylor

    2012-08-01

    Full Text Available The chemical mechanism leading to SOA formation and ageing is expected to be a multigenerational process, i.e. a successive formation of organic compounds with higher oxidation degree and lower vapor pressure. This process is here investigated with the explicit oxidation model GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere. Gas phase oxidation schemes are generated for the C8–C24 series of n-alkanes. Simulations are conducted to explore the time evolution of organic compounds and the behavior of secondary organic aerosol (SOA formation for various preexisting organic aerosol concentration (COA. As expected, simulation results show that (i SOA yield increases with the carbon chain length of the parent hydrocarbon, (ii SOA yield decreases with decreasing COA, (iii SOA production rates increase with increasing COA and (iv the number of oxidation steps (i.e. generations needed to describe SOA formation and evolution grows when COA decreases. The simulated oxidative trajectories are examined in a two dimensional space defined by the mean carbon oxidation state and the volatility. Most SOA contributors are not oxidized enough to be categorized as highly oxygenated organic aerosols (OOA but reduced enough to be categorized as hydrocarbon like organic aerosols (HOA, suggesting that OOA may underestimate SOA. Results show that the model is unable to produce highly oxygenated aerosols (OOA with large yields. The limitations of the model are discussed.

  20. Modeling SOA formation from the oxidation of intermediate volatility n-alkanes

    Directory of Open Access Journals (Sweden)

    J. Lee-Taylor

    2012-06-01

    Full Text Available The chemical mechanism leading to SOA formation and ageing is expected to be a multigenerational process, i.e. a successive formation of organic compounds with higher oxidation degree and lower vapor pressure. This process is here investigated with the explicit oxidation model GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere. Gas phase oxidation schemes are generated for the C8–C24 series of n-alkanes. Simulations are conducted to explore the time evolution of organic compounds and the behavior of secondary organic aerosol (SOA formation for various preexisting organic aerosol concentration (COA. As expected, simulation results show that (i SOA yield increases with the carbon chain length of the parent hydrocarbon, (ii SOA yield decreases with decreasing COA, (iii SOA production rates increase with increasing COA and (iv the number of oxidation steps (i.e. generations needed to describe SOA formation and evolution grows when COA decreases. The simulated oxidative trajectories are examined in a two dimensional space defined by the mean carbon oxidation state and the volatility. Most SOA contributors are not oxidized enough to be categorized as highly oxygenated organic aerosols (OOA but reduced enough to be categorized as hydrocarbon like organic aerosols (HOA, suggesting that OOA may underestimate SOA. Results show that the model is unable to produce highly oxygenated aerosols (OOA with large yields. The limitations of the model are discussed.

  1. Surface kinetics modeling of silicon and silicon oxide plasma etching. III. Modeling of silicon oxide etching in fluorocarbon chemistry using translating mixed-layer representation

    International Nuclear Information System (INIS)

    Silicon oxide etching was modeled using a translating mixed-layer model, a novel surface kinetic modeling technique, and the model showed good agreement with measured data. Carbon and fluorine were identified as the primary contributors to deposition and etching, respectively. Atomic fluorine flux is a major factor that determines the etching behavior. With a chemistry having a small amount of atomic fluorine (such as the C4F8 chemistry), etching yield shows stronger dependence on the composition change in the gas flux

  2. Dynamic Modeling, Model-Based Control, and Optimization of Solid Oxide Fuel Cells

    Science.gov (United States)

    Spivey, Benjamin James

    2011-07-01

    Solid oxide fuel cells are a promising option for distributed stationary power generation that offers efficiencies ranging from 50% in stand-alone applications to greater than 80% in cogeneration. To advance SOFC technology for widespread market penetration, the SOFC should demonstrate improved cell lifetime and load-following capability. This work seeks to improve lifetime through dynamic analysis of critical lifetime variables and advanced control algorithms that permit load-following while remaining in a safe operating zone based on stress analysis. Control algorithms typically have addressed SOFC lifetime operability objectives using unconstrained, single-input-single-output control algorithms that minimize thermal transients. Existing SOFC controls research has not considered maximum radial thermal gradients or limits on absolute temperatures in the SOFC. In particular, as stress analysis demonstrates, the minimum cell temperature is the primary thermal stress driver in tubular SOFCs. This dissertation presents a dynamic, quasi-two-dimensional model for a high-temperature tubular SOFC combined with ejector and prereformer models. The model captures dynamics of critical thermal stress drivers and is used as the physical plant for closed-loop control simulations. A constrained, MIMO model predictive control algorithm is developed and applied to control the SOFC. Closed-loop control simulation results demonstrate effective load-following, constraint satisfaction for critical lifetime variables, and disturbance rejection. Nonlinear programming is applied to find the optimal SOFC size and steady-state operating conditions to minimize total system costs.

  3. A mathematical model for the bacterial oxidation of a sulfide ore concentrate

    Energy Technology Data Exchange (ETDEWEB)

    Nagpal, S.; Dahlstrom, D. (Univ. of Utah, Salt Lake City, UT (United States). Dept. of Chemical Engineering); Oolman, T. (Radian Corp., Austin, TX (United States))

    1994-03-05

    The effect of dilution rate and feed solids concentration on the bacterial leaching of a pyrite/arsenopyrite ore concentrate was studied. A mathematical model was developed for the process based on the steady-state data collected over the range of dilution rates (20 to 110 h) and feed solids concentrations (6 to 18% w/v) studied. A modified Monod model with inhibition by arsenic was used to model bacterial ferrous ion oxidation rates. The model assumes that (1) pyrite and arsenopyrite leaching occurs solely by the action of ferric iron produced from the bacterial oxidation of ferrous iron and (2) bacterial growth rates are proportional to ferrous ion oxidation rate. The equilibrium among the various ionic species present in the leach solution that are likely to have a significant effect on the bioleach process were included in the model.

  4. Relativistic density functional theory modeling of plutonium and americium higher oxide molecules

    Science.gov (United States)

    Zaitsevskii, Andréi; Mosyagin, Nikolai S.; Titov, Anatoly V.; Kiselev, Yuri M.

    2013-07-01

    The results of electronic structure modeling of plutonium and americium higher oxide molecules (actinide oxidation states VI through VIII) by two-component relativistic density functional theory are presented. Ground-state equilibrium molecular structures, main features of charge distributions, and energetics of AnO3, AnO4, An2On (An=Pu, Am), and PuAmOn, n = 6-8, are determined. In all cases, molecular geometries of americium and mixed plutonium-americium oxides are similar to those of the corresponding plutonium compounds, though chemical bonding in americium oxides is markedly weaker. Relatively high stability of the mixed heptoxide PuAmO7 is noticed; the Pu(VIII) and especially Am(VIII) oxides are expected to be unstable.

  5. Oxidative metabolism in YAC128 mouse model of Huntington's disease.

    Science.gov (United States)

    Hamilton, James; Pellman, Jessica J; Brustovetsky, Tatiana; Harris, Robert A; Brustovetsky, Nickolay

    2015-09-01

    Alterations in oxidative metabolism are considered to be one of the major contributors to Huntington's disease (HD) pathogenesis. However, existing data about oxidative metabolism in HD are contradictory. Here, we investigated the effect of mutant huntingtin (mHtt) on oxidative metabolism in YAC128 mice. Both mHtt and wild-type huntingtin (Htt) were associated with mitochondria and the amount of bound Htt was four-times higher than the amount of bound mHtt. Percoll gradient-purified brain synaptic and non-synaptic mitochondria as well as unpurified brain, liver and heart mitochondria, isolated from 2- and 10-month-old YAC128 mice and age-matched WT littermates had similar respiratory rates. There was no difference in mitochondrial membrane potential or ADP and ATP levels. Expression of selected nuclear-encoded mitochondrial proteins in 2- and 10-month-old YAC128 and WT mice was similar. Cultured striatal and cortical neurons from YAC128 and WT mice had similar respiratory and glycolytic activities as measured with Seahorse XF24 analyzer in medium containing 10 mm glucose and 15 mm pyruvate. In the medium with 2.5 mm glucose, YAC128 striatal neurons had similar respiration, but slightly lower glycolytic activity. Striatal neurons had lower maximal respiration compared with cortical neurons. In vivo experiments with YAC128 and WT mice showed similar O2 consumption, CO2 release, physical activity, food consumption and fasted blood glucose. However, YAC128 mice were heavier and had more body fat compared with WT mice. Overall, our data argue against respiratory deficiency in YAC128 mice and, consequently, suggest that mitochondrial respiratory dysfunction is not essential for HD pathogenesis. PMID:26041817

  6. Optical modeling of nickel-base alloys oxidized in pressurized water reactor

    Energy Technology Data Exchange (ETDEWEB)

    Clair, A. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS, Universite de Bourgogne, 9 avenue Alain Savary, BP 47870, 21078 Dijon cedex (France); Foucault, M.; Calonne, O. [Areva ANP, Centre Technique Departement Corrosion-Chimie, 30 Bd de l' industrie, BP 181, 71205 Le Creusot (France); Finot, E., E-mail: Eric.Finot@u-bourgogne.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS, Universite de Bourgogne, 9 avenue Alain Savary, BP 47870, 21078 Dijon cedex (France)

    2012-10-01

    The knowledge of the aging process involved in the primary water of pressurized water reactor entails investigating a mixed growth mechanism in the corrosion of nickel-base alloys. A mixed growth induces an anionic inner oxide and a cationic diffusion parallel to a dissolution-precipitation process forms the outer zone. The in situ monitoring of the oxidation kinetics requires the modeling of the oxide layer stratification with the full knowledge of the optical constants related to each component. Here, we report the dielectric constants of the alloys 600 and 690 measured by spectroscopic ellipsometry and fitted to a Drude-Lorentz model. A robust optical stratification model was determined using focused ion beam cross-section of thin foils examined by transmission electron microscopy. Dielectric constants of the inner oxide layer depleted in chromium were assimilated to those of the nickel thin film. The optical constants of both the spinels and extern layer were determined. - Highlights: Black-Right-Pointing-Pointer Spectroscopic ellipsometry of Ni-base alloy oxidation in pressurized water reactor Black-Right-Pointing-Pointer Measurements of the dielectric constants of the alloys Black-Right-Pointing-Pointer Optical simulation of the mixed oxidation process using a three stack model Black-Right-Pointing-Pointer Scattered crystallites cationic outer layer; linear Ni-gradient bottom layer Black-Right-Pointing-Pointer Determination of the refractive index of the spinel and the Cr{sub 2}O{sub 3} layers.

  7. Analytical model of LDMOS with a single step buried oxide layer

    Science.gov (United States)

    Yuan, Song; Duan, Baoxing; Cao, Zhen; Guo, Haijun; Yang, Yintang

    2016-09-01

    In this paper, a two-dimensional analytical model is established for the Single-Step Buried Oxide SOI structure proposed by the authors. Based on the two-dimensional Poisson equation, the analytic expression of the surface electric field and potential distributions for the device is achieved. In the SBOSOI (Single-Step Buried Oxide Silicon On Insulator) structure, the buried oxide layer thickness changes stepwise along the drift region, and the electric field in the oxide layer also varies with the different buried oxide layer thickness. These variations will modulate the surface electric field distribution through the electric field modulation effects, which makes the surface electric field distribution more uniform. As a result, the breakdown voltage of the device is improved by 60% compared with the conventional SOI structure. To verify the accuracy of the analytical model, the device simulation software ISE TCAD is utilized, the analytical values are in good agreement with the simulation results by the simulation software. The results verified the established two-dimensional analytical model for SBOSOI structure is valid, and it also illustrates the breakdown voltage enhancement by the electric field modulation effect sufficiently. The established analytical models will provide the physical and mathematical basis for further analysis of the new power devices with the patterned buried oxide layer.

  8. Conditional Induction of Oxidative Stress in RPE: A Mouse Model of Progressive Retinal Degeneration.

    Science.gov (United States)

    Biswal, Manas R; Ildefonso, Cristhian J; Mao, Haoyu; Seo, Soo Jung; Wang, Zhaoyang; Li, Hong; Le, Yun Z; Lewin, Alfred S

    2016-01-01

    An appropriate animal model is essential to screening drugs or designing a treatment strategy for geographic atrophy. Since oxidative stress contributes to the pathological changes of the retinal pigment epithelium (RPE), we are reporting a new mouse AMD model of retinal degeneration by inducing mitochondrial oxidative stress in RPE. Sod2 the gene for manganese superoxide dismutase (MnSOD) was deleted in RPE layer using conditional knockout strategy. Fundus microscopy, SD-OCT and electroretinography were used to monitor retinal structure and function in living animals and microscopy was used to assess pathology post mortem. Tissue specific deletion of Sod2 caused elevated signs of oxidative stress, RPE dysfunction and showed some key features of AMD. Due to induction of oxidative stress, the conditional knockout mice show progressive reduction in ERG responses and thinning of outer nuclear layer (ONL) compared to non-induced littermates. PMID:26427390

  9. Aerobic oxidation of lignin models using a base metal vanadium catalyst.

    Science.gov (United States)

    Hanson, Susan K; Baker, R Tom; Gordon, John C; Scott, Brian L; Thorn, David L

    2010-06-21

    Dipicolinate vanadium(V) complexes oxidize lignin model complexes pinacol monomethyl ether (A), 2-phenoxyethanol (B), 1-phenyl-2-phenoxyethanol (C), and 1,2-diphenyl-2-methoxyethanol (D). With substrates having C-H bonds adjacent to the alcohol moiety (B-D), the C-H bond is broken in pyridine-d(5) solvent, yielding 2-phenoxyacetaldehyde from B, 2-phenoxyacetophenone from C, and benzoin methyl ether from D. In DMSO-d(6) solvent the reaction is slower, and both C-H and C-C bond cleavage products are observed for D. The vanadium(IV) products of these reactions have been identified and characterized. Catalytic oxidation of C and D has been demonstrated using air and (dipic)V(O)O(i)Pr. For both substrates, the C-C bond between the alcohol and ether groups is broken in the catalytic oxidation. 1-Phenyl-2-phenoxyethanol is oxidized to a mixture of phenol, formic acid, benzoic acid, and 2-methoxyacetophenone. The products of oxidation of 1,2-diphenyl-2-methoxyethanol depend on the solvent; in DMSO benzaldehyde and methanol are the major products, while benzoic acid and methyl benzoate are the major products obtained in pyridine solvent. Phenyl substituents on the model complex facilitate the oxidation, with relative rates of oxidation D > C > B. PMID:20491453

  10. Role of oxidative stress in surgical cavernous nerve injury in a rat model.

    Science.gov (United States)

    Wang, Hui; Ding, Xie-Gang; Li, Shi-Wen; Zheng, Hang; Zheng, Xin-Min; Navin, Shrestha; Li, Lu; Wang, Xing-Huan

    2015-06-01

    This study investigates the role of oxidative stress in surgical cavernous nerve (CN) injury in a rat model. Eighty-four male Sprague-Dawley rats were randomly divided into three groups: group 1, sham-operated rats; group 2, bilateral CN-crushed rats; and group 3, bilateral CN-transection-and-sutured-immediately rats. Oxidative stress was evaluated by malondialdehyde levels, super oxide dismutase (SOD) activities, and glutathione peroxidase (GPX) activities in serum. Erectile function was assessed by CN electrostimulation at 3 months with mean maximal intracavernous pressure (ICP) and maximal ICP per mean arterial pressure. Nerve injury was assessed by toluidine blue staining of CNs and nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase staining of penile tissue. GPX protein expression and nitrotyrosine-3 (NT-3) levels in penile tissue were measured. Erectile function and the number of myelinated axons of CNs and NADPH-diaphorase-positive nerve fibers were statistically decreased between groups, from sham to crush to transection. For markers, both nerve-injury groups showed increased oxidative stress markers at early time points, with the transection group showing greater oxidative stress than the crushed group and values normalizing to sham levels by week 12. GPX expression and NT-3 levels in penile tissue were in concordance with the results of SOD and GPX. These results show that oxidative stress plays an important role in injured CNs, and different methods of CN injury can lead to different degrees of oxidative stress in a rat model. PMID:25597854

  11. Modeling Nitrous Oxide Production during Biological Nitrogen Removal via Nitrification and Denitrification: Extensions to the General ASM Models

    DEFF Research Database (Denmark)

    Ni, Bing-Jie; Ruscalleda, Maël; Pellicer i Nàcher, Carles;

    2011-01-01

    Nitrous oxide (N2O) can be formed during biological nitrogen (N) removal processes. In this work, a mathematical model is developed that describes N2O production and consumption during activated sludge nitrification and denitrification. The well-known ASM process models are extended to capture N2...

  12. Modeling and experimental evaluation of the diffusion bonding of the oxide dispersion strengthened steel PM2000

    Science.gov (United States)

    Sittel, Wiebke; Basuki, Widodo W.; Aktaa, Jarir

    2015-10-01

    A modeling based optimization process of the solid state diffusion bonding is presented for joining ferritic oxide dispersion strengthened steels PM2000. An optimization study employing varying bonding temperatures and pressures results in almost the same strength and toughness of the bonded compared to the as received material. TEM investigations of diffusion bonded samples show a homogeneous distribution of oxide particles at the bonding seam similar to that in the bulk. Hence, no loss in strength or creep resistance due to oxide particle agglomeration is found, as verified by the mechanical properties observed for the joint.

  13. THERMODYNAMIC MODELING OF THE SURFACE LAYER STRUCTURE ON INCONEL 600 OXIDIZED IN A CONTROLLED ATMOSPHERE

    Directory of Open Access Journals (Sweden)

    Abdallah Haouam

    2012-03-01

    Full Text Available Samples of Inconel 600 were isothermally oxidized in a controlled atmosphere with a special mounting at high-temperature oxidation. Along with this experimental study, a simulation of thermodynamic behavior of the material in the same oxidation conditions was carried out using the Thermo-Calc code. The thermodynamic modeling is able to predict the phase nature and its distribution in the structure of the surface layer resulting from the corrosion of the material in thermodynamic equilibrium in the absence of mechanical stress. The results of this simulation are supplemented to results obtained from the analysis by glow discharge spectrometry (GDS which is performed on the samples tested.

  14. Oxidative Stress Associated with Neuronal Apoptosis in Experimental Models of Epilepsy

    Directory of Open Access Journals (Sweden)

    Marisela Méndez-Armenta

    2014-01-01

    Full Text Available Epilepsy is considered one of the most common neurological disorders worldwide. Oxidative stress produced by free radicals may play a role in the initiation and progression of epilepsy; the changes in the mitochondrial and the oxidative stress state can lead mechanism associated with neuronal death pathway. Bioenergetics state failure and impaired mitochondrial function include excessive free radical production with impaired synthesis of antioxidants. This review summarizes evidence that suggest what is the role of oxidative stress on induction of apoptosis in experimental models of epilepsy.

  15. Submicro-battery effect and selective bio-oxidation model of gold-bearing arsenopyrite by Thiobacillus ferrooxidans

    Institute of Scientific and Technical Information of China (English)

    杨洪英; 杨立; 赵玉山; 陈刚; 吕久吉; 范有静

    2002-01-01

    Through the study by electronic probe it was found that many new cracks and holes appear on the surface of gold-bearing arsenopyrite crystal oxidized by Thiobacillus ferrooxidans, which are along with some directions. Then the selective bio-oxidation model of gold-bearing arsenopyrite was set up. The selective bio-oxidation resulting from the submicro-battery effect of gold/ arsenopyrite mineral pairs naturally forms in the gold-bearing arsenopyrite crystal. Thiobacillus ferrooxidans has priority to oxidize the place of gold-rich and oxidizes selectedly along with the crystal border, crystal face and crack. The bacteria oxidation process of gold-bearing arsenopyrite is divided into three stages: the first stage is the surface oxidation, the second stage is restraining oxidation and the third stage is the filament oxidation, bacteria oxidize along with cracks of arsenopyrite.

  16. A shrinking core model for the electro-deoxidation of metal oxides in molten halide salts

    International Nuclear Information System (INIS)

    A shrinking core model is developed and applied to the electro-deoxidation of metal oxides (such as TiO2, SiO2, NiO, Cr2O3 and Nb2O3). Among these the reduction of TiO2 is the most complex due to reduction by formation of a number of lower oxides and perovskite formation under certain experimental conditions. Hence, TiO2 is chosen as the model material for this reduction. First, a single stage model is adopted for the reduction of TiO2 to Ti and it is shown that an additional term for the oxygen concentration in the shell must be added to get the accurate values of oxygen concentration unless the concentration at the exterior of the grain is zero. Subsequently, a multi-stage model for the successive reduction of titanium oxides to titanium is proposed. It uses a shrinking core of the oxides in the order starting from TiO2 to Ti3O5 to Ti2O3 to TiO to Ti. An analytical solution is developed for the transient differential equation resulting in a series solution for the concentration of oxygen in the lower oxides. Subsequently, a solution based on the pseudo-steady assumption is also developed. It is shown that for the parameters chosen, at certain values of dimensionless applied current density, Id, (∼0.1) the transient and pseudo-steady state solutions agree in terms of the dimensionless time it takes for the core to shrink completely. The proposed model could be applied to other metal oxides such as SiO2, NiO, Cr2O3, Nb2O3 and other metal oxides that are reduced using the Fray-Farthing-Chen (FFC) process mechanism. This can be used for a reactor scale model or for performing a parametric study of the current density and the grain size

  17. Modeling for multilevel switching in oxide-based bipolar resistive memory

    International Nuclear Information System (INIS)

    We report a physical model for multilevel switching in oxide-based bipolar resistive memory (ReRAM). To confirm the validity of the model, we conduct experiments with tantalum-oxide-based ReRAM of which multi-resistance levels are obtained by reset voltage modifications. It is also noticeable that, in addition to multilevel switching capability, the ReRAM exhibits extremely different switching timescales, i.e. of the order of 10−7 s to 100 s, with regard to reset voltages of only a few volts difference which can be well explained by our model. It is demonstrated that with this simple model, multilevel switching behavior in oxide bipolar ReRAM can be described not only qualitatively but also quantitatively. (paper)

  18. Radiolytic modelling of spent fuel oxidative dissolution mechanism. Calibration against UO 2 dynamic leaching experiments

    Science.gov (United States)

    Merino, J.; Cera, E.; Bruno, J.; Quiñones, J.; Casas, I.; Clarens, F.; Giménez, J.; de Pablo, J.; Rovira, M.; Martínez-Esparza, A.

    2005-11-01

    Calibration and testing are inherent aspects of any modelling exercise and consequently they are key issues in developing a model for the oxidative dissolution of spent fuel. In the present work we present the outcome of the calibration process for the kinetic constants of a UO 2 oxidative dissolution mechanism developed for using in a radiolytic model. Experimental data obtained in dynamic leaching experiments of unirradiated UO 2 has been used for this purpose. The iterative calibration process has provided some insight into the detailed mechanism taking place in the alteration of UO 2, particularly the role of rad OH radicals and their interaction with the carbonate system. The results show that, although more simulations are needed for testing in different experimental systems, the calibrated oxidative dissolution mechanism could be included in radiolytic models to gain confidence in the prediction of the long-term alteration rate of the spent fuel under repository conditions.

  19. Radiolytic modelling of spent fuel oxidative dissolution mechanism. Calibration against UO2 dynamic leaching experiments

    International Nuclear Information System (INIS)

    Calibration and testing are inherent aspects of any modelling exercise and consequently they are key issues in developing a model for the oxidative dissolution of spent fuel. In the present work we present the outcome of the calibration process for the kinetic constants of a UO2 oxidative dissolution mechanism developed for using in a radiolytic model. Experimental data obtained in dynamic leaching experiments of unirradiated UO2 has been used for this purpose. The iterative calibration process has provided some insight into the detailed mechanism taking place in the alteration of UO2, particularly the role of ·OH radicals and their interaction with the carbonate system. The results show that, although more simulations are needed for testing in different experimental systems, the calibrated oxidative dissolution mechanism could be included in radiolytic models to gain confidence in the prediction of the long-term alteration rate of the spent fuel under repository conditions

  20. Theoretical modeling of heterogeneous catalysts based on platinum and cerium oxide

    OpenAIRE

    Bruix Fusté, Albert

    2014-01-01

    This thesis focuses on the computational study of models for platinum catalysts supported on cerium oxide (CeO2) which are of technological relevance. In these catalysts, ceria is often found acting as a non-inert support, leading to complex metal-support interactions (MSI) that modify the properties of both the oxide and the supported metal. First principles computational methods based on the Density functional Theory (DFT) have been used to study the nature of these interactions and their e...

  1. Effects of Laminaria japonica polysaccharides on exercise endurance and oxidative stress in forced swimming mouse model

    OpenAIRE

    Yan, Feiwei; Hao, Haitao

    2016-01-01

    Background Polysaccharides are the major active ingredients responsible for the bioactivities of Laminaria japonica. However, the effects of L. japonica polysaccharides (LJP) on exercise endurance and oxidative stress have never been investigated. Therefore, this study was conducted to investigate the effects of LJP on exercise endurance and oxidative stress in a forced swimming mouse model. The animals were divided into four groups, namely the control (C), LJP-75, LJP-150, and LJP-300 groups...

  2. Model-based Interpretation of the Performance and Degradation of Reformate Fueled Solid Oxide Fuel Cells

    OpenAIRE

    Kromp, Alexander

    2013-01-01

    Solid oxide fuel cells offer great prospects for the sustainable, clean and safe conversion of various fuels into electrical energy. In this thesis, the performance-determining loss processes for the cell operation on reformate fuels are elucidated via electrochemical impedance spectroscopy. Model-based analyses reveal the electrochemical fuel oxidation mechanism, the coupling of fuel gas transport and reforming chemistry and the impact of fuel impurities on the degradation of each loss process.

  3. A simple model to estimate the optimal doping of p - Type oxide superconductors

    Directory of Open Access Journals (Sweden)

    Adir Moysés Luiz

    2008-12-01

    Full Text Available Oxygen doping of superconductors is discussed. Doping high-Tc superconductors with oxygen seems to be more efficient than other doping procedures. Using the assumption of double valence fluctuations, we present a simple model to estimate the optimal doping of p-type oxide superconductors. The experimental values of oxygen content for optimal doping of the most important p-type oxide superconductors can be accounted for adequately using this simple model. We expect that our simple model will encourage further experimental and theoretical researches in superconducting materials.

  4. Simple electrolyzer model development for high-temperature electrolysis system analysis using solid oxide electrolysis cell

    International Nuclear Information System (INIS)

    An electrolyzer model for the analysis of a hydrogen production system using a solid oxide electrolysis cell has been developed, and the effects of principal parameters have been estimated via sensitivity studies based on the developed model. The main parameters considered were current density, area-specific resistance, temperature, pressure, molar fraction, and flow rates in the inlet and outlet. A simple model is also estimated for a high-temperature hydrogen production system that integrates the solid oxide electrolysis cell with a very high temperature reactor. (author)

  5. Simple Electrolyzer Model Development for High-Temperature Electrolysis System Analysis Using Solid Oxide Electrolysis Cell

    International Nuclear Information System (INIS)

    An electrolyzer model for the analysis of a hydrogen-production system using a solid oxide electrolysis cell (SOEC) has been developed, and the effects for principal parameters have been estimated by sensitivity studies based on the developed model. The main parameters considered are current density, area specific resistance, temperature, pressure, and molar fraction and flow rates in the inlet and outlet. Finally, a simple model for a high-temperature hydrogen-production system using the solid oxide electrolysis cell integrated with very high temperature reactors is estimated.

  6. Modelling of Physical, Chemical, and Material Properties of Solid Oxide Fuel Cells

    Directory of Open Access Journals (Sweden)

    Jakub Kupecki

    2015-01-01

    Full Text Available This paper provides a review of modelling techniques applicable for system-level studies to account for physical, chemical, and material properties of solid oxide fuel cells. Functionality of 0D to 3D models is discussed and selected examples are given. Author provides information on typical length scales in evaluation of power systems with solid oxide fuel cells. In each section, proper examples of previous studies done in the field of 0D–3D modelling are recalled and discussed.

  7. Kinetic Model of Hypophosphite Oxidation on a Nickel Electrode in D2O Solution

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Kinetic model of hypophosphite oxidation on a nickel electrode was studied in D2Osolution in order to reach a better understanding of the oxidation mechanism. In the model the electrooxidation of hypophosphite undergo a H abstraction of hypophosphite from the P-H bond to form the phosphorus-centered radical PHO2-, which subsequently is electrochemically reacted with water to form the final product, phosphite. The kinetic equations were derived, and the kinetic parameters were obtained from a comparison of experimental results and the kinetic equations. The process of hypophosphite electrooxidation could be well simulated by this model

  8. Experimental and kinetic modeling study of C2H4 oxidation at high pressure

    DEFF Research Database (Denmark)

    Lopez, Jorge Gimenez; Rasmussen, Christian Lund; Alzueta, Maria;

    2009-01-01

    A detailed chemical kinetic model for oxidation of C2H4 in the intermediate temperature range and high pressure has been developed and validated experimentally. New ab initio calculations and RRKM analysis of the important C2H3 + O-2 reaction was used to obtain rate coefficients over a wide range...... bar, varying the reaction stoichiometry from very lean to fuel-rich conditions. Model predictions are generally satisfactory. The governing reaction mechanisms are outlined based on calculations with the kinetic model. Under the investigated conditions the oxidation pathways for C2H4 are more complex...

  9. Modeling of enhancement of nonlinearity in oxide and chalcogenide glasses by introduction of nanometals

    Energy Technology Data Exchange (ETDEWEB)

    Zakery, A. [Department of Physics, College of Science, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)]. E-mail: zakeri@physics.susc.ac.ir; Shahmirzaee, H. [Department of Physics, College of Science, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)

    2007-02-12

    In this Letter we extended T-matrix to calculate the nonlinear susceptibilities of a composite nonlinear host and guest medium, and then applied this model to calculate the nonlinear susceptibilities of oxide and chalcogenide glasses by introduction of nanometals. The results of the model is in good agreement with experimental ones.

  10. Modeling of enhancement of nonlinearity in oxide and chalcogenide glasses by introduction of nanometals

    International Nuclear Information System (INIS)

    In this Letter we extended T-matrix to calculate the nonlinear susceptibilities of a composite nonlinear host and guest medium, and then applied this model to calculate the nonlinear susceptibilities of oxide and chalcogenide glasses by introduction of nanometals. The results of the model is in good agreement with experimental ones

  11. Modeling of enhancement of nonlinearity in oxide and chalcogenide glasses by introduction of nanometals

    Science.gov (United States)

    Zakery, A.; Shahmirzaee, H.

    2007-02-01

    In this Letter we extended T-matrix to calculate the nonlinear susceptibilities of a composite nonlinear host and guest medium, and then applied this model to calculate the nonlinear susceptibilities of oxide and chalcogenide glasses by introduction of nanometals. The results of the model is in good agreement with experimental ones.

  12. Parameterising secondary organic aerosol from α-pinene using a detailed oxidation and aerosol formation model

    Directory of Open Access Journals (Sweden)

    J.-F. Müller

    2011-08-01

    Full Text Available A new 10-product parameter model for α-pinene secondary organic aerosol (SOA is presented, based on simulations with the detailed model BOREAM (Biogenic hydrocarbon Oxidation and Related Aerosol formation Model. The parameterisation takes into account the influence of temperature, type of oxidant, NOx-regime, photochemical ageing and water uptake, and is suitable for use in global chemistry transport models. BOREAM is validated against recent photooxidation smog chamber experiments, for which it reproduces SOA yields to within a factor of 2 in most cases. In the simple chemical mechanism of the parameter model, oxidation of α-pinene generates peroxy radicals, which, upon reaction with NO or HO2, yield products corresponding to high or low-NOx conditions, respectively. The model parameters – i.e. the temperature-dependent stoichiometric coefficients and partitioning coefficients of the 10 semi-volatile products – are obtained from simulations with BOREAM, including a prescribed diurnal cycle for the radiation, oxidant and emission levels, as well as a deposition sink for the particulate and gaseous products. The effects of photooxidative ageing are implicitly included in the parameterisation, since it is based on near-equilibrium SOA concentrations, obtained through simulations of a two-week period. Modelled SOA mass yields are about ten times higher in low-NOx than in high-NOx conditions, with yields of about 50 % in the low-NOx OH-initiated oxidation of α-pinene, considerably more than in previous parameterisations based on smog chamber experiments. The parameterisation is only moderately sensitive to the assumed oxidant levels. However, photolysis of species in the particulate phase is found to strongly reduce SOA yields. Water uptake is parameterised using fitted activity coefficients, resulting in a good agreement with the full model.

  13. Modeling of iron oxide reduction in a plasma jet by the products of methane conversion

    International Nuclear Information System (INIS)

    Iron oxide scale, which consists of FeO and Fe3O4, has been accumulated in Belarus in a large amount as a waste of the Belarus metallurgical works and heat-treatment departments of machine-building factories. Currently, the reduction of iron oxide for further use of pure iron powder for producing machine parts via the powder metallurgy route is an urgent problem. In this work, a heat transfer model for the reduction of iron oxide particles in a plasmatron is developed, which permits calculating the temperature, heating rate and particle velocity. Thermodynamic modeling (TM) in different temperature intervals accounting for possible phase transitions is used for determining the composition of gas phase necessary for the reduction of iron oxide. The results of modeling permit estimating the optimal process parameters, which provide complete reduction of the iron oxide powder to iron: the temperature interval, initial methane-to-oxygen ratio and the mass ratio of iron oxide to the gas mixture. (authors)

  14. Wet oxidation lumped kinetic model for wastewater organic burden biodegradability prediction.

    Science.gov (United States)

    Verenich, Svetlana; Kallas, Juha

    2002-08-01

    In many cases, treatment of wastewaters requires a combination of processes that very often includes biological treatment. Wet oxidation (WO) in combination with biotreatment has been successfully used for the treatment of refractory wastes. Therefore, information about the biodegradability of wastewater solutes and particulates after wet oxidation is very important. The present work proposes a model that can describe the oxidation process via organic concentration characteristics such as chemical oxygen demand (COD), biochemical oxygen demand (BOD), and immediately available BOD (IA BOD) and so can allow the prediction of biodegradability (i.e., BOD/COD ratio). The reaction mechanism includes the destruction of nonbiodegradable substances bytwo pathways: oxidation to carbon dioxide and water and oxidation to larger biodegradable compounds with their further degradation to smaller ones measured via IA BOD. The destruction of small biodegradable compounds to end products is also included in the model. The experiments were performed at different temperatures (170-200 degrees C) and partial oxygen pressures (0.5-1.5 MPa) in a batch stainless steel high-pressure autoclave. The model of concentrated thermomechanical pulp circulation water was selected for the experiments. The proposed model correlates with the experimental data well and it is compared with other WO models in the literature. PMID:12188362

  15. Modeling and Structural Optimization of Solid Oxide Fuel Cells

    DEFF Research Database (Denmark)

    Panagakos, Grigorios

    dealing with this problem. On the one hand, we attempt to perform optimization of a Solid Oxide Fuel Cell in the macro scale. Focusing on the anode interconnect, we wish to come up with an optimum interconnect design. This can be achieved in principal, since the interconnect needs to satisfy two major...... requirements. On the one hand, it needs to secure the intake of fuel into the cell, fact that would require an as low hydraulic resistance as possible, i.e. ideally an open channel and on the other hand to exhibit an as high as possible electronic conductance, which in the ideal case would mean an area blocked...... approaches and this is one of the first attempts to apply this combination of set of tools to fuel cells. Describing in a nutshell the methodology followed, we use Comsol's ability to create Matlab scripts which incorporate the desired physics of the problem (Partial Differential Equations, treating the...

  16. Thin Film Models of Magnesium Orthovanadate Catalysts for Oxidative Dehydrogenation

    Energy Technology Data Exchange (ETDEWEB)

    SAULT,ALLEN G.; MUDD,JASON E.; MILLER,JAMES E.; RUFFNER,JUDITH A.; RODRIGUEZ,MARK A.; TISSOT JR.,RALPH G.

    2001-03-01

    Magnesium vanadates are potentially important catalytic materials for the conversion of alkanes to alkenes via oxidative dehydrogenation. However, little is known about the active sites at which the catalytic reactions take place. It may be possible to obtain a significant increase in the catalytic efficiency if the effects of certain material properties on the surface reactions could be quantified and optimized through the use of appropriate preparation techniques. Given that surface reactivity is often dependent upon surface structure and that the atomic level structure of the active sites in these catalysts is virtually unknown, we desire thin film samples consisting of a single magnesium vanadate phase and a well defined crystallographic orientation in order to reduce complexity and simplify the study of active sites. This report describes the use of reactive RF sputter deposition to fabricate very highly oriented, stoichiometric Mg{sub 3}(VO{sub 4}){sub 2} thin films, and subsequent studies of the reactivity of these films under reaction conditions typically found during oxidative dehydrogenation. We demonstrate that the synthesis methods employed do in fact result in stoichiometric films with the desired crystallographic orientation, and that the chemical behavior of the films closely approximates that of bulk, high surface area Mg{sub 3}(VO{sub 4}){sub 2} powders. We further use these films to demonstrate the effects of oxygen vacancies on chemical behavior, demonstrate that surface composition can vary significantly under reaction conditions, and obtain the first evidence for structure sensitivity in Mg{sub 3}(VO{sub 4}){sub 2} catalysts.

  17. Parameterization of oxide film models with respect to SCC initiation of 316SS under PWR conditions

    International Nuclear Information System (INIS)

    Engineering alloys, such as austenitic stainless steels and nickel-based alloys used in nuclear power plants, protect themselves from their high temperature water environment by forming a passive oxide layer. The oxide layer makes the materials resistant to uniform corrosion but, potentially, makes them susceptible to stress corrosion cracking. Generally the passive oxide layer consists of a compact oxide inner layer and a porous, deposited, hydroxide outer layer. In the compact layer, matter and charge are transported by diffusion - migration of defects such as anion and cation vacancies, interstitial cations, electrons and holes. The oxide layer interacts with the substrate material and the solution at its interfaces. The inner layer grows into the substrate at the metal-film interface and dissolves at the film-solution interface. The oxide film can be modelled using Point Defect (PDM) and Mixed Conduction (MCM) Models. The PDM analytically addresses generation, transport and consumption of point defects such as vacancies and interstitials. The associated MCM treats the coupling between ionic point defects and electron transport. Using these models allows the computation of oxidation and dissolution rates, as well as the rate of vacancy injection into the substrate as a function of the composition of a Fe-Cr-Ni alloy, pH, potential and temperature of the primary coolant. Parameterization of such models is performed against the evolution of the oxide layer thickness versus exposure time, compositional profiles of Fe, Cr, Ni and O through the oxide layer and in-situ electrochemical impedance spectroscopic (EIS) measurements. In the present work, we demonstrate the parameterization of a one-dimensional model (transport of O and Cr via a vacancy mechanism, Fe and Ni via an interstitialcy mechanism, constant field strength) for 316-type stainless steel in PWR water. Preliminary results for a two-dimensional model (transport of O and Cr via a vacancy mechanism, Fe and

  18. Effect of glutathione on brain nitric oxide levels in an experimental epilepsy mouse model

    Institute of Scientific and Technical Information of China (English)

    Aylin Akcali; Sadrettin Pence; Naciye Kurtul; Mehmet Bosnak; Munife Neyal

    2009-01-01

    BACKGROUND: Oxidative stress plays an important role in the pathophysiology of epilepsy. Glutathione, known as one of the compounds of antioxidant defense, has been shown to inhibit convulsions. Nitric oxide has a proconvulsant effect on a pentylenetetrazole-induced animal model. OBJECTIVE: To evaluate the effects of glutathione administration on nitric oxide levels in brain regions of convulsive and kindling pentylenetetrazole-induced seizure models. DESIGN, TIME, AND SETTING: A randomized, controlled, animal experiment. The study was performed at the Department of Physiology, Gaziantep University and Department of Chemistry-Biochemistry, Kahramamaras Sutcu Imam University in 2006.MATERIALS: Pentylenetetrazole and glutathione were purchased from Sigma, USA. METHODS: A total of 80 mice were assigned to 8 groups (n=10): normal control, saline control (1 mL normal saline), convulsive pentylenetetrazole (single intraperitoneal administration of pentylenetetrazole, 60 mg/kg), convulsive pentylenetrazole plus glutathione (single administration of 60 mg/kg pentylenetetrazole and 200 mg/kg glutathione), five-dose glutathione (intraperitoneal injection of 200 mg/kg glutathione respectively at 1, 3, 5, 7, and 10 days), single-dose glutathione (single administration of 200 mg/kg glutathione), pentylenetetrazole kindling (intraperitoneal administration of pentylenetetrazole of 40 mg/kg at 1, 3, 5, 7, and 10 days), and pentylenetetrazole kindling plus glutathione group (intraperitoneal injection of 40 mg/kg pentylenetetrazole and 200 mg/kg glutathione respectively at 1, 3, 5, 7, and 10 days). MAIN OUTCOME MEASURES: All mice were sacrificed 1 hour after the last administration. Brain nitric oxide levels were determined by spectrophotometry. RESULTS: There were no significant differences in nitric oxide levels between the normal control, saline control, five-dose glutathione, and single-dose glutathione groups (P>0.05). Nitric oxide levels in the cerebral hemisphere and

  19. A functional group oxidation model (FGOM for SOA formation and aging

    Directory of Open Access Journals (Sweden)

    X. Zhang

    2013-06-01

    Full Text Available Secondary organic aerosol (SOA formation from a volatile organic compound (VOC involves multiple generations of oxidation that include functionalization and fragmentation of the parent carbon backbone and likely particle-phase oxidation and/or accretion reactions. Despite the typical complexity of the detailed molecular mechanism of SOA formation and aging, a relatively small number of functional groups characterize the oxidized molecules that constitute SOA. Given the carbon number and set of functional groups, the volatility of the molecule can be estimated. We present here a functional group oxidation model (FGOM that represents the process of SOA formation and aging. The FGOM contains a set of parameters that are to be determined by fitting of the model to laboratory chamber data: total organic aerosol concentration, and O : C and H : C atomic ratios. The sensitivity of the model prediction to variation of the adjustable parameters allows one to assess the relative importance of various pathways involved in SOA formation. An analysis of SOA formation from the high- and low-NOx photooxidation of four C12 alkanes (n-dodecane, 2-methylundecane, hexylcyclohexane, and cyclododecane using the FGOM is presented, and comparison with the statistical oxidation model (SOM of Cappa et al. (2013 is discussed.

  20. A Functional Group Oxidation Model (FGOM for SOA formation and aging

    Directory of Open Access Journals (Sweden)

    X. Zhang

    2012-12-01

    Full Text Available Secondary organic aerosol (SOA formation from a volatile organic compound (VOC involves multiple generations of oxidation that include functionalization and fragmentation of the parent carbon backbone and, likely, particle-phase oxidation and/or accretion reactions. Despite the typical complexity of the detailed molecular mechanism of SOA formation and aging, a relatively small number of functional groups characterize the oxidized molecules that constitute SOA. Given the carbon number and set of functional groups, the volatility of the molecule can be estimated. We present here a Functional Group Oxidation Model (FGOM that represents the process of SOA formation and aging. The FGOM contains a set of parameters that are to be determined by fitting of the model to laboratory chamber data: total organic aerosol concentration, and O:C and H:C atomic ratios. The sensitivity of the model prediction to variation of the adjustable parameters allows one to assess the relative importance of various pathways involved in SOA formation. An analysis of SOA formation from the high- and low-NOx photooxidation of four C12 alkanes (n-dodecane, 2-methylundecane, hexylcyclohexane, and cyclododecane using the FGOM is presented, and comparison with the Statistical Oxidation Model (SOM of Cappa et al. (2012 is discussed.

  1. Analytical model of LDMOS with a double step buried oxide layer

    Science.gov (United States)

    Yuan, Song; Duan, Baoxing; Cao, Zhen; Guo, Haijun; Yang, Yintang

    2016-09-01

    In this paper, a two-dimensional analytical model is established for the Buried Oxide Double Step Silicon On Insulator structure proposed by the authors. Based on the two-dimensional Poisson equation, the analytic expressions of the surface electric field and potential distributions for the device are achieved. In the BODS (Buried Oxide Double Step Silicon On Insulator) structure, the buried oxide layer thickness changes stepwise along the drift region, and the positive charge in the drift region can be accumulated at the corner of the step. These accumulated charge function as the space charge in the depleted drift region. At the same time, the electric field in the oxide layer also varies with the different drift region thickness. These variations especially the accumulated charge will modulate the surface electric field distribution through the electric field modulation effects, which makes the surface electric field distribution more uniform. As a result, the breakdown voltage of the device is improved by 30% compared with the conventional SOI structure. To verify the accuracy of the analytical model, the device simulation software ISE TCAD is utilized, the analytical values are in good agreement with the simulation results by the simulation software. That means the established two-dimensional analytical model for BODS structure is valid, and it also illustrates the breakdown voltage enhancement by the electric field modulation effect sufficiently. The established analytical models will provide the physical and mathematical basis for further analysis of the new power devices with the patterned buried oxide layer.

  2. Modeling and parametric simulations of solid oxide fuel cells with methane carbon dioxide reforming

    International Nuclear Information System (INIS)

    Highlights: ► A 2D model is developed for solid oxide fuel cells (SOFCs). ► CH4 reforming by CO2 (MCDR) is included. ► SOFC with MCDR shows comparable performance with methane steam reforming SOFC. ► Increasing CO electrochemical oxidation greatly enhances the SOFC performance. ► Effects of potential and temperature on SOFC performance are also discussed. - Abstract: A two-dimensional model is developed to simulate the performance of solid oxide fuel cells (SOFCs) fed with CO2 and CH4 mixture. The electrochemical oxidations of both CO and H2 are included. Important chemical reactions are considered in the model, including methane carbon dioxide reforming (MCDR), reversible water gas shift reaction (WGSR), and methane steam reforming (MSR). It’s found that at a CH4/CO2 molar ratio of 50/50, MCDR and reversible WGSR significantly influence the cell performance while MSR is negligibly small. The performance of SOFC fed with CO2/CH4 mixture is comparable to SOFC running on CH4/H2O mixtures. The electric output of SOFC can be enhanced by operating the cell at a low operating potential or at a high temperature. In addition, the development of anode catalyst with high activity towards CO electrochemical oxidation is important for SOFC performance enhancement. The model can serve as a useful tool for optimization of the SOFC system running on CH4/CO2 mixtures

  3. Performance model for large area solid oxide fuel cells

    Science.gov (United States)

    Klotz, Dino; Schmidt, Jan Philipp; Weber, André; Ivers-Tiffée, Ellen

    2014-08-01

    A parameter set obtained from a 1 cm2 size electrode cell is used to develop and calibrate a one-dimensional spatially resolved model. It is demonstrated that this performance model precalculates the evolving operating parameters along the gas channel of a large-sized cell. Input parameters are: (i) number of discretization elements N, accounting for anodic gas conversion, (ii) anodic gas flow rate and composition and (iv) operating voltage. The model calculations based on data from the 1 cm2 cell are scaled to be equivalent to a larger cell with 16 cm2 electrode size which is used to validate the performance model. The current/voltage characteristics can be predicted very accurately, even when anodic gas flow rates vary by as much as a factor of four. The performance model presented herein simulates the total overvoltage and does so in a broad range of operation conditions. This is done with an accuracy of the simulated current better than 6.1% for UOP = 0.85 V, 3.8% for UOP = 0.8 V and 3.7% for UOP = 0.75 V. It is hoped that these equations will form the basis of a greater model, capable of predicting all the conditions found throughout any industrial stack.

  4. Microstructural Modeling of Thermal Conductivity of High Burn-up Mixed Oxide Fuel

    International Nuclear Information System (INIS)

    Predicting the thermal conductivity of oxide fuels as a function of burn-up and temperature is fundamental to the efficient and safe operation of nuclear reactors. However, modeling the thermal conductivity of fuel is greatly complicated by the radially inhomogeneous nature of irradiated fuel in both composition and microstructure. In this work, radially and temperature-dependent models for effective thermal conductivity were developed utilizing optical micrographs of high burn-up mixed oxide fuel. The micrographs were employed to create finite element meshes with the OOF2 software. The meshes were then used to calculate the effective thermal conductivity of the microstructures using the BISON fuel performance code. The new thermal conductivity models were used to calculate thermal profiles at end of life for the fuel pellets. These results were compared to thermal conductivity models from the literature, and comparison between the new finite element-based thermal conductivity model and the Duriez-Lucuta model was favorable

  5. Modelling and engineering of stress based controlled oxidation effects for silicon nanostructure patterning

    International Nuclear Information System (INIS)

    Silicon nanostructure patterning with tight geometry control is an important challenge at the bottom level. In that context, stress based controlled oxidation appears to be an efficient tool for precise nanofabrication. Here, we investigate the stress-retarded oxidation phenomenon in various silicon nanostructures (nanobeams, nanorings and nanowires) at both the experimental and the theoretical levels. Different silicon nanostructures have been fabricated by a top-down approach. Complex dependence of the stress build-up on the nano-object’s dimension, shape and size has been demonstrated experimentally and physically explained by modelling. For the oxidation of a two-dimensional nanostructure (nanobeam), relative independence to size effects has been observed. On the other hand, radial stress increase with geometry downscaling of a one-dimensional nanostructure (nanowire) has been carefully emphasized. The study of shape engineering by retarded oxidation effects for vertical silicon nanowires is finally discussed. (paper)

  6. An improved model to evaluate the oxidation kinetics of uranium dioxide during dry storage

    International Nuclear Information System (INIS)

    During dry air storage, the oxidation of the spent fuel in case of cladding and container failure (accidental scenario) could be detrimental for further handling of the spent fuel rod and for the safety of the facilities. Recently, the phase transition sequence during the first step of parabolic oxidation kinetic has been challenged again and two well-distinguished intermediate products, U4O9 and U3O7 have been identified. Moreover, these observations have shown that the three phases (UO2, U4O9 and U3O7) occur together. Starting from a previous model of grain oxidation based on finite difference approach, a new model, describing the parabolic oxidation kinetic, has been developed based on the oxygen atom diffusion. This model allows in one hand to take into account the occurrence of the three phases and in another hand to describe accurately the plateau behaviour. A comparison between the model and literature data obtained on non-irradiated powders has been carried out and shows that this model can describe the weight gain evolution as a function of time for different temperatures. The diffusion coefficients of oxygen in the two phases (U4O9 and U3O7) were obtained by fitting the model results to experimental data. The comparison with the values given in literature is quite good

  7. Plutonium chemistry: a synthesis of experimental data and a quantitative model for plutonium oxide solubility

    International Nuclear Information System (INIS)

    The chemistry of plutonium is important for assessing potential behavior of radioactive waste under conditions of geologic disposal. This paper reviews experimental data on dissolution of plutonium oxide solids, describes a hybrid kinetic-equilibrium model for predicting steady-state Pu concentrations, and compares laboratory results with predicted Pu concentrations and oxidation-state distributions. The model is based on oxidation of PuO2 by water to produce PuO2+x, an oxide that can release Pu(V) to solution. Kinetic relationships between formation of PuO2+x, dissolution of Pu(V), disproportionation of Pu(V) to Pu(IV) and Pu(VI), and reduction of Pu(VI) are given and used in model calculations. Data from tests of pyrochemical salt wastes in brines are discussed and interpreted using the conceptual model. Essential data for quantitative modeling at conditions relevant to nuclear waste repositories are identified and laboratory experiments to determine rate constants for use in the model are discussed

  8. Modelling of cladding oxidation by air under severe accident conditions with the MAAP 4 code

    International Nuclear Information System (INIS)

    In a nuclear power plant, air ingress into the vessel is a potential risk in some low probable situations of severe accidents. Air is a highly oxidizing atmosphere that can lead to an enhanced core oxidation and degradation affecting the release of FP. This is particularly true speaking about ruthenium release, which can be significantly increased in the presence of air. This is a key issue due to the high radio-toxicity of ruthenium and its ability to form highly volatile oxides. The oxygen affinity is decreasing in priority from the Zircaloy cladding, to fuel and ruthenium inclusions. It is consequently of great need to understand the phenomena governing cladding oxidation by air as a prerequisite for the source term issues in such scenarios. As a first step, a phenomenological study has been carried out to characterize nitriding of the Zircaloy claddings. In summary, nitriding occurs preferentially when the oxygen has been consumed locally or in case of total oxygen starvation and when the cladding was slightly pre-oxidized. Just like oxidation, nitriding can be modeled in a simplified form as a cladding weight gain in terms of thickness. The model implemented in MAAP takes this into account as well as re-oxidation of the nitrides, in the case where oxygen is available again (especially during a reflood). Several correlations were thus integrated and a new one, called “KIT-EDF”, was developed, based on KIT separate-effect tests. The model has been implemented and validated against QUENCH-16 and QUENCH-10 experiments, studying the oxidation in air atmosphere of an assembly pre-oxidized in steam and finally quenched with water. The simulations give encouraging results since the modeling of nitriding effects has increased hydrogen production during reflood, as experimentally observed. The results of this study lead us to identify a number of perspectives for the future, namely taking into account the changes in the structure of the oxide layer during a

  9. A General Mechanistic Model of Solid Oxide Fuel Cells

    Institute of Scientific and Technical Information of China (English)

    SHI Yixiang; CAI Ningsheng

    2006-01-01

    A comprehensive model considering all forms of polarization was developed. The model considers the intricate interdependency among the electrode microstructure, the transport phenomena, and the electrochemical processes. The active three-phase boundary surface was expressed as a function of electrode microstructure parameters (porosity, coordination number, contact angle, etc.). The exchange current densities used in the simulation were obtained by fitting a general formulation to the polarization curves proposed as a function of cell temperature and oxygen partial pressure. A validation study shows good agreement with published experimental data. Distributions of overpotentials, gas component partial pressures, and electronic/ionic current densities have been calculated. The effects of a porous electrode structure and of various operation conditions on cell performance were also predicted. The mechanistic model proposed can be used to interpret experimental observations and optimize cell performance by incorporating reliable experimental data.

  10. Oxidative stress during aging and in Alzheimer's disease : a comparative study of oxidative damage and antioxidant enzymatic activities in mouse models and human brain tissue

    OpenAIRE

    Schüssel, Katrin

    2005-01-01

    The hypothesis that oxidative stress plays a role in the pathogenesis of Alzheimer’s disease (AD) was tested by studying oxidative damage, acitvities of antioxidant enzymes and levels of reactive oxygen species (ROS) in several models. To this end, mouse models transgenic for mutant presenilin (PS1M146L) as well as mutant amyloid precursor protein (APP) and human post mortem brain tissue from sporadic AD patients and age-matched controls were studied. Aging leads to an upregulation of antioxi...

  11. Experimental and modeling study of the oxidation of n- and iso-butanal

    KAUST Repository

    Veloo, Peter S.

    2013-09-01

    Understanding the kinetics of large molecular weight aldehydes is essential in the context of both conventional and alternative fuels. For example, they are key intermediates formed during the low-temperature oxidation of hydrocarbons as well as during the high-temperature oxidation of oxygenated fuels such as alcohols. In this study, an experimental and kinetic modeling investigation of n-butanal (. n-butyraldehyde) and iso-butanal (. iso-butyraldehyde or 2-methylpropanal) oxidation kinetics was performed. Experiments were performed in a jet stirred reactor and in counterflow flames over a wide range of equivalence ratios, temperatures, and pressures. The jet stirred reactor was utilized to observe the evolution of stable intermediates and products for the oxidation of n- and iso-butanal at elevated pressures and low to intermediate temperatures. The counterflow configuration was utilized for the determination of laminar flame speeds. A detailed chemical kinetic interpretative model was developed and validated consisting of 244 species and 1198 reactions derived from a previous study of the oxidation of propanal (propionaldehyde). Extensive reaction pathway and sensitivity analysis was performed to provide detailed insight into the mechanisms governing low-, intermediate-, and high-temperature reactivity. The simulation results using the present model are in good agreement with the experimental laminar flame speeds and well within a factor of two of the speciation data obtained in the jet stirred reactor. © 2013 The Combustion Institute.

  12. Detailed kinetic modeling study of n-pentanol oxidation

    KAUST Repository

    Heufer, Karl Alexander

    2012-10-18

    To help overcome the world\\'s dependence upon fossil fuels, suitable biofuels are promising alternatives that can be used in the transportation sector. Recent research on internal combustion engines shows that short alcoholic fuels (e.g., ethanol or n-butanol) have reduced pollutant emissions and increased knock resistance compared to fossil fuels. Although higher molecular weight alcohols (e.g., n-pentanol and n-hexanol) exhibit higher reactivity that lowers their knock resistance, they are suitable for diesel engines or advanced engine concepts, such as homogeneous charge compression ignition (HCCI), where higher reactivity at lower temperatures is necessary for engine operation. The present study presents a detailed kinetic model for n-pentanol based on modeling rules previously presented for n-butanol. This approach was initially validated using quantum chemistry calculations to verify the most stable n-pentanol conformation and to obtain C-H and C-C bond dissociation energies. The proposed model has been validated against ignition delay time data, speciation data from a jet-stirred reactor, and laminar flame velocity measurements. Overall, the model shows good agreement with the experiments and permits a detailed discussion of the differences between alcohols and alkanes. © 2012 American Chemical Society.

  13. Modeling selenate adsorption behavior on oxides, clay minerals, and soils using the triple layer model

    Science.gov (United States)

    Selenate adsorption behavior was investigated on amorphous aluminum oxide, amorphous iron oxide, goethite, clay minerals: kaolinites, montmorillonites, illite, and 18 soil samples from Hawaii, and the Southwestern and the Midwestern regions of the US as a function of solution pH. Selenate adsorpti...

  14. Thermal conductivity modeling of water containing metal oxide nanoparticles

    Institute of Scientific and Technical Information of China (English)

    Ahmad Azari

    2015-01-01

    The nano particles have demonstrated great potential to improve the heat transfer characteristics of heat transfer fluids. Possible parameters responsible for this increase were studied. The heat transfer profile in the nanolayer region was combined with other parameters such as volume fraction, particle radius thermal conductivity of the fluid, particle and nanolayer, to formulate a thermal conductivity model. Results predicting the thermal conductivity of nanofluids using the model were compared with experimental results as well as studies by other researchers. The comparison of the results obtained for the CuO/water and TiO2/water nanofluids studied shows that the correlation proposed is in closest proximity in predicting the experimental results for the thermal conductivity of a nanofluid. Also, a parametric study was performed to understand how a number of factors affect the thermal conductivity of nanofluids using the developed correlation.

  15. Physiologically based pharmacokinetic models for trichloroethylene and its oxidative metabolites.

    OpenAIRE

    Fisher, J W

    2000-01-01

    Trichloroethylene (TCE) pharmacokinetics have been studied in experimental animals and humans for over 30 years. Compartmental and physiologically based pharmacokinetic (PBPK) models have been developed for the uptake, distribution, and metabolism of TCE and the production, distribution, metabolism, and elimination of P450-mediated metabolites of TCE. TCE is readily taken up into systemic circulation by oral and inhalation routes of exposure and is rapidly metabolized by the hepatic P450 syst...

  16. Grazing incidence Fe-line telescopes using W/B4C multilayers

    DEFF Research Database (Denmark)

    Joensen, Karsten D.; Gorenstein, Paul; Christensen, Finn Erland;

    1994-01-01

    Traditional high-Z coated X-ray telescopes for the >= 1 keV range all have a loss of throughput with higher energies, owing to the inverse proportionality between the critical angle and energy. We have shown that this can, to some degree, be countered by employing multilayers on the outermost...

  17. A $B_4C$-silicon target for the detection of neutrino interactions

    CERN Document Server

    Barichello, G; Daniels, D C; do Couto e Silva, E; Dumps, Ludwig; Ellis, M; Ferrère, D; Gómez-Cadenas, J J; Gössling, C; Gouanère, M; Hernando, J A; Huta, W; Jiménez, J M; Kokkonen, J; Kuznetsov, V E; Linssen, Lucie; Long, J; Lisowski, B; Lupi, A; Runólfsson, O; Schmidt, B; Soler, F J P; Steele, D; Stipcevic, M; Veltri, M; Voillat, D

    1998-01-01

    This note describes the construction of a target for neutrino interactions composed of passive boron carbide plates interleaved with silicon microstrip detectors. The target contains four layers of passive material with a total mass of 45 kg and 600 single--sided silicon microstrip detectors with a total surface of 1.14 m$^2$ distributed over five layers. It is installed in the NOMAD spectrometer at the CERN SPS neutrino beam. During the 1997 run about 8000 \

  18. Machinability Studies on Turning Al 6061alloy with 10% Reinforcement of B4C on MMC

    Directory of Open Access Journals (Sweden)

    Srivathsan A.

    2016-01-01

    Full Text Available Aluminum Boron Carbide Metal Matrix Composites (Al-MMC have revolutionized aeronautical and automobile industries, in the recent times due to their exceptional mechanical and physical properties. However it is seen that the machinability of these composites is greatly reduced by the hardness of constituent reinforcement particles. Moreover these constituent reinforcement particles serve as disadvantage by increasing tool wear accompanying undesirable depression in life of tool. This paper presents the experimental investigations on turning of Al6061 matrix metal reinforced with 10 % by weight of boron carbide (B4Cp particles - which was fabricated using Stir casting method. Fabricated samples are turned on medium duty lathe of 2kW spindle power with Polycrystalline Diamond (PCD inserts of 1500 grade at various cutting conditions by varying parameters. Hence, parameters such as power consumed by main spindle, machined surface roughness and tool wear are studied and recorded. Furthermore, study results are supported using concurring images obtained from Scanning Electron Microscopy (SEM. It is observed that surface finish and power consumed for 1500 grade insert are comparatively better at higher cutting speeds. Additionally it is observed that tool wear is strongly dependent on abrasive hard reinforcement particles.

  19. Evidence of amorphisation of B4C boron carbide under slow, heavy ion irradiation

    Science.gov (United States)

    Gosset, D.; Miro, S.; Doriot, S.; Victor, G.; Motte, V.

    2015-12-01

    Boron carbide is widely used either as armor-plate or neutron absorber. In both cases, a good structural stability is required. However, a few studies have shown amorphisation may occur in severe conditions. Hard impacts lead to the formation of amorphous bands. Some irradiations in electronic regime with H or He ions have also shown amorphisation of the material. Most authors however consider the structure is not drastically affected by irradiations in the ballistic regime. Here, we have irradiated at room temperature dense boron carbide pellets with Au 4 MeV ions, for which most of the damage is in the ballistic regime. This study is part of a program devoted to the behavior of boron carbide under irradiation. Raman observations have been performed after the irradiations together with transmission electron microscopy (TEM). Raman observations show a strong structural damage at moderate fluences (1014/cm2, about 0.1 dpa), in agreement with previous studies. On the other hand, TEM shows the structure remains crystalline up to 1015/cm2 then partially amorphises. The amorphisation is heterogeneous, with the formation of nanometric amorphous zones with increasing density. It then appears short range and long range disorder occurs at quite different damage levels. Further experiments are in progress aiming at studying the structural stability of boron carbide and isostructural materials (α-B, B6Si,…).

  20. On regularities of interaction in B4C-Me4-6B systems

    International Nuclear Information System (INIS)

    An investigation has been made into refractories which are compatible with boron carbide and prospecting for manufacturing composite materials with enhanced physicomechanical properties. It is revealed that valent electron redistribution in the process of MeB2 type compound formation is determined by electronic structure of transition metals that reflects the possibility of formation of stable electron configurations

  1. Oxidation flow reactors (OFRs): overview of recent field and modeling studies

    Science.gov (United States)

    Jimenez, Jose-Luis; Palm, Brett B.; Peng, Zhe; Hu, Weiwei; Ortega, Amber M.; Li, Rui; Campuzano-Jost, Pedro; Day, Douglas A.; Stark, Harald; Brune, William H.; de Gouw, Joost; Schroder, Jason

    2016-04-01

    Oxidation flow reactors (OFRs) are popular tools for studying SOA formation and aging in both laboratory and field experiments. In an OFR, the concentration of an oxidant (OH, O3, or NO3) can be increased, leading to hours-months of equivalent atmospheric oxidation during the several-minute OFR residence time. Using gas- and particle-phase measurements from several recent field campaigns, we demonstrate SOA formation after oxidation of ambient air in an OFR. Typically, more SOA formation is observed from nighttime air than daytime air. This indicates that the concentration of SOA-forming gases in ambient air is relatively higher at night. Measured ambient VOCs are not able to explain the magnitude of SOA formation in the OFR, suggesting that typically unmeasured S/IVOCs (possibly VOC oxidation products or direct emissions) play a substantial intermediary role in ambient SOA formation. We also present highlights from recent OFR oxidant chemistry modeling studies. HOx, Ox, and photolysis chemistry was modeled for two common OH production methods (utilizing 185+254 nm UV light, or 254 nm only). OH exposure (OHexp) can be estimated within a factor of ~2 using model-derived equations, and can be verified in situ using VOC decay measurements. OHexp is strongly dependent on external OH reactivity, which may cause significant OH suppression in some circumstances (e.g., lab/source studies with high precursor concentrations). UV light photolysis and reaction with oxygen atoms are typically not major reaction pathways. Modeling the fate of condensable low-volatility organic gases (LVOCs) formed in an OFR suggests that LVOC fate is dependent on particle condensational sink. E.g., for the range of particle condensational sink at a remote pine forest, anywhere from 20-80% of produced LVOCs were predicted to condense onto aerosols for an OHexp of ~1 day, with the remainder lost to OFR or sampling line walls. Similar to large chamber wall loss corrections, a correction is needed

  2. Extending the models for iron and sulfur oxidation in the extreme Acidophile Acidithiobacillus ferrooxidans

    Directory of Open Access Journals (Sweden)

    Holmes David S

    2009-08-01

    Full Text Available Abstract Background Acidithiobacillus ferrooxidans gains energy from the oxidation of ferrous iron and various reduced inorganic sulfur compounds at very acidic pH. Although an initial model for the electron pathways involved in iron oxidation has been developed, much less is known about the sulfur oxidation in this microorganism. In addition, what has been reported for both iron and sulfur oxidation has been derived from different A. ferrooxidans strains, some of which have not been phylogenetically characterized and some have been shown to be mixed cultures. It is necessary to provide models of iron and sulfur oxidation pathways within one strain of A. ferrooxidans in order to comprehend the full metabolic potential of the pangenome of the genus. Results Bioinformatic-based metabolic reconstruction supported by microarray transcript profiling and quantitative RT-PCR analysis predicts the involvement of a number of novel genes involved in iron and sulfur oxidation in A. ferrooxidans ATCC23270. These include for iron oxidation: cup (copper oxidase-like, ctaABT (heme biogenesis and insertion, nuoI and nuoK (NADH complex subunits, sdrA1 (a NADH complex accessory protein and atpB and atpE (ATP synthetase F0 subunits. The following new genes are predicted to be involved in reduced inorganic sulfur compounds oxidation: a gene cluster (rhd, tusA, dsrE, hdrC, hdrB, hdrA, orf2, hdrC, hdrB encoding three sulfurtransferases and a heterodisulfide reductase complex, sat potentially encoding an ATP sulfurylase and sdrA2 (an accessory NADH complex subunit. Two different regulatory components are predicted to be involved in the regulation of alternate electron transfer pathways: 1 a gene cluster (ctaRUS that contains a predicted iron responsive regulator of the Rrf2 family that is hypothesized to regulate cytochrome aa3 oxidase biogenesis and 2 a two component sensor-regulator of the RegB-RegA family that may respond to the redox state of the quinone pool

  3. Trimetazidine prevents oxidative changes induced in a rat model of sporadic type of Alzheimer's disease.

    Directory of Open Access Journals (Sweden)

    Gholamreza Hassanzadeh

    2015-01-01

    Full Text Available Oxidative stress plays a major role in the pathogenesis of Alzheimer's disease (AD of sporadic origin. The expression of DHCR24 (Seladin-1, marker for neuronal oxidative stress and degeneration, has been reported to be altered in the brains of AD patients. In the present study, we investigated the effect of trimetazidine (TMZ on the hippocampal oxidative parameters and the expression of DHCR24 (Seladin-1 in an animal model of sporadic AD. Male rats were pre-treated with TMZ (25 mg/kg after which injected with intracerebroventricular-streptozotocin (ICV-STZ/Saline. Following 2, 7 and 14 days, animals of different groups were sacrificed with their brain excised to detect the hippocampal lipid peroxidation, superoxide dismutase (SOD, catalase activity, DHCR24 (Seladin-1 expression and possible histopathological changes. ICV-STZ administration induced significant oxidative changes in the hippocampus. Meanwhile, TMZ pre-treatment showed to ameliorate the oxidative stress, which was demonstrated by a significant rise in the hippocampal SOD and catalase activity, as well as a significant decrease in the malondialdehyde (MDA level. TMZ administration also increased the expression of DHCR24 (Seladin-1 gene in the hippocampus. In conclusion, our findings indicated a neuroprotective effect of TMZ possibly related to its antioxidant activity resulting in the up-regulation of DHCR24 (Seladin-1. Such TMZ effects may be beneficial in minimizing oxidative stress in sporadic Alzheimer's disease and possible prevention of disease progression.

  4. Trimetazidine prevents oxidative changes induced in a rat model of sporadic type of Alzheimer's disease.

    Science.gov (United States)

    Hassanzadeh, Gholamreza; Hosseini, Amir; Pasbakhsh, Parichehr; Akbari, Mohammad; Ghaffarpour, Massoud; Takzare, Nasrin; Zahmatkesh, Maryam

    2015-01-01

    Oxidative stress plays a major role in the pathogenesis of Alzheimer's disease (AD) of sporadic origin. The expression of DHCR24 (Seladin-1), marker for neuronal oxidative stress and degeneration, has been reported to be altered in the brains of AD patients. In the present study, we investigated the effect of trimetazidine (TMZ) on the hippocampal oxidative parameters and the expression of DHCR24 (Seladin-1) in an animal model of sporadic AD. Male rats were pre-treated with TMZ (25 mg/kg) after which injected with intracerebroventricular-streptozotocin (ICV-STZ)/Saline. Following 2, 7 and 14 days, animals of different groups were sacrificed with their brain excised to detect the hippocampal lipid peroxidation, superoxide dismutase (SOD), catalase activity, DHCR24 (Seladin-1) expression and possible histopathological changes. ICV-STZ administration induced significant oxidative changes in the hippocampus. Meanwhile, TMZ pre-treatment showed to ameliorate the oxidative stress, which was demonstrated by a significant rise in the hippocampal SOD and catalase activity, as well as a significant decrease in the malondialdehyde (MDA) level. TMZ administration also increased the expression of DHCR24 (Seladin-1) gene in the hippocampus. In conclusion, our findings indicated a neuroprotective effect of TMZ possibly related to its antioxidant activity resulting in the up-regulation of DHCR24 (Seladin-1). Such TMZ effects may be beneficial in minimizing oxidative stress in sporadic Alzheimer's disease and possible prevention of disease progression. PMID:25597600

  5. Thermodynamic and kinetic aspects on the selective surface oxidation of binary, ternary and quarternary model alloys

    International Nuclear Information System (INIS)

    Segregation and selective oxidation phenomena of minor alloying elements during annealing of steel sheets lead to the formation of bare spots after hot dip galvanizing. In order to understand the influence of common alloying elements on the surface chemistry after annealing, model alloys of binary (Fe-2Si, Fe-2Mn and Fe-0.8Cr), ternary (Fe-2Mn-2Si, Fe-2Mn-0.8Cr and Fe-2Si-0.8Cr) and quarternary (Fe-2Mn-2Si-0.8Cr) systems were investigated. The specimens were annealed for 60 s at 820 deg. C in N2-5% H2 gas atmospheres with different dew points -80 and -40 deg. C, respectively. Surface chemistry of the annealed specimens was obtained by using X-ray photoelectron spectroscopy (XPS). The field emission scanning electron microscopy (FE-SEM) was used to view surface morphology. At low dew point -80 deg. C, apart from the thermodynamical calculations such as solubility product of oxides and their critical solute concentrations, kinetics play a decisive role on the selective oxidation, i.e. oxygen competition. As expected, the amount of external selective oxidation of alloying elements are well pronounced at higher dew point -40 deg. C. An attempt has been made to explain the dominant process of Si and Mn on Cr-oxidation and segregation. It is observed that annealing of quarternary system at higher dew point shifts the Cr-oxidation from external to internal

  6. A model for the release of low-volatility fission products in oxidizing conditions

    International Nuclear Information System (INIS)

    A thermodynamic and kinetic model has been developed for calculating low-volatility fission-product releases from UO2 at high temperatures in oxidizing conditions. Volatilization of the UO2 matrix is assumed to be the rate controlling process. Oxidation kinetics of the UO2 are modelled by either interfacial rate control, gas phase oxidant transport control, or solid-state diffusion of oxygen. The vapour pressure of UO3 in equilibrium with the oxidizing fuel is calculated from thermodynamic data, and volatilization rates are determined using a model for forced convective mass transport. Low-volatility fission-product releases are calculated from the volume of vapourized fuel. Model calculations are conservative compared to experimental data for Zr, La, Ce and Nb fission-product releases from irradiated UO2 exposed to air at 1973-2350 K. The implications of this conservatism are discussed in terms of possible rate control by processes other than convective mass transport of UO3. Coefficients for effective surface area (based on experimental data) and for heterogeneous rate controlling reaction kinetics are introduced to facilitate agreement between calculations and the experimental data.

  7. A detailed approach to model transport, heterogeneous chemistry, and electrochemistry in solid-oxide fuel cells

    OpenAIRE

    Janardhanan, Vinod

    2007-01-01

    This book lays out a numerical framework for the detailed description of heterogeneous chemistry, electrochemistry and porous media transport in solid-oxide fuel cells (SOFC). Assuming hydrogen as the only electrochemically active species, a modified Butler-Volmer equation is used to model the electrochemical charge transfer.

  8. Recent modelling improvements in fuel performance code GERMINAL for SFR oxide fuel pins

    International Nuclear Information System (INIS)

    Objectives for the new code GERMINAL V2: – To strengthen the modelling of mixed oxide fuel pin: - FE computations for thermal analysis & mechanics; new mechanical behaviour’s laws; - State-of-the-art evolution for fuel physics. – To extend the simulation capability: - Materials with different behaviour, specific physics (fuel loaded with minor actinides); - By completing the validation base

  9. Quantitative model of the oxidation of methane at high pressure. II. Mechanism of autoacceleration

    Energy Technology Data Exchange (ETDEWEB)

    Vedeneev, V.I.; Gol' denberg, M.Ya.; Gorban' , N.I.; Teitel' boim, M.A.

    1988-07-01

    A quantitative model of the oxidation of methane at high pressures is analyzed with the aid of a mathematical approach to complex chemical schemes that has been developed. A two-stage mechanism of autoacceleration is identified. The key elementary reactions that determine the kinetics of the process are established.

  10. Experimental and Kinetic Modeling Study of Methanol Ignition and Oxidation at High Pressure

    DEFF Research Database (Denmark)

    Aranda, V.; Christensen, J. M.; Alzueta, Maria;

    2013-01-01

    conditions studied, the onset temperature for methanol oxidation was not dependent on the stoichiometry, whereas increasing pressure shifted the ignition temperature toward lower values. Model predictions of the present experimental results, as well as rapid compression machine data from the literature, were...

  11. Characterization of subcritical water oxidation with in situ monitoring and self-modeling curve resolution

    International Nuclear Information System (INIS)

    In this paper, a subcritical water oxidation (SBWO) process was monitored using self-modeling curve resolution (SMCR) of in situ UV-Vis measurements to estimate time-dependant composition profiles of reactants, intermediates and products. A small laboratory scale reactor with UV-Vis fiber-optic probes and a flow cell was used to demonstrate the usefulness of SMCR for monitoring the destruction of model compounds phenol, benzoic acid, and aniline in a dilute aqueous solutions. Hydrogen peroxide was used as the oxidizing reagent at moderate temperature (150-250 deg. C) and pressure (60-90 atm) in a single phase. By use of in situ monitoring, reaction times were easily determined and conditions for efficient oxidations were easily diagnosed without the need for time consuming off-line reference measurements. For selected runs, the destruction of the model compound was confirmed by gas chromatography and chemical oxygen demand (COD) measurements. Suspected intermediate oxidation products were easily detected by the use of UV-Vis spectrometry and self-modeling curve resolution, but could not be detected by gas chromatography

  12. Hydrogen oxidation at high pressure and intermediate temperatures: experiments and kinetic modeling

    DEFF Research Database (Denmark)

    Hashemi, Hamid; Christensen, Jakob Munkholt; Gersen, Sander;

    2015-01-01

    conditions ( U = 1.03 and 0.05). At very oxidizing conditions (O 2 atmosphere, U = 0.0009), the temperature for onset of reaction was reduced to 775–798 K. The data were interpreted in terms of a detailed chemical kinetic model, drawn mostly from work of Burke and coworkers. In the present study, the rate...

  13. Biodegradation and cometabolic modeling of selected beta blockers during ammonia oxidation.

    Science.gov (United States)

    Sathyamoorthy, Sandeep; Chandran, Kartik; Ramsburg, C Andrew

    2013-11-19

    Accurate prediction of pharmaceutical concentrations in wastewater effluents requires that the specific biochemical processes responsible for pharmaceutical biodegradation be elucidated and integrated within any modeling framework. The fate of three selected beta blockers-atenolol, metoprolol, and sotalol-was examined during nitrification using batch experiments to develop and evaluate a new cometabolic process-based (CPB) model. CPB model parameters describe biotransformation during and after ammonia oxidation for specific biomass populations and are designed to be integrated within the Activated Sludge Models framework. Metoprolol and sotalol were not biodegraded by the nitrification enrichment culture employed herein. Biodegradation of atenolol was observed and linked to the activity of ammonia-oxidizing bacteria (AOB) and heterotrophs but not nitrite-oxidizing bacteria. Results suggest that the role of AOB in atenolol degradation may be disproportionately more significant than is otherwise suggested by their lower relative abundance in typical biological treatment processes. Atenolol was observed to competitively inhibit AOB growth in our experiments, though model simulations suggest inhibition is most relevant at atenolol concentrations greater than approximately 200 ng·L(-1). CPB model parameters were found to be relatively insensitive to biokinetic parameter selection suggesting the model approach may hold utility for describing pharmaceutical biodegradation during biological wastewater treatment. PMID:24112027

  14. Development of the Monolith Froth Reactor for Catalytic Wet Oxidation of CELSS Model Wastes

    Science.gov (United States)

    Abraham, Martin; Fisher, John W.

    1995-01-01

    The aqueous phase oxidation of acetic acid, used as a model compound for the treatment of CELSS (Controlled Ecological Life Support System) waste, was carried out in the monolith froth reactor which utilizes two-phase flow in the monolith channels. The catalytic oxidation of acetic acid was carried out over a Pt/Al2O3 catalyst, prepared at The University of Tulsa, at temperatures and pressures below the critical point of water. The effect of externally controllable parameters (temperature, liquid flow rate, distributor plate orifice size, pitch, and catalyst distance from the distributor plate) on the rate of acetic acid oxidation was investigated. Results indicate reaction rate increased with increasing temperature and exhibited a maximum with respect to liquid flow rate. The apparent activation energy calculated from reaction rate data was 99.7 kJ/mol. This value is similar to values reported for the oxidation of acetic acid in other systems and is comparable to intrinsic values calculated for oxidation reactions. The kinetic data were modeled using simple power law kinetics. The effect of "froth" feed system characteristics was also investigated. Results indicate that the reaction rate exhibits a maximum with respect to distributor plate orifice size, pitch, and catalyst distance from the distributor plate. Fundamental results obtained were used to extrapolate where the complete removal of acetic acid would be obtained and for the design and operation of a full scale CELSS treatment system.

  15. Kinetic modeling of low temperature oxidation of copper nanoparticles by O2

    International Nuclear Information System (INIS)

    Highlights: • Low temperature oxidation of copper nanoparticles resulted in hollow Cu2O particles. • A mechanism is proposed to explain the outward growth of Cu2O. • The reaction involves simultaneously growth and nucleation processes of Cu2O. • Adsorption is the rate determining step below the slowdown of the reaction. • A kinetic model is proposed and confronted to the experimental data. - Abstract: The mechanism and kinetics of copper nanoparticles oxidation at low temperature were investigated using thermogravimetry (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Isothermal and isobaric studies of the oxidation reaction were carried out at various temperatures. It was found that working under an oxygen partial pressure of 1 kPa in the temperature range 125–145 °C leads to reaction where nucleation of the oxide phase is in competition with its growth. The study of the dependency of the growth rate on the oxygen partial pressure under 10 kPa has shown the adsorption of oxygen at the surface of the oxide to be the rate-determining step. A mechanism and a kinetic model have been established to interpret the experimental curves

  16. Kinetic modeling of the oxidative degradation of additive free PE in bleach disinfected water

    Science.gov (United States)

    Mikdam, Aïcha; Colin, Xavier; Billon, Noëlle; Minard, Gaëlle

    2016-05-01

    The chemical interactions between PE and bleach were studied at 60°C in immersion in bleach solutions kept at a free chlorine concentration of 100 ppm and a pH of 5 or 7.2. It was found that the polymer undergoes a severe oxidation from the earliest weeks of exposure, in a superficial layer whose thickness (of about 50-70 µm) is almost independent of the pH value, although the superficial oxidation rate is faster in acidic than in neutral medium. Oxidation leads to the formation and accumulation of a large variety of carbonyl products (mostly ketones and carboxylic acids) and, after a few weeks, to a decrease in the average molar mass due to the large predominance of chain scissions over crosslinking. A scenario was elaborated for explaining such unexpected results. According to this scenario, the non-ionic molecules (Cl2 and ClOH) formed from the disinfectant in the water phase, would migrate deeply into PE and dissociate into highly reactive radicals (Cl• and HO•) in order to initiate a radical chain oxidation. A kinetic model was derived from this scenario for predicting the general trends of the oxidation kinetics and its dependence on environmental factors such as temperature, free chlorine concentration and pH. The validity of this model was successfully checked by comparing the numerical simulations with experimental data.

  17. Modeling the Electrochemical Hydrogen Oxidation and Evolution Reactions on the Basis of Density Functional Theory Calculations

    DEFF Research Database (Denmark)

    Skulason, Egill; Tripkovic, Vladimir; Björketun, Mårten;

    2010-01-01

    Density functional theory calculations have been performed for the three elementary steps―Tafel, Heyrovsky, and Volmer―involved in the hydrogen oxidation reaction (HOR) and its reverse, the hydrogen evolution reaction (HER). For the Pt(111) surface a detailed model consisting of a negatively char...... detailed kinetic model based entirely on the DFT reactions and show that the exchange current follows a volcano curve when plotted against the H adsorption free energy in excellent agreement with experimental data....

  18. Oxidative stress contributes to outcome severity in a Drosophila melanogaster model of classic galactosemia

    Directory of Open Access Journals (Sweden)

    Patricia P. Jumbo-Lucioni

    2013-01-01

    Classic galactosemia is a genetic disorder that results from profound loss of galactose-1P-uridylyltransferase (GALT. Affected infants experience a rapid escalation of potentially lethal acute symptoms following exposure to milk. Dietary restriction of galactose prevents or resolves the acute sequelae; however, many patients experience profound long-term complications. Despite decades of research, the mechanisms that underlie pathophysiology in classic galactosemia remain unclear. Recently, we developed a Drosophila melanogaster model of classic galactosemia and demonstrated that, like patients, GALT-null Drosophila succumb in development if exposed to galactose but live if maintained on a galactose-restricted diet. Prior models of experimental galactosemia have implicated a possible association between galactose exposure and oxidative stress. Here we describe application of our fly genetic model of galactosemia to the question of whether oxidative stress contributes to the acute galactose sensitivity of GALT-null animals. Our first approach tested the impact of pro- and antioxidant food supplements on the survival of GALT-null and control larvae. We observed a clear pattern: the oxidants paraquat and DMSO each had a negative impact on the survival of mutant but not control animals exposed to galactose, and the antioxidants vitamin C and α-mangostin each had the opposite effect. Biochemical markers also confirmed that galactose and paraquat synergistically increased oxidative stress on all cohorts tested but, interestingly, the mutant animals showed a decreased response relative to controls. Finally, we tested the expression levels of two transcripts responsive to oxidative stress, GSTD6 and GSTE7, in mutant and control larvae exposed to galactose and found that both genes were induced, one by more than 40-fold. Combined, these results implicate oxidative stress and response as contributing factors in the acute galactose sensitivity of GALT-null Drosophila and, by

  19. Experimental and Modeling Investigation of the Low-Temperature Oxidation of Dimethyl Ether.

    Science.gov (United States)

    Rodriguez, Anne; Frottier, Ophélie; Herbinet, Olivier; Fournet, René; Bounaceur, Roda; Fittschen, Christa; Battin-Leclerc, Frédérique

    2015-07-16

    The oxidation of dimethyl ether (DME) was studied using a jet-stirred reactor over a wide range of conditions: temperatures from 500 to 1100 K; equivalence ratios of 0.25, 1, and 2; residence time of 2 s; pressure of 106.7 kPa (close to the atmospheric pressure); and an inlet fuel mole fraction of 0.02 (with high dilution in helium). Reaction products were quantified using two analysis methods: gas chromatography and continuous wave cavity ring-down spectroscopy (cw-CRDS). cw-CRDS enabled the quantification of formaldehyde, which is one of the major products from DME oxidation, as well as that of hydrogen peroxide, which is an important branching agent in low-temperature oxidation chemistry. Experimental data were compared with data computed using models from the literature with important deviations being observed for the reactivity at low-temperature. A new detailed kinetic model for the oxidation of DME was developed in this study. Kinetic parameters used in this model were taken from literature or calculated in the present work using quantum calculations. This new model enables a better prediction of the reactivity in the low-temperature region. Under the present JSR conditions, error bars on predictions were given. Simulations were also successfully compared with experimental flow reactor, jet-stirred reactor, shock tube, rapid compression machine, and flame data from literature. The kinetic analysis of the model enabled the highlighting of some specificities of the oxidation chemistry of DME: (1) the early reactivity which is observed at very low-temperature (e.g., compared to propane) is explained by the absence of inhibiting reaction of the radical directly obtained from the fuel (by H atom abstraction) with oxygen yielding an olefin + HO2·; (2) the low-temperature reactivity is driven by the relative importance of the second addition to O2 (promoting the reactivity through branching chain) and the competitive decomposition reactions with an inhibiting

  20. Application of the Generic Modeling Template Approach to Unsaturated Fatty Acid Oxidation and Crystallization Systems

    DEFF Research Database (Denmark)

    Fedorova, Marina; Papadakis, Emmanouil; Meisler, Kresten Troelstrup; Sin, Gürkan; Gani, Rafiqul

    In this work, a couple of applications of the template-based approach for model development are presented. The computer-aided template concept has been developed based on a model decomposition technique and has been implemented as a software tool, which provides a user-friendly interface for...... following the modelling workflow steps, guidance through the steps , as well as providing additional information and comments. The application of the tool is highlighted with two case studies: oxidation of unsaturated acid with hydrogen peroxide and modeling of a crystal lization operation for the...... paracetamol-ethanol system....

  1. Influence of modelled soil biogenic NO emissions on related trace gases and the atmospheric oxidizing capacity

    OpenAIRE

    Steinkamp, J.; Ganzeveld, L. N.; Wilcke, W.; Lawrence, M G

    2009-01-01

    The emission of nitric oxide (NO) by soils (SNOx) is an important source of oxides of nitrogen (NOx=NO+NO2) in the troposphere, with estimates ranging from 4 to 21 Tg of nitrogen per year. Previous studies have examined the influence of SNOx on ozone (O-3) chemistry. We employ the ECHAM5/MESSy atmospheric chemistry model (EMAC) to go further in the reaction chain and investigate the influence of SNOx on lower tropospheric NOx, O-3, peroxyacetyl nitrate (PAN), nitric acid (HNO3), the hydroxyl ...

  2. In-pile steam oxidation of model HTGR fuel elements

    International Nuclear Information System (INIS)

    Model HTGR fuel elements were exposed to various concentrations of steam while being irradiated under several sets of temperature conditions in the Oak Ridge Research Reactor. In one test, catalysis by iron impurities in the graphite casing of the fuel element caused a highly localized attack on the graphite by the steam; this resulted in the formation of deep pits in the casing. Furthermore, the iron impurities were sufficiently mobile to cause pitting attack on the pyrolytic carbon coatings of the fuel particles as well. The presence of steam induced a rapid increase in the release of gaseous fission products. However, the cessation of steam ingress in the primary system resulted in a pronounced, but correspondingly smaller, reduction in the level of gaseous release. The incidence of fuel failure was greater than anticipated; however, even though the coatings of greater than 30% of the fuel had failed, the release of fission products beyond the fuel element itself was largely confined to iodine and the noble gases. A novel mode of fuel failure was observed under the rather severe conditions of the tests; this involved the attack of the pyrolytic carbon coatings on intact particles by uncoated fragments of uranium fuel kernel material from failed particles

  3. An Abnormal Nitric Oxide Metabolism Contributes to Brain Oxidative Stress in the Mouse Model for the Fragile X Syndrome, a Possible Role in Intellectual Disability

    Science.gov (United States)

    Lima-Cabello, Elena; Garcia-Guirado, Francisco; Calvo-Medina, Rocio; el Bekay, Rajaa; Perez-Costillas, Lucia; Quintero-Navarro, Carolina; Sanchez-Salido, Lourdes

    2016-01-01

    Background. Fragile X syndrome is the most common genetic cause of mental disability. Although many research has been performed, the mechanism underlying the pathogenesis is unclear and needs further investigation. Oxidative stress played major roles in the syndrome. The aim was to investigate the nitric oxide metabolism, protein nitration level, the expression of NOS isoforms, and furthermore the activation of the nuclear factor NF-κB-p65 subunit in different brain areas on the fragile X mouse model. Methods. This study involved adult male Fmr1-knockout and wild-type mice as controls. We detected nitric oxide metabolism and the activation of the nuclear factor NF-κBp65 subunit, comparing the mRNA expression and protein content of the three NOS isoforms in different brain areas. Results. Fmr1-KO mice showed an abnormal nitric oxide metabolism and increased levels of protein tyrosine nitrosylation. Besides that, nuclear factor NF-κB-p65 and inducible nitric oxide synthase appeared significantly increased in the Fmr1-knockout mice. mRNA and protein levels of the neuronal nitric oxide synthase appeared significantly decreased in the knockout mice. However, the epithelial nitric oxide synthase isoform displayed no significant changes. Conclusions. These data suggest the potential involvement of an abnormal nitric oxide metabolism in the pathogenesis of the fragile X syndrome. PMID:26788253

  4. An Abnormal Nitric Oxide Metabolism Contributes to Brain Oxidative Stress in the Mouse Model for the Fragile X Syndrome, a Possible Role in Intellectual Disability

    Directory of Open Access Journals (Sweden)

    Elena Lima-Cabello

    2016-01-01

    Full Text Available Background. Fragile X syndrome is the most common genetic cause of mental disability. Although many research has been performed, the mechanism underlying the pathogenesis is unclear and needs further investigation. Oxidative stress played major roles in the syndrome. The aim was to investigate the nitric oxide metabolism, protein nitration level, the expression of NOS isoforms, and furthermore the activation of the nuclear factor NF-κB-p65 subunit in different brain areas on the fragile X mouse model. Methods. This study involved adult male Fmr1-knockout and wild-type mice as controls. We detected nitric oxide metabolism and the activation of the nuclear factor NF-κBp65 subunit, comparing the mRNA expression and protein content of the three NOS isoforms in different brain areas. Results. Fmr1-KO mice showed an abnormal nitric oxide metabolism and increased levels of protein tyrosine nitrosylation. Besides that, nuclear factor NF-κB-p65 and inducible nitric oxide synthase appeared significantly increased in the Fmr1-knockout mice. mRNA and protein levels of the neuronal nitric oxide synthase appeared significantly decreased in the knockout mice. However, the epithelial nitric oxide synthase isoform displayed no significant changes. Conclusions. These data suggest the potential involvement of an abnormal nitric oxide metabolism in the pathogenesis of the fragile X syndrome.

  5. Development and Assessment of a Thermo-kinetic model on Mixed Oxide (MOX) Fuels using Dictra

    International Nuclear Information System (INIS)

    MOX fuels containing recycled plutonium are currently used in PWR throughout France. Moreover, mixed oxide fuels is the recommended fuel type for Gen IV SFR's. Thus it is of paramount importance to understand the diffusion properties within the fuel matrix. Mixed oxide fuels such as uranium-plutonium dioxide exhibits a non-stoichiometric range over a wide temperature scale. Atomic transport properties are governed by the defects in the fuel. The DICTRA-based model considers diffusion across non-stoichiometric ranges described by experimentally available data. Before considering mixed oxide fuels, the binaries UO2±x and PuO2-x are assessed. A vacancy and interstitial diffusion-model for oxygen is applied to U-O and Pu-O systems as a function of defect structures, derived from CALPHAD-type thermodynamic descriptions. Oxygen and metal self-diffusion coefficients are assessed for a mobility database. Chemical diffusion coefficients are derived using the Darken relation and defect migration energies are evaluated. A diffusion model of the oxides in the C1 phase with O/M=1.85-2.15 at various temperatures is presented. (author)

  6. Modeling of tunneling current in ultrathin MOS structure with interface trap charge and fixed oxide charge

    Institute of Scientific and Technical Information of China (English)

    Hu Bo; Huang Shi-Hua; Wu Feng-Min

    2013-01-01

    A model based on analysis of the self-consistent Poisson-Schrodinger equation is proposed to investigate the tunneling current of electrons in the inversion layer of a p-type metal-oxide-semiconductor (MOS) structure.In this model,the influences of interface trap charge (ITC) at the Si-SiO2 interface and fixed oxide charge (FOC) in the oxide region are taken into account,and one-band effective mass approximation is used.The tunneling probability is obtained by employing the transfer matrix method.Further,the effects of in-plane momentum on the quantization in the electron motion perpendicular to the Si-SiO2 interface of a MOS device are investigated.Theoretical simulation results indicate that both ITC and FOC have great influence on the tunneling current through a MOS structure when their densities are larger than 1012 cm-2,which results from the great change of bound electrons near the Si-SiO2 interface and the oxide region.Therefore,for real ultrathin MOS structures with ITC and FOC,this model can give a more accurate description for the tunneling current in the inversion layer.

  7. Methanol oxidation at platinum electrodes in acid solution: comparison between model and real catalysts

    Directory of Open Access Journals (Sweden)

    A. V. TRIPKOVIC

    2006-12-01

    Full Text Available Methanol oxidation in acid solution was studied at platinum single crystals, Pt(hkl, as the model catalyst, and at nanostructural platinum supported on high surface area carbon, Pt/C, as the real catalyst. The linear extrapolation method was used to determine the beginning of hydroxyl anion adsorption. Structural sensitivity of the adsorption was proved and a correlation with the onset of the methanol oxidation current was established at all catalysts. Bisulfate and chloride anions were found to decrease the methanol oxidation rate, but probably did not influence the reaction parth. The specific activity for the reaction increased in the sequence Pt(110 < Pt/C < Pt(111, suggesting that the activity of the supported Pt catalyst can be correlated with the activities of the dominating crystal planes on its surface.

  8. Nitronate monooxygenase, a model for anionic flavin semiquinone intermediates in oxidative catalysis.

    Science.gov (United States)

    Gadda, Giovanni; Francis, Kevin

    2010-01-01

    Nitronate monooxygenase (NMO), formerly referred to as 2-nitropropane dioxygenase, is an FMN-dependent enzyme that uses molecular oxygen to oxidize (anionic) alkyl nitronates and, in the case of the enzyme from Neurospora crassa, (neutral) nitroalkanes to the corresponding carbonyl compounds and nitrite. Over the past 5 years, a resurgence of interest on the enzymology of NMO has driven several studies aimed at the elucidation of the mechanistic and structural properties of the enzyme. This review article summarizes the knowledge gained from these studies on NMO, which has been emerging as a model system for the investigation of anionic flavosemiquinone intermediates in the oxidative catalysis of organic molecules, and for the effect that branching of reaction intermediates has on both the kinetic parameters and isotope effects associated with enzymatic reactions. A comparison of the catalytic mechanism of NMO with other flavin-dependent enzymes that oxidize nitroalkane and nitronates is also presented. PMID:19577534

  9. Modeling anti-Trypanosoma cruzi activity of N-oxide containing heterocycles.

    Science.gov (United States)

    Boiani, Mariana; Cerecetto, Hugo; Gonzalez, Mercedes; Gasteiger, Johann

    2008-01-01

    In the present study a systematic approach was used to model the anti-T. cruzi activity of a series of N-oxide containing heterocycles belonging to four chemical families with a wide structural diversity. The proposed mode of action implies the reduction of the N-oxide moiety; however, the biochemical mechanism underlying the anti-T. cruzi activity is still unkown. For structural representation two types of descriptors were analyzed: quantum chemical (AM1) global descriptors and properties coded by radial distribution function (RDF). Both types of descriptors point to the relevance of electronic properties. The local-RDF (LRDF) identified an electrophilic center at 4.1-4.9 A from the oxygen atom of the N-oxide moiety, although other properties are required to explain the biological activity. While the mode of action of N-oxide containing heterocycles is still unknown, the results obtained here strengthen the importance of the electrophilic character of the molecule and the possible participation of the heterocycle in a reduction process. The ability of these descriptors to distinguish among activity classes was assessed using Kohonen neural networks, and the best clustering descriptors were later used for model building. Different learning algorithms were used for model development, and stratified 10-fold cross-validation was used to evaluate the performance of each classifier. The best results were obtained using k-nearest neighbors (k-NN) and decision tree (J48) methods combined with global descriptors. Since tree-based methods are easily translated into classification rules, the J48 model is a useful tool in the de novo construction of new N-oxide containing heterocycle lead structures. PMID:18163603

  10. Alternative Fabrication Routes toward Oxide-Dispersion-Strengthened Steels and Model Alloys

    Science.gov (United States)

    Bergner, Frank; Hilger, Isabell; Virta, Jouko; Lagerbom, Juha; Gerbeth, Gunter; Connolly, Sarah; Hong, Zuliang; Grant, Patrick S.; Weissgärber, Thomas

    2016-07-01

    The standard powder metallurgy (PM) route for the fabrication of oxide-dispersion-strengthened (ODS) steels involves gas atomization to produce a prealloyed powder, mechanical alloying (MA) with fine oxide powders, consolidation, and finally thermal/thermomechanical treatment (TMT). It is well established that ODS steels with superior property combinations, for example, creep and tensile strength, can be produced by this PM/MA route. However, the fabrication process is complex and expensive, and the fitness for scaling up to the industrial scale is limited. At the laboratory scale, production of small amounts of well-controlled model systems continues to be desirable for specific purposes, such as modeling-oriented experiments. Thus, from the laboratory to industrial application, there is growing interest in complementary or alternative fabrication routes for ODS steels and related model systems, which offer a different balance of cost, convenience, properties, and scalability. This article reviews the state of the art in ODS alloy fabrication and identifies promising new routes toward ODS steels. The PM/AM route for the fabrication of ODS steels is also described, as it is the current default process. Hybrid routes that comprise aspects of both the PM route and more radical liquid metal (LM) routes are suggested to be promising approaches for larger volumes and higher throughput of fabricated material. Although similar uniformity and refinement of the critical nanometer-sized oxide particles has not yet been demonstrated, ongoing innovations in the LM route are described, along with recent encouraging preliminary results for both extrinsic nano-oxide additions and intrinsic nano-oxide formation in variants of the LM route. Finally, physicochemical methods such as ion beam synthesis are shown to offer interesting perspectives for the fabrication of model systems. As well as literature sources, examples of progress in the authors' groups are also highlighted.

  11. Modeling the oxidative coupling of methane:Heterogeneous chemistry coupled with 3D flow field simulation

    Institute of Scientific and Technical Information of China (English)

    Yaghobi Nakisa; Ghoreishy Mir Hamid Reza

    2009-01-01

    The oxidative coupling of methane (OCM) over titanate perovskite catalyst has been developed by three-dimensional numerical simulations of flow field coupled with heat transfer as well as heterogeneous kinetic model.The reaction was assumed to take place both in the gas phase and on the catalytic surface.Kinetic rate constants were experimentally obtained using a ten step kinetic model.The simulation results agree quite well with the data of OCM experiments,which were used to investigate the effect of temperature on the selectivity and conversion obtained in the methane oxidative coupling process.The conversion of methane linearly increased with temperature and the selectivity of C2 was practically constant in the temperature range of 973-1073 K.The study shows that CFD tools make it possible to implement the heterogeneous kinetic model even for high exothermic reaction such as OCM.

  12. A grey box model of glucose fermentation and syntrophic oxidation in microbial fuel cells.

    Science.gov (United States)

    de Los Ángeles Fernandez, Maria; de Los Ángeles Sanromán, Maria; Marks, Stanislaw; Makinia, Jacek; Gonzalez Del Campo, Araceli; Rodrigo, Manuel; Fernandez, Francisco Jesus

    2016-01-01

    In this work, the fermentative and oxidative processes taking place in a microbial fuel cell (MFC) fed with glucose were studied and modeled. The model accounting for the bioelectrochemical processes was based on ordinary, Monod-type differential equations. The model parameters were estimated using experimental results obtained from three H-type MFCs operated at open or closed circuits and fed with glucose or ethanol. The experimental results demonstrate that similar fermentation processes were carried out under open and closed circuit operation, with the most important fermentation products being ethanol (with a yield of 1.81molmol(-1) glucose) and lactic acid (with a yield of 1.36molmol(-1) glucose). A peak in the electricity generation was obtained when glucose and fermentation products coexisted in the liquid bulk. However, almost 90% of the electricity produced came from the oxidation of ethanol. PMID:26512864

  13. Detection and quantification of protein oxidation in sarcopenic models: a mass spectrometry study.

    Science.gov (United States)

    Pasha, Sabah; Tveen Jensen, Karina; Pitt, Andrew R; Spickett, Corinne M

    2014-10-01

    Oxidised biomolecules in aged tissue could potentially be used as biomarkers for age-related diseases; however, it is still unclear whether they causatively contribute to ageing or are consequences of the ageing process. To assess the potential of using protein oxidation as markers of ageing, mass spectrometry (MS) was employed for the identification and quantification of oxidative modifications in obese (ob/ob) mice. Lean muscle mass and strength is reduced in obesity, representing a sarcopenic model in which the levels of oxidation can be evaluated for different muscular systems including calcium homeostasis, metabolism and contractility. Several oxidised residues were identified by tandem MS (MS/MS) in both muscle homogenate and isolated sarcoplasmic reticulum (SR), an organelle that regulates intracellular calcium levels in muscle. These modifications include oxidation of methionine, cysteine, tyrosine, and tryptophan in several proteins such as sarcoplasmic reticulum calcium ATPase (SERCA), glycogen phosphorylase, and myosin. Once modifications had been identified, multiple reaction monitoring MS (MRM) was used to quantify the percentage modification of oxidised residues within the samples. Preliminary data suggests proteins in ob/ob mice are more oxidised than the controls. For example SERCA, which constitutes 60-70% of the SR, had approximately a 2-fold increase in cysteine trioxidation of Cys561 in the obese model when compared to the control. Other obese muscle proteins have also shown a similar increase in oxidation for various residues. Further analysis with complex protein mixtures will determine the potential diagnostic use of MRM experiments for analysing protein oxidation in small biological samples such as muscle needle biopsies. PMID:26461380

  14. Rhesus monkey lens as an in vitro model for studying oxidative stress

    International Nuclear Information System (INIS)

    Lenses from young rhesus monkeys were incubated in the presence of H2O2 or oxygen radical generating systems to determine their suitability as a model for investigating lenticular oxidative stress. Additionally, direct comparisons were made between the effects found with the monkey lenses and those observed with cultured rat lenses exposed to the same oxidizing systems. As in earlier studies with rat lenses the monkey lenses exhibited impaired ability to actively accumulate from the medium radioactively labelled rubidium and choline following exposure to oxidative stress. Based on the effects of various scavengers of oxygen radicals it appeared that the mechanisms responsible for lens damage were the same for both rat and monkey lenses. However, rat lenses were damaged by lower concentrations of oxidants than were monkey lenses. It was concluded that oxidative stress affects both rat and monkey lenses by similar mechanisms but that lenses from monkeys, and probably other primates, are more resistant to these effects because they have better endogenous antioxidant defenses

  15. Model-fitting approach to kinetic analysis of non-isothermal oxidation of molybdenite

    International Nuclear Information System (INIS)

    The kinetics of molybdenite oxidation was studied by non-isothermal TGA-DTA with heating rate 5degC.min-1. The model-fitting kinetic approach applied to TGA data. The Coats-Redfern method used of model fitting. The popular model-fitting gives excellent fit non-isothermal data in chemically controlled regime. The apparent activation energy was determined to be about 34.2 kcalmol-1 With pre-exponential factor about 108 sec-1 for extent of reaction less than 0.5

  16. Process flow model of solid oxide fuel cell system supplied with sewage biogas

    OpenAIRE

    Van herle, Jan; Favrat, Daniel; Maréchal, François; Bucheli, Olivier; Leuenberger, Sacha; Membrez, Yves

    2004-01-01

    A model for a 1000 kW class solid oxide fuel cell (SOFC) system running on biogas from a sewage sludge digestion plant was implemented in a process flow scheme using external steam reforming. The model stack consisted of planar anode supported cells operated at 800 degreesC displaying state-of- the-art electrochemical performance (0.15 W/cm(2) at 80% fuel utilisation). Real annual data from an existing sewage plant were used as input to the model. From the input of 43 m(3)/h biogas (63% ...

  17. Dynamic modelling of nitrous oxide emissions from three Swedish sludge liquor treatment systems

    DEFF Research Database (Denmark)

    Lindblom, E.; Arnell, M.; Flores-Alsina, X.;

    2014-01-01

    The objective of this paper is to model the dynamics and validate the results of nitrous oxide (N2O)emissions from three Swedish nitrifying/denitrifying, nitritation and anammox systems treating real anaerobic digester sludge liquor. The Activated Sludge Model No. 1 is extended to describe N2O......) a moving-bed biofilm reactor. Results show that the calibrated model is partly capable of reproducing the behaviour of N2O as well as the nitritation/nitrification/denitrification dynamics. However, the results emphasize that additional work is required before N2O emissions from sludge liquor treatment...

  18. Dynamic modelling of nitrous oxide emissions from three Swedish sludge liquor treatment systems

    DEFF Research Database (Denmark)

    Lindblom, E.; Arnell, M.; Flores-Alsina, X.;

    2016-01-01

    The objective of this paper is to model the dynamics and validate the results of nitrous oxide (N2O)emissions from three Swedish nitrifying/denitrifying, nitritation and anammox systems treating real anaerobic digester sludge liquor. The Activated Sludge Model No. 1 is extended to describe N2O......) a moving-bed biofilm reactor. Results show that the calibrated model is partly capable of reproducing the behaviour of N2O as well as the nitritation/nitrification/denitrification dynamics. However, the results emphasize that additional work is required before N2O emissions from sludge liquor treatment...

  19. Reaction modelling of Iron Oxide Bromination in the UT-3 thermochemical cycle for Hydrogen production from water

    International Nuclear Information System (INIS)

    Analysis modelling of the iron oxide bromination had been carried out using experiment data from the iron oxide bromination in the UT-3 thermochemical cycle. Iron oxide in the form of pellets were made of the calcination of the mixture of iron oxide, silica, graphite and cellulose at 1473 K. Thermobalance reactor was used to study the kinetic reactions of the iron oxide bromination at a temperature of 473 K for 2 - 6 hours. The data collected from the experiments were used as input for the common models. However, none of these models could not explain the result of the experiments. A new model, a combination of two kinetic reactions : exposed particle and coated particle was created and worked successfully

  20. Oxidation of elemental mercury in the atmosphere; Constraints imposed by global scale modelling

    Energy Technology Data Exchange (ETDEWEB)

    Bergan, Torbjoern; Rodhe, Henning [Stockholm Univ. (Sweden). Dept. of Meteorology

    2000-05-01

    Based on the global mercury model published by Bergan et al. (1999), we present here further results from simulations where the central theme has been to evaluate the role of ozone and the hydroxyl radical as possible gas phase oxidants for the oxidation of elemental mercury in the atmosphere. The magnitude of natural and man-made mercury emissions are taken from recent literature estimates and the flux from land areas is assumed to vary by season. We consider only two mercury reservoirs, elemental mercury, Hg{sup 0}, and the more soluble divalent form, Hgll. Wet and dry deposition of Hgll is explicitly treated. Applying monthly mean fields of ozone for the oxidation of gas phase Hg{sup 0} and using the reaction rate by Hall (1995) yields a global transformation of Hg{sup 0} to Hgll which is too slow to keep the simulated concentration of Hg{sup 0} near observed values. This shows that there are additional important removal processes for Hg{sup 0} or that the reaction rate proposed by Hall (1995) is too slow. A simulation in which the oxidation rate was artificially increased, so that the global turn-over time of Hg{sup 0} was one year and the simulated average concentration of Hg{sup 0} was realistic, produced latitudinal and seasonal variations in Hg{sup 0} that did not support the hypothesis that gas phase reaction with O{sub 3} is the major oxidation process for Hg{sup 0}. Recent studies indicate that OH may be an important gas phase oxidant for Hg{sup 0}. Using OH as the oxidant and applying the preliminary oxidation rate by Sommar et al. (1999) gave an unrealistically large removal of Hg{sup 0} from the atmosphere. From calculations using a slower reaction rate, corresponding to a turn-over time of Hg{sup 0} of one year, we calculated concentrations of both Hg{sup 0} in surface air and Hgll in precipitation which correspond, both in magnitude and temporal variation, to seasonal observations in Europe and North America. This result supports the suggestion that

  1. Ionic conductivity studies of solid oxide fuel cell electrolytes and theoretical modeling of an entire solid oxide fuel cell

    Science.gov (United States)

    Pornprasertsuk, Rojana

    Because of the steep increase in oil prices, the global warming effect and the drive for energy independence, alternative energy research has been encouraged worldwide. The sustainable fuels such as hydrogen, biofuel, natural gas, and solar energy have attracted the attention of researchers. To convert these fuels into a useful energy source, an energy conversion device is required. Fuel cells are one of the energy conversion devices which convert chemical potentials into electricity. Due to their high efficiency, the ease to scale from 1 W range to megawatts range, no recharging requirement and the lack of CO2 and NOx emission (if H2 and air/O 2 are used), fuel cells have become a potential candidate for both stationary power generators and portable applications. This thesis has been focused primarily on solid oxide fuel cell (SOFC) studies due to its high efficiency, varieties of fuel choices, and no water management problem. At the present, however, practical applications of SOFCs are limited by high operating temperatures that are needed to create the necessary oxide-ion vacancy mobility in the electrolyte and to create sufficient electrode reactivities. This thesis introduces several experimental and theoretical approaches to lower losses both in the electrolyte and the electrodes. Yttria stabilized zirconia (YSZ) is commonly used as a solid electrolyte for SOFCs due to its high oxygen-ion conductivity. To improve the ionic conductivity for low temperature applications, an approach that involves dilating the structure by irradiation and introducing edge dislocations into the electrolyte was studied. Secondly, to understand the activation loss in SOFC, the kinetic Monte Carlo (KMC) technique was implemented to model the SOFC operation to determining the rate-limiting step due to the electrodes on different sizes of Pt catalysts. The isotope exchange depth profiling technique was employed to investigate the irradiation effect on the ionic transport in different

  2. Acetaldehyde partial oxidation on the Au(111) model catalyst surface: C-C bond activation and formation of methyl acetate as an oxidative coupling product

    Science.gov (United States)

    Karatok, Mustafa; Vovk, Evgeny I.; Shah, Asad A.; Turksoy, Abdurrahman; Ozensoy, Emrah

    2015-11-01

    Partial oxidation of acetaldehyde (CH3CHO) on the oxygen pre-covered Au(111) single crystal model catalyst was investigated via Temperature Programmed Desorption (TPD) and Temperature Programmed Reaction Spectroscopy (TPRS) techniques, where ozone (O3) was utilized as the oxygen delivery agent providing atomic oxygen to the reacting surface. We show that for low exposures of O3 and small surface oxygen coverages, two partial oxidation products namely, methyl acetate (CH3COOCH3) and acetic acid (CH3COOH) can be generated without the formation of significant quantities of carbon dioxide. The formation of methyl acetate as the oxidative coupling reaction product implies that oxygen pre-covered Au(111) single crystal model catalyst surface can activate C-C bonds. In addition to the generation of these products; indications of the polymerization of acetaldehyde on the gold surface were also observed as an additional reaction route competing with the partial and total oxidation pathways. The interplay between the partial oxidation, total oxidation and polymerization pathways reveals the complex catalytic chemistry associated with the interaction between the acetaldehyde and atomic oxygen on catalytic gold surfaces.

  3. Modeling selenite adsorption envelopes on oxides, clay minerals, and soils using the triple layer model

    Science.gov (United States)

    Selenite adsorption behavior was investigated on amorphous aluminum and iron oxides, clay minerals: kaolinite, montmorillonite, and illite, and 45 surface and subsurface soil samples from the Southwestern and Midwestern regions of the USA as a function of solution pH. Selenite adsorption decreased ...

  4. CFD Model Of A Planar Solid Oxide Electrolysis Cell For Hydrogen Production From Nuclear Energy

    International Nuclear Information System (INIS)

    A three-dimensional computational fluid dynamics (CFD) model has been created to model high temperature steam electrolysis in a planar solid oxide electrolysis cell (SOEC). The model represents a single cell as it would exist in an electrolysis stack. Details of the model geometry are specific to a stack that was fabricated by Ceramatec2, Inc. and tested at the Idaho National Laboratory. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT2. A solid-oxide fuel cell (SOFC) model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, Nernst potential, operating potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Mean model results are shown to compare favorably with experimental results obtained from an actual ten-cell stack tested at INL

  5. THERMAL AND ELECTROCHEMICAL THREE DIMENSIONAL CFD MODEL OF A PLANAR SOLID OXIDE ELECTROLYSIS CELL

    Energy Technology Data Exchange (ETDEWEB)

    Grant Hawkes; Jim O& #39; Brien; Carl Stoots; Steve Herring; Mehrdad Shahnam

    2005-07-01

    A three-dimensional computational fluid dynamics (CFD) model has been created to model high-temperature steam electrolysis in a planar solid oxide electrolysis cell (SOEC). The model represents a single cell, as it would exist in an electrolysis stack. Details of the model geometry are specific to a stack that was fabricated by Ceramatec , Inc. and tested at the Idaho National Laboratory. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT2. A solid-oxide fuel cell (SOFC) model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, Nernst potential, operating potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Mean model results are shown to compare favorably with experimental results obtained from an actual ten-cell stack tested at INL.

  6. Mesoscale modeling of combined aerosol and photo-oxidant processes in the Eastern Mediterranean

    Science.gov (United States)

    Lazaridis, M.; Spyridaki, A.; Solberg, S.; Smolík, J.; Zdímal, V.; Eleftheriadis, K.; Aleksanropoulou, V.; Hov, O.; Georgopoulos, P. G.

    2005-03-01

    Particulate matter and photo-oxidant processes in the Eastern Mediterranean have been studied using the UAM-AERO mesoscale air quality model in conjunction with the NILU-CTM regional model. Meteorological data were obtained from the RAMS prognostic meteorological model. The modeling domain includes the eastern Mediterranean area between the Greek mainland and the island of Crete. The modeling system is applied to study the atmospheric processes in three periods, i.e. 13-16 July 2000, 26-30 July 2000 and 7-14 January 2001. The spatial and temporal distributions of both gaseous and particulate matter pollutants have been extensively studied together with the identification of major emission sources in the area. The modeling results were compared with field data obtained in the same period. The objective of the current modeling work was mainly to apply the UAM-AERO mesoscale model in the eastern Mediterranean in order to assess the performed field campaigns and determine that the applied mesoscale model is fit for this purpose. Comparison of the modeling results with measured data was performed for a number of gaseous and aerosol species. The UAM-AERO model underestimates the PM10 measured concentrations during summer and winter campaigns. Discrepancies between modeled and measured data are attributed to unresolved particulate matter emissions. Particulate matter in the area is mainly composed by sulphate, sea salt and crustal materials, and with significant amounts of nitrate, ammonium and organics. During winter the particulate matter and oxidant concentrations were lower than the summer values.

  7. Effects of nitric oxide-related compounds in the acute ketamine animal model of schizophrenia

    OpenAIRE

    Kandratavicius, Ludmyla; Balista, Priscila Alves; Wolf, Daniele Cristina; Abrao, Joao; Evora, Paulo Roberto; Rodrigues, Alfredo Jose; Chaves, Cristiano; Maia-de-Oliveira, Joao Paulo; Leite, Joao Pereira; Dursun, Serdar Murat; Baker, Glen Bryan; Guimaraes, Francisco Silveira; Hallak, Jaime Eduardo Cecilio

    2015-01-01

    Background Better treatments for schizophrenia are urgently needed. The therapeutic use of the nitric oxide (NO)-donor sodium nitroprusside (SNP) in patients with schizophrenia has shown promising results. The role of NO in schizophrenia is still unclear, and NO modulation is unexplored in ketamine (KET) animal models to date. In the present study, we compared the behavioral effects of pre- and post-treatment with SNP, glyceryl trinitrate (GTN), and methylene blue (MB) in the acute KET animal...

  8. A planar anode-supported Solid Oxide Fuel Cell model with internal reforming of natural gas

    OpenAIRE

    Chinda, Penyarat; Chanchaona, Somchai; Brault, Pascal; Wechsatol, Wishsanuruk

    2011-01-01

    Abstract Solid Oxide Fuel Cells (SOFCs) are of great interest due to their high energy efficiency, low emission level, and multiple fuel utilization. SOFC can operate with various kinds of fuels such as natural gas, carbon monoxide, methanol, ethanol, and hydrocarbon compounds, and they are becoming one of the main competitors among environmentally friendly energy sources for the future. In this study, a mathematical model of a co-flow planar anode-supported...

  9. Operando X-ray Investigation of Electrode/Electrolyte Interfaces in Model Solid Oxide Fuel Cells

    OpenAIRE

    Volkov, Sergey; Vonk, Vedran; Khorshidi, Navid; Franz, Dirk; Kubicek, Markus; Kilic, Volkan; Felici, Roberto; Huber, Tobias M.; Navickas, Edvinas; Rupp, Ghislain M.; Fleig, Jürgen; Stierle, Andreas

    2016-01-01

    We employed operando anomalous surface X-ray diffraction to investigate the buried interface between the cathode and the electrolyte of a model solid oxide fuel cell with atomic resolution. The cell was studied under different oxygen pressures at elevated temperatures and polarizations by external potential control. Making use of anomalous X-ray diffraction effects at the Y and Zr K-edges allowed us to resolve the interfacial structure and chemical composition of a (100)-oriented, 9.5 mol % y...

  10. Performance Model for High-Power Lithium Titanate Oxide Batteries based on Extended Characterization Tests

    DEFF Research Database (Denmark)

    Stroe, Ana-Irina; Swierczynski, Maciej Jozef; Stroe, Daniel Ioan;

    2015-01-01

    Lithium-ion (Li-ion) batteries are found nowadays not only in portable/consumer electronics but also in more power demanding applications, such as stationary renewable energy storage, automotive and back-up power supply, because of their superior characteristics in comparison to other energy...... model for a commercially available 13Ah high-power lithium titanate oxide battery cell based on laboratory-performed extended characterization tests....

  11. Application of polymer model for calculation of oxides activity in B2O3 based melts

    International Nuclear Information System (INIS)

    Possibility of using equations of polymer model for calculation of oxide activity in boron silicate systems is shown. Correlation of calculation and experimental values of MnO activity in MnO-B2O3 MnO-B2O3-SiO2 melts testifies to the fact, that boron coordination number with respect to oxygen in these systems is constant and equals three. 6 refs., 1 figs., 1 tab

  12. Kinetic Modelling for the Assay of Nortriptyline Hydrochloride Using Potassium Permanganate as Oxidant

    OpenAIRE

    Rahman, Nafisur; Khan, Sumaiya

    2014-01-01

    Kinetic methods for accurate determination of nortriptyline hydrochloride have been described. The methods are based on the oxidation of nortriptyline hydrochloride with KMnO4 in acidic and basic media. In acidic medium, the decrease in absorbance at 525.5 nm and in basic medium, the increase in absorbance at 608.5 nm were measured as a function of time. The variables affecting the reactions were carefully investigated and optimised. Kinetic models such as initial rate, rate constant, variabl...

  13. Recombinant human deoxyribonuclease attenuates oxidative stress in a model of eosinophilic pulmonary response in mice.

    Science.gov (United States)

    da Cunha, Aline Andrea; Nuñez, Nailê Karine; de Souza, Rodrigo Godinho; Vargas, Mauro Henrique Moraes; Silveira, Josiane Silva; Antunes, Géssica Luana; Schmitz, Felipe; de Souza Wyse, Angela Terezinha; Jones, Marcus Herbert; Pitrez, Paulo Márcio

    2016-02-01

    The inflammatory cells infiltrating the airways produce several mediators, such as reactive oxygen species (ROS). ROS and the oxidant-antioxidant imbalance might play an important role in the modulation of airways inflammation. In order to avoid the undesirable effects of ROS, various endogenous antioxidant strategies have evolved, incorporating both enzymatic and non-enzymatic mechanisms. Recombinant human deoxyribonuclease (rhDNase) in clinical studies demonstrated a reduction in sputum viscosity, cleaving extracellular DNA in the airways, and facilitating mucus clearance, but an antioxidant effect was not studied so far. Therefore, we evaluated whether the administration of rhDNase improves oxidative stress in a murine model of asthma. Mice were sensitized by two subcutaneous injections of ovalbumin (OVA), on days 0 and 7, followed by three lung challenges with OVA on days 14, 15, and 16. On days 15 and 16, after 2 h of the challenge with OVA, mice received 1 mg/mL of rhDNase in the lungs. Bronchoalveolar lavage fluid and lung tissue were obtained on day 17, for inflammatory and oxidative stress analysis. We showed that rhDNase did not alter the population of inflammatory cells, such as eosinophil cells, in OVA-treated rhDNase group but significantly improved oxidative stress in lung tissue, by decreasing oxygen reactive species and increasing superoxide dismutase/catalase ratio, glutathione peroxidase activity, and thiol content. Our data provide the first evidence that rhDNase decreases some measures of oxidative stress and antioxidant status in a murine model of asthma, with a potential antioxidant effect to be further studied in human asthma. PMID:26738487

  14. Prediction of iodide adsorption on oxides by surface complexation modeling with spectroscopic confirmation.

    Science.gov (United States)

    Nagata, Takahiro; Fukushi, Keisuke; Takahashi, Yoshio

    2009-04-15

    A deficiency in environmental iodine can cause a number of health problems. Understanding how iodine is sequestered by materials is helpful for evaluating and developing methods for minimizing human health effects related to iodine. In addition, (129)I is considered to be strategically important for safety assessment of underground radioactive waste disposal. To assess the long-term stability of disposed radioactive waste, an understanding of (129)I adsorption on geologic materials is essential. Therefore, the adsorption of I(-) on naturally occurring oxides is of environmental concern. The surface charges of hydrous ferric oxide (HFO) in NaI electrolyte solutions were measured by potentiometric acid-base titration. The surface charge data were analyzed by means of an extended triple-layer model (ETLM) for surface complexation modeling to obtain the I(-) adsorption reaction and its equilibrium constant. The adsorption of I(-) was determined to be an outer-sphere process from ETLM analysis, which was consistent with independent X-ray absorption near-edge structure (XANES) observation of I(-) adsorbed on HFO. The adsorption equilibrium constants for I(-) on beta-TiO(2) and gamma-Al(2)O(3) were also evaluated by analyzing the surface charge data of these oxides in NaI solution as reported in the literature. Comparison of these adsorption equilibrium constants for HFO, beta-TiO(2), and gamma-Al(2)O(3) based on site-occupancy standard states permitted prediction of I(-) adsorption equilibrium constants for all oxides by means of the Born solvation theory. The batch adsorption data for I(-) on HFO and amorphous aluminum oxide were reasonably reproduced by ETLM with the predicted equilibrium constants, confirming the validity of the present approach. Using the predicted adsorption equilibrium constants, we calculated distribution coefficient (K(d)) values for I(-) adsorption on common soil minerals as a function of pH and ionic strength. PMID:19176225

  15. Modeling arsenite oxidation by chemoautotrophic Thiomonas arsenivorans strain b6 in a packed-bed bioreactor

    International Nuclear Information System (INIS)

    Arsenic is a major toxic pollutant of concern for the human health. Biological treatment of arsenic contaminated water is an alternative strategy to the prevalent conventional treatments. The biological treatment involves a pre-oxidation step transforming the most toxic form of arsenic, As (III), to the least toxic form, As (V), respectively. This intermediate process improves the overall efficiency of total arsenic removal from the contaminated water. As (III) oxidation by the chemoautotrophic bacterium Thiomonas arsenivorans strain b6 was investigated in a fixed-film reactor under variable influent As (III) concentrations (500–4000 mg/L) and hydraulic residence times (HRTs) (0.2–1 day) for a duration of 137 days. During the entire operation, seven steady-state conditions were obtained with As (III) oxidation efficiency ranging from 48.2% to 99.3%. The strong resilience of the culture was exhibited by the recovery of the bioreactor from an As (III) overloading of 5300 ± 400 mg As (III)/L day operated at a HRT of 0.2 day. An arsenic mass balance revealed that As (III) was mainly oxidized to As (V) with unaccounted arsenic (≤ 4%) well within the analytical error of measurement. A modified Monod flux expression was used to determine the biokinetic parameters by fitting the model against the observed steady-state flux data obtained from operating the bioreactor under a range of HRTs (0.2–1 day) and a constant influent As (III) concentration of 500 mg/L. Model parameters, k = 0.71 ± 0.1 mg As (III)/mg cells h, and Ks = 13.2 ± 2.8 mg As (III)/L were obtained using a non-linear estimation routine and employing the Marquardt–Levenberg algorithm. Sensitivity analysis revealed k to be more sensitive to model simulations of As (III) oxidation under steady-state conditions than parameter Ks. -- Highlights: ► As (III) oxidation. ► Biokinetic parameters. ► Model validation and sensitivity analysis.

  16. Development and verification of models for cladding oxidation in the early stages of a severe accident

    International Nuclear Information System (INIS)

    Models have been developed for fuel cladding oxidation in the early stages of a severe accident. The models take account of the crucibilization effect of the zirconium dioxide layer on preventing the Zircaloy melt from flowing down, inner surface oxidation, and the steam starvation effect. The models have been included in the core thermal-hydraulic code SEFDAN. The SEFDAN code has been applied to analyses of severe fuel damage tests in the PBF and NRU facilities, and the TMI-2 accident. The calculated results are in good agreement with the measured or observed results. The analyses indicate that the fuel cladding temperature would have reached the melting point of zirconium dioxide in the PBF.SFD tests and in the TMI-2 accident, and that the fuel temperature would have reached the melting point of uranium dioxide in the PBF.SFD scoping test and TMI-2. In leading fuel rods to such high temperatures, the crucibilization effect of the zirconium dioxide layer plays an essential role, because it retains the molten Zircaloy and sustains the zirconium-water reaction of the molten Zircaloy. In addition, the significant role of the inner surface oxidation on temperature escalation and hydrogen generation rate has been revealed in the analyses of the NRU.FLHT-2 test. (author). 16 refs, 7 figs

  17. The modeling of a standalone solid-oxide fuel cell auxiliary power unit

    Science.gov (United States)

    Lu, N.; Li, Q.; Sun, X.; Khaleel, M. A.

    In this research, a Simulink model of a standalone vehicular solid-oxide fuel cell (SOFC) auxiliary power unit (APU) is developed. The SOFC APU model consists of three major components: a controller model; a power electronics system model; and an SOFC plant model, including an SOFC stack module, two heat exchanger modules, and a combustor module. This paper discusses the development of the nonlinear dynamic models for the SOFC stacks, the heat exchangers and the combustors. When coupling with a controller model and a power electronic circuit model, the developed SOFC plant model is able to model the thermal dynamics and the electrochemical dynamics inside the SOFC APU components, as well as the transient responses to the electric loading changes. It has been shown that having such a model for the SOFC APU will help design engineers to adjust design parameters to optimize the performance. The modeling results of the SOFC APU heat-up stage and the output voltage response to a sudden load change are presented in this paper. The fuel flow regulation based on fuel utilization is also briefly discussed.

  18. Adsorption of Pentachlorophenol onto Oxide and Clay Minerals: Surface Reaction Model and Environmental Implications

    Institute of Scientific and Technical Information of China (English)

    WU Daqing; DIAO Guiyi; YUAN Peng; PENG Jinlian

    2006-01-01

    The adsorption of pentachlorophenol (PCP) onto quartz, kaolinite, illite, montmorillonite and iron oxides has been investigated by batch equilibrium techniques. The pH-dependent isotherms are curves with peak values, the position of which is at about pH= 5-6 depending on the mineral species. Based on distribution of both speciation of surface hydroxyls on minerals and PCP in solution a surface reaction model involving surface complexation and surface electrostatic attraction is presented to fit the pH-dependent isotherms, and both reaction constants are calculated. The results show that on quartz and phyllosilicate minerals the predominant adsorption reaction is surface complexation,meanwhile both of surface electrostatic attraction and surface complexation are involved on the iron oxide minerals. The reaction constants of surface electrostatic adsorption are usually one to three orders in magnitude, larger than that of surface complexation. The concentration-dependent isotherms can be well fitted by Langmuir equation with the correlation coefficient R>0.93 for kaolinite and iron oxides. The maximum adsorption is found in the order: hematite > lepidocrocite > goethite > kaolinite >quartz > montmorillonite ≈ illite, which can be interpreted by consideration of both reaction mechanism and surface hydroxyl density. The significant adsorption of PCP onto mineral surfaces suggests that clay and iron oxide minerals will play an important role as HIOCs are adsorbed in laterite or latertoid soil, which is widespread in South China.

  19. Physiological and Metabolic Effects of Carbon Monoxide Oxidation in the Model Marine Bacterioplankton Ruegeria pomeroyi DSS-3

    OpenAIRE

    Cunliffe, Michael

    2013-01-01

    Ruegeria pomeroyi expresses carbon monoxide (CO) dehydrogenase and oxidizes CO; however, CO has no effect on growth. Nuclear magnetic resonance (NMR) spectra showed that CO has no effect on cellular metabolite profiles. These data support ecosystem models proposing that, even though bacterioplankton CO oxidation is biogeochemically significant, it has an insignificant effect on bacterioplankton productivity.

  20. Modeling a full scale oxidation ditch system, coupling hydrodynamics and biological kinetics using ASM1 model

    International Nuclear Information System (INIS)

    Optimising the aeration in oxidation ditch aims on one hand, a better wastewater quality and on the other hand, a reduction of the energy expenses of the treatment. given that the energy expenses relative to the aeration represents 60 to 80% of the operating costs of a wastewater treatment plant and given that the biological activity is strictly dependent on dissolved oxygen, the transfer of oxygen is considered as one of the key parameters of the process. (Author) 8 refs.

  1. Modelling the growth of methane-oxidizing bacteria in a fixed biofilm

    DEFF Research Database (Denmark)

    Bilbo, Carl Morten; Arvin, Erik; Holst, Helle;

    1992-01-01

    Methane-oxidizing bacteria were grown in a fixed biofilm reactor in order to study their ability to degrade chlorinated aliphatic hydrocarbons. Focus is on the growth behaviour of the mixed culture. The growth is described by a model that includes methanotrophic bacteria in the active biomass...... of the observability of the system reveals that several of the coefficients cannot be determined explicitly due to the complexity of the model and the limited amount of variables measured. Estimation procedures based on least squares methods are employed and parameter estimates and confidence intervals are computed...

  2. Modelling the growth process of porous aluminum oxide film during anodization

    Science.gov (United States)

    Aryslanova, E. M.; Alfimov, A. V.; Chivilikhin, S. A.

    2015-11-01

    Currently it has become important for the development of metamaterials and nanotechnology to obtain regular self-assembled structures. One such structure is porous anodic alumina film that consists of hexagonally packed cylindrical pores. In this work we consider the anodization process, our model takes into account the influence of layers of aluminum and electrolyte on the rate of growth of aluminum oxide, as well as the effect of surface diffusion. In present work we consider those effects. And as a result of our model we obtain the minimum distance between centers of alumina pores in the beginning of anodizing process.

  3. Two-parameter stochastic resonance in a model of electrochemical oxidation of formic acid on Pt

    Institute of Scientific and Technical Information of China (English)

    皮宗新; 辛厚文

    2002-01-01

    Stochastic resonance (SR) is shown in a two-parameter system, a model of electro-chemical oxidation of formic acid on Pt. The driving current and the saturation coverage for carbon monoxide are two control parameters in this model. Modulation of an excitable focal stable state close to a Hopf bifurcation by a weak periodic signal in one parameter and noise in the other parameter is found to give rise to SR. The results indicate that the noise can enlarge a weak peri-odic signal and lead the system to be ordered. The scenario and novel aspects of SR in this system are discussed.

  4. Modelling the growth of methane-oxidizing bacteria in a fixed biofilm

    DEFF Research Database (Denmark)

    Bilbo, Carl Morten; Arvin, Erik; Holst, Helle; Spliid, Henrik

    1992-01-01

    Methane-oxidizing bacteria were grown in a fixed biofilm reactor in order to study their ability to degrade chlorinated aliphatic hydrocarbons. Focus is on the growth behaviour of the mixed culture. The growth is described by a model that includes methanotrophic bacteria in the active biomass...... fraction. The inactive biomass fraction consists of exocellular polymers and biodegradable and inert particulate biomass. The model describes the oxygen respiration in detail. Yield coefficients, decay constants and hydrolysis constants are estimated based on the oxygen respiration. An analysis of the...

  5. Is the lobster cockroach Nauphoeta cinerea a valuable model for evaluating mercury induced oxidative stress?

    Science.gov (United States)

    Rodrigues, N R; Nunes, M E M; Silva, D G C; Zemolin, A P P; Meinerz, D F; Cruz, L C; Pereira, A B; Rocha, J B T; Posser, T; Franco, J L

    2013-08-01

    Organic and inorganic forms of mercury are highly neurotoxic environmental contaminants. The exact mechanisms involved in mercury neurotoxicity are still unclear. Oxidative stress appears to play central role in this process. In this study, we aimed to validate an insect-based model for the investigation of oxidative stress during mercury poisoning of lobster cockroach Nauphoeta cinerea. The advantages of using insects in basic toxicological studies include the easier handling, rapid proliferation/growing and absence of ethical issues, comparing to rodent-based models. Insects received solutions of HgCl2 (10, 20 and 40mgL(-1) in drinking water) for 7d. 24h after mercury exposure, animals were euthanized and head tissue samples were prepared for oxidative stress related biochemical determinations. Mercury exposure caused a concentration dependent decrease in survival rate. Cholinesterase activity was unchanged. Catalase activity was substantially impaired after mercury treatment 40mgL(-1). Likewise, GST had a significant decrease, comparing to control. Peroxidase and thioredoxin reductase activity was inhibited at concentrations of 20mgL(-1) and 40mgL(-1) comparing to control. These results were accompanied by decreased GSH levels and increased hydroperoxide and TBARS formation. In conclusion, our results show that mercuric compounds are able to induce oxidative stress signs in insect by modulating survival rate as well as inducing impairments on important antioxidant systems. In addition, our data demonstrates for the first time that Nauphoeta cinerea represents an interesting animal model to investigate mercury toxicity and indicates that the GSH and thioredoxin antioxidant systems plays central role in Hg induced toxicity in insects. PMID:23466093

  6. Tungsten oxide in polymer electrolyte fuel cell electrodes-A thin-film model electrode study

    Energy Technology Data Exchange (ETDEWEB)

    Wickman, Bjoern, E-mail: bjorn.wickman@chalmers.s [Competence Centre for Catalysis, Department of Applied Physics, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); Wesselmark, Maria; Lagergren, Carina; Lindbergh, Goeran [Applied Electrochemistry, School of Chemical Science and Engineering, KTH, SE-100 44 Stockholm (Sweden)

    2011-10-30

    Highlights: > Platinum and tungsten oxide thin-film electrocatalysts. > Single cell fuel cell evaluation. > Hydrogen-tungsten bronze formation. > CO oxidation on platinum on tungsten oxide. - Abstract: Thin films of WO{sub x} and Pt on WO{sub x} were evaporated onto the microporous layer of a gas diffusion layer (GDL) and served as model electrodes in the polymer electrolyte fuel cell (PEFC) as well as in liquid electrolyte measurements. In order to study the effects of introducing WO{sub x} in PEFC electrodes, precise amounts of WO{sub x} (films ranging from 0 to 40 nm) with or without a top layer of Pt (3 nm) were prepared. The structure of the thin-film model electrodes was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy prior to the electrochemical investigations. The electrodes were analyzed by cyclic voltammetry and the electrocatalytic activity for hydrogen oxidation reaction (HOR) and CO oxidation was examined. The impact of Nafion in the electrode structure was examined by comparing samples with and without Nafion solution sprayed onto the electrode. Fuel cell measurements showed an increased amount of hydrogen tungsten bronzes formed for increasing WO{sub x} thicknesses and that Pt affected the intercalation/deintercalation process, but not the total amount of bronzes. The oxidation of pre-adsorbed CO was shifted to lower potentials for WO{sub x} containing electrodes, suggesting that Pt-WO{sub x} is a more CO-tolerant catalyst than Pt. For the HOR, Pt on thicker films of WO{sub x} showed an increased limiting current, most likely originating from the increased electrochemically active surface area due to proton conductivity and hydrogen permeability in the WO{sub x} film. From measurements in liquid electrolyte it was seen that the system behaved very differently compared to the fuel cell measurements. This exemplifies the large differences between the liquid electrolyte and fuel cell systems. The thin-film model

  7. Steam oxidation of boron carbide–stainless steel liquid mixtures

    International Nuclear Information System (INIS)

    In the framework of nuclear reactor core meltdown accidents studies, the oxidation kinetics of boron carbide–stainless steel liquid mixtures exposed to argon/steam atmospheres was investigated at temperatures up to 1527 °C. A B–Cr–Si–O liquid protective layer forms on the surface of the mixtures in contact with steam. This protective layer gradually transforms into a Cr2O3-rich slag. Important quantities of liquid can be projected from the melt during oxidation. These projections are favoured by high B4C contents in the melt, high steam partial pressures and low temperatures. In addition to stainless steel–boron carbide melts, simpler compositions (pure 304L stainless steel, iron–boron, iron–boron carbide and stainless steel–boron) were studied, in order to identify the basic oxidation mechanisms.

  8. Kinetics of ethylcyclohexane pyrolysis and oxidation: An experimental and detailed kinetic modeling study

    KAUST Repository

    Wang, Zhandong

    2015-07-01

    Ethylcyclohexane (ECH) is a model compound for cycloalkanes with long alkyl side-chains. A preliminary investigation on ECH (Wang et al., Proc. Combust. Inst., 35, 2015, 367-375) revealed that an accurate ECH kinetic model with detailed fuel consumption mechanism and aromatic growth pathways, as well as additional ECH pyrolysis and oxidation data with detailed species concentration covering a wide pressure and temperature range are required to understand the ECH combustion kinetics. In this work, the flow reactor pyrolysis of ECH at various pressures (30, 150 and 760Torr) was studied using synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (PIMS) and gas chromatography (GC). The mole fraction profiles of numerous major and minor species were evaluated, and good agreement was observed between the PIMS and GC data sets. Furthermore, a fuel-rich burner-stabilized laminar premixed ECH/O2/Ar flame at 30Torr was studied using synchrotron VUV PIMS. A detailed kinetic model for ECH high temperature pyrolysis and oxidation was developed and validated against the pyrolysis and flame data performed in this work. Further validation of the kinetic model is presented against literature data including species concentrations in jet-stirred reactor oxidation, ignition delay times in a shock tube, and laminar flame speeds at various pressures and equivalence ratios. The model well predicts the consumption of ECH, the growth of aromatics, and the global combustion properties. Reaction flux and sensitivity analysis were utilized to elucidate chemical kinetic features of ECH combustion under various reaction conditions. © 2015 The Combustion Institute.

  9. Bartter/Gitelman syndromes as a model to study systemic oxidative stress in humans.

    Science.gov (United States)

    Maiolino, Giuseppe; Azzolini, Matteo; Rossi, Gian Paolo; Davis, Paul A; Calò, Lorenzo A

    2015-11-01

    Reactive oxygen species (ROS) are intermediates in reduction-oxidation reactions that begin with the addition of one electron to molecular oxygen, generating the primary ROS superoxide, which in turn interacts with other molecules to produce secondary ROS, such as hydrogen peroxide, hydroxyl radical, and peroxynitrite. ROS are continuously produced during metabolic processes and are deemed to play an important role in cardiovascular diseases, namely, myocardial hypertrophy and fibrosis and atherosclerosis, via oxidative damage of lipids, proteins, and deoxyribonucleic acid. Angiotensin II (Ang II) is a potent vasoactive agent that also exerts mitogenic, proinflammatory, and profibrotic effects through several signaling pathways, in part involving ROS, particularly superoxide and hydrogen peroxide. Moreover, Ang II stimulates NADPH oxidases, leading to higher ROS generation and oxidative stress. Bartter/Gitelman syndrome patients, despite elevated plasma renin activity, Ang II, and aldosterone levels, exhibit reduced peripheral resistance, normal/low blood pressure, and blunted pressor effect of vasoconstrictors. In addition, notwithstanding the activation of the renin-angiotensin system and the increased plasma levels of Ang II, these patients display decreased production of ROS, reduced oxidative stress, and increased antioxidant defenses. In fact, Bartter/Gitelman syndrome patients are characterized by reduced levels of p22(phox) gene expression and undetectable plasma peroxynitrite levels, while showing increased plasma antioxidant power and expression of antioxidant enzymes, such as heme oxygenase-1. In conclusion, multifarious data suggest that Bartter and Gitelman syndrome patients are a model of low oxidative stress and high antioxidant defenses. The contribution offered by the study of these syndromes in elucidating the molecular mechanisms underlying this favorable status could offer chances for new therapeutic targets in disease characterized by high

  10. Oxidation of Catechol using Titanium Silicate (TS-1 Catalyst: Modeling and Optimization

    Directory of Open Access Journals (Sweden)

    Sonali Sengupta

    2013-12-01

    Full Text Available The oxidation of catechol was studied in an eco-friendly process with commercial titanium silicate-1 (TS-1 catalyst and hydrogen peroxide as oxidant in absence of all mass transfer effects. The process was opti-mized by Box-Behnken design in terms of three independent process variables such as reaction tempera-ture, moles of hydrogen peroxide per mole of catechol and catalyst amount whose optimum values of the process variables were found to be 60 °C, 13.2 and 1.24 g respectively for maximum conversion of 75.8 %. The effects of different process parameters such as mole ratio of hydrogen peroxide to catechol, catalyst par-ticle size, catalyst amount, temperature and reaction time were studied. A pseudo first order kinetic model was fitted with the experimental rate data. The apparent activation energy for the reaction was found to be 11.37 kJ/mole.  © 2013 BCREC UNDIP. All rights reservedReceived: 22nd April 2013; Revised: 25th October 2013; Accepted: 1st November 2013[How to Cite: Sengupta, S., Ghosal, D., Basu, J.K. (2013. Oxidation of Catechol using Titanium Silicate (TS-1 Catalyst: Modeling and Optimization. Bulletin of Chemical Reaction Engineering & Catalysis, 8 (2: 167-177. (doi:10.9767/bcrec.8.2.4759.167-177][Permalink/DOI: http://dx.doi.org/10.9767/bcrec.8.2.4759.167-177

  11. Model complexes of key intermediates in fungal cytochrome P450 nitric oxide reductase (P450nor).

    Science.gov (United States)

    McQuarters, Ashley B; Wirgau, Nathaniel E; Lehnert, Nicolai

    2014-04-01

    Denitrifying bacteria and fungi efficiently detoxify the toxic metabolite nitric oxide (NO) through reduction to nitrous oxide (N2O) using nitric oxide reductase (NOR) enzymes. In fungi, for example Fusarium oxysporum, NO is reduced by a Cytochrome P450 NOR (P450nor). This enzyme contains a heme b center coordinated to a proximal cysteinate ligand in the active site. In the proposed mechanism of P450nor, the ferric heme binds NO first to form a ferric heme-nitrosyl complex, which is subsequently reduced by NAD(P)H to generate a ferrous HNO species as the next key intermediate. Recently, key progress has been made in our understanding of the electronic structures and fundamental reactivity of these important intermediates, using suitable model complexes. In this review, model complexes of ferric heme-nitrosyls with varied axial anionic ligands (such as N-donors, O-donors, and S-donors) are discussed first. Then, the generation and reactivity of ferrous heme-HNO complexes is summarized and related back to the mechanism of P450nor. PMID:24658055

  12. Bifunctional nanostructured model catalysts: Metal/oxide interaction controls initial NO{sub x} storage mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Staudt, Thorsten; Desikusumastuti, Aine; Happel, Markus; Lykhach, Yaroslava; Laurin, Mathias; Libuda, Joerg [Lehrstuhl fuer Physikalische Chemie II, Friedrich-Alexander-Universitaet Erlangen-Nuernberg (Germany); Qin, Zhihui; Shaikhutdinov, Shamil [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany); Rohr, Friedemann [Umicore AG and Co. KG, Hanau (Germany)

    2009-07-01

    In order to get detailed insights into the underlying mechanism and microkinetics, we investigated the initial NO{sub x} uptake on a model nitrogen storage and reduction (NSR) catalyst. This model system is prepared under UHV conditions by co-deposition of noble metal particles (Pd) and Ba-containing oxide particles, representing the storage compound, onto an ordered alumina film on a NiAl(110) substrate. Using a combination of vibrational spectroscopy (IRAS), molecular-beam methods (MB) and scanning tunnelling microscopy (STM), we were able to show that the reaction mechanism is critically controlled by the metal-oxide interaction between the active noble metal particles and the NO{sub x} storage compound. We suggest that a reverse spillover of activated oxygen species from the NO{sub x} storage compound to the noble metal is facilitated by the strong interaction between both components. A partial oxidation of the metal particles and a simultaneous stabilization of surface nitrite intermediates are a consequence of this process.

  13. Effect of Mannitol on Hyaluronic Acid Stability in Two in Vitro Models of Oxidative Stress

    Directory of Open Access Journals (Sweden)

    Marguerite Rinaudo

    2014-07-01

    Full Text Available In this paper, we propose the evaluation of the mannitol’s ability to reduce hyaluronic acid (HA degradation using two different models of oxidative stress. Firstly, a solution of hyaluronan and a solution of the same HA including mannitol in PBS buffer were submitted to an oxidative stress generated by the addition of xanthine + xanthine oxidase generating oxygen free radicals. Different enzyme concentrations were used and the HA properties were studied after 24 h of contact at ambient temperature. Decreases of the viscosity of the solution were assessed by rheometry (viscous and elastic module and that of HA molecular weight was determined by steric exclusion chromatography. Rheologic behavior was assessed on identical HA solutions subjected to another model of oxidative stress imposed by addition of hydrogen peroxide. The influence of mannitol concentration on HA degradation was also demonstrated. Whatever the stress applied, it appears very clearly that mannitol protects hyaluronic acid from mediated oxygen free radicals degradation. These in vitro results suggest that mannitol could be a simple way to significantly increase the intra-articular residence time of the injected hyaluronic acid and therefore might improve viscosupplementation effectiveness.

  14. Model study of multiphase DMS oxidation with a focus on halogens

    Directory of Open Access Journals (Sweden)

    R. von Glasow

    2004-01-01

    Full Text Available We studied the oxidation of dimethylsulfide (DMS in the marine boundary layer (MBL with a one-dimensional numerical model and focused on the influence of halogens. Our model runs show that there is still significant uncertainty about the end products of the DMS addition pathway, which is especially caused by uncertainty in the product yield of the reaction of the intermediate product methyl sulfinic acid (MSIA with OH. BrO strongly increases the importance of the addition branch in the oxidation of DMS even when present at mixing ratios smaller than 0.5pmol mol-1. The inclusion of halogen chemistry leads to higher DMS oxidation rates and smaller DMS to SO2 conversion efficiencies. The DMS to SO2 conversion efficiency is also drastically reduced under cloudy conditions. In cloud-free model runs between 5 and 15% of the oxidized DMS reacts further to particulate sulfur, in cloudy runs this fraction is almost 100%. Sulfate production by HOClaq and HOBraq is important in cloud droplets even for small Br- deficits and related small gas phase halogen concentrations. In general, more particulate sulfur is formed when halogen chemistry is included. A possible enrichment of HCO3- in fresh sea salt aerosol would increase pH values enough to make the reaction of S(IV* (=SO2,aq+HSO3-+SO32- with O3 dominant for sulfate production. It leads to a shift from methyl sulfonic acid (MSA to non-sea salt sulfate (nss-SO42- production but increases the total nss-SO42- only somewhat because almost all available sulfur is already oxidized to particulate sulfur in the base scenario. We discuss how realistic this is for the MBL. We found the reaction MSAaq+OH to contribute about 10% to the production of nss-SO42- in clouds. It is unimportant for cloud-free model runs. Overall we find that the presence of halogens leads to processes that decrease the albedo of stratiform clouds in the MBL.

  15. Assessment of nitric oxide (NO) redox reactions contribution to nitrous oxide (N2 O) formation during nitrification using a multispecies metabolic network model.

    Science.gov (United States)

    Perez-Garcia, Octavio; Chandran, Kartik; Villas-Boas, Silas G; Singhal, Naresh

    2016-05-01

    Over the coming decades nitrous oxide (N2O) is expected to become a dominant greenhouse gas and atmospheric ozone depleting substance. In wastewater treatment systems, N2O is majorly produced by nitrifying microbes through biochemical reduction of nitrite (NO2(-)) and nitric oxide (NO). However it is unknown if the amount of N2O formed is affected by alternative NO redox reactions catalyzed by oxidative nitrite oxidoreductase (NirK), cytochromes (i.e., P460 [CytP460] and 554 [Cyt554 ]) and flavohemoglobins (Hmp) in ammonia- and nitrite-oxidizing bacteria (AOB and NOB, respectively). In this study, a mathematical model is developed to assess how N2O formation is affected by such alternative nitrogen redox transformations. The developed multispecies metabolic network model captures the nitrogen respiratory pathways inferred from genomes of eight AOB and NOB species. The performance of model variants, obtained as different combinations of active NO redox reactions, was assessed against nine experimental datasets for nitrifying cultures producing N2O at different concentration of electron donor and acceptor. Model predicted metabolic fluxes show that only variants that included NO oxidation to NO2(-) by CytP460 and Hmp in AOB gave statistically similar estimates to observed production rates of N2O, NO, NO2(-) and nitrate (NO3(-)), together with fractions of AOB and NOB species in biomass. Simulations showed that NO oxidation to NO2(-) decreased N2O formation by 60% without changing culture's NO2(-) production rate. Model variants including NO reduction to N2O by Cyt554 and cNor in NOB did not improve the accuracy of experimental datasets estimates, suggesting null N2O production by NOB during nitrification. Finally, the analysis shows that in nitrifying cultures transitioning from dissolved oxygen levels above 3.8 ± 0.38 to <1.5 ± 0.8 mg/L, NOB cells can oxidize the NO produced by AOB through reactions catalyzed by oxidative NirK. PMID:26551878

  16. Application of a shape accommodating HIP densification model to high temperature yttria oxide material

    International Nuclear Information System (INIS)

    As the need for higher operating temperatures increases, there will be a greater need for materials that can withstand +2,000 C and oxidizing conditions. Y2O3, a high-temperature oxide, was selected on the basis of its high melting point and resistance to surface recession at 2,000 C. The need for processing such a high temperature material demands alternative approaches to production of reliable parts. Hot isostatic pressing offers a route to reliable production of parts for high temperature applications. This study developed empirical relationships to account for the shape of particles and attempts to modify the Ashby, Easterling and Arzt model by incorporating the morphological characteristics into the description of effective pressure on the particle contacts

  17. Hydrogen embrittlement of zircaloy-4: behavior, damage mechanism, interaction with the oxide layer, finite element modelling

    International Nuclear Information System (INIS)

    Zircaloy-4 is used as structural parts in the fuel assemblies in the PWR type reactors. In the operating conditions, this material is oxidized by the primary circuit water. This oxidation leads to hydrogen embrittlement. The aim of the thesis is the characterization and the simulation of this embrittlement. Traction tests have been performed on samples, with and without hydrides to characterize the material behaviour. They showed a transversal anisotropy. The influence of the hydrides on the material ductility has been determined. A quantitative germination law has been proposed, taking into account the plastic deformation and the hydrogen content. A modified Gurson-Tvergaard model has been used to represent the material behaviour and rupture. Then the behaviour parameters identified have been introduced in a numerical simulation using the finite element method. (A.L.B.)

  18. Characterization of Solid Oxide Fuel Cell Components Using Electromagnetic Model-Based Sensors

    Energy Technology Data Exchange (ETDEWEB)

    Zilberstein, Vladimir; Craven, Chris; Goldfine, Neil

    2004-12-28

    In this Phase I SBIR, the contractor demonstrated a number of capabilities of model-based sensors such as MWM sensors and MWM-Arrays. The key results include (1) porosity/microstructure characterization for anodes, (2) potential for cathode material characterization, (3) stress measurements in nickel and cobalt, and (4) potential for stress measurements in non-magnetic materials with a ferromagnetic layer. In addition, potential applications for manufacturing quality control of nonconductive layers using interdigitated electrode dielectrometers have been identified. The results indicate that JENTEK's MWM technology can be used to significantly reduce solid oxide fuel cell production and operating costs in a number of ways. Preliminary investigations of solid oxide fuel cell health monitoring and scale-up issues to address industry needs have also been performed.

  19. Multi-scale Model of Residual Strength of 2D Plain Weave C/SiC Composites in Oxidation Atmosphere

    Science.gov (United States)

    Chen, Xihui; Sun, Zhigang; Sun, Jianfen; Song, Yingdong

    2016-06-01

    Multi-scale models play an important role in capturing the nonlinear response of woven carbon fiber reinforced ceramic matrix composites. In plain weave carbon fiber/silicon carbon (C/SiC) composites, the carbon fibers and interphases will be oxidized at elevated temperature and the strength of the composite will be degraded when oxygen enters micro-cracks formed in the as-produced parts due to the mismatch in thermal properties between constituents. As a result of the oxidation on fiber surface, fiber shows a notch-like morphology. In this paper, the change rule of fiber notch depth is fitted by circular function. And a multi-scale model based upon the change rule of fiber notch depth is developed to simulate the residual strength and post-oxidation stress-strain curves of the composite. The multi-scale model is able to accurately predict the residual strength and post-oxidation stress-strain curves of the composite. Besides, the simulated residual strength and post-oxidation stress-strain curves of 2D plain weave C/SiC composites in oxidation atmosphere show good agreements with experimental results. Furthermore, the oxidation time and temperature of the composite are investigated to show their influences upon the residual strength and post-oxidation stress-strain curves of plain weave C/SiC composites.

  20. Modeling and experimental validation of CO heterogeneous chemistry and electrochemistry in solid oxide fuel cells

    Energy Technology Data Exchange (ETDEWEB)

    Yurkiv, Vitaly

    2010-12-17

    In the present work experimental and numerical modeling studies of the heterogeneously catalyzed and electrochemical oxidation of CO at Nickel/yttria-stabilized zirconia (YSZ) solid oxide fuel cell (SOFC) anode systems were performed to evaluate elementary charge-transfer reaction mechanisms taking place at the three-phase boundary of CO/CO{sub 2} gas-phase, Ni electrode, and YSZ electrolyte. Temperature-programmed desorption and reaction experiments along with density functional theory calculations were performed to determine adsorption/desorption and surface diffusion kinetics as well as thermodynamic data for the CO/CO{sub 2}/Ni and CO/CO{sub 2}/YSZ systems. Based on these data elementary reaction based models with four different charge transfer mechanisms for the electrochemical CO oxidation were developed and applied in numerical simulations of literature experimental electrochemical data such as polarization curves and impedance spectra. Comparison between simulation and experiment demonstrated that only one of the four charge transfer mechanisms can consistently reproduce the electrochemical data over a wide range of operating temperatures and CO/CO{sub 2} gas compositions. (orig.) [German] In der vorliegenden Arbeit wurden experimentelle und numerische Untersuchungen zur heterogen katalysierten und elektrochemischen Oxidation von CO an Anodensystemen (bestehend aus Nickel und yttriumdotiertem Zirkoniumdioxid, YSZ) von Festoxidbrennstoffzellen (engl. Solid Oxide Fuel Cells, SOFCs) ausgefuehrt, um den mikroskopischen Mechanismus der an der CO/CO{sub 2}-Gasphase/Ni-Elektrode/YSZ-Elektrolyt- Dreiphasen-Grenzflaeche ablaufenden Ladungsuebertragungsreaktion aufzuklaeren. Temperaturprogrammierte Desorptionsmessungen (TPD) und Temperaturprogrammierte Reaktionsmessungen (TPR) sowie Dichtefunktionaltheorierechnungen wurden ausgefuehrt, um adsorptions-, desorptions- und reaktionskinetische sowie thermodynamische Daten fuer die CO/CO{sub 2}/Ni- und CO/CO{sub 2}/YSZ

  1. Mathematical Modeling of Ammonia Electro-Oxidation on Polycrystalline Pt Deposited Electrodes

    Science.gov (United States)

    Diaz Aldana, Luis A.

    The ammonia electrolysis process has been proposed as a feasible way for electrochemical generation of fuel grade hydrogen (H2). Ammonia is identified as one of the most suitable energy carriers due to its high hydrogen density, and its safe and efficient distribution chain. Moreover, the fact that this process can be applied even at low ammonia concentration feedstock opens its application to wastewater treatment along with H 2 co-generation. In the ammonia electrolysis process, ammonia is electro-oxidized in the anode side to produce N2 while H2 is evolved from water reduction in the cathode. A thermodynamic energy requirement of just five percent of the energy used in hydrogen production from water electrolysis is expected from ammonia electrolysis. However, the absence of a complete understanding of the reaction mechanism and kinetics involved in the ammonia electro-oxidation has not yet allowed the full commercialization of this process. For that reason, a kinetic model that can be trusted in the design and scale up of the ammonia electrolyzer needs to be developed. This research focused on the elucidation of the reaction mechanism and kinetic parameters for the ammonia electro-oxidation. The definition of the most relevant elementary reactions steps was obtained through the parallel analysis of experimental data and the development of a mathematical model of the ammonia electro-oxidation in a well defined hydrodynamic system, such as the rotating disk electrode (RDE). Ammonia electro-oxidation to N 2 as final product was concluded to be a slow surface confined process where parallel reactions leading to the deactivation of the catalyst are present. Through the development of this work it was possible to define a reaction mechanism and values for the kinetic parameters for ammonia electro-oxidation that allow an accurate representation of the experimental observations on a RDE system. Additionally, the validity of the reaction mechanism and kinetic parameters

  2. Fuel/Oxidizer Injector Modeling in Sub- and Super-Critical Regimes for Deep Throttling Cryogenic Engines Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Accurate CFD modeling of fuel/oxidizer injection and combustion is needed to design and analyze liquid rocket engines. Currently, however, there is no mature...

  3. Thermodynamic Modeling of Oxide Phases in the Mn-O System

    Science.gov (United States)

    Kang, Youn-Bae; Jung, In-Ho

    2016-06-01

    A critical evaluation and thermodynamic modeling for thermodynamic properties of all oxide phases and phase diagrams in the Mn-O system are presented. Optimized Gibbs energy parameters for the thermodynamic models of the oxide phases were obtained which reproduce all available and reliable experimental data within error limits from 298 K (25 °C) to above the liquidus temperature at compositions covering from MnO to MnO2, and oxygen partial pressure from 10-15 to 102 (bar). The optimized thermodynamic properties and phase diagrams are believed to be the best estimates presently available. Two spinel phases (α - and β -Mn3O4) were modeled using Compound Energy Formalism (CEF) with the use of physically meaningful parameters. Valence states of the spinels are interpreted based on the available thermopower measurement, for which Mn4+ was considered in the cubic spinel (β -Mn3O4). The present Mn3O4 spinel solutions can be integrated into a larger spinel solution database, which has been already developed. The database of the model parameters can be used along with a software for Gibbs energy minimization in order to calculate any type of phase diagram sections and thermodynamic properties.

  4. Oxidative DNA damage background estimated by a system model of base excision repair

    Energy Technology Data Exchange (ETDEWEB)

    Sokhansanj, B A; Wilson, III, D M

    2004-05-13

    Human DNA can be damaged by natural metabolism through free radical production. It has been suggested that the equilibrium between innate damage and cellular DNA repair results in an oxidative DNA damage background that potentially contributes to disease and aging. Efforts to quantitatively characterize the human oxidative DNA damage background level based on measuring 8-oxoguanine lesions as a biomarker have led to estimates varying over 3-4 orders of magnitude, depending on the method of measurement. We applied a previously developed and validated quantitative pathway model of human DNA base excision repair, integrating experimentally determined endogenous damage rates and model parameters from multiple sources. Our estimates of at most 100 8-oxoguanine lesions per cell are consistent with the low end of data from biochemical and cell biology experiments, a result robust to model limitations and parameter variation. Our results show the power of quantitative system modeling to interpret composite experimental data and make biologically and physiologically relevant predictions for complex human DNA repair pathway mechanisms and capacity.

  5. Lightning NOx Statistics Derived by NASA Lightning Nitrogen Oxides Model (LNOM) Data Analyses

    Science.gov (United States)

    Koshak, William; Peterson, Harold

    2013-01-01

    What is the LNOM? The NASA Marshall Space Flight Center (MSFC) Lightning Nitrogen Oxides Model (LNOM) [Koshak et al., 2009, 2010, 2011; Koshak and Peterson 2011, 2013] analyzes VHF Lightning Mapping Array (LMA) and National Lightning Detection Network(TradeMark) (NLDN) data to estimate the lightning nitrogen oxides (LNOx) produced by individual flashes. Figure 1 provides an overview of LNOM functionality. Benefits of LNOM: (1) Does away with unrealistic "vertical stick" lightning channel models for estimating LNOx; (2) Uses ground-based VHF data that maps out the true channel in space and time to NOx from lightning return stroke; (7) NOx computed for several other lightning discharge processes (based on Cooray et al., 2009 theory): (a) Hot core of stepped leaders and dart leaders, (b) Corona sheath of stepped leader, (c) K-change, (d) Continuing Currents, and (e) M-components; and (8) LNOM statistics (see later) can be used to parameterize LNOx production for regional air quality models (like CMAQ), and for global chemical transport models (like GEOS-Chem).

  6. Polymerisation, basicity, oxidation state and their role in ionic modelling of silicate melts

    Directory of Open Access Journals (Sweden)

    R. Moretti

    2005-06-01

    Full Text Available In order to describe and quantify the reactivity of silicate melts, the ionic notation provided by the Temkin formalism has been historically accepted, giving rise to the study of melt chemical equilibria in terms of completely dissociated ionic species. Indeed, ionic modelling of melts works properly as long as the true extension of the anionic matrix is known. This information may be attained in the framework of the Toop-Samis (1962a,b model, through a parameterisation of the acid-base properties of the dissolved oxides. Moreover, by combining the polymeric model of Toop and Samis with the «group basicity» concept of Duffy and Ingram (1973, 1974a,b, 1976 the bulk optical basicity (Duffy and Ingram, 1971; Duffy, 1992 of molten silicates and glasses can be split into two distinct contributions, i.e. the basicity of the dissolved basic oxides and the basicity of the polymeric units. Application to practical cases, such as the assessment of the oxidation state of iron, require bridging of the energetic gap between the standard state of completely dissociated component (Temkin standard state and the standard state of pure melt component at P and T of interest. On this basis it is possible to set up a preliminary model for iron speciation in both anhydrous and hydrous aluminosilicate melts. In the case of hydrous melts, I introduce both acidic and basic dissociation of the water component, requiring the combined occurrence of H+ cations, OH- free anions and, to a very minor extent, of T-OH groups. The amphoteric behaviour of water revealed by this study is therefore in line with the earlier prediction of Fraser (1975.

  7. A two-dimensional, finite-difference model of the oxidation of a uranium carbide fuel pellet

    International Nuclear Information System (INIS)

    The oxidation of spent uranium carbide fuel, a candidate fuel for Generation IV nuclear reactors, is an important process in its potential reprocessing cycle. However, the oxidation of uranium carbide in air is highly exothermic. A model has therefore been developed to predict the temperature rise, as well as other useful information such as reaction completion times, under different reaction conditions in order to help in deriving safe oxidation conditions. Finite difference-methods are used to model the heat and mass transfer processes occurring during the reaction in two dimensions and are coupled to kinetics found in the literature

  8. Metal-ceramic composite development based on its modelling results

    Science.gov (United States)

    Dvilis, E. S.; Khasanov, O. L.; Khasanov, A. O.; Petyukevich, M. S.

    2016-02-01

    The modeling (and its experimental verification) of packing and deformation of the composites consisted of aluminum-magnesium alloy AMg6, B4C powder and W nano-powder has been performed. The powder compositions were determined using discrete element modeling of the composite particles packing based on the particle size distribution functions of real powders. The models of maximum mixture packing densities have been rendered.

  9. Application of random pore model for synthesis gas production by nickel oxide reduction with methane

    International Nuclear Information System (INIS)

    Highlights: • Random pore model was modified for bulk flow effect in NiO + CH4 reaction. • The NiO + CH4 reaction produced synthesis gas with H2/CO ratio near two. • The structural changes and product layer resistance were accounted. • Inherent kinetic constants and concentration dependency were determined. • Conversion–time profiles were predicted well by the mathematical model. - Abstract: Recently, there is a great interest in the noncatalytic gas–solid reactions between methane, as an environmentally friendly reducing agent, and metal oxides to yield synthesis gas and the related metal at low temperatures. In the present work, reduction of nickel oxide with methane was investigated. It has been proven that it is possible to produce metallic nickel and synthesis gas, simultaneously. The thermogravimetry measurements and instantaneous mass spectrometry analysis of the gaseous products have been performed for the NiO + CH4 reaction. In addition, the complete mathematical model was developed by applying the random pore model to predict the conversion–time profiles at the temperature range of 600–750 °C. Some important parameters such as concentration dependency, external mass transfer resistance, solid structural changes, product layer resistance, and pore size distribution have been considered in this sophisticated mathematical model. In addition, the random pore model has been modified for consideration of the bulk flow effect. Results obtained from this kinetic study indicate that the model performs well in predicting the experimental data. However by neglecting the bulk flow effect, there are lower predicted rate constants for this reaction. The analysis of the gaseous products showed that the synthesis gas could be produced with a H2/CO ratio near two

  10. Modelling and performance evaluation of solid oxide fuel cell for building integrated co- and polygeneration

    Energy Technology Data Exchange (ETDEWEB)

    Kazempoor, P. [Empa Swiss Federal Laboratories for Materials Science and Technology, Building Science and Technology Laboratory, Duebendorf (Switzerland); Mechanical Engineering Department, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Dorer, V. [Empa Swiss Federal Laboratories for Materials Science and Technology, Building Science and Technology Laboratory, Duebendorf (Switzerland); Ommi, F. [Mechanical Engineering Department, Tarbiat Modares University, Tehran (Iran, Islamic Republic of)

    2010-12-15

    Models of fuel cell based combined heat and power systems, used in building energy performance simulation codes, are often based on simple black or grey box models. To model a specific device, input data from experiments are often required for calibration. This paper presents an approach for the theoretical derivation of such data. A generic solid oxide fuel cell (SOFC) system model is described that is specifically developed for the evaluation of building integrated co- or polygeneration. First, a detailed computational cell model is developed for a planar SOFC and validated with available numerical and experimental data for intermediate and high temperature SOFCs with internal reforming (IT-DIR and HT-DIR). Results of sensitivity analyses on fuel utilisation and air excess ratio are given. Second, the cell model is extended to the stack model, considering stack pressure losses and the radiative heat transfer effect from the stack to the air flow. Third, two system designs based on the IT-DIR and HT-DIR SOFCs are modelled. Electric and CHP efficiencies are given for the two systems, as well as performance characteristics, to be used in simulations of building integrated co- and polygeneration systems. (Copyright copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. An extension of a high temperature creep model to account for fuel sheath oxidation

    International Nuclear Information System (INIS)

    Starting from the high-temperature creep model for Zircaloy fuel sheathing, the NIRVANA (developed by AECL), a multilayer model, is proposed in this paper: it includes the outer oxide plus alpha retained layers, and the inner core of beta or alpha plus beta material, all constrained to deform with the same creep rate. The model has been incorporated into the SPARA fuel computer code developed for the transient analysis of fuel rod behaviour in the CIRENE prototype reactor, but it is in principle valid for all Zircaloy fuel sheathings. Its predictions are compared with experimental results from burst tests on BWR and PWR type sheaths; the tests were carried out at CNEN under two research contracts with Ansaldo Meccanico Nucleare and Sigen-Sopren, respectively

  12. Modelling TCE degradation by a mixed culture of methane-oxidizing bacteria

    DEFF Research Database (Denmark)

    Broholm, Kim; Christensen, Thomas Højlund; Jensen, Bjørn K.

    1992-01-01

    A model describing the growth of bacteria and the degradation of methane and trichloroethylene (TCE) based on the concept of competitive inhibition is proposed. The model has been applied to laboratory batch experiments representing different initial TCE concentrations (50–4300 μg/l) and initial...... methane concentrations (0.53–3.2 mg/l). The proposed model simulated successfully the data obtained for initial methane concentration (less than 1.8 mg/l), causing constant experimental growth conditions during the experiments. This indicates that the interactions between methane and TCE degradation can...... treatment processes and in situ bioremediation schemes for degradation of TCE by methane-oxidizing bacteria....

  13. Modelling of liquid metal flow and oxide film defects in filling of aluminium alloy castings

    Science.gov (United States)

    Dai, X.; Jolly, M.; Yang, X.; Campbell, J.

    2012-07-01

    The liquid metal flow behaviours in different runner system designs have important effects on the mechanical strength of aluminium alloy castings. In this paper, a new model has been developed which is a two-dimensional program using a finite difference technique and the Marker and Cell (MAC) method to simulate the flow of liquid metal during filling a mould. In the program the Eulerian method has been used for the liquid metal flow, while the Oxide Film Entrainment Tracking Algorithm (OFET) method (a Lagrangian method) has been used to simulate the movement of the oxide film on the liquid metal surface or in the liquid metal flow. Several examples have been simulated and tested and the relevant results were obtained. These results were compared with measured bending strengths. It was found that the completed program was capable of simulating effectively the filling processes of different runner systems. The simulation results are consistent with the experiment. In addition, the program is capable of providing clearer images for predicting the distribution of the oxide film defects generated during filling a mould.

  14. Impaired pulmonary artery contractile responses in a rat model of microgravity: role of nitric oxide

    Science.gov (United States)

    Nyhan, Daniel; Kim, Soonyul; Dunbar, Stacey; Li, Dechun; Shoukas, Artin; Berkowitz, Dan E.

    2002-01-01

    Vascular contractile hyporesponsiveness is an important mechanism underlying orthostatic intolerance after microgravity. Baroreceptor reflexes can modulate both pulmonary resistance and capacitance function and thus cardiac output. We hypothesized, therefore, that pulmonary vasoreactivity is impaired in the hindlimb-unweighted (HLU) rat model of microgravity. Pulmonary artery (PA) contractile responses to phenylephrine (PE) and U-46619 (U4) were significantly decreased in the PAs from HLU vs. control (C) animals. N(G)-nitro-L-arginine methyl ester (10(-5) M) enhanced the contractile responses in the PA rings from both C and HLU animals and completely abolished the differential responses to PE and U4 in HLU vs. C animals. Vasorelaxant responses to ACh were significantly enhanced in PA rings from HLU rats compared with C. Moreover, vasorelaxant responses to sodium nitroprusside were also significantly enhanced. Endothelial nitric oxide synthase (eNOS) and soluble guanlyl cyclase expression were significantly enhanced in PA and lung tissue from HLU rats. In marked contrast, the expression of inducible nitric oxide synthase was unchanged in lung tissue. These data support the hypothesis that vascular contractile responsiveness is attenuated in PAs from HLU rats and that this hyporesponsiveness is due at least in part to increased nitric oxide synthase activity resulting from enhanced eNOS expression. These findings may have important implications for blood volume distribution and attenuated stroke volume responses to orthostatic stress after microgravity exposure.

  15. Levels of oxidative stress parameters and the protective effects of melatonin in psychosis model rat testis

    Institute of Scientific and Technical Information of China (English)

    Bekir S.Parlaktas; Birsen Ozyurt; Huseyin Ozyurt; Ayten T.Tunc; Ali Akbas

    2008-01-01

    Aim: To evaluate the effects of melatonin on antioxidant enzyme levels and histopathologic changes in dizocilpine (MK-801)-induced psychosis model rat testis. Methods: A total of 24 adult male Wistar-Albino rats were divided into three groups with 8 in each. Group Ⅰ was used as control. Rats in Group Ⅱ were injected with MK-801 (0.5 mg/kg body weight i.p. for 5 days). In addition to MK-801, melatonin (50 mg/kg body weight i.p. once a day for 5 days) was injected into the rats in Group Ⅲ. The testes were harvested bilaterally for biochemical and histopathological examinations. Antioxidant enzyme activities, malondialdehyde, protein carbonyl and nitric oxide (NO) levels in tes-ticular tissues were analyzed using spectrophotometric analysis methods. Histopathological examinations of the testes were also performed. Results: MK-801 induced testicular damage, which resulted in significant oxidative stress (OS) by increasing the levels of antioxidant enzymes. The malondialdehyde, protein carbonyl and NO levels were increased in testicular tissues of rats. Treatment with melatonin led to significant decrease in oxidative injury.Administration of melatonin also reduced the detrimental histopathologic effects caused by MK-801. Conclusion:The results of the present study showed that MK-801 cause OS in testicular tissues of rats and treatment with melatonin can reduce the harmful effects of MK-801.

  16. Oxidative desulfurization of model diesel via dual activation by a protic ionic liquid

    Energy Technology Data Exchange (ETDEWEB)

    Lü, Hongying, E-mail: hylv@ytu.edu.cn; Wang, Shunan; Deng, Changliang; Ren, Wanzhong; Guo, Baocun

    2014-08-30

    Highlights: • A protic ionic liquid, [Hnmp]HCOO, was used as in ODS. • The mechanism of ODS was involved in dual activation by the PIL. • The [Hnmp]HCOO exhibited high catalytic activity in ODS. • The amounts of PILs and oxidant dosage play vital roles in desulfurization system. • This system can be recycled five times with an unnoticeable decrease in activity. - Abstract: A novel and green carboxylate-anion-based protic ionic liquid (PIL), [Hnmp]HCOO, was prepared through a simple and atom economic neutralization reaction between N-methyl-2-pyrrolidonium (NMP) and formic acids. Both FT-IR spectra and {sup 1}H NMR confirmed its simple salt structure. [Hnmp]HCOO exhibited so high catalytic activity that the dibenzothiophene (DBT) removal reached 99% at 50 °C in 3 h under conditions of V{sub PIL}/V{sub model} {sub oil} = 1:10 and H{sub 2}O{sub 2}/DBT (O/S, molar ratio) = 5. The catalytic oxidation reactivity of S-compounds was found to be in the order of DBT > 4,6-dimethyldibenzothiophene (4,6-DMDBT) > benzothiophene (BT). The investigation on mechanism showed that oxidative desulfurization was realized through dual activation of PIL. Moreover, [Hnmp]HCOO can be recycled for five times with an unnoticeable decrease in desulfurization activity.

  17. FEAT4.1: modeling of sheath oxidation and heat flow in CANDU fuel elements

    International Nuclear Information System (INIS)

    This paper describes recent developments in the AECL-developed computer program, FEAT (Finite Element Analysis for Temperature), which is used to assess the thermal integrity of CANDU ® fuel elements. The FEAT code is used to calculate temperatures in the fuel pellet and in the Zircaloy sheath of a CANDU fuel element under normal operating conditions (NOC), as well as the temperature peaking due to end flux peaking during a transient such as a postulated loss of coolant accident (LOCA). For normal operation of high burnup fuel, the Zircaloy oxidation effect on fuel temperatures needs to be considered due to the long residence time in the reactor. The oxide layer on the coolant side of the fuel sheath has a lower thermal conductivity than that of Zircaloy. Therefore, the heat flow from the fuel element to coolant will be reduced resulting in increased fuel pellet and sheath temperatures. To ensure that the FEAT code is suitable for application in analysis of advanced fuels such as the ACR®-1000 fuel, a number of model developments and code improvements were conducted based on the existing version FEAT 4.0, including the modeling of sheath oxidation and its effect on heat flow in the fuel element, time-dependence of end flux peaking during the postulated LOCA (Loss Of Coolant Accident) conditions, pre-processing and postprocessing of analysis data. This paper describes the theories for the models, as well as other improvements, and verification and validation of the new FEAT version (i.e., FEAT 4.1). (author)

  18. Paricalcitol may improve oxidative DNA damage on experimental amikacin-induced nephrotoxicity model.

    Science.gov (United States)

    Bulut, Gulay; Basbugan, Yildiray; Ari, Elif; Erten, Remzi; Bektas, Havva; Alp, Hamit Hakan; Bayram, Irfan

    2016-06-01

    This study aimed to investigate the possible protective effect of paricalcitol on experimental amikacin-induced nephrotoxicity model in rats. Wistar albino rats (n = 32) were allocated into four equal groups of eight each, the control (Group C), paricalcitol (Group P), amikacin-induced nephrotoxicity (Group A), and paricalcitol-treated amikacin-induced nephrotoxicity (Group A + P) groups. Paricalcitol was given intra-peritoneally at a dose of 0.4 μg/kg/d for 5 consecutive days prior to induction of amikacin-induced nephrotoxicity. Intra-peritoneal amikacin (1.2 g/kg) was used to induce nephrotoxicity at day 4. Renal function parameters, oxidative stress biomarkers, oxidative DNA damage (8-hydroxy-2'-deoxyguanosine/deoxyguanosine ratio), kidney histology, and vascular endothelial growth factor (VEGF) immunoexpression were determined. Group A + P had lower mean fractional sodium excretion (p deoxyguanosine/deoxyguanosine ratio (8-OHdG/dG ratio) (p < 0.001) were significantly lower; superoxide dismutase (p = 0.024) and glutathione peroxidase (p = 0.007) activities of renal tissue were significantly higher in group A + P than in group A. The mean scores of tubular necrosis (p = 0.024), proteinaceous casts (p = 0.038), medullary congestion (p = 0.035), and VEGF immunoexpression (p = 0.018) were also lower in group A + P when compared with group A. This study demonstrates the protective effect of paricalcitol in the prevention of amikacin-induced nephrotoxicity in an experimental model. Furthermore, it is the first study to demonstrate that paricalcitol improves oxidative DNA damage in an experimental acute kidney injury model. PMID:26983906

  19. Thermodynamic database development-modeling and phase diagram calculations in oxide systems

    Institute of Scientific and Technical Information of China (English)

    Arthur D. Pelton

    2006-01-01

    The databases of the FactSage thermodynamic computer system have been under development for 30 years. These databases contain critically evaluated and optimized data for thousands of compounds and hundreds of multicomponent solutions of solid and liquid metals, oxides, salts, sulfides, etc. The databases are automatically accessed by user-friendly software that calculates complex multiphase equilibria in large multicomponent systems for a wide variety of possible input/output constraints. The databases for solutions have been developed by critical evaluation/optimization of all available phase equilibrium and thermodynamic data. The databases contain parameters of models specifically developed for different types of solutions involving sublattices, ordering, etc. Through the optimization process, model parameters are found which reproduce all thermodynamic and phase equilibrium data within experimental error limits and permit extrapolation into regions of temperature and composition where data are unavailable. The present article focuses on the databases for solid and liquid oxide phases involving 25 elements. A short review of the available databases is presented along with the models used for the molten slag and the solid solutions such as spinel, pyroxene, olivine, monoxide, corundum, etc. The critical evaluation/optimization procedure is outlined using examples from the A12O3-SiO2-CaO-FeO-Fe2O3 system. Sample calculations are presented in which the oxide databases are used in conjunction with the FactSage databases for metallic and other phases. In particular, the use of the FactSage module for the calculation of multicomponent phase diagrams is illustrated.

  20. Experimental and model analysis of the co-oxidative behavior of syngas feed in an Intermediate Temperature Solid Oxide Fuel Cell

    Science.gov (United States)

    Donazzi, A.; Rahmanipour, M.; Maestri, M.; Groppi, G.; Bardini, L.; Pappacena, A.; Boaro, M.

    2016-02-01

    By means of model analysis, we show that, in the presence of syngas, the electro-oxidation of H2 and that of CO occur in parallel and contemporarily on Samaria-doped Ceria (Sm0.2Ce0.8O1.9, SDC) Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). The activation of a co-oxidative route is a most distinguishing feature of Ce-based cells, compared to traditional SOFCs. SDC electrolyte supported IT-SOFCs with Cu-Pd-CZ80 composite anodes and LSCF cathodes were tested under a wide range of operating conditions. Polarization and EIS measurements were collected at 600 °C and 650 °C with syngas mixtures (2.3-0.4H2/CO ratio), H2/N2 mixtures (from 97 to 30% H2 v/v) and CO/CO2 mixtures (from 97 to 50% CO v/v). A 1D, dynamic and heterogeneous model of the cell was applied to analyze the polarization and the EIS curves. The kinetics of the reactions of H2 electro-oxidation, CO electro-oxidation and O2 reduction were individually investigated and global power law rates were derived. The syngas experiments were simulated on a fully predictive basis and no parameter adjustment, confirming that the polarization behavior could be best reproduced exclusively by assuming the presence of the co-oxidative route. The IT-SOFCs were also exposed to biogas mixtures, revealing that the dry-reforming reaction was active.

  1. Reactive magnesium oxide cements: geochemical modelling of pH profile and solid phase composition

    International Nuclear Information System (INIS)

    Due to a range of technical and sustainability advantages, reactive magnesium oxide cements (MgO) are a potential alternative to Portland cement (PC) for conditioning intermediate level radioactive waste (ILW). MgO cements consist of a mixture of hydraulic cement and reactive magnesium oxide to which pozzolans such as silica fume (SF) may be added. While favourable, the mechanical and chemical properties of MgO matrices still require further investigation to ensure effective immobilisation of contaminants. In this study a solubility-speciation model was developed using PHREEQC to simulate blends based on low and high contents of MgO, including SF as a supplementary material. Analyses aimed at characterising binding systems focusing on their equilibrium pH with pure water and saturation index (SI) of solid phases. The geochemical model successfully confirmed that the equilibrium pH is inversely proportional to the fraction of MgO and SF present in the hydrated paste. Comparison with data available on literature mostly gave a consistent picture and the model provided reasonable predictions of existent solid phases. (authors)

  2. Experimental and modeling study of the low-temperature oxidation of large alkanes

    CERN Document Server

    Biet, Joffrey; Warth, Valérie; Glaude, Pierre-Alexandre; Battin-Leclerc, Frédérique

    2008-01-01

    This paper presents an experimental and modeling study of the oxidation of large linear akanes (from C10) representative from diesel fuel from low to intermediate temperature (550-1100 K) including the negative temperature coefficient (NTC) zone. The experimental study has been performed in a jet-stirred reactor at atmospheric pressure for n-decane and a n-decane/n-hexadecane blend. Detailed kinetic mechanisms have been developed using computer-aided generation (EXGAS) with improved rules for writing reactions of primary products. These mechanisms have allowed a correct simulation of the experimental results obtained. Data from the literature for the oxidation of n-decane, in a jet-stirred reactor at 10 bar and in shock tubes, and of n-dodecane in a pressurized flow reactor have also been correctly modeled. A considerable improvement of the prediction of the formation of products is obtained compared to our previous models. Flow rates and sensitivity analyses have been performed in order to better understand ...

  3. Iodine's impact on tropospheric oxidants: a global model study in GEOS-Chem

    Science.gov (United States)

    Sherwen, T.; Evans, M. J.; Carpenter, L. J.; Andrews, S. J.; Lidster, R. T.; Dix, B.; Koenig, T. K.; Sinreich, R.; Ortega, I.; Volkamer, R.; Saiz-Lopez, A.; Prados-Roman, C.; Mahajan, A. S.; Ordóñez, C.

    2016-02-01

    We present a global simulation of tropospheric iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic iodine sources, standard gas-phase iodine chemistry, and simplified higher iodine oxide (I2OX, X = 2, 3, 4) chemistry, photolysis, deposition, and parametrized heterogeneous reactions. In comparisons with recent iodine oxide (IO) observations, the simulation shows an average bias of ˜ +90 % with available surface observations in the marine boundary layer (outside of polar regions), and of ˜ +73 % within the free troposphere (350 hPa yield a total bromine- and iodine-driven tropospheric O3 burden decrease of 14.4 % compared to a simulation without iodine and bromine chemistry in the model, and a small increase in OH (1.8 %). This is a significant impact and so halogen chemistry needs to be considered in both climate and air quality models. 1 Here OX is defined as O3 + NO2 + 2NO3 + PAN + PMN+PPN + HNO4 + 3N2O5 + HNO3 + BrO + HOBr + BrNO2+2BrNO3 + MPN + IO + HOI + INO2 + 2INO3 + 2OIO+2I2O2 + 3I2O3 + 4I2O4, where PAN = peroxyacetyl nitrate, PPN = peroxypropionyl nitrate, MPN = methyl peroxy nitrate, and MPN = peroxymethacryloyl nitrate.

  4. Evidence of oxidative injury during aging of the liver in a mouse model.

    OpenAIRE

    Colantoni, Alessandra; Idilman, Ramazan; De Maria, Nicola; Duffner, Lisa A.; VAN THIEL, DAVID H.; Witte, Pamela L.; Kovacs, Elizabeth J.

    2001-01-01

    The aim of the present study was to determine whether oxidative stress contributes to aging of the liver in a mouse model. Liver was obtained from young (3–5 months old) and aged (18–24 months old) mice. No age-induced gross changes in liver morphology were detected by light microscopy. Apoptosis was measured using the fragment end labeling of DNA for the immunohistochemical identification of the apoptotic nuclei. The total apoptotic cells represented 1% of the total cells in livers of young ...

  5. A coarse-grained model for polyethylene oxide and polyethylene glycol: conformation and hydrodynamics

    OpenAIRE

    Lee, Hwankyu; de Vries, Alex H.; Marrink, Siewert-Jan; Pastor, Richard W.

    2009-01-01

    A coarse-grained (CG) model for polyethylene oxide (PEO) and polyethylene glycol (PEG) developed within the framework of the MARTINI CG force field (FF) using the distributions of bonds, angles, and dihedrals from the CHARMM all-atom FF is presented. Densities of neat low molecular weight PEO agree with experiment, and the radius of gyration R-g = 19.1 angstrom +/- 0.7 for 76-mers of PEO (M-w approximate to 3400), in excellent agreement with neutron scattering results for an equal sized PEG. ...

  6. Ability of silybin and its derivatives to prevent protein oxidation in different model systems

    DEFF Research Database (Denmark)

    Purchartová, K.; Baron, C.P.; Křen, V.

    2013-01-01

    to prevent activation of hemoglobin (Hb) to highly reactive hypervalent heme protein species (ferrylHb and perferrylHb) was examined. Indeed, Hb cytotoxicity has been associated with the generation of protein radicals, which are formed when the ferric iron of Hb (Fe3+) is oxidised by H2O2 to (Fe4......+) to form perferrylHb and ferrylHb, with the later also bearing a radical on its protein. The relationship between the structural properties of silybin and its derivatives and their ability to prevent oxidation of Hb was investigated in model system in the presence or the absence of lipids. The...... protein species....

  7. The effect of consuming oxidized oil supplemented with fiber on lipid profiles in rat model

    Directory of Open Access Journals (Sweden)

    Shila Shafaeizadeh

    2011-01-01

    Conclusions: Pectin consumption could decrease serum malondialdehyde and cholesterol in the diet that contains oxidized oil. Pectin supplementation could decrease the detrimental effects of thermally oxidized oil.

  8. Measurement-based modelling of bromine-induced oxidation of mercury above the Dead Sea

    Directory of Open Access Journals (Sweden)

    E. Tas

    2012-03-01

    Full Text Available Atmospheric mercury depletion events (AMDEs outside the polar region – driven by high levels of gaseous Br and BrO (i.e., BrOx – were observed recently in the warm Dead Sea boundary layer. The efficient oxidation of gaseous elemental mercury (GEM under temperate conditions by BrOx was unexpected considering that the thermal back dissociation reaction of HgBr is about 2.5 orders of magnitude higher under Dead Sea temperatures compared to polar temperatures, and hence was expected to significantly slow down GEM oxidation under warm temperatures. The goal of this modelling study was to improve understanding of the interaction of reactive bromine and mercury during Dead Sea AMDEs using numerical simulations based on a comprehensive measurement campaign in summer 2009.

    Our analysis is focused on daytime AMDE when chemical processes dominate concentration changes. Best agreements between simulations and observations were achieved using rate constants for kHg+Br and kHg+BrO of 2.7 × 10−13 cm3 molecule−1 s−1 and 1.5 × 10−13 cm3 molecule−1 s−1, respectively. Our model also predicted that a rate constant kHg+BrO of 5.0 × 10−14 cm3 molecule−1 s−1 may be considered as a minimum, which is higher than most reported values. These rate constants suggest that BrO could be a more efficient oxidant than Br in the troposphere as long as [Br]/[BrO] ratios are smaller than ~0.2 to 0.5. Under Dead Sea conditions, these kinetics demonstrate a high efficiency and central role of BrOx for AMDEs, with relative contributions to GEM depletion of more than ~90%. Unexpectedly, BrO was found to be the dominant oxidant with relative contributions above 80%. The strong contribution of BrO could explain why the efficiency of GEM

  9. Comprehensive Assessment of Oxidatively Induced Modifications of DNA in a Rat Model of Human Wilson's Disease.

    Science.gov (United States)

    Yu, Yang; Guerrero, Candace R; Liu, Shuo; Amato, Nicholas J; Sharma, Yogeshwar; Gupta, Sanjeev; Wang, Yinsheng

    2016-03-01

    Defective copper excretion from hepatocytes in Wilson's disease causes accumulation of copper ions with increased generation of reactive oxygen species via the Fenton-type reaction. Here we developed a nanoflow liquid chromatography-nanoelectrospray ionization-tandem mass spectrometry coupled with the isotope-dilution method for the simultaneous quantification of oxidatively induced DNA modifications. This method enabled measurement, in microgram quantities of DNA, of four oxidative stress-induced lesions, including direct ROS-induced purine cyclonucleosides (cPus) and two exocyclic adducts induced by byproducts of lipid peroxidation, i.e. 1,N(6)-etheno-2'-deoxyadenosine (εdA) and 1,N(2)-etheno-2'-deoxyguanosine (εdG). Analysis of liver tissues of Long-Evans Cinnamon rats, which constitute an animal model of human Wilson's disease, and their healthy counterparts [i.e. Long-Evans Agouti rats] showed significantly higher levels of all four DNA lesions in Long-Evans Cinnamon than Long-Evans Agouti rats. Moreover, cPus were present at much higher levels than εdA and εdG lesions. In contrast, the level of 5-hydroxymethyl-2'-deoxycytidine (5-HmdC), an oxidation product of 5-methyl-2'-deoxycytidine (5-mdC), was markedly lower in the liver tissues of Long-Evans Cinnamon than Long-Evans Agouti rats, though no differences were observed for the levels of 5-mdC. In vitro biochemical assay showed that Cu(2+) ions could directly inhibit the activity of Tet enzymes. Together, these results suggest that aberrant copper accumulation may perturb genomic stability by elevating oxidatively induced DNA lesions, and by altering epigenetic pathways of gene regulation. PMID:26362317

  10. Mass transfer model for two-layer TBP oxidation reactions: Revision 1

    International Nuclear Information System (INIS)

    To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the Canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. Bubbles containing reaction products enhance the rate of transfer of water from the aqueous layer to the organic layer. These bubbles are generated by the oxidation of TBP and its reaction products in the organic layer and by the oxidation of butanol in the aqueous layer. Butanol is formed by the hydrolysis of TBP in the organic layer. For aqueous-layer bubbling to occur, butanol must transfer into the aqueous layer. Consequently, the rate of oxidation and bubble generation in the aqueous layer strongly depends on the rate of transfer of butanol from the organic to the aqueous layer. This report presents measurements of mass transfer rates for the mixing of water and butanol in two-layer, TBP-aqueous mixtures, where the top layer is primarily TBP and the bottom layer is comprised of water or aqueous salt solution. Mass transfer coefficients are derived for use in the modeling of two-layer TBP-nitric acid oxidation experiments

  11. Modeling of Nitrous Oxide Production from Nitritation Reactors Treating Real Anaerobic Digestion Liquor.

    Science.gov (United States)

    Wang, Qilin; Ni, Bing-Jie; Lemaire, Romain; Hao, Xiaodi; Yuan, Zhiguo

    2016-01-01

    In this work, a mathematical model including both ammonium oxidizing bacteria (AOB) and heterotrophic bacteria (HB) is constructed to predict N2O production from the nitritation systems receiving the real anaerobic digestion liquor. This is for the first time that N2O production from such systems was modeled considering both AOB and HB. The model was calibrated and validated using experimental data from both lab- and pilot-scale nitritation reactors. The model predictions matched the dynamic N2O, ammonium, nitrite and chemical oxygen demand data well, supporting the capability of the model. Modeling results indicated that HB are the dominant contributor to N2O production in the above systems with the dissolved oxygen (DO) concentration of 0.5-1.0 mg O2/L, accounting for approximately 75% of N2O production. The modeling results also suggested that the contribution of HB to N2O production decreased with the increasing DO concentrations, from 75% at DO = 0.5 mg O2/L to 25% at DO = 7.0 mg O2/L, with a corresponding increase of the AOB contribution (from 25% to 75%). Similar to HB, the total N2O production rate also decreased dramatically from 0.65 to 0.25 mg N/L/h when DO concentration increased from 0.5 to 7.0 mg O2/L. PMID:27125491

  12. Modeling of Nitrous Oxide Production from Nitritation Reactors Treating Real Anaerobic Digestion Liquor

    Science.gov (United States)

    Wang, Qilin; Ni, Bing-Jie; Lemaire, Romain; Hao, Xiaodi; Yuan, Zhiguo

    2016-01-01

    In this work, a mathematical model including both ammonium oxidizing bacteria (AOB) and heterotrophic bacteria (HB) is constructed to predict N2O production from the nitritation systems receiving the real anaerobic digestion liquor. This is for the first time that N2O production from such systems was modeled considering both AOB and HB. The model was calibrated and validated using experimental data from both lab- and pilot-scale nitritation reactors. The model predictions matched the dynamic N2O, ammonium, nitrite and chemical oxygen demand data well, supporting the capability of the model. Modeling results indicated that HB are the dominant contributor to N2O production in the above systems with the dissolved oxygen (DO) concentration of 0.5–1.0 mg O2/L, accounting for approximately 75% of N2O production. The modeling results also suggested that the contribution of HB to N2O production decreased with the increasing DO concentrations, from 75% at DO = 0.5 mg O2/L to 25% at DO = 7.0 mg O2/L, with a corresponding increase of the AOB contribution (from 25% to 75%). Similar to HB, the total N2O production rate also decreased dramatically from 0.65 to 0.25 mg N/L/h when DO concentration increased from 0.5 to 7.0 mg O2/L. PMID:27125491

  13. Selective oxidation of sulfurs and oxidation desulfurization of model oil by 12-tungstophosphoric acid on cobalt-ferrite nanoparticles as magnetically recoverable catalyst

    Institute of Scientific and Technical Information of China (English)

    Ezzat Rafiee; Nasibeh Rahpeyma

    2015-01-01

    Silica-coated CoFe2O4 nanoparticles were prepared and used as a support for the immobilization of 12-tungstophosphoric acid, to produce a new magnetically separable catalyst. This catalyst was characterized using X-ray diffraction, wavelength-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, laser par-ticle size analysis, and vibrating sample magnetometry. The catalyst showed high activity in the selective oxidation of thioethers and thiophenes to the corresponding sulfones under mild condi-tions. The catalytic activity of the nanocatalyst in the oxidative desulfurization of model oil was investigated. The effect of nitrogen-containing compounds on sulfur removal from the model oil was also evaluated. The catalyst showed high activity in the oxidative desulfurization of diesel. The cata-lyst can be readily isolated from the oxidation system using an external magnet and no obvious loss of activity was observed when the catalyst was reused in four consecutive runs.

  14. Experimental study and modelling of the high temperature mechanical behavior of oxide dispersion strengthened ferritic steels

    International Nuclear Information System (INIS)

    The strength of metals, and therefore their maximum operating temperature, can be improved by oxide dispersion strengthening (ODS). Numerous research studies are carried out at the French Atomic Energy Commission (CEA) in order to develop a cladding tube material for Gen IV nuclear power reactors. Oxide dispersion strengthened steels appear to be the most promising candidates for such application, which demands a minimum operating temperature of 650 C. The present dissertation intends to improve the understanding of the mechanical properties of ODS steels, in terms of creep lifetime and mechanical anisotropy. The methodology of this work includes mechanical tests between room temperature and 900 C as well as macroscopic and polycrystalline modelling. These tests are carried out on a Fe-14Cr1W0,26Ti + 0,3 Y2O3 ODS ferritic steel processed at CEA by mechanical alloying and hot extrusion. The as-received material is a bar with a circular section. The mechanical tests reveal the high mechanical strength of this steel at high temperature. A strong influence of the strain rate on the ductility and the mechanical strength is also observed. A macroscopic mechanical model has been developed on the basis of some experimental statements such as the high kinematic contribution to the flow stress. This model has a strong ability to reproduce the mechanical behaviour of the studied material. Two different polycrystalline models have also been developed in order to reproduce the mechanical anisotropy of the material. They are based on its specific grain morphology and crystallographic texture. The discrepancy between the predictions of both models and experimental results reveal the necessity to formulate alternate assumptions on the deformation mechanisms of ODS ferritic steels. (author)

  15. 3D CFD Electrochemical And Heat Transfer Model Of An Internally Manifolded Solid Oxide Electrolysis Cell

    International Nuclear Information System (INIS)

    A three-dimensional computational fluid dynamics (CFD) electrochemical model has been created to model high-temperature electrolysis cell performance and steam electrolysis in an internally manifolded planar solid oxide electrolysis cell (SOEC) stack. This design is being evaluated at the Idaho National Laboratory for hydrogen production from nuclear power and process heat. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. A solid-oxide fuel cell (SOFC) model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, operating potential, steam-electrode gas composition, oxygen-electrode gas composition, current density and hydrogen production over a range of stack operating conditions. Single-cell and five-cell results will be presented. Flow distribution through both models is discussed. Flow enters from the bottom, distributes through the inlet plenum, flows across the cells, gathers in the outlet plenum and flows downward making an upside-down ''U'' shaped flow pattern. Flow and concentration variations exist downstream of the inlet holes. Predicted mean outlet hydrogen and steam concentrations vary linearly with current density, as expected. Effects of variations in operating temperature, gas flow rate, oxygen-electrode and steam-electrode current density, and contact resistance from the base case are presented. Contour plots of local electrolyte temperature, current density, and Nernst potential indicate the effects of heat transfer, reaction cooling/heating, and change in local gas composition. Results are discussed for using this design in the electrolysis mode. Discussion of thermal neutral voltage, enthalpy of reaction, hydrogen production, cell thermal

  16. Three-dimensional three-phase model for simulation of hydrodynamics, oxygen mass transfer, carbon oxidation, nitrification and denitrification in an oxidation ditch.

    Science.gov (United States)

    Lei, Li; Ni, Jinren

    2014-04-15

    A three-dimensional three-phase fluid model, supplemented by laboratory data, was developed to simulate the hydrodynamics, oxygen mass transfer, carbon oxidation, nitrification and denitrification processes in an oxidation ditch. The model provided detailed phase information on the liquid flow field, gas hold-up distribution and sludge sedimentation. The three-phase model described water-gas, water-sludge and gas-sludge interactions. Activated sludge was taken to be in a pseudo-solid phase, comprising an initially separated solid phase that was transported and later underwent biological reactions with the surrounding liquidmedia. Floc parameters were modified to improve the sludge viscosity, sludge density, oxygen mass transfer rate, and carbon substrate uptake due to adsorption onto the activated sludge. The validation test results were in very satisfactory agreement with laboratory data on the behavior of activated sludge in an oxidation ditch. By coupling species transport and biological process models, reasonable predictions are made of: (1) the biochemical kinetics of dissolved oxygen, chemical oxygen demand (COD) and nitrogen variation, and (2) the physical kinematics of sludge sedimentation. PMID:24525069

  17. Numerical modelling of methane-powered micro-tubular, single-chamber solid oxide fuel cell

    Energy Technology Data Exchange (ETDEWEB)

    Akhtar, N. [School of Applied Mathematics, University of Birmingham, B15 2TT (United Kingdom); Department of Chemical Engineering, University of Birmingham, B15 2TT (United Kingdom); Decent, S.P. [School of Applied Mathematics, University of Birmingham, B15 2TT (United Kingdom); Kendall, K. [Department of Chemical Engineering, University of Birmingham, B15 2TT (United Kingdom)

    2010-12-01

    An experimentally validated, two-dimensional, axisymmetric, numerical model of micro-tubular, single-chamber solid oxide fuel cell (MT-SC-SOFC) has been developed. The model incorporates methane full combustion, steam reforming, dry reforming and water-gas shift reaction followed by electrochemical oxidation of produced hydrogen within the anode. On the cathode side, parasitic combustion of methane along with the electrochemical oxygen reduction is implemented. The results show that the poor performance of single-chamber SOFC as compared to the conventional (dual-chamber) SOFC (in case of micro-tubes) is due to the mass transport limitation on the anode side. The gas velocity inside the micro-tube is far too low when compared to the gas-chamber inlet velocity. The electronic current density is also non-uniform over the cell length, mainly due to the short length of the anode current collector located at the cell outlet. Furthermore, the higher temperature near the cell edges is due to the methane combustion (very close to the cell inlet) and current collection point (at the cell outlet). Both of these locations could be sensitive to the silver current collecting wire as silver may rupture due to cell overheating. (author)

  18. Reactive Transport Modeling of Microbe-mediated Fe (II) Oxidation for Enhanced Oil Recovery

    Science.gov (United States)

    Surasani, V.; Li, L.

    2011-12-01

    Microbially Enhanced Oil Recovery (MEOR) aims to improve the recovery of entrapped heavy oil in depleted reservoirs using microbe-based technology. Reservoir ecosystems often contain diverse microbial communities those can interact with subsurface fluids and minerals through a network of nutrients and energy fluxes. Microbe-mediated reactions products include gases, biosurfactants, biopolymers those can alter the properties of oil and interfacial interactions between oil, brine, and rocks. In addition, the produced biomass and mineral precipitates can change the reservoir permeability profile and increase sweeping efficiency. Under subsurface conditions, the injection of nitrate and Fe (II) as the electron acceptor and donor allows bacteria to grow. The reaction products include minerals such as Fe(OH)3 and nitrogen containing gases. These reaction products can have large impact on oil and reservoir properties and can enhance the recovery of trapped oil. This work aims to understand the Fe(II) oxidation by nitrate under conditions relevant to MEOR. Reactive transport modeling is used to simulate the fluid flow, transport, and reactions involved in this process. Here we developed a complex reactive network for microbial mediated nitrate-dependent Fe (II) oxidation that involves both thermodynamic controlled aqueous reactions and kinetic controlled Fe (II) mineral reaction. Reactive transport modeling is used to understand and quantify the coupling between flow, transport, and reaction processes. Our results identify key parameter controls those are important for the alteration of permeability profile under field conditions.

  19. Photochemical modelling of photo-oxidant levels over the Swiss plateau and emission reduction scenarios

    International Nuclear Information System (INIS)

    During summertime high pressure conditions, high photo-oxidant (O3, H2O2, PAN and others) levels are frequently observed in the planetary boundary layer in central Europe. It is well known that close to the earth's surface ozone is formed by complex reactions involving VOC, NOx, and sunlight. Substantial reductions of both precursors are needed to reduce photo-oxidant levels. In this context the reductions of the abundance of the precursors and the variation of their ratios is of great importance. Here we report model calculations from the Harwell Photochemical Trajectory Model of the levels of O3, H2O2 and PAN along a trajectory over the Swiss Plateau from Lake Constance to Lake Geneva. These calculations are in satisfactory agreement with measurements made during the intensive observation period of the research program POLLUMET (Pollution and Meteorology in Switzerland). Sensitivity calculations of emission reduction scenarios indicate that on the Swiss Plateau the ozone production may be mainly NOx-limited; under conditions where the CO levels are closer to the upper limit within the range (120-600 ppbv). The calculated peak ozone level reduction caused by an exclusive NOx-emission reduction is about three times larger than that caused by an exclusive VOC reduction. The combined reduction of all precursor compounds is the most efficient strategy, although it is only marginally more efficient than the NOx-reduction scenario alone. (author) figs., tabs., 75 refs

  20. Cardiovascular disease-related parameters and oxidative stress in SHROB rats, a model for metabolic syndrome.

    Directory of Open Access Journals (Sweden)

    Eunice Molinar-Toribio

    Full Text Available SHROB rats have been suggested as a model for metabolic syndrome (MetS as a situation prior to the onset of CVD or type-2 diabetes, but information on descriptive biochemical parameters for this model is limited. Here, we extensively evaluate parameters related to CVD and oxidative stress (OS in SHROB rats. SHROB rats were monitored for 15 weeks and compared to a control group of Wistar rats. Body weight was recorded weekly. At the end of the study, parameters related to CVD and OS were evaluated in plasma, urine and different organs. SHROB rats presented statistically significant differences from Wistar rats in CVD risk factors: total cholesterol, LDL-cholesterol, triglycerides, apoA1, apoB100, abdominal fat, insulin, blood pressure, C-reactive protein, ICAM-1 and PAI-1. In adipose tissue, liver and brain, the endogenous antioxidant systems were activated, yet there was no significant oxidative damage to lipids (MDA or proteins (carbonylation. We conclude that SHROB rats present significant alterations in parameters related to inflammation, endothelial dysfunction, thrombotic activity, insulin resistance and OS measured in plasma as well as enhanced redox defence systems in vital organs that will be useful as markers of MetS and CVD for nutrition interventions.

  1. Intrinsic point defects in zinc oxide. Modeling of structural, electronic, thermodynamic and kinetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Erhart, P.

    2006-07-01

    The present dissertation deals with the modeling of zinc oxide on the atomic scale employing both quantum mechanical as well as atomistic methods. The first part describes quantum mechanical calculations based on density functional theory of intrinsic point defects in ZnO. To begin with, the geometric and electronic structure of vacancies and oxygen interstitials is explored. In equilibrium oxygen interstitials are found to adopt dumbbell and split interstitial configurations in positive and negative charge states, respectively. Semi-empirical self-interaction corrections allow to improve the agreement between the experimental and the calculated band structure significantly; errors due to the limited size of the supercells can be corrected by employing finite-size scaling. The effect of both band structure corrections and finite-size scaling on defect formation enthalpies and transition levels is explored. Finally, transition paths and barriers for the migration of zinc as well as oxygen vacancies and interstitials are determined. The results allow to interpret diffusion experiments and provide a consistent basis for developing models for device simulation. In the second part an interatomic potential for zinc oxide is derived. To this end, the Pontifix computer code is developed which allows to fit analytic bond-order potentials. The code is subsequently employed to obtain interatomic potentials for Zn-O, Zn-Zn, and O-O interactions. To demonstrate the applicability of the potentials, simulations on defect production by ion irradiation are carried out. (orig.)

  2. Comparison between two methane reforming models applied to a quasi-two-dimensional planar solid oxide fuel cell model

    International Nuclear Information System (INIS)

    Up to recently 2-D solid oxide fuel cell (SOFC) modelling efforts were based on global kinetic approaches for the methane steam reforming and water gas shift reactions (WGS) or thermodynamic equilibrium. Lately detailed models for elementary heterogeneous chemical kinetics of reforming (HCR) over Ni-YSZ anode became available in literature. Both approaches were employed in a quasi 2-D model of a planar high temperature electrolyte supported (ESC) SOFC and simulations were carried out for three different fuel gas compositions: pre-reformed natural gas (high CH4 content), and two different biomass derived producer gases (low CH4 content). The results show that the HCR predicts much slower reforming rates which leads to a more evenly distributed solid temperature but smaller power output and thus electrical efficiency. The two models result into predictions that differ greatly if high methane content fuels are used and for such cases the decision upon the modelling scheme to follow should be based on experimental investigations.

  3. Structure, Raman spectra and defect chemistry modelling of conductive pyrochlore oxides

    DEFF Research Database (Denmark)

    Poulsen, F.W.; Glerup, M.; Holtappels, P.

    2000-01-01

    Mixed ionic-electronic conducting pyrochlore structure oxides, with Pr and Gd on the A site and Zr, Mn, Ce, Sn, In, Mo, and Ti on the B site, were characterised by X-ray powder diffraction and Raman spectroscopy. Mn and In have a solubility around x = 0.1-0.2 in Pr2Zr2-xMnxO7 and Pr2Sn2-xInxO7......-O(x) and V-O on the O site, interstitial oxygens O-i", and delocalised electrons and electron holes. Four mass action law expressions govern such a model. The defect model can rationalise why home-valent doping, i.e. substitution of Zr(4+) by Ce(4+), can lead to an increase in ionic conductivity...

  4. Fenton Process Coupled to Ultrasound and UV Light Irradiation for the Oxidation of a Model Pollutant

    Directory of Open Access Journals (Sweden)

    Karen E. Barrera-Salgado

    2016-01-01

    Full Text Available The Fenton process coupled to photosonolysis (UV light and Us, using Fe2O3 catalyst supported on Al2O3, was used to oxidize a model pollutant like acid green 50 textile dye (AG50. Dye degradation was followed by AG50 concentration decay analyses. It was observed that parameters like iron content on a fixed amount of catalyst supporting material, catalyst annealing temperature, initial dye concentration, and the solution pH influence the overall treatment efficiency. High removal efficiencies of the model pollutant are achieved. The stability and reusability tests of the Fe2O3 catalyst show that the catalyst can be used up to three cycles achieving high discoloration. Thus, this catalyst is highly efficient for the degradation of AG50 in the Fenton process.

  5. A computational fluid dynamics model of a solid oxide fuel cell

    Energy Technology Data Exchange (ETDEWEB)

    Sudaprasert, K.; Travis, R.P.; Martinez Botas, R.F.

    2005-03-15

    In this work a three-dimensional model of a solid oxide fuel cell (SOFC) has been developed and is used to predict the temperature, concentration distribution and velocity profile across the cell. This model employs Users' Subroutines in a commercial computational fluid dynamics (CFD) code to simulate the electrochemical reactions. The results show both fuel concentration and current density decreasing along the flow direction. The temperature differences are significant with the hottest point located in middle of the active area. Increasing the operating temperature is shown to reduce the effect of polarization that hampers the cell performance, although other issues such as thermal stresses and reduced material choices are more significant. (Author)

  6. Modeling of diffusion mechanism of conductive channel oxidation in a Pt/NiO/Pt memory switching structure

    Science.gov (United States)

    Sysun, V. I.; Bute, I. V.; Boriskov, P. P.

    2016-09-01

    The transition process from the low resistance state into the high resistance state in a Pt/NiO/Pt memory switching structure has been studied by numerical modeling. Detailed analysis shows, that thermally induced diffusion oxidation by nickel vacancies is the key factor for distortion of the channel metallic conductivity. Spatial dynamics of the process of oxidation defines channel narrowing mainly in its central part, and also sets the critical current through the structure sufficient for final rupture of the channel and the transition to high resistance state. The increase in critical current above the limit even by 10% reduces the switching time by an order of magnitude, which is in agreement with experiments. The developed radial diffusion model of conductive channel (or filaments) oxidation may be suitable for the analysis of switching effect a number of other ReRAM oxide structures.

  7. A planar anode-supported Solid Oxide Fuel Cell model with internal reforming of natural gas

    Science.gov (United States)

    Chinda, P.; Chanchaona, S.; Brault, P.; Wechsatol, W.

    2011-05-01

    Solid Oxide Fuel Cells (SOFCs) are of great interest due to their high energy efficiency, low emission level, and multiple fuel utilization. SOFC can operate with various kinds of fuels such as natural gas, carbon monoxide, methanol, ethanol, and hydrocarbon compounds, and they are becoming one of the main competitors among environmentally friendly energy sources for the future. In this study, a mathematical model of a co-flow planar anode-supported solid oxide fuel cell with internal reforming of natural gas has been developed. The model simultaneously solves mass, energy transport equations, and chemical as well as electrochemical reactions. The model can effectively predict the compound species distributions as well as the cell performance under specific operating conditions. The main result is a rather small temperature gradient obtained at 800 °C with S/C = 1 in classical operating conditions. The cell performance is reported for several operating temperatures and pressures. The cell performance is specified in terms of cell voltage and power density at any specific current density. The influence of electrode microstructure on cell performance was investigated. The simulation results show that the steady state performance is almost insensitive to microstructure of cells such as porosity and tortuosity unlike the operating pressure and temperature. However, for SOFC power output enhancement, the power output could be maximized by adjusting the pore size to an optimal value, similarly to porosity and tortuosity. At standard operating pressure (1 atm) and 800 °C with 48% fuel utilization, when an output cell voltage was 0.73 V, a current density of 0.38 A cm-2 with a power density of 0.28 W cm-2 was predicted. The accuracy of the model was validated by comparing with existing experimental results from the available literature.

  8. Modeling on oxide dependent 2DEG sheet charge density and threshold voltage in AlGaN/GaN MOSHEMT

    Science.gov (United States)

    Panda, J.; Jena, K.; Swain, R.; Lenka, T. R.

    2016-04-01

    We have developed a physics based analytical model for the calculation of threshold voltage, two dimensional electron gas (2DEG) density and surface potential for AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOSHEMT). The developed model includes important parameters like polarization charge density at oxide/AlGaN and AlGaN/GaN interfaces, interfacial defect oxide charges and donor charges at the surface of the AlGaN barrier. The effects of two different gate oxides (Al2O3 and HfO2) are compared for the performance evaluation of the proposed MOSHEMT. The MOSHEMTs with Al2O3 dielectric have an advantage of significant increase in 2DEG up to 1.2 × 1013 cm‑2 with an increase in oxide thickness up to 10 nm as compared to HfO2 dielectric MOSHEMT. The surface potential for HfO2 based device decreases from 2 to ‑1.6 eV within 10 nm of oxide thickness whereas for the Al2O3 based device a sharp transition of surface potential occurs from 2.8 to ‑8.3 eV. The variation in oxide thickness and gate metal work function of the proposed MOSHEMT shifts the threshold voltage from negative to positive realizing the enhanced mode operation. Further to validate the model, the device is simulated in Silvaco Technology Computer Aided Design (TCAD) showing good agreement with the proposed model results. The accuracy of the developed calculations of the proposed model can be used to develop a complete physics based 2DEG sheet charge density and threshold voltage model for GaN MOSHEMT devices for performance analysis.

  9. A novel parameter estimation method for metal oxide surge arrester models

    Indian Academy of Sciences (India)

    Mehdi Nafar; Gevork B Gharehpetian; Taher Niknam

    2011-12-01

    Accurate modelling and exact determination of Metal Oxide (MO) surge arrester parameters are very important for arrester allocation, insulation coordination studies and systems reliability calculations. In this paper, a new technique, which is the combination of Adaptive Particle Swarm Optimization (APSO) and Ant Colony Optimization (ACO) algorithms and linking the MATLAB and EMTP, is proposed to estimate the parameters of MO surge arrester models. The proposed algorithm is named Modified Adaptive Particle Swarm Optimization (MAPSO). In the proposed algorithm, to overcome the drawback of the PSO algorithm (convergence to local optima), the inertia weight is tuned by using fuzzy rules and the cognitive and the social parameters are self-adaptively adjusted. Also, to improve the global search capability and prevent the convergence to local minima, ACO algorithm is combined to the proposed APSO algorithm. The transient models of MO surge arrester have been simulated by using ATP-EMTP. The results of simulations have been applied to the program, which is based on MAPSO algorithm and can determine the fitness and parameters of different models. The validity and the accuracy of estimated parameters of surge arrester models are assessed by comparing the predicted residual voltage with experimental results.

  10. Parameter Identification of the 2-Chlorophenol Oxidation Model Using Improved Differential Search Algorithm

    Directory of Open Access Journals (Sweden)

    Guang-zhou Chen

    2015-01-01

    Full Text Available Parameter identification plays a crucial role for simulating and using model. This paper firstly carried out the sensitivity analysis of the 2-chlorophenol oxidation model in supercritical water using the Monte Carlo method. Then, to address the nonlinearity of the model, two improved differential search (DS algorithms were proposed to carry out the parameter identification of the model. One strategy is to adopt the Latin hypercube sampling method to replace the uniform distribution of initial population; the other is to combine DS with simplex method. The results of sensitivity analysis reveal the sensitivity and the degree of difficulty identified for every model parameter. Furthermore, the posteriori probability distribution of parameters and the collaborative relationship between any two parameters can be obtained. To verify the effectiveness of the improved algorithms, the optimization performance of improved DS in kinetic parameter estimation is studied and compared with that of the basic DS algorithm, differential evolution, artificial bee colony optimization, and quantum-behaved particle swarm optimization. And the experimental results demonstrate that the DS with the Latin hypercube sampling method does not present better performance, while the hybrid methods have the advantages of strong global search ability and local search ability and are more effective than the other algorithms.

  11. Microstrain in nanostructured nickel oxide studied using isotropic and anisotropic models

    International Nuclear Information System (INIS)

    Nanostructured nickel oxide, NiO is synthesized through a novel chemical route using nickel chloride and ethanol amine as starting materials. The prepared samples are annealed at higher temperatures, viz. 350 °C, 400 °C, 500 °C and 600 °C. The samples are characterized using XRD, TEM, antioxidant activity and DC conductivity measurements. The crystallite size and microstrain in the samples are studied using Williamson-Hall (W-H) analysis assuming uniform deformation model, uniform deformation stress model and uniform deformation energy density model. The results obtained using three models yield microstrain values which decreases with increase of crystallite size. The average crystallite size and the microstrain of the samples measured from modified W-H plot using uniform energy density model are found to be most suitable. The study shows that the microstrain in nanostructured NiO originates due to the presence of Ni2+ and O2− vacancies and it is confirmed by the measurement of antioxidant activity and dc conductivity of the samples in vacuum and air ambience

  12. Modeling a reversible solid oxide fuel cell as a storage device within AC power networks

    Energy Technology Data Exchange (ETDEWEB)

    Ren, J.; Roscoe, A.J.; Burt, G. [Department of Electronic and Electrical Engineering, Royal College, University of Strathclyde, Glasgow (United Kingdom); Gamble, S.R.; Irvine, J.T.S. [School of Chemistry, University of St. Andrews, Purdie Building, St. Andrews (United Kingdom)

    2012-10-15

    A reversible solid oxide fuel cell (RSOFC) system, consisting of a RSOFC stack, heat store, and electrical inverters to convert DC to AC power, is shown by computer modeling to have the potential to efficiently store electrical energy. This paper describes the modeling of a single RSOFC, based on a proposed cell geometry, empirical data on the resistivities of the components, and calculation of activation and diffusion polarization resistances from electrochemical theory. Data from ac impedance spectroscopy measurements on symmetrical cells are used to model RSOFC impedance. A RSOFC stack is modeled by electrically linking the individual cells inside a pressurized vessel. A phase change heat store is added to improve energy storage efficiency. The model is implemented in MATLAB {sup registered} /Simulink {sup registered}. Two competing inverter control schemes are compared, trading off DC bus ripple against AC power quality. It is found that selection of appropriate DC bus capacitance is important in certain scenarios, with potential system cost implications. It is shown that the system can store electrical energy at an efficiency of 64% over a single discharge-charge cycle, i.e., hydrogen to electricity and heat to hydrogen. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Modelling of chalcopyrite oxidation reactions in the Outokumpu flash smelting process

    Energy Technology Data Exchange (ETDEWEB)

    Ahokainen, T.; Jokilaakso, A. [Helsinki Univ. of Technology, Otaniemi (Finland)

    1996-12-31

    A mathematical model for simulating oxidation reactions of chalcopyrite particles together with momentum, heat and mass transfer between particle and gas phase in a flash smelting furnace reaction shaft is presented. In simulation, the equations governing the gas flow are solved numerically with a commercial fluid flow package, Phoenics. The particle phase is introduced into the gas flow by a Particle Source In Cell (PSIC) - technique, where a number of discrete particles is tracked in a gas flow and the relevant source terms for momentum, mass, and heat transfer are added to the gas phase equations. The gas phase equations used are elliptic in nature and the fluid turbulence is described by the (k-{epsilon}) -model. Thermal gas phase radiation is simulated with a six-flux radiation model. The chemical reactions of concentrate particles are assumed to happen at two sharp interfaces, and a shrinking core model is applied to describe the mass transfer of chemical species through the reaction product layer. In a molten state, the oxygen consumption is controlled by a film penetration concept. The reacting concentrate particles are a mixture of chalcopyrite and silica. Also a certain amount of pure inert silica is fed to the process as flux. In the simulations the calculation domain includes the concentrate burner and a cylindrical reaction shaft of an industrial scale flash smelting furnace. Some examples about the simulations carried out by the combustion model are presented. (author)

  14. An analytical model of hydrogen evolution and oxidation reactions on electrodes partially covered with a catalyst.

    Science.gov (United States)

    Kemppainen, Erno; Halme, Janne; Lund, Peter D

    2016-05-11

    Our previous theoretical study on the performance limits of the platinum (Pt) nanoparticle catalyst for the hydrogen evolution reaction (HER) had shown that the mass transport losses at a partially catalyst-covered planar electrode are independent of the catalyst loading. This suggests that the two-dimensional (2D) numerical model used could be simplified to a one-dimensional (1D) model to provide an easier but equally accurate description of the operation of these HER electrodes. In this article, we derive an analytical 1D model and show that it indeed gives results that are practically identical to the 2D numerical simulations. We discuss the general principles of the model and how it can be used to extend the applicability of existing electrochemical models of planar electrodes to low catalyst loadings suitable for operating photoelectrochemical devices under unconcentrated sunlight. Since the mass transport losses of the HER are often very sensitive to the H2 concentration, we also discuss the limiting current density of the hydrogen oxidation reaction (HOR) and how it is not necessarily independent of the reaction kinetics. The results give insight into the interplay of kinetic and mass-transport limitations at HER/HOR electrodes with implications for the design of kinetic experiments and the optimization of catalyst loadings in the photoelectrochemical cells. PMID:27137703

  15. Modeling mass transfer in solid oxide fuel cell anode: II. H2/CO co-oxidation and surface diffusion in synthesis-gas operation

    Science.gov (United States)

    Bao, Cheng; Jiang, Zeyi; Zhang, Xinxin

    2016-08-01

    Following the previous work on comparing performance of Fickian, Stefan-Maxwell and dusty-gas model for mass transfer in single fuel system, this article is focused on the electrochemistry and transport in the anode of solid oxide fuel cell using H2sbnd H2Osbnd COsbnd CO2sbnd N2 hybrid fuel. Under the standard framework of the dusty-gas model combined with the Butler-Volmer equation, it carries out a macroscopic area-specific modeling work. More specifically, two variables of hydrogen current fraction and enhancement factor are well defined and solved for the electrochemical co-oxidation of H2 and CO, and the diffusion equivalent circuit model is introduced to describe more comprehensively the resistance of mass transfer including molecular/Knudsen diffusion and surface diffusion. The model has been validated well in full region of Vsbnd I performance of an experimental anode-supported button cell. An approximate analytical solution of the hydrogen current fraction is also presented for explicit computation. Comparison between the results by different approaches for the effective diffusivity shows the importance of right mass-transfer modeling.

  16. Quantitative analysis of anaerobic oxidation of methane (AOM) in marine sediments: A modeling perspective

    Science.gov (United States)

    Regnier, P.; Dale, A. W.; Arndt, S.; LaRowe, D. E.; Mogollón, J.; Van Cappellen, P.

    2011-05-01

    Recent developments in the quantitative modeling of methane dynamics and anaerobic oxidation of methane (AOM) in marine sediments are critically reviewed. The first part of the review begins with a comparison of alternative kinetic models for AOM. The roles of bioenergetic limitations, intermediate compounds and biomass growth are highlighted. Next, the key transport mechanisms in multi-phase sedimentary environments affecting AOM and methane fluxes are briefly treated, while attention is also given to additional controls on methane and sulfate turnover, including organic matter mineralization, sulfur cycling and methane phase transitions. In the second part of the review, the structure, forcing functions and parameterization of published models of AOM in sediments are analyzed. The six-orders-of-magnitude range in rate constants reported for the widely used bimolecular rate law for AOM emphasizes the limited transferability of this simple kinetic model and, hence, the need for more comprehensive descriptions of the AOM reaction system. The derivation and implementation of more complete reaction models, however, are limited by the availability of observational data. In this context, we attempt to rank the relative benefits of potential experimental measurements that should help to better constrain AOM models. The last part of the review presents a compilation of reported depth-integrated AOM rates (ΣAOM). These rates reveal the extreme variability of ΣAOM in marine sediments. The model results are further used to derive quantitative relationships between ΣAOM and the magnitude of externally impressed fluid flow, as well as between ΣAOM and the depth of the sulfate-methane transition zone (SMTZ). This review contributes to an improved understanding of the global significance of the AOM process, and helps identify outstanding questions and future directions in the modeling of methane cycling and AOM in marine sediments.

  17. Simulating secondary organic aerosol in a regional air quality model using the statistical oxidation model - Part 1: Assessing the influence of constrained multi-generational ageing

    Science.gov (United States)

    Jathar, S. H.; Cappa, C. D.; Wexler, A. S.; Seinfeld, J. H.; Kleeman, M. J.

    2016-02-01

    Multi-generational oxidation of volatile organic compound (VOC) oxidation products can significantly alter the mass, chemical composition and properties of secondary organic aerosol (SOA) compared to calculations that consider only the first few generations of oxidation reactions. However, the most commonly used state-of-the-science schemes in 3-D regional or global models that account for multi-generational oxidation (1) consider only functionalization reactions but do not consider fragmentation reactions, (2) have not been constrained to experimental data and (3) are added on top of existing parameterizations. The incomplete description of multi-generational oxidation in these models has the potential to bias source apportionment and control calculations for SOA. In this work, we used the statistical oxidation model (SOM) of Cappa and Wilson (2012), constrained by experimental laboratory chamber data, to evaluate the regional implications of multi-generational oxidation considering both functionalization and fragmentation reactions. SOM was implemented into the regional University of California at Davis / California Institute of Technology (UCD/CIT) air quality model and applied to air quality episodes in California and the eastern USA. The mass, composition and properties of SOA predicted using SOM were compared to SOA predictions generated by a traditional two-product model to fully investigate the impact of explicit and self-consistent accounting of multi-generational oxidation.Results show that SOA mass concentrations predicted by the UCD/CIT-SOM model are very similar to those predicted by a two-product model when both models use parameters that are derived from the same chamber data. Since the two-product model does not explicitly resolve multi-generational oxidation reactions, this finding suggests that the chamber data used to parameterize the models captures the majority of the SOA mass formation from multi-generational oxidation under the conditions

  18. Simulating secondary organic aerosol in a regional air quality model using the statistical oxidation model – Part 1: Assessing the influence of constrained multi-generational ageing

    Directory of Open Access Journals (Sweden)

    S. H. Jathar

    2015-09-01

    Full Text Available Multi-generational oxidation of volatile organic compound (VOC oxidation products can significantly alter the mass, chemical composition and properties of secondary organic aerosol (SOA compared to calculations that consider only the first few generations of oxidation reactions. However, the most commonly used state-of-the-science schemes in 3-D regional or global models that account for multi-generational oxidation (1 consider only functionalization reactions but do not consider fragmentation reactions, (2 have not been constrained to experimental data; and (3 are added on top of existing parameterizations. The incomplete description of multi-generational oxidation in these models has the potential to bias source apportionment and control calculations for SOA. In this work, we used the Statistical Oxidation Model (SOM of Cappa and Wilson (2012, constrained by experimental laboratory chamber data, to evaluate the regional implications of multi-generational oxidation considering both functionalization and fragmentation reactions. SOM was implemented into the regional UCD/CIT air quality model and applied to air quality episodes in California and the eastern US. The mass, composition and properties of SOA predicted using SOM are compared to SOA predictions generated by a traditional "two-product" model to fully investigate the impact of explicit and self-consistent accounting of multi-generational oxidation. Results show that SOA mass concentrations predicted by the UCD/CIT-SOM model are very similar to those predicted by a two-product model when both models use parameters that are derived from the same chamber data. Since the two-product model does not explicitly resolve multi-generational oxidation reactions, this finding suggests that the chamber data used to parameterize the models captures the majority of the SOA mass formation from multi-generational oxidation under the conditions tested. Consequently, the use of low and high NOx yields

  19. Polyhydroxylated fullerene nanoparticles attenuate brain infarction and oxidative stress in rat model of ischemic stroke

    Science.gov (United States)

    Vani, Javad Rasouli; Mohammadi, Mohammad Taghi; Foroshani, Mahsa Sarami; Jafari, Mahvash

    2016-01-01

    Oxidative stress is the common underlying mechanism of damage in ischemic stroke. Therefore, we aimed to evaluate the possible protective effects of polyhydroxylated fullerene derivatives on brain infarction and oxidative/nitrosative stress in a rat model of ischemic stroke. The experiment was performed by four groups of rats (each; n=12); Sham, Control ischemia, and ischemic treatment groups (Pretreatment and Posttreatment). Brain ischemia was induced by 90 min middle cerebral artery occlusion (MCAO) followed by 24 hours reperfusion. Rats received fullerene nanoparticles at dose of 1 mg/kg 30 min before MCAO and immediately after beginning of reperfusion. Infarct volume, contents of malondialdehyde (MDA), glutathione (GSH) and nitrate as well as superoxide dismutase (SOD) activity were assessed 24 hours after termination of MCAO. Brain infarct volume was 310 ± 21 mm3 in control group. Administration of fullerene nanoparticles before and after MCAO significantly decreased the infarct volume by 53 % (145 ± 45 mm3) and 81 % (59 ± 13 mm3), respectively. Ischemia also enhanced MDA and nitrate contents of ischemic hemispheres by 45 % and 25 % , respectively. Fullerene nanoparticles considerably reduced the MDA and nitrate contents of ischemic hemispheres before MCAO by 58 % and 17 % , respectively, and after MCAO by 38 % and 21 % , respectively. Induction of MCAO significantly decreased GSH content (19 % ) and SOD activity (52 % ) of ischemic hemispheres, whereas fullerene nanoparticles increased the GSH content and SOD activity of ischemic hemispheres by 19 % and 52 % before MCAO, respectively, and 21 % and 55 % after MCAO, respectively. Our findings indicate that fullerene nanoparticles, as a potent scavenger of free radicals, protect the brain cells against ischemia/reperfusion injury and inhibit brain oxidative/nitrosative damage.

  20. Carnosine and taurine treatments diminished brain oxidative stress and apoptosis in D-galactose aging model.

    Science.gov (United States)

    Aydın, A Fatih; Çoban, Jale; Doğan-Ekici, Işın; Betül-Kalaz, Esra; Doğru-Abbasoğlu, Semra; Uysal, Müjdat

    2016-04-01

    D-galactose (GAL) has been used as an animal model for brain aging and antiaging studies. GAL stimulates oxidative stress in several tissues including brain. Carnosine (CAR; β-alanil-L-histidine) and taurine (TAU; 2-aminoethanesulfonic acid) exhibit antioxidant properties. CAR and TAU have anti-aging and neuroprotective effects. We investigated the effect of CAR and TAU supplementations on oxidative stress and brain damage in GAL-treated rats. Rats received GAL (300 mg/kg; s.c.; 5 days per week) alone or together with CAR (250 mg/kg/daily; i.p.; 5 days per week) or TAU (2.5% w/w; in rat chow) for 2 months. Brain malondialdehyde (MDA), protein carbonyl (PC) and glutathione (GSH) levels and superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), glutathione transferase (GST) and acetylcholinesterase (AChE) activities were determined. Expressions of B cell lymphoma-2 (Bcl-2), Bax and caspase-3 were also evaluated in the brains by immunohistochemistry. GAL treatment increased brain MDA and PC levels and AChE activities. It decreased significantly brain GSH levels, SOD and GSH-Px but not GST activities. GAL treatment caused histopathological changes and increased apoptosis. CAR and TAU significantly reduced brain AChE activities, MDA and PC levels and elevated GSH levels in GAL-treated rats. CAR, but not TAU, significantly increased low activities of SOD and GSH-Px. Both CAR and TAU diminished apoptosis and ameliorated histopathological findings in the brain of GAL-treated rats. Our results indicate that CAR and TAU may be effective to prevent the development of oxidative stress, apoptosis and histopathological deterioration in the brain of GAL-treated rats. PMID:26518192