Calculations of the Thermodynamic Properties of Glasses and Melts in the Na<Subscript>2</Subscript>O-SiO<Subscript>2</Subscript> and B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> Systems on the Basis of the Generalized Lattice Theory of Associated Solutions

The possibility of calculating the thermodynamic properties of binary glass-forming systems containing both modifier (Na₂O) and glass-former (B₂O₃) oxides with the use of the vacancy variant of the generalized lattice theory of associated solutions is demonstrated for glasses and melts in the Na₂O-SiO₂ and B₂O₃-SiO₂ systems.     

Effect of CO<Subscript>2</Subscript> concentration on the performance of different thermodynamic models for prediction of CH<Subscript>4</Subscript>+CO<Subscript>2</Subscript>+H<Subscript>2</Subscript>O hydrate equilibrium conditions

Accurate prediction of phase equilibria regarding CH₄ replacement in hydrate phase with high pressure CO₂ is an important issue in modern reservoir engineering. In this work we investigate the possibility of establishing a thermodynamic framework for predicting the hydrate equilibrium conditions for evaluation of CO₂ injection scenarios. Different combinations of equations of state and mixing rules are applied and the most accurate thermodynamic models at different CO₂ concentration ranges are proposed.     

Phase equilibria in the Ho<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

The phase formation is investigated and the phase diagram of the Ho₂O₃-SrAl₂O₄ system is constructed. A ternary compound, namely, Ho₂SrAl₂O₇, is revealed. It is established that this compound undergoes incongruent melting.     

Phase Equilibria in the Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> System

The phase equilibria are investigated and the phase diagram is constructed for the Gd₂O₃-SrAl₂O₄ pseudobinary join of the Gd₂O₃-SrO-Al₂O₃ ternary oxide system. One ternary compound, namely, Gd₂SrAl₂O₇, is revealed in the Gd₂O₃-SrAl₂O₄ join. It is found that this compound undergoes congruent melting.     

Phase Diagram and Glass Formation in the Sb<Subscript>2</Subscript>S<Subscript>3</Subscript>-AgI System

The phase diagram, the glass formation, and the physicochemical properties of glass-forming and crystalline compositions in the Sb₂S₃-AgI system are investigated. Glasses in this system are moisture-resistant and have high refractive indices. These materials can be used in optical devices operating in the long-wavelength spectral range and as membranes for chemical sensors. The phase diagram of the Sb₂S₃-AgI system is constructed from the data of X-ray powder diffraction and differential thermal analyses.     

Glass formation and the phase diagram of crystalline components in the Sb<Subscript>2</Subscript>S<Subscript>3</Subscript>-PbI<Subscript>2</Subscript> system

Glasses in the Sb₂S₃-PbI₂ system are synthesized, and their physicochemical properties are investigated. The glasses possess high refractive indices (up to 3 or greater). The phase diagram of the Sb₂S₃-PbI₂ system is constructed from the data of differential thermal and X-ray powder diffraction analyses. The diagram exhibits an eutectic behavior. The eutectic is located at a content of 47 mol % PbI₂ and at a temperature of 370 ± 5°C.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Samoilenko, Mohammad Arif, Novikov, Filatov, Blinov.     

Effect of heat release conditions on the phase composition of the combustion products of a Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Al/C thermite mixture

An X-ray method was used to study the phase composition of the combustion products of a Fe₂O₃/TiO₂/Al/C thermite composite mixture, in particular, during combustion of samples under cooling by water. The data of the experiments are compared with the results of thermodynamic calculations. A probable explanation of the reasons of the angular displacement of the line of iron in the X-ray spectrum of the combustion products and a mechanism for the crystallization of an eutectic TiC + α-Fe mixture from the melt of the Ti/Fe/C ternary system. The composition of the combustion products was found to be different from the equilibrium one, which is manifested in the presence of defects in the carbon sublattice of titanium carbide. A probable explanation of the deficiency of carbon is proposed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 4, pp. 39–43, July–August, 2008.     

Kinetics of crystal nucleation of Na<Subscript>2</Subscript>O · 2CaO · 3SiO<Subscript>2</Subscript>-based solid solutions in glasses of the Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript>—CaSiO<Subscript>3</Subscript> pseudobinary join

The kinetics of crystal nucleation is investigated in sodium calcium silicate glasses of two compositions (22.4 and 24.4 mol % Na₂O), which belong to the Na₂SiO₃—CaSiO₃ pseudobinary join and, according to the phase diagram, lie in the region of the formation of solid solutions between the compositions Na₂O · 2CaO · 3SiO₂ and Na₂O · CaO · 2SiO₂. The stationary rate of crystal nucleation of Na₂O · 2CaO · 3SiO₂-based solid solutions is measured as a function of temperature. It is shown that the maximum stationary rate of nucleation increases with an increase in the sodium oxide content in the initial glasses. The experimental data are analyzed in the framework of the classical nucleation theory.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Soboleva, Yuritsyn, Ugolkov.     

The Structure of Fusion-Cast High-Chrome Oxide Refractories in the Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> - MgO - Al<Subscript>2</Subscript>O<Subscript>3</Subscript> System

The phase composition and structure of fusion-cast refractories composed of 57.0 – 84.2% Cr₂O₃, 4.3 – 36.1% MgO, 2.0 – 9.7% Al₂O₃, and 2.4 – 6.9% SiO₂ have been studied by petrographic and x-ray spectral microprobe analysis methods. Refractories high in MgO with modulus M = (Cr₂O₃ +Al₂O₃)/MgO = 1.64 – 3.1 are shown to consist of spinel phase Mg(Cr, Al)₂O₄ and silicate glass. Refractory materials (80.8 – 84.2% Cr₂O₃, 4.3 – 4.7% MgO, 2.0 – 9.7% Al₂O₃, and 2.7 – 6.9% SiO₂ with M = 18.7 – 20.2) are three-phase systems composed of spinel, escolaite, and glass phase. These materials, owing to their high corrosion resistance, have promising potentiality for practical applications.__________Translated from Novye Ogneupory, No. 12, pp. 69 – 74, December, 2004.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Crystallization of glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The crystallization of strontium borate glasses containing 16.7–43.0 mol % SrO is investigated. New crystalline compounds of the hypothetical compositions 2SrO · 3B₂O₃ (metastable) and SrO · 5B₂O₃ (stable below 750°C), as well as the metastable diborate modification β-SrO · 2B₂O₃, are revealed, and their X-ray powder diffraction data are obtained. It is demonstrated that, with a deficit of strontium oxide, the 4SrO · 7B₂O₃ compound forms solid solutions. Strontium triborate SrO · 3B₂O₃, which was previously prepared only through the dehydration of crystal hydrates, is produced using crystallization of glasses. The thermal stability of this compound is studied. The influence of the dispersity on the stability of different crystalline phases is discussed. Variants of the phase diagram for the SrO · B₂O₃-B₂O₃ system in the case of monolithic and dispersed samples are proposed from analyzing the experimental results and the data available in the literature.     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

Electrical conductivity of CuI-AsI<Subscript>3</Subscript>-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> and CuI-SbI<Subscript>3</Subscript>-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> chalcogenide films prepared by chemical deposition

The electrical conductivity of chalcogenide semiconductor films in the CuI-AsI₃-As₂Se₃ and CuI-SbI₃-As₂Se₃ systems, which have been prepared by chemical deposition from mono-n-butylamine, has been studied as a function of the temperature and film composition. It has been established that the electrical conductivity of the CuI-AsI₃-As₂Se₃ and CuI-SbI₃-As₂Se₃ films is predominantly determined by the copper iodide content. It has been demonstrated that the electrical properties of the chalcogenide glasses and the related films are characterized by the same values to within the experimental error, which is explained by the same model of dissolution of vitreous semiconductors in amines with the retention of the electrical properties of chalcogenide glasses after the deposition of films from their solutions.     

Structure and electrical conductivity of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The temperature-concentration dependence of the electrical conductivity of glasses in the Na₂SO₄-NaPO₃ and Na₂O-P₂O₅ systems has been investigated. Based on the obtained experimental data (IR spectra, density, microhardness, sound velocity, and paper chromatography), it has been demonstrated that SO₄²⁻ ions form terminal groups through the incorporation into polyphosphate fragments of the structure of glasses in the Na₂SO₄-NaPO₃ system. An increase in the electrical conductivity of glasses in this system by a factor of ∼1000 (as compared to NaPO₃) at 25°C and a decrease in the activation energy for electrical conduction from 1.40 to 1.10 eV have been interpreted from the viewpoint of the decrease in the dissociation energy E _d of polar sulfate phosphate structural chemical fragments formed in the glass bulk upon introduction into sodium metaphosphate Na₂SO₄. This leads to an increase in the number of dissociated sodium ions, which are charge carriers, and to a decrease in the energy (E _a) of their activation shift in the sublattice formed by sulfate phosphate fragments of the structure.     

Modeling the methyldiethanolamine-piperazine scrubbing system for CO<Subscript>2</Subscript> removal: Thermodynamic analysis

Aqueous solutions of methyldiethanolamine (MDEA) and piperazine (PZ) are commonly used solvent nowadays. In this work a thermodynamic analysis with the Electrolyte-NRTL model has been performed for systems composed of acidic gases and MDEA + PZ aqueous solution. ASPEN Plus® has been used for thermodynamic modeling. Values of binary interaction parameters for liquid phase activity coefficients have been estimated from regressions of experimental data. Moreover, the influence of the interactions between ion pairs and MDEA or PZ molecular species has been analyzed. The final aim is to obtain a reliable tool for design and simulation of absorption and stripping columns, fundamentals also in order to carry out energy saving studies.

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Investigation into the formation of phases with a Ba<Subscript>2</Subscript>Ti<Subscript>9</Subscript>O<Subscript>20</Subscript>-type structure in the BaO-TiO<Subscript>2</Subscript> and BaO-SrO-TiO<Subscript>2</Subscript> systems

The mechanism of formation of barium titanate Ba₂Ti₉O₂₀ in the BaO-TiO₂ and BaO-SrO-TiO₂ systems is investigated using initial mixtures prepared by three methods, namely, mechanical grinding of the initial reactants, coprecipitation from aqueous solutions of salts, and the sol-gel technique. It is established that, irrespective of the preparation procedure, the formation of Ba₂Ti₉O₂₀ proceeds through the formation of the intermediate phases BaTi₄O₉ and BaTi₅O₁₁. The nature of the intermediate phases is determined by the homogeneity and dispersion of the initial mixture, as well as by the stability of the intermediate phase. The most optimum conditions for the synthesis of Ba₂Ti₉O₂₀ are provided by the formation of BaTi₅O₁₁ as an intermediate phase upon heat treatment of the coprecipitation products in the nanocrystalline state. The metastability and structural defects in the BaTi₅O₁₁ intermediate phase encourage a decrease in the temperature of the final heat treatment by 100–150°C in the course of the preparation of Ba₂Ti₉O₂₀ single-phase ceramics.     

Electronic and magnetic properties of SnO<Subscript>2</Subscript>/CrO<Subscript>2</Subscript> thin superlattices

In this article, using first-principles electronic structure calculations within the spin density functional theory, alternated magnetic and non-magnetic layers of rutile-CrO₂ and rutile-SnO₂ respectively, in a (CrO₂) _n (SnO₂) _n superlattice (SL) configuration, with n being the number of monolayers which are considered equal to 1, 2, ..., 10 are studied. A half-metallic behavior is observed for the (CrO₂) _n (SnO₂) _n SLs for all values of n. The ground state is found to be FM with a magnetic moment of 2 μ_B per chromium atom, and this result does not depend on the number of monolayers n. As the FM rutile-CrO₂ is unstable at ambient temperature, and known to be stabilized when on top of SnO₂, the authors suggest that (CrO₂) _n (SnO₂) _n SLs may be applied to spintronic technologies since they provide efficient spin-polarized carriers.     

Determination of the Specific Heat of the Normal Alkanes C<Subscript>7</Subscript>-C<Subscript>11</Subscript>

Using precise experimental data on the specific heat at constant pressure C _p of the normal alkanes C₇-C₁₁ over a wide parameter range, the C _p values are determined on the liquid and vapor branches of the boundary curve from the normal boiling point to 0.98T _c. In the coordinates C _p-P _s-T _s, orthogonal projections of the reduced phase diagram of these hydrocarbons are constructed and analyzed. Existing generalized expressions for C _p of the liquid and gas phases of the normal alkanes C₅-C₁₁ on the boundary curve as a function of temperature are evaluated, and new expressions for C _p are proposed.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 4, 2005, pp. 476–480.Original Russian Text Copyright © 2005 by Kuznetsov, Gorbachev.     

Phase equilibria in the LaAlO<Subscript>3</Subscript>-LaSrAlO<Subscript>4</Subscript> system

The phase equilibria are investigated and the phase diagram is constructed for the LaAlO₃-LaSrAlO₄ pseudobinary join of the La₂O₃-SrO-Al₂O₃ ternary oxide system. One ternary compound, namely, La₂SrAl₂O₇, is found in the LaAlO₃-LaSrAlO₄ join. The crystallographic, thermal, and some other physicochemical characteristics of the compounds are reported.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Popova, Tugova, Zvereva, Gusarov.