Mass spectrometric study and modeling of the thermodynamic properties of SrO-Al2 O3 melts at high temperatures.

RATIONALE: The SrO-Al2 O3 system holds promise as a base for a wide spectrum of advanced materials, which may be synthesized or applied at high temperatures. Therefore, studying vaporization and high-temperature thermodynamic properties of this system is of great practical importance. METHODS: Samples of the SrO-Al2 O3 system were obtained by solid-state synthesis and identified by X-ray fluorescence analysis, X-ray phase analysis, scanning electron microscopy, electron probe microanalysis, simultaneous thermal analysis, and thermogravimetric analysis. The thermodynamic properties of the SrO-Al2 O3 system were studied by the Knudsen effusion mass spectrometric (KEMS) method and were fitted by the Redlich-Kister and Wilson polynomials. The thermodynamic values obtained were also optimized within the generalized lattice theory of associated solutions (GLTAS). RESULTS: The vapor composition, temperature, and concentration dependences of the partial vapor pressures over the samples under study as well as the SrO activities in melts of the SrO-Al2 O3 system were determined by the KEMS method. Usage of the Redlich-Kister and Wilson polynomials allowed calculation of the excess Gibbs energies, enthalpies of mixing, and excess entropies in the concentration range 0-33 mol% of SrO at temperatures of 2450 and 2550 K. CONCLUSIONS: Significant negative deviations from the ideality were observed in the melts of the SrO-Al2 O3 system at 2450, 2550, and 2650 K. The Wilson polynomial was found to be the optimal approach to describe the thermodynamic properties in the system studied. Optimization of the experimental data using the GLTAS approach allowed the characteristic features of the thermodynamic description of the SrO-Al2 O3 system to be elucidated and explained.

High-temperature mass spectrometric study and modeling of ceramics based on the Al2 O3 -SiO2 -ZrO2 system.

RATIONALE: Materials based on the Al2 O3 -SiO2 -ZrO2 system are promising for a wide range of high-temperature technological applications, such as thermal barrier coatings in the aviation and space industry or advanced materials in nuclear power reactors. Experimental studies of the ceramics based on this system by the Knudsen effusion mass spectrometric (KEMS) method are of significant interest in designing technological processes for the synthesis and exploitation of the Al2 O3 -SiO2 -ZrO2 materials. METHODS: Samples of ceramics in the Al2 O3 -SiO2 -ZrO2 system, including the Al2 O3 -ZrO2 and SiO2 -ZrO2 binaries, were prepared by solid-state synthesis. Analysis of the samples was performed by X-ray fluorescence and diffraction techniques. The vapor composition and thermodynamic properties of the components in this system were determined by KEMS. The derived thermodynamic functions were optimized within the generalized lattice theory of associated solutions (GLTAS). RESULTS: In the temperature range 1900-2600 K, the SiO, Al, AlO, Al2 O, ZrO, ZrO2 , and O vapor species were identified over the samples in the systems under study. For the thermodynamic properties to be determined correctly, the samples of the Al2 O3 -SiO2 -ZrO2 system had to be vaporized at temperatures less than 2000 K, where data could be obtained only for the SiO species. The SiO2 activities obtained were taken as the experimental basis for the modeling within the GLTAS approach. This allowed evaluation of the component activities and excess Gibbs energy, and assessment of the relative number of bonds of different types. CONCLUSIONS: At 1920 K, the Al2 O3 -SiO2 -ZrO2 system is characterized by negative deviations of its thermodynamic properties from the ideal behavior. The consistency of the obtained modeling results was illustrated by comparison of the values derived from the data for the ternary and the boundary binary systems and thereby indicates the reasonable uniformity of the energy parameters of the lattice model derived in the calculations, which may be used in further modeling of multicomponent systems.

Constitutive chitosanase from Bacillus thuringiensis B-387 and its potential for preparation of antimicrobial chitooligomers.

The article proves the ability of the entomopathogenic strain B. thuringiensis var. dendrolimus B-387 to high the constitutive production (3-12.5 U/mL) of extracellular chitosanase, that was found for the first time. The enzyme was purified in 94-fold by ultrafiltration, affinity sorption and cation-exchange chromatography and characterized biochemically. The molecular mass of the chitosanase determined using SDS-PAGE is 40 kDa. Temperature and pH-optima of the enzyme are 55 °C and pH 6.5, respectively; the chitosanase was stable under 50-60 °C and pH 4-10.5. Purified chitosanase most rapidly (Vmax ~ 43 µM/mL × min, KM ~ 0.22 mg/mL, kcat ~ 4.79 × 104 s-1) hydrolyzed soluble chitosan of the deacetylation degree (DD) 85% by endo-mode, and did not degrade colloidal chitin, CM-cellulose and some other glucans. The main reaction products of the chitosan enzymolysis included chitobiose, chitotriose and chitotetraose. In addition to small chitooligosaccharides (CHOs), the studied chitosanase also generated low-molecular weight chitosan (LMWC) with average Mw in range 14-46 kDa and recovery 14-35%, depending on the enzyme/substrate ratio and incubation temperature. In some cases, the chitosan (DD 85 and 50%) oligomers prepared using crude chitosanase from B. thuringiensis B-387 indicated higher antifungal and antibacterial activities in vitro in comparison with the initial polysaccharides. The data obtained indicate the good prospect of chitosanase B-387 for the production of bioactive CHOs.

High-temperature mass spectrometric study of thermodynamic properties in the TiO2 -Al2 O3 -SiO2 system and modeling.

RATIONALE: The TiO2 -Al2 O3 -SiO2 system is the base for various glass-ceramic materials, which have great practical value for a large number of modern technologies. Many TiO2 -Al2 O3 -SiO2 materials are synthesized or applied at high temperatures, which justifies the relevance of the present study. METHODS: The samples in the TiO2 -Al2 O3 -SiO2 system were synthesized using the method of induction melting in a cold crucible. The thermodynamic properties of the TiO2 -Al2 O3 -SiO2 system were studied using the Knudsen effusion mass spectrometric method. The derived thermodynamic functions were optimized within the generalized lattice theory of associated solutions (GLTAS) approach and compared with the results of calculation using the semiempirical Kohler, Muggianu, Toop, Redlich-Kister, and Wilson methods based on the corresponding data in the binary systems. RESULTS: The SiO2 selective vaporization from the samples under study was shown at temperatures above 1940 K. The thermodynamic properties in the TiO2 -Al2 O3 -SiO2 system, including the TiO2 -SiO2 system, were obtained in the temperature range 1965-2012 K and were optimized using GLTAS to obtain the consistent concentration dependences of the component activities and excess Gibbs energies. CONCLUSIONS: Positive deviations from the ideal behavior were observed in the TiO2 -Al2 O3 -SiO2 system at high temperatures. Comparison of these values with the results of the modeling based on the GLTAS approach allowed the recommendations regarding the optimal semiempirical methods for the excess Gibbs energy calculation in different concentration ranges to be made.

Mass spectrometric study and modeling of the thermodynamic properties in the Gd2 O3 -ZrO2 -HfO2 system at high temperatures.

RATIONALE: Materials based on the Gd2 O3 -ZrO2 -HfO2 system are promising for a wide range of high-temperature technological applications, such as for obtaining thermal barrier coatings in the aviation and space industry, as well as advanced materials in nuclear power applications. Experimental studies of the ceramics based on this system by the Knudsen effusion mass spectrometric method provides such valuable information as the vapor composition over the samples and enables derivation of the thermodynamic functions. METHODS: Samples of ceramics in the Gd2 O3 -ZrO2 -HfO2 system were synthesized and analyzed by X-ray fluorescence and diffraction techniques. The vaporization processes and partial pressures of the vapor species over the samples were obtained by the high-temperature mass spectrometric method using the ion current comparison method. The derived thermodynamic functions were optimized within the Generalized Lattice Theory of Associated Solutions (GLTAS) approach. RESULTS: At the temperature of 2600 K, the GdO, ZrO, ZrO2 , HfO, and O vapor species were found over the samples, but only for the GdO and ZrO species were accurate experimental data on the partial pressures obtained. In all the ceramic samples, the Gd2 O3 activity was determined. On this experimental basis, modeling within the GLTAS approach was performed. It allowed the evaluation of the Gd2 O3 , ZrO2 , and HfO2 activities in the system under study and a rough approximation of the excess Gibbs energy as a function of composition to be obtained. CONCLUSIONS: At 2600 K the Gd2 O3 -ZrO2 -HfO2 system is characterized by negative deviations of its thermodynamic properties from the ideal behavior. Consistency of the obtained modeling results indicate reasonable uniformity of the energy parameters of the lattice model derived in calculations of the hafnia-containing oxide systems, which may be used in further modeling of multicomponent systems.

Vaporization and thermodynamic properties of the SrO-Al2 O3 system studied by Knudsen effusion mass spectrometry.

RATIONALE: Strontium aluminates can be used as refractory construction materials at temperatures up to 2000°Ð¡ or as the materials for immobilization of long-lived radioactive waste. The SrО-Al2 O3 system is one of the more complicated oxide systems used for the creation of new radio-transparent materials. The exploitation of such materials at high temperatures demands the knowledge of the thermal stability of the compounds and solid solutions formed in the SrО-Al2 O3 system. METHODS: The synthesis of the samples in the SrO-Al2 O3 system was carried out by a ceramic method at 1250°C. The characterization of the samples was accomplished with the use of X-ray diffraction (XRD). The vaporization of the samples under study was performed from a twin tungsten effusion cell using the Knudsen effusion mass spectrometry method. RESULTS: The temperature dependences of partial pressures of vapor species over 4SrO·Al2 O3 , 3SrO·Al2 O3 , SrO·Al2 O3 , SrO·2Al2 O3 and SrO·6Al2 O3 in a wide range of temperatures were determined. The component activities, the Gibbs energies of mixing and the standard enthalpies of individual strontium aluminates were obtained. CONCLUSIONS: The thermodynamic properties of the SrO-Al2 O3 system at high temperatures are characterized by negative deviation from ideality. The vaporization processes and thermodynamic properties of the SrO-Al2 O3 system were obtained for the first time.

Simple method for ultrasound assisted «click¼ modification of azido-chitosan derivatives by CuAAC.

New quaternized chitosan derivatives HT-TMC were synthesized as a result of copper catalyzed azide-alkyne [3 + 2] cycloaddition (CuAAC). The structure of the HT-TMC was verified by 2D NMR. The synthesis was carried out as a result of the formation of Cu(I) in situ, under the action of ultrasound in aerobic conditions in the presence of acetic acid and metallic copper (copper turnings). The new derivatives were characterized by increased pH range of solubility (DS range 18-76%) and the presence of antibacterial and fungicidal activities. The proposed catalytic system makes it possible to easily and efficiently obtain new derivatives of chitosan as a result of ultrasound-promoted CuAAC.

Evaluation of Antibacterial and Antifungal Properties of Low Molecular Weight Chitosan Extracted from Hermetia illucens Relative to Crab Chitosan.

This study shows the research on the depolymerisation of insect and crab chitosans using novel enzymes. Enzyme preparations containing recombinant chitinase Chi 418 from Trichoderma harzianum, chitinase Chi 403, and chitosanase Chi 402 from Myceliophthora thermophila, all belonging to the family GH18 of glycosyl hydrolases, were used to depolymerise a biopolymer, resulting in a range of chitosans with average molecular weights (Mw) of 6-21 kDa. The depolymerised chitosans obtained from crustaceans and insects were studied, and their antibacterial and antifungal properties were evaluated. The results proved the significance of the chitosan's origin, showing the potential of Hermetia illucens as a new source of low molecular weight chitosan with an improved biological activity.

High-temperature mass spectrometric study of the thermodynamic properties in the Sm2 O3 -ZrO2 -HfO2 system.

RATIONALE: The Sm2 O3 -ZrO2 -HfO2 system is a promising base for the development of a wide spectrum of new refractory materials. Reliable data on thermodynamic properties in this system are of significant importance for planning the preparation and application of high-temperature ceramics. Especially, they can be useful for calculation of the unknown phase equilibria in this system. METHODS: The thermodynamic properties of the Sm2 O3 -ZrO2 -HfO2 system were studied by the high-temperature mass spectrometric method. The samples in the system under consideration synthesized by the solid-state method were vaporized from a tungsten twin effusion cell using a MS-1301 magnetic sector mass spectrometer. Ionization of the vapor species effusing from the cell was carried out by electrons at an energy of 25 eV. RESULTS: It was shown that, at temperatures below 2500 K, the main vapor species over the ceramics based on the Sm2 O3 -ZrO2 -HfO2 system were SmO, Sm, and O corresponding to vapor composition over pure Sm2 O3 . The SmO, Sm, and O partial vapor pressures over the samples and the Sm2 O3 activities were obtained in the temperature range 2319-2530 K. This allowed the excess Gibbs energy values to be determined. For comparison, the excess Gibbs energies in the Sm2 O3 -ZrO2 -HfO2 system were also calculated by the semi-empirical Kohler, Toop, Redlich-Kister, and Wilson methods and optimized by the statistical thermodynamic Generalized Lattice Theory of Associated Solutions (GLTAS). CONCLUSIONS: The thermodynamic data calculated by the semi-empirical approaches at 2423 K were shown to be lower than the experimental values. However, the Toop and Wilson methods were found to be useful for evaluation of the excess Gibbs energy values at the Sm2 O3 mole fraction less and higher than 0.32, respectively. The self-consistent thermodynamic description of the Sm2 O3 -ZrO2 -HfO2 system was derived at high temperatures by optimization of the experimental results using the GLTAS.

Vaporization and thermodynamics of the Cs2 O-MoO3 system studied using high-temperature mass spectrometry.

RATIONALE: Cesium and molybdenum are fission products of uranium dioxide fuel in nuclear reactors, which interact with each other depending on the oxygen potential of the fuel. This leads to formation of various compounds of the Cs2 O-MoO3 system, which are exposed to high temperatures during operation of a reactor or a severe accident at a nuclear power plant. This is why the study of the vaporization and thermodynamics of compounds in the Cs2 O-MoO3 system is important. METHODS: Synthesis of the compounds in the Cs2 O-MoO3 system was carried out by sintering Cs2 MoO4 and MoO3 . Characterization of the samples was accomplished with the use of XRD, TGA/DSC/DTA, IR spectroscopy, and ICP emission spectroscopy. Vaporization of the samples under study was carried out from a platinum effusion cell using an MS-1301 mass spectrometer developed for high-temperature studies of low-volatility substances. RESULTS: The temperature dependences of partial pressures of vapor species were determined over pure MoO3 and Cs2 MoO4 in the ranges 870-1000 K and 1030-1198 K, respectively. MoO3 , Mo2 O6 , Mo3 O9 , Mo4 O12 , and Mo5 O15 were shown to be the main vapor species over the Cs2 O-MoO3 system in the temperature range 850-1020 K. The component activities, Gibbs energies of mixing, and excess Gibbs energies were obtained as functions of the component concentration at 900, 950, and 1000 K. CONCLUSIONS: The thermodynamic properties of the Cs2 O-MoO3 system found in the study evidenced negative deviations from ideality. The MoO3 and Cs2 MoO4 partial molar enthalpies of mixing, the Cs2 MoO4 partial vaporization enthalpy, and the total enthalpy of mixing in the Cs2 O-MoO3 system at 1000 K were obtained for the first time.

High-temperature mass spectrometric study of vaporization and thermodynamics of the Cs2 O-B2 O3 system: Review and experimental investigation.

RATIONALE: The compounds in the Cs2 O-B2 O3 system are of particular interest for nuclear applications since cesium borates may be formed during accidents in nuclear reactors, affecting the rate of release of radiotoxic isotopes into the environment. Thus, information on the vaporization and thermodynamic properties of cesium borates is necessary for simulation and modeling of the isotope release processes taking place during the nuclear reactor accidents. METHODS: Compounds in the Cs2 O-B2 O3 system were synthesized by the co-crystallization method with subsequent sintering. The sample characterization was carried out using XRD, TGA/DSC/DTA, IR spectroscopy, and ICP atomic emission spectroscopy. The vaporization and thermodynamics of the samples under consideration were investigated using an MS-1301 mass spectrometer and a single molybdenum effusion cell. The electron ionization method was employed for ionization of the vapor species with an electron energy of 30 eV. The scale of the ionizing voltage was calibrated according to the traditional technique by measuring the appearance energy of gold in the mass spectrum of the vapor over pure gold. RESULTS: The main vapor species over the samples in the Cs2 O-B2 O3 system were CsBO2 and Cs2 B2 O4 in the temperature range 789-1215 K and in the concentration range 0.1-0.5 mole fraction of Cs2 O. The temperature dependences of the CsBO2 and Cs2 B2 O4 partial pressures over cesium borate were obtained in the temperature range 767-990 K. The CsBO2 and B2 O3 activities, the Gibbs energies of mixing, the excess Gibbs energies, the partial mole enthalpies of mixing, and total enthalpies of mixing were determined as functions of temperature and composition of the condensed phase. CONCLUSIONS: As the Cs2 O and B2 O3 activity values evidenced, negative deviations from the ideal behavior were observed in the Cs2 O-B2 O3 system in the temperature range 800-1000 K. The total enthalpies of mixing and the Gibbs energies of mixing in the Cs2 O-B2 O3 system were compared with the literature data, illustrating their mutual agreement.

Mass spectrometric study of ceramics in the Sm2 O3 -ZrO2 -HfO2 system at high temperatures.

RATIONALE: Systems containing zirconia, hafnia, and rare earth oxides are indispensable in various areas of high-temperature technologies as a basis of ultra-high refractory ceramics. Exposure of these materials to high temperatures may result in unexpected selective vaporization of components or phase transitions in the condensed phase leading to changes in physicochemical properties. Consequently, reliable application of the ceramics based on systems such as Sm2 O3 -ZrO2 -HfO2 is impossible without data on its vaporization processes and thermodynamic properties, which may be used to predict the physicochemical characteristics of the ultra-high refractory ceramics. METHODS: Ceramics based on the Sm2 O3 -ZrO2 -HfO2 system were obtained by solid-state synthesis and characterized by X-ray fluorescence and X-ray phase analyses. The vaporization and thermodynamics of the system considered were examined by the high-temperature mass spectrometric method using a MS-1301 magnetic sector mass spectrometer with a tungsten twin effusion cell. Vapor species effusing from the cell were ionized by electrons with an energy of 25 eV. RESULTS: The main vapor species over the Sm2 O3 -ZrO2 -HfO2 system were shown to be SmO, Sm, and O at a temperature of 2373 K, indicating selective vaporization of Sm2 O3 from the samples. The partial pressures of these vapor species and the Sm2 O3 activities were determined in the Sm2 O3 -ZrO2 -HfO2 system and allowed the excess Gibbs energies to be evaluated. These excess Gibbs energy values were compared with the results obtained by the semi-empirical and statistical thermodynamic approaches. CONCLUSIONS: The data obtained in this study showed negative deviations from the ideal behavior in the Sm2 O3 -ZrO2 -HfO2 system at 2373 K. The results calculated according to the semi-empirical methods and statistical thermodynamic Generalized Lattice Theory of Associated Solutions were in agreement with each other. Thus, this evidenced the desirability of further experimental investigation of the Sm2 O3 -ZrO2 -HfO2 system by the high-temperature mass spectrometric method.

Obtaining chitin, chitosan and their melanin complexes from insects.

Interest in insects as a source of valuable biologically active substances has significantly increased over the past few years. Insects serve as an alternative source of chitin, which forms up to 40% of their exoskeleton. Chitosan, a deacetylated derivative of chitin, attracts the attention of scientists due to its unique properties (sorption, antimicrobial, film-forming, wound healing). Furthermore, some insect species are unique and can be used to obtain chitin- and chitosan-melanin complexes in the later stages of ontogenesis. Due to the synergistic effect, chitosan and melanin can enhance each other's biological activity, providing a wide range of potential applications.

Thermodynamic properties of gaseous BaSnO2 and Ba2 O2 studied by Knudsen effusion mass spectrometry.

RATIONALE: BaSnO3 is an interesting technical and industrial ceramic, with uses in many areas of electronic technology. Currently, there is great interest in this ceramic material because of its potential as a transparent conductive oxide. Due to its good chemical stability, it is also used as a surface processing material in the synthesis of electroluminophores. When heated, the stannates of alkaline earth metals can pass into the vapor phase with or without dissociation. Until the present investigation, gaseous salts where SnO plays the role of an anion-forming oxide had been unknown. The formation enthalpy of gaseous Ba2 O2 also needed to be determined. METHODS: Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species, equilibrium constants and enthalpies of the studied gas-phase reactions, as well as the formation and atomization enthalpies of gaseous BaSnO2 and Ba2 O2 : a mixture of BaO and SnO2 was evaporated from a platinum effusion cell. For the evaporation of gold (pressure standard), a molybdenum effusion cell was used. A theoretical study of gaseous BaSnO2 and Ba2 O2 was performed by several quantum chemistry methods. RESULTS: Ba, BaO, Ba2 O2 , SnO and BaSnO2 were found to be the main species in the vapor over the BaO-SnO2 mixture in the temperature range of 1680-1920 K. The standard formation enthalpies of gaseous BaSnO2 and Ba2 O2 were determined on the basis of the equilibrium constants of the studied gas-phase reactions. Energetically favorable structures of these gaseous species were found and vibrational frequencies were evaluated in the harmonic approximation. The formation enthalpy of gaseous Ba2 O2 was clarified; in addition, the formation enthalpies of gaseous SrSnO3 and CaSnO3 were estimated. CONCLUSIONS: The thermal stability of gaseous BaSnO2 was confirmed by Knudsen effusion mass spectrometry. The reaction enthalpies of gaseous BaSnO2 from gaseous barium and tin oxides were theoretically evaluated and the obtained values were found to be in reasonable agreement with the experimental ones.

Vaporization and thermodynamics of ceramics in the Sm2 O3 -Y2 O3 -HfO2 system.

RATIONALE: The Sm2 O3 -Y2 O3 -HfO2 system holds promise for applications in the sphere of high-temperature technologies, particularly the development of ultra-high-temperature ceramics. However, the reliability of refractory materials is dependent on the possible selective vaporization of their components leading to changes in their physicochemical properties. Thus, information about vaporization processes and thermodynamic properties of ceramics based on the Sm2 O3 -Y2 O3 -HfO2 system may be of importance for the production of high-temperature materials as well as for the prediction of the physicochemical properties of ultra-high-temperature ceramics. METHODS: The Knudsen effusion mass spectrometric method was used, with an MS-1301 magnetic mass spectrometer equipped with a tungsten twin effusion cell used to examine the samples in the Sm2 O3 -Y2 O3 -HfO2 system. Electron ionization of vapor species effusing from the cell was carried out at an ionization energy of 25 eV. RESULTS: It was shown that at a temperature of 2373 K, selective vaporization of Sm2 O3 and Y2 O3 occurred in the samples of the Sm2 O3 -Y2 O3 -HfO2 system, with the main vapor species being SmO, Sm, YO, and O. The partial pressures of these vapor species were obtained by the ion current comparison method. The Sm2 O3 activities in the Sm2 O3 -Y2 O3 -HfO2 system were determined and allowed the evaluation of the excess Gibbs energies at 2373 K. The direction of change of the condensed phase of the samples because of selective vaporization of the components was examined. CONCLUSIONS: The Sm2 O3 -Y2 O3 -HfO2 system was characterized by negative deviations from the ideal behavior at 2373 K. The excess Gibbs energies evaluated in the present study were approximated using the Redlich-Kister representation and visualized in the form of curves of constant values in the concentration triangle. The data obtained in the Sm2 O3 -Y2 O3 -HfO2 system were optimized using the Barker-Guggenheim theory of associated solutions.

Thermochemical study of gaseous indium-arsenic sulfosalt.

RATIONALE: Sulfide systems are often used at high temperatures, when vaporization of the components is enabled. Sulfide ores are used as sources of various metals and nonmetals and gaseous sulfides, and sulfosalts may also play a role in the atmosphere chemistry of hot rocky exoplanets. To predict the existence and thermal stability of gaseous sulfides and sulfosalts it is important to know their thermodynamic characteristics. In this study the sulfosalt of indium and arsenic was obtained in the gaseous phase for the first time. METHODS: High-temperature Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species over indium and arsenic sulfides. A molybdenum double two-temperature cell was used to create the conditions of coexistence of indium and arsenic sulfides. A theoretical study of gaseous As4 S4 and In2 AsS2 was performed using both B3LYP, M06, PBE0 and TPSSh hybrid DFT functionals and an ab initio wave function-based MP2(Full) method. RESULTS: Gaseous In2 AsS2 has been identified during vaporization of In6 S7 and As2 S3 from the molybdenum double two-temperature cell. The structure and molecular parameters of gaseous In2 AsS2 were determined using quantum chemical calculations. Energetically favorable structures of gaseous In2 S, AsS, As4 S4 and In2 AsS2 were found and vibrational frequencies were evaluated in the harmonic approximation. The formation enthalpy of gaseous In2 AsS2 (186 ± 37 kJ mol-1 ) was derived as a result of measurements of the equilibrium constants of two independent gas-phase reactions. CONCLUSIONS: The gaseous sulfosalt of indium and arsenic was obtained for the first time. The formation enthalpy of the In2 AsS2 (g) molecule at 298 K was evaluated both experimentally and theoretically. The thermal stability of the gaseous sulfosalt is less than that of the gaseous oxyacid salts.

Vaporization and thermodynamics of ceramics in the Y2 O3 -ZrO2 -HfO2 system.

RATIONALE: The Y2 O3 -ZrO2 -HfO2 system is a promising base for a wide range of high-temperature materials including ultra-high-temperature ceramics. At high temperatures of synthesis and application of these ceramics the components may vaporize selectively, leading to changes in chemical composition and exploitation properties of the materials. Therefore, study of the vaporization processes of ceramics based on the Y2 O3 -ZrO2 -HfO2 system is of great importance. The thermodynamic properties of the Y2 O3 -ZrO2 -HfO2 system obtained in the present study can be used for the prediction and modeling of the physicochemical properties of ultra-high-temperature ceramics. METHODS: The present study was carried out by the high-temperature Knudsen effusion mass spectrometric method using the MS-1301 mass spectrometer, which was designed to study the physicochemical properties of non-volatile compounds. Vapor species effusing from the tungsten twin effusion cell, which was used for vaporization of the samples under study, were ionized by electron ionization with an ionization energy of 30 eV. RESULTS: The gaseous phase over the samples of the Y2 O3 -ZrO2 -HfO2 system was shown to consist of the YO, ZrO, ZrO2 , HfO and O vapor species at a temperature of 2660 K. The YO, ZrO, ZrO2 , HfO and O partial vapor pressures were obtained in a wide concentration range by the complete isothermal vaporization method, which allowed determination of the activities of Y2 O3 , ZrO2 and HfO2 , Gibbs energies of mixing and excess Gibbs energies of the Y2 O3 -ZrO2 -HfO2 system at 2660 K. CONCLUSIONS: Negative deviations from the ideal behavior were shown in the solid solutions of the Y2 O3 -ZrO2 -HfO2 system at 2660 K. The excess Gibbs energies found in the present study were approximated using the Redlich-Kister representation. The possibility of application of the Kohler method to estimate the excess Gibbs energies of the Y2 O3 -ZrO2 -HfO2 system was considered.

Thermodynamic properties of gaseous cerium phosphate studied by Knudsen effusion mass spectrometry.

Gaseous CePO2 has been identified by Knudsen effusion mass spectrometry during vaporization of CeO2 and magnesium diphosphate from tungsten double, two-temperature effusion cell. Structure and molecular parameters of gaseous cerium phosphate under study were determined using quantum chemical calculations. On the basis of equilibrium constants measured for gas-phase reaction, standard formation enthalpy of CePO2 was determined to be -508 ± 41 kJ â‹… mol-1 at the temperature 298 K.

Vaporization and thermodynamics of ceramics based on the La2 O3 -Y2 O3 -HfO2 system studied by the high-temperature mass spectrometric method.

RATIONALE: Materials based on the La2 O3 -Y2 O3 -HfO2 system are promising for the production of highly refractory ceramics, e.g., thermal barrier coatings and molds for casting of elements of gas turbine engines. When these ceramics are synthesized or used at high temperatures, selective vaporization of components may take place, resulting in changes in the physicochemical properties of the materials. Consequently, development of materials based on the La2 O3 -Y2 O3 -HfO2 system requires information on vaporization in this system as well as on its thermodynamics, without which prediction and modeling of their physicochemical properties are impossible. METHODS: Vaporization processes and thermodynamic properties in the La2 O3 -Y2 O3 -HfO2 system were studied by the high-temperature Knudsen effusion mass spectrometric method using a MS-1301 mass spectrometer. Electron ionization of vapor species was employed at an ionization energy of 25 eV. The samples under study and reference substances were vaporized from a tungsten twin effusion cell. RESULTS: At 2337 K the main vapor species over samples in the La2 O3 -Y2 O3 -HfO2 system were shown to be LaO, YO and O. The partial pressures of the vapor species mentioned and the La2 O3 and Y2 O3 activities in the samples were obtained at 2337 K. The Gibbs energies of mixing and excess Gibbs energies were found in the solid solution of this system. CONCLUSIONS: Vaporization of ceramics based on the La2 O3 -Y2 O3 -HfO2 system at 2337 K led to selective transition of La2 O3 and Y2 O3 to the gaseous phase, with the La2 O3 vaporization rate being higher than that of Y2 O3 . The directions of composition changes of samples due to their vaporization at 2337 K were determined. In the solid solution of this system negative deviations from ideal behavior were found. The ability to estimate the excess Gibbs energies in the solid solution of the La2 O3 -Y2 O3 -HfO2 system by the Kohler method was shown.

Chitin and Cellulose Processing in Low-Temperature Electron Beam Plasma.

Polysaccharide processing by means of low-temperature Electron Beam Plasma (EBP) is a promising alternative to the time-consuming and environmentally hazardous chemical hydrolysis in oligosaccharide production. The present paper considers mechanisms of the EBP-stimulated destruction of crab shell chitin, cellulose sulfate, and microcrystalline cellulose, as well as characterization of the produced oligosaccharides. The polysaccharide powders were treated in oxygen EBP for 1-20 min at 40 °C in a mixing reactor placed in the zone of the EBP generation. The chemical structure and molecular mass of the oligosaccharides were analyzed by size exclusion and the reversed phase chromatography, FTIR-spectroscopy, XRD-, and NMR-techniques. The EBP action on original polysaccharides reduces their crystallinity index and polymerization degree. Water-soluble products with lower molecular weight chitooligosaccharides (weight-average molecular mass, Mw = 1000-2000 Da and polydispersity index 2.2) and cellulose oligosaccharides with polymerization degrees 3-10 were obtained. The ¹H-NMR analysis revealed 25-40% deacetylation of the EBP-treated chitin and FTIR-spectroscopy detected an increase of carbonyl- and carboxyl-groups in the oligosaccharides produced. Possible reactions of ß-1,4-glycosidic bonds' destruction due to active oxygen species and high-energy electrons are given.