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.

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.

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.

Development of Novel Polyamide-Imide/DES Composites and Their Application for Pervaporation and Gas Separation.

Novel polymer composites based on polyamide-imide Torlon and deep eutectic solvent (DES) were fabricated and adapted for separation processes. DES composed of zinc chloride and acetamide in a ratio of 1:3 M was first chosen as a Torlon-modifier due to the possibility of creating composites with a uniform filling of the DES through the formation of hydrogen bonds. The structure of the membranes was investigated by scanning electron microscopy and X-ray diffraction analysis; thermal stability was determined by thermogravimetric analysis and mass spectrometry. The surface of the composites was studied by determining the contact angles and calculating the surface tension. The transport properties were investigated by such membrane methods as pervaporation and gas separation. It was found that the inclusion of DES in the polymer matrix leads to a significant change in the structure and surface character of composites. It was also shown that DES plays the role of a plasticizer and increases the separation performance in the separation of liquids and gases. Torlon/DES composites with a small amount of modifier were effective in alcohol dehydration, and were permeable predominantly to water impurities in isopropanol. Torlon/DES-5 demonstrates high selectivity in the gas separation of O2/N2 mixture.

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.

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.

Asymmetric Membranes Based on Copolyheteroarylenes with Imide, Biquinoline, and Oxazinone Units: Formation and Characterization.

Modern ultrafiltration requires novel perfect membranes with narrow pore size, high porosity, and minimal pore tortuosity to achieve high separation performance. In this work, copolyamic acid (co-PAA) was synthesized and used for the preparation of asymmetric porous membranes by phase inversion technique. Several co-PAA membranes were heated up to 250 °C; during heating, they undergo solid-phase transformation into co-polybenzoxazinoneimide (co-PBOI) via dehydration and cyclization. Comparative characterization of both co-PAA and co-PBOI membranes was realized by scanning electron microscopy, mechanical testing, thermogravimetric analysis, and ultrafiltration experiments. Membrane calibration was carried out using a mixture of seven proteins with different molecular weights. During heat treatment, the molecular weight cut-off of the membranes decreased from 20 × 103 g/mol (co-PAA) to 3 × 103 g/mol (co-PBOI). Abnormally low dispersions of rejection (0.3 for co-PAA and 0.45 for co-PBOI) were observed for the studied membranes; this fact indicates that the membranes possess enhanced resolving power.

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.

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.

Evaluation of relative electron ionization cross-sections for some oxides and oxyacid salts.

RATIONALE: The total or relative cross-sections for the ionization of polyatomic molecules by electron ionization are essential data in a wide range of applications. In addition to the total ionization cross-sections, relative ionization cross-sections are sometimes also required. Accurate values of electron ionization cross-sections of high-temperature vapor species are of importance in mass spectrometric investigations. So the need for experimental ionization cross-section data for high-temperature vapor species is vital. METHODS: Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum or tungsten effusion cells containing samples of pure Au and CeO2 . The vapor compositions over the CeO2 -Mo and CeO2 -W systems were determined by Knudsen effusion mass spectrometry. The method of ion currents comparison was used to measure partial pressures. The enthalpies of the reactions under study were calculated using the third law procedure. RESULTS: The standard formation enthalpies of cerium molybdates and tungstates were determined from the relative ionization cross-sections of molybdenum, tungstate, cerium, and cerium salts. Cross-sections were calculated by different methods: simple adding atomic cross-sections with correction factor, using known ratios of complex ions, adding oxide cross sections. The traditional approach to determination of ionization cross-sections exploiting the values of atomic cross-sections and the additivity rules as well as literature experimental data was used. CONCLUSIONS: The enthalpies of formation of gaseous cerium molybdates and tungstates were evaluated by measurements of the reaction enthalpies for several independent reactions. The best agreement was obtained with the data from the analysis of experimentally determined relative ionization cross-sections, and using ionization cross-sections of polyatomic molecules recommended by Drowart et al. The widely used additivity method, in spite of the additional corrections introduced, gives the worst convergence of the values under consideration.

High-temperature mass spectrometric study of the vaporization processes and thermodynamic properties of samples in the Bi2 O3 -P2 O5 -SiO2 system.

RATIONALE: The Bi2 O3 -P2 O5 -SiO2 system possesses a number of valuable properties that may be of use for various practical applications, both for obtaining new materials, e.g. optical fibers, and for replacing systems based on toxic lead silicate. Information on vaporization processes and thermodynamic properties obtained in the present study will be useful for the development of synthetic methods and approaches for modeling the thermodynamic properties of materials based on this system. METHODS: High-temperature Knudsen effusion mass spectrometry was used to study the vaporization processes and to determine the thermodynamic properties of the components in the Bi2 O3 -P2 O5 -SiO2 system. Measurements were performed with a MS-1301 magnetic sector mass spectrometer. Vaporization was carried out using an iridium-plated molybdenum twin effusion cell containing the sample under study and pure bismuth(III) oxide as a reference substance. Electron ionization at an energy of 30 eV was employed in the study. RESULTS: At a temperature of 950 K, Bi and O2 were found to be the main vapor species over the samples studied. The Bi2 O3 activity as a function of composition in the Bi2 O3 -P2 O5 -SiO2 system was derived from the obtained Bi partial pressures. The excess Gibbs energy of the system studied was calculated at 950 K and 1273 K. The possibility of using the Kohler method for the calculation of thermodynamic properties in the Bi2 O3 -P2 O5 -SiO2 system was illustrated. CONCLUSIONS: The excess Gibbs energy of the Bi2 O3 -P2 O5 -SiO2 system obtained in the present study using the Knudsen mass spectrometric method at 950 K and 1273 K demonstrated significant negative deviations from ideal behavior. The excess Gibbs energy values calculated by the Kohler method were shown to be in good agreement with those obtained from experimental data. Copyright © 2016 John Wiley & Sons, Ltd.

Thermodynamics of gaseous barium cerate studied by Knudsen effusion mass spectrometry.

RATIONALE: BaCeO3 species, which are known to be excellent proton conductors, are potential candidates as electrolytes in hydrogen concentrators and fuel cells. Oxides of barium and cerium, with their reactivity can, in turn, form gaseous associates - complex molecules with two different types of atoms (not including oxygen). To predict the possibility of the existence of gaseous associates formed by barium and cerium oxides it is important to know their thermodynamic characteristics. Until the present investigation, gaseous cerates were unknown. METHODS: High-temperature Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species over the BaO-CeO2 system, and the formation enthalpies of gaseous CeO2 and BaCeO3 were derived. Measurements of partial pressures and reaction enthalpies were performed with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum and tungsten effusion cells containing the samples under study and pure gold as a reference substance. A theoretical study of gaseous cerium dioxide and barium cerate was performed by several quantum chemical methods: DFT M06, DFT PBE0 and MP2. RESULTS: In the temperature range 1900-2120 K, CeO and CeO2 were found to be the main vapor species over the solid CeO2 . Ba, BaO, CeO, CeO2 and BaCeO3 species were found in the vapor over the BaO-CeO2 mixture. On the basis of the equilibrium constant of the gaseous reaction BaO + CeO2  = BaCeO3 , the standard formation enthalpy of gaseous BaCeO3 (-1065 ± 25 kJ/mol) at 298  K was determined. Energetically favorable structures of gaseous CeO2 and BaCeO3 were found and vibrational frequencies were evaluated in the harmonic approximation. CONCLUSIONS: The stability of BaCeO3 gaseous species was confirmed by high-temperature mass spectrometry. Gas-phase reactions involving gaseous barium and cerium oxides with gaseous barium cerate were studied. The enthalpies of the formation reactions of gaseous barium cerate from gaseous BaO and CeO2 were evaluated theoretically and the obtained values were in agreement with the experimental ones. Copyright © 2016 John Wiley & Sons, Ltd.

Thermodynamic study of gaseous tin molybdates by high-temperature mass spectrometry.

RATIONALE: Molybdenum and tin are components of various construction materials which are often used at high temperature and in an oxidizing atmosphere. Oxides of molybdenum and tin, with their high reactivity, can, in their turn, form a number of gaseous compounds. To predict the possibility of the existence of gaseous associates formed by tin and molybdenum oxides it is important to know their thermodynamic characteristics. Until the present investigation only a few gaseous salts of tin were known. METHODS: High-temperature Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species over the SnO(2) -MoO(3) system. The formation enthalpies of gaseous SnMoO(4), Sn(2) MoO(5) and SnMo(2)O(7) were derived. Measurements were performed with a MS-1301 mass spectrometer. Vaporization was carried out using a molybdenum effusion cell containing the samples under study and pure gold as the reference substance. A theoretical study of gaseous tin molybdates was performed by several quantum chemical methods: wave function based explicitly correlated F12 methods and DFT M0(6) methods. RESULTS: In the temperature range of 1200-1400 K, SnO, Sn(2)O(2), SnMoO(4), Sn(2) MoO(5), SnMo(2)O(7), MoO(3), Mo(2)O(6) and Mo(3)O(9) were found to be the main vapor species over the samples studied. On the basis of the equilibrium constants of gaseous reactions, the standard formation enthalpies of gaseous SnMoO(4) (-699 ± 29 kJ/mol), Sn(2) MoO(5) (-1001 ± 38 kJ/mol) and SnMo(2)O(7) (-1456 ± 60 kJ/mol) at 298 K were determined. Energetically favorable structures were found and vibrational frequencies were evaluated in the harmonic approximation. CONCLUSIONS: The stability of gaseous species, SnMoO(4), Sn(2) MoO(5) and SnMo(2)O(7), was confirmed by high-temperature mass spectrometry. A number of gas-phase reactions involving tin-containing gaseous salts were studied. The enthalpies of reactions of gaseous tin molybdates were evaluated theoretically and the obtained values are in agreement with those obtained experimentally.

Gaseous titanium molybdates and tungstates: thermodynamic properties and structures.

RATIONALE: Titanium is a component of various construction materials, which is often used at high temperature and in an oxidizing atmosphere. Thermally stable even at high temperatures, titanium compounds may appear in the condensed phase. To predict the possibility of existence of gaseous associates formed by titanium oxides it is important to know their thermodynamic characteristics. Until the present investigation no gaseous salts of titanium were known. METHODS: Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum and tungsten effusion cells containing samples of pure Au, Ti3O5 and SiO2. A theoretical study of gaseous titanium molybdates and tungstates in different spin states was performed by quantum chemical density functional theory (DFT) B3LYP and M06 methods. RESULTS: On the basis of the equilibrium constants of gaseous reactions, the standard formation enthalpies of gaseous TiMoO3 (-424 ± 28 kJ/mol), TiWO3 (-400 ± 22 kJ/mol), TiMoO4 (-795 ± 29 kJ/mol), TiWO4 (-750 ± 24 kJ/mol), TiMoO5 (-1146 ± 23 kJ/mol) and TiWO5 (-1125 ± 22 kJ/mol) at 298 K were determined. Energetically favorable structures were localized and vibrational frequencies were evaluated in the harmonic approximation. Natural atomic charges, bond orders, and valence indices were calculated for all relevant structures. CONCLUSIONS: The stability of gaseous species TiMoOn and TiWOn (n = 3, 4, 5) was confirmed by high-temperature mass spectrometry. A number of gas-phase reactions involving titanium-containing gaseous salts were studied. Enthalpies of reactions of gaseous TiXOn (X = Mo, W; n = 3, 4, 5) formation were evaluated theoretically and the obtained values are in agreement with the experimental ones.

Mass spectrometric study of thermodynamic properties in the Yb2O3-ZrO2 system at high temperatures.

RATIONALE: Materials based on the Yb2O3-ZrO2 system have many industrial applications such as high-temperature solid electrolytes, ceramics with special properties and most importantly for thermal barrier coatings. As their synthesis and use take place at high temperatures, information on the vaporization processes, thermodynamic properties and phase equilibria of this system at high temperatures is of great importance. METHODS: Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using two tungsten effusion cells containing the sample under study and pure Yb2O3. The values of component activities in the Yb2O3-ZrO2 system were also calculated using the CALPHAD approach. RESULTS: The Yb and O vapor species were identified over the samples studied at 2400 K. Using these data the ZrO2 activities, chemical potentials of components and the Gibbs energies of the solid solution formation were calculated in this system. The thermodynamic values were also obtained as the result of modeling of the Yb2O3-ZrO2 system based on the CALPHAD approach using the data available on the phase diagram of this system and calorimetric measurements only. CONCLUSIONS: The thermodynamic functions found in the Yb2O3-ZrO2 system at 2400 K, such as the activities of components and the Gibbs energy of formation, displayed negative deviation from ideality. Mutual agreement was observed between the experimental thermodynamic values and the results of calculations based on the CALPHAD approach.

High-temperature mass spectrometric determinations of relative ionization cross-sections of gaseous TiO, TiO2, VO, VO2, YO, HfO and GeO molecules.

RATIONALE: Accurate values of electron ionization cross-sections of high-temperature vapor species are of importance in mass spectrometric investigations as well as in a variety of other fields. However, the present experimental techniques are subject to many inherent difficulties or are limited in applicability and so far have yielded relatively few reliable values. Theoretical calculations are not sufficiently accurate. So the need for experimental ionization cross-section data for these species is very important. METHODS: Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum effusion cells containing samples of pure Au, V2O3, Ti3O5, GeO2 and Y2O3-HfO2 systems. RESULTS: The VO, VO2, TiO, TiO2, YO, HfO and GeO vapor species were identified over the samples studied. The partial pressures of Au and the oxides were measured by a complete isothermal vaporization method. The relative ionization cross-sections σ(Au)/σ(i) were determined for the gaseous oxides studied. The results were compared with the literature data. CONCLUSIONS: The inapplicability of the 'additivity rule' is shown. This finding is in good agreement with a tendency to changing ionization cross-sections in the Periodic Table row of gaseous M, МО and МО2 species.