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.

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.

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.

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.

High-temperature mass spectrometric study of thermodynamic properties in the UO2 -ZrO2 system.

RATIONALE: The UO2 -ZrO2 solid solution at high temperatures is the key system of modern nuclear science and technology in the context of the safety operation of nuclear cycles, the consequences of severe accidents, and the incorporation of nuclear waste. Urgent needs of the continuation of experimental studies of this system at temperatures up to 3000 K are aimed at preventing severe accidents similar to Chernobyl and Fukushima when the thermodynamic approach is used for the prediction of high-temperature behavior of materials. METHODS: This investigation was carried out using the Knudsen effusion mass spectrometric method using the MS-1301 magnetic sector mass spectrometer. The samples in the UO2 -ZrO2 system were vaporized from a tungsten effusion cell. Vapor species effusing from the cell were ionized at an electron ionization energy of 70 eV. RESULTS: The vaporization and thermodynamics of pure UO2 and ZrO2 as well as of the samples in the UO2 -ZrO2 system were studied in the range 2000-2730 K. The temperature dependences of the partial vapor pressures of UO and UO2 over pure UO2 were obtained at 2060-2456 K, which agreed with the literature results. The partial vapor pressures of UO, UO2 , ZrO, and ZrO2 , the vaporization rates, and the UO2 and ZrO2 activities in the UO2 -ZrO2 solid solutions were determined at 2370, 2490, 2570, and 2730 K. CONCLUSIONS: The component activities and excess Gibbs energies of the UO2 -ZrO2 system indicated a change in deviations from the ideal behavior from positive to negative with the temperature increase from 2370 to 2730 K. The thermodynamic functions of formation from the oxides of the solid solutions in the UO2 -ZrO2 system such as Gibbs energies as well as the enthalpies and entropies of formation were obtained for the first time at 2550 K in the composition range 0.89-1.00 ZrO2 mole fraction.

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.

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.

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.

High-temperature mass spectrometric study of the vaporization processes and thermodynamic properties in the Gd2 O3 -Y2 O3 -HfO2 system.

RATIONALE: The refractory properties of the Gd2 O3 -Y2 O3 -HfO2 system are considered promising for the production of many high-temperature materials, e.g., thermal barrier coatings and casting molds for gas turbine engine blades. At high temperatures, components of the Gd2 O3 -Y2 O3 -HfO2 system may vaporize selectively and this may significantly change the physicochemical properties of the materials. Therefore, information on vaporization processes and thermodynamic properties of the Gd2 O3 -Y2 O3 -HfO2 system is of great importance. METHODS: The vaporization processes and thermodynamic properties of the Gd2 O3 -Y2 O3 -HfO2 system were studied using high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using a tungsten twin effusion cell containing the samples under study and pure Gd2 O3 as a reference substance. Electron ionization at an energy of 25 eV was employed in the present study. RESULTS: It was shown that at a temperature of 2500 K the vapor over the samples in the Gd2 O3 -Y2 O3 -HfO2 system consisted of the GdO, YO and O vapor species. The Gd2 O3 and Y2 O3 activities in the samples in the Gd2 O3 -Y2 O3 -HfO2 system as well as their vaporization rates were derived from the partial pressures of the vapor species. Using these data the HfO2 activities, the Gibbs energy of mixing and the excess Gibbs energy in this system were calculated at 2500 K. CONCLUSIONS: The thermodynamic properties of the Gd2 O3 -Y2 O3 -HfO2 system, i.e., the component activities in the samples and the excess Gibbs energy, obtained in the present study at 2500 K, exhibited negative deviations from ideal behavior. The concentration dependence of excess Gibbs energy of the Gd2 O3 -Y2 O3 -HfO2 system was approximated with an empirical equation. Copyright © 2017 John Wiley & Sons, Ltd.

Mass spectrometric study of thermodynamic properties in the Gd2 O3 -Y2 O3 system at high temperatures.

RATIONALE: The Gd2 O3 -Y2 O3 system possesses a number of practical applications, one of the most important of them being production of casting molds for gas turbine engine blades. The components of this system are often added to zirconia or hafnia to obtain high-temperature ceramics which are used for the development of thermal barrier coatings. However, Gd2 O3 and Y2 O3 are more volatile than zirconia or hafnia and may vaporize selectively during synthesis or usage of high-temperature materials which may lead to changes in their physicochemical properties. Therefore, information on the vaporization processes and thermodynamic properties of the Gd2 O3 -Y2 O3 system is of great importance. METHODS: High-temperature Knudsen effusion mass spectrometry was used to study the vaporization processes and to determine the thermodynamic properties of the Gd2 O3 -Y2 O3 system. Measurements were performed with a MS-1301 mass spectrometer. Vaporization was carried out using a tungsten twin effusion cell containing the sample under study and pure Gd2 O3 as a reference substance. Electron ionization at an energy of 25 eV was employed. RESULTS: At the temperature of 2630 K, GdO, YO and O vapor species were identified over the samples in the Gd2 O3 -Y2 O3 system. The Gd2 O3 and Y2 O3 activities and the vaporization rates of samples as functions of composition in the Gd2 O3 -Y2 O3 system were derived from the partial pressures of the vapor species mentioned. Using these data the Gibbs energy of mixing and excess Gibbs energy of the hexagonal solid solution in this system were calculated at 2630 K. CONCLUSIONS: The thermodynamic properties of the Gd2 O3 -Y2 O3 system, such as the activities of components and the excess Gibbs energy, obtained in the present study using Knudsen mass spectrometry at 2630 K, demonstrated significant negative deviations from ideal behavior. The vaporization rates of the samples were found to decrease as the Y2 O3 content increased. Copyright © 2016 John Wiley & Sons, Ltd.

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.

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.