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Development of the advanced materials based on the TiO2‐SiO2‐ZrO2 system is hindered by lack of the information on its thermodynamic properties and phase equilibria. In the present study, the samples in the TiO2‐SiO2‐ZrO2 system were prepared by solid‐state synthesis and analyzed by X‐ray microanalysis, fluorescence, and diffraction techniques. The thermodynamic properties in this system were evaluated by Knudsen effusion mass spectrometric (KEMS) method and optimized within the generalized lattice theory of associated solutions (GLTAS). The main vapor species over the silica‐containing samples vaporized from the tungsten cell at the temperature 1973 K were SiO, O, WO2, and WO3. The vapor over the samples in the TiO2‐ZrO2 system at 2356 K was composed mainly of TiO, TiO2, O, WO2, and WO3. The activity of components in the samples and the partial pressures of the identified vapor species were determined. At 1973 K, the TiO2‐SiO2‐ZrO2 system is characterized by positive deviations from the ideality. The observed weak dependence of the SiO2 activity on the SiO2 content suggests the presence of a broad field of immiscibility on the phase diagram in the concentration range 40–100 mol. % SiO2. The thermodynamic data on the TiO2‐SiO2‐ZrO2 system obtained by KEMS can be of great value for calculation of the phase equilibria. [ABSTRACT FROM AUTHOR]

Rationale: The SrO–Al2O3 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–Al2O3 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–Al2O3 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–Al2O3 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–Al2O3 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–Al2O3 system to be elucidated and explained. [ABSTRACT FROM AUTHOR]

Rationale: Materials based on the Al2O3‐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 Al2O3‐SiO2‐ZrO2 materials. Methods: Samples of ceramics in the Al2O3‐SiO2‐ZrO2 system, including the Al2O3‐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, Al2O, 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 Al2O3‐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 Al2O3‐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. [ABSTRACT FROM AUTHOR]

Rationale: The TiO2–Al2O3–SiO2 system is the base for various glass–ceramic materials, which have great practical value for a large number of modern technologies. Many TiO2–Al2O3–SiO2 materials are synthesized or applied at high temperatures, which justifies the relevance of the present study. Methods: The samples in the TiO2–Al2O3–SiO2 system were synthesized using the method of induction melting in a cold crucible. The thermodynamic properties of the TiO2–Al2O3–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–Al2O3–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–Al2O3–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. [ABSTRACT FROM AUTHOR]

Rationale: Materials based on the Gd2O3‐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 Gd2O3‐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 Gd2O3 activity was determined. On this experimental basis, modeling within the GLTAS approach was performed. It allowed the evaluation of the Gd2O3, 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 Gd2O3‐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. [ABSTRACT FROM AUTHOR]

Rationale: The Sm2O3-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 Sm2O3-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 Sm2O3-ZrO2-HfO2 system were SmO, Sm, and O corresponding to vapor composition over pure Sm2O3. The SmO, Sm, and O partial vapor pressures over the samples and the Sm2O3 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 Sm2O3-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 Sm2O3 mole fraction less and higher than 0.32, respectively. The self-consistent thermodynamic description of the Sm2O3-ZrO2-HfO2 system was derived at high temperatures by optimization of the experimental results using the GLTAS. [ABSTRACT FROM AUTHOR]

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 Sm2O3‐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 Sm2O3‐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 Sm2O3‐ZrO2‐HfO2 system were shown to be SmO, Sm, and O at a temperature of 2373 K, indicating selective vaporization of Sm2O3 from the samples. The partial pressures of these vapor species and the Sm2O3 activities were determined in the Sm2O3‐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 Sm2O3‐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 Sm2O3‐ZrO2‐HfO2 system by the high‐temperature mass spectrometric method. [ABSTRACT FROM AUTHOR]

Thermodynamic properties and vaporization processes of the Gd 2 O 3 -HfO 2 and Gd 2 O 3 -ZrO 2 systems were studied by the Knudsen effusion mass spectrometric method (KEMS). The samples used in the present study were synthesized by sintering of pure oxides. The vapor species over the systems at the temperature 2600 K were GdO, ZrO, HfO, ZrO 2 , and atomic oxygen. The partial pressures of the vapor species, the component activities, and the excess Gibbs energies were obtained in the binary systems studied. It was illustrated that thermodynamic properties found in both systems had the negative deviations from ideality. The thermodynamic data found in the present study were also discussed using the results of modeling of the component activities based on the generalized lattice theory of associated solutions. Correlations were shown between the observed changes in the thermodynamic behavior of the Gd 2 O 3 -HfO 2 and Gd 2 O 3 -ZrO 2 systems and the relative number of bonds formed in the condensed phase when the second coordination sphere was taken into consideration. • Vapor composition was identified over the Gd 2 O 3 -HfO 2 and Gd 2 O 3 -ZrO 2 systems. • Vapor pressures and component activities were found in the samples at 2600 K. • The activity data were optimized using the Barker theory. • Negative deviations from ideality in the Gd 2 O 3 -HfO 2 and Gd 2 O 3 -ZrO 2 systems were shown. • Correlation between thermodynamic properties and numbers of bonds was established. [ABSTRACT FROM AUTHOR]

Ceramics based on the Sm 2 O 3 –Y 2 O 3 and Sm 2 O 3 –HfO 2 systems is promising for development of advanced refractory materials including casting molds for gas turbine engine blades and thermal barrier coatings. Vaporization processes and thermodynamic properties of the Sm 2 O 3 –Y 2 O 3 and Sm 2 O 3 –HfO 2 systems were studied by the Knudsen effusion mass spectrometric method. The samples used in the present study were synthesized by the solid-state method. Composition of the vapor over these systems at the temperature 2373 K was the same as over pure oxides. Temperature dependences of the partial pressures of the SmO and Sm vapor species were obtained over pure Sm 2 O 3 in the temperature range 2265–2668 K and over Sm 2 Hf 2 O 7 in the temperature range 2222–2650 K. The partial pressures of the vapor species, the component activities, and the excess Gibbs energies were determined over a wide concentration ranges in the Sm 2 O 3 –Y 2 O 3 and Sm 2 O 3 -HfO 2 systems at the temperature 2373 K. These thermodynamic functions exhibited negative deviations from the ideality and were compared with the data available for the La 2 O 3 –Y 2 O 3 , Gd 2 O 3 –Y 2 O 3 , ZrO 2 –Y 2 O 3 and La 2 O 3 –HfO 2 , Gd 2 O 3 –HfO 2 , Nd 2 O 3 –HfO 2 systems. Thermodynamic properties of these binary systems containing yttria and hafnia with rare earth oxides were discussed in the frame of the Generalized Lattice Theory of Associated Solutions. Correlations were found between the observed changes in the thermodynamic behavior of the systems mentioned and the relative number of bonds in the condensed phases when the second coordination sphere was taken into consideration. • Vapor compositions were identified over Sm 2 O 3 –Y 2 O 3 and Sm 2 O 3 –HfO 2 systems. • Partial pressures of vapor species and component activities were determined at 2373 K. • Excess Gibbs energies indicated negative deviations from ideality in the systems considered. • Correlation between thermodynamic properties and calculated number of bonds was shown. • The results were compared with the data for other yttria- and hafnia-containing systems. [ABSTRACT FROM AUTHOR]