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Materials based on the GdSamples of ceramics in the GdAt the temperature of 2600 K, the GdO, ZrO, ZrOAt 2600 K the Gd

The evolutionary development of structural heat-resistant superalloys has led to creation of high-temperature niobium-silicon based natural composite materials (CM) which are promising for manufacturing of aircraft gas turbine engine blades with an operating temperature of up to 1350°C. To impart the necessary properties (heat resistance, heat resistance, creep resistance, fracture toughness, manufacturability, etc.) CM are doped with modifiers, e.g., B, Ge, Sn, Zr. When using the technology of mechanical alloying for production of niobium-silicon based composites Fe and Ni can enter the material as technical impurities. The quality of materials is the first concern in the aerospace industry. Accurate determination the matrix, alloying and impurity elements in the CM composition is necessary for quality control of the semi-products and off-the-shelf CM. We improved the method of ICP AES with microwave sample preparation for determination of the chemical composition of niobium-silicon based composite materials. The analytical lines of B, Ge, Sn, Zr, Fe, and Ni free of significant spectral overlap are used. The range of the determinable contents (wt.%) is: Nb — 40 – 80; B, Ge, Zr — 1 – 5; Sn — 1 – 2.5; Fe — 0.01 – 10; Ni — 0.01 – 5. To evaluate the metrological characteristics of the method, model solutions similar in composition to the composites analyzed, prepared from certified solutions of the ions, were used as reference samples. State standard reference samples of ferroniobium and titanium alloys similar in composition to Nb – Si based CM were used to verify the accuracy of the technique in spiked tests. The repeatability and intermediate precision indices did not exceed 2 and 4 %rel., respectively, for all the elements studied.

The SmThe thermodynamic properties of the SmIt was shown that, at temperatures below 2500 K, the main vapor species over the ceramics based on the SmThe 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 Sm

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.

The ceramics based on the Y2O3-ZrO2 system is promising for development of refractory materials including ultra-high temperature ceramics. In the present study the samples of the Y2O3-ZrO2 system were synthesized by the solid-state method. The vaporization processes and thermodynamic properties of the Y2O3-ZrO2 system were studied by the Knudsen effusion mass spectrometric method. The vapor composition, the YO, ZrO, ZrO2 and O partial pressures over the samples as well as the Y2O3 and ZrO2 activities of the Y2O3-ZrO2 system were determined at the temperature 2660 K. Thermodynamic properties (i.e. excess Gibbs energies) of the Y2O3-ZrO2 system obtained in the present study can be described in terms of the subregular solution model.

Rationale The 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 the 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 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.

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 SmCeramics based on the SmThe main vapor species over the SmThe data obtained in this study showed negative deviations from the ideal behavior in the Sm

The purpose of the present study was to examine the thermodynamic properties and vaporization processes in the Sm2O3–ZrO2 system by the Knudsen effusion mass spectrometric method (KEMS). The samples in the system under consideration were synthesized by the solid-state method using a high-energy ball mill. Vapor over the Sm2O3–ZrO2 system consisted of SmO, Sm, and O in the temperature range 2200–2540 K. Concentration dependences of the SmO and Sm partial vapor pressures, the component activities, and excess Gibbs energies were obtained at a temperature of 2452 K in the compositional range of 0.23–0.73 Sm2O3 mole fraction. These data evidenced negative deviations from the ideal behavior and a possibility to use the subregular solution model to describe the concentration dependences of the thermodynamic properties in the Sm2O3–ZrO2 system. Correlations were found between the observed changes in the thermodynamic behavior of the system mentioned and the relative number of bonds when the second coordination sphere was taken into consideration in the condensed phase calculated by the Generalized Lattice Theory of Associated Solutions.

RATIONALE The refractory properties of the Gd2O3-Y2O3-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 Gd2O3-Y2O3-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 Gd2O3-Y2O3-HfO2 system is of great importance. METHODS The vaporization processes and thermodynamic properties of the Gd2O3-Y2O3-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 Gd2O3 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 Gd2O3-Y2O3-HfO2 system consisted of the GdO, YO and O vapor species. The Gd2O3 and Y2O3 activities in the samples in the Gd2O3-Y2O3-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 Gd2O3-Y2O3-HfO2 system, i.e., the components 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 Gd2O3-Y2O3-HfO2 system was approximated with an empirical equation.

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.

The SmThe 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 SmIt was shown that at a temperature of 2373 K, selective vaporization of SmThe Sm

The YThe 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.The gaseous phase over the samples of the YNegative deviations from the ideal behavior were shown in the solid solutions of the Y

Materials based on the LaVaporization processes and thermodynamic properties in the LaAt 2337 K the main vapor species over samples in the LaVaporization of ceramics based on the La

The refractory properties of the GdThe vaporization processes and thermodynamic properties of the GdIt was shown that at a temperature of 2500 K the vapor over the samples in the GdThe thermodynamic properties of the Gd

The GdHigh-temperature Knudsen effusion mass spectrometry was used to study the vaporization processes and to determine the thermodynamic properties of the GdAt the temperature of 2630 K, GdO, YO and O vapor species were identified over the samples in the GdThe thermodynamic properties of the Gd