Knudsen Effusion Mass Spectrometric Method Research Articles

Development of the High‐Temperature Knudsen Effusion Mass Spectrometry in the Nordic Countries

In this article, a brief review of the development of the Knudsen effusion mass spectrometric (KEMS) approach in the Theoretical Metallurgy Department of the KTH Royal Institute of Technology and in the in the Laboratory of Metallurgy of the Helsinki University of Technology and modifications of quadrupole model QMG420 mass spectrometers, is presented. The thermodynamic data obtained from vaporization of standards, such as NaCl, CsCl, B2O3, and Ag, and of the B2O3–Al2O3 and ZnO–P2O5 systems is compared with the data obtained using a magnetic MS1301 mass spectrometer. For the first time, composition of the vapor phase over the Dy2O3–DyF3, CaO–CaCl2, and Cu–Mg systems and the partial pressures of components at high temperatures are investigated. The experimental data obtained for the investigated systems are used for prediction of the vaporization processes and modeling of thermodynamic properties and high‐temperature phase equilibria in the multicomponent systems used in metallurgy. An account is given of the detailed studies of the vaporization processes and thermodynamic properties of some multicomponent systems composed of oxides, fluorides, and carbonates forming mold powders for continuous casting of steel. Some new directions of the ongoing studies by the KEMS method are summarized.

Molecular structure, thermodynamic and spectral characteristics of chloroboron(III) subphthalocyanine and its dodecafluorinated derivative

A comprehensive study of the structural, spectral and energetic properties of chloroboron(III) complexes of subphthalocyanine (H[Formula: see text]SubPc, for the first time) and dodecafluorosubphthalocyanine (F[Formula: see text]SubPc, reinvestigation) was performed by mass-spectroscopy (MS), gas-phase electron diffraction (GED), IR spectroscopy and quantum-chemical (QC) calculations. A synchronous GED/MS method showed that at T = 630 K and T = 540 K, thermally stable H[Formula: see text]SubPc and F[Formula: see text]SubPc molecular forms are present in the gas phase. The geometric structure of free molecules has been determined, in which the N3-B-Cl fragment has the structure of a distorted tetrahedron, and the phthalocyanine skeleton has a dome shape. QC calculations of the geometry agree well with the GED results. The similarities and differences of the molecular structure in the gas and solid phases were discussed. It is shown, that despite the similarity of most geometric parameters, the H[Formula: see text]SubPc and F[Formula: see text]SubPc have significant differences in electronic characteristics, which determines the differences in their physicochemical properties. The interpretation of the experimental IR spectra was carried out. The distribution of potential energy of normal vibrations over the internal vibrational coordinates has been analyzed. The sublimation enthalpies of H[Formula: see text]SubPc ([Formula: see text]H[Formula: see text](589 K) = 135(5) kJ ⋅ mol[Formula: see text] and F[Formula: see text]SubPc ([Formula: see text]H[Formula: see text](516 K) = 189(3) kJ ⋅ mol[Formula: see text] were determined by the mass spectrometric Knudsen effusion method. The obtained data is important for designing processes employed in fabricating optoelectronic devices based on subphthalocyanines by PVD. Experimental geometric parameters for free molecules and vibrational frequencies can be used to calculate the thermodynamic functions of gaseous H[Formula: see text]SubPc and F[Formula: see text]SubPc.

High‐temperature Mass Spectrometric Study and Modeling of the Thermodynamic Properties of the TiO2‐SiO2‐ZrO2 System

AbstractDevelopment 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.

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

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. 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). 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. Significant negative deviations from the ideality were observed in the melts of the SrO-Al2 O3 system at 2450, 2550, and 2650 K. The Wilson polynomial was found to be the optimal approach to describe the thermodynamic properties in the system studied. Optimization of the experimental data using the GLTAS approach allowed the characteristic features of the thermodynamic description of the SrO-Al2 O3 system to be elucidated and explained.

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

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

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

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. 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. 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. 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.

Thermodynamics and vaporization of ceramics based on the Gd2O3-ZrO2 and Gd2O3-HfO2 systems studied by KEMS

Thermodynamic properties and vaporization processes of the Gd2O3-HfO2 and Gd2O3-ZrO2 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, ZrO2, 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 Gd2O3-HfO2 and Gd2O3-ZrO2 systems and the relative number of bonds formed in the condensed phase when the second coordination sphere was taken into consideration.

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

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. 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. 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. 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.

The hafnia-based ceramics containing lanthana or samaria: Mass spectrometric study and calculation of the thermodynamic properties at high temperatures

The thermodynamic properties and vaporization processes of the ceramics based on the La2O3-Y2O3-ZrO2-HfO2 and Sm2O3-Y2O3-ZrO2-HfO2 systems were studied using the Knudsen effusion mass spectrometric method (KEMS) at high temperatures. The ceramic samples in the systems mentioned were synthesized by the solid-state method. Vapor composition over the samples studied, the partial pressures of the vapor species, vaporization rates, and the lanthanoid oxide activities were determined in the temperature ranges 2339–2459 K and 2373–2461 K for the lanthana-containing and samaria-containing systems, respectively. The samples in the La2O3-Y2O3-ZrO2-HfO2 system were shown to be more volatile than those in the Sm2O3-Y2O3-ZrO2-HfO2 system. The data obtained evidenced negative deviations from the ideal behavior in the systems mentioned. Experimental thermodynamic data found at the temperature 2373 K were compared with the corresponding values calculated using the semi-empirical Kohler, Redlich-Kister, and Wilson approaches, as well as the Generalized Lattice Theory of Associated Solutions (GLTAS). It was shown that the data calculated by the semi-empirical methods were underestimated as compared to experimental values obtained using KEMS. It should be underlined that modeling based on GLTAS allowed more reliable data on the lanthanoid oxide activities in hafnia-based ceramics containing lanthana and samaria to be obtained in comparison with the semi-empirical methods mentioned.

Thermodynamics and vaporization of the Sm2O3–ZrO2 system studied by Knudsen effusion mass spectrometry

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.

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

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. 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. 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. 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.

Thermodynamic approach for prediction of oxide materials properties at high temperatures

Abstract Modern high-temperature technologies and methods of production of advanced materials impose new requirements on the quality of information on physicochemical properties of oxide systems at high temperatures. Normally, thermodynamic approach for these purposes is the most fundamental and essential. Great attention was paid by M.M. Shultz to extensive development of this approach in the studies of oxide melts, crystals, glasses, ceramics, and coatings using calorimetric, EMF, and high temperature mass spectrometric methods. Advantages of the thermodynamic approach were illustrated by examples of application of the Knudsen effusion mass spectrometric method to studies of oxide systems and materials, which were crucial for the further development of space and aviation industry, energetics, instrument making, communication engineering, metallurgy, energy-saving, and environmental safety. In the discussion of the regularities of vaporization processes and changes of thermodynamic properties in oxide systems, a number of particular systems based on silica and hafnia was considered in detail. Modeling was carried out for these systems using the Generalized Lattice Theory of Associated Solutions. The obtained results assert a necessity for creation of the national thermodynamic data- and model bases essential for further prediction of phase equilibria in oxide systems and materials at high temperatures.

Ceramics based on the Sm2O3–Y2O3 and Sm2O3–HfO2 systems at high temperatures: Thermodynamics and modeling

Ceramics based on the Sm2O3–Y2O3 and Sm2O3–HfO2 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 Sm2O3–Y2O3 and Sm2O3–HfO2 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 Sm2O3 in the temperature range 2265–2668 K and over Sm2Hf2O7 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 Sm2O3–Y2O3 and Sm2O3-HfO2 systems at the temperature 2373 K. These thermodynamic functions exhibited negative deviations from the ideality and were compared with the data available for the La2O3–Y2O3, Gd2O3–Y2O3, ZrO2–Y2O3 and La2O3–HfO2, Gd2O3–HfO2, Nd2O3–HfO2 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.

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

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. 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. 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. 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.

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. 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. 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. 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.

Mass-Spectrometric Study of Evaporation of Perovskite

The evaporation of perovskite CaTiO3 at 1700–2200 K was studied by the high-temperature mass-spectrometric Knudsen effusion method. The molecular components typical of simple oxides and a small amount of complex gaseous oxide CaTiO3 were identified in the gas phase over perovskite. The partial vapor pressures of the molecular components of the gas phase over perovskite were compared with those corresponding to simple oxides; it was found that the character of evaporation of perovskite is mainly affected by the calcium component.

Thermodynamics and vaporization of ceramics based on the Y2O3-ZrO2 system studied by KEMS

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.

Thermodynamic description of the Gd2O3-Y2O3-HfO2 and La2O3-Y2O3-HfO2 systems at high temperatures

Thermodynamic properties of the Gd2O3-Y2O3-HfO2 and La2O3-Y2O3-HfO2 systems were obtained by Knudsen effusion mass spectrometric method at the temperatures 2500 K and 2337 K, respectively. Description of the thermodynamic properties of these systems was obtained using the Barker theory. It was illustrated that negative deviations from the ideality in these systems were related to the formation of the Me-O-Y and Y-O-Hf bonds in the solid solutions. Accuracy of the optimization of the thermodynamic data in the Gd2O3-Y2O3-HfO2 system using the Barker theory was checked in comparison with the traditional Redlich-Kister approximation approach.

Thermodynamic properties of the La2O3-HfO2 system at high temperatures

The La2O3-HfO2 system is a base for many advanced materials used in high temperature technologies and nuclear industry. Information on vaporization processes and thermodynamic properties of ceramics based on the La2O3-HfO2 system is important to prevent the La2O3 selective vaporization during their synthesis or usage. The study was carried out by the Knudsen effusion mass spectrometric method. At 2337 K LaO and O were the main vapor species over the samples in the La2O3-HfO2 system. The dependence of the La2O3 activities on composition in the La2O3-HfO2 system was obtained by the differential mass spectrometric method. The HfO2 activities, excess Gibbs energies and Gibbs energies of mixing were evaluated in the solid solutions of the La2O3-HfO2 system at 2337 K using the Gibbs-Duhem equation and showed significant negative deviations from ideality. The solid solution presumably with the pyrochlore structure was characterized with the strongest negative deviations.

Mass Spectrometry Study of the Thermodynamic Properties of Spinel Solid Solutions

The partial pressure values of vapor species over spinel solid solutions and the boundary of the solid spinel solutions in the MgAl2O4 (solid solution) + Al2O3 region are determined on the basis of the data obtained by Knudsen effusion mass spectrometric method in the temperature range 2000–2200 K. The obtained thermodynamic information is compared to the information available in the literature. The values of oxide activities, Gibbs energies, enthalpies and entropies of formation of solid solutions show a slightly negative deviations from ideality.