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Rationale: Ceria‐based systems are of great interest because of their unique properties. Such systems may be used as anode materials for SOFCs or in oxygen sensors. The exploitation of these materials often requires high temperatures. In such conditions, the partial or complete evaporation of materials is possible. Therefore, knowledge of the values of partial pressures and thermodynamic properties is essential to predict and/or prevent possible consequences and accidents. Methods: Knudsen effusion mass spectrometry was used to determine partial pressures of vapor species over the SrO–CeO2 and CaO‐CeO2 systems. Measurements of partial pressures were performed with a MS‐1301 mass spectrometer. Vaporization was carried out using molybdenum or tungsten effusion cells. A theoretical study of gaseous strontium and calcium cerates was performed by several quantum chemical methods: density functional theory (DFT) M06, DFT PBE0, and MP2. Results: The minimum value of relative electron ionization cross‐section for CeO2 was estimated. In the temperature range of 2218–2249 K above the SrO‐CeO2 system and of 2128–2208 K above the CaO‐CeO2 system, gaseous M, MO, MO, CeO2, O, O2 and MCeO3 (M = Sr, Ca) were found. Energetically favorable structures of gaseous SrCeO3 and CaCeO3 were found, and vibrational frequencies were evaluated in the "rigid rotor‐harmonic oscillator" approximation. On the basis of the equilibrium constants of gaseous reaction MO + CeO2 = MCeO3, the standard formation enthalpy of gaseous SrCeO3 (−913 ± 26 kJ/mol) and of gaseous CaCeO3 (−917 ± 26 kJ/mol) at 298 K were determined. Conclusions: The estimated value of relative electron ionization cross‐section for CeO2 is in agreement with the general rule applicable for dioxides. The stability of SrCeO3 and CaCeO3 gaseous species was confirmed by KEMS. Gas‐phase reactions involving gaseous SrO (CaO) and CeO2 with gaseous SrCeO3(CaCeO3) were studied. Enthalpy of formation reaction of gaseous SrCeO3(CaCeO3) from gaseous SrO (CaO) were evaluated theoretically, and the obtained value is in agreement with the experimental one. [ABSTRACT FROM AUTHOR]

Rationale: The compounds in the Cs2O‐B2O3 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 Cs2O‐B2O3 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 Cs2O‐B2O3 system were CsBO2 and Cs2B2O4 in the temperature range 789–1215 K and in the concentration range 0.1–0.5 mole fraction of Cs2O. The temperature dependences of the CsBO2 and Cs2B2O4 partial pressures over cesium borate were obtained in the temperature range 767–990 K. The CsBO2 and B2O3 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 Cs2O and B2O3 activity values evidenced, negative deviations from the ideal behavior were observed in the Cs2O‐B2O3 system in the temperature range 800–1000 K. The total enthalpies of mixing and the Gibbs energies of mixing in the Cs2O‐B2O3 system were compared with the literature data, illustrating their mutual agreement. [ABSTRACT FROM AUTHOR]

Rationale: The Sm2O3‐Y2O3‐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 Sm2O3‐Y2O3‐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 Sm2O3‐Y2O3‐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 Sm2O3 and Y2O3 occurred in the samples of the Sm2O3‐Y2O3‐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 Sm2O3 activities in the Sm2O3‐Y2O3‐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 Sm2O3‐Y2O3‐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 Sm2O3‐Y2O3‐HfO2 system were optimized using the Barker‐Guggenheim theory of associated solutions. [ABSTRACT FROM AUTHOR]

Rationale: The Y2O3‐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 Y2O3‐ZrO2‐HfO2 system is of great importance. The thermodynamic properties of the Y2O3‐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 Y2O3‐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 Y2O3, ZrO2 and HfO2, Gibbs energies of mixing and excess Gibbs energies of the Y2O3‐ZrO2‐HfO2 system at 2660 K. Conclusions: Negative deviations from the ideal behavior were shown in the solid solutions of the Y2O3‐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 Y2O3‐ZrO2‐HfO2 system was considered. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 systemmay 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 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 Gd2O3-Y2O3-HfO2 system was approximated with an empirical equation. [ABSTRACT FROM AUTHOR]