Vaporization and thermodynamic properties of lanthanum hafnate

Лопатин

et al. 2021

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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 Cs2O–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 Cs2O–MoO3 system is important. Methods Synthesis of the compounds in the Cs2O–MoO3 system was carried out by sintering Cs2MoO4 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 Cs2MoO4 in the ranges 870–1000 K and 1030–1198 K, respectively. MoO3, Mo2O6, Mo3O9, Mo4O12, and Mo5O15 were shown to be the main vapor species over the Cs2O–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 Cs2O–MoO3 system found in the study evidenced negative deviations from ideality. The MoO3 and Cs2MoO4 partial molar enthalpies of mixing, the Cs2MoO4 partial vaporization enthalpy, and the total enthalpy of mixing in the Cs2O–MoO3 system at 1000 K were obtained for the first time.

Section: Methodsmentioning

confidence: 99%

Vaporization and thermodynamics of the Cs₂O–MoO₃ system studied using high‐temperature mass spectrometry

Лопатин

et al. 2021

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“…Determination of the partial pressures of the vapor species over the samples was performed according to the Hertz‐Knudsen equation:

p ((), i) = \frac{q_{i}}{stL} \sqrt{\frac{2 πRT}{M_{i}}},

where q i is the mass of the sample that vaporized in the form of the i vapor species with the mole mass M i during vaporization time t at temperature T , L is the Clausing coefficient, R is the gas constant, and s is the area of the effusion orifice. The features of the application and limitations of the complete isothermal vaporization method for evaluation of the composition changes in multicomponent samples because of selective vaporization of components have been considered repeatedly …”

Section: Methodsmentioning

confidence: 99%

Vaporization and thermodynamics of ceramics in the Y₂O₃‐ZrO₂‐HfO₂ system

Каблов

et al. 2019

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Rationale:The Y 2 O 3 -ZrO 2 -HfO 2 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 Y 2 O 3 -ZrO 2 -HfO 2 system is of great importance. The thermodynamic properties of the Y 2 O 3 -ZrO 2 -HfO 2 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 Y 2 O 3 -ZrO 2 -HfO 2 system was shown to consist of the YO, ZrO, ZrO 2 , HfO and O vapor species at a temperature of 2660 K. The YO, ZrO, ZrO 2 , 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 Y 2 O 3 , ZrO 2 and HfO 2 , Gibbs energies of mixing and excess Gibbs energies of the Y 2 O 3 -ZrO 2 -HfO 2 system at 2660 K. Conclusions: Negative deviations from the ideal behavior were shown in the solid solutions of the Y 2 O 3 -ZrO 2 -HfO 2 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 Y 2 O 3 -ZrO 2 -HfO 2 system was considered.

“…Selective La 2 O 3 vaporization was found to take place at that temperature, and the condensed phase was enriched with HfO 2 . Significant negative deviations from ideal behavior were shown in the solid solutions in the La 2 O 3 ‐HfO 2 system at 2445 K …”

Section: Introductionmentioning

confidence: 99%

“…that the main vapor species over pure HfO 2 over the wide temperature range 2250-3040 K are HfO and O. The temperature dependence of the The vaporization and thermodynamics in the La 2 O 3 -HfO 2 system were studied by the high-temperature mass spectrometric method in the concentration range from La 2 Hf 2 O 7 to pure hafnia at a temperature of 2445 K 34. Selective La 2 O 3 vaporization was found to take place at that temperature, and the condensed phase was enriched with HfO 2 .…”

mentioning

confidence: 99%

Vaporization and thermodynamics of ceramics based on the La₂O₃‐Y₂O₃‐HfO₂ system studied by the high‐temperature mass spectrometric method

Каблов

et al. 2018

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Vaporization of ceramics based on the La O -Y O -HfO system at 2337 K led to selective transition of La O and Y O to the gaseous phase, with the La O vaporization rate being higher than that of Y O . 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 La O -Y O -HfO system by the Kohler method was shown.