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

Vorozhtcov

Лопатин

et al. 2021

Self Cite

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.

Section: Resultsmentioning

confidence: 99%

“…The Sm 2 O 3 activities a Sm 2 O 3 in the Sm 2 O 3 ‐ZrO 2 ‐HfO 2 system were obtained by Equation , as suggested in our earlier studies 38,48 :

a_{{Sm}_{2} O_{3}} = \frac{{I^{3}}_{{SmO}^{+}}}{I {°^{3}}_{{italicSmO}^{+}}} \times \frac{I °_{{italicSm}^{+}}}{I_{{Sm}^{+}}},

where the ° symbol refers to the standard of determination of the Sm 2 O 3 activity.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

(][, {Sm}_{2} O_{3}) = 2 ()(, SmO) + ()(, O),

(][, {Sm}_{2} O_{3}) = 2 ()(, Sm) + 3 ()(, O),

where hereinafter formulae in parentheses and square brackets correspond to the gaseous and condensed phases, respectively.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mass spectrometric study of ceramics in the Sm₂O₃‐ZrO₂‐HfO₂ system at high temperatures

Vorozhtcov

Лопатин

et al. 2021

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High‐temperature mass spectrometric study of the thermodynamic properties in the Sm₂O₃‐ZrO₂‐HfO₂ system

Каблов

Vorozhtcov

et al. 2022

Self Cite

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.

Mass spectrometric study and modeling of the thermodynamic properties in the Gd₂O₃‐ZrO₂‐HfO₂ system at high temperatures

Каблов

Шилов

et al. 2022

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Rationale: Materials based on the Gd 2 O 3 -ZrO 2 -HfO 2 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 Gd 2 O 3 -ZrO 2 -HfO 2 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, ZrO 2 , 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 Gd 2 O 3 activity was determined. On this experimental basis, modeling within the GLTAS approach was performed. It allowed the evaluation of the Gd 2 O 3 , ZrO 2 , and HfO 2 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 Gd 2 O 3 -ZrO 2 -HfO 2 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. | INTRODUCTIONA search for new compositions of the zirconia-hafnia ceramics stabilized by rare earth oxides is interesting, first of all, in view of the advantages they may provide when used as materials for thermal barrier coatings 1-6 and for casting moulds and cores in the production of gas turbine engine blades. [7][8][9] Investigation of the thermodynamic properties of the Gd 2 O 3 -ZrO 2 -HfO 2 ceramics in addition to the data