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

et al. 2020

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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.

([], Y_{2} O_{3}) = 2 ((), YO) + ((), O),

([], {HfO}_{2}) = ((), HfO) + ((), O) .

…”

Section: Introductionmentioning

confidence: 99%

“…The YO partial vapor pressures ( p° ( i )) over Y 2 O 3 and the HfO partial vapor pressures over HfO 2 were determined as functions of temperature in the ranges 2257–2703 K and 2550–2863 K, respectively:

\log p^{o} ((),, YO, Pa) = - \frac{35387 \pm 388}{T} + ((), 13.52 \pm 0.17),

\log p^{o} ((),, HfO, Pa) = - \frac{37922 \pm 773}{T} + ((), 14.08 \pm 0.10) .

…”

Section: Introductionmentioning

confidence: 99%

Vaporization and thermodynamics of ceramics in the Sm₂O₃‐Y₂O₃‐HfO₂ system

Каблов

et al. 2020

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“…The ZrO 2 vaporization processes were investigated using the classical Knudsen effusion method and the Knudsen effusion mass spectrometric approach 42–47,49,50 . Some details of these studies are summarized and presented in Table 2.…”

Section: Introductionmentioning

confidence: 99%

“…According to the results obtained by the Knudsen effusion mass spectrometric method, 45,50 the Zr + , ZrO + , and ZrO 2 + ions were identified in the mass spectra of vapor over ZrO 2 in the temperature range 2600–2900 K. It was shown 45,50 that the Zr + ion was formed in the mass spectra of vapor over ZrO 2 as a product of dissociative ionization. Thus, the ZrO 2 sublimation at the temperature range 2200–2900 K may be described according to the following equations 42–47,49,50 :

([], {ZrO}_{2}) = ((), ZrO) + ((), O),

([], {ZrO}_{2}) = ((), {ZrO}_{2}) .

It was shown 45,51 that, in this temperature range, the congruently subliming zirconia composition under equilibrium conditions in vacuum corresponds to ZrO 1.96 . A detailed discussion of the opportunity to use the partial vapor pressure of ZrO 2 over ZrO 1.96 for thermodynamic calculations was reported by Stolyarova, 52 taking into consideration the experimental results found earlier 45,51 .…”

Section: Introductionmentioning

confidence: 99%

“…The authors 45 underlined that they had to resort in this case to the common practice of the identity of thermodynamic properties of the stoichiometric (ZrO 2 ) and substoichiometric zirconia (ZrO 1.96 ) in the condensed phase. Based on this experimental observation, the thermodynamic activity of zirconia was further determined using the partial pressures of the ZrO 2 vapor species in the binary and ternary zirconia‐containing systems with the following rare‐earth oxides 49,52–59 : Y 2 O 3 , Nd 2 O 3 , Lu 2 O 3 , Pr 2 O 3 , La 2 O 3 , and CeO 2 .…”

Section: Introductionmentioning

confidence: 99%

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High‐temperature mass spectrometric study of thermodynamic properties in the UO₂–ZrO₂ system

Kurata

et al. 2020

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Rationale 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. Methods 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. Results 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. Conclusions 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.

High‐temperature mass spectrometric study of thermodynamic properties in the TiO₂–Al₂O₃–SiO₂ system and modeling

Shemchuk

et al. 2022

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Rationale The TiO2–Al2O3–SiO2 system is the base for various glass–ceramic materials, which have great practical value for a large number of modern technologies. Many TiO2–Al2O3–SiO2 materials are synthesized or applied at high temperatures, which justifies the relevance of the present study. Methods The samples in the TiO2–Al2O3–SiO2 system were synthesized using the method of induction melting in a cold crucible. The thermodynamic properties of the TiO2–Al2O3–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. Results The SiO2 selective vaporization from the samples under study was shown at temperatures above 1940 K. The thermodynamic properties in the TiO2–Al2O3–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. Conclusions Positive deviations from the ideal behavior were observed in the TiO2–Al2O3–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.