Thermodynamic properties of the La2 O3 -ZrO2 system by Knudsen effusion mass spectrometry at high temperature

S M Shugurov; O Yu Kurapova; S I Lopatin; V G Konakov; E A Vasil'eva

doi:10.1002/rcm.7997

Thermodynamic properties of the La₂ O₃ -ZrO₂ system by Knudsen effusion mass spectrometry at high temperature

Rapid Commun Mass Spectrom. 2017 Dec 15;31(23):2021-2029. doi: 10.1002/rcm.7997.

Authors

S M Shugurov¹, O Yu Kurapova¹, S I Lopatin¹, V G Konakov¹, E A Vasil'eva¹

Affiliation

¹ Institute of Chemistry, St Petersburg State University, 26 Universitetskii avenu, 198504, St Petersburg, Russian Federation.

PMID: 28940769
DOI: 10.1002/rcm.7997

Abstract

Rationale: Zirconia doped with a lanthanum oxide system is of high interest due to its exceptional thermal stability for the development of high-performance ceramics. It possesses the beneficial properties of pure zirconia, such as heat resistance, mechanical strength and inertness, but also eliminates its main disadvantage, i.e. brittleness. At high temperatures, components of such systems may vaporize selectively, leading to significant change in composition, and hence, the thermal resistance, phase stability and performance of the ceramic materials. Therefore, information on the vaporization processes and thermodynamic properties of the La₂ O₃ -ZrO₂ system is of great importance.

Methods: Knudsen effusion mass spectrometry was used to study the vaporization processes and thermodynamic properties of solid solutions in the La₂ O₃ -ZrO₂ system at 2110 K. Pure La₂ O₃ was used as a reference substance. Comprehensive characterization of the precursors and ceramics was performed via SEM, STA, XRD and PSD analysis.

Results: Zirconia-doped lanthania precursor powders and ceramics with La₂ O₃ of 33.3, 50, 70 and 90 mol.% content were manufactured by solid-state synthesis and the original cryochemical technique. La, LaO, ZrO and ZrO₂ were found to be the main vapor species over the samples studied. The activities and thermodynamic properties of La₂ O₃ were calculated. Via XRD analysis it was shown that the phase composition of xLa₂ O₃ -(100-x)ZrO₂ powders (x = 0.33, 0.5, 0.7 and 0.9 mol. fraction) significantly depends on the synthesis technique chosen.

Conclusions: According to the XRD results combined with Rietveld refinement of the patterns, 33.3 La₂ O₃ -66.7 ZrO₂ ceramics after solid-state synthesis are composed of well-formed cubic pyrochlore-type La₂ Zr₂ O₇ with 5 wt.% admixture of monoclinic and cubic ZrO₂ whereas 33.3 La₂ O₃ -66.7 ZrO₂ precursor powders after cryochemical synthesis correspond to low-crystalline La(OH)₃ . The components of the La₂ O₃ -ZrO₂ system evaporate separately: there is no temperature range where lanthanum and zirconium gaseous species are present together. It was found that the activities of lanthania have low negative deviation from the ideal case.