Vaporization features of CeO2[sbnd]ZrO2 solid solutions at high temperature

Abstract

Ceria-zirconia solid solutions are the important materials for the application in catalysis and the energy conversion. However, the existing data on the thermodynamic properties of ceria-zirconia solid solutions which is used to distinguish their stability is controversial. In the present work, equilibrium ceria-zirconia solid solutions with 90, 50, 24 and 9 mol.% CeO2 were manufactured using the original sol-gel reverse co-precipitation method with further prolonged thermal treatment for 5–50 h at 973–1373 K. Comprehensive characterizations of the precursor powders obtained were performed via SEM, STA, XRD, ESCA and PSD-analysis. According to XRD observations combined with Rietvield refinement and ESCA the equilibrium solid solutions without an admixture of Ce3+ in the condensed phase were obtained after the calcination of samples at 1373 K. Knudsen effusion mass spectrometry was used to study the vaporization processes and the thermodynamic properties of solid solutions in the CeO2ZrO2 system at 2150 K. Similar dependence of the CeO2 activity on the condensed phase composition was obtained for solid solutions with various ceria contents, which ensured the equilibrium evaporation. The schematic evaporation process for xCeO2-(100-x)ZrO2 solid solutions at 2100–2500 K was suggested for the first time. It was found, that high temperature behavior of CeO2ZrO2 system significantly differs from its behavior at lower temperatures, i.e. 873–1373 K, when Ce (IV) to Ce (III) reduction takes place.