Abstract
The effect of preparation method on the chemical stability of sinterable (La, Ca)CrO3-δ powder was investigated. The ceramic method (powder mixing method) resulted in inhomogeneous distributions of the calcium content (x) in the perovskite phase (La1-xCaxCrO3-δ) after calcining at a temperature from 1223 to 1373K. More homogeneous powder was obtained by the liquid mixing method. The distribution of calcium content caused a large amount of second phases such as calcium oxychromates (Cam(CrO4)n) in a powder prepared by the ceramic method, and an excess amount of the second phase remained as Ca5(CrO4)3OH on the surface of the ceramics after sintering at 1573K. During a treatment in an H2+H2O gaseous mixture at 1273K for 627h, Cam(CrO4)n decomposed to CaO and α-CaCr2O4, and the decomposition was enhanced by the existence of silicon-containing impurities. The liquid mixing method minimized the amount of Cam(CrO4)n, and resulted in sufficient chemical stability in H2+H2O.
