EFFECT OF PREPARATION METHOD ON CHEMICAL-STABILITY OF SINTERABLE CALCIUM-DOPED LANTHANUM CHROMITES

The effect of preparation method on the chemical stability of sinterab le (La, Ca) CrO3-delta powder was investigated. The ceramic method (po wder mixing method) resulted in inhomogeneous distributions of the cal cium content (x) in the perovskite phase (La1-xCaxCrO3-delta) after ca lcining at a temperature from 1223 to 1373 K. 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 oxychro mates (Ca(m)(CrO4)n) in a powder prepared by the ceramic method, and a n excess amount of the second phase remained as Ca5(CrO4)3OH on the su rface of the ceramics after sintering at 1573 K. During a treatment in an H-2 + H2O gaseous mixture at 1273 K for 627 h, Ca(m)(CrO4)n decomp osed to CaO and alpha-CaCr2O4, and the decomposition was enhanced by t he existence of silicon-containing impurities. The liquid mixing metho d minimized the amount of Cam(CrO4)n, and resulted in sufficient chemi cal stability in H-2 + H2O.