Lanthanum zirconate (La 2 Zr 2 O 7 ) was prepared by coprecipitating lanthanum nitrate and zirconyl oxychloride at pH 10, followed by ethanol washing. The initial high surface area of ∼304 m 2 ؒg −1 decreased very rapidly with increased sintering temperature and decreased to an immeasurably small value after heating at 1200°C for 15 h. The major parameters studied were phase evolution, crystallite size, porosity, surface area reduction, and shrinkage during sintering. Three temperature regions were identified based on these studies: below the crystallization temperature, between the crystallization temperature and ∼1100°C, and above 1100°C. The main contribution of surface area reduction in the region 800°-1100°C was due to surface diffusion; the main contribution above 1100°C was due to grain-boundary diffusion coupled with surface diffusion.

samples. The effect of steam on the thermal stability of La 2 O 3 ⅐11Al 2 O 3 has also been studied. La 2 O 3 ⅐11Al 2 O 3 sample is found to be stable in steam.

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