In-situ synthesis of rodlike LaAl11O18 in Al2O3 powder by a coprecipitation method

Composite powders of rodlike LaAl11O18 grains distributed in an Al2O3 matrix were prepared by a coprecipitation method using La(NO3)3·6H2O and Al(NO)3·9H2O as starting materials. The formation temperature of the LaAl11O18 phase was analyzed by XRD and the morphology of the synthesized powders was observed by SEM with EDX analysis. The results showed that the rodlike LaAl11O18 phase could be formed at low temperature and that it was distributed homogeneously in the equiaxed Al2O3 powder. The average aspect ratio of the LaAl11O18 grains and the average grain size of the Al2O3 obtained by calcining the dried gel at 1500°C for 1 h were 3–5 and 0.6 μm, respectively. TEM and HREM were used to characterize the rodlike LaAl11O18 grains and showed that the crystallographic orientation of the LaAl11O18 grain for the elongated direction was [001].