Pore morphology in cryochemically prepared alumina powders and their sulphate precursors

Cryochemically prepared alumina and yttria-doped alumina powders and their sulphate precursors were examined in the SEM and TEM. The TEM examination revealed a typical chained agglomerate structure with subnamometre-sized porosity within the agglomerates and micrometre-sized porosity between the agglomerates. The SEM examination showed that the sulphate solutions had separated into water channels and immiscible hydrates upon freezing. The water channels had ovulated and spheroidized as they were freezing. This morphology was maintained through vacuum drying and calcining.