Calcination of microporous BeO powders

Abstract

Two microporous BeO powders which differed only in that in one the mean pore width was < 6 Å and in the other was ∼6–20 Å, were used to study the effect of molecular size pores upon the micro-structural changes during calcination. As with macroporous oxides, the mean pore width increased with increasing calcination temperature and pores < 6 Å width were eliminated by ∼500°C. Since significant crystal growth in vacuo is not observed at such low temperatures, the initial presence of these very small pores has no significant effect upon crystal growth during calcination at high temperatures. The elimination of pores of width < 6 Å is accompanied by a decrease in intra-aggregate pore volume (which is not observed on elimination of larger micropores) and this leads to a lower temperature of aggregate densification for the oxide containing the smallest pores. In the presence of H₂O vapour the processes of pore and crystal growth occur at significantly lower temperatures than in vacuo but aggregate densification is not enhanced.