SOL-GEL PREPARATION AND CRYSTALLIZATION OF BARIUM OSUMILITE GLASS

Partial-alkoxide (PAR) and all-alkoxide (AAR) routes for preparing sto ichiometric barium osumilite (BaMg2Al6Si9O30) have been developed. Sin tering to 89% (PAR) and 86% (AAR) of the estimated theoretical densiti es are achieved after 1 h at 1150 and 1100 degrees C, respectively. Bo th types of gel are amorphous after calcination for 5 h at 650 degrees C. Crystallisation of gel powders using a constant heating rate of 10 degrees C/min starts at approximately 980 degrees C with mullite for PAR and hexacelsian for AAR as the first phases to crystallise. Barium osumilite initially crystallises at 1000 degrees C and becomes the do minant phase after 3 h at 1200 degrees C. The presence of celsian, hex acelsian and cordierite are, however, unavoidable even at high tempera tures, and isothermal crystallisation of the gel powders for 1 h at 12 50 degrees C does not result in single phase barium osumilite.