GEL TO GLASS CONVERSION AND CRYSTALLIZATION OF ALKOXY-DERIVED BARIUM ALUMINOSILICATE GEL

Barium aluminosilicate (BaAl2Si2O8) gel was prepared by hydrolyzing mixed alkoxide precursors. Differential thermal (DTA) and thermal gravimetric (TGA) analyses of the oven-dried (at 70-degrees-C) gel were performed to examine its thermal and weight-loss characteristics, respectively. Thermal conversion of the gel into 'BaAl2Si2O8 glass' and its subsequent crystallization were monitored by studying the changes of specific surface area (BET method) and microstructural features (by scanning electron microscopy (SEM)) and by X-ray powder diffraction (XRD) analysis. The results indicated that BaAl2Si2O8 glass can be produced at approximately 1000-degrees-C by the sol-gel process. Studies also showed that gel-derived BaAl2SiO8 glass crystallizes into hexacelsian phase in the approximately 1000-1020-degrees-C range. However, when 800-degrees-C heated organic-free gel is mixed with 5 wt% lithium oxide (Li2O), it Crystallizes into the (monoclinic) celsian phase at the same temperature (1000-1020-degrees-C).