Microstructure characteristics for anorthite composite glass with nucleating agents of TiO2 under non-isothermal crystallization

Abstract

The anorthite-based composite glass doped with TiO2 and B2O3 was prepared by quenching of molten droplets. Phase development and crystals microstructure of glass were investigated under non-isothermal conditions. A glass transition temperature of 770degreesC and an exothermal peak around 870degreesC in the DTA trace was associated with anorthite crystallization (CaAl2Si2O8). For glass specimens under nucleation and crystallization heat-treatment, the final predominant phase was identified as anorthite. Anorthite crystals show preferential nucleation at specific sites with rutile TiO2 crystals precipitated from the glassy matrix and anorthite crystallization is governed by heterogeneous volume nucleation. The introduced TiO2 plays the role of nucleating agents to reduce the crystallization temperature lower than 900degreesC for anorthite-based glass-ceramics. Chemical compositions could be related to the crystal microstructures on different characteristic regions. It was observed that the sintering aid of B2O3 neither reacted with nor dissolved in the anorthite or rutile TiO2 crystals, and remained a glassy phase in the matrix. Occurrence of acicular precipitations was attributed to the orientation growth of TiO2 crystals. Anorthite crystals were observed to grow with the forms of feathery-spherical particles, having a tendency to coalescence into a huge domain. (C) 2002 Elsevier Science Ltd. All rights reserved.