Microstructure characteristics for anorthite composite glass with nucleating agents of TiO 2 under non-isothermal crystallization

Abstract

The anorthite-based composite glass doped with TiO 2 and B 2O 3 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 770°C and an exothermal peak around 870°C in the DTA trace was associated with anorthite crystallization (CaAl 2Si 2O 8). 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 TiO 2 crystals precipitated from the glassy matrix and anorthite crystallization is governed by heterogeneous volume nucleation. The introduced TiO 2 plays the role of nucleating agents to reduce the crystallization temperature lower than 900°C 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 B 2O 3 neither reacted with nor dissolved in the anorthite or rutile TiO 2 crystals, and remained a glassy phase in the matrix. Occurrence of acicular precipitations was attributed to the orientation growth of TiO 2 crystals. Anorthite crystals were observed to grow with the forms of feathery-spherical particles, having a tendency to coalescence into a huge domain.