Crystallization, microstructure and expansivity of spodumeneorthoclase glasses

Abstract

The crystallization behaviour was investigated for some glasses, within the system spodumene-orthoclase, during different heat treatments by DTA, XRD and SEM. Kaolin and quartz sand were used as starting materials for the glass preparation and melting. The base glasses were stable through the heat treatments and did not show any crystallization propensity, whereas TiO2 additions catalyze the crystallization tendency in the glasses. The crystallization process involved the formation of β-spodumene and leceite in addition to the metastable high quartz, which disappeared at higher temperatures (>900 °C). Translucent glass-ceramies, containing uniform and nonuniform microstructures, were obtained in the ease of domination of high quartz and β-spodumene, respectively. Little difference in the coefficient of thermal expansion (CTE) was noted in the base glasses (64 to 66 ∙ 10^-7 at 20 to 500 °C) and the TiOs doped glasses (60 to 69 ∙ 10^-7 K^-1 at 20 to 500 °C). Change in CTE in the TiOs doped glass ceramie samples from 37 to 69 ∙ 10^-7 at 20 to 300 °C depends mainly on the content of crystallized β-spodumene in addition to the residual glass. However, an increase in β-spodumene content in the crystallized glass-ceramies lowers the value of CTE and vice versa.