Crystallization of some aluminosilicate glasses

The crystallization behaviour of some glasses within the spodumene-willemite-diopside system is described. DTA, XRD and polarizing microscopy were used for this investigation. Increase of the calculated spodumene and/or willemite contents enhanced batch melting, internal nucleation, and lowered the temperatures of crystallization onset in the glass. Stable β-spodumene, willemite, and diopside phases were directly developed from the melts, whereas, metastable β-eucryptite ss and β-Zn2SiO4 ss phases initially crystallized out from the glass. These latter phases were transformed into the stable β-spodumene ss and willemite forms above 900°C and around 840°C respectively. Diopside was generally difficult to crystallize out from the glasses. Some crystalline glasses exhibited very low thermal expansion coefficients (−8 to 16 × 10−7/°C); this was discussed in terms of the type and relative proportions of the constituent phases.