Crystallization of some aluminosilicate glasses

The crystallization behaviour of some glasses within the spodumene-willemit e-diopside system is described. DTA. XRD and polarizing microscopy were use d for this investigation. Increase of the calculated spodumene and/or wille mite contents enhanced batch melting, internal nucleation, and lowered the temperatures of crystallization onset in the glass. Stable P-spodumene, wil lemite, and diopside phases were directly developed from the melts, whereas , metastable beta -eucryptite ss and beta -Zn2SiO4 ss phases initially crys tallized out from the glass. These latter phases were transformed into the stable beta -spodumene ss and willemite forms above 900 degreesC and around 840 degreesC respectively. Diopside was generally difficult to crystallize out from the glasses. Some crystalline glasses exhibited very low thermal expansion coefficients (-8 to 16 x 10(-7)/degreesC); this was discussed in terms of the type and relative proportions of the constituent phases. (C) 2 001 Elsevier Science Ltd and Techna S.r.l. All rights reserved.