EFFECT OF HEAT-TREATMENT TEMPERATURE ON THE PROPERTIES OF A LITHIUM ALUMINOSILICATE GLASS

The effects of isochronal heat treatments on the properties of a lithium aluminosilicate glass have been measured. Heat treatment of the base glass at temperatures between 700-degrees and 1100-degrees-C initially results in phase separation of the glass, followed by the formation of beta-quartz solid solution (ss) at about 850-degrees-C. The beta-quartz(ss) converts to beta-spodumene in the temperature range between 950-degrees and 1000-degrees-C. The dependence of the properties of the material on the heat-treatment temperature is controlled by phase separation below 850-degrees-C, by the rapid crystallization of beta-quartz(ss) between 850-degrees and 900-degrees-C, and by the lack of change in morphology with heat treatment above 900-degrees-C. The effects of heat treatment on the properties of this material are explained on the basis of the changes in the composition and morphology of the residual amorphous and crystalline phases.