THERMAL-ANALYSIS OF A SIO2-AL2O3-CAO-CAF2 GLASS

A SiO2-Al2O3-CaO-CaF2 ionomer glass was investigated using thermal analysis, X-ray diffraction, and scanning electron microscopy. The purpose of this investigation was to control the susceptibility of the glass to acid attack. The differential thermal analysis trace exhibited a sharp glass transition at about 645-degrees-C and two exotherms. The first exotherm corresponded to liquid-liquid phase separation followed by crystallization of fluorite. The second, much larger, exotherm was the result of crystallization of the remaining glass phase to form anorthite. Prolonged heat treatment below the glass-transition temperature demonstrated that crystallization of fluorite can occur without prior liquid-liquid phase separation.