Transparent glass-ceramics obtained during cooling

This paper examines the microstructure of glass-ceramics obtained during cooling melts of different compositions in the ternary Li2O-Al2O3-SiO2 system. The effects of MgO, ZnO, and TiO2 additions revealed necessary to attain the crystallisation during cooling. The microstructure of the transparent glass-ceramics, once obtained with a 15-min soak in the temperature range of 700-800 degreesC, is stable at room temperature. An interesting colour change has been noted during the treatment and TEM investigations confirmed that such coloration is produced by phase separation. The crystalline phase evolved are mixed titanates of Mg and Zn which develop from the phase separated glass, soon after T-g, and grow to form the nucleation centres for other crystalline phases. The evolution from phase separated glass to glass-ceramic has been followed by modulated DSC and NMR spectroscopies.