Effect of cooling rate on crystallization in an aluminophosphosilicate melt

The effect of cooling rate on spontaneous crystallization behaviour of an aluminophosphosilicate melt is studied by means of differential scanning calorimetry, x-ray diffraction, scanning electron microscopy and viscometry. Cooling rates of 160, 2100 and 12 000 K/s are attained by subjecting the glass melt to the casting, pressing and fibre drawing processes, respectively. Results show that phase separation occurs in the melt during cooling, and leads to the internal nucleation and opalescence in the studied glass. The degree of phase separation increases with decreasing cooling rate. Hence, the opalescence of the glass can be tuned by adjusting the cooling rate. This makes the production of opal glasses or transparent glass ceramics more efficient and with some energy savings, since the conventional isothermal treatment procedure can be left out.