Effect of different nucleation catalysts on the crystallization of Li2O-ZnO-MgO-Al2O3-SiO2 glasses

Based on local raw materials, a range of LiZnMg aluminosilicate glasses were prepared to investigate the influence of TiO2, Cr2O3, and ZrO2 on the crystallization behaviour and thermal expansion characteristics. Differential thermal analysis showed that the crystallization propensity increases in the order TiO2 > Cr2O3 > ZrO2. Virgilite, beta-spodumene ss, gahnite, enstatite and cristobalite were formed in the prepared glass-ceramics. The microstructure of glass-ceramic samples showed growths of rounded and subrounded grains in the basesample, whereas, somewhat rod-like and accumulated growths appeared in samples containing ZrO2. However, a rather homogeneous texture of accumulated growths was developed in glass-ceramics containing TiO2 and Cr2O3. The coefficient of thermal expansion of parent glasses was sensitive to the type of nucleating agent added (Cr2O3 > TiO2 > ZrO2) varying from 24.8 x 10(-7) to 65.1 X 10(-7) degrees C-1 being almost unchanged with the heat-treatment. The microhardness values of glass-ceramic samples were in the 763-779 kg/mm(2) range. (C) 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved.