Effect of different nucleation catalysts on the crystallization of Li 2O–ZnO–MgO–Al 2O 3–SiO 2 glasses

Abstract

Based on local raw materials, a range of LiZnMg aluminosilicate glasses were prepared to investigate the influence of TiO 2, Cr 2O 3, and ZrO 2 on the crystallization behaviour and thermal expansion characteristics. Differential thermal analysis showed that the crystallization propensity increases in the order TiO 2 > Cr 2O 3 > ZrO 2. Virgilite, β-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 base sample, whereas, somewhat rod-like and accumulated growths appeared in samples containing ZrO 2. However, a rather homogeneous texture of accumulated growths was developed in glass-ceramics containing TiO 2 and Cr 2O 3. The coefficient of thermal expansion of parent glasses was sensitive to the type of nucleating agent added (Cr 2O 3 > TiO 2 > ZrO 2) varying from 24.8 × 10 −7 to 65.1 × 10 −7 °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.