Crystallization behaviour, microstructure and mechanical properties of cordierite–mullite glass ceramics

The crystallization behaviour of a glass ceramic with the composition SiO2 49.0, Al2O3 38.35, MgO 8.19, BaO 1.50, V2O5 2.96 wt.% was investigated by DTA, XRD and SEM. It was shown that the specimen developed a fine microstructure comprised of mullite and cordierite crystals after heating at the DTA peak temperature of 1056 °C. Heating the glass at higher temperatures of 1200–1400 °C resulted in much coarser microstructures but the above mentioned phases were preserved. The activation energy for crystallization, E, and Avrami exponent, n, were determined for this glass specimen as 116.3 ± 6.2 kJ mol−1 and 0.9 ± 0.2, respectively, for fine particle size and 172 ± 11 kJ mol−1 and 1.4 ± 0.2 for coarse particle size specimens, indicating predominately surface and mixed bulk-surface crystallization mechanisms for the fine and coarse particle size specimens, respectively. The highest bending strength value obtained was 159 ± 13.2 MPa for the specimen crystallized at 1056 °C for 2 h.