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 degrees C. Heating the glass at higher temperatures of 1200-1400 degrees 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 degrees C for 2 h. (C) 2009 Elsevier B.V. All rights reserved.