Microstructural characterization and physical properties of a slag-based glass-ceramic crystallized at 950 and 1100°C

Glass-ceramic materials were developed from Turkish blast-furnace slags mixed with 3 and 5 wt% titania (TiO2) On the basis of the DTA and the dilatometry analyses, nucleation experiments were carried out at 725 degrees C and crystallization was performed at 950 and at 1100 degrees C. DTA and X-ray diffraction studies conducted on the glass samples devitrified at 950 degrees C revealed glassy regions and small amounts of gehlenite (Ca2Al2SiO7) and merwinite (Ca3MgSi2O8) phases whereas complete transformation to melilite solid solution of akermanite (Ca2MgSi2O7) and gehlenite phases occurred for those crystallized at 1100 degrees C. Optical microscopy and SEM investigations on the slag glass-ceramic crystallized at 950 degrees C revealed large crystals due to surface crystallization whereas bulk crystallization was evident for those crystallized at 1100 degrees C. For both cases, the crystalline size decreased with increasing nucleant content. Wear, hardness, fracture toughness and bending properties of the slag based glass-ceramic material were enhanced with the increase in nucleant content and the crystallization temperature. (C) 1997 Elsevier Science Limited.