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°C and crystallization was performed at 950 and at 1100°C. DTA and X-ray diffraction studies conducted on the glass samples devitrified at 950°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°C. Optical microscopy and SEM investigations on the slag glass-ceramic crystallized at 950°C revealed large crystals due to surface crystallization whereas bulk crystallization was evident for those crystallized at 1100°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.