EFFECT OF CaO/SiO₂ AND HEAT TREATMENT ON THE MICROSTRUCTURE OF GLASS-CERAMICS FROM BLAST FURNACE SLAG

Glass-ceramics, with molten blast furnace (BF) slag as the major raw material, were prepared successfully by the melting method. The effect of the CaO/SiO₂ ratio in the molten BF slag and heat treatment on the viscosity and microstructure of glass-ceramics produced from BF slag were traced using the melt property tester, DSC, XRD and SEM. The results showed that increasing the CaO/SiO₂ ratio of BF slag caused a decrease not only in the viscosity of the BF slag at high temperature but also in the nucleation and crystallization temperature for the preparation of glass-ceramics. The content of akermanite-gehlenite increased as the CaO/SiO₂ ratio increased from 0.30 to 0.63. With increasing nucleation and crystallization temperature, the crystalline phases remain unchanged, but the crystal shape changes from granular to flaky. The optimum CaO/SiO₂ ratio was found to be 0.44, resulting in diopside as the main crystalline phase, augite as the secondary crystalline phase and a small mount of akermanite-gehlenite after appropriate heat treatment i.e. nucleation at 775°C and crystallization at 920°C.