Sinterability, structural evolution and pinhole elimination of high strength self-glazed glass-ceramics sintered from granite sludge by instant glaze firing

Granite sludge from the cutting and polishing of granite blocks should be utilized to prevent environmental pollution. This study focuses on the preparation of high-strength self-glazed glass-ceramics from granite sludge by combining dense sintering and instant glaze firing. Thermal analyses including thermogravimetry, differential scanning calorimetry and thermal expansion were used to evaluate the sinterability of the granite powder and to determine the dense sintering temperature. For the instant glaze firing of the sintered glass-ceramics, the structural evolution was analyzed by X-ray diffraction and solid-state nuclear resonance to clarify glaze formation and glass network stability, respectively. Glaze formation resulted from the dissolution of quartz and feldspars and the reduced glass viscosity, as indicated by the thermochemical calculation. As the glaze firing temperature was increased, the thickness of the surface glaze increased. The coefficient of thermal expansion of the glazed glass-ceramics indicates a residual compressive stress in the surface glaze. The elimination of glaze pinholes was achieved by reducing the amount of ferrous minerals and increasing the glaze firing rate. Under the optimum conditions, the flexural strength and surface glossiness of the glazed glass-ceramic were 112.5 MPa and 54.7 GU respectively, enabling the scalable production of high-strength self-glazed glass-ceramics from granite sludge for application in decorative tiles.