Two-step Sintering and Foaming Mechanism of Porous Glass-ceramics from Granite Powder

Porous glass-ceramics were prepared by using a two-step sintering process, i.e., low-temperature sintering and high-temperature foaming, with granite powder as the raw material and SiC as the foaming agent. The effects of sintering and foaming temperature on pore structure, crystal phase composition and compressive strength of the porous glass-ceramics were systematically studied by using XRD, SEM, TG-DSC and ceramic bending tester. Foaming mechanism of the glass-ceramics was analyzed. With increasing sintering temperature, flexural strength and bulk density of the glass-ceramics without foaming agent first increased and then decreased, while the optimum sintering temperature was 1120 ℃. With increasing foaming temperature, anorthite and quartz in the glass-ceramics gradually dissolved into the glass phase. Meanwhile, the crystallinity decreased, the pore size increased, and both the apparent density and compressive strength decreased. However, the specific strength reached a maximum value of 5.36 kN·m·kg^-1 at 1220 ℃, with a porosity of 59.7%. In contrast to the open pore structure of the one-step sintered sample, the two-step sintered sample shows a closed pore structure. Specific strength of the porous glass-ceramic prepared by using the two-step sintering is superior to that of sample prepared by using the one-step sintering method.