Abstract
The effects of pretreament on the sintering was studied with spherical silica powders prepared by the hydrolysis of Si(OC2H5)4.(1) Calcination or autoclaving prevented the fracture of compacts in firing.(2) The thermal shrinkage of the compacts of calcined powder occurred slowly near the calcination temperature, while the compacts of commercial silica gel shrank rapidly at lower temperature. The shrinking behavior of the autoclaved-powders was intermediate between calcined-powders and commercial silica gel.(3) The bulk density and Vickers hardness of sintered compacts increased as the firing temperature was raised. Relative density of 99.8% was obtained at 1200° and 1150°C for calcined-powder and autoclaved-powder respectively.(4) Spherical silica particles remained when fired at 1000°C, but the compacts became vitreous at 1150°-1200°C.(5) The transparent sintered compacts were obtained when about 0.3μm diameter particles were sintered at 1200°C for 5h.The sintering property of spherical silica powders was improved by precalcinaton, but the same effects of calcination were obtained from 400° to 800°C. Further, the sintering of spherical silica powders was improved when autoclaved in the presence of water.
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