Abstract
Powder compacts with mullite composition (3Al2O3⋅2SiO2) were prepared by mixing γ-alumina and colloidal silica, followed by pressurized filtration. The compacts were sintered by means of viscous flow of amorphous silica phase at relatively low temperature (1200-1250°C) under various water vapor pressures with dew points of -35, +25 and +60°C, and the effect of partial pressure of water vapor on the viscous sintering of mullite was investigated. Densification was enhanced with an increase in water vapor pressure. It was attributed to the fact that the water vapor terminates the silica network, which lowers the viscosity of amorphous silica. Apparent viscosity in the viscous sintering could be determined by applying theoretical models derived in the system composed of only vitreous phase. A compact with nearly full density (≅99%) was obtained under high water vapor pressures by optimizing sintering temperature and time.
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