Pressure Slip Casting of Submicron Alumina Powder

Compacts are formed by pressure (0.9MPa) slip casting from a submicron Al₂O₃ powder using sheet filter. The process is compared with the conventional one using plaster mold. Two types of filters are; 1. acetyl-cellulose sheet with the thickness of 125μm and the hole size of 0.2 μm backed by a plate of porous aluminum; 2. plaster mold reinforced by analuminum tube. An Al₂O₃ powder with the average particle size of 0.22μm and the purity of 99.99% is dispersed in a ball mill to prepare slips with coefficients of viscosity in the range of 400~600mPa⋅sec. The results obtained are summarized as followes: 1. The rate of increase in the depth of the cake formed from the slip is represented by a constant K=L²/t (L:the thickness of the cake [mm], t:the time [min]). The value of K is 0.08mm²/min in conventional slip casting with the plaster mold and about 1.0mm²/min in pressure slip casting with the plaster mold or the cellulose sheet. 2. The sintering of the compacts are obstracted by the contamination from a plaster mold. The thickness of the contaminated layer in the compacts is about a few millimeter from the cake-mold interface. 3. Density of 99 to 99.5% and bending strength above 700MPa are obtained in the alumina compacts sintered at 1250°C for 1.5hr, in the pressure slip casting with the acetyl-cellulose sheet filter.