Dewatering of spontaneous-coagulation-cast alumina ceramic gel by filtrating with low pressure

Water removal in colloidal processing is a tough and crucial problem because deformation and cracking of the wet body easily happen during the drying process. Inspired by conventional pressure filtration (PF), we combined spontaneous coagulation casting (SCC) with PF to partially remove water from the gelled sample before drying for the purpose of lessening the risk of cracking and shortening the drying period. The effect of pressure, holding time, and solid loading on the particle packing ratio of wet samples, the drying process, and the bulk density and homogeneity of green and sintered bodies was surveyed systemically. The PF process of 0.4 MPa for 2 h was optimized based on dewatering ratio from ceramic slurries. The particle packing ratio of the pressure-filtrated samples increased with the solid loading of ceramic slurries, and 61 vol% was obtained for the slurry with 56 vol% solid loading. The drying time of the pressure-filtrated samples was shortened by as much as 42%–53% compared with that of the gelled samples, and the linear shrinkage for the pressure-filtrated samples during drying was only approximately 0.5%, much smaller than that of the gelled samples (2.4%–4.6%). Furthermore, the bulk density of the pressure-filtrated green bodies was more than 2% higher than that of the gelled green bodies, and more homogeneous green bodies were obtained by PF than by SCC. The alumina ceramic with 98.8% relative density and a homogenous density distribution was obtained after being sintered at 1550 °C for 2 h.