Effects of pH and Concentration of Aqueous Alumina Suspensions on Pressure Filtration Rate and Green Microstructure of Consolidated Powder Cake

Pressure filtration rate, packing density and microstructural fluctuation in a consolidated powder cake were studied with 5-50 vol% aqueous suspensions of single crystal alumina particles of 0.5 μm size under a pressure range of 200 to 400 kPa. The decreased height of the suspension during the pressure filtration followed tm of time, where m was in the range form 0.57 to 0.67 at 10 vol% solids (depending on pH of the suspensions) and approached 0.5 at around 20 vol% solids. The consolidation time was longest for the weakly charged particles near the isoelectric point because of the formation of a uniform distribution of small pore channels in the cake. The positively charged particles were densely agglomerated during pressure filtration but the formation of relatively large pore channels between dense particle clusters shortened the filtration time. The packing density of the formed cake increased in the following order: weakly charged particles near the isoelectric point