The Effect of Electric Field on Pressure Filtration of Ceramic Suspensions

Abstract

The consolidation behavior of Al2O3 and indium tin oxide (ITO, 90% In2O3–10% SnO2) particles 150–200 nm in size was examined using a pressure filtration apparatus at a constant compressive rate under an electric field. The relation of applied pressure (ΔPt) with volume of dehydrated filtrate (Vf) was compared with the established filtration theory (theory I) for a well‐dispersed suspension and the newly developed filtration theory (theory II) for a flocculated suspension. The experimental results without polyelectrolyte dispersant deviated from theory I when ΔPt exceeded a critical pressure (ΔPtc). This deviation is associated with the phase transition from a dispersed suspension to a flocculated suspension at ΔPtc. A good agreement was shown between the developed theory II and experimental results after the phase transition. When a dispersant (polyacrylic ammonium, PAA) was added to alumina, ITO, or Al2O3–ITO mixed powder suspensions, the consolidation behavior of the particles was controlled by the dissociation and amounts of adsorbed and free PAA. The addition of a large amount of highly charged PAA enhanced the repulsive interaction between PAA‐adsorbed particles, and the consolidation behavior was explained by theory I. The adsorption of neutral PAA on the particles reduced the repulsive interaction, and the consolidation behavior was well explained by theory II. The phase transition from dispersed to flocculated suspension was very sensitive to the electric field during the pressure filtration. The ΔPtc for the suspension with and without PAA decreased drastically when a low electric field was applied. The final packing density of the flocculated particles was greatly increased by the application of a weak electric field. However, the dense structure under high pressure was relaxed to a low‐density structure when the stored elastic strain energy was released.