Colloidal processing of aluminum oxide powder for membrane applications

The properties of dip-coating slips were varied by adjusting pH, by using nonionic or ionic additive polymers and by using different electrolytes and concentrations. Electrostatic stabilization of the slip with poly(vinyl alcohol) (PVA) addition led to the smallest particle size resulting in the highest density and the lowest permeability of the dip coated layer. Only small amounts of nonionic PVA adsorbed on the particles, which decreased the zeta potential slightly by charge shielding. The measured particle size decreased when the PVA concentration increased. The PVA addition did not affect the isoelectric point (i.e.p.) of the alumina particles. Strongly adsorbed sodium poly(metacrylic acid) (Na-PMAA) changed the pHiep from ∼9 to ∼4. The smallest particle size was measured at pH values 7-9. The zeta potential of particles with Na-PMAA addition decreased when the ionic strength was increased. Low zeta potential values resulted in flocculation of the slip and larger flock size. The flocculated slips led to fast growth, high porosity and high permeability of the layer. © 2002 Elsevier Science Ltd and Techna S.r.l. All rights reserved.