Electrical Properties, Rheology and Packing Density of Colloidal Alumina Particles

Abstract

The mobility of positively and negatively charged alumina particles in concentrated suspensions was analyzed with monitoring the electrical conductivity of the suspensions. The decreased mobility (u) at a lower charge (Q) was due to increased attractive interaction. The increase of volume fraction of moderately charged particles resulted in the decrease of u value because of the increased repulsive interaction with decreased interparticle distance. Too strong repulsive interaction between highly charged particles suppressed the migration of dispersed particles. The mobility of negatively charged particles was lower than that of positively charged particles at a similar Q value because of a stronger effect of chemical bonding between hydrated particle surface. The apparent viscosity of acidic suspensions was lower than that of basic suspensions. This result was also discussed based on three important effects of charge, concentration and nature of hydrated surface of alumina particles. The green densities of alumina compacts consolidated by filtration through gypsum molds were higher for the acidic suspensions than for the basic suspensions.