Effect of the surface active agents on the rheology of aqueous alumina slips

Abstract

In order to understand the properties of concentrated alumina slips with particular reference to their stability behavior, both electrophoresis and rheology experiments were carried out on three commercial alumina powders in three cationic surface active agents. The results suggest that all three commercial alumina powders used in this investigation are associated with some surface impurity that resembles sodium citrate and all three additives are adsorbed on the alumina particle surface. The net surface negative charge decreased with the addition of the additives for additive concentrations below 1% (wt), and above 1% (wt) it appears that the additive remains electrophoretically neutral. While the slips prepared in water and the additive solutions for concentrations above 1% (wt) were very stable, with low viscosity and Newtonian type fluid behavior, the alumina dispersions containing 0.5% (wt) additive solutions were flocculated and exhibited pseudo plastic fluid type properties. It appears that while at low additive concentrations, both the rheology of the slip and the electrophoretic mobility of the alumina particles is governed by the electrostatic interactions, steric effects are responsible for the state of the slip at high concentrations.