Interactions in aqueous Al2O3–AlN suspensions during the HAS process

Hydrolysis-assisted solidification (HAS) is a new method for net-shaping ceramic green parts from aqueous suspensions. It is based on the thermally activated hydrolysis of aluminium nitride powder added to a concentrated suspension of a ceramic powder. During hydrolysis, water is consumed and ammonia is formed. The cumulative effect of water consumption and the change in zeta-potential due to a pH change leads to an exponential increase of viscosity until the fluid character of the suspension is lost and a moist solid is obtained. In the present paper the contribution of changing interparticle forces arising from the pH shift is described. The electrokinetic properties of AlN powder and their influence on the viscosity of acidic or alkaline aqueous alumina suspensions before and during hydrolysis are presented and discussed.