Evaluation of dispersability of gamma alumina prepared by homogeneous precipitation

Abstract

Aqueous dispersions of Γ-alumina powder synthesized by homogeneous precipitation (HP) were investigated and compared with a commercial gamma alumina (TM300). As the isoelectric point (IEP) of the two powders was found to be at the same pH (8.5), the rheological properties of the suspensions were determined under controlled rate conditions, varying the pH and solid loading. It was found that the pH used in a suspension affects its rheological properties and consequently the final density of the slip cast body, obtaining the highest density for the heated bodies at pH values below the IEP. The pH limit to maintain Newtonian flow is dependent on the solid content and the type of alumina used. Thus, a TM300 35% solid-loaded suspension requires a pH of 4, whereas HP alumina requires only a pH of 3.75 to behave as a Newtonian fluid. Both suspensions were slip cast and the green bodies were heated at four distinct temperatures. Lastly, the relative densities of the heated bodies were measured by the Archimedes method, and in all cases, lower relative densities were obtained for HP alumina. © 2012 The Ceramic Society of Japan.