Effect of deflocculants on the densification and mechanical properties of sol–gel alumina

Abstract

Boehmite precipitate prepared at pH=8.5 was oven-dried and calcined at different temperatures and their powder characteristics were determined. The colloidal precipitate (20 wt.%) was dispersed in aqueous medium containing 0.1 wt.% of different deflocculants. The boehmite suspensions containing these deflocculants were centrifuged, oven-dried and calcined. The powder was then compacted into pellets using uniaxial press at 180 MPa and sintered at 1600 °C. The compacts prepared with deflocculants were found to give higher sintered density and mechanical properties than the compacts prepared without deflocculants. When the deflocculants were used, the densification and fracture toughness of the compacts obey the following order: polyamino benzoic acid>ammoinum polyacrylate>ammonium citrate>polyethylene amine>acrylic acid>ammonium carbonate>ammonium tartarate>citric acid.