Processing of aqueous alpha-Al2O3, alpha-SiO2 and alpha-SiC suspensions with polyelectrolytes.

The preparation of aqueous alpha-Al2O3, alpha-SiO2 and alpha-SiC suspensions with polyelectrolytes, ie. the NH4+ salt of polymethacrylic acid (PMA-NH4+) and the acidic form of polyethylene imine (PEI-H+), is investigated It is based on the adsorption of these polyelectrolytes which in turn depends mainly on the nature of the polyelectrolyte, and the charge density that develops on the powder surface in water. The efficiency of these dispersants is primarily attributed to the electrostatic interaction between -COO- groups of PMA-NH4+ and positive sites on the alumina surface at pH 8-9 as well as between -NH2+- groups of PEI-H+ and negative sites of the silica surface or of the oxidized surface of silicon carbide in acidic media. Good dispersion and stability of dispersions are then obtained through electrostatic and steric stabilization. As an application, the preparation of an Al2O3-SiC aqueous mixed slurry was investigated as a preliminary step in the processing of Al2O3/SiC nanocomposites. (C) 1997 Elsevier Science Limited.