Processing of Aqueous α0Al_2O_3, α-SiO_2 and α-SiC Suspensions with Polyelectrolytes

摘要

The preparation of aqueous α-Al_2O_3, α-SiO_2 and α-SiC suspensions with polyelectrolytes, i.e. the NH~+_4 salt of polymethacrylic acid (PMA-AH_4~+) 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-NH_4~+ and positive sites on the alu- mina surface at pH 8-9 as well as between-NH_2~+- groups of PEI-NH_4~+ and negative sites of the silica surface or of the oxidized surface of silicon carbide in acidic media.