Stabilization of ethanol-based alumina suspensions

Al2O3 powders have been successfully dispersed in ethanol by varying the suspension acidity. An operational pH (O.pH) was defined to measure the acidity of these ethanol-based suspensions. The isoelectric point of Al2O3 in ethanol was at an O.pH of 8. According to Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, suspensions between an O.pH of 3.5-10.5 possessed only attractive inter-particle potential. Suspensions below 3.5 had high zeta potential, fine particle size, and were Newtonian. However, suspensions at high pH were shear thinning and consisted of agglomerates, despite their high zeta potential. The use of citric acid as a dispersant has also been investigated. At an O.pH of 3, optimum additions of citric acid between 0.6 and 1.0 wt% decreased the particle size, resulted in repulsive inter-particle potentials and increased the solid loading capacity to 15 vol% from 2 vol% while maintaining Newtonian behavior and similar viscosity to suspensions at O.pH 2. Addition of citric acid created agglomerated suspensions that were negatively charged at O.pH 10.5 (obtained by adding NH4OH), but positively charged suspensions at O.pH 13.6 (obtained by adding tetramethylammonium hydroxide).