Rheological properties of aqueous alpha Al2O3 suspensions: Influence of dispersant concentration

The effects of concentration of polyacrylic acid as a dispersant on rheolog ical properties of aqueous alumina suspensions have been investigated under steady and oscillatory shear conditions. At solid volume fractions between 0.45 and 0.6, a high degree of particle stabilization is achieved when 0.2 wt% of polyacrylic acid is added. At lower dispersant concentrations, susp ensions exhibit pronounced irreversible thixotropic behaviour, whereas at h igher dispersant concentrations, time dependent effects on the flow propert ies are not detectable. When the saturation adsorption limit of the polyele ctrolyte on Al2O3 is reached, further addition of the dispersant appreciabl y changes the flow behaviour, as well as the viscoelastic response of inves tigated suspensions. The data under steady shear are described by applicati on of the generalized Casson model, and for the analysis of viscoelastic da ta the generalized Maxwell model is used.