EFFECTIVENESS OF A DISPERSANT FOR THE THICKENING OF ALUMINA SLURRIES WHILE RETAINING THE FLUIDITY

Concentrated alumina slurries were fluidized in an optimum amount of polyacrylates (PAA) in the content region where a good dispersion was obtained. Dispersion was necessary, but not sufficient for fluidization. The expected role of PAA in the thickening was retention of a water-reducing ability to retain the fluidity. Thickening of the alumina slurry to the limit of retaining the fluidity was achieved by the amount of PAA at which the flow point showed a minimum. The flow of alumina slurries around the limit was approximated by the Bingham model which was characterized by the yield stress and the Bingham viscosity. The flow curves of the slurries containing insufficient PAA had a yield stress which decreased with increasing amount of PAA and disappeared at an optimum amount of PAA to give a minimum flow point. The yield stress again increased retaining the low Bingham viscosity with increasing amount of PAA, to exceed the optimum amount for molecular weights smaller than 1 0 000. On the other hand, the Bingham viscosity increased without increasing the yield stress with increasing amount of PAA, to exceed the optimum amount for molecular weights larger than 20000. The effect of PAA on the dispersion and flow behaviour could be explained by the electrostatic stabilization based on the Derjaguin-Landau, Verwey-Overbeek (DLVO) theory for the PAA with a molecular weight smaller than 10 000, and by the steric stabilization for the PAA with a molecular weight larger than 20 000.