Dispersion of aluminum hydroxide coated Si3N4 powders with ammonium polyacrylate dispersant

Si3N4 powders coated with aluminum hydroxide were prepared and dispersed in water with ammonium polyacrylate (NH4PA) to produce 11.8 vol.% slips. The influence of the Al(OH)3 coating on the rheological behavior of 11.8 vol.% aqueous Si3N4 slips with NH4PA was investigated. The coating of Al(OH)3 on Si3N4 particles resulted in a bayerite-like surface with a small amount of gibbsite-like structure which improved the adsorption of a NH4PA dispersant and effectively reduced the viscosity of the 11.8 vol.% slurries. The viscosity values of slips with 0.11 wt.% NH4PA at pH 9.5 decreased from 33 mPa s for the uncoated powder to about 2 mPa s for the coated powders. Lower viscosity values and higher maximum packing fraction of the coated Si3N4 slips with respect to the uncoated one were found in the pH range studied (9.1–10.3) due to the greater NH4PA adsorption of the coated powders.