Ammonium polyacrylate adsorption on "aluminium hydroxides and oxyhydroxide" coated silicon nitride powders

Si3N4 powders coated with pseudoboehmite, Al hydroxide with a OH/Al mol rat io (R) lower than 3 and bayerite, were prepared from different coating solu tions and dispersed in water with an ammonium polyacrylate (NH(4)PA) to pro duce 11.8 vol% slips. The coated powders showed isoelectric points at pH 7, 7.5 and 7.5 close to that of the precipitate coatings of pseudoboehmite, A l hydroxide (R < 3) and bayerite, respectively, indicating that the surface coverages were almost complete. The bayerite coated powders had the lowest specific surface area values. The coatings on Si3N4 particles were shown t o improve the adsorption of NH(4)PA dispersant on Si3N4 The maximum adsorpt ion of the polyelectrolyte at pH 9.5 increased from 0.01 for the uncoated p owder to 0.03, 0.055 and 0.08 mg/m(2) for the coated powders with pseudoboe hmite, Al hydroxide (R < 3) and bayerite, respectively. (C) 2000 Elsevier S cience Ltd and Techna S.r.l. All rights reserved.