Changes in beta-sialon suspension behaviour due to surface oxidation, milling, surfactant and sintering additive

Results of a study of the behaviour of aqueous suspensions of carbothermall y prepared beta -sialon are presented. The influence of an oxidation treatm ent, attrition milling, sintering additive (Y2O3) and addition of a deflocc ulant (Dolapix CE 64) on the stabilisation behaviour of the suspensions was studied. Obtained results show that the surface properties of beta -sialon particles are affected, as expected, by the oxidation treatment (isoelectr ic point, pH(iep) approximate to 2.1) and by attrition milling of the power (pH(iep) approximate to 4.6). In the presence of Y2O3 the suspension of be ta -sialon becomes less stable (pH(iep) approximate to 3.4), the viscosity is increased and the stable pH range is reduced. This behaviour is explaine d in terms of surface composition of p-sialon, the solubility of yttria in acidic solution and the possibility of precipitation of yttrium-hydroxy com plexes on p-sialon surface at higher pH while increasing the pH. Addition o f the deflocculant increases the absolute zeta potential and changes the su spension behaviour from shear thickening to shear thinning. Low viscosity s uspensions with 60 wt% beta -sialon and 10 wt% Y2O3 can be prepared at pH > 10, such that they can be used for slip casting. (C) 2000 Elsevier Science Ltd and Techna S.r.l. All rights reserved.