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

Results of a study of the behaviour of aqueous suspensions of carbothermally prepared ß-sialon are presented. The influence of an oxidation treatment, attrition milling, sintering additive (Y2O3) and addition of a deflocculant (Dolapix CE 64) on the stabilisation behaviour of the suspensions was studied. Obtained results show that the surface properties of ß-sialon particles are affected, as expected, by the oxidation treatment (isoelectric point, pHiep ˜ 2.1) and by attrition milling of the power (pHiep ˜ 4.6). In the presence of Y2O3 the suspension of ß-sialon becomes less stable (pHiep ˜ 3.4 ), the viscosity is increased and the stable pH range is reduced. This behaviour is explained in terms of surface composition of ß-sialon, the solubility of yttria in acidic solution and the possibility of precipitation of yttrium-hydroxy complexes on ß-sialon surface at higher pH while increasing the pH. Addition of the deflocculant increases the absolute zeta potential and changes the suspension behaviour from shear thickening to shear thinning. Low viscosity suspensions with 60 wt% ß-sialon and 10 wt% Y2O3 can be prepared at pH>10, such that they can be used for slip casting.