Aqueous processing of carbothermally prepared Ca-alpha-SiAlON and beta-SiAlON powders: Powder and suspension characterisation

Properties of carbothermally prepared Ca-alpha-SiAlON and beta-SiAlON powde rs and aqueous suspensions thereof were determined The isoelectric points o f Ca-alpha-SiAlON and beta-SiAlON were 3.4 and 4.6. After addition of deflo cculant, Dolapix CE64, the behaviour of both suspensions is nearly identica l. The isoelectric points become 5.5 and 5.3, respectively. Despite differe nces in bulk composition, grain size distribution, grain size and shape, bo th SiAlON suspensions show a similar dependence of a zeta potential on pH. Optimum slip casting properties, i.e. lowest viscosity values (below 10 mPa s), the highest absolute zeta potential values, the smallest floc size and sediment volume were found between pH 10-11 for both powders. The potentia ls of the different suspension characterisation techniques were compared an d zeta potential and viscosity measurements were found the most convenient. (C) 1999 Elsevier Science Ltd. All rights reserved.