Processing of Al2O3/SiC nanocomposites—part 1: aqueous colloidal processing

An aqueous sol preparation route was investigated for the production of Al2O3/SiC nanocomposites. Different alumina and silicon carbide powders were used as well as two polyelectrolyte dispersing agents. The alumina powders were dispersed first, via wet ball milling, with silicon carbide being added during a second milling stage. Dispersed sols were prepared with silicon carbide powders having an average particle size ranging from 0.5 μm down to 50 nm. The rheological characteristics of the sols were determined and used together with the results from TEM studies of the sols to ascertain the spatial arrangement of sol particles or ‘sol architecture’. It was found that whilst a polydispersion approach is suitable for the coarser SiC powders, this cannot be applied to very fine particles. Rather, the pH of the sol has to be lowered to encourage heterocoagulation.