Surface oxidation and dispersion behaviour of phenolic resin coated α-SiC powder in aqueous medium

The surface oxidation and dispersion behaviour of phenolic resin coated alpha-SiC powder in aqueous medium has been studied. For comparison purpose a pure alpha-SiC powder was also studied. Zeta potential and viscosity studies revealed that the phenolic resin coated SiC powder requires an electrostatic stabilisation, whereas, the pure SiC powder requires an electrosteric stabilisation in order to produce aqueous SiC slurries with high solids content. The decomposition behaviour of phenolic resin was assessed by differential scanning calorimetry and thermogravimetry techniques. The influence of aqueous processing on the surface characteristics of pure and the phenolic resin coated powders was assessed by means of Fourier transform infrared spectroscopy and by estimating the bulk density of their gelcast samples sintered at 2150 degrees C for 1 h. Various characterisation results revealed that the phenolic resin coating slightly effects the dispersion behaviour of SiC powder in the aqueous medium but it protects powder from surface oxidation during aqueous processing. Sintered properties suggest that in order to obtain a dense SIC body with a bulk density of > 3-13 g cm(-3) (similar to 97.5% of the theoretical density) following an aqueous gelcasting technique, the phenolic resin (similar to 5%) coated SiC powder should possess an average particle/agglomerate size of < 11.0 mu m, compact (green) density of > 1.67 g cm(-3) and B content of > 0.5%.