Microstructure of silicon carbide nano powder–polycarbosilane–solvent mixed slurries and observed shear rate dependence in slurry viscosity

SiC powder, polycarbosilane and xylene mixed slurries were prepared for microstructure observation and viscosity measurement. Slurries with averaged primary SiC size of 270 or 50 nm revealed existence of isolated secondary particles smaller than 1 μm in optical microscope observation. These secondary particles showed a Brownian motion in a xylene-PCS medium. On the other hand, slurry with an averaged primary SiC size of 20 nm revealed existence of large secondary particles in the size of 2–5 μm. The apparent area occupied with these secondary particles was far larger than that occupied by secondary particles of 270 or 50 nm in spite of a low SiC content. It was suggested that the secondary particles observed in the 20 nm slurry possessed small spaces among the primary SiC particles. Viscosity measurement presented that apparent viscosity of the slurry was high in general when the primary SiC particle size was small. In particular, the 20 nm SiC slurries showed quite high viscosity even at a SiC content of 5–6 mass%, which almost corresponded to that of 40 mass% for a SiC 270 nm slurry. Shear thinning effect was also remarkable when the primary SiC particle size was small.