Dispersion and densification of nano Si-(Al)-C powder with amorphous/nanocrystalline bimodal microstructure

The dispersion behavior and densification of nano Si-(Al)-C powder with amorphous/nanocrystalline bimodal microstructure were investigated. The Si-C powders synthesized by a mechanical alloying (MA) process had a near-spherical shape with an average particle size of 170 nm. A solid loading of 62 vol% was achieved using polyethyleneimine (PEI) as a dispersant. The optimum dispersant amount was 1 wt% based on zeta potential, sedimentation, and viscosity analysis data. The high zeta potential value (73 mV) compared with that of the commercially available SiC (65 mV) was caused by modified surface properties and consequent promotion of the cationic dispersant adsorption. A Si-Al-C slurry containing 6.5 wt% of sintering additives with a solid loading of 60 vol% was also prepared. The relative density of the dried Si-Al-C slurry was 63.3% without additional compaction, which could be densified at 1650 degrees C at a pressure of 20 MPa using a spark plasma sintering furnace.