Property improvement of silicon nitride suspensions for gel casting by surface grafting of carbon black

In order to obtain silicon nitride ceramics with high strength and high porosity applicable for harsh environment, in-situ fabrication of silicon carbide nano reinfercement phase was employed to improve properties of the material. To enhance the stability of gel casting slurry, free radical graft of acrylamide onto carbon black surface was achieved by using a redox initiating system consisting of ceric ions (Ce⁴⁺) and hydroxyl groups. Multi-component suspension was prepared by this grafted carbon black and silicon nitride powder. The factors effecting the grafting reaction were discussed. The grafting was proved by infrared spectrophotometer (IR), thermogravimetry (TG) and transmission electronic microscopy (TEM) analysis. The research shows that grafted carbon black has excellent dispersion stability, the block of reaction is weakened greatly after surface modification, and uniform multi-component suspension can be prepared, which has benefits for silicon nitride gel casting techniques.