Solidifying Concentrated Si3N4 Suspensions for Gelcasting by Ultrasonic Effects

Ultrasonic wave were used to accelerate the solidification of Si3N4 suspensions for gelcasting. Different zones of the suspension solidified simultaneously under ultrasonic effect and structure defects in the green body caused by asynchronous solidification of the suspension could be avoided. It was found that the amount of initiator and catalyst for the polymerization of acrylamide monomers in the suspension can be reduced significantly and the flexibility of gelcasting processing could be improved. The mechanisms of the ultrasonic effect can be explained as following: on one hand, ultrasonic can increase the temperature of the suspension homogeneously; on the other hand, ultrasonic activates monomers, initiator and catalyst, and then boosts the reaction that initiator decomposes and generates free radicals and accelerates the polymerization rate of acrylamide monomers greatly.