The Study On Gelcasting Forming Process Of Si₃N₄ Ceramic Material

The main focuses of this thesis are gelcasting forming technique in aspects of low-toxicity monomer and coaxial nozzle system used to fabricate Si3N4 hollow spheres.In this work, the low-toxicity monomer NMA was instead of the monomer AM, and controlling parameters of polymerization was discussed from the point of view of dynamics. The influence factors on polymerization such as the content of monomer, cross-linker and initiator, temperature and pH were studied utilizing the Taguchi statistical method. The result of experiment showed the optimum value of above elements when NMA was polymerization. The content of monomer is 20wt. %; the key of initiator is its concentration; the temperature of polymerization and body drying should be below 65oC; the range of pH for polymerization is from 2 to 11. The importance of factors were identified by analyzing their relative scores , namely D(Temperature)＞A(Monomer content)＞B(The ration of monomer to cross-linker)=C(Initiator content)=E(pH)。Based on spray drying-coaxial nozzle system and gelcasting technology, this paper presented a novel method-gelcasting coaxial nozzle system (GCNS) that was used to fabricate ceramic hollow spheres and introduced the equipment self-assemble. In this dissertation, Si3N4 hollow spheres were prepared using this GCNS and controlling parameters of this process were optimized, which included forming medium that is methyl silicon oil, the temperature of reaction in range of 80～90℃, the air flow injecting into coaxial nozzle that must be discontinuous, and drying method –drying in forming medium. The results of the experiment showed that surface performance of Si3N4 powder is the key factor of the performance of slurry. The weight percent of slurry that was made of Si3N4 coated powders was raised to 42%. The obvious difference of the slurry used to GCNS from traditional gelcasting forming technique was that the amount of PVA was added into the slurry as binder, which was to help the slurry form liquid film easily. The content of PVA is about 20-40wt. % used to the slurry of GCNS. The weight percent of initiator is 1-1.5wt. %.