Gelcasting Of Aqueous Silicon Carbide/Carbon Black Slurry

Advanced ceramic forming processes are key techniques for producing ceramic components with large dimensions and complicate shapes in order to increase materials reliability and reduce the manufacturing costs. Gelcasting is one of the most promising methods among all the advanced ceramic forming techniques. In this thesis, SiC/carbon black slurry with low viscosity and high solid loading was prepared and the mechanism of free-radical polymerization of acrylamide in SiC/carbon black slurry was proposed. Homogenous dense RBSC green bodies were prepared through gelcasting process. The main results of the research are listed as follows:For the first time, the polymerization process of acrylamide monomer in SiC/carbon black slurry was studied systematically and the polymerization mechanism was put forward. One conception of reducing the activity of free radical in polymerization system by adding acetylacetone was put forward. Controllable free-radical polymerization of acrylamide in concentrated SiC/carbon black aqueous suspensions can be achieved by adding acetylacetone to prolong the idle time and the conversion of polymerization. The result is very important and useful for gelcasting of ceramic suspension containing carbon materials.For the first time, SiC/carbon black slurries with high solid loading were studied systematically. The researches indicated that dispersion of carbon black was the key factor to affect the achievement of obtaining high solid loading SiC/carbon black slurries. Relationship between dispersion of carbon black particles and function groups on carbon black surface was investigated. SiC/carbon black slurries with 65% solid loading was prepared through increasing the contents of carboxylic and lactonic functions of carbon black, powder mixing in batches and optimal process condition. The slurry showed pseudoplastic characteristics, and can satisfy the requirement of gelcasting process.Heat evolution of the system was measured to characterize the polymerization process of acrylamide monomer in ceramic slurry. The conversion of polymerization process of acrylamide monomer can be calculated by heat evolution. The measurement with a measuring error of about 5% was proven effective for several ceramic slurries. Drying procedure, pore size distribution, microstructure and density uniformity of SiC/carbon black green bodies were studied systematically. SiC/carbon black green bodies with complicated shapes have been fabricated through gelcasting process. Theshrinkage of green body was 0.3% and the density deviation was 0.32%. After infiltrated with molten silicon, the shrinkage of sintering body had another 0.2%. The researches indicated gelcasting processing combined with reaction-bonded technique was a promising method for producing silicon carbide components with large dimension and complicate shape.Chen YufengDirected by Prof. Fan Qisheng...