SiC_W/Al₂O₃ Ceramic Composites Prepared By In-situ Carbothermal Reaction From Kaolinite

SiCw/Al2O3 ceramic was widely used because of its forbearing high temperature, oxygenation and abrasion and it had higher mechanical properties than that of single phase A12O3 ceramic. When SiCw was added into Al2O3 phase, the mechanical properties including fracture toughness, bending strength, thermal shock resistance were improved. So far it became one of the most attractive composite ceramic.In this paper, the main purpose of the study is to explore a new method to synthesize advanced SiCw/Al2O3 composites with relatively low cost. SiCw/Al2O3 composite powder was produced by in-situ carbothermic from kaolinite. The composites powder was sintered by hot pressing sintering that no stained composites can be obtained. The thermodynamics, dynamics, the phases and microstructure of composites were analyzed, which in order to show the mechanism. The whole carbothermal reduction should be done step by step. Firstly, kaolinite was dehydrated and transformed to mullite and silicon dioxide (amorphous). Then as the formation of SiO vapor-phase, SiO2 was reduced to SiC. At last mullite phase was reduced to SiC and Al2O3, the structure of Al2O3 coated by SiCw formed at last. The SiC whiskers grew along the fixed axis normal to the (111) direction. Effects of technological parameters on products were studied simultaneously. The results indicated that pure and uniformLy distributed SiC whiskers and A12O3 particles can be obtained at 1500?for holding 2 h when the molar ratio of kaolinite/carbon was 1/8 and the argon flow was 80 mL/min. The SiC whiskers displayed an ideal aspect ratio of more than 25 with a length is over 5?m and a diameter is 200 nm.Using kailinite/polymer compounds as materials, kaolinite/DMSO intercalation compounds were prepared by using dimethylsulphoxide as intercalation agent and the polymer monomer can be intercalated between the layers of kaolinite by displacing intercalated dimethylsulphoxide from kaolinite/DMSO intercalation compound. It polymerized by heating to finally prepare kaolinite/polymer intercalation compound. The polymer intercalationed the layer of kaolinite, changed the vibration hydroxy of interbed of kaolinite, and high intercalation ratio was got. SiCw/Al2O3 composite powder was produced by in-situ carbothermic reduction.There is large distinction on the process between kaolinite/C and kaolinite/polymer system.The distinction could be attributed to the driving force. Solid state reaction rate is controlled by diffusion which with the slowly diffusion rate in solid structure. But in the kaolinite/polymer system, kaolinite flakes are evenly dispersed in polymer because of the intercalation impact. Kaolinite/polymer compounds transform into kaolinite and carbon laminated structures after carbonation reaction with temperature increasing. Therefore kaolinite and carbon contract with a molecular level, the reactants have no use for long range diffusion in carbothermic reaction under high temperature, which increasing the driving force and decreasing the temperature of carbothermic reduction.It was also found that different additives have a beneficial effect on the microstructure and properties of SiCw/Al2O3 composites. The composites will be the good mechanic properties. Additives Y2O3 and A12O3 micro powder have a beneficial effect on the microstructure and properties of SiCw/Al2O3 composites. Products with additive of 3wt% of Y2O3 had a higher relatively density of 97.2%, tensile strength of 345.69MPa and better microstructure.