Preparation Of Silicon Carbide Ceramic Foams Combined With In-situ Mullite Whiskers

SiC ceramic foams is widely used in the area of filtration at high temperature. However, domestic SiC ceramic foams generally has shortage of low intensity and instability or other shortcomings, therefore its usage is limited. In this paper, use organic foam impregnation method and in-situ synthesis method to prepare silicon carbide ceramic foams reinforced by mullite whisker. Use XRD, SEM, mechanical testing and other means to analysis how different process parameters affect mullite whiskers, performance of composite slurry and composite ceramic foams, phase, microstructure and so on.The fabrication of the mullite whiskers is investigated, synthesis mullite by aluminum hydroxide, alumina which react with kaolin respectively. The effect of vanadium pentoxide, aluminum fluoride addition on the ratio of length and diameter of mullite whiskers is studied. The results showed that aluminum hydroxide and kaolin, with addition of 3.5%aluminum fluoride and 4%vanadium pentoxide, sintered at 1400℃for 2h, the morphology of mullite whiskers can be homogeneous, with a diameter of 0.3-0.5μm, ratio of length and diameter is about 10 to 30; when alumina and kaolin, with addition of 3.5%aluminum fluoride,4.5%vanadium pentoxide, sintered at 1450℃for 2h, the morphology can be uniform diameter of about 0.5～1μm, ratio of length and diameter about 8 to 30 of the mullite whiskers.The influence of additives, pH value on the composite slurry of impregnation is studied. The results showed that the performance of composite slurry was best with addition of 0.4%mass fraction of the dispersant TMAH and 0.1%mass fraction defoamer B199; when pH value was 10, the absolute value of Zeta potential was 44.6mV; prepared composite slurry which solid content was up to 80%, uniform stability, good rheology and fit for impregnation.Experimental results showed that in situ growth mullite whisker can effectively enhance the performance of silicon carbide ceramic foams, in situ mullite whisker combined with silicon carbide ceramic foams mainly composite by silicon carbide, mullite, whiskers, combining phase, and the combination of different phase was very close, the distribution of mullite whiskers was uniform and formed a network structure; when the mullite content was 25%, the compressive strength of silicon carbide ceramic foams prepared by alumina to synthesis mullite whiskers was up to 2.1MPa, pore rate was 23.1%, the largest thermal shock resistance was up to 21 times; when used aluminum hydroxide to prepare mullite whiskers combined with silicon carbide ceramic foams, the compressive strength was 1.76MPa, pore rate was 24.7%, the maximum thermal shock resistance was 16 times. In the silicon mullite whiskers combined with silicon carbide ceramic foams, the enhancement mechanism of mullite whisker was mainly load transfer, deflection of crack, whisker bridging and whisker pull out.