Preparation And Properties Of Mullite/SiC Porous Ceramic By In-situ Reactive Sintering

SiC-based porous ceramic have been widely used in the filed of high-temperature filtration system because they have high thermal stability, large surface areas, high mechanical property, resistance to chemical attack, good filtration performance, and so on. In this thesis, mullite/SiC porous ceramic were prepared by in-situ reactive sintering. SiC powder served as substrate material, and Guangxi white clay and Al2O3 were added. In addition, graphite, active carbon and carbon black were used for pore former. CMC used as binders. The influence of preparation processing, SiC particle size, content of mullite, and the kind and content of pore former on microstructures, phase composition, porosity and bulk density, and the flexural strength have been systematically studied. The result shows as follows:(1) The effect of preparation process on properties of muttile/SiC porous ceramic has been depth investigited. The result shows when sintering temperature varied from 1250℃ to 1450℃, the porosity of mullite/SiC porous ceramic firstly increased and then gradually decreased, the bulk density increased, on the contrary, the flexural strength of samples slightly decreased and then gradually increased. The porosity and flexural strength of the sample sintered at 1450℃ were 27.0% and 40.4 MPa. When holding time varied from 2 h to 4 h, with it increased, the liquid phase of samples raised, the porosity of samples decreased, the flexural strength and bulk density gradully increased. The most suitable holding time is 3 h. Under different molding pressures, the relationship between the porosity and flexural strength of samples defer to the Rice formula.(2) The effect of particle size on properties of muttile/SiC porous ceramic has been investigited. The result shows that with the particle size increased, the porosity and flexural strength of samples decreased, the bulk density increased. when the sample sintered at 1350℃ with the particle size was 6.5 microns, the porosity and the flexural strength were 45.8% and 55.4 MPa. when the sample sintered at 1250℃ with the particle size was the 75 microns, the porosity and the flexural strength were 27.6% and 15.2 MPa. The sample has the smaller of silicon carbide particle size, the higer particle surface activity will be, and the more mullite has.(3) The effect of the content of mullite on properties of muttile/SiC porous ceramic has been depth investigited. The result shows that when the particle size was 75 microns, the content of mullite was 10 wt%, the porosity and flexural strength were 28.1% and 6.25 MPa; the particle size was 13 microns, the content of mullite was 30 wt%, the porosity and flexural strength were 31.2% and 54.3 MPa. With the higher of the content of mullite and more liquid phase which were introduced by Al2O3 and Guanxi clay, the sintered of samples can promote.(4) The effect of kind and content of pore former on properties of muttile/SiC porous ceramic has been investigited. The result shows that adding carbon black had the highest porosity, and the porosity of samples with the activated carbon was the lowest, and the flexural strength was the opposite. The content of carbon black added at 25 wt%, the porosity was 52.6%, the flexural strength was so small; the content of activated carbon at 5 wt%, the porosity and flexural strength were 35.2% and 73.7 MPa. Graphite as the pore former, with the content increased, the porosity of the sample increased and the flexural strength decreased. When the content of graphite varied from 0 wt% to 30 wt%, the porosity increased from 30.6% to 46.3%, the flexural strength decreased from 26.8 MPa to 6.5 MPa. The relationship curve of porosity and flexural strength of samples also deferred to the Rice formula.