The Research On Preparation And Characterization Of Porous SiC/Mullite Ceramics

SiC porous ceramic is a new functional material, which can be widely applied inthe fields of energy, environmental protection, biological, military project andchemistry industry for its excellent performances of both the porous ceramic andSiCs’, such as low density, high specific surface area, thermal stability, abrasionresistance and chemical stability. Mullite is the sole stable compound among theAl2O3-SiO₂system. Mullite has many excellent characteristics, such as low heatconduction coefficient and thermal expansion coefficient, high resistance to creepdegeneration and thermal stability. Above all, SiC/Mullite porous ceramic has a broadprospect of application and market.In our research, SiC, kaolinite and A1₂O₃were main raw materials and theSiC/Mullite porous ceramic was prepared by adding pore-foaming agent. The effectsof sintering temperature, pore-foaming agent, mkaolinite/mA1₂O₃, additive, holding timeand molding pressure on the porosity, volume density, flexural strength, thermalshock resistance and oxidation resistance performance of the porous ceramic werediscussed. The phase composition and fracture morphology of the sample werecharacterized by XRD and SEM. Through systematic research, the main researchconclusions are as follows:（1）The samples used amylum and carbon black as pore agents sintered atdifferent temperatures. The results reveal that pore content was10wt%, the porositywas31.40%, the strength retention rate was31.86%, oxidation weight gain was0.72%after thermal shock resistance and oxidation resistance tests of the sample.（2）On the basis of the pore-forming agent content was10wt%, the effect of massratio of kaolin and Al2O3on the properties of porous ceramics were also studied, asthe ratio increased, bending strength first increased and then decreased. The resultsindicate that when the mass ratio of kaolin and Al2O3was1.00, Al2O3was slightlyhigher than the proportion of synthetic theory mullite, the mechanical properties ofthe composites were the best that flexural strength was42.50MPa.（3）The effect of three different additives of MgO, Cr₂O₃, Y₂O₃on theperformance of the porous ceramics were also studied when the pore-forming agentcontent was10wt%and the mass ratio of kaolin and Al2O3was1.00. Thecomprehensive performance of prepared porous ceramics were the best, while MgOaddition amount up to2wt%, porosity was32.84%, volume density was1.864g/cm3, flexural strength reached up to44.58MPa.（4）The paper discussed holding time and molding pressure for the influence ofporous ceramics properties. The optimal results of SiC/mullite were obtained asfollows: When the molding pressure was100MPa, the sintering temperature was1350℃, the holding time was2h, the porosity, the flexural strength of the sinteredsample’s properties were32.84%,44.58MPa, respectively. After thermal shockresistance and oxidation resistance test of the sample, the thermal shock strengthretention rate was32.30%, the oxidation weight gain rate was0.57%.