Study On Microstructures And Properties Of SiC Foam Ceramics Prepared By The Organic Foam Impregnation Method

SiC foam ceramics have well thermal stability, large specific surface area andexcellent mechanical properties, which are mainly applied to high temperature wastegas and molten metal filer, so it possesses broad application prospect. The sinteringtemperature of SiC foam ceramics can be lowed effectively and its mechanicalproperty also can be improved by adding the appropriate additives, thus theapplication scope of SiC foam ceramics can be expanded.The SiC foam ceramics was prepared by organic foam impregnation andpressureless sintering method, with polyurethane foam as the precursor, α-SiC as rawmaterial, polyvinyl alcohol as the precursor surface modifier, carboxyl methylcellulose and ludox as the slurry adhesive, Al₂O₃and Al₂O₃+MgO as sintering aidsrespectively. The effects of sintering temperature, types and content of sinteringadditives on the microstructures and properties of SiC foam ceramics were studied.Phases and microstructures of SiC ceramic foam are analyzed using X-ray diffraction（XRD） and scanning electron microscope （SEM）, and the mechanical properties ofSiC foam ceramics are investigated by the compression test.The results show that the sintering temperature can be reduced and the sinteringrate can be improved by forming the mullite phases through the reaction between theAl₂O₃and SiC on the surface of SiO₂. When sintered at1450°C, porosity decreasesand the compressive strength of SiC foam ceramics firstly increases and thendecreases with increasing content of sintering additives. The compressive strengthreaches the maximum when the content of sintering additives is20wt%. Whencontent of sintering additives is20wt%, both the porosity and compressive strengthfirstly increase and then decrease with increasing sintering temperature, and reachesthe maximum at1450°C.When Al₂O₃+MgO sintering additives are introduced into materials, not only mullite phases form, but also acicular forsterite phases generate. Thus the sinteringtemperature can be reduced, the sintering process can be promoted, and themechanical properties can also be effectively improved. With the increasement ofsintering additives content, both porosity and compressive strength firstly increasethen decrease, and they reach the maximum when the content of sintering additives is8wt%. When the content of sintering additives is8wt%, with the increase ofsintering temperature, the porosity and compressive strength reach the maximum at1450°C. The compressive strength and porosity of SiC foam ceramics can basicallymeet the usage requirements.