Preparation Of SiC Ceramic Materials By Reaction Melt Infiltration And Study On Microstructure And Performances Of The Materials

Reaction-bonded Silicon Carbide(RBSC) is a multiple phase ceramic composedwith SiC and free Silicon, and in some situation it contains free Carbon as well. Themelting point of Silicon is not high and its chemical stability is not well either, soRBSC ceramic can not be used at temperature above the melting point of Silicon. Andperformance of the materials, such as mechanical performance at high temperature,corrosion resistance and resistivity, has been affected too. In order to improve theseperformances, we must control the content and distribution effectively. The purposeof this subject study is to explore the possibility to prepare RBSC materials whoseperformances are different from the common ones, and to discuss the influencingfactors to the microstructure and performance of materials and there regularity.Another purpose of this study is to generalize the relationship between microstructureand performance of the RBSC ceramic materials.In this paper, The RBSC ceramics had been prepared by dry pressing, whichexhibit density of 3.17 g/cm~3 or fracture strength of 625MPa. The influence ofprocessing parameter to microstructure of green body and density of the ceramicswere discussed.Results of the experiment indicate that suitable distribution of pore size withdouble peak of the green body is good to the process of liquid silicon infiltration andincreasing the sintering temperature properly can promote the reaction completethoroughly. Purification to the stuff is good to promote the fracture strength ofmaterial.During the study, I discovered that, due to the and high oxygen content, it isdifficult for you to get RBSC ceramics with high mechanic properties if the stuff istoo thin. The strength is not up to the density, and the material which density is 3.10g/cm~3 has the biggest fracture strength. With the increasing of the sintering densities,the fracture strength of RBSC ceramics increases firstly, then decreases. During theincreasing period, the fracture strength has the nearly linearity relation with thecapacity content of free silicon. The thinner free silicon is, the more uniformdistribution is, the higher fracture strength of the material is. Usually, the smaller thegrain size is, the higher the fracture strength of the RBSC multiphase ceramic is.RBSC ceramic has good oxidation resistance in the normal atmospheric pressure. The lower content of free silicon is, the better oxidation resistance material gets. Withthe same content of free silicon, material that has bigger grain size has betteroxidation resistance.RBSC ceramic has good corrosion resistance of acid except the HF, while hasweak corrosion resistance of the HF and alkali. The chemical corrosion resistance ofhigh density material is evidently better than the one with medium density. The highdensity RBSC ceramic with minor free carbon has better corrosion resistance than thecompact material with the same density, especially in the acid.RBSC ceramic has better electrical conductivity if it contains more free silicon,which may has relationship with the purity of Silicon that the experiment used. Andthe thinner grain size the material has, the worse electrical conductivity it has.The study testify that you can improve the performance of RBSC ceramic bydecreasing the content of free Silicon in RBSC ceramic or improving its distributionuniformity, and reducing structure macula of the material. However, the result ofcorrosion experiment on high density material indicates that it is unrealistic toimprove the mechanical performance of RBSC ceramic at temperature above themelting point of Silicon by promoting the material density.