Study On Room Temperature Freezing Casting Of Porous Carbon Preform And Properties Of The Reaction Sintered Body

Compared with traditional aqueous based freezing casting, room temperaturefreezing casting is superior, for it is much easier to put into practice and needless offreezing equipments. The aim of this paper is to make porous carbon preform withfine porous structure by room temperature freezing casting,the preform has somehigh performances that can react with melting silicon well during liquid siliconinfiltration process, the reaction formed SiC generated in that way has dense,homogeneous structure, and the flexural strength of it is much higher. In order toachieve that goal, this paper has studied the preparing process of camphene basedcarbon slurry, the casting process for making porous carbon preform, themicrostructure of the porous carbon preform, the relationship between reactionformed SiC’s microstructure and the mechanical performance of it. The main contentsand conclusions of the research were listed as following:1.The main factors which will effect the rheological behavior of the camphenebased carbon slurry has been studied. such as carbon resource, dispersant and thedosage of it, solid content, the additive and so on. The results show that: Both of thecharcoal powder and carbon N990are suitable dispersed in camphene when usemodificated polyester as dispersant, but the reaction performance of the charcoalpowder is much better, so the charcoal powder is used as carbon resource; DispersantCH5was selected as dispersant when preparing camphene based charcoal powderslurry, the suitable dosage of it is3wt%to the mass of charcoal powder; When thesolid content of the slurry is improved, the viscosity of the slurry is raise, and therheological behavior of the slurry is changed from Newtonian fluid to Bingham fluid;The viscosity of the slurry will raise when adding some dosage of polystyrene whichact as the binder in the porous carbon preforms; The rheological behavior of the slurryhas the tendency to changed from Bingham fluid to Shear thickening fluid whenadding methyl cellulose which used as pore maker.2.The casting conditions which will effect the linear shrinkage and homogeneitydegree of the microstructure of the preform were studied, such as casting at room temperature, relatively low temperature casting and room temperature freezing castingassisted with vibration, The sublimation behavior of the porous carbon preform undera stable room environment has been studied also.The result show that: The shrinkageof the porous carbon preform is largest when casting under relatively low temperature;The shrinkage during sintering is the main cause responsible for the dimension changeof the preform; The circle crack is much easier to generated on the surface of thepreforms during sublimation process when the preforms was casting under roomtemperature; When the porous carbon preforms were casting under room temperatureassisted with vibration,there will leaving larger cylinder pore in the preform due to thefully growth of camphene dendrite; The relatively homogenous microstructure will begenerated when casting at relatively low temperature; The sublimation behavior of theporous carbon preform under a stable room environment is agree with exponentialfunction.3.The microstructure of the porous carbon preform and reaction sintered SiCwere studied, the microstructure of the reaction sintered SiC and the mechanicalperformance was also studied. The results shows: The porous carbon preform has twokinds of pore structure, they are the larger cylinder pores and smaller irregular pores,the porous carbon preforms were not suitable for reaction sinter and the reactionformed SiC has large macroscopy defects; When adding methyl cellulose, thehomogeneity degree of the porous carbon preform and the reaction performance wasimproved largely;When the charcoal powder content slurry is40vol%in the slurry,the scatter degree of the flexural strength of the reaction formed SiC is narrowed byincrease the content of methyl cellulose; When the mmethyl cellulose:mcharcoal powder=10wt%,the scatter degree of the flexural strength of the reaction formed SiC was alsonarrowed by increasing the content of charcoal powder; The density, average flexuralstrength, Weibull modulus, Vicker’s hardness of the best reaction formed SiCproduced in this paper were2.96g/cm3,429.02MPa,13.27,27.52GPa,respectively.