Preparation Of Porous Silicon Carbide Ceramics By Gel-casting And Cordierite Bonding Method

In this paper,SiC is used as the raw material,and the in-situ cordierite combination method is adopted.Kaolin,talc powder and aluminum oxide are used as oxide binder,which are identified as synthetic cordierite phase raw materials(hereinafter referred to as cordierite production materials).The ratio between the three is fixed,which with amorphous SiO2 derived from the oxidation of the surface of SiC at high temperature is used to form a cordierite phase to bind the SiC particles,so as to achieve the purpose of reducing the sintering temperature.It is formed by gel-casting method,and the sintering process is optimized to effectively control the discharge of organic matter process,so that the polymer is carbonized and volatilized to form pores,and acts as a pore-forming agent.SiC porous ceramics with low thermal expansion coefficient and good mechanical properties.By studying the ratios of SiC and cordierite production materials,organic monomers additions,and the rate of organic discharge,sintering temperatures,etc.on the structure and performance of SiC porous ceramics,to obtain the optimal ratio between SiC and cordierite production materials,the best monomer addition,the best sintering temperature and the rate of organic discharge,optimize the sintering process of silicon carbide porous ceramics.On this basis,in order to further reduce the sintering temperature,a rare earth oxide sintering aid(CeO2)was added to study the effect of CeO2 on the structure and properties of the SiC porous ceramics,and an appropriate amount of sintering aid was added to prepare SiC porous ceramics with excellent performance.When the ratio of SiC to cordierite forming material is 3:1(that is,containing 75wt%SiC),at a sintering temperature of 1300? at a discharge of organic matter rate of 10?/min,the cordierite in the prepared porous ceramic sample The phase has good crystallinity,and the porosity is about 54.72%.The microstructure of its cross-section has a uniform pore shape and regular shape.There is a well-developed neck at the bottom of the pore,its compressive strength is 18.65 MPa,and its thermal expansion coefficient is 7.08×10-6?-1.As the amount of organic monomer added gradually increases,the Viscosity of the mixed slurry decreases and its fluidity increases.The addition of the organic monomer is beneficial to prepare a mixed slurry with high solid phase content,low viscosity,and good fluidity.The pore forming process mainly uses the added organic monomer to oxidize in the sintering process to form the gas phase and leave the pores.Therefore,the porosity of SiC porous ceramics increases with the increase of organic monomer.When the addition amount of organic monomer is 9 wt%,the raw material composition of SiC and cordierite is used in the ratio of 3:1,the mixed slurry prepared by ball mill has lower viscosity,better fluidity,and is more suitable for setting Glue injection molding process;and at a discharge of organic matter rate of 5?/min,porous ceramics prepared at a sintering temperature of 1300?have a higher porosity of 55.76%.When the sintering temperature is increased,the characteristic peak and peak strength of the cordierite phase in the porous ceramic sample is enhanced,the crystallinity is high,and its content is high,which promotes the formation of the cordierite phase,effectively exerts the bonding effect of the cordierite phase,and makes the ceramic structure The densified compressive strength increases and the thermal expansion coefficient decreases.When the sintering temperature is 1300?,the porous ceramic samples prepared by sintering have regular pore shape,uniform distribution,good neck joint development,and the best comprehensive performance.Compared with the porous ceramic sample sintered at a discharge of organic matter rate of 10?/min,the pores in the microstructure of the ceramic sample sintered at a discharge of organic matter rate of 5?/min are more obvious honeycomb structures.And the arrangement is close,the shape is regular,the distribution is uniform,with higher compressive strength and lower coefficient of thermal expansion.Comprehensive analysis shows that the addition of 9 wt%of organic monomers at a discharge of organic matter rate of 5?/min and a sintering temperature of 13000C,the SiC porous ceramics obtained after sintering have excellent properties,of which the porosity is 55.76%,and the compressive strength is 30.54 MPa,and its thermal expansion coefficient is the lowest,and it is 6.39×10-6?-1.The addition of CeO2can promote the formation of cordierite phase,and the liquid phase sintering phenomenon occurs during the sintering process,which makes the crystal grains closely combined,the porous ceramics become denser,the compressive strength increases,and the porosity decreases,but the overall is higher than 40%The coefficient of thermal expansion decreases,but when excess CeO2 is added(more than about 3 wt%),the coefficient of thermal expansion begins to increase.Therefore,the amount of CeO2 addition can be selected at 3 wt%.At this time,the porosity is 42.58%,the compressive strength is 51.07 MPa,and the thermal expansion coefficient is 5.37×10-6?-1.