Preparation And Properties Of Silicon Carbide Based Porous Materials

Silicon carbide ceramics are one of the indispensable and promising ceramic materials nowadays.Compared with other ceramics,SiC has higher specific strength,specific modulus,hardness,thermal stability,and better oxidation resistance.So,it has been widely used in metallurgy,chemical engineering,aerospace,and semiconductor industry.In order to improve the properties of single-phase SiC porous ceramics,in this study,SiC-Al2O3 porous materials were fabricated from the powders of commercial silicon carbide and fused corundum by polymeric foam replication method.Effects of sintering temperatures(1250℃,1350℃,1450℃)and addition amounts of V2O5(0-3%)on a few key properties of as-prepared porous materials such as appearances,microstructures,phase compositions,sintering properties,cold compressive strength and thermal shock resistance have been investigated.In the second part,SiC-FexSiy porous materials were synthesized at different temperatures for 4h,with industrial silicon carbide,iron oxide and activated carbon as raw materials.Effects of w(Fe2O3+C)and sintering temperature(1500-1600℃)on the phase compositions,microstructures,sintering properties,cold compressive strength and oxidation resistance of SiC-FexSiy porous materials were systematically investigated.The preparation processes of silicon carbide based porous materials were also analyzed.The following conclusions were obtained:(1)During the sintering process of the SiC-Al2O3 porous materials,SiC was oxidized in air and formed SiO2,then part of as-formed SiO2 reacted with Al2O3 to produce Al6Si2O13 ceramic reinforced phase.The cold compressive strength and thermal shock resistance of as-prepared porous materials were found to be remarkably improved.(2)Increasing the sintering temperature and adding an appropriate amount of V2O5 could improve the properties of SiC-Al2O3 porous material.When adding 1%V2O5 in mass fraction,the porous materials prepared at 1450℃ for 2h showed the best overall performance.Their apparent porosity is 69.08%,the cold compressive strength is 2.46MPa,and the thermal shock resistance cycles is 25 times(between 1200℃ and room temperature in air).(3)Sintering temperature and w(Fe2O3+C)have significant effects on the properties of SiC-FexSiy porous materials.When w(Fe2O3+C)was 21%and sintered at 1550℃ for 4 h,the materials exhibited the best overall performance.Their apparent porosity is 46%,the average pore diameter is 6.1μm,the cold compressive strength is 8.8MPa,and the thermal shock resistance cycles is 49 times(45 times in air cooling and 4 times in water cooling).In addition,their oxidation resistance is also excellent.(4)The synthesis process of the SiC-FexSiy porous materials includes carbothermal reduction stage and in-situ synthesis stage.The carbothermal reduction stage provides sufficient porosity for the materials,which can be referred to as the pore-forming stage.The in-situ synthesis stage generates FexSiy reinforcement phase,which can be known as the self-enhancement stage.