Effects of sintering additives on microstructure and properties of porous SiC ceramics with high porosity

The porous SiC ceramics were fabricated by gel-casting and pressureless sintering process in air atmosphere with a solid loading of 10% slurry constituting of tert-butyl alcohol,acrylamide,SiC powder and sintering additives.The effects of two kinds of sintering additives,Al2O3 and Al2O3+SiO2,on the porosity,microstructure and mechanical properties of the porous SiC ceramics were studied.The results show that the sintering additive of Al2O3+SiO2 obviously improves the sinterability of SiC ceramics,and compared with that only using Al2O3 as sintering additive,both sintering temperature of SiC specimen and formation temperature of mullite phase are decreased by about 50 ℃.The median pore diameter of the porous SiC ceramics is about 2 μm and presents single peak distribution.The compressive strength of the porous SiC ceramics increases with increasing the sintering temperature,whereas the porosity has little change.Using Al2O3+SiO2 as sintering additive,the porosity and compressive strength of SiC porous ceramics sintered at 1 400 ℃ reach 70.57% and 17.74 MPa,respectively.