Fabrication of Mullite Bonded Porous SiC Ceramics via Sol-Gel Coated Precursor

In the present work oxide bonded porous SiC ceramics were fabricated using surface modified sol-gel mullite coated SiC particles. The coated powder was characterized by measuring zeta potential at different pH, XRD analysis, thermal analysis and FTIR spectroscopy. To observe the role of mullite source on the properties of final ceramics two other sources of mullite (commercial mullite and synthesized mullite through sol-gel route) were also used. Porous SiC ceramics were prepared by sintering powder compact of mullite coated SiC/SiC+mullite particles in air at 1300 degrees C for 3h keeping the mullite content same. The morphologies, phase composition, porosity, pore size distribution and mechanical strength of porous ceramics were examined as a function of mullite source. It was observed that the coating of SiC particles by sol-gel mullite precursor effectively reduced the % SiC oxidation degree from 51 to 33%. The ceramics obtained from sol-gel coated precursor had a flexural strength of approximate to 23MPa at porosity of approximate to 45 vol% and ceramics fabricated from SiC with sol-gel derived mullite powder had a flexural strength of approximate to 25MPa at porosity of approximate to 42 vol%. Microstructure observations revealed that neighbouring SiC particles were bonded by well-developed neck consisting of needle-shaped mullite grown in a siliceous matrix.