Properties of mullite-bonded SiC ceramics from mullite precursor sol coated SiC powder and crystallization kinetics of mullite formation

Mullite bonded -bonded porous silicon carbide (SiC) ceramics were fabricated by sintering sol–gel mullite-coated SiC particles. The coated powder was characterized by measuring zeta potential at different pH, X-ray photoelectron spectroscopy (XPS), XRD analysis and thermal analysis. The thermal oxidation behaviour of coated SiC powder was examined by thermogravimetry (TG)-Differential thermal analysis (DTA) technique in dry air. Mullite formation exhibited two exothermic peaks; the first 1195–1213°C and the second at 1319–1358°C. The activation energy for mullite crystallization in the first step ranged from 884 to 1250 KJ mole− 1 and in second step it ranged from 759 to 1018 KJ mole− 1. Characterization of resulting SiC ceramics were done by XRD, SEM, TEM, EDS, porosity, pore size distribution analysis and measurement of mechanical strength. The ceramics with porosity ∼42 vol.-% exhibited flexural strength of ∼23 MPa. Microstructure observations revealed that neighbouring SiC particles were bonded by well-developed neck consisting of needle-shaped mullite grown in a siliceous matrix.