Sanchita Baitalik

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°C for 3 h 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 ∼23 MPa at porosity of ∼45 vol% and ceramics fabricated from SiC with sol-gel derived mullite powder had a flexural strength of ∼25 MPa at porosity of ∼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.

Properties of Porous SiC Ceramics Processed by Gelation and Consolidation of Boehmite Coated SiC Suspensions

ABSTRACT SiC powder was dispersed in various concentrations of boehmite sol. The boehmite coated SiC powder was characterized by zeta potential measurement, TEM and FT-IR analyses. Mullite bonded porous SiC ceramics were fabricated by sintering boehmite coated SiC powder compact via a pressureless sintering in air at 1300oC and were characterized by XPS, XRD, SEM analyses. The sintered ceramics have an interconnected open porous network with near uniform pore diameter. Rod shaped mullite crystals were observed in the neck region that bonded the SiC particles together. Effect of boehmite sol concentration on phase composition, microstructure, flexural strength, porosity and pore size distribution was studied. The ceramics synthesized from 30 wt% boehmite sol coated SiC powder contained 26 wt% mullite with ∼30 vol% porosity. GRAPHICAL ABSTRACT

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.