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

Abstract

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 o 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.

Effect of mechanical activation on mullite formation in an alumina-silica ceramics system at lower temperature

“…Hence, mechanical activation as reported in this study is key to achieving a much lower mullitization temperature. Baitalik et al (2015) in their study sought to keep mullite content same in an SiC/SiC ϩ mullite composite structure in air at 1,300°C for 3 h. Notably, sintering at this temperature of 1,300°C kept the mullite content intact. No information of intense milling was recorded for this study, hence the relatively high temperature needed to keep the mullite content in the composite intact.…”

“…It is worthy of note that in their study, no mechanical activation was to the best of our knowledge reported to disorder the structure of the materials, hence the high temperatures reported in main conversion to mullite. Baitalik et al (2015) in their work observed the role of mullite source on the properties of final ceramics by using two sources of mullite (commercial mullite and synthesized mullite through sol-gel route). Porous SiC ceramics were prepared by sintering powder compact of mullite coated SiC/ SiC ϩ mullite particles in air at 1,300°C for 3 h keeping the mullite content same.…”