Insitu Synthesis and Characterization of Mullite-Carbon Refractory Ceramic Composite from Okpella Kaolin and Graphite

Abstract

Mullite fibres were developed within the carbon matrix through high temperature reaction sintering of kaolinite to produce mullite-carbon refractory ceramic composite. The effects of sintering temperatures on the phases developed and the physico-mechanical properties of the mullite-carbon refractory ceramic composite produced was investigated. The kaolin clay was sourced from Okpella, Edo State, Nigeria. The raw kaolin and graphite were prepared for characterization, to determine their mineralogical phases. Kaolin was thoroughly blended with 40 vol. % graphite in a ball mill. The test samples that contain homogeneous mixture of kaolin and graphite were produced via uniaxial compaction. The compacted samples were subjected to firing (sintering) at 1300˚C, 1400˚C and 1500˚C held at the temperature for an hour. The sintered samples were then characterized for the developed phases using x‐ray diffractometry analysis, microstructural morphology using ultra‐high resolution field emission scanning electron microscope, various physical and mechanical properties were determined. The results obtained from microstructural morphology of the samples revealed the evolution of mullite, that turns needle-like shaped fibre as the temperature was raised to 1500°C. Other phases synthesized in the samples were cristobalite and microcline. The mineralogical phase of the samples revealed the increments in the evolution of mullite and also the variation in other phase attained as the sintering temperature was raised from 1300°C to 1500°C for the sample having the same composition. It was concluded that sample with optimum physico-mechanical properties is obtained at 1400°C.