Chemical, phase and structural change of mullite synthesized during sintering of kaolin

Abstract Mullite is of great technological relevance but rarely occurs in nature and as a result different approaches have been adopted in its synthesis from alumina bearing minerals. In this study, chemical, phase and structural change of mullite synthesized from sintering of natural kaolinite clay is investigated. Thoroughly beneficiated kaolinite clay powder was obtained from Nigeria and uniaxially pressed into cylindrical compact of 40 × 30 mm followed by sintering at temperatures of 1200°C and 1300°C, respectively. The chemical composition, microstructure change, phase transformation, and reaction bonding were carried out using EDXRF, SEM, XRD, and FT‐IR, respectively, to assess the synthesized mullite. The results showed that a well‐dispersed primary mullite phase was obtained which was fully developed at increased temperature of 1300°C. Better mullite phase was also obtained with increasing alumina content at more elevated temperature of 1300°C while Si‐O‐Al bonding of mullite crystals was also obtained from the FT‐IR spectra. However, the needle‐shaped mullite structure was not achieved which might be attributed to the sintering temperatures 1200°C‐1300°C utilized.