Preparation and properties of porous mullite-based ceramics fabricated by solid state reaction

In this study, the effect of the alumina particle size on the formation of mullite using a silica gel powder and micro- and nano-scale Al2O3 powders as raw materials was investigated. The optimized Al2O3 source was then reacted with the silica gel to prepare porous mullite-based ceramics. The results revealed that the highly reactive nano-Al2O3 powder could form mullite at a relatively low firing temperature. Therefore, the nano-Al2O3 powder was used to prepare porous mullite-based ceramics by firing at 1600 degrees C, 1650 degrees C and 1700 degrees C. The pore size of the prepared porous mullite-based ceramics ranges from tens to hundreds of micrometres, with the apparent porosity being 42.8-58.0%. Further, the mullite content in the samples increased with increasing firing temperature, and a higher firing temperature promoted sintering, resulting in improved strength of the sample. After calcination at 1700 degrees C, the mullite content in the sample reached 81.8%, and the sample showed excellent thermal shock resistance. The strengths of the samples before and after thermal shock were found to be 23.6 and 15.58 MPa, with the residual strength ratio being 66%.