Synthesis of high‐performance mullite ceramics based on associated rare‐earth kaolin

Abstract The objective of this work was to prepare high‐purity, high‐strength mullite ceramics from low‐cost, associated rare‐earth kaolin (AREK). A reaction sintering process using calcined AREK and γ‐Al ₂ O ₃ powders was used to synthesize high‐performance mullite ceramics. Mineralogical, morphological, and chemical characteristics of AREK were given. The effects of associated REEs in kaolin and sintering temperature on the microstructural evolution, phase transformation, and physical properties of mullite were studied. The results showed that the mullite contents were 98.8%, the maximum aspect ratio was 8.22 μm, the relative density was 93.04%, and the micro‐Vickers hardness and flexural strength were 10.63 GPa and 184.24 MPa, after sintering at 1500°C for 4 h. For comparison, calcined without rare‐earth kaolin was also employed as a raw material to synthesize mullite ceramics, and the mullite content prepared by sintering the two kaolin clays at 1320–1480°C for 4 h was quite similar. However, mullite prepared using AREK forms secondary mullite in the temperature range of 1480–1500°C with a significantly higher mullite content, and therefore, the advantages of preparing mullite based on AREK as the raw material are high purity, low mullitization temperature, and high strength.