Synthesis of Low-Thermal-Expansion Cordierite Ceramics Using Kaolin-Group Minerals

Abstract

Cordierite (2MgO·2Al2O3·5SiO2) in the MgO·Al2O3·SiO2 system exhibits a low thermal expansion coefficient, high thermal shock resistance, low dielectric constant, and excellent electrical insulation properties. However, the material has a narrow sintering-temperature range. If the sintering temperature is too low, the crystal structure of cordierite does not form sufficiently; conversely, if it is slightly higher than ideal, the material decomposes into postelite, spinel, and mullite, leading to a significant increase in its thermal expansion coefficient. To overcome this problem, we adjusted the composition of cordierite by mixing it with predetermined amounts of kaolin minerals. After sintering at 1340℃, the resulting ceramic showed satisfactory physical properties, such as bulk density, absorption rate, and porosity. The optimal mixing conditions included a MgO/Al2O3 molar ratio of 1.006 and SiO2/Al2O3 molar ratio of 2.4277. Given its low thermal expansion coefficient(2.20 × 10−6/℃ at 800℃ and 2.57 × 10−6/℃ at 1000℃) and favorable physical and shrinkage properties, the cordierite prepared in this work may have potential applications in the development of kiln furniture materials for sintering next-generation secondary battery cathode materials.