Cordierite Ceramics Prepared from Poor Quality Kaolin for Electric Heater Supports: Sintering Process,Phase Transformation,Microstructure Evolution and Properties

To efficiently utilize the kaolin, an economical way of preparing cordierite ceramic with high performance for electric heater supports was put forward. In this study, sintering process, phase transformation, microstructure evolutions were systematically studied by heating microscope, X-ray diffraction, scanning electronic microscope and thermal analysis. Properties (physical properties, electrical properties and coefficient of thermal expansion (CTE)) were tested for comprehensive performance evaluation. The results showed that the utilization of poor quality kaolin broadened the firing range of cordierite ceramic which was from 1 200 to 1 380 °C. Microstructure becomes loose with increasing of the pore size, which had significant influence on bending strength and electrical properties. High content of K₂O in poor quality kaolin was the reason for liquid phase generation in sintering process, which further leads to microstructural changes. The cordierite ceramic sintered at 1 320 °C had the properties as follows: CTE of 1.98×10^-6 °C^-1 (500 °C), bending strength of 90 MPa, apparent porosity of 15.1%, dielectric constant of 7.5 (100 Hz), and volume resistivity of 1.05×10⁹ Ω·cm (100 Hz). The comprehensive properties are very suitable for use as electric heater supports.