Thermal conductivity and specific heat of kaolinite: Evolution with thermal treatment

The structure and microstructure of a standard reference kaolin clay change significantly with thermal treatment. The consequences in terms of thermal conductivity and specific heat have been studied. Thermal conductivity measurements were made, using the laser flash technique, on the green body and samples subjected to thermal treatments at different temperatures between 700 and 1400 °C. The results show that the green body and kaolin treated at temperatures below 1050 °C exhibit low values of effective thermal conductivity, less than 0.3 W m−1 K−1. Higher temperature treatment yields a strong increase in thermal conductivity up to 3 W m−1 K−1. Through complementary characterization based on X-ray diffraction and scanning electron microscopy, this evolution as well as that of the specific heat is interpreted in terms of structural reorganisation of the clay, microstructural changes and crystallisation of mullite and cristobalite.