Reaction mechanism and microstructure evolution of andalusite with zirconia

The reaction process of zircon (ZrSiO4) in the andalusite (Al2SiO5)–zirconia system was studied at the temperatures from 1270 to 1460 °C. Phase compositions and microstructures of reaction products were analyzed by X-ray diffraction analysis, scanning electron microscopy and energy-dispersive spectrometer. The results show that andalusite starts to react with ZrO2 to form zircon and mullite at 1270 °C. As the temperature rises, the amount of zircon gradually increases. The reaction process is in accordance with the nuclei and growth models: Amorphous silica formed by the decomposition of andalusite reacts with zirconia to form zircon crystal nucleus, and the nucleus continues to develop and encapsulate the ZrO2. Then, the amorphous silica reacts with zirconia through the product layer of zircon. The time exponent of m illustrates that the reaction between andalusite and zirconia is not an isokinetic process. The reaction rate constant increases with the rise of temperature. The activation energy of the reaction is 127.28 kJ mol−1.