Study of mullite formation in porcelain stoneware applying isoconversional and IKP methods

The growth process of mullite in a porcelain stoneware body has been studied under isoconversional, isokinetic relationship and invariant kinetic parameters. Activation energy for mullite crystallisation of over 589–628 kJ mol−1 and a Ln A over 50–59 min−1 was obtained. The model was Johnson–Melh–Avrami with n = 1.5. The model chosen implies quick nucleation and subsequent one or three-dimensional growth. Isoconversional methods show an independent activation energy variation in mid range conversion degrees. Lower and higher conversion degrees show different reactions in mullite formation. Results obtained with the methods employed here are in agreement with a previous paper where the Kissinger non-isothermal method and Ligero et al. approximation were applied.