Crystallisation kinetics of β-spodumene in lithium aluminosilicate sol-gel glasses

beta-spodumene (LiAlSi2O6) is one of the crystalline phase of the lithium aluminosilicate (LAS) glass-ceramics, having a low thermal expansion coefficient. The sol-gel process is an advantageous processing route for LAS materials, compared to melting, as it avoids lithium oxide losses and formation of undesired crystalline phases. It is very important to understand the crystallisation kinetics in order to assess the amount of the different crystalline phases formed for a given thermal cycle. This study reports the application of the non-isothermic method for evaluation of crystallization kinetic parameters, based on differential thermal analysis (DTA) experiments under constant heating rates (10, 12,15 and 20 degrees C min(-1)) up to 1000 degrees C. The Johnson-Mehl-Avrami (JMA) theory, modified with distinct approaches, lead to Avrami coefficients, n, in the range of 2.1-2.4 and apparent activation energies, E-a, of 345-362 kJ mol(-1). A simultaneous tridimensional and bidimensional crystal growth mechanism for a constant number of nuclei is proposed for beta-spodumene crystallization.