Effect of Fluorine on the Crystallization of Li_2O-Al_2O_3-SiO_2 Glasses

The nucleation and crystallization behavior of Li2O-Al2O3-SiO2 glasses with varied amounts of Fluorine content were investigated by the differential thermal analysis (DTA), X-ray diffraction (XRD) and the scanning electron microscopy (SEM). The results show that with the increase of the fluorine concentration, the crystallization peak temperature (Tp) decreases, the crystallization activation energy (E) decreases, the Avrami exponent (n) increases.. The onset of the precipitation of LixAlxSi1-xO2 crystal and its transformation to β-spodumene all shift to lower temperature and the grain size increases with the fluorine added. The values of the Avrami exponent (n) and the crystallization activation energy (E) agree well with the scanning electron microscopy observation of equivalent axis grain crystal. The results suggest that the fluorine promotes the initial crystallization and ion diffusion in the glass system.