GLASS-CERAMICS FROM FLY-ASH WITH ADDED LI2O

The effects of the addition of Li2O to fly ash on the devitrification behaviour of the derived glass are investigated with the aid of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The phases crystallizing first for the as-quenched glass and the glass sample previously nucleated are different. Solid solutions of lithium-magnesium silicate (Li(2+2x)Mg(1-x)SiO4) and a small quantity of beta-eucryptite (LiAlSiO4) solid solution are formed from the as-quenched glass, while only solid solutions of lithium-magnesium silicate are formed from the sample previously nucleated. In both cases, these crystalline phases are then converted, at higher temperatures, into a large amount of beta-eucryptite solid solution together with small quantities of diopside crystals (CaMgSi2O6). Kinetic parameters for nucleation and crystal growth were estimated from the DTA curves. The temperature of maximum nucleation rate was 620-degrees-C and the activation energy for crystal growth E = 316 kJ mol-1. The crystal morphology was investigated by SEM, and the crystal shape was consistent with the morphological index n calculated by DTA. The glass-ceramic obtained from a previously nucleated glass showed a fine-grained texture.