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 differ ential thermal analysis (DTA), X-ray diffraction (XRD) and scanning el ectron microscopy (SEM). The phases crystallizing first for the as-que nched glass and the glass sample previously nucleated are different. S olid solutions of lithium-magnesium silicate (Li(2+2x)Mg(1-x)SiO4) and a small quantity of beta-eucryptite (LiAlSiO4) solid solution are for med 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 te mperatures, into a large amount of beta-eucryptite solid solution toge ther with small quantities of diopside crystals (CaMgSi2O6). Kinetic p arameters for nucleation and crystal growth were estimated from the DT A curves. The temperature of maximum nucleation rate was 620-degrees-C and the activation energy for crystal growth E = 316 kJ mol-1. The cr ystal morphology was investigated by SEM, and the crystal shape was co nsistent with the morphological index n calculated by DTA. The glass-c eramic obtained from a previously nucleated glass showed a fine-graine d texture.