NUCLEATION AND CRYSTAL-GROWTH IN A FLY-ASH DERIVED GLASS

The devitrification behaviour of a fly ash derived glass, examined by differential thermal analysis (DTA), X-ray diffraction and scanning electron microscopy (SEM), is reported and discussed. The crystallized phases were identified as mullite (3Al2O3.2SiO2) and anorthite (CaO.Al2O3.2SiO2). Kinetic parameters for nucleation and crystal growth were estimated from the DTA curves. The temperature of maximum nucleation rate was 790-degrees-C and the activation energy for crystal growth E = 370 kJ mol-1. The crystal morphology was investigated by SEM and the crystal shape found to be consistent with the morphological index n calculated by DTA. The glass-ceramic obtained from a previously nucleated glass showed a fine-grained texture.