Crystallization behaviour of glasses produced from fly ash

The crystallization behaviour of fly ash based glass samples annealed at 60 0 degreesC for 2 and 10 It was investigated by DTA, XRD and SEM. On the bas is of DTA, nucleation experiments of two glass samples were carried out at 680 and 687 degreesC for 5 h and crystallization experiments were performed at 924 and 892 degreesC for 20 min. The Avrami constant for both glass sam ples was calculated as 4, which indicates bulk crystallization, predicted b y the Ozawa equation. Using the modified Kissinger equation, activation ene rgies of crystal growth were determined as 318 and 312 kJ/moI for samples a nnealed at 2 and 10 h, respectively. Single peak analysis technique proved that the activation energy is independent of DTA heating rate. SEM observat ions indicated that the produced glass-ceramic samples have fine grained mi crostructure. The crystallized phase was identified as diopside [Ca(Mg,Al)( Si,Al)(2)O-6] by X-ray diffraction analysis. The results of Vickers microha rdness tests showed that the hardness values of the produced glass-ceramic samples decreased with the increase in holding time at the annealing temper ature. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.