In¯uence of the Nucleation Time-lag on the Activation Energy in Non-isothermal Crystallization

In the present work, the in¯uence of the nucleation time-lag on the non-isothermal glass crystallization is discussed. Di€erential thermal analysis (DTA) results of an iron-rich glass nucleated by Cr 2 O 3 were obtained at di€erent heating rates. The activation energy of crystallization, E c , and the Avrami parameter, m, estimated by Kissinger's and Ozawa's equations were shown to be dependent on the heating rate. The value of E c , obtained at 2.5, 5 and 7.5 K/min heating rates was calculated as 299 kJ/mol, while the value of E c , obtained at 10, 15 and 20 K/min was as 499 kJ/mol. The value of m forìow' and`high' heating rates were 2.57 and 1.45, respectively. The results were interpreted on the basis of the non-steady state nature of the nucleation process. It was assumed that at high heating rates no nucleation takes place and the crystals grow on a existing ®xed number of nuclei; the activation energy of crystal growth, E g , can be estimated by applying the Kissinger equations. At low heating rates nucleation occurs and the number of nuclei formed is in-¯uenced by the heating rate; E g can be estimated by the Matusita and Sakka equation. Ó 2001 Published by Elsevier Science B.V.