Study of non-isothermal crystallization of Eu3+ doped Zn2SiO4 powders through the application of various macrokinetic models

Abstract

Various macrokinetic models (Avrami, Evans, Tobin, Malkin, Dietz, Nakamura, and modified first-order models) were applied to describe non-isothermal crystallization kinetics of Eu3+ doped zinc silicate powders prepared via the sol-gel method. Analysis of the experimental data was carried out using a direct-fitting method such that the experimental data were fitted directly to each macrokinetic model using a non-linear multivariable regression computation procedure. Comparison of kinetic parameters obtained from the non-linear computation approach to those obtained from the traditional analytical procedure suggested that applicability and reliability of the direct-fitting method were satisfactory. Judging from the quality of the fit, only Nakamuras model properly describe the temperature dependence of the relative crystallinity, which resulted in the total rejection of the Tobin model in describing the crystallization. With detailed kinetic examination it was concluded that crystallization mechanism of alpha-willemite doped samples combusted in a microwave oven (MW) follows interface controlled growth with an increasing nucleation rate, attached with geometric process-rate function obeying the improved (corrected) Nakamuras model. It was found that the presence of non integer Avrami exponent values may indicate that crystallization occurs by more than one reaction mechanism, including the occurrence of autocatalytic behavior of a given system. (C) 2013 Elsevier B.V. All rights reserved.