Bratati Das and Ashis Bhattacharjee* Pages 1 - 14 ( 14 )
Background: Melting is generally treated in terms of thermodynamics and the thermodynamic treatment disregards the melting process as a kinetic phenomenon. But from the kinetic view point, any process can be characterized by the activation energy and pre-exponential factor and these parameters are derivable from the temperature dependence of the process rate. Exploring such dependence for melting presents a fundamental problem because essentially this process occurs at a single temperature. The temperature region of melting cannot be extended beyond this temperature which makes it impossible to study the temperature dependence of the melting rate and derive the respective kinetic parameters.
Objective: The objective of present study is to explore the mechanism of the melting process of maliec anhydride in the framework of certain phase transition models. Taking melting as just other first order phase transitions, occurring via the formation of the nuclei of the new phase and their growth, focus is on the nucleation and growth models.
Method: Non-isothermal thermogravimetry as well as differential scanning calorimetry studies have been performed. Using isoconversional kinetic analysis, temperature dependence of activation energy of melting has been obtained. Nucleation and growth models have been employed to regenerate the temperature dependence of activation energy to compare with observed one. The nucleation and growth models have been used to derive theoretical temperature dependencies for the effective activation energy of melting. The theoretical dependencies are then compared with the experimental ones estimated by means of isoconversional kinetic analysis. The purpose of this whole analysis is to obtain kinetic insights into melting of crystals of malice anhydride under normal conditions.
Observations: Thermogravimetry measurements indicate that melting is followed by concomitant evaporation, whereas DSC study shows the two processes to appear in two different temperature regions and these differences are held due to experimental conditions. From statistical analysis, the growth model seems more suitable for the interpretation of the melting kinetics of maliec anhydride.
Maliec anhydride, thermogravimetry, DSC, isoconversional kinetics, melting mechanism
Department of Physics, Visva-Bharati University, Santiniketan –731235, Department of Physics, Visva-Bharati University, Santiniketan –731235