Thermal analysis of Micro, Nano- and Non-Crystalline Materials by Jaroslav Šesták & Peter Šimon

Author:Jaroslav Šesták & Peter Šimon
Language: eng
Format: epub
Publisher: Springer Netherlands, Dordrecht

11.9.5 Non-Arrhenian Character of Crystallization and Glass Transition

As discussed in the paper by Ozawa [58], crystallization is a complicated process, so that sometimes it is not well understood. The following two points are essential to be considered:1.In general, crystallization proceeds by two elementary processes, that is, nucleation and growth. The temperature ranges of these processes differ from each other (see Fig. 11.1).

2.Generally, the Arrhenius law does not hold for these processes, except in special cases. For both processes, the temperature dependences are so complicated that the rate constants decrease below the melting temperature with increasing temperature, and they increase in a lower temperature range with increasing temperature, as shown by the bell curves in Fig 11.1 depicting the rates of nucleation and crystal growth. Approximate relationships for the constant rate of heating or cooling hitherto used for nonisothermal kinetics of chemical reactions are based on the Arrhenius law. Therefore, these relationships cannot be generally applied for nonisothermal kinetics of crystallization [58].

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