Activation energy for crystallization

Crystallization kinetics have been studied by differential thermal analysis (92,94,95). The heat of fusion of the crystalline phase is approximately 96 kj/kg (23 kcal/mol), and the activation energy for crystallization is 104 kj/mol (25 kcal/mol). The extent of crystallinity may be calculated from the density of amorphous polymer (d = 1.23), and the crystalline density (d = 1.35). Using this method, polymer prepared at —40° C melts at 73°C and is 38% crystalline. Polymer made at +40° C melts at 45°C and is about 12% crystalline. 

A similar analysis can be made for the crystallization rate in determining an apparent activation energy for crystal growth, Ec, assuming... 

Lu K, Wang JT (1991) Activation energies for crystal nucleation and growth in amorphous alloys. Mater Sci EnginA133 500-503... 

Fig. 8. Crystallization of an amorphous alloy (a) into a stable (cy) or metastable compound (C2). The values given in parentheses represent an order of magnitude estimate of the activation energy for crystallization A act and the crystallization enthalpy AHcr.

The above equations may be applied to diffusion, dissolution or crystallization processes k can be taken as the relevant rate constant. For example, a plot of logX G versus T would give a so-called activation energy for crystal growth, E cryst log versus T gives EwiS8 log7) versus where... 

Where E is the activation energy for crystallization, Tp is the peak temperature and R is the universal gas constant, m is known as the dimensionality of growth and here ni = n. In order to derive from this equation, one must know the value of n. The n value can be obtained from the slope of the plot of ln[-ln(l-a)] Vs. InP at constant temperature. In order to evaluate... 

The activation energy for crystallization was determined to be 411 and 315 kj/mol by Kissinger (Equation 58) and Augis Bennett (Equation 60) method, respectively (Fig. 28a-b) (Liu Duh, 2007). Comparing with this study, previous works on near equiatomic NiTi films showed that the activation energy was 370-419 kJ/mol (Chen Wu 1999 Seeger Ryder, 1994). 

Matusita, K., Komatsu, T. Yokota, R. (1984). Kinetics of non-isothermal crystallization process and activation energy for crystal growth in amorphous materials. Journal of Materials Science, 19, pp. 291-296,0022-2461... 

Figure 29. Variations of activation energy for crystallization of the PEN/CNT nanoeomposites with various CNT contents.

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