Activation energy of crystallization

Figure 3.19 Arrhenius plot to determine the activation energy of crystallization. Based on the slope of the line in this example, E =100 kJ/mol.

Previously shown was how the activation energy of crystallization may be determined using DTA/DSC (section 3.6). A technique for determining the activation energy of a decomposition reaction using TG will now be developed. 

As we concluded above, the activation energy of crystallization corresponds to that of crystal growth. The activation energies of different zeolites are close. For example, for mordenite and zeolite A, the calculated values mentioned above are 10 to 11 kcal/mole i.e., activation energy is equivalent to the energy of 2 hydrogen bonds. It can be connected with the necessity of dehydration of the silicate... 

The enthalpy of crystallization, AH, equilibrium temperature, Teq, and activation energy of crystallization, Uact, values are summarized in Table 1. 

The dependence of the crystallization temperature (T ) on the heating rate (j) can be used to obtain experimental values for the activation energy of crystallization (Luborsky and Liebermann, 1978 Scott, 1978). The method of analysis is based on the results of Kissinger (1957). For a first-order rate process one may write... 

Nano-diamond was found to irrflu-ence crystallization behavior and activation energy of crystallization of polyphenylene... 

The activation energy of crystallization can also be determined by an approximation proposed by Augis and Bennett (Augis Bennett, 1978). The relation used by them is of the form ... 

This method has an extra advantage over the modifed Ozawa method employed in the literature for the determination of activation energy of crystallization that the intercept of In (jS/ Tp) against 1000/ Tp gives the value of pre-exponential... 

Table 3. Activation energy of crystallization of as-prepared and annealed samples of SessGessPbg and SessGesoPbi2 glassy systems using different theoritical models...

Table 2. Avrami exponent (n) and activation energy of crystallization (Ext) in terms of incubation time during isothermal annealing and the activation energy of crystallization (Eiso) determined from a Kissinger plot for the ball-milled amorphous Ti5oCui8Ni22Al4Sn6 alloy and its composite containing 10 vol.% TiC Reprinted from (Zhang, et al., 2006a), with permission from American Institute of Physics.

The kinetics of mica crystallization in DICOR glass-ceramic was studied by Bapta et al. (1996). The formal kinetic parameters were established according to the JMAK equation (Eq. 1-6 in Section 1.4.3). The activation energy of crystallization was determined as 203 kj moT the formal reaction order n as 3.4 0.2 and the pre-exponential factor as 2.88 x 10 s ... 

A Constant, E Activation energy of crystal growth, N = Nr+ No/a, Nr is the number of crystal nuclei at the unit volume formed during heat treatment at nucleation temperature, and No/a is the number of crystal nuclei at the unit volume formed during the rise in temperature at speed a. 

For further clarification, the activation energy of crystallization, E, is calculated for glasses by using the modified Ozawa equation ... 

The kinetics of non-isothermal crystallization using differential scanning calorimeUy (DSC) has been a known approach to study the crystallization behavior of polymers. The analysis was commonly performed through the use of modified Avrami [1 ], Ozawa [5] and other methods [6-7]. Kissinger method [8] was often used to obtain the activation energy of crystallization. These methods have been helpful to differentiate the crystallization behavior between materials. 

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