**3.3.2 Amorphous alloys**

Non-isothermal crystallization kinetic investigation of Se58Ge42-xPbx (*x* = 9, 12) alloy studied by Deepika et al. is given here as an example of the crystallization kinetics in amorphous alloys. In their study, glassy alloys of Se58Ge33Pb9 and Se58Ge30Pb12 were prepared by meltquenching technique and after realizing thermal analyses, the samples were annealed at 633 and 643 K, which lie between the first and second crystallization, respectively. The activation energy of crystallization for the first and second crystallization stages of Se58Ge33Pb9 and Se58Ge30Pb12 glassy systems was derived using the approximation methods developed by the Kissinger (Equation 58), Matusita (Equation 59), Augis and Bennett (Equation 60). The values of activation energy of crystallization of as-prepared and annealed samples using different theoretical models are given in Table 3 (Deepika et al., 2009).


Table 3. Activation energy of crystallization of as-prepared and annealed samples of Se58Ge33Pb9 and Se58Ge30Pb12 glassy systems using different theoritical models (Deepika et al., 2009)

From Table 3, it is observed that activation energy of crystallization decreases after annealing. This means that group of atoms in the glassy state requires less amount of energy to jump to crystalline state hence, making the sample less stable and more prone to crystallization. This is again an indication of the fact that annealing of glass leads it to a quicker crystallization. The crystallization mechanism of crystals decreases to one dimension from two and three dimensions after annealing, suggesting a decrease from bulk nucleation to surface nucleation in annealed samples.

It is also observed that activation energies of amorphous alloys calculated by means of the different theoretical models differ substantially from each other. This difference in the activation energy as calculated with the different models may be attributed to the different approximations used in the models.
