KJMAKolmogorov-Johnson-Mehl-Avrami Theory
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In its original form KJMA theory considered that nucleation sites were uniform randomly located in space.
So far, three different approaches have been proposed for morphological modeling of polymer crystallization, i.e., the Voronoi tessellation model, the modified KJMA model, and the cellular model.
To this end, we incorporate the KJMA approach modified to study nonisothermal crystallization of copper by Kruger (16) and Woldt (17).
If one considers the KJMA exponent from the standpoint of volumetric changes, a relative effect obtainable from the thermomechanical measurements becomes worth investigating.
Transformation of Eq 1 to nonisothermal kinetics is based on the discretization of the time dependence of the temperature, i.e., approximation of continuous temperature-time curves by subsequent isothermal steps, with each step (N) obeying the isothermal KJMA kinetics.
By simple algebra, taking logarithms twice to reduce the equation to the traditional KJMA notation, one obtains
Previous attempts to apply the extension of isothermal KJMA kinetics to the nonisothermal case for polymeric materials differ from our approach in two aspects.
Application of the modified KJMA analysis to the nonisothermal and isothermal experiments is shown in Figs.
Application of KJMA kinetics to isothermal and nonisothermal calorimetric studies resulted in exponents with values [nearly equal to]4 for the isothermal case and [nearly equal to]2 for the nonisothermal case.