Jeziorny Method Should Be Avoided in Avrami Analysis of Nonisothermal Crystallization

Abstract

The Jeziorny method treats nonisothermal crystallization data by replacing the variable temperature (T) values with the corresponding values of time and substituting them into the isothermal Avrami plot, ln[−ln(1 − α)] vs. lnt. For isothermal data, the slope of this plot is the Avrami exponent, n and the intercept is the rate constant, kA. This does not hold for nonisothermal data. Theoretical analysis suggests that in the case of nonisothermal data the intercept cannot be interpreted as kA, and its “correction” by dividing over the temperature change rate β is devoid of any meaning. In turn, the slope cannot be interpreted as n. It is demonstrated that the slope changes with time and its value depends not only on n but also on the temperature, temperature range, and activation energy of crystallization. Generally, the value of the slope is likely to markedly exceed the n value. The theoretical results are confirmed by analysis of simulated data. Overall, the Jeziorny method as well as other techniques that substitute nonisothermal data into the isothermal Avrami plot should be avoided as invalid and useless for any reasonable Avrami analysis. It is noted that n can be estimated from the nonlinear plot of ln[−ln(1 − α)] vs. T.

Nonisothermal Crystallization Kinetics by DSC: Practical Overview

“…Furthermore, Equation (17) indicates that, typically, the slope value should significantly exceed the correct m values [33]. This inference is consistent with previous reports [61,64,65].…”

“…A failure of the method to determine the correct values of m is well demonstrated for simulated [64] and experimental data [65]. A recent theoretical analysis of the method shows [33] that for nonisothermal data, the slope of the Avrami plot ln[−ln(1 − α)] vs. lnt does not yield the expected value of m. Instead, the value of the slope has a rather complex form [33]:…”

“…This is done to streamline integration with the aim of obtaining simple equations for parameterizing the process rate. Without going into unnecessary technical details, it is easy to arrive at an approximately linear equation of this kind [29][30][31][32][33]:…”

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“…where 𝑘(𝑇) = 𝐴𝑒 −𝐸 𝑎 𝑅𝑇 -rate constant, β -heating rate However, as Vyazovkin states [29], this transformation contradicts the basic principle of equating physical quantities and also leads to incorrect Avrami indices, usually larger than the actual value. It should be noted that the Jeziorny's method is often used to calculate the Avrami index of non-isothermal crystallization kinetics of amorphous metallic glasses due to the developed algorithm for the interpretation of the polymer crystallization mechanism.…”

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“…Compared with PET, the carbon residue of PET/GQDs nanocomposites at 550 °C did not increase but decreased. This is because The crystallization process of PET/GQDs nanocomposites can be investigated via the DSC method [38][39][40]. Based on the previous results, 0.5 wt% GQDs had a good crystallization effect on PET.…”