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Comments and recommendations on the use of the Avrami equation for physico‐chemical kinetics
Author(s) -
Khanna Y. P.,
Taylor T. J.
Publication year - 1988
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760281605
Subject(s) - avrami equation , thermodynamics , kinetics , exponent , materials science , activation energy , constant (computer programming) , chemistry , crystallization , physics , computer science , classical mechanics , linguistics , philosophy , programming language , crystallization of polymers
Over the last four decades, numerous reports have appeared on the physico‐chemical kinetics, especially crystallization kinetics, based on the Avrami equation, ϕ = exp [− Kt n ] where ϕ is the fraction of material unchanged at time t , K is an overall rate constant and “ n ” is the Avrami exponent indicative of process mechanism. The usage of the Avrami equation has been limited to the determination of “ n ” and its temperature dependence. It is shown that the evaluation of K and the activation energy (E) using this equation is erroneous since K and E are both influenced by “ n ” although such would be unexpected from the Avrami equation. On the other hand, if one uses a modified expression, ϕ = exp[− Kt ] n , then in addition to the value of “ n ”, correct values of K and E are obtained. This retains the original correspondence of the Avrami equation to nuclea‐tion and crystal growth processes but extends its applicability to (i) correctly evaluate K and E parameters, and (ii) correctly compare transformation rates when the systems differ in their n values. Experimental data are presented to support these conclusions.