Vyazovkin Isoconversional Method
The Vyazovkin’s isoconversional method is a widely recommended integral approach for accurate determination of activation energies, Ea [1]. In the link bellow, a free MS-EXCEL macro is available for download, where this method was implemented.
In this program, the activation energy at a specific conversion fraction, α, is obtained by determining the Ea value that minimizes the equation:
(1)
where
(2)
In the equations above, Eα and Tα are the activation energy and temperature at a conversion fraction α, respectivelly, obtained from independent experimental runs i and j, performed at different heating rates, β. In the macro, the integral is numerically evaluated by using the trapezoidal rule and a uniform grid spacing, that is continuaslly decreased, until a difference in the integral values smaller than 10-6, between consecutive interactions, is obtained. Different activation energy values are then used in the equations above and, the activation energy for the process, determined as the value of Eα that gives the lower result for equation 1. This macro was developed for the work presented in reference [2]. If you find this Macro useful for your research, please cite this reference.
[1] S. Vyazovkin; Journal of Computational Chemistry 1997, 18, 393-402.