Kinetic equations for diffusion-controlled precipitation reactions

Abstract

In the past it has been suggested that the Johnson-Mehl-Avrami Kolmogorov (JMAK) equation can be used to describe the progress of a large number of nucleation and growth reactions, including diffusion-controlled precipitation reactions, provided that nucleation is random. However, its validity has only been proved for reactions with a linear growth and not for diffusion-controlled precipitation reactions. Here, the ability of the JMAK equation to fit the experimental data of diffusion-controlled precipitation reactions has been compared with the Austin-Rickett (AR) equation ?=1?{[k(T)t]n+1}-1 In all cases studied the AR equation provides a better fit to the data and the obtained integer and half-integer values of n can be interpreted in terms of the physics of the transformation processes. The latter is mostly not possible for n values obtained from the JMAK equation. It is concluded that for the purpose of interpreting data of precipitation reactions, the AR equation is more appropriate than the JMAK equation. Note: See www.eprints.soton.ac.uk/18827/ for improved analysis.