A New Model for Diffusion-controlled Precipitation Reactions Using the Extended Volume Concept

In this work a new model for diffusion-controlled precipitation reactions is derived, analysed and tested against a wide range of data. The model incorporates elements of the extended volume concept and combines this with a new treatment of soft impingement of diffusion fields. The model derivation involves an integration over isoconcentration regions in the parent phase in the extended volume, which leads to a single analytical equation describing the relation the fraction transformed, α, and the extended volume fraction, αext, as: α = {exp(-2αext)-1}/(2αext) + 1 The model is compared to a range of new and old data on diffusion-controlled reactions including precipitation reactions and exsolution reactions, showing a very good performance, outperforming classical and recent models. The model allows new interpretation of existing data which, for the first time, show a consistent analysis, in which Avrami constants, n, equal values that are always consistent with transformation theory. Published as: Starink, M.J. (2014) Thermochimica Acta, 596, pp. 109-119