A new computational treatment of reactive diffusion in binary systems

Reactive diffusion is usually explained and simulated for a binary A-B diffusion couple used as a starting configuration. Various solution concepts for reactive diffusion are shortly discussed. If sharp interfaces between the developed new and/or parent phases with infinite mobility are assumed and act as ideal sources and sinks for vacancies, then the local equilibrium conditions at the interface are enforced. This is pronounced as jump in chemical composition given by a phase equilibrium diagram, and the corresponding local mass balance (conservation) at the interface must be taken into account. This represents a classical concept. However, there exist two further solution concepts, one working with the thermodynamic factors and the other one utilizing chemical potentials as unambiguous functions of the chemical composition. All three concepts are compared based on the solution of the same reference example by means of finite difference technique. Drastic differences appear between results obtained by the classical sharp interface concept as well as the chemical potential based concept (both providing identical results) compared to the use of the thermodynamic factor concept. The analysis of the results of simulations indicates that the solution concept based on thermodynamic factors produces artifacts in the treatment of reactive diffusion, if the most accurate discretization scheme is used.