On locking strains in mechanochemistry of chemical reactions fronts

A. B. Freidin ; L. L. Sharipova ; N. F. Morozov

Čebyševskij sbornik, Tome 18 (2017) no. 3, pp. 475-487

Résumé

The influence of stresses and strains on the chemical reaction rate is studied basing on the concept of the chemical affinity tensor. The reaction between a deformable solid and diffusive gaseous constituents is considered. The reaction is localized at the reaction front and consumes all the matter supplied by the diffusion. Silicon oxidation and lithiation are examples of such a reaction. Tensorial nature of the chemical reaction is manifestation of the fact that in the case of deformable material the reaction is to be considered not in a point but at an oriented area element. A kinetic equation takes the form of the dependence of the reaction rate at the oriented area element on the normal component of the chemical affinity tensor. Stress-strain state affects the reaction rate as it affects the chemical affinity tensor. If the normal component of the affinity tensor is negative then the reaction at the oriented area element is impossible. Strains and stresses at which the normal component of the affinity tensor cannot be positive at any orientation or concentration of the diffusive constituent form forbidden zones in strain or stress space. A procedure for forbidden zones construction is developed. The use of the jump relationships for stresses and strains allows to present the normal component of the chemical affinity tensor as a dependence on strains/stresses on one side of the reaction front and the normal to the front. Then it is shown that the boundaries of the zone are determined by maximum and minimum of a quadratic form that was earlier studied for phase transitions zones construction. The location and sizes of the zone depend on the input of the chemical energies of the constituents relatively to strain energies. Besides the deformations which correspond to forbidden regions, blocking deformations are also considered which can be unblocked and started-up due to inelastic strains or diffusion.

Détail

Keywords: chemical affinity tensor, mechanochemistry, chemical reaction front kinetics, blocking strains, forbidden regions.