Stress-Assisted Reaction at a Solid-Fluid Interface

On the interface between a solid and a fluid, a reaction can occur in which atoms either leave the solid to join the fluid, or leave the fluid to join the solid. If the solid is in addition subject to a mechanical load, two outcomes may be expected. The reaction may proceed uniformly, so that the interface remains flat as the solid recedes or extends. Alternatively, the reaction may cause the interface to roughen and develop sharp cracks, leading to fracture. This paper reviews the current understanding of the subject. The solid-fluid is a thermodynamic system: the solid is in elastic equilibrium with the mechanical load, but not in chemical equilibrium with the fluid. Thermodynamic forces that drive the interfacial reaction include chemical energy difference between the solid and the fluid, elastic energy stored in the solid, and interfacial energy. The reaction is taken to be thermally activated. A kinetic law is adopted in which the stress affects both the activation energy and the driving force of the interface reaction. A linear perturbation analysis identifies the stability condition, which differs substantially from the well known stability condition based on the driving force alone. Large perturbations are examined by assuming that the interface varies as a family of cycloids, from slight waviness to sharp cracks. An analytic elasticity solution is used to compute the stress field in the solid, and a variational method to evolve the shape of the interface.