The kinetics of solid state reactions accompanied by fracture: I. Reaction of ion exchange in lime-soda glass

Reaction of Na+ to Li+ ion exchange in lime-soda glass was investigated as an example of a solid state reaction accompanied by fracture. The reaction proceeds at contact between the glass and lithium-containing melted salts and causes cracking of the glass and formation of combined reaction-fracture front. It is shown that both disordered and ordered pattern of cracking can be observed in different conditions. Results of the experimental investigation are compared with the existing models describing the stationary propagation of the combined reaction-fracture front. It turned out that the models describe satisfactorily only the case of disordered morphology of fracture. We suppose that the phenomenon of ordered fracture is connected with some factors providing a stable propagation of ordered system of cracks which have not been considered in the existing models yet. It is shown that the ordered fracture in the case under consideration can be caused by the effect of spatial separation of the diffusion and fracture fronts due to local crystallization of the reaction melt occurring near the reaction zone in definite conditions.