Transport phenomena during aqueous corrosion of silicate glass—New insights from theoretical analysis of diffusion with a moving boundary

Incongruent corrosion of silicate glass is modeled as a moving-boundary transport problem, where the moving boundary contributes convective transport and the ion exchange provides diffusive transport. Here, the convection-diffusion transport equation is solved with two models—one couples the moving boundary to the diffusion process while the other has an independent moving boundary trajectory. These models are shown to replicate the aqueous corrosion of soda lime silica (SLS) in neutral and acidic conditions. The sigmoidal sodium concentration profiles at the glass surface are explained by the Gaussian convolution caused by experimental methods, not by a concentration-dependent diffusion coefficient. By fitting the experimental data with physically meaningful transport models, the driving force for the diffusion and leaching of sodium from the glass is found to be the ingress of hydrous species into the SLS glass (H₂O in neutral condition and H⁺ in acidic condition), instead of the concentration gradient of sodium.