Mutual diffusivity, network dilation, and salt bath poisoning effects in ion-exchanged glass

Chemically strengthened glass produced via the ion exchange process has found many interesting applications due to its high strength and damage resistance. It is known that salt bath poisoning has a strong effect on mutual diffusivity during the ion exchange process. Salt bath poisoning occurs when cations previously in the glass contaminate the molten bath nominally consisting of a larger substituting cation. In this work, we introduce a simple two-level model describing the impact of salt bath poisoning on the mutual diffusion coefficient. The model is compared to experimentally measured values of mutual diffusivity over a wide range of salt bath poisoning and glass composition. The model is shown to agree well with the experimental data. We also quantify the dependence of the activation energy for mutual diffusivity on the initial concentration of the substituting cation in the base glass composition. Finally, we address the issue of network dilation during ion exchange, showing that the magnitude of the “network dilation anomaly” is lower for aluminosilicate glasses as compared to soda lime float glasses, enabling them to achieve closer to their ideal values of strength.