Title: Thermodynamics and Kinetics of Silicate Glasses submitted to Binary Ion Exchange: Equilibrium Conditions and Interdiffusion Kinetics

Abstract: Ion exchange processes between an ions reservoir and a solid matrix are modeled under the assumption that near interface volumes achieve equilibrium in a much faster time than the overall process time, while in the bulk of the solid matrix, ions are transported by an interdiffusion kinetic process. Ion exchange equilibrium conditions are established within the framework of classical thermodynamics. The result is defined in terms of the chemical potential of exchanging ionic species. The proposed original derivation is performed making use of the thermodynamics of subsystems. This result is fundamental to allow the development of the equilibrium theory for the evaluation of near-surface equilibrium concentrations and ion exchange isotherms. Interaction energies of the exchanging components within the subsystems matrices can be further determined. The kinetics of the ion exchange process in silicate glass is further discussed to find connections with the near-surface equilibrium condition. Within the framework of the proposed model, interdiffusion equations can be derived from having the boundary condition established by the thermodynamic equilibrium at the near interface. It has been found that the thermodynamic factor of the interdiffusion coefficient is related to the interaction energy of the exchanging ions in the glass allowing a new approach to the interpretation of past experimental results.