Résumé
Role of Al on the chemical durability of SiO2-B2O3-Al2O3-CaO-Na2O glassesJean-Marc Delaye, Kamalesh Damodaran, Sumit Tiwari, Mélanie Taron, Stéphane GinCEA, DES, ISEC, DPME, SEME, University of Montpellier, Marcoule, F-30207 Bagnols-sur-Cèze, FranceEmail : jean-marc.delaye@cea.fr It has been shown experimentally that Al2O3 has a great impact on the chemical durability of SiO2-B2O3-Al2O3-CaO-Na2O glasses In glasses with a low Al2O3 content, a rapid release of Si into the solution is observed, followed by a sudden stop of the glass alteration. Conversely, glasses with a higher Al2O3 content exhibit a longer period before the Si and B releases into the solution diminish. These observations can be formally expressed by defining a characteristic time for chemical durability, which exhibits a strong positive correlation with the Al2O3 content (see Figure 1). Additionally, this characteristic time is influenced by the SiO2 content. Figure 1 : Change of the chemical durability characteristic time versus the Al2O3 content in a series of SiO2-B2O3-Al2O3-CaO-Na2O glasses. [1]To gain deeper insights into these experimental findings, classical molecular dynamics (MD) simulations were conducted using potentials fitted to simulate SiO2-Al2O3-CaO-Na2O glasses in contact with water. The parameters of the force field were fine-tuned through Force Matching, followed by refinement based on experimental data [2]. Employing the Potential Mean Force method to simulate hydrolysis processes enabled us to explain the impact of Al on glass durability. Specifically, we noted that an increase in the Al2O3 content in the glass composition resulted in a substantial augmentation of hydrolysis energies within the Si local environments. Simultaneously, the energy required to reform the Si-O bonds decreased. This phenomenon could account for a delay in the reduction of the alteration rate with higher Al2O3 content [3].Utilizing a new Monte Carlo approach capable of simulating glass alteration by modeling both water diffusion within the glass and hydrolysis mechanisms, various alteration scenarios were explored in SiO2-B2O3-Al2O3-Na2O glasses. The calculations suggest that a rapid release of Si into the solution can result in the formation of a Si-enriched and dense external layer, contributing to a quick reduction of the alteration rate. Conversely, when the release of Si into the solution is more gradual, minimal structural changes occur at the glass-water interface. In such cases, a more widespread and slower relaxation of the alteration layer may be responsible for the decline in the alteration rate. [1] M. Taron PhD, “Simulation à l’échelle nanoscopique du transport réactif : application à la dissolution des verres nucléaires”, Montpellier University, Sept. 2022.[2] T. Mahadevan, S. Baroni, M. Taron, S. Gin, J.C. Du, J.-M. Delaye, J. Non Cryst. Solids, 592 (2022) 121746.[3] K. Damodaran, J.-M. Delaye, A. Kalinichev, S. Gin, Acta Materialia, 225 (2022) 117478.