Impact of calcium and pH on ISG alteration at basic pH: Mechanism of formation and transport properties of the gel layer
Article
Cagnon, B, Gin, S, Cabié, M et al. (2025). Impact of calcium and pH on ISG alteration at basic pH: Mechanism of formation and transport properties of the gel layer
. JOURNAL OF NUCLEAR MATERIALS, 610 10.1016/j.jnucmat.2025.155796
Cagnon, B, Gin, S, Cabié, M et al. (2025). Impact of calcium and pH on ISG alteration at basic pH: Mechanism of formation and transport properties of the gel layer
. JOURNAL OF NUCLEAR MATERIALS, 610 10.1016/j.jnucmat.2025.155796
The dissolution of International Simple Glass (ISG) was investigated at 90 °C, elevated concentration of dissolved silica and in the presence of calcium, with a specific emphasis on basic pH conditions. The leaching solution was labelled with 29Si, 18O and 44Ca in part of the experiments to elucidate the dissolution mechanisms. Based on the isotopic signatures of the gel layer analyzed using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), it was concluded that oxygen atoms mostly originate from the solution for all investigated conditions, while silicon atoms almost exclusively originate from the glass. A negative correlation was found between the initial concentration of calcium in solution and the gel layer thickness, suggesting either the formation of a passivating (Si, Ca)-rich layer, a catalytic effect of Ca on the gel densification or a combination of both. In addition, the pH-dependence of the diffusion coefficient of B within the gel was found to be stronger in the basic pH range than in the acidic pH range, which was suggested to originate from the change in coordination of B species at pH90 °C ∼ 8.5. Overall, these results suggest that in a (Ca, Si)-rich solution at basic pH, the durability of ISG is stronger than previously thought, as the diffusion coefficient of B under such conditions are lower than expected based on literature.
