Aqueous corrosion of borosilicate glass under acidic conditions: A new corrosion mechanism

One important application of borosilicate glass is its use as a nuclear waste form to immobilize high-level nuclear waste. Understanding the corrosion mechanism of borosilicate glasses in aqueous solutions is essential to reliably predict their long-term behavior in the worst-case scenario of glass-groundwater contact in a geologic repository. Traditional models evaluate the long-term corrosion process on the basis of diffusion-controlled hydration and ion exchange reactions that are followed by solid-state reconstruction of the hydrolyzed glass network. Here we report textural, chemical, and 18O and 26Mg isotope tracer results from corrosion experiments with a borosilicate glass in an acidic aqueous solution (initial pH ≈ 0, T = 150 °C, 6 to 336 h) that contradict such a paradigm. We propose a new mechanistic model for glass corrosion under acidic conditions that is based on congruent (stoichiometric) dissolution of the glass that is spatially and temporally coupled to the precipitation of amorphous silica at an inward moving reaction front. The model potentially provides a novel framework to understand apparently contradictory observations made under more moderate conditions and to evaluate the long-term aqueous durability of silicate glasses.