Origin and consequences of silicate glass passivation by surface layers

TLDR

Silicate glasses are durable, but their long‑term suitability for confining highly radioactive waste over hundreds of thousands of years remains uncertain. The study aims to understand the mechanisms of aqueous corrosion that determine the long‑term durability of silicate glasses. Corrosion proceeds by water ingress that releases mobile elements and triggers in‑situ silicate repolymerization, producing a passivating layer that equilibrates with pore and bulk solutions and functions as a sub‑nanometre molecular sieve. In silica‑saturated solution, the glass corrodes initially but rapidly slows as a stable passivating layer forms, achieving the required low corrosion rate and providing insights for optimizing nuclear glass design.

Abstract

Silicate glasses are durable materials, but are they sufficiently durable to confine highly radioactive wastes for hundreds of thousands years? Addressing this question requires a thorough understanding of the mechanisms underpinning aqueous corrosion of these materials. Here we show that in silica-saturated solution, a model glass of nuclear interest corrodes but at a rate that dramatically drops as a passivating layer forms. Water ingress into the glass, leading to the congruent release of mobile elements (B, Na and Ca), is followed by in situ repolymerization of the silicate network. This material is at equilibrium with pore and bulk solutions, and acts as a molecular sieve with a cutoff below 1 nm. The low corrosion rate resulting from the formation of this stable passivating layer enables the objective of durability to be met, while progress in the fundamental understanding of corrosion unlocks the potential for optimizing the design of nuclear glass-geological disposal.