Exafs for studying corrosion of glass surfaces

The technique of glancing angle EXAFS is introduced and applied to the study of aqueous corrosion at the surface of sodium borosilicate glass. In particular, the structural roles of iron and uranium are compared at loadings typical for nuclear waste disposal. The structural chemistry observed at the surface is rich in detail and adds considerably to the qualitative picture for the leaching of oxide glasses obtained from conventional surface analytical probes. Both metald migrate to the surface as corrosion progresses, iron more rapidly than uranium. There is evidence for mineralisation of the modifiers at the surface following leaching and, in the case of uranium, as a result of polishing. Indeed the uranyl configuration of U⁶⁺ is particularly sensitive to changes just beyond the oxygen ligand. Wet and dry surfaces can be distinguished and square planar clustering can be identified. The sequence of events is interpreted in terms of ion migration and water infusion taking place along percolation channels within the borosilicate network.