Acid leaching reorganizes hierarchical nanoporous alteration layers on borosilicate glass

Abstract Aqueous corrosion of silicate glass produces surface alteration layers whose formation may involve both leaching/in situ reorganization and interface-coupled dissolution–precipitation (ICDP). Here, selective acid leaching combined with focused ion beam scanning electron microscopy tomography, transmission electron microscopy–energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy was used to probe aluminum in a hierarchical nanoporous layer formed on borosilicate glass. Acid leaching removed aluminum almost completely while retaining a continuous porous silicate layer, consistent with an acid-soluble hydroxylated Al-containing secondary phase located outside, rather than incorporated into, the silicate network. Its removal thinned the segmented solid phase and altered the depth-dependent porosity. Associated shifts in optical reflectance and water-droplet spreading were consistent with changes in layer thickness and pore structure. These findings support contributions from both ICDP-type and leaching/in situ reorganization processes and identify aluminum speciation as an important factor governing alteration-layer structure and response.