Elemental distribution analysis of mesoporous structure on silicate glass surface corroded in the K2HPO4 aqueous solution

The Hierarchical Nanoporous Layer (HNL) glass, formed through alkaline corrosion, exhibits unique properties, including low reflectivity and superhydrophilicity. Despite these notable features, the precise mechanism responsible for its spontaneous formation has yet to be fully understood. While glass–water interactions typically follow either the classic leaching/in-situ reorganization model or the interface-coupled dissolution-precipitation (ICDP) model, reports detailing such highly specific, hierarchically graded alteration layers remain scarce. Consequently, investigating HNL formation serves as a highly valuable case study contributing to a comprehensive understanding of complex glass corrosion mechanisms. To determine the governing mechanism, we conducted an analysis of the cross-sectional microstructure and elemental distribution utilizing scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS). The findings revealed the onset of a Na-depleted diffusion layer even before significant structural changes, which subsequently progressed beneath the fully developed HNL. Furthermore, detailed analysis of the reaction interface revealed a gradual concentration gradient extending approximately 30 nm, which contrasts with the sharp boundary predicted by the ICDP model. These observations strongly suggest that HNL formation is primarily driven by diffusion-controlled kinetics consistent with the leaching/in-situ reorganization mechanism, offering valuable insights into the functionalization of glass surfaces as well as the broader mechanisms of glass corrosion.