Effect of heat treatment on the surface chemical structure of glass: Oxygen speciation from in situ XPS analysis

Abstract

AbstractCompositional changes in unleached and acid‐leached soda‐lime silicate surfaces were tracked with in‐vacuo heating and X‐ray Photoelectron Spectroscopy. Surface oxygen speciation was determined using a stoichiometry‐based algorithm via elemental composition, instead of the typical O 1s peak‐fitting approach. Accurate surface hydroxyl quantification is shown to require dehydration at temperatures near 200°C. On the unleached surface, no change in surface hydroxyl density (~2.5 OH/nm2) is observed in the temperature range of 200°C‐500°C after the initial dehydration. However, repolymerization in the network (non‐bridging oxygen→bridging oxygen) is observed due to volatilization of sodium. The acid‐leached surface undergoes sodium out‐diffusion from the bulk at sub‐Tg temperatures with laterally resolved inhomogeneity and shows a reduction in the concentration of hydroxyls from 4.5 OH/nm2 (200°C) to 3.2 OH/nm2 (500°C) accompanied by an increase in bridging oxygen. These results suggest that when [OH] > 2.5~3/nm2, vicinal OH undergo dehydroxylation with evolution of water, whereas when [OH] < 2.5/nm2, most OHs are non‐interacting and isolated (at temperatures below Tg). Furthermore, at temperatures exceeding 300°C, sodium has enough thermal energy to desorb in vacuum and diffuse from the bulk (depending on the abundance & local structure).