New insight into atmospheric alteration of alkali-lime silicate glasses

A mixed alkali lime silicate glass altered in atmospheric conditions (80 °C/85%RH, Relative Humidity) for various lengths of time was characterized at all scales. The altered glass forms a hydrated solid phase bearing about 10 wt% of H2O in the form of Si-OH groups and molecular water. No alkali depletion was observed after ageing tests. Structural results from 1H, 23Na and 29Si MAS NMR point out the close proximity of Si-OH, H2O and Na+ species. This study gives new insight into the mechanisms of the atmospheric alteration, essential to conservation strategies in industry and cultural heritage.