Glass corrosion mechanisms: A multiscale analysis
Abstract Ancient to modern glass used for stained glass windows, representative of the main composition types (Ca-rich, Na- and Ca-rich and K-rich) were treated with boiling concentrated H2SO4 (338 °C) and/or in molten NaOH (320 °C, with or without water addition). Subsequent annealings in air or in molten KNO3 (334 °C) were also performed. Microstructures and corrosion habits were analysed by optical microscopy. Modifications of the silicate network and corrosion products were studied by Raman and IR spectroscopies, dilatometry, microhardness, and TGA. Only K-rich silicate glasses are drastically modified by concentrated sulphuric acid. The alkali leaching takes place in three steps: i) K+–H+ (not H3O+) exchange, partly reversible, inducing glass contraction and cracking, ii) a complete, irreversible H+/K+ ion exchange, iii) a (small) hydration of the formed porous, multicracked lixiviated silica-rich solid crust. The thermal treatment of the crust induces a water loss (~ 0.6 wt.% at