Mechanical strength improvement of a soda-lime–silica glass by thermal treatment under flowing gas

The incidence of thermal treatments in air, N2 or NH3, on the mechanical properties of a soda-lime silica glass is presented. The effects of the treatment time and temperature were studied. Ammonia treatments lead to the most important compositional changes near the surface: SIMS and XPS techniques revealed a significant depletion in alkali and alkaline earth cations and a limited incorporation of nitrogen. IR-reflexion spectroscopy provided evidence for compositional changes near the surface, from a typical soda-lime glass towards a silica glass composition. The affected surface layer is typically about 1 μm deep and leads to significant changes of the local mechanical properties. Nanoindentation measurements showed that hardness increases whereas Youngʹs modulus decreases both by ∼10% in a 300 nm thick surface layer. A significant increase of the indentation fracture toughness (Kc) from 0.72 to 0.89 MPa.m1/2 was also noticed. The different processes leading to the cationic migration and to the changes of the glass surface properties were discussed.