The self-healing behavior of radial cracks generated by Vickers indentation in float glass is analyzed when heat treated at 6201C under various atmospheres. Results evidence that two main driving forces influence radial crack evolution: release of residual stresses induced by initial indentation and capillary forces due to surface energy minimization. Depending on the viscosity level, viscous flow allows crack morphological changes driven by capillarity forces or not. Our results evidence that at 6201C, the viscosity of the glass surrounding cracks can be significantly reduced by water diffusion and glass hydrolysis, or increased by glass des-hydration, as a function of the humidity level of the furnace atmosphere. Hydration and des-hydration of glass are shown to play a major role in the crack morphology changes during healing, respectively, favoring or impeding morphological changes driven by capillarity forces.T. Rouxel-contributing editor
General studies of phase transitions PACS 64.70.F--Liquid-Vapour transitions PACS 67.25.bh -Quantum fluids and solids : 4 He -Films and restricted geometries.Abstract. -We report on thermodynamic and optical measurements of the condensation process of 4 He in three silica aerogels of different microstructures. For the two base-catalysed aerogels, the temperature dependence of the shape of adsorption isotherms and of the morphology of the condensation process show evidence of a disorder driven transition, in agreement with recent theoretical predictions. This transition is not observed for a neutral-catalysed aerogel, which we interpret as due to a larger disorder in this case.
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