No abstract

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.

No abstract

A thin-film-heater method is setup to measure the thermal conductivity of super insulating materials such as silica aerogels. The experimental setup is purposely designed for insulating materials and allows direct measurement of the thermal conductivity. Few experimental data are available in the literature concerning thermal conductivity of aerogels even though these materials are of major interest in thermal insulation. More data are necessary in order to understand thermal transport and to validate existing models. Monolithic and granular silica aerogels are investigated. Our experimental technique enables to quantify the influence of important parameters, such as air pressure and distribution of grain sizes, on the insulating performance of this material.

No abstract

No abstract

Room‐temperature microplastic phenomena in oxide glasses are attributed to the combined effects of densification and shear flow, the origin of which, however, remains speculative. Using atomic force microscopy imaging to analyze the imprint topology created by microindentation in mixed alkali alumino‐phosphate glasses, we show that the amount of matter displaced at the surface is correlated with the alkali mobility. These results lead to the conclusion that mobile alkali assists shear flow processes produced by indentation at room temperature and that these processes correspond to plastic rather than viscous flow.