Impregnation Studies Of Partially Densified Aerogels - Glasses Preparation

Silica aerogels are porous materials whose porosity lies between 98 and 0 %. This large range of porosity is obtained from alcogels of various initial density (by diluting the initial solutions). In order to obtain partially densified aerogels (P.D.A.) the corresponding aerogels are then oxidized and submitted to various isothermal heat treatments performed in a temperature range where the aerogels sinter. Due to their wide porosity scale, PDA are good candidates to be used as host materials. First, the visible light transmission (350-800 nm) against the material density gives information about the microscopic evolution of the porosity. Then, the hydrodynamical properties of the impregnating solutions versus the PDA porosity are studied. The permeability defined as the flow rate of liquid depending on the pressure can afford information about the nature of the porosity. The capillary rise permits characterization of the influence of the surface tension on the penetration of the impregnating liquids. Absorption-desorption measurements give information about the gas flow in these porous materials.