Influence of specific surface area of pyrogenic silicas on their heat of immersion in water and on their surface properties assessed using inverse gas chromatography

The heat of immersion and the surface properties of pyrogenic silicas were examined using microcalorimetry and inverse gas chromatography at finite concentration (FC-IGC). The microcalorimetric measurements showed a regular decrease of the heat of immersion, in water, per area unit with an increase in the surface areas. The desorption isotherms were established using FC-IGC. It is observed that BET constant value goes through a minimum, whereas the shapes of distribution function of the adsorption energies of isopropanol are changing. All results could be interpreted using a model of formation of the pyrogenic silica in the flame, which explains the change of surface functionality and geometry occurring around 200 m 2/g. Specific surface area of pyrogenic silicas influences the heat of immersion in water par area unit, while inverse gas chromatography at finite concentration evidences the change of surface properties occurring around 200 m 2/g.