Heat of immersion studies on characterized silicas

Abstract

A differential wetting calorimeter suitable for measuring heats of immersion of solids in either aqueous solutions or dry organic solvents is described. With this apparatus the heats of immersion of a number of well-characterized Aerosil silicas in both water and benzene have been measured. The heat of immersion of unannealed silicas in water is dependent on the temperature of the wetting process. For annealed silicas this temperature dependence is not always present. These results indicate that the heat of wetting contains terms which reflect disturbances of the liquid layers surrounding the solid. Also, for microporous adsorbents the heats of wetting cannot be reliably expressed in terms of heats per unit area of surface when the area is determined by the B.E.T. method.