Analysis of Anhydrous and Hydrated Surface Energies of gamma-Al2O3 by Water Adsorption Microcalorimetry

Surface energies have postulated importance to catalysis, crystal growth,. sintering, polymorphism, and many other fields. importance is even more critical when dealing with nanostructured materials, where the surface-to-volume ratio is considerably higher and the surface term. accounts for a much larger fraction of the total free energy. Here we present a novel approach to experimentally assess the average anhydrous and hydrated surface energies of oxides, and used the method to determine, the surface energy of gamma alumina The method uses a water adsorption setup combined with a microcalorimeter where the heat of adsorption can be monitored as a function of the adsorbed amount Maintaining a closed system, the approach enables the correlation of the molecular configuration of absorbed water with the thermodynamic data, and hence the definition of the point where a liquid water configuration exists (at high relative humidity). This information allows the calculation of the surface energy at room temperature for any coverage state by using the adsorption calorimetric data For gamma alumina, a close relationship between the water adsorption behavior and the surface energy was observed, evidencing that higher surface energies are associated with highly energetic dissociative behaviors of water and a continuous surface energy decrease upon water adsorption. Three adsorption stages were clearly observed from the combination of adsorption isotherm and microcalorimetric data, consistently with presented models.