The reactivity of oxides with water vapor
Abstract A Tian-Calvet microcalorimeter has been used to determine the heat of interaction of water vapor with a range of oxides at 303 K. New data for SiO 2 , TiO 2 , ZnAl 2 O 4 and CaO are reported which, together with already established results for Al 2 O 3 , enable an overall view to be given of the hydrophilic behavior of oxides. The change of the differential heat of adsorption with uptake for a given oxide allows the proportions of surface with high and low hydrophilicity, and with hydrophobicity if present, to be assessed. For the highly hydrophilic oxide CaO, the interaction occurs in depth, but this is suppressed when Mn ions are introduced in solid solution in CaO. The change from hydrophilic to hydrophobic behavior in oxides is correlated with the gradation from ionic to covalent bonding.