Structure and dynamics of ammonia adsorbed on graphitized carbon black. Part 1.—Adsorption isotherms and thermodynamic properties

Abstract

Isotherms of ammonia on a graphitized carbon black (Vulcan III) have been measured at temperatures of 163.4, 172.6, 182.0, 191.5, 201.5 and 211.0 K, using a microbalance. They are all of Type III. Values of isosteric heats and differential entropies of adsorption have been determined. The isosteric heat is comparable with the latent heat of evaporation of the liquid but much less than the latent heat of sublimation of the solid. This has the effect that, below the melting point of bulk ammonia, the amount adsorbed at a given relative pressure decreases with decreasing temperature. This type of behaviour is uncommon and seems to be characteristic of systems in which heterogeneous nucleation takes place.