Heats and entropies of adsorption of N2 on grafoil at 79.3 K

Abstract

An adiabatic calorimeter has been constructed to measure heats of physical adsorption of gases on exfoliated graphite (Grafoil) with an accuracy of 1% or better. Its use is illustrated by the determination of differential and integral heats and entropies of adsorption of N₂ on Grafoil at T= 79.3 K and for the range of surface coverages 0.011 < θ < 1.2. The effects of surface heterogeneity, of interactions between the adsorbed molecules and of a transition from a fluid to a registered solid surface phase are clearly delineated. Monte Carlo calculations confirm the magnitude of the heat of adsorption and its dependence on surface coverage. The analysis of the entropy yields some information about the degrees of freedom of the adsorbed molecules in the low-coverage region.