The Adsorption of Non-polar Gases on Alkali Halide Crystals. I. The Low-temperature Adsorption of Non-polar Gases on Cubic Sodium Chloride

The low-temperature adsorption of non-polar gases (argon, oxygen, nitrogen and carbon dioxide) on cubic sodium chloride was investigated. The present results on the isosteric heats of adsorption for these four gases indicate that the non-uniformity of the surface considerably predominate in the low coverage region and the mutual interaction between the adsorbed molecules is also distinguished in the region of the comparatively high coverage. The entropies of the adsorbed materials (argon, oxygen and nitrogen) were experimentally determined and compared with the calculated values of the two-dimensional gas. These results show that the adsorbed molecules have the nature of the two-dimensional gas at least in the region of θ=0.3∼0.9. The present results indicate that the phase change (a gaseous film→a condensed film) of argon or oxygen may occur at about θ=0.9, but this fact is somewhat uncertain.