Physical adsorption of gases on graphite

Abstract

Isotherms for adsorption of nitrogen, carbon monoxide, oxygen, argon, krypton and nitric oxide on graphitized and ungraphitized samples of carbon black (Sterling FT) have been measured at ca. 78 K. The adsorption isotherms for krypton and nitric oxide on the graphitized sample are sharply stepwise, indicating two-dimensional condensation. The isotherms for nitrogen, carbon monoxide, oxygen and argon have been used to plot the amount adsorbed on the ungraphitized sample against amount adsorbed on the graphitized sample at the same pressure. This provides a method for comparing multilayer adsorption of different gases on the two surfaces. Discontinuities in the “comparison plot” correspond to second-layer completion, and it is suggested that the influence of the surface extends beyond the second adsorbate layer. Anomalous behaviour of argon is attributed to a more open packed structure on the ungraphitized surface.