Anomalies in standard gas adsorption isotherms of N2 and Ar on graphite at 77 K

Pronounced hysteresis due to pores, and a distinct step near a relative pressure of 0.4, appeared in the adsorption-desorption isotherms of N₂ and Ar at 77 K for both natural graphite and natural graphite subjected to various treatments. The step stems from the adsorption of a second layer. By applying the same method as that used to determine Point B, the amount of gas adsorbed up to the completion of a second layer was read from the isotherm and the relationship between the surface area of pores and the amount of surface oxygen was investigated.