(250f) On the Crossing of Low Temperature Adsorption Isotherms of Argon on Graphite Surface

Low temperature adsorption isotherms of argon on graphite are studied using Grand Canonical Monte Carlo simulation. The goal of this investigation is to see whether the phenomenon of crossing of isotherms (when plotted against the reduced pressure) is reproduced by the simulation, and to gain insight into the microscopic reasons for the crossing. Simulations were carried out with adsorption of argon on a structureless surface at 71.11, 73.52, 74.96 and 78.47 K. The results were plotted against the pressure scaled against the GEMC simulated vapour pressure. If surface mediation is not accounted for, the simulated isotherms do not cross; however they do when surface mediation is taken into consideration. This is another support for the possible existence of the surface mediation, a phenomenon that has been shown to be necessary for the correct description of adsorption isotherms of noble gases and other gases on graphitized thermal carbon black.