ADSORPTION ON PRE-PLATED GRAPHITE - DISPLACEMENT TRANSITION FOR THE (KRYPTON CYCLOHEXANE) AND (METHANE CARBON-TETRACHLORIDE) FILMS

The displacement, by krypton adsorption, of a cyclohexane monolayer pre-adsorbed on graphite has been studied between 77 and 84 K by means of volumetric measurements. A displacement critical temperature of 80.25 K has been determined. From volumetric measurements of methane adsorption at 77 K on graphite pre-plated with carbon tetrachloride, a displacement of the pre-adsorbed layer has also been shown to occur, according to a continuous process. This displacement has been confirmed by a structural characterization of the film, by means of neutron diffraction. During this transition, two two-dimensional solid phases coexist on the surface of graphite. One of them exhibits a structure close to that of pure adsorbed carbon tetrachloride at the same temperature. The other structure is close to that of pure methane. Its crystal parameter decreases with increasing adsorbed amounts of methane.