CAPILLARY CONDENSATION OF XE ON EXFOLIATED GRAPHITE

Multilayer adsorptions of xenon on the loosely packed form and the strongly compressed form of exfoliated graphite were investigated by pressure-volume and X-ray diffraction techniques. The adsorption isotherm of Xe at 107 K on the loosely packed substrate showed four layering transitions, as well as the hysteresis loop between adsorption and desorption branches. From the measurement of X-ray diffraction at each stage of the adsorption, it was found that bulk crystallites of Xe started to appear just after the formation of a bilayer even on the loosely packed formed, and some of them remained in coexistence with a monolayer in desorption. Thus, the hysteresis loop is directly associated with the capillary condensation of Xe within pores of this substrate. The adsorption isotherm of nitrogen at 77 K also showed hysteresis loop and confirmed the presence of the mesopores having widths of ca. 40 A with the assumption of slitshaped pores in the loosely packed exfoliated graphite. The strong compression of the exfoliated graphite caused the formation of the pores with widths larger than ca. 80 Å. © 1990, American Chemical Society. All rights reserved.