These temperatures are above the critical hysteresis temperature
and the isotherms are reversible as shown in Fig. 7. At
130 K, adsorption proceeds by filling the neck, followed by condensation
in the cavity. At higher temperatures there is more fluctuation
in the cavity than at lower temperatures, as seen in the
snapshot plot for Point D3. It could be argued that at high temperatures
adsorption is a process of compressing the adsorbate, and
desorption is one of rarefaction, resulting in reversible isotherms.
An interesting point is that the 130 K isotherm, although reversible,
shows a sharp change in density when the cavity is filled. This
could be viewed as condensation in a poorly defined bubble as
pressure is increased and cavitation of the condensed fluid when
pressure is decreased. This implies that cavitation can occur in a
reversible isotherm, i.e. independent of the appearance of a hysteresis
loop, a feature which has not been recognized in the previous
literature.