Phase behaviour of argon and krypton adsorbed in mesoporous Vycor glass

Abstract

The phase behaviour of Ar and Kr adsorbed in Vycor glass at pressures and temperatures above the bulk triple point and below the bulk critical point has been investigated. Ar is found to condense in the pores ∼2 K above the bulk transition and freeze ∼10 K below the bulk transition. In contrast the condensation transition for Kr is shifted up by 4 K and freezing shifted down by 15 K. There is a pronounced hysteresis (4–6 K) at the liquid/solid phase boundary and a lesser amount (∼2 K) at the gas/liquid boundary. We find clear differences between the pore filling and emptying processes at the gas/liquid phase boundary and evidence of pore blocking on desorption. In addition microbubbles or large gas–liquid interfaces are thought to occur when Kr condenses in the pores but this effect is absent in Ar. Finally, solid Ar in the pores melts in a more continuous way than Kr.