Physical adsorption on patchwise heterogeneous surfaces. 5. Phase transitions in krypton films on graphitized carbon black in the temperature range 104-129 K

Abstract

Adsorption isotherms of krypton on graphitized carbon black were measured with a high-precision volumetric adsorption apparatus in the temperature range of 104.5-129.0 K. Three of the isotherms were measured up to more than five statistical adsorbed layers. Isosteric heats and equilibrium spreading pressures were calculated from the adsorption isotherms and aided interpretation of the data. The existence of both a fluid to in-registry solid and an in-registry solid to out-of-registry solid phase transition in the adsorbed krypton films is clear below 122 K. At temperatures of 122 K and above the fluid krypton changes continuously to the out-of-registry solid. Thus, a phase diagram enclosing the in-registry solid adsorbed film was defined. The dispersion force contribution to the surface free energy of graphitized carbon black was calculated to be 154.7 mN/m.