Physical adsorption of gases. Part 2.—Mixture of xenon and krypton on Pyrex

The adsorptions of xenon, krypton and a xenon + krypton mixture on Pyrex have been measured at temperatures of 77–90°K. Equilibrium pressures have been measured in the range 3 × 10–10–2×10–5 torr, the partial pressures in the mixed gas phase being measured by an omegatron mass analyzer. Heats and entropies of adsorption are evaluated as a function of coverage. A method is developed for computing the adsorption of a gas on a heterogeneous surface. The surface is treated as a number of patches with differing adsorption parameters. The procedure is based on a numerical integration routine for high speed computers. Xenon and krypton adsorptions can be described by the same three-patch model of the surface. On the major part of the Pyrex surface, adsorbed krypton is non-localized whereas adsorbed xenon is localized. Even at low coverage the high mobility of the adsorbed krypton is lost when krypton is adsorbed in admixture with an excess of xenon.