PHYSICAL ADSORPTION OF VAPOR ON ICE .2. N-ALKANES

Physical adsorption studies of simple nonpolar hydrocarbon vapors on ice are described. The isotherms obtained cover a temperature range of from -96°C to -30°C, or up to roughly the temperature where drastic sintering occurs. Results are compared to existing data for hydrocarbon adsorption on liquid water. At temperatures below that of about -35°C, adsorption behavior is characterized by low adsorption energies, with isosteric heats lower than the heat of condensation at low coverages and rising to that of the heat of condensation as coverage increases to multilayer formation. As the temperature is increased to -35°C and above, adsorption behavior dramatically changes to that similar to adsorption on liquid water, marked by abnormally high adsorption heats at low coverage which drop to the heat of condensation as coverage increases. The explanation proposed is that H2O molecules in the ice surface are actively involved in the adsorption process at the higher temperatures, in a similar manner to the case of hydrocarbon adsorption on liquid water. © 1969.