The Adsorption of Water Vapor by Porous Glass

Porous glass is a good getter for water vapor in semiconductor devices. This article presents a fundamental study of the physical adsorption of water on multiform porous Vycor over the range 30°–150°C and 10 −3 to 25 torr water vapor pressure, with surface coverages up to a third of a monolayer. The adsorption isotherms, for which a general equation is given, are of the Freundlich type. Differential heats and entropies of adsorption have been determined, and from the latter it is concluded that the film of adsorbed water is intermediate in nature between rigidly localized and completely mobile. Kinetic studies give the result that the amount adsorbed is proportional to . The effects of various drying procedures on the subsequent adsorptive capacity of the glass are considered in some detail and the mechanism of surface dehydration inferred.