The Surface Chemistry of Condensation Nuclei: III. The Adsorption of Water Vapor on “Doped” Silver Iodide

Abstract

Adsorption isotherms at 10C for water vapor on ?pure? silver iodide and silver iodide doped with 0.60 avid 0.12 weight per cent of potassium nitrate have been determined by a volumetric method. It has been demonstrated that the addition of hygroscopic contaminants to silver iodide increases its efficiency in the nucleation of ice from supercooled water vapor. The adsorption of water vapor on the 0.12% doped material is identical on an equal surface area basis to that on pure AgI to a relative pressure of 0.4; above this pressure, water vapor adsorption on the doped material is much greater than on the pure material. Water vapor adsorption on the 0.60% doped sample is much greater at all relative pressures than on the other materials. It is shown that the impurity content of AgI prepared by precipitation techniques is less than 0.1%. The results are discussed in terms of the nature of the adsorbing surface as affected by the presence of the hygroscopic contaminant.