Water Vapor Affinity of Potassium Bromide Coated with Potassium Oleate

Abstract

Abstract The amounts of adsorbed water and the isosteric heats for water vapor adsorption on fine crystals of KBr treated with various amounts of potassium oleate (KOI) were measured. In the adsorption isotherm of untreated KBr, a slight stepped rise of the amount adsorbed was observed, and this step is considered to be due to the two-dimensional condensation of water molecules adsorbed on the uniform surfaces of KBr particles. The monolayer capacity, determined from the adsorption isotherm of KBr by the point B method, agreed with the value calculated according to an adsorptive structure based on the two assumptions that all the surfaces of the KBr particles consist of (100) planes and that one water molecule is adsorbed per regularly distributed Br− site. A small amount of pre-adsorbed KOI was recognized to prevent the water vapor adsorption on KBr, and conversely, this effect disappeared with increasing KOI content while the hygroscopicity of the sample increased markedly. This abnormal increase in the adsorbed amount suggests that the adsorbed water molecules penetrate into the multilayer films of KOI on the KBr.