Influence of Adsorbed Water on Surface State of Sodium Chloride Powder

Abstract

NaCl powder sample was prepared by the recipe mentioned in the previous paper. Water adsorption isotherms on the samples outgassed in the temperature range from 250C to 3600C and their surface area values were determined. Effect of the amount of presorbed water on the isotherms was also tested.
Each of the isotherms showed a stepped rise in the adsorbed amount at the vapor pressure forming two layers completely. ln the case of outgassing at 250C, reproducib!e isotherms were obtained for the repeated adserption up to forming three layers. The sample outgassed after ferming eight layers showed 20% decrease in the monolayer capacity. When the presorbed amount exceeded the amount necessary to form 2.7 layers, a surface area of the sample began to decrease.
The outgassing at temperatures above 200 C decreased the height of a stepped rise of the isotherm, and the subsequent outgassing at 250C 1owered the water adsorption ability. Corresponding to the above phenemena, the surface area of the sample more decreased by adsorbing water than that of the sample untreated.