Adsorption of water vapour on ionic solids containing preadsorbed sodium oleate. Part 2.—Calcium carbonate

Publisher Website
Google Scholar
Abstract
Krypton adsorption isotherms at 76 K on calcium carbonate prepared by thermal decomposition of calcium oxalate have a stepwise appearance, and the step is eliminated by pre-adsorption of sodium oleate from aqueous solution. The effective cross-sectional are of an adsorbed water molecule at 293 K on pure CaCO3 is ca. 28 × 10–20 m2, which together with the low coverage isosteric heats of ca. 33 kJ mol–1, increasing to just above the heat of liquefaction of water with increasing coverage, indicates that cooperative adsorption of water occurs at localized sites. Pre-adsorption of sodium oleate at surface coverage below the theoretical monolayer decreases the subsequent adsorption of water vapour, but at higher concentrations the trend is reversed and a film of oleate, equivalent to ca. 6 theoretical layers, shows a marked increase in water vapour adsorption with hysteresis persisting to very low pressures. It is suggested that the first two layers of oleate ions have a laminar structure, with higher layers forming a similar structure to that of solid sodium oleate.

This publication has 0 references indexed in Scilit: