Infrared and gravimetric studies of the adsorption of water on barium sulphate

Abstract

Barium sulphate precipitated from aqueous solution contains bulk water which can be removed by prolonged evacuation at 773 K. Infrared spectra of barium sulphate exposed to water vapour show that both associative and dissociative adsorption of water occurs. Water is desorbed from multilayers by evacuation at ca. 298 K and from the first monolayer by evacuation at 383 K. Water in the first monolayer is adsorbed partly at weak Lewis acidic Ba²⁺ cations and partly via hydrogen-bonding interactions with exposed sulphate anions. Hydroxyl groups exist either in low-area planes or at defect or edge sites and are also removed by heat treatment at ca. 383 K.