Water Vapor Adsorption on Kaolinitic Clays

Abstract

The water vapor adsorption and desorption on various kaolinitic clays were studied. The adsorption isotherms showed a multi-layer adsorption (type II isotherm) but hysteresis was not observed under the present measurement conditions. The order of the water film thickness, calculated from the water vapor adsorption isotherms, is Motoyama Kibushi Clay≥Jinya Kibushi Clay=Motoyama Gairome Clay> Hara Gairome Clay>Georgia Kaolin>Kanpaku Kaolin in the range of relative humidity from 10 to 90% at 40°C. This order corresponds to the order of plasticities well known from experience. It was found that the water film thickness of weathering-origin clays was thicker than that of hydrothermal-origin clays. The difference is considered to be due to the different amounts of adsorbed cations on the kaolinitic clay surface.