Abstract
The specific surface areas of ten soil samples (clay content 1—72 %, organic carbon content 0.8—11.5 %) were determined by water vapor and nitrogen gas adsorption. The surface areas obtained by application of the BET equation to water vapor sorption at p/po 0.12—0.42 (21—195 m2/g) were, on the average, 80 % of the areas determined by water vapor sorption at p/po 0.20, range 27—229 m2/g. A BET water monolayer coverage was formed on the soil surface at p/po 0.12—0.20. The BET water area correlated closely with the one-point water area (p/po 0.20). The surface area determined by nitrogen gas adsorption ranged from 0.3 to 21 m2/g and did not correlate closely with water areas. The water surface areas were closely related to soil organic carbon content, while the nitrogen area was primarily related to soil clay content.
Highlights
The specific surface area of soils and clays is conventionally determined by low-temperature adsorption isotherms of non-polar gases like nitrogen
Areas determined by onepoint adsorption of water at a relative humidity (p/p0 ) of 20 % are as useful as areas determined by water vapor adsorption isotherms
The disagreement of surface areas determined by water vapor and nitrogen adsorption is explained to be due to the fact that only the external area is estimated by nitrogen adsorption, while water vapor adsorption estimates the total surface area
Summary
The specific surface area of soils and clays is conventionally determined by low-temperature adsorption isotherms of non-polar gases like nitrogen. According to Quirk (1955), surface areas determined by water vapor adsorption are only approximations to the areas determined by nitrogen adsorption. The previous study (Niskanen and Mäntylahti 1987 a) showed that soil surface areas determined by water vapor adsorption at p/p 20 % were closely related to soil clay and organic carbon content. The aim of this investigation was to study water vapor sorption on soil and to compare surface areas determined by the aid of water vapor sorption isotherms and by water vapor sorption at p/pG 0.20 with areas determined by nitrogen gas adsorption
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