TABLE OF CONTENTS The theory of monolayer adsorption developed by Brunauer, Emmett, and Teller (1938) is used for surface area measurements of sediments and other materials. Molecular adsorption is produced by van der Waals forces, which cause condensation of liquids and without which no adsorption would occur. Adsorption occurs at the most active site of the solid surface and then progresses to areas of lesser activity; finally, pore-filling will occur as gas condenses in the pores of the solid. Normally only a monolayer of gas molecules covers the surface area of the solid, which is exposed to the gas at the temperature of condensation. When only a monolayer of gas is adsorbed on the surface, one can calculate the surface area that was covered by the gas molecules from the amount of gas that was adsorbed. The adsorption isotherm of nitrogen (volume adsorbed vs. the relative pressure at constant temperature) is generally used for surface area measurements of sediments, grains, and powders. The volume of gas physically adsorbed as a unimolecular layer is determined by arranging the adsorption parameters in the form of a straight line:
where: P = equilibrium vapor pressure.
P N2 = pressure of saturated nitrogen vapor at the test temperature.
V = volume of nitrogen adsorbed at pressure P and the test temperature.
V m = volume of gas required to form a monolayer.
C = dimensionless constant related to the heart of adsorption.
A plot of P/(P N2 - P) versus P /P N2
