ABSTRACT
The plots of P/V(P0 – P) against P/P0 should therefore exhibit a straight line with slope (C – 1)/(VmC) and intercept 1/(V
pressure range 0.05-0.35. The slope (C – 1)/(V m C) and intercept values 1/V
cally or by linear regression. Therefore, the monolayer capacity V m can be derived from the reciprocal
of the summation between the slope and intercept values, as shown in
V C V C V C
5 2
1 1 1
(8.7)
To calculate the surface areas of powders, another important value is the cross-sectional area A of the adsorbate molecules. The surface area S (m2) of the powder can be obtained from the product of the monolayer capacity V
S V AN5 3 2
22 4 10 3. (m ) 2
(8.8)
where N A is Avogadro’s number. A reasonable estimation of the cross-sectional area of an adsorbate
molecule is generally obtained from the liquid density of the adsorptive at measurement temperature using Equation 8.9 with several assumptions: (a) the shape of an adsorptive molecule is spherical, (b) the liquid structure of the adsorptive is the closest packing structure with 12 nearest neighbors, and (c) the adsorptive molecules are adsorbed on the particle surface with the 6 nearest neighbors in the close-packed hexagonal arrangement:
A MN5
. ρ A
(8.9)
The factor 1.091 in Equation 8.9 is a packing factor deduced from the assumptions described above.
