Micromeritics FlowSorb III 2305 Operator's Manual page 73

FlowSorb III
One form of the well-known BET equation* that describes the adsorption of a
gas upon a solid surface is
where
V
P
0
V
m
C
The surface area S of the sample giving the monolayer adsorbed gas volume
Vm
(STP)
where
A
M
N
Single-Point Surface Area
The constant C of equation 1 is typically a relatively large number, i.e., C>1,
from which equation 1 reduces very nearly to
Now if P/P
* Brunauer, S., Emmett, P.H., and Teller, E., J. Am. Chem. Soc. 60, 309A (1938).
Aug 00
THEORY
(P/P )/V[1-(P/P )] = 1/(V
0 0
= the volume (at standard temperature and pressure, STP) of gas
adsorbed at pressure P
= the saturation pressure which is the vapor pressure of liquified gas
at the adsorbing temperature
= the volume of gas (STP) required to form an adsorbed monomolecular
layer
= a constant related to the energy of adsorption
is then calculated from
S = Vm N/M
A
= Avogadro's number which expresses the number of gas molecules
in a mole of gas at standard conditions,
= the molar volume of the gas, and
= the area of each adsorbed gas molecule as given in Appendix B.
(P/P )/V[1-(P/P )] = (1/V
0 0
>>1/C, equation 3 can be further represented by
0
(P/P )/V[1-(P/P )] = (1/V
0 0
C)+[(C-1)/(V C)]P/P
m m 0
)[(1/C)+(P/P )]
m 0
)(P/P )
m 0
Appendix A
(1)
(2)
(3)
(4)
A-1