Micromeritics FlowSorb III 2305 Operator's Manual page 76

Appendix A
Multipoint Surface Area
A straight line usually results between P/P
experimental data are plotted as (P/P
the abscissa. Relative pressures within this prescribed range are typically obtained
with gas compositions between about 5% and 25% N
Equation 1 shows then that the slope and intercept of this line are, respectively,
(C-1)/V
The FlowSorb is calibrated by injecting into it an accurately measured volume of
each gas mixture at ambient conditions, calculating the volume of this gas at
standard conditions, and setting the instrument to indicate thereafter adsorbed and
desorbed gas volumes at standard conditions. When 1 mL of gas mixture is in-
jected, its volume V at STP is given by
The sample specific surface area S in square meters per gram is calculated from
equation 2 using appropriate constants and slope and intercept values once the
plot is made. Using the constants given above, this relationship becomes
or simply
A-4
C and 1/(V C) and that both the values of V
m m
273.2
V = 1.00 x
Rm.Temp.
23
S = 6.023 x 10 x 16.2 x 10
S = 4.353/(slope + intercept)
values from about 0.05 to 0.25 when
0
)/V[1-(P/P )] on the ordinate against P/P
0 0
with the remainder He.
2
m
Atm.Press.
x
760
-20
/22414 (slope + intercept)
FlowSorb III
as
0
and C can be determined.
(8)
(9)
(10)
Aug 00