Micromeritics Gemini VII 2390a, Operator'S Manual, Page: 323 / 426

Gemini VII Appendix C
239-42828-01 - Dec 2012 C-29
Dubinin-Astakhov
V
 
log
Vo
 
RT

E
0
---------
N
Po
P
------- log

N
– log =
The Dubinin-Astakhov equation is a follows:
where
V = volume adsorbed at equilibrium pressure (cm
3
/g STP)
Vo = the micropore capacity (cm
3
/g STP)
Po = saturation vapor pressure of gas at temperature T (mmHg)
P = equilibrium pressure (mmHg)
T = analysis bath temperature (K)
R = the gas constant (0.0083144 kJ/mol)
E
0
= characteristic energy (kJ/mole)
N = Astakhov exponent, may be optimized or user entered from the Dubinin
Report Options dialog

= the affinity coefficient of the analysis gas relative to the Po gas, from the
Dubinin Adsorptive Options dialog

For each point designated for Dubinin-Astakhov calculations, the following calculations are done:
LV = log(V)
LP
Po
P
------- log
N
=
A least-squares fit is performed on the (LP,LV) designated pairs where LP is the independent variable
and LV is the dependent variable. If the user selected
Yes
for the
Optimize Astakhov Exponent
prompt, a systematic search for the optimum value of N is conducted by recalculating the linear regres-
sion and selecting the value of N that gives the smallest standard error of the y-intercept. The exponent
N is optimized to within 10
-4
. If the optimum value for N is not found in this range, an exponent of 2 is
used. The following are calculated:
a.) Slope (S cm
3
/g STP)
b.) Y-intercept (YI cm
3
/g STP)
c.) Error of the slope (S
ERR
cm
3
/g STP)
d.) Error of the y-intercept (YI
ERR
cm
3
/g STP)
e.) Optimized Astakhov exponent (N)
f.) Correlation coefficient