Micromeritics Gemini VII 2390a, Operator'S Manual

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Appendix F Gemini VII
F-14 239-42828-01 - Dec 2012
quently leads to inconsistencies when carried to small mesopore sizes. If the thickness curve used is
too steep, it finally will predict a larger increment of adsorptive for a given pressure increment than is
actually observed; since a negative pore volume is non-physical, the algorithm must stop. Conversely,
if the thickness curve used underestimates film thinning, accumulated error results in the calculation of
an overly large volume of (possibly nonexistent) small pores.
The use of equation (1) represents an improvement over the traditional algorithm. Kernel functions
corresponding to various classical Kelvin-based methods have been calculated for differing geometries
and included in the list of models.
Models Included
t
3.54
5.00 –
P
/Po
 
ln
----------------------
 
 
1/3
=
Kelvin Equation with Halsey Thickness Curve
N2 - Halsey Thickness Curve
The kernel function is calculated using the Halsey equation with standard parameters:
The nitrogen properties used in the Kelvin equation are:
N2 - Halsey Thickness Curve
The calculation is the same as above except that cylindrical geometry is assumed.
Geometry
Slit
Substrate
Average
Category:
Porosity
Method:
Nitrogen at 77 K
Surface tension =
8.88 dynes cm
-1
Molar density =
0.02887 g cm
-3
Geometry
Cylinder
Substrate
Average
Category:
Porosity
Method:
Nitrogen at 77 K
Reference
: G. Halsey, J. Chem. Phys 16, 931 (1948).