Principle Of Operation - Micromeritics FlowSorb III 2305 Operator's Manual

FlowSorb III

Principle of Operation

The surface area of granulated and powdered solids or porous materials is meas-
ured with the FlowSorb III by determining the quantity of a gas that adsorbs as a
single layer of molecules, a so-called monomolecular layer, on a sample. This ad-
sorption is done at or near the boiling point of the adsorbate gas. Under specific
conditions, the area covered by each gas molecule is known within relatively nar-
row limits. The area of the sample is thus calculable directly from the number of
adsorbed molecules, which is derived from the gas quantity at the prescribed con-
ditions, and the area occupied by each.
For a nitrogen and helium mixture of 30 volume percent nitrogen, conditions most
favorable for the formation of a monolayer of adsorbed nitrogen are established
at atmospheric pressure and the temperature of liquid nitrogen. Parameters defining
the conditions at which the monolayer forms are incorporated in the multipoint
analysis result by the data treatment. Atmospheric pressure and ice water
temperature may establish appropriate conditions for a n-butane and helium mix-
ture. Other gases at other conditions are also usable.
In general, a surface area result obtained by the multipoint method using nitrogen
as the adsorbate is somewhat more reliable than a single point one, and nitrogen
gas is preferable over other gases. Unless special circumstances dictate, nitrogen
is recommended.
Refer to Appendix A for additional information on FlowSorb theory.
Mar 2012
Principle of Operation
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