This document describes a method for the evaluation of porosity and pore size distribution by physical
adsorption (or physisorption). The method is limited to the determination of the quantity of a gas
adsorbed per unit mass of sample as a function of pressure at a controlled, constant temperature [1-
9]. Commonly used adsorptive gases for physical adsorption characterization include nitrogen, argon,
krypton at the temperatures of liquid nitrogen and argon (77 K and 87 K respectively) as well as CO2 (at
273K). Traditionally, nitrogen and argon adsorption at 77K and 87 K, respectively, allows one to assess
pores in the approximate range of widths 0,45nm to 50 nm, although improvements in temperature
control and pressure measurement now allow larger pore widths to be evaluated. CO2 adsorption
at 273K can be applied for the microporous carbon materials exhibiting so-called ultramicropores.
Krypton adsorption at 77 K and 87 K is used to determine the surface area or porosity of materials with
small surface area or for the analysis of thin porous films. The method described here is suitable for a
wide range of porous materials. This standard focuses on the determination of pore size distribution
from as low as 0,4 nm up to ca.100 nm, but will not focus on the assessment of surface area which is
described in a dedicated standard (ISO 9277:2010).
The procedures which have been devised for the determination of the amount of gas adsorbed may be
divided into two groups: (i) those which depend on the measurement of the amount of gas removed
from the gas phase,i.e manometric (volumetric) methods; (ii) those which involve the measurement
of the uptake of the gas by the adsorbent (i.e. direct determination of increase in mass by gravimetric
In practice, static or dynamic techniques may be used to determine the amount of gas adsorbed.
However, the manometric method is generally considered the most suitable technique for undertaking
physisorption measurements with nitrogen, argon, and krypton at cryogenic temperatures (i.e., 77K and
87 K, the boiling temperature of nitrogen and argon, respectively) with the goal of obtain pore volume
and pore size information. Hence, here we will focus only on the application of the manometric method.