Nitrogen can be absorbed into the pores. From the adsorption regularity, when the relative pressure of nitrogen is greater than 0.4, the nitrogen gas generated in the suction hole becomes condensed liquid nitrogen, and adsorption is greatly increased. As the Microporous, it can be show capillary condensationphenomenon at a lower pressure. For the macroporous, they will need to be filled with liquid nitrogen at a higher pressure. Capillary condensation pressure and Pore is in line with the Kelvin equation.
The pore size is divided by several stages. We can measure adsorption isotherm, the adsorption volume for each incremental change, and the calculated volume corresponding to the pore size. The pore volume is calculated with variation, i.e., pore size distribution.