Threewell-defined stages were identified: (1) a slow increase in nitrogen
uptake at a low relative pressure, corresponding to monolayermultilayer
adsorption on the porewalls; (2) intermediate relative pressures
indicative of capillary condensation within the mesopores; and
(3) high relative pressures indicating an external crystal multi-layer
adsorption of nitrogen and all the other pores are filled when the pressure
to reach saturation (P/P0 = 1.0). The isotherms belonged to Type
IV in the definition of IPCC and indicated that N2 is condensed in the
pores at high relative pressures. There was a hysteresis loop of the H2
style, since the pores had a narrow inlet and wide hole (Wang, 2005).