Ultramicropores in microporous carbon fibres evidenced by helium adsorption at 4.2 K

The adsorption isotherms of He on activated carbon fibres at 4.2 K have been determined gravimetrically. The He adsorption isotherms were of typical type I and were analysed by the Dubinin–Radushkevich plots, giving the micropore volumes which are greater than those obtained from the N2 adsorption isotherm at 77 K by 20–50%. The excess amount of He adsorption was ascribed to the presence of ultramicropores which cannot be assessed by N2 molecules.