title: Two confined phases of argon adsorbed inside open single walled carbon nanotubes.
abstract: Isothermal adsorption of Ar on single walled carbon nanotubes (SWNTs) has been studied at 77 and 87 K. The SWNTs have been grown by laser vaporization of a graphite pellet containing 0.6% (atomic) Ni/Co catalyst. The nanotubes have been prepared for argon adsorption measurements by prolonged outgassing of as-grown material in a vacuum at room temperature (295 K), at elevated temperatures of up to 475 K, and by oxidization for 2 h in dry air at 470 K. Formation of two condensed phases of Ar in the interior of SWNTs has been observed at 77 K. The low-density phase is formed at 155(5) microTorr, while the high-density phase, at 120(5) microTorr. At 87 K, only a single phase has been observed at 185(5) microTorr. Condensation at both 77 and 87 K appears to be the first-order phase transition. Onset of the quasi-one-dimensional linear (one-channel) phase and the quasi-two-dimensional monolayer (six-channel) phase formation on the external surface of bundles has been observed at 77 K near 0.0017 and 0.8 Torr, respectively, and at 87 K near 0.018 and 5 Torr, respectively. Isosteric heats of adsorption for the one-channel phase, the first external layer, and the second external layer have been determined to be equal to 137, 107, and 70 meV, respectively.
authors.affiliation: Steacie Institute for Molecular Sciences, National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada.
authors.forename: Zygmunt J
authors.initials: ZJ
authors.lastname: Jakubek
authors.forename: Benoit
authors.initials: B
authors.lastname: Simard
mesh_terms: D000327:Adsorption; D001128:Argon / Q000737:chemistry*; D020650:Combinatorial Chemistry Techniques / Q000379:methods*; D037742:Nanotubes, Carbon / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D013816:Thermodynamics
chemical_list: D037742:Nanotubes, Carbon; D001128:Argon