B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
G.V. Kurdyumov Institute for Metal Physics, National Academy of Sciences of Ukraine 36 Academician Vernadsky Blvd., Kyiv 03142, Ukraine
Received Jule 10, 2017
By dissociating CO molecules on an iron-nickel catalyst in a temperature range of 400–550 °C, was obtained a carbon nanocondensate containing multi-walled carbon nanotubes. The x-ray diffraction method shows that the resulting condensate contains two phases of different density and degree of order. An increase of the synthesis temperature leads to increase of density and decrease of the phase difference, which is due to in-crease in the nondefectiveness of carbon layers and their quantity in multi-walled carbon nanotubes. The studies of the sorption kinetics and the subsequent desorption of hydrogen by synthesized samples in the temperature range of 7–120 K showed that with temperature lowering from 120 to 65 K, an increase in the H2 sorption characteristic times was observed for all samples, which is indicative for thermally activated diffusion. At temperatures below 65 K, the characteristic times of hydrogen sorption were slightly dependant on temperature, which can be explained by predominance of the diffusion tunnel mechanism over the thermoactivation mechanism. In the temperature range of 7–20 K we observed pecularities of the temperature dependence of the characteristic times, apparently caused by formation of a mono-layer of H2 molecules on the inner surface of the nanotube cavities. The dependence of the activation energy of hydrogen diffusion on the synthesis temperature of the samples correlates well with the data obtained by x-ray spectroscopy: an increase in the activation energy occurs as the relative amount of the highly ordered carbon phase increases.