The present work is devoted to the search for new electrode materials for lowtemperature thermionic energy converters (TECs). As shown, the carbon nanostructures (СNS) adding to pure powdered titanium in an amount of 3-9% wt. and their subsequent mechanical mixing leads to the formation of composites that acquire new qualities that were not present in any of their original pure constituents. Thus, the significant changes in the mechanical and electrical characteristics of composites are observed. For example, the electrical conductivity is changed up to 2 orders in initial state of composites as well as its maximum values after samples' compaction are increased (1.6-5 times) in comparison with both the pure Ti powder and the pure thermally extended graphite (TEG) in corresponding compression states. Such changes are caused by the presence of contacts between the metal particles and the CNS in the metal-nanocarbon composites and, accordingly, the possibility of the transition of free charges, including hot charges, from the metal to the CNS.
The specific electrical conductivity (σ) of mechanical mixture consisting of particles LaNi 5 and multi-walled carbon nanotubes was studied under compression. Founded that the conductivity of mechanical mixture with micro particles LaNi 5 (diameter 28 ± 6 mkm) and 51 wt. % CNT is executed to the order of magnitude σ of CNT. Growth mechanism of specific electrical conductivity of mechanical mixture LaNi 5 with CNTs is due the process of ordering and the transfer electrons from the metal to CNTs. At this concentration, the mechanism of electron transfer from the metal particles to the CNT is most optimal.
A carbon nanocondensate containing multiwalled carbon nanotubes has been produced by dissociation of CO molecules on an iron-nickel catalyst at temperatures of 400–500 °C. X-ray diffraction is used to show that this condensate contains two phases with different densities and degrees of ordering. Elevated synthesis temperatures lead to a higher density and smaller differences in the phases, which are related to increased freedom from defects in the carbon layers and a greater number of layers in the multiwalled carbon nanotubes. Studies of the sorption and subsequent desorption kinetics of hydrogen by the synthesized samples at temperatures of 7–120 K showed that when the temperature is lowered from 120 to 65 K, an increased sorption time for H2, which is typical of thermally activated diffusion, was observed in all the samples. At temperatures below 65 K the characteristic hydrogen sorption times depended weakly on temperature; this can be explained by a predominance of tunnel diffusion over thermally activated diffusion. At temperatures of 7–20 K, the temperature dependence of the characteristic times had features that appear to be related to the formation of a monolayer of H2 molecules on the inner surface of the nanotube cavities. The dependence of the hydrogen diffusion activation energy on the temperature at which the samples were synthesized correlates well with x-ray spectroscopy data: n rise in the activation energy is observed as the relative amount of the highly ordered carbon phase increases.
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