4He Sorption in Graphene Oxide at Low Temperatures

The sorption and subsequent desorption of 4He gas by grapheme oxide (GO) and hydrazine-reduced grapheme oxide (RGO-Hz) powders have been investigated in the temperature interval 2 – 25 K. It is found that the Hz-reduction of GO increases the sorptive capacitance of RGO-Hz by a factor of 3.3 in com-parison with GO. It is assumed that the sorptive capacity of the RGO-Hz sample increases because the O2-containing groups are removed in the process of Hz-reduction of GO, which makes the interlayer space ac-cessible for sorption When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3520

Quantum effects in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with ⁴He

The radial thermal expansion αr of bundles of single-walled carbon nanotubes saturated with ⁴He impurities to the molar concentration 9.4% has been investigated in the interval 2.5–9.5 K using the dilatometric method. In the interval 2.1–3.7 K α r is negative and is several times higher than the negative αr for pure nanotube bundles. This most likely points to ⁴He atom tunneling between different positions in the nanotube bundle system. The excess expansion was reduced with decreasing ⁴He concentration

Thermal expansion of solid solutions Kr-CH₄ at temperatures of liquid helium

A negative contribution of the CH₄ impurity to the thermal expansion of the solution has been revealed in the dilatometric studies of solid Kr + 0.76% CH4, Kr + 5.25% CH₄, and Kr + 10.5% CH₄ solutions at 1-23 K. It is shown that the negative contribution results from changes in the occupancy of the ground state of the A-modifications of isolated CH₄ molecules. Assuming that the CH₄ impurity singles and clusters contribute to the thermal expansion independently, we can estimate their contributions. The contribution of the singles to the thermal expansion of the solid solution is negative. The energies of the first excitational rotational states were determined for singles and two-body and three-body clusters of the CH₄ molecules

The effect of O₂ impurities on the low-temperature radial thermal expansion of bundles of closed single-walled carbon nanotubes

The effect of oxygen impurities upon the radial thermal expansion αr of bundles of closed single-walled carbon nanotubes has been investigated in the temperature interval 2.2–48 K by the dilatometric method. Saturation of bundles of nanotubes with oxygen caused an increase in the positive αr-values in the whole interval of temperatures used. Also, several peaks appeared in the temperature dependence αr(T) above 20 K. The low temperature desorption of oxygen from powders consisting of bundles of single-walled nanotubes with open and closed ends has been investigated

Quantum phenomena in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with ³He. A giant isotope effect

The radial thermal expansion αr of bundles of single-walled carbon nanotubes saturated with ³He up to the molar concentration 9.4% has been investigated in the temperature interval 2.1–9.5 K by high-sensitivity capacitance dilatometry. In the interval 2.1–7 K a negative αr was observed, with a magnitude which exceeded the largest negative αr values of pure and ⁴He-saturated nanotubes by three and two orders of magnitude, respectively. The contributions of the two He isotope impurities to the negative thermal expansion of the nanotube bundles are most likely connected with the spatial redistribution of ⁴He and ³He atoms by tunneling at the surface and inside nanotube bundles. The isotope effect turned out to be huge, probably owing to the higher tunneling probability of ³He atoms

The low-temperature radial thermal expansion of single-walled carbon nanotube bundles saturated with nitrogen

The effect of a N₂ impurity on the radial thermal expansion coefficient αr of single-walled carbon nanotube bundles has been investigated in the temperature interval 2.2–43K by the dilatometric method. Saturation of nanotube bundles with N₂ caused a sharp increase in the positive magnitudes of αr in the whole temperature range used and a very high and wide maximum in the thermal expansion coefficient αr(T) at T~28 K. The lowtemperature desorption of the impurity from the N₂-saturated powder of bundles of single-walled carbon nanotubes with open and closed ends has been investigated

4He Sorption in Graphene Oxide at Low Temperatures

The sorption and subsequent desorption of 4He gas by grapheme oxide (GO) and hydrazine-reduced grapheme oxide (RGO-Hz) powders have been investigated in the temperature interval 2 – 25 K. It is found that the Hz-reduction of GO increases the sorptive capacitance of RGO-Hz by a factor of 3.3 in com-parison with GO. It is assumed that the sorptive capacity of the RGO-Hz sample increases because the O2-containing groups are removed in the process of Hz-reduction of GO, which makes the interlayer space ac-cessible for sorption When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3520

Radial thermal expansion of single-walled carbon nanotube bundles at low temperatures

For the first time the linear coefficient of the radial thermal expansion has been measured on a system of SWNT bundles at low temperatures (2.2–120 K). The measurements were performed using a dilatometer with a sensitivity of 2·10⁻⁹ cm. The cylindrical sample 7 mm high and 10 mm in diameter was obtained by compressing powder. The resulting bundles of the nanotubes were oriented perpendicular to the sample axis. The starting powder contained over 90% of SWNTs with the outer diameter 1.1 nm, the length varying within 5–30 μm. The change of sign of the radial thermal expansion coefficient at 5.5 K was observed

Radial thermal expansion of pure and Xe-saturated bundles of single-walled carbon nanotubes at low temperatures

The radial thermal expansion coefficient ar of pure and Xe-saturated bundles of single-walled carbon nanotubes (CNT) has been measured in the interval 2.2-120 K. The coefficient is positive above T = 5.5 K and negative at lower temperatures. The experiment was made using a low-temperature capacitance dilatometer with a sensitivity of 2·10⁻⁹ cm and the sample was prepared by compacting a CNT powder such that the pressure applied oriented the nanotube axes perpendicular to the axis of the cylindrical sample. The data show that individual nanotubes have a negative thermal expansion while the solid compacted material has a positive expansion coefficient due to expansion of the intertube volume in the bundles. Doping the nanotubes with Xe caused a sharp increase in the magnitude of ar in the whole range of temperatures used, and a peak in the dependence ar(T) in the interval 50-65 K. A subsequent decrease in the Xe concentration lowered the peak considerably but had little effect on the thermal expansion coefficient of the sample outside the region of the peak. The features revealed have been explained qualitatively

Argon effect on thermal expansion of fullerite C₆₀

The linear thermal expansion of compacted Ar-doped fullerite C₆₀(ArxC₆₀) is investigated at 2-12 K using dilatometric method. The thermal expansion of ArxC₆₀ was also studied after partial desaturation of argon from fullerite. It is revealed that argon doping resulted in the considerable change of the temperature dependence of the thermal expansion of fullerite. An explanation of the observed effects is proposed