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 thermal conductivity of solid krypton—methane solutions

The dynamic interaction of a quantum rotor with its crystalline environment has been studied by measurement of the thermal conductivity of the Kr₁–c(CH₄)c solid solutions at c = 0.05–0.75 in the temperature region 2–40 K. The thermal resistance of the solutions was mainly determined by the resonance scattering of phonons on CH₄ molecules with the nuclear spin I = 1 (the nuclear spin of the T species). The influence of the nuclear spin conversion on the temperature dependence of the thermal conductivity к(T) leads to a well-defined minimum on к(T). The temperature of the minimum depends on the CH₄ concentration. It was shown that the nonmonotonic increase of the anisotropic molecular field with the CH₄ concentration is caused by a compensation effect due to corrections in the mutual orientations of the neighboring rotors at c > 0.5. The temperature dependence of Kr₁–c(CH₄)c is described within the Debye model of thermal conductivity taking into account the lower limit of the phonon mean free path. It is shown that phonon–rotation coupling is responsible for the anomalous temperature dependence of the thermal resistance at varying temperature. It increases strongly when the quantum character of the CH₄ rotation at low temperatures changes to a classical one at high temperatures. A thermal conductivity jump (a sharp increase in к(T) within a narrow temperature range) was also observed. The temperature position of the jump varies from 9.7 to 8.4 K when the CH₄ concentration changes from 0.25 to 0.45

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

Extraordinary temperature dependence of isochoric thermal conductivity of crystalline CO₂ doped with inert gases

The isochoric thermal conductivities of solid (CO₂)₀,₉₀₅Kr₀,₀₉₅ and (CO2)₁₋xXex(x = 0.052 and 0.097) solution of different densities was investigated in the temperature interval from 150 K to the onset of melting. An unusual effect of point defects on the thermal conductivity has been detected. In pure CO₂ at T >150 K the isochoric thermal conductivity decreases smoothly with increasing temperature. In contrast, the thermal conductivity of solid CO₂/Kr and CO₂/Xe solutions first decreases passing through a minimum at 200–210 K and then starts to increase with temperature up to the onset of melting. This behavior of the isochoric thermal conductivity is attributed to the rotation of the CO₂ molecules which gains more freedom as the spherically symmetrical inert gas atoms dissolve in CO₂

Experimental low-temperature heat capacity of one-dimensional xenon adsorbate chains in the grooves of carbon c-SWNT bundles

The experimental studies of the heat capacity of 1D chains of xenon atoms adsorbed in the outer grooves of bundles of closed single-walled carbon nanotubes CXe have been first made at temperature range 2–30 K with the adiabatic calorimeter. The experimental data CXe have been compared with theory [A. Šiber, Phys. Rev. B 66, 235414 (2002)]. The experimental and theoretical heat capacity curves are close below 8 K. Above 8 K the experimental curve CXe (T) exceeds the theoretical one and excess capacity CXe (T) increases monotonously with temperature. We assume that the CXe (T) caused mainly by the increase of the distance between the neighboring xenon atoms in the chain with increasing temperature

Isochoric thermal conductivity of solid nitrogen

The isochoric thermal conductivity of solid nitrogen has been investigated on four samples of different densities in the temperature interval from 20 K to the onset of melting. In α-N₂ the isochoric thermal conductivity exhibits a dependence weaker than Λ1/T; in β-N₂ it increases slightly with temperature. The experimental results are discussed within a model in which the heat is transported by low-frequency phonons or by «diffusive» modes above the mobility edge. The growth of the thermal conductivity in β-N₂ is attributed to the decreasing «rotational» component of the total thermal resistance, which occurs as the rotational correlations between the neighboring molecules become weaker

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