N. A. Vinnikov

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

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

Kinetics of He4 gas sorption by fullerite C60. Quantum effects

The kinetics of helium gas sorption by C60 powder and subsequent desorption of the He4 impurity from the saturated powder is studied in the temperature interval 2–292K. Evidence is obtained supporting the existence of two stages in the temperature dependences of sorption and desorption. These stages originate in different times taken by helium to occupy octahedral and tetrahedral interstices in the C60 lattice. The characteristic times of sorption and desorption coincide. It is found that the temperature dependences of the characteristic times for occupying the octahedral and tetrahedral interstices are nonmonotonic. When the temperature is lowered from 292to79.3K, the characteristic times increase, which indicates thermally activated diffusion of helium in C60. With a further reduction to T=10K, the characteristic times decrease by more than an order of magnitude. Below 8K the characteristic times of sorption and desorption are temperature-independent. This suggests tunnel diffusion of He4 in C60.

Influence of dissolved oxygen on the thermal expansion and polyamorphism of fullerite C60

The temperature dependence of the coefficient of linear thermal expansion alpha of O-2-C-60 solutions with 20% and 80% filling of the octahedral cavities with oxygen is investigated in the temperat ...

Hydrogen sorption and radial thermal expansion of bundles of single-walled nanotubes irradiated by γ-rays in hydrogen atmosphere

The influence of radiation exposure in hydrogen atmosphere on the radial thermal expansion of single-walled carbon nanotubes and on their sorption of hydrogen is studied. The irradiation was carried out with cobalt-60 γ-rays (with an energy of 1.2 MeV and an irradiation dose of 1.5·107 rad) in the normal hydrogen atmosphere under pressure 1 atm and at temperature of 300 K. The sorption and desorption of hydrogen by samples of nanotubes were investigated over the temperature range 15–1170 K before and after irradiation. It was found that the irradiation of carbon nanotubes (CNTs) in hydrogen atmosphere leads to considerable increasing an amount of hydrogen sorbed by the sample. The irradiation in hydrogen atmosphere resulted in increasing absolute values of radial thermal expansion of CNTs bundles over the temperature range investigated (2–120 K). The effects of hydrogen physically and chemically sorbed in bundles of CNTs on the radial thermal expansion of the irradiated samples were distinguished.

Thermal expansion of solutions of deuteromethane in fullerite C60 at low temperatures. Isotopic effect

The thermal expansion of CD4 solutions in the orientational glass C60 with molar concentration of deuteromethane 20 and 50% has been investigated in the temperature range 2.5–23 K. The orientation ...

Tunneling effects in the kinetics of helium and hydrogen isotopes desorption from single-walled carbon nanotube bundles

The kinetics of desorption both helium isotopes and molecules of hydrogen and deuterium from open-ended or γ-irradiated single-walled carbon nanotube bundles was investigated in temperature range of 10–300 K. The gases desorption rates obey the Arrhenius law at high temperatures, deviate from it with temperature reduction and become constant at low temperatures. These results indicate the quantum nature of gas outflow from carbon nanotube bundles. We had deduced the crossover temperature below which the quantum corrections to the effective activation energy of desorption become significant. This temperature follows linear dependence against the inverse mass of gas molecule and is consistent with theoretical prediction.

Quantum effects in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with He4

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 ...

Kinetics of 3He, 4He, H2, D2, Ne, and N2 sorption by bundles of single-walled carbon nanotubes. Quantum effects

This is a study of the low temperature kinetics of the sorption and subsequent desorption of 3He, 4He, H2, D2, Ne, and N2 by bundles of single-wall carbon nanotubes with closed ends (c-SWNT). The characteristic times of the sorption and desorption processes are the same to within the experimental error. Annealing a sample of bundles at 500 °C greatly reduces the characteristic times and changes their temperature dependences. The effect of annealing decreased with increasing molecular weight of the dissolved gas. At temperatures below 16 K the sorption times for 3He, 4He, H2, and D2 depends weakly on temperature, which suggests a tunnel character of the sorption for these impurities by nanotube bundles. The effect of γ-irradiation of nanotube bundles on the sorption and desorption of hydrogen is qualitatively similar to the effect of annealing.

Diffusion of H2 and Ne impurities in fullerite C60. Quantum effects

The kinetics of sorption and subsequent desorption of normal H2 and Ne gases in C60 powder has been investigated in the temperature range 12–292 K using the method of direct pressure measurement. The measured characteristic times for filling the octahedral interstitial sites of fullerite with gas molecules were used to obtain the temperature dependences of the diffusion coefficients in fullerite for H2 and Ne. Upon cooling down below room temperature the diffusion coefficients of the impurities were found to initially decrease in both solid state solutions and then rise steeply below 90 K (H2) or 100 K (Ne). At the lowest temperatures reached in the experiments, the temperature dependence of the diffusion leveled. The features revealed are attributed to the competition between the thermally activated diffusion, which is dominant at comparatively high temperatures, and the quantum diffusion, which prevails at low temperatures.

Hydrogen sorption by the bundles of single-wall carbon nanotubes, irradiated in various gas media

The effect of radioactive irradiation on H2 sorption by bundles of single-wall carbon nanotubes (SWNTs) has been investigated in various gas media. The samples were irradiated with γ-quanta (1.2 MeV) of 60Co ((1.5–1.7) × 107 rad) radiation at room temperature in deuterium, nitrogen, and oxygen atmosphere (P = 1 atm), and in a vacuum. The processes of H2 sorption and desorption in the SWNT bundles were investigated before and after irradiation in the temperature interval 12–1270 K. It is found that irradiation in a gas environment has a significant effect both on the low-temperature H2 sorption induced by the weak physical interaction, and the chemical H2 sorption by the SWNT bundles. A phenomenological model has been proposed to explain the defect generation in carbon nanotubes irradiated in gas media.