V. G. Manzhelii

Thermal Conductivity of Methane-Hydrate

The thermal conductivity of the methane hydrate CH4 (5.75H2O) was measured in the interval 2–140 K using the steady-state technique. The thermal conductivity corresponding to a homogeneous substance was calculated from the measured effective thermal conductivity obtained in the experiment. The temperature dependence of the thermal conductivity is typical for the thermal conductivity of amorphous solids. It is shown that after separation of the hydrate into ice and methane, at 240 K, the thermal conductivity of the ice exhibits a dependence typical of heavily deformed fine-grain polycrystal. The reason for the glass-like behavior in the thermal conductivity of clathrate compounds has been discussed. The experimental results can be interpreted within the phenomenological soft-potential model with two fitting parameters.

On the polyamorphism of fullerite-based orientational glasses.

The dilatometric investigation in the temperature range of 2–28 K shows that a first-orderpolyamorphous transition occurs in the orientational glasses based on C60 doped with H2, D2 andXe. A polyam ...

Negative thermal expansion of fullerite C60 at liquid helium temperatures

The thermal expansion of fullerite C60 has been measured in the temperature range 2–9 K. A compacted fullerite sample with a diameter of about 6 mm and height of 2.4 mm was used. It was found that ...

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

The radial thermal expansion coefficient alphar of pure and Xe-saturated bundles of single-walled carbon nanotubes (CNTs) is measured in the interval 2.2–120 K. The coefficient is positive above T ...

Heat transfer in the orientationally disordered phase of solid methane

Abstract The isochoric thermal conductivity of the orientationally disordered (OD) phase of solid methane has been studied at molar volumes 30.5 and 31.1 cm3/mol from 35 to 140 K. Above the order–disorder transition temperature, the isochoric thermal conductivity of methane first grows with temperature, passes through a smooth maximum and then decreases up to the melting temperature. The thermal conductivity maximum shifts towards higher temperatures as the density of the samples increases. The unusual temperature dependence of the isochoric thermal conductivity of methane is attributed to the interaction between phonons and correlated molecular rotations. The contributions of phonon–phonon scattering (Umklapp-processes) and phonon scattering at excitations of the rotational molecule motion to thermal resistance are discussed.

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.

Thermal expansion and polyamorphism of N2–C60 solutions

The linear coefficients alpha(T) of N-2-C-60 solutions with 9.9% and 100% of the C-60 lattice thermal expansion interstitials filled with N-2 are investigated in the interval 2.2-24 K. The dependen ...

Specific features of thermal expansion and polyamorphism in CH4–C60 solutions at low temperatures

The temperature dependence of the linear thermal expansion coefficient alpha(T) is investigated in the temperature range of 2.5 to 23 K for two different CH4-C-60 solutions in which CH4 molecules o ...

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 ...