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The thermal expansion of fullerite C60 doped with a 4He impurity at T ∼2 K has been investigated by the method of low temperature precision dilatometry in the interval T = 2.2−24 K. The character and the derived values of the thermal expansion coefficients were strongly dependent on the concentration of the 4He impurity in fullerite. In the interval T = 2.2−5 K the thermal expansion of the 4He x−C60 system is negative, which is attributed to the tunnel movement of the 4He atoms in the cavity system of the C60 crystal lattice and at the crystallite surface. The contribution of this process to the thermal expansion decreases as the impurity (4He) concentration increases and the probability of 4He tunneling between the crystal lattice cavities and the impurity-free areas of the grain surface diminishes. In the temperature interval T = 4.5−24 K the thermal expansion of the 4He x−C60 system is influenced predominantly by the mutual transformations of different orientation glass modifications of fullerite. Owing to their tunnel character the transformations make a negative contribution to the process of thermal expansion entailing a hysteresis and other anomalies observed in this temperature interval. The intensity of the processes provoked by the tunneling-encouraged phase transformations of the orientational glasses of C60 increases with the 4He concentration in fullerite.

For the first time, a solid phase of the C60@{H2O} n mixture has been obtained through joint condensation of water vapor and fullerene C60 on a cooled substrate. When heated to room temperature and melted, the mixture C60@{H2O} n forms a stable solution without applying any treatment such as shaking or sonication. The visible and UV spectroscopic analysis of the product shows that the absorption spectrum of the solution prepared by melting the mixture condensed at T1 = 90 K exhibits features characteristic of C60 molecules in pure fullerite films at λ1 = 344 nm, λ2 = 265 nm, and λ3 = 220 nm. The absorption spectrum of the mixture condensed at T2 = 223 K has no features in the long-wavelength region (λ1 = 344 nm), which may be attributed to the functionalization of fullerene vapors in the process of condensation at higher temperatures of the substrate.

Scanning electron microscopy, X-ray diffraction, and thermoprogrammed desorption methods were used to study the effect of treatment with a pulsed high-frequency discharge in a hydrogen atmosphere on the morphology, structure, and sorption characteristics of thermally reduced graphene oxide (TRGO). The TRGO treatment with pulsed gas discharge was shown to enhance the physical sorption of hydrogen by 1.5 times. It can be assumed that the increase in sorption capacity is due to a change in the distance between adjacent carbon surfaces in packets of graphene planes, due to the chemical interaction with the hydrogen ionized during the discharge.

Measurements of heat capacity at constant pressure of thermally reduced graphene oxide (trGO) and graphite oxide (GtO) were performed in the temperature range from 1.8 to 275 K by thermal relaxation method. Above 15 K, the specific heat values of trGO and GtO are close to each other within 20%. Below 10 K, the ratio of the specific heat of trGO to the specific heat of GtO increases with decreasing temperature and reaches 5 at 2 K. It was found that the temperature dependence of the specific heat of trGO is of a complex character. There are temperature ranges in which of the specific heat of trGO is close to either linear or T2.5.

The authors have studied the effect of small (≤ 1 wt%) additions of thermally reduced graphene oxide on the microhardness and microindentation kinetics in two types of polymers: polystyrene (i.e. thermoplastic with a glass transition temperature of Tg ≈ 373 K) and polyester resin (i.e. thermosetting plastic, Tg ≈ 300 K). The room temperature creep of nanocomposites under an indenter is described using a three-element rheological Kelvin–Voigt model. The study determines the parameters of this model and how graphene oxide (GO) affects them. In a polystyrene nanocomposite with 0.3 wt % graphene oxide, unrelaxed and relaxed elastic moduli, and the modulus characterizing high-elastic deformation, increase by 11%, 40% and 87%, respectively, as compared to the initial polystyrene; at the same time, microhardness increases by 38% and 45% for the different series of samples. The results obtained indicate that the presence of graphene oxide in the nanocomposite severely restricts the mobility of molecular segments. The addition of 0.3 wt% graphene oxide to polyester resin is accompanied by an increase in the mechanical glass transition temperature of the resin by at least 5 K. This leads to a change in the relaxation state of this polymer: while at room temperature the polyester resin behaves like an elastomer, a polyester resin nanocomposite with 0.3 wt% graphene oxide exhibits glassy properties. At room temperature, the microhardness of polyester resin-glass fabric-graphene oxide nanocomposites with a GO content of 0.5 and 1 wt% increases by 20% and 80% respectively, as compared to that of a polyester resin-glass fabric composite. The authors have obtained the temperature dependences of the microhardness of nanocomposites with a polyester matrix in the range 77–298 K, and have also identified temperature regions where the microdeformation of composites is reversible, which is associated with the formation of crazes with a lower glass transition temperature.

The features of hydrogen sorption by a wide range of nanostructures — fullerite C60, carbon nanotubes, graphene structures, nanodispersed carbon, including Pd-containing nanoclusters, ordered silicon-oxide-based nanostructures (the MCM-41 family) and silicon-oxide aerogel — have been reviewed. Special attention is given to the sorption characteristics of carbon nanostructures that have been exposed to various modifying treatments (oxidation, gamma-ray irradiation in gas atmosphere, action of pulsed high frequency gas discharge). Two mechanisms of physical low-temperature sorption of hydrogen have been revealed to predominate in such nanostructures in different temperature intervals. At the lowest temperatures (8–12 K), the sorption can actually proceed without thermal activation: it is realized through the tunnel motion of hydrogen molecules along the nanostructure surfaces. The periodic structure of the potential relief, allowed by the surface frame of carbon and silicon-oxide nanostructures, along the rather low interpit barriers are beneficial for the formation of low-dimensional (including quantum) hydrogen-molecule systems practically without thermally activated diffusion. In such nanostructures, the hydrogen diffusion coefficients are actually independent of temperature at 8–12 K. At higher temperatures (12–295 K), a thermally activated mechanism of hydrogen diffusion prevails. The periodic structure of fullerite C60 contains periodic interstitial cavities, separated by rather low potential barriers. Their sizes are sufficient to accommodate impurity hydrogen molecules and, thus, allow diffusion processes, which can also have a tunnel nature. It is shown that gamma-irradiation and high-frequency gas discharge processing increase markedly the quantity of hydrogen strongly bonded to carbon nanostructures.

Using X-ray diffraction and thermo-programmed desorption, the present study investigated the effect of treatment with pulsed high-frequency discharge in a hydrogen environment on the structure and sorption characteristics of the carbon synthetic nanoporous sorbent SCN (spherical carbonite saturated). Treatment with SCN by a pulsed gas discharge led to chemisorption of 0.4% hydrogen by weight, as well as 1.7 times greater physical sorption of hydrogen. We can assume this increase in sorption capacity is due to changes in the equivalent pore sizes that result from chemical interaction of the carbon atoms of SCN with hydrogen ionized during the discharge process.PACS: 61.43.Gt Powders; porous materials; 52.77.–j Plasma applications; 88.30.R– Hydrogen storage.

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.

The sorption and desorption of hydrogen by mesoporous MCM-41 silicate material is studied at temperatures ranging from 6.8 to 290 K. It is found that a thermally activated mechanism with an estimated activation energy Ea ≈ 466 K predominates in the H2 sorption kinetics of an MCM-41 sample for temperatures of 60–290 K. For temperatures of 17–60 K the diffusion coefficient of H2 molecules in MCM-41 is almost entirely temperature independent, which is typical when a tunneling diffusion mechanism predominates over the thermally activated mechanism. Within the 8–17 K range, a change in the mobility of H2 molecules in the channels of MCM-41 is observed that appears to correspond to the formation of a monolayer (or its destruction during heating) and subsequent layers of hydrogen which have condensed on the inner surfaces of the channels. This process has an activation energy Em ≈ 21.2 K. At temperatures below 8 K the diffusion coefficients of H2 depend weakly on temperature. This presumably corresponds to a cha...

5 Figuras.- 2 Tablas.- This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Low Temp. Phys.45, 422 (2019) and may be found at http://dx.doi.org/10.1063/1.5093523, The effect of thermal reduction of graphene oxide on the hydrogen sorption and desorption kinetics was studied by temperature-programmed desorption in the 7–120 K temperature range. The heat treatment of graphene oxide samples resulted in a decrease in the activation energy for hydrogen diffusion by more than an order of magnitude (by a factor of 12–13) compared with the initial graphite oxide. This change in the activation energy is, most likely, caused by exfoliation (loosening) of the graphite oxide carbon sheets upon the thermal removal of intercalated water, which changes the sorption character by decreasing the influence of the opposite walls in the interlayer spaces., The authors are grateful to Prof. A.I. Prokhvatilov for the fruitful discussion of the results of the study, and to the National Academy of Sciences of Ukraine for the financial support within the framework of the program “Fundamental Problems of the Development of New Nanomaterials and Nanotechnologies” (Project No. 0115U001397).

The temperature dependence of the linear thermal expansion coefficients (LTEC) of a single crystal of a-(BEDT-TTF)2NH4Hg(SCN)4 where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene was studied by the method of precision capacitive dilatometry in the temperature range 2-250 K along the crystallographic direction b* (perpendicular to the crystal layers). Negative values of LTEC were found below 4 K. Probably it is due to charge fluctuations as the temperature approaches the temperature of transition to the superconducting state Tc. It has been suggested that the bends on temperature dependence of LTEC observed in the temperature range 25-45 K are related to order-disorder arrangement of NH4+ ions. Weak maximum of the LTEC, detected at a temperature of about 200-220 K, can be caused by the processes of charge redistribution and the associated intermolecular interaction fluctuations., 8 pages, 2 figures

Sorption and desorption of 4He by a mesoporous silicate material MCM-41 was studied in the temperature range of 1.5–290 K. It was shown that for T = 25–290 K the thermal activation mechanism is dominant in the sorption kinetics of 4He atoms by an MCM-41 sample. Its activation energy was estimated as Ea ≈ 164.8 K. For T = 12–23 K, the diffusion of 4He atoms in the MCM-41 was practically independent of temperature, which typically occurs when the tunnelling mechanism of diffusion dominates over the thermally activated one. A change in the mobility of 4He atoms in MCM-41 channels was observed at T = 6–12 K, which may be indicative of the formation upon cooling (or decay upon heating) of a 4He monolayer and subsequent multilayers on the inner surfaces of the channels. Below 6 K, the diffusion coefficients of 4He are only weakly temperature dependent, which may be attributed to the behavior of quantum 4He liquid in the MCM-41 channels covered with several layers of 4He atoms.

The effects of radiation exposure in a hydrogen atmosphere on hydrogen sorption by a synthetic porous carbon nanosorbent, SCN (spherical carbonite saturated). The exposure was created by γ-rays from cobalt-60 (photon energy 1.2 MeV, irradiation dose 4.8 × 107 rad) in a normal hydrogen atmosphere at a pressure of 1 atm and a temperature of 300 K. The processes of hydrogen sorption-desorption by SCN samples before and after irradiation were studied in a temperature interval of 15–1173 K. It was found that the irradiation of SCN in a hydrogen atmosphere significantly increased the amount hydrogen sorbed in the sample. We conducted a comparison with the results of earlier studies investigating the influence of irradiation on the sorption of hydrogen by single-walled carbon nanotubes. The amount of physically sorbed hydrogen in the synthetic SCN sorbent that was irradiated in the hydrogen atmosphere, is four times greater than the amount of hydrogen that was physically sorbed by the single-walled carbon nanotubes that were irradiated under similar conditions. At a temperature below 25 K, the hydrogen diffusion in the SCN was almost temperature independent for the porous subsystem with the highest diffusion coefficients, which is typical for cases when the tunnel diffusion mechanism dominates the thermodynamic mechanism.

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.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Low Temperature Physics 43, 383 (2017) and may be found at https://doi.org/10.1063/1.4979362, The kinetics of the sorption and the subsequent desorption of 4He by the starting graphite oxide (GtO) and the thermally reduced graphene oxide samples (TRGO, Treduction = 200, 300, 500, 700 and 900 °C) have been investigated in the temperature interval 1.5–20 K. The effect of the annealing temperature on the structural characteristics of the samples was examined by the x-ray diffraction (XRD) technique. On lowering the temperature from 20 to 11–12 K, the time of 4He sorption increased for all the samples, which is typically observed under the condition of thermally activated diffusion. Below 5 K the characteristic times of 4He sorption by the GtO and TRGO-200 samples were only weakly dependent on temperature, suggesting the dominance of the tunnel mechanism. In the same region (T, Financial support from Spanish Ministry MINECO and the European Regional Development Fund (Project No. ENE2013-48816-C5-5-R), the Regional Government of Aragon and the European Social Fund DGA-ESF (Project No. T66) and Targeted Comprehensive Fundamental Research Program of NASU (Project No. 6/16-H) is gratefully acknowledged.

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.

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.

The effect of 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 sharply increased the positive values of αr in the entire experimental temperature range and resulted in a very high, wide maximum in the thermal expansion coefficient αr(T) at T∼28K. Low-temperature impurity desorption from N2-saturated powder consisting of bundles of single-walled carbon nanotubes with open and closed ends has been investigated.

The radial thermal expansion coefficient (a)r of pure and Xe-saturated bundles of single-walled carbon nanotubes 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 2x10-9 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 (a)r in the whole range of temperatures used, and a peak in the dependence (a)r (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., Comment: 12 pages,6 figures

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 ...

Orientational glasses with CO molecules occupying 26 and 90% of the octahedral interstitial sites in the C60 lattice have been investigated by the dilatometric method in a temperature interval of 2 ...

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 ...

New carbon materials are the most intensively studied objects now. This is due to the wide range of industrial applications, because of the unique unusual physical properties of these materials - high mechanical strength, electrical conductivity, chemical resistance, abrasion resistance, sorption capacity. However, in practical application nanosystems it must take into consideration that carbon nanostructure quite easily adsorb different particles (atoms and molecules). Saturation of impurity particles significantly affects the physical properties of carbon nanostructures and products based on them, in particular at low temperatures.

The kinetics of the sorption and subsequent desorption of gaseous 3He in a C60 fullerite powder has been studied in the temperature range of 2–292 K. The temperature dependences of the diffusion coefficients of 3He and 4He impurities in fullerite have been plotted using the measured characteristic times of filling of octahedral and tetrahedral interstices, as well as previous data. These temperature dependences of the diffusion coefficients of 3He and 4He impurities in fullerite are qualitatively similar. A decrease in the temperature from 292 to 79 K is accompanied by a decrease in the diffusion coefficients, which corresponds to the dominance of the thermally activated diffusion of helium isotopes in fullerite. A further decrease in the temperature to 8–10 K leads to an increase in the diffusion coefficients by more than an order of magnitude. The diffusion coefficients of 3He and 4He are independent of the temperature below 8 K, indicating the tunnel character of the diffusion of helium in C60 fullerite. The isotope effect is manifested in the difference between the absolute values of the diffusion coefficients of 3He and 4He atoms at the same temperatures.

The kinetics of sorption and subsequent desorption of argon gas by a C60 powder has been investigated in the temperature interval 58-290 K. The temperature dependence of the coefficients of Ar diffusion in fullerite has been obtained using the measured characteristic times of sorption. The diffusion coefficients of Ar decrease monotonically with lowering temperature in the whole range of the investigated temperatures, which corresponds to the thermally activated diffusion of Ar atoms in fullerite. The glass transition in fullerite induces an order-of-magnitude decrease in the activation energy of Ar diffusion in fullerite. Most likely this is because new directions may appear due to the glass transition in which the barriers separating the interstitial voids in the C60 lattice are significantly lower, Comment: 8 pages, 4 figures

The effect of oxygen impurities upon the radial thermal expansion (ar) 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 ar-values in the whole interval of temperatures used. Also, several peaks appeared in the temperature dependence ar(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, Comment: 7 pages, 3 figures

The radial thermal expansion (ar) 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 (ar) is negative and is several times higher than the negative (ar) 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., 4 pages, 1 figure, will be published in Fiz.Nizk Temp. #7, 2010

The kinetics of helium gas sorption by a C60 powder and subsequent desorption of the 4He impurity from the saturated powder has been investigated in the temperature interval T = 2-292 K. Evidence is obtained that supports the existence of two stages in the temperature dependences of sorption and desorption. The stages account for the different times taken by helium to occupy the 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 of occupying the octahedral and tetrahedral interstices are nonmonotonic. As the temperature is lowered from 292 K to 79.3 K, the characteristic times increase, which indicates a predominance of thermally activated diffusion of helium in C60. On a further decrease to T = 10 K the characteristic times reduce over an order of magnitude. Below 8 K the characteristic times of sorption and desorption are temperature-independent. This suggests a tunnel character of 4He diffusion in C60., Comment: 6 pages, 2 figures

The effect of a normal H2 impurity upon the radial thermal expansion (Ar) of SWNT bundles has been investigated in the interval T = 2.2-27 K using the dilatometric method. It is found that H2 saturation of SWNT bundles causes a shift of the temperature interval of the negative thermal expansion towards lower (as compared to pure CNTs) temperatures and a sharp increase in the magnitude of (Ar) in the whole range of temperatures investigated. The low temperature desorption of H2 from a powder consisting of bundles of SWNTs, open and closed at the ends, has been investigated., Comment: 10 pages, 2 figures

The temperature dependence of the linear thermal expansion coefficient α(T) has been investigated in the temperature range of 2.5 to 23 K for two different CH4–C60 solutions in which CH4 molecules occupied 24 and 50% of the octahedral interstitial sites of the C60 lattice. In both cases, α(T) exhibits hysteresis, suggesting the existence of two types of orientational glass associated with these solutions. The temperature of the first-order phase transition between these two glasses was estimated and the behavior of these two glasses compared. The characteristic times of thermalization τ1, reorientation of the C60 molecules τ2, and of the phase transformation between the glasses τ', have been estimated for these solutions. Both the temperature dependence of α(T) and the characteristic thermalization time τ1are found to have features near the phase transition temperature and an explanation has been put forward to explain these observed features.

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.

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.

The programmed thermal desorption method is used at temperatures of 7–95 K to study the sorption and subsequent desorption of hydrogen by a sample of silica aerogel. Physical sorption of hydrogen owing to the weak van-der-Waals interaction of hydrogen molecules with the silicon dioxide walls of the pores of the sample was observed over the entire temperature range. The total capacity of the aerogel sample for hydrogen was ∼1.5 mass %. It was found that when the sample temperature was lowered from 95 to 60 K, the characteristic sorption times for hydrogen by the silica aerogel increase; this is typical of thermally activated diffusion (Ea ≈ 408 K). For temperatures of 15–45 K the characteristic H2 sorption times depended weakly on temperature, presumably because of the predominance of a tunnel mechanism for diffusion over thermally activated diffusion. Below 15 K the characteristic sorption times increase somewhat as the temperature is lowered; this may be explained by the formation of a monolayer of H2 molecules on the surface of the aerogel grains.

Sorption and the subsequent desorption of 4He, H2, Ne, N2, CH4, and Kr gas impurities by graphene oxide(GO), glucose-reduced GO (RGO-Gl) and hydrazine-reduced GO (RGO-Hz) powders have been investigated in the temperature interval 2¿290 K. It has been found that the sorptive capacity of the reduced sample RGO-Hz is three to six times higher than that of GO. The reduction of GO with glucose has only a slight effect on its sorptive properties. The temperature dependences of the diffusion coefficients of the GO, RGO-Gl and RGO-Hz samples have been obtained using the measured characteristic times of sorption. It is assumed that the tempera-ture dependences of the diffusion coefficients are determined by the competition of the thermally activated and tunneling mechanisms, the tunneling contribution being dominant at low temperatures.

Linear thermal expansion coefficient (LTEC) of single crystal k-(D4-BEDT-TTF)2Cu[N(CN)2]Br was studied across the crystal layers in the temperature range 2-290 K using the method of precise capacitive dilatometry. Below Tc = 11,6 K the LTEC of the sample had a small negative value, which is apparently due to the transition from the paramagnetic metal in the superconducting state. There was a bend of temperature dependence of the LTEC, which shows broad peak around 40 K and can be attributed to the elastic lattice anomaly around the end-point of Mott boundary. A sharp jump in the LTEC values and hysteresis was observed in the area of Tg ~ 75-77 K, what is likely explained by the transition in a glass-like state. The isotope effect in the thermal expansion is discusses, which manifested itself in a shift of the phase transitions in comparison with fully deuterated BEDT-TTF sample., 11 pages, 6 figures

Linear coefficient of thermal expansion α(T) of single crystal (BEDT–TTF)2Cu[N(CN)2]C1 was studied along the crystal layers using the method of precise capacitive dilatometry in the temperature range 2–285 K. It is positive in this direction over the entire temperature range. Anomalies of thermal expansion were observed at 29–30 K and 74–80 K. The anomaly near 30 K is, apparently, due to the transition between the paramagnetic phase and the antiferromagnetic insulator state. Peak of α(T) at 78 K corresponds to a phase transition related to orientational disordering of ethylene groups in dimers of BEDT–TTF. A broad maximum of α(T) in the temperature range 40–70 K, is apparently explained by fluctuations of charge within the dimers, and by spin fluctuations, which first increase with increasing temperature, and then decrease in process of thermal disordering of dimers.

The radial thermal expansion {\alpha}r 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 {\alpha}r was observed, with a magnitude which exceeded the largest negative {\alpha}r 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., Comment: 3 pages, 1 figure, 16 references

The sorption of 4He by graphene oxide powders thermally reduced at T = 200, 300, 500, 700, 900 °C has been investigated in the interval 1.5–290 K. The measured dependence of the quantity of sorbed helium upon the reduction temperature shows up as a nonmonotonic curve. The highest quantities of helium were sorbed by the samples reduced at T = 300 and 900 °C. It is assumed that the thermal reduction of graphite oxide by heating it to 300 °C causes evaporation of the water intercalated in the spacings of the carbon layers, this results in exfoliation of the graphene planes, which enhances the sorptive capacity. Heating the samples to 900 °C generates numerous defects in the carbon planes, as a result, the interlayer spacings become accessible for sorption, which enhances the sorptive capacity.