The conductivity of thermally reduced graphene oxide (GO) measured at various reduction stages shows that the samples demonstrate transition to the conducting state within a narrow range of annealing ...temperatures (150-170 °С). The conductivity in this temperature region increases by about five orders of magnitude to indicate that the percolation mechanism is responsible for this transition. According to this mechanism, the above temperature range is associated with formation of a certain number of conductive channels composed of GO fragments reduced to the conducting state. Thus, it is a new type of percolation transition, since increased conductivity is a result of increased conductivity of the particles due to thermal treatment rather than a result of increased concentration of conducting particles. A further temperature growth is associated with increased number of conducting GO fragments and the number of conducting channels, and some smoother conductivity increase. The XPS spectra of partially reduced GO samples indicate correlation between increased conductivity of GO fragments and plasmon oscillations revealed as XPS peaks. The current-voltage characteristics measured for the samples of partially reduced GO indicate a non-ohmic conductivity which manifests as increased conductivity versus voltage dependence. This is due to the fact that electrical resistance of the percolation channels is the sum of resistances of conductive GO fragments and contact resistances which depend on the voltage drop at the contact and, therefore, on the voltage applied.
Divertor Thomson Scattering on Globus-M2 Ermakov, N. V.; Zhiltsov, N. S.; Kurskiev, G. S. ...
Plasma physics reports,
12/2023, Letnik:
49, Številka:
12
Journal Article
Recenzirano
We present the first Thomson scattering (TS) measurements of electron temperature in the lower divertor of the Globus-M2 tokamak. The divertor TS diagnostics is designed for local measurements of the
...T
e
(
z
,
t
) in the range of 1–100 eV and
n
e
(
z
,
t
) in the range of
m
–3
. Parameters of the probing Nd:YAG laser are as follows 1064 nm/2 J/100 Hz/3 ns. The probing chord is launched vertically at
R
= 24 cm and covers areas of the inner leg, vicinity of separatrix and private flux region. Along probing chord of 110 mm, 9 spatial points were realized. Advanced filter polychromators were used to analyze Thomson scattering spectra.
Thomson scattering of the core edge and divertor plasma regions of a tokamak with reactor technologies is discussed. The rationale and choice of technical solutions are given, the composition of the ...Thomson scattering diagnostic complex is discussed, as well as an estimate of the accuracy of measuring both electron temperature and density. Particular attention is paid to ensuring the functionality of the proposed diagnostics in the reactor mode of the tokamak operation and the results of testing diagnostic equipment in the experiments on Globus-M2 tokamak.
Surface strengthening of structural steels with carbon nanomaterials using laser and electron-beam heating is studied. It is shown that during laser treatment the maximum microhardness of a modified ...layer is achieved in a strengthened zone up to 70 μm thick with
q
= 9 × 10
4
W/cm
2
, and with electron beam treatment in a strengthened zone up to 300 μm thick with
q
= 4.6 × 10
4
W/cm
2
. It is established that in both cases with optimum treatment regimes strengthening is due to forming martensite, a cellular structure, and grain disintegration.
There has been developed an approach to the production of graphene as a result of the thermal reduction of graphene oxide (GO). GO has been synthesized by the use of the modified Hummers method with ...utilization of sodium nitrate and concentrated sulfuric acid. A paper-like material of 40 - 60 μm in thickness and 1.2 g/cm3 in density was formed on a filter after deposition from dispersion. The material was cut onto samples of about 15×25 mm2 in size which were experienced to the thermal treatment at various temperatures between 100 and 800 °C. This resulted in a set of GO samples reduced to various degrees. The degree of reduction was determined on the basis of measurements of the conductivity. Along with that the evolution of samples density was studied as the annealing temperature was enhanced. The analysis of the X-ray photoelectron spectra of partially reduced GO permitted the determination of the dynamics of changing the chemical composition of the material in the process of the thermal treatment. The analysis of Raman spectra of the GO samples indicates rather high degree of the disordering of the material. A possibility of the usage of the material produced as a nanocarbon coating in experiments on the interaction of high intense liquid flows with a wall surface is discussed.
The electrical properties of a polymer composite with carbon nanotube additives have been analyzed. The state of the system near the percolation threshold, when charge is transferred along a single ...percolation path, has been considered. For this state, the current–voltage characteristics of a percolation chain made up of carbon nanotubes have been calculated under the assumption that the contact resistance between neighboring nanotubes is much higher than the intrinsic resistance of the nanotubes. According to recent data, the distance between neighboring (contacting) nanotubes has been assumed to be randomly distributed. It has been shown that, under the given conditions, the current–voltage characteristic is essentially nonlinear. This indicates the nonohmic conductivity of the composites. The dependence of the current–voltage characteristic on the spread of the contact distribution over distances has been discussed.
A Thermal Accumulator Based on Phase-Change Materials Bocharov, G. S.; Vagin, A. O.; Grigoriev, I. S. ...
Doklady. a journal of the Russian Academy of Sciences. Physics,
06/2022, Letnik:
67, Številka:
6
Journal Article
Recenzirano
The concept of a water thermal accumulator based on phase-change materials (PCMs) has been proposed and analyzed. In such a system, energy accumulation (release) occurs due to a phase transition in ...PCMs, and water is used as a working fluid. The thermal accumulator consists of identical modules, the number of which determined by the quantity of accumulated energy. Each module represents a double concentric tube, in which the inner cavity is filled with flowing water and the outer cavity is filled with PCMs. The PCM used is paraffin wax, which has a specific melting enthalpy of 216 J/g. To increase the PCM heat conductivity coefficient, an additive of thermally reduced graphene oxide is used. The passage of hot water through the inner tube results in the melting of paraffin wax, which accumulates the thermal energy corresponding to the melting enthalpy. This energy is recovered when cold water is passed through the system containing the melted paraffin wax and heated as a result of paraffin wax solidification. Some estimates of thermal accumulator regimes and the results of calculating the unsteady longitudinal and transversal temperature distributions at different time moments are given.
—
In this paper, we examine the key features of the preparation of graphene by chemical vapor deposition on copper substrates differing in geometry (foil and wire). Along with graphene, we analyze ...impurity structures forming on the surface of copper substrates as a result of graphene synthesis and discuss their origin and possible ways of eliminating them.
Samples of thermally reduced graphene oxide are studied using differential cross sections for photoelectron inelastic energy losses. We compare different procedures for recovering cross sections from ...the photoelectron energy spectra resulting from multiple inelastic scattering. It is shown that the cross section for inelastic energy losses (which uniquely characterizes allotropes of carbon) in the sample containing the minimal amount of carbon oxides corresponds the best to pyrolytic graphite.
The evolution of energy spectra of X-ray photoelectron spectroscopy observed with increasing annealing temperature of graphene oxide (GO) samples is being investigated. The main attention in the work ...is focused on the region investigation determined by multiple electron energy losses due to π and π + σ plasmon excitations. Such a study allows one to understand an entire structural evolution of GO during thermal reduction process. π plasmon peak becomes prominent only for the samples annealed at the temperatures above 200 °C. Comparison of acquired graphene oxide spectrum (annealed at 1000 °C) with spectrum of highly oriented pyrolytic graphite (HOPG) has been carried out.
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