The paper proposes a modified Maxwell formula applied to the calculation of the thermal conductivity of nanofluids. It is shown that the use of elongated particles or chains of nanoparticles leads to a significant increase in thermal conductivity. Theoretical estimates based on the proposed model are in good agreement with experimental data.

Graphite-like (metal!) regions and diamond-like (dielectric!) regions in carbon nanostructures are very closely spaced. Based on this unique feature, a model of thermal emf produced due to the drag of electrons by ballistic phonons is developed and a model of thermal conduction during heat transfer through the graphite-like/diamond-like region interface is proposed. Experiments with a thermoelectric generator based on film carbon nanostructures are analyzed. Models of a thermoelectric generator based on a composite of a graphite-like matrix containing diamond nanoparticles and graphene impurities are proposed. These models both demonstrate the above-mentioned phenomena and predict the achievement of the maximum thermoelectric conversion efficiency.

A method of calculating the size distribution of supercritical nuclei in the presence of flows in a melt or in a vapor for the first-order phase transition, namely, for crystallization or condensation, has been proposed. The method is confirmed by the comparison with the results of experimental studies of centrifugal casting of Al.

Models of field (cold, autoelectron) emission from various types of carbon nanostructures, other than graphene, are described. The experimental results are compared with theoretical predictions.

We show an experimental evidence of the domination of absorption over scattering in absorbance spectra of detonation nanodiamonds. We perform absorbance measurements on the UV-vis spectrophotometer equipped with an integrating sphere and compare them with conventional absorbance spectra. Additionally, we measure the scattering light intensity at the cuvette side wall (scattering at 90 degrees angle). The obtained experimental data were interpreted using photon random-walk simulations in turbid media and the Kubelka-Munk approach. The scattering cross sections and indicatrices were obtained by Mie theory. We discover that despite being very close to the lambda(-4) power law (like Rayleigh scattering) the light extinction by the primary 4-nm diamond crystallites is due to absorption only and scattering can be neglected. That is the reason why previously absorption and scattering contributions were confused. The scattering is governed only by the agglomerates of 100 nm and larger in size remaining in the hydrosols and their fraction can be effectively controlled by centrifugation. Only Mie theory reproduces correctly the close to lambda(-2) scattering by the agglomerates accounting for the weird interplay between their size, fractal dimension, and dielectric properties. Finally, using the obtained absorbance spectra we estimate the fraction of nondiamond phase in nanodiamonds and their agglomerates.

Abstract Thin carbon films consisting of separate nanometer-scale sp2 carbon islands with smooth vacuum boundary deposited on Si wafers were found to be capable of low-field electron emission – starting from macroscopic field magnitudes as low as ∼1 V/µm. For such films, we suggest a novel model of emission facilitation by thermoelectric field associated with heat generation concentrated in nanosized areas. Quantitative estimates performed on the basis of this hypothesis for typical experimental conditions gave estimates for local thermoelectric field magnitude and lateral non-uniformity of surface potential as high as ∼100 V/μm and a few Volts, respectively. Thus, the suggested model explains the low-field emission capability of smooth-surface nanocarbon films observed in many previous experiments.

We demonstrate that it is technologically possible to obtain graphite-like films which can be used for the creation of a thermoelectric generator. The proposed technology ensures uniformity and rather small thickness of these films and allows them to be formed on a diamond-like film substrate with deposited contacts at acceptable interface. Measurements show that the electron-phonon drag effect in this system ensures thermo-emf values about 100 times as large as those provided by the diffusion process. Arrangement of the graphite-like material on a diamond-like film substrate also favors increase in the thermo-emf, which is a manifestation of the electron–ballistic phonon drag. It is established that conditions necessary for the creation of a thermoelectric generator can be achieved based on the proposed carbon nanostructures.

A model describing peculiarities of field emission from carbon nanomaterials is considered. The model is based on inclusion by drag of electrons by ballistic phonons in the temperature gradient range in the emission center. The model does not require any additional assumptions concerning a special energy structure of the emission center. Quantitative estimates of the thermopower coefficient obtained based on the emission model are in good agreement with experimental results.

Nanodiamond (ND) is one of the most attractive allotropic modification of carbon due to their unique physical and chemical properties. In the present review the current state of science and technology in the field of NDs is analyzed. ND can be used in various application and in different form e.g. as a dispersion phase in suspension, as a filler in composites, etc., so the sedimentation stability of ND in different media are under scrutiny. Thus, theoretical aspects of ND suspension coagulation mechanisms and the methods avoiding it were considered. The dependence of rheological behavior on particles modification was discussed as well. Various methods for the preparation and modification of NDs to obtain particles of various sizes on a nanometer scale with different physicochemical properties were reviewed. The area of practical application for NDs was considered on the example of polymer composites. The various manufacturing methods, mechanical properties and medical aspects for thermosetting, thermoplastic and elastomer ND composites were summarized.

A specific distribution of supercritical nuclei, taking into account the presence of the macroscopic motion, i.e., rotation, has been found in this work. A calculation method of size distribution of heavily postcritical nucleation centers is proposed. The distribution of supercritical nucleation centers in the presence of flow effect, which was obtained here theoretically, is confirmed by an experimental investigation of the centrifugal casting of Al.

We have recently shown that the sol-gel transition occurs in hydrosol of detonation nanodiamond (DND) particles with size of 4-5 nm. Here we study properties of the hydrosol. Namely, we study the dependence of dynamic viscosity and shear stress on DND concentrations. Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) were used for characterization of the hydrosol structure. Deagglomeration of diamond nanoparticles in preparation of the hydrosol was carrying out without mechanical milling. In contrast with previous studies viscosity was measured by rotational viscometer. The observed effects can be explained by the model, that assumes existence of particle chains connected to each other by electrostatic interaction. Moreover, the potential of this interaction is non-spherically symmetric. Such chains of DND particles are present in hydrosols even at the concentration of about 1 wt%.

The structural, electrical, and optical properties of thin graphite-like films produced by magnetron- assisted sputtering onto crystalline silicon and quartz at substrate temperatures in the range from 320 to 620°C are studied. From analysis of the Raman spectra, it is established that, as the substrate temperature is elevated, the crystallite size increases and the concentration of structural defects and the content of amorphous carbon in the phase composition of the films decrease. It is found that, as the substrate temperature is elevated, the maximum of the absorption intensity in the ultraviolet spectral region of the optical absorption spectra shifts to longer wavelengths and the absorption intensity in the visible and near-infrared spectral regions increases. As the deposition temperature is elevated, the conductivity of the films increases from 0.2 Ω –1 cm –1 at 320°C to 30 Ω –1 cm –1 at 620°C.

The effect of rotation flow emerging under centrifugal casting on the first-order phase transition, i.e., crystallization, has been studied using the example of producing a gradient composite material of AK12 aluminum alloy in a mixture with basalt fibers. It has been shown that a material with a hardened surface can be created. Distribution of admixtures in the main material when there is macroscopic motion has been found.

In this paper we propose a method for ultrafine fractionation of nanodiamonds using the differential centrifugation in the fields up to 215000g. The developed protocols yield 4-6 nm fraction giving main contribution to the light scattering intensity. The desired 4-6 nm fraction can be obtained from various types of initial nanodiamonds: three types of detonation nanodiamonds differing in purifying methods, laser synthesis nanodiamonds and nanodiamonds made by milling. The characterization of the obtained hydrosols was conducted with Dynamic Light Scattering, Zeta potential measurements, powder XRD and TEM. According to powder XRD and TEM data ultracentrifugation also leads to a further fractionation of the primary diamond nanocrystallites in the hydrosols from 4 to 2 nm.

Possibility of growth of diamond single crystals from nanodiamond particles by oriented attachment mechanism under influence of organic substances has been suggested and experimentally confirmed.It has been found that diamond single crystals ranging up to 1.5 mu m are formed from the 4-5 nm nanodiamond particles at high pressures and high temperatures treatment (HPHT: P similar to 7 GPa, T similar to 1300 degrees C). It has been experimentally shown that the necessary condition for the formation of the diamond single crystals is an addition of substances containing C-H groups into HPHT chamber.The formation of the diamond single crystals has been confirmed by several experimental methods, including Raman scattering, scanning electron microscopy (SEM) and electron energy loss spectroscopy (EELS). Analysis of experimental results has shown that mechanism of oriented-attachment growth is responsible for formation of diamond single crystals. A model explained details of the mechanism has been suggested. (C) 2017 Elsevier B.V. All rights reserved.

There is a new idea to enhance the Seebeck coefficient using electron drag by a heat flux and decrease the thermal conductivity by heat dissipation at the interfaces between graphite- and diamond-like areas in a composite formed from carbon nanostructures. The proposed thermoelectric converter is based on a thin (20–50 nm) graphite-like layer located at an ultra-short distance from the diamond-like area. According to estimation, a thermoelectric power higher than in the case of diffusion by a factor of 103 can be attained. Under ideal conditions, this allows a room-temperature thermoelectric efficiency of 150 to be obtained. The results of investigations within project no. 16-19-00075 of the Russian Science Foundation are substantiated.

A model of a thermoelectric generator is proposed, in which composite materials obtained by sintering diamond nanoparticles are used as the main component. To increase the useful conversion of heat into electric current, it is proposed to use the effect of electron drag by ballistic phonons. To reduce the ineffective heat spread, it is proposed to use the effect of thermal resistance of the boundaries between the graphite-like and diamond-like phases of the composite. An experimental confirmation of the existence of an optimal volume ratio between graphite-like and diamond-like phases of the composite is predicted and obtained. The highest achieved value of thermoelectric coefficient in the actual structure is 80 mu V K-1 ( which means 20 times increase compared to that of composites not of the optimal structure), with a thermal conductivity of 50 W m(-1) K-1. These results were obtained with constant electrical conductivity. The combined influence of these two effects in case of the ideal composite structure should result in an increase of the thermoelectric efficiency parameter by three orders of magnitude.

We submit results of the study of hydrosols of the single crystalline diamond nanoparticles ranging of 4 5 nm, obtained by detonation synthesis. The stable hydrosols with negative and positive zeta potentials were obtained from industrial powder after additional purification and subsequent annealing in air or in hydrogen. Unusual behavior of the hydrosols was revealed with increasing concentration of diamond nanoparticles. The state is characterized by giant viscosity value and is reversible unlike SiO2 hydrogel. Formation of the state has been explained in the frame of model that assumes the polyhedral shape of diamond nanoparticles and consequently non-spherical surface charge distribution. Stability of hydrosol was determined in accordance to the Derjaguin- Landau- Vervey- Overbeek (DLVO) theory, although as it is clear from the DLVO theory, that the double electrical layer in hydrosol is not spherical in that case. This non-sphericity results in gel formation at a smaller threshold concentration than that of DLVO theory prediction. The suggested model is supported by experimental data on particle size distribution, obtained by dynamic light scattering, by small angle neutron scattering and by theoretical estimation of the threshold concentrations. (C) 2016 Elsevier Ltd. All rights reserved.

The distribution of heavily post-critical nucleation centers in the nucleation kinetics subject to the macroscopic flow effect has been successfully obtained. Examples of rotary and convective motions during the centrifugal casting are considered. The obtained distribution has been confirmed by an experimental investigation of the composite material AK12 (boron carbide (B4C)) crystallization.