A. N. Kirichenko

Fulleride of aluminum nanoclusters

Properties of nanocomposites composed of fullerene C60 chemically bonded to Al nanocrystals are reported. The nanocomposites of Al–C60 create a class of new material of fulleride of aluminum nanoclusters. New nanostructured and modified by C60 aluminum-based material has been sintered from fulleride of aluminum nanoclusters. Key features of this material are creating covalent bonds Al–C60 and preserving C60 during sintering. Addition of several wt % of C60 essentially improves (by a factor of 3 to 10, up to 7 GPa) the hardness of initial aluminum.

Longer Carbon Nanotubes by Controlled Catalytic Growth in the Presence of Water Vapor

One of the most important problems in the synthesis of carbon nanotubes is the problem of controlling their morphology, namely, length, aspect ratio, alignment and so forth. Catalytic synthesis of carbon nanotubes in a suspended bed reactor allowed for the study of the possibilities of controlling the growth of nanotubes by introducing a certain amount of water vapor and carbon-containing materials in the reaction zone. The synthesized long carbon nanotubes were studied by Raman spectroscopy, transmission and scanning electron microscopy. We found that water concentration influences both yield and structure of nanotubes. It is shown that the yield of centimeter-long nanotubes can be maximized at an optimum H2O/C ratio, while deviations dramatically change morphology and thickness of the nanotubes.

C60 three-dimensional polymerization by impulse heating effect

Impulse laser heating combined with a quick sample cooling in a diamond anvil cell provides unique conditions for the 3D polymerization reaction of C60. The reaction proceeds under the 8–10 GPa pressure and 2700 K temperature in the case of heating-cooling cycle time around 0.1 μs. Such a short heating time permits to increase the maximal temperature of the fullerite sample by 1700 K on conditions that C60 are still surviving. As a result, the pressure of the phase transition to 3D polymerized fullerite phase with 519 GPa bulk modulus was essentially decreased. Furthermore, the transition has proceeded at quasi-hydrostatic conditions without activation by applying a plastic deformation.

Graphite-to-diamond (13C) direct transition in a diamond anvil high-pressure cell

13C-graphite treated in a diamond anvil high-pressure cell was studied by high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and electron energy loss spectroscopy. It was found that 13C-diamond and lonsdaleite originate after the treatment under high pressure and shear deformation.

Transformation-deformation bands in C60 after the treatment in a shear diamond anvil cell

The C60 fullerene has been investigated by high-resolution transmission electron microscopy and electron energy loss spectroscopy in a shear diamond anvil cell after applying pressure and shear deformation treatment of fcc phase. Shear transformation-deformation bands are revealed consisting of shear-strain-induced nanocrystals of linearly polymerized fullerene and polytypes, the triclinic, monoclinic, and hcp C60, fragments of amorphous structures, and voids. Consequently, after pressure release, the plastic strain retains five high pressure phases, which is potentially important for their engineering applications. Localized shear deformation initially seems contradictory because high pressure phases of C60 are stronger than the initial low pressure phase. However, this was explained by transformation-induced plasticity during localized phase transformations. It occurs due to a combination of applied stresses and internal stresses from a volume reduction during phase transformations. Localized phase transformations and plastic shear deformation promote each other, which produce positive mechanochemical feedback and cascading transformation-deformation processes. Since the plastic shear in a band is much larger than is expected based on the torsion angle, five phase transformations occur in the same region with no transformation outside the band. The results demonstrate that transformation kinetics cannot be analyzed in terms of prescribed shear, and methods to measure local shear should be developed.

Transport properties of nanocomposite thermoelectric materials based on Si and Ge

The modification of transport properties (thermal conductivity, electrical conductivity, and See-beck coefficient) of nanostructured thermoelectrics based on Ge and Si-Ge with inclusions of the second phase has been investigated experimentally. In the Ge-C60 nanocomposite, modifying inclusions are the fullerene C60 located along the germanium grain boundaries and 1- to 5-nm SiC nanocrystals in the Si-Ge-SiC nanocomposite. In particular, the presence of these inclusions in the nanocomposite leads to an increase of the Seebeck coefficient in the temperature range above 600 K and, in general, to an increase in the thermoelectric figure of merit ZT by a factor of 1.5–2 as compared to the corresponding characteristics of nanostructured thermoelectrics based on Si-Ge without modifying inclusions of the second phase.

Phase diagram of carbon and the factors limiting the quantity and size of natural diamonds

Phase diagrams of carbon, and those focusing on the graphite-to-diamond transitional conditions in particular, are of great interest for fundamental and applied research. The present study introduces a number of experiments carried out to convert graphite under high-pressure conditions, showing a formation of stable phase of fullerene-type onions cross-linked by sp3-bonds in the 55-115 GPa pressure range instead of diamonds formation (even at temperature 2000-3000 K) and the already formed diamonds turn into carbon onions. Our results refute the widespread idea that diamonds can form at any pressure from 2.2 to 1000 GPa. The phase diagram built within this study allows us not only to explain the existing numerous experimental data on the formation of diamond from graphite, but also to make assumptions about the conditions of its growth in Earths crust.

Sonochemical Preparation and Subsequent Fixation of Oxygen-Free Graphene Sheets at N,N-Dimethyloctylamine-Aqua Boundary

In this study, the syntheses of oxygen-free graphene sheets and the method of its fixation at an oil-aqua interface were presented. The graphene sheets were prepared by exfoliation of synthetic graphite powder in an aqua-organic medium under ultrasound irradiation. N,N-Dimethyloctylamine- (DMOA-) aqua emulsion was used as the liquid medium, and pH was equal to 3. The obtained graphene nanosuspension was fractionated by sedimentation and decanted according to the weight. The graphene nanoparticle fractions, differing in configuration and number of layers, have been characterized using transmission electron microscopy (TEM), electron diffraction, HRTEM, Raman spectroscopy, and electron energy loss spectroscopy (EELS). It was found that using a DMOA-aqua mixture as the liquid medium in ultrasonic treatment of synthetic graphite leads to the formation of oxygen-free 1-2-layer graphene sheets attached to the DMOA-aqua interface. The proposed method differs from known ones by using a small amount of more environmentally friendly organic substances. It allows to obtain large quantities of oxygen-free graphene, and finally unconverted graphite can be directed for reuse. The proposed method allows to obtain both 2D graphene sheets with micron linear dimensions and 3D packages with a high content of defects. Both these species are in demand in areas related to the development of new materials with unique electrophysical properties.

Hydrogen adsorption in the series of carbon nanostructures: Graphenes–graphene nanotubes–nanocrystallites

A comparative analysis of hydrogen absorption capability is performed for the first time for three types of carbon nanostructures: graphenes, oriented carbon nanotubes with graphene walls (OCNTGs), and pyrocarbon nanocrystallites (PCNs) synthesized in the pores of TRUMEM ultrafiltration membranes with mean diameters (Dm) of 50 and 90 nm, using methane as the pyrolized gas. The morphology of the carbon nanostructures is studied by means of powder X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). Hydrogen adsorption is investigated via thermogravimetric analysis (TGA) in combination with mass-spectrometry. It is shown that only OCNTGs can adsorb and store hydrogen, the desorption of which under atmospheric pressure occurs at a temperature of around 175°C. Hydrogen adsorption by OCNTGs is quantitatively determined and found to be about 1.5% of their mass. Applying certain assumptions, the relationship between the mass of carbon required for the formation of single-wall OCNTGs in membrane pores and the surface area of pores is established. Numerical factor Ψ = mdep/mcalc, where mdep is the actual mass of carbon deposited upon the formation of OCNTGs and mcalc is the calculated mass of carbon necessary for the formation of OCNTGs is introduced. It is found that the dependence of specific hydrogen adsorption on the magnitude of the factor has a maximum at Ψ = 1.2, and OCNTGs can adsorb and store hydrogen in the interval 0.4 to 0.6 < Ψ < 1.5 to 1.7. Possible mechanisms of hydrogen adsorption and its relationship to the structure of carbon nanoformations are examined.

Synthesis of carbon nanostructures in an RF induction plasmatron

The method and results of synthesizing carbon nanotubes and onion-like structures by the sublimation of a mixture of a carbon powder with a catalyst (Y2(CO3)3) in the plasma flow of an inert gas (argon) generated in an rf plasmatron are described. Carbon vapors are condensed into fullerene-containing soot onto various materials (Al, Cu, Ti, stainless steel) placed in the working chamber of an experimental setup. The composition of the synthesized soot is analyzed by modern highly informative methods (Raman spectroscopy, transmission electron microscopy, X-ray diffraction). Single-wall carbon nanotubes of a small diameter (1.2 nm) and onion-like structures 10–20 nm in size are formed in experiments. In a reference experiment on a mixture of argon and methane, a material, which consists of a mixture of amorphous carbon, nanosized graphite, and graphite with a crystallite size of several microns, is synthesized. The effect of the substrate material, the gas pressure, and the plasma flow velocity on the formation of carbon nanotubes is studied.