UDC 546.27:548.33
A. R. Oganov (Stony Brook, USA) V. L. Solozhenko (Villetaneuse, France)
Boron: a hunt for superhard polymorphs
Boron is a unique element, being the only element, all known polymorphs of which are superhard, and all of its crystal structures are distinct from any other element. The electron-deficient bonding in boron explains its remarkable sensitivity to even small amounts of impurity atoms and allows boron to form peculiar chemical compounds with very different elements. These complications made the study of boron a great challenge, creating also a unique and instructive chapter in the history of science. Strange though it may sound, the discovery of boron in 1808 was ambiguous, with pure boron polymorphs established only starting from the 1950s—1970s, and only in 2007 was the stable phase at ambient conditions determined. The history of boron research from its discovery to the latest discoveries pertaining to the phase diagram of this element, the structure and stability of β-boron, and the establishment of a new high-pressure polymorph, γ-boron, are reviewed.
Keywords: boron, structure, polymorphism, phase diagram.
UDC 621.921.34-492.2:620.22-419
A. A. Bochechka (Kyiv)
Analysis of the driving forces of the sintering process of diamond powders of micro- and nanoranges at high pressure
It is shown that during sintering of diamond powders, there is no summation of the Laplace pressure and the external pressure acting on the system. Modeling of the pore shape showed that there are possible cases when the capillary forces are directed against the external forces. An equation is proposed that describes the ultimate compaction of the diamond particle system in this case. Experimental values of the density of diamond polycrystals sintered from diamond powders of different dispersion are well described by this equation within the measurement error. To improve sintering, additives are needed that form chemical compounds with carbon and bind diamond nanoparticles during sintering.
Keywords: sintering, high pressures, Laplace pressure, diamond nanopowders, diamond micropowders, pore shape.
UDC 661.88
A. A. Sivkov, E. P. Naiden, A. Ya. Pak (Tomsk, Russia)
Dynamic synthesis of ultradispersed crystalline phases of the C—N system
The results of exploratory studies on the dynamic synthesis of crystalline covalent carbon nitride C3N4 in a hypervelocity pulsed jet of carbon electric discharge plasma flowing into a space with a nitrogen atmosphere are presented. The plasma source is a high-current pulsed coaxial magnetoplasma accelerator with a graphite accelerating channel. The obtained data show the possibility of synthesizing ultradisperse covalent carbon nitride.
Keywords: hypervelocity jet, carbon plasma, dynamic synthesis, ultradisperse crystalline covalent carbon nitride.
UDC 544.3:621.762
A. F. Lisovsky (Kiev)
Thermodynamics of impregnation of nanodispersed materials
The results of a thermodynamic study of the impregnation of porous bodies formed from macro- or nanoparticles are presented. Thermodynamic functions describing this process are derived, and criteria determining the conditions for spontaneous impregnation in the studied porous materials are substantiated.
Keywords: thermodynamics, nanocomposition, impregnation.
UDC 533.951:548.33
A. V. Kurdyumov, V. F. Britun, V. V. Yarosh, N. I. Borimchuk, A. I. Danilenko, V. B. Zelyavsky (Kiev)
Phase Transformations of Carbon Black under High-Temperature Shock Compression
The article presents studies of carbon black transformation into diamond and an amorphous carbon phase with an intermediate density (2.9 g/cm³) under high-temperature shock compression (20–32 GPa, 2500–3500 K). Compression conditions that provide the maximum yield of these phases are determined. The transformation patterns are analyzed under the assumption that the amorphous phase is an intermediate structure on the path of transformation of turbostratic carbon into diamond.
Keywords: phase transformations, high pressures, shock compression, carbon black, amorphous carbon, diamond.
UDC 539.23
A. S. Gavrilov, A. P. Voznyakovsky, L. V. Agibalova (St. Petersburg, Russia)
Study of Polydispersity of Detonation Synthesis Nanocarbons by Dynamic Light Scattering
The article presents the results of studying the effect of ultrasonic exposure time on the distribution of detonation synthesis nanocarbons in an aqueous medium. Optimum values of ultrasonic treatment parameters are determined. The effect of modifying detonation synthesis nanodiamond powders with fullerene C60 and dibutyl tin dilaurate is described. It is shown that irreversible adsorption of C60 and dibutyl tin dilaurate is observed during the modification of these powders. Modification of nanocarbons with fullerene leads to a significant shift in the polydispersity curves toward smaller particle sizes.
Keywords: nanocarbons, detonation synthesis, polydispersity, fullerenes, modification, ultrasonic action, dynamic light scattering.
UDC 537.876:535.2
S. P. Starik, O. G. Gontar, O. M. Kutsay (m. Kiev)
Methodology for decoupling complex problems from synthesis and analysis of optical spherical coatings using dry melt
A mathematical model of optics problems for a spherical medium with heterogeneous spheres is examined. The formulation and analysis of the solutions to the problems of synthesis and analysis of the optics of spherical media as mathematical optimization problems has been analyzed. A security program has been created that allows you to carry out their decoupling within the framework of this model. The influx of volumetric heterogeneity of the carbon sphere on photometric and ellipsometric characteristics is theoretically shown. Modeling of different types of interference rich-spherical coatings from the upper diamond-like ball, which is simultaneously a functionally active optical ball and the unique role of a dry melt, was carried out.
Key words: dry melt, wrapped problem, optical ball coating, optical constants, heterogeneity of the ball.
UDC 621.923
P. G. Matyukha, V. V. Gabitov (Donetsk)
Specific cost of grinding steel R6M5F3 depending on the method of dressing and electrical discharge effects on the working surface of the cubonite wheel
Using the criterion of minimum specific cost, a comparison was made of the dressing methods and the grinding process of steel R6M5F3 with electrical discharge effects on the working surface of the cubonite wheel on a metal bond. It was found that the electrical discharge dressing method provides an order of magnitude lower specific cost of grinding compared to the abrasive method. Electrical discharge effects on the working surface of the wheel during grinding increase the specific cost of processing, in connection with which grinding is advisable to perform periodic dressing by the electrical discharge method during processing.
Keywords: specific grinding cost, vanadium high-speed steel, cubic bonited wheels, electrical discharge effects.
UDC 621.623
Yu. D. Filatov, V. P. Yashchuk, A. Yu. Filatov (Kiev) U. Heisel, M. Storchak (Stuttgart, Germany) Guy Monteil (Besancon, France)
Assessment of roughness and reflectivity of surfaces of products made of non-metallic materials during finishing diamond-abrasive processing
It is shown that the roughness of surfaces that are formed during various technological operations of finishing diamond-abrasive processing of non-metallic materials determines their angular diagrams of reflection and scattering, characterized by a speckle structure. It is established that the scattering indicatrix is formed due to the reflection of light by homogeneous areas of texture formations on the surface and their boundaries. The parameter that responds to changes in the roughness of the treated surfaces is the peak width in the scattering indicatrix against the background of a virtually unchanged pedestal.
Keywords: surface roughness, grinding, polishing, angular diagrams of reflection and scattering of light, scattering indicatrix.
UDC 621.539.4
E. B. Soroka (Kyiv)
Ensuring the stability of PVD coatings by creating a discrete topography with specified parameters
It is shown that in PVD coatings, which are characterized by significant residual compressive stresses, it is possible to prevent the swelling of the coating with its subsequent destruction by forming discrete coatings with specified parameters. The maximum permissible length of a discrete section of the coating, all other things being equal, will be different on bases made of different materials. The creation of a discrete topography improves the self-organization of the base-coating system and expands the possibilities of using vacuum-plasma coatings.
Keywords: PVD coatings, compressive stress, discrete topography.
UDC 681.324.06
V. N. Kulakovsky, A. A. Lebedeva, I. V. Skvortsov, E. M. Chistyakov, K. Z. Gordashnik, V. N. Kolodnitsky (Kiev)
Integrated model of the subject area “Superhard materials”
An integrated model of the subject area “Superhard materials” has been developed, including a system of multi-level ontologies. The system of materials science ontology “Superhard materials” uses a terminological thesaurus and contains concepts of problem-oriented knowledge corresponding to the scientific directions developed at the V. N. Bakul Institute of Superhard Materials of the National Academy of Sciences of Ukraine.
Keywords: knowledge base, ontology, thesaurus, model, subject area.