UDC 541.16
AND. L. Ivanovsky (Ekaterinburg, Russia)
The search for superhard carbon: between graphite and diamond
A brief overview of the works of recent years (2009–2012) aimed at the search for new 3D (sp3) allotropic modifications of carbon with increased hardness, performed using computer materials science methods, is presented. Attention is paid to the principles of building structural models, methods of stability analysis and estimation of microhardness of new carbon materials.
Key words: new 3D (sp3) allotropes of carbon, structure, modeling, stability, microhardness.
UDC 544.473-039.63
G. P. Bogatyreva†, T. M. Zakharova, V. L. Veselovskyi, H. G. Tsapyuk, O. AND. Beda, V. G. Poltoratsky (Kyiv)
Mo2C as a support for Cu–Co–Fe oxide catalysts in the CO oxidation reaction
The physicochemical characteristics of Cu–Co–Fe oxide catalysts supported on molybdenum carbide and their catalytic activity in the CO oxidation reaction were studied. It was shown that for more effective use of Mo2C as a support for catalysts, it should be treated with a mixture of HF + HNO3 acids in order to increase the defectivity of the structure.
Keywords: CO oxidation, oxide catalysts, molybdenum carbide.
UDC 549.2: 539.1
V. A. Belous, A. S. Kuprin (Kharkov)
S. N. Dub (Kyiv)
V. D. Ovcharenko, G. N. Tolmacheva,
E. N. Reshetnyak (Kharkov)
I. I. Timofeeva, P. M. Lytvyn (Kyiv)
Structure and mechanical properties of protective Ti–Al–Si–N coatings deposited from separated vacuum arc plasma
The protective coatings of the Ti–Al–Si–N system were deposited by the vacuum-arc method during sputtering of the 78Ti–16Al–6Si cathode in nitrogen. The phase composition and substructure of the coating of the Ti–Al–Si–N system were studied by X-ray structural analysis, the topography of the coating was determined by atomic force microscopy, the chemical composition was determined by the X-ray fluorescence method, and the hardness and modulus of elasticity of the coating were determined by the nanoindentation method. It was established that in the Ti–Al–Si–N system, with increasing nitrogen pressure in the deposition chamber, there is a transition from nanocrystalline (up to 0.04 Pa) to nanocomposite (0.04–0.66 Pa) and X-ray amorphous (0.66–1.1 Pa) coatings, and at a pressure of 2.7 Pa, the amount of the crystalline phase again sharply increases. Optimal mechanical properties and maximum thermal stability are provided by coatings with a nanocrystalline structure and nanocomposite ones with a low content of the amorphous phase, the hardness of which reaches 47 GPa.
Key words: thin Ti–Al–Si–N coatings, nanocomposites, vacuum arc, nanoindentation.
UDC 622.24.051:536.2:004.942
IN. AND. Dutka (Kyiv)
Computer modeling of the temperature field in the process of sintering carbide composites using induction and radiant heating
A computer model of the temperature field of a high-temperature installation for sintering powder samples from ceramic materials using induction and radiant heating has been developed. For the numerical solution of the system of equations describing the processes of induction and radiant heating, the finite element method was used in combination with a finite-difference procedure in time, which is based on the Newton-Raphson scheme, and when modeling radiant heat transfer, the radiation method was used. A numerical analysis of the temperature field in the technological installation during the sintering process was performed. A comparison of the numerical results and the results of temperature measurements on the surface of the infiltrator during the sintering of a composite mixture with a silicon carbide framework is presented; based on the agreement of the calculation results with the measurement results, a conclusion was made about the adequacy of the computer model.
Keywords: computer modeling, induction and radiant heating, sintering, carbide composites.
UDC 691.327:666.973.6
M. AND. Tsysar (Kyiv)
Investigation of the topological features of the formation of the surface relief of titanium nitride films on a silicon substrate during diffusion mass transfer and annealing by scanning tunneling microscopy
The peculiarities of the structure and properties of nanostructured films of titanium nitride on a silicon substrate are considered, and a physical-mathematical model of the formation of their surface relief based on the deformation theory is constructed. The dependence of the surface corrugation wavelength on the film thickness was obtained. The topography of the surface relief formed as a result of diffusion mass transfer and changed during annealing was studied. The amplitude of the formed corrugations is determined.
Key words: titanium nitride nanostructured film, diffusion mass transfer, annealing, scanning tunneling microscope, probe, tip, boron-doped semiconductor diamond.
UDC 621.923
AND. IN. Burdin, P. G. Matyuha (Donetsk)
Diamond grinding of the composition VK8–steel 45 with control of the cutting ability of the wheel by the electroerosion method
The optimal mechanical and electrical modes of grinding the VK8-steel 45 composition with periodic electroerosion effect on the working surface of the wheel, which ensure increased productivity and reduced unit cost of processing, are determined in comparison with the grinding wheel filled with electroerosion method.
Key words: grinding modes, composition VK8–steel 45.
UDC [621.7.015:620.191.35]:679.822
AND.IN.Voloshyn, L. AND. Litvinov, E. IN. Slyunyn (Kharkov)
Effect of crystallographic orientation on sapphire surface roughness during diamond processing
The effect of crystallographic orientation of sapphire and its annealing on surface roughness during diamond grinding and polishing was studied.
Keywords: sapphire, grinding, polishing, annealing, surface roughness, crystallographic orientation.
UDC 546.27:536.424
O. O. Kurakevych (Paris, France)
V. L. Solozhenko (Villetaneuse, France)
Crystal structure of dense pseudo-cubic boron allotrope, pc-B52, by powder X-ray diffraction
During past years, a number of reports have been published on synthesis of tetragonal allotrope of boron, t-B52 phase. However, no unambiguous characterization of the crystal structure has been performed to the present time, while remarkable variation of the a/c lattice-parameter ratio raises strong doubts about its uniqueness. Here the Rietveld refinement of the crystal structure of the high pressure-high temperature boron phase synthesized by a direct solid-state transformation of rhombohedral β-B106 at 20 GPa and 2500 K has been reported for the first time. Although this boron allotrope belongs to the t-B52 type, its structure can be considered as pseudo-cubic with the a/c ratio of Ö2.
Keywords: allotropy, boron, crystal structure, dense phase.