UDC 536.42:539.89
V. L. Solozhenko, A. A. Kurakevich (Paris, France) N. A. Dubrovinskaya, L. S. Dubrovinsky (Bayreuth, Germany)
Synthesis of superhard composites in the B—C system
Phase transformations of turbostratic graphite-like BCx phases at a pressure of 20 GPa and temperatures up to 2300 K were studied by X-ray diffractometry and scanning electron microscopy of quenched samples. It was found that, regardless of stoichiometry, the studied phases decompose into boron-doped diamond and boron carbide. The resulting two-phase composite materials have semiconductor properties and high hardness, which in the case of BC3 is comparable to the hardness of a diamond single crystal.
UDC 536.42:544.454.3
V. V. Danilenko (Kyiv)
Features of Carbon Condensation in a Detonation Wave and Conditions for Optimal Synthesis of Nanodiamonds
The conditions for the synthesis of detonation nanodiamonds are analyzed by comparing the phase diagram of nanocarbon and detonation parameters. For non-porous explosives used in the synthesis, the initial pressure and temperature of detonation are in the region of liquid nanocarbon, therefore, during the process of carbon condensation in a detonation wave, coagulation of carbon clusters occurs and at pressures above 16.5 GPa, carbon nanodroplets are formed, which then crystallize into nanodiamonds on the isentrope of expansion of detonation products in the pressure range of 16.5-10 GPa. The commonality of the processes of nanodiamond and soot formation is shown. The positions of the amorphization lines of carbon nanodroplets on the phase diagram are calculated depending on their size. It was found that nanodroplets of 2 nm and smaller cannot crystallize. The effect of explosive charge detonation conditions (detonation imperfection, scale factor, effect of the shell around the charge, coagulation and separation of clusters in moving detonation products) on the synthesis of nanodiamonds was analyzed. Due to the release of surface energy during cluster coagulation with an increase in their size from 2 to 6-8 nm, the calculated cluster temperature increases by 600 K. The conditions for the optimal synthesis of detonation nanodiamonds were formulated.
UDC 548.736.15:621.921.34
V. V. Lysakovsky, M. A. Serga, V. N. Kvasnitsa, S. A. Ivakhnenko (Kiev)
New simple forms of synthetic diamond single crystals
New forms of diamond single crystal growth grown by the temperature gradient method are described. Simple forms (047), (123), (127), (134), (135), (145) (149) (345) and (469) have not been previously observed in single crystals of synthetic diamond. Goniometric measurements of their indices showed that the index values most likely correspond to the dissolution faces and do not significantly affect the habit form of the obtained single crystals of synthetic diamond.
UDC 621.762:669.018.45:533.92
P. I. Loboda, Yu. I. Bogomol, M. O. Sisoev, G. P. Kisla (m. Kiev)
Structure and power of supersolid materials based on pseudobinary systems of borides, separated by zone melting
The structure, mechanical and electrophysical properties of supersolid materials created on the basis of pseudobinary systems of borides and separated by the method of zone melting have been studied. The mechanical strength of the materials changes due to the molding process of a straight structure, and the electrical strength changes as a result of the purification of the materials in the process of moving the zone to the melt.
UDC 621.762.242:669.27
V. P. Bondarenko, A. A. Matveychuk, I. V. Savchuk, A. N. Vaschenko, T. V. Gomelyako (Kiev)
Study of the combined process of tungsten reduction-carbidization from its oxide WO3 in a methane-hydrogen gas environment without using graphite
The conditions for obtaining tungsten carbide WC by combining the processes of tungsten reduction and carbidization in a methane-hydrogen gas environment without using graphite linings are specified. The patterns of formation of tungsten and tungsten carbide powder particles in open and closed reactors are described. The role of external and internal diffusion processes is revealed. The effect of methane amount in methane-hydrogen medium on the rate and completeness of the combined reduction-carbidization process in an open-type reactor, as well as on the rate and features of tungsten particle growth in a closed-type reactor was studied.
UDC 661.551:546.621
V. G. Lutsenko (Kyiv)
Composition and properties of dispersed silicon carbide obtained from rice husk
The effect of pyrolysis temperature on the composition and properties of dispersed SiC obtained from rice husk was studied. The fibrous fraction of silicon carbide was isolated and its content was determined using sieve analysis and sedimentation in aqueous solutions. Silicon carbide of various morphologies contains at least 85 ‰ (by weight) of the 3C polytype. Nanoscale twinning, quantum wells, conductivity type inversion and anomalous chemical properties of both SiC particles and whiskers are noted.
UDC 669.018.045
V. E. Semenenko, A. S. Posukhov, N. N. Pilipenko (Kharkiv)
High-strength and wear-resistant eutectic composites
The heat resistance and wear resistance of quasi-eutectic system composites are studied metal—interstitial phase with a regular structure. The microhardness of composites of different dispersion was determined. A monolithic structurally stable Ni-Cr-Si-B coating was obtained on carbon steel and its tribotechnical characteristics were determined.
UDC 621.922.029
M. A. Grigoryan (Yerevan)
Characteristics of interacting reliefs of a diamond roller and a grinding wheel
The results of processing the profilograms of the reliefs of a diamond roller and a grinding wheel during dressing are presented. It was found that the height parameters of the microgeometry of newly finished and run-in rollers, as well as newly dressed and run-in grinding wheels, differ. The height parameters and the number of cutting edges are different for tools with different grain sizes.
UDC 621.921.34-492.2
N. V. Novikov, G. F. Nevstruev, G. D. Il’nitskaya, V. I. Kushch, V. N. Kolodnitsky (Kyiv)
Quality assessment of superhard material powders. Part 1. Theoretical foundations of the quality characteristics assessment method
A new method for assessing the quality characteristics of superhard material powders is proposed. It allows determining not only the known weighted average value of the powder quality characteristic based on the measured quality characteristic indicators, but also obtaining additional information on the powder composition and its homogeneity. In addition, the developed method allows predicting the results of separating the powder under study into a number of powders of different quality. The theoretical foundations of the method and practical methods for its application for assessing the quality characteristics of superhard material powders are developed and presented.