UDC 548.39.:539.2
N. A. Bondarenko, A. N. Zhukovsky, V. A. Mechnik (Kyiv)
Analysis of the main theories of sintering materials. 1. Sintering under isothermal and non-isothermal conditions (review)
The material available in the literature on the theories of sintering crystalline powders under various conditions is systematized and an analysis of the main factors influencing the kinetics of this process is given. The issues, the solution of which will allow a deeper understanding of the nature of physical phenomena occurring in the process of manufacturing composite materials using powder metallurgy methods, are discussed.
UDC 539.89:621.762.5:621.921.34-492.2
A. A. Shulzhenko, A. A. Bochechka, G. S. Oleynik, P. A. Nagorny, L. A. Romanko, V. S. Gavrilova (Kiev)
Compacting ultrafine diamond powder in a high-pressure steel apparatus
The temperature dependence and compaction kinetics of detonation synthesis diamond nanopowder, preliminarily degassed in a vacuum, in a high-pressure steel apparatus were studied. It was shown that continuous physical boundaries arise when particles contact along the same planes, and diffusion processes are completely suppressed under the studied thermobaric conditions. Powder degassing allows reducing the sintering temperature by one and a half times without reducing the degree of compaction.
UDC 536.7:661.657
V. L. Solozhenko (Paris), V. Z. Turkevich, D. V. Turkevich (Kyiv)
Phase diagram of the B—B2O3 system at high pressures
Phase relationships in the B—B2O3 system were studied using in situ synchrotron radiation diffraction at 2.5 and 5.0 GPa in the temperature range of 300–2500 K. Quenched products of boron and boron (III) oxide interaction were studied using X-ray diffractometry. The obtained results were used to find unknown parameters in phenomenological models of phases competing in the B—B2O3 system at high pressures. A thermodynamic analysis of the B—B2O3 system was performed and its phase diagram was constructed at pressures of 0.1 MPa and 5 GPa. It was found that the system contains only one thermodynamically stable boron suboxide B6O, which forms eutectic equilibria with boron and boron oxide, and with B2O3 this equilibrium is degenerate.
UDC 621.762.5
S.A. Kukharenko, A.E. Shilo, E.K. Bondarev (Kiev)
Sintering in glass systems in the presence of a liquid phase
The sintering of glass powders in the Na2O—B2O3—SiO2 and PbO—ZnO—B2O3—SiO2 systems, as well as their mixtures, was studied. It was shown that the sintering process changes as a result of crystallization. The introduction of diamonds and cubic boron nitride into glass powders affects the change in shrinkage during sintering of composites. Sintering of lead-containing glass powders obeys the viscous flow mechanism.
UDC 538.95:553.65:537.311
I. Kh. Abdukadirova (Tashkent)
Thermoradiation effects of changes in some electrophysical properties of a crystalline dielectric
The radiation effects of changes in temperature-frequency dependences of a number of electrophysical properties of one of the widely used crystalline dielectrics — α-Al2O3 in the temperature range of 50-4000 °C and frequencies of 0.3-30 kHz were studied. The main patterns of temperature dependences of dielectric losses of the original and radiation-treated crystals were established. A nonlinear temperature dependence of dielectric losses, permeability, dielectric loss coefficient and active conductivity on alternating current were revealed, as well as the appearance of features such as kinks and maxima (around 100 and 2500 °C) on the corresponding dependences in the radiation-treated crystal. The regularity of the change in the dependence of electrical properties on the radiation frequency is established, its effect on the amplitude of additional dielectric absorption is shown. The correlation of the features of the change in some electrical parameters as a function of temperature and frequency is noted. The nature of radiation-induced additional dielectric absorption is discussed.
UDC 544.72:621.921.34-488
L. Yu. Ostrovskaya, V. M. Perevertaylo, V. S. Zhuravlev (Kiev) V. G. Ralchenko, A. V. Savelyev, S. V. Terekhov (Moscow)
Study of the wettability of nanocrystalline diamond films doped with nitrogen
The role of the nitrogen doping impurity in changing the contact angle of wetting of nanocrystalline diamond films with various liquid media (water, glycerol, tin, as well as electrolytes with different pH, simulating biological fluids) is considered. Experiments on chemical modification of the film surface by hydrogenation in microwave plasma of hydrogen and oxidation during annealing in air indicate significantly broader possibilities for controlling the wettability of nanocrystalline diamond films in comparison with microcrystalline ones. Wetting with model liquids allows us to evaluate the prospects of using these films for biomedical applications.
UDC: 666.233:519.711.3
M. A. Serga, S. N. Shevchuk (Kyiv)
Modeling of temperature fields in a cell for growing diamond single crystals with stimulated nucleation
The influence of the configuration of the resistive system of the cell for growing of diamond single crystals using heat sinks on the distribution of thermal fields in the growth volume. Using the finite difference method, the temperature distribution in the growth volume was obtained when growing diamond single crystals using heat sinks made of nickel and silicon carbide. Based on the results obtained, the use of heat sinks is promising when growing single diamond single crystals for a single-crystal tool.
UDC 621.941:004.032.26
A. G. Naidenko, L. N. Devin (Kyiv)
Using the acoustic emission method to search for diagnostic features when analyzing the process of turning aluminum alloys with diamond-hard alloy cutters
A study of acoustic emission signals was conducted to search for diagnostic features when turning an aluminum workpiece with a cutter made of a diamond-hard alloy plate. It was found that the most informative is the frequency range of the signal between the peaks on the spectrogram of its envelope. The amplitude of this part of the spectrum is sensitive to changes in cutting depth and feed.