G. N. Makarenko

Comparative Study of the Chemical Resistance of Titanium Nitride and Stainless Steel in Media of the Oral Cavity

We have shown that TiN powders practically do not react with biochemical media in the body. Using the polarization curve method, x-ray phase analysis, and Auger-electron spectroscopy of the electrode surface, we have studied the reaction of titanium nitride and 12Kh18N10T stainless steel with distilled water, a 3% solution of NaCl, HCl, and gastric juice. We have demonstrated the high corrosion resistance of both materials in H2O (which is also typical for saliva); but in the presence of salt and when gastric juice is ejected from the esophagus into the oral cavity, the corrosion resistance of steel may decrease by several orders of magnitude compared with TiN. In the case of a titanium nitride electrode, we have also established the mechanism of the protective (inhibiting) action of organic reagents contained in the biochemical media, while stainless steel dissolves in gastric juice significantly more rapidly than in hydrochloric acid with the same pH 2.0.

Features of Carbothermal Synthesis of Aluminum Nitride under Nitrogen Pressure

Aluminum nitride is synthesized by the carbothermal method from a mixture of aluminum oxide and carbon black under a nitrogen pressure of 0.2-0.3 MPa at 1800-1900°C and with an isothermal soaking time of 3 h. The best results are obtained with synthesis at 1800°C and a nitrogen pressure of 0.3 MPa from a charge of stoichiometric composition. Powder with an AlN content up to 99 mass% consists of isometric grains with a narrow size range (2-6 μm). Introduction of lithium carbonate into the original mixture worsens the results.

Chemical stability of silicon nitride powders in biochemical media

We have used chemical and x-ray analysis to study the stability and phase composition of silicon nitride powders with different panicle size ranges and morphology in biochemical media (physiological solution, gastric juice, blood serum) at 37°C. We have established the high solubility of Si3N4 in physiological solution and blood serum. The solubility increases with the dispersity of the powder in all the media. We explain this behavior of silicon nitride in biochemical media using modern theories of bioinorganic catalysis.

Mechanism of Interaction of Silicon Nitride Powders with Biochemical Media and their Toxic Effect

For a simulation of toxic effect of silicon nitride powders (in different dispersion state) on human organism, the rates of conversion and mechanisms of interaction with physiological Ringer-Lock solution, gastric juice, blood serum and inorganic media with the same pH were studied. for the alkali and neutral biochemical media, the mechanism of bioinorganic catalysis was established, the Ca2+— ions play the role of catalyst. The results of study were confirmed by toxic tests using a priming of white rats with Si3N4 powders and the further analysis of their blood indexes as well as morphological state of lungs and liver after 1, 3 and 6 months.

Reaction of aluminum nitride powder with biochemical media

The effect of particle size and morphology on the degree of dissolution of commercial AlN powder, fiber crystals, and nanoparticles in physiological solution, blood serum, gastric juice, and control media with the same values of pH was determined. The reaction mechanism of AlN powder with biochemical media and its toxic effect are discussed.

Oxidation of boron silicide and materials based on it

Boron silicide and compounds based on it containing titanium, chromium, nickel, and yttrium and scandium oxides are studied for their oxidation in air from room temperature to 1300°C. It is shown that chromium boride markedly improves the heat resistance of B4Si over a wide temperature range (700–1300°C) probably as a result chromium-oxide dissolution in borosilicate glass and alteration of its structure. A favorable effect of yttrium and scandium oxides as well of nickel silicide appears at above 100°C as a result of forming complex oxide compounds in the scale.

Formation of Diborides of Groups IV–VI Transition Metals During Mechanochemical Synthesis

Fine powders of diborides of groups IV–VI transition metals (TiB2, HfB2, NbB2, TaB2, CrB2, Mo2B5, and W2B5) were produced by mechanochemical synthesis and low-temperature heat treatment of activated charges. The particle size of the powders was ≤1 μm. It is revealed that processes of formation of diborides of groups IV–VI transition metals differ within period and group. Diborides Ti and Nb formed discontinuously. Diborides Hf and Ta formed after the formation of lower boride phases, whereas higher borides Cr, Mo, and W formed in almost a single-phase state only after a low-temperature treatment of preliminarily mechanoactivated charges. The differences were analyzed from the point of view of the donor-acceptor capacity of the atoms of boron and diboride-forming transition metals.

Use of Binary Titanium–Chromium Diboride for Producing Protective Coatings on a Nickel Substrate

The production of composite electrolytic coatings on a nickel substrate using binary titanium–chromium diboride obtained by mechanical synthesis was studied. The influence of heat treatment parameters on the phase composition and structure of the coatings was examined. It is shown that these coatings substantially increase the wear resistance of structural medium-carbon steel.

Highly Dispersed Powders in Boride–Silicide Systems

Nanosized composite powders with a composition of titanium diboride–silicides of group IV–VI transition metals are obtained in boride–silicide systems by mechanochemical synthesis for 5–30 min. The initiation effect of TiB2 on the formation of silicide phases during joint mechanochemical synthesis is shown. It is established that the powder particles are 40–70 nm in size. The powders tend to agglomerating. The properties of hot-pressed compacted TiB2–20 wt.% MoSi2 samples are studied: ultimate bending strength 421 ± 29 MPa; microhardness 25 ± 0.8 GPa. Electrolytic Ni–TiB2–MoSi2 coating possesses high wear-resistance in sliding friction and can be recommended for hardening and recovering the surfaces of machinery and mechanical parts.

Phase Formation During Nitriding of Vanadium Disilicide

The evolution of microstructural and phase transformations during nitriding of mechanically preactivated vanadium disilicide powder is investigated by X-ray diffraction, chemical analysis, and transmission electron microscopy. It is established that, in the initial stage of nitriding (1000–1100°C), the phase formation is accompanied by the dispersion of near-surface zones of VSi2 particles and the formation of V2N and α-modification silicon nitride. With increase in the nitriding temperature, the phase formation is accompanied by the delamination of particles and the formation of mainly VN and silicon nitride of α- and α-modifications. Nitriding of a mechanically activated vanadium disilicide powder at 1400°C enables synthesizing a fine silicon nitride–vanadium nitride composite powder in a single process. The synthesized powder is formed as loose aggregates consisting of 50 nm particles.