Composites based on melamine and titanium dioxide at different initial ratios 4 : 1, 6 : 1, 8 : 1, and 10 : 1 were obtained by polymerization in air at a temperature of 550°C. The morphology of the samples was investigated, and the elemental mapping of the sample composition was carried out using scanning electron microscopy. It was found that the initial melamine particles have a size of more than 20 μm, and its polymerization leads to the formation of g-C3N4 layers up to 5 μm in size. TiO2 particles have an average size of 150 nm, and the resulting g-C3N4/TiO2 heterostructures consist of particles with a size of 20–30 nm, which form agglomerates of about 2 μm in size. It was shown that the specific surface area decreases from 67 to 41 m2/g with increasing melamine content in the initial mixture. A single-phase composition TiN0.24O1.88 was formed when the initial components were mixed at a ratio of 4 : 1. When the ratio of the initial melamine and titanium dioxide was increased to 8 : 1 and 10 : 1, a two-phase system was formed, which consisted of Ti0.72O2 in an amount from 12 to 13

The synthesis conditions, structure details, and electrical conductivity of cation- and anion-deficient scheelite-like solid solutions Sr1 − 1.5x – yBix + yФ0.5xMo1 – yVyO4 and Sr1 − 1.5xBixФ0.5xMo1 – yVyO4 – d, where Ф is a cation vacancy, have been studied. The homogeneity ranges of solid solutions were determined, and their structural features were studied using a set of methods. The morphology of ceramic samples was studied by scanning electron microscopy. The total electrical conductivity of the compounds was measured by impedance spectroscopy in the temperature range 400–650°C. To estimate the contribution of the electron and proton components to the total electrical conductivity of solid solutions, the electrical conductivity characteristics were measured in a humid atmosphere and at various partial pressures of oxygen. The Arrhenius plots of the electrical conductivity were analyzed.

High-entropy alloys attract researcher’s attention due to the presence of a set of new properties. The paper considers the factors affecting the structure of high-entropy alloys (HEAs) based on the elements Ti, Zr, Hf, V, and Nb. The structure data of four-component Ti25Zr25V25Nb25 and five-component Ti20Zr20Hf20V20Nb20 alloys, which were obtained under the same melting and cooling conditions in an arc furnace, are presented. The data of the EDX analysis showed that the chemical composition of the alloys corresponded to the nominal one. Analysis of micrographs of the ingots surface allows us to conclude that the applied melting mode led to overheating of the four–component alloy, but not for the five-component one. It was experimentally found that the primary formation of the four-component alloy occurs faster than that of the five-component one, but further remelting under overheating conditions leads to multiphase structure formation. The maximum content of BCC solid solution (98%) in Ti25Zr25V25Nb25 alloy was achieved during the first remelting, another phase was FCC solid solution (2%). The maximum content of BCC solid solution (95%) in Ti20Zr20Hf20V20Nb20 alloy was obtained by repeated remelting, BCC, HCP solid solutions, and the Laves phase were presented in the amount of 3% or less. The crystal lattice parameters of the BCC main phases for the Ti25Zr25V25Nb25 and Ti20Zr20Hf20V20Nb20 alloys were 3.270 and 3.362 Å, respectively. It was established that to obtain refractory HEAs with a single-phase structure it is important both fulfilment of thermodynamic conditions and correct choice of time-temperature conditions of melting and crystallization for each specific alloy composition.

Electrical resistivity and magnetic susceptibility of Al-Ni-Co-Cu-Zr alloys with different component ratios are studied in a wide temperature range including both solid and liquid states. The abnormal behavior of properties is discovered in the temperature range 700-1200 K. The increase of magnetic atoms concentration (mainly cobalt) in the alloys composition leads to increase of properties anomalies. Some parameters of the electronic structure - paramagnetic Curie temperature, effective magnetic moment and density of electron states at Fermi level - are calculated from the experimental data.

In this work were studied density (by gamma-absorption method) and electrical resistivity (by contactless method in rotating magnetic field) of Al–Ni–Co–Ce glass-forming alloys with different ratios of transition metals. It was found the existence of a wide two-phase zone was established and jump-like changes in properties at solidus and liquidus temperatures. Increasing of cobalt content from 2 to 4 at % leads to 2% decrease of density and 3% increase of electrical resistivity in crystalline and liquid states. Temperature coefficients of change in properties were calculated. Density hysteresis was detected, which occurs when melts are overheated above 1350 K. This fact is related to the disintegration of large-scale microheterogeneities that exist in melts during heating. It is shown that these results can be used to optimize the process of obtaining rapidly hardened alloys.

We have studied for the first time the feasibility of using Al2O3 and Al : Zn (1 : 1) coatings produced by supersonic plasma spraying for protecting GdTbDyHoSc and GdTbDyHoY high-entropy rare-earth (RE) alloys from corrosion in a salt-fog chamber. The results demonstrate that, under salt fog conditions, Al2O3 coatings break down through local surface activation, resulting in pitting corrosion, with a considerable fraction of the coating on the main material remaining intact. The alloys coated with Al : Zn (1 : 1) exhibit lower corrosion resistance under salt fog conditions as a consequence of electrochemical corrosion. Interaction of Al2O3 with NaCl limits the suitability of such coatings for protecting high-entropy RE alloys under salt fog conditions. Limitations refer to the specimen test time and coating thickness.

The paper presents a methodology for the synthesis of iron complex with hydrazine hydrate Fe(N2H4)xCly. 2 H 4 ) x Cl y . The Fe(N2H4)xCly 2 H 4 ) x Cl y complex was investigated by X-ray phase analysis and scanning electron microscopy. Upon hydrolysis, the Fe(N2H4)xCly 2 H 4 ) x Cl y complex forms a composite sorbent, which is Fe3O4 3 O 4 in a shell of Fe(N2H4)xCly 2 H 4 ) x Cl y complex. The composite sorbent can be used to treat wastewater from Cr(VI) ions and is effective in the pH range of 2 to 12. Based on the adsorption and electrokinetic potential data, a conclusion about the nature of the terminal groups of the adsorbent was made, a scheme of the structure of its electrical double layer and the adsorption mechanism were proposed. Depending on the conditions, Cr(VI) can be adsorbed on the composite sorbent or reduced to Cr(III). The efficiency of the composite sorbent in the removal of Cr(VI) ions was tested on a sample of real wastewater.

A natural iron-bearing oxysulfide, named cafeosite after its chemical composition, is a unique example of a mineral that simultaneously contains iron in three oxidation states: Fe3+, Fe2+, and intermediate between Fe2+ and Fe-0 involved in metallic-type FeFe bonding. Cafeosite was discovered in metamorphosed carbonaceous chondrite Dhofar 225, which is classified as CM-anomalous but likely related to the CY (Yamato-type) group. The mineral occurs as tiny anhedral grains that coalesce into irregular aggregates up to 20 mu m, commonly encrusted by micrometer-thick troilite or pyrrhotite rims. The grains are randomly disseminated within a chondrite matrix composed of thermally altered phyllosilicates. Associated accessory minerals are troilite, pyrrhotite, Fe-rich, Al-bearing olivine, unknown Al-bearing Fe sulfide, Al-rich chromite, kamacite, awaruite, pentlandite, escolaite, and perovskite. In reflected light, cafeosite is gray, with no internal reflections. Anisotropy is moderate, bireflectance in gray hues. Infrared microspectroscopy did not reveal any bands attributable to (OH)(-), H2O or CO32- vibrations. Owing to the small grain size, the crystal structure of the mineral has been studied using synthetic analog, which was found to be isostructural with natural cafeosite based on electron backscatter diffraction (EBSD) data. Cafeosite is orthorhombic, space group Cmce (#64), a 17.4856(9), b 11.1516 (5), c 11.1543(5) angstrom, V 2175.0(2) angstrom(3), Z = 8, D-x = 4.11 g cm(-3). The crystal structure has been solved and refined to R-1 = 0.039 for 1105 unique reflections. Chemical composition of both natural and synthetic cafeosite corresponds to the formula Ca4Fe32+Fe23+(square Fe-1-x(x))O6S4 where (square Fe-1-x(x)) denotes structural vacancy partially occupied by semimetallic-type Fe (x = 0.2-0.3). The ideal endmember formula of the mineral is Ca4Fe32+Fe23+square O6S4. Cafeosite was likely formed from previously altered precursor material of Dhofar 225, which, like common CM chondrites, consisted of phyllosilicates, Ca-bearing carbonates, tochilinite-like sulfides-hydroxides and pyrrhotite. During thermal metamorphism at temperatures between 750 and 900 degrees C, sulfides-hydroxides were partly sintered with calcined carbonates and iron oxides, resulting in cafeosite formation. Due to varying and redox-dependent contents of Fe3+ and Fe2+, as well as the presence of metallic-type Fe in the structure, cafeosite could be regarded as a single-phase redox indicator alternative to the known triple-phase buffers, for example, iron-magnetite-pyrrhotite (IM-Po), iron-wustite-pyrrhotite (IW-Po) and magnetite-wustite-pyrrhotite (MW-Po) systems. Discovery of cafeosite provides insight into a previously obscured aspect of CY-chondrite formation: the redox conditions of thermal metamorphism on carbonaceous asteroids.

The refractory metal carbides TiC, ZrC, HfC, NbC, and TaC have excellent physical, chemical, and mechanical properties as materials for ultra-high temperature ceramics. The most refractory of them are TaC and HfC, the melting temperatures of which approach 4000°C. The high hardness, strength, and wear resistance of refractory carbides is also noteworthy. Therefore, natural interest in high-entropy carbides (HECs) based on them is grounded: they are becoming an important class of new ceramic materials, since they potentially have more advanced applied properties. However, the production of such materials by classical metallurgical methods is a difficult problem. In modern investigations, HEC samples are most often synthesized using expensive special equipment (plasma spark sintering methods, high-energy planetary mills, etc.) and relatively long preparation of precursors for sample fabrication. Here, we describe a new approach to synthesizing a multicomponent (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C carbide using an electrochemical process at a temperature not exceeding 1173 K. This technique is based on the phenomenon of currentless metal transfer in molten salts. After sequential metal transfer, the sample is washed from an electrolyte and then sintered in a vacuum furnace. According to X-ray diffraction analysis, the resulting HEC is a single-phase fcc solid solution. The X-ray diffraction pattern of the synthesized sample is in good agreement with the X-ray diffraction pattern calculated by the Debye formula for a supercell of 64 000 atoms. A compacted HEC sample is prepared by pressing a pellet 10 mm in diameter in a mold with the addition of cobalt as a matrix metal. After vacuum sintering, the sample is polished for examination in a scanning electron microscope. Elemental mapping of the sample surface is performed; it demonstrates a satisfactory distribution of the metals that make up the HEC. The measured microhardness of the sample turned out to be lower than the values reported by other authors, which can be due to some residual porosity of the sample.

Electrical resistivity of Co 48 Fe 25 Si 4 B 19 Nb 4 amorphous alloy and with small additions of rare-earth metals ( = Nd, Sm, Tb, Yb) was studied using the AC four-probe method. It was found that these alloys have a specific behavior of electrical resistivity after crystallization-temperature dependences of resistivity at cooling are non-linear and can be fitted as ln R~ T -1/4 . Keywords: amorphous alloys, metallic glasses, electrical resistivity, rare-earth metals.

Doped bismuth vanadates (Bi4V2–xMexO11–δ, Bi4V2-xMe0,5xMe'0,5xO11–δ, Bi4V2–xMe0,25xMe'0,25xMe''0,25xMe'''0.25xO11–δ, x = 0,2; Me,Me',Me'',Me'''=Mg,Ca,Cu,Ni) were obtained by solid-phase synthesis. The certification of the powdered samples was carried out by X-ray analysis. The parameters of the unit cell of the samples were determined. The transport characteristics were estimated by the method of impedance spectroscopy. The equivalent cell schemes for the different temperature regions were selected.

The influence of the conditions of mechanical activation of a mixture of Cu–12 wt. % Sn with different content of the modifier Cu9 Al4 on the structural-phase composition and morphology of the formed composites was studied by the methods of X-ray diffraction analysis, optical and electron microscopy. With the mechanochemical introduction of 10 wt. % of the modifying additive into the matrix of mechanosynthesized tin bronze, the product mainly forms a ternary solid solution of aluminum and tin in copper, Al0.05Cu0.9Sn0.05. In the case of 20 wt. % of the modifying additive, the product contains a solid solution of tin in copper Cu0.9Sn0.1 and an intermetallic compound Cu9 Al4. Studies of the mechanical and tribotechnical characteristics of the material obtained by sintering under pressure showed that the intensity of wear of bronze of the mechanochemically synthesized powder Cu–12 wt. % Sn is slightly less than that of industrial bronze BrTPh10-1, the friction coefficient f decreases by a factor of 1.4, and the range of its values is quite wide f = 0.7–0.9. Modification of mechanically synthesized Cu–12 wt. % Sn bronze with the Cu9 Al4 intermetallic compound makes it possible to reduce wear by a factor of 1.4–1.8 and significantly reduces the friction coefficient (by a factor of 2). A stable value of f = 0.5 is achieved for the MA composition Cu–12 wt. % Sn + 20 wt. % Cu9 Al4. The introduction of an intermetallic compound increases the microhardness of the alloys by a factor of 1.6–2.0 (up to Hμ = 2730 MPa) relative to the bronze alloy BrTPh10-1and mechanically synthesized bronze.

We consider a new method for the preparation of refractory high-entropy alloys (HEAs) AlTiZrVNb, which consists in the joint aluminothermic reduction of metals from their oxides. It was determined that V and Nb undergo reduction to a greater extent, and about 90% of their amounts transfer into the metal phase. Metals Ti and Zr undergo reduction to a lesser extent, with 76 and 50% of their amounts transitioning into the metal phase, respectively. The obtained alloy has a multiphase structure consisting of C14 Laves phases, Zr5Al3-type phases, and a B2-type ordered phase, which plays the role of a matrix. The microhardness of the alloy is 6.37 GPa, which is similar to the values of refractory HEAs. The structure of the obtained alloy has a similar structure throughout its bulk, namely, coarse-grained with a number of pores, partly filled with non-metallic inclusions of aluminum oxide.

Equiatomic Al-Ni-Co-Cu-Zr alloy was produced by arc melting. Rapidly quenched rods were prepared by suction casting method. Density, electrical resistivity and thermal analysis of the alloy were investigated experimentally. Basing on X-ray diffraction it was shown that the structure of the alloy consists of two competing solid solutions: BCC-ZrNi2Al (Heusler-type phase) and & gamma;-phase Cu9Al4. In addition, pure cooper and Cu3Al, Cu5Zr7Ni5 intermetallic compounds were determined. Rapid quenching of this alloy leads to the formation of solid solutions based on BCC-ZrNi2Al and high-temperature Cu3Al phase. It is shown that the alloy in crystalline state has a linear density change up to solidus temperature. A region of resistivity decrease with increasing temperature is found out for the first time. The melting process goes in a wide temperature range (above 250 K) where 4 thermal reactions were detected. Density and electrical resistivity changes here non-linearly. In liquid state there are no thermal effects in the alloy and temperature dependencies of density and electrical resistivity can be fitted by linear functions.

A wuestite phase metastable at room temperature in the form of a whisker conglomerate was found on the surface of nanoporous iron obtained by electrochemical dealloying (selective anodic dissolution of a less noble metal) of ferromanganese. The features of the further oxidation of iron by TG-DSC and Х-ray phase analysis with a temperature sweep were studied. A wide range of coexistence of three forms of iron oxides and relative stability of the magnetite phase up to 900°C were described.

Министерство науки и высшего образования Российской Федерации Российское химическое общество им.Д.И.Менделеева Секция по химической термодинамике и термохимии Научного совета РАН по физической химии Сибирское Отделение Российской Академии Наук Институт неорганической химии им.А.В.Николаева СО РАН

Впервые исследована возможность использования Al 2 O 3 - и Al : Zn (1 : 1)-покрытий, нанесенных методом сверхзвукового плазменного напыления, в качестве защитных для высокоэнтропийных сплавов (ВЭС) редкоземельных элементов (РЗМ) GdTbDyHoSc и GdTbDyHoY от коррозии в камере соляного тумана. Показано, что покрытие Al 2 O 3 в условиях соляного тумана разрушается по механизму локальной активации поверхности, появляется питтинговая коррозия и при этом сохраняется значительная доля покрытия на основном материале. Образцы с покрытием Al : Zn (1 : 1) в условиях соляного тумана показывают меньшую стойкость вследствие электрохимической коррозии. Взаимодействие Al 2 O 3 с NaCl делает данное покрытие ограниченно годным для защиты сплавов РЗМ ВЭС в условиях соляного тумана. Ограничения касаются времени испытания образцов и толщины нанесенного покрытия.

Microcrystalline powders of rutile and anatase were milled in a high-energy planetary mill down to obtain nanosized TiO2 powders (the size of coherent scattering region (CSR) about 30 nm and 60 nm, respectively). The resulting powders were characterized by HRTEM, Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the xi-potential of the aqueous suspensions was determined. High-energy milling made it possible to significantly increase the ability of TiO2 to remove chromium from aqueous solutions. The effectiveness of the powders for not only Cr(VI) removing but also total chromium adsorption under UV-irradiation and short wavelength visible light has been shown. This is important, since Cr(III) does not remain in the aqueous medium and cannot be oxidized back to Cr(VI) under the influence of some environmental factors. It is possible to remove more than 99.9 % of total chromium and 100 % of chromium hexavalent from a 50 mg center dot L-1 solution of Cr(VI) using milled anatase. XPS showed that, upon the photoadsorption, Cr(VI) is reduced to Cr(III). The presence of an acetate buffer in the solution promotes the most efficient removal of chromium. This work shows a simple way to obtain a highly effective material with potential applications for the removal of high toxic hexavalent chromium from industrial wastewater. The milled anatase sample was successfully tested to remove Cr (VI) from a real wastewater sample.

Refractory metal carbides TiC, ZrC, HfC, NbC and TaC have excellent physical, chemical and mechanical properties as materials for ultra-high temperature ceramics. Of these, the most refractory are TaC and HfC, whose melting points approach 4000°C. It should be noted the high hardness, strength and wear resistance of refractory carbides. Hence, there is a natural interest in high-entropy carbides based on them, which are becoming an important class of new ceramic materials, since they potentially have more advanced applied properties. However, obtaining such materials by classical metallurgical methods is a difficult task. In modern research, samples of high-entropy carbides are most often synthesized using expensive special equipment (methods of plasma-spark sintering, high-energy planetary mills, etc.) and a relatively long preparation of precursors for sample production. This paper describes a new approach to the synthesis of multicomponent carbide (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C using an electrochemical process at a temperature not exceeding 1173 K. The method is based on the phenomenon of currentless metal transfer in molten salts. After the step-by-step transfer of metals, the sample was washed from the electrolyte, then sintered in a vacuum furnace. According to X-ray phase analysis, the resulting high-entropy carbide is a single-phase solid solution with an FCC structure. The diffraction pattern of the synthesized sample is in good agreement with the calculated diffraction pattern obtained by the Debye formula for a supercell of 64 000 atoms. A compact sample of high-entropy carbide was produced by pressing a tablet 10 mm in diameter with the addition of cobalt as a matrix metal. After vacuum sintering, the sample was ground to prepare for examination on a scanning electron microscope. Elemental mapping of the sample surface was performed, which showed a satisfactory distribution of metals that make up the high-entropy carbide. The measured microhardness of the sample turned out to be less than the values found in the publications of other authors, which may be due to some residual sample porosity.

X-ray diffraction analysis and optical and electron microscopy have been used to study the effect of mechanical activation conditions of the Cu–12% Sn mixture with different Cu 9 Al 4 modifier contents on the structure and phase composition and morphology of formed composites. The mechanochemical introduction of 10 wt % of the modifying additive into the matrix of mechanically synthesized tin bronze mainly results in the formation of a ternary Al 0.05 Cu 0.9 Sn 0.05 solid solution of aluminum and tin in copper. In the case of the 20 wt % modifying additive, the final product contains a Cu 0.9 Sn 0.1 tin solid solution in copper and Cu 9 Al 4 intermetallics. Studies of the mechanical and tribological characteristics of the material prepared by sintering under a pressure showed that the intensity of wear of the material based on the Cu–12 wt % Sn mechanochemically synthesized bronze is insignificant lower than that of commercial bronze alloy CuSn10P; the coefficient of friction ( f ) decreases by ~1.3 times and the range of its values is sufficiently wide, f = 0.7–0.9. The modification of the Cu–12 wt % Sn mechanically synthesized bronze with the Cu 9 Al 4 intermetallics allowed us to decrease the intensity of wear by 1.3 to 1.6 times and to substantially decrease the coefficient of friction (by 1.2 to 1.6 times). The stable value f = 0.5 is reached for the mechanically activated Cu‒12 wt % Sn + 20 wt % Cu 9 Al 4 composition. The introduction of the intermetallics results in the increase in the microhardness of the alloys by 1.6 to 2 times (to H μ = 2730 MPa) compared to those of CuSn10P and mechanically synthesized bronzes.