Vol 63, No 11 (2018)

Cesium-containing complex oxides Cs[MgR_0.5P_1.5O₆], where R = B, Al, or Fe, were prepared from solutions containing H₃BO₃, metal nitrates, and H₃PO₄/NH₄H₂PO₄. The chemical and phase transformations occurring during the synthesis of these oxides were elucidated by differential thermal analysis (DTA) and X-ray powder diffraction (XRD. Optimal synthesis parameters were found. The boron compound was found to be formed at 800°C, and the aluminum and iron compounds, at 1200°C. All compounds have the pollucite structure (cubic system, space group I4₁32). A comparative analysis of the synthesis of complex oxides under study from various precursors that differed from one another in metal and phosphorus chemical species was carried out.

Interaction between silica hydrogel isolated from serpentines (Mg(Fe))₆[Si₄O₁₀](OH)₈, sodium hydroxide NaOH, and strontium chloride SrCl₂ in aqueous medium was studied by DTA and X-ray powder diffraction (XRD). Stirring of the boiling aqueous suspension prepared from these reagents under the atmospheric pressure for 2 h yields hydrated strontium silicate species: Sr₃Si₂O₇ · 4H₂O and Sr₃Si₂O₇ · 3H₂O or their mixtures, whose heating to 810–825°C is accompanied by some phase transformations: strontium metasilicate Sr₃Si₃O₉ or strontium orthosilicate Sr₂SiO₄ is formed after bound water is removed in the range 250–350°C, and strontium silicate SrSiO₃ is formed at higher temperatures. Sr₂SiO₄ single phase is observed upon heat treatment to 700–750°C. The optimal molar ratio of the reagents was found to favor Sr₂SiO₄ formation.

MgO@SiO₂ core–shell nanoparticles were manufactured, and a synthetic protocol was developed to prepare MgO nanoparticles where the SiO₂ shell thickness was less than 10 nm. The influence of synthesis parameters on the formation of MgO@SiO₂ nanoparticles was studied. The fact of a SiO₂ shell being formed on the MgO surface was established and the sizes of the thus-prepared MgO@SiO₂ nanoparticles were determined by TEM and Fourier-transform IR spectroscopy.

Multiple regression equations linking properties of nanocomposites synthesized by thermolysis of unsaturated nickel dicarboxylates in an argon medium and magnetic characteristics have been obtained by processing experimental data. The equations obtained enable one to predict the magnetic characteristics on the basis of data on the phase composition of the nanocomposite, the content of nickel, and average diameter of nickel-containing nanoparticles; moreover, information on the effect of characteristics on the magnetic properties can be obtained.

The influence of conditions of heat treatment of a solution [Zn(H₂O)(O₂C₅H₇)₂] in 1-butanol (temperature 125–185°C, treatment times 2, 4, and 6 h) on dispersion and microstructure of the formed nanocrystalline and poorly aggregated zinc oxide, promising component for optoelectronics, including as receptor materials of chemical gas sensors, was investigated. IR spectroscopy showed that the precursor decomposition occurs through the cleavage of the C^β–C^γ bond of the ligand to form acetone and butyl acetate. It was determined that at the minimum treatment temperature and time (125°C, 2 h) ZnO nanoparticles are nearly spherical, and under hard conditions, rodlike particles are formed. At 125°C (treatment times 4 and 6 h), rodlike particles are organized into dense agglomerates resembling bundles in shape, and at the higher temperatures there is no aggregation of ZnO nanoparticles. The high CO selectivity and sensitivity (4–100 ppm) was revealed for oxide coatings obtained by screen printing using ZnO nanopowders synthesized at 125°C (treatment times 2 and 4 h).

Vaporization of cobalt(II) pivalate [Co(Piv)₂] (1, HPiv = HO₂CCMe₃) and cobalt(II) oxopivalate [Co₄O(Piv)₆] (2) complexes has been studied by Knudsen effusion technique in combination with mass-spectral analysis of gas phase composition. The congruent sublimation of the prepared compounds has occurred, it has been accompanied by partial thermal decomposition in the case of complex 1. Saturated vapor over complex 1 has been found to consist mainly of monomeric Co(Piv)₂, dimeric Co₂(Piv)₄, and small amount of tetrameric Co₄(Piv)₈ molecules, as well as Co₄O(Piv)₆, CO₂, and 2,2,4,4-tetramethylpentanone ones. Saturated vapor over complex 2 contains only Co₄O(Piv)₆ species. The absolute values of partial pressure and sublimation enthalpies of gas phase components have been calculated.

Quantum-chemical calculations of the structure and relative thermodynamic stability of tetranuclear clusters M_xN_{4 – x}O₆(OMе)₁₀ (M, N = Re, Ru; x = 4–0) including geometric isomers of bimetallic clusters are performed to establish the possibility of replacing Re atoms by Ru atoms while maintaining a cyclic tetranuclear structure. As the initial model, the structure of Re₄O₆(OPri)₁₀ was chosen which is an almost regular rhombus. The values of the metal–metal and metal–oxygen interatomic distances are calculated, and features of their variation under the transition from mononuclear to heteronuclear clusters and from neutral clusters to anions are discussed. Differences between the relative thermodynamic stability of homometallic and heterometallic tetranuclear clusters, including the geometric isomers of the latter, are discussed.

Quantum-chemical modeling of the structure, electronic properties, and stability of hexagonal manganese clusters (MnA_kB_i)_m · nH₂O (A, B = O, SO₄, H₂SO₄; i, k = 0, 1, 2; n = 3–15, m = 3, 6, 12) has been performed by the density functional theory method with gradient correction (PBE and B3LYP). It has been demonstrated that the hexagonal manganese clusters can react with water to release oxygen and ozone (upon the transition to low-lying excited states, for example, on heating or exposure to light). The release of ozone from the (MnO₂)_n clusters (n = 3, 6, 12, …) requires the smallest energy input. It has been revealed that the interaction with hydrogen in the gas phase can lead to the adsorption of ozone onto the cluster surface.

The composition and structure of the Cu²⁺ coordination cores in the previously synthesized [CuCl(HNPv)] · H₂O, [CuCl(HIPv)] · H₂O, [Cu(AOc)(HNPv)], [Cu(AOc)(HIPv)], [Cu(NO₃)(HNPv)], and [Cu(NO₃)(HIPv)] complexes, where HNPv and HIPv pyruvic acid nicotinoyl and isonicotinoyl hydrazones, respectively, have been determined. The binuclear complex [Cu₂(HNPv)₂(H₂O)2(μ-Cl)] has been synthesized for the first time and characterized by elemental analysis and IR, EPR, and EXAFS spectroscopy. Its dimeric structure has been proved by magnetic susceptibility measurement and EPR.

A new method to produce ultra-high-temperature ceramic composites under rather mild conditions (1700°C, 30 MPa, treatment time 15 min) was applied to synthesize a relatively dense (ρ_rel = 84.5%) HfB₂–30 vol % SiC material containing nanocrystalline silicon carbide (average crystallite size ∼37 nm). The elemental and phase compositions, microstructure, and some mechanical properties of this material and also its thermal behavior in an air flow within the temperature range 20–1400°C were investigated. Using a high-frequency induction plasmatron, a study was made of the effect of a supersonic dissociated air flow on the surface of the produced ultra-high-temperature ceramic composite shaped as a flat-end cylindrical sample installed into a copper water-cooled holder. On 40-min exposure of the sample to the supersonic dissociated air flow, the sample did not fail, and the weight loss was 0.04%. Although the heat flux was high, the temperature on the surface did not exceed 1400–1590°C, which could be due to the heat transfer from the sample to the water-cooled model. The thickness of the oxidized layer under these conditions was 10–20 μm; no SiC-depleted region formed. Specific features of the microstructure of the oxidized surface layer of the sample were noted.

The phase diagram of system DyCuS₂–EuS has been first constructed, and the phase equilibria in the Cu₂S–Dy₂S₃–EuS triangle at 970 K have been studied. Compound EuDyCuS₃ (1DyCuS₂ : 1EuS), space group Pnma, a = 10.1901(3) Å, b = 3.9270(1) Å, c = 12.8468(3) Å, melts incongruently at 1727 ± 7 K according to the reaction: EuDyCuS_3solid ↔ 0.17 SS EuS (90 mol % EuS, 10 mol % DyCuS₂) + 0.83 liq (42 mol % EuS, 58 mol % DyCuS₂), ΔH = 2.9 ± 0.6 kJ/mol; microhardness of the phase is 3080 ± 35 MPa. Compound EuDyCuS₃ is transparent in the range 3000–1800 cm^–1. In system DyCuS₂–EuS, the solid solution (SS) based on EuS extends from 91 to 100 mol % at 1770 K and from 92 to 100 mol % at 1170 K. In γ-DyCuS₂, 2 mol % EuS dissolves at 1487 K. The eutectic is formed between compounds DyCuS₂ and EuDyCuS3 at 12 mol % EuS, T = 1487 ± 8 K. In system Cu₂S−Dy₂S₃−EuS, 10 secondary systems have been isolated. At 970 K, tie-lines are located between compound EuDyCuS₃ and solid solutions based on compounds β-Cu₂S, EuS, DyCuS₂, β-(DyCu₃S₃), and EuDy₂S₄; between DyCuS₂ and the solid solution of α-Dy₂S₃, DyCuS₂, and EuDy₂S₄.

The influence of external settings on the mineral assemblage of plutonic rocks is studied. The equilibrium compositions of phases formed during melting–crystallization of quartz monzodiorite are calculated by physicochemical modeling (PCM) methods. It is shown that, by changing the temperature and atmosphere of melt formation, one can change the mineral assemblage of the crystallizing solid phase that can be used in stone casting and in the production of mineral fibers.

Stabilization of Cu²⁺ ions in aqueous and aqueous ammonia solutions of copper acetate was studied for a wide range of ammonia concentrations. The structure of copper acetate hydrate complexes was shown to markedly change upon dissolution in water. In aqueous solutions, copper is stabilized as strongly bound Cu²⁺ associates (dimers) in a distorted octahedral environment composed of water molecules and acetate groups oxygen atoms in equatorial positions with strong exchange interaction via acetate groups. In solutions of copper acetate in aqueous ammonia, the concentration of ammonia has a crucial effect on the ordering of Cu²⁺ ions in associates. At high ammonia concentration, disordered copper tetra-ammoniate associates with the \({d_{{x^2} - {y^2}}}\) ground state are formed, whereas at low ammonia concentration, bulky Cu²⁺ ion associate structures are generated, with the \({d_{{x^2} - {y^2}}}\) ground state, hydroxyl groups in the equatorial plane, and water molecules in the axial positions.