Vol 54, No 2 (2018)

Colloidal zinc sulfide solutions have been prepared by reacting zinc trifluoroacetate and thioacetamide in methyl methacrylate as a reaction medium, and europium and terbium salts have been added to the solution. Using methyl methacrylate block polymerization, we have synthesized PMMA/ZnS, PMMA/ZnS:Eu(III), PMMA/ZnS:Tb(III), and PMMA/ZnS:Eu(III),Tb(III) composites. The luminescence of the composites is due to charge recombination at energy levels of structural defects and impurities in ZnS and also to ⁵D₀ → ⁷F_j and ⁵D₄ → ⁷F_j electronic transitions of the Eu³⁺ and Tb³⁺ ions. It depends on the composition and structure of the composites, excitation wavelength, and other factors. The mutual effects of the ZnS and the Eu³⁺ and Tb³⁺ ions show up as changes in the position and relative intensity of luminescence bands in the spectra of the composites.

Mesoporous calcium phosphate granules ranging in mesopore size from 11 to 19 nm have been prepared using cryogenic processing (–18°C) of gels and extrusion of calcium phosphate paste. The granules based on acid calcium phosphates have a relatively small specific surface area (45 m²/g) in comparison with the neutral and basic calcium phosphates (84–155 m²/g). Preclinical in vivo trials on rats show that the presence of calcium phosphate granules in a bone defect considerably accelerates reparative osteogenesis in comparison with a control group of animals.

Using mechanochemical synthesis, we have prepared zirconium borohydride, Zr(BH₄)₄, as a precursor for ZrB₂ film growth by chemical vapor deposition. We have carried out the thermodynamic modeling of phase formation processes in the Zr–B–(N)–H and Zr–B–(N)–H–O systems in a wide temperature range, from 100 to 2500°C, at various p_(H2)/p_(Zr(BH4)4) and p_(NH3)/p_(Zr(BH4)4) partial pressure ratios in the starting gas mixtures. A process has been proposed for the growth of zirconium diboride films by Zr(BH₄)₄ decomposition using two techniques: chemical vapor deposition and plasma-enhanced chemical vapor deposition. We also developed a process for the growth of multilayer ZrB₂-and BC_xN_y-based structures.

An unactivated mixture of aluminum hydroxide (gibbsite) and lithium carbonate and a mixture mechanically activated in an AGO-2 planetary mill were heat-treated in air and under vacuum (0.05 Pa) at temperatures of up to 800–850°C, and the phase composition of the heat treatment products was determined by in situ X-ray diffraction. The results demonstrate that, in the case of the unactivated mixture or after mechanical activation for 1 min, heat treatments in air and under vacuum lead to the formation of α-LiAlO₂ and γ-LiAlO₂, respectively. After mechanical activation for 5 or 10 min, heat treatment both in air and under vacuum leads to γ-LiAlO₂ formation. A possible mechanism behind the effect of the reaction medium on the phase composition of LiAlO₂ is analyzed.

The Pb₈La₂(GeO₄)₄(VO₄)₂ and Pb₈Nd₂(GeO₄)₄(VO₄)₂ germanatovanadates with the apatite structure have been prepared by solid-state reactions, by sequentially firing stoichiometric mixtures of PbO, La₂O₃ (Nd₂O₃), GeO₂, and V₂O₅ in air at temperatures of 773, 873, 973, and 1073 K. The effect of temperature on the heat capacity of the resultant polycrystalline samples has been studied by differential scanning calorimetry at temperatures from 350 to 950 K using polycrystalline samples. The experimental C_p(T) data have been used to evaluate the thermodynamic functions of the lead lanthanum and lead neodymium germanatovanadates.

The separation factors of metal impurities for potassium dihydrogen phosphate crystallization from nonstoichiometric solutions have been experimentally determined. Based on the results obtained, a method has been proposed that makes it possible to obtain a material containing aluminum, iron, chromium, and titanium at a level of ~5 × 10^–2 ppm by weight from commercially available raw materials. In this method, a KH₂PO₄ solution is purified due to partial crystallization of the macrocomponent, so that the above impurities are concentrated in the solid phase. The purified solution is then boiled down with KOH additions.

Polished sections of individual ferrospheres 30 to 40 μm in size, with single-block and blocky structures and a variable glass phase content, have been studied using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer system. The results demonstrate that the single-block globules consist of sintered magnetite crystallites containing Al₂O₃, MgO, and CaO as impurities and are formed from the pyrite of the initial coal. Characteristically, the ferrospheres with a variable glass phase content differ in the composition of local areas on polished sections of the globules, which attests to inhomogeneity of the melt droplets they formed from. We have identified groups of globules whose overall composition, as well as the composition of their local areas, meet general equations for the interrelation between the concentrations of their components: SiO₂ = f(FeO) and SiO₂ = f(Al₂O₃). Comparison of the coefficients of the SiO₂ = f(Al₂O₃) dependence for the globules with the silicate modulus (SiO₂/Al₂O₃) of the aluminosilicate mineral components of the coal indicates that the formation of this type of globules involves pyrite–anorthite or pyrite–albite associates containing quartz impurities. The composition of the spinel ferrite in the globules produced with the participation of anorthite comprises FeO, Al₂O₃, MgO, and CaO in concentrations of 85–96, 1.7–10, 0.1–1.8, and 0.3–2.8 wt %, respectively. In the albite-based globules, the respective concentrations are 81–92, 0.7–5.9, 1.0–5.7, and 2.2–5.6 wt %. The crystallite size and shape are determined by the size of the local melt areas where the total concentration of spinel-forming oxides exceeds 85 wt %.

Ceramic (1–x)Ba(Ti1–yZry)O₃ · xPbTiO₃ (0 ≤ x, у ≤ 1) samples have been characterized by X-ray diffraction and dielectric measurements. The results have been used to map out the phase diagram of the system, which demonstrates the variation in the phase composition of the samples. It has been shown that, in the composition regions adjacent to the BaTiO₃–PbTiO₃ side and BaZrO₃ corner of the composition triangle, the samples consist of perovskite solid solutions that have tetragonal and cubic structures, respectively, at room temperature. In the intermediate composition region, the samples consist of different perovskite solid solutions similar in composition and structure. We have obtained composition dependences of the unit-cell symmetry and parameters for the solid solutions, their ferroelectric Curie temperature T_C, characteristic dielectric relaxation temperatures, dielectric permittivity ε, and dielectric loss tangent tanδ (at temperatures from 100 to 800 K and frequencies from 25 to 106 Hz) and analyzed the evolution of their dielectric properties with increasing BaZrO₃ content: from ferroelectric to properties of ferroelectric relaxors, reentrant relaxors, and dielectric relaxors of the dipole glass type.