


Vol 63, No 4 (2018)
- Year: 2018
- Articles: 20
- URL: https://journal-vniispk.ru/0036-0236/issue/view/10287
Synthesis and Properties of Inorganic Compounds
Study of the Thermal Behavior of Wedge-Shaped Samples of HfB2–45 vol % SiC Ultra-High-Temperature Composite in a High-Enthalpy Air Flow
Abstract
By spark plasma sintering, HfB2–45 vol % SiC ultra-high-temperature ceramic was prepared, from which wedge-shaped samples were cut. The behavior of the samples was examined in a flow of dissociated air produced by an induction plasmatron, where the surface temperature of the leading edges of the samples reached ~2700°C. The dependence of the temperature distribution gradient on the distance from the leading edges of the samples was experimentally investigated. For the samples after the experiments, the elemental and phase compositions were determined, and features of the surface microstructure in various regions of the sample and on its polished surface were studied.



Phase Equilibria in LiYF4–LiLuF4 System and Heat Conductivity of LiY1–xLuxF4 Single Crystals
Abstract
Single crystals of LiY1–xLuxF4 (x = 0, 0.25, 0.5, 0.65, 0.9) solid solution were grown by Bridgman–Stockbarger technique. Melting points determined by DSC monotonically varied with composition from 831 to 841 K when x increased. Interval between liquidus and solidus curves is not larger 1°C. This feature extremely favors to the growth of homogeneous single crystals from melt. Heat conductivity (κ) of solid solution is lower than that of LiYF4 and LiLuF4 components. In the region 0.25 ≤ x ≤ 0.65 at 300 K, κ = 4 ± 0.1 W/(m K).



Synthesis of MgFe1.6Ga0.4O4 by Gel Combustion Using Glycine and Hexamethylenetetramine
Abstract
A powderlike material of composition MgFe1.6Ga0.4O4 was synthesized by gel combustion using a glycine–hexamethylenetetramine mixture. The gel produced by the synthesis was studied by thermal analysis (TGA/DSC) and IR spectroscopy. This mixture was shown to be efficient for obtaining homogeneous nanosized MgFe1.6Ga0.4O4. The morphology of the powders was characterized by scanning electron microscopy and X-ray powder diffraction analysis.



Synthesis and Optical Properties of Fe@Au, Ni@Au Bimetallic Core–Shell Nanoparticles
Abstract
Fe@Au and Ni@Au core–shell nanoparticles (NPs) were synthesized by liquid-phase reduction of iron and nickel compounds by sodium borohydride in an aqueous medium. Transmission electron microscopy, X-ray powder diffraction, and spectrophotometry were used to confirm the structure of the NPs and to determine their shape and the average core and shell size.



New Approach to the Preparation of Doped Lithium Niobate Batches for Single Crystal Growth
Abstract
Technological approaches have been developed to the preparation of single-phase lithium niobate batches doped with magnesium, zinc, iron, and rarer-earth elements (TR = La, Pr, Nd, Sm, Gd, Dy, or Er) from high-purity niobium-containing solutions to avoid niobium pentoxide separation, its mixing with lithium carbonate, and LiNbO3 preparation from this mixture by a solid-phase reaction. Two process flowsheets have been proposed, being applicable over the entire ranges of the studied dopant concentrations. Optimal parameters for preparing single-phase LiNbO3 batches of tailored compositions have been determined. The batches prepared by the developed technology are intended for growing doped optical-quality lithium niobate single crystals.



Synthesis and Selected Physicochemical Properties of Complex Na2[Zr(MoO4)3]
Abstract
The interaction of Zr(NO3)4 and Na2MoO4 in an aqueous medium has been studied by the method of residual concentrations at 20°C. The compound Nа2[Zr(MoO4)3] is formed starting at the molar ratio Zr(NO3)4/Na2MoO4 ≥ 0.66. The compound has been characterized by X-ray diffraction, IR spectroscopy, and thermal analysis.



Coordination Compounds
Structural Features of [{MoO2(Lbi)}2(μ-O)] Based Oxomolybdenum(VI) Complexes with Five-Coordinate Molybdenum(VI)
Abstract
Structural features of eight binuclear complexes with the general formula [{MoO2(Lbin)}2(μ-O)] (I–VIII) (Lbi is a bidentate chelate ligand, n = 1–8), in which the coordination number of Mo atoms is five, are considered. The parameter τ = (A–B)/60, where A and B are the greatest bond angles among the ten bond angles at the Mo atoms in coordination pentahedra, can be used as a criterion characterizing the coordination polyhedron of the molybdenum atom in complexes I–VIII. The parameter τ is zero for an ideal square pyramid and unity for an ideal trigonal bipyramid.



Structure of an Unordinary 1-D Cobalt(II) Polymer Formed upon the Dissolution of the Mononuclear Co(OOPh)2[O(H)Me]4 Adduct in Chloroform
Abstract
The structure of the 1-D {[Co2(μ,η2-OOCPh)(μ-OOCPh)2(O(H)Me)2](μ-OOCPh)(HCCl3)}n polymer formed upon the dissolution of single crystals of the mononuclear Co(OOPh)2[O(H)Me]4 adduct containing coordinated labile methanol molecules in boiling chloroform was studied by X-ray diffraction.



Theoretical Inorganic Chemistry
Separation and Concentration of Rare Earths by Recycling Liquid–Liquid Chromatography with Multiple Sample Injection: A Computational Study
Abstract
Our computational studies into the separation of two- and three-component mixtures of rareearth salts by recycling liquid–liquid chromatography (RLC) with multiple sample injection show that this method considerably enhances metal separation efficiency and makes it possible to concentrate one of the components of mixture.



Theoretical Study of the Structure and Stability of Stepwise Hydrogenated Aluminum Clusters Al44Hn (n = 1−24)
Abstract
The energies and structural and spectroscopic characteristics of a series of model stepwise hydrogenated aluminum clusters Al44Hn (n = 1−24) obtained by successive introduction of hydrogen atoms into various surface positions of the Al44 cluster have been calculated by the density functional theory method (B3LYP). According to these calculations, the [Al39] surface layer of the cage retains a closed “nested doll” shape with a pentaatomic inner core [Al5]. With increasing n, both the surface layer and the core tend to experience increasing asymmetric distortions. The surface is corrugated and undergoes significant axial and equatorial extensions and contractions, some of the Al−H two-center terminal bonds are transformed into threecenter hydrogen bridges, and some Al atoms are displaced from the surface layer to the outer sphere and are bound to the surface through hydrogen bridges. The inner core [Al5] at n = 24 loses its bipyramidal shape and shifts to the surface layer so that one or two of its atoms are “built-in” into the concave regions of the surface layer. The calculated average energies of Al−H bonds are within the range ~55.5 ± 2.5 kcal/mol. The averaged energies of the Al44Hn → Al44Hn–2 + Н2 dissociation reactions with elimination of a hydrogen molecule are on the order of a few kilocalories per mole and are evidence of small exothermicity (or isothermicity) of these reactions. For the Al44H, Al44H2, and Al44H6 clusters as an example, the relative stabilities of isomers with terminal Al−H bonds in various nonequivalent positions of the [Al39] surface layer are compared.



Physical Methods of Investigation
MALDI-TOF Mass Spectrometry of Nanosized MoO2. Structure and Relative Stability of Isomers of Lower Molybdenum Oxide Cations
Abstract
MALDI-TOF was used to study molybdenum dioxide (MoO2) containing a nanosized fraction. The composition of cationic clusters of nonstoichiometric lower molybdenum oxides in the gas phase was determined, and the thermodynamic stabilities and configurations of isomers were calculated for selected symmetric molecular structures and for cations MoSO8+and Mo5O9+. Molecular orbital analysis was performed for two trigonal-bipyramidal clusters Mo5O8 and Mo5O9. Changes in molybdenum–molybdenum interatomic distances in going from MoO8+ and Mo5O9+ cations to neutral clusters are discussed.



Effect of the Synthesis Conditions on the Crystal, Local, and Electronic Structures of Ce2x4+Ce2-2x3+M2O7 + x (M = Zr, Hf)
Abstract
The effect of synthesis conditions (type of cations, annealing temperature, reductive or oxidative atmosphere) on the chemical composition and structure of compounds formed in the MO2–CeO2/Ce2O3 systems (M = Zr, Hf) was studied by X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The isothermal annealing of the precursors at temperatures below 1000°C in air gives Ce0.5M0.5O2 powders with fluorite type cubic structure (space group Fm3̅m). High-temperature annealing above 1000°C gives rise to additional tetragonal (space group P42/nmc) (for zirconates) or monoclinic (space group P21/a) (for hafnates) phases. The annealing in a hydrogen atmosphere affords the compounds Ce2x4+Ce2-2x3+M2O7 + x with an intermediate oxidation state of cerium and the x value depending on both the reduction conditions and the pre-annealing parameters. Vacuum annealing at 1400°C considerably decreases the content of Ce(IV) in the samples and affords a pyrochlore structure (space group Fd3̅m) with predominating Ce(III) cations.



The Effect of CdSe and InP Quantum Dots on the Interaction of ZnO with NO2 under Visible Light Irradiation
Abstract
Nanocomposites based on nanocrystalline ZnO and CdSe and InP nanocrystals (quantum dots) have been synthesized by chemical precipitation and high-temperature colloidal synthesis. The microstructure parameters of the oxide matrix and the size of the CdSe and InP nanocrystals have been determined. A correlation was established between the spectral dependence of the photoconductivity of nanocomposites and the optical absorption spectra of quantum dots. The influence of CdSe and InP quantum dots on the interaction of ZnO with NO2 under visible light irradiation has been studied. It has been shown that the synthesized nanocomposites can be used to detect NO2 under illumination with green light without additional thermal heating.



Magnetic Phase Diagram of Solid Solutions in the CoCr2S4–Cu0.5Ga0.5Cr2S4 System
Abstract
The magnetic phase diagram of solid solutions in the CoCr2S4–Cu0.5Ga0.5Cr2S4 system was constructed. The widest concentration range (0.38 < x < 1) in the diagram represents solid solutions based on the ferrimagnetic semiconductor CoCr2S4 (TC = 223 K), which exhibits unusual properties in the magnetic ordering region while measuring the temperature dependence of the dynamic susceptibility. The magnetic properties were studied with a Quantum Design PPMS-9 platform within the temperature range 5–300 K in a 100-Oe constant magnetic field and/or a varying (100-, 500-, and 1000-Hz) magnetic field with an amplitude of 1 Oe.



Synthetic Calcium Aluminosilicate Monolith: Transformations in an Aqueous Medium
Abstract
Investigations of the evolution of the phase composition, texture, and physical properties of SCAS monoliths with a set of spectroscopic, diffractometric, and thermal methods have shown that during the leach test an amorphous phase is accumulated and its composition changes. This is beneficial as regards stability of SCAS monoliths to the action of hydrosphere and makes them promising materials for the manufacture of matrices for immobilization of hazardous (toxic) wastes.



Physicochemical Analysis of Inorganic Systems
Physicochemical Interaction in the TlInSe2–TlInP2Se6 System
Abstract
Phase equilibria in the TlInSe2–TlInP2Se6 system have been studied for the first time by classic physicochemical analysis methods (differential thermal analysis (DTA), X-ray diffraction, and microstructural analysis (MSA)), and its phase diagram has been plotted. The system belongs to the eutectic type (Rooseboom V type) and forms boundary solid solutions based on the initial complex selenides.



Ternary Systems LiBr–LiVO3–Li2CrO4 and KBr–KVO3–K2CrO4
Abstract
The binary system KVO3–K2CrO4 and two ternary systems, LiBr–LiVO3–Li2CrO4 and KBr–KVO3–K2CrO4, were studied. In the ternary systems, the compositions and melting points of eutectic alloys were determined by differential thermal analysis: (49.0 mol % LiBr, 5.0 mol % LiVO3, 46.0 mol % Li2CrO4, 400°C) and (17.0 mol % KBr, 78.0 mol % KVO3, 5.0 mol % K2CrO4, 458°C), respectively.



Physical Chemistry of Solutions
Equilibrium Compositions of HF Solutions in N,N-Dimethylformamide
Abstract
For HF solutions in DMF, concentration-dependent fractions of DMF molecules (α(DMF)) that remain unassociated and that enter heteroassociates (HAs) of 1 : 1, 4 : 1, and 12 : 1 molecular stoichiometries were obtained by two independent methods, namely, from an analysis of IR spectra and by calculating the material balance. The experimental way was shown to be enough exact in determining the ratio between the solvent molecules in four different states up to ~83 mol % HF. The equilibrium compositions of HF–DMF solutions were estimated over the entire range of concentrations. Starting with [HF] of ~25 mol %, more than one-half HF molecules are associated, and at [HF] of ~50–92 mol %, at least 90% of the HF molecules are associated. The equilibrium composition of HF–organic solvent (Solv) solutions in which HAs of 1 : 1, 1 : 4, and 1 : 12 molecular stoichiometries are formed, can be described by a single set of α(HF–Solv) versus concentration plots.



Scandium Extraction with Benzo-15-crown-5 from Neutral Nitrate–Trichloroacetate Solutions
Abstract
A systematic study for scandium extraction with benzo-15-crown-5 in chloroform from trichloroacetate solutions has been performed. The presence of free trichloroacetic acid in extraction system has been found to prevent scandium transfer into organic phase. Scandium is extracted from neutral trichloroacetate solutions as partially hydrolyzed trichloroacetate complexes, the extracted compound includes two crown ether molecules. The presence of nitrate anions has no effect on scandium distribution ratios and nitrate anion is not involved in extracted compound composition. Optimal process conditions for selective scandium recovery from concentrated solutions of rare-earth nitrates in the presence of lithium trichloroacetate with high separation factors (>100) on the use of B15C5 as extractant have been determined.



The Effect of Concentration Parameters on Complexation in the Iron(0)–Iron(II)–Glycine–Water System
Abstract
The processes of formation of iron(II) complexes in aqueous glycine solutions in the pH range of 1.0–8.0 at 298 K and ionic strength of 1 mol/L (NaClO4) are studied using Clark and Nikolskii’s oxidation potential method. The type and number of coordinated ligands, the nuclearity, and the total composition of the resulting complexes are determined. The following complex species are formed in the investigated system: [Fe(OH)(H2O)5]+, [FeHL(H2O)5]2+, [Fe(HL)(OH)(H2O)4]+, [Fe(OH)2(H2O)4]0, [Fe2(HL)2(OH)2(H2O)8]2+, and [Fe(HL)2(H2O)4]2+. Their formation constants are calculated by the successive iterations method using Yusupov’s theoretical and experimental oxidation function. The model parameters of the resulting coordination compounds are determined.


