


Vol 61, No 11 (2016)
- Year: 2016
- Articles: 22
- URL: https://journal-vniispk.ru/0036-0236/issue/view/10178
Synthesis and Properties of Inorganic Compounds
SiO2–TiO2 binary aerogels: Synthesis in new supercritical fluids and study of thermal stability
Abstract
A comparative analysis of properties of SiO2–TiO2 binary aerogels prepared by supercritical drying using different supercritical fluids (isopropanol, hexafluoroisopropanol, methyl tert-butyl ether, and CO2) has been performed. The use of different supercritical fluids allows preparation of both homogeneous amorphous SiO2–TiO2 binary aerogels (by supercritical drying in hexafluoroisopropanol and CO2) and composite aerogels containing nanocrystalline anatase (by supercritical drying in isopropanol and methyl tert-butyl ether). The thermal treatment of the aerogels at temperatures up to 600°C does not lead to considerable change in the porous structure and phase composition of the aerogels.



How xerogel carbonization conditions affect the reactivity of highly disperse SiO2–C composites in the sol–gel synthesis of nanocrystalline silicon carbide
Abstract
A transparent silicon polymer gel was prepared by sol–gel technology to serve as the base in the preparation of highly disperse SiO2–C composites at various temperatures (400, 600, 800, and 1000°C) and various exposure times (1, 3, and 6 h) via pyrolysis under a dynamic vacuum (at residual pressures of ~1 × 10–1 to 1 × 10–2 mmHg). These composites were X-ray amorphous; their thermal behavior in flowing air in the range 20–1200°C was studied. The encapsulation of nascent carbon, which kept it from oxidizing in air and reduced the reactivity of the system in SiC synthesis, was enhanced as the carbonization temperature and exposure time increased. How xerogel carbonization conditions affect the micro- and mesostructure of the xerogel was studied by ultra-small-angle neutron scattering (USANS). Both the carbonization temperature and the exposure time were found to considerably influence structure formation in highly disperse SiO2–C composites. Dynamic DSC/DTA/TG experiments in an inert gas flow showed that the increasing xerogel pyrolysis temperatures significantly reduced silicon carbide yields upon subsequent heating of SiO2–C systems to 1500°C, from 35–39 (400°C) to 10–21% (1000°C).



Preparation of double pyrophosphates in aqueous systems chromium(III) salt−sodium pyrophosphate
Abstract
The specifics of preparation of chromium double pyrophosphates in systems Cr(NO3)3–Na4P2O7–H2O, CrCl3–Na4P2O7–C2O, and KCr(SO4)2–Na4P2O7–H2O are discussed. Changes in pH of the mentioned systems have been studied depending of the component ratio. The effects of the deposition duration and sodium pyrophosphate concentration on pH have been studied for system Cr(NO3)3–Na4P2O7–H2O. Phase composition has been determined for compounds prepared in systems Cr(NO3)3–Na4P2O7–H2O and KCr(SO4)2–Na4P2O7–H2O. It has been found that the acid residue anions do not substantially affect the formation of a continuous series of compounds consisting of hydroxy and hydro combinations of chromium ions and pyrophosphate ion, whereas cations can have an effect. System KCr(SO4)2–Na4P2O7–C2O is less sensitive to reaction conditions than systems in which normal salts Cr(NO3)3 and CrCl3 act as a source of Cr3+ cation. A product stable over time can be prepared in system KCr(SO4)2–Na4P2O7–C2O; after heat treatment at 900°C, it is a mixture of KCrP2O7 and a-CrPO4 phases.



Influence of La(III) on the reactivity and sensor properties of nanocrystalline SnO2
Abstract
Synthesis of Sn(IV) and La(III) based nanocomposites has been effectuated. According to the data obtained by XRD and TPR-H2 methods, it is supposed that La in nanocompites is located in amorphous La2Sn2O7 segregation. The effect of La(III) on the adsorption properties of SnO2 surface and concentration of chemisorbed oxygen was determined. Sensor properties of obtained materials towards 10 ppm of CO in air were studied by in situ DC conductance measurements. It is shown that La introduction allows to increase sensor response of SnO2 during CO detection in air.



Formation of carbon phases under hydrothermal conditions
Abstract
The formation of carbon phases by reacting formaldehyde with sulfuric acid under hydrothermal conditions was studied. The final products of the reaction were found to be amorphous carbon, diamond-like carbon, α- and β-graphite phases, fullerenes C60 and C70, fullerites, carbolite, and chaoite. Hydrocarbons of various compositions were detected in reaction products, namely cyclic hydrocarbons, including aromatic ones, and naphthene hydrocarbons. A formation scheme is suggested for carbon structures.



Effect of the introduction procedure and concentration of yttrium cations on the crystal structure of (1–x)ZrO2 · xY2O3 powders
Abstract
An integrated study of the crystal and local structures of complex oxides (1–x)ZrO2 · xY2O3 (x = 0.005–0.18, YSZ), precipitated from solutions of metal salts and annealed in air, was carried out. For the use of deposition from solutions, reverse co-precipitation was found to be the method of choice for introducing yttrium cations into YSZ, ensuring the maximum stabilization effect of high-temperature phases. An increase in the yttrium content induces polymorphic transformations, monoclinic phase (P21/a) → tetragonal phase (P42/nmc) (for x = 0.02) → cubic phase (Fm\(\bar 3\)m) (for x = 0.08), in the samples prepared at temperatures of ≤1000°C. A Raman study of the local structure of YSZ powders confirmed the formation of a single-phase tetragonal structure for the 2YSZ and 3YSZ samples and identified trace amounts of the tetragonal phase for the 8YSZ and 18YSZ samples with the cubic structure.



Synthesis of nanosized iron(III) oxide and study of its formation features
Abstract
Nanosized iron(III) oxide has been obtained by thermolysis of iron(III) acetylacetonate using diphenyl ether as a dispersion medium. It has been shown that increase in thermolysis temperature from 180 to 250°C allows one to half the average size of Fe2O3 nanoparticles. The introduction of surfactant into dispersion medium also leads to decrease of the average size of particles down to 4 nm. The phase composition of the prepared nano-Fe2O3 has been established, the possibility to reduce nano-Fe2O3 into iron metal has been shown by temperature-programmed reduction



Morphology of calcium carbonate prepared via homogeneous synthesis
Abstract
The morphology of calcium carbonate prepared via homogeneous synthesis from carbonate–chloride solutions was studied. The precipitates were investigated by scanning electron microscopy (SEM) and Xray diffraction. The effects of the ratio between the chloride and carbonate components of a solution on the morphology, crystal structure, and particle size of precipitated calcium carbonate were illustrated.



Coordination Compounds
Four- and five-coordinate metal atoms in a supramolecular polymeric assembly of silver(I) with (4-methyl-2-quinolylthio)acetate
Abstract
The coordination compound [Ag2L2(H2O)2] · 2H2O (I), L = C12H10NO2S has been synthesized by the reaction of AgNO3 with 4-methyl-2-quinolylthioacetic acid (HL) preliminarily neutralized with an equimolar amount of NBu4OH. Its crystal structure has been determined, and luminescence properties have been studied. Crystals of I are monoclinic, space group C2/c, a = 31.239(6) Å, b = 12.056(2) Å, c = 16.846(3) Å, β = 122.17(3)°, V = 5370.4(2) Å3, ρcalc = 1.861 g/cm3, Z = 16. The structure is formed by two crystallographically nonequivalent silver atoms Ag(1) and Ag(2) and two tridentate bridging ligands L coordinated through the S, N, and O atoms. These atoms, together with water molecules, form the coordination environments of the metal atoms with CN = 5 and 4, respectively. The Ag+ ions and the tridentate ligands form infinite [Ag4L4]n bands extended in the [001] direction. The presence of outer-sphere water molecules involved in O–H···O hydrogen bonding is responsible for the formation of a supramolecular framework structure. The photoluminescence spectrum of compound I shows two bands at ~450 and ~485 nm corresponding to the blue spectral range.



Crystal structure of EuCeCuS3
Abstract
The crystal structure of EuCeCuS3, a complex sulfide synthesized for the first time, has been solved using X-ray powder diffraction data. Crystals are rhombic, space group Pnma, Ba2MnS3 structural type, a = 8.1023(1) Å, b = 4.0386(1) Å, c = 15.9022(2) Å, V = 520.36(1) Å3, Z = 4, ρcalcd = 5.767 g/cm3. The Eu,CeS7 polyhedron incorporates the Eu and Ce atoms, which are randomly disordered over two crystallographic sites. The bond lengths dEu,Ce–S range from 2.885 to 3.044 Å.



Structural features of monomeric octahedral d2-rhenium(V) monooxo complexes with the oxygen atoms of monodentate acido ligands OЕRn– (n = 1, 2; Е = Si, B, S; R = Me3, F3, О2CF3)
Abstract
Some structural features of mononuclear octahedral rhenium(V) oxo complexes (I–VI) with the oxygen atoms of monodentate acido ligands OЕRn– (n = 1, 2; Е = Si, B, S; R = Me3, F3, О2CF3) have been considered. The Re–O(OЕR)trans bonds in complexes I–V (Е = Si, B; R = Me3, F3) are elongated due to the structural manifestation of the trans-effect of multiply bonded oxo ligands. The Re–O{S(O2CF3)}cis bond in cis-position to the O(oxo) ligand in complex VI is shortened in comparison with Rе–O(ST).



New binuclear complex of bis(2,4,6,8-tetramethyl-2,4,6,8- tetraazabicyclo(3.3.0)octane-3,7-dione-O,O')-diaquatetrakis(nitrato-O,O')-dimanganese(II) monohydrate: Synthesis and crystal structure
Abstract
The centrosymmetric binuclear manganese(II) nitrate complex with a bicyclic bis-carbamide, namely, 2,4,6,8-tetramethyl-2,4,6,8-tetraazabicyclo(3.3.0)octane-3,7-dione, or mebicar (Mk) [Mn(C8H14N4O2)(H2O)(NO3)2]2 · H2O (I), has been synthesized for the first time. The structure of complex I has been solved (CCDC no. 1435139). Crystals of complex I are monoclinic, space group P21/c, a = 12.8108(11) Å, b = 10.0662(2) Å, c = 18.6367(17) Å, β = 136.512(16)°, V = 1654.0(4) Å3, ρcalcd = 1.659 g/cm3, Z = 2. Each manganese atom is coordinated to the two oxygen atoms of two Mk molecules related by the symmetry codes (1–x, 2–y, 1–z) and to two bidentate nitrate anions and one water molecule. The coordination polyhedron of the manganese atom is a strongly distorted pentagonal bipyramid. The Mn···Mn distance in the complex is 8.7261(9) Å.



Structure of two new compounds of fluoroquinolone antibiotics with mineral acids
Abstract
New compounds of sparfloxacin (C19H22F2N4O3, SfH) and levofloxacin (C18H20FN3O4, LevoH) with mineral acids, namely, sparfloxacinium bromide (SfH · HBr, I) and levofloxacindium diperchlorate (LevoH · 2HClO4, II), have been synthesized and characterized by X-ray diffraction. Crystallographic data are a = 7.7151(7) Å, b = 26.109(3) Å, с = 10.008(1) Å, β = 103.556(1)°, V = 1959.7(3) Å3, space group P21/n, Z = 4 for I and a = 9.727(6) Å, b = 20.440(12) Å, с = 12.286(7) Å, β = 104.327(8)°, V = 2367(2)Å3, space group P21, Z = 4 for II. The structures of these compounds are stabilized by intra- and intermolecular hydrogen bonds and π–π interaction between SfH2+ or LevoH32+ ions.



Theoretical Inorganic Chemistry
Quantum-chemical modeling of lithiation of a silicon–silicon carbide composite
Abstract
With the aim of searching for promising anode materials for lithium-ion batteries, quantum-chemical modeling of the introduction of lithium into a silicon layer supported by nitrogen-doped silicon carbide at Li: Si ratios of 1: 1, 2: 1, and 3: 1 has been performed by the density functional theory method with inclusion of gradient correction and periodic boundary conditions. It has been demonstrated that the absorption of lithium by silicon is energetically more favorable than the formation of a metal layer on the silicon surface. As the lithium concentration increases, the energy difference decreases; i.e., the introduction of lithium into silicon becomes increasingly less favorable, the network of silicon atoms is broken down into smaller and smaller pieces, while the layer thickness increases threefold.



Physical Methods of Investigation
Study of tin dioxide–sodium stannate composite obtained by decomposition of peroxostannate as a potential anode material for lithium-ion batteries
Abstract
A tin dioxide–sodium stannate composite has been obtained by the thermal treatment of sodium peroxostannate nanoparticles at 500°C in air. X-ray powder diffraction study has revealed that the composite includes crystalline phases of cassiterite SnO2, sodium stannate Na2Sn2O5, and sodium hexahydroxostannate Na2Sn(OH)6. Scanning electron microscopy has shown that material morphology does not change considerably as compared with the initial tin peroxo compound. Electrochemical characteristics have been compared for the anodes of lithium-ion batteries based on tin dioxide–sodium stannate composite and anodes based on a material manufactured by the thermal treatment of graphene oxide–tin dioxide–sodium stannate composite at 500°C in air.



Rhodium complexation with phosphoryl-containing calix[4]resorcine
Abstract
Complexation of rhodium compounds with phosphoryl-containing calix[4]resorcine in ethanol and acetone has been considered. The structure and properties of the synthesized complexes have been studied by IR and Raman spectroscopy, 1H and 31P NMR, EPR, UV-Vis spectroscopy, and TG/DSC. The effect of the solvent nature and conformation of a macrocyclic ligand on the structure of the resulting complexes has been observed. It has been demonstrated that one of the key factors responsible for complexation in EtOH is self-association of the ligand without the participation of the solvent. Complex formation in acetone is determined by its high ionizing ability. In diamagnetic complexes, the macrocyclic ligand is coordinated to the central atom through the phosphoryl oxygen atoms. For triaquatrichlororhodium in an aprotic medium, coordination occurs through the oxygen atoms of resorcinol moieties, which is accompanied by the formation of resorcinol radical anion and conversion of the diethoxyphosphorylaryl groups into ethoxyhydroxyphosphorylaryl moieties.



Kinetics of the formation of precipitates and the physicochemical properties of technetium-99 and rhenium sulfides according to small-angle X-ray scattering and ultramicrocentrifugation data
Abstract
The interaction of technetium and rhenium with sulfides in aqueous solutions was studied by small-angle X-ray scattering and ultramicrocentrifugation. It was shown that, although the stoichiometry of technetium sulfide corresponds to the formula Tc2S7–x, the oxidation state of technetium in it is +4 and the excess sulfur is bound into a disulfide group so that its formula can correctly be written as [Tc3(µ3-S)(µ2-S2)3(S2)(3n–n)/n)]n. The determination of the solubility of technetium sulfide is complicated by its tendency to form colloids, which was the reason why the above methods were chosen to find features of its formation and describe its solubility in solutions.



Synthesis of nanodispersed anatase by tetrabutoxy titanium hydrolysis
Abstract
Nanodispersed titanium oxyhydrate was obtained by tetrabutoxy titanium hydrolysis in the presence of a chelating agent, acetylacetone. The introduction of a chelating agent to tetrabutoxy titanium hydrolysis in a water–ethanol mixture allows one to control the hydrolysis rate. According to X-ray powder diffraction data, amorphous titanium oxyhydrate after annealing at 400°C transforms to anatase, the crystallites of which are 6.2–8.4 nm in size. Transmission electron microscopy showed that the anatase particles are close to spheres 5–9 nm in diameter. The amorphous materials were studied by differential thermal analysis, thermogravimetric analysis, and mass spectrometric analysis of released gases. The benzene adsorption by the produced materials was determined. The nitrogen adsorption isotherms of two samples were constructed, and the specific surface area of the anatase particles and the pore size were found (148.5 and 98 m2/g, and 4.4 and 4.0 nm, respectively).



Synthesis and study of high-temperature heat capacity of erbium orthovanadate
Abstract
Orthovanadate ErVO4 has been prepared by solid-phase synthesis from a stoichiometric mixture of high pure V2O5 and chemically pure Er2O3 by multistage calcination in air in the temperature range 873–1273 K. The effect of temperature (380–1000 K) on the heat capacity of orthovanadate ErVO4 was studied by hightemperature calorimetry. Thermodynamic properties of erbium orthovanadate (enthalpy change H°(T)–H°(380 K), entropy change S°(T)–S°(380 K), and reduced Gibbs energy Φ°(T)) have been calculated from the experimental Cp = f(T) data. It has been shown that the specific heat varies in a row of oxides and orthovanadates of Gd-Lu naturally depending on the radius of the R3+ ion within the third and fourth tetrads.



Studies of natural kaolinite and its modified forms
Abstract
Modified forms of the natural and annealed at 700°C kaolinite have been fabricated by treatment using hydrochloric acid of different concentrations. The resulting samples were investigated using X-ray fluorescence spectroscopy, X-ray diffraction analysis, IR spectroscopy, and positron annihilation spectroscopy, scanning electron microscopy, etc. The dependencies of elements contents, dye adsorption, specific surface area, and specific internal volume on the concentration of hydrochloric acid have been determined. It has been demonstrated that the changes in the structure of annealed kaolinite were significantly increased by the increase of the concentration of acid, and also there were proportional changes in the values of specific surface area, internal volume, and dye adsorption. Changes in the structural parameters of natural kaolinite depend on the acid concentration in a less degree. Modification with acid results in obtaining solutions that contain metal chlorides. Precipitation of these metals in the form of oxides on the surface of kaolinite particles results in fabrication of new sorbents, whose yield is close to the quantitative one, whereas the kaolinite sorption characteristics become improved. Further kaolinite modification by cellulose under similar conditions results in fabrication of a new, more efficient sorbent. It has been demonstrated that natural kaolinite treated with 12% hydrochloric acid had lower friction coefficient than the annealed one.



Physicochemical Analysis of Inorganic Systems
Phase diagram of the NaF–CaF2 system and the electrical conductivity of a CaF2-based solid solution
Abstract
The phase diagram of the NaF–CaF2 system was studied by thermal analysis and X-ray powder diffraction analysis with the determination of the chemical composition. The system was found to be of the eutectic type. A narrow range of the existence of solid solution Ca1–xNaxF2–x was established. The NaF solubility reaches a maximal value of x = 0.035 at 1200 ± 50°C (the temperature at which there is a diffuse phase transition in fluorite). At 920 ± 25°C, the NaF solubility reaches a minimum (<0.4 mol %) and increases again to 2.2 ± 0.2 mol % at a eutectic temperature (818°C). The ionic conductivity increases by three orders of magnitude after adding NaF to CaF2.



Physical Chemistry of Solutions
Extraction of rare earth elements with 2-[2'-(methoxydiphenylphosphoryl)phenyldiazenyl]-4-tert-butylphenol in the presence of 1-butyl-3-methylimidazolium and trioctylmethylammonium picrates
Abstract
Extraction of micro amounts of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y with solutions of 2-[2'-(methoxydiphenylphosphoryl)phenyldiazenyl]-4-tert-butylphenol in 1,2-dichloroethane in the presence of 1-butyl-3-methylimidazolium and trioctylmethylammonium picrates has been studied. The stoichiometry of extracted complexes has been determined, the effect of HNO3 concentration in aqueous phase on the efficiency of rare earth elements recovery into organic phase has been considered.


