Density and microhardness of glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The density d at a temperature of 25°C is measured by the hydrostatic weighing method, the Vickers microhardness H _V is determined, and the fluctuation free volume fraction f _g is calculated for glasses in the SrO-B₂O₃-SiO₂ system with a constant strontium oxide content in the range from 35 to 45 mol %. It is demonstrated that the quantities H _V and f _g decrease and the density d increases with an increase in the SrO content.     

AC Conductivity and Dielectric Behavior of Silicophosphate Glass Doped by Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>

Silicophosphate glasses of nominal composition (P₂ O ₅ 50%-SiO₂ 30%-Na₂O 20%) and Nd₂ O ₃ additive (0.5 and 2 wt%) were prepared and dielectric behavior has been studied over a temperature range (302–483 K) in the frequency range (0.5 - 3243 kHz). Frequency dependence of AC conductivity (σ _ac), has been explored using the universal power law. Disparity of the frequency exponent (s) with temperature was examined in terms of diverse conduction mechanisms. The principal conduction mechanisms were found correlated to both barrier hopping (CBH) and quantum mechanical tunneling (QMT) models. Temperature dependence of σ _ac (ω) showed a linear increase with different frequencies. In addition, the capacitance, loss tangent, dielectric loss and dielectric constant were calculated over variable temperature ranges and frequencies.     

Stability of polymer structures based on fullerene C<Subscript>60</Subscript> under their oxidation with oxygen

A comparative study of the oxidative destruction of the monomer face-centered cubic (FCC) lattice and various polymer [dimeric (D), orthorhombic (O), tetragonal (T), and rhombohedral (R)] phases of C₆₀ in an atmosphere of oxygen has been performed in the temperature range of 100–500°C with the use of a flow microunit connected to a gas chromatograph. From direct measurements of the content of CO₂ in the gaseous products of destruction, the temperature dependences of oxidation rates are measured for the materials under study. It has been established that, with respect to stability against oxidative destruction, different forms of C₆₀ may be arranged as follows: the monomer FCC phase of C₆₀ > D > O > T > R. The reasons behind this tendency are discussed.     

Cluster Self-Organization of Intermetallic Systems: Two-Layer Quasi-Spherical Nanocluster Precursors K69 and K26 in the Crystal Structure of Li<Subscript>26</Subscript>Na<Subscript>58</Subscript>Ba<Subscript>38</Subscript> (<Emphasis Type="Italic">cF</Emphasis>488)

The geometric and topological analysis of the crystal structure of intermetallic Li₂₆Na₅₈Ba₃₈ (cF488, a = 27.335 Å, V = 20 424 ų, F-43m) is carried out using computer methods (ToposPro software package). The analysis method is based on determining the chemical composition and structure of an intermetallic cluster precursor and constructing a basic 3D network of the structure in the form of a graph whose nodes correspond to the position of their centers of gravity. Using the method of the complete decomposition of the 3D factor graph of the crystal structure into cluster substructures, we find two types of framework-forming nanoclusters, namely, K69 of the 1@16@52 composition and K26 of the 0@4@22 composition with point symmetry g =–43m. The symmetric and topological code of self-assembly of 3D structures from nanocluster precursors is reconstructed in the following form: primary chain → microlayer → microframework. Clusters Ba5, Na₆(Na₄), and Na₂В are determined as spacers occupying voids in the 3D framework of nanoclusters K69 and K26.     

Modeling Self-Organization Processes in Crystal Forming Systems. Symmetry and Topology Codes of Cluster Self-Assembly of Crystal Structure of Na<Subscript>44</Subscript>Tl<Subscript>7</Subscript> (Na<Subscript>6</Subscript>Tl)

The geometrical and topological analysis of the crystal structure of intermetallide Na₄₄Tl₇ (Na₆Tl, a = 24.154 Å, V = 14091.8 ų, space group F-43m) is carried out. The algorithms of the combinatorial-topological analysis, which ensure the recovery of the symmetrical and topological code (program) of the cluster self-assembly of the crystal structure of an intermetallide, are developed. The topological type of the basic 3D network for two types of cluster precursors corresponds to a simple cubic 3D network P _c with CN = 6 and basic 2D network of type 4⁴. There are eight cluster precursors in the unit cell: four K86 and four K50. The cluster precursor K86 made from 86 atoms is formed from eight icosahedra i-TlNa₁₂ linked by the apices. The center of the cluster precursor K86 is at the position 4a (0, 0, 0) with the point symmetry g = –43m. The 50-atomic cluster precursor K50 consists of six i-TlNa₁₂ icosahedra. The center of the cluster precursor K50 is in the partial position 4b (0, 0, 0) with the point symmetry g = –43m. The symmetrical and topological codes of the self-assembly of 3D structures from nanocluster precursors K86 and K50 are reconstructed in the following form: primary chain → microlayer → microframework.     

Synthesis and investigation of Ag-Cs-<Emphasis Type="Italic">X</Emphasis> (<Emphasis Type="Italic">X</Emphasis> = I,Br, Cl) glasses doped with Er<Superscript>3+</Superscript>

The glass formation and crystallization of ErI₃-doped melts in the Ag-Cs-Pb-X (X = I, Br, Cl) are investigated in the section corresponding to the cation ratio Ag: Cs: Pb = 59: 39: 2 with ErI₃ contents of 0.2–7.5 mol %. The glass transition, crystallization, and melting temperatures are determined for a number of compositions. The primary crystalline phases that precipitate from melts upon crystallization are identified. It is demonstrated that the iodide, bromide, and chloride glasses containing up to 0.5 mol % ErI₃ have the lowest crystallization ability. An increase in the ErI₃ content leads to the precipitation of unidentified erbium-containing phases from melts upon cooling and to an increase in the crystallization ability of glasses. The spectral and luminescence properties of the glass of the composition 52Ag · 17AgCl · 39CsBr · 2PbCl₂ + 0.5 mol % ErI₃ are studied in the range of the ⁴ I _13/2 → ⁴ I _15/2 transition of the Er³⁺ ion. It is found that the lifetime of the ⁴ I _13/2 → ⁴ I _15/2 level of the Er³⁺ ion is equal to 10 ms.     

Thermal behavior of layered perovskite-like compounds in the Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>-BiFeO<Subscript>3</Subscript> system

The thermal properties of compounds of the general formula Bi _{m + 1} Fe _{m ? 3} Ti₃O_{3m + 3}, which are layered perovskite-like phases of the Aurivillius type, are investigated as a function of their composition. It is demonstrated that the temperature of decomposition of the Bi _{m + 1} Fe _{m ? 3} Ti₃O_{3m + 3} compounds decreases with an increase in the thickness of perovskite-like layers alternating in the structure and that the composition dependence of the temperature of the structural transition observed in these compounds exhibits a more complex behavior. The linear thermal expansion coefficients of all the compounds under investigation are found to be virtually independent of the composition.     

Crystallization and thermal transformations in nanocrystals of the YPO<Subscript>4</Subscript>-LuPO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

Nanocrystals of yttrium lutetium phosphates of the general formula Y_1?x Lu_xPO₄ · nH₂O are synthesized. The temperature dependence of the nanocrystal size is investigated in the range 200–1100°C. The formation of a series of continuous solid solutions belonging to the tetragonal crystal system is revealed, and the limits of their thermal stability are determined.     

Raman spectra and surface structure of CaO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass leached in potassium hydroxide solutions

It is difficult to research on the surface structure of amorphous phase in fly ash during leaching reaction due to crystalline phase and complex structure. In the present work, in order to reveal the effects of leaching reaction on the surface structure of amorphous phase in fly ash, the modelling CaO-Fe₂O₃-Al₂O₃-SiO₂ glass was prepared by the traditional melting methods. The leaching reaction of CaO-Fe₂O₃-Al₂O₃-SiO₂ glass with 7.5 M KOH was investigated by spectroscopy, spectrophotometer and wet chemical method. The results show that the content of Q ¹, Q ², Q ³ and Q ⁴ of glass without corrosion was 4.21, 9.51, 23.03 and 52.55%, respectively, which shows that the network polymerization of glass is compact. The leaching reaction of glass can be described by the following equation: dS/dt = k/(r + S ₀). Leaching in KOH for various times induces the content of Q ⁴ and Q ¹ to be decreased, and Q ² and Q ³ increased, resulted in the depolymerization of network and the surface glass dissolved in alkaline solution to form a gel phase. In stage one of leaching reaction, the rate of iron ion leached from glass surface was slow, which resulted in the small slope of straight-line relationship of leaching curve. In the following stage, the leaching rate of iron ion increased with the prolongation of time.     

Crystal structure and thermal expansion of ammonium pentaborate NH<Subscript>4</Subscript>B<Subscript>5</Subscript>O<Subscript>8</Subscript>

Anhydrous ammonium pentaborate NH₄B₅O₈ has been synthesized by thermal dehydration of larderellite NH₄[B₅O₇(OH)₂] · H₂O at a temperature of 290°C for 7 h. The crystal structure has been determined from the X-ray powder diffraction data: a = 7.58667(5) Å, b = 12.00354(8) Å, c = 14.71199(8) Å, R _p = 6.23, R _wp = 7.98, R _B = 12.7, R _F = 8.95, and β-KB₅O₈ structure type. The double interpenetrating framework is formed by pentaborate groups, each consisting of a boron-oxygen tetrahedron and four triangles, in which all oxygen atoms are bridging. The thermal behavior of the NH₄B₅O₈ compound has been investigated using thermal X-ray diffraction. As for other pentaborates of this type, the thermal expansion of the NH₄B₅O₈ compound is anisotropic and reaches a maximum along the a axis. The thermal expansion coefficients are as follows: α _a = 39 × 10^?6, α _b = 6 × 10^?6, α _c = 20 × 10^?6, and α _V = 65 × 10^?6 °C^?1.     

CO and CO<Subscript>2</Subscript> methanation over Ni catalysts supported on alumina with different crystalline phases

The effect of alumina crystalline phases on CO and CO₂ methanation was investigated using alumina-supported Ni catalysts. Various crystalline phases, such as α-Al₂O₃, θ-Al₂O₃, δ-Al₂O₃, η-Al₂O₃, γ-Al₂O₃, and κ-Al₂O₃, were utilized to prepare alumina-supported Ni catalysts via wet impregnation. N₂ physisorption, H₂ chemisorption, temperature-programmed reduction with H₂, CO₂ chemisorption, temperature-programmed desorption of CO₂, and X-ray diffraction were employed to characterize the catalysts. The Ni/θ-Al₂O₃ catalyst showed the highest activity during both CO and CO₂ methanation at low temperatures. CO methanation catalytic activity appeared to be related to the number of Ni surface-active sites, as determined by H₂-chemisorption. During CO₂ methanation, Ni dispersion and the CO₂ adsorption site were found to influence catalytic activity. Selective CO methanation in the presence of excess CO₂ was performed over Ni/γ-Al₂O₃ and Ni/δ-Al₂O₃; these substrates proved more active for CO methanation than for CO₂ methanation.     

SHS of Y<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>-based mineral-like ceramics: Influence of green density

Explored was the influence of compacting pressure (P) and green density (ρ) on the properties of Zr-doped mineral-like pyrochlore ceramics Y₂(Ti_{1 – x} Zr _x )₂O₇ (x ≤ 0.3) prepared by SHS method. The optimal ρ values that provide minimal porosity and maximal mechanical strength of synthesized ceramics were found. An increase in ρ was found to decrease combustion temperature and increase pyrochlore lattice parameter a. Green density was also found to affect phase composition of the SHS-produced ceramics under study.     

Solution-Combustion Synthesis of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> as a Cathode Material for Lithium-Ion Batteries

A cathode material for lithium-ion batteries–LiNi_1/3Co_1/3Mn_1/3O₂–was prepared by solution combustion synthesis and characterized by XRD, SEM, and galvanostatic charge/discharge cycling. The sample calcined at 950°C for 10 h showed best charge/discharge performance. An initial discharge capacity (C) of 150.5 mA h g^–1 retained 95.7% of its value after 75 charge/discharge cycles at I_c = 14 mA g^–1 (0.2C rate), I_d = 70 mA g^–1 (0.5C rate).     

Transport properties of solid electrolytes based on <Emphasis Type="Italic">Me</Emphasis>Sm<Subscript>2</Subscript>S<Subscript>4</Subscript>

The solid-solution regions in the MeSm₂S₄-MeS and MeSm₂S₄-Sm₂S₃ (Me = Ca, Ba) systems are revealed. The average ion, cation, and anion transport number of the synthesized solid electrolytes xSm₂S₃[Ca(Ba)S] · (100 ? x)Ca(Ba)Sm₂S₄ (x = 1?10 mol %) are determined by the electromotive force (emf) method with the use of concentration cells with and without transfer. In the phases under investigation, the ion transfer in the temperature range 673–723 K is provided by sulfide ions (\(t_{S^2 } \) = 1.00±0.02). The diffusion coefficients of S^2? ions in the solid electrolytes are determined by potentiostatic chronoamperometry. A vacancy mechanism of defect formation is proposed. It is demonstrated that the transport characteristics of the solid electrolytes based on the CaSm₂S₄ compound are worse than those of the solid electrolytes based on the BaSm₂S₄ compound.     

Crystal structure of Pb<Subscript>6</Subscript>O[(Si<Subscript>6</Subscript>Al<Subscript>2</Subscript>)O<Subscript>20</Subscript>]

The crystal structure of Pb₆O[(Si₆Al₂)O₂₀)] is investigated using X-ray diffraction. The compound has tetragonal symmetry, space group I4/mmm, a = 11.7162(10) Å, c = 8.0435(12) Å, and V = 1104.13(2) ų. The structure is refined to R ₁ = 0.036 for 562 unique reflections with [F ₀] ≥ 4σF. The structure contains two symmetrically independent positions of the Pb²⁺ cations coordinated by five O atoms (Pb²⁺-O^2? = 2.34–2.68 Å). The TO₄ tetrahedra (T = Si, Al) form tubular [(Si₆Al₂)O₂₀] chains extended along the c axis. The O₄ oxygen atom is not bonded to the Si and Al atoms and is octahedrally coordinated by six Pb atoms with the formation of an oxo-centered OPb₆ octahedron. The assumption is made that, in some of lead silicate and aluminosilicate glasses, a number of oxygen atoms are located outside the tetrahedral structure and represent segregation centers of the Pb²⁺ cations due to the formation of oxo-centered complexes.     

Synthesis and Thermoelectric Properties of Ceramics Based on Bi<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Co<Subscript>1.7</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Oxide

Layered ceramics based on bismuth–calcium cobaltite with varied cobalt oxide contents is synthesized by the solid-phase method, the ceramics phase composition is determined, and the microstructure, thermal expansion, electroconductivity, and thermal electromotive force are investigated. The formation of just one compound, ternary oxide composed of Bi₂Ca₂Co_1.7O _y , is established within the quasi-binary Bi₂Ca₂O₅–CoO _z system. The effect of the cobalt oxide content on the Bi₂Ca₂Co _x O _y ceramics’ microstructure and physicochemical properties is analyzed. The single-phased ceramic sample Bi₂Ca₂Co_1.7O _y demonstrated the highest power factor value among all the investigated samples—26.0 μW/(m K²) at a temperature of 300 K. This sample showed the lowest value of the thermal linear expansion coefficient of 9.72 × 10^–6 K^–1.     

Synthesis and crystal structure of the low-temperature modification of Li<Subscript>12</Subscript>Zn<Subscript>4</Subscript>(P<Subscript>2</Subscript>O<Subscript>7</Subscript>)<Subscript>5</Subscript>

The crystal structure of a low-temperature modification of the Li₁₂Zn₄(P₂O₇)₅ compound has been determined by full-profile analysis from the X-ray powder diffraction data. The compound crystallizes in the monoclinic crystal system (a = 5.130(1) Å, b = 13.454(1) Å, c = 8.205(1) Å, β = 90.36(1)°, space group P2₁/n, Z = 4) and has a framework structure in which the zinc and lithium atoms statistically occupy equivalent positions.     

Perovskite-type MgCNi<Subscript>3</Subscript> superconductors as prepared by combined sintering-ETE process and SHS reaction: Structural and superconducting properties

Complete conversion of the elements into the Perovskite-type MgCNi₃ compound has been achieved in the following two-stage process: (1) isothermal treatment (sintering) of starting powder compacts and (2) their subsequent electrothermal explosion (ETE) under uniaxial pressure. For comparison, similar reaction was also performed by mere sintering and by SHS. The bulk anti-perovskite MgCNi₃ superconductor was prepared from Mg-C-3Ni powder compacts. Isothermal treatments failed in the formation of the perovskite-type compound as a sole product. The hexagonal MgCNi₃ phase obtained by combined sintering-ETE route was found to have the lattice constants a = 3.0845 Å and c = 3.5259Å. The grains of the MgCNi₃ obtained by sintering-ETE process are fine, well compacted, and more homogenous than those prepared by sintering or SHS. The structure of materials was characterized by XRD, SEM, and EDS. The superconducting properties were detected using the temperature dependence of magnetization M as measured in ZFC and FC experiments at H = 15 Oe. For our MgCNi₃, the superconducting transition temperature T _c is around 7 K.     

Partition of <Emphasis Type="Italic">n</Emphasis>-Butanol Among Phases and Solubilization Ability of Winsor type III Microemulsions

The partition of n-butanol in Winsor type III (W-III) microemulsions was investigated in this work. Three kinds of anionic surfactants (sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (DSS), and sodium dodecyl benzene sulfonate (SDBS)) and two kinds of anionic/cationic surfactant mixtures (SDS/octadecyl trimethyl ammonium chloride (OTAC) mixtures and DSS/OTAC mixtures) were studied. Internal standard gas chromatography was employed in n-butanol content analysis. The results showed that no water exists in the excess oil (EO) phase and no oil exists in the excess water (EW) phase. For the W-III microemulsions obtained by salinity scanning, relatively constant n-butanol content in the EO (11–12 v%) and EW (1–4 v%) was found under different salinities. Accurate measurement of n-butanol content in each phase is important for those systems having low solubilization ability. For the W-III microemulsions prepared using SDS/OTAC surfactant mixture, the percentage of n-butanol distributed into the interfacial layer decreased while the fraction of n-butanol in the interfacial layer first increased sharply and then tended to be stable with the addition of n-butanol. For the different optimum W-III microemulsion systems tested, most of the surfactant-to-alcohol molar ratio data are near 1:3, but obvious deviation could be observed for some data. On the basis of the accurate measurement of n-butanol content in the EO and EW phases, the standard free energy, ΔG _o→in ^* (T = 298.15 K) of n-butanol transferring from the EO phase to the interfacial region was calculated. The results show negative ΔG _o→in ^* values. For microemulsions with the same components, n-butanol content is an important factor influencing the ΔG _o→in ^* value, and a high absolute value of ΔG _o→in ^* leads to high solubilization ability.     

Effect of the Molecular Structure on the Adsorption Properties of Cationic Surfactants at the Air–Water Interface

The surface activity and thermodynamic properties of adsorption at the air–water interface of two series of cationic surfactants based on isourea: the O-dodecyl-N,N′-diisopropylisourea hydrochloride, hydrobromide, and hydroiodide and the O-tridecafluorooctyl-N,N′-diisopropylisourea hydrochloride and hydrobromide were studied. The effect of structural parameters as the nature of the halide counter ion and the nature of the non-polar chain on the surface activity and thermodynamic properties of adsorption were investigated. The surface parameters, the maximum surface excess concentration (Γ _max), the minimum area per molecule (A _min) at the aqueous solution-air interface, effectiveness of surface tension reduction (π_CMC), and efficiency of surface tension reduction (pC ₂₀) were estimated. The standard Gibbs free energy of adsorption, (ΔG°_ads) change has been calculated at different temperatures.