Synthesis and isoconversional kinetic study of the formation of LiNiPO<Subscript>4</Subscript> from Ni<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>·8H<Subscript>2</Subscript>O as a new precursor

The nanosized LiNiPO₄ was successfully synthesized by a solid-state reaction between the new Ni₃(PO₄)₂·8H₂O precursor and Li₃PO₄ at 700 °C in air atmosphere. The formation of LiNiPO₄ was generated via three thermal decomposition steps. The samples were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscopy, atomic absorption/atomic emission spectrophotometers, and thermogravimetric/differential thermal gravimetric/differential thermal analysis techniques. The activation energy (E_α) values of the three steps were calculated by Vyazovkin method and determined to be 90.39?±?5.79, 197.81?±?7.46, and 308.66?±?12.03 kJ mol^?1, respectively. The average E_α values from this method are very close to E_α from KAS method. The most probable mechanism functions g(α) of three steps were evaluated by using the masterplots method and found to be the F_1/3 (first step), F_3/2 (second step), and D₄ (final step), respectively. The pre-exponential factors (A) values of three steps were obtained based on the E_α and g(α). The kinetic triplet parameters of the formation of LiNiPO₄ from the new precursor are reported in the first time.     

A theoretical study on the dynamics of the gas phase reaction of NH<Subscript>2</Subscript>(<Superscript>2</Superscript>B<Subscript>1</Subscript>) with HO<Subscript>2</Subscript>(<Superscript>2</Superscript>A″)

Quasi-classical trajectory calculations and stochastic one-dimensional chemical master equation simulation methods are used to study the dynamics of the reaction of amidogen radical [NH₂(²B₁)] with hydroperoxyl radical [HO₂(²A″)] on the lowest singlet electronic state. The title complex reaction takes place on a multi-well multichannel potential energy surface consisting of three deep potential wells and one van der Waals complex. In quasi-classical trajectory calculations a new analytical potential energy surface based on CCSD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) ab initio method was driven and used to study the dynamics of the title reaction. In quasi-classical trajectory calculations, the reactive cross sections and reaction probabilities are determined for 200–2000 K relative translational energies to calculate the rate constants. The same ab initio method was used to have the necessary data for solving the one-dimensional chemical master equation to calculate the rate constants of different channels. In solving the master equation, the Lennard-Jones potential model was used to form the collision between the collider gases. The fractional populations of different intermediates and products in the early stages of the reaction were examined to determine the role of the energized intermediates and the van der Waals complex on the dynamics of the title reaction. Although the calculated total rate constants from both methods are in good agreement with the reported experimental values in the literature, the quasi-classical trajectory simulation predicts the formation of NH₂O + OH as the major channel in the title reaction in accordance with the previous studies (Sumathi and Peyerimhoff, Chem. Phys. Lett., 263:742–748, 1996), while the stochastic master equation simulation predicts the formation of HNO + H₂O as the major products.     

Theoretical study on the ion–molecule reaction of HCN<Superscript>+</Superscript> with NH<Subscript>3</Subscript>

A detailed theoretical study is carried out at the B3LYP/6-311G(d,p) and CCSD(T)/6-311++G(3df,2pd) (single-point) levels as an attempt to investigate the mechanism of the little understand ion–molecule reaction between HCN⁺ and NH₃. Various possible reaction pathways are considered. It is shown that six dissociation products P ₁ (NH₃ ⁺ + HCN), P ₂ (NH₄ ⁺ + CN), P ₃ (NH₃ ⁺ + HNC), P ₉ (HCNH⁺ + NH₂) P ₁₀ (NCNH₃ ⁺ + H), and P ₁₂ (HNCNH₂ ⁺ + H) are both thermodynamically and kinetically feasible. Among these products, P ₁ is the most competitive product with predominant abundance. P ₃ and P ₉ may be the second feasible products with comparable yields. P ₁₂ may be the least possible product followed by the almost negligible P ₂ and P ₁₀ . Because the isomers and transition states involved in the HCN⁺ + NH₃ reaction all lie below the reactant, the title reaction is expected to be rapid, which is consistent with the measured large rate constant in experiment. The title reaction may have a potential relevance in Titan’s atmosphere, where the temperature is very low. Furthermore, our calculated results are compared with the previous experimental findings.     

Tree of phases of the quinary reciprocal system Li,K || F,Br, MoO<Subscript>4</Subscript>, WO<Subscript>4</Subscript> and study of the stable tetrahedron LiF–KBr–Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>–Li<Subscript>2</Subscript>WO<Subscript>4</Subscript>

The quinary reciprocal system Li, K || F, Br, MoO₄, WO₄ was partitioned into simplexes using graph theory by writing an adjacency matrix and solving a logical expression. A tree of phases of the system was constructed. The tree of phases has a linear structure and consists of four stable partitioning tetrahedra, two stable pentatopes, and three stable hexatopes. In the quinary reciprocal system Li, K || F, Br, MoO₄, WO₄, crystallizing phases were predicted. The stable tetrahedron LiF–KBr–Li₂MoO₄–Li₂WO₄ of the quinary reciprocal system Li, K || F, Br, MoO₄, WO₄ was studied by differential thermal analysis and X-ray powder diffraction. There are no invariant equilibrium points in the tetrahedron. Continuous series of solid solutions Li₂Mo_xW_1–xO₄ do not decompose.     

Kinetics and mechanism of the low-temperature oxidation of carbon monoxide with oxygen on a PdCl<Subscript>2</Subscript>–CuCl<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

A systematic study of the kinetics of the low-temperature oxidation of carbon monoxide with oxygen on a PdCl₂–CuCl₂/γ-Al₂O₃ supported catalyst was carried out over a wide range of the partial pressures of oxygen, water, and CO in order to test hypotheses on the reaction mechanism. It was shown that, as the temperature was increased from 20 to 38°C, rate of formation of CO₂ decreased and the apparent activation energy was about–40 kJ/mol. The hypotheses of different degrees of complexity concerning the reaction mechanism were formulated based on physicochemical data and a Langmuir–Hinshelwood model. Mechanisms in which carbon dioxide is formed on the interaction of the surface Pd(I) and Pd(II) complexes that include carbon monoxide and water with the surface complex of Cu(I) that coordinates oxygen were recognized as the most probable.     

Effect of ionic conductivity of a PAN–PC–LiClO<Subscript>4</Subscript> solid polymeric electrolyte on the performance of a TiO<Subscript>2</Subscript> photoelectrochemical cell

A nanoparticle TiO₂ solid-state photoelectrochemical cell has been fabricated. The effect of ionic conductivity of a solid electrolyte of polyacrylonitrile (PAN)–propylene carbonate (PC)–lithium perchlorate (LiClO₄) on the performance of a photoelectrochemical cell of indium tin oxide (ITO)/TiO₂/PAN–PC–LiClO₄/graphite has been investigated. A nanoparticle TiO₂ film was deposited onto ITO-covered glass substrate by controlled hydrolysis technique. A solid electrolyte of PAN–LiClO₄ with PC plasticizer prepared by solution casting technique was used as a redox couple medium. The room temperature conductivity of the electrolyte was determined by AC impedance spectroscopy technique. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows a photovoltaic effect under illumination. The short-circuit current density, J _sc, and open-circuit voltage, V _oc, vary with the conductivity of the electrolyte. The highest J _sc of 2.82 μA cm⁻² and V _oc of 0.56 V were obtained at the conductivity of 4.2 × 10⁻⁴ Scm⁻¹ and at the intensity of 100 mW cm⁻².     

Phase formation in the system Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>–MgMoO<Subscript>4</Subscript>–Sc<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phase formation in the system Li₂MoO₄–MgMoO₄–Sc₂(MoO₄)₃ was studied by X-ray powder diffraction analysis and differential thermal analysis. Ternary molybdate LiMgSc(MoO₄)₃ was synthesized, which crystallizes in the triclinic system (space group P\(\bar 1\)). In the Li₂Mg₂(MoO₄)₃–Li₃Sc(MoO₄)₃ section, a continuous solid solution in the rhombic system was found to form (space group Pnma).     

Synthesis of nanopowders and physicochemical properties of ceramic matrices of the LaPO<Subscript>4</Subscript>–YPO<Subscript>4</Subscript>–(H<Subscript>2</Subscript>O) and LaPO<Subscript>4</Subscript>–HoPO<Subscript>4</Subscript>–(H<Subscript>2</Subscript>O) systems

Sol-gel method was used to synthesize nanosize powders in the LaPO₄–YPO₄–(H₂O) and LaPO₄–HoPO₄–(H₂O) systems. Dense ceramic samples with high microhardness (up to 25 GPa) were formed from these powders by sintering at temperatures of up to 1600°C. The isomorphic capacity of the monoclinic LaPO₄ matrix for the second component (yttrium or holmium) simulating radioactive nuclides of the actinide-rare-earth fraction was found to be high. The composites are stable in aqueous solutions, which is indicated by the low concentration of lanthanum and yttrium ions during leaching test (~10^–7 g L^–1). The results obtained in the study can be used to develop new high-efficiency ceramic matrices for solidification of the actinide-rare-earth fraction of liquid wastes formed in processing of the spent nuclear fuel.     

Photocatalytic Conversion of a FeCl<Subscript>3</Subscript>–CCl<Subscript>4</Subscript>–ROH System

The photocatalytic transformations of carbon tetrachloride and aliphatic primary alcohols in the presence of iron trichloride and a molar ratio of components FeCl₃: CCl₄: ROH = 1: 300: 2550 were studied. CCl₄ is transformed into chloroform and hexachloroethane after exposure to a mercury lamp (250 W) to the FeCl₃–CCl₄–ROH system at 20°C, whereas the primary ROH alcohols are selectively oxidized into acetals (1,1-dialkoxyalkanes). The maximum conversion of CCl₄ reaches 80%. The kinetics and mechanism of the photocatalytic conversion of the FeCl₃–CCl₄–ROH system are considered.     

Study of the stable tetrahedron LiVO<Subscript>3</Subscript>–Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>–KBr–LiKMoO<Subscript>4</Subscript> of the quaternary reciprocal system Li,KǁBr,VO<Subscript>3</Subscript>,MoO<Subscript>4</Subscript>

Phase equilibria in the stable tetrahedron LiVO₃–Li₂MoO₄–KBr–LiKMoO₄ of the quaternary reciprocal system Li,K∥Br,VO₃,MoO₄ were studied by differential thermal analysis. The composition (mol %) and melting point of the alloy corresponding to a quaternary eutectic were determined: (24.2% LiVO₃, 10.4% Li₂MoO₄, 13.5% KBr, 51.9% LiKMoO₄, 407°С).     

Separation of hafnium from tungsten by extraction chromatography with TOA in HCl–H<Subscript>2</Subscript>O<Subscript>2</Subscript> mixture

In order to measure ¹⁸²Hf by accelerator mass spectrometry (AMS), a chemical procedure for separation of hafnium from tungsten has been developed by extraction chromatography. The extraction chromatographic behavior of hafnium and tungsten has been studied using tri-n-octylamine (TOA) as the stationary phase, HCl–H₂O₂ mixture and NH₃·H₂O as the mobile phase. The effects of H₂O₂ concentration, column loading and column dimensions are investigated. Hf and W with microgram amounts are successfully separated on a chromatographic column (Ø5 × 196 mm), on which Hf is hardly retained after completely eluted with 6 M HCl–1% H₂O₂ and W strongly adsorbed is then eluted with 3 M NH₃·H₂O. The decontamination factor for tungsten is 3.0 × 10⁵ and the recovery of hafnium is better than 99% using a single column separation.     

Physicochemical Analysis of the System Zr(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>–Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>–H<Subscript>2</Subscript>SO<Subscript>4</Subscript>–H<Subscript>2</Subscript>O at 25°С

The solubility in the quaternary water–salt system Zr(SO₄)₂ · 4Н₂О–Na₂SO₄–H₂SO₄–H₂O at 25°C was studied. It was found that, in the system, there is crystallization of not only Na₂SO₄ and Zr(SO₄)₄ · 4H₂O, but also sodium sulfate zirconates Na₂Zr(SO₄)₂(OH)₂ · 0.3H₂O, Na₄Zr(SO₄)₄ · 3H₂O, and Na₂Zr(SO₄)₂ · 3H₂O and two new compounds, S₁ and S₂, which are presumably Na₂ZrO(SO₄)₂ · 2H₂O and Na₂Zr₂O₂(SO₄)₃ · 6H₂O.     

Study of the NaF–NaBr–Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> system

The NaBr–D (Na₃FSO₄) quasi-binary system and the NaF–NaBr–Na₂SO₄ ternary system were studied by differential thermal analysis. The melting points and compositions of eutectic mixtures were determined, and in-, mono-, and divariant equilibrium states were described.     

A study on the effect of synthesis parameters on the size of nickel particles in sol–gel derived Ni–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites

The present work deals with the synthesis of Ni–SiO₂–Al₂O₃ nanocomposites fabricated by embedding nickel oxide particles, obtained from hexahydrated nickel nitrate [Ni(NO₃)₂ · 6H₂O], in matrixes with different molar percents of Silica/Alumina, through sol–gel method based on hydrolysis and condensation of tetraethylorthosilicate (TEOS) and Aluminum Isopropoxide [Al(OC₃H₇)₃] alkoxides. Due to the various factors, e.g., pH, EtOH/TEOS/H₂O ratio, Si/Ni ratio etc., influencing the nickel grain size of the nanocomposites, Taguchi robust design method of system optimization was used to determine the percent of contribution (%ρ) of each factor. The nanocomposites were reduced in a flow of hydrogen and nitrogen gas at 700 °C for half an hour. The nickel grain size in the nanocomposites was determined by utilizing Scherrer`s method and XRD patterns. The smallest nickel grain size obtained from the Taguchi orthogonal array was about 24 nm, later confirmed by TEM observations. After optimization of the controlling factors, a nickel grain size of 15.4 nm was obtained. It was found that the SiO₂/Al₂O₃ molar ratio of the matrix had the most influence on the nickel grain size (29.22%) and the Water/TEOS molar ratio stood in second place (21.44%). It was illustrated that the starting temperature of the aluminum isopropoxide had the least influence on the nickel grain size.     

Multicomponent systems LiCl–LiBr–Li<Subscript>2</Subscript>SO<Subscript>4</Subscript> and LiCl–LiBr–Li<Subscript>2</Subscript>SO<Subscript>4</Subscript>–Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>

Phase equilibria in the LiCl–LiBr–Li₂SO₄ ternary system and the LiCl–LiBr–Li₂SO₄–Li₂MoO₄ quaternary system were studied by differential thermal analysis. The compositions and temperatures of minima in the ternary and quaternary systems were determined to be (31.2 mol % LiCl, 46.8 mol % LiBr, 22.0 mol % Li₂SO₄, 460°C) and (25.2 mol % LiCl, 30.2 mol % LiBr, 14.6 mol % Li₂SO₄, 30.0 mol % Li₂MoO₄, 411°C), respectively.     

Thermodynamic study of solid solutions in the SnTe–AgSbTe<Subscript>2</Subscript> system by means of EMF with solid electrolyte Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript>

The results from studying the SnTe–AgSbTe₂ system by means of EMF with the solid electrolyte Ag₄RbI₅ in the temperature range of 300–430 K are presented. The formation of a wide (≥80 mol % of AgSbTe₂) region of solid solutions based on SnTe is confirmed. Partial thermodynamic functions ΔG?, ΔH?, and ΔS? of silver in alloys are calculated from the equations for the EMF temperature dependences. Based on the literature data regarding solid-phase equilibria in the Ag₂Te–SnTe–Sb₂Te₃–Te system, potential-determining reactions are identified that allow us to calculate the standard thermodynamic formation functions and standard entropies of solid solutions (2SnTe) _x (AgSbTe₂)_1?x (х = 0.2, 0.4, 0.6, 0.8, and 0.9).     

Experimental and theoretical characterization of Fe<Subscript>2</Subscript>Cr trinuclear-oxo-centered complex with a CF<Subscript>2</Subscript>ClCOO<Superscript>–</Superscript> bridge

In this work, an atrinuclear-oxo-centered complex of the CrFe₂ type with the CF₂ClCOO^– bridging ligand is newly synthesized. The complex is characterized by experimental and theoretical methods. The optimized geometry and theoretical vibrational frequencies are computed using the density functional theory (DFT) method. Also, the AIM analysis was applied to study changes in topological parameters such as the electron density at critical points of all the bonds of the complex. In the optimized geometry of the complex, three metal ions form a trigonal-planar structure with a μ₃-O atom in its center. Each of M³⁺ metal ions has an octahedral coordination environment of oxygen atoms. The DFT results are in agreement with the experimental ones, confirming the validity of the optimized geometry for the complex.     

The Sections GeSnSb<Subscript>4</Subscript>Te<Subscript>8</Subscript>–GeTe and GeSnSb<Subscript>4</Subscript>Te<Subscript>8</Subscript>–SnTe of the Quasi-Ternary System GeTe–Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–SnTe

By differential thermal, X-ray powder diffraction, and microstructural analyses and microhardness and density measurements, phase equilibria in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe were studied and their state diagrams were constructed. It was determined that these sections are quasi-binary sections of the eutectic type of the GeTe–Sb₂Te₃–SnTe system. The coordinates of the eutectic points in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe are (40 mol % GeTe, 700 K) and (30 mol % SnTe, 750 K), respectively. Regions of solid solutions based on the initial components in the sections were identified. Alloys in the regions of solid solutions are p-type semiconductors.     

Theoretical analysis of the system Li,K, Ca,Ba||F,WO<Subscript>4</Subscript>: Physicochemical properties of the system LiF–K<Subscript>2</Subscript>WO<Subscript>4</Subscript>–BaF<Subscript>2</Subscript>–CaF<Subscript>2</Subscript>–BaWO<Subscript>4</Subscript>

The differentiation of the quaternary reciprocal system Li, K, Ca, Ba||F, WO₄ was performed based on the graph theory using special software. Stable and metastable complexes of the system were found using a matrix of reciprocal pairs of salts. For the first time, by a set of physicochemical analysis methods (differential thermal, visual polythermal, and X-ray powder diffraction analyses), based on the method of thermal analysis of successive projections of the composition polytope, the quaternary system LiF–K₂WO₄–CaF₂–BaF₂–BaWO₄, which is a stable complex of the quaternary reciprocal system Li, K, Ca, Ba||F, WO₄, was studied and the coordinates of invariant points were determined.