Experimental investigation of the formation of double phosphates in the LaPO4–NaF system

In the course of segregation smelting of rare-earth and rare metal raw materials with a fluxing agent (NaF), two immiscible melts form, one of which is a silicate melt and the other is a phosphate–salt melt. The silicate melt is enriched with Fe₂O₃, Al₂O₃, SiO₂, and Nb₂O₅, and the phosphate–salt melt is dominated by P₂O₅, TR₂O₃, Sc₂O₃, and Y₂O₃, and also with Ca, Sr, and Ba oxides. Chemical reactions between lanthanum orthophosphate and sodium fluoride in the LaPO₄–NaF system were studied for developing a technology for processing the phosphate–salt (rare-earth metal) melt. It was found that a metathesis reaction gives double phosphate Na₃La[PO₄]₂ and binary fluoride NaLaF₄. The products of crystallization of melts in the LaPO₄–NaF system decompose in weak mineral acids unlike those in conventional technology for processing monazite raw material.     

Benchmarking and analysis of 6Li neutron depth profiling of lithium ion cell electrodes

The University of Texas at Austin Neutron Depth Profiling (UT-NDP) facility was utilized to analyze varying cathode compositions in lithium battery materials. Battery materials included LiCoO₂, LiMn_1/3Ni_1/3Co_1/3O₂, and LiFePO₄. The cells were made at The University of Texas at Austin as coin cells with lithium anodes. The NDP analysis method for Li in battery materials was benchmarked between two facilities and with computational models.     

Towards insight into properties and stabilities of complexes of ozone with CO2, CS2 and SCO species

The MP2 method in combination with the aug-cc-pVXZ (X = D and T) basis set has been carried out to examine the complexes between O₃ and isostructure species of CO₂, CS₂ and SCO. Two, two and four minima have been located on the potential energy surfaces of O₃–CO₂, O₃–CS₂ and O₃–SCO complexes, respectively. The results reveal that the stabilization of complexes should be in the order O₃–CS₂ > O₃–SCO > O₃–CO₂.     

Sol–gel preparation and electrochemical properties of La-doped Li4Ti5O12 anode material for lithium-ion battery

A sol–gel method using Ti(OC₄H₉)₄, LiCH₃COO·2H₂O, and La(NO₃)₃·6H₂O as starting materials and ethyl acetoacetate as chelating agent to prepare pure and lanthanum (La)-doped Li₄Ti₅O₁₂ is reported. The structure and morphology of the active materials characterized by powder X-ray diffraction and scanning electron microscopy analysis indicate that doping with a certain amount of La³⁺ does not affect the structure of Li₄Ti₅O₁₂, but can restrain the agglomeration of the particles during heat treatment. The electrochemical properties measured by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling tests show that La-doped Li₄Ti₅O₁₂ presents a much improved electrochemical performance due to a decrease in charge transfer resistance. At current densities of 1 and 5 C, the La-doped Li₄Ti₅O₁₂ exhibits excellent reversible capacities of 156.16 and 150.79 mAh?g^?1, respectively. The excellent rate capability and good cycling performance make La-doped Li₄Ti₅O₁₂ a promising anode material for lithium-ion batteries in energy storage systems.     

Effects of acid treatment on electrochemical properties of Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript>·LiNi<Subscript>0.5</Subscript>Co<Subscript>0.45</Subscript>Fe<Subscript>0.05</Subscript>O<Subscript>2</Subscript> cathode materials

A new composite, Li₂MnO₃·LiNi_0.5Co_0.45Fe_0.05O₂, can be synthesized by a solid-state method and preconditioned with 5 wt% HCl, H₂SO₄, or H₃PO₄ solution to achieve H⁺/Li⁺ exchange. The effects of acid treatment on the structure, morphology, and electrochemical properties of Li₂MnO₃·LiNi_0.5Co_0.45Fe_0.05O₂ cathode materials are analyzed. The X-ray powder diffraction patterns imply that the hexagonal α-NaFeO₂ structure (space group R\(\bar{3}\)m) of the materials is not changed by the acid treatment. The scanning electron microscope images show that particles become spherical with smooth surfaces after acid treatment, and the Brunauer–Emmett–Teller analysis reveals that the specific surface area increases. The charge–discharge test demonstrates that acid-treated Li₂MnO₃·LiNi_0.5Co_0.45Fe_0.05O₂ cathode materials deliver higher initial coulombic efficiencies than untreated material, owing to the improvement of the catalytic reduction activity of oxygen released during the initial charge process. Furthermore, Li₂MnO₃·LiNi_0.5Co_0.45Fe_0.05O₂ treated with HCl displays the best electrochemical performance, with the acid treatment improving the initial coulombic efficiency from 66.0 to 82.2%. Thus, acid treatment can effectively improve the electrochemical performance of electrode materials in Li-ion batteries.     

The Effect of Sc<Subscript>2</Subscript>O<Subscript>3</Subscript> on the Physicochemical Properties of Low-Melting Cryolite Melts КF–AlF<Subscript>3</Subscript> and КF–NaF–AlF<Subscript>3</Subscript>

Quasibinary phase diagrams of the system “low-melting cryolite–Sc₂O₃” the potential media for synthesizing alloyed alloys Al–Sc are plotted by the method of thermal analysis. The phase diagrams of (KF–NaF–AlF₃)–Sc₂O₃ with different content of NaF and the cryolite ratio (CR) 1.3 and 1.5 are the diagrams with simple eutectics. The liquidus temperature of the (KF–AlF₃)–Sc₂O₃ system increases with the increase in the Sc₂O₃ concentration due to the formation of a high-melting compound: potassium hexafluoroscandiate К₃ScF₆. The solubility of Sc₂O₃ in low-melting cryolite melts KF–NaF–AlF₃ increases with the increase in temperature and CR. In contrast Al₂O₃, the solubility of Sc₂O₃ in melts containing KF–AlF₃ with CR = 1.3–1.5 is much lower than in cryolite melts containing NaF. The conductivity of low-melting cryolite melts measured by the method of impedance spectroscopy decreases in proportion to the Sc₂O₃ concentration in the similar way as in salt melts containing Al₂O₃. Based on the experimental data obtained, the compositions of low-melting cryolite melts are proposed for the synthesis of doped Al–Sc alloys.     

Ordered mesoporous Pt/Fe3O4–CeO2 heterostructure gel particles with enhanced catalytic performance for the reduction of 4-nitrophenol

The unique physicochemical properties of ordered mesoporous transition metal oxides have attracted more and more attention. The hydrolysis process of metal oxide precursors is difficult to control, and it is difficult to synthesize an ordered mesoporous transition metal oxide material using the conventional template method. Ordered mesoporous Pt/Fe₃O₄–CeO₂ heterostructure gel materials with excellent catalytic properties were successfully prepared using aerogel technology and the chemical deposition method. The Pt/Fe₃O₄–CeO₂ material was an n–n combined heterostructured semiconductor material which consisted of a magnetic Fe₃O₄ layer, a CeO₂ core and Pt noble metal doped nanoparticles. A layer of Fe₃O₄ thin film was formed on the surface of ordered mesoporous Pt/CeO₂ gel matrix material using the chemical deposition method. The intriguing heterostructural features could facilitate reactant diffusion and exposure of active sites which could enhance synergistic catalytic effects between the Pt nanoparticles and CeO₂ nanoparticles. Compared with Pt/CeO₂, the prepared Pt/Fe₃O₄–CeO₂ showed enhanced catalytic activity in the reduction of 4-nitrophenol at room temperature. The catalytic activity of the heterostructure catalysts was systematically investigated using 4-nitrophenol reduction as a model reaction. The results showed that the Pt (0.1%)/Fe₃O₄–CeO₂ sample exhibited the optimal catalytic performance toward catalytic reduction of 4-nitrophenol to 4-aminophenol. The study provided a method for the preparation of heterostructure nanocatalysts with high efficiency, which would be effective for application in various catalytic reactions.     

Thermal characterization and compatibility studies of perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) oxide with Cr2O3 at high temperature

The chemical compatibility of perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (BSCF) oxides with Cr₂O₃ has been examined between room temperature and 1,100 °C. Differential thermal analysis and thermogravimetric analysis were used to analyze the thermal behavior of BSCF–Cr₂O₃ binary mixtures in all composition ranges (0–100 mass% BSCF). The reaction products were identified by X-ray analysis after heating at 700–1,100 °C. As we expected, it was found that perovskite-type BSCF oxide had a poor chemical compatibility with the Cr₂O₃ oxide. In particular, the decomposition process of the BSCF–Cr₂O₃ binary mixture is quite complex and it starts at about 700–750 °C. The mixtures of BSCF and Cr₂O₃ oxides reacted forming mixed complex oxides based on (Ba/Sr)FeO₃, (Co/Fe)CrO₄, and (Ba/Sr)CrO₄ mixtures.     

Structural and Temperature Dependent Electrical Conductivity Properties of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> CO-Doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

In the present work, Dy₂O₃ and Sm₂O₃ double-doped Bi₂O₃-based materials are synthesized by exploiting the solid-state synthesis method. The structural and temperature dependent electrical properties of these ternary ceramic samples, which are candidate materials for solid oxide fuel cell (SOFCs) electrolyte, are determined by means of a powder X-ray diffractometer (XRD), the four point-probe method (FPPM), and the thermal-gravimetry/differential thermal analysis (TG/DTA). As a result of the XRD measurements, the fluorite-type fcc δ-phase with a stable structure is obtained for higher values of the dopant oxide material, which are the samples with the maximum content of fixed 20% Dy₂O₃ and 15% and 20% Sm₂O₃. The samples with the stable δ-phase structure have higher conductivities. The highest electrical conductivity is found for the (Bi₂O₃)0.6(Dy₂O₃)_0.2(Sm₂O₃)_0.2 sample, which was 2.5×10^–2 (Ohm cm)^–1 at 750 °C. The activation energies are also calculated from the Arrhenius charts, which were determined from the FPPM measurements. The lowest activation energy is found as 0.85 eV for the sample with the highest electrical conductivity.     

Compositional Analysis of Cement Raw Meal by Near-Infrared (NIR) Spectroscopy

Abstract

A rapid and accurate method is presented to determine CaCO₃, SiO₂, Fe₂O₃, and Al₂O₃ in cement raw meal using near-infrared (NIR) spectroscopy. Multiplicative scatter correction (MSC) was employed to eliminate the scattering signal and partial least squares (PLS) regression was used to build the analysis model. The results demonstrated good performance by this approach for the determination of CaCO₃, SiO₂, Fe₂O₃, and Al₂O₃. NIR spectroscopy exhibits the feasibility to characterize the quality of cement raw meal. Compared with prompt gamma neutron activation analysis (PGNAA) and X-ray fluorescence (XRF), this method is more efficient and safer.     

Detection of 13 mycotoxins in feed using modified QuEChERS with dispersive magnetic materials and UHPLC–MS/MS

An analytical method for the simultaneous determination of 13 mycotoxins in feed by magnetic dispersive solid‐phase extraction combined with ultra‐high performance liquid chromatography and tandem mass spectrometry was developed. The samples were extracted with acetonitrile/water (80:20, v/v, containing 3% acetic acid), and separated by centrifugation after salting‐out, and then treated with magnetic adsorbents to remove interferences. The separation of target mycotoxins was performed on an ACQUITY UPLC HSS T3 column using a mobile phase consisting of 1 mmol/L ammonium acetate with 0.1% formic acid and methanol by gradient elution. Good linearities for the 13 mycotoxins were achieved with correlation coefficients over 0.99, and the recoveries of mycotoxins were in the range of 89.3–112.6% at spiking at levels of 5, 20, and 100 μg/kg, with relative standard deviations of 0.9–10.4%. Based on the functional magnetic materials (MDN@Fe₃O₄, PSA@Fe₃O₄, ZrO_2@Fe₃O₄) applied in dispersive solid‐phase extraction, the pretreatment process is more convenient and it is beneficial to reduce the experimental cost by reusing the recycled magnetic materials. It is a simple, rapid, and environmentally friendly analytical method for the determination of mycotoxins in feed.     

Pyrolysis–gas chromatographic analysis of poly(vinyl chloride). II. In situ absorption of HCl during pyrolysis and combustion of PVC

A pyrolysis–gas chromatographic technique for measuring the amount of hydrogen chloride released during the high temperature pyrolysis of poly(vinyl chloride) resins, plastisols, copolymers and compounds containing inert fillers has been developed. The technique, which is also applicable to the analysis of chlorinated polyethylene and chlorinated poly(vinyl chloride), is based on the use of a standard precursor of HCl, poly(vinyl chloride) homopolymer. The analysis has been successfully used to measure the degree of in situ absorption of HCl during pyrolysis by certain basic fillers [K₂CO₃, CaCO₃, CaO, MgO, Al(OH)₃, Na₂CO₃, Al₂O₃ and LiOH] dispersed in a poly(vinyl chloride)–o-dioctyl phthalate matrix. Combustion of a number of combustion residues (chloride determination) revealed that the amount of HCl absorbed by the basic filler was independent of the method of degradation (pyrolysis or combustion). Flammability measurements of those matrices having the same composition indicate that in situ absorption of HCl during combustion has little effect on the overall flammability of these materials.     

Sol–gel preparation and characterization of Bi4(Si1−xGex)3O12 solid solutions

Micro-crystals of Bi₄(Ge_xSi_1?x)₃O₁₂ (x = 0, 0.25, 0.5, 0.75, 1) solid solution series were synthesized by a sol–gel method, using stoichiometric Si(OC₂H₅)₄, GeO₂, Bi(NO₃)₃·5H₂O as the starting materials. The as-prepared series were studied by X-ray diffraction, Raman spectra, differential thermal analysis, and fluorescence spectra. Experiments showed that single phase of Bi₄(Si_1?xGe_x)₃O₁₂ was obtained by the sol–gel method. For all the composition, Bi₄Si₃O₁₂ and Bi₄Ge₃O₁₂ can completely dissolve into each other. The refined cell parameters were in proportion to the composition. Bi₄Ge₃O₁₂ showed the strongest fluorescence emission while Bi₄Si₃O₁₂ showed the weakest fluorescence emission.     

Investigations on the use of chemical modifiers for the direct determination of trace impurities in Al2O3 ceramic powders by slurry electrothermal evaporation coupled with inductively-coupled plasma mass spectrometry (ETV–ICP–MS)

The direct determination of trace impurities in Al₂O₃ ceramic basic powders by ICP–MS using electrothermal evaporation (ETV) with slurry sampling has been investigated. To increase interference-free analyte volatilization, the use of the palladium-group modifiers (PGM) IrCl₃, Pd(NO₃)₂, and PdCl₂ for the determination of Ca, Fe, Ga, Mg, Mn, Na, Ni, and V in Al₂O₃ powders was studied. Their role, which in ETV–ICP–MS and ETV– ICP–OES is to stabilize the investigated analyte during the ashing phase, to increase vaporization of the matrix, and to reduce transport losses was investigated. Optimum analysis results were obtained with PdCl₂ modifier when 500 ng Pd was used for a sample weight of 100 μg Al₂O₃ injected into the ETV. Calibration was performed by standard addition with aqueous solutions of the analytes. The RSDs calculated from triplicate analysis ranged form 5 to 10%. Detection limits between 0.07 μg g^–1 (Ga) and 1.1 μg g^–1 (Na) were achieved. The accuracy was proven for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V by analyzing an NIST standard reference Al₂O₃ material (SRM 699) with a middle grain size of 16.4 μm. The analytical method was used for the analysis of Al₂O₃ powder (AKP 30, Sumitomo, Japan) with impurities in the low μg g^–1 range and a middle grain size of 1.1 μm. The results obtained for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V were comparable with those obtained by ICP–MS subsequent to conventional decomposition with hydrochloric acid at high pressure.     

Preparation and characterization of bismuth silicate nanopowders

Bismuth silicate (Bi₄Si₃O₁₂) nanopowders were prepared by the sol-gel method. Tetraethyl orthosilicate (TEOS) and Bi₂O₃ were used as the starting materials. The precursors were heat-treated at 750°C for 2 h. The size distribution of Bi₄Si₃O₁₂ nanopowders is 40–100 nm. The thermogravimetry and differential thermal analysis (TG-DTA) curves, the X-ray diffraction (XRD) patterns and the transmission electron microscopy (TEM) microphotograph of Bi₄Si₃O₁₂ were discussed. Compared with crystal materials, the excitation and emission spectra of Bi₄Si₃O₁₂ nanopowders indicated a blue shift. Translated from Chinese Journal of Inorganic Chemistry, 2006, 22(7): 1327–1329 (in Chinese)     

Vapour phase synthesis of quinoline from aniline and glycerol over mixed oxide catalysts

The vapour phase synthesis of quinoline from aniline and glycerol (1:2 mole ratio) in a single step was investigated over ZnO–Cr₂O₃, CuO–ZnO/Al₂O₃, MoO₃–V₂O₅/Al₂O₃ and NiO–MoO₃/Al₂O₃ catalysts in the presence of air at 623–723 K under normal atmospheric pressure. Among these catalysts investigated, the CuO–ZnO/Al₂O₃ combination effectively performed this reaction with high activity and selectivity.     

Comparison of photocatalytic and antibacterial activities of allotropes of graphene doped Sm2O3 nanocomposites: Optical,thermal, and structural studies

This study mainly focuses on the synthesis of two allotropes of graphene, graphene oxide (GO) and reduced graphene oxide (rGO), by the modified Hummers' method and chemical reduction method, respectively. Sm₂O₃/GO and Sm₂O₃/rGO nanocomposites were further synthesized in the presence of the cationic surfactant CTAB via the sol–gel method followed by the reflux method. Synthesized nanocomposites were subjected to characterization by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and UV–Visible spectroscopy to explore structural, thermal, optical, and photocatalytic properties. Characteristic FTIR peaks were observed in nanocomposites, and the bond length of the Sm-O bond was calculated. The Coats-Redfern method was employed to calculate the kinetics and thermodynamic parameters. Hexagonal crystallite shapes of Sm₂O₃/GO and Sm₂O₃/rGO nanocomposites with 11.8 and 13.13 nm crystallite sizes and 3.9 and 2.5 eV optical band gaps were observed. The photocatalytic efficiency of Sm₂O₃/GO and Sm₂O₃/rGO nanocomposites was assessed against the degradation of methylene blue in the presence of sunlight, and its degradation was confirmed through FTIR. The antimicrobial activities were also performed against the bacterial strains Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus.     

The thermodynamic method for selecting oxygen carriers used for chemical looping air separation

Chemical looping air separation (CLAS) has been suggested as a new and energy saving method for producing oxygen from air. The selection of suitable oxygen carriers is the key issue for CLAS system. This paper shows a comprehensive thermodynamic method for selecting oxygen carriers used for CLAS through studying the properties of 34 different oxygen releasing reactions referring to 18 elements at different temperatures. The research mainly includes analysis of oxygen releasing capacity by calculating the Gibbs free energy change (ΔG) and the equilibrium partial pressure of oxygen of the reduction or oxidation reaction at different temperatures. Oxygen content and transport capacity were calculated. The spontaneous reaction temperatures for oxygen releasing reactions were presented to determine the operating temperatures. Also, the minimum demand of the steam for the reduction reaction was discussed. On the basis of the comprehensive thermodynamic study, the oxide systems of CrO₂/Cr₂O₃, PbO₂/Pb₃O₄, PbO₂/PbO, Pb₃O₄/PbO, MnO₂/Mn₂O₃, and Ag₂O/Ag have been found suitable for the CLAS process in low temperatures (500–800 K). The systems of PdO₂/PdO, PdO₂/Pd, PdO/Pd, MnO₂/MnO, and MnO₂/Mn₃O₄ were suitable for medium temperatures (800–1100 K) CLAS process. And Co₃O₄/CoO, CuO/Cu₂O, Mn₂O₃/Mn₃O₄, and OsO₂/Os systems only worked successfully in high temperatures (1100–1400 K). In addition, the CaO₂/CaO system was not suitable for CLAS because of the reaction with steam. The various binders such as SiO₂, TiO₂, Al₂O₃, Y₂O₃, ZrO₂, and YSZ which have been used for CLC could also be the supports for CLAS oxygen carriers.     

Structure,chemical stability and electrical properties of BaCe0.9Y0.1O3−δ modified with V2O5

Wet vacuum impregnation method was applied in order to evaluate the possibility of the formation of the material in BaCe_0.9Y_0.1O_3?δ–V₂O₅ system. Single-phase BaCe_0.9Y_0.1O_3?δ samples, synthesised by solid-state reaction method, were impregnated with the solution of vanadium(V) oxide precursor. Multi-step, multi-cycle impregnation procedure was applied to enhance the impregnation efficiency. Partial decomposition of Y-doped BaCeO₃ in contact with the solution of the precursor, resulting in the formation of vanadium containing phases (CeVO₄ and BaV₂O₆) on the materials surface, was observed. However, the presence of vanadium was also confirmed for the inner parts of the materials. The synthesised materials were submitted for exposition test to evaluate their chemical stability towards CO₂/H₂O. All BaCe_0.9Y_0.1O₃-based materials modified by impregnation revealed higher chemical stability in comparison with single-phase un-modified BaCe_0.9Y_0.1O_3?δ, since the amount of barium carbonate formed during the exposition was significantly lower. The total electrical conductivity of the received multi-phase materials was generally slightly lower than for the reference BaCe_0.9Y_0.1O_3?δ sample, since the presence of the additional phases had a blocking effect on materials conductivity. The values of BaCeO₃ lattice parameters and the Seebeck coefficient did not show the modification of the defects structure of Y-doped BaCeO₃ during applied synthesis procedure.

     

Determination of oxygen in oxides by carrier gas hot extraction analysis with simultaneous COx detection

The determination of oxygen by carrier gas hot extraction is the most popular method for oxygen analysis, but its application to high oxygen contents in oxides requires a critical look at the basic assumptions of the method. The process was studied for various oxides (Al₂O₃, Bi₂O₃, Cr₂O₃, Fe₂O₃, MoO₃, NiO, TiO₂, WO₃, Y₂O₃, and ZrO₂) using a modern analyser with IR-detectors for CO₂ and CO. There was a difference specific to oxides that must be known to get the required analytical results with high precision and accuracy. High amounts of CO₂ were formed particularly from Bi₂O₃, Fe₂O₃, MoO₃, NiO, and WO₃. The reaction rate can be controlled with delayed heating of the furnace, so that an oxide sample weight of up to 100 mg can be used. Received: 13 April 1999 / Revised: 24 June 1999 / Accepted: 28 June 1999