Oxides Of Various Compositions Research Articles

Synthesis and characterisation of mesoporous MgAl2O4 hollow spheres as a high-value product in a waste recovery strategy

Micrometre-scale hollow sphere-shaped MgAl2O4 powders were synthesised using a spray-drying method, followed by calcination. An aqueous solution of mixed Mg2+ and Al3+ salts, derived from aluminium slag and serpentine tailings, served as a source of magnesium and aluminium. The secondary raw materials were subjected to acid leaching, and the refined leachates were used to prepare a spray-dried MgAl2O4 precursor, which was heat-treated at temperatures ranging from 550 °C to 1100 °C for 1 h. Characterisation of the resulting MgAl2O4 spinel powders was performed using various physicochemical techniques, including thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and physical adsorption using N2 (BET). The prepared MgAl2O4 spinel demonstrated several unique properties, including ultrafine particles with a uniform distribution (1–5 μm) and minimal particle agglomeration, high sintering activity (beginning at 550 °C), high purity, high specific surface area (110 m2 g-1/750 °C), and open porosity with a narrow pore size distribution (3–7 nm). These properties make the prepared MgAl2O4 spinel a highly valuable product for waste recovery strategies. The simplicity, efficiency, and cost-effectiveness of this process also predispose it to large-scale production of functional mixed metal oxides of various compositions for use in industries such as energy storage, sensing, and 3D printing fillers.

Effect of Mo-doping in SnO2 thin film photoanodes for water oxidation

New semiconducting metal oxides of various compositions are of great interest for efficient solar water oxidation. In this report, Mo-doped SnO2 (Mo:SnO2) thin films deposited by reactive magnetron co-sputtering in the Ar and O2 gas environment are studied. The Sn to Mo ratio in the films can be controlled by changing the O2 partial pressure and the deposition power of the Sn and Mo targets. Increasing the Mo concentration in the film leads to the increase in the oxygen vacancy density, which limits the maximum achievable photocurrent density. The thin films exhibit a direct band gap of 2.7 eV, the maximum achievable photocurrent density of 0.6 mA cm−2 at 0 VRHE and the onset potential of 0.14 VRHE. The incident photon to current transfer (IPCE) efficiency of 22% is shown at a 450 nm wavelength. The initial performance of the Mo:SnO2 thin films is evaluated for solar water oxidation.

Distribution of O atoms on partially oxidized metal targets, and the consequences for reactive sputtering of individual metal oxides

We investigate the oxidation of a wide range of metal surfaces by ab-initio calculations. We go through a wide range of metals (Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Ag, Au, Zn, Cd, Al) and surface oxygen coverages (ΘO). Calculations of the adsorption energy per O atom (Eads_min) are followed by characterizing the preferred distribution of O atoms on a partially oxidized surface (considering up to 329 distributions per metal). We find that individual metals exhibit qualitatively different Eads_min(ΘO) dependencies and thermodynamical preferences: (i) decreasing Eads_min(ΘO) and heterogeneous distribution of O atoms (stoichiometric oxide + metal; e.g. Al or La), (ii) increasing Eads_min(ΘO) and homogeneous distribution of O atoms (substoichiometric oxide; e.g. Ti or Zr), (iii) concave Eads_min(ΘO) and homogeneous distribution of O atoms at low ΘO and heterogeneous at high ΘO (e.g. Sc or Y), etc. This is of crucial importance for the quantities such as secondary electron emission yield, which are guaranteed to correspond to a weighted average of those of stoichiometric oxide and metal only in the case of heterogeneous O atom distribution. The results are correlated with formation enthalpies of oxides of various compositions, surface atomic densities of individual metals, and experimental results such as the time dependence of the magnetron voltage during sputter cleaning of oxidized metal targets. Furthermore, we demonstrate use of these results by presenting static and dynamic Monte Carlo simulations of sputtering.

Abrasive Wear Resistance of Alloyed Electric-Arc Coatings from Flux-Cored Wires

We study the structure, abrasive and gas-abrasive wear resistances of electric-arc coatings from fluxcored wires of domestic and TAFA, Praxair, EnDoTec DO, and Castolin-EuTronic leading foreign companies at room and elevated temperatures. It is shown that the wear resistance of the coatings sprayed from two heterogeneous flux-cored wires is twice higher than the wear resistance of ShKh15 steel in tests with fixed abrasive due to its elevated cohesive strength, low level of residual stresses, and high hardness. It is discovered that, in tests with nonfixed abrasive, a coating obtained from the EnDoTec DO*390N flux-cored wire has the highest wear resistance due to the presence of tungsten, vanadium, and niobium carbides in its charge. It was established that, at room temperature, the gas-abrasive wear resistance of the coatings remains equal to the wear resistance of 12Kh1МF steel or is much lower than the wear resistance of steel. As the temperature increases over 400°С, the gas-abrasive wear resistance of the coatings increases due of the formation of oxides of various compositions.

Dissolution of Manganese Oxides of Various Compositions in Sulfuric Acid Solutions Studied by Kinetic Methods

The dissolution of manganese oxides in sulfuric acid solutions of various concentrations has been studied by kinetic methods. We have investigated the dissolution of manganese oxides of various compositions in sulfuric acid solutions of various concentrations. The composition of the manganese oxides and the sulfuric acid concentration have been shown to influence the dissolution rate. We have calculated kinetic parameters of the dissolution of manganese oxides in sulfuric acid solutions (dissolution rate, activation energy for dissolution, and reaction orders) and proposed a model for the dissolution of manganese oxides in sulfuric acid solutions.

Reactions of manganese oxides with sulfuric acid solutions studied by kinetic and electrochemical methods

Reactions of manganese oxides of various compositions with sulfuric acid solutions have been studied by kinetic and electrochemical methods. The surface composition of the manganese oxides has been shown to vary during the dissolution process. We present mathematical dependences of the dissolution rate on kinetic parameters of the electrolyte solution for the oxides of various compositions and interpret the behavior of the manganese oxide with various compositions during dissolution in sulfuric acid solutions of various concentrations.

Mixed-oxide nanoparticles in a polyethylene matrix

We have synthesized and characterized mixed oxides of various compositions which are excellent precursors for the preparation of cathode materials for lithium ion batteries. The materials consist of mixed oxide nanoparticles about 2 nm in size, stabilized in a hydrocarbon matrix. We describe the fabrication of such materials and present transmission and scanning electron microscopy and X-ray diffraction data for them and their basic electrochemical characteristics.

Thermodynamic explanation of the universal correlation between oxygen evolution activity and corrosion of oxide catalysts.

In recent years, the oxygen evolution reaction (OER) has attracted increased research interest due to its crucial role in electrochemical energy conversion devices for renewable energy applications. The vast majority of OER catalyst materials investigated are metal oxides of various compositions. The experimental results obtained on such materials strongly suggest the existence of a fundamental and universal correlation between the oxygen evolution activity and the corrosion of metal oxides. This corrosion manifests itself in structural changes and/or dissolution of the material. We prove from basic thermodynamic considerations that any metal oxide must become unstable under oxygen evolution conditions irrespective of the pH value. The reason is the thermodynamic instability of the oxygen anion in the metal oxide lattice. Our findings explain many of the experimentally observed corrosion phenomena on different metal oxide OER catalysts.

Ionic liquid-mediated synthesis of meso-scale porous lanthanum-transition-metal perovskites with high CO oxidation performance.

Lanthanum-transition-metal perovskites with robust meso-scale porous frameworks (meso-LaMO3) are synthesized through the use of ionic liquids. The resultant samples demonstrate a rather high activity for CO oxidation, by taking advantage of unique nanostructure-derived benefits. This synthesis strategy opens up a new opportunity for preparing functional mesoporous complex oxides of various compositions.

Combined Functional Biocoatings on the VT-6 Alloy

Electrochemical oxidation of spark-deposited coatings from intermetallic TiAl3 and TiN–3AlN nitride ceramics in 3% NaCl solution leads to a nanosized surface layer composed of titanium oxides of various composition: from higher to lower oxides toward the substrate. The highest corrosion resistance is shown by the intermetallic coating, which is confirmed by anodic oxidation polarization curves and layerwise Auger spectroscopy of protective titanium and aluminum oxide films. A combined biocoating is produced as follows: electrospark deposition of TiAl3 layer onto VT-6 alloy—electrochemical oxidation in 3% NaCl solution—deposition of hydroxyapatite layer—laser fusion. Energy-dispersive X-ray spectroscopy has revealed a wide adhesion area at the interface between the spark-deposited coating and hydroxyapatite, which agrees with smooth variation in microhardness in this area. The coating shows strong adhesion to the substrate and biocompatibility with the bone tissue.

Transformations of mixed molybdenum-vanadium oxides in the oxidation of hydrocarbons by molecular oxygen

Structural-morphological transformations of molybdenum-vanadium mixed oxide catalysts of varying composition in the oxidation of hydrocarbons are studied by X-ray diffraction analysis, electron microscopy, electron paramagnetic resonance technique, and Raman scattering spectroscopy. It is shown that the catalytic reactions, which are analyzed in detail for oxides of various compositions, cause a considerable restructuring of the mixed oxides.

Effect of Direct Transport Current and Heat Treatment on Resistive Properties of Bismuth-Based Ceramic High-Temperature Superconducting Oxides of Various Compositions

The effect of direct transport current (I) and heat treatment on resistive properties of bismuth-based ceramic high-temperature superconducting oxides of various compositions is studied by temperature dependent resistivity (r) measurements at fixed points in the vicinity of liquid nitrogen temperature in the presence of Earth's uncompensated magnetic field. It is shown that the observed results are significantly dependent on the sample preparation and post-processing conditions as well as on the measurement temperature. The results obtained are interpreted within the framework of the theory of Josephson weak links modified under the impact of self magnetic field of the sample’s transport current. An attempt is also done to find an analogy between the dependence of the characteristic parameters on the transport current in the case of heat treatment and on the dose when the samples are irradiated by various types of ionizing radiation.

Structural and spectroscopic properties of high temperature prepared ZrO2–TiO2 mixed oxides

ZrO₂-TiO₂ mixed oxides of various composition, with the molar fraction of TiO₂ ranging from 0.1% to 15%, have been prepared via sol-gel synthesis and then calcined at 1273 K to check both their thermal stability and physicochemical properties. These solids are usually employed in photocatalytic processes and as active phase supports in heterogeneous catalysis. As indicated by X-ray diffraction and Raman spectroscopy, solid solutions based on Ti ions diluted in the ZrO₂ matrix are formed in the whole range of Ti molar fraction examined. Materials with low Ti loading (0.1%–1%) are basically constituted by the monoclinic phase of ZrO₂ while the tetragonal phase becomes prevalent at 15% of TiO₂ molar fraction. The presence of Ti ions modify the electronic structure of the solid as revealed by investigation of the optical properties. The typical band gap transition of ZrO₂ undergoes, in fact, a red shift roughly proportional to the Ti loading which reach the remarkable value of 1.6 eV for the sample with 10% of molar Ti concentration. Comparing chemical analysis of the solids with XPS data it has been put into evidence that the titanium ions distribution into the solid is not uniform and the concentration of Ti⁴⁺ tend tomore » be higher in subsurface layers than in the crystal bulk. The introduction of titanium ions in the structure increases the reducibility of the solid. Annealing under vacuum at various temperatures causes oxygen depletion with consequent reduction of the solid which shows up mainly in terms of formation of Ti³⁺ reduced centres which are characterized by a typical EPR signal. Ti³⁺ defects forms, as also forecast by theoretical modelling of the solid, as their energy is lower than that of other possible reduced defective centers. The reduced solids are able to transfer electrons to adsorbed oxygen molecules in mild condition resulting in the formation of surface superoxide anions (O₂⁻) which are stabilized on surface Zr⁴⁺ or, alternatively, on Ti⁴⁺ ions according to the sample composition. - Graphical abstract: The presence of Ti in ZrO₂ modifies UV–vis and electronic properties of mixed oxides. Highlights: • ZrO₂–TiO₂ mixed oxides have been prepared via sol–gel synthesis. • Solids with low Ti loading are constituted by the monoclinic phase of ZrO₂. • The presence of Ti ions modify the electronic structure of the solid. • The introduction of titanium ions increases the reducibility of the solid.« less

Effect of nano-oxide concentration on the mechanical properties of a maxillofacial silicone elastomer

Contemporary silicone-based elastomeric prostheses tend to degrade over time because of the effect of mechanical loading. Little has been reported on how the mechanical properties of a maxillofacial prosthetic elastomer may be affected by the addition of nanosized oxide particles used as an opacifier. The purpose of this study was to evaluate the effect of different concentrations of nanosized oxides of various composition on the mechanical properties of a commercially available silicone elastomer. Nanosized oxides (Ti, Zn, or Ce) were added in various concentrations (0.5%, 1.0%, 1.5%, 2.0%, 2.5%, or 3.0% by weight) to a commercial silicone elastomer (A-2186), commonly used for fabricating extraoral maxillofacial prostheses. Silicone elastomer A-2186 without nanosized oxides served as a control group. Specimens (n=5) were polymerized according to manufacturer's recommendations and tested for tensile strength (ASTM D412) and tear strength (ASTM D624), and percent elongation in a universal testing machine. Uniformity of particle dispersion within the processed elastomer was assessed using scanning electron microscopic imaging. For each property, a 2-way ANOVA was performed evaluating the effect of oxide type and strength, and Fisher's PLSD test was used for pairwise comparisons (alpha=.05). SEM examination indicated that all 3 nanosized oxides distribute evenly throughout the silicone specimens, except for the 3.0% group, which are partly agglomerated. The 2.0% and 2.5% groups of all nanosized oxides demonstrated significantly higher tensile and tear strengths and percent elongation (P<.001) than the control group. CeO(2) had significantly lower tensile strength than TiO2 and ZnO (P<.05). The ZnO group had significantly higher tear strength than TiO(2) and CeO(2) (P <.05). Most of specimens became somewhat harder when compared with the control group. CeO(2) group had significantly higher Shore A hardness than TiO(2) and ZnO (P<.001). There was no significant difference of percent elongation among the type of nanosized oxides. Incorporation of Ti, Zn, or Ce nano-oxides at concentrations of 2.0% and 2.5% improved the overall mechanical properties of the silicone A-2186 maxillofacial elastomer.

The interaction of CH3Cl, CH2Cl2, CHCl3, and CCl4 with ozone on the surface of ice under stratospheric conditions

The interaction of ozone with chlorinated methanes adsorbed on a thin ice film was studied over the temperature range 77–292 K. Ozone was shown to oxidize chlorinated methanes starting with 210 K to produce chlorine oxides of various compositions. The products formed in the oxidation of chlorinated methanes with ozone over the temperature range 77–292 K were analyzed by IR Fourier transform spectroscopy. Along with carbon dioxide and water, chlorine oxides in high oxidation states were predominantly formed.

Effect of genesis on the properties and hydrogen reducibility of NiO-ZnO mixed oxides

The physico-chemical properties and reactivity tested by hydrogen reduction have been studied for two series of NiO-ZnO mixed oxides of various composition. The solid nickel oxide or zinc oxide in interaction with the solution of nitrate of the second component were used as the precursors in each series. The differences in some physico-chemical parameters of the samples in both series were correlated with their reduction behaviour, followed both in iso- and non-isothermal regime. Moreower, the influence of various factors modifying the reactivity of mixed oxides was also investigated and the results were compared with those obtained from earlier studied analogous systems of quite different origin.

Properties of NiO–ThO2 Mixed Oxides From Hydroxides and Their Hydrogen Reducibility Behaviour

Some physico-chemical properties of NiO–ThO2 mixed oxides of various compositions have been investigated. The presence of strongly bound constitutional water in the hydrogel of reactive forms of thorium dioxide, determined by their origin (thermal decomposition of mixed hydroxides) caused the different reduction behaviour as compared with other mixed oxide systems containing the only, thermodynamically less stabile reducible component. The significant effects of the thermal treatment in oxygen atmosphere, pre-irradiation by the gamma rays or accelerated electrons under various conditions (in air or in water suspension) as well as of surface chemical activation with a platinum complex on the reactivity of mixed oxides or reoxidized samples during their hydrogen reduction have been also proved.

Effect of annealing on aging characteristics of MgO-CaO film as a protective layer for AC PDP

The present generation of AC plasma display panels (AC PDP) requires further improvement because of poor voltage characteristics and high production cost. The voltage characteristics of AC PDPs are greatly affected by a protective layer because it is directly exposed to the gas plasma. To replace the conventional MgO protective layer in order to improve the voltage characteristics, panels with various protective layers of an MgO-CaO system were prepared by an e-beam evaporation method. Among the oxides of various composition of the MgO-CaO system, a panel with an Mg0.9Ca0.1O protective layer had the lowest firing and sustaining voltages. But, it exhibited poor aging characteristics, compared to the conventional MgO protective layer. A post annealing process was introduced so as to improve the surface properties and aging characteristics of the Mg0.9Ca0.1O protective layer in this work. The annealing process was performed in nitrogen gas as a function of holding time at 400 °C. From XRD analyses, the (111) orientation formed in the as-deposited Mg0.9Ca0.1O thin film remained unchanged after the annealing process. However, the surface morphology of the Mg0.9Ca0.1O protective layer, which is closely related to its aging characteristics was greatly affected by the annealing conditions. The refractive index of the Mg0.9Ca0.1O thin film was increased by the annealing process at 400 °C for 5 h, which is probably due to an increase in film density. The sustaining voltage of the annealed Mg0.9Ca0.1O film is lower in the initial aging period but higher than that of the as-deposited Mg0.9Ca0.1O film after obtaining a stable voltage. However, the annealing in nitrogen gas made the aging process much shorter, compared to that of the as-deposited Mg0.9Ca0.1O film. The aging characteristic of the Mg0.9Ca0.1O protective layer was found to be greatly improved by the annealing process in nitrogen gas at 400 °C for 5 h.

97/01913 Iron distribution among phases in high- and low-sulfur coal fly ash

Moessbauer spectroscopy, reflected-light optical microscopy, scanning-electron microscopy, wet chemical, and X-ray diffraction studies were conducted on six fly ash samples. The fly ashes, representing the combustion by-products of coals with total sulfur contents of less than 2% to greater than 4%, ranged from 17.6 to 32.0% Fe{sub 2}O{sub 3} by XRF analysis. Wet chemical analysis was used to determine the Fe{sup 3+}/{summation}Fe content of the ashes, which ranged from 72% to 83%. Optical analysis of the ashes indicated that the spinel, encompassing iron oxides of various compositions, ranges from 4.0 to 12.6% (vol.). Moessbauer analyses confirmed the presence of three Fe-bearing phases: magnetite, hematite (possibly of two different compositions), and glass. The variation in the Fe-oxidation state follows the variation in the sulfur, consequently pyrite, content of the feed coal.

Radiation influencing of the reactivity of NiO-Bi 2O 3 mixed oxides during their hydrogen reduction

The basic physico-chemical properties of NiO-Bi 2O 3 mized oxides of various composition and their chemical reactivity during hydrogen reduction as a test reaction were studied. The reduction rate was found to be a nonmonotonic function of composition of the samples which can be positively affected by heat treatment in various atmospheres. Gamma-preirradiation of the system in air with a dose of 1 MGy led to an acceleration in the process of reduction, whereas irradiation of the samples in water suspension with the same dose caused a conspicuous decrease in the reduction rate. The sensitivity of the mixed oxides under study towards heat treatment and ionizing radiation, as well as their reactivity in general, decreased with increasing content of Bi 2O 3. The negative radiation effect appears to be correlable with an increase in surface oxidation ability, whereas positive influencing of the reduction rate can be correlated with an increased concentration of stabilized charge defects (non-equilibrium electrons), enhancing the reactivity of an interface.