Reduction of Oxide Mixtures of (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + CuO) and (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) by Low-Temperature Hydrogen Plasma

The paper presents experimental results pertaining to the reduction of oxide mixtures namely (Fe₂O₃ + CuO) and (Fe₂O₃ + Co₃O₄), by low-temperature hydrogen plasma in a microwave hydrogen plasma set-up, at microwave power 750 W and hydrogen flow rate 2.5 × 10^?6 m³ s^?1. The objective was to examine the effect of addition of CuO or Co₃O₄, on the reduction of Fe₂O₃. In the case of the Fe₂O₃ and CuO mixture, oxides were reduced to form Fe and Cu metals. Enhancement of reduction of iron oxide was marginal. However, in the case of the Fe₂O₃ and Co₃O₄ mixture, FeCo alloy was formed within compositions of Fe₇₀Co₃₀, to Fe₃₀Co₇₀. Since the temperature was below 841 K, no FeO formed during reduction and the sequence of Fe₂O₃ reduction was found to be Fe₂O₃ → Fe₃O₄ → Fe. Reduction of Co₃O₄ preceded that of Fe₂O₃. In the beginning, the reduction of oxides led to the formation of Fe–Co alloy that was rich in Co. Later Fe continued to enter into the alloy phase through diffusion and homogenization. The lattice strain of the alloy as a function of its composition was measured. In the oxide mixture in which excessive amount of Co₃O₄ was present, all the Co formed after reduction could not form the alloy and part of it appeared as FCC Co metal. The crystallite size of the alloy was in the range of 22–30 nm. The crystal size of the Fe–Co alloy reduced with an increase in Co concentration.     

Gold nanoparticles fabricated by pulsed laser ablation in supercritical CO2

Nanosecond pulsed laser ablation (PLA) of gold plate with an excitation wavelength of 532?nm was carried out in supercritical CO₂ (scCO₂) to fabricate gold nanoparticles. Surface morphology of the gold plate after irradiation and the crater depth after PLA were observed by scanning electron microscopy and laser scanning microscopy, while extinction spectra of gold nanoparticles collected in the glass slide was measured by UV?CVis spectrophotometer. The gold plate was ablated at various scCO₂ densities and irradiation times at constant temperature of 40??C. The ablation was also conducted at atmospheric condition with air to evaluate the environmental dependence of ablation. Both surface morphology of the irradiated gold plate and crater depth formation were significantly affected by the changes in scCO₂ density, the surrounding environment, and irradiation time. As expected, the increasing scCO₂ density resulted in a deeper ablation crater, however, the deepest crater was obtained at a density of 0.63?g/cm³ or pressure of 10?MPa. Gold nanoparticles generated by PLA in scCO₂ have been confirmed at the spectra band near 530?nm.     

Preparation of size‐controlled In2O3 nanoparticles

Highly crystalline and monodisperse In₂O₃ nanoparticles were successfully prepared by thermal decomposition of In(dipy)₃Cl₃·2H₂O in oleylamine and oleic acid under inert atmosphere. The size of In₂O₃ nanoparticles could be readily tuned from 10–15 nm to 40–50 nm, depending on the molar ratio of precursor to combined solvent in the reaction system. As‐synthesized In₂O₃ nanoparticles have a center‐body cubic structure as characterized by powder X‐ray diffraction and selected‐area electron diffraction. Transmission electron microscopy images showed that In₂O₃ nanoparticles have a narrow size distribution. A relatively strongly PL peak centered at 378 nm could be clearly seen when 10–15 nm In₂O₃ nanoparticles redispersed in cyclohexane were excited at 275 nm at room temperature. Copyright © 2007 John Wiley & Sons, Ltd.     

High temperature oxidation of HP40 alloy under H2–H2O and air atmospheres: a surface study

In the present work, high temperature oxidation of HP40 alloy was carried out at 1050 °C under H₂–H₂O and air atmospheres; the influence of atmosphere on surface morphology and composition was studied. Octahedral crystals with considerable spalled regions are present on the surface of alloy oxidized under air, the oxide scale composes of MnCr₂O₄, Cr₂O₃ and (Fe, Ni)Cr₂O₄ and spalled regions exhibit base alloy and SiO₂‐rich regions. The surface of alloy oxidized under H₂–H₂O is fully covered by small granular crystals and blade‐type structures without spallation, and the oxide scale composes of MnCr₂O₄ and Cr₂O₃. Moreover, X‐ray photoelectron spectroscopy analysis shows considerable difference in chemical valence states of Mn, Cr and O elements on both alloy surfaces, and hydroxyl compounds exist on the alloy oxidized under H₂–H₂O atmosphere. Copyright © 2017 John Wiley & Sons, Ltd.     

A Hydrogen-Deficient Nickel–Cobalt Double Hydroxide for Photocatalytic Overall Water Splitting

Developing highly efficient and low-cost photocatalysts for overall water splitting has long been a pursuit for converting solar power into clean hydrogen energy. Herein, we demonstrate that a nonstoichiometric nickel–cobalt double hydroxide can achieve overall water splitting by itself upon solar light irradiation, avoiding the consumption of noble-metal co-catalysts. We employed an intensive laser to ablate a NiCo alloy target immersed in alkaline solution, and produced so-called L-NiCo nanosheets with a nonstoichiometric composition and O²⁻/Co³⁺ ions exposed on the surface. The nonstoichiometric composition broadens the band gap, while O²⁻ and Co³⁺ ions boost hydrogen and oxygen evolution, respectively. As such, the photocatalyst achieves a H₂ evolution rate of 1.7 μmol h⁻¹ under AM 1.5G sunlight irradiation and an apparent quantum yield (AQE) of 1.38 % at 380 nm.     

Growth and field crystallization of anodic films on Ta–Nb alloys

The growth behavior of amorphous anodic films on Ta–Nb solid solution alloys has been investigated over a wide composition range at a constant current density of 50 A m⁻² in 0.1 mol dm⁻³ ammonium pentaborate electrolyte. The anodic films consist of two layers, comprising a thin outer Nb₂O₅ layer and an inner layer consisting of units of Ta₂O₅ and Nb₂O₅. The outer Nb₂O₅ layer is formed as a consequence of the faster outward migration of Nb⁵⁺ ions, compared with Ta⁵⁺ ions, during film growth under the high electric field. Their relative migration rates are independent of the alloy composition. The formation ratio, density, and capacitance of the films show a linear relation to the alloy composition. The susceptibility of the anodic films to field crystallization during anodizing at constant voltage increases with increasing niobium content of the alloy.     

Nanoporous platinum–cobalt alloy for electrochemical sensing for ethanol,hydrogen peroxide,and glucose

Nanoporous platinum–cobalt (NP–PtCo) alloy with hierarchical nanostructure is straightforwardly fabricated by dealloying PtCoAl alloy in a mild alkaline solution. Selectively etching Al resulted in a hierarchical three-dimensional network nanostructure with a narrow size distribution at 3 nm. The as-prepared NP–PtCo alloy shows superior performance toward ethanol and hydrogen peroxide (H₂O₂) with highly sensitive response due to its unique electrocatalytic activity. In addition, NP–PtCo also exhibits excellent amperometric durability and long-term stability for H₂O₂ as well as a good anti-interference toward ascorbic acid, uric acid, and dopamine. The hierarchical nanoporous architecture in PtCo alloy is also highly active for glucose sensing electrooxidation and sensing in a wide linear range. The NP–PtCo alloy holds great application potential for electrochemical sensing with simple preparation, unique catalytic activity, and high structure stability.     

High-temperature oxidation of FeCrAl alloy with alumina–silica–ceria coatings deposited by sol–gel method

One-layer protective coatings made up of SiO₂–Al₂O₃ or SiO₂–Al₂O₃–CeO₂ oxides were synthesized on a FeCrAl alloy substrate by the sol–gel method from sols containing tetraethyl orthosilicate, aluminum tri-sec-butoxide and cerium(III) 2,4-pentanedionate as the precursors. Coating solutions with the Si:Al:Ce molar ratio of 3:1:0, 3:1:0.1; 3:1:0.01, and 3:1:0.001 were used. The composition and morphology of the obtained gels were examined by TG/DSC, XRD, and SEM techniques. It was found that a small addition of cerium affected the morphology of the forming coatings and improved the FeCrAl alloy resistance to high-temperature oxidation (in air at T = 900 °C for t = 100 h). The oxidation of all the investigated samples conformed to the parabolic rate. The protection effectiveness of the one-layer coatings after 100 h of high-temperature oxidation was as high as 70 %.     

A Hydrogen‐Deficient Nickel–Cobalt Double Hydroxide for Photocatalytic Overall Water Splitting

Developing highly efficient and low‐cost photocatalysts for overall water splitting has long been a pursuit for converting solar power into clean hydrogen energy. Herein, we demonstrate that a nonstoichiometric nickel–cobalt double hydroxide can achieve overall water splitting by itself upon solar light irradiation, avoiding the consumption of noble‐metal co‐catalysts. We employed an intensive laser to ablate a NiCo alloy target immersed in alkaline solution, and produced so‐called L‐NiCo nanosheets with a nonstoichiometric composition and O^2?/Co³⁺ ions exposed on the surface. The nonstoichiometric composition broadens the band gap, while O^2? and Co³⁺ ions boost hydrogen and oxygen evolution, respectively. As such, the photocatalyst achieves a H₂ evolution rate of 1.7 μmol h^?1 under AM 1.5G sunlight irradiation and an apparent quantum yield (AQE) of 1.38 % at 380 nm.     

β-Ga2O3 nanowires sheathed with boron nitrogen

A new synthetic route was developed to obtain β-Ga₂O₃ nanowires by heating mixed B and Ga₂O₃ powder precursor at 1600 °C under Ar atmosphere. The nanowires have widths of 30–60 nm and perfect crystallinity. When the heating of B and Ga₂O₃ powder precursor was carried out in N₂ atmosphere, β-Ga₂O₃ nanowires sheathed with BN layers (3–5 nm) were yielded. The structure and composition of the products were characterized. The growth scenario for the β-Ga₂O₃ nanowires as well as the formation of outer BN sheaths was also discussed.     

Defect chemistry and VUV optical properties of the BaMgAl10O17:Eu-Ba0.75Al11O17.25:Eu solid solution

The optical properties of the BaMgAl₁₀O₁₇:Eu²⁺ (BAM)-Ba_0.75Al₁₁O_17.25:Eu²⁺ (BAL) solid solution have been studied using VUV excitation, emission and reflectance spectroscopy. Three unique Eu²⁺ emission centers are observed in a ratio that depends on the composition of the host and the dopant concentration. Two of the emission centers are assigned to Eu on normal Beevers-Ross sites and Eu on anti Beevers-Ross sites. The defect chemistry of this system is modeled based on the known behavior of the spinel (MgO·nAl₂O₃) system. Based on this model, the third Eu center can be assigned either to Eu near Al vacancies or to Eu associated with O atoms in the cation layer. In undoped materials exciton emission is observed, peaking at 263 nm in BAM and 285 nm in BAL. This emission may be the mechanism of host-to-activator energy transfer in these phosphors.     

State of disperse alloy particles catalyzing hydrocarbon decomposition by the carbide cycle mechanism: TEM and EDX studies of the Cu-Ni/Al2O3 and Cu-Co/Al2O3 catalysts

The state of disperse bimetallic alloy particles in the Cu-Ni/Al₂O₃ and Cu-Co/Al₂O₃ catalysts during their carbonization in butadiene-1,3 is studied by high-resolution electron microscopy and energy-dispersive X-ray analysis. During the formation of carbon nanofilaments by the carbide cycle mechanism, the catalyst is in a dissipative state such that the bimetallic particles vary in composition and have an anomalous component distribution in their bulk. The extrapolation of this state provides insight into the processes occurring in the dissipative system.     

Effect of the phase composition of the starting mixture on the formation of the layered perovskite-like compound Bi<Subscript>7</Subscript>Fe<Subscript>3</Subscript>Ti<Subscript>3</Subscript>O<Subscript>21</Subscript>

The effect of the phase composition of the starting mixture on the formation of the layered perovskite-like compound Bi₇Fe₃Ti₃O₂₁ in the Bi₂O₃-TiO₂-Fe₂O₃ system is reported. The rate-limiting process in the formation of this compound is reactant mass transfer to the reaction zone.     

Topotactical growth of thick perovskite oxynitride layers by nitridation of single crystalline oxides

Thick films of the perovskite-related oxynitrides LaTiO₂N, NdTiO₂N, SrNbO₂N and SrTaO₂N were synthesised by nitridation of single crystals of the corresponding oxides with general composition ABO_3.5. The oxide crystals were obtained by optical floating zone growth. They correspond to n = 4 member of the A_nB_nO_3n+2 family of layered perovskites and were reacted at temperatures between 900 °C and 1050 °C to form the oxynitrides. Electron probe microanalysis proved the presence of nitrogen in a surface layer of a few micrometer thickness. Cross-section SEM revealed additional thin stripes of oxynitride within the bulk of the crystals, indicating that nitrogen is incorporated preferably parallel to the perovskite-type layers, which in turn are connected in a zipper-type mechanism. The formation of the desired perovskite-type oxynitrides was confirmed by X-ray diffraction. Pole figure measurements proved an epitaxial orientation ABO₂N (110)[001]  ABO_3.5 (001)[100]. The mosaicity of the oxynitrides both in polar and azimuthal direction was very small (<2°) indicating a nearly single crystalline quality of the surface layer. The nitridation of the crystals results in a dramatic change in colour. Optical spectroscopy revealed shifts of the absorption edge by more than 200 nm to longer wavelengths with respect to the parent oxides, corresponding to a reduction of the band gap energies by 1.4–1.8 eV.     

Corrosion behavior of Mg,AZ31, and AZ91 alloys in dilute NaCl solutions

Corrosion behavior of extruded Mg, extruded AZ31 alloy, and cast AZ91 alloy was investigated by electrochemical measurements in dilute NaCl solutions. Corrosion products and passivation films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. All specimens exhibit the corrosion and passivation zones in dilute NaCl solutions. The aluminum content and alloy microstructure influence the corrosion and passivation processes. AZ91 alloy shows the broadest passivation zone followed by AZ31 alloy and Mg. AZ91 alloy reveals a highest corrosion resistance, and preferential attack is located at the primary Mg phase. Its relatively fine β-phase (Mg₁₇Al₁₂) network and Al₂O₃/Al(OH)₃ compounds produced on the passivation film are the main factors which limit the corrosion progress as compared with AZ31 alloy and Mg. The thick passivation product on AZ31 alloy is the key factor which restricts the corrosion attack in dilute solutions.     

Characterization of high-temperature superconductors by electron microprobe analysis

In order to optimize the physical properties of HTSC small single crystals grown from a melt for basic studies of their physical properties the influence of the environment on their impurity content was investigated by EPMA. This requires quantitative analysis of all elements being present in the crystals. The accuracy of results was affected by problems with the choice and quality of standards, by contamination but also by malfunction of microprobe electronics. The HTSC materials were found to react with mills, milling balls, crucibles and the atmosphere. These problems are being discussed and some reactions being studied for Y₁Ba₂Cu₃O_6+x (0 < x < 1) HTSC in A1₂O₃ and ZrO₂ crucibles. The crystals grown contain reproducible amounts of impurities depending on boundary conditions and exhibit a zone structure in composition particularly for Y and Ba within their range of homogeneity.     

Single red up-conversion luminescence of Er sensitized layered Y2Ti2O7 phosphor

High color purity red emission with single band successfully achieved in a new Er³⁺, Tm³⁺ co-doped Y₂Ti₂O₇ system under 1550 nm excitation, value of red to green emission ratio of the samples is more than 10³. Efficient up-conversion luminescence can be obtained while the ⁴I_13/2 level of Er³⁺ pumped by 1500 nm directly based on the large absorption section and long luminescence lifetime, and red emission composition will greatly enhanced by co-doping with Tm³⁺ ions, color purity of red emission under 1550 nm excitation is much higher than that of 980 nm. The quenching concentration of Er³⁺ ions is up to 28 mol% in Y₂Ti₂O₇ rely on the layer distribution of cations, which can further improve the red emission color purity.     

Formation of Pd–Ag nanoparticles in supported catalysts based on the heterobimetallic complex PdAg<Subscript>2</Subscript>(OAc)<Subscript>4</Subscript>(HOAc)<Subscript>4</Subscript>

The formation of Pd–Ag nanoparticles deposited from the heterobimetallic acetate complex PdAg₂(OAc)₄(HOAc)₄ on α-Al₂O₃, γ-Al₂O₃, and MgAl₂O₄ has been investigated by high-resolution trans-mission electron microscopy, temperature-programmed reduction, and IR spectroscopy of adsorbed CO. The reduction of PdAg₂(OAc)₄(HOAc)₄ supported on γ-Al₂O₃ and MgAl₂O₄ takes place in two steps (at 15–245 and 290–550°C) and yields Pd–Ag particles whose average size is 6–7 nm. The reduction of the Pd–Ag catalyst supported on α-Al₂O₃ occurs in a much narrower temperature range (15–200°C) and yields larger nanoparticles (~10–20 nm). The formation of Pd–Ag alloy nanoparticles in all of the samples is demonstrated by IR spectroscopy of adsorbed CO, which indicates a marked weakening of the absorption band of the bridged form of adsorbed carbon monoxide and a >30-cm^–1 bathochromic shift of the linear adsorbed CO band. IR spectroscopic data for PdAg₂/α-Al₂O₃ suggest that Pd in this sample occurs as isolated atoms on the surface of bimetallic nanoparticles, as is indicated by the almost complete absence of bridged adsorbed CO bands and by a significant weakening of the Pd–CO bond relative to the same bond in the bimetallic samples based on γ-Al₂O₃ and MgAl₂O₄ and in the monometallic reference sample Pd/γ-Al₂O₃.     

Scanning Auger analysis for the clarification of oxidation and interdiffusion processes during laser ablation of YBa2Cu3O7-x on alloy/oxide substrates

Scanning Auger investigations are reported on layer systems consisting of a metallic substrate, an oxide buffer layer and the YBa₂Cu₃O_7?x (YBCO) high temperature superconductor. By bending the samples under UHV conditions the internal interfaces have been made accessible for the Auger analysis. The examination of the interfaces have shown that an oxidation of the substrate alloy had taken place during the deposition of the YBCO in spite of the buffer layer already being present. Additionally, segregated sulphur has been found on the substrate/buffer interface, which can lead to a loss of adhesion of the layer system. By line scan investigations on samples prepared by ball cratering a carbon enriched zone of approximately 50 nm thickness has been detected at the interface of buffer and YBCO.     

Nonlinear Optical Susceptibility of Fe2O3 Thin Film Synthesized by a Modified Sol-Gel Method

The homogeneous transition metal oxide Fe₂O₃ thin films are synthesized in a modified sol-gel process by spin coating. The third order nonlinear optical susceptibility of the film is about 2 × 10^–9 esu at 488 nm wavelength by the z-scan method with a 180 femtosecond pulse laser beam. The film is expected to be useful for the application of nonlinear optical devices.