Characterization of Ni–Pd alloy as anode for methanol oxidative fuel cell

Electrochemical deposition of Ni–Pd alloy films of various compositions from bath solution containing ethylenediamine (EDA) was carried out to use as anode material for methanol oxidative fuel cell in H₂SO₄ medium. Electronic absorption spectrum of bath solution containing Ni²⁺, Pd²⁺ ions and EDA indicated the formation of a four coordinate square planar metal–ligand complex of both the metal ions. X-ray diffraction (XRD) patterns of the deposited alloy films show an increase in Pd–Ni alloy lattice parameter with increase in Pd content, and indicate the substitution of Pd in the lattice. A nano/ultrafine kind of crystal growth was observed in the alloy film deposited at low current density (2.5 mA cm⁻²). X-ray photoelectron spectroscopic (XPS) studies on the successively sputtered films showed the presence of Ni and Pd in pure metallic states and the surface concentration ratio of Ni to Pd is less than bulk indicating the segregation of Pd on the surface. Electro-catalytic oxidation of methanol in H₂SO₄ medium is found to be promoted on Ni–Pd electrodeposits. The anodic peak current characteristics to oxidation reaction on Ni–Pd was found typically high when compared to pure nickel and the relative increase in surface area by alloying the Ni by Pd was found to be as much as 300 times.     

Color centers and charge state recharge in γ-irradiated Yb:YAP

Gamma-ray irradiation induced color centers and charge state recharge of impurity and doped ion in 10 at.% Yb:YAP have been studied. The change in the additional absorption (AA) spectra is mainly related to the charge exchange of the impurity Fe²⁺, Fe³⁺ and Yb³⁺ ions. Two impurity color center bands at 255 and 313 nm were attributed to Fe³⁺ and Fe²⁺ ions, respectively. The broad AA band centered at 385 nm may be associated with the cation vacancies and F-type center. The transition Yb³⁺ → Yb²⁺ takes place in the process of γ-irradiation. Oxygen annealing and γ-ray irradiation lead to an opposite effect on the absorption properties of the Yb:YAP crystal. In the air annealing process, the transition Fe²⁺ → Fe³⁺ and Yb²⁺ → Yb³⁺ take place and the color centers responsible for the 385 nm band was destroyed.     

Effects of adsorbent dose, its particle size and initial arsenic concentration on the removal of arsenic, iron and manganese from simulated ground water by Fe3+ impregnated activated carbon

This paper presents the observations of the study on arsenic removal from a contaminated ground water (simulated) by adsorption onto Fe³⁺ impregnated granular activated carbon (GAC-Fe). Fe²⁺, Fe³⁺ and Mn²⁺ have also been considered along with arsenic species in the water sample. Similar study has also been done with untreated granular activated carbon (GAC) for comparison. The effects of adsorbent dose, particle size of adsorbent and initial arsenic concentration on the removal of As(T), As(III), As(V), Fe²⁺, Fe³⁺ and Mn²⁺ have been discussed. Under the experimental conditions, the optimum adsorbent doses for GAC-Fe and GAC have been found to be 8 g/l and 24 g/l, respectively with an agitation time of 15 h. Particle size of the adsorbents (both GAC and GAC-Fe) has shown negligible effect on the removal of arsenic and Fe species. However, for Mn removal the effect of adsorbent particle size is comparatively more. Percentage removal of As(T), As(V) and As(III) increase with the decrease in initial arsenic concentration (As₀). However, the increase in percentage removal of all the arsenic species with decrease in As₀ are less for higher value of As₀ (3000–500 ppb) than those of the lower value of As₀ (500–10 ppb). The % removal of As(T), As(III), As(V), Fe, and Mn were 95%, 92.4%, 97.6%, 99% and 41.2%, respectively when 8 g/l GAC-Fe was used at the As₀ value of 200 ppb. However, for GAC these values were 55.5%, 44%, 71%, 98% and 97%. The pH and temperature of the study were 7 ± 0.1 and 30 ± 1 °C, respectively.     

Assessment of electrical and optical properties of heavily Fe-implanted semi-insulating InP

We report total compensation of InP layers n-doped to levels as high as n=2×10¹⁸ cm⁻³ by high temperature (>200°C) MeV Fe implantation and annealing. The electronic density and the active Fe (in the form of the Fe²⁺/Fe³⁺ deep acceptor states) profiles are obtained from the comparison between the current–voltage (I–V) characteristics and the outcome of a numerical simulation. These results are confirmed by photo-induced current transient spectroscopy (PICTS) experiments, which show a correlation between the Fe activation and the background doping concentration. A deeper insight into the properties of the Fe²⁺/Fe³⁺ centers is gained by Fourier transform infrared (FTIR) photoluminescence measurements, showing intense and sharp emission peaks at 3.5 μm, associated with Fe intracenter transitions. The corresponding lifetimes have been studied by time resolved integrated photoluminescence measurements.     

Preparation and activity evaluation of p-n junction photocatalyst NiO/TiO2

p–n Junction photocatalyst NiO/TiO₂ was prepared by sol–gel method using Ni(NO₃)₂·6H₂O and tetrabutyl titanate [Ti(OC₄H₉)₄] as the raw materials. The p–n junction photocatalyst NiO/TiO₂ was characterized by UV–vis diffuse reflection spectrum, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr₂O₇²⁻ and photocatalytic oxidation of rhodamine B. The results show that, for photocatalytic reduction of Cr₂O₇²⁻, the optimum percentage of doped-NiO is 0.5% (mole ratio of Ni/Ti). The photocatalytic activity of the p–n junction NiO/TiO₂ is much higher than that of TiO₂ on the photocatalytic reduction of Cr₂O₇²⁻. However, the photocatalytic activity of the p–n junction photocatalyst NiO/TiO₂ is much lower than that of TiO₂ on the photocatalytic oxidation of rhodamine B. Namely, the p–n junction photocatalyst NiO/TiO₂ has higher photocatalytic reduction activity, but lower photocatalytic oxidation activity. Effects of heat treatment on the photocatalytic activity of p–n junction photocatalyst NiO/TiO₂ were investigated. The mechanisms of influence on the photocatalytic activity were also discussed by the p–n junction principle.     

Wet oxidative method for removal of 2,4,6-trichlorophenol in water using Fe(III), Co(II), Ni(II) supported MCM41 catalysts

Chlorophenols in water are resistant to biological oxidation and they have to be destroyed by chemical oxidation. In the present work, Fe(III), Co(II) and Ni(II) incorporated MCM41 mesoporous solids were used as catalysts for oxidation of 2,4,6-trichlorophenol in water with or without the oxidant, H₂O₂. The catalysts were prepared by impregnation and were characterized by XRD and FTIR measurements. The parent MCM41, Fe(III), Co(II) and Ni(II) impregnated MCM41 had cation exchange capacity of 20.5, 25.5, 24.2, 26.0 mequiv./100 g, respectively. The catalysts were used after calcination at 773–873 K for 5 h. The reactions were carried out in a high pressure stirred reactor at 0.2 MPa (autogenous) and 353 K under various reaction conditions. The conversion achieved with Fe(III), Co(II) and Ni(II) incorporated MCM41 in 5 h is respectively 59.4, 50.0 and 65.6% with 2,4,6-TCP:H₂O₂ molar ratio of 1:1, and 60.2, 60.9 and 68.8% in absence of H₂O₂. The oxidation has a first order rate coefficient of (1.2–4.8) × 10⁻³ min⁻¹. The results show that introduction of Fe(III), Co(II) and Ni(II) into MCM-41 through impregnation produces very effective catalysts for wet oxidation of 2,4,6-trichlorophenol.     

Improvements in mechanical properties of TiB2 ceramics tool materials by the dispersion of Al2O3 particles

TiB₂–Al₂O₃ composites with Ni–Mo as sintering aid have been fabricated by a hot-press technique at a lower temperature of 1530 °C for 1 h, and the mechanical properties and microstructure were investigated. The microstructure consists of dispersed Al₂O₃ particles in a fine-grained TiB₂ matrix. The addition of Al₂O₃ increases the fracture toughness up to 6.02 MPa m^1/2 at an amount of 40 vol.% Al₂O₃ and the flexural strength up to 913.86 MPa at an amount of 10 vol.% Al₂O₃. The improved flexural strength of the composites is a result of higher density than that of monolithic TiB₂. The increase of fracture toughness is a result of crack bridging by the metal grains on the boundaries, and crack deflection by weak grain boundaries due to the bad wetting characters between Ni–Mo and Al₂O₃.     

Microstructural changes in oxygen-irradiated zirconium-based alloy characterised by X-ray diffraction techniques

We have carried out irradiation with 116 MeV O⁵⁺ ions on Zr–1Sn–1Nb–0.1Fe (ZIRLO) alloy at different doses and the microstructural parameters of the irradiated samples have been characterised by X-ray Diffraction Line Profile Analysis (XRDLPA). The average volume-weighted and surface-weighted domain size, microstrain and dislocation density have been estimated as a function of dose. There was a drastic decrease in domain size from unirradiated sample to the sample at a dose of 1 × 10¹⁷ O⁵⁺/m², but these values saturated with increasing dose of irradiation. The values of microstrain were found to increase with dose. The dislocation density increased almost by an order of magnitude for the samples irradiated with 1 × 10¹⁸ O⁵⁺/m² and 5 × 10¹⁸ O⁵⁺/m² as compared to the unirradiated samples.     

Stabilization of copper sludge by high-temperature CuFe2O4 synthesis process

Copper sludge was stabilized by high-temperature CuFe₂O₄ ferritization technique with different sintering temperature, isothermal time and Fe³⁺/M²⁺ molar ratio. Copper is stabilized by inserting the copper ion into the stable CuFe₂O₄ structure by ferritization. The result indicates that sintering temperature above 800 °C would be proper temperature range for CuFe₂O₄ synthesis. When the Fe³⁺/M²⁺ molar ratio of sludges are above the stoichiometric ratio of 2, copper ion in sludge would be stabilized and hence be kept from leaching out. From the result of relative XRD intensity ratio, the equilibrium of the ferritization reaction could be reached by prolonging the isothermal time to 10 h. Judging by the TCLP results, the optimum ferritization parameters are Fe³⁺/M²⁺ molar ratio equal to 3.5, sintering temperature at 800 °C and isothermal time above 10 h.     

Structural characterization of basalt-based glass–ceramic coatings

There are a lot of technologically interesting characteristics of glass–ceramics, which are hard, wear resistant, oxidation and corrosion resistant ceramic materials. In the present study, the production of the basalt-based glass–ceramic coating by atmospheric plasma spray technique and their structural characterization were reported. Basalt-based glass coating was performed on AISI 1040 steel substrate which was pre-coated with Ni–5 wt% Al by using plasma spray gun. Basalt coatings of the glass form were crystallized at 800, 900 and 1000 °C for 1–4 h in orders to transform to the glass–ceramic structure. The presence of augite [(CaFeMg)SiO₃], diopside [Ca(Mg_0.15Fe_0.85)(SiO₃)₂] and aluminian diopside [Ca(Mg,Al)(Si,Al)₂O₆] crystalline phases formed in the basalt-based glass–ceramic coating layer was detected by X-ray diffraction analysis. Optical microscopy with micrometer was used for metallographic examinations. Differential scanning calorimeter was used for determining the crystallization temperature of glass form basalt-based coatings. Microhardness measurements were carried out on the basalt-based glass–ceramic coating layer with Vickers indenter. The hardness of coating layers is changing between 1009 and 1295 HV_0.05 depending on crystallization temperature and process times. It was found that, the higher the crystallization temperature, the more the crystalline phases were resulted. In addition, the lower the crystallization temperature and the longer the treatment time, the harder the coating layer became.     

Fe-substituted tobermorites: Synthesis and characterization by Mössbauer spectroscopy and other techniques

The isomorphous substitution of Fe³⁺ for Si⁴⁺ in the tobermorite (Ca₅Si₆H₂O₁₈·4H₂O) structure and its effects on the cation exchange properties of tobermorites were investigated. Fe³⁺- substituted 11Å tobermorites were synthesized under hydrothermal conditions. The cation exchange capacities of these Fe³⁺-substituted tobermorites ranged between 82–122 meq/100g while specific Cs sorption ranged from 420–800 K_d. ⁵⁷Fe Mossbauer Spectroscopy, in addition to other techniques, was used to investigate the Fe-substitution in the tobermorite structure. None of the Mossbauer spectra revealed any absorption line due to Fe²⁺. The observed spectra were fitted to one or more closely overlapping quadrupole doublets. The assignment of Fe³⁺ among the available tetrahedral and octahedral sites was made based on the distinct differences in the observed isomer shifts. The extent of Fe³⁺_IV vs. Fe³⁺_VI site occupancies was determined from the corrected intensities of the respective quadrupole doublets.     

Spectroscopic evidence of inhomogeneous distribution of Nd in YVO4, YPO4 and YAsO4 crystals

Nd³⁺ : YVO₄ is one of the most interesting laser hosts for micro and diode-pumped solid state lasers. We have studied magnetic and optical properties of Nd³⁺ in three zircon type crystals YMO₄ (M=V, As, P). In particular, Nd³⁺ ions exhibit in the three hosts a multisite character observed in the absorption and emission spectra. However, the emission and its dynamics are strongly dependant on the reabsorption mechanisms. In Nd : YVO₄, single crystals containing 7 ± 1 × 10¹⁸ Nd³⁺ ions/cm³, the lifetime is 95 ± 2 μs in good agreement with the calculated radiative lifetime. Electron Paramagnetic Resonance (EPR) measurements are performed to identify the nature of the different substitution sites for Nd³⁺ ions. Nd³⁺ ions are found to be inhomogeneously distributed in tetragonal D_2d symmetry sites, in isolated ions, “shallow clusters” and pairs. Proportions of the different local environments depend on the total neodymium concentration. For instance, 15% of the Nd³⁺ ions are gathered in Nd³⁺–Nd³⁺ pairs for 7.2 ± 0.2 × 10¹⁹ Nd³⁺ ions/cm³.     

Structural properties of swift heavy ion beam irradiated Fe/Si bilayers

The Fe/Si multilayers were prepared by electron beam evaporation in a cryo-pumped vacuum deposition system. Ag⁺ and Au⁺ ions of 100 MeV at two different fluencies such as 1 × 10¹² ions/cm² and 1 × 10¹³ ions/cm² at a pressure of 10^− 7 torr were used to irradiate the Fe/Si samples. The irradiated samples were analyzed by High-Resolution XRD and it reveals that the irradiated films are having polycrystalline nature and it confirms the formation of the β-FeSi₂. The structural parameters such as crystallite size (D), strain (ε) and dislocation density (δ) have been evaluated from the XRD spectrum. The role of the substrates and the influence of swift heavy ions on the formation of β-FeSi₂ have been discussed in this paper.     

Crystal structure, thermal expansion and electrical conductivity of Nd0.7Sr0.3Fe1−xCoxO3 (0≤x≤0.8)

The crystal structure, thermal expansion and electrical conductivity of the solid solution Nd_0.7Sr_0.3Fe_1−xCo_xO₃ for 0≤x≤0.8 were investigated. All compositions had the GdFeO₃-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction (XRPD). The pseudo-cubic lattice constant decreased continuously with x. The average linear thermal expansion coefficient (TEC) in the temperature range from 573 to 973 K was found to increase with x. The thermal expansion curves for all values of x displayed rapid increase in slope at high temperatures. The electrical conductivity increased with x for the entire temperature range of measurement. The calculated activation energy values indicate that electrical conduction takes place primarily by the small polaron hopping mechanism. The charge compensation for the divalent ion on the A-site is provided by the formation of Fe⁴⁺ ions on the B-site (in preference to Co⁴⁺ ions) and vacancies on the oxygen sublattice for low values of x. The large increase in the conductivity with x in the range from 0.6 to 0.8 is attributed to the substitution of Fe⁴⁺ ions by Co⁴⁺ ions. The Fe site has a lower small polaron site energy than Co and hence behaves like a carrier trap, thereby drastically reducing the conductivity. The non-linear behaviour in the dependence of log σT with reciprocal temperature can be attributed to the generation of additional charge carriers with increasing temperature by the charge disproportionation of Co³⁺ ions.     

基于FeI2/Ni2+溶液还原制备低成本的高导电性及催化性纸张石墨

采用基于FeI₂/ Ni(NO₃)₂溶液的温和化学法还原制备低成本的纸张型石墨烯, 并对其导电与催化性能进行了研究。研究结果表明: 在pH=1.5, 温度为95℃的条件下处理6 h, 得到电导率高达30231 S/m的纸张型石墨烯, 这是由于作为强路易斯酸的Fe²⁺促进了亲核取代反应, 提高了还原效率, 从而提高了纸张型石墨烯的电导率; 而Ni²⁺通过减少溶液中的H⁺来抑制Fe²⁺的水解, 从而保证Fe²⁺对石墨烯的充分还原以及达到保护环境的目的。此外, 基于此还原工艺制备的纸张型石墨烯在I^-/I^3-电解液中可以获得接近铂电极的电流密度, 表明制备出的纸张型石墨烯具有较好的催化性能,并可以为电子提供快速的传出通道, 使其在太阳能电池中表现出较好的应用前景。     

Effect of impurities on the oxidation mechanism of nickel at 800°C

Abstract

The effect of impurities on the oxidation mechanism of nickel was studied on commercial nickel grades compared to a pure nickel. On the basis of oxidation kinetics, SEM and STEM microstructural and analytical investigations allowed us to identify the oxidation mechanism for both types of nickel at 800°C. The morphology of the oxide scale notably differs according to the purity of the nickel. For oxidised commercial grades, a duplex structure was observed with an outer columnar layer and an inner layer made of equiaxed grains. The inner NiO/outer NiO interface is planar without any segregation, while the NiO/Ni interface is convoluted with large cavities. Mn, Ti and sometimes also silicon impurities were detected at this latter interface. Below the NiO/Ni interface, in the underlying nickel, large internal oxidation was observed. The observed microstructure was quite different for the pure nickel. A single porous NiO layer, composed of equiaxed grains, was observed. The NiO/Ni interface was facetted and no porosity was detected. The presence and localisation of impurities, as well as morphological changes through the scale in the nickel grades, were taken into account to explain the modification of oxidation kinetics with substrate purity.     

Neutron collimator with rectangular beam profile

Several Soller slit-type neutron collimators which give rectangular profiles of transmission as a function of angular divergence have been constructed. The collimators accept a beam of realistic dimensions – greater than 12×22 mm² in all cases. The blades of the collimators are 280 μm thick wafers of single-crystal silicon each coated with a Ni–Gd–Ni multilayer on one side. Tests at a neutron wavelength of 7.5 Å confirm that the transmission profiles are rectangular. Tests at a wavelength of 4.2 Å show that two such collimators rocked against each other give dramatically enhanced transmission and resolution by comparison with conventional collimators. This is the first such demonstration of increased counting rates in a scan on an instrument from rectangular profile collimators, an effect expected but not produced for over 40 years.     

On the interpretation of Fe Mössbauer spectra from CdTe thin films with substitutions of Fe, In, and Sb

⁵⁷Fe Mössbauer spectra of well characterized CdTe thin films with substitutions of Fe, In and Sb were recorded and interpreted according to the changes in the ionic radii and electronic properties of these substitutions relative to Cd in the CdTe framework. The literature reports of certain correlations among the iron valence, Fe²⁺ or Fe³⁺, and the crystallinity of the films are critically discussed and an explanation of their origin is provided. The Mössbauer results also allow direct understanding of the effect of In and Sb substitutions on the properties of the films.     

Synthesis and spectral properties of Ce[Ag(CN)2]3

Cerium ion luminescence in crystalline hosts forms the basis of many blue phosphor and scintillator technologies. We report the synthesis of luminescent single crystals of cerium dicyanoargentate. The luminescence properties are characterized using both steady-state and time-resolved spectroscopy. The broad, overlapping dicyanoargentate and Ce³⁺ emissions are decomposed into three Gaussians, revealing the characteristic dicyanoargentate emission at 350 nm while the Ce³⁺ 5d–4f transitions are observed at 359 nm and 391 nm. Excitation measurements show that the 4f–5d Ce³⁺ absorption overlaps the 320 nm emission of the dicyanoargentate ions, leading to a strong coupling between the dicyanoargentate energy donors and Ce³⁺ acceptors. We conclude that the cerium is excited through an energy transfer process from the dicyanoargentate species, resulting in strong room temperature luminescence.     

基于磁性1-(2-吡啶偶氮)-2-萘酚的金属离子去除剂的制备研究

利用1-(2-吡啶偶氮)-2-萘酚(PAN)与金属离子形成络合物,再采用共沉淀法,加入Fe³⁺和Fe²⁺,使其形成具有磁性的Fe₃O₄-PAN-Mⁿ⁺;以水合肼为还原剂,将金属离子还原制备Fe₃O₄-PAN-M^0,再采用磁铁将其从待测体系中进行富集和分离,简化了分离的过程。该产物有望进一步用于环境体系中的有机小分子监测。