Effect of tin addition on microstructure and electrochemical properties of rolled AZ61-Sn magnesium anodic materials

Microstructure characterization,corrosion behavior,and electrochemical properties of magnesium anode materials containing 1-3 wt.% Sn in AZ61 alloy were studied by optical microscopy,X-ray diffraction(XRD) ,scanning electron microscopy(SEM) ,and energy-dispersive spectroscopy(EDS) ,constant current method,potential polarization,and drainage.The results showed that amount of Mg2Sn phase increased,and recrystallization ratio of Sn-contained Mg alloys during rolling process was improved with increasing of Sn content.This resulted in uniform and refined grains.The results also demonstrated that discharge potential was improved and hydrogen release rate was reduced with the addition of Sn.As the current density increased,the release hydrogen rate was rising,owing to negative variance effect of magnesium alloys.The current efficiency gets to 87% at 20 mA/cm2.The main components of the corrosion products are easy-to-peel-off MgO and Al2O3 that can lead to more negative and stable work potential and accelerate battery reaction continuously.     

Al-Ga doped nanostructured carbon as a novel material for hydrogen production in water

Production of hydrogen using Al-Ga doped nanostructured carbon in pure water is studied. The XRD and BET techniques were used for sample analyses. Dehydrogenation data of aluminum on the ordered mesoporous carbon were collected at 353 K. In the present work the oxidation rate of activated aluminum and water is investigated depending on eutectic composition and reaction temperature. The H₂ generation rate increases with the rise of temperature. Incorporated Al-Ga-OMC nanocomposite had faster (hydrogen production rate was 112 ml H₂ min⁻¹ g⁻¹) and more efficient (hydrogen production yield was 100%) dehydrogenation kinetics than incorporated Al-OMC nanocomposite and ball-miled active aluminum.     

Corrosion and electrochemical behaviors of pure aluminum in novel KOH‐ionic liquid‐water solutions

The corrosion and electrochemical behaviors of pure aluminum in KOH‐ionic liquid‐water solutions with variable volume ratios of water and the ionic liquid 1‐butyl‐3‐methyl imidazolium tetrafluoroborate (BMIMBF₄) were for the first time investigated by means of hydrogen collection, polarization curve, galvanostatic discharge, and electrochemical impedance spectroscopy (EIS). The results of hydrogen collection experiments showed that aluminum has a low corrosion rate in KOH‐BMIMBF₄‐H₂O solutions, and the corrosion rate decreases with increase in BMIMBF₄ content in the electrolytes. The results of electrochemical experiments revealed that aluminum is electrochemically active over a very wide potential window in the KOH‐BMIMBF₄‐H₂O solutions, and its electrochemically kinetic mechanism is similar to that in the corresponding aqueous solution; the increase in KOH and water contents in the electrolytes may improve the anodic dissolution performance of aluminum. It was found that aluminum presents excellent galvanostatic discharge performance in the 2.0 M KOH BMIMBF₄‐H₂O mixed solution with 60% water.     

Electrochemical Processes at the Bi<Superscript>0</Superscript>–Bi<Superscript>3+</Superscript> Interface in Chloride Melts

For rational design of technological schemes for production of high-grade bismuth and to improve electrochemical bismuth refining, knowledge of physicochemical properties of low-valent bismuth compounds and the mechanisms underlying processes occurring at the Bi⁰–Bi³⁺ interface in molten salts is necessary. For this purpose, the kinetics and mechanism of formation of low-valent bismuth compounds in the Bi⁰–BiCl₃–ZnCl₂–NH₄Cl system by UV–Vis spectroscopy was studied. Chemical interactions between metallic bismuth and Bi³⁺ species in the melt give rise to Bi+ intermediates and [Bi₅]³⁺ clusters, which are registered by their characteristic absorption bands at approximately 18000 and 14000 cm^–1. The kinetic parameters for the Bi⁺ and [Bi₅]³⁺ formations are estimated from the dependence of intensities of these absorption bands on the time of contact between metallic bismuth and Bi³⁺ species in the melt. The rate constants characterizing the Bi⁺ and [Bi₅]³⁺ formations are estimated to be 3.33 × 10^–3 and 2.31 × 10^–3 s^–1, respectively. The mechanism of anodic bismuth dissolution is proposed, and the cathodic and anodic current efficiencies for bismuth are determined.     

Electrochemical hydrogenation and corrosion behaviour of LaCo4.8M0.2 alloys

Hydrogen absorption properties and the corrosion characteristics of three LaCo_4.8M_0.2 alloys (where M ≡ antimony, magnesium or bismuth) have been investigated using electrochemical techniques. Absorption of hydrogen and corrosion behaviour of LaCo_4.8M_0.2 alloys have been compared with LaCo₅ intermetallic compound. Typical potentiokinetic polarisation curves in 6 M potassium hydroxide solution showed that modification of LaCo₅ by partial substitution of antimony, magnesium or bismuth for cobalt resulted in lower anodic currents in the passive range. The substitution does not significantly affect the shape of potentiokinetic polarisation curves in 0.5 M sulphate solutions for pH 2 and 7. Partial substitution of cobalt with bismuth in LaCo₅ alloy increases the effectiveness of absorption of cathodically evolved hydrogen in strong alkaline solutions.     

Kinetics of interaction of Mg-based mechanically activated alloys with hydrogen

Parameters of interaction of hydrogen with magnesium powders and structure of powder magnesium alloys alloyed with different metals and oxides (such as Fe, Ni, Al, Cu, Ti, Pd, NiPd, V₂O₅, and VH₂) prepared by mechanical activation under either argon or hydrogen atmosphere in a vibration mill have been studied. The mechanically activated alloys absorb to 7 wt% hydrogen at 300°C for 20 min. For most of the additions used, the effect of the grain size and type of addition on the rate of hydrogen absorption was found to manifest itself only at the stage of the formation of the MgH₂ phase upon mechanical activation in the hydrogen atmosphere; virtually no effect is observed upon subsequent hydrogenation. The temperature of the hydrogen desorption also depends only slightly on the addition kind. The increase in the hydrogenation rate of the Mg-based alloys resulting from the mechanical activation was shown to be due to the formation of a specific structural state of the particle surface, which exhibits a high catalytic activity for the hydrogen sorption. A study of the mechanically activated alloys by proton nuclear magnetic resonance showed a substantial increase in the rate of proton spin-lattice relaxation as compared to that observed for MgH₂ produced by direct hydrogenation. This can be due to the interaction of protons with paramagnetic centers formed at the imperfect surface of mechanically activated Mg particles.     

Dependence of the surface charge and the fluorine adsorption by γ-aluminum oxide on the solution temperature

The dependence of the surface charge of the γ-aluminum oxide and the fluorine adsorption on the solution temperature (20, 30, and 40°C), the pH (3.5–10), and the equilibrium concentration of fluorine in the solution (from 1.0 × 10⁻³ to 1.5 × 10⁻¹ M/l) is studied by the method of potentiometric titration and adsorption variations with the view to elucidate the nature of the processes that take place upon the removal of fluorine with the use of ECDM sludge of an aluminum alloy that was calcined at a temperature of 800 °C. The adsorption isotherms were processed using the Freundlich, Langmuir, and BET equations. The best coincidence with the experimental data is obtained with the use of the Langmuir equation. It is shown that both the solution temperature increase and the amount of fluorine adsorbed by the sample surface shift the pH_PZC to a more acid range. The fluoride adsorption occurs due to the exchange of the OH⁻-groups of the hydrated oxide surface for fluorine ions due to the interaction of the charged AlOH₂⁺ centers of the surface with F⁻ ions and due to the formation of hydrogen bonds of F⁻ and uncharged AlOH centers.     

Doped sodium aluminium hydrides as hydrogen storage materials-characterizations and mechanistic insights

The dehydriding and rehydriding of sodium aluminium hydride,NaAlH ₄, is kinetically enhanced and rendered reversible in the solid state upon doping with a small amount of catalyst species, such as titanium, zirconium or tin. The catalyst doped hydrides appear to be good candidates for development as hydrogen carriers for onboard proton exchange membrane (PEM) fuel cells because of their relatively low operation temperatures (120–150 °C) and high hydrogen carrying capacities (4–5 wt.%). However, the nature of the active catalyst species and the mechanism of catalytic action are not yet known. In particular, using combinations of Ti and Sn compounds as dopants, a cooperative catalyst effect of the metals Ti and Sn in enhancing the hydrogen uptake and release kinetics is hereby reported. In this paper, characterization techniques including XRD, XPS, TEM, EDS and SEM have been applied on this material. The results suggest that the solid state phase changes during the hydriding and dehydriding processes are assisted through the interaction of a surface catalyst. A mechanism is proposed to explain the catalytic effect of the Sn/Ti double dopants on this hydride.     

The influence of hydrogen on the stress-corrosion cracking of low-strength Al-Mg alloys

There is growing evidence for hydrogen uptake in aluminum alloys and its contribution to the crack growth of high-strength aluminum alloys, but less evidence for low-strength alloys. This paper summarizes the evidence for hydrogen uptake in a low-strength alloy, AA5083, and its contribution to the stress-corrosion cracking of this alloy. A key factor is the anodic dissolution of grain boundary β phase (Al₃Mg₂) and the associated hydrogen reduction that accompanies this dissolution. For more information, contact R.H. Jones, Pacific Northwest National Laboratory, P.O. Box 999, MSIN p8–15, Richland, WA 99352-0999; (509) 376–4276; fax (509) 376-0418; e-mail rh.jones@pnl.gov.     

A spectroscopic and electrochemical investigation of the oxidation pathway of glycyl-d,l-methionine and its N-acetyl derivative induced by gold(III)

The ¹H nuclear magnetic resonance spectroscopy was applied to study the reaction of the dipeptide glycyl-d,l-methionine (H-Gly-d,l-Met-OH) and its N-acetylated derivative (Ac-Gly-d,l-Met-OH) with hydrogen tetrachloridoaurate(III) (H[AuCl₄]). The corresponding peptide and [AuCl₄]^– were reacted in 1:1, 2:1, and 3:1 molar ratios, and all reactions were performed at pD 2.45 in 0.01 M DCl as solvent and at 25°C. It was found that the first step of these reactions is coordination of Au(III) to the thioether sulfur atom with formation of the gold(III)-peptide complex [AuCl₃(R-Gly-Met-OH-S)] (R=H or Ac). This intermediate gold(III) complex further reacts with an additional methionine residue to generate the R-Gly-Met-OH chlorosulfonium cation as the second intermediate product, which readily undergoes hydrolysis to give the corresponding sulfoxide. The oxidation of the methionine residue in the reaction between H-Gly-d,l-Met-OH and [AuCl₄]^– was five times faster (k ₂ = 0.363 ± 0.074 M^-1s^-1) in comparison to the same process with N-acetylated derivative of this peptide (k ₂ = 0.074 ± 0.007 M^-1s^-1). The difference in the oxidation rates between these two peptides can be attributed to the free terminal amino group of H-Gly-d,l-Met-OH dipeptide. The mechanism of this redox process is discussed and, for its clarification, the reaction of the H-Gly-d,l-Met-OH dipeptide with [AuCl₄]^– was additionally investigated by UV-Vis and cyclic voltammetry techniques. From these measurements, it was shown that the [AuCl₂]^– complex under these experimental conditions has a strong tendency to disproportionate, forming [AuCl₄]^– and metallic gold. This study contributes to a better understanding of the mechanism of the Au(III)-induced oxidation of methionine and methionine-containing peptides in relation to the severe toxicity of anti-arthritic and anticancer gold-based drugs.     

Properties of metallic cements formed upon the interaction of mechanochemically synthesized copper alloys with liquid gallium and its eutectics: Interaction of Cu/Bi composites with liquid gallium

Atomic force microscopy and scanning electron microscopy were used to study the structure of metallic cements that are formed upon the interaction of Cu/Bi mechanocomposites with liquid gallium at room temperature. It has been established that the intermetallic compound CuGa₂, which is the basic component of this metallic cement, is formed as tetragonal crystals 1–4 μm in size with a characteristic layeredspiral growth. The second phase—bismuth—is adsorbed at the growth steps in the form of disperse formations 70–250 nm in size; local bismuth accumulations of micron size are also observed. It is shown that in the metallic cement that is formed at room temperature regions of incompletely reacted Cu/Bi composite are retained.     

Deposition of diamond-like films of hydrogenized carbon

Diamond-like films of hydrogenized carbon on metal substrates were produced by deposition from methane activated by capacitive electric discharge (AD) within the frequency range of 5–250 Hz and with a relative pulse duration of the charge of 1.5–17. Variations in the charge parameters (frequency, relative pulse duration, current density, methane pressure, the value of gas flow), substrate temperature, and geometry of the vacuum chamber affect the deposition rate, properties, and structures of films within a wide range. Diamondlike films of hydrogenized carbon represented nanocomposite material. The size of sp ² clusters was 5–6 nm, whereas the sp ³/sp ² ratio of carbon and the content of bound hydrogen decreased with increasing substrate temperature and current density and decreasing methane pressure.     

Mechanism of the initial stages of iron passivation in acidic sulfate solutions

Anodic and cathodic potentiostatic current transients of freshly formed iron (99.95%) electrodes in 0.5 M aqueous acidic (pH 1.7–3.2) sulfate solutions are examined. The initial stages of iron passivation are confirmed to be determined by the following several processes each prevailing in a definite period: the formation of surface charge-transfer complexes (H₂O) _δ+ ^ads (first 3–5 ms) and their transformation into adsorbed OH⁻ groups (subsequent 10–50 ms) with the concurrent adsorption of hydrogen atoms H_ads by iron.     

Conditions and mechanism of the ionization and dissociation of water. Predictions based on nonempirical calculations

Based on the results of quantum chemical modeling of neutral and charged water clusters, mechanisms of the ionization and dissociation of water explaining the regularities discovered in experiments are proposed. There are two possible ways of the water and ice ionization, namely, (i) directly from the ground electronic state of the neutral system provided that the high-frequency stretching vibrations of molecules, which determine the formation of H₃O⁺ and OH⁻ ionic fragments, are sufficiently excited, and (ii) via the intermediate transfer to the excited electronic state where hydronium radicals may appear at a certain excess energy. The formation of atomic hydrogen may also take place in the processes of two kinds, namely, (i) the dissociation of the electronically excited water clusters and (ii) the recombination of an electron, appeared upon ionization, with a hydronium cation that leads to the spontaneous detachment of a hydrogen atom. The processes may proceed either successively or simultaneously in a time period compared to the characteristic or even resolution time of the experiment, which may result in incorrect estimation of the quantum yields of hydrated electrons and hydrogen atoms in terms of standard procedures. Original Russian Text ? Yu.V. Novakovskaya, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 3, pp. 235–243.     

Ti55合金电子束焊缝氢致延迟裂纹的扩展机理

钛合金广泛应用于军事航空领域 ,但是一些钛合金在焊接条件下 ,焊缝会产生氢致延迟裂纹 ,其致裂机理尚不十分清楚。通过充氢CT(Compacttension)试件的恒载拉伸试验 ,研究了氢浓度对Ti5 5合金电子束焊缝裂纹尖端应力强度因子门槛值Kth及裂纹扩展速率da/dt的影响规律 ,分析了氢致延迟裂纹扩展的机理。结果表明 ,氢在Ti5 5合金焊缝中的固溶度约为 79× 10 -4%。当充氢浓度C0 低于 79× 10 -4%时 ,随着焊缝氢浓度C0 的增大 ,裂纹开始扩展的应力强度因子门槛值Kth迅速减小 ,而裂纹扩展速率da/dt随着C0 的增大而增大 ;C0 为 79× 10 -4%时 ,Kth为最小值并呈恒值特征。裂纹尖端应力场诱导氢原子扩散导致氢化物TiH2 析出是Ti5 5合金电子束焊缝氢致延迟裂纹扩展的主要机制     

Influences on the H<Subscript>2</Subscript>-sorption properties of Mg of Co (with various sizes) and CoO addition by reactive grinding and their thermodynamic stabilities

We attempted to improve the H₂-sorption properties of Mg by mechanical grinding under H₂ (reactive grinding) with Co (with various particle sizes) and with CoO. The thermodynamic stabilities of the added Co and CoO were also investigated. CoO addition has the best influence and addition of smaller particles of Co (0.5–1.5 μm) has a better effect than the addition of larger particles of Co on the H₂-sorption properties of Mg. The activated Mg+10 wt.% CoO sample has about 5.54 wt% hydrogen-storage capacity at 598 K and the highest hydriding rate, showing an H_a value of 2.39 wt.% after 60 min at 598 K, 11.2 bar H₂. The order of the hydriding rates after activation is the same as that of the specific surface areas of the samples. The reactive grinding of Mg with Co or CoO and hydriding-dehydriding cycling increase the H₂-sorption rates by facilitating nucleation of magnesium hydride or α solid solution of Mg and H (by creating defects on the surface of the Mg particles and by the additive), and by making cracks on the surface of Mg particles and reducing the particle size of Mg, thus shortening the diffusion distances of hydrogen atoms. The cobalt oxide is stable even after 14 hydriding cycles at 598 K under 11.2 bar H₂. Discharge capacities are measured for the sampple Mg+10 wt.%CoO and Mg+10wt.%Co (0.5−1.5 μm) with good hydrogen-storage properties.     

A novel indicator system for catalytic spectrophotometric determination and speciation of inorganic selenium species （Se（Ⅳ）, Se（Ⅵ）） at trace levels in natural lake and river water samples

A novel catalytic kinetic method is proposed for the determination of Se(IV), Se(VI), and total inorganic selenium in water based on the catalytic effect of Se(IV) on the reduction of Celestine blue by sodium sulfide at pH 7.0 phosphate buffer. The fixed-time method was adopted for the determination and speciation of inorganic selenium. Under the optimum conditions, the two calibration graphs are linear with a good correlation coefficient in the range 2–20 and 20–200 μg·L⁻¹ of Se(IV) for the fixed-time method at 30°C. The experimental and theoretical detection limits of the developed kinetic method were found to be 0.21 and 2.50 μg·L⁻¹ for the fixed-time method (3 min). All of the variables that affect the sensitivity at 645 nm were investigated, and the optimum conditions were established. The interference effect of various cations and anions on the Se(IV) determination was also studied. The selectivity of the selenium determination was greatly improved with the use of the strongly cation exchange resin such as Amberlite IR120 plus as long as chelating agents of thiourea and thiosulphate. The proposed kinetic method was validated statistically and through recovery studies in natural water samples. The relative standard deviations (RSDs) for ten replicate measurements of 2, 10, and 20 μg·L⁻¹ of Se(IV) change between 0.35% and 5.58%, while the RSDs for ten replicate measurements of 3, 6, and 12 μg·L⁻¹ of Se(VI) change between 0.49% and 1.61%. Analyses of a certified standard reference material (NIST SRM 1643e) for selenium using the fixed-time method showed that the proposed kinetic method has good accuracy. The Se(IV), Se(VI), and total inorganic selenium in lake and river water samples have been successfully determined by this method after selective reduction of Se(VI) to Se(IV).     

High-resolution microstructural investigations of interfaces between light metal alloy substrates and cold gas-sprayed coatings

Interfaces between light metal alloys, aluminum AA7022, and magnesium AZ91, and optimized cold gassprayed zinc-based coatings are characterized. The analyses include scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). Investigations by SEM show a seam with intensive mixing of the substrate and coating material, which is indicated by different values of gray due to element contrast. In energy-dispersive spectroscopy analyses, increased zinc concentrations compared with the substrate material are detected in <1 μm thick vortexes inside the seam. The TEM investigations prove that these areas consist of a homogeneous solid solution and submicron-sized or nanosized intermetallic phases with different concentrations of aluminum, zinc, and magnesium. Because diffusion processes cannot result in the observed microstructure. local melting followed by precipitation of intermetallic phases is concluded as the consequence of the intensive mechanical interaction at the substrate-coating interface during particle impact during the cold gas spraying of zinc on magnesium or aluminum substrates. The original version of this paper was published in the CD ROM Thermal Spray Commects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and HW International Institute of Welding, Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany.     

Carburization resistance of nickel-base, heat-resisting alloys

Cast heat-resisting alloys containing 45 or 60 wt% nickel were isothermally carburized in flowing gas mixtures of H₂–5CH₄ (volume percent) at temperatures of 900–1,100 °C, and their performance compared with that of standard commercial grades containing 30–35% nickel. Chromium-rich M₇C₃ and M₂₃C₆ precipitated internally in all materials, to depths which increased according to parabolic kinetics. Comparison of the rate constants with those predicted from Wagner’s diffusion theory showed that carbon diffusion through a chromium-depleted alloy matrix was the rate-controlling process. The 45% nickel alloys carburized more slowly than the 30–35% nickel grades as a result of decreased carbon solubility and diffusivity at the higher nickel level. The 60% nickel alloys also contained aluminum. At higher temperatures, diffusion of aluminum to the surface led to A1₂O₃ scale formation and enhanced carburization resistance. The degree of protection obtained depended on alloy aluminum content. P. Becker—On secondment from Schmidt & Clemens GmbH, Post Fach 1140, 51779 Lindlar, Germany.