Search

In this study, the discharge performance of Mg-6 wt% Al alloy anodes with varying Ca and Zn contents was evaluated by electrochemical studies and surface analyses. The results indicated that the cell voltage and anode efficiencies changed according to the alloy compositions and discharge currents. The 6 wt%Al-1wt%Zn-1wt%Ca (AZX611) alloy was discovered to exhibit the highest cell voltage of 0.678 V and anode efficiency of 64% at the discharge current of 10 mA cm-2. Although the calculated charge corresponding to the mass loss of AZX611 was equal to the sum of the calculated charge stemming from the captured H2 and the discharge current, the other alloys yielded smaller values. The discharge products of these alloys were analyzed by X-ray diffraction to locate the peaks related to metallic Mg species. The electrochemical impedance spectroscopy analysis of the AZX611 alloy, conducted under the discharged state using a proposed equivalent circuit, revealed a close relationship between the resistance in the high frequency loop and the anode efficiency. [ABSTRACT FROM AUTHOR]

We propose a new method to evaluate residual stress based on the analysis of a portion of a Debye ring with two-dimensional synchrotron x-ray diffraction. The residual stress of a nickel-based alloy GH3535 evaluated by the proposed method is determined to be – 1149±34 MPa based on the quantitative analysis of the deformation of the (200) reflection, and the residual stress obtained by analyzing THE (111) plane is –933± 68 MPa. The results demonstrate that the GH3535 alloy surface is highly compressive, as expected for a polishing surface treatment. The proposed method provides insight into the field of residual stress measurement and quantitative understanding of the residual stress states in GH3535. [ABSTRACT FROM AUTHOR]

The formation of PtxIry alloy nanoparticles (NPs), having a controlled bulk and surface composition over a wide range of Ir content (35-90 at% Ir), was reported in our recent work. While this prior work did examine the activity of these NPs toward the methanol oxidation reaction (MOR), this was done only per mass of catalyst and only under RT conditions. Here, the MOR activity is reported based on the real surface area of the NPs, determined using several electrochemical methods as well as TEM analysis, in both room temperature (RT) and 60°C methanol-containing 0.5 M H2SO4 solutions. These more comprehensive results suggest that the bi-functional effect of Ir on Pt activity plays the most significant role in catalyzing the MOR, with the optimum Ir content found to be ca. 35 at% and 50 at% at low and high potentials, respectively, at both temperatures. This demonstrates that less Ir is needed when the CO production rate is low, as is the case for methanol oxidation at the low potentials desired in operating direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

The galvanostatic anodizing behavior of additive manufactured (AM) Al-Si10-Mg alloy was studied in H2SO4 electrolyte. The analysis of the voltage vs time response was complemented with a systematic characterization of the anodic oxide layer using a variety of techniques. In addition, a cast alloy of approximately the same chemical composition as that of the AM specimens was used as a reference in this study. Significant differences were found in the voltage-time characteristics of the samples analyzed. Besides, an anisotropic anodizing behavior was observed in the additive manufactured specimens. Due to the fine silicon microstructure present in the additive manufactured samples, the anodic oxide growth was much more obstructed than for the cast alloy. Nevertheless, even though the oxide layer was generally thinner in the AM samples for the same conditions and anodizing time, a much more continuous and uniform oxide layer was found in the additive manufactured specimens compared to the cast alloy. The porous structure was found to be greatly affected by the fine distribution of the silicon phase in the AM parts. [ABSTRACT FROM AUTHOR]

Various examples of induced codeposition have been over time reported in the literature and partly understood. In particular, Brenner discussed as early as 1963 in his book "Electrodeposition of alloys" evidence of the induced deposition of Germanium; attempts to understand such mechanism however are lacking. In this work, the electrochemical co-deposition of Cu-Ge thin films from an alkaline tartrate-complexing electrolyte was investigated by combined cyclic voltammetry and quartz crystal microbalance of the unitary and alloy electrolytes. Ge undergoes reduction from Ge4+ (GeO32-) to Ge1- (GeH) in a two-step process and forms a self-limiting deposit, the thickness of which is a function of the Ge ion concentration and pH. Cu2+ deposition is strongly inhibited by the presence of Ge species above -1.2 V Ag/AgCl, while at more negative potentials a signature of alloy codeposition is present, in parallel with hydrogen evolution. Oxygen deposition is significant when Ge is at or above 25 at%. Induced codeposition is rationalized in terms of the activation of the Ge-H bond by Cu, resulting possibly in the formation of adsorbed species containing H-Cu-Ge, whereby H is dissociated, resulting in alloy growth in parallel with formation of a significant amount of H2 gas. [ABSTRACT FROM AUTHOR]

Direct electro-reduction of mixed powders of chromium oxide (Cr2O3) and nickel oxide (NiO) to the intermetallic compound Cr1.12Ni2.88 was successfully demonstrated in CaCl2 molten salt at 900°C. The reduction mechanism was investigated by cyclic voltammetry using a metallic cavity electrode (MCE) as well as the characterizations of some partially electrolyzed products and Ni-Cr alloy prepared from constant voltage electrolysis by terminating the reduction process after different times, which were characterized by means of XRD and SEM et al. It was found that the reduction starts with the formation of Ni metal, accompanied with the formation of an intermediate product CaCr2O4. Then, the intermediate product CaCr2O4 is further electro-reduced to Cr, which is directly alloyed with the newly-formed Ni to form the Ni-Cr intermetallic compound. At the same time, pure Cr phase could not be detected by the XRD or EDXA when the Cr content is relatively low in the NiO-Cr2O3 mixture. Intermetallic compound with the target stoichiometry containing 6000 ppm oxygen is obtained after 4 h electro-reduction in CaCl2 molten salt at 900°C. [ABSTRACT FROM AUTHOR]

CuGaS2 solar energy thin film is fabricated with electrochemical deposition of precursor from deep eutectic solvent (DES) based on choline chloride and urea (commercially known as Reline) to eliminate the interference of hydrogen evolution reaction (HER). The process involves electrodeposition of Cu-Ga precursor on molybdenum substrate from Reline and subsequential annealing in sulfur vapor. The formation of CuGa2 alloy in precursor is observed and pure ternary chalcopyrite CuGaS2 phase in good polycrystalline structure without secondary phase is obtained after thermal treatment. The influence of applied deposition potential on the crystalline phase, morphology, compositions and carrier concentration of the films were investigated. The Cu/Ga ratio decreases with decreasing the deposition potential benefiting the formation of a pure crystallized CuGaS2 thin film. A relative positive deposition potential results in a larger crystalline size benefitting the photoelectrical conversion. Impedance spectroscopy test demonstrates the semiconductor property of the synthesized CuGaS2 polycrystalline thin film is p-type and the carrier concentration increases with negative shift of deposition potential. [ABSTRACT FROM AUTHOR]

Kinetics of passive film growth on a CoCrMo biomedical alloy have been studied using the Electrochemical Quartz Crystal Microbalance technique (EQCM) in phosphate buffer solution at room temperature and 37°C. CoCrMo layers were deposited on the quartz crystals by physical vapor deposition (PVD) reaching a dense and compact deposition film with fine-grain structure. EQCM measurements were performed under potentiodynamic and potentiostatic conditions (at applied passive and transpassive potentials). Furthermore, ex-situ X-ray Photoelectron Spectroscopy (XPS) analysis of the each tested sample was performed at the end of the electrochemical test. The use of EQCM allows distinguishing between electrochemical oxidation, passive and transpassive dissolution and passive film growth. In the passive domain the passive film thickness stabilizes within 200 to 400 s after an initial fast growth. The increase in current at the onset of the transpassive domain does not affect the passive dissolution rate. Only at higher potential dissolution rate increases due to the dissolution of Cr(VI), Co(III) and Mo(VI) species. The observed constant mass loss rate at transpassive potentials indicates that the passive film at these potentials is cracked or porous. Increasing temperature accelerates the mass loss through the oxide/electrolyte interface enhancing the passive and transpassive dissolution and increasing the thickness of the oxide film. [ABSTRACT FROM AUTHOR]

The oxidation behavior of Mn1.5CO1.5O4 (MCO)-coated Haynes 230 (H230) and Crofer 22 APU was investigated between 700 and 900°C. The oxidation kinetics of the coated alloys was compared with that of base alloys at 800°C. An apparent two-stage kinetics behavior of the MC0-coated Crofer 22 APU was observed. The coating effectively reduced the oxidation rate constants of Crofer 22 APU by 5.5 times, whereas it did not seem to affect the oxidation kinetics of H230. The oxidation activation energies of the coated alloys suggest distinctly different oxidation mechanisms between the coated H230 and Crofer 22 APU. A Cr-modified spinel was observed in the interface region between the metal oxide scale and the spinel coating after long-term oxidation for both alloys. A semiquantitative model of oxidation kinetics was developed to explain the different behaviors observed. Apparently, the Cr-modified spinel may play a more important role on H230 during long-term oxidation. The heat-treatment of H230 in the reducing environment used for the MCO coating application processes appeared to debit oxidation resistance of the base alloy. The optimization of the MCO application process is expected to benefit oxidation resistance as well as chromia containment on H230. [ABSTRACT FROM AUTHOR]

In this work, we describe the synthesis of porous Au structures by galvanic displacement reaction using porous Si exhibiting arrays of parallel pores with diameters near 100 nm as template material. Two metal ions were used as Au precursors: tetrachloroaurate(III) and bis(ethylenediamine)Au(III). Fluoride was employed to etch the Si oxides that form as a result of the displacement reaction. The porous metal layer that forms with tetrachloroaurate(III) is an agglomerate of spherical particles with Ca. 100 nm diameter. Metallization with bis(ethylenediamine)Au(III) preserves the morphology of the original porous Si layer, Creating a porous Au layer containing an array of parallel pores with Ca. 100 nm diameter. The displacement process is under diffusion control for both reagents. The expansion rate of the porous metal layer into the substrate agrees well with a simple one- dimensional reaction-diffusion model entailing the displacement of Si in a large extent. The electrochemical behavior of the synthesized porous Au layers was studied by voltammetry. [ABSTRACT FROM AUTHOR]

Electrochemical codeposition of a series of face-centered cubic NixPt1-x alloys is demonstrated (0.1 < x < 0.95). The alloy composition is a monotonic function of potential. The Pt-rich NixPt1-x alloys are formed at potentials positive to that required to deposit elemental Ni. Codeposition is ascribed to the negative enthalpy of NixPt1-x alloy formation that proceeds via a Ni underpotential deposition reaction in concert with Pt deposition. Interestingly, this process occurs at higher Ni underpotentials than anticipated based on extrapolated literature data from thermochemical measurements and ab initio calculations of alloy formation. In contrast, Ni-rich NixPt1-x alloys are produced at Ni overpotentials although the films are formed under conditions where pure Ni deposition is otherwise kinetically hindered. The alloy composition corresponding to the transition from underpotential to overpotential deposition is a function of the PtCl4/NiCl2 electrolyte composition. The films were found to be bright and specular over the full range of compositions studied (grain size < 10 nm). Atomic force microscopy yielded root-mean-square roughness values on the order of 5 nm for Ni-rich deposits up to 2.5 μm thick. [ABSTRACT FROM AUTHOR]

Metal-gate work function Φm modulation using Hf alloys was achieved by the interdiffusion of bilayer metallic films each with a thickness of less than or equal to 10 nm. For a bilayer stack comprising a Hf layer on a Ni layer, varying the Hf/Ni metal thickness ratio from 0 (single-layer Ni stack) to 1.4 achieved Φm tunability from 4.74 to 4.2 eV after forming gas anneal (FGA) at 420°C. Interdiffusion in Hf/Pt stack and Pt/Pt-Hf stack was also explored, and the largest Φm shift of ~0.5 eV from single-layer Pt and Pt-Hf stack, respectively, was obtained after annealing at 700°C for 30 s. The observed Φm shift correlated to the extent of metal interdiffusion and was found to be strongly dependent on the metal thickness and anneal temperature. The Hf/Pt stack was further employed to demonstrate Φm tunability of thin interdiffused metal layers on HfO2 and HfLaOx high-k gate dielectrics. Through process optimization, the interdiffusion of thin metallic layers allows precise dual-gate Φm control for advanced transistors. [ABSTRACT FROM AUTHOR]

Tungsten (W) has been selected as the divertor material in ITER based on its promising thermal and mechanical properties. Despite these advantages, continued investigation has revealed W to undergo extreme surface morphology evolution in response to relevant fusion operating conditions. These complications spur the need for further exploration of W and other innovative plasma facing components (PFCs) for future fusion devices. Recent literature has shown that alloying of W with other refractory metals, such as tantalum (Ta), results in the enhancement of key PFC properties including, but not limited to, ductility, hydrogen isotope retention, and helium ion (He+) radiation tolerance. In the present study, pure W and W–Ta alloys are exposed to simultaneous and sequential low energy, He+ and deuterium (D+) ion beam irradiations at high (1223 K) and low (523 K) temperatures. The goal of this study is to cultivate a complete understanding of the synergistic effects induced by dual and sequential ion irradiation on W and W–Ta alloy surface morphology evolution. For the dual ion beam experiments, W and W–Ta samples were subjected to four different He+: D+ ion ratios (100% He+, 60% D+  +  40% He+, 90% D+  +  10% He+ and 100% D+) having a total constant He+ fluence of 6  ×  1024 ion m−2. The W and W–Ta samples both exhibit the expected damaged surfaces under the 100% He+ irradiation, but as the ratio of D+/He+ ions increases there is a clear suppression of the surface morphology at high temperatures. This observation is supported by the sequential experiments, which show a similar suppression of surface morphology when W and W–Ta samples are first exposed to low energy He+ irradiation and then exposed to subsequent low energy D+ irradiation at high temperatures. Interestingly, this morphology suppression is not observed at low temperatures, implying there is a D–W interaction mechanism which is dependent on temperature that is driving the suppression of the microstructure evolution in both the pure W and W–Ta alloys. Minor irradiation tolerance enhancement in the performance of the W–Ta samples is also observed. [ABSTRACT FROM AUTHOR]

In this study, Ge1−xSnx alloy films are co-sputtered on Si(100) substrates using RF magnetron sputtering at different substrate temperatures. Scanning electron micrographs, atomic force microscopy (AFM), Raman spectroscopy, and x-ray photoemission spectroscopy (XPS) are conducted to investigate the effect of substrate temperature on the structural and optical properties of grown GeSn alloy films. AFM results show that RMS surface roughness of the films increases from 1.02 to 2.30 nm when raising the substrate temperature. This increase could be due to Sn surface segregation that occurs when raising the substrate temperature. Raman spectra exhibits the lowest FWHM value and highest phonon intensity for a film sputtered at 140 °C. The spectra show that decreasing the deposition temperature to 140 °C improves the crystalline quality of the alloy films and increases nanocrystalline phase formation. The results of Raman spectra and XPS confirm Ge–Sn bond formation. The optoelectronic characteristics of fabricated metal-semiconductor-metal photodetectors on sputtered samples at room temperature (RT) and 140 °C are studied in the dark and under illumination. The sample sputtered at 140 °C performs better than the RT sputtered sample. [ABSTRACT FROM AUTHOR]

In-depth clarification of hydrogen interaction with noble metal nanoparticles and nanoalloys is essential for further development and design of efficient catalysts and hydrogen storage nanomaterials. This issue becomes even more challenging for nanoalloys of bulk-immiscible metals. The hydrogen interaction with bulk-immiscible Pd–Rh nanoalloys (3–6 nm) supported on mesoporous carbon is studied by both laboratory and large scale facility techniques. X-ray diffraction (XRD) reveals a single phase fcc structure for all nanoparticles confirming the formation of nanoalloys in the whole composition range. In situ extended x-ray absorption fine structure (EXAFS) experiments suggest segregated local structures into Pd-rich surface and Rh-rich core coexisting within the nanoparticles. Hydrogen sorption can be tuned by chemical composition: Pd-rich nanoparticles form a hydride phase, whereas Rh-rich phases do not absorb hydrogen under ambient temperature and pressure conditions. The thermodynamics of hydride formation can be tailored by the composition without affecting hydrogen capacity at full hydrogenation. Furthermore, for hydrogen absorbing nanoalloys, in situ EXAFS reveals a preferential occupation of hydrogen for the interstitial sites around Pd atoms. To our knowledge, this is the first study providing insights into the hydrogen interaction mechanism with Pd–Rh nanoalloys that can guide the design of catalysts for hydrogenation reactions and the development of nanomaterials for hydrogen storage. [ABSTRACT FROM AUTHOR]

Topologically non-trivial surface states were reported first on Sbx bulk crystals. In this study we present transport measurements performed on thin Sbx-films (up to 24 nm thickness) grown epitaxially on Si(111) with various Sb-concentrations (up to x = 0.22). The analysis of the temperature dependency allowed us to distinguish between different transport channels originating from surface and bulk bands as well as impurity states. At temperatures below 30 K the transport is mediated by surface states while at higher temperatures activated transport via bulk channels sets in. The surface state conductivity and bulk band gaps can be tuned by the Sb-concentration and film thickness, respectively. For films as thin as 4 nm the surface state transport is strongly suppressed in contrast to Bi(111) films grown under identical conditions. The impurity channel is of intrinsic origin due to the growth and alloy formation process and turns out to be located at the buried interface. [ABSTRACT FROM AUTHOR]

The first-principles calculations based on density functional theory combined with cluster expansion techniques and Monte Carlo (MC) simulations were used to study the phase diagrams of both wurtzite (WZ) and zinc-blende (ZB) Cd1–xZnxS alloys. All formation energies are positive for WZ and ZB Cd1–xZnxS alloys, which means that the Cd1–xZnxS alloys are unstable and have a tendency to phase separation. For WZ and ZB Cd1–xZnxS alloys, the consolute temperatures are 655 K and 604 K, respectively, and they both have an asymmetric miscibility gap. We obtained the spatial distributions of Cd and Zn atoms in WZ and ZB Cd0.5Zn0.5S alloys at different temperatures by MC simulations. We found that both WZ and ZB phases of Cd0.5Zn0.5S alloy exhibit phase segregation of Cd and Zn atoms at low temperature, which is consistent with the phase diagrams. [ABSTRACT FROM AUTHOR]

The influence of the RE-rich phase distribution in the precursor alloys on the anisotropy of the hydrogenation disproportionation desorption recombination (HDDR) processed powders is investigated. The homogenized ingot alloy and the as-cast strip casting (SC) alloy with a uniform RE-rich grain boundary phase lead to high anisotropy of the refined powders, acquiring degrees of alignment (DOA) of 0.62 and 0.54, respectively. The RE-rich phase aggregation results in a deteriorated DOA of the powders due to the drastic disproportionation rate, while a thin and uniform RE-rich phase distribution is beneficial for DOA. A reaction model of the initial particle microstructure is proposed for optimizing the HDDR powder anisotropy. [ABSTRACT FROM AUTHOR]

An in situ ultrahigh-strength ductile Al50Sc50 bulk alloy is produced by the copper mold casting method with a composite microstructure of micron-/submicron-sized grains and nanoscale twins. According to the microstructural investigations, hierarchical nanotwinned lamellar AlSc bundles with embedded micron-/submicron-sized Al2Sc and AlSc2 are observed. The as-cast alloy displays a unique act of ultrahigh strength of ∼1.85 GPa together with pronounced work hardening and a large plasticity of ∼14%. Further microstructural investigations on deformed specimens indicate that abundant hierarchical nanotwinned lamellar AlSc bundles are effective to dissipate localization of shear stress or block dislocations from spreading throughout the alloy and hinder the propagation of microcracks formed by local stress transition. [ABSTRACT FROM AUTHOR]

Structural, electronic, and magnetic properties of a Heusler-type CoFeCrAl alloy have been investigated experimentally and by model calculations, with a focus on the alloy’s spin-gapless semiconductivity. The as-quenched samples are ferrimagnetic at room temperature with a Curie temperature of about 456 K, which increases to 540 K after vacuum annealing at 600 °C for 2 h. The saturation magnetizations of the as-quenched and 600 °C-annealed samples are 1.9 µB/f.u. and 2.1 µB/f.u., respectively, which are very close to the value predicted by the Slater–Pauling curve. The resistivity shows a nearly linear decrease with increasing temperature, from about 930 µΩ cm at 5 K to about 820 µΩ cm at 250 K, with dρ/dT of about  −5   ×   10−7 Ω cm K−1. We explain this high resistivity and its temperature dependence as imperfect spin-gapless semiconducting behavior, with a negative band-gap parameter of 0.2 eV. [ABSTRACT FROM AUTHOR]

Highly mismatched semiconductor alloys such as GaNxAs1 − x and GaBixAs1 − x have several novel electronic properties, including a rapid reduction in energy gap with increasing x and also, for GaBiAs, a strong increase in spin-orbit-splitting energy with increasing Bi composition. We review here the electronic structure of such alloys and their consequences for ideal lasers. We then describe the substantial progress made in the demonstration of actual GaInNAs telecommunication (telecom) lasers. These have characteristics comparable to conventional InP-based devices. This includes a strong Auger contribution to the threshold current. We show, however, that the large spin-orbit-splitting energy in GaBiAs and GaBiNAs could lead to the suppression of the dominant Auger recombination loss mechanism, finally opening the route to efficient temperature-stable telecomm and longer wavelength lasers with significantly reduced power consumption. [ABSTRACT FROM AUTHOR]

The formation energies and electronic structures of Ni-rich Ni-Mn-Ga alloys have been investigated by first-principles calculations using the pseudopotential plane wave method based on density functional theory. The results show that the alloying Ni prefers to occupy the Mn site directly in Ni9Mn3Ga4 and to occupy the Mn site and drive the displaced Mn atom to the Ga site in Ni9Mn4Ga3, which is in accordance with the experimental result. According to the lattice constants and the density of states analyses, these site preference behaviours are closely related to the smaller lattice distortion and the lower-energy electronic structure when the excess Ni occupies the Mn site. The effect of Ni alloying on martensitic transformation is discussed and the enhancement of martensitic transformation temperature by Ni alloying is estimated by the calculated formation energy difference between austenite and martensite phases. [ABSTRACT FROM AUTHOR]

Presents an abstract of the study `Transient Analysis of Hydrogen Absorption by Alloy Particles Using Shrinkage Core Model,' by W. Zhang and S. Srinivasan to be presented at the 188th Electrochemical Society Meeting on October 8-13, 1995.