Alloy Formation Process Research Articles

Defect-rich CoRu alloy embedded in the porous carbon serving as highly-efficient and bifunctional electrocatalyst for overall water splitting over a wide pH range

Exploring highly-efficient and pH-universal overall water splitting electrocatalysts are critical but keep challenging. Herein, a highly-efficient, dual-function and pH-universal electrocatalyst consisting of CoRu alloy nanoparticles embedded in the carbon matrix (CoRu/C) was successfully synthesized through an acid etching-pyrolysis conversion process using ZIF-67 as a precursor. Benefiting from the rich crystal defects created during the alloy formation process that could serve as active catalytic sites and the optimized electronic structure, the as-obtained CoRu/C electrocatalyst required overpotentials of only 18 and 37 mV to reach a current density of 10 mA cm−2 for hydrogen evolution reaction (HER) and 184 and 170 mV for oxygen evolution reaction (OER) in 1.0 M KOH and 0.5 M H2SO4 aqueous solution, respectively. For practical application, the CoRu/C catalyst only needs a cell voltage of 1.49 and 1.45 V in a two-electrode overall water splitting system to achieve a current density of 10 mA cm−2 in alkaline and acidic medium, respectively. The present work paves a new way for the design and construction of efficient bifunctional electrocatalyst for overall water splitting, and would inspire widespread research interest in the field of energy storage and conversion.

Temperature and concentration dependence of the electrochemical PtHg4 alloy formation for mercury decontamination

New and improved methods to remove toxic mercury from contaminated waters and waste streams are highly sought after. Recently, it was shown that electrochemical alloy formation of PtHg4 on a platinum surface with mercury ions from solution can be utilized for decontamination, with several advantages over conventional techniques. Herein, we examine the alloy formation process in more detail by mercury concentration measurements using inductively coupled plasma mass spectrometry in batch measurements as well as electrochemical quartz crystal microbalance analysis both in batch and in flowing water with initial mercury concentrations ranging from 0.25 to 75000 µg L−1 Hg2+. Results show that mercury is effectively removed from all solutions and the rate of alloy formation is constant over time, as well as for very thick layers of PtHg4. The apparent activation energy for the electrochemical alloy formation was determined to be 0.29 eV, with a reaction order in mercury ion concentration around 0.8. The obtained results give new insights that are vital in the assessment and further development of electrochemical alloy formation as a method for large scale mercury decontamination.

Синтез трехкомпонентного сплава на основе алюминия методом селективного лазерного плавления

Introduction. The technology of selective laser melting is one of the key technologies in Industry 4.0, which allows manufacturing products of any complex geometric shape, reducing significantly the amount of material used, reducing the lead time and obtaining a new alloy from elementary powders in the melting process. To understand the process of alloy formation under laser exposure, it is necessary to know the initial data of powders, which significantly affect the quality of the products obtained. The purpose of this study is to determine the requirements for the structural-phase state, elemental composition of aluminum, silicon and magnesium powders and further preparation of Al-Si-Mg (Al — 91 wt.%, Si — 8 wt.%, Mg — 1 wt.%) powder mixture for laser synthesis. The initial powders of aluminum PA-4 (GOST 6058-73), silicon (GOST 2169-69) and magnesium MPF-4 (GOST 6001-79) and powder composition Al-Si-Mg are studied using X-ray diffraction and X-ray phase analysis. The shape and sizes of particles are determined by the studies of raster electronic images. By the method of selective laser melting, samples are obtained from a powder composition under constant and pulsed laser exposure. The composition is prepared by mixing powders in a globe mill. Results and discussion. It is shown that the initial powders of aluminum, silicon and magnesium are single-phase. Particles with a size of 20–64 µm, recommended for selective laser melting, are used to obtain a powder composition. By mixing the powders for one hour, spherical particles are obtained, which is preferable for laser melting. The results of grinding the samples after laser melting showed that the samples obtained under constant laser exposure at the following mode parameters: P = 80 W, V = 300 mm/s, s = 90 μm, h = 25 μm have the greatest mechanical strength. Conclusions. The described study shows the possibility of synthesizing products from a powder composition of aluminum, silicon and magnesium by selective laser melting.

Low‐Pt NiNC‐Supported PtNi Nanoalloy Oxygen Reduction Reaction Electrocatalysts—In Situ Tracking of the Atomic Alloying Process

AbstractWe report and analyze a synthetic strategy toward low‐Pt platinum‐nickel (Pt‐Ni) alloy nanoparticle (NP) cathode catalysts for the catalytic electroreduction of molecular oxygen to water. The synthesis involves the pyrolysis and leaching of Ni‐organic polymers, subsequent Pt NP deposition, followed by thermal alloying, resulting in single Ni atom site (NiNC)‐supported PtNi alloy NPs at low Pt weight loadings of only 3–5 wt %. Despite low Pt weight loading, the catalysts exhibit more favorable Pt‐mass activities compared to conventional 20–30 wt % benchmark PtNi catalysts. Using in situ microscopic techniques, we track and unravel the key stages of the PtNi alloy formation process directly at the atomic scale. Surprisingly, we find that carbon‐encapsulated metallic Ni@C structures, rather than NiNx sites, act as the Ni source during alloy formation. Our materials concepts offer a pathway to further decrease the overall Pt content in hydrogen fuel cell cathodes.

Laser Assisted Synthesis of Surfactant-Free Au-Ag Alloy Nanoparticles in Water

Surfactant-free nontoxic Au-Ag alloy nanoparticles were synthesized via re-irradiation of laser generated mono metallic colloidal mixtures with 532 nm radiations from Nd: YAG nanosecond laser. The impact of re-irradiating laser energy in alloy formation kinetics was investigated. The alloy formation process was analyzed with UV-Visible absorption spectra at different time intervals of laser irradiation. The generated nanoparticles were characterized with dynamic light scattering size analysis, zeta potential studies, and HRTEM imaging. Photothermal properties of the samples were investigated employing thermal lens method. Alloy formation became faster with a slight blue shift in the plasmonic band wavelength with increase in irradiation energy. Reduction in nanoparticle size and stability were also observed at high irradiation energies.

Electrochemical Separation of Uranium from Dysprosium in Molten Salt/Liquid Metal Extraction System

The electrochemical behavior of Dy3+ and U3+ ions on inert Mo and active Ga (Ga-Al) electrodes were studied vs Cl−/Cl2 reference electrode in fused 3LiCl-2KCl eutectic at the temperature range of 723–823 K by transient electrochemical technique. The electrode reactions, associated with the electrodeposition of metallic dysprosium (uranium) and with the processes of alloy formation were investigated. The apparent standard potential of Me(III)/Me(Ga) and Me(III)/Me(Ga-Al) couples were calculated. The principal thermodynamic properties of dysprosium and uranium alloys were determined. The separation factor of dysprosium/uranium couple on liquid gallium and gallium-aluminum electrodes was calculated. The efficiency of separation of Dy from U was estimated.

Novel approach of in-situ nickel capture technology to recycle silver and palladium from waste nickel-rich multilayer ceramic capacitors

Abstract Waste multilayer ceramic capacitors (MLCCs) are important secondary resource containing silver and palladium. Current methods of directly recovering precious metals from waste MLCCs have certain deficiencies in terms of environmental protection, recovery efficiency and purity. Capture technology has advantages of high enrichment efficiency and less pollution. Nickel can be used as the capture agent. Therefore, this study proposed a novel approach to recycle silver and palladium from waste nickel-rich MLCCs by in-situ nickel capture technology without adding additional capture agent. SiO2 and Al2O3 were selected as the slag former. Silver and palladium were enriched in the alloy and separated from the slag. The recovery rates of silver and palladium were 98.31% and 98.62% under the optimal conditions. Through the microstructure and component analysis of the alloy, nickel and silver formed two phases and palladium existed in silver phase. Furthermore, the capture mechanism was proposed as the separation process of metals and slag, and alloy formation process. Recycling of slag can be achieved by crystallization. This study proposed a green and efficient process to recycle silver and palladium in waste nickel-rich MLCCs and provided a theoretical basis for capture technology to recycle waste MLCCs.

One-Pot Synthesis of PtNi Alloy Nanoparticle-Supported Multiwalled Carbon Nanotubes in an Ionic Liquid Using a Staircase Heating Process.

High-performance PtNi alloy nanoparticle-supported multiwalled carbon nanotube composite (PtNi/MWCNT) electrocatalysts can be prepared via one-pot preparation for oxygen reduction reaction. This route of preparation utilizes the pyrolytic decomposition of metal precursors, such as Pt(acac)2 with Ni precursors, nickel bis(trifluoromethanesulfonyl)amide (Ni[Tf2N]2) or nickel acetylacetonate (Ni(acac)2), in an ionic liquid (IL), N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide ([N1,1,1,3][Tf2N]). Currently, there is insufficient information concerning the effect of difference in preparation conditions on the formation mechanism and catalytic activity of PtNi/MWCNT. In this article, a staircase heating process was used to investigate the PtNi alloy nanoparticle formation mechanism and catalytic activity of the resulting PtNi/MWCNT. We found that the alloy formation process, composition, and crystal structure, which directly affect the electrocatalytic activity, strongly depended on the Ni precursor species and heating process. The catalytic performance of certain PtNi/MWCNTs collected during the staircase heating process was better than that of PtNi/MWCNTs produced via the conventional heating process.

Optimization of the Sintering Parameters for Materials Manufactured by Powder Injection Molding

The properties of sintered and heat-treated steels produced from the Catamold 8740 material by powder injection molding were examined. Parts made of the Catamold 8740 low-alloy mild carbon steel are used in the military, automotive, and other industries where high reliability and resistance to dynamic loads are required. The Catamold 8740 chemical homogeneity was studied as a function of powder injection molding parameters: heating rate, sintering temperature, holding time, and subsequent heat treatment. Microscopic analysis showed that Catamold 8740 was a mechanical mixture of powders in various sizes (carbonyl iron, nickel, Fe–Mo, Fe–Cr, Fe–Si-Mo, Fe–Si). When the heating rate of the Catamold 8740 powder mixture increased from 2 to 5 °C/min, the microstructural heterogeneity caused by uneven compaction decreased and the alloy formation process activated at 900–1340°C. The impact strength of Charpy V-notch test samples changed from 10.39 to 11.52 J/cm2 with higher sintering temperature and heating rate increasing from 2 °C/min (1270°C) to 5 °C/min (1340°C). When holding time increased from 30 to 90 min at a sintering temperature of 1340°C, the material became denser, the pores rounded, and the ferrite matrix homogeneous. However, the impact strength decreased by a factor of 1.4 because of coarser grain sizes and brittle fracture. Heat treatment processes reduced the impact strength after sintering. The results obtained were used to optimize the powder injection molding parameters. The influence of chemical and dimensional inhomogeneity of the starting Catamold 8740 powders and sintering kinetics on the structure and mechanical properties of parts operating under impact loads was established.

Functional Galvanic Coatings of the Cr-Zn System

The authors have studied the influence of the electric current density, temperature, electrolyte composition on the properties of electroplating Chromium-Zinc deposits. The dependence of the maximum yield of metal on the physico-chemical characteristics of the solutions for electroplating of Chromium and Cr-Zn alloy has been shown. Chromium-Zinc coatings have been obtained from electrolytes based on chromic acid in the presence of organic additive (4-methylaminophenol). Abrupt nonlinear changes in density, viscosity, surface tension, specific electrical conductivity due to structural transformations in electrolytes are observed at the concentration of zinc sulphate of 4070 gramm / litr (further in the text - g/l), and the organic additive of 2-5 g/l. The obtained model has been applied to predict the optimal electrolyte compositions for the processes of Cr-Zn alloy formation, which will allow reducing the research efforts concerning the electrochemical studies of the given process when chromic acid solutions are used. The coatings exhibit high hardness, corrosion resistance, wear resistance, low internal stresses.

Preparation of a Nickel–Holmium Alloy Coating in an Equimolar HoCl3-Containing NaCl–KCl Melt

Cyclic voltammetry is used to study the electrolytic reduction of holmium ions on a nickel electrode in a holmium chloride-containing equimolar molten mixture of sodium and potassium chlorides in a temperature range of 1073–1173 K. The potentials of formation of nickel–holmium intermetallic compounds (IMCs) are determined. Nickel–holmium intermetallic compounds are synthesized by controlled potential electrolysis. Under the selected electrolysis conditions, the prepared coating is shown to be single-phase and its composition corresponds to the HoNi2 stoichiometry. The coefficients of reaction diffusion of holmium in nickel are calculated and the activation energy of alloy-formation process is determined.

Rational Design of Ir-M Nanoalloy for PEMFC Cathode Application: Combined Computational and Experimental Study

Despite recent efforts on replacing a noble Pt to less expensive catalysts for improving oxygen reduction reaction (ORR) for PEMFC (polymer electrolyte membrane fuel cell) application, the performance and stability of a noble Pt catalyst remains superior. In this presentation, we have systematically designed the novel Ir-based ORR catalyst for the PEMFC application via the combined density functional theory (DFT) and experimental approach.First, we computationally screened the potential M element and near-surface composition in Ir3M nanoalloy (M = 3d, 4d, 5d metals) for the purpose of enhancing the activity and durability of catalyst in ORR by considering Gibbs free energy change for alloy formation process, oxygen binding energy and segregation energy of inside M element toward surface layer under vacuum and oxygen environment. Our DFT-based screening identified the pure Ir monolayer on the top of Ir3­Cr, Ir3­V, Ir3­Re, and Ir3­Tc alloy cores as the promising candidates for improving ORR activity and durability. Next, a pure Ir monolayer on the top of Ir3­Cr core (which was expected to show the most enhanced ORR activity among the computationally-screened candidates) was experimentally prepared via physical vapor deposition method (PVD) and electrochemically evaluated for confirming our DFT prediction. We successfully synthesized a 3nm Ir-covered (Ir skinlayer) Ir3­Cr nanoparticle whose surface lattice distance was contracted by 1.03% compared to the pure Ir case. The specific activity (at 0.7 V vs RHE) of a Ir skinlayer/Ir3Cr catalyst with the very high durability (showing only 0.05 % decrease from the initial activity after 3000 potential cycles) was 12.3 times higher than a Ir catalyst. The detail mechanism on the enhanced activity in Ir-M alloy was also examined. Our theoretical and experimental study highlight the general methodology for designing metal-based alloy catalysts for the application to ORR in PEMFC and such method can be further extended to the development of the next-level electrocatalyst for energy conversion.

A Study of the Pore Surface State of Porous TiNi-based Materials Obtained by SHS at Various Ignition Temperatures

Structural features of porous TiNi-based materials obtained by SHS at temperatures of synthesis beginning of400 Cand600 Chave been investigated. It is found that finely porous material with a porosity P=75 % was obtained at the temperature of400 C. A surface of pore walls contains a dendritic relief, oxycarbidenitride layer and a multitude of secondary phase particles. Phase and chemical composition of the material is non-uniform. SHS material obtained at the synthesis beginning temperature of600 °Cis characterized as a coarse-porosity one P=65 %. Nano- and micropores are practically absent. The oxycarbidenitride surface layer with a variable thickness is substantially free of secondary inclusions due to the more complete processes of alloy formation. This layer has an own substructure based on carbonitride and oxynitride layers.

Surface state conductivity in epitaxially grown Bi1−xSbx(111) films

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.

Electrochemical Formation and Phase Control of Mg–Cu Alloys

AbstractMg–Cu alloys with different phases were electrodeposited in a molten LiCl–KCl eutectic mixture containing a small amount (0.5 mol %) of MgCl2 at 673 K. The electrochemical behavior of the MgII ion and alloy formation processes were studied at inert molybdenum (Mo) and active copper (Cu) electrodes in the molten salts, respectively. Different electrochemical techniques, such as cyclic voltammetry, square‐wave voltammetry, chronoamperometry, and open‐circuit potentiometry were carried out to investigate the electrochemical formation mechanism of Mg–Cu alloys. Three signals, corresponding to the formation of metal Mg and two different Mg–Cu alloy phases, are observed when using cyclic voltammetry, square‐wave voltammetry, and open‐circuit potentiometry. Chronoamperometry studies indicate the different interfacial properties of the magnesium metal versus the Mg–Cu alloys. The results of X‐ray diffraction and scanning electron microscopy show that the MgCu2 and Mg2Cu phases could be obtained at −2.30 and −2.38 V (vs. Pt), respectively.

Synergetic role of Li(+) during Mg electrodeposition/dissolution in borohydride diglyme electrolyte solution: voltammetric stripping behaviors on a Pt microelectrode indicative of Mg-Li alloying and facilitated dissolution.

We describe a voltammetric and spectroscopic study of Mg electrodeposition/dissolution (MgDep/Dis) in borohydride diglyme electrolyte solution containing Li(+) carried out on a Pt ultramicroelectrode (UME, r = 5 μm). The data reveal Li(+) cation facilitation that has not been previously recognized in studies made using macroelectrodes. While a single broad, asymmetric stripping peak is expected following MgDep on a Pt macroelectrode in 0.1 M Mg(BH4)2 + 1.5 M LiBH4 diglyme solution on a Pt UME, the stripping reveals three resolved oxidation peaks, suggesting that MgDep/Dis consists of not only a Mg/Mg(2+) redox reaction but also contributions from Mg-Li alloying/dissolution reaction processes. Detailed XPS, SIMS, ICP, and XRD studies were performed that confirm the importance of Mg-Li alloy formation processes, the nature of which is dependent on the reduction potential used during the MgDep step. Based on the electrochemical and surface analysis data, we propose an electrochemical mechanism for MgDep/Dis in a borohydride diglyme electrolyte solution that, in the presence of 1.5 M Li(+) ions, proceeds as follows: (1) Mg(2+) + 2e(-) ⇌ Mg; (2) (1 - x)Mg(2+) + xLi(+) + (2 - x)e(-) ⇌ Mg(1-x)Lix, 0 < x ≤ 0.02; and (3) (1 - y)Mg(2+) + yLi(+) + (2 - y)e(-) ⇌ Mg(1-y)Liy, 0.02 < y ≤ 0.09. Most significantly, we find that the potential-dependent MgDep/Dis kinetics are enhanced as the concentration of the LiBH4 in the diglyme electrolyte is increased, a result reflecting the facilitating influences of reduced uncompensated resistance and the enhanced electro-reduction kinetics of Mg(2+) due to Mg-Li alloy formation.

The Electrochemical Co-reduction of Mg-Al-Y Alloys in the LiCl-NaCl-MgCl2-AlF3-YCl3 Melts

The electrochemical formation of Mg-Al-Y alloys was studied in the LiCl-NaCl-MgCl2 melts by the addition of AlF3 and YCl3 on a molybdenum electrode at 973 K (700 degrees C). In order to reduce the volatilization of salt solvent in the electrolysis process, the volatile loss of LiCl-NaCl-MgCl2 and LiCl-KCl-MgCl2 melts was first measured in the temperature range from 873 K to 1023 K (600 degrees C to 750 degrees C). Then, the electrochemical behaviors of Mg(II), Al(III), Y(III) ions and alloy formation processes were investigated by cyclic voltammetry, chronopotentiometry, and open circuit chronopotentiometry. The cyclic voltammograms indicate that the under-potential deposition of magnesium and yttrium on pre-deposited Al leads to formation of Mg-Al and Al-Y intermetallic compounds. The Mg-Al-Y alloys were prepared by galvanostatic electrolysis in the LiCl-NaCl-MgCl2-AlF3-YCl3 melts and characterized by X-ray diffraction and scanning electron microscopy with energy dispersive spectrometry. Composition of the alloys was analyzed by inductively coupled plasma-atomic emission spectrometer, and current efficiency was also determined by the alloy composition. (C) The Minerals, Metals & Materials Society and ASM International 2014

Metal-enhanced Ge1−xSnx alloy film growth on glass substrates using a biaxial CaF2 buffer layer

The Ge1−xSnx(111) alloy formation process at the early stage and later stage of Ge deposition on a biaxial Sn/CaF2 (capping layer + NR)/glass substrate at an elevated growth temperature.

High Magnetic Moment of FeCo Nanoparticles Produced in Polyol Medium

High magnetization Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">55</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">45</sub> alloy nanoparticles have been successfully synthesized by the polyol reduction process followed by annealing under argon. The diethylene glycol was used as solvent and reducing agent simultaneously in this process. All the synthesized samples of FeCo nanoparticles were annealed at 873 K for different times. The alloy formation processes, the evolution of the microstructure, and the magnetic properties have been investigated before and after samples annealing. The X-ray diffraction (XRD) of the synthesized product before annealing shows that a cobalt ferrite is spinel structure of crystallite size of about 10 nm. XRD analysis of the samples annealed at 873 K for different times also shows that of the FeCo alloy has been obtained by reducing the cobalt ferrite. It has been confirmed that the formation of a body-centered cubic (bcc) single-phase structure where the wt% increases with annealing times leading to a pure phase after annealing during 4 h. These results are confirmed by transmission electron microscopy study. The saturation magnetization of the Fe-Co alloys increases with annealing time, indicating an increasing homogeneity in composition and the single bcc FeCo phase formation. The highest saturation magnetization of 235 Am2 · kg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with a low coercivity of 7.5 mT was obtained for the Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">55</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">45</sub> nanoparticles annealed during 4 h. The anisotropy constant K has been extracted and we have shown that increases with the annealing time.

Structural, magnetic, and electronic properties of high moment FeCo nanoparticles

Soft-magnetic Fe55Co45 alloy nanoparticles have been successfully synthesized by the polyol reduction process followed by annealing under argon. The diethylene glycol (DEG) was used as solvent and reducing agent simultaneously in this process. The synthesized samples of nanoparticles were annealed at 873K for different times. The alloy formation processes, the evolution of the microstructure, the magnetic properties, and the DOS calculation have been investigated before and after samples annealing. The X-ray diffraction of the synthesized product before annealing shows that a cobalt ferrite is spinel structure of crystallite size of about 10nm. X-ray diffraction analysis of the samples annealed at 873K for different times also shows that of the FeCo alloy has been obtained by reducing the cobalt ferrite. It has been confirmed the formation of a body-centered-cubic (bcc) single phase structure where the wt.% increases with annealing times leading to a pure phase after annealing during 4h. These results are confirmed by transmission electron microscopy study. The saturation magnetization of the Fe–Co alloys increases with annealing time, indicating an increasing homogeneity in composition and the single bcc FeCo phase formation. The highest saturation magnetization of 235emug−1with a low coercivity of 76Oe was obtained for the Fe55Co45nanoparticles annealed during 4h. The local random anisotropy constant KL has been extracted. This work presents also detailed information about total, and atom projected density of state functions, as well as the magnetic moment for different atoms in Fe55Co45 alloys and cobalt ferrite.