Bulk Metal Research Articles

The mechanics of the friction-assisted lateral extrusion process

The friction-assisted lateral extrusion process (FALEP) is gaining attention as a candidate for fabricating high-performance ultrafine grain alloys for potential industrial applications. It consists of extruding metal in bulk or powder form into a solid sheet in a single operation to obtain ultrafine-grained (UFG) structures. The sheet has high yield strength due to its UFG microstructure and a shear-type crystallographic texture that is fundamentally different from the textures of sheets obtained by rolling. Apart from its single-step feature, FALEP requires lower forces than in rolling, so less energy is required to achieve large reductions. The present work introduces analytical elastic/plastic continuum calculations for the mechanics of the FALEP process. The results of the calculations demonstrate the great advantages of FALEP with respect to rolling and equal/non-equal channel angular pressings.Graphical

Interfacial Properties of Anisotropic Monolayer SiAs Transistors

The newly prepared monolayer (ML) SiAs is expected to be a candidate channel material for next-generation nano-electronic devices in virtue of its proper bandgap, high carrier mobility, and anisotropic properties. The interfacial properties in ML SiAs field-effect transistors are comprehensively studied with electrodes (graphene, V2CO2, Au, Ag, and Cu) by using ab initio electronic structure calculations and quantum transport simulation. It is found that ML SiAs forms a weak van der Waals interaction with graphene and V2CO2, while it forms a strong interaction with bulk metals (Au, Ag, and Cu). Although ML SiAs has strong anisotropy, it is not reflected in the contact property. Based on the quantum transport simulation, ML SiAs forms n-type lateral Schottky contact with Au, Ag, and Cu electrodes with the Schottky barrier height (SBH) of 0.28 (0.27), 0.40 (0.47), and 0.45 (0.33) eV along the a (b) direction, respectively, while it forms p-type lateral Schottky contact with a graphene electrode with a SBH of 0.34 (0.28) eV. Fortunately, ML SiAs forms an ideal Ohmic contact with the V2CO2 electrode. This study not only gives a deep understanding of the interfacial properties of ML SiAs with electrodes but also provides a guide for the design of ML SiAs devices.

Frictional shear stress-induced incomplete martensitic transformation in mono-crystalline B2-CuZr spherulites

An austenitic B2-CuZr phase, when deformed, can undergo a martensitic transformation (MT) that produces a martensitic B19′-CuZr phase, resulting in remarkable transformation-induced plasticity (TRIP) and shape memory effects in B2-structured alloys. However, the shear mechanism as well as the crystallographic characteristics, which underlie the MT and, in turn, the TRIP and shape memory effects, remain unclear and somewhat controversial. Here we report that a single shear on {110}B2<001>B2, along with {1 1 5.5}B2 being the habit plane, are responsible for the MT in B2-CuZr, where {110}B2 and <001>B2 are the shear plane and the shear direction, respectively. These were revealed by determining unambiguously the orientation relationship between B2 and B19′, co-existing in individual spherulites contained in a B2-CuZr-containing bulk metal glass-matrix composite (BMGC). This exotic microstructure, featuring a core-shell like distribution in each single spherulite in which all the 12 possible martensite (B19′) variants constitute the core and the parent B2 forms the shell, was made from an incomplete MT in originally mono-crystalline B2 spherulites of the as-cast BMGC when subjected to moderately applied frictional shear stresses upon mechanical grinding. Finite element analysis suggests that a core-shell like shear stress distribution inside a B2 spherulite, caused by the confinement of the stiffer glass matrix, may account for it. These results provide direct experimental evidence to elucidate the B2→B19′ MT and its variant selections under various stress states, and pave the way for developing ductile B2-structured alloys, including but not limited to, shape memory intermetallics, high entropy alloys and B2-containing composite materials.

MXene guides microwaves through 3D polymeric structures

With the advances in space technology, weight reduction of components has been a paramount, yet challenging task. Additive manufacturing with high-performance polymers can realize lightweight and complex geometries that can also be manufactured on board. Yet polymers are electromagnetically inefficient for applications requiring electrical conductivity, such as guiding microwave signals. This work presents high-efficiency and lightweight additively-manufactured microwave components enabled by MXene coating. The waveguiding functionality was observed from 8 to 33 GHz, covering low earth orbit (LEO) frequencies, with a power-handling capability of up to 10 dB and a transmission coefficient of 93 %. After a single dip-coating cycle, the polymer waveguide performed only 2 % below an eight times heavier metallic equivalent. Frequency/polarization filtering was enabled by implementing special geometries, and a range of microwave functionalities, including resonance, was demonstrated. The MXene-coated components can replace 3D-printed and bulk metals, greatly decreasing weight and cost in space, and also in various terrestrial applications.

Topological Conversion of Nickel Foams to Monolithic Single‐Atom Catalysts

AbstractSingle‐atom catalysts have emerged as a promising class of catalysts due to their tailored coordination environments on the support, which can improve a variety of catalytic reactions, making them a highly desirable research subject in materials science with significant potential for industrial applications. However, traditional synthesis methods mainly obtain low‐yield powder catalysts without macroscopic mechanical strength, and also require tedious procedures, limiting their practicability. Here, monolithic carbon fibers are prepared with single atomic Ni sites directly from bulk metal. The synchronous support growth and metal diffusion realizes the effective atomization of nickel foam, and the innovative strategy of topological growth within a confined space results in robust and tough monolith. The application of this single‐atom‐monolith is demonstrated as a free‐standing electrode for highly efficient electrochemical CO2 reduction. The proposed synthesis strategy allows feasible preparation of functional single‐atom catalysts for potential industrial applications with advantages of using low‐cost raw materials, enabling large‐scale production, and providing processable, moldable monolithic materials.

Cationic Al oxo-hydroxide clusters: syntheses, molecular structures, and functional applications

Al oxo-hydroxide clusters, synthesized through the hydrolysis of Al³⁺ solutions, are expected to bridge the gap between metal-aqua complexes and bulk metal oxides/hydroxides. These clusters exhibit remarkable diversity in structure...

A low Pt-loaded electrode electrochemically synthesized from bulk metal for electrocatalytic applications

A Pt/WC1−x/WO3 self-supported electrode is fabricated from bulk metals by a electrochemical method. The interfacial effect of Pt and WC1−x/WO3 regulates the adsorption/desorption and transfer of Hads, thus optimizing the electrocatalytic performance.

Oxidation of fine aluminum particles: thermally induced transformations in particle shells and kinetics of oxide nucleation.

This paper investigates the process of oxidation of fine aluminum powder, consisting of spherical Al particles of 'metal core/oxide shell' type, when heated in air at temperatures below 550 °C. The highly dispersed aluminum powder 'Alex' used in this work (particle size: 0.05-1.5 μm and number average particle diameter (DN): 0.11 μm) was produced by electric explosion of a thin Al wire in argon with subsequent passivation in an oxygen-containing atmosphere. For the first time, the influence of the particle size on the oxidation process has been identified. During the reaction, individual γ-Al2O3 oxide nuclei grow at the surface of Al particles with diameters less than 300 nm without laterally overlapping to form a protective passivating layer, as typically occurs during the oxidation of micron-sized particles or bulk metal. The localization of γ-Al2O3 nuclei is determined by the regions where peeling of the primary amorphous oxide film from the surface of the metal core of an Al particle occurs due to the thermal decomposition of aluminum hydroxides (T ≈ 350 °C) present within the particle shells. A significant increase in the contributions of the following factors leads to a high oxidation rate: the diffusion within the disordered structure of a particle core and the surface diffusion of cations (Ea = 80.6 ± 5.3 kJ mol-1, 400-450 °C), the surface and grain boundary diffusion of oxygen during the growth of γ-Al2O3 crystallites (Ea = 108.3 ± 11.2 kJ mol-1, 470-500 °C) and the surface and grain boundary transport of anions through an amorphous and underlying nanocrystalline oxide layer with a constant thickness (Ea = 205.1 ± 8.6 kJ mol-1, 520-550 °C). The results obtained make it possible to expand the theoretical understanding of the manifestations of the size effect in solid-phase reactions and take into account its influence in practice.

Oxygen vacancy chemistry in oxide cathodes.

Secondary batteries are a core technology for clean energy storage and conversion systems, to reduce environmental pollution and alleviate the energy crisis. Oxide cathodes play a vital role in revolutionizing battery technology due to their high capacity and voltage for oxide-based batteries. However, oxygen vacancies (OVs) are an essential type of defect that exist predominantly in both the bulk and surface regions of transition metal (TM) oxide batteries, and have a crucial impact on battery performance. This paper reviews previous studies from the past few decades that have investigated the intrinsic and anionic redox-mediated OVs in the field of secondary batteries. We focus on discussing the formation and evolution of these OVs from both thermodynamic and kinetic perspectives, as well as their impact on the thermodynamic and kinetic properties of oxide cathodes. Finally, we offer insights into the utilization of OVs to enhance the energy density and lifespan of batteries. We expect that this review will advance our understanding of the role of OVs and subsequently boost the development of high-performance electrode materials for next-generation energy storage devices.

Multi-spectroscopic study of electrochemically-formed oxide-derived gold electrodes.

Oxide-derived metals are produced by reducing an oxide precursor. These materials, including gold, have shown improved catalytic performance over many native metals. The origin of this improvement for gold is not yet understood. In this study, operando non-resonant sum frequency generation (SFG) and ex situ high-pressure X-ray photoelectron spectroscopy (HP-XPS) have been employed to investigate electrochemically-formed oxide-derived gold (OD-Au) from polycrystalline gold surfaces. A range of different oxidizing conditions were used to form OD-Au in acidic aqueous medium (H3PO4, pH = 1). Our electrochemical data after OD-Au is generated suggest that the surface is metallic gold, however SFG signal variations indicate the presence of subsurface gold oxide remnants between the metallic gold surface layer and bulk gold. The HP-XPS results suggest that this subsurface gold oxide could be in the form of Au2O3 or Au(OH)3. Furthermore, the SFG measurements show that with reducing electrochemical treatments the original gold metallic state can be restored, meaning the subsurface gold oxide is released. This work demonstrates that remnants of gold oxide persist beneath the topmost gold layer when the OD-Au is created, potentially facilitating the understanding of the improved catalytic properties of OD-Au.

Enhancing the electrochemical performance of Sn-Zn alloy anode foil for lithium-ion batteries through microstructure design via accumulative roll bonding technique

In this study, we introduce a novel method for designing microstructures of Sn-45Zn alloy foils utilizing the accumulative roll bonding (ARB) technique, which is one of severe plastic deformation techniques that have been used for refining the microstructures of bulk metals. The electrochemical properties of Sn-Zn foil anodes with various microstructures achieved through the ARB method followed by annealing are investigated in lithium-ion batteries. The degree and characteristics of microstructural damage during electrochemical cyclic tests are also examined in detail to provide insights into the microstructural parameters that critically influence the capacity and cyclic behavior of the Sn-Zn alloy foil anode. Our findings suggest that the ARB-processed Sn-Zn alloy foil, characterized by nearly ultrafine grains composed of Sn and Zn phases with the Zn phase forming a continuous network, exhibits superior battery capacity and cycle life compared to the sample processed using the conventional rolling method. This superiority can be attributed to its unique microstructure obtained through ARB, which reduces pore density, suppresses pore interlinkage, decreases charge transport resistance and nucleation overpotential, and enhances Li-ion diffusivity in the electrode.

Enhanced oil dehalogenation during catalytic pyrolysis of WEEE-derived plastics over Fe- and Ca-modified zeolites

Pyrolysis affords the conversion of plastics from Waste of Electrical and Electronic Equipment (WEEE) into oils with potential applications in the production of valuable chemicals and the formulation of liquid fuels. However, the presence of significant concentrations of halogens (Cl and Br) in these wastes represents an important limitation as it can lead to the generation of hazardous species that negatively affect the environment. In this work, the catalytic pyrolysis of a real WEEE plastic has been investigated using a reaction system that operates with continuous feeding of the raw material. The catalysts assayed include bulk metal oxides (Fe2O3 and CaO) and zeolites (ZSM-5 and USY), as well as hybrid solids obtained by supporting those metal oxides on the zeolites. Pre-treatment of the raw WEEE plastics by water washing allows the Cl concentration to be significantly reduced, but it does not affect the Br content. Thermal pyrolysis produces an oil fraction with a high yield (> 70 wt%) and a large concentration of halogens (700 ppm), even though the char produced effectively retains more than 90% of Br and Cl contained in the feedstock. During catalytic pyrolysis, the halogen content of the oil is further reduced obtaining the best dehalogenation results with the metal-modified zeolites. This fact evidences a synergetic effect derived from the high metal dispersion achieved over the zeolitic supports. Fe/ZSM-5 is the most promising catalyst, showing an almost constant dehalogenation activity along the time-on-stream and producing an oil enriched in monoaromatic hydrocarbons (mainly styrene).

One‐Stop Hybrid Printing of Bulk Metal and Polymer for 3D Electronics

Additive manufacturing (AM), so‐called 3D printing, has reshaped manufacturing technologies with attractive alternatives to the traditional centralized, subtractive‐based mass production. Further functionalities like multimaterial AM (MMAM) are essential for mainstream manufacturing. With MMAM of electrical traces, the traditional printed circuit board can be transformed to freeform 3D electronics using the entire volumetric space. Although research groups attempt MMAM for freeform 3D electronics, achieving easy integration of the electrical traces with high conductance into dielectric substrates in a streamlined and simplified process remains challenging. Herein, an in‐house developed printer, named Synkròtima, is demonstrated for one‐stop printing of 3D dielectric parts with fully embedded and structured conductive features via drop‐on‐demand printing of molten metal for the first time. Printed traces show 12 times lower electrical resistance of at 230 μm linewidth than the lines from conductive inks. Printed traces with 100 μm dot spacing reveal exemplary shape fidelity with a standard deviation of only 7 μm. Quantitative estimation of adhesion of metal traces to dielectric reveals a mean shear‐off force of 7.20 N which is half of what is obtained for reflow soldered electronics. Demonstrators with embedded functional electrical circuits, directly interconnected components, and 3D out‐of‐plane metal structures are printed via Synkròtima.

High Temperature Corrosion of Inconel 625 and Pure Nickel in Contact with Fluoride Melts

Considering the fact that fossil fuels are not inexhaustible, and they pollute the environment, the automotive industry is transitioning from internal combustion to electric engines. As a result, batteries are becoming a strategic component of cars and thus battery ingredients are considered as important raw materials. Therefore, these batteries need to be recycled as well, since the natural resources for producing them are limited and some of the elements like nickel which are used in these batteries can be hazardous if left in the environment. In order to recycle electric batteries, furnaces with high temperature corrosion resistance are necessary. Maintaining these furnaces for longer periods is of great interest and necessitates it for the challenges to be dealt with, especially in case of high temperature corrosion.In the present study, high temperature corrosion behavior of Inconel 625 is compared with pure nickel. Both metals have been exposed to fluoride melts (to mimic the recycling process) for different durations of time. The performances of these two bulk metals are investigated mainly through scanning electron microscope and X-ray diffraction. Element leaching, oxidation, depth of internal attack and depletion profile are among the main parameters studied here. Experiments are carried out both in dry and humid condition to see how humidity changes the reactions. Since there are different alloying elements in Inconel 625, and humidity is involved, pure nickel is used as the baseline to see the effect of different parameters involved. Filtered air is used as the main environment in this study and lithium fluoride is used as the main salt.

Impacts of E-Beam Irradiation on Polycrystalline Metals in Both Bulk and Thin Film Forms

This study aims to explore the impact of e-beam irradiation on the mechanical and structural characteristics of four different polycrystalline metals (Ni, Cr, V, and Ti), in both bulk and thin film forms. Thin metal films are fabricated using magnetron sputtering. The primary goal is to identify suitable metal candidates for growing thin films, which could serve as exit windows for e-beam accelerators. This selection is based on their properties, power dissipation capabilities, and the effects of irradiation on mechanical attributes such as hardness, ductility, defect density, and strength.For the bulk polycrystalline metal samples, a series of nanoindentation tests has been conducted before and after e-beam irradiation to investigate changes in hardness and elastic modulus. Additionally, to compare performance with the bulk samples, thin metal films are subjected to the same procedure before and after irradiation, allowing for the evaluation of film hardness, moduli, and creep properties. Results indicate that irradiated bulk samples of Ni, Cr, and V become harder, whereas Ti experiences softening. There is no significant irradiation effect on modulus for all for polycrystalline metal samples. To understand the underlying reasons behind these effects, both the fabricated metal films and bulk metal samples undergo comprehensive characterization tests for their microstructural properties, elastic behavior, and chemical composition. This involves the utilization of SEM with EDS, FESEM and AFM to analyze microstructure and surface attributes of the films, followed by X-ray diffraction to gain insight into film morphology and lattice orientation.

Electrochemical Top-Down Synthesis of Nanostructured Electrocatalysts for Polymer Electrolyte Membrane Fuel Cells

Nanostructured catalysts are a promising class of materials to meet the requirements for the energy transition away from fossil fuels towards alternative, carbon-free, energy carriers, such as hydrogen. These catalyst materials boost the efficiency of energy conversion devices, such as fuel cells or electrolyzers, by accelerating their fundamental electrochemical reactions. Bottom-up synthetic routes for nanostructured materials often involve multiple synthesis steps and the use of surfactants, reducing agents or stabilizers. This results in complex and extensive synthesis protocols.[1] In recent years, a novel top-down synthesis approach to form metal nanoparticles has been established, in which bulk metal wires are immersed in an electrolyte and subsequently subjected to a high alternating potential. This leads to the generation of nanoparticles dispersed in the electrolyte.[2] There is no need for reducing agents, surfactants, or precursor solutions. The complete synthesis can be performed in one pot involving one main step with consequent washing and drying of the nanoparticles.In this study, we synthesized Pt-based nanoparticles supported on Vulcan® carbon support (Pt/C) and tested their electrochemical activity towards the oxygen reduction reaction (ORR) for polymer electrolyte membrane fuel cells (PEMFCs). Firstly, we elucidated the influence of synthesis parameters such as potential amplitude, frequency, electrolyte composition, and concentration on the size and shape of Pt nanoparticles.[3] We continued with the synthesis of more complex nanostructures, such as Pt alloy nanoparticles. This introduces strain and ligand effects at the surface of the nanoparticles, which increases the electrocatalytic activity for the ORR. We demonstrated the facile, simple, and surfactant-free synthesis of highly active PtxPr/C[4] and PtxCu/C, as two examples for Pt alloy catalysts for the ORR, and give an outlook on other systems, such as PtxGd/C.

Filiform Corrosion on Polyester Powder-Coated Aluminum

Filiform corrosion initiates and grows locally at macroscopic defects in coatings on metal substrates. While typically not detrimental to the bulk metal properties, the filiform corrosion results in threadlike filaments that propagate parallel to the surface underneath the coating. Herein, we present a study correlating the electrochemical and structural properties of polyester powder coatings onto 6022 aluminum to their associated resistance to filiform corrosion. Filiforms are propagated using a modified EN 3665 method and tracked temporally via bright field microscopy. Results including electrochemical impedance spectroscopy, open-circuit potential tracking, and potentiostatic experiments were used to evaluate coating barrier properties. Coating morphologies of pre- and post-corrosion samples are evaluated using SEM and EDX. Mechanical properties of free-standing polyester films are also characterized. The combined electrochemical and mechanical data are used to derive polyester coating design criterion to maximize resistance to filiform corrosion.

Growth mechanism for dendrite-free lithium regulated deposition

The unhealthy electrodeposition leads to uncontrolled growth and random fracture of Li, causing safety problems. Here we elaborate on the growth mechanism of Li on different substrates by integrating overpotential testing and Gibbs free energy calculating. Induced nucleation sites are brought into the substrate to trap Li preferentially, reducing the primary deposition barrier and contributing to the uniform nucleation of Li. The Li grows along the sites where the pits grow on the carbon substrate. The secure connection between the metal and the substrate can be used to stabilize the bulk metal. In addition, the external magnetic field during electrodeposition homogenizes the direction of ion movement and promotes uniform deposition. At the same time, the 3D frame distributes the ion flux homogenization, providing enough space to mitigate the volume change. The design of the substrate provides a unique inside-out growth path for metal, which guides the uniform deposition of Li and effectively inhibits the growth of dendrites. The electrochemical performance using CC/Co3O4/Li electrode is significantly improved in the full battery with sulfur as the cathode. This work explores the growth mechanism of Li metal and guides stable dendrite-free Li electrode fabrication.

Microwave ignition characteristics and distinction of typical nanothermites under different electromagnetic radiation

As a commonly used agent in micro-nano satellites and other small pyrotechnics, it is crucial to understand the response of nanothermite to microwave due to the growing interest in space and the increasingly complex electromagnetic environment. Microwaves can penetrate typical energetic materials and interact with them spatially and holistically. There are two ways of microwave radiation to the samples: microwave drill (contact) and single mode resonator (non-contact). To date, all previous studies were carried out in a single environment, and only for a single thermite system. In this work, the ignition performance of three representative nanothermite systems (Al/CuO, Al/MnO2, Al/Fe3O4) under two microwave ignition devices (custom-made microwave drill and single mode resonator) was first systematically studied, which contain both magnetic and non-magnetic, as well as high and low reactivity. The results showed that the relationship between ignition delay time and power basically accorded with exponential function. The ignition delay time decreased rapidly with the increase of power and finally stabilized within a fixed range. Compare to the metal oxide, pure Al was insensitive to microwave. However, the mechanism of the two ignition processes was different. The ignition sequence of the nanothermites was the same as metal oxides, indicating that the metal oxide was the decisive factor and driver of nanothermite ignition under microwave drill. For the ignition in resonator, the nanothermite behaved like bulk metal, reflecting most of the electromagnetic energy away. The ignition sequence was consistent with the aluminum content in the composites, implying nAl was the determining factor. To further analyze the ignition mechanism, the hot wire and laser sensitivity of nanothermites were also compared.

Mass Production and Vast Application States of Bulk Metallic Glasses

Since the first synthesis of bulk metallic glasses (BMGs) by copper mold casting in 1990, much effort has been devoted to the searching of new BMG composition, the clarification of fundamental and engineering properties for BMGs and their industrialization. At present, BMGs have been formed in a large number of multicomponent alloy systems where the empirical three component rule is satisfied. Nowadays, commercialized BMGs are classified to Zr-based and Fe-based alloy groups. When we look at the industrialization of Zr-Al-Ni-Cu-based BMGs, the first commercialization was made for golf clubs in Japan in 1998, followed by watch parts etc. Since then, Zr-based BMGs have been used continuously up to 2013, though their application scale was in a limited state. Since 2014, the application scale was significantly extended in collaboration with the rapid developments of smartphones and electric vehicles. At present, the mass production facilities for Zr-based BMGs have been significantly developed and variety of BMG products have been produced. On the other hand, Fe-based soft magnetic BMGs were found in 1995. Their BMGs have also been used on a huge number of pieces in various kinds of electronic-magnetic instruments. These recent application states for Zr- and Fe-based BMGs are introduced together with new nanocrystalline Fe-based soft magnetic alloys developed through the derivation of alloy composition from Fe-based BMGs.