Search Results (101)

The widespread implementation of next-generation Li metal anodes is limited, in part, due to the formation of dendritic and/or mossy electrodeposits during cycling. These morphologies can lead to battery failure due to the formation of short circuits and significant volumetric expansion at the anode. One strategy to control the electrodeposition of Li metal is to use lithiophilic materials at the anode. Here, we evaluate the impact of Ag and Au on the early stages of Li metal electrodeposition and cycling. The alloying substrates decrease the voltage for Li reduction and improve Li wetting/adhesion. We probe volumetric expansion directly through dilatometry measurements and find that the degree of volumetric expansion is less when lithium is cycled on an alloying substrate compared to a non-alloying substrate (Cu). Dilatometry experiments reveal that Au has the least amount of volumetric expansion and coin cell cycling experiments indicate that Ag yields more stable cycling compared to Au or Cu. The evaluation of in situ cross-sectional images of cycled coin cells shows that Ag has the lowest volumetric expansion in a coin cell format. Full article

Electrochemical nitrogen reduction reaction (NRR) has emerged as a promising approach for sustainable ammonia synthesis under ambient conditions, offering a low-energy alternative to the traditional Haber–Bosch process. However, the development of efficient and sustainable electrocatalysts for NRR remains a significant challenge. Noble metals, known for their exceptional chemical stability under electrocatalytic conditions, have garnered considerable attention in this field. In this study, we report the successful synthesis of nanoporous CuAuPtPd quasi-high-entropy alloy (quasi-HEA) prism arrays through “melt quenching” and “dealloying” techniques. The as-obtained alloy demonstrates remarkable performance as an NRR electrocatalyst, achieving an impressive ammonia synthesis rate of 17.5 μg h⁻¹ mg⁻¹ at a potential of −0.2 V vs. RHE, surpassing many previously reported NRR catalysts. This work not only highlights the potential of quasi-HEAs as advanced NRR electrocatalysts but also provides valuable insights into the design of nanoporous multicomponent materials for sustainable energy and catalytic applications. Full article

Non-radiative decay of surface plasmon (SP) offers a novel paradigm for efficient conversion of photons into carriers. However, the narrow bandwidth of SP has been a significant obstacle to the widespread applications. Previously, research and applications mainly focused on noble metals such as Au, Ag, and Cu. In this article, we report an Ag-Al alloy material, μ-Ag₃Al, in which the surface plasmon operating bandwidth is 1.7 times that of Ag and hot carrier transport properties are comparable with those of AuAl. The results show that μ-Ag₃Al allows efficient direct interband electronic transitions from ultraviolet (UV) to near infrared range. Spherical nanoparticles of μ-Ag₃Al exhibit the localized surface plasmon resonance (LSPR) effect in the ultraviolet region. Its surface plasmon polariton (SPP) shows strong non-radiative decay at 3.36 eV, which is favorable for the generation of high-energy hot carriers. In addition, the penetration depth of SPP in μ-Ag₃Al remains high across the UV to the near-infrared range. Moreover, the transport properties of hot carriers in μ-Ag₃Al are comparable with those in Al, borophene and Au-Al intermetallic compounds. These properties can provide guidance for the design of plasmon-based photodetectors, solar cells, and photocatalytic reactors. Full article

Ammonia (NH₃) represents a promising zero-emission fuel in hydrogen fuel cells. Membrane reactors for NH₃ decomposition based on Pd-alloys have demonstrated high NH₃ conversion, high hydrogen diffusivity, and high hydrogen selectivity, which allows for the production of high-purity H₂ without the need for gas separation or purification. However, it is observed that Pd-alloy membranes are to a various degree prone to H₂ flux inhibition in the presence of NH₃. Hence, finding proper means to tailor the surface adsorption properties through, e.g., alloying is imperative to further improve the technology. In the current work, hydrogen and ammonia co-adsorption phenomena on M(1 1 1) and Pd₃M(1 1 1) (M = Pd, Ru, Ag, Au, Cu) surfaces are studied using density functional theory calculations. It is shown that the surface adsorption properties are strongly dependent on the surface composition, which can be linked to the corresponding electronic structure at the membrane surface. Full article

Surface nanopatterning induced by ion beam irradiation allows for the creation of patterns on large areas of a wide variety of materials. However, surface composition plays a crucial role in the process. In this study, we investigate the bombardment of a metallic alloy, specifically an Au-Cu system with different compositions, discussing differences in the formation of patterns compared to pure materials. Mixtures with compositions ranging from 35 to 65 at.% Cu exhibit a dampening effect on ripple height and depth. At intermediate angles of incidence, horizontal displacement is minimized and sputtering maximized; conversely, at grazing angles, sputtering is minimized and horizontal displacement becomes dependent on material mobility. It is, therefore, evident that sputtering determines the patterning for intermediate angles. However, an analysis of the redistribution factor as a function of the angle of incidence shows that the weight of the redistribution is much lower than that of sputtering in alloys of similar composition at grazing angles due to the amorphization process. This point is confirmed by the data on displaced atoms obtained from the relocation cross-sections. Full article

To avoid wear and tear of the slip ring due to electrical corrosion, the slip ring needs to undergo the running-in process under atmospheric conditions without current after assembly. To address the urgent demand for long-service capability space conductive slip rings in the aerospace field, the running-in behavior and failure mechanism between the AgCuNi alloy and Au-electroplated layer are investigated using a ball-on-disc tribometer in this paper. The results show that the transfer film composed of Au plays an important role in modifying the friction during the sliding process. With the accumulation of wear debris composed of Ag on the disc, the contact material of the friction pair changed from Au and Au to Au, Ag and Au, so the surface roughness of wear tracks increased. Finally, the transfer film broke, which made the layer fail. This paper reveals the key element failure mechanism that causes transfer film failure in the running-in contact area, which is used to reveal the friction behavior and failure mechanism of slip ring friction pair materials, and provides a basis for the selection of running-in parameters during the running-in process of slip rings before power-on operation. Full article

Understanding the tribological properties of alloy-based sliding electrical contacts is crucial for both fundamental research and practical applications. Here, to explore the friction, wear, and contact resistance of a AgCuNi alloy/Au-electroplated layer during sliding, a ball-on-disk tribometer was coupled with a source meter. The experiments were conducted under various conditions including a current ranging from 0 to 1.0 A, a normal load ranging from 0.5 to 3.0 N, and a sliding speed of 40 mm/s. The results indicate that the wear of the friction pair is aggravated by both the current and the increase in the normal load. When the current was 0.5 A, the wear loss reached its lowest point. However, as the current increased from 0.5 A to 1.0 A, there was an intensification in Ag transfer from the alloy ball to the Au-electroplated layer, resulting in an increase in wear loss. Both the normal load and current have significant effects on both friction coefficient and contact resistance. The variation in contact resistance over time follows a similar pattern to that of the friction coefficient over time. The formation of a transfer film plays a crucial role in determining contact resistance, wear resistance, and friction coefficient. The experiment demonstrates that optimizing the normal load and current can adjust both the contact resistance and friction coefficient, thereby prolonging service life and ensuring the stability of contacts. Full article

In order to obtain electronic contacts with good performance, Au-Cu alloy coatings with different gold contents were prepared on copper substrates by direct current electrodeposition and were tested against electrochemical corrosion and arc corrosion. The experimental results showed that the hardness of the Au-Cu alloy was in the range of 115.2 HV~171.6 HV, which meets the requirements of electronic contact materials. The polarization curve (Tafel) test and electrochemical impedance spectroscopy (EIS) test results indicated that the electrochemical corrosion resistance of Au-Cu alloy plating was much better than pure copper. With the rise of gold content in the alloy coatings, the corrosion resistance of the alloy coatings enhanced gradually. Compared with pure copper, the Au-Cu alloy coatings showed more stable contact resistance. After 1000 contacts, the resistivity of the alloy with 75% gold varied from 72 mΩ to 78 mΩ, whereas under the same conditions, the resistivity of copper changed from 14 mΩ to 78 mΩ. Anode-type material transfer occurred after 1000 contacts with a reduction in the total mass of each contact element. The mass loss of Au₇₅Cu₂₅ and Au₈₆Cu₁₄ contact elements was lower than that of pure copper. The Au-Cu alloy coatings displayed excellent arc corrosion resistance when the gold content in the alloy plating was higher than 75%. Full article

To realize highly sensitive SAW devices, novel Al–Cu thin films were developed using a combinatorial sputtering system. The Al–Cu sample library exhibited a wide range of chemical compositions and electrical resistivities, providing valuable insights for selecting optimal materials for SAW devices. Considering the significant influence of electrode resistivity and density on acoustic wave propagation, an Al–Cu film with 65 at% Al was selected as the IDT electrode material. The selected Al–Cu film demonstrated a resistivity of 6.0 × 10⁻⁵ Ω-cm and a density of 4.4 g/cm³, making it suitable for SAW-based microfluidic actuator applications. XRD analysis revealed that the Al–Cu film consisted of a physical mixture of Al and Cu without the formation of Al–Cu alloy phases. The film exhibited a fine-grained microstructure with an average crystallite size of 7.5 nm and surface roughness of approximately 6 nm. The SAW device fabricated with Al–Cu IDT electrodes exhibited excellent acoustic performance, resonating at 143 MHz without frequency shift and achieving an insertion loss of −13.68 dB and a FWHM of 0.41 dB. In contrast, the Au electrode-based SAW device showed significantly degraded acoustic characteristics. Moreover, the SAW-based microfluidic module equipped with optimized Al–Cu IDT electrodes successfully separated 5 μm polystyrene (PS) particles even at high flow rates, outperforming devices with Au IDT electrodes. This enhanced performance can be attributed to the improved resonance characteristics of the SAW device, which resulted in a stronger acoustic radiation force exerted on the PS particles. Full article

The ability to fabricate bimetallic clusters with atomic precision offers promising prospects for elucidating the correlations between their structures and properties. Nevertheless, achieving precise control at the atomic level in the production of clusters, including the quantity of dopant, characteristic of ligands, charge state of precursors, and structural transformation, have remained a challenge. Herein, we report the synthesis, purification, and characterization of a new bimetallic hydride cluster, [AuCu₁₁(H){S₂P(OⁱPr)₂}₆(C≡CPh)₃] (AuCu₁₁H). The hydride position in AuCu₁₁H was determined using DFT calculations. AuCu₁₁H comprises a ligand-stabilized defective fcc Au@Cu₁₁ cuboctahedron. AuCu₁₁H is metastable and undergoes a spontaneous transformation through ligand exchange into the isostructural [AuCu₁₁(Cl){S₂P(OⁱPr)₂}₆(C≡CPh)₃] (AuCu₁₁Cl) and into the complete cuboctahedral [AuCu₁₂{S₂P(OⁱPr)₂}₆(C≡CPh)₄]⁺ (AuCu₁₂) through an increase in nuclearity. These structural transformations were tracked by NMR and mass spectrometry. Full article

Sn-10Bi low-bismuth-content solder alloy provides a potential alternative to the currently used Sn-Ag-Cu series due to its lower cost, excellent ductility, and strengthening resulting from the Bi solid solution and precipitation. This study primarily investigates the interfacial evolution and shear strength characteristics of Sn-10Bi joints on a Ni/Au surface finish during the as-soldered and subsequent isothermal aging processes. To improve the joint performance, a 0.2 or 0.5 wt.% dopant of Zn was incorporated into Sn-10Bi solder. The findings demonstrated that a 0.2 or 0.5 wt.% Zn dopant altered the composition of the intermetallic compound (IMC) formed at the interface between the solder and Ni/Au surface finish from Ni₃Sn₄ to Ni₃(Sn, Zn)₄. The occurrence of this transformation is attributed to the diffusion of Zn atoms into the Ni₃Sn₄ lattice, resulting in the substitution of a portion of the Sn atoms by Zn atoms, thereby forming the Ni₃(Sn, Zn)₄ IMC during the soldering process, which was also verified by calculations based on first principles. Furthermore, a 0.2 or 0.5 wt.% Zn dopant in Sn-10Bi significantly inhibited the Ni₃(Sn, Zn)₄ growth after both the soldering and thermal aging processes. Zn addition can enhance the shear strength of solder joints irrespective of the as-soldered or aging condition. The fracture mode was determined by the aging durations—with the brittle mode occurring for as-soldered joints, the ductile mode occurring for aged joints after 10 days, and again the brittle mode for joints after 40 days of aging. Full article

To meet the demands for high-temperature performance and lightweight materials in aerospace engineering, the Au-Ni solder is often utilized for joining dissimilar materials, such as Ti₃Al-based alloys and Ni-based high-temperature alloys. However, the interaction between Ti and Ni can lead to the formation of brittle phases, like Ti₂Ni, TiNi, and TiNi₃, which diminish the mechanical properties of the joint and increase the risk of crack formation during the welding process. Cu doping has been shown to enhance the mechanical properties and high-temperature stability of the Au-Ni brazed joint’s central area. Due to the difficulty in accurately controlling the solid solution content of Cu in the Au-Ni alloy, along with the high cost of Au, traditional experimental trial-and-error methods are insufficient for the development of Au-based solders. In this study, first principles calculations based on density functional theory were employed to analyze the effect of Cu content on the stability of the Au-2.0Ni-xCu (x = 0, 0.25, 0.5, 0.75, 1.0, 1.25 wt%) alloy phase structure. The thermal properties of the alloy were determined using Gibbs software fitting. The results indicate that the Au-2.0Ni-0.25Cu alloy exhibits the highest plastic toughness (B/G = 5.601, ν = 0.416, Cauchy pressure = 73.676 GPa) and a hardness of 1.17 GPa, which is 80% higher than that of Au-2.0Ni. This alloy balances excellent strength and plastic toughness, meeting the mechanical performance requirements of brazed joints. The constant pressure specific heat capacity (C_p) of the Au-2.0Ni-xCu alloy is higher than that of Au-2.0Ni and increases with Cu content. At 1000 K, the C_p of the Au-2.0Ni-0.25Cu alloy is 35.606 J·mol⁻¹·K⁻¹, which is 5.88% higher than that of Au-2.0Ni. The higher C_p contributes to enhanced high-temperature stability. Moreover, the linear expansion coefficient (CTE) of the Au-2.0Ni-0.25Cu alloy at 1000 K is 8.76 × 10⁻⁵·K⁻¹, only 0.68% higher than Au-2.0Ni. The lower CTE helps to reduce the risk of solder damage caused by thermal stress. Therefore, the Au-2.0Ni-0.25Cu alloy is more suitable for brazing applications in high-temperature environments due to its excellent mechanical properties and thermal stability. This study provides a theoretical basis for the performance optimization and engineering application of the Au-2.0Ni-xCu alloy as a gold-based solder. Full article

This paper investigates the mineralogical and geochemical characteristics, as well as the possible sources, of gold, silver, platinum group elements (PGE), copper, and lead found in the beach sands along Egypt’s Mediterranean coast. Using scanning electron microscopy and electron probe micro-analysis, this study determines the morphology and micro-chemistry of separated grains to assess their economic potential and how various minerals respond to different transport distances. The analysis reveals that gold grains are of high purity (94.11 to 98.55 wt.%; average 96 wt.% Au) and are alloyed with Ag (1.28–2.32 wt.%) and Cu (0.16–3.15 wt.%). Two types of gold grains were identified, indicating differences in transport distances. Variations in morphology, surface features, inclusion types, rims, and chemistry of the native metals, including gold grains, suggest differences in composition, weathering degree, transport distance, deposit types, and host rocks. The average Ag concentration in gold grains (1.86 wt.%) suggests a link to mesothermal or supergene deposits. Most silver, copper, and lead grains are spherical, with some variations in shape. Silver grains have 71.66–95.34 wt.% Ag (avg. 82.67 wt.%). Copper grains have 92.54–98.42 wt.% Cu (avg. 94.22 wt.%). Lead grains contain 74.22–84.45 wt.% Pb (avg. 79.26 wt.%). The identified platinum group minerals (PGM) belong to the Pt–Fe alloys and sperrylite, both of which are PPGE-bearing minerals. These metals likely originate from the weathering of upstream Nile tributaries surrounded by igneous and metamorphic rocks from Ethiopian and Central African regions, with a minor contribution from the Egyptian Eastern Desert Mountains. Full article

Ternary gold alloys (TGAs) are highly regarded for their excellent electrical properties. Electrical resistivity is a crucial indicator for evaluating the electrical performance of TGAs. To explore new promising TGAs with lower resistivity, we developed a reverse design approach integrating machine learning techniques and proactive searching progress (PSP) method. Compared with other models, the support vector regression (SVR) was determined to be the most optimal model for resistivity prediction. The training and test sets yielded R² values of 0.73 and 0.77, respectively. The model interpretation indicated that lower electrical resistivity was associated with the following conditions: a van der Waals Radius (V_rt) of 0, a V_r (another van der Waals Radius) of less than 217, and a mass attenuation coefficient of MoKα (M_acm) greater than 77.5 cm²g⁻¹. Applying the PSP method, we successfully identified eight candidates whose resistivity was lower than that of the sample with the lowest resistivity in the dataset by more than 53–60%, e.g., Au_1.000Cu_4.406Pt_1.833 and Au_1.000Pt_2.232In_1.502. Finally, the candidates were validated to possess low resistivity through the pattern recognition method. Full article

In this article, an attempt was made to join DP600 steel and Ti6Al4V titanium alloy sheets by resistance spot-welding (RSW) using an interlayer in the form of Cu and Au layers fabricated through the cold-spraying process. The welded joints obtained by RSW without an interlayer were also considered. The influence of Cu and Au as an interlayer on the resulting microstructure as well as mechanical properties (shear force and microhardness) of the joints were determined. A typical type of failure of Ti6Al4V/DP600 joints produced without the use of an interlayer is brittle fracture. The microstructure of the resulting joint consisted mainly of the intermetallic phases FeTi and Fe₂Ti. The microstructure of the Ti6Al4V/Au/DP600 joint contained the intermetallic phases Ti₃Au, TiAu, and TiAu4. The intermetallic phases TiCu and FeCu were found in the microstructure of the Ti6Al4V/Cu/DP600 joint. The maximum tensile/shear stress was 109.46 MPa, which is more than three times higher than for a welded joint fabricated without the use of Cu or Au interlayers. It has been observed that some alloying elements, such as Fe, can lower the martensitic transformation temperature, and some, such as Au, can increase the martensitic transformation temperature. Full article