Search Results (63)

The development of stable, non-toxic electrolytes is essential for electrodepositing large-area coatings. This study presents a novel low-cyanide electrolyte, offering a viable alternative to traditional cyanide-based solutions for the electroplating of gold–copper alloys. Compared to conventional baths, the new formulation offers safer handling and environmental compatibility without compromising performance. Electrolyte compositions were optimized via cyclic voltammetry, and coatings were deposited using direct current, pulse current, and reverse pulse current methods. The novel low-cyanide electrolyte system achieved a 99.1% reduction in cyanide use compared with the commercial formulation. Coatings produced with pulse current and reverse pulse current deposition exhibited structural, morphological, and mechanical properties comparable to those obtained from cyanide-based electrolytes. Overall, the low-cyanide electrolyte represents a safer, high-performance alternative to traditional cyanide-based systems. Full article

A prototype of an industrial installation for the deposition of self-restoring nitride coatings on the surface of reed switch contacts using electro-spark erosion alloying was developed, manufactured, and tested under the laboratory conditions at LLC Nitron. It was shown that the coatings are formed inside a bulb of reed switches at the final stage of their production following the impact from the spark breakdown between the contacts, stimulated via alternating magnetic and electric fields. The nitrogen concentration in the surface layers of the nitride coatings, estimated by means of X-ray microanalysis, was ca. 19 at. % and their thickness, measured by time-of-flight secondary ion mass spectrometry via sputter depth profiling, ranged between 250 and 350 nm. The novelty of the presented work consists of the development of an innovative piece of equipment, the operating principle and design of which are protected by intellectual property rights (four Russian patents). The technological approach implemented in this installation differs from the industrial galvanic technology due to its high level of environmental safety and economic efficiency, since it does not require the use of gold, ruthenium, or other high-priced metals. Full article

The gold standard materials used for frameworks of full-arch implant-supported fixed prostheses (ISFPs) have traditionally been metal alloys, but recently, high-performance polymers such as polyetherketones and fibre-reinforced resins have been gaining popularity despite the lack of evidence of load-bearing capacity. The aim of the present study was to evaluate the displacements and strains of milled polymeric frameworks for full-arch ISFPs using 3D digital image correlation. Methods: Twelve frameworks were milled from four polymeric materials (three per group): polyetheretherketone (PEEK), polyetherketoneketone (PEKK), poly(methyl methacrylate) (PMMA) and fibre-reinforced composite (FRC). Each framework was fitted with titanium links and screwed to implant analogues embedded in resin and tested for static load-bearing capacity up to 200N. Displacements were captured with two high-speed photographic cameras and analysed with a video correlation system on three spatial axes, U, V, and W, along with principal tensile, compressive and von Mises strains. Results: PEEK exhibited the highest displacement, indicating greater flexibility, while FRC showed the lowest displacement, suggesting enhanced rigidity. Von Mises strain analysis revealed that PMMA and PEEK experienced higher strain, whereas PEKK and FRC demonstrated lower strain distribution. Bayesian ANOVA provided strong evidence for material differences. Conclusion: FRC exhibited superior load-bearing characteristics, reinforcing its potential as a viable clinical alternative to metal-based ISFPs. Full article

As cyanide ion (CN⁻), an ecologically harmful pollutant, has received incessant attention with growing industrialization on a global scale, the capability of on-site monitoring of CN⁻ contamination becomes increasingly crucial. In this work, we have fabricated a simplistic plasmonic-sensing platform for CN⁻, which can be combined with the human naked eye for visual monitoring. The main sensor part consisted of β-Cyclodextrin (β−CD)-decorated gold-rich silver bimetallic alloy nanoparticles (β−CD-Ag/Au-rich alloy NPs), while a sensing analysis was performed by a spectrophotometer or smartphone, where optical data gathered by its camera were analyzed by RGB color sensing. Upon the introduction of various CN⁻ quantities into β−CD-Ag/Au-rich alloy NPs, the spectral peak of the surface plasmon resonance (SPR) shifted from 488 nm to 496 nm. This redshift indicated a strong etching reaction between alloy NPs and CN⁻, demonstrating a ultrahigh detection sensitivity, i.e., a limit of detection (LOD) of 0.24 nM. During the formation of metal-cyano complexes in the CN⁻-induced etching response of β−CD-Ag/Au-rich alloy NPs, we observed a naked-eye discernible color change from brownish-red to colorless, allowing for naked-eye monitoring. The smartphone could also analyze the colorimetric response for such an etching process via RGB color sensing, demonstrating a LOD of 1.35 nM, being still less than the maximum concentration (1.91 nM) in drinking water, which is allowable by the World Health Organization (WHO). The straightforwardness and very high sensitivity of the proposed technique for CN⁻ detection using alloy nanoparticles with a smartphone may hold promise for simplistic, affordable in-field examinations of CN⁻ in water. Full article

Additive manufacturing (AM) is a layerwise production process that creates three-dimensional objects according to a digital model. This technology has demonstrated to be a promising alternative to conventional manufacturing methods for various industrial sectors, such as aerospace, automotive, biomedical, and energy. AM offers several advantages, like design flexibility, material efficiency, functional integration, and rapid prototyping. As regards metal parts, conventional AM techniques using infrared laser sources face some limitations in processing high-reflectivity and high-conductivity materials or alloys, such as aluminum, copper, gold, and silver. These materials have low absorption of infrared radiation, which results in unstable and shallow melt pools, poor surface quality, and high porosity. To overcome these challenges, green and blue laser sources have been proposed for AM processes. This review provides an overview of the recent developments and applications of green and blue laser sources for powder bed fusion of copper and its alloys, focusing on the effects of process parameters on the melt pool dynamics, microstructure formation, and thermal and electrical properties of the fabricated parts. This review also presents the main applications of AM of copper and its alloys together with potential opportunities for future developments. Full article

Developing an efficient recycling route for spent single-use medical devices is essential for recovering precious metals. The proposed complete hydrometallurgical route goes through the initial pyrolysis and acid digestion steps, expanding upon our previous relevant work in the field, followed by solvent extraction, stripping, and precipitation procedures. In this study, a complete hydrometallurgical process was developed for the recovery of gold, platinum, iridium, and tantalum, separating them from other metals, i.e., from iron, chromium, and nickel, also present in the examined medical devices, i.e., (i) diagnostic electrophysiology catheters, containing gold, (ii) diagnostic guide wires, containing platinum and iridium alloys, and (iii) self-expanding stents, containing tantalum. This study reports the experimental results of selecting an efficient extractant, stripping, and precipitation agent, along with the effects of key factors that influence each consecutive step of the process, i.e., agent concentration, aqueous to organic phase ratio, contact time, and pH, using simulated metal solutions and also applying the obtained optimal conditions to the treatment of real sample solutions. For the selective separation of gold, Aliquat 336 was used to extract it in the organic phase; it was then stripped using a thiourea solution and precipitated by utilizing an iron sulfate (II) solution and proper pH adjustment. The selective separation of platinum was achieved by using Aliquat 336 for the organic phase extraction and a perchlorate acid solution for stripping it back into the aqueous solution and adding a sodium bromate solution to precipitate it. Due to the similar chemical behavior, the selective recovery of iridium followed the same processes as that of platinum, and the separation between them was achieved through selective precipitation, as heating the solution and adjusting the pH value resulted in the selective precipitation of iridium. Lastly, the selective recovery of tantalum consists of extraction by using Alamine 336, then stripping it back to the aqueous phase by using sodium chloride, and precipitation by using potassium salt solution and proper pH adjustment. A total recovery of 88% for Au, 86% for Pt, 84% for Ir, and 80% for Ta was obtained, thus achieving a high uptake of precious metals from the examined real spent/waste samples. Full article

Gold compositional studies have been advocated to resolve genetic relationships between alluvial and in situ occurrences based on the assumption that the P-T-X conditions at the sites of mineral deposition are reflected in common compositional signatures of gold. Here, we explore two refinements to a simple ‘same or different’ approach, namely (i) in situ gold sources at different localities may correspond to multiple stages of mineralization and, therefore, different gold grade, and (ii) any duplication of gold signatures between localities requires fluid conduits compatible with the prevailing structural framework. The high-grade gold paragenetic stage at the Cononish Mine, Scotland, is characterized by relatively low Ag alloy associated with Ag-Au and Ag tellurides. This signature is replicated in the inclusion signature of alluvial gold from the adjacent drainage and is also present in two other drainages for which there are no known in situ sources. There is a strong correlation between the spatial extent of this signature and the fault linkage zone, but outside this zone, gold exhibits other compositional signatures. The study shows how structural considerations provide an independent and robust framework to evaluate genetic relationships suggested by compositional studies of alluvial gold in areas where the source location and economic potential are unknown. Full article

Proton Exchange Membrane Fuel Cells (PEMFCs) are promising technology to convert chemical energy from dihydrogen in electrical energy. HT-PEMFCs are working at high temperatures (above 120 °C) and with doped orthophosphoric acid H₃PO₄ PBI membranes. In such devices, bipolar metallic plates are used to provide reactive gas inside the fuel cell and collect the electrical current. The metallic elements used as bipolar plates, end plates, and interconnectors in acid electrolyte and gaseous fuel cells are severely damaged by a combination of oxidation (due in particular to the use of oxygen, whether pure or contained in the air) and corrosion (due in particular to acid effluents from the electrolyte). This degradation rapidly leads to the loss of the electrical conductivity of the metallic elements and today requires the use of very specific alloys, possibly coated with pure gold. The solution investigated in the present study is the use of a protective coating based on single-phase nitrides obtained by reactive magnetron sputtering or reactive HiPIMS (High-Power Impulse Magnetron Sputtering). The influence of the microstructure on the physical–chemical properties was studied. The electrochemical properties were quantified following two approaches. First, the corrosion current of the developed coatings was measured at room temperature and at higher temperatures using the Linear Sweep Voltammetry (LSV) technique. Then, Electrochemical Impedance Spectroscopy (EIS) measurements were performed to better identify and evaluate their corrosion-resistance performances. 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

In recent years, additive manufacturing (AM) has played a significant role in various fashion industries, especially the textile and jewelry manufacturing sectors. This review article delves deeply into the wide range of methods and materials used to make intricately designed jewelry fabrication using the additive manufacturing (AM) process. The Laser Powder Bed Fusion (L-PBF) process is examined for its suitability in achieving complex design and structural integrity in jewelry fabrication even with respect to powder metallurgy methods. Moreover, the review explores the use of precious materials, such as gold, silver, copper, platinum, and their alloys in additive manufacturing. Processing precious materials is challenging due to their high reflectivity and thermal conductivity, which results in poor densification and mechanical properties. To address this issue, the review article proposes three different strategies: (i) adding alloying elements, (ii) coating powder particles, and (iii) using low-wavelength lasers (green or blue). Finally, this review examines crucial post-processing techniques to improve surface quality, robustness, and attractiveness. To conclude, this review emphasizes the potential of combining additive manufacturing (AM) with traditional craftsmanship for creating jewelry, exploring the potential future directions and developments in the field of additive manufacturing (AM) for jewelry fabrication. Full article

Metallic nanoparticles have gained attention in technological fields, particularly photonics. The creation of silver/gold (Ag/Au) alloy NPs upon laser exposure of an assembly of these NPs was described. First, using the Nd: YAG pulsed laser ablation’s second harmonic at the same average power and exposure time, Ag and Au NPs in distilled water were created individually. Next, the assembly of Ag and Au NP colloids was exposed again to the pulsed laser, and the effects were examined at different average powers and exposure times. Furthermore, Ag/Au alloy nanoparticles were synthesized with by raising the average power and exposure time. The absorption spectrum, average size, and shape of alloy NPs were obtained by using an ultraviolet-visible (UV–Vis) spectrophotometer and transmission electron microscope instrument. Ag/Au alloy NPs have been obtained in the limit of quantum dots (<10 nm). The optical band gap energies of the Ag/Au alloy colloidal solutions were assessed for different Ag/Au alloy NP concentrations and NP sizes as a function of the exposure time and average power. The experimental data showed a trend toward an increasing bandgap with decreasing nanoparticle size. The nonlinear optical characteristics of Ag/Au NPs were evaluated and measured by the Z-scan technique using high repetition rate (80 MHz), femtosecond (100 fs), and near-infrared (NIR) (750–850 nm) laser pulses. In open aperture (OA) Z-scan measurements, Ag, Au, and Ag/AuNPs present reverse saturation absorption (RSA) behavior, indicating a positive nonlinear absorption (NLA) coefficient. In the close-aperture (CA) measurements, the nonlinear refractive (NLR) indices (n₂) of the Ag, Au, and Ag/Au NP samples were ascribed to the self-defocusing effect, indicating an effective negative nonlinearity for the nanoparticles. The NLA and NLR characteristics of the Ag/Au NPs colloids were found to be influenced by the incident power and excitation wavelength. The optical limiting (OL) effects of the Ag/Au alloy solution at various excitation wavelengths were studied. The OL effect of alloy NPs is greater than that of monometallic NPs. The Ag/Au bimetallic nanoparticles were found to be more suitable for optical-limiting applications. Full article

Huge amounts of Au and Ag are recovered from the hazardous waste lead anode slime. The conventional extraction of precious metals from lead anode slime is based on pyrometallurgical and electrolytic processes, which are seriously conditioned by the separation of harmful elements As and Sb. In this paper, an innovative and efficient oxidation–vacuum volatilization–carbon reduction process was proposed to separate and enrich Ag and Au from lead anode slime. Before vacuum volatilization, selective oxidation of the lead anode slime was performed. Then, vacuum volatilization and vacuum carbon reduction were used to obtain a gold- and silver-rich alloy. The feasibility of the process was verified experimentally and theoretically. The effects of temperature and time on vacuum volatilization separation and reduction enrichment were investigated. The experimental results showed that the Ag content in the resulting gold- and silver-rich alloy was as high as 67.58%, Au was as high as 4287 g/t, and the efficiencies for the recovery of Ag and Au from the lead anode slime were 99.25% and 99.91%, respectively. The gold- and silver-rich alloy can be directly used to produce Ag ingots. Moreover, no gas or wastewater was discharged in this process, so Ag and Au were recovered in a sustainable and cleaner manner. Full article

The aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) plays a pivotal role in the synthesis of renewable, biodegradable plastics and sustainable chemicals. Although supported gold nanoclusters (NCs) exhibit significant potential in this process, they often suffer from low selectivity. To address this challenge, a series of gold-M (M means Ni, Fe, Cu, and Pd) bimetallic NCs catalysts were designed and synthesized to facilitate the selective oxidation of HMF to FDCA. Our findings indicate that the introduction of doped metals, particularly Ni and Pd, not only improves the reaction rates for HMF tandem oxidation but also promotes high yields of FDCA. Various characterizations techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (CO-DRIFTS), and temperature-programmed desorption of oxygen (O₂-TPD), were employed to scrutinize the structural and electronic properties of the prepared catalysts. Notably, an electronic effect was observed across the Au-based bimetallic catalysts, facilitating the activation of reactant molecules and enhancing the catalytic performance. This study provides valuable insights into the alloy effects, aiding in the development of highly efficient Au-based bimetallic catalysts for biomass conversions. Full article

Small-size gold nanoparticles (AuNPs) are showing large potential in various fields, such as photothermal conversion, sensing, and medicine. However, current synthesis methods generally yield lower, resulting in a high cost. Here, we report a novel uni-micelle method for the controlled synthesis of monodisperse gold nanocrystals, in which there is only one kind micelle containing aqueous solution of reductant while the dual soluble Au (III) precursor is dissolved in oil phase. Our synthesis includes the reversible phase transfer of Au (III) and “uni-micelle” synthesis, employing a Au (III)-OA complex as an oil-soluble precursor. Size-controlled monodisperse AuNPs with a size of 4–11 nm are synthesized by tuning the size of the micelles, in which oleylamine (OA) is adsorbed on the shell of micelles and enhances the rigidity of the micelles, depressing micellar coalescence. Monodisperse AuNPs can be obtained through a one-time separation process with a higher yield of 61%. This method also offers a promising way for the controlled synthesis of small-size alloy nanoparticles and semiconductor heterojunction quantum dots. Full article