Search Results (53)

Solid oxide fuel cells (SOFCs) have been considered as alternative energy conversion devices because of their high energy conversion efficiency, fuel flexibility, and cost efficiency without precious metal catalysts. In current SOFCs, the cermet anode consists of nickel and ion-conducting ceramic materials, and solid oxide electrolytes and ceramic cathodes have been used. SOFCs normally operate at high temperatures because of the lower ion conductivity of ceramic components at low temperatures, and they have weaknesses in terms of mechanical strength and durability against thermal shock originating from the properties of ceramic materials. To solve these problems, metal-supported solid oxide fuel cells (MS-SOFCs) have been designed. SOFCs using metal substrates, such as Ni-based and Cr-based alloys, provide significant advantages, such as a low material cost, ruggedness, and tolerance to rapid thermal cycling. In this article, SOFCs are introduced briefly, and the types of metal substrate used in MS-SOFCs, as well as the advantages and disadvantages of each metal support, are reviewed. 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

Numerous mineral microinclusions discovered in the Triassic Ildeus mafic–ultramafic intrusion are dominated by base metal sulfides, gold, silver, and their alloys, as well as rare earth element (REE) minerals. These mineral microinclusions were formed through both the magmatic differentiation of the Ildeus intrusion and the multi-stage interaction of intrusive rocks with late-magmatic, post-magmatic and post-collisional fluids. A comparison of the results of our microinclusions study with ore mineralization discovered within the Ildeus intrusion suggests that microinclusion assemblages in igneous rocks are, in some cases, precursors of potentially economic mineralization. In the case of the Ildeus rocks, sulfide microinclusions correspond to potentially economic disseminated nickel–cobalt sulfide ores, while microinclusions of gold and its alloys correlate with intrusion-hosted, erratic gold mineralization. The occurrence of silver and rare earth element minerals in Ildeus plutonic rocks indicates the possible presence of silver and REE mineralization, which is supported by sub-economic whole-rock silver and REE grades in parts of the Ildeus intrusion. The results of our investigation suggest that studies of mineral microinclusions in magmatic rocks may be useful in the evaluation of their metallogenic specialization and ore-forming potential and could possibly be utilized as an additional prospecting tool in the regional exploration for precious, base, and rare metals. Full article

Developing cost-effective and high-performance non-precious metal-based electrocatalysts for hydrogen evolution reaction is of crucial importance toward sustainable hydrogen energy systems. Herein, we prepare a novel hybrid electrode featuring intermetallic Fe₂Mo nanoparticles anchored on the hierarchical nanoporous copper skeleton as robust hydrogen evolution electrocatalyst by simple and scalable alloying and dealloying methods. By virtue of the highly active intermetallic Fe₂Mo nanoparticles and unique bicontinuous nanoporous copper skeleton facilitating ion/molecule transportation, nanoporous Fe₂Mo/Cu electrode shows excellent hydrogen evolution reaction electrocatalysis, with a low Tafel slope (~71 mV dec⁻¹) to realize ampere-level current density of 1 A cm⁻² at a low overpotential of ~200 mV in 1 M KOH electrolyte. Furthermore, nanoporous Fe₂Mo/Cu electrode exhibits long−term stability exceeding 400 h to maintain ~250 mA cm⁻² at an overpotential of 150 mV. Such outstanding electrocatalytic performance enables the nanoporous Fe₂Mo/Cu electrode to be an attractive hydrogen evolution reaction catalyst for water splitting in the hydrogen economy. Full article

Metal alloys continue to be, and are expected to remain, essential materials for fabricating prosthetic elements due to their unique properties, particularly their high strength, durability, and appropriate modulus of elasticity, which make them well-suited for such applications. However, commonly used non-precious metal alloys exhibit lower corrosion resistance compared to precious metal alloys. This reduced resistance leads to the release of metal ions from the alloy into the oral environment. Adverse biological responses to metal alloys can be mitigated through various surface modifications, most commonly by applying coatings. These coatings are typically ceramic, including oxides, nitrides, and carbides. In this study, the mechanical properties (hardness, modulus of elasticity, adhesion, and thickness) of complex Si(C,N) coatings applied to a prosthetic Ni-Cr alloy were investigated. Depending on the proportions of N, C, and Si in the coating, the hardness ranged from 12 to 15 GPa, while the modulus of elasticity varied between 130 and 170 GPa. Adhesion strength, measured via the scratch test method, was within an acceptable range. Microscopic analysis revealed that the coatings had a thickness of 2 to 2.5 μm, exhibiting a homogeneous, columnar structure. In conclusion, the properties of the fabricated Si(C,N) coatings are deemed satisfactory for their intended use as protective layers for prosthetic and orthodontic components. Full article

High entropy alloys (HEAs) have been widely studied due to their special crystal structure, but their bulk structure and low specific surface area limit their further application in broader fields. In this work, the dealloying of precious metal Cu₃₅Pd₃₅Ni₂₅Ag₅ quasi-HEAs is performed. Porous noble metals with micro prism array structure and porous noble metal PdO/Ag₂O/NiO oxides with nano “ligament/pore” structure are obtained by constant potential dealloying and free dealloying, respectively. In this way, the porosification of quasi-HEAs and noble metal oxides is achieved. Moreover, the effects of dealloying parameters on pore morphology and phase structure of dealloyed materials are studied, and the evolution mechanisms of pore structures of different dealloying products are discussed. The work provides strategies for the preparation of porous precious metal quasi-HEAs and porous noble metal oxides by the dealloying method. These products present great potential for application as functional materials in hot fields such as catalysis and energy storage. Full article

The hydrogen economy, as an emerging paradigm for sustainable energy, relies on efficient hydrogen oxidation (HOR) and hydrogen evolution reactions (HER). These reactions require effective catalysts to enhance reaction kinetics and reduce costs. Platinum (Pt) is widely used but faces issues such as high cost and CO poisoning. Non-precious metal catalysts, particularly Ni-based alloys, are being explored as viable alternatives. This study introduces a ternary MoWNi alloy catalyst synthesized via microwave-assisted methods and annealing. The MoWNi alloy catalyst achieves a current density of 3.5 mA·cm⁻² at an overpotential of 100 mV in HOR and requires only 25 mV overpotential to reach a current density of 10 mA·cm⁻² in HER, making it comparable to commercial 20% Pt/C catalysts. Notably, the catalyst also exhibits superior stability and resistance to CO toxicity. These findings underscore the potential of MoWNi alloy catalysts in advancing hydrogen-based energy systems. Full article

Superelastic metastable β-Ti-Nb alloys are attractive low-modulus materials for use in biomedical implants. The antibacterial properties of silver and its ability to lower the modulus of Ti-Nb-based transforming alloys make it an appealing ternary addition, but the Ti-Nb-Ag system is poorly characterised at present. This study elucidates the microstructure, equilibrium phases, and mechanical behaviour of a systematic series of Ti–24Nb–XAg (X = 0, 2, 6) (at.%) alloys. The mutual solubility of Nb and Ag in Ti overcame the immiscibility of Nb and Ag and produced an alloy with a single-phase β microstructure for low Ag concentrations. However, at silver concentrations above approximately 5 at.%, the solubility limit was reached and precipitates began to form. These precipitates were found to form quickly during recrystallisation, refining the grain size by Zener pinning, and persisted even after a 500 h heat treatment at 1100 °C. All three alloys showed non-linear-elastic behaviour typical of transforming alloys. The addition of up to 2 at.% Ag to Ti–24Nb was found to decrease the elastic modulus, suppress formation of the ω phase, and cause the critical transformation stress to decrease, though the transformation stress increased above that of Ti–24Nb when 6 at.% Ag is added. These results indicate that Ti-Nb-Ag alloys are a promising candidate for developing new low-modulus implants. Full article

It is a great challenge to prepare efficient and stable electrocatalysts for hydrogen evolution (HER) using non-precious metals. In this study, a series of PtCo/Ti₃C₂T_x-Y (Y: 16, 32, and 320, Y indicates the quality of Co(NO₃)₂) catalysts were synthesized by loading PtCo alloy on Ti₃C₂T_x. The PtCo/Ti₃C₂T_x-32 catalyst showed the best HER performance, reaching a current density of 10 mA cm⁻² with low overpotential (36 and 101 mV) and small Tafel slopes (66.37 and 105.17 mV dec⁻¹) in 0.5 mol L⁻¹ H₂SO₄ and 1 mol L⁻¹ KOH solution. The excellent HER activity of PtCo/Ti₃C₂T_x-32 can be attributed as follows: Ti₃C₂T_x has a unique two-dimensional structure, which can provide a large number of attachment sites for the PtCo alloy, hence exposing more active sites; on the other hand, it can also provide a fast and efficient conductive network for electron transport during electrocatalytic processes, thus enhancing the connectivity between electrolyte and catalyst. PtCo alloy makes the PtCo/Ti₃C₂T_x catalyst more hydrophilic, accelerating the release rate of bubbles. The DFT calculation results showed that the energy barrier of HER is reduced because the charge around Pt is redistributed by Co after alloying Pt and Co, so that the PtCo/Ti₃C₂T_x catalyst has a suitable ΔG_H* value. This study can be expected to provide some references for the design and synthesis of Ti₃C₂T_x-supported alloy electrocatalysts with high activity and stability for HER. Full article

A silver-rich lead alloy was obtained through the recycling of two metallurgical wastes: these are lead paste obtained from spent lead–acid batteries and a jarosite residue obtained from the hydrometallurgical production of zinc. Mixtures of both wastes were pyrometallurgically treated with sodium carbonate in a silicon carbide crucible at 1200 °C. The alloy and slag produced were analyzed by atomic absorption spectrometry, X-ray diffraction, and scanning electron microscopy with energy-dispersive spectra. High silver recovery was obtained in a Pb-Ag alloy for a mixture ratio of 30% Na₂CO₃–40% lead paste–30% jarosite, reaching a silver grade of 126 ppm. The slags produced for the highest jarosite content allow the compound formation of Na₂(SO₄) and Na₂Fe(SO₄)₂, which have high sulfur-fixing, avoiding SO₂ release and contributing to the minimization of atmospheric pollution. The novel pyrometallurgical route addresses not only the valorization of precious metals such as silver and lead but also the reduction in accumulated industrial waste. 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

Ammonia is known as an alternative hydrogen supplier because of its high hydrogen content and convenient storage and transport. Hydrogen production from ammonia decomposition also provides a source of hydrogen for fuel cells. While catalysts composed of ruthenium metal atop various support materials have proven to be effective for ammonia decomposition, non-precious-metal-based catalysts are attracting more attention due to desires to reduce costs. We prepared a series of Fe, Co, Ni, Mn, and Cu monometallic catalysts and their alloys as catalysts over proton-conducting ceramics via the impregnation method as precious-metal-free ammonia decomposition catalysts. While Co and Ni showed superior performance compared to Fe, Mn, and Cu on a BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−б (BZCYYb) support as an ammonia decomposition catalyst, the cost of Fe is much lower than that of other metals. Alloying Fe with Co can significantly increase the conversion and stability and lower the overall cost of materials. The measured ammonia decomposition rate of FeCo/BZCYYb reached 100% at 600 °C, and the ammonia decomposition rate was almost unchanged during the long-term test of 200 h, which reveals its good catalytic activity for ammonia decomposition and thermal stability. When the metallic catalyst remained unchanged, BZCYYb also exhibited better performance compared to other commonly used oxide supports. Finally, when ammonia cracked using our alloy catalyst was fed to solid oxide fuel cells (SOFCs), the peak power densities were very close to that achieved with a simulated fully cracked gas stream, i.e., 75% H₂ + 25% N₂, thus proving the effectiveness of this new type of ammonia decomposition catalyst. Full article

Traditionally, precious metals are processed by either lost-wax casting or the casting of semi-finished products followed by cold or hot working, machining, and surface finishing. Long process chains usually conclude in a high material input factor and a significant amount of new scrap to be refined. The maturing of Additive Manufacturing (AM) technologies is advantageous with regard to resources among other criteria by opening up new processing techniques like laser-based powder bed fusion (LPBF) for the production of near net shape metal products. This paper gives an insight into major advantages of the powder-based manufacturing of precious metal components over conventional methods focusing on product carbon footprints (PCF). Material Flow Cost Accounting (MFCA) for selected applications show energy and mass flows and inefficient recoverable losses in detail. An extended MFCA approach also shows the greenhouse gas (GHG) savings from avoiding recoverable material losses and provides PCF for the products. The PCF of the precious metals used is based on a detailed Life Cycle Assessment (LCA) of the refining process of end-of-use precious metals. In the best case, the refining of platinum from end-of-life recycling, for example, causes 60 kg CO_2e per kg of platinum. This study reveals recommended actions for improvements in efficiency and gives guidance for a more sustainable production of luxury or technical goods made from precious metals. This exemplary study on the basis of an industrial application shows that the use of AM leads to a carbon footprint of 2.23 kg CO_2e per piece in comparison with 3.17 kg CO_2e by conventional manufacturing, which means about a 30 percent reduction in GHG emissions and also in energy, respectively. Full article

A high-noble Au–Pt–Ge porcelain-fused-to-metal (PFM) dental alloy without the known adverse metallic elements and with the addition of germanium (Ge) was produced as a more cost-effective alternative to other precious alloying metals, with investigations for determining the functionality and clinical use of this alloy. The thermomechanical, biocompatibility, durability, workability and economic characteristics of the produced dental alloy were investigated. These properties were investigated with in vitro biocompatibility testing on human gingival fibroblasts (HGFs); static immersion testing for metal ion release; DSC analysis; hardness, tensile testing, density and coefficient of thermal expansion (CTE) measurements; metallographic and SEM/EDX microstructure investigations; and finally with the production of a test PFM dental bridge. The results of the thermomechanical testing showed alloy properties suitable for dental restorations and clinical use, with somewhat lower mechanical properties, making the alloy not suitable for extensive multiunit fixed restorations. The microstructure investigations showed segregations of Ge in the homogeneous alloy matrix, which reduce the alloy’s mechanical properties. The produced PFM dental bridge showed excellent workability of the alloy in a dental laboratory setting, as well as a high standard of the final dental restoration. The ion release was negligible, well below any harmful quantities, while the cell viability examination showed significantly higher viability ratings on polished alloy samples as compared to as-cast samples. The results showed that a dental substructure in direct contact with oral tissue and fluids should be highly polished. The performed investigations showed that the produced PFM dental alloy is suitable for clinical use in producing high-quality dental restorations with high biocompatibility for patients prone to metal allergies. 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