Search Results (46)

With the opening of complex service routes, the importance of the service performance of brake pads under long slope braking conditions is increasing. It is necessary to analyze the slope braking adaptability of current brake pad products. This work takes the copper-based powder metallurgy brake pads of a certain in-service high-speed train as the research object and conducts friction and wear behavior tests of the brake pads based on a full-scale brake test bench. Through microscopic observation and damage analysis, the differences in friction and wear behavior of the brake pads under stop braking and slope braking conditions are compared, revealing the wear mechanism and damage evolution characteristics of the brake pads. The results show that under the impact of high speed, high braking force, and severe thermal load in the stop braking conditions, the uneven wear of brake pads is high, and the eccentric wear of friction blocks is affected by both the friction radius and friction direction. The friction surface has a large number and size of damages, and the stability of the friction interface is poor. The brake pad exhibits a composite wear mechanism dominated by abrasive wear and brittle fracture induced exfoliation. In the slope braking condition, under the action of low speed, low braking force, and long-term stable thermal load, the uneven wear of the brake pads is relatively low, the surface damage size is small, and the friction block only has eccentric wear along the friction direction. The brake pad mainly initiates cracks along the interface of the components, which propagate parallel to the friction surface, exhibiting a progressive delamination and flaking exfoliation mechanism with a low wear rate. Although the friction interface of the brake pad is relatively stable under slope braking conditions, the cumulative delamination wear of the brake pads under long-term braking action needs further attention. Full article

The expansion of copper mining operations has led to the accumulation of a large amount of phyllite waste rock. Re-purposing this material into manufactured sand presents a promising solution for its large-scale consumption. In this study, phyllite waste rock from the Dexing Copper Mine was used as raw materials to prepare manufactured sand. A precise mineralogical analysis was conducted using Tescan Integrated Mineral Analyzer (TIMA) to determine the mineral composition, intergeneration and distribution relationships, particle size and shape, and elemental distribution. The performance of the resulting manufactured sand was comprehensively evaluated. Key findings showed a needle and flake particle content of 5.2%, a methylene blue (MB) value of 1.3, and a stone powder content of 9%. The physical properties, including solidity, crushing index, density, and porosity, as well as mica content, complied with the national standard GB14684-2022 (Sand for Construction). Additionally, phyllite-sand concrete exhibited a third-month expansion rate below the standard limit of 0.1%, indicating no potential risk for alkali-silica reaction. The radioactive index of the material met the standard requirements, posing no radiation hazard. However, the excessive sulfur compounds in phyllite present a risk of corrosion of the concrete structures, necessitating mitigation measures. Full article

Residual-free eutectic Au80Sn20 soldering is still the dominant assembly technology for optoelectronic devices such as high-power lasers, LEDs, and photodiodes. Due to the high cost of gold, alternatives are desirable. This paper investigates the thermal performance of copper-based sintering for optoelectronic submodules on first and second level to obtain thermally efficient thin bondlines. Sintered interconnects obtained by a new particle-free copper ink, based on complexed copper salt, are compared with copper flake and silver nanoparticle sintered interconnects and benchmarked against AuSn solder interconnects. The copper ink is dispensed and predried at 130 °C to facilitate in situ generation of Cu nanoparticles by thermal decomposition of the metal salt before sintering. Submounts are then sintered at 275 °C for 15 min under nitrogen with 30 MPa pressure, forming uniform 2–5 µm copper layers achieving shear strengths above 31 MPa. Unpackaged LEDs are bonded on first level using the copper ink but applying only 10 MPa to avoid damaging the semiconductor dies. Thermal performance is evaluated via transient thermal analysis. Results show that copper ink interfaces approach the performance of thin AuSn joints and match silver interconnects at second level. However, at first level, AuSn and sintered interconnects of commercial silver and copper pastes remained superior due to the relative inhomogeneous thickness of the thin Cu copper layer after predrying, requiring higher bonding pressure to equalize surface inhomogeneities. Full article

The use of copper and its alloys in architecture, especially in arid regions, is growing, driven by visual appeal, functional advantages, and sustainability. Changes in visual and colorimetric appearances and patina formation were evaluated for architectural Cu metal, brass (CuZn15), bronze (CuSn4), and a golden alloy (CuZn5Al5). Coupons were exposed over 4 years in Dubai, United Arab Emirates, at a test site located 2 km from the seashore under unsheltered conditions, and at various surface inclinations. Comparative exposures were conducted in Brest, France, at sites of increasing distance from the seashore. Visual appearance was assessed by colorimetry and optical imaging; patina cross-sections were characterized by means of scanning electron microscopy and elemental analysis (SEM/EDS), and crystalline phase identification was conducted by means of x-ray diffraction (XRD). All Dubai surfaces developed red-yellowish, heterogeneous patinas with embedded sand and dust, reducing lightness and visual appeal. Inclination had minor effect, although some extent of spallation occurred on downward-facing CuSn4. Even the corrosion-resistant CuZn5Al5 alloy lost its golden hue due to the incorporation of sand and dust into the patina. In Brest, appearance depended on the distance from the seashore, with green-blue patinas near the sea and red-yellowish farther inland, similar to Dubai. Cleaning may restore some luster, but the desert exposure generally reduced the long-term aesthetic performance of all materials. Full article

Thin films of manganese–nickel–cobalt oxide with graphene (G@MNCO) were deposited on copper foam using electrochemical deposition. NiCo₂O₄ is the main phase in these films. As the proportion of graphene in the precursor solution increases, the oxygen vacancies in the samples also increase. The microstructure of these samples evolves into hierarchical vertical flake structures. Cyclic voltammetry measurements conducted within the potential range of 0–1.2 V reveal that the electrode with the highest graphene content achieves the highest specific capacitance, approximately 475 F/g. Furthermore, it exhibits excellent cycling durability, maintaining 95.0% of its initial capacitance after 10,000 cycles. The superior electrochemical performance of the graphene-enhanced, manganese-doped nickel–cobalt oxide electrode is attributed to the synergistic contributions of the hierarchical G@MNCO structure, the three-dimensional Cu foam current collector, and the binder-free fabrication process. These features promote quicker electrolyte ion diffusion into the electrode material and ensure robust adhesion of the active materials to the current collector. Full article

Copper (II) oxide nanoparticles (CuO NPs) attract much attention as a promising antimicrobial agent. We studied the antibacterial properties of three types of CuO NPs against Escherichia coli bacteria: flake-shaped particles with a diameter of 50–200 nm and a thickness of 10–20 nm (CuO-CD synthesized by chemical deposition), spherical particles with a size of 20–90 nm (CuO-EE obtained by electrical explosion), and rod-shaped particles with a length of 100–200 nm and a diameter of 30 × 70 nm (CuO-CS commercial sample). We tested how the shape, size, and concentration of the NPs, and composition of the dispersion medium affected the properties of the CuO NPs. We prepared dispersions based on distilled water, a 0.9% NaCl solution, and the LB broth by Lennox and used Triton X-100 and sodium dodecyl sulfate (SDS) as stabilizers. The concentration of NPs was 1–100 mg L⁻¹. We showed that the dispersion medium composition and stabilizer type had the greatest influence on the antibacterial effects of CuO NPs. We observed the maximum antibacterial effect for all CuO NP types dispersed in water without a stabilizer, as well as in LB broth with the SDS stabilizer. The maximum inhibition of culture growth was observed under the influence of CuO-EE (by 30%) and in the LB broth with the SDS stabilizer (by 1.3–1.8 times depending on the type of particles). In the saline solution, the antibacterial effects were minimal; in some cases, the CuO NPs even promoted bacterial culture growth. SDS increased the antibacterial effects of NPs in broth and saline but decreased them in water. Finally, among the particle types, CuO-CS turned out to be the most bactericidal, which is probably due to their rod-shaped morphology and small diameter. At the same time, the concentration and aggregation effects of CuO NPs in the colloidal systems we studied did not have a linear action on their antibacterial properties. These results can be used in the development of antibacterial coatings and preparations based on CuO NPs to achieve their maximum efficiency, taking into account the expected conditions of their use. Full article

Radar sensors are critical for obstacle detection and navigation, especially for automated driving. Using the use-case “printing of heating coils on the inside of the front housing (primary radome)” needed for de-icing in winter, it is demonstrated that additive manufacturing (AM) can provide economic and functional benefits for manufacturing of the sensors. AM will allow significant cost reduction by eliminating parts and simplifying the manufacturing process. Different AM technologies for the coils were investigated, first, by applying the conductive traces by fused deposition modeling (FDM), and, second, by printing copper particle-free inks and pastes. The metal layers were electrically and mechanically characterized using a profilometer to measure the trace dimension and a four-point probe to measure the resistance. It was revealed that low-cost conductive filaments with low resistivity and current carrying capacity are commercially still not available. The best option sourced was a copper–polyester-based filament with 6000 µΩcm after printing. Therefore, low-cost particle-free copper inks and commercial copper flake paste were selected to print the heating coil. The Cu particle-free inks were amine-based Cu (II) formate complexes, where the Cu exists in an ionic form. Using contactless printing processes such as ink-jet printing or pneumatic dispensing, the traces could be deposited onto the low-melting temperature (225 °C) polymeric radome structure. After printing, the material needed to be sintered to form the conductive copper traces. To avoid damaging the polymer radome during sintering, two different processes were investigated: low-temperature (<150 °C) sintering in an oven for 30 min or fast laser sintering. The sintered Cu layers achieved the following specific electric resistivities when slowly sintered in the oven: paste 4 µΩcm and ink 8.8 µΩcm. Using laser sintering, the ink achieved 3.2 µΩcm because the locally high temperature provides better sintering. Also, the adhesion was significantly increased to (5 B). Therefore, laser sintering is the preferred technology. In addition, it allows fast processing directly after printing. Commercial equipment is available where printing and laser sintering is integrated. The potential of low-cost copper material and the integration in additive manufacturing of electronic systems using radar sensors as an example are demonstrated in this paper. Full article

Adsorption chillers are distinguished by their low electricity consumption, lack of moving parts and exceptional reliability. However, their considerable weight, due to the low sorption capacity of conventional adsorbents, remains a key limitation. This study investigates the effect of introducing thermally conductive additives—aluminium powder, copper powder and graphite flakes—at 5, 15 and 25 wt.% to silica-gel-based adsorbent beds on the enhancement of heat transfer. In contrast to other works, this study also includes a novel analysis of the thermal properties of dry sorbents, since the moisture content affects the thermal conductivity. Additives improve the thermal conductivity, as measured by the laser flash method (LFA), of the bed by up to 20.7% while maintaining a reasonable sorption capacity, as measured by the dynamic vapor sorption (DVS). Additions of copper at 5–15 wt.% and graphite flakes at 15–25 wt.% provide an optimal compromise between thermal conductivity and sorption capacity. Aluminium powder, on the other hand, offers flexibility over a wider range (5–25 wt.%). The increased thermal conductivity of these modified materials is expected to lead to more efficient heat transport, which suggests the hypothesis that it could reduce the cycle time and increase the efficiency of adsorption chillers. Full article

Photovoltaic–thermal (PVT) applications have been widely studied in recent years, though commercialisation has become critical due to their operational characteristics and size. In this study, a portable PVT system was developed for mobilisation with assistance from an organic phase-change material (PCM). Two different PCM composites were developed using the PCM with charcoal (PCM + C) and charcoal and metal flakes (PCM + C + M). Considering the portability of the PVT system, conventional metal-container-based PCM storage units were avoided, and the shape-stabilised PCMs (SS-PCMs) were fitted directly on the back surface of the PV module. Further, a serpentine copper tube was placed on the SS-PCMs to extract heat energy for hot water applications. It was found that PV_PCM+C+M exhibited a higher cooling rate, with peak reductions of 24.82 °C and 4.19 °C compared to the PV_noPCM and PV_PCM+C, respectively. However, PV_PCM+C exhibited a higher outlet water temperature difference of 11.62 °C. Secondly, an increase of more than 0.2 litres per minute showed a declining trend in cooling in the PV module. Considering the primary concern of electrical power generation, it was concluded that PV_PCM+C+M is suitable for PVT mobilisation applications, owing to it having shown the highest thermal cooling per 190 g of PCM and a 1-Watt (TCPW) cooling effect of 2.482 °C. In comparison, PV_PCM+C achieved a TCPW cooling effect of 1.399 °C. Full article

Recent advancements in nanotechnology have improved the application of copper oxide (CuO) nanostructures, known for their diverse antibacterial, electrical, catalytic, optical, and pharmacological properties, which depend on nanoparticle morphology. This study investigated two synthesis methods for structured CuO: microwave-assisted hydrolysis and ultrasound using copper acetate and KOH, and an eco-friendly method involving cholesterol-free egg white albumin and Solanum lycopersicum extract. Characterization techniques, including XRD, FTIR, and SEM-EDS, were utilized to analyze the produced CuO. XRD confirmed high-purity monoclinic CuO structures in the sample obtained via the chemical method, while characteristic peaks of tenorite and dolerophanite were observed in the albumin-synthesized sample. ATR-FTIR analysis revealed O-H stretching bands around 3400 cm⁻¹, indicating adsorbed H-OH or -OH and strong Cu-O bond peaks at 434 cm⁻¹. The CuO synthesized via microwave and ultrasound methods displayed superior crystallinity compared to commercial CuO. SEM illustrated various morphologies, such as flakes, microspheres, and irregular polyhedra, influenced by the presence of proteins and organic acids. Antibacterial tests demonstrated the effective inhibition of Escherichia coli and Enterococcus faecalis, confirming the potential of CuO as a promising antibacterial agent. Overall, the findings highlight the effectiveness of green chemistry in developing crystalline CuO for various applications. Full article

In this paper, two kinds of copper-containing steels with copper contents of 2.31 and 6.01 wt.% were designed. By comparing with commercial Q355, the bactericidal properties of copper in seawater containing sulfate-reducing bacteria (SRB) and its influence on the corrosion process of steel were revealed. The corrosion rate, morphology of products, and bactericidal action of copper were tracked by scanning electron microscopy, X-ray diffraction, confocal microscopy, and electrochemical analysis techniques. It was found that the resistance of copper-containing steel to bacterial corrosion was obviously better than that of non-copper-containing steel. At 28 days, the weight loss rates in the SRB environment for 0Ni2Cu6 samples increased by merely 5.43%, which was nearly half that of Q355 of 9.75%. Cu-containing steels exhibited potent antibacterial action, with the ε-Cu phase altering the corrosion byproduct composition from brittle flakes to robust particles and inhibiting the production of H₂S. The killed bacteria adhered to the surface of the steel and slowed down the corrosion of the steel. The confocal laser scanning microscope and electrochemical experiments showed that a dense CuFeO₄ film formed on the substrate, impeding corrosive ion penetration, and an upsurge in Cu content markedly enhanced the material’s anti-corrosion and antimicrobial attributes. Full article

The Ti₃SiC₂TiSi_x ceramic composite was synthesized in situ from a mixture of 3Ti:1.5Si:1.2C powders under pressures ranging from 2 to 5 GPa and temperatures of 1150 °C to 1400 °C. At medium and high temperatures (4–5 GPa and 1400 °C), Ti₃SiC₂ dissolves into the cubic TiC phase. SEM analysis revealed that the high-pressure-produced multilayer structure of Ti₃SiC₂ remained intact. The friction properties of Ti₃SiC₂-TiSi_x composites combined with copper and aluminum were studied under both dry and lubricated conditions. After the break-in period, the Ti₃SiC₂-TiSi_x/Al combination exhibited the lowest friction coefficient: approximately 0.2. In dry-sliding conditions, the friction coefficient varies between 0.5 and 0.8. The wear mechanisms for Ti₃SiC₂-TiSi_x composites paired with aluminum primarily involve pear groove wear and adhesive wear during dry friction. Irregularly shaped aluminum balls accumulate in the pear grooves and adhere to each other. With increasing sintering pressure, the average friction coefficient of Ti₃SiC₂-TiSi_x composites against Cu ball pairs first increases and then decreases. The wear rate of the samples did not vary significantly as the sintering pressure increased, whereas the wear rate of Cu balls decreased with increasing sintering pressure. The adhesive wear of the Ti₃SiC₂-TiSi_x composite with its Cu counterpart is stronger than that of the Al counterpart. Abrasive chips of Cu balls appeared in flake form and adhered to the contact interface. Full article

In this study, ultrasound treatment was used to exfoliate commercially available graphite flakes into reduced graphene oxide (rGO) dispersed in ethanol. After centrifugation, solid copper chloride trihydrate was added, resulting in a green liquor containing Cu(II), Cu(I), and rGO. These liquors exhibited good and rapid photocatalytic activity in the degradation of eosin and bromophenol blue dyes (elimination in a few seconds) under visible-light irradiation. UV–visible spectroscopy confirmed the presence of rGO and Cu species. The size and morphology of the rGO sheets were investigated by several methods (SAXS, wide-angle XRD, SEM, and TEM). Negative UV peaks indicated light emission, which was independently verified by fluorescence. Intense plasmon peaks, with absorbances greater than 10, were observed after adding copper chloride salt. These plasmons were eliminated by a high dilution before the described catalytic tests were performed. Full article

The physical properties as well as thermal and electrical stability of copper particles can be improved by surface protection, which mainly depends on the coating material. Our study was, therefore, focused on the rheological, thermal, mechanical and electrical characterization of polymer composites by comparing uncoated (Cu), silver-coated (Cu@Ag) and silica-coated (Cu@Si) copper flakes in low-density polyethylene at various volume concentrations (up to 40%). Interactions among particles were investigated by rheological properties, as these indicate network formation (geometrical entanglement), which is important for mechanical reinforcement as well as establishing an electric pathway (electrical percolation). The results showed that geometrical and electrical percolation were the same for Cu and Cu@Si, ~15%, while, surprisingly, Cu@Ag exhibited much lower percolation, ~7.5%, indicating the fusion of the Ag coating material, which also decreased crystal growth (degree of crystallinity). Furthermore, the magnitude of the rheological and mechanical response remained the same for all investigated materials, indicating that the coating materials do not provide any load transfer capabilities. However, they profoundly affect electron transfer, in that, Cu@Ag exhibited superior conductivity (74.4 S/m) compared to Cu (1.7 × 10⁻⁴ S/m) and Cu@Si (1.5 × 10⁻¹⁰ S/m). The results obtained are important for the design of advanced polymer composites for various applications, particularly in electronics where enhanced electrical conductivity is desired. Full article

Recycling lithium-ion batteries provides sustainable raw materials. Crushing and separation are necessary for extracting metals, like lithium, from batteries. Crushing a battery carries a risk of fire or explosion. Fully discharging the battery is crucial for safe production. Discharging batteries in a salt solution is a simple and cost-effective large-scale process. However, it is important to note that there is a potential risk of corrosion and loss of battery elements when batteries are immersed in a salt solution. The purpose of this study is to investigate the effectiveness of two distinct methodologies at enhancing the voltage drop of a cylindrical battery when immersed in a salt solution while preventing corrosion. These techniques involve the application of iron and copper accelerators. A 20 wt.% salt water solution was chosen based on the research of several researchers. As the current flows through the metal parts, it encounters electrical resistance and forms an electric circuit with the electrolyte solution. This interaction converts electrical energy into various physical–electrical–electrochemical phenomena, leading to a decrease in battery voltage. Research revealed that the battery can be discharged up to 100% within 4 h without causing corrosion to its components. Another point to note is that if copper conductors are used, it is possible to decrease the battery voltage by around 90% within 8 h. The gap between the copper conductor and the battery had a direct impact on the battery’s discharge rate. Reducing the distance significantly increased the discharge rate, as confirmed by experimental evidence. This discharge mechanism was thoroughly described in a schematic, and, to further explain the electrochemical reaction, the Pourbaix diagram was utilized for both the Fe-Na-Cl and Cu-Na-Cl systems. Moreover, our theoretical predictions were validated through a chemical and mineralogical analysis of the precipitates that formed in the solution. Full article