Two 11th- and 12th-century entrance doors from the Basilica di San Marco in Venice, made of different copper alloys and woods, were non-invasively examined in situ. The chemical composition of the ...metals, the way in which different metal parts were joined together, the tree species used to construct the supporting structures and the age of the wood are determined. A portable ED-XRF instrument and optical microscopes were used. The doors were also photographed to produce high-resolution orthophotos and 3D models. The metal parts of the doors were made of leaded tin-bronze and quaternary Cu-Sn-Zn-Pb alloys and were mounted on a wooden multi-layer structure of larch and silver fir; the dendrochronological dates of some of the larch boards are 1965, teminus post quem.
The microstructural evolution and recrystallization behavior of a single-phase Cu–18Ni–17Zn alloy during annealing has been investigated. The strengthening effects of the solute atom concentration, ...grain size, and recrystallized volume fraction have also been studied. The results have shown that the difference in yield strengths for the fully recrystallized samples mainly depended on the grain boundary strengthening effect. This is attributed to a constant (∼41 MPa) solid-solution strengthening contribution in the completely recrystallized Cu–18Ni–17Zn alloy. When compared with pure copper, this alloy exhibited a high Hall-Petch constant (∼0.36 MPa m1/2), which is due to the higher grain boundary interface energy. A discontinuous recrystallization occurred in the alloy in the temperature range 400 °C–500 °C. Furthermore, the yield strength was linearly correlated to the recrystallized volume fraction in the partial recrystallized samples. Moreover, the addition of Ni and Zn increased the recrystallization temperature and slowed the recrystallization kinetics. The activation energy for the recrystallization was estimated as 92.6 ± 5.1 kJ/mol in the cold-rolled Cu–Ni–Zn alloy, which indicates that the grain boundary migration during recrystallization was mainly controlled by diffusion along the grain boundaries. In addition, the recrystallized grains preferentially nucleated at shear bands with high strain energies in the Cu–Ni–Zn alloy during annealing. As the regions of shear banding were completely consumed, new recrystallized nuclei formed at the grain corners. The limited number of nucleation sites resulted in a low Avrami exponent value that ranged from 0.41 to 0.61.
Cu-Cr-Zr-Ti alloy specimens have been fabricated by selective laser melting (SLM) technology with a high relative density. Their microstructure and mechanical properties at room conditions as related ...to elevated temperatures have been investigated after solution annealing and aging of the material and compared to hot-rolled samples. The microstructure of the SLM material consists of grains elongated along build direction with the size in the range from 30 to 250µm. The mechanical test showed that the SLM material has 195–211MPa ultimate tensile strength (UTS) and 11–16% elongation at break at 20°С. Samples produced parallel to the build direction show slightly higher UTS and elongation at break in comparison with samples fabricated perpendicular to the build direction. The UTS of the SLM samples is approximately 20–25% lower compared to the hot-rolled samples. The study revealed that SLM technology can be successfully utilized to produce complex-shaped copper alloy parts with high density and good mechanical properties.
•High density Cu-Cr-Zr-Ti specimens have been fabricated by selective laser melting.•Mechanical tests showed good results at room and elevated temperatures.•SLM parameters optimization and HIP treatment are suggested to reduce porosity.
Ni–Mn-based Heusler alloys are known to demonstrate magnetic shape memory and giant magnetocaloric effect (MCE). These effects depend on the phases, crystallographic and magnetic phase transitions, ...and the crystallographic texture characteristics. These structural characteristics, in turn, are a function of the processing parameters. In the current work, Nisub.55.5Mnsub.18.8Gasub.24Sisub.1.7 Heusler alloy was processed by melt-spinning under a helium atmosphere. This process results in a fine microstructure. The ribbon that was produced with a narrower nozzle width, faster wheel speed, and higher cast temperature, indicating a faster cooling rate, had double the magnetic entropy change close to room temperature. However, the other ribbon demonstrated a large entropy change over a broader temperature range, extending its usability. The effect of the melt-spinning process parameters on the developing microstructure, crystallographic structure and texture, transformation temperatures, and the magnetic entropy change were studied to explain the difference in magnetocaloric behavior.
Ni.sub.55Fe.sub.19Ga.sub.26 ribbons obtained by melt-spinning technique exhibit a martensitic transformation from L2.sub.1 cubic austenite phase to 14 M martensite phase above room temperature. We ...have taken advantage of the existence of thermal hysteresis of the martensitic phase transition (~ 11 K) to analyze the effect of isothermal treatments on the reverse martensitic transformation, which has been analyzed by means of interrupted heating using differential scanning calorimetry. The experimental findings clearly indicate a time-depending effect in the martensitic transformation at temperatures between the austenite start and finish temperatures. Moreover, it has been observed that two successive martensitic transformations take place after the isothermal arrest was performed.
•Increased photoactivity of hybridized/supported CuO–ZnO and CuS–ZnS systems.•Higher efficiency of the CuO–ZnO/NCP than CuS–ZnS/NCP.•Res shifts of band gaps of the supported coupled semicondcutors ...whit respect to monocomponent one.
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Photocatalytic activity of the coupled ZnO–CuO and ZnS–CuS semiconductors supported onto clinoptilolite nanoparticles (CNP) and micronized one (CMP) was studied in photodegradation of benzophenone (BP) aqueous solution. The ZnO–CuO/CNP (or MCP) and ZnS–CuS/CNP (or MCP) catalysts were prepared via calcination and sulfiding of their Zn(II)–Cu(II) ion-exchanged samples, respectively. XRD patterns confirmed loading of the mentioned semiconductors onto the zeolite, and nano dimension of the catalysts was confirmed by XRD and TEM results. Typical Tauc plots obtained from UV–vis DRS spectra showed red shifts for the band gap energies of the supported coupled semiconductors with respect to the supported monocomponent ones especially for ZnO/NCP and ZnS/NCP catalysts. Also, in both indirect and direct transitions, these red shifts were more considerable in the oxidic systems with respect to the sulfidic systems. Accordingly, the supported oxidic systems showed better photocatalytic activity than the sulfidic one. In the oxidic systems changing the dose of CuO played important role while in the sulfidic systems ZnS played considerable role in the degradation of BP. In the used systems, CuO and ZnS played the main e/h generators in the oxidic and sulfidic systems, respectively, while ZnO and CuS played the preventer e/h recombination. Based on the results, production of e/h is the rate limiting step in the used systems. The maximum degradation activity of the catalysts was obtained at: 0.12gL−1 of ZnO0.80–CuO3.18/NCP and 0.10gL−1 of ZnS1.39–CuS2.88/NCP catalysts, initial BP concentration of 30mgL−1 at pH 7.5.
Copper is a significant platform for CO2 electroreduction catalysts because it is the only known metal to produce multi-carbon products but suffers from poor selectivity. In the early stages of the ...reaction pathway, a selectivity-determining step dictates if the pathway leads to formate (a dead-end) or to CO (and on to multi-carbon products). Therefore, controlling the adsorption of key intermediates, in order to steer the reaction pathway as desired, is critical for selective CO2 electroreduction. Alloying copper is a strategy in which the composition and electronic properties of the alloy surface can be finely tuned to alter the reaction intermediate adsorption behavior. Herein, through in situ Raman spectroscopy and density functional theory (DFT) calculations, we investigate a composition-dependent selectivity toward CO and formate during CO2 electroreduction on a range of Cu–Sn alloy catalysts. We find that the selectivity shifts from CO to formate generation as the Sn content in the alloy catalyst increases because of a shift in adsorption preference from the C-bound *COOH intermediate to the O-bound *OCHO intermediate. Theoretical DFT calculation results indicate that this selectivity shift is due to a gradual weakening of *COOH adsorption and strengthening of *OCHO that occurs with increasing Sn content. A combination of theoretical Bader charge analysis and experimental X-ray photoelectron spectroscopy revealed the origin of such transformation: upon alloying, charge is redistributed from Sn to Cu, which creates regions of localized positive charge on the Sn sites. Therefore, with increasing tin content, these localized positive sites hinder the nucleophilic attack of the CO2 carbon, making *COOH adsorption (and the CO pathway) less favorable.
With the use of electrolytic Cu powder, Zr powder, Si powder and nickel-coated Bsub.4C powder as cladding powders, in-situ synthesized ZrBsub.2-SiC reinforced copper matrix composite coatings were ...prepared by laser cladding on the surface of the copper substrate to improve the surface hardness and wear resistance. Under the condition of a laser energy density at 60 kJ/cmsup.2, the macroscopic surface of the composite coating was continuously flat. The microstructure and phase of the cladding coating were analyzed by means of XRD and SEM. The reinforcements with nano-scale particle and micron-scale needle-like structures were in-situ synthesized in the cladding coating, and the content of the reinforcement phase decreased slightly from the coating surface to the substrate. The phase analysis results showed that the reinforcements included ZrBsub.2 and SiC. When the content of the reinforcement was increased to 30 wt%, microhardness also increased from 48 HVsub.0.2 to 309 HVsub.0.2, which was about 5.6 times that of the copper matrix. The wear resistance of the composite coatings was characterized by current-carrying wear tests. By keeping the sliding speed and load constant, the wear rate decreased with an increase in the reinforcement content, and the wear mechanism changed from adhesive wear to abrasive wear. The wear rate of the composite coating with the current was higher than that without the current due to its electric ablation and high temperature.
Monodisperse bimetallic Pd–Cu nanoparticles with controllable size and composition were synthesized by a one‐step multiphase ethylene glycol (EG) method. Adjusting the stoichiometric ratio of the Pd ...and Cu precursors afforded nanoparticles with different compositions, such as Pd85–Cu15, Pd56–Cu44, and Pd39–Cu61. The nanoparticles were separated from the solution mixture by extraction with non‐polar solvents, such as n‐hexane. Monodisperse bimetallic Pd–Cu nanoparticles with narrow size‐distribution were obtained without the need for a size‐selection process. Capping ligands that were bound to the surface of the particles were removed through heat treatment when the as‐prepared nanoparticles were loaded onto a Vulcan XC‐72 carbon support. Supported bimetallic Pd–Cu nanoparticles showed enhanced electrocatalytic activity towards methanol oxidation compared with supported Pd nanoparticles that were fabricated according to the same EG method. For a bimetallic Pd–Cu catalyst that contained 15 % Cu, the activity was even comparable to the state‐of‐the‐art commercially available Pt/C catalysts. A STEM‐HAADF study indicated that the formation of random solid‐solution alloy structures in the bimetallic Pd85–Cu15/C catalysts played a key role in improving the electrochemical activity.
Army of two: Supported bimetallic Pd–Cu nanoparticles, which were synthesized by a one‐step multiphase method, showed enhanced electrocatalytic activity towards MeOH oxidation, comparable to the state‐of‐the‐art commercially available Pt/C catalysts.
