Copper-gold Alloys Research Articles

Dealloying of gold-copper alloy nanowires: From hillocks to ring-shaped nanopores.

We report on a novel fabrication approach of metal nanowires with complex surface. Taking advantage of nodular growth triggered by the presence of surface defects created intentionally on the substrate as well as the high tilt angle between the magnetron source axis and the normal to the substrate, metal nanowires containing hillocks emerging out of the surface can be created. The approach is demonstrated for several metals and alloys including gold, copper, silver, gold–copper and gold–silver. We demonstrate that applying an electrochemical dealloying process to the gold–copper alloy nanowire arrays allows for transforming the hillocks into ring-like shaped nanopores. The resulting porous gold nanowires exhibit a very high roughness and high specific surface making of them a promising candidate for the development of SERS-based sensors.

Phenomenological Model for Gold-Copper Electrodeposition: Application to Thick Coatings

Pure gold-copper alloys are known to be difficult to electrodeposit because of a strong variation in composition after a few microns have been deposited. Commissariat àl’Energie Atomique (CEA) studied the phenomenon and showed that the decrease in gold’s content is accompanied by an evolution of the microstructure that could be attributed to the free cyanide released near the cathode. During electrolysis, free cyanides provoke a decrease of the copper overpotential (until copper reduction is stopped) and promote the formation of Cu(CN)43− that conduct to an instantaneous three-dimensional nucleation of copper. This phenomenological model well explains why the growth mechanism changes and why only gold is deposited for thick deposits. On the basis of this model, CEA has developed a specific process using ultrasonic waves in order to remove the free cyanides from the cathode. This process allows CEA to perform thick gold-copper deposits with a constant concentration in copper through all the thickness. By controlling the applied potential, different thick alloys with a concentration of copper between 0 wt% up to 40 wt% can be deposited.

STEM characterization of Gold-Copper anisotropic nanocrystals

Alloy nanoparticles are an important group of nanomaterials exhibiting size, shape, structure and composition dependent properties. In bulk, gold-copper alloys exhibits ordered phases Au3Cu (L12), AuCu (L10), AuCu3 (L12) [1]. Theses phases could be modified in temperature and composition at the nanoscale. For instance, ligands play an important role in the synthesis of bi-metallic nanoparticles because they influence the final shape and size of the nanoparticle. The most common method used to synthesize alloyed nanoparticles is wet-chemistry that make use of phosphoric acids, polymeric chains or thiol groups as surfactants in organic solvents such as toluene that control the spatial and shape distribution of the nanoparticles. However, the knowledge of the internal structure of the crystals provides insights to understand the crystal growth of the nanosystem. In recent years it has been reported the relationship between shape and internal features such as stacking faults and twin boundaries on nanowires and decahedral particles [2]. This features (twins, stacking faults and other defects) can modified the final shape of nanoparticles. Some other factors that affect in the same way are the concentration of the reactants and the temperature ranges. Therefore, in this work we present a systematic study on gold-copper bimetallic system to analyze the internal structure of ultrathin nanowires, decahedral nanostars and nanocubes. Modifying few conditions during the synthesis, such as metal concentrations and surfactant used, namely hexadecylamine (HDA), octadecylamine (ODA), oleylamine (OLA) or 1-dodecanethiol (DDT), we obtained Au-Cu nanocrystals with the different morphologies aforementioned. Through high resolution transmission electron microscopy (HRTEM), High Angle Annular Dark Field (HAADF) imaging and Energy Dispersive X-Ray Spectroscopy (EDS) we have obtained atomic resolution that allow us to describe the internal structure of the synthesized particles.

Reaction Pathway and Free Energy Landscape of Catalytic Oxidation of Carbon Monoxide Operated by a Novel Supported Gold–Copper Alloy Cluster

An insight into the catalytic activities of pure gold (Au8) and gold-alloy (CuAu7) clusters supported on either MgO(100) or graphene has been undertaken in the search for an efficient, yet commercially appealing production of Au-based nanocatalysts. The present set of first-principles dynamical simulations shows that the gold and gold–copper alloy clusters destabilize to various extents on MgO but preserve their structures on the graphene support at room temperature. Consequently, the Cu atom remains embedded inside the Au cluster on MgO, whereas it can be easily exposed on the cluster surface on the graphene substrate. This feature appears to be a general key issue to trigger the catalytic reaction and discloses new perspectives for a rational synthesis of supported Au-based catalysts relying on the intrinsic chemical character of Cu which possesses a stronger affinity to oxygen than Au. Indeed, the Cu atom acts as an active site for the approach of O2 and keeps the molecule bound to the cluster. We clarified that the catalytic oxidation of CO occurs on the graphene-supported CuAu7 in a highly selective Langmuir–Hinshelwood type reaction, addressing the long-standing controversy about the actual reaction mechanism for this type of catalysis. Our findings contribute to the development of efficient and commercially appealing supported alloy clusters driven by a proper choice of dopants and supports, thus reducing the use of expensive gold.

For Whom the Bells Fall: Metals from the Cenote Sagrado, Chichén Itzá

Bells of copper and copper alloys and gold–copper alloys were deposited in events at the Cenote Sagrado at Chichén Itzá, Mexico during the site's primary occupation (ad 750–1050) and in later centuries. Housed in three museums in the United States and Mexico, bells (n = 38) were evaluated for traces of fabrication and alteration using Vis–UV–IR optical microscopy. Bulk compositions were determined through p‐ED‐XRF. Phases and compositional variation by depth were characterized through XRD and RBS. The technological styles of bell groups were ascribed to communities of metallurgical practice, from West and Central Mexico to Costa Rica and Panama.

Determination of the k-Values of Copper-Gold Alloys with ED- and WD-EPMA - Results of an Inter-Laboratory Comparison

1. BAM Federal Institute for Materials Research and Testing, Division 6.8 Surface Analysis and Interfacial Chemistry, 12200 Berlin, Germany. 2. National Institute of Standards and Technology (NIST), Materials Measurement Science Division, Microanalysis Research Group, Gaithersburg, MD 20899, USA. 3. BAM Federal Institute for Materials Research and Testing, Division 1.4 Process Analytical Technology, 12200 Berlin, Germany.

The short-range order and ordering energies in gold-copper polycrystalline alloys that are rich in gold

The concentration dependence of the short-range order parameters in gold-rich polycrystalline disordered solid gold-copper solutions was investigated using the X-ray diffuse-scattering method. On the X-ray diffuse-scattering patterns of disordered alloys with 75, 83, and 90% gold, diffuse maximums that are typical of short-range order were absent in the region of the possible superstructure reflex (100), but in the region of the possible reflex (110), an intensity rise on the scattering patterns was revealed that noticeably depended on the gold concentration. The application of the method, taking the effects of static displacements on the considered coordination spheres into account, allowed the determination of short-range order parameters for nine coordination spheres. The spectra of short-range order parameters, which was calculated using the least-squares method, had the long-range sign-alternating representation that is inherent in the Cu3Au superstructure. The absolute values of short-range order parameters were detected to decrease with an increase of the gold content in the alloys. The concentration dependence and small values of ordering energy of investigated polycrystalline alloys were revealed on the first coordination sphere using the Clapp-Moss method.

Copper oxides: kinetics of formation and semiconducting properties. Part I. Polycrystalline copper and copper-gold alloys

The anodic formation of Cu(I) and Cu(II) oxides on polycrystalline copper and copper-gold alloys (4 and 15 at% Au) in deoxygenated 0.1 M KOH was examined by voltammetry, chronoamperometry, and chronopotentiometry with a synchronous registration of photocurrent and photopotential, in situ spectroscopy of photocurrent as well as XPS and SEM measurements. The band gap of p-Cu2O is 2.2 eV for indirect optical transitions independent of the concentration of gold in Cu-Au alloy. It grows on CuOH or n-Cu2O underlayer. The increase of anodic potential results in a thickening of oxide film which is a mixture of Cu(I) and Cu(II) oxides. The latter is a p-type semiconductor with a low photosensitivity. The rate of oxide formation on the alloys is lower than on copper. The structure-dependent properties of the oxide phase on the alloys and copper are different. Copper is prone to corrosive oxidation even in deoxygenated alkaline solution by the traces of molecular oxygen. The corrosive growth of Cu(I) oxide film occurs according to the parabolic law. After the cathodic polarization, the surface of copper remains free of corrosive oxide no longer than 15–20 min. The preliminary anodic formation even of a thin Cu2O film as well as the alloying of copper with gold suppresses the corrosive oxidation of copper.

A colorimetric probe for ascorbic acid based on copper-gold nanoparticles in electrospun nylon

We report on a colorimetric probe based on copper-gold alloy nanoparticles (NPs). The probe is capable of selectively detecting ascorbic acid (AA) as a result of the distance-dependent colour change of the nanoparticles immobilized in an electrospun nylon-6 nanofiber. The resulting white nanofibres undergo a colour change to blue as a result of the aggregation of the NPs induced by AA in the pH range 2–7. The probe is selective for AA even in the presence of dopamine, uric acid, saccharides, amino acids and certain organic acids. It covers the 1.76 x10−2 mg L−1 to 1.76 x105 mg L−1 concentration range, and exhibits a limit of detection of 1.76 x10−2 mg L−1 based on visual detection. Its application was demonstrated by the determination of ascorbic acid in fruit juices, urine, serum, and vitamin C tablets.

Effect of thermo-mechanical treatment on properties improvement and microstructure changes in copper–gold alloy

This paper reports on the changes in hardness, microhardness, electrical conductivity and microstructure using the optical and scanning electron microscopy of the copper-based alloy with 4.5at.% gold, during the complex thermo-mechanical treatment, which is used to create the conditions for development of anneal hardening effect. It was shown that the increase of deformation degree during both the prefinal and final rolling resulted in the increase of hardness, microhardness and electrical conductivity values, due to changes in the microstructure caused by the cold plastic deformation. The differences in the initial microstructure of the homogenized and quenched samples created the different deformation strengthening rates. Low-temperature annealing of the finally rolled samples contributed to a further increase of the above properties due to the anneal hardening effect. The improvement of the properties during the annealing was accomplished in two stages, and the best combination of properties was achieved in the second stage of hardening after annealing at 260°C. Minor changes in the microstructure were noticeable during the annealing at 260°C, but the EDS analysis showed a significant change in the concentration of gold atoms within the grain.

Electroreduction of Carbon Dioxide on Copper-Based Electrodes: Activity of Copper Single Crystals and Copper–Gold Alloys

The activity of copper single-crystal and copper–gold alloyed (Au1Cu99, Au10Cu90, Au20Cu80, Au50Cu50) electrodes for CO2 electroreduction has been investigated in aqueous phosphate buffer solutions by cyclic voltammetry and potentiostatic long-term electrolysis. In addition to H2, four species were identified in the gaseous phase by chromatography after electrolyses: CO, CH4, C2H4 and traces of C2H6. At copper electrodes, the major carbon-containing products are CO and CH4. Analysis of the data indicates that the fraction of methane increases in the order Cu (poly) < Cu (100) < Cu (111), whereas a concomitant decrease of the carbon monoxide fraction is observed. The selectivity of low-index faces towards methane formation is consistent with a mechanism involving CO(ads) and H(ads). Analytical information obtained after potentiostatic electrolyses at copper–gold alloys shows that the CO production increases markedly with the Au content, while the fraction of CH4 diminishes. Amongst all the examined electrodes, the Au50Cu50 alloy appears to be the most efficient substrate for the conversion of CO2 into carbon-containing gaseous products.

Flow Injection Analysis of Ellagic Acid in Cosmetic Skin-Whitening Creams Using a Dendritic Nanostructured Copper-Gold Alloy Plated Screen-Printed Carbon Electrode

Flow Injection Analysis of Ellagic Acid in Cosmetic Skin-Whitening Creams Using a Dendritic Nanostructured Copper-Gold Alloy Plated Screen-Printed Carbon Electrode

The Possibility of New Ordering Reaction in Cu-50 mass% Au Alloy

Among the large number of superlattices, there is a special group which may be classified as long period superlattices, the copper-gold system provides a classical example of such structure. Despite that historically, the copper-gold alloys containing about 25 atom percent gold were among the first investigated alloys, it still represents a subject of numerous studies. In the present work, we study all the possible phase transitions in the binary intermetallic alloy Cu3Au using differential scanning calorimetry (DSC) and differential dilatometry. A new important anomaly due certainly to a new ordered reaction has been detected at low temperature range by these two methods. To confirm this new reaction, we have used other techniques as high resolution transmission electron microscopy (HRTEM), electrical resistivity and microhardness measurements. The kinetics parameters as activation energy Eact and Avrami exponent n have also been calculated respectively by Starink and John Mehl Avrami Kolmogorov (JMAK) methods.

Understanding the effect of thermal treatments on the structure of CuAu/SiO2 catalysts and their performance in propene oxidation

The synthesis and catalytic application of supported CuAu is discussed. Different thermal treatments of a dried precursor of copper nitrate and tetrachloroauric acid on silica lead to catalysts with significantly different structures and properties. Direct calcination gives a catalyst which contains very large gold ensembles with minimal interaction with the copper present. Hydrogen reduction of the dried precursor leads to the formation of copper–gold alloy nanoparticles. Subsequent high temperature calcination de-alloys the copper from the gold to a significant extent. The presence of gold stabilises the formation of Cu+ on this catalyst. The activity and selectivity observed in the oxidation of propene with molecular oxygen, with or without co-fed hydrogen, depends on the pre-treatment, reaction conditions and the ratio of copper to gold in the catalyst. A number of different catalytic active sites are identified and discussed.

Combined neutron and synchrotron X-ray microprobe analysis: attempt to disclose 3600 years-old secrets of a unique bronze age metal artifact

Over the most recent years, micro-analytical facilities based on neutron beams as well as synchrotron X-ray radiation advanced to indispensable instruments in the context of investigating artwork and archaeological artifacts. Using a combined approach of neutron and X-ray micro-beam techniques we investigated a uniquely decorated flanged axe dated into the Early Bronze Age (2200–1600 BC). This axe found in Central Europe is in view of its very early dating and striking parallels to Greek objects one of the most important artifacts concerning the provenance of its particular decoration technique. Neutron tomography was employed to obtain a full three-dimensional structural analysis of the object. Complementary, X-ray microprobe investigations were used to produce two-dimensional chemical and crystallographic images with high spatial resolution. The analysis of the internal structural details of the historical object provides invaluable information regarding manufacturing techniques and material properties. Important insights were obtained for different steps of the object creation including the body casting, the smithing, and—most important—the unique damascening decoration. The compositional analysis and the chemical imaging yield crucial information about the provenance of the metallic raw materials used. The technical and structural peculiarities observed for the axe of Thun-Renzenbuhl reveal distinct differences as compared to Mediterranean objects. Additionally, the chemical analysis of the copper inlays used as part of the decoration point towards the usage of pure copper metal, again in contrast to the more ‘exotic’ copper–gold alloys employed in the Mediterranean damascening decorations. Contradictory to the widely accepted conception of a strong influence of Mediterranean cultures, the present findings point towards a considerable influence of Bronze Age Central Europe by cultures located in the Balkan Peninsula and Caucasus region.

Nonenzymatic glucose sensor based on gold–copper alloy nanoparticles on defect sites of carbon nanotubes by spontaneous reduction

Gold (Au) and copper (Cu) alloy catalysts were deposited on the defect sites of carbon nanotubes by spontaneous reduction among AuCl 4 −, Cu 2+ and oxygen-containing functional groups. Compared with AuCu alloy catalysts prepared by adsorption methods and electrochemical deposition methods, AuCu alloy catalysts show excellent catalytic ability to glucose by spontaneous reduction. The linear range of nonenzymatic sensors that were prepared by spontaneous reduction for glucose detection is 0.08–9.26 mM, and detection limit is 4 μM. In addition, there are high sensitivity (22 μA mM −1), reproducibility (96%) and stability (95% after 60 days). Selectivity of this nonenzymatic sensor for ascorbic, uric acid and acetaminophen was also obtained.

Current bonding systems for resin-bonded restorations and fixed partial dentures made of silver–palladium–copper–gold alloy

Summary This review article describes about the bonding systems for noble metal alloys, bonding techniques of restorations and fixed partial dentures (FPDs) made of Ag–Pd–Cu–Au alloys, and their clinical performance. Thione monomers, 6-(4-vinylbenzyl- n- propyl) amino-1,3,5-triazine-2,4-dithione (VTD), 6-methacryloyloxyhexyl-2-thiouracil-5-carboxylate (MTU-6), and 10-methacryloxydecyl 6,8-dithiooctanoate (MDDT), has been proved effective for bonding noble metal alloys. An acrylic adhesive consists of the tri- n -butylborane (TBB) initiator, methyl methacrylate (MMA) monomer liquid with 5% 4-methacryloyloxyethyl trimellitate anhydride (4-META), and poly(methyl methacrylate) (PMMA), is being used for bonding metallic restorations to abutment surfaces. Clinical performance of restorations and FPDs made of Ag–Pd–Cu–Au alloys is overall excellent when they are seated with the currently available noble metal bonding systems.

A MAZAPA PHASE COPPER FIGURINE FROM ATETELCO, TEOTIHUACAN: DATA AND SPECULATIONS

AbstractExcavations of the Mazapan phase at the Atetelco complex at Teotihuacan by Ruben Cabrera and colleagues produced a small human copper figurine. Studies of Mesoamerican metallurgy have indicated that metallurgy was introduced to western Mexico arounda.d.700 from Colombia, and Ecuador. This particular figurine is a remarkable find. The dates (a.d.800–900) precede those of copper artifacts in the central Highlands. The manufacturing method (an open-backed casting) is rare in Mesoamerica but common in Colombia and Panama. Open-backed cast figurines that do appear in Mesoamerica come from the Cenote of Sacrifice, are made from copper-gold alloys, and were imported from lower Central America or Colombia. The Atetelco figurine is made from a copper-arsenic alloy. Copper-arsenic alloy objects are common in western Mexico (aftera.d.1150) and Ecuador and northern Peru (after abouta.d.300). The major question concerning the Atetelco figurine is whether it was fashioned in Ecuador or Colombia and imported, or whether it was produced in western Mexico. Our study of artifact chemistry, fabrication methods, and provenience indicate that the weight of the evidence points to western Mexico. We suggest that this fabrication technique (lost-wax castings of open-backed human figurines), while introduced from Colombia and lower Central America, never became a major component of the Mesoamerican metallurgical tradition.

ChemInform Abstract: Application of Copper—Gold Alloys in Catalysis: Current Status and Future Perspectives

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Dependence of radiation from a laser-produced plasma on the plasma composition

Results are reported from calculations of how the radiation spectrum from a laser-produced plasma depends on the gold concentration in a target made of a gold-copper alloy. Calculations were carried out with the SND code by using the photon absorption coefficients obtained from the THERMOS code. The experimental data are interpreted by comparing them with the calculated results.