Silver-copper Alloys Research Articles

Silver surface enrichment in ancient coins studied by micro-PIXE

The surface enrichment of archeological silver–copper alloys, either intentional or due to corrosion processes, has been known for many years. The most used non-destructive techniques, such as particle-induced X-ray emission (PIXE) and X-ray fluorescence (XRF) are surface techniques, with penetration depths typically ranging from a few microns to a few tens of microns. Therefore, these techniques could produce results which are not representative of the bulk composition of the alloy.In order to gain insight into the silver enrichment process and the effects on the data obtained with these techniques, a set of silver roman denarii were cross sectioned and analyzed at the Centro Nacional de Aceleradores micro-PIXE facility. Elemental maps show silver surface enriched layers up to 250μm thick. Besides, silver-enriched surface layers are not found for alloys with 96–98wt.% Ag.

Formation of single-walled bimetallic coinage alloy nanotubes in confined carbon nanotubes: molecular dynamics simulations

The growth of single-walled bimetallic Au-Ag, Au-Cu and Ag-Cu alloy nanotubes (NTs) and nanowires (NWs) in confined carbon nanotubes (CNTs) has been investigated by using the classical molecular dynamics (MD) method. It is found that three kinds of single-walled gold-silver, gold-copper and silver-copper alloy NTs could indeed be formed in confined CNTs at any alloy concentration, whose geometric structures are less sensitive to the alloy concentration. And an extra nearly pure Au (Cu) chain will exist at the center of Au-Ag (Au-Cu and Ag-Cu) NTs when the diameters of the outside CNTs are big enough, thus producing a new type of tube-like alloy NWs. The bonding energy differences between the mono- and hetero-elements of the coinage metal atoms and the quasi-one-dimensional confinement from the CNT play important roles in suppressing effectively the "self-purification" effects, leading to formation of these coinage alloy NTs. In addition, the fluid-solid phase transition temperatures of the bimetallic alloy NTs are found to locate between those of the corresponding pure metal tubes. Finally, the dependences of the radial breathing mode (RBM) frequencies and the tube diameters of the alloy NTs on the alloying concentration were obtained, which will be very helpful for identifying both the alloying concentration and the alloy tube diameters in future experiments.

Improving the quality of strips made of a copper-silver alloy

An unconventional technology is developed for producing commercial batches of cold-drawn rectangular strips that are made of a copper-silver alloy for use as current conductors in the rotors of turbogenerators. The effect of the draft on the strength and ductility characteristics is studied. A product with suitable mechanical properties is obtained and high electrical conductivity is attained in the alloy.

Understanding silver hollow wares of the eighteenth and nineteenth centuries: Is there a role for X-ray fluorescence?

Open architecture energy dispersive X-ray fluorescence (XRF) has been used extensively for the study of historic silver alloys since 1970. Silver alloy analyses are carried out to address questions about an object's provenance, technology of manufacture, authenticity, and condition. However, the data generated from this surface analysis technique rarely represent the bulk alloy composition. Quantitative analysis of historic silver alloys using XRF non-destructively is challenging due to: the objects’ curved and irregular surfaces (absence of ideal and reproducible geometries); element segregation in copper–silver alloys; limited availability of alloy standards for instrument calibration; post-manufacturing acid treatments that dissolve surface copper from the alloy (pickling); the presence of firescale (copper oxides) or other corrosion/tarnish layers; and surface inhomogeneities introduced by polishing. This study represents an attempt to quantify these sources of error, and, where possible, to provide analytical protocols that can minimize or even eliminate them. Examples are provided using English and American silver hollow wares from the New York Historical Society.

A note on the analysis of metal threads

The present work demonstrates by means of two practical examples the extreme importance of examination of cross sections of metal threads to obtain an overview of their structure and of the different materials employed in their manufacture. Problems that might be caused by disturbance of surface features during polishing were prevented by covering the sample before embedding with a layer of nickel, using electroless deposition. Results from scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) showed that, although the mean chemical composition of both metal wires is the same, their metallurgical structure is completely different: one consisting of pure silver with inclusions of copper particles and the other a silver–copper alloy.

Low Temperature Formation of Silver and Silver-Copper Alloy Nano-Particles Using Plasma Enhanced Hydrogenation and Their Optical Properties

In this paper, a novel method of producing nanoparticles at low temperatures using hydrogen bombardment of thin films, deposited on glass substrates, is introduced. Silver nanoparticles were obtained by this method in our Plasma Enhanced Chemical Vapor Deposition system. Optical and morphological characteristics of these nanoparticles were extensively studied for various conditions of plasma treatment, such as plasma power density, temperature, duration of hydrogen bombardment, thickness of the initial thin metallic film etc. In addition, Ag-Cu alloy nanoparticles on glass substrates were also achieved. The process of nanoparticle formation in this method shows that several kinds of metals and semiconductors nanoparticles can be obtained using this approach. Scanning Electron Microscopy, Atomic Force Microscopy and Transmission Electron Microscopy were used to analyze the nanostructures.

Rapid penetration of bismuth from solid Bi2Te3 along grain boundaries in Cu and Cu-based alloys

As well known, bismuth rapidly penetrates into copper grain boundaries at about 550 °C and embrittles copper. In the experiments, the authors have used solid Bi2Te3 for the embrittlement of pure copper and copper-based solid solutions containing iron and silver. The investigated alloys were heated in the closed volume together with Bi2Te3 for a short time (5–90 min) at 570 °C in the hydrogen atmosphere. Bi2Te3 did not contact with copper samples during annealing. After that, the samples were bent and grain boundary cracks were formed (with the depth about 10–500 μm). Experiment showed that silver accelerates the embrittlement in the contrast to iron. The cracks in the silver–copper alloys were deeper than in the iron–copper ones. It was assumed that the depth of cracks is equal to the penetration depth. The reasons for this phenomenon were discussed in terms of the impurities effect on the grain boundary segregation.

Silver loss during the oxidative refining of silver–copper alloys

The high temperature oxidative refining of molten silver–copper alloys is accompanied by silver losses to the slag. Typically, borosilicate slags are utilized as a flux and air or oxygen is injected into the molten alloy. The majority of the copper can be selectively oxidized to copper oxide, but some silver is also lost to the slag. In this research, the mechanism of silver loss has been investigated. Firstly, TGA and DTA studies of molten silver–copper alloys were performed, in order to elucidate the oxidation processes occurring at the gas–metal interface in the bubble. Secondly, the silver losses to the slag in the high temperature refining tests were quantified. Thirdly, the slag was characterized using XRD and the morphology of the silver in the slag was examined. Fourthly, a pseudo-equilibrium model of the refining process was developed and this was utilized to suggest methods for minimizing the silver loss to the slag. Finally, possible methods for recovering the silver from the slag are discussed.

Crystallization of sputtered amorphous silicon induced by silver–copper alloy with high crystalline volumeratio

Silver–copper alloy-induced crystallization of sputtered a-Si has been studied. In this alloy, Cu acts as a catalyst to accelerate the crystallization, while Ag acts as a new kind of buffer layer, different from Al 2O 3 and Si 3N 4, to obtain well-crystallized poly-Si films with short annealing time and free of post-treatment for ohmic contact. When the Cu content is limited to below 30%, Ag can effectively slow down the diffusion of Cu into Si and decrease the Cu–silicide nuclei density to improve the crystalline volume ratio from 80% to over 90%. A 1:4 ratio of Cu to Ag yields the best result. The crystalline volume ratio and Hall mobility reach nearly 100% and 29.4 cm 2/V s, respectively. This high quality poly-Si film demonstrates a promising application in solarcells.

Studies on the Effect of Base Metal Composition in Pulse Plating of Silver over Silver Alloy

This research attempt is made to study the effect of base metal composition in pulse plating of silver over silver alloy.The effect of pulse parameters due to the electro deposition of silver over 50% silver alloy is studied and the results arecompared with the results obtained from the study of the effect of pulse parameters because of the electro deposition of75% silver alloy. The surfaces are characterized by scanning electron microscopy and X-ray techniques. Higher thepurity of silver, finer is the grain size. It is also evident that 75% silver alloy has more corrosion resistant than 50%silver alloy. It is suggested that the properties are improved in pulse plating if the concentration of silver in silver copperalloy is more.

First-principles study of the mechanism of ethylene epoxidation over Ag–Cu particles

Silver–copper alloys have been proposed as catalysts for ethylene epoxidation due to their superior selectivity compared to pure silver, the predominant catalyst for this reaction. Under reaction conditions it has been previously shown that, rather than a two-dimensional (2D) Ag–Cu alloy, a thin copper oxide-like layer forms on top of silver, and several possible surface structures were identified (Phys. Rev. Lett., 2010, 104, 035503). By means of density-functional theory calculations, we study the mechanism of ethylene epoxidation catalyzed by the thin oxide-like surface structures. We identify different reaction pathways that will compete and/or synergetically interplay in the catalysis. In general, the reaction mechanism is structure-dependent and the reaction does not always proceed through the formation of (meta)stable intermediates, in contrast to clean Ag and the 2D alloy. Analyzing the competing reactions, we discuss how the addition of Cu improves the selectivity and stress the overall importance of accounting for the effect of ambient conditions.

Influence of solidification rates on a Directional Solidification process for the production of Functionally Graded Materials

This paper is concerned in assessing the possibility of the use of a Directional Solidification (DS) process in order to produce functionally graded materials. It will be assessed the influence of the relative displacement rate between heating coil and mould, in order to evaluate the produced cooling rates along the casting and consequent metallurgical and mechanical properties on the obtained component. A copper-silver alloy, which is prompt to macro-segregation occurrence, will be used. Results demonstrate that the process, which is able to originate DS castings, may also be used for FGMs production.

Copper-Silver Alloy for Advanced Barrierless Metallization

In this study we observed significantly improved properties, over a pure copper (Cu) film, for a copper-silver alloy film made with a pure copper film co-sputtered with a minute amount of either Ag0.3N0.4 or Ag1.2N0.7 on a barrierless Si substrate. In either case, no noticeable interaction between the film␣and the Si substrate was found after annealing at 600°C for 1 h. The Cu(Ag0.3,N0.4) film was thermally stable after annealing at 400°C for 240 h. The film’s resistivity was ∼2.2 μΩ cm after annealing at 600°C, while its leakage current was found to be lower than that of a pure Cu film by three orders of magnitude. The adhesion of the Cu(Ag1.2,N0.7) film to the Si substrate was approximately seven times that of a pure Cu film to a silicon substrate. Hence, a Cu film doped with Ag and N seems to be a better candidate for both barrierless metallization and the making of superior interconnects.

Phase separation in immiscible silver–copper alloy thin films

Far from equilibrium, immiscible nanocrystalline Ag–Cu alloy thin films of nominal composition Ag–40 at.% Cu have been deposited by co-sputter deposition. Both X-ray and electron diffraction studies indicate that the as-deposited films largely consist of nanocrystalline grains of a single alloyed face-centered cubic (fcc) phase. However, detailed three-dimensional atom probe tomography studies on the same films give direct evidence of a nanoscale phase separation within the columnar grains of the as-deposited Ag–Cu films. Subsequent annealing of these films at 200 °C leads to two effects; a more pronounced nanoscale separation of the Ag and Cu phases, as well as the early stages of recrystallization leading to the breakdown of the columnar grain morphology. Finally, annealing at a higher temperature of 390 °C for a long period of time leads to complete recrystallization, grain coarsening, and a complete phase separation into fcc Cu and fcc Ag phases.

Electromigration in electroplated Cu(Ag) alloy thin films investigated by means of single damascene Blech structures

Electromigration failure of copper interconnects in microelectronics evokes a need for materials with improved resistance against electromigration effects. Copper–silver alloy thin films are a promising material for the next generation of interconnects and were investigated with respect to their electromigration resistance. The investigations were done by atom drift experiments by means of Blech structures fabricated in single damascene technology with two different Ta-based liner systems. Electromigration induced atom drift could be demonstrated. The resistance against electromigration of Cu(Ag) films appears to be slightly higher than for pure Cu films. However, significant experimental errors are still present. Additionally, de-alloying effects were observed.

The Effect of DC Plating Parameters on the Composition and Morphology of Silver-copper Alloy

This research attempts to optimize the parameters for DC plating of silver on silver alloy of two differentcompositions namely 50% and 75% silver alloy. In the Silver –copper alloy, the surface morphology and compositionof the electro deposit are influenced by current density, silver concentration in the bath, applied current type andaddition of additive. It has been found that concentration of silver in silver alloy has an effect in weight electrodeposited over cathode in DC plating. The surface morphology is studied by taking SEM micrograph for thetwo different compositions of silver alloy and grain size is measured using XRD analysis. Higher the purity of silver,finer is the grain size. It has been observed that with the increase of silver in the sample, the amount of silverdeposited, hence the thickness of the deposit varies for the same current and voltage settings.

Anodic oxidation of Ag-Cu alloys in sulfuric acid solutions when reaction products are unstable

Based on the impedance models of porous layer, anodic behavior of silver as a component of Ag-Cu alloys in aqueous sulfuric acid solutions is analyzed. It is shown that, in order to adequately describe the electrochemical process, chemical decomposition of superficial passivating silver-sulfate layer should be taken into account. Decomposition rate constants of the layer on silver-copper alloys of diverse composition are calculated.

Influence of synthesis conditions on the nanostructure of immiscible copper–silver alloy thin films

Far from equilibrium, immiscible nanocrystalline Cu–Ag alloy thin films of nominal composition Cu–30(±5) at.% Ag were deposited by co-sputtering. While films deposited at ∼300 K exhibit a two-phase mixture of face-centered cubic (fcc) Ag + fcc Cu, those deposited either at ∼100 K or at low power (∼40 W) exhibit an fcc Cu–25 at.% Ag solid solution, excess fcc Ag and small fractions of a metastable hexagonal (4H) Cu–Ag phase. Increasing the sputtering gas pressure leads to phase separation into fcc Cu, fcc Ag and metastable 4H Cu–Ag.

Corrosion behavior of palladium–silver–copper alloys in model saliva

Objectives Palladium–silver system alloyed with other metals represents one of possible material choices in prosthetics. Its corrosion properties are influenced by minority components added in order to obtain the properties required for stomatological purposes. The objective of this work was to ascertain the influence of copper on the corrosion mechanism of palladium–silver alloys. Methods Corrosion properties of four palladium–silver–copper alloys were compared with the behavior of the palladium–silver binary system. Standard electrochemical measurements in a model saliva solution were complemented with an XPS analysis of the specimens surface. Experimental data were compared with the results of thermodynamic analysis. Results The foregoing study revealed formation of a saline layer of insoluble silver compounds as the dominant feature of the corrosion mechanism in a binary system. This process is suppressed in ternary alloys where electrochemical reactions of copper take place on the alloy-electrolyte phase boundary leading to the formation of a layer based on copper oxides. Significance The alloying of the palladium–silver binary system with copper results in an important change in the corrosion behavior of ternary alloys. A change in the mechanism of interaction with the environment leads to susceptibility to non-uniform corrosion.

CrossRef Listing of Deleted DOIs

The enthalpies of mixing of liquid copper with liquid silver and with solid titanium, zirconium, and hafnium have been measured by high temperature reaction calorimetry at 1371 to 1373 K. A least squares treatment of the data for copper-silver alloys yields the following expression for the molar enthalpy of mixing: ΔHmix = ϰAgϰCu(17.66 − 5.46 ϰAg) kJ mol−1. The enthalpies of solution of solid titanium, zirconium, and hafnium in dilute solutions in liquid copper are all exothermic; the following values were found: -2.0 kJ mol−1 for Ti, -52.5 kJ mol−1 for Zr, and -46.3 kJ mol−1 for Hf. These values are all significantly less exothermic than predicted by the semiempirical theory of Miedema. The enthalpies of formation of congruent melting intermetallic phases in the systems Cu-Ti, Cu-Zr, and Cu-Hf were measured by drop calorimetry or by solution calorimetry in liquid copper. The enthalpies of formation of the solid alloys have been compared with corresponding data for the liquid alloys.