Copper-silver System Research Articles

Catalysis on Mono- and Bimetallic Nanoparticles of the Silver–Copper System Cu<sub><i>n</i></sub>Ag<sub><i>m</i></sub>

The purpose of this work is to study the catalytic properties of mono- and bimetallic nanoparticles of the copper-silver system of variable composition supported on aluminum oxide in the conversion reactions of protium modifications and deuterium-hydrogen exchange. From a comparison of the temperature dependences of the specific catalytic activity of the samples in the two reactions under study, a conclusion was drawn about different reaction mechanisms. It has been shown that, compared to bulk metals, nanoparticles of the CunAgm composition have catalytic properties in a wide temperature range, up to 77 K. In the chemical reaction of isotope exchange in molecular hydrogen, a synergistic effect is observed, which indicates the interaction of metals in biparticles.

Bimetallic Copper-Silver Systems Supported on Natural Clinoptilolite: Long-Term Changes in Nanospecies’ Composition and Stability

Long-term changes in species of copper-silver bimetallic systems on natural clinoptilolite obtained by ion exchange of Cu2+ and Ag+ and then reduced at different temperatures were studied. Even after storage under ambient conditions, XRD and UV-Vis diffuse reflectance spectra indicate the presence of nanospecies and larger particles of reduced copper and silver. Scanning electron microscopy of aged bimetallic samples, reduced at the highest temperature (450 °C) and the pristine sample for their preparation, also aged, showed the presence of silver particles with a size of about 100 nm. They are formed in the initial ion-exchanged sample (without reduction) due to the degradation of Ag+ ions. The particles in the reduced sample are larger; in both samples they are evenly distributed over the surface. The presence of silver affects the stability and the mechanism of decomposition/oxidation of reduced copper species, and this stability is higher in bimetallic systems. The decomposition pattern of recently reduced species includes the formation of smaller nanoparticles and few-atomic clusters. This can occur, preceding the complete oxidation of Cu to ions. Quasicolloidal silver, which is present in fresh bimetallic samples reduced at lower temperatures, transforms after aging into Ag8 clusters, which indicates the stability of these nanospecies on natural clinoptilolite.

Synthesis and antibacterial activity of silver-copper nano-composites formed by microwave assisted chemical reduction

Abstract Bimetallic copper silver systems are promising antibacterial agents with wider activity range and enhanced activity than single metallic systems. In this study we present the synthesis of copper silver bimetallic composites utilizing a fast, microwave assisted chemical reduction method. The method requires low reaction times and yields nano-composites with a morphology best described as nano silver decorated copper particles. Water leaching studies show that copper follows a fast exponential leaching kinetics compared to silver. The release of silver remains slow and is sustained over a much longer period compared to copper. Consequently, the antibacterial effects of the composites will be dictated by the fast leaching copper and modulated by the composition of silver in the composite. The antibacterial effects of the composite on pseudomonas aeruginosa bacterium confirm this effect.

Comparison of Spectra of Grain Boundaries Spontaneously Formed in Cu-Ag and Cu-In Systems

Spectra of grain boundaries existing in the polycrystalline copper-silver system (positive enthalpy of mixing) have been studied in comparison with those of the copper-indium system (negative enthalpy of mixing). Spectra of grain boundaries are formed spontaneously upon an increase in the temperature, occurrence of eutectic and peritectic reactions, and subsequent relaxation of structures in the two-phase solid/liquid region of phase diagrams. It has been shown that the rate of grain growth and the relation between different grain boundary types in the total spectrum depend on the enthalpy of mixing.

Laser method of microscopic sensor synthesis for liquid and gas analysis using glucose and H2S as an example

Laser-induced deposition of metals from a solution has been used as a new method for the synthesis of microcomposite materials in the copper-silver system. It was shown that the obtained materials have good sensory properties with respect to the determination of d-glucose in aqueous solutions. It is also shown that it can be used for gas sensors. Control of sensory properties can be done by changing the method of deposition. X-ray diffraction, EDX, and impedance spectroscopy were used to characterize the materials obtained and it was shown that laser sequential deposition and coprecipitation of two metals give different results. An explanation of the results was proposed. It explains them by the eutectic nature of the interaction in the copper-silver system.

Phase transitions in copper–silver alloys under high pressure torsion

AbstractThe influence of high pressure torsion (HPT) on the formation and decomposition of solid solutions in the copper–silver system has been studied. The investigated Cu-8 wt.% Ag alloy was annealed at two different temperatures, 500 and 650°C, and quenched. The samples consisted of (Cu) solid solution in the matrix with (Ag) precipitates. During HPT a steady-state value of torsion torque was reached after about 1.5 anvil rotations. After HPT (5 anvil rotations) the composition of the (Cu) solid solution in both samples had become equal. In other words, the concentration of silver in the (Cu) matrix annealed at 650°C decreased and in the sample annealed at 500°C increased. Moreover, a similar process took place in (Ag) precipitates as well. The concentration of copper in (Ag) particles in the sample annealed at 650°C decreased and in the sample annealed at 500°C increased. Thus, the composition of (Cu) and (Ag) solid solutions reached at steady-state during HPT does not depend on that before HPT. The composition of the (Cu) and (Ag) solid solutions after HPT is as high as if the samples were annealed at a certain intermediate temperature about 600 ± 20°C.

Room-temperature grain boundary diffusion data measured from historical artifacts

Abstract Diffusion processes in typical metals are considered to be slow at room temperature but there are many applications for which very long-term use is envisaged and stability needs to be assured over a timescale of 10 000 years, where even slow processes can be important. It is clearly impractical to make diffusion measurements under controlled conditions for this length of time, so it is common to perform accelerated tests at higher temperatures and extrapolate the necessary information from the measurements so obtained. We have tested the validity of this type of extrapolation for room-temperature, grain boundary diffusion in the copper–silver system, by measuring low-temperature diffusion profiles in antique samples of Sheffield Plate. We present experimental measurements and analysis, along with a comparison to modern diffusivity data extrapolated in the usual manner.

Low-Temperature Grain Boundary Diffusion Data Measured from Historical Artifacts

ABSTRACTDiffusion processes in typical metals are slow at room temperature but there are many applications for which very long-term use is envisaged and stability needs to be assured over a timescale of 10, 000 years, where even slow processes can be important. It is common to perform accelerated tests at higher temperatures and extrapolate the necessary information from the measurements so obtained. We have tested the validity of this type of extrapolation for room-temperature, grain boundary diffusion in the copper-silver system, by measuring low-temperature diffusion profiles in antique samples of Sheffield plate.

Isothermal solidification kinetics of diffusion brazing

Diffusion brazing (DB) is a process that produces interface-free joints that approach the bulk properties of the material that is to be joined. Solid-state diffusion of the melting point depressant (MPD) element into the joint metal causes the solid/liquid (S/L) interface to advance until the joint is solidified. The time required to complete this isothermal solidification stage was modeled using a moving boundary analysis. Precision measurements of the interlayer width as a function of time were made on the copper-silver system. The bonding apparatus consisted of a suspended load feedback system that prevented leakage of joint metal due to extrusion or surface wetting, thus preserving mass balance. The interlayer width vs bonding time measurements obtained were found to be within a factor of 4 of the theoretical model. The difference was ascribed to the difficulty in accurately measuring the actual liquid width and loss of silver due to vaporization. Large spherical protrusions grow during bonding, which further roughens the interface. However, experimental and predicted concentration profiles of silver were found to be in complete agreement. As the liquid remaining in the grain boundary grooves is diffused away, porosity can develop due to volume changes. By holding the joint at temperature for extended periods, complete solidification followed by homogenization will occur. Selecting the appropriate bonding temperature to achieve a specified maximum concentration of braze metal at the joint is dependent on both the isothermal solidification and homogenization kinetics.

Oxidation of methanol on the surfaces of copper-silver alloys

The catalytic oxidation of methanol on copper, silver and copper - silver alloys has been studied in a large range of temperature changes, alloy compositions, reaction gas mixture compositions and flow rates. A reaction mechanism is proposed and the reaction conditions providing for highest catalytic activity and selectivity are outlined. It is possible using the scheme, to explain why copper is not so suitable as a catalyst as silver. A correlation has been established between the phase diagram of the bimetallic copper-silver system and its catalytic activity. Some copper-silver alloys prove suitable to be used as industrial catalysts for the oxidation of methanol to formaldehyde.

Wetting and spreading in the CuAg system

Sessile drop experiments were made in the copper-silver system at the eutectic temperature and 900°C. Wetting, or acute contact angles, were observed for specimens in chemical thermodynamic equilibrium. Spreading occurred when the substrate was not in chemical equilibrium with the liquid. The interface does not remain aligned with the free surface of the substrate only in the presence of reactions.

THE SOMMERFELD MODEL AND THE HEAT OF SOLUTION OF AN ALLOY

An approximately self-consistent method, using a Sommerfeld model, and incorporating an approximation to the second-order perturbation energy (Lennard-Jones 1930), is used to calculate the heat of solution of both monovalent–monovalent and monovalent–polyvalent alloy systems. The heat of solution, as given by the second-order approximation, varies directly with the square of the perturbing potential, and inversely with the mean total energy of the free electrons in the solvent. Varley's (1954.) result resembles this, except that his expression varies inversely with the mean kinetic energy of the free electrons in the pure solute. The first-order approximation to the energy of the alloy system is identical, except for a change of sign, with the expression suggested by Friedel (1952, 1954) for the heat of solution. The charge accumulation about a solute site is found to vary directly with the strength of the perturbation, and inversely with the mean energy of the free electrons in the solvent. Varley obtained a comparable expression; however, his function varies inversely with the mean kinetic energy of the free electrons in the pure solute. The calculated charge accumulations in the copper–silver system, and for gold dissolved in silver, agree qualitatively with those of Arafa (1949) and Huang (1948).

Galvanic Cell Measurements in the Copper–Silver System

Galvanic Cell Measurements in the Copper–Silver System

A Calculation of the Solubility Limits of the Copper-Silver System

A calculation is made of the change in the energy of a monovalent metal when one of its atoms is replaced by an atom of a different monovalent metal, not necessarily of the same atomic volume. From a knowledge of this energy the heat of solution can be determined and thereby, through the usual thermodynamic relations, also the solubility limits. Numerical calculations have been carried out for the copper-silver system and the theory shows in this case the existence of narrow solubility limits, in agreement with the known phase diagram. The theoretical values of the heats of solution are compared with those required to give the observed solubility limits.