Thermodynamic studies of the surface and transport properties in Ag–In and Ag–Sb liquid alloys

The surface tension, surface concentration, viscosity and mutual diffusion co-efficients of the Ag–In and Ag–Sb liquid alloys have been calculated using energetics and derivables from a statistical mechanical framework which recognises the formation of atom clusters of self associates. Our calculations suggest the existence of some form of local order in the systems. Ag–In showed higher tendencies to heterocoordination in the bulk-manifested higher values of mutual diffusion coefficient throughout the concentration range. The viscosity values of Ag–In and Ag–Sb were calculated using the expression reported by Kucharsky which relates the viscosity of a liquid binary alloy to the activity coefficients of the liquid alloy components that are raised to some power m. This exponent m is a fitted parameter. The calculated viscosity values for Ag–Sb had some reasonable agreement with experiment above 0.5 atomic fraction of Sb, using a fitted parameter value of m = 4.5. The fitted parameter value for the viscosity of Ag–In is expected to be in the range 1.5 ≤ m ≤ 3.5.     

Structural and energetic asymmetry in liquid Ag–Al alloys

The thermodynamic and microscopic structure of Ag–Al liquid alloy at 1273?K has been studied by using regular associated solution model. This model has been utilised to determine the complex concentration in a regular associated solution of Ag and Al. We have then used the complex concentration to calculate the free energy of mixing, enthalpy of mixing, entropy of mixing, activity and concentration fluctuations in long wavelength limit S _CC(0) and the Warren–Cowley short-range parameter α ₁. The analysis suggests that heterocoordination leading to the formation of complex Ag₃Al is likely to exist in the liquid but is of a weakly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Ag-rich region. The alloy behaves like a segregating system in Al-rich region.     

Thermal stability of Ag–Au,Cu–Au,and Ag–Cu bimetallic nanoparticles supported on highly oriented pyrolytic graphite

The formation of Ag–Au, Cu–Au, and Ag–Cu bimetallic particles on the surface of highly oriented pyrolytic graphite was studied by X-ray photoelectron spectroscopy. Samples with the core–shell structure of particles were prepared by sequential thermal vacuum deposition. The thermal stability of the samples was studied over a wide range of temperatures (25-400°C) under ultrahigh-vacuum conditions. The heating of the samples to ~250°C leads to the formation of bimetallic alloy particles with a relatively uniform distribution of metals in the bulk. The thermal stability of the samples with respect to sintering depends on the nature of the supported metals. Thus, the Ag–Au particles exhibited the highest thermal resistance (~350°C) under ultrahigh-vacuum conditions, whereas the Ag–Cu particles agglomerated even at ~250°C.     

Solvothermal preparation,and characterization,of Cu–Ag nanoparticles

Cu–Ag nanoparticles have been successfully synthesized by one-pot solvothermal treatment of a mixture of AgNO₃ and Cu(OAc)₂·H₂O in ethylene glycol solution at 180 °C for 10 h. The samples were characterized by UV–visible absorption, X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). The results showed that Cu–Ag nanoparticles and a small amount of phase-separated Cu–Ag alloy nanoparticles with an average diameter of 100 ± 30 nm were synthesized by the solvothermal treatment procedure. The mechanism of formation is discussed.     

A 3-D inorganic–organic hybrid based on saturated Wells–Dawson polyoxoanion and K+, linked by an Ag–Ag bond

A 3-D complex K₂[Ag₂(biim)₂]₂P₂W₁₈O₆₂ (biim?=?biimidazole) (1) has been hydrothermally synthesized and characterized by IR, thermogravimetric, and single-crystal X-ray diffraction. Single-crystal X-ray structural analysis reveals that 1 exhibits a 1-D wavelike chain constructed from µ₃-bridging oxygen atoms of [P₂W₁₈O₆₂]^6? and [Ag₂(biim)₂]²⁺. The K⁺ link to six oxygen atoms of three P₂W₁₈ clusters and 12 equatorial terminal oxygen atoms of P₂W₁₈ clusters link to six K⁺, resulting in a 3-D framework with a relatively short Ag–Ag bond [2.836?Å]. The electrochemical behavior of 1 modified carbon paste electrode (1-CPE) has been studied. The results indicate that 1-CPE has remarkable stability.     

Fabrication and photoluminescence properties of Ag0 and Ag0–Er3+ containing plasmonic glass nanocomposites in the K2O–ZnO–SiO2 system

Here, we report the preparation of nano silver (Ag) and nano Ag-erbium (Ag–Er) co-embedded potassium–zinc-silicate based monolithic glass nanocomposites by a controlled heat-treatment process of precursor glasses. The nanocomposites were characterized by differential scanning calorimeter, dilatometer, UV–Visible absorption spectrophotometer, X-ray diffractometer and transmission electron microscope and spectroflurimeter. A strong surface plasmon resonance (SPR) band is observed around 430 nm in all the heat-treated glass nanocomposite samples due to the formation of Ag⁰ nanoparticles (NP). The Ag-glass nanocomposite samples display nearly 2-fold enhanced photoluminescence (PL) at 470 nm upon excitation at 290 nm until the size of the NP increases to the value equals to the mean free path of conduction electrons inside the particles. On contrary to this, the photoluminescence spectra of Er³⁺ ions exhibit a gradual decrease of NIR emission at 1540 nm due to ⁴I_13/2 → ⁴I_15/2 transition under excitation at 523 nm in the heat-treated glass nanocomposites which happened due to excitation energy transfer of Er³⁺ ions to the Ag NP, acting as ‘plasmonics diluents’ for Er³⁺ ions. These nanocomposites have huge potential for various nanophotonic applications.     

Comparative toxicity study of Ag, Au, and Ag–Au bimetallic nanoparticles on Daphnia magna

A comparative assessment of the 48-h acute toxicity of aqueous nanoparticles synthesized using the same methodology, including Au, Ag, and Ag–Au bimetallic nanoparticles, was conducted to determine their ecological effect in freshwater environments through the use of Daphnia magna, using their mortality as a toxicological endpoint. D. magna are one of the standard organisms used for ecotoxicity studies due to their sensitivity to chemical toxicants. Particle suspensions used in toxicity testing were well-characterized through a combination of absorbance measurements, atomic force or electron microscopy, flame atomic absorption spectrometry, and dynamic light scattering to determine composition, aggregation state, and particle size. The toxicity of all nanoparticles tested was found to be dose and composition dependent. The concentration of Au nanoparticles that killed 50% of the test organisms (LC₅₀) ranged from 65–75 mg/L. In addition, three different sized Ag nanoparticles (diameters = 36, 52, and 66 nm) were studied to analyze the toxicological effects of particle size on D. magna; however, it was found that toxicity was not a function of size and ranged from 3–4 μg/L for all three sets of Ag nanoparticles tested. This was possibly due to the large degree of aggregation when these nanoparticles were suspended in standard synthetic freshwater. Moreover, the LC₅₀ values for Ag–Au bimetallic nanoparticles were found to be between that of Ag and Au but much closer to that of Ag. The bimetallic particles containing 80% Ag and 20% Au were found to have a significantly lower toxicity to Daphnia (LC₅₀ of 15 μg/L) compared to Ag nanoparticles, while the toxicity of the nanoparticles containing 20% Ag and 80% Au was greater than expected at 12 μg/L. The comparison results confirm that Ag nanoparticles were much more toxic than Au nanoparticles, and that the introduction of gold into silver nanoparticles may lower their environmental impact by lowering the amount of Ag which is bioavailable.     

Synthesis and characterization of Sibunit-supported Pd–Ga,Pd–Zn,and Pd–Ag catalysts for liquid-phase acetylene hydrogenation

Pd/Sibunit and Pd–M/Sibunit (M = Ga, Zn, or Ag) catalysts have been synthesized, and their catalytic properties in liquid-phase acetylene hydrogenation have been investigated. Doping of the palladium catalyst with a metal M leads to the formation of the Pd₂Ga, PdZn, or Pd_0.46Ag_0.54 bimetallic compound. The bimetallic particles are much smaller (1.6–2.0 nm) than the monometallic palladium particles (4.0 nm). Doping with zinc raises the ethylene selectivity by 25% without affecting the activity of the catalyst. Specific features of the effect of each of the dopants on palladium are reported.     

The Influence of Ag and Ag(In) Alloy on Y–Ba–Cu–O Equilibrium Diagram Around the Y-123 Superconducting Phase

We studied the chemical compatibility of Ag, Ag(In)alloy, Y₂BaCuO₅ (the so-called Y-211 green phase) and YBa₂Cu₃O_7–δ (Y-123) phase in order to check if better grain growth and alignment with minimum contamination were possible during the Y-123melt texturing. We demonstrate that the addition of silver to Y-123 always led to an enhanced texture. The typical microstructure of the composite Y-123 plus Y-211 (that is believed essential for high critical currents in these High Tc superconductors) was not disturbed by addition of silver up to 7.5 wt%, while higher concentrations of metal led to a degradation of the texture. DTA–TG analysis was used to investigate the influence of Ag and Ag(In) alloy on the Y–Ba–Cu–O equilibria around the Y-123 phase. We found a very unexpected thermal behaviour, similar to an eutectic equilibrium, when the silver concentration was increased to35 wt%. We believe that this effect was essentially due to the increasingly higher concentration of silver that could react with the secondary phases present in the melt. This revised version was published online in July 2006 with corrections to the Cover Date.     

Theoretical Study on the Structures and Thermal Properties of Ag–Pt–Ni Trimetallic Clusters

The structures and thermal properties of Ag–Pt–Ni ternary nanoclusters varying with different compositions and sizes are studied by Monte Carlo and molecular dynamics simulations. It can be found that silver atoms tend to occupy the surface and platinum atoms favor the subsurface occupation, whereas the inner is occupied by nickel atoms due to the different surface energies and lattice parameters. In addition, there is a non-monotonous relationship between the melting points and compositions of Ag–Pt–Ni ternary nanoclusters according to molecular dynamics simulations. In addition, a linear decrease in melting point with \(N^{ - 1/3}\) is found for both monometallic and trimetallic clusters. This behavior is consistent with Pawlow’s law.     

Study and 3D modeling of the phase diagram of the Ag–Ge–Se system

In view of the contradictoriness of the literature data, phase equilibria in the Ag–Ge–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and an isothermal section at room temperature of the phase diagram were constructed, and so was the projection of the liquidus surface. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was shown that, in the system, a single ternary compound, Ag₈GeSe₆, forms, which undergoes congruent melting at 1175 K and a polymorphic transformation at 321 K. The formation of the compounds Ag₂GeSe₃ and Ag₈GeSe₅, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

SERS of 7-azaindole adsorbed on Ag doped sol–gel film and Ag sol: a comparative investigation

Surface enhanced Raman scattering (SERS) studies have been undertaken on Ag doped sol–gel derived film with 7-azaindole (7-AI) used as the reference compound. The enhancement factor in the film is comparable with the result of the chloride aggregated silver citrate sol. Along with the spectral observation and assignments of the frequencies, the significance of colloidal sol–gel film in which the size of the metal is in the dimensions of nanometers have been discussed.     

Crystal structure of natural Ag–Cu–Pb–Bi sulfide

The crystal structure of a natural sulfide Cu_3,44Ag_0,56Pb₂Bi₆S₁₃ (Сmcm, Z = 4, a = 3.973(1) Å, b = 13.370(2) Å, c = 42.182(7) Å, R = 0.059) is determined. The structure has seven cation positions: two of them (Cu and Ag) are in a tetrahedral environment of sulfur atoms; one (Pb), in a special position (mm2), has a coordination polyhedron in the form of a bicapped trigonal prism; and the other cation positions are surrounded by sulfur atoms forming distorted octahedra. The mirror symmetry plane perpendicular to the c translation causes microtwinning by cutting a layer of trigonal prisms framed by tetrahedron ribbons. These layers are divided by those composed by edge-linked octahedra with a diagonal ribbon of five octahedra (N = 5). The cation and anion positions are ordered by individual sublattices with pseudohexagonal subcells on the m planes perpendicular to the a translation, which concentrate the positions of all the atoms. Supposedly, this natural sulfide is the previously described (1885) yet unconfirmed alaskaite mineral from the lillianite–heyrovskyite homological series and may be isostructural to the ourayite mineral.     

Temperature and Oxygen Partial Pressure Dependences of the Surface Tension of Liquid Sn–Ag and Sn–Cu Lead-free Solder Alloys

Summary. Temperature dependence of the surface tension of liquid Sn–Ag and Sn–Cu base lead-free solder alloys and oxygen partial pressure dependence of liquid Sn–Ag alloy were evaluated using the experimental data obtained, respectively, by the constrained drop method and the sessile drop method in the previous studies [1, 2]. The temperature dependences of the surface tension have maximum positive values when the mol fraction of Ag and Cu is about 0.7, while those for pure liquid Sn, Ag, and Cu have negative values. The calculated values based on Butler’s equations were found to be in reasonable agreement with those of the experimental data. The oxygen partial pressure dependences of the surface tension of liquid Sn–Ag alloys at 1253 K have a minimum value when the mol fraction of Ag is about 0.9 and the oxygen partial pressure is less than about 10⁻¹³ atm. From this, it is considered that the oxygen adsorption increased by adding Ag to Sn when the mol fraction of Ag is less than 0.9.     

Thermal and Microstructural Analysis of the Y–Ba–Cu–O/Ag Equilibrium Around the Critical Composition YBa2Cu3Ox/Ag 35 mass%

We studied the Y–Ba–Cu–O/Ag equilibrium diagram in oxygen atmosphere around the composition YBa₂Cu₃O_x/Ag35 mass%. We found a high thermal effect: the peritectic decomposition temperature of Y-123 phase is lowered from 1040 to 940°C. We demonstrate here that the nature of the phenomenon is not chemical. We explained it as the result of a mechanical segregation of Y-123 decomposition products from Y-123 phase, performed by silver. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solid-Phase Surface Adsorption in Ag–Au|F–, H2O and Ag–Au|ClO–4, H2O Systems: Allowing for the Solid-Solution Nonideality

Integral and differential (with respect to the composition) isotherms of changes in the interfacial free energy (_m– ), the charge density q, and the surface composition X _Au of alloys equilibrated with an aqueous surface-inactive electrolyte are obtained in terms of a finite-thickness interfacial layer, with use of concentration dependences of activity coefficients of components of a polycrystalline binary alloy. Using ac measurements of the double-layer parameters, it is stated that the surface-active component in the Ag–Au|F^–, H₂O and Ag–Au|ClO^– ₄, H₂O systems at 298 K is gold. The Ag–Au solid solution shows negative deviations from Raoult's law, except for the compositions X _Au 0.04 and X _Au 0.80, where the solid solution properties approach those of an ideal solution.     

Experimental Study and 3D Modeling of the Phase Diagram of the Ag–Sn–Se System

In connection with the contradictoriness of literature data, phase equilibria in the Ag–Sn–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and the isothermal section at room temperature of the phase diagram were constructed, and a projection of the liquidus surface was built. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was demonstrated that, in the system, two ternary compounds, Ag₈SnSe₆ and Ag_xSn_{2 – x}Se₂ (0.84 < x < 1.06), form. The former melts congruently at 1015 K and undergoes a polymorphic transformation at 355 K, and the latter melts with decomposition by a peritectic reaction at 860 K. The formation of the compound Ag₂SnSe₃, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a limited number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

First Principles Calculations Toward Understanding SERS of 2,2′-Bipyridyl Adsorbed on Au,Ag, and Au–Ag Nanoalloy

First principles electrodyanmics and quantum chemical simulations are performed to gain insights into the underlying mechanisms of the surface enhanced Raman spectra of 22BPY adsorbed on pure Au and Ag as well as on Au–Ag alloy nanodiscs. Experimental SERS spectra from Au and Ag nanodiscs show similar peaks, whereas those from Au–Ag alloy reveal new spectral features. The physical enhancement factors due to surface nano-texture were considered by numerical FDTD simulations of light intensity distribution for the nano-textured Au, Ag, and Au–Ag alloy and compared with experimental results. For the chemical insights of the enhancement, the DFT calculations with the dispersion interaction were performed using Au₂₀, Ag₂₀, and Au₁₀Ag₁₀ clusters of a pyramidal structure for SERS modeling. Binding of 22BPY to the clusters was simulated by considering possible arrangements of vertex and planar physical as well as chemical adsorption models. The DFT results indicate that 22BPY prefers a coplanar adsorption on a (111) face with trans-conformation having close energy difference to cis-conformation. Binding to pure Au cluster is stronger than to pure Ag or Au–Ag alloy clusters and adsorption onto the alloy surface can deform the surface. The computed Raman spectra are compared with experimental data and assignments for pure Au and Ag models are well matching, indicating the need of dispersion interaction to reproduce strong Raman signal at around 800 cm^–1. This work provides insight into 3D character of SERS on nanorough surfaces due to different binding energies and bond length of nanoalloys. © 2018 Wiley Periodicals, Inc.