Mixed Ag Research Articles

Chemisorption Effects on Colloidal Lead Nanoparticles

A stable aqueous lead sol (10 nm particles) is formed upon the γ-irradiation of Pb(ClO4)2 in the presence of (poly)ethyleneimine. Lead nanoparticles have an absorption band at 218 nm with e = 3.2 × 104 M-1 cm-1; the band appears at the wavelength that is expected for a surface plasmon oscillation. The changes in the shape of the absorption band, which occur upon the interaction of the nanoparticles with various solutes, are described and interpreted. Oxygen, nitrous oxide, carbon tetrachloride, and chloroform oxidize colloidal lead particles to Pb2+. Carbon disulfide oxidizes only surface lead atoms to yield a layer of PbS precursor. The oxidation of lead particles by the ions of noble metals is investigated for Ag+ and Cu2+. Silver ions oxidize lead nanoparticles incompletely, which is explained by the formation of mixed Ag−Pb structures. Cu2+ ions also do not completely oxidize lead particles, although Cu particles with a low Pb content can be obtained.

Improvement of morphological stability of Ag thin film on a TiN layer with a thin interposing metal layer

The morphological stability of Ag thin film on a TiN layer with a thin interposing metal layer has been investigated. Due to the formation of Ag spikes at the Ag/Si interface, a diffusion barrier is needed to buffer the interdiffusion of Ag with Si. TiN films deposited by physical vapor deposition (PVD) or metalorganic chemical vapor deposition (MOCVD) were used. A Au or Ti (∼3 nm) layer was used as the glue layer between Ag and TiN. In a Ag/Au/TiN system, a mixed Ag–Au layer is stable on PVD-TiN at temperatures as high as 450 °C. In Ag/Ti/TiN systems, the thermal stability of Ag on CVD-TiN is superior to that on PVD-TiN. Ag layers were found to be discontinuous after annealing at 300 and 350 °C on PVD-TiN and CVD-TiN systems, respectively.

Alternating magnetic field losses in high- Tc superconducting multifilament tapes with a mixed matrix of Ag and BaZrO 3

Alternating magnetic field losses for the new (Bi, Pb) 2Sr 2Ca 2Cu 3O 10 multifilament tapes with a mixed Ag–BaZrO 3 matrix for coupling loss reduction have been measured at 77 K and at frequencies up to 100 Hz. Due to the presence of oxide barriers around the filaments, the effective transverse electrical resistivity in the matrix is increased by a factor of eight, with a corresponding modification of the frequency dependence of the coupling losses. This result is a very promising step in the development of low loss high- T c superconductors for 50 Hz applications. For larger Δ B values, it seems feasible to reduce the coupling losses at 50 Hz to a tolerable level by both, applying high-resistive barriers and changing the conductor dimensions, away from the extremely flat tape geometry. A saturation loss criterion is derived for twisted flat multifilament tapes.

Seasonal dynamics of colored dissolved material in the Sargasso Sea

Observations from the Sargasso Sea have shown that the light attenuation spectrum is a function of both phytoplankton pigments and a detrital-like component that varies independently. Here we examine the nature and dynamics of these detrital-like variations by analyzing a time-depth series of visible and ultraviolet light absorption spectra for colored (chromophoric) dissolved materials [CDOM; ag(λ)] and detrital particulates [ad(λ)] collected at the US JGOFS Bermuda Atlantic time-series study (BATS) site. At 440nm, CDOM absorption, ag(440), made up of on an average more than one-half of the total non-water absorption coefficient, while detrital particulate absorption, ad(440), was generally a minor constituent. The vertically integrated stock of CDOM (0–140m) increased from the beginning of spring until the end of summer in 1994 and 1995, although near-surface values (⩽40m) were strongly depressed near the surface at the peak of summer. This summertime reduction of the mixed layer ag(λ) is likely due to photooxidation of CDOM to optically inactive forms. Further, values of CDOM absorption were unrelated directly to indices of total water column dissolved organic carbon (DOC) stocks measured at BATS. We hypothesize that CDOM is produced as a by-product of the microbial breakdown of DOC and is destroyed due to photooxidation. Summertime CDOM dynamics at this site can be quantified with these two processes, as mixing below the summertime mixed layer can be assumed to be small. Our results imply, for the first time in the blue ocean, a link between microbial community activity and CDOM dynamics and clearly provide an explanation for the nature of non-chlorophyll light attenuation observed in the Sargasso Sea.

Synthesis, identification and thermal analysis of coprecipitates of silver-(cobalt, nickel, copper and zinc) oxalate

The coprecipitates Ag 2M(C 2O 4) 2 · nH 2O (M  CO 2+, Nit 2+, Cue 2+ or Zn 2+) have been prepared and identified by means of IR, elemental analysis, XRD, SEM and (DTA/TGA). The XRD and SEM data indicate that, the coprecipitates are solid solutions. The thermal decomposition of the compounds in dynamic air and N 2 flow has been studied. It is established that, the atmosphere plays a significant role upon the nature of decomposition as well as the type of thermoproducts and their thermal stability. The present study gives also an idea about the nature of interaction of the water of crystallization. The mixed oxide obtained from the thermal decomposition of Ag 2Ni(C 2O 4) 2 · 2H 20 in air and N 2 has been investigated. The XRD and SEM results suggest the formation of a mixed lattice oxide Ag 2NiO 2.

An investigation of superionic conduction in the mixed system Ag 1 − xCu xI-Ag 2O-P 2O 5 (0.05 ≤ x ≤ 0.25)

This work deals with the preparation and characterization of different compositions in the mixed system 80% (Ag 1 − x Cu x I)-20% (2Ag 2O · P 2O 5) (0.05 ≤ x≤ 0.25). Solid samples were synthesized by quenching the appropriate molten mixtures and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), complex impedance and transport number techniques. The XRD data have indicated the formation of glassy phases mixed with AgI or other polycrystalline phases. From the DSC measurements it is clear that a glass transition temperature around 327 K is exhibited by these specimens. The complex impedance studies carried out in the frequency range 65.5 kHz −1 Hz and transport number analysis suggest that the best conducting composition, namely 80% (Ag 0.9Cu 0.1I)-20% (2Ag 2O · P 2O 2), would possess a silver ionic conductivity of 8.64 × 10 −3 S cm −1 at room temperature.

Thermopower of an asymmetric cell, Ag¦AgI¦Ag 2S, involving a mixed conductor Ag 2S as an information transmitter

We have examined both theoretically and experimentally the thermopower of an asymmetric thermocell, Ag¦α-AgI¦Ag 2S, which involves a mixed conductor (Ag 2S) as a possible electrode for the system of an electrolyte with common ions (AgI). It has been found that the mixed conductor probe allows one to measure the thermopower of the electrolyte under the Soret equilibrium condition which would be impossible to realize in a symmetric thermocell, Ag ¦ α-AgI ¦ Ag. Upon comparison of the stationary state thermopowers from the symmetric and asymmetric cells, the transported entropy of Ag in Agi turns out to be equal to the standard entropy of metallic Ag.

Ion-beam-activated processes on the surfaces of solids

The paper presents an overview of results concerning phenomena related to ion-beam-activated deposition of thin films in the case when the amount of replenished impurities is larger than the amount of sputtered atoms. Metallic films were sputter-deposited on silicon during simultaneous He +, Ne +, Ar + high-energy (50–175 keV) irradiation. It is shown that high-energy ion-activated oxygen adsorption at the silicon-silver interface from residual gases depends on ion mass, energy and ion flux density. The critical value of electronic energy deposition rate (1.2 × 10 21 eV cm −3 s −1) when oxygen removal prevails on the ion-activated adsorption was found to be common for all ions studied. A phenomenological model describing ion-activated oxygen adsorption is proposed. The trim calculations and ion-induced integral stress measurements in silicon substrate were used to explain formation of the silicon-enriched region in the mixed Ag Si layer.

A POTENTIOMETRIC STUDY OF THE COMPLEXATION OF ALIPHATIC ACYCLIC MONOAMINES WITH Ag(I) IN 1 M NITRATE

Abstract Complexation of 12 aliphatic monoamines with Ag(I) has been studied in 1M KNO3 at 25°C using a potentiometric titration technique, performing pH and pAg measurements. To study these ternary systems, the binary systems (Ag-OH, L-H, H-OH) were first investigated. The model used for background Ag(I) hydrolysis is consistent with the literature. Graphical techniques were used for the calculation of formation constants of silver-amine complexes. The estimates were further refined using the Superquad program. Evidence has been found for the formation of mixed Ag(I)-hydroxo ligand complexes only with aliphatic primary monoamines.

Frequency response analysis of the fast ion conducting system cuprous iodide — Silver chromate

Preparation and characterization of new superionic conductors have been considered to be an essential component in the area of solid state ionics. The details of frequency response analysis carried out in terms of impedance (Z), conductivity (σ) and modulus (M) diagrams on a series of compositions in the mixed system CuIAg 2CrO 4 exhibiting Ag + ionic conductivity over the temperature range 290–400 K and in the frequency range 65.5 kHz–1Hz are presented in this paper. The frequency - dependent conductivity spectra have been found to obey the Jonscher's power law over the temperature range under investigation. The observed temperature dependence of conductivity has indicated that a low activation energy is associated with the composition possessing high conductivity and vice versa. The separation of grain - boundary and electrode polarisations from the bulk impedances has been made feasible through the impedance spectra. A long tail in the low-frequency region and a tendency to peak at higher frequencies in the modulus diagram have shown that it is possible to effectively suppress the information concerning grain-boundary and electrode effects in the modulus formalism. Modulus and impedance spectra have indicated the non-Debye type of polarisation in the above material.

Impedance and modulus spectroscopic studies on the fast ion conducting system CuIAg 2MoO 4

This paper deals with a detailed analysis of impedance ( z) and conductivity (σ) spectra, as well as modulus ( M) diagrams of the mixed system CuIAg 2MoO 4, exhibiting Ag + ionic conductivity over the temperature range 290–400 K and in the frequency range, 65.5 kHz-1 Hz. The observed conductivity spectra could be attributed to Jonscher's power law dependence. Impedance spectra have enabled the separation of bulk properties from electrode effects. The modulus spectra have exhibited a long tail pattern in the low frequency region and a tendency to peak at higher frequencies thereby suppressing the electrode effects at low frequencies in the modulus formalism. A comparative study of modulus spectra and the impedance patterns has indicated the non-Debye type of frequency dispersion in the mixed system.

Initial growth of silver on Ge(111) studied by scanning tunneling microscopy.

Scanning tunneling microscopy (STM) has been used to study the Ge(111) surface after submonolayer depositions of Ag. At the lowest coverages a (4\ifmmode\times\else\texttimes\fi{}4) reconstruction, with small insets of a (3\ifmmode\times\else\texttimes\fi{}1) edge structure, is observed. Based on the STM images we propose a mixed Ag and Ge adatom structure for the (4\ifmmode\times\else\texttimes\fi{}4) reconstruction, in which the adatoms have local (1\ifmmode\times\else\texttimes\fi{}1) and (2\ifmmode\times\else\texttimes\fi{}2) arrangements corresponding to a Ag coverage of 6/16 monolayers. The (3\ifmmode\times\else\texttimes\fi{}1) structure appears to have a configuration similar to the Si(111)/Ag-(3\ifmmode\times\else\texttimes\fi{}1) reconstruction, although in this case it has a much more limited extension, restricted to a few unit cells in the near vicinity of step edges and phase boundaries. At higher coverages, after the completion of a full (4\ifmmode\times\else\texttimes\fi{}4)/(3\ifmmode\times\else\texttimes\fi{}1) surface, a (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} structure appears showing STM images similar to those previously published for the Si(111)/Ag system.

Hot-grotto therapy : ST. Germano in Agnano - Naples, Italy

Composition–activity relationships are important when developing synergistic properties in multimetallic nanoparticles in catalytic reactions. This paper reports findings regarding correlations between catalytic activities and bimetallic compositions of carbon electrode-supported AuAg nanoparticles in the electrocatalytic oxidation of glucose in alkaline solutions. Electrocatalytic activities were characterized using voltammetric and electrolytic techniques, and were also compared with those obtained with gold and silver nanoparticle catalysts under the same conditions. Results from cyclic voltammograms at bimetallic AumAg100−m (m: at%) nanoparticle modified-electrodes in H2SO4 solutions suggested that synthesized Au82Ag18 and Au73Ag27 nanoparticles were composed by atomically mixed Ag and Au atoms, and not composed of Ag and Au metal domains, in other words, they were homogeneous. On the other hand, Au40Ag60 and Au17Ag83 nanoparticles were heterogeneous, composed of Ag and Au metal domains. Homogeneously bimetallic AumAg100−m nanoparticles showed improvements in electrocatalytic activity for glucose, and heterogeneous bimetallic nanoparticles did not show any improvements. The electrolytic product was strongly dependant on the composition ratio of Ag, regardless of whether nanoparticles were homogeneous or heterogeneous. AumAg100−m (100 − m = ca. 30) nanoparticles showed synergistic catalytic activities with both characteristic properties of Aunano and Agnano nanoparticles.

Superconducting fluctuation effects at a silver-germanium interface.

Structures consisting of various layers of Ag and Ge were fabricated in ultrahigh vacuum by quench condensation onto substrates held at liquid-helium temperatures. The electrical conductances of these structures measured ino situ exhibited incomplete superconducting transitions and superconducting fluctuation effects. It is suggested that these may be a consequence of phenomena occurring at a Ag-Ge interface, rather than properties of atomically mixed Ag and Ge.

Syntheses and some properties of binary fluorides of silver, copper and nickel

Thermally unstable highest-oxidation-state transition metal polymeric fluorides (e.g. AgF 3, NiF 4) are precipitated from anhydrous hydrogen fluoride (AHF) solutions of their salts by addition of fluoroacids (A) such as BF 3, PF 5 or AsF 5 [1]: MF x y− + yA → MF (x−y) + yAF −. Red, diamagnetic AgF 3 precipitated by AsF 5 from AHF solutions of AgF 4 − salts is reduced with excess of AsF 5 by following equation: AgF 3 + AsF 5 → AgFAsF 6 + 1/2F 2. While such reduction does not occur with BF 3 this acid is therefore preferred for the preparation of stoichiometric AgF 3. Silver trifluoride is thermodinamically unstable and loses F 2 in contact with AHF according to the equation: 3AgF 3 → Ag 3F 8 + 1/2F 2. The formation of Ag 3F 8 by the interaction of one mole of Ag(II) and two moles of Ag(III) confirmed that the material formed in the degradation of AgF 3 is a mixed valence material Ag(II)Ag(III) 2F 8. Interaction of AgF + with AuF 4 − (1:1) in AHF yields maroon Ag(II)Ag(III)F 5. Silver trifluoride is isostructural with AuF 3. Its powerful oxidizing properties are in accord with the tight binding of its valence shell d orbital electrons. CuF 6 3− salts interact quantitavely with liquid AHF already at −60° yielding bright red CuF 3: CuF 6 3− + 3xHF → CuF 3 + 3F(HF) x −. The oxidizing properties of above-mentioned fluorides will be discussed.

Glass formation and anomalous annealing effects in the mixed oxyanion system AgIAg 2SO 4Ag 2WO 4

The glass-forming region in the ternary mixed anion system AgIAg 2SO 4Ag 2SO 4Ag 2WO 4 has been delineated and the enthalpic manifestation of the glass transition has been examined. By selecting compositions along the tie-line 60AgI · (40 − x)Ag 2SO 4 · xAg 2WO 4 and varying x it was possible to study the effect of replacing the SO 4 2− ion by the larger WO 4 2− ion, at a fixed AgI content. The glass-to-liquid transition is found to evolve over an unusually wide range of temperature in the ternary glasses relative to the binary ones indicating that the mixing of anions of different sizes leads to a dramatic broadening of the spectrum of structural relaxation times. Consistent with this observation, the DSC scans of annealed ternary samples reveal prominent pre- T g endothermic peaks which have previously been seen only in polymer melts (such as pure PVC) known for highly non-exponential relaxation. Possible structural origins, and applications of the T g broadening phenomenon are discussed.

Electron-transfer processes with substituted group 5 metal carbonyls. Synthesis, crystal and molecular structure of Ag 3M 3(CO) 12(Me 2PCH 2CH 2PMe 2) 3, M = Nb, Ta, the first structurally characterized carbonyl derivatives of niobium(0) and tantalum(0)

Some new tetracarbonyl derivatives of tantalum(I), TaI(CO) 4LL (LL = tmeda, dppm, 2,2′-dipy), have been obtained by diiodine oxidation of [Ta(CO) 6] − in the presence of the bidentate ligand. Dicyclopentadienylcobalt(II) does not react with the tetracarbonyl dppe derivatives of niobium(I) and tantalum(I), MI(CO) 4dppe, whereas the corresponding pentamethyl substituted complex, CoCp 2 ★, carries out the two-electron transfer to form [CoCp 2 ★][M(CO) 4dppe]. Finally, oxidation of the [M(CO) 4dmpe] − anion, M = Nb, Ta, with the silver(I) salts AgNO 2 and AgBF 4 gave the hexanuclear mixed metal clusters Ag 3M 3(CO) 12(dmpe) 3, which were studied by X-ray diffraction methods. Crystals of Ag 3Nb 3(CO) 12(dmpe) 3 are rhombohedric, space group R 3 c, hexagonal setting, No. 167, a 14.323(1), c 44.772(4) Å, V 7954.6 Å 3, Z = 6, D calc 1.739 g cm −3, μ(Cu- K α) 162.93 cm −1, F(000) = 4068; R = 0.044. Crystals of the tantalum derivative are isotypic: a 14.274(5), c 44.55(3) Å, V 7860.6 Å 3, Z = 6, D calc 2.095 g cm −3, μ(Mo- K α) 78.82 cm −1, F(000) = 4644, R = 0.029. The coordination geometry around the group 5 metal may be described as a distorted square antiprism, the coordination sites being filled with the four carbonyl groups, the two silver atoms and the two phosphorous atoms of the bidentate ligand. The central core of the clusters is constituted by two almost regular interpenetrated equilateral triangles of silver and niobium (or tantalum) atoms. Both metal clusters react with dry hydrogen iodide giving silver metal and MI(CO) 4(dmpe).

Hexafluoro antimonates(V) of divalent metals, synthesis and properties

Solvolysis of metal(II) fluorosulfates in liquid antimony(V) fluoride according to:[Formula: see text]with M = Sn, Ni, Pd, Cu, or Ag, is found to be a clean, efficient route to the hexafluoro antimonates of the corresponding metals. Two of the compounds reported here display unusual features: Pd(SbF6)2 is, like its fluorosulfate precursor, paramagnetic with the Pd2+ ion in a 3A2g ground state, and an analysis of the ligand field spectrum is presented; Ag(SbF6)2 is, unlike a recently reported paramagnetic, blue, valence isomer, diamagnetic and nearly white in color. Formulation as a mixed valency compound Ag(I)Ag(III)(SbF6)4 is suggested. Low temperature magnetic susceptibility measurements (where appropriate), Raman, and IR data are reported. The hexafluoro antimonates of Ni, Pd, and Cu show antiferromagnetic exchange at very low temperatures. Pd(SbF6)2 shows very weak ferromagnetism below 10 K. Keywords: fluoroantimonates of divalent metals, synthesis and solvolysis in SbF5, vibrational spectra, magnetic susceptibility measurements.

Radioluminescence of silver halide optical fibers

The radioluminescence of mixed Ag halide optical fibers (AgClxBr1−x, where 0 < x < 1) is investigated in the range 20–200°C. The main feature in the emission spectrum of the Cl-rich fibers is a broad band centered at 520 nm, which behaves as exp(E/kT), with E ≈ 0.06 eV. It indicates a competition between nonradiative processes and radiative recombinations of electrons with self-trapped holes. In the Br-rich samples the emission is mainly in the 600–700-nm range and is ascribed to holes trapped at Ag vacancies near divalent and trivalent cationic impurities. An intense new band in the infrared appears in some of the Cl-rich fibers and in all the Br-rich fibers following annealing at 250°C. It is ascribed to the migration of cationic impurities, or of the Ag vacancies that charge compensate them, and to the formation of new complex point defects.

Stability constants for aqueous silver/bromide/thiocyanate complexes

Stability constants for aqueous Ag +/Br −, Ag +/SCN −, and mixed Ag +/Br −/SCN − complexes are determined at 25° C by using data generated potentiometrically in solutions having ionic strengths of 0.4, 1.0, and 2.0 m. Monte Carlo numerical methods which yield apparent stability constants for these complexes as well as confidence limits are described in detail. Explicit consideration of speciation shows that under useful precipitation conditions (high bromide and low thiocyanate), a significant fraction of soluble silver is present as AgBr n (SCN) 1− n− m m complexes. The most prevalent mixed complexes under these conditions are AgBr (SCN) − (log β 11=8.0 ± 0.5) and AgBr 2(SCN) 2− (log β 21=9.2 ± 0.3). The free energies of formation of the other tri- and tetra-coordinate mixed complexes are nearly indistinguishable (log β 12=9.3 ± 0.5; log β 31=9.0 ± 0.6; log β 22=9.6 ± 0.9; log β 13=10.3 ±0.5).