Silver interface reactions with

G. Interface Reactions with Gold, Silver, and Palladium... 

The state-of-the-art mirror system now in use is a glass second-surface silver mirror backed with copper and paint, as shown in Fig. 2. For this system, the characterization and study of the glass/silver, silver/copper, and copper/paint interfaces before and after various stages of use are clearly required to understand the multilayer mirror stack. The methods of characterization outlined in Sec. 2.4 of Ref. 3, especially those of ISS, XPS, AES, and SIMS, are clearly applicable to this problem. In ter facial degradation reactions may begin at the silver/glass interface... 

The existence of a current hump near Tc is confirmed by several additional facts. In the first place, these are deduced from the results of the quantitative treatment of the impedance spectra of the HTSC/solid electrolyte system [147]. This approach consists of calculating from the experimental complex-plane impedance diagrams the parameters characterizing the solid electrolyte, the polarization resistance of the reaction with the participation of silver, and the double-layer capacitance (Cdi) for each rvalue (measured with an accuracy of up to 0.05°). Temperature dependence of the conductance and capacitance of the solid electrolyte (considered as control parameters) were found to be monotonic, while the similar dependences of two other parameters exhibited anomalies near Tc- The existence of a weakly pronounced minimum of Cji near Tc, which is of great interest in itself, was interpreted by the authors as the result of sharp reconstruction of the interface in the course of superconducting transition [145]. 

The decomposition of copper(II) squarate, as with the copper(II) carboxylates, proceeded to completion in two distinct rate processes with stepwise cation reduction [113]. The first step (nr < 0.5) fitted zero-order kinetics withii = 150 15 kJ mof between 530 and 590 K. The second step was approximately first-order with an increase in to 210 20 kJ mol and reaction temperature, 590 to 670 K. No reaction interface could be identified in scanning electron microscopic studies. Silver squarate decomposed [114] between 473 and 510 K without melting, by a predominantly deceleratory reaction with E = 190 8 kJ mol. ... 

We conclude that we are observing reaction at the polymer-silver interface that results in reflectance loss. This interface reaction could result from degradation of the bulk polymer or its additives, initiation at the polymer/mirror interface, or reaction with the ambient atmosphere. 

We have observed mirror failure due to physical delamination and chemical reaction (a) at the mlrror/backing interface apparently due to inadequate protection from the atmosphere by the backing and, (b) at the polymer/mirror Interface due to reaction with a light-sensitive antioxidant or possibly with the degrading polymer. For both silver and aluminum mirrors, interfacial reactions were only observed at the back surface of the mirror regardless of how the mirror was put down or assembled. 

The best bioelectric interfaces are combinations of metals and their metallic salts, usually chlorides. The metal salt is used as a coating on the base metal and acts as an intermediary in the electrode-electrolyte processes. Silver in combination with a chloride coating is the most widely used biopotential recording electrode. Silver chemically reacts in chloride-bearing fluids such as saline, skin sweat, and body fluids containing potassium and sodium chloride. After a few hours of immersion, a silver electrode will become coated with a thin layer of silver chlorides. This occurs by the spontaneous reaction ... 

Methanol oxidation on Ag polycrystalline films interfaced with YSZ at 500°C has been in investigated by Hong et al.52 The kinetic data in open and closed circuit conditions showed significant enhancement in the rate of C02 production under cathodic polarization of the silver catalyst-electrode. Similarly to CH3OH oxidation on Pt,50 the reaction exhibits electrophilic behavior for negative potentials. However, no enhancement of HCHO production rate was observed (Figure 8.48). The rate enhancement ratio of C02 production was up to 2.1, while the faradaic efficiencies for the reaction products defined from... 

In topochemical reactions all steps, including that of nucleation of the new phase, occur exclusively at the interface between two solid phases, one being the reactant and the other the product. As the reaction proceeds, this interface gradually advances in the direction of the reactant. In electrochemical systems, topochemical reactions are possible only when the reactant or product is porous enough to enable access of reacting species from the solution to each reaction site. The number of examples electrochemical reactions known to follow a truly topochemical mechanism is very limited. One of these examples are the reactions occurring at the silver (positive) electrode of silver-zinc storage batteries (with alkaline electrolyte) ... 

Despite the fact that the electrodeposition of copper and silver at the water-DCE and the water-dichloromethane interfaces has been generally regarded as the first experimental evidence for heterogeneous ET at externally biased ITIES [171], a very limited amount of work has dealt with this type of process. This reaction has also theoretical interest because the molecular liquid-liquid interface can be seen as an ideal substrate for electrochemical nucleation studies due to the weak interactions between the interface and the newly formed phase and the lack of preferential nucleation sites always present at metallic electrodes. 

The essential difference between the hydroxylamine reaction and the hydrazine reaction appears to be that silver nuclei are formed in the solution much more readily by hydrazine than by hydroxylamine. At sufficiently low pH and in the absence of copper, hydroxylamine does not readily form nuclei in the solution, and the catalytic reduction of the silver chloride occurs essentially at a solid interface with the silver nuclei. Hydrazine, on the other hand, readily forms nuclei in the solution and an important fraction of the total reaction involves the catalytic reduction of dissolved silver chloride. This would account for the well-known photographic properties of the two agents. Hydroxylamine is a cleanworking developer which, under proper conditions, yields little fog. Hydrazine shows much less selectivity and, although it develops an image, it also yields a relatively high fog density. 

Under the usual conditions of commercial practice, the development reaction does not occur entirely at the silver/silver halide interface. Some reduction of silver ions from solution takes place. Such reduction presumably can occur at any point on the silver/solution interface, and the mechanism should be the same as that for post-fixation physical development. The relative extent of the physical development in comparison with that at the silver/silver halide interface will depend upon the silver halide solvent action of the developing solution and upon the rate of the direct development. 

Experiments illustrating these various possible reactions have been carried out notably by Reinders (Z it. Roll. Ghem. xiii, 235, 1913) and by Hofmann (Zeit. Phys. Ghem. Lxxxiii. 385,. 1913). Finely divided calcium sulphate is preferentially wetted by water in the presence of liquids, such as chloroform and benzene which are frequently termed non-polar or slightly polar. Silver iodide suspensions in water will go into the dineric interface in contact with ether, chloroform and benzene, but are removed from the water by preferential wetting in the case of butyl and amyl alcohols, whilst the reverse holds true in the case of aqueous suspensions of arsenious sulphide. 

The procedure to fabricate colloidal silver, (Ag°) , spherical nanoparticles is similar to that already described (see Section 9.3.3) The Cu( AOT)2 is replaced by the silver derivative. The relative concentration of Na(AOT), Ag(AOT)2, and the reducing agent remain the same. Control of the particle size is obtained from 2 nm to 6 nm (67). To stabilize the particles and to prevent their growth, 1 p.l/mL of pure dodecanethiol is added to the reverse micellar system containing the particles. This induces a selective reaction at the interface, with covalent attachment, between thio derivatives and silver atoms (68). The micellar solution is evaporated at 60°C, and a solid mixture of dodecanethiol-coated nanoparticles and surfactant is obtained. To remove the AOT and excess dodecanethiol surfactant, a large amount of ethanol is added and the particles are dried and dispersed in heptane. A slight size selection occurs, and the size distribution drops from 43% to 37%. The size distribution is reduced through the size selected precipitation (SSP) technique (38). 

The application of surface-enhanced Raman spectroscopy (SERS) for monitoring redox and other processes at metal-solution interfaces is illustrated by means of some recent results obtained in our laboratory. The detection of adsorbed species present at outer- as well as inner-sphere reaction sites is noted. The influence of surface interaction effects on the SER spectra of adsorbed redox couples is discussed with a view towards utilizing the frequency-potential dependence of oxidation-state sensitive vibrational modes as a criterion of reactant-surface electronic coupling effects. Illustrative data are presented for Ru(NH3)63+/2+ adsorbed electrostatically to chloride-coated silver, and Fe(CN)63 /" bound to gold electrodes the latter couple appears to be valence delocalized under some conditions. The use of coupled SERS-rotating disk voltammetry measurements to examine the kinetics and mechanisms of irreversible and multistep electrochemical reactions is also discussed. Examples given are the outer- and inner-sphere one-electron reductions of Co(III) and Cr(III) complexes at silver, and the oxidation of carbon monoxide and iodide at gold electrodes. 

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