Silver surface diffusion

GP 2[ [R 3a[The sputtered silver on aluminum alloy (AlMg3) platelets, machined by thin-wire pEDM, were smooth and dense. On prolonged operation under reaction conditions, small silver particles are generated by surface diffusion so that also the blank aluminum platelet surface is exposed (20 vol.-% ethylene, 80 vol.-% oxygen 3 bar 0.23-2 s 250 °C) [43]. 

They measured the zero potential point of the system, which depends on the halide concentration and type as described by the equations above. They were able to measure the effect of diffusion of species to the electrode and were able to determine a mixed potential of the electrode where the forward transfer of electrons from the silver was equal to the rate of reduction of the oxidant. This is shown diagram-matically in Figure 31. Nickel et al. found that the adsorption of halide to the silver surface did not influence the potential if the halide layer was less than 5 pm thick, but they did note that at a clean silver surface the silver halide formation began at a higher potential than expected, which they attributed to the high solubility of microscopic silver on the surface. 

With this value and. Isd < 8 nm, the propagation rate constant can be calculated from eq. (2.38) to be kv < 18 x 10 cm s V which is about 60 times as low as the experimental value of 1.0 cm s V The obvious conclusion is that surface diffusion plays a subordinate role in the electrochemical deposition of silver, in any case less than 1% [5.24, 5.30]. 

Ignatiev that Li diffuses into graphite even at liquid nitrogen temperature to leave only a submonolayer of Li on the surface. Diffusion of other alkali metals (Na, K, and Rb) into silver has also been observed by Lambert and co-workers but is significant only at high temperatures (> 870 K). Li diffuses more readily because of its small size. The atomic radii for Li, Na, K, Rb and Cs are 1.55, 1.90, 2.35, 2.48 and 2.67 A respectively. 

Calculations have shed light on the mechanism of formation of silver particles by the action of light on silver halide. We find that surface defect sites present a particularly favorable trapping level for electrons. After this trapping step, silver ions diffuse to the electron, forming a deeper trap for additional electrons. 

A similar reanalysis of the work of Rhead on silver gave results that were just as striking. Interpretation of thermal grooving data as the result of surface diffusion yielded a of 55,500 compared to reference values of 12,000 for other methods of measuring surface diffusion was 10 ... 

The value of a, which is in accordance with those expected from growth models including surface diffiision [8], confirms previous conclusions about the electrodissolution mechanism of silver in acid aqueous solutions derived from electrochemical kinetic data, in which a relevant role was played by the surface diffusion of silver atoms at low overpotential. 

The elementary steps of the silver halide photographic process are discussed in reference [127]. The surface diffusion rates of silver atoms on a single silver crystal surface were found to increase by orders of magnitude in the presence of chemisorbed sulfur. Could sulfur-induced sensitization of the photographic process be related to this observation ... 

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