THE METAL–SOLUTION SILVER ION EXCHANGE

Abstract

The exchange of silver ions between silver nitrate solutions and surfaces of metallic silver was studied, using radioactive silver (Ag110, 270 day half-life) as a tracer. Marked differences in behavior of surfaces prepared in different ways were observed. Crystalline (annealed and etched) surfaces exchanged rapidly to a depth of a few atomic layers, and about 80% of the acquired radioactivity was removed as quickly by exchange with inactive silver nitrate solution. Highly polished surfaces exchanged up to ten times as great an extent as the etched annealed surfaces, but required 40 hours' immersion to attain their maximum activity. The deactivation of polished surfaces by inactive solutions was inversely proportional to the period of immersion in active solution, with surfaces immersed for 17 hr. or more retaining all but 30% of their acquired activity. Abraded surfaces exchanged quickly and retained most of their activity, the extent of the exchange depending upon the ratio of “worked” to “unworked” material on the surface. Some evidence of comparatively rapid diffusion in the polish layers was obtained. The interior of cold-worked silver when exposed to the nitrate solution behaved similarly to abraded surfaces. Mechanisms for the behavior of these different types of surface are offered, and the data of other workers discussed.