De-alloying at elevated temperatures and at 298 k-similarities and differences

When a component is selectively removed from an alloy at elevated temperature, the surface often becomes unstable, and corrosion rates are high. This is in accord with a constant and relatively short interdiffusion distance in the alloy which is on the order of the spacing between neighboring penetrations. For volatile reaction products, surface roughening produces a porous alloy network which is enriched in the more noble component(s). The porous structure is interconnecting and open to the gas phase. Wagner's geometrical consideration appears to be important for the onset of the surface instability and the development of the porous layer. Pore size and pore-to-pore spacing decrease with temperature. The temperature dependence extends down to 298 K based on data for other alloys corroded in aqueous electrolytes. Other similarities, as well as differences, with selective corrosion processes at ambient temperatures are discussed based on data obtained over a broad range of temperature.