Corrosion of Homogeneous Alloys

Concerning ambient-temperature corrosion of solid alloys, a preliminary note in Chap. 3 on thermodynamics was that bulk/surface equilibria of alloy components cannot normally be expected, because solid-state diffusion usually is too slow to counteract selective dissolution rates of components. The situation is different for liquid amalgams, as they can be mechanically stirred. Also, liquid amalgam surfaces are uniform down to atomic distances. For solid alloys, slow bulk-to-surface diffusion usually will instead leave the surface depleted with respect to ‘fast’ components, and enriched with respect to ‘slow’ components, and the result is an overall decrease in corrosion rate. The crystallografic structure of solid surfaces suggests that the main effect is blocking of kink sites active in metal dissolution, and this supposition will further below be seen to account for what may be described as fine-tuning of concepts, which we do not, however, immediately need to approach.