Zinc-coated (galvanized) steel has been used successfully in applications in which bare (or painted, ungalvanized) steel would suffer corrosive attack. In general, galvanic coupling to zinc, as either an anode or a coating, is an effective means for combatting steel corrosion. Because of this, the use of galvanized steel has increased markedly, stimulated primarily by automobile manufacturers seeking to extend the corrosion warranties on automobiles.1
Although effective, zinc coatings are not without a number of drawbacks that warrant efforts to improve them. For example, because of the widely differing electrode potentials between zinc and steel (–1.05 and –0.69 VSCE, respectively, in air-saturated NaCl solutions), the zinc corrodes at a rapid rate to protect the steel. This is reflected in the limited lifetimes of galvanized unpainted siding. The basic electrochemistry controlling the situation is shown in Figure 1 for a system controlled by oxygen reduction. The zinc sacrificially...
