Corrosion protection of galvanized steel pipe in acidic media by surface amalgamation

AbstractA procedure for corrosion protection of galvanized steel in slightly acidic media has been proposed, based on surface amalgamation by contact with Hg2+ solutions. The treatment procedure and the changes it effects in the morphology of the Fe–Zn alloyed layers of galvanized coatings are described. The amalgamated layer reaches a thickness of 75 μm and includes the η and ζ layers, penetration into the ζ layer being by grain boundary diffusion. A reduction in the corrosion rate of surface amalgamated galvanized pipe in contact with slightly acidic media, ranging from ten fold at pH 4–6 to one hundred fold at pH <4, is due to cathodic control resulting from the high overvoltage for hydrogen discharge on Zn–Hg alloys.