THE INFLUENCE OF DICHROMATE AND CERIUM PASSIVATION TREATMENTS ON THE DISSOLUTION OF SN ZN COATINGS/

The electrochemical behaviour of an 80Sn-20Zn electro-deposited alloy following passivation in a dichromate solution and a cerium-containing solution, was studied. It was found that both the dichromate and ceri um passivation procedures lead to an increase in the corrosion protect ion afforded by the 80Sn-20Zn electrodeposit. This was attributed to a reduction in the rate of the zinc dissolution reaction from the elect ro-deposit which in turn extended the cathodic protection periods of t he deposit. Passivation of the electro-deposited alloy in the cerium-c ontaining solution lead to the precipitation of cerium oxides/hydroxid es in a non-uniform manner over the surface. This precipitated film of cerium had the appearance of a cracked-mud layer. Nevertheless, the a dditional corrosion protection afforded by the cerium passivation trea tment was equivalent to that provided by the dichromate passivation tr eatment. (C) 1997 Elsevier Science Ltd.