Molybdate based passivation of zinc

In order to reduce corrosion rates, zinc plated parts are usually chromated. Recently chromates have caused increasingly environmental concern, for both allergic effects among workers touching chro-mated parts and toxic effects on fish, plants and bacteria. A molybdate based alternative has been developed to replace chromates in several passivation applica-tions. Depending on the environment in which the passivated parts are to be exposed, the protection that this alternative treatment provides range from less efficient to more efficient as compared to chromate. These aspects as well as issues such as; cost, stability, layer composition and test results from several different corrosion tests will be discussed.