The Study of Passivization on Galvanised Metal Sheet in Different Environments

Lee, Chee Kiat (2012) The Study of Passivization on Galvanised Metal Sheet in Different Environments. Final Year Project (Other), Tunku Abdul Rahman University College.

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Abstract

Hot-dip galvanized coatings protect steel by providing both cathodic and barrier protection. When there are concerns with environmental to which the galvanized steel will be exposed, passivation treatments, for example, can be used to prevent the formation of wet storage stain. Wet storage stain is caused by the newly galvanized surfaces being covered by moisture, such as rain, or condensation and having no air flow over the surface. Water reacts with the zinc metal on the surface to form zinc oxide and zinc hydroxide. Passivation agent is able to delay the formation of zinc oxides and hydroxides, normally last about six weeks before being consumed. By that time, galvanized steel begins to form its protective zinc patina. Hexavalent chrome passivation on galvanized steel had been used in most of industries. Yet since year 2000, more countries had started to ban the use of hexavalent chrome. Hexavalent chrome is known to be carcinogenic. From a health standpoint, hexavalent chromium is a form of toxic chromium which will lead to health hazard and requires special disposal procedures. Therefore there is a need for a chromium- free coating in galvanized metal. New passivation system based on phosphate can replace the current hexavalent chrome with same or even higher corrosion protection in certain environments. Passivation coating is such an economic way to protect the specimen and enhance the performance of the specimen as good as chromes coating.