Post Treatment of Galvanized Coating to Improve Corrosion Resistance

Singh, D D N (1997) Post Treatment of Galvanized Coating to Improve Corrosion Resistance. In: Workshop on Hot Dip Galvanizing - HODGA-97, 6-7, January 1997, National Metallurgical Laboratory, Jamshedpur.



In electromotive force (EMF) series,zinc occupies a place much lower than iron (E0Zn = -0.76V and for iron E0,Fe = -0.44V). Thus thermodynamically, Zn is very unstable comp ared to iron and in practice, it is indeed fond to corrode sacrificially in contact of iron in most of the envir-onments.In dry environment having plenty of supply of oxygen and carbon di oxide, the corrosion rate of zinc, however, is about 25 times less than iron. lt is a very surprising fact and reason is attributed to the formation of passive layer on the zinc surface. Zinc surface combines with Oxygen to form ZnO. If CO, is also available, the upper layer is converted into zinc carbonate. These comp-ounds provide protection to the surface in absence of moisture. However, if ingress of moisture and other gases take place to the surface, these protective films are damaged and an onset of deterioration of metal/coating takes place as a result of formation of zinc hydroxide, Zn(OH)2. This initial discolouration of the zinc surface is known as white rusting.

Item Type:Conference or Workshop Item (Paper)
Official URL/DOI:
Uncontrolled Keywords:Electromotive force; oxygen; carbon dioxide; zinc surface
Divisions:Corrosion and Surface Engineering
ID Code:4290
Deposited By:Sahu A K
Deposited On:16 Nov 2011 13:08
Last Modified:26 Dec 2011 14:25
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