microsoft word - anti corrosive coating

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1 1.1 INTRODUCTION Steel is a suitable construction material for a wide range of structures because of its favorable mechanical properties and high speed fabrication 1 . Corrosion may lead to damage of unprotected steel exposed in different environmental conditions. Corrosion is an electrochemical reaction process which leads to continuous loss of metal or metal alloys 2 . Energy is needed to extract metals from their mineral state to the pure state. The same amount of energy is emitted during the formation of its chemical compounds or in other words during the process of corrosion. Corrosion returns the metal to its combined state in chemical compounds that are similar or even identical to the minerals from which the metals were extracted .Thus corrosion has been called extractive metallurgy in reverse. 1.2 MECHANISM OF CORROSION Corrosion reactions are electrochemical in nature. Surface of iron goes into solution as ferrous ions at anodic sites 3 . Iron atoms undergoes oxidation to ions they release electron whose negative charge will quickly buildup in the metal and prevent anodic reaction, or corrosion 4. Corrosion returns the metal to its combined state in chemical compounds that are similar or even identical to the minerals from which the metals were extracted. Thus corrosion has been called extractive metallurgy in reverse 5,6 . The dissolution will only continue if the electrons released ca n pass to a site on the metal surface where a cathodic reaction is possible. At a cathodic site the electrons react with some reducible component of the electrolyte and are themselves removed from the metal. The rates of the anodic and cathodic reactions must be equivalent according to Faraday’s Laws, being determined by the total flow of electrons from anodes to cathodes which is called the “corrosion current”, I Corr . Since the corrosion current must also flow through the electrolyte by ionic conduction the conductivity of the electrolyte will influence the way in which corrosion cells operate.

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