Three Types Of Electrochemical Theory Of Corrosion

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CHEMISTRY ASSIGNMENT

STUDENT NAME : SYED HAMMAD AHMED
CLASS : F.E MECHANICAL ENGINEERING SECTION C
TEACHER'S NAME : MISS HIRA SULTAN
DATE :
Table of Contents

Serial No. Topics Page No.
1 Corrosion 3
2 Electrochemical Theory of Corrosion 3
3 Types of Electrochemical Theory of Corrosion 4  Oxygen Absorption 4  Hydrogen Evolution 5  Galvanic Corrosion 6-7  Concentration Cell Corrosion 8-10
4 References 10

Corrosion

Corrosion is the usual process and it occurs because of natural inclination of metals to make their more stable compounds, usually oxides. Ores are chemical compounds in which most metals exist in natural form. In the refining process, metal is extracted from its ore by
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This type of Corrosion occurs when the two non-similar metals are dipped partially or are immersed in solution or when the metal comes in contact with a liquid which is conducting. A Galvanic cell forms on the surface of metal and Therefore, some part of metal surface acts as anode and other as cathode. The chemical in the environment and humidity acts as an electrolyte. So the Oxidation of anodic part takes place and therefore corrosion product is formed on the surface of the metal between cathode and anode. To understand this theory, let us take a example of corrosion of Iron. Oxidation of metal happens at anode while the reduction process occurs at cathode. By taking rusting of Iron as an example, the reaction can be explained as that it may occur in two …show more content…
It is also called Galvanic coupling. It happens due to electrochemical attack on the metal surface, which is exposed to an electrolyte of changing aeration and changing electrolyte. It occurs due to different air concentrations metal surfaces are exposed to. Therefore, metal surface acquire different potential between different aerated areas. It has been found experimentally that poor-oxygenated parts are anodic.
Examples:

 The metal part immersed in water or in a conducting liquid is called water line corrosion.  The metal part partially buried in soil.

If the metal is partially immersed in the electrolyte, the area above the liquid is more aerated and becomes cathodic area and that area which is in the liquid becomes less exposed to air and there suffers corrosion. For a given current between two dissimilar metals, if the current density, and hence the rate of dissolution of the less noble metal (anode) will be greater the smaller the would be surface area of the anode. The use of unfavorable surface area ratios has led to many expensive and often spectacular failures.

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