Engineering Chemistry

3

Science of Corrosion

3.1 Introduction

Corrosion can be defined as the slow degradation or deterioration of a metallic material from the metallic surface due to unwanted attack by the atmosphere gases, soil, chemical, or electrochemical reaction with its environment (gaseous or liquid medium).

Degradation or deterioration means reduction in the useful properties of the material which includes:

• Decaying of surfaces of metals
• Weakening of the material due to loss of cross sectional area.
• Loss of properties such as malleability, ductility.
• Cracking of polymer due to sunlight.

3.1.1 Causes

It has been found that most metals (exceptions noble metals like Au, Pt, etc.) exist in nature is combined forms as their oxides, carbonates, sulphates, sulphides, ...