**5. Chemistry of corrosion**

In general, metals are having unique properties like opaque, lustrous, conductivity, malleable and ductile in nature and are readily forms metallic bonds with other metals and ionic bonds with non-metals [15, 16]. The metals that have overlapping conduction bands and valence bands in their electronic structure.

**5**

*Corrosion Inhibitors*

(Fe2O3).

**Figure 1.**

*Corrosion cycle process.*

**6. Classification**

At anode:

• Wet and Dry corrosion.

M (metal) → Mn+

*DOI: http://dx.doi.org/10.5772/intechopen.80542*

Metals are obtained from their ore by the expenditure of large amounts of energy. Metals store heat as potential energy during the smelting and refining process and release this energy during the corrosion process after reacting with the environment. These metals can therefore be regarded as being in a metastable state and will tend to lose their energy by reverting to compounds more or less similar to their original states, for example the starting material for iron and steel making and the corrosion product rust has the same chemical composition

The energy stored during melting and released during corrosion supplies the driving potential for the corrosion process to take place. Since most metallic compounds, and especially corrosion products, have little mechanical strength, a severely corroded piece of metal is quite useless for its original purpose [17]. Metals such as Mg, Al, Zn, and Fe which require larger amount of energy for refining are more susceptible to corrosion than metals which require lesser amount for refining

such as gold, silver, platinum. A corrosion cycle is shown below (**Figure 1**).

Corrosion has been classified into different methods. They are

• Electrochemical corrosion and chemical corrosion (or)

• Low temperature corrosion and high temperature corrosion (or)

temperature conditions. The corrosion process involves two reactions.

+ ne<sup>−</sup> (oxidation)

Mn + (metal ion) → Forms compound such as oxide

Mn + (metal ion) → Dissolves in solution

Wet corrosion occurs when the metal is in contact with an electrolytic conducting liquid or when two dissimilar metals or alloys are either immersed or dipped partially in the electrolytic conducting solutions. This is always associated with low

**Figure 1.** *Corrosion cycle process.*

*Corrosion Inhibitors*

**3. Corrosion definition**

extracted [13].

Corrosion costs manifest in the form of premature deterioration or failure necessitating maintenance, repairs and replacement of damaged parts.. Corrosion has a vast environmental and economic impact on all the surfaces of national infrastructure like highways, bridges, buildings, chemical processing units, waste water treatment and virtually on all metallic objects in our day to day life use [10]. Other than material loss, corrosion interferes not only with environment, also affects human safety and industrial operations severely. Awareness to corrosion and adaptation of timely and appropriate control measures hold the key in the abatement of corrosion failures [11].

The spontaneous oxidation of metal is termed as corrosion [12], that is, Corrosion is the deterioration or destruction of metals and alloys in the presence of an environment by chemical or electrochemical means. The medium in which the metal undergoes corrosion is termed as corrosive or aggressive medium. Corrosion products formed are chemical compounds containing the metal in the oxidized form with the exception of gold and platinum, all other metals corrode and transform themselves into substances similar to the mineral ores from which they are

The corrosion affects severely on the safe, reliable and efficient operation of equipment and structures than the simple loss of a mass of metal [14]. Failures of all kind of machineries and the need for expensive replacements may occur even though the amount of metal destroyed is quite small. Some of the major harmful

Nuclear plant shutdown due to failure, for example, nuclear reactor during

• Safety requirement measures from a fire hazard or explosion or release of toxic

• Health problems, for example, drinking water contamination with lead is likely

In general, metals are having unique properties like opaque, lustrous, conductivity, malleable and ductile in nature and are readily forms metallic bonds with other metals and ionic bonds with non-metals [15, 16]. The metals that have overlapping

conduction bands and valence bands in their electronic structure.

• Replacement of corroded equipment resulting in heavy expenditure.

**4. Adverse economic and social effects of corrosion**

• High cost preventive maintenance such as painting.

• Loss of product from a corroded container.

effects of corrosion can be listed below:

decontamination process.

• Loss of efficiency.

due to corrosion.

**5. Chemistry of corrosion**

product.

**4**

Metals are obtained from their ore by the expenditure of large amounts of energy. Metals store heat as potential energy during the smelting and refining process and release this energy during the corrosion process after reacting with the environment. These metals can therefore be regarded as being in a metastable state and will tend to lose their energy by reverting to compounds more or less similar to their original states, for example the starting material for iron and steel making and the corrosion product rust has the same chemical composition (Fe2O3).

The energy stored during melting and released during corrosion supplies the driving potential for the corrosion process to take place. Since most metallic compounds, and especially corrosion products, have little mechanical strength, a severely corroded piece of metal is quite useless for its original purpose [17]. Metals such as Mg, Al, Zn, and Fe which require larger amount of energy for refining are more susceptible to corrosion than metals which require lesser amount for refining such as gold, silver, platinum. A corrosion cycle is shown below (**Figure 1**).
