Electrochemical nature of aqueous corrosion

The electrons generated from each metal atom that is oxidized must be transferred to and become a part of another chemical species in what is termed a reduction reaction.

Or a metal may be totally reduced from an ionic to a neutral metallic state according to:

N^(n+) + neˉ —> N

• For metallic materials, the corrosion process is normally electrochemical, i.e, a chemical reaction in which there is transfer of electrons from one chemical species to another.
• Aqueous corrosion is an electrochemical reaction of materials due to a wet environment, resulting in the deterioration of the material and its vital properties.

Electrochemical Nature of Aqueous Corrosion

Corrosion has been the subject of scientific study for about 150 years. Historically, corrosion has meant the destructive oxidation of metals. But today engineering applications include a multitude of nonmetallic materials.

Significance and purposes of corrosion prevention and control

the hypothetical metal M that has a valence number of n (or n valence electrons) may experience oxidation according to the reaction:

M —> M^(n+) + neˉ

in which M becomes an “n+” positively charged ion and in the process loses its “n” valence electrons (eˉ) ; is used to symbolize an electron.

Group 6

the term “corrosion” now signifies the degradation and loss of function by exposure to the operational environment of all materials. Corrosion can have a great impact on the safety and reliability of an extremely wide range of articles of commerce, and its economic impact .

It plays a critical role in determining the life-cycle performance, safety, and cost of engineered products and systems of value to the national defense and the general health and welfare of the public.

Technology areas where corrosion plays an important role include:

energy production

Transportation

water distribution and sewerage, & etc

studies have concluded that a wider application of our understanding of the corrosion phenomenon could reduce the cost of corrosion to the nation even more.1

Technology areas where corrosion plays an important role include:

• energy production
• Transportation
• water distribution and sewerage, & etc

studies have concluded that a wider application of our understanding of the corrosion phenomenon could reduce the cost of corrosion to the nation even more.

Other examples in which oxidation are:

Fe —> Fe^(2+) + 2eˉ

Al —> Al^(3+) + 3eˉ

The site at which oxidation takes place is called the anode; oxidation is sometimes called an anodic reaction.

Corrosion of Fe in water:

In De-aerated water (oxygen is removed):

•The nail in the de-aerated tube

– Anodic reaction:

Fe → Fe^(+2) + 2eˉ

– Cathodic reaction (water without dissolved O2):

2H2O + 2eˉ → H2 + 2OHˉ

– Overall:

Fe + 2H2O → Fe(OH)2 + H2

In Aerated water (oxygen is dissolved):

The nail in the aerated tube

– Anodic reaction:

Fe → Fe^(+2) + 2eˉ

– Cathodic reaction (water with dissolved O2):

O2 + H2O + 4e- → 4OHˉ

– Overall:

2Fe + O2 + H2O → 2Fe(OH)2

Common cathodic reactions:

near the surface of seawater:

O2 + H2O + 4eˉ → 4OHˉ

in de-aerated water :

2H2O + 2eˉ → H2 + 2OHˉ

in aerated acids:

O2 + 4H^(+) + 4eˉ → 4H2Oˉ

in general:

N^(+n) + neˉ → N

Corrosion or anodic reaction of metals:

M → M^(+n) + neˉ (general corrosion reaction of a metal)

Fe → Fe^(+2) + 2eˉ iron corrosion

Al → Al^(+3) + 3eˉ aluminum corrosion

Cu → Cu^(+2) + 2eˉ copper corrosion

The electrons generated from each metal atom that is oxidized must be transferred to and become a part of another chemical species in what is termed a reduction reaction.

Or a metal may be totally reduced from an ionic to a neutral metallic state according to:

N^(n+) + neˉ —> N

For example, some metals undergo corrosion which have a high concentration of hydrogen (H) ions; the H ions are reduced as follows:

2H^(+) + 2eˉ —> H2

The location at which reduction occurs is called the cathode.

The electrons generated from each metal atom that is oxidized must be transferred to and become a part of another chemical species in what is termed a reduction reaction.

Or a metal may be totally reduced from an ionic to a neutral metallic state according to:

N^(n+) + neˉ —> N