Basic Concept of Corrosion

The concept of corrosion was introduced by Louis Jacques Thenard in 1819. In the past olden days, Romans used to cover utensils made of copper with tin lids and tin covers. The concept of corrosion was understood by Romans earlier and followed some tips to overcome it. Many people have done research on it and  proposed certain advanced methods to overcome the corrosion

Basic Concept of corrosion and its features:

The basic concept of corrosion starts with a metal. A metal when reacts with oxygen, sulfur, and an electrolyte. They form respective oxides, sulfates, carbonates, and rust on their surface that leads to the damage of the entire piece or the surface.

Features:

The corroded area has rust which is a layer of oxide.

The metals which are noble gold, silver didn’t immediately react with oxides. Hence the concept of corrosion is not applicable to noble metals.

Alloys with high content of iron may rust.

Drawbacks:

1) It reduces the appearance and affects the quality of metal, alloy

2) Strength of the metal.

3) Permeability of gases and liquids.

It is an electrochemical phenomenon, during this electronic chemical phenomenon the above changes are observed.

The basic concept of corrosion – Rusting methodology:

The main concept of corrosion with steps are:

1) If the metals react with oxygen then that surface is considered an anode

2) These electrons released by oxidation move from one spot to another spot and reduce the amount of oxygen in the presence of H.

3) Hence it forms H₂CO₃.

4) It forms carbonate because the air contains CO₂ and moisture.

5) The hydrogen ion here in water behaves as a cathode.

Hence the carbonate which is rust is formed on the surface.

The basic concept of corrosion  & Types

1) Galvanic corrosion.

2) Uniform corrosion.

3) Pitting corrosion.

Galvanic- the concept of corrosion

When two metals that are not chemically reactive are in contact, the corrosion occurs at the junction or the joints of the metal. This type of corrosion is observed in the following example:

When the Zinc is in contact with the steel in the saltwater environment then the rust occurs on the junction of the two metals.

Choosing the metals which are galvanically related to each other then there will be less chance of corrosion to occur.

Uniform corrosion (The concept of corrosion)

This type of corrosion spreads all over the surface of the metal, resulting in the uniform loss of the entire metal piece.

The cast iron and the steel corrodes uniformly. Coating with protective paint and galvanising the entire surface helps in not forming rust.

Pitting corrosion:

Pitting corrosion’s basic concept of corrosion revolves around the formation of pits on the metal surface. Here this type of corrosion causes cavities.Usage of cold-applied epoxy materials reduces the pitting corrosion process. This type of pitting corrosion overcoming method has been adopted since 1960. This type of pitting corrosion is observed on iron metal bars.80-grit sandpaper has also been used the remove the rust on the surface.

In other words, the concept of corrosion with overvoltage is an irreversible process. The difference between potentials of electrodes causes overvoltage which evolves the gas.

Application of overvoltage concept:

Electrodeposition of metals in solution:

The electrodeposition of the metals is the surface coating process where different ions from different electrolytes get deposited on the surface, it is also known as electroplating where the process of deposition is controlled by using electricity.

Process:

Here the anode and cathode are placed in the electrolyte. The cathode is a metal. When the electricity passes the charges move from the anode to the cathode resulting in the forming of a layer on the cathode bar. Hence forming a layer on the metal surface.

Copper electroplating is the most useful process for metals to avoid rusting. Nickel or copper is used to coat the surface.

The materials commonly used for electroplating:

• zinc
• nickel
• brass
• gold
• iron

Application of overvoltage concept:

The application of the overvoltage concept on metals is nothing but the overpotential between two potentials during the current passage. This voltage is considered as overvoltage. The application of overvoltage concept can also be described with the following scenario:

When a metal is placed in water then the metal piece presumes itself as a potential, later if the metal piece undergoes corrosion then the metal’s potential varies which is referred to as overpotential.

The chemical equation equations for the above process:

At cathode:

Cu ->Cu²⁺ + 2e^–

At anode:

2e^– ->Cu²⁺

These ions deposit on the cathode to form a layer.

Galvanising with zinc:

The process of applying zinc on the metal surface which may be applied on steel or iron to prevent rusting

Alloying: This process reduces the corrosion process which has more metals that are less reactive to oxygen

Example: Stainless steel- iron and carbon, chromium, nickel, titanium, manganese, molybdenum.

Because of the chromium, it forms chromium oxide when it reacts with oxygen from water, which is a protective layer.

Conclusion

Thus rusting is the one that affects and the above method of application of overvoltage concept helps in the reduction of the corrosion the electroplating, galvanising, alloying methods are used to reduce the corrosion effect on the metals. Along with these methods applying grease can also reduce the effect of corrosion. Oiling is also a methodology to prevent rusting. Since oil and greases don’t react with water and oxygen they form a layer that reduces the corrosion