Question

what is corrosion ????????​

Answer 1

question :-

⏩what is corrosion ????

Answer:

⏩Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, carbonate or sulfide. It is the gradual destruction of materials by chemical and/or electrochemical reaction with their environment.

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Answer 2

Answer:

DEFINATION

→→→→→→→ Corrosion can be defined as the process through which refined metals are converted into more stable compounds such as metal oxides, metal sulfides, or metal hydroxides. The rusting of iron involves the formation of iron oxides via the action of atmospheric moisture and oxygen.

Factors Affecting Corrosion :-

1. Exposure of the metals to air containing gases like CO2, SO2, SO3 etc.
2. Exposure of metals to moisture especially salt water (which increases the rate of corrosion).
3. Presence of impurities like salt (eg. NaCl).
4. Temperature: An increase in temperature increases corrosion.
5. Nature of the first layer of oxide formed: some oxides like Al2O3 forms an insoluble protecting layer which can prevent further corrosion. Others like rust easily crumble and expose the rest of the metal.
6. Presence of acid in the atmosphere: acids can easily accelerate the process of corrosion.

Types of Corrosion :-

(1). Crevice Corrosion:-

Whenever there is a difference in ionic concentration between any two local areas of a metal, a localized form of corrosion know as crevice corrosion can occur. Examples of areas where crevice corrosion can occur are gaskets, the undersurface of washers, and bolt heads.

Example: All grades of aluminium alloys and stainless steels undergo crevice corrosion.

(ii) Stress Corrosion Cracking :-

Stress Corrosion Cracking can be abbreviated to ‘SCC’ and refers to the cracking of the metal as a result of the corrosive environment and the tensile tress placed on the metal. It often occurs at high temperatures.

Example: Stress corrosion cracking of austenitic stainless steel in chloride solution.

(iii) Intergranular Corrosion :-

Intergranular corrosion occurs due to the presence of impurities in the grain boundaries that separate the grain formed during the solidification of the metal alloy. It can also occur via the depletion or enrichment of the alloy at these grain boundaries.

Example: Aluminum-base alloys are affected by IGC.

(iv) Galvanic Corrosion

When there exists an electric contact between two metals that are electrochemically dissimilar and are in an electrolytic environment, galvanic corrosion can arise. It refers to the degradation of one of these metals at a joint or at a junction. A good example of this type of corrosion would be the degradation that occurs when copper, in a salt-water environment, comes in contact with steel.

Example: When aluminium and carbon steel are connected and immersed in seawater, aluminium corrodes faster and steel is protected.

(iv) Pitting Corrosion :-

Pitting Corrosion is very unpredictable and therefore is difficult to detect. It is considered one of the most dangerous types of corrosion. It occurs at a local point and proceeds with the formation of a corrosion cell surrounded by the normal metallic surface. Once this ‘Pit’ is formed, it continues to grow and can take various shapes. The pit slowly penetrates metal from the surface in a vertical direction, eventually leading to structural failure it left unchecked.

Example: Consider a droplet of water on a steel surface, pitting will initiate at the centre of the water droplet (anodic site).

(v) Uniform Corrosion :-

This is considered the most common form of corrosion wherein an attack on the surface of the metal is executed by the atmosphere. The extent of the corrosion is easily discernible. This type of corrosion has a relatively low impact on the performance of the material.

Example: A piece of zinc and steel immersed in diluted sulphuric acid would usually dissolve over its entire surface at a constant rate.