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Chapter 21 – Corrosion and its prevention

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

You might have noticed how the iron railings in your balcony or terrace are shiny and bright when these are new but after a few weeks, the appearance of a reddish-brown layer on them? This is true for grills, nails, decor items made of copper, or even silver accessories. While copper starts to turn greenish over a period; silver starts to blacken. The reddish-brown layer on iron, the black layer on silver, and the green layer on the copper are all examples of corrosion.

Corrosion is a problem that causes extensive damages to things made out of metal. It includes bridges, railings, window grills, bodies of ships, locomotives, car bodies, and all other metallic objects. It is an irreversible reaction; which is why it is so very important to understand the basics of corrosion and its prevention properly. Use an advanced learning app like MSVgo that helps you understand the fundamentals of corrosion (and preventing it) in an engaging and immersive manner with the help of animations and visualizations.

Let us now understand corrosion and its prevention in detail.

Corrosion is a natural irreversible chemical reaction in which chemically-active metals convert from their pure state to corroded substances, in the presence of moisture or air.

Corrosion Examples And Reactions

  1. Notice the silver earrings of your mom and sister turn black when left exposed to air – the coating formed is known as silver sulphide the silver reacts with sulphur.
    2Ag(s) + H2S(g) → Ag2S(s) + H+2+(g)
  2. Similarly, copper vessels or artifacts start to turn green – this is because of the formation of copper oxide.
    2Cu(s) + ½ O2(g) → Cu2O(s)
    Cu2O(s) + ½ O2(g) → 2CuO(s) (black in colour)
  3. Iron, we already know rusts in the presence of moisture – rust is chemically known as iron oxide.
    Fe2O3 + xH2O → Fe2O3.xH2O (rust)

These are the factors that cause corrosion:

  • Moisture is one of the most common reasons causing metals to corrode.
  • Corrosive gases like ammonia, sulphur oxides, hydrogen oxides, and chlorine cause corrosion too.
  • Often, the presence of bacteria and dirt in the atmosphere also accelerate the process of metal corrosion.
  • The presence of acids and impurities plays a role in corrosion too.
  • When the temperature is high, the chances of corrosion increases.
  1. Uniform corrosion – This is one of the most common forms of corrosion where the chemical process occurs uniformly throughout the entire surface that is exposed to the surrounding atmosphere. For example, when zinc is submerged in sulphuric acid, the reaction will occur uniformly across the entire surface.
  2. Two-metal corrosion – It is also called galvanic corrosion. This happens when two electrochemically dissimilar metals are in electric contact in a corrosive solution. There is electron flow between the metals; as a result, a galvanic reaction sets-in, in which one metal will corrode at the joint. The metal which is less-resistant is anodic, and the more-resistant metal becomes cathodic.
  3. Crevice corrosion – This type of degradation occurs in the crevices of reactive metals when exposed to corrosives.
  4. Stress corrosion – When a metal crack as it is left exposed to a corrosive environment, is called stress corrosion. This type mostly happens at a higher temperature.
  5. Intergranular corrosion – when there are impurities in the granular structure, Intergranular corrosion sets in. It results in the formation of depleted layers at the grain boundaries.
  • Painting and oiling – Applying a good-quality layer of paint or oil or grease on the surface of the metal prevents its surface from being exposed to factors that cause corrosion.
  • Galvanizing – In this method, a thin layer of zinc covers the surface of the iron, which prevents it from rusting.
  • Anodising – In this process, where an oxide coating made from aluminum is produced on the surface of the metal through an electrolytic process. It is a thick layer that acts as a protective covering and resists wear and tear and corrosion of the surface.
  • Alloying – In this process, the metal is converted into alloys – for example, pure iron rusts; therefore, by mixing with 0.05% carbon, an alloy is formed. Stainless steel is an iron alloy formed by mixing iron with nickel and chromium, and stainless steel does not rust.
  • Chrome plating – In this process, a thin layer of chromium is electroplated onto the surface of the metal which opposes corrosion.

Corrosion is one of the most common chemical reactions that happen in our everyday life. It happens when metals react or are acted upon by other substances like oxygen, acids, moisture, etc.

  1. How can corrosion be prevented?

Corrosion can be prevented by methods like painting, galvanizing, anodizing, alloying, and chrome-plating.

  1. What is corrosion and its prevention class 10?

Corrosion is the degradation of reactive metals, and you need to study it in class 10 in Chemistry as this is a natural process and needs to be prevented.

  1. What are 3 ways to prevent corrosion?

The best three ways to prevent corrosion are painting, alloying and chrome-plating.

  1. What is corrosion? Give examples.

Rust is a common example of corrosion. Silver turning black and copper turning green are other two common examples.

  1. How do you protect aluminum from corrosion?

Aluminum is the only reactive metal that does not corrode. A protective layer on the surface prevents it from corrosion.

For a better understanding of corrosion and its prevention, use a powerful app like MSVgo that will act as a catalyst in your learning experience. This is because it enables clear understanding in an animated setup with visualization aids and techniques.

High School Physics

  • Alternating Current
  • Atoms
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  • Dual nature of Radiation and Matter
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High School Chemistry

  • Acids, Bases and Salts
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  • Absorption and Movement of Water in Plants
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Middle School Science

  • Acids, Bases And Salts
  • Air and Its Constituents
  • Basic Biology
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Middle School Math

  • Addition
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