Write the different types of oxide films formed on the metal surface. Explain the oxide film which is more protective against corrosion.

Write the different types of oxide films formed on the metal surface. Explain the oxide film which is more protective against corrosion.
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1 Answer

Answer :

Types of oxide films

1. Stable porous oxide film

2. Stable non porous oxide film

3. Unstable oxide film

4. Volatile oxide film

i) Stable nonporous oxide film ii) Unstable oxide films are protective against corrosion.

Stable Non-porous oxide film:-

In this case the volume of metal oxide formed is more than volume of the metal from which it is formed. Hence this film is a continuous film and it does not possess any pores in the structure. Hence this film is protective oxide film.Once formed it acts as barrier and protect the metal from further corrosion.


Unstable oxide film :-

In this case, metal oxide formed is unstable it decomposes back into the metal and oxygen as soon as it is formed.

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Hence corrosion is not possible in this case.

Example: - Such type of oxide film is formed in the metals like Ag, Au, and Pt.

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