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CORROSION (destruction of metal surface) (Chemical corrosion (or) dry…
CORROSION (destruction of metal surface)
Chemical corrosion (or) dry corrosion
Corrosion by other gases
Hydrogen embrittlement
the process by which metals such as steel become brittle due to diffusion of hydrogen into the metal.
Decarburisation of steel
when the metal is heated to high temperatures where carbon in the steel reacts with hydrogen
Corrosion by oxygen
All metal corrodes at high temp. except noble metals
Types of oxide layer
Unstable oxide layer
Au, Ag, Pt form unstable oxide layer which decomposes soon after the for- mation, thereby preventing further
corrosion
Volatile oxide layer
Molybdenum forms a volatile oxide film of MoO3 which accelerates corrosion.
Stable oxide layer
It is a more dense and tightly bound layer on the surface of the metal, preventing further corrosion.
Electrochemical corrosion (or) Wet corrosion
Galvanic corrosion
Two metals are connected more active metal undergoes corrosion
prevention
prevented by using insulators in between them
Differential aeration corrosion
Less aerated undergoes corrosion
Types
Pitting corrosion
Localized form of corrosion by which cavities or "holes" on metal surface
Crevice corrosion
Crevice can be formed between two metals or a metal and non-metallic material.
Wire fence corrosion
The wires cross are less accessible to air than the rest hence corrosion takes
place at the wire crossings
Pipeline corrosion
Unprotected pipelines, buried in the ground, exposed to the atmosphere, or submerged in water
