➢Material science and engineering:-
CORROSION
❖ It is a process of decomposition degradation of material at its surface due to formation of metal oxide, metal hydro-oxide, metal salts which are known as scale.
❖ On the basis of mechanism there are two types of corrosion
a) Dry corrosion
b) Wet corrosion
c)Dry corrosion
❖ It is also known chemical corrosion because chemical reaction of certain gases like,
o2, cl2, Sulphur etc. forms scale at metal surface. It is called dry corrosion because in this metal surface is not exposed to any liquid.
Mechanism of DRY-CORROSION
❖ When the metal is exposed to temperature it becomes +vely charged by releasing
electrons.
❖ This released electron is gained by oxygen present in atmosphere and become Electronegative
❖ The negatively charged oxygen combines with positive charged metal to form metal oxide at the surface of metal and is known as scale which is a cause of corrosion.
M M2+ + 2 ∆ e-2-2
WET CORROSION
➢ When corrosion occurs under moist
or wet condition then it is known as
wet corrosion.
➢ Wet corrosion can be also defined as
degradation or decomposition of
material when the material is in
contact with any conducting liquid
particle.
➢ Presence of conducting liquid at the
surface of material which transfers
the electrons is necessary condition
for wet corrosion.
➢ Following are the conditions required for wet corrosion:-
➢ There must be separate anodic & cathodic areas to create electrode potential required for flow of electrons.
➢ There must be metal path connecting anode & cathode.
➢ Anodic reactions:-
➢ Anodic areas on the material are those areas from where electrons are released & where
metal ions are formed.
➢ Cathodic reaction:-
➢ Cathodic areas are those which is surrounded by oxygen where gain of electrons tales place to form hydroxyl ions.
FACTORS AFFECTING CORROSION
➢ 1.Environment: The environment plays a significant role in corrosion because it provides the medium through which the corrosion process occurs. Different environments cancan accelerate corrosion. Some common corrosive environments include:
➢ Moisture: Water, humidity, and moisture accelerate corrosion by facilitating the electrochemical reactions involved in the corrosion process.
➢ Acids and Bases: Acids and bases can increase the corrosiveness of an environment by providing ions that promote corrosion reactions.
➢ Salts: Saltwater and salty atmospheres contain ions that enhance the corrosive process, making materials more susceptible to corrosion.
➢ Pollutants: Pollutants in the air or water, such as sulfur compounds and industrial emissions, can accelerate corrosion by providing additional corrosive agents.
➢ Material Properties: The properties of the material being corroded also influence the corrosion corrosion process.
Some key material properties include:
➢ Chemical Composition: The chemical composition of a material determines its susceptibility to corrosion. Some materials are inherently more resistant to corrosion due to their chemical makeup.
➢ Microstructure: The microstructure of a material affects its corrosion resistance.Grain boundaries, phases, and defects in the material can influence corrosion susceptibility.
➢ Passivity: Some materials form protective oxide layers (passive films) that inhibit further corrosion. The ability of a material to passivate can significantly affect its corrosion resistance.
➢ Alloying Elements: Alloying elements can improve a material's corrosion resistance by altering its chemical composition and microstructure.
#mechanical engineering
