Name: METAL CORROSION,ITS PREVENTION AND ELECTROCHEMISTRY
Uploaded: 2021-12-03
Duration: 4 min 26 s
Description: . . Unit V: METAL CORROSION, ITS PREVENTION. AND ELECTROCHEMISTRY.

. . Unit V: METAL CORROSION, ITS PREVENTION. AND ELECTROCHEMISTRY. 

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. . ❖ Metal corrosion –. It is defined as the process of chemical or electrochemical. 

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It is defined as the process of chemical or electrochemical

decay or destruction of a metal due to the action of surrounding
medium is called as corrosion.

A)  Atmospheric corrosion
B)  Immersed  corrosion

The corrosion occurs metals come in contact directly with

atmospheric gases like O2, CO2 and moisture etc. It is of two 
types-

. . 1. Corrosion due to oxygen or oxidation corrosion.
2. Corrosion due to other gases.. 

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1. Corrosion due to oxygen or oxidation corrosion.
2. Corrosion due to other gases.

The metallic surfaces when exposed to air undergo oxidation

and the process is represented by the general equation

The film so produced can be classified into

a)  Porous (Non-protective)
b) Non- porous (Protective)

. . B. Immersed corrosion or Electrochemical corrosion-. 

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B. Immersed corrosion or Electrochemical corrosion-

The corrosion which is brought about through ionic reactions in

the presence of solution as a conducting medium When two
dissimilar metals are in contact with each other is called as Immersed
corrosion.

1. Galvanic cell corrosion or Daniel cell:
When two dissimilar metals are electrically connected and

dipped in an electrolyte solution.  The e.m.f. developed is due to two 
separate reactions taking place at the electrode. Zn acts as a anode 
and Cu acts as a cathode.

Zn (solid)             Zn++ (aq) +2e-
(Oxidation)

Cu++ (aq)+ 2e-
Cu (solid)                    (Reduction)

. . Galvanic cell. Working of Daniell Cell Salt badge + cathode (Reduction) (Oxidation) Zn zn2• zn:• znS04 I cu: cusog. 

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Working of Daniell Cell
Salt badge
+ cathode
(Reduction)
(Oxidation)
Zn
zn2•
zn:• znS04
I cu:
cusog

. . Hydrogen Evolution. This type of corrosion occurs when metals are exposed to acidic. 

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This  type of corrosion occurs when metals are exposed to acidic

environments like industrial waste , solutions of non –oxidising  acids.

HYDROGEN EVOLUTION MECHANISM
At Anode:
At Cathode:
2FC+
S•el

. . Galvanizing. It is the process of coating iron or steel with a thin coat. 

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It is the process of coating iron or steel with a thin coat

Iron sheet
Dil H2S04
Drying
chamber
Washing bath
Pair of
hot rollers
NH4Cl-flux
Hot
air
Molten zinc at
425-4600c
Galvanised
sheet
Annealing
chamber
Excess zinc
removed
- . O. Galvanization of steel sheet

. . Tinning process. TINNING OF STEEL SHEET Tek. It is the process of covering iron or steel sheets with a thin coat of tin to prevent it from corrosion.. 

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It is the process of covering iron or steel sheets with 
a thin coat of tin to prevent it from corrosion.

. . Electrochemistry. • A cell is a device chemical reaction takes place. • Electrolytic cell- Electrical energy is converted into chemical. 

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• A cell is a device chemical reaction takes place.          
• Electrolytic cell- Electrical energy is converted into chemical

• Electrochemical cell- Chemical energy is converted into

• Electrolyte-
•
The substance which is in aqueous solution liberates ions

and allows the electric current to pass through it, resulting in 
the chemical decomposition is known as electrolyte.

• Strong electrolyte- These are highly ionised and hence , high

degree of ionisation are called strong electrolyte.

• Weak electrolyte-These are partially ionised in solution have a

low degree of ionisation  are called weak electrolyte.

. . Ionisation and Electrolytic dissociation. •
Ionisation –. 

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•
It is defined as the process of  breaking up of a substance into

•
It is defined as the process of splitting up of an electrovalent

compound into ions is known as electrolytic dissociation.

•
Electrode potential – There are two types

•
The tendency of an electrode to lose electrons is a direct measure  of

its tendency to get oxidised is called oxidation potential.

•
The tendency of an electrode to gain electrons is a direct measure of

its tendency to  get reduced is called reduction potential.

. . Applications of Electrolyte. Electroplating –. 

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The process of producing metallic coating of more

resistant metals ( like silver, gold,nickel chromium ) on the base 
metal with the help of electric current is called electroplating.

Battery
Key
Copper
plate
Metallic
spoon
cuso
solution

. . Electro refining. It is process in which a pure metal can be obtained from pure metal by. 

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It is process in which a pure metal can be obtained from pure metal by

Key
e-
Cathode—
+ Anode
Acidified copper
sulphate solution
Tank
Impurities
(anode mud)

. . Faraday ,s First Law. This law states that the weight of a substance deposited at an
electrode during electrolysis, is directly proportional to the
quantity of electricity passed through the electrolyte.. 

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This law states that the weight of a substance deposited at an
electrode during electrolysis, is directly proportional to the
quantity of electricity passed through the electrolyte.

W - grams is the weight of substance
Q - the quantity of electricity

W ∝
c × t      where  Q = number of coulombs

c = current in amperes
t =  time in seconds.

W = z × c × t    where  z = constant (E.C.E.)

. . 1. Wt. of copper deposited (W1) ∝
Chemical equivalent of copper (E1). 

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1. Wt. of copper deposited (W1) ∝
Chemical equivalent of copper (E1)

2. Wt. of silver deposited (W2) ∝
Chemical equivalent of  silver (E2)

This law states that when the same quantity of electricity is passed through 
different electrolytes arranged in series, the weights of substances deposited at 
the respective electrodes are directly proportional to their chemical equivalents.

METAL CORROSION,ITS PREVENTION AND ELECTROCHEMISTRY

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