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What is Electrodeposition? (Factors Affecting the Quality of Electrodeposition)
What is Electrodeposition?
An electrolytic process by which one metal is deposited over other metal or non-metal is known as electrodeposition.
Electrodeposition is widely used for decorative, protective and functional purposes. The process of electrodeposition includes −
Electroplating − It is the process of deposition of metal over any metallic or non-metallic surfaces for protecting the metals from corrosion.
Electro metallization − It is a process by which a metal can be deposited on a conducting base for decorative or protective purposes.
Electro typing − It is a process used to reproduce printing, set up typing and medals, etc.
Electro forming − It is a process used for reproduction of objects by electrodeposition in order to increase their durability.
Electro facing − It is a process of coating of metallic surfaces with a harder metal by electrodeposition in order to increase their durability.
Factors Affecting the Quality of Electrodeposition
The factors on which the quality of electrodeposition depends are described below.
Nature of Electrolyte
The nature of electrolyte used in the electrodeposition process greatly affects the formation of smooth deposit. A smooth deposit can be provided by employing the electrolyte from which complex ions can be obtained.
Current Density
The process of electrodeposition depends upon the rate at which crystals grow and the rate at which fresh nuclei are formed. Therefore, the deposit of metal will be uniform and fine grained if the current density is used at the rate higher than at which the nuclei are formed.
The deposition will be strong and porous if the rate of nuclei formation is very high due to very high current density.
Conductivity
The electrolytic solution of good conductivity provides economy in power consumption and also reduces the tendency to form tress and rough deposits.
Temperature of Solution
The low temperature of the electrolytic solution results in the formation of small crystal of metal while the high temperature causes the formation of large crystals.
In addition, the high temperature gives the following beneficial results −
Increased conductivity,
Increased solubility of slats,
Decreased occlusion of hydrogen in the deposit metal, etc.
Electrolytic Concentration
The increased concentration of electrolyte results in higher current density. Thus, by increasing the electrolytic concentration, a uniform and fine-grain deposit can be obtained.
Polarization
As we know, the rate of metal deposition increases with the increase in current density up to a certain limit after which electrolyte surrounding the base metal becomes so much depleted of metal ions that the further increase in the current density does not cause increase in rate of deposition. The use of current density beyond this limit results in the electrolysis of water and liberation of hydrogen on the cathode. This liberated hydrogen on the cathode blankets the base metal that reduces the rate of metal deposition. This phenomenon is known as polarization.
The polarization can be reduced by reversing the current at regular intervals.
Addition of Agents
The addition of acids or other substances to the electrolyte decreases the resistance of the electrolytic solution. Also, some additional agents like gums, dextrose, etc. influence the nature of the deposit. The nuclei of the crystal absorb the additional agents added in the electrolyte. This prevents its large growth and hence the deposition will be fine grained.
Throwing Power
Throwing power is the ability of the electrolyte to produce uniform deposit on an article of irregular shape. As the distance between the various potions of the cathode and anode will be different because of irregular shape of the cathode. Therefore, it is necessary that the electrolyte should have relatively better throwing power so that uniform deposit can be produced.
The throwing power of an electrolyte can be increased in two ways as −
By increasing the distance between the anode and cathode.
By reducing the voltage drop at the cathode surface.
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