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Electroplating

Electroplating is a process of depositing a thin layer of a fine and superior metal (like chromium, zinc, nickel, gold etc.) over the article of a baser and cheaper metal (like iron, copper, brass), with the help of electric current.

 

Electroplating is very useful because of the following reasons:

  • Surface protection e.g. nickel plating of iron to prevent corrosion.
  • Makes the article attractive e.g., electroplating of silver or gold on brass etc.
  • Repair of finer machine parts.

Process

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The process of electroplating involves the following steps:

  • Before electroplating the metal surface is cleaned thoroughly. Firstly, an alkaline solution is used to remove grease and then it is treated with acid to remove any oxide layer. It is then washed with water.
  • The article to be electroplated is made cathode since metallic ions are positive and thus get deposited on the cathode.
  • The anode is made of pure metal, which is to be coated on the article.
  • The electrolyte is the salt of the metal to be coated on the article.
  • A direct (D.C.) current is passed through the electrolyte. The anode dissolves, depositing the metal ions from the solution on the article in the form of a metallic coating. The passage of low current is continued for a long time to ensure an even coating.
  • To obtain a thin, coherent and bright deposit, the conditions of low current density, optimum temperature and low metal ion concentration are found to be helpful.
The choice of electrolyte for use in the electroplating bath is very important. A good electrolyte should have the following characteristics.
  • It should be highly soluble in water.
  • Its solution should be a reasonably good conductor of electricity.
  • Its solution should be stable towards oxidation, reduction and hydrolysis.
  • It should be reasonably priced.

Now let us study electroplating with nickel and silver, both of which qualify as good protective coatings.

a) Electroplating with Nickel

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  • Electrolyte - Aqueous solution of nickel sulphate
  • Cathode - Article to be electroplated (nail)
  • Anode - Block of nickel metal.
  • Dissociation of nickel sulphate -

nickel electroplating

 

b) Electroplating with Silver

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  • Electrolyte - Aqueous solution of sodium argento cyanide Na[Ag(CN)2].
  • Cathode - Article to be electroplated (spoon).
  • Anode - Block of silver metal
  • Dissociation of sodium argento cyanide:

silver electroplating

 


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