Electroplating Process


What is Electroplating?

In the word ‘Electroplating’, ‘electro’ refers to electric current and ‘plating’ refers to an act of outer covering of some materials with a thin layer of a different metal.

Thus, electroplating definition is given as the process of plating a layer of any metal on other material by passing an electric current.


Electroplating is mainly done for avoiding corrosion of metals and for decorative purposes.Electroplating is a widely used process in many industries like automobiles, airplanes, electronics, jewelry, toys and many more.


Electroplating is conducted in an electrolytic cell. The metal to be electroplated is connected to the cathode. The electrolyte consists of the salt solution of metal with which electroplating has to be done. The electrolyte ionizes to give positively charged ions (metal ions) which move towards the anode for electroplating the desired object.

The main reason for performing electroplating are:

  1. To make better appearance of the objects (e.g., shiny)

  2. To protect the objects from corrosion 

  3. To enhance or give special engineering or mechanical features to abrasion, lubricity etc. 

The Anode and Cathode

In the process of electroplating, an external source of electric current is usually applied. This takes place in an electrolytic cell. The electrode connected to the positive terminal of the battery is called anode, while the electrode connected to the negative terminal of the battery is called cathode. The electrochemical reduction reaction takes place at the cathode (negative terminal). The electrochemical oxidation reaction takes place at the anode (positive terminal).

  • The object on which electroplating takes place is made the cathode (negative terminal)

  • The metal which is going to be plated as a layer on the object is made the anode (positive terminal).

  • The salt solution of the metal which is to be deposited is taken as electrolyte.

The anode is given the direct current, where oxidation reaction occurs making its metal ions dissolved in the electrolyte solution. 

These dissolved metal ions from the electrolytic solution become less as they get deposited on cathode. 

How does Electroplating Work?

Let us read about some more information about electroplating.

Electroplating process:

To understand the process of electroplating, let us take an example of electroplating iron objects with copper.

  • Here, the iron object on which electroplating takes place is made the cathode (negative terminal).

  • The copper metal which is going to be plated as a layer on the iron object is made the anode (positive terminal).

  • The copper sulphate solution is taken as electrolyte.

Procedure:

  • Dissolve two teaspoonfuls of copper sulphate in 250 mL of distilled water in a clean and dry beaker. To increase conduction, add a few drops of dilute sulphuric acid to copper sulphate solution. Take a copper plate of 10 cm x 4cm size and a spoon made of iron. Use sandpaper to clean the copper plate and iron spoon. Rinse the copper plate and iron spoon with water and dry them. 

  • Place the copper plate inside the copper sulphate solution and connect it to the positive terminal of a battery. This copper plate becomes the anode or positive electrode.

  • Place the iron spoon inside the copper sulphate solution at a distance away from the copper plate and connect it to the positive terminal of a battery. This iron spoon becomes the cathode or negative electrode.

  • Now, allow the current to pass for about 15 minutes. Now remove the copper plate and iron spoon from the solution and observe them. We will find that a small amount of the copper plate has dissolved and the surface of the iron spoon has got a reddish layer of copper all over it. Hence, the iron spoon has been electroplated with copper.

  • Copper sulphate solution contains copper ions and sulphate ions. When an electric current is allowed to pass through the copper sulphate solution, 

  • The free copper ions from the copper sulphate solution get attracted to the negative ions of the iron spoon connected to the negative terminal of the battery and become copper atoms. These copper atoms get deposited on the iron spoon as a thin layer of copper all over its surface.

  • The copper plate connected to the positive terminal of the battery, dissolves by forming positively charged copper ions. These copper ions enter into the copper sulphate solution. In this manner the lost copper ions to the negative electrode (iron spoon) are restored in the copper sulphate solution by the positive electrode, and this process continues so that the copper ions in the electrolyte remain the same. 

Hence, during the copper plating of iron spoon, copper metal is transferred from the copper plate to iron spoon through copper sulphate solution from positive electrode to negative electrode.

Uses of Electroplating

Electroplating is a very useful process in coating thin metal layers on different metals and other objects. This is done to,

  • Give a shiny look on the objects, by changing its appearance.

  • To avoid corrosion of the objects.

  • To make the objects scratch resistant.

  • To avoid spoiling of more reactive metals by coating less reactive metal on more reactive metals.

  • To manufacture ornaments by coating costlier silver and gold coatings on less expensive metals.


Examples:

  • Chromium having shiny appearance, does not corrode and resists scratches. Chromium is, however, highly expensive and making the complete object out of chromium might be uneconomical. Thus, the object is made from a cheap metal and chromium plating is done over it. Thus, chromium plating is done on a number of objects like car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims etc.

  • Many jewelry items are manufactured at low prices by electroplating silver and gold on less expensive metals. These ornaments have the look of silver or gold but are much cheaper.

  • Tin cans which are used for storing food, are made by electroplating tin on iron. Due to the less reactive nature of tin than iron, food is protected and does not get spoiled from contact with iron.

  • Iron, being very strong, is used in building bridges and in automobiles. It, however, has a drawback that it undergoes corrosion and forms rust. Hence, a zinc coating is electroplated on iron to prevent it from corrosion and rusting.