Electrolysis is the chemical process by which an electric current is passed through a liquid or solution (called the electrolyte) in which there are charged particles called ions. The electric current causes chemical reactions to take place. These chemical reaction involve the oxidation or reduction of the ions in the electrolyte. This process is explained in the article on Electrochemistry.
Industrial Applications
Electrochemistry is used in several important applications in industry. One of the most important of these is Electroplating. This process involves the use of electrolysis to put a thin layer of one metal onto the surface of another.
Protective Coating
Why would this be an important process? A layer of one metal on another is useful for various reasons. First, it can protect the metal beneath. Chromium-plating is a very popular way of protecting steel components. Chromium does not corrode, unlike steel which is very prone to rust. It is resistant to scratches and wear and also gives an attractive, shiny finish. Articles which are often plated with chromium metal include bath taps, electric kettles, towel rails and car bumpers.
Precious Metals
A second reason for the use of electroplating is for precious items. Cheaper metals can be plated with silver or gold to make attractive items which cost a fraction of the price.
So how is it done?
Electrolytes and Electrodes
An electrolytic cell suitable for plating must have the correct electrolyte and electrodes. The object to be plated is connected to the electrical circuit so that it is the negative electrode or cathode. The electrolyte must be a solution containing positive ions of the metal to be plated onto the object. The positive electrode or anode can be of the metal to be plated or of an inert material such as graphite.
Reduction of Ions
When the electrical circuit is connected, the object to be plated becomes negatively charge because the current pumps electrons towards it. It attracts the positive ions in the solution, which are ions of the metal, for example silver ions. When the silver ions reach the cathode, they each receive an electron from the surface of the cathode and become neutral silver atoms, which attach themselves to the surface of the object. So the object is plated by silver.
Brush Plating
This method requires a large quantity of solution of electrolyte, sufficient for the complete immersion object to be plated. Another method has been developed however, called brush plating. This uses a brush which has been saturated in the electrolyte and connected as the anode to an electrical circuit. The object to be plated is connected as the cathode so that when the brush is placed on the object, the circuit is completed and electrolysis takes place. This is useful for localised plating and the plating of large objects.
