An alloy is a homogeneous mixture of two or more metals or of one or more metals with certain non-metallic elements.
The properties of alloys are often different from those of its components. Pure gold is too soft to be used. The addition of small percentage of copper enhances its strength and utility.
An amalgam is an alloy of mercury with another metal. These alloys are formed through metallic bonding with the electrostatic force of attraction between the electrons and the positively charged metal ions. Silver tin amalgam is used for dental filling.
Reasons for alloying:
i. To modify appearance and colour
ii. To modify chemical activity.
iii. To lower the melting point.
iv. To increase hardness and tensile strength.
v. To increase resistance to electricity.
· By fusing the metals together. E.g. Brass is made by melting zinc and copper.
· By compressing finely divided metals. E.g. Wood metal: an alloy of lead, tin, bismuth and cadmium powder is a fusible alloy.
Alloys as solid solutions:
Alloys can be considered solid solutions in which the metal with high concentration is solvent and other metals are solute.
For example, brass is a solid solution of zinc (solute) in copper (solvent).
Based on the presence or absence of Iron, alloys can be classified into:
· Ferrous alloys: Contain Iron as a major component. A few examples of ferrous alloys are Stainless Steel, Nickel Steel etc.
· Non-ferrous alloys: These alloys do not contain Iron as a major component. For example, Aluminium alloy, Copper alloy etc.
Copper Alloys (Non- ferrous), Aluminium Alloys (Non- ferrous), Iron Alloys(Ferrous)