4.2A Metal and alloys

4.2A Metal and alloys

Extracting metal from ore 

Metal ore is a rock containing a metal, or a metal compound, in a high enough concentration to make it economic to extract the metal.

• Iron ores such as magnetite or hematite contain iron oxide. It is obtained through blast furnace. 
• Aluminium ore such as bauxite, is difficult to decompose and expensive, it is obtained through an expensive process called electrolysis which consumer large amount of energy.

Grain size

As metals solidifies from liquid state, the atoms arrange themselves into a regular pattern known as a lattice structure or metallic structure.  

A metal once solidified, it will form a particular structure and it will either be: 

1. Close packed hexagonal - weak, poor strength to weight ratio. (Zinc & magnesium)
2. Face centred cubic - very ductile, good electrical conductors. (Aluminium, copper, gold, silver & lead) 
3. Body centred cubic - hard & tough. (Chromium & tungsten)

Most metals are crystalline in structure. (made up of separate crystals)

• A grain boundary is the border between two grains, or crystallites.
• Grains can be changed when a metal is processed or turned into an alloy.
• Each of the individual grains can vary in size. Depending on the size of the grain the metal will have different physical properties.
• If the grain is heated then slowly cooled the metal will contain larger grains and if the metal is heated then quickly cooled it will have smaller grains.
• metals with smaller grains are more malleable because there are more grain boundaries so it can bend easier without breaking.
• Metals with has a large grain will break easier because the grain boundaries are longer and diverge in many different directions making it harder to bend so it just breaks.
• Each metals have different grains and therefore there are many different uses.

Modifying physical properties

Design criteria for super alloys 

Recovery and disposal