Lecture 9 – Aluminium: Introduction, Extraction & Alloys

ACKNOWLEDGEMENT:

Figure	Source of Figure
Figure 8	http://wps.prenhall.com

Aluminium:

Aluminium is a highly demanded metal. It is used to make:

1. Air craft bodies
2. Car bodies
3. Kitchen uses

It is extremely reactive, as seen from its position in the Reactivity series, but apparently unreactive as Aluminium has a natural tendency to coat itself with oxygen on its body. This oxide layer on aluminium makes it completely unreactive and corrosion resistant.

Ore:

The highly demanded aluminium metal is obtained from its ore, Bauxite, Al₂O₃.

Extraction of Aluminium:

1. The ore is washed thoroughly with water to remove rocks, clay and sand impurities.
2. The clean ore has a high melting point of over 2000°C ; to make the extraction more economical and feasible, it is dissolved in cryolite which lowers its melting point to 1000°C.
3. The mixture is melted at and molten bauxite and cryolite is electrolyzed using Carbon electrodes.
• Figure 8:
  
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4. Oxide ions travel to the anode and are oxidized to Oxygen gas by losing electrons.
  
5. Aluminium ions travel to the cathode and are reduced to Aluminium metal by gaining electrons.

6. The overall equation of the reaction can be written as: 

7. In this process Carbon anodes have to be periodically replaced as oxygen evolved at the anode oxidizes it to carbon dioxide.

Table 5: Aluminium alloys