Refining of Aluminium (Hoope’s process):
This process is based on electrolysis of a fused mixture of AlF3, BaF2 and NaF saturated with Al2O3. The bath consist of two layers (a) lower molten Al-Cu alloy and (b) upper molten fluorides. Aluminium metal is deposited at the top of the upper layer which contains hanging carbon cathodes. Crude Al is introduced at the bottom layer as show in Figure 1.1.
On electrolysis, Al from Al-Cu alloy goes into solution in the middle layer as Al3+ leaving impurities at the anode. Al3+ is reduced at the cathode and deposited at the top of molten fluorides. The aluminium layer grows and is draw off occasionally.
- Aluminium is used for making utensils due to less weight, resistance to corrosion and good conductor of heat.
- It is used for preparing aeroplane bodies and certain structural material.
- Aluminium is used in reflecting mirrors for reflecting heat and light.
- It is also used to prepare the electric goods.
- It is used to prepare useful alloys.
Aluminium bronze is an alloy of Al (10%) and Cu (90%). It is used in imitation jewellary due to high tensile strength and golden colour.
Duralumin (Al, 92.5%; Mg, 1.5%; Cu, 2%; Ni, 4%;) is an alloy of Al used in aircraft due to tensile strength (as high as that of steel) and light Weight.