Metallurgy of aluminium

                       
                                   Metallurgy of aluminium

     
                                                  It is solid in state
  • Symbol : Al
  • Color : Silvery white
  • Atomic number : 13
  • Electronic
  • configuration:2, 8, 3
  • Valency : 3
  • Atomic mass : 27
  • Position in the periodic table: period=3, group=13 (III A)
      
The important ores of aluminium are as follows:
Name of the ore is
  • Bauxite Al2O3.2H2O
  • Cryolite Na3AlF6
  • Corundum Al2O3
  • The chief ore of aluminium is  bauxite (Al2O3.2H2O).
                                            




Extraction of aluminium from bauxite  involves two stages:
1 st STAGE

 Conversion of Bauxite into Alumina by Baeyer’s Process

The conversion of Bauxite into Alumina involves the following steps:

    i.Bauxite ore is finely grounded and heated under pressure with concentrated caustic soda
solution at 150°C to obtain sodium meta aluminate.
 Al2O3.2H2O + 2NaOH → 2NaAlO2 + 3H2O
Bauxite Sodium Meta aluminate

    ii.On diluting sodium meta aluminate with water, aluminium hydroxide precipitate is
obtained.
NaAlO2 + 2H2O → NaOH + Al(OH)3
   iii.The precipitate is filtered, washed, dried and ignited at 1000°C to get alumina.
                                          2Al(OH)3 → Al2O3 + 3H2O

 Reduction of Alumina by Hall’s process

Aluminium is produced by the electrolytic reduction of fused alumina (Al2O3) in
the electrolytic cell.
  •   Cathode : Iron tank lined with graphite
  • Anode : A bunch of graphite rods suspended in molten electrolyte
  • Electrolyte : Pure alumina + moltencryolite + fluorspar (fluorspar lowers thefusion temperature of electrolyte)
  • Temperature : 900-950°C
  • Voltage used : 5-6V


The overall equation for aluminium extraction is
 2Al2O→ 4Al + 3O2
Aluminium deposits at cathode and oxygen gas is liberated at anode

Properties of Aluminium
Physical properties:
  • It is a silvery white metal.
  • It has low density and it is light
  • It is malleable and ductile.
  • It is a good conductor of heat andelectricity.
  • Melting point: 675°C
  • It can be well polished to produce attractive shiny appearance.
Chemical properties:
Reaction with air: 
It is not affected by dry air.On heating at 800°C,aluminium burns
very brightly forming its oxide and nitride.

4Al + 3O2 → 2Al2O3 
2Al + N2 → 2AlN 
Reaction with water: 
Water has no reaction on aluminium due to the layer ofoxide on it.When steam is passed over red hot aluminium, hydrogen is produced.

2Al + 3H2O → Al2O3 + 3H2↑
Reaction with alkalis: It reacts with strong caustic alkalis forming aluminates.

2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2


Reaction with acids: With dilute and con. HCl it liberates H2 gas.
2Al + 6HCl → 2AlCl3 + 3H2


DO YOU KNOW
           Dilute or concentrated nitric acid does not attack aluminium. But it renders aluminium passive due to the formation of an oxide film on its surface.
Reducing action :  Aluminium is a powerful reducing agent. When a mixture of aluminium powder and iron oxide is ignited, the latter is reduced to metal. This process is known as aluminothermic process.
Fe2O3 + 2Al → 2Fe + Al2O3
Uses of aluminium

  • House hold utensils  
  • Electrical cable industry
  • Aeroplanes and other industrial parts
  • Thermite welding Aluminium metal
  • Aluminium wires
                        

                                        


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