Aluminium is the most important non-ferrous metal after copper. Al is famous for its remarkable properties like very high strength-to-weight ratio, ease at which it can be rolled, extruded, cast, formed and machined. Having a high strength-to-weight ratio and corrosion resistance makes it a suitable option to replace steel. Further, aluminium is a good conductor of heat and electricity and much cheaper to copper, aids in Al as replacement for copper.
Ores
| # |
Ore |
Formula |
%\( Al_{2}O_{3} \) |
| 1 |
Gibbsite |
\( (Al_{2}O_{3}.3H_{2}O ) \) |
65.4 |
| 2 |
Diaspore |
\( (Al_{2}O_{3}.H_{2}O ) \) |
85.4 |
| 3 |
Bauxite |
Gibbsite + Diaspore |
58-67 |
Generally ore content, TiO2 (5-10%), silica (0.5-2.0%) and remaining Fe2O3
Properties
| # |
Property |
Value |
| 1 |
Appearance |
Silvery gray metallic |
| 2 |
Melting point |
933.47 K (660.32 °C) |
| 3 |
Density |
2.70 g/cm3 |
| 4 |
Crystal structure |
FCC |
| 5 |
Young's modulus |
70 GPa |
Application of Aluminium
-
Having high ductility and flow properties, Al can be easily extruded and form in various shapes like vessels and containers.
-
In packaging industry, for making decorative item and protective surfaces.
-
In kitchenware, chemical and brewing inductry and milk processing as Al have good corrosion resistance and non-toxic property.
-
In structural construction and transpotation application as Al have good mechanical property and high strength-to-weight ratio.
-
In electrical conductors as Al have good electrical and thermal conductivity
-
In roofing systems and thermal insulation as Al have high reflectivity and low emissivity
-
Can be used as deoxidizers as Al have high affinity towards oxygen.
Extraction of Aluminium :
(1) Carbothermic reduction of bauxite : Extraction of Al using this route is
not commercially adopted as -
- Cabothermic reduction requires a very high temperature i.e., 2000 °C
- At high temperature it produces undesirable aluminium carbide
- As this process has a very high operating temperature, so refractories required for such condition is very expensive and rare.
(2) Electrolysis of Al-salt in aq. solution : The extraction of Al is
not feasible by this route because decomposion of aqueous solution occure at lower votltage than that needed for electrodeposition of Al ions. The aqueous solution decomposited to evolve H
2 and we need 1.67 volt more for Al-deposition
(3) Extration of aluminium by Hall-Heroult process :
Aluminium is produced from Bauxite (mixture of gibbsite and diaspore) in a two-step process that consists of leaching of bauxite to get pure alumina and smelting to produce Aluminium from that obtained alumina. Hall-Heroult process used highly pure alumina (SiO
2 < 5%), as having high SiO
2 is bad for elctrodes (in HH-process) because they tends to stick on the elctrodes and cause problems. So it is highly recomended to produce high purity of alumina using bayer's process. And generally to obtain such purity we stop bayer's process at early stage.
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