what is the role of graphite rod in the electrometallurgy of aluminium???
Graphite rod is used as an anode and graphite line iron as cathode during the electrolysis of alumina. During the electrolysis aluminium is liberated at the cathode and oxygen at the anode. This oxygen reacts with the graphite anode to for CO and CO2 preventing the oxygen evolved from oxidizing aluminium.Thus the role of graphite in electrometallurgy of aluminium is to prevent the liberation of oxygen so that the aluminium is not oxidized by oxygen.
Graphite being cheaper is also an advantage.
In the electrometallurgy of aluminium, a fused mixture of purified alumina (Al2O3), cryolite (Na3AlF6) and fluorspar (CaF2) is electrolysed. In this electrolysis, graphite is used as the anode and graphite-lined iron is used as the cathode. During the electrolysis, Al is liberated at the cathode, while CO and CO2 are liberated at the anode, according to the following equation.
If a metal is used instead of graphite as the anode, then O2 will be liberated. This will not only oxidise the metal of the electrode, but also convert some of the Al liberated at the cathode back into Al2O3. Hence, graphite is used for preventing the formation of O2 at the anode. Moreover, graphite is cheaper than other metals.