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Electrochemical Principles of Metallurgy

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Electrochemical Principles of Metallurgy - Lesson Summary

The principles of metallurgy are effective in the reduction of metal ions to their respective metals in their solution (or) molten states. The reduction is carried out through electrolysis (or) using reducing elements. Such methods are based on electrochemical principles.

          Mn+     +              A                  →        M           +        An+
Metal ion        reducing Element           Metal            Reduced ion

These electrochemical principles are explained in

                ΔG°  = -nE°F
          n = Number of Electrons Gained
         E° = Electrode Potential of Redox Couple

The value of E0 for a metal depends on its reactivity. Thus, it differs from metal to metal. More reactive metals have high E0, whereas less reactive metals have low E0. It is difficult to reduce metals that have high E0.

If the difference between the E0 values of two metals is positive, then the value of ∆G0 will be negative.

Hence, the less reactive metal will come out of the solution and the more reactive metal will go into the solution.

            An+     +                 B                      →           A              +       Bn+
Less Metal ion   More reducing Element      Less Reactive Metal  More Reduced ion

Ex: The reduction of copper (II) to copper in the presence of iron.

           Cun+       +      Fe     →         Cu      +           Fen+
Copper(II) ion        Iron             Copper               Iron(II) ion

In a simple electrolysis process, the positive ions always move towards the negative electrode called the cathode.

Precautions to be taken:

  • · Consider the reactivity of the metal produced in the electrolysis.
  • · Use suitable material as the electrodes.
  • · Sometimes flux is needed to increase the conductivity of the molten mass.


Metallurgy of aluminium:

Addition of cryolite and fluorspar as flux to aluminium oxide because pure aluminium oxide is a bad conductor of heat and electricity. The fused substance is used as the electrolyte.

During this process, the electrolyte is taken in a steel container lined with carbon, which acts as the cathode. A bunch of graphite rods immersed in the electrolyte act as the anode. This process is also known as the Hall-Heroult process. When current is passed, all the Al+3 ions move towards the cathode. Oxygen is liberated at the anode, which reacts with the carbon atoms of the anode to form carbon monoxide and carbon dioxide.

Cathode:    Al3+   +   3e-         →     Al(l)

Anode   :    C(s)   +   O2-        →     CO(g) + 2e-
                      
C(s)   +   2O2-      →     CO2(g) + 4e-

Generally, copper is extracted from its low concentrated ores by a process known as "hydrometallurgy". In this process, a solution containing Cu+2 ions is treated with a scrap of iron or hydrogen.

         Cu+2          +      Fe          →          Cu        +     Fe+2
Copper(II) ion          Iron                     Copper          Ferrous(II) ion

         Cu+2          +          H2          →          Cu        +         2H+
Copper(II) ion          Hydrogen                Copper         Hydrogen ion

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