Refining and Corrosion in Metals

REFINING OF METALS

  • The metals produced by various reduction processes are not very pure.
  • They contain impurities, which must be removed to obtain pure metals.
  • The most widely used method for refining impure metals is electrolytic refining -the process of removal of impurities to get pure metal using electricity is known as electrolytic refining
  • In this process, the impure metal is made the anode and a thin strip of pure metal is made the cathode.
  • A solution of the metal salt is used as an electrolyte.
electrolytic refining of copper
electrolytic refining of copper

 

  • On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte.
  • An equivalent amount of pure metal from the electrolyte is deposited on the cathode.
  • The soluble impurities go into the solution, whereas,
  • the insoluble impurities settle down at the bottom of the anode and are known as anode mud.

 CORROSION

  • The surface of some metals, such as iron, is corroded when they are exposed to moist air for a long period of time.
  • This phenomenon is known as corrosion.
  • corrosion of iron also known as rusting of iron

      corrosion of iron also known as rusting of iron

PREVENTION FROM CORROSION

  • Paint
  • Oil or grease
  • Plastic coating
  • Tin plating – cover metal by molten tin
  • Electroplating
  • chrome plating
  • anodizing – protect metal by formation of thick metal oxide coating of generally aluminium
  • making alloys
  • Galvanization – cover metal by molten zinc
  • Galvanization is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
galvanized steel protected from rust
galvanized steel protected from rust
  • The galvanized article is protected against rusting even if the zinc coating is broken.
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