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.

• 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

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.

• The galvanized article is protected against rusting even if the zinc coating is broken.