5.4    Ceramics

Ceramics

• A ceramic is an inorganic non-metallic solid which is prepared by heating a substance or mixture of substances to a high temperature
• Ceramics often contain silicon dioxide, magnesium oxide and aluminium This gives ceramics their giant covalent or ionic structures.
• Properties of ceramics:

i.   Very high melting and boiling points

• This is because most ceramics contain giant covalent or ionic structures. The covalent or ionic bonds holding them together is very strong, a lot of energy is required to overcome it

ii.   Does not conduct electricity or heat

• This is because there are no delocalised electrons or free moving ions present. Therefore most of them are electrical insulators

iii.   Chemically unreactive

• This is because all the electrons are held firmly in strong covalent bonds and not available for a reaction

iv. Very hard

• This is because the ionic or covalent bonds holding them is very strong

Uses of ceramics

• Ceramics containing magnesium oxide are used:
  • as electrical insulators in industrial electrical cables
  • as a refractory in furnace linings because it has a high melting point
  • in fire-resistant wall boards

• Ceramics containing aluminium oxide are used:
  • as a refractory in furnace linings because it has a high melting point
  • as an abrasive for grinding hard materials because they do not conduct heat or melt when heat is given off during grinding
  • in transparent aluminium oxide-scandium windows
  • in high temperature and high voltage electrical insulators
  • in the replacement of artificial hip joints

• Ceramics containing silicon dioxide are used:
  • as a refractory in furnace linings because it has a high melting point
  • as a abrasive, for example in sandpaper
  • in the manufacture of glass