8.3 - Composition of Ceramics and Its Uses

Meaning, Composition and Production

• A ceramic is a solid made from inorganic, non-metallic substances.
• It is produced by shaping the material and hardening it at high temperature.
• Most ceramics contain metal compounds, non-metal compounds or metalloid compounds, such as:
  • aluminium oxide, $\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$;
  • titanium carbide, $\mathrm{TiC}$;
  • silicon carbide, $\mathrm{SiC}$.

Basic Properties and Particle Explanation

• Ceramics are generally:
  • hard and strong;
  • highly resistant to heat;
  • chemically inert;
  • heat and electrical insulators;
  • brittle and easily broken.
• Atoms in ceramics are joined by strong covalent bonds and ionic bonds. Therefore, ceramics melt only at very high temperatures and resist compression.
• The strongly bonded atoms are arranged irregularly and cannot slide over one another. A strong applied force breaks the bonds, so ceramics are brittle and weak under tension.
• Their electrons cannot move freely, so ceramics do not conduct heat or electricity.

Traditional and Advanced Ceramics

Classification	Composition, properties and uses
Traditional ceramics	Made from clay such as kaolin, $\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3\cdot 2Si{\mathrm{O}}_2\cdot 2{\mathrm{H}}_2\mathrm{O}$. Clay is mixed with water to make a soft, mouldable mixture and then fired at high temperature. Used for bricks, pottery and crockery.
Advanced ceramics	Made from inorganic compounds such as oxides, carbides and nitrides. They have greater resistance to heat and abrasion, are more chemically inert and may possess superconductivity.

• Silicon carbide is hard and strong, so it is used for cutting discs.
• Silicon carbide withstands thermal shock and has high heat resistance, so it is also used for brake discs.
• Tungsten carbide is hard and abrasion-resistant, so it is used for rings.

Applications of Ceramics

Field	Application
Medicine	Zirconia ceramic is used for dental implants; alumina ceramic is used for knee bones; superconducting ceramics are used in Magnetic Resonance Imaging (MRI) machines.
Transportation	Ceramic components are used in jet engines.
Energy production	Ceramics serve as electrical insulators in high-voltage locations such as power stations.
House construction	Ceramic building materials are suitable because they are hard, strong, chemically inert, heat-resistant and electrical insulators.