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Saturday, 2 January 2016

Structure of Crystalline Ceramics

          The properties of ceramic materials, like all materials, are dictated by the type of atoms present, the types of bonding between the atoms, and the way the atoms are packed together. The type of bonding and structure helps determine what type of properties a material will have. Most ceramic phases, like metals, have crystalline structure. Ceramic crystal's are formed by either a pure ionic bond, a pure covalent bond or by bonds that possess the ionic as well as covalent characteristics.

Ionic Bonds 
         
          The strength of an ionic bond depends on the size of the charge on each ion. The greater the number of electrons being shared, is the greater the force of attraction, or the stronger the covelent bond. This gives ceramic materials of relatively high stability.
          These type of bonds result in high elastic modulus and hardness, high melting points, low thermal expansion, and good chemical resistance. On the other hand, ceramics are also hard and often brittle (unless the material is toughened by reinforcements or other means) , which leads to failure.
Covalent Bonds
       
          In general, ceramics possess high hardness, high melting point and low electrical conductivity at room temperature.they have good chemical resistance and thermal insulation properties. they are also brittle at low temperatures.

          The ceramic crystals structures are, however, invariably more complex as compared to those of metals, since atoms of different sizes and electronic configurations are assembled together.
               Common crystal structures found in crystalline ceramics particularly those of oxide type include the following: 
                        Rocksalt structure
                        Ilmenite structure
                        Wurzite structure
                          Fluorite structure
                        Zinc blende structure

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