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Give the preperation, properties and uses of dolomite bricks.
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Dolomite is magnesium lime stone with the composition, $CaMg(CO_3)_2$

Properties:

  1. Dolomite bricks are more porous and possess more softness, shrinkage and less strength than magnesia bricks.
  2. They can be used upto 2300°C without load and upto 1650°C under a load of 3.5Kg/cm2

Preparation:

  1. Dolomite is calcined, powdered and mixed with binding material and water. Mixing is performed in edge runner and then allowed to age by keeping it in wet condition.
  2. The mixture is moulded to bricks which are air dried and burnt to a temperature ranging between 1200°C to 1650°C.
  3. For preparing stabilized dolomite bricks, dolomite is mixed with serpentine$(MgO\cdot SiO_2)$ and the mixture is calcined to form di- and tri-calcium silicates which do not absorb water and carbon dioxide.
  4. The calcined mixture is mixed with a binding agent (usually silicate) and moulded into bricks which when burnt at about 1500°C for about a day gives stabilized dolomite bricks.

Uses:

  1. It is generally used as a repairing material rather than as a direct refractory because of its defects like:
    great porosity, shrinkage and softness.
  2. However, stabilized dolomite bricks are used in electric furnaces, bessemer convertors, open-hearth furnaces, etc and as a cheap substitute for magnesia bricks.
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