Write preparation properties and uses of - (i) Dolomite bricks (ii) Silicon carbide
1 Answer

1. Dolmite bricks

  • Preparation: Dolmite bricks are made by mixing calcined dolmite (CaO+MgO mixture in equimolecular preparations) with silicate binder. They are fired at 1500 °C for about 24 hours
  • Properties: Dolmite bricks possess less strength, more softness and porosity, greater shrinkage and high hygroscopicity than magnasite bricks. However, they can withstand a load of 3.5 kg/cm2 at 1650 °C. They are also not very resistant to thermal shocks.
  • Uses: Dolmite is rarely used as a direct refractory, but it is useful as repair material.
  • Stabilized dolmite bricks are, however used for basic electric furnace linings.
  • Bessemer converters, open-hearth furnaces, ladle-linings etc. and as a cheap substitute for magnesite bricks.

2. Silicon carbide:

  • Preparation: It is a bluish-black crystalline artificial mineral with hardness between corundum and diamond.
  • It is made by subjecting a mixture of silica and carbon (coke or coal) to high temperature (1650-2200 °C) in an electric furnace

  • It is very hard, chemically unreactive, can withstand the action of high temperature without damage, but it is not tough and is somewhat brittle. It is mainly used in cutting-wheels, abrasive papers and clothes. It is extensively used for grinding of materials of low tensile strengths like cast iron, brass, bronze and many more.

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