Refractories:

• It is defined as any material that can withstand very high temperature, without degrading or softening.
• It retains its strength at high temperature.

• It confines heat and at the same time it resist the abrasive and corrosive action of molten metals, slags and gases at high operating temperatures.. Refractory are essential materials of construction in metallurgy, engineering and chemical industries. It is used for construction of the linings of the tanks, furnaces, kilns, converters etc.

   

Preparation, Properties and Uses of Carborundum bricks:

Preparation of Carborundum bricks:

• Carborundum is called Silicon Carbide (SiC). It is made in an electric furnace at a very high temperature of around$1500\ ^\circ C$ from sand (60%) and coke (40%) with addition of saw-dust and little salt.
• Saw-dust evolves gases when burnt and increases porosity of the charge. Also, salt reacts with iron and other impurities to form volatile chlorides and increases the porosity of the product. Carborundum removed from the furnace is then mixed with bonding agent like clay, shaped, dried and fired. The particles are mixed with glue, pressed and dried at$2000\ ^\circ C$, and bonds of inter-crystalline Carborundum develop.

Properties:

• They have properties like high thermal conductivity and low thermal expansion. It tend to oxidise to silica, when heated in air at a temperature range of 900 -$1000\ ^\circ C$.
• Clay-bonded Carborundum bricks can be used upto$1750 \ ^\circ C$ as it softens around this temperature.
• Self bonded product has high refractories, superior strength, high density, high abrasion resistance and high chemical resistance.

Uses: 

• Carborundum bricks are used for partition kilns, coke ovens, recuperators and floor of heat treatment furnaces.
• They are used as heating elements in furnaces in the form of rods and bars because of its high electrical conductivity.