Refractories and Other Ceramics

Definition: Refractories are constructional materials which must their duties at high temperature. Hence, they must have a high fusion point. The clay which is used for manufacturing refractories and refractory linings is called fire clay. This type of clay can resist high temperature without melting or becoming soft.

Use of Refractories: They are used in building works for setting stones in ovens and fire places. They are used for the manufacture of fire bricks and chimney posts. They are also used as lining of sand melting furnace of glass factory and iron-ores melting furnaces in steel plant. Fire bricks are used for the construction of boilers, combustion chambers and chimney flues.

                                                              Refractories and Other Ceramics 

Composition of Fire Clays: Fire clay should contain a higher percentage of silica and alumina and very small quantity of lime and magnesia, iron oxide and Alkalies. Silica (Sio2) becomes soft at about 2800 and finally fuses and becomes a glassy substance at about 3200. It melts around 3300. Due to this high softening and melting point, it is, therefore, used as a principal materials in the manufacture of refractories and fire bricks. Alumina (Al2o3) has still higher softening fusion temperature. It melts at about 3800. It is, therefore, uses combination with silica to manufacture refractories to resist high heat and temperature. But the presence of time, magnesia, iron oxide, and alkalies act like fluxes to lower the softening and fusion point and temperature. So silica and alumina are nondetrimentals and lime, magnesia, iron oxide and alkalies are termed as detrimentals in fire clay. The following chart show the approximate composition of fire clays depending upon the special use.

Silixa    60 to 96 percent ,Alumina    2 to 36,Oxide    2 to 5.

Manufacture of Refractory Bricks: Fire bricks are manufactured from fire clay and the different steps in the manufacturing process such as digging, weathering, tempering and moulding of fire bricks are same as those of ordinary bricks but the burning is generally carried out in a superior type of kiln under carefully graduated temperature control.