Classification of Refractories

Classification of Refractories-

On the basis of chemical behaviour -

1. Acid Refractories - combine readily with bases. Their chief constituent is silica: quartz, sand,ganister and silica bricks.

2. Basic Refractories - consist mainly of basic oxides: magnesite and dolomite.

3. Natural Refractories - consist of materials which do not combine with either basic or acidic oxides: silicon carbide, chromite and carbon.



On the basis of use -

1. Siliceous Refractories - containing not less than 93 per cent SiO2 are used for roof, metallurgical furnaces and glass tanks. This is an acid refractory made from hard, dense quartzite and sand

stone.

2. Alumino silicate Refractories -  may be semi-acid type containing silica (over 65 per cent),chamotte with 30–45 % alumina are used in brickwork, lining of furnances; alumina (less than 35 per cent) or high-alumina variety with more than 45 per cent alumina are used in glass industry for furnace brickwork. Aluminosilicate items are used to line cupolas, coke ovens etc.

3. Magnesia Refractories - consist chiefly of MgO (80–85%) and their refractoriness may be as high as 2000° C. In is an important basic refractory. It finds application in extractive metallurgy.

4. Chromous Refractories - are obtained from chromous iron ore blended with magnesia and alumina. Their refractoriness is 1800–2000° C and they withstand attack by iron ore slags. They

are used in steel making furnaces.

 

5. Carbonaceous Refractories - are manufactured from graphite or coke. These have refractoriness above 1700° C and are resistant to attack by molten slags.