Answer:

• Preparation of Dolomite Bricks:-

1. Dolomite is magnesium lime stone with the composition,$Ca Mg (CO_3)_2$. It occurs in nature. Calcined dolomite particles are united with the help of magnesium silicate, iron ore, basic slags, tar, etc. (binding materials). 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° to 1650°C. Stabilised dolomite bricks. For preparing such bricks, dolomite is mixed with serpentine$(MgO.SiO_2)$ and the mixture is calcined to form di- and hi-calcium silicates which do not absorb water and carbon dioxide.
3. 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. Such bricks are quite stable towards basic slags.

• Properties of Dolomite Bricks:-

1. Dolomite brick is less strong, more porous and has more shrinkage than magnesia bricks.
2. Dolomite bricks are more resistant to slags and spatting than magnesia bricks. This is due to the fact that dicalciunt silicate present in dolomite brick is more resistant than magnesium silicate to dust and slag containing lime and iron compounds.
3. Dolomite bricks are porous and soft and wear away quickly.
4. They also have great volume shrinkage and so they are not very useful refractories.
5. Dolomite is rarely used as a direct refractory, but is useful as repair material.

• Uses:-

1. Dolomite bricks have been used for basic electric furnace linings, Bessemer converters, open hearth fur-naces, ladle linings etc.
2. Dolomite is generally used as a repairing material rather than as a direct refractory because of its defects like great porosity, shrinkage and softness.