B) Physical form

Broadly speaking refractory materials are either bricks or monolithic.

Shaped refractories are in the form the bricks of some standard dimensions. These refractories are machine pressed and have uniform properties. Special shapes with required dimensions are hand molded and are used for particular kilns and furnaces. Different types are:

1. Ramming refractory material is in loose dry form with graded particle size. They are mixed with water for use. Wet ramming masses are used immediately on opening.
   
   
2. Castables refractory materials contain binder such as aluminate cement which imparts hydraulic setting properties when mixed with water. These materials are installed by casting and are also known as refractory concretes.
   
   
3. Mortars are finely ground refractory materials, which become plastic when mixed with water. These are used to fill the gap created by a deformed shell, and to make wall gas tight to prevent slag penetration. Bricks are joined with mortars to provide a structure.
   
   
4. Plastic refractories are packed in moisture proof packing and pickings are opened at the time of use. Plastic refractories have high resistance to corrosion.

Monolithic refractories

Monolithic refractories are replacing conventional brick refractories in steelmaking and other metal extraction industries. Monolithic refractories are loose materials which can be used to form joint free lining. The main advantages of monolithic linings are

• Grater volume stability
• Better spalling tendency
• Elimination of joint compared with brick lining
• Can be installed in hot standby mode
• Transportion is easier

Monolithic refractories can be installed by casting, spraying etc.

Ramming masses are used mostly in cold condition so that desired shapes can be obtained with accuracy.