Properties required in a refractory

The diversified applications of refractory materials in several different types of industries require diversified properties to meet the physico-chemical and thermal requirements of different phases. In some industrial units more than one phase are present e.g. in steel-making vessels slag /metal /gases are simultaneously present in the vessel at high temperatures. In the heat treating furnaces solid/reducing or oxidizing gases are simultaneously present. Below are briefly described the properties of the refractory materials:

Refractoriness  
Refractoriness is a property at which a refractory will deform under its own load. The refractoriness is indicated by PCE (Pyrometric cone equivalent). It should be higher than the application temperatures.
 
Refractoriness decreases when refractory is under load. Therefore more important is refractoriness under load (RUL) rather than refractoriness.


Porosity and Slag permeability    
Porosity affects chemical attack by molten slag, metal and gases. Decrease in porosity increases strength and thermal Conductivity.

Strength 
It is the resistance of the refractory to compressive loads, tension and shear stresses.In taller furnaces, the refractory has to support a heavy load; hence strength under the combined effect of temperature and load, i.e. refractoriness under load is important.

Specific gravity   
Specific gravity of the refractory is important to consider the weight of a brick. Cost of bricks of higher specific gravity is more that of lower specific gravity. But strength of bricks of higher specific gravity is greater than one with lower specific gravity.