Classification of Refractory
1) Acid refractories
2) Basic Refractories
3) Neutral Refractories
Acid refractories
The raw material used for silica bricks is ganister, a fine grained quartzite rock containing 97 to 98 %. The rock is crushed ground with water and mixed with 2 % lime. The mixture is moulded into bricks in a power press allowed to dry and then ultimately bagged in high temperature kiln at 1500 oC -1600 o C. The lime being basic reacts chemically with acidic SiO2and fuses at number of places .in a brick and gives it strength. The bricks expand by about 3.5%after high temperature backing is finished. Silica bricks are extremely hard, refractory and able to withstand a load of 3.5 Kg per sq. cm. at 1600o C .Their ability to withstand fluctuation in temperature is very poor.
Silica bricks are suitable for furnaces which are most of the time exposed to uniformly high temperature.