Silica bricks contain 90% to 95% SiO2 and about 2% lime is added during grinding to furnish the bond.

Basic raw materials used for their manufacture are quartz, quartzite, ganister, sand, sandstone, etc.

For their manufacture, the siliceous rock is crushed and ground with 2% lime and water.

The thick paste is then made into bricks either by hand moulding or by machine-pressing.

The bricks are dried in air or in heated rooms and then, burnt in kilns.

During heating, temperature is slowly raised, in about 24 hours, to about 1500°C and this is maintained for nearly 12 hours, so as to allow quartzite to be converted into cristobalite.

Then, cooling is done carefully and it takes about 1 to 2 weeks.

During cooling, cristobalite is slowly changed into tridymite, so that a mixture of tridymite and cristobalite results in final bricks.

Uses:

• The main applicaiton of silica bricks are roofs of open-hearth furnaces, open-hearth steel making furnaces.
• They are also used in coke-oven walls, cowper stove domes, roofs of electric furnaces, linings of acid converters, glass furnaces, etc.
• Because of their high thermal conductivity, they are also used in by-products coke-ovens and gas retort settings.