Classification And Features Of Silica Refractories

Silica refractories refer to the type of refractories containing not less than 93% silica. The main types of silica refractories include common silica brick, high quality silica brick, special silica brick and quartz products. 

Silica brick is made of silica stones containing not less than 96% SiO2 with addition of mineralization agents (iron scale, lime) and binders(molasses, sulfite pulp waste) by kneading, molding, drying and firing. The more SiO2 silica stones contain, the better its refractory performance. Impurities such as Al2O3, K2O and Na2O are harmful and can reduce the refractoriness. Impurities like Fe2O3, CaO and MgO can work as fluxes. The raw materials for manufacturing high quality silica brick should be treated through special chemical methods to remove impurities. 

 

The main chemical composition of silica bricks includes 94-98% SiO2, 0.2-2.0% Al2O3, 1.5-3.5% CaO, 0.3-3.0% Fe2O3 and 0-0.5% R2O.

 

Silica bricks can be categorized into many types according to its application, including coke oven brick, hot stove brick, EAF brick, glass furnace brick, etc.. Besides, new types are developed and put into production, such as chrome silica brick, SiC silica brick and Si3N4 silica brick. 

 

According to the shapes, it can divided into standard brick, common brick, shaped brick and special brick. 

 

Since Silica brick belongs to acid refractories, it has great resistance to acid slags and bad resistance to alkali slags. Its softening temperature under load is as high as 1640-1670℃. Its volume is stable at high temperature in the long term use. 

 

It mainly comprises of tridymite, cristobalite and a small amount of quartz and glass phase. At low temperature, it has big volume changes due to the crystal transformation of tridymite, cristobalite and residual quartz. Thus, it has bad volume stability at low temperature. Under 800℃, it should be cooled and heated slowly to avoid cracks. So it is not suitable to furnaces and kilns that have sudden temperature changes under 800℃. 

 

The properties and manufacturing process of silica brick are closely related to the crystal transformation of SiO2. True specific gravity is an important indicator for its quality. A small true specific gravity means high content of tridymite and cristobalite, low content of quartz and small residual linear expansion. 

 

Silica brick is mainly used in the carbonization chamber and combustion chamber of coke ovens, the crown of grass furnaces and firing kilns of silicate products.