Consideration for the Use of Silica Brick

Silica brick is a type of refractory product mainly composed of SiO2 (>93%). It is made of quartzite as the raw material and a small amount of mineralizing agents by firing at high temperature. its mineral composition mainly include tridymite, cristobalite, quartz and a small amount of residual glass phase. 

Silica brick belongs to acid refractory materials and has good resistance to acid slags. It is easy to be corroded by basic slags and alkali oxides such as Al2O3, K2O and Na2O, but it has good resistance to oxides such as Fe2O3. One advantage of silica brick is its high softening temperature under load, within 1640-1680℃, close to the melting points of tridymite and cristobalite (1670, 1713℃).

 

Silica brick has irreversible volume expansion after calcining again due to the continuous transformation of the residual quartz in the brick. Above 300℃ and  close to the melting points of tridymite and cristobalite, silica brick has stable volume. When heated to 1450℃, there is about 1.5-2.2% volume expansion. The expansion will seal the brick joints and ensure the good tightness and structure strength of masonry. 

The main drawback of silica brick is its low thermal shock resistance (1-4 heat cycles in water). Another is low refractoriness(1690-1730℃). These drawbacks greatly limit its applications. Silica brick is mainly used in coke ovens, glass furnaces, acidic steelmaking furnaces and other thermal equipment. 

 

The two points should be taken into consideration during the use of silica brick:

1) Since silica brick has rapid volume expansion due to crystalline transformation, avoid extreme temperature changes around 600℃ during preheating and cooling. 

2) Avoid direct contact with basic slags.