The General Properties of Silica Brick

The silica brick is an acid refractory material with excellent resistance to acid slags. It is mainly composed of SiO2 (>93%). 

Silica brick is made of quartzite as raw material with addition of a small amount of mineralizing agents by firing at high temperature. Its mineral composition is tridymite, cristobalite, a small amount of residual quartz and glass phase which coexist at high temperature.

 

The silica brick has excellent resistance to acid slags but is easily eroded by the basic slags.  It is easily eroded by oxides such as A1203, K2O and Na2O but has good resistance to oxides such as CaO, FeO and Fe2O3. 

 

It has high deformation temperature under load, close to the melting point of tridymite, cristobalite (1670 ℃, 1713 ℃), fluctuating between 1640-1680℃.

 

Silica brick will have irreversible volume expansion caused by the continuous transformation of quartz after fired again. Between 300℃ and close to the melting points of tridymite and cristobalite, silica brick has stable volume and 1.5-2.2% volume expansion after heated to 1450℃. This volume expansion will make the joints sealed and ensure the masonry has good air tightness and structural strength. 

 

The drawback of silica brick are bad thermal shock (1-4 times heat exchange in water) and low refractoriness (1690~1730℃). Those have its application greatly limited. It is mainly used in the coke oven, glass furnace, acid steel furnaces and other thermal equipment.

When silica brick is used, the following points should be paid attention to:

1) Since the silica brick has rapid volume expansion between 200-300℃ and at 573℃, when preheating the furnaces and kilns, rise the temperature slowly at 600℃ and avoid rapid temperature changes when cooled below 600℃. 

2) Avoid contact with the basic slag.