Silica brick is an acid refractory material with good resistance to acid slag erosion. The softening temperature under load is as high as 1640-1670 degrees Celsius, and its volume is relatively stable under high temperature for long-term use.
The mineral phase composition of silica bricks is mainly tridymite and cristobalite, with a small amount of quartz and glass. Tridymite, cristobalite and residual quartz have large volume changes due to changes in crystal form at low temperatures, so the thermal stability of silica bricks at low temperatures is very poor. During use, it should be heated and cooled slowly below 800 degrees Celsius to avoid cracks. Therefore, it is not suitable for use in kilns with sudden temperature changes below 800 degrees Celsius.
The nature and process of silica bricks are closely related to the crystal transformation of SiO2. Therefore, the true specific gravity is an important quality index of silica bricks. The general requirement is below 2.38, and high-quality silica bricks should be below 2.35. The real specific gravity is small, which reflects that the amount of tridymite and cristobalite in the brick is large, and the amount of residual quartz is small, so the residual linear expansion is small, and the strength decreases during use. Silica exists in seven crystalline and one amorphous variants. These variants can be divided into two main groups: the first variants are quartz, tridymite and cristobalite, which have very different crystal structures and are very slow to transform into each other; the second variants are subspecies of the above variants ──αβ and γ types, their structures are similar, and they transform quickly into each other. In theory, the mutual transformation relationship between them.
The raw material for making silica bricks is silica. The higher the SiO2 content of the silica raw material, the higher the refractoriness. The most harmful impurities are Al2O3, K2O, Na2O, etc., which seriously reduce the refractoriness of refractory products. Silica bricks use silica with a SiO2 content of not less than 96% as raw materials, add mineralizers (such as iron scale, milk of lime) and binders (such as molasses, sulfurous acid pulp waste liquid), after kneading, molding, drying, and firing And other processes made.
It is mainly used for the partition wall of the carbonization chamber and the combustion chamber of the coke oven, the heat storage chamber and the sediment chamber of the steelmaking open hearth furnace, the soaking furnace, the refractory material of the glass melting furnace, and the vault of the kiln for firing ceramics, etc. Load-bearing parts. It is also used in the high-temperature load-bearing parts of hot blast stoves and the top of acid open hearth furnaces.
