Dense High Thermal Conductivity Silica Bricks

General Refractory Materials

Main Advantages of Compacted High Thermal Conductivity Silica Bricks

Good thermal conductivity, thermal conductivity of compacted silica bricks increased by more than 20%

Higher density, good wear resistance, good environmental benefits

Can improve the thermal efficiency of coke ovens, blast furnace hot blast furnaces, and carbon calcining furnaces

1. Silica bricks are made of high-purity quartz stone that is calcined and selected and mixed with a small amount of lime milk. Part of the aggregate can be used after the waste silica bricks are crushed. High-grade silica brick raw materials must undergo special chemical treatment to remove impurities.

2. Chemical composition The general chemical composition of silica bricks is Si0293→98%, Al2O30.2←2.0%, Ga01.5～3.5%, Fe2O30.3～3.0%, R200←0.5%. According to the current standards in my country, silica bricks for coke ovens and glass pool furnaces are Si02＞93%.

3. Crystalline phase composition

It is not difficult to see from the above chemical composition that the crystal phase composition of silica bricks is mainly Si02 crystals and a small amount of silicate crystals such as calcium silicate. There is almost no glass phase in silica bricks. There are many types of Si02 crystals, including quartz, tridymite and cristobalite. Among them, they can be divided into three types: α, β, and γ.

 

Among the crystal phases of silica bricks, the highest melting point is Si02 crystals, which are 1725℃. It is impossible for silica bricks to be composed of 100% pure SiO2. This is not only because the purity of the raw materials is difficult to achieve, but also because it is impossible to combine SiO2 crystals together, so there are other components. The crystals composed of these components and a small amount of glass phase have low melting points, which play a role in combining SiO2 crystal particles, so they are called binders. The large particles of SiO2 crystals in the brick are called aggregates. The corrosion resistance and temperature resistance of the binder are worse than those of the aggregate. However, too little binder will make the aggregate loose. Therefore, the correct selection of the amount of binder is an important issue in the manufacture of silica bricks.

The proportions of various crystal phases in silica bricks are generally: quartz 1%←15% (the quality is better in the direction indicated by the arrow), tridymite 30→50%, and cristobalite 40←60%. The aggregate contains the most cristobalite, and there will be a small amount of unconverted quartz in the center, while the tridymite content is very small. There are many needle-shaped crystals of tridymite in the binder, as well as a small amount of calcium silicate and glass phase.

The biggest disadvantage of silica bricks is that they have poor heat shock resistance below 700℃. This is mainly caused by the transformation of various crystal forms of Si02. The raw material of silica bricks, natural silica, is mainly quartz crystals, and quartz is stable below 870℃. 870～1470℃ is the stable temperature of tridymite, and 1470～1725℃ is the stable temperature of cristobalite. In fact, when quartz is heated to above 870℃, almost no tridymite is generated. When there is an appropriate amount of mineralizer, quartz begins to transform into semi-stable cristobalite at 1250℃, and the transformation is completed around 1600℃.

High load softening temperature

Another feature of silica bricks is the high load softening temperature. This is a common feature of single oxide refractory materials. The reason is that the SiO2 content is very high. In addition to SiO2 crystals, there are few other low-melting point substances in silica bricks. And when these low-melting substances melt, they will dissolve a lot of SiO2, making it very viscous. The refractoriness of clay bricks and silica bricks is the same at 1710℃. The softening point of clay bricks is only 1300℃, while the softening point of silica bricks can reach 1630℃. Even sillimanite bricks with a refractoriness of up to 1780℃ have a load softening temperature of 1600℃. Therefore, silica bricks have good strength at high temperatures.

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