Refractory Bricks

Performance and working principles of 9 common refractory bricks used in glass kilns

Jan 30,2024

In the configuration design of glass kiln lining, shaped refractory bricks are mainly used. According to the working conditions and environment of different parts of the glass kiln, the materials and properties of the refractory bricks used are also different. The following are the 9 most commonly used refractory bricks for glass kiln linings in my country:

01 silica brick

Silica bricks are acidic refractory materials. Silica bricks for glass kilns are siliceous refractory products mainly made of phosphorus quartz and used to build high-temperature parts of glass kilns. Their load deformation temperature is relatively high, with a fluctuation range of 1640~1680°C. Close to the melting points of phosphoquartz and cristobalite (1670°C, 1713°C). High-quality silica bricks have the characteristics of high purity and density, high softening temperature under load, low reburning change, good high temperature creep resistance, high normal temperature compressive strength, reasonable mineral phase composition, low true density, and accurate size. As the current photovoltaic glass furnaces become larger and larger, the glass melting temperature is also high. The silica bricks are limited by low refractoriness (1690~1730℃) and poor thermal shock stability (heat exchange in water is 1~4 times). It cannot meet the requirements for the use of large roofs in the melting section, but the superstructure of the cooling section has become the best choice.

02 clay bricks

Clay bricks are acidic refractory materials. As the Al2O3 content in the bricks increases, the acidity gradually weakens, and its thermal conductivity is the lowest among all refractory materials. Although its refractoriness is as high as 1700°C, its load softening temperature is only about 1300°C. When it is corroded by a large amount of R2O, the softening temperature will further drop to about 1050°C, so it cannot bear load and pressure when used at high temperatures. The thermal expansion rate of clay bricks is the smallest among commonly used refractory materials. At the same time, because clay bricks have fine crystals, small pores and even distribution, stress can be easily buffered. Therefore, they have strong thermal shock resistance in a wide range and can be used in kilns. Important parts such as flue material selection.

03 High alumina brick

Aluminosilicate refractory materials with an Al2O3 content greater than 48% are collectively called high-aluminum refractory materials. It is divided into 3 levels according to the Al2O3 content:

Class I: Al2O3>75%;

Grade II: Al2O3 60%~75%;

Grade III: Al2O3 48%~60%.

In the range of Al2O3 content less than 71.8%, as the Al2O3 content increases, the main crystal phase mullite in high-aluminum products increases; in the range of Al2O3 greater than 71.8%, as the Al2O3 content increases, the amount of mullite decreases and The amount of corundum increases. The refractory properties of the product increase with the increase in Al2O3 content. Compared with clay refractory materials, the outstanding advantages of high-aluminum refractory materials are high refractoriness and load softening temperature. High-aluminum refractory materials products have higher thermal conductivity than clay products. The thermal shock resistance of high-aluminum refractory products is between clay products and siliceous products, and can be used as insulation layer bricks for glass furnaces.

04 Sillimanite Bricks

Compared with clay bricks, sillimanite bricks and mullite bricks have a higher high-temperature load softening point, a dense fine-grained structure, and are less likely to cause bubbles in the glass liquid, making them extremely suitable for the discharge port structure.

05 mullite bricks

The main crystal phase of mullite bricks is mullite. The refractory degree of mullite is about 1850℃, high load softening temperature, low high temperature creep rate, good thermal shock resistance, and acidic slag erosion resistance. The options are: Vertical flue substructure and horizontal flue interior surfaces.

06 Fused Mullite Brick

Fused mullite uses high-alumina bauxite as raw material, and different bauxites are formulated into the composition of mullite (3Al2O3-2SiO2). The mass percentage is: Al2O372%, SiO2 28%. The main crystal phases are mullite and corundum, and the glass phase is filled between the crystal phases. Its resistance to glass liquid erosion is stronger than that of sintered refractory materials, but not as good as that of fused refractory materials. Adding a small amount (7%~8.5%) of zirconium dioxide can make the mullite crystal smaller and the brick structure denser. The mullite can be increased to 60%~70%, which relatively reduces the content of the glass phase and reduces the Cracks in the product. Fused mullite bricks have low thermal expansion coefficient, good thermal shock resistance, and strong resistance to glass liquid erosion.

07 Fused zirconium corundum brick

Fused zirconium corundum bricks belong to the Al2O3-ZrO2-SiO2 system (AZS bricks for short). According to the ZrO2 content, it can be divided into three levels: 33%, 36%, and 41%. Compared with fused mullite bricks, fused zirconium corundum bricks have better resistance to glass liquid erosion. The main reasons are:

① The main crystal phases in zirconium corundum bricks are corundum and baddeleyite that coexist closely. Both crystal phases have good corrosion resistance.

② Between the glass phase filling in the zirconium corundum brick and the above-mentioned crystal phase, this glass phase is corroded by high-temperature glass liquid to form albite glass with higher viscosity. The viscosity is higher because a certain amount of ZrO2 is melted in it. This is A layer of high-viscosity glass remains on the surface of the brick and is not easy to spread, thus protecting the brick body. The corrosion resistance of fused zirconium corundum bricks increases with the increase of ZrO2 content. Among them, the melting temperature of ZrO2 is as high as about 2700°C, and it has high resistance to acids, alkali, glass liquid and other media.

Fused zirconium corundum bricks are not only used in parts that are in contact with molten glass due to high temperatures and severe erosion, but are also widely used in the superstructure of glass melting furnaces.

08 Fused corundum brick

Fused corundum brick a-b-Al2O3 (94.5%~96.5%) is made of high-purity alumina as raw material, introducing a small amount of soda ash, and melting at 2000~2200℃. The crystal structure is composed of 45%~55% a-Al2O3 It is composed of 45% to 60% b-Al2O3 phase. Since a larger amount of b-Al2O3 is intertwined between a-Al2O3 crystals, the original a-Al2O3 tubular microstructure becomes a scaly structure, and the crystals are also smaller than their individual counterparts. It is much smaller when it exists, so its corrosion resistance is second only to a-Al2O3, but the thermal deformation resistance of the brick is greatly improved, so it becomes the best choice for large refractory materials in the passage pool wall and the clarification area of the melting part.

The corrosiveness of refractory materials at high temperatures is: AZS-41#>AZS-36#>AZS-33#〉a-b-Al2O3. This is because the main crystal phase in the fused zirconium corundum brick is densely coexisting corundum (a- Al2O3) and baddeleyite (ZrO2), both crystal phases have good corrosion resistance. The corrosion resistance of fused zirconium corundum increases with the increase of ZrO2 content. Due to the high strength requirements of the bricks, and considering that the volatile matter of the glass liquid is easy to accumulate here, the furnace bricks should be 33# fused AZS bricks. Similarly, the corners of the pool wall are even more eroded by the glass liquid, and the glass liquid Volatile matter and alkali vapor are more likely to accumulate here. Generally, fused bricks with higher ZrO2 content should be selected, and 41# fused AZS bricks are the best.

09 Zirconium-containing refractory bricks

Zirconium-containing refractory products are refractory products made from zirconium oxide (ZrO2) and zircon (ZrSiO4). Zirconia series products, zircon stone series products, zirconium mullite and zirconium corundum series products all belong to this type of products. According to different production processes, zirconium-containing refractory products are divided into sintered products, cast products and unsintered products. Zirconium-containing refractory products have the characteristics of high melting point, low thermal conductivity, good chemical stability, especially good corrosion resistance to molten glass.

The properties of zirconium-containing refractories depend on the properties of ZrO2. The melting point of dense and stabilized zirconia is 2677°C, and the service temperature reaches 2500°C. The bulk density fluctuates between 4.5 and 5.5g/cm3 due to the purity of the raw materials and the manufacturing method. The bulk density of dense zirconia products can reach 5.75g/cm3. The mechanical strength of zirconia products is very high, and the strength is maintained until 1300~1500℃. The thermal conductivity of ZrO2 is much lower than that of all other oxide materials. This characteristic of ZrO2 can be used as a high-temperature insulation layer.

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