Silica bricks used in glass furnaces are silicon-based refractory products mainly composed of flake quartz. They are used for the construction of high-temperature areas such as glass tanks and kilns. Silica bricks for glass furnaces should have the following characteristics:
High temperature stability: They should maintain dimensional stability even in the presence of temperature fluctuations. Due to the high load softening temperature and low creep rate of silica bricks, the glass furnace can remain unchanged and structurally stable at 1600°C.
No contamination of glass melt: The main component of silica bricks is SiO2. If there are any chippings or surface droplets during use, it does not affect the quality of the glass melt.
Chemical erosion resistance: The silica bricks in the upper structure are subjected to the erosion of gases containing R2O in the glass raw materials. A smooth metamorphic layer is formed on the surface, which reduces the erosion rate and provides protection.
Low bulk density: This helps reduce the weight of the furnace.
(2) According to the Chinese Building Materials Industry Standard (JC/T616=1996), high-quality silica bricks for glass furnaces are classified into three grades based on their unit weight: XBG-96 for a unit weight not exceeding 15kg, ZBG-96 for 15-25kg, and DBG-96 for 25-40kg.
2.Kaolin Brick
Kaolin bricks are refractory materials made from kaolin clay with an Al2O3 content of 40%~44%. There are three production methods: pressing, ramming, and casting. The production processes of the first two methods are similar to general refractory materials. In 1964, China successfully experimented with the casting method and officially put it into production. It mainly uses calcined bauxite (75%) mixed with soft clay to form a slurry. Water glass is added as a diluent to give the slurry good fluidity. NaCl and NH4Cl are added as thickening agents to accelerate the solidification of the slurry. The slurry is poured into gypsum molds, demolded, dried with electricity, and then fired in a kiln. Current products include large pool bricks (for pool bottoms or walls), feeder trough bricks, heat exchanger cylinder bricks, and crucibles, among others. The advantages of the casting method are that the products have a dense and uniform structure, good resistance to glass corrosion, and a higher degree of mechanization in production. The disadvantage is that there may be larger dimensional tolerances and slight distortion at times.
3.High Alumina Brick
Properties of high alumina bricks as refractory materials:
Chemically bonded high alumina bricks have good thermal shock stability, high load softening temperature, high compressive strength at room temperature, and certain resistance to chemical erosion.
4.1 Silicon Carbide Brick
Compared to clay bricks, silicon carbide bricks and mullite bricks have higher high-temperature load softening points. They have a dense fine-grained structure and are less likely to generate bubbles in the glass melt, making them extremely suitable for applications in feeder troughs, plungers, nozzles, and crucibles. They are only used as pool kiln bricks in special cases.
4.2 Mullite Brick
Mullite electric fusion brick is a type of refractory product in the alumina-silicon series that is cast into a certain shape after high-temperature melting, with mullite as the main crystal phase. The properties of mullite bricks are mainly determined by mullite as the main crystal phase. Mullite bricks have a refractoriness of around 1850°C, high load softening temperature, low creep rate at high temperatures, good thermal shock resistance, and resistance to acidic slag erosion.
Mullite bricks should not come into contact with alkaline substances above 1450°C, as it would cause the decomposition of mullite. In a reducing atmosphere above 1370°C, mullite will also decompose, with some SiO2 turning into gaseous SiO2 and leaving the brick. At temperatures above 1650°C, even in a non-reducing atmosphere and under relatively low oxygen partial pressure, mullite will decompose.
5.Magnesite BrickRefractory materials that are primarily composed of magnesium oxide (MgO) and have forsterite (Mg2SiO4) as the main crystalline phase are collectively referred to as magnesite refractory materials. Currently, the main varieties of refractory materials include the following:
5.1 Magnesite Brick and Magnesite-Silica Brick
Ordinary magnesite brick: Made from sintered magnesite, with an approximate MgO content of 91%. It is a magnesite refractory product directly bonded by silicates. This is a widely used magnesite product in both production and applications.
Directly bonded magnesite brick: Made from high-purity sintered magnesia, with a MgO content of over 95%. It is a magnesite refractory product directly bonded between forsterite grains.
Magnesia-silica brick: Made from high-silicon sintered magnesite, with a SiO2 content of 5%~11% and a CaO/SiO2 molar ratio ≤ 1. It is a magnesite refractory product bonded by magnesite olivine.
5.2 Magnesite-chrome brick: Made primarily from sintered magnesite, with the addition of a suitable amount of chromite. It has a Cr2O3 content of 8%~20% and is a magnesite refractory product bonded by magnesite-chrome spinel.
5.3 Magnesite Olivine Brick and Magnesia-Calcia Brick
Magnesite olivine brick: It is a refractory material with magnesite olivine as the main crystal phase. It is mainly made from olivine rock and pure olivine as the primary raw materials. The shaped products are called magnesite olivine bricks.
Magnesia-calcia brick: Made from high-calcium sintered magnesite, with a CaO content of 6%~10% and a CaO/SiO2 molar ratio > 2. It is a magnesite refractory product bonded by dicalcium silicate.
5.4 Magnesia-Alumina Brick
Magnesia-alumina brick is an alkaline refractory material with a composition of approximately 85% MgO and 5%-10% Al2O3. The main crystal phase of magnesia-alumina brick is forsterite, with magnesia-alumina spinel as the matrix (magnesia-alumina spinel replaces calcined magnesite in magnesite brick as the binder for forsterite).
Note: Please be aware that the content provided is for informational purposes only and may not include all possible varieties and details about magnesite and magnesite-related bricks.
6.Electric Fused Cast Refractories
6.1 Electric Fused Mullite Brick
Electric fused mullite brick is made from high-alumina bauxite. The impure bauxite is formulated into the composition of mullite (with a mass percentage of 3Al2O3·2SiO2, which is approximately Al2O3 72% and SiO2 28%). It is melted at around 2300°C, cast into a sand mold at 1850°C, and then annealed to relieve stress. The main crystal phases are mullite and corundum, with a glass phase filling the gaps between the crystals. It has a stronger resistance to glass liquid corrosion compared to sintered refractories but is not as strong as other electric fused refractories. Adding a small amount (7%-8.5%) of zirconia can reduce the size of the mullite crystals, make the brick more dense, increase the mullite content to 60%-70%, relatively decrease the content of the glass phase, and reduce cracks in the products. Electric fused mullite brick has low thermal expansion coefficient, good thermal shock resistance, and strong resistance to glass liquid erosion.
6.2 Electric Fused Zirconia Corundum Brick
6.3 Electric Fused Corundum Brick
(1) Electric fused corundum brick is made from high-purity alumina as the raw material, with a small amount of pure alkali added, and is melted at 2000-2200°C. The production process is similar to that of high-alumina products. The particle distribution should follow the principle of closest packing, using multi-stage ratios and increasing the amount of fine powder to improve the bulk density of the products and promote the sintering of the bricks. Aluminum oxide exists in various crystal forms, including electric fused α-Al2O3 brick, electric fused α-β-Al2O3 brick, and electric fused β-Al2O3 brick.
6.4 Electric Fused Chrome Corundum Brick
In AZS-33 brick, 10%-30% of Cr2O3 (mainly replacing Al2O3) is introduced, and the brick is produced by non-shrinkage casting to form electric fused chrome zircon corundum brick (referred to as AZCS brick, French designation ER2161). The surface and interior of the brick are dark green in color. The brick contains 4.5% shrinkage and no connected pores. The formation of aluminum-chromium spinel solid solution Al2O3·Cr2O3 (approximately 56%, with the remaining being corundum and glass phase) increases the viscosity of the glass phase and greatly improves the resistance to glass corrosion. It is 3.4 times that of ER1681 and 2.6 times that of ER1711. However, Cr2O3 can cause discoloration of the glass melt and cannot be used for colorless transparent glass. At the same time, its foaming index is not ideal, so it is an ideal material for the upper structure of tank furnaces.
6.5 Electric Fused Quartz Brick
The production process of electric fused quartz brick is the same as that of quartz glass. It uses high-purity quartz sand (with a SiO2 content of over 99.5%) as the raw material and a small amount of Na2O as a mineralizer. The material is melted in a graphite resistance furnace (1750-1800°C). After melting, the molten material is quickly removed, rolled into bricks, and then mechanically processed after cooling in the air. It has an extremely low thermal expansion coefficient and good thermal shock resistance. It has strong resistance to borosilicate glass corrosion but is not resistant to sodium-calcium-silicate glass corrosion. When the brick is held at temperatures above 1150°C for a long time, it gradually crystallizes into beta-quartz, consisting only of crystals without a glass phase. The onset temperature of load softening can be increased to 1720-1730°C.
7.Zirconium-Containing Refractory Brick
7.1 Zircon Stone Brick
7.2 Sintered Zirconia Corundum Brick
Sintered zirconia corundum brick is made from zircon stone and alumina, with a ZrO2 content generally below 20%. Zircon stone and alumina undergo a solid-phase reaction at 1400-1450°C, resulting in a microstructure with a uniform distribution of two phases: mullite and monoclinic zirconia. This irreversible reaction is also known as an in-situ reaction. The measured starting temperature of the reaction is 1397°C, between 1400-1425°C and 1500°C.
7.3 Zirconia Brick
(1) Zirconia brick is a refractory product mainly produced from zirconia. There are two main manufacturing methods: sintering and fusion casting. Zirconia exists in three crystal phases: monoclinic, tetragonal, and cubic. When zirconia is heated to around 1100°C, it undergoes a phase transformation from monoclinic to tetragonal, accompanied by a volume shrinkage of 7%; conversely, it expands in volume. Tetragonal zirconia transforms into cubic phase above 2300°C. The densities of the three crystal phases are 5.68 g/cm3 (monoclinic), 6.10 g/cm3 (tetragonal), and 6.27 g/cm3 (cubic), respectively.
(2) Zirconia has a high melting point, high temperature structural strength, and excellent resistance to acid and alkali erosion.
7.4 Zircon Mullite Brick
Zircon mullite brick is a cast refractory product made from mullite and zirconia. It has a dense crystal structure, high load softening temperature, good thermal stability, high mechanical strength at room and high temperatures, good wear resistance, good thermal conductivity, and excellent resistance to erosion.
7.5 Electric Fused Zirconia Corundum Brick
Electric fused zirconia corundum brick is made from AZS blocks or electric fused AZS waste bricks, with a small amount of kaolin or alumina added as a binder. When heated to a certain temperature, the electric fused AZS aggregate infiltrates the glass phase and reacts with the binder to form mullite, allowing the brick body to sinter. The firing temperature is in the range of 1600-1700°C. The chemical and phase composition of the fused blocks is highly uniform, with a low glass phase content. The chemical and phase composition of the waste bricks is less uniform, with a higher glass phase content (15%-25%). The chemical composition range of the combined products is as follows: Al2O3 50%-60%, ZrO2 20%-30%, SiO2 14%-20%.
