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Performance and Working Principles of 9 Common Refractory Bricks for Glass Kilns
2026-05-08
01 Silica Bricks
Silica bricks are acidic refractory materials. Specifically, silica bricks designed for glass kilns are siliceous refractory products—primarily composed of cristobalite and quartz—used for lining the high-temperature zones of glass melting furnaces. They exhibit a high load deformation temperature, ranging from 1640°C to 1680°C, which approaches the melting points of cristobalite and tridymite (1670°C and 1713°C, respectively). High-quality silica bricks are characterized by high purity and density, a high load-softening temperature, low re-firing shrinkage, excellent resistance to high-temperature creep, high compressive strength at room temperature, an optimal mineral phase composition, low true density, and precise dimensions. With the current trend toward increasingly large-scale photovoltaic glass kilns—accompanied by higher glass melting temperatures—silica bricks face limitations due to their relatively low refractoriness (1690°C to 1730°C) and poor thermal shock resistance (typically withstanding only 1 to 4 thermal cycles when quenched in water). Consequently, they are unable to meet the structural requirements for the large crown arches in the melting zone; however, they remain the unrivaled choice for the superstructure of the cooling zone.
Silica bricks details :
https://www.skrefractory.com/high-quality-silica-brick-use-for-industry-furnace-product/
02 Clay Bricks
Clay bricks are acidic refractory materials; as the Al₂O₃ content within the bricks increases, their acidity gradually diminishes. Among all refractory materials, they possess the lowest thermal conductivity. Although their refractoriness reaches as high as 1700°C, their load-softening temperature is only around 1300°C. Furthermore, when subjected to significant corrosion by R₂O, this softening temperature drops even further to approximately 1050°C; consequently, they cannot bear structural loads or withstand compressive stress during high-temperature applications. Clay bricks exhibit the lowest coefficient of thermal expansion among commonly used refractory materials. Moreover, due to their fine crystalline structure and small, uniformly distributed pores, internal stresses are readily buffered; as a result, they demonstrate strong resistance to thermal shock across a wide temperature range, making them suitable for use in secondary critical areas of kilns and furnaces, such as flues.
Clay bricks details :
03 High-Alumina Bricks
Aluminosilicate refractory materials with an Al2O3 content exceeding 48% are collectively referred to as high-alumina refractory materials. Based on their Al2O3 content, they are classified into three grades:
Grade I: Al2O3 > 75%;
Grade II: Al2O3 60%–75%;
Grade III: Al2O3 48%–60%.
Within the range where the Al2O3 content is less than 71.8%, the proportion of mullite—the primary crystalline phase in high-alumina products—increases as the Al2O3 content rises. Conversely, within the range where the Al2O3 content exceeds 71.8%, the quantity of mullite decreases while the quantity of corundum increases as the Al2O3 content increases. The refractory properties of these products improve in tandem with an increase in their Al2O3 content. Compared to clay-based refractory materials, high-alumina refractories possess distinct advantages, notably their high refractoriness and high refractoriness under load (RUL). Furthermore, high-alumina refractory products exhibit higher thermal conductivity than their clay-based counterparts. The thermal shock resistance of high-alumina refractory products falls between that of clay-based products and silica-based products; consequently, they are suitable for use as skewbacks within the thermal insulation layer of the main arch in glass melting furnaces.
high alumina brick details :
04 Sillimanite Bricks
Compared to clay bricks, sillimanite and mullite bricks exhibit a higher softening point under high-temperature load. Characterized by a dense, fine-grained structure, they are less prone to inducing bubble formation in molten glass, making them exceptionally suitable for structural components at the glass discharge port.
Sillimanite Bricks details :
05 Mullite Bricks
The primary crystalline phase of mullite bricks is mullite. Mullite possesses a refractoriness of approximately 1850°C, high refractoriness under load, a low high-temperature creep rate, excellent thermal shock resistance, and resistance to acidic slag corrosion; it is a suitable choice for the lower structures of vertical flues as well as the internal surfaces of horizontal flues.
Details :
06 Fused Mullite Bricks
Fused mullite is manufactured using high-alumina bauxite as the raw material. Various bauxite sources are blended to achieve the stoichiometric composition of mullite (3Al2O3·2SiO2), with mass percentages of 72% Al2O3 and 28% SiO2. The primary crystalline phases consist of mullite and corundum, while a glassy phase fills the interstitial spaces between the crystals. Its resistance to corrosion by molten glass is superior to that of sintered refractory materials, though it is not quite as robust as other types of fused refractory materials. The addition of a small amount (7%–8.5%) of zirconium dioxide serves to refine the mullite crystals and densify the brick's microstructure; this increases the mullite content to 60%–70%, thereby relatively reducing the proportion of the glassy phase and minimizing cracking in the finished product. Fused mullite bricks are characterized by a low coefficient of thermal expansion, excellent thermal shock resistance, and strong resistance to corrosion by molten glass.
07 Fused Cast Zircon-Corundum Bricks
Fused cast zircon-corundum bricks belong to the Al2O3-ZrO2-SiO2 system (abbreviated as AZS bricks). Based on their ZrO2 content, they are classified into three grades: 33%, 36%, and 41%. Compared to fused cast mullite bricks, fused cast zircon-corundum bricks exhibit superior resistance to corrosion by molten glass. The primary reasons for this are:
① The dominant crystalline phases in zircon-corundum bricks are corundum and baddeleyite (monoclinic zirconia), which coexist in a dense, interlocking structure; both of these crystalline phases possess excellent corrosion resistance.
② The glassy phase within the zircon-corundum bricks fills the interstitial spaces between the aforementioned crystalline phases. When subjected to corrosion by high-temperature molten glass, this glassy phase transforms into a high-viscosity albite-rich glass. Its viscosity is further enhanced by the dissolution of a certain amount of ZrO2 into the matrix. This layer of highly viscous glass remains on the brick's surface, resisting diffusion and thereby protecting the underlying brick body. The corrosion resistance of fused cast zircon-corundum bricks improves as their ZrO2 content increases. Notably, ZrO2 possesses an extremely high melting point—approximately 2700°C—and demonstrates exceptional resistance to corrosive media such as acids, alkalis, and molten glass.
Fused cast zircon-corundum bricks are utilized not only in areas exposed to molten glass characterized by high temperatures and severe corrosion but are also widely employed in the superstructure of glass melting furnaces.
details : https://www.skrefractory.com/fused-casting-azs33-36-41-block-product/
08 Fused Corundum Bricks
Fused corundum bricks [α-β-Al2O3 (94.5%–96.5%)] are manufactured using high-purity alumina as the raw material, with the addition of a small amount of soda ash, and are fused at temperatures ranging from 2000°C to 2200°C. The crystalline structure consists of 45%–55% α-Al2O3 and 45%–60% β-Al2O3 phases. Because a relatively large quantity of β-Al2O3 is interwoven among the α-Al2O3 crystals, the original tubular microstructure of the α-Al2O3 is transformed into a lamellar (scaly) structure; furthermore, the crystals are significantly finer than they would be if existing independently. Consequently, while its resistance to corrosion is second only to that of pure α-Al2O3, the brick's resistance to thermal deformation is substantially enhanced. This makes it the optimal choice of refractory material for the walls of the glass flow channel and for the main arch (crown) in the refining zone of the melting furnace.
At high temperatures, the relative resistance of refractory materials to corrosion follows this order: AZS-41# > AZS-36# > AZS-33# > α-β-Al2O3. This is because the primary crystalline phases in fused zirconia-corundum bricks are a dense, coexisting mixture of corundum (α-Al2O3) and baddeleyite (ZrO2), both of which possess excellent corrosion resistance. The corrosion resistance of fused zirconia-corundum increases in direct proportion to its ZrO2 content. Given the high strength requirements for arch abutment bricks—and considering that volatile substances from the molten glass tend to accumulate in this area—it is recommended that the arch abutment bricks in a glass melting furnace be selected from the AZS-33# fused refractory series. By the same token, corner sections of the furnace pool walls are subjected to even more intense scouring by the molten glass, and volatile glass substances and alkali vapors accumulate there more readily; therefore, it is generally advisable to select fused refractory bricks with a higher ZrO2 content, with the AZS-41# fused refractory brick being the optimal choice.
09 Zirconia Refractory Bricks
Zirconia-containing refractory products are refractory materials manufactured using zirconia (ZrO2) and zircon (ZrSiO4) as raw materials. This category encompasses zirconia-series products, zircon-series products, as well as zircon-mullite and zircon-corundum series products. Based on their manufacturing processes, zirconia-containing refractory products are classified into sintered products, fused-cast products, and unfired products. These materials are characterized by a high melting point, low thermal conductivity, and excellent chemical stability—specifically, they exhibit superior resistance to corrosion by molten glass.
The properties of zirconia-containing refractory materials are fundamentally determined by the properties of ZrO2 itself. Zirconia products exhibit exceptionally high mechanical strength, a level of strength that is effectively maintained even at temperatures ranging from 1300°C to 1500°C. Furthermore, the thermal conductivity of ZrO2 is significantly lower than that of any other oxide-based refractory material. This specific characteristic of ZrO2 makes it an ideal material for use in high-temperature thermal insulation layers.