Aluminosilicate refractory materials with an Al2O3 content greater than 48% are collectively called high-aluminum refractory materials. Its final product is the high alumina brick most commonly used in thermal kilns. According to the Al2O3 content, high alumina bricks can be divided into three grades:
Class I: Al2O3>75%;
Class II: Al2O360%~75%;
Grade III: Al2O348%~60%.
Classified according to mineral composition: low mullite and mullite (Al2O348%~71.8%); mullite-corundum and corundum-mullite (Al2O371.8%~95%); corundum (Al2O395 %~100%). In the range of Al2O3 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 decreases. The number increases. The fire resistance of the product increases with the increase in Al2O3 content.
High alumina bricks refer to aluminosilicate or pure alumina sintered products containing more than 48% Al2O3. Generally, high alumina refractory bricks contain less than 80% Al2O3, and those containing more than 80% Al2O3 are called corundum bricks.
Compared with clay bricks, the outstanding advantages of high alumina fire bricks are high refractoriness and load softening temperature.
1. Refractory resistance
The refractoriness of high aluminum bricks fluctuates widely, generally between 1770 and 2000°C. It is mainly affected by the Al2O3 content and increases with the increase of the Al2O3 content in the product. At the same time, the refractoriness is also affected by the content and type of impurities, and is related to the mineral structure of the product.
2. Load softening temperature
The softening deformation temperature of high alumina bricks under load is greater than 1400°C, and increases with the increase of Al2O3 content. For products with an Al2O3 content of less than 71.8%, the load softening temperature depends on the quantity ratio of mullite and glass phases, and increases with the increase in the quantity of mullite. The amount and nature of the glass phase have a significant impact on the load softening point. When the Al2O3 content is 71.8% to 90%, it is a mullite or corundum product. As the Al2O3 content increases, the glass phase volume basically remains unchanged. Although corundum increases, the mullite decreases; therefore, the softening temperature under load does not increase. Significantly. After the Al2O3 content exceeds 90%, as the Al2O3 content increases, the number of glass phases decreases and the load softening temperature increases significantly, from 1630°C when Al2O3 is 90% to 1900°C when Alz03 is 100%. The load softening temperature increases with the increase in Al2O3 content. improve.
3. Thermal conductivity
High-aluminum refractory products have higher thermal conductivity than clay products. The reason is that there is less glass with low thermal conductivity in high-aluminum products, while the amount of mullite and corundum crystals with better thermal conductivity increases, which improves the thermal conductivity of the product. Thermal conductivity decreases as temperature increases.
The thermal conductivity of high alumina bricks is different from clay bricks and silica bricks. The thermal conductivity of high aluminum refractory bricks decreases as the temperature increases. When the Al2O3 content in high alumina firebricks is higher, the more mullite and corundum crystals there are, the more obvious the tendency of thermal conductivity to decrease as the temperature increases. But above 1000℃, the decrease rate decreases. The thermal conductivity of clay bricks and silica bricks increases with temperature, showing a linear relationship, and does not change near 1000°C. At normal temperature, the thermal conductivity of high aluminum refractory bricks is 2 to 3 times greater than that of clay bricks, but their thermal conductivities are basically similar above 1000°C.
Varieties with low Al2O3 content in high alumina bricks are similar to clay bricks in load softening point and thermal shock resistance. However, as the Al2O3 content increases, the load softening point and thermal shock resistance gradually increase. These characteristics of high alumina refractory bricks make them a high-temperature type of clay bricks, so they can be used in high-temperature parts of glass melting furnaces. Varieties with low porosity can be used in high-temperature parts of the regenerator, such as the roof and upper walls of the regenerator.
