High alumina refractory brick is referred to as high alumina brick. Its main mineral composition is mullite, corundum and glass phase. As the Al2O3 content of high alumina bricks increases, the amount of mullite and corundum phases also increases, the glass phase decreases accordingly, and the refractory resistance and high temperature performance of the products increase accordingly. An increase in the amount of glass phase and a decrease in viscosity will destroy the structure of high alumina bricks. In particular, the presence of KO and NaO not only reduces the temperature at which the liquid phase is generated, but also reduces the viscosity of the liquid phase, resulting in a rapid decline in the high-temperature strength of the product. For high-aluminum products with an Al2O3 content of less than 72%, the only high-temperature stable crystal phase is mullite, which increases with the increase in Al2O3 content; for high-aluminum products with an Al2O3 content of more than 72%, the high-temperature stable crystal phases are mullite and For corundum, as the Al2O3 content increases, the amount of corundum increases and the amount of mullite decreases, which accordingly increases the high-temperature strength of the product.
Therefore, high alumina bricks are divided into three levels according to the content of AL2O3. The first-level high alumina bricks have Al2O3 greater than 75%; the second-level high alumina bricks have 60%-75% Al2O3; and the third-level high alumina bricks have an aluminum content of 48%-60%. , Al2O3 less than 48% are collectively called clay bricks.
The properties of third-grade high alumina bricks and clay bricks are similar, and their main crystal phases are mullite and glass phases. Because its high-temperature performance is better than that of clay bricks, third-level high-aluminum products can be used wherever clay bricks can be used. The main crystal phase of second-level high-alumina bricks is mullite. The high-temperature performance of this type of product is significantly better than that of clay bricks: the main crystal phases of first-class high-alumina bricks are mullite and corundum. Since corundum has higher chemical stability and fire resistance than mullite, the higher the corundum content in the product. , the higher the high temperature resistance and erosion resistance of the product. However, the thermal expansion coefficient of corundum is much larger than that of mullite, so the higher the corundum content, the lower its thermal shock resistance.
The important working properties of high alumina bricks are load softening temperature and high temperature creep. The load softening temperature increases with the increase of the AL2O3 content of the product, as shown in the figure below. The load softening temperature of high alumina bricks with an Al2O3 content below 70% depends on the quantitative ratio between the mullite crystal phase and the liquid phase. For mullite-corundum products with an Al2O3 content between 70% and 90%, as the Al2O3 Increase, the load softening temperature does not increase significantly. This is because the Fe2O3 and TiO2 components in the raw material increase slightly with the increase of Al2O3, which changes the quantity and properties of the high-temperature liquid phase. The mullite crystal phase partially softens at high temperatures, and the corundum quantity Although there is an increase, it cannot form a skeleton, resulting in no significant increase in the softening temperature under load. Only when the Al2O3 content in the product is greater than 90%, or even reaches more than 95%, the main crystal phase in the product is corundum, the direct bonding rate between crystal grains is significantly improved, and the liquid phase only exists in the gaps between the crystal grains, and its load The softening temperature is significantly increased.
The high temperature creep behavior of high alumina bricks is expressed by creep rate. The torsional creep rates of the first-level and second-level high alumina bricks are similar. At 1200°C, the creep rate is 0.25~0.29×10-5R.h, while the third-level high alumina bricks are 3.5×10 at the same temperature. -5r·h, 10 times higher than the first and second grade high alumina bricks.
Phase analysis shows that the glass phase content in first- and second-level high alumina bricks is 7% to 9%, and that in third-level high alumina bricks is 20%. The creep rate is not only related to the glass phase content, but also to the composition and its composition of the glass phase. Related to high temperature viscosity. The liquid viscosity of the third-level high alumina brick at 1200°C is only half of that of the first-level high alumina brick and 26% of that of the second-level high alumina brick. Therefore, in the creep behavior of the third-level high alumina bricks, the glass phase plays a leading role, while in addition to the glass effect in the first- and second-level bricks, grain boundary creep plays an important role. The higher the direct bonding rate between the crystal phases, the greater the effect of grain boundary creep. The more obvious it is. Obviously, improving the purity of raw materials, changing the chemical and mineral composition of the matrix, reducing the number of glass phases and adjusting the composition of the glass phase during production are the keys to improving high-temperature creep properties. It can also improve high temperature volume stability and slag resistance.
The thermal shock stability of high alumina bricks is poor, which is closely related to the phase composition of the product. In production, measures such as adjusting the particle composition of the mud and improving the particle structure characteristics of the product are usually used to appropriately improve its thermal shock stability. Adding an appropriate amount of synthetic cordierite, zircon powder, etc. to the ingredients to produce high thermal shock stability and high aluminum products has achieved certain results.
High alumina bricks are widely used as lining materials for thermal equipment used in industrial production fields such as metallurgy, machinery manufacturing, petrochemical industry, power and light industry.
