The main mineral composition of high alumina brick is mullite, corundum, and glass phase. As the AL2O3 content of high alumina brick increases, the number of mullite and corundum phases increases, the glass phase decreases accordingly, and the refractoriness and high-temperature performance of the product increases.
The increase in the number of glass phases and the decrease in viscosity will destroy the structure of high alumina brick, especially the presence of KO and NaO will not only lower the temperature of the generated liquid phase but also reduce the viscosity of the liquid phase, resulting in a rapid decrease in the high-temperature strength of the product.
For the high alumina products with AL2O3 content below 72%, the high-temperature stable phase is mullite, which increases with the AL2O3 content.
For the high alumina products with AL2O3 content above 72%, the high-temperature stable crystalline phase is mullite and corundum, which increases with AL2O3 content, the number of corundum increases and the number of mullite decreases, which increases the high-temperature strength of the products accordingly.
02. Three Grades Of High Alumina Brick
Therefore, high alumina brick is divided into three grades according to the level of AL2O3 content, the first-grade high alumina brick AL2O3 is more than 75%. Second-grade high alumina brick AL2O3 is 60%-75%. Third-grade high alumina brick aluminum content of 48%-60%, AL2O3 below 48% is collectively known as clay bricks.
Third-grade high alumina brick and clay brick performance are similar, its main crystal phase is mullite and glass phase. Because its high-temperature performance is better than clay brick, can use clay brick occasions can use three high alumina products, and two high alumina brick of the main crystal phase for mullite.
The high-temperature performance of this kind of product is better than clay brick: the main crystal phase of first-grade high alumina brick is mullite and corundum because the chemical stability and refractories of corundum are higher than mullite, so the higher the content of corundum in the products, the higher the high-temperature resistance and erosion resistance of the products. However, the coefficient of thermal expansion of corundum is much larger than that of mullite, thus the higher the corundum content, the lower its thermal shock resistance.
03. High-Temperature Properties Of High Alumina Brick
The essential working property of high alumina brick is the load softening temperature and high-temperature creep, the load softening temperature increases with the increase of the AL2O3 content of the product.
The load softening temperature of high alumina brick with AL2O3 content below 70% depends on the ratio between the number of mullite crystalline phase and liquid phase, and the load softening temperature of mullite-corundum products with AL2O3 content between 70% and 90% does not increase significantly with the increase of AL2O3. This is due to the FE2O3 and TIO2 components in the raw material slightly increasing with the increase of AL2O3, which changed the number and nature of the high-temperature liquid phase, the mullite crystalline phase partially softened at high temperatures, although the number of corundum increased. But can not form a skeleton, thus leading to no significant increase in load-softening temperature.
Only when the content of AL2O3 in the product is more than 90%, or even 95%, the main crystalline phase in the product is corundum, the direct bonding rate between the grains is obviously increased, and the liquid phase only exists in the space between the grains, so the load softening temperature is significantly increased.
The poor thermal shock stability of high alumina brick is closely related to the composition of the product’s physical phase. In production, usually adjust the particle composition of the clay, improve the particle structure characteristics of the product, and other measures to properly improve its thermal shock stability.
In the ingredients to add the appropriate amount of synthetic cordierite, zircon micro powder, etc., manufacturing high thermal shock stability of high aluminum products, and achieved some success.
Mainly used for masonry lime kiln, boiler, calcium carbide furnace, blast furnace, hot blast furnace, electric furnace roof, blast furnace, reflection furnace, and rotary kiln lining. In addition, high alumina bricks are also widely used as lattice bricks for storage heat in flat furnaces, plug heads for pouring systems, water spout bricks, etc.
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