High alumina bricks refer to sintered products containing more than 48% of Al2O3, alumina silicate or pure alumina. Generally, high-alumina bricks contain less than 80% of Al2O3, and those containing more than 80% of Al2O3 are called corundum bricks.
Compared with clay bricks, high-alumina bricks have the outstanding advantages of high refractoriness and high load softening temperature. In the use of industrial kilns, there are five common types of high-alumina bricks.
(1) Ordinary high aluminum bricks
Ordinary high aluminum bricks have become the preferred material in many thermal kilns due to their unique composition and excellent performance. Its mineral composition mainly includes mullite, corundum and glass phase. The ratio and content of these three directly determine the overall performance of high-alumina bricks.
With the gradual increase of the content of alumina (Al2O3), the content of mullite and corundum also shows a corresponding growth trend, while the content of glass phase gradually decreases. This change not only significantly improves the refractoriness of high-alumina bricks, but also makes their performance in high-temperature environments more stable and outstanding.
Compared with traditional clay products, ordinary high-alumina bricks show more excellent refractory performance. This is not only reflected in their higher refractoriness, but also in their ability to maintain a longer stable state during use, thereby effectively extending the service life of the kiln. This advantage has led to the wide application of high-alumina bricks in various thermal kilns. Whether it is metallurgy, glass, ceramics or other industries that require high-temperature treatment, high-alumina bricks have won market recognition for their outstanding performance.
(2) High-load soft high alumina bricks
High-load soft high-alumina bricks stand out for their outstanding performance and have become the preferred material for many high-temperature environments. Compared with ordinary high-alumina bricks, high-load soft high-alumina bricks have undergone unique optimization and improvement in the matrix and binder parts, thereby achieving significant performance improvements.
In the matrix part, high-load soft high-alumina bricks not only add precious tri-stone concentrate, but also cleverly introduce high-alumina materials such as corundum powder and high-aluminum corundum powder based on the theoretical composition of the chemical composition after burning close to mullite. The addition of these high-alumina materials not only enhances the structural stability of the brick body, but also further improves its refractory performance.
In terms of the selection of binders, high-load soft high-alumina bricks have also made great efforts. It uses high-quality ball clay as a binder, and flexibly selects different clay composite binders or mullite binders according to different varieties and needs. This refined selection and design enables high-load soft high-alumina bricks to form a tighter and stronger structure during the firing process, thereby further improving its load softening temperature.
(3) Low creep high alumina bricks
In order to improve the creep resistance of high-alumina bricks, we adopted the technical strategy of unbalanced reaction. The core of this strategy is to carefully select and add high-quality raw materials such as tri-stone minerals and activated alumina according to the actual operating temperature of the kiln, so that the composition of the matrix is as close to or completely reaches the composition of mullite as possible. This is because mullite, as a high-performance refractory mineral, has excellent mechanical and thermal properties, which can significantly improve the overall high-temperature performance of the material.
In the process of achieving mullite formation of the matrix, we strictly controlled the ratio of alumina (Al₂O₃) to silica (SiO₂), which is the key to ensuring complete mullite formation of the matrix. Through this fine regulation, we successfully reduced the content of the glass phase and further improved the creep resistance of the material.
(4) Phosphate-bonded high-alumina bricks
Phosphate-bonded high-alumina bricks play an irreplaceable role in many high-temperature industrial furnaces with their unique preparation process and excellent performance. This product uses high-quality, dense special or first-grade high-alumina bauxite clinker as the main raw material, cleverly uses phosphate solution or aluminum phosphate solution as a binder, and uses a semi-dry machine pressing process, and then undergoes precise heat treatment at 400 to 600°C, ultimately creating a chemically bonded high-performance refractory product.
It is worth noting that phosphate-bonded high-alumina bricks belong to the category of unfired bricks. In order to effectively avoid the shrinkage of products that may occur during use, we carefully introduce heat-expanding raw materials such as kyanite and silica into our ingredients. The addition of these raw materials not only effectively alleviates the shrinkage of the products, but also further improves their overall stability.
Compared with ceramic-bonded fired high-alumina bricks, phosphate-bonded high aluminum bricks show obvious advantages in anti-stripping performance. However, there is still room for improvement in terms of load softening temperature and erosion resistance. To make up for this deficiency, we cleverly add a small amount of high-quality materials such as fused corundum and mullite during the preparation process. The addition of these materials not only significantly strengthens the matrix, but also further improves the high temperature resistance and erosion resistance of the products.
(5) Micro-expanding high-alumina bricks
Micro-expanding high-alumina bricks are mainly made of high-quality high-alumina bauxite as the main raw material, and are cleverly added with selected three-stone concentrates. They are carefully crafted by strictly following the production process of high-alumina bricks.
In order to enable high alumina bricks to expand appropriately during use, we pay special attention to the selection of three-stone concentrates and the control of their particle size. By carefully selecting suitable tri-stone concentrates and strictly controlling the firing temperature, we have successfully caused some of the selected tri-stone minerals to undergo mullitization reaction, while retaining some unreacted tri-stone minerals. These residual tri-stone minerals will further undergo mullitization reaction (i.e. primary or secondary mullitization) during use, accompanied by volume expansion, thus giving high-alumina bricks unique micro-expansion properties.
Micro-expansion high-alumina bricks play an irreplaceable role in various high-temperature industrial kilns due to their unique micro-expansion properties and excellent resistance to slag penetration. Whether it is metallurgy, glass, ceramics or other industries that require high-temperature treatment, micro-expansion high-alumina bricks can provide solid guarantees for the production of enterprises with their excellent performance and stable quality.
