Special Grade High-Alumina Bricks
Special grade high-alumina bricks are composed of 88% alumina bauxite clinker, 85% aluminum powder, and a binder. The 88% alumina bauxite is crushed into granules. These granules are mixed in proportion and thoroughly blended in a mixer. The mixture is then pressed into semi-finished products using a hydraulic press. The semi-finished products are fired in a tunnel kiln at a temperature of 1470°C. The final product has an aluminum content of 85%.
Special grade high-alumina bricks are dense refractory bricks with high compressive strength and density. The firing temperature for special grade high-alumina bricks is higher than that of ordinary high-alumina bricks, and their service life is twice that of ordinary high-alumina refractory bricks. The raw material for special grade high-alumina bricks is special grade alumina bauxite clinker calcined in a rotary kiln, with an alumina content of over 85% and a bulk density of 2.6-2.8. Bauxite clinker powder and fine powder are added, along with a certain proportion of sillimanite powder. Paper pulp solution is used as a binder. The process involves mixing different particle sizes, kneading, forming, drying, and firing in an oxidizing atmosphere at 1470°C to produce the refractory brick.
Comparison with Ordinary High-Alumina Bricks
The raw materials used for special grade high-alumina bricks are different from those used for ordinary high-alumina bricks. The most significant difference is the alumina content. Ordinary high-alumina bricks use materials with an alumina content of 55%-75%, and a bulk density of 2.3-2.5. Therefore, there is a significant difference in quality between different types of high-alumina bricks.
Key Properties of High-Alumina Bricks
The refractoriness of high-alumina bricks is a critical indicator, as is bulk density. Each type of high-alumina brick has different refractoriness and bulk density. The refractoriness of ordinary high-alumina bricks is not less than 1750°C, while that of special grade high-alumina bricks is 1800°C, with a higher bulk density and greater density. The crystalline phases of high-alumina bricks consist of mullite, glassy phase, and corundum. The higher the alumina content, the greater the proportion of corundum. As the alumina content increases, the mullite content also increases, and the formation of long-columnar mullite crystals in high-alumina refractory bricks creates a robust network structure that helps to increase the load-softening temperature of the bricks.
Special grade high-alumina bricks have an alumina content of 85% and a high load-softening temperature. With a high alumina content, the proportion of corundum in the structure increases, and the mullite crystals cannot form a complete network structure. Instead, a relatively loose corundum-mullite framework is formed. Additionally, as the alumina content increases, the iron content in the glassy phase decreases, and the viscosity of the liquid phase decreases. The load-softening temperature of special grade high-alumina bricks is minimally affected by the alumina content. However, when the alumina content exceeds 90%, the corundum forms a stable framework. Due to the high purity of the raw materials, the impurity content is low, and the amount of glassy phase is minimal. Therefore, as the alumina content increases, the load-softening strength also increases, resulting in greater density. In summary, the purity of the raw materials, the chemical and mineral composition of the matrix, and the amount of glassy phase are key factors in improving the high-temperature structural strength, thermal shock stability, and slag resistance of special grade high-alumina bricks.
Applications
Special grade high-alumina bricks are used in various parts of industrial furnaces, including electric furnace roofs, blast furnaces, hot blast stoves, blast furnace hearths, cupola furnaces, reverberatory furnaces, transition zones of rotary kilns, and lime kilns.