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In the field of refractory materials, alumina refractory materials, with their excellent high-temperature stability and wide applicability, have become indispensable important materials in industrial production. This article will delve into the production process of alumina refractory materials, especially focusing on the key points of their unique production process and the manufacturing process of transparent alumina products, showcasing their exquisite craftsmanship and excellent performance.
Alumina refractory materials, especially those using high-purity raw materials with Al₂O₃ content greater than 99%, are meticulously manufactured using high-temperature ceramic processes and are acclaimed as "corundum special refractory materials". The core of their production process lies in the precise treatment of raw materials and scientific forming and sintering technology.
Raw Material Pretreatment
This is the first step in the production process of alumina refractory materials. Industrial alumina raw materials are pre-fired at 1350~1600℃ to ensure the transformation of γ-Al₂O₃ into stable α-Al₂O₃, while reducing the shrinkage rate of the product and effectively preventing cracking. This process lays a solid foundation for subsequent forming and sintering.
Fine Milling
The pre-treated raw alumina refractory materials need to be further milled to achieve a requirement where particles smaller than 5μm account for more than 90%. If a mill with iron balls or liners is used, strict acid washing and iron removal treatments are required to ensure product purity.
Forming and Drying
The forming stage uses various methods such as slip casting or mechanical pressing, flexibly chosen based on the shape and requirements of the product. Slip casting is mostly used for hollow products like crucibles and tubes, while mechanical pressing combines fine powder and coarse particles under high pressure by adding a binder. The formed bodies need to be dried to reduce moisture content to 1%~1.5%, ensuring sintering quality.
High-Temperature Sintering
Sintering is a critical step in the production of alumina refractory materials. The firing temperature is generally controlled at 1600-1800℃, and for pure alumina products, it is no less than 1800℃. Adding sintering aids (such as TiO₂) can lower the firing temperature to 1600-1650℃, promoting densification and enhancing product performance.
Transparent alumina products, as high-end products among alumina refractory materials, have a more refined production process based on the basic process.
Selection of Ultra-Pure Raw Materials
Transparent alumina products require extremely high purity of raw materials, using ultra-pure alumina raw materials with Al₂O₃ content above 99.9%. These materials are often produced through special methods such as ammonium aluminum sulfate and undergo strict calcination processes to ensure stable physical and chemical properties.
Fine Milling and Impurity Control
During the milling process, not only must the particle fineness meet very high standards (most are smaller than 1μm), but the material and wear rate of the milling balls and jars must also be strictly controlled to prevent impurity contamination. Appropriate dispersants and impurity removal processes are used to ensure the purity and dispersion of the raw materials.
Precise Use of Additives
To inhibit the growth of alumina grains and improve the transparency of the product, precise amounts of MgO, Y₂O₃, or La₂O₃ inhibitors are needed. These additives react with Al₂O₃ under suitable conditions to form a uniform microstructure, thereby increasing the light transmittance of the product.
Careful Control of Sintering Process
The sintering process of transparent alumina products needs to be conducted in an H₂ or vacuum environment to eliminate pores within the grains and inhibit grain growth. By increasing the firing temperature and extending the holding time, further densification and enhancement of light transmittance can be achieved.
In summary, the production process of alumina refractory materials covers multiple steps from raw material pretreatment to high-temperature sintering, each of which requires strict control to ensure the excellent performance of the product. The manufacturing of transparent alumina products further pursues the ultimate in craftsmanship and technology, showcasing high-tech and high-precision in the field of refractory materials.
