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The production and application of Brown Fused Alumina (BFA) necessitate a comprehensive understanding of its fundamental chemical and physical properties. Due to the regional characteristics of BFA’s production and usage, both producers and consumers are intimately familiar with the specific quality requirements of this material.
To ensure the high quality of the final product, the production process of BFA must adhere to strict technical conditions. This includes a thorough understanding of the product’s applications, the production process, and the factors affecting BFA’s grinding and refractory properties.
Brown Fused Alumina is produced through a reduction process of calcined bauxite in an electric arc furnace, with coke and coal commonly used as reducing agents. During the smelting process, impurities in the bauxite, such as iron oxide, silicon dioxide, and titanium dioxide, are primarily retained in their oxide forms rather than being reduced to metals. The presence of these oxides in BFA significantly impacts its performance.
Understanding BFA’s physical structure is crucial for preventing quality issues. Microscopic examination reveals that BFA is primarily composed of α-alumina grains, which are bonded together by a small amount of glassy slag. A typical BFA consists of over 95% α-alumina crystals, which are composed of Al2O3 solid solutions containing Ti2O3. The glassy slag is mainly composed of silicon dioxide, titanium dioxide, and other trace oxides present in the electric arc furnace, forming the glass phase.
The solubility of these oxides in the α-alumina grain structure is low, making the content of glassy slag and the distribution of impurities between the α-alumina grains key factors affecting BFA’s performance. The α-alumina grants BFA high hardness and a high melting point, while the presence of the glass phase and impurities increases the material’s toughness or resistance to fracture.
For BFA that meets typical technical conditions, the ideal ratio of silicon dioxide to titanium dioxide in the glass phase should be adjusted based on specific applications and performance requirements, rather than simply approaching a 1:1 ratio. If the glass phase contains too much silicon dioxide, the excess silicon dioxide may react with alumina to form mullite (2SiO2·3Al2O3), potentially reducing BFA’s toughness.
On the other hand, if there is an excess of titanium dioxide (TiO2) in BFA, it may react with alumina to form aluminum titanate (TiO2·Al2O3). The formation of this third phase can weaken the interface between the α-alumina grains and the glass phase. The difference in thermal expansion coefficients among the three phases may also cause cracks between grains during heating, affecting the material’s performance.
In summary, the production and application of Brown Fused Alumina require an in-depth understanding of its chemical composition, physical structure, and the impact of impurities. By precisely controlling the production process and material composition, the performance of BFA can be optimized to meet the demands of various applications.