Calcined alumina is a high-purity inorganic non-metallic material produced by calcining industrial-grade alumina at high temperatures. Its chemical composition is Al₂O₃, and depending on the calcination temperature and process, it can form various crystal structures such as α-Al₂O₃ and γ-Al₂O₃. α-Al₂O₃ exhibits high hardness, high melting point (approximately 2054°C), and strong chemical stability; while γ-Al₂O₃ has a high specific surface area and good adsorption properties. It typically appears as a white powder, and its particle size can be precisely controlled to suit specific applications, ranging from submicron to micron size. Its density is approximately 3.9–4.0 g/cm³, and it is insoluble in water and most acids, reacting only with strong alkalis at high temperatures.
Calcined alumina has key applications in the ceramics industry
1. Improved mechanical properties:
Adding calcined alumina to ceramic raw materials can significantly enhance the hardness, strength, and wear resistance of the ceramic. Because alumina itself has high hardness and rigidity, it strengthens the crystalline structure within the ceramic, making it more resistant to damage from external impacts and abrasion. This makes it suitable for producing high-performance products such as ceramic floor tiles and wear-resistant industrial ceramic components.
2. Improved thermal properties:
Calcined alumina has a low coefficient of thermal expansion, which effectively reduces the thermal expansion rate of ceramics and enhances their thermal stability. This minimizes the risk of cracking due to thermal stress during high-temperature firing and under fluctuating temperature conditions, making it suitable for producing high-temperature ceramics, kiln components, refractory ceramics, and other products requiring high thermal stability.
3. Improved electrical properties:
Its excellent electrical insulation and dielectric properties make calcined alumina a key raw material for electronic ceramics. In the production of electronic components such as circuit boards and ceramic capacitors, it enhances the insulation performance and dielectric constant stability of the ceramics, ensuring the normal operation of electronic devices.
4. Enhanced chemical stability:
Calcined alumina has stable chemical properties, which strengthens the resistance of ceramics to acid and alkali corrosion, maintaining their structural integrity in harsh chemical environments. This makes it widely used in chemical engineering ceramics and corrosion-resistant ceramic pipes.
5. Promotion of sintering densification:
As a sintering aid, under certain conditions, it can lower the sintering temperature of ceramics, promoting grain growth and densification during the firing process, reducing porosity, and improving the density and gloss of the ceramics, thus optimizing the appearance and quality of ceramic products.
The application of calcined alumina varies across different types of ceramics
1. Building ceramics:
In the production of ceramic floor tiles, calcined alumina is commonly used to enhance the wear resistance and hardness of the tiles, enabling them to withstand frequent foot traffic and abrasion. Furthermore, by adjusting the amount added, the thermal stability of the tiles can be optimized, preventing cracking and deformation due to temperature changes. For wall tiles, it improves the gloss and hardness of the glaze, enhances its stain resistance, and facilitates easy cleaning and maintenance.
2. Electronic Ceramics:
This is a core raw material in the field of electronic ceramics. When used in manufacturing integrated circuit substrates, its high insulation properties, good thermal conductivity, and stable dielectric properties effectively enhance circuit integration and operational stability. In the production of ceramic capacitors, it allows for precise control of the dielectric constant, meeting the capacitance performance requirements of various electronic devices.
3. Special Ceramics:
Calcined alumina is a key raw material in the production of special ceramics such as alumina ceramic cutting tools, ceramic bearings, and high-temperature structural ceramics. By controlling its particle size, purity, and crystal structure, high-performance ceramic products with high strength, hardness, high-temperature resistance, and corrosion resistance can be produced, widely used in high-end fields such as mechanical processing, aerospace, and new energy.
4. Everyday Ceramics:
Adding an appropriate amount of calcined alumina to everyday ceramics can improve the mechanical strength of the ceramics and reduce breakage during use. It also helps to improve the whiteness and transparency of the ceramics, enhancing the aesthetic appeal and quality of the product.
