By Cathy | 01 April 2024 | 0 Comments
The alpha-alumina family: from properties to preparation to applications
Aluminum oxide has many phase transitions, with more than a dozen transition phases and a thermodynamically stable phase, i.e., α-alumina. α-alumina, due to its special structure, has the characteristics of high-temperature resistance, hardness, etc., and also has high chemical stability, and is commonly used in the reinforcing and toughening of a wide range of products to enhance wear resistance, densification, fracture toughness, etc.. As a catalytic carrier, refractory material, integrated circuit board base, aerospace wing leading edge, etc., its stable performance brings versatile uses and has high application prospects.
α-Alumina has stable properties as well as versatile properties and applications. Due to its excellent synthetic design and complete industrialization system, it has a wide range of applications in petrochemical, refractory materials, construction materials, military industry and weapons.
Structure and properties of α-alumina
α-Al2O3 is a tripartite crystal system, with oxygen ions arranged in a hexagonal close-packed arrangement and aluminum ions located in the center of the octahedron, filling 2/3 of the octahedral gap and keeping the furthest distance from each other to comply with the principle of Bubbleley incompatibility. This structure gives α-Al2O3 a strong structural stability. The transformation paths of the alumina crystallites to each other are related to the preparation conditions, and the crystallites are present in the form to some extent mixed at various stages during the temperature increase. Until after 1200°C, the substance obtains enough energy to complete the macroscopic volume change and internal structural rearrangement, and the crystal lattice is converted from Fcc to Hcp, which finally turns into the thermodynamically stable phase α-Al2O3.Relationship between various crystal types of aluminum oxide
However, in actual products, α-Al2O3, as a solid substance at room temperature, usually has certain unsaturated structures and defects on its surface. Suspension bonds and exposed aluminum and oxygen atoms give α-Al2O3 certain Lewis acid and alkali properties, and, at the same time, some surface adsorption capacity, which can be used as a modified adsorption point for catalytic carriers in order to pick up the active centers of various functions and build a complete catalytic system. Because of such surface structure, the aqueous phase dispersion of α-Al2O3 particles is not high, and the addition of dispersant, improved ball milling and ultrasonication can increase its dispersion in aqueous solution.Types of alpha-alumina and preparation methods
The alumina industry commonly produces α-Al2O3 by electrolysis of cryolite-alumina melts, and the production methods have expanded from alkali methods to other methods such as acid, combined acid-base and thermal methods. As the high-temperature stabilized phase of alumina, α-Al2O3 is often obtained above a roasting temperature of 1200 °C. The alumina is also produced in the form of a high-temperature stabilized phase, α-Al2O3.
Applications of α-Alumina
α-Al2O3 is commonly used in industrial fillers, catalysis and other applications due to its special structure and physicochemical properties.α-Alumina has stable properties as well as versatile properties and applications. Due to its excellent synthetic design and complete industrialization system, it has a wide range of applications in petrochemical, refractory materials, construction materials, military industry and weapons.
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