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Aluminium oxide, A new generation of indispensable hard materials

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Update time : 2019-08-19 15:25:00
Aluminium oxide is a white solid, a compound of aluminum and oxygen, and has a molecular formula of Al₂O₃. It is also known as bauxite in mining, ceramics and materials science.
As an important chemical material, spherical alumina has a series of excellent properties such as high hardness, high strength, corrosion resistance and high temperature resistance. Spherical alumina has the above properties, and is widely used in ceramic materials, chemical mechanical polishing abrasives, catalysts and catalyst carriers due to its size and morphology. In a broad sense, alumina can be divided into two major categories: aqueous alumina and anhydrous alumina.
 
Aqueous alumina
Aqueous alumina is also known as hydrated alumina, and six variants of alumina hydrate have been identified. Alumina trihydrate, including industrial aluminum hydroxide (α-Al₂O₃·H₂O), mayalite (β₁-Al₂O₃·H₂O) and boraxite (β₂-Al₂O₃·H₂O): alumina monohydrate, including boehmite (α) -Al₂O₃·H₂O), diaspore (β-Al₂O₃·H₂O): pseudo-boehmite (Al₂O₃·1.3-2.2H₂O).
 
Anhydrous alumina
At present, there are at least eight different crystal forms of alumina: ρ-(amorphous), χ-(amorphous), η-(cubic system), γ-(cubic system), θ-(monoclinic crystal) (), δ- (tetragonal), κ- (hexagon) and α-(hexagonal) alumina. They are all isomers, in which α-Al₂O₃ is a thermally stable phase after high temperature heat treatment, and the other is an unstable transition state alumina.
 
In general, for various crystal forms of alumina, their chemical and physical properties are greatly different, such as density, pore structure, specific surface area, thermal stability and the like. When alumina is prepared by different preparation methods, even if it is the same crystal form, its properties are greatly different.
 
Χ-, ρ-Al₂O₃: belongs to amorphous alumina, which is the product of rapid dehydration and quenching of precursors. It is commonly known as “quick powder” and is called FCA (Flash Calcined Alumina) abroad. It has strong hydration activity and water absorption, and is often used as a binder and water absorbing agent. It has been widely used in many fields.
η- Al₂O₃: The product of the precursor dehydrated at a low temperature generally has a large specific surface area, but has poor thermal stability and is prone to crystal transformation at high temperatures.

γ- Al₂O₃: has strong adsorption capacity and catalytic activity and is called activated alumina. Generally, the specific surface area is large, the bulk density is small, the special pore structure is obtained, the thermal stability and the mechanical strength are good, and the performance thereof is easily changed, so the application field is extremely wide.

θ-,δ-,κ- Al₂O₃: The product of the precursor dehydrated at temperatures above 600 °C, almost free of structural water, its specific surface area and pore volume are generally small, but its thermal stability is better, can be used for high temperature The catalytic carrier of the reaction.

α-Al₂O₃: Also known as corundum, it is the final thermostable crystalline form after dehydration of transitional alumina. It is the most widely used type of alumina crystal, and the crystal is completely free of water. The structure is compact, its specific surface area is usually very small, the melting point is as high as 2050 ° C, and it has high hardness, high strength, wear resistance and corrosion resistance. It is commonly used in abrasive materials, high temperature resistant materials and ceramic composite materials.
 
Crystalline transformation of alumina
Calcined aqueous alumina at different temperatures, the water in the structure is continuously removed, the spatial arrangement of aluminum atoms and oxygen atoms is also constantly changing, and the alumina changes from amorphous to crystalline, gradually forming a variety of unstable transitions alumina. When the temperature exceeds 1200 ° C, a lattice remodeling phase transition occurs, and the oxygen atom arrangement is converted into a hexagonal closely packed structure, thereby forming a thermally stable phaseα-Al₂O₃.

TRUNNANO (Luoyang Trunnano Tech Co., Ltd ) is a professional Aluminium oxide  manufacturer with over 12 years experience in chemical products research and development. If you are looking for high quality Aluminium oxide, please feel free to contact us and send an inquiry.
 
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