Alumina powder morphology

- Jul 02, 2020-

Alumina powder is an ultrafine particle with a size range of 1-100 nm. Due to the reduction of the particle size of the powder, it exhibits many peculiar effects such as quantum size effect, small size effect, surface effect and macroscopic quantum tunneling effect, making it exhibit a series of new physical and chemical properties, such as: excellent mechanical and mechanical properties , Special magnetic properties, high conductivity and diffusion rate, large specific surface area and high reactivity, electromagnetic wave absorption and other properties.

Alumina has a complicated shape and is a product of dehydration of aluminum hydroxide. It has eight crystal forms of ρ, χ, κ, η, γ, δ, θ, and α. Alumina of different crystal forms has been widely used in various industrial sectors. ρ,χ alumina is used as a desiccant for gas, liquid and solid. γ-Al2O3 belongs to the cubic close-packed configuration with a tetragonal crystal system, which is very similar to the spinel (MgAl2O4) structure. Al3+ is distributed in the 8 tetrahedral voids and 16 octahedral voids in the spinel, which is equivalent to replacing the 3 Mg2+ positions in the MgAl2O4 spinel with 2 Al3+, so it is also called the lack of spinel structure. γ-Al2O3 is formed by dehydration of hydrated alumina at a temperature of 400-800°C. This Al2O3 is insoluble in water, but soluble in acid or alkali, heated to 1273K, and converted to α-Al2O3 after a certain holding time. So it is unstable at high temperature. γ-Al2O3 is disordered. This disorder is mainly determined by the disorder of aluminum atoms. It is precisely because of the disorder of aluminum atoms that the preparation conditions are controlled to produce γ-Al2O3。

η, γ-type alumina is used as a catalyst and carrier in hydrogenation, dehydrogenation, desulfurization, cracking and other petrochemical industries, as a filler in rubber, plastics and papermaking; α-type alumina is also known as steel jade, white crystal, diamond-shaped hexahedron It can be used as a catalyst carrier. When directly oxidizing ethylene to produce ethylene oxide, alpha-alumina loaded with silver is used as a catalyst. In addition, alpha-alumina is high-temperature alumina with high hardness and strength. It is widely used in Ceramics, glass, refractory materials, abrasives, etc. 

The ultra-fine Al2O3 powder can solve the high selectivity and high reactivity of the catalyst due to its large surface area, large pore volume, concentrated pore distribution and high number of reactive centers. Therefore, it is widely used as a catalyst for automobile exhaust purification, catalytic combustion, petroleum refining, hydrodesulfurization and polymer synthesis.

The ultra-fine Al2O3 powder has a huge surface and interface, and is very sensitive to the external environment moisture. Changes in the ambient temperature quickly cause changes in the surface or interface ion valence and electron transport. In the range of 30% to 80% humidity, the AC impedance changes linearly, with fast response speed, high reliability, high sensitivity, long anti-aging life, resistance to the invasion and pollution of other gases, and can maintain detection in dust and smoke environment The accuracy is ideal for moisture-sensitive sensors and hygroelectric thermometer materials. In addition, ultra-fine Al2O3 is a commonly used substrate material, with good electrical insulation, chemical durability, heat resistance, strong radiation resistance, high dielectric constant, uniform surface, low cost, can be used in semiconductor devices and large-scale The substrate material of integrated circuits is widely used in microelectronics, electronics and information industries. 

High-purity ultra-fine alumina has the advantages of true specific gravity, high Mohs hardness, corrosion resistance and easy sintering. Due to its fine structure, uniform structure, specific grain boundary structure, high temperature stability and good processing performance, insulation resistance Heat can be compounded with a variety of materials and other characteristics, mainly used in the electronics industry, biochemical ceramics, structural ceramics, functional ceramics, etc. It is one of the basic materials in high-tech fields such as electronics, machinery, aviation, chemical industry.