At present, the world’s alumina powder produced by Bayer process accounts for more than 90% of the total output, most of which are used to make metal aluminum, and less than 10% are used for other purposes.
Alumina powder is alumina, chemical symbol: Al2O3, molecular weight 102, pure alumina is white amorphous powder, commonly known as bauxite, density 3.9-4.0g/cm3, melting point 2050℃, boiling point 2980℃, insoluble in water, amphoteric Oxide, soluble in inorganic acid and alkaline solution, there are four allotropes β-alumina δ-alumina v-alumina a-alumina, and there are mainly two variants of α type and γ type , Industrially can be extracted from bauxite.
In the crystal lattice of α-type alumina, oxygen ions are densely packed in hexagons, and Al3+ is symmetrically distributed in the octahedral coordination center surrounded by oxygen ions. The lattice energy is large, so the melting point and boiling point are high. α-type alumina is insoluble in water and acid. It is also called aluminum oxide in industry. It is the basic raw material for making metal aluminum. It is also used to make various refractory bricks, refractory crucibles, refractory tubes, and high temperature test instruments; it can also be used as abrasive , Flame retardants, fillers, etc.; high-purity α-type alumina is also the raw material for the production of artificial corundum, artificial ruby and sapphire; it is also used for the production of modern large-scale integrated circuits.
γ-type alumina is produced by dehydration of aluminum hydroxide at a low temperature of 140-150°C. It is also called activated alumina and aluminum glue in industry. In its structure, oxygen ions are approximately densely packed in vertical planes, and Al3+ is irregularly distributed in the octahedral and tetrahedral voids surrounded by oxygen ions. γ-type alumina is insoluble in water, but can be dissolved in strong acid or strong alkali solution. When it is heated to 1200℃, it is completely converted into α-type alumina. γ-type alumina is a porous material, with an internal surface area of up to several hundred square meters per gram, with high activity and strong adsorption capacity. Industrial products are often colorless or slightly pink cylindrical particles with good pressure resistance. It is commonly used adsorbent, catalyst and catalyst carrier in petroleum refining and petrochemical industry; it is used as deacidification agent for transformer oil and turbine oil in industry; it is also used for chromatography analysis; in laboratory, it is neutral strong desiccant Its drying capacity is no less than that of phosphorus pentoxide. After use, it can be regenerated and reused after heating at 175°C for 6-8h.
