The difference between calcined alumina and ordinary alumina
Pure calcined alumina is a white amorphous powder, commonly known as alumina, density 3.9-4.0g / cm3, melting point 2050 ℃, boiling point 2980 ℃, insoluble in water, calcined alumina mainly α-and γ-two Variants, industrially available from bauxite extraction. Bauxite (Al2O3 • H2O and Al2O3 • 3H2O) is the main mineral of aluminum in nature. After being crushed, it is impregnated with high temperature calcined sodium oxide solution to obtain sodium aluminate solution. The residue is removed by filtration and the filtrate is cooled down and calcined and oxidized Aluminum crystal, after a long time stirring, sodium aluminate solution will be precipitated precipitation of aluminum hydroxide precipitation; precipitation will be washed out, and then at 950-1200 ℃ temperature calcined to get α-alumina powder, the mother liquor can be recycled use. This method by the Austrian scientist Bayer (K.J.Bayer) invented in 1888, today is still the main method of industrial production of alumina, known as "Bayer law." In the α-alumina lattice, the oxygen ions are closely packed hexagonal, Al3 + symmetrically distributed in the oxygen ion surrounded by octahedral coordination center, lattice can be great, so the melting point, the boiling point is high. Α-alumina is insoluble in water and acid, the industry also known as aluminum oxide, aluminum is the basic system of raw materials; also used for making all kinds of refractory bricks, refractory crucible, refractory tube, high temperature laboratory equipment; , Flame retardants, fillers, etc .; high purity α-alumina or the production of artificial corundum, artificial ruby and sapphire raw materials; also used in the production of modern large-scale integrated circuit board.
Γ-calcined alumina is aluminum hydroxide in the 140-150 ° C under low temperature dehydration in the system, also known as activated alumina industry, aluminum. The structure of oxygen ions close to the cubic surface close to the accumulation of Al3 + irregularly distributed in the oxygen ions surrounded by octahedral and tetrahedral voids. Γ-alumina insoluble in water, soluble in strong acid or alkali solution, it will be heated to 1200 ℃ on all converted to α-alumina. Γ-alumina is a porous material, the internal surface area per gram up to several hundred square meters, high activity and high adsorption capacity. Industrial products are often colorless or microstrip pink cylindrical particles, good pressure resistance. In the oil refining and petrochemical industry is commonly used in the adsorbent, catalyst and catalyst carrier; in the industry is transformer oil, turbine oil deacidification, but also for chromatography; in the laboratory is a neutral strong desiccant , Its drying capacity as much as phosphorus pentoxide, after use in 175 ℃ heating 6-8h can be recycled after repeated use.
At present the world's production of alumina with Bayer method to account for more than 90% of the total output, the majority of aluminum oxide for the system of aluminum, for less than 10% of other uses.
Γ-calcined alumina is aluminum hydroxide in the 140-150 ° C under low temperature dehydration in the system, also known as activated alumina industry, aluminum. The structure of oxygen ions close to the cubic surface close to the accumulation of Al3 + irregularly distributed in the oxygen ions surrounded by octahedral and tetrahedral voids. Γ-alumina insoluble in water, soluble in strong acid or alkali solution, it will be heated to 1200 ℃ on all converted to α-alumina. Γ-alumina is a porous material, the internal surface area per gram up to several hundred square meters, high activity and high adsorption capacity. Industrial products are often colorless or microstrip pink cylindrical particles, good pressure resistance. In the oil refining and petrochemical industry is commonly used in the adsorbent, catalyst and catalyst carrier; in the industry is transformer oil, turbine oil deacidification, but also for chromatography; in the laboratory is a neutral strong desiccant , Its drying capacity as much as phosphorus pentoxide, after use in 175 ℃ heating 6-8h can be recycled after repeated use.
At present the world's production of alumina with Bayer method to account for more than 90% of the total output, the majority of aluminum oxide for the system of aluminum, for less than 10% of other uses.
