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Alumina Raw Materials
Aluminum oxide is an inorganic substance with the chemical formula Al2O3. It is a high-hardness compound with a melting point of 2054°C and a boiling point of 2980°C. Aluminum oxide is an ionic crystal that can be ionized at high temperatures and is often used to make refractory materials.
Industrial alumina is prepared from bauxite (Al2O3·3H2O) and diaspore. For Al2O3 with high purity requirements, it is generally prepared by chemical methods. There are many isomorphous crystals of Al2O3, more than 10 of which are known, and there are mainly three crystal forms, namely α-Al2O3, β-Al2O3, and γ-Al2O3. Different structures have different properties, and they are almost completely converted into α-Al2O3 at high temperatures above 1300°C.
Alumina is a stable oxide of aluminum with the chemical formula Al2O3. It is also called bauxite in mining, ceramics and materials science.
Properties: a white solid that is insoluble in water, odorless, tasteless, extremely hard, easy to absorb moisture but not deliquescent, and non-hygroscopic after burning. Alumina is a typical amphoteric oxide, soluble in inorganic acids and alkaline solutions, almost insoluble in water and non-polar organic solvents. Corundum is α-shaped and belongs to the hexagonal closest packing. It is an inert compound, slightly soluble in acid and alkali and resistant to corrosion.
Storage: sealed and dry.
Uses: used as analytical reagents, dehydration of organic solvents, adsorbents, catalysts for organic reactions, abrasives, polishing agents, raw materials for smelting aluminum, and refractory materials.
Alumina contains the elements aluminum and oxygen. If the bauxite raw material is chemically treated to remove oxides of silicon, iron, titanium, etc., the product is a high-purity alumina raw material, and the Al2O3 content is generally above 99%. The mineral phase is composed of 40% to 76% γ-Al2O3 and 24% to 60% α-Al2O3. γ-Al2O3 can be transformed into α-Al2O3 at 950 to 1200°C, and a significant volume shrinkage occurs at the same time.
There are many variants of Al2O3, the most common ones are α and γ types, which are both white crystals.
The corundum in nature is α type, which belongs to the hexagonal closest packing, with a high melting point and hardness, insoluble in acid and alkali, corrosion resistance, and good insulation.
The γ type can be obtained by heating aluminum hydroxide with aluminum hydroxide or aluminum ammonium alum at 723K. It is insoluble in water, but has strong water absorption, strong adsorption capacity and catalytic activity.
The β-form has ion conductivity and allows Na+ to pass through.
China has rich bauxite resources, with a proven conservative reserve of 2.3 billion tons, ranking fourth in the world, and has the resource conditions to develop the alumina industry. Therefore, there are rich types of alumina. For example: bauxite, calcined alumina and ordinary industrial alumina, α-alumina, abrasive alumina, activated alumina, etc. And alumina is widely used.
Corundum powder has high hardness and can be used as abrasive and polishing powder. Alumina sintered at high temperature is called artificial corundum or artificial gemstone, which can be used to make mechanical bearings or diamonds in watches.
Alumina is also used as a high-temperature refractory material to make refractory bricks, crucibles, porcelain, artificial gemstones, etc. Alumina is also a raw material for aluminum smelting.
Calcination of aluminum hydroxide can produce γ-Al2O3. γ-Al2O3 has strong adsorption and catalytic activity, and can be used as an adsorbent and catalyst.
α-alumina is insoluble in water and acid and is the basic raw material for making metallic aluminum. It is also used to make various refractory bricks, refractory crucibles, refractory tubes, and high-temperature resistant experimental instruments. It can also be used as abrasives, flame retardants, fillers, etc. High-purity α-alumina is also the raw material for producing artificial corundum, artificial ruby and sapphire. It is also used to produce the substrate of modern large-scale integrated circuits.
The main component of corundum is α-Al2O3. It is a barrel-shaped or cone-shaped trigonal crystal. It has a glassy or diamond luster. The density is 3.9-4.1g/cm3, the hardness is 9, and the melting point is 2000±15℃. It is insoluble in water, acid and alkali. It is resistant to high temperatures. The colorless and transparent ones are called white jade, the red ones containing trace trivalent chromium are called rubies; the blue ones containing divalent iron, trivalent iron or tetravalent titanium are called sapphires; the dark gray and dark black ones containing a small amount of ferric oxide are called corundum powder. It can be used as bearings for precision instruments, diamonds, grinding wheels, polishing agents, refractory materials and electrical insulators for watches. The colorful ones can be used as decorative gems. Artificial ruby single crystals can be used to make laser materials. In addition to natural minerals, it can be made by melting aluminum hydroxide with hydrogen-oxygen flame.
Aluminum oxide is the reason why metal aluminum is not easily corroded in the air. Pure aluminum reacts easily with oxygen in the air to form a thin film of aluminum oxide covering the aluminum surface exposed to the air. This aluminum oxide film prevents the aluminum from further oxidation. The thickness and properties of the oxide film can be enhanced by a process called anodizing (anodic corrosion protection).
Application of alumina ceramics in the ceramic industry. Alumina ceramics are a ceramic material with Al₂O₃ as the main raw material and corundum as the main crystal phase. It has the advantages of high mechanical strength, high hardness, low high-frequency dielectric loss, high high-temperature insulation resistance, good chemical corrosion resistance and thermal conductivity.
Rongsheng High Aluminum Raw Material Manufacturer
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