What Is Alumina?

Aluminum oxide is an inorganic substance with the chemical formula Al2O3. It is a high-hardness compound with a melting point of 2054 ℃ and a boiling point of 2980 ℃. It is an ionizable ionic crystal at high temperatures and is commonly used to manufacture refractory materials. Industrial alumina is prepared from bauxite (Al2O3 · 3H2O) and boehmite. Al2O3 with high purity requirements is generally prepared by chemical methods. Al2O3 has many homogeneous and heterogeneous crystals, with over 10 known types, mainly consisting of three crystal forms, namely α - Al2O3 β-Al2O3,γ-Al2O3. Among them, the structure and properties are different, and it is almost completely transformed into α - Al2O3 at high temperatures above 1300 ℃. Aluminum oxide belongs to amphoteric oxides, which can react with acids to form corresponding aluminum salts and water and react with strong alkaline solutions to form aluminum salts and water. This characteristic makes alumina highly flexible in chemical reactions. Structurally, the crystal structure of alumina is diverse, with the most common being alpha alumina (also known as corundum type alumina), which belongs to the trigonal crystal system and has extremely high hardness (second only to diamond). It is one of the hardest oxides in nature and is often used as an abrasive and polishing agent. In addition, there are various crystal forms such as β - alumina and γ - alumina, which can transform into each other under different conditions and exhibit different physical and chemical properties.
Aluminum oxide has many applications. It can be used as a high-temperature refractory material to make refractory bricks, crucibles, porcelain, artificial gemstones, etc. Aluminum oxide is also a raw material for aluminum smelting. Calcination of aluminum hydroxide can produce γ -. Gamma Al ₂ O3 has strong adsorption capacity and catalytic activity and can be used as an adsorbent and catalyst. The main component of corundum is alpha Al ₂ O3. A cubic crystal in the shape of a barrel or cone. 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 ℃. Insoluble in water, acid, and alkali. High-temperature resistance. Colorless and transparent materials are called white jade, while red materials containing trace amounts of trivalent chromium are called ruby; Blue sapphire containing divalent iron, trivalent iron, or tetravalent titanium is called sapphire; Corundum powder is a dark gray or dark colored substance containing a small amount of iron oxide. Can be used as bearings for precision instruments, diamonds for clocks, grinding wheels, polishing agents, refractory materials, and electrical insulators. Colorful gemstones can be used for decoration. Artificial ruby single crystal can be used as a material for laser production. In addition to natural minerals, aluminum hydroxide can be produced by melting it with a hydrogen-oxygen flame.
Meanwhile, aluminum oxide is the reason why metallic aluminum is not easily corroded in air. Pure aluminum metal easily reacts with oxygen in the air, forming a thin layer of aluminum oxide film covering the surface of aluminum exposed to the air. This layer of aluminum oxide film can prevent aluminum from being further oxidized. The thickness and properties of oxide films can be strengthened through a treatment process called anodizing (anodic corrosion prevention).
Aluminum oxide is suitable for various dry and wet treatment processes, and can finely polish the rough surface of any workpiece, making it one of the most economical abrasives. This sharp synthetic abrasive with water chestnuts has a hardness second only to diamond, making it particularly suitable for use when strict requirements are placed on iron pollution. Used for the roughest cutting, it can also be made into a pebble shape for processing precision-sized workpieces to achieve extremely low roughness. Due to its high density, sharpness, and water chestnut structure, it is one of the fastest-cutting abrasives.
In ceramic technology, alumina is divided into calcined alumina and ordinary industrial alumina. Calcined alumina is an essential raw material for producing antique bricks, while industrial alumina can be used to produce microcrystalline stones. In traditional glazes, alumina is commonly used for whitening. Due to the popularity of antique bricks and microcrystalline stones in the market, the amount of alumina used has also been increasing year by year.
Therefore, alumina ceramics have emerged in the ceramic industry - alumina ceramics are a ceramic material mainly made of Al ₂ O Ⅲ as the main raw material and corundum as the main crystal phase. Due to its excellent comprehensive technical properties such as high mechanical strength, high hardness, low high-frequency dielectric loss, high-temperature insulation resistance, good chemical corrosion resistance and thermal conductivity, etc.