In the lattice of α-type alumina, oxygen ions are closely packed in hexagons, and Al3 + is symmetrically distributed in the coordination center of the octahedron surrounded by oxygen ions. The lattice energy is large, so the melting point and boiling point are high. Alpha-alumina is insoluble in water and acid. It is also called aluminum oxide in industry. It is the basic raw material for making aluminum metal. It is also used to make various refractory bricks, refractory crucibles, refractory tubes, and high-temperature-resistant experimental instruments. , 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 to produce the board base of modern large-scale integrated circuits.
γ-alumina
γ-alumina is made by dehydration of aluminum hydroxide in the low temperature environment of 140-150 ℃. It is also called activated alumina and aluminum glue in industry. In its structure, the oxygen ions are approximately closely packed with cubic centers, and Al3 + is irregularly distributed in the octahedral and tetrahedral voids surrounded by oxygen ions. γ-alumina is insoluble in water and can be dissolved in strong acid or alkali solution. It will be converted into α-alumina when heated to 1200 ℃. γ-alumina is a kind of porous material, the internal surface area per gram is up to hundreds of square meters, and it has high activity and strong adsorption capacity. Industrial products are often colorless or pinkish cylindrical particles with good pressure resistance. It is a commonly used adsorbent, catalyst and catalyst carrier in petroleum refining and petrochemical industry; it is a deacidifier for transformer oil and turbine oil in industry, and it is also used for chromatographic analysis; it is a neutral strong desiccant in the laboratory , Its drying ability is no less than that of phosphorus pentoxide, after use, it can be regenerated and reused by heating below 175 ℃ for 6-8h.
The alumina produced by the Bayer method accounts for more than 90% of the total output in the world. Most of the alumina is used to make metal aluminum and less than 10% is used for other purposes.
Electrolytic alumina
The main process of industrialized large-scale production of electrolytic aluminum is a molten salt electrochemical process, which can be expressed as follows with a simple chemical formula:
Molten salt electrolysis
Main reaction: Al₂O₃ + 2C —————— → 2Al + CO₂ ↑ + CO ↑ ⑴
Anode 960 ～ 990 ℃ cathode
Side reaction: AlF₃ + C → Al + CF₃⑵
3NaFAlF₃ + C → Al + NaF + CF₄ + F₂ ⑶
NaF + C → Na + CF₄ ⑷
Beta alumina
There is also a kind of β-Al₂O₃, which has ion conductivity (allows Na to pass), and uses β-alumina as the electrolyte to make a sodium-sulfur battery. Because the storage capacity per unit weight of this storage battery is large, large current discharge can be performed, so it has broad application prospects. The negative electrode of this battery is molten sodium, the positive electrode is sodium polysulfide (Na₂Sx), and the electrolyte is β-alumina (sodium ion conductor)
The temperature range of this storage battery can reach 620 ～ 680K, and its storage capacity is 3 ～ 5 times that of lead storage battery. The production of caustic soda using β-Al₂O₃ ceramics as a membrane for electrolyzed saline solution has the characteristics of high product purity and low pollution.
Abrasive alumina
Alumina is suitable for a variety of dry and wet treatment processes, and can polish the rough surface of any workpiece finely.
It is one of the most affordable abrasives. This sharp and rhomboid synthetic abrasive has a hardness second only to diamond, and is especially suitable for use when there are strict requirements for iron pollution. For the roughest cutting, it can also be made into a pebble shape to process precision-sized workpieces to achieve extremely low roughness. Due to its high density, sharp, diamond-shaped structure, it is currently one of the fastest cutting abrasives.
Alumina is made of brown corundum by electrofusion of high-quality bauxite, and high-quality aluminate is used to produce powdered corundum and white corundum. Their natural crystal structure gives them high hardness and fast cutting performance. At the same time they are often used as raw materials for consolidated abrasives and coated abrasives.
Alumina can be recycled many times, and the number of cycles is related to the material grade and the specific process. Most standard abrasive blasting equipment can be used.
Applicable industrial scope: aerospace industry, automotive industry, consumer product processing, casting / die casting, OEM distributors, semiconductor industry and other different fields.
Applicable process range: surface pretreatment before electroplating, painting, glazing and PTFE coating; deburring and descaling of aluminum and alloy products; mold cleaning; metal sandblasting pretreatment; dry and wet grinding; Precision optical refraction; grinding of minerals, metals, glass and crystals; glass engraving and paint additives.
Activated alumina
Technical index
Activated alumina appearance: Activated alumina is white spherical porous particles with uniform particle size, smooth surface, large mechanical strength and strong hygroscopicity. It does not swell or crack after water absorption. It has strong adsorption for fluorine, and is mainly used for the removal of fluorine in drinking water in high-fluorine areas.
Activated alumina has the ability to selectively adsorb gas, water vapor and some liquid moisture. After the adsorption is saturated, it can be heated at about 175-315 ° C to remove water and resurrect. Adsorption and resurrection can be performed multiple times. In addition to being used as a desiccant, it can also absorb lubricating oil vapor from contaminated oxygen, hydrogen, carbon dioxide, natural gas, etc. And can be used as a catalyst and catalyst carrier and chromatographic analysis carrier.
Under certain operating conditions and regeneration conditions, the drying depth of the product is up to the dew point temperature-70 degrees.
Ceramic effect
Alumina is divided into calcined alumina and ordinary industrial alumina. Calcined alumina is an essential raw material for the production of antique bricks, while industrial alumina can be used to produce microcrystalline stone. In traditional glazes, alumina is often used for whitening. Since antique bricks and microcrystalline stone are favored by the market, the amount of alumina is also increasing year by year.
Therefore, alumina ceramics came into being in the ceramic industry-alumina ceramics is a ceramic material that uses Al 2 O 3 as the main raw material and corundum as the main crystal phase. Because of its high mechanical strength, high hardness, and high-frequency dielectric Low loss, high temperature insulation resistance, good chemical resistance and good thermal conductivity and other excellent comprehensive technical performance advantages.