Jul 16, 2020 Viewed: 534 Tags: aluminum   Anodized  

Common sense of alumina

Summary: Alumina is usually called "aluminum oxide". It is a white powder, which is a covalent compound. It has a melting point of 2050 ° C, a boiling point of 3000 ° C, and a true density of 3.6g / cm3.


It has good fluidity, is insoluble in water, and can be dissolved in molten cryolite. It is the main raw material in aluminum electrolytic production.


Name Alumina; Corundum; White Jade; Ruby; Sapphire; Corundum Powder; Corundum


Chemical formula Al2O3


Appearance white crystalline powder or solid


Physical properties


Unit amount 101.96 amu


Melting point 2303 K


Boiling point 3250 K


Density 3.97 kg / m ..


Crystal Structure Trigonal System (hex)


Thermochemical properties


ΔfH0liquid -1620.57 kJ / mol


ΔfH0solid -1675.69 kJ / mol


S0liquid, 1 bar 67.24 J / mol? K


S0solid 50.9 J / mol? K


  safety


Ingestion Low risk


Inhalation May cause irritation or lung injury.


Skin low risk


Narrow eyes low risk


使用 Unless otherwise specified, SI units and standard temperature and pressure are used.


Alumina is a compound of aluminum and oxygen, and its molecular formula is Al2O3. It is also called bauxite in mining, ceramics and materials science.


Emergency response


Isolate leaking contaminated areas and restrict access. It is recommended that emergency handlers wear dust masks (full-face masks) and wear protective clothing. Avoid dust, sweep up carefully, place in a bag and transfer to a safe place. If a large amount of leakage, cover with plastic cloth, canvas. Collect, recycle or transport to waste disposal site for disposal.


preparation


Strongly heated aluminum hydroxide can obtain amorphous white alumina powder. 2Al (OH) 3 → Al 2 O 3 + 3H 2 O


use


1. The main components of ruby and sapphire are alumina, which show different colors due to other impurities. Ruby contains chromium oxide and is red, while sapphire contains iron oxide and titanium oxide and is blue.


2. Among the main constituents of aluminite, aluminate, the content of alumina is the highest. Industrially, ferrite is purified into alumina through the Bayer process, and then converted into aluminum metal by the Hall-Heroult process.


3. Aluminum oxide is the reason why aluminum metal is not easily corroded in the air. Pure metallic aluminum easily reacts with oxygen in the air, forming a thin aluminum oxide film covering the aluminum surface exposed to the air. This aluminum oxide film prevents aluminum from continuing to oxidize. The thickness and properties of this oxide film can be enhanced by a process called anodization (anodic corrosion protection).


4. Aluminum is a good conductor of electricity and heat. Because of its high hardness, the crystal form of aluminum is suitable for use as abrasive materials and cutting tools.


5. Alumina powder is often used as a medium for color analysis.


6. In August 2004, a scientist working at 3M Corporation in the United States developed an alloy synthesized from aluminum and rare earth elements to produce a strengthened glass called transparent alumina.


Materials Corundum powder has high hardness and can be used as abrasive, polishing powder, high-temperature sintered alumina, called artificial corundum or artificial gem, and 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 gems, etc. Alumina is also a raw material for aluminum smelting. Calcined aluminum hydroxide can produce γ-Al2O3. γ-Al2O3 has strong adsorption and catalytic activity, and can be used as an adsorbent and catalyst. Corundum is mainly composed of α-Al2O3. Barrel or cone-shaped trigonal crystals. Glassy or diamondy. The density is 3.9 ~ 4.1g / cm3, the hardness is 9, and the melting point is 2000 ± 15 ℃. Insoluble in water, and insoluble in acids and bases. High temperature resistance. Those who are colorless and transparent are called white jade, and red that contains a small amount of trivalent chromium is called ruby; blue that contains divalent iron, trivalent iron, or tetravalent titanium is called sapphire; dark gray and dark black that contain a small amount of ferric oxide Called corundum powder. Can be used as bearings for precision instruments, diamonds, grinding wheels, polishing agents, refractory materials and electrical insulators for watches and clocks. Gorgeous for decorative gems. Material of artificial ruby single crystal can make laser. In addition to natural minerals, it can be obtained by melting aluminum hydroxide with a hydrogen-oxygen flame.


The chemical formula of alumina is Al2O3, and the molecular weight is 101.96. The main component of bauxite. White powder. With different crystal forms, α-Al2O3 and γ-Al2O3 are common. Corundum in nature is α-Al2O3, hexagonal close-packed crystals. The melting point of α-Al2O3 is 2015 ± 15 ℃, density is 3.965g / cm3, hardness is 8.8, and it is insoluble in water, acid or alkali. γ-Al2O3 belongs to cubic close-packed crystals. It is insoluble in water, but soluble in acid and alkali. It is a typical amphoteric oxide.


Al2O3 + 6H + = 2Al3 ++ 3H2O


Al2O3 + 2OH- = 2AlO2- + H2O


Alumina preparation and application:


1. Manufacturing method of alumina film mainly composed of α-type crystal structure, alumina film mainly composed of α-type crystal structure, and film containing the same


2. Manufacturing method of α-type alumina powder


3. Method for producing α-alumina powder and α-alumina powder obtained by the method


Q4. Alpha-alumina powder and production method thereof


Ⅴ. Alpha-alumina powder and its manufacturing method


Q6. Alpha-alumina and manufacturing method thereof


7. Preparation method of α-alumina pellets


8. Preparation method of α-alumina nano powder


IX. Alpha-alumina fine powder and manufacturing method thereof


10. Manufacturing method of α-alumina powder


Q11. Preparation method of β-alumina


Q12. Preparation method of γ-alumina


13. θ-Alumina in-situ coated monolithic catalyst carrier


14. Method for joint production of alumina and calcium aluminate cement by Bayer process


15. Fluidization process of red mud water suspension in the production of alumina by Bayer process


Aluminum burns in the air and combines with oxygen to form alumina. The chemical equation can be written as △


What is alumina


Pure alumina is a white amorphous powder, commonly known as alumina, with a density of 3.9-4.0g / cm3, a melting point of 2050 ° C and a boiling point of 2980 ° C. It is insoluble in water. There are mainly two types of alumina: alpha and gamma. Can be extracted from bauxite.


Bauxite is the main mineral of aluminum in nature. After being crushed, it is impregnated with a high-temperature sodium hydroxide solution to obtain a sodium aluminate solution. The residue is filtered off, the filtrate is cooled, and aluminum hydroxide crystals are added. After long-term stirring, aluminum The sodium hydroxide solution will separate out the aluminum hydroxide precipitate; the precipitate is separated and washed, and then calcined at a temperature of 950-1200 ° C to obtain α-type alumina powder, and the mother liquor can be recycled. This method was invented by the Austrian scientist Bayer (KJ Bayer) in 1888, and it is still the main method for industrial production of alumina today, known as the "Bayer method".


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. 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 alpha 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 circuit board substrates.


γ-type alumina is produced by dehydrating aluminum hydroxide under 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 densely packed in the vertical direction, and Al3 + is irregularly distributed in the octahedral and tetrahedral voids surrounded by the oxygen ions. γ-type alumina is insoluble in water, and can be dissolved in strong acid or alkali solution. When it is heated to 1200 ℃, it will be completely converted into α-type alumina. γ-type alumina is a porous substance with an internal surface area of up to several hundred square meters per gram and high activity and strong adsorption capacity. Industrial products are often colorless or slightly 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 is also used for chromatographic analysis; it is a neutral strong desiccant in the laboratory , Its drying capacity is no less than that of phosphorus pentoxide, and it can be reused after heating for 6-8h at 175 ℃.


At present, the alumina produced by the Bayer process in the world accounts for more than 90% of the total output. Most of the alumina is used for making aluminum metal, and less than 10% is used for other purposes.





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