Aluminium - a chemical element of group III of the Periodic Table. Content in the earth first ranked among the metals - 8.13%, and the third place after oxygen and silicon. There's more than 250 minerals of aluminum, which are mainly concentrated near the surface of the earth, and over 40% of them belong to the aluminosilicate.
The only method of obtaining aluminum metal is the electrolysis. The main raw material for the process - alumina (A12O3) receive different hydrochemical methods by processing minerals containing aluminum compound.
Aluminum has a high chemical activity, the energy of its compounds with oxygen, sulfur, and carbon is very high. Among the stress it is the most electronegative element. In normal conditions, interacting with oxygen, aluminum, coated with a thin but a solid film of aluminum oxide A1203 which protects from further oxidation, which causes its high corrosion resistance. However, in the presence of aluminum or environmental Hg, Na, Mg, Ca, Si, Cu, and some other elements of the strength of the oxide film and its protective properties are greatly reduced.
Molten aluminum reacts with the oxide and carbon dioxide and water vapor. Greatest interest is the solubility of hydrogen in aluminum, since the presence of hydrogen in the metal affects the mechanical properties of aluminum and its alloys. Hydrogen in aluminum in quantities exceeding the solid solubility is seen as harmful impurities.
Aluminium has amphoteric properties, ie react with acids to form the corresponding salts, and the interaction with alkalis - aluminates. This feature greatly enhances the recovery of aluminum from ore of different composition. Aluminum is dissolved in sulfuric and hydrochloric acids, and in alkalis, but concentrated nitric acid and an organic aluminum do not work.
The main aluminum ore bauxite include, nepheline, alunite and some other compounds, but the most important is the bauxite ore, which is almost completely run all foreign alumina refineries. Bauxite - a complex ore consisting of oxides and hydroxides of Al, Fe, Si and Ti as impurities and presence of calcium carbonate and magnesium hydrosilicates (chlorite), sulfides and sulfates (mainly iron) and organic compounds. In nature monomineralic bauxite extremely rare, are more common ore of mixed type.
Aluminium - chemical element of the third group of the periodic table.
|Coefficient of linear expansion
The density of solid and molten aluminum is reduced with increasing its purity:
|Density at 20°С||2,727||2,706||2,703||2,6996||2,6989||2,69808|
As you increase the purity, its melting point of aluminum is increasing:
|Melting point, °С||657||658||659,7||659,8||660,24|
Thermal conductivity of aluminum increases with the degree of purity. For commercial aluminum (99.49 and 99.70%) thermal conductivity at 200 ° C is equal to 209 and 222 W / (m × K). For electrolytically refined aluminum 99.9% thermal conductivity at 190 ° C increases to 343 W / (m × K). Impurities of copper, magnesium and manganese in aluminum lower its thermal conductivity. For example, the addition of 2% Mn to aluminum reduces the thermal conductivity from 209 to 126 W / (m × K).
Aluminium has a high electrical conductivity.
The electrical conductivity of aluminum affected by a number of factors: the degree of deformation, heat treatment and so on, a crucial role is played by the nature of the impurities present in the aluminum. Impurities in their negative influence on the electrical conductivity of aluminum can be placed in the following order: Cr, V, Mn, Ti, Mg, Ag, Cu, Zn, Si, Fe Ni.
The most negative impact on the resistance of aluminum have impurities Cr, V, Mn and Ti. Therefore, in aluminum, is intended for the electrical industry, the amount of Cr + V + Mn + Ti should not exceed 0.015%.
The main impurities in aluminum - silicon, iron, copper, zinc, and titanium. When small amounts of silicon in aluminum (0.06%), the value Fe: Si is relatively little effect on its electrical resistance. With increasing silicon content up to 0,15-0,16%, Effect Fe: Si increases.
With the increase of the degree of purity of aluminum increases its ability to reflect light. Thus, the degree of reflection of white light from the rolled aluminum sheet (foil), depending on the purity of the metal, according to increases in the following way: for Al 99.2% -75%, Al 99.5% -84% and 99.8% for aluminum -86%. Leaf surface, made of electrolytically refined 99.996% pure aluminum reflects 90% of incident white light.
The mechanical properties of aluminum depends on the purity of the form and modes of processing, temperature and other factors. With increasing purity strength and hardness of aluminum decreases and ductility increases. Modulus at 20 ° C for metal purity is 99.25% 69.65 GPa, and for electrolytically refined aluminum of 99.98% purity 65.71 GPa. As the temperature decreases the strength of aluminum, and the ductility increases.
At a temperature near the melting point of the mechanical properties of the contaminated aluminum can rapidly deteriorate due to the weakening of the grain boundaries and intergranular fracture. Temperature sharp weakening in cast aluminum purity 99.988% is 654 ° C, and the purity of 99.998% - 656 ° C.
Aluminum has a high capacity for deformation, the ductility increases with increasing purity. Aluminium 99,995% can be subjected to very large hoods, such as the diameter of 80 to a diameter of 0.1 mm.
By increasing the strength of aluminum deformation increases and the elongation decreases.
Doping of high purity aluminum increases its strength but reduces the ductility at room and at low temperatures. For example, the addition of 0,5% Fe to 99.99% pure aluminum increases the σv from 88.3 to 219.7 MPa (cold-worked metal) and from 49.0 to 99.1 MPa (annealed aluminum).
If you look at the history, it is in 1825 were the first to obtain a small sample of light and flexible metal, and in 1886, after the development of the method of electrolysis of alumina, aluminum began its triumphal march across the planet. Aluminium is a non-ferrous metal, which, thanks to the formation of a solid oxide film in contact with oxygen, has one of the highest corrosion resistance. This is certainly an attractive feature is complemented by the following set of physical and chemical characteristics:
This priority characteristics allow to use aluminum in all sectors of the global economy. To increase the strength of the metal in the alloy is often added copper, magnesium, silicon and zinc in varying proportions. Each alloy has individual properties. Aluminum is successfully used as an additive in a variety of non-ferrous alloys to improve the corrosion properties.
Today aluminum offers the consumer a lot of necessary items, from the popular aluminum wire and finishing sheets for the production and finishing of the fuselage airliners.
Currently, the scope of the aluminum products include various sectors of the economy. The chemical industry use aluminum to manufacture equipment for use in aggressive area. Aluminium is used for the production of aircraft parts, ships and vehicles. It is present in the container, cans and other packaging for the food industry. Aluminium used in household appliances, building materials and construction.
Applications of aluminum can be divided into the following groups:
Options for use of aluminum in industrial and household purposes increase year by year, stimulating demand for this light and ductile metal.
Aluminum - lightweight metal with high corrosion and mechanical properties. With doping and heat treatment of aluminum alloys we receive different grades. The main alloying elements - copper, magnesium, manganese, silicon and zinc. Methods of heat treatment: annealing, cold deformation, hardening, artificial and natural aging. Aluminum is found in many non-ferrous metals and is used for cladding. Thanks to it, aluminum increased corrosion resistance and ductility of materials.
Used for aluminum electrolysis of alumina in molten cryolite. Electrolytic refining rid of impurities and metal are as clean as possible. Then it is poured into bars or ingots, which are rolled into concrete products hot or cold method.
Aluminum construction unpretentious and capable long time without maintenance. They are highly flexible and can withstand heavy loads. All this allows to use it to build and upgrade a variety of structures.
|Grade list of pure aluminum and aluminum alloys|
|USA||ISO R209||Alcan||NF A02-004||DIN 1700||DIN 17007||BS, BS-L, DTD||UNI||JIS|