Aluminum Prices, Occurrence, Extraction and Use

Aluminum (often in the Anglo-American language area also aluminum) is a chemical element with the element symbol Al and the atomic number 13. In the periodic table aluminum belongs to the third main group and to the 13. IUPAC Group, the Boron Group, formerly known as the Earth Metal Group. There are numerous aluminum compounds.

Aluminum is a silvery-white light metal. In the earth's envelope, it is the third most abundant element, after oxygen and silicon, and the most abundant metal in the earth's crust.

In materials technology, "aluminum" is understood as meaning all materials based on the element aluminum. These include pure aluminum (at least 99,0% Al), high-purity aluminum (min 99,7% Al) and, in particular, the aluminum alloys, which have strengths comparable to steel, at only one third of its density.

Aluminum, which occurs in nature only in the form of chemical compounds but not as metal, was discovered in the early 19. Century. In the early 20. Century began industrial mass production.

The extraction takes place in aluminum smelters starting from the mineral bauxite, first in the Bayer process, which is used to extract aluminum oxide, and then in the Hall-Héroult process of a fused-salt electrolysis process, in which aluminum is recovered. 2016 115 million tons of aluminum oxide (Al2O3) were produced worldwide. This has yielded 54,6 million tonnes of primary aluminum.

The metal is very base and reacts at freshly cut points at room temperature with air and water to alumina. However, this immediately forms a thin, impermeable to air and water layer (passivation), thus protecting the aluminum from corrosion. Pure aluminum has a low strength; it is much higher for alloys. The electrical and thermal conductivity is high, which is why aluminum is used for light cables and heat exchangers.

One of the best known products is aluminum foil. Others include components in vehicles and machinery, electrical wiring, pipes, cans and household items. Aluminum recycling achieves worldwide rates of about 40%.

History

1782 first suggested to Lavoisier that algae soil (alumina, derived from Latin alumen 'alum') was an oxide of a previously unknown element in Marggraf's 1754 from an alum solution. Finally, 1825 succeeded in rendering it to the Danish Hans Christian Ørsted by reacting aluminum chloride (AlCl3) with potassium amalgam, whereby potassium served as a reducing agent:

Davy, who had also been trying for a long time at the presentation of the new element, introduced from 1807 the name variants alumium, aluminum and aluminum, of which the last two in English to this day coexist.

1827 succeeded Friedrich Wöhler with the same method as Ørsted, but using metallic potassium as a reducing agent to obtain pure aluminum. Henri Étienne Sainte-Claire Deville refined the Wöhler trial in 1846 and published it in a book to 1859. Through this improved process, the yield of aluminum production increased, and as a result, the price of aluminum, which had previously been higher than that of gold, dropped to one-tenth within ten years.

1886 was independently developed by Charles Martin Hall and Paul Héroult to name the electrolysis process for the production of aluminum named after them: the Hall-Héroult process. 1889 Carl Josef Bayer developed the Bayer process named after him for the isolation of pure alumina from bauxites. Aluminum is still produced industrially today according to this principle.

At the end of the 19. At the turn of the 20th century, the metal was so well-known that it was dubbed metal ships made from aluminia.

occurrence

Aluminum is the third most abundant element of the earth's crust, making it the most abundant metal, accounting for 7,57% by weight of oxygen and silicon. However, due to its base character, it occurs almost exclusively in bound form. The largest amount is chemically bound in the form of aluminosilicates, in which it occupies the position of silicon in oxygen tetrahedra in the crystal structure. These silicates are for example part of clay, gneiss and granite.

Rarely is alumina found in the form of the mineral corundum and its varieties ruby ​​(red) and sapphire (colorless, of different colors). The colors of these crystals are based on admixtures of other metal oxides. Corundum has the highest aluminum content of a compound with almost 53 percent. A similarly high proportion of aluminum is found in the even rarer minerals Akdalait (about 51 percent) and Diaoyudaoit (about 50 percent). Altogether (2017) 1156 aluminum-containing minerals are known so far.

The only economically important raw material for aluminum production is bauxite. Deposits are located in southern France (Les Baux), Guinea, Bosnia and Herzegovina, Hungary, Russia, India, Jamaica, Australia, Brazil and the United States. Bauxite contains approximately 60 percent aluminum hydroxide (Al (OH) 3 and AlO (OH)), such as 30 percent iron oxide (Fe2O3) and silica (SiO2).

In the production one distinguishes primary aluminum, called also metallurgical aluminum, which is won from bauxite, and secondary aluminum from aluminum scrap. The recycling only needs about 5 percent of the energy of primary production.

Aluminum as a mineral

Due to the passivation, aluminum rarely occurs in nature elementary (dignified). Aluminum 1978 was first discovered by BV Oleinikov, AV Okrugin, NV Leskova in mineral samples from the Billeekh Intrusion and the Dyke OB-255 in the Republic of Sakha (Yakutia) in the Russian Far Eastern Federal District. In total, around 20 sites (stand 2019) for solid aluminum have been known worldwide, including in Azerbaijan, Bulgaria, the People's Republic of China (Guangdong, Guizhou, Jiangsu and Tibet) and in Venezuela. In addition, solid aluminum could be detected in rock samples from the moon, which brought the probe of the Luna 20 mission from the crater Apollonius.

Due to its extreme rarity, aluminum does not have any significance as a source of raw materials, but as a solid element aluminum is still recognized as an independent mineral by the International Mineralogical Association (IMA: 1980-085a). According to the classification of minerals according to Strunz (9 edition) aluminum is classified under the system number 1.AA.05 (elements - metals and intermetallic compounds - copper cupalite family - copper group). In the outdated 8. Edition of the Strunz'schen Mineral classification of aluminum, however, is not yet listed. Only in the last 2018 updated "Lapis mineral directory", which is based on this form of system numbering out of consideration for private collectors and institutional collections, the mineral received the system and mineral no. I / A.3-05. The classification of minerals according to Dana, which is predominantly used in English-speaking countries, leads the element mineral under the system no. 01.01.01.05.

In nature, dignified aluminum usually occurs in the form of granular mineral aggregates and micro-nuggets, but in rare cases can also develop tabular crystals up to about one millimeter in size. Fresh mineral samples are of shiny metallic, silvery white color. In the air, the surfaces darken due to oxidation and appear gray. Aluminum leaves a dark gray line on the slab.

Depending on the locality, aluminum often contains impurities from other metals (Cu, Zn, Sn, Pb, Cd, Fe, Sb) or occurs as ingrown or microcrystalline fused with hematite, ilmenite, magnetite, moissanite and pyrite or jarosite.

Type material, ie mineral samples from the type locality of the mineral, is stored in the Geological Museum of the Academy of Sciences in Yakutsk in the Russian republic of Sakha (Yakutia).

Scheme of molten electrolysis

Recovery

Aluminum metal is produced electrolytically from an alumina melt. Since these are difficult to isolate from the omnipresent on the ground aluminosilicates, the large-scale extraction is made of the relatively rare, silicate-poor bauxite. For the extraction of pure alumina from silicates, there are proposals for a long time, the implementation of which is still not economically possible.

The alumina / hydroxide mixture contained in the ore is first digested with sodium hydroxide solution (Bayer process, tube reactor or autoclave digestion) to rid it of impurities such as iron and silicon oxide, and is then predominantly used in fluidized bed plants (but also in Rotary kilns) to alumina (Al2O3) fired.

The dry digestion (Deville method), however, has no meaning. The finest-milled, unpurified bauxite was calcined together with soda and coke in rotary kilns at around 1200 ° C and the resulting sodium aluminate was subsequently dissolved with sodium hydroxide solution.

The production of the metal takes place in aluminum smelters by fused-salt electrolysis of aluminum oxide by the cryolite-alumina process (Hall-Héroult process). To lower the melting point, the aluminum oxide is melted together with cryolite (eutectic at 963 ° C). [36] During electrolysis, aluminum forms at the bottom of the vessel and oxygen at the anode, which is combined with the graphite (carbon) of the anode reacts to carbon dioxide and carbon monoxide. The graphite blocks forming the anode burn off so slowly and are replaced from time to time. The graphite cathode (vessel bottom) is inert to aluminum. The liquid aluminum collecting at the bottom is sucked off with a suction pipe.

Due to the high binding energy due to the trivalent aluminum, the process is quite energy-intensive. For each kilogram of raw aluminum produced, 12,9 must be used up to 17,7 kilowatt-hours of electrical energy. A reduction of the power requirement is only possible to a small extent, because the potentials for energetic optimizations are largely developed. Aluminum production is therefore economical only in the vicinity of cheap available electrical energy, for example, in addition to hydropower plants, such as in Rheinfelden or (former) in Ranshofen near the Inns.

 

Features

Physical Properties

Aluminum solidifies exclusively in a cubic surface-centered space grid in the space group Fm3m (room group no. 225). The lattice parameter for pure aluminum is 0,4049 nm (corresponds to 4,05 Å) for 4 formula units per unit cell.

Spaces occur with a density of 1,3 × 10-4 at 500 ° C, at room temperature they are only 10-12. Quenching may also result in larger vacancy densities at room temperature, which is important for some properties of aluminum materials because the voids promote diffusion. Reshaping at room temperature can increase the vacancy density on 10-4. The dislocation density is 10-7, a typical area for metals, and leads to the good formability of aluminum. Stacking faults could not be detected with aluminum, which is explained by the high stacking fault energy from 103 to 200 (10-7 J / cm²). As a result, the increase in strength during cold rolling and forging is minimal and some aluminum materials even tend to soften afterward.

density

With a density of 2,6989 g / cm³ (about one third of steel), aluminum is a typical light metal, which makes it an interesting material for lightweight construction. The density of the alloys usually deviates only by about + 3% to -2%. Special alloys with lithium have an 15% lower density. Aluminum is one of the lightest materials, surpassed only by magnesium.

Mechanical properties

Aluminum is a relatively soft and tough metal. The tensile strength of absolutely pure aluminum is 45 N / mm², the yield strength at 17 N / mm² and the elongation at break at 60%, whereas for commercially pure aluminum the tensile strength is 90 N / mm², the yield strength at 34 N / mm² and the Elongation at 45%. In contrast, the tensile strength of its alloys is up to 710 N / mm² (alloy 7068). Its modulus of elasticity is about 70 GPa, a value often quoted. Pure aluminum is given a value of 66,6 GPa, but the values ​​vary from 60 to 78 GPa. The G-modulus is 25,0 kN / mm², the transverse contraction number (Poisson's number) is 0,35.

Thermal properties

The melting temperature is 660,2 ° C and the boiling temperature is 2470 ° C. The melting temperature is significantly lower than that of copper (1084,6 ° C), cast iron (1147 ° C) and iron (1538 ° C), which makes aluminum a good casting material.

At a transition temperature of 1,2 K, pure aluminum becomes superconducting.

The thermal conductivity is relatively high with 235 W / (K m). Although the thermal conductivity of copper is about twice as high, but the density is about four times greater, which is why aluminum is used for heat exchangers in vehicles. The coefficient of thermal expansion is quite high due to the rather low melting point with 23,1 μm · m-1 · K-1.

The shrinkage, ie the volume decrease during solidification is 7,1%.

Electrical Properties

Since thermal and electrical conductivity in metals are dominated by the same mechanisms, aluminum is with also a very good electrical conductor. In the ranking of the elements with the highest specific conductivity, aluminum, as well as the thermal conductivity, is in fourth place behind silver, copper and gold. The combination of high specific conductance, low density, high availability and (compared to other materials) low cost aluminum in electrical engineering - especially in power engineering, where large conductor cross sections are needed - has become the most important conductor material besides copper.

Magnetic properties

Aluminum is paramagnetic, so it is attracted by magnets, but the effect is very weak. Magnetic susceptibility at room temperature is 0,62 × 10-9 m³ / kg, which makes aluminum practically non-magnetic.

Chemical properties

The pure light metal aluminum has a dull, silver-gray appearance due to a very thin forming in the air thin oxide layer. This passivating oxide layer makes pure aluminum very corrosion resistant at 4 to 9 pH values, reaching a thickness of about 0,05 μm.

This oxide layer also protects against further oxidation, but is a hindrance in the electrical contacting and soldering. It can be reinforced by electrical oxidation (anodization) or chemically.

The oxide layer can be dissolved by means of complex formation reactions. An extraordinarily stable and water-soluble neutral complex enters into aluminum in neutral chloride solution. The following reaction equation illustrates the process:

This is preferably done at locations where the oxide layer of the aluminum has already been damaged. It comes there through the formation of holes for pitting corrosion. If the chloride solution then can come to the free metal surface, other reactions take place. Aluminum atoms can be oxidized with complexation:

If ions of nobler metals are present in the solution, they are reduced and deposited on the aluminum. This principle is based on the reduction of silver ions present on the surface of tarnished silver as silver sulfide to silver.

Aluminum reacts vigorously with aqueous sodium hydroxide solution (NaOH) (and a little less vigorously with aqueous sodium carbonate solution) to produce hydrogen. This reaction is exploited in chemical pipe cleaning agents. The reaction of aluminum with NaOH proceeds in two steps: the reaction with water and the complexation of the hydroxide to sodium aluminate.

In the reaction with water

initially aluminum hydroxide is formed.

As a rule, the surface is subsequently dried, during which the hydroxide is converted into the oxide:

However, this does not happen in the reaction of aluminum in aqueous sodium hydroxide solution.

Now follows the 2. Step, the complexation of the hydroxide to sodium aluminate:

As a result of the complexing, the gelatinous hydroxide becomes water-soluble and can be transported away from the metal surface. As a result, the aluminum surface is no longer protected against the further attack of the water and step 1 runs off again.

As with the reaction of aluminum with acids, three moles of hydrogen gas can be produced per mole of aluminum with this method.

Aluminum reacts with bromine at room temperature under the flame. It should be noted that the resulting aluminum bromide reacts with water to form aluminum hydroxide and hydrobromic acid.

With mercury, aluminum forms an amalgam. When mercury comes into direct contact with aluminum, that is, when the aluminum oxide layer is mechanically destroyed at this point, mercury eats holes in the aluminum; Underwater then grows over it alumina in the form of a small cauliflower. Therefore, mercury is classified in aviation as a dangerous good and "corrosive liquid" compared to aluminum materials.

Aluminum also reacts violently with hydrochloric acid with evolution of hydrogen, and it is slowly dissolved by sulfuric acid. It is passivated in nitric acid.

In powder form (particle size smaller than 500 μm), aluminum is highly reactive, especially if it is not phlegmatized due to its large surface area. Aluminum then reacts with water giving off hydrogen to aluminum hydroxide. Finest, not phlegmatized aluminum powder is also called Pyroschliff. Non-phlegmatized aluminum dust is very dangerous and ignites spontaneously when exposed to air.

isotope

In nature, only the isotope 27Al occurs; Aluminum is one of the pure elements. This isotope, which is stable and contains 14 neutrons and 13 protons in the core, does not absorb neutrons, which is why aluminum is also used in nuclear reactors. All other isotopes are artificially produced and are radioactive. The most stable of these isotopes is 26Al with a half-life of one million years. By electron capture or beta decay, this results in 26Mg, by trapping a neutron and subsequent gamma decay 27Al. The isotopes 24Al to 29Al (except 26Al and 27Al) have half-lives between a few seconds and a few hundred seconds. 23Al decays with a half-life of only 0,13 seconds.

aluminum alloys

Aluminum alloys are alloys that are predominantly made of aluminum.

Aluminum can be alloyed with numerous metals to promote certain properties or to suppress other undesirable properties. With some alloys, the formation of the protective oxide layer (passivation) is greatly disturbed, as a result of which the components produced from it are sometimes susceptible to corrosion. Almost all high-strength aluminum alloys are affected by the problem.

There are aluminum wrought alloys, which are intended for further processing by rolling, forging and extrusion and cast materials. These are used in foundries.

In general, aluminum alloys are divided into the two major groups of kneading and casting alloys:

Cast aluminum alloys.

Typical cast aluminum alloys contain silicon as a major alloying element (AlSi), but there are also grades of copper or magnesium cast alloys.

wrought aluminum alloys, they have a share of about 75% and are subdivided further according to the main alloying element (s) in
Pure aluminum with aluminum contents from 99,0% to 99,9%. They are very easy to work, have low strength and good corrosion resistance.

Aluminum-copper alloys (AlCu): They have medium to high strength, are curable, but susceptible to corrosion and poorly weldable. They can contain additives of magnesium or manganese.

Aluminum-manganese alloys (AlMn): They have low to medium strength, are corrosion resistant and easy to process.

Aluminum-magnesium alloys (AlMg, without AlMgSi): They have medium strengths, are non-hardenable, corrosion resistant, easy to form and weld. Most varieties also contain manganese (AlMg (Mn)).

Aluminum-magnesium-silicon alloys (AlMgSi): They have medium to high strength, are easy to machine by welding and extrusion, hardenable and corrosion resistant.

Aluminum-zinc-magnesium alloys (AlZnMg): Copper-free grades have medium to high strengths and are easily weldable. Copper-containing grades (AlZnMg (Cu)) have high strengths - in the case of 7075 over 500 MPa - are not processed by fusion welding, but well by machining (milling, drilling).

Special alloysFor example, aluminum-lithium alloys with particularly low density, or free-cutting alloys that are particularly easy to machine.

In addition, a distinction is made between naturally hard alloys - which can not be hardened by a heat treatment - and curable:

Typical natural hard wrought aluminum alloys are: AlMg, AlMn, AlMgMn, AlSi
Curing wrought alloys - Strength enhancement by precipitation hardening of alloying elements with additional aging annealing at 150 to 190 ° C. Typical curable aluminum wrought alloys are: AlMgSi, AlCuMg, AlZnMg. The first high-strength, hardenable aluminum alloy AlCuMg got 1907 the trade name duralumin, briefly called "Dural".

 

Temporal development of worldwide primary aluminum production

Economical importance

Aluminum is the second most important metallic material after steel. 2016 produced 115 million tons worldwide.

The price of aluminum on the world market since 1980 has been around the value of 2000 dollars per tonne (purity of 99,7%). However, it is relatively volatile, falling 2016 to around 1500 dollars per ton, while returning 2017 close to 2000 dollars.

Usage

Aluminum has a high specific strength. Compared to steel, aluminum components are about half as heavy with the same strength, but have a larger volume. That is why it is often used in lightweight construction, ie where low mass is required, which, for example, contributes to reduced fuel consumption in means of transport, especially in the aerospace industry. For this reason, it also gained in importance in the automotive industry; In the past, the high material price, the poorer weldability and the problematic fatigue strength and the deformation properties in the event of accidents (low energy absorption capacity in the so-called crumple zone) stood in the way. The hood of the Washington Monument, a 3 kg heavy casting, was considered one of the largest aluminum workpieces by 1884. In the construction of small and medium-sized ships and boats, the corrosion resistance of aluminum to saltwater is estimated. Vehicle manufacturing (including ships, aircraft and rail vehicles) made 2010 the largest contributor to the worldwide use of aluminum, accounting for approximately 35 percent.

In aluminum alloys, strengths are achieved which are only slightly inferior to those of steel. Therefore, the use of aluminum for weight reduction is appropriate wherever material costs play a minor role. Aluminum and duralumin are widely used in aircraft construction and space technology in particular. Most of the structure of today's commercial aircraft is riveted from aluminum sheets of various thicknesses and alloys.

Continuously cast round bars of aluminum

vehicle construction

In vehicles, their mass plays a role: the lighter a vehicle is, the lower the fuel consumption. In Germany, almost 50% of aluminum is used in vehicle construction (as of: 2015).

Cars

In cars, aluminum materials are used for various engine components - including the engine block, the cylinder pistons for the special piston alloys exist, the cylinder heads - where especially the low thermal expansion and corrosion susceptibility and the high heat resistance are crucial; together with the good castability, since these components are usually cast. Further applications in vehicles are for gearbox housings, as heat shields and as heat exchangers - in the last two in the form of pure aluminum. In the chassis aluminum is used as forgings for rear axles, axle, wishbones and wheels. In the bodywork aluminum is used for doors, hoods, bumpers and fenders, as well as in the body structure.

Commercial Vehicles

For commercial vehicles, aluminum is used for sideboards, tail lifts, superstructures, load securing, compressed air tanks, fuel tanks and underbody protection. For light commercial vehicles, lightweight construction with aluminum is strongly influenced by the statutory maximum load per axle: with a lower vehicle weight, a higher payload is possible.

rail vehicles

Rail vehicles also use plenty of aluminum. The prerequisite for this were two important other developments: certain welding processes that are suitable for aluminum materials (TIG welding / MIG welding) in the 1950ers and the extrusion of large profiles. The use of aluminum has changed the overall design of rail vehicles. Until about 1970, constructions made of steel tubes were common, then increasingly welded aluminum profiles.

Aircraft

Already in the initial phase of aviation aluminum materials were used, 1903 for example Magnalium for the fittings of an airplane, which still consisted largely of wood, wire and cloth. The first flyable all-metal aircraft dates from the year 1915, but consisted of sheet steel in shell construction. The decisive development for the use of aluminum in the aircraft industry came from 1906 Alfred Wilm, who found a curable aluminum-copper alloy with the duralumin, which has very high strengths and is therefore ideal for lightweight construction. Can be used for aircraft AlCu and AlZnMg. The total mass of aircraft goes back to 60% on aluminum. The compound of stamped sheet metal, cut or driven, milled from the solid or made of profiles workpieces is usually done by riveting, since the most commonly used materials are bad weldable.

Electrical Engineering

Aluminum is a good conductor of electricity. After silver, copper and gold, it has the fourth highest electrical conductivity of all metals. For a given electrical resistance, an aluminum conductor has a smaller mass, but a larger volume than a copper conductor. For this reason, copper is usually used as an electrical conductor when volume plays a dominant role, for example with the windings in transformers. Aluminum has advantages as an electrical conductor when weight plays an important role, for example in the conductors of overhead lines. In order to reduce weight, aluminum cables are also used in aircraft such as the Airbus A380.

Among other things, aluminum is also processed into busbars in substations and in live castings. For electrical installations, there are copper-clad aluminum cables, the copper coating is to improve the contact. Raw material prices are primarily crucial in this application area, as aluminum is less expensive than copper. For overhead lines in electric railways, however, it is unsuitable due to its poor contact and sliding properties, in this area primarily copper is used despite the higher weight.

When contacted under pressure aluminum is problematic because it tends to creep. In addition, it covers air with an oxide layer. After prolonged storage or contact with water, this insulating layer is so thick that it must be removed before contacting. Especially in contact with copper, bimetallic corrosion occurs. With improper contacts in terminals, aluminum conductors can result in failures and cable fires as a result of loosening contacts. However, crimp connections with matching sleeves and tools are safe. As an intermediate layer between copper and aluminum, Cupal connectors can avoid contact problems.

Noteworthy is the slight decrease in the specific electrical conductivity of aluminum with the addition of alloying constituents, whereas copper shows a significant reduction in conductivity when contaminated.

The largest aluminum producers in the world
In thousands of tons (2018)

Rank	Country	Production	capacity
1	People's Republic of China	33.000	47.800
2	India	3.700	4.060
3	Russia	3.700	3.900
4	Canada	2.900	3.270
5	United Arab Emirates	2.600	2.600
6	Australia	1.600	1.720
7	Norway	1.300	1.430
8	Bahrain	1.000	1.050
9	United States	890	1.790
10	to Iceland	870	870

 

Electronics

The electronics industry uses aluminum for its good processability and good electrical and thermal conductivity.

In integrated circuits, only aluminum was used as interconnect material until the 2000 years. Until the Xnumxer years, it was also used as a material for the gate control gate of metal-insulator-semiconductor field-effect transistors (MOSFET and MOS-FET). In addition to the low resistivity, good adhesion to and low diffusion in silicon oxides (insulation material between the tracks) and ease of structuring with dry etching are crucial for use. However, since the beginning of the 1980 years aluminum has increasingly been replaced by copper as a conductor material, even though more complex structuring methods (see damascene and dual damascene process) and diffusion barriers are required. The higher manufacturing overhead is outweighed by the lower resistivity, which significantly increases in the case of small structures in aluminum much earlier and outweighs other properties (eg, electromigration behavior), and the aluminum processes could meet the increased demands (clock frequency, power dissipation, etc.) in no longer satisfy circuits operating at high frequencies (see also RC element).

However, aluminum is still used in microelectronic products, so it is used because of its good contactability by other metals in the last interconnect levels to make electrical contact with the solder balls used in the flip-chip mounting. The situation is similar in the case of power semiconductors, in which all conductor track planes generally consist of aluminum. In general, and in particular for power semiconductors, the material is used for bonding wires (connecting wires between the chip and the housing connection).

With the introduction of high-k + metal-gate technology, aluminum has become more important in the area of ​​the gate after more than 25 years of abstinence, and is also used as a work-process adjuster.

Packaging and containers

In the packaging industry, aluminum is processed into beverage and tin cans as well as aluminum foil. It makes use of the property of absolute barrier effect against oxygen, light and other environmental influences. Crucial to the use of aluminum as packaging is not the low density, but the good workability by rolling and the non-toxicity. Thin films are produced in thicknesses of six microns and then used mostly in composite systems, for example in Tetra Paks. Plastic films can be provided with a thin layer by vapor deposition with aluminum, which then has a high (but not complete) barrier function. The reason for this barrier effect is not the pure aluminum, but the passive layer of boehmite. If this is injured, gas can flow unimpeded through the material aluminum. Pure aluminum, AlMn (alloys with manganese) and AlMg (alloys with magnesium) are mostly used.

Aluminum also makes pans and other kitchen utensils, such as the classic Italian espresso maker, as well as travel and military utensils.

Aluminum is processed for a variety of containers and housings because it is easy to machine by forming. Aluminum objects are often protected by an anodized layer against oxidation and abrasion.

2017 accounted for 17% of European aluminum use on packaging.

Optics and lighting technology

Due to its high reflectivity, aluminum is used as a mirror coating of surface mirrors, among others in scanners, motor vehicle headlamps and SLR cameras, but also in infrared measurement technology. It also reflects ultraviolet radiation unlike silver. Aluminum mirror coatings are usually protected by a protective layer against corrosion and scratches.

Architecture and construction

Aluminum powder and aluminum pastes are used to produce aerated concrete. Compounds such as aluminum hydroxysulfate, aluminum dihydroxyformate or amorphous aluminum hydroxide are used as alkali-free shotcrete accelerators.

Construction and functional materials

Aluminum is used as a construction material for load-bearing parts of buildings and as a functional material as decorative, corrosion-resistant parts. In addition to the weather resistance, the good processability is crucial, especially in the case of manual production. The construction industry is the main customer for aluminum profiles. Aluminum is mainly used for window frames, doors and elements of facades. The facade of the Imperial War Museum in Manchester is particularly well known. The aluminum-manganese alloys, which have low strength and good corrosion resistance, are mainly used. In some cases, aluminum is also used for bridge construction, where otherwise steel construction predominates. Alloys with higher strength, including AlMg and AlSi, are used for structural engineering. Sheets and composite panels made of aluminum alloys achieve fire protection classes from 'non-combustible' to 'normally flammable'. A house fire develops 1000 ° C heat in a full fire, which, regardless of the fire protection class, burns holes in the aluminum alloy, which flows or drips down between 600 ° C and 660 ° C.

 

Other applications

In rocketry, the fuel of solid rockets consists of a maximum of 30 percent of aluminum powder, which releases a lot of energy when burned. Aluminum is used in fireworks (see also pyrotechnics), where it provides depending on the grain and mixture for colored effects. Also in pop sets it is often used.

In aluminothermics, aluminum is used to recover other metals and semi-metals by using the aluminum to reduce the oxides. An important method of aluminothermy is the thermite reaction, in which aluminum is reacted with ferric oxide. In this highly exothermic reaction temperatures up to 2500 ° C and liquid iron, which is used for aluminothermic welding, z. B. for joining railway tracks. Further applications of the reducing effect of aluminum are made possible for laboratory use by using aluminum amalgam.

Aluminum serves as a pigment for colors (silver or gold bronze). Colored anodized it is part of many decorative materials such as baubles, gift ribbons and tinsel. For coating surfaces, it is used in aluminizing.

With aluminum heating elements of iron and coffee machines are pressed.

Before it was possible to make zinc plate processable by adding titanium as so-called titanium zinc, aluminum sheet was used for façade and roof elements (see lightweight roof) as well as gutters.

Because of its high thermal conductivity, aluminum is used as the material for extruded heat sinks and heat-dissipating base plates. Aluminum electrolytic capacitors use aluminum as electrode material and housing material, furthermore it is used for the production of antennas and waveguides.

Aluminum occurs in some alloys. In addition to the aluminum alloys, which are predominantly made of aluminum, the aluminum alloys, aluminum brass, isabelline, aluminum and copper in the devard ash alloy, as the main alloying element for magnesium alloys, as well as in Alnico and Sendust, two iron alloys with special magnetic properties , Aluminum is also found in many titanium alloys, especially in Ti-6Al-4V, the variety that makes up about 50% of all titanium alloys. There is aluminum with 6 mass percent included.

application

During processing a distinction is made between cast alloys and wrought alloys:

Cast alloys are processed in foundries and cast in molds that are already fully or substantially in line with the final product. This is followed by finishing by grinding. Cast alloys are often melted from scrap metal.
Wrought alloys are cast into ingots in the steel mills and then rolled there to produce plates, sheets, rods and foils. From thick plates and other solid blanks, parts are made by machining (milling, drilling and turning). Other massive blanks can be processed by forging into individual pieces or by extrusion to profiles. The latter is particularly common in aluminum. Sheets are processed by punching, bending and deep drawing.

Thereafter, the items are joined by welding, riveting, soldering and similar methods.

Pour

The casting of aluminum is called cast aluminum. Due to its comparatively low melting point of 660 ° C (cast iron about 1150 ° C, steel 1400 ° C to 1500 ° C) and its good castability, it is one of the materials frequently used in the foundry. AlSi, special cast alloys with silicon, even have melting points around 577 ° C. The aluminum content of all products produced in foundries is about 11% (cast iron 76%, cast iron 9%) and is therefore by far the most important non-ferrous metal (non-ferrous metals) in the foundry, even before 1,5% copper. The share of non-ferrous metal casting of aluminum is about 87%. In Germany, 2011 processed about 840.000 tons of aluminum in foundries; About 76% of non-ferrous metal casting is lost to the automotive industry.

The low melting point is followed by a lower energy input during the melting process and a lower temperature load on the molds. Aluminum is basically suitable for all casting processes, in particular for die casting or aluminum diecasting, with which even complicated shaped parts can be manufactured. The foundry processes special aluminum casting alloys, mostly aluminum-silicon alloys. In the smelters, on the other hand, mostly wrought alloys are produced, which are intended for further processing by rolling, forging and extrusion. These are shed in the smelting works to ingots (ingot casting) or to round bars, which theoretically can be endless (continuous casting). Continuous casting has been increasingly used since the 1930 years. There are special systems that can produce up to 96 round bars simultaneously with casting lengths between 3 and 7 meters and sometimes up to 10 meters. The diameters range from 75 to 700 mm. Sheets are sometimes made by casting directly on a roller that cools the melt. The raw sheet is then directly cold rolled without hot rolling, saving costs of up to 60%.

Forming procedures

About 74 percent of the aluminum is processed by forming. This includes, among other things, rolling, forging, extrusion and bending.

Pure and ultra-pure aluminum can be well formed due to the low strength and solidifies in cold forming, with large changes in shape are possible. The solidification can be eliminated by recrystallization annealing. Wrought alloys with AlMg and AlMn achieve their higher strength through the alloying elements and by cold working. The hardenable alloys AlMgSi, AlZnMg, AlCuMg and AlZnMgCu precipitate strengthening phases during forming; they are relatively difficult to reshape.

roll

Cast billets are often further processed by rolling, either to thick plates which are then by milling to finished products, to sheets that are further processed by punching and bending or films. During rolling, the microstructure of the materials changes: small spherical components, which are often present after casting, are flattened and elongated. On the one hand, the microstructure becomes finer and more uniform, but on the other hand also direction-dependent. The capacity of an aluminum hot rolling mill is about 800.000 tons per year. Ingots with up to 30 tons of mass are processed. They have dimensions of up to 8,7 meters in length, 2,2 meters in width and 60 cm in thickness. Even larger bars can be processed technically, but the texture quality then decreases. After hot rolling, the material is usually present in thicknesses from about 20 to 30 mm. This is followed by cold rolling to final thickness. Cold rolling mills have capacities from 300.000 to 400.000 annual tons. Composites can be made by roll-plating. One or two sides of a layer of another material is applied. Frequently, a layer of corrosion-resistant pure aluminum is applied to corrosion-susceptible core material.

extrude

Aluminum can be formed by extrusion into complicated construction profiles; This is a great advantage in the production of hollow profiles (eg for window frames, bars, beams), heat sink profiles or in the antenna technology. The production of semi-finished products or components is done from starting material such as ingots, sheet metal or cylinders. Aluminum alloys are much better extruded than other materials, which is why a large proportion of the aluminum is processed by this process. The starting material is pressed through a hollow tool. The result is endless material that is sawed off in the desired length. It can also be made of complicated cross-sections, for example hollow sections or which with undercuts. However, the cross section is constant over the length. With high-strength alloys, large minimum wall thicknesses are required and the pressing takes a long time, which is why the medium-strength, hardenable alloys are preferred. The curing is usually carried out directly afterwards. In extrusion, the material is heated to temperatures of about 450 to 500 ° C to increase the formability, which is also used for solution annealing. Immediately after extrusion, the workpiece is cooled by air or water and thus quenched which leads to higher strengths.

Other

A mixing process of casting and forging is Cobapress, which is specially designed for aluminum and is widely used in the automotive industry. Modern rolling mills are very expensive, but also very productive.

Cutting involves turning, drilling and milling. Aluminum materials are easy to chip. Their exact properties, however, depend on the alloy and microstructure state. It should be noted that the temperatures occurring during processing can be quickly within the range of the melting point. However, with the same cutting parameters as with steel, aluminum results in less mechanical and thermal stress. As a cutting material carbide is often used for hypoeutectic or diamond for the highly abrasive hypereutectic alloys. In particular, the machining of anodized workpieces requires hard tools to avoid wear by the hard anodized coating. The grinding dust produced during grinding of aluminum can lead to an increased risk of explosion.

Welding and soldering

In principle, all aluminum materials are suitable for welding, but pure aluminum tends to pores in the weld. In addition, the aluminum melt tends to react with the atmosphere, which is why almost always welded under inert gas. Well suited are MIG and plasma welding as well as TIG welding. In the latter case, when using alternating current, the noble gas argon is used as protective gas, and helium at direct current.

Both carbon dioxide and solid-state lasers are suitable for laser welding, but not for all alloys. Because of the high thermal conductivity, the melt solidifies very quickly, so that the weld tends to pores and cracks. Resistance spot welding requires, compared to steel, higher electrical currents and shorter welding times, and in some cases special equipment, as the standard welding equipment for steel is not suitable. For electron beam welding, all alloys are suitable, but magnesium and tin tend to evaporate during the welding process. Manual arc welding is rarely used, usually for refining castings. Soldering is difficult because of the forming oxide layer in the air. Both hard and soft soldering with special fluxes are used. Alternatively, aluminum can be soldered without flux with ultrasound, while the oxide layer is broken mechanically during the soldering process.

Aluminum in nature and organisms
Aluminum in the human body

Aluminum is not an essential trace element and is considered unnecessary for the human diet. In the human body are on average about 50 to 150 milligrams of aluminum. These are distributed to approximately 50 percent of the lung tissue, to 25 percent on the soft tissues and to another 25 percent on the bones. Aluminum is thus a natural part of the human body.

99 to 99,9 Percent of the amount of aluminum commonly consumed in food (10 to 40 mg per day) is excreted unestablished through the faeces. Chelating agents (complexing agents) such as citric acid can increase absorption to 2 to 3 percent. Also, the intake of aluminum salts through the gastrointestinal tract is low; but it varies depending on the chemical compound and its solubility, pH, and the presence of complexing agents. It is estimated that 1 ‰ or 3 ‰ of aluminum obtained in food or in drinking water are absorbed in the gastrointestinal tract. The elimination of water-soluble aluminum salts into the organism takes place within a few days, primarily through the kidneys via the urine, less through the faeces. In dialysis patients with impaired renal function, there is therefore an increased risk of accumulation in the body with toxic effects, such as bone softening and damage to the central nervous system; In addition, dialysis patients are exposed to a higher supply of aluminum due to pharmaceutical products (phosphate binders) which are necessary for them. Aluminum, which is not excreted by the kidneys, gets into the bones. There it is comparatively very slowly eliminated, so that it is assumed by model estimates that about 1-2% of the re-absorbed dose accumulate in the body. [115] In one life, one accumulates about 35 mg of aluminum in the body.

In the blood, Al3 + is predominantly bound (about 80%) to transferrin. 16 percent is present as [Al (PO4) (OH)], 1,9 percent as a citrate complex, 0,8 percent as Al (OH) 3, and 0,6 percent as [Al (OH) 4] -. The blood of the newborn already contains aluminum ions that originate from the material circulation. Serum levels of about 6-10 μg / L are similar to those of adults.

plants

Aluminum in the form of various salts (phosphates, silicates) is a constituent of many plants and fruits, as dissolved Al compounds are absorbed by the soil from the soil due to rain. This is increasingly the case when acid soils are affected by acid rain (see also Forest damage ).

Much of the soil in the world is chemically acidic. If the pH is below 5,0, Al3 + ions are taken up by the roots of the plants. This is the case for half of the cultivable land in the world. The ions in particular damage the root growth of the fine roots. The plant, if it is not tolerant to aluminum, is then under stress. Numerous enzymes and signal-transmitting proteins are affected; the consequences of the poisoning are not yet completely known. In acidic metal-rich soils, Al3 + is the ion with the greatest potential for damage. From the model plant Arabidopsis transgenes are known, which increase their aluminum tolerance and tolerant varieties are also known in crops.

For example, acid rain in Sweden in the 1960 years acidified the lakes, causing more Al3 + ions to dissolve and kill sensitive fish. In Norway, too, this correlation was established during a research project in the 1970er years.

At pH values ​​above 5,0, aluminum is bound as a polymeric hydroxy cation on the surface of silicates. At pH values ​​from 4,2 to 5, the proportion of mobile cations is increasing.

When increasing the concentration of sulfuric acid by acid rain, aluminum hydroxysulfate forms: [116]

toxicity

In renal impairment and in dialysis patients, the uptake of aluminum leads to progressive encephalopathy (memory and speech disorders, listlessness and aggression) by brain cell loss and progressive dementia, fractured osteoporosis (arthritis) and anemia (because aluminum has the same memory whiteness) like iron). This was observed in the 1970er years in long-term hemodialysis patients by strong aluminum intake ("Dialysis Encephalopathy Syndrome").

Especially with regard to the use in deodorants and food additives, the health effects of aluminum are discussed controversially. For example, aluminum has been the subject of several controversial factors associated with Alzheimer's disease.

According to a study by the Federal Institute for Risk Assessment (BfR) of July 2007, in the general case at the time of the study's creation, no Alzheimer's risk from aluminum was identified from commodities because of the comparatively small amount; however, as a precaution, do not store acidic foods in contact with aluminum pots or foil. 2014 re-evaluated the use of aluminum-containing deodorants and cosmetics by the Federal Institute for Risk Assessment in February: Aluminum salts from such products can be absorbed through the skin, and regular use for decades could potentially contribute to health problems.

The British Alzheimer's Society, based in London, argues that the studies produced by 2008 have not demonstrated convincingly a causal relationship between aluminum and Alzheimer's disease. Nevertheless, there are some studies, such as For example, the PAQUID cohort study in France, with a health data evaluation of 3777 persons aged 65 years since 1988 to the present, in which an aluminum exposure is indicated as a risk factor for Alzheimer's disease. Thus, many senile plaques with elevated aluminum levels were found in brains of Alzheimer's patients. However, it is unclear whether aluminum accumulation is a consequence of Alzheimer's disease or aluminum is causally associated with Alzheimer's disease. The German Alzheimer's Association sees no convincing connection between aluminum intake and Alzheimer's disease.

Aluminum is one of the non-essential trace elements, toxicity mainly depends on the amount: 0,01 mg / l aluminum in the blood is considered normal value, values ​​above 0,06 mg / l speak for excessive exposure and values ​​above 0,2 mg / l in the blood are considered toxic.

Prices for aluminum

Prices for aluminum alloys

Prices for aluminum scrap

Prices for aluminum ingot