AluminiumOverview
Physical characteristiscs
Chemical characteristics.
Isotopes
Production and refinement
Recycling
Compounds
Applications
Applications of compounds.
Popular reactions
Overview
Aluminium (or aluminum) is a chemical element in the boron group with symbol Al and atomic number 13.
It is silvery white, and it is not soluble in water under normal circumstances.
Aluminium is the third most abundant element (after oxygen and silicon), and the most abundant metal, in the Earth's crust.
( It is arranged as ,O,Si,Al,Fe,Ca,Na...)
It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals.
The chief ore of aluminium is bauxite.
Aluminium is remarkable for the metal's low density and for its ability to resist corrosion due to the phenomenon of passivation. Structural components made from aluminium and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.
Despite its prevalence in the environment, aluminium salts are not known to be used by any form of life.
In keeping with its pervasiveness, aluminium is well tolerated by plants and animals.
Owing to their prevalence, potential beneficial (or otherwise) biological roles of aluminium compounds are of continuing interest.
Physical characteristiscs
Aluminium is a
relatively soft,
durable,
lightweight,
ductile and
malleable metal
with appearance ranging from silvery to dull gray, depending on the surface roughness.
It is nonmagnetic and does not easily ignite.
A fresh film of aluminium serves as a good reflector (approximately 92%) of visible light and an excellent reflector (as much as 98%) of medium and far infrared radiation.
The yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa.
Aluminium has about one-third the density and stiffness of steel. It is easily machined, cast, drawn and extruded.
Aluminium atoms are arranged in a face-centered cubic (fcc) structure.
Aluminium has a stacking-fault energy of approximately 200 mJ/m2.Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density.
Aluminium is capable of being a superconductor, with a superconducting critical temperature of 1.2 Kelvin and a critical magnetic field of about 100 gauss .
Chemical characteristics.
Corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation.
4Al(s) + 3O2(g) → 2Al2O3(s)
The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper.This corrosion resistance is also often greatly reduced by aqueous salts, particularly in the presence of dissimilar metals.
Owing to its resistance to corrosion, aluminium is one of the few metals that retain silvery reflectance in finely powdered form, making it an important component of silver-colored paints.
Aluminium mirror finish has the highest reflectance of any metal in the 200–400 nm (UV) and the 3,000–10,000 nm (far IR) regions; in the 400–700 nm visible range it is slightly outperformed by tin and silver and in the 700–3000 (near IR) by silver, gold, and copper.
Aluminium is oxidized by water to produce hydrogen and heat:
2 Al + 3 H2O → Al2O3 + 3 H2
This conversion is of interest for the production of hydrogen. Challenges include circumventing the formed oxide layer which inhibits the reaction and the expenses associated with the storage of energy by regeneration of the Al metal.
Isotopes
Aluminium has many known isotopes, whose mass numbers range from 21 to 42; however,
only 27Al (stable isotope) and 26Al (radioactive isotope, t1/2 = 7.2×105 y) occur naturally.
27Al has a natural abundance above 99.9%.
26Al is produced from argon in the atmosphere by spallation caused by cosmic-ray protons.
Aluminium isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites.
The ratio of 26Al to 10Be has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales.
Cosmogenic 26Al was first applied in studies of the Moon and meteorites. Meteoroid fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial 26Al production. After falling to Earth, atmospheric shielding drastically reduces 26Al production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that 26Al was relatively abundant at the time of formation of our planetary system.
(Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.)
Production and refinement
Aluminium forms strong chemical bonds with oxygen.
Compared to most other metals, it is difficult to extract from ore, such as bauxite, due to the high reactivity of aluminium and the high melting point of most of its ores. ( For example, direct reduction with carbon, as is used to produce iron, is not chemically possible because aluminium is a stronger reducing agent than carbon. )
Indirect carbothermic reduction can be carried out using carbon and Al2O3, which forms an intermediate Al4C3 and this can further yield aluminium metal at a temperature of 1900–2000 °C. This process is still under development; it requires less energy and yields less CO2 than the Hall-Héroult process,
the major industrial process for aluminium extraction.
Electrolytic smelting of alumina was originally cost-prohibitive in part because of the high melting point of alumina, or aluminium oxide, (about 2,000 °C (3,600 °F).
Many minerals, however, will dissolve into a second already molten mineral, even if the temperature of the melt is significantly lower than the melting point of the first mineral.
Molten cryolite was discovered to dissolve alumina at temperatures significantly lower than the melting point of pure alumina without interfering in the smelting process.
In the Hall-Héroult process, alumina is first dissolved into molten cryolite with calcium fluoride and then electrolytically reduced to aluminium at a temperature between 950 and 980 °C (1,740 to 1,800 °F).
Cryolite is a chemical compound of aluminium and sodium fluorides: (Na3AlF6). Although cryolite is found as a mineral in Greenland, its synthetic form is used in the industry.
The aluminium oxide itself is obtained by refining bauxite in the Bayer process.
The electrolytic process replaced the Wöhler process, which involved the reduction of anhydrous aluminium chloride with potassium.
Both of the electrodes used in the electrolysis of aluminium oxide are carbon. Once the refined alumina is dissolved in the electrolyte, it disassociates and its ions are free to move around.
The reaction at the cathode is:
Al3+ + 3 e− → Al
Here the aluminium ion is being reduced.
The aluminium metal then sinks to the bottom and is tapped off, usually cast into large blocks called aluminium billets for further processing.
At the anode, oxygen is formed:
2 O2− → O2 + 4 e−
To some extent, the carbon anode is consumed by subsequent reaction with oxygen to form carbon dioxide.
The anodes in a reduction cell must therefore be replaced regularly, since they are consumed in the process.
The cathodes do erode, mainly due to electrochemical processes and metal movement.
After five to ten years, depending on the current used in the electrolysis, a cell has to be rebuilt because of cathode wear.
( Cathode contains carbon. In the process above oxygen is formed at cathode. So C(s) reacts with O2(g) and form CO2(g). That is the reason to rebuilt. )
Aluminium electrolysis with the Hall-Héroult process consumes a lot of energy, but alternative processes were always found to be less viable economically and/or ecologically.
The worldwide average specific energy consumption is approximately 15±0.5 kilowatt-hours per kilogram of aluminium produced (52 to 56 MJ/kg).
The most modern smelters achieve approximately 12.8 kW·h/kg (46.1 MJ/kg). (Compare this to the heat of reaction, 31 MJ/kg, and the Gibbs free energy of reaction, 29 MJ/kg.)
Reduction line currents for older technologies are typically 100 to 200 kiloamperes; state-of-the-art smelters operate at about 350 kA. Trials have been reported with 500 kA cells.
The Hall-Heroult process produces aluminium with a purity of above 99%. Further purification can be done by the Hoope process.
The process involves the electrolysis of molten aluminium with a sodium, barium and aluminium fluoride electrolyte. The resulting aluminium has a purity of 99.99%.
Electric power represents about 20% to 40% of the cost of producing aluminium, depending on the location of the smelter.
Aluminium production consumes roughly 5% of electricity generated in the U.S.
Smelters tend to be situated where electric power is both plentiful and inexpensive, such as the United Arab Emirates with excess natural gas supplies and Iceland and Norway with energy generated from renewable sources.
The world's largest smelters of alumina are
- People's Republic of China,
- Russia, and
- Quebec and
- British Columbia in Canada.
In 2005, the People's Republic of China was the top producer of aluminium with almost a one-fifth world share, followed by Russia, Canada, and the USA, reports the "British Geological Survey."
Over the last 50 years, Australia has become a major producer of bauxite ore and a major producer and exporter of alumina (before being overtaken by China in 2007).
Australia produced 68 million tonnes of bauxite in 2010. The Australian deposits have some refining problems, some being high in silica, but have the advantage of being shallow and relatively easy to mine.
Recycling
Aluminium is theoretically 100% recyclable without any loss of its natural qualities.
According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of aluminium in use in society (i.e. in cars, buildings, electronics etc.) is 80 kg. Much of this is in more-developed countries (350–500 kg per capita) rather than less-developed countries (35 kg per capita). Knowing the per capita stocks and their approximate lifespans is important for planning recycling.
Recovery of the metal via recycling has become an important use of the aluminium industry. Recycling was a low-profile activity until the late 1960s, when the growing use of aluminium beverage cans brought it to the public awareness.
Recycling involves melting the scrap, a process that requires only 5% of the energy used to produce aluminium from ore, though a significant part (up to 15% of the input material) is lost as dross (ash-like oxide).
The dross can undergo a further process to extract aluminium.
In Europe aluminium experiences high rates of recycling, ranging from 42% of beverage cans, 85% of construction materials and 95% of transport vehicles.
Recycled aluminium is known as secondary aluminium, but maintains the same physical properties as primary aluminium. Secondary aluminium is produced in a wide range of formats and is employed in 80% of alloy injections. Another important use is for extrusion.
White dross from primary aluminium production and from secondary recycling operations still contains useful quantities of aluminium that can be extracted industrially.
The process produces aluminium billets, together with a highly complex waste material.
This waste is difficult to manage. It reacts with water, releasing a mixture of gases (including, among others, hydrogen, acetylene, and ammonia), which spontaneously ignites on contact with air; contact with damp air results in the release of copious quantities of ammonia gas. Despite these difficulties, the waste has found use as a filler in asphalt and concrete.
Compounds
Oxidation state +3
The vast majority of compounds, including all Al-containing minerals and all commercially significant aluminium compounds, feature aluminium in the oxidation state 3+. The coordination number of such compounds varies, but generally Al3+ is six-coordinate or tetracoordinate. Almost all compounds of aluminium(III) are colorless.
Halides
All four trihalides are well known. Unlike the structures of the three heavier trihalides, aluminium fluoride (AlF3) features six-coordinate Al. The octahedral coordination environment for AlF3 is related to the compactness of fluoride ion, six of which can fit around the small Al3+ centre. AlF3 sublimes (with cracking) at 1,291 °C (2,356 °F). With heavier halides, the coordination numbers are lower.
The other trihalides are dimeric or polymeric with tetrahedral Al centers.
These materials are prepared by treating aluminium metal with the halogen, although other methods exist. Acidification of the oxides or hydroxides affords hydrates. In aqueous solution, the halides often form mixtures, generally containing six-coordinate Al centres, which are feature both halide and aquo ligands. When aluminium and fluoride are together in aqueous solution, they readily form complex ions such as
[AlF(H2O)5]2+,
AlF3(H2O)3, and
[AlF6]3−. I
n the case of chloride, polyaluminium clusters are formed such as
[Al13O4(OH)24(H2O)12]7+.
Oxide and hydroxides
Aluminium forms one stable oxide, known by its mineral name corundum. Sapphire and ruby are impure corundum contaminated with trace amounts of other metals.
The two oxide-hydroxides, AlO(OH), are boehmite and diaspore. T
here are three trihydroxides:
bayerite,
gibbsite, and
nordstrandite,
which differ in their crystalline structure (polymorphs).
Most are produced from ores by a variety of wet processes using acid and base.
Heating the hydroxides leads to formation of corundum.
These materials are of central importance to the production of aluminium and are themselves extremely useful.
Carbide, nitride, and related materials
Aluminium carbide (Al4C3) is made by heating a mixture of the elements above 1,000 °C (1,832 °F).
The pale yellow crystals consist of tetrahedral aluminium centres. It reacts with water or dilute acids to give methane. The acetylide, Al2(C2)3, is made by passing acetylene over heated aluminium.
Aluminium nitride (AlN)
is the only nitride known for aluminium. Unlike the oxides it features tetrahedral Al centres. It can be made from the elements at 800 °C (1,472 °F). It is air-stable material with a usefully high thermal conductivity. Aluminium phosphide (AlP) is made similarly, and hydrolyses to give phosphine:
Oxidation states +1 and +2
Although the great majority of aluminium compounds feature Al3+ centres, compounds with lower oxidation states are known and sometime of significance as precursors to the Al3+ species.
Aluminium(I)
AlF, AlCl and AlBr exist in the gaseous phase when the trihalide is heated with aluminium. The composition AlI is unstable at room temperature with respect to the triiodide:
3 AlI → AlI3 + 2 Al
A stable derivative of aluminium monoiodide is the cyclic adduct formed with triethylamine, Al4I4(NEt3)4.
Also of theoretical interest but only of fleeting existence are Al2O and Al2S. Al2O is made by heating the normal oxide, Al2O3, with silicon at 1,800 °C (3,272 °F) in a vacuum.[34] Such materials quickly disproportionates to the starting materials.
Aluminium(II)
Very simple Al(II) compounds are invoked or observed in the reactions of Al metal with oxidants. For example, aluminium monoxide, AlO, has been detected in the gas phase after explosion and in stellar absorption spectra.More thoroughly investigated are compounds of the formula R4Al2 where R is a large organic ligand.
AlP + 3 H2O → Al(OH)3 + PH3
Applications
Aluminium is the most widely used non-ferrous metal.
Global production of aluminium in 2005 was 31.9 million tonnes.
It exceeded that of any other metal except iron (837.5 million tonnes).
Forecast for 2012 is 42–45 million tonnes, driven by rising Chinese output.
( You know what chinese are rewritting each fields in the present )
Aluminium is almost always alloyed, which markedly improves its mechanical properties, especially when tempered. For example, the common aluminium foils and beverage cans are alloys of 92% to 99% aluminium.
The main alloying agents are
copper,
zinc,
magnesium,
manganese, and
silicon (e.g., duralumin)
and the levels of these other metals are in the range of a few percent by weight.
Some of the many uses for aluminium metal are in:
Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles, etc.) as sheet, tube, castings, etc.
Packaging (cans, foil, etc.)
Construction (windows, doors, siding, building wire, etc.).
A wide range of household items, from cooking utensils to baseball bats, watches.
Street lighting poles, sailing ship masts, walking poles, etc.
Outer shells of consumer electronics, also cases for equipment e.g. photographic equipment.
Electrical transmission lines for power distribution
MKM steel and Alnico magnets
Super purity aluminium (SPA, 99.980% to 99.999% Al), used in electronics and CDs.
Heat sinks for electronic appliances such as transistors and CPUs.
Substrate material of metal-core copper clad laminates used in high brightness LED lighting.
Powdered aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and thermite.
Aluminium can be reacted with hydrochloric acid or with sodium hydroxide to produce hydrogen gas.
A variety of countries, including France, Italy, Poland, Finland, Romania, Israel, and the former Yugoslavia, have issued coins struck in aluminium or aluminium-copper alloys.
Some guitar models sport aluminium diamond plates on the surface of the instruments, usually either chrome or black. Kramer Guitars and Travis Bean are both known for having produced guitars with necks made of aluminium, which gives the instrument a very distinct sound.
Aluminium is usually alloyed – it is used as pure metal only when corrosion resistance and/or workability is more important than strength or hardness. A thin layer of aluminium can be deposited onto a flat surface by physical vapour deposition or (very infrequently) chemical vapour deposition or other chemical means to form optical coatings and mirrors.
Applications of compounds.
Alumina
Aluminium oxide (Al2O3) and the associated oxy-hydroxides and trihydroxides are produced or extracted from minerals on a large scale. The great majority of this material is converted to metallic aluminium. About 10% of the production capacity is used for other applications. A major use is as an absorbent, for example alumina will remove water from hydrocarbons, to enable subsequent processes that are poisoned by moisture. Aluminium oxides are common catalysts for industrial processes, e.g. the Claus process for converting hydrogen sulfide to sulfur in refineries and for the alkylation of amines. Many industrial catalysts are "supported", meaning generally that an expensive catalyst (e.g., platinum) is dispersed over a high surface area material such as alumina. Being a very hard material (Mohs hardness 9), alumina is widely used as an abrasive and the production of applications that exploit its inertness, e.g., in high pressure sodium lamps.
Sulfates
Several sulfates of aluminium find applications.
Aluminium sulfate (Al2(SO4)3(H2O)18) is produced on the annual scale of several billions of kilograms. About half of the production is consumed in water treatment. The next major application is in the manufacture of paper. It is also used as a mordant, in fire extinguisher, as a food additive, in fireproofing, and in leather tanning. Aluminium ammonium sulfate, which is also called ammonium alum, (NH4)Al(SO4)2·12H2O, is used as a mordant and in leather tanning. Aluminium potassium sulfate ([Al(K)](SO4)2)(H2O)12 is used similarly. The consumption of both alums is declining.
Chlorides
Aluminium chloride (AlCl3) is used in petroleum refining and in the production of synthetic rubber and polymers. Although it has a similar name, aluminium chlorohydrate has fewer and very different applications, e.g. as a hardening agent and an antiperspirant. It is an intermediate in the production of aluminium metal.
Niche compounds
Given the scale of aluminium compounds, a small scale application could still involve thousands of tonnes. One of the many compounds used at this intermediate level include aluminium acetate, a salt used in solution as an astringent. Aluminium borate (Al2O3·B2O3) is used in the production of glass and ceramics. Aluminium fluorosilicate (Al2(SiF6)3) is used in the production of synthetic gemstones, glass and ceramic. Aluminium phosphate (AlPO4) is used in the manufacture: of glass and ceramic, pulp and paper products, cosmetics, paints and varnishes and in making dental cement. Aluminium hydroxide (Al(OH)3) is used as an antacid, as a mordant, in water purification, in the manufacture of glass and ceramic and in the waterproofing of fabrics. Lithium aluminium hydride is a powerful reducing agent used in organic chemistry. Organoaluminiums are used as Lewis acids and cocatalysts. For example, methylaluminoxane is a cocatalyst for Ziegler-Natta olefin polymerization to produce vinyl polymers such as polyethene.
Popular reactions
Al(s) + O2(g) → Al2O3(s)
Al(s) + HCl(aq) → AlCl3(aq) + H2(g)
Al(s) + H2SO4(aq) → Al2(SO4)3(aq) + H2(g)
Al(s) + NaOH(aq) → Al(OH)3(s) + Na(aq)
(recently this reaction is neglected and the below one is used for both (aq) and (conc) solutions )
Al(s) + NaOH(conc) → NaAlO2(aq)
Al(s) + P(s) → AlP(s)
Al(s) + N2(g) → AlN(s)
Al(s) + F2(g) → AlF3(s)
Al(s) + Cl2(g) → AlCl3(s)
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