Home About us Products Services Contact us Bookmark
:: wikimiki.org ::
Aluminum

Aluminum

x Aluminium or aluminum (Symbol Al) (see the spelling section below) is a silvery and ductile member of the poor metal group of chemical elements. Its atomic number is 13. Aluminium is found primarily as the ore bauxite and is remarkable for its resistance to oxidation (due to the phenomenon of passivation), its strength, and its light weight. Aluminium is used in many industries to make millions of different products and is very important to the world economy. Structural components made from aluminium are vital to the aerospace industry and very important in other areas of transportation and building in which light weight, durability, and strength are needed.

Properties

transport Aluminium is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. Aluminium is nontoxic (as the metal) nonmagnetic and non-sparking. Pure aluminium has a tensile strength of about 49 megapascals (MPa) and 700 MPa if it is formed into an alloy. Aluminium is about one-third as dense as steel or copper; is malleable, ductile, and easily machined and cast; and has excellent corrosion resistance and durability due to the protective oxide layer. It is also nonmagnetic and nonsparking and is the second most malleable metal (after gold) and the sixth most ductile. ductile

Applications

Whether measured in terms of quantity or value, the use of aluminium exceeds that of any other metal except iron, and it is important in virtually all segments of the world economy. Pure aluminium has a low tensile strength, but readily forms alloys with many elements such as copper, zinc, magnesium, manganese and silicon. When combined with thermo-mechanical processing these aluminium alloys display a marked improvement in mechanical properties. Aluminium alloys form vital components of aircraft and rockets as a result of their high strength to weight ratio. When aluminium is evaporated in a vacuum it forms a coating that reflects both visible light and radiant heat. These coatings form a thin layer of protective aluminium oxide that does not deteriorate as silver coatings do. In particular, nearly all modern mirrors are made using a thin reflective coating of aluminium on the back surface of a sheet of float glass. Telescope mirrors are also coated with a thin layer of aluminium, but are front coated to avoid internal reflections even though this makes the surface more susceptible to damage. Telescope Diet Coke.]] Some of the many uses for aluminium are in:
- Transportation (automobiles, airplanes, trucks, railroad cars, marine vessels, etc.)
- Packaging (cans, foil, etc.)
- Water treatment
- Construction (windows, doors, siding, building wire, etc.
- Consumer durable goods (appliances, cooking utensils, etc.)
- Electrical transmission lines (aluminium conductors are half the weight of copper for equal conductivity and lower in price[http://www.metalprices.com])
- Machinery.
- Although non-magnetic itself, aluminium is used in MKM steel and Alnico magnets.
- Super purity aluminium (SPA, 99.980% to 99.999% Al) is used in electronics and CDs.
- Powdered aluminium is commonly used for silvering in paint. Aluminium flakes may also be included in undercoat paints, particularly wood primer — on drying, the flakes overlap to produce a water resistant barrier.
- Anodised aluminium is more stable to further oxidation, and is used in various fields of construction.
- Most modern computer CPU heat sinks are made of aluminium due to its ease of manufacture and good heat conductivity. Copper heat sinks are smaller although more expensive and harder to manufacture. Aluminium oxide, alumina, is found naturally as corundum (rubies and sapphires), emery, and is used in glass making. Synthetic ruby and sapphire are used in lasers for the production of coherent light. Aluminium oxidises very energetically and as a result has found use in solid rocket fuels, thermite, and other pyrotechnic compositions. Aluminium is also a superconductor, with a superconduting critical temperature of 1.2 Kelvin.

Engineering use

Improper use of aluminium can result in problems, particularly in contrast to iron or steel, which appear "better behaved" to the intuitive designer, mechanic, or technician. The reduction by two thirds of the weight of an aluminium part compared to a similarly sized iron or steel part seems enormously attractive, but it should be noted that it is accompanied by a reduction by two thirds in the stiffness of the part. Therefore, although direct replacement of an iron or steel part with a duplicate made from aluminium may still give acceptable strength to withstand peak loads, the increased flexibility will cause three times more deflection in the part. Where failure is not an issue but excessive flex is undesirable due to requirements for precision of location or efficiency of transmission of power, simple replacement of steel tubing with similarly sized aluminium tubing will result in a degree of flex which is undesirable; for instance, the increased flex under operating loads caused by replacing steel bicycle frame tubing with aluminium tubing of identical dimensions will cause misalignment of the power-train as well as absorbing the operating force. To increase the rigidity by increasing the thickness of the walls of the tubing increases the weight proportionately, so that the advantages of lighter weight are lost as the rigidity is restored. Aluminium can best be used by redesigning the part to suit its characteristics; for instance making a bicycle of aluminium tubing which has an oversize diameter rather than thicker walls. In this way, rigidity can be restored or even enhanced without increasing weight. The limit to this process is the increase in susceptibility to what is termed "crippling" failure, where the deviation of the force from any direction other than directly along the axis of the tubing causes folding of the walls of the tubing. For instance, a common aluminium soft drink can should be able to support an enormous weight directly along its axis; in practice, however, the walls of the can buckle, crumple, and/or fold up under even a mild force, due to minute deviations from the precise axial direction, making possible the common pastime of flattening an empty can by slamming it against one's forehead. The latest models of the Corvette automobile, among others, are a good example of redesigning parts to make best use of aluminium's advantages. The aluminium chassis members and suspension parts of these cars have large overall dimensions for stiffness but are lightened by reducing cross-sectional area and removing unneeded metal; as a result, they are not only equally or more durable and stiff as the usual steel parts, but they possess an airy gracefulness which most people find attractive. Similarly, aluminium bicycle frames can be optimally designed so as to provide rigidity where required, yet have flexibility in terms of absorbing the shock of bumps from the road and not transmitting them to the rider. The strength and durability of aluminium varies widely, not only as a result of the components of the specific alloy, but also as a result of the particular manufacturing process; for this reason, it has from time to time gained a bad reputation. For instance, a high frequency of failure in many early aluminium bicycle frames in the 1970s resulted in just such a poor reputation; with a moment's reflection, however, the widespread use of aluminium components in the aerospace and automotive high performance industries, where huge stresses are undergone with vanishingly small failure rates, proves that properly built aluminium bicycle components should not be unusually unreliable, and this has subsequently proved to be the case. Similarly, use of aluminium in automotive applications, particularly in engine parts which must survive in difficult conditions, has benefited from development over time. An Audi engineer commented about the V12 engine, producing over 500 horsepower (370 kW), of an Auto Union race car of the 1930s which was recently restored by the Audi factory, that the aluminium alloy of which the engine was constructed would today be used only for lawn furniture and the like. Even the aluminium cylinder heads and crankcase of the Corvair, built as recently as the 1960s, earned a reputation for failure and stripping of threads in holes, even as large as spark plug holes, which is not seen in current aluminium cylinder heads. Often, aluminium's sensitivity to heat must also be considered. Even a relatively routine procedure such as welding is complicated by the fact that aluminium will melt long before it gets even dully red hot; therefore, unlike steel or iron, where the experienced welder can know from its hue how close the metal is to the melting point, welding aluminium requires a degree of expertise incorporating an almost intuitive sense of the metal's temperature, or else the part suddenly and without warning melts into a puddle. Aluminium also will accumulate internal stresses and strains under conditions of overheating; while not immediately obvious, the tendency of the metal to "creep" under sustained stresses results in delayed distortions, for instance the commonly observed warping or cracking of aluminium automobile cylinder heads after an engine is overheated, sometimes as long as years later, or the tendency of welded aluminium bicycle frames to gradually twist out of alignment from the stresses accumulated during the welding process. For this reason, many uses of aluminium in the aerospace industry avoid heat altogether by joining parts using adhesives; this was also used for some of the early aluminium bicycle frames in the 1970s, with unfortunate results when the aluminium tubing corroded slightly, loosening the bond of the adhesive and leading to failure of the frame. Stresses from overheating aluminium can be relieved by heat-treating the parts in an oven and gradually cooling, in effect annealing the stresses; this can also result, however, in the part becoming distorted as a result of these stresses, so that such heat-treating of welded bicycle frames, for instance, results in a significant fraction becoming misaligned. If the misalignment is not too severe, once cooled they can be bent back into alignment with no negative consequences; of course, if the frame is properly designed for rigidity (see above), this will require enormous force.

Household wiring

Because of its high conductivity and relatively low price compared to copper at the time, aluminium was introduced for household electrical wiring to a large degree in the United States in the 1960s. Unfortunately, many of the wiring fixtures at the time were not designed to accept aluminium wire. More specifically:
- The greater coefficient of thermal expansion of aluminium, causes the wire to expand and contract relative to the dissimilar metal screw connection, eventually loosening the connection.
- Pure aluminium has a tendency to "creep" under steady sustained pressure (to a greater degree as the temperature rises), again producing a degree of looseness in an initially tight connection.
- Galvanic corrosion from the dissimilar metals increases the electrical resistance of the connection. In combination, these properties caused connections between electrical fixtures and aluminium wiring to overheat which resulted in several fires. As a result, aluminium household wiring has become unpopular, and in many jurisdictions is not permitted in very small sizes in new construction. However, aluminium wiring can be safely used with fixtures whose connections are designed to avoid loosening and overheating. Older fixtures of this type are marked "Al/Cu", and newer ones are marked "CO/ALR". Otherwise, aluminium wiring can be terminated by crimping it to a short "pigtail" of copper wire, which can be treated as any other copper wire. A properly done crimp, requiring high pressure produced by the proper tool, is tight enough not only to eliminate any thermal expansion of the aluminium, but also to exclude any atmospheric oxygen and thus prevent corrosion between dissimilar metals. New alloys are used for aluminium building wire today in combination with aluminium terminations. Connections made with these standard industry products are as safe and reliable as copper connections. :See also:Aluminum wire

History

The oldest suspected (although unprovable) reference to aluminium is in Pliny the Elder's Naturalis Historia: One day a goldsmith in Rome was allowed to show the Emperor Tiberius a dinner plate of a new metal. The plate was very light, and almost as bright as silver. The goldsmith told the Emperor that he had produced the metal from ordinary clay. He also assured the Emperor that only he, himself, and the gods knew how to produce this metal from clay. The Emperor became very interested, and, as a financial expert, he was also worried. He feared that all his treasures of gold and silver would fall in value if people started producing this bright metal from clay. Therefore, instead of giving the goldsmith the recognition the latter had anticipated, he ordered him to be beheaded. [http://www.findarticles.com/p/articles/mi_m2843/is_n3_v19/ai_16836663 Notes] - [http://www.world-aluminium.org/history/antiquity.html Source] The ancient Greeks and Romans used salts of this metal as dyeing mordants and as astringents for dressing wounds, and alum is still used as a styptic. Further Joseph Needham suggested finds in 1974 showed the ancient Chinese used aluminium (see the link for "Notes" above). In 1761 Guyton de Morveau suggested calling the base alum 'alumine'. In 1808, Humphry Davy identified the existence of a metal base of alum, which he named (see Spelling below for more information on the name). Friedrich Wöhler is generally credited with isolating aluminium (Latin alumen, alum) in 1827 by mixing anhydrous aluminium chloride with potassium. However, the metal had been produced for the first time two years earlier in an impure form by the Danish physicist and chemist Hans Christian Ørsted. Therefore almanacs and chemistry sites often list Øersted as the discoverer of aluminium.[http://www.chemicalelements.com/elements/al.html#isotopes Source] Still it would further be P. Berthier who discovered aluminium in bauxite ore and successfully extracted it. The Frenchman Henri Saint-Claire Deville improved Wöhler's method in 1846 and described his improvements in a book in 1859, chief among these being the substitution of sodium for the considerably more expensive potassium. The American Charles Martin Hall of Oberlin, OH applied for a patent (400655) in 1886 for an electrolytic process to extract aluminium using the same technique that was independently being developed by the Frenchman Paul Héroult in Europe. The invention of the Hall-Héroult process in 1886 made extracting aluminium from minerals cheaper, and is now the principal method in common use throughout the world. Upon approval of his patent in 1889, Hall, with the financial backing of Alfred E. Hunt of Pittsburgh, PA, started the Pittsburgh Reduction Company, renamed to Aluminum Company of America in 1907, later shortened to Alcoa. Alcoa Aluminium was selected as the material to be used for the apex of the Washington Monument, at a time when one ounce cost twice the daily wages of a common worker in the project. [http://www.tms.org/pubs/journals/JOM/9511/Binczewski-9511.html Source] Germany became the world leader in aluminium production soon after Adolf Hitler seized power. By 1942, however, new hydroelectric power projects such as the Grand Coulee Dam gave the United States something Nazi Germany could not hope to compete with, namely the capability of producing enough aluminium to manufacture sixty thousand warplanes in four years. [http://www.phpsolvent.com/wordpress/?page_id=341]

Natural occurrence

Although aluminium is an abundant element in Earth's crust (believed to be 7.5% to 8.1%), it is very rare in its free form and was once considered a precious metal more valuable than gold. Napoleon III of France had a set of aluminium plates reserved for his finest guests. Others had to make do with gold ones. Aluminium has been produced in commercial quantities for just over 100 years. Aluminium was, when it was first discovered, extremely difficult to separate from its ore. Aluminium is among the most difficult metals on earth to refine, despite the fact that it is one of the planet's most common. The reason is that aluminium is oxidised very rapidly and that its oxide is an extremely stable compound that, unlike rust on iron, does not flake off. The very reason for which aluminium is used in many applications is why it is so hard to produce. Recovery of this metal from scrap (via recycling) has become an important component of the aluminium industry. Recycling involves simply melting the metal, which is far less expensive than creating it from ore. Refining aluminium requires enormous amounts of electricity; recycling it requires only 5% of the energy to produce it. A common practice since the early 1900s, aluminium recycling is not new. It was, however, a low-profile activity until the late 1960s when the exploding popularity of aluminium beverage cans finally placed recycling into the public consciousness. Other sources for recycled aluminium include automobile parts, windows and doors, appliances, containers and other products. Aluminium is a reactive metal and it is hard to extract it from its ore, aluminium oxide (Al2O3). Direct reduction, with carbon for example, is not economically viable since aluminium oxide has a melting point of about 2000°C. Therefore, it is extracted by electrolysis — the aluminium oxide is dissolved in molten cryolite and then reduced to the pure metal. By this process, the actual operational temperature of the reduction cells is around 950 to 980°C. Cryolite was originally found as a mineral on Greenland, but has been replaced by a synthetic cryolite. Cryolite is a mixture of aluminium, sodium, and calcium fluorides: (Na3AlF6). The aluminium oxide (a white powder) is obtained by refining bauxite, which is red since it contains 30 to 40% iron oxide. This is done using the so-called Bayer process. Previously, the Deville process was the predominant refining technology. The electolytic 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 ore is in the molten state, its ions are free to move around. The reaction at the negative cathode is :Al3+ + 3e- → Al Here the aluminium ion is being reduced (electrons are added). The aluminium metal then sinks to the bottom and is tapped off. At the positive electrode (anode) oxygen gas is formed: :2O2- → O2 + 4e- This carbon anode is then oxidised by the oxygen. The anodes in a reduction must therefore be replaced regularly, since they are consumed in the process: :O2 + C → CO2 Contrary to the anodes, the cathodes are not consumed during the operation, since there is no oxygen present at the cathode. The carbon cathode is protected by the liquid aluminium inside the cells. Cathodes do erode, mainly due to electrochemical processes. After 5 to 10 years, depending on the current used in the electrolysis, a cell has to be reconstructed completely, because the cathodes are completely worn. 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 world-wide 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 reach approximately 12.8 kW·h/kg (46.1 MJ/kg). Reduction line current for older technologies are typically 100 to 200 kA. State-of-the-art smelters operate with about 350 kA. Trials have been reported with 500 kA cells. Electric power represents about 20 to 40% of the cost of producing aluminium, depending on the location of the aluminium smelter. Smelters tend to be located where electric power is plentiful and inexpensive, such as South Africa, the South Island of New Zealand, Australia, China, Middle-East, Russia, Iceland and Quebec in Canada. China is currently (2004) the top world producer of aluminium. Suriname depends on aluminium exports for 70% of its export earnings.[http://www.cia.gov/cia/publications/factbook/geos/ns.html#Econ]

Isotopes

Aluminium has nine isotopes, whose mass numbers range from 23 to 30. Only Al-27 (stable isotope) and Al-26 (radioactive isotope, t1/2 = 7.2 × 105 y) occur naturally, however Al-27 has a natural abundance of 100%. Al-26 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 Al-26 to beryllium-10 has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales. Cosmogenic Al-26 was first applied in studies of the Moon and meteorites. Meteorite fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial Al-26 production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further Al-26 production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that Al-26 was relatively abundant at the time of formation of our planetary system. Possibly, the energy released by the decay of Al-26 was responsible for the remelting and differentiation of some asteroids after their formation 4.6 billion years ago.

Clusters

In the journal Science of 14 January 2005 it was reported that clusters of 13 aluminium atoms (Al13) had been made to behave like an iodine atom; and, 14 aluminium atoms (Al14) behaved like an alkaline earth atom. The researchers also bound 12 iodine atoms to an Al13 cluster to form a new class of polyiodide. This discovery is reported to give rise to the possibility of a new characterisation of the periodic table: superatoms. The research teams were led by Shiv N. Khanna (Virginia Commonwealth University) and A. Welford Castleman Jr (Penn State University). [http://www.science.psu.edu/alert/Castleman1-2005.htm]

Precautions

Aluminium is one of the few abundant elements that appears to have no beneficial function in living cells, but a few percent of people are allergic to it — they experience contact dermatitis from any form of it: an itchy rash from using styptic or antiperspirant products, digestive disorders and inability to absorb nutrients from eating food cooked in aluminium pans, and vomiting and other symptoms of poisoning from ingesting such products as Rolaids , Amphojel, and Maalox (antacids). In other persons, aluminium is not considered as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amounts, although the use of aluminium cookware, popular because of its corrosion resistance and good heat conduction, has not been shown to lead to aluminium toxicity in general. Excessive consumption of antacids containing aluminium compounds and excessive use of aluminium-containing antiperspirants are more likely causes of toxicity. It has been suggested that aluminium may be linked to Alzheimer's disease, although that research has recently been refuted; aluminium accumulation may be a consequence of the Alzheimer's damage, not the cause. In any event, if there is any toxicity of aluminium it must be via a very specific mechanism, since total human exposure to the element in the form of naturally occurring clay in soil and dust is enormously large over a lifetime. Care must be taken to prevent aluminium from coming into contact with certain chemicals that can cause it to corrode quickly. For example, just a small amount of mercury applied to the surface of a piece of aluminium can break up the normal aluminium oxide barrier usually present. Within a few hours, even a heavy structural beam can be significantly weakened. For this reason, mercury thermometers are not allowed on many airliners, as aluminium is a common structural component in aircraft.

Spelling

Etymology / Nomenclature history

In 1808, Humphry Davy originally proposed the name alumium while trying to isolate the new metal electrolytically from the mineral alumina. In 1812 he changed the name to aluminum to match its Latin root. The same year, an anonymous contributor to the Quarterly Review objected to aluminum, and proposed the name aluminium. :Aluminium, for so we shall take the liberty of writing the word, in preference to aluminum, which has a less classical sound. (Q. Review VIII. 72, 1812) This had the advantage of conforming to the -ium suffix precedent set by other newly discovered elements of the period: potassium, sodium, magnesium, calcium, and strontium (all of which Davy had isolated himself). Nevertheless, -um spellings for elements were not unknown at the time: platinum, which had been known to Europeans since the 16th century, molybdenum, which was discovered in 1778, and tantalum, which was discovered in 1802, all have spellings ending in -um. Curiously, the United States adopted the -ium for most of the 19th century with aluminium appearing in Webster's Dictionary of 1828. However in 1892 Charles Martin Hall used the -um spelling in an advertising handbill for his new efficient electrolytic method for the production of aluminium, despite using the -ium spelling in all of his patents filed between 1886 and 1903. It has consequently been suggested that the spelling on the flyer was a simple spelling mistake rather a deliberate choice to use the -um spelling. Hall's domination of production of the metal ensured that the spelling aluminum became the standard in North America, even though the Webster Unabridged Dictionary of 1913 continued to use the -ium version. In 1926, the American Chemical Society officially decided to use aluminum in its publications, and American dictionaries typically label the spelling aluminium as a British variant.

Present day spelling

In the English-speaking world, the spellings (and associated pronunciations) aluminium and aluminum are both in common use in both scientific and nonscientific contexts. In the United States, the spelling aluminium is largely unknown, and the spelling aluminum predominates. Elsewhere in the English-speaking world the spelling aluminium predominates, and the spelling aluminum is largely unknown. However, in Canada both spellings are common, due to the multiple influences on the language of its proximity to the United States, its British colonial past and the large number of native French speakers. Outside English, the "ium" spelling is widespread: the word is aluminium in French and German, and identical or similar forms are used in many other languages. Consequently it is the more common of the two spellings in global terms, even though there may be more users of aluminum in the English-speaking world. The International Union of Pure and Applied Chemistry (IUPAC) adopted aluminium as the standard international name for the element in 1990, but three years later recognised aluminum as an acceptable variant. Hence their periodic table includes both, but places aluminium first [http://www.iupac.org/reports/periodic_table/index.html]. IUPAC officially prefers the use of aluminium in its internal publications, although several IUPAC publications use the spelling aluminum.[http://www.iupac.org/cgi-bin/htsearch?sort=score&restrict=www.iupac.org%2Fpublications%2Fci&config=htdig&restrict=&exclude=www.iupac.org%2Fgoldbook%2F&words=aluminum&submit=]

Chemistry

Oxidation state 1


- AlH is produced when aluminium is heated at 1500 °C in an atmosphere of hydrogen.
- Al2O is made by heating the normal oxide, Al2O3, with silicon at 1800 °C in a vacuum.
- Al2S can be made by heating Al2S3 with aluminium shavings at 1300 °C in a vacuum. It quickly disproportionates to the starting materials. The selenide is made in a parallel manner.
- AlF, AlCl and AlBr exist in the gaseous phase when the tri-halide is heated with aluminium.

Oxidation state 2


- Aluminium suboxide, AlO can be shown to be present when aluminium powder burns in oxygen.

Oxidation state 3


- Fajans rules show that the simple trivalent cation Al3+ is not expected to be found in anhydrous salts or binary compounds such as Al2O3. The hydroxide is a weak base and aluminium salts of weak bases, such as carbonate, can't be prepared. The salts of strong acids, such as nitrate, are stable and soluble in water, forming hydrates with at least six molecules of water of crystallization.
- Aluminium hydride, (AlH3)n, can be produced from trimethylaluminium and an excess of hydrogen. It burns explosively in air. It can also be prepared by the action of aluminium chloride on lithium hydride in ether solution, but cannot be isolated free from the solvent.
- Aluminium carbide, Al4C3 is made by heating a mixture of the elements above 1000 °C. The pale yellow crystals have a complex lattice structure, and react with water or dilute acids to give methane. The acetylide, Al2(C2)3, is made by passing acetylene over heated aluminium.
- Aluminium nitride, AlN, can be made from the elements at 800 °C. It is hydrolysed by water to form ammonia and aluminium hydroxide.
- Aluminium phosphide, AlP, is made similarly, and hydrolyses to give phosphine.
- Aluminium oxide, Al2O3, occurs naturally as corundum, and can be made by burning aluminium in oxygen or by heating the hydroxide, nitrate or sulfate. As a gemstone, its hardness is only exceeded by diamond, boron nitride and carborundum. It is almost insoluble in water.
- Aluminium hydroxide may be prepared as a gelatinous precipitate by adding ammonia to an aqueous solution of an aluminium salt. It is amphoteric, being both a very weak acid, and forming aluminates with alkalis. It exists in various crystalline forms.
- Aluminium sulfide, Al2S3, may be prepared by passing hydrogen sulfide over aluminium powder. It is polymorphic.
- Aluminium fluoride, AlF3, is made by treating the hydroxide with HF, or can be made from the elements. It consists of a giant molecule which sublimes without melting at 1291 °C. It is very inert. The other trihalides are dimeric, having a bridge-like structure.
- Organo-metallic compounds of empirical formula AlR3 exist and, if not also giant molecules, are at least dimers or trimers. They have some uses in organic synthesis, for instance trimethylaluminium.
- Alumino-hydrides of the most electropositive elements are known, the most useful being lithium aluminium hydride, Li[AlH4]. It decomposes into lithium hydride, aluminium and hydrogen when heated, and is hydrolysed by water. It has many uses in organic chemistry. The aluminohalides have a similar structure.

Aluminium in popular culture


- In the film Star Trek IV: The Voyage Home, Scotty devises the fictional material transparent aluminum.

See also


- Alloys of aluminium.

References


- [http://periodic.lanl.gov/elements/13.html Los Alamos National Laboratory – Aluminum]
- [http://www.worldwidewords.org/articles/aluminium.htm World Wide Words] A history of the spelling of aluminium from a British viewpoint.
- Oxford English Dictionary Entries "aluminum" and "aluminium", available by subscription. [http://www.oed.com]

External links


- [http://www.webelements.com/webelements/elements/text/Al/index.html WebElements.com – Aluminium]
- [http://www.world-aluminium.org/ World Aluminium]
- [http://www.indexmundi.com/en/commodities/minerals/aluminum/aluminum_table12.html World production of primary aluminum, by country]
- [http://www.saanet.org/kashipur/docs/seenalum.htm Social and Environmental Impact of the Aluminium Industry]
- [http://153rd.com/sam/as/physics/aluminium/normal/redirect.html Sam's Aluminium Information Site] Patents
- US[http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=400664.WKU.&OS=PN/400664&RS=PN/400664 400664] – Process of reducing aluminum from its floride salts by electrolysis – C. M. Hall Category:Chemical elements Category:Poor metals Category:Pigments Category:Pyrotechnic chemicals Category:Rocket fuels ko:알루미늄 ja:アルミニウム simple:Aluminium th:อะลูมิเนียม

Spelling

Proper spelling is the writing of a word or words with all necessary letters and diacritics present in an accepted, conventional order. It is one of the elements of orthography and a prescriptive element of language. As a means of transcribing the sounds of language into alphabetic letters, spelling, however officially sanctioned, often offers but a rough and inconsistant approximation. Whereas uniformity in the spelling of words is one of the features of a standard language in modern times, and official languages usually prescribe standard spelling, Minority languages and regional languages often lack this trait. Furthermore, it is a relatively recent development in various major languages in national contexts, linked to the compiling of dictionaries, the founding of national academies, and other institutions of language maintenance, including compulsory mass education. Learning proper spelling by rote is a traditional element of elementary education. In the US, the ubiquity of the phonics method of teaching reading, which emphasizes the importance of "sounding out" spelling in learning to read, also puts a premium on the prescriptive learning of spelling. For these reasons, divergence from standard spelling is often perceived as an index of stupidity, illiteracy, or lower class standing. The intelligence of Dan Quayle, for instance, was repeatedly disparaged for correcting a student's spelling of potato as potatoe at an elementary school spelling bee in Trenton, New Jersey on June 15, 1992. In fact, "potatoe" is a variant historical spelling now in disuse. Divergent spelling is also popular advertising technique used to attract attention: qwik, donut, or tonite, for example. Spelling evolves, often from a principle of alphabetic thrift rather than phonetic rectitude: catalogue becomes catalog. Despite this, in countries such as the US and UK without official spelling policies, many vestigial and foreign spelling conventions work simultaneously. In countries where there is a national language maintenance policy, such as the Netherlands and Germany, spelling reforms were driven to make spelling a better index of pronunciation. Since traditional language teaching methods emphasized written language over spoken language, a second-language speaker can have a better spelling ability than a native in spite of having a worse command of the language. The International Phonetic Alphabet (IPA) aims to provide a medium of alphabetic characters to transcribe all sounds in all languages.

See also


- Misspelling
- Spelling reform
  - Reforms of French orthography
  - German spelling reform of 1996
  - Reforms of Russian orthography
  - Shavian alphabet
- Phonemic orthography
- Spelling pronunciation
- English spelling
  - List of English words with diacritics
- Greek orthography
  - Monotonic orthography
  - Polytonic orthography
- Latin spelling and pronunciation
- Russian orthography
- Grapheme
- Official script Category:Writing

Poor metal

The poor metals or post-transition metals are the metallic elements of the p-block of the periodic table, occurring between the metalloids and the transition metals. They are more electropositive than the transition metals, but less so than the alkali metals and alkaline earth metals. Their melting and boiling points are generally lower than those of the transition metals, and they are also softer. The poor metals are aluminium, gallium, indium, tin, thallium, lead, and bismuth, and sometimes included are germanium, antimony and polonium. Elements 113 to 116 are provisionally included in this category, and are known temporarily as: ununtrium, ununquadium, ununpentium and ununhexium.

See also


- Periodic table
Category:Periodic table

- ja:卑金属 th:โลหะหลังทรานซิชั่น

Atomic number

The atomic number (Z) is a term used in chemistry and physics to represent the number of protons found in the nucleus of an atom. In an atom of neutral charge, the number of electrons also equals the atomic number. The atomic number originally meant the number of an element's place in the periodic table. When Mendeleev arranged the known chemical elements grouped by their similarities in chemistry, it was noticeable that placing them in strict order of atomic mass resulted in some mismatches. Iodine and tellurium, if listed by atomic mass, appeared to be in the wrong order, and would fit better if their places in the table were swapped. Placing them in the order which fit chemical properties most closely, their number in the table was their atomic number. This number appeared to be approximately proportional to the mass of the atom, but, as the discrepancy showed, reflected some other property than mass. The anomalies in this sequence were finally explained after research by Henry Gwyn Jeffreys Moseley in 1913. Moseley discovered a strict relationship between the x-ray diffraction spectra of elements, and their correct location in the periodic table. It was later shown that the atomic number corresponds to the electric charge of the nucleus — in other words the number of protons. It is the charge which gives elements their chemical properties, rather than the atomic mass. The atomic number is closely related to the mass number (although they should not be confused) which is the number of protons and neutrons in the nucleus of an atom. The mass number often comes after the name of the element, e.g. carbon-14 (used in carbon dating).

See also


- Periodic table
- List of elements by number
- Effective atomic number Category:Chemical properties Category:Nuclear physics als:Ordnungszahl ko:원자 번호 ja:原子番号 simple:Atomic number th:เลขอะตอม

Bauxite

Bauxite is a naturally occurring, heterogeneous material composed primarily of one or more aluminium hydroxide minerals, plus various mixtures of silica, iron oxide, titania, aluminium silicates, and other impurities in minor or trace amounts. Bauxite is a sedimentary rock produced by in situ chemical weathering typically under tropical to subtropical climate conditions. The principal aluminium hydroxide minerals found in varying proportions with bauxites are gibbsite and the polymorphs boehmite and diaspore. Bauxites are typically classified according to their intended commercial application: abrasive, cement, chemical, metallurgical, refractory, etc. The bulk of world bauxite production (approximately 85%) is used as feed for the manufacture of alumina via a wet chemical caustic leach method commonly known as the Bayer process. Subsequently, the majority of the resulting alumina produced from this refining process is in turn employed as the feedstock for the production of aluminium metal by the electrolytic reduction of alumina in a molten bath of natural or synthetic cryolite (Na3AlF6), the Hall-Heroult process. Bauxite is the raw material most widely used in the production of alumina on a commercial scale. Other raw materials, such as anorthosite, alunite, coal wastes, and oil shales, offer additional potential alumina sources. Although it would require new plants using new technology, alumina from these nonbauxitic materials could satisfy the demand for primary metal, refractories, aluminium chemicals, and abrasives. Synthetic mullite, produced from kyanite and sillimanite, substitutes for bauxite-based refractories. Although more costly, silicon carbide and alumina-zirconia substitute for bauxite-based abrasives.

History

Bauxite was named after the village Les Baux de Provence in southern France, where it was first discovered in 1821 by the geologist Pierre Berthier. Knighted in 1832, Sir Berthier went on to establish the Berthier Museum of Geology in Tours. Due to the exhaustion of its bauxite mines, France has almost completely ceased the exploitation of bauxite since 1991. French mines were located in the Var, Bouches-du-Rhône and Herault départements.

World Bauxite Mine Production, Reserves, and Reserve Base

(x1000 tonne) Mine production Reserves Reserve base 2000 2001 ------------------------------------------------------------------- Australia 53,800 53,500 3,800,000 7,400,000 Brazil 14,000 14,000 3,900,000 4,900,000 China 9,000 9,200 720,000 2,000,000 Guinea 15,000 15,000 7,400,000 8,600,000 Guyana 2,400 2,000 700,000 900,000 India 7,370 8,000 770,000 1,400,000 Jamaica 11,100 13,000 2,000,000 2,500,000 Russia 4,200 4,000 200,000 250,000 Suriname 3,610 4,000 580,000 600,000 United States NA NA 20,000 40,000 Venezuela 4,200 4,400 320,000 350,000 Other countries 10,800 10,200 4,100,000 4,700,000 ------------------------------------------------------------------- World total (rounded) 135,000 137,000 24,000,000 34,000,000 (Numbers for 2001 estimated)

External links


- [http://minerals.usgs.gov/minerals/pubs/commodity/bauxite/ USGS Minerals Information: Bauxite]
- [http://www.mii.org/Minerals/photoal.html Mineral Information Institute] Category:Sedimentary rocks ko:보크사이트 ja:ボーキサイト

Passivation

Passivation is the process of making a material "passive" in relation to another material prior to using the materials together. For example, prior to storing hydrogen peroxide in an aluminium container, the container can be passivated by rinsing it with a dilute solution of nitric acid and peroxide alternating with deionized water. The nitric acid and peroxide oxidizes and dissolves any impurities on the inner surface of the container, and the deionized water rinses away the acid and oxidized impurities. In the context of corrosion, passivation is the spontaneous formation of a hard non-reactive surface film that inhibits further corrosion. This layer is usually an oxide or nitride that is a few atoms thick. Under normal conditions of pH and oxygen concentration, passivation is seen in such materials as aluminium, magnesium, copper, stainless steel, titanium, and silicon. Ordinary steel can form a passivating layer in alkali environments, as rebar does in concrete. The conditions necessary for passivation are recorded in Pourbaix diagrams. Some corrosion inhibitors help the formation of a passivation layer on the surface of the metals they come in contact with.

Passivation of specific materials:


- Aluminum may be protected from oxidation by anodizing or allodizing.
- Iron based materials, including steel, may be somewhat protected by promoting oxidation ("rust") and then converting the oxidation to a metalophosphate by using phosphoric acid and further protected by surface coating. As the uncoated surface is water soluable a preferred method is to form maganese compounds by a process known as parkerizing™/

Further Reading

ASTM A967 provides advice for the passivation of stainless steel parts. Category:Metallurgy Category:Corrosion ja:不動態

Aerospace

:This article is about the field of research and industry; for the corporation, see The Aerospace Corporation Aerospace refers to the broad field of air and space travel and the associated research. Aerospace is a very diverse industry, which has an immediate impact on the lives of almost everyone. space]

Overview

In most industrial countries, the aerospace industry is a cooperation of public and private industries. For example, several countries have a space program under the command of the government, such as NASA in the United States, ESA in Europe, the Canadian Space Agency in Canada, RKA in Russia and China National Space Administration in China. Along with these public space programs, many companies produce technical tools and components such as spaceships and satellites. Some known companies involved in space programs include Lockheed Martin, Northrop Grumman, Airbus and Boeing. These companies are also involved in other areas of aerospace such as the construction of aircraft. Many countries have air transport companies, such as Air France and Air India.

History

The field of aerospace got its beginning with the first powered flight at Kitty Hawk on December 17, 1903, by the Wright brothers. From there, aerospace has grown to be one of the most exciting, diverse, and fast paced fields of today. From the first wood-and-cloth plane of Wilbur and Orville Wright to the first trip to the moon on Apollo 11 to the new and exciting aircraft being developed by companies like Boeing, Airbus, or Bombardier, aerospace has come a long way in a little over a century.

See also


- Aeronautics
- Astronautics
- Aerospace engineering
- General aviation
- Space travel
- Space exploration

External link


- [http://dictionary.reference.com/search?q=aerospace Aerospace definition], from Dictionary.com Category:Space exploration

Transport

:For other article subjects named transport, see Transport (disambiguation). Transportation redirects here, for other uses, see Transportation (disambiguation). Transport or transportation is the movement of people, goods, signals and information from one place to another. The term is derived from the Latin trans ("across") and portare ("to carry").

Aspects of transport

The field of transport has several aspects: loosely they can be divided into a triad of infrastructure, vehicles, and operations. Infrastructure includes the transport networks (roads, railways, airways, canals, pipelines, etc.) that are used, as well as the nodes or terminals (such as airports, railway stations, bus stations and seaports). The vehicles generally ride on the networks, such as automobiles, bicycles, buses, trains, airplanes. The operations deal with the control of the system, such as traffic signals and ramp meters, railroad switches, air traffic control, etc, as well as policies, such as how to finance the system (for example, the use of tolls or gasoline taxes). Broadly speaking, the design of networks are the domain of civil engineering and urban planning, the design of vehicles of mechanical engineering and specialized subfields such as nautical engineering and aerospace engineering, and the operations are usually specialized, though might appropriately belong to operations research or systems engineering.

Modes of transport

Modes are combinations of networks, vehicles, and operations, and include walking, the road transport system, rail transport, ship transport and modern aviation.

Categories of transport


- (Non-human) Animal-powered transport
- Aviation
- Cable transport
- Conveyor transport
- Human-powered transport
- Hybrid transport
- Ship transport
- Space transport
- Transport on other planets
- Proposed future transport

Transport and communications

Transport and communication are both substitutes and complements. Though it might be possible that sufficiently advanced communication could substitute for transport, one could telegraph, telephone, fax, or email a customer rather than visiting them in person, it has been found that those modes of communication in fact generate more total interactions, including interpersonal interactions. The growth in transport would be impossible without communication, which is vital for advanced transportation systems, from railroads which want to run trains in two directions on a single track, to air traffic control which requires knowing the location of aircraft in the sky. Thus, it has been found that the increase of one generally leads to more of the other.

Transport and land use

There is a well-known relationship between the density of development, and types of transportation. Intensity of development is often measured by area of Floor Area Ratio (FAR), the ratio of useable floorspace to area of land. As a rule of thumb, FARs of 1.5 or less are well suited to automobiles, those of six and above are well suited to trains. The range of densities from about two up to about four is not well served by conventional public or private transport. Many cities have grown into these densities, and are suffering traffic problems. Personal rapid transit could provide a solution to this problem. Land uses support activities. Those activities are spatially separated. People need transport to go from one to the other (from home to work to shop back to home for instance). Transport is a "derived demand," in that transport is unnecessary but for the activities pursued at the ends of trips. Good land use keeps common activities close (e.g. housing and food shopping), and places higher-density development closer to transportation lines and hubs. Poor land use concentrates activities (such as jobs) far from other destinations (such as housing and shopping). There are economies of agglomeration. Beyond transportation some land uses are more efficient when clustered. Transportation facilities consume land, and in cities, pavement (devoted to streets and parking) can easily exceed 20 percent of the total land use. An efficient transport system can reduce land waste.

Transport, energy, and the environment

Transport is a major use of energy, and transport burns most of the world's petroleum. Hydrocarbon fuels produce carbon dioxide, a greenhouse gas widely thought to be the chief cause of global climate change, and petroleum-powered engines, especially inefficient ones, create air pollution, including nitrous oxides and particulates (soot). Although vehicles in the United States have been getting cleaner because of environmental regulations, this has been offset by an increase in the number of vehicles and more use of each vehicle. Other environmental impacts of transport systems include traffic congestion, toxic runoff from roads and parking lots that can pollute water supplies and aquatic ecosystems, and automobile-oriented urban sprawl, which can consume natural habitat and agricultural lands. Low-pollution fuels can reduce pollution. Low pollution fuels may have a reduced carbon content, and thereby contribute less in the way of carbon dioxide emissions, and generally have reduced sulfur, since sulfur exhaust is a cause of acid rain. The most popular low-pollution fuel at this time is liquified natural gas. Hydrogen is an even lower-pollution fuel that produces no carbon dioxide, but producing and storing it economically is currently not feasible. Other alternative renewable energy sources such as biodiesel are being researched heavily. Another strategy is to make vehicles more efficient, which reduces pollution and waste by reducing the energy use. Electric vehicles use efficient electric motors, but their range is limited by either the extent of the electric transmission system or by the storage capacity of batteries. Electrified public transport generally uses overhead wires or third rails to transmit electricity to vehicles, and is used for both rail and bus transport. Battery electric vehicles store their electric fuel onboard in a battery pack. Another method is to generate energy using fuel cells, which may eventually be two to five times as efficient as the internal combustion engines currently used in most vehicles. Another effective method is to streamline ground vehicles, which spend up to 75% of their energy on air-resistance, and to reduce their weight. Regenerative braking is possible in all electric vehicles and recaptures the energy normally lost to braking, and is becoming common in rail vehicles. In internal combustion automobiles and buses, regenerative braking is not possible, unless electric vehicle components are also a part of the powertrain, these are called hybrid electric vehicles. Shifting travel from automobiles to well-utilized public transport can reduce energy consumption and traffic congestion. Use of non-motorized modes walking and bicycling also reduces the consumption of fossil fuels. However, as most areas get wealthier, the use of these modes declines. There are a few wealthy cities where bicycling comprises a significant share of trips, including Copenhagen, Denmark and Groningen, Netherlands. A number of other cities, including London, Paris, New York, Bogotá, Chicago, and San Francisco, are creating networks of bicycle lanes and bicycle paths to encourage bicycling by increasing safety from traffic.

Transport Research

Transport research facilities are mainly attached to universities or are steered by the state. In most countries (not in France and Spain) one can see now how laboratories are brought into PPP-operation, where industry takes over part of the share. Some major players in Europe:
- Transport Research Laboratory [http://www.trl.co.uk/ TRL UK]
- [http://www.vtt.fi/transport/ VTT FI]
- [http://www.lcpc.fr LCPC FR]
- [http://www.inrets.fr INRETS FR]
- [http://www.certu.fr CERTU FR]
- [http://www.dlr.de/dlr/Verkehr DLR DE]
- [http://www.crf.it CRF IT]
- [http://www.vv.tno.nl TNO NL]
- [http://www.cedex.es/ CEDEX ES]
- [http://www.cemt.org/jtrc/ Joint OECD-ECMT Transport Research Centre]
- [http://www.cemt.org/index.htm European Conference of Ministers of Transport] USA:
- http://www.its.berkeley.edu Institute of Transportation Studies, University of California, Berkeley
- National Transportation Research Center
- [http://www.trb.org/ Transportation Research Board] The European Commission supports the co-operation and collaboration amongst the transport laboratories by funding projects like EXTR@Web and [http://www.intransnet.org Intransnet]. Especially the transition from planned economy to achieving a stable position on the market will be a challenge for laboratories in the new member states. Another EU-project [http://www.etra.cc etra.cc]is coping with those problems.

See also


- List of transport topics
- Transportation reference tables
- Historic transport Category:Commercial item transport and distribution
- Category:Technology ko:교통 ja:交通 simple:Transport th:การขนส่ง

Oxidation

Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. This can be a simple redox process, such as the combustion of carbon to yield carbon dioxide, it could be the reduction of carbon by hydrogen to yield methane, or it could be the oxidation of sugar in the human body, through a series of very complex electron transfer processes. The term redox comes from the two concepts of reduction and oxidation. :Oxidation describes the loss of an electron by a molecule, atom, or ion; loss of hydrogen, or gain of oxygen. It also means an increase in oxidation number. :Reduction describes the uptake of an electron by a molecule, atom, or ion; loss of oxygen and gain of hydrogen. It also means a decrease in oxidation number. These two terms go together, because in a chemical reaction, one cannot occur without the other; electrons lost by one compound must be gained by another. Reduction can also be considered to be the reducing of an atom's positive charge, and oxidation its opposite (gaining positive charge). oxygen

Oxidizing and reducing agents

Substances that have the ability to oxidize (Commonwealth English oxidise) other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. Put in another way, the oxidant removes electrons from the other substance, and is thus reduced itself. Oxidants are usually chemical substances with elements in high oxidation numbers (e.g. H2O2, MnO4-, CrO3, Cr2O72-, OsO4) or highly electronegative substances that can gain one or two extra electrons by oxidizing a substance (O2, O3, F2, Cl2, Br2). Substances that have the ability to reduce other substances are said to be reductive and are known as reductive agents, reductants, or reducers. Put in another way, the reductant transfers electrons to the substance. Reductants in chemistry are very diverse. Metal reduction - electropositive elemental metals can be used (Li, Na, Mg, Fe, Zn, Al). These metals donate or give away electrons readily. Other kinds of reductants are hydride transfer reagents (NaBH4, LiAlH4), these reagents are widely used in organic chemistry, primarily in the reduction of carbonyl compounds to alcohols. Another useful method is reductions involving hydrogen gas (H2) with a palladium, platinum, or nickel catalyst. These catalytic reductions are primarily used in the reduction of carbon-carbon double or triple bonds. The chemical way to look at redox processes is that the reductant transfers electrons to the oxidant. Thus, at the end of the reaction, the reductant will have been oxidized and the oxidant will have been reduced.

Former meaning (oxygen/hydrogen)

Formerly, oxidation simply meant the addition of oxygen or the removing of hydrogen (hence the name oxidation), and reduction was removal of oxygen or the addition of hydrogen. Currently, however, the terms are normally used in a more general sense, describing electron movement.

Examples of redox reactions

A good example is the reaction between hydrogen and fluorine: :H2 + F2 → 2HF We can write this overall reaction as two half-reactions: an oxidation reaction: :H2 → 2H+ + 2e- and a reduction reaction: :F2 + 2e- → 2F- Elements always have an oxidation number of zero. In the first half reaction hydrogen is oxidized from an oxidation number of zero to an oxidation number of +1. In the second half reaction fluorine is reduced from an oxidation number of zero to an oxidation number of −1. When adding the reactions together the electrons cancel: :H2 → 2H+ + 2e- :+ 2e- + F2 → 2F- : --------------------- :H2 + F2 → 2H+ + 2F- And the ions combine to form hydrogen fluoride: 2H+ + 2F- → 2HF

Other examples


- iron(II) oxidizes to iron(III): :Fe2+ → Fe3+ + e-
- hydrogen peroxide reduces to hydroxide: :H2O2 + 2 e- → 2 OH- overall equation for the above: :2Fe2+ + H2O2 + 2H+ → 2Fe3+ + 2H2O
- denitrification, nitrate reduces to nitrogen: :2NO3- + 10e- + 12 H+ → N2 + 6H2O
- iron oxidizes to iron(III) oxide and oxygen is reduced forming iron(III) oxide (commonly known as rusting or tarnishing): :4Fe + 3O2 → 2 Fe2O3.
- Combustion of hydrocarbons produces water, carbon dioxide, some partially oxidized forms such as carbon monoxide, and heat energy. Complete oxidation of materials containing carbon produces carbon dioxide.
- In organic chemistry, stepwise oxidation of a hydrocarbon produces water and, successively, an alcohol, an aldehyde or a ketone, carboxylic acid, and then a peroxide.

Redox reactions in biology

Much biological energy is stored and released by means of redox reactions. Photosynthesis involves the reduction of carbon dioxide into sugars and the oxidation of water into molecular oxygen. The reverse reaction, respiration, oxidizes sugars to produce carbon dioxide and water. As intermediate steps, the reduced carbon compounds are used to reduce nicotinamide adenine dinucleotide (NAD+), which then contributes to the creation of a proton gradient, which drives the synthesis of adenosine triphosphate (ATP) and is maintained by the reduction of oxygen. In animal cells, mitochondria perform similar functions. See Membrane potential article. The term redox state is often used to describe the balance of NAD+/NADH and NADP+/NADPH in a biological system such as a cell or organ. The redox state is reflected in the balance of several sets of metabolites (e.g., lactate and pyruvate, beta-hydroxybutyrate and acetoacetate) whose interconversion is dependent on these ratios. An abnormal redox state can develop in a variety of deleterious situations, such as hypoxia, shock, and sepsis.

See also


- Bioremediation
- Calvin cycle
- Citric acid cycle
- Electrochemical cell
- Electrochemistry
- Galvanic cell
- Membrane potential
- Thermic reaction

External links


- [http://www.shodor.org/UNChem/advanced/redox/redoxcalc.html Redox Reactions Calculator]
- [http://www.chemguide.co.uk/inorganic/redox/definitions.html#top Redox reactions at Chemguide] Category:Electrochemistry ko:산화·환원 반응 ja:酸化還元反応

Steel

Steel is a metal alloy whose major component is iron, with carbon being the primary alloying material. Carbon acts as a hardening agent, preventing iron atoms, which are naturally arranged in a lattice, from sliding past one another. Varying the amount of carbon and its distribution in the alloy controls qualities such as the hardness, elasticity, ductility, and tensile strength of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but is also more brittle. One classical definition is that steels are iron–carbon alloys with up to 1.5 percent carbon by weight; alloys with higher carbon content than this are known as cast iron. Currently there are several classes of steels in which carbon is replaced with other alloying materials, and carbon, if present, is undesired. A more recent definition is that steels are iron-based alloys that can be plastically formed (pounded, rolled, etc.).

Iron and steel

plastically Iron, like most metals, is not found in the Earth's crust in a native state. Iron can be found in the crust only in combination with oxygen or sulfur. Typically Fe2O3—the form of iron oxide found as the mineral hematite, and FeS2—Pyrite. Iron oxide is a soft sandstone-like material with limited uses on its own. Iron is extracted from ore by removing the oxygen by combining it with a preferred chemical partner such as carbon. This process, known as smelting, was first applied to metals with lower melting points. Copper melts at just over 1000 °C, while tin melts around 250 °C. Both temperatures could be reached with ancient methods that have been used for at least 6000 years (since the Bronze Age). Since the oxidation rate itself increases rapidly beyond 800 °C, it is important that smelting take place in a fairly oxygen-free environment. Unlike copper and tin, liquid iron dissolves carbon quite readily, so that smelting results in an alloy containing too much carbon to be called steel. Bronze Age Even in the narrow range of concentrations that make up steel, mixtures of carbon and iron can form into a number of different structures, or allotropes, with very different properties; understanding these is essential to making quality steel. At room temperature, the most stable form of iron is the body-centered cubic structure ferrite or α-iron, a fairly soft metallic material that can dissolve only a small concentration of carbon (no more than 0.021 wt% at 910 °C). Above 910 °C ferrite undergoes a phase transition from body-centered cubic to a face-centered cubic configuration, called austenite or γ-iron, which is similarly soft and metallic but can dissolve considerably more carbon (as much as 2.04 wt% carbon at 1146 °C). As carbon-rich austenite cools, the mixture attempts to revert to the ferrite phase, resulting in an excess of carbon. One way for carbon to leave the austenite is for cementite to precipitate out of the mix, leaving behind iron that is pure enough to take the form of ferrite, and resulting in a cementite-ferrite mixture. Cementite is a stochiometric phase with the chemical formula of Fe3C. Cementite forms in regions of higher carbon content while other areas revert to ferrite around it. Self-reinforcing patterns often emerge during this process, leading to a patterned layering known as pearlite due to its pearl-like appearance, or the similar but less beautiful bainite. Perhaps the most important allotrope is martensite, a chemically metastable substance with about four to five times the strength of ferrite. Martensite has a very similar unit cell structure to austenite, and identical chemical composition. As such, it requires extremely little thermal activation energy to form. The heat treatment process for most steels involves heating the alloy until austenite forms, then quenching the hot metal in water or oil, cooling it so rapidly that the transformation to ferrite or perlite does not have time to take place. The transformation into martensite, by contrast, occurs almost immediately, due to a lower activation energy. Martensite has a lower density than austenite, so that the transformation between them results in a change of volume. In this case, expansion occurs. Internal stresses from this expansion generally take the form of compression on the crystals of martensite and tension on the remaining ferrite, with a fair amount of shear on both constituents. If quenching is done improperly, these internal stresses can cause a part to shatter as it cools; at the very least, they cause internal work hardening and other microscopic imperfections. At this point, if its carbon content is high enough to produce a significant concentration of martensite, the metal resembles spring steel: extremely hard, but very brittle. Often, steel undergoes further heat treatment at a lower temperature to destroy some of the martensite (by allowing enough time for cementite, etc., to form) and help settle the internal stresses and defects. This softens the steel, producing a more ductile and fracture-resistant metal. Because time is so critical to the end result, this process is known as tempering, source of the term tempered steel. Other materials are often added to the iron-carbon mixture to tailor the resulting properties. Nickel and manganese in steel add to its tensile strength and make austenite more chemically stable, chromium increases the hardness and melting temperature, and vanadium also increases the hardness while reducing the effects of metal fatigue. Large amounts of chromium and nickel (often 18 and 8 %, respectively) are added to stainless steel so that a hard oxide forms on the metal surface to inhibit corrosion. Tungsten interferes with the formation of cementite, allowing martensite to form with slower quench rates, resulting in high speed steel. On the other hand sulfur, nitrogen, and phosphorus make steel more brittle, so these commonly found elements must be removed from the ore during processing. When iron is smelted from its ore by commercial processes, it contains more carbon than is desirable. To become steel, it must be melted and reprocessed to remove the correct amount of carbon, at which point other elements can be added. Once this liquid is cast into ingots, it usually must be "worked" at high temperature to remove any cracks or poorly mixed regions from the solidification process, and to produce shapes such as plate, sheet, wire, etc. It is then heat-treated to produce a desirable crystal structure, and often "cold worked" to produce the final shape. In modern steelmaking these processes are often combined, with ore going in one end of the assembly line and finished steel coming out the other. These can be streamlined by a deft control of the interaction between work hardening and tempering.

History of iron and steelmaking

Iron was in limited use long before it became possible to smelt it. The first signs of iron use come from Ancient Egypt and Sumer, where around 4000 BC small items, such as the tips of spears and ornaments, were being fashioned from iron recovered from meteorites (see Iron: History). About 6% of meteorites are composed of an iron-nickel alloy, and iron recovered from meteorite falls allowed ancient peoples to manufacture small numbers of iron artifacts. Meteoric iron was also fashioned into tools in precontact North America. Beginning around the year 1000, the Thule people of Greenland began making harpoons and other edged tools from pieces of the Cape York meteorite. These artifacts were also used as trade goods with other Arctic peoples: tools made from the Cape York meteorite have been found in archaeological sites more than 1000 miles (1600 km) away. When the American polar explorer Robert Peary shipped the largest piece of the meteorite to the American Museum of Natural History in New York City in 1897, it still weighed over 33 tons. The name for iron in several ancient languages means "sky metal" or something similar. In distant antiquity, iron was regarded as a precious metal, suitable for royal ornaments.

The Iron Age

ton Beginning between 3000 BC to 2000 BC increasing numbers of smelted iron objects (distinguishable from meteoric iron by their lack of nickel) appear in Anatolia, Egypt and Mesopotamia (see Iron: History). The oldest known samples of iron that appear to have been smelted from iron oxides are small lumps found at copper-smelting sites on the Sinai Peninsula, dated to about 3000 BC. Some iron oxides are effective fluxes for copper smelting; it is possible that small amounts of metallic iron were made as a by-product of copper and bronze production throughout the Bronze Age. In Anatolia, smelted iron was occasionally used for ornamental weapons: an iron-bladed dagger with a bronze hilt has been recovered from a Hattic tomb dating from 2500 BC. Also, the Egyptian ruler Tutankhamun died in 1323 BC and was buried with an iron dagger with a golden hilt. An Ancient Egyptian sword bearing the name of pharaoh Merneptah as well as a battle axe with an iron blade and gold-decorated bronze haft were both found in the excavation of Ugarit (see Ugarit). The early Hittites are known to have bartered iron for silver, at a rate of 40 times the iron's weigh, with Assyria. Iron did not, however, replace bronze as the chief metal used for weapons and tools for several centuries, despite some attempts. Working iron required more fuel and significantly more labor than working bronze, and the quality of iron produced by early smiths may have been inferior to bronze as a material for tools. Then, between 1200 and 1000 BC, iron tools and weapons displaced bronze ones throughout the near east. This process appears to have begun in the Hittite Empire around 1300 BC, or in Cyprus and southern Greece, where iron artifacts dominate the archaeological record after 1050 BC. Mesopotamia was fully into the Iron Age by 900 BC, central Europe by 800 BC. The reason for this sudden adoption of iron remains a topic of debate among archaeologists. One prominent theory is that warfare and mass migrations beginning around 1200 BC disrupted the regional tin trade, forcing a switch from bronze to iron. Egypt, on the other hand, did not experience such a rapid transition from the bronze to iron ages: although Egyptian smiths did produce iron artifacts, bronze remained in widespread use there until after Egypt's conquest by Assyria in 663 BC. Iron smelting at this time was based on the bloomery, a furnace where bellows were used to force air through a pile of iron ore and burning charcoal. The carbon monoxide produced by the charcoal reduced the iron oxides to metallic iron, but the bloomery was not hot enough to melt the iron. Instead, the iron collected in the bottom of the furnace as a spongy mass, or bloom, whose pores were filled with ash and slag. The bloom then had to be reheated to soften the iron and melt the slag, and then repeatedly beaten and folded to force the molten slag out of it. The result of this time-consuming and laborious process was wrought iron, a malleable but fairly soft alloy containing little carbon. Wrought iron can be carburized into a mild steel by holding it in a charcoal fire for prolonged periods of time. By the beginning of the Iron Age, smiths had discovered that iron that was repeatedly reforged produced a higher quality of metal. Quench-hardening was also known by this time. The oldest quench-hardened steel artifact is a knife found on Cyprus at a site dated to 1100 BC.

Developments in China

Archaeologists and historians debate whether bloomery-based ironworking ever spread to China from the West. Around 500 BC, however, metalworkers in the southern state of Wu developed an iron smelting technology that would not be practiced in Europe until late medieval times. In Wu, iron smelters achieved a temperature of 1130°C, hot enough to be considered a blast furnace. At this temperature, iron combines with 4.3% carbon and melts. As a liquid, iron can be cast into molds, a method far less laborious than individually forging each piece of iron from a bloom. Cast iron is rather brittle and unsuitable for striking implements. It can, however, be decarburized to steel or wrought iron by heating it in air for several days. In China, these ironworking methods spread northward, and by 300 BC, iron was the material of choice throughout China for most tools and weapons. A mass grave in Hebei province, dated to the early third century BC, contains several soldiers buried with their weapons and other equipment. The artifacts recovered from this grave are variously made of wrought iron, cast iron, malleabilized cast iron, and quench-hardened steel, with only a few, probably ornamental, bronze weapons. During the Han Dynasty (202 BC–AD 220), Chinese ironworking achieved a scale and sophistication not reached in the West until the eighteenth century. In the first century, the Han government established ironworking as a state monopoly and built a series of large blast furnaces in Henan province, each capable of producing several tons of iron per day. By this time, Chinese metallurgists had discovered how to puddle molten pig iron, stirring it in the open air until it lost its carbon and became wrought iron. (In Chinese, the process was called chao, literally, stir-frying.) Also during this time, Chinese metallurgists had found that wrought iron and cast iron could be melted together to yield an alloy of intermediate carbon content, that is, steel. According to legend, the sword of Liu Bang, the first Han emperor, was made in this fashion. Some texts of the era mention "harmonizing the hard and the soft" in the context of ironworking; the phrase may refer to this process.

India

Perhaps as early as 300 BC, although certainly by AD 200, high quality steel was being produced in southern India by what Europeans would later call the crucible technique. In this system, high-purity wrought iron, charcoal, and glass were mixed in crucibles and heated until the iron melted and absorbed the carbon. The resulting high-carbon steel, called پولاد (pulâd) in Persian and wootz by later Europeans, was exported throughout much of Asia. A solid pillar of rust-resistant steel forged in 4th century AD and now standing for many centuries next to the Kutab Minar in Delhi is a testimony of the steel manufaturing skills of Indian artisans. The famous Damascus sword was made of steel imported from India.

Middle East

By the 9th century, smiths in the Abbasid caliphate had developed techniques for forging wootz to produce steel blades of unusual flexibility and sharpness (Damascus steel). The secret of forging this kind of steel was lost, even in the Middle East, by around 1600, and only recently have metallurgists found methods for reproducing its properties.

Ironworking in medieval Europe

The middle ages in Europe saw the construction of progressively larger bloomeries. By the 8th century, smiths in northern Spain had developed a style that become known as a Catalan forge, a furnace about 1 meter (3 feet) tall, capable of smelting up to 150 kg (350 lb) of iron in each batch. In succeeding centuries, smiths in the Frankish empire and later the Holy Roman Empire scaled up this basic design, increasing the height of the flue to as tall as 5 meters (16 feet) and smelting as much as 350 kg (750 lb) of iron in each batch. These larger furnaces required more draft than could be provided by human power, and forging the large blooms that resulted was also beyond the capabilities of a single man. To this end, waterwheels were employed to power the bellows and hammers. Eventually, the scaling up of the bloomery reached a point where the furnace was hot enough to produce cast iron. Although the brittle cast iron may initially have been a nuisance to the smith, as it was too brittle to be forged, the spread of cannon to Europe in the 1300s provided an application for iron casting, cast iron cannonballs. The oldest known blast furnace in Europe was constructed at Lapphyttan in Sweden, sometime between 1150 and 1350. Other early European blast furnaces were built throughout the Rhine valley: blast furnaces were in operation near Liège (a city in modern-day Belgium) in the 1340s, and at Massevaux in France by 1409. The first English blast furnace was not built until 1496, when Henry VII commissioned a new ironworks at Newbridge, in a part of Sussex known as the Weald. Despite this late start, the production of English iron foundries rapidly grew, in no small part due to foreign craftsmen hired by Henry to bring the craft of iron casting to England. In 1543, William Levett, a Wealden ironmaster, and Peter Baude, a French craftsman in Henry VIII's employ, cast the Weald's first one-piece iron cannon. English iron cannons gained a reputation for being superior to, and less expensive than, the bronze cannons made elsewhere in Europe, and at least initially, efforts to copy them outside the Weald failed. The superiority of English cannons over Spanish ones has been credited as one factor in England's 1588 defeat of the Spanish Armada. In 1619, Jan Andries Moerbeck, a Dutch ironmaster, began importing Wealden iron ore for comparison to the ore available on the Continent. One difference he observed was that the English ore contained some calcareous material, and soon after, Dutch ironmasters introduced the use of limestone as a flux in the blast furnace. This practice improved the separation of slag from the cast iron and improved the quality of Continental cast iron.

Ironworking in early modern Europe