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Anodising

Anodising

Anodising, or anodizing, is a process used to protect aluminum from abrasion and corrosion and to allow it to be dyed in a wide range of colors. The process derives its name from the fact that the part to be treated forms the anode portion of an electrical circuit in this electrolytic process. Anodized aluminum can be found on paintball guns, carabiners, and other extreme sports equipment due to its aesthetic properties but also the protection it offers to aluminum. The aluminum oxide coating is grown from and into the surface of the aluminum. Because of this (unlike coatings), it is not prone to peeling or cracking. It also possesses excellent thermal and electrical insulation qualities.

Chemistry

Aluminum naturally forms a passivating oxide layer which provides moderate protection against corrosion. The layer is strongly adherent to the metal surface (as compared to corrosion in steel, where rust puffs up and flakes off, exposing new metal to corrosion), and it will regrow quickly if scratched off. In anodization, this layer of aluminum oxide is grown on the surface of the aluminum from the action of the current being passed through the part, which is bathed in an acid solution. The conditions are controlled to prevent the phenomenon of passivation from occurring, allowing the formation of an oxide layer many times thicker than would otherwise form. This oxide layer increases both the hardness and the corrosion resistance of the aluminum. The oxide forms as microscopic hexagonal "pipe" crystals of corundum, each having a central hexagonal pore (which is also the reason that an anodized part can take on color in the dyeing process).

Dyeing

pore Where appearance is important, the oxide surface can be dyed before the sealing stage, as the dye enters the pores in the oxide surface. The number of dye colors is almost endless; however, lighter colors tend to look better than darker ones. Alternatively, metal (usually tin) can be electrolytically deposited in the pores of the anodic coating to provide colors that are more light-fast (resistant to fading). Metal dye colors range from pale champagne to black. Bronze shades are preferred for architectural use. After dyeing, the surface is usually sealed by using hot water or steam to convert the oxide into its hydrated form, reducing the porosity of the surface as the oxide swells.

Related processes

Aluminum and its alloys are not the only materials that can be anodized. Titanium can be anodized and the coating can create an attractive blue color without dyes. The color formed is dependent on the thickness of the oxide; it is caused by the interference of light reflecting off the oxide surface with light traveling through it and reflecting off the underlying metal surface. Titanium nitride coatings can also be formed, which have a brown or golden color and have the same wear and corrosion benefits as anodization.

External links

- [http://www.coatfab.com/anodising.htm Coating and Fabrications Magazine]
- [http://www.hard-anodising.co.uk/tap.asp Hard Anodising Ltd] Category:Chemical processes Category:Metallurgy Category:Corrosion

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: :2O^2- → 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, t_1/2 = 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.

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

Corrosion

Corrosion is deterioration of useful properties in a material due to reactions with its environment. Weakening of steel due to oxidation of the iron atoms is a well-known example of electrochemical corrosion. This type of damage usually affects metallic materials, and typically produces oxide(s) and/or salt(s) of the original metal. Corrosion also includes the dissolution of ceramic materials and can refer to discolouration and weakening of polymers by the sun's ultraviolet light. Most structural alloys corrode merely from exposure to moisture in the air, but the process can be strongly affected by exposure to acids, bases, salts and organic chemicals. It can be concentrated locally to form a pit or crack, or it can extend across a wide area to produce general deterioration; efforts to reduce corrosion sometimes merely redirect the damage into less visible, less predictable forms.

Corrosion in nonmetals

Most ceramic materials are almost entirely immune to corrosion. The strong ionic and/or covalent bonds that hold them together leave very little free chemical energy in the structure; they can be thought of as already corroded. When corrosion does occur, it is almost always a simple dissolution of the material or chemical reaction, rather than an electrochemical process. A common example of corrosion protection in ceramics is the lime added to soda-lime glass to reduce its solubility in water; though it is not nearly as soluble as pure sodium silicate, normal glass does form sub-microscopic flaws when exposed to moisture. Due to its brittleness, such flaws cause a dramatic reduction in the strength of a glass object during its first few hours at room temperature. The degradation of polymeric materials is due to a wide array of complex and often poorly-understood physiochemical processes. These are strikingly different from the other processes discussed here, and so the term "corrosion" is only applied to them in a loose sense of the word. Because of their large molecular weight, very little entropy can be gained by mixing a given mass of polymer with another substance, making them generally quite difficult to dissolve. While dissolution is a problem in some polymer applications, it is relatively simple to design against. A more common and related problem is swelling, where small molecules infiltrate the structure, reducing strength and stiffness and causing a volume change. Conversely, many polymers (notably flexible vinyl) are intentionally swelled with plasticizers, which can be leached out of the structure, causing brittleness or other undesirable changes. The most common form of degradation, however, is a decrease in polymer chain length. Mechanisms which break polymer chains are familiar to biologists because of their effect on DNA: ionizing radiation (most commonly ultraviolet light), free radicals, and oxidizers such as oxygen, ozone, and chlorine. Additives can slow these process very effectively, and can be as simple as a UV-absorbing pigment (i.e., titanium dioxide or carbon black). Plastic shopping bags often do not include these additives so that they break down more easily as litter. The remainder of this article is about electrochemical corrosion.

Electrochemical theory

One way to understand the structure of metals on the basis of particles is to imagine an array of positively-charged ions sitting in a negatively-charged "gas" of free electrons. Coulombic attraction holds these oppositely-charged particles together, but there are other sorts of negative charge which are also attracted to the metal ions, such as the negative ions (anions) in an electrolyte. For a given ion at the surface of a metal, there is a certain amount of energy to be gained or lost by dissolving into the electrolyte or becoming a part of the metal, which reflects an atom-scale tug-of-war between the electron gas and dissolved anions. The quantity of energy then strongly depends on a host of variables, including the types of ions in a solution and their concentrations, and the number of electrons present at the metal's surface. In turn, corrosion processes cause electrochemical changes, meaning that they strongly affect all of these variables. The overall interaction between electrons and ions tends to produce a state of local thermodynamic equilibrium that can often be described using basic chemistry and a knowledge of initial conditions.

Galvanic series

In a given environment (one standard medium is aerated, room-temperature seawater), one metal will be either more noble or more active than the next, based on how strongly its ions are bound to the surface. Two metals in electrical contact share the same electron gas, so that the tug-of-war at each surface is translated into a competition for free electrons between the two materials. The noble metal will tend to take electrons from the active one, while the electrolyte hosts a flow of ions in the same direction. The resulting mass flow or electrical current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a Galvanic series, and can be a very useful design guideline when choosing materials.

Resistance to corrosion

Some metals are more intrinsically resistant to corrosion than others, either due to the fundamental nature of the electrochemical processes involved or due to the details of how reaction products form. Otherwise, many techniques can be used during an item's manufacture and use to protect its materials from damage.

Intrinsic chemistry

Galvanic series The materials most resistant to corrosion are those for which corrosion is thermodynamically unfavorable. Any corrosion products of gold or platinum tend to decompose spontaneously into pure metal, which is why these elements can be found in metallic form on Earth, and is a large part of their intrinsic value. More common "base" metals can only be protected by more temporary means. Some metals have naturally slow reaction kinetics, even though their corrosion is thermodynamically favorable. These include such metals as zinc, magnesium, and cadmium. While corrosion of these metals is continuous and ongoing, it happens at an acceptably slow rate. An extreme example is graphite, which releases large amounts of energy upon oxidation, but has such slow kinetics that it is effectively immune to electrochemical corrosion under normal conditions.

Passivation

Given the right conditions, a thin film of corrosion products can form on a metal's surface spontaneously, acting as a barrier to further oxidation. When this layer stops growing at less than a micrometre thick under the conditions that a material will be used in, the phenomenon is known as passivation (rust, for example, usually grows to be much thicker, and so is not considered passivation, and the oxide layer is not protective anyway). While this effect is in some sense a property of the material, it serves as an indirect kinetic barrier: the reaction is often quite rapid unless and until an impermiable layer forms. Passivation in air and water at moderate pH is seen in such materials as aluminium, stainless steel, titanium, and silicon. These conditions required for passivation are specific to the material. The effect of pH is recorded using Pourbaix diagrams, but many other factors are influential. Some conditions that inhibit passivation include: high pH for aluminum, low pH or the presence of chloride ions for stainless steel, high temperature for titanium (in which case the oxide dissolves into the metal, rather than the electrolyte) and fluoride ions for silicon. On the other hand, sometimes unusual conditions can bring on passivation in materials that are normally unprotected, as the alkaline environment of concrete does for steel rebar. Exposure to a liquid metal such as mercury or hot solder can often circumvent passivation mechanisms.

Surface treatments

solder

Applied coatings

Plating, painting, and the application of enamel are the most common anti-corrosion treatments. They work by providing a barrier of corrosion-resistant material between the damaging environment and the (often cheaper, tougher, and/or easier-to-process) structural material. Aside from cosmetic and manufacturing issues, there are tradeoffs in mechanical flexibility versus resistance to abrasion and high temperature. Platings usually fail only in small sections, and if the plating is more noble than the substrate (i.e., chromium on steel), a galvanic couple will cause any exposed area to corrode much more rapidly than an unplated surface would. For this reason, it is often wise to plate with a more active metal such as zinc or cadmium.

Reactive coatings

If the environment is controlled (especially in recirculating systems), corrosion inhibitors can often be added to it. These form an electrically insulating and/or chemically impermeable coating on exposed metal surfaces, to suppress electrochemical reactions. Such methods obviously make the system less sensitive to scratches or defects in the coating, since extra inhibitors can be made available wherever metal becomes exposed. Chemicals that inhibit corrosion include some of the salts in hard water (Roman water systems are famous for their mineral deposits), chromates, phosphates, and a wide range of specially-designed chemicals that resemble surfactants (i.e. long-chain organic molecules with ionic end groups). surfactant

Anodization

Aluminium alloys often undergo a surface treatment known as anodization in a chemical bath near the end of their manufacture. Electrochemical conditions in the bath are carefully adjusted so that uniform pores several nanometers wide appear in the metal's oxide film. These pores allow the oxide to grow much thicker than passivating conditions would allow. At the end of the treatment, the pores are allowed to close, forming a harder-than-usual (and therefore more protective) surface layer. If this coating is scratched, normal passivation processes take over to protect the damaged area.

Cathodic protection

Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. It is a method used to protect metal structures from corrosion. Cathodic protection systems are most commonly used to protect steel, water, and fuel pipelines and tanks; steel pier piles, ships, and offshore oil platforms. For effective CP, the potential of the steel surface is polarized (pushed) more negative until the metal surface has a uniform potential. With a uniform potential, the driving force for the corrosion reaction is halted. For galvanic CP systems, the anode material corrodes under the influence of the steel, and eventually it must be replaced. The polarization is caused by the current flow from the anode to the cathode, driven by the difference in electrochemical potential between the anode and the cathode. For larger structures, galvanic anodes cannot economically deliver enough current to provide complete protection. Impressed Current Cathodic Protection (ICCP) systems use anodes connected to a DC power source (a cathodic protection rectifier). Anodes for ICCP systems are tubular and solid rod shapes of various specialized materials. These include high silicon cast iron, graphite, mixed metal oxide, platinum and niobium coated wire and others.

Corrosion in passivated materials

Passivation is extremely useful in alleviating corrosion damage, but care must be taken not to trust it too thoroughly. Even a high-quality alloy will corrode if its ability to form a passivating film is compromised. Because the resulting modes of corrosion are more exotic and their immediate results are less visible than rust and other bulk corrosion, they often escape notice and cause problems among those who are not familiar with them.

Pitting corrosion

Certain conditions, such as low availability of oxygen or high concentrations of species such as chloride which compete as anions, can interfere with a given alloy's ability to re-form a passivating film. In the worst case, almost all of the surface will remain protected, but tiny local fluctuations will degrade the oxide film in a few critical points. Corrosion at these points will be greatly amplified, and can cause corrosion pits of several types, depending upon conditions. While the corrosion pits only nucleate under fairly extreme circumstances, they can continue to grow even when conditions return to normal, since the interior of a pit is naturally deprived of oxygen. In extreme cases, the sharp tips of extremely long and narrow pits can cause stress concentration to the point that otherwise tough alloys can shatter, or a thin film pierced by an invisibly small hole can hide a thumb sized pit from view. These problems are especially dangerous because they are difficult to detect before a part or structure fails. Pitting remains among the most common and damaging forms of corrosion in passivated alloys, but it can be prevented by control of the alloy's environment, which often includes ensuring that the material is exposed to oxygen uniformly (i.e., eliminating crevices).

Fretting

Many useful passivating oxides are also effective abrasives, particularly TiO₂ and Al₂O₃. Fretting corrosion occurs when particles of corrosion product continuously abrade away the passivating film as two metal surfaces are rubbed together. While this process does often damage the frets of musical instruments, they were named separately.

Weld decay and knifeline attack

Stainless steel can pose special corrosion challenges, since its passivating behavior relies on the presence of a minor alloying component (Chromium, typically only 18%). Due to the elevated temperatures of welding or during improper heat treatment, chromium carbides can form in the grain boundaries of stainless alloys. This chemical reaction robs the material of chromium in the zone near the grain boundary, making those areas much less resistant to corrosion. This creates a galvanic couple with the well-protected alloy nearby, which leads to weld decay (corrosion of the grain boundaries near welds) in highly corrosive environments. Special alloys, either with low carbon content or with added carbon "getters" such as titanium and niobium (in types 321 and 347, respectively), can prevent this effect, but the latter require special heat treatment after welding to prevent the similar phenomenon of knifeline attack. As its name applies, this is limited to a small zone, often only a few micrometres across, which causes it to proceed more rapidly. This zone is very near the weld, making it even less noticeable¹.

Economic impact

The US Federal Highway Administration released a study, entitled Corrosion Costs and Preventive Strategies in the United States, in 2002 on the direct costs associated with metallic corrosion in nearly every U.S. industry sector. The study showed that for 1998 the total annual estimated direct cost of corrosion in the U.S. was approximately $276 billion (approximately 3.1% of the US gross domestic product). FHWA Report Number:FHWA-RD-01-156. The NACE International [http://www.nace.org website] has a [http://www.nace.org/nace/content/publicaffairs/cost_corr_pres/cost_corrosion_files/frame.htm summary] slideshow of the report findings. Jones¹ writes that electrochemical corrosion causes between $8 billion and $128 billion in economic damage per year in the United States alone, degrading structures, machines, and containers.

References

- Principles and Prevention of Corrosion, 2nd edition. Denny A. Jones. Upper Saddle River, New Jersey: Prentice Hall, 1996. ISBN 0-13-359993-0.

External links

- http://www.corrosion-doctors.org/

Dyed

A dye can generally be described as a colored substance that has an affinity to the substrate to which it is being applied. The dye is usually used as an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber. In contrast, a pigment generally has no affinity for the substrate, and is insoluble. Archaeological evidence shows that, particularly in India and the Middle East, dyeing has been carried out for over 5000 years. The dyes were obtained from either animal, vegetable or mineral origin, with no or very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, but only a few have ever been used on a commercial scale.

Organic dyes

The first man-made organic dye, mauveine, was discovered by William Henry Perkin in 1856. Many thousands of dyes have since been prepared and, because of vastly improved properties imparted upon the dyed materials, quickly replaced the traditional natural dyes. Dyes are now classified according to how they are used in the dyeing process. Acid dyes are water-soluble anionic dyes that are applied to fibers such as silk, wool, nylon and modified acrylic fibers using neutral to acid dyebaths. Attachment to the fiber is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fiber. Acid dyes are not substantive to cellulosic fibers. Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibers, but find some use for wool and silk. Usually acetic acid is added to the dyebath to help the uptake of the dye onto the fiber. Basic dyes are also used in the coloration of paper. Direct or substantive dyeing is normally carried out in a neutral or slightly alkaline dyebath, at or near boiling point, with the addition of either sodium chloride (NaCl) or sodium sulfate (Na₂SO₄). Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains. Mordant dyes require a mordant, which improves the fastness of the dye against water, light and perspiration. The choice of mordant is very important as different mordants can change the final colour significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques. The most important mordant dyes are the synthetic mordant dyes, or chrome dyes, used for wool; these comprise some 30% of dyes used for wool, and are especially useful for black and navy shades. The mordant, potassium dichromate, is applied as an after-treatment. Vat dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water soluble alkali metal salt of the dye, which, in this leuco form, has an affinity for the textile fibre. Subsequent oxidation reforms the original insoluble dye. Reactive dyes utilize a chromophore containing a substituent that is capable of directly reacting with the fibre substrate. The covalent bonds that attach reactive dye to natural fibers make it among the most permanent of dyes. "Cold" reactive dyes, such as Procion MX, Cibacron F, and Drimarene K, are very easy to use because the dye can be applied at room temperature. Reactive dye is by far the best choice for dyeing cotton and other cellulose fibers at home or in the art studio. Disperse dyes were originally developed for the dyeing of cellulose acetate, and are substantially water insoluble. The dyes are finely ground in the presence of a dispersing agent and then sold as a paste, or spray-dried and sold as a powder. They can also be used to dye nylon, triacetate, polyester and acrylic fibres. In some cases, a dyeing temperature of 130 °C is required, and a pressurised dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fibre. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding. Azo dyeing is a technique in which an insoluble azoic dye is produced directly onto or within the fibre. This is achieved by treating a fibre with both diazoic and coupling components. With suitable adjustment of dyebath conditions the two components react to produce the required insoluble azo dye. This technique of dyeing is unique, in that the final colour is controlled by the choice of the diazoic and coupling components.

Natural dyes

Animal origin

These include tyrian purple (vat dye), kermes and cochineal (mordant dyes) and techelet.

Vegetable origin

Substantive dyes include safflower and turmeric, while indigo and woad are vat dyes. Mordant dyes include alizarin (madder), dyer's broom, brazilwood, quercitron bark, weld and old fustic. Cudbear is unclassified.

Inorganic dyes

These include eosin and iron buff.

Food dyes

One other class which describes the role of dyes, rather than their mode of use, is the food dye. Because food dyes are classed as food additives, they are manufactured to a higher standard than some industrial dyes. Food dyes can be direct, mordant and vat dyes, and their use is strictly controlled by legislation. Many are azoic dyes, although anthraquinone and triphenylmethane compounds are used for colours such as green and blue. Some naturally-occurring dyes are also used.

Other

A number of other classes have also been established, including:
- Oxidation bases, for mainly hair and fur
- Sulfur dyes, for textile fibres
- Leather dyes, for leather
- Fluorescent brighteners, for textile fibres and paper
- Solvent dyes, for wood staining and producing coloured lacquers, solvent inks, colouring oils, waxes.
- Carbene dyes, a recently developed method for colouring multiple substrates

Chemical classification

External links

- [http://www.pburch.net/dyeing/aboutdyes.shtml About Dyes] Category:Dyes ja:染料 simple:Dye

Electrical circuit

An electrical network or electrical circuit is an interconnection of electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. It can be as small as an integrated circuit on a silicon chip, or as large as an electricity distribution or transmission network. A circuit is a network that has a closed loop i.e. a return path. A network is a connection of 2 or more simple circuit elements, and may not be a circuit. The goal when designing electrical networks for signal processing is to apply a predefined operation on potential differences (measured in volts) or currents (measured in amperes). Typical functions for these electrical networks are amplification, oscillation and analog linear algorithmic operations such as addition, subtraction, multiplication, division, differentiation and integration. In the case of power distribution networks, engineers design the circuit to transport the energy as efficiently as possible while at the same time taking into account economic factors, network safety and redundancy. These networks use components such as power lines, cables, circuit breakers, switches and transformers. To design any electrical circuits, electrical engineers need to be able to predict the voltages and currents in the circuit. Linear circuits can be analysed to a certain extent by hand because complex number theory gives engineers the ability to treat all linear elements using a single mathematical representation. A number of electrical laws apply to all electrical networks. These include
- Kirchhoff's current law: the sum of all currents entering a node is equal to the sum of all currents leaving the node.
- Kirchhoff's voltage law: the directed sum of the electrical potential differences around a circuit must be zero.
- Ohm's law: the voltage across a resistor is the product of its resistance and the current flowing through it.
- the Y-delta transform
- Norton's theorem: any two-terminal collection of voltage sources and resistors is electrically equivalent to an ideal current source in parallel with a single resistor.
- Thevenin's theorem: any two-terminal combination of voltage sources and resistors is electrically equivalent to a single voltage source in series with a single resistor.
- Millman's method: the voltage on the ends of branches in parallel is equal to the sum of the currents flowing in every branch divided by the total equivalent conductance.
- See also Analysis of resistive circuits. Other more complex laws may be needed if the network contains nonlinear or reactive components. Non-linear self-regenerative hetrodyning systems can be approximated. Applying these laws results in a set of simultaneous equations that can be solved either by hand or by a computer.

Network simulation software

In more complex circuits, engineers need to turn to circuit simulation software. SPICE and EMTP are the most famous of these.

Linearization around operating point

When faced with a new circuit, the software first tries to find a steady state solution. This is a solution where all nodes conform to Kirchhoff's Current Law and the voltages across and through each element of the circuit conform to the voltage/current equations governing that element. Once the steady state solution is found, the operating points of each element in the circuit are known. For a small signal analysis, every non-linear element can be linearized around its operation point to obtain the small-signal estimate of the voltages and currents. This is an application of Ohm's Law. The resulting linear circuit matrix can be solved with Gauss-Jordan elimination.

Piece-wise linear approximation

This type of simulator uses piece-wise linear approximations of the equations governing the elements of a circuit. This approximation comes down to splitting the circuit into two parts: a completely linear network with a number of terminals that connect to ideal diodes. Every time a diode switches from on to off or vice versa, the linear network is configured differently. Increasing the accuracy of the simulation can be achieved by adding more detail to the approximation of equations, this will increase the running time of the simulation. This flexibility allows an engineer to make a trade-off between simulation time and the precision of the results, something that is not easily done with the previous simulation technique. An example for a software using this technique is the Simulink toolbox PLECS.

External articles

; Main
- "[http://www.allaboutcircuits.com All About Electric Circuits]" (2003) : online textbooks covering electricity and electronics.
- [http://www.discovercircuits.com/ Discover Circuits] : resource for engineers, hobbyists, inventors & consultants. ;Simulator
- [http://www.falstad.com/circuit/ Circuit simulator applet]: voltage and current visualization (Java) Category:Electronics Category:Electrical engineering __NOTOC__ ja:電気回路

Paintball marker

A paintball marker or paintball gun is the primary device used in the game of paintball to mark an opposing player with paint. It uses an expanding gas (usually CO₂, N₂ or Air) to force a paintball through a barrel with a muzzle velocity of approximately 300 ft/s (100 m/s). This velocity is sufficient for most paintballs to break upon impact, but not fast enough to cause tissue damage beyond mild bruising. Nearly every commercial field has, and strictly enforces, a rule limiting the muzzle velocity of a paintball to 300 ft/s or less. Because being hit in an eye by a paintball can result in permanent blindness or visual impairment, it is important that players always wear proper eye and face protection when around a paintball marker and nearly every commercial paintball field has, and strictly enforces, a rule requiring certified eye and face protection while on the field. A marker consists of four main components. These are:
- Body
- Hopper
- Tank
- Barrel The vast majority of modern paintball markers have the previous components. There is, however, a strong following of stock-class players who use markers with a purposefully low rate of fire and ammo capacity. Stock-class guns are usually pump-action paintball guns powered by either 12-gram CO₂ cartridges or small CO₂ tanks. Also note the trend in using the term "marker" instead of "gun." This term started with speedball paintball in an effort to make it sound more like a game, and to separate paintball equipment from guns intended to injure or kill. Some hardcore woodsballers, however, scoff at the term "marker". =Body=

Internals

There are four major types of paintball marker firing systems.

Electro-pneumatic

An electro-pneumatic firing system is controlled electronically. This allows the marker to fire with very little effort. It also enables markers to have multiple firing modes, such as three-shot bursts, six-shot bursts or even fully automatic. However, virtually all tournaments and paintball fields only allow semiautomatic mode (one trigger pull, one shot). Because of this, some high-end markers ship with a control board only allowing semiautomatic, and for fully auto modes the board will need to be replaced. Others rely on LCD screens to indicate that a mode besides semiautomatic has been selected. Many newer electro-pneumatic markers incorporate anti-chop eyes (ACE) which use lasers to detect whether or not a paintball is in the breech when the trigger is pulled, in order to prevent ball chopping. This feature usually appears in the form of one of two systems: either reflective, in which the laser bounces off the ball, or break-beam, in which the laser hits a receiver at the other end so that the beam is "broken" if a ball is present. The latter is more efficient and is used in high-end markers. Examples include the Bob Long Intimidator Series, the Dye Matrix and DM5, various WDP Angels, the AKALMP Excaliburs and Vikings, Smart Parts Shockers, Impulses and Ions, and Eclipse Ego.

Mechanical

In these firing systems, the action is controlled solely through mechanical means. Many mechanical markers have a hammer which, when cocked, is held back by a catch connected to the trigger (trigger sear). These markers also have a spring whose purpose is to push the hammer forward. When the trigger is pulled, the catch is released and the hammer is allowed to slam into the valve. This diverts the flow of air from a tank, through the bolt and into the paintball, propelling it out the barrel. Excess air not used to propel the ball is then used to recock the hammer. This type of marker is called a blow-back design and is the most common approach used. Common examples of blow-back markers are the Kingman Spyder and Tippmann lines.

Pump

Pulling the trigger in these markers releases a blast of gas, propelling the paintball through its barrel. It is the player's responsibility, however, to pump the gun. This resets the hammer and allows a paintball to drop into the breach. Stock markers are always pump.

Electro-mechanical guns

In these markers, a hybrid approach is used – the mechanical firing of the marker is driven by an electric coil. This allows for the short, light trigger associated with electronic markers on an otherwise mechanical marker. Common examples of this are Kingman markers with ESP triggers and the E-Mag by Airgun Designs.

Bolt Position While Firing

Open bolt

"Open bolt" means the bolt is back when the marker is cocked, leaving a paintball in the chamber at all times. The bolt is the internal part of the marker that the High Pressured Air, CO₂ or N₂ travels through to propel the ball. The blow-back mechanism is the most common open bolt mechanism. On these blow-back markers, when you release the trigger sear it allows the bolt to move forward. At the bottom of the bolt is a hole allowing air to travel through it, so when the bolt is released and moved to a certain point the air will travel through it. Most markers, high-end or low-end, work this way. The other form of open bolt marker is the blow-forward, the most common example of which is Spyder.

Closed bolt

Pumps and Autocockers are closed bolt markers. On these markers the bolt is forward, or closed, when cocked. Once a shot is fired the bolt moves back, allowing another ball to drop in the chamber, and then moves back to its closed position. In a pump marker this recocking process is done by hand. An autococker is very similar to a pump, but the autococker uses parts called the 3-way, the ram, and the LPR (low pressure regulator) to cock itself. This system is believed by some to improve the accuracy of each shot because the bolt does not move when the air is released. There have been numerous tests on the subject, but the most scientific ones that use machines to fire rounds instead of humans have shown that there is negligible, if any, improvement in the accuracy and consistency of shots. =Hopper= Hoppers, also known as loaders, hold paintballs for the marker to fire. There are many different variations, but the primary feed methods are gravity, agitating, and force-feed. While agitating and force-feed hoppers result in a higher possible rate of fire, they may fail. The most common causes of malfunction are dead batteries and contact with moisture.

Gravity

Gravity loaders are a simple plastic container with a hole at the bottom. The paint is simply pulled down by gravity. These loaders are especially popular with the Tippmann 98 and other less expensive mechanical markers.

Agitating

Agitating hoppers use a propeller to encourage, or agitate the paintballs into loading. This helps increase the rate of fire. The A-5, manufactured by Tippman uses an agitation device built into the marker itself. This agitator is cycled during the normal cocking action of the gun and is not electronic. It therefore requires no batteries and is not as sensitive to moisture.

Force-feed

Force-feed hoppers can use a propeller, spring, or belt loaded system to force balls at an accelerated rate into a marker. The most popular force-fed hoppers are the [http://www.odysseypaintball.com/halob.html Odyssey HALO] and [http://www.viewloader.com/product.asp?item_num=5020&fam=Electronic+Loaders Viewloader EVLution II]. Force-fed loaders are used when a high rate-of-fire is required, such as in competition. This type of loader is used by all professional teams and can reach speeds over 20 balls-per-second. Some also include other features, which may include information about how many balls are remaining in your hopper, or how many balls per second you can shoot. There are also clips similar to ones used on guns; these are more expensive, gun specific, and may hold fewer balls. Another type of force-feed hopper is called the [http://www.qloader.com q-loader]. This 'clip style' loader can hold up to one hundred rounds at a time and can unload them very quickly, allowing thirty-five balls per second. As a forced hopper, it allows the player to shoot with the marker upside down, sideways or from any other position. Unlike many other clip-based hoppers, it is not marker-specific. =Tank= The tank holds a compressed gas used to accelerate the paintballs and, in the case of most semi-automatic markers, cock the marker. The tank is usually filled with liquid CO₂, compressed N₂ or compressed Air. A CO₂ tank stores the gas in the tank as a liquid and when it is released must boil into a gas before it can be used. This process leads to some commonly known problems such as inconsistent velocity and freezing. It especially has problems in cold weather which makes the boiling process slow down and increases the chance for liquid CO₂ to get inside the marker and damage some part of it. CO₂ tanks are measured in terms of the amount of liquid it can store (in Ounces). High Pressure Air (HPA) is stored in the tank as a gas, so the problems of CO₂ needing to boil are not an issue. HPA uses a regulator to control the pressure that is released resulting in a consistent velocity. HPA tanks have two measurements: PSI and In³. Stock Class paintball markers must be fed using 12g CO₂ cartridges. =Barrels=

Specifications

Length

Generally barrels are twelve, fourteen, sixteen, eighteen, or twenty inches. Some people have had custom barrels made which may reach up to forty-eight inches. There is no accuracy nor efficiency benefit for barrels beyond eleven inches long; however, longer barrels generally make less noise than shorter barrels by allowing excess gas to escape more slowly. Longer barrels cause players to "sight in" faster than they would with shorter barrels and thus give the perception that longer barrels are more accurate. Barrel lengths that exceed sixteen inches have no further reduction in sound nor any gain in accuracy. Barrels longer than this also require more propellant to keep the paintball at speed while traveling the length of the barrel after the initial acceleration, and can produce a noticeable decrease in gas efficiency.

Porting

Most barrels are ported (or vented), which means that holes are drilled into the front of the barrel allowing the propellant to dissipate, decreasing both the turbulence of the air column following the ball out of the barrel as well as the sound signature of the marker. It should be noted that excess porting can vastly decrease a marker's gas efficiency since the porting will cause the gas to escape the barrel before the ball is at optimum velocity. Any porting in a barrel reduces its effective length to the section without ports. For example; if a 16 inch barrel has porting that starts 6 inches past the threads then it has an effective barrel length of 6 inches. There is no way for the gas to propel the ball at optimum velocity unless either more gas, more pressure, or both are used, resulting in decreased gas efficiency. The most effective porting is a series of small diameter holes drilled in a spiral pattern. To optimize this pattern, the holes should be drilled past eleven inches, although they can be drilled before this length.

Threading

Most modern paintball markers have barrels that screw into the front receiver. Barrel threading must be matched to that of the marker. Common threads are Angel, Autococker, Impulse/Ion, Shocker, Spyder, and Tippman.

Bore

The Bore is the interior diameter of the barrel. Two and three-piece barrels allow the barrel bore to be matched to the paint diameter. Paint to barrel matching is especially important in certain closed-bolt markers, especially autocockers, because small paint in a large barrel can roll out the front of barrel.

Construction

Barrels are manufactured in three types: one piece, two piece, and three piece. The type of barrel is usually irrelevant because the quality of the barrel has a much greater impact on accuracy.

One piece

One piece barrels are machined from a single piece of material, usually aluminum. The standard paintball size is .68 caliber and these barrels are honed to have an inner diameter anywhere from .68 caliber to .69 caliber. Most one piece barrels have a stepped bore after 8 inches that increases to around .70 caliber.

Two piece

Two piece barrels, made from two pieces of machined material, consist of a "front" and "back". The back attaches to the marker and is machined with a pre-specified bore between .682 and .695 caliber. These barrels are machined with varying dimensions to better match the size of the barrel to the size of the paint being put through it. The front is usually has the same bore as the largest back the manufacturer offers.

Three piece

Three-piece barrels, instead of having multiple backs each with a different bore, have only a single back. A series of inserts, or sleeves, with differing bores are inserted into the back. The front is then screwed on to keep the sleeve in place. Sleeves are generally offered in either aluminum or stainless steel. This type offers the most flexibility in that the user needs only one set of sleeves and a rear for each marker they own. They can also select front sections to make the barrel length they prefer. This type also generally offers the widest selection of barrel diameters, usually .680, .681, .682, .683, .684, and so on up to .696 caliber.

Other

The Flatline barrel, manufactured by Tippmann Sports is designed to decrease the parabolic travel of fired paint. The barrel is curved such that accellerating paint contacts the top of the barrel, imparting backspin. This backspin generates lift (known as the "Magnus Effect"), resulting in a flatter arc. This is especially beneficial in woodsball or scenario paintball where overhanging branches limit the range of traditional barrels. It is available for the Tippmann model 98 and A-5. There are conversion kits to allow the use of the flatline barrels on some other markers, as well. The Apex barrel, manufactured by [http://www.bentippmann.com/ Ben Tippmann Paintball Design] also imparts spin to the ball. Unlike the flatline barrel, however, the Apex can impart spin at any degree and at several magnitudes. It's possible to impart back, top, or sidespin. This allows balls to arc around some obstacles, or have them drop over bunkers. The magnitude of spin can also be varied, allowing for a gentle curve or a sudden hook. It is availble with threads for most markers. =Stock Class= Stock Class is a set of commonly agreed upon but unofficial rules for paintball markers. The marker must have a horizontal paintball feed, which means that the marker must be tilted (rocked) forward or backward to feed the next shot. The marker may not be semi-automatic, which means that it requires pumping or cocking prior to each shot being fired (in other words "rock and cock"). The marker must must be powered by 12 gram powerlets, which limits the amount of shots to 15-30 depending on the efficiency of the marker. The paintball may only hold 10 paintballs in it, allowing the marker to hold a maximum of 11 paint balls at a time. The marker may not have porting on the barrel (porting is putting holes in the end of the barrel for decreasing the sound of firing). Very few fields or tournaments require full stock class compliance, and instead use what is commonly called "Modified Stock Class" rules. These rules usually allow constant air (CO₂ or high pressure air) instead of 12 grams, feed tubes that hold 15 paintballs, and allow porting on the barrel since porting was found to have a positive effect on the accuracy of the paintball. Different fields can allow or not allow rules as they see fit. Arguably the most popular stock class marker is the Phantom made by CCI, and can been seen [http://www.phantomonline.com/paintballguns/paintballguns.htm here].

Why stock class?

Stock class aims to retain the way paintball was at its birth, before electronic markers, high rates of fire, and overshooting. Players play stock class for different reasons: some grew up playing paintball this way and don't like the direction the industry has taken the sport, some play this way to save money, some simply enjoy the challenge of not being able to rely on a fast marker to get eliminations.

Fringe or Mainstream?

Stock class was the way paintball started, and as the technology evolved, so did the players. As stock class faded from memories, players joining the sport knew that a fast marker was the only way to compete. But as time drew on, stock class players could be found playing speedball against the high-end markers. This brought stock class back into the minds of the older players and introduced it to a new generation of players. The popularity of stock class play has been steadily increasing for the past few years, as seen in increased demand in sales and trades on popular forums. Category:Paintball

Extreme sport

Extreme sport (practically synonymous with the term action sport) is a general term for sports featuring speed, height, danger or spectacular stunts. A feature of such activities in the view of some is their alleged capacity to induce a so-called ‘‘adrenaline rush’’ in participants (a misnomer, since often the rush or high obtained is a product of increased levels of dopamine endorphins and serotonin). Extreme sports are often associated with young adults wishing to push themselves to the limits of their physical ability and fear, in turn pushing the boundaries of a particular sport. This youthful demographic accounts too for extreme sports’ frequent association with youth culture, not restricted to clothing fashions and music. Some contend that the distinction between an extreme sport and a conventional one is as much to do with marketing as it is to do with perceptions about levels of danger involved or the amount of adrenaline generated. Snowboarding thus has a more extreme ‘‘image’’ than skiing due to differing marketing strategies and the fact of being a newer sport, even though skiing is a faster and at least equally dangerous activity. Furthermore a sport like Rugby Union, though dangerous and adrenaline-inducing, would not fall into the category of extreme sports due to its traditional image. The term gained popularity with the advent of the X Games, a made-for-television collection of events. Advertisers were quick to recognise the appeal of the event to the public, as a consequence competitors and organisers are not wanting for sponsorship these days. The high profile of extreme sports and the culture surrounding them has also led people to invent jokey parodies, such as Extreme ironing, urban housework, extreme croquet, extreme unicycling, 'house gymnastics', and extreme wheelbarrow. Some purists repudiate the stereoypical "adrenaline junkie" tag. The practitioners would claim they enjoy developing their physical and/or mental skills, seek mastery of inhospitable environments, look to escape from the mundane rigours of day-to-day existence, or simply love the wilderness environment in which many of these sports take place. 'Bob Drury', a paraglider pilot says "We do these things not to escape life, but to prevent life escaping us". Some of the sports have existed for decades and their proponents span generations, some going on to become well known personalities. Rock climbing and ice climbing have spawned publicly recognisable names such as Edmund Hillary, Chris Bonington and more recently Joe Simpson. Another example is surfing, which was originally invented centuries ago by the native inhabitants of Hawaii. Several so-called extreme sports, including snowboarding, were included in the 2002 Winter Olympic Games.

List of some extreme sports

The following are sometimes classed as extreme sports:
- BASE jumping
- BMX freestyle
- Bouldering
- Buildering
- Bungee jumping
- Elevator surfing
- Extreme skiing
- Free-diving
- Caving
- Free running / Parkour
- Cave diving
- Climbing
- Whitewater kayaking
- Kitesurfing
- Kneeboarding
- Mountain biking
- Mountain boarding
- Paintballing
- Parachuting
- Paragliding
- Paramotoring
- Poweriser
- Whitewater rafting
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