1.
Inch
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The inch is a unit of length in the imperial and United States customary systems of measurement now formally equal to 1⁄36 yard but usually understood as 1⁄12 of a foot. Derived from the Roman uncia, inch is also used to translate related units in other measurement systems. The English word inch was a borrowing from Latin uncia not present in other Germanic languages. The vowel change from Latin /u/ to English /ɪ/ is known as umlaut, the consonant change from the Latin /k/ to English /tʃ/ or /ʃ/ is palatalisation. Both were features of Old English phonology, inch is cognate with ounce, whose separate pronunciation and spelling reflect its reborrowing in Middle English from Anglo-Norman unce and ounce. In many other European languages, the word for inch is the same as or derived from the word for thumb, the inch is a commonly used customary unit of length in the United States, Canada, and the United Kingdom. It is also used in Japan for electronic parts, especially display screens, for example, three feet two inches can be written as 3′ 2″. Paragraph LXVII sets out the fine for wounds of various depths, one inch, one shilling, an Anglo-Saxon unit of length was the barleycorn. After 1066,1 inch was equal to 3 barleycorns, which continued to be its legal definition for several centuries, similar definitions are recorded in both English and Welsh medieval law tracts. One, dating from the first half of the 10th century, is contained in the Laws of Hywel Dda which superseded those of Dyfnwal, both definitions, as recorded in Ancient Laws and Institutes of Wales, are that three lengths of a barleycorn is the inch. However, the oldest surviving manuscripts date from the early 14th century, john Bouvier similarly recorded in his 1843 law dictionary that the barleycorn was the fundamental measure. He noted that this process would not perfectly recover the standard, before the adoption of the international yard and pound, various definitions were in use. In the United Kingdom and most countries of the British Commonwealth, the United States adopted the conversion factor 1 metre =39.37 inches by an act in 1866. In 1930, the British Standards Institution adopted an inch of exactly 25.4 mm, the American Standards Association followed suit in 1933. By 1935, industry in 16 countries had adopted the industrial inch as it came to be known, in 1946, the Commonwealth Science Congress recommended a yard of exactly 0.9144 metres for adoption throughout the British Commonwealth. This was adopted by Canada in 1951, the United States on 1 July 1959, Australia in 1961, effective 1 January 1964, and the United Kingdom in 1963, effective on 1 January 1964. The new standards gave an inch of exactly 25.4 mm,1.7 millionths of a longer than the old imperial inch and 2 millionths of an inch shorter than the old US inch. The United States retains the 1/39. 37-metre definition for survey purposes and this is approximately 1/8-inch in a mile
2.
Iron
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Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series and it is by mass the most common element on Earth, forming much of Earths outer and inner core. It is the fourth most common element in the Earths crust, like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen, fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon. A certain proportion of carbon steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with metals are by far the most common industrial metals because they have a great range of desirable properties. Iron chemical compounds have many uses, Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens, among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with oxygen in hemoglobin and myoglobin. Iron is also the metal at the site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants. A human male of average height has about 4 grams of iron in his body and this iron is distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test, the data on iron is so consistent that it is often used to calibrate measurements or to compare tests. An increase in the content will cause a significant increase in the hardness. Maximum hardness of 65 Rc is achieved with a 0. 6% carbon content, because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the properties of iron at high pressures and temperatures have also been studied extensively
3.
Alloy
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An alloy is a mixture of metals or a mixture of a metal and another element. Alloys are defined by a metallic bonding character, an alloy may be a solid solution of metal elements or a mixture of metallic phases. Intermetallic compounds are alloys with a stoichiometry and crystal structure. Zintl phases are sometimes considered alloys depending on bond types. Alloys are used in a variety of applications. In some cases, a combination of metals may reduce the overall cost of the material while preserving important properties, in other cases, the combination of metals imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength. Examples of alloys are steel, solder, brass, pewter, duralumin, bronze, the alloy constituents are usually measured by mass. Alloys are usually classified as substitutional or interstitial alloys, depending on the arrangement that forms the alloy. They can be classified as homogeneous, or heterogeneous or intermetallic. An alloy is a mixture of elements, which forms an impure substance that retains the characteristics of a metal. Alloys are made by mixing two or more elements, at least one of which is a metal and this is usually called the primary metal or the base metal, and the name of this metal may also be the name of the alloy. The other constituents may or may not be metals but, when mixed with the base, they will be soluble. The mechanical properties of alloys will often be different from those of its individual constituents. A metal that is very soft, such as aluminium, can be altered by alloying it with another soft metal. Although both metals are soft and ductile, the resulting aluminium alloy will have much greater strength. Adding a small amount of carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel
4.
Aluminium
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Aluminium or aluminum is a chemical element in the boron group with symbol Al and atomic number 13. It is a silvery-white, soft, nonmagnetic, ductile metal, Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is combined in over 270 different minerals. The chief ore of aluminium is bauxite, Aluminium is remarkable for the metals low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the industry and important in transportation and structures, such as building facades. The oxides and sulfates are the most useful compounds of aluminium, despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals. Because of these salts abundance, the potential for a role for them is of continuing interest. Aluminium is a soft, durable, lightweight, ductile. It is nonmagnetic and does not easily ignite, a fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation. The yield strength of aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has about one-third the density and stiffness of steel and it is easily machined, cast, drawn and extruded. Aluminium atoms are arranged in a cubic structure. Aluminium has an energy of approximately 200 mJ/m2. Aluminium is a thermal and electrical conductor, having 59% the conductivity of copper. Aluminium is capable of superconductivity, with a critical temperature of 1.2 kelvin. Aluminium is the most common material for the fabrication of superconducting qubits, the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts, particularly in the presence of dissimilar metals. In highly acidic solutions, aluminium reacts with water to form hydrogen, primarily because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium
5.
Nickel
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Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a golden tinge. Nickel belongs to the metals and is hard and ductile. Meteoric nickel is found in combination with iron, a reflection of the origin of elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earths inner core, use of nickel has been traced as far back as 3500 BCE. Nickel was first isolated and classified as an element in 1751 by Axel Fredrik Cronstedt. The elements name comes from a mischievous sprite of German miner mythology, Nickel, an economically important source of nickel is the iron ore limonite, which often contains 1–2% nickel. Nickels other important ore minerals include garnierite, and pentlandite, major production sites include the Sudbury region in Canada, New Caledonia in the Pacific, and Norilsk in Russia. Nickel is slowly oxidized by air at room temperature and is considered corrosion-resistant, historically, it has been used for plating iron and brass, coating chemistry equipment, and manufacturing certain alloys that retain a high silvery polish, such as German silver. About 6% of world production is still used for corrosion-resistant pure-nickel plating. Nickel-plated objects sometimes provoke nickel allergy, Nickel has been widely used in coins, though its rising price has led to some replacement with cheaper metals in recent years. Nickel is one of four elements that are ferromagnetic around room temperature, alnico permanent magnets based partly on nickel are of intermediate strength between iron-based permanent magnets and rare-earth magnets. The metal is valuable in modern times chiefly in alloys, about 60% of world production is used in nickel-steels, other common alloys and some new superalloys comprise most of the remainder of world nickel use, with chemical uses for nickel compounds consuming less than 3% of production. As a compound, nickel has a number of chemical manufacturing uses. Nickel is a nutrient for some microorganisms and plants that have enzymes with nickel as an active site. Nickel is a metal with a slight golden tinge that takes a high polish. It is one of four elements that are magnetic at or near room temperature. Its Curie temperature is 355 °C, meaning that bulk nickel is non-magnetic above this temperature, the unit cell of nickel is a face-centered cube with the lattice parameter of 0.352 nm, giving an atomic radius of 0.124 nm
6.
Cobalt
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Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt is found in the Earths crust only in chemically combined form, the free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal. In 1735, such ores were found to be reducible to a new metal, today, some cobalt is produced specifically from various metallic-lustered ores, for example cobaltite, but the main source of the element is as a by-product of copper and nickel mining. The copper belt in the Democratic Republic of the Congo, Central African Republic, cobalt is primarily used in the preparation of magnetic, wear-resistant and high-strength alloys. The compounds, cobalt silicate and cobalt aluminate give a deep blue color to glass, ceramics, inks, paints. Cobalt occurs naturally as only one isotope, cobalt-59. Cobalt-60 is an important radioisotope, used as a radioactive tracer. Cobalt is the center of coenzymes called cobalamins, the most common example of which is vitamin B12. As such, it is a trace dietary mineral for all animals. Cobalt in inorganic form is also a micronutrient for bacteria, algae, cobalt is a ferromagnetic metal with a specific gravity of 8.9. The Curie temperature is 1,115 °C and the moment is 1. 6–1.7 Bohr magnetons per atom. Cobalt has a relative permeability two-thirds that of iron, metallic cobalt occurs as two crystallographic structures, hcp and fcc. The ideal transition temperature between the hcp and fcc structures is 450 °C, but in practice, the difference is so small that random intergrowth of the two is common. Cobalt is a weakly reducing metal that is protected from oxidation by an oxide film. It is attacked by halogens and sulfur, heating in oxygen produces Co3O4 which loses oxygen at 900 °C to give the monoxide CoO. The metal reacts with fluorine at 520 K to give CoF3, with chlorine, bromine and iodine and it does not react with hydrogen gas or nitrogen gas even when heated, but it does react with boron, carbon, phosphorus, arsenic and sulfur. At ordinary temperatures, it reacts slowly with mineral acids, and very slowly with moist, common oxidation states of cobalt include +2 and +3, although compounds with oxidation states ranging from −3 to +5 are also known. A common oxidation state for simple compounds is +2 and these salts form the pink-colored metal aquo complex 2+ in water
7.
Copper
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Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of copper has a reddish-orange color. Copper is one of the few metals that occur in nature in directly usable metallic form as opposed to needing extraction from an ore and this led to very early human use, from c.8000 BC. Copper used in buildings, usually for roofing, oxidizes to form a green verdigris, Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as agents, fungicides, and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the hemoglobin in fish. In humans, copper is found mainly in the liver, muscle, the adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight. The filled d-shells in these elements contribute little to interatomic interactions, unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper, at the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form. The softness of copper partly explains its high conductivity and high thermal conductivity. The maximum permissible current density of copper in open air is approximately 3. 1×106 A/m2 of cross-sectional area, Copper is one of a few metallic elements with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air, as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. A green layer of verdigris can often be seen on old structures, such as the roofing of many older buildings. Copper tarnishes when exposed to sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper, 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper, both have a spin of 3⁄2
8.
Titanium
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Titanium is a chemical element with symbol Ti and atomic number 22. It is a transition metal with a silver color, low density. Titanium is resistant to corrosion in sea water, aqua regia, titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791, and it is named by Martin Heinrich Klaproth for the Titans of Greek mythology. The metal is extracted from its principal mineral ores by the Kroll, the most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments. Other compounds include titanium tetrachloride, a component of smoke screens and catalysts, and titanium trichloride, the two most useful properties of the metal are corrosion resistance and strength-to-density ratio, the highest of any metallic element. In its unalloyed condition, titanium is as strong as some steels, there are two allotropic forms and five naturally occurring isotopes of this element, 46Ti through 50Ti, with 48Ti being the most abundant. Although they have the number of valence electrons and are in the same group in the periodic table. As a metal, titanium is recognized for its high strength-to-weight ratio and it is a strong metal with low density that is quite ductile, lustrous, and metallic-white in color. The relatively high melting point makes it useful as a refractory metal and it is paramagnetic and has fairly low electrical and thermal conductivity. Commercial grades of titanium have ultimate tensile strength of about 434 MPa, equal to that of common, low-grade steel alloys, titanium is 60% denser than aluminium, but more than twice as strong as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys achieve tensile strengths of over 1400 MPa, however, titanium loses strength when heated above 430 °C. Titanium is not as hard as some grades of heat-treated steel, it is non-magnetic, machining requires precautions, because the material might gall unless sharp tools and proper cooling methods are used. Like steel structures, those made from titanium have a limit that guarantees longevity in some applications. The metal is an allotrope of an hexagonal α form that changes into a body-centered cubic β form at 882 °C. The specific heat of the α form increases dramatically as it is heated to this transition temperature but then falls, similar to zirconium and hafnium, an additional omega phase exists, which is thermodynamically stable at high pressures, but metastable at ambient pressures. This phase is usually hexagonal or trigonal and can be considered to be due to a soft longitudinal acoustic phonon of the β phase causing collapse of planes of atoms, like aluminium and magnesium, titanium metal and its alloys oxidize immediately upon exposure to air. Titanium readily reacts with oxygen at 1,200 °C in air and it is, however, slow to react with water and air at ambient temperatures because it forms a passive oxide coating that protects the bulk metal from further oxidation. When it first forms, this layer is only 1–2 nm thick but continues to grow slowly
9.
Ferromagnetism
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Not to be confused with Ferrimagnetism, for an overview see Magnetism. Ferromagnetism is the mechanism by which certain materials form permanent magnets. In physics, several different types of magnetism are distinguished, an everyday example of ferromagnetism is a refrigerator magnet used to hold notes on a refrigerator door. The attraction between a magnet and ferromagnetic material is the quality of magnetism first apparent to the ancient world, permanent magnets are either ferromagnetic or ferrimagnetic, as are the materials that are noticeably attracted to them. Only a few substances are ferromagnetic, the common ones are iron, nickel, cobalt and most of their alloys, some compounds of rare earth metals, and a few naturally occurring minerals, including some varieties of lodestone. Historically, the term ferromagnetism was used for any material that could exhibit spontaneous magnetization and this general definition is still in common use. In particular, a material is ferromagnetic in this sense only if all of its magnetic ions add a positive contribution to the net magnetization. If some of the magnetic ions subtract from the net magnetization, if the moments of the aligned and anti-aligned ions balance completely so as to have zero net magnetization, despite the magnetic ordering, then it is an antiferromagnet. These alignment effects only occur at temperatures below a critical temperature. Among the first investigations of ferromagnetism are the works of Aleksandr Stoletov on measurement of the magnetic permeability of ferromagnetics. The table on the right lists a selection of ferromagnetic and ferrimagnetic compounds, ferromagnetism is a property not just of the chemical make-up of a material, but of its crystalline structure and microstructure. There are ferromagnetic metal alloys whose constituents are not themselves ferromagnetic, called Heusler alloys, conversely there are non-magnetic alloys, such as types of stainless steel, composed almost exclusively of ferromagnetic metals. Amorphous ferromagnetic metallic alloys can be made by rapid quenching of a liquid alloy. These have the advantage that their properties are isotropic, this results in low coercivity, low hysteresis loss, high permeability. One such typical material is a transition metal-metalloid alloy, made from about 80% transition metal, a relatively new class of exceptionally strong ferromagnetic materials are the rare-earth magnets. They contain lanthanide elements that are known for their ability to carry large magnetic moments in well-localized f-orbitals, a number of actinide compounds are ferromagnets at room temperature or exhibit ferromagnetism upon cooling. PuP is a paramagnet with cubic symmetry at room temperature, in its ferromagnetic state, PuPs easy axis is in the <100> direction. In NpFe2 the easy axis is <111>, above TC ≈500 K NpFe2 is also paramagnetic and cubic
10.
Coercivity
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An analogous property, electric coercivity, is the ability of a ferroelectric material to withstand an external electric field without becoming depolarized. Thus coercivity measures the resistance of a material to becoming demagnetized. Coercivity is usually measured in oersted or ampere/meter units and is denoted HC and it can be measured using a B-H analyzer or magnetometer. Ferromagnetic materials with high coercivity are called magnetically hard materials, and are used to permanent magnets. Materials with low coercivity are said to be magnetically soft, the latter are used in transformer and inductor cores, recording heads, microwave devices, and magnetic shielding. Typically the coercivity of a material is determined by measurement of the magnetic hysteresis loop, also called the magnetization curve. The apparatus used to acquire the data is typically a vibrating-sample or alternating-gradient magnetometer, the applied field where the data line crosses zero is the coercivity. If an antiferromagnet is present in the sample, the coercivities measured in increasing and decreasing fields may be unequal as a result of the exchange bias effect, the coercivity of a material depends on the time scale over which a magnetization curve is measured. The magnetization of a material measured at an applied reversed field which is smaller than the coercivity may, over a long time scale. Relaxation occurs when reversal of magnetization by domain wall motion is thermally activated and is dominated by magnetic viscosity, at the coercive field, the vector component of the magnetization of a ferromagnet measured along the applied field direction is zero. There are two modes of magnetization reversal, single-domain rotation and domain wall motion. When the magnetization of a material reverses by rotation, the component along the applied field is zero because the vector points in a direction orthogonal to the applied field. When the magnetization reverses by domain wall motion, the net magnetization is small in every vector direction because the moments of all the individual domains sum to zero, magnetization curves dominated by rotation and magnetocrystalline anisotropy are found in relatively perfect magnetic materials used in fundamental research. The role of walls in determining coercivity is complicated since defects may pin domain walls in addition to nucleating them. The dynamics of domain walls in ferromagnets is similar to that of grain boundaries, common dissipative processes in magnetic materials include magnetostriction and domain wall motion. The coercivity is a measure of the degree of magnetic hysteresis, the squareness and coercivity are figures of merit for hard magnets although energy product is most commonly quoted. The 1980s saw the development of rare-earth magnets with high energy products, since the 1990s new exchange spring hard magnets with high coercivities have been developed. com
11.
Magnet
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A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet, a force that pulls on other materials, such as iron. A permanent magnet is a made from a material that is magnetized. An everyday example is a refrigerator used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are attracted to a magnet, are called ferromagnetic. These include iron, nickel, cobalt, some alloys of rare-earth metals, ferromagnetic materials can be divided into magnetically soft materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically hard materials, which do. To demagnetize a saturated magnet, a magnetic field must be applied. Hard materials have high coercivity, whereas soft materials have low coercivity, an electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of soft material such as steel. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the local strength of magnetism in a material is measured by its magnetization. Ancient people learned about magnetism from lodestones, which are naturally magnetized pieces of iron ore, the word magnet in Greek meant stone from Magnesia, a part of ancient Greece where lodestones were found. Lodestones, suspended so they could turn, were the first magnetic compasses, the earliest known surviving descriptions of magnets and their properties are from Greece, India, and China around 2500 years ago. The properties of lodestones and their affinity for iron were written of by Pliny the Elder in his encyclopedia Naturalis Historia, by the 12th to 13th centuries AD, magnetic compasses were used in navigation in China, Europe, the Arabian Peninsula and elsewhere. The magnetic flux density is a vector field, the magnetic B field vector at a given point in space is specified by two properties, Its direction, which is along the orientation of a compass needle. Its magnitude, which is proportional to how strongly the compass needle orients along that direction, in SI units, the strength of the magnetic B field is given in teslas. A magnets magnetic moment is a vector that characterizes the overall magnetic properties. For a bar magnet, the direction of the moment points from the magnets south pole to its north pole. In SI units, the moment is specified in terms of A·m2
12.
Rare-earth magnet
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Rare-earth magnets are strong permanent magnets made from alloys of rare earth elements. The magnetic field produced by rare-earth magnets can exceed 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla. There are two types, neodymium magnets and samarium-cobalt magnets, magnetostrictive rare-earth magnets such as Terfenol-D also have applications—e. g. in loudspeakers. Rare earth magnets are brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping. The term rare earth can be misleading as these metals are not particularly rare or precious, however, they form compounds with the transition metals such as iron, nickel, and cobalt, and some of these have Curie temperatures well above room temperature. Rare earth magnets are made from these compounds, the greater strength of rare earth magnets is mostly due to two factors. First, their structures have very high magnetic anisotropy. This means a crystal of the material preferentially magnetizes along a specific crystal axis but is difficult to magnetize in other directions. The resistance of the lattice to turning its direction of magnetization gives these compounds a very high magnetic coercivity. This is a consequence of incomplete filling of the f-shell, which can contain up to 7 unpaired electrons, in a magnet it is the unpaired electrons, aligned so they spin in the same direction, which generate the magnetic field. This gives the materials high remanence, the maximum energy density BHmax is proportional to Js2 so these materials have the potential for storing large amounts of magnetic energy. The magnetic energy product BHmax of neodymium magnets is about 18 times greater than ordinary magnets by volume and this allows rare earth magnets to be smaller than other magnets which produce the same field strength. Rare earth magnets have higher remanence, much higher coercivity and energy product, the table below compares the magnetic performance of the two types of rare earth magnet, neodymium and samarium-cobalt, with other types of permanent magnets. Source, Samarium–cobalt magnets, the first family of rare earth magnets invented, are used than neodymium magnets because of their higher cost. However, samarium–cobalt has a higher Curie temperature, creating a niche for these magnets in applications where high strength is needed at high operating temperatures. They are highly resistant to oxidation, but sintered samarium-cobalt magnets are brittle and prone to chipping and cracking, neodymium magnets, invented in the 1980s, are the strongest and most affordable type of rare-earth magnet. They are made of an alloy of neodymium, iron, and boron, neodymium magnets are used in numerous applications requiring strong, compact permanent magnets, such as electric motors for cordless tools, hard disk drives, magnetic holddowns, and jewelry clasps. They have the highest magnetic field strength and have a higher coercivity, corrosion can cause unprotected magnets to spall off a surface layer, or to crumble into a powder
13.
Cavity magnetron
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The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities. Electrons pass by the openings to these cavities and cause radio waves to oscillate within, the frequency of the microwaves produced, the resonant frequency, is determined by the cavities physical dimensions. An early form of magnetron was invented by H. Gerdien in 1910, another form of magnetron tube, the split-anode magnetron, was invented by Albert Hull in 1920, but it wasnt capable of high frequencies and was of little use. Similar devices were experimented with by many teams through the 1920s and 1930s, the cavity magnetron tube was later improved by John Randall and Harry Boot in 1940 at the University of Birmingham, England. The compact cavity magnetron tube drastically reduced the size of radar sets so that they could be easily installed in night-fighter aircraft, anti-submarine aircraft. In the post-war era the magnetron became less used in the radar role. This was because the output changes from pulse to pulse. This makes the signal unsuitable for pulse-to-pulse comparisons, which is used for detecting and removing clutter from the radar display. The magnetron remains in use in some radars, but has much more common as a low-cost microwave source for microwave ovens. In this form, approximately one billion magnetrons are in use today, in a conventional electron tube, electrons are emitted from a negatively charged, heated component called the cathode and are attracted to a positively charged component called the anode. The idea of using a grid for control was patented by Lee de Forest, one concept used a magnetic field instead of an electrical charge to control current flow, leading to the development of the magnetron tube. In this design, the tube was made with two electrodes, typically with the cathode in the form of a rod in the center. The tube was placed between the poles of a horseshoe magnet arranged such that the field was aligned parallel to the axis of the electrodes. With no magnetic field present, the tube operates as a diode, in the presence of the magnetic field, the electrons will experience a force at right angles to their direction of motion, according to the left-hand rule. In this case, the electrons follow a path between the cathode and anode. The curvature of the path can be controlled by varying either the field, using an electromagnet. At very high magnetic field settings the electrons are forced back onto the cathode, at the opposite extreme, with no field, the electrons are free to flow straight from the cathode to the anode. There is a point between the two extremes, the value or Hull cut-off magnetic field, where the electrons just reach the anode
14.
Magnetic field
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A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any point is specified by both a direction and a magnitude, as such it is represented by a vector field. The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter in the SI, B is measured in teslas and newtons per meter per ampere in the SI. B is most commonly defined in terms of the Lorentz force it exerts on moving electric charges, Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. In quantum physics, the field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields are used throughout modern technology, particularly in electrical engineering. The Earth produces its own field, which is important in navigation. Rotating magnetic fields are used in electric motors and generators. Magnetic forces give information about the carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits, noting that the resulting field lines crossed at two points he named those points poles in analogy to Earths poles. He also clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them, almost three centuries later, William Gilbert of Colchester replicated Petrus Peregrinus work and was the first to state explicitly that Earth is a magnet. Published in 1600, Gilberts work, De Magnete, helped to establish magnetism as a science, in 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law. Charles-Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated, building on this force between poles, Siméon Denis Poisson created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic H-field is produced by magnetic poles, three discoveries challenged this foundation of magnetism, though. First, in 1819, Hans Christian Ørsted discovered that an electric current generates a magnetic field encircling it, then in 1820, André-Marie Ampère showed that parallel wires having currents in the same direction attract one another. Finally, Jean-Baptiste Biot and Félix Savart discovered the Biot–Savart law in 1820, extending these experiments, Ampère published his own successful model of magnetism in 1825. This has the benefit of explaining why magnetic charge can not be isolated. Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism, in 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field
15.
Neodymium magnet
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A neodymium magnet, the most widely used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed in 1982 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet commercially available. They have replaced other types of magnets in the applications in modern products that require strong permanent magnets, such as motors in cordless tools, hard disk drives. However, compounds of neodymium with transition metals such as iron can have Curie temperatures well above room temperature, the strength of neodymium magnets is due to several factors. The tetragonal Nd2Fe14B crystal structure has exceptionally high uniaxial magnetocrystalline anisotropy and this means a crystal of the material preferentially magnetizes along a specific crystal axis, but is very difficult to magnetize in other directions. The resistance of the lattice to turning its direction of magnetization gives the compound a very high coercivity. The neodymium atom also can have a magnetic dipole moment because it has 7 unpaired electrons in its electron structure as opposed to 3 in iron. In a magnet it is the electrons, aligned so they spin in the same direction. This gives the Nd2Fe14B compound a high saturation magnetization and typically 1.3 teslas, therefore, as the maximum energy density is proportional to Js2, this magnetic phase has the potential for storing large amounts of magnetic energy. This magnetic energy value is about 18 times greater than ordinary magnets by volume and this property is higher in NdFeB alloys than in samarium cobalt magnets, which were the first type of rare-earth magnet to be commercialized. In practice, the properties of neodymium magnets depend on the alloy composition, microstructure. In 1982, General Motors and Sumitomo Special Metals discovered the Nd2Fe14B compound, the research was initially driven by the high raw materials cost of SmCo permanent magnets, which had been developed earlier. GM focused on the development of melt-spun nanocrystalline Nd2Fe14B magnets, while Sumitomo developed full-density sintered Nd2Fe14B magnets, GM commercialized its inventions of isotropic Neo powder, bonded Neo magnets, and the related production processes by founding Magnequench in 1986. The company supplied melt-spun Nd2Fe14B powder to bonded magnet manufacturers, the Sumitomo facility became part of the Hitachi Corporation, and currently manufactures and licenses other companies to produce sintered Nd2Fe14B magnets. Hitachi holds more than 600 patents covering neodymium magnets, chinese manufacturers have become a dominant force in neodymium magnet production, based on their control of much of the worlds sources of rare earth mines. The United States Department of Energy has identified a need to find substitutes for rare earth metals in permanent magnet technology, the Advanced Research Projects Agency-Energy has sponsored a Rare Earth Alternatives in Critical Technologies program, to develop alternative materials. In 2011, ARPA-E awarded 31.6 million dollars to fund Rare-Earth Substitute projects, the ingots are pulverized and milled, the powder is then sintered into dense blocks. The blocks are then heat-treated, cut to shape, surface treated and magnetized, in 2015, Nitto Denko Corporation of Japan announced their development of a new method of sintering neodymium magnet material
16.
Tesla (unit)
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The tesla is a unit of measurement of the strength of a magnetic field. It is a unit of the International System of Units. One tesla is equal to one weber per square metre, the unit was announced during the General Conference on Weights and Measures in 1960 and is named in honour of Nikola Tesla, upon the proposal of the Slovenian electrical engineer France Avčin. The strongest fields encountered from permanent magnets are from Halbach spheres, the strongest field trapped in a laboratory superconductor as of June 2014 is 21 T. This may be appreciated by looking at the units for each, the unit of electric field in the MKS system of units is newtons per coulomb, N/C, while the magnetic field can be written as N/. The dividing factor between the two types of field is metres per second, which is velocity, in ferromagnets, the movement creating the magnetic field is the electron spin. In a current-carrying wire the movement is due to moving through the wire. One tesla is equivalent to,10,000 G, used in the CGS system, thus,10 kG =1 T, and 1 G = 10−4 T.1,000,000,000 γ, used in geophysics. Thus,1 γ =1 nT.42.6 MHz of the 1H nucleus frequency, thus, the magnetic field associated with NMR at 1 GHz is 23.5 T. One tesla is equal to 1 V·s/m2 and this can be shown by starting with the speed of light in vacuum, c = −1/2, and inserting the SI values and units for c, the vacuum permittivity ε0, and the vacuum permeability μ0. Cancellation of numbers and units then produces this relation, for those concerned with low-frequency electromagnetic radiation in the home, the following conversions are needed most,1000 nT =1 µT =10 mG,1,000,000 µT =1 T. For the relation to the units of the field, see the article on permeability
17.
Earth's magnetic field
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Its magnitude at the Earths surface ranges from 25 to 65 microteslas. The North geomagnetic pole, located near Greenland in the hemisphere, is actually the south pole of the Earths magnetic field. Unlike a bar magnet, Earths magnetic field changes over time because it is generated by a geodynamo, however, at irregular intervals averaging several hundred thousand years, the Earths field reverses and the North and South Magnetic Poles relatively abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past, such information in turn is helpful in studying the motions of continents and ocean floors in the process of plate tectonics. The magnetosphere is the region above the ionosphere that is defined by the extent of the Earths magnetic field in space. The Earths magnetic field serves to deflect most of the solar wind, one stripping mechanism is for gas to be caught in bubbles of magnetic field, which are ripped off by solar winds. The study of past magnetic field of the Earth is known as paleomagnetism, reversals also provide the basis for magnetostratigraphy, a way of dating rocks and sediments. The field also magnetizes the crust, and magnetic anomalies can be used to search for deposits of metal ores, humans have used compasses for direction finding since the 11th century A. D. and for navigation since the 12th century. Although the magnetic declination does shift with time, this wandering is slow enough that a simple compass remains useful for navigation, using magnetoception various other organisms, ranging from some types of bacteria to pigeons, use the Earths magnetic field for orientation and navigation. At any location, the Earths magnetic field can be represented by a three-dimensional vector, a typical procedure for measuring its direction is to use a compass to determine the direction of magnetic North. Its angle relative to true North is the declination or variation, facing magnetic North, the angle the field makes with the horizontal is the inclination or magnetic dip. The intensity of the field is proportional to the force it exerts on a magnet, another common representation is in X, Y and Z coordinates. The intensity of the field is measured in gauss, but is generally reported in nanoteslas. A nanotesla is also referred to as a gamma, the tesla is the SI unit of the Magnetic field, B. The Earths field ranges between approximately 25,000 and 65,000 nT, by comparison, a strong refrigerator magnet has a field of about 10,000,000 nanoteslas. A map of intensity contours is called an isodynamic chart, as the World Magnetic Model shows, the intensity tends to decrease from the poles to the equator. A minimum intensity occurs in the South Atlantic Anomaly over South America while there are maxima over northern Canada, Siberia, the inclination is given by an angle that can assume values between -90° to 90°. In the northern hemisphere, the field points downwards and it is straight down at the North Magnetic Pole and rotates upwards as the latitude decreases until it is horizontal at the magnetic equator
18.
Isotropy
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Isotropy is uniformity in all orientations, it is derived from the Greek isos and tropos. Precise definitions depend on the subject area, exceptions, or inequalities, are frequently indicated by the prefix an, hence anisotropy. Anisotropy is also used to describe situations where properties vary systematically, Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. Within mathematics, isotropy has a few different meanings, Isotropic manifolds A manifold is isotropic if the geometry on the manifold is the same regardless of direction, a manifold can be homogeneous without being isotropic, but if it is inhomogeneous, it is necessarily anisotropic. Isotropic quadratic form A quadratic form q is said to be if there is a non-zero vector v such that q =0. In complex geometry, a line through the origin in the direction of a vector is an isotropic line. Isotropic coordinates Isotropic coordinates are coordinates on a chart for Lorentzian manifolds. Isotropy group An isotropy group is the group of isomorphisms from any object to itself in a groupoid, Isotropic position A probability distribution over a vector space is in isotropic position if its covariance matrix is the identity. This follows from invariance of the Hamiltonian, which in turn is guaranteed for a spherically symmetric potential. Kinetic theory of gases is also an example of isotropy and it is assumed that the molecules move in random directions and as a consequence, there is an equal probability of a molecule moving in any direction. Thus when there are molecules in the gas, with high probability there will be very similar numbers moving in one direction as any other hence demonstrating approximate isotropy. Fluid dynamics Fluid flow is isotropic if there is no directional preference, an example of anisotropy is in flows with a background density as gravity works in only one direction. The apparent surface separating two differing isotropic fluids would be referred to as an isotrope, thermal expansion A solid is said to be isotropic if the expansion of solid is equal in all directions when thermal energy is provided to the solid. Electromagnetics An isotropic medium is one such that the permittivity, ε, and permeability, μ, of the medium are uniform in all directions of the medium, optics Optical isotropy means having the same optical properties in all directions. The individual reflectance or transmittance of the domains is averaged if the macroscopic reflectance or transmittance is to be calculated, cosmology The Big Bang theory of the evolution of the observable universe assumes that space is isotropic. It also assumes that space is homogeneous and these two assumptions together are known as the Cosmological Principle. As of 2006, the observations suggest that, on scales much larger than galaxies, galaxy clusters are Great features. Here homogeneous means that the universe is the same everywhere and isotropic implies that there is no preferred direction, in the study of mechanical properties of materials, isotropic means having identical values of a property in all directions
19.
Remanence
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Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material after an external magnetic field is removed. It is also the measure of that magnetization, colloquially, when a magnet is magnetized it has remanence. The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, the equivalent term residual magnetization is generally used in engineering applications. Where it is unwanted, it can be removed by degaussing, sometimes the term retentivity is used for remanence measured in units of magnetic flux density. The default definition of magnetic remanence is the remaining in zero field after a large magnetic field is applied. The effect of a hysteresis loop is measured using instruments such as a vibrating sample magnetometer. In physics this measure is converted to an average magnetization and denoted in equations as Mr, if it must be distinguished from other kinds of remanence, then it is called the saturation remanence or saturation isothermal remanence and denoted by Mrs. In engineering applications the residual magnetization is often measured using a B-H Analyzer and this is represented by a flux density Br. This value of remanence is one of the most important parameters characterizing permanent magnets, neodymium magnets, for example, have a remanence approximately equal to 1.3 teslas. Often a single measure of remanence does not provide information on a magnet. For example, magnetic tapes contain a number of small magnetic particles. Magnetic minerals in rocks may have a range of magnetic properties. One way to look inside these materials is to add or subtract small increments of remanence, one way of doing this is first demagnetizing the magnet in an AC field, and then applying a field H and removing it. This remanence, denoted by Mr, depends on the field and it is called the initial remanence or the isothermal remanent magnetization. Another kind of IRM can be obtained by first giving the magnet a saturation remanence in one direction and this is called demagnetization remanence or DC demagnetization remanence and is denoted by symbols like Md, where H is the magnitude of the field. Yet another kind of remanence can be obtained by demagnetizing the saturation remanence in an ac field and this is called AC demagnetization remanence or alternating field demagnetization remanence and is denoted by symbols like Maf. If the particles are noninteracting single-domain particles with uniaxial anisotropy, there are simple linear relations between the remanences, another kind of laboratory remanence is anhysteretic remanence or anhysteretic remanent magnetization. This is induced by exposing a magnet to an alternating field plus a small dc bias field
20.
Curie temperature
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In physics and materials science, the Curie temperature, or Curie point, is the temperature at which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism. The Curie temperature is named after Pierre Curie, who showed that magnetism was lost at a critical temperature, the force of magnetism is determined by the magnetic moment, a dipole moment within an atom which originates from the angular momentum and spin of electrons. Permanent magnetism is caused by the alignment of magnetic moments and induced magnetism is created when disordered magnetic moments are forced to align in an magnetic field. For example, the magnetic moments change and become disordered at the Curie temperature. Higher temperatures make magnets weaker, as spontaneous magnetism occurs below the Curie temperature. Magnetic susceptibility above the Curie Temperature can be calculated from the Curie–Weiss law, in analogy to ferromagnetic and paramagnetic materials, the Curie temperature can also be used to describe the phase transition between ferroelectricity and paraelectricity. In this context, the parameter is the electric polarisation that goes from a finite value to zero when the temperature is increased above the Curie temperature. Magnetic moments are permanent dipole moments within the atom which are made up from electrons angular momentum and spin, by the relation μl = el/2me, electrons inside atoms contribute magnetic moments from their own angular momentum and from their orbital momentum around the nucleus. Magnetic moments from the nucleus are insignificant in contrast to magnetic moments from electrons, thermal contribution will result in higher energy electrons causing disruption to their order and alignment between dipoles to be destroyed. Ferromagnetic, paramagnetic, ferrimagnetic and antiferromagnetic materials have different structures of intrinsic magnetic moments and it is at a materials specific Curie temperature where they change properties. The transition from antiferromagnetic to paramagnetic occurs at the Néel temperature which is analogous to Curie temperature, orientations of magnetic moments in materials Ferromagnetic, paramagnetic, ferrimagnetic and antiferromagnetic structures are made up of intrinsic magnetic moments. If all electrons within the structure are paired, these cancel out due to having opposite spins. Thus even with a magnetic field will have different properties. A material is only above its Curie temperature. Paramagnetic materials are non-magnetic when a field is absent and magnetic when a magnetic field is applied. When the magnetic field is absent the material has disordered magnetic moments, that is, when the magnetic field is present the magnetic moments are temporarily realigned parallel to the applied field, the atoms are symmetrical and aligned. The magnetic moment in the direction is what causes an induced magnetic field. For paramagnetism this response to a magnetic field is positive
21.
Incandescence
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Incandescence is the emission of electromagnetic radiation from a hot body as a result of its temperature. The term derives from the Latin verb incandescere, to glow white, incandescence is a special case of thermal radiation. Incandescence usually refers specifically to visible light, while thermal radiation refers also to infrared or any electromagnetic radiation. For a detailed discussion of the intensity and spectrum of incandescence, see the article and this limit is called the Draper point. The incandescence does not vanish below that temperature, but it is too weak in the spectrum to be perceivable. At higher temperatures, the substance becomes brighter and its changes from red towards white. Incandescence is exploited in incandescent light bulbs, in which a filament is heated to a temperature at which a fraction of the falls in the visible spectrum. The majority of the radiation however, is emitted in the part of the spectrum. If the filament could be hotter, efficiency would increase, however. More efficient light sources, such as fluorescent lamps and LEDs, sunlight is the incandescence of the white hot surface of the sun. The word incandescent is also used figuratively to describe a person who is so angry that they are imagined to glow or burn red hot or white hot, red heat List of light sources Figurative use, Rangers 1 Unirea-Urziceni 4 etc
22.
Brittleness
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A material is brittle if, when subjected to stress, it breaks without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength, breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses and some polymers, such as PMMA, many steels become brittle at low temperatures, depending on their composition and processing. When used in science, it is generally applied to materials that fail when there is little or no evidence of plastic deformation before failure. One proof is to match the broken halves, which should fit exactly since no plastic deformation has occurred, when a material has reached the limit of its strength, it usually has the option of either deformation or fracture. Improving material toughness is therefore a balancing act and this principle generalizes to other classes of material. Naturally brittle materials, such as glass, are not difficult to toughen effectively, the first principle is used in laminated glass where two sheets of glass are separated by an interlayer of polyvinyl butyral, which as a viscoelastic polymer absorbs the growing crack. The second method is used in toughened glass and pre-stressed concrete, a demonstration of glass toughening is provided by Prince Ruperts Drop. Brittle polymers can be toughened by using metal particles to initiate crazes when a sample is stressed, the least brittle structural ceramics are silicon carbide and transformation-toughened zirconia. A different philosophy is used in materials, where brittle glass fibres. When strained, cracks are formed at the interface, but so many are formed that much energy is absorbed. The same principle is used in creating metal matrix composites, generally, the brittle strength of a material can be increased by pressure. Supersonic fracture is crack motion faster than the speed of sound in a brittle material and this phenomenon was first discovered by scientists from the Max Planck Institute for Metals Research in Stuttgart and IBM Almaden Research Center in San Jose, California. Izod impact strength test Charpy impact test Fractography Forensic engineering Ductility Strengthening mechanisms of materials Lewis, Peter Rhys, Reynolds, K, Gagg, rösler, Joachim, Harders, Harald, Bäker, Martin. Mechanical behaviour of engineering materials, metals, ceramics, polymers, and composites
23.
United States dollar
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The United States dollar is the official currency of the United States and its insular territories per the United States Constitution. It is divided into 100 smaller cent units, the circulating paper money consists of Federal Reserve Notes that are denominated in United States dollars. The U. S. dollar was originally commodity money of silver as enacted by the Coinage Act of 1792 which determined the dollar to be 371 4/16 grain pure or 416 grain standard silver, the currency most used in international transactions, it is the worlds primary reserve currency. Several countries use it as their currency, and in many others it is the de facto currency. Besides the United States, it is used as the sole currency in two British Overseas Territories in the Caribbean, the British Virgin Islands and Turks and Caicos Islands. A few countries use the Federal Reserve Notes for paper money, while the country mints its own coins, or also accepts U. S. coins that can be used as payment in U. S. dollars. After Nixon shock of 1971, USD became fiat currency, Article I, Section 8 of the U. S. Constitution provides that the Congress has the power To coin money, laws implementing this power are currently codified at 31 U. S. C. Section 5112 prescribes the forms in which the United States dollars should be issued and these coins are both designated in Section 5112 as legal tender in payment of debts. The Sacagawea dollar is one example of the copper alloy dollar, the pure silver dollar is known as the American Silver Eagle. Section 5112 also provides for the minting and issuance of other coins and these other coins are more fully described in Coins of the United States dollar. The Constitution provides that a regular Statement and Account of the Receipts and that provision of the Constitution is made specific by Section 331 of Title 31 of the United States Code. The sums of money reported in the Statements are currently being expressed in U. S. dollars, the U. S. dollar may therefore be described as the unit of account of the United States. The word dollar is one of the words in the first paragraph of Section 9 of Article I of the Constitution, there, dollars is a reference to the Spanish milled dollar, a coin that had a monetary value of 8 Spanish units of currency, or reales. In 1792 the U. S. Congress passed a Coinage Act, Section 20 of the act provided, That the money of account of the United States shall be expressed in dollars, or units. And that all accounts in the offices and all proceedings in the courts of the United States shall be kept and had in conformity to this regulation. In other words, this act designated the United States dollar as the unit of currency of the United States, unlike the Spanish milled dollar the U. S. dollar is based upon a decimal system of values. Both one-dollar coins and notes are produced today, although the form is significantly more common
24.
Loudspeaker
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A loudspeaker is an electroacoustic transducer, which converts an electrical audio signal into a corresponding sound. The most widely used type of speaker in the 2010s is the speaker, invented in 1925 by Edward W. Kellogg. The dynamic speaker operates on the basic principle as a dynamic microphone. Besides this most common method, there are several technologies that can be used to convert an electrical signal into sound. The sound source must be amplified or strengthened with a power amplifier before the signal is sent to the speaker. Speakers are typically housed in an enclosure or speaker cabinet which is often a rectangular or square box made of wood or sometimes plastic. The enclosures materials and design play an important role in the quality of the sound, where high fidelity reproduction of sound is required, multiple loudspeaker transducers are often mounted in the same enclosure, each reproducing a part of the audible frequency range. In this case the individual speakers are referred to as drivers, drivers made for reproducing high audio frequencies are called tweeters, those for middle frequencies are called mid-range drivers, and those for low frequencies are called woofers. Smaller loudspeakers are found in such as radios, televisions, portable audio players, computers. Larger loudspeaker systems are used for music, sound reinforcement in theatres and concerts, the term loudspeaker may refer to individual transducers or to complete speaker systems consisting of an enclosure including one or more drivers. To adequately reproduce a range of frequencies with even coverage, most loudspeaker systems employ more than one driver. Individual drivers are used to different frequency ranges. The drivers are named subwoofers, woofers, mid-range speakers, tweeters, the terms for different speaker drivers differ, depending on the application. In two-way systems there is no mid-range driver, so the task of reproducing the mid-range sounds falls upon the woofer and tweeter, home stereos use the designation tweeter for the high frequency driver, while professional concert systems may designate them as HF or highs. When multiple drivers are used in a system, a network, called a crossover. Loudspeaker driver of the type pictured are termed dynamic to distinguish them from earlier drivers, or speakers using piezoelectric or electrostatic systems, or any of several other sorts. Johann Philipp Reis installed an electric loudspeaker in his telephone in 1861, it was capable of reproducing clear tones, alexander Graham Bell patented his first electric loudspeaker as part of his telephone in 1876, which was followed in 1877 by an improved version from Ernst Siemens. In 1898, Horace Short patented a design for a loudspeaker driven by compressed air, he sold the rights to Charles Parsons
25.
Casting (metalworking)
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In metalworking, casting means a process, in which liquid metal is poured into a mold, that contains a hollow cavity of the desired shape, and is then allowed to cool and solidify. The solidified part is known as a casting, which is ejected or broken out of the mold to complete the process. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods, Casting processes have been known for thousands of years, and widely used for sculpture, especially in bronze, jewellery in precious metals, and weapons and tools. Traditional techniques include casting, plaster mold casting and sand casting. The modern casting process is subdivided into two categories, expendable and non-expendable casting. It is further broken down by the material, such as sand or metal. Expendable mold casting is a classification that includes sand, plastic, shell, plaster. This method of mold casting involves the use of temporary, non-reusable molds, sand casting is one of the most popular and simplest types of casting, and has been used for centuries. Sand casting allows for smaller batches than permanent mold casting and at a reasonable cost. Not only does this method allow manufacturers to create products at a low cost, from castings that fit in the palm of your hand to train beds, it can all be done with sand casting. Sand casting also allows most metals to be cast depending on the type of sand used for the molds, sand casting requires a lead time of days, or even weeks sometimes, for production at high output rates and is unsurpassed for large-part production. Green sand has almost no weight limit, whereas dry sand has a practical part mass limit of 2. Minimum part weight ranges from 0. 075–0.1 kg, the sand is bonded together using clays, chemical binders, or polymerized oils. Sand can be recycled many times in most operations and requires little maintenance, plaster casting is similar to sand casting except that plaster of paris is substituted for sand as a mold material. Plaster casting is an alternative to other molding processes for complex parts due to the low cost of the plaster. The biggest disadvantage is that it can only be used with low melting point non-ferrous materials, such as aluminium, copper, magnesium, and zinc. Shell molding is similar to casting, but the molding cavity is formed by a hardened shell of sand instead of a flask filled with sand. The sand used is finer than sand casting sand and is mixed with a resin so that it can be heated by the pattern, because of the resin and finer sand, it gives a much finer surface finish
26.
Sintering
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Sintering is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. Sintering happens naturally in mineral deposits or as a process used with metals, ceramics, plastics. The atoms in the materials diffuse across the boundaries of the particles, fusing the particles together, the study of sintering in metallurgy powder-related processes is known as powder metallurgy. An example of sintering can be observed when ice cubes in a glass of water adhere to each other, examples of pressure-driven sintering are the compacting of snowfall to a glacier, or the forming of a hard snowball by pressing loose snow together. The word sinter comes from the Middle High German sinter, a cognate of English cinder, the driving force for densification is the change in free energy from the decrease in surface area and lowering of the surface free energy by the replacement of solid-vapor interfaces. It forms new but lower-energy solid-solid interfaces with a decrease in free energy occurring. On a microscopic scale, material transfer is affected by the change in pressure, If the size of the particle is small, these effects become very large in magnitude. For properties such as strength and conductivity, the area in relation to the particle size is the determining factor. The variables that can be controlled for any material are the temperature. Through time, the radius and the vapor pressure are proportional to 2/3 and to 1/3. The source of power for solid-state processes is the change in free or chemical energy between the neck and the surface of the particle. The pore elimination occurs faster for a trial with many pores of uniform size, for the latter portions of the process, boundary and lattice diffusion from the boundary become important. Sintering is part of the process used in the manufacture of pottery. These objects are made from such as glass, alumina, zirconia, silica, magnesia, lime, beryllium oxide. Some ceramic raw materials have an affinity for water and a lower plasticity index than clay. Sintering is performed at high temperature, besides, second and/or third external force could be used. Commonly used second external force is pressure, so, the sintering that performed just using temperature is generally called pressureless sintering. Pressureless sintering is possible with graded metal-ceramic composites, with a nanoparticle sintering aid, a variant used for 3D shapes is called hot isostatic pressing
27.
Precipitation hardening
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In superalloys, it is known to cause yield strength anomaly providing excellent high-temperature strength. Since dislocations are often the dominant carriers of plasticity, this serves to harden the material, the impurities play the same role as the particle substances in particle-reinforced composite materials. Unlike ordinary tempering, alloys must be kept at elevated temperature for hours to allow precipitation to take place and this time delay is called aging. Solution treatment and aging is sometimes abbreviated STA in metals specs, note that two different heat treatments involving precipitates can alter the strength of a material, solution heat treating and precipitation heat treating. Solid solution strengthening involves formation of a solid solution via quenching. Precipitation heat treating involves the addition of impurity particles to increase a materials strength, precipitation hardening via precipitation heat treatment is the main topic of discussion in this article. Nucleation occurs at a high temperature so that the kinetic barrier of surface energy can be more easily overcome. These particles are allowed to grow at lower temperature in a process called aging. This is carried out under conditions of low solubility so that thermodynamics drive a total volume of precipitate formation. Diffusions exponential dependence upon temperature makes precipitation strengthening, like all heat treatments, too little diffusion, and the particles will be too small to impede dislocations effectively, too much, and they will be too large and dispersed to interact with the majority of dislocations. Precipitation strengthening is possible if the line of solid solubility slopes strongly toward the center of a phase diagram, while a large volume of precipitate particles is desirable, a small enough amount of the alloying element should be added that it remains easily soluble at some reasonable annealing temperature. Elements used for strengthening in typical aluminum and titanium alloys make up about 10% of their composition. While binary alloys are easily understood as an academic exercise. A large number of other constituents may be unintentional, but benign, in some cases, such as many aluminum alloys, an increase in strength is achieved at the expense of corrosion resistance. The addition of large amounts of nickel and chromium needed for corrosion resistance in stainless steels means that traditional hardening and tempering methods are not effective, however, precipitates of chromium, copper, or other elements can strengthen the steel by similar amounts in comparison to hardening and tempering. The strength can be tailored by adjusting the annealing process, with lower initial temperatures resulting in higher strengths, the lower initial temperatures increase the driving force of nucleation. More driving force means more nucleation sites, and more sites means more places for dislocations to be disrupted while the part is in use. Many alloy systems allow the temperature to be adjusted
28.
Hardware disease
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Hardware disease is a common term for bovine traumatic reticuloperitonitis. It is usually caused by the ingestion of a sharp, metallic object and these pieces of metal settle in the reticulum and can irritate or penetrate the lining. It is most common in cattle, but is occasionally seen in beef cattle. It is very rarely reported in any other ruminants and it can be difficult to conclusively diagnose, but can be prevented by the oral administration of a magnet before the animal reaches the age of one. Cattle commonly swallow foreign objects, because they do not use their lips to discriminate between materials and they do not completely chew their feed before swallowing, sharp metallic objects, such as nails or wire, are the common initiators of hardware disease. The object travels into the rumen and is pushed into the reticulum along with the rest of the feed. In some cases, contractions of the reticulum can push the object through part of the wall into the peritoneal cavity. In rare cases, the object penetrates the entire wall of the reticulum and can pierce the heart sac. Compression by the uterus in late pregnancy, straining during parturition, diagnosis is typically based on history and clinical findings when the veterinarian examines the cow. Symptoms of hardware disease vary depending on where the object penetrates, the cow exhibits an arched back, a reluctance to move and a slow, careful gait. The cow may groan when lying down, getting up, defecating and urinating, the heart rate is normal or slightly elevated, and the respiration is shallow and rapid. In dairy cows, there is often a decrease in milk production, laboratory tests are not always necessary, but increases in fibrinogen and total plasma protein often result from hardware disease and may be diagnosed with a blood sample. Electronic metal detectors can be used, but not all heavy sharp objects will be metal, radiographs are also used and are advantageous because the location of the metallic body can be identified. However, if the object is not metallic or dense enough the radiograph is of no use. If there is inflammation in either the Peritoneal cavity or the Pericardium, if hardware disease is suspected, a magnet should be administered orally through a tube into the rumen. Depending on the type of magnet used, inserting a second magnet could cause internal pinching which could lead to serious complications, a broad-spectrum antibiotic should also be given to control infection. The cow should be confined and movement limited in the hopes that the reticulum can repair the hole, surgery is necessary in some cases and involves rumenotomy with a physical removal of the object. In some advanced cases that don’t respond to medical or surgical therapy, good feed management is also important, in smaller operations, some farmers pass metal detectors or magnets over the feed
29.
Electric motor
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An electric motor is an electrical machine that converts electrical energy into mechanical energy. The reverse of this is the conversion of energy into electrical energy and is done by an electric generator. In normal motoring mode, most electric motors operate through the interaction between an electric motors magnetic field and winding currents to generate force within the motor, small motors may be found in electric watches. General-purpose motors with highly standardized dimensions and characteristics provide convenient mechanical power for industrial use, the largest of electric motors are used for ship propulsion, pipeline compression and pumped-storage applications with ratings reaching 100 megawatts. Electric motors may be classified by electric power source type, internal construction, application, type of motion output, perhaps the first electric motors were simple electrostatic devices created by the Scottish monk Andrew Gordon in the 1740s. The theoretical principle behind production of force by the interactions of an electric current. The conversion of energy into mechanical energy by electromagnetic means was demonstrated by the British scientist Michael Faraday in 1821. A free-hanging wire was dipped into a pool of mercury, on which a permanent magnet was placed, when a current was passed through the wire, the wire rotated around the magnet, showing that the current gave rise to a close circular magnetic field around the wire. This motor is often demonstrated in experiments, brine substituting for toxic mercury. Though Barlows wheel was a refinement to this Faraday demonstration. In 1827, Hungarian physicist Ányos Jedlik started experimenting with electromagnetic coils, after Jedlik solved the technical problems of the continuous rotation with the invention of the commutator, he called his early devices electromagnetic self-rotors. Although they were used only for instructional purposes, in 1828 Jedlik demonstrated the first device to contain the three components of practical DC motors, the stator, rotor and commutator. The device employed no permanent magnets, as the fields of both the stationary and revolving components were produced solely by the currents flowing through their windings. His motor set a record which was improved only four years later in September 1838 by Jacobi himself. His second motor was powerful enough to drive a boat with 14 people across a wide river and it was not until 1839/40 that other developers worldwide managed to build motors of similar and later also of higher performance. The first commutator DC electric motor capable of turning machinery was invented by the British scientist William Sturgeon in 1832, following Sturgeons work, a commutator-type direct-current electric motor made with the intention of commercial use was built by the American inventor Thomas Davenport, which he patented in 1837. The motors ran at up to 600 revolutions per minute, and powered machine tools, due to the high cost of primary battery power, the motors were commercially unsuccessful and Davenport went bankrupt. Several inventors followed Sturgeon in the development of DC motors but all encountered the same battery power cost issues, no electricity distribution had been developed at the time
30.
Pickup (music technology)
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The signal from a pickup can also be recorded directly, using a DI box or broadcast on the radio or television. Most electric guitars and electric basses use magnetic pickups, acoustic guitars, upright basses and fiddles often use a piezoelectric pickup. A magnetic pickup consists of a permanent magnet with a core of such as alnico or ferrite. The pickup is most often mounted on the body of the instrument, Magnetic pickups used with string basses can be attached to the bridge. The permanent magnet creates a field, the motion of the vibrating steel strings disturbs the field, changing magnetic flux. The pickup is then connected with a cable to an amplifier which amplifies the signal to a sufficient magnitude of power to drive a loudspeaker. A pickup can also be connected to recording equipment via a patch cable, there may also be an internal preamplifier device mounted in an acoustic guitar or in an external box. When a preamp is used in way, it is between the pickup and cable and can significantly reduce the equivalent impedance of the pickup coil. The output voltage of magnetic pickups varies between 100 mV rms to over 1 V rms for some of the higher output types, some high-output pickups achieve this by employing very strong magnets, thus creating more flux and thereby more output. This can be detrimental to the sound because the magnets pull on the strings can cause problems with intonation as well as damp the strings. Other high-output pickups have more turns of wire to increase the voltage generated by the strings movement, however, this also increases the pickups output resistance/impedance, which can affect high frequencies if the pickup is not isolated by a buffer amplifier or a DI unit. The turns of wire in proximity to each other have an equivalent self-capacitance that and this resonance can accentuate certain frequencies, giving the pickup a characteristic tonal quality. The more turns of wire in the winding, the higher the output voltage, the inductive source impedance inherent in this type of transducer makes it less linear than other forms of pickups, such as piezo-electric or optical. The tonal quality produced by this nonlinearity is, however, subject to taste, the external load usually consists of resistance and capacitance between the hot lead and shield in the guitar cable. The electric cable also has a capacitance, which can be a significant portion of the overall system capacitance and this arrangement of passive components forms a resistively-damped second-order low-pass filter. Single coil pickups act like an antenna and are prone to pick up mains hum along with the musical signal. Mains hum consists of a signal at a nominal 50 or 60 Hz, depending on local alternating current frequency. The changing magnetic flux caused by the mains current links with the windings of the pickup, the pickups also are sensitive to the electromagnetic field from nearby cathode ray tubes in video monitors or televisions
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Microphone
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A microphone, colloquially nicknamed mic or mike, is a transducer that converts sound into an electrical signal. Several different types of microphone are in use, which employ different methods to convert the air pressure variations of a wave to an electrical signal. Microphones typically need to be connected to a preamplifier before the signal can be recorded or reproduced, in order to speak to larger groups of people, a need arose to increase the volume of the human voice. The earliest devices used to achieve this were acoustic megaphones, some of the first examples, from fifth century BC Greece, were theater masks with horn-shaped mouth openings that acoustically amplified the voice of actors in amphitheatres. In 1665, the English physicist Robert Hooke was the first to experiment with an other than air with the invention of the lovers telephone made of stretched wire with a cup attached at each end. German inventor Johann Philipp Reis designed an early sound transmitter that used a strip attached to a vibrating membrane that would produce intermittent current. Better results were achieved with the transmitter design in Scottish-American Alexander Graham Bells telephone of 1876 – the diaphragm was attached to a conductive rod in an acid solution. These systems, however, gave a poor sound quality. The first microphone that enabled proper voice telephony was the carbon microphone and this was independently developed by David Edward Hughes in England and Emile Berliner and Thomas Edison in the US. Although Edison was awarded the first patent in mid-1877, Hughes had demonstrated his working device in front of many witnesses some years earlier, the carbon microphone is the direct prototype of todays microphones and was critical in the development of telephony, broadcasting and the recording industries. Thomas Edison refined the carbon microphone into his carbon-button transmitter of 1886 and this microphone was employed at the first ever radio broadcast, a performance at the New York Metropolitan Opera House in 1910. In 1916, E. C. Wente of Western Electric developed the next breakthrough with the first condenser microphone, in 1923, the first practical moving coil microphone was built. The Marconi Skykes or magnetophon, developed by Captain H. J. Round, was the standard for BBC studios in London and this was improved in 1930 by Alan Blumlein and Herbert Holman who released the HB1A and was the best standard of the day. Also in 1923, the microphone was introduced, another electromagnetic type, believed to have been developed by Harry F. Olson. Over the years these microphones were developed by companies, most notably RCA that made large advancements in pattern control. With television and film technology booming there was demand for high fidelity microphones, electro-Voice responded with their Academy Award-winning shotgun microphone in 1963. During the second half of 20th century development advanced quickly with the Shure Brothers bringing out the SM58, digital was pioneered by Milab in 1999 with the DM-1001. The latest research developments include the use of optics, lasers and interferometers
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Sensor
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A sensor is always used with other electronics, whether as simple as a light or as complex as a computer. Moreover, analog sensors such as potentiometers and force-sensing resistors are still widely used, applications include manufacturing and machinery, airplanes and aerospace, cars, medicine, robotics and many other aspects of our day-to-day life. A sensors sensitivity indicates how much the output changes when the input quantity being measured changes. For instance, if the mercury in a thermometer moves 1 cm when the changes by 1 °C. Some sensors can also affect what they measure, for instance, Sensors are usually designed to have a small effect on what is measured, making the sensor smaller often improves this and may introduce other advantages. Technological progress allows more and more sensors to be manufactured on a scale as microsensors using MEMS technology. In most cases, a microsensor reaches a higher speed. Most sensors have a transfer function. The sensitivity is defined as the ratio between the output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is the slope of the transfer function. Converting the sensors electrical output to the measured units requires dividing the output by the slope. In addition, an offset is added or subtracted. For example -40 must be added to the output if 0 V output corresponds to -40 C input, for an analog sensor signal to be processed, or used in digital equipment, it needs to be converted to a digital signal, using an analog-to-digital converter. The full scale range defines the maximum and minimum values of the measured property, the sensitivity may in practice differ from the value specified. This is called a sensitivity error and this is an error in the slope of a linear transfer function. If the output differs from the correct value by a constant. This is an error in the y-intercept of a transfer function. Nonlinearity is deviation of a transfer function from a straight line transfer function
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International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
34.
Aluminium alloy
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Aluminium alloys are alloys in which aluminium is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, there are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. About 85% of aluminium is used for products, for example rolled plate, foils. Cast aluminium alloys yield cost-effective products due to the low melting point, the most important cast aluminium alloy system is Al–Si, where the high levels of silicon contribute to give good casting characteristics. Aluminium alloys are used in engineering structures and components where light weight or corrosion resistance is required. Alloys composed mostly of aluminium have been important in aerospace manufacturing since the introduction of metal-skinned aircraft. Aluminium-magnesium alloys are both lighter than aluminium alloys and much less flammable than alloys that contain a very high percentage of magnesium. Aluminium alloy surfaces will develop a white, protective layer of aluminium oxide if left unprotected by anodizing and/or correct painting procedures, referred to as dissimilar-metal corrosion, this process can occur as exfoliation or as intergranular corrosion. Aluminium alloys can be heat treated. This causes internal element separation, and the metal then corrodes from the inside out, Aluminium alloy compositions are registered with The Aluminum Association. Aluminium alloys with a range of properties are used in engineering structures. Alloy systems are classified by a system or by names indicating their main alloying constituents. Selecting the right alloy for a given application entails considerations of its strength, density, ductility, formability, workability, weldability. A brief historical overview of alloys and manufacturing technologies is given in Ref. Aluminium alloys are used extensively in aircraft due to their high strength-to-weight ratio. On the other hand, pure aluminium metal is too soft for such uses. Aluminium alloys typically have an elastic modulus of about 70 GPa, therefore, for a given load, a component or unit made of an aluminium alloy will experience a greater deformation in the elastic regime than a steel part of identical size and shape. Though there are aluminium alloys with somewhat-higher tensile strengths than the commonly used kinds of steel, with completely new metal products, the design choices are often governed by the choice of manufacturing technology. Extrusions are particularly important in regard, owing to the ease with which aluminium alloys, particularly the Al–Mg–Si series
