1.
British Army
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The British Army is the principal land warfare force of the United Kingdom. As of 2017 the British Army comprises just over 80,000 trained Regular, or full-time, personnel and just over 26,500 trained Reserve, or part-time personnel. Therefore, the UK Parliament approves the continued existence of the Army by passing an Armed Forces Act at least once every five years, day to day the Army comes under administration of the Ministry of Defence and is commanded by the Chief of the General Staff. Repeatedly emerging victorious from these decisive wars allowed Britain to influence world events with its policies and establish itself as one of the leading military. In 1660 the English, Scottish and Irish monarchies were restored under Charles II, Charles favoured the foundation of a new army under royal control and began work towards its establishment by August 1660. The Royal Scots Army and the Irish Army were financed by the Parliament of Scotland, the order of seniority of the most senior line regiments in the British Army is based on the order of seniority in the English army. At that time there was only one English regiment of dragoons, after William and Marys accession to the throne, England involved itself in the War of the Grand Alliance, primarily to prevent a French invasion restoring Marys father, James II. Spain, in the two centuries, had been the dominant global power, and the chief threat to Englands early transatlantic ambitions. The territorial ambitions of the French, however, led to the War of the Spanish Succession and the Napoleonic Wars. From the time of the end of the Seven Years War in 1763, Great Britain was the naval power. As had its predecessor, the English Army, the British Army fought the Kingdoms of Spain, France, and the Netherlands for supremacy in North America and the West Indies. With native and provincial assistance, the Army conquered New France in the North American theatre of the Seven Years War, the British Army suffered defeat in the American War of Independence, losing the Thirteen Colonies but holding on to Canada. The British Army was heavily involved in the Napoleonic Wars and served in campaigns across Europe. The war between the British and the First French Empire of Napoleon Bonaparte stretched around the world and at its peak, in 1813, the regular army contained over 250,000 men. A Coalition of Anglo-Dutch and Prussian Armies under the Duke of Wellington, the English had been involved, both politically and militarily, in Ireland since being given the Lordship of Ireland by the Pope in 1171. The campaign of the English republican Protector, Oliver Cromwell, involved uncompromising treatment of the Irish towns that had supported the Royalists during the English Civil War, the English Army stayed in Ireland primarily to suppress numerous Irish revolts and campaigns for independence. Having learnt from their experience in America, the British government sought a political solution, the British Army found itself fighting Irish rebels, both Protestant and Catholic, primarily in Ulster and Leinster in the 1798 rebellion. The Haldane Reforms of 1907 formally created the Territorial Force as the Armys volunteer reserve component by merging and reorganising the Volunteer Force, Militia, Great Britains dominance of the world had been challenged by numerous other powers, in the 20th century, most notably Germany
2.
Challenger 2
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The FV4034 Challenger 2 is a British main battle tank in service with the armies of the United Kingdom and Oman. It was designed and built by the British company Vickers Defence Systems, Vickers Defence Systems began to develop a successor to Challenger 1 as a private venture in 1986. A £90 million deal for a vehicle was finalised in January 1989. In June 1991, the Ministry of Defence placed a £520 million order for 140 vehicles, production began in 1993 and the units tanks were delivered in July 1994, replacing the Challenger 1. The tank entered service with the British Army in 1998, with the last delivered in 2002 and it is expected to remain in service until 2035. The Royal Army of Oman ordered 18 Challenger 2s in 1993, the Challenger 2 is an extensive redesign of the Challenger 1. Although the hull and automotive components seem similar, they are of a design and build than those of the Challenger 1. The tanks drive system provides a 550 km range, with a road speed of 59 km/h. The Challenger 2 is equipped with a 120-millimetre 55-calibre long L30A1 tank gun, the Challenger 2 is also armed with a L94A1 EX-347.62 mm chain gun and a 7.62 mm L37A2 machine gun. Fifty eight main armament rounds and 4,200 rounds of 7.62 mm ammunition are carried, the Challenger 2 is considered to be one of the best protected tanks in the world. The turret and hull are protected with second generation Chobham armour, on one occasion, in August 2006, during the post-invasion stage of the Iraq War, an RPG-29 was fired at a Challenger 2 that was climbing over a ramp. The armour on its front underside hull, which was not augmented with an explosive reactive armour package, was damaged, the tank subsequently returned to base under its own power and was quickly repaired and back on duty the following day. As a response to the incident, the reactive armour package was replaced with a Dorchester block. It has seen service in Bosnia, Kosovo and Iraq. The Challenger 2 is the vehicle of this name, the first being the A30 Challenger. The second was the Persian Gulf War era Challenger 1, which was the British armys main battle tank from the early 1980s to the mid-1990s, Vickers Defence Systems began to develop a successor to Challenger 1 as a private venture in 1986. Following the issue of a Staff Requirement for a next-generation tank, the demonstration phase contained three milestones for progress, with dates of September 1989, March 1990, and September 1990. At the last of these milestones, Vickers was to have met 11 key criteria for the tanks design, in June 1991, after competition with other tank manufacturers designs, the MoD placed a £520 million order for 127 MBTs and 13 driver training vehicles
3.
Main battle tank
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A main battle tank, also known as a battle tank or universal tank, is a tank that fills the armor-protected direct fire and maneuver role of many modern armies. Through the 1960s, the MBT replaced almost all other tanks, today, main battle tanks are considered a key component of modern armies. Modern MBTs seldom operate alone, as they are organized into armoured units which involve the support of infantry and they are also often supported by surveillance or ground-attack aircraft. In World War I, tanks were classed into light, medium, and heavy based on weight, as tank combat evolved, tank design suffered from a number of limitations due largely to engine power and transmission capability. A designer could produce a tank with high maneuverability, armour, or a large gun, the first prioritised maneuverability, and thus had a limit on weight. These were known variously as cavalry tanks, light tanks, medium tanks and these tanks had different uses depending on the countrys tank doctrine, but were generally used to exploit holes in the enemy lines and run far into the rear areas in self-supporting armoured groups. This would disrupt enemy logistics and command-and-control, as well as delay the movement of reserves to the front and it was believed operations of this sort would undermine or completely destroy the ability for the front-line troops to continue battle. The second class prioritised armour and thus weighed more, limiting maneuverability and these were known as infantry tanks, heavy tanks, or assault tanks. They were generally designed to assault enemy lines, working in concert with front-line infantry, as these were expected to move forward at the same speed as the men, higher speeds were not required and the engine power could instead be used to carry a much greater load. Infantry tanks featured much larger amounts of armour, heavier guns, as the nature of tank warfare evolved, tanks designed for other specialised roles also saw development. This included dedicated tank destroyers, and engineer tanks such as Hobarts Funnies, Tank destroyers had varied successes, and often ended up engaging enemy infantry instead of their intended targets. German assault gun armoured vehicles like the Sturmgeschütz III were found effective in an anti-tank role, in spite of a great amount of theory and pre-war testing, the plans for armoured combat quickly proved themselves outdated. The battlefield did not bog down like it did in World War I and this was especially evident in the great sweeping battles in North Africa and the Soviet Union, where armoured forces executed drives of hundreds of miles. In these cases the problems with having two became especially evident, the tanks able to go toe-to-toe with the enemy were generally found miles to the rear. Those able to maintain the drive were lightly armoured, and proved easy prey for enemy anti-tank guns, as these evolved, the tanks own weapons had to grow larger in order to deal with enemy tanks with the same level of armour. This evolution led to the development of a more general-purpose medium tank, medium tanks formed the bulk of the tank combat forces. Generally these designs massed about 25-30 tonnes, were armed with cannons around 75 mm, notable examples include the Soviet T-34, the German Panzer IV, and the US M4 Sherman. The widespread production of designs led to most others being pushed out of service or into niche roles
4.
Metal
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A metal is a material that is typically hard, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable—that is, they can be hammered or pressed permanently out of shape without breaking or cracking—as well as fusible and ductile, about 91 of the 118 elements in the periodic table are metals, the others are nonmetals or metalloids. Some elements appear in both metallic and non-metallic forms, astrophysicists use the term metal to collectively describe all elements other than hydrogen and helium, the simplest two, in a star. The star fuses smaller atoms, mostly hydrogen and helium, to larger ones over its lifetime. In that sense, the metallicity of an object is the proportion of its matter made up of all chemical elements. Many elements and compounds that are not normally classified as metals become metallic under high pressures, the atoms of metallic substances are typically arranged in one of three common crystal structures, namely body-centered cubic, face-centered cubic, and hexagonal close-packed. In bcc, each atom is positioned at the center of a cube of eight others, in fcc and hcp, each atom is surrounded by twelve others, but the stacking of the layers differs. Some metals adopt different structures depending on the temperature, atoms of metals readily lose their outer shell electrons, resulting in a free flowing cloud of electrons within their otherwise solid arrangement. This provides the ability of metallic substances to easily transmit heat, while this flow of electrons occurs, the solid characteristic of the metal is produced by electrostatic interactions between each atom and the electron cloud. This type of bond is called a metallic bond, Metals are usually inclined to form cations through electron loss, reacting with oxygen in the air to form oxides over various timescales. Examples,4 Na + O2 →2 Na2O2 Ca + O2 →2 CaO4 Al +3 O2 →2 Al2O3, the transition metals are slower to oxidize because they form a passivating layer of oxide that protects the interior. Others, like palladium, platinum and gold, do not react with the atmosphere at all, some metals form a barrier layer of oxide on their surface which cannot be penetrated by further oxygen molecules and thus retain their shiny appearance and good conductivity for many decades. The oxides of metals are generally basic, as opposed to those of nonmetals, exceptions are largely oxides with very high oxidation states such as CrO3, Mn2O7, and OsO4, which have strictly acidic reactions. Painting, anodizing or plating metals are good ways to prevent their corrosion, however, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two form an electrochemical cell, and if the coating is less reactive than the coatee. Metals in general have high conductivity, high thermal conductivity. Typically they are malleable and ductile, deforming under stress without cleaving, in terms of optical properties, metals are shiny and lustrous. Sheets of metal beyond a few micrometres in thickness appear opaque, although most metals have higher densities than most nonmetals, there is wide variation in their densities, lithium being the least dense solid element and osmium the densest
5.
Plastic
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Plastic is a material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and can be molded into solid objects. Plastics are typically organic polymers of high mass, but they often contain other substances. They are usually synthetic, most commonly derived from petrochemicals, due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials, such as wood, stone, horn and bone, leather, paper, metal, glass, and ceramic, in most of their former uses. In developed countries, about a third of plastic is used in packaging, other uses include automobiles, furniture, and toys. In the developing world, the ratios may be different - for example, the worlds first fully synthetic plastic was bakelite, invented in New York in 1907 by Leo Baekeland who coined the term plastics. Toward the end of the century, one approach to this problem was met with wide efforts toward recycling, the word plastic is derived from the Greek πλαστικός meaning capable of being shaped or molded, from πλαστός meaning molded. The common word plastic should not be confused with the technical adjective plastic, used for insulating parts in electrical fixtures, paper laminated products, thermally insulation foams. Problems include the probability of moldings naturally being dark colors, One of the most expensive commercial polymers. It forms the basis of artistic and commercial acrylic paints when suspended in water with the use of other agents, polytetrafluoroethylene – Heat-resistant, low-friction coatings, used in things like non-stick surfaces for frying pans, plumbers tape and water slides. It is more known as Teflon. Urea-formaldehyde – One of the aminoplasts and used as an alternative to phenolics. Used as an adhesive and electrical switch housings. Early plastics were bio-derived materials such as egg and blood proteins, in 1600 BC, Mesoamericans used natural rubber for balls, bands, and figurines. Treated cattle horns were used as windows for lanterns in the Middle Ages, materials that mimicked the properties of horns were developed by treating milk-proteins with lye. In the 1800s, as industrial chemistry developed during the Industrial Revolution, the development of plastics also accelerated with Charles Goodyears discovery of vulcanization to thermoset materials derived from natural rubber. Parkesine is considered the first man-made plastic, the plastic material was patented by Alexander Parkes, In Birmingham, UK in 1856. It was unveiled at the 1862 Great International Exhibition in London, parkesine won a bronze medal at the 1862 Worlds fair in London
6.
Ceramic
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A ceramic is an inorganic, non-metallic, solid material comprising metal, non-metal or metalloid atoms primarily held in ionic and covalent bonds. This article gives an overview of ceramic materials from the point of view of materials science, the crystallinity of ceramic materials ranges from highly oriented to semi-crystalline, vitrified, and often completely amorphous. Most often, fired ceramics are either vitrified or semi-vitrified as is the case with earthenware, stoneware, varying crystallinity and electron consumption in the ionic and covalent bonds cause most ceramic materials to be good thermal and electrical insulators. With such a range of possible options for the composition/structure of a ceramic, the breadth of the subject is vast. Many composites, such as fiberglass and carbon fiber, while containing ceramic materials, are not considered to be part of the ceramic family. The earliest ceramics made by humans were pottery objects or figurines made from clay, either by itself or mixed with materials like silica, hardened, sintered. Later ceramics were glazed and fired to create smooth, colored surfaces, decreasing porosity through the use of glassy, ceramics now include domestic, industrial and building products, as well as a wide range of ceramic art. In the 20th century, new materials were developed for use in advanced ceramic engineering. The word ceramic comes from the Greek word κεραμικός, of pottery or for pottery, from κέραμος, potters clay, tile, the earliest known mention of the root ceram- is the Mycenaean Greek ke-ra-me-we, workers of ceramics, written in Linear B syllabic script. The word ceramic may be used as an adjective to describe a material, product or process, or it may be used as a noun, either singular, or, more commonly, as the plural noun ceramics. A ceramic material is an inorganic, non-metallic, often crystalline oxide, nitride or carbide material, some elements, such as carbon or silicon, may be considered ceramics. Ceramic materials are brittle, hard, strong in compression, weak in shearing and they withstand chemical erosion that occurs in other materials subjected to acidic or caustic environments. Ceramics generally can withstand high temperatures, such as temperatures that range from 1,000 °C to 1,600 °C. Glass is often not considered a ceramic because of its amorphous character. However, glassmaking involves several steps of the process and its mechanical properties are similar to ceramic materials. Traditional ceramic raw materials include minerals such as kaolinite, whereas more recent materials include aluminium oxide. The modern ceramic materials, which are classified as advanced ceramics, include silicon carbide, both are valued for their abrasion resistance, and hence find use in applications such as the wear plates of crushing equipment in mining operations. Advanced ceramics are used in the medicine, electrical, electronics industries. Crystalline ceramic materials are not amenable to a range of processing
7.
Atmosphere of Earth
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The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earths gravity. The atmosphere of Earth protects life on Earth by absorbing solar radiation, warming the surface through heat retention. By volume, dry air contains 78. 09% nitrogen,20. 95% oxygen,0. 93% argon,0. 04% carbon dioxide, and small amounts of other gases. Air also contains an amount of water vapor, on average around 1% at sea level. The atmosphere has a mass of about 5. 15×1018 kg, the atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The Kármán line, at 100 km, or 1. 57% of Earths radius, is used as the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km, several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition. The study of Earths atmosphere and its processes is called atmospheric science, early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann. The three major constituents of air, and therefore of Earths atmosphere, are nitrogen, oxygen, water vapor accounts for roughly 0. 25% of the atmosphere by mass. The remaining gases are often referred to as gases, among which are the greenhouse gases, principally carbon dioxide, methane, nitrous oxide. Filtered air includes trace amounts of other chemical compounds. Various industrial pollutants also may be present as gases or aerosols, such as chlorine, fluorine compounds, sulfur compounds such as hydrogen sulfide and sulfur dioxide may be derived from natural sources or from industrial air pollution. In general, air pressure and density decrease with altitude in the atmosphere, however, temperature has a more complicated profile with altitude, and may remain relatively constant or even increase with altitude in some regions. In this way, Earths atmosphere can be divided into five main layers, excluding the exosphere, Earth has four primary layers, which are the troposphere, stratosphere, mesosphere, and thermosphere. It extends from the exobase, which is located at the top of the thermosphere at an altitude of about 700 km above sea level, to about 10,000 km where it merges into the solar wind. This layer is composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen. The atoms and molecules are so far apart that they can travel hundreds of kilometers without colliding with one another, thus, the exosphere no longer behaves like a gas, and the particles constantly escape into space. These free-moving particles follow ballistic trajectories and may migrate in and out of the magnetosphere or the solar wind, the exosphere is located too far above Earth for any meteorological phenomena to be possible
8.
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
9.
United States Army
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The United States Armed Forces are the federal armed forces of the United States. They consist of the Army, Marine Corps, Navy, Air Force, from the time of its inception, the military played a decisive role in the history of the United States. A sense of unity and identity was forged as a result of victory in the First Barbary War. Even so, the Founders were suspicious of a permanent military force and it played an important role in the American Civil War, where leading generals on both sides were picked from members of the United States military. Not until the outbreak of World War II did a standing army become officially established. The National Security Act of 1947, adopted following World War II and during the Cold Wars onset, the U. S. military is one of the largest militaries in terms of number of personnel. It draws its personnel from a pool of paid volunteers. As of 2016, the United States spends about $580.3 billion annually to fund its military forces, put together, the United States constitutes roughly 40 percent of the worlds military expenditures. For the period 2010–14, the Stockholm International Peace Research Institute found that the United States was the worlds largest exporter of major arms, the United States was also the worlds eighth largest importer of major weapons for the same period. The history of the U. S. military dates to 1775 and these forces demobilized in 1784 after the Treaty of Paris ended the War for Independence. All three services trace their origins to the founding of the Continental Army, the Continental Navy, the United States President is the U. S. militarys commander-in-chief. Rising tensions at various times with Britain and France and the ensuing Quasi-War and War of 1812 quickened the development of the U. S. Navy, the reserve branches formed a military strategic reserve during the Cold War, to be called into service in case of war. Time magazines Mark Thompson has suggested that with the War on Terror, Command over the armed forces is established in the United States Constitution. The sole power of command is vested in the President by Article II as Commander-in-Chief, the Constitution also allows for the creation of executive Departments headed principal officers whose opinion the President can require. This allowance in the Constitution formed the basis for creation of the Department of Defense in 1947 by the National Security Act, the Defense Department is headed by the Secretary of Defense, who is a civilian and member of the Cabinet. The Defense Secretary is second in the chain of command, just below the President. Together, the President and the Secretary of Defense comprise the National Command Authority, to coordinate military strategy with political affairs, the President has a National Security Council headed by the National Security Advisor. The collective body has only power to the President
10.
Fused quartz
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Fused quartz or fused silica is glass consisting of silica in amorphous form. It differs from traditional glasses in containing no other ingredients, which are added to glass to lower the melt temperature. Fused silica, therefore, has high working and melting temperatures, the optical and thermal properties of fused quartz are superior to those of other types of glass due to its purity. For these reasons, it use in situations such as semiconductor fabrication. It has better ultraviolet transmission than most other glasses, and so is used to make lenses and its low coefficient of thermal expansion also makes it a useful material for precision mirror substrates. Fused quartz is produced by fusing high-purity silica sand, which consists of quartz crystals, quartz contains only silicon and oxygen, although commercial quartz glass often contains impurities. The most dominant impurities are aluminium and titanium, melting is effected at approximately 1650 °C using either an electrically heated furnace or a gas/oxygen-fuelled furnace. This results in a transparent glass with a purity and improved optical transmission in the deep ultraviolet. Fused quartz is normally transparent, the process of fusion results in a material that is translucent, the material can however appear opaque owing to the presence of small air bubbles trapped within the material. The water content is determined by the manufacturing process, flame fused material always has a higher water content due to the combination of the hydrocarbons and oxygen fuelling the furnace forming hydroxyl groups within the material. An IR grade material typically has an content of <10 parts per million, most of the applications of fused silica exploit its wide transparency range, which extends from the UV to the near IR. Fused silica is the key starting material for optical fiber, used for telecommunications, vacuum tubes with silica envelopes allowed for radiation cooling by incandescent anodes. Because of its strength fused silica was used in deep diving vessels such as the Bathysphere, the combination of strength, thermal stability, and UV transparency makes it an excellent substrate for projection masks for photolithography. EPROMs are recognizable by the transparent fused quartz window which sits on top of the package, through which the chip is visible. Due to the stability and composition it is used in semiconductor fabrication furnaces. Fused quartz has nearly ideal properties for fabricating first surface mirrors such as used in telescopes. The material behaves in a way and allows the optical fabricator to put a very smooth polish onto the surface and produce the desired figure with fewer testing iterations. These lenses are used for UV photography, as the glass has a lower extinction rate than lens made with more common flint or crown glass formulas
11.
Glass
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Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, for example, window panes, tableware, and optoelectronics. The most familiar, and historically the oldest, types of glass are silicate glasses based on the chemical compound silica, the primary constituent of sand. The term glass, in usage, is often used to refer only to this type of material. Many applications of silicate glasses derive from their optical transparency, giving rise to their use as window panes. Glass can be coloured by adding metallic salts, and can also be painted and printed with vitreous enamels and these qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures, because glass can be formed or moulded into any shape, it has been traditionally used for vessels, bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also used for paperweights, marbles. Some objects historically were so commonly made of glass that they are simply called by the name of the material, such as drinking glasses. Porcelains and many polymer thermoplastics familiar from everyday use are glasses and these sorts of glasses can be made of quite different kinds of materials than silica, metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications, like glass bottles or eyewear, polymer glasses are a lighter alternative than traditional glass, silica is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, fused quartz is a glass made from chemically-pure SiO2. It has excellent resistance to shock, being able to survive immersion in water while red hot. However, its high melting-temperature and viscosity make it difficult to work with, normally, other substances are added to simplify processing. One is sodium carbonate, which lowers the transition temperature. The soda makes the glass water-soluble, which is undesirable, so lime, some magnesium oxide. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass, soda-lime glasses account for about 90% of manufactured glass. Most common glass contains other ingredients to change its properties, lead glass or flint glass is more brilliant because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium also increases the refractive index, iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium oxide can be used for glass that absorbs UV wavelengths
12.
Steel
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Steel is an alloy of iron and other elements, primarily carbon, that is widely used in construction and other applications because of its high tensile strength and low cost. Steels base metal is iron, which is able to take on two forms, body centered cubic and face centered cubic, depending on its temperature. It is the interaction of those allotropes with the elements, primarily carbon. In the body-centred cubic arrangement, there is an atom in the centre of each cube. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that otherwise occur in the lattices of iron atoms. The carbon in steel alloys may contribute up to 2. 1% of its weight. Steels strength compared to pure iron is possible at the expense of irons ductility. With the invention of the Bessemer process in the mid-19th century and this was followed by Siemens-Martin process and then Gilchrist-Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron, further refinements in the process, such as basic oxygen steelmaking, largely replaced earlier methods by further lowering the cost of production and increasing the quality of the product. Today, steel is one of the most common materials in the world and it is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations, the noun steel originates from the Proto-Germanic adjective stakhlijan, which is related to stakhla. The carbon content of steel is between 0. 002% and 2. 1% by weight for plain iron–carbon alloys and these values vary depending on alloying elements such as manganese, chromium, nickel, iron, tungsten, carbon and so on. Basically, steel is an alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction, too little carbon content leaves iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy, commonly called pig iron, while iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include, manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium. Additional elements are important in steel, phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper. Alloys with a higher than 2. 1% carbon content, depending on other element content, cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties
