1.
Bronze
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These additions produce a range of alloys that may be harder than copper alone, or have other useful properties, such as stiffness, ductility, or machinability. The archeological period where bronze was the hardest metal in use is known as the Bronze Age. In the ancient Near East this began with the rise of Sumer in the 4th millennium BC, with India and China starting to use bronze around the same time, everywhere it gradually spread across regions. The Bronze Age was followed by the Iron Age starting from about 1300 BC and reaching most of Eurasia by about 500 BC, the discovery of bronze enabled people to create metal objects which were harder and more durable than previously possible. Bronze tools, weapons, armor, and building such as decorative tiles were harder and more durable than their stone. It was only later that tin was used, becoming the major ingredient of bronze in the late 3rd millennium BC. Tin bronze was superior to arsenic bronze in that the process could be more easily controlled. Also, unlike arsenic, metallic tin and fumes from tin refining are not toxic, the earliest tin-alloy bronze dates to 4500 BCE in a Vinča culture site in Pločnik. Other early examples date to the late 4th millennium BC in Africa, Susa and some ancient sites in China, Luristan, ores of copper and the far rarer tin are not often found together, so serious bronze work has always involved trade. Tin sources and trade in ancient times had a influence on the development of cultures. In Europe, a source of tin was the British deposits of ore in Cornwall. In many parts of the world, large hoards of bronze artefacts are found, suggesting that bronze also represented a store of value, in Europe, large hoards of bronze tools, typically socketed axes, are found, which mostly show no signs of wear. With Chinese ritual bronzes, which are documented in the inscriptions they carry and from other sources and these were made in enormous quantities for elite burials, and also used by the living for ritual offerings. Pure iron is soft, and the process of beating and folding sponge iron to wrought iron removes from the metal carbon. Careful control of the alloying and tempering eventually allowed for wrought iron with properties comparable to modern steel, Bronze was still used during the Iron Age, and has continued in use for many purposes to the modern day. Among other advantages, it does not rust, the weaker wrought iron was found to be sufficiently strong for many uses. Archaeologists suspect that a disruption of the tin trade precipitated the transition. The population migrations around 1200–1100 BC reduced the shipping of tin around the Mediterranean, limiting supplies, there are many different bronze alloys, but typically modern bronze is 88% copper and 12% tin
2.
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
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.
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.
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
6.
Brass
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Brass is a metal alloy made of copper and zinc, the proportions of zinc and copper can be varied to create a range of brasses with varying properties. It is an alloy, atoms of the two constituents may replace each other within the same crystal structure. By comparison, bronze is principally an alloy of copper and tin, however, bronze and brass may also include small proportions of a range of other elements including arsenic, phosphorus, aluminium, manganese, and silicon. The term is applied to a variety of brasses. Modern practice in museums and archaeology increasingly avoids both terms for objects in favour of the all-embracing copper alloy. It is also used in zippers, Brass is often used in situations in which it is important that sparks not be struck, such as in fittings and tools used near flammable or explosive materials. Brass has higher malleability than bronze or zinc, the relatively low melting point of brass and its flow characteristics make it a relatively easy material to cast. By varying the proportions of copper and zinc, the properties of the brass can be changed, allowing hard, the density of brass is 8.4 to 8.73 grams per cubic centimetre. Today, almost 90% of all alloys are recycled. Because brass is not ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a powerful magnet, Brass scrap is collected and transported to the foundry where it is melted and recast into billets. Billets are heated and extruded into the form and size. The general softness of brass means that it can often be machined without the use of cutting fluid, aluminium makes brass stronger and more corrosion-resistant. Aluminium also causes a highly beneficial hard layer of oxide to be formed on the surface that is thin, transparent. Tin has an effect and finds its use especially in seawater applications. Combinations of iron, aluminium, silicon and manganese make brass wear and tear resistant, to enhance the machinability of brass, lead is often added in concentrations of around 2%. Since lead has a melting point than the other constituents of the brass. The pattern the globules form on the surface of the brass increases the available surface area which in turn affects the degree of leaching. In addition, cutting operations can smear the lead globules over the surface and these effects can lead to significant lead leaching from brasses of comparatively low lead content
7.
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
8.
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
9.
Manganese
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Manganese is a chemical element with symbol Mn and atomic number 25. It is not found as an element in nature, it is often found in minerals in combination with iron. Manganese is a metal with important industrial metal alloy uses, particularly in stainless steels, by the mid-18th century, Swedish chemist Carl Wilhelm Scheele had used pyrolusite to produce chlorine. Scheele and others were aware that pyrolusite contained a new element, johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, which he did by reducing the dioxide with carbon. Manganese phosphating is used for rust and corrosion prevention on steel, ionized manganese is used industrially as pigments of various colors, which depend on the oxidation state of the ions. The permanganates of alkali and alkaline earth metals are powerful oxidizers, Manganese dioxide is used as the cathode material in zinc-carbon and alkaline batteries. In biology, manganese ions function as cofactors for a variety of enzymes with many functions. Manganese enzymes are essential in detoxification of superoxide free radicals in organisms that must deal with elemental oxygen. Manganese also functions in the complex of photosynthetic plants. The element is a trace mineral for all known living organisms but is a neurotoxin. In larger amounts, and apparently with far greater effectiveness through inhalation, Manganese is a silvery-gray metal that resembles iron. It is hard and very brittle, difficult to fuse, Manganese metal and its common ions are paramagnetic. Manganese tarnishes slowly in air and oxidizes like iron in water containing dissolved oxygen, naturally occurring manganese is composed of one stable isotope, 55Mn. Eighteen radioisotopes have been isolated and described, the most stable being 53Mn with a half-life of 3.7 million years, 54Mn with a half-life of 312.3 days, and 52Mn with a half-life of 5.591 days. All of the radioactive isotopes have half-lives of less than three hours, and the majority of less than one minute. Manganese also has three meta states, Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before the supernova explosion. 53Mn decays to 53Cr with a half-life of 3.7 million years, because of its relatively short half-life, 53Mn is relatively rare, produced by cosmic rays impact on iron. Manganese isotopic contents are combined with chromium isotopic contents and have found application in isotope geology
10.
Silicon
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Silicon is a chemical element with symbol Si and atomic number 14. A hard and brittle crystalline solid with a metallic luster. It is a member of group 14 in the table, along with carbon above it and germanium, tin, lead. It is not very reactive, although more reactive than germanium, Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earths crust. It is most widely distributed in dusts, sands, planetoids, over 90% of the Earths crust is composed of silicate minerals, making silicon the second most abundant element in the Earths crust after oxygen. Most silicon is used commercially without being separated, and often with little processing of the natural minerals, such use includes industrial construction with clays, silica sand, and stone. Silicate is used in Portland cement for mortar and stucco, and mixed with sand and gravel to make concrete for walkways, foundations. Silicates are used in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass, Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Elemental silicon also has an impact on the modern world economy. Most free silicon is used in the refining, aluminium-casting. Silicon is the basis of the widely used synthetic polymers called silicones, Silicon is an essential element in biology, although only tiny traces are required by animals. However, various sea sponges and microorganisms, such as diatoms and radiolaria, silica is deposited in many plant tissues, such as in the bark and wood of Chrysobalanaceae and the silica cells and silicified trichomes of Cannabis sativa, horsetails and many grasses. Silicon is a solid at room temperature, with a point of 1,414 °C. Like water, it has a density in a liquid state than in a solid state and it expands when it freezes. With a relatively high conductivity of 149 W·m−1·K−1, silicon conducts heat well. In its crystalline form, pure silicon has a gray color, like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a cubic crystal structure with a lattice spacing of 0.5430710 nm. The outer electron orbital of silicon, like that of carbon, has four valence electrons, the 1s, 2s, 2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six
11.
Zinc
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Zinc is a chemical element with the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table, in some respects zinc is chemically similar to magnesium, both elements exhibit only one normal oxidation state, and the Zn2+ and Mg2+ ions are of similar size. Zinc is the 24th most abundant element in Earths crust and has five stable isotopes, the most common zinc ore is sphalerite, a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States, Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity. Zinc metal was not produced on a large scale until the 12th century in India and was unknown to Europe until the end of the 16th century, the mines of Rajasthan have given definite evidence of zinc production going back to the 6th century BC. To date, the oldest evidence of pure zinc comes from Zawar, in Rajasthan, alchemists burned zinc in air to form what they called philosophers wool or white snow. The element was named by the alchemist Paracelsus after the German word Zinke. German chemist Andreas Sigismund Marggraf is credited with discovering pure metallic zinc in 1746, work by Luigi Galvani and Alessandro Volta uncovered the electrochemical properties of zinc by 1800. Corrosion-resistant zinc plating of iron is the application for zinc. Other applications are in batteries, small non-structural castings. A variety of compounds are commonly used, such as zinc carbonate and zinc gluconate, zinc chloride, zinc pyrithione, zinc sulfide. Zinc is an essential mineral perceived by the public today as being of exceptional biologic and public health importance, Zinc deficiency affects about two billion people in the developing world and is associated with many diseases. In children, deficiency causes growth retardation, delayed sexual maturation, infection susceptibility, enzymes with a zinc atom in the reactive center are widespread in biochemistry, such as alcohol dehydrogenase in humans. Consumption of excess zinc can cause ataxia, lethargy and copper deficiency, Zinc is a bluish-white, lustrous, diamagnetic metal, though most common commercial grades of the metal have a dull finish.6 pm. The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C, above 210 °C, the metal becomes brittle again and can be pulverized by beating. Zinc is a conductor of electricity. For a metal, zinc has relatively low melting and boiling points, the melting point is the lowest of all the transition metals aside from mercury and cadmium. Many alloys contain zinc, including brass, Other metals long known to form binary alloys with zinc are aluminium, antimony, bismuth, gold, iron, lead, mercury, silver, tin, magnesium, cobalt, nickel, tellurium, and sodium
12.
Arsenic
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Arsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in minerals, usually in combination with sulfur and metals. It has various allotropes, but only the form is important to industry. The primary use of arsenic is in alloys of lead. Arsenic is a common dopant in semiconductor electronic devices. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, a few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic are a dietary element in rats, hamsters, goats, chickens. However, arsenic poisoning occurs in multicellular life if quantities are larger than needed, Arsenic contamination of groundwater is a problem that affects millions of people across the world. The three most common allotropes are metallic gray, yellow, and black arsenic, with gray being the most common. Gray arsenic adopts a structure consisting of many interlocked, ruffled, six-membered rings. Because of weak bonding between the layers, gray arsenic is brittle and has a relatively low Mohs hardness of 3.5. Nearest and next-nearest neighbors form an octahedral complex, with the three atoms in the same double-layer being slightly closer than the three atoms in the next. This relatively close packing leads to a density of 5.73 g/cm3. Gray arsenic is a semimetal, but becomes a semiconductor with a bandgap of 1. 2–1.4 eV if amorphized, gray arsenic is also the most stable form. Yellow arsenic is soft and waxy, and somewhat similar to tetraphosphorus, both have four atoms arranged in a tetrahedral structure in which each atom is bound to each of the other three atoms by a single bond. This unstable allotrope, being molecular, is the most volatile, least dense, solid yellow arsenic is produced by rapid cooling of arsenic vapor, As 4. It is rapidly transformed into gray arsenic by light, the yellow form has a density of 1.97 g/cm3. Black arsenic is similar in structure to red phosphorus, black arsenic can also be formed by cooling vapor at around 100–220 °C
13.
Corrosion
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Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the dedicated to controlling and stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfur, rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide or salt of the original metal, corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids, many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the surface, such as passivation and chromate conversion. However, some corrosion mechanisms are less visible and less predictable, in a galvanic couple, the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate, what type of metal to use is readily determined by following the galvanic series. For example, zinc is used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the industry and also anywhere water contacts pipes or metal structures. Factors such as size of anode, types of metal. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials, galvanic corrosion is often prevented by the use of sacrificial anodes. In any given environment, one metal will be more noble or more active than others. Two metals in electrical contact share the same electrons, so that the tug-of-war at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a series and is useful in predicting and understanding corrosion
14.
Tarnish
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Tarnish is a thin layer of corrosion that forms over copper, brass, silver, aluminum, magnesium and other similar metals as their outermost layer undergoes a chemical reaction. Tarnish does not always result from the effects of oxygen in the air. For example, silver needs hydrogen sulfide to tarnish, although it may tarnish with oxygen over time and it often appears as a dull, gray or black film or coating over metal. Tarnish is a phenomenon that is self-limiting, unlike rust. Only the top few layers of the metal react, and the layer of tarnish seals, tarnish actually preserves the underlying metal in outdoor use, and in this form is called patina. The formation of patina is necessary in such as copper roofing, and outdoor copper, bronze. Patina is the given to tarnish on copper based metals. Tarnish is a product of a reaction between a metal and a nonmetal compound, especially oxygen and sulfur dioxide. It is usually a metal oxide, the product of oxidation, sometimes it is a metal sulfide. The metal oxide sometimes reacts with water to make the hydroxide, using a thin coat of polish can prevent tarnish from forming over these metals. Tarnish can be removed by using wool, sandpaper, emery paper. Gentler abrasives, like calcium carbonate, are used by museums to clean tarnished silver as they cannot damage or scratch the silver. Herman Silver Restoration, Conservation & Preservation – the most thoroughly researched and practiced silver care information on the Web, common causes of gold tarnishing & prevention
15.
Redox
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Redox is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a process and a complementary oxidation process, two key concepts involved with electron transfer processes. Redox reactions include all chemical reactions in which atoms have their oxidation state changed, in general, the chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in terms, Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom. Reduction is the gain of electrons or a decrease in state by a molecule, atom. As an example, during the combustion of wood, oxygen from the air is reduced, the reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. Redox is a portmanteau of reduction and oxidation, the word oxidation originally implied reaction with oxygen to form an oxide, since dioxygen was historically the first recognized oxidizing agent. Later, the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions, ultimately, the meaning was generalized to include all processes involving loss of electrons. The word reduction originally referred to the loss in weight upon heating a metallic ore such as an oxide to extract the metal. In other words, ore was reduced to metal, antoine Lavoisier showed that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the atom gains electrons in this process. The meaning of reduction then became generalized to all processes involving gain of electrons. Even though reduction seems counter-intuitive when speaking of the gain of electrons, it help to think of reduction as the loss of oxygen. Since electrons are charged, it is also helpful to think of this as reduction in electrical charge. The electrochemist John Bockris has used the words electronation and deelectronation to describe reduction and oxidation processes respectively when they occur at electrodes and these words are analogous to protonation and deprotonation, but they have not been widely adopted by chemists. The term hydrogenation could be used instead of reduction, since hydrogen is the agent in a large number of reactions. But, unlike oxidation, which has been generalized beyond its root element, the word redox was first used in 1928. The processes of oxidation and reduction occur simultaneously and cannot happen independently of one another, the oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction
16.
Sulfur
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Sulfur or sulphur is a chemical element with symbol S and atomic number 16. It is abundant, multivalent, and nonmetallic, under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a yellow crystalline solid at room temperature. Chemically, sulfur reacts with all elements except for gold, platinum, iridium, tellurium, though sometimes found in pure, native form, sulfur usually occurs as sulfide and sulfate minerals. Being abundant in native form, sulfur was known in ancient times, being mentioned for its uses in ancient India, ancient Greece, China, in the Bible, sulfur is called brimstone. Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from natural gas, the greatest commercial use of the element is the production of sulfuric acid for sulfate and phosphate fertilizers, and other chemical processes. The element sulfur is used in matches, insecticides, and fungicides, many sulfur compounds are odoriferous, and the smells of odorized natural gas, skunk scent, grapefruit, and garlic are due to organosulfur compounds. Hydrogen sulfide gives the characteristic odor to rotting eggs and other biological processes, sulfur is an essential element for all life, but almost always in the form of organosulfur compounds or metal sulfides. Three amino acids and two vitamins are organosulfur compounds, many cofactors also contain sulfur including glutathione and thioredoxin and iron–sulfur proteins. Disulfides, S–S bonds, confer mechanical strength and insolubility of the keratin, found in outer skin, hair. Sulfur is one of the chemical elements needed for biochemical functioning and is an elemental macronutrient for all organisms. Sulfur is derived from the Latin word sulpur, which was Hellenized to sulphur, the spelling sulfur appears toward the end of the Classical period. In 12th-century Anglo-French, it was sulfre, in the 14th century the Latin ph was restored, for sulphre, the parallel f~ph spellings continued in Britain until the 19th century, when the word was standardized as sulphur. Sulfur was the form chosen in the United States, whereas Canada uses both, the IUPAC adopted the spelling sulfur in 1990, as did the Nomenclature Committee of the Royal Society of Chemistry in 1992, restoring the spelling sulfur to Britain. Sulfur forms polyatomic molecules with different chemical formulas, the best-known allotrope being octasulfur, cyclo-S8. The point group of cyclo-S8 is D4d and its dipole moment is 0 D. Octasulfur is a soft, bright-yellow solid that is odorless and it melts at 115.21 °C, boils at 444.6 °C and sublimes easily. At 95.2 °C, below its melting temperature, cyclo-octasulfur changes from α-octasulfur to the β-polymorph, the structure of the S8 ring is virtually unchanged by this phase change, which affects the intermolecular interactions. At higher temperatures, the viscosity decreases as depolymerization occurs, molten sulfur assumes a dark red color above 200 °C
17.
Exhaust gas
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Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline, petrol, biodiesel blends, diesel fuel, fuel oil, or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack and it often disperses downwind in a pattern called an exhaust plume. A2013 study by MIT indicates that 53,000 early deaths occur per year in the United States alone because of vehicle emissions. According to another study from the university, traffic fumes alone cause the death of 5,000 people every year just in the United Kingdom. The largest part of most combustion gas is nitrogen, water vapor, and carbon dioxide, Exhaust gas temperature is important to the functioning of the catalytic converter of an internal combustion engine. It may be measured by an exhaust gas temperature gauge, EGT is also a measure of engine health in gas-turbine engines. During the first two minutes after starting the engine of a car that has not been operated for several hours, inefficient catalytic converter under cold conditions, Catalytic converters are very inefficient until up to their operating temperature. This time has much reduced by moving the converter closer to the exhaust manifold. The small converter handles the start-up emissions, which enough time for the larger main converter to heat up. Further improvements can be realised in many ways, including heating, thermal battery, chemical reaction preheating, flame heating. The requirements were phased in beginning with 2004 vehicles and all new cars, in spark-ignition engines the gases resulting from combustion of the fuel and air mix are called exhaust gases. The composition varies from petrol to diesel engines, but is around these levels, The 10% oxygen for diesel is likely if the engine was idling and it is much less if the engine is running under load. People exposed to it should wear a gas mask, in aircraft gas turbine engines, exhaust gas temperature is a primary measure of engine health. Typically the EGT is compared with an engine power indication called engine pressure ratio. For example, at full power EPR there will be a maximum permitted EGT limit, once an engine reaches a stage in its life where it reaches this EGT limit, the engine will require specific maintenance in order to rectify the problem. The amount the EGT is below the EGT limit is called EGT margin, the EGT margin of an engine will be greatest when the engine is new, or has been overhauled. For most airlines, this information is monitored remotely by the airline maintenance department by means of ACARS. In jet engines and rocket engines, exhaust from propelling nozzles which in some applications shows shock diamonds, Flue gas Flue gas emissions from fossil fuel combustion In steam engine terminology the exhaust is steam that is now so low in pressure that it can no longer do useful work
18.
Combustion
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Combustion in a fire produces a flame, and the heat produced can make combustion self-sustaining. Combustion is often a sequence of elementary radical reactions. Solid fuels, such as wood, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the required to produce more of them. Combustion is often hot enough that light in the form of either glowing or a flame is produced, a simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. The bond energies in the play only a minor role, since they are similar to those in the combustion products. The heat of combustion is approximately -418 kJ per mole of O2 used up in the combustion reaction, uncatalyzed combustion in air requires fairly high temperatures. Complete combustion is stoichiometric with respect to the fuel, where there is no remaining fuel, thermodynamically, the chemical equilibrium of combustion in air is overwhelmingly on the side of the products. Thus, the smoke is usually toxic and contains unburned or partially oxidized products. Since combustion is rarely clean, flue gas cleaning or catalytic converters may be required by law, fires occur naturally, ignited by lightning strikes or by volcanic products. Combustion was the first controlled chemical reaction discovered by humans, in the form of campfires and bonfires, usually, the fuel is carbon, hydrocarbons or more complicated mixtures such as wood that contains partially oxidized hydrocarbons. Combustion is also currently the only used to power rockets. Combustion is also used to destroy waste, both nonhazardous and hazardous, oxidants for combustion have high oxidation potential and include atmospheric or pure oxygen, chlorine, fluorine, chlorine trifluoride, nitrous oxide and nitric acid. For instance, hydrogen burns in chlorine to form hydrogen chloride with the liberation of heat, although usually not catalyzed, combustion can be catalyzed by platinum or vanadium, as in the contact process. In complete combustion, the reactant burns in oxygen, producing a number of products. When a hydrocarbon burns in oxygen, the reaction will yield carbon dioxide. When elements are burned, the products are primarily the most common oxides, carbon will yield carbon dioxide, sulfur will yield sulfur dioxide, and iron will yield iron oxide. Nitrogen is not considered to be a combustible substance when oxygen is the oxidant, Combustion is not necessarily favorable to the maximum degree of oxidation, and it can be temperature-dependent. For example, sulfur trioxide is not produced quantitatively by the combustion of sulfur, NOx species appear in significant amounts above about 2,800 °F, and more is produced at higher temperatures
19.
Seawater
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Seawater, or salt water, is water from a sea or ocean. On average, seawater in the oceans has a salinity of about 3. 5% This means that every kilogram of seawater has approximately 35 grams of dissolved salts. Average density at the surface is 1.025 kg/l, seawater is denser than both fresh water and pure water because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases, at typical salinity, it freezes at about −2 °C. The coldest seawater ever recorded was in 2010, in a stream under an Antarctic glacier, seawater pH is typically limited to a range between 7.5 and 8.4. However, there is no universally accepted reference pH-scale for seawater, although the vast majority of seawater has a salinity of between 31 g/kg and 38 g/kg, seawater is not uniformly saline throughout the world. Where mixing occurs with fresh water runoff from river mouths, near melting glaciers or vast amounts precipitation, the most saline open sea is the Red Sea, where high rates of evaporation, low precipitation and low river run-off, and confined circulation result in unusually salty water. The salinity in isolated bodies of water can be considerably greater still, historically, several salinity scales were used to approximate the absolute salinity of seawater. A popular scale was the Practical Salinity Scale where salinity was measured in practical salinity units, the current standard for salinity is the Reference Salinity scale with the salinity expressed in units of g/kg. The density of surface seawater ranges from about 1020 to 1029 kg/m3, depending on the temperature, at a temperature of 25 °C, salinity of 35 g/kg and 1 atm pressure, the density of seawater is 1023.6 kg/m3. Deep in the ocean, under pressure, seawater can reach a density of 1050 kg/m3 or higher. The density of seawater also changes with salinity, brines generated by seawater desalination plants can have salinities up to 120 g/kg. The density of typical seawater brine of 120 g/kg salinity at 25 °C, seawater pH is limited to the range 7.5 to 8.4. The speed of sound in seawater is about 1,500 m/s, and varies with temperature, salinity. The thermal conductivity of seawater is 0.6 W/mK at 25 °C, the thermal conductivity decreases with increasing salinity and increases with increasing temperature. Seawater contains more dissolved ions than all types of freshwater, however, the ratios of solutes differ dramatically. Bicarbonate ions also constitute 48% of river water solutes but only 0. 14% of all seawater ions, differences like these are due to the varying residence times of seawater solutes, sodium and chlorine have very long residence times, while calcium tends to precipitate much more quickly. The most abundant dissolved ions in seawater are sodium, chloride, magnesium, sulfate and its osmolarity is about 1000 mOsm/l
20.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
21.
Aluminium oxide
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Aluminium oxide or aluminum oxide is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. It is the most commonly occurring of several aluminium oxides, and it is commonly called alumina, and may also be called aloxide, aloxite, or alundum depending on particular forms or applications. It occurs naturally in its crystalline polymorphic phase α-Al2O3 as the mineral corundum, varieties of form the precious gemstones ruby. Al2O3 is significant in its use to produce metal, as an abrasive owing to its hardness. Corundum is the most common naturally occurring form of aluminium oxide. Rubies and sapphires are gem-quality forms of corundum, which owe their characteristic colors to trace impurities, rubies are given their characteristic deep red color and their laser qualities by traces of chromium. Sapphires come in different colors given by various other impurities, such as iron, Al2O3 is an electrical insulator but has a relatively high thermal conductivity for a ceramic material. Aluminium oxide is insoluble in water, in its most commonly occurring crystalline form, called corundum or α-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools. Aluminium oxide is responsible for the resistance of aluminium to weathering. Metallic aluminium is very reactive with oxygen, and a thin passivation layer of aluminium oxide forms on any exposed aluminium surface. This layer protects the metal from further oxidation, the thickness and properties of this oxide layer can be enhanced using a process called anodising. A number of alloys, such as bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. Aluminium oxide was taken off the United States Environmental Protection Agencys chemicals lists in 1988, aluminium oxide is on EPAs Toxics Release Inventory list if it is a fibrous form. Al2O3 +6 HF →2 AlF3 +3 H2O Al2O3 +2 NaOH +3 H2O →2 NaAl4 The most common form of aluminium oxide is known as corundum. The oxygen ions form a hexagonal close-packed structure with aluminium ions filling two-thirds of the octahedral interstices. In terms of its crystallography, corundum adopts a trigonal Bravais lattice with a group of R-3c. The primitive cell contains two units of aluminium oxide. Each has a crystal structure and properties
22.
Tin
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Tin is a chemical element with symbol Sn and atomic number 50. It is a metal in group 14 of the periodic table. It is obtained chiefly from the mineral cassiterite, which contains tin dioxide, Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, and has two main oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, metallic tin is not easily oxidized in air. The first alloy used on a scale was bronze, made of tin and copper. After 600 BC, pure metallic tin was produced, pewter, which is an alloy of 85–90% tin with the remainder commonly consisting of copper, antimony, and lead, was used for flatware from the Bronze Age until the 20th century. In modern times, tin is used in alloys, most notably tin/lead soft solders. Another large application for tin is corrosion-resistant tin plating of steel, inorganic tin compounds are rather non-toxic. Because of its low toxicity, tin-plated metal was used for packaging as tin cans. However, overexposure to tin may cause problems with metabolizing essential trace elements such as copper and zinc, Tin is a soft, malleable, ductile and highly crystalline silvery-white metal. When a bar of tin is bent, a sound known as the tin cry can be heard from the twinning of the crystals. Tin melts at the low temperature of about 232 °C, the lowest in group 14, the melting point is further lowered to 177.3 °C for 11 nm particles. β-tin, which is stable at and above room temperature, is malleable, in contrast, α-tin, which is stable below 13.2 °C, is brittle. α-tin has a cubic crystal structure, similar to diamond. α-tin has no properties at all because its atoms form a covalent structure in which electrons cannot move freely. It is a dull-gray powdery material with no common uses other than a few specialized semiconductor applications and these two allotropes, α-tin and β-tin, are more commonly known as gray tin and white tin, respectively. Two more allotropes, γ and σ, exist at temperatures above 161 °C, in cold conditions, β-tin tends to transform spontaneously into α-tin, a phenomenon known as tin pest. Commercial grades of tin resist transformation because of the effect of the small amounts of bismuth, antimony, lead
23.
Algae
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Algae is an informal term for a large, diverse group of photosynthetic organisms which are not necessarily closely related, and is thus polyphyletic. Included organisms range from unicellular genera, such as Chlorella and the diatoms, to forms, such as the giant kelp. Most are aquatic and autotrophic and lack many of the cell and tissue types, such as stomata, xylem, and phloem. No definition of algae is generally accepted, one definition is that algae have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells. Some authors exclude all prokaryotes thus do not consider cyanobacteria as algae, Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria, diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, and the roots, leaves, and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago, the singular alga is the Latin word for seaweed and retains that meaning in English. Although some speculate that it is related to Latin algēre, be cold, a more likely source is alliga, binding, entwining. The Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it, the Latinization, fūcus, meant primarily the cosmetic rouge. It could be any color, black, red, green, accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name Fucus appears in a number of taxa, most algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and presumably represent reduced endosymbiotic cyanobacteria, however, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three groups of algae. Their lineage relationships are shown in the figure in the upper right, many of these groups contain some members that are no longer photosynthetic
24.
Lichen
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A lichen is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi in a symbiotic relationship. The combined lichen has properties different from those of its component organisms, Lichens come in many colours, sizes, and forms. The properties are sometimes plant-like, but lichens are not plants, Lichens may have tiny, leafless branches, flat leaf-like structures, flakes that lie on the surface like peeling paint, or other growth forms. A macrolichen is a lichen that is either bush-like or leafy, here, macro and micro do not refer to size, but to the growth form. Common names for lichens may contain the word moss, and lichens may superficially look like and grow with mosses, Lichens do not have roots that absorb water and nutrients as plants do, but like plants, they produce their own food by photosynthesis. When they grow on plants, they do not live as parasites, Lichens occur from sea level to high alpine elevations, in many environmental conditions, and can grow on almost any surface. Lichens are abundant growing on bark, leaves, mosses, on other lichens and they grow on rock, walls, gravestones, roofs, exposed soil surfaces, and in the soil as part of a biological soil crust. Different kinds of lichens have adapted to survive in some of the most extreme environments on Earth, arctic tundra, hot dry deserts, rocky coasts and they can even live inside solid rock, growing between the grains. It is estimated that 6% of Earths land surface is covered by lichen, there are about 20,000 known species of lichens. Some lichens have lost the ability to reproduce sexually, yet continue to speciate, Lichens may be long-lived, with some considered to be among the oldest living things. They are among the first living things to grow on fresh rock exposed after an event such as a landslide, the long life-span and slow and regular growth rate of some lichens can be used to date events. In American English, lichen is pronounced the same as the verb liken, in British English, both this pronunciation and one rhyming with kitchen /ˈlɪtʃən/) are used. Lichens grow in a range of shapes and forms. The shape of a lichen is determined by the organization of the fungal filaments. The nonreproductive tissues, or vegetative body parts, is called the thallus, Lichens are grouped by thallus type, since the thallus is usually the most visually prominent part of the lichen. Thallus growth forms typically correspond to a few basic internal structure types, Common names for lichens often come from a growth form or color that is typical of a lichen genus. When a crustose lichen gets old, the center may start to crack up like old-dried paint, old-broken asphalt paving and this is called being rimose or areolate, and the island pieces separated by the cracks are called areolas. The areolas appear separated, but are connected by an underlying prothallus or hypothallus, when a crustose lichen grows from a center and appears to radiate out, it is called crustose placodioid
25.
Barnacle
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A barnacle is a type of arthropod constituting the infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters and they are sessile suspension feeders, and have two nektonic larval stages. Around 1,220 barnacle species are currently known, the name Cirripedia is Latin, meaning curl-footed. Barnacles are encrusters, attaching themselves permanently to a hard substrate, the most common, acorn barnacles, are sessile, growing their shells directly onto the substrate. The order Pedunculata attach themselves by means of a stalk, free-living barnacles are attached to the substratum by cement glands that form the base of the first pair of antennae, in effect, the animal is fixed upside down by means of its forehead. In some barnacles, the cement glands are fixed to a long, muscular stalk, a ring of plates surrounds the body, homologous with the carapace of other crustaceans. These consist of the rostrum, two plates, two carinolaterals, and a carina. In sessile barnacles, the apex of the ring of plates is covered by an operculum, the plates are held together by various means, depending on species, in some cases being solidly fused. Inside the carapace, the lies on its back, with its limbs projecting upwards. Segmentation is usually indistinct, and the body is more or less divided between the head and thorax, with little, if any, abdomen. Adult barnacles have few appendages on their heads, with only a single, vestigial pair of antennae, attached to the cement gland. The six pairs of limbs are referred to as cirri. Barnacles have no heart, although a sinus close to the esophagus performs similar function. The blood vascular system is minimal, similarly, they have no gills, absorbing oxygen from the water through their limbs and the inner membrane of their carapaces. The excretory organs of barnacles are maxillary glands, the main sense of barnacles appears to be touch, with the hairs on the limbs being especially sensitive. The adult also has an eye, although this is probably only capable of sensing the difference between light and dark. This eye is derived from the naupliar eye. Barnacles have two larval stages, the nauplius and the cyprid, before developing into a mature adult
26.
Mussel
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Mussel is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, a few species have colonised hydrothermal vents associated with deep ocean ridges. In most marine mussels the shell is longer than it is wide, the external colour of the shell is often dark blue, blackish, or brown, while the interior is silvery and somewhat nacreous. The common name mussel is also used for many freshwater bivalves, freshwater mussel species inhabit lakes, ponds, rivers, creeks, canals, and they are classified in a different subclass of bivalves, despite some very superficial similarities in appearance. They are classified with the Heterodonta, the group which includes most of the bivalves commonly referred to as clams. The mussels external shell is composed of two hinged halves or valves, the valves are joined together on the outside by a ligament, and are closed when necessary by strong internal muscles. Mussel shells carry out a variety of functions, including support for soft tissues, protection from predators, the periostracum is composed of a protein called conchin, and its function is to protect the prismatic layer from abrasion and dissolution by acids. Like most bivalves, mussels have an organ called a foot. In freshwater mussels, the foot is large, muscular, and it is used to pull the animal through the substrate in which it lies partially buried. It does this by repeatedly advancing the foot through the substrate, expanding the end so it serves as an anchor and it also serves as a fleshy anchor when the animal is stationary. In marine mussels, the foot is smaller, tongue-like in shape, in this pit, a viscous secretion is exuded, entering the groove and hardening gradually upon contact with sea water. This forms extremely tough, strong, elastic, byssal threads that secure the mussel to its substrate allowing it to remain sessile in areas of high flow, in cooking, the byssus of the mussel is known as the beard and is removed before the mussels are prepared. Both marine and freshwater mussels are filter feeders, they feed on plankton, a mussel draws water in through its incurrent siphon. The water is brought into the branchial chamber by the actions of the cilia located on the gills for ciliary-mucus feeding. The wastewater exits through the excurrent siphon, the labial palps finally funnel the food into the mouth, where digestion begins. Marine mussels are usually found clumping together on wave-washed rocks, each attached to the rock by its byssus, the clumping habit helps hold the mussels firm against the force of the waves. At low tide mussels in the middle of a clump will undergo less water loss because of capture by the other mussels. Both marine and freshwater mussels are gonochoristic, with male and female individuals
27.
Stainless steel
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In metallurgy, stainless steel, also known as inox steel or inox from French inoxydable, is a steel alloy with a minimum of 10. 5% chromium content by mass. Stainless steel is notable for its resistance, and it is widely used for food handling. Stainless steel does not readily corrode, rust or stain with water as ordinary steel does, however, it is not fully stain-proof in low-oxygen, high-salinity, or poor air-circulation environments. There are various grades and surface finishes of stainless steel to suit the environment the alloy must endure, Stainless steel is used where both the properties of steel and corrosion resistance are required. Stainless steel differs from carbon steel by the amount of chromium present, unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film is active and accelerates corrosion by making it easier for more iron oxide to form, since iron oxide has lower density than steel, the film expands and tends to flake and fall away. In comparison, stainless steels contain sufficient chromium to undergo passivation and this layer prevents further corrosion by blocking oxygen diffusion to the steel surface and stops corrosion from spreading into the bulk of the metal. Passivation occurs only if the proportion of chromium is high enough, Stainless steel’s resistance to corrosion and staining, low maintenance, and familiar lustre make it an ideal material for many applications. Storage tanks and tankers used to transport orange juice and other food are made of stainless steel. This also influences its use in kitchens and food processing plants, as it can be steam-cleaned and sterilized. High oxidation resistance in air at ambient temperature is achieved with addition of a minimum of 13% chromium. The chromium forms a layer of chromium oxide when exposed to oxygen. The layer is too thin to be visible, and the metal remains lustrous, the layer is impervious to water and air, protecting the metal beneath, and this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, corrosion resistance can be adversely affected if the component is used in a non-oxygenated environment, a typical example being underwater keel bolts buried in timber. When stainless steel parts such as nuts and bolts are forced together, when forcibly disassembled, the welded material may be torn and pitted, a destructive effect known as galling. Galling can be avoided by the use of materials for the parts forced together, for example bronze and stainless steel. However, two different alloys electrically connected in a humid, even mildly acidic environment may act as a voltaic pile, nitronic alloys, made by selective alloying with manganese and nitrogen, may have a reduced tendency to gall. Additionally, threaded joints may be lubricated to provide a film between the two parts and prevent galling, low-temperature carburizing is another option that virtually eliminates galling and allows the use of similar materials without the risk of corrosion and the need for lubrication
28.
Plain bearing
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A plain bearing is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore, the journal slides over the bearing surface, the simplest example of a plain bearing is a shaft rotating in a hole. A simple linear bearing can be a pair of flat surfaces designed to allow motion, e. g. a drawer, plain bearings, in general, are the least expensive type of bearing. They are also compact and lightweight, and they have a high load-carrying capacity, the design of a plain bearing depends on the type of motion the bearing must provide. The three types of motions possible are, Journal bearing, This is the most common type of plain bearing, it is simply a shaft rotating in a bearing. In locomotive and railroad car applications a journal bearing specifically referred to the plain bearing once used at the ends of the axles of railroad wheel sets, axlebox bearings today are no longer plain bearings but rather are rolling-element bearings. Linear bearing, This bearing provides linear motion, it may take the form of a circular bearing, thrust bearing, A thrust bearing provides a bearing surface for forces acting axial to the shaft. One example is a propeller shaft, integral plain bearings are built into the object of use as a hole prepared in the bearing surface. Industrial integral bearings are made from cast iron or babbitt. Integral bearings are not as common because bushings are easier to accommodate, depending on the material, an integral bearing may be less expensive but it cannot be replaced. If an integral bearing wears out, the item may be replaced or reworked to accept a bushing, integral bearings were very common in 19th-century machinery, but became progressively less common as interchangeable manufacture became popular. For example, a common integral plain bearing is the hinge, a bushing, also known as a bush, is an independent plain bearing that is inserted into a housing to provide a bearing surface for rotary applications, this is the most common form of a plain bearing. Common designs include solid, split, and clenched bushings, a sleeve, split, or clenched bushing is only a sleeve of material with an inner diameter, outer diameter, and length. A flanged bushing is a sleeve bushing with a flange at one end extending outward from the OD. The flange is used to locate the bushing when it is installed or to provide a thrust bearing surface. Sleeve bearings of inch dimensions are almost exclusively dimensioned using the SAE numbering system. The numbering system uses the format -XXYY-ZZ, where XX is the ID in sixteenths of an inch, YY is the OD in sixteenths of an inch, a linear bushing is not usually pressed into a housing, but rather secured with a radial feature. Two such examples include two retaining rings, or a ring that is molded onto the OD of the bushing that matches with a groove in the housing
29.
Landing gear
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Landing gear is the undercarriage of an aircraft or spacecraft and may be used for either takeoff or landing. For aircraft it is generally both, for aircraft, the landing gear supports the craft when it is not flying, allowing it to take off, land, and taxi without damage. Faster aircraft usually have retractable undercarriages, which folds away during flight to reduce air resistance or drag, for launch vehicles and spacecraft landers, the landing gear is typically designed to support the vehicle only post-flight, and are typically not used for takeoff or surface movement. Aircraft landing gear usually includes wheels equipped with shock absorbers, or more advanced air/oil oleo struts, for runway. Some aircraft are equipped with skis for snow or floats for water, the undercarriage is a relatively heavy part of the vehicle, it can be as much as 7% of the takeoff weight, but more typically is 4–5%. The taildragger arrangement was common during the early era, as it allows more room for propeller clearance. Most modern aircraft have tricycle undercarriages, taildraggers are considered harder to land and take off, and usually require special pilot training. Sometimes a small wheel or skid is added to aircraft with tricycle undercarriage. Concorde, for instance, had a tail bumper wheel. Both Boeinga largest WW II bomber, the B-29 Superfortress and the 1960s-introduction Boeing 727 trijet airliner each have a tail bumper. Some aircraft with conventional landing gear have a fixed tailwheel. Another arrangement sometimes used is central main and nose gear with outriggers on the wings and this may be done where there is no convenient location on either side to attach the main undercarriage or to store it when retracted. Examples include the Lockheed U-2 spy plane and the Harrier Jump Jet, to decrease drag in flight some undercarriages retract into the wings and/or fuselage with wheels flush against the surface or concealed behind doors, this is called retractable gear. If the wheels rest protruding and partially exposed to the airstream after being retracted, most retraction systems are hydraulically operated, though some are electrically operated or even manually operated. This adds weight and complexity to the design, in retractable gear systems, the compartment where the wheels are stowed are called wheel wells, which may also diminish valuable cargo or fuel space. Pilots confirming that their landing gear is down and locked refer to three green or three in the green, a reference to the electrical indicator lights from the nosewheel/tailwheel and the two main gears. Red lights indicate the gear is in the position, amber lights indicate that the landing gear is in transit. Multiple redundancies are usually provided to prevent a failure from failing the entire landing gear extension process
30.
Aircraft
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An aircraft is a machine that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the lift of an airfoil. The human activity that surrounds aircraft is called aviation, crewed aircraft are flown by an onboard pilot, but unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Aircraft may be classified by different criteria, such as type, aircraft propulsion, usage. Each of the two World Wars led to technical advances. Consequently, the history of aircraft can be divided into five eras, Pioneers of flight, first World War,1914 to 1918. Aviation between the World Wars,1918 to 1939, Second World War,1939 to 1945. Postwar era, also called the jet age,1945 to the present day, aerostats use buoyancy to float in the air in much the same way that ships float on the water. They are characterized by one or more large gasbags or canopies, filled with a relatively low-density gas such as helium, hydrogen, or hot air, which is less dense than the surrounding air. When the weight of this is added to the weight of the aircraft structure, a balloon was originally any aerostat, while the term airship was used for large, powered aircraft designs – usually fixed-wing. In 1919 Frederick Handley Page was reported as referring to ships of the air, in the 1930s, large intercontinental flying boats were also sometimes referred to as ships of the air or flying-ships. – though none had yet been built, the advent of powered balloons, called dirigible balloons, and later of rigid hulls allowing a great increase in size, began to change the way these words were used. Huge powered aerostats, characterized by an outer framework and separate aerodynamic skin surrounding the gas bags, were produced. There were still no fixed-wing aircraft or non-rigid balloons large enough to be called airships, then several accidents, such as the Hindenburg disaster in 1937, led to the demise of these airships. Nowadays a balloon is an aerostat and an airship is a powered one. A powered, steerable aerostat is called a dirigible, sometimes this term is applied only to non-rigid balloons, and sometimes dirigible balloon is regarded as the definition of an airship. Non-rigid dirigibles are characterized by a moderately aerodynamic gasbag with stabilizing fins at the back and these soon became known as blimps. During the Second World War, this shape was adopted for tethered balloons, in windy weather
31.
String (music)
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A string is the vibrating element that produces sound in string instruments such as the guitar, harp, piano, and members of the violin family. Strings are lengths of a material that a musical instrument holds under tension so that they can vibrate freely. Wound strings have a core of one material, with an overwinding of other materials and this is to make the string vibrate at the desired pitch, while maintaining a low profile and sufficient flexibility for playability. This enabled stringed instruments to be made with less thick bass strings, on string instruments that the player plucks or bows directly, this enabled instrument makers to use thinner strings for the lowest-pitched strings, which made the lower-pitch strings easier to play. The end of the string that mounts to the tuning mechanism is usually plain. Depending on the instrument, the other, fixed end may have either a plain, loop. When a ball or loop is used with a guitar, this ensures that the string stays fixed in the bridge of the guitar, when a ball or loop is used with a violin-family instrument, this keeps the string end fixed in the tailpiece. Fender Bullet strings have a cylinder for more stable tuning on guitars equipped with synchronized tremolo systems. Strings for some instruments may be wrapped with silk at the ends to protect the string, the color and pattern of the silk often identifies attributes of the string, such as manufacturer, size, intended pitch, etc. There are several varieties of wound strings available, the simplest wound strings are roundwound—with round wire wrapped in a tight spiral around either a round or hexagonal core. Such strings are usually simple to manufacture and the least expensive and they have several drawbacks, however, Roundwound strings have a bumpy surface profile that produce friction on the players fingertips. This causes squeaking sounds when the fingers slide over the strings. Roundwound strings higher friction surface profile may hasten fingerboard and fret wear, when the core is round, the winding is less secure and may rotate freely around the core, especially if the winding is damaged after use. Flatwound strings also have either a round or hex core, however, the winding wire has a rounded square cross-section that has a shallower profile when tightly wound. This makes for more playing, and decreased wear for frets. Squeaking sounds due to fingers sliding along the strings are also decreased significantly, flatwound strings also have a longer playable life because of smaller grooves for dirt and oil to build up in. On the other hand, flatwound strings sound less bright than roundwounds, flatwounds also usually cost more than roundwounds because of less demand, less production, and higher overhead costs. Manufacturing is also difficult, as precise alignment of the flat sides of the winding must be maintained
32.
Engine
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An engine or motor is a machine designed to convert one form of energy into mechanical energy. Heat engines burn a fuel to heat, which is then used to create a force. Electric motors convert electrical energy into motion, pneumatic motors use compressed air. In biological systems, molecular motors, like myosins in muscles, use energy to create forces. The word engine derives from Old French engin, from the Latin ingenium–the root of the word ingenious. Pre-industrial weapons of war, such as catapults, trebuchets and battering rams, were called siege engines, the word gin, as in cotton gin, is short for engine. Most mechanical devices invented during the revolution were described as engines—the steam engine being a notable example. However, the steam engines, such as those by Thomas Savery, were not mechanical engines. In this manner, an engine in its original form was merely a water pump. Devices converting heat energy into motion are commonly referred to simply as engines, examples of engines which exert a torque include the familiar automobile gasoline and diesel engines, as well as turboshafts. Examples of engines which produce thrust include turbofans and rockets, the term motor derives from the Latin verb moto which means to set in motion, or maintain motion. Thus a motor is a device that imparts motion, motor and engine later came to be used largely interchangeably in casual discourse. However, technically, the two words have different meanings, however, rocketry uses the term rocket motor, even though they consume fuel. A heat engine may also serve as a prime mover—a component that transforms the flow or changes in pressure of a fluid into mechanical energy. An automobile powered by a combustion engine may make use of various motors and pumps. Another way of looking at it is that a motor receives power from an external source, simple machines, such as the club and oar, are prehistoric. More complex engines using human power, animal power, water power, wind power and these were used in cranes and aboard ships in Ancient Greece, as well as in mines, water pumps and siege engines in Ancient Rome. The writers of those times, including Vitruvius, Frontinus and Pliny the Elder, treat these engines as commonplace, by the 1st century AD, cattle and horses were used in mills, driving machines similar to those powered by humans in earlier times
33.
Naval architecture
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Naval architecture also known as naval engineering, is an engineering discipline dealing with the engineering design process, shipbuilding, maintenance, and operation of marine vessels and structures. Naval architecture involves basic and applied research, design, development, design evaluation, preliminary design of the vessel, its detailed design, construction, trials, operation and maintenance, launching and dry-docking are the main activities involved. Ship design calculations are required for ships being modified. Naval architecture also involves formulation of safety regulations and damage control rules, the word vessel includes every description of watercraft, including non-displacement craft, WIG craft and seaplanes, used or capable of being used as a means of transportation on water. The principal elements of architecture are, Hydrostatics concerns the conditions to which the vessel is subjected to while at rest in water. This involves computing buoyancy, and other properties, such as trim. Hydrodynamics concerns the flow of water around the hull, bow, and stern. Resistance – resistance towards motion in water primarily caused due to flow of water around the hull, powering calculation is done based on this. Propulsion – to move the vessel through water using propellers, thrusters, water jets, engine types are mainly internal combustion. Some vessels are powered using nuclear or solar energy. Ship motions – involves motions of the vessel in seaway and its responses in waves, controllability – involves controlling and maintaining position and direction of the vessel. Arrangements involves concept design, layout and access, fire protection, allocation of spaces, ergonomics, construction depends on the material used. Other joining techniques are used for materials like fibre reinforced plastic. Traditionally, naval architecture has been more craft than science, the suitability of a vessels shape was judged by looking at a half-model of a vessel or a prototype. Ungainly shapes or abrupt transitions were frowned on as being flawed and this included rigging, deck arrangements, and even fixtures. Subjective descriptors such as ungainly, full, and fine were used as a substitute for the precise terms used today. A vessel was, and still is described as having a ‘fair’ shape and these tools are used for static stability, dynamic stability, resistance, powering, hull development, structural analysis, green water modelling, and slamming analysis. Data is regularly shared in international conferences sponsored by RINA, Society of Naval Architects, computational Fluid Dynamics is being applied to predict the response of a floating body in a random sea
34.
Propeller
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A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the blade, and a fluid is accelerated behind the blade. Their disadvantages are higher mechanical complexity and higher cost, the principle employed in using a screw propeller is used in sculling. It is part of the skill of propelling a Venetian gondola but was used in a less refined way in parts of Europe. For example, propelling a canoe with a paddle using a pitch stroke or side slipping a canoe with a scull involves a similar technique. In China, sculling, called lu, was used by the 3rd century AD. In sculling, a blade is moved through an arc. The innovation introduced with the propeller was the extension of that arc through more than 360° by attaching the blade to a rotating shaft. Propellers can have a blade, but in practice there are nearly always more than one so as to balance the forces involved. The origin of the screw propeller starts with Archimedes, who used a screw to lift water for irrigation and bailing boats and it was probably an application of spiral movement in space to a hollow segmented water-wheel used for irrigation by Egyptians for centuries. Leonardo da Vinci adopted the principle to drive his theoretical helicopter, in 1784, J. P. Paucton proposed a gyrocopter-like aircraft using similar screws for both lift and propulsion. At about the time, James Watt proposed using screws to propel boats. This was not his own invention, though, Toogood and Hays had patented it a century earlier, by 1827, Czech-Austrian inventor Josef Ressel had invented a screw propeller which had multiple blades fastened around a conical base. He had tested his propeller in February 1826 on a ship that was manually driven. He was successful in using his bronze screw propeller on an adapted steamboat and his ship Civetta with 48 gross register tons, reached a speed of about six knots. This was the first ship successfully driven by an Archimedes screw-type propeller, after a new steam engine had an accident his experiments were banned by the Austro-Hungarian police as dangerous. Josef Ressel was at the time a forestry inspector for the Austrian Empire, but before this he received an Austro-Hungarian patent for his propeller. This new method of propulsion was an improvement over the paddlewheel as it was not so affected by either ship motions or changes in draft as the burned coal
35.
ATEX directive
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The ATEX directive consists of two EU directives describing what equipment and work environment is allowed in an environment with an explosive atmosphere. ATEX derives its name from the French title of the 94/9/EC directive, as of July 2003, organizations in EU must follow the directives to protect employees from explosion risk in areas with an explosive atmosphere. The ATEX 94/9/EU that is dedicated to the manufacturer has changed, still applicable up to 19 April 2016 the ATEX 94/9/EC will be removed and replaced by a new directive. This new ATEX directive 2014/34/EU will be mandatory for manufacturer on 20 April 2016 as is stated in article 44 of the directive. Promised for a time, this new ATEX directive has been published together with 8 other directives in the frame of NEW LEGISLATIVE FRAMEWORK ALIGNMENT PACKAGE.11.2011 under reference COM763 final. The classification given to a zone, and its size and location, depends on the likelihood of an explosive atmosphere occurring. Areas classified into zones must be protected from sources of ignition. Equipment and protective systems intended to be used in zoned areas must meet the requirements of the directive, Zone 0 and 20 require Category 1 marked equipment, zone 1 and 21 require Category 2 marked equipment and zone 2 and 22 require Category 3 marked equipment. Zone 0 and 20 are the zones with the highest risk of an explosive atmosphere being present, equipment in use before July 2003 is allowed to be used indefinitely provided a risk assessment shows it is safe to do so. The aim of directive 94/9/EC is to allow the trade of ‘ATEX’ equipment and protective systems within the EU by removing the need for separate testing. The regulations apply to all equipment intended for use in explosive atmospheres, whether electrical or mechanical, there are two categories of equipment I for mining and II for surface industries. The directive also covers components essential for the use and safety devices directly contributing to the safe use of the equipment in scope. These latter devices may be outside the potentially explosive environment, manufacturers/suppliers must ensure that their products meet essential health and safety requirements and undergo appropriate conformity procedures. Once certified, the equipment is marked by the ‘CE’ and ‘Ex’ symbol to identify it as approved under the ATEX directive, the technical dossier must be kept for a period of 10 years. Certification ensures that the equipment or protective system is fit for its intended purpose, there are four ATEX classification to ensure that a specific piece of equipment or protective system is appropriate and can be safely used in a particular application,1. The ATEX as an EU directive finds its US equivalent under the HAZLOC standard and this standard given by the Occupational Safety and Health Administration defines and classifies hazardous locations such as explosive atmospheres. Atmospheric conditions are referred to as ambient temperatures and pressures. That is to say temperatures of –20 °C to 40 °C, hazard - Dusts Zone 20 - A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently
36.
Jewellery
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Jewellery or jewelry consists of small decorative items worn for personal adornment, such as brooches, rings, necklaces, earrings, and bracelets. Jewellery may be attached to the body or the clothes, for many centuries metal, often combined with gemstones, has been the normal material for jewellery, but other materials such as shells and other plant materials may be used. It is one of the oldest type of archaeological artefact – with 100, historically, the most widespread influence on jewellery in terms of design and style have come from Asia. Jewellery may be made from a range of materials. Gemstones and similar such as amber and coral, precious metals, beads, and shells have been widely used. In most cultures jewellery can be understood as a symbol, for its material properties, its patterns. Jewellery has been made to nearly every body part, from hairpins to toe rings. The word jewellery itself is derived from the jewel, which was anglicised from the Old French jouel. In British English, Indian English, New Zealand English, Hiberno-English, Australian English, both are used in Canadian English, though jewelry prevails by a two to one margin. Numerous cultures store wedding dowries in the form of jewellery or make jewellery as a means to store or display coins, alternatively, jewellery has been used as a currency or trade good, an example being the use of slave beads. Many items of jewellery, such as brooches and buckles, originated as functional items. Jewellery can also symbolise group membership or status, wearing of amulets and devotional medals to provide protection or ward off evil is common in some cultures. These may take the form of symbols, stones, plants, animals, body parts, in creating jewellery, gemstones, coins, or other precious items are often used, and they are typically set into precious metals. Alloys of nearly every metal known have been encountered in jewellery, bronze, for example, was common in Roman times. Modern fine jewellery usually includes gold, white gold, platinum, palladium, titanium, most contemporary gold jewellery is made of an alloy of gold, the purity of which is stated in karats, indicated by a number followed by the letter K. American gold jewellery must be of at least 10K purity, many whimsical fashions were introduced in the extravagant eighteenth century. Cameos that were used in connection with jewellery were the attractive trinkets along with many of the objects such as brooches, ear-rings. Some of the necklets were made of pieces joined with the gold chains were in and bracelets were also made sometimes to match the necklet
37.
Water supply
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Water supply is the provision of water by public utilities commercial organisations, community endeavors or by individuals, usually via a system of pumps and pipes. However, about 14% did not have access to a water source and had to use unprotected wells or springs, canals. A clean water supply - in particular water that is not polluted with fecal matter from lack of sanitation - is the single most important determinant of public health. Destruction of water supply and/or sanitation infrastructure after major catastrophes poses the threat of severe epidemics of waterborne diseases. Water supply systems get water from a variety of locations after appropriate treatment, including groundwater, surface water, the water treatment steps include, in most cases, purification, disinfection through chlorination and sometimes fluoridation. Treated water then flows by gravity or is pumped to reservoirs. In the U. S, the single family home uses about 69.3 gallons of water per day. This includes toilet use, washing machine use, showers, baths, tap use, many of the 3.5 billion people having access to piped water receive a poor or very poor quality of service, especially in developing countries where about 80% of the world population lives. Water supply service quality has many dimensions, continuity, water quality, pressure, and it is estimated that about half of the population of developing countries receives water on an intermittent basis. Drinking water quality has a micro-biological and a physico-chemical dimension, there are thousands of parameters of water quality. For more details, please see the entries on water quality, water treatment. Water pressures vary in different locations of a distribution system, Water mains below the street may operate at higher pressures, with a pressure reducer located at each point where the water enters a building or a house. In poorly managed systems, water pressure can be so low as to only in a trickle of water or so high that it leads to damage to plumbing fixtures. Typical UK pressures are 4–5 bar for an urban supply, however, some people can get over eight bars or below one bar. A single iron main pipe may cross a valley, it will have the same nominal pressure. So people at the bottom of a 100-foot hill will get about 3 bars more than those at the top, the effective pressure also varies because of the pressure loss due to supply resistance even for the same static pressure. An urban consumer may have 5 metres of 15 mm pipe running from the main, so the kitchen tap flow will be fairly unrestricted. A rural consumer may have a kilometre of rusted and limed 22 mm iron pipe, for this reason, the UK domestic water system has traditionally employed a cistern feed system, where the incoming supply is connected to the kitchen sink and also a header/storage tank in the attic
38.
Oil
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An oil is any neutral, nonpolar chemical substance that is a viscous liquid at ambient temperatures and is both hydrophobic and lipophilic. Oils have a carbon and hydrogen content and are usually flammable. The general definition of oil includes classes of compounds that may be otherwise unrelated in structure, properties. Oils may be animal, vegetable, or petrochemical in origin and they are used for food, fuel, medical purposes, lubrication, and the manufacture of many types of paints, plastics, and other materials. Specially prepared oils are used in religious ceremonies and rituals as purifying agents. First attested in English 1176, the oil comes from Old French oile, from Latin oleum, which in turn comes from the Greek ἔλαιον, olive oil, oil. The earliest attested forms of the word are the Mycenaean Greek
39.
Petrochemical
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Petrochemicals, also called petroleum distillates, are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from fossil fuels, such as coal or natural gas. The two most common classes are olefins and aromatics. Oil refineries produce olefins and aromatics by fluid catalytic cracking of petroleum fractions, chemical plants produce olefins by steam cracking of natural gas liquids like ethane and propane. Aromatics are produced by catalytic reforming of naphtha, Olefins and aromatics are the building-blocks for a wide range of materials such as solvents, detergents, and adhesives. Olefins are the basis for polymers and oligomers used in plastics, resins, fibers, elastomers, lubricants, global ethylene and propylene production are about 115 million tonnes and 70 million tonnes per annum, respectively. Aromatics production is approximately 70 million tonnes, the largest petrochemical industries are located in the USA and Western Europe, however, major growth in new production capacity is in the Middle East and Asia. There is substantial inter-regional petrochemical trade, primary petrochemicals are divided into three groups depending on their chemical structure, Olefins includes ethylene, propylene, and butadiene. Ethylene and propylene are important sources of chemicals and plastics products. Butadiene is used in making synthetic rubber, aromatics includes benzene, toluene, and xylenes. Benzene is a raw material for dyes and synthetic detergents, manufacturers use xylenes to produce plastics and synthetic fibers. Synthesis gas is a mixture of carbon monoxide and hydrogen used to make ammonia, ammonia is used to make the fertilizer urea and methanol is used as a solvent and chemical intermediate. The prefix petro- is an abbreviation of the word petroleum, since petro- is Ancient Greek for rock. Therefore, the correct term would be oleochemicals. However, the term oleochemical is used to describe chemicals derived from plant, benzene, toluene and xylenes, as a whole referred to as BTX and primarily obtained from petroleum refineries by extraction from the reformate produced in catalytic reformers. Methane and BTX are used directly as feedstocks for producing petrochemicals, the output ethylene capacity of large steam crackers ranged up to as much as 1.0 –1.5 Mt per year. Steam crackers are not to be confused with steam reforming plants used to produce hydrogen, like commodity chemicals, petrochemicals are made on a very large scale. Petrochemical manufacturing units differ from commodity chemical plants in that often produce a number of related products
40.
Welding
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In addition to melting the base metal, a filler material is typically added to the joint to form a pool of molten material that cools to form a joint that is usually stronger than the base material. Pressure may also be used in conjunction with heat, or by itself, although less common, there are also solid state welding processes such as friction welding or shielded active gas welding in which metal does not melt. Some of the best known welding methods include, Oxy-fuel welding - also known as oxyacetylene welding or oxy welding, uses fuel gases and oxygen to weld and cut metals. Shielded metal arc welding – also known as stick welding or electric welding, the electrode holder holds the electrode as it slowly melts away. Slag protects the weld puddle from atmospheric contamination, gas tungsten arc welding – also known as TIG, uses a non-consumable tungsten electrode to produce the weld. The weld area is protected from contamination by an inert shielding gas such as argon or helium. Flux-cored arc welding – almost identical to MIG welding except it uses a special tubular wire filled with flux, it can be used with or without shielding gas, submerged arc welding – uses an automatically fed consumable electrode and a blanket of granular fusible flux. The molten weld and the arc zone are protected from contamination by being submerged under the flux blanket. Electroslag welding – a highly productive, single pass welding process for thicker materials between 1 inch and 12 inches in a vertical or close to vertical position. Electric resistance welding - a welding process that produces coalescence of laying surfaces where heat to form the weld is generated by the resistance of the material. In general, an efficient method, but limited to relatively thin material, many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. While often a process, welding may be performed in many different environments, including in open air, under water. Welding is an undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes. Until the end of the 19th century, the welding process was forge welding. Arc welding and oxyfuel welding were among the first processes to develop late in the century, Welding technology advanced quickly during the early 20th century as the world wars drove the demand for reliable and inexpensive joining methods. Developments continued with the invention of laser welding, electron beam welding, magnetic pulse welding. Today, the continues to advance. Robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods, the history of joining metals goes back several millennia
41.
Metal inert gas welding
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Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from contaminants in the air. The process can be semi-automatic or automatic, a constant voltage, direct current power source is most commonly used with GMAW, but constant current systems, as well as alternating current, can be used. Originally developed for welding aluminium and other materials in the 1940s. The cost of inert gas limited its use in steels until several years later, further developments during the 1950s and 1960s gave the process more versatility and as a result, it became a highly used industrial process. Today, GMAW is the most common industrial welding process, preferred for its versatility, speed, unlike welding processes that do not employ a shielding gas, such as shielded metal arc welding, it is rarely used outdoors or in other areas of air volatility. A related process, flux cored arc welding, often does not use a shielding gas, the principles of gas metal arc welding began to be understood in the early 19th century, after Humphry Davy discovered the short pulsed electric arcs in 1800. Vasily Petrov independently produced the electric arc in 1802. It was not until the 1880s that the technology developed with the aim of industrial usage. At first, carbon electrodes were used in arc welding. By 1890, metal electrodes had been invented by Nikolay Slavyanov, in 1920, an early predecessor of GMAW was invented by P. O. Nobel of General Electric. It used an electrode wire and direct current, and used arc voltage to regulate the feed rate. It did not use a gas to protect the weld. In 1926 another forerunner of GMAW was released, but it was not suitable for practical use, in 1948, GMAW was developed by the Battelle Memorial Institute. It used a smaller diameter electrode and a constant voltage power source developed by H. E. Kennedy and it offered a high deposition rate, but the high cost of inert gases limited its use to non-ferrous materials and prevented cost savings. In 1953, the use of carbon dioxide as an atmosphere was developed. It quickly became the most popular GMAW variation, the spray-arc transfer variation was developed in the early 1960s, when experimenters added small amounts of oxygen to inert gases. More recently, pulsed current has been applied, giving rise to a new method called the pulsed spray-arc variation, GMAW is one of the most popular welding methods, especially in industrial environments. It is used extensively by the metal industry and, by extension
42.
Argon
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Argon is a chemical element with symbol Ar and atomic number 18. It is in group 18 of the table and is a noble gas. Argon is the third-most abundant gas in the Earths atmosphere, at 0. 934% and it is more than twice as abundant as water vapor,23 times as abundant as carbon dioxide, and more than 500 times as abundant as neon. Argon is the most abundant noble gas in Earths crust, comprising 0. 00015% of the crust, nearly all of the argon in Earths atmosphere is radiogenic argon-40, derived from the decay of potassium-40 in the Earths crust. In the universe, argon-36 is by far the most common argon isotope, the name argon is derived from the Greek word ἀργόν, neuter singular form of ἀργός meaning lazy or inactive, as a reference to the fact that the element undergoes almost no chemical reactions. The complete octet in the atomic shell makes argon stable. Its triple point temperature of 83.8058 K is a fixed point in the International Temperature Scale of 1990. Argon is produced industrially by the distillation of liquid air. Argon is also used in incandescent, fluorescent lighting, and other gas-discharge tubes, Argon makes a distinctive blue-green gas laser. Argon is also used in fluorescent glow starters, Argon has approximately the same solubility in water as oxygen and is 2.5 times more soluble in water than nitrogen. Argon is colorless, odorless, nonflammable and nontoxic as a solid, liquid or gas, Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperature. Although argon is a gas, it can form some compounds under extreme conditions. Argon fluorohydride, a compound of argon with fluorine and hydrogen that is stable below 17 K, has been demonstrated. Although the neutral ground-state chemical compounds of argon are presently limited to HArF, ions, such as ArH+, and excited-state complexes, such as ArF, have been demonstrated. Theoretical calculation predicts several more argon compounds that should be stable but have not yet been synthesized, Argon was suspected to be a component of air by Henry Cavendish in 1785. Argon was first isolated from air in 1894 by Lord Rayleigh and Sir William Ramsay at University College London by removing oxygen, carbon dioxide, water and they had determined that nitrogen produced from chemical compounds was 0. 5% lighter than nitrogen from the atmosphere. The difference was slight, but it was important enough to attract their attention for many months and they concluded that there was another gas in the air mixed in with the nitrogen. Argon was also encountered in 1882 through independent research of H. F. Newall, each observed new lines in the color spectrum of air that did not match known elements
43.
Coins of the Australian dollar
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Coins of the Australian dollar were introduced on 14 February 1966, although they did not at that time include one-dollar or two-dollar coins. The dollar was equivalent in value to 10 shillings in the former currency, produced by the Royal Australian Mint, all current coins portray Her Majesty Elizabeth II, Queen of Australia, on the obverse, with the present effigy having been designed by Ian Rank-Broadley. This is matched with designs by the Australian-born artist Stuart Devlin on the reverse. They now comprise 50c, 20c, 10c and 5c coins – all still referred to as though actually 75% copper and 25% nickel. The 50c coin originally had a shape, and contained 80% silver and 20% copper. It was made to almost identical dimensional specifications as the British 26 pence half crown and it was changed to a 12-sided shape for 1969 and all following years, but the 12 sided issue was minted as a specimen piece in 1966-67 to test the design. It has since issued in both standard and commemorative designs. The standard designs on both versions of the coin are the same, the obverse carries the effigy of the sovereign, nearly all the Australian round 50-cent coins from 1966 that remain in existence are now only traded for their bullion value. They are often confused with the round 50c coin from New Zealand with the date 1967-2006, gold one-dollar and two-dollar coins were introduced in the 1980s. The one-dollar coin was introduced in 1984, to replace the banknote of the same value, the two-dollar coin, also replacing a banknote, was introduced in 1988. These have content of 2% nickel, 6% aluminium and 92% copper, thus, all Australian coins in use currently are composed of more than half copper. The two-dollar coin is smaller in diameter than the one-dollar coin, the one- and two-cent coins were discontinued in 1991 due to the metal exceeding face value and were withdrawn from circulation. Australian coins have medallic orientation, as do most other Commonwealth coinage, Japanese yen coinage and this is in contrast to coin orientation, which is used in United States coinage. Many special versions of the 10c, 20c, 50c, $1 and $2 coins have been produced, for some years, all the coins are replaced with a different design for that year. In other cases, only a few coins have the new design, in 2012, a commemorative $2 coin was produced depicting a poppy for Remembrance Day and in 2013, a coloured purple coin for the 60th anniversary of Queen Elizabeth IIs coronation. In 2016 a commemorative 25c coin was produced for Anzac day with 4 million coins minted, the Royal Australian Mint regularly releases collectable coins, one of the most famous of which is the gold two hundred dollar coin. Australian collectable coins are all legal tender and can be used directly as currency or converted to normal coinage at a bank, metals include aluminium bronze, silver, gold and bi-metal coins. Nugget coins are issued in ounces and fractions or kilograms and come in gold and platinum, list of people who have appeared on Australian currency Coins of the New Zealand dollar Swedish rounding
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Coins of the New Zealand dollar
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This article concerns the coins of the New Zealand dollar. Prior to 10 July 1967, the New Zealand pound, using the £sd system, was the currency of New Zealand, Coins of the pound tend to follow the size, weight, and composition of their British counterparts. The main coins in usage were the halfpenny, penny, threepence, sixpence, shilling, florin, and halfcrown. Decimalisation of the New Zealand currency occurred on 10 July 1967, on the same day, new decimal coins were introduced to replace the existing pound coins. The first coins of the New Zealand dollar were 1c, 2c, 5c, 10c, 20c, the 1c, 2c, and 50c coins were new sizes, with the 1c and 2c minted in bronze, and 50c in cupronickel. The new 5c, 10c, and 20c were the size, weight, and value as the former sixpence, shilling. Indeed, until 1970, the 10 cents coin bore the additional legend One Shilling, the obverse designs of all the coins featured Arnold Machins portrait of Elizabeth II, with the legend ELIZABETH II NEW ZEALAND. The initial designs for the sides of the coins introduced in 1967 were rejected by the Royal Mint. Several more designs were produced, followed by a public debate. James Berrys designs were accepted for most of the coins, although he was asked to rework his design for the 5c coin. In 1986, the portrait of Elizabeth II on New Zealand coins was changed to Raphael Makloufs new portrait of the Queen, towards the end of the 1980s, the 1c and 2c were becoming of little value, and it was decided to withdraw these coins from circulation. The last coins of denominations were minted for circulation in 1987. The coins were withdrawn from circulation, before finally being demonetised on 1 May 1990. After the withdrawal of these coins, cash transactions were normally rounded to the nearest 5 cents, some larger retailers, in the interests of public relations, elected to round the total price down. Alternatively, many retailers rounded all their prices to the nearest 5 cents to avoid the issue entirely—so a New Zealand shopper often encountered products for sale at prices like $4.95. On 11 February 1991, $1 and $2 coins were introduced to replace the $1 and these coins were minted in aluminium bronze, and were the first New Zealand coins to be minted to metric specifications. At the same time, because the new $1 coin depicted a kiwi, the new 20c coins depicted a Māori carving of Pukaki, a chief of the Ngati Whakaue iwi. Coins with kiwi design, however, outnumbered coins with the new design until they were replaced with the new 20c coins, all depicting the later design, in 1999, Ian Rank-Broadleys portrait of the Queen was introduced and the legend rearranged to read NEW ZEALAND ELIZABETH II
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Royal Australian Mint
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The Royal Australian Mint is the sole producer of all of Australias circulating coins. Opened in 1965 and situated in the Australian federal capital city of Canberra, in the suburb of Deakin, before the opening of the Australian mint, Australian coins were struck at branches of the Royal Mint - the Sydney Mint, Melbourne Mint and Perth Mint. The Royal Australian Mint is the first mint in Australia not to be a branch of the Royal Mint in London, the only other operational mint in Australia is the Perth Mint. Planning for the mint started in 1959 when it was proposed to move the Royal Mint branch in Melbourne to Canberra and it was officially opened by The Duke of Edinburgh on 22 February 1965, coinciding with decimal currency, which was introduced into circulation on 14 February 1966. The new mint cost A$5 million to build, with an additional $4 million for equipment, some staff from the Melbourne mint relocated to Canberra to operate the new mint. The mint consists of two buildings, a building, and a process building. The administration building houses the engravers, a laboratory, and a basement where coinage is measured to ensure correct size. The mint is an Australian Public Service agency, staffed through the Department of the Treasury, during 1984-1986 renovations were carried out to support the increasing demand for the production of collector coins, and also to improve the visitor facilities. Visitors can mint their own legal tender coin using visitor presses, the mint serves primarily to manufacture Australias legal tender precious metal coins. Notes are produced by Note Printing Australia in Melbourne, the mint also produces medals for military and civilian honours, most notably the Order of Australia. The mint produced medals for the 2000 Summer Olympics in conjunction with the Perth Mint, the Royal Australian Mint also produces tokens made for commercial organisations such as casinos, car washes etc. Since its opening, the mint has produced over fourteen billion coins and has the capacity to two million coins per day. In November 2001, the mint issued the worlds first coin with a double hologram, the mint also creates bi-metallic coins, and colour printed coins. On 11 December 2005 the Joint Standing Committee on Public Works tabled a report recommending the refurbishment of the Royal Australian Mint with a projected cost of A$41.2 million. Work was planned to commence in October 2006 with completion dates of June 2008 for the process building, the refurbishment also planned to introduce industrial robots to the manufacturing process. The work was completed in 2009, and the mint is now open to the public, in 2014, the Abbott Government announced a scoping study into selling the Royal Australian Mint. List of mints Royal Australian Mints official website
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Mexican peso
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The Mexican peso is the currency of Mexico. Modern peso and dollar currencies have a origin in the 15th–19th century Spanish dollar, most continuing to use its sign. The Mexican peso is the 8th most traded currency in the world, the third most traded currency originating from the Americas, the current ISO4217 code for the peso is MXN, prior to the 1993 revaluation, the code MXP was used. The peso is subdivided into 100 centavos, represented by ¢, as of March 31,2017, the pesos exchange rate was $19.94 per Euro and $18.71 per U. S. dollar. The name was used in reference to pesos oro or pesos plata. The Spanish word peso means weight, the peso was originally the name of the eight-real coins issued in Mexico by Spain. These were the so-called Spanish dollars or pieces of eight in wide circulation in the Americas, in 1863, the first issue was made of coins denominated in centavos, worth one hundredth of the peso. This was followed in 1866 by coins denominated one peso, coins denominated in reales continued to be issued until 1897. In 1905, the content of the peso was reduced by 49. 3%. However, from 1918 onward, the weight and fineness of all the coins declined, until 1977. On January 1,1993 the Bank of Mexico introduced a new currency, one new peso, or N$1.00, was equal to 1000 of the obsolete MXP pesos. The ISO4217 code, however, remained unchanged as MXN, thanks to the stability of the Mexican economy and the growth in foreign investment, the Mexican peso is now among the 15 most traded currency units in recent years. The first coins of the currency were 1 centavo pieces minted in 1863. Emperor Maximilian, ruler of the Second Mexican Empire from 1864–1867 and his portrait was on the obverse, with the legend Maximiliano Emperador, the reverse shows the imperial arms and the legends Imperio Mexicano and 1 Peso and the date. They were struck from 1866 to 1867, the New Mexican republic continued to strike the 8 reales piece, but also began minting coins denominated in centavos and pesos. In addition to copper 1 centavo coins, silver coins of 5,10,25 and 50 centavos and 1 peso were introduced between 1867 and 1869, gold 1, 2½,5,10 and 20-peso coins were introduced in 1870. The obverses featured the Mexican eagle and the legend Republica Mexicana, the reverses of the larger coins showed a pair of scales, those of the smaller coins, the denomination. One-peso coins were made from 1865 to 1873, when 8 reales coins resumed production, in 1882, cupro-nickel 1,2 and 5 centavos coins were issued but they were only minted for two years
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