Osmium is a chemical element with symbol Os and atomic number 76. It is a hard, bluish-white transition metal in the platinum group, found as a trace element in alloys in platinum ores. Osmium is the densest occurring element, with an experimentally measured density of 22.59 g/cm3. Manufacturers use its alloys with platinum and other platinum-group metals to make fountain pen nib tipping, electrical contacts, in other applications that require extreme durability and hardness; the element's abundance in the Earth's crust is among the rarest. Osmium is the densest stable element. Calculations of density from the X-ray diffraction data may produce the most reliable data for these elements, giving a value of 22.587±0.009 g/cm3 for osmium denser than the 22.562±0.009 g/cm3 of iridium. Osmium is a hard but brittle metal that remains lustrous at high temperatures, it has a low compressibility. Correspondingly, its bulk modulus is high, reported between 395 and 462 GPa, which rivals that of diamond; the hardness of osmium is moderately high at 4 GPa.
Because of its hardness, low vapor pressure, high melting point, solid osmium is difficult to machine, form, or work. Osmium forms compounds with oxidation states ranging from −2 to +8; the most common oxidation states are +2, +3, +4, +8. The +8 oxidation state is notable for being the highest attained by any chemical element aside from iridium's +9 and is encountered only in xenon, ruthenium and iridium; the oxidation states −1 and −2 represented by the two reactive compounds Na2 and Na2 are used in the synthesis of osmium cluster compounds. The most common compound exhibiting the +8 oxidation state is osmium tetroxide; this toxic compound is formed. It is a volatile, water-soluble, pale yellow, crystalline solid with a strong smell. Osmium powder has the characteristic smell of osmium tetroxide. Osmium tetroxide forms. With ammonia, it forms the nitrido-osmates OsO3N−. Osmium tetroxide is a powerful oxidizing agent. By contrast, osmium dioxide is black, non-volatile, much less reactive and toxic.
Only two osmium compounds have major applications: osmium tetroxide for staining tissue in electron microscopy and for the oxidation of alkenes in organic synthesis, the non-volatile osmates for organic oxidation reactions. Osmium pentafluoride is known; the lower oxidation states are stabilized by the larger halogens, so that the trichloride, tribromide and diiodide are known. The oxidation state +1 is known only for osmium iodide, whereas several carbonyl complexes of osmium, such as triosmium dodecacarbonyl, represent oxidation state 0. In general, the lower oxidation states of osmium are stabilized by ligands that are good σ-donors and π-acceptors; the higher oxidation states are stabilized by strong σ- and π-donors, such as O2− and N3−. Despite its broad range of compounds in numerous oxidation states, osmium in bulk form at ordinary temperatures and pressures resists attack by all acids and alkalis, including aqua regia. Osmium has seven occurring isotopes, six of which are stable: 184Os, 187Os, 188Os, 189Os, 190Os, 192Os.
186Os undergoes alpha decay with such a long half-life ×1015 years 140000 times the age of the universe, that for practical purposes it can be considered stable. Alpha decay is predicted for all seven occurring isotopes, but it has been observed only for 186Os due to long half-lives, it is predicted that 184Os and 192Os can undergo double beta decay but this radioactivity has not been observed yet.187Os is the descendant of 187Re and is used extensively in dating terrestrial as well as meteoric rocks. It has been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons; this decay is a reason. However, the most notable application of osmium isotopes in geology has been in conjunction with the abundance of iridium, to characterise the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the non-avian dinosaurs 65 million years ago. Osmium was discovered in 1803 by William Hyde Wollaston in London, England.
The discovery of osmium is intertwined with that of platinum and the other metals of the platinum group. Platinum reached Europe as platina, first encountered in the late 17th century in silver mines around the Chocó Department, in Colombia; the discovery that this metal was not an alloy, but a distinct new element, was published in 1748. Chemists who studied platinum dissolved it in aqua regia to create soluble salts, they always observed a small amount of a insoluble residue. Joseph Louis Proust thought. Victor Collet-Descotils, Antoine François, comte de Fourcroy, Louis Nicolas Vauquelin observed iridium in the black platinum residue in 1803, but did not obtain enough material for further experiments; the two French ch
Niobium known as columbium, is a chemical element with symbol Nb and atomic number 41. It is a soft, crystalline, ductile transition metal found in the minerals pyrochlore and columbite, hence the former name "columbium", its name comes from Greek mythology Niobe, the daughter of Tantalus, the namesake of tantalum. The name reflects the great similarity between the two elements in their physical and chemical properties, making them difficult to distinguish; the English chemist Charles Hatchett reported a new element similar to tantalum in 1801 and named it columbium. In 1809, the English chemist William Hyde Wollaston wrongly concluded that tantalum and columbium were identical; the German chemist Heinrich Rose determined in 1846 that tantalum ores contain a second element, which he named niobium. In 1864 and 1865, a series of scientific findings clarified that niobium and columbium were the same element, for a century both names were used interchangeably. Niobium was adopted as the name of the element in 1949, but the name columbium remains in current use in metallurgy in the United States.
It was not until the early 20th century. Brazil is the leading producer of an alloy of 60 -- 70 % niobium with iron. Niobium is used in alloys, the largest part in special steel such as that used in gas pipelines. Although these alloys contain a maximum of 0.1%, the small percentage of niobium enhances the strength of the steel. The temperature stability of niobium-containing superalloys is important for its use in jet and rocket engines. Niobium is used in various superconducting materials; these superconducting alloys containing titanium and tin, are used in the superconducting magnets of MRI scanners. Other applications of niobium include welding, nuclear industries, optics and jewelry. In the last two applications, the low toxicity and iridescence produced by anodization are desired properties. Niobium is considered a technology-critical element. Niobium was identified by English chemist Charles Hatchett in 1801, he found a new element in a mineral sample, sent to England from Connecticut, United States in 1734 by John Winthrop F.
R. S. and named the mineral columbite and the new element columbium after Columbia, the poetical name for the United States. The columbium discovered by Hatchett was a mixture of the new element with tantalum. Subsequently, there was considerable confusion over the difference between columbium and the related tantalum. In 1809, English chemist William Hyde Wollaston compared the oxides derived from both columbium—columbite, with a density 5.918 g/cm3, tantalum—tantalite, with a density over 8 g/cm3, concluded that the two oxides, despite the significant difference in density, were identical. This conclusion was disputed in 1846 by German chemist Heinrich Rose, who argued that there were two different elements in the tantalite sample, named them after children of Tantalus: niobium and pelopium; this confusion arose from the minimal observed differences between niobium. The claimed new elements pelopium and dianium were in fact identical to niobium or mixtures of niobium and tantalum; the differences between tantalum and niobium were unequivocally demonstrated in 1864 by Christian Wilhelm Blomstrand and Henri Etienne Sainte-Claire Deville, as well as Louis J. Troost, who determined the formulas of some of the compounds in 1865 and by Swiss chemist Jean Charles Galissard de Marignac in 1866, who all proved that there were only two elements.
Articles on ilmenium continued to appear until 1871. De Marignac was the first to prepare the metal in 1864, when he reduced niobium chloride by heating it in an atmosphere of hydrogen. Although de Marignac was able to produce tantalum-free niobium on a larger scale by 1866, it was not until the early 20th century that niobium was used in incandescent lamp filaments, the first commercial application; this use became obsolete through the replacement of niobium with tungsten, which has a higher melting point. That niobium improves the strength of steel was first discovered in the 1920s, this application remains its predominant use. In 1961, the American physicist Eugene Kunzler and coworkers at Bell Labs discovered that niobium-tin continues to exhibit superconductivity in the presence of strong electric currents and magnetic fields, making it the first material to support the high currents and fields necessary for useful high-power magnets and electrical power machinery; this discovery enabled — two decades — the production of long multi-strand cables wound into coils to create large, powerful electromagnets for rotating machinery, particle accelerators, particle detectors.
Columbium was the name bestowed by Hatchett upon his discovery of the metal in 1801. The name reflected; this name remained in use in American journals—the last paper published by American Chemical Society with columbium in its title dates from 1953—while niobium was used in Europe. To end this confusion, the name niobium was chosen for element 41 at the 15th Conference of the Union of Chemistry in Amsterdam in 1949. A year this name was adopted by the International Union of Pure and Applied Chemistry after 100 years of controversy, despite the chronological precedence of the name columbium; this was a compromise of sorts.
Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, their mixtures, which are called alloys. A special type of alloy was invented in 1995, when Taiwanese scientists invented the world's first high-entropy alloys of metals that can withstand the highest temperatures and pressures for use in industrial and technological applications such as state of the art race cars, submarines, nuclear reactors, jet airplanes, nuclear weapons, long range hypersonic missiles and many other areas of technology. Metallurgy is used to separate metals from their ore. Metallurgy is the technology of metals: the way in which science is applied to the production of metals, the engineering of metal components for usage in products for consumers and manufacturers; the production of metals involves the processing of ores to extract the metal they contain, the mixture of metals, sometimes with other elements, to produce alloys.
Metallurgy is distinguished from the craft of metalworking, although metalworking relies on metallurgy, as medicine relies on medical science, for technical advancement. The science of metallurgy is subdivided into physical metallurgy. Metallurgy is subdivided into ferrous metallurgy and non-ferrous metallurgy. Ferrous metallurgy involves processes and alloys based on iron while non-ferrous metallurgy involves processes and alloys based on other metals; the production of ferrous metals accounts for 95 percent of world metal production. The roots of metallurgy derive from Ancient Greek: μεταλλουργός, metallourgós, "worker in metal", from μέταλλον, métallon, "metal" + ἔργον, érgon, "work"; the word was an alchemist's term for the extraction of metals from minerals, the ending -urgy signifying a process manufacturing: it was discussed in this sense in the 1797 Encyclopædia Britannica. In the late 19th century it was extended to the more general scientific study of metals and related processes. In English, the pronunciation is the more common one in the Commonwealth.
The pronunciation is the more common one in the USA, is the first-listed variant in various American dictionaries. The earliest recorded metal employed by humans appears to be gold, which can be found free or "native". Small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period, c. 40,000 BC. Silver, copper and meteoric iron can be found in native form, allowing a limited amount of metalworking in early cultures. Egyptian weapons made from meteoric iron in about 3000 BC were prized as "daggers from heaven". Certain metals, notably tin and copper, can be recovered from their ores by heating the rocks in a fire or blast furnace, a process known as smelting; the first evidence of this extractive metallurgy, dating from the 5th and 6th millennia BC, has been found at archaeological sites in Majdanpek and Plocnik, in present-day Serbia. To date, the earliest evidence of copper smelting is found at the Belovode site near Plocnik; this site produced a copper axe from 5500 BC.
The earliest use of lead is documented from the late neolithic settlement of Yarim Tepe in Iraq, "The earliest lead finds in the ancient Near East are a 6th millennium BC bangle from Yarim Tepe in northern Iraq and a later conical lead piece from Halaf period Arpachiyah, near Mosul. As native lead is rare, such artifacts raise the possibility that lead smelting may have begun before copper smelting." Copper smelting is documented at this site at about the same time period, although the use of lead seems to precede copper smelting. Early metallurgy is documented at the nearby site of Tell Maghzaliyah, which seems to be dated earlier, lacks pottery. Other signs of early metals are found from the third millennium BC in places like Palmela, Los Millares, Stonehenge. However, the ultimate beginnings cannot be ascertained and new discoveries are both continuous and ongoing. In the Near East, about 3500 BC, it was discovered that by combining copper and tin, a superior metal could be made, an alloy called bronze.
This represented a major technological shift known as the Bronze Age. The extraction of iron from its ore into a workable metal is much more difficult than for copper or tin; the process appears to have been invented by the Hittites in about 1200 BC. The secret of extracting and working iron was a key factor in the success of the Philistines. Historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations; this includes the ancient and medieval kingdoms and empires of the Middle East and Near East, ancient Iran, ancient Egypt, ancient Nubia, Anatolia, Ancient Nok, the Greeks and Romans of ancient Europe, medieval Europe and medieval China and medieval India and medieval Japan, amongst others. Many applications and devices associated or involved in metallurgy were established in ancient China, such as the innovation of the blast furnace, cast iron, hydraulic-powered trip hammers, double acting piston bellows. A 16th century book by Georg Agricola called De re metallica describes the developed and complex processes of mining metal ores, metal extraction and metallurgy of the time.
Agricola has been described as the "father of metallurgy". Extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted
Engineering is the application of knowledge in the form of science and empirical evidence, to the innovation, construction and maintenance of structures, materials, devices, systems and organizations. The discipline of engineering encompasses a broad range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied mathematics, applied science, types of application. See glossary of engineering; the term engineering is derived from the Latin ingenium, meaning "cleverness" and ingeniare, meaning "to contrive, devise". The American Engineers' Council for Professional Development has defined "engineering" as: The creative application of scientific principles to design or develop structures, apparatus, or manufacturing processes, or works utilizing them singly or in combination. Engineering has existed since ancient times, when humans devised inventions such as the wedge, lever and pulley; the term engineering is derived from the word engineer, which itself dates back to 1390 when an engine'er referred to "a constructor of military engines."
In this context, now obsolete, an "engine" referred to a military machine, i.e. a mechanical contraption used in war. Notable examples of the obsolete usage which have survived to the present day are military engineering corps, e.g. the U. S. Army Corps of Engineers; the word "engine" itself is of older origin deriving from the Latin ingenium, meaning "innate quality mental power, hence a clever invention."Later, as the design of civilian structures, such as bridges and buildings, matured as a technical discipline, the term civil engineering entered the lexicon as a way to distinguish between those specializing in the construction of such non-military projects and those involved in the discipline of military engineering. The pyramids in Egypt, the Acropolis and the Parthenon in Greece, the Roman aqueducts, Via Appia and the Colosseum, Teotihuacán, the Brihadeeswarar Temple of Thanjavur, among many others, stand as a testament to the ingenuity and skill of ancient civil and military engineers.
Other monuments, no longer standing, such as the Hanging Gardens of Babylon, the Pharos of Alexandria were important engineering achievements of their time and were considered among the Seven Wonders of the Ancient World. The earliest civil engineer known by name is Imhotep; as one of the officials of the Pharaoh, Djosèr, he designed and supervised the construction of the Pyramid of Djoser at Saqqara in Egypt around 2630–2611 BC. Ancient Greece developed machines in both military domains; the Antikythera mechanism, the first known mechanical computer, the mechanical inventions of Archimedes are examples of early mechanical engineering. Some of Archimedes' inventions as well as the Antikythera mechanism required sophisticated knowledge of differential gearing or epicyclic gearing, two key principles in machine theory that helped design the gear trains of the Industrial Revolution, are still used today in diverse fields such as robotics and automotive engineering. Ancient Chinese, Greek and Hungarian armies employed military machines and inventions such as artillery, developed by the Greeks around the 4th century BC, the trireme, the ballista and the catapult.
In the Middle Ages, the trebuchet was developed. Before the development of modern engineering, mathematics was used by artisans and craftsmen, such as millwrights, clock makers, instrument makers and surveyors. Aside from these professions, universities were not believed to have had much practical significance to technology. A standard reference for the state of mechanical arts during the Renaissance is given in the mining engineering treatise De re metallica, which contains sections on geology and chemistry. De re metallica was the standard chemistry reference for the next 180 years; the science of classical mechanics, sometimes called Newtonian mechanics, formed the scientific basis of much of modern engineering. With the rise of engineering as a profession in the 18th century, the term became more narrowly applied to fields in which mathematics and science were applied to these ends. In addition to military and civil engineering, the fields known as the mechanic arts became incorporated into engineering.
Canal building was an important engineering work during the early phases of the Industrial Revolution. John Smeaton was the first self-proclaimed civil engineer and is regarded as the "father" of civil engineering, he was an English civil engineer responsible for the design of bridges, canals and lighthouses. He was a capable mechanical engineer and an eminent physicist. Using a model water wheel, Smeaton conducted experiments for seven years, determining ways to increase efficiency. Smeaton introduced iron gears to water wheels. Smeaton made mechanical improvements to the Newcomen steam engine. Smeaton designed the third Eddystone Lighthouse where he pioneered the use of'hydraulic lime' and developed a technique involving dovetailed blocks of granite in the building of the lighthouse, he is important in the history, rediscovery of, development of modern cement, because he identified the compositional requirements needed to obtain "hydraulicity" in lime.
Rhenium is a chemical element with symbol Re and atomic number 75. It is a silvery-gray, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion, rhenium is one of the rarest elements in the Earth's crust. Rhenium has the third-highest melting point and second-highest boiling point of any element at 5903 K. Rhenium resembles manganese and technetium chemically and is obtained as a by-product of the extraction and refinement of molybdenum and copper ores. Rhenium shows in its compounds a wide variety of oxidation states ranging from −1 to +7. Discovered in 1908, rhenium was the second-last stable element to be discovered, it was named after the river Rhine in Europe. Nickel-based superalloys of rhenium are used in the combustion chambers, turbine blades, exhaust nozzles of jet engines; these alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element. The second-most important use is as a catalyst: rhenium is an excellent catalyst for hydrogenation and isomerization, is used for example in catalytic reforming of naphtha for use in gasoline.
Because of the low availability relative to demand, rhenium is expensive, with price reaching an all-time high in 2008/2009 US$10,600 per kilogram. Due to increases in rhenium recycling and a drop in demand for rhenium in catalysts, the price of rhenium has dropped to US$2,844 per kilogram as of July 2018. Rhenium was the second last-discovered of the elements; the existence of a yet-undiscovered element at this position in the periodic table had been first predicted by Dmitri Mendeleev. Other calculated information was obtained by Henry Moseley in 1914. In 1908, Japanese chemist Masataka Ogawa announced that he had discovered the 43rd element and named it nipponium after Japan. However, recent analysis indicated the presence of rhenium, not element 43, although this reinterpretation has been questioned by Eric Scerri; the symbol Np was used for the element neptunium, the name "nihonium" named after Japan, along with symbol Nh, was used for element 113. Element 113 was discovered by a team of Japanese scientists and was named in respectful homage to Ogawa's work.
Rhenium is considered to have been discovered by Walter Noddack, Ida Noddack, Otto Berg in Germany. In 1925 they reported that they had detected the element in platinum ore and in the mineral columbite, they found rhenium in gadolinite and molybdenite. In 1928 they were able to extract 1 g of the element by processing 660 kg of molybdenite, it was estimated in 1968 that 75% of the rhenium metal in the United States was used for research and the development of refractory metal alloys. It took several years from that point before the superalloys became used. Rhenium is a silvery-white metal with one of the highest melting points of all elements, exceeded by only tungsten and carbon, it has one of the highest boiling points of all elements. It is one of the densest, exceeded only by platinum and osmium. Rhenium has a hexagonal close-packed crystal structure, with lattice parameters a = 276.1 pm and c = 445.6 pm. Its usual commercial form is a powder, but this element can be consolidated by pressing and sintering in a vacuum or hydrogen atmosphere.
This procedure yields a compact solid having a density above 90% of the density of the metal. When annealed this metal is ductile and can be bent, coiled, or rolled. Rhenium-molybdenum alloys are superconductive at 10 K. Rhenium metal superconducts at 1.697±0.006 K. In bulk form and at room temperature and atmospheric pressure, the element resists alkalis, sulfuric acid, hydrochloric acid, dilute nitric acid, aqua regia. Rhenium has one stable isotope, rhenium-185, which occurs in minority abundance, a situation found only in two other elements. Occurring rhenium is only 37.4% 185Re, 62.6% 187Re, unstable but has a long half-life. This lifetime can be affected by the charge state of rhenium atom; the beta decay of 187Re is used for rhenium-osmium dating of ores. The available energy for this beta decay is one of the lowest known among all radionuclides; the isotope rhenium-186m is notable as being one of the longest lived metastable isotopes with a half-life of around 200,000 years. There are twenty-five other recognized radioactive isotopes of rhenium.
Rhenium compounds are known for all the oxidation states between −3 and +7 except −2. The oxidation states +7, +6, +4, +2 are the most common. Rhenium is most available commercially as salts of perrhenate, including sodium and ammonium perrhenates; these are white, water-soluble compounds. The most common rhenium chlorides are ReCl6, ReCl5, ReCl4, ReCl3; the structures of these compounds feature extensive Re-Re bonding, characteristic of this metal in oxidation states lower than VII. Salts of 2− feature a quadruple metal-metal bond. Although the highest rhenium chloride features Re, fluorine gives the d0 Re derivative rhenium heptafluoride. Bromides and iodides of rhenium are well known. Like tungsten and molybdenum, with which it shares chemical similarities, rhenium forms a variety of oxyhalides; the oxychlorides are most common, include ReOCl4, ReOCl3. The most common oxide is the volatile colourless Re2O7. Rhenium trioxide ReO3 adopts a perovskite-like structure. Other oxides include
A chemical substance is a form of matter having constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. Chemical substances can be chemical compounds, or alloys. Chemical elements may not be included in the definition, depending on expert viewpoint. Chemical substances are called'pure' to set them apart from mixtures. A common example of a chemical substance is pure water. Other chemical substances encountered in pure form are diamond, table salt and refined sugar. However, in practice, no substance is pure, chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, gases, or plasma, may change between these phases of matter with changes in temperature or pressure. Chemical substances may be converted to others by means of chemical reactions. Forms of energy, such as light and heat, are not matter, are thus not "substances" in this regard.
A chemical substance may well be defined as "any material with a definite chemical composition" in an introductory general chemistry textbook. According to this definition a chemical substance can either be a pure chemical element or a pure chemical compound. But, there are exceptions to this definition; the chemical substance index published by CAS includes several alloys of uncertain composition. Non-stoichiometric compounds are a special case that violates the law of constant composition, for them, it is sometimes difficult to draw the line between a mixture and a compound, as in the case of palladium hydride. Broader definitions of chemicals or chemical substances can be found, for example: "the term'chemical substance' means any organic or inorganic substance of a particular molecular identity, including – any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature". In geology, substances of uniform composition are called minerals, while physical mixtures of several minerals are defined as rocks.
Many minerals, mutually dissolve into solid solutions, such that a single rock is a uniform substance despite being a mixture in stoichiometric terms. Feldspars are a common example: anorthoclase is an alkali aluminum silicate, where the alkali metal is interchangeably either sodium or potassium. In law, "chemical substances" may include both pure substances and mixtures with a defined composition or manufacturing process. For example, the EU regulation REACH defines "monoconstituent substances", "multiconstituent substances" and "substances of unknown or variable composition"; the latter two consist of multiple chemical substances. For example, charcoal is an complex polymeric mixture that can be defined by its manufacturing process. Therefore, although the exact chemical identity is unknown, identification can be made to a sufficient accuracy; the CAS index includes mixtures. Polymers always appear as mixtures of molecules of multiple molar masses, each of which could be considered a separate chemical substance.
However, the polymer may be defined by a known precursor or reaction and the molar mass distribution. For example, polyethylene is a mixture of long chains of -CH2- repeating units, is sold in several molar mass distributions, LDPE, MDPE, HDPE and UHMWPE; the concept of a "chemical substance" became established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate. He deduced; this is now known as the law of constant composition. With the advancement of methods for chemical synthesis in the realm of organic chemistry. However, there are some controversies regarding this definition because the large number of chemical substances reported in chemistry literature need to be indexed. Isomerism caused much consternation to early researchers, since isomers have the same composition, but differ in configuration of the atoms. For example, there was much speculation for the chemical identity of benzene, until the correct structure was described by Friedrich August Kekulé.
The idea of stereoisomerism – that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement – was another crucial step in understanding the concept of distinct chemical substances. For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers. An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmuted into another element through a nuclear reaction; this is so, beca
Chromium is a chemical element with symbol Cr and atomic number 24. It is the first element in group 6, it is a steely-grey, lustrous and brittle transition metal. Chromium boasts a high usage rate as a metal, able to be polished while resisting tarnishing. Chromium is the main additive in stainless steel, a popular steel alloy due to its uncommonly high specular reflection. Simple polished chromium reflects 70% of the visible spectrum, with 90% of infrared light being reflected; the name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, because many chromium compounds are intensely colored. Ferrochromium alloy is commercially produced from chromite by silicothermic or aluminothermic reactions and chromium metal by roasting and leaching processes followed by reduction with carbon and aluminium. Chromium metal is of high value for hardness. A major development in steel production was the discovery that steel could be made resistant to corrosion and discoloration by adding metallic chromium to form stainless steel.
Stainless steel and chrome plating together comprise 85% of the commercial use. In the United States, trivalent chromium ion is considered an essential nutrient in humans for insulin and lipid metabolism. However, in 2014, the European Food Safety Authority, acting for the European Union, concluded that there was not sufficient evidence for chromium to be recognized as essential. While chromium metal and Cr ions are not considered toxic, hexavalent chromium is both toxic and carcinogenic. Abandoned chromium production sites require environmental cleanup. Chromium is the fourth transition metal found on the periodic table, has an electron configuration of 3d5 4s1, it is the first element in the periodic table whose ground-state electron configuration violates the Aufbau principle. This occurs again in the periodic table with other elements and their electron configurations, such as copper and molybdenum; this occurs. In the previous elements, the energetic cost of promoting an electron to the next higher energy level is too great to compensate for that released by lessening inter-electronic repulsion.
However, in the 3d transition metals, the energy gap between the 3d and the next-higher 4s subshell is small, because the 3d subshell is more compact than the 4s subshell, inter-electron repulsion is smaller between 4s electrons than between 3d electrons. This lowers the energetic cost of promotion and increases the energy released by it, so that the promotion becomes energetically feasible and one or two electrons are always promoted to the 4s subshell. Chromium is the first element in the 3d series where the 3d electrons start to sink into the inert core. Chromium is a strong oxidising agent in contrast to the tungsten oxides. Chromium is hard, is the third hardest element behind carbon and boron, its Mohs hardness is 8.5, which means that it can scratch samples of quartz and topaz, but can be scratched by corundum. Chromium is resistant to tarnishing, which makes it useful as a metal that preserves its outermost layer from corroding, unlike other metals such as copper and aluminium. Chromium has a melting point of 1907 °C, low compared to the majority of transition metals.
However, it still has the second highest melting point out of all the Period 4 elements, being topped by vanadium by 3 °C at 1910 °C. The boiling point of 2671 °C, however, is comparatively lower, having the third lowest boiling point out of the Period 4 transition metals alone behind manganese and zinc. Chromium has an unusually high specular reflection in comparison to that of other transition metals. At 425 μm, chromium was found to have a relative maximum reflection of about 72% reflectance, before entering a depression in reflectivity, reaching a minimum of 62% reflectance at 750 μm before rising again to reflecting 90% of 4000 μm of infrared waves.. When chromium is formed into a stainless steel alloy and polished, the specular reflection decreases with the inclusion of additional metals, yet is still rather high in comparison with other alloys. Between 40% and 60% of the visible spectrum is reflected from polished stainless steel; the explanation on why chromium displays such a high turnout of reflected photon waves in general the 90% of infrared waves that were reflected, can be attributed to chromium's magnetic properties.
Chromium has unique magnetic properties in the sense that chromium is the only elemental solid which shows antiferromagnetic ordering at room temperature. Above 38 °C, its magnetic ordering changes to paramagnetic.. The antiferromagnetic properties, which cause the chromium atoms to temporarily ionize and bond with themselves, are present because the body-centric cubic's magnetic properties are disproportionate to the lattice periodicity; this is due to the fact that the magnetic moments at the cube's corners and the cube centers are not equal, but are still antiparallel. From here, the frequency-dependent relative permittivity of chromium, deriving from Maxwell's equations in conjunction with chromium's antiferromagnetivity, leaves chromium with a high infrared and visible light reflectance. Chromium metal left standing in air is passivated by oxidation, forming a th