Concentrated solar power
Concentrated solar power systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight, or solar thermal energy, onto a small area. Electricity is generated when the concentrated light is converted to heat, which drives a heat engine connected to an electrical power generator or powers a thermochemical reaction. CSP had a world's total installed capacity of 4,815 MW in 2016, up from 354 MW in 2005; as of 2017, Spain accounted for half of the world's capacity, at 2,300 MW, making this country the world leader in CSP. The United States follows with 1,740 MW. Interest is notable in North Africa and the Middle East, as well as India and China; the global market has been dominated by parabolic-trough plants, which accounted for 90% of CSP plants at one point. The largest CSP projects in the world are the Ivanpah Solar Power Facility in the United States and the Mojave Solar Project in the United States. In most cases, CSP technologies cannot compete on price with photovoltaic solar panels, which have experienced huge growth in recent years due to falling prices and much smaller operating costs.
CSP needs large amount of direct solar radiation, its energy generation falls with cloud cover. This is in contrast with photovoltaics, which can produce electricity from diffuse radiation. However, the advantage of CSP over PV is that as a thermal technology, running a conventional thermal power block, a CSP plant can store the heat of solar energy in molten salts, which enables these plants to continue to generate electricity whenever it is needed, whether day or night; this makes CSP a dispatchable form of solar. This is valuable in places where there is a high penetration of PV, such as California because an evening peak is being exacerbated as PV ramps down at sunset. CSP has other uses than electricity. Researchers are investigating solar thermal reactors for the production of solar fuels, making solar a transportable form of energy in the future; these researchers use the solar heat of CSP as a catalyst for thermochemistry to break apart molecules of H2O, to create hydrogen from solar energy with no carbon emissions.
By splitting both H2O and CO2, other much-used hydrocarbons – for example, the jet fuel used to fly commercial airplanes – could be created with solar energy rather than from fossil fuels. In 2017, CSP represented less than 2% of worldwide installed capacity of solar electricity plants. However, in recent years falling prices of CSP plants are making this technology competitive with other base-load power plants using fossil and nuclear fuel in high moisture and dusty atmosphere at sea level, such as the United Arab Emirates. Base-load CSP tariff in the dry Atacama region of Chile reached below ¢5.0/kWh in 2017 auctions. A legend has it that Archimedes used a "burning glass" to concentrate sunlight on the invading Roman fleet and repel them from Syracuse. In 1973 a Greek scientist, Dr. Ioannis Sakkas, curious about whether Archimedes could have destroyed the Roman fleet in 212 BC, lined up nearly 60 Greek sailors, each holding an oblong mirror tipped to catch the sun's rays and direct them at a tar-covered plywood silhouette 49 m away.
The ship caught fire after a few minutes. In 1866, Auguste Mouchout used a parabolic trough to producе steam for the first solar steam engine; the first patent for a solar collector was obtained by the Italian Alessandro Battaglia in Genoa, Italy, in 1886. Over the following years, invеntors such as John Ericsson and Frank Shuman developed concentrating solar-powered dеvices for irrigation, refrigеration, locomоtion. In 1913 Shuman finished a 55 HP parabolic solar thermal energy station in Maadi, Egypt for irrigation; the first solar-power system using a mirror dish was built by Dr. R. H. Goddard, well known for his research on liquid-fueled rockets and wrote an article in 1929 in which he asserted that all the previous obstacles had been addressed. Professor Giovanni Francia designed and built the first concentrated-solar plant, which entered into operation in Sant'Ilario, near Genoa, Italy in 1968; this plant had the architecture of today's power tower plants with a solar receiver in the center of a field of solar collectors.
The plant was able to produce 1 MW with superheated steam at 100 bar and 500 °C. The 10 MW Solar One power tower was developed in Southern California in 1981. Solar One was converted into Solar Two in 1995, implementing a new design with a molten salt mixture as the receiver working fluid and as a storage medium; the molten salt approach proved effective, Solar Two operated until it was decommissioned in 1999. The parabolic-trough technology of the nearby Solar Energy Generating Systems, begun in 1984, was more workable; the 354 MW SEGS was the largest solar power plant in the world, until 2014. No commercial concentrated solar was constructed from 1990 when SEGS was completed until 2006 when the Compact linear Fresnel reflector system at Liddell Power Station in Australia was built. Few other plants were built with this design although the 5 MW Kimberlina Solar Thermal Energy Plant opened in 2009. In 2007, 75 MW Nevada Solar One was built, a trough design and the first large plant since SEGS.
Between 2009 and 2013, Spain built over standardized in 50 MW blocks. Due to the success of Solar Two, a commercial power plant, called Solar Tres Power Tower, was buil
Cementite is a compound of iron and carbon, more an intermediate transition metal carbide with the formula Fe3C. By weight, it is 93.3 % iron. It has an orthorhombic crystal structure, it is a hard, brittle material classified as a ceramic in its pure form, is a found and important constituent in ferrous metallurgy. While cementite is present in most steels and cast irons, it is produced as a raw material in the iron carbide process, which belongs to the family of alternative ironmaking technologies; the name cementite originated from the research of Floris Osmond and J. Werth, where the structure of solidified steel consists of a kind of cellular tissue in theory, with ferrite as the nucleus and Fe3C the envelope of the cells; the carbide therefore cemented the iron. In the iron–carbon system it is a common constituent because ferrite can contain at most 0.02wt% of uncombined carbon. Therefore, in carbon steels and cast irons that are cooled, a portion of the carbon is in the form of cementite.
Cementite forms directly from the melt in the case of white cast iron. In carbon steel, cementite precipitates from austenite as austenite transforms to ferrite on slow cooling, or from martensite during tempering. An intimate mixture with ferrite, the other product of austenite, forms a lamellar structure called pearlite. While cementite is thermodynamically unstable being converted to austenite and graphite at higher temperatures, it does not decompose on heating at temperatures below the eutectoid temperature on the metastable iron-carbon phase diagram. Cementite changes from ferromagnetic to paramagnetic at its Curie temperature of 480 K. A natural iron carbide occurs in iron meteorites and is called cohenite after the German mineralogist Emil Cohen, who first described it; as carbon is one of the possible minor light alloy components of metallic planetary cores, the high-pressure/high-temperature properties of cementite as a simple proxy for cohenite are studied experimentally. The figure shows the compressional behaviour at room temperature.
There are other forms of metastable iron carbides that have been identified in tempered steel and in the industrial Fischer-Tropsch process. These include epsilon carbide, hexagonal close-packed Fe2-3C, precipitates in plain-carbon steels of carbon content > 0.2%, tempered at 100-200 °C. Non-stoichiometric ε-carbide dissolves above ~200 °C, where Hägg carbides and cementite begin to form. Hägg carbide, monoclinic Fe5C2, precipitates in hardened tool steels tempered at 200-300 °C. Characterization of different iron carbides is not at all a trivial task, X-ray diffraction is complemented by Mössbauer spectroscopy. Smith, William F.. Foundations of Materials Science and Engineering. McGraw-Hill. ISBN 978-0-07-295358-9. Durand-Charre, Madeleine. Microstructure of Steels and Cast Irons. Springer. ISBN 978-3-642-05897-4. Mössbauer Spectroscopy of Iron Carbides: From Prediction to Experimental Confirmation http://www.nature.com/articles/srep26184 Comprehensive review on cementite Crystal structure of cementite at NRL Crystal Structure of Cementite, Cambridge University Alternative Ironmaking Technologies L.
J. E. Cohen Nature of Carbides of Iron, Bulletin 631 US Bureau of Mines Pycalphad: Thermodynamic calculation of cementite http://pycalphad.readthedocs.org/en/latest/examples/CementiteAnalysis.html based on Hallstedt, Bengt. "Thermodynamic properties of cementite". Calphad. 34: 129–133. Doi:10.1016/j.calphad.2010.01.004. Ester Esna du Plessis The Crystal Structures of Iron Carbides, Ph. D. Thesis, University of Johannesburg, 2006 https://ujcontent.uj.ac.za/vital/access/manager/Repository/uj:1863 Le Caer, G.. "Characterization by Moessbauer spectroscopy of iron carbides formed by Fischer-Tropsch synthesis". The Journal of Physical Chemistry. 86: 4799–4808. Doi:10.1021/j100221a030. Bauer-Grosse, E.. "Formation of Fe7C3 and Fe5C2 type metastable carbides during the crystallization of an amorphous Fe75C25 alloy". Journal of Non-Crystalline Solids. 44: 277–286. Doi:10.1016/0022-309390030-2
Sodium-potassium alloy, colloquially called NaK, is an alloy of two alkali metals and potassium, and, liquid at room temperature. Various commercial grades are available. NaK is reactive with water and may catch fire when exposed to air, so must be handled with special precautions. NaK containing 40% to 90% potassium by weight is liquid at room temperature; the eutectic mixture consists of 77% potassium and 23% sodium, is liquid from −12.6 to 785 °C, has a density of 866 kg/m3 at 21 °C and 855 kg/m3 at 100 °C, making it less dense than water. It is reactive with water and is stored under hexane or other hydrocarbons, or under an inert gas if high purity and low levels of oxidation are required; when stored in air, it may ignite. This superoxide reacts explosively with water and organics. NaK will sink in lighter mineral oil, it is unsafe to store in this manner. A large explosion took place at the Oak Ridge Y-12 facility on December 8, 1999, when NaK cleaned up after an accidental spill and inappropriately treated with mineral oil was scratched with a metal tool.
The liquid alloy attacks PTFE. NaK has a high surface tension, which makes large amounts of it pull into a bun-like shape, its specific heat capacity is 982 J/kg⋅K, one quarter of that for water, but heat transfer is higher over a temperature gradient due to higher thermal conductivity. Metropolis Monte Carlo simulations indicate an amorphous solid may form at the eutectic concentration below a temperature range of 140 K to 170 K with rapid cooling. NaK has been used as the coolant in experimental fast neutron nuclear reactors. Unlike commercial plants, these are shut down and defuelled. Use of lead or pure sodium, the other materials used in practical reactors, would require continual heating to maintain the coolant as a liquid. Use of NaK overcomes this; the Dounreay Fast Reactor is an example. The Soviet RORSAT radar satellites were powered by a BES-5 reactor, cooled with NaK. In addition to the wide liquid temperature range, NaK has a low vapor pressure, important in the vacuum of space. An unintended consequence of the usage as a coolant on orbiting satellites has been the creation of additional space debris.
NaK coolant has leaked from a number of satellites, including Kosmos 1818 and Kosmos 1867. The coolant self-forms into frozen droplets of solid sodium-potassium of up to several centimeters in size; these solid objects are a source of space debris. The Danamics LMX Superleggera CPU cooler uses NaK to transport heat from the CPU to its cooling fins. Sodium-potassium alloys are used as desiccants in drying solvents prior to distillation, although they are inferior to molecular sieves. NaK-77, a eutectic alloy of sodium-potassium, can be used as a hydraulic fluid in high-temperature and high-radiation environments, for temperature ranges of 10 to 1,400 °F, its bulk modulus at 1,000 °F is higher than of a hydraulic oil at room temperature. Its lubricity is poor, so positive-displacement pumps are unsuitable and centrifugal pumps have to be used. Addition of caesium shifts the useful temperature range to −95 to 1,300 °F. NaK-77 alloy was tested in hydraulic and fluidic systems for the Supersonic Low Altitude Missile.
Industrially, NaK is produced in a reactive distillation. In this continuous process, a distillation column is fed with potassium sodium. In the reaction zone, potassium chloride reacts with sodium to form sodium potassium; the lighter-boiling potassium is enriched in an upper fractionating zone and drawn at the column head while molten sodium chloride is withdrawn from the bottom. Liquid metal
Gold is a chemical element with symbol Au and atomic number 79, making it one of the higher atomic number elements that occur naturally. In its purest form, it is a bright reddish yellow, soft and ductile metal. Chemically, gold is a group 11 element, it is solid under standard conditions. Gold occurs in free elemental form, as nuggets or grains, in rocks, in veins, in alluvial deposits, it occurs in a solid solution series with the native element silver and naturally alloyed with copper and palladium. Less it occurs in minerals as gold compounds with tellurium. Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of nitric acid and hydrochloric acid, which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic objects, giving rise to the term acid test. Gold dissolves in alkaline solutions of cyanide, which are used in mining and electroplating.
Gold dissolves in mercury, forming amalgam alloys. A rare element, gold is a precious metal, used for coinage and other arts throughout recorded history. In the past, a gold standard was implemented as a monetary policy, but gold coins ceased to be minted as a circulating currency in the 1930s, the world gold standard was abandoned for a fiat currency system after 1971. A total of 186,700 tonnes of gold exists above ground, as of 2015; the world consumption of new gold produced is about 50% in jewelry, 40% in investments, 10% in industry. Gold's high malleability, resistance to corrosion and most other chemical reactions, conductivity of electricity have led to its continued use in corrosion resistant electrical connectors in all types of computerized devices. Gold is used in infrared shielding, colored-glass production, gold leafing, tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine; as of 2017, the world's largest gold producer by far was China with 440 tonnes per year.
Gold is the most malleable of all metals. It can be drawn into a monoatomic wire, stretched about twice before it breaks; such nanowires distort via formation and migration of dislocations and crystal twins without noticeable hardening. A single gram of gold can be beaten into a sheet of 1 square meter, an avoirdupois ounce into 300 square feet. Gold leaf can be beaten thin enough to become semi-transparent; the transmitted light appears greenish blue, because gold reflects yellow and red. Such semi-transparent sheets strongly reflect infrared light, making them useful as infrared shields in visors of heat-resistant suits, in sun-visors for spacesuits. Gold is a good conductor of electricity. Gold has a density of 19.3 g/cm3 identical to that of tungsten at 19.25 g/cm3. By comparison, the density of lead is 11.34 g/cm3, that of the densest element, osmium, is 22.588±0.015 g/cm3. Whereas most metals are gray or silvery white, gold is reddish-yellow; this color is determined by the frequency of plasma oscillations among the metal's valence electrons, in the ultraviolet range for most metals but in the visible range for gold due to relativistic effects affecting the orbitals around gold atoms.
Similar effects impart a golden hue to metallic caesium. Common colored gold alloys include the distinctive eighteen-karat rose gold created by the addition of copper. Alloys containing palladium or nickel are important in commercial jewelry as these produce white gold alloys. Fourteen-karat gold-copper alloy is nearly identical in color to certain bronze alloys, both may be used to produce police and other badges. White gold alloys can be made with nickel. Fourteen- and eighteen-karat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. Blue gold can be made by alloying with iron, purple gold can be made by alloying with aluminium. Less addition of manganese, aluminium and other elements can produce more unusual colors of gold for various applications. Colloidal gold, used by electron-microscopists, is red. Gold has only one stable isotope, 197Au, its only occurring isotope, so gold is both a mononuclidic and monoisotopic element. Thirty-six radioisotopes have been synthesized, ranging in atomic mass from 169 to 205.
The most stable of these is 195Au with a half-life of 186.1 days. The least stable is 171Au. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of proton emission, α decay, β+ decay; the exceptions are 195Au, which decays by electron capture, 196Au, which decays most by electron capture with a minor β− decay path. All of gold's radioisotopes with atomic masses above 197 decay by β− decay. At least 32 nuclear isomers have been characterized, ranging in atomic mass from 170 to 200. Within that range, only 178Au, 180Au, 181Au, 182Au, 188Au do not have isomers. Gold's most stable isomer is 198m2Au with a half-life of 2.27 days. Gold's least stable isomer is 177m2Au with a half-life of only 7 ns. 184m1Au has three decay paths: β+ decay, isomeric
Potassium is a chemical element with symbol K and atomic number 19. It was first isolated from the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals. All of the alkali metals have a single valence electron in the outer electron shell, removed to create an ion with a positive charge – a cation, which combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium is a soft silvery-white alkali metal that oxidizes in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, burning with a lilac-colored flame, it is found dissolved in sea water, is part of many minerals. Potassium is chemically similar to sodium, the previous element in group 1 of the periodic table, they have a similar first ionization energy, which allows for each atom to give up its sole outer electron. That they are different elements that combine with the same anions to make similar salts was suspected in 1702, was proven in 1807 using electrolysis.
Occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, it is the most common radioisotope in the human body. Potassium ions are vital for the functioning of all living cells; the transfer of potassium ions across nerve cell membranes is necessary for normal nerve transmission. Fresh fruits and vegetables are good dietary sources of potassium; the body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys. Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps. Heavy crop production depletes the soil of potassium, this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production; the English name for the element potassium comes from the word "potash", which refers to an early method of extracting various potassium salts: placing in a pot the ash of burnt wood or tree leaves, adding water and evaporating the solution.
When Humphry Davy first isolated the pure element using electrolysis in 1807, he named it potassium, which he derived from the word potash. The symbol "K" stems from kali, itself from the root word alkali, which in turn comes from Arabic: القَلْيَه al-qalyah "plant ashes". In 1797, the German chemist Martin Klaproth discovered "potash" in the minerals leucite and lepidolite, realized that "potash" was not a product of plant growth but contained a new element, which he proposed to call kali. In 1807, Humphry Davy produced the element via electrolysis: in 1809, Ludwig Wilhelm Gilbert proposed the name Kalium for Davy's "potassium". In 1814, the Swedish chemist Berzelius advocated the name kalium for potassium, with the chemical symbol "K"; the English and French speaking countries adopted Davy and Gay-Lussac/Thénard's name Potassium, while the Germanic countries adopted Gilbert/Klaproth's name Kalium. The "Gold Book" of the International Union of Physical and Applied Chemistry has designated the official chemical symbol as K.
Potassium is the second least dense metal after lithium. It is a soft solid with a low melting point, can be cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray on exposure to air. In a flame test and its compounds emit a lilac color with a peak emission wavelength of 766.5 nanometers. Neutral potassium atoms have 19 electrons, one more than the stable configuration of the noble gas argon; because of this and its low first ionization energy of 418.8 kJ/mol, the potassium atom is much more to lose the last electron and acquire a positive charge than to gain one and acquire a negative charge. This process requires so little energy that potassium is oxidized by atmospheric oxygen. In contrast, the second ionization energy is high, because removal of two electrons breaks the stable noble gas electronic configuration. Potassium therefore does not form compounds with the oxidation state of higher. Potassium is an active metal that reacts violently with oxygen in water and air.
With oxygen it forms potassium peroxide, with water potassium forms potassium hydroxide. The reaction of potassium with water is dangerous because of its violent exothermic character and the production of hydrogen gas. Hydrogen reacts again with atmospheric oxygen, producing water, which reacts with the remaining potassium; this reaction requires only traces of water. Because of the sensitivity of potassium to water and air, reactions with other elements are possible only in an inert atmosphere such as argon gas using air-free techniques. Potassium does not react with most hydrocarbons such as mineral kerosene, it dissolves in liquid ammonia, up to 480 g per 1000 g of ammonia at 0 °C. Depending on the concentration, the ammonia solutions are blue to yellow, their electrical conductivity is similar to that of liquid metals. In a pure solution, potassium reacts with ammonia to form KNH2, but this reaction is accelerated by minute amounts of transition metal s
A fire sprinkler or sprinkler head is the component of a fire sprinkler system that discharges water when the effects of a fire have been detected, such as when a predetermined temperature has been exceeded. Fire sprinklers are extensively used worldwide, with over 40 million sprinkler heads fitted each year. In buildings protected by properly designed and maintained fire sprinklers, over 99% of fires were controlled by fire sprinklers alone. In 1812, British inventor Sir William Congreve patented a manual sprinkler system using perforated pipes along the ceiling; when someone noticed a fire, a valve outside the building could be opened to send water through the pipes. It was not until a short time that, as a result of a large furniture factory that burned down, Hiram Stevens Maxim was consulted on how to prevent a recurrence and invented the first automatic fire sprinkler, it would report the fire to the fire station. Maxim was unable to sell the idea elsewhere. Henry S. Parmalee of New Haven, Connecticut created and installed the first automatic fire sprinkler system in 1874, using solder that melted in a fire to unplug holes in the otherwise sealed water pipes.
He was the president of Mathusek Piano Works, invented his sprinkler system in response to exorbitantly high insurance rates. Parmalee patented his idea and had great success with it in the U. S. calling his invention the "automatic fire extinguisher". He traveled to Europe to demonstrate his method to stop a building fire before total destruction. Parmalee's invention did not get as much attention as he had planned, as most people could not afford to install a sprinkler system. Once he realized this, he turned his efforts to educating insurance companies about his system, he explained that the sprinkler system would reduce the loss ratio, thus save money for the insurance companies. He knew that he could never succeed in obtaining contracts from the business owners to install his system unless he could ensure for them a reasonable return in the form of reduced premiums. In this connection, he was able to enlist the interest of two men, who both had connections in the insurance industry; the first of was Major Hesketh, a cotton spinner in a large business in Bolton, Chairman of the Bolton Cotton Trades Mutual Insurance Company.
The Directors of this Company and its Secretary, Peter Kevan, took an interest in Parmalee’s early experiments. Hesketh got Parmalee his first order for sprinkler installations in the cotton spinning mills of John Stones & Company, at Astley Bridge, Bolton; this was followed soon afterwards by an order from the Alexandra Mills, owned by John Butler of the same town. Although Parmalee got two sales through its efforts, the Bolton Cotton Trades Mutual Insurance Company was not a big company outside of its local area. Parmalee needed a wider influence, he found this influence in James North Lane, the Manager of the Mutual Fire Insurance Corporation of Manchester. This company was founded in 1870 by the Textile Manufacturers' Associations of Lancashire and Yorkshire as a protest against high insurance rates, they had a policy of encouraging risk management and more the use of the most up-to-date and scientific apparatus for extinguishing fires. Though he put tremendous effort and time into educating the masses on his sprinkler system, by 1883 only about 10 factories were protected by the Parmalee sprinkler.
Back in the U. S. Frederick Grinnell, manufacturing the Parmalee sprinkler, designed the more effective Grinnell sprinkler, he increased sensitivity by removing the fusible joint from all contact with the water, and, by seating a valve in the center of a flexible diaphragm, he relieved the low-fusing soldered joint of the strain of water pressure. By this means, the valve seat was forced against the valve by the water pressure, producing a self-closing action; the greater the water pressure, the tighter the valve. The flexible diaphragm had a more important function, it caused the valve and its seat to move outwards until the solder joint was severed. Grinnell got a patent for his version of the sprinkler system, he took his invention to Europe, where it was a much bigger success than the Parmalee version. The Parmalee system was withdrawn, opening the path for Grinnell and his invention. Fire sprinkler application and installation guidelines, overall fire sprinkler system design guidelines are provided by the National Fire Protection Association 13, 13D, 13R.
California and Illinois require sprinklers in at least some new residential construction. Fire sprinklers can be open orifice. Automatic fire sprinklers operate at a predetermined temperature, utilizing a fusible element, a portion of which melts, or a frangible glass bulb containing liquid which breaks, allowing the plug in the orifice to be pushed out of the orifice by the water pressure in the fire sprinkler piping, resulting in water flow from the orifice; the water stream impacts a deflector, which produces a specific spray pattern designed in support of the goals of the sprinkler type. Modern sprinkler heads are designed to direct spray downwards. Spray nozzles are available to provide spray in various patterns; the majority of automatic fire sprinklers operate individually in a fire. Contrary to motion picture representation, the entire sprinkler system does not activate, unless the system is a special deluge type. Open orifice sprinklers are only used in water spray systems or deluge sprinklers systems.
They are identical to the automatic sprinkler on which they are based, with the heat-sensitive operating element removed. Automa
Mercury is a chemical element with symbol Hg and atomic number 80. It is known as quicksilver and was named hydrargyrum. A heavy, silvery d-block element, mercury is the only metallic element, liquid at standard conditions for temperature and pressure. Mercury occurs in deposits throughout the world as cinnabar; the red pigment vermilion is obtained by synthetic mercuric sulfide. Mercury is used in thermometers, manometers, sphygmomanometers, float valves, mercury switches, mercury relays, fluorescent lamps and other devices, though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being phased out in clinical environments in favor of alternatives such as alcohol- or galinstan-filled glass thermometers and thermistor- or infrared-based electronic instruments. Mechanical pressure gauges and electronic strain gauge sensors have replaced mercury sphygmomanometers. Mercury remains in use in scientific research applications and in amalgam for dental restoration in some locales.
It is used in fluorescent lighting. Electricity passed through mercury vapor in a fluorescent lamp produces short-wave ultraviolet light, which causes the phosphor in the tube to fluoresce, making visible light. Mercury poisoning can result from exposure to water-soluble forms of mercury, by inhalation of mercury vapor, or by ingesting any form of mercury. Mercury is a silvery-white liquid metal. Compared to other metals, it is a fair conductor of electricity, it has a freezing point of −38.83 °C and a boiling point of 356.73 °C, both the lowest of any stable metal, although preliminary experiments on copernicium and flerovium have indicated that they have lower boiling points. Upon freezing, the volume of mercury decreases by 3.59% and its density changes from 13.69 g/cm3 when liquid to 14.184 g/cm3 when solid. The coefficient of volume expansion is 181.59 × 10−6 at 0 °C, 181.71 × 10−6 at 20 °C and 182.50 × 10−6 at 100 °C. Solid mercury can be cut with a knife. A complete explanation of mercury's extreme volatility delves deep into the realm of quantum physics, but it can be summarized as follows: mercury has a unique electron configuration where electrons fill up all the available 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d, 6s subshells.
Because this configuration resists removal of an electron, mercury behaves to noble gases, which form weak bonds and hence melt at low temperatures. The stability of the 6s shell is due to the presence of a filled 4f shell. An f shell poorly screens the nuclear charge that increases the attractive Coulomb interaction of the 6s shell and the nucleus; the absence of a filled inner f shell is the reason for the somewhat higher melting temperature of cadmium and zinc, although both these metals still melt and, in addition, have unusually low boiling points. Mercury does not react with most acids, such as dilute sulfuric acid, although oxidizing acids such as concentrated sulfuric acid and nitric acid or aqua regia dissolve it to give sulfate and chloride. Like silver, mercury reacts with atmospheric hydrogen sulfide. Mercury reacts with solid sulfur flakes. Mercury dissolves many metals such as silver to form amalgams. Iron is an exception, iron flasks have traditionally been used to trade mercury.
Several other first row transition metals with the exception of manganese and zinc are resistant in forming amalgams. Other elements that do not form amalgams with mercury include platinum. Sodium amalgam is a common reducing agent in organic synthesis, is used in high-pressure sodium lamps. Mercury combines with aluminium to form a mercury-aluminium amalgam when the two pure metals come into contact. Since the amalgam destroys the aluminium oxide layer which protects metallic aluminium from oxidizing in-depth small amounts of mercury can corrode aluminium. For this reason, mercury is not allowed aboard an aircraft under most circumstances because of the risk of it forming an amalgam with exposed aluminium parts in the aircraft. Mercury embrittlement is the most common type of liquid metal embrittlement. There are seven stable isotopes of mercury, with 202Hg being the most abundant; the longest-lived radioisotopes are 194Hg with a half-life of 444 years, 203Hg with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lives.
199Hg and 201Hg are the most studied NMR-active nuclei, having spins of 1⁄2 and 3⁄2 respectively. Hg is the modern chemical symbol for mercury, it comes from hydrargyrum, a Latinized form of the Greek word ὑδράργυρος, a compound word meaning "water-silver" – since it is liquid like water and shiny like silver. The element was named after the Roman god Mercury, known for his mobility, it is associated with the planet Mercury. Mercury is the only metal for which the al