Glass is a non-crystalline, amorphous solid, transparent and has widespread practical and decorative uses in, for example, window panes and optoelectronics. The most familiar, the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica, the primary constituent of sand; the term glass, in popular usage, is used to refer only to this type of material, familiar from use as window glass and in glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of 75% silicon dioxide, sodium oxide from sodium carbonate, calcium oxide called lime, several minor additives. Many applications of silicate glasses derive from their optical transparency, giving rise to their primary use as window panes. Glass will transmit and refract light. Glass can be coloured by adding metallic salts, can be painted and printed with vitreous enamels; these qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows.
Although brittle, silicate glass is durable, many examples of glass fragments exist from early glass-making cultures. Because glass can be formed or moulded into any shape, it has been traditionally used for vessels: bowls, bottles and drinking glasses. In its most solid forms it has been used for paperweights and beads; when extruded as glass fiber and matted as glass wool in a way to trap air, it becomes a thermal insulating material, when these glass fibers are embedded into an organic polymer plastic, they are a key structural reinforcement part of the composite material fiberglass. Some objects were so made of silicate glass that they are called by the name of the material, such as drinking glasses and eyeglasses. Scientifically, the term "glass" is defined in a broader sense, encompassing every solid that possesses a non-crystalline structure at the atomic scale and that exhibits a glass transition when heated towards the liquid state. Porcelains and many polymer thermoplastics familiar from everyday use are glasses.
These sorts of glasses can be made of quite different kinds of materials than silica: metallic alloys, ionic melts, aqueous solutions, molecular liquids, polymers. For many applications, like glass bottles or eyewear, polymer glasses are a lighter alternative than traditional glass. Silicon dioxide is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, branching rootlike structures called fulgurites. Fused quartz is a glass made from chemically-pure silica, it has excellent resistance to thermal shock, being able to survive immersion in water while red hot. However, its high melting temperature and viscosity make it difficult to work with. Other substances are added to simplify processing. One is sodium carbonate; the soda makes the glass water-soluble, undesirable, so lime, some magnesium oxide and aluminium oxide are added to provide for a better chemical durability. The resulting glass is called a soda-lime glass. Soda-lime glasses account for about 90% of manufactured glass.
Most common glass contains other ingredients to change its properties. Lead glass or flint glass is more "brilliant" because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion and was used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eyeglasses. Iron can be incorporated into glass to absorb infrared radiation, for example in heat-absorbing filters for movie projectors, while cerium oxide can be used for glass that absorbs ultraviolet wavelengths; the following is a list of the more common types of silicate glasses and their ingredients and applications: Fused quartz called fused-silica glass, vitreous-silica glass: silica in vitreous, or glass, form. It has low thermal expansion, is hard, resists high temperatures, it is the most resistant against weathering. Fused quartz is used for high-temperature applications such as furnace tubes, lighting tubes, melting crucibles, etc.
Soda-lime-silica glass, window glass: silica + sodium oxide + lime + magnesia + alumina. Is transparent formed and most suitable for window glass, it has a high thermal expansion and poor resistance to heat. It is used for windows, some low-temperature incandescent light bulbs, tableware. Container glass is a soda-lime glass, a slight variation on flat glass, which uses more alumina and calcium, less sodium and magnesium, which are more water-soluble; this makes it less susceptible to water erosion. Sodium borosilicate glass, Pyrex: silica + boron trioxide + soda + alumina. Stan
Ebonite is a brand name for hard rubber first obtained by vulcanizing natural rubber for prolonged periods. Besides natural rubber, Ebonite linseed oil, its name comes from its intended use as an artificial substitute for ebony wood. The material is known generically as hard rubber and has been called vulcanite, although that name now refers to the mineral vulcanite. Charles Goodyear's brother Nelson Goodyear experimented with the chemistry of ebonite composites. In 1851 he used zinc oxide as a filler. Hugh Silver was responsible for giving it its name; the sulfur percentage and the applied temperatures and duration during vulcanizing are the main variables that determine the technical properties of the hard rubber polysulfide elastomer. The occurring reaction is addition of sulfur at the double bonds, forming intramolecular ring structures, so a large portion of the sulfur is cross-linked in the form of intramolecular addition; as a result of having a maximum sulfur content up to 40%, it may be used to resist swelling and minimize dielectric loss.
The strongest mechanical properties and greatest heat resistance is obtained with sulfur contents around 35% while the highest impact strength can be obtained with a lower sulfur content of 30%. The rigidity of hard rubber at room temperature is attributed to the van der Waals forces between the intramolecular sulfur atoms. Raising the temperature increases the molecular vibrations that overcome the van der Waals forces making it elastic. Hard rubber has a content mixture dependent density around 1.1 to 1.2. When reheated hard rubber exhibits shape-memory effect and can be easy reshaped within certain limits. Depending on the sulfur percentage hard rubber has a thermoplastic transition or softening temperature of 70 to 80 °C; the material is brittle, which produces problems in its use in battery cases for example, where the integrity of the case is vital to prevent leakage of sulfuric acid. It has now been replaced by carbon black -filled polypropylene. Under the influence of the ultraviolet portion in daylight hard rubber oxidizes and exposure to moisture bonds water with free sulfur on the surface creating sulfates and sulfuric acid at the surface that are hygroscopic.
The sulfates condense water from the air, forming a hydrophilic film with favorable wettability characteristics on the surface. These aging processes will discolor the surface grayish green to brown and cause rapid deterioration of electric surface resistivity. Ebonite contamination was problematic; the ebonite was rolled between metal foil sheets, which were peeled off, leaving traces of metal behind. For electronic use the surface was ground to remove metal particles. Hard rubber was used in early 20th century bowling balls, it has been used in electric plugs, tobacco pipe mouthpieces, hockey pucks, fountain pen bodies and nib feeds, saxophone and clarinet mouthpieces as well as complete humidity-stable clarinets. Hard rubber is seen as the wheel material in casters, it is commonly used in physics classrooms to demonstrate static electricity, because it is at or near the negative end of the triboelectric series. Hard rubber was used in the cases of automobile batteries for years, thus establishing black as their traditional colour long after stronger modern plastics like polypropylene were substituted.
It was used for decades in hair combs made by Ace, now part of Newell Rubbermaid, although the current models are known to be produced with plastics. Ebonite is used as an anticorrosive lining for various vessels that contain diluted hydrochloric acid, it forms bubbles when storing hydrofluoric acid at temperatures above room temperature, or for prolonged durations
Shungite is a black, non-crystalline mineraloid consisting of more than 98 weight percent of carbon. It was first described from a deposit near Shunga village, in Karelia, from where it gets its name. Shungite has been reported to contain trace amounts of fullerenes; the term "shungite" was used in 1879 to describe a mineraloid with more than 98 percent carbon. More the term has been used to describe shungite-bearing rocks, leading to some confusion. Shungite-bearing rocks have been classified purely on their carbon content, with Shungite-1 having a carbon content in the range 98-100 weight percent and Shungite-2, -3, -4 and -5 having contents in the ranges 35-80 percent, 20-35 percent, 10-20 percent and less than 10 percent, respectively. In a further classification, shungite is subdivided into bright, semi-bright, semi-dull and dull on the basis of their luster. Shungite has two main modes of occurrence, disseminated within the host rock and as mobilised material. Migrated shungite, bright shungite, has been interpreted to represent migrated hydrocarbons and is found as either layer shungite, layers or lenses near conformable with the host rock layering, or vein shungite, found as cross-cutting veins.
Shungite may occur as clasts within younger sedimentary rocks. Shungite has to date been found in Russia; the main deposit is in the Lake Onega area of Karelia, at Zazhoginskoye, near Shunga, with another occurrence at Vozhmozero. Two other much smaller occurrences have been reported in Russia, one in Kamchatka in volcanic rocks and the other formed by the burning of spoil from a coal mine at high temperature in Chelyabinsk. Other occurrences have been described from Austria, Democratic Republic of Congo and Kazakhstan. Shungite has been regarded as an example of abiogenic petroleum formation, but its biological origin has now been confirmed. Non-migrated shungite is found directly stratigraphically above deposits that were formed in a shallow water carbonate shelf to non-marine evaporitic environment; the shungite bearing sequence is thought to have been deposited during active rifting, consistent with the alkaline volcanic rocks that are found within the sequence. The organic-rich sediments were deposited in a brackish lagoonal setting.
The concentration of carbon indicates elevated biological productivity levels due to high levels of nutrients available from interbedded volcanic material. The stratified shungite-bearing deposits that retain sedimentary structures are interpreted as metamorphosed oil source rocks; some diapiric mushroom-shaped structures have been identified, which are interpreted as possible mud volcanoes. Layer and vein shungite varieties, shungite filling vesicles and forming the matrix to breccias, are interpreted as migrated petroleum, now in the form of metamorphosed bitumen; the Shunga deposit contains an estimated total carbon reserve of more than 250 gigatonnes. It is found within a sequence of Palaeoproterozoic metasedimentary and metavolcanic rocks that are preserved in a synform; the sequence is dated by a gabbro intrusion, which gives a date of 1980±27 Ma, the underlying dolostones, which give an age of 2090±70 Ma. There are nine Shungite-bearing layers within the Zaonezhskaya Formation, from the middle of the preserved sequence.
Of these the thickest is layer six, known as the "Productive horizon", due to its concentration of shungite deposits. Four main deposits are known from the area, the Shungskoe, Maksovo and Nigozero deposits; the Shungskoe deposit is the most studied and is mined out. Shungite has been used as a folk medical treatment since the early 18th century. Peter the Great set up Russia's first spa in Karelia to make use of the water purifying properties of shungite, which he had himself experienced, he instigated its use in providing purified water for the Russian army. The anti-bacterial properties of shungite have been confirmed by modern testing. Shungite has been used since the middle of the 18th century as a pigment for paint, is sold under the names "carbon black" or "shungite natural black". In the 1970s, shungite was exploited in the production of an insulating material, known as shungisite. Shungisite is prepared by heating rocks with low shungite concentrations to 1090–1130 °C and is used as a low density filler
International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is helpful in distinguishing between serials with the same title. ISSN are used in ordering, interlibrary loans, other practices in connection with serial literature; the ISSN system was first drafted as an International Organization for Standardization international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard; when a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in electronic media; the ISSN system refers to these types as electronic ISSN, respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is assigned a linking ISSN the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.
The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits; the last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code can be expressed as follows: NNNN-NNNC where N is in the set, a digit character, C is in; the ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, C=5. To calculate the check digit, the following algorithm may be used: Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, 2, respectively: 0 ⋅ 8 + 3 ⋅ 7 + 7 ⋅ 6 + 8 ⋅ 5 + 5 ⋅ 4 + 9 ⋅ 3 + 5 ⋅ 2 = 0 + 21 + 42 + 40 + 20 + 27 + 10 = 160 The modulus 11 of this sum is calculated. For calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right.
The modulus 11 of the sum must be 0. There is an online ISSN checker. ISSN codes are assigned by a network of ISSN National Centres located at national libraries and coordinated by the ISSN International Centre based in Paris; the International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change. Since the ISSN applies to an entire serial a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components.
Separate ISSNs are needed for serials in different media. Thus, the print and electronic media versions of a serial need separate ISSNs. A CD-ROM version and a web version of a serial require different ISSNs since two different media are involved. However, the same ISSN can be used for different file formats of the same online serial; this "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, the Web, it makes sense to consider only content, independent of media; this "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier, as ISSN-independent initiative, consolidated in the 2000s. Only in 2007, ISSN-L was defined in the
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite and is the main component of pearls and the shells of marine organisms and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale, it is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous. Calcium carbonate shares the typical properties of other carbonates. Notably it reacts with acids, releasing carbon dioxide:CaCO3 + 2 H+ → Ca2+ + CO2 + H2Oreleases carbon dioxide upon heating, called a thermal decomposition reaction, or calcination, to form calcium oxide called quicklime, with reaction enthalpy 178 kJ/mol:CaCO3 → CaO + CO2Calcium carbonate will react with water, saturated with carbon dioxide to form the soluble calcium bicarbonate. CaCO3 + CO2 + H2O → Ca2This reaction is important in the erosion of carbonate rock, forming caverns, leads to hard water in many regions.
An unusual form of calcium carbonate is the hexahydrate, ikaite, CaCO3·6H2O. Ikaite is stable only below 8 °C; the vast majority of calcium carbonate used in industry is extracted by quarrying. Pure calcium carbonate, can be produced from a pure quarried source. Alternatively, calcium carbonate is prepared from calcium oxide. Water is added to give calcium hydroxide carbon dioxide is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate: CaO + H2O → Ca2 Ca2 + CO2 → CaCO3↓ + H2O The thermodynamically stable form of CaCO3 under normal conditions is hexagonal β-CaCO3. Other forms can be prepared, the denser orthorhombic λ-CaCO3 and μ-CaCO3, occurring as the mineral vaterite; the aragonite form can be prepared by precipitation at temperatures above 85 °C, the vaterite form can be prepared by precipitation at 60 °C. Calcite contains calcium atoms coordinated by six oxygen atoms, in aragonite they are coordinated by nine oxygen atoms.
The vaterite structure is not understood. Magnesium carbonate has the calcite structure, whereas strontium carbonate and barium carbonate adopt the aragonite structure, reflecting their larger ionic radii. Calcite and vaterite are pure calcium carbonate minerals. Industrially important source rocks which are predominantly calcium carbonate include limestone, chalk and travertine. Eggshells, snail shells and most seashells are predominantly calcium carbonate and can be used as industrial sources of that chemical. Oyster shells have enjoyed recent recognition as a source of dietary calcium, but are a practical industrial source. Dark green vegetables such as broccoli and kale contain dietarily significant amounts of calcium carbonate, they are not practical as an industrial source. Beyond Earth, strong evidence suggests the presence of calcium carbonate on Mars. Signs of calcium carbonate have been detected at more than one location; this provides some evidence for the past presence of liquid water.
Carbonate, is found in geologic settings and constitutes an enormous carbon reservoir. Calcium carbonate occurs as aragonite and dolomite as significant constituents of the calcium cycle; the carbonate minerals form the rock types: limestone, marble, travertine and others. In warm, clear tropical waters corals are more abundant than towards the poles where the waters are cold. Calcium carbonate contributors, including plankton, coralline algae, brachiopods, echinoderms and mollusks, are found in shallow water environments where sunlight and filterable food are more abundant. Cold-water carbonates do exist at higher latitudes but have a slow growth rate; the calcification processes are changed by ocean acidification. Where the oceanic crust is subducted under a continental plate sediments will be carried down to warmer zones in the asthenosphere and lithosphere. Under these conditions calcium carbonate decomposes to produce carbon dioxide which, along with other gases, give rise to explosive volcanic eruptions.
The carbonate compensation depth is the point in the ocean where the rate of precipitation of calcium carbonate is balanced by the rate of dissolution due to the conditions present. Deep in the ocean, the temperature pressure increases. Calcium carbonate is unusual in. Increasing pressure increases the solubility of calcium carbonate; the carbonate compensation depth can range from 4,000 to 6,000 meters below sea level. Calcium carbonate can preserve fossils through permineralization. Most of the vertebrate fossils of the Two Medicine Formation—a geologic formation known for its duck-billed dinosaur eggs—are preserved by CaCO3 permineralization; this type of preservation conserves high levels of detail down to the microscopic level. However, it leaves specimens vulnerable to weathering when exposed to the surface. Trilobite populations were once thought to have composed the majority of aquatic life during the Cambrian, due to the fact that their calcium carbonate-rich shells were more preserved than those of other species, which had purely chitinous shells.
The main use of calcium ca
Vulcanization is a chemical process, invented by Charles Goodyear, used to harden rubber. Vulcanization traditionally referred to the treatment of natural rubber with sulfur and this remains the most common example, however the term has grown to include the hardening of other rubbers via various means. Examples include silicone rubber via room temperature vulcanizing and chloroprene rubber using metal oxides. Vulcanization can therefore be defined as the curing of elastomers, it works by forming cross-links between sections of polymer chain which results in increased rigidity and durability, as well as other changes in the mechanical and electrical properties of the material. Vulcanization, in common with the curing of other thermosetting polymers, is irreversible; the word vulcanization is derived from the Roman god of fire. In contrast with thermoplastic processes, vulcanization, in common with the curing of other thermosetting polymers, is irreversible. Five types of curing systems are in common use: Sulfur systems Peroxides Metallic oxides Acetoxysilane Urethane crosslinkers By far the most common vulcanizing methods depend on sulfur.
Sulfur, by itself, does not vulcanize synthetic polyolefins. Accelerated vulcanization is carried out using various compounds that modify the kinetics of crosslinking, this mixture is referred to as a cure package; the main polymers subjected to sulfur vulcanization are polyisoprene and styrene-butadiene rubber, which are used for most street-vehicle tires. The cure package is adjusted for the substrate and the application; the reactive sites—cure sites—are allylic hydrogen atoms. These C-H bonds are adjacent to carbon-carbon double bonds. During vulcanization, some of these C-H bonds are replaced by chains of sulfur atoms that link with a cure site of another polymer chain; these bridges contain between one and several atoms. The number of sulfur atoms in the crosslink influences the physical properties of the final rubber article. Short crosslinks give the rubber better heat resistance. Crosslinks with higher number of sulfur atoms give the rubber good dynamic properties but less heat resistance.
Dynamic properties are important for flexing movements of the rubber article, e.g. the movement of a side-wall of a running tire. Without good flexing properties these movements form cracks, make the rubber article fail; the vulcanization of neoprene or polychloroprene rubber is carried out using metal oxides rather than sulfur compounds which are presently used with many natural and synthetic rubbers. In addition, because of various processing factors, the choice of accelerator is governed by different rules to other diene rubbers. Most conventionally used accelerators are problematic when CR rubbers are cured and the most important accelerant has been found to be ethylene thiourea, although being an excellent and proven accelerator for polychloroprene, has been classified as reprotoxic; the European rubber industry has started a research project SafeRubber to develop a safer alternative to the use of ETU. Room-temperature vulcanizing silicone is constructed of reactive oil-based polymers combined with strengthening mineral fillers.
There are two types of room-temperature vulcanizing silicone: RTV-1. Acetoxysilane, when exposed to humid conditions, will form acetic acid; the curing process progresses through to its core. The product is either in a fluid or paste form. RTV-1 silicone has good adhesion and durability characteristics; the Shore hardness can be varied between 18 and 60. Elongation at break can range from 150% up to 700%, they have excellent aging resistance due to superior resistance to UV weathering. RTV-2. RTV-2 remains flexible from −80 to 250 °C. Break-down occurs at temperatures above 350 °C, leaving an inert silica deposit, non-flammable and non-combustible, they can be used for electrical insulation due to their dielectric properties. Mechanical properties are satisfactory. RTV-2 is used to make flexible moulds, as well as many technical parts for industry and paramedical applications. Polymer stabilizers Vulcanized fibre
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