Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" sound in its physical properties, except that humans cannot hear it; this limit varies from person to person and is 20 kilohertz in healthy young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz. Ultrasound is used in many different fields. Ultrasonic devices are used to detect objects and measure distances. Ultrasound imaging or sonography is used in medicine. In the nondestructive testing of products and structures, ultrasound is used to detect invisible flaws. Industrially, ultrasound is used for cleaning and accelerating chemical processes. Animals such as bats and porpoises use ultrasound for locating prey and obstacles. Scientists are studying ultrasound using graphene diaphragms as a method of communication. Acoustics, the science of sound, starts as far back as Pythagoras in the 6th century BC, who wrote on the mathematical properties of stringed instruments.
Echolocation in bats was discovered by Lazzaro Spallanzani in 1794, when he demonstrated that bats hunted and navigated by inaudible sound, not vision. Francis Galton in 1893 invented the Galton whistle, an adjustable whistle that produced ultrasound, which he used to measure the hearing range of humans and other animals, demonstrating that many animals could hear sounds above the hearing range of humans; the first technological application of ultrasound was an attempt to detect submarines by Paul Langevin in 1917. The piezoelectric effect, discovered by Jacques and Pierre Curie in 1880, was useful in transducers to generate and detect ultrasonic waves in air and water. Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz". In air at atmospheric pressure, ultrasonic waves have wavelengths of 1.9 cm or less. The upper frequency limit in humans is due to limitations of the middle ear. Auditory sensation can occur if high‐intensity ultrasound is fed directly into the human skull and reaches the cochlea through bone conduction, without passing through the middle ear.
Children can hear some high-pitched sounds that older adults cannot hear, because in humans the upper limit pitch of hearing tends to decrease with age. An American cell phone company has used this to create ring signals that are only audible to younger humans, but many older people can hear the signals, which may be because of the considerable variation of age-related deterioration in the upper hearing threshold; the Mosquito is an electronic device that uses a high pitched frequency to deter loitering by young people. Bats use a variety of ultrasonic ranging techniques to detect their prey, they can detect frequencies beyond 100 kHz up to 200 kHz. Many insects have good ultrasonic hearing, most of these are nocturnal insects listening for echolocating bats; these include many groups of moths, praying mantids and lacewings. Upon hearing a bat, some insects will make evasive manoeuvres to escape being caught. Ultrasonic frequencies trigger a reflex action in the noctuid moth that causes it to drop in its flight to evade attack.
Tiger moths emit clicks which may disturb bats' echolocation, in other cases may advertise the fact that they are poisonous by emitting sound. Dogs and cats' hearing range extends into the ultrasound; the wild ancestors of cats and dogs evolved this higher hearing range to hear high-frequency sounds made by their preferred prey, small rodents. A dog whistle is a whistle that emits ultrasound, used for calling dogs; the frequency of most dog whistles is within the range of 23 to 54 kHz. Toothed whales, including dolphins, can hear ultrasound and use such sounds in their navigational system to orient and to capture prey. Porpoises have the highest known upper hearing limit at around 160 kHz. Several types of fish can detect ultrasound. In the order Clupeiformes, members of the subfamily Alosinae have been shown to be able to detect sounds up to 180 kHz, while the other subfamilies can hear only up to 4 kHz. Ultrasound generator/speaker systems are sold as electronic pest control devices, which are claimed to frighten away rodents and insects, but there is no scientific evidence that the devices work.
An ultrasonic level or sensing system requires no contact with the target. For many processes in the medical, pharmaceutical and general industries this is an advantage over inline sensors that may contaminate the liquids inside a vessel or tube or that may be clogged by the product. Both continuous wave and pulsed systems are used; the principle behind a pulsed-ultrasonic technology is that the transmit signal consists of short bursts of ultrasonic energy. After each burst, the electronics looks for a return signal within a small window of time corresponding to the time it takes for the energy to pass through the vessel. Only a signal received during this window will qualify for additional signal processing. A popular consumer application of ultrasonic ranging was the Polaroid SX-70 camera, which included a lightweight transducer system to focus the camera automatically. Polaroid licensed this ultrasound technology and it became the basis of a variety of ultrasonic products. A common ultrasound application is an automatic door opener, where an ultrasonic sensor detects a person's approach and opens the door.
Ultrasonic sensors are used to detect intruders. The flow in pipes or open channels can be measured by ultrasonic flowmeters, which measure the average veloci
Samarium iodide is an inorganic compound with the formula SmI2. When employed as a solution for organic synthesis, it is known as "Kagan's reagent". SmI2 is a green solid and its solutions are green as well, it is a strong one-electron reducing agent, used in organic synthesis. In samarium iodide, the metal centers are seven-coordinate with a face-capped octahedral geometry. In its ether adducts, samarium remains heptacoordinate with five ether and two terminal iodide ligands. Samarium iodide is prepared in nearly quantitative yields from samarium metal and either diiodomethane or 1,2-diiodoethane; when prepared in this way, its solutions is most used without purification of the inorganic reagent. Solid, solvent-free SmI2 forms by high temperature decomposition of samarium iodide. Samarium iodide is a powerful reducing agent – for example it reduces water to hydrogen, it is available commercially as a dark blue 0.1 M solution in THF. Samarium iodide is a reagent for carbon-carbon bond formation, for example in a Barbier reaction between a ketone and an alkyl iodide to form a tertiary alcohol: R1I + R2COR3 → R1R2CR3 Typical reaction conditions use SmI2 in THF in the presence of catalytic NiI2.
Esters react but aldehydes give by-products. The reaction is convenient in that it is very rapid. Although samarium iodide is considered a powerful single-electron reducing agent, it does display remarkable chemoselectivity among functional groups. For example and sulfoxides can be reduced to the corresponding sulfide in the presence of a variety of carbonyl-containing functionalities; this is due to the slower reaction with carbonyls as compared to sulfones and sulfoxides. Furthermore, hydrodehalogenation of halogenated hydrocarbons to the corresponding hydrocarbon compound can be achieved using samarium iodide, it can be monitored by the color change that occurs as the dark blue color of SmI2 in THF discharges to a light yellow once the reaction has occurred. The picture shows the dark colour disappearing upon contact with the Barbier reaction mixture. Work-up is with dilute hydrochloric acid, the samarium is removed as aqueous Sm3+. Carbonyl compounds can be coupled with simple alkenes to form five, six or eight membered rings.
Tosyl groups can be removed from N-tosylamides instantaneously, using SmI2 in conjunction with a base. The reaction is effective for the synthesis of sensitive amines such as aziridines: In the Markó-Lam deoxygenation, an alcohol could be instantaneously deoxygenated by reducing their toluate ester in presence of SmI2; the applications of SmI2 have been reviewed. The book "Organic Synthesis Using Samarium Diiodide" published in 2009 gives a detailed overview of reactions mediated by SmI2
Wilhelm Rudolph Fittig
Wilhelm Rudolph Fittig was a German chemist. Fittig discovered the pinacol coupling reaction, mesitylene and biphenyl, he studied the action of sodium on hydrocarbons. He discovered the Fittig reaction or Wurtz–Fittig reaction for the synthesis of alkylbenzenes, he proposed a diketone structure for benzoquinone and isolated phenanthrene from coal tar, he discovered and synthesized the first lactones and investigated structures of piperine naphthalene and fluorene. Fittig studied chemistry at the University of Göttingen, graduating as Ph. D. with a dissertation on acetone in 1858, under the supervision of Heinrich Limpricht and Friedrich Wöhler. He subsequently held several appointments at Göttingen, becoming Wöhler's assistant in 1858, privatdozent in 1860 and extraordinary professor in 1870. In 1870 he was appointed full professor at University of Tübingen and in 1876 at Strassburg, where the laboratories were erected from his designs. Fittig's research covered wide areas of organic chemistry.
The aldehydes and ketones provided material for his earlier work. He observed that aldehydes and ketones may suffer reduction in neutral and sometimes acid solution to secondary and tertiary glycols, substances which he named pinacones; the unsaturated acids received much attention, he discovered the internal anhydrides of oxyacids, termed lactones. He discovered what is now known as the pinacol rearrangement, whereby 1,2-diols rearrange to aldehydes or ketones under acid catalysis, his work involved the preparation of 2,3-dimethyl-2,3-butanediol from acetone, followed by the rearrangement to 3,3-dimethylbutanone, oxidised with dichromate to trimethylacetic acid. Fittig's interpretation of his results was incorrect and the products formed were not identified until more than a decade when Aleksandr Butlerov independently prepared trimethylacetic acid and confirmed it was the same product as Fittig had prepared. In 1855, Charles-Adolphe Wurtz showed that when sodium acted upon alkyl iodides, the alkyl residues combined to form more complex hydrocarbons.
This process is now known as the Wurtz-Fittig reaction. His investigations on Perkin's reaction led him to an explanation of its mechanism which appeared to be more in accordance with the facts; the question, however, is one of much difficulty, the exact course of the reaction appears to await solution. These researches incidentally solved the constitution of coumarin, the odoriferous principle of woodruff. Fittig and Erdmann's observation that γ-phenyl structural analog of isocrotonic acid yielded α-naphthol by loss of water was of much importance, since it afforded valuable evidence as to the constitution of naphthalene, they investigated certain hydrocarbons occurring in the high boiling point fraction of the coal tar distillate and solved the constitution of phenanthrene. We owe much of our knowledge of the alkaloid piperine to Fittig, who in collaboration with Ira Remsen established its constitution in 1871. Fittig has published two used textbooks, his researches have been recognized by many scientific societies and institutions, the Royal Society awarding him the Davy medal in 1906.
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed.. "Fittig, Rudolf". Encyclopædia Britannica. Cambridge University Press. Genealogy database entry, University of Illinois
Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; the chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the aerospace industry and important in transportation and building industries, such as building facades and window frames; the oxides and sulfates are the most useful compounds of aluminium. Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals; because of these salts' abundance, the potential for a biological role for them is of continuing interest, studies continue.
Of aluminium isotopes, only 27Al is stable. This is consistent with aluminium having an odd atomic number, it is the only aluminium isotope that has existed on Earth in its current form since the creation of the planet. Nearly all the element on Earth is present as this isotope, which makes aluminium a mononuclidic element and means that its standard atomic weight equates to that of the isotope; the standard atomic weight of aluminium is low in comparison with many other metals, which has consequences for the element's properties. All other isotopes of aluminium are radioactive; the most stable of these is 26Al and therefore could not have survived since the formation of the planet. However, 26Al is produced from argon in the atmosphere by spallation caused by cosmic ray protons; the ratio of 26Al to 10Be has been used for radiodating of geological processes over 105 to 106 year time scales, in particular transport, sediment storage, burial times, erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of 3s23p1, with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Aluminium can easily surrender its three outermost electrons in many chemical reactions; the electronegativity of aluminium is 1.61. A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; this crystal system is shared by some other metals, such as copper. Aluminium metal, when in quantity, is shiny and resembles silver because it preferentially absorbs far ultraviolet radiation while reflecting all visible light so it does not impart any color to reflected light, unlike the reflectance spectra of copper and gold.
Another important characteristic of aluminium is its low density, 2.70 g/cm3. Aluminium is a soft, lightweight and malleable with appearance ranging from silvery to dull gray, depending on the surface roughness, it is nonmagnetic and does not ignite. A fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation; the yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has stiffness of steel, it is machined, cast and extruded. Aluminium atoms are arranged in a face-centered cubic structure. Aluminium has a stacking-fault energy of 200 mJ/m2. Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity, with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.
Aluminium is the most common material for the fabrication of superconducting qubits. Aluminium's corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the bare metal is exposed to air preventing further oxidation, in a process termed passivation; the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts in the presence of dissimilar metals. In acidic solutions, aluminium reacts with water to form hydrogen, in alkaline ones to form aluminates—protective passivation under these conditions is negligible; because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium. However, because
Zinc chloride is the name of chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, are soluble in water. ZnCl2 itself is hygroscopic and deliquescent. Samples should therefore be protected from sources of moisture, including the water vapor present in ambient air. Zinc chloride finds wide application in textile processing, metallurgical fluxes, chemical synthesis. No mineral with this chemical composition is known aside from the rare mineral simonkolleite, Zn58Cl2·H2O. Four crystalline forms of ZnCl2 are known: α, β, γ, δ, in each case the Zn2+ ions are tetrahedrally coordinated to four chloride ions. Here a, b, c are lattice constants, Z is the number of structure units per unit cell, ρ is the density calculated from the structure parameters; the pure anhydrous orthorhombic form changes to one of the other forms on exposure to the atmosphere, a possible explanation is that the OH− ions originating from the absorbed water facilitate the rearrangement.
Rapid cooling of molten ZnCl2 gives a glass. The covalent character of the anhydrous material is indicated by its low melting point of 275 °C. Further evidence for covalency is provided by the high solubility of the dichloride in ethereal solvents, where it forms adducts with the formula ZnCl2L2, where L = ligand such as O2. In the gas phase, ZnCl2 molecules are linear with a bond length of 205 pm. Molten ZnCl2 has a high viscosity at its melting point and a comparatively low electrical conductivity, which increases markedly with temperature. A Raman scattering study of the melt indicated the presence of polymeric structures, a neutron scattering study indicated the presence of tetrahedral complexes. Five hydrates of zinc chloride are known: ZnCl2n with n = 1, 1.5, 2.5, 3 and 4. The tetrahydrate ZnCl24 crystallizes from aqueous solutions of zinc chloride. Anhydrous ZnCl2 can be prepared from zinc and hydrogen chloride: Zn + 2 HCl → ZnCl2 + H2Hydrated forms and aqueous solutions may be prepared by treating Zn metal with hydrochloric acid.
Zinc oxide and zinc sulfide react with HCl: ZnS + 2 HCl → ZnCl2 + H2SUnlike many other elements, zinc exists in only one oxidation state, 2+, which simplifies purification of the chloride. Commercial samples of zinc chloride contain water and products from hydrolysis as impurities; such samples may be purified by recrystallization from hot dioxane. Anhydrous samples can be purified by sublimation in a stream of hydrogen chloride gas, followed by heating the sublimate to 400 °C in a stream of dry nitrogen gas; the simplest method relies on treating the zinc chloride with thionyl chloride. Molten anhydrous ZnCl2 at 500–700 °C dissolves zinc metal, and, on rapid cooling of the melt, a yellow diamagnetic glass is formed, which Raman studies indicate contains the Zn2+2 ion. A number of salts containing the tetrachlorozincate anion, are known. "Caulton's reagent", V2Cl36Zn2Cl6 is an example of a salt containing Zn2Cl2−6. The compound Cs3ZnCl5 contains tetrahedral ZnCl2−4 and Cl− anions. No compounds containing the ZnCl4−6 ion have been characterized.
Whilst zinc chloride is soluble in water, solutions cannot be considered to contain solvated Zn2+ ions and Cl− ions, ZnClxH2O species are present. Aqueous solutions of ZnCl2 are acidic: a 6 M aqueous solution has a pH of 1; the acidity of aqueous ZnCl2 solutions relative to solutions of other Zn2+ salts is due to the formation of the tetrahedral chloro aqua complexes where the reduction in coordination number from 6 to 4 further reduces the strength of the O–H bonds in the solvated water molecules. In alkali solution in the presence of OH− ion various zinc hydroxychloride anions are present in solution, e.g. Zn3Cl2−, Zn2Cl2−2, ZnOHCl2−3, Zn58Cl2·H2O precipitates; when ammonia is bubbled through a solution of zinc chloride, the hydroxide does not precipitate, instead compounds containing complexed ammonia are produced, Zn4Cl2·H2O and on concentration ZnCl22. The former contains the Zn62+ ion, the latter is molecular with a distorted tetrahedral geometry; the species in aqueous solution have been investigated and show that Zn42+ is the main species present with Zn3Cl+ present at lower NH3:Zn ratio.
Aqueous zinc chloride reacts with zinc oxide to form an amorphous cement, first investigated in the 1855 by Stanislas Sorel. Sorel went on to investigate the related magnesium oxychloride cement, which bears his name; when hydrated zinc chloride is heated, one obtains a residue of ZnCl e.g. ZnCl2·2H2O → ZnCl + HCl + H2OThe compound ZnCl2·½HCl·H2O may be prepared by careful precipitation from a solution of ZnCl2 acidified with HCl, it contains a polymeric anion n with balancing monohydrated hydronium ions, H5O2+ ions. The formation of reactive anhydrous HCl gas formed when zinc chloride hydrates are heated is the basis of qualitative inorganic spot tests; the use of zinc chloride as a flux, sometimes in a mixture with ammonium chloride, involves the production of HCl and its subsequent reaction with surface oxides. Zinc chloride forms two salts with ammonium chloride: 2ZnCl4 and 3ClZnCl4, which decompose on heating liberating HCl, just as zinc chloride hydrate does; the action of zinc chloride/ammonium chloride fluxes, for example, in the hot-dip galvanizing process produces H2 gas and ammonia fumes.
Cellulose dissolves in aqueous solutions of ZnCl2, zinc-cellulose complexes have been detected. Cellulose dissolves in molten ZnCl2 hydrate and carboxylation and acetylation performed on the cellulose polymer. Thus, although m
Montmorillonite is a soft phyllosilicate group of minerals that form when they precipitate from water solution as microscopic crystals, known as clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite group, is a 2:1 clay, meaning that it has two tetrahedral sheets of silica sandwiching a central octahedral sheet of alumina; the particles are plate-shaped with a thickness of 0.96 nm. Members of this group include saponite. Montmorillonite is a subclass of smectite, a 2:1 phyllosilicate mineral characterized as having greater than 50% octahedral charge; the substitution of lower valence cations in such instances leaves the nearby oxygen atoms with a net negative charge that can attract cations. In contrast, beidellite is smectite with greater than 50% tetrahedral charge originating from isomorphous substitution of Al for Si in the silica sheet; the individual crystals of montmorillonite clay are not bound hence water can intervene, causing the clay to swell. The water content of montmorillonite is variable and it increases in volume when it absorbs water.
Chemically, it is hydrated sodium calcium aluminium magnesium silicate hydroxide 0.3322·nH2O. Potassium and other cations are common substitutes, the exact ratio of cations varies with source, it occurs intermixed with chlorite, illite and kaolinite. Montmorillonite can be transformed within cave environments; the natural weathering of the cave can leave behind concentrations of aluminosilicates which were contained within the bedrock. Montmorillonite can form in solutions of aluminosilicates. High HCO3 - concentrations and long periods of time can aid in its formation. Montmorillonite can transform to palygorskite under dry conditions and to halloysite-10Å in acidic conditions. Halloysite-10Å can further transform into halloysite-7Å by drying. Montmorillonite is used in the oil drilling industry as a component of drilling mud, making the mud slurry viscous, which helps in keeping the drill bit cool and removing drilled solids, it is used as a soil additive to hold soil water in drought-prone soils, used in the construction of earthen dams and levees, to prevent the leakage of fluids.
It is used as a component of foundry sand and as a desiccant to remove moisture from air and gases. Montmorillonite clays have been extensively used in catalytic processes. Cracking catalysts have used montmorillonite clays for over 60 years. Other acid-based catalysts use acid-treated montmorillonite clays. Similar to many other clays, montmorillonite swells with the addition of water. Montmorillonites expand more than other clays due to water penetrating the interlayer molecular spaces and concomitant adsorption; the amount of expansion is due to the type of exchangeable cation contained in the sample. The presence of sodium as the predominant exchangeable cation can result in the clay swelling to several times its original volume. Hence, sodium montmorillonite has come to be used as the major constituent in nonexplosive agents for splitting rock in natural stone quarries in an effort to limit the amount of waste, or for the demolition of concrete structures where the use of explosive charges is unacceptable.
This swelling property makes montmorillonite-containing bentonite useful as an annular seal or plug for water wells and as a protective liner for landfills. Other uses include as an anticaking agent in animal feed, in paper making to minimize deposit formation, as a retention and drainage aid component. Montmorillonite has been used in cosmetics. In a fine powder form, it can be used as a flocculant in ponds. Tossed on the surface as it drops into the water, making the water "clouded", it attracts minute particles in the water and settles to the bottom, cleaning the water. Koi and goldfish actually feed on the "clump" which can aid in the digestion of the fish, it is sold in pond supply shops. Sodium montmorillonite is used as the base of some cat litter products, due to its adsorbent and clumping properties. Montmorillonite can be calcined to produce a porous material; this calcined clay is sold as a soil conditioner for playing fields and other soil products such as for use as bonsai soil as an alternative to akadama.
Montmorillonite is effective as an adsorptive of heavy metals. For external use, montmorillonite has been used to treat contact dermatitis. Montmorillonite clay is added to some dog and cat foods as an anti-caking agent and because it may provide some resistance to environmental toxins, though research on the subject is not yet conclusive. Montmorillonite was first described in 1847 for an occurrence in Montmorillon in the department of Vienne, more than 50 years before the discovery of bentonite in the US, it is known by other names. Montmorillonite is known to cause micelles to assemble together into vesicles; these structures resemble cell membranes on many cells. It can help nucleotides to assemble into RNA which will end up inside the vesicles; this could have generated complex RNA polymers that could reproduce the RNA trapped within the vesicles. This process may have played a part in abiogenesis. Minerals similar to montmorillonites have been found on Mars. Abiogenesis Dispersion Emulsion dispersion Sodification