Aluminium nitride is a nitride of aluminium. Its wurtzite phase is a wide band gap semiconductor material, giving it potential application for deep ultraviolet optoelectronics. AlN was first synthesized in 1877, but it was not until the middle of the 1980s that its potential for application in microelectronics was realized due to its high thermal conductivity for an electrically insulating ceramic. Aluminium nitride is stable at high temperatures in inert atmospheres and melts about 2200 °C. In a vacuum, AlN decomposes at ~1800 °C. In the air, surface oxidation occurs above 700 °C, at room temperature, surface oxide layers of 5-10 nm have been detected; this oxide layer protects the material up to 1370 °C. Above this temperature bulk oxidation occurs. Aluminium nitride is stable in hydrogen and carbon dioxide atmospheres up to 980 °C; the material dissolves in mineral acids through grain boundary attack, in strong alkalies through attack on the aluminium nitride grains. The material hydrolyzes in water.
Aluminium nitride is resistant to attack from most molten salts, including cryolite. Aluminum nitride can be patterned with a Cl2-based reactive ion etch. AlN is synthesized by the carbothermal reduction of aluminium oxide in the presence of gaseous nitrogen or ammonia or by direct nitridation of aluminium; the use of sintering aids, such as Y2O3 or CaO, hot pressing is required to produce a dense technical grade material. Epitaxially grown thin film crystalline aluminium nitride is used for surface acoustic wave sensors deposited on silicon wafers because of AlN's piezoelectric properties. One application is an RF filter, used in mobile phones, called a thin film bulk acoustic resonator; this is a MEMS device. Aluminium nitride is used to build piezoelectric micromachined ultrasound transducers, which emit and receive ultrasound and which can be used for in-air rangefinding over distances of up to a meter. Metallization methods are available to allow AlN to be used in electronics applications similar to those of alumina and beryllium oxide.
AlN nanotubes as inorganic quasi-one-dimensional nanotubes, which are isoelectronic with carbon nanotubes, have been suggested as chemical sensors for toxic gases. There is much research into developing light-emitting diodes to operate in the ultraviolet using gallium nitride based semiconductors and, using the alloy aluminium gallium nitride, wavelengths as short as 250 nm have been achieved. In May 2006, an inefficient AlN LED emission at 210 nm was reported. There are multiple research efforts in industry and academia to use aluminum nitride in piezoelectric MEMS applications; these include resonators and microphones. Among the applications of AlN are opto-electronics, dielectric layers in optical storage media, electronic substrates, chip carriers where high thermal conductivity is essential, military applications, as a crucible to grow crystals of gallium arsenide and semiconductor manufacturing. Boron nitride Aluminium phosphide Indium nitride Aluminium oxynitride Jaime Andrés Pérez Taborda.
C. Caicedo. "Deposition pressure effect on chemical and optical properties of binary Al-nitrides". Optics & Laser Technology. 69: 92–103. Bibcode:2015OptLT..69...92P. Doi:10.1016/j.optlastec.2014.12.009. Hdl:10261/129916
Simplified molecular-input line-entry system
The simplified molecular-input line-entry system is a specification in the form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules; the original SMILES specification was initiated in the 1980s. It has since been extended. In 2007, an open standard called. Other linear notations include the Wiswesser line notation, ROSDAL, SYBYL Line Notation; the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. Acknowledged for their parts in the early development were "Gilman Veith and Rose Russo and Albert Leo and Corwin Hansch for supporting the work, Arthur Weininger and Jeremy Scofield for assistance in programming the system." The Environmental Protection Agency funded the initial project to develop SMILES. It has since been modified and extended by others, most notably by Daylight Chemical Information Systems.
In 2007, an open standard called "OpenSMILES" was developed by the Blue Obelisk open-source chemistry community. Other'linear' notations include the Wiswesser Line Notation, ROSDAL and SLN. In July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is considered to have the advantage of being more human-readable than InChI; the term SMILES refers to a line notation for encoding molecular structures and specific instances should be called SMILES strings. However, the term SMILES is commonly used to refer to both a single SMILES string and a number of SMILES strings; the terms "canonical" and "isomeric" can lead to some confusion when applied to SMILES. The terms are not mutually exclusive. A number of valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol. Algorithms have been developed to generate the same SMILES string for a given molecule; this SMILES is unique for each structure, although dependent on the canonicalization algorithm used to generate it, is termed the canonical SMILES.
These algorithms first convert the SMILES to an internal representation of the molecular structure. Various algorithms for generating canonical SMILES have been developed and include those by Daylight Chemical Information Systems, OpenEye Scientific Software, MEDIT, Chemical Computing Group, MolSoft LLC, the Chemistry Development Kit. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database; the original paper that described the CANGEN algorithm claimed to generate unique SMILES strings for graphs representing molecules, but the algorithm fails for a number of simple cases and cannot be considered a correct method for representing a graph canonically. There is no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, double bond geometry; these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES.
A notable feature of these rules is. The term isomeric SMILES is applied to SMILES in which isotopes are specified. In terms of a graph-based computational procedure, SMILES is a string obtained by printing the symbol nodes encountered in a depth-first tree traversal of a chemical graph; the chemical graph is first trimmed to remove hydrogen atoms and cycles are broken to turn it into a spanning tree. Where cycles have been broken, numeric suffix labels are included to indicate the connected nodes. Parentheses are used to indicate points of branching on the tree; the resultant SMILES form depends on the choices: of the bonds chosen to break cycles, of the starting atom used for the depth-first traversal, of the order in which branches are listed when encountered. Atoms are represented by the standard abbreviation of the chemical elements, in square brackets, such as for gold. Brackets may be omitted in the common case of atoms which: are in the "organic subset" of B, C, N, O, P, S, F, Cl, Br, or I, have no formal charge, have the number of hydrogens attached implied by the SMILES valence model, are the normal isotopes, are not chiral centers.
All other elements must be enclosed in brackets, have charges and hydrogens shown explicitly. For instance, the SMILES for water may be written as either O or. Hydrogen may be written as a separate atom; when brackets are used, the symbol H is added if the atom in brackets is bonded to one or more hydrogen, followed by the number of hydrogen atoms if greater than 1 by the sign + for a positive charge or by - for a negative charge. For example, for ammonium. If there is more than one charge, it is written as digit.
Aluminium bromide is any chemical compound with the empirical formula AlBrx. Aluminium tribromide is the most common form of aluminium bromide, it is sublimable hygroscopic solid. The dimeric form of aluminium tribromide predominates in the solid state, in solutions in noncoordinating solvents, in the melt, in the gas phase. Only at high temperatures do these dimers break up into monomers: Al2Br6 → 2 AlBr3 ΔH°diss = 59 kJ/molThe species aluminium monobromide forms from the reaction of HBr with Al metal at high temperature, it disproportionates near room temperature: 6/n "n" → Al2Br6 + 4 AlThis reaction is reversed at temperatures higher than 1000 °C. Aluminium monobromide has been crystallographically characterized in the form the tetrameric adduct Al4Br44; this species is electronically related to cyclobutane. Theory suggest that the diatomic aluminium monobromide condenses to a dimer and a tetrahedral cluster Al4Br4, akin to the analogous boron compound. Al2Br6 consists of two AlBr4 tetrahedra.
The molecular symmetry is D2h. The monomer AlBr3, observed only in the vapor, can be described as D3h point group; the atomic hybridization of aluminium is described as sp2. The Br-Al-Br bond angles are 120 °. By far the most common form of aluminium bromide is Al2Br6; this species exists as hygroscopic colorless solid at standard conditions. Typical impure samples are yellowish or red-brown due to the presence of iron-containing impurities, it is prepared by the reaction of HBr with Al: 2 Al + 6 HBr → Al2Br6 + 3 H2Alternatively, the direct bromination occurs also: 2 Al + 3 Br2 → Al2Br6 Al2Br6 dissociates to give the strong Lewis acid, AlBr3. Regarding the tendency of Al2Br6 to dimerize, it is common for heavier main group halides to exist as aggregates larger than implied by their empirical formulae. Lighter main group halides such as boron tribromide do not show this tendency, in part due to the smaller size of the central atom. Consistent with its Lewis acidic character, water hydrolizes Al2Br6 with evolution of HBr and formation of Al-OH-Br species.
It reacts with alcohols and carboxylic acids, although less vigorously than with water. With simple Lewis bases, Al2Br6 forms adducts, such as AlBr3L. Aluminium tribromide reacts with carbon tetrachloride at 100 °C to form carbon tetrabromide: 4 AlBr3 + 3 CCl4 → 4 AlCl3 + 3 CBr4and with phosgene yields carbonyl bromide and aluminium chlorobromide: AlBr3 + COCl2 → COBr2 + AlCl2BrAl2Br6 is used as a catalyst for the Friedel-Crafts alkylation reaction. Related Lewis acid-promoted reactions include as epoxide ring openings and decomplexation of dienes from iron carbonyls, it is a stronger Lewis acid than the more common Al2Cl6. Aluminium tribromide is a reactive material
Aluminium oxide or aluminum oxide is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. It is the most occurring of several aluminium oxides, identified as aluminium oxide, it is called alumina and may be called aloxide, aloxite, or alundum depending on particular forms or applications. It occurs in its crystalline polymorphic phase α-Al2O3 as the mineral corundum, varieties of which form the precious gemstones ruby and sapphire. Al2O3 is significant in its use to produce aluminium metal, as an abrasive owing to its hardness, as a refractory material owing to its high melting point. Corundum is the most common occurring crystalline form of aluminium oxide. Rubies and sapphires are gem-quality forms of corundum, which owe their characteristic colors to trace impurities. Rubies are given their characteristic deep red color and their laser qualities by traces of chromium. Sapphires come in different colors given by various other impurities, such as titanium. Al2O3 is an electrical insulator but has a high thermal conductivity for a ceramic material.
Aluminium oxide is insoluble in water. In its most occurring crystalline form, called corundum or α-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools. Aluminium oxide is responsible for the resistance of metallic aluminium to weathering. Metallic aluminium is reactive with atmospheric oxygen, a thin passivation layer of aluminium oxide forms on any exposed aluminium surface; this layer protects the metal from further oxidation. The thickness and properties of this oxide layer can be enhanced using a process called anodising. A number of alloys, such as aluminium bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance; the aluminium oxide generated by anodising is amorphous, but discharge assisted oxidation processes such as plasma electrolytic oxidation result in a significant proportion of crystalline aluminium oxide in the coating, enhancing its hardness. Aluminium oxide was taken off the United States Environmental Protection Agency's chemicals lists in 1988.
Aluminium oxide is on the EPA's Toxics Release Inventory list. Aluminium oxide is an amphoteric substance, meaning it can react with both acids and bases, such as hydrofluoric acid and sodium hydroxide, acting as an acid with a base and a base with an acid, neutralising the other and producing a salt. Al2O3 + 6 HF → 2 AlF3 + 3 H2O Al2O3 + 2 NaOH + 3 H2O → 2 NaAl4 The most common form of crystalline aluminium oxide is known as corundum, the thermodynamically stable form; the oxygen ions form a nearly hexagonal close-packed structure with the aluminium ions filling two-thirds of the octahedral interstices. Each Al3+ center is octahedral. In terms of its crystallography, corundum adopts a trigonal Bravais lattice with a space group of R3c; the primitive cell contains two formula units of aluminium oxide. Aluminium oxide exists in other, phases, including the cubic γ and η phases, the monoclinic θ phase, the hexagonal χ phase, the orthorhombic κ phase and the δ phase that can be tetragonal or orthorhombic.
Each has properties. Cubic γ-Al2O3 has important technical applications; the so-called β-Al2O3 proved to be NaAl11O17. Molten aluminium oxide near the melting temperature is 2/3 tetrahedral, 1/3 5-coordinated, with little octahedral Al-O present. Around 80% of the oxygen atoms are shared among three or more Al-O polyhedra, the majority of inter-polyhedral connections are corner-sharing, with the remaining 10–20% being edge-sharing; the breakdown of octahedra upon melting is accompanied by a large volume increase, the density of the liquid close to its melting point is 2.93 g/cm3. The structure of molten alumina is temperature dependent and the fraction of 5- and 6-fold aluminium increases during cooling, at the expense of tetrahedral AlO4 units, approaching the local structural arrangements found in amorphous alumina. Aluminium hydroxide minerals are the main component of the principal ore of aluminium. A mixture of the minerals comprise bauxite ore, including gibbsite and diaspore, along with impurities of iron oxides and hydroxides and clay minerals.
Bauxites are found in laterites. Bauxite is purified by the Bayer process: Al2O3 + H2O + NaOH → NaAl4 Al3 + NaOH → NaAl4Except for SiO2, the other components of bauxite do not dissolve in base. Upon filtering the basic mixture, Fe2O3 is removed; when the Bayer liquor is cooled, Al3 precipitates. NaAl4 → NaOH + Al3The solid Al3 Gibbsite is calcined to give aluminium oxide: 2 Al3 → Al2O3 + 3 H2OThe product aluminium oxide tends to be multi-phase, i.e. consisting of several phases of aluminium oxide rather than corundum. The production process can therefore be optimized to produce a tailored product; the type of phases present affects, for example, the solubility and pore structure of the aluminium oxide product which, in turn, affects the cost of aluminium production and pollution control. Known as alundum or aloxite in the mining and materials science communities, aluminium oxide finds wide use. Annual world production of aluminium oxide in 2015 was 115 million tonnes, over 90% of, used in the manufacture of aluminium metal.
The major uses of speciali
Aluminium chloride known as aluminium trichloride, is the main compound of aluminium and chlorine. It is white, but samples are contaminated with iron chloride, giving it a yellow color; the solid has boiling point. It is produced and consumed in the production of aluminium metal, but large amounts are used in other areas of the chemical industry; the compound is cited as a Lewis acid. It is an example of an inorganic compound that reversibly changes from a polymer to a monomer at mild temperature. AlCl3 adopts three different structures, depending on the state. Solid AlCl3 is a sheet-like layered cubic close packed layers. In this framework, the Al centres exhibit octahedral coordination geometry. In the melt, aluminium trichloride exists with tetracoordinate aluminium; this change in structure is related to the lower density of the liquid phase versus solid aluminium trichloride. Al2Cl6 dimers are found in the vapour phase. At higher temperatures, the Al2Cl6 dimers dissociate into trigonal planar AlCl3, structurally analogous to BF3.
The melt conducts electricity poorly, unlike more-ionic halides such as sodium chloride. The hexahydrate consists of octahedral 3+ centers and chloride counterions. Hydrogen bonds anions; the hydrated form of aluminium chloride has an octahedral molecular geometry, with the central aluminum ion surrounded by six water ligand molecules. This means that the hydrated form cannot act as a Lewis acid since it cannot accept electron pairs, thus this cannot be used as a catalyst in Friedel-Crafts alkylation of aromatic compounds. Anhydrous aluminium chloride is a most powerful Lewis acid, capable of forming Lewis acid-base adducts with weak Lewis bases such as benzophenone and mesitylene, it forms tetrachloroaluminate in the presence of chloride ions. Aluminium chloride reacts with calcium and magnesium hydrides in tetrahydrofuran forming tetrahydroaluminates. Aluminium chloride is hygroscopic, having a pronounced affinity for water, it fumes in moist air and hisses when mixed with liquid water as the Cl− ions are displaced with H2O molecules in the lattice to form the hexahydrate Cl3.
The anhydrous phase cannot be regained on heating as HCl is lost leaving aluminium hydroxide or alumina: Al6Cl3 → Al3 + 3 HCl + 3 H2OOn strong heating, aluminium oxide is formed from the aluminium hydroxide via: 2 Al3 → Al2O3 + 3 H2OAqueous solutions of AlCl3 are ionic and thus conduct electricity well. Such solutions are found to be indicative of partial hydrolysis of the Al3 + ion; the reactions can be described as: 3+ ⇌ 2+ + H+Aqueous solutions behave to other aluminium salts containing hydrated Al3+ ions, giving a gelatinous precipitate of aluminium hydroxide upon reaction with dilute sodium hydroxide: AlCl3 + 3 NaOH → Al3 + 3 NaCl Aluminium chloride is manufactured on a large scale by the exothermic reaction of aluminium metal with chlorine or hydrogen chloride at temperatures between 650 to 750 °C. 2 Al + 3 Cl2 → 2 AlCl3 2 Al + 6 HCl → 2 AlCl3 + 3 H2Aluminum chloride may be formed via a single displacement reaction between copper chloride and aluminum metal. 2 Al + 3 CuCl2 → 2 AlCl3 + 3 CuIn the US in 1993 21,000 tons were produced, not counting the amounts consumed in the production of aluminium.
Hydrated aluminium trichloride is prepared by dissolving aluminium oxides in hydrochloric acid. Metallic aluminum readily dissolves in hydrochloric acid ─ releasing hydrogen gas and generating considerable heat. Heating this solid does not produce anhydrous aluminium trichloride, the hexahydrate decomposes to aluminium hydroxide when heated: Al6Cl3 → Al3 + 3 HCl + 3 H2OAluminium forms a lower chloride, aluminium chloride, but this is unstable and only known in the vapour phase. AlCl3 is the most used Lewis acid and one of the most powerful, it finds application in the chemical industry as a catalyst for Friedel–Crafts reactions, both acylations and alkylations. Important products are ethylbenzene, it finds use in polymerization and isomerization reactions of hydrocarbons. The Friedel–Crafts reaction is the major use for aluminium chloride, for example in the preparation of anthraquinone from benzene and phosgene. In the general Friedel–Crafts reaction, an acyl chloride or alkyl halide reacts with an aromatic system as shown: The alkylation reaction is more used than the acylation reaction, although its practice is more technically demanding because the reaction is more sluggish.
For both reactions, the aluminium chloride, as well as other materials and the equipment, should be dry, although a trace of moisture is necessary for the reaction to proceed. A general problem with the Friedel–Crafts reaction is that the aluminium chloride catalyst sometimes is required in full stoichiometric quantities, because it complexes with the products; this complication sometimes generates a large amount of corrosive waste. For these and similar reasons, more recyclable or environmentally benign catalysts have been sought. Thus, the use of aluminium chloride in some applications is being displaced by zeolites. Aluminium chloride can be used to introduce aldehyde groups onto aromatic rings, for example via the Gattermann-Koch reaction which uses carbon monoxide, hydrogen chloride and a copper chloride co-catalyst. Aluminium chloride finds a wide variety of other applications in organic chemistry. For example, it can catalyse the "ene reaction", such as the addition of 3-but
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics describes the behaviour of visible and infrared light; because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays and radio waves exhibit similar properties. Most optical phenomena can be accounted for using the classical electromagnetic description of light. Complete electromagnetic descriptions of light are, however difficult to apply in practice. Practical optics is done using simplified models; the most common of these, geometric optics, treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics; the ray-based model of light was developed first, followed by the wave model of light.
Progress in electromagnetic theory in the 19th century led to the discovery that light waves were in fact electromagnetic radiation. Some phenomena depend on the fact that light has both particle-like properties. Explanation of these effects requires quantum mechanics; when considering light's particle-like properties, the light is modelled as a collection of particles called "photons". Quantum optics deals with the application of quantum mechanics to optical systems. Optical science is relevant to and studied in many related disciplines including astronomy, various engineering fields and medicine. Practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, telescopes, microscopes and fibre optics. Optics began with the development of lenses by Mesopotamians; the earliest known lenses, made from polished crystal quartz, date from as early as 700 BC for Assyrian lenses such as the Layard/Nimrud lens. The ancient Romans and Greeks filled glass spheres with water to make lenses.
These practical developments were followed by the development of theories of light and vision by ancient Greek and Indian philosophers, the development of geometrical optics in the Greco-Roman world. The word optics comes from the ancient Greek word ὀπτική, meaning "appearance, look". Greek philosophy on optics broke down into two opposing theories on how vision worked, the "intromission theory" and the "emission theory"; the intro-mission approach saw vision as coming from objects casting off copies of themselves that were captured by the eye. With many propagators including Democritus, Epicurus and their followers, this theory seems to have some contact with modern theories of what vision is, but it remained only speculation lacking any experimental foundation. Plato first articulated the emission theory, the idea that visual perception is accomplished by rays emitted by the eyes, he commented on the parity reversal of mirrors in Timaeus. Some hundred years Euclid wrote a treatise entitled Optics where he linked vision to geometry, creating geometrical optics.
He based his work on Plato's emission theory wherein he described the mathematical rules of perspective and described the effects of refraction qualitatively, although he questioned that a beam of light from the eye could instantaneously light up the stars every time someone blinked. Ptolemy, in his treatise Optics, held an extramission-intromission theory of vision: the rays from the eye formed a cone, the vertex being within the eye, the base defining the visual field; the rays were sensitive, conveyed information back to the observer's intellect about the distance and orientation of surfaces. He summarised much of Euclid and went on to describe a way to measure the angle of refraction, though he failed to notice the empirical relationship between it and the angle of incidence. During the Middle Ages, Greek ideas about optics were resurrected and extended by writers in the Muslim world. One of the earliest of these was Al-Kindi who wrote on the merits of Aristotelian and Euclidean ideas of optics, favouring the emission theory since it could better quantify optical phenomena.
In 984, the Persian mathematician Ibn Sahl wrote the treatise "On burning mirrors and lenses" describing a law of refraction equivalent to Snell's law. He used this law to compute optimum shapes for curved mirrors. In the early 11th century, Alhazen wrote the Book of Optics in which he explored reflection and refraction and proposed a new system for explaining vision and light based on observation and experiment, he rejected the "emission theory" of Ptolemaic optics with its rays being emitted by the eye, instead put forward the idea that light reflected in all directions in straight lines from all points of the objects being viewed and entered the eye, although he was unable to explain how the eye captured the rays. Alhazen's work was ignored in the Arabic world but it was anonymously translated into Latin around 1200 A. D. and further summarised and expanded on by the Polish monk Witelo making it a standard text on optics in Europe for the next 400 years. In the 13th century in medieval Europe, English bishop Robert Grosseteste wrote on a wide range of scientific topics, discussed light from four different perspectives: an epistemology of light, a metaphysics or cosmogony of light, an etiology or physics of light, a theology of light, basing it on the works Aristotle and Platonism.
Grosseteste's most famous disciple, Roger Bacon, wrote w
Ammonium aluminium sulfate
Ammonium aluminium sulfate known as ammonium alum or just alum, is a white crystalline double sulfate encountered as the dodecahydrate, formula Al2·12H2O. It is used in small amounts in a variety of niche applications; the dodecahydrate occurs as the rare mineral tschermigite. Ammonium alum is made from sulfuric acid and ammonium sulfate, it forms a solid solution with potassium alum. Pyrolysis leaves alumina; such alumina is used in the production of grinding powders and as precursors to synthetic gems. Ammonium alum is not a major industrial chemical or a useful laboratory reagent, but it is cheap and effective, which invites many niche applications, it is used in water purification, in vegetable glues, in porcelain cements, in deodorants and in tanning, dyeing and in fireproofing textiles. The pH of the solution resulting from the topical application of ammonium alum with perspiration is in the acid range, from 3 to 5. Ammonium alum is a common ingredient in animal repellant sprays. Alum was once a common pickling ingredient used to promote crispness in preserved vegetables, due to the way it reacts with natural pectin.
It has fallen out of use from a suspected link to Alzheimer's Disease, is no longer recommended for pickling, but is still known as E number E523. Aluminium sulfate related to ammonium alum, is considered nontoxic up to LD50 of 6207 mg/kg