The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium; the melting point of a substance depends on pressure and is specified at a standard pressure such as 1 atmosphere or 100 kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point; because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point. For most substances and freezing points are equal. For example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures.
For example, agar melts at 85 °C and solidifies from 31 °C. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances, the freezing point of water is not always the same as the melting point. In the absence of nucleators water can exist as a supercooled liquid down to −48.3 °C before freezing. The chemical element with the highest melting point is tungsten, at 3,414 °C; the often-cited carbon does not melt at ambient pressure but sublimes at about 3,726.85 °C. Tantalum hafnium carbide is a refractory compound with a high melting point of 4215 K. At the other end of the scale, helium does not freeze at all at normal pressure at temperatures arbitrarily close to absolute zero. Many laboratory techniques exist for the determination of melting points. A Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip, revealing its thermal behaviour at the temperature at that point. Differential scanning calorimetry gives information on melting point together with its enthalpy of fusion.
A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window and a simple magnifier. The several grains of a solid are placed in a thin glass tube and immersed in the oil bath; the oil bath is heated and with the aid of the magnifier melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, optical detection is automated; the measurement can be made continuously with an operating process. For instance, oil refineries measure the freeze point of diesel fuel online, meaning that the sample is taken from the process and measured automatically; this allows for more frequent measurements as the sample does not have to be manually collected and taken to a remote laboratory. For refractory materials the high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees.
The spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source, calibrated as a function of temperature. In this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer. For temperatures above the calibration range of the source, an extrapolation technique must be employed; this extrapolation is accomplished by using Planck's law of radiation. The constants in this equation are not known with sufficient accuracy, causing errors in the extrapolation to become larger at higher temperatures. However, standard techniques have been developed to perform this extrapolation. Consider the case of using gold as the source. In this technique, the current through the filament of the pyrometer is adjusted until the light intensity of the filament matches that of a black-body at the melting point of gold.
This establishes the primary calibration temperature and can be expressed in terms of current through the pyrometer lamp. With the same current setting, the pyrometer is sighted on another black-body at a higher temperature. An absorbing medium of known transmission is inserted between this black-body; the temperature of the black-body is adjusted until a match exists between its intensity and that of the pyrometer filament. The true higher temperature of the black-body is determined from Planck's Law; the absorbing medium is removed and the current through the filament is adjusted to match the filament intensity to that of the black-body. This establishes a second calibration point for the pyrometer; this step is repeated to carry the calibration to hi
Barium oxide, BaO, is a white hygroscopic non-flammable compound. It has a cubic structure and is used in cathode ray tubes, crown glass, catalysts, it is harmful to human skin and if swallowed in large quantity causes irritation. Excessive quantities of barium oxide may lead to death, it is prepared by heating barium carbonate with coke, carbon black or tar or by thermal decomposition of barium nitrate. Barium oxide is used for example, those in cathode ray tubes, it replaced lead oxide in the production of certain kinds of glass such as optical crown glass. While lead oxide raised the refractive index, it raised the dispersive power, which barium oxide does not alter. Barium oxide has use as an ethoxylation catalyst in the reaction of ethylene oxide and alcohols, which takes place between 150 and 200 °C, it is a source of pure oxygen through heat fluctuation. It oxidises to BaO2 by formation of a peroxide ion; the complete peroxidation of BaO to BaO2 occurs at moderate temperatures but the increased entropy of the O2 molecule at high temperatures means that BaO2 decomposes to O2 and BaO at 1175K.
The reaction was used as a large scale method to produce oxygen before the air separation became the dominant method in the beginning of the 20th century. The method was named after its inventors the Brin process. Barium oxide is made by heating barium carbonate, it may be prepared by thermal decomposition of barium nitrate. It is formed through the decomposition of other barium salts. 2Ba + O2 → 2BaO BaCO3 → BaO + CO2 Barium oxide is an irritant. If it contacts the skin or the eyes or is inhaled it causes redness. However, it is more dangerous, it can cause nausea and diarrhea, muscle paralysis, cardiac arrhythmia, can cause death. If ingested, medical attention should be sought immediately. Barium oxide should not be released environmentally. Barium International Chemical Safety Card 0778
European Chemicals Agency
The European Chemicals Agency is an agency of the European Union which manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, Evaluation and Restriction of Chemicals. ECHA is the driving force among regulatory authorities in implementing the EU's chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and addresses chemicals of concern, it is located in Finland. The agency headed by Executive Director Bjorn Hansen, started working on 1 June 2007; the REACH Regulation requires companies to provide information on the hazards and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most used substances have been registered; the information is technical but gives detail on the impact of each chemical on people and the environment.
This gives European consumers the right to ask retailers whether the goods they buy contain dangerous substances. The Classification and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU; this worldwide system makes it easier for workers and consumers to know the effects of chemicals and how to use products safely because the labels on products are now the same throughout the world. Companies need to notify ECHA of the labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100 000 substances; the information is available on their website. Consumers can check chemicals in the products. Biocidal products include, for example, insect disinfectants used in hospitals; the Biocidal Products Regulation ensures that there is enough information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation; the law on Prior Informed Consent sets guidelines for the import of hazardous chemicals.
Through this mechanism, countries due to receive hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have serious effects on human health and the environment are identified as Substances of Very High Concern 1; these are substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment and do not break down. Other substances considered. Companies manufacturing or importing articles containing these substances in a concentration above 0,1% weight of the article, have legal obligations, they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy. Once a substance has been identified in the EU as being of high concern, it will be added to a list; this list is available on ECHA's website and shows consumers and industry which chemicals are identified as SVHCs.
Substances placed on the Candidate List can move to another list. This means that, after a given date, companies will not be allowed to place the substance on the market or to use it, unless they have been given prior authorisation to do so by ECHA. One of the main aims of this listing process is to phase out SVHCs where possible. In its 2018 substance evaluation progress report, ECHA said chemical companies failed to provide “important safety information” in nearly three quarters of cases checked that year. "The numbers show a similar picture to previous years" the report said. The agency noted that member states need to develop risk management measures to control unsafe commercial use of chemicals in 71% of the substances checked. Executive Director Bjorn Hansen called non-compliance with REACH a "worry". Industry group CEFIC acknowledged the problem; the European Environmental Bureau called for faster enforcement to minimise chemical exposure. European Chemicals Bureau Official website
Barium ferrate is the chemical compound of formula BaFeO4. This is a rare compound containing iron in the +6 oxidation state; the ferrate ion has two unpaired electrons. It is isostructural with BaSO4, contains the tetrahedral 2− anion; the ferrate anion is paramagnetic due to its two unpaired electrons and it has a tetrahedral molecular geometry. X-ray diffraction has been used to determine the orthorhombic unit cell structure of nanocrystalline BaFeO4, it has a pnma space group with b = 0.5512 nm and c = 0.7214 nm. The accuracy of the X-Ray diffraction data has been verified by the lattice fringe intervals from High-Resolution Transmission Electron Microscopy and cell parameters calculated from Selected Area Diffraction. Infra-red peaks of barium ferrate are observed at 870, 812, 780 cm−1. BaFeO4 has a magnetic moment of x Am2 with a Weiss constant of -89 K. There are two methods for producing ferrate: wet synthetic methods; the dry synthetic method is performed using a thermal technique. Primary experiments indicate an improvement in the purity of the synthesized barium ferrate by performing the reaction at low temperature in the absence of carbon dioxide and by filtering and drying the precipitate.
Addition of a soluble sodium barium salt to an alkali metal ferrate solution produces a maroon precipitate of barium ferrate, a crystal which has the same structure as barium chromate and has the same solubility. The wet method employs electrochemical techniques. Barium ferrate, BaFeO4, can be prepared by adding barium oxide to a mixture NaClO and ferric nitrate at room temperature; the precipitate formed can be filtered and washed with a 1:1 hexane and diethyl ether mixture in order to remove water and other impurities. The following is the reaction for the synthesis of barium ferrate using the wet method: Ba2 → BaO + H2O NaClO + FeNO3 + BaO → BaFeO4 + NaCl + NO The reaction for the formation of barium ferrate is vigorous and strong chlorine odor. Barium ferrate can be purified by washing with petroleum spirit. Further purification can be done by 3 to 5 washes with 95% ethanol followed by another wash with petroleum spirit. Stirring the reaction and repeating the washing process three times produces a dry precipitate.
Barium ferrate is used as an oxidizing reagent in organic syntheses. Its other applications include removal of color, removal of cyanide, killing bacteria and contaminated and waste water treatment. Salts of ferrate are energetic cathode materials in “super-iron” batteries. Cathodes containing ferrate compounds are referred to as “super-iron” cathodes due to their oxidized iron basis, multiple electron transfer, high intrinsic energy. Among all ferrate salts, barium ferrate sustains unusually facile charge transfer, important for the high power domain of alkaline batteries. Barium ferrate is the most stable of the ferrate compounds; the formula, BaFeO4 • H2O, was determined by H. Rose, it has the most definite composition. Prior to drying, barium ferrate can be decomposed by all soluble acids, including carbonic acid. After the salt has been dried once, it does not decompose easily. If carbon dioxide is passed through water on which hydrated barium is suspended, barium ferrate will decompose to form barium carbonate, ferric hydroxide and oxygen gas.
Dried barium ferrate is decomposed by hydrochloric acid, releasing chlorine. The irreversible reaction of digesting barium chromate with a solution of sodium ferrate forms barium ferrate, the color of the solution is changed from red to yellow due to the sodium chromate, formed. Alkaline sulfates decompose barium ferrate that has not been dried, forming barium sulfate, ferric hydroxide and oxygen gas. Barium ferrate, appears to be one of the most insoluble salts known. Potassium ferrate Ferrate Barium
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.
Barium ferrite, abbreviated BaFe, BaM, is the chemical compound with the formula BaFe12O19. This and related ferrite materials are components in magnetic stripe cards and loudspeaker magnets. BaFe is described as Ba2+1219; the Fe3+ centers are ferromagnetically coupled. This area of technology is considered to be an application of the related fields of materials science and solid state chemistry. Barium ferrite is a magnetic material, has a high packing density, is a metal oxide. Studies of this material date at least as far back as 1931, it has found applications in magnetic card strips and magnetic tapes. One area in particular it has found success in is long-term data storage; the Fe3+ centers, with a high-spin d5 configuration, are ferromagnetically coupled. This area of technology is considered to be an application of the related fields of materials science and solid state chemistry. A related family of industrially useful "hexagonal ferrites" are known containing barium. In contrast to the usual spinel structure, these materials feature hexagonal close-packed framework of oxides.
Furthermore, some the oxygen centers are replaced by Ba2+ ions. Formulas for these species include BaFe12O19, BaFe15O23, BaFe18O27. A one-step hydrothermal process can be used to form crystals of barium ferrite, by mixing barium chloride, ferrous chloride, potassium nitrate, sodium hydroxide with a hydroxide to chloride concentration ratio of 2:1. Nanoparticles are prepared from ferric nitrate, barium chloride, sodium citrate, sodium hydroxide; the typical preparation, however, is by calcining barium carbonate with iron oxide: BaCO3 + 6 Fe2O3 → Δ BaFe12O19 + CO2 Barium ferrite has been considered for long term data storage. The material has proven to be resistant to a number of different environmental stresses, including humidity and corrosion; because ferrites are oxidized it can not be oxidized any further. This is one reason ferrites. Barium ferrite proved to be resistant to thermal demagnetization, another issue common with long term storage; when barium ferrite magnets increase in temperature, their high intrinsic coercivity improves, this is what makes it more resistant to thermal demagnetization.
Ferrite magnets are the only type of magnets that become more resistant to demagnetization as temperature increases. This characteristic of barium ferrite makes it a popular choice in motor and generator designs and in loudspeaker applications. Ferrite magnets can be used in temperatures up to 300 °C, which makes it a perfect to be used in the applications mentioned above. Ferrite magnets are good insulators and don't allow any electrical current to flow through them and they are brittle which shows their ceramic characteristics. Ferrite magnets have good machining properties, which allows for the material to be cut in many shapes and sizes. Barium ferrites are robust ceramics that are stable to moisture and corrosion-resistant. BaFe is an oxide so it does not break down due to oxidation as much as a metal alloy might. Metal particles have been used to store data on tapes and magnetic strips but they have reached their limit for high capacity data storage. In order to increase their capacity by on data tape the MP had to increase the tape length by and track density by over which made it necessary to reduce the size of the individual particles.
As the particles were reduced in size, the passivizing coating needed to prevent the oxidation and deterioration of the MP had to become thicker. This presented a problem for as the passivation coating got thicker it became harder to achieve an acceptable signal to noise ratio. Barium ferrite out classes MP because BaFe is in its oxidized state and so is not restricted in its size by a protective coating. Due to its hexagonal pattern it is easier to organize compared to the unorganized rod like MP. Another factor is the difference in the size of the particles, in MP the size ranges from 40-100 nm while the BaFe is only 20 nm. So the smallest MP particle is still double the size of the BaFe particles. Barium ferrite is used in applications such as recording media, permanent magnets, magnetic stripe cards. Due to the stability of the material, it is able to be reduced in size, making the packing density much greater. Earlier media devices utilized doped acicular oxide materials to yield the coercivity values necessary to record.
In recent decades, barium ferrite has replaced acicular oxides. ID cards using barium ferrite are made with a magnetic fingerprint that identifies them, allowing readers to self-calibrate. Barium ferrite is a common material for speaker magnets; the materials can be formed into any shape and size using a process called sintering, whereby powdered barium ferrite is pressed into a mold, heated until it fuses together. The barium ferrite turns into a solid block; the magnets have an excellent resistance to demagnetization, allowing them to still be useful in speaker units over a long period of time. Barium ferrite is used for Linear Tape-Open storage. Barium ferrite might lead to future improvements in LTO tapes because of its high
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