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Halon 2600
Hexafluoroethane is an organofluorine compound with the chemical formula . It is a non-flammable colorless odorless gas negligibly soluble in water and slightly soluble in methanol. Its structure is . It is an extremely potent and long-lived greenhouse gas. It is the perfluorocarbon counterpart to the hydrocarbon ethane. Physical properties Hexafluoroethane's Phase (matter), solid phase has two Polymorphism (materials science), polymorphs. In the scientific literature, different phase transition temperatures have been stated. The latest works assign it at 103 K (−170 °C). Below 103 K it has a slightly disordered structure, and over the transition point, it has a Cubic crystal system, body centered cubic structure. The critical point is at 19.89 °C (293.04 K) and 30.39 Bar (unit), bar. Table of densities: Vapor density is 4.823 (air = 1), Relative density, specific gravity at 21 °C is 4.773 (air = 1) and specific volume at 21 °C is 0.1748 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Tetrafluoride
Tetrafluoromethane, also known as carbon tetrafluoride or R-14, is the simplest perfluorocarbon (Carbon, CFluorine, F4). As its IUPAC name indicates, tetrafluoromethane is the perfluorinated counterpart to the hydrocarbon methane. It can also be classified as a haloalkane or halomethane. Tetrafluoromethane is a useful refrigerant but also a potent greenhouse gas. It has a very high bond strength due to the nature of the carbon–fluorine bond. Bonding Because of the multiple carbon–fluorine bonds, and the high electronegativity of fluorine, the carbon in tetrafluoromethane has a significant positive partial charge which strengthens and shortens the four carbon–fluorine bonds by providing additional Ionic bond, ionic character. Carbon–fluorine bonds are the strongest single bonds in organic chemistry. Additionally, they strengthen as more carbon–fluorine bonds are added to the same carbon atom. In the one-carbon organofluorine compounds represented by molecules of fluorometh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Greenhouse Gas
Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about , rather than the present average of .Le Treut, H., R. Somerville, U. Cubasch, Y. Ding, C. Mauritzen, A. Mokssit, T. Peterson and M. Prather, 2007:Chapter 1: Historical Overview of Climate Change. In:Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. olomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.) Cambridge University Press, Cambridge, United Kingdom and New Y ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semiconductor
A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping levels are present in the same crystal, they form a semiconductor junction. The behavior of charge carriers, which include electrons, ions, and electron holes, at these junctions is the basis of diodes, transistors, and most modern electronics. Some examples of semiconductors are silicon, germanium, gallium arsenide, and elements near the so-called " metalloid staircase" on the periodic table. After silicon, gallium arsenide is the second-most common semiconductor and is used in laser diodes, solar cells, microwave-frequency integrated circuits, and others. Silicon is a critical element for fabricating most electronic circuits. Semiconductor devices can display a range of different useful properties, such as passing current more easil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Etching (microfabrication)
Etching is used in microfabrication to chemically remove layers from the surface of a wafer (electronics), wafer during manufacturing. Etching is a critically important process module in fabrication, and every wafer undergoes many etching steps before it is complete. For many etch steps, part of the wafer is protected from the etchant by a "masking" material which resists etching. In some cases, the masking material is a photoresist which has been patterned using photolithography. Other situations require a more durable mask, such as silicon nitride. Etching media and technology The two fundamental types of etchants are liquid-phase ("wet") and plasma (physics), plasma-phase ("dry"). Each of these exists in several varieties. Wet etching The first etching processes used liquid-phase ("wet") etchants. This process is now largely outdated but was used up until the late 1980s when it was superseded by dry plasma etching. The wafer can be immersed in a bath of etchant, wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Specific Volume
In thermodynamics, the specific volume of a substance (symbol: , nu) is the quotient of the substance's volume () to its mass (): :\nu = \frac It is a mass-specific intrinsic property of the substance. It is the reciprocal of density (rho) and it is also related to the molar volume and molar mass: :\nu = \rho^ = \frac The standard unit of specific volume is cubic meters per kilogram (m3/kg), but other units include ft3/lb, ft3/slug, or mL/g. Specific volume for an ideal gas is related to the molar gas constant () and the gas's temperature (), pressure (), and molar mass (): : \nu = \frac It's based on the ideal gas law, PV = , and the amount of substance In chemistry, the amount of substance (symbol ) in a given sample of matter is defined as a ratio () between the particle number, number of elementary entities () and the Avogadro constant (). The unit of amount of substance in the International ..., n = m/M Applications Specific volume is commonly applied to: * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Relative Density
Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nearly always measured with respect to water at its densest (at ); for gases, the reference is air at room temperature (). The term "relative density" (abbreviated r.d. or RD) is preferred in SI, whereas the term "specific gravity" is gradually being abandoned. If a substance's relative density is less than 1 then it is less dense than the reference; if greater than 1 then it is denser than the reference. If the relative density is exactly 1 then the densities are equal; that is, equal volumes of the two substances have the same mass. If the reference material is water, then a substance with a relative density (or specific gravity) less than 1 will float in water. For example, an ice cube, with a relative density of about 0.91, will float. A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vapor Density
Vapour density is the density of a vapour in relation to that of hydrogen. It may be defined as mass of a certain volume of a substance divided by mass of same volume of hydrogen. :vapour density = mass of ''n'' molecules of gas / mass of ''n'' molecules of hydrogen gas . :vapour density = molar mass of gas / molar mass of H2 :vapour density = molar mass of gas / 2.01568 :vapour density = × molar mass (and thus: molar mass = ~2 × vapour density) For example, vapour density of mixture of NO2 and N2O4 is 38.3. Vapour density is a dimensionless quantity. Vapour density = density of gas / density of hydrogen (H2) Alternative definition In many web sources, particularly in relation to safety considerations at commercial and industrial facilities in the U.S., vapour density is defined with respect to air, not hydrogen. Air is given a vapour density of one. For this use, air has a molecular weight of 28.97 atomic mass units, and all other gas and vapour molecular weights are div ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bar (unit)
The bar is a metric unit of pressure defined as 100,000 Pa (100 kPa), though not part of the International System of Units (SI). A pressure of 1 bar is slightly less than the current average atmospheric pressure on Earth at sea level (approximately 1.013 bar). By the barometric formula, 1 bar is roughly the atmospheric pressure on Earth at an altitude of 111 metres at 15 °C. The bar and the millibar were introduced by the Norwegian meteorologist Vilhelm Bjerknes, who was a founder of the modern practice of weather forecasting, with the bar defined as one megadyne per square centimetre. The SI brochure, despite previously mentioning the bar, now omits any mention of it.. The bar has been legally recognised in countries of the European Union since 2004. British Standard BS 350:2004 ''Conversion Factors for Units''. The US National Institute of Standards and Technology (NIST) deprecates its use except for "limited use in meteorology" and lists ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cubic Crystal System
In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals. There are three main varieties of these crystals: *Primitive cubic (abbreviated ''cP'' and alternatively called simple cubic) *Body-centered cubic (abbreviated ''cI'' or bcc) *Face-centered cubic (abbreviated ''cF'' or fcc) Note: the term fcc is often used in synonym for the ''cubic close-packed'' or ccp structure occurring in metals. However, fcc stands for a face-centered cubic Bravais lattice, which is not necessarily close-packed when a motif is set onto the lattice points. E.g. the diamond and the zincblende lattices are fcc but not close-packed. Each is subdivided into other variants listed below. Although the ''unit cells'' in these crystals are conventionally taken to be cubes, the primitive unit cells often are not. Bravais lattices The three Bravais latices ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Transition
In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic State of matter, states of matter: solid, liquid, and gas, and in rare cases, plasma (physics), plasma. A phase of a thermodynamic system and the states of matter have uniform physical property, physical properties. During a phase transition of a given medium, certain properties of the medium change as a result of the change of external conditions, such as temperature or pressure. This can be a discontinuous change; for example, a liquid may become gas upon heating to its boiling point, resulting in an abrupt change in volume. The identification of the external conditions at which a transformation occurs defines the phase transition point. Types of phase transition States of matter Phase transitions commonly refer to when a substance tran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymorphism (materials Science)
In crystallography, polymorphism is the phenomenon where a compound or element can crystallize into more than one crystal structure. The preceding definition has evolved over many years and is still under discussion today. Discussion of the defining characteristics of polymorphism involves distinguishing among types of transitions and structural changes occurring in polymorphism versus those in other phenomena. Overview Phase transitions (phase changes) that help describe polymorphism include polymorphic transitions as well as melting and vaporization transitions. According to IUPAC, a polymorphic transition is "A reversible transition of a solid crystalline phase at a certain temperature and pressure (the inversion point) to another phase of the same chemical composition with a different crystal structure." Additionally, Walter McCrone described the phases in polymorphic matter as "different in crystal structure but identical in the liquid or vapor states." McCrone also def ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase (matter)
In the physical sciences, a phase is a region of material that is chemically uniform, physically distinct, and (often) mechanically separable. In a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, and the humid air is a third phase over the ice and water. The glass of the jar is a different material, in its own separate phase. (See .) More precisely, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, magnetization and chemical composition. The term ''phase'' is sometimes used as a synonym for state of matter, but there can be several immiscible phases of the same state of matter (as where oil and water separate into distinct phases, both in the liquid state). Types of phases Distinct phases may be described as different states of matter such as gas, liquid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
