An avalanche is an event that occurs when a cohesive slab of snow lying upon a weaker layer of snow fractures and slides down a steep slope. Avalanches are triggered in a starting zone from a mechanical failure in the snowpack when the forces of the snow exceed its strength but sometimes only with gradual widening. After initiation, avalanches accelerate and grow in mass and volume as they entrain more snow. If the avalanche moves fast enough, some of the snow may mix with the air forming a powder snow avalanche, a type of gravity current. Slides of rocks or debris, behaving in a similar way to snow, are referred to as avalanches; the remainder of this article refers to snow avalanches. The load on the snowpack may be only due to gravity, in which case failure may result either from weakening in the snowpack or increased load due to precipitation. Avalanches initiated by this process are known as spontaneous avalanches. Avalanches can be triggered by other loading conditions such as human or biologically related activities.
Seismic activity may trigger the failure in the snowpack and avalanches. Although composed of flowing snow and air, large avalanches have the capability to entrain ice, rocks and other surficial material. However, they are distinct from slushflows which have higher water content and more laminar flow, mudslides which have greater fluidity, rock slides which are ice free, serac collapses during an icefall. Avalanches are not rare or random events and are endemic to any mountain range that accumulates a standing snowpack. Avalanches are most common during winter or spring but glacier movements may cause ice and snow avalanches at any time of year. In mountainous terrain, avalanches are among the most serious objective natural hazards to life and property, with their destructive capability resulting from their potential to carry enormous masses of snow at high speeds. There is no universally accepted classification system for different forms of avalanches. Avalanches can be described by their size, their destructive potential, their initiation mechanism, their composition and their dynamics.
Most avalanches occur spontaneously during storms under increased load due to snowfall. The second largest cause of natural avalanches is metamorphic changes in the snowpack such as melting due to solar radiation. Other natural causes include rain, earthquakes and icefall. Artificial triggers of avalanches include skiers and controlled explosive work. Contrary to popular belief, avalanches are not triggered by loud sound. Avalanche initiation can start at a point with only a small amount of snow moving initially. However, if the snow has sintered into a stiff slab overlying a weak layer fractures can propagate rapidly, so that a large volume of snow, that may be thousands of cubic meters, can start moving simultaneously. A snowpack will fail; the load is straightforward. However, the strength of the snowpack is much more difficult to determine and is heterogeneous, it varies in detail with properties of the snow grains, density, temperature, water content. These properties may all metamorphose in time according to the local humidity, water vapour flux and heat flux.
The top of the snowpack is extensively influenced by incoming radiation and the local air flow. One of the aims of avalanche research is to develop and validate computer models that can describe the evolution of the seasonal snowpack over time. A complicating factor is the complex interaction of terrain and weather, which causes significant spatial and temporal variability of the depths, crystal forms, layering of the seasonal snowpack. Slab avalanches form in snow, deposited, or redeposited by wind, they have the characteristic appearance of a block of snow cut out from its surroundings by fractures. Elements of slab avalanches include the following: a crown fracture at the top of the start zone, flank fractures on the sides of the start zones, a fracture at the bottom called the stauchwall; the crown and flank fractures are vertical walls in the snow delineating the snow, entrained in the avalanche from the snow that remained on the slope. Slabs can vary in thickness from a few centimetres to three metres.
Slab avalanches account for around 90% of avalanche-related fatalities in backcountry users. The largest avalanches form turbulent suspension currents known as powder snow avalanches or mixed avalanches; these consist of a powder cloud. They can form from any type of snow or initiation mechanism, but occur with fresh dry powder, they can exceed speeds of 300 kilometres per hour, masses of 10000000 tonnes. In contrast to powder snow avalanches, wet snow avalanches are a low velocity suspension of snow and water, with the flow confined to the track surface; the low speed of travel is due to the friction between the sliding surface of the track and the water saturated flow. Despite the low speed of travel, wet snow avalanches are capable of generating powerful destructive forces, due to the large mass and density; the body of the flow of a wet snow avalanche can plough through soft snow, can scour boulders, earth and other vegetation.
Anatase is a mineral form of titanium dioxide. The mineral is always encountered as a black solid, although the pure material is colorless or white. Two other mineral forms of TiO2 are known and rutile. Anatase is always found as small and developed crystals, like rutile, a more occurring modification of titanium dioxide, it crystallizes in the tetragonal system; the common pyramid of anatase, parallel to the faces of which there are perfect cleavages, has an angle over the polar edge of 82°9', the corresponding angle of rutile being 56°52½'. It was on account of this steeper pyramid of anatase that the mineral was named, by René Just Haüy in 1801, from the Greek anatasis, "extension", the vertical axis of the crystals being longer than in rutile. There are important differences between the physical characters of anatase and rutile: the former is less hard and dense. Anatase is optically negative whereas rutile is positive, its luster is more adamantine or metallic-adamantine than that of rutile.
Two growth habits of anatase crystals may be distinguished. The more common occurs as simple acute double pyramids with an indigo-blue to black color and steely luster. Crystals of this kind are abundant at Le Bourg-d'Oisans in Dauphiné, where they are associated with rock-crystal and axinite in crevices in granite and mica-schist. Similar crystals, but of microscopic size, are distributed in sedimentary rocks, such as sandstones and slates, from which they may be separated by washing away the lighter constituents of the powdered rock; the plane of anatase is the most thermodynamically stable surface and is thus the most exposed facet in natural and synthetic anatase. Crystals of the second type have numerous pyramidal faces developed, they are flatter or sometimes prismatic in habit; such crystals resemble xenotime in appearance and, were for a long time supposed to belong to this species, the special name wiserine being applied to them. They occur attached to the walls of crevices in the gneisses of the Alps, the Binnenthal near Brig in canton Valais, being a well-known locality.
Occurring pseudomorphs of rutile after anatase are known. While anatase is not an equilibrium phase of TiO2, it is stable near room temperature. At temperatures between 550 and about 1000 °C, anatase converts to rutile; the temperature of this transformation depends on the impurities or dopants as well as on the morphology of the sample. Due to its potential application as a semiconductor, anatase is prepared synthetically. Crystalline anatase can be prepared in laboratories by chemical methods such as sol-gel method. Examples include controlled hydrolysis of titanium ethoxide. Dopants are included in such synthesis processes to control the morphology, electronic structure, surface chemistry of anatase. Another name in use for this mineral is octahedrite, a name which, indeed, is earlier than anatase, given because of the common octahedral habit of the crystals. Other names, now obsolete, are dauphinite, from the well-known French locality. List of minerals Adularia Delustrant
Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying the genetic instructions used in the growth, development and reproduction of all known organisms and many viruses. DNA and ribonucleic acid are nucleic acids; the two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases, a sugar called deoxyribose, a phosphate group; the nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules, with hydrogen bonds to make double-stranded DNA; the complementary nitrogenous bases are divided into two groups and purines. In DNA, the pyrimidines are cytosine. Both strands of double-stranded DNA store the same biological information.
This information is replicated as and when the two strands separate. A large part of DNA is non-coding, meaning that these sections do not serve as patterns for protein sequences; the two strands of DNA are thus antiparallel. Attached to each sugar is one of four types of nucleobases, it is the sequence of these four nucleobases along the backbone. RNA strands are created using DNA strands as a template in a process called transcription. Under the genetic code, these RNA strands specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells, DNA is organized into long structures called chromosomes. Before typical cell division, these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms store most of their DNA inside the cell nucleus as nuclear DNA, some in the mitochondria as mitochondrial DNA, or in chloroplasts as chloroplast DNA. In contrast, prokaryotes store their DNA only in circular chromosomes.
Within eukaryotic chromosomes, chromatin proteins, such as histones and organize DNA. These compacting structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA was first isolated by Friedrich Miescher in 1869, its molecular structure was first identified by Francis Crick and James Watson at the Cavendish Laboratory within the University of Cambridge in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Raymond Gosling, a post-graduate student of Rosalind Franklin. DNA is used by researchers as a molecular tool to explore physical laws and theories, such as the ergodic theorem and the theory of elasticity; the unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro- and nano-fabrication. Among notable advances in this field are DNA origami and DNA-based hybrid materials. DNA is a long polymer made from repeating units called nucleotides.
The structure of DNA is dynamic along its length, being capable of coiling into tight loops and other shapes. In all species it is composed of two helical chains, bound to each other by hydrogen bonds. Both chains are coiled around the same axis, have the same pitch of 34 angstroms; the pair of chains has a radius of 10 angstroms. According to another study, when measured in a different solution, the DNA chain measured 22 to 26 angstroms wide, one nucleotide unit measured 3.3 Å long. Although each individual nucleotide is small, a DNA polymer can be large and contain hundreds of millions, such as in chromosome 1. Chromosome 1 is the largest human chromosome with 220 million base pairs, would be 85 mm long if straightened. DNA does not exist as a single strand, but instead as a pair of strands that are held together; these two long strands coil in the shape of a double helix. The nucleotide contains both a segment of the backbone of a nucleobase. A nucleobase linked to a sugar is called a nucleoside, a base linked to a sugar and to one or more phosphate groups is called a nucleotide.
A biopolymer comprising multiple linked nucleotides is called a polynucleotide. The backbone of the DNA strand is made from alternating sugar residues; the sugar in DNA is 2-deoxyribose, a pentose sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings; these are known as the 3′-end, 5′-end carbons, the prime symbol being used to distinguish these carbon atoms from those of the base to which the deoxyribose forms a glycosidic bond. When imagining DNA, each phosphoryl is considered to "belong" to the nucleotide whose 5′ carbon forms a bond therewith. Any DNA strand therefore has one end at which there is a phosphoryl attached to the 5′ carbon of a ribose and another end a
Mt. Baker Ski Area
Mt. Baker Ski Area is a ski resort in the northwest United States, located in Whatcom County, Washington, at the end of State Route 542; the base elevation is at 3,500 feet. It is about 10 miles south of the international border with Canada; the ski area is home to the world's greatest recorded snowfall in one season, 1,140 inches, recorded during the 1998–99 season. Mt. Baker enjoys the unofficially highest average annual snowfall of any resort in the world, with 641 inches; the ski area is known for numerous challenging in-bounds routes and for the many backcountry opportunities that surround it. The backcountry is accessible from several chairlifts, access is permitted from the resort following the Mt. Baker Ski Area backcountry policy; the lifts at Mt. Baker referred to by number. All are fixed-grip quads. Chairs 3 and 4 access the same point from different sides of the mountain using a continuous loop of cable. Chair 1 runs from the Heather Meadows Lodge upper base area to the top of Panorama Dome.
There is a midpoint station on this lift, where other riders can catch it halfway down the mountain, allowing for speedy runs on Austin, Pan Face, North Face, Chicken Ridge, the famed Chute. Accessible from Chair 1 is the Canyon and the rest of the Chair 6 terrain. Chair 2 is located at the Heather Meadows Lodge upper base area; this is a chair for beginners. Chair 3 allows customers either to access the Raven Hut Lodge area or return down to Chairs 2 and 3. Chair 4 runs from the Raven Hut Lodge area and back up to the top of Chair 3. Chair 5 replaced two parallel double chairs and accesses intermediate terrain, as well as the experts-only Gabl's run and the Elbow backcountry area. Chair 6 runs to the top of Panorama Dome. Chair 7 is the only chair. From it, one can access the Raven Hut Lodge area. Chair 8 is the longest chair on the mountain and features longer groomed runs as well as access to the Hemispheres and Shuksan Arm backcountry areas. Additionally, there are two handle-tow surface lifts for beginners, one located at White Salmon and one at Heather Meadows.
As of 2017, Mt. Baker does not have a terrain park. Future expansion is limited, according to an interview with the General Manager, Duncan Howat: Due to the remote location of the ski area — 37 miles out on a dead-end road — Howat said it will never become a full-scale ski resort with hotels and condos. For starters, there aren't any public utilities up there to support more development. In 1989, when the ski area began developing a second base area known as the White Salmon Lodge, it first had to build all the necessary infrastructure: a parking lot, a water catchment and filtration system, a sewage treatment system, a power generator. "We'll improve the current infrastructure, but as far as going off into some new territory and build new chairlifts, that won't happen," Howat said. "We've got some new plans, but I'm not gonna let it out yet." Started in 1985, this slalom snowboard race through the natural halfpipe has evolved into an international event. The Legendary Banked Slalom attracts many professionals from around the world as competitors and allows amateurs of all ages and abilities to compete on the same course over the same period with the professionals.
The winner in each category receives an embroidered Carhartt jacket. Mt. Baker Ski Area is featured in ski and snowboard films and still photography due to its picturesque setting, plentiful snowfall, the availability of accessed advanced terrain; the Call of The Wild was filmed at Mt. Baker in 1934–35. Featured in Season 5, Episode 14 of the TV series, "Frasier", entitled "The Ski Lodge"; the ski season begins in late November and ends in late April. Usual operating hours are 9:00 a.m. to 3:30 p.m. 1921–26: Mt. Baker highway constructed to Heather Meadows. 1927: Mount Baker Lodge opened. Mt. Baker Ski Club organized. 1930: First ski tournament at Heather Meadows. 1931: Mt. Baker Lodge destroyed by fire. 1935: Pacific Northwest Ski Association downhill tournament, held on northeast face of Table Mountain. 1935–36: "Ski escalator" installed. 1937–38: First rope tow installed, Otto Lang ski school. 1953: The first chairlift, Pan Dome, is constructed at the ski area. 1977: Six chairs and four rope tows operate.
They are referenced by name instead of number. 1981–88: One rope tow is removed, chairs are now numbered instead of named. 1989–90: The first quad chair is installed in the White Salmon area. One more rope tow is removed. 1991–98: Chair 8 opens. 1996: White Salmon Day Lodge opens. 2002: Chair 4 and Chair 5 doubles replaced with Chair 5 quad. 2011: Chairs 1 and 6 designated as "Experts only". Official website WSDOT: road conditions NOAA Weather Report for Mt. Baker Ski Resort - White Salmon Base Area NOAA Weather Report for Mt. Baker Ski Resort - Heather Meadows Base Area Northwest Mountain Weather Telemetry Plots - Previous ten days weather Trail maps from previous years
State of matter
In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid and plasma. Many other states are known to exist, such as glass or liquid crystal, some only exist under extreme conditions, such as Bose–Einstein condensates, neutron-degenerate matter, quark-gluon plasma, which only occur in situations of extreme cold, extreme density, high-energy; some other states remain theoretical for now. For a complete list of all exotic states of matter, see the list of states of matter; the distinction is made based on qualitative differences in properties. Matter in the solid state maintains a fixed volume and shape, with component particles close together and fixed into place. Matter in the liquid state maintains a fixed volume, but has a variable shape that adapts to fit its container, its particles move freely. Matter in the gaseous state has both variable shape, adapting both to fit its container, its particles are neither close together nor fixed in place.
Matter in the plasma state has variable volume and shape, but as well as neutral atoms, it contains a significant number of ions and electrons, both of which can move around freely. The term phase is sometimes used as a synonym for state of matter, but a system can contain several immiscible phases of the same state of matter. In a solid, constituent particles are packed together; the forces between particles are so strong that the particles cannot move but can only vibrate. As a result, a solid has a stable, definite shape, a definite volume. Solids can only cut. In crystalline solids, the particles are packed in a ordered, repeating pattern. There are various different crystal structures, the same substance can have more than one structure. For example, iron has a body-centred cubic structure at temperatures below 912 °C, a face-centred cubic structure between 912 and 1,394 °C. Ice has fifteen known crystal structures, or fifteen solid phases, which exist at various temperatures and pressures.
Glasses and other non-crystalline, amorphous solids without long-range order are not thermal equilibrium ground states. Solids can be transformed into liquids by melting, liquids can be transformed into solids by freezing. Solids can change directly into gases through the process of sublimation, gases can change directly into solids through deposition. A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a constant volume independent of pressure; the volume is definite if the pressure are constant. When a solid is heated above its melting point, it becomes liquid, given that the pressure is higher than the triple point of the substance. Intermolecular forces are still important, but the molecules have enough energy to move relative to each other and the structure is mobile; this means that the shape of a liquid is determined by its container. The volume is greater than that of the corresponding solid, the best known exception being water, H2O; the highest temperature at which a given liquid can exist is its critical temperature.
A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will expand to fill the container. In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small, the typical distance between neighboring molecules is much greater than the molecular size. A gas occupies the entire container in which it is confined. A liquid may be converted to a gas by heating at constant pressure to the boiling point, or else by reducing the pressure at constant temperature. At temperatures below its critical temperature, a gas is called a vapor, can be liquefied by compression alone without cooling. A vapor can exist in equilibrium with a liquid, in which case the gas pressure equals the vapor pressure of the liquid. A supercritical fluid is a gas whose temperature and pressure are above the critical temperature and critical pressure respectively. In this state, the distinction between liquid and gas disappears. A supercritical fluid has the physical properties of a gas, but its high density confers solvent properties in some cases, which leads to useful applications.
For example, supercritical carbon dioxide is used to extract caffeine in the manufacture of decaffeinated coffee. Like a gas, plasma does not have definite volume. Unlike gases, plasmas are electrically conductive, produce magnetic fields and electric currents, respond to electromagnetic forces. Positively charged nuclei swim in a "sea" of freely-moving disassociated electrons, similar to the way such charges exist in conductive metal, where this electron "sea" allows matter in the plasma state to conduct electricity. A gas is converted to a plasma in one of two ways. E.g. Either from a huge voltage difference between two points, or by exposing it to high temperatures. Heating matter to high temperatures causes electrons to leave the atoms, resulting in the presence of free electrons; this creates a so-called ionised plasma. At high temperatures, such as those present in stars, it is assumed that all electrons are "free", that a high-energy plasma is bare nuclei swimming in a
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At room temperature and pressure, another solid form of carbon known as graphite is the chemically stable form, but diamond never converts to it. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are utilized in major industrial applications such as cutting and polishing tools, they are the reason that diamond anvil cells can subject materials to pressures found deep in the Earth. Because the arrangement of atoms in diamond is rigid, few types of impurity can contaminate it. Small numbers of defects or impurities color diamond blue, brown, purple, orange or red. Diamond has high optical dispersion. Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometers in the Earth's mantle, although a few have come from as deep as 800 kilometers. Under high pressure and temperature, carbon-containing fluids dissolved minerals and replaced them with diamonds.
Much more they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites. Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures or from hydrocarbon gas by chemical vapor deposition. Imitation diamonds can be made out of materials such as cubic zirconia and silicon carbide. Natural and imitation diamonds are most distinguished using optical techniques or thermal conductivity measurements. Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as allotropes depending on the type of chemical bond; the two most common allotropes of pure carbon are graphite. In graphite the bonds are sp2 orbital hybrids and the atoms form in planes with each bound to three nearest neighbors 120 degrees apart. In diamond they are sp3 and the atoms form tetrahedra with each bound to four nearest neighbors. Tetrahedra are rigid, the bonds are strong, of all known substances diamond has the greatest number of atoms per unit volume, why it is both the hardest and the least compressible.
It has a high density, ranging from 3150 to 3530 kilograms per cubic metre in natural diamonds and 3520 kg/m³ in pure diamond. In graphite, the bonds between nearest neighbors are stronger but the bonds between planes are weak, so the planes can slip past each other. Thus, graphite is much softer than diamond. However, the stronger bonds make graphite less flammable. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity, as well as wide bandgap and high optical dispersion. Diamond's ignition point is 720 -- 800 °C in 850 -- 1000 °C in air; the equilibrium pressure and temperature conditions for a transition between graphite and diamond is well established theoretically and experimentally. The pressure changes linearly between 1.7 GPa at 0 K and 12 GPa at 5000 K. However, the phases have a wide region about this line where they can coexist. At normal temperature and pressure, 20 °C and 1 standard atmosphere, the stable phase of carbon is graphite, but diamond is metastable and its rate of conversion to graphite is negligible.
However, at temperatures above about 4500 K, diamond converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at 2000 K, a pressure of 35 GPa is needed. Above the triple point, the melting point of diamond increases with increasing pressure. At high pressures and germanium have a BC8 body-centered cubic crystal structure, a similar structure is predicted for carbon at high pressures. At 0 K, the transition is predicted to occur at 1100 GPa; the most common crystal structure of diamond is called diamond cubic. It is formed of unit cells stacked together. Although there are 18 atoms in the figure, each corner atom is shared by eight unit cells and each atom in the center of a face is shared by two, so there are a total of eight atoms per unit cell; each side of the unit cell is 3.57 angstroms in length. A diamond cubic lattice can be thought of as two interpenetrating face-centered cubic lattices with one displaced by 1/4 of the diagonal along a cubic cell, or as one lattice with two atoms associated with each lattice point.
Looked at from a <1 1 1> crystallographic direction, it is formed of layers stacked in a repeating ABCABC... pattern. Diamonds can form an ABAB... structure, known as hexagonal diamond or lonsdaleite, but this is far less common and is formed under different conditions from cubic carbon. Diamonds occur most as euhedral or rounded octahedra and twinned octahedra known as macles; as diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. The crystals can be elongated. Diamonds are found coated in nyf, an opaque gum-like skin; some diamonds have opaque fibers. They are referred to as opaque if the fibers
Supercooling known as undercooling, is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid. A liquid crossing its standard freezing point will crystalize in the presence of a seed crystal or nucleus around which a crystal structure can form creating a solid. Lacking any such nuclei, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs. Homogeneous nucleation can occur above the glass transition temperature, but if homogeneous nucleation has not occurred above that temperature, an amorphous solid will form. Water freezes at 273.15 K, but it can be "supercooled" at standard pressure down to its crystal homogeneous nucleation at 224.8 K. The process of supercooling requires that water be pure and free of nucleation sites, which can be achieved by processes like reverse osmosis or chemical demineralization, but the cooling itself does not require any specialised technique.
If water is cooled at a rate on the order of 106 K/s, the crystal nucleation can be avoided and water becomes a glass—that is, an amorphous solid. Its glass transition temperature is much colder and harder to determine, but studies estimate it at about 136 K. Glassy water can be heated up to 150 K without nucleation occurring. In the range of temperatures between 231 K and 150 K, experiments find only crystal ice. Droplets of supercooled water exist in stratus and cumulus clouds. An aircraft flying through such a cloud sees an abrupt crystallization of these droplets, which can result in the formation of ice on the aircraft's wings or blockage of its instruments and probes, unless the aircraft is equipped with an appropriate de-icing system. Freezing rain is caused by supercooled droplets; the process opposite to supercooling, the melting of a solid above the freezing point, is much more difficult, a solid will always melt at the same temperature for a given pressure. For this reason, it is the melting point, identified, using melting point apparatus.
It is possible, at a given pressure, to superheat a liquid above its boiling point without it becoming gaseous. Supercooling is confused with freezing-point depression. Supercooling is the cooling of a liquid below its freezing point without it becoming solid. Freezing point depression is when a solution can be cooled below the freezing point of the corresponding pure liquid due to the presence of the solute. Constitutional supercooling, which occurs during solidification, is due to compositional solid changes, results in cooling a liquid below the freezing point ahead of the solid–liquid interface; when solidifying a liquid, the interface is unstable, the velocity of the solid–liquid interface must be small in order to avoid constitutional supercooling. Supercooled zones are observed when the liquidus temperature gradient at the interface is larger than the temperature gradient. ∂ T L ∂ x | x = 0 > ∂ T ∂ x or m ∂ C L ∂ x | x = 0 > ∂ T ∂ x The slope of the liquidus phase boundary on the phase diagram is m = ∂ T L / ∂ C L The concentration gradient is related to points, C L S and C S L, on the phase diagram: ∂ C L ∂ x | x = 0 = − C L S − C S L D / v For steady-state growth C S L = C 0 and the partition function k = C S L C L S can be assumed to be constant.
Therefore, the minimum thermal gradient necessary to create a stable solid front is as expressed below. ∂ T ∂ x < m C 0 v k D For more information, see the equation of In order to survive extreme