HOME

TheInfoList




The melting point (or, rarely, liquefaction point) of a substance is the
temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concept ...

temperature
at which it changes
state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper in Columbia, South Carolina, Un ...
from
solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied ...

solid
to
liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers to a fluid flow, flow in which the material density is constant within a fluid par ...

liquid
. At the melting point the solid and liquid phase exist in
equilibrium List of types of equilibrium, the condition of a system in which all competing influences are balanced, in a wide variety of contexts. Equilibrium may also refer to: Film and television * Equilibrium (film), ''Equilibrium'' (film), a 2002 scien ...
. The melting point of a substance depends on
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

pressure
and is usually specified at a
standard pressure Standard temperature and pressure are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure ...
such as 1
atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet or other material body, that is held in ...
or 100
kPa The pascal (symbol: Pa) is the SI derived unit SI derived units are units of measurement ' Measurement is the number, numerical quantification (science), quantification of the variable and attribute (research), attributes of an object or event, ...
. 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 substances to supercool, the freezing point can easily appear to be below its actual value. When the "characteristic freezing point" of a substance is determined, in fact, the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice, that is, the
melting point The melting point (or, rarely, liquefaction point) of a substance is the at which it changes from to . At the melting point the solid and liquid phase exist in . The melting point of a substance depends on and is usually specified at a such ...
."


Examples

For most substances,
melting Melting, or Enthalpy of fusion, fusion, is a physical process that results in the phase transition of a chemical substance, substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the applic ...

melting
and
freezing Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid o ...

freezing
points are approximately equal. For example, the melting point ''and'' freezing point of
mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

mercury
is . However, certain substances possess differing solid-liquid transition temperatures. For example,
agar Agar ( or ), or agar-agar, is a jelly-like substance, obtained from red algae Red algae, or Rhodophyta ( , ; ), are one of the oldest groups of eukaryotic algae Algae (; singular alga ) is an informal term for a large and diverse group of ...
melts at and solidifies from ; such direction dependence is known as
hysteresis Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of t ...

hysteresis
. The melting point of ice at 1 atmosphere of pressure is very close to ; this is also known as the ice point. In the presence of
nucleating substances
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 Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isoc ...
liquid down to before freezing. The metal with the highest melting point is
tungsten Tungsten, or wolfram, is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have ...

tungsten
, at ; this property makes tungsten excellent for use as
electrical filament image of the tungsten Tungsten, or wolfram, is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting on ...
s in
incandescent lamp image of the tungsten filament of an incandescent light bulb An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire #Filament, filament heated until it glows. The filament is enclosed in a gla ...

incandescent lamp
s. The often-cited
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
does not melt at ambient pressure but sublimes at about ; a liquid phase only exists above pressures of and estimated (see carbon phase diagram).
Tantalum hafnium carbide Tantalum is a chemical element with the Symbol (chemistry), symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain from Greek mythology. Tantalum is a rare, hard, blue-gray, lustre (mineralogy), lu ...
(Ta4HfC5) is a
refractory A refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperature Temperature is a physical quantity that expresses hot and cold. ...
compound with a very high melting point of . Quantum mechanical computer simulations have predicted that the alloy HfN0.38C0.51 will have an even higher melting point (about 4400 K), which would make it the substance with the highest melting point at ambient pressure. This prediction was later confirmed by experiment. At the other end of the scale,
helium Helium (from el, ἥλιος, helios Helios; Homeric Greek: ), Latinized as Helius; Hyperion and Phaethon are also the names of his father and son respectively. often given the epithets Hyperion ("the one above") and Phaethon ("the shining" ...

helium
does not freeze at all at normal pressure even at temperatures arbitrarily close to
absolute zero Absolute zero is the lowest limit of the thermodynamic temperature Thermodynamic temperature is the measure of ''absolute temperature'' and is one of the principal parameters of thermodynamics. A thermodynamic temperature reading of zero deno ...
; a pressure of more than twenty times normal
atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. ...
is necessary.


Melting point measurements

Many
laboratory techniques A laboratory (, ; colloquially lab) is a facility that provides controlled conditions in which scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-E ...
exist for the determination of melting points. A Kofler bench is a metal strip with a temperature gradient (range from room temperature to 300 °C). Any substance can be placed on a section of the strip, revealing its thermal behaviour at the temperature at that point.
Differential scanning calorimetry Differential scanning calorimetry (DSC) is a thermoanalytical technique in which the difference in the amount of heat In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than Work (thermodynam ...

Differential scanning calorimetry
gives information on melting point together with its
enthalpy of fusion The enthalpy of fusion of a substance, also known as (latent) heat of fusion is the change in its enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It ...
. A basic melting point apparatus for the analysis of crystalline solids consists of an
oil bath An oil bath is a type of heated bath used in a laboratory A laboratory (, ; colloquially lab) is a facility that provides controlled conditions in which science, scientific or technological research, experiments, and measurement may be perfor ...

oil bath
with a transparent window (most basic design: a Thiele tube) and a simple magnifier. Several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated (and stirred) and with the aid of the magnifier (and external light source) melting of the individual crystals at a certain temperature can be observed. A metal block might be used instead of an oil bath. Some modern instruments have automatic optical detection. The measurement can also 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.


Techniques for refractory materials

For refractory materials (e.g. platinum, tungsten, tantalum, some carbides and nitrides, etc.) the extremely high melting point (typically considered to be above, say, 1800 °C) may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical
pyrometer Image:Pyrometer 040824.jpg, upA sailor checking the temperature of a ventilation system. A pyrometer is a type of remote-sensing thermometer used to measure the temperature of distant objects. Various forms of pyrometers have historically existed. ...
. 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 that has been previously 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 Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of th ...
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 (mp = 1063 °C). 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 the pyrometer and this black-body. The temperature of the black-body is then adjusted until a match exists between its intensity and that of the pyrometer filament. The true higher temperature of the black-body is then determined from Planck's Law. The absorbing medium is then 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 higher temperatures. Now, temperatures and their corresponding pyrometer filament currents are known and a curve of temperature versus current can be drawn. This curve can then be extrapolated to very high temperatures. In determining melting points of a refractory substance by this method, it is necessary to either have black body conditions or to know the
emissivity work iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is ...
of the material being measured. The containment of the high melting material in the liquid state may introduce experimental difficulties. Melting temperatures of some refractory metals have thus been measured by observing the radiation from a black body cavity in solid metal specimens that were much longer than they were wide. To form such a cavity, a hole is drilled perpendicular to the long axis at the center of a rod of the material. These rods are then heated by passing a very large current through them, and the radiation emitted from the hole is observed with an optical pyrometer. The point of melting is indicated by the darkening of the hole when the liquid phase appears, destroying the black body conditions. Today, containerless laser heating techniques, combined with fast pyrometers and spectro-pyrometers, are employed to allow for precise control of the time for which the sample is kept at extreme temperatures. Such experiments of sub-second duration address several of the challenges associated with more traditional melting point measurements made at very high temperatures, such as sample vaporization and reaction with the container.


Thermodynamics

For a solid to melt,
heat In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these ...

heat
is required to raise its temperature to the melting point. However, further heat needs to be supplied for the melting to take place: this is called the
heat of fusion The enthalpy of fusion of a substance, also known as (latent) heat of fusion is the change in its enthalpy Enthalpy is a property of a thermodynamic system A thermodynamic system is a body of matter and/or radiation, confined in space by walls ...
, and is an example of
latent heat Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system A thermodynamic system is a body of matter In classical physics and general chemistry, matter is any su ...
. From a thermodynamics point of view, at the melting point the change in
Gibbs free energy In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quan ...
(ΔG) of the material is zero, but the
enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant p ...

enthalpy
(''H'') and the
entropy Entropy is a scientific concept as well as a measurable physical property that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics ...

entropy
(''S'') of the material are increasing (ΔH, ΔS > 0). Melting phenomenon happens when the Gibbs free energy of the liquid becomes lower than the solid for that material. At various pressures this happens at a specific temperature. It can also be shown that: : \Delta S = \frac Here ''T'', ''ΔS'' and ''ΔH'' are respectively the
temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concept ...

temperature
at the melting point, change of entropy of melting and the change of enthalpy of melting. The melting point is sensitive to extremely large changes in
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

pressure
, but generally this sensitivity is orders of magnitude less than that for the
boiling point The boiling point of a substance is the temperature at which the vapor pressure 280px, The ''pistol test tube'' experiment. The tube contains alcohol and is closed with a piece of cork. By heating the alcohol, the vapors fill in the space, inc ...
, because the solid-liquid transition represents only a small change in volume. If, as observed in most cases, a substance is more dense in the solid than in the liquid state, the melting point will increase with increases in pressure. Otherwise the reverse behavior occurs. Notably, this is the case of water, as illustrated graphically to the right, but also of Si, Ge, Ga, Bi. With extremely large changes in pressure, substantial changes to the melting point are observed. For example, the melting point of silicon at ambient pressure (0.1 MPa) is 1415 °C, but at pressures in excess of 10 GPa it decreases to 1000 °C. Melting points are often used to characterize organic and inorganic compounds and to ascertain their
purity Purity may refer to: Books * ''Pureza'' (novel), a 1937 Brazilian novel by José Lins do Rego * ''Purity'' (novel), a 2015 novel by Jonathan Franzen **Purity (TV series), ''Purity'' (TV series), a TV series based on the novel *''Purity'', a 2012 ...
. The melting point of a pure substance is always higher and has a smaller range than the melting point of an impure substance or, more generally, of mixtures. The higher the quantity of other components, the lower the melting point and the broader will be the melting point range, often referred to as the "pasty range". The temperature at which melting begins for a mixture is known as the "solidus" while the temperature where melting is complete is called the "liquidus". Eutectics are special types of mixtures that behave like single phases. They melt sharply at a constant temperature to form a liquid of the same composition. Alternatively, on cooling a liquid with the eutectic composition will solidify as uniformly dispersed, small (fine-grained) mixed crystals with the same composition. In contrast to crystalline solids,
glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by ...

glass
es do not possess a melting point; on heating they undergo a smooth
glass transition The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous In condensed matter physics Condensed matter physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη ...
into a
viscous liquid In condensed matter physics Condensed matter physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that s ...
. Upon further heating, they gradually soften, which can be characterized by certain softening points.


Freezing-point depression

The freezing point of a
solvent A solvent (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...

solvent
is depressed when another compound is added, meaning that a
solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute and the water the solvent. In chemistry ...
has a lower freezing point than a pure solvent. This phenomenon is used in technical applications to avoid freezing, for instance by adding salt or ethylene glycol to water.


Carnelley's rule

In
organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and th ...
, Carnelley's rule, established in 1882 by Thomas Carnelley, states that ''high
molecular symmetry Molecular symmetry in chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds c ...
is associated with high melting point''. Carnelley based his rule on examination of 15,000 chemical compounds. For example, for three
structural isomer In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a chemical compound, compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct chemical bond, bon ...
s with
molecular formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes ...
C5H12 the melting point increases in the series
isopentane Isopentane, also called methylbutane or 2-methylbutane, is a branched-chain saturated hydrocarbon In organic chemistry, a hydrocarbon is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are gene ...

isopentane
−160 °C (113 K)
n-pentane Pentane is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, catenat ...
−129.8 °C (143 K) and
neopentane Neopentane, also called 2,2-dimethylpropane, is a double-branched-chain alkane , the simplest alkane In organic chemistry, an alkane, or paraffin (a historical trivial name In chemistry, a trivial name is a nonsystematic name for a chemical su ...
−16.4 °C (256.8 K).
HaynesHaynes may refer to: People *Haynes (surname) Places In Australia: * Haynes, Western Australia In the United Kingdom: *Haynes, Bedfordshire **Haynes Church End In the United States: *Haynes, Arkansas *Haynes, North Dakota *Haynes, Ohio *Haynes To ...
, pp. 6.153–155.
Likewise in
xylene Xylene (from ''xylon'', "wood"), xylol or dimethylbenzene is any one of three s of dimethylbenzene, or a combination thereof. With the formula (CH3)2C6H4, in each of the three compounds two hydrogen atoms in the ring are substituted by two s. ...
s and also dichlorobenzenes the melting point increases in the order meta, ortho and then para.
Pyridine Pyridine is a basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming language In computer science Computer science deals with the theoretical foundations of informati ...

Pyridine
has a lower symmetry than
benzene Benzene is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come from a once-living organ ...

benzene
hence its lower melting point but the melting point again increases with
diazine Diazines are a group of organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenatio ...
and
triazine Triazines are a class of nitrogen-containing heterocycles. The parent molecules' molecular formula is . They exist in three isomeric forms, 1,3,5-triazines being common. Structure The triazines have planar six-membered benzene-like ring but w ...
s. Many cage-like compounds like
adamantane Adamantane is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ...

adamantane
and
cubane Cubane (C8H8) is a synthetic hydrocarbon In organic chemistry, a hydrocarbon is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen ...
with high symmetry have relatively high melting points. A high melting point results from a high
heat of fusion The enthalpy of fusion of a substance, also known as (latent) heat of fusion is the change in its enthalpy Enthalpy is a property of a thermodynamic system A thermodynamic system is a body of matter and/or radiation, confined in space by walls ...
, a low
entropy of fusion The entropy of fusion is the increase in entropy Entropy is a scientific concept as well as a measurable physical property that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are us ...
, or a combination of both. In highly symmetrical molecules the crystal phase is densely packed with many efficient intermolecular interactions resulting in a higher enthalpy change on melting. 180 px, Like many high symmetry compounds, tetrakis(trimethylsilyl)silane has a very high melting point (m.p.) of 319-321 °C. It tends to sublime, so the m.p. determination requires that the sample be sealed in a tube.


Predicting the melting point of substances (Lindemann's criterion)

An attempt to predict the bulk melting point of crystalline materials was first made in 1910 by Frederick Lindemann. The idea behind the theory was the observation that the average amplitude of thermal vibrations increases with increasing temperature. Melting initiates when the amplitude of vibration becomes large enough for adjacent atoms to partly occupy the same space. The Lindemann criterion states that melting is expected when the vibration root mean square amplitude exceeds a threshold value. Assuming that all atoms in a crystal vibrate with the same frequency ''ν'', the average thermal energy can be estimated using the
equipartition theorem In , the equipartition theorem relates the of a system to its average . The equipartition theorem is also known as the law of equipartition, equipartition of energy, or simply equipartition. The original idea of equipartition was that, in , e ...
asSorkin, S., (2003)
Point defects, lattice structure, and melting
Thesis, Technion, Israel.
: E = 4\pi^2 m \nu^2~u^2 = k_ T where ''m'' is the atomic mass, ''ν'' is the
frequency Frequency is the number of occurrences of a repeating event per unit of time A unit of time is any particular time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparen ...

frequency
, ''u'' is the average vibration amplitude, ''k''B is the
Boltzmann constant The Boltzmann constant ( or ) is the proportionality factor In mathematics, two varying quantities are said to be in a Binary relation, relation of proportionality, Multiplication, multiplicatively connected to a Constant (mathematics), c ...
, and ''T'' is the
absolute temperature Thermodynamic temperature is a quantity defined in thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of ...

absolute temperature
. If the threshold value of ''u2'' is ''c2a2'' where ''c'' is the Lindemann constant and ''a'' is the
atomic spacing Atomic spacing refers to the distance between the Atomic nucleus, nuclei of atoms in a material. This space is extremely large compared to the size of the atomic nucleus, and is related to the chemical bonds which bind atoms together. In solid mate ...
, then the melting point is estimated as : T_ = \cfrac . Several other expressions for the estimated melting temperature can be obtained depending on the estimate of the average thermal energy. Another commonly used expression for the Lindemann criterion is : T_ = \cfrac . From the expression for the Debye frequency for ''ν'', we have : T_ = \cfrac where ''θ''D is the
Debye temperature In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is gover ...
and ''h'' is the
Planck constant The Planck constant, or Planck's constant, is a fundamental physical constant A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that is generally believed to be both universal in nature an ...
. Values of ''c'' range from 0.15 to 0.3 for most materials.Nelson, D. R., (2002)
Defects and geometry in condensed matter physics
Cambridge University Press,


Melting point prediction

In February 2011, Alfa Aesar released over 10,000 melting points of compounds from their catalog as
open data Open Data is the idea that some data should be freely available to everyone to use and republish as they wish, without restrictions from copyright, patents or other mechanisms of control. The goals of the open-source data movement are similar ...

open data
. This dataset has been used to create a
random forest Random forests or random decision forests are an ensemble learning In statistics and machine learning, ensemble methods use multiple learning algorithms to obtain better predictive inference, predictive performance than could be obtained fro ...
model for melting point prediction which is now freely available.Predict melting point from SMILES
Qsardb.org. Retrieved on 13 September 2013.
Open melting point data are also available from '' Nature Precedings''. High quality data mined from patents and also modelsOCHEM melting point models
ochem.eu. Retrieved on 18 June 2016.
developed with these data were published by Tetko ''et al''.


Table


See also

*
Hagedorn temperature The Hagedorn temperature, ''T''H, is the temperature in theoretical physics where hadronic matter (i.e. ordinary matter) is no longer stable, and must either "evaporate" or convert into quark matter; as such, it can be thought of as the "boiling poi ...
* Highest melting point *
Liquidus The liquidus temperature, TL or Tliq, specifies the temperature above which a material is completely liquid, and the maximum temperature at which crystal A crystal or crystalline solid is a solid Solid is one of the four fundamental ...
*
List of elements by melting point This is a list of the 118 chemical elements which have been Timeline of chemical element discoveries, identified as of 2021. A chemical element, often simply called an element, is a species of atoms which all have the same number of protons in thei ...
*
Melting points of the elements (data page) Melting, or Enthalpy of fusion, fusion, is a physical process that results in the phase transition of a chemical substance, substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the applic ...
*
Phase diagram A phase diagram in physical chemistry Physical chemistry is the study of macroscopic The macroscopic scale is the length scale on which objects or phenomena are large enough to be visible with the naked eye, without magnifying optical ins ...

Phase diagram
*
Phases of matter In the physical sciences Physical science is a branch of natural science Natural science is a branch A branch ( or , ) or tree branch (sometimes referred to in botany Botany, also called , plant biology or phytology, is the s ...
* Simon–Glatzel equation * Slip melting point * Solidus temperature *
Triple point In , the triple point of a substance is the and at which the three (, , and ) of that substance coexist in .. It is that temperature and pressure at which the curve, curve and the curve meet. For example, the triple point of occurs at a tem ...
*
Zone melting Zone melting (or zone refining, or floating-zone method, or floating-zone technique) is a group of similar methods of purifying crystals, in which a narrow region of a crystal is melted, and this molten zone is moved along the crystal. The molte ...


References


Citations


Sources

; Works cited *


External links


Melting and boiling point tables vol. 1
by Thomas Carnelley (Harrison, London, 1885–1887)
Melting and boiling point tables vol. 2
by Thomas Carnelley (Harrison, London, 1885–1887)
Patent mined data
Over 250,000 freely downloadable melting point data. Also downloadable a
figshare
{{DEFAULTSORT:Melting Point Atmospheric thermodynamics Physical quantities Phase transitions Threshold temperatures