NationMaster - Encyclopedia: Freezing

In physics and chemistry, freezing is the process whereby a liquid turns to a solid when cold enough. The freezing point is the temperature at which this happens. Melting, the process of turning a solid to a liquid, is almost the exact opposite of freezing. All known liquids undergo freezing when the temperature is lowered with the sole exception of helium, which remains fluid at absolute zero and can only be solidified under pressure. For most substances, the melting and freezing points are the same temperature, however, certain substances possess differing solid-liquid transition temperatures. For example, agar melts at 85 °C (185 °F) and solidifies from 31 °C to 40 °C (89.6 °F to 104 °F); this process is known as thermal hysteresis. A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... For other uses, see Chemistry (disambiguation). ... For other uses, see Liquid (disambiguation). ... This box: For other uses, see Solid (disambiguation). ... The melting point of a crystalline solid is the temperature range at which it changes state from solid to liquid. ... For other uses, see Temperature (disambiguation). ... In physics, melting is the process of heating a solid substance to a point (called the melting point) where it turns into a liquid. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Superfluidity is a phase of matter characterised by the complete absence of viscosity. ... For other uses, see Absolute Zero (disambiguation). ... This does not adequately cite its references or sources. ... Thermal hysteresis. ...

Crystallization

Most liquids freeze by crystallization, formation of crystalline solid from the uniform liquid. This is a first-order thermodynamic phase transition, which means that as long as solid and liquid coexist, the equilibrium temperature of the system remains constant and equal to the melting point. Crystallization consists of two major events, nucleation and crystal growth. Nucleation is the step where the molecules start to gather into clusters, on the nanometer scale, arranging in a defined and periodic manner that defines the crystal structure. The crystal growth is the subsequent growth of the nuclei that succeed in achieving the critical cluster size. Frost crystallization on a shrub. ... Frost crystallization on a shrub. ... For other uses, see Crystal (disambiguation). ... This diagram shows the nomenclature for the different phase transitions. ... The melting point of a crystalline solid is the temperature range at which it changes state from solid to liquid. ... Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ... Crystals are entities of atoms, ions or even polymer strings in which the subunits (i. ... A nanometre (American spelling: nanometer) is 1. ... Periodicity is the quality of occurring at regular intervals (e. ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ...

Supercooling

In spite of the second law of thermodynamics, crystallization of pure liquids usually begins at lower temperature than the melting point, due to high activation energy of homogeneous nucleation. The creation of a nucleus implies the formation of an interface at the boundaries of the new phase. Some energy is expended to form this interface, based on the surface energy of each phase. If a hypothetical nucleus is too small, the energy that would be released by forming its volume is not enough to create its surface, and nucleation does not proceed. Freezing does not start until the temperature is low enough to provide enough energy to form stable nuclei. In presence of irregularities on the surface of the containing vessel, solid or gaseous impurities, pre-formed solid crystals, or other nucleators, heterogeneous nucleation may occur, where some energy is released by the partial destruction of the previous interface, rising the supercooling point to be near or equal to the melting point. The melting point of water at 1 atmosphere of pressure is very close to 0 °C (32 °F, 273.15 K), and in the presence of nucleating substances the freezing point of water is close to the melting point, but in the absence of nucleators water can super cool to −42 °C (−43.6 °F, 231 K) before freezing. Under high pressure (2,000 atmospheres) water will super cool to as low as −70°C (−94°F, 203 K) before freezing^[1]. Supercool redirects here. ... The second law of thermodynamics is an expression of the universal law of increasing entropy. ... The melting point of a crystalline solid is the temperature range at which it changes state from solid to liquid. ... The sparks generated by striking steel against a flint provide the activation energy to initiate combustion in this Bunsen burner. ... Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ... Surface energy quantifies the disruption of chemical bonds that occurs when a surface is created. ... Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ... Supercool redirects here. ... Standard atmosphere (symbol: atm) is a unit of pressure. ...

Vitrification

Certain materials, such as glass or glycerol, may harden without crystallizing; these are called amorphous solids. Amorphous materials as well as some polymers do not have a true freezing point as there is no abrupt phase change at any specific temperature. Instead, there is a gradual change in their viscoelastic properties over a range of temperatures. Such materials are characterized by a glass transition temperature which may be roughly defined as the "knee" point of the material's density vs. temperature graph. A vitrification experiment for the study of nuclear waste disposal at Pacific Northwest National Labs Vitrification is a process of converting a material into a glass-like amorphous solid which is free of any crystalline structure, either by the quick removal or addition of heat, or by mixing with an... This article is about the material. ... Glycerine, Glycerin redirects here. ... Wax and paraffin are amorphous. ... Viscoelasticity, also known as anelasticity, describes materials that exhibit both viscous and elastic characteristics when undergoing plastic deformation. ... The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids (rubbery state). ...

Freezing of biological fluids

Most living organisms accumulate cryoprotectants such as anti-nucleating proteins, polyols, and glucose to protect themselves against frost damage by sharp ice crystals. Most plants, in particular, can safely reach temperatures of −4°C to −12°C. Certain bacteria, notably Pseudomonas syringae, produce specialized proteins that serve as potent ice nucleators, which they use to force ice formation on the surface of various fruits and plants at about −2°C^[2]. The freezing causes injuries in the epithelia and makes the nutrients in the underlying plant tissues available to the bacteria. ^[3] A cryoprotectant is a substance that is used to protect biological tissue from freezing damage (damage due to ice formation). ... A cryoprotectant is a substance that is used to protect biological tissue from freezing damage (damage due to ice formation). ... Antifreeze proteins AFPs or ice structuring proteins ISPs refer to a class of polypeptides produced by certain vertebrates, plants, fungi and bacteria that permit their survival in subzero environments. ... Frost on black pipes Frost is a solid deposition of water vapor from saturated air. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Binomial name Pseudomonas syringae Van Hall, 1904 Pseudomonas syringae is a rod shaped, Gram-negative bacterium, with polar flagella. ...

Food preservation

Freezing is a common method of food preservation which slows both food decay and the growth of micro-organisms. Besides the effect of lower temperatures on reaction rates, freezing makes water less available for bacterial growth. Frozen food is food preserved by the process of freezing. ... Various preserved foods Food preservation is the process of treating and handling food in such a way as to stop or greatly slow down spoilage to prevent foodborne illness while maintaining nutritional value, density, texture and flavor. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... Iron rusting - a chemical reaction with a slow reaction rate. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ...

References

A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

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