| 词条 | Regelation |
| 释义 |
The phenomenon works best with high thermal conductivity materials such as copper, since latent heat of fusion from the top side needs to be transferred to the lower side to supply latent heat of melting.In short, the phenomenon in which ice converts to liquid due to applied pressure and then re-converts to ice once the pressure is removed is called regelation. Regelation was discovered by Michael Faraday. It occurs only for substances such as ice, that have the property of expanding upon freezing, for the melting points of those substances decrease with the increasing external pressure. The melting point of ice falls by 0.0072 °C for each additional atm of pressure applied. For example, a pressure of 500 atmospheres is needed for ice to melt at −4 °C.[2] Surface meltingFor a normal crystalline ice far below its melting point, there will be some relaxation of the atoms near the surface. Simulations of ice near to its melting point show that there is significant melting of the surface layers rather than a symmetric relaxation of atom positions. Nuclear magnetic resonance provided evidence for a liquid layer on the surface of ice. In 1998, using atomic force microscopy, Astrid Döppenschmidt and Hans-Jürgen Butt measured the thickness of the liquid-like layer on ice to be roughly 32 nm at −1 °C, and 11 nm at −10 °C.[3] The surface melting can account for the following:
Examples of regelationA glacier can exert a sufficient amount of pressure on its lower surface to lower the melting point of its ice. The melting of the ice at the glacier's base allows it to move from a higher elevation to a lower elevation. Liquid water may flow from the base of a glacier at lower elevations when the temperature of the air is above the freezing point of water. MisconceptionsIce skating is given as an example of regelation; however the pressure required is much greater than the weight of a skater. Additionally, regelation does not explain how one can ice skate at sub-zero (°C) temperatures.[4]Compaction and creation of snow balls is another example from old texts. Again the pressure required is far greater than can be applied by hand. A counter example is that cars do not melt snow as they run over it. Latest progressA supersolid skin that is elastic, hydrophobic, thermally more stable covers both water and ice. The skins of water and ice are characterized by an identical H-O stretching phonons of 3450 cm^-1. Neither the case of liquid forms on ice nor ice layer covers water, but the supersolid skin slipperizes ice and toughens the water skin[5] Hydrogen bond (O:H-O) relaxation under compression. Compression shortens and stiffens the O:H nonbond and simultaneously lengthens and softens the H-O covalent bond, and negative pressure effect oppositely [6] Melting point is proportional to the cohesive energy of the covalent bond. Therefore, compression lower the Tm.[7] See also
Further reading
References1. ^{{cite journal|doi=10.1098/rspa.1973.0013|title=Pressure Melting and Regelation of Ice by Round Wires|year=1973|last1=Drake|first1=L. D.|last2=Shreve|first2=R. L.|journal=Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=332|issue=1588|pages=51 |bibcode = 1973RSPSA.332...51D }} {{States of matter}}2. ^Glossary of Meteorology: Regelation {{webarchive|url=https://web.archive.org/web/20060225201328/http://amsglossary.allenpress.com/glossary/search?id=regelation1 |date=2006-02-25 }}, American Meteorological Society, 2000 3. ^{{cite journal|last1=Döppenschmidt|first1=Astrid|last2=Butt|first2=Hans-Jürgen|date=2000-07-11|title=Measuring the Thickness of the Liquid-like Layer on Ice Surfaces with Atomic Force Microscopy|journal=Langmuir|volume=16|issue=16|pages=6709–6714|doi=10.1021/la990799w}} 4. ^White, James. The Physics Teacher, 30, 495 (1992). 5. ^{{cite journal|last1=Zhang|first1=Xi|title=A common superslid skin covering both water and ice.|journal=PCCP|date=October 2014|volume=16|issue=42|pages=22987–22994|display-authors=etal|bibcode=2014PCCP...1622987Z|doi=10.1039/C4CP02516D|pmid=25198167|url=https://dr.ntu.edu.sg/bitstream/10220/24509/1/A%20common%20supersolid%20skin%20covering%20both%20water%20and%20ice.pdf|arxiv=1401.8045}} 6. ^{{cite book|last1=Sun|first1=Changqing|title=Relaxation of the Chemical Bond.|date=2014|publisher=Springer|isbn=978-981-4585-20-0|page=807}} 7. ^{{cite journal|last1=Sun|first1=Chang Qing|title=Hidden force opposing compression of ice|journal=Chem. Sci.|date=2012|volume=3|pages=1455–1460|display-authors=etal}} 1 : Thermodynamics |
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