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#REDIRECT [[Magnetic refrigeration]] |
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== Magnetocaloric effect == |
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Magnetocaloric effect is the reversible change in temperature caused by material's exposure to magnetic field. |
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Its basic nature can be understood and remembered from two roots of the word: [[magnet]], and [[calory]] (old unit for [[temperature]]). |
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Most notable example of magnetocaloric effect is the one of chemical element [[gadolinium]] and some of its [[alloys]]. Gadolinium's temperature increases when substance enters magnetic field. When gadolinium leaves magnetic field, the temperature drops back to lower level, as Gadolinium cools down. |
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The effect was actually discovered in pure [[iron]] in 1881 by [[E. Warburg]]. Originally, the effect measured about 0.5 to 2 K per [[Tesla]] of change in magnetic field. Nowadays modern alloys of gadolinium produce 3 to 4 K per Tesla of Δ in magnetic field. |
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== Magnetic refrigerators == |
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Refrigerators have been demonstrated based on magnetocaloric effect in laboratories using magnetic fields of about 5T produced by a [[superconducting magnet]] (for comparison, this is about 100,000 times the Earth's magnetic field). |
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The theory says the external magnetic field causes spins of atoms to align, decreasing material's heat capacity. Therefore the material heats up, provided that energy cannot be lost. This heat is then conducted away by water and after the magnetocaloric material departs the field (or field is removed) it is cooler than before the procedure was applied. |
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This effect could save our [[ozone]] layer if the technology is perfected to use room temperature materials instead of superconducting magnets which by themselves have to be cooled down probably to the temperature of liquid [[nitrogen]] (77 K) or to even lower temperatures, cooled with expensive liquid [[helium]]. Consequently, the technology may not be found suitable for home appliances, but for experimental and industrial use only. |
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Recent research emphasises use of '''<math>Ga_{5}(Si_{x}Ge_{1-x})_{4}</math>''' alloy, which is cheaper than pure gadolinium and may live up to commerical use, but other materials are being researched and tested too. |
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== Links == |
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[http://www.accessscience.com/Encyclopedia/3/39/Est_399200_frameset.html?doi Magnetocaloric effect] |
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[http://www.physlink.com/Education/AskExperts/ae488.cfm What is magnetocaloric effect and what materials exhibit this effect the most?] |
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[http://www.sciencenews.org/pages/sn_arc98/3_28_98/fob3.htm Magnetocaloric materials keep fridges cool by C. Wu] |
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[http://www.eurekalert.org/features/doe/2001-11/dl-mrs062802.php Magnetic refrigerator successfully tested] |
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Latest revision as of 19:17, 12 August 2006
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