Physics

Lifting the Lid on Undercooled Metals

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Science  30 May 2003:
Vol. 300, Issue 5624, pp. 1343-1345
DOI: 10.1126/science.300.5624.1343e

As the temperature of molten metals is reduced below the melt temperature, Tm, they tend to solidify and crystallize. In many instances, however (for example, if the number of nucleation sites can be suppressed), it is possible to maintain the metal as a liquid at temperatures well below Tm. Up to now, the mechanism giving rise to this undercooling has been unclear. Some 50 years ago, it was proposed that the local structure of the liquid may contain a significant amount of icosahedral ordering that would present a barrier to long-range ordering and prevent the metal from solidifying. However, direct verification has so far been lacking. Kelton et al. now remove the ambiguities that may arise with the presence of interfaces by using an electrostatic levitation technique to isolate the molten metal and then perform x-ray scattering to provide direct confirmation of the formation of the icosahedral phase within the liquid metal.—ISO

Phys. Rev. Lett. 90, 195504 (2003).

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