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Name: Melanie
Status: Student
Grade: Other
Location: CA
Country: USA
Date: July 2006


Question:
If a metallic material is cooled through the melting temperature at an extremely rapid rate, it will form a noncrystalline solid (i.e., a metallic glass). Will the electrical conductivity of the noncrystalline metal be greater or less than its crystalline counterpart? Why?



Replies:
Hi Melanie,

Intriguing question! Amorphous metals made by extreme rapid cooling of normal elemental metals have lower thermal conductivity than their normal (crystalline) versions. I have not been able to find any specific data on electrical conductivity, but I expect that since metals that are good thermal conductors also are almost without exception, good electrical conductors, amorphous metals will have poorer electrical conductivity as well. Amorphous versions of pure metals are not easy to produce, and are limited to very thin sheet thicknesses. This is because the method used to produce them is to "squirt" a thin film of the molten metal onto a large, cold metal wheel. If the metal is more than a few thousandths of an inch thick, it cannot cool fast enough and a crystalline layer results. Their extreme thinness means comparison with "normal" metals is more difficult.

The increased resistivity of amorphous metals results from their internal molecular disorder, as compared to the more orderly crystal structure of crystalline metals.

As a matter of interest, the largest single use of amorphous metal today is in the manufacturing of electronic shoplifting protection devices (those little rectangular plastic "thingies" that are stuck to merchandise you buy). You can tear apart one of the those devices if you would like to have a sample of amorphous metal. There are two strips of metal inside; one can easily be seen to be amorphous metal. The world's largest manufacturer of amorphous metals is VacuumSchmelze in Germany (the name means "Vacuum Melting, which how the metal is melted before squirting onto the cold metal wheel).

Regards,

Bob Wilson



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