Conductivity of Metallic Glass

name         Melanie
status       student
grade        other
location     CA

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?
--------------------------------------
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
====================================================================