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Extraction of Metals

Smart Alloys.

A smart alloy is a smart material that can remember its original shape.
The technical name for a smart alloy is a shape memory alloy (SMA).

Examples of this type of alloy are nickel-titanium
copper-zinc-aluminium and copper-aluminium-nickel.

When a smart alloy is bent or twisted (called deforming)
it keeps its new shape until it is heated.
When the temperature is raised above a certain level
the alloy returns to its original shape.

Nickel-titanium smart alloys are the most successful
but the most expensive. The material is called Nitinol.
Nitinol is is used to make dental braces, spectacle frames and stents.

Dental braces are wires which are used to correct the growth of teeth.
Nitinol can provide a constant force on the teeth
as it tries to return them to the correct shape.

Spectacles are glasses which people use to see better.
The frames often get bent and
Nitinol frames can return to their original shape on warming.

A stent is a tube inserted into a damaged blood vessel.
The stent strengthens the blood vessel to prevent it
collapsing or bursting. Small nitinol stents are inserted cold
and expand inside the blood vessel to the correct diameter
as the stent warms up to the patient's body temperature.

The disadvantages of smart alloys are their high cost
and their increased metal fatigue.
Metal fatigue happens when bending or twisting
of a metal causes it to break.

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