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Why do we remember the shape of a paper clip ?

Like a miracle : take a paper clip , unfold it and deform , then holding the tip of the pliers gently hold it briefly over a candle flame and it becomes again the same as before . How is this possible?

Take your time to try , it will not work with each clip . ” Privileged “ are those of a special alloy metal called “shape memory” . When heated, they ” remember “ what they looked like in the process of production before being chilled, and return to it’s original state .

The most successful one is nitinolat alloy – of nickel and titanium.  Copper and zinc , copper, nickel and aluminum work better. They can exist in two structures – the high temperature austenite and martensite low . The transition between them is provided by the temperature changes.


“Remember “ metals are used in many fields – from medicine to aerospace . For example, stent expansion artery is inserted easily into the blood vessel and unfolds only when it reaches its destination . Extensive use in braces to correct teeth , and frames of glasses – not a tragedy if someone sits on them and bent. Especially valuable are those alloys in the manufacture of artificial satellites , in particular for the part of the solar panels. They are sent into space folded to occupy less space in the rocket , and deploy them only when heated by the sun. They find a place even in underwired bras . The transition from one phase to another can be effected not only by a change in temperature. There are materials that ” remember “ the shape with the help of magnetic fields.


Memory metals are used in automobiles – Spring example. Nitinolat occurs in fire sensors in robotics . It is believed that in the future these metals will produce artificial limbs – arms and legs that can be tailored to each individual patient. By having a good memory metals will make active structures that will move as prosthetic muscles.

The effect of metal shape memory was discovered in 1932 by Swedish researcher Arne Olader in an alloy of gold and cadmium. Nitinolat was born in 1962 at Naval Research Laboratory in the U.S..