SHAPE MEMORY ALLOYS e.g. Nitinol &
Magnetic Shape Memory Alloys
Brown's Chemistry Revision Notes - Smart Materials and Materials Science
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general survey of materials - natural & synthetic, properties & uses
GCSE Level (~US grades 9-10) Chemistry Revision
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list of keywords mentioned on these 'smart materials' pages:
Carbon fibres * Chromogenic
materials * Electrochromic materials
* Gore-Tex * Halochromic materials * High
performance polymers * Kevlar * Lycra *
Magnetic shape memory alloys * Magnetostrictive
materials * Nitinol *
pH sensitive polymers *
Photochromic materials *
Photomechancal materials * Piezoelectric
effect materials *
Self-healing materials * Shape
memory alloys *
Shape memory polymers * Spandex
* Temperature responsive polymers
* Thermochromic materials *
PART 2 SHAPE
MEMORY ALLOYS (metals)
Shape memory alloys remember their shape! Return to their desired shape - smart
SHAPE MEMORY ALLOYS
(SMAs) are metallic alloy
materials in which deformation (change in shape) can be induced and
recovered through temperature changes or stress changes.
An SMA subjected to a mechanical
stress or shear force will undergo a reversible deformation, usually
over a narrow temperature range.
Shape-Memory Alloys are metals
that, after being strained, at a certain temperature revert back to their
The crystal structure changes
above their transformation temperature causes them to return to their
SMAs can involve relatively
large forces produced by any resistance encountered in their transformation
and, reversibly, a large mechanical movement effect as the strain
This enable the shape to be
recovered if the temperature is altered back.
The overall phenomena is that a
material is mechanically deformed, then heated, and then rapidly
reverts to its 'remembered' shape.
Basically, bend a piece of shape
memory alloy so it is out of shape, warm it up, and it returns to its
Shape memory alloys cab used in
various devices e.g.
thermostats for temperature
on-off switches for clamping
devices such as pipe couplings where a loose sleeve can be caused to
contract and clamp tightly by heating or cooling to induce the shape recall
Titanium and nickel
metals are the two main components of Nitinol 'smart alloys'.
belongs to a group of shape memory alloys (SMA) which can
'remember their original shape'.
For example they can regain
there original shape on heating e.g. used in thermostats in
cookers , coffer makers etc.
When nitinol is cool you
can bend it, i.e. it can be quite flexible, BUT if you bend it
(stress it) to far, it might stay bent and not regain its correct
However, if you heat the
'stressed' nitinol object above a certain threshold temperature, it
relaxes and regains its original remembered shape!
They can be designed
to regain their original shape after release of a physical
stress e.g. used in 'bendable' eyeglass frames, very handy if
you tread on them. Place them into a bowl of warm water and your
glasses frame regains its shape!
Nitinol is used in dental braces.
The dental brace is
designed to return to the correct dental shape on warming.
The cold dental brace is
stressed on placing in position on the teeth.
As the nitinol brace
warms up, it 'remembers' and returns to its 'designed shape' and
pulls the teeth into their correct position in your mouth!
Nitinol shape memory
alloys are used to make stents.
Stents are fine
tubes used to treat damaged blood vessels which restrict the
flow of blood.
mesh tubes are inserted into blood vessels to maintain the inner
diameter of a blood vessel.
Once inserted, the
fine tubes warm up and expand to allow the flow of blood.
Nitinol is an
acronym for 'Nickel Titanium Naval Ordinance Laboratory' betraying,
like so many technological developments, its military origins, but
now acquiring many 'peaceful' uses.
MAGNETIC SHAPE MEMORY ALLOYS -
change in shape under the influence of externally applied magnetic field.
The reverse can also occur so
that the magnetization of the material can change under the influence of a mechanical stress
For example, magnetic shape memory alloys are
metallic materials that change their shape in response to a significant change in the
external magnetic field.
TOP OF PAGE
INDEX of SMART MATERIALS PAGES
CHROMOGENIC MATERIALS - Thermochromic, Photochromic & Electrochromic Materials
SHAPE MEMORY ALLOYS e.g. Nitinol & Magnetic Shape Memory Alloys
SHAPE MEMORY POLYMERS, pH and temperature sensitive-responsive polymers,
performance polymers like KEVLAR
GORETEX, THINSULATE and TEFLON-PTFE
PIEZOELECTRIC EFFECT (PIEZOELECTRIC MATERIALS) and PHOTOMECHANICAL MATERIALS
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