today we're talking about weird
materials that we use in space in robots
and in your mouth I'm talking about
shape memory alloys like the name says
these are metals that remember different
shapes to understand how these metals
work we've got to talk about atoms and
organizing let's talk about atoms first
atoms are tiny bits of matter that you
cannot see with your eye yet they make
up everything in our world from the
chair that you're sitting on to your
cell phone atoms have some surprising
ways of behaving - we'll talk about that
shortly now how big is an atom well
imagine pulling one of your hairs out of
your head and whittling it like a stick
100,000 times one of those shavings
would be the width of an atom they're
that small now let's talk about atoms
and organizing you may not know this but
atoms arrange themselves similar to the
way we humans arrange ourselves
sometimes they sit in rows like we do on
a bus or an airplane we call that
seating arrangement of Fay's other times
they sit diagonal from each other sort
of like seats in a movie theater or
sports stadium this is another phase
when atoms move from one seating to
another this is called a phase change
phase changes are all around us
you may already know about waters phases
solid liquid and gas many other
materials have phases like that - some
of them have several solid phases ok
back to those shape memory alloys we
mentioned before when we say that the
metals remember their different shapes
what we're really saying is they
remember different seating arrangements
of atoms when the atoms rearrange the
metal moves from one shape to another
let's look at a phase change in action
here I have a metal wire that is made
out of nickel and titanium this metal
wire is a shape-memory alloy and I'm
going to make it switch between its
different shapes using heat from a
lighter watch this
I'm going to wrap this wire around my
finger and then heat amazing that wire
returns to a straight line when I heat
it let's try that again
I'm going to wrap it around my finger
and heat it yep that's still amazing not
only is it amazing this is weird because
metals generally don't do that here's a
paper clip when I heat it I get nothing
what we're seeing is the shape memory
wire changing phases when it gets hot
when the wire is cold atoms are in a
diagonal arrangement like the movie
theater seating we talked about before
we call this a monoclinic arrangement
and scientists will call this phase
martensite when I heated up the wire the
atoms moved into columns like airplane
seating this is a cubic arrangement
scientists will call this phase
austenite so when we added the heat the
atoms shifted positions seamlessly and
they'll do this forever they have this
coordinated motion just like members of
a tireless marching band each makes a
small shift but all together those small
shifts create a totally different
pattern so that's pretty cool but where
do we use these materials well if you
look in the sky tonight shape-memory
alloys are at work on Mars they're used
to move panels on the Mars rover so that
it can study the environment like our
metal straighten when it was heated the
metals holding the panels will move when
electrically heated when we stop heating
the shape-memory metal the panel will
return back due to an opposing spring
back on earth shape-memory alloys are
used to open up clogged arteries as
stents which are small collapsible
springs that force open passages
shape-memory alloys are also used to
move robots toy butterflies teeth and
braces and for a perfect fit every time
shape-memory wires are used as under
wires in bras now you know Victoria's
Secret by popping a bra to the dryer
it'll be brand new
every time so whether it's on Mars or in
your mouth small atomic movements can
create huge changes and understanding
the way atoms behave allows us to make
cereals that make our world a better
place