From robots to braces to the Mars Rover, see how a special kind of metal called shape memory alloys advance technology in everyday ways that we don't always realize.
00:00Today we're talking about weird materials that we use in space, in robots, and in your mouth.
00:21I'm talking about shape memory alloys. Like the name says, these are metals that remember different
00:28shapes. To understand how these metals work, we've got to talk about atoms and organizing.
00:34Let's talk about atoms first. Atoms are tiny bits of matter that you cannot see with your eye,
00:40yet they make up everything in our world, from the chair that you're sitting on to your cell phone.
00:46Atoms have some surprising ways of behaving too. We'll talk about that shortly.
00:51Now, how big is an atom? Well, imagine pulling one of your hairs out of your head
00:56and whittling it like a stick 100,000 times. One of those shavings would be the width of an atom.
01:03They're that small. Now let's talk about atoms and organizing.
01:08You may not know this, but atoms arrange themselves similar to the way we humans arrange ourselves.
01:14Sometimes they sit in rows, like we do on a bus or an airplane. We call that seating arrangement a phase.
01:21Other times, they sit diagonal from each other, sort of like seats in a movie theater or sports stadium.
01:27This is another phase. When atoms move from one seating to another, this is called a phase change.
01:34Phase changes are all around us. You may already know about water's phases, solid, liquid, and gas.
01:42Many other materials have phases like that too. Some of them have several solid phases.
01:48Okay, back to those shape memory alloys we mentioned before.
01:51When we say that the metals remember their different shapes,
01:55what we're really saying is they remember different seating arrangements of atoms.
01:59When the atoms rearrange, the metal moves from one shape to another.
02:04Let's look at a phase change in action.
02:07Here I have a metal wire that is made out of nickel and titanium.
02:11This metal wire is a shape memory alloy, and I'm going to make it switch between its different shapes using heat from a lighter.
02:19Watch this. I'm going to wrap this wire around my finger and then heat it.
02:26Amazing! That wire returns to a straight line when I heat it.
02:31Let's try that again. I'm going to wrap it around my finger and heat it.
02:36Yup, that's still amazing. Not only is it amazing, this is weird because metals generally don't do that.
02:43Here's a paper clip. When I heat it, I get nothing.
02:47What we're seeing is the shape memory wire changing phases when it gets hot.
02:52When the wire is cold, atoms are in a diagonal arrangement like the movie theater seating we talked about before.
02:58We call this a monoclinic arrangement, and scientists will call this phase martensite.
03:04When I heated up the wire, the atoms moved into columns like airplane seating.
03:09This is a cubic arrangement. Scientists will call this phase austenite.
03:14So when we added the heat, the atoms shifted positions seamlessly, and they'll do this forever.
03:20They have this coordinated motion just like members of a tireless marching band.
03:24Each makes a small shift, but altogether those small shifts create a totally different pattern.
03:30So that's pretty cool, but where do we use these materials?
03:34Well, if you look in the sky tonight, shape memory alloys are at work, on Mars.
03:39They're used to move panels on the Mars rover so that it can study the environment.
03:44Like our metal straightened when it was heated, the metals holding the panels will move when electrically heated.
03:50When we stop heating the shape memory metal, the panel will return back due to an opposing spring.
03:56Back on Earth, shape memory alloys are used to open up clogged arteries as stents, which are small, collapsible springs that force open passages.
04:06Shape 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 underwires in bras.
04:17Now you know Victoria's secret. By popping a bra into the dryer, it'll be brand new every time.
04:24So whether it's on Mars or in your mouth, small atomic movements can create huge changes.
04:30And understanding the way atoms behave allows us to make materials that make our world a better place.
