Nitinol Wire (G Hernandez Scipio)

Author

Gloria E. Hernandez Scipio

Principle(s) Illustrated

• Crystal Structure

• Mixture of two different metals

• Heating casing a physical molecular change

• Memory Wire

Standards

• NGSS Science & engineering standards

• NGSS Cross-cutting concept standards

• NGSS Disciplinary core idea standards

Questioning Script

Prior knowledge & experience:

Smart materials respond to things that happen around them. This activity demonstrates the properties of one smart material: Nitinol. Nitinol is a mixture of two different metals: nickel and titanium. Nitinol stands for Ni (nickel), Ti (titanium), and Naval Ordnance Laboratory, the place where it was discovered in 1965. What makes Nitinol so smart? Find out!

In this activity, you will demonstrate the shape memory properties of Nitinol by shaping and heating samples.

Root question:

Can a metal actually be smart?

Bend the metal into any type of shape. Now try to straighten it back out. Can you do it? What happens if we apply heat?

• • Extension Question: If you bend a paper clip, or other wire out of shape, and then heat it up, what happens? Try it! How does Nitinol behave differently from other wires? What are the differences between Nitinol and other wires?

Target response:

• • Everything around us is made of tiny building blocks called atoms.

  • Nitinol is made up of two kinds of atoms: Nickel atoms and Titanium atoms.

  • They are arranged in an organized pattern called a crystal structure. Most

  • solids have a crystal structure, but Nitinol is special because it has two

  • different crystal structures, also called solid phases. At colder temperatures,

  • Nitinol’s atoms are in one arrangement, called martensite. At higher

  • temperatures, Nitinol’s atoms are in a slightly different crystal structure,

  • called austenite. When you heat Nitinol, you give the atoms energy to move from the martensite structure to the austenite structure, and as it cools back down, they move back. The atoms in the Nitinol move just a little bit, but this makes a huge difference in how the metal feels and behaves. At lower temperatures, Nitinol is soft and easy to bend. At hotter temperatures, it is stiff and springy.

    • • • • How does that make Nitinol a smart material? When it’s in its low-temperature structure, when you heat it up, it will change to its high-temperature structure. It bounces back to its original shape when that change happens. When you heated the wire up using the hair dryer, you caused the Nitinol to change from one phase to the other, and it went back to the shape it was in before you bent it. This gives Nitinol its other name, memory metal.

  • Conclusion: Nitinol reacts to a change in its environment – temperature - so it is a smart material. Nitinol and some other metal mixtures have shape memory, which has made them useful in a lot of inventions, like wires for braces, staples that hold broken bones together, coffee pots that turn off when the water is hot enough, and trick spoons that bend when you try to stir your tea!

Common Misconceptions:

State common misconceptions

Photographs and Movies

References

Educational Innovations

Penn State Nanoscience Activities with Nitinol