Shape Memory Alloy at a glance
Background
Imagine bending a metal wire out of shape and then watching it spring back to its original form just by heating it up! In this lesson, students will explore how Nitinol, a shape memory alloy made of nickel and titanium, can do just that. They'll discover that Nitinol has two different phases: one at high temperatures (austenite) and one at low temperatures (martensite).
When the metal is cool, it’s softer and can be bent or twisted. But when you heat it up, the atoms rearrange themselves back into the stronger, high-temperature phase, and the metal returns to its original shape. This ability to “remember” its shape makes Nitinol an incredibly useful material in many products we use every day, like retractable antennas, braces, and even eyeglass frames.
Students will also compare Nitinol to regular steel wire, which doesn’t have these shape memory properties, to better understand what makes Nitinol special. By the end of this lesson, students will see how tiny changes on the atomic level can lead to big effects in the materials we use.
Lesson Objective
Students will learn about the shape memory effect in metals, specifically how nitinol, an alloy of nickel and titanium, can return to its original shape when heated. They will compare this effect with that of regular steel wire, which does not exhibit the same property.
Experiment Description
In this experiment, students will deform nitinol wire and then heat it in hot water to observe how it returns to its original shape. They will also test steel wire under the same conditions to see the difference in behavior and understand the concept of phase change in materials.
Materials List
- 6 inches of nitinol wire
- 6 inches of steel wire
- Glass beaker
- Hotplate
- Needle nose pliers
- Water
Safety Precautions
- Always wear safety glasses to protect against splashing water, and use beaker tongs to handle the hot beaker.
- Avoid touching the beaker, water, or wires until they have cooled completely to prevent burns.
The Experiment
1. Fill the beaker with water.
2. Place the beaker on the hot plate and turn to the high temperature setting. The water should be heated to just below boiling.
3. Bend the nitinol wire to a desired shape.
4. Place the nitinol wire in the hot water.
5. The nitinol wire should immediately return to its original shape.
6. Remove the nitinol wire from the beaker using the pliers and show it to the students.
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