L.O: To understand what an alloy is and why they have different properties to the pure metals they are made from

HOT SCIENCE!!!

Watch what happens to this unusual bit of wire!

What do you observe.Can you think of some objects which this property would be useful for?

What is this material?

The wire is an alloy. An alloy is a mixture containing one or more metal elements. By changing the amount of each element in an alloy, material scientists can custom-make alloys to fit a given job.

More specifically the hot wire is a smart material which can change one or more of its physical characteristics under the influence of an external stimulus. This type is called a Shape memory alloy

You are now going to look at some other shape memory alloys. Complete the worksheet as you do.

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Shape memory alloys

Shape memory alloy is a type of smart material made from metals that returns to its original shape after being deformed.

A smart material can change one or more of its physical characteristics under the influence of an external stimulus.

Nitinol is a shape memory alloy made from nickel and titanium.

Nitinol is also now used extensively in medicine.

This material can be used to make a pair of glasses that ‘remembers’ its shape and does not break when crushed.

• Smart alloys can change shape because of the way the atoms re-arrange into different forms at different temperatures

• e.g. water and ice have different arrangements of particles, depending on temperature

A smart alloy has a low temperature form and a high temperature form:

Arrangement of atoms at room temperature

Arrangement of atoms when heated

When the smart wire cools down it ‘remembers’ its high temperature form A and will return to the high temperature form when heated

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Nitinol springs

Uses of smart alloys

e.g. Thermostat in kettles: (when it starts to boil steam makes the alloy change shape and switch off the current)

1. devices that cause movement when the temperature changes

e.g. Hubble space telescope: smart alloys used in construction of solar panels: initially folded, but when exposed to solar radiation the alloy returned to its remembered shape and the panels opened

2. device returns to a particular shape when heated

3. shape change is restricted, creating stress

e.g. braces made from smart alloy – when the alloy warms up in the mouth it goes back to its original shape, pushing teeth into the right position

4. devices that cause movement when an electrical current passes through

wing flaps on aircraft robotic

arm

5. Superelastic alloys have a memory and when bent or stretched will return to their original shape

Superelastic alloys are used in spectacle frames

One-way smart alloy:Changes shape when heated but stays the same when cooled – needs a force to make them change back to B

Two-way smart alloy: Changes shape when heated and when cooled down

Superelastic alloy: shape not affected by temperature – needs a force to change from A to B but will change back when force is released