Chapter 9

Question 1

Smart material

Answer 1

Materials that react to an external stimulus

Question 2

Thermochromic pigments

Answer 2

Pigments, inks, and dyes that react to heat by changing colour

Irreversible versions are available to indicate when a critical temperature has been reach, useful for products such as medical supplies

Appearance - powder that’s added to a variety of materials

Characteristics - change colour with heat, usually reversible

Uses - flexible thermometers, temperature indicator, clothing

Question 3

Photochromic pigment

Answer 3

React to levels of light by changing colour (caused by the UV Rays in sunlight)

Appearance - compound that is added to a variety of materials

Characteristics - change colour via light, normally reversible

Uses - novelty goods, paint, clothes

Case study:
The most common application of photochromic particles is the use of silver halides in sunglasses

It allows the lens of the glasses to darken in high levels of sunlight, and become clear again when the light level is lower

It may take up to 2 minutes to fully darkness, and will eventually lose the ability to become clear again

Question 4

Shape Memory Alloy

Answer 4

This material can return to a preset shape, even after being deformed significantly, via heat or electricity

The most common SMA is Nitinol, an alloy of nickel and titanium. To set the shape memory, you hold Nitinol in the desired position and heat it up to 540°C. When it cools it can be deformed in any shape. When reheated to 70°C it will spring back to its preset shape. This can also be achieved by passing an electric current through it

Appearance - grey metal wire

Characteristic - shape can be programmed at 540°C, returns to preset shape at 70°C

Uses - glasses grams, dental braces, fire sprinklers

Question 5

Self - healing materials

Answer 5

Bio concrete uses a special mixture of bacteria to fill in fractures with limestone when water seeps into cracks

Question 6

Quantum tunnelling composite

Answer 6

Can be both a conductor or an insulator. The more pressure is applied, the closer the conductive particles are to each other, making the material more conductive

Used in touch sensitive devices and wearable technology

Question 7

Piezoelectric

Answer 7

Although it’s technically not a conductor it can produce an electrical voltage when put under pressure

Used in mobile phone speakers and microphones, and for glass lighter ignition