Chapter 9 Flashcards
Smart material
Materials that react to an external stimulus
Thermochromic pigments
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
Photochromic pigment
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
Shape Memory Alloy
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
Self - healing materials
Bio concrete uses a special mixture of bacteria to fill in fractures with limestone when water seeps into cracks
Quantum tunnelling composite
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
Piezoelectric
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