C2 MATERIAL CHOICES Flashcards
What different properties can describe how a material behaves?
- melting point
- tensile strength
- compressive strength
- stiffness
- hardness
- density
What does the effectiveness and durability of a product depend on?
the materials used to make it
By finding the mean..
it’ll be nearest to the true value
What are examples of natural materials?
cotton, paper, plant and silk and wool from animals
how are synthetic materials manufacture?
chemical reactions of raw materials
What are other natural raw materials?
extracted from earths crust - limestone, iron ore and crude oil
why have synthetic materials replaced natural materials?
- natural materials are in short supply
- designed to give particular properties
- cheaper and made in quantity needed
What is crude oil?
a mixture of thousands of hyrdrocarbons
What is made when fuel burns in oxygen?
carbon dioxide and water
how is crude oil separated?
by fractional distillation
what happens during fractional distillation?
- the oil is heated - turned into all gases
- the distillation tower gets cooler as it gets higher
- has molecule condense into liquids when they cool
what is a polymer
a large molecule made by joining many smaller molecules called monomers. - chain of carbon atoms
how is a polymer made?
a process called polymerisation
what is PET?
polyethylenetetraphthalate - polymer used to make drink bottles. clear, strong, low density and does not shatter.
between molecules, the stronger the force…
- the more energy is needed to separate the molecules
- the higher the melting point
what does the properties of polymers depend on?
how the molecules are arranged
What is LDPE (low density polyethene)?
Long molecules with branches. The branches keep molecule chains apart, so the forces between different molecules are weak - e.g plastic bags, are weak, flexible my soft and have low melting points
what is HDPE (high density polyethene)?
Has long chains but no branches so the molecules are aligned close to each other. HDPE is much stronger and is used to make long-lasting items which are hard and stuff, such as water pipes
HDPE has a degree of crystallinity. what does this mean?
This means there are lots of areas with regular patterns in the way the molecules line up.
What are plasticisers?
Used to make a polymer softer. they are small molecules inserted into polymer chains to keep them apart, wearing the forces between them.
what is PVC suitable for and why?
for rain coats - it’s harder wrong and waterproof but also flexible
What can you do with thermoplastics?
you can soften it and when heated, it can be moulded into any shape
why don’t thermosetting plastics melt?
they do not soften when heated. They contain cross-links which lock the molecules together so they cannot melt.
How can you increase crystallinity?
by removing branches in the main polymer chain and making the chains as flat as possible. This is so that the molecule chains can line up neatly.
Why would you draw polymers through a tiny hole when heated?
It makes the molecule chains line up, increasing crystallinity and forming higher tensile strength fibre - bullet proof vests have been made in this way.
What are nanoparticles?
- material containing up to a thousand atoms
- occur naturally, such as salt in sea spray
- occur by accident, such as solid particulates made when fuel burns
- can be designed in laboratories
What is nanotechnology?
The use and control of very small structures
How small is an atom?
about one-tenth of a nanometer in diameter
what is nanotechnology measured in?
nanometers (nm)
surface area increases when….
a lump of solid is cut up into bits
What are silver nanoparticles used for? why?
put into plasters, wound dressing, socks, - plastics made into food containers. silver nanoparticles are very good killing bacteria.
What is titanium oxide nanoparticles used for? why?
put into sunscreen. make the sunscreen transparent and absorb UV light
What are composites?
nanoparticles can be mixed with other materials like metals, ceramic and plastic
