Ceramics, Composites, Polymers Flashcards
(15 cards)
Properties of fibre glass
Low density
Strong
Waterproof
Flexible
Properties of plywood
Low density
Strong
What is fibreglass made from?
A polymer matrix with glass fibres.
What is carbon fibre?
A polymer matrix which is strong and light.
What is concrete made from?
From aggregate embedded in cement.
What is wood made from?
Wood is a natural composite made from cellulose fibres held by an organic polymer matrix.
What are polymers?
Polymers are made from long carbon chains.
Their properties depend on their density and the different groups attached to the chain.
What happens to thermosoftening polymers and what are they made up of?
Some will soften quite easily. They will then re-set when they cool down. They are made up of individual polymer chains that are tangled together.
What happens to thermosetting polymers when heated?
Thermosetting polymers do not melt when we heat them. These have strong covalent bonds forming
‘cross-links’ between their polymer chains.
How is LDPE formed?
Using very high pressures and a trace of oxygen, ethene forms LDPE. The polymer chains are randomly branched and cannot pack closely together, hence its lower density.
How is HDPE formed?
Using a catalyst at 50°C and a slightly raised pressure, ethene makes HDPE. This is made up of straighter poly(ethene) chains.
They can pack more closely together than branched chains, hence its higher density of HDPE.
Difference between HDPE and LDPE
HDPE has a higher density and softening temperature and is stronger than LDPE.
LDPE is more flexible and transparent
Why are ceramics brittle?
Ceramics are brittle because the strong bonds between the tightly packed ions stop them from moving when stress is applied, and the repulsion between like-charged ions makes it hard for the layers to slide, causing them to break instead of bend.
How are ceramics made?
Clay is mixed with water, which helps create ionic and covalent compounds. Once mixed, this mixture is shaped and then heated, resulting in a ceramic pot.
Formation of ceramics
It starts with wet clay, which has water molecules in it.
When this wet clay is heated up, it transforms into a strong ceramic material because the heat helps bond the particles together.
