4.7 Ceramics, Composites & Polymers

Question 1

In chemistry, what is meant by a material’s strength?

Answer 1

The resistance of a material to an applied force

Question 2

In chemistry, what is meant by a material’s melting point?

Answer 2

The temperature at which a solid melts into a liquid

Question 3

In chemistry, what is meant by a material’s conductivity?

Answer 3

How well a material conducts electricity

Question 4

In chemistry, what is meant by a material’s hardness?

Answer 4

How well a material can resist being scratched or indented (hard materials don’t scratch)

Question 5

In chemistry, what is meant by a material’s brittleness?

Answer 5

How easily a material breaks when a force is applied (brittle materials snap easily)

Question 6

In chemistry, what is meant by a material’s stiffness?

Answer 6

How well a material can resist bending (a stiff material won’t bend very much

Question 7

What are the two types of materials that ceramics can be made of?

Answer 7

• Glass
• Ceramics

Question 8

Ceramics

Answer 8

Ceramics are hard to define, but are basically a group of hard, brittle, heat-resistant, and corrosion - resistant materials.

Question 9

How are ceramics made?

Answer 9

They are made by shaping and then firing a nonmetallic material, such as clay, at a high temperature. Two main groups of ceramics are clay ceramics and glass.

Question 10

Ceramics - Clay (2)

Answer 10

• Clay is a mixture of materials formed from weathered and decomposed rock. It’s soft when it’s wet, which makes it easy to mould into different shapes required for pottery or bricks.
• It is hardened by firing at very high temperatures. It has a high compressive strength so it’s used as a building material - clay bricks can withstand the weight of lots more bricks on top of them.

Question 11

Ceramics - Glass (3)

Answer 11

• Glass is generally transparent, strong and a good thermal insulator. Also, it can be moulded when hot and can be brittle when thin.
• The majority of glass made is soda-lime glass which is made by heating lime, sand (silicon oxide) and sodium carbonate (soda) until they melt. When the mixture cools it comes out as glass.
• Borosilicate glass is made by heating sand with boron trioxide. Borosilicate glass has a much higher melting point than soda-lime glass.

Question 12

What do ‘clay ceramics’ include? (3)

Answer 12

• Brick
• China
• Porcelain

Question 13

Which three materials are used to make soda-lime glass?

Answer 13

• Limestone
• Sand
• Sodium carbonate

Question 14

Composites (2)

Answer 14

• Composites, such as fibreglass, are made of one material (the reinforcement) embedded in another (the matrix/binder). The materials could be embedded on a bulk scale, such as with concrete that’s reinforced with steel, or they could be made up of nanoparticles of one substance embedded in another.
• The properties of a composite depend on the properties of the materials it is made from. For example: carbon fibre composites have been made using carbon atoms bonded together to make carbon fibres or carbon nanotubes, held together in a polymer resin matrix. These composites are expensive to make but they’re strong and have a low density so they’re used to make aeroplanes and sports car.

Question 15

What two components are composites made from?

Answer 15

• The reinforcement: often long solid fibres or fragments
• The matrix: which binds the reinforcement together. Usually something that starts soft and then hardens

Question 16

What does LDPE stand for?

Answer 16

Low-density poly(ethene)

Question 17

Which type of poly(ethene) is most flexible, but weakest?

Answer 17

LDPE: low-density poly(ethene)

Question 18

Which type of polymers melt easily when heated?

Answer 18

Thermosoftening polymers

Question 19

Alloys have ____________ properties to the metals they’re made from

Answer 19

different

Question 20

Alloys - Bronze

Answer 20

Bronze is an alloy of copper and tin. It’s harder than copper and is used to make ornaments.

Question 21

Alloys - Brass

Answer 21

Brass is made from copper and zinc. It’s more malleable than bronze and is used in situations where low friction is required, such as in water taps and door fittings.

Question 22

Alloys - Gold alloys

Answer 22

Gold alloys are used to make jewellery. They contain metals such as zinc, copper and silver which harden the gold.

Question 23

Alloys - Aluminium alloys

Answer 23

Aluminium alloys are used to make aircraft. Aluminium has a low density but pure aluminium is too soft for making aeroplanes, so it’s alloyed with other metals to make it stronger.

Question 24

Why are alloys harder than pure metals?

Answer 24

This is because different elements have differently sized atoms. So when another element is mixed with a pure metal, the new element’s atoms distort the layers of metal atoms, making it more difficult for them to slide over each other.

Question 25

Alloys - Steel (3)

Answer 25

• Steel is an alloy of iron and carbon. It’s harder than iron, and also stronger (as long as the amount of carbon doesn’t get greater than about 1%).
• Steel that contains chromium and nickel doesn’t rust - this is stainless steel.
• A lot of things are made from steel - bridges, engine parts, cutlery, cars, etc.

Question 26

Alloys - Iron

Answer 26

Iron on its own will rust (corrode) fairly quickly, but steel is much less likely to rust.