Materials: Topic 5, Ceramics and Composites

Question 1

List the different types of ceramics

Answer 1

• Engineering Ceramics
– Crystalline Ceramics
– Glass (amorphous)
– (Glass Ceramics)
• Traditional Clay based
• Rocks and Minerals
• Cement and Concrete
• Ceramic composites

Question 2

General thermal behaviour of ceramics

Answer 2

• High melting point
• Refractory
• Insulator

Question 3

General mechanical behaviour of ceramics

Answer 3

– Brittle
– Hard
– Stiff
– Wear Resistant
– Prone to thermal shock

Question 4

General physical behaviour of ceramics

Answer 4

– Chemically Inert
– Electrical Insulaor
– Non-magnetic

Question 5

Some other ceramic properties

Answer 5

• Low fracture strength
• Low tensile strength
• High compressive strength
• Good Creep resistance
• Excellent Wear Resistance
• Low Density (cf Metals)
• Chemical Resistance: oxides cannot
oxidise
• Difficult to make into shapes: High Tm
chemical inertness, hardness…..

Question 6

Name some natural ceramics

Answer 6

Stone (durable: Stonehenge, cheap and freely available), limestone, sandstone, granite: aluminosilicate.

Question 7

What is concrete?

Answer 7

• Cement paste + aggregate
• Compression: up to 120 MPa
– comparable to Al
• Tension:

Question 8

Why is reinforcing concrete with steel so effective?

Answer 8

The thermal expansion of concrete matches that of steel. This means that steel reinforced concrete
made in July does not crack in December.

Alkalinity of the concrete pacifies the steel so corrosion does not occur.

Question 9

What is a composite?

Answer 9

Composites contain a chemically and/or physically distinct phase distributed within another continuous phase.

Question 10

The two ‘phases’ on a composite are called?

Answer 10

Reinforcing phase - usually fibres

Matrix phase: Polymer (most common), metallic or ceramic

Question 11

Types of composites:

Answer 11

• Biocomposites– Wood, horn or shell, natural fibre,
biopolymers.

• Carbon-carbon composites – Formula 1 car or jet fighter disc brakes
• Ceramic matrix composites – Heat resisting tiled surface of the space shuttle
• Metal matrix composites – Antenna boom on Hubble Space Telescope
• Polymer matrix composites – Boat hulls or water tanks

Question 12

What is the function of the matrix?

Answer 12

• To allow the reinforcement to be fabricated into a functional shape.
• To transmit the load to the fibres (via an interface) throughout the composite.
• To protect the reinforcement from damage.

Question 13

What is the function of the reinforcement?

Answer 13

• Reinforcements are added to monolithic materials to enhance physical properties.
• Typical reinforcements are metals, ceramics, carbon
or polymers in the form of fibres, particulates and
preforms.
• Typically reinforcements range in size from 5 to 150
mm

Question 14

Pros of composites

Answer 14

• Properties can be tailored
• Durable
• Parts count can be reduced

Question 15

Cons of composites

Answer 15

• Energy costs can be high
• Material costs can be high
• Difficult to recycle