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Synthetic Materials
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Worksheet 1 A synthetic fibre that replaces silk
Time to Think (p. 9)
1.
Nylon stockings were much cheaper than silk stockings, and they were
smoother, stronger and more elastic.
2.
Fabrics made from nylon is soft, light, strong, elastic, and resistant to chemicals.
3.
A water molecule is given out.
4.
Diacid has two acid groups and diamine has two amino groups. Each acid
group of diacid and each amino group of diamine can react to form strong
bonds.
5.
Both of the monomers of nylon and silk are joined by strong bonds formed
between acid groups and amino groups.
6.
Swimwear, curtain, string or rope, raincoat, racket string, dental floss, etc.
7.
Biological washing powder can digest silk, which is a protein. So it cannot be
used for clothes made from silk. However, it can be used for nylon fabrics
because nylon is not a protein.
8.
Polyester, acrylic, Dacron, Teflon, etc.
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Synthetic Materials
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Worksheet 2 Composite materials
Time to Think (p. 15)
1.
The wall of the houses may be hard and strong, but may be brittle and may not
be resistant to weathering and fire.
2.
In a mud brick, the mud resists compression and the straw stands tearing. Thus
the composite material has good compressive strength and good tensile
strength.
3.
The matrix material is cement and the reinforcement materials are small stones
and sand.
4.
Steel rods make the cement stronger so that it is more capable of standing
compression and bending.
5.
CFRP is lighter and stronger than metals, and can block the spread of a crack
that appears on the body.
6.
Fibreglass can undergo more elongation before it breaks than carbon fibre
composite.
7.
(a) Wood is made up of a large number of thick-walled cells. The cell wall of
these cells contains an organic matrix embedded with fine fibres of
cellulose and lignin. The cellulose fibres make the wood tough and strong.
Lignin gives the wood additional strength and rigidity.
(b) Bone is made up of an organic matrix embedded with protein fibres and
calcium salts. The protein fibres make the bone strong and flexible. The
calcium salts make the bone hard and rigid.
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Synthetic Materials
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Worksheet 3 Metal with memory
Time to Think (p. 21)
1.
They wanted to test the flexibility of the alloy strip. They were surprised to
observe that the metal strip immediately reverted to its original shape when it
was heated with a lighter.
2.
Buehler and Wang thought that the property change of Nitinol might be due to
a change in the atomic arrangement or crystal structure of the alloy.
3.
Pressure has no effect on the shape of the A-phase, but will change the shape of
the M-phase.
4.
The A-phase has a symmetrical cube-like crystal structure which is very rigid
and cannot be deformed by pressure easily. The M-phase has a less symmetrical
crystal structure which is less rigid and can be deformed easily by pressure.
5.
A dental brace made from SMA applies a constant pressure on the teeth. The
wire does not need to be retightened when it contracts as the teeth move, unlike
the conventional stainless steel wires.
6.
The stent expands to its original shape when its temperature rises to that of
body temperature.
7.
The SMA wire can exert a constant force to hold the separated parts of a
fractured bone tightly together until the fracture of the bone heals.
8.
No definite answers. Students may obtain the relevant information on websites
such as:
http://www.stanford.edu/~richlin1/sma/sma.html
http://webdocs.cs.ualberta.ca/~database/MEMS/sma_mems/sma.html
http://en.wikipedia.org/wiki/Shape_memory_alloy
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