10.3 - Using Materials

What is corrosion?

The destruction of materials by chemical reactions with substances in the environment, e.g. rusting.

How is corrosion prevented?

Applying a coating that acts as a barrier, such as greasing, painting, or electroplating, stopping the air or water coming into contact with the metal.

Describe the sacrificial protection method.

• Some coatings are reactive and may contain corrosion inhibitors or a more reactive metal.

• If two metals are in contact the more reactive metal will corrode instead of the less reactive one.

• For example, zinc is used to galvanize iron and when scratched, provides sacrificial protection because zinc is more reactive than iron.

Describe the compounds and the uses of bronze, brass, gold and silver and copper and zinc, aluminum-magnesium and steels.

• Bronze - an alloy of copper and tin, used for making statues and decorative objects.

• Brass - an alloy of copper and zinc used for producing water taps and door fittings.

• Gold used as jewelry is usually an alloy with silver, copper, and zinc (The proportion of gold in the alloy is measured in carats, with pure gold being 24 carat, e.g. 18 carat is 75% gold).

• Aluminum-magnesium alloys are low density and used in aerospace manufacturing.

• Steels - alloys of iron that contain specific amounts of carbon and other metals.

  • High carbon steel is strong but brittle.

  • Low carbon steel is softer and easily shaped.

  • Steels containing chromium and nickel (stainless steels) are hard and resistant to corrosion.

How are the properties of polymers determined?

• Depends on what monomers they are made from and the conditions under which they are made.

• For example, low density (LD) and high density (HD) poly(ethene) are produced from ethene, using different catalysts and reaction conditions.

Describe the structures of thermosoftening polymers.

• Thermosoftening polymers soften easily on heating and can then be remolded, keeping the new shape on cooling.

• The polymer molecules are attracted to each other by weak intermolecular forces.

Describe the structures of thermosetting polymers

• Thermosetting polymers do not melt on heating.

• The polymer molecules are linked to each other by strong cross-links.

How is soda-lime glass made?

Heating a mixture of sand, sodium carbonate, and limestone.

How is borosilicate glass made?

Made from sand and boron trioxide, melts at higher temperatures than soda-lime glass.

How are clay ceramics made?

Made by shaping wet clay and then heating in a furnace (including pottery and bricks).

How are composites formed?

• Fibers or fragments of one material (reinforcement) are surrounded by a binder/matrix material that holds these fibers/fragments together.

• E.g. fiberglass - glass fibers bound together in a polymer, used for making storage tanks.