resources - corrosion

Question 1

what is meant by corrosion?

Answer 1

the destruction of materials by chemical reactions with substances in the environment

Question 2

how to carry out experiment on the conditions required for rusting?

Answer 2

RUSTING only applies to iron and alloys of iron (steel) (in other metals it is corroding)

• first test tube, is a iron nail in distilled water, open to air
• second test tube, iron nail in distilled water. water has been boiled to remove any dissolved air. water covered by oil to prevent any air in the test tube from dissolving in the water (water + no air)
• third test tube we have anhydrous calcium chloride powder which removes any water from the air in the test tube. placed rubber bung to prevent moist air entering (air + no water)
• leave for several days + look for changes
  test tube 1: iron nail covered in rust
  test tube 2 + 3: no rust
  conclusion: rusting requires air + water

Question 3

why is corrosion a big problem?

Answer 3

damages materials

Question 4

how to prevent corrosion?

Answer 4

• using a barrier between the environment and the materials that we want to protect. use grease or paint or coat material in metal which is called electroplating.

Question 5

why is aluminium popular?

Answer 5

it naturally reacts with oxygen in the air to form a thin layer of aluminium oxide. this porches metal underneath from any further corrosion

Question 6

why do iron nails get coated in a layer of zinc?

Answer 6

coating a metal in zinc is called galvanising. these are galvanised nails. layer of zinc acts as a barrier against air and water, preventing the iron from corroding. however if zinc gets scratched, it still prevents corrosion as zinc more reactive than iron. means zinc corrodes instead of metal. this is sacrificial protection (using a more reactive metal)
(on ships zinc bars replaced every couple of years)