Corrosion/preventative measures Flashcards
What is corrosion
Reaction of metal with its surrounding, such as air and water
What happens when an object rusts
Iron+oxygen+water —> hydrated iron(III)oxide
Rusting is a redox reaction
It is called rusting when iron or steel is corroded
What are the methods to prevent rusting/reduce it
Painting
Coating with oil, grease or plastic
Plating with zinc (galvanising)
Plating with tin
How does Painting reduce rusting
Paint prevents air and water reaching the surface of the metal, but when it chips rusting starts on the exposed part of the metal
How does coating with oil, grease or plastic reduce corrosion
Prevents the metal being exposed to the air and water, however if the coating is damaged rusting starts on the exposed metals
What is sacrificial protection
Involves using a metal more reactive than iron such as zinc or magnesium. The more reactive metal will corrode first , protecting the iron/steel by ‘sacrificing ‘ itself.
This method is useful when painting is difficult.
What is galvanising
Galvanising involves dipping the metal object in molten zinc. After it has cooled and solidified the thin layer of zinc stops air/water reaching the iron/steel below and acts as a sacrificial metal so the object is protected even if the zinc layer is damaged
Disadvantage of tin plating
Tin is less reactive than iron, so if the tin layer is damaged the steel will act as the sacrificial metal and will rust faster than normal