1. CORROSION

2. CORROSION
Corrosion is a chemical change, in which a metal loses its
properties because of a chemical reaction with its
environment.
Corrosion is a very slow process, can take decades
depending on the metal involved.
Corrosion looks different for different types of metals.

3. IRON (Rusting)
The corrosion of iron-based
metals is called RUSTING
Iron reacts with oxygen to
form IRON OXIDE
The oxygen can come from
AIR or WATER

4. IRON (Rusting)
Rusting iron is POROUS

5. What’s Porous?

6. IRON (RUSTING)
SoWhat?
Rusted metal will absorb water and “flake off”
This exposes fresh un-rusted metal to water or
oxygen
This new metal will rust
Costs billions of dollars

7. Rust is Porous

10. ALUMINUM
Reacts with oxygen in the
air to make
ALUMINUM OXIDE
The aluminum develops a
layer of rust, preventing
further corrosion.

11. SILVER

12. SILVER
Silver does not rust, but
tarnishes very slowly.
Silver reacts with hydrogen
sulfide found in food or water
In this reaction, silver turns into
silver sulfide.
Silver Sulfide:
Called “tarnish”
A blue/black colour

13. Spoon made of silver
SILVER SPOON COVERED IN SILVER SULFIDE (TARNISH)

14. SILVER
Let’s make silver tarnish quickly!
Materials
1 piece of silver material
2 hard boiled eggs (only the yolk)
1 zip lock bag
Procedure
Boil eggs, remove egg yolks
Place in ziplock bag, overnight in freezer

15. SILVER

16. Preventing Corrosion
Key – keep metal
surface from having
contact with oxygen

17. Preventing Corrosion
Materials to paint:
Paint
Oil
Rust proof paint
Prevention is based on stopping the metal from being
exposed to OXYGEN in either air or water.