CORROSION : CORROSION CORROSION : 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. IRON (Rusting) : 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 IRON (Rusting) : IRON (Rusting) Rusting iron is POROUS What’s Porous? : What’s Porous? What’s Porous? : What’s Porous? IRON (RUSTING) : IRON (RUSTING) So What?
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 Rust is Porous : Rust is Porous ALUMINUM : ALUMINUM Reacts with oxygen in the air to make ALUMINUM OXIDE The aluminum develops a layer of rust, preventing further corrosion. SILVER : SILVER SILVER : 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.
A blue/black colour Slide 14: Spoon made of silver SILVER SPOON COVERED IN SILVER SULFIDE (TARNISH) SILVER : SILVER Let’s make silver tarnish quickly!
1 piece of silver material
2 hard boiled eggs (only the yolk)
1 zip lock bag
Boil eggs, remove egg yolks
Place in ziplock bag, overnight in freezer SILVER : SILVER Preventing Corrosion : Preventing Corrosion Key – keep metal surface from having contact with oxygen Preventing Corrosion : Preventing Corrosion Materials to paint:
Rust proof paint
Prevention is based on stopping the metal from being exposed to OXYGEN in either air or water.