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) 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) Rusting iron is POROUS

What’s Porous?

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

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

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

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

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

SILVER

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

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.