Science 9 - Corrosion

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CORROSION
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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.

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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

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IRON (Rusting)

• Rusting iron is POROUS

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Whats Porous?
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Whats Porous?
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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

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Rust is Porous
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ALUMINUM

• Reacts with oxygen in the air to make ALUMINUM
  OXIDE

• The aluminum develops a layer of rust, preventing
  further corrosion.

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SILVER
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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

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

• Lets 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

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SILVER
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Preventing Corrosion

• Key keep metal surface from having contact with
  oxygen

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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.