Corrosion Flashcards
What are the three types of corrosion?
Dry
Wet (Single Metal or Galvanic metal)
Stress
What is a Metal? List some…
A metal is solid at an ordinary temperature, lustrous on a freshly cut surface, malleable, fusible, ductile to some degree, usually good electrical and thermal conductivity.
Examples of metals:
- iron, gold, silver, aluminium
What is an Alloy? List some…
A metal that is made by combining two or more metallic elements, especially to give greater strength or resistance to corrosion
Examples: Steel or Stainless Steel
What is oxidation in terms of rust?
A chemical reaction that takes place when a substance comes into contact with oxygen or another oxidizing substance.
Water and air together is essential for rust
How can oxidation protect some metals?
Some metals have an oxide layer which prevents it from further oxidation.
Rust will eventually just erode some materials where it goes from metal with strength to fluffy stuff with no strength.
what are three factors that govern corrosion?
- Environment
- type of metal (some are more prone/reactive than others)
- protection
What are some corrosive envrionments?
Costal and Marine environments
- due to the salt found in water
Industrial Environments
- Due to the emissions (gas and acids)
Farming Environments
- nitrates from fertilisers.
what is corrosion accelerated by
Warm temperatures, acid’s and salts.
What is wet corrosion for a single metal?
Effects mainly steel, but it is a reaction between electron transfer which causes an imbalance.
The Cathode Gains an Electron and the Anode looses an electron
What is dry corrosion for a single metal?
This is when oxidation happens (protects majority of metals), but it must be able to make contact with the surface of the metal.
Whta is stress corrosion?
happen when you bend metal which causes electrons to move around and eventually the metal will break.
What is galvanic corrosion (two dissimilar metals)?
type of wet corrosion when two or more dissimilar metals are brought into electrical contact in the presence of an electrolyte (water or moisture).
Where does galvanic corrosion most commonly occur?
In high moisture, high humidity or water.
Explain this Diagram
INSERT DIAGRAM
One of the metals becomes an anode (gives electrons (-)) and corrodes faster than normal
One of the metals becomes a cathode (takes electrons (+)) and corrodes slower than normal
Cathodes and Anodes can be determined by a graph
What metals are considered anodes (Least noble - corrodes quicker)?
Magnesium, Zinc, Aluminium Alloys
