6.4 Flashcards
What two actions causes corrosion?
Chemical or electrochemical
What is erosion?
Destruction by a mechanical action
Why does corrosion occur?
Because the metals are trying to return to there natural state
What is a noble metal?
When a metal is chemically pure (i.e gold and platinum)
What goes through an anoxic change?
The metal that is being attacked
What goes through an cathodic change?
The corrosive agent
What is a passive film on a metal?
When the metal itself produces an invisible oxide film to protect itself from corrosion
What metals are said to be corrosion resistant?
Aluminium and pure titanium
What is electrochemical action also known as?
Galvanic action
What is needed for galvanic corrosion to take place?
Two dissimilar metals and an electrolyte
What is microbiological corrosion?
Corrosion caused from bacteria, fungi, moulds
What is stress corrosion?
Intergranular cracking of the metal
What colour is rust when formed from steel and iron?
Dark colours (i.e red and brown)
What colour is corrosion when formed on aluminium?
White
What is the worst metal to put with aluminium?
Mercury
What colour is rust from magnesium?
Grey
What colour is rust from copper?
Green
How are copper wires on aircraft protected?
Plating with tin or nickel
What is electrolytic corrosion?
When an external source of current is applied
When does electrolytic corrosion normally take place?
When a battery leaks
In the galvanic scale what is a metal known as if it is moat corrosive?
Anodic
In the galvanic scale what is a metal known as if it is less corrosive?
Cathodic
What is the most common type of corrosion?
Pitting corrosion
What is exfoliation corrosion?
When the surface is lifted by corrosion in the grain boundary (like delamination)
What is fretting corrosion?
When two objects rub together when designed not to
What is aerobic bacteria?
Requires oxygen to live
What is meant by anaerobic bacteria?
When oxygen is not needed
What is fungi?
Micro-organisms that feed on organic materials
