Corrosion Flashcards
What is Corrosion?
Natural phenomenon where metal is converted into oxide.
What is chemical corrosion?
The metal wants to get back to normal.
What is electrochemical (galvanic) corrosion?
Dissimilar metals make electrical contact
Rate depends on contact surface size
Two changes in corrosion
Attacked metal: Anodic
Reducing agent: Cathodic
What is microbiological corrosion?
Bacteria, fungi, mould. On fuel, etc
Can produce ammonia
What is Stress corrosion?
Intergranular - cracks
What is Filiform corrosion?
Looks like worms under paint
O2 cell concentration
Humid surface
Lead to intergranular if not removed
What is Alclad?
Highly resistant to corrosion attack
What is passive film?
Tightly bound surface layer, prevents further corrosion
What is common corrosion?
Loose and porous film + electrolyte
Penetrates easily
Effects of corrosion on Steel, Aluminium, Magnesium, Copper
Rust
White powder
Grey powder and severe pitting
Green powder
Influencing factors on corrosion
Moisture Temperature Type of material Electrolytes Oxygen Mechanical stresses
What is Stress corrosion?
Dark rings and lines around rivets (smoking rivets)
Fretting gap
What is Pitting corrosion?
Common in Magnesium and Aluminium Alloy
White powder
Starts on surface, extends vertically
Decreases strength
What is Fretting?
Between 2 highly loaded surfaces, move against each other
Protective oxide film is removed
