M6.4 Corrosion Flashcards
What is corrosion?
Metal is oxidised, forms salts and oxides
Why does corrosion form?
Difference in electrode potentials when in contact with electrolyte
What are the 3 requirements for corrosion to form?
. Electrical potential difference
. Conductive path
. Electrolyte covering areas
How can you prevent corrosion?
. Dry and clean surface
. Cleanliness
What is a passive film?
Invisible oxide layer
What corrosion will occur in grains?
. Intergranular
. Pitting
Describe galvanic corrosion
. 2 dissimilar metals
. Further apart on scale are more reactive
What is electrolytic corrosion?
Electrolyte and current through 2 metals
What’s the difference between galvanic and electrolytic corrosion?
Galvanic - interaction between 2 metals
Electrolytic - cause by external source of current
What is microbiological corrosion?
. Bacteria, fungi, mould
. Aircraft fuel tanks
What’s are the 2 bacteria categories?
Anaerobic, aerobic
What is stress corrosion and what’s it formed by?
. SCC
. Unexpected failure
. Tensile or cycled loading
. Dye penetrate inspecting
What is filiform corrosion?
. Oxygen concentrated
. On coatings
. Worms
What is pitting corrosion?
. Holes in materials
What is inter-granular corrosion?
. Cracking
. Allow other corrosions to enter
. Use films to prevent
What is exfoliation corrosion?
. Advanced of intergranular
. Go down grains
What’s fretting corrosion?
. Occurs due to vibration
. Rubbing removes protective films
. Use lube to prevent
What is crevice corrosion?
. Enter through nut edges
. Sealing
What is mercury corrosion?
. Chemical reactions
. Attacks grain boundary
What do noble metals have resistance to?
Surface attacks
Explain dry corrosion
. Lacks moisture
. Dry conditions
. Slow process
What’s wet corrosion?
. Humidity over 60%
. Moisture presence
