6.4 Corrosion Flashcards
What is the difference between corrosion and erosion
Erosion occurs due to mechanical actions
Why do metals such as gold and silver not corrode
As they are noble metals and are chemically pure
What is galvanic corrosion
The corrosion of two different dissimilar metals in the presence of an electrolyte
What is microbiological corrosion
From bacteria fungi or moulds
How can corrosion of magnesium be identified
A grey powder
What is filiform corrosion
Produces a worm like track of corrosion
Usually when relative humidity is 78-90%
Can lead to inter granular if not removed
What is pitting corrosion
First appears as a white powdery deposit. It starts on the surface and extends vertically in to the material
What is the most common type of corrosion on aluminium and magnesium
Pitting
What is inter granular corrosion
Attacks the grain boundaries with sometimes no indication on the surface
What is exfoliation corrosion
An advanced form of inter granular corrosion.
Where is exfoliation corrosion most common
Wrought products
What is fretting corrosion
Damage that can be caused in between two highly loaded surfaces which are not meant to move against each other
What is crevice corrosion
A type of concentration cell corrosion. This is corrosion of metal in a metal to metal joint, and corrosion at the edge of a joint. Seals of joints and gaps and use of protective coatings in the fraying surface area can reduce crevice corrosion
