Corrosion Flashcards
Metal corrosion
the deterioration of the metal by chemical or electrochemical attack.
three conditions necessary for corrosion to occur?
the presence of an electrolyte, an anode and a cathode and a conductor.
Electro-chemical attack?
the process of one metal giving up electrons (anode) to another metal (cathode). To replace the electrons the anode loses, it gains them from the electrolyte. The anode corrodes the cathode does not.
direct chemical attack?
occurs when a caustic agent comes in direct contact with the bare surface metal and produces corrosive by products.
What is an Electro-chemical attack comparable with? Why?
An electro-chemical attack is comparable with a dry cell battery because both have an electrolytic reaction.
What is an anode?
.
the positive plate that gives up electrons to the cathode and corrodes.
What is a cathode?
the negative plate that gains electrons from the anode
What can a mechanic do to prevent corrosion from ever occurring?
by using a protective coating, adequate cleaning, keeping drain holes free of obstructions, and sealing the aircraft against water during foul.
Uniform Surface corrosion
An even dulling of the surface caused by exposure to corrosive agents.
Pitting corrosion
Next step after uniform surface. Pits or clumps of white powder appear on anodic area
Inter-granular corrosion
Internal corrosion along grain boundaries
Exfoliation corrosion
An extreme case of intergranular corrosion that causes metal layers to delaminate
Galvanic corrosion
Occurs When two dissimilar metals with different potentials come into direct contact and set off an electron flow.
Concentration Cell corrosion
Occurs when two metals are joined together and moisture settles in creating a corrosion cell.
Stress corrosion
Occurs When a metal is subjected to a tensile stress in a corrosive environment.
Fretting corrosion
Occurs when slight movements wear away small particles of metal on two tightly fitted surfaces
six causes of corrosion
Wind erosion
Air moisture
Salt water
Spilled battery acids
Caustic cleaning solutions.
Improper heat treatment
Name ten areas where corrosion is likely to form on an aircraft.
Exhaust trails
Bilge areas
Wheel wells
Exterior skins
Galleys
Battery compartments
Lavatories
Flap recesses
Seat tracks
Fuel tanks
What are the steps in treating aluminum alloy of corrosion?
Fine clean parts
Strip paint
Remove corrosion with powdered pumice and scotch brite pad. For severe corrosion, use an aluminum wire brush
Neutralize remaining corrosion salts with 5% chromic acid solution
rinse off after 5 minutes.
Restore the parts protective coating.
Name the various protective coatings available for aluminum alloys.
Alclad
Alodine
Anodizing
Organic Coatings
How are ferrous metals treated of corrosion
strip parts of dirt and paint
Remove corrosion mechanically with scotchbrite and steel wire brush
Restore protective coating
Name the various protective coatings available for ferrous metals
Galvanizing with a coat of zinc
Cadmium plating
Metal spraying with molten aluminum
Case Hardening.
How is magnesium treated of corrosion?
with a hog bristle brush, nylon pad or glass bead blasting.
How can galvanic corrosion be prevented?
By placing a dielectric tape
How is the inside of structural steel tubing protected against corrosion?
Using Hot linseed oil
How is corrosion treated on highly stressed steel parts? Why?
with the use of abrasive papers, small power buffers and buffing compounds
What is the most likely cause of intergranular corrosion?
The most likely cause of intergranular corrosion is improper quenching during the heat treatment process.
An anodized surface which has been broken can be repaired by which chemical
treatment?
by a chemical conversion material such as Alodine.
