M6.4

Question 1

What is corrosion

Answer 1

Chemical or electrochemical reactions cause metals to be oxidised, forming salts and oxides of the metal.

Question 2

Galvanic Corrosion

Answer 2

• 2 dissimilar metals make electrical contact in the presence of an electrolyte
• metals from less noble group corrode easier when in contact with more noble metals

Question 3

Electrolytic corrosion

Answer 3

• Due to an electrolyte and the flow of electrical current between 2 metals
• casued by electromotive force (EMF)

Question 4

What is a microbiological attack?

Answer 4

-bacteria, fungi or moulds (commonly found in aircraft fuel tanks and are the greatest corrosion problems)

Question 5

Microbial corrosion can be minimised by?

Answer 5

• scheduled drainage of water from fuel tanks
• inspections for bacteria, remove bacteria after
• application to prevent further growth

Question 6

Examples of where microbial corrosion can occur?

Answer 6

• fuel tanks
• toilets
• galleys
• bilge sump

Question 7

What is the common place for stress corrosion

Answer 7

Between rivets in a stressed skin

Question 8

Filiform corrosion?

Answer 8

• humidity 78% - 90%
• special form of oxygen-concentration cell corrosion
• if not removed, it can lead to inter-granular corrosion, especially around fasteners + seams
• worm like trace beneath paint film

Question 9

Pitting corrosion?

Answer 9

• produces holes in material
• common on aluminium and magnesium
• decreases materials strength

Question 10

Inter-granular corrosion?

Answer 10

• cracking and tends to accelerate over time

Question 11

Exfoliation Corrosion?

Answer 11

• advanced form of inter-granular corrosion

Question 12

Fretting corrosion?

Answer 12

• erosion corrosion which occurs due to vibration and slipping
• rubbing action removes protective film, continued rubbing leads to active metal released in atmosphere
• use lubrication to help reduce friction

Question 13

Mercury Corrosion?

Answer 13

• small amounts can lead to serious corrosion problems
• attacks aluminium through a chemical reaction (amalgamation)
• dangerous to aircraft + people

Question 14

What is the cause of corrosion

Answer 14

• deterioration of metal due to reaction between different metals and their operational environment
• thicker components are more prone to corrosion due to variation in their composition

Question 15

Noble metals

Answer 15

• such as silver, gold, platinum
• resistance to surface attack and their improved electrical and thermal conductivity

Question 16

Wet corrosion

Answer 16

• where relative humidity is >60%

Question 17

Corrosion prone areas?

Answer 17

• exhaust area, battery compartment, lavatories and galleys, bilge areas, wheel well and landing gear area, external skin areas,