M6.4 Corrosion

Question 1

What’s formed when alkalis or acids react with metals

Answer 1

Metallic salts

Question 2

Why does corrosion occur

Answer 2

occurs because of the metals’ tendency to return to their natural state

Question 3

Why aren’t noble metals as susceptible to corrosion

Answer 3

because they are chemically pure in their natural state.

Question 4

What happens in relation to the anode and cathode in corrosion

Answer 4

Anode - donates electrons
Cathode- receives electrons from anode

Question 5

What metals can produce a passive film

Answer 5

Stainless steel
Pure aluminium
Titanium

Question 6

What three requirements must be met In order for electrolysis corrosion to form

Answer 6

Potential difference in the metal
Electrolyte
Conductive path between the two areas of potential difference

Question 7

What’s galvanic corrosion

Answer 7

when two dissimilar metals make electrical contact in the presence of an electrolyte which causes erosion to occur

Question 8

How does the galvanic scale affect the rates of corrosion

Answer 8

The further they are away from each other on the galvanic scale the faster the reaction will occur

Question 9

What’s the difference between galvanic corrosion and electrolytic corrosion.

Answer 9

Electrolytic corrosion is caused by an external current whereas galvanic describes the difference between two metals

Question 10

What’s microbiological corrosion

Answer 10

Corrosion caused by bacteria or fungi growing due to water and fuel meeting

Question 11

What two sections can bacteria be classified into

Answer 11

Aerobic and anaerobic

Question 12

How does low humidity affect the growth of fungi

Answer 12

It slows down the growth

Question 13

What are the ideal conditions for microorganisms

Answer 13

20-40 degrees and 85-100% humidity

Question 14

How can Microbiological corrosion be minimised

Answer 14

with a maintenance programme that includes:

A scheduled draining of water from the fuel tanks.
Inspections that look for a milky-white substance, indicating that microbial growth is present, followed by removing the microbial growth.
An application of biocide to prevent further growth

Question 15

What main areas of the aircraft are affected by microbiological corrosion

Answer 15

The galley,toilets and fuel tank

Question 16

What’s stress corrosion caused by

Answer 16

Due to the surface being put under tension due to a load being applied to it

Question 17

What’s filliform corrosion

Answer 17

oxygen-concentration cell corrosion or crevice corrosion that occurs on metal surfaces with an organic coating system

Question 18

How can filiform corrosion be identified

Answer 18

Worm like trace under paint film

Question 19

Under what environmental conditions does filiform corrosion usually occur under

Answer 19

78-90% humidity and slightly acidic surface

Question 20

What can happen if filiform corrosion isn’t removed

Answer 20

Can lead to inter-granular corrosion

Question 21

What’s the most common type of corrosion on magnesium and aluminium

Answer 21

Pitting

Question 22

What’s pitting corrosion

Answer 22

localised form of corrosion that produces holes in the material

Question 23

How is intergranual corrosion created

Answer 23

Due to not being quenched within the given 10 second time period after being heated

Question 24

What type of metal is exfoliation corrosion occur in

Answer 24

Wrought metals

Question 25

What’s fretting corrosion

Answer 25

Corrosion caused by two surfaces under a load vibrating or slightly rubbing together

Question 26

What can be done to prevent fretting from occurring

Answer 26

Applying a lubricant or a sealant

Question 27

What causes crevice corrosion

Answer 27

Stagnant water in a scratch or divot of a surface which causes and imbalance of o2 which causes a potential difference

Question 28

What’s the chemical reaction called when mercury attacks aluminium

Answer 28

Amalgamation

Question 29

In what conditions does wet erosion occur in

Answer 29

Humidity exceeding 60%

Question 30

What’s skydrol’s importance in chemical attacks

Answer 30

Found within hydraulic fluid and cam cause sever corrosion and embrittlement of titanium alloys at temps of above 120degress

Question 31

What are some factors that affect metal corrosion and the rate in which it occurs

Answer 31

Presence of a dissimilar, less corrodible metal (galvanic corrosion)
Anode and cathode surface areas (galvanic corrosion)
Temperature
Heat treatment and grain direction
Presence of electrolytes (hard water, saltwater, battery fluids etc.)
Availability of oxygen
Presence of different concentrations of the same electrolyte
Presence of biological organisms
Mechanical stress on the corroding metal
Time of exposure to a corrosive environmen

Question 32

What are the corrosion prone areas on an aircraft

Answer 32

Under galley
Toilets
Exhaust areas
Undercarriage
Battery compartment
Bilge areas
Wheels and landing gear
External skin

Question 33

What types of corrosion is copper particularly susceptible to

Answer 33

Intergranualr and surface

Question 34

Whats produced when copper begins to corrode

Answer 34

A blueish greenish costing on surface

Question 35

Is magnesium susceptible to corrosion if so what type

Answer 35

Pitting and yes extremely

Question 36

Is titanium susceptible to corrosion and if so what

Answer 36

No

Question 37

Is nickel susceptible to corrosion if so what type

Answer 37

No unless under extreme temp

Question 38

Is cadmium and zinc susceptible to corrosion

Answer 38

Yes
Evident due to white to brown to black mottling of the surface