M6.4 Corrosion Flashcards

1
Q

What’s formed when alkalis or acids react with metals

A

Metallic salts

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2
Q

Why does corrosion occur

A

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

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3
Q

Why aren’t noble metals as susceptible to corrosion

A

because they are chemically pure in their natural state.

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4
Q

What happens in relation to the anode and cathode in corrosion

A

Anode - donates electrons
Cathode- receives electrons from anode

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5
Q

What metals can produce a passive film

A

Stainless steel
Pure aluminium
Titanium

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6
Q

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

A

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

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7
Q

What’s galvanic corrosion

A

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

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8
Q

How does the galvanic scale affect the rates of corrosion

A

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

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9
Q

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

A

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

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10
Q

What’s microbiological corrosion

A

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

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11
Q

What two sections can bacteria be classified into

A

Aerobic and anaerobic

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12
Q

How does low humidity affect the growth of fungi

A

It slows down the growth

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13
Q

What are the ideal conditions for microorganisms

A

20-40 degrees and 85-100% humidity

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14
Q

How can Microbiological corrosion be minimised

A

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

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15
Q

What main areas of the aircraft are affected by microbiological corrosion

A

The galley,toilets and fuel tank

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16
Q

What’s stress corrosion caused by

A

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

17
Q

What’s filliform corrosion

A

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

18
Q

How can filiform corrosion be identified

A

Worm like trace under paint film

19
Q

Under what environmental conditions does filiform corrosion usually occur under

A

78-90% humidity and slightly acidic surface

20
Q

What can happen if filiform corrosion isn’t removed

A

Can lead to inter-granular corrosion

21
Q

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

22
Q

What’s pitting corrosion

A

localised form of corrosion that produces holes in the material

23
Q

How is intergranual corrosion created

A

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

24
Q

What type of metal is exfoliation corrosion occur in

A

Wrought metals

25
What’s fretting corrosion
Corrosion caused by two surfaces under a load vibrating or slightly rubbing together
26
What can be done to prevent fretting from occurring
Applying a lubricant or a sealant
27
What causes crevice corrosion
Stagnant water in a scratch or divot of a surface which causes and imbalance of o2 which causes a potential difference
28
What’s the chemical reaction called when mercury attacks aluminium
Amalgamation
29
In what conditions does wet erosion occur in
Humidity exceeding 60%
30
What’s skydrol’s importance in chemical attacks
Found within hydraulic fluid and cam cause sever corrosion and embrittlement of titanium alloys at temps of above 120degress
31
What are some factors that affect metal corrosion and the rate in which it occurs
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
32
What are the corrosion prone areas on an aircraft
Under galley Toilets Exhaust areas Undercarriage Battery compartment Bilge areas Wheels and landing gear External skin
33
What types of corrosion is copper particularly susceptible to
Intergranualr and surface
34
Whats produced when copper begins to corrode
A blueish greenish costing on surface
35
Is magnesium susceptible to corrosion if so what type
Pitting and yes extremely
36
Is titanium susceptible to corrosion and if so what
No
37
Is nickel susceptible to corrosion if so what type
No unless under extreme temp
38
Is cadmium and zinc susceptible to corrosion
Yes Evident due to white to brown to black mottling of the surface