6.4 Corrosion✅(6)

Question 1

How does corrosion occur?

Answer 1

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

Question 2

What is erosion

Answer 2

destruction through mechanical action

Question 3

What is the advantage of a passive film produced on the surface of aluminium and titanium

Answer 3

-prevents further surface oxidisation

Question 4

Can corrosion be prevented?

Answer 4

No

Question 5

Corrosion is a natural process, and its prevention is almost impossible, but it can be controlled (T or F)

Answer 5

T

Question 6

What is the best way to control corrosion?

Answer 6

• Cleanliness

Question 7

What is galvanic corrosion?

Answer 7

• When 2 dissimilar metals (more noble & less noble) make electrical contact in the presence of an electrolyte

Question 8

Metals from the less noble group corrode easier when they are in contact with more noble metals (T or F)

Answer 8

T

Question 9

What is electrolytic corrosion?

Answer 9

Due to an electrolyte and the flow of an electrical current between the 2 metals, caused by an externally induced electromotive force (EMF)

Question 10

Galvanic corrosion describes the interaction between two different metals (T or F)

Answer 10

T

Question 11

Electrolytic corrosion is caused by an external source of current (T or F)

Answer 11

T

Question 12

Bacteria can be classified into 2 categories which are

Answer 12

• aerobic
• anaerobic

Question 13

What is a microbial attack?

Answer 13

• includes actions of bacteria, fungi or moulds (commonly found in aircraft fuel tanks)

Question 14

Microbial growth occurs at the interface of water and fuel (T or F)

Answer 14

T

Question 15

How can microbial composition be minimised

Answer 15

• scheduled water drainage from fuel tanks
• Inspection for milky white substance
• application of biocide to prevent further growth

Question 16

What are the two main areas that are susceptible to corrosion on an aircraft

Answer 16

• toilets
• galleys

Question 17

What is stress corrosion cracking (SCC)

Answer 17

• growth of crack formation in a corrosive environment

Question 18

What is a common place for stress corrosion

Answer 18

• between rivets in a stressed skin

Question 19

What is Filiform corrosion

Answer 19

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

Question 20

Filiform corrosion occurs when the relative humidity of the air is what?

Answer 20

78%-90%

Question 21

What occurs if filiform corrosion is not removed

Answer 21

leads to intergranular corrosion (especially around fasteners and seams)

Question 22

What is pitting corrosion

Answer 22

localised form of corrosion that produces holes in the material

Question 23

What is the most common type of corrosion on aluminium and magnesium

Answer 23

pitting corrosion

Question 24

Pitting corrosion is dangerous because of the vertical extension, which decreases the materials strength (T or F)

Answer 24

T

Question 25

What is intergranular corrosion

Answer 25

usually presents itself as cracking and tends to accelerate over time

Question 26

What is exfoliation corrosion

Answer 26

advanced form of intergranular corrosion

Question 27

Exfoliation is most prone to occur in what products

Answer 27

wrought products

Question 28

What is fretting corrosion

Answer 28

special type of erosion-corrosion which occurs due to vibration and slipping

Question 29

How is fretting identified

Answer 29

- black or grey-brown powder/paste

Question 30

What can help reduce rubbing friction and prevent fretting corrosion

Answer 30

lubricant or sealant

Question 31

What is a crevice corrosion?

Answer 31

- attacks metal surface through a stagnant solution in the crevices

Question 32

Even small amounts of mercury can lead to serious corrosion problems for various metals and alloys (T or F)

Answer 32

T

Question 33

Mercury attacks aluminium through a chemical reaction known as what?

Answer 33

amalgamation

Question 34

Disadvantages of mercury

Answer 34

- damaging to aircraft structures - mercury vapours is dangerous for people

Question 35

Why are noble metals such as silver, gold and platinum used in aircraft assemblies

Answer 35

- because of their resistance to surface attack - and improved electrical and thermal conductivity

Question 36

Copper and copper alloys are also relatively corrosion resistant (T or F)

Answer 36

T

Question 37

How is severe copper corrosion evident by

Answer 37

accumulation of green to blue copper salts

Question 38

What is dry corrosion

Answer 38

- metals form a thin oxide layer due to the reaction of metals with oxygen

Question 39

What is wet corrosion

Answer 39

- takes place in humidity exceeds 60%

Question 40

If an alkaline or acidic liquid contacts metal, corrosion forms. This is known as?

Answer 40

direct chemical attack

Question 41

Examples of corrosion prone areas?

Answer 41

- exhaust areas - battery compartment - lavatories and galley access - bilge areas - wheel well (LG area)

Question 42

Aluminium is generally corrosion resistant (T or F)

Answer 42

T

Question 43

When a anodised coating is damaged, how can it be partially restored?

Answer 43

by chemical surface treatment

Question 44

What is the corrosion product of aluminium

Answer 44

white-to-grey powdery material

Question 45

What is the corrosion product of copper

Answer 45

bluish-green coating on surface of material

Question 46

Is magnesium highly susceptible to corrosion

Answer 46

yes

Question 47

magnesium is particularly susceptible to what type of corrosion

Answer 47

pitting corrosion

Question 48

What material is highly corrosion resistant?

Answer 48

titanium

Question 49

If titanium is in contact with zinc and cadmium plated parts, what can occur

Answer 49

promote cracking

Question 50

Thicker structural components are more prone to corrosive attacks due to variations in their composition (T OR F)

Answer 50

T

Question 51

What attacks can occur on copper components

Answer 51

- staining - tarnish