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mod 6 > 6.4 corrosion m > Flashcards

6.4 corrosion m Flashcards

1
Q

when does corrosion from on a metal?

A

whenever there is a difference in electrode potentials between parts of metal structure when in contact with an electrolyte

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2
Q

what do alkalis react with metals to create?

A

metallic salts (corrosion)

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3
Q

wat is used as a surface treatment for painting?

A

phosphoric acid solution

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4
Q

wat are ferrous metals subjected to but what is more vulnerable?

A

subject to damage but aluminium is more vulnerable to strong alkaline solutions than acids

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5
Q

corrosion should be distinguished from erosion but how is this done?

A

mechanical action

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6
Q

why does corrosion occur?

A

because of metals tendency to return to its original state

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7
Q

d noble metals corrode easily?

A

no because they are chemically pure in there natural state

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8
Q

where do all corrosive attacks start?

A

on the metal surface

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9
Q

what is the metal surface known as?

A

as electrolyte

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10
Q

what does the corrosion process involve?

A

two chemical changes
anodic and cathodic

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11
Q

what does the anode look like?

A

like it is being eten away

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12
Q

what happens in an anodic reaction?

A

electrolyte donates electrons into the internal circuit so the anode is oxidized

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13
Q

wat happens in a cathodic reaction?

A

receive electrons from anode and the electrons reduce the oxygen and water monocles into hydroxide ions and mixes with metal ions

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14
Q

what are examples of metals that produce corrosion products?

A

stainless steal
titanium

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15
Q

wen can the electrolyte easily penetrate and continue the corrosion process?

A

when the corrosion film is lose and prosperous

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16
Q

where does corrosion tend to form?

A

on less resistant surfaces but can also happen in boundary’s in between layers

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17
Q

what can corrosion in boundary layers result in?

A

pits and intergranular corrosion

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18
Q

what metals tend to lose electrons easily?

A

magnesium and aluminum

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19
Q

do metals corrode faster when thy lose more or fewer electrons?

A

when they lose more more easily

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20
Q

why may metals be corrosive resistant?

A

when they produce a passive oxide film on there surface

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21
Q

for corrosion to form what requirements must be met?

A

an electrical potential difference with the metal
a conductive path between the two areas of potential difference
some form of electrolyte or fluid covering the two areas

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22
Q

can corrosion be prevented?

A

no but can be controlled

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23
Q

what is one of the best way to control corrosion?

A

cleanliness

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24
Q

when does galvanic corrosion?

A

when two dissimilar metals make electrical contact in the presence of electrolyte

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25
Q

metals from what group corrode easier?

A

less noble groups

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26
Q

what metals will more actively corrode on the galvanic scale?

A

further apart on the galvanic scale

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27
Q

what is electrolytic corrosion?

A

when electrolyte and the flow of an electrical current between two metals

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28
Q

what does galvanic corrosion describe?

A

the interaction between two different metals

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29
Q

wat is an electrolytic corrosion caused by?

A

external source of current

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30
Q

wat does microbiological corrosion include?

A

actions of bacteria fungi or mold found in the fuel tanks

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31
Q

bacteria can be classified in to two category’s what are they?

A

aerobic
anaerobic

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32
Q

what does aerobic bacteria require?

A

require oxygen to live

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33
Q

how dos aerobic bacteria accelerate corrosion?

A

by oxidizing Sulphur to produce sulfuric acid

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34
Q

when does anerobic oxygen live?

A

can only survive when free oxygen is no present

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35
Q

what is fungi?

A

micro organisms that feed on organic materials

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36
Q

what slows the growth of microbes?

A

low humidity

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37
Q

what are ideal growth conditions for most micro organisms?

A

temperatures of 20 °C - 40 °C
relative humidity of 85% - 100%.

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38
Q

where does microbiological growth occur?

A

a the interface of water an fuel

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39
Q

what does the growth of fungus produce?

A

organic acids
alcohols
esters

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40
Q

Microbial corrosion can be minimized with a maintenance programmed that includes what?

A

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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41
Q

wa are the two main areas susceptible to corrosion?

A

toilets and galleys

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42
Q

what is stress corosion?

A

growth of crack formation in corrosive environment

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43
Q

what can stress corrosion lead to?

A

unexpected and sudden failure of normally ductile metal alloys when subjected to tensile strength or cyclic loading

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44
Q

wat is a common place for stress corrosion?

A

between rivets in a stressed skin

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45
Q

what can sow the extent of stress corrosion?

A

dye penetrant

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46
Q

what is filiform corrosion?

A

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

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47
Q

how is filiform corrosion identified?

A

a worm like trace of corrosion produced beneath the paint film

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48
Q

when does filiform corrosion occur?

A

when the relative humidity of the air is 78% - 90% and the surface is slightly acidic

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49
Q

where does filiform corrosion start?

A

at breaches in the coating system as well as in fastener heads and extends along the surface of the painted sheet underneath the coating

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50
Q

what can happen if filiform corrosion is not removed?

A

can lead to intergranular corrosion

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51
Q

what is the most common type of corrosion on aluminum and magnesium?

A

pitting corrosion

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52
Q

wat is pitting corrosion?

A

a localized form of corrosion that produces holes in the material

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53
Q

what can holes in materials from pitting corrosion also cause?

A

act as stress risers and acid in forming stress croon

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54
Q

how is intergranular corrosion presented?

A

as cracking and tends to accelerate over time

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55
Q

what are the protective coatings for intergranular corrosion?

A

paint
primer
cladded alliminum

56
Q

exfoliation corrosion is an advanced form of what?

A

intergranular corrosion

57
Q

where is exfoliation most prone?

A

extrusions
thick sheets
thin plates with elongated flat type grain structure

58
Q

what is fretting corrosion?

A

special type of erosion corrosion which occurs vibration and slipping

58
Q

how is fretting identified?

A

black or gray brown powder paste

59
Q

what helps reduce rubbing friction?

A

lubricate or sealant

60
Q

what is crevice corrosion?

A

attacks the metal surface through as stagnant solution

61
Q

describe crevice corrosion?

A

sever localized corrosion at narrow gaps between assemblies

62
Q

is mercury corrosion common on aircraft?

A

not commonly found

63
Q

what is the attack on aluminum through mercery called?

A

amalgamation

64
Q

how does a mercury attack happen?

A

mercury rapidly attacks the grain boundary’s of the aluminum

64
Q
A
65
Q

what is corrosion?

A

deterioration of a metal due to its reaction between different metals and their operational environment

66
Q

are thicker or thinner materials more prone to corrosion?

A

thicker

67
Q

what will effect the rate and type of corrosion?

A

operational stresses

68
Q

what is a major factor in corrosion?

A

composition of the material

69
Q

what are aircraft materials selected on?

A

the material strength and the cost
corrosion resistance is a secondary consideration

70
Q

what contaminates are in air and gas?

A

chlorides
surfaces
nitrates

71
Q

what climates increase corrosion?

A

warm moisture found climates

72
Q

why are noble metals used in aircraft assemblies?

A

because of there resistance to surface attack and there improved electrical and thermal conductivity

73
Q

how can copper corrosion be removed?

A

mechanically removed then the area is treated with a chromic acid solution

74
Q

can corrosion occur in dry conditions?

A

yes

75
Q
A
76
Q

what do most metals form in dry room temp conditions?

A

a thin oxide layer

77
Q

what does aluminum carry?

A

a thin but highly protective oxide layer

78
Q

how is dry corrosion explained?

A

by absorption mechanisms

79
Q

what type of surfaces does dry corrosion occur on?

A

heterogenous and homogenous

80
Q

is dry corrosion uniform?

A

yes

81
Q

is dry corrosion a quick or slow process?

A

slow process

82
Q

where does wet corrosion occur?

A

when the relative humidity exeads 60%

83
Q

what can wet corrosion result in?

A

pitting and stress cracking corrosion

84
Q

does corrosion happen quicker in freshwater or saltwater?

A

saltwater

85
Q

when is corrosion known as wet corrosion?

A

takes place from electrochemical attack with presence of moisture of conducting medium

86
Q

what type of surfaces does wet corrosion occur on?

A

heterogenous surfaces

87
Q

what is wet corrosion explained by?

A

electrochemical mechanism

88
Q

is we corrosion uniform?

A

no

89
Q

where does wet corrosion happen but where does it accumulate?

A

takes place at anode but accumulates at cathode

90
Q

what is a direct chemical attack?

A

when an alkaline or acid liquid contacts metal

91
Q

when there is no current flow or definitive anodic or cathodic area ho can a direct chemical attack still happen?

A

formation of protective film on the surface
mechanical removal of protective films
flexing on the metal surface
changes in temperature

92
Q

what can cause sever corrosion and embrittlement of titanium alloys but above what temp?

A

phosphate ester hydraulic fluid
when above 120 degrease Celsius`

93
Q
A
94
Q

what can happen when materials are placed under to much stress?

A

corrosion can occur and the material can crack

95
Q

what must happen to corrosion prone areas?

A

must be cleaned, inspected and treated more frequently than less corrosive areas

96
Q

what re corrosion prone areas?

A

exhaust areas
battery components
lavs and gallys
bilge areas
wheel wells and landing gear
external skin areas

97
Q

why is a battery compartment a corrosion prone area?

A

fumes from overheated battery’s

98
Q

what must we do with led battery’s?

A

clean and neutralize frequently

99
Q

why are lavs and galleys corrosive?

A

spilled food and waste products spilled on the floor

100
Q

what must we do to bilge areas to prevent corrosion?

A

keep clean and free of contaminates

101
Q

what is the wheel well and landing gear exposed to?

A

mud
salt
gavel
flying debris

102
Q

when inspecting landing gears and wheel wells where should attention be focused?

A

high strength steel compartments
exposed surfaces
exposed seiches
areas where water can be trapped
wheels
rigid tubing

103
Q

what are aircraft surfaces usually covered with?

A

a protective finish but it is still susceptible to corrosion

104
Q

are areas subject to high operational areas more or less likely to corrode?

A

more likely

105
Q

what can cause damage to the original surface protection?

A

trimming
drilling
reverting

106
Q

id aluminum corrosive resistant?

A

generally corrosive resistant

107
Q

what corrosion types can attack aluminum ?

A

surface
galvanic
pitting
intergranular

108
Q

what are some aluminum parts connected with?

A

anodized coating

108
Q

how can the white to gray powdery material be removed form aluminum?

A

mechanical polishing with a softer material

109
Q

what is the corrosive product of aluminum?

A

white to gray powder

109
Q

how can the white to gray powder be removed?

A

mechanical polishing with a matirial softer than the metal

110
Q

what are some aluminum parts protected by?

A

a anodized coating

110
Q

what do anodizing do?

A

increases the thickness of the oxide film

111
Q

what will happen if the anodized coating is damaged in service?

A

the costing will be partially restored by chemical surface treatment

112
Q

what can degrade the performance of copper and copper alloy components?

A

minor amounts of corrosion on copper

113
Q

what is the product of corrosion on copper?

A

bluish green coating on the surface

114
Q

what type of corrosion is copper susceptible to?

A

surface and intergranular corrosion

115
Q

what is magnesium’s susceptibility to corrosion?

A

highly susceptible

116
Q

what should happen when the protective coting fails on magnisium?

A

should be repaired promptly and completed repaired to avoid serious structural damage

117
Q

is magnesium corrosion easy to detect?

A

yes possibly the easiest

118
Q

what does corrosion on magnesium look like?

A

lifting of the paint film as white spots on the surface which rapidly develop in to snow like mounds or whiskers

119
Q

what does correction of corrosion on magnesium look like?

A

remove corrosion by applying chemical conversion coat and protective finish

120
Q

does titanium corrode easily?

A

no highly corrosive resistant

121
Q

when may titanium see degradation of its structural prophies?

A

when in repeated contact with chlorinated solvents at high temps

122
Q

what does titanium do to adjacent parts?

A

cause sever corrosion through galvanic corrosion

123
Q

how can the prevention o the titanium part crossing adjacent surfaces be done?

A

galvanically isolated through barrier coatings or films

124
Q

what can promote cracking in titanium?

A

contact with zinc or cadmium plated parts

125
Q

when are alloys with a nickel basis often used?

A

challenging environments that require good resistance against high and low temperatures

126
Q

how can corrosion on nickel alloys be identified?

A

green powdery deposit on the surface

127
Q

what does cadmium coating protect?

A

steel parts and provides compatible surface when a part contacts another material

128
Q

what does a corrosive attack on cadmium look like?

A

white to brown to black motting on the surface

129
Q

when does the cadmium plate protect the metal up until?

A

until actual iron rust appears

130
Q

when will steel begin to pit?

A

when exposed to harsh corrosive environments

131
Q

what type of corrosion is stainless steel highly suseptiable to?

A

crevice and stress corrosion cracking in moist salt laden environments and can cause galvanic corrosion for any other metal they are in contact with

132
Q

how can corrosion of stainless steel be prevented?

A

by keeping it clean

mod 6 (12 decks)

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