6.4 corrosion

Question 1

what is corrosion

Answer 1

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

Question 2

where does corrosion form

Answer 2

on metals where there is a a difference in electrode potentials between 2 parts of a metal structure which are in contact with an electrolyte

Question 3

what acid is aluminum susceptible to

Answer 3

sulphuric acid

Question 4

what is aluminium more vulnerable to: alkaline or acid

Answer 4

alkaline

Question 5

do noble metals corrode easily?

Answer 5

no

Question 6

is metal an electrode or electrolyte

Answer 6

electrode
water is the electrolyte

Question 7

how is aluminium and titanium naturally protectedf

Answer 7

they produce a passive oxide film which is impermeable and prevent further surface oxidisation

Question 8

what are the 3 requirements for corrosion to occur

Answer 8

electrical potential difference
conductive path
electrolyte

Question 9

what is one of the best ways to prevent corrosion

Answer 9

cleanliness of the surface

Question 10

what is galvanic corrosion

Answer 10

two dissimilar metals (more noble and less noble) make electrical contact in the presence of an electrolyte

Question 11

what is electrolytic corosion

Answer 11

corrosion due to eleectrolyte and emf

Question 12

where is microbiological corrosion commonly found

Answer 12

fuel tanks

Question 13

what are the ideal growth conditions for micro-organisms

Answer 13

humidity of 85%-100%
temps of 20-40c

Question 14

how can microbial corrosion be prevented

Answer 14

scheduled draining of water in fuel tanks
inspections for milky white substance
biocide

Question 15

what other areas are microbial corrosion common

Answer 15

galleys
toilets

Question 16

how is stress corrosion caused

Answer 16

cyclic loading
tensile stress

Question 17

where is a common place for stress corrosion

Answer 17

between rivets in a stressed skin
around pressed in bushings
tapered pipe fittings

Question 18

what is filiform corrosion

Answer 18

worm like trace of corrosion
crevice corrosion
beneath the paint film

Question 19

when does filiform corrosion occur

Answer 19

when relative humidity is 78-90%

Question 20

if filiform corrosion is not removed what happens

Answer 20

it can lead to interangular corrosion

Question 21

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

Answer 21

pitting corrosion

Question 22

what is pitting corrosion

Answer 22

holes on surfaCE

Question 23

why is pitting corosion dangerous

Answer 23

decreases material strength

Question 24

what is intergranular corrosion

Answer 24

cracking which tends to accelerate over time
a combination of chemical and electrolytic actions attacj material along grain boundary

Question 25

what is exfoliation

Answer 25

advanced form of intergranular

Question 26

in which products is exfoliation more common

Answer 26

wrought products

Question 27

what is fretting corosion

Answer 27

occurs due to vibration and slipping

Question 28

how does fretting work

Answer 28

rubbing removes protective layer on material

Question 29

how is fretting identifyied

Answer 29

black or grey/brown powder/paste

Question 30

what is crevice corrosion

Answer 30

attacks metal through stagnant water in crevice

Question 31

where can crevice corrosion be seen

Answer 31

around the edges of nuts and rivet heads

Question 32

what is mercury corrosion

Answer 32

mercury can corrode various metals and alloys especially aluminium

Question 33

what is the chemical reaction in mercury corrosion

Answer 33

amalgamation

Question 34

are thicker structural components more or less susceptible to corrosion

Answer 34

more susceptible due to variations in their composition

Question 35

what are corrosion prone areas example

Answer 35

exhaust battery compartment lav and gallies bilge areas wheel well landing gears external skin

Question 36

is aluminium generally corrosion resistant

Answer 36

yes

Question 37

what does anodising do

Answer 37

increases the thickness of oxide film on aluminium naturally protective film

Question 38

is titanium susceptible to corrosion

Answer 38

no it is highly corrosion resistant

Question 39

what is a special form of oxygen concentration cell corrosion or crevice corrosion that occurs on metal surfaces

Answer 39

filiform corrosion

Question 40

what is exfoliation corrosion

Answer 40

advanced form of intergrangular

Question 41

if intergranular is left untreated what happens

Answer 41

becomes exfoliation