6.4 Corrosion✅(6) Flashcards
How does corrosion occur?
chemical or electrochemical reactions cause metals to be oxidised, forming salts and oxides of the metal
What is erosion
destruction through mechanical action
What is the advantage of a passive film produced on the surface of aluminium and titanium
-prevents further surface oxidisation
Can corrosion be prevented?
No
Corrosion is a natural process, and its prevention is almost impossible, but it can be controlled (T or F)
T
What is the best way to control corrosion?
- Cleanliness
What is galvanic corrosion?
- When 2 dissimilar metals (more noble & less noble) make electrical contact in the presence of an electrolyte
Metals from the less noble group corrode easier when they are in contact with more noble metals (T or F)
T
What is electrolytic corrosion?
Due to an electrolyte and the flow of an electrical current between the 2 metals, caused by an externally induced electromotive force (EMF)
Galvanic corrosion describes the interaction between two different metals (T or F)
T
Electrolytic corrosion is caused by an external source of current (T or F)
T
Bacteria can be classified into 2 categories which are
- aerobic
- anaerobic
What is a microbial attack?
- includes actions of bacteria, fungi or moulds (commonly found in aircraft fuel tanks)
Microbial growth occurs at the interface of water and fuel (T or F)
T
How can microbial composition be minimised
- scheduled water drainage from fuel tanks
- Inspection for milky white substance
- application of biocide to prevent further growth
What are the two main areas that are susceptible to corrosion on an aircraft
- toilets
- galleys
What is stress corrosion cracking (SCC)
- growth of crack formation in a corrosive environment
What is a common place for stress corrosion
- between rivets in a stressed skin
What is Filiform corrosion
special form of oxygen-concentration cell corrosion or crevice corrosion that occurs on metal surfaces with organic coating system
Filiform corrosion occurs when the relative humidity of the air is what?
78%-90%
What occurs if filiform corrosion is not removed
leads to intergranular corrosion (especially around fasteners and seams)
What is pitting corrosion
localised form of corrosion that produces holes in the material
What is the most common type of corrosion on aluminium and magnesium
pitting corrosion
Pitting corrosion is dangerous because of the vertical extension, which decreases the materials strength (T or F)
T
What is intergranular corrosion
usually presents itself as cracking and tends to accelerate over time
What is exfoliation corrosion
advanced form of intergranular corrosion
Exfoliation is most prone to occur in what products
wrought products
What is fretting corrosion
special type of erosion-corrosion which occurs due to vibration and slipping
How is fretting identified
- black or grey-brown powder/paste
What can help reduce rubbing friction and prevent fretting corrosion
lubricant or sealant
What is a crevice corrosion?
- attacks metal surface through a stagnant solution in the crevices
Even small amounts of mercury can lead to serious corrosion problems for various metals and alloys (T or F)
T
Mercury attacks aluminium through a chemical reaction known as what?
amalgamation
Disadvantages of mercury
- damaging to aircraft structures
- mercury vapours is dangerous for people
Why are noble metals such as silver, gold and platinum used in aircraft assemblies
- because of their resistance to surface attack
- and improved electrical and thermal conductivity
Copper and copper alloys are also relatively corrosion resistant (T or F)
T
How is severe copper corrosion evident by
accumulation of green to blue copper salts
What is dry corrosion
- metals form a thin oxide layer due to the reaction of metals with oxygen
What is wet corrosion
- takes place in humidity exceeds 60%
If an alkaline or acidic liquid contacts metal, corrosion forms. This is known as?
direct chemical attack
Examples of corrosion prone areas?
- exhaust areas
- battery compartment
- lavatories and galley access
- bilge areas
- wheel well (LG area)
Aluminium is generally corrosion resistant (T or F)
T
When a anodised coating is damaged, how can it be partially restored?
by chemical surface treatment
What is the corrosion product of aluminium
white-to-grey powdery material
What is the corrosion product of copper
bluish-green coating on surface of material
Is magnesium highly susceptible to corrosion
yes
magnesium is particularly susceptible to what type of corrosion
pitting corrosion
What material is highly corrosion resistant?
titanium
If titanium is in contact with zinc and cadmium plated parts, what can occur
promote cracking
Thicker structural components are more prone to corrosive attacks due to variations in their composition (T OR F)
T
What attacks can occur on copper components
- staining
- tarnish
