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01-1a-509 > -1 chapter 3 > Flashcards

-1 chapter 3 Flashcards

1
Q

Corrosion is

A

the
electrochemical deterioration of a material or its
properties due to its chemical reaction with the
surrounding environment. This reaction occurs because
of the tendency of metals to return to their naturally
occurring state, usually oxide or sulfide ores.

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2
Q

ATOM.

A

The smallest unit of an element, made
up of a positively charged nucleus surrounded by a
system of negatively charged electrons.

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3
Q

how many elements are there?

A

over 100- including metals (such as aluminum,
magnesium, gold, platinum, iron, nickel, titanium,
cadmium, chromium, copper, silver, lead, beryllium,
zinc), and non-metals (such as carbon, boron, sulfur,
chlorine, hydrogen, oxygen, nitrogen, and helium).

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4
Q

ELECTRON.

A

A negatively charged subatomic

particle.

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5
Q

Electrons

flow through liquid solutions only in the presence of

A

ions

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6
Q

ION.

A

An atom or group of atoms or molecules
which has acquired a net electric charge by gaining
(negative ion) or losing (positive ion) electrons.

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7
Q

ELECTROLYTE

A 
A liquid (usually water) solution
containing ions.
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8
Q

When a metal

corrodes

A

the atoms lose electrons and become positively

charged

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9
Q

Four conditions must

exist before metal corrosion can occur.

A

-A metal which has a tendency to corrode must
be present (the corroding metal is called the anode);
-A dissimilar conductive material (the cathode),
which has less tendency to corrode than the anode,
must be present (a dissimilar metal may be a different
metal, a protected part of the same metal, or conductive
plastic);
-A conductive liquid (electrolyte) must connect the
anode and cathode (so that ions can carry electric
current between them); and
-Electrical contact between the anode and cathode
(usually in the form of metal-to-metal contact) must
exist so that electrons can move between the anode
and the cathode.

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10
Q

corrosion products form, they often

precipitate onto the corroding surface as

A

a powdery

deposit.

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11
Q

The best time to prevent

corrosion is

A

the design stage

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12
Q

When two dissimilar
metals make electrical contact in the presence of an
electrolyte, the rate at which corrosion occurs depends
on the difference in their activities

A

The greater the difference in activity, the faster corrosion occurs but, when the corroding metal is
larger than the less active metal, corrosion will be slow
and superficial.

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13
Q

Higher temperature

environments tend to produce

A

more rapid corrosion due
to accelerated chemical reactions and, in humid
environments, higher concentration of water vapor in
the air.

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14
Q

UNIFORM SURFACE CORROSION

A

Uniform
surface corrosion is probably the most common type of
corrosion. It results from a direct chemical attack on a
metal surface that proceeds uniformly over the entire
exposed surface

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15
Q

GALVANIC CORROSION

A

Galvanic corrosion
occurs when different metals are in contact with each
other and an electrolyte, such as sea water.

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16
Q

PITTING CORROSION

A

Pitting is a form of
extremely localized attack that results in holes in the
metal

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17
Q

INTERGRANULAR CORROSION

A

Intergranular corrosion is an attack on the grain
boundaries of the metal. A highly magnified cross
section of any commercial alloy shows the granular structure of the metal.

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18
Q

EXFOLIATION CORROSION

A

Exfoliation is an advanced form of
intergranular corrosion where the surface grains of a
metal are lifted up by the force of expanding corrosion
products occurring at the grain boundaries.

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19
Q

CREVICE CORROSION.

A

Crevice corrosion
occurs because the environment of the local area is
very different from the larger environment.
Crevice corrosion is
one of the most familiar types of corrosion.

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20
Q

Active/Passive Cells

A

Metals which depend
on a tightly adhering passive film, such as the oxide
film on corrosion resistant steel, are prone to rapid
corrosive attack by active/passive cells

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21
Q

FILIFORM CORROSION

A

Filiform corrosion is
a form of crevice corrosion which occurs on metal
surfaces having a thin (~4 mils) organic protective
coating. It is recognized by its characteristic wormlike
trace of corrosion products beneath the coating

22
Q

EROSION CORROSION

A

Erosion corrosion is
the increase in the rate of attack on a metal due to the
action of a corrosive fluid against the metal surface.

23
Q

STRESS CORROSION

A

Also called stress
corrosion cracking (SCC). Stress corrosion is the intergranular or transgranular
cracking of a metal caused by the combined effects of
constant tensile stress (internal or applied) and corrosion.

24
Q

CORROSION FATIGUE

A

Corrosion fatigue is the cracking of metals caused by

the combined effects of cyclic stress and corrosion.

25
Q

FRETTING CORROSION

A

Fretting corrosion
occurs at contact areas between materials under load
subject to repeated vibration.

26
Q

HOT CORROSION

A

Also called high
temperature oxidation. Corrosion in the absence of
water can occur at high temperatures, such as those
found in turbine engine combustors, turbine sections,
and afterburners

27
Q

ALUMINUM

A

Aluminum is highly anodic, as evidenced by its position
in the galvanic series table. It is anodic to most other
metals, and, when in contact with them, galvanic
corrosion of the aluminum will occur. Aluminum alloys
are subject to pitting, intergranular corrosion, and
stress corrosion cracking

28
Q

MAGNESIUM

A

These alloys are highly susceptible to
corrosion when the metal surface is exposed to the
environment without a protective finish. The corrosion
products are white powdery snow-like mounds

29
Q

STEEL

A

Corrosion of steel is easily recognized because the

corrosion product is red rust

30
Q

STAINLESS STEEL

A

The main reason for the existence of stainless
steels is their resistance to corrosion. Stainless steels
are much more resistant to common rusting, chemical
action, and high temperature oxidation than ordinary
steels, due to the formation of an invisible oxide film, or passive layer, on the surface of these alloys.
-Stainless steels are susceptible to crevice
corrosion and stress corrosion cracking in moist, salt
laden environments. Exposure to saltwater can cause
pitting. The corrosion product of stainless steel is a
roughened surface with a red, brown, or black stain.

31
Q

TITANIUM

A

Under certain conditions,
chlorides and some chlorinated solvents may induce
stress corrosion cracking of certain titanium alloys.
Titanium and its alloys are highly corrosion resistant.

32
Q

CADMIUM

A

. Cadmium,
when coupled with steel, is anodic and protects the steel
by galvanic action. Corrosion on cadmium is evident
by white to brown to black mottling of the surface

33
Q

CHROMIUM

A

Chromium is used as a protective
plating. Chromium plating is also used to provide a
smooth, wear-resistant surface and to reclaim worn
parts

34
Q

NICKEL

A

Pure nickel is used as an electroless coating and
is subject to pitting corrosion. Flaking of the nickel
coating can also occur when an underlying metal
corrodes

35
Q

COPPER AND COPPER ALLOYS

A

Copper and copper-based alloys (brass and bronze) are considered corrosion resistant, with corrosion usually
limited to staining and tarnish. Copper corrosion is evidenced by the accumulation of blue or blue-green corrosion products on the corroded part. Sometimes copper or copper alloy surfaces tarnish to a dull gray-green color (patina) and the surface will remain relatively smooth.

36
Q

SILVER

A

. Silver does not
corrode in the ordinary sense, although it will tarnish in
the presence of sulfur.

37
Q

GOLD

A

Gold is a noble metal (pure
metal in nature) and does not normally corrode; however,
a slight deposit will appear as a darkening of reflecting
surfaces. Tarnish removal is critical on gold components
because of the very thin coatings used.

38
Q

TIN

A

Tin has the best combination of
solderability and corrosion resistance of any metallic
coating. However, tin has a tendency to grow “whiskers”
on tin plated wire and other plated applications.

39
Q

GRAPHITE/CARBON FIBER COMPOSITES

A

They are an important class of
aviation materials because of their high strength-toweight ratios and high stiffness Since carbon is the least active
metal in the galvanic series, it will accelerate the corrosion of any aircraft metal to which it is coupled.
Insulation between graphite or carbon epoxy composites and other metals is necessary to prevent
dissimilar metal attack on the attached part.

40
Q

ENCAPSULANTS AND CONFORMAL

COATINGS

A

Encapsulants and conformal coatings are
used to envelop an avionic component, module or assembly. These materials are considered nearly as
effective as hermetic sealing.

41
Q

Natural conditions in the environment which affect the

corrosion process are:

A

moisture, temperature, salt
atmospheres, ozone, sand, dust, and solar radiation.
Corrosion may also be promoted by biological sources,
including animals, insects, and microorganisms.

42
Q

Manmade conditions, which also affect the corrosion

process, include:

A

industrial pollution, manufacturing
operations, packaging, storage conditions, and
shipment.

43
Q

MOISTURE

A

Moisture is present in air as a gas
(water vapor) or as finely divided droplets of liquid (mist
or fog). It often contains contaminants such as chlorides,
sulfates, and nitrates, which increase its corrosive effects.

44
Q

SALT ATMOSPHERES

A

Salt forms a strong
electrolyte when dissolved in water, which causes rapid
corrosion of unprotected metal surfaces. The primary
source of the world’s salt is the ocean, which is 3.5% to
3.9% salt. Normal sea winds can carry from 10 to 100
pounds of seasalt per cubic mile of air.

45
Q

OZONE

A

Ozone is a particularly active form of
oxygen which is formed naturally during thunderstorms,
by arcing in electrical devices, and by photochemical
reactions in smog. When ozone is absorbed by
electrolyte solutions in contact with metals, it increases
the rate of corrosion.

46
Q

SOLAR RADIATION

A

The two ranges of solar
radiation most damaging to materials are ultraviolet (the
range that causes sunburn) and infrared (the range that
makes sunlight feel warm). On earth, maximum solar
radiation occurs in the tropics and equatorial regions,
but considerable damage occurs in the temperate zones
as a result of solar heating, photochemical effects, and
combinations of these two phenomena.

47
Q

TEMPERATURE

A

High temperature either
improves or impairs the performance of avionic
equipment, depending on conditions. Corrosion and
other harmful processes (outgassing, decomposition)
increase as temperature rises.

48
Q

PRESSURE

A

These environments create the familiar
corona, arcing, and poor cooling problems in avionic
equipment. Another problem is that of cyclic low and
high pressures. These varying pressures create leaky
seals and cause breathing. Breathing promotes
condensation and creates a corrosive environment.

49
Q

SAND, DUST, AND VOLCANIC ASH

A

Some of
the least recognized contributors to corrosion are sand,
dust, and volcanic ash. They often contain a number of
tar products, ashes, and soot. Sand, dust and volcanic
ash are hygroscopic and, when present on internal or
external surfaces of aircraft or electronic parts, can
absorb and hold moisture.

50
Q

CLIMATE

A

Warm, moist air, normally found in
tropical climates, tends to accelerate corrosion. Cold,
dry air, normally found in arctic climates, tends to
reduce corrosion rates. Corrosion does not occur in
very dry conditions.

51
Q

All personnel should familiarize

themselves with their local environment, such as

A

moisture, temperature, atmospheric pressure, salt,
water, sand, and dust. The type of aircraft, aircraft
mission, and ground operations also influence the rate
of corrosion.

01-1a-509 (6 decks)

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