Chapter 3: Corrosion Theory

Front 1

The chemical or electrochemical deterioration of a material.

Back 1

Corrosion

Front 2

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

Back 2

Atom

Front 3

A negatively charged subatomic particle

Back 3

Electron

Front 4

An atom or group of atoms or molecules which has acquired a net electric charge by gaining or losing electrons

Back 4

Ion

Front 5

A liquid (usually water) solution containing ions.

Back 5

Electrolyte

Front 6

All metals will corrode to some extent in a natural environment.

Back 6

Theory of Corrosion

Front 7

What four conditions must exist before metal corrosion can occur?

Back 7

1. A metal that has a tendency to corrode must be present (anode).

2. A dissimilar conductive material must be present (cathode).

3. A conductive liquid must connect the anode and cathode. (Electrolyte).

4. Electrical contact between the anode and cathode must exist.

Front 8

All corrosive attacks begin where?

Back 8

On the surface of the metal.

Front 9

Factors that influence corrosion

Back 9

1. Type of Material

2. Heat Treatment and Grain Direction

3. Dissimilar Metals

4. Anode and cathode surface area

5. Presence of electrolytes

6. Electrolyte concentration

7. Availability of oxygen

Front 10

The best time to prevent corrosion is?

Back 10

At the design stage

Front 11

Highest Corrosion Potential

Back 11

Lithium, Magnesium alloys, and zinc (plates)

Front 12

More factors that influence corrosion

Back 12

High temperatures, biological organisms, mechanical stress, length of exposure

Front 13

How many types of corrosion are there?

Back 13

12

Front 14

Most common type of corrosion, that results from a direct chemical attack on the metal surface. Coating/sealing the exposed surface will protect it from this type of attack.

Back 14

Uniform surface Corrosion

Front 15

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

Back 15

Galvanic corrosion

Front 16

Extremely localized corrosion attack that results in holes in the metal.

Back 16

Pitting corrosion

Front 17

a corrosion attack on the grain boundaries of the metal. Frequently the grain boundaries are anodic to the metal within the grain.

Back 17

Intergranular Corrosion

Front 18

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.

Back 18

Exfoliation Corrosion

Front 19

One of the most familiar types of corrosion. May occur in any crevice where a stagnant solution has pooled.

Back 19

Crevice corrosion

Front 20

A form of crevice corrosion which occurs on metal surfaces having a thin organic protective coating. Recognized by its characteristic wormlike trace of corrosion products beneath the coating.

Back 20

Filiform corrosion

Front 21

The increase in the rate of attack on a metal due to the action of a corrosive fluid against the metal surface. Characterized by grooves, gullies, waves, rounded holes, and or valleys in the metal surface.

Back 21

Erosion Corrosion

Front 22

The Intergranular or transgranular cracking of a metal caused by the combined effects of constant tensile stress.

Back 22

Stress corrosion

Front 23

The cracking of metals caused by the combined effects of cyclic stress and corrosion. No metal is immune to reduction.

Back 23

Corrosion Fatigue

Front 24

Occurs at contact areas between materials under load subject to repeated vibration.

Back 24

Fretting Corrosion

Front 25

Also known as high temperature oxidation.

Back 25

Hot corrosion

Front 26

NAME THE ALLOY:

Susceptible to surface pitting, Intergranular, exfoliation, stress, fatigue cracking, and fretting. Appearance of corrosion is a white to gray powder.

Back 26

Aluminum Alloy

Front 27

NAME THE ALLOY:

Highly susceptible to pitting. Corrosion appears as white, powdery, snow like mounds, and white spots on the surface.

Back 27

Magnesium Alloy

Front 28

NAME THE ALLOY

Susceptible to surface oxidation, pitting, surface corrosion, and Intergranular corrosion. Appears as a reddish-brown oxide (or rust).

Back 28

Carbon and Low Alloy Steel

Front 29

NAME THE ALLOY

Susceptible to uniform surface corrosion. Appears as a white powdery deposit to brown or black mottling of the surface

Back 29

Cadmium

Front 30

Natural conditions in the environment that affect the corrosion process.

Back 30

Moisture, temperature, salt, atmospheres, ozone, sand, dust, and solar radiation.

Front 31

Aluminum and magnesium form corrosion products that are white oxides or what?

Back 31

Hydroxides

Front 32

The most common type of corrosion (and the one that can be most effectively treated by maintenance personnel) is what corrosion?

Back 32

Electrochemical

Front 33

There are over how many elements?

Back 33

100

Front 34

What cannot move through metal conductors?

Back 34

Ions

Front 35

Branch of science concerned with chemical reactions at surfaces in contact with electrolytes?

Back 35

Electrochemistry

Front 36

How many conditions must exist before metal corrosion can occur?

Back 36

Four

Front 37

Corroding metal is called the what?

Back 37

Anode

Front 38

When corrosion products form, they often precipitate onto the corroding surface as a what?

Back 38

Powdery deposit

Front 39

Since corrosion products occupy more volume than the original metal, the paint surfaces may become blistered, flaked, chipped, or appear what?f

Back 39

Lumpy

Front 40

The best time to prevent corrosion is at what stage?

Back 40

Design

Front 41

The most commonly used metals in aircraft construction are aluminum, steel, titanium, and what else?

Back 41

Magnesium

Front 42

Most alloys are made up entirely of small crystalline regions called what?

Back 42

Grains

Front 43

Many alloys used in aircraft construction are sensitive to a form of corrosion known as what?

Back 43

Stress corrosion cracking.

Front 44

What corrosion is probably the most common type?

Back 44

Uniform Surface

Front 45

What corrosion occurs when different metals are in contact with each other and an electrolyte

Back 45

Galvanic

Front 46

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

Back 46

Pitting

Front 47

What are most susceptible to pitting damage?

Back 47

Stainless steels

Front 48

What corrosion is an attack on the grain boundaries of the metal?

Back 48

Intergranular

Front 49

What 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?

Back 49

Exfoliation

Front 50

What corrosion occurs because the environment of the local area is very different from the larger environment?

Back 50

Crevice

Front 51

What corrosion is a form of crevice corrosion which occurs on metal surfaces having a thin organic protective coating?

Back 51

Filiform

Front 52

Filiform corrosion occurs when the relative humidity of the air is between 65 abd90%, and the air temperature is between what?

Back 52

70 and 100 degrees

Front 53

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

Back 53

Erosion

Front 54

What corrosion is the Intergranular or transgranular cracking of a metal caused by the combined effects of constant tensile stress and corrosion?

Back 54

Stress

Front 55

Aluminum allow can fail by stress corrosion cracking when subjected to a stress which is only what percent of its rated strength?

Back 55

10%

Front 56

What is the cracking of metals caused by the combined effects of cyclic stress and corrosion?

Back 56

Corrosion fatigue

Front 57

What corrosion occurs at contact areas between materials under load subject to repeated vibration?

Back 57

Fretting

Front 58

What are the most widely used materials for aircraft construction?

Back 58

Aluminum and aluminum alloys

Front 59

Some aluminum parts are protected with an electrochemically applied oxide coating called what?

Back 59

Anodize

Front 60

What are the lightest structural metals used for aircraft and missile airframes?

Back 60

Magnesium Alloys

Front 61

What are used for gears, bearings, and high strength bolts, and for mountings, racks, brackets, and hardware in avionic systems?

Back 61

Stainless steels

Front 62

Titanium and titanium allows find numerous uses in aircraft, engines, and missiles at temperatures up to what?

Back 62

1000 degrees

Front 63

What is used as a coating to protect steel hardware such as bolts, washers, and screws, and as plating on electrical connectors?

Back 63

Cadmium

Front 64

What is used as a protective plating?

Back 64

Chromium

Front 65

What is a brittle gold-aluminum compound formed when bonding gold to aluminum?

Back 65

"Purple Plague"

Front 66

What is used as a plating material over copper in waveguides, microminiature circuits, wires, contacts, and rf shielding?

Back 66

Silver

Front 67

What has the best combination of solder ability and corrosion resistance of any metallic coating?

Back 67

Tin

Front 68

Graphite or carbon fiber composites are materials which consist of reinforcing fibers in a matrix made of organic resin and what?

Back 68

Epoxy

Front 69

What in addiction to conformal coating are used to envelop an avionic component, module or assembly?

Back 69

Encapsulants

Front 70

What compounds are used to encase a part or component such as in an electrical connector?

Back 70

Potting

Front 71

Rubbers and what else are used for insulation, seals, gaskets, caps, tubing, films, and coatings?

Back 71

Elastomers

Front 72

What is present in air as a gas or as finely divided droplets?

Back 72

Moisture

Front 73

What formation results from condensation of moisture?

Back 73

Electrolyte

Front 74

What percentage is salt of the ocean?

Back 74

3.5 to 3.9

Front 75

Normal sea winds can carry from 10 to how many pounds of sea salt per cubic mile of air?

Back 75

100

Front 76

Most fungus growth is inhibited by temperatures above what temperature?

Back 76

104

Front 77

What attack includes the action of bacteria, fungi, or molds?

Back 77

Microbial attack

Front 78

Bacteria may be either aerobic of what else?

Back 78

anaerobic

Front 79

What bacteria require oxygen to live?

Back 79

Aerobic

Front 80

Most front line combat aircraft average how many hours per day in flight operations?

Back 80

1 to 2

Front 81

Equipment should be properly packaged in accordance with what to minimize damage during shipment?

Back 81

MIL-STD-2073-1