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Materials > Corrosion > Flashcards

Corrosion Flashcards

1
Q

What is corrosion?

A

Corrosion is the destructive and unintentional degradation of a material caused by its enviroment

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2
Q

What are the four key features of corrosion

A
  1. Anode
  2. Cathode
  3. Electrolyte
  4. Metallic Path
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3
Q

What are the 5 effects of corrosion?

A
  1. Reduces strength
  2. Decreases operational life
  3. Metallic properties are lost
  4. Wastage of metal
  5. Contamination of fluids in vessels and pipes
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4
Q

What is the anode?

A

The metal where electrons are released at the anode, which is the more reactive metal

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5
Q

What is the cathode?

A

The metal which gains the electrons

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6
Q

What happens in oxidation?

A

The metal atoms lose electrons

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7
Q

What happens in reduction?

A

The surrounding environment gains electrons

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8
Q

What is the electrolyte?

A

The electrically conductive solution that must be present for corrosion to occur

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9
Q

What is the metallic path?

A

The two electrodes are connected by a metallic conductor

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10
Q

What are the four characteristics of an anodic reaction?

A
  1. Oxidation of metal to an ion with a charge
  2. Release of electrons
  3. Shift to a higher valence state
  4. The process of oxidation in most metals results in corrosion
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11
Q

What are three common corrosion cells?

A
  1. Galvanic corrosion cells
  2. Concentration cells
  3. Electrolytic cells
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12
Q

Name four corrosive atmospheres

A
  1. Industrial
  2. Marine
  3. Rural
  4. Indoor
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13
Q

What is the equation for the Pilling-Bedworth ratio?

A

P-B Ratio = AoPm/AmPo

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14
Q

What can be said about the oxide film for metals with a P-B ratio of < 1, < 2 and > 2

A

< 1 - tend to be porous and non-protective
< 2 - tend to be protective
> 2 - Compressive stresses present

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15
Q

What 3 factors does the corrosion rate depend on?

A
  1. Chloride content
  2. Oxygen Availability
  3. Temperature
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16
Q

What are the 7 common corrosion mechanisms?

A
  1. Corrosion fatigue
  2. Stress corrosion cracking (SCC)
  3. Oxygen pitting corrosion
  4. Galvanic attack
  5. Caustic attack
  6. Intergranular corrosion
  7. Hydrogen embrittlement
17
Q

What are 4 protective measures?

A
  1. Protective coatings (Anodic coatings, Cathodic coatings)
  2. Alloying (Shifting electrode potential, protective surface film)
  3. Electrochemical methods (Sacrificial anode)
  4. Design
18
Q

Do metals corrode faster at a higher or lower temperature?

A

Higher temperature

19
Q

What 2 things should be done to avoid galvanic corrosion?

A
  1. Choose metals that are close in the galvanic series?

2. Insulate dissimilar metals

Materials (9 decks)

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