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CH-109 Applied Chemistry (BME-2021) > Corrosion > Flashcards

Corrosion Flashcards

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1
Q

What is dry corrosion?

A 
Direct attack on metals by
oxygen at low or high
temperatures, in the
absence of moisture. It leads
to oxidation corrosion. The
resultant metal oxide is
known as a corrosion
product.
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2
Q

What is anode reaction for dry corrosion?

A

M = M(2+) + e(-)

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3
Q

What is cathode reaction for dry corrosion?

A

(1/2) O2 + 2e(-) = O(2-)

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4
Q

What is overall reaction for dry corrosion?

A

M + 1/2 O2 = M(+2) + O(-2) = MO

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5
Q

What are the types of films resulting from dry corrosion?

A

Stable, unstable, porous, and volatile.

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6
Q

What is a stable film?

A

Stable oxide layer adhered tightly to the metal surface. They act as a protective coating and prevent further corrosion. (Example: Pb, Cu, etc.)

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7
Q

What is a unstable film?

A

Metals decompose reversibly leading to an unstable films - continuous corrosion. (Example: Au, Ag, etc.)

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8
Q

What is a porous film?

A

Cracks in the surface of film that allow oxygen to pass through thereby allowing continuous corrosion. (Example: Li, Na, etc.)

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9
Q

What is a volatile film?

A

Film evaporates as soon as it forms exposing fresh metal surface to further attack. (Example: Mo etc.)

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10
Q

What is specific volume ratio?

A

Volume of metal oxide film formed / volume of metal ion consumed

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11
Q

What is the condition for stable porous film?

A

Specific volume ratio > 1

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12
Q

What is the condition for unstable porous film?

A

Specific volume ratio < 1

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13
Q

What is Pilling and Bedworth Rule.

A

Specific volume ratio > 1 for stable porous film and < 1 for unstable porous film.

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14
Q

What gases (other than oxygen) can also cause corrosion?

A

Cl2, SO2, H2, S, CO2, F2, and NOx

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15
Q

What is the formula for corrosion of silver by chlorine?

A

Cl2 + 2Ag = 2AgCl

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16
Q

What is the formula for corrosion of tin by chlorine?

A

Sn + 2Cl2 = SnCl4

17
Q

What is electrochemical corrosion?

A

Two dissimilar metals are partially dipped in an electrolyte.

18
Q

What is anode mechanism for electrochemical corrosion?

A

M = M(n+) + ne(-) (Oxidation)

19
Q

What are the main mechanisms for cathode in electrochemical corrosion?

A
  1. Hydrogen evolution mechanism

2. Oxygen absorption mechanism.

20
Q

What is Hydrogen evolution mechanism?

A

Occurs in an acidic environment to all metals

above hydrogen in electrochemical series

21
Q

What is Oxygen absorption mechanism?

A

Occurs in the presence of neutral electrolyte

(NaCl) and atmospheric oxygen.

22
Q

What is galvanic / dissimilar metal corrosion?

A

Refers to corrosion damage induced when two dissimilar materials are coupled in a
corrosive electrolyte.

23
Q

What are the conditions for galvanic corrosion?

A
  1. Electrochemically dissimilar metals.
  2. Metals must be in electrical contact.
  3. Metals must be exposed to an electrolyte.
24
Q

What is Differential Aeration Corrosion / (concentration-cell corrosion)?

A

Occurs when two or more areas of a metal surface are in contact with different concentrations of the same solution or different concentrations of dissolved oxygen in the electrolyte.

25
Q

What is the Galvanic series?

A

Establishes the corrosion behavior of metals and alloys in unpolluted sea water without their protective films.

26
Q

How is the galvanic series ordered?

A

Metals occupying higher positions in the series undergo corrosion in a vigorous manner.

27
Q

What are the factors that influence the rate of corrosion?

A
  1. Nature of metal
  2. Nature of environment
  3. Presence of corrosive gases and chemically active particles increases corrosion.
  4. Acidic medium is more corrosive than alkaline
    medium.
28
Q

How do impurities affect rate of galvanic corrosion?

A

Impurities increase rate of corrosion.

29
Q

What are the main corrosion control methods?

A
  1. Modification of metal.
  2. Modification of environment.
  3. Cathodic protection.
  4. Protective coating.
  5. Anodic inhibitors.
30
Q

What is galvanizing?

A

Galvanizing, or galvanization, is a manufacturing process where a coating of molten zinc is applied to steel or iron to offer protection and prevent rusting.

31
Q

How is corrosion affected by temperature?

A

Increases

32
Q

How is corrosion affected by temperature?

A

Increases

33
Q

What are types of cathodic protection?

A

Sacrifical anode, and impressed current protection

CH-109 Applied Chemistry (BME-2021) (6 decks)

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