Chapter 2 Advanced Corrosion

Question 1

Describe passivation:

Answer 1

The production of a tightly adherent layer formed from the corrosion product (oxide, carbonate, chloride, sulfate, etc.)

Question 2

Describe the following factors and how they affect corrosion:

• Oxygen:
• Temperature:
• Chemical Salts:
• Humidity (or wetness):
• Pollutants and acid gases:

Answer 2

Oxygen: oxygen increases the rate of corrosion
Temperature: corrosion usually accelerated with increasing temperature
Chemical salts: increase the rate of corrosion by increasing the efficiency of the electrolyte.
Humidity: (or wetness): the wetter the environment, the more corrosion is likely to occur.
Pollutants and acid gases: acid rain, chemical byproducts and chlorides all promote corrosion.

Question 3

Two broad categories of corrosion can be described as:

Answer 3

General and localized

Question 4

Describe galvanic corrosion:

Answer 4

Galvanic corrosion is an electrochemical action of two dissimilar metals in the presence of an electrolyte and an electron conductive path, which occurs when dissimilar metals come into contact.

Question 5

Describe cathodic protection:

Answer 5

Cathodic protection is the reduction or elimination of corrosion by making the structure to be protected a cathode by means of an impressed current or attachment to a galvanic anode.

Question 6

The two primary types of cathodic protection are:

Answer 6

Impressed current and galvanic ( sacrificial).

Question 7

Impressed current power sources include:

Answer 7

Rectified commercial power
Solar cells
Generators
Fuel cells wind-powered cells
Thermoelectric cells

Question 8

Describe cathodic disbondment:

Answer 8

Cathodic disbondment is the separation of the coating from the surface through hydroxyl (OH-) formation due to increased ( made more negative) potential.