Chapter 2 - advanced corrosion Flashcards
Describe passivation.
Passivation is the formation of a protective oxide film on the surface reducing its chemical activity and its ability to corrode.
Describe the following factors and how they affect corrosion.
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.
Two broad categories of corrosion can be described as?
General and localized
Describe galvanic corrosion.
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.
Describe cathodic protection.
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.
The two primary types of cathodic protection are?
Impressed current and galvanic ( sacrificial).
Impressed current power source include?
Rectified commercial power Solar cells Generators Fuel cells wind-powered cells Thermoelectric cells
Describe cathodic disbondment.
Cathodic disbondment is the separation of the coating from the surface through hydroxyl (OH-) formation due to increased ( made more negative) potential.
General corrosion is ?
A result in a relatively uniform loss of material over the entire surface
Localized corrosion is?
It occurs at discrete sites on the metal surface. areas adjacent are normally corroded to a much lesser extent. If at all.
