1. Q: What is corrosion? A: Corrosion is the deterioration of materials,
typically metals, due to chemical or electrochemical reactions with their
environment, resulting in the loss of material properties and structural integrity.
2. Q: What are the four basic requirements for electrochemical corrosion?
ANSWER Anode, cathode, electrolyte, and metallic connection between anode
and cathode.
3. Q: What is the difference between uniform and localized corrosion?
ANSWER Uniform corrosion occurs evenly across the surface, while localized
corrosion attacks specific areas, such as pitting, crevice corrosion, or stress
corrosion cracking.
4. Q: Define galvanic corrosion. ANSWER Galvanic corrosion occurs when
two dissimilar metals are in electrical contact in the presence of an electrolyte,
causing the more active metal to corrode preferentially.
5. Q: What is the galvanic series? ANSWER A ranking of metals and alloys
based on their corrosion potential in a specific environment, typically seawater,
arranged from most active (anodic) to most noble (cathodic).
6. Q: What is pitting corrosion? ANSWER A form of localized corrosion that
creates small holes or pits in the metal surface, often initiated by breakdown of
passive films in the presence of aggressive ions like chlorides.
7. Q: Explain crevice corrosion. ANSWER Localized corrosion that occurs in
confined spaces where oxygen depletion and accumulation of aggressive
species create conditions favorable for accelerated attack.
8. Q: What is intergranular corrosion? ANSWER Corrosion that occurs
preferentially along grain boundaries, often due to depletion of alloying
elements or precipitation of secondary phases at grain boundaries.
,9. Q: Define stress corrosion cracking (SCC). ANSWER The growth of
cracks in a corrosive environment under the combined influence of sustained
tensile stress and specific environmental conditions.
10. Q: What is erosion corrosion? ANSWER The acceleration of corrosion
due to high-velocity fluid flow that removes protective films and increases mass
transport of corrosive species to the metal surface.
11. Q: Explain the concept of passivity in metals. ANSWER Passivity is the
spontaneous formation of a thin, protective oxide film on metal surfaces that
significantly reduces the corrosion rate despite thermodynamic favorability for
corrosion.
12. Q: What is the Pourbaix diagram? ANSWER A diagram showing regions
of thermodynamic stability for different species of an element as a function of
pH and electrode potential, useful for predicting corrosion behavior.
13. Q: Define corrosion rate. ANSWER The rate at which a material
deteriorates due to corrosion, typically expressed in terms of penetration rate
(mils per year or mm per year) or weight loss.
14. Q: What is the difference between corrosion rate and corrosion current
density? ANSWER Corrosion rate is the actual material loss, while corrosion
current density is the electrochemical current associated with the corrosion
process, related by Faraday's law.
15. Q: What is the mixed potential theory? ANSWER A theory explaining
that the corrosion potential of a corroding metal is determined by the
intersection of anodic and cathodic polarization curves.
16. Q: Define overpotential. ANSWER The additional potential beyond the
equilibrium potential required to drive an electrochemical reaction at a
measurable rate.
17. Q: What is the Tafel equation? ANSWER An equation describing the
relationship between overpotential and current density for electrochemical
reactions: η = a + b log(i).
18. Q: Explain the concept of polarization. ANSWER The shift in electrode
potential from its equilibrium value when current flows, caused by activation,
concentration, or resistance effects.
19. Q: What is cathodic protection? ANSWER A corrosion control technique
that reduces corrosion by making the metal structure the cathode of an
electrochemical cell.
, 20. Q: What are the two types of cathodic protection systems? ANSWER
Galvanic (sacrificial anode) systems and impressed current cathodic protection
(ICCP) systems.
21. Q: What is anodic protection? ANSWER A corrosion control method that
maintains a metal in its passive state by applying an anodic current to keep the
potential in the passive region.
22. Q: Define corrosion inhibitors. ANSWER Chemical substances that, when
added in small concentrations to a corrosive environment, significantly reduce
the corrosion rate of metals.
23. Q: What are the main types of corrosion inhibitors? ANSWER Anodic
inhibitors, cathodic inhibitors, mixed inhibitors, and volatile corrosion inhibitors
(VCIs).
24. Q: What is selective leaching? ANSWER A corrosion process where one
component of an alloy is preferentially removed, leaving behind a porous,
weakened structure.
25. Q: Give an example of selective leaching. ANSWER Dezincification of
brass, where zinc is preferentially leached out, leaving a porous copper
structure.
26. Q: What is hydrogen embrittlement? ANSWER The loss of ductility and
tensile strength in metals due to the absorption of atomic hydrogen, which can
lead to cracking and failure.
27. Q: What is the critical pitting potential? ANSWER The minimum
potential above which stable pits can initiate and propagate in a given
environment.
28. Q: Define repassivation potential. ANSWER The potential below which
existing pits become unstable and cease to propagate.
29. Q: What is the difference between general and localized corrosion
rates? ANSWER General corrosion rate represents uniform attack across the
surface, while localized rates can be orders of magnitude higher in specific
areas.
30. Q: What is crevice corrosion potential? ANSWER The potential above
which crevice corrosion can initiate and sustain in a given environment.
31. Q: Explain the autocatalytic nature of pitting corrosion. ANSWER Once
initiated, pits create acidic, chloride-rich conditions that accelerate further
attack, making the process self-sustaining.
typically metals, due to chemical or electrochemical reactions with their
environment, resulting in the loss of material properties and structural integrity.
2. Q: What are the four basic requirements for electrochemical corrosion?
ANSWER Anode, cathode, electrolyte, and metallic connection between anode
and cathode.
3. Q: What is the difference between uniform and localized corrosion?
ANSWER Uniform corrosion occurs evenly across the surface, while localized
corrosion attacks specific areas, such as pitting, crevice corrosion, or stress
corrosion cracking.
4. Q: Define galvanic corrosion. ANSWER Galvanic corrosion occurs when
two dissimilar metals are in electrical contact in the presence of an electrolyte,
causing the more active metal to corrode preferentially.
5. Q: What is the galvanic series? ANSWER A ranking of metals and alloys
based on their corrosion potential in a specific environment, typically seawater,
arranged from most active (anodic) to most noble (cathodic).
6. Q: What is pitting corrosion? ANSWER A form of localized corrosion that
creates small holes or pits in the metal surface, often initiated by breakdown of
passive films in the presence of aggressive ions like chlorides.
7. Q: Explain crevice corrosion. ANSWER Localized corrosion that occurs in
confined spaces where oxygen depletion and accumulation of aggressive
species create conditions favorable for accelerated attack.
8. Q: What is intergranular corrosion? ANSWER Corrosion that occurs
preferentially along grain boundaries, often due to depletion of alloying
elements or precipitation of secondary phases at grain boundaries.
,9. Q: Define stress corrosion cracking (SCC). ANSWER The growth of
cracks in a corrosive environment under the combined influence of sustained
tensile stress and specific environmental conditions.
10. Q: What is erosion corrosion? ANSWER The acceleration of corrosion
due to high-velocity fluid flow that removes protective films and increases mass
transport of corrosive species to the metal surface.
11. Q: Explain the concept of passivity in metals. ANSWER Passivity is the
spontaneous formation of a thin, protective oxide film on metal surfaces that
significantly reduces the corrosion rate despite thermodynamic favorability for
corrosion.
12. Q: What is the Pourbaix diagram? ANSWER A diagram showing regions
of thermodynamic stability for different species of an element as a function of
pH and electrode potential, useful for predicting corrosion behavior.
13. Q: Define corrosion rate. ANSWER The rate at which a material
deteriorates due to corrosion, typically expressed in terms of penetration rate
(mils per year or mm per year) or weight loss.
14. Q: What is the difference between corrosion rate and corrosion current
density? ANSWER Corrosion rate is the actual material loss, while corrosion
current density is the electrochemical current associated with the corrosion
process, related by Faraday's law.
15. Q: What is the mixed potential theory? ANSWER A theory explaining
that the corrosion potential of a corroding metal is determined by the
intersection of anodic and cathodic polarization curves.
16. Q: Define overpotential. ANSWER The additional potential beyond the
equilibrium potential required to drive an electrochemical reaction at a
measurable rate.
17. Q: What is the Tafel equation? ANSWER An equation describing the
relationship between overpotential and current density for electrochemical
reactions: η = a + b log(i).
18. Q: Explain the concept of polarization. ANSWER The shift in electrode
potential from its equilibrium value when current flows, caused by activation,
concentration, or resistance effects.
19. Q: What is cathodic protection? ANSWER A corrosion control technique
that reduces corrosion by making the metal structure the cathode of an
electrochemical cell.
, 20. Q: What are the two types of cathodic protection systems? ANSWER
Galvanic (sacrificial anode) systems and impressed current cathodic protection
(ICCP) systems.
21. Q: What is anodic protection? ANSWER A corrosion control method that
maintains a metal in its passive state by applying an anodic current to keep the
potential in the passive region.
22. Q: Define corrosion inhibitors. ANSWER Chemical substances that, when
added in small concentrations to a corrosive environment, significantly reduce
the corrosion rate of metals.
23. Q: What are the main types of corrosion inhibitors? ANSWER Anodic
inhibitors, cathodic inhibitors, mixed inhibitors, and volatile corrosion inhibitors
(VCIs).
24. Q: What is selective leaching? ANSWER A corrosion process where one
component of an alloy is preferentially removed, leaving behind a porous,
weakened structure.
25. Q: Give an example of selective leaching. ANSWER Dezincification of
brass, where zinc is preferentially leached out, leaving a porous copper
structure.
26. Q: What is hydrogen embrittlement? ANSWER The loss of ductility and
tensile strength in metals due to the absorption of atomic hydrogen, which can
lead to cracking and failure.
27. Q: What is the critical pitting potential? ANSWER The minimum
potential above which stable pits can initiate and propagate in a given
environment.
28. Q: Define repassivation potential. ANSWER The potential below which
existing pits become unstable and cease to propagate.
29. Q: What is the difference between general and localized corrosion
rates? ANSWER General corrosion rate represents uniform attack across the
surface, while localized rates can be orders of magnitude higher in specific
areas.
30. Q: What is crevice corrosion potential? ANSWER The potential above
which crevice corrosion can initiate and sustain in a given environment.
31. Q: Explain the autocatalytic nature of pitting corrosion. ANSWER Once
initiated, pits create acidic, chloride-rich conditions that accelerate further
attack, making the process self-sustaining.
