Category: Corrosion Engineering Objective Questions

Corrosion Engineering Objective Questions & Answers on “Modern Theory Principles – Thermodynamics – 2”.

1. Which of the following is a cathode and anode respectively in the Ag-Fe system?
a) Iron (Fe) and Silver (Ag)
b) Silver (Ag) and Iron (Fe)
c) Gold (Ag) and Iron (Fe)
d) Iron (Fe) and Gold (Ag)
Answer: b
Clarification: In the Ag-Fe system, Silver (Ag) (+0.80V) acts as a cathode as the standard hydrogen potential is relatively higher than the Iron (Fe) (-0.44V) and Iron acts as anode due to relatively less standard hydrogen potential.

2. An electrochemical reaction is always a combination of oxidation half-cell and a reduction of half-cell.
a) True
b) False
Answer: a
Clarification: Corrosion is usually an electrochemical process which is a combination of oxidation half-cell and reduction half-cell. Oxidation and reduction reactions are simultaneous in nature and it is also called Redox reactions.

3. What is the cathodic and anodic reactions respectively of Cu-Ag system?
a) Ag==>Ag⁺²+2e and Cu⁺²+2e==>Cu
b) Cu==>Cu⁺²+2e and Ag==>Ag⁺²+2e
c) 2Ag⁺¹+2e==>2Ag and Cu==>Cu⁺²+2e
d) 2Ag==>2Ag⁺¹+2e and Cu⁺²+2e==>Cu
Answer: c
Clarification: Standard hydrogen potential of silver (Ag) is +0.80V and copper is +0.34V.
Cathodic reaction: 2Ag⁺¹+2e==>2Ag
Anodic reaction: Cu==>Cu⁺²+2e

4. Which of the following type of reaction is shown in the given figure?

a) Non-spontaneous reaction
b) Equilibrium reaction
c) Neither spontaneous nor non-spontaneous reaction
d) Spontaneous reaction
Answer: d
Clarification: Spontaneous reaction is a reaction in which the change in Gibbs free energy is negative. It means the free energy of reactants is more than the free energy of products.

5. Which of the following diagrams shows the stability of metals over a range of pH and potential of a system?
a) Phase diagrams
b) Pourbaix diagrams
c) Phase diagrams and Pourbaix diagrams
d) Colling curves
Answer: b
Clarification: Pourbaix diagrams show the stability of metal over a range of pH and potential of a system. It also includes native zone, passive zone, and corrosive zone. It is also called as potential-pH diagrams.

6. What is depicted in the given figure?

a) Phase diagram of the Fe-C system
b) Pourbaix diagram for Fe-O₂ system
c) Pourbaix diagram for Fe-H₂O system
d) Colling curve pure iron
Answer: c
Clarification: Pourbaix diagram is a diagram that shows the stability of species of a metal over a range of pH and potential of a system. Given figures represents the pourbaix diagram of the Fe-H₂O system.

7. Which of the following zone of given Pourbaix diagram indicates the immune zone?

a) Zone 1
b) Zone 2
c) Zone 3
d) Zone 4
Answer: a
Clarification: The Immune zone is the zone of the pourbaix diagram in which the stability of native metal in zero oxidation state is high. It is the zone in which no corrosion or passivation takes place.

8. Which of the following zone(s) of given Pourbaix diagrams indicate a passive zone?

a) Zone 1 and 2
b) Zone 2 and 3
c) Zone 2, 3 and 6
d) Zone 4 and 5
Answer: d
Clarification: Passive zone is the zone in the pourbaix diagram in which the passivation of metal takes place. It is the operating zone in various industries to minimize corrosion and to increase the efficiency of the process.

9. Which of the following is/are the applications of Pourbaix diagrams?
a) Predicting the spontaneous direction of reactions
b) To reduce corrosion attack
c) To reduce corrosion attack, to predict the direction of spontaneous reaction and to estimate the composition of corrosion product
d) To estimate the composition of corrosion product
Answer: c
Clarification: Applications of Pourbaix diagrams:
i. Predicting the spontaneous direction of reactions
ii. To reduce corrosion attack
iii. To estimate the composition of corrosion product.

10. Which of the following is/are the limitations of Pourbaix diagrams?
a) Rate of reaction is can’t be predicted
b) It neglects the impurities of working conditions
c) Stability of metallic species is predicted
d) Rate of reaction is not predicted and it neglects the impurities of working conditions
Answer: d
Clarification: Limitations of Pourbaix diagrams:
i. Rate of reaction can’t be predicted
ii. It neglects the impurities of working conditions
iii. Alloying elements of alloys are also neglected.

Corrosion Engineering MCQs on “Eight Forms – Cavitation and Fretting Corrosion”.

1. Which of the following type of corrosion is caused by the formation and collapse of vapor bubbles in a liquid near the metal surface?
a) Filiform corrosion
b) Fretting corrosion
c) Cavitation damage
d) Crevice corrosion
Answer: c
Clarification: Cavitation damage is the special form of erosion-corrosion that occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface.

2. Which of the following equipment encounters cavitation damage in the service?
a) Hydraulic turbines
b) Ship propellers
c) Pump impellers
d) Hydraulic turbines, ship propellers, and pump impellers
Answer: d
Clarification: Cavitation damage occurs in hydraulic turbines, ship propellers, pump impellers, and other surfaces where high-velocity liquid flow and pressure changes are encountered.

3. Which of the following condition is/are correct regarding the boiling point of a liquid with an increase in pressure?
a) Decreases up to triple point
b) Increases up to triple point
c) Increases up to the critical point
d) Decreases up to the critical point
Answer: a
Clarification: As the pressure of a liquid decreases, its boiling point decreases up to its triple point. As the pressure increases its increases up to a critical point.
Example: At higher altitudes boiling point of liquids reaches low as atmospheric pressure decreased.

4. Which of the following will result due to cavitation damage of a metal?
a) Mechanical action
b) Chemical dissolution
c) Both mechanical action and chemical dissolution
d) Neither mechanical action nor chemical dissolution
Answer: c
Clarification: Cavitation damage is the special form of erosion-corrosion that occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface. It results in the mechanical and chemical dissolution of metal.

5. Cavitation damaged can be reduced by changing the design to minimize hydrodynamic pressure differences in process streamflow.
a) False
b) True
Answer: b
Clarification: Cavitation damaged can indeed be reduced by changing the design to minimize hydrodynamic pressure differences in process streamflow. It reduces the impingement area and force of the stream.

6. Which of the following type of corrosion is depicted in the given figure?

a) Fretting corrosion
b) Crevice corrosion
c) Cavitation damage
d) Pitting corrosion
Answer: c
Clarification: Cavitation damage is depicted in the given figure. It occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface. And it results in mechanical action and chemical dissolution of metal.

7. Which of the following type of corrosion that occurs at contact areas between materials under load subjected to vibration or relative motion?
a) Fretting corrosion
b) Crevice corrosion
c) Cavitation damage
d) Pitting corrosion
Answer: a
Clarification: Fretting corrosion is the special type of erosion-corrosion that occurs at the contact areas between materials under load subjected to vibration or relative motion.

8. Which of the following is/are the other names of fretting corrosion?
a) Friction oxidation
b) Wear oxidation
c) False brinelling
d) Friction oxidation, wear oxidation and false brinelling
Answer: d
Clarification: Fretting corrosion is one of the special types of erosion-corrosion. It also called friction oxidation, wear oxidation, chafing, and false brinelling. Because it gets initiated with wear or friction and oxides debris are formed during corrosion.

9. Which of the following is/are the classic cases of fretting corrosion?
a) Bolted tie plates on railroad rails
b) Press-fitted ball bearing race on a shaft
c) On ball bearings
d) Bolted tie plates on railroad rails and press-fitted ball bearing race on a shaft
Answer: d
Clarification: Fretting corrosion occurs at contact areas between materials under load subjected to vibration or repeated relative motion. And it doesn’t occur on materials in continuous motion such as on ball bearings.

10. Which of the following is/are the basic requirements for the occurrence of fretting corrosion?
a) The interface must be under load
b) Vibration or repeated relative motion between the two surfaces
c) The interface must be under load and vibration or repeated relative motion between the two surfaces
d) The relative motion should be high
Answer: c
Clarification: The basic requirements for the occurrence of fretting corrosion are:
i. The interface must be under load
ii. Vibration or repeated relative motion between the two surfaces
iii. The load and the relative motion of the interface must be sufficient to produce deformation.

11. Which of the following is/are the preventive measures of fretting corrosion?
a) Lubricate with low-viscosity, high-tenacity oil
b) Increasing surface hardness by shot-peening or cold working
c) Use gaskets to absorb vibrations
d) Lubricate with low-viscosity, high-tenacity oil, increasing surface hardness by shot-peening and use gaskets to absorb vibrations
Answer: d
Clarification: Preventive measures to minimize fretting corrosion:
i. Lubricate with low-viscosity, high-tenacity oil, and greases
ii. Increasing surface hardness by shot-peening or cold working
iii. Use gaskets to absorb vibrations and exclude oxygen at bearing surfaces
iv. Increase the load to decrease slip between two metals.

Corrosion Engineering Questions and Answers for Campus interviews on “Cathodic and Anodic Protection – 2”.

1. Which of the corrosion prevention method is used for reducing the maintenance cost of highway and bridges?
a) Sacrificial anode
b) Impressed current supply
c) Anodic protection
d) Use of inhibitors
Answer: b
Clarification: Impressed current supply is used as the corrosion prevention for reducing maintenance costs of big metallic structures such as highways and bridges. It also used to reduce the corrosion of reinforced steel.

2. Which of the following is depicted in the given figure?

a) Anodic protection
b) Impressed current supply
c) Stray current effect
d) Sacrificial anode
Answer: c
Clarification: The given figure depicts the stray current effect that usually caused to the dense pipelines in the vicinity of a tank or pipeline protected by the impressed current system.

3. Anodic protection is based on the formation of a protective film on metals by external applied anodic currents.
a) True
b) False
Answer: a
Clarification: Anodic protection is one of the corrosion prevention methods that is based on the formation of a protective film on metals by external applied anodic currents.

4. Which of the following metals can be protected using anodic protection?
a) Nickel and iron
b) Nickel, iron, and titanium
c) Titanium only
d) Nickel, iron, titanium, and magnesium
Answer: b
Clarification: Anodic protection can be used only for active-passive transition metals as it provides external current for the formation of a passive oxide layer. Active-passive transition metals include nickel, iron, aluminum, titanium, and its alloys.

5. A potentiostat is an electronic device that maintains a metal at a constant potential to a reference electrode.
a) True
b) False
Answer: a
Clarification: A potentiostat is an electronic device that maintains a metal at a constant potential to a reference electrode. It is required to protect a metal anodically by a passivating metal surface.

6. Which of the following corrosion prevention method is depicted in the given figure?

a) Sacrificial anode
b) Impressed current supply method
c) Use of inhibitors
d) Anodic protection
Answer: d
Clarification: Anodic protection of a storage tank is depicted in the given figure. A potentiostat is used to maintain the constant potential for a metallic structure against the reference electrode that results in passivity.

7. Which of the following auxiliary cathode is used for anodic protection?
a) Graphite
b) Platinized titanium
c) Platinum-clad electrode
d) Aluminum electrode
Answer: c
Clarification: It is necessary to have an inert auxiliary cathode such as a platinum-clad electrode as the anode provides external electric current to passivates the metallic structure.

8. Which of the following reference electrode is used in anodic protection?
a) Standard hydrogen electrode
b) Copper/copper sulfate reference electrode
c) Standard hydrogen electrode and calomel electrode
d) Calomel electrode
Answer: d
Clarification: The Calomel electrode is used to measure the potential maintained during the operation. It is connected to the third terminal of potentiostat whereas metal and auxiliary cathode are connected to first and second terminals respectively.

9. Which of the following is/are the advantages of anodic protection than cathodic protection?
a) Availability in extremely corrosive conditions
b) Low current requirement
c) Availability in extremely corrosive conditions and low current requirement
d) Very low installation cost
Answer: c
Clarification: Advantages of anodic protection than cathodic protection is:
i. Availability in extremely corrosive conditions
ii. Low current requirement.

10. Which of the following is/are the unique advantages of anodic protection?
a) To monitor instantaneous corrosion rate
b) Operating conditions can be established in the lab
c) It is applicable for all type of metals
d) To monitor instantaneous corrosion rate and operating conditions can be established in the lab
Answer: d
Clarification: Unique advantages of anodic protection are:
i. To monitor the instantaneous corrosion rate of a metal
ii. Operating condition of anodic protection can be precisely established in the lab.

Corrosion Engineering for Campus Interviews,

Corrosion Engineering Multiple Choice Questions on “Modern Theory Principles – Polarization – 1”.

1. What is meant by an anode?
a) An electrode at which reduction process takes place
b) An electrode at which oxidation process takes place
c) An electrode at which neither the oxidation nor reduction takes place
d) An electrode at which both oxidation and reduction takes place
Answer: b
Clarification: An electrode at which the oxidation process takes place is known as anode whereas the electrode at which reduction process takes place is known as the cathode.

2. Which of the following is correct regarding Polarization?
a) It is the deviation from equilibrium potential
b) It results from the change in net current flow
c) Magnitude is measured in terms of overvoltage
d) It is the deviation from equilibrium potential that occurred due to the change in net current flow and its magnitude is measured in terms of overvoltage.
Answer: d
Clarification: Polarization is the deviation from equilibrium potential that occurred due to the change in net current flow and its magnitude is measured in terms of overvoltage.

3. What is the symbol of overvoltage?
a) Alpha (α)
b) Beta (β)
c) Eta (η)
d) Delta (Δ)
Answer: c
Clarification: The magnitude of polarization is measured in terms of over voltage and it is denoted with symbol Eta (η). It is the difference of corrosion potential (E_corr) and the standard potential of an electrode.

4. Exchange current density is the current per unit area of either oxidation or reduction process at the equilibrium.
a) True
b) False
Answer: a
Clarification: Exchange current density is the current per unit area of either oxidation or reduction process at the equilibrium. Type of metal and environment are the factors of exchange current density and it is denoted by i₀.

5. What is the formula to calculate rate of oxidation or rate of reduction during equilibrium?
a) r₀=r_R=i₀nF
b) r₀=r_R=i₀/nF
c) r₀=r_R=i₀n/F
d) r₀=r_R=nF/i₀
Answer: b
Clarification: Equilibrium is defined as the state at which rate of oxidation is equal to the rate of reduction. And the formula to calculate rate of oxidation or reduction is r₀=r_R=i₀/nF where i₀ is exchange current density, n is number of electrons involved and F is faraday’s constant.

6. Which of the following metal shows the highest exchange current density for hydrogen-hydrogen ion as per given figure?

a) Mercury
b) Iron
c) Platinized platinum
d) Platinum
Answer: c
Clarification: Platinized platinum shows the highest exchange current density for hydrogen-hydrogen ion due to its high inertness and electrically conductivity. The order follows as (i₀)_Pt^H+/H2>(i₀)_Fe^H+/H2>(i₀)_Hg^H+/H2.

7. Which of the following is the controlling factor of Activation polarization?
a) The activation energy of a reaction
b) Diffusion of ions in the solution
c) The temperature of a solution
d) The velocity of a solution
Answer: a
Clarification: Activation polarization is the mechanism of polarization that depends on the activation energy of a reaction. Activation energy is the minimum energy required for reacting species to undergo chemical reactions.

8. Which of the following mentioned is/are the types of polarization?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Activation, concentration and resistance polarization
Answer: d
Clarification: Types of polarization:

9. What is the relationship between reaction rate and overvoltage for activation polarization?
a) n_a=±βlog(i₀/i)
b) n_a=±βlog(I/i₀)
c) n_a=±βlog(1-i₀/i)
d) n_a=±βlog(1-i/i₀)
Answer: b
Clarification: The relationship between reaction rate and overvoltage for activation polarization can be noted as n_a=±βlog(I/i₀) where β is a Tafel constant and i₀ is exchange current density.

10. What is depicted in the given figure?

a) Concentration polarization of hydrogen-hydrogen ion
b) Resistance polarization of hydrogen-hydrogen ion
c) Activation polarization of hydrogen-hydrogen ion
d) Both activation and concentration polarization of hydrogen-hydrogen ion
Answer: c
Clarification: The given figure depicts the activation polarization of the hydrogen-hydrogen ion electrode. Curve1 indicates the cathodic polarization whereas curve2 indicates the anodic polarization.