Category: Corrosion Engineering Objective Questions

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.

Corrosion Engineering Multiple Choice Questions on “Corrosion Prevention – Coatings – 1”.

1. A thin coating of metallic and inorganic materials can provide a satisfactory barrier between the metal and its environment.
a) True
b) False
Answer: a
Clarification: A thin coating of metallic, inorganic, and organic material can provide a satisfactory barrier between the metal and its environment. Because it minimizes the exposure of native metal to the corrosive environment.

2. Which of the following is/are the purposes of coatings?
a) To acts as a sacrificial metal
b) To act as an effective barrier
c) Either to act as sacrificial metal or to act as an effective barrier
d) Neither to act as sacrificial metal nor to act as an effective barrier
Answer: c
Clarification: Coatings are the relatively thin material portion on the surfaces of native metal to avoid direct exposure to the corrosive environment. The purpose of coatings is either to act as sacrificial metal or to act as an effective barrier.

3. Which of the following is/are the methods to apply metallic coatings?
a) Electrode position
b) Flame spraying
c) Cladding
d) Electrode position, flame spraying, and cladding
Answer: d
Clarification: Methods to apply metallic coatings are:
i. Electrode position
ii. Flame spraying
iii. Cladding
iv. Hot dipping
v. Vapor deposition.

4. What is the reason for the localized attack on the base metal due to the porosity of coatings?
a) Crevice formation
b) Galvanic effect
c) Initiation of pits
d) Crevice formation and galvanic effect
Answer: b
Clarification: The localized attack on the base metal due to the porosity of coatings is dueto two-metal corrosion or galvanic effect. Because metal coating and base metal are electrically connected in a corrosive environment.

5. Which of the following is/are the examples for metal-coated articles?
a) Silverware
b) Galvanized steel
c) Tin cans
d) Silverware, galvanized steel, and tin cans
Answer: d
Clarification: Sacrificial metals such as zinc, tin, and precious metals such as silver, gold, platinum is used as metallic coatings for various applications. Silverware, galvanized steel, and tin cans are examples of metallic coatings.

6. What is meant by electrodeposition?
a) Immersing native metal in a solution of the metal to be plated
b) Hot rolling of two metals together to get a composite sheet
c) A wire or powder through melting flame is blown onto the surface to be protected
d) Coating metal is vaporized electrically to deposit on the metals to be coated
Answer: a
Clarification: Electrode position is an immersion of native metal in a solution of the metal to be plated with direct current passing through them. It is also called electroplating.

7. Which of the following is/are the factors of electroplating that effects efficiency?
a) Temperature and composition of the bath
b) Composition of bath and time
c) Temperature, the composition of the bath, time and current density
d) Current density and composition of the bath
Answer: c
Clarification: Factors that affect the efficiency of electroplating are:
i. Temperature
ii. Current density
iii. Time
iv. Composition of bath.

8. What is the general purpose of each coating in a three-layered coating of an automobile bumper?
a) Inner coating – adhesion, intermediate coating – corrosion protection and top layer – appearance
b) Inner coating – corrosion protection, intermediate coating – adhesion and top layer – appearance
c) All layers for corrosion resistance
d) All layers for appearance
Answer: a
Clarification: In general, multiple layered metallic structures consist of inner coating for adhesion such as copper, intermediate coating for corrosion resistance such as nickel and top coatings for appearance such as chromium.

9. What is meant flame spraying metallic coating?
a) Hot rolling of two metals together to get a composite sheet
b) A wire or powder through melting flame is blown onto the surface to be protected
c) Coating metal is vaporized electrically to deposit on the metals to be coated
d) Immersing native metal in a solution of the metal to be plated
Answer: b
Clarification: Flame spraying metallic coating is a method of metal coating in which a wire or powder through the melting flame is blown onto the surface to be protected. Oxygen, acetylene, and propane are used for melting flame.

10. Which of the following is/are the application of flame spraying?
a) Bridges
b) Refrigeration equipment
c) Ship hulls
d) Bridges, refrigeration equipment and ship hulls
Answer: d
Clarification: Application of flame spraying include vessels of all kinds, bridges, ship hulls, refrigeration equipment, and many fabricated steel products. Low melting point metals such as zinc, tin, and lead are used.

11. What is meant by metal cladding?
a) Immersing native metal in a solution of the metal to be plated
b) Coating metal is vaporized electrically to deposit on the metals to be coated
c) Hot rolling of two metals together to get a composite sheet
d) A wire or powder through melting flame is blown onto the surface to be protected
Answer: c
Clarification: Metal cladding is a method of hot rolling two metals together to get a composite sheet. High-strength aluminum alloys and commercial pure aluminum are rolled together to provide the corrosion barrier.

12. Cladding is a great economical advantage in that the corrosion barrier as the expensive material is backed up by inexpensive material by minimizing corrosion.
a) True
b) False
Answer: a
Clarification: Cladding is a great economical advantage in that the corrosion barrier as the expensive material is backed up by inexpensive material by minimizing corrosion.

13. What is meant by vapor deposition?
a) A wire or powder through melting flame is blown onto the surface to be protected
b) Coating metal is vaporized electrically to deposit on the metals to be coated
c) Hot rolling of two metals together to get a composite sheet
d) Immersing native metal in a solution of the metal to be plated
Answer: b
Clarification: Vapor deposition is a method of metal coating in that coating metal is vaporized electrically to deposit on the metals to be coated. It is usually used for high strength parts for missiles and rockets.

14. What is meant by diffusion coatings?
a) Immersing native metal in a solution of the metal to be plated
b) Coating metal is vaporized electrically to deposit on the metals to be coated
c) Heat treatment to cause alloy formation by diffusion of one metal into the other
d) Hot rolling of two metals together to get a composite sheet
Answer: c
Clarification: Diffusion coatings involve heat treatment to cause alloy formation by diffusion of one metal into the other. It is also called as surface alloying. It improves various properties such as wear-resistance and corrosion resistance at the surface.

15. Which of the following is/are the types of diffusion coatings?
a) Sherardizing – zinc
b) Chromizing – chromium
c) Alonizing – aluminum
d) Sherardizing – zinc, chromizing – chromium and alonizing – aluminum
Answer: d
Clarification: Types of diffusion coatings:
i. Sherardizing – zinc
ii. Chromizing – chromium
iii. Alonizing – aluminum
iv. Carburizing – carbon
v. Nitriding – nitrogen.

Corrosion Engineering Questions & Answers for Exams on “Modern Theory Principles – Polarization – 2”.

1. Which of the following is/are correct regarding concentration polarization?
a) Diffusion of ions in the bulk solution is the controlling factor
b) It usually operates at a high current density
c) It is a continuation of Activation polarization
d) It is a continuation of activation polarization, diffusion of ions in the bulk solution is the controlling factor and it usually operates at high current densities
Answer: d
Clarification: Concentration polarization is the mechanism of polarization in which diffusion of ions in the bulk solution is the controlling factor, it is a continuation of activation polarization and it usually operates at high current densities.

2. What is depicted in the given figure?

a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Activation and concentration polarization
Answer: b
Clarification: The given figure depicts the concentration polarization of a reaction. It is the mechanism of polarization in which the diffusion of ions in the bulk solution is the controlling factor. It usually encounters at high-density currents and low concentration solution.

3. What is the formula to determine limiting diffusion current density (i_L) of concentration polarization?
a) i_L=xnFC_B/D
b) i_L=DC_B /nFx
c) i_L=DnFC_B/x
d) i_L=x/DnFC_B
Answer: c
Clarification: i_L=DnFC_B/x is the formula to determine the limiting diffusion current density (i_L) of concentration polarization. Where I_L is the limiting diffusion current density, D is the diffusion coefficient, C_B concentration of ions in bulk solution and x is the thickness of diffusion layer.

4. Agitation will increase the limiting diffusion current density of concentration polarization.
a) True
b) False
Answer: a
Clarification: Agitation tends to decrease the thickness of the diffusion layer by supply enough ions to the metal interface hence there will be an increase in limiting diffusion current density of concentration polarization.

5. Which of the following is/are correct regarding the given figure?

a) Velocity, temperature, and concentration are the factors that influence limiting current density
b) Limiting current density decreases with an increase in velocity, temperature, and concentration
c) Limiting current density increase with the increase in velocity, temperature, and concentration
d) Velocity, temperature, and concentration are the factors that influence limiting current density and it increases as it increases
Answer: d
Clarification: The given figure shows the increase in limiting diffusion current density of concentration polarization with an increase in velocity, temperature, or concentration. It is due to the relatively high availability of reacting species at the interface and decrease in thickness of the diffusion layer.

6. Which of the following type(s) of polarization is depicted in the given figure?

a) Activation polarization
b) Concentration polarization
c) Activation and concentration polarization
d) Resistance polarization
Answer: c
Clarification: The given figure depicts the cathodic polarization of an element with activation and concentration polarizations. Concentration polarization is the continuation of activation polarization at higher current densities.

7. Which of the following is/are correct regarding resistance polarization?
a) Activation energy at the interface is the controlling factor
b) The resistance of transition between electrodes and electrolytes
c) Diffusion of ions in the bulk solution is the controlling factor
d) The resistance of reacting ions for diffusion is the controlling factor
Answer: b
Clarification: Resistance polarization is the type of polarization in which there is a resistance of transition between electrodes and electrolytes. But this polarization has a negligible effect on corrosion kinetics.

8. Which two scientists present the first formal presentation on mixed potential theory?
a) Wagner and Traud
b) Wagner and Evans
c) Traud and Nernst
d) Wilsmore and Nernst
Answer: d
Clarification: Mixed potential theory is the electrochemical hypothesis of modern corrosion presented by Wagner and Traud in the year 1938. It relates the potentials and currents of the corrosion system to determine corrosion potential (E_corr) and corrosion current (i_corr).

9. Which of the following is/are the hypothesis of mixed potential theory?
a) Any electrochemical reaction can be divided into two or more partial reactions
b) No net accumulation of electric charge during the reaction
c) Any electrochemical reaction can be divided into two or more partial reactions and no net accumulation of electric charge during the reaction
d) Electrochemical reactions can’t be divided into partial reactions
Answer: c
Clarification: Hypothesis of mixed potential theory:
i. Any electrochemical reactions can be divided into two or more partial reactions
ii. No net accumulation of electric charge during the reaction.

10. Which of the following is depicted in the given mixed potential schematic?

a) Dissolution of zinc
b) Oxidation of hydrogen
c) Reduction of zinc
d) Dissolution of copper
Answer: a
Clarification: The given mixed potential schematic depicts the dissolution of zinc. It shows the anodic polarization of zinc, cathodic polarization of hydrogen, and resulting in E_corr and i_corr.