250+ TOP MCQs on Corrosion Prevention – Coatings – 1 and Answers

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.