This set of Corrosion Engineering Multiple Choice Questions & Answers (MCQs) focuses on “ Corrosion Prevention – Inhibitors”.
1. An inhibitor is a chemical substance that added in small concentrations to an environment, to decrease the corrosion rate.
a) True
b) False
View Answer
Explanation: An inhibitor is a chemical substance that added in small concentrations to an environment, to decrease the corrosion rate. It is also regarded as a retarding catalyst.
2. Which of the following is/are the types of inhibitors?
a) Adsorption inhibitors
b) Scavengers
c) Vapor-phase inhibitors
d) Adsorption inhibitors, scavengers, and vapor-phase inhibitors
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Explanation: Following are the types of inhibitors:
i. Adsorption inhibitors
ii. Scavengers
iii. Vapor-phase inhibitors
iv. Hydrogen-evolution poisons
v. Oxidizers.
3. Which of the following is an example of adsorption-type inhibitors?
a) Arsenic
b) Sodium sulfite
c) Organic amines
d) Chromates
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Explanation: Adsorption-type inhibitors are the type of inhibitors that adsorb on the surface of cathode or anode and alter its surface. Organic amines are examples of adsorption-type inhibitors.
4. Which of the following inhibitors are effective in acid solutions?
a) Oxidizers
b) Hydrogen-evolution poisons
c) Vapor-phase inhibitors
d) Oxidizers and hydrogen-evolution poisons
View Answer
Explanation: Cathodic reduction of hydrogen ions to a hydrogen atom is the main driving force for the metallic dissolution in many acidic environments. It can be reduced or minimized with hydrogen-evolution poisons.
5. Which of the following is/are the examples of Hydrogen-evolution poisons?
a) Arsenic and Antimony
b) Sodium sulfite and hydrazine
c) Chromates and ferric salts
d) Organic amines
View Answer
Explanation: Hydrogen-evolution poisons are the inhibitors that retard the rate of evolution of hydrogen gas in an acidic environment. Arsenic and Antimony are examples of hydrogen-evolution poisons.
6. Which of the following is/are the examples of scavengers?
a) Arsenic and Antimony
b) Chromates and ferric salts
c) Sodium sulfite and hydrazine
d) Organic amines
View Answer
Explanation: Scavengers are the type of inhibitors that removes corrosive reagents from the solution. Sodium sulfite and hydrazine are examples of scavengers. 2Na2SO3+O2==>2Na2SO4 is the scavenging action of sodium sulfite.
7. Oxidizers such as chromates, nitrates, and ferric salts inhibit the corrosion of metal and alloys that demonstrate active-passive transition.
a) False
b) True
View Answer
Explanation: Oxidizers such as chromates, nitrates, and ferric are one type of inhibitors that inhibit the corrosion of metal and alloys that demonstrate active-passive transition. Active-passive transition metals include iron and stainless steel.
8. Which of the following is/are the characteristics of the vapor phase inhibitor?
a) It has a very high vapor pressure
b) Inhibit the atmospheric corrosion without being contact with the metal surface
c) Effective in closed spaces
d) It has very high vapor pressure, inhibit atmosphere corrosion without being contact with the metal surface and very effective in closed spaces
View Answer
Explanation: Vapor-phase inhibitors are very similar to organic adsorption-type inhibitors. Characteristics of vapor-phase inhibitors are:
i. It has a very high vapor pressure
ii. Inhibit the atmospheric corrosion without being contact with the metal surface
iii. Effective in closed spaces.
9. Which of the following phenomenon in which the inhibiting effect is sometimes greater than that would be achieved by either of the two or substances alone?
a) Galvanic effect
b) Cathodic protection
c) Synergistic effect
d) Inhibiting effect
View Answer
Explanation: When two or more inhibiting substances are added to a corrosive system, the inhibiting effect is sometimes greater than that achieved by either of the two or more substances alone. This is called a synergistic effect.
10. Which of the following is/are the limitations of inhibitors?
a) It contaminates the environment
b) Inhibitors are toxic
c) Its efficiency decreases with time and temperature
d) It contaminates the environment, toxic in nature, and its efficiency decreases with time and temperature.
View Answer
Explanation: Limitations of inhibitors:
i. It contaminates the environment
ii. Inhibitors are toxic in nature
iii. Its efficiency decreases with time and temperature
iv. It should not be used directly or indirectly in the preparation of food.
11. Which of the following inhibitor is used for aluminum in the hydrogen peroxide environment?
a) 2% boron trifluoride
b) Alkali metal nitrates
c) Sodium silicate
d) Benzoic acid
View Answer
Explanation: Inhibitors are the chemical compounds that decrease the corrosion rate of metal in a specific environment. Alkali metal nitrates are used as inhibitors for the aluminum metal in the hydrogen peroxide environment.
12. Which of the following inhibitor is used for steel in 80% pure sulfuric acid?
a) 2% boron trifluoride
b) Sodium silicate
c) Alkali metal nitrates
d) Benzoic acid
View Answer
Explanation: Inhibitors are very specific to a particular metal, environment, and the concentration of an environment. 2% boron trifluoride inhibitor is used for steel in 80% pure sulfuric acid.
13. Which of the following inhibitor is used for steel in the water?
a) Sodium silicate
b) Alkali metal nitrates
c) Benzoic acid
d) 2% boron trifluoride
View Answer
Explanation: Inhibitors are the chemical compounds that decrease the corrosion rate of metal in a specific environment. Benzoic acid is used as an inhibitor for steel in water.
14. Which of the following phenomenon that occurs on metal surface during inhibition?
a) Adsorption only
b) Adsorption and phase layers
c) Phase layers only
d) Neither adsorption nor phase layers
View Answer
Explanation: Inhibitors are the chemical compounds that decrease the corrosion rate of metal in a specific environment. Inhibition can be caused by both adsorption and phase layers on the metal surface.
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