Corrosion Engineering online quiz on “Modern Theory Applications – Corrosion Rate Measurement”.
1. What is meant by anodic protection?
a) Accompanying the sacrificial metal with metallic structure
b) Prevention of corrosion by impressed cathodic current by supply electrons
c) Prevention of corrosion by the impressed anodic current is used to transform from active to a passive state
d) Additions of oxidizers and oxidizing agents for the formation of an oxide layer
Answer: c
Clarification: Anodic protection is one of the corrosion prevention or protection method in which the impressed anodic current is used to transform from active to a passive state.
2. The optimum potential for anodic protection is in the mid of passive region since it permits slight variations.
a) True
b) False
Answer: a
Clarification: Anodic protection is a corrosion prevention method in which anodic current of certain potential is provided to the metallic structure to transform from active to a passive state. The optimum potential for anodic protection is in the mid of passive region since it permits slight variations.
3. Which of the following noble metals will improve the corrosion resistance of titanium and chromium on galvanic coupling?
a) Platinum
b) Palladium
c) Rhodium
d) Platinum, palladium, and rhodium
Answer: d
Clarification: Noble metals such as platinum, palladium, and rhodium on galvanic coupling will improve the corrosion resistance of titanium and chromium by spontaneous passivation. It is due to the mixed potential of the couple lies in the passive region of titanium and chromium.
4. Stainless steels containing small quantities of platinum passivates more readily in the presence of oxygen, ferric salts, and other oxidizing agents.
a) False
b) True
Answer: b
Clarification: Stainless steels containing small quantities of platinum passivates more readily in the presence of oxygen, ferric salts, and other oxidizing agents. It is due to the resultant mixed potential of an alloy that reaches a passive region quickly.
5. Which of the following electrochemical methods is/are used to determine the corrosion rate?
a) Tafel extrapolation
b) Linear polarization
c) Tafel extrapolation and linear polarization
d) Neither Tafel extrapolation nor linear polarization
Answer: c
Clarification: Tafel extrapolation and linear polarization are the two electrochemical methods used to determine the corrosion rate. These methods are extensively used for laboratory and industrial corrosion tests.
6. The applied current cathodic polarization curve of a corroding metal is non-linear at low currents, but it becomes linear at higher currents on a semilogarithmic plot.
a) False
b) True
Answer: b
Clarification: The cathodic polarization curve is the curve drawn by measuring over voltage between reference and the working electrode on a semilogarithmic plot. It is non-linear at low currents whereas it becomes linear at higher currents.
7. Which of the following is/are the advantages of Tafel extrapolation?
a) It can measure extremely low corrosion rates
b) It can be used for continuously monitoring the corrosion rate of a system
c) It can be used for continuously monitoring the corrosion rate of a system with high accuracy and measures extremely low corrosion rates
d) It can be performed rapidly with high accuracy
Answer: c
Clarification: Advantages of Tafel extrapolation are:
- It can measure extremely low corrosion rates
- It can be used for continuously monitoring the corrosion rate of a system
- It can be performed rapidly with high accuracy.
8. Which of the following is/are the limitations of Tafel extrapolation?
a) For reasonable accuracy, the Tafel region must be extended
b) It can be applied to systems containing one reduction process only
c) Much interference from concentration polarization
d) It can be applied to systems containing one reduction process, for reasonable accuracy the Tafel region must be extended and there will be much interference from concentration polarization
Answer: d
Clarification: Limitations of Tafel extrapolation are:
- For reasonable accuracy, the Tafel region must be extended
- It can be applied to systems containing one reduction process only
- Much interference from concentration polarization.
9. What is the range of current density around corrosion potential that will observe that the applied current density is a linear function of the electrode potential?
a) 10 mV more noble or active around corrosion potential
b) 5 mV more noble or active around corrosion potential
c) 10 V more noble or active around corrosion potential
d) 5 V more noble or active around corrosion potential
Answer: a
Clarification: In around 10 millivolts around corrosion potential, it is observed that the applied current density is a linear function of the electrode potential. It is known as a linear polarization curve.
10. What is the formula to determine the slope of linear polarization curve?
a) ΔE/Δi =[2.3*icorr*(βa+βb)]/[βa*βb]
b) ΔE/Δi=[βa+βb]/[2.3*icorr*(βa*βb)]
c) ΔE/Δi=[βa*βb]/[2.3*icorr*(βa+βb)]
d) ΔE/Δi=[2.3*icorr*(βa*βb)]/[βa+βb]
Answer: c
Clarification: The slope of linear polarization curve is determined by using ΔE/Δi=[βa*βb]/[2.3*icorr*(βa+βb)] where βa , βb are Tafel slopes of anodic and cathodic reactions and icorr is the current density at the intersection point of anodic and cathodic reaction.
11. Which of the following industries uses Tafel extrapolation or linear polarization to measure low corrosion rates?
a) Nuclear industries
b) Pharmaceutical industries
c) Food processing industries
d) Nuclear, pharmaceutical and food processing industries
Answer: d
Clarification: Nuclear, pharmaceutical, and food processing industries are the industries that use Tafel extrapolation or linear polarization where measuring low corrosion rates is important. Traces of impurities or contamination in these industries could lead to catastrophic failure.