Corrosion Engineering online test on “High-Temperature Corrosion – 2”.
1. In general, all oxides are nonstoichiometric in nature their composition varies from an ideal molecular formula.
a) True
b) False
Answer: a
Clarification: In general, all oxides are nonstoichiometric in nature their compositions vary from an ideal molecular formula. It is due to the excess or deficiency in metallic ions or equivalent oxygen ions.
2. Which of the following is/are correct regarding the measurement of the rate of oxidation?
a) Weight loss per unit area of metal is the measure of the rate of oxidation
b) Either weight loss or weight gain per unit area of metal is the measure of the rate of oxidation
c) Weight gain per unit area of metal is the measure of the rate of oxidation
d) Neither weight loss nor weight gain per unit area of metals is the measure of the rate of oxidation
Answer: c
Clarification: Rate of oxidation is usually measured and expressed in terms of weight gain per unit area of metal. As oxidation results in the conversion from metal M (x gms) to metallic oxides MOn (x+n*16 gms).
3. Diffusion-controlled oxidation can be minimized by decreasing the concentration of ionic defects in the scale.
a) False
b) True
Answer: b
Clarification: diffusion-controlled oxidation can be minimized by decreasing the concentration of ionic defects in the scale. These defects include Frenkel defect, Schottky defect, and many crystallographic defects.
4. What are the types of oxidation rate laws?
a) Linear and parabolic law
b) Cubic and logarithmic law
c) Linear, parabolic and cubic law
d) Linear, parabolic, cubic and logarithmic law
Answer: d
Clarification: Oxidation rate laws are classified based on the variation of oxidation rate in different metals. They are linear, parabolic, cubic, and logarithmic laws.
5. Which of the following oxidation rate law is depicted as x in the given figure?
a) Linear law
b) Parabolic law
c) Cubic law
d) Parabolic law
Answer: a
Clarification: The given figure depicts the graphical representation of oxidation laws. Linear oxidation law is denoted by letter x. Linear law states that weight gain per unit metal is directly proportional to the time of exposure.
6. Which of the following oxidation rate law is depicted as z in the given figure?
a) Linear law
b) Parabolic law
c) Cubic law
d) Parabolic law
Answer: c
Clarification: The given figure depicts the graphical representation of oxidation laws. Cubic law is denoted as letter z and it states that cube of weight gain per unit metal is directly proportional to the time of exposure.
7. Which of the following is/are correct regarding linear oxidation law?
a) Weight gain per unit area of the metal is directly proportional to the exposure time
b) It is a characteristic of porous or cracked scale
c) Sodium is an example that follows linear oxidation law
d) Weight gain per unit area of metal is directly proportional to exposure time, it is characteristic of porous or cracked scale and sodium follows linear oxidation law
Answer: d
Clarification: Linear oxidation law:
- Weight gain per unit area of the metal is directly proportional to the exposure time
- It is characteristics of porous or cracked scale
- Sodium follows linear oxidation law.
8. Which of the following metal doesn’t follow linear oxidation law?
a) Sodium
b) Aluminum
c) Niobium
d) Potassium
Answer: b
Clarification: Linear oxidation law states that an increase in weight per unit area of metal is directly proportional to the time of exposure. Metals such as sodium, potassium, tantalum, and niobium follow linear oxidation law whereas aluminum follows the logarithmic oxidation law.
9. Which of the following is/are true regarding parabolic oxidation rate law?
a) It was proposed by C. Wagner
b) It states that square of weight loss is directly proportional to the time of exposure
c) It was proposed by C. Wagner which states that square of weight loss is directly proportional to the time of exposure and it resembles non-steady-state diffusion-controlled reactions
d) It resembles non-steady-state diffusion-controlled reactions
Answer: c
Clarification: True statements regarding parabolic oxidation rate law:
- It was proposed by C. Wagner
- It states that square of weight loss is directly proportional to the time of exposure
- It resembles non-steady-state diffusion-controlled reactions.
10. Which of the following metals follows logarithmic oxidation law?
a) Aluminum
b) Copper
c) Iron
d) Aluminum, copper, and iron
Answer: d
Clarification: Logarithmic law is observed in thin sections of oxide layers at low temperatures. Metals such as aluminum, copper, iron, and other metals follow logarithmic oxidation rate law.