# Engineering Materials and Metallurgy Questions and Answers – Types of Corrosion and Oxidation

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This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Types of Corrosion and Oxidation”.

1. Which code is followed by the corrosion of metals?
a) Burger’s vector
b) Pilling–Bedworth
d) Miller’s theorem

Explanation: The Pilling-Bedworth ratio is the ratio of the volume of the basic cell of a metal oxide to the volume of the basic cell of an equivalent or standard metal. It is used to find out the likeliness of the metal to corrode or resist it.

2. What is the Faraday’s constant?
a) 96.49 kC mol-1
b) 99.01 kC mol-1
c) 100.3 kC mol-1
d) 104.49 kC mol-1

Explanation: The Faraday’s constant is used to determine the magnitude of electric charge per mole of electrons. It is denoted as F and is named after Michael Faraday. The accurate value of this constant is 96485.33289(59) C mol-1.

3. How is the Faraday’s constant defined?
a) F = e NA
b) F = e / NA
c) F = e + NA
d) F = NA / e

Explanation: The Faraday’s constant is used to determine the magnitude of electric charge per mole of electrons. It is denoted by F = e NA. Here, e is the charge of an electron and NA is Avogadro’s constant.
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4. What is the free energy of formation value for Al2O3?
a) 419 kJ mol-1
b) 1045 kJ mol-1
c) 1576 kJ mol-1
d) 2562 kJ mol-1

Explanation: The free energy of formation of metal oxides is denoted by ΔG and is noted at 25oC. This value is 1045 kJ mol-1 for Cr2O3 and 1576 kJ mol-1 for Al2O3.

5. What is the Piling-Bedworth ratio of MgO?
a) 0.41
b) 0.79
c) 1.71
d) 2.03

Explanation: The Pilling-Bedworth ratio is the ratio of the volume of the basic cell of a metal oxide to the volume of the basic cell of an equivalent or standard metal. This ratio is 0.41, 0.79, 1.71, and 2.03 for K2O, MgO, Cu2O, and Cr2O3 in that order.

7. A galvanic cell set up due to differences in the concentration of metal ion is known as ________
a) Concentration ion
b) Concentration cell

Explanation: A region in the electrolyte where the metal ions are less in number is known as anodic. Such differences in concentration of metal ion may result in the formation of a galvanic cell known as concentration cell.

8. A galvanic cell formed due to residual stresses is known as ________
a) Stress cell
b) Residual cell
c) Residual ion

Explanation: A galvanic cell can be formed due to various residual stresses in a metal. The stressed region is more active and anodic in nature. These cells can be formed due to dislocation density in a cold worked metal or in a polycrystalline metal.

9. The phenomenon where the density of metal is exceptionally low due to increasing potential is known as _______
a) Polarization
b) Ionization
c) Passivation
d) Canonization

Explanation: When the potential of metal increases, its current density increases. However, after the critical value, it is lowered suddenly and remains constant for a while. This is known as passivation.

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