# Phase Transformation Questions and Answers – Influence of Interface on Equilibrium

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This set of Phase Transformation Questions and Answers for Freshers focuses on “Influence of Interface on Equilibrium”.

1. The surface of a single crystal (of a pure element) is an example of a_________
a) Solid-Vapor interface
b) Solid-Liquid interface
c) Solid-Solid interface
d) Liquid-Liquid interface

Explanation: The surface of a single crystal (of a pure element) is an example of a Solid-Vapor interface. These crystals are material whose constituents are arranged in a highly ordered fashion and they form the crystal lattice which extends in all the direction.

2. Grain boundaries are an example of a_________
a) Solid-Vapor interface
b) Solid-Liquid interface
c) Solid-Solid interface
d) Liquid-Liquid interface

Explanation: Grain boundaries are example of homo phase interface which is a type of solid-solid interface. Grain boundaries are strongly affected by the change in orientation involved. If the angles of disorientation are small, less than about 3 degree, they can be readily accommodated by the formation of a two-dimensional network of dislocations.

3. Solidification front is an example of_________
a) Solid-Vapor interface
b) Solid-Liquid interface
c) Solid-Solid interface
d) Liquid-Liquid interface

Explanation: Solidification front is an example of Solid-Liquid interface and it is one among the 3 interfaces concerned with a crystalline structure.

4. For a particular or given diffusion coefficient, which among the following interface moves the slowest?
a) Coherent
b) Semi coherent
c) Incoherent
d) Mixed

Explanation: For a given diffusion coefficient the coherent interface moves the slowest and then the semi coherent and the fastest one is the incoherent interface.

5. If the α/β(α,β are phases) interfacial energy is given as 10N/mm and the particles are spherical with a radius 2.5mm, ΔP (extra pressure due to curvature of α/β) is given approximately by_________
a) 8 N/mm2
b) 4 N/mm2
c) 3 N/mm2
d) 2 N/mm2

Explanation: If γ is the α/β interfacial energy and the particles are spherical with a radius r, ΔP (extra pressure due to curvature of α/β) is given approximately by ΔP = 2*γ/r. So substituting the respective values we get the value as ΔP = 2*10/2.5 = 8 N/mm2.

6. There is an increase in free energy due to interfacial energy is known as a capillarity effect or the Gibbs-Thomson effect. Find the increase in this free energy if the interfacial energy, the molar volume and the radius of the spherical particle are given as 10 (kJ/mm2), 6mm3/mol and 4mm respectively?
a) 40 kJmol-1
b) 30 kJmol-1
c) 50 kJmol-1
d) 60 kJmol-1

Explanation: This increase in the Gibbs free energy can be calculated using the formula
G = (2γV)/r
Hence substituting this value of interfacial energy, molar volume and radius in the equation we get the increase in energy as (2*10*6)/4 = 30 kJmol-1.

7. MnS in steel is an example of _____
a) Coherent interface
b) Semi coherent interface
c) Incoherent interface
d) Mixed interface

Explanation: It is an example of incoherent interface because inclusion in alloys have incoherent interface. When the interface plane has a very different atomic configuration in the two adjacent phases, there is no possibility of good matching across the interface, hence it turn out to be an Incoherent interface.

8. The free energy increase due to interfacial energy is known as_____
a) Gibbs-Thomson effect
b) Perkins effect
c) Nano effect
d) Hauls effect

Explanation: Free energy increase due to interfacial energy is known as a capillarity effect or the Gibbs-Thomson effect. And this can be calculated if the interfacial energy, molar volume and the radius of the spherical particles are known.

9. If the surface area of the large particle remains unchanged the increase in free energy will be due to the____
a) Motion of spherical particle
b) Vibration of spherical particle
c) Increase in the interfacial area of the spherical particle
d) Decrease in the interfacial area of the spherical particle

Explanation: This happens because under this condition the increase in free energy is directly proportional to the radius of the spherical particle.

10. Generic high angle grain boundaries are typically___________
a) Coherent interface
b) Semi coherent interface
c) Incoherent interface
d) Mixed interface

Explanation: Definition of the incoherent surface says that when the interface plane has a very different atomic configuration in the two adjacent phases, there is no possibility of good matching across the interface and in case of the high angle grain boundaries are notably more disordered, with large areas of poor fit and a comparatively open structure hence they are typically incoherent in nature.

11. The structure of interface plays a key role in determining its energy. Which among the energy considerations play a major role when their sizes are large and small respectively?
a) Interfacial and elastic
b) Elastic and interfacial
c) Interfacial in both cases
d) Elastic in both cases 