Engineering Questions with Answers - Multiple Choice Questions
Materials Science MCQ’s – Phase Transformation Kinetics
What is/are the phenomenon involved in phase transformation?
d) Nucleation and growth
Explanation: Formation of a nucleus or tiny particles of the new phase is nucleation and increase in size of the nucleus at the expense of the parent phase is growth.
How many types of nucleation process are there and what are they?
a) 2 and (fusion and fission)
b) 2 and (Heterogeneous and Homogeneous)
c) 2 and (Heterogeneous and fusion)
d) 4 and (fusion, fission, Heterogeneous and Homogeneous)
Explanation: Two types of nucleation – Heterogeneous and Homogeneous whereas fusion and fission are nuclear reactions.
What reactions come under supercooling?
b) Eutectic and Peritectic
c) Eutectic and Eutectoid
d) Peritectic and Eutectoid
Explanation: Driving force to nucleate increases as we increase T.
What are the characteristics of large supercooling in nucleation?
a) Few nuclei, large crystals
b) Rapid nucleation, many nuclei, small crystals
c) Rapid nucleation, many nuclei, large crystals
d) Few nuclei, small crystals
Explanation: Nuclei (seeds) act as a template to grow crystals and for nucleus will help in a rate of the addition of atoms to the nucleus must be faster than the rate of loss.
At what temperature does supercooling is needed in homogeneous nucleation?
b) 100- 250°C
Explanation: Nuclei form in the bulk of liquid metal so requires supercooling (typically 80-300°C max).
From the following figure if blue curve represent growth rate what does red and green curve represent respectively?
a) Nucleation rate, over all transformation rate
b) Over all transformation rate, Nucleation rate
c) Nucleation rate, finer grain size
d) Over all transformation rate, finer grain size
Explanation: The overall transformation rate is the product of nucleation and growth rates.
Which is the most important thermodynamic parameter in Homogenous nucleation?
a) Free energy G
b) Enthalpy H
c) Entropy S
d) Free energy G, Enthalpy H, Entropy S
Explanation: G is important as a phase transformation will occur immediately only when G has a negative value.
What does phase transformation involve?
a) Transformation rates kinetics
b) Movement/rearrangement of atoms
c) Changes in microstructure
d) Transformation rate kinetics, rearrangement of Atoms, Changes in microstructure
Explanation: Formation of a new phase having a distinct physical/chemical character and a different structure than that of the parent phase.
Below the critical radius the tiny particles are _______ and are called _______
a) unstable, grains
b) stable, grains
c) unstable, embryo
d) stable, embryo
Explanation: The tiny particle of the solid that forms first will get stabilized only when it achieves a critical radius (r*). Below the critical radius, it is considered unstable and is said to be an embryo.