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1. What is/are the phenomenon involved in phase transformation?
a) Nucleation
b) Growth
c) Fission
d) Nucleation and growth

View Answer

Answer: d [Reason:] 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.

2. 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 andfusion)
d) 4 and (fusion, fission, Heterogeneous and Homogeneous)

View Answer

Answer: b [Reason:] Two types of nucleation – Heterogeneous and Homogeneous where as fusion and fission are nuclear reactions.

3. What reactions come under supercooling?
a) Peritectic
b) Eutectic and Peritectic
c) Eutectic and Eutectoid
d) Peritectic and Eutectoid

View Answer

Answer: c [Reason:] Driving force to nucleate increases as we increase T.

4. 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

View Answer

Answer: b [Reason:] Nuclei (seeds) act as template to grow crystals and for nucleus will help inrate of addition of atoms to nucleus must be faster than rate of loss.

5. At what temperature does supercooling is needed in homogenous nucleation?
a) 0.1-10ºC
b) 100- 250°C
c) 80-300°C
d) 10-15°C

View Answer

Answer: c [Reason:] Nuclei form in the bulk of liquid metal so requires supercooling (typically 80-300°C max).

6. From the following figure if blue curve represent growth rate what does red and green curve represent respectively?
materials-science-questions-answers-online-test-q6
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

View Answer

Answer: a [Reason:]The overall transformation rate is the product of nucleation and growth rates.

7. What are thermodynamic parametersofhomogeneous nucleation?
a) Free energy G
b) Enthalpy H
c) Entropy S
d) Free energy G, Enthalpy H, Entropy S

View Answer

Answer: d [Reason:] G is important as a phase transformation will occur immediately only when G has a negative value.

8. What does phase transformation involve?
a)Transformation rates kinetics
b) Movement/rearrangement of atoms
c) Changes in microstructure
d) Transformation rateskinetics, rearrangement of Atoms, Changes in microstructure

View Answer

Answer: d [Reason:] Formation of a new phase having a distinct physical/chemical character and a different structure than that of the parent phase.

9. Below the critical radius the tiny particles are _______ and are called _______
a) unstable, grains
b) stable, grains
c) unstable, embryo
d) stable, embryo

View Answer

Answer: c [Reason:] 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 beembryo.

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