Which schematic shows the rate of solid nucleation from a pure liquid metal versus undercooling T=T m-T, where T m is freezing temperature and T is liquid temperature?

GATE 2024 MT – Question 22

Physical Metallurgy · Nucleation solidification and transformations · 1 mark · Multiple choice

Which schematic shows the rate of solid nucleation from a pure liquid metal versus undercooling $\Delta T=T_m-T$, where $T_m$ is freezing temperature and $T$ is liquid temperature?

Graph A
Graph B
Graph C
Graph D

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Correct answer: (A) Graph A

Explanation

At small undercooling the nucleation barrier is large, so the rate is low.

Increasing undercooling lowers the barrier and raises the rate, but very low temperature eventually suppresses atomic mobility.

The competition produces a maximum, represented by **A**.