2. For heterogeneous nucleation on the mould wall; what is the importance of the width of the
crack at its mouth on the mould surface? Under what condition(s) crystalline metallic phase will
not nucleate from liquid retained in a mold-wall crevice even much below Tm? Explain using
schematic diagram ..
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(a) For heterogeneous nucleation on the mould wall; what is the importance of the width of the
crack at its mouth on the mould surface? Under what condition(s) crystalline metallic phase will
not nucleate from liquid retained in a mold-wall crevice even much below Tm? Explain using
schematic diagram. 2+2=4
(b) Estimate the number of crystal-like clusters in 1 mm3
of copper at its melting point for
spherical clusters containing 100 atoms. Given: The atomic volume of liquid
copper ()=1.6 x 10-29 m3
, Solid -liquid interfacial energy (SL) = 0.177 J m-2 , Boltzmann
constant (k) = 1.38 X 10-23 J K-1, Melting Temperature (TM) = 1356 K. 4
[Hint: the number spherical clusters of radius r
no= total number of atoms in the spherical cluster].
(c) The equilibrium shape of a coherent precipitate can be predicted by using -plot. How will
you determine the equilibrium shape of an incoherent precipitate using strain energy? 2
[Hint: Think and answer