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Solidification: Cooling Curves, Concept of Nucleation and Growth

The document discusses cooling curves and the concepts of nucleation and growth during solidification. It explains that cooling curves show the change in phase from liquid to solid over time, with pure metals and alloys solidifying at a constant temperature. For alloys, the temperature does not remain constant during solidification. It also describes how nucleation is the initial formation of crystalline structures from liquid atoms, which then grow as more atoms join, in a step-by-step process transforming the material from liquid to solid phase.

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126 views5 pages

Solidification: Cooling Curves, Concept of Nucleation and Growth

The document discusses cooling curves and the concepts of nucleation and growth during solidification. It explains that cooling curves show the change in phase from liquid to solid over time, with pure metals and alloys solidifying at a constant temperature. For alloys, the temperature does not remain constant during solidification. It also describes how nucleation is the initial formation of crystalline structures from liquid atoms, which then grow as more atoms join, in a step-by-step process transforming the material from liquid to solid phase.

Uploaded by

venkatachalapathy.th
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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SOLIDIFICATION

Cooling curves, concept of nucleation and growth


Dr Pradeep Kumar Jha
MIED, IIT ROORKEE

1
COOLING CURVES

• Cooling curve is a line graph that represents the change


of phase of matter ( for metals, typically from liquid to
solid)

• In pure metals and alloys with eutectic composition,


solidification occurs at a constant temperature

• In case of alloys, temperature does not remain constant


during solidification.
2
NUCLEATION AND GROWTH

• During phase transformation, free energy change


determines the rate of transformation.

• At equilibrium melting point, free energy of solid as well


as liquid phase are equal.

• For transformation to be possible and to proceed


simultaneously, free energy change must be negative.

3
• Once condition of spontaneous occurrence of phase
transformation is satisfied, formation of crystalline
configuration among few atoms of liquid starts.

• Further, more and more atoms leave the liquid and join
the crystalline configuration.

• Transformation from liquid to solid state is a step to step


process and can be divided into two steps, occurring
one after the other: formation of tiny stable particles of
solid phase (nucleation)and increase in size of these
particles (growth).

4
THANKS

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