Solidification

Solidification - Solidification Introduction Unit...

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Unformatted text preview: Solidification Introduction: Unit operations: Chemical engineers can describe a system at any stage by specifying: chemistry, temperature and pressure Materials engineers need to add the “full processing history”, beginning with solidification. Engineering materials are “history dependent” Solidification: Materials change state to lower their energy Solidification requires a release of energy Vol release = (4/3) π r 3 ∆ E v ∆ E v is the volume free energy Energy must be provided to create new interfacial surface Surface Energy = 4 π r 2 σ σ is the energy per unit of surface area For small values of r, r 2 is greater than r 3 , while the reverse is true for large values of r. Therefore the net energy change takes the form of the figure to the left. A cluster of atoms (embryo) must first grow to the size of the critical radius to form a stable nucleus that can then further grow into a solid crystal The value of the critical radius depends on the temperature of the liquid, i.e. ∆ E v How can we promote nucleation?...
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Solidification - Solidification Introduction Unit...

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