L29 - Nucleation and crystallization At T > Tf atoms have...

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Dr. P. Lucas U of A MSE 110 Nucleation and crystallization At T > T f , atoms have enough thermal energy kT to overcome the attractive forces and remain free to translate in a high entropy state: the liquid phase. G liq <G cryst At T < T f , the atoms can’t overcome the attractive energy and stabilize to a lower energy configuration by forming bonds. G cryst <G liq The formation of that ordered crystalline materials is therefore associated with the release of the enthalpy of fusion H f . The free energy difference between the liquid and solids corresponds to the thermodynamic driving force towards formation of a crystalline nuclei and is proportional to its volume: The surface tension is the driving force toward dissolution of that nuclei and is proportional to its surface: The total driving force toward formation of nuclei during random fluctuation in the supercooled liquid is: Past a critical radius r* G cryst decreases and the nuclei has a high probability of developing into a stable crystal. SUMMARY FROM LAST CLASS 3 3 4 r g G V π × = 2 4 r g G S π × = 2 3 3 4 4 r g r g G S V Cryst π π × + × =
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Dr. P. Lucas U of A MSE 110 Crystal growth GLASS FORMATION Once a stable nucleus is formed, other atoms diffuse to its surface and the nuclei grows into a large crystalline grain.
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