ENGR 240 - 11.9.07

ENGR 240 11.9.07 - ENGR 240 November 9 2007 Phase transformations o Nucleation and Growth Fundamentals Nucleation formation of small

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ENGR 240 – November 9, 2007 Phase transformations o Nucleation and Growth Fundamentals Nucleation – formation of small particles (nuclei) of a new phase o Liquid-solid o Solid-solid Growth – increase in size of the nuclei Nucleation Homogeneous nucleation formation of spherical nuclei uniformly dispersed throughout parent phase. o Liquid-solid Liquid phase Solid phase Radius of nuclei γ – Surface free energy of solid-liquid interference Energy associated with formation of nuclei Heterogeneous nucleation get help with the formation of nuclei from impurities (solid particles in a liquid), grain boundaries, dislocations, some surface, etc. Less energy is required for the formation of nuclei Liquid phase Solid phase radius of nucleus (solid Phase) γ - Surface energy o θ - Contact angle o ΔG Gibbs free energy F(H, S, T) Phase transformation occurs when –ΔG Two components to ΔG for transformation Difference in free energy between phases o ΔG i = (4/3)πr
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This note was uploaded on 04/07/2008 for the course ENGR 240 taught by Professor Gross during the Fall '07 term at Bucknell.

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ENGR 240 11.9.07 - ENGR 240 November 9 2007 Phase transformations o Nucleation and Growth Fundamentals Nucleation formation of small

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