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3.14/3.40J/22.71J Recap Diffusion Process & Surface Evolution

3.14/3.40J/22.71J Recap Diffusion Process & Surface Evolution. Ting-Yun Huang 2012 Nov. 15 th. Outline. Diffusion of 1-2-v system: Interdiffusivity Kirkendall Effect Different diffusion mechanisms Fast diffusion path and lattice diffusion Capillary force/Surface energy.

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3.14/3.40J/22.71J Recap Diffusion Process & Surface Evolution

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  1. 3.14/3.40J/22.71J RecapDiffusion Process & Surface Evolution Ting-Yun Huang 2012 Nov. 15th

  2. Outline • Diffusion of 1-2-v system: Interdiffusivity • Kirkendall Effect • Different diffusion mechanisms • Fast diffusion path and lattice diffusion • Capillary force/Surface energy

  3. Diffusion of 1-2-v system: Interdiffusivity • Crystal frame • From crystal frame to lab frame (observed) • Interdiffusivity: • Note that D is usually concentration dependent, thus the here only applies to small region

  4. Kirkendall Effect Direct exchange mechanism Kirkendall’s experimental setup. Use Mo as fictitious marker. Ring mechanism JOM.49 (6) (1997), pp. 15-19.

  5. Kirkendall Effect • Vacancy Mechanism • Criticism from Mehl • The measured Zn concentration varies, and the diffusivity is different in Zn and Cu. • Nanoparticle system. JOM.49 (6) (1997), pp. 15-19.

  6. Kirkendall Effect- Nanoscale • Hollow nanocrystals • Kirkendall effect forming the nano porous materials • Applications: due to large surface area, can be applied to nano-reactorand catalysts, etc. Yin et al., 304 (5671): 711-714, Science

  7. Diffusion of different mechanisms • Di: diffusivity, controlled by migration energy. • xi:molar fraction of sites • i: denotes the species, can be vacancy, interstitials. • : the migration energy of the species • : the formation energy of the species • Vacancy mechanism/Interstitial mechanism

  8. Fast diffusion path and lattice diffusion • Dsurface(T)>>DGBs(T)~Dcores(T)>>Dlattice(T) • for 0<T<Tmelt • Mixed diffusion mechanism • Lattice + Grain boundaries • Lattice + Dislocation core

  9. Surface energy/Young-Laplace Pressure • : n dependent. (n: unit normal) • Wulff construction/Faceting of crystals

  10. Questions? Comments? THANK YOU!

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