Lecture note 25 (12-01-2011)

Lecture note 25 (12-01-2011) - * . Its next jump will with...

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1 MAE 581 Advanced Materials Science Lecture note 25 Diffusion Diffusion is a non-equilibrium thermodynamic process Correlation effects We must first return to the mean square displacement in the case of an isotope A * diffusing in A by means of vacancies. The situation after A * has changed place once (from site 6 to 7) is shown in the close-packed plane in Fig. 8.4. Next to A * is a vacancy which has jumped from 7 to 6. Its next jump will with equal probability be an exchange with any one of its nearest neighbors (the vacancy has the same interaction with A * as with A). The situation is quite different for A
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Unformatted text preview: * . Its next jump will with the greatest probability be back to 6 rather than 1-5 simply because the vacancy which made the earlier jump possible is still there. The preferred reverse jump which is directly correlated with the preceding jump falsifies the calculation of the mean square displacement which is made statistically without correlation. It also demolishes the earlier assumption that the self-diffusion coefficient in A defined by is identical with the actually measureable isotope diffusion coefficient 2 3 Interstitial mechanism of diffusion 4...
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This note was uploaded on 01/16/2012 for the course MAE 581 taught by Professor Fu during the Fall '11 term at SUNY Buffalo.

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Lecture note 25 (12-01-2011) - * . Its next jump will with...

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