Phase transitions - 6
Channel: bhadeshia123
Date: 03/11/2022

Diffusion is at first sightly difficult to appreciate for the solid state. A number of mechanisms have been proposed historically. This includes a variety of ring mechanisms where atoms simply swap positions, but controversy remained because the strain energies associated with such swaps made the theories uncertain. One possibility is that diffusion occurs by atoms jumping into vacancies. But the equilibrium concentration of vacancies is typically 10^{-6}, which is  small. The theory was therefore not generally accepted until an elegant experiment by Smigelskas and Kirkendall.

This talk deals with the mechanism of diffusion, for both interstitial and substitutional solutes. It ends with an understanding of uphill diffusion where the chemical potential gradient opposes that of the concentration.

More information on
https://www.phase-trans.msm.cam.ac.uk/teaching.html

H. K. D. H. Bhadeshia