Question

Among the four atomic diffusion mechanisms, what mechanisms can assist atomic self-diffusion and what cannot?

Answer 1

Atomic diffusion is a diffusion process where the movement of thermally activated atoms in a solid results in net transfer of atoms. There are different kinds of atomic diffusion which includes vacancy diffusion which is the most energertically favourable process involving the interchange of places by an atom and neighbouring vacancy. The unit step in this procees is the atom breaks its bonds and jumps into neighbouring vacant site. In interstitial diffusion atoms are samll enough to occupy interstitial sites by jumping from one site to another. Substitutional diffusion generally proceeds by the vacancy mechanism and it is slower than interstitial diffusion. A self diffusion or direct excahnge mechanism consists of three or four atmos in a ring which move continuously thereby interchanging their positions which requires exceptionally high energy for the process to occur. A self interstitial is more mobile than vacancy and requires a small aount of activation energy. vacany and susbtitutional diffusions assists self diffusion mechanisms whereas interstsitial doesnt.