Question

Question from Transport Phenomena in Material Processing, D.R. Poirer & G.H. Geiger

#12.10

Describe the conditions under which the following terms are applicable: (1) self diffusion, (2)

tracer diffusion, (3) chemical diffusion, (4) interstitial diffusion, (5) substitutional diffusion,

(6) interdiffusion, and (7) intrinsic diffusion.

Answer 1

1. Self diffusion

~ diffusion is the thermal motion of a liquid or gas particles at the temperature above absolute temperature and its rate is a function of temperature, viscosity, mass, and concentration gradient and when this concentration gradient is absent the diffusion is then governed by self diffusion. It occurs where same type atoms exchange places

2. Tracer diffusion

~it is a spontaneous mixing of molecules without a concentration gradient and it is identical to the self diffusion.

3. Chemical diffusion.

~ this diffusion occurs in the condition where there is concentration gradient or chemical potentional, the entropy of the system increases and it brings the system to the equilibrium state.

4.Interstitial diffusion.

~this occurs at very microscopic level at the level of atoms this diffusion occurs at the interstitial site and the atoms are very small.