Question

5. It is believed that interstitial diffusion is faster than vacancy diffusion. Can you show this by comparing the values of diffusion coefficients of a pair of cases (one values for each type of diffusion) from Table 5.2.. -(5 points)

Answer 1

Diffusion coefficient is the magnitude of the molar flux through any flowing space per unit concentration of the gradient and the direction of the gradient is out of the plane. It can also be related with the kinematic viscosity if the metals are in liquid state. Low diffusion coefficient would mean low kinematic viscosity if in liquid state and if the viscosity will be less then the diffusion in the metal will occur at a faster rate. So as if we compare the values of the diffusion coefficients from the table 5.2. Take an example from both type of diffusion in BCC structure and we can compare the rates and it will be found that the values of the diffusion coefficients is less in interstitial diffusion is very less as compared to the vacancy diffusion and the difference is about 10 times and so it can be seen that the diffusion rate in the interstitial diffusion will be very high with respect to the vacancy distribution. We can compare any two samples from each case in BCC as well as the FCC structure and the results will be same for the coefficients as it would be less for the interstitial diffusion.

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