# Diffusion Coefficient Calculation | Nitrogen in FCC Iron

• tkjacobsen
K. JacobsenIn summary, the person is asking for help in calculating the diffusion coefficient for a Nitrogen atom in fcc iron. They have already calculated the minimum energy path for diffusion in one direction and are seeking a standard method for estimating the diffusion coefficient for interstitial diffusion. They are provided with the formula D = (r^2)(v)/(6)exp((-G_m)/(kT)) and are given references for further reading. They express gratitude for the helpful response.
tkjacobsen
[SOLVED] Diffusion coefficient.

Hi everybody

I have a Nitrogen atom sitting at the octahedral site in fcc iron. I have calculated the minimum energy path (diffusion path) when moving the Nitrogen atom to the neighboring octahedral site.

My question is:
How can i calculate the diffusion coefficient? (only considering the diffusion in that one direction)

Hi tkjacobsen, welcome to PF. The standard way is to estimate $D$ for interstitial diffusion is

$$D=\frac{r^2 \nu}{6} \exp\left(\frac{-G_m}{kT}\right)$$

where $r$ is the distance between sites, $\nu$ is the attempt frequency (the characteristic vibration frequency in the crystal), and $G_m$ is the energy barrier involved in jumping from one interstitial site to another.

Edit: Sorry, I really should have given a reference. Try Allen and Balluffi's Kinetics of Materials, Porter and Easterling's Phase Transformations in Metals and Alloys, or any good kinetics book.

Last edited:
Thanks alot, this was exactly what I was looking for.

Best Regards
T.

## 1. What is the diffusion coefficient?

The diffusion coefficient is a measure of how easily and quickly a substance can move through a material. It is a fundamental parameter in diffusion processes and is used to calculate the rate of diffusion.

## 2. How is the diffusion coefficient calculated?

The diffusion coefficient is calculated using Fick's laws of diffusion, which describe the relationship between the concentration gradient, diffusion coefficient, and diffusion flux. The diffusion coefficient can also be determined experimentally through diffusion experiments.

## 3. Why is the diffusion coefficient important in studying nitrogen in FCC iron?

Nitrogen is an important element in steel production and its diffusion in FCC iron can affect the material's properties. The diffusion coefficient is crucial in predicting the rate and extent of nitrogen diffusion, which can impact the strength, ductility, and corrosion resistance of the steel.

## 4. How does temperature affect the diffusion coefficient of nitrogen in FCC iron?

The diffusion coefficient of nitrogen in FCC iron increases with an increase in temperature. This is because as the temperature increases, the kinetic energy of the atoms increases, allowing them to move more easily through the material, resulting in a higher diffusion coefficient.

## 5. Can the diffusion coefficient of nitrogen in FCC iron be modified?

Yes, the diffusion coefficient can be modified by altering the composition and microstructure of the iron, as well as the temperature and time of the diffusion process. This can be achieved through techniques such as alloying, heat treatment, and surface treatments.

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