Understanding the Kirkendall Effect and Its Impact on Diffusion in Materials

[mhill]

could someone explain me this effect ??

i know that , is due to the diffusion of atoms by the existence of 'vacancies' deffects that allow the diffusion.

the problem is that this is what i know, for example in the German Wikipedia there is a good image but i do not how to interpretate (image of Kirkendall effect)

http://upload.wikimedia.org/wikipedia/commons/4/4c/KirkendallSceme1.png

if someone can help, thank you.

 

[DiffusionGuy]

In essence, the Kirkendall effect describes the differing diffusion rates that exists between two or more dissimilar layers (e.g. thin films). If one is able to insert markers on the interface between the layers of a sample (call it an A/B thin film system), one would see that the markers migrate into one layer, depending on the difference of the diffusion coefficient of element A in B and B in A. So, if A diffuses faster into B, the markers will move into layer A.

One way to described this effect is with Darken's equation, D_effective = X_AD_B + X_BD_A, where D_A is the diffusion coefficient of element A in B, D_B is the diffusion coefficient of B in A, and D_effective is the effective diffusion coefficient.

 

[charng]

The Kirkendall Effect is a phenomenon that occurs in materials undergoing diffusion, where there is an unequal rate of diffusion between two different types of atoms or molecules. This leads to the formation of voids or vacancies in the material, resulting in an uneven distribution of atoms and a change in the material's properties. This effect was first observed by American scientist Edgar Kirkendall in the 1940s and has since been studied extensively in various materials and applications.

The image you have referenced from the German Wikipedia shows a schematic of the Kirkendall Effect in a diffusion couple. The diffusion couple is made up of two different materials, A and B, with different diffusion coefficients (a measure of how quickly atoms can move through a material). As the atoms from material A diffuse into material B, they create vacancies in material A and form a layer of material B on the surface of material A. At the same time, the atoms from material B diffuse into material A, but at a slower rate due to its lower diffusion coefficient. This unequal diffusion results in a void or "gap" between the two materials, as shown in the image.

The Kirkendall Effect has significant implications in materials science and engineering, as it can lead to changes in the microstructure and properties of materials. Understanding this effect is important in the design and development of materials for various applications, such as in the production of semiconductors, metals, and ceramics. By studying the Kirkendall Effect, scientists and engineers can better control and manipulate the diffusion process to create materials with desired properties and performance. I hope this explanation has helped you understand the Kirkendall Effect better.