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Atomic diffusion in polycrystalline materials is therefore often modeled using an effective diffusion coefficient, which is a combination of lattice, and grain boundary diffusion coefficients. In general, surface diffusion occurs much faster than grain boundary diffusion, and grain boundary diffusion occurs much faster than lattice diffusion.
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical potential.
Each atomic species can be given its own intrinsic diffusion coefficient ~ and ~, expressing the diffusion of a certain species in the whole system. The interdiffusion coefficient D ~ {\displaystyle {\tilde {D}}} is defined by the Darken's equation as:
The diffusion requires atomic contact between the surfaces due to the atomic motion. The atoms migrate from one crystal lattice to the other one based on crystal lattice vibration. [2] This atomic interaction sticks the interface together. [1] The diffusion process is described by the following three processes: surface diffusion; grain boundary ...
Surface diffusion is a general process involving the motion of adatoms, molecules, and atomic clusters (adparticles) at solid material surfaces. [1] The process can generally be thought of in terms of particles jumping between adjacent adsorption sites on a surface, as in figure 1.
The Kirkendall effect is the motion of the interface between two metals that occurs due to the difference in diffusion rates of the metal atoms. The effect can be observed, for example, by placing insoluble markers at the interface between a pure metal and an alloy containing that metal, and heating to a temperature where atomic diffusion is reasonable for the given timescale; the boundary ...
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The atomic packing factor is the proportion of space filled by these spheres which can be worked out by calculating the total volume of the spheres and dividing by the volume of the cell as follows: A P F = N p a r t i c l e V p a r t i c l e V unit cell {\displaystyle \mathrm {APF} ={\frac {N_{\mathrm {particle} }V_{\mathrm {particle} }}{V ...