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The self-diffusion coefficient of neat water is: 2.299·10 −9 m 2 ·s −1 at 25 °C and 1.261·10 −9 m 2 ·s −1 at 4 °C. [2] Chemical diffusion occurs in a presence of concentration (or chemical potential) gradient and it results in net transport of mass. This is the process described by the diffusion equation.
Diffusion is a stochastic process due to the inherent randomness of the diffusing entity and can be used to model many real-life stochastic scenarios. Therefore, diffusion and the corresponding mathematical models are used in several fields beyond physics, such as statistics , probability theory , information theory , neural networks , finance ...
Thermophoresis (also thermomigration, thermodiffusion, the Soret effect, or the Ludwig–Soret effect) is a phenomenon observed in mixtures of mobile particles where the different particle types exhibit different responses to the force of a temperature gradient. This phenomenon tends to move light molecules to hot regions and heavy molecules to ...
Tunneling diffusion is a physical manifestation of the quantum tunneling effect involving particles tunneling across diffusion barriers. It can occur in the case of low diffusing particle mass and low E diff , and has been observed in the case of hydrogen diffusion on tungsten and copper surfaces. [ 16 ]
This allows us to study the effects of diffusion in a discrete manner to understand the movement of individual atoms, molecules, plasma etc. In such a process, the movements of diffusing species (atoms, molecules, plasma etc.) are treated as a discrete entity, following a random walk through the CVD reactor, boundary layer, material structures etc.
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 ...
The diffusion coefficient in solids at different temperatures is generally found to be well predicted by the Arrhenius equation: = where D is the diffusion coefficient (in m 2 /s), D 0 is the maximal diffusion coefficient (at infinite temperature; in m 2 /s),
A thermal force on a gas due to a temperature gradient, also called thermal diffusion or Thermal transpiration. It is used to drive a gas pump with no moving parts called a Knudsen pump. It is the currently accepted theory for the rotation of the Crookes radiometer. Diffusion in a temperature gradient, also called thermodiffusion or thermophoresis.