Atomic diffusion

Other air molecules (e.g. oxygen, nitrogen) have lower mobilities and thus diffuse more slowly through the balloon wall.

The rate of transport is governed by the diffusivity and the concentration gradient.

Diffusing particles migrate from point vacancy to point vacancy by the rapid, essentially random jumping about (jump diffusion).

For a single atom in a defect-free crystal, the movement can be described by the "random walk" model.

the atom will have moved, on average, a distance of: If the jump frequency is given by

For example, along the grain boundaries and certain crystalline defects such as dislocations there is more open space, thereby allowing for a lower activation energy for diffusion.

H + ions diffusing in an O 2- lattice of superionic ice
Atomic diffusion across a 4-coordinated lattice. Note that the atoms often block each other from moving to adjacent sites. As per Fick’s law , the net flux (or movement of atoms) is always in the opposite direction of the concentration gradient .