In materials science, dispersion is the fraction of atoms of a material exposed to the surface.
In general, D = NS/N, where D is the dispersion, NS is the number of surface atoms and NT is the total number of atoms of the material.
[1] It is an important concept in heterogeneous catalysis, since only atoms exposed to the surface can affect catalytic surface reactions.
Dispersion increases with decreasing crystallite size and approaches unity at a crystallite diameter of about 0.1 nm.
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