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· When two materials inter-diffuse,
their diffusion coefficients in the other matrix may be different due to different
lattice dimensions or lattice structure e.g. DB> DA
· The position of the boundary in a
diffusion couple will change as the diffusion occurs. This is known as the
Kirkendall effect.
· The mean diffusion
coefficient in a region with mole fractions of the constituents XA
and XB is given by: < D > = XBDA+
XADB
· The change
in the position of the boundary is illustrated opposite and taken as the equal
concentration point.
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