Isothermal Diffusion in an Uncharged Multicomponent System

This equation shows that a gradient in concentration c can induce a flow of component/. Dfj is called a cross-diffusion coefficient. Equation (13.6.4a) can be expressed in matrix form 

To complete the picture we must find Jj from Jid. Combining Eqs. (13.5.7) and (13. 5.1 lb) gives 

This gives Ji as a linear combination of the fluxes J/. This can also be expressed as 

Substituting Eq. (13.6.5) into Eq. (13.6.8) then gives the desired laboratory-fixed fluxes 

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