Ficks First Law for Binary Mixtures

Your objectives in studying this section are to be able to  

Write down Fick s first law for diffusion in a binary, isothermal, isobaric mixture. 

Define the Fick diffusivity and establish the relation between the Fick dif-fusivity and the Maxwell-Stefan diffusivity for a binary system. 

At about the same time that Maxwell and Stefan were developing their ideas of diffusion in multicomponent mixtures, Adolf Fick and others were attempting to uncover the basic diffusion equations through experimental studies involving binary mixtures (Fick, 1855). The result of Fick s work was the law that bears his name. The Fick equation for a binary mixture in an isothermal, isobaric system is 

The correlation and prediction of Fick and MS diffusion coefficients is discussed in the section that follows. The Fick diffusivity incorporates two aspects (1) the significance of an inverse drag coefficient (D), and (2) thermodynamic nonideality (T). Consequently, the physical interpretation of the Fick diffusion coefficient is less transparent than for the MS diffusivity. 

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