Fick’s 2nd Law

A solution of Fick s 2nd Law often used for absorption testing is... 

In the kinetics of formation of carbides by reaction of the metal with CH4, the diffusion equation is solved for the general case where carbon is dissolved into the metal forming a solid solution, until the concentration at the surface reaches saturation, when a solid carbide phase begins to develop on the free surface. If the carbide has a thickness at a given instant and the diffusion coefficient of carbon is D in the metal and Dn in the carbide, Fick s 2nd law may be written in the form (Figure 8.1)... 

Diffusion in the unsteady state before equilibrium is described by Fick s 2nd law of diffusion ... 

An example of a transfer function based on a physical model is the Nemst impedance of a transport controlled electrode reaction. The impedance spectra in Fig. 7-14, which were obtained on a rotating platinum disk electrode at the equilibrium potential of the iron hexacyanoferrate redox system, exhibit the typical shape of a transport-controlled process. The transfer function cannot be described by a limited number of electrical circuit elements but must be derived from the differential equations of Fick s 2nd law and the appropriate boundary conditions. For finite linear diffusion, the so-called Nemst impedance Z can be derived theoretically... 

Drag bioavailability depends upon both the rate and extent of absorption. Permeation through the stratum comeum occurs by passive diffusion, a process well described by Fick s 1st and 2nd laws. Consider the steady-state situation shown in Figure 8.2. Assume that the drag concentration in the formulation (Cv) is constant and that, on the other side of the membrane, sink conditions prevail (i.e. due to the efficient... 

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