Diffusion in a Semi-Infinite Solid Media

The typical application of these models involves transient chemodynamics within the solid yielding equations for the concentration profiles and the flux to the adjoining fluid media. The applications involve chemicals in soils and sediments for idealized scenarios of uniform concentration, Co(g/m ) at f = 0, from the interface at y = 0 downward in the y-direction to infinity. Within the solid chemical transport is by Fickian diffusion with coefficient I e(m /s). At times, f 0, the surface concentration is assumed zero causing chemical quantities to move from the solid into the adjoining fluid phase. 

Diffusion with reactive decay. For this case, the time-varying concentration profile in the solid is given by 

Both of the above equations apply when k = 0, which is no reactive decay. 

Diffusion with reactive decay and mass transfer to the adjoining fluid phase. This case extends the previous one by including a MTC, k (m/s), on the fluid side to capture this transport resistance. The concentration profile equation for the same idealized initial solid phase conditions is 

2 Diffusion and Advection in a Semi-Infinite Soeid Media 

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