Determination of diffusivity using the characteristic function for the regular regime.

A new method is proposed for determining diffusivity from experiments in desorption of a component migrating through a medium such as solution and porous solid. In this analysis the equation representing the desorption from a plane sheet whose surface concentration is zero is solved numerically to establish an expression describing the process. Thus it becomes possible to deduce the concentration dependence of the diffusivity for a wide range of concentrations from a single desorption experiment. Application of this method to desorption rate curves obtained numerically shows that the method has good practicality when the diffusivity increases with concentration.