Multiphase Systems in Electric Fields

These equations show that the A and B fluxes are composed of both a drift term and a reaction term. The drift term stems from the electric field. The reaction term was already deduced in the kinetics of heterogeneous reactions. From Eqns. (8.78) and (8.79), we obtain the reaction product s rate of thickness increase to be 

rv vanishes as soon as rA = rB (DA = B) and is essentially proportional to U°(=F-U°) if the applied voltage is high enough. The correction term (rA - rB)-AG° accounts for the diffusion potential which arises in the reaction product. Also, from Eqns. (8.80) and (8.81), we can see that the growth of ABX2 is parabolic only for long times. 

The foregoing analysis has been concerned with ionic conducting crystals. In metal systems, to a first order, the applied voltage has no influence on the reaction rate of the a/y/0 system. In a semiconducting reaction couple, the electric current (under the same conditions as before) is 

Equation (8.82) can be compared with Eqn. (8.76) for ionic crystals. After eliminating Vp, we obtain for jyA 

If the electrodes are reversible for X ( -X2), and the reacting system is surrounded by X2(g), then A/ux vanishes. Since jA (and similarly jB) is responsible for the 

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