Adsorption impedance Surface coverage

Adsorption is, of course, of major importance in the inhibition of corrosion by organic compounds (adsorption inhibitors) that have the ability to adsorb strongly on the metal surface, thus impeding the dissolution reaction and reducing the corrosion rate. It follows that the coverage of a metal surface by adsorbed inhibitor can be evaluated from the relationship... 

Ion adsorption has been suggested as a cause of surface states (Rajeschwar, 1982) and it may well be one cause, particularly if the potential of the semiconductor is positive to that of the flatband potential. On p-Si in a solution containing N(Bu)4, to take a specific example, the density of surface states obtained from impedance spectroscopy is shown in Fig. 10.17 (Gonzalez-Martin, 1993). It is seen that the concentration of surface states increases exponentially in the cathodic direction until the expected limit (toward complete coverage) is seen. 

The kinetic parameter whose evolution governs the impedance is the concentration of the intermediate Bads in the adsorbed phase. If Q is the fraction of the electrode surface covered by this adsorbate and j3 is the superficial concentration for a complete coverage by Bads> by assuming a Langmuir adsorption isotherm, the surface concentration of Bads is cb = j30. 

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