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Studies on the pitting corrosion of zinc in aqueous solutions I. Variations of the potential of the zinc electrode in relation to the concentration of the aggressive anion
Author(s) -
El Din A. M. Shams,
El Haleem S. M. Abd
Publication year - 1974
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19740250803
Subject(s) - chemistry , inorganic chemistry , zinc , potassium chromate , ion , chromate conversion coating , aqueous solution , iodide , amalgam (chemistry) , bromide , chloride , electrode potential , desorption , adsorption , halide , electrode , corrosion , electrochemistry , chromium , organic chemistry
The way in which the stationary potential of a zinc electrode previously treated with various passivating and inhibiting solutions changes in the present of the chloride, bromide and iodide ions is studied in solutions of potassium chromate, disodium hydrogen phosphate and sodium tungstanate. It is shown that the potential change as a function of the halogenide concentration follows a S shaped curve. The potentials are established after an induction period the duration of which decreases as the concentration of the aggressive anion increases and/or the concentration of the inhibiting anion decreases. A linear relationship is obtained for the maximum permissible concentration of the aggressive anion at a given concentration of the inhibiting anion. This relationship is theoretically derived from the defect resulting from the specifical adsorption of both ions at the metal surface. While e.g. a temperature increase shifts the potential in pure chromate solutions to more positive potentials, thus improving the protective effect, the permissible concentration of the aggressive anion is simultaneously decreased. This phenomenon suggests that in these conditions the desorption of the inhibiting anions is increased.