Abstract
The purpose of this study is to prove that the Channel Flow Double Electrode (CFDE) technique can be used to detect chromous ions, with a view to improving the materialbalance during a Fe-Cr repassivation sequence. The chromous ions are produced under flowingconditions by potentiostatic activation of a chromium single-crystal electrode and are thenoxidised downstream on a gold electrode. The experimental collection efficiency Nexp is the ratioof the collecting current for the oxidation of Cr2 to the steady state current of the dissolution ofchromium metal. The latter current is calculated using Faradays law, from the amount of materialdissolved after a long term activation. The value of Nexp is very close to the theoretical collectionefficiency N0 and it seems to be independent of the flow velocity in the range 40–120 cm s−1.This result is discussed and compared with the literature. Moreover as chromous ions arethermodynamically unstable in acidic media, an estimation of the limiting rate constant, k, of Cr2oxidation reaction is calculated to be less than 0.7 s−1.
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