Transpassive dissolution of chromium and Cr/Fe alloys in solutions of isopropanol in 1 M H 2SO 4

Abstract

Transpassive dissolution of pure chromium and Cr/Fe(Ni) alloys containing 16–71% Cr has been investigated in 1 M H 2SO 4 containing 1 M isopropanol. The Cr (VI) species generated at the surface of the electrode in the course of the overall anodic process react nearly exclusively after their chemical dissolution from the electrode surface with the alcohol homogeneously in solution. The other possibility in terms of a surface reaction, which would regenerate the Cr(III) state, is observed only to a minor extent. Turnover factors of the Cr 2O 3 film are only between 0 and 1.1. This is quite in contrary to the behaviour of a ceramic Cr 2O 3 layer on Ti, where turnover factors of 100 are possible, and electroorganic oxidations via heterogeneous redox catalysis can be accomplished. Differences in the two electrodes eventually responsible for this very different behaviour, are discussed in detail.