Abstract
The behaviour of three types of nickel (99·99% {111} single crystal, 99·99% polycrystalline and commercial purity grade polycrystalline) has been investigated in 1N perchloric acid. The electrochemical results and the optical microscopy observations of the surface during and after controlled dissolution are compared with the ones previously obtained under the same conditions in 1N sulphuric acid and in 1N hydrochloric acid.
From an analysis of all our data a mechanistic model of nickel dissolution is deduced. It interprets the value of 60 mV for the anodic Tafel slope, found for the high purity nickel, and it considers, as the rate determining step, two possible reactions: (i)proton transfer from the intermediate NiOH2 +, electrochemically formed, to a water molecule, and (ii) the movement ofadspecies such as NiOHads from kinks to plane surfaces. The prevailing control of one of these two steps depends on the type of the anion and the purity of the nickel surface.
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