Abstract
The reduction dissolution of magnetite was investigated in the acidic perchlorate solutions of various pH values by means of the potential sweep method and impedance measurement, with special interest in the mechanism of oxide dissolution. In a certain potential region, the current potential diagram exhibited a peak, both the positive and negative branch of which obeyed a Butler—Volmer type relation. The rate of the dissolution in this potential region was controlled by a transfer of ion across the Helmholtz layer. The positive branch of the peak depended on the pH of solution. The rate of dissolution was found to be controlled by an anion-removal process. The negative branch of the peak was independent of pH and the transfer of ferrous ion was rate-controlling. From the impedance measurement, the faradaic formation of a surface layer with non-stoichiometric composition was suggested. The impedance behaviour at low frequencies corresponded well to the stationary dissolution behaviour.
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