Dissolution of iron oxide under potential control

The behaviour of magnetite (Fe3O4), a potentially damaging corrosion product of steel, has been investigated in acidic solution and the results are reported and discussed herein. A review of some of the literature on the structure and electrochemistry of magnetite and on the electrochemical dissolution of crystals is presented. Emphasis is laid upon work concerned with the dissolution of magnetite, especially in acidic and/or at cathodic potentials. A preliminary examination of the electrochemical behaviour of magnetite in terms of its current/potential characteristics and the response to potential perturbations of both stationary and non-stationary magnetite electrodes is given. The effect of an applied potential on the dissolution rate of magnetite in acidic perchlorate solution and the variation with time of both the dissolution and electronic currents is described also. It is shown that, over a wide range of potential, dissolution of magnetite occurs via a solid-state reduction of ferric to ferrous ions with subsequent transfer of ferrous ions into solution. It is shown also that while a relationship exists between the applied potential and the dissolution rate, it is complex and in the main reflects the relationship between the applied potential and the electronic current. It has been possible to conclude that at elevated temperatures, potential regions exist within which the electronic current is controlled by a solution-state process and suggests that it is the mass-transport of protons which is the rate-controlling factor.