Dissolution of Magnetite Coupled with Iron of Various Surface Areas

Abstract

The effect of the galvanic coupling between magnetite and iron on their dissolution was investigated in aqueous solutions containing ethylenediaminetetraacetic acid (EDTA) in the presence and absence of ferrous ion, in which magnetite dissolved reductively. Four different area ratios between iron to magnetite were studied: 1:1600, 1:400, 1:100, and 1:25 (marked as couple 1 through couple 4 hereafter). The objective was to simulate the presence of a magnetite film partially removed from an iron surface in the course of chemical cleaning when coupling conditions occur with variable area ratios. Measurements of the couple's potential (Ecouple) and individual currents of magnetite (Imag) and iron (IFe) (marked as mag1 through mag4 and Fe1 through Fe4 hereafter) have shown that as the iron area increases the reductive dissolution of magnetite is accelerated. At the same time, the potential of the couple shifts to more negative values, becoming closer to the potential of Fe under the same conditions. Electrochemical impedance spectroscopy (EIS) and cyclic sweep measurements have shown that the dissolution of magnetite increases as the Fe area increases. This result can be attributed to the autocatalytic effect caused by ferrous ions resulting from iron dissolution on the reductive dissolution of magnetite. This is confirmed by comparison with magnetite dissolution under the same conditions without coupling. The dissolution rate was increased when Fe2+ was added to the medium.