Electrochemical Behavior of Iron Rust in Neutral Solution

Abstract

Rust electrodes were prepared by fixing a piece of rust plate, which was formed on pure iron during four months exposure in urban environment, on an acrylic plate with a conductive adhesive. The galvanostatic catholic polarization of them was studied in 0.1M Na2SO4 solution at 20C.The rest potential gradually recovered after polarization current was switched off and approached the value which depended on the amount of charge passed through the rust electrode. The change in the amount of crystalline substances in the rust plate was observed by X-ray diffraction.As the reduction proceeded, the amount of lepidocrocite (FeOOH) decreased, crystalline magnetite (Fe3O4) increased and goethite (a-FeOOH) did not change. The bulk of electrochemically active substances, which we call "intermediate substances," could not be identified by X-ray diffraction but their behavior was estimated from that of crystalline substances. After sufficient reduction, the intermediate substances were converted to crystalline magnetite which could not be oxidized any more electrochemically.The rest potential of the rust electrodes is controlled by the equilibrium potential of the intermediate substances which is defined by solid state Fe(III)/ Fe(II) redox system. From our findings, "an overlapping dual electrode" model is proposed for rusted steel in aqueous solution, namely an equilibrium electrode of solid state system overlaps on the corroding electrode controlled by the reduction of oxygen.

<i>In-Situ</i> Observation of Initial Stage Cosmetic Corrosion Behavior under Wet and Dry Conditions

“…Suzuki et al analyzed the rust layer of pure iron formed in an exposure test by a cathodic constant current method and concluded that magnetite is not easily oxidized by air when it has been reduced to crystalline magnetite. 18) As mentioned above, crystalline magnetite was detected by the XRD analysis in the present study. Therefore, the magnetite was not oxidized by air or the water film in this case because the magnetite consisted of crystalline magnetite.…”

“…The second possibility is that the oxidation reaction of magnetite does not occur even in contact with oxygen in the gas phase or water film. This second possibility is discussed by Suzuki et al 18) as follows. Suzuki et al analyzed the rust layer of pure iron formed in an exposure test by a cathodic constant current method and concluded that magnetite is not easily oxidized by air when it has been reduced to crystalline magnetite.…”

M&ouml;ssbauer Spectroscopic Study of Rust Formed on a Weathering Steel and a Mild Steel Exposed for a Long Term in an Industrial Environment

“…The atmospheric corrosion is electrochemical in nature. 52) It is widely reported that rust is electrochemically highly active, [13][14][15][16][17][18] and therefore the rust on the corroding steel surfaces is affected by the potential of steel. Due to the is also adherent and tight.…”

“…Because the rust is reduced just after wetting of the dry surface as cathodic reaction by the negative electrode potential, and during drying the oxygen reduction as cathodic reaction takes place on the reduced rust surface in the pore system of the rust. [11][12][13][14][15][16][17][18][19][20][21][22] In spite of the importance of the rust on the corrosion behavior of steels, limited numbers of studies have mentioned the rust constituents formed on the steel surfaces. The crystalline rust, which is detected by X-ray diffraction technique, has been well characterized, and the composition change of the crystalline rust with the exposure duration have * Graduate Student, Osaka University.…”

Effect of Environmental Cation Species on Corrosion near Shear Cut Edge of 55%Al–Zn Alloy Coated Steel Sheet

“…It is suggested that this phenomenon of increased current is caused by the reduction reaction of the iron rust on the Fe electrode. 17) In other words, the cathodic reaction is suppressed on the Fe electrode of the galvanic electrode in MgCl 2 SST. This corresponds with the corrosion suppression of the coating near the cut edge of the galvanic specimen in MgCl 2 SST shown in Fig.…”