Untitled

Freezing Enhances Leaching of Ferrous Ions but Hinders Reductive Dissolution of Ferric Ions from Iron Oxides

“…Also, if dissolved ion species are supplied from the electrode by its reduction, the redox reaction of Fe 2+ /Fe 3+ ( E 0 = 0.77 vs SHE) is observable in this potential window. In actuality, former studies using the magnetite electrode observed the Fe 2+ /Fe 3+ redox couple on voltammograms even when ferrous or ferric ions were not added to solutions, suggesting that dissolved iron species are supplied from magnetite. − …”

“…Figure a shows CVs recorded using the magnetite electrode at 25 °C, where the potential ( E ) was scanned in the potential range, E = 0.3 → −0.5 → 0.8 → 0.3 V (vs Ag/AgCl). CV is well characterized by one redox couple (anodic peak A 1 and cathodic peak C 1 ) at E ∼ 0.4 V and one cathodic peak (C 2 ) at E ∼ −0.1 V. Former studies assigned the C 1 /A 1 couple to the redox of dissolved Fe 2+ /Fe 3+ and C 2 to the reduction of ferric ions on the surface of the magnetite crystal (Fe magn III ). − Thus, dissolved Fe 2+ , which is supplied at C 2 , is oxidized to Fe 3+ at A 1 , and then, Fe 3+ is reduced at C 1 in the subsequent cathodic scan to give the C 1 /A 1 redox couple. Because dissolved iron species does not exist in the original solution, the A 1 /C 1 redox couple did not appear when the potential was initially scanned in the anodic direction, that is, E = 0.3 → 0.8 V, as shown in Figure b.…”

Contribution of electrochemical dissolution during pickling of low carbon steel in acidic solutions

“…Additional cathodic reactions should therefore be considered. According to references [5,8,27], reductive dissolution of magnetite is also expected in this potential range, i.e.,…”

“…continuous parallel sublayers deposited on the substrate and made of wüstite (FeO), magnetite (Fe 3 O 4 ) and hematite (Fe 2 O 3 ) [2] . In order to obtain information on the behaviour of passive films, a large amount of work has been carried out on pure iron oxides (bulk oxides, sintered powders or sputtered layers on a membrane) [3][4][5][6][7][8][9], and it has been shown that the electronic properties of synthetic iron oxides are in good agreement with the behaviour of natural passive films on iron.…”

“…Since it is known that iron oxide dissolution in acid solutions is simultaneously a chemical and an electrochemical process [5,[7][8][9], another difficulty is to find experimental methods which allow the two mechanisms to be distinguished. While electrochemical methods provide information on the rate of electrochemical dissolution, additional analytical techniques are necessary to determine the total dissolution rate.…”