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The influence of a magnetic field on the non-electrochemical dissolution of iron
Journal of Electroanalytical Chemistry 624 (2008) 327–328
Contents lists available at ScienceDirect
Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem
Short Communication
The influence of a magnetic field on the non-electrochemical dissolution of iron G. Bech-Nielsen a, M. Jaskuła b,* a b
IPL, Technical University of Denmark, Lyngby, Copenhagen, Denmark Jagiellonian University, Department of Physical Chemistry and Electrochemistry, Cracow, Poland
a r t i c l e
i n f o
Article history: Received 20 March 2008 Received in revised form 28 July 2008 Accepted 5 August 2008 Available online 17 August 2008
a b s t r a c t The influence of magnetic field on the rate of chemical reaction with a proton transfer is explained on the basis of quantum effects and spin relaxation. A model of chemical dissolution of iron under the influence of magnetic field was proposed. Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Chemical dissolution of iron Influence of magnetic field
Electrochemical dissolution of metals is well established and accounts closely for most cases of corrosion attack. However, since about 1960 it has been shown convincingly for several metals, including iron, that also a purely chemical, potential independent dissolution takes place. For iron it has been shown that while the anodic dissolution has a positive reaction order wrt pH, the chemical dissolution has a negative one [1]. Also influence of anions can be assumed for the chemical dissolution. Vorkapic and Drazic [2] found that touching the corroding iron electrode with a magnet decreased the dissolution rate. About a few hundreds papers report that there is an influence of the magnetic field on the rate of various chemical and electrochemical reactions. The extensive reviews were made by Steiner and Ulrich [3] for chemical and by Fahidy [4] for electrochemical reactions. One of the most interesting systems is iron the corrosion of which was investigated in various electrolytes. According to Chiba [5], the magnetic field affected remarkably the anodic reaction (Fe ? Fe2+ + 2e) and promoted the oxidation of Fe2+ to Fe3+ in HCl solution. Wang and Chen [6] explain observed effects by assuming an additional magnetic overpotential that could be attributed to the reduction of diamagnetic ion hydrate on the iron/solution interface and the adsorption of Fe2+ on the iron surface, which are responsible for the changes of electrical double layer structure and the increase of activity in the corrosion system. Only a few authors contest wide-spread opinions about the influence of magnetic field on the mechanism of reactions. For example, Koehler and Bund [7] found no influence of magnetic field on the electron transfer reaction and explain the observed effects by
* Corresponding author. Tel.: +48 12 663 22 69; fax: +48 12 634 05 15. E-mail addresses: [email protected] (G. Bech-Nielsen), [email protected] (M. Jaskuła). 0022-0728/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2008.08.003
working of magnetodynamic forces. However, the problem considered here is a non-electrochemical reaction. A model for the chemical dissolution of iron, accounting for the influence of pH and anion concentration, has been presented by Bech-Nielsen and Reeve [8]. However, influence of magnetic field could not be identified in this model, but a clue may be found in recent work in a different field. A paper by Lundager Madsen [9] shows that smaller crystals of calcium carbonate are formed in a magnetic field, when precipitation takes place between calcium ions and hydrogen carbonate ions, but not when carbonate ions are predominant or when heavy water and deuterated chemicals are used. The effect is ascribed to faster deprotonation of the hydrogen carbonate ion as a result of quantum effects influencing closely neighbouring protons. Replacement of protons with deuterons excludes the quantum effects. It is possible to identify a step in the model for chemical dissolution of iron [8], which could be similarly influenced by a magnetic field. The model is formulated as follows:
Fe0 þ 2X () Fe0 ðXÞ2
ð1Þ
x¼0
Fe0 ðXÞ2 þ H3 Oþ ð()ÞFe0 ðXÞH3 Oþx¼0 þ X Fe0 ðXÞH3 Oþx¼0 ) FeðXÞH3 OþxPd 0
Fe
ðXÞH3 OþxPd
þ
þH )
Fe2þ aq
þ H2 þ X þ H2 O
ð2Þ ð3Þ ð4Þ
Step (1) is the common starting step for chemical and electrochemical dissolution. X is an anion. x = 0 and x P d mean ‘‘at the iron surface” and ‘‘outside the double layer”, respectively. With a low coverage of the product in (2), this step will be rate controlling, and a reaction order wrt pH of 1 is predicted. Rate control by step (3) will arise as a result of maximum coverage by the product in (2).
328
G. Bech-Nielsen, M. Jaskuła / Journal of Electroanalytical Chemistry 624 (2008) 327–328
Influence of Magnetic Field 1-2`
log (i)
1-2
2.4 2.2 2 1.8 1.6 1.4 1.2 1 -4
1-3 1-2`-3 1-2-3
-3.5
-3
-2.5
-2
-1.5
-pH Fig. 1. Schematic diagram showing logarithmically the limiting reactions 1-2, 1-3 and 1-20 , the latter lower than 1-2 due to the magnetic field. The curved parts marked 1-2-3 and 1-20 -3 show the rates of the reactions in the region of transition between the limiting reactions. The resultant rate, i, in a transition between limiting 10 consecutive reactions ia and ib, is calculated by the relation: 1=i ¼ 1=ia þ 1=ib .
Then a reaction order wrt pH of zero is predicted. A reported value of 0.45 [2] indicates partial control by steps (2) and (3) and a rather high coverage by the product in (2). Then a magnetic field might influence reaction (2) in a similar way as with the hydrogen carbonate ion, since the adsorbed complex contains protons at the closest distance. Thus, a higher rate for reaction (2) will decrease the rate of dissolution. The diagram in Fig. 1 illustrates schematically the course of reactions, with a transition from step (+2) as the rate determining
one to step (3) in the absence of a magnetic field, and, with a magnetic field, with the transition from a step (20 ) (only replacing step (2) at higher coverage by the product in this step). The diagram was constructed according to the principles for consecutive reactions described earlier [10]. However, as the diagram has been drawn, a lowering of the dissolution rate can hardly be expected to be more than a factor of ca. 1.5, much less than reported by Vorkapic and Drazic [2], and it may thus be assumed that a more direct influence of the magnetic field is involved, maybe slowing down the rate of reaction (3) as well. It should finally be noted that the present suggestion is strongly dependent on the validity of the arguments presented by Lundager Madsen [9] in favour of quantum effects affecting proton transfer in a magnetic field. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
Ya.M. Kolotyrkin, G.M. Florianovich, Z. Phys. Chem. 231 (1966) 145. L.Z. Vorkapic, D.M. Drazic, Corros. Sci. 19 (1979) 643. U. Steiner, T. Ulrich, Chem. Rev. 89 (1) (1989) 51–147. T. Fahidy, Mod. Aspects Electrochem. 32 (1999) 333–354. A. Chiba, T. Ogawa, Nippon Kagaku Kaishi (3) (1988) 357. Chen Wang, Junming Chen, Zhongguo Fushi Yu Fanghu Xuebao 14 (2) (1994) 123–128. S. Koehler, A. Bund, J. Phys. Chem. B 110 (2006) 1485–1489. G. Bech-Nielsen, J.C. Reeve, Dansk Kemi 61 (1980) 261. H.E. Lundager Madsen, J. Crystal Growth 267 (2004) 251. G. Bech-Nielsen, J.C. Reeve, Electrochim. Acta 27 (1982) 1321.
Contents lists available at ScienceDirect
Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem
Short Communication
The influence of a magnetic field on the non-electrochemical dissolution of iron G. Bech-Nielsen a, M. Jaskuła b,* a b
IPL, Technical University of Denmark, Lyngby, Copenhagen, Denmark Jagiellonian University, Department of Physical Chemistry and Electrochemistry, Cracow, Poland
a r t i c l e
i n f o
Article history: Received 20 March 2008 Received in revised form 28 July 2008 Accepted 5 August 2008 Available online 17 August 2008
a b s t r a c t The influence of magnetic field on the rate of chemical reaction with a proton transfer is explained on the basis of quantum effects and spin relaxation. A model of chemical dissolution of iron under the influence of magnetic field was proposed. Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Chemical dissolution of iron Influence of magnetic field
Electrochemical dissolution of metals is well established and accounts closely for most cases of corrosion attack. However, since about 1960 it has been shown convincingly for several metals, including iron, that also a purely chemical, potential independent dissolution takes place. For iron it has been shown that while the anodic dissolution has a positive reaction order wrt pH, the chemical dissolution has a negative one [1]. Also influence of anions can be assumed for the chemical dissolution. Vorkapic and Drazic [2] found that touching the corroding iron electrode with a magnet decreased the dissolution rate. About a few hundreds papers report that there is an influence of the magnetic field on the rate of various chemical and electrochemical reactions. The extensive reviews were made by Steiner and Ulrich [3] for chemical and by Fahidy [4] for electrochemical reactions. One of the most interesting systems is iron the corrosion of which was investigated in various electrolytes. According to Chiba [5], the magnetic field affected remarkably the anodic reaction (Fe ? Fe2+ + 2e) and promoted the oxidation of Fe2+ to Fe3+ in HCl solution. Wang and Chen [6] explain observed effects by assuming an additional magnetic overpotential that could be attributed to the reduction of diamagnetic ion hydrate on the iron/solution interface and the adsorption of Fe2+ on the iron surface, which are responsible for the changes of electrical double layer structure and the increase of activity in the corrosion system. Only a few authors contest wide-spread opinions about the influence of magnetic field on the mechanism of reactions. For example, Koehler and Bund [7] found no influence of magnetic field on the electron transfer reaction and explain the observed effects by
* Corresponding author. Tel.: +48 12 663 22 69; fax: +48 12 634 05 15. E-mail addresses: [email protected] (G. Bech-Nielsen), [email protected] (M. Jaskuła). 0022-0728/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2008.08.003
working of magnetodynamic forces. However, the problem considered here is a non-electrochemical reaction. A model for the chemical dissolution of iron, accounting for the influence of pH and anion concentration, has been presented by Bech-Nielsen and Reeve [8]. However, influence of magnetic field could not be identified in this model, but a clue may be found in recent work in a different field. A paper by Lundager Madsen [9] shows that smaller crystals of calcium carbonate are formed in a magnetic field, when precipitation takes place between calcium ions and hydrogen carbonate ions, but not when carbonate ions are predominant or when heavy water and deuterated chemicals are used. The effect is ascribed to faster deprotonation of the hydrogen carbonate ion as a result of quantum effects influencing closely neighbouring protons. Replacement of protons with deuterons excludes the quantum effects. It is possible to identify a step in the model for chemical dissolution of iron [8], which could be similarly influenced by a magnetic field. The model is formulated as follows:
Fe0 þ 2X () Fe0 ðXÞ2
ð1Þ
x¼0
Fe0 ðXÞ2 þ H3 Oþ ð()ÞFe0 ðXÞH3 Oþx¼0 þ X Fe0 ðXÞH3 Oþx¼0 ) FeðXÞH3 OþxPd 0
Fe
ðXÞH3 OþxPd
þ
þH )
Fe2þ aq
þ H2 þ X þ H2 O
ð2Þ ð3Þ ð4Þ
Step (1) is the common starting step for chemical and electrochemical dissolution. X is an anion. x = 0 and x P d mean ‘‘at the iron surface” and ‘‘outside the double layer”, respectively. With a low coverage of the product in (2), this step will be rate controlling, and a reaction order wrt pH of 1 is predicted. Rate control by step (3) will arise as a result of maximum coverage by the product in (2).
328
G. Bech-Nielsen, M. Jaskuła / Journal of Electroanalytical Chemistry 624 (2008) 327–328
Influence of Magnetic Field 1-2`
log (i)
1-2
2.4 2.2 2 1.8 1.6 1.4 1.2 1 -4
1-3 1-2`-3 1-2-3
-3.5
-3
-2.5
-2
-1.5
-pH Fig. 1. Schematic diagram showing logarithmically the limiting reactions 1-2, 1-3 and 1-20 , the latter lower than 1-2 due to the magnetic field. The curved parts marked 1-2-3 and 1-20 -3 show the rates of the reactions in the region of transition between the limiting reactions. The resultant rate, i, in a transition between limiting 10 consecutive reactions ia and ib, is calculated by the relation: 1=i ¼ 1=ia þ 1=ib .
Then a reaction order wrt pH of zero is predicted. A reported value of 0.45 [2] indicates partial control by steps (2) and (3) and a rather high coverage by the product in (2). Then a magnetic field might influence reaction (2) in a similar way as with the hydrogen carbonate ion, since the adsorbed complex contains protons at the closest distance. Thus, a higher rate for reaction (2) will decrease the rate of dissolution. The diagram in Fig. 1 illustrates schematically the course of reactions, with a transition from step (+2) as the rate determining
one to step (3) in the absence of a magnetic field, and, with a magnetic field, with the transition from a step (20 ) (only replacing step (2) at higher coverage by the product in this step). The diagram was constructed according to the principles for consecutive reactions described earlier [10]. However, as the diagram has been drawn, a lowering of the dissolution rate can hardly be expected to be more than a factor of ca. 1.5, much less than reported by Vorkapic and Drazic [2], and it may thus be assumed that a more direct influence of the magnetic field is involved, maybe slowing down the rate of reaction (3) as well. It should finally be noted that the present suggestion is strongly dependent on the validity of the arguments presented by Lundager Madsen [9] in favour of quantum effects affecting proton transfer in a magnetic field. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
Ya.M. Kolotyrkin, G.M. Florianovich, Z. Phys. Chem. 231 (1966) 145. L.Z. Vorkapic, D.M. Drazic, Corros. Sci. 19 (1979) 643. U. Steiner, T. Ulrich, Chem. Rev. 89 (1) (1989) 51–147. T. Fahidy, Mod. Aspects Electrochem. 32 (1999) 333–354. A. Chiba, T. Ogawa, Nippon Kagaku Kaishi (3) (1988) 357. Chen Wang, Junming Chen, Zhongguo Fushi Yu Fanghu Xuebao 14 (2) (1994) 123–128. S. Koehler, A. Bund, J. Phys. Chem. B 110 (2006) 1485–1489. G. Bech-Nielsen, J.C. Reeve, Dansk Kemi 61 (1980) 261. H.E. Lundager Madsen, J. Crystal Growth 267 (2004) 251. G. Bech-Nielsen, J.C. Reeve, Electrochim. Acta 27 (1982) 1321.