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New Approaches to Study Magnesium Corrosion Behavior

D avila Gabbardo, Aline
http://rave.ohiolink.edu/etdc/view?acc_num=osu1555375316744396

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
New technologies and applications for Mg require further improvements of its corrosion resistance. Fundamental comprehension of the Mg corrosion mechanisms is necessary to address the issue, as the Mg corrosion behavior is unexpected from the theory of electrochemical kinetics. The anomalous hydrogen evolution phenomenon (anomalous HE) exhibited by Mg, also known as the negative difference effect (NDE), is still an unresolved issue. Recent research suggests that the anomalous HE is a consequence of a surface change during dissolution. The proposed mechanisms debate the location of the phenomenon on the surface. The phenomenon is proposed to happen at the corroded areas behind the corrosion front, in the dark corrosion products left behind the corrosion front and/or at the active dissolving sites. New techniques and experimental data are needed to further address the discussion. Some researchers believe that the anomalous HE phenomenon observed during Mg corrosion is associated with the actual active dissolving sites. Selective accumulation or re-deposition of impurities at these active dissolving surfaces is a possible explanation for the anomalous HE behavior because most impurities are cathodically polarized on an Mg matrix and can support the hydrogen evolution reaction (HER) at a high rate. However, many recent studies have presented results that contradict this model. Some authors have pointed out the dominant role of the active surfaces in the phenomenon, but none has provided undisputed evidence for why active surfaces are more catalytic for the HER. In this work, two methods are used to study the anomalous HE phenomenon on Mg with the aim to provide further experimental evidence towards an explanation: the 2D pit growth method and the scratched electrode technique. The first method is called 2D pitting because the sample is a thin metallic film deposited on an inert substrate, so the pit depth is constant and limited to the film thickness. By analyzing 2D pit growth, it is possible to accurately track the active dissolving surface and to measure the anodic, net and cathodic current densities. The hydrogen evolution current density was shown to increase with increasing applied potentials in the ohmic/activation control region, which is direct evidence for the anomalous HE behavior. In addition, the results clearly demonstrated that the anomalous HE phenomenon happens at the active dissolving site, which in this case is the pit wall. The 2D pits were also evaluated at high applied potentials where a salt film precipitated on the active dissolving surface. The results showed that the anomalous HE rate decreased in the transport control region approaching zero at the limiting current density. In this case, the rate of hydrogen evolution was limited by water diffusion through the salt film to reach the active surface. The scratched electrode technique uses a diamond scribe to create a scratch on the metal surface during potentiostatic experiments. This enables the measurement of corrosion kinetics of freshly generated metallic surfaces. The technique was used to evaluate the anodic and cathodic reaction rates of bare (film free) ultra high purity Mg surfaces. Active dissolving sites can be considered film free surfaces. It was shown that the catalytic activity for the HER increased on the scratch surface and this increased catalytic activity persisted until repassivation.
Gerald Frankel (Advisor)
Jenifer Locke (Committee Member)
Christopher Taylor (Committee Member)
175 p.
Materials Science

Recommended Citations

Citations

  • D avila Gabbardo, A. (2019). New Approaches to Study Magnesium Corrosion Behavior [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555375316744396

    APA Style (7th edition)

  • D avila Gabbardo, Aline. New Approaches to Study Magnesium Corrosion Behavior. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1555375316744396.

    MLA Style (8th edition)

  • D avila Gabbardo, Aline. "New Approaches to Study Magnesium Corrosion Behavior." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555375316744396

    Chicago Manual of Style (17th edition)

osu1555375316744396
402
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This open access ETD is published by The Ohio State University and OhioLINK.