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LI-XIAOJI Dissertation April 8.pdf (7.74 MB)

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Understanding Liquid-Air Interface Corrosion of Steel in Simplified Liquid Nuclear Waste Solutions

Li, Xiaoji
http://rave.ohiolink.edu/etdc/view?acc_num=osu1365506823

Abstract Details

2013, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
Carbon steel is susceptible to the liquid-air interface (LAI) corrosion in liquid nuclear waste and in simulants, but a precise understanding of the mechanism is still missing. This work aimed to expand the understanding of the LAI corrosion mechanism. LAI corrosion was found to initiate at the very top of the meniscus in the form of pits under potentiostatic polarization condition. Gas bubbles were often observed to collect on corrosion product in the meniscus after extensive LAI corrosion. Additionally, LAI corrosion initiated later than crevice corrosion in the presence of a crevice. The effect of meniscus geometry on LAI corrosion initiation depends on the precise triple phase boundary rather than the opening angle of the meniscus geometry. Deaeration accelerated LAI corrosion. LAI corrosion was not enhanced by wetting the surface immediately above the meniscus. A pre-existing passive film boundary in the bulk solution could not eliminate LAI corrosion. Cyclic potentiodynamic polarization measurements were conducted, but could not distinguish the solution aggressiveness in terms of passive current density and pitting potential at varied alkaline pHs and concentrations of nitrate and nitrite ions. In addition, linear polarization resistance and electrochemical impedance spectroscopy measurements at OCP in the meniscus and bulk solution could not confirm the hypothesis that the meniscus solution would become increasingly aggressive to initiate LAI corrosion. Efforts were made to generate direct supporting evidence for several hypotheses. The use of a small pH electrode did not confirm existence of a pH gradient before initiation of LAI corrosion. Similarly, no IR drop was present in the meniscus prior to LAI corrosion initiation. In situ Raman spectroscopy was applied to monitor concentration changes of nitrate, sulfate and nitrite with time in the meniscus during LAI corrosion. A proposed mechanism of nitrate ion enhancement and nitrite ion depletion at the meniscus was not verified. Results showed that both aggressive ion (nitrate or sulfate) and inhibiting ion (nitrite) concentrations exhibited no variation before LAI corrosion initiation, as well as the nitrate-to-nitrite concentration ratio. The cathodic reduction kinetics in simplified waste simulants were also studied electrochemically. Both cyclic voltammetry and cathodic polarization measurements indicate that the nitrite reduction reaction exhibits faster kinetics than the nitrate reduction reaction at larger cathodic overpotential. However, the cathodic reactions at OCP are not dominated by the reduction of nitrate and nitrite. The varied availability of oxygen to the electrode surface clearly distinguishes the cathodic kinetics among varied immersion conditions. Lastly, nitrogenous gases, such as NO2, NO, N2O and sometimes NH3, were detected using gas chromatography-mass spectroscopy and gas detector tube methods, but only after extensive LAI corrosion. The reduction of nitrate or nitrite to the gases is probably promoted by the local acidification in the meniscus region generated by the hydrolysis of cations after extensive LAI corrosion propagation. Based on this work, it is likely that LAI corrosion is related to the local acidification at the top of meniscus. This mechanism is consistent with all known facts about LAI corrosion.
Gerald Frankel (Advisor)
Rudolph Buchheit (Committee Member)
Yogeshwar Sahai (Committee Member)
254 p.
Materials Science
Liquid nuclear Waste; liquid-air interface corrosion; LAI corrosion; meniscus; carbon steel; electrochemical measurements; in-situ Raman spectroscopy; nitrate ion; nitrite ion; oxygen concentration cell; ohmic potential drop; salt concentration cell

Recommended Citations

Citations

  • Li, X. (2013). Understanding Liquid-Air Interface Corrosion of Steel in Simplified Liquid Nuclear Waste Solutions [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365506823

    APA Style (7th edition)

  • Li, Xiaoji. Understanding Liquid-Air Interface Corrosion of Steel in Simplified Liquid Nuclear Waste Solutions. 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1365506823.

    MLA Style (8th edition)

  • Li, Xiaoji. "Understanding Liquid-Air Interface Corrosion of Steel in Simplified Liquid Nuclear Waste Solutions." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365506823

    Chicago Manual of Style (17th edition)

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