Induction periods during anodic polarization of zinc in aqueous oxalic acid solutions

The anodic polarization of zinc in aqueous solutions of oxalic acid was investigated. The polarizations were carried out in electrolytes with concentrations between 0.005 and 0.500 mol dm−3, at constant current densities (1 ÷ 40 mA cm−2). In the course of anodic polarization, induction periods were...

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Bibliographic Details
Published in:Materials chemistry and physics 2019-02, Vol.223, p.727-736
Main Authors: Lilov, E., Lilova, V., Girginov, Ch, Kozhukharov, S., Tsanev, A., Yancheva, D.
Format: Article
Language:English
Subjects:
Anodic polarization
Aqueous solutions
Current density
Electrode polarization
Electrolytes
High voltages
Induction periods
Mathematical models
Measurement methods
Metal surfaces
Oxalic acid
Photomicrographs
Thin films
X ray photoelectron spectroscopy
Zinc
Zinc oxide
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Summary:The anodic polarization of zinc in aqueous solutions of oxalic acid was investigated. The polarizations were carried out in electrolytes with concentrations between 0.005 and 0.500 mol dm−3, at constant current densities (1 ÷ 40 mA cm−2). In the course of anodic polarization, induction periods were distinctly recorded, and their durations were found to be strongly dependent on both the electrolyte concentration and the applied current density. By employing XPS and XRD diffraction methods and performing ATR-FTIR measurements, it was established that the layers formed on the metal surface are composed of crystalline zinc oxalate dihydrate, covered with thin ZnO external layers. Furthermore, a conceptual model was developed which qualitatively explains the mechanism of appearance of the observed induction periods. This model perceives the roughness variation of the electrode surface during anodic polarization. The obtained AFM images and SEM micrographs confirm the assumptions made in the presented model. During the polarization of zinc in aqueous solutions of oxalic acid, high voltages are reached, which makes them suitable for forming ZnC2O4.2H2O coatings. [Display omitted] •Anodic galvanostatic polarizations are performed on pure Zn in oxalic acid solutions.•The acid concentrations and the current densities were varied in large ranges.•Distinguishable induction periods were registered in all the investigated cases.•A conceptual model is created for explication of the investigated systems behavior.•The proposed model was verified by the experimental results.
ISSN:0254-0584
1879-3312
DOI:10.1016/j.matchemphys.2018.11.044