Faculty of Technology and Metallurgy

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Author: search.filters.author.Grcev, Toma

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    Electrochemical passivation of niobium in KOH solutions
    (CROATIAN CHEMICAL SOC, 2006-12)
    ;
    Prusi, Abdurauf
    ;
    Grcev, Toma
    ;
    Arsov, Ljubomir
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    Electrochemical characterization of the passive films formed on niobium surfaces in H2SO4 solutions
    (National Library of Serbia, 2006)
    ;
    Prusi, Abdurauf
    ;
    Grcev, Toma
    ;
    Arsov, Ljubomir
    The electrochemical formation and characteristics of passive films on niobium surfaces in aqueous H2SO4 solutions were studied using open circuit potential and cyclic voltammetry. In the potential region between -1.0 and 1.2 V(NHE), the cyclic voltammetry data showed that the active/passive transition involves slow metal dissolution followed by the formation of semiconducting passive oxide films. The possible electrochemical reactions and the change of the oxidation steps of some niobium oxides occurring in the passive film during the polarization are proposed. A strong influence of the natural air-formed oxide film on the chemical composition of the passive film was shown. This influence makes chemical structure of thin passive films more complicated than that of thick anodic films. It is shown that the passive films consists of more or less stable oxides, such as NbO, NbO2 and Nb2O5. The Raman spectra revealed that the thin passive films were amorphous, while the films formed at higher voltages consist, primarily, of well-crystallized Nb2O5.
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    Active/Passive Transition of Niobium in Strong Acid and Alkaline Solutions
    (Sociedade Portuguesa de Electroquímica, 2006)
    ;
    Abdurauf, Prusi
    ;
    Grcev, Toma
    ;
    Arsov,Ljubomir
    By cyclic voltammetry the active/passive transition of Nb electrode has been investigated in concentration range from 0.1 M to 10 M aqueous solutions of H2SO4 and KOH. Results indicate the strong influence of the concentration and electrolyte nature to the active/passive transitions and stability of passive films. Depending on electrolyte concentrations, at potential of 1 V the calculated thickness of passive films varied from 2.2 nm to 3.2 nm. For the same concentrations of H2SO4 and KOH the formed passive films in KOH are thicker than in H2SO4. By multiple cycle sequences in which the final anodic potential is gradually enlarged, the barrier properties of passive films on Nb electrode were confirmed. In the first positive scan after the active/passive transition, no cathodic or reactivation peaks for both 1 M H2SO4 and KOH were observed. Only for higher concentrations of KOH (> 2 M) the small reactivation process was recorded. In concentration of 5 M and 10 M KOH, if after the passive film formation the Nb electrodes were maintained for 15 min at cathodic potential of -1.55 (SHE), the cyclic voltammograms indicated the complete dissolution of passive films. The voltammetric data have confirmed that the Nb electrode is more resistant in concentrated H2SO4 than in concentrated KOH solutions.