The anodic behaviour of niobium—I. The state of the art

D’Alkaine, C.V.; Souza, L.M.M. de; Nart, Francisco Carlos

doi:10.1016/0010-938x(93)90262-f

Cited by 44 publications

(17 citation statements)

References 36 publications

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“…30 In order to avoid the formation of Nb hydrides 40,41 of a wide non-stoichiometric composition 42 which are usually formed at about −1.5 V vs. SHE, 30 all polarization diagrams were recorded starting from the same cathodic potential limit of −1.35 V vs. SCE, i.e., about −1.0 V vs. SHE (after 10 s at the open circuit potential). As can be seen in Fig.…”

Section: Polarization Diagramsmentioning

confidence: 99%

Semiconducting properties of oxide films formed onto an Nb electrode in NaOH solutions

Jović

2008

JSCS

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In this paper, the results of the potentiostatic formation of homogeneous and heterogeneous, nano-crystalline passive films of Nb 2 O 5 onto an Nb electrode in NaOH solutions of different concentrations at potentials lower than 3.0 V vs. SCE are presented. The semiconducting properties of such films were investigated by EIS measurements. After fitting the EIS results by appropriate equivalent circuits, the space charge capacitance (C sc ) and space charge resistance (R sc ) of these films were determined. The donor density (N sc ), flat band potential (E fb ) and thickness of the space charge layer (d sc ) for such oxide films were determined from the corresponding Mott-Schottky (M-S) plots. It is shown that all oxide films were n-type semiconductors in a certain potential range.

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Section: Polarization Diagramsmentioning

confidence: 99%

Semiconducting properties of oxide films formed onto an Nb electrode in NaOH solutions

Jović

2008

JSCS

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“…Being a valve metal, niobium passivates with a high corrosion resistance in most common aqueous media [1][2][3][4] . The passive films, constituted of amorphous niobium pentoxide 3 , can be easily thickened by anodic polarisation [3][4][5][6][7] ; the oxide growth occurs by high-field ion migration in the film 8,9 .…”

Section: Introductionmentioning

confidence: 99%

Electrochemical characterization of thin passive films on Nb electrodes in H3PO4 solutions

Biaggio¹,

Bocchi²,

Rocha‐Filho³

et al. 1997

J. Braz. Chem. Soc.

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The electrical and semiconducting properties of thin anodic passive films potentiostatically formed (1 V ≤ E f ≤ 5 V vs. sce) on polycrystalline niobium electrodes in aqueous 0.5 mol/L H3PO4 solutions (pH 1.3) were studied, at room temperature, using electrochemical impedance spectroscopy. The data were analysed with a transfer function using a non-linear fitting routine, assuming that the resistance of the film is coupled in series with the faradaic impedance of the Nb(0) → Nb(V) reaction, and these in parallel with the capacitance of the passive film/electrolyte interface. The relative permittivity of the films was estimated as about 44. The number concentration of donors (ND) in the films was found to decrease with E f (i.e., with increasing film thickness). A flat band potential value of -0.72 V was also obtained from Mott-Schottky plots.Utilizando-se a espectroscopia de impedância eletroquímica, foram estudadas as propriedades elétricas e semicondutoras de filmes anódicos passivos formados potenciostaticamente (1 V ≤ E f ≤ 5 V vs. ecs) sobre eletrodos de nióbio policristalino em soluções aquosas de H3PO4 0,5 mol/L (pH 1,3), a temperatura ambiente. Os dados foram analisados com uma função de transferência usando uma rotina de ajuste não-linear, supondo que a resistência do filme está acoplada em série com a impedância faradaica da reação Nb(0) → Nb(V) e estas em paralelo com a capacitância da interface filme/eletrólito. A permissividade relativa dos filmes foi estimada como cerca de 44. Encontrou-se que a concentração em número de doadores (ND) nos filmes decresce com E f (isto é, à medida que a espessura do filme aumenta). A partir de gráficos de Mott-Schottky, também obteve-se um valor de -0,72 V para o potencial de banda plana.

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“…Thus the processes represented by peaks P A and P C correspond to a redox pair, which becomes more irreversible with cycling or with increasing potential scan rate. The growing distance between anodic and cathodic peaks may be related with the ageing processes of the film 22 , which dehydrates, getting less conductive and rendering its reduction and further reoxidation more difficult. The increase of the intensity of these peaks with the progressive cicling is a probable consequence of increasing the active area of the electrode, due to higher rugosity of the surface, resulting from the dissolution processes.…”

Section: Resultsmentioning

confidence: 99%

Passivation of iron in solutions containing borate using rotating ring-disc measurements

Martini¹,

Müller²

1999

J. Braz. Chem. Soc.

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Investigou-se o comportamento eletroquímico do ferro em soluções neutras de perclorato de sódio contendo pequenas concentrações de borato de sódio, através da técnica de voltametria cíclica e empregando-se eletrodo rotatório de disco e anel. Nas soluções de perclorato, a passivação do ferro ocorreu após o pico anódico correspondente à zona ativa, no qual foi observada a dissolução de espécies Fe 2+ e Fe 3+. Quando é adicionado borato à solução, tanto a densidade de corrente do pico anódico quanto a quantidade de espécies ativas de ferro solúveis diminuem. Para uma concentração constante de perclorato e borato, o aumento do pH do meio mostrou ser menos efetivo na promoção da passivação do ferro do que a presença de borato. Os resultados demonstraram que a interação entre o íon borato e a superfície eletródica ocorre por adsorção química, de acordo com a isoterma de Langmuir.The electrochemical behavior of iron in neutral solutions of perchlorate and low borate concentrations was investigated using cyclic voltammetry and the rotating ring-disc electrode techniques. In solutions containing just perchlorate, iron passivation was observed at potentials higher than the potential of an anodic peak corresponding to the active range at which the dissolution of Fe 2+ and Fe 3+ species was detected. When borate is added to the solution, this anodic peak decreased as well as the amount of the active soluble species. The increase of pH, keeping the borate and perchlorate concentrations constant, was found to be less effective at promoting iron passivation than the increase of borate concentration. The results demonstrated that the interaction between borate ion and the electrode surface occurs by chemical adsorption according to the Langmuir isotherm.

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The anodic behaviour of niobium—I. The state of the art

Cited by 44 publications

References 36 publications

Semiconducting properties of oxide films formed onto an Nb electrode in NaOH solutions

Semiconducting properties of oxide films formed onto an Nb electrode in NaOH solutions

Electrochemical characterization of thin passive films on Nb electrodes in H3PO4 solutions

Passivation of iron in solutions containing borate using rotating ring-disc measurements

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