Electrochemical impedance spectroscopic studies on niobium anodic dissolution in HF

Rao, Mandula Tirumala; Ramanathan, Surash

doi:10.1007/s10008-017-3634-z

Cited by 14 publications

(16 citation statements)

References 61 publications

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“…1) has a negative slope, as described in detail in the literature. 20 At a more anodic potential in the passive region (300 mV vs. OCP), in addition to the high frequency capacitive loop and low frequency capacitive loop with negative differential resistance, a mid-frequency pseudo-inductive loop is also seen (Fig. 3c).…”

Section: Resultsmentioning

confidence: 95%

“…This active-passive transition behavior is typical of the valve metals Nb, Ta and Ti in HF solutions. 4,18,20,26 In comparison, another valve metal, Zr, exhibits limited passivation and the current decreases only slightly after the transition. 27 The peak potential and current values for the data shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The dissolution of Nb in 500 mM HF was studied using potentiodynamic polarization and EIS, and a four-step mechanism involving two adsorbed species based on reaction mechanism analysis was proposed. 20 It was proposed that chemical and electrochemical dissolution occur in two parallel pathways.…”

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confidence: 99%

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On the Anodic Dissolution of Tantalum and Niobium in Hydrofluoric Acid

Meethal

Rao

Sapra

et al. 2018

J. Electrochem. Soc.

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Ta and Nb are group V valve metals which resist corrosion. Anodic dissolution of Ta and Nb in acidic fluoride media of varying HF concentration is investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. Polarization curves showed a clear active and passive region in all the solutions employed in this study. At a given HF concentration, Nb anodic polarization currents are larger compared to those of Ta. EIS of Ta and Nb exhibited a low frequency capacitive loop in active region, and a low frequency negative differential resistance in the passive region. The surface of Ta and Nb was characterized using XPS, and it reveals the presence of both sub oxide and pentoxide. The electrochemical results could be explained by a four step mechanism involving sub-oxide and pentoxide intermediates. The analysis shows that direct dissolution of sub-oxide occurs via an electrochemical pathway and is facilitated by HF − 2 species and HF in undissociated form. On the other hand, chemical dissolution of pentoxide, which occurs in parallel, is facilitated by the HF species in undissociated form.

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Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

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On the Anodic Dissolution of Tantalum and Niobium in Hydrofluoric Acid

Meethal

Rao

Sapra

et al. 2018

J. Electrochem. Soc.

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“…6b are allowed to hold negative values to represent the inductance. Previously, the dissolution of Ta, Nb, Zr, and Ti in HF has been observed and modeled with inductive loops of EIS data [9,[39][40][41]. The two inductance loops and the mid-frequency capacitance loop obtained (Fig.…”

Section: Electrochemical Impedance Analysis Of Ti and Air-oxidized Timentioning

confidence: 97%

Studies on Corrosion of Titanium and Air-Oxidized Titanium in Fluorinated Nitric Acid

Jayaraj

Padinhateeri

Ningshen

et al. 2019

Trans Indian Inst Met

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Titanium (Ti) is a lustrous transition metal which possesses excellent corrosion resistance in several aggressive environments but is attacked by acidic fluoride media. In this work, the addition of fluoride ion to nitric acid on the corrosion behavior of Ti and air-oxidized Ti was studied. Air oxidation of Ti at 800°C for 5 h resulted in the formation of an intact rutile TiO 2 layer with a thickness of about 35 lm. The corrosion resistance was investigated from the polarization resistance (R P ) values which were obtained from linear polarization and electrochemical impedance spectroscopy (EIS) measurements. A decrease in the R P value of Ti with the addition of fluoride ion in nitric acid was observed, and this indicated the formation of an unstable layer, which resulted in accelerated dissolution. The several order increase in the R P value of air-oxidized Ti in nitric acid containing fluoride ions pointed the improved resistance to corrosion. The diffusivity of species through the air-oxidized TiO 2 layer was estimated from the electrochemical equivalent circuit (EEC) analysis of EIS data. Even though the diffusivity increased by several orders with the addition of fluoride ions, air-oxidized Ti provided better protection against nitric acid containing fluoride ions than Ti. The corrosion rates of Ti and air-oxidized Ti in boiling nitric acid containing fluoride ions were also estimated from weight loss experiments. Even in boiling fluorinated nitric acid, airoxidized Ti provided better corrosion protection, with corrosion rates of about 1000 times less than that of Ti.

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“…The model successfully predicted the major characteristics of the polarization curves, and the results predicted that the chemical and the electrochemical dissolution steps were affected by the concentration of HF − 2 and HF, respectively. Anodic dissolution of other valve metals such as Ti 18,19 and Nb 20 have been characterized using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Compared to the polarization data, which is obtained at the dc limit, electrochemical impedance spectra (EIS) contain more information about the system, as they are acquired in a wide range of frequencies.…”

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confidence: 99%

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

Amrutha

Rao

Ramanathan

2018

J. Electrochem. Soc.

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Anodic dissolution of Zr in 10 mM HF was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. The surface state of the electrode was analyzed using X-ray photon spectroscopy, and the surface morphology was characterized using atomic force microscopy. EIS data acquired at multiple dc potentials were subjected to mechanistic analysis. Reaction mechanism analysis approach reveals that at least four intermediates are required to describe the observed results. The intermediates are likely to be Zr sub-oxides, oxyfluorides and ZrO 2 . The proposed mechanism successfully predicts the major features observed in polarization and impedance spectra. At low overpotentials, the fractional surface coverage of Zr 3+ species is higher than that of Zr 4+ species, and the electrochemical dissolution rate is higher than the chemical dissolution rate. As the overpotential increases, the surface is covered with Zr 4+ species and chemical dissolution rate becomes comparable to electrochemical dissolution rate. Although the surface is covered with Zr 4+ species at higher overpotentials, significant chemical and electrochemical dissolution processes continue to occur and hence Zr is not protected in acidic fluoride media under anodic conditions. © The Author Zirconium and alloys containing Zr are extensively used in the nuclear power industry as fuel cladding agents, in chemical industries as an alloying component, and in biomedical implants.1-4 The wide acceptance of this metal and its alloys is due to their superior mechanical strength, and high resistance toward corrosion, and H 2 embrittlement.5-8 These properties are due to the formation of a stable, protective passive film of ZrO 2 .9-11 Although Zr exhibits excellent corrosion resistance in most of the harsh environments, it readily dissolves in acidic fluoride media. 6,7,12,13 Earlier scientific reports on Zr dissolution are mostly based on conventional techniques, such as weight loss measurements, 14 measurement of volume of H 2 gas evolved, 7 and steady-state polarization techniques.15 Prono et al. 16 have analyzed the polarization of Zr in 0.12 M NaF + 7 M HNO 3 and proposed a seven-step mechanism comprising three competitive paths to describe the dissolution. This analysis was limited to the modeling of polarization data obtained at a single concentration. In our previous work, Zr anodic dissolution mechanism in the acidic fluoride medium was studied using the mechanistic analysis of current potential polarization data in various HF solutions.17 A mechanism containing two adsorbed intermediates and two dissolution steps, shown in Eq. 1, was proposed. The model successfully predicted the major characteristics of the polarization curves, and the results predicted that the chemical and the electrochemical dissolution steps were affected by the concentration of HF − 2 and HF, respectively. Anodic dissolution of other valve metals such as Ti 18,19 and Nb 20 have been characterized using potentiodynamic polarization and electrochemical imped...

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Electrochemical impedance spectroscopic studies on niobium anodic dissolution in HF

Cited by 14 publications

References 61 publications

On the Anodic Dissolution of Tantalum and Niobium in Hydrofluoric Acid

On the Anodic Dissolution of Tantalum and Niobium in Hydrofluoric Acid

Studies on Corrosion of Titanium and Air-Oxidized Titanium in Fluorinated Nitric Acid

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

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