Kinetics of anodic dissolution of Zr in acidic fluoride media

Amrutha, M. S.; Ramanathan, Surash

doi:10.1007/s10008-016-3342-0

Cited by 9 publications

(19 citation statements)

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“…Recently, the zirconium dissolution kinetics in solutions containing different concentrations of HF was determined by modeling the polarization data measured in multiple HF concentrations. 27 It is important to note that more than one model can easily provide excellent model fits when data from only pure HF solutions are analyzed, since the individual species concentrations are correlated. However, when results of Ti dissolving in solutions containing HF as well as KF or H 2 SO 4 are included in the analysis, the predictor correlations are broken and many mechanisms would fail to predict the trends correctly, enabling identification of the appropriate mechanism.…”

Section: H190mentioning

confidence: 99%

Effect of HF Concentration on Anodic Dissolution of Titanium

Amrutha

Fasmin

Ramanathan

2017

J. Electrochem. Soc.

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Anodic dissolution of Ti metal in varying concentrations of hydrofluoric acid (10-1000 mM HF) was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. Polarization curves obtained at all concentrations of HF solution showed that current initially rises with potential, and decreases at higher potentials. Complex plane plot of the impedance spectra of Ti dissolution in 25 and 50 mM HF solutions exhibited three capacitive loops in the active region and a capacitive behavior with negative resistance in the passive region. The surface was characterized using X-ray photoelectron spectroscopy. A four step mechanism with chemical and electrochemical dissolution steps was employed to model Ti dissolution. The analysis shows that the simulated results match the polarization trends satisfactorily in all the solutions investigated. The model predicts that HF − 2 and remaining HF are the species that influence chemical and electrochemical dissolution steps respectively. The estimates of surface coverage values of the adsorbed species showed that with increasing over potential, the metal surface was progressively covered with oxide film, while an increase in nominal HF concentration leads to a decrease in fractional surface coverage. Titanium is used as engineering material in medical implants, aerospace applications, and in industrial applications by virtue of its low density, high strength and high corrosion resistance.1 Due to the presence of a tenacious passive oxide layer on its surface, Ti is highly corrosion resistant in most of the harsh chemical environments. 2,3However, the oxide layer readily dissolves in acidic fluoride medium. The anodic dissolution phenomena of Ti in fluoride media is important not only in corrosion but also in several technologies and industrial applications such as pickling of Ti, 4 manufacture of Ti based automobile parts, 5 and formation of self-organized TiO 2 nano tubes. 2,3,6Ti dissolution in fluoride medium has been studied extensively, and its dissolution in acidic fluoride media depends mainly on the concentrations of various species formed by HF dissolution, pH of the solution and temperature.3,6-8 Straumanis and Chen measured the volume of hydrogen produced during Ti dissolution in HF and proposed that the reaction order is 0.66 when the HF concentration is below 0.2 N and unity when it is more than 0.2 N.9 Ti dissolution in a solution of 0.1 N HF + 1 M HCl was measured at various temperatures, and the order was reported to be 0.76 while the activation energy was 6.9 kcal/mol. 10 HF, in combination with HNO 3 and a few other additives such as acetic acid, H 3 PO 4 , dodecyl benzene sulfonic acid, carbamide, sodium benzoate or sodium nitrate, have been used for chemical milling of In Ti pickling, addition of nitric acid is used to prevent hydride formation at the metal surface, which can lead to hydrogen embrittlement. 16 Ti dissolution in HF + HNO 3 solution is modeled using a mechanistic approach with Ti 3+ and TiO 2 as intermediate species. 1...

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Section: H190mentioning

confidence: 99%

Effect of HF Concentration on Anodic Dissolution of Titanium

Amrutha

Fasmin

Ramanathan

2017

J. Electrochem. Soc.

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“…Zr metal shows unusual behavior in the passive region compared to the other valve metals. 5,17,29 However, since the current decreases at least slightly with potential, this region is termed as passive. The data shows significant fluctuations in the current values in the passive region, which was found to be the case in all repeat runs.…”

Section: Resultsmentioning

confidence: 99%

“…These fluctuations are likely due to continuous oxide formation and destruction. 17,29 The polarization data along with impedance spectra, were subjected to mechanistic modeling, as described in the later part of this paper.…”

Section: Resultsmentioning

confidence: 99%

“…These findings are comparable to the surface coverage plots obtained for 10 mM HF solution using the mechanism shown in Eq. 1, 17 which did not distinguish between the various forms of Zr oxides and oxy fluorides.…”

mentioning

confidence: 83%

“…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.…”

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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

Rao

Ramanathan

2017

J Solid State Electrochem

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Kinetics of anodic dissolution of Zr in acidic fluoride media

Cited by 9 publications

References 50 publications

Effect of HF Concentration on Anodic Dissolution of Titanium

Effect of HF Concentration on Anodic Dissolution of Titanium

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

Electrochemical impedance spectroscopic studies on niobium anodic dissolution in HF

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