On the Anodic Dissolution of Tantalum and Niobium in Hydrofluoric Acid

Meethal, Ranjith Punathil; Rao, Mandula Tirumala; Sapra, Sanjeev; Suni, Ian Ivar; Ramanathan, Surash

doi:10.1149/2.0691805jes

Cited by 15 publications

(7 citation statements)

References 56 publications

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“…Bojinov et al 31 used the surface charge approach to describe the dissolution of Nb in acidic fluoride medium. The anodic dissolution mechanism of Ti, Zr, Nb and Ta in hydrofluoric acid has been reported earlier [32][33][34][35][36][37][38] where a four step mechanism with two adsorbed intermediate species and two dissolution pathways were proposed. In summary, the corrosion rate of Ti and Zr and several alloys of valve metals in conc.…”

mentioning

confidence: 69%

“…All the four valve metals exhibit passivation at sufficiently large anodic potentials in HF solutions. 32,33,35,36,38,42 Since the Tafel extrapolation cannot be used in the passive region, the polarization data above the transition potential (peak in the current potential plot) in the anodic region is not considered for the Tafel analysis. In the cathodic region, the polarization data up to an over-potential of −150 mV was used for Ti and Zr, and up to −200 mV was used for Nb and Ta.…”

Section: Methodsmentioning

confidence: 99%

“…To break the predictor correlation, experiments were also conducted in HF solutions with addition of H 2 SO 4 or KF. 32,33,35,38,42 Surface characterization.-The surfaces of the bare metal and corroded samples used in the weight loss experiments, under the least and the most corrosive conditions as described in the results and discussion, were characterized using SEM and optical surface profile 3D images. The SEM examination was performed in Inspect F50 (FEI), which is a field emission gun based high resolution scanning electron microscope.…”

Section: = -Dmentioning

confidence: 99%

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Studies on Group IV and V Valve Metal Corrosion in Acidic Fluoride Media

Rao¹,

Meethal²,

Amrutha³

et al. 2020

J. Electrochem. Soc.

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Dissolution rates of Ti, Zr, Nb and Ta in acidic fluoride media of different concentrations at various temperatures were measured by weight loss method, and were complemented by electrochemical measurements at room temperatures. A mathematical model to estimate the corrosion rate of these four valve metals based on the overall reaction mechanism for metal dissolution as well as H2 evolution is developed from the weight loss experiments. Valve metal dissolution process occurs through two independent pathways assisted by (HF2)− and equilibrium HF species. Except Ti, the dissolution of other valve metals studied are not significantly influenced by the H2 evolution reaction. Among the four metals evaluated, Nb offers the best corrosion resistance at high temperature and high HF concentration. The corrosion resistance of all four valve metals estimated from linear polarization, electrochemical spectroscopy and Tafel extrapolation in various concentrations of solutions match well. For Ti, dissolution rates calculated from Tafel extrapolation were lower than those based on weight loss experiments, while for Zr, Nb and Ta, they were mostly higher than those based on weight loss experiments.

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mentioning

confidence: 69%

Section: Methodsmentioning

confidence: 99%

Section: = -Dmentioning

confidence: 99%

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Studies on Group IV and V Valve Metal Corrosion in Acidic Fluoride Media

Rao¹,

Meethal²,

Amrutha³

et al. 2020

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: 96%

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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“…On the other hand, EIS deals with materials in which ionic conductivity dominates over electronic conductivity [2]. To date, this technique has been applied in a wide range of applications, such as supercapacitors [3][4][5], corrosion [6][7][8][9][10][11], solar cells [12][13][14], electrolysers [15][16][17][18], electrochemical sensors [19][20][21], batteries [22][23][24][25], and fuel cells [26][27][28][29], amongst others. Today, it is considered as one of the fundamental electrochemical techniques [30].…”

Section: Introductionmentioning

confidence: 99%

Optimization of the Perturbation Amplitude for EIS Measurements Using a Total Harmonic Distortion Based Method

Giner-Sanz

Ortega

Pérez-Herranz

2018

J. Electrochem. Soc.

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Ohm's generalized law defines the concept of impedance. This law, and thus the definition itself, are only valid if the system fulfills the linearity condition. However, electrochemical systems are typically highly nonlinear. Consequently, the linearity condition can only be achieved in these systems if a low perturbation amplitude is used for performing EIS measurements. Nevertheless, the use of low amplitude perturbations leads to low signal-to-noise ratios, which result in high measurement errors. The concept of optimum amplitude arises from this tradeoff: the perturbation has to have an amplitude big enough in order to minimize the measurement errors (i.e. maximize the SNR), but at the same time, the perturbation has to have an amplitude small enough to avoid the generation of significant nonlinear effects that would distort the measured EIS spectra. In a previous work, a linearity assessment quantitative method based on the total harmonic distortion parameter was developed. In this work, the aforementioned THD method was applied for the perturbation amplitude selection for EIS measurements in a highly nonlinear model system: the cathodic electrode of an alkaline water electrolyser. The THD method successfully obtained the optimum amplitudes both, for a constant amplitude strategy and for a frequency dependent strategy. The THD method also allowed to obtain the noise structure and to quantify the nonlinear effects. This method is slightly superior to the ℘ method, a method based on the harmonic analysis of the output signal that was developed in earlier works.

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On the Anodic Dissolution of Tantalum and Niobium in Hydrofluoric Acid

Cited by 15 publications

References 56 publications

Studies on Group IV and V Valve Metal Corrosion in Acidic Fluoride Media

Studies on Group IV and V Valve Metal Corrosion in Acidic Fluoride Media

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

Optimization of the Perturbation Amplitude for EIS Measurements Using a Total Harmonic Distortion Based Method

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