Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

Abstract

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...

Investigation of Acetic Acid Effect on Carbon Steel Corrosion in CO2–H2S Medium: Mechanistic Reaction Pathway and Kinetics

“…Energy-dispersive spectroscopy (EDS) measurements also confirm the presence of sulfur, oxygen, and carbon species on the surface at all acetic acid concentrations (results are not shown here). A similar approach is reported in the literature. ,, It is also noted that the solubility of ferrous acetate is higher than that of other ferrous-based corrosion products; thus, one might not expect the presence of an acetate layer on the carbon steel surface. Here, Fe ad 1 + and Fe ad 3 2+ correspond to the sulfides of iron, and similarly, Fe ad 2 + and Fe ad 4 2+ correspond to the carbonates/oxides of iron.…”

“…The reaction pathway of the anodic dissolution process could be retrieved from the EIS data via the reaction mechanism analysis approach . The dissolution mechanism of Fe in various corrosive media is investigated using the RMA approach. − In the present work, the following multistep mechanism, which involves four intermediate adsorbate species, is proposed to describe the impedance patterns obtained from EIS measurements. where Fe ad 1 + , Fe ad 2 + , Fe ad 3 2+ , and Fe ad 4 2+ represent species of different oxidation states (+1 and +2) adsorbed on the carbon steel surface, whose steady-state surface coverage values are given by θ 1 , θ 2 , θ 3 , and θ 4 , respectively. As the system contains CO 2 as well as H 2 S, the formation of both FeCO 3 and FeS is thermodynamically feasible.…”

“…A similar approach is reported in the literature. 27,28,32 It is also noted that the solubility of ferrous acetate is higher than that of other ferrous-based corrosion products; thus, one might not expect the presence of an acetate layer on the carbon steel surface. Here, Fe was tested with acquired EIS data, the data simulated from the suggested mechanism match well with the EIS experimental data.…”

Kinetics of carbon steel dissolution in ammonium chloride solution containing sodium thiosulfate

“…Thus, the following four‐step mechanism (Mechanism 2) with two intermediate adsorbates and of same charge (+2) was considered. Recently, Amrutha et al also employed the same approach to describe the Zr dissolution in HF medium …”

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

“…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.…”