Electrochemical Impedance Spectroscopic Study of Passive Zirconium

Abstract

The development of deterministic models for predicting the accumulation of corrosion damage to zirconium and Zircaloys in pressurized water reactor ͑PWR͒ coolant environments requires the acquisition of values for various model parameters. In the present work, the point defect model ͑PDM͒ was further developed to account for the properties of passive films comprising hydride barrier layers and porous oxide outer layers that form on zirconium and Zircaloys in high-temperature, hydrogenated aqueous solutions. The model parameter values were extracted from electrochemical impedance spectroscopic data for zirconium in hydrogenated, borate buffer solution ͓0.1 M B͑OH͒ 3 + 0.001 M LiOH, pH 6.94͔ at 250°C by optimization. The results indicate that the corrosion resistance of zirconium in high-temperature, hydrogenated aqueous solutions is dominated by the outer layer, as was found to be the case for nonhydrogenated solutions where a defective oxide barrier layer forms. The impedance model based on the PDM provides a good account of the growth of the bi-layer passive films described above, and the extracted model parameter values might be used, for example, for predicting the accumulation of general corrosion damage to Zircaloy fuel cladding in PWR operating environments.

Influences of structure and composition on the photoelectrochemical behaviour of anodic films on Zr and Zr–20at.%Ti

“…For 100 V anodic film on Ti-80 at.%Zr, according to the composition depth profile obtained by RBS [40], x Ti = 0.2 and x Zr = 0.8 can be inserted in Eq. (7). Concerning the electronegativity values, we assume and χ Ti = 1.656, obtained as the arithmetic mean between the electronegativity obtained by using Eq.…”

“…These features make ZrO 2 very useful in a wide range of applications in the ceramic engineering [1], as oxygen sensor in fuel cell [2] and as catalytic support medium [3]. Zirconia is one of the most radiation-resistant ceramics currently known [4,5] and therefore has a particular importance in the nuclear industry, where zirconium-based alloys are frequently employed due to their excellent mechanical properties and good corrosion resistance [6,7]. Moreover, in the last years ZrO 2 has been proposed as a gate dielectric material in metaloxide semiconductor devices [8,9].…”

Kinetic parameters of the oxidation of zirconium alloys in simulated WWER water – Effect of KOH content

“…In recent years, electrochemical impedance spectroscopy (EIS) has been extensively used to characterise the oxide films on zirconium alloys [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. However, mainly ex situ measurements in aqueous electrolytes at room temperature, or experiments in a gaseous atmosphere following oxidation in high-temperature water have been reported.…”

“…Very recently, a kinetic approach to the anodic behaviour of pure Zr in both deaerated and hydrogenated boric acid-lithium hydroxide solutions has been proposed on the basis of the point defect model (PDM) and validated against EIS data obtained at 250°C [22,23]. On the other hand, some of us have adapted the mixed-conduction model (MCM) for oxide films [24,25] to quantitatively describe the in situ impedance data for several Zircaloy 2-type alloys in simulated boiling water reactor (BWR) coolant at 300°C [20].…”

The electrochemistry of carbon steel in simulated concrete pore water in boom clay repository environments

“…The model developed in this work to interpret the impedance data is based upon the Point Defect Model (PDM) and incorporates elements of our previous work [3][4][5][6], Figure 1. Briefly, we have taken the total differential of the expression for the passive current density under non-steady state conditions in terms of the independent variables [voltage, barrier layer thickness, and concentration of metal interstitials at the barrier layer/solution (outer layer) interface (see Figure 2)] and we assume that these independent variables and the passive current density undergo sinusoidal variations with time.…”