Zsolt Kerner

Impedance of rough capacitive electrodes: The role of surface disorder

The interfacial impedance of solid electrodes in the absence of Faradaic reactions usually deviates from purely capacitive behaviour; this effect is enhanced on rough electrodes. We present a qualitative experiment showing that capacitance dispersion on solid electrodes is due to surface disorder (i.e. heterogeneities on the atomic scale) rather than roughness (i.e. geometric irregularities much larger than those on the atomic scale).

Measurement of adsorption rates of anions on Au(111) electrodes by impedance spectroscopy

We have measured impedance spectra on Au(111) electrode in aqueous perchlorate solutions containing specifically adsorbing anions (SO42−, Cl−, Br− and I−) of about 10−4 M concentrations at potentials where the dominant electrode process is the adsorption of the above anions. Accordingly, the impedance spectra have been analyzed in terms of the Frumkin–Melik-Gaykazyan adsorption impedance theory. With SO42−, Cl− we found the adsorption rates to be immeasurably high; with Br− and I− the apparent rate coefficients could be determined. For the halide anions this quantity increases in the order of Cl−>Br−>I−; and rapidly decreases with increasing electrode potential and coverage. We attribute this change to the decrease of the occupancy related hindrance factor overcompensates the increase of the rate coefficient.

In situ electrochemical impedance spectroscopy of Zr-1%Nb under VVER primary circuit conditions

Oxide layers were grown on tubular samples of Zr–1%Nb under conditions simulating those in VVER-type pressurised water reactors, viz. in near-neutral borate solutions in an autoclave at 290 °C. These samples were investigated using electrochemical impedance spectroscopy which was found to be suitable to follow in situ the corrosion process. A –CPEox∥Rox– element was used to characterise the oxide layer on Zr–1%Nb. Both the CPEox coefficient, σox, and the parallel resistance, Rox, were found to be thickness dependent. The layer thickness, however, can only be calculated after a calibration procedure. The temperature dependence of the CPEox element was also found to be anomalous while the temperature dependence of Rox indicates that the oxide layer has semiconductor properties. The relaxation time – defined as (Roxσox)1/α – was found to be quasi-independent of oxidation time and temperature; thus it is characteristic to the oxide layer on Zr–1%Nb.

Oxide layers of Zr–1% Nb under PWR primary circuit conditions

Abstract Oxide layers were grown on Zr–1% Nb under conditions simulating those in VVER-type pressurised water reactors (PWRs), viz. in borate solutions in an autoclave at 290°C. The layers were characterised by various methods: their respective thickness values were determined by weight gain measurements, Rutherford backscattering (RBS), nuclear reaction analysis (NRA) and scanning electron microscopy (SEM); the electrical properties were tested by electrochemical impedance spectroscopy. The results show that the oxide layer on Zr–1% Nb is homogeneous and somewhat thicker than that on Zircaloy-4.

Investigation of Local Corrosion Degradation Developed on a Pipeline System in Service Period

Corrosion degradation was observed in a nuclear power plant spent fuel cooling system. A systematic and comprehensive investigation program was developed which was negatively influenced by the limit of sampling (contaminated material). Corrosion tests, mechanical and microstructural investigations were carried out and also microbiological effect was examined. Major contributors to the degradation were identified.

Corrosion Resistance of Nanosized Silicon Carbide-Rich Composite Coatings Produced by Noble Gas Ion Mixing

Ion beam mixing has been used to produce a silicon carbide (SiC)-rich nanolayer for protective coating. Different C/Si/C/Si/C/Si(substrate) multilayer structures (with individual layer thicknesses falling in the range of 10-20 nm) have been irradiated by Ar+ and Xe+ ions at room temperature in the energy and fluence ranges of 40-120 keV and 1-6 × 1016 ion/cm2, respectively. The effects of ion irradiation, including the in-depth distribution of the SiC produced, was determined by Auger electron spectroscopy depth profiling. The thickness of the SiC-rich region was only some nanometers, and it could be tailored by changing the layer structure and the ion irradiation conditions. The corrosion resistance of the layers was investigated by potentiodynamic electrochemical test in 4 M KOH solution. The measured corrosion resistance of the SiC-rich layers was orders of magnitude better than that of pure silicon, and a correlation was found between the corrosion current density and the effective areal density of the SiC.