J.J. Noël

Localized Dissolution of Millscale-Covered Pipeline Steel Surfaces

Abstract Electrochemical impedance spectroscopy, corrosion potential measurements, and surface analysis by scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDX) and Raman spectroscopy were used to investigate the localized dissolution of millscale-covered pipeline steel surfaces. The porous millscale originally present on the pipe surface exerts an influence on the corrosion of the pipeline and may contribute to the eventual onset of stress corrosion cracking (SCC). Three regions in the corrosion potential-time plot were observed after exposure to an aqueous environment, corresponding to the initial attempts at breakdown of the millscale, coupling of the dissolution of the underlying steel to reductive dissolution of the millscale, and active corrosion of the steel at the base of pores in the film supported by water reduction either on the metal or on the millscale surface. The corrosion rate increases as the dissolved carbon dioxide (CO2) concentration increases. Changes in the solu...

The Effects of Simulated Fission Products in the Reduction of Hydrogen Peroxide on Simulated Nuclear Fuel Electrodes

The electrochemical reduction of hydrogen peroxide (H 2 O 2 ) has been studied on a series of simulated nuclear fuel (SIMFUEL) materials with different amounts of simulated fission products. Steady-state polarization measurements under diffusion-compensated conditions show that the reaction proceeds with a weak dependence on applied potential and fractional reaction orders with respect to H 2 O 2 . A mechanism for H 2 O 2 reduction on SIMFUEL materials is proposed to explain these features. It is found that the activity of the material for the H 2 O 2 reduction reaction increases with the doping level. This increase can be attributed to noble metal particles present in the SIMFUEL. This enhanced reactivity is most apparent at low overpotentials, where H 2 O 2 reduction proceeds significantly faster on the noble metal particles than on the UO 2+x lattice.

Effect of Sulfide on Carbon Steel Corrosion in Anaerobic Near-Neutral pH Saline Solutions

Severe corrosion damage may occur when gas transmission pipelines are exposed, at disbonded coating locations, to trapped waters containing sulfide. This scenario has been investigated in long-term...

An Experimental Basis for a Mixed Potential Model for Nuclear Fuel Corrosion within a Failed Waste Container

A mixed-potential model to predict the corrosion behaviour of nuclear fuel inside a failed carbon steel-lined copper waste container in a granitic repository is briefly described. A number of experiments underway to improve the mechanistic form of the model and to provide the necessary input data are discussed. A primary emphasis is placed on the consequences of the accumulation of corrosion product deposits on the fuel surface on the development of aggressive local chemistries, the cathodic reduction of H 2 O 2 and potential for scavenging of H 2 O 2 by the products of carbon steel corrosion (in particular H 2 ).

Anodic Oxide Growth and Hydrogen Absorption on Zr in Neutral Aqueous Solution: A Comparison to Ti

Anodization and subsequent cathodic polarization of a thin-film sample of Zr were studied with in situ neutron reflectometry and electrochemical impedance spectroscopy (EIS). The results show the originally 485 A thick sputter-deposited film generally behaved similar to a bulk electrode in neutral Na 2 SO 4 solution. The anodic oxide, grown by applying 0.5 V potential steps, contained a significant amount of hydrogen in one form or another. The observed anodization ratio was somewhat higher than the literature value determined by coulometry, while the Pilling Bedworth ratio was in good agreement with published data. Oxide layer thickening, accelerated immediately after an anodic polarization was applied, persisted for many hours, suggesting the migration of ions continues for an extended time. The oxide cracked when the applied potential reached 1.5 V and its thickness reached ∼100 A causing loss of passivation. Surprisingly, the EIS behavior of the sample with cracked oxide could still be well represented by a single time-constant equivalent circuit consisting of a capacitor and a leakage resistor, albeit with much lower resistance. This indicates that the cracked and intact regions of the electrode behave essentially independent as parallel electrodes. The proposed modified equivalent circuit can explain a number of other unusual observations, including those seen under cathodic polarization.

The Influence of Environmental Conditions and Passive Film Properties on the MIC of Engineered Barriers in the Yucca Mountain Repository

A combination of gamma radiation fields, the absence of moisture, and the high temperatures on the drip shield (DS) and waste package (WP) should combine to suspend microbial activity on the DS/WP surfaces for many tens of thousands of years. This lack of microbial activity, coupled with the corrosion resistance of the titanium Grade7 (Ti-7 drip shield) and the Alloy-22 (waste package) materials make microbially induced corrosion (MIC) of these engineered barrier materials extremely unlikely.

Influence of Noble Metal Particles on Redox Reactions on Uranium Dioxide Surfaces

The influence of rare-earth doping and noble metal inclusions (ε-particles) on H2O2 and O2 reduction and H2 oxidation on UO2 surfaces has been studied electrochemically. These reactions are important in determining the corrosion behaviour of nuclear fuel inside failed waste containers under permanent waste disposal conditions. Experiments were conducted on SIMFUEL electrodes doped with various amounts of non-radioactive elements in proportions appropriate to simulate the chemical effects of in-reactor irradiation. The results show that ε-particles catalyze all of these reactions. These results indicate that ε-particles can act as catalytic anodes and cathodes depending on the redox conditions prevailing within a failed container.

The Influence of Temperature on the Passive Film Properties of ASTM Grade-7 Titanium

The influence of temperature on the passivity of highly corrosion-resistant alloys is often critical to their industrial performance. We have been studying the effects of temperature (up to ~150°C) on Ti alloys, such as ASTM Grade-7 (Ti-7), in neutral saline solutions, using open circuit potential measurements and electrochemical impedance spectroscopy (EIS). As the temperature increased, up to ~80°C, the oxide film resistance increased and the capacitance decreased, consistent with thickening of, and defect annealing within, the passive film. At higher temperatures, the passive film displayed decreasing resistance and increasing capacitance, and a second time constant developed at low frequencies, indicating the introduction of pores or cracks into the oxide. Thus, this thin oxide film ruptures under certain conditions, leading to a temporary loss of corrosion protection. Such oxide breakdown and repair yields potential transients (“electrochemical noise”), which contain information on the electrochemical behaviour of the material.

Influence of Temperature on the Corrosion of Uranium Dioxide Nuclear Fuel

The anodic dissolution of UO{sub 2} has been studied at 60 deg. C and the results compared to previous observations at 22 deg. C. The rate of oxidation / dissolution was determined electrochemically at constant potentials in the range -500 mV to 500 mV (vs. SCE). The composition of the electrochemically oxidized surface was determined by X-Ray Photoelectron Spectroscopy (XPS). The onset of oxidation (UO{sub 2} {yields} UO{sub 2+x}) occurred at approximately the same potential (-400 mV) at both temperatures. However, the conversion of U{sub V} to U{sub VI}, and hence to soluble UO{sub 2}{sup 2+}, was accelerated by temperature. This acceleration of dissolution caused the development of acidity at localized sites on the fuel surface at lower (less oxidizing) potentials ({>=} 100 mV) at 60 deg. C than at 22 deg. C ({>=} 350 mV)