Application of a constant cathodic current to an electrode in an alkaline Cu(II) lactate solution results in oscillation of the electrode potential during the electrodeposition of copper/cuprous oxide layered nanostructures. The electrochemical quartz crystal microbalance (EQCM) is used for in situ phase analysis measurements of the nanoscale layers and the results are compared with bulk XRD measurements. The EQCM is also used to estimate the layer thicknesses and overall modulation wavelength of the nanostructures. We propose that Cu2O is deposited during the positive spikes in electrode potential, while a composite of Cu and Cu2O is deposited during the more negative plateau region of the oscillation. The modulation wavelength calculated from the EQCM is in good agreement with that observed with scanning electron microscopy. The EQCM is shown to be a useful tool for estimating layer thicknesses and phase compositions for layers that are too thin to be examined by other instrumental techniques.

Layered nanostructures of copper metal and cuprous oxide are electrodeposited from alkaline solutions of Cu(II) lactate at room temperature. No subsequent heat treatment is necessary to effect crystallization. The electrode potential spontaneously oscillates during constant-current deposition. At a fixed current density the oscillation period decreases as either the pH or temperature is increased. The oscillations are periodic in stirred solution, but show period doubling and evidence of quasi-periodic or chaotic behavior in unstirred solution. The phase composition and resistivity of the films can be controlled by varying the applied current density. The resistivity of the films can be varied over ten orders of magnitude. Scanning electron microscopy shows that the films are layered.

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The five-metal epsilon particle represents an important component with respect to the corrosion of spent nuclear fuel as it is the principal host for 99Tc. This radionuclide has a high solubility in oxidizing environments (as TcO4 -), a half-life of 213,000 years, and has been proposed as a monitor for the corrosion rate of spent fuel. As such, an understanding of the corrosion processes affecting epsilon particles may have important implications on our ability to accurately assess radionuclide release rates from spent nuclear fuel.Non-radioactive metal powders were mixed in an atomic percent ratio of 40% Mo, 30% Ru, 15% Pd, 10% Re, and 5% Rh (Re used as a surrogate for Tc), a composition that simulates epsilon particles in spent reactor fuel [1,2]. The powders were electric arc-melted in the presence of an Ar-purged atmosphere. Scanning electron microscopy images of the as-cast samples denote a primary sample heterogeneity, with two distinct zones, each composed of a mixture of very fine-grained Mo-, Mo-Ru-Re, and Mo-Ru-Pd rich crystals. Results from vapor hydration tests (200°C) for time periods up to 35 days indicate the formation of Mo- and Reenriched alteration phases. Phase growth was enhanced when air was periodically replenished in the test vessels suggesting that oxide and/or hydroxide alteration phases may play a role in the corrosion process. MCC-1 tests (90°C) were conducted for time periods up to 182 days in leachant solutions that were prepared with either a) deionized water or b) deionized water acidified with nitric acid to a pH of 3.0. Solutions from the deionized water tests progressively decreased in pH with increasing reaction time (5.5 to 4.0), while the pH values remained at a near-constant value of 3.0 in the acidified solutions. Solution results indicate a preferential release of Mo followed by Re. Normalized Re/Mo release ratios varied from 0.20 to 0.86, and increased as a function of reaction time and acidity. Release of the platinum group metals (Pd, Rh, and Ru) was relatively insignificant in comparison to Mo and Re.

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