We have developed a cleaning procedure for aluminum alloys for effective minimization of surface-adsorbed sub-micrometer particles and nonvolatile residue. The procedure consists of a phosphoric acid etch followed by an alkaline detergent wash. To better understand the mechanism whereby this procedure reduces surface contaminants, we characterized the aluminum surface as a function of cleaning step using surface enhanced Raman spectroscopy (SERS). SERS indicates that phosphoric acid etching re-establishes a surface oxide of different characteristics, including deposition of phosphate and increased hydration, while the subsequent alkaline detergent wash appears to remove the phosphate and modify the new surface oxide, possibly leading to a more compact surface oxide. We also studied the zeta potential of <5 microm pure aluminum and aluminum alloy 6061-T6 particles to determine how surface electrostatics may be affected during the cleaning process. The particles show a decrease in the magnitude of their zeta potential in the presence of detergent, and this effect is most pronounced for particles that have been etched with phosphoric acid.

Dated: Phys. Rev. B in press as of April 15, 2002) Temperature dependent extended x-ray absorption fine structure (EXAFS) spectra were measured for a 3.3 at% Ga stabilized Pu alloy over the range T = 20 -300 K. EXAFS data were acquired at both the Ga K-edge and the Pu LIII-edge. Curve-fits were performed to the first shell interactions to obtain pair-distance distribution widths, σ, as a function of temperature. The temperature dependence of σ(T ) was accurately modeled using a correlated-Debye model for the lattice vibrational properties, suggesting Debye-like behavior in this material. Using this formalism, we obtain pair-specific correlated-Debye temperatures, ΘcD, of 110.7 ±1.7 K and 202.6 ±3.7 K, for the Pu-Pu and Ga-Pu pairs, respectively. The result for the Pu-ΘcD value compares well with previous vibrational studies on δ-Pu. In addition, our results represent the first unambiguous determination of Ga-specific vibrational properties in PuGa alloys, i.e, ΘcD for the Ga-Pu pair. Because the Debye temperature can be related to a measure of the lattice stiffness, these results indicate the Ga-Pu bonds are significantly stronger than the Pu-Pu bonds. This effect has important implications for lattice stabilization mechanisms in these alloys.

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Chromia-forming ferritic stainless steel (FSS) is a highly promising interconnect material for application in solid oxide fuel cells. In this study, initial oxidation of chromium oxides was performed at 500–800 °C to understand the evolution of materials at an early stage. The structural variations in oxide scales were analyzed through scanning electron microscopy, energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffractometry (XRD), laser confocal microscopy (LSCM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Surface electrochemical properties were investigated through electrochemical impedance spectroscopy to understand how the heat treatment temperature affected surface impedance. Treatment temperatures higher than 700 °C facilitate the diffusion of Cr and Mn, thus allowing ferritic spinels to form on the surface and leading to high electrical conductivity.