Alessandra Beni

Flow microcapillary plasma mass spectrometry-based investigation of new Al–Cr–Fe complex metallic alloy passivation

Al-Cr-Fe complex metallic alloys are new intermetallic phases with low surface energy, low friction, and high corrosion resistance down to very low pH values (0-2). Flow microcapillary plasma mass spectrometry under potentiostatic control was used to characterize the dynamic aspect of passivation of an Al-Cr-Fe gamma phase in acidic electrolytes, allowing a better insight on the parameters inducing chemical stability at the oxyhydroxide-solution interface. In sulfuric acid pH 0, low element dissolution rates (in the µg cm(-2) range after 60 min) evidenced the passive state of the Al-Cr-Fe gamma phase with a preferential over-stoichiometric dissolution of Al and Fe cations. Longer air-aging was found to be beneficial for stabilizing the passive film. In chloride-containing electrolytes, ten times higher Al dissolution rates were detected at open-circuit potential (OCP), indicating that the spontaneously formed passive film becomes unstable. However, electrochemical polarization at low passive potentials induces electrical field generated oxide film modification, increasing chemical stability at the oxyhydroxide-solution interface. In the high potential passive region, localized attack is initiated with subsequent active metal dissolution.

Real space crystallography of a complex metallic alloy: high-angle annular dark-field scanning transmission electron microscopy of o-Al4(Cr,Fe)

High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) has been performed along the low-index zone axes of the o-Al4(Cr,Fe) complex metallic alloy to obtain a real-space representation of the crystal structure and to elucidate the materials inherent structural disorder. By comparing experiments with multislice STEM simulations, the model previously suggested by X-ray diffraction is further refined to provide a new set of positions and occupancies for the transition metal atoms. Pmnb is suggested as the new space group for the o-Al4(Cr,Fe) phase. A nonperiodic layer-type modulation, averaged out in bulk diffraction methods, is detected, corroborating the need for complementing bulk diffraction analysis with real-space imaging to derive the true crystal structure of Al4(Cr,Fe).

Meeting Report: Exploratory Workshop on Soft X-rays and Electrochemical Energy Storage and Converters

From June 3–5, 2013, the Swiss Federal Laboratories for Materials Science and Technology (EMPA) and the Swiss Light Source held an international workshop on soft X-rays and electrochemical energy storage and converters at EMPA in Dübendorf, Switzerland. A total of 30 scientists from Europe, India, Korea, and the Americas presented state-of-the-art soft X-ray and electron spectroscopy methodologies, some of which combined operando or in-situ experiments with electroanalytical methods employing synchrotron radiation.