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Southfield, MI, United States

Song G.-L.,General Motors | Liu M.,Meda Engineering and Technical Services
Corrosion Science | Year: 2013

The corrosion of aluminum alloy AlSi8Cu3Fe(Zn) in ethanol and ethanol solutions containing 10. vol.% water and 10. vol.% acetic acid, respectively, was investigated by means of electrochemical impedance spectroscopy (EIS), polarization curve, immersion, optical microscopy, scanning electron microscopy and element mapping. The Al alloy in the ethanol and its solutions exhibited a capacitive loop in the measured Nyquist EIS spectra at high frequencies, which can be attributed to the ethanol's dielectric response. Addition of 10. vol.% acetic acid increased the ethanol corrosivity more significantly than the same amount of water addition. The Al-Si-Cu-Mg precipitated zones in the alloy were susceptible to corrosion attack due to the micro-galvanic effect by the Cu-containing precipitates. © 2013 Elsevier Ltd. Source

Poirier E.,Meda Engineering and Technical Services | Dailly A.,General Motors
Physical Chemistry Chemical Physics | Year: 2012

The description of experimental gas adsorption data in terms of an accurate model is key to understand the adsorption mechanism and its limits. As a basic feature such a model should predict correctly the conditions under which saturation occurs. However, in the absence of bulk condensation properties for a supercritical adsorbate this matter remains open to discussions. In this study, the decreasing region of excess hydrogen adsorption isotherms measured down to 50 K is used to determine the adsorbed phase volume, density and pressure corresponding to saturation. The experimental method developed for these key measurements addresses the challenges of very low temperature adsorption measurements at high pressure. Therefore, the modifications specially made to a cryostat used in conjunction with a Sievert apparatus to reach high temperature stability (±10 mK) down to 40 K are presented. The approach is implemented on the novel nanoporous materials UMCM-1 and NOTT-112 over 50-77 K and 0-40 bar. The derived hydrogen saturation properties are found to be consistent with a Dubinin-Astakhov model. Importantly, the measured adsorbed hydrogen phase volume also compares well with the pore volume obtained from Ar porosimetry. The found saturation properties provide a physical basis to calculate consistent absolute adsorption isotherms and enthalpies, and to project the ultimate adsorption capacity of a conceptual material with a maximized specific surface area. The present findings provide additional evidence that the common view on supercritical adsorption, in which it is assumed that no liquid is formed and that the only possible mechanism involves monolayer coverage, does not hold in many nanoporous materials. © 2012 the Owner Societies. Source

Song G.-L.,General Motors | Liu M.,Meda Engineering and Technical Services
Corrosion Science | Year: 2012

This paper presents an investigation on the effect of substrate pretreatment on the corrosion of Electroless E-coating coated AZ31 Mg alloy. Immersion, salt spray, cyclic exposure, AC electrochemical impedance spectroscopy (EIS), XPS analysis and XRD examination results show that the coating protection performance can be significantly improved if the substrate surface is properly dehydrated at a high temperature after wet-cleaning. A simple " wet. +. dry" process involving acid-etching. +. dehydration can be a practical surface preparation technique for the Electroless E-coating on Mg alloys in industry. A surface dehydration model is proposed to explain the coating formation and protection performance. © 2012 Elsevier Ltd. Source

Song G.-L.,General Motors | Mishra R.,General Motors | Xu Z.,Meda Engineering and Technical Services
Electrochemistry Communications | Year: 2010

Rolled AZ31 Mg alloy, which has great potential applications in the automobile industry, is detected to be highly crystallographic textured. Its rolling surface (RS), mainly consisting of (0001) crystallographic planes, is first time measured to be more electrochemically stable and corrosion resistant than its cross-section surface (CS) mainly composed of crystallographic planes (10̄10) and (11̄20) in 5 wt.% NaCl. The different corrosion performances of these crystallographic planes can be ascribed to their different anodic and cathodic reaction activities. A theoretical analysis confirms that the different electrochemical activities of RS and CS surfaces originate from the different surface energy levels of the (0001), (10̄10) and (11̄20) crystallographic planes. © 2010 Elsevier B.V. All rights reserved. Source

Lewis L.H.,Northeastern University | Pinkerton F.E.,General Motors | Bordeaux N.,Northeastern University | Mubarok A.,University of Massachusetts Amherst | And 4 more authors.
IEEE Magnetics Letters | Year: 2014

Meteorites, likely the oldest source of magnetic material known to mankind, are attracting renewed interest in the science and engineering community. Worldwide focus is on tetrataenite, a uniaxial ferromagnetic compound with the tetragonal L10 crystal structure comprised of nominally equiatomic Fe-Ni that is found naturally in meteorites subjected to extraordinarily slow cooling rates, as low as 0.3 K per million years. Here, the favorable permanent magnetic properties of bulk tetrataenite derived from the meteorite NWA 6259 are quantified. The measured magnetization approaches that of Nd-Fe-B (1.42 T) and is coupled with substantial anisotropy (1.0-1.3 MJ/m3) that implies the prospect for realization of technologically useful coercivity. A highly robust temperature dependence of the technical magnetic properties at an elevated temperature (20-200 °C) is confirmed, with a measured temperature coefficient of coercivity of -0.005%/K, over one hundred times smaller than that of Nd-Fe-B in the same temperature range. These results quantify the extrinsic magnetic behavior of chemically ordered tetrataenite and are technologically and industrially significant in the current context of global supply chain limitations of rare-earth metals required for present-day high-performance permanent magnets that enable operation of a myriad of advanced devices and machines. © 2014 IEEE. Source

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