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O'Grady W.E.,U.S. Navy | Roeper D.F.,EXCET Incorporated | Natishan P.M.,U.S. Navy
Journal of Physical Chemistry C | Year: 2011

We generated molecular simulations of Cl - interacting at different sites in aluminum oxide models and carried out FEFF8 calculations to obtain the local l-projected density of states (LDOS) spectra. These are compared to our earlier experimental X-ray absorption near-edge structure (XANES) data in order to study the interactions of chloride ions with the passive oxide film on aluminum as a function of electrochemical potential at the Cl K edge. This led to a number of new insights in the mechanism of the breakdown of the passive film in chloride solutions. Importantly, we show the chloride first attacks the hydroxyl components of the aluminum oxide, penetrates the oxide film, and finally attacks the metal surface. © 2011 American Chemical Society.

Garsany Y.,Excet Inc. | Singer I.L.,U.S. Navy | Swider-Lyons K.E.,U.S. Navy
Journal of Electroanalytical Chemistry | Year: 2011

Evaluation of Pt/Vulcan carbon (Pt/VC) electrocatalysts for the oxygen reduction reaction (ORR) is dependent on the quality of the electrocatalyst- coated thin film electrode used for rotating disk electrode (RDE) methodology. Traditionally, films are made by dropping a catalyst ink on an inverted, stationary glassy-carbon electrode, and then air-drying it, but the resulting films are irreproducible and often have poor quality. We present a drying procedure for making reproducible, smooth thin electrocatalyst films, by rotating the electrocatalyst ink on the glassy-carbon electrode substrate at 700 rpm while it is drying. The differences between the morphologies of films made with the rotational versus the stationary drying methods are illustrated with 3D optical profilometry and scanning electron microscopy. Film thickness and uniformity was determined by optical interferometric profilometry for films prepared with both drying methods. The stationary drying method leads to a non-uniform film with thicknesses varying from 0.042 μm in the center of the disk electrode to 4.5 μm towards the edge of the electrode. The rotational drying method yields a uniform film thickness of about 0.8 μm over the entire electrode surface. The difference in these film morphologies is quantified for the ORR electrocatalytic activity of a 19.7% and 40% Pt/VC electrocatalyst. The platinum mass and area-specific activities for the ORR are on average 72% and 56% higher for electrocatalyst made by this rotational drying method, compared to those made from the stationary drying method. © 2011 Elsevier B.V. All rights reserved.

Natishan P.M.,U.S. Navy | O'Grady W.E.,Excet Inc.
Journal of the Electrochemical Society | Year: 2014

Metals and alloys such as aluminum (Al), stainless steels, and nickel-based alloys exhibit corrosion resistance in a wide range of environments due to the presence of protective, passive oxides. However, in environments that contain aggressive anions such as chloride, Cl?, the passive film becomes unstable and degrades locally causing film breakdown and pitting corrosion. A number of theories describing the initiation of pitting corrosion have been postulated and discussed but to date there is no consensus on the mechanism of breakdown. Since all current mechanisms require Cl- interactions for oxide film breakdown in Cl- containing environments, the question is what is the nature of the interaction of aggressive anions such as Cl- with the passive film, adsorption and/or absorption, leading to pitting? This communication focuses on the interaction of Cl- with the passive oxide film on pure aluminum by reviewing and summarizing the available experimental data concerning Cl- interactions. It should also be noted that the observations for Cl- interactions with Al reviewed and summarized herein might not be applicable to all metals and alloys. © The Author(s) 2014. Published by ECS. All rights reserved. Published by ECS.

Lall A.A.,Excet Inc. | Terray A.,U.S. Navy | Hart S.J.,U.S. Navy
Optics Express | Year: 2010

Laser separation of particles is achieved using forces resulting from the momentum exchange between particles and photons constituting the laser radiation. Particles can experience different optical forces depending on their size and/or optical properties, such as refractive index. Thus, particles can move at different speeds in the presence of an optical force, leading to spatial separations. In this paper, we present a theoretical analysis on laser separation of non-absorbing aerosol particles moving at speeds (1-10 cm/sec) which are several orders of magnitude greater than typical particle speeds used in previous studies in liquid medium. The calculations are presented for particle deflection by a loosely focused Gaussian 1064 nm laser, which simultaneously holds and deflects particles entrained in flow perpendicular to their direction of travel. The gradient force holds the particles against the viscous drag for a short period of time. The scattering force simultaneously pushes the particles, perpendicular to the flow, during this period. Our calculations show particle deflections of over 2500 μm for 15 μm aerosol particles, and a separation of over 1500 μm between 5 μm and 10 μm particles when the laser is operated at 10W. We show that a separation of about 421 μm can be achieved between two particles of the same size (10 μm) but having a refractive index difference of 0.1. Density based separations are also possible. Two 10 μm particles with a density difference of 600 kg/m3 can be separated by 193 μm. Examples are shown for separation distances between polystyrene, poly(methylmethacrylate), silica and water particles. These large laser guided deflections represent a novel achievement for optical separation in the gas phase. © 2010 Optical Society of America.

Garsany Y.,EXCET INC | Ge J.,University of Hawaii at Manoa | St-Pierre J.,University of Hawaii at Manoa | Rocheleau R.,University of Hawaii at Manoa | Swider-Lyons K.E.,U.S. Navy
Journal of the Electrochemical Society | Year: 2014

Rotating disk electrode (RDE) voltammetry has been touted as a simple means for benchmarking the oxygen reduction reaction (ORR) activity of platinum-based electrocatalysts in proton exchange membrane fuel cells. In practice, the RDE methodology has been highly variable across laboratories, with up to 20% differences in values for the Pt electrochemical surface area and 10x differences in mass activity and area-specific activity reported from the same standard Pt/C electrocatalyst.We confirm that the same ORR activities can be replicated across laboratories when a detailed experimental protocol is followed. From our work and others', we conclude that dominant factors in the RDE experimental protocol include the ink formulation, electrocatalyst film quality and the electrochemical procedures. We make a recommendation for procedures for the reproducible characterization of Pt/C commercial catalysts, present simple metrics for researchers to use for a quick check of their results, and also propose new benchmark values for two Pt/C standards. © 2014 The Electrochemical Society. All rights reserved.

Permenter M.G.,Excet Inc. | Lewis J.A.,U.S. Army | Jackson D.A.,U.S. Army
PLoS ONE | Year: 2011

Many heavy metals, including nickel (Ni), cadmium (Cd), and chromium (Cr) are toxic industrial chemicals with an exposure risk in both occupational and environmental settings that may cause harmful outcomes. While these substances are known to produce adverse health effects leading to disease or health problems, the detailed mechanisms remain unclear. To elucidate the processes involved in the toxicity of nickel, cadmium, and chromium at the molecular level and to perform a comparative analysis, H4-II-E-C3 rat liver-derived cell lines were treated with soluble salts of each metal using concentrations derived from viability assays, and gene expression patterns were determined with DNA microarrays. We identified both common and unique biological responses to exposure to the three metals. Nickel, cadmium, chromium all induced oxidative stress with both similar and unique genes and pathways responding to this stress. Although all three metals are known to be genotoxic, evidence for DNA damage in our study only exists in response to chromium. Nickel induced a hypoxic response as well as inducing genes involved in chromatin structure, perhaps by replacing iron in key proteins. Cadmium distinctly perturbed genes related to endoplasmic reticulum stress and invoked the unfolded protein response leading to apoptosis. With these studies, we have completed the first gene expression comparative analysis of nickel, cadmium, and chromium in H4-II-E-C3 cells.

Lewis J.A.,U.S. Army | Gehman E.A.,Mitre Corporation | Baer C.E.,Excet Inc. | Jackson D.A.,U.S. Army
BMC Genomics | Year: 2013

Background: The principal toxicity of acute organophosphate (OP) pesticide poisoning is the disruption of neurotransmission through inhibition of acetylcholinesterase (AChE). However, other mechanisms leading to persistent effects and neurodegeneration remain controversial and difficult to detect. Because Caenorhabditis elegans is relatively resistant to OP lethality-particularly through the inhibition of AChE-studies in this nematode provide an opportunity to observe alterations in global gene expression following OP exposure that cannot be readily observed in less resistant organisms. Results: We exposed cultures of worms in axenic, defined medium to dichlorvos under three exposure protocols. In the first, worms were exposed continuously throughout the experiment. In the second and third, the worms were exposed for either 2 or 8 h, the dichlorvos was washed out of the culture, and the worms were allowed to recover. We then analyzed gene expression using whole genome microarrays from RNA obtained from worms sampled at multiple time points throughout the exposure. The worms showed a time-dependent increase in the expression of genes involved in stress responses. Early in the exposure, the predominant effect was on metabolic processes, while at later times, an immune-like response and cellular repair mechanisms dominated the expression pattern. Following removal of dichlorvos, the gene expression in the worms appeared to relatively rapidly return to steady-state levels. Conclusion: The changes in gene expression observed in the worms following exposure to dichlorvos point towards two potential mechanisms of toxicity: inhibition of AChE and mitochondrial disruption. © 2013 Lewis et al.; licensee BioMed Central Ltd.

Garsany Y.,Excet Inc. | Garsany Y.,U.S. Navy | Dutta S.,Dynalene Inc. | Swider-Lyons K.E.,U.S. Navy
Journal of Power Sources | Year: 2012

We use cyclic and rotating disk electrode voltammetry to study glycol-based coolant formulations to show that individual constituents have either negligible or significant poisoning effects on the nanoscale Pt/carbon catalysts used in proton exchange membrane fuel cells. The base fluid in all these coolants is glycol (1, 3 propanediol), commercially available in a BioGlycol coolant formulation with an ethoxylated nonylphenol surfactant, and azole- and polyol-based non-ionic corrosion inhibitors. Exposure of a Pt/Vulcan carbon electrode to glycol-water or glycol-water-surfactant mixtures causes the loss of Pt electrochemical surface area (ECSA), but the Pt ECSA is fully recovered in clean electrolyte. Only mixtures with the azole corrosion inhibitor cause irreversible losses to the Pt ECSA and oxygen reduction reaction (ORR) activity. The Pt ECSA and ORR activity can only be recovered to within 70% of its initial values after aggressive voltammetric cycling to 1.50 V after azole poisoning. When poisoned with a glycol mixture containing the polyol corrosion inhibitor instead, the Pt ECSA and ORR activity is completely recovered by exposure to a clean electrolyte. The results suggest that prior to incorporation in a fuel cell, voltammetric evaluation of the constituents of coolant formulations is worthwhile. © 2012 Elsevier B.V.

Nilles J.M.,Excet Inc. | Connell T.R.,Excet Inc. | Durst H.D.,Edgewood Chemical Biological Center
Analyst | Year: 2010

We explore a thermal separation technique for use with Direct Analysis in Real Time (DART). By applying gas temperature ramping, we are able to disburse a mixture of compounds in time. The three components were selected to create a challenging mixture that would not likely be discerned solely using exact mass capabilities. While the thermal separation technique is of low resolution, it preserves the inherent rapid, non-contact, ambient characteristics of the ion source. © 2010 The Royal Society of Chemistry.

Garsany Y.,EXCET INC | Baturina O.A.,U.S. Navy | Swider-Lyons K.E.,U.S. Navy | Kocha S.S.,Nissan Motor Co.
Analytical Chemistry | Year: 2010

A tutorial is provided for methods to accurately and reproducibly determine the activity of Pt-based electrocatalysts for the oxygen reduction reaction in proton exchange membrane fuel cells and other applications.The impact of various experimental parameters on electrocatalyst activity is demonstrated, and explicit experimental procedures and measurement protocols are given for comparison of electrocatalyst activity to fuel cell standards. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.). © 2010 American Chemical Society.

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