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Song G.-L.,United Materials and Systems
Corrosion Science | Year: 2010

Many practical galvanic corrosion problems can be simplified into a one-dimensional mathematical equation. In this study, theoretical expressions for galvanic potentials and currents of one-dimensional systems are deduced and some critical parameters involved in the potential and current equations are systematically discussed. The developed analytical approach is then applied to some practical galvanic corrosion cases, such as a steel-Al joint exposed to bio-fuel E85, a galvanic couple separated by a passive spacer and a scratched organic coating. It is demonstrated that the analytical approach can examine the reliability of a computer modeled galvanic corrosion process and help understand the mechanism behind the computer modeled galvanic corrosion behavior. © 2009 Elsevier Ltd. All rights reserved. Source

Sassin M.B.,U.S. Navy | Mansour A.N.,United Materials and Systems | Pettigrew K.A.,Nova Research Inc. | Rolison D.R.,U.S. Navy | Long J.W.,U.S. Navy
ACS Nano | Year: 2010

We describe a simple self-limiting electroless deposition process whereby conformai, nanoscale iron oxide (Fe0x,) coatings are generated at the interior and exterior surfaces of macroscopically thick (∼90 μm) carbon nanofoam paper substrates via redox reaction with aqueous K2Fe0 4. The resulting Fe0x,-carbon nanofoams are characterized as device-ready electrode structures for aqueous electrochemical capacitors and they demonstrate a 3-to-7 fold increase in charge-storage capacity relative to the native carbon nanofoam when cycled in a mild aqueous electrolyte (2.5 M Li2SO4), yielding mass-, volume-, and footprint-normalized capacitances of 84 F g-1,121Fcm-3, and 0.85 F cm -2, respectively, even at modest Fe0x,loadings (27 wt %). The additional charge-storage capacity arises from faradaic pseudocapacitance of the Fe0x, coating, delivering specific capacitance >300 Fg -1 normalized to the content of Fe0x, as FeOOH, as verified by electrochemical measurements and in situ X-ray absorption spectroscopy. The additional capacitance is electrochemically addressable within tens of seconds, a time scale of relevance for high-rate electrochemical charge storage. We also demonstrate that the addition of borate to buffer the Li 2S04 electrolyte effectively suppresses the electrochemical dissolution of the Fe0x, coating, resulting in <20% capacitance fade over 1000 consecutive cycles. © 2010 American Chemical Society. Source

Cai M.,College of William and Mary | Outlaw R.A.,College of William and Mary | Quinlan R.A.,College of William and Mary | Quinlan R.A.,United Materials and Systems | And 4 more authors.
ACS Nano | Year: 2014

The growth and electrical characteristics of vertically oriented graphene nanosheets grown by radio frequency plasma-enhanced chemical vapor deposition from C2H2 feedstock on nickel substrates and used as electrodes in symmetric electric double layer capacitors (EDLC) are presented. The nanosheets exhibited 2.7 times faster growth rate and much greater specific capacitance for a given growth time than CH4 synthesized films. Raman spectra showed that the intensity ratio of the D band to G band versus temperature initially decreased to a minimum value of 0.45 at a growth temperature of 750°C, but increased rapidly with further temperature increase (1.15 at 850°C). The AC specific capacitance at 120 Hz of these EDLC devices increased in a linear fashion with growth temperature, up to 265 μF/cm2 (2 μm high film, 850°C with 10 min growth). These devices exhibited ultrafast frequency response: the frequency response at -45°phase angle reached over 20 kHz. Consistent with the increase in D band to G band ratio, the morphology of the films became less vertical, less crystalline, and disordered at substrate temperatures of 800°C and above. This deterioration in morphology resulted in an increase in graphene surface area and defect density, which, in turn, contributed to the increased capacitance, as well as a slight decrease in frequency response. The low equivalent series resistance varied from 0.07 to 0.08 Ω and was attributed to the significant carbon incorporation into the Ni substrate. © 2014 American Chemical Society. Source

Di Pisa C.,Queen Mary, University of London | Aliabadi M.H.,Imperial College London | Young A.,United Materials and Systems
International Journal for Numerical Methods in Engineering | Year: 2012

In this paper, the dual boundary element method is combined with a multiregion formulation to simulate plate assembly undergoing large deflection. The incremental load approach is used to treat the geometrical nonlinearity, and radial basis functions are used to approximate the derivatives of the large deflection terms. The dual reciprocity method is used to transfer all the domain integrals to the boundary. Once the solution at the boundary is obtained for the assembly, a J -integral for large deflection is implemented to extract the fracture parameters. © 2011 John Wiley & Sons, Ltd. Source

Sharp S.L.,Orbital Sciences Corp | Paine J.S.N.,United Materials and Systems | Blotter J.D.,Brigham Young University
Journal of Intelligent Material Systems and Structures | Year: 2010

A new geometrically unique ultrasonic motor (USM) was designed, prototyped, and tested. USMs operate by vibrating a drive tip in an elliptical motion while in periodic contact with a driven surface. Piezoelectric elements are used to create the elliptical motions and are driven at near resonance frequencies to create the needed displacements for the motor to operate. The motor in this article consists of an arched frame, a center ground, and two piezoelectric elements connected to the center ground. Several finite element models were developed to design the motor and to predict performance. The models predicted a linear motor capable of pushing up to 5 N and a maximum speed of 0.4 m/s. A prototype frame was built out of tool steel and run against an oxide ceramic plate. The prototype motor achieved a maximum speed of 55.6 mm/s and a push force of 0.348 N at a preload of 6 N. The prototype frames steady-state displacements were approximately 20% of the expected output from the finite element models. Reasons for these discrepancies are discussed and investigated. © The Author(s), 2010. Source

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