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 Î© and was attributed to the significant carbon incorporation into the Ni substrate. © 2014 American Chemical Society.
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.
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.
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.
Yin Y.,University of Miami |
Zhou J.,University of Miami |
Mansour A.N.,United Materials and Systems |
Zhou X.,University of Miami
Journal of Power Sources | Year: 2011
NaI/I2 mediators and activated carbon were added into poly(ethylene oxide) (PEO)/lithium aluminate (LiAlO2) electrolyte to fabricate composite electrodes. All solid-state supercapacitors were fabricated using the as prepared composite electrodes and a Nafion 117 membrane as a separator. Cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge measurements were conducted to evaluate the electrochemical properties of the supercapacitors. With the addition of NaI/I2 mediators, the specific capacitance increased by 27 folds up to 150 F g-1. The specific capacitance increased with increases in the concentration of mediators in the electrodes. The addition of mediators also reduced the electrode resistance and rendered a higher electron transfer rate between mediator and mediator. The stability of the all-solid-state supercapacitor was tested over 2000 charge/discharge cycles. © 2011 Elsevier B.V. All rights reserved.
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.
Park C.-S.,United Materials and Systems |
Priya S.,United Materials and Systems
Journal of the American Ceramic Society | Year: 2011
We report the structural, electrical, and magnetoelectric (ME) properties of cofired ME laminate composites synthesized using tape-casting approach. Compositions corresponding to 0.2Pb(Zn1/3Nb2/3)-0. 8Pb(Zr0.5Ti0.5)O3 [PZNT] and (Ni 0.6Cu0.2Zn0.2) Fe2O3 [NCZF] were used as piezoelectric and magnetostrictive phases, respectively. In order to reduce the sintering temperature of the ferrite layer, NZF was modified with Cu and thereafter the laminate composite was successfully sintered at 930°C. The interface between PZNT and NCZF was found to exhibit strong bonding with no structural defects, which was correlated with cross diffusion of ions. The laminate composite was found to exhibit the ME coefficient of 82 mVÂ·(cmÂ·Oe)-1 at Hdc=67 Oe and was able to detect a small DC magnetic field of 1 μT under Hac=1 Oe at 1 kHz. This sensitivity was attributed to the effectiveness of elastic coupling in the laminate structure. Fabrication of cofired laminate composites with high magnetic field sensitivity will lead to their wide-scale application. © 2010 The American Ceramic Society.
Swait T.J.,United Materials and Systems |
Jones F.R.,United Materials and Systems |
Hayes S.A.,United Materials and Systems
Composites Science and Technology | Year: 2012
A practical structural health monitoring system based on measuring changes in the electrical resistance of a carbon fibre composite structure is presented. Electrical contact with the fibres is provided by flexible printed circuit boards which are interleaved with the carbon fibre plies during the lamination of the composite. The resistance between opposite pairs of contacts was measured before and after an impact load which caused barely visible impact damage (BVID) in the panel. It was found that even low levels of impact damage produced measurable changes in resistance in the vicinity of the damage. Therefore was demonstrated that electrical resistance measurements are a practical means of locating BVID. Various parameters were studied in order to better understand the mechanisms involved and optimise the system for improved sensitivity and accuracy. The location of the contacts in the through thickness direction, the spacing and orientation of the contacts and the residual thermal stress of the laminate were all investigated and recommendations made. A structural health monitoring system for composites based on electrical resistance has several important potential benefits over acoustic, ultrasonic or optical methods; it adds little parasitic mass, causes no reduction in mechanical integrity, can be carried out on structures either in or out of service conditions and is very simple in concept, implementation and data interpretation. © 2012 Elsevier Ltd.
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.94K | Year: 2011
The primary purpose of this proposal is to develop and demonstrate a new technology for manufacturing an ultra-low-cost precision optical telescope mirror which can be scaled up for use in very large UV/optical and/or infrared telescopes. This proposal will demonstrate prototype manufacturing of a precision mirror in the 0.25 to 0.5 meter class, with a specific scale up roadmap to 1 to 2+ meter class system which can be rated for space flight. Material behavior, processing parameters, optical performance, and mounting techniques will be demonstrated. The potential for scale-up will be addressed from a processing and infrastructure point of view. The Phase 1 deliverable will be a 0.25 meter proof-of-concept mirror. Its optical performance assessment and all data on the processing and properties of its substrate material will be determined.UMS proposes to demonstrate the feasibility of forming a polymer derived 'bulk ceramic' mirror substrate with a 'fully dense' optical surface. This mirror substrate with fully dense surface, will be optically figured, polished and coated with a reflective metal system typically used in a commercial terrestrial telescope.
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.93K | Year: 2009
The primary purpose of this proposal is to develop and demonstrate a new technology for manufacturing an ultra-low-cost precision optical telescope mirror which can be scaled up for use in very large UV/optical and/or infrared telescopes. The Phase 1 deliverable will be a 0.25 meter precision mirror. Its optical performance assessment and all data on the processing and properties of its substrate material will be determined. The unique manufacturing processes employed allow for integration of mirror and support features, significantly increasing both cost reduction and quality improvement potential.