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Atlanta, GA, United States

Jiang Y.,South China University of Technology | Jiang Z.-J.,South China University of Technology | Cheng S.,South China University of Technology | Liu M.,South China University of Technology | Liu M.,GA Institute of Technology
Electrochimica Acta | Year: 2014

A 3-dimensional porous graphene material (PGM) has been synthesized using a simple two-step process: hydrothermal reaction and calcination. Hydrothermal reaction of graphene oxide (GO) in the presence of resorcinol and glutaraldehyde leads to covalent grafting of partially reduced GO with glutaraldehyde and the deposition of phenolic resin. Subsequent calcination of the composite consisting of phenolic resin deposited on partially reduced GO in the presence of KOH produces structurally stable, highly porous graphene material with a specific surface area of ∼1,066 ± 2 m2 g-1. When used as an active electrode material in a lithium battery, the PGM exhibits an initial discharge capacity of ∼1,538 mAh g-1, which is significantly higher than those of graphite and other carbonaceous materials reported previously. More importantly, when cycled at higher discharge/charge rates, the PGM-based electrodes still deliver large capacities and excellent cycling performance, demonstrating great potential for high-performance lithium-ion batteries. The attractive electrochemical performance of the PGM is attributed to its unique porous structure with large specific surface area and the presence of more disordered carbon atoms produced by the KOH activation. © 2014 Elsevier Ltd. All rights reserved. Source


Jiang Y.,South China University of Technology | Jiang Z.-J.,South China University of Technology | Yang L.,South China University of Technology | Cheng S.,South China University of Technology | And 2 more authors.
Journal of Materials Chemistry A | Year: 2015

The encapsulation of transition metal oxide (TMO) particles in a graphene hollow shell to form a core-void-shell structure is an attractive way to improve the electrochemical performance of TMO-based electrodes for lithium ion batteries (LIBs). First, the continuous graphene shell may enhance the electrical conductivity of the electrodes and thus facilitate current collection and charge transfer associated with lithium storage. Second, the unique shell structure may suppress the aggregation of the core TMO particles while the void space between the core and shell may accommodate the large volume changes of the core during charge-discharge cycling, which enhances electrode stability against cycling. Third, the high specific surface area may improve the accessibility of active electrode materials to the electrolyte, which could effectively reduce the solid-state diffusion length and thus enhance Li ion transport and rate capability. When tested in a LIB, a Fe3O4@rGO composite electrode exhibits an initial reversible capacity of 1236.6 mA h g-1, which is much higher than that of an electrode based on bare Fe3O4, a physical mixture of Fe3O4 and graphene, or other forms of Fe3O4 reported in the literature. In addition, the cycling performance and rate capacity are also much better. The results clearly demonstrate that this unique electrode architecture is ideally suited for LIBs and other electrochemical energy storage and conversion devices. © The Royal Society of Chemistry 2015. Source


Senesi M.,Georgia Institute of Technology | Ruzzene M.,Georgia Institute of Technology | Ruzzene M.,GA Institute of Technology
Journal of the Acoustical Society of America | Year: 2011

A frequency selective acoustic transducer (FSAT) is proposed for directional sensing of guided waves. The considered FSAT design is characterized by a spiral configuration in wavenumber domain, which leads to a spatial arrangement of the sensing material producing output signals whose dominant frequency component is uniquely associated with the direction of incoming waves. The resulting spiral FSAT can be employed both for directional sensing and generation of guided waves, without relying on phasing and control of a large number of channels. The analytical expression of the shape of the spiral FSAT is obtained through the theoretical formulation for continuously distributed active material as part of a shaped piezoelectric device. Testing is performed by forming a discrete array through the points of the measurement grid of a scanning laser Doppler vibrometer. The discrete array approximates the continuous spiral FSAT geometry, and provides the flexibility to test several configurations. The experimental results demonstrate the strong frequency dependent directionality of the spiral FSAT and suggest its application for frequency selective acoustic sensors, to be employed for the localization of broadband acoustic events, or for the directional generation of Lamb waves for active interrogation of structural health. © 2011 Acoustical Society of America. Source


Grant
Agency: National Science Foundation | Branch: | Program: STTR | Phase: Phase I | Award Amount: 149.99K | Year: 2007

This Small Business Technology Transfer (STTR) Phase I project is directed towards the design, development, and evaluation of a unique ultra-high-speed precision micro-milling machine with a micro-spindle/motor assembly along with in situ metrology sensors. The proposed micro-milling machine is an integral part of an overall micro-manufacturing system. Micro-manufacturing refers to the creation of high-precision three-dimensional (3D) products using a variety of materials and possessing features with sizes ranging from tens of micrometers to a few millimeters. While micro-scale technologies are well established in the semiconductor and microelectronics fields, the same cannot be said for manufacturing products involving complex 3D geometry and high accuracies in non-silicon materials. At the same time, the trends in industrial and military products that demand miniaturization, design flexibility, reduced energy consumption, and high accuracy continue to accelerate -- especially in the medical, biotechnology, telecommunications, and energy fields. Mohawk Innovative Technologies, in partnership with the Georgia Institute of Technology, will develop a unique ultra-high-speed precision micro-milling machine, which will have the capability of being used both in milling (for machining softer metals) and in grinding (for harder metals and ceramics). The principal advantage of the proposed micro-milling machine, besides the state-of-the-art in situ metrology, is the higher precision obtained through the implementation of the ultra-high-speed spindle that will decrease the cutting forces and thus tool vibrations. In Phase II, the proposed ultra-high-speed precision micro-milling machine will be further evaluated and modified to demonstrate the fabrication of complex parts for a variety of industries including defense, aerospace, healthcare and energy. The proposed desktop system will be designed with considerations of affordability, portability and versatility to assist in the development of new businesses and industries, and high value jobs.


Grant
Agency: National Science Foundation | Branch: | Program: STTR | Phase: Phase I | Award Amount: 150.00K | Year: 2007

This Small Business Technology Transfer Research (STTR) Phase I project explores the technical feasibility and commercial potential of an innovative process for converting immiscible polymer wastes into self-reinforced high-performance composites. The process entails creating fibers with sheath/core morphology to self-reinforce the resulting composites and eliminate separation steps. The new recycling protocol will be initially implemented in PP/nylon blends and tested in carpet recycling. The Phase I project addresses the following critical questions: a) Can the new method be used effectively in enhancing the mechanical properties of immiscible polymer blends? and b) What are the major factors that should be considered in scaling up the process prototype? The successful completion of this project will yield a novel enabling processing route for making self-reinforced polymer composites from recycled PP/nylon cost effectively. For the carpet recycling market alone, it holds the promise of reducing more than 4 billion pounds/yr of existing landfilled carpet waste and converting them into value-added products. This will both reduce the carpet waste stream going to the landfill and reduce the demand for the petroleum-based raw materials used in plastics manufacturing. The elimination of complicated sorting and separation steps further implies less energy consumption in manufacturing. The lightness of the resultant products can further enhance fuel efficiency in transportation.

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