Sample records for air diffusion cathode

  1. Air cathode structure manufacture

    DOEpatents

    Momyer, William R. (Palo Alto, CA); Littauer, Ernest L. (Los Altos Hills, CA)

    1985-01-01

    An improved air cathode structure for use in primary batteries and the like. The cathode structure includes a matrix active layer, a current collector grid on one face of the matrix active layer, and a porous, nonelectrically conductive separator on the opposite face of the matrix active layer, the collector grid and separator being permanently bonded to the matrix active layer. The separator has a preselected porosity providing low IR losses and high resistance to air flow through the matrix active layer to maintain high bubble pressure during operation of the battery. In the illustrated embodiment, the separator was formed of porous polypropylene. A thin hydrophobic film is provided, in the preferred embodiment, on the current collecting metal grid.

  2. Degradation characteristics of air cathode in zinc air fuel cells

    NASA Astrophysics Data System (ADS)

    Ma, Ze; Pei, Pucheng; Wang, Keliang; Wang, Xizhong; Xu, Huachi; Liu, Yongfeng; peng, Guanlin

    2015-01-01

    The zinc air fuel cell (ZAFC) is a promising candidate for electrical energy storage and electric vehicle propulsion. However, its limited durability has become a major obstacle for its successful commercialization. In this study, 2-cell stacks, 25 cm cells and three-electrode half-cells are constructed to experimentally investigate the degradation characteristics of the air cathode. The results of electrochemical tests reveal that the peak power density for the 25 cm2 cell with a new air cathode is 454 mW cm-2, which is twice as the value of the used air cathode. The electrochemical impedance analysis shows that both the charge transfer resistance and the mass transfer resistance of the used air cathodes have increased, suggesting that the catalyst surface area and gas diffusion coefficient have decreased significantly. Additionally, the microstructure and morphology of the catalytic layer (CL) and gas diffusion layer (GDL) are characterized by scanning electron microscopes (SEM). SEM results confirm that the micropores in CL and GDL of the used air cathode are seriously clogged, and many catalyst particles are lost. Therefore, the performance degradation is mainly due to the clogging of micropores and loss of catalyst particles. Furthermore, hypotheses of degradation mechanism and mitigation strategies for GDL and CL are discussed briefly.

  3. Air humidity and water pressure effects on the performance of air-cathode microbial fuel cell cathodes

    NASA Astrophysics Data System (ADS)

    Ahn, Yongtae; Zhang, Fang; Logan, Bruce E.

    2014-02-01

    To better understand how air cathode performance is affected by air humidification, microbial fuel cells were operated under different humidity conditions or water pressure conditions. Maximum power density decreased from 113030mWm-2 with dry air to 98080mWm-2 with water-saturated air. When the cathode was exposed to higher water pressures by placing the cathode in a horizontal position, with the cathode oriented so it was on the reactor bottom, power was reduced for both with dry (1030130mWm-2) and water-saturated (390190mWm-2) air. Decreased performance was partly due to water flooding of the catalyst, which would hinder oxygen diffusion to the catalyst. However, drying used cathodes did not improve performance in electrochemical tests. Soaking the cathode in a weak acid solution, but not deionized water, mostly restored performance (96060mWm-2), suggesting that there was salt precipitation in the cathode that was enhanced by higher relative humidity or water pressure. These results showed that cathode performance could be adversely affected by both flooding and the subsequent salt precipitation, and therefore control of air humidity and water pressure may need to be considered for long-term MFC operation.

  4. A dual pore carbon aerogel based air cathode for a highly rechargeable lithium-air battery

    NASA Astrophysics Data System (ADS)

    Wang, Fang; Xu, Yang-Hai; Luo, Zhong-Kuan; Pang, Yan; Wu, Qi-Xing; Liang, Chun-Sheng; Chen, Jing; Liu, Dong; Zhang, Xiang-hua

    2014-12-01

    Cathode structure plays a vital role in lithium-air battery for that it can provide space for discharged products accommodation and free path for oxygen, e- and Li+ transport. However, pore blockage, cathode passivation and degradation all result in low discharge rates and poor cycling capability. To get rid of these predicaments, a novel highly conductive dual pore carbon aerogel based air cathode is fabricated to construct a lithium-air battery, which exhibits 18 to 525 cycles in the LiTFSI/sulfolane electrolyte at a current density varying from 1.00mAcm-2 to 0.05mAcm-2, accompanied by a high energy efficiency of 78.32%. We postulate that the essence lies in that the as-prepared air cathode inventively create a suitable tri-phase boundary reaction zone, facilitating oxygen and Li+ diffusion in two independant pore channels, thus realizing a relative higher discharge rate capability, lower pore blockage and cathode passivation. Further, pore structure, carbon loading, rate capability, discharge depth and the air's effect are exploited and coordinated, targeting for a high power and reversible lithium-air battery. Such nano-porous carbon aerogel air cathode of novel dual pore structure and material design is expected to be an attractive alternative for lithium-air batteries and other lithium based batteries.

  5. Oxide diffusion in innovative SOFC cathode materials.

    PubMed

    Hu, Y; Thorton, V; Pirovano, C; Capoen, E; Bogicevic, C; Nuns, N; Mamede, A-S; Dezanneau, G; Vannier, R N

    2014-01-01

    Oxide diffusion was studied in two innovative SOFC cathode materials, Ba(2)Co(9)O(14) and Ca(3)Co(4)O(9)+? derivatives. Although oxygen diffusion was confirmed in the promising material Ba(2)Co(9)O(14), it was not possible to derive accurate transport parameters because of an oxidation process at the sample surface which has still to be clarified. In contrast, oxygen diffusion in the well-known Ca(3)Co(4)O(9)+? thermoelectric material was improved when calcium was partly substituted with strontium, likely due to an increase of the volume of the rock salt layers in which the conduction process takes place. Although the diffusion coefficient remains low, interestingly, fast kinetics towards the oxygen molecule dissociation reaction were shown with surface exchange coefficients higher than those reported for the best cathode materials in the field. They increased with the strontium content; the Sr atoms potentially play a key role in the mechanism of oxygen molecule dissociation at the solid surface. PMID:25407246

  6. Temporal variations of cathode performance in air-cathode single-chamber microbial fuel cells with different separators

    NASA Astrophysics Data System (ADS)

    Ma, Jinxing; Wang, Zhiwei; Suor, Denis; Liu, Shumeng; Li, Jiaqi; Wu, Zhichao

    2014-12-01

    An ideal separator is essential for efficient power production from air-cathode single-chamber microbial fuel cells (MFCs). In this study, we use different kinds of membranes as separators, including Nafion 117 proton exchange membrane, polyethersulfone and poly(vinylidene fluoride) microfiltration membranes. Temporal variations of cathode performance are monitored during the experiment. Results show that MFCs with microfiltration membranes present higher power output but deterioration is still observed after about 600-h operation. With the utilization of appropriate separators (e.g., polyethersulfone membrane), biofouling, cation fouling and chemical scale fouling of the cathodes are alleviated while reaction fouling seems inevitable. Moreover, it is found that Coulombic efficiency (CE) and energy efficiency (EE) are also related to the cathode performance. Despite relatively high oxygen diffusivity (1.49נ10-5cm2s-1), CE and EE of the MFC with 0.1?m pore-size polyethersulfone membrane can reach 92.8% and 13.7%, respectively, when its average power density registers 403.5mWm-2. This phenomenon might be attributed to the finding that the overall substrate consumption rate due to oxygen reduction and respiration is almost constant in the air-cathode MFCs. Oxygen leakage into the electrolyte can be inhibited due to the efficient oxygen reduction reaction on the surface of the cathode.

  7. Using cathode spacers to minimize reactor size in air cathode microbial fuel cells Qiao Yang a

    E-print Network

    Using cathode spacers to minimize reactor size in air cathode microbial fuel cells Qiao Yang January 2012 Available online 30 January 2012 Keywords: Microbial fuel cell Spacer Oxygen demand Scale up a b s t r a c t Scaling up microbial fuel cells (MFCs) will require more compact reactor designs

  8. High Performance Cathodes for Li-Air Batteries

    SciTech Connect

    Xing, Yangchuan

    2013-08-22

    The overall objective of this project was to develop and fabricate a multifunctional cathode with high activities in acidic electrolytes for the oxygen reduction and evolution reactions for Li-air batteries. It should enable the development of Li-air batteries that operate on hybrid electrolytes, with acidic catholytes in particular. The use of hybrid electrolytes eliminates the problems of lithium reaction with water and of lithium oxide deposition in the cathode with sole organic electrolytes. The use of acid electrolytes can eliminate carbonate formation inside the cathode, making air breathing Li-air batteries viable. The tasks of the project were focused on developing hierarchical cathode structures and bifunctional catalysts. Development and testing of a prototype hybrid Li-air battery were also conducted. We succeeded in developing a hierarchical cathode structure and an effective bifunctional catalyst. We accomplished integrating the cathode with existing anode technologies and made a pouch prototype Li-air battery using sulfuric acid as catholyte. The battery cathodes contain a nanoscale multilayer structure made with carbon nanotubes and nanofibers. The structure was demonstrated to improve battery performance substantially. The bifunctional catalyst developed contains a conductive oxide support with ultra-low loading of platinum and iridium oxides. The work performed in this project has been documented in seven peer reviewed journal publications, five conference presentations, and filing of two U.S. patents. Technical details have been documented in the quarterly reports to DOE during the course of the project.

  9. Battery with modular air cathode and anode cage

    DOEpatents

    Niksa, Marilyn J. (Painesville, OH); Pohto, Gerald R. (Mentor, OH); Lakatos, Leslie K. (Mentor, OH); Wheeler, Douglas J. (Cleveland Heights, OH); Niksa, Andrew J. (Painesville, OH); Schue, Thomas J. (Huntsburg, OH); Turk, Thomas R. (Mentor, OH)

    1988-01-01

    A battery assembly of the consumable metal anode type has now been constructed for ready assembly as well as disassembly. In a non-conductive and at least substantially inert cell body, space is provided for receiving an open-structured, non-consumable anode cage. The cage has an open top for facilitating insertion of an anode. A modular cathode is used, comprising a peripheral current conductor frame clamped about a grid reinforced air cathode in sheet form. The air cathode may be double gridded. The cathode frame can be sealed, during assembly, with electrolyte-resistant-sealant as well as with adhesive. The resulting cathode module can be assembled outside the cell body and readily inserted therein, or can later be easily removed therefrom.

  10. Battery with modular air cathode and anode cage

    DOEpatents

    Niksa, Marilyn J. (Painesville, OH); Pohto, Gerald R. (Mentor, OH); Lakatos, Leslie K. (Mentor, OH); Wheeler, Douglas J. (Cleveland Heights, OH); Niksa, Andrew J. (Painesville, OH); Schue, Thomas J. (Huntsburg, OH)

    1987-01-01

    A battery assembly of the consumable metal anode type has now been constructed for ready assembly as well as disassembly. In a non-conductive and at least substantially inert cell body, space is provided for receiving an open-structured, non-consumable anode cage. The cage has an open top for facilitating insertion of an anode. A modular cathode is used, comprising a peripheral current conductor frame clamped about a grid reinforced air cathode in sheet form. The air cathode may be double gridded. The cathode frame can be sealed, during assembly, with electrolyte-resistant-sealant as well as with adhesive. The resulting cathode module can be assembled outside the cell body and readily inserted therein, or can later be easily removed therefrom.

  11. Lithium AMTEC with gas-diffusion cathode

    SciTech Connect

    Lysenko, G.P. [Moscow Aviation Inst. (Russian Federation)

    1996-12-31

    To determine optimal geometrical parameters of a gas-diffusion electrode for the alkali metal AMTEC, there has been developed a model of such an electrode of regular structure made up by identical electrically conducting spherical particles having contact with the solid electrolyte and each other over circular surfaces. Calculations run using this model allowed to assess the gas-diffusion electrode geometry. Theoretical and experimental performance of sodium AMTEC have been compared which showed their good match. However, sodium solid electrolytes due to decomposition at the operating temperatures rather quickly loses its surface`s properties. Use of modified lithium oxide as a lithium electrolyte proved stable performance of solid electrolyte at the temperatures up to 1,200 K with lithium working fluid.

  12. Electricity Generation Using an Air-Cathode Single Chamber

    E-print Network

    power generation in an air-cathode MFC containing carbon electrodes in the presence and absence/L with the PEM-MFC and 103 mg/L in the MFC without a PEM (1000 resistor). Similar results on the effect power densities in this range will likely require systems that do not contain a polymeric PEM in the MFC

  13. Two types of diffusions at the cathode/electrolyte interface in IT-SOFCs

    SciTech Connect

    Li Zhipeng, E-mail: LI.Zhipeng@nims.go.jp [Global Research Center for Environment and Energy based on Nanomaterials Science, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044 (Japan); Mori, Toshiyuki [Global Research Center for Environment and Energy based on Nanomaterials Science, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044 (Japan); Auchterlonie, Graeme John [Centre for Microscopy and Microanalysis, University of Queensland, St. Lucia, Brisbane, Queensland 4072 (Australia); Zou Jin [Centre for Microscopy and Microanalysis, University of Queensland, St. Lucia, Brisbane, Queensland 4072 (Australia); Division of Materials, University of Queensland, St. Lucia, Brisbane, Queensland 4072 (Australia); Drennan, John [Centre for Microscopy and Microanalysis, University of Queensland, St. Lucia, Brisbane, Queensland 4072 (Australia)

    2011-09-15

    Analytical transmission electron microscopy, in particular with the combination of energy dispersive X-ray spectroscopy (EDX) and electron energy-loss spectroscopy (EELS), has been performed to investigate the microstructure and microchemistry of the interfacial region between the cathode (La{sub 0.6}Sr{sub 0.4}Co{sub 0.8}Fe{sub 0.2}O{sub 3}, LSCF) and the electrolyte (Gd-doped ceria, GDC). Two types of diffusions, mutual diffusion between cathode and electrolyte as well as the diffusion along grain boundaries, have been clarified. These diffusions suggest that the chemical stability of LSCF and GDC are not as good as previously reported. The results are more noteworthy if we take into consideration the fact that such interdiffusions occur even during the sintering process of cell preparation. - Graphical Abstract: Two types of diffusions, the mutual diffusion and the diffusion along grain boundaries, occurred at the cathode/electrolyte interface of intermediate temperature solid state fuel cells, during cell preparation. The mutual diffusion is denoted by black arrows and the diffusion along grain boundaries assigned by pink arrows. Highlights: > All the cations in cathode (LSCF) and electrolyte (GDC) can mutually diffuse into each other. > Diffusing elements will segregate at grain boundaries or triple junctions around the cathode/electrolyte interface. > Two types of diffusions, the mutual diffusion and diffusion along grain boundaries, have been clarified thereafter.

  14. Oxygen diffusion in solid oxide fuel cell cathode and electrolyte materials: mechanistic insights from atomistic simulations

    E-print Network

    Yildiz, Bilge

    Oxygen diffusion in solid oxide fuel cell cathode and electrolyte materials: mechanistic insights to drive fast ionic transport. 1. Introduction The interest in Solid Oxide Fuel Cell (SOFC) technology of the cell. Of particular concern are the cathode and electrolyte which have major contributions

  15. Pre-acclimation of a wastewater inoculum to cellulose in an aqueouscathode MEC improves power generation in aircathode MFCs

    Microsoft Academic Search

    Shaoan Cheng; Patrick Kiely; Bruce E. Logan

    2011-01-01

    Cellulose has been used in two-chamber microbial fuel cells (MFCs), but power densities were low. Higher power densities can be achieved in aircathode MFCs using an inoculum from a two-chamber, aqueouscathode microbial electrolysis cell (MEC). Aircathode MFCs with this inoculum produced maximum power densities of 1070mWm?2 (cathode surface area) in single-chamber and 880mWm?2 in two-chamber MFCs. Coulombic efficiencies ranged from

  16. Hydrogen Diffusion and EAC of Pipeline Steels Under Cathodic Protection

    Microsoft Academic Search

    M. Cabrini; T. Pastore

    Pipeline steels can show Environmental Induced Cracking phenomena under slow straining with Hydrogen Embrittlement mechanism\\u000a under cathodic protection. Hydrogen evolution can take place due to cathodic protection normally used in order to protect\\u000a the pipeline against general corrosion. The steel is polarized at cathodic potentials in the range ?0.8 to ?1.1 V vs SCE,\\u000a but very negative values could be

  17. Prediction of Room Air Diffusion for Reduced Diffuser Flow Rates

    E-print Network

    Gangisetti, Kavita

    2011-02-22

    and analytical tool for investigating ventilation inside the system and thus to increase thermal comfort and improve indoor air quality. The room air supply diffuser flow rates can be reduced for less loading with the help of a variable air volume unit...

  18. Diffusion of air (1); phosgene (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Brnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) air; (2) phosgene

  19. Bent paths of a positive streamer and a cathode-directed spark leader in diffuse discharges preionized by runaway electrons

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Tarasenko, Viktor F.; Shao, Tao; Beloplotov, Dmitry V.; Lomaev, Mikhail I.; Wang, Ruixue; Sorokin, Dmitry A.; Yan, Ping

    2015-03-01

    Diffuse discharges preionized by runaway electrons can produce large-area homogeneous discharges at elevated pressures, which is an intriguing phenomenon in the physics of pulsed discharges. In this paper, runaway-electron-preionized diffuse discharge (REP DD) was obtained in a wide pressure range (0.05-0.25 MPa), and under certain conditions a positive streamer and a cathode-directed spark leader could be observed to propagate at some angles to the applied (background) electric field lines. For a 16-mm gap at an air pressure of 0.08-0.1 MPa, the percentage of pulses in which such propagation is observed is about 5%-50% of their total number, and in the other pulses such bent paths could not be observed because there is even no streamer or cathode-directed spark leader in diffuse discharges. In our opinion, such propagation of the positive streamer and the cathode-directed spark leader at some angle to the background electric field lines owes to different increase rates of the electron density in different regions of the discharge volume under REP DD conditions. Therefore, during the formation of a REP DD, the increase of the electron density is inhomogeneous and nonsimultaneous, resulting in an electron density gradient at the ionization wave front.

  20. Prediction of Room Air Diffusion for Reduced Diffuser Flow Rates

    E-print Network

    Gangisetti, Kavita

    2011-02-22

    profiles for (a) free axisymmetric jets (b) attached jets??. . 18 8 Computational domain ............................................................................... 27 9 Nozzle diffuser and its orientation... openings with a small aspect ratio. These jets are three dimensional and axisymmetric - at least at some distance from the diffuser opening. ? Linear air jets ?are formed by linear slots or rectangular openings with a large aspect ratio. These jet flows...

  1. Poly(vinylidene fluoride-co-hexafluoropropylene) phase inversion coating as a diffusion layer to enhance the cathode performance in

    E-print Network

    Poly(vinylidene fluoride-co-hexafluoropropylene) phase inversion coating as a diffusion layer(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) phase inversion coating was developed as a cathode diffusion

  2. Metallized graphite as an improved cathode material for aluminium/air batteries

    NASA Astrophysics Data System (ADS)

    Mukherjee, Ambick; N. Basumallick, Indra

    1993-06-01

    This paper reports the fabrication of metallized (Pt, Ni, Cu, Fe, Co) graphite cathodes by an electrodeposition method from an appropriate electrolytic bath, together with the performance characteristics of specially-designed aluminium/air cells that utilize these cathodes. In these cells, the aluminium electrodes were separated by a glass-jacket separator. The latter prevents mixing of hydrogen gas evolved due to the corrosion of the aluminium electrode. While the open-circuit voltage of the cells is virtually invariant, the short-circuit current and discharge behaviour are markedly dependent upon the choice of catalytic metal. The discharge profiles are improved markedly for cells with a Pt-, Ni- or Cu-coated graphite air cathode, but the reverse is found for Fe- and Co-coated cathodes. The behaviour is explained in terms of chemisorption and the better catalytic activity of Pt, Ni and Cu. These results suggest that Ni- and Cu-coated graphite air cathodes are promising low-cost and efficiennt electrodes for aluminium/air batteries.

  3. Polyelectrolyte-single wall carbon nanotube composite as an effective cathode catalyst for air-cathode microbial fuel cells.

    PubMed

    Wu, Huanan; Lu, Min; Guo, Lin; Bay, Leonard Guan Hong; Zhang, Zheng; Li, Sam Fong Yau

    2014-01-01

    Polyelectrolyte-single wall carbon nanotube (SCNT) composites are prepared by a solution-based method and used as metal-free cathode catalysts for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). In this study, two types of polyelectrolytes, polydiallyldimethylammonium chloride (PDDA) and poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] (PEPU) are applied to decorate the SCNTs and the resulting catalysts exhibit remarkable catalytic ability toward ORR in MFC applications. The enhanced catalytic ability could be attributed to the positively charged quaternary ammonium sites of polyelectrolytes, which increase the oxygen affinity of SCNTs and reduce activation energy in the oxygen reduction process. It is also found that PEPU-SCNT composite-based MFCs show efficient performance with maximum power density of 270.1 mW m(-2), comparable to MFCs with the benchmark Pt/C catalyst (375.3 mW m(-2)), while PDDA-SCNT composite-based MFCs produce 188.9 mW m(-2). These results indicate that PEPU-SCNT and PDDA-SCNT catalysts are promising candidates as metal-free cathode catalysts for ORR in MFCs and could facilitate MFC scaling up and commercialization. PMID:25429448

  4. Isotope effect of mercury diffusion in air.

    PubMed

    Koster van Groos, Paul G; Esser, Bradley K; Williams, Ross W; Hunt, James R

    2014-01-01

    Identifying and reducing impacts from mercury sources in the environment remains a considerable challenge and requires process based models to quantify mercury stocks and flows. The stable isotope composition of mercury in environmental samples can help address this challenge by serving as a tracer of specific sources and processes. Mercury isotope variations are small and result only from isotope fractionation during transport, equilibrium, and transformation processes. Because these processes occur in both industrial and environmental settings, knowledge of their associated isotope effects is required to interpret mercury isotope data. To improve the mechanistic modeling of mercury isotope effects during gas phase diffusion, an experimental program tested the applicability of kinetic gas theory. Gas-phase elemental mercury diffusion through small bore needles from finite sources demonstrated mass dependent diffusivities leading to isotope fractionation described by a Rayleigh distillation model. The measured relative atomic diffusivities among mercury isotopes in air are large and in agreement with kinetic gas theory. Mercury diffusion in air offers a reasonable explanation of recent field results reported in the literature. PMID:24364380

  5. Study of an unitised bidirectional vanadium/air redox flow battery comprising a two-layered cathode

    NASA Astrophysics Data System (ADS)

    grosse Austing, Jan; Nunes Kirchner, Carolina; Hammer, Eva-Maria; Komsiyska, Lidiya; Wittstock, Gunther

    2015-01-01

    The performance of a unitised bidirectional vanadium/air redox flow battery (VARFB) is described. It contains a two-layered cathode consisting of a gas diffusion electrode (GDE) with Pt/C catalyst for discharging and of an IrO2 modified graphite felt for charging. A simple routine is shown for the modification of a graphite felt with IrO2. A maximum energy efficiency of 41.7% at a current density of 20 mA cm-2 as well as an average discharge power density of 34.6 mW cm-2 at 40 mA cm-2 were obtained for VARFB operation at room temperature with the novel cathode setup. A dynamic hydrogen electrode was used to monitor half cell potentials during operation allowing to quantify the contribution of the cathode to the overall performance of the VARFB. Four consecutive cycles revealed that crossover of vanadium ions took place and irreversible degradation processes within the reaction unit lead to a performance decrease.

  6. Effect of nitrate on the performance of single chamber air cathode microbial fuel cells

    E-print Network

    Tullos, Desiree

    Effect of nitrate on the performance of single chamber air cathode microbial fuel cells Chontisa Accepted 26 August 2008 Published online 11 September 2008 Keywords: Microbial fuel cell Denitrification microbial fuel cells (MFCs) has drawn much attention recently as a new approach of waste- water treatment

  7. Polarization effects in a porous air cathode due to the influence of the anode in an alkaline air-metal cell

    Microsoft Academic Search

    J. Mrha; N.-E. Brring; S. U. Falk

    1973-01-01

    Experiments in 6 N KOH at room temperature with air-zinc and air-cadmium cells show clearly that the anodes have an influence on the polarization of the porous air cathode. The electrolyte volume is also found to have an effect. At a constant load of 30 mA\\/cm2 the polarization curve for oxygen reduction at the air cathode was, depending on cell

  8. Increased performance of single-chamber microbial fuel cells using an improved cathode structure

    E-print Network

    Increased performance of single-chamber microbial fuel cells using an improved cathode structure Maximum power densities by air-driven microbial fuel cells (MFCs) are considerably influenced by cathode reserved. Keywords: Microbial fuel cell; Air cathode; Diffusion layer; PTFE coating; Coulombic efficiency 1

  9. Metal-air batteries: from oxygen reduction electrochemistry to cathode catalysts.

    PubMed

    Cheng, Fangyi; Chen, Jun

    2012-03-21

    Because of the remarkably high theoretical energy output, metal-air batteries represent one class of promising power sources for applications in next-generation electronics, electrified transportation and energy storage of smart grids. The most prominent feature of a metal-air battery is the combination of a metal anode with high energy density and an air electrode with open structure to draw cathode active materials (i.e., oxygen) from air. In this critical review, we present the fundamentals and recent advances related to the fields of metal-air batteries, with a focus on the electrochemistry and materials chemistry of air electrodes. The battery electrochemistry and catalytic mechanism of oxygen reduction reactions are discussed on the basis of aqueous and organic electrolytes. Four groups of extensively studied catalysts for the cathode oxygen reduction/evolution are selectively surveyed from materials chemistry to electrode properties and battery application: Pt and Pt-based alloys (e.g., PtAu nanoparticles), carbonaceous materials (e.g., graphene nanosheets), transition-metal oxides (e.g., Mn-based spinels and perovskites), and inorganic-organic composites (e.g., metal macrocycle derivatives). The design and optimization of air-electrode structure are also outlined. Furthermore, remarks on the challenges and perspectives of research directions are proposed for further development of metal-air batteries (219 references). PMID:22254234

  10. Bifunctional quaternary ammonium compounds to inhibit biofilm growth and enhance performance for activated carbon air-cathode in microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Li, Nan; Liu, Yinan; An, Jingkun; Feng, Cuijuan; Wang, Xin

    2014-12-01

    The slow diffusion of hydroxyl out of the catalyst layer as well as the biofouling on the surface of cathode are two problems affecting power for membrane-less air-cathode microbial fuel cells (MFCs). In order to solve both of them simultaneously, here we simply modify activated carbon air-cathode using a bifunctional quaternary ammonium compound (QAC) by forced evaporation. The maximum power density reaches 104112mWm-2 in an unbuffered medium (0.5gL-1 NaCl), which is 17% higher than the control, probably due to the accelerated anion transport in the catalyst layer. After 2 months, the protein content reduced by a factor of 26 and the power density increases by 33%, indicating that the QAC modification can effectively inhibit the growth of cathodic biofilm and improve the stability of performance. The addition of NaOH and QAC epoxy have a negative effect on power production due to the clogging of pores in catalyst layer.

  11. A new approach to in situ sediment remediation based on air-cathode microbial fuel cells

    Microsoft Academic Search

    Yong Yuan; Shungui Zhou; Li Zhuang

    2010-01-01

    PurposeAs an attempt to remove the back color and odor of the organic-rich sediment, a novel tubular air-cathode MFC (TAC-MFC) was\\u000a constructed and employed for in situ sediment remediation. The biodegradation of organic matter in sediment was stimulated\\u000a by providing anodic electrode as an electron acceptor. The TAC-MFC was more favorable for application than typical sediment-type\\u000a MFCs, whose performances are

  12. Performance of MnO2 Crystallographic Phases in Rechargeable Lithium-Air Oxygen Cathode

    NASA Astrophysics Data System (ADS)

    Oloniyo, Olubukun; Kumar, Senthil; Scott, Keith

    2012-05-01

    Manganese dioxide (MnO2) has been shown to be effective for improving the efficiency of cathodes in lithium-air cells. Different crystallographic phases including ?-, ?-, and ?-MnO2 nanowires, ?-MnO2 nanospheres, and ?-MnO2 nanowires on carbon ( ?-MnO2/C) were synthesized using the hydrothermal method. Their physical properties were examined using x-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area measurements, and scanning electron microscopy (SEM) and found to be in agreement with the literature. Electrochemical properties of the synthesized catalyst particles were investigated by fabricating cathodes and testing them in a lithium-air cell with lithium hexafluorophosphate in propylene carbonate (LiPF6/PC) and tetra(ethylene glycol)dimethyl ether (LiTFSi/TEGDME) electrolytes. ?-MnO2 had the highest discharge capacity in the LiTFSi/TEGDME electrolyte (2500 mAh/g), whilst ?-MnO2/C in LiPF6/PC showed a significantly higher discharge capacity of 11,000 mAh/g based on total mass of the catalytic cathode. However, the latter showed poor capacity retention compared with ?-MnO2 nanowires, which was stable for up to 30 cycles. The reported discharge capacity is higher than recorded in previous studies on lithium-air cells.

  13. Graphite fiber brush anodes for increased power production in air-cathode microbial fuel cells.

    PubMed

    Logan, Bruce; Cheng, Shaoan; Watson, Valerie; Estadt, Garett

    2007-05-01

    To efficiently generate electricity using bacteria in microbial fuel cells (MFCs), highly conductive noncorrosive materials are needed that have a high specific surface area (surface area per volume) and an open structure to avoid biofouling. Graphite brush anodes, consisting of graphite fibers wound around a conductive, but noncorrosive metal core, were examined for power production in cube (C-MFC) and bottle (B-MFC) air-cathode MFCs. Power production in C-MFCs containing brush electrodes at 9600 m2/m3 reactor volume reached a maximum power density of 2400 mW/m2 (normalized to the cathode projected surface area), or 73 W/m3 based on liquid volume, with a maximum Coulombic efficiency (CE) of 60%. This power density, normalized by cathode projected area, is the highest value yet achieved by an air-cathode system. The increased power resulted from a reduction in internal resistance from 31 to 8 Q. Brush electrodes (4200 m2/m3) were also tested in B-MFCs, consisting of a laboratory media bottle modified to have a single side arm with a cathode clamped to its end. B-MFCs inoculated with wastewater produced up to 1430 mW/m2 (2.3 W/m3, CE = 23%) with brush electrodes, versus 600 mW/m2 with a plain carbon paper electrode. These findings show that brush anodes that have high surface areas and a porous structure can produce high power densities, and therefore have qualities that make them ideal for scaling up MFC systems. PMID:17539547

  14. Inhibition of microbial growth on air cathodes of single chamber microbial fuel cells by incorporating enrofloxacin into the catalyst layer.

    PubMed

    Liu, Weifeng; Cheng, Shaoan; Sun, Dan; Huang, Haobin; Chen, Jie; Cen, Kefa

    2015-10-15

    The inevitable growth of aerobic bacteria on the surface of air cathodes is an important factor reducing the performance stability of air cathode single-chamber membrane-free microbial fuel cells (MFCs). Thus searching for effective methods to inhibit the cathodic microbial growth is critical for the practical application of MFCs. In this study, enrofloxacin (ENR), a broad spectrum fluoroquinolone antibiotic, was incorporated into the catalyst layer of activated carbon air cathodes (ACACs) to inhibit the cathodic microbial growth. The biomass content on ACACs was substantially reduced by 60.2% with ENR treatment after 91 days of MFCs operation. As a result of the inhibited microbial growth, the oxygen reduction catalytic performance of the ENR treated ACACs was much stable compared to the fast performance decline of the untreated control. Consequently, a quite stable electricity production was obtained for the MFCs with the ENR treated ACACs, in contrast with a 22.5% decrease in maximum power density of the MFCs with the untreated cathode. ENR treatment of ACACs showed minimal effects on the anode performance. These results indicate that incorporating antibiotics into ACACs should be a simple and effective strategy to inhibit the microbial growth and improve the long-term stability of the performance of air cathode and the electricity production of MFCs. PMID:25957076

  15. Plant air systems safety study: Portsmouth Gaseous Diffusion Plant

    SciTech Connect

    Not Available

    1982-05-01

    The Portsmouth Gaseous Diffusion Plant Air System facilities and operations are reviewed for potential safety problems not covered by standard industrial safety procedures. Information is presented under the following section headings: facility and process description (general); air plant equipment; air distribution system; safety systems; accident analysis; plant air system safety overview; and conclusion. (JGB)

  16. Diffusion of diphosphoric acid tetraethyl ester (1); air (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Brnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) diphosphoric acid tetraethyl ester; (2) air

  17. Temperature dependence of OH diffusion in air and He

    NASA Astrophysics Data System (ADS)

    Liu, Yong; Ivanov, Andrey V.; Molina, Mario J.

    2009-02-01

    Although accurate knowledge of OH diffusion under atmospheric conditions is important, only one experimental study has been carried out at room temperature. Here, we report laboratory measurements of the OH diffusion coefficient in He and in a mixture of He and air over the range 218-318 K, using a temperature-controlled flow tube coupled to a low-pressure chemical ionization mass spectrometer. The results, which show a strong, almost square dependence of the diffusion coefficient on temperature in He and air, are consistent with predictions obtained from our theoretical calculations for diffusion of its polar diffusive analogue, H2O, using the 6-12 Lennard-Jones potential model with the collision parameters of water. This supports our hypothesis that the diffusion of OH can be accurately represented in the atmosphere by water, its polar diffusive analogue.

  18. A Single-Chamber Microbial Fuel Cell without an Air Cathode

    PubMed Central

    Nimje, Vanita Roshan; Chen, Chien-Cheng; Chen, Hau-Ren; Chen, Chien-Yen; Tseng, Min-Jen; Cheng, Kai-Chien; Shih, Ruey-Chyuan; Chang, Young-Fo

    2012-01-01

    Microbial fuel cells (MFCs) represent a novel technology for wastewater treatment with electricity production. Electricity generation with simultaneous nitrate reduction in a single-chamber MFC without air cathode was studied, using glucose (1 mM) as the carbon source and nitrate (1 mM) as the final electron acceptor employed by Bacillus subtilis under anaerobic conditions. Increasing current as a function of decreased nitrate concentration and an increase in biomass were observed with a maximum current of 0.4 mA obtained at an external resistance (Rext) of 1 K? without a platinum catalyst of air cathode. A decreased current with complete nitrate reduction, with further recovery of the current immediately after nitrate addition, indicated the dependence of B. subtilis on nitrate as an electron acceptor to efficiently produce electricity. A power density of 0.0019 mW/cm2 was achieved at an Rext of 220 ?. Cyclic voltammograms (CV) showed direct electron transfer with the involvement of mediators in the MFC. The low coulombic efficiency (CE) of 11% was mainly attributed to glucose fermentation. These results demonstrated that electricity generation is possible from wastewater containing nitrate, and this represents an alternative technology for the cost-effective and environmentally benign treatment of wastewater. PMID:22489190

  19. Anode and Cathode Spots in High-Voltage Nanosecond-Pulse Discharge Initiated by Runaway Electrons in Air

    NASA Astrophysics Data System (ADS)

    Shao, Tao; Victor, F. Tarasenko; Yang, Wen-jin; Dmitry, V. Beloplotov; Zhang, Cheng; Mikhail, I. Lomaev; Yan, Ping; Dmitry, A. Sorokin

    2014-08-01

    We report the experimental results with nanosecond-pulse discharges formed in the air gap between a flat electrode and a sharp electrode. The appearance of anode and cathode spots on the electrodes is studied experimentally. It is considered that bright spots on the flat cathode with positive polarity of the sharp electrode are formed due to the explosive electron emission on the cathode and the dynamic displacement current in the gap. It is also shown that with negative polarity of the sharp electrode, bright spots on the flat anode are formed after changing the polarity of the flat electrode due to the discharge oscillatory mode. Under these conditions, the explosive electron emission firstly forms on the sharp cathode. With negative polarity of the sharp electrode of the subnanosecond-pulse pulser, the runaway electron beam current is measured behind the anode foil with a time resolution of no more than 100 ps.

  20. In situ Fourier transform infrared-diffuse reflection spectroscopy of direct methanol fuel cell anodes and cathodes

    SciTech Connect

    Fan, Q.; Pu, C.; Smotkin, E.S. [Illinois Inst. of Tech., Chicago, IL (United States). Dept. of Chemical and Environmental Engineering

    1996-10-01

    In situ Fourier transform infrared-diffuse reflection spectroscopy (FTIR-DRS) was used to study both the adsorbed and desorbed species produced on high surface area anodes and cathodes of direct methanol/oxygen fuel cells. The authors investigated platinum-ruthenium and platinum black as anodes. The cathodes studied were platinum black. The primary product detected on both Pt-black and Pt-Ru anodes at low methanol/water vapor ratios (P{sub methanol}: 15.2 kPa) was CO{sub 2}. Consistent with previous work, CO adsorption is more prevalent on Pt-black than on Pt-RU. In addition to CO and CO{sub 2}, vibrational modes due to formic acid, methylformate, and formaldehyde are detected by FTIR-DRS under potentiostatic control. At higher methanol/water vapor ratios (P{sub methanol}: 38.0 kPa) and low potentials (0.10 to 0.50 V), formaldehyde is the only product at the Pt-Ru anode. Methylformate and formic acid vibrational modes appear at potentials from 0.60 to 0.80 V. CO{sub 2} and methanol are observed at open circuit on the cathode side as a result of methanol permeation from the anode to the cathode region. CO{sub 2} increases in the cathode region with increasing anode potential.

  1. Enhancement of diffuse reflectance using air tunnel structure.

    PubMed

    Jang, Jae Eun; Lee, Gae Hwang; Song, Byoung Gwon; Cha, Seung Nam; Jung, Jae Eun

    2013-02-01

    Submicrometer air gap structure has formed on diffuse reflection structure to improve light reflectance. Covering polymer or liquid on a diffuse reflector to make optical components induces the severe decrease of the total reflectance, since the diffuse reflected angle of some light rays is larger than the critical angle and the rays travel to the medium until meeting a proper small incident angle. The reflectance drops to 68% of the original value with just a polymer coating on the diffuse reflector. The formation of an air tunnel structure between the polymer layer and the diffuse reflector makes a symmetrical reflective index matching state and recovers 95% of the original reflectance. Due to the simple fabrication process and the chemical stability, the structure can be applied to various optical components and reflective display devices. PMID:23381414

  2. Accelerated OH(-) transport in activated carbon air cathode by modification of quaternary ammonium for microbial fuel cells.

    PubMed

    Wang, Xin; Feng, Cuijuan; Ding, Ning; Zhang, Qingrui; Li, Nan; Li, Xiaojing; Zhang, Yueyong; Zhou, Qixing

    2014-04-01

    Activated carbon (AC) is a promising catalyst for the air cathode of microbial fuel cells (MFCs) because of its high performance and low cost. To increase the performance of AC air cathodes, the acceleration of OH(-) transport is one of the most important methods, but it has not been widely investigated. Here we added quaternary ammonium to ACs by in situ anchoring of a quaternary ammonium/epoxide-reacting compound (QAE) or ex situ mixing with anion exchange resins in order to modify ACs from not only the external surface but also inside the pores. In 50 mM phosphate buffer solution (PBS), the in situ anchoring of QAE was a more effective way to increase the power. The highest power density of 2781 36 mW/m(2), which is 10% higher than that of the control, was obtained using QAE-anchored AC cathodes. When the medium was switched to an unbuffered NaCl solution, the increase in maximum power density (885 25 mW/m(2)) was in accordance with the anion exchange capacity (0.219 mmol/g). The highest power density of the anion exchange resin-mixed air cathode was 51% higher than that of the control, indicating that anion exchange is urgently needed in real wastewaters. Excess anchoring of QAE blocked both the mesopores and micropores, causing the power output to be inhibited. PMID:24597673

  3. Diffusion barriers in modified air brazes

    DOEpatents

    Weil, Kenneth Scott; Hardy, John S; Kim, Jin Yong; Choi, Jung-Pyung

    2013-04-23

    A method for joining two ceramic parts, or a ceramic part and a metal part, and the joint formed thereby. The method provides two or more parts, a braze consisting of a mixture of copper oxide and silver, a diffusion barrier, and then heats the braze for a time and at a temperature sufficient to form the braze into a bond holding the two or more parts together. The diffusion barrier is an oxidizable metal that forms either a homogeneous component of the braze, a heterogeneous component of the braze, a separate layer bordering the braze, or combinations thereof. The oxidizable metal is selected from the group Al, Mg, Cr, Si, Ni, Co, Mn, Ti, Zr, Hf, Pt, Pd, Au, lanthanides, and combinations thereof.

  4. Diffusion barriers in modified air brazes

    DOEpatents

    Weil, Kenneth Scott (Richland, WA); Hardy, John S. (Richland, WA); Kim, Jin Yong (Richland, WA); Choi, Jung-Pyung (Richland, WA)

    2010-04-06

    A method for joining two ceramic parts, or a ceramic part and a metal part, and the joint formed thereby. The method provides two or more parts, a braze consisting of a mixture of copper oxide and silver, a diffusion barrier, and then heats the braze for a time and at a temperature sufficient to form the braze into a bond holding the two or more parts together. The diffusion barrier is an oxidizable metal that forms either a homogeneous component of the braze, a heterogeneous component of the braze, a separate layer bordering the braze, or combinations thereof. The oxidizable metal is selected from the group Al, Mg, Cr, Si, Ni, Co, Mn, Ti, Zr, Hf, Pt, Pd, Au, lanthanides, and combinations thereof.

  5. ANALYTICAL DIFFUSION MODEL FOR LONG DISTANCE TRANSPORT OF AIR POLLUTANTS

    EPA Science Inventory

    A steady-state two-dimensional diffusion model suitable for predicting ambient air pollutant concentrations averaged over a long time period (e.g., month, season, or year) and resulting from the transport of pollutants for distances greater than about 100 km from the source is de...

  6. Non-catalyzed microbial fuel cell (MFC) with open air cathode for bioelectricity generation during acidogenic wastewater treatment

    Microsoft Academic Search

    S. Venkata Mohan; S. Srikanth; P. N. Sarma

    2009-01-01

    Single chambered mediatorless microbial fuel cell (MFC Nafion-117 membrane) fabricated with non-catalyzed electrodes was operated with open-air cathode to evaluate bioelectricity generation from domestic wastewater under acidogenic conditions (pH, 6) using anaerobic mixed consortia as anodic biocatalyst. Experimental data illustrated the feasibility of bioelectricity generation from domestic wastewater treatment. A steady increase in MFC performance was observed from the first

  7. Anolyte recirculation effects in buffered and unbuffered single-chamber air-cathode microbial fuel cells.

    PubMed

    Zhang, Liang; Zhu, Xun; Kashima, Hiroyuki; Li, Jun; Ye, Ding-ding; Liao, Qiang; Regan, John M

    2015-03-01

    Two identical microbial fuel cells (MFCs) with a floating air-cathode were operated under either buffered (MFC-B) or bufferless (MFC-BL) conditions to investigate anolyte recirculation effects on enhancing proton transfer. With an external resistance of 50 ? and recirculation rate of 1.0 ml/min, MFC-BL had a 27% lower voltage (9.7% lower maximal power density) but a 64% higher Coulombic efficiency (CE) than MFC-B. MFC-B had a decreased voltage output, batch time, and CE with increasing recirculation rate resulting from more oxygen transfer into the anode. However, increasing the recirculation rate within a low range significantly enhanced proton transfer in MFC-BL, resulting in a higher voltage output, a longer batch time, and a higher CE. A further increase in recirculation rate decreased the batch time and CE of MFC-BL due to excess oxygen transfer into anode outweighing the proton-transfer benefits. The unbuffered MFC had an optimal recirculation rate of 0.35 ml/min. PMID:25514399

  8. Continuous electricity generation by a graphite granule baffled air-cathode microbial fuel cell.

    PubMed

    Feng, Yujie; Lee, He; Wang, Xin; Liu, Yaolan; He, Weihua

    2010-01-01

    A baffled air-cathode microbial fuel cell (BAFMFC) was designed and operated under continuous flow. With glucose fed as substrate, an average voltage of 652 mV was obtained under the external resistance of 1000 Omega (30 degrees C). The maximum power density was 15.2 W/m(3) with the chemical oxygen demand (COD) removal rate of 88.0%. The overall resistance was 13.7 Omega while ohmic internal resistance was 10.8 Omega. Average COD removal rate was 69.7-88.0%, when COD loading varied from 4.11 kg COD/(m(3)NACd) to 16.0 kg COD/(m(3)NACd). The liquid from corn stover steam explosion process (COD=7160+/-50mg/L) was treated by BAFMFC, and the maximum power density was 10.7 W/m(3) with the average COD removal rate was 89.1%. The present study indicated BAFMFC can be comparable to the traditional anaerobic baffled reactor in COD removal rate for high-concentration wastewater and have an advantage in energy harvest from wastewater. PMID:19748267

  9. Application of nitrogen-doped carbon powders as low-cost and durable cathodic catalyst to air-cathode microbial fuel cells.

    PubMed

    Shi, Xinxin; Feng, Yujie; Wang, Xin; Lee, He; Liu, Jia; Qu, Youpeng; He, Weihua; Kumar, S M Senthil; Ren, Nanqi

    2012-03-01

    Given few in-depth studies available on the application of nitrogen-doped carbon powders (NDCP) to air-cathode microbial fuel cells (ACMFCs), a low-cost and durable catalyst of NDCP was prepared and used as cathodic catalyst of ACMFCs. Compared to the untreated carbon powders, the N-doped treatment significantly increased the maximum power density (MPD) of ACMFC. A two-step pretreatment of heat treatment and hydrochloric acid immersion can further obviously increase the MPD. With a reasonably large loading of catalyst, the MPD of NDCP based ACMFC was comparable to that of carbon-supported platinum (Pt/C) based ACMFC, while the cost was dramatically reduced. The pretreatment increased the key nitrogen functional groups, pyridinic-like and pyrrolic-like nitrogen. A third new key nitrogen functional group, nitrogen oxide, was discovered and the mechanism of its contribution was explained. Compared to the inherent deterioration problem of Pt/C, NDCP exhibited high stability and was superior for long-term operation of ACMFCs. PMID:22265594

  10. Effect of helium injection on diffusion dominated air ingress accidents in pebble bed reactors

    E-print Network

    Yurko, Joseph Paul

    2010-01-01

    The primary objective of this thesis was to validate the sustained counter air diffusion (SCAD) method at preventing natural circulation onset in diffusion dominated air ingress accidents. The analysis presented in this ...

  11. Using ammonium bicarbonate as pore former in activated carbon catalyst layer to enhance performance of air cathode microbial fuel cell

    NASA Astrophysics Data System (ADS)

    Li, Da; Qu, Youpeng; Liu, Jia; He, Weihua; Wang, Haiman; Feng, Yujie

    2014-12-01

    The rolling catalyst layers in air cathode microbial fuel cells (MFCs) are prepared by introducing NH4HCO3 as pore former (PF) with four PF/activated carbon mass ratios of 0.1, 0.2, 0.3 and 1.0. The maximum power density of 8928mWm-2 is obtained by cathodes with the mass ratio of 0.2, which is 33% higher than that of the control reactor (without PF, 67122mWm-2). Pore analysis indicates the porosity increases by 38% and the major pore range concentrates between 0.5?m-0.8?m which likely facilitates to enrich the active reaction sites compared to 0.8?m-3.0?m in the control and other PF-cathodes. In addition, pore structure endows the cathode improved exchange current density by 2.4 times and decreased charge transfer resistance by 44%, which are the essential reasons to enhance the oxygen reduction. These results show that addition of NH4HCO3 proves an effective way to change the porosity and pore distribution of catalyst layers and then enhance the MFC performance.

  12. Nitrogen removal in a single-chamber microbial fuel cell with nitrifying biofilm enriched at the air cathode.

    PubMed

    Yan, Hengjing; Saito, Tomonori; Regan, John M

    2012-05-01

    Nitrogen removal is needed in microbial fuel cells (MFCs) for the treatment of most waste streams. Current designs couple biological denitrification with side-stream or combined nitrification sustained by upstream or direct aeration, which negates some of the energy-saving benefits of MFC technology. To achieve simultaneous nitrification and denitrification, without extra energy input for aeration, the air cathode of a single-chamber MFC was pre-enriched with a nitrifying biofilm. Diethylamine-functionalized polymer (DEA) was used as the Pt catalyst binder on the cathode to improve the differential nitrifying biofilm establishment. With pre-enriched nitrifying biofilm, MFCs with the DEA binder had an ammonia removal efficiency of up to 96.8% and a maximum power density of 900 25 mW/m(2), compared to 90.7% and 945 42 mW/m(2) with a Nafion binder. A control with Nafion that lacked nitrifier pre-enrichment removed less ammonia and had lower power production (54.5% initially, 750 mW/m(2)). The nitrifying biofilm MFCs had lower Coulombic efficiencies (up to 27%) than the control reactor (up to 36%). The maximum total nitrogen removal efficiency reached 93.9% for MFCs with the DEA binder. The DEA binder accelerated nitrifier biofilm enrichment on the cathode, and enhanced system stability. These results demonstrated that with proper cathode pre-enrichment it is possible to simultaneously remove organics and ammonia in a single-chamber MFC without supplemental aeration. PMID:22386083

  13. Soot formation in hydrocarbon\\/air laminar jet diffusion flames

    Microsoft Academic Search

    P. B. Sunderland; G. M. Faeth

    1996-01-01

    Soot processes along the axes of round laminar jet diffusion flames were studied, considering ethane, propane, n-butane, ethylene, propylene, and 1,3-butadiene burning in air at pressures of 2599 kPa. Measurements included soot volume fractions, temperatures, soot structure, concentrations of major gas species and gas velocities. As distance increased along the axes of the flames, significant soot formation began when temperatures

  14. Surface Exchange and Bulk Diffusivity of LSCF as SOFC Cathode: Electrical Conductivity Relaxation and Isotope Exchange Characterizations

    SciTech Connect

    Li, Yihong; Gerdes, Kirk; Horita, Teruhisa; Liu, Xingbo

    2013-05-05

    The oxygen diffusion coefficient (D) and surface exchange coefficient (k) of a typical SOFC cathode material, La{sub 0.6}Sr{sub 0.4}Co{sub 0.2}Fe{sub 0.8}O{sub 3-?} (LSCF) were characterized by both electrical conductivity relaxation (ECR) and oxygen isotope exchange (IE) methods. Conductivity relaxation experiments were conducted at 800C for small step changes in partial pressure of oxygen (P{sub O{sub 2}} ), both decreasing and increasing, from 0.02 atm to 0.20 atm. The results revealed P{sub O{sub 2}} dependent hysteresis with the reduction process requiring more equilibration time than oxidation. Analysis of the experimental data indicated that the surface exchange coefficient is a function of the final oxygen partial pressure in an isothermal system. In addition, both forward and backward oxygen reduction reaction constants, which are vital for the fundamental understanding of SOFC cathode reaction mechanisms, are investigated based on the relationship between surface exchange coefficient and P{sub O{sub 2}} . The direct comparisons between the results from both ECR and IE were presented and the possible experimental errors in both methods were discussed.

  15. Improved performance of air-cathode single-chamber microbial fuel cell for wastewater treatment using microfiltration membranes and multiple sludge inoculation

    Microsoft Academic Search

    Jian Sun; Yongyou Hu; Zhe Bi; Yunqing Cao

    2009-01-01

    Substantial optimization and cost reduction are required before microbial fuel cells (MFCs) can be practically applied. We show here the performance improvement of an air-cathode single-chamber MFC by using a microfiltration membrane (MFM) on the water-facing side of the cathode and using multiple aerobic sludge (AES), anaerobic sludge (ANS), and wetland sediment (WLS) as anodic inoculums. Batch test results show

  16. Degrading a mixture of three textile dyes using photo-assisted electrochemical process with BDD anode and O?-diffusion cathode.

    PubMed

    Khataee, Alireza; Safarpour, Mahdie; Vahid, Behrouz; Akbarpour, Amaneh

    2014-01-01

    In this paper, degradation of a mixture of three azo dyes was studied by the photo-assisted electrochemical process using an O?-diffusion cathode containing carbon nanotubes and boron-doped diamond (BDD) anode. The concentration of three textile dyes (C.I. Acid Orange 8 (AO8), C.I. Acid Orange 10 (AO10), and C.I. Acid Orange 12 (AO12)) was determined simultaneously despite the severe overlap of their spectra. For this purpose, partial least square (PLS), as a multivariate calibration method, was utilized based on recording UV-Vis spectra during the decolorization process. Moreover, the central composite design was used for the modeling of photo-assisted electrochemical decolorization of the aqueous solutions containing three dyes. The investigated parameters were the initial concentration of three dyes, applied current and reaction time. Analysis of variance (ANOVA) revealed that the obtained regression models match the experimental results well with R (Khataee et al. 2010, Clean-Soil Air Water 38 (1):96-103, 2010) of 0.972, 0.971, and 0.957 for AO8, AO10, and AO12, respectively. Three-dimensional surface and contour plots were applied to describe the relation between experimental conditions and the observed response. The results of TOC analysis confirmed good ability of proposed photo-assisted electrochemical process for degradation and mineralization of textile industry wastewater. PMID:24723345

  17. Increasing power generation for scaling up single-chamber air cathode microbial fuel cells

    E-print Network

    surface area to reactor volume), but the impact of cathode size on power generation depended to the anode area) (Fan et al., 2008), or 1.55 kW/m3 (power normalized to the reactor vol- ume) (Fan et al technology could advance to con- ventional anaerobic digesters in the term of power density, under optimized

  18. The performance of phosphorus (P)-doped activated carbon as a catalyst in air-cathode microbial fuel cells.

    PubMed

    Chen, Zhihao; Li, Kexun; Pu, Liangtao

    2014-10-01

    To observe the influence of P-doped activated carbon (AC) in air-cathode microbial fuel cells (MFCs), AC was treated with H3PO4 (1M) at 80C and 400C respectively, and then was used as catalyst layer in the air-cathode. The maximum power densities were: 109633mW/m(2) (SP2, AC treated at 400C), 95436mW/m(2) (SP1, AC treated at 80C), which were 55%, 35% higher than the control (70827mW/m(2), untreated AC), respectively. The results of electrochemical impedance spectroscopy (EIS) and the Brunauer-Emmett-Teller (BET) showed that the total resistance was decreased and the pore structure was changed. The analysis of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) demonstrated that P-doped functional group was produced in SP2, which caused the 15% greater power density than SP1 by increasing O2 adsorption. What is more important, the chemically modified method is simple and economical. PMID:25151475

  19. Study of the Durability of Doped Lanthanum Manganite and Cobaltite Cathode Materials under Real World Air Exposure Atmospheres

    SciTech Connect

    Singh, Prabhakar; Mahapatra, Manoj; Ramprasad, Rampi; Minh, Nguyen; Misture, Scott

    2014-11-30

    The overall objective of the program is to develop and validate mechanisms responsible for the overall structural and chemical degradation of lanthanum manganite as well as lanthanum ferrite cobaltite based cathode when exposed to real world air atmosphere exposure conditions during SOFC systems operation. Of particular interest are the evaluation and analysis of degradation phenomena related to and responsible for (a) products formation and interactions with air contaminants, (b) dopant segregation and oxide exolution at free surfaces, (c) cation interdiffusion and reaction products formation at the buried interfaces, (d) interface morphology changes, lattice transformation and the development of interfacial porosity and (e) micro-cracking and delamination from the stack repeat units. Reaction processes have been studied using electrochemical and high temperature materials compatibility tests followed by structural and chemical characterization. Degradation hypothesis has been proposed and validated through further experimentation and computational simulation.

  20. A quantitative analysis of numerical diffusion introduced by advection algorithms in air quality models

    NASA Astrophysics Data System (ADS)

    Odman, Mehmet Talat

    Methodologies that quantify numerical diffusion errors associated with advection algorithms are discussed. Diffusion errors in four flux-form advection schemes are analyzed, and the order of accuracy of each scheme is determined. The relationship between numerical diffusion and important parameters of air quality models such as the grid resolution, Courant number, and the wavelength of pollutant plume are described. Then, numerical diffusion introduced by the least diffusive advection scheme (among the four analyzed here) is compared with explicit horizontal diffusion introduced by two parameterizations, one for subgrid-scale diffusion and another for grid-scale diffusion. This quantitative analysis of numerical diffusion can be used for improving the formulation of horizontal diffusion as well as the treatment of subgrid-scale plumes in air quality models.

  1. 14CO2-in-air sampling with passive diffusion samplers.

    PubMed

    Wood, M J; Surette, R A; Mohindra, J K; Patterson, J G

    1998-02-01

    Passive diffusion samplers designed for measuring HTO-in-air have been evaluated for measuring 14CO2-in-air. Controlled exposures to HTO-in-air, 14CO2-in-air, and a combination of the two gases were carried out. The sampling rate of the 14CO2-in-air was found to be approximately 0.7 that of HTO-in-air. This value is consistent with the calculated relative sampling rates based on the diffusion coefficients of the gases. Passive diffusion samplers currently used for sampling HTO-in-air at CANDU facilities have been shown to be suitable for also measuring 14CO2-in-air and HTO-in-air simultaneously when prepared with the appropriate sampling solution. PMID:9450595

  2. Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution

    PubMed Central

    Basirun, Wan Jeffrey; Sookhakian, Mehran; Baradaran, Saeid; Endut, Zulkarnain; Mahmoudian, Mohammad Reza; Ebadi, Mehdi; Yousefi, Ramin; Ghadimi, Hanieh; Ahmed, Sohail

    2015-01-01

    Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6?M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13?mW cm?2, in contrast to MnO2, which produced a maximum power density of 9.2?mW cm?2. The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms. PMID:25765731

  3. Graphene oxide electrocatalyst on MnO? air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution.

    PubMed

    Basirun, Wan Jeffrey; Sookhakian, Mehran; Baradaran, Saeid; Endut, Zulkarnain; Mahmoudian, Mohammad Reza; Ebadi, Mehdi; Yousefi, Ramin; Ghadimi, Hanieh; Ahmed, Sohail

    2015-01-01

    Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6?M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13?mW cm(-2), in contrast to MnO2, which produced a maximum power density of 9.2?mW cm(-2). The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms. PMID:25765731

  4. Ignition time of hydrogen-air diffusion flames

    NASA Astrophysics Data System (ADS)

    Snchez, Antonio L.; Fernndez-Tarrazo, Eduardo; Boivin, Pierre; Lin, Amable; Williams, Forman A.

    2012-11-01

    The ignition time of hydrogen-air diffusion flames is a quantity of utmost interest in a large number of applications, with implications regarding the viability of supersonic combustion and the safe operation of gas turbines. The underlying chemistry and the associated ignition history are very different depending on the initial temperature and pressure. This article addresses conditions that place the system above the so-called second explosion limit, as is typically the case in SCRAMJET operation, so that a branched-chain explosion characterizes the ignition process. The roles of local radical accumulation, molecular transport, and chemical reaction in nonpremixed ignition are clarified by considering the temporal evolution of an unstrained mixing layer formed between two semi-infinite spaces of hydrogen and air. The problem is formulated in terms of a radical-pool mass fraction, whose evolution in time is studied with a WKB expansion that exploits the disparity of chemical time scales present in the problem, leading to an explicit expression for the ignition time. The applicability of the analytical results for obtaining predictions of ignition distances in supersonic-combustion applications is also considered.

  5. Full-scale thermal performance tests of alternative diffusers when operating with cold air

    SciTech Connect

    Hu, S.C.; Barber, J.M.; Chiang, H.

    1999-07-01

    This paper discusses an experimental study of the direct delivery of cold air into a full-scale environmental chamber using different diffusers, i.e., a multi-cone circular ceiling diffuser, a vortex diffuser, and a nozzle-type diffuser. Comparisons have been made of mean flow patterns, temperature distribution, thermal comfort using the PD model and the ADPI model, and condensation risk. The results show that both the vortex diffuser and the nozzle-type diffuser are capable of providing a very good indoor thermal comfort environment compared with that provided by the multi-cone circular diffuser, which tends to create cold air dumping in the occupied zone. The vortex diffuser exhibits a higher induction effect than the nozzle-type diffuser. However, the airspeed generated by the vortex diffuser is generally lower than that of the nozzle-type diffuser. Both the vortex diffuser and the nozzle-type diffuser can be considered to have condensation-free characteristics, although some vapor film was observed in the early stage of a hard start-up test for the nozzle-type diffuser.

  6. The Importance of Nanometric Passivating Films on Cathodes forLi - Air Batteries

    SciTech Connect

    Adams, Brian D.; Black, Robert; Radtke, Claudio; Williams, Zach; Mehdi, Beata L.; Browning, Nigel D.; Nazar, Linda F.

    2014-12-23

    Recently, there has been a transition from fully carbonaceous positive electrodes for the aprotic lithium oxygen battery to alternative materials and the use of redox mediator additives, in an attempt to lower the large electrochemical overpotentials associated with the charge reaction. However, the stabilizing or catalytic effect of these materials can become complicated due to the presence of major side-reactions observed during dis(charge). Here, we isolate the charge reaction from the discharge by utilizing electrodes prefilled with commercial lithium peroxide with a crystallite size of about 200-800 nm. Using a combination of S/TEM, online mass spectrometry, XPS, and electrochemical methods to probe the nature of surface films on carbon and conductive Ti-based nanoparticles, we show that oxygen evolution from lithium peroxide is strongly dependent on their surface properties. Insulating TiO2 surface layers on TiC and TiN - even as thin as 3 nm*can completely inhibit the charge reaction under these conditions. On the other hand, TiC, which lacks this oxide film, readily facilitates oxidation of the bulk Li2O2 crystallites, at a much lower overpotential relative to carbon. Since oxidation of lithium oxygen battery cathodes is inevitable in these systems, precise control of the surface chemistry at the nanoscale becomes of upmost importance.

  7. Lithium Diffusion & Magnetism in Battery Cathode Material LixNi1/3Co1/3Mn1/3O2

    NASA Astrophysics Data System (ADS)

    Mnsson, M.; Nozaki, H.; Wikberg, J. M.; Pra, K.; Sassa, Y.; Dahbi, M.; Kamazawa, K.; Sedlak, K.; Watanabe, I.; Sugiyama, J.

    2014-12-01

    We have studied low-temperature magnetic properties as well as high-temperature lithium ion diffusion in the battery cathode materials LixNi1/3Co1/3Mn1/3O2 by the use of muon spin rotation/relaxation. Our data reveal that the samples enter into a 2D spin-glass state below TSG ? 12 K. We further show that lithium diffusion channels become active for T >= Tdiff ~ 125 K where the Li-ion hopping-rate [v(T)] starts to increase exponentially. Further, v(T) is found to fit very well to an Arrhenius type equation and the activation energy for the diffusion process is extracted as Ea ? 100 meV.

  8. Efficient salt removal in a continuously operated upflow microbial desalination cell with an air cathode

    E-print Network

    Efficient salt removal in a continuously operated upflow microbial desalination cell with an air of salt removal. During the 4-month operation, the UMDC constantly removed salts and generated bio-electricity. At a hydraulic retention time (HRT) of 4 days (salt solution) and current production of $62 mA, the UMDC was able

  9. Improved performance of membrane free single-chamber air-cathode microbial fuel cells with nitric acid and ethylenediamine surface modified activated carbon fiber felt anodes

    Microsoft Academic Search

    Nengwu Zhu; Xi Chen; Ting Zhang; Pingxiao Wu; Ping Li; Jinhua Wu

    2011-01-01

    Surface modifications of anode materials are important for enhancing power generation of microbial fuel cell (MFC). Membrane free single-chamber air-cathode MFCs, MFC-A and MFC-N, were constructed using activated carbon fiber felt (ACF) anodes treated by nitric acid and ethylenediamine (EDA), respectively. Experimental results showed that the start-up time to achieve the maximum voltages for the MFC-A and MFC-N was shortened

  10. Manganese cobaltite/polypyrrole nanocomposite-based air-cathode for sustainable power generation in the single-chambered microbial fuel cells.

    PubMed

    Khilari, Santimoy; Pandit, Soumya; Das, Debabrata; Pradhan, Debabrata

    2014-04-15

    Manganese cobaltite nanorods (MnCo2O4 NRs) were prepared and tested as potential air-cathode catalyst for the single-chambered microbial fuel cells (sMFC). The power generation of sMFC increases with MnCo2O4 NRs loading to the cathode. The Polypyrrole (PPy) and Vulcan XC were used as conducting support to the MnCo2O4 NRs to form composites either by in situ or by mechanical mixing in the cathode fabrication. The cyclic voltammetry, linear sweep voltammetry and electrochemical impedance studies reveal that the in situ-MnCo2O4 NRs/PPy composite has higher catalytic activity than that of mechanically mixed-MnCo2O4NRs/PPy composite because of higher interfacial contact between MnCo2O4 NRs and PPy. The maximum volumetric power density with in situ-MnCo2O4 NRs/PPy, mechanically mixed-MnCo2O4 NRs/PPy, MnCo2O4 NRs/Vulcan XC and catalyst-free (only Vulcan XC) cathode was measured to be 6.11, 5.05, 4.22, and 1.77 W/m(3), respectively, in the sMFC. This suggests that PPy is not only a better conducting support than that of conventionally used Vulcan XC but also the cathode composite fabrication process is important for enhanced performance. The synergetic effect of MnCo2O4 NRs and PPy was found to play an important role for the improved energy recovery and it could be applied as an efficient and inexpensive cathode catalyst for the sMFC. PMID:24333931

  11. Mutual diffusion occurring at the interface between La?.?Sr?.?Co?.?Fe?.?O? cathode and Gd-doped ceria electrolyte during IT-SOFC cell preparation.

    PubMed

    Li, Zhi-Peng; Toshiyuki, Mori; Auchterlonie, Graeme John; Zou, Jin; John, Drennan

    2011-07-01

    The microstructure and local chemistry of the interface between the screen-printed La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3) (LSCF) thin film cathode and Gd-doped ceria (GDC) electrolyte substrate have been investigated. Elemental distribution analyses, by energy-dispersive X-ray spectroscopy operated in scanning transmission electron microscopy (STEM) mode, illustrate that all constituent elements in GDC and LSCF mutually diffuse across the LSCF/GDC interface, with equal diffusion length. This leads to the formation of mutual diffusion zones at the LSCF/GDC interfaces, with the resultant mixture of diffusing ions being associated with specific valence state changes, as verified by STEM electron energy loss spectroscopy analyses. Moreover, this mutual diffusion can result in microstructural changes, where superstructure formation is accompanied by enhancement of oxygen vacancy ordering at this region. Such mutual diffusion and associated microstructure evolution is considered to be detrimental to fuel cell efficiency and should be suppressed by lowering cell fabrication temperatures. PMID:21675745

  12. Performance of low cost scalable air-cathode microbial fuel cell made from clayware separator using multiple electrodes.

    PubMed

    Ghadge, Anil N; Ghangrekar, Makarand M

    2015-04-01

    Performance of scalable air-cathode microbial fuel cell (MFC) of 26 L volume, made from clayware cylinder with multiple electrodes, was evaluated. When electrodes were connected in parallel with 100 ? resistance (R ext), power of 11.46 mW was produced which was 4.48 and 3.73 times higher than individual electrode pair and series connection, respectively. Coulombic efficiency of 5.10 0.13% and chemical oxygen demand (COD) removal of 78.8 5.52% was observed at R ext of 3 ?. Performance under different organic loading rates (OLRs) varying from 0.75 to 6.0 g CODL(-1)d(-1) revealed power of 17.85 mW (47.28 mA current) at OLR of 3.0 g CODL(-1)d(-1). Internal resistance (R int) of 5.2 ? observed is among the least value reported in literature. Long term operational stability (14 months) demonstrates the technical viability of clayware MFC for practical applications and potential benefits towards wastewater treatment and electricity recovery. PMID:25693451

  13. A small-scale air-cathode microbial fuel cell for on-line monitoring of water quality.

    PubMed

    Di Lorenzo, Mirella; Thomson, Alexander R; Schneider, Kenneth; Cameron, Petra J; Ieropoulos, Ioannis

    2014-12-15

    The heavy use of chemicals for agricultural, industrial and domestic purposes has increased the risk of freshwater contamination worldwide. Consequently, the demand for efficient new analytical tools for on-line and on-site water quality monitoring has become particularly urgent. In this study, a small-scale single chamber air-cathode microbial fuel cell (SCMFC), fabricated by rapid prototyping layer-by-layer 3D printing, was tested as a biosensor for continuous water quality monitoring. When acetate was fed as the rate-limiting substrate, the SCMFC acted as a sensor for chemical oxygen demand (COD) in water. The linear detection range was 3-164 ppm, with a sensitivity of 0.05 ?A mM(-1) cm(-2) with respect to the anode total surface area. The response time was as fast as 2.8 min. At saturating acetate concentrations (COD>164 ppm), the miniature SCMFC could rapidly detect the presence of cadmium in water with high sensitivity (0.2 ?g l(-1) cm(-2)) and a lower detection limit of only 1 ?g l(-1). The biosensor dynamic range was 1-25 ?g l(-1). Within this range of concentrations, cadmium affected only temporarily the electroactive biofilm at the anode. When the SCMFCs were again fed with fresh wastewater and no pollutant, the initial steady-state current was recovered within 12 min. PMID:25005554

  14. N-type Cu2O doped activated carbon as catalyst for improving power generation of air cathode microbial fuel cells.

    PubMed

    Zhang, Xi; Li, Kexun; Yan, Pengyu; Liu, Ziqi; Pu, Liangtao

    2015-07-01

    A novel n-type Cu2O doped activated carbon (AC) air cathode (Cu/AC) was developed as an alternative to Pt electrode for oxygen reduction in microbial fuel cells (MFCs). The maximum power density of MFCs using this novel air cathode was as high as 139076mWm(-2), almost 59% higher than the bare AC air cathode. Specifically, the resistance including total resistance and charge transfer resistance significantly decreased comparing to the control. Tafel curve also showed the faster electro-transfer kinetics of Cu/AC with exchange current density of 1.0310(-3)Acm(-2), which was 69% higher than the control. Ribbon-like Cu2O was deposited on the surface of AC with the mesopore surface area increasing. Cubic Cu2O crystals exclusively expose (111) planes with the interplanar crystal spacing of 2.48, which was the dominate active sites for oxygen reduction reaction (ORR). N-type Cu2O with oxygen vacancies played crucial roles in electrochemical catalytic activity. PMID:25863207

  15. Electrochemical properties of graphene flakes as an air cathode material for Li-O2 batteries in an ether-based electrolyte.

    PubMed

    Kim, Se Young; Lee, Ho-Taek; Kim, Kwang-Bum

    2013-12-14

    We employed graphene flakes as an air-cathode material for Li-O2 batteries and investigated their electrochemical properties in the dimethyl ether electrolyte. Graphene flakes were prepared by microwave-assisted reduction of graphene oxide, and their electrochemical properties were compared with those of Ketjen Black and carbon nanotubes. The catalytic effect of the prepared graphene flake-air cathode was demonstrated using cyclic voltammetry and discharge-charge testing performed under a limited discharge capacity. The catalytic effect of graphene flakes was also supported by morphological and spectroscopic analysis of the discharge-charge products formed on the graphene surface. Scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy revealed that Li2O2, Li2O, and Li2CO3 were the main discharge products on all carbon-air cathode surfaces. Raman spectroscopy revealed that LiRCO3 was additionally formed on Ketjen Black and carbon nanotubes during the first discharge; however, its formation was not observed on the graphene flakes. The catalytic effect of the graphene flakes and the absence of LiRCO3 in the discharge product could explain the higher Coulombic efficiency in the discharge-charge tests. PMID:24166701

  16. A best fit approach to estimating multiple diffuse source terms using ambient air monitoring data and an air dispersion model.

    PubMed

    MacQueen, Donald; Bertoldo, Nicholas; Wegrecki, Anthony

    2013-08-01

    Lawrence Livermore National Laboratory uses CAP88-PC Version 1.0 modeling software to demonstrate compliance with the Code of Federal Regulations Title 40 Part 61 Subpart H (National Emission Standards for Emissions of Radionuclides Other Than Radon From Department of Energy Facilities). Annual air emissions from both well characterized stack sources and difficult to characterize diffuse sources must be assessed. This paper describes a process that uses a mathematical optimization routine to find a set of estimated diffuse source terms that together with the measured stack source terms provides a best fit of modeled air concentrations to measured air concentrations at available sampling locations. The estimated and measured source terms may then be used in subsequent CAP88-PC modeling to estimate dose at the off-site maximally exposed individual. LLNL has found this process to be an effective way to deal with the required assessment of diffuse sources that have otherwise been difficult to assess. PMID:23803667

  17. A diffusion approximation approach to stochastic modeling of air conditioning type loads

    E-print Network

    Roy, Teresa Henryka

    1981-01-01

    A DIFFUSION APPROXIMATION APPROACH TO STOCHASTIC MODELING OF AIR CONDITIONING TYPE LOADS A Thesis by TERESA HENRYKA ROY Submitted to the Graduate Colleqe of Texas A&M University in partial fulfillment of the requirement for the degree... of MASTER OF SCIENCE August 1981 Major Subject: Electrical Engineering A DIFFUSION APPROXIMATION AP99OACH TD STOCHASTIC MODELING OF AIR CONDITIONING TYPE LOADS A Thesis by TERESA HENRYKA ROY Approved as to style and content by: (Chairman...

  18. Soot microstructure in steady and flickering laminar methane\\/air diffusion flames

    Microsoft Academic Search

    Jie Zhang; Constantine M. Megaridis

    1998-01-01

    An experimental investigation is presented to identify the mechanisms responsible for the enhanced sooting behavior of strongly flickering methane\\/air jet diffusion flames when compared to their steady counterparts. The work extends the implementation of thermophoretic sampling in flickering, co-flow, laminar, diffusion flames. Acoustic forcing of the fuel flow rate is used to phase lock the periodic flame flicker close to

  19. MEASUREMENT OF EFFECTIVE AIR DIFFUSION COEFFICIENTS FOR TRICHLOROETHENE IN UNDISTURBED SOIL CORES. (R826162)

    EPA Science Inventory

    Abstract In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm2/s over a range of air...

  20. Long-term calibration monitoring of Spectralon diffusers BRDF in the air-ultraviolet

    Microsoft Academic Search

    Georgi T. Georgiev; James J. Butler

    2007-01-01

    Long-term calibration monitoring of the bidirectional reflectance distribution function (BRDF) of Spectralon diffusers in the air-ultraviolet is presented. Four Spectralon diffusers were monitored in this study. Three of the diffusers, designated as H1, H2, and H3, were used in the prelaunch radiance calibration of the Solar Backscatter Ultraviolet\\/2 (SBUV\\/2) satellite instruments on National Oceanic and Atmospheric Administration (NOAA) 14 and

  1. Diffusion of Clean Indoor Air Ordinances in the Southwestern United States

    Microsoft Academic Search

    Everett M. Rogers; Jeffery C. Peterson

    2008-01-01

    The authors investigate the process through which clean indoor air ordinances were considered in 10 communities in the southwestern United States and key factors that influenced diffusion and adoption. Clean indoor air ordinances, which ban smoking in public places, were adopted in approximately 1,409 U.S. communities from 1986 to April 2004. The authors gathered data from 10 communities in New

  2. EXTINCTION STUDIES OF PROPANE/AIR COUNTERFLOW DIFFUSION FLAMES: THE EFFECTIVENESS OF AEROSOLS

    EPA Science Inventory

    The fire suppression effectiveness of solid aerosols as suitable halon replacements has examined. Experiments were performed in a counterflow diffusion burner, consisting of two 1 cm i.d. tubes separated by 1 cm. Aerosols were delivered to propane/air flames in the air flow. Both...

  3. Prediction of Air Mixing From High Sidewall Diffusers in Cooling Mode: Preprint

    SciTech Connect

    Ridouane, E. H.; Gawlik, K.

    2011-02-01

    Computational fluid dynamics modeling was used to evaluate the performance of high sidewall air supply in cooling mode. The research focused on the design, placement, and operation of air supply diffusers located high on a sidewall and return grilles located near the floor on the same sidewall. Parameters of the study are the supply velocity, supply temperature, diffuser dimensions and room dimensions. Thermal loads characteristic of high performance homes were applied at the walls and room temperature was controlled via a thermostat. The results are intended to provide information to guide the selection of high sidewall supply diffusers to provide proper room mixing for cooling of high performance homes.

  4. Generation of large-scale, barrier-free diffuse plasmas in air at atmospheric pressure using array wire electrodes and nanosecond high-voltage pulses

    NASA Astrophysics Data System (ADS)

    Teng, Yun; Li, Lee; Liu, Yun-Long; Liu, Lun; Liu, Minghai

    2014-10-01

    This paper introduces a method to generate large-scale diffuse plasmas by using a repetition nanosecond pulse generator and a parallel array wire-electrode configuration. We investigated barrier-free diffuse plasmas produced in the open air in parallel and cross-parallel array line-line electrode configurations. We found that, when the distance between the wire-electrode pair is small, the discharges were almost extinguished. Also, glow-like diffuse plasmas with little discharge weakening were obtained in an appropriate range of line-line distances and with a cathode-grounding cross-electrode configuration. As an example, we produced a large-scale, stable diffuse plasma with volumes as large as 18 15 15 cm3, and this discharge region can be further expanded. Additionally, using optical and electrical measurements, we showed that the electron temperature was higher than the gas temperature, which was almost the same as room temperature. Also, an array of electrode configuration with more wire electrodes had helped to prevent the transition from diffuse discharge to arc discharge. Comparing the current waveforms of configurations with 1 cell and 9 cells, we found that adding cells significantly increased the conduction current and the electrical energy delivered in the electrode gaps.

  5. Scalable air cathode microbial fuel cells using glass fiber separators, plastic mesh supporters, and graphite fiber brush anodes.

    PubMed

    Zhang, Xiaoyuan; Cheng, Shaoan; Liang, Peng; Huang, Xia; Logan, Bruce E

    2011-01-01

    The combined use of brush anodes and glass fiber (GF1) separators, and plastic mesh supporters were used here for the first time to create a scalable microbial fuel cell architecture. Separators prevented short circuiting of closely-spaced electrodes, and cathode supporters were used to avoid water gaps between the separator and cathode that can reduce power production. The maximum power density with a separator and supporter and a single cathode was 75 1 W/m(3). Removing the separator decreased power by 8%. Adding a second cathode increased power to 154 1 W/m(3). Current was increased by connecting two MFCs connected in parallel. These results show that brush anodes, combined with a glass fiber separator and a plastic mesh supporter, produce a useful MFC architecture that is inherently scalable due to good insulation between the electrodes and a compact architecture. PMID:20566288

  6. Effect of pressure on structure and NO sub X formation in CO-air diffusion flames

    NASA Technical Reports Server (NTRS)

    Maahs, H. G.; Miller, I. M.

    1979-01-01

    A study was made of nitric oxide formation in a laminar CO-air diffusion flame over a pressure range from 1 to 50 atm. The carbon monoxide (CO) issued from a 3.06 mm diameter port coaxially into a coflowing stream of air confined within a 20.5 mm diameter chimney. Nitric oxide concentrations from the flame were measured at two carbon monoxide (fuel) flow rates: 73 standard cubic/min and 146 sccm. Comparison of the present data with data in the literature for a methane-air diffusion flame shows that for flames of comparable flame height (8 to 10 mm) and pseudoequivalence ratio (0.162), the molar emission index of a CO-air flame is significantly greater than that of a methane-air flame.

  7. Measurement of thermal diffusivity of air using photopyroelectric interferometry

    E-print Network

    Mandelis, Andreas

    the thermal diffusivity of ambient gases with optimal precision is introduced. The technique is based on destructive PPE interferometric detection inside a thermal-wave resonant cavity with an optically transparent-to-noise ratio and the measurement dynamic range and precision by suppressing the large optically transmitted

  8. Laboratory-scale analysis of effect of plume spacing of air diffuser system on destratification efficiency.

    PubMed

    Kim, J Y; Park, S H; Kim, S H; Park, H

    2006-10-01

    This paper presents a study conducted to develop guidelines for the design of an air bubble destratification system, with particular concern given to plume spacing. To investigate the effect of plume spacing on the destratification efficiency of the system, we first conducted a dimensional analysis that included major variables in bubble hydrodynamics. Then, we conducted laboratory experiments with various plume spacings and water depths under non-linear stratification conditions, and we evaluated the destratification efficiencies. Our results showed that the highest efficiency was obtained with a plume spacing of 0.75 times the water depth. Our study has shown that the overall efficiency of an air diffuser system can be increased by changing the spacing between diffusers and that plume spacing should be a major design parameter for future air diffuser systems. PMID:17144263

  9. NITRIC ACID-AIR DIFFUSION COEFFICIENT: EXPERIMENTAL DETERMINATION

    EPA Science Inventory

    Trace gaseous HNO3 in air is removed in a laminar flow nylon tube. The HNO3 deposition pattern was obtained by sectioning the tube, extracting with an aqueous solution, and measuring the concentration by ion chromatography. Mass transport analysis of the deposition pattern demons...

  10. Centrifugal Compressor Surge Margin Improved With Diffuser Hub Surface Air Injection

    NASA Technical Reports Server (NTRS)

    Skoch, Gary J.

    2002-01-01

    Aerodynamic stability is an important parameter in the design of compressors for aircraft gas turbine engines. Compression system instabilities can cause compressor surge, which may lead to the loss of an aircraft. As a result, engine designers include a margin of safety between the operating line of the engine and the stability limit line of the compressor. The margin of safety is typically referred to as "surge margin." Achieving the highest possible level of surge margin while meeting design point performance objectives is the goal of the compressor designer. However, performance goals often must be compromised in order to achieve adequate levels of surge margin. Techniques to improve surge margin will permit more aggressive compressor designs. Centrifugal compressor surge margin improvement was demonstrated at the NASA Glenn Research Center by injecting air into the vaned diffuser of a 4:1-pressure-ratio centrifugal compressor. Tests were performed using injector nozzles located on the diffuser hub surface of a vane-island diffuser in the vaneless region between the impeller trailing edge and the diffuser-vane leading edge. The nozzle flow path and discharge shape were designed to produce an air stream that remained tangent to the hub surface as it traveled into the diffuser passage. Injector nozzles were located near the leading edge of 23 of the 24 diffuser vanes. One passage did not contain an injector so that instrumentation located in that passage would be preserved. Several orientations of the injected stream relative to the diffuser vane leading edge were tested over a range of injected flow rates. Only steady flow (nonpulsed) air injection was tested. At 100 percent of the design speed, a 15-percent improvement in the baseline surge margin was achieved with a nozzle orientation that produced a jet that was bisected by the diffuser vane leading edge. Other orientations also improved the baseline surge margin. Tests were conducted at speeds below the design speed, and similar results were obtained. In most cases, the greatest improvement in surge margin occurred at fairly low levels of injected flow rate. Externally supplied injection air was used in these experiments. However, the injected flow rates that provided the greatest benefit could be produced using injection air that is recirculating between the diffuser discharge and nozzles located in the diffuser vaneless region. Future experiments will evaluate the effectiveness of recirculating air injection.

  11. Pore Scale Modeling of the Reactive Transport of Chromium in the Cathode of a Solid Oxide Fuel Cell

    SciTech Connect

    Ryan, Emily M.; Tartakovsky, Alexandre M.; Recknagle, Kurtis P.; Khaleel, Mohammad A.; Amon, Cristina

    2011-01-01

    We present a pore scale model of a solid oxide fuel cell (SOFC) cathode. Volatile chromium species are known to migrate from the current collector of the SOFC into the cathode where over time they decrease the voltage output of the fuel cell. A pore scale model is used to investigate the reactive transport of chromium species in the cathode and to study the driving forces of chromium poisoning. A multi-scale modeling approach is proposed which uses a cell level model of the cathode, air channel and current collector to determine the boundary conditions for a pore scale model of a section of the cathode. The pore scale model uses a discrete representation of the cathode to explicitly model the surface reactions of oxygen and chromium with a cathode material. The pore scale model is used to study the reaction mechanisms of chromium by considering the effects of reaction rates, diffusion coefficients, chromium vaporization, and oxygen consumption on chromiums deposition in the cathode. The study shows that chromium poisoning is most significantly affected by the chromium reaction rates in the cathode and that the reaction rates are a function of the local current density in the cathode.

  12. Characterization of bacterial and archaeal communities in air-cathode microbial fuel cells, open circuit and sealed-off reactors.

    PubMed

    Shehab, Noura; Li, Dong; Amy, Gary L; Logan, Bruce E; Saikaly, Pascal E

    2013-11-01

    A large percentage of organic fuel consumed in a microbial fuel cell (MFC) is lost as a result of oxygen transfer through the cathode. In order to understand how this oxygen transfer affects the microbial community structure, reactors were operated in duplicate using three configurations: closed circuit (CC; with current generation), open circuit (OC; no current generation), and sealed off cathodes (SO; no current, with a solid plate placed across the cathode). Most (98%) of the chemical oxygen demand (COD) was removed during power production in the CC reactor (maximum of 640??10mW/m(2)), with a low percent of substrate converted to current (coulombic efficiency of 26.5??2.1%). Sealing the cathode reduced COD removal to 7%, but with an open cathode, there was nearly as much COD removal by the OC reactor (94.5%) as the CC reactor. Oxygen transfer into the reactor substantially affected the composition of the microbial communities. Based on analysis of the biofilms using 16S rRNA gene pyrosequencing, microbes most similar to Geobacter were predominant on the anodes in the CC MFC (72% of sequences), but the most abundant bacteria were Azoarcus (42 to 47%) in the OC reactor, and Dechloromonas (17%) in the SO reactor. Hydrogenotrophic methanogens were most predominant, with sequences most similar to Methanobacterium in the CC and SO reactor, and Methanocorpusculum in the OC reactors. These results show that oxygen leakage through the cathode substantially alters the bacterial anode communities, and that hydrogenotrophic methanogens predominate despite high concentrations of acetate. The predominant methanogens in the CC reactor most closely resembled those in the SO reactor, demonstrating that oxygen leakage alters methanogenic as well as general bacterial communities. PMID:23775270

  13. Measurement of Hydrogen Peroxide in Ambient Air by Impinger and Diffusion Scrubber

    Microsoft Academic Search

    Roger L. Tanner; Ji Shen

    1990-01-01

    Two methods for the determination of gaseous hydrogen peroxide in ambient air were tested during the Carbon Species Methods Comparison Study conducted at Glendora, CA, August 1220, 1986. Air was sampled by the BNL dual impinger\\/diffusion scrubber apparatus after ambient ozone removal by addition of NO. Sampling was done during daylight hours (? 08002000 hours) from a sampling line shared

  14. A correlation of air-coupled ultrasonic and thermal diffusivity data for CFCC materials

    SciTech Connect

    Pillai, T.A.K. [Univ. of Wisconsin, LaCrosse, WI (United States). Dept. of Physics; Easler, T.E.; Szweda, A. [Dow Corning Corp., Midland, MI (United States). Advanced Ceramics Program] [and others

    1997-01-01

    An air-coupled (non contact) through-transmission ultrasonic investigation has been conducted on 2D multiple ply Nicalon{trademark} SiC fiber/SiNC CFCC panels as a function of number of processing cycles. Corresponding thermal diffusivity imaging was also conducted. The results of the air-coupled ultrasonic investigation correlated with thermal property variations determined via infrared methods. Areas of delaminations were detected and effects of processing cycles were also detected.

  15. Long-term calibration monitoring of Spectralon diffusers BRDF in the air-ultraviolet.

    PubMed

    Georgiev, Georgi T; Butler, James J

    2007-11-10

    Long-term calibration monitoring of the bidirectional reflectance distribution function (BRDF) of Spectralon diffusers in the air-ultraviolet is presented. Four Spectralon diffusers were monitored in this study. Three of the diffusers, designated as H1, H2, and H3, were used in the prelaunch radiance calibration of the Solar Backscatter Ultraviolet/2 (SBUV/2) satellite instruments on National Oceanic and Atmospheric Administration (NOAA) 14 and 16. A fourth diffuser, designated as the 400 diffuser, was used in the prelaunch calibration of the Ozone Mapping and Profiler Suite (OMPS) instrument scheduled for initial flight in 2009 on the National Polar Orbiting Environmental Satellite System Preparatory Project. The BRDF data of this study were obtained between 1994 and 2005 using the scatterometer located in the National Aeronautics and Space Administration Goddard Space Flight Center Diffuser Calibration Laboratory. The diffusers were measured at 13 wavelengths between 230 and 425 nm at the incident and scatter angles used in the prelaunch calibrations of SBUV/2 and OMPS. Spectral features in the BRDF of Spectralon are also discussed. The comparison shows how the air-ultraviolet BRDF of these Spectralon samples changed over time under clean room deployment conditions. PMID:17994141

  16. Long-term calibration monitoring of Spectralon diffusers BRDF in the air-ultraviolet

    NASA Astrophysics Data System (ADS)

    Georgiev, Georgi T.; Butler, James J.

    2007-11-01

    Long-term calibration monitoring of the bidirectional reflectance distribution function (BRDF) of Spectralon diffusers in the air-ultraviolet is presented. Four Spectralon diffusers were monitored in this study. Three of the diffusers, designated as H1, H2, and H3, were used in the prelaunch radiance calibration of the Solar Backscatter Ultraviolet/2 (SBUV/2) satellite instruments on National Oceanic and Atmospheric Administration (NOAA) 14 and 16. A fourth diffuser, designated as the 400 diffuser, was used in the prelaunch calibration of the Ozone Mapping and Profiler Suite (OMPS) instrument scheduled for initial flight in 2009 on the National Polar Orbiting Environmental Satellite System Preparatory Project. The BRDF data of this study were obtained between 1994 and 2005 using the scatterometer located in the National Aeronautics and Space Administration Goddard Space Flight Center Diffuser Calibration Laboratory. The diffusers were measured at 13 wavelengths between 230 and 425 nm at the incident and scatter angles used in the prelaunch calibrations of SBUV/2 and OMPS. Spectral features in the BRDF of Spectralon are also discussed. The comparison shows how the air-ultraviolet BRDF of these Spectralon samples changed over time under clean room deployment conditions.

  17. Enzymatic fuel cells: integrating flow-through anode and air-breathing cathode into a membrane-less biofuel cell design.

    PubMed

    Rincn, Rosalba A; Lau, Carolin; Luckarift, Heather R; Garcia, Kristen E; Adkins, Emily; Johnson, Glenn R; Atanassov, Plamen

    2011-09-15

    One of the key goals of enzymatic biofuel cells research has been the development of a fully enzymatic biofuel cell that operates under a continuous flow-through regime. Here, we present our work on achieving this task. Two NAD(+)-dependent dehydrogenase enzymes; malate dehydrogenase (MDH) and alcohol dehydrogenase (ADH) were independently coupled with poly-methylene green (poly-MG) catalyst for biofuel cell anode fabrication. A fungal laccase that catalyzes oxygen reduction via direct electron transfer (DET) was used as an air-breathing cathode. This completes a fully enzymatic biofuel cell that operates in a flow-through mode of fuel supply polarized against an air-breathing bio-cathode. The combined, enzymatic, MDH-laccase biofuel cell operated with an open circuit voltage (OCV) of 0.584 V, whereas the ADH-laccase biofuel cell sustained an OCV of 0.618 V. Maximum volumetric power densities approaching 20 ?W cm(-3) are reported, and characterization criteria that will aid in future optimization are discussed. PMID:21775124

  18. A THEORETICAL ANALYSIS OF NITRIC OXIDE PRODUCTION IN A METHANE/AIR TURBULENT DIFFUSION FLAME

    EPA Science Inventory

    The report gives results of a theoretical analysis of nitric oxide production in a methane/air turbulent diffusion flame. In the coherent flame model used, the chemical reactions take place in laminar flame elements which are lengthened by the turbulent fluid motion and shortened...

  19. Transient Behaviour of Laminar Counterflow Hydrogen-Air Diffusion Flames with Complex Chemistry

    Microsoft Academic Search

    N. DARABIHA

    1992-01-01

    The nonsteady behaviour of counterflow diffusion hydrogen-air flames is studied in this article, using a finite difference implicit method and a complex kinetics model. The flame responses to step and sinusoidal strain rale variations are obtained for flames submitted to moderate strain rates and also to strain rates corresponding to extinction conditions. Frequency response curves are obtained for both cases

  20. Effects of water-contaminated air on blowoff limits of opposed jet hydrogen-air diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Jentzen, Marilyn E.; Wilson, Lloyd G.; Northam, G. Burton

    1988-01-01

    The effects of water-contaminated air on the extinction and flame restoration of the central portion of N2-diluted H2 versus air counterflow diffusion flames are investigated using a coaxial tubular opposed jet burner. The results show that the replacement of N2 contaminant in air by water on a mole for mole basis decreases the maximum sustainable H2 mass flow, just prior to extinction, of the flame. This result contrasts strongly with the analogous substitution of water for N2 in a relatively hot premixed H2-O2-N2 flame, which was shown by Koroll and Mulpuru (1986) to lead to a significant, kinetically controlled increase in laminar burning velocity.

  1. Fuel cell stack with passive air supply

    DOEpatents

    Ren, Xiaoming; Gottesfeld, Shimshon

    2006-01-17

    A fuel cell stack has a plurality of polymer electrolyte fuel cells (PEFCs) where each PEFC includes a rectangular membrane electrode assembly (MEA) having a fuel flow field along a first axis and an air flow field along a second axis perpendicular to the first axis, where the fuel flow field is long relative to the air flow field. A cathode air flow field in each PEFC has air flow channels for air flow parallel to the second axis and that directly open to atmospheric air for air diffusion within the channels into contact with the MEA.

  2. A diffusion denuder for the measurement of semivolatile organic compounds in ambient air

    SciTech Connect

    Krieger, M.S.

    1993-01-01

    Semivolatile organic compounds, such as polychlorinated biphenyls and polycyclic aromatic hydrocarbons, are present in the atmosphere in the gas phase and adsorbed to particles. Their atmospheric fate and transport is controlled by their partitioning between these two phases. Therefore, the accurate determination of this partitioning is important in understanding their movement through the atmosphere and their ultimate fate. Current air sampling techniques probably do not give accurate gas-particle partitioning data because of sampling artifacts inherent in the sampling process. An alternative sampling process, based on a diffusion denuder, was developed. A diffusion denuder is a tube or set of tubes through which an atmospheric sample is passed. The inside of the tube(s) is coated with a material which collects the components of interest. The authors' denuder uses capillary gas chromatographic columns as the sampling tubes. Diffusion denuders are not susceptible to the sampling artifacts that are encountered with current air sampling techniques because they collect gas-phase molecules before collection of particles. The denuder was used to collect semivolatile organic compounds from a variety of samples, including diesel exhaust, wood smoke, tobacco smoke, indoor air, and ambient air. Results from the indoor air samples demonstrate the effectiveness of on-line thermal desorption. Indoor air and ambient air measurements demonstrate that the air concentrations measured with the denuder were not different from those measured with conventional samplers. Results from combustion samples and from scanning electron microscopy indicated that particle transmission through the denuder was acceptable. Finally, the gas-particle partitioning of fourteen polycyclic aromatic hydrocarbons was measured in Indianapolis, Indiana, using the denuder. Comparable heat of desorption values to those determined by conventional sampling methods were obtained.

  3. Exploration of ion migration mechanism and diffusion capability for Na3V2(PO4)2F3 cathode utilized in rechargeable sodium-ion batteries

    NASA Astrophysics Data System (ADS)

    Song, Weixin; Ji, Xiaobo; Wu, Zhengping; Yang, Yingchang; Zhou, Zhou; Li, Fangqian; Chen, Qiyuan; Banks, Craig E.

    2014-06-01

    NASICON-type Na3V2(PO4)2F3 is employed as a promising cathode for sodium-ion batteries in order to explore the ion-migration mechanism and diffusion capability. Two kinds of Na sites, namely Na(1) site and Na(2) site exist in the crystal structure per formula unit to accommodate a total of three sodium ions. The ion at Na(2) site with half occupation extracts first and inserts the last due to its high chemical potential, while the whole extraction/insertion of two ions between 1.6 and 4.6V vs. Na+/Na can produce three plateaus in charge/discharge processes because of the reorganization of ions. The first discharge capacity of 111.6mAhg-1 with retention of 97.6% after 50 cycles could be obtained by electrochemical testing at 0.091C. Electrochemical activation and/or structural reorganization of the system by cycling could improve the diffusion coefficient of sodium with a comparatively large magnitude of 10-12cm2s-1, though many influences on the resistance factors also can be attributed to the cycling process. Such work is of fundamental importance to the progression of sodium-based batteries to be fully realized and be implemented over existing Li-ion based batteries.

  4. Sequential anodecathode configuration improves cathodic oxygen reduction and effluent quality of microbial fuel cells

    Microsoft Academic Search

    Stefano Freguia; Korneel Rabaey; Zhiguo Yuan; Jrg Keller

    2008-01-01

    The reduction of oxygen at the cathode and the diffusion of protons from the anode to the cathode are currently perceived as two major bottlenecks of microbial fuel cells (MFCs). To address these issues, we have designed an MFC configuration in which the effluent of an acetate-fed anode was used as a feed for an aerated, biocatalysed cathode. The development

  5. Active Flow Control Integrated Diffuser for increased Energy Efficiency in Variable Air Volume Systems

    NASA Astrophysics Data System (ADS)

    van der Schijff, Hermanus; Menicovich, David; Vollen, Jason; Amitay, Michael

    2013-11-01

    An experimental investigation was performed to study the application of flow control on an HVAC diffuser using synthetic jets distributed evenly along the diffuser edges. The study was conducted on 1:3 scale typical office space (150 ft2) , which included a simulated scale HVAC system supplied by compressed air. Two different jet momentum coefficients were investigated for two inlet flow rates of 40 and 60 CFM. The flow field was measured using hot wire anemometry and Particle Image Velocimetry. Current Variable Air Volume HVAC systems vary the incoming airflow to adjust to changing temperature conditions in the conditioned space. However, when the air flow rate drops below ideal, air distribution becomes inefficient. This study demonstrates the effectiveness of synthetic jets at controlling the incoming airflow and the distribution in the room, showing ability to affect throw coefficient parameters for different flow rates within the test chamber. The use of such devices has the potential to improve air quality and air distribution in building while simultaneously lowering energy demands of HVAC systems.

  6. Strain-induced extinction of hydrogen-air counterflow diffusion flames - Effects of steam, CO2, N2, and O2 additives to air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.

    1992-01-01

    A fundamental study was performed using axisymmetric nozzle and tubular opposed jet burners to measure the effects of laminar plug flow and parabolic input velocity profiles on the extinction limits of H2-air counterflow diffusion flames. Extinction limits were quantified by 'flame strength', (average axial air jet velocity) at blowoff of the central flame. The effects of key air contaminants, on the extinction limits, are characterized and analyzed relative to utilization of combustion contaminated vitiated air in high enthalpy supersonic test facilities.

  7. Active flow control integrated diffuser (afcid) for increased energy efficiency in variable air volume systems

    NASA Astrophysics Data System (ADS)

    Van Der Schijff, Hermanus P.

    Variable air volume (VAV) air terminals are designed to save energy by reducing airflow into a given space based on occupancy and required load. Systems are typically designed to operate at peak load, however as load is reduced, performance is compromised due to inadequate throw. As a result, fans are installed to adjust for the losses, negating many of the energy savings. Additionally flow is vectored by the use of vanes, a basic passive type of flow control. An experimental investigation was performed to study the application of flow control on that of a HVAC diffuser using synthetic jets distributed evenly along the diffuser edge parallel to the flow field. The study was conducted on a 1:3 scale typical office space (150 ft2), which included a simulated scale HVAC system supplied by compressed air. Two different jet blowing ratios were investigated for system loads of 60% and 90%. The flow field was established using hot wire anemometry and Particle Image Velocimetry (PIV). This study demonstrates the effectiveness of synthetic jet based active flow control at controlling airflow, showing ability to affect throw parameters for changing flow rates within the test chamber. Vectoring of up to 20% and improvement in jet spread of 200% was demonstrated. The use of such devices has the potential to improve air quality and air distribution in building while simultaneously lowering energy demands of HVAC systems.

  8. Microbial community structures differentiated in a single-chamber air-cathode microbial fuel cell fueled with rice straw hydrolysate

    PubMed Central

    2014-01-01

    Background The microbial fuel cell represents a novel technology to simultaneously generate electric power and treat wastewater. Both pure organic matter and real wastewater can be used as fuel to generate electric power and the substrate type can influence the microbial community structure. In the present study, rice straw, an important feedstock source in the world, was used as fuel after pretreatment with diluted acid method for a microbial fuel cell to obtain electric power. Moreover, the microbial community structures of anodic and cathodic biofilm and planktonic culturewere analyzed and compared to reveal the effect of niche on microbial community structure. Results The microbial fuel cell produced a maximum power density of 137.6??15.5mW/m2 at a COD concentration of 400mg/L, which was further increased to 293.33??7.89mW/m2 through adjusting the electrolyte conductivity from 5.6 mS/cm to 17 mS/cm. Microbial community analysis showed reduction of the microbial diversities of the anodic biofilm and planktonic culture, whereas diversity of the cathodic biofilm was increased. Planktonic microbial communities were clustered closer to the anodic microbial communities compared to the cathodic biofilm. The differentiation in microbial community structure of the samples was caused by minor portion of the genus. The three samples shared the same predominant phylum of Proteobacteria. The abundance of exoelectrogenic genus was increased with Desulfobulbus as the shared most abundant genus; while the most abundant exoelectrogenic genus of Clostridium in the inoculum was reduced. Sulfate reducing bacteria accounted for large relative abundance in all the samples, whereas the relative abundance varied in different samples. Conclusion The results demonstrated that rice straw hydrolysate can be used as fuel for microbial fuel cells; microbial community structure differentiated depending on niches after microbial fuel cell operation; exoelectrogens were enriched; sulfate from rice straw hydrolysate might be responsible for the large relative abundance of sulfate reducing bacteria. PMID:24433535

  9. Compact lanthanum hexaboride hollow cathode.

    PubMed

    Goebel, Dan M; Watkins, Ronald M

    2010-08-01

    A compact lanthanum hexaboride hollow cathode has been developed for space applications where size and mass are important and research and industrial applications where access for implementation might be limited. The cathode design features a refractory metal cathode tube that is easily manufactured, mechanically captured orifice and end plates to eliminate expensive e-beam welding, graphite sleeves to provide a diffusion boundary to protect the LaB6 insert from chemical reactions with the refractory metal tube, and several heater designs to provide long life. The compact LaB(6) hollow cathode assembly including emitter, support tube, heater, and keeper electrode is less than 2 cm in diameter and has been fabricated in lengths of 6-15 cm for different applications. The cathode has been operated continuously at discharge currents of 5-60 A in xenon. Slightly larger diameter versions of this design have operated at up to 100 A of discharge current. PMID:20815605

  10. Effect of varied air flow on flame structure of laminar inverse diffusion flames.

    SciTech Connect

    Shaddix, Christopher R.; Williams, Timothy C.; Blevins, Linda Gail; Mikofski, Mark A. (University of California Berkeley)

    2004-03-01

    The structure of laminar inverse diffusion flames (IDFs) of methane and ethylene was studied using a cylindrical co-flowing burner. Several flames of the same fuel flow-rate yet various air flow-rates were examined. Heights of visible flames were obtained using measurements of hydroxyl (OH) laser-induced fluorescence (LIF) and visible images. Polycyclic aromatic hydrocarbon (PAH) LIF and soot laser-induced incandescence (LII) were also measured. In visible images, radiating soot masks the blue region typically associated with the flame height in normal diffusion flames (NDFs). Increased air flow-rates resulted in longer flames. PAH LIF and soot LII indicated that PAh and soot are present on the fuel side of the flame and that soot is located closer to the reaction zone than PAH. Ethylene flames produced significantly higher PAH LIF and soot LII signals than methane flames, which is consistent with the sooting propensity of ethylene.

  11. Characteristics of Gaseous Diffusion Flames with High Temperature Combustion Air in Microgravity

    NASA Technical Reports Server (NTRS)

    Ghaderi, M.; Gupta, A. K.

    2003-01-01

    The characteristics of gaseous diffusion flames have been obtained using high temperature combustion air under microgravity conditions. The time resolved flame images under free fall microgravity conditions were obtained from the video images obtained. The tests results reported here were conducted using propane as the fuel and about 1000 C combustion air. The burner included a 0.686 mm diameter central fuel jet injected into the surrounding high temperature combustion air. The fuel jet exit Reynolds number was 63. Several measurements were taken at different air preheats and fuel jet exit Reynolds number. The resulting hybrid color flame was found to be blue at the base of the flame followed by a yellow color flame. The length and width of flame during the entire free fall conditions has been examined. Also the relative flame length and width for blue and yellow portion of the flame has been examined under microgravity conditions. The results show that the flame length decreases and width increases with high air preheats in microgravity condition. In microgravity conditions the flame length is larger with normal temperature combustion air than high temperature air.

  12. On the homogeneity of a diffuse barrier discharge in atmospheric air between flat cylindrical electrodes

    NASA Astrophysics Data System (ADS)

    Malashin, M. V.; Moshkunov, S. I.; Khomich, V. Yu.; Shershunova, E. A.

    2015-05-01

    The degree of homogeneity of a diffuse dielectric barrier discharge in millimeter air gaps under atmospheric pressure has been analyzed. This analysis is based on the glow-brightness distribution in the discharge gap cross section with allowance for a cylindrical electrode shape. It is shown that the degree of discharge homogeneity depends on both the repetition frequency of voltage pulses applied to the discharge gap and the barrier material.

  13. Lateral diffusion of amphiphiles and macromolecules at the air/water interface

    SciTech Connect

    Kim, Sanghoon; Yu, Hyuk [Univ. of Wisconsin, Madison, WI (United States)

    1992-05-14

    We report a lateral diffusion study on the air/water interface of a surface-active protein, bacterial lipase from Pseudomonas fluorescens, and vinyl polymer, poly(tert-butyl methacrylate), with the technique of fluorescence recovery after photobleaching. For the validation of implementating the technique and the calibration of our instrument, we relied on a phospholipid system that Peters and Beck have used earlier and found that our results were in accord with theirs within 20% in absolute magnitude. For both the phospholipid and lipase, we analyzed the lateral diffusion data in terms of the free area model of Sackmann and Traeuble. We conclude that the results of lipase could be interpreted by invoking a conformational change induced by lateral compression in the monolayer state and those of the polymer, by postulating the quenching of the diffusion process when its concentration crosses over from the dilute regime to the semidilute regime. 37 refs., 11 figs., 2 tabs.

  14. Improvement of microbial fuel cell cathodes using cost-effective polyvinylidene fluoride

    NASA Astrophysics Data System (ADS)

    Qiu, Zhaozheng; Su, Min; Wei, Liling; Han, Hongliang; Jia, Qibo; Shen, Jianquan

    2015-01-01

    In this study polyvinylidene fluoride (PVDF) is investigated as an alternative to polytetrafluoroethylene (PTFE) for air-cathode diffusion layers (DLs) in microbial fuel cells (MFCs) for the improvement of MFC power generation. It is found that the cathode fabricated with PVDF achieves a higher maximum power density (MPD) than a PTFE cathode. Successive PVDF or PVDF/carbon black DLs are applied on the base layers in order to optimize cathode performance. The results show significant improvements in such performances as the coulombic efficiency (CE), MPD, and water loss. In electrochemical tests, the cathode coated with four PVDF DLs has the largest current response at a given applied potential, yielding the highest MPD of 0.123 mW cm-2 (normalized to the projected cathode surface area) and largest CE (10.7%) in the MFC test. Carbon black is added to the DLs in order to test its effect on the MFC power generation. Cathodes made from pure PVDF DLs perform better than those containing PVDF/carbon black DLs in electrochemical and MFC tests. In addition, a smaller MFC (28 mL) produces a much higher MPD than a larger MFC (700 mL), resulting in an increase in the CE.

  15. Effects of plume spacing and flowrate on destratification efficiency of air diffusers.

    PubMed

    Yum, Kyungtaek; Kim, Sung Hoon; Park, Heekyung

    2008-07-01

    This study adopts techniques of computational fluid dynamics (CFD) to analyze the combined effect of adjacent plumes of an air-diffuser system on its destratification efficiency. Lab experiments were carried out to calibrate and verify the CFD models in thermally stratified freshwater. The CFD simulation and lab experiment results were analyzed to relate destratification efficiency with four non-dimensional variables. The results indicate that destratification number, D(N), has the best relationship that includes air flowrate, stratification frequency, water depth, and bubble slip velocity. Since plume spacing and air flowrate are the major control variables of the system, especially in the field, two charts showing the relationships between destratification efficiency, plume spacing, and destratification number are developed for guiding their control in its design and operation. PMID:18577490

  16. Arduino-based control system for measuring ammonia in air using conditionally-deployed diffusive samplers

    NASA Astrophysics Data System (ADS)

    Ham, J. M.; Williams, C.; Shonkwiler, K. B.

    2012-12-01

    Arduino microcontrollers, wireless modules, and other low-cost hardware were used to develop a new type of air sampler for monitoring ammonia at strong areal sources like dairies, cattle feedlots, and waste treatment facilities. Ammonia was sampled at multiple locations on the periphery of an operation using Radiello diffusive passive samplers (Cod. RAD168- and RAD1201-Sigma-Aldrich). However, the samplers were not continuously exposed to the air. Instead, each sampling station included two diffusive samplers housed in specialized tubes that sealed the cartridges from the atmosphere. If a user-defined set of wind and weather conditions were met, the Radiellos were deployed into the air using a micro linear actuator. Each station was solar-powered and controlled by Arduinos that were linked to a central weather station using Xbee wireless modules (Digi International Inc.). The Arduinos also measured the total time of exposure using hall-effect sensors to verify the position of the cartridge (i.e., deployed or retracted). The decision to expose or retract the samplers was made every five minutes based on wind direction, wind speed, and time of day. Typically, the diffusive samplers were replaced with fresh cartridges every two weeks and the used samplers were analyzed in the laboratory using ion chromatography. Initial studies were conducted at a commercial dairy in northern Colorado. Ammonia emissions along the Front Range of Colorado can be transported into the mountains where atmospheric deposition of nitrogen can impact alpine ecosystems. Therefore, low-cost air quality monitoring equipment is needed that can be widely deployed in the region. Initial work at the dairy showed that ammonia concentrations ranged between 600 to 1200 ppb during the summer; the highest concentrations were downwind of a large anaerobic lagoon. Time-averaged ammonia concentrations were also used to approximate emissions using inverse dispersion models. This methodology provides a relatively low-cost technique for measuring the spatial and seasonal variations in ammonia near strong areal sources.

  17. Flickering of thoriated and lanthanized tungsten cathodes

    NASA Astrophysics Data System (ADS)

    Hoebing, Thomas; Hermanns, Patrick; Bergner, Andre; Ruhrmann, Cornelia; Traxler, Hannes; Wesemann, Ingmar; Mentel, Juergen; Awakowicz, Peter

    2014-10-01

    Tungsten cathodes in HID-lamps are commonly doped with rare earth oxides to reduce the work function ?. A popular dopant ThO2 decreases ? from 4.55 eV to 3.0 eV and, therewith, reduces the cathode temperature. La2O3-cathodes seem to represent an alternative, since the reduction of ? is comparable to that of thoriated cathodes. But a temporally unstable arc attachment can be observed at cathodes doped with La2O3. At thoriated cathodes, this flickering can also be detected, but less pronounced. It is attributed to a temporal increase of ?, induced by a transient shortage of La at the cathode tip. The arc attachment moves from the tip to colder areas of the cathode, where a high amount of La is present. Reasons for a temporal increase of ? can be attributed to an insufficient transport of oxides from the interior of the cathode and an insufficient return of vaporized La by an ion current from the arc plasma to the cathode. Enrichments of La/Th compounds are formed on the cathode surface providing emitter material in case of a shortage at the tip. Cathode coverage and diffusion in the interior of the electrode, ThO2- and La2O3-electrodes behave differently. Differences and their influence on the stability of the arc will be presented.

  18. Cathode flow control for fuel cell power plant

    Microsoft Academic Search

    G. W. Scheffler; G. Vartanian

    1989-01-01

    The patent describes a cathode air flow control system for use in a fuel cell power plant to minimize oxygen starvation of fuel cells in the power plant. The system comprising: means forming a fresh air inlet for admitting air into the cathodes of the fuel cells in the power plant; means in the fresh air inlet for varying the

  19. Wastewater treatment, energy recovery and desalination using a forward osmosis membrane in an air-cathode microbial osmotic fuel cell

    E-print Network

    Wastewater treatment, energy recovery and desalination using a forward osmosis membrane in an air Keywords: Forward osmosis Desalination Fouling Microbial osmotic fuel cell a b s t r a c t A microbial osmotic fuel cell (MOFC) has a forward osmosis (FO) membrane situated between the electrodes that enable

  20. A novel method for effective diffusion coefficient measurement in gas diffusion media of polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    Yang, Linlin; Sun, Hai; Fu, Xudong; Wang, Suli; Jiang, Luhua; Sun, Gongquan

    2014-07-01

    A novel method for measuring effective diffusion coefficient of porous materials is developed. The oxygen concentration gradient is established by an air-breathing proton exchange membrane fuel cell (PEMFC). The porous sample is set in a sample holder located in the cathode plate of the PEMFC. At a given oxygen flux, the effective diffusion coefficients are related to the difference of oxygen concentration across the samples, which can be correlated with the differences of the output voltage of the PEMFC with and without inserting the sample in the cathode plate. Compared to the conventional electrical conductivity method, this method is more reliable for measuring non-wetting samples.

  1. Sustained diffusive alternating current gliding arc discharge in atmospheric pressure air

    NASA Astrophysics Data System (ADS)

    Zhu, Jiajian; Gao, Jinlong; Li, Zhongshan; Ehn, Andreas; Aldn, Marcus; Larsson, Anders; Kusano, Yukihiro

    2014-12-01

    Rapid transition from glow discharge to thermal arc has been a common problem in generating stable high-power non-thermal plasmas especially at ambient conditions. A sustained diffusive gliding arc discharge was generated in a large volume in atmospheric pressure air, driven by an alternating current (AC) power source. The plasma column extended beyond the water-cooled stainless steel electrodes and was stabilized by matching the flow speed of the turbulent air jet with the rated output power. Comprehensive investigations were performed using high-speed movies measured over the plasma column, synchronized with simultaneously recorded current and voltage waveforms. Dynamic details of the novel non-equilibrium discharge are revealed, which is characterized by a sinusoidal current waveform with amplitude stabilized at around 200 mA intermediate between thermal arc and glow discharge, shedding light to the governing mechanism of the sustained spark-suppressed AC gliding arc discharge.

  2. Limiting current and wide range air\\/fuel ratio sensors using the same YSZ?A1 2O 3 layers as electrolyte and diffusion barrier

    Microsoft Academic Search

    Jong-Heun Lee; Chang-Soon Kwon; Hoin Kim; Byung-Ki Kim

    1996-01-01

    A limiting current-type oxygen sensor using the same YSZ?A12O3 layers as electrolyte and diffusion barrier was designed to increase thermal shock resistance, case of fabrication, and long-term stability of the sensor. The limiting current of the sensor originated from the limited O2 diffusion towards the cathode side from all directions of the sensor because the microstructures of the electrolyte and

  3. Shapes of Nonbuoyant Round Luminous Laminar-Jet Diffusion Flames in Coflowing Air. Appendix F

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Urban, David L. (Technical Monitor)

    2000-01-01

    The shapes (luminous flame boundaries) of steady nonbuoyant round luminous hydrocarbon-fueled laminar-jet diffusion flames in coflowing air were studied both experimentally and theoretically. Flame shapes were measured from photographs of flames burning at low pressures in order to minimize the effects of buoyancy. Test conditions involved acetylene-, propylene. and 1,3-butadiene-fueled flames having initial reactant temperatures of 300 K, ambient pressures of 19-50 kPa, jet-exit Reynolds numbers of 18-121, and initial air/fuel velocity ratios of 0.22-32.45 to yield luminous flame lengths of 21-198 mm. The present flames were close to the laminar smoke point but were not soot emitting. Simple expressions to estimate the shapes of nonbuoyant laminar-jet diffusion flames in coflow were found by extending an earlier analysis of Mahalingam et al. These formulas provided a good correlation of present measurements except near the burner exit where self-similar approximations used in the simplified analysis are no longer appropriate.

  4. Mineralization of sulfanilamide by electro-Fenton and solar photoelectro-Fenton in a pre-pilot plant with a Pt/air-diffusion cell.

    PubMed

    El-Ghenymy, Abdellatif; Cabot, Pere Llus; Centellas, Francesc; Garrido, Jos Antonio; Rodrguez, Rosa Mara; Arias, Conchita; Brillas, Enric

    2013-05-01

    The mineralization of sulfanilamide solutions at pH 3.0 was comparatively studied by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) using a 2.5 L pre-pilot plant containing a Pt/air-diffusion cell coupled with a solar photoreactor. Organics were primordially oxidized by hydroxyl radical (OH) formed from Fenton's reaction between H?O? generated at the cathode and added Fe(2+) and/or under the action of sunlight. A mineralization up to 94% was achieved using SPEF, whereas EF yielded much poorer degradation. The effect of current density and Fe(2+) and drug concentrations on the degradation rate, mineralization current efficiency and energy cost per unit DOC mass of EF and/or SPEF was examined. The sulfanilamide decay always followed a pseudo first-order kinetics, being more rapid in SPEF due to the additional generation of OH induced by sunlight on Fe(III) species. Catechol, resorcinol, hydroquinone and p-benzoquinone were identified as aromatic intermediates. The final solutions treated by EF contained Fe(III) complexes of maleic, fumaric, oxamic and mainly oxalic acids, which are hardly destroyed by OH. The quick photolysis of Fe(III)-oxalate complexes by sunlight explains the higher oxidation ability of SPEF. The N content of sulfanilamide was mainly mineralized as NH?? ion and in much lesser extent as NO?? ion, whereas most of its initial S was converted into SO?? ion. PMID:23561569

  5. Exploratory investigation of the use of area suction to eliminate air-flow separation in diffusers having large expansion angles

    NASA Technical Reports Server (NTRS)

    Holzhauser, Curt A; Hall, Leo P

    1956-01-01

    Tests were made at a mean inlet Mach number of 0.2 with area suction applied to conical diffusers with expansion angles of 30 degrees and 50 degrees and exit to inlet area ratios of 2. Air-flow separation was eliminated with suction mass flows of 3 and 4 percent of the inlet mass flows for the 30 degrees and 50 degrees diffusers, respectively.

  6. Cathodic electrocatalyst layer for electrochemical generation of hydrogen peroxide

    NASA Technical Reports Server (NTRS)

    Rhodes, Christopher P. (Inventor); Tennakoon, Charles L. K. (Inventor); Singh, Waheguru Pal (Inventor); Anderson, Kelvin C. (Inventor)

    2011-01-01

    A cathodic gas diffusion electrode for the electrochemical production of aqueous hydrogen peroxide solutions. The cathodic gas diffusion electrode comprises an electrically conductive gas diffusion substrate and a cathodic electrocatalyst layer supported on the gas diffusion substrate. A novel cathodic electrocatalyst layer comprises a cathodic electrocatalyst, a substantially water-insoluble quaternary ammonium compound, a fluorocarbon polymer hydrophobic agent and binder, and a perfluoronated sulphonic acid polymer. An electrochemical cell using the novel cathodic electrocatalyst layer has been shown to produce an aqueous solution having between 8 and 14 weight percent hydrogen peroxide. Furthermore, such electrochemical cells have shown stable production of hydrogen peroxide solutions over 1000 hours of operation including numerous system shutdowns.

  7. Moisture diffusivity in quinoa ( Chenopodium quinoa Willd.) seeds: Effect of air temperature and initial moisture content of seeds

    Microsoft Academic Search

    Mara C. Gely; Estela M. Santalla

    2007-01-01

    The moisture diffusivity in quinoa (Chenopodium quinoa Willd.) seeds were evaluated as a function of the air drying temperature and the initial moisture content of seeds obtaining values between 2.5310?12m2\\/s (30C, 12.87% d.b.) and 7.6710?11m2\\/s (90C, 23.44% d.b.). From a statistical analysis based on a factorial experiment, moisture diffusivity showed higher dependence with drying air temperature than with the initial

  8. Resistivity network and structural model of the oxide cathode for CRT application

    Microsoft Academic Search

    Abbass A. Hashim; D. S. Barratt; A. K. Hassan; Jan H. Evans-Freeman; V. Nabok

    2006-01-01

    In this paper, the electrical properties of oxide cathode and oxide cathode plus, supplied by LG Philips Displays, have been investigated in relation to different cathode activation regimes and methods. Oxide cathode activation treatment for different durations has been investigated. The formations of the compounds associated to the diffusion of reducing elements (Mg, Al, and W) to the Ni cap

  9. Thermal and electrochemical decomposition of lithium peroxide in non-catalyzed carbon cathodes for Li-air batteries.

    PubMed

    Beyer, H; Meini, S; Tsiouvaras, N; Piana, M; Gasteiger, H A

    2013-07-14

    The decomposition of lithium peroxide during the charging process of lithium-air batteries is investigated. A novel preparation method for electrodes in the discharged state, i.e., prefilled with Li2O2 using polyethylene oxide as a binder, is presented. The composition and reactivity of Li2O2-prefilled electrodes are examined by thermal analysis coupled with on-line mass spectrometry. Voltage profiles and gas evolution during the charging process of Li2O2-prefilled electrodes in battery cells are correlated with the thermal decomposition process of Li2O2 and its impact on other electrode compounds. It is found that both thermal Li2O2 decomposition and the electrochemical decomposition of Li2O2 during charging enhance the oxidation of the electrolyte, the binder, and/or carbon, which is suggested to be due to the formation of "nascent" oxygen during Li2O2 decomposition into O2 and Li2O (thermally) or into O2 and lithium ions (electrochemically). PMID:23715054

  10. Water Diffusivity and Quality Attributes of Fresh and Partially Osmodehydrated Cactus Pear (Opuntia Ficus Indica) Subjected to Air-Dehydration

    Microsoft Academic Search

    M. A. Ruiz-Cabrera; G. Flores-Gmez; R. Gonzlez-Garca; A. Grajales-Lagunes; M. Moscosa-Santillan; M. Abud-Archila

    2008-01-01

    Water diffusivity, vitamin C degradation, and color change were assessed in two batches of cactus pear that were dried; one by regular air-drying; and the other one by applying partial osmodehydration followed by air-drying. The drying was done with a convection oven at 40, 50, 60, and 70C. The pretreatment was performed by immersing the samples for 3 hours in

  11. Shapes of Nonbuoyant Round Luminous Hydrocarbon/Air Laminar Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Sunderland, P. B.; Urban, D. L.; Yuan, Z.-G.

    1999-01-01

    The shapes (luminous flame boundaries) of round luminous nonbuoyant soot-containing hydrocarbon/air laminar jet diffusion flames at microgravity were found from color video images obtained on orbit in the Space Shuttle Columbia. Test conditions included ethylene- and propane-fueled flames burning in still air at an ambient temperature of 300 K, ambient pressures of 35-130 kPa, initial jet diameters of 1.6 and 2.7 mm, and jet exit Reynolds numbers of 45-170. Present test times were 100-200 s and yielded steady axisymmetric flames that were close to the laminar smoke point (including flames both emitting and not emitting soot) with luminous flame lengths of 15-63 mm. The present soot-containing flames had larger luminous flame lengths than earlier ground-based observations having similar burner configurations: 40% larger than the luminous flame lengths of soot-containing low gravity flames observed using an aircraft (KC-135) facility due to reduced effects of accelerative disturbances and unsteadiness; roughly twice as large as the luminous flame lengths of soot-containing normal gravity flames due to the absence of effects of buoyant mixing and roughly twice as large as the luminous flame lengths of soot-free low gravity flames observed using drop tower facilities due to the presence of soot luminosity and possible reduced effects of unsteadiness. Simplified expressions to estimate the luminous flame boundaries of round nonbuoyant laminar jet diffusion flames were obtained from the classical analysis of Spalding (1979); this approach provided Successful Correlations of flame shapes for both soot-free and soot-containing flames, except when the soot-containing flames were in the opened-tip configuration that is reached at fuel flow rates near and greater than the laminar smoke point fuel flow rate.

  12. Soot Oxidation in Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix K

    NASA Technical Reports Server (NTRS)

    Xu, F.; El-Leathy, A. M.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    Soot oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round jets burning in coflowing air considering acetylene, ethylene, propylene and propane as fuels. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation mainly occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of stable major gas species (N2, H2O, H2, O2, CO, CO2, CH4, C2H2,C2H4, C2H6, C3H6, and C3H8) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by the deconvoluted Li/LiOH atomic absorption technique and flow velocities by laser velocimetry. It was found that soot surface oxidation rates are not particularly affected by fuel type for laminar diffusion flames and are described reasonably well by the OH surface oxidation mechanism with a collision efficiency of 0.10, (standard deviation of 0.07) with no significant effect of fuel type in this behavior; these findings are in good agreement with the classical laminar premixed flame measurements of Neoh et al. Finally, direct rates of surface oxidation by O2 were small compared to OH oxidation for present conditions, based on estimated O2 oxidation rates due to Nagle and Strickland-Constable (1962), because soot oxidation was completed near the flame sheet where O2 concentrations were less than 1.2% by volume.

  13. Soot Surface Oxidation in Laminar Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix I

    NASA Technical Reports Server (NTRS)

    Xu, F.; El-Leathy, A. M.; Kim, C. H.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2003-01-01

    Soot surface oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round fuel jets burning in coflowing dry air considering acetylene-nitrogen, ethylene, propyiene-nitrogen, propane and acetylene-benzene-nitrogen in the fuel stream. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of major stable gas species (N2, H2O, H2, O2, CO, CO2, CH4, C2H2, C2H6, C3H6, C3H8, and C6H6) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by deconvoluted Li/LiOH atomic absorption and flow velocities by laser velocimetry. For present test conditions, it was found that soot surface oxidation rates were not affected by fuel type, that direct rates of soot surface oxidation by O2 estimated from Nagle and Strickland-Constable (1962) were small compared to observed soot surface oxidation rates because soot surface oxidation was completed near the flame sheet where O2 concentrations were less than 3% by volume, and that soot surface oxidation rates were described by the OH soot surface oxidation mechanism with a collision efficiency of 0.14 and an uncertainty (95% confidence) of +/- 0.04 when allowing for direct soot surface oxidation by O2, which is in reasonably good agreement with earlier observations of soot surface oxidation rates in both premixed and diffusion flames at atmospheric pressure.

  14. Soot Oxidation in Laminar Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix D

    NASA Technical Reports Server (NTRS)

    Xu, F.; El-Leathy, A. M.; Faeth, G. M.

    2000-01-01

    Soot oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round jets burning in coflowing air considering acetylene, ethylene, proplyene and propane as fuels. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation mainly occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of stable major gas species (N2, H2O, H2, 02, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H6, and C3H8) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by the deconvoluted Li/LiOH atomic absorption technique and flow velocities by laser velocimetry. It was found that soot surface oxidation rates are not particularly affected by fuel type for laminar diffusion flames and are described reasonably well by the OH surface oxidation mechanism with a collision efficiency of 0.10, (standard deviation of 0.07) with no significant effect of fuel type in this behavior; these findings are in good agreement with the classical laminar premixed flame measurements of Neoh et al. Finally, direct rates of surface oxidation by O2 were small compared to OH oxidation for present conditions, based on estimated O2 oxidation rates due to Nagle and Strickland-Constable, because soot oxidation was completed near the flame sheet where O2 concentrations were less than 1.2% by volume.

  15. Shapes of Nonbuoyant Round Luminous Hydrocarbon/Air Laminar Jet Diffusion Flames. Appendix H

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Sunderland, P. B.; Urban, D. L.; Yuan, Z.-G.; Ross, Howard B. (Technical Monitor)

    2000-01-01

    The shapes (luminous flame boundaries) of round luminous nonbuoyant soot-containing hydrocarbon/air laminar jet diffusion flames at microgravity were found from color video images obtained on orbit in the Space Shuttle Columbia. Test conditions included ethylene- and propane-fueled flames burning in still air at an ambient temperature of 300 K ambient pressures of 35-130 kPa, initial jet diameters of 1.6 and 2.7 mm, and jet exit Reynolds numbers of 45-170. Present test times were 100-200 s and yielded steady axisymmetric flames that were close to the laminar smoke point (including flames both emitting and not emitting soot) with luminous flame lengths of 15-63 mm. The present soot-containing flames had larger luminous flame lengths than earlier ground-based observations having similar burner configurations: 40% larger than the luminous flame lengths of soot-containing low gravity flames observed using an aircraft (KC-135) facility due to reduced effects of accelerative disturbances and unsteadiness; roughly twice as large as the luminous flame lengths of soot-containing normal gravity flames due to the absence of effects of buoyant mixing and roughly twice as large as the luminous flame lengths of soot-free low gravity flames observed using drop tower facilities due to the presence of soot luminosity and possible reduced effects of unsteadiness, Simplified expressions to estimate the luminous flame boundaries of round nonbuoyant laminar jet diffusion flames were obtained from the classical analysis of Spalding; this approach provided successful correlations of flame shapes for both soot-free and soot-containing flames, except when the soot-containing flames were in the opened-tip configuration that is reached at fuel flow rates near and greater than the laminar smoke point fuel flow rate.

  16. Soot Formation in Laminar Acetylene/Air Diffusion Flames at Atmospheric Pressure. Appendix J

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation--O2, CO2, H2O, O, and OH-are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.

  17. Soot Formation in Laminar Acetylene/Air Diffusion Flames at Atmospheric Pressure. Appendix H

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation-O2, CO2, H2O, O, and OH-are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.

  18. Soot Formation in Laminar Acetylene/Air Diffusion Flames at Atmospheric Pressure. Appendix C

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2000-01-01

    The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation-O2, CO2, H2O, O, and OH-are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.

  19. Comparison of annular diffusion denuder and high volume air samplers for measuring per- and polyfluoroalkyl substances in the atmosphere.

    PubMed

    Ahrens, Lutz; Shoeib, Mahiba; Harner, Tom; Lane, Douglas A; Guo, Rui; Reiner, Eric J

    2011-12-15

    Overestimation of the particle phase concentration collected on glass-fiber filters (GFFs) has been reported for perfluoroalkyl carboxylic acids (PFCAs) using conventional high volume air samplers. In this study, per- and polyfluoroalkyl substances (PFASs) were determined in the gas and particulate phases using colocated annular diffusion denuder and high volume air samplers at a semiurban site in Toronto, Canada, in winter 2010. Samples were analyzed for 7 PFAS classes (i.e., PFCAs, perfluoro-alkane sulfonic acids (PFSAs), fluorotelomer alcohols (FTOHs), fluorotelomer methacrylates (FTMACs), fluorotelomer acrylates (FTACs), perfluorooctane sulfonamides (FOSAs), and perfluorooctane sulfonamidoethanols (FOSEs)). The gas diffusion coefficients for individual PFASs were calculated and the denuder performance was evaluated. Modeled subcooled liquid vapor pressures (p(L)) correlated well with the vapor phase breakthrough for the denuder and high volume air systems. Total air concentrations for PFASs measured using annular diffusion denuders and high volume samplers were in agreement within a factor of 4; however, much greater differences were observed for measurements of gas-particle partitioning. Vapor phase PFSAs and PFCAs can adsorb to the GFF using high volume air samplers, resulting in much higher particle-associated fractions for these chemicals compared to the annular diffusion denuder sampler. This effect was not observed for the FTOHs, FTMACs, FTACs, FOSAs, and FOSEs. Thus, for investigations of gas-particle partitioning of PFSAs and PFCAs, the diffusion denuder sampler is the preferred method. The results of this study improve our understanding of the gas-particle partitioning of PFASs, which is important for modeling their long-range transport in air. PMID:22066738

  20. Two-phase computational fluid dynamics assessment of bubble plume in air-diffuser destratification.

    PubMed

    Yum, K; Ahn, J; Park, H; Ko, I H

    2005-09-01

    Hydrodynamic flow patterns and behavior induced by bubble plumes in a linearly stratified fluid are studied. To optimize an air-diffuser destratification system, we used computational fluid dynamics software to develop a two-phase (air-water) destratification model. The model enables us to simulate complicated stratification conditions with different densities and source strengths. We conducted laboratory experiments to verify the model in thermally stratified fresh water. The computational fluid dynamics model performs well when the plume number ranges from 30 to 600. We successfully explain various phenomena, including the hydrodynamic behavior of bubble plumes and turbulent three dimension flow patterns. Our approach provides a level of detail not possible with other one-dimensional plume models. Contrary to the findings of other researchers, our experiments and computational fluid dynamics simulation indicate that the energy conversion efficiency increases as plume number increases; moreover, the three flow types do not occur in the same plume number regimes defined in other research. The difference is apparently due to the effect of the bubble size. PMID:16196412

  1. Diamond p-n junction cold cathode

    NASA Astrophysics Data System (ADS)

    Kennel, Elliot B.; Zaibyshev, Vladimir Z.; Kucherov, Rafail Y.; Svensson, C. Robert; Davis, Paul R.; Mackie, William A.

    1993-06-01

    This effort successfully demonstrated that intercalated graphite fibers are outstanding cathode materials. Such fibers are stable in air at ambient temperature and offer current densities of over 100 Amps/sq cm at 10 volts bias voltage (at 700 K). Ambient temperature cathodes also offer high current capability at somewhat higher bias voltage. Cesiated graphite and diamond both exhibit these characteristics, but graphite intercalation compounds are stable in air whereas the diamond/cesium system is not. The graphite cathodes do not require a cesium reservoir in order to function.

  2. Experimental Method Development for Estimating Solid-phase Diffusion Coefficients and Material/Air Partition Coefficients of SVOCs

    EPA Science Inventory

    The solid-phase diffusion coefficient (Dm) and material-air partition coefficient (Kma) are key parameters for characterizing the sources and transport of semivolatile organic compounds (SVOCs) in the indoor environment. In this work, a new experimental method was developed to es...

  3. 14 Diffusive CO2 Flux at the Air-Water Interface of the Robert-Bourassa Hydroelectric Reservoir in

    E-print Network

    Long, Bernard

    14 Diffusive CO2 Flux at the Air-Water Interface of the Robert-Bourassa Hydroelectric Reservoir Hydroelectric reservoirs and lakes in boreal Qubec produce greenhouse gases (GHG) mainly in the form of CO2 of the interface. When applied to the Robert- Bourassa hydroelectric reservoir in boreal Qubec, this model

  4. Headgroup Immersion Depth and Its Effect on the Lateral Diffusion of Amphiphiles at the Air/Water Interface

    E-print Network

    Majda, Marcin

    Headgroup Immersion Depth and Its Effect on the Lateral Diffusion of Amphiphiles at the Air/water interface to characterize the lateral mobilities of several long alkyl chain ferrocene amphiphiles strongly on the headgroup polarity, demonstrating that the immersion depth of the amphiphiles is the key

  5. Enhanced nitrogen removal in single-chamber microbial fuel cells with increased gas diffusion areas.

    PubMed

    Yan, Hengjing; Regan, John M

    2013-03-01

    Single-chamber microbial fuel cells (MFCs) with nitrifiers pre-enriched at the air cathodes have previously been demonstrated as a passive strategy for integrating nitrogen removal into current-generating bioelectrochemical systems. To further define system design parameters for this strategy, we investigated in this study the effects of oxygen diffusion area and COD/N ratio in continuous-flow reactors. Doubling the gas diffusion area by adding an additional air cathode or a diffusion cloth significantly increased the ammonia and COD removal rates (by up to 115% and 39%), ammonia removal efficiency (by up to 134%), the cell voltage and cathode potentials, and the power densities (by a factor of approximately 2). When the COD/N ratio was lowered from 13 to 3, we found up to 244% higher ammonia removal rate but at least 19% lower ammonia removal efficiency. An increase of COD removal rate by up to 27% was also found when the COD/N ratio was lowered from 11 to 3. The Coulombic efficiency was not affected by the additional air cathode, but decreased by an average of 11% with the addition of a diffusion cloth. Ammonia removal by assimilation was also estimated to understand the ammonia removal mechanism in these systems. These results showed that the doubling of gas diffusion area enhanced N and COD removal rates without compromising electrochemical performance. PMID:23097182

  6. Evaluation of passive diffusion bag and dialysis samplers in selected wells at Hickam Air Force Base, Hawaii, July 2001

    USGS Publications Warehouse

    Vroblesky, Don A.; Pravecek, Tasha

    2002-01-01

    Field comparisons of chemical concentrations obtained from dialysis samplers, passive diffusion bag samplers, and low-flow samplers showed generally close agreement in most of the 13 wells tested during July 2001 at Hickam Air Force Base, Hawaii. The data for chloride, sulfate, iron, alkalinity, arsenic, and methane appear to show that the dialysis samplers are capable of accurately collecting a passive sample for these constituents. In general, the comparisons of volatile organic compound concentrations showed a relatively close correspondence between the two different types of diffusion samples and between the diffusion samples and the low-flow samples collected in most wells. Divergence appears to have resulted primarily from the pumping method, either producing a mixed sample or water not characteristic of aquifer water moving through the borehole under ambient conditions. The fact that alkalinity was not detected in the passive diffusion bag samplers, highly alkaline waters without volatilization loss from effervescence, which can occur when a sample is acidified for preservation. Both dialysis and passive diffusion bag samplers are relatively inexpensive and can be deployed rapidly and easily. Passive diffusion bag samplers are intended for sampling volatile organic compounds only, but dialysis samplers can be used to sample both volatile organic compounds and inorganic solutes. Regenerated cellulose dialysis samplers, however, are subject to biodegradation and probably should be deployed no sooner than 2 weeks prior to recovery. 1 U.S. Geological Survey, Columbia, South Carolina. 2 Air Florce Center for Environmental Excellence, San Antionio, Texas.

  7. Rechargeability of Li-air cathodes pre-filled with discharge products using an ether-based electrolyte solution: implications for cycle-life of Li-air cells.

    PubMed

    Meini, Stefano; Tsiouvaras, Nikolaos; Schwenke, K Uta; Piana, Michele; Beyer, Hans; Lange, Lukas; Gasteiger, Hubert A

    2013-07-21

    The instability of currently used electrolyte solutions and of the carbon support during charge-discharge in non-aqueous lithium-oxygen cells can lead to discharge products other than the desired Li2O2, such as Li2CO3, which is believed to reduce cycle-life. Similarly, discharge in an O2 atmosphere which contains H2O and CO2 impurities would lead to LiOH and Li2CO3 discharge products. In this work we therefore investigate the rechargeability of model cathodes pre-filled with four possible Li-air cell discharge products, namely Li2O2, Li2CO3, LiOH, and Li2O. Using Online Electrochemical Mass Spectrometry (OEMS), we determined the charge voltages and the gases evolved upon charge of pre-filled electrodes, thus determining the reversibility of the formation/electrooxidation reactions. We show that Li2O2 is the only reversible discharge product in ether-based electrolyte solutions, and that the formation of Li2CO3, LiOH, or Li2O is either irreversible and/or reacts with the electrolyte solution or the carbon during its oxidation. PMID:23748698

  8. Dynamic Weakening (Extinction) of Simple Hydrocarbon-air Counterflow Diffusion Flames by Oscillatory Inflows

    NASA Technical Reports Server (NTRS)

    Pellett, G.; Kabaria, A.; Panigrahi, B.; Sammons, K.; Convery, J.; Wilson, L.

    2005-01-01

    This study of laminar non-premixed HC-air flames used an Oscillatory-input Opposed Jet Burner (OOJB) system developed from a previously well-characterized 7.2-mm Pyrex-nozzle OJB system. Over 600 dynamic Flame Strength (FS) measurements were obtained on unanchored (free-floating) laminar Counterflow Diffusion Flames (CFDF's). Flames were stabilized using plug inflows having steady-plus-sinusoidal axial velocities of varied magnitude, frequency, f, up to 1600 Hz, and phase angle from 0 (most data) to 360 degrees. Dynamic FS is defined as the maximum average air input velocity (U(sub air), at nozzle exit) a CFDF can sustain before strain-induced extinction occurs due to prescribed oscillatory peak-to-peak velocity inputs superimposed on steady inputs. Initially, dynamic flame extinction data were obtained at low f, and were supported by 25-120 Hz Hot-Wire cold-flow velocity data at nozzle exits. Later, expanded extinction data were supported by 4-1600 Hz Probe Microphone (PM) pk/pk P data at nozzle exits. The PM data were first obtained without flows, and later with cold stagnating flows, which better represent speaker-diaphragm dynamics during runs. The PM approach enabled characterizations of Dynamic Flame Weakening (DFW) of CFDF's from 8 to 1600 Hz. DFW was defined as % decrease in FS per Pascal of pk/pk P oscillation, namely, DFW = - 100 d(U(sub air) / U(sub air),0Hz) / d(pkpk P). The linear normalization with respect to acoustic pressure magnitude (and steady state (SS) FS) led to a DFW unaffected by strong internal resonances. For the C2H4/N2-air system, from 8 to 20 Hz, DFW is constant at 8.52 plus or minus 0.20 (% weakening)/Pa. This reflects a quasi-steady flame response to an acoustically induced dU(sub air)/dP. Also, it is surprisingly independent of C2H4/N2 mole fraction due to normalization by SS FS. From 20 to approximately 150 Hz, the C2H4/N2 air-flames weakened progressively less, with an inflection at approximately 70 Hz, and became asymptotically insensitive (DFW approximately 0) at approximately 300 Hz, which continued to 1600 Hz. The DFW of CH4-air flames followed a similar pattern, but showed much greater weakening than C2H4/N2-air flames; i.e., the quasi-steady DFW (8 to approximately 15 Hz) was 44.3 %/Pa, or approximately 5x larger, even though the 0 Hz (SS) FS was only 3.0 x smaller. The quasi-steady DFW's of C3H8-air and C2H6-air were intermediate at 34.8 and 20.9 %Pa, respectively. The DFW profiles of all four fuels, at various frequencies, correlated well but non-linearly with respective SS FS's. Notably, the DFW profile for C3H8 air fell more rapidly in the range greater than 15 to 60 Hz, compared with the 1- and 2-carbon fuels. This may indicate a shift in chemical kinetics, and/or O2 transport to a flame that moved closer to the fuel-side. In conclusion, Dynamic Flame Weakening limits appear significant and unique for each fuel, and correlate closely, but non-linearly, with Steady-State Flame Strengths at any given frequency. For reasons unknown, the dynamic flames didn't weaken more at intermediate frequencies (e.g., at 20-50 Hz) than they did at low frequencies (less than 15 Hz), where quasi-steady weakening appears to dominate. Quasi-steady flame weakening ostensibly represents a transient input strain rate maximum that just exceeds the steady-state strain-rate-limited extinction limit for a few cycles. Clearly, further detailed mechanistic understanding is needed in the fall-off region.

  9. New insights in the polarization resistance of anode-supported solid oxide fuel cells with La0.6Sr0.4Co0.2Fe0.8O3 cathodes

    SciTech Connect

    Lu, Zigui; Hardy, John S.; Templeton, Jared W.; Stevenson, Jeffry W.

    2011-01-01

    In this study, the polarization resistance of the La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) solid oxide fuel cell (SOFC) cathode was investigated by I-V sweep and electrochemcial impedance spectroscopy under a series of dc bias voltages and cathode environments (i.e. stagnant air, flowing air, and flowing oxygen) at temperatures from 550 to 750 C. In flowing oxygen, the polarization resistance of the fuel cell decreased considerably with the applied current density. A linear relationship was observed between the ohmic-free over-potential and the logarithm of the current density of the fuel cell at all the measuring temperatures. In stagnant or flowing air, a new arc related to the molecular oxygen diffusion in the pores of the cathode was identified at high temperatures and high current densities. The magnitude of this arc increased with the applied current density due to the decreased oxygen partial pressure at the interface of the cathode and the electrolyte. It is found that the performance of the fuel cell in air is mainly determined by the oxygen diffusion process. Elimination of this process by flowing oxygen to the cathode improved the cell performance significantly. At 750 C, for a fuel cell with a laser-deposited Sm0.2Ce0.8O1.9 (SDC) interlayer, an extraordinarily high power density of 2.6 W cm-2 at 0.7 V was achieved in flowing oxygen, as a result of reduced ohmic and polarization resistance of the fuel cell, which were 0.06 ? cm2 and 0.03 ? cm2, respectively. The results indicate that optimization of the microstructure of the LSCF cathode or adoption of a new cell design which can mitigate the diffusion problem in the cathode might enhance cell performance significantly.

  10. Numerical study of the effects of gravity on soot formation in laminar coflow methane\\/air diffusion flames under different air stream velocities

    Microsoft Academic Search

    Wenjun Kong; Fengshan Liu

    2009-01-01

    Numerical simulations of laminar coflow methane\\/air diffusion flames at atmospheric pressure and different gravity levels were conducted to gain a better understanding of the effects of gravity on soot formation by using relatively detailed gas-phase chemistry and complex thermal and transport properties coupled with a semi-empirical two-equation soot model. Thermal radiation was calculated using the discrete-ordinates method coupled with a

  11. High current diffuse dielectric barrier discharge in atmospheric pressure air for the deposition of thin silica-like films

    NASA Astrophysics Data System (ADS)

    Starostin, S. A.; Premkumar, P. Antony; Creatore, M.; de Vries, H.; Paffen, R. M. J.; van de Sanden, M. C. M.

    2010-02-01

    The diffuse dielectric barrier discharge in atmospheric pressure air was applied for the thin film deposition on polymeric web in industrially relevant roll-to-roll configuration. The silica-like film deposition was performed using the admixture of hexamethyldisiloxane precursor to air flow. Fast discharge imaging at 2 ?s exposure time confirms plasma uniformity in a single current pulse time scale. Morphology and composition analyses indicate that the process results in ultrasmooth films (roughness comparable to initial substrate roughness) and shows the possibility to synthesize carbon-free layers.

  12. Hollow cathode apparatus

    NASA Technical Reports Server (NTRS)

    Aston, G. (inventor)

    1984-01-01

    A hollow cathode apparatus is described, which can be rapidly and reliably started. An ignitor positioned upstream from the hollow cathode, generates a puff of plasma that flows with the primary gas to be ionized through the cathode. The plasma puff creates a high voltage breakdown between the downstream end of the cathode and a keeper electrode, to heat the cathode to an electron-emitting temperature.

  13. Development of a diffuse air-argon plasma source using a dielectric-barrier discharge at atmospheric pressure

    SciTech Connect

    Tang Jie; Jiang Weiman; Zhao Wei; Wang Yishan; Li Shibo; Wang Haojing [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119 (China)] [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119 (China); Duan Yixiang [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119 (China) [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119 (China); Research Center of Analytical Instrumentation, Sichuan University, Chengdu 610064 (China)

    2013-01-21

    A stable diffuse large-volume air plasma source was developed by using argon-induced dielectric-barrier discharges at atmospheric pressure. This plasma source can be operated in a filamentary discharge with the average areal power density of 0.27 W/cm{sup 2} and the gas temperature of 315{+-}3 K. Spatial measurement of emission spectrum and temperature indicates that this plasma is uniform in the central region along the transverse direction. It is also found that the formation of diffuse air plasma mainly lies in the creation of sufficient seed electrons by the Penning effect through collisions between two argon or nitrogen metastables at low electric fields.

  14. A new measurement method for nitrogen oxides in the air using an annular diffusion scrubber coated with titanium dioxide

    Microsoft Academic Search

    Yuichi Komazaki; Hiroki Shimizu; Shigeru Tanaka

    1999-01-01

    A new convenient measurement method of nitrogen oxides (NOx) in the ambient air was developed. The collection of NOx is performed by an annular diffusion scrubber coated with a mixture of titanium dioxide (TiO2) and hydroxyapatite (Ca10(PO4)6(OH)2) and the analysis is carried out by ion chromatography with conductivity detection. Under ultraviolet light (UV) illumination, TiO2 produces reactive oxygen species such

  15. Nanotube cathodes.

    SciTech Connect

    Overmyer, Donald L.; Lockner, Thomas Ramsbeck; Siegal, Michael P.; Miller, Paul Albert

    2006-11-01

    Carbon nanotubes have shown promise for applications in many diverse areas of technology. In this report we describe our efforts to develop high-current cathodes from a variety of nanotubes deposited under a variety of conditions. Our goal was to develop a one-inch-diameter cathode capable of emitting 10 amperes of electron current for one second with an applied potential of 50 kV. This combination of current and pulse duration significantly exceeds previously reported nanotube-cathode performance. This project was planned for two years duration. In the first year, we tested the electron-emission characteristics of nanotube arrays fabricated under a variety of conditions. In the second year, we planned to select the best processing conditions, to fabricate larger cathode samples, and to test them on a high-power relativistic electron beam generator. In the first year, much effort was made to control nanotube arrays in terms of nanotube diameter and average spacing apart. When the project began, we believed that nanotubes approximately 10 nm in diameter would yield sufficient electron emission properties, based on the work of others in the field. Therefore, much of our focus was placed on measured field emission from such nanotubes grown on a variety of metallized surfaces and with varying average spacing between individual nanotubes. We easily reproduced the field emission properties typically measured by others from multi-wall carbon nanotube arrays. Interestingly, we did this without having the helpful vertical alignment to enhance emission; our nanotubes were randomly oriented. The good emission was most likely possible due to the improved crystallinity, and therefore, electrical conductivity, of our nanotubes compared to those in the literature. However, toward the end of the project, we learned that while these 10-nm-diameter CNTs had superior crystalline structure to the work of others studying field emission from multi-wall CNT arrays, these nanotubes still had a thin coating of glassy carbon surrounding them in a sheath-like manner. This glassy carbon, or nano-crystalline graphite, is likely to be a poor conductor due to phonon scattering, and should actually be deleterious for extracting electrons with electric fields. While we did not achieve the field emission reported for single-wall carbon nanotubes that spurred the idea for this project, at the year's very end, we had a breakthrough in materials growth and learned to control the growth of very-small diameter nanotubes ranging from 1.4 to 7 nm. The 1.4-nm nanotubes are single-walled and grow at only 530 C. This is the lowest temperature known to result in single-wall carbon nanotubes, and may be very important for many applications that where certain substrates could not be used due to the high temperatures commonly used for CNT growth. Critically important for field emission, these small diameter nanotubes, consisting of only a few concentric graphene cylindrical walls, do not show the presence of a poorly-conductive sheath material. Therefore, these nanotubes will almost definitely have superior field emission properties to those we already measured, and it is possible that they could provide the necessary field emission to make this project successful. Controlled spacing and lengths of these single-wall nanotubes have yet to be explored, along with correlating their structures to their improved field emission. Unfortunately, we did not discover the methods to grow these highly-crystalline and small diameter CNTs until late in the year. Since we did not achieve the necessary emission properties by mid-year, the project was ''prematurely'' terminated prior to the start of the second year. However, it should be noted that with the late developments, this work has not hit the proverbial ''brick wall''. Clearly the potential still exists to reproduce and even exceed the high emission results reported for randomly-oriented and curly single-wall carbon nanotubes, both in terms of total field emitting currents and perhaps more importantly, in reproducibility.

  16. Diffusion

    NSDL National Science Digital Library

    Christopher Thomas (None; )

    2006-11-09

    Diffusion is the movement of particles from an area of high concentration to an area of low concentration. The molecules move until equilibrium is reached. If a perfume is sprayed on one side of the room, the perfume molecules will eventually spread out all over the room until there are equal concentrations of the molecules throughout the space.

  17. Effects of H2O, CO2, and N2 air contaminants on critical airside strain rates for extinction of hydrogen-air counterflow diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Guerra, Rosemary

    1989-01-01

    Dish-shaped counterflow diffusion flames centered by opposing laminar jets of H2 and clean and contaminant O2/N2 mixtures in an argon bath at 1 atm were used to study the effects of contaminants on critical airside strain. The jet velocities for both flame extinction and restoration are found for a wide range of contaminant and O2 concentrations in the air jet. The tests are also conducted for a variety of input H2 concentrations. The results are compared with those from several other studies.

  18. Nonlinear analysis of polymer electrolyte fuel cell dynamics with cathode two-phase flow

    NASA Astrophysics Data System (ADS)

    Burkholder, Michael; Litster, Shawn

    2013-11-01

    Water management in polymer electrolyte fuel cells (PEFCs) must be optimized to minimize parasitic costs. Removing water with excessive air flow rates at low-current, low-power conditions can be very parasitic, but these conditions can be unstable from the two-phase slug flow in the cathode air-delivery microchannels that occurs from the intrinsically low air and water flow rates. In this work, we use nonlinear analysis to understand the effect that varying currents and air flow rates have on PEFC dynamics. We estimate the dimension and entropy invariants indicative of dynamical complexity and stability from a reconstructed state space embedded using PEFC voltage data. We show that the estimated invariants can be correlated to the channel two-phase flow regime. We also investigate autocorrelation in the voltage signal by using diffusion analysis to estimate Hurst exponents. Lastly, we propose a reduced order map for application to real time PEFC water management.

  19. Diffusion sampler testing at Naval Air Station North Island, San Diego County, California, November 1999 to January 2000

    USGS Publications Warehouse

    Vroblesky, Don A.; Peters, Brian C.

    2000-01-01

    Volatile organic compound concentrations in water from diffusion samplers were compared to concentrations in water obtained by low-flow purging at 15 observation wells at the Naval Air Station North Island, San Diego, California. Multiple diffusion samplers were installed in the wells. In general, comparisons using bladder pumps and diffusion samplers showed similar volatile organic carbon concentrations. In some wells, sharp concentration gradients were observed, such as an increase in cis-1,2-dichloroethene concentration from 100 to 2,600 micrograms per liter over a vertical distance of only 3.4 feet. In areas where such sharp gradients were observed, concentrations in water obtained by low-flow sampling at times reflected an average concentration over the area of influence; however, concentrations obtained by using the diffusion sampler seemed to represent the immediate vicinity of the sampler. When peristaltic pumps were used to collect ground-water samples by low-flow purging, the volatile organic compound concentrations commonly were lower than concentrations obtained by using diffusion samplers. This difference may be due to loss of volatiles by degassing under negative pressures in the sampling lines induced while using the peristaltic pump, mixing in the well screen, or possible short-circuiting of water from an adjacent depth. Diffusion samplers placed in buckets of freephase jet fuel (JP-5) and Stoddard solvent from observation wells did not show evidence of structural integrity loss during the 2 months of equilibration, and volatile organic compounds detected in the free-phase fuel also were detected in the water from the diffusion samplers.

  20. Diffusion

    NSDL National Science Digital Library

    Since the advent of the internet, a number of artists and related organizations have become interested in utilizing the web to promulgate new forms of artistic creation and their subsequent dissemination. Supported by the Arts Council of England, these Diffusion eBooks are essentially pdf files that readers can download, print out and make into booklets. As the site suggests, "the Diffusion format challenges conventions of interactivity-blending the physical and the virtual and breaking the dominance of mouse and screen as the primary forms of human computer interaction...the format's aim is to take the reader away from the screen and computer and engage them in the process of production." There are a number of creative booklets available here for visitors, complete with instruction on how to assemble them for the desired effect. For anyone with even a remote interest in the possibilities afforded by this rather curious new form of expression, this website is worth a look.

  1. A new measurement method for nitrogen oxides in the air using an annular diffusion scrubber coated with titanium dioxide

    NASA Astrophysics Data System (ADS)

    Komazaki, Yuichi; Shimizu, Hiroki; Tanaka, Shigeru

    A new convenient measurement method of nitrogen oxides (NO x) in the ambient air was developed. The collection of NO x is performed by an annular diffusion scrubber coated with a mixture of titanium dioxide (TiO 2) and hydroxyapatite (Ca 10(PO 4) 6(OH) 2) and the analysis is carried out by ion chromatography with conductivity detection. Under ultraviolet light (UV) illumination, TiO 2 produces reactive oxygen species such as super oxide (O 2-), hydroxyl radical (OH) and peroxyhydroxyl radical (HO 2), by which nitric oxide (NO) is oxidized to nitrogen dioxide (NO 2), and is further oxidized to nitric acid (HNO 3). The yielded HNO 3 and NO 2 are effectively adsorbed on the surface of TiO 2 and hydroxyapatite. The collection efficiencies of NO and NO 2 by the annular diffusion scrubber coated with the catalysts under UV illumination are higher than 98%, respectively, at the air flow rate of 0.2-1.0 l min -1. After the collection of NO x, by feeding deionized water into the annular diffusion scrubber, HNO 3 and NO 2 which adsorbed on the catalysts are extracted as forms of nitrite ion (NO 2-) and nitrate ion (NO 3-). The extraction efficiencies of NO and NO 2 are almost 100%. The activity of the washed catalysts can be completely recovered by drying with the purified air. Further, a simultaneous separated measurement of NO and NO 2 can be performed by utilizing the UV illumination dependence. This method was applied to the measurement of NO x in the ambient air. The NO x concentration measured by this method was in good agreement with that obtained using the chemiluminescence NO x analyzer.

  2. Improvements to a Transport Model of Asphalt Binder Oxidation in Pavements: Pavement Temperature Modeling, Oxygen Diffusivity in Asphalt Binders and Mastics, and Pavement Air Void Characterization

    E-print Network

    Han, Rongbin

    2012-07-16

    in pavements. In this model, oxygen transport and reaction were described mathematically as two interlinked steps: 1) diffusion and/or flow of oxygen from the atmosphere above the pavement into the interconnected air voids in the pavement; and 2) diffusion...

  3. CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting, Devon Island, Canada

    E-print Network

    Chappellaz, Jrme

    CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting and the effects of summer melting. The 14 CO2 profile from the permeable firn includes the 1963 thermonuclear peak no indication of alteration by summer melting, which is attributed to a high degree of convective and diffusive

  4. Investigations of cathode phenomena in pseudospark discharges

    NASA Astrophysics Data System (ADS)

    Felsner, P.; Stetter, M.; Hartmann, W.; Linsenmeyer, A.; Christiansen, J.; Frank, K.

    1994-11-01

    The cathode phenomena during the conduction phase of a pseudospark discharge are investigated with different cathode materials: Cu, Mo, Ni, Ta, and W/Re. The discharge gas was hydrogen with a gas pressure of 40 Pa. At a pulse duration of 2.7 microsecond and a maximum current of 9 kA, i.e., at a transferred charge of 11 mC/discharge, mass erosion rates of the cathode materials showed no significant material dependence after 10(exp 6) discharges. Fast framing photography (end-on, exposure time: 5 ns) of the light emission from the cathode surface revealed several small spots simultaneously, distributed over a cathode surface of 1 sq cm. The distribution of metal and hydrogen spectral lines at the cathode surface and in the gap were compared. Metal lines are localized on the cathode surface, whereas the hydrogen Balmer beta-line is diffuse over the electrodes surfaces and the gap. Polished electrodes showed, after a single pulse, about 10(exp 7) craters with 0.5-5 micrometer diameter. This is leading to a local current density of about 10(exp 8) A/sq cm in a single crater.

  5. Analysis and experimental study on formation conditions of large-scale barrier-free diffuse atmospheric pressure air plasmas in repetitive pulse mode

    SciTech Connect

    Li, Lee, E-mail: leeli@mail.hust.edu.cn; Liu, Lun; Liu, Yun-Long; Bin, Yu; Ge, Ya-Feng; Lin, Fo-Chang [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electric and Electronic Engineering, HuaZhong University of Science and Technology (HUST), Wuhan 430074 (China)

    2014-01-14

    Atmospheric air diffuse plasmas have enormous application potential in various fields of science and technology. Without dielectric barrier, generating large-scale air diffuse plasmas is always a challenging issue. This paper discusses and analyses the formation mechanism of cold homogenous plasma. It is proposed that generating stable diffuse atmospheric plasmas in open air should meet the three conditions: high transient power with low average power, excitation in low average E-field with locally high E-field region, and multiple overlapping electron avalanches. Accordingly, an experimental configuration of generating large-scale barrier-free diffuse air plasmas is designed. Based on runaway electron theory, a low duty-ratio, high voltage repetitive nanosecond pulse generator is chosen as a discharge excitation source. Using the wire-electrodes with small curvature radius, the gaps with highly non-uniform E-field are structured. Experimental results show that the volume-scaleable, barrier-free, homogeneous air non-thermal plasmas have been obtained between the gap spacing with the copper-wire electrodes. The area of air cold plasmas has been up to hundreds of square centimeters. The proposed formation conditions of large-scale barrier-free diffuse air plasmas are proved to be reasonable and feasible.

  6. Analysis and experimental study on formation conditions of large-scale barrier-free diffuse atmospheric pressure air plasmas in repetitive pulse mode

    NASA Astrophysics Data System (ADS)

    Li, Lee; Liu, Lun; Liu, Yun-Long; Bin, Yu; Ge, Ya-Feng; Lin, Fo-Chang

    2014-01-01

    Atmospheric air diffuse plasmas have enormous application potential in various fields of science and technology. Without dielectric barrier, generating large-scale air diffuse plasmas is always a challenging issue. This paper discusses and analyses the formation mechanism of cold homogenous plasma. It is proposed that generating stable diffuse atmospheric plasmas in open air should meet the three conditions: high transient power with low average power, excitation in low average E-field with locally high E-field region, and multiple overlapping electron avalanches. Accordingly, an experimental configuration of generating large-scale barrier-free diffuse air plasmas is designed. Based on runaway electron theory, a low duty-ratio, high voltage repetitive nanosecond pulse generator is chosen as a discharge excitation source. Using the wire-electrodes with small curvature radius, the gaps with highly non-uniform E-field are structured. Experimental results show that the volume-scaleable, barrier-free, homogeneous air non-thermal plasmas have been obtained between the gap spacing with the copper-wire electrodes. The area of air cold plasmas has been up to hundreds of square centimeters. The proposed formation conditions of large-scale barrier-free diffuse air plasmas are proved to be reasonable and feasible.

  7. Pulsed mode cathode

    NASA Technical Reports Server (NTRS)

    Myers, Roger M. (inventor); Rawlin, Vinvent K. (inventor)

    1994-01-01

    A cathode in an MPD thruster has an internal heater and utilizes low work function material. The cathode is preheated to operating temperature, and then the thruster is fired by discharging a capacitor bank in a pulse forming network.

  8. Surface diffusion control of the photocatalytic oxidation in air/TiO2 heterogeneous reactors

    E-print Network

    Tsekov, R

    2015-01-01

    The diffusion of superoxide radical anions on the surface of TiO2 catalysts is theoretically considered as an important step in the kinetics of photocatalytic oxidation of toxic pollutants. A detailed analysis is performed to discriminate the effects of rotation, anion and adsorption bonds vibrations on the diffusion coefficient. A resonant dependence of the diffusivity on the lattice parameters of the TiO2 surface is discovered showing that the most rapid diffusion takes place when the lattice parameters are twice larger than the bond length of the superoxide radical anions. Whereas the rotation and vibrations normal to the catalyst surface are important, the anion bond vibrations do not affect the diffusivity due to their low amplitudes as compared to the lattice parameters.

  9. Pressed boride cathodes

    NASA Technical Reports Server (NTRS)

    Wolski, W.

    1985-01-01

    Results of experimental studies of emission cathodes made from lanthanum, yttrium, and gadolinium hexaborides are presented. Maximum thermal emission was obtained from lanthanum hexaboride electrodes. The hexaboride cathodes operated stably under conditions of large current density power draw, at high voltages and poor vacuum. A microtron electron gun with a lanthanum hexaboride cathode is described.

  10. Effects of H2O, CO2, and N2 Air Contaminants on Critical Airside Strain Rates for Extinction of Hydrogen-Air Counterflow Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Wilson, L. G.; Northam, G. B.; Guerra, Rosemary

    1989-01-01

    Coaxial tubular opposed jet burners (OJB) were used to form dish shaped counterflow diffusion flames (CFDF), centered by opposing laminar jets of H2, N2 and both clean and contaminated air (O2/N2 mixtures) in an argon bath at 1 atm. Jet velocities for flame extinction and restoration limits are shown versus wide ranges of contaminant and O2 concentrations in the air jet, and also input H2 concentration. Blowoff, a sudden breaking of CFDF to a stable ring shape, occurs in highly stretched stagnation flows and is generally believed to measure kinetically limited flame reactivity. Restore, a sudden restoration of central flame, is a relatively new phenomenon which exhibits a H2 dependent hysteresis from Blowoff. For 25 percent O2 air mixtures, mole for mole replacement of 25 percent N2 contaminant by steam increased U(air) or flame strength at Blowoff by about 5 percent. This result is consistent with laminar burning velocity results from analogous substitution of steam for N2 in a premixed stoichiometric H2-O2-N2 (or steam) flame, shown by Koroll and Mulpuru to promote a 10 percent increase in experimental and calculated laminar burning velocity, due to enhanced third body efficiency of water in: H + O2 + M yields HO2 + M. When the OJB results were compared with Liu and MacFarlane's experimental laminar burning velocity of premixed stoichiometric H2 + air + steam, a crossover occurred, i.e., steam enhanced OJB flame strength at extinction relative to laminar burning velocity.

  11. Low cost fuel cell diffusion layer configured for optimized anode water management

    DOEpatents

    Owejan, Jon P; Nicotera, Paul D; Mench, Matthew M; Evans, Robert E

    2013-08-27

    A fuel cell comprises a cathode gas diffusion layer, a cathode catalyst layer, an anode gas diffusion layer, an anode catalyst layer and an electrolyte. The diffusion resistance of the anode gas diffusion layer when operated with anode fuel is higher than the diffusion resistance of the cathode gas diffusion layer. The anode gas diffusion layer may comprise filler particles having in-plane platelet geometries and be made of lower cost materials and manufacturing processes than currently available commercial carbon fiber substrates. The diffusion resistance difference between the anode gas diffusion layer and the cathode gas diffusion layer may allow for passive water balance control.

  12. A plasma-cathode electron source designed for industrial use

    Microsoft Academic Search

    Igor Osipov; Nikolai Rempe

    2000-01-01

    The article presents a description of the principle of operation, the design, and the performance data of a plasma-cathode electron source. Plasma is produced in a hollow-cathode reflex discharge operating in an axial magnetic field. The discharge unit is filamentless. Air is used as the working gas. The electron source generates a focused continuous electron beam of current up to

  13. Rate of water equilibration in vapor-diffusion crystallization: dependence on the residual pressure of air in the vapor space.

    PubMed

    DeTitta, G T; Luft, J R

    1995-09-01

    The kinetics of water equilibration in vapor-diffusion crystallization experiments are sensitive to the residual pressure of air in the vapor chamber. Experiments with sitting droplets of 10%(w/v) PEG, allowed to equilibrate with reservoirs of 20%(w/v) PEG, were conducted at pressures ranging from 80 to 760 mm Hg. Equilibrations were interrupted after one, four, five and seven days to assess their progress. Even down to the lowest pressures examined it was found that a decrease in pressure leads to an increase in the rate of equilibration. The residual pressure of air in the vapor chamber can be varied to tailor the time course of equilibration in macromolecular crystal growth experiments. PMID:15299810

  14. Three-Dimensional Reconstruction of Porous LSCF Cathodes D. Gostovic,*,z

    E-print Network

    Florida, University of

    , 2007. Available electronically October 15, 2007. Solid oxide fuel cells SOFCs are efficient to reconstruct a cathode and the cathode/ electrolyte interface. Experimental Square LSCF symmetric cell cathodes volume totaled 1065 m3 from the free air surface to the dense yttria-stabilized zirconia electrolyte

  15. Sublimation kinetics and diffusion coefficients of TNT, PETN, and RDX in air by thermogravimetry.

    PubMed

    Hikal, Walid M; Weeks, Brandon L

    2014-07-01

    The diffusion coefficients of explosives are crucial in their trace detection and lifetime estimation. We report on the experimental values of diffusion coefficients of three of the most important explosives in both military and industry: TNT, PETN, and RDX. Thermogravimetric analysis (TGA) was used to determine the sublimation rates of TNT, PETN, and RDX powders in the form of cylindrical billets. The TGA was calibrated using ferrocene as a standard material of well-characterized sublimation rates and vapor pressures to determine the vapor pressures of TNT, PETN, and RDX. The determined sublimation rates and vapor pressures were used to indirectly determine the diffusion coefficients of TNT, PETN, and RDX for the first time. A linear log-log dependence of the diffusion coefficients on temperature is observed for the three materials. The diffusion coefficients of TNT, PETN, and RDX at 273 K were determined to be 5.7610(-6)m(2)/sec, 4.9410(-6)m(2)/s, and 5.8910(-6)m(2)/s, respectively. Values are in excellent agreement with the theoretical values in literature. PMID:24840410

  16. Limits on the TeV flux of diffuse gamma rays as measured with the HEGRA air shower array

    NASA Astrophysics Data System (ADS)

    HEGRA Collaboration; Aharonian, F. A.; Akhperjanian, A. G.; Barrio, J. A.; Bernlhr, K.; Bojahr, H.; Bolz, O.; Brst, H.; Contreras, J. L.; Cortina, J.; Denninghoff, S.; Fonseca, V.; Gebauer, H. J.; Gonzalez, J. C.; Gtting, N.; Heinzelmann, G.; Hermann, G.; Heusler, A.; Hofmann, W.; Horns, D.; Ibarra, A.; Iserlohe, C.; Jung, I.; Kankanyan, R.; Kestel, M.; Kettler, J.; Kohnle, A.; Konopelko, A.; Kornmayer, H.; Kranich, D.; Krawczynski, H.; Lampeitl, H.; Lopez, M.; Lorenz, E.; Lucarelli, F.; Magnussen, N.; Mang, O.; Meyer, H.; Mirzoyan, R.; Moralejo, A.; On~a, E.; Padilla, L.; Panter, M.; Plaga, R.; Plyasheshnikov, A.; Prahl, J.; Phlhofer, G.; Rauterberg, G.; Rhode, W.; Rhring, A.; Rowell, G. P.; Sahakian, V.; Samorski, M.; Schilling, M.; Schrder, F.; Siems, M.; Stamm, W.; Tluczykont, M.; Vlk, H. J.; Wiedner, C.; Wittek, W.

    2002-07-01

    Using data from the HEGRA air shower array, taken in the period from April 1998 to March 2000, upper limits on the ratio I?/ICR of the diffuse photon flux I? to the hadronic cosmic ray flux ICR are determined for the energy region 20-100 TeV. The analysis uses a gamma-hadron discrimination which is based on differences in the development of photon- and hadron-induced air showers after the shower maximum. A method which is sensitive only to the non-isotropic component of the diffuse photon flux yields an upper limit of I?/ICR (at 54 TeV) <2.010-3 (at the 90% confidence level) for a sky region near the inner galaxy (/20< galactic longitude /<60 and /|galactic latitude /|<5). A method which is sensitive to both the isotropic and the non-isotropic component yields global upper limits of I?/ICR (at 31 TeV) <1.210-2 and I?/ICR (at 53 TeV) <1.410-2 (at the 90% confidence level).

  17. Combustion rate limits of hydrogen plus hydrocarbon fuel: Air diffusion flames from an opposed jet burner technique

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Guerra, Rosemary; Wilson, Lloyd G.; Reeves, Ronald N.; Northam, G. Burton

    1987-01-01

    Combustion of H2/hydrocarbon (HC) fuel mixtures may be considered in certain volume-limited supersonic airbreathing propulsion applications. Effects of HC addition to H2 were evaluated, using a recent argon-bathed, coaxial, tubular opposed jet burner (OJB) technique to measure the extinction limits of counterflow diffusion flames. The OJB flames were formed by a laminar jet of (N2 and/or HC)-diluted H2 mixture opposed by a similar jet of air at ambient conditions. The OJB data, derived from respective binary mixtures of H2 and methane, ethylene, or propane HCs, were used to characterize BLOWOFF and RESTORE. BLOWOFF is a sudden breaking of the dish-shaped OJB flame to a stable torus or ring shape, and RESTORE marks sudden restoration of the central flame by radial inward flame propagation. BLOWOFF is a measure of kinetically-limited flame reactivity/speed under highly stretched, but relatively ideal impingement flow conditions. RESTORE measures inward radial flame propagation rate, which is sensitive to ignition processes in the cool central core. It is concluded that relatively small molar amounts of added HC greatly reduce the reactivity characteristics of counterflow hydrogen-air diffusion flames, for ambient initial conditions.

  18. LAMINAR METHANE-AIR DIFFUSION FLAME WITH CHLORINE IMPURITIES: PRELIMINARY RESULTS

    EPA Science Inventory

    The extended abstract gives preliminary results of exploratory tests, conducted by adding chlorine to the fuel side of a well characterized methane-air flame, to study the fundamental processes accompanying the combustion of chlorinated hydrocarbons. (NOTE: Formation of products ...

  19. The electrical conductivity of Norway spruce needle diffusate as affected by certain air pollutants.

    PubMed

    Keller, T

    1986-06-01

    Four-year-old potted Norway spruce (Picea abies (L.) Karst.) grafts established with scion material from three mature trees, were exposed to either long-term fumigation with SO(2), with and without water stress, or long-term ozone fumigation. The electrical conductivity of the needle diffusate was measured after the needles had been washed with chloroform and then leached in distilled water. Although none of the treatments caused visible symptoms of injury, SO(2) fumigation and water stress both caused an increase in diffusate conductivity, but the effects were not synergistic. Ozone fumigation lowered both conductivity and nutrient ion concentration in the leachate. PMID:14975911

  20. Synchrotron Investigations of SOFC Cathode Degradation

    SciTech Connect

    Idzerda, Yves

    2013-09-30

    The atomic variations occurring in cathode/electrolyte interface regions of La{sub 1-x}Sr{sub x}Co{sub y}Fe{sub 1-y}O{sub 3-?} (LSCF) cathodes and other SOFC related materials have been investigated and characterized using soft X-ray Absorption Spectroscopy (XAS) and diffuse soft X-ray Resonant Scattering (XRS). X-ray Absorption Spectroscopy in the soft X-ray region (soft XAS) is shown to be a sensitive technique to quantify the disruption that occurs and can be used to suggest a concrete mechanism for the degradation. For LSC, LSF, and LSCF films, a significant degradation mechanism is shown to be Sr out-diffusion. By using the XAS spectra of hexavalent Cr in SrCrO4 and trivalent Cr in Cr2O3, the driving factor for Sr segregation was identified to be the oxygen vacancy concentration at the anode and cathode side of of symmetric LSCF/GDC/LSCF heterostructures. This is direct evidence of vacancy induced cation diffusion and is shown to be a significant indicator of cathode/electrolyte interfacial degradation. X-ray absorption spectroscopy is used to identify the occupation of the A-sites and B-sites for LSC, LSF, and LSCF cathodes doped with other transition metals, including doping induced migration of Sr to the anti-site for Sr, a significant cathode degradation indicator. By using spatially resolved valence mapping of Co, a complete picture of the surface electrochemistry can be determined. This is especially important in identifying degradation phenomena where the degradation is spatially localized to the extremities of the electrochemistry and not the average. For samples that have electrochemical parameters that are measured to be spatially uniform, the Co valence modifications were correlated to the effects of current density, overpotential, and humidity.

  1. A membraneless air-breathing hydrogen biofuel cell based on direct wiring of thermostable enzymes on carbon nanotube electrodes.

    PubMed

    Lalaoui, Nomie; de Poulpiquet, Anne; Haddad, Raoudha; Le Goff, Alan; Holzinger, Michael; Gounel, Sbastien; Mermoux, Michel; Infossi, Pascale; Mano, Nicolas; Lojou, Elisabeth; Cosnier, Serge

    2015-04-16

    A biocathode was designed by the modification of a carbon nanotube (CNT) gas-diffusion electrode with bilirubin oxidase from Bacillus pumilus, achieving high current densities up to 3 mA cm(-2) for the reduction of O2 from air. A membraneless air-breathing hydrogen biofuel cell was designed by combination of this cathode with a functionalized CNT-based hydrogenase anode. PMID:25845356

  2. Field evaluation of two diffusive samplers and two adsorbent media to determine 1,3-butadiene and benzene levels in air

    Microsoft Academic Search

    Bo Strandberg; Anna-Lena Sunesson; Margit Sundgren; Jan-Olof Levin; Gerd Sllsten; Lars Barregard

    2006-01-01

    Two types of diffusive samplers, both of which are compatible with thermal desorption, but differ in their geometrySKC-Ultra (badge-type) and Radiello (radial symmetry-type)were evaluated indoors and outdoors under varying temperature, humidity and wind speed conditions, using the graphitized adsorbents Carbopack X or Carbograph 5 to measure 1,3-butadiene and benzene in ambient air. The results obtained by diffusive sampling were compared

  3. Noise control of pneumatic percussion drills. [considering air exhaust flow diffusion and vibration damping

    NASA Technical Reports Server (NTRS)

    Darabont, A.; Soiman, S.

    1974-01-01

    Noise sources in pneumatic drills are studied bringing to light the fact that air exhaust is the most important source. The present state of the art of noise control is discussed for pneumatic percussion drills abroad, indicating the different solutions adopted in this respect. Drills produced in Rumania are described and the results of noise measurements are shown.

  4. A simulation study of short-range atmospheric dispersion for hypothetical air-borne effluent releases using different turbulent diffusion methods

    Microsoft Academic Search

    C. V. Srinivas; R. Venkatesan; K. M. Somayaji; R. Indira

    2009-01-01

    Radiological impact due to hypothetical air-borne effluent releases for an upcoming fast reactor (PFBR), at a tropical coastal\\u000a site in Kalpakkam is studied using the HYSPLIT dispersion model. Short range air dispersion simulations are conducted with\\u000a HYSPLIT for a weakly forced synoptic condition on 3rd March, 2008 with three turbulent diffusion methods, i.e., standard velocity\\u000a deformation (A), short range isotropic

  5. Hollow-Cathode Source Generates Plasma

    NASA Technical Reports Server (NTRS)

    Deininger, W. D.; Aston, G.; Pless, L. C.

    1989-01-01

    Device generates argon, krypton, or xenon plasma via thermionic emission and electrical discharge within hollow cathode and ejects plasma into surrounding vacuum. Goes from cold start up to full operation in less than 5 s after initial application of power. Exposed to moist air between operations without significant degradation of starting and running characteristics. Plasma generated by electrical discharge in cathode barrel sustained and aided by thermionic emission from emitter tube. Emitter tube does not depend on rare-earth oxides, making it vulnerable to contamination by exposure to atmosphere. Device modified for use as source of plasma in laboratory experiments or industrial processes.

  6. Improvement of Cathode Reaction of a Mediatorless Microbial Fuel Cell

    Microsoft Academic Search

    JAE KYUNG JANG; BYUNG HONG KIM

    2004-01-01

    Oxygen diffuses through the cation-specific membrane, reducing the coulomb yield of the fuel cell. In the present study, attempts were made to enhance current generation from the fuel cell by lowering the oxygen diffusion, including the uses of ferricyanide as a cathode mediator and of a platinum-coated graphite electrode. Ferricyanide did not act as a mediator as expected, but as

  7. Discharge characteristics of lithium\\/molten nitrate thermal battery cells using silver salts as solid cathode materials

    Microsoft Academic Search

    G. E. McManis; M. H. Miles; A. N. Fletcher

    1985-01-01

    Thermal battery cells using molten nitrate electrolytes and liquid lithium anodes have been evaluated using several silver salts with low solubility in molten nitrates as solid cathode materials. These cathode materials do not readily diffuse into the anolyte and, thus, do not have parasitic reactions with the lithium anode. Furthermore, the solid cathode materials have voltammetric characteristics as favorable as

  8. Increased performance of single-chamber microbial fuel cells using an improved cathode structure

    Microsoft Academic Search

    Shaoan Cheng; Hong Liu; Bruce E. Logan

    2006-01-01

    Maximum power densities by air-driven microbial fuel cells (MFCs) are considerably influenced by cathode performance. We show here that application of successive polytetrafluoroethylene (PTFE) layers (DLs), on a carbon\\/PTFE base layer, to the air-side of the cathode in a single chamber MFC significantly improved coulombic efficiencies (CEs), maximum power densities, and reduced water loss (through the cathode). Electrochemical tests using

  9. Diffusion-related exciton decay processes in air-suspended single-walled carbon nanotubes studied by photoluminescence microscopy

    NASA Astrophysics Data System (ADS)

    Ishii, A.; Yoshida, M.; Kato, Y. K.

    2014-03-01

    In carbon nanotubes, exciton diffusion causes complex photoluminescence properties through end quenching and exciton-exciton annihilation. In order to clarify the effects of these processes in air-suspended carbon nanotubes, where they are isolated from the surroundings, we perform photoluminescence measurements on over a hundred individual nanotubes. Nanotube length dependence is investigated by measuring emission from nanotubes suspended over trenches with various widths[2] and excitation power dependence is also investigated on each nanotube. We analyze the results by calculating the effects of end quenching as a function of the tube length using a first-passage approach.[3] At low excitation powers where the exciton-exciton annihilation is negligible, this model gives intrinsic exciton diffusion lengths and relative values of photoluminescence action cross section. For higher excitation powers, Monte Carlo simulations are used to quantitatively evaluate the exciton-exciton annihilation rates and spatial profiles of the exciton density. Work supported by KAKENHI, SCOPE, KDDI Foundation, The Sumitomo Foundation, and the Photon Frontier Network Program of MEXT, Japan.

  10. Simultaneous Raman/LIF measurements of major species and NO in turbulent H2/air diffusion flames

    NASA Astrophysics Data System (ADS)

    Meier, W.; Vyrodov, A. O.; Bergmann, V.; Stricker, W.

    1996-07-01

    A single-pulse spontaneous Raman scattering apparatus, based on a flashlamp-pumped dye laser, was used to determine the concentrations of the major species and the temperature in turbulent H2/N2/air jet diffusion flames. The concentrations of nitric oxide were simultaneously measured by Laser-Induced Fluorescence (LIF) after excitation of the A 2 ? +- X 2 ? transition with a Nd: YAG-pumped dye laser. Some fundamentals of the employed methods, including the calibration procedure, quenching corrections, and accuracy are discussed. Besides a detailed study of the experimental technique, a main goal of the presented investigations was the generation of comprehensive data sets of high accuracy from well-defined turbulent flames which allow for a quantitative comparison with model calculations. Two flames with different fuel dilution and Reynolds numbers were investigated in a pattern of typically 100 measuring locations each comprising 300 single shots. In addition, four flames with different flow velocities but same fuel composition were compared with respect to their temperature and NO concentration profiles. The results show that differential diffusion plays an important role in these flames, especially near the flame base, where the temperature is increased above the adiabatic flame temperature and deviations from adiabatic equilibrium are large. The correlations between NO and mixture fraction and NO and temperature reveal characteristic features of the different flames.

  11. Monitoring of workers exposed to a mixture of toluene, styrene and methanol vapours by means of diffusive air sampling, blood analysis and urinalysis

    Microsoft Academic Search

    Toshio Kawai; Tomojiro Yasugi; Kazunori Mizunuma; Shun'ichi Horiguchi; Ikuharu Morioka; Kazuhisa Miyashita; Yoko Uchida; Masayuki Ikeda

    1992-01-01

    Summary Exposure of 34 male workers to combined toluene, styrene and methanol was monitored by personal diffusive sampling of solvent vapours in breathing zone air, analysis of shift-end blood for the 3 solvents and analysis of shift-end urine for hippuric, mandelic and phenylglyoxylic acids and methanol. The exposure of most of the workers was below current occupational exposure limits. Regression

  12. International Innovation and Diffusion of Air Pollution Control Technologies: The Effects of NOX and SO2 Regulation in the US, Japan, and Germany

    Microsoft Academic Search

    David Popp

    2004-01-01

    Using patent data from the United States, Japan, and Germany, this paper examines both the innovation and diffusion of air pollution control equipment. Whereas the United States was an early adopter of stringent sulfur dioxide (SO2) standards, both Japan and Germany introduced stringent nitrogen dioxide (NOX) standards much earlier than the US. Nonetheless, in both cases, tightened standards in the

  13. Lightweight Cathodes For Nickel Batteries

    NASA Technical Reports Server (NTRS)

    Britton, Doris L.

    1996-01-01

    Lightweight cathodes for rechargeable nickel-based electrochemical cells undergoing development. In cathodes, mats of nickel fibers are substrates providing structural support of, and electrical contact with, active cathode material. Offers specific energies greater than sintered nickel plaque cathodes. Electrodes used in rechargeable batteries for applications in which weight major concern, including laptop computers, cellular phones, flashlights, soldiers' backpacks, and electric vehicles.

  14. Investigation and improvement of SOFC composite cathodes

    NASA Astrophysics Data System (ADS)

    Bidrawn, Fred

    The focus of this dissertation is on the preparation, performance, and long term stability of SOFC composite cathodes prepared by infiltration methods. The majority of the work that follows aims to improve the understanding of the processes contributing to cathode deactivation and to propose strategies to lessen the extent of this deactivation. Through this understanding of the factors governing cathode performance, improvements can be made in overall cathode performance which can in turn lead to lower operating temperatures. The fuel cells used in this work were prepared by tapecasting and infiltration methods. Composite YSZ-perovskite electrodes were prepared by infiltration of stoichiometric ratios of perovskite precursor nitrate salts into a porous YSZ scaffold. First, the influence of ionic conductivity on the performance of solid oxide fuel cell cathodes was studied for electrodes prepared by infiltration of 40-wt% La0.8Ca0.2FeO3 (LCF), La0.8 Sr0.2FeO3 (LSF), and La0.8Ba0.2 FeO3 (LBF) into porous YSZ scaffolds. Although ionic conductivity varied by over an order of magnitude, no significant difference was observed in the performance of each material, suggesting that oxygen ion diffusion through perovskite film is not a rate limiting step for the oxygen reduction process within the cathode. Next, the effect of various infiltrated dopants on the performance of SOFC cathodes was examined. The addition of dopants had little influence on the 1123-K composite electrodes but all dopants tested improved the performance of the 1373-K, suggesting that the improved performance is related to structural changes in the electrode, rather than to improved catalytic properties or ionic conductivity. Based on these results, a model was developed to understand the performance of these electrodes. Two rate-limiting cases are considered for oxygen transfer into the YSZ fins: diffusion through the perovskite film or reactive adsorption of O2 at the perovskite surface. In agreement with the experimental results, an important implication from the model is that ionic conductivity of the pervoskite phase does not limit performance, for most commonly used perovskites, and that surface adsorption is likely limiting. Finally, strategies for improving cathode performance and stability are discussed.

  15. A model of hollow cathode plasma chemistry

    NASA Technical Reports Server (NTRS)

    Katz, I.; Anderson, J. R.; Polk, J. E.; Brophy, J. R.

    2002-01-01

    We have developed a new model of hollow cathode plasma chemistry based on the observation that xenon ion mobility is diffusion limited due to resonant charge exchange reactions. The model shows that vapor phase barium atoms are ionized almost immediately and electric fields accelerate the ions upstream from the emission zone. We have also applied the model to the orifice region, where the resultant ion generation profile correlates with previously reported orifice erosion.

  16. Cathodes - Technological review

    NASA Astrophysics Data System (ADS)

    Cherkouk, Charaf; Nestler, Tina

    2014-06-01

    Lithium cobalt oxide (LiCoO2) was already used in the first commercialized Li-ion battery by SONY in 1990. Still, it is the most frequently used cathode material nowadays. However, LiCoO2 is intrinsically unstable in the charged state, especially at elevated temperatures and in the overcharged state causing volume changes and transport limitation for high power batteries. In this paper, some technological aspects with large impact on cell performance from the cathode material point of view will be reviewed. At first it will be focused on the degradation processes and life-time mechanisms of the cathode material LiCoO2. Electrochemical and structural results on commercial Li-ion batteries recorded during the cycling will be discussed. Thereafter, advanced nanomaterials for new cathode materials will be presented.

  17. Cathodes - Technological review

    SciTech Connect

    Cherkouk, Charaf; Nestler, Tina [Institut fr Experimentelle Physik, Technische Universitt Bergakademie Freiberg, Leipziger Strae 23, 09596 Freiberg (Germany)

    2014-06-16

    Lithium cobalt oxide (LiCoO{sub 2}) was already used in the first commercialized Li-ion battery by SONY in 1990. Still, it is the most frequently used cathode material nowadays. However, LiCoO{sub 2} is intrinsically unstable in the charged state, especially at elevated temperatures and in the overcharged state causing volume changes and transport limitation for high power batteries. In this paper, some technological aspects with large impact on cell performance from the cathode material point of view will be reviewed. At first it will be focused on the degradation processes and life-time mechanisms of the cathode material LiCoO{sub 2}. Electrochemical and structural results on commercial Li-ion batteries recorded during the cycling will be discussed. Thereafter, advanced nanomaterials for new cathode materials will be presented.

  18. Analysis of turbulent free jet hydrogen-air diffusion flames with finite chemical reaction rates

    NASA Technical Reports Server (NTRS)

    Sislian, J. P.

    1978-01-01

    The nonequilibrium flow field resulting from the turbulent mixing and combustion of a supersonic axisymmetric hydrogen jet in a supersonic parallel coflowing air stream is analyzed. Effective turbulent transport properties are determined using the (K-epsilon) model. The finite-rate chemistry model considers eight reactions between six chemical species, H, O, H2O, OH, O2, and H2. The governing set of nonlinear partial differential equations is solved by an implicit finite-difference procedure. Radial distributions are obtained at two downstream locations of variables such as turbulent kinetic energy, turbulent dissipation rate, turbulent scale length, and viscosity. The results show that these variables attain peak values at the axis of symmetry. Computed distributions of velocity, temperature, and mass fraction are also given. A direct analytical approach to account for the effect of species concentration fluctuations on the mean production rate of species (the phenomenon of unmixedness) is also presented. However, the use of the method does not seem justified in view of the excessive computer time required to solve the resulting system of equations.

  19. Comparison of passive diffusion bag samplers and submersible pump sampling methods for monitoring volatile organic compounds in ground water at Area 6, Naval Air Station, Whidbey Island, Washington

    USGS Publications Warehouse

    Huffman, Raegan L.

    2002-01-01

    Ground-water samples were collected in April 1999 at Naval Air Station Whidbey Island, Washington, with passive diffusion samplers and a submersible pump to compare concentrations of volatile organic compounds (VOCs) in water samples collected using the two sampling methods. Single diffusion samplers were installed in wells with 10-foot screened intervals, and multiple diffusion samplers were installed in wells with 20- to 40-foot screened intervals. The diffusion samplers were recovered after 20 days and the wells were then sampled using a submersible pump. VOC concentrations in the 10-foot screened wells in water samples collected with diffusion samplers closely matched concentrations in samples collected with the submersible pump. Analysis of VOC concentrations in samples collected from the 20- to 40-foot screened wells with multiple diffusion samplers indicated vertical concentration variation within the screened interval, whereas the analysis of VOC concentrations in samples collected with the submersible pump indicated mixing during pumping. The results obtained using the two sampling methods indicate that the samples collected with the diffusion samplers were comparable with and can be considerably less expensive than samples collected using a submersible pump.

  20. Arcjet cathode phenomena

    NASA Technical Reports Server (NTRS)

    Curran, Francis M.; Haag, Thomas W.; Raquet, John F.

    1989-01-01

    Cathode tips made from a number of different materials were tested in a modular arcjet thruster in order to examine cathode phenomena. Periodic disassembly and examination, along with the data collected during testing, indicated that all of the tungsten-based materials behaved similarly despite the fact that in one of these samples the percentage of thorium oxide was doubled and another was 25 percent rhenium. The mass loss rate from a 2 percent thoriated rhenium cathode was found to be an order of magnitude greater than that observed using 2 percent thoriated tungsten. Detailed analysis of one of these cathode tips showed that the molten crater contained pure tungsten to a depth of about 150 microns. Problems with thermal stress cracking were encountered in the testing of a hafnium carbide tip. Post test analysis showed that the active area of the tip had chemically reacted with the propellant. A 100 hour continuous test was run at about 1 kW. Post test analysis revealed no dendrite formation, such as observed in a 30 kW arcjet lifetest, near the cathode crater. The cathodes from both this test and a previously run 1000 hour cycled test displayed nearly identical arc craters. Data and calculations indicate that the mass losses observed in testing can be explained by evaporation.

  1. Arcjet Cathode Phenomena

    NASA Technical Reports Server (NTRS)

    Curran, Francis M.; Haag, Thomas W.; Raquet, John F.

    1989-01-01

    Cathode tips made from a number of different materials were tested in a modular arcjet thruster in order to examine cathode phenomena. Periodic disassembly and examination, along with the data collected during testing, indicated that all of the tungsten-based materials behaved similarly despite the fact that in one of these samples the percentage of thorium oxide was doubled and another was 25 percent rhenium. The mass loss rate from a 2 percent thoriated rhenium cathode was found to be an order of magnitude greater than that observed using 2 percent thoriated tungsten. Detailed analysis of one of these cathode tips showed that the molten crater contained pure tungsten to a depth of about 150 microns. Problems with thermal stress cracking were encountered in the testing of a hafnium carbide tip. Post test analysis showed that the active area of the tip had chemically reacted with the propellant. A 100 hour continuous test was run at about 1 kW. Post test analysis revealed no dendrite formation, such as observed in a 30 kW arcjet lifetest, near the cathode crater. The cathodes from both this test and a previously run 1000 hour cycled test displayed nearly identical arc craters. Data and calculations indicate that the mass losses observed in testing can be explained by evaporation.

  2. Cathode materials review

    NASA Astrophysics Data System (ADS)

    Daniel, Claus; Mohanty, Debasish; Li, Jianlin; Wood, David L.

    2014-06-01

    The electrochemical potential of cathode materials defines the positive side of the terminal voltage of a battery. Traditionally, cathode materials are the energy-limiting or voltage-limiting electrode. One of the first electrochemical batteries, the voltaic pile invented by Alessandro Volta in 1800 (Phil. Trans. Roy. Soc. 90, 403-431) had a copper-zinc galvanic element with a terminal voltage of 0.76 V. Since then, the research community has increased capacity and voltage for primary (nonrechargeable) batteries and round-trip efficiency for secondary (rechargeable) batteries. Successful secondary batteries have been the lead-acid with a lead oxide cathode and a terminal voltage of 2.1 V and later the NiCd with a nickel(III) oxide-hydroxide cathode and a 1.2 V terminal voltage. The relatively low voltage of those aqueous systems and the low round-trip efficiency due to activation energies in the conversion reactions limited their use. In 1976, Wittingham (J. Electrochem. Soc., 123, 315) and Besenhard (J. Power Sources 1(3), 267) finally enabled highly reversible redox reactions by intercalation of lithium ions instead of by chemical conversion. In 1980, Goodenough and Mizushima (Mater. Res. Bull. 15, 783-789) demonstrated a high-energy and high-power LiCoO2 cathode, allowing for an increase of terminal voltage far beyond 3 V. Over the past four decades, the international research community has further developed cathode materials of many varieties. Current state-of-the-art cathodes demonstrate voltages beyond any known electrolyte stability window, bringing electrolyte research once again to the forefront of battery research.

  3. Thermionic cathode life test studies

    NASA Technical Reports Server (NTRS)

    Forman, R.; Elmer, P.

    1980-01-01

    An update on the life testing of commerical, high current density impregnated tungsten cathodes is presented. The B-type cathodes, operated at a current density of 2 A/cm2 and a cathode temperature of 1100 C have now been run satisfactorily for more than four years. The M-cathode, at the same current density but at an operating temperature of only 1010 C, have been tested for more than three years. The M-cathodes show no degradation in current over their present operating life whereas the current from the B-cathodes degrade about 6 percent after four years of operation.

  4. DEVELOPMENT OF PLUTONIUM RECOVERY PROCESS BY MOLTEN SALT ELECTROREFINING WITH LIQUID CADMIUM CATHODE

    Microsoft Academic Search

    Masatoshi Iizuka; Koich Uozumi; Tadashi Inoue; Takashi Iwai; Osamu Shirai; Yasuo Arai

    The effects of electrochemical conditions on the behaviour of plutonium and adequate conditions for recovery at liquid cadmium cathode (LCC) used in pyrometallugical reprocessing were studied with small, not stirred electrodes. Cathodic current density adequate for plutonium collection at LCC was considered to be controlled by diffusion plutonium ion in molten salt and proportional to its concentration. It was shown

  5. Evaluation of passive diffusion bag samplers, dialysis samplers, and nylon-screen samplers in selected wells at Andersen Air Force Base, Guam, March-April 2002

    USGS Publications Warehouse

    Vroblesky, Don A.; Joshi, Manish; Morrell, Jeff; Peterson, J.E.

    2003-01-01

    During March-April 2002, the U.S. Geological Survey, Earth Tech, and EA Engineering, Science, and Technology, Inc., in cooperation with the Air Force Center for Environmental Excellence, tested diffusion samplers at Andersen Air Force Base, Guam. Samplers were deployed in three wells at the Main Base and two wells at Marianas Bonins (MARBO) Annex as potential ground-water monitoring alternatives. Prior to sampler deployment, the wells were tested using a borehole flowmeter to characterize vertical flow within each well. Three types of diffusion samplers were tested: passive diffusion bag (PDB) samplers, dialysis samplers, and nylon-screen samplers. The primary volatile organic compounds (VOCs) tested in ground water at Andersen Air Force Base were trichloroethene and tetrachloroethene. In most comparisons, trichloroethene and tetrachloroethene concentrations in PDB samples closely matched concentrations in pumped samples. Exceptions were in wells where the pumping or ambient flow produced vertical translocation of water in a chemically stratified aquifer. In these wells, PDB samplers probably would be a viable alternative sampling method if they were placed at appropriate depths. In the remaining three test wells, the trichloroethene or tetrachloroethene concentrations obtained with the diffusion samplers closely matched the result from pumped sampling. Chloride concentrations in nylon-screen samplers were compared with chloride concentrations in dialysis and pumped samples to test inorganic-solute diffusion into the samplers across a range of concentrations. The test showed that the results from nylon-screen samplers might have underestimated chloride concentrations at depths with elevated chloride concentrations. The reason for the discrepancy in this investigation is unknown, but may be related to nylon-screen-mesh size, which was smaller than that used in previous investigations.

  6. Lifetime Modeling of Xenon Hollow Cathodes Used in Electric Propulsion

    NASA Astrophysics Data System (ADS)

    Kovaleski, Scott

    2001-10-01

    Xenon hollow cathodes with barium calcium aluminate impregnated tungsten inserts are widely used in electric propulsion. These high current, low power cathodes are employed in ion thrusters, Hall thrusters, and on the International Space Station in plasma contactors. The entitlement lifetime of a thermionic emission cathode impregnated with barium-containing compounds is determined by the evolution and transport of barium away from the emitter surface. A model is being developed to study the process of barium transport and loss from the emitter insert in hollow cathodes. A thermodynamic model of the chemical process of barium evolution has been adapted from that of Lipeles and Kan^1. The model accounts for the diffusion of barium and barium oxide gas through the xenon expellant and loss of barium-containing gases through the cathode orifice as well as loss by condensation. Axial barium density profiles are presented and cathode lifetimes are estimated. Results of the model are compared with experimental results from the extensive hollow cathode life test database at the NASA Glenn Research Center. 1. Lipeles, R.A., Kan, H.K.A., Appl. Surf. Sci. 16, 189(1983).

  7. Filtered cathodic arc source

    DOEpatents

    Falabella, S.; Sanders, D.M.

    1994-01-18

    A continuous, cathodic arc ion source coupled to a macro-particle filter capable of separation or elimination of macro-particles from the ion flux produced by cathodic arc discharge is described. The ion source employs an axial magnetic field on a cathode (target) having tapered sides to confine the arc, thereby providing high target material utilization. A bent magnetic field is used to guide the metal ions from the target to the part to be coated. The macro-particle filter consists of two straight solenoids, end to end, but placed at 45[degree] to one another, which prevents line-of-sight from the arc spot on the target to the parts to be coated, yet provides a path for ions and electrons to flow, and includes a series of baffles for trapping the macro-particles. 3 figures.

  8. A compartment model of alveolar-capillary oxygen diffusion with ventilation-perfusion gradient and dynamics of air transport through the respiratory tract.

    PubMed

    Jaworski, Jacek; Redlarski, Grzegorz

    2014-08-01

    This paper presents a model of alveolar-capillary oxygen diffusion with dynamics of air transport through the respiratory tract. For this purpose electrical model representing the respiratory tract mechanics and differential equations representing oxygen membrane diffusion are combined. Relevant thermodynamic relations describing the mass of oxygen transported into the human body are proposed as the connection between these models, as well as the influence of ventilation-perfusion mismatch on the oxygen diffusion. The model is verified based on simulation results of varying exercise intensities and statistical calculations of the results obtained during various clinical trials. The benefit of the approach proposed is its application in simulation-based research aimed to generate quantitative data of normal and pathological conditions. Based on the model presented, taking into account many essential physiological processes and air transport dynamics, comprehensive and combined studies of the respiratory efficiency can be performed. The impact of physical exercise, precise changes in respiratory tract mechanics and alterations in breathing pattern can be analyzed together with the impact of various changes in alveolar-capillary oxygen diffusion. This may be useful in simulation of effects of many severe medical conditions and increased activity level. PMID:24950449

  9. Joule heat generation in thermionic cathodes of high-pressure arc discharges

    SciTech Connect

    Benilov, M. S.; Cunha, M. D. [Departamento de Fisica, CCCEE, Universidade da Madeira, Largo do Municipio, 9000 Funchal (Portugal)

    2013-02-14

    The nonlinear surface heating model of plasma-cathode interaction in high-pressure arcs is extended to take into account the Joule effect inside the cathode body. Calculation results are given for different modes of current transfer to tungsten cathodes of different configurations in argon plasmas of atmospheric or higher pressures. Special attention is paid to analysis of energy balances of the cathode and the near-cathode plasma layer. In all the cases, the variation of potential inside the cathode is much smaller than the near-cathode voltage drop. However, this variation can be comparable to the volt equivalent of the energy flux from the plasma to the cathode and then the Joule effect is essential. Such is the case of the diffuse and mixed modes on rod cathodes at high currents, where the Joule heating causes a dramatic change of thermal and electrical regimes of the cathode. The Joule heating has virtually no effect over characteristics of spots on rod and infinite planar cathodes.

  10. Development of a tubular microbial fuel cell (MFC) employing a membrane electrode assembly cathode

    Microsoft Academic Search

    Jung Rae Kim; Giuliano C. Premier; Freda R. Hawkes; Richard M. Dinsdale; Alan J. Guwy

    2009-01-01

    Tubular microbial fuel cells (MFC) with air cathode might be amenable to scale-up but with increasing volume a mechanically robust, cost-effective cathode structure is required. Membrane electrode assemblies (MEA) are investigated in a tubular MFC using cost-effective cation (CEM) or anion (AEM) exchange membrane. The MEA fabrication mechanically combines a cathode electrode with the membrane between a perforated cylindrical polypropylene

  11. Effect of dielectric material on bipolar nanosecond pulse diffuse dielectric barrier discharge in air at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Tang, Kai; Wang, Wenchun; Yang, Dezheng; Zhang, Shuai; Yang, Yang; Liu, Zhijie

    2013-08-01

    In this paper, dielectric plates made by ceramic, quartz and polytetrafluoroethylene (PTFE) respectively are employed to generate low gas temperature, diffuse dielectric barrier discharge plasma by using a needle-plate electrode configuration in air at atmospheric pressure. Both discharge images and the optical emission spectra are obtained while ceramic, quartz and PTFE are used as dielectric material. Plasma gas temperature is also calculated by comparing the experimental emission spectra with the best fitted spectra of N2 (C3?u ? B3?g 1-3) and N2 (C3?u ? B3?g 0-2). The effects of different pulse peak voltages and gas gap distances on the emission intensity of N2 (C3?u ? B3?g, 0-0, 337.1 nm) and the plasma area on dielectric surface are investigated while ceramic, quartz and PTFE are used as dielectric material. It is found that the permittivity of dielectric material plays an important role in the discharge homogeneity, plasma gas temperature, emission spectra intensity of the discharge, etc. Dielectric with higher permittivity i.e., ceramic means brighter discharge luminosity and stronger emission spectra intensity of N2 (C3?u ? B3?g, 0-0, 337.1 nm) among the three dielectric materials. However, more homogeneous, larger plasma area on dielectric surface and lower plasma gas temperature can be obtained under dielectric with lower permittivity i.e., PTFE. The emission spectra intensity and plasma gas temperature of the discharge while the dielectric plate is made by quartz are smaller than that while ceramic is used as dielectric material and bigger than that when PTFE is used as dielectric material.

  12. Lattice Expansion of LSCF-6428 Cathodes Measured by In-situ XRD during SOFC Operation

    SciTech Connect

    Hardy, John S.; Templeton, Jared W.; Edwards, Danny J.; Lu, Zigui; Stevenson, Jeffry W.

    2012-01-03

    A new capability has been developed for analyzing solid oxide fuel cells (SOFCs). This paper describes the initial results of in-situ x-ray diffraction (XRD) of the cathode on an operating anode-supported solid oxide fuel cell. It has been demonstrated that XRD measurements of the cathode can be performed simultaneously with electrochemical measurements of cell performance or electrochemical impedance spectroscopy (EIS). While improvements to the technique are still to be made, the XRD pattern of a lanthanum strontium cobalt ferrite (LSCF) cathode with the composition La0.6Sr0.4Co0.2Fe0.8O3-? (LSCF-6428) was found to continually but gradually change over the course of more than 60 hours of operation in air under typical SOFC operating conditions. It was determined that the most significant change was a gradual increase in the cubic lattice parameters of the LSCF from 3.92502 (as determined from the integration of the first 20 hours of XRD patterns) to 3.92650 (from the integration of the last 20 hours). This analysis also revealed that there were several peaks from unidentified minor phases that increased in intensity over this timeframe. After a temporary loss of airflow early in the test, the cell generated between 225 and 250 mW/cm2 for the remainder of the test. A large low frequency arc in the impedance spectra suggests the cell performance was gas diffusion limited and that there is room for improvement in air delivery to the cell.

  13. Hydrogen evolution cathode

    Microsoft Academic Search

    Gray

    1984-01-01

    An improved hydrogen evolution cathode with a conductive metal core and an integral Raney-type catalytic surface predominantly derived from an adherent ternary aluminide Beta structured intermetallic crystalline precursory outer portion of the metal core is disclosed. The precursory outer portion preferably has molybdenum and titanium added to give a precursor alloy having the formula Ni \\/SUB x\\/ Mo \\/SUB y\\/

  14. Emission from ferroelectric cathodes

    Microsoft Academic Search

    S. E. Sampayan; G. J. Caporaso; C. L. Holmes; E. J. Lauer; D. Prosnitz; D. O. Trimble; G. A. Westenskow

    1994-01-01

    We have recently initiated an investigation of electron emission from ferroelectric cathodes. Our experimental apparatus consisted of an electron diode and a 250 kV, 12 Omega, 70 ns pulsed high voltage power source. A planar triode modulator driven by a synthesized waveform generator initiates the polarization inversion and allows inversion pulse tailoring. The pulsed high voltage power source is capable

  15. DARHT 2 kA Cathode Development

    SciTech Connect

    Henestroza, E.; Houck, T.; Kwan, J.W.; Leitner, M.; Miram, G.; Prichard, B.; Roy, P.K.; Waldron, W.; Westenskow, G.; Yu, S.; Bieniosek, F.M.

    2009-03-09

    In the campaign to achieve 2 kA of electron beam current, we have made several changes to the DARHT-II injector during 2006-2007. These changes resulted in a significant increase in the beam current, achieving the 2 kA milestone. Until recently (before 2007), the maximum beam current that was produced from the 6.5-inch diameter (612M) cathode was about 1300 A when the cathode was operating at a maximum temperature of 1140 C. At this temperature level, the heat loss was dominated by radiation which is proportional to temperature to the fourth power. The maximum operating temperature was limited by the damage threshold of the potted filament and the capacity of the filament heater power supply, as well as the shortening of the cathode life time. There were also signs of overheating at other components in the cathode assembly. Thus it was clear that our approach to increase beam current could not be simply trying to run at a higher temperature and the preferred way was to operate with a cathode that has a lower work function. The dispenser cathode initially used was the type 612M made by SpectraMat. According to the manufacturer's bulletin, this cathode should be able to produce more than 10 A/cm{sup 2} of current density (corresponding to 2 kA of total beam current) at our operating conditions. Instead the measured emission (space charge limited) was 6 A/cm{sup 2}. The result was similar even after we had revised the activation and handling procedures to adhere more closely to the recommend steps (taking longer time and nonstop to do the out-gassing). Vacuum was a major concern in considering the cathode's performance. Although the vacuum gauges at the injector vessel indicated 10{sup -8} Torr, the actual vacuum condition near the cathode in the central region of the vessel, where there might be significant out-gassing from the heater region, was never determined. Poor vacuum at the surface of the cathode degraded the emission (by raising the work function value). We reexamined all the components in the cathode region and eliminated those parts that were suspected to be potential sources of contamination, e.g., feed-throughs with zinc coating. Finally, we considered a change in the cathode type, by using a different combination of impregnation and coating. Since the ETA-II accelerator at LLNL used a 12.5 cm diameter 311XW (barium oxide doped with scandium and coated with a osmium-tungsten thin film) cathode and emitted 2200A of beam current (i.e. 18 A/cm{sup 2}), it was reasonable to assume that DARHT can adopt this type of cathode to produce 2 kA (i.e., 10A/cm{sup 2}). However, it was later found that the 311XW has a higher radiation heat loss than the 612M and therefore resulted in a maximum operating temperature (as limited by filament damage) below that required to produce the high current. With the evidence provided by systematic emission tests using quarter-inch size cathodes, we confirmed that the 311XM (doped with scandium and has a osmium-ruthenium (M) coating) had the best combination of low work function and low radiation heat loss. Subsequently a 6.5-inch diameter 311XM cathode was installed in DARHT and 2 kA beam current was obtained on June 14, 2007. In testing the quarter-inch size cathode, we found that the beam current was sensitive to the partial pressure of various gases in the vacuum chamber. Furthermore, there was a hysteresis effect on the emission as a function of temperature. The phenomenon suggested that the work function of the cathode was dependent on the dynamic equilibrium between the diffusion of the impregnated material to the surface and the contamination rate from the surrounding gas. Water vapor was found to be the worst contaminant amongst the various gases that we have tested. Our data showed that the required vacuum for emitting at 10 A/cm{sup 2} is in the low 10{sup -8} Torr range.

  16. Improved Rare-Earth Emitter Hollow Cathode

    NASA Technical Reports Server (NTRS)

    Goebel, Dan M.

    2011-01-01

    An improvement has been made to the design of the hollow cathode geometry that was created for the rare-earth electron emitter described in Compact Rare Earth Emitter Hollow Cathode (NPO-44923), NASA Tech Briefs, Vol. 34, No. 3 (March 2010), p. 52. The original interior assembly was made entirely of graphite in order to be compatible with the LaB6 material, which cannot be touched by metals during operation due to boron diffusion causing embrittlement issues in high-temperature refractory materials. Also, the graphite tube was difficult to machine and was subject to vibration-induced fracturing. This innovation replaces the graphite tube with one made out of refractory metal that is relatively easy to manufacture. The cathode support tube is made of molybdenum or molybdenum-rhenium. This material is easily gun-bored to near the tolerances required, and finish machined with steps at each end that capture the orifice plate and the mounting flange. This provides the manufacturability and robustness needed for flight applications, and eliminates the need for expensive e-beam welding used in prior cathodes. The LaB6 insert is protected from direct contact with the refractory metal tube by thin, graphite sleeves in a cup-arrangement around the ends of the insert. The sleeves, insert, and orifice plate are held in place by a ceramic spacer and tungsten spring inserted inside the tube. To heat the cathode, an insulating tube is slipped around the refractory metal hollow tube, which can be made of high-temperature materials like boron nitride or aluminum nitride. A screw-shaped slot, or series of slots, is machined in the outside of the ceramic tube to constrain a refractory metal wire wound inside the slot that is used as the heater. The screw slot can hold a single heater wire that is then connected to the front of the cathode tube by tack-welding to complete the electrical circuit, or it can be a double slot that takes a bifilar wound heater with both leads coming out the back. This configuration replaces the previous sheathed heater design that limited the cycling-life of the cathode.

  17. Ring laser gyro cathode arrangement

    SciTech Connect

    Council, T.

    1986-03-11

    This patent describes a ring laser gyro having a body with a cavity forming a closed loop path, a cathode and a pair of anodes, each of which is in communication with the cavity and means establishing a gas discharge between the cathode and each of the anodes to provide a pair of counter-rotating beams traveling through the cavity. An improved cathode arrangement is described consisting of: a metal cathode member having a lower edge; an annular groove in a surface of the gyro body, the lower edge of the cathode member being disposed within the groove; and a cover extending about the cathode member and secured to the gyro body, the cover supporting the cathode member.

  18. Characterization of Atomic and Electronic Structures of Electrochemically Active SOFC Cathode Surfaces

    SciTech Connect

    Kevin Blinn; Yongman Choi; Meilin Liu

    2009-08-11

    The objective of this project is to gain a fundamental understanding of the oxygen-reduction mechanism on mixed conducting cathode materials by means of quantum-chemical calculations coupled with direct experimental measurements, such as vibrational spectroscopy. We have made progress in the elucidation of the mechanisms of oxygen reduction of perovkite-type cathode materials for SOFCs using these quantum chemical calculations. We established computational framework for predicting properties such as oxygen diffusivity and reaction rate constants for adsorption, incorporation, and TPB reactions, and formulated predictions for LSM- and LSC-based cathode materials. We have also further developed Raman spectroscopy as well as SERS as a characterization tool for SOFC cathode materials. Raman spectroscopy was used to detect chemical changes in the cathode from operation conditions, and SERS was used to probe for pertinent adsorbed species in oxygen reduction. However, much work on the subject of unraveling oxygen reduction for SOFC cathodes remains to be done.

  19. UPDATING APPLIED DIFFUSION MODELS

    EPA Science Inventory

    Most diffusion models currently used in air quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Cooperative Agreement with the Environmental Protection Agency, the American Meteorological Socie...

  20. Oxygen-Diffusion and Structural Modification in Air-Annealed Superconducting Bi2Sr2CaCu2Oy Single Crystals

    NASA Astrophysics Data System (ADS)

    Zhao, Xiao-ru; Wu, Wen-bin; Sun, Xue-feng; Wang, Liang-bin; Zhou, Gui-en; Li, Xiao-Guang; Zhang, Yu-heng; Kitazawa, Koichi

    1997-12-01

    Bi2Sr2CaCu2Oy single crystals were air-annealed at 300, 400, 600 and 750C for 20 h in consequence. Measurements of ac susceptibility and x-ray diffraction showed that at annealing temperature below 400C, the change of Tc was dominated by oxygen-diffusion involved in pervoskite unit and was strongly sample-dependent. This diffusion from pervoskite unit occurred earlier than that from Bi-O layers. At annealing temperature over 400C, with the intercalation of excess oxygen into Bi-O layers, the hole concentration in the crystal was redistributed so that Bi-O reservoir fully determined superconductivity. From the changes of non-uniform strain in annealing process, it was found that structural modification was also closely correlated to superconductivity.

  1. Cold cathodes for CFAs

    Microsoft Academic Search

    K. F. Ramacher; M. S. Worthington; G. R. MacPhail

    2000-01-01

    Summary form only given. Application of cold cathode technology for use in crossed-field amplifiers (CFAs) has been limited by the characteristics of the materials, usually platinum (Pt) or beryllium (Be\\/BeO), used as the emitter. A case in point is the L-4717, used as the second stage amplifier (baby Amplitron) in the SPS-48-C\\/E transmitters. This tube, which uses a thermionic emitter,

  2. Two-dimensional imaging of molecular hydrogen in H2-air diffusion flames using two-photon laser-induced fluorescence

    NASA Technical Reports Server (NTRS)

    Lempert, W.; Kumar, V.; Glesk, I.; Miles, R.; Diskin, G.

    1991-01-01

    The use of a tunable ArF laser at 193.26 nm to record simultaneous single-laser-shot, planar images of molecular hydrogen and hot oxygen in a turbulent H2-air diffusion flame. Excitation spectra of fuel and oxidant-rich flame zones confirm a partial overlap of the two-photon H2 and single-photon O2 Schumann-Runge absorption bands. UV Rayleigh scattering images of flame structure and estimated detection limits for the H2 two-photon imaging are also presented.

  3. Quantifying the Water Content in the Cathode of Enzyme Fuel Cells via Neutron Imaging

    SciTech Connect

    Aaron, D [Georgia Institute of Technology; Borole, Abhijeet P [ORNL; Hussey (NIST), Daniel [National Institute of Standards and Technology (NIST); Jacobson, David [National Institute of Standards and Technology (NIST); Yiacoumi, Sotira [Georgia Institute of Technology; Tsouris, Costas [ORNL

    2011-01-01

    Neutron imaging was used to study cathode water content over time in a three-dimensional-cathode enzyme fuel cell (EFC). A porous carbon felt cathode allowed air to flow through the electrode. A solution with laccase and a mediator formed an aqueous layer on the electrode surface. Water loss was observed in situ via neutron imaging for varying experimental conditions, including flow rates of hydrogen and air, cathode inlet humidity, volume of enzyme solution, and its composition. Cathode water loss occurred for all experimental conditions, but the loss rate was noticeably reduced when a high-salt-concentration enzyme solution was used in the cathode in conjunction with increased humidity in the air feed stream. Results from neutron imaging and power density analysis were used in analyzing the causes that could contribute to EFC water loss. An increase in temperature due to the exothermic cathode reaction is considered a plausible cause of cathode water loss via evaporation. This is the first reported application of neutron imaging as a technique to study EFC water management. The results suggest that neutron imaging can be employed to provide a better understanding of EFC phenomena and thereby contribute to design and operational improvements of EFCs.

  4. Atmospheric glow discharge plasmas using a microhollow cathode device

    Microsoft Academic Search

    Adam Lodes; Randy Curry

    2009-01-01

    Glow discharges are known to have relatively high electron densities even while maintaining stability. Applications of these discharges are numerous and include plasma reflectors and absorbers of electromagnetic radiation, surface treatment, thin film deposition and gas lasers. Microhollow cathode devices have been shown to be excellent high electron density (up to 1016\\/cm3) sources of glow plasma atmospheric air discharges. Under

  5. Air-cooled, hydrogen-air fuel cell

    NASA Technical Reports Server (NTRS)

    Shelekhin, Alexander B. (Inventor); Bushnell, Calvin L. (Inventor); Pien, Michael S. (Inventor)

    1999-01-01

    An air-cooled, hydrogen-air solid polymer electrolyte (SPE) fuel cell with a membrane electrode assembly operatively associated with a fluid flow plate having at least one plate cooling channel extending through the plate and at least one air distribution hole extending from a surface of the cathode flow field into the plate cooling channel.

  6. Linear air-fuel sensor development

    SciTech Connect

    Garzon, F. [Los Alamos National Lab., NM (United States); Miller, C. [General Motors, Flint, MI (United States). GM/Delphi E. Division

    1996-12-14

    The electrochemical zirconia solid electrolyte oxygen sensor, is extensively used for monitoring oxygen concentrations in various fields. They are currently utilized in automobiles to monitor the exhaust gas composition and control the air-to-fuel ratio, thus reducing harmful emission components and improving fuel economy. Zirconia oxygen sensors, are divided into two classes of devices: (1) potentiometric or logarithmic air/fuel sensors; and (2) amperometric or linear air/fuel sensors. The potentiometric sensors are ideally suited to monitor the air-to-fuel ratio close to the complete combustion stoichiometry; a value of about 14.8 to 1 parts by volume. This occurs because the oxygen concentration changes by many orders of magnitude as the air/fuel ratio is varied through the stoichiometric value. However, the potentiometric sensor is not very sensitive to changes in oxygen partial pressure away from the stoichiometric point due to the logarithmic dependence of the output voltage signal on the oxygen partial pressure. It is often advantageous to operate gasoline power piston engines with excess combustion air; this improves fuel economy and reduces hydrocarbon emissions. To maintain stable combustion away from stoichiometry, and enable engines to operate in the excess oxygen (lean burn) region several limiting-current amperometric sensors have been reported. These sensors are based on the electrochemical oxygen ion pumping of a zirconia electrolyte. They typically show reproducible limiting current plateaus with an applied voltage caused by the gas diffusion overpotential at the cathode.

  7. Simulation of CO-H2-air Turbulent Diffusion Flame by the Combustion Model Combined Chemical Equilibrium Method with the Eddy Dissipation Concept Model

    NASA Astrophysics Data System (ADS)

    Fukumoto, Kazui; Ogami, Yoshifumi

    This research aims at building a turbulent diffusion combustion model based on chemical equilibrium and kinetics for simplifying complex chemical mechanisms. This paper presents the combustion model based on chemical equilibrium combined with an eddy dissipation concept model (CE-EDC); the model is validated by simulating a CO-H2-air turbulent diffusion flame. In the CE-EDC model, the reaction rate of fuels and intermediate species are estimated by using the equations of the EDC model. Then, the reacted fuels and intermediate species are assumed to be in chemical equilibrium; the amounts of the other species are determined by the Gibbs free energy minimization method by using the amounts of the reacted fuels, intermediate species, and air as reactants. An advantage of the CE-EDC model is that the amounts of the combustion products can be determined without using detailed chemical mechanisms. Moreover, it can also predict the amounts of the intermediate species. The obtained results are compared with Correa's experimental data and Gran's computational data by using the EDC model, which uses the complex chemical mechanisms. The mole fractions of CO, H2, H2O, OH, temperature, and mixture fraction obtained by using our CE-EDC model were in good agreement with these reference data. Using the present CE-EDC model, amounts of combustion products can be calculated by using a reduced chemical mechanism and the Gibbs free energy minimization theory. The accuracy of this model is in the same order as that of the EDC model.

  8. Cathode spot division in vacuum arcs with solid metal cathodes

    Microsoft Academic Search

    B. E. Djakov; R. Holmes

    1971-01-01

    Studies of cathode spot division have been made for vacuum arcs with solid metal cathodes of zinc, lead, copper, aluminium and bismuth for discharge currents in the range 5-150 A. The distribution function of the number of spots is Gaussian for fixed experimental conditions. Above a certain current i0 the mean number of spots increases linearly with current except for

  9. Photoluminescence and visible diffuse-reflection spectroscopic evidence of samarium reduction in air-fired samples of mixed samarium: strontium tetraborate precipitates.

    PubMed

    Brown, Telvin M; Jeffreys, Mareo C; Pehaire, Mario; Stump, Nathan A

    2013-03-01

    Photoluminescence and visible diffuse-reflection spectroscopies have provided evidence of the reduction of samarium to the divalent state in samarium-doped strontium borate and pure samarium borate samples. The samples were prepared by the air firing of homogeneous precipitates of divalent strontium and trivalent samarium ions from aqueous solutions with saturated sodium tetraborate. The use of this method in the preparation of divalent lanthanide ions has not been reported previously. Reduced samarium was observed in fired tetraborate precipitates prepared with solutions containing 1, 5, 10, 25, 50, 75, and 90 mole percent samarium versus strontium. Divalent samarium also was identified in fired precipitates of trivalent samarium solutions precipitated with tetraborate. Sm(2+) was identified as the primary emitting species in each of the eight compositions. However, diffuse-reflection spectroscopy indicated the presence of trivalent samarium in the studied samples, ranging from minimal for samples prepared with low samarium concentrations to nearly exclusive when pure samarium was studied. Quenching of the characteristic emission associated with the trivalent species is believed to result in the absence of the emission features arising from residual samarium(III) in the products. Although the absence of trivalent samarium emission enhanced the ability of emission spectroscopy to identify small amounts of divalent samarium, indicating that reduction had occurred, it limited the ability of this method to determine the extent of the reduction. Diffuse-reflection spectroscopy's ability to look at both species provided a much better analysis of the extent of samarium reduction. PMID:23452491

  10. Ring cusp/hollow cathode discharge chamber performance studies

    NASA Technical Reports Server (NTRS)

    Vaughn, J. A.; Wilbur, P. J.

    1988-01-01

    An experimental study performed to determine the effects of hollow cathode position, anode position, and ring cusp magnetic field configuration and strength on discharge chamber performance is described. The results are presented in terms of comparative plasma ion energy cost, extracted ion fraction, and beam profile data. Results show that the rate of primary electron loss to the anode decreases as the anode is moved downstream of the ring cusp toward the screen grid and that the loss rate of ions to hollow cathode surfaces are excessive if the cathode is located upstream of a point of peak magnetic flux density at the discharge chamber centerline. Moreover, the fraction of the ions produced that are lost to discharge chamber walls and ring magnet surfaces is reduced by positioning of the magnet rings so the plasma density is uniform over the grid surface, and adjusting their strength to a level where it is sufficient to prevent excessive ion losses by Bohm diffusion.

  11. Diffuse CO 2 soil degassing and CO 2 and H 2S concentrations in air and related hazards at Vulcano Island (Aeolian arc, Italy)

    NASA Astrophysics Data System (ADS)

    Carapezza, M. L.; Barberi, F.; Ranaldi, M.; Ricci, T.; Tarchini, L.; Barrancos, J.; Fischer, C.; Perez, N.; Weber, K.; Di Piazza, A.; Gattuso, A.

    2011-10-01

    La Fossa crater on Vulcano Island is quiescent since 1890. Periodically it undergoes "crises" characterized by marked increase of temperature (T), gas output and concentration of magmatic components in the crater fumaroles (T may exceed 600 C). During these crises, which so far did not lead to any eruptive reactivation, the diffuse CO 2 soil degassing also increases and in December 2005 an anomalous CO 2 flux of 1350 tons/day was estimated by 1588 measurements over a surface of 1.66 km 2 extending from La Fossa crater to the inhabited zone of Vulcano Porto. The crater area and two other anomalously degassing sites (Levante Beach and Palizzi) have been periodically investigated from December 2004 to August 2010 for diffuse CO 2 soil flux. They show a marked variation with time of the degassing rate, with synchronous maxima in December 2005. Carbon dioxide soil flux and environmental parameters have been also continuously monitored for over one year by an automatic station at Vulcano Porto. In order to assess the hazard of the endogenous gas emissions, CO 2 and H 2S air concentrations have been measured by Tunable Diode Laser profiles near the fumaroles of the crater rim and of the Levante Beach area, where also the viscous gas flux has been estimated. In addition, CO 2 air concentration has been measured both indoor and outdoor in an inhabited sector of Vulcano Porto. Results show that in some sites usually frequented by tourists there is a dangerous H 2S air concentration and CO 2 exceeds the hazardous thresholds in some Vulcano houses. These zones should be immediately monitored for gas hazard should a new crisis arise.

  12. Electrochemical characterization of cobalt-encapsulated nickel as cathodes for MCFC

    E-print Network

    Popov, Branko N.

    of the cobalt- encapsulated electrode. Impedance data from the modied electrode indicate that the oxygen. Simultaneously, the Ni2 cation diffuses to the anode side of the electrolyte and is then reduced in the hydrogen atmosphere to metallic nickel. The diffusion of Ni2 cation fuels more dissolution of nickel from the cathode

  13. Hot hollow cathode gun assembly

    DOEpatents

    Zeren, J.D.

    1983-11-22

    A hot hollow cathode deposition gun assembly includes a hollow body having a cylindrical outer surface and an end plate for holding an adjustable heat sink, the hot hollow cathode gun, two magnets for steering the plasma from the gun into a crucible on the heat sink, and a shutter for selectively covering and uncovering the crucible.

  14. Cheaper Hydride-Forming Cathodes

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.; Blue, Gary

    1990-01-01

    Hydride-forming cathodes for electrochemical experiments made of materials or combinations of materials cheaper and more abundant than pure palladium, according to proposal. Concept prompted by needs of experimenters in now-discredited concept of electrochemical nuclear fusion, cathodes useful in other electrochemical applications involving generation or storage of hydrogen, deuterium, or tritium.

  15. Optical study of a diffuse bipolar nanosecond pulsed dielectric barrier discharge with different dielectric thicknesses in air

    NASA Astrophysics Data System (ADS)

    Liu, Z. J.; Wang, W. C.; Zhang, S.; Yang, D. Z.; Jia, L.; Dai, L. Y.

    2012-12-01

    In this paper, a bipolar nanosecond high-voltage pulse power supply with about 20 ns rising time is employed to generate a diffuse dielectric barrier discharge using dielectric plates of different thicknesses. Dielectric thickness, which is regarded as an important discharge parameter, can improve diffuse discharge characteristics. Both the images of the diffuse dielectric barrier discharge and the optical emission spectra with different dielectric thicknesses are recorded successfully under severe electromagnetic interference. The effects of the discharge gap distance, pulse peak voltage, and pulse repetition rate on the emission intensity of N2 (C3? u ? B3? g ) of nanosecond pulsed dielectric barrier discharge with different dielectric thicknesses were investigated. It was found that increasing dielectric thickness is not conducive to acquiring a larger area of diffuse discharge. Also, the intensity of discharge decays and the discharge volume constricts in a horizontal direction with increasing dielectric thickness. The experimental result also shows that the emission intensity of N2 (C3? u ? B3? g ) decreases with the increase of the dielectric thickness and the discharge gap distance, but rises with both increasing both pulse peak voltage and pulse repetition rate.

  16. A low diffusive Lagrange-remap scheme for the simulation of violent air-water free-surface flows.

    E-print Network

    Boyer, Edmond

    using a five-equation model. In this paper, we explore a simplified variant approach for gas-liquid solver for the solution of the volume-averaged equations, and a low diffusive compressive scheme on various flow reference problems: dam break, sloshing of a tank filled with water, water-water impact

  17. A low diffusive Lagrange-Remap scheme for the simulation of violent air-water free-surface flows.

    E-print Network

    using a five-equation model. In this paper, we explore a simplified variant approach for gas-liquid for the solution of the volume-averaged equations, and a low diffusive compressive scheme for the advection flow reference problems: dam break, sloshing of a tank filled with water, water-water impact

  18. Cathodic hydrodimerization of nitroolefins

    PubMed Central

    Weling, Michael

    2015-01-01

    Summary Nitroalkenes are easily accessible in high variety by condensation of aldehydes with aliphatic nitroalkanes. They belong to the group of activated alkenes that can be hydrodimerized by cathodic reduction. There are many olefins with different electron withdrawing groups used for cathodic hydrodimerization, but not much is known about the behaviour of the nitro group. Synthetic applications of this group could profit from the easy access to nitroolefins in large variety, the CC bond formation with the introduction of two nitro groups in a 1,4-distance and the conversions of the nitro group by reduction to oximes and amines, the conversion into aldehydes and ketones via the Nef reaction and base catalyzed condensations at the acidic CH bond. Eight 1-aryl-2-nitro-1-propenes have been electrolyzed in an undivided electrolysis cell to afford 2,5-dinitro-3,4-diaryl hexanes in high yield. The 4-methoxy-, 4-trifluoromethyl-, 2-chloro- and 2,6-difluorophenyl group and furthermore the 2-furyl and 2-pyrrolyl group have been applied. The reaction is chemoselective as only the double bond but not the nitro group undergoes reaction, is regioselective as a ,-coupling with regard to the nitro group and forms preferentially two out of six possible diastereomers as major products. PMID:26199673

  19. Emission from ferroelectric cathodes

    NASA Astrophysics Data System (ADS)

    Sampayan, S. E.; Caporaso, G. J.; Holmes, C. L.; Lauer, E. J.; Prosnitz, D.; Trimble, D. O.; Westenskow, G. A.

    1993-05-01

    The authors have recently initiated an investigation of electron emission from ferroelectric cathodes. The experimental apparatus consisted of an electron diode and a 250 kV, 12 ohm, 70 ns pulsed high voltage power source. A planar triode modulator driven by a synthesized waveform generator initiates the polarization inversion and allows inversion pulse tailoring. The pulsed high voltage power source is capable of delivering two high voltage pulses within 50 (mu)s of each other and is capable of operating at a sustained repetition rate of 5 Hz. The initial measurements indicate that emission current densities above the Child-Langmuir Space Charge Limit, J(sub CL), are possible. They explain this effect to be based on a non-zero initial energy of the emitted electrons. They also determined that this effect is strongly coupled to relative timing between the inversion pulse and application of the main anode-cathode pulse. They also have initiated brightness measurements of the emitted beam and estimate a preliminary lower bound to be on the order of 10(exp 9) A/sq m-rad(exp 2) for currents close to J(sub CL) and factor of two less at currents over 4J(sub CL). As in previous measurements at this laboratory, they performed the measurement using a pepper pot technique. Beamlet profiles are recorded with a fast phosphor and gated cameras. They describe their apparatus and preliminary measurements.

  20. Emission from ferroelectric cathodes

    SciTech Connect

    Sampayan, S.E.; Caporaso, G.J.; Holmes, C.L.; Lauer, E.J.; Prosnitz, D.; Trimble, D.O.; Westenskow, G.A.

    1993-05-17

    We have recently initiated an investigation of electron emission from ferroelectric cathodes. Our experimental apparatus consisted of an electron diode and a 250 kV, 12 ohm, 70 ns pulsed high voltage power source. A planar triode modulator driven by a synthesized waveform generator initiates the polarization inversion and allows inversion pulse tailoring. The pulsed high voltage power source is capable of delivering two high voltage pulses within 50 ns of each other and is capable of operating at a sustained repetition rate of 5 Hz. Our initial measurements indicate that emission current densities above the Child-Langmuir Space Charge Limit are possible. We explain this effect to be based on a non-zero initial energy of the emitted electrons. We also determined that this effect is strongly coupled to relative timing between the inversion pulse and application of the main anode-cathode pulse. We also have initiated brightness measurements of the emitted beam. As in our previous measurements at this Laboratory, we performed the measurement using a pepper pot technique. Beam-let profiles are recorded with a fast phosphor and gated cameras. We describe our apparatus and preliminary measurements.

  1. Emission from ferroelectric cathodes

    NASA Astrophysics Data System (ADS)

    Sampayan, S. E.; Caporaso, G. J.; Holmes, C. L.; Lauer, E. J.; Prosnitz, D.; Trimble, D. O.; Westenskow, G. A.

    1994-02-01

    We have recently initiated an investigation of electron emission from ferroelectric cathodes. Our experimental apparatus consisted of an electron diode and a 250 kV, 12 ?, 70 ns pulsed high voltage power source. A planar triode modulator driven by a synthesized waveform generator initiates the polarization inversion and allows inversion pulse tailoring. The pulsed high voltage power source is capable of delivering two high voltage pulses within 50 ?s of each other and is capable of operating at a sustained repetition rate of 5 Hz. Our initial measurements indicate that emission current densities above the Child-Langmuir space charge limit, JCL, are possible. We explain this effect to be based on a non-zero initial energy of the emitted electrons. We also determined that this effect is strongly coupled to relative timing between the inversion pulse and application of the main anode-cathode pulse. We also have initiated brightness measurements of the emitted beam and estimate a preliminary lower bound to be on the order of 10 9 A/m 2rad 2. As in our previous measurements at this Laboratory, we performed the measurement using a pepper pot technique. Beamlet profiles are recorded with a fast phosphor and gated cameras. We describe our apparatus and preliminary measurements.

  2. Air breathing direct methanol fuel cell

    DOEpatents

    Ren, Xiaoming (Los Alamos, NM); Gottesfeld, Shimshon (Los Alamos, NM)

    2002-01-01

    An air breathing direct methanol fuel cell is provided with a membrane electrode assembly, a conductive anode assembly that is permeable to air and directly open to atmospheric air, and a conductive cathode assembly that is permeable to methanol and directly contacting a liquid methanol source. Water loss from the cell is minimized by making the conductive cathode assembly hydrophobic and the conductive anode assembly hydrophilic.

  3. Extinguishment of methane diffusion flames by inert gases in coflow air and oxygen-enriched microgravity environments

    Microsoft Academic Search

    Fumiaki Takahashi; Gregory T. Linteris; Viswanath R. Katta

    2011-01-01

    Extinguishment of laminar coflow diffusion flames in microgravity (?g) have been studied experimentally and computationally. The ?g experiments were conducted using a methane cup-burner flame aboard the NASA Reduced-Gravity Aircraft. Transient computations with full methane chemistry and a gray-gas radiation model were performed to reveal the flame structure and extinguishment processes. In ?g, as an inert gas (N2, He, or

  4. Using the tabulated diffusion flamelet model ADF-PCM to simulate a lifted methane-air jet flame

    Microsoft Academic Search

    Jean-Baptiste Michel; Olivier Colin; Christian Angelberger; Denis Veynante

    2009-01-01

    Two formulations of a turbulent combustion model based on the approximated diffusion flame presumed conditional moment (ADF-PCM) approach [J.-B. Michel, O. Colin, D. Veynante, Combust. Flame 152 (2008) 80-99] are presented. The aim is to describe autoignition and combustion in nonpremixed and partially premixed turbulent flames, while accounting for complex chemistry effects at a low computational cost. The starting point

  5. Using the tabulated diffusion flamelet model ADF-PCM to simulate a lifted methaneair jet flame

    Microsoft Academic Search

    Jean-Baptiste Michel; Olivier Colin; Christian Angelberger; Denis Veynante

    2009-01-01

    Two formulations of a turbulent combustion model based on the approximated diffusion flame presumed conditional moment (ADF-PCM) approach [J.-B. Michel, O. Colin, D. Veynante, Combust. Flame 152 (2008) 8099] are presented. The aim is to describe autoignition and combustion in nonpremixed and partially premixed turbulent flames, while accounting for complex chemistry effects at a low computational cost. The starting point

  6. Photoemission experiments of a large area scandate dispenser cathode

    NASA Astrophysics Data System (ADS)

    Zhang, Huang; Liu, Xing-guang; Chen, Yi; Chen, De-biao; Jiang, Xiao-guo; Yang, An-min; Xia, Lian-sheng; Zhang, Kai-zhi; Shi, Jin-shui; Zhang, Lin-wen

    2010-09-01

    A 100-mm-diameter scandate dispenser cathode was tested as a photocathode with a 10 ns Nd:YAG laser (266 nm) on an injector test stand for linear induction accelerators. This thermionic dispenser cathode worked at temperatures ranging from room temperature to 930 C (below or near the thermionic emission threshold) while the vacuum was better than 410 -7 Torr. The laser pulse was synchronized with a 120 ns diode voltage pulse stably and they were in single pulse mode. Emission currents were measured by a Faraday cup. The maximum peak current collected at the anode was about 100 A. The maximum quantum efficiency measured at low laser power was 2.410 -4. Poisoning effect due to residual gas was obvious and uninterrupted heating was needed to keep cathode's emission capability. The cathode was exposed to air one time between experiments and recovered after being reconditioned. Photoemission uniformity of the cathode was also explored by changing the laser spot's position.

  7. Dispenser cathode high power gridded klystron gun

    Microsoft Academic Search

    R. B. True; M. F. Kirshner; L. Turek; G. R. Good; R. J. Hansen; T. M. Bemis; R. J. Bartkowski

    2004-01-01

    This paper describes the design and performance of a new shadow gridded gun useful for high power radar klystrons. The gun features an M-type dispenser cathode having heater power identical to a larger diameter cathode oxide cathode gun used in one application. It is known that dispenser cathodes are more tolerant of arcs, poisoning, and other effects that can ruin

  8. A novel cathode for alkaline water electrolysis

    Microsoft Academic Search

    Weikang Hu; Xuejun Cao; Fupeng Wang; Yunshi Zhang

    1997-01-01

    A novel cathode with a multilayer structure was developed. Mm-based hydride alloys served as the hydrogen absorbing alloy of the novel cathode. A Ni-Mo alloy coating was used as the electrocatalyst of the cathode. The experimental results showed that the novel cathode not only had highly catalytic activity for HER, but also exhibited excellent durability and stability under the conditions

  9. A novel cathode for alkaline water electrolysis

    Microsoft Academic Search

    Weikang Hu; Xuejun Cao; Fupeng Wang; Yunshi Zhang

    1997-01-01

    A novel cathode with a multilayer structure was developed. Mm-based hydride alloys served as the hydrogen absorbing alloy of the novel cathode. A Ni-Mo alloy coating was used as the electrocatalyst of the cathode. The experimental results showed that the novel cathode not only had highly catalytic activity for HER (hydrogen evolution reaction), but also exhibited excellent durability and stability

  10. High current hollow cathode phenomena

    NASA Technical Reports Server (NTRS)

    Friedly, Verlin J.; Wilbur, Paul J.

    1990-01-01

    Experimental results show that the energies of ions produced near a hollow cathode orifice can be several times the anode-to-cathode potential difference generally considered available to accelerate them. These energies (of order 50 eV) are sufficient to induce substantial sputter erosion rates. Increases in discharge current (to 60 A) cause the energies and current densities of these jet ions to increase substantially. A model describing jet ion generation is proposed. The effects of discharge current on cathode internal pressure are also examined experimentally and described phenomenologically.

  11. Effects of heat loss, preferential diffusion, and flame stretch on flame-front instability and extinction of propane/air mixtures

    NASA Technical Reports Server (NTRS)

    Ishizuka, S.; Miyasaka, K.; Law, C. K.

    1982-01-01

    Flame configurations, flame-front cellular instability, and extinction of propane/air mixtures in the stagnation-point flow are experimentally studied for their dependence on downstream heat loss, preferential diffusion, and flame stretch. Boundaries for lean- and rich-limit extinction, stabilization of corrugated flames, and local extinction caused by sharp curvatures are mapped for varying propane concentrations and freestream velocities. Flame location and temperature at extinction are determined as functions of stagnation surface temperature, extent of preheating, propane concentration, and freestream velocity. Results substantiate the theoretical predictions of the different extinction modes for lean and rich flames in the absence of downstream heat loss, and yield useful insight on the extinction characteristics when finite downstream heat loss does exist. It is further shown that flame-front instability occurs only for rich mixtures in accordance with preferential diffusion considerations, and that flame stretch has a stabilizing effect such that flame-front instability is completely inhibited before the onset of extinction.

  12. Characteristics of DC and pulsed hollow cathode glow discharge

    SciTech Connect

    Atta Khedr, M. [Old Dominion Univ., Norfolk, VA (United States). Physical Electronics Research Inst.; Hefny, A.A.; Hamdy, H.; Shahen, F. [Cairo Univ., Beni Suef (Egypt). Physics Dept.; Gamal, Y. [Cairo Univ., Giza (Egypt). National Inst. of Laser Enhanced Sciences

    1998-12-31

    The investigation of the characteristics of hollow cathode glow discharge and plasma produced are important in different applications, applied physics, technology, and environment, hollow cathode UV light sources, hollow cathode gas lasers, and air treatment. In this work the authors have studied the characteristics of two types of hollow cathode glow discharge and plasmas produced. One kind is plasma has a large area in low gas pressure (0.1 to 10 Torr) using three electrodes, the second is confined in a small area inside the two hollow electrodes under high gas pressure (20--400 Torr). The gases used were He, Ar and dry air. The results show that the current and voltage are dependent on the gas pressure. The lifetime of plasma is considered at value 300 {micro}s. The electron temperature and light intensity have an optimum value at threshold conditions of gas pressure. Increasing the gas pressure cause the plasma is exited due to the change of the gas conductivity, the plasma is confined in a small area at higher pressure and started to be off. The increasing of the gas molecules that is decreasing the mean free path of electrons and the thermal absorption increase.

  13. Magnetic-cusp, cathodic-arc source

    DOEpatents

    Falabella, Steven (Livermore, CA)

    1995-01-01

    A magnetic-cusp for a cathodic-arc source wherein the arc is confined to the desired cathode surface, provides a current path for electrons from the cathode to the anode, and utilizes electric and magnetic fields to guide ions from the cathode to a point of use, such as substrates to be coated. The magnetic-cusp insures arc stability by an easy magnetic path from anode to cathode, while the straight-through arrangement leads to high ion transmission.

  14. Cold cathode vacuum discharge tube

    DOEpatents

    Boettcher, Gordon E. (Albuquerque, NM)

    1998-01-01

    A cold cathode vacuum discharge tube, and method for making same, with an interior surface of the trigger probe coated with carbon deposited by carbon vapor deposition (CVD) or diamond-like carbon (DLC) deposition. Preferably a solid graphite insert is employed in the probe-cathode structure in place of an aluminum bushing employed in the prior art. The CVD or DLC probe face is laser scribed to allow resistance trimming to match available trigger voltage signals and to reduce electrical aging.

  15. Cold cathode vacuum gauging system

    DOEpatents

    Denny, Edward C. (Knoxville, TN)

    2004-03-09

    A vacuum gauging system of the cold cathode type is provided for measuring the pressure of a plurality of separate vacuum systems, such as in a gas centrifuge cascade. Each casing is fitted with a gauge tube assembly which communicates with the vacuum system in the centrifuge casing. Each gauge tube contains an anode which may be in the form of a slender rod or wire hoop and a cathode which may be formed by the wall of the gauge tube. The tube is provided with an insulated high voltage connector to the anode which has a terminal for external connection outside the vacuum casing. The tube extends from the casing so that a portable magnet assembly may be inserted about the tube to provide a magnetic field in the area between the anode and cathode necessary for pressure measurements in a cold cathode-type vacuum gauge arrangement. The portable magnetic assembly is provided with a connector which engages the external high voltage terminal for providing power to the anode within in the gauge tube. Measurement is made in the same manner as the prior cold cathode gauges in that the current through the anode to the cathode is measured as an indication of the pressure. By providing the portable magnetic assembly, a considerable savings in cost, installation, and maintenance of vacuum gauges for pressure measurement in a gas centrifuge cascade is realizable.

  16. Opposed jet burner studies of silane-methane, silane-hydrogen and hydrogen diffusion flames with air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Guerra, Rosemary; Wilson, L. G.; Northam, G. B.

    1986-01-01

    An atmospheric pressure tubular opposed jet burner technique was used to characterize certain diffusion-flame transitions and associated burning rates for N2-diluted mixtures of highly-reactive fuels. Presented are: (1) details of the technique, with emphasis on features permitting the study of flames involving pyrophoric gases and particle-forming combustion reactions: (2) discoveries on the properties of these flames which correspond to physically and chemically distinct stages of silane and hydrogen combustion; and (3) unburnt gas velocity data obtained from flames based on SiH4-CH4-N2, SiH4-H2-N2, and H2-N2 fuel mixtures, and plotted as functions of combustible-fuel mole fraction and fuel/oxygen molar input flow ratios. In addition, these burning velocity results are analyzed and interpreted.

  17. Opposed jet burner studies of silane-methane, silane-hydrogen, and hydrogen diffusion flames with air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Guerra, Rosemary; Wilson, L. G.; Northam, G. B.

    1986-01-01

    An atmospheric pressure tubular opposed jet burner technique was used to characterize certain diffusion-flame transitions and associated burning rates for N2-diluted mixtures of highly-reactive fuels. The paper presents: (1) details of the technique, with emphasis on features permitting the study of flames involving pyrophoric gases and particle-forming combustion reactions; (2) discoveries on the properties of these flames which correspond to physically and chemically distinct stages of silane and hydrogen combustion; and (3) unburnt gas velocity data obtained from flames based on SiH4-CH4-N2, SiH4-H2-N2, and H2-N2 fuel mixtures, and plotted as functions of combustible-fuel mole fraction and fuel/oxygen molar input flow ratios. In addition, these burning velocity results are analyzed and interpreted.

  18. Seasonal, anthropogenic, air mass, and meteorological influences on the atmospheric concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs): Evidence for the importance of diffuse combustion sources

    SciTech Connect

    Lee, R.G.M.; Green, N.J.L.; Lohmann, R.; Jones, K.C. [Lancaster Univ. (United Kingdom)] [Lancaster Univ. (United Kingdom)

    1999-09-01

    Sampling programs were undertaken to establish air polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) concentrations at a semirural site on the northwest coast of England in autumn and summer and to investigate factors causing their variability. Changing source inputs, meteorological parameters, air masses, and the impact of a festival when it is customary to light fireworks and bonfires were investigated. Various lines of evidence from the study point to diffuse, combustion-related sources being a major influence on ambient air concentrations. Higher PCDD/F concentrations were generally associated with air masses that had originated and moved over land, particularly during periods of low ambient temperature. Low concentrations were associated with air masses that had arrived from the Atlantic Ocean/Irish Sea to the west of the sampling site and had little or no contact with urban/industrialized areas. Concentrations in the autumn months were 2 to 10 times higher than those found in the summer.

  19. Improved materials and processes of dispenser cathodes

    NASA Astrophysics Data System (ADS)

    Longo, R. T.; Sundquist, W. F.; Adler, E. A.

    1984-08-01

    Several process variables affecting the final electron emission properties of impregnated dispenser cathodes were investigated. In particular, the influence of billet porosity, impregnant composition and purity, and osmium-ruthenium coating were studied. Work function and cathode evaporation data were used to evaluate cathode performance and to formulate a model of cathode activation and emission. Results showed that sorted tungsten powder can be reproducibly fabricated into cathode billets. Billet porosity was observed to have the least effect on cathode performance. Use of the 4:1:1 aluminate mixture resulted in lower work functions than did use of the 5:3:2 mixture. Under similar drawout conditions, the coated cathodes showed superior emission relative to uncoated cathodes. In actual Pierce gun structures under accelerated life test, the influence of impregnated sulfur is clearly shown to reduce cathode performance.

  20. The Maximum Drop-Height of a Droplet in a Vertical Countercurrent Water-Air Heat and Moisture Exchange Tower Attached to a Main Fan Diffuser in a Coal Mine

    NASA Astrophysics Data System (ADS)

    Chen, S.; Cui, H.; Wang, H.; Zhao, J.

    2014-10-01

    A vertical countercurrent water-air heat and moisture exchange tower attached to a main fan diffuser is designed. To reduce water loss blown away by the airflow from the exchange tower, the forces acting on droplets are analysed. Droplet motion may be classified under four conditions: (1) downward initial acceleration; (2) upward initial acceleration; (3) droplet blown away by airflow; (4) droplet suspension. With droplet break-up neglected, a general equation for the maximum droplet drop-height is presented and numerical calculations are performed. Equations for the maximum drop-height under Conditions 3 and 4 are deduced, and the equation for Condition 3 is applied to an engineering case study. The effect of air velocity on the maximum drop-height is more significant than that of other factors. The conclusions provide a novel approach to optimizing the design of vertical countercurrent water-air heat and moisture exchange towers attached to main fan diffusers.

  1. Improved Sinterability and Performance of Lanthanum Ferrite SOFC Cathodes

    SciTech Connect

    Simner, Steve P.; Anderson, Michael D.; Stevenson, Jeffry W.

    2003-10-01

    Strontium-doped lanthanum ferrite (LSF) materials have shown considerable promise as solid oxide fuel cell (SOFC) cathodes. When used in conjunction with an anode-supported yttria-stabilized zirconia (YSZ) electrolyte assembly, power densities of 0.7-0.9 W/cm2 at 750 C and 0.7V can be achieved. However, this performance relies on the incorporation of a doped ceria interlayer between the YSZ electrolyte and LSF cathode. In the case of Sr-doped lanthanum manganites and cobaltites the ceria interlayer acts as a reaction barrier and prevents the formation of poorly conducting Sr- and La- zirconate phases. LSF, on the other hand, does not appear to react with YSZ to form the aforementioned zirconate phases even if reacted at 1400 C ({approx}250 C above the typical firing temperature for LSF). Instead, when sintered in direct contact with YSZ, Zr4+ cations diffuse into the perovskite where they occupy B-site positions, and result in decreased electrical (and possibly ionic) conductivity of the cathode. As expected the Zr diffusion exhibits thermal dependence, and is typically observed at temperatures ?1000 C. The current cathode of choice, La0.8Sr0.2FeO3-? (LSF-20), has an optimized (in terms of adherence and microstructure) sintering temperature of {approx}1150 C. Therefore, application of this cathode directly on YSZ results in the aforementioned LSF-YSZ interaction, and subsequently relatively poor performance. Hence, the need for the protective ceria interlayer. Recently, the authors have considered changes in the LSF-20 chemistry to facilitate enhanced cathode sintering <1000 C in an attempt to avoid the LSF-YSZ reaction. Modifications must be subtle in nature since high cation dopant levels can result in the formation of poorly conducting zirconate phases, typically observed with manganites and cobaltites. A composition that appears somewhat promising is a slightly A-site deficient lanthanum ferrite with a marginal amount of Cu dopant on the B-site, (La0.8Sr0.2)0.98Fe0.98Cu0.02O3-?. This composition can be sintered onto YSZ at 950 C, and to date has indicated power densities of 1.3-1.8 W/cm2 at 750 C and 0.7V ({approx}1.5-2.0 times greater than the performance exhibited for a cell with an LSF-20 cathode and ceria interlayer). Other transition metal dopants and degrees of non-stoichiometry are also under investigation.

  2. Laboratory development and field evaluation of a new diffusive sampler to collect nitrogen oxides in the ambient air.

    PubMed

    De Santis, F; Dogeroglu, T; Fino, A; Menichelli, S; Vazzana, C; Allegrini, I

    2002-04-01

    Diffusive samplers for the determination of NO(x) and NO2 based on collection on a coated carbon paper filter have been developed. NO is first oxidized to NO2 and then collected on the reactive surface. When NO2 and NOx samplers are exposed simultaneously, NO can be calculated by difference. The sampler has been derived from a Palmes design as recently modified by Bertoni et al. for the determination of BTX (benzene, toluene, xylenes). Laboratory tests were conducted in controlled atmosphere to evaluate linearity, uptake rate, face velocity effects, sample stability, influence of relative humidity, precision and accuracy. The samplers are capable of reliable measurements of the two species at common levels of a polluted atmosphere in urban settings yielding average concentration levels over 1 month and beyond. The uptake rate of NO2 was found to be 11.7 mL/min in a very good agreement (within 5%) with the value calculated from theory. The measured uptake rate for NO(x) was determined in experiments involving sampling at different concentration levels in comparison to chemiluminescence (CL) measurements. The precision of the measurements for co-located passive samplers was better than 5%. The accuracy of the data collected is within +/-20% of the actual value measured by CL. The laboratory and field results show that the NO(x) and NO2 samplers meet the data quality goal requested by the first EU Directive 1999/30/EU for these pollutants. PMID:12240650

  3. Pyrometric cathode temperature measurements in metal halide lamps

    NASA Astrophysics Data System (ADS)

    Schmidt, M.; Schneidenbach, H.; Kettlitz, M.

    2013-10-01

    Time-averaged temperature distributions along the electrodes of vertically operated high-intensity discharge lamps with cylindrical quartz burners filled with mercury and additives of NaI, TlI and DyI3 have been measured. The lamps have been driven by 120 Hz switched-dc currents between 0.4 and 1.78 A and the measurements have been performed during the cathodic phase at the lower electrode. All considered currents are characterized by a diffuse arc attachment. For the correction of disturbing effects the measured distributions have been fitted with solutions of the quasi-one-dimensional and steady-state energy balance of a rod-shaped tungsten cathode. A model of the near-cathode layer in a multi-species plasma has been applied for the determination of the boundary layer characteristics where the work function has been treated as a free parameter. The required plasma component concentrations have been estimated from spectroscopic measurements in the arc column. The fit procedure includes the adjustment of the extension of the lateral arc attachment region which has a distinct impact on the determined tip temperature, power input from the plasma into the cathode and the work function. For the latter the tungsten value has been verified in the pure Hg lamp, but strong deviations result in the case of a TlI admixture. The lamp with DyI3 clearly shows the gas-phase emitter effect of lowering the work function induced by Dy.

  4. Generation Of Atmospheric Pressure Non-Thermal Plasma By Diffusive And Constricted Discharges In Rest And Flowing Gases (Air And Nitrogen)

    NASA Astrophysics Data System (ADS)

    Akishev, Y.; Grushin, M.; Karalnik, V.; Kochetov, I.; Napartovich A.; Trushkin N.

    2010-07-01

    Weekly ionized non-thermal plasma (NTP) is of great interest for many applications because of its strong non-equilibrium state wherein an average electron energy Te exceeds markedly gas temperature Tg, i.e. electrons in the NTP are strongly overheated compared to neutral gas. Energetic electrons due to frequent collisions with the neutrals excite and dissociate effectively atoms and molecules of the plasma-forming gas that results in a creation of physically-, and bio-chemically active gaseous medium in a practically cold background gas. At present there are many kinds of plasma sources working at low and atmospheric pressure and using MW, RF, low frequency, pulsed and DC power supplies for NTP generation. The NTP at atmospheric pressure is of considerable interest for practice. A reason is that sustaining the NTP at atmospheric pressure at first allows us to avoid the use of expensive vacuum equipment and second gives opportunity to use the NTP for treatment of the exhausted gases and polluted liquids. The second opportunity cannot be realized at all with use of the NTP at low pressure. Main subject of this talk is low current atmospheric pressure gas discharges powering with DC power supplies. Plasma forming gases are air and nitrogen which are much cheaper compared to rare gases like He or Ar. Besides, great interest to molecular nitrogen as plasma forming gas is caused first of all its unique capability to accumulate huge energy in vibration, electron (metastables) and dissociated (atomic) states providing high chemical reactivity of the activated nitrogen. All active particles mentioned above have a long lifetime, and they can be therefore transported for a long distance away from place of their generation. Different current modes (diffusive and constricted) of these discharges are discussed. Experimental and numerical results on generation of chemically active species in the diffusive and constricted mode are presented. Some data on the usage of the atmospheric pressure NTP for gas cleanup, surface treatment and sterilization are given.

  5. Performance of anode-supported solid oxide fuel cell with La 0.85Sr 0.15MnO 3 cathode modified by sol-gel coating technique

    NASA Astrophysics Data System (ADS)

    Yoon, Sung Pil; Han, Jonghee; Nam, Suk Woo; Lim, Tae-Hoon; Oh, In-Hwan; Hong, Seong-Ahn; Yoo, Young-Sung; Lim, Hee Chun

    Yttria-stabilized zirconia (8 mol%; YSZ) or samaria-doped ceria (Sm 0.2Ce 0.8O 2; SDC)-modified La 0.85Sr 0.15MnO 3 (LSM) composite cathodes were fabricated by formation of an YSZ or SDC film at the triple-phase boundary (TPB) of LSM/YSZ/gas. The YSZ film greatly enlarged the number of electrochemical reaction sites (ERSs) by increasing the TPB. The composite cathode was formed on thin YSZ electrolyte (about 30 ?m thickness) supported on an anode and then I-V characterization and ac impedance analyses were performed at temperatures between 700 and 800 C. As a result of the impedance analysis on the cell at 800 C, with humidified hydrogen as the fuel and air as the oxidant, the element R1 around the frequency of 1000 Hz is identified as the anode polarization, R2 around the frequency of 100 Hz is identified as the cathode polarization and R3 below the frequency of 10 Hz is the resistance of gas phase diffusion through the anode. The maximum power densities of the cell modified by the SDC sol-gel coating were about 0.53 W/cm 2 at 750 C and about 0.19 W/cm 2 at 650 C. The result implied that deposition of SDC in the pore surface of the cathode increased the area of the TPB, resulting in a decrease of cathode polarization and improved cell performance.

  6. Air cell

    NASA Astrophysics Data System (ADS)

    Okamura, Okiyoshi; Wakasa, Masayuki; Tamanoi, Yoshihito

    1991-04-01

    The present invention relates to an air cell. This air cell provides a compact light-weight power source for model aircraft permitting them to fly for an extended period so that they may be used for such practical purposes as crop dusting, surveying, and photographing. The cell is comprised of a current collector so disposed between a magnesium, zinc, or aluminum alloy cathode and a petroleum graphite anode that it is in contact with the anode. The anode is formed by adding polytetrafluoroethylene dispersion liquid in a mixture of active carbon and graphite powder, pouring the mixture into a mold and heating it to form the anode. It is fabricated by a plurality of anode sections and is formed with at least one hole so that it can provide a cell which is compact in size and light in weight yet is capable of generating a high output. The anode, the cathode, and a separator are wetted by an electrolytic liquid. The electrolyte is continuously supplied through the life of the cell.

  7. High-current-density, high brightness cathodes for free electron laser applications

    SciTech Connect

    Green, M.C. (Varian Associates, Palo Alto, CA (USA). Palo Alto Microwave Tube Div.)

    1987-06-01

    This report discusses the following topics: brightness and emittance of electron beams and cathodes; general requirements for cathodes in high brightness electron guns; candidate cathode types; plasma and field emission cathodes; true field emission cathodes; oxide cathodes; lanthanum hexaborides cathodes; laser driven thermionic cathodes; laser driven photocathodes; impregnated porous tungsten dispenser cathodes; and choice of best performing cathode types.

  8. PEMFC air loop model and control

    Microsoft Academic Search

    S. Caux; J. Lachaize; M. Fadel; P. Schott; L. Nicod

    2005-01-01

    This paper presents the control of air supply of a proton exchange membrane fuel cell-PEMFC-system. This control is based on a species balance model in the cathode (oxygen) compartment which must be controlled to stay not only at a constant pressure but also to follow a desired air flow. Desired air flow combined with sufficient hydrogen flow enables the production

  9. Air breathing direct methanol fuel cell

    DOEpatents

    Ren, Xiaoming (Los Alamos, NM)

    2002-01-01

    An air breathing direct methanol fuel cell is provided with a membrane electrode assembly, a conductive anode assembly that is permeable to air and directly open to atmospheric air, and a conductive cathode assembly that is permeable to methanol and directly contacting a liquid methanol source.

  10. Diffusion Geometry Diffusion Geometry

    E-print Network

    Hirn, Matthew

    Diffusion Geometry Diffusion Geometry for High Dimensional Data Matthew J. Hirn July 3, 2013 #12;Diffusion Geometry Introduction Embedding of closed curve Figure: Left: A closed, non-self-intersecting curve in 3 dimensions. Right: Its embedding as a circle. #12;Diffusion Geometry Introduction Cartoon

  11. Investigating Microbial Fuel Cell Bioanode Performance Under Different Cathode Conditions

    SciTech Connect

    Borole, Abhijeet P [ORNL; Hamilton, Choo Yieng [ORNL; Aaron, D [Georgia Institute of Technology; Tsouris, Costas [ORNL

    2009-01-01

    A compact, three-in-one, flow-through, porous, electrode design with minimal electrode spacing and minimal dead volume was implemented to develop a microbial fuel cell (MFC) with improved anode performance. A biofilm-dominated anode consortium enriched under a multimode, continuous-flow regime was used. The increase in the power density of the MFC was investigated by changing the cathode (type, as well as catholyte strength) to determine whether anode was limiting. The power density obtained with an air-breathing cathode was 56 W/m3 of net anode volume (590 mW/m2) and 203 W/m3 (2160 mW/m2) with a 50-mM ferricyanide- based cathode. Increasing the ferricyanide concentration and ionic strength further increased the power density, reaching 304 W/m3 (3220 mW/m2, with 200 mM ferricyanide and 200 mM buffer concentration). The increasing trend in the power density indicated that the anode was not limiting and that higher power densities could be obtained using cathodes capable of higher rates of oxidation. The internal solution resistance for the MFC was 5 6 X, which supported the improved performance of the anode design. A new parameter defined as the ratio of projected surface area to total anode volume is suggested as a design parameter to relate volumetric and area-based power densities and to enable comparison of various MFC configurations.

  12. Observation of radio frequency ring-shaped hollow cathode discharge plasma with MgO and Al electrodes for plasma processing

    SciTech Connect

    Ohtsu, Yasunori, E-mail: ohtsuy@cc.saga-u.ac.jp; Matsumoto, Naoki [Department of Electrical and Electronic Engineering, Graduate School of Science and Engineering, Saga University, 1 Honjo-machi, Saga 840-8502 (Japan)

    2014-05-15

    Various high-density plasma sources have been proposed for plasma processing. Especially, the hollow cathode discharge is one of the powerful ones. In this work, radio-frequency (RF) driven ring-shaped hollow cathode discharges with high secondary-electron emission have been investigated, using an aluminum (Al) cathode, coated or not with magnesium oxide (MgO). The thickness of MgO thin film is approximately 200?nm. The RF discharge voltage for the coated cathode is almost the same as that for the uncoated one, in a wide range of Ar gas pressure, from 5.3 to 53.2?Pa. The results reveal that the plasma density has a peak at an Ar gas pressure of 10.6?Pa for both cathodes. The plasma density for the coated cathode is about 1.53 times higher than that for the uncoated one, at various gas pressures. To the contrary, the electron temperature for the coated cathode is lower than temperature obtained with the uncoated cathode, at various gas pressures. Radial profiles of electron saturation current, which is proportional to plasma flux, are also examined for a wide range of gas pressure. Radial profiles of electron temperature at various axial positions are almost uniform for both cathodes so that the diffusion process due to density gradient is dominant for plasma transport. The secondary electrons emitted from the coated cathode contribute to the improvement of the plasma flux radial profile obtained using the uncoated cathode.

  13. Decay of the zincate concentration gradient at an alkaline zinc cathode after charging

    NASA Technical Reports Server (NTRS)

    Kautz, H. E.; May, C. E.

    1979-01-01

    The transport of the zincate ion to the alkaline zinc cathode was studied by observing the decay of the zincate concentration gradient at a horizontal zinc cathode after charging. This decay was found to approximate first order kinetics as expected from a proposed boundary layer model. The concentrations were calculated from polarization voltages. The decay half life was shown to be a linear function of the thickness of porous zinc deposit on the cathode indicating a very rapid transport of zincate through porous zinc metal. The rapid transport is attributed to an electrochemical mechanism. From the linear dependence of the half life on the thickness the boundary layer thickness was found to be about 0.010 cm when the cathode was at the bottom of the cell. No significant dependence of the boundary layer thickness on the viscosity of electrolyte was observed. The data also indicated a relatively sharp transition between the diffusion and convection transport regions. When the cathode was at the top of the cell, the boundary layer thickness was found to be roughly 0.080 cm. The diffusion of zincate ion through asbestos submerged in alkaline electrolyte was shown to be comparable with that predicted from the bulk diffusion coefficient of the zincate ion in alkali.

  14. Properties of ceramic honeycomb cathodes

    NASA Astrophysics Data System (ADS)

    Friedman, M.; Myers, M. C.; Chan, Y.; Sethian, J. D.

    2008-04-01

    A high current electron beam was emitted from slabs of ceramic honeycomb that were placed 2mm in front of the primary electron emitters. Inside the ceramic honeycomb pores, the primary electrons are multiplied many folds by a secondary emission process creating plasma from which the electron beam was emitted. Measurements show that there was no anode-cathode gap closure during the pulse duration and a uniform current density distribution was observed on the anode. Contrary to the measurements of "conventional" large area field emission cathodes, no transit time instability was observed.

  15. Cold cathode vacuum discharge tube

    DOEpatents

    Boettcher, G.E.

    1998-03-10

    A cold cathode vacuum discharge tube, and method for making same, are disclosed with an interior surface of the trigger probe coated with carbon deposited by carbon vapor deposition (CVD) or diamond-like carbon (DLC) deposition. Preferably a solid graphite insert is employed in the probe-cathode structure in place of an aluminum bushing employed in the prior art. The CVD or DLC probe face is laser scribed to allow resistance trimming to match available trigger voltage signals and to reduce electrical aging. 15 figs.

  16. Cold cathode vacuum discharge tube

    DOEpatents

    Boettcher, G.E.

    1998-04-14

    A cold cathode vacuum discharge tube, and method for making same, with an interior surface of the trigger probe coated with carbon deposited by chemical vapor deposition (CVD) or diamond-like carbon (DLC) deposition are disclosed. Preferably a solid graphite insert is employed in the probe-cathode structure in place of an aluminum bushing employed in the prior art. The CVD or DLC probe face is laser scribed to allow resistance trimming to match available trigger voltage signals and to reduce electrical aging. 14 figs.

  17. Nickel-titanium-phosphate cathodes

    Microsoft Academic Search

    Ilias Belharouak; Khalil Amine

    2008-01-01

    Cathode materials having an improved electronic conductivity allowing for faster kinetics in the electrochemical reaction, as well as higher conductivity to meet the power requirements for many consumer applications, especially at low temperatures. The cathode material comprises a compound from the family of compounds where the basic unit is generally represented by Li.sub.xNi.sub.0.5TiOPO.sub.4. The structure of Li.sub.xNi.sub.0.5TiOPO.sub.4 includes corner sharing

  18. Titanium diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, Daniele J.; Liang, Yan

    2014-12-01

    Diffusion of Ti has been characterized in natural olivine and synthetic forsterite. Experiments on the natural olivines were run under buffered conditions (IW and NNO), and those on synthetic forsterite were run in air. Titanium diffusion appears relatively insensitive to crystallographic orientation and oxygen fugacity under the range of investigated conditions, and diffusivities are similar for Fe-bearing olivine and forsterite. For Ti diffusion in synthetic forsterite, we obtain the following Arrhenius relation for diffusion over the temperature range 900-1400 C:

  19. Some new results on electron transport in the atmosphere. [Monte Carlo calculation of penetration, diffusion, and slowing down of electron beams in air

    NASA Technical Reports Server (NTRS)

    Berger, M. J.; Seltzer, S. M.; Maeda, K.

    1972-01-01

    The penetration, diffusion and slowing down of electrons in a semi-infinite air medium has been studied by the Monte Carlo method. The results are applicable to the atmosphere at altitudes up to 300 km. Most of the results pertain to monoenergetic electron beams injected into the atmosphere at a height of 300 km, either vertically downwards or with a pitch-angle distribution isotropic over the downward hemisphere. Some results were also obtained for various initial pitch angles between 0 deg and 90 deg. Information has been generated concerning the following topics: (1) the backscattering of electrons from the atmosphere, expressed in terms of backscattering coefficients, angular distributions and energy spectra of reflected electrons, for incident energies T(o) between 2 keV and 2 MeV; (2) energy deposition by electrons as a function of the altitude, down to 80 km, for T(o) between 2 keV and 2 MeV; (3) the corresponding energy depostion by electron-produced bremsstrahlung, down to 30 km; (4) the evolution of the electron flux spectrum as function of the atmospheric depth, for T(o) between 2 keV and 20 keV. Energy deposition results are given for incident electron beams with exponential and power-exponential spectra.

  20. A probability density function Eulerian Monte Carlo field method for large eddy simulations: Application to a turbulent piloted methane/air diffusion flame (Sandia D)

    SciTech Connect

    Mustata, Radu; Valino, Luis; Jimenez, Carmen [LITEC Consejo Superior de Investigaciones Cientificas, Maria de Luna 10, 50018, Zaragoza (Spain); Jones, W.P.; Bondi, S. [Department of Mechanical Engineering, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom)

    2006-04-15

    The Eulerian stochastic field method is applied to the solution of the modeled evolution equation for the subgrid joint probability density function (JPDF) of the reacting scalars in a large eddy simulation (LES) of a piloted methane/air diffusion flame (Sandia Flame D). A simple model for subgrid scale (SGS) stresses and fluxes and a global four-step mechanism for combustion are combined in the formulation. Test cases with varying mesh sizes and numbers of stochastic fields were completed. The differences in the results obtained with the two grids were very small and this indicates that the mesh resolution was sufficient. However, incorporation of the JPDF, via the stochastic field solution method, improved the quality of predictions significantly, particularly those quantities related to reaction, such as temperature. Eight stochastic fields were shown to be enough to characterize the influence of SGS fluctuations on filtered species formation rate to reasonable accuracy and at moderate computational cost. With the exceptions of H{sub 2} and CO, good agreement between measured and computed mean and RMS profiles of velocity, composition, and temperature was achieved. The discrepancies in H{sub 2} and CO concentrations are attributable to limitations in the global chemistry mechanism used in the LES. Overall the results serve to highlight the potential of the Eulerian stochastic field method in LES. (author)

  1. Novel Cathodes Prepared by Impregnation Procedures

    SciTech Connect

    Eduardo Paz

    2006-09-30

    (1) We showed that similar results were obtained when using various LSM precursors to produce LSM-YSZ cathodes. (2) We showed that enhanced performance could be achieved by adding LSCo to LSMYSZ cathodes. (3) We have preliminary results showing that there is a slow deactivation with LSFYSZ cathodes.

  2. The cathode spot of a vacuum arc

    Microsoft Academic Search

    G A Lyubimov; V I Rakhovski?

    1978-01-01

    In this review we analyze the current state of experiments and theory relating to the cathode spot of a vacuum arc. We discuss technical features of the experimental study of the near-cathode region of a vacuum arc with high time and space resolution. We discuss in detail the experimental data on such basic parameters characterizing the cathode spot as velocity,

  3. Argon-ion gas laser cathode construction

    Microsoft Academic Search

    1984-01-01

    An improved argon-ion gas laser utilizes a dispenser-type cathode and within the cathode shroud mounts a preignition electrode and a heat shield enabling the cathode to be operated efficiently and within a 900°⁻¹°⁵°sup 0\\/ C. temperature range over an extended period of time.

  4. Conflicting roles of nickel in controlling cathode performance in lithium ion batteries.

    PubMed

    Gu, Meng; Belharouak, Ilias; Genc, Arda; Wang, Zhiguo; Wang, Dapeng; Amine, Khalil; Gao, Fei; Zhou, Guangwen; Thevuthasan, Suntharampillai; Baer, Donald R; Zhang, Ji-Guang; Browning, Nigel D; Liu, Jun; Wang, Chongmin

    2012-10-10

    A variety of approaches are being made to enhance the performance of lithium ion batteries. Incorporating multivalence transition-metal ions into metal oxide cathodes has been identified as an essential approach to achieve the necessary high voltage and high capacity. However, the fundamental mechanism that limits their power rate and cycling stability remains unclear. The power rate strongly depends on the lithium ion drift speed in the cathode. Crystallographically, these transition-metal-based cathodes frequently have a layered structure. In the classic wisdom, it is accepted that lithium ion travels swiftly within the layers moving out/in of the cathode during the charge/discharge. Here, we report the unexpected discovery of a thermodynamically driven, yet kinetically controlled, surface modification in the widely explored lithium nickel manganese oxide cathode material, which may inhibit the battery charge/discharge rate. We found that during cathode synthesis and processing before electrochemical cycling in the cell nickel can preferentially move along the fast diffusion channels and selectively segregate at the surface facets terminated with a mix of anions and cations. This segregation essentially can lead to a higher lithium diffusion barrier near the surface region of the particle. Therefore, it appears that the transition-metal dopant may help to provide high capacity and/or high voltage but can be located in a "wrong" location that may slow down lithium diffusion, limiting battery performance. In this circumstance, limitations in the properties of lithium ion batteries using these cathode materials can be determined more by the materials synthesis issues than by the operation within the battery itself. PMID:22985059

  5. New Cathode Materials for Intermediate Temperature Solid Oxide Fuel Cells

    SciTech Connect

    Allan J. Jacobson

    2006-06-30

    Operation of SOFCs at intermediate temperatures (500-800 C) requires new combinations of electrolyte and electrode materials that will provide both rapid ion transport across the electrolyte and electrode-electrolyte interfaces and efficient electrocatalysis of the oxygen reduction and fuel oxidation reactions. This project concentrates on materials and issues associated with cathode performance that are known to become limiting factors as the operating temperature is reduced. The specific objectives of the proposed research are to develop cathode materials that meet the electrode performance targets of 1.0 W/cm{sup 2} at 0.7 V in combination with YSZ at 700 C and with GDC, LSGM or bismuth oxide based electrolytes at 600 C. The performance targets imply an area specific resistance of {approx}0.5 {Omega}cm{sup 2} for the total cell. The research strategy is to investigate both established classes of materials and new candidates as cathodes, to determine fundamental performance parameters such as bulk diffusion, surface reactivity and interfacial transfer, and to couple these parameters to performance in single cell tests. In this report, further measurements of the oxygen deficient double perovskite PrBaCo{sub 2}O{sub 5.5+{delta}} are reported. The high electronic conductivity and rapid diffusion and surface exchange kinetics of PBCO suggest its application as cathode material in intermediate temperature solid oxide fuel cells. Preliminary measurements in symmetric cells have shown low ASR values at 600 C. Here we describe the first complete cell measurements on Ni/CGO/CGO/PBCO/CGO cells.

  6. Cathodic protection diagnostic expert system

    SciTech Connect

    Van Blaricum, V.L.; Kumar, A. (Army Construction Engineering Research Labs., Champaign, IL (United States)); Park, Y.T. (Soong Sil Univ., Seoul (Korea, Republic of). Dept. of Computer Science)

    1994-12-01

    A knowledge-based diagnostic system has been developed for troubleshooting cathodic protection systems. The expert system is designed to work in conjunction with a database that stores inventory and field measurement information and flags problem areas. The system is described, and examples of troubleshooting using the system are presented.

  7. Offshore platform cathodic protection retrofits

    SciTech Connect

    Turnipseed, S.P. [Chevron Research and Technology Co., Richmond, CA (United States)

    1996-10-01

    Cathodic protection (CP) is the primary technique used for underwater corrosion control on the majority of offshore steel structures. Offshore platforms are often kept in service far beyond their original design life. Refurbishment of the CP system is required when adequate protection can no longer be maintained. Various offshore platform CP retrofit designs are discussed.

  8. Prevent corrosion by cathodic protection

    Microsoft Academic Search

    1989-01-01

    Corrosion can be minimized by coating the steel pipe line with a high quality insulating material such as a high density polyethylene jacket or an epoxy film and then providing it cathodic protection by means of sacrificial anodes or an impressed current system. However, there are a number of other considerations that may be applicable to a gas utility's pipe

  9. Magnetic-cusp, cathodic-arc source

    DOEpatents

    Falabella, S.

    1995-11-21

    A magnetic-cusp for a cathodic-arc source wherein the arc is confined to the desired cathode surface, provides a current path for electrons from the cathode to the anode, and utilizes electric and magnetic fields to guide ions from the cathode to a point of use, such as substrates to be coated. The magnetic-cusp insures arc stability by an easy magnetic path from anode to cathode, while the straight-through arrangement leads to high ion transmission. 3 figs.

  10. Cathodes for molten-salt batteries

    NASA Technical Reports Server (NTRS)

    Argade, Shyam D.

    1993-01-01

    Viewgraphs of the discussion on cathodes for molten-salt batteries are presented. For the cathode reactions in molten-salt cells, chlorine-based and sulfur-based cathodes reactants have relatively high exchange current densities. Sulfur-based cathodes, metal sulfides, and disulfides have been extensively investigated. Primary thermal batteries of the Li-alloy/FeS2 variety have been available for a number of years. Chlorine based rechargable cathodes were investigated for the pulse power application. A brief introduction is followed by the experimental aspects of research, and the results obtained. Performance projections to the battery system level are discussed and the presentation is summarized with conclusions.

  11. Cathode effects on thrust subsystem performance predictability.

    NASA Technical Reports Server (NTRS)

    Goldstein, R.; Pawlik, E. V.

    1972-01-01

    Development of a model of mercury vapor electron bombardment thrustor hollow cathode operation. The proposed model predicts that the primary electron emission mechanism is thermionic when sufficient low work function material is present, that the cathode is heated by power extracted from the plasma to a temperature sufficient to emit the current demanded by the external circuit; that for a given total arc current, attempts to reduce cathode temperature by changes in the external thermal coupling will affect only the amount of power extracted from the plasma; and that depletion of low work function material in the cathode results in higher cathode temperature.

  12. Cathodes for molten-salt batteries

    NASA Astrophysics Data System (ADS)

    Argade, Shyam D.

    1993-02-01

    Viewgraphs of the discussion on cathodes for molten-salt batteries are presented. For the cathode reactions in molten-salt cells, chlorine-based and sulfur-based cathodes reactants have relatively high exchange current densities. Sulfur-based cathodes, metal sulfides, and disulfides have been extensively investigated. Primary thermal batteries of the Li-alloy/FeS2 variety have been available for a number of years. Chlorine based rechargable cathodes were investigated for the pulse power application. A brief introduction is followed by the experimental aspects of research, and the results obtained. Performance projections to the battery system level are discussed and the presentation is summarized with conclusions.

  13. The performance of perovskites and spinels as catalysts for oxygen reduction in solid oxide fuel cell cathodes

    NASA Astrophysics Data System (ADS)

    Martin, Boris E.

    The lack of understanding of the catalytic process at the state-of-the-art cathode material surface in solid oxide fuel cells, (La0.8Sr 0.2)0.98MnO3+delta (LSM), has hindered the design of better catalysts. The objectives of this study were to design a system enabling the comparison of catalytic activities of different cathode materials independently of morphological factors, as well as to resolve catalytic processes at the LSM surface. The selection and optimization of potential cathode materials were performed on the basis of thermal expansion, four-probe dc-conductivity and thermoelectric power measurements in air. The materials studied as potential cathodes were tungsten, niobium and molybdenum doped barium cobaltite perovskites, copper manganese, cobalt manganese and cobalt ferrite spinels as well as strontium doped lanthanum cobalt ferrites and lanthanum manganite perovskites. The doped barium cobaltites were found lo offer superior electrical conductivity when octahedral site transition metal average valence was mixed 3+ /4+ compared to mixed 2+/3+. On the other hand, the loss of conductivity associated with octahedral site doping rendered these materials inadequate for solid oxide fuel cells (SOFC) cathode applications. Copper manganese spMd was found to exhibit electrical conductivity as high as 200 S.cm-1 at 1073 K and thermal expansion 11 ppm/K between 298 K and 1200 K. Thermal and chrono-potentiometric studies were used to determine the oxygen diffusivity, in cobalt and strontium doped lanthanum iron perovskites (LSCF), and revealed that the activation of strontium doped lanthanum manganese perovskites (LSM) under cathodic bias is kinetically limited by its rate of oxygen surface exchange, suggesting that the cathodic activation of LSM is due to its change in oxygen content under bias. The electronic defect structure of the cubic spinels was resolved in a defect reaction model involving the thermally activated redox of Cu + and Mn4+ to Cu2+ and Mn3+, as well as the disproportionation of Jahn-Teller ion Mn3+ into Mn2+ and Mn4+ and demonstrated that copper doping enhanced the amount of Mn4+ on octahedral sites. Cyclic voltammetry and potential-dependent electrochemical impedance spectroscopy studies of dense (La0.8Sr0.2)0.98MnO3+delta polycrystalline films revealed that the rate determining step in the oxygen reduction reaction, in the conditions of our study was the first charge transfer between oxygen ad-atoms and octahedral manganese III, as described by (S)Oad + MnxMn?O -adS +MnMn. The catalytic activity of CuzMn3-- zO4 cubic spinets was found superior to that of LSM and of stoichiometrie CoFe2O4 and Co2MnO 4 spinal at intermediate temperature, suggesting that the Mn 3+/Mn4+ redox couple on octahedral sites plays a major role in the catalysis of the oxygen reduction reaction on those transition metal oxide surfaces.

  14. Effect of formation of biofilms and chemical scale on the cathode electrode on the performance of a continuous two-chamber microbial fuel cell.

    PubMed

    Chung, Kyungmi; Fujiki, Itto; Okabe, Satoshi

    2011-01-01

    A two-chamber MFC system was operated continuously for more than 500 days to evaluate effects of biofilm and chemical scale formation on the cathode electrode on power generation. A stable power density of 0.57 W/m(2) was attained after 200 days operation. However, the power density decreased drastically to 0.2 W/m(2) after the cathodic biofilm and chemical scale were removed. As the cathodic biofilm and chemical scale partially accumulated on the cathode, the power density gradually recovered with time. Microbial community structure of the cathodic biofilm was analyzed based on 16S rRNA clone libraries. The clones closely related to Xanthomonadaceae bacterium and Xanthomonas sp. in the Gammaproteobacteria subdivision were most frequently retrieved from the cathodic biofilm. Results of the SEM-EDX analysis revealed that the cation species (Na(+) and Ca(2+)) were main constituents of chemical scale, indicating that these cations diffused from the anode chamber through the Nafion membrane. However, an excess accumulation of the biofilm and chemical scale on the cathode exhibited adverse effects on the power generation due to a decrease in the active cathode surface area and an increase in diffusion resistance for oxygen. Thus, it is important to properly control the formation of chemical scale and biofilm on the cathode during long-term operation. PMID:20923722

  15. Domain structure in Delithiated LiFePO 4 , a cathode material for Li ion Battery Applications

    Microsoft Academic Search

    M. Kinyanjui; A. Chuvilin; U. Kaiser; P. Axmann; M. Wohlfahrt-Mehrens

    Delithiation is a basic step in the operation of the Li ion battery and it involves the extraction of Li ions from the lattice\\u000a of the cathode material and insertion into the lattice of the anode. LiFePO4 is a cathode material whose wide application in high energy Li ion batteries, is limited by low ion and electron diffusion\\u000a [1]. Partially

  16. Thermionic cathode life-test studies

    NASA Technical Reports Server (NTRS)

    Forman, R.; Smith, D. H.

    1979-01-01

    A NASA-Lewis Research Center program for life testing commercial, high-current-density thermionic cathodes has been in progress since 1971. The purpose of the program is to develop long-life power microwave tubes for space communications. Four commercial-type cathodes are being evaluated in this investigation. They are the 'Tungstate', 'S' type, 'B' type, and 'M' type cathodes, all of which are capable of delivering 1 A/ sq cm or more of emission current at an operating temperature in the range of 1000-1100 C. The life test vehicles used in these studies are similar in construction to that of a high-power microwave tube and employ a high-convergence electron-gun structure; in contrast to earlier studies that used close-space diodes. These guns were designed for operation at 2 A/sq cm of cathode loading. The 'Tungstate' cathodes failed at 700 h or less and the 'S' cathode exhibited a lifetime of about 20,000 h. One 'B' cathode has failed after 27,000 h, the remaining units continuing to operate after up to 30,000 h. Only limited data are now available for the 'M' cathode, because only one has been operated for as long as 19,000 h. However, the preliminary results indicate the emission current from the 'M' cathode is more stable than the 'B' cathode and that it can be operated at a true temperature approximately 100 C lower than for the 'B' cathode.

  17. Temperature Distributions in Hollow Cathode Emitters

    NASA Technical Reports Server (NTRS)

    Polk, Jay; Marrese, Colleen; Thornber, Ben; Dang, Lisa; Johnson, Lee

    2004-01-01

    Life-limiting processes in hollow cathodes are determined largely by the temperature of the emitter. To support development of cathode life models we have developed a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used determine the axial temperature profile. Thermocouples on the orifice plate provide measurements ofthe external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. Initial measurements of the temperature distribution in a hollow cathode with the same geometry as a cathode that failed after operating at 12 A emission current for 27800 hours are discussed.

  18. A plasma-cathode electron source designed for industrial use

    NASA Astrophysics Data System (ADS)

    Osipov, Igor; Rempe, Nikolai

    2000-04-01

    The article presents a description of the principle of operation, the design, and the performance data of a plasma-cathode electron source. Plasma is produced in a hollow-cathode reflex discharge operating in an axial magnetic field. The discharge unit is filamentless. Air is used as the working gas. The electron source generates a focused continuous electron beam of current up to 0.3 A at an accelerating voltage of up to 60 kV. Owing to the absence of hot electrodes, the system operates reliably under severe gas conditions with a long lifetime. The electron source is currently used as a component of electron-beam welding flow lines. The use of the electron source for electron-beam facing of composite powdered materials is also discussed.

  19. A Computational and Experimental Study of Coflow Laminar Methane/Air Diffusion Flames: Effects of Fuel Dilution, Inlet Velocity, and Gravity

    NASA Technical Reports Server (NTRS)

    Cao, S.; Ma, B.; Bennett, B. A. V.; Giassi, D.; Stocker, D. P.; Takahashi, F.; Long, M. B.; Smooke, M. D.

    2014-01-01

    The influences of fuel dilution, inlet velocity, and gravity on the shape and structure of laminar coflow CH4-air diffusion flames were investigated computationally and experimentally. A series of nitrogen-diluted flames measured in the Structure and Liftoff in Combustion Experiment (SLICE) on board the International Space Station was assessed numerically under microgravity (mu g) and normal gravity (1g) conditions with CH4 mole fraction ranging from 0.4 to 1.0 and average inlet velocity ranging from 23 to 90 cm/s. Computationally, the MC-Smooth vorticity-velocity formulation was employed to describe the reactive gaseous mixture, and soot evolution was modeled by sectional aerosol equations. The governing equations and boundary conditions were discretized on a two-dimensional computational domain by finite differences, and the resulting set of fully coupled, strongly nonlinear equations was solved simultaneously at all points using a damped, modified Newton's method. Experimentally, flame shape and soot temperature were determined by flame emission images recorded by a digital color camera. Very good agreement between computation and measurement was obtained, and the conclusions were as follows. (1) Buoyant and nonbuoyant luminous flame lengths are proportional to the mass flow rate of the fuel mixture; computed and measured nonbuoyant flames are noticeably longer than their 1g counterparts; the effect of fuel dilution on flame shape (i.e., flame length and flame radius) is negligible when the flame shape is normalized by the methane flow rate. (2) Buoyancy-induced reduction of the flame radius through radially inward convection near the flame front is demonstrated. (3) Buoyant and nonbuoyant flame structure is mainly controlled by the fuel mass flow rate, and the effects from fuel dilution and inlet velocity are secondary.

  20. Studies of the cathode region of the dc glow discharge

    SciTech Connect

    Den Hartog, E.A.

    1989-01-01

    Laser-based spectroscopic diagnostics are employed to gain an increased understanding of the cathode region of a dc helium glow discharge. A pair of diagnostics are used to determine the density (n{sub e}) and temperature (T{sub e}) of low energy electrons confined in the negative glow. The first diagnostic is based on the observed suppression of 2{sup 1}S metastables in the negative glow due to electron collisions. The reaction primarily responsible for the suppression is the metastable spin conversion reaction which converts 2{sup 1}S metastables to 2{sup 3}S metastables. 2{sup 1}S and 2{sup 3}S metastable densities and 2{sup 1}P resonant atom densities are mapped as a function of position, and the maps are analyzed to determine a relation between n{sub e} and T{sub e}. A second relation between n{sub e} and T{sub e} is determined by measuring the electron impact transfer rate between Rydberg levels. The intersection of the two relations yields n{sub e} and T{sub e} for the low energy electrons in the negative glow. Empirical determinations of the current balance at the cathode surface and metastable production are compared to results of Monte Carlo simulations. The current balance comparison leads to the prediction of a field reversal at the cathode fall-negative glow boundary. As a consequence of this field reversal a simple model of the negative glow is suggested, in which the plasma in the negative glow diffuses toward the anode in an ambipolar-like process. Ion production in the negative glow is determined from Monte Carlo simulations. An equation is written balancing production and diffusion losses. This equation is written balancing production and diffusion losses. This equation leads to a third relation between n{sub e} and T{sub e} which is compared to the earlier results.

  1. Design model for the baffle aperture region of a hollow cathode thruster

    NASA Technical Reports Server (NTRS)

    Brophy, J. R.; Wilbur, P. J.

    1981-01-01

    A current balance on the main discharge chamber of an electron bombardment thruster is carried out. It is shown that the discharge current is the sum of the net cathode emission current, the beam current, and the ion current to cathode potential surfaces. Measurements of ion currents outside the virtual anode surface in a SERT II divergent magnetic field thruster show that relatively few ions cross this surface. This implies that ions are directed preferentially toward the anode and cathode pole pieces. A simple theoretical model useful as an aid in the design of the baffle aperture region of a hollow cathode equipped thruster is developed. The electron diffusion process through the aperture is modeled in accordance with the Bohm diffusion theory. The model is shown to yield consistent results for a given thruster geometry over substantial changes in operating conditions. The model's design usefulness is limited by a factor of two uncertainty observed over different thruster/cathode region geometries and by the accuracy to which the plasma parameters required as inputs to the model can be specified.

  2. Non-isothermal electrochemical model for lithium-ion cells with composite cathodes

    NASA Astrophysics Data System (ADS)

    Basu, Suman; Patil, Rajkumar S.; Ramachandran, Sanoop; Hariharan, Krishnan S.; Kolake, Subramanya Mayya; Song, Taewon; Oh, Dukjin; Yeo, Taejung; Doo, Seokgwang

    2015-06-01

    Transition metal oxide cathodes for Li-ion batteries offer high energy density and high voltage. Composites of these materials have shown excellent life expectancy and improved thermal performance. In the present work, a comprehensive non-isothermal electrochemical model for a Lithium ion cell with a composite cathode is developed. The present work builds on lithium concentration-dependent diffusivity and thermal gradient of cathode potential, obtained from experiments. The model validation is performed for a wide range of temperature and discharge rates. Excellent agreement is found for high and room temperature with moderate success at low temperatures, which can be attributed to the low fidelity of material properties at low temperature. Although the cell operation is limited by electronic conductivity of NCA at room temperature, at low temperatures a shift in controlling process is seen, and operation is limited by electrolyte transport. At room temperature, the lithium transport in Cathode appears to be the main source of heat generation with entropic heat as the primary contributor at low discharge rates and ohmic heat at high discharge rates respectively. Improvement in electronic conductivity of the cathode is expected to improve the performance of these composite cathodes and pave way for its wider commercialization.

  3. Preliminary assessment of using tree-tissue analysis and passive-diffusion samplers to evaluate trichloroethene contamination of ground water at Site SS-34N, McChord Air Force Base, Washington, 2001

    USGS Publications Warehouse

    Cox, S.E.

    2002-01-01

    Two low-cost innovative sampling procedures for characterizing trichloroethene (TCE) contamination in ground water were evaluated for use at McChord Air Force Base (AFB) by the U.S. Geological Survey, in cooperation with the U.S. Air Force McChord Air Force Base Installation Restoration Program, in 2001. Previous attempts to characterize the source of ground-water contamination in the heterogeneous glacial outwash aquifer at McChord site SS-34N using soil-gas surveys, direct-push exploration, and more than a dozen ground-water monitoring wells have had limited success. The procedures assessed in this study involved analysis of tree-tissue samples to map underlying ground-water contamination and deploying passive-diffusion samplers to measure TCE concentrations in existing monitoring wells. These procedures have been used successfully at other U.S. Department of Defense sites and have resulted in cost avoidance and accelerated site characterization. Despite the presence of TCE in ground water at site SS-34N, TCE was not detected in any of the 20 trees sampled at the site during either early spring or late summer sampling. The reason the tree tissue procedure was not successful at the McChord AFB site SS-34N may have been due to an inability of tree roots to extract moisture from a water table 30 feet below the land surface, or that concentrations of TCE in ground water were not large enough to be detectable in the tree tissue at the sampling point. Passive-diffusion samplers were placed near the top, middle, and bottom of screened intervals in three monitoring wells and TCE was observed in all samplers. Concentrations of TCE from the passive-diffusion samplers were generally similar to concentrations found in samples collected in the same wells using conventional pumping methods. In contrast to conventional pumping methods, the collection of ground-water samples using the passive-diffusion samples did not generate waste purge water that would require hazardous-waste disposal. In addition, the results from the passive-diffusion samples may show that TCE concentrations are stratified across some screened intervals. The overall results of the limited test of passive-diffusion samplers at site SS-34N were similar to more detailed tests conducted at other contaminated sites across the country and indicate that further evaluation of the use of passive-diffusion samplers at McChord site SS-34N is warranted.

  4. Formation of stable direct current microhollow cathode discharge by venturi gas flow system for remote plasma source in atmosphere

    SciTech Connect

    Park, Ki Wan; Lee, Tae Il; Hwang, Hyeon Seok; Noh, Joo Hyon; Baik, Hong Koo [Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Song, Kie Moon [Department of Applied Physics, Konkuk University, Chungju (Korea, Republic of)

    2008-02-11

    We introduce a microhollow cathode configuration with venturi gas flow to ambient air in order to obtain glow discharge at atmospheric pressure. Stable microhollow cathode discharge was formed in a 200 {mu}m diameter at 9 mA and the optimum value of gas velocityxdiameter for hollow cathode effect was obtained in our system. In order to confirm hollow cathode effect, we measured the enhancement of E/N strength for 200 {mu}m (0.31 m{sup 2}/s) and 500 {mu}m (0.78 m{sup 2}/s) air discharge at 8 mA under the velocity of 156 m/s. As a result, an increase of 46.7% in E/N strength of the discharge of 200 {mu}m hole was obtained compare to that of 500 {mu}m.

  5. Conflicting Roles Of Nickel In Controlling Cathode Performance In Lithium-ion Batteries

    SciTech Connect

    Gu, Meng; Belharouak, Ilias; Genc, Arda; Wang, Zhiguo; Wang, Dapeng; Amine, Khalil; Gao, Fei; Zhou, Guangwen; Thevuthasan, Suntharampillai; Baer, Donald R.; Zhang, Jiguang; Browning, Nigel D.; Liu, Jun; Wang, Chong M.

    2012-09-17

    A variety of approaches are being made to enhance the performance of lithium ion batteries. Incorporating multi-valence transition metal ions into metal oxide cathodes has been identified as an essential approach to achieve the necessary high voltage and high capacity. However, the fundamental mechanism that limits their power rate and cycling stability remains unclear. The power rate strongly depends on the lithium ion drift speed in the cathode. Crystallographically, these transition metal-based cathodes frequently have a layered structure. In the classic wisdom, it is accepted that lithium ion travels swiftly within the layers moving out/in of the cathode during the charge/discharge. Here, we report the unexpected discovery of a thermodynamically driven, yet kinetically controlled, surface modification in the widely explored lithium nickel manganese oxide cathode material, which may inhibit the battery charge/discharge rate. We found that during cathode synthesis and processing before electrochemical cycling in the cell nickel can preferentially move along the fast diffusion channels and selectively segregate at the surface facets terminated with a mix of anions and cations. This segregation essentially blocks the otherwise fast out/in pathways for lithium ions during the charge/discharge. Therefore, it appears that the transition metal dopant may help to provide high capacity and/or high voltage, but can be located in a wrong location that blocks or slows lithium diffusion, limiting battery performance. In this circumstance, limitations in the properties of Li-ion batteries using these cathode materials can be determined more by the materials synthesis issues than by the operation within the battery itself.

  6. Sulfur-vanadium oxide gel composites as thin film cathodes for rechargeable lithium batteries

    SciTech Connect

    Mukherjee, S.P.; Gavrilov, A.B.; Skotheim, T.A.

    1998-07-01

    A class of novel electroactive cathode materials based on composites produced from elemental sulfur and vanadium oxide xerogels or aerogels has been developed as models for lithium battery applications. The use of elemental sulfur in rechargeable lithium batteries has been hindered due to certain limitations such as, very low electronic conductivity and the out-diffusion of polysulfides during the cycling process which reduces the cycling efficiency. Vanadium oxide xerogels and aerogels have certain desirable characteristic physico-chemical properties, such as, high surface areas with nono-scale interconnecting porosity, high electronic conductivity, non- or nanocrystallinity, and oxidation reduction catalytic activity. Since these properties may improve the performance of sulfur based rechargeable batteries, a family of composite cathodes containing elemental sulfur and vanadium oxide gels were produced. The performance of the composites cathodes, in thin film form, were evaluated in coin cells and AA cells with metallic lithium anodes and liquid electrolytes. The multifunctional role of vanadium oxide gels on the cell performance of the cells having composite cathodes has been qualitatively explored. Results indicate that the cathodes having xerogel composites based on vanadium oxide sol from vanadium oxide isopropoxide can be made with high sulfur content (80 wt %) and with low carbon content (5 wt %) and without any polymer binder. This shows the contribution of adhesive properties and electronic conductivity of vanadium oxide xerogels. A significant suppression of polysulfide out-diffusion is observed with appropriate processing of the composite cathodes. It is anticipated that the nanoscale interconnecting porosity of gels plays an important role in this behavior. An excellent rate capability is observed with the vanadium-oxide sulfur composite cathodes indicating the contribution of intrinsic electrochemical properties of the vanadium oxide.

  7. Filters for cathodic arc plasmas

    DOEpatents

    Anders, Andre (Albany, CA); MacGill, Robert A. (Richmond, CA); Bilek, Marcela M. M. (Engadine, AU); Brown, Ian G. (Berkeley, CA)

    2002-01-01

    Cathodic arc plasmas are contaminated with macroparticles. A variety of magnetic plasma filters has been used with various success in removing the macroparticles from the plasma. An open-architecture, bent solenoid filter, with additional field coils at the filter entrance and exit, improves macroparticle filtering. In particular, a double-bent filter that is twisted out of plane forms a very compact and efficient filter. The coil turns further have a flat cross-section to promote macroparticle reflection out of the filter volume. An output conditioning system formed of an expander coil, a straightener coil, and a homogenizer, may be used with the magnetic filter for expanding the filtered plasma beam to cover a larger area of the target. A cathodic arc plasma deposition system using this filter can be used for the deposition of ultrathin amorphous hard carbon (a-C) films for the magnetic storage industry.

  8. Barium-Dispenser Thermionic Cathode

    NASA Technical Reports Server (NTRS)

    Wintucky, Edwin G.; Green, M.; Feinleib, M.

    1989-01-01

    Improved reservoir cathode serves as intense source of electrons required for high-frequency and often high-output-power, linear-beam tubes, for which long operating lifetime important consideration. High emission-current densities obtained through use of emitting surface of relatively-low effective work function and narrow work-function distribution, consisting of coat of W/Os deposited by sputtering. Lower operating temperatures and enhanced electron emission consequently possible.

  9. Diffusion, Osmosis, and Dialysis

    NSDL National Science Digital Library

    Molecular Literacy Project

    Materials such as water, nutrients, dissolved gases, ions and waste are constantly moving across a cell's membrane. In this activity, students interact with models of diffusion and osmosis and observe the net flow of molecules in air, in cells, and across a cell's semi-permeable membrane. Students will be able to: Determine that diffusion results from random motion and/or collisions of particles; learn that particles diffuse from high concentration to low concentration; explore simple diffusion across a semi-permeable membrane; connect the process to dialysis.

  10. Arc-cathode interaction study

    NASA Technical Reports Server (NTRS)

    Zhou, X.; Heberlein, J.

    1992-01-01

    Insufficient electrode life and uncertainties in that life are major problems hampering the development in many plasma application areas which make use of plasma torches, arc heaters, and arc jet thrusters. In spite of a considerable amount of work published dealing with arc-cathode phenomena, our present understanding is still incomplete because different physical phenomena dominate for different combinations of experimental parameters. The objective of our present research project is to gain a better understanding of the behavior of arc-cathode surface interaction over a wide range of parameters, and furthermore to develop guidelines for better thermal design of the electrode and the selection of materials. This report will present the research results and progress obtained on the arc-cathode interaction studies at the University of Minnesota. It includes results which have been obtained under programs other than the NASA funded program. Some of the results have been submitted in an informal interim progress report, and all of the results have been presented in a seminar during a visit to the NASA Lewis Research Center on October 16, 1992.

  11. Characterization of hollow cathode, ring cusp discharge chambers. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Vaughn, Jason A.

    1989-01-01

    An experimental study into the effects of changes in such physical design parameters as hollow cathode position, anode position and ring cusp magnetic field configuration and strength on discharge chamber performance, is described. The results are presented in terms of comparative plasma ion energy cost, extracted ion fraction and ion beam profile data. Such comparisons are used to demonstrate specific means by which changes in these design parameters induce changes in performance, i.e., through changes in the loss rates of primary electrons to the anode, of ions to discharge chamber walls or of ions to cathode and anode surfaces. Results show: (1) the rate of primary electron loss to the anode decreases as the anode is moved downstream of the ring cusp toward the screen grid, (2) the loss rate of ions to hollow cathode surfaces are excessive if the cathode is located upstream of a point of peak magnetic flux density on the discharge chamber centerline, and (3) the fraction of the ions produced that are lost to discharge chamber walls and ring magnet surfaces is reduced by positioning the magnet rings so the plasma density is uniform over the grid surface and so there are no steep magnetic flux density gradients near the walls through which ions can be lost by Bohm diffusion. The uniformity of the plasma density at the grids can also be improved by moving the point of primary electron injection into the discharge chamber off of the chamber centerline. Other results show the discharge chamber losses decrease when a filament cathode is substituted for a hollow cathode to the extent of the hollow cathode operating power. When plasma ion energy cost is determined in such a way that the cost of operating the hollow cathode is subtracted out, the performance using either electron source is similar.

  12. Oxygen transport in the internal xenon plasma of a dispenser hollow cathode

    SciTech Connect

    Capece, Angela M., E-mail: acapece@pppl.gov; Shepherd, Joseph E. [California Institute of Technology, Pasadena, California 91125 (United States); Polk, James E.; Mikellides, Ioannis G. [Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, California 91109 (United States)

    2014-04-21

    Reactive gases such as oxygen and water vapor modify the surface morphology of BaO dispenser cathodes and degrade the electron emission properties. For vacuum cathodes operating at fixed temperature, the emission current drops rapidly when oxygen adsorbs on top of the low work function surface. Previous experiments have shown that plasma cathodes are more resistant to oxygen poisoning and can operate with O{sub 2} partial pressures one to two orders of magnitude higher than vacuum cathodes before the onset of poisoning occurs. Plasma cathodes used for electric thrusters are typically operated with xenon; however, gas phase barium, oxygen, and tungsten species may be found in small concentrations. The densities of these minor species are small compared with the plasma density, and thus, their presence in the discharge does not significantly alter the xenon plasma parameters. It is important, however, to consider the transport of these minor species as they may deposit on the emitter surface and affect the electron emission properties. In this work, we present the results of a material transport model used to predict oxygen fluxes to the cathode surface by solving the species conservation equations in a cathode with a 2.25?mm diameter orifice operated at a discharge current of 15?A, a Xe flow rate of 3.7 sccm, and 100?ppm of O{sub 2}. The dominant ionization process for O{sub 2} is resonant charge exchange with xenon ions. Ba is effectively recycled in the plasma; however, BaO and O{sub 2} are not. The model shows that the oxygen flux to the surface is not diffusion-limited; therefore, the high resistance to oxygen poisoning observed in plasma cathodes likely results from surface processes not considered here.

  13. New Cathode Materials for Intermediate Temperature Solid Oxide Fuel Cells

    SciTech Connect

    Allan J. Jacobson

    2004-07-23

    Operation of SOFCs at intermediate temperatures (500-800 C) requires new combinations of electrolyte and electrode materials that will provide both rapid ion transport across the electrolyte and electrode - electrolyte interfaces and efficient electrocatalysis of the oxygen reduction and fuel oxidation reactions. This project concentrates on materials and issues associated with cathode performance that are known to become limiting factors as the operating temperature is reduced. The specific objectives of the proposed research are to develop cathode materials that meet the electrode performance targets of 1.0 W/cm{sup 2} at 0.7 V in combination with YSZ at 700 C and with GDC, LSGM or bismuth oxide based electrolytes at 600 C. The performance targets imply an area specific resistance of {approx}0.5 {Omega}cm{sup 2} for the total cell. The research strategy is to investigate both established classes of materials and new candidates as cathodes, to determine fundamental performance parameters such as bulk diffusion, surface reactivity and interfacial transfer, and to couple these parameters to performance in single cell tests. The initial choices for study are perovskite oxides based on Sr substituted LaFeO{sub 3}, where significant data in single cell tests exists at PNNL for cathodes on both YSZ and CSO/YSZ, and Ln{sub 2}NiO{sub 4} compositions. A key component of the research strategy is to evaluate for each cathode material composition, the key performance parameters, including ionic and electronic conductivity, surface exchange rates, stability with respect to the specific electrolyte choice, and thermal expansion coefficients. Results on electrical conductivity relaxation measurements on additional compositions in the La{sub 2}NiO{sub 4+x} and Pr{sub 2}NiO{sub 4+x} series are presented in this report. Studies of the inter-diffusion of amorphous SrFeO{sub 3-x} and LaFeO{sub 3-x} bilayer films prepared by pulsed laser deposition are described. Such studies are a preliminary to the combinatorial synthesis approach discussed in previous reports.

  14. Development program on a cold cathode electron gun

    NASA Technical Reports Server (NTRS)

    Spindt, C. A.; Holland, C. E.

    1985-01-01

    During this phase of the cathode development program, SRI improved the multiple electron beam exposure system used to print hole patterns for the cathode arrays, studied anisotropic etch processes, conducted cathode investigations using an emission microscope, reviewed possible alternate materials for cathode fabrication, studied cathode storage techniques, conducted high power operation experiments, and demonstrated high-current-density operation with small arrays of tips.

  15. Hollow cathode, quasi-steady MPD arc

    NASA Technical Reports Server (NTRS)

    Parmentier, N.; Jahn, R. G.

    1971-01-01

    A quasi-steady MPD accelerator has been operated with four different hollow cathodes over a power range from 5 kilowatts to 5 megawatts. The absolute level of the argon mass flow, as well as the fractional division of the flow between the cathode and the six standard chamber injectors, is varied over a range of 1 to 12 grams per second. For a fixed total current, it is observed that the voltage increases monotonically with mass flow rate, compared to the usual experience with solid cathodes where the voltage decreases with mass flow rate. For a fixed percentage of flow through the cathode, each hollow cathode configuration displays a minimum impedance at a particular value of the total mass flow. It is asserted that in order to keep the discharge inside the hollow cathode the magnetic pressure and gasdynamic pressure have to match inside the cavity.

  16. Decay of the zincate concentration gradient at an alkaline zinc cathode after charging

    NASA Technical Reports Server (NTRS)

    Kautz, H. E.; May, C. E.

    1979-01-01

    The study was carried out by observing the decay of the zincate concentration gradient at a horizontal zinc cathode after charging. This decay was found to approximate first order kinetics as expected from a proposed boundary layer model. The decay half life was shown to be a linear function of the thickness of porous zinc deposit on the cathode indicating a very rapid transport of zincate through porous zinc metal. The rapid transport is attributed to an electrochemical mechanism. The data also indicated a relatively sharp transition between the diffusion and convection transport regions. The diffusion of zincate ion through asbestos submerged in alkaline electrolyte was shown to be comparable with that predicted from the bulk diffusion coefficient of the zincate ion in alkali.

  17. Anion reduction dominated cathodic limit of metal-free ionic liquid: experimental and theoretical proofs.

    PubMed

    Lo, Nai-Chang; Chen, Hsing-Yin; Chuang, Wan-Jung; Lu, Chi-Yu; Chen, Ping-Yu; Chen, Po-Yu

    2013-11-01

    The cathodic limit of the electrochemical window in the second-generation ionic liquids (composed of air- and water-stable metal-free cations and anions) is traditionally believed to be determined by the reduction of the cation. More and more exceptions, however, were found in various ionic liquids. In this study, the cathodic limit of the electrochemical window in 1-butyl-1-methylpyrrolidinium salicylate ionic liquid (BMP-SAL IL) was studied. It has been found that the cathodic limit of BMP-SAL is determined by the reduction of SAL(-) anion rather than the reduction of BMP(+) cation. The cyclic voltammetric behavior, NMR spectra, and MALDI-TOF MS spectra of BMP-SAL recorded before and after the IL was electrolyzed at the cathodic limit provide sufficient evidence that the major reaction at the cathodic limit of BMP-SAL is the reduction of SAL(-) anion. The theoretical calculations support the experimental data, and the results indicate that anion reduction dominated cathodic limit should be a common phenomenon in ionic liquids. PMID:24107181

  18. A direct density modulation cathode in magnetron

    SciTech Connect

    Li, Wei; Zhang, Jun; Liu, Yong-gui; Yang, Han-wu; Shu, Ting [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073 (China)] [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073 (China)

    2013-09-15

    A direct Density Modulation Cathode (DMC) in magnetron is proposed in this paper. By removing the velocity modulation process, electron spokes corresponding to the dominant operating mode can be quickly formed when the DMC is used. Based on theoretical analysis, particle-in-cell simulations and experimental investigations are carried out for demonstration. The final results show that compared with conventional solid cathode and transparent cathode, the DMC can increase 68% and even 146% of relative microwave widths, respectively.

  19. Pyrite cathode material for a thermal battery

    NASA Astrophysics Data System (ADS)

    Pemsler, J. P.; Litchfield, J. K.

    1991-02-01

    The present invention relates in general to a synthetic cathode material for a molten salt battery and, more particularly, to a process of providing and using synthetic pyrite for use as a cathode in a thermal battery. These batteries, which have been successfully used in a number of military applications, include iron disulfide cathode material obtained as benefacted or from natural occurring pyrite deposits, or as a byproduct of flotation concentrate from the processing of base or noble metal ores.

  20. Pyrite cathode material for a thermal battery

    SciTech Connect

    Pemsler, J.P.; Litchfield, J.K.

    1991-02-07

    The present invention relates in general to a synthetic cathode material for a molten salt battery and, more particularly, to a process of providing and using synthetic pyrite for use as a cathode in a thermal battery. These batteries, which have been successfully used in a number of military applications, include iron disulfide cathode material obtained as benefacted or from natural occurring pyrite deposits, or as a byproduct of flotation concentrate from the processing of base or noble metal ores.

  1. Cathode spot observation in vacuum arc of zinc cathode under oxygen gas flow

    Microsoft Academic Search

    Ryuichi Miyano; Youhei Fujimura; Hirofumi Takikawa; Tateki Sakakibara; Masayuki Nagao

    2000-01-01

    Magnetically steered cathode spot(s) of a vacuum arc with a zinc (Zn) cathode was (were) observed using a high-speed video camera. The camera can take 4,500 frames per second of 256 by 256 pixels. The transverse magnetic flux density for steering the cathode spot was 1.0 and 5.5 mT at the bottom of the cathode (64 mm in diameter) shoulder.

  2. Cathode spot motion in vacuum arc of zinc cathode under oxygen gas flow

    Microsoft Academic Search

    Ryuichi Miyano; Youhei Fujimura; Hirofumi Takikawa; Tateki Sakakibara; Masayuki Nagao

    2001-01-01

    Magnetically steered cathode spot(s) of a vacuum arc with a zinc (Zn) cathode was(were) observed using a high-speed video camera. The camera can take 4500 frames per second of 256256 pixels. The transverse magnetic flux density for steering the cathode spot was 1.0 and 5.5 mT at the bottom of the cathode (64 mm in diameter) shoulder. The arc was

  3. A Two Frequency Thermionic Cathode Electron Gun

    NASA Astrophysics Data System (ADS)

    Edelen, Jon; Biedron, Sandra; Harris, John; Lewellen, John; Milton, Stephen

    2014-03-01

    When an un-gated thermionic cathode is operated in an RF gun, some fraction of the emitted electrons will return to the cathode due to the change in sign of the electric field in the gun. This back-bombardment current causes heating of the cathode, and this reduces the ability of the cathode heater to control the bunch charge. In this paper, we investigate the use of a two frequency TM010 / TM020 electron gun to mitigate this effect. Simulations revealed that for a 100-pC bunch charge operating at 10MV/m gradient the harmonic field produced a 63% reduction in the back-bombardment power.

  4. Development of High Energy Cathode (PNNL)

    SciTech Connect

    Zhang, Jiguang; Liu, Jun

    2011-01-01

    Lithium ion batteries with high energy densities are required to reach DOEs goal on early commercialization of electrical vehicles, including HEV, PHEV and EV. To increase the energy of cathode, voltage or/and capacity of cathode need to be increased. During FY10, we have investigated cathode materials with high operation voltages, for example LiMnPO4, and renewable organic cathode with high capacities. Environmentally friendly materials and low cost synthesis approaches have been intentionally explored during our efforts.

  5. Emission properties of explosive field emission cathodes

    SciTech Connect

    Roy, Amitava; Patel, Ankur; Menon, Rakhee; Sharma, Archana; Chakravarthy, D. P. [Accelerator and Pulse Power Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Patil, D. S. [Laser and Plasma Technology Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India)

    2011-10-15

    The research results of the explosive field emission cathode plasma expansion velocity and the initial emission area in the planar diode configuration with cathodes made of graphite, stainless steel, polymer velvet, carbon coated, and carbon fiber (needle type) cathodes are presented. The experiments have been performed at the electron accelerator LIA-200 (200 kV, 100 ns, and 4 kA). The diode voltage has been varied from 28-225 kV, whereas the current density has been varied from 86-928 A/cm{sup 2} with 100 ns pulse duration. The experimentally obtained electron beam diode perveance has been compared with the 1 dimensional Child-Langmuir- law. It was found that initially only a part of the cathode take part in the emission process. The plasma expands at 1.7-5.2 cm/{mu}s for 4 mm anode-cathode gap for various cathode materials. It was found that the plasma expansion velocity increases with the decrease in the cathode diameter. At the beginning of the accelerating pulse, the entire cathode area participates in the electron emission process only for the multiple needle type carbon fiber cathode.

  6. Experimental measurements on the current balance at the cathode of a cylindrical hollow cathode glow discharge

    Microsoft Academic Search

    H. Helm

    1979-01-01

    The contribution of positive ions, photons and metastable particles to the secondary emission of electrons from the cathode of an argon glow discharge with cylindrical cathode is measured by sampling the plasma species through a small orifice in the cathode wall and analyzing them in a high vacuum region. Additional experiments are made with a second apparatus which enables the

  7. Synthesis, Characterization and Performance of Cathodes for Lithium Ion Batteries

    NASA Astrophysics Data System (ADS)

    Zhu, Jianxin

    Lithium ion batteries provide a high energy density, higher voltage as well as a long shelf life compared to traditionally used lead acid, NiMH and NiCd batteries. Thus, they are a very promising energy storage system for our daily life. As one of the most important components in a battery, cathode materials have been investigated intensively in recent years as they play a key role in determining the cell voltage and discharge capacity in a battery. Both layered Li(Ni1/3Co1/3Mn1/3)O 2 (NCM) and olivine-structured LiFePO4 (LFP) materials are promising cathode candidates. However, these cathodes also have some disadvantages that have hindered further commercialization. The main issue with NCM is its rapid performance decay upon cycling. In addition, LFP is hindered by a low rate capacity and low lithium ion diffusivity. We studied the crystal growth behavior and performance of both Li(Ni 1/3Co1/3Mn1/3)O2 and LiFePO4 cathodes in order to develop synthesis-structure-function relationships. Three different crystal growth behaviors were observed for the NCM annealing process: surface, volume and grain boundary diffusion. Further exploration of the mechanism of NCM performance decay revealed that microstructural changes were related to the strain accommodation ability in this system and that nanostructured materials were more stable during cycling. In the LFP synthesis, we observed both oriented attachment (OA) and Ostwald ripening (OR) during growth in a triethylene-glycol system. Both polycrystalline and single crystalline particles evolved as a function of a time-dependent pH change. Thus, the lithium ion diffusion rate of LiFePO4 was improved by tailoring the morphology and size though our modification of the precursor environment, revealing that polycrystalline LFP displayed better performance than single crystalline particles. Finally, the electronic conductivity of LiFePO4 was successfully increased via a polymer solution coating method. By producing more uniform, thin and coherent coatings on LiFePO4 particles, we were able to produce batteries with significantly less carbon (i.e., 0.41 wt.%) while has comparable performance (discharge capacity of 80mAh/g at 2C) compared to traditionally synthesized carbon-coated LiFePO4 with higher carbon loadings (ca. 2.64 wt.%). This will enable us to produce batteries with higher active material loading and therefore, significantly larger energy densities.

  8. New mechanically rechargeable zinc-air batteries

    Microsoft Academic Search

    J. Giltner

    1975-01-01

    This report describes the design, development and testing of new mechanically rechargeable zinc-air batteries. Following research and development of a low cost silver-mercury cathode catalyst, prototype battery tests were conducted. Cycle life tests at 3.5 amperes indicated satisfactory performance through at least 26 cycles when this test was terminated for the final hardware build. The cathode bi-cell design utilized the

  9. H+ diffusion and electrochemical stability of Li1+x+yAlxTi2-xSiyP3-yO12 glass in aqueous Li/air battery electrolytes

    NASA Astrophysics Data System (ADS)

    Ding, Fei; Xu, Wu; Shao, Yuyan; Chen, Xilin; Wang, Zhiguo; Gao, Fei; Liu, Xingjiang; Zhang, Ji-Guang

    2012-09-01

    It is well known that LATP (Li1+x+yAlxTi2-xSiyP3-yO12) glass is a good lithium (Li)-ion conductor. However, the interaction between LATP glass and H+ ions in aqueous electrolytes (including the diffusion and surface adsorption of H+ ions) needs to be well understood before the long-term application of LATP glass in an aqueous electrolyte can be realized. In this work, we investigate H+-ion diffusion in LATP glass and their interactions with the glass surface using both experimental and modeling approaches. Our results indicate that the apparent H+-related current observed in the initial cyclic voltammetry scan should be attributed to the adsorption of H+ ions on the LATP glass rather than the bulk diffusion of H+ ions. Furthermore, density functional theory calculations indicate that the H+-ion diffusion energy barrier (3.21eV) is much higher than that for Li+ ions (0.79eV) and Na+ ions (0.79eV) in a NASICON-type LiTi2(PO4)3 material. As a result, H+-ion conductivity in LATP glass is negligible at room temperature. However, significant surface corrosion was found after the LATP glass in a strong alkaline electrolyte. Therefore, to prevent LATP glass from corrosion, appropriate electrolytes must be developed for long-term operation of LATP in aqueous Li-air batteries.

  10. Development of aqueous-lithium batteries with a focus on cathodes

    NASA Astrophysics Data System (ADS)

    Vanvoorhis, Dewey J.

    Topics dealing with the advancement of the aqueous-lithium battery technology are discussed. First, results are presented from the characterization of various cathode candidates for the aqueous-lithium systems: both water and oxygen reducing. Among the water reducing cathodes, nickel and ruthenium cathodes have proven to be the best candidates. Planar nickel and ruthenium electrodes have been studied in 8M KOH using electrochemical impedance spectroscopy (EIS) and equivalent circuits at -1.2, -1.25, -1.35, -1.45, and -1.7 VSCE. Aging characteristics based on EIS are presented for the nickel and ruthenium electrodes at -1.25 and -1.45 V SCE. Electrochemical rate constants are also reported from the EIS data, which are based on the Volmer-Heyrovsky mechanism of the hydrogen evolution reaction (HER). The kinetic parameters obtained from the mechanistic model agree with both the AC results obtained at all five cathodic overpotentials tested and the DC experimental results form nickel in 8M KOH. Among the oxygen reducing cathodes, four commercially available air cathodes form E-TEK, ERC, and Alupower were used to characterize the lithium-air system for a wide range of discharge rates. Secondly, a commercially available cation exchange membrane, NafionRTM 90209, has proven to be an effective means of controlling the electrolyte concentration of the battery if operating in an ocean environment. Finally, the characterization of aqueous-lithium single-celled batteries is presented for both lithium-air and lithium-water batteries. A novel idea for a lithium-water battery is also described, and results are presented for 8 days of continuous prototype operation. The specific energy density of the prototype, 4 kW-hr/kg, has almost doubled that of previous designed lithium-water systems, and the faradaic efficiency of the prototype exceeds 90%. The lithium-water prototype demonstrated that the system is promising, and efforts should continue for its development.

  11. Diffusivity fractionations of H2(16)O/H2(17)O and H2(16)O/H2(18)O in air and their implications for isotope hydrology.

    PubMed

    Barkan, Eugeni; Luz, Boaz

    2007-01-01

    We have determined the isotope effects of (17)O and (18)O substitution of (16)O in H(2)O on molecular diffusivities of water vapor in air by the use of evaporation experiments. The derived diffusion fractionation coefficients (17)alpha(diff) and (18)alpha(diff) are 1.0146 +/- 0.0002 and 1.0283 +/- 0.0003, respectively. We also determined, for the first time, the ratio ln((17)alpha(diff))/ln((18)alpha(diff)) as 0.5185 +/- 0.0002. This ratio, which is in excellent agreement with the theoretical value of 0.5184, is significantly smaller than the ratio in vapor-liquid equilibrium (0.529). We show how this new experimental information gives rise to (17)O excess in meteoric water, and how it can be applied in isotope hydrology. PMID:17705344

  12. Nanostructured MnO2-Based Cathodes for Li-Ion/Polymer Cells

    NASA Technical Reports Server (NTRS)

    Skandan, Ganesh; Singhal, Amit

    2005-01-01

    Nanostructured MnO2-based cathodes for Li-ion/polymer electrochemical cells have been investigated in a continuing effort to develop safe, high-energy-density, reliable, low-toxicity, rechargeable batteries for a variety of applications in NASA programs and in mass-produced commercial electronic equipment. Whereas the energy densities of state-of-the-art lithium-ion/polymer batteries range from 150 to 175 W h/kg, the goal of this effort is to increase the typical energy density to about 250 W h/kg. It is also expected that an incidental benefit of this effort will be increases in power densities because the distances over which Li ions must diffuse through nanostructured cathode materials are smaller than those through solid bulk cathode materials.

  13. Processes For Cleaning a Cathode Tube and Assemblies In A Hollow Cathode Assembly

    NASA Technical Reports Server (NTRS)

    Patterson, Michael J. (Inventor); Verhey, Timothy R. R. (Inventor); Soulas, George C. (Inventor)

    2001-01-01

    The present invention is a process for cleaning a cathode tube and other subassemblies in a hollow cathode assembly. In the disclosed process, hand covering elastomer gloves are used for handling all cathode assembly parts. The cathode tube and other subassemblies are cleaned with a lint-free cloth damped with acetone, then wiped with alcohol, immersed in ethyl alcohol or acetone, and ultrasonic agitation is applied, heating to 60 C. for ethyl alcohol or 56 C. for acetone. The cathode tube and other subassemblies are dried by blowing with nitrogen gas.

  14. One-step fabrication of membraneless microbial fuel cell cathode by electropolymerization of polypyrrole onto stainless steel mesh.

    PubMed

    Feng, Chunhua; Wan, Qunyi; Lv, Zhisheng; Yue, Xianjun; Chen, Yanfeng; Wei, Chaohai

    2011-05-15

    A unique one-step method for fabrication of a membraneless microbial fuel cell (MFC) cathode was developed by coating a conductive polymer onto stainless steel mesh. The resulting polypyrrole/anthraquinone-2-sulfonate (PPy/AQS) film was synthesized via electropolymerization using AQS as the dopants. The scanning electron microscopy results indicated that the PPy/AQS film was uniformly formed on the metal mesh electrode without cracks on its surface and featuring a globular structure. Being equipped with such a cathode that was able to catalyze oxygen reduction and prevent water leakage, the membraneless MFC allowed power generation over 250h and exhibited a maximum power density of 575mWm(-2). Increasing film thickness seemed to result in a reduction in power performance due to the increased ohmic resistance of the cathode material and the enhanced difficulty for oxygen diffusion inside the cathode. PMID:21454069

  15. Electrolytic cell with improved hydrogen evolution cathode

    Microsoft Academic Search

    Gray

    1984-01-01

    An electrolytic cell having an improved hydrogen evolution cathode, said cathode being characterized by a conductive metal core and an integral Raney-type catalytic surface predominantly derived from an adherent ternary aluminide Beta structured intermetallic crystalline precursory outer portion of the metal core is disclosed. The precursory outer portion preferably has molybdenum and titanium added to give a precursor alloy having

  16. Electrolytic cell with improved hydrogen evolution cathode

    Microsoft Academic Search

    Gray

    1984-01-01

    An electrolytic cell having an improved hydrogen evolution cathode said cathode being characterized by a conductive metal core and an integral Raney-type catalytic surface predominantly derived from an adherent ternary aluminide Beta structured intermetallic crystalline precursory outer portion of the metal core is disclosed. The precursory outer portion preferably has molybdenum and titanium added to give a precursor alloy having

  17. Genetic algorithms for inverse cathodic protection problems

    Microsoft Academic Search

    Luiz C Wrobel; Panayiotis Miltiadou

    2004-01-01

    Cathodic protection (CP) is a corrosion prevention technique which uses electrochemical properties of metals to insure that the structure to be protected becomes the cathode of an electrolytic cell. The technique is commonly used for protecting metallic structures placed in aggressive environments, e.g. ship hulls, offshore structures and underground pipelines.Mathematical models of CP problems require appropriate boundary conditions given by

  18. Photovoltaic powered regulated cathodic protection system

    Microsoft Academic Search

    Wagdy R. Anis; Hany A. Alfons

    1994-01-01

    The cathodic protection (CP) system objective is to protect metallic structures against corrosion caused by chemical reaction between metallic structures and surrounding mediums, such as soil or water. To overcome such a problem, a sacrificing anode is connected to the protected structure (which acts as a cathode) through a DC power supply. As a result, a current passes from the

  19. Measuring system for enhanced cathodic corrosion protection

    Microsoft Academic Search

    Franco Ferraris; Marco Parvis; Emma Angelini; Sabrina Grassini

    2012-01-01

    Buried metallic artifacts in soil or seawater are exposed to high risk of corrosion due to the contact with the surrounding aggressive environment. The protection of a wide range of iron-based artifacts is carried out by means of cathodic protection (CP)systems. CP is a technique used to control the corrosion of a metal surface by making it the cathode of

  20. Model for designing planar magnetron cathodes

    SciTech Connect

    Garcia, M.

    1997-09-30

    This report outlines an analytical model of the distribution of plasma in the cathode fall of a planar magnetron cathode. Here I continue commentary on previous work, and introduce an ion sheath model to describe the discharge dark space below the magnetron halo.

  1. Bimetallic Cathode Materials for Lithium Based Batteries

    E-print Network

    Bimetallic Cathode Materials for Lithium Based Batteries Frontiers in Materials Science Seminar for implantable cardiac defibrillators (ICDs) are based on the Lithium/Silver vanadium oxide (SVO, Ag2V4O11 to the favorable battery characteristics associated with Ag2VO2PO4 cathodes. Website/Bio Information: http://www.cbe.buffalo.edu/people/full_time/e_takeuchi.php

  2. High energy density battery with cathode composition

    Microsoft Academic Search

    D. Nalewajek; R. E. Eibeck; B. Sukornick

    1985-01-01

    A cell which employs an active metal anode such as lithium and a liquid organic electrolyte that is improved by the use of a cathode comprised of carbon fluoride chloride is described. The cathode comprises a carbon fluoride chloride of the general formula (C \\/SUB y\\/ F \\/SUB x\\/ Cl \\/SUB z\\/ ) \\/SUB n\\/ wherein y is 1 to

  3. Multi-cathode unbalanced magnetron sputtering systems

    NASA Technical Reports Server (NTRS)

    Sproul, William D.

    1991-01-01

    Ion bombardment of a growing film during deposition is necessary in many instances to ensure a fully dense coating, particularly for hard coatings. Until the recent advent of unbalanced magnetron (UBM) cathodes, reactive sputtering had not been able to achieve the same degree of ion bombardment as other physical vapor deposition processes. The amount of ion bombardment of the substrate depends on the plasma density at the substrate, and in a UBM system the amount of bombardment will depend on the degree of unbalance of the cathode. In multi-cathode systems, the magnetic fields between the cathodes must be linked to confine the fast electrons that collide with the gas atoms. Any break in this linkage results in electrons being lost and a low plasma density. Modeling of the magnetic fields in a UBM cathode using a finite element analysis program has provided great insight into the interaction between the magnetic fields in multi-cathode systems. Large multi-cathode systems will require very strong magnets or many cathodes in order to maintain the magnetic field strength needed to achieve a high plasma density. Electromagnets offer the possibility of independent control of the plasma density. Such a system would be a large-scale version of an ion beam enhanced deposition (IBED) system, but, for the UBM system where the plasma would completely surround the substrate, the acronym IBED might now stand for Ion Blanket Enhanced Deposition.

  4. Kinetic mechanism of molecular energy transfer and chemical reactions in low-temperature air-fuel plasmas.

    PubMed

    Adamovich, Igor V; Li, Ting; Lempert, Walter R

    2015-08-13

    This work describes the kinetic mechanism of coupled molecular energy transfer and chemical reactions in low-temperature air, H2-air and hydrocarbon-air plasmas sustained by nanosecond pulse discharges (single-pulse or repetitive pulse burst). The model incorporates electron impact processes, state-specific N2 vibrational energy transfer, reactions of excited electronic species of N2, O2, N and O, and 'conventional' chemical reactions (Konnov mechanism). Effects of diffusion and conduction heat transfer, energy coupled to the cathode layer and gasdynamic compression/expansion are incorporated as quasi-zero-dimensional corrections. The model is exercised using a combination of freeware (Bolsig+) and commercial software (ChemKin-Pro). The model predictions are validated using time-resolved measurements of temperature and N2 vibrational level populations in nanosecond pulse discharges in air in plane-to-plane and sphere-to-sphere geometry; temperature and OH number density after nanosecond pulse burst discharges in lean H2-air, CH4-air and C2H4-air mixtures; and temperature after the nanosecond pulse discharge burst during plasma-assisted ignition of lean H2-mixtures, showing good agreement with the data. The model predictions for OH number density in lean C3H8-air mixtures differ from the experimental results, over-predicting its absolute value and failing to predict transient OH rise and decay after the discharge burst. The agreement with the data for C3H8-air is improved considerably if a different conventional hydrocarbon chemistry reaction set (LLNL methane-n-butane flame mechanism) is used. The results of mechanism validation demonstrate its applicability for analysis of plasma chemical oxidation and ignition of low-temperature H2-air, CH4-air and C2H4-air mixtures using nanosecond pulse discharges. Kinetic modelling of low-temperature plasma excited propane-air mixtures demonstrates the need for development of a more accurate 'conventional' chemistry mechanism. PMID:26170427

  5. NEW CATHODE MATERIALS FOR INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELLS

    SciTech Connect

    Allan J. Jacobson

    2004-05-11

    Operation of SOFCs at intermediate temperatures (500-800 C) requires new combinations of electrolyte and electrode materials that will provide both rapid ion transport across the electrolyte and electrode-electrolyte interfaces and efficient electrocatalysis of the oxygen reduction and fuel oxidation reactions. This project concentrates on materials and issues associated with cathode performance that are known to become limiting factors as the operating temperature is reduced. The specific objectives of the proposed research are to develop cathode materials that meet the electrode performance targets of 1.0 W/cm{sup 2} at 0.7 V in combination with YSZ at 700 C and with GDC, LSGM or bismuth oxide based electrolytes at 600 C. The performance targets imply an area specific resistance of {approx}0.5 {Omega}cm{sup 2} for the total cell. The research strategy is to investigate both established classes of materials and new candidates as cathodes, to determine fundamental performance parameters such as bulk diffusion, surface reactivity and interfacial transfer, and to couple these parameters to performance in single cell tests. The initial choices for study are perovskite oxides based on Sr substituted LaFeO{sub 3}, where significant data in single cell tests exists at PNNL for cathodes on both YSZ and CSO/YSZ, and of Ln{sub 2}NiO{sub 4} compositions. A key component of the research strategy is to evaluate for each cathode material composition, the key performance parameters, including ionic and electronic conductivity, surface exchange rates, stability with respect to the specific electrolyte choice, and thermal expansion coefficients. Results on electrical conductivity relaxation measurements on La{sub 2}NiO{sub 4+x} and Pr{sub 2}NiO{sub 4+x} samples are reported and compared with results from previous studies. Studies of the crystallization of amorphous SrFeO{sub 3-x} and LaFeO{sub 3-x} films prepared by pulsed laser deposition are reported. Such studies are a preliminary to the combinatorial synthesis approach described in the first report.

  6. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, Viswanath R.

    2007-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm) (Fig. 1, left). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated (Fig. 1, right). A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  7. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, V. R.

    2006-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated. A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  8. Hydrothermal Synthesis of Nanostructured Manganese Oxide as Cathodic Catalyst in a Microbial Fuel Cell Fed with Leachate

    PubMed Central

    Haoran, Yuan; Lifang, Deng; Tao, Lu; Yong, Chen

    2014-01-01

    Much effort has been devoted to the synthesis of novel nanostructured MnO2 materials because of their unique properties and potential applications as cathode catalyst in Microbial fuel cell. Hybrid MnO2 nanostructures were fabricated by a simple hydrothermal method in this study. Their crystal structures, morphology, and electrochemical characters were carried out by FESEM, N2-adsorption-desorption, and CV, indicating that the hydrothermally synthesized MnO2 (HSM) was structured by nanorods of high aspect ratio and multivalve nanoflowers and more positive than the naturally synthesized MnO2 (NSM), accompanied by a noticeable increase in oxygen reduction peak current. When the HSM was employed as the cathode catalyst in air-cathode MFC which fed with leachate, a maximum power density of 119.07?mW/m2 was delivered, 64.68% higher than that with the NSM as cathode catalyst. Furthermore, the HSM via a 4-e pathway, but the NSM via a 2-e pathway in alkaline solution, and as 4-e pathway is a more efficient oxygen reduction reaction, the HSM was more positive than NSM. Our study provides useful information on facile preparation of cost-effective cathodic catalyst in air-cathode MFC for wastewater treatment. PMID:24723824

  9. Hydrothermal synthesis of nanostructured manganese oxide as cathodic catalyst in a microbial fuel cell fed with leachate.

    PubMed

    Haoran, Yuan; Lifang, Deng; Tao, Lu; Yong, Chen

    2014-01-01

    Much effort has been devoted to the synthesis of novel nanostructured MnO2 materials because of their unique properties and potential applications as cathode catalyst in Microbial fuel cell. Hybrid MnO2 nanostructures were fabricated by a simple hydrothermal method in this study. Their crystal structures, morphology, and electrochemical characters were carried out by FESEM, N2-adsorption-desorption, and CV, indicating that the hydrothermally synthesized MnO2 (HSM) was structured by nanorods of high aspect ratio and multivalve nanoflowers and more positive than the naturally synthesized MnO2 (NSM), accompanied by a noticeable increase in oxygen reduction peak current. When the HSM was employed as the cathode catalyst in air-cathode MFC which fed with leachate, a maximum power density of 119.07?mW/m(2) was delivered, 64.68% higher than that with the NSM as cathode catalyst. Furthermore, the HSM via a 4-e pathway, but the NSM via a 2-e pathway in alkaline solution, and as 4-e pathway is a more efficient oxygen reduction reaction, the HSM was more positive than NSM. Our study provides useful information on facile preparation of cost-effective cathodic catalyst in air-cathode MFC for wastewater treatment. PMID:24723824

  10. Stabilization mechanisms of aluminum-titanium bilayer cathodes in organic solar cells

    NASA Astrophysics Data System (ADS)

    Cao, Huanqi; Tanaka, Masaki; Ishikawa, Ken

    2013-09-01

    A major concern in organic solar cells today is to continue to improve their stability. Aluminum-titanium bilayer cathodes have been reported to prolong the shelf-lives of organic solar cells to be more than 3 months in air without encapsulation. However, the stabilization mechanism was unsolved, and further investigation into the mechanism was required. We probed the surface morphology of different cathodes with atomic force microscope and explored elemental depth profiles in different devices with time of flight-secondary ion mass spectrometry to analyze the mechanism, in addition to optimization of the cell structure. Based on the experimental observations, we attribute the improved shelf-lives to three functions of the bilayer cathodes, e.g., the elimination of large cracks, the suppression of interdiffusion, and the sustainable oxygen scavenging. These findings provide information useful for rationally designing efficient structures that stabilize organic solar cells.

  11. Experimental And Theoretical Studies On The Characteristics Of Low-Pressure Glow Discharge With Liquid Cathode

    NASA Astrophysics Data System (ADS)

    Shutov, D.; Ivanov, A.; Smirnov, S.; Rybkin v.

    2010-07-01

    The characteristics of low-pressure air glow discharge with liquid cathode (electrolytic cathode low-pressure discharge, ELCLPD) has been investigated. Distilled water was utilized as a cathode. The electric field strength, gas temperature as well as emission intensity of some bands of N2(C3?u?B3 ?g) were measured at pressure from 76 to 760 torr at fixed discharge current of 40 mA. Based upon these data, the reduced electric field strength, E/N, effective vibrational temperatures for N2(C3?u, X1Sg+) and rotational temperatures for N2(X1Sg+) were investigated. The electron energy distribution function (EEDF) and some electron parameters (average energy, electron density) were obtained on the base of numerical solution of the Boltzmann kinetic equation.

  12. Specific features of an electric discharge operating between an electrolytic anode and a metal cathode

    SciTech Connect

    Gaisin, A. F.; Sarimov, L. R. [Kazan State Technical University (Russian Federation)

    2011-06-15

    Results are presented from experimental studies of a high-current electric discharge operating between an St45 steel cathode and a service water anode in a wide range of air pressures. Peculiarities of discharge ignition and specific features of cathode and anode spots were revealed. The behavior of the current density on a service water anode was investigated for the first time. Comparison of the current densities j on the steel cathode and service water anode shows that, in the parameter range under study, Hehl's law is not satisfied on the water anode. The two-dimensional distribution of the potential inside and on the surface of the service water anode was measured.

  13. Analysis of cathode geometry to minimize cathode erosion in direct current microplasma jet

    NASA Astrophysics Data System (ADS)

    Causa, Federica; Ghezzi, Francesco; Dellasega, David; Caniello, Roberto; Grosso, Giovanni

    2012-12-01

    Microplasma jets are now widely used for deposition, etching, and materials processing. The present study focuses on the investigation of the influence of cathode geometry on deposition quality, for microplasma jet deposition systems in low vacuum. The interest here is understanding the influence of hydrogen on sputtering and/or evaporation of the electrodes. Samples obtained with two cathode geometries with tapered and rectangular cross-sections have been investigated experimentally by scanning electron microscopy and energy dispersion X-ray spectroscopy. Samples obtained with a tapered-geometry cathode present heavy contamination, demonstrating cathode erosion, while samples obtained with a rectangular-cross-section cathode are free from contamination. These experimental characteristics were explained by modelling results showing a larger radial component of the electric field at the cathode inner wall of the tapered cathode. As a result, ion acceleration is larger, explaining the observed cathode erosion in this case. Results from the present investigation also show that the ratio of radial to axial field components is larger for the rectangular geometry case, thus, qualitatively explaining the presence of micro-hollow cathode discharge over a wide range of currents observed in this case. In the light of the above findings, the rectangular cathode geometry is considered to be more effective to achieve cleaner deposition.

  14. Cathode for an electrochemical cell

    DOEpatents

    Bates, John B. (Oak Ridge, TN); Dudney, Nancy J. (Knoxville, TN); Gruzalski, Greg R. (Oak Ridge, TN); Luck, Christopher F. (Knoxville, TN)

    2001-01-01

    Described is a thin-film battery, especially a thin-film microbattery, and a method for making same having application as a backup or primary integrated power source for electronic devices. The battery includes a novel electrolyte which is electrochemically stable and does not react with the lithium anode and a novel vanadium oxide cathode. Configured as a microbattery, the battery can be fabricated directly onto a semiconductor chip, onto the semiconductor die or onto any portion of the chip carrier. The battery can be fabricated to any specified size or shape to meet the requirements of a particular application. The battery is fabricated of solid state materials and is capable of operation between -15.degree. C. and 150.degree. C.

  15. Sodium monolayers on thermionic cathodes

    NASA Astrophysics Data System (ADS)

    Almansttter, Jrgen; Eberhard, Bernd; Gnther, Klaus; Hartmann, Thomas

    2002-07-01

    Under certain conditions alkali vapours form dipole monolayers on metallic electrodes that can lower the work function of the bulk material. In this case, the power balance of the electrode, the electrode fall voltage and the electrode loss power can change considerably. To verify this effect a pyrometric technique was adapted and optimized for the diagnostics of tungsten electrodes in high pressure sodium discharges. Using an already verified model of thermally emitting cathodes the effect was observed in a Na DC discharge and the range of existence was investigated. An interpretation of the results is given using a Langmuir description of forming the Na monolayers and first-principles electronic structure calculations using a pseudopotential plane wave method to solve the Kohn-Sham equations of density-functional theory.

  16. Numerical and Physical Simulation of the Low-Velocity Air Flow in a Diffuser with a Circular Cavity in the Case of Suction of the Air from the Central Cylindrical Body Positioned in the Cavity

    NASA Astrophysics Data System (ADS)

    Isaev, S. A.; Guvernyuk, S. V.; Zubin, M. A.; Baranov, P. A.; Ermakov, A. M.

    2015-01-01

    Comparative analysis of the results of solution of the steady-state Reynolds equations closed with the use of the shear-stress transfer model for the air fl ow in a divergent channel with suction of the air from the surface of the cylindrical central body positioned in the circular vortex cavity built in the lower wall of the channel with the corresponding experimental data has been performed.

  17. AFM as an analysis tool for high-capacity sulfur cathodes for LiS batteries

    PubMed Central

    Srgel, Seniz; Costa, Rmi; Carl, Linus; Galm, Ines; Caas, Natalia; Pascucci, Brigitta; Friedrich, K Andreas

    2013-01-01

    Summary In this work, material-sensitive atomic force microscopy (AFM) techniques were used to analyse the cathodes of lithiumsulfur batteries. A comparison of their nanoscale electrical, electrochemical, and morphological properties was performed with samples prepared by either suspension-spraying or doctor-blade coating with different binders. Morphological studies of the cathodes before and after the electrochemical tests were performed by using AFM and scanning electron microscopy (SEM). The cathodes that contained polyvinylidene fluoride (PVDF) and were prepared by spray-coating exhibited a superior stability of the morphology and the electric network associated with the capacity and cycling stability of these batteries. A reduction of the conductive area determined by conductive AFM was found to correlate to the battery capacity loss for all cathodes. X-ray diffraction (XRD) measurements of Li2S exposed to ambient air showed that insulating Li2S hydrolyses to insulating LiOH. This validates the significance of electrical ex-situ AFM analysis after cycling. Conductive tapping mode AFM indicated the existence of large carbon-coated sulfur particles. Based on the analytical findings, the first results of an optimized cathode showed a much improved discharge capacity of 800 mAg(sulfur)?1 after 43 cycles. PMID:24205455

  18. Study on aluminate of cathode emission active substances

    Microsoft Academic Search

    Li Zhishun; Wang Yuchun

    2010-01-01

    Microwave tubes are used at the field of radar, electron counterwork and communication widely. The cathode is the heart of the microwave tube. The impregnated aluminate Ba-W cathode is used most widely. Along with the development of microwave technology, the high performance cathode is necessary with big current density, long life. The performance of cathode is decided by aluminate of

  19. Carbon fiber paper cathodes for lithium ion batteries

    Microsoft Academic Search

    Andrew K Kercher; Jim Kiggans; Nancy J Dudney

    2010-01-01

    A novel lithium ion battery cathode structure was produced which has the potential for excellent capacity retention and good thermal management. In these cathodes, the active cathode material (lithium iron phosphate) was carbon bonded to a thermally and electrically conductive carbon fiber paper (CFP) support. Electrochemical testing was performed on Swagelok cells consisting of CFP cathodes and lithium anodes. High

  20. Coated porous carbon cathodes for lithium ion batteries

    Microsoft Academic Search

    Andrew K Kercher; Nancy J Dudney; Jim Kiggans; James William Klett

    2008-01-01

    Coated porous carbon cathodes for automotive lithium batteries are being developed with the goal of overcoming the problems with capacity fade and poor thermal management in conventional polymer-bonded cathodes. The active cathode material (lithium iron phosphate nanoparticles) is carbon-bonded to the porous carbon support material. Cathodes have been developed with high specific energy and power and with good cycling behavior.

  1. The virtual cathode as a transient double sheath

    NASA Technical Reports Server (NTRS)

    Intrator, T.; Cho, M. H.; Wang, E. Y.; Hershkowitz, N.; Diebold, D.

    1988-01-01

    The two-dimensional plasma potential measurements are given of a space-charge dominated double sheath near a hot cathode. Laboratory data show that a virtual cathode is a self-consistent solution only for a transient cathode-plasma system. Slow charge exchange ions get trapped in the potential dip that forms the virtual cathode and eventually destroy it.

  2. Batteries: Overview of Battery Cathodes

    SciTech Connect

    Doeff, Marca M

    2010-07-12

    The very high theoretical capacity of lithium (3829 mAh/g) provided a compelling rationale from the 1970's onward for development of rechargeable batteries employing the elemental metal as an anode. The realization that some transition metal compounds undergo reductive lithium intercalation reactions reversibly allowed use of these materials as cathodes in these devices, most notably, TiS{sub 2}. Another intercalation compound, LiCoO{sub 2}, was described shortly thereafter but, because it was produced in the discharged state, was not considered to be of interest by battery companies at the time. Due to difficulties with the rechargeability of lithium and related safety concerns, however, alternative anodes were sought. The graphite intercalation compound (GIC) LiC{sub 6} was considered an attractive candidate but the high reactivity with commonly used electrolytic solutions containing organic solvents was recognized as a significant impediment to its use. The development of electrolytes that allowed the formation of a solid electrolyte interface (SEI) on surfaces of the carbon particles was a breakthrough that enabled commercialization of Li-ion batteries. In 1990, Sony announced the first commercial batteries based on a dual Li ion intercalation system. These devices are assembled in the discharged state, so that it is convenient to employ a prelithiated cathode such as LiCoO{sub 2} with the commonly used graphite anode. After charging, the batteries are ready to power devices. The practical realization of high energy density Li-ion batteries revolutionized the portable electronics industry, as evidenced by the widespread market penetration of mobile phones, laptop computers, digital music players, and other lightweight devices since the early 1990s. In 2009, worldwide sales of Li-ion batteries for these applications alone were US$ 7 billion. Furthermore, their performance characteristics (Figure 1) make them attractive for traction applications such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (EVs); a market predicted to be potentially ten times greater than that of consumer electronics. In fact, only Liion batteries can meet the requirements for PHEVs as set by the U.S. Advanced Battery Consortium (USABC), although they still fall slightly short of EV goals. In the case of Li-ion batteries, the trade-off between power and energy shown in Figure 1 is a function both of device design and the electrode materials that are used. Thus, a high power battery (e.g., one intended for an HEV) will not necessarily contain the same electrode materials as one designed for high energy (i.e., for an EV). As is shown in Figure 1, power translates into acceleration, and energy into range, or miles traveled, for vehicular uses. Furthermore, performance, cost, and abuse-tolerance requirements for traction batteries differ considerably from those for consumer electronics batteries. Vehicular applications are particularly sensitive to cost; currently, Li-ion batteries are priced at about $1000/kWh, whereas the USABC goal is $150/kWh. The three most expensive components of a Li-ion battery, no matter what the configuration, are the cathode, the separator, and the electrolyte. Reduction of cost has been one of the primary driving forces for the investigation of new cathode materials to replace expensive LiCoO{sub 2}, particularly for vehicular applications. Another extremely important factor is safety under abuse conditions such as overcharge. This is particularly relevant for the large battery packs intended for vehicular uses, which are designed with multiple cells wired in series arrays. Premature failure of one cell in a string may cause others to go into overcharge during passage of current. These considerations have led to the development of several different types of cathode materials, as will be covered in the next section. Because there is not yet one ideal material that can meet requirements for all applications, research into cathodes for Li-ion batteries is, as of this writ

  3. A analysis of the cathode coupled amplifier

    E-print Network

    Hetlinger, Forrest James

    1951-01-01

    AN ANALySIS 0 TH CATHODE COOFL D ~iPLIPIER A Thesis by FORREST JACKS RETLING-. . R Approved as to style and content by: Chairman of Committee 'Head of Department August, 1951 AN ANALYSIS OF THE CATHODE COUPLED. AMPLIFIER by FORHEST JAMES... Circuit Introduction and Review of the Literature The cathode-coupled amplifier c1rcuit is shown in Fi~re l. It can be seen that, if the circuit is fed with signal voltages esl and es& of opposite phase, 1t will behave much like the ordinary push...

  4. Cathode for molten carbonate fuel cell

    DOEpatents

    Kaun, Thomas D. (New Lenox, IL); Mrazek, Franklin C. (Hickory Hills, IL)

    1990-01-01

    A porous sintered cathode for a molten carbonate fuel cell and method of making same, the cathode including a skeletal structure of a first electronically conductive material slightly soluble in the electrolyte present in the molten carbonate fuel cell covered by fine particles of a second material of possibly lesser electronic conductivity insoluble in the electrolyte present in the molten carbonate fuel cell, the cathode having a porosity in the range of from about 60% to about 70% at steady-state cell operating conditions consisting of both macro-pores and micro-pores.

  5. Cells having cathodes containing polycarbon disulfide materials

    DOEpatents

    Okamoto, Y.; Skotheim, T.A.; Lee, H.S.

    1995-08-15

    The present invention relates to an electric current producing cell which contains an anode, a cathode having as a cathode-active material one or more carbon-sulfur compounds of the formula (CS{sub x}){sub n}, in which x takes values from 1.2 to 2.3 and n is greater or equal to 2, and where the redox process does not involve polymerization and de-polymerization by forming and breaking S--S bonds in the polymer backbone. The cell also contains an electrolyte which is chemically inert with respect to the anode and the cathode. 5 figs.

  6. High power microwave generation from coaxial virtual cathode oscillator using graphite and velvet cathodes

    NASA Astrophysics Data System (ADS)

    Menon, Rakhee; Roy, Amitava; Singh, S. K.; Mitra, S.; Sharma, Vishnu; Kumar, Senthil; Sharma, Archana; Nagesh, K. V.; Mittal, K. C.; Chakravarthy, D. P.

    2010-05-01

    High power microwave (HPM) generation studies were carried out in KALI-5000 pulse power system. The intense relativistic electron beam was utilized to generate HPMs using a coaxial virtual cathode oscillator. The typical electron beam parameters were 350 kV, 25 kA, and 100 ns, with a few hundreds of ampere per centimeter square current density. Microwaves were generated with graphite and polymer velvet cathode at various diode voltage, current, and accelerating gaps. A horn antenna setup with diode detector and attenuators was used to measure the microwave power. It was observed that the microwave power increases with the diode voltage and current and reduces with the accelerating gap. It was found that both the peak power and width of the microwave pulse is larger for the velvet cathode compared to the graphite cathode. In a coaxial vircator, velvet cathode is superior to the graphite cathode due to its shorter turn on time and better electron beam uniformity.

  7. Low temperature aluminum reduction cell using hollow cathode

    DOEpatents

    Brown, Craig W. (Seattle, WA); Frizzle, Patrick B. (Seattle, WA)

    2002-08-20

    A method of producing aluminum in an electrolytic cell containing alumina dissolved in an electrolyte. A plurality of non-consumable anodes are disposed substantially vertically in the electrolyte along with a plurality of monolithic hollow cathodes. Each cathode has a top and bottom and the cathodes are disposed vertically in the electrolyte and the anodes and the cathodes are arranged in alternating relationship. Each of the cathodes is comprised of a first side facing a first opposing anode and a second side facing a second opposing anode. The first and second sides are joined by ends to form a reservoir in the hollow cathode for collecting aluminum therein deposited at the cathode.

  8. A microbial fuel cell with improved cathode reaction as a low biochemical oxygen demand sensor

    Microsoft Academic Search

    Kui Hyun Kang; Jae Kyung Jang; Hyunsoo Moon; Byung Hong Kim

    2003-01-01

    Mediator-less microbial fuel cells (MFC) enriched with oligotrophic microbes were optimized through enhance- ment of cathode reaction and lowering O2 diffusion into the anode compartment as a low BOD sensor. The optimization of the MFC has greatly improved the maximum current and coulomb yield. The oligotroph-type MFC could be used as a low BOD sensor with high operational stability, good

  9. Effective Secondary Electron Yield of a Cathode for Plasma Display Panel

    Microsoft Academic Search

    Yukio Murakami; Hideomi Matsuzaki; Hiroshi Murakami; Nobuaki Ikuta

    2001-01-01

    In order to improve the discharge characteristics of a plasma display panel (PDP), the availability gamma^\\\\prime\\/gamma of the secondary electrons from the PDP cathodes is investigated, which is determined by the back-diffusion effect in the discharge gas. We carried out a Monte-Carlo simulation (MCS) under conditions which were varied: the gas composition, the initial energy distribution of emitted electrons due

  10. 24-HOUR DIFFUSIVE SAMPLING OF 1,3-BUTADIENE IN AIR ONTO CARBOPACK X SOLID ADSORBENT FOLLOWED BY THERMAL DESORPTION/GC/MS ANALYSIS - FEASIBILITY STUDY

    EPA Science Inventory

    Diffusive sampling of 1,3-butadiene for 24 hr onto the graphitic adsorbent Carbopack X packed in a stainless steel tube badge (6.3 mm o.d., 5 mm i.d., and 90 mm in length) with analysis by thermal desorption/gas chromatography (GC)/mass spectrometry (MS) has been evaluated in con...

  11. DESCRIPTION OF ATMOSPHERIC TRANSPORT PROCESSES IN EULERIAN AIR QUALITY MODELS

    EPA Science Inventory

    Key differences among many types of air quality models are the way atmospheric advection and turbulent diffusion processes are treated. Gaussian models use analytical solutions of the advection-diffusion equations. Lagrangian models use a hypothetical air parcel concept effecti...

  12. Effect of cathode surface area and separately stabilized cathodes on high power glow discharges for CO2 laser excitation

    Microsoft Academic Search

    D. R. Evans; J. E. Harry

    1988-01-01

    Results are presented which indicate the importance of the cathode surface area and the advantage of using separately stabilized cathodes for the excitation of high power CO2 lasers. The results indicate that operation of a glow discharge with multiple cathodes of adequate surface area enables operation in the abnormal glow region at higher currents than with a single cathode of

  13. Effect of cathode surface area and separately stabilized cathodes on high power glow discharges for CO2 laser excitation

    Microsoft Academic Search

    D. R. Evans; J. E. Harry

    1988-01-01

    Results are presented which indicate the importance of the cathode surface area and the advantage of using separately stabilized cathodes for the excitation of high power CO lasers. The results indicate that operation of a glow discharge with multiple cathodes of adequate surface area enables operation in the abnormal glow region at higher currents than with a single cathode of

  14. High current density cathode for electrorefining in molten electrolyte

    DOEpatents

    Li, Shelly X.

    2010-06-29

    A high current density cathode for electrorefining in a molten electrolyte for the continuous production and collection of loose dendritic or powdery deposits. The high current density cathode eliminates the requirement for mechanical scraping and electrochemical stripping of the deposits from the cathode in an anode/cathode module. The high current density cathode comprises a perforated electrical insulated material coating such that the current density is up to 3 A/cm.sup.2.

  15. Li/SOCl2 cell performance with modified cathodes

    NASA Astrophysics Data System (ADS)

    Doddapaneni, Narayan; Hoff, Gerald F.

    The performance of Li/SOCl2 cells with ceramic doped cathodes was evaluated during discharge and external short circuit conditions. Modified cathodes, doped with up to 30 percent by weight of ceramic fibers, produced identical specific cathode capacities. The inclusion of modified cathodes in Li/SOCl2 cells reduces the short circuit peak currents by as much as 35 percent compared to cells with undoped cathodes.

  16. Brewery wastewater treatment using air-cathode microbial fuel cells

    Microsoft Academic Search

    Yujie Feng; Xin Wang; Bruce E. Logan; He Lee

    2008-01-01

    Effective wastewater treatment using microbial fuel cells (MFCs) will require a better understanding of how operational parameters\\u000a and solution chemistry affect treatment efficiency, but few studies have examined power generation using actual wastewaters.\\u000a The efficiency of wastewater treatment of a beer brewery wastewater was examined here in terms of maximum power densities,\\u000a Coulombic efficiencies (CEs), and chemical oxygen demand (COD)

  17. Interfacial phenomena on selected cathode materials

    SciTech Connect

    Kostecki, Robert; Matsuo, Yoshiaki; McLarnon, Frank

    2001-06-22

    We have carried out a series of surface studies of selected cathode materials. Instrumental techniques such as Raman microscopy, surface enhanced Raman spectroscopy (SERS), and atomic force microscopy were used to investigate the cathode surfaces. The goal of this study was to identify detrimental processes which occur at the electrode/electrolyte interface and can lead to electrode degradation and failure during cycling and/or storage at elevated temperatures.

  18. Noble gas mixture hollow cathode lasers

    Microsoft Academic Search

    M. Jnossy; L. Csillag; Z. Donk; K. Rzsa

    1993-01-01

    A review of noble gas mixture ion lasers operating cw in hollow cathode discharges is given. The basic properties of hollow\\u000a cathode discharges and the main principles of tube construction are described. For the He?Kr, He?Ar and He?Ne?Xe systems laser\\u000a transitions, excitation mechanisms, operation of the lasers and questions of lasers for practical use are discussed. The single\\u000a frequency operation

  19. Advances in cold cathode physics and technology

    SciTech Connect

    Nation, J.A. [Cornell Univ., Ithaca, NY (United States)] [Cornell Univ., Ithaca, NY (United States); Schaechter, L. [Technion, Haifa (Israel). Electrical Engineering Dept.] [Technion, Haifa (Israel). Electrical Engineering Dept.; Mako, F.M.; Len, L.K.; Peter, W. [FM Technologies, Inc., Fairfax, VA (United States)] [FM Technologies, Inc., Fairfax, VA (United States); Tang, C.M. [Creatv MicroTech, Inc., Potomac, MD (United States)] [Creatv MicroTech, Inc., Potomac, MD (United States); Srinivasan-Rao, T. [Brookhaven National Lab., Upton, NY (United States)] [Brookhaven National Lab., Upton, NY (United States)

    1999-05-01

    The authors review recent progress in the physics and technology of cold cathode electron emitters. The characteristics of emission from field emitter arrays, photocathodes, and ferroelectrics are presented, together with a summary of the understanding of the physics involved. The paper concludes with a description of L-band micropulse gun, based on secondary emission in an RF cavity. Emphasis is placed on cathode development for electron guns to drive microwave tubes and RF accelerators.

  20. A calcium aluminate electride hollow cathode

    NASA Astrophysics Data System (ADS)

    Rand, Lauren Paula

    The development and testing of a hollow cathode utilizing C12A7 (12CaO?Al 2O3) electride as an insert are presented. Hollow cathodes are an integral part of electric propulsion thrusters on satellites and ground-based plasma sources for materials engineering. The power efficiency and durability of these components are critical, especially when used in flight applications. A low work function material internal to the cathode supplies the electrons needed to create the cathode plasma. Current state-of-the- art insert materials are either susceptible to poisoning or need to be heated to temperatures that result in a shortened cathode lifetime. C12A7 electride is a ceramic in which electrons contained in sub-nanometer sized lattice cages act as a conductive medium. Due to its unique atomic structure and large size, C12A7 electride has a predicted work function much lower than traditional insert materials. A novel, one-step fabrication process was developed that produced an amorphous form of C12A7 electride that had a measured work function 0.76 eV. A single electride hollow cathode was operated on xenon for over 60 hours over a two-month period that included 20 restarts and 11 chamber vent pump-down sequences with no sign of degradation, and on iodine for over 20 hours with no apparent reactivity issues. The operations of cathodes with three different orifice sizes were compared, and their effects on the interior cathode plasma modeled in a zero- dimensional phenomenological model.

  1. Development of plasma cathode electron guns

    NASA Astrophysics Data System (ADS)

    Oks, Efim M.; Schanin, Peter M.

    1999-05-01

    The status of experimental research and ongoing development of plasma cathode electron guns in recent years is reviewed, including some novel upgrades and applications to various technological fields. The attractiveness of this kind of e-gun is due to its capability of creating high current, broad or focused beams, both in pulsed and steady-state modes of operation. An important characteristic of the plasma cathode electron gun is the absence of a thermionic cathode, a feature which leads to long lifetime and reliable operation even in the presence of aggressive background gas media and at fore-vacuum gas pressure ranges such as achieved by mechanical pumps. Depending on the required beam parameters, different kinds of plasma discharge systems can be used in plasma cathode electron guns, such as vacuum arcs, constricted gaseous arcs, hollow cathode glows, and two kinds of discharges in crossed EB fields: Penning and magnetron. At the present time, plasma cathode electron guns provide beams with transverse dimension from fractional millimeter up to about one meter, beam current from microamperes to kiloamperes, beam current density up to about 100 A/cm2, pulse duration from nanoseconds to dc, and electron energy from several keV to hundreds of keV. Applications include electron beam melting and welding, surface treatment, plasma chemistry, radiation technologies, laser pumping, microwave generation, and more.

  2. Model for designing planar magnetron cathodes

    SciTech Connect

    Garcia, M.

    1997-05-30

    Planar magnetron cathodes have arching magnetic field lines which concentrate plasma density to enhance ion bombardment and sputtering. Typical parameters are: helium at 1 to 300 milli-torr, 200 to 2000 gauss at the cathode, 200 to 800 volts, and plasma density decreasing by up to ten times within 2 to 10 cm from the cathode. A 2D, quasineutral, fluid model yields formulas for the plasma density: n(x,y), current densities: j(x,y), j{sub e}(x,y), j{sub +}(x,y), the electric field: E{sub y}(y), and the voltage between the cathode surface and a distant plasma. An ion sheath develops between the cathode and the quasineutral flow. The thickness of this sheath depends on processes in the quasineutral flow. Experiments shows that T{sub e} (3 {yields} 8 eV) adjusts to ensure that {alpha}{sub 0}{tau} {approx} 2.5 in helium, for ionization rate {alpha}{sub 0} (10{sup 4} {yields} 10{sup 5} s{sup -1}), and electron transit time to the unmagnetized plasma {tau} (10 {yields} 100 {micro}s). Helium glow discharge cathode fall {alpha}{sub 0}{tau} is about 2.5, though this occurs at much higher voltage.

  3. Thermal-wave resonant-cavity measurements of the thermal diffusivity of air: A comparison between cavity-length and modulation-frequency scans

    Microsoft Academic Search

    J. Shen; A. Mandelis; B. D. Aloysius

    1996-01-01

    The application of a thermal-wave resonant cavity to thermal-diffusivity measurements of gases has been investigated. The cavity was constructed using a thin aluminum foil wall as the intensitv-modulated laser-beam oscillator source opposite a pyroclectric polyvilidene fluoride wall acting as a signal transducer. Theoretically, cavity-length and modulation-frequency scans both produce resonance-like extrema in lock-in in-phase and quadrature curses. These extrema can

  4. Diffusive exchange of polycyclic aromatic hydrocarbons across the air-water interface of the Patapsco River, an urbanized subestuary of the Chesapeake Bay

    Microsoft Academic Search

    Holly A. Bamford; John H. Offenberg; Randolph K. Larsen; Fung-Chi Ko; Joel E. Baker

    1999-01-01

    Air-water exchange fluxes of 13 polycyclic aromatic hydrocarbons (PAHs) were determined along a transect in the Patapsco River from the Inner Harbor of Baltimore, MD, to the mainstem of the northern Chesapeake Bay. Sampling took place at six sites during three sampling intensives (June 1996, February 1997, and July 1997) and at one site every ninth day between March 1997

  5. Hydrogen production through steam electrolysis: Control strategies for a cathode-supported intermediate temperature solid oxide electrolysis cell

    Microsoft Academic Search

    J. Udagawa; P. Aguiar; N. P. Brandon

    2008-01-01

    Hydrogen production via steam electrolysis may involve less electrical energy consumption than conventional low temperature water electrolysis, reflecting the favourable thermodynamics and kinetics at elevated temperatures. The present paper reports on the development of a one-dimensional dynamic model of a cathode-supported planar intermediate temperature solid oxide electrolysis cell (SOEC) stack with air flow introduced through the cells. The model, which

  6. Proton exchange membrane fuel cell cathode contamination - Acetylene

    NASA Astrophysics Data System (ADS)

    Zhai, Y.; St-Pierre, Jean

    2015-04-01

    Acetylene adsorption on PEMFC electrodes and contamination in single cells are investigated with 300 ppm acetylene at a cathode held at 80 C. The results of adsorption experiments suggest that acetylene adsorbs readily on electrodes and is reduced to ethylene and ethane under an open circuit potential of H2/N2, as the adsorbates can be electro-oxidized at high potentials. The cell voltage response shows that 300 ppm acetylene results in a cell performance loss of approximately 88%. The voltage degradation curve is divided into two stages by an inflection point, which suggests that potential-dependent processes are involved in acetylene poisoning. These potential-dependent processes may include acetylene oxidation and reduction as well as accumulation of intermediates on the electrode surface. Electrochemical impedance spectroscopy analysis suggests that acetylene affects the oxygen reduction reaction and may also affect mass transport processes. Acetylene also may be reduced in the steady poisoning state of the operating cell. After neat air operation, the cyclic voltammetry results imply that the cathode catalyst surface is almost completely restored, with no contaminant residues remaining in the MEA. Linear scanning voltammetry measurements show no change in hydrogen crossover caused by contamination, and polarization curves confirm complete recovery of cell performance.

  7. Diffusion /Osmosis

    NSDL National Science Digital Library

    Jensen

    2007-11-26

    This project is use to review the concepts of diffusion and osmosis 1. Watch the tutorials on diffusion and osmosis. Take the online quiz at the end of each one. Diffusion Animation Osmosis Animation 2. Do the interactive lab on diffusion. Stop when you get to the calculating water potential section. Diffusion/Osmosis Interactive Demo 3. Play the Quia review games. Quia Games- matching/concetration Quia Jeopardy 4. Check out the Elodea leaf cells. Be able to ...

  8. Self-organization in cathode boundary layer discharges

    NASA Astrophysics Data System (ADS)

    Takano, Nobuhiko

    Cathode boundary layer (CBL) discharge, which has been developed as a UV light source, operates in a direct current between a planar cathode and a ring-shape anode that are separated by a dielectric with an opening of the same diameter as the anode. The nonthermal CBL discharges operate in a medium pressure range down to 30 Torr, emitting excimer radiation when operated with noble gases. The radiant excimer emittance at 172 nm in xenon reaches 1.7 W/cm2, and a maximum excimer efficiency of 6% has been obtained. The high excimer radiant emittance, in addition to low cost and simple geometry compared to other UV sources, makes CBL discharges an excellent choice for deep UV lamps and a candidate for integrated flat UV panels (Moselhy et al. 2004). It has been found that CBL discharges spontaneously give rise to regularly arranged filaments, i.e., self-organization, at a low current, e.g., less than 0.2 mA at 75 Torr (Schoenbach et al. 2004). In this thesis, the self-organization of direct current xenon discharges in the CBL configuration and parallel-plate geometry have been studied for a pressure range from 30 to 140 Torr and currents from 20 muA to 1 mA. Comprehensive examinations have been performed to investigate the behavior of those filaments by the use of optical, electrical, and spectral measurements. Side-on and end-on observations of the discharges have provided information on axial structure and distance of the filaments from the cathode fall. The electrical measurement has recorded a discrete I-V characteristic associated with the change of the numbers of the filaments. The spectral measurement provides scaling information on the relative population of high-lying states (1s 4, 1s5, and 2p6) of excited xenon atoms. Moreover, temperature measurement has revealed that the thermal electron emission from the cathode surface is negligible for the formation of filaments. The reactor geometry with parallel-plate electrodes analogously gives self-organization. The gas species, the cathode material, and the reactor geometry are varied to facilitate the understanding of the CBL xenon discharges and the self-organization. When krypton is used instead of xenon, rather homogeneous plasma far from organized pattern formation is observed with decreasing current. Of the tested aluminum, copper, and tungsten cathodes, the aluminum cathode achieved higher excimer intensity at 250 Torr than that of the molybdenum cathode by a factor of two. The diameter of the plasma reactor was reduced to 300 mum, and it gave rise to a single filament, illuminating with an enhanced excimer power density of 500 mW/cm2 at 62 Torr. Three mechanisms of these self-organizations are given and discussed in this thesis. The first mechanism explains that the axial electric field can initiate instability. This instability is caused by N-shaped negative differential conductivity (NNDC) in the vicinity of negative glow, which is attributed to electron-electron collisions. Positive feedback of the current density and the electric field due to the NNDC causes fluctuation to develop. Another positive feedback effect of the gas temperature is that the first Townsend coefficient can become dominant as, the current density increases. The filaments are assumed to undergo Coulomb force from the positively charged cathode fall channels and positive space charges on the surface of the surrounding dielectric spacer. The calculations, based on these assumptions on the Coulombic interactions, showed good agreement with experimental data. The second mechanism for the pattern formation is presented as to the development of Turing instability. The discussion is based on the idea that the regular arrangement of filaments is merely a result of general phenomena such as diffusion, ionization, or drift. A reaction-diffusion process with respect to the variation of local current density j and voltage v is the physical effect in the discharge. The numerical calculation was performed and obtained was a 2-D patterned structure exhibiting resemblance to the observed pattern. The tran

  9. Development of Ni1-xCoxO as the cathode/interconnect contact for solid oxide fuel cells

    SciTech Connect

    Lu, Zigui; Xia, Guanguang; Templeton, Joshua D.; Li, Xiaohong S.; Nie, Zimin; Yang, Zhenguo; Stevenson, Jeffry W.

    2011-06-01

    A new type of material, Ni1-xCoxO, was developed for solid oxide fuel cell (SOFC) cathode/interconnect contact applications. The phase structure, coefficient of thermal expansion, sintering behavior, electrical property, and mechanical bonding strength of these materials were evaluated against the requirements of the SOFC cathode/interconnect contact. A dense cathode/interconnect contact layer was developed through reaction sintering from Ni and Co metal powders. An area specific resistance (ASR) as low as 5.5 mohm.cm2 was observed after 1000 h exposure in air at 800 C for the LSM/Ni0.33Co0.67O/AISI441 assembly. Average mechanical strengths of 6.8 and 5.0 MPa were obtained for the cathode/contact/cathode and interconnect/contact/interconnect structures, respectively. The significantly low ASR was probably due to the dense structure and therefore improved electrical conductivity of the Ni0.33Co0.67O contact and the good bonding of the interfaces between the contact and the cathode, and between the contact and the interconnect.

  10. Efficient multilayer electrophosphorescence white polymer light-emitting diodes with aluminum cathodes

    Microsoft Academic Search

    Tengling Ye; Minrong Zhu; Jiangshan Chen; Dongge Ma; Chuluo Yang; Wenfa Xie; Shiyong Liu

    2011-01-01

    By simply doping Li2CO3 in an alcohol soluble neutral conjugated polymer poly[9,9-bis(6?-diethoxylphosphorylhexyl)fluorene] (PF-EP), we demonstrate highly efficient multilayer electrophosphorescence white polymer light-emitting diodes with air-stable Al cathode. From the mechanism studies, we find that the phosphate groups can make Li ions movable in the PF-EP film, resulting in great improvement in the electron injection and transport ability of PF-EP. The

  11. Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells: III. Role of volatile boron species on LSM/YSZ and LSCF

    SciTech Connect

    Zhou, Xiao Dong; Templeton, Jared W.; Zhu, Zihua; Chou, Y. S.; Maupin, Gary D.; Lu, Zigui; Brow, R. K.; Stevenson, Jeffry W.

    2010-09-02

    Boron oxide is a key component to tailor the softening temperature and viscosity of the sealing glass for solid oxide fuel cells. The primary concern regarding the use of boron containing sealing glasses is the volatility of boron species, which possibly results in cathode degradation. In this paper, we report the role of volatile boron species on the electrochemical performance of LSM/YSZ and LSCF cathodes at various SOFC operation temperatures. The transport rate of boron, ~ 3.2410-12 g/cm2sec was measured at 750C with air saturated with 2.8% moisture. A reduction in power density was observed in cells with LSM/YSZ cathodes after introduction of the boron source to the cathode air stream. Partial recovery of the power density was observed after the boron source was removed. Results from post-test secondary ion mass spectroscopy (SIMS) analysis the partial recovery in power density correlated with partil removal of the deposited boron by the clean air stream. The presence of boron was also observed in LSCF cathodes by SIMS analysis, however the effect of boron on the electrochemical performance of LSCF cathode was negligible. Coverage of triple phase boundaries in LSM/YSZ was postulated as the cause for the observed reduction in electrochemical performance.

  12. CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting, Devon Island, Canada

    Microsoft Academic Search

    Ian D. Clark; Lori Henderson; Jrme Chappellaz; David Fisher; Roy Koerner; Douglas E. J. Worthy; Tom Kotzer; Ann-Lise Norman; Jean-Marc Barnola

    2007-01-01

    Firn air and ice have been sampled and analyzed for trace gases (CO2, N2O, CH4, and CO) and isotopes (14C, 13C, and 18O of CO2; 3H of ice) at 3 m intervals from the surface to the depth of closure at 60 m on the Devon Island Ice Cap, a low-elevation permanent glacier in the Canadian Arctic Islands, to investigate

  13. Multiple cathodic reaction mechanisms in seawater cathodic biofilms operating in sediment microbial fuel cells.

    PubMed

    Babauta, Jerome T; Hsu, Lewis; Atci, Erhan; Kagan, Jeff; Chadwick, Bart; Beyenal, Haluk

    2014-10-01

    In this study, multiple reaction mechanisms in cathodes of sediment microbial fuel cells (SMFCs) were characterized by using cyclic voltammetry and microelectrode measurements of dissolved oxygen and pH. The cathodes were acclimated in SMFCs with sediment and seawater from San Diego Bay. Two limiting current regions were observed with onset potentials of approximately +400 mVAg/AgCl for limiting current I and -120 mVAg/AgCl for limiting current II. The appearance of two catalytic waves suggests that multiple cathodic reaction mechanisms influence cathodic performance. Microscale oxygen concentration measurements showed a zero surface concentration at the electrode surface for limiting current II but not for limiting current I, which allowed us to distinguish limiting current II as the conventional oxygen reduction reaction and limiting current I as a currently unidentified cathodic reaction mechanism. Microscale pH measurements further confirmed these results. PMID:25154833

  14. Micro-engineered cathode interface studies

    SciTech Connect

    Doshi, R.; Kueper, T.; Nagy, Z.; Krumpelt, M.

    1997-08-01

    The aim of this work is to increase the performance of the cathode in solid oxide fuel cells (SOFCs) operating at 1,000 C by decreasing the polarization resistance from 0.2 {Omega}-cm{sup 2} at 300 mA/cm{sup 2}. Decreased polarization resistance will allow operation at higher current densities. This work is in support of the Westinghouse tubular SOFC technology using YSZ electrolyte and strontium doped lanthanum manganite (LSM) cathode. As a result of work performed last year at Argonne National Laboratory and information derived from the literature, the limitations at the cathode/electrolyte interface can be classified into two main areas. First, the ionic conductivity of the LSM cathode material is low which limits the reaction zone to an area very close to the interface, while the rest of the cathode thickness acts essentially as current collector with channels for gas access. Second, the electronic conductivity in YSZ is very low which limits the reaction zone to areas that are the boundaries between LSM and YSZ rather than the YSZ surface away from LSM at the interface. Possible solutions to this problem being pursued are: (1) introducing an ionic conducting YSZ phase in LSM to form a porous two-phase mixture of LSM and YSZ; (2) applying a thin interlayer between the electrolyte and the cathode where the interlayer has high ionic and electronic conductivity and high catalytic activity for reduction of O{sub 2}; (3) increasing the ionic conductivity in the LSM by suitable doping; and (4) increasing the electronic conductivity in the electrolyte by doping or by depositing an appropriate mixed conducting layer on the YSZ before applying the cathode.

  15. Ring cusp/hollow cathode discharge chamber performance studies. [ion propulsion

    NASA Technical Reports Server (NTRS)

    Vaughn, J. A.; Wilbur, Paul J.

    1988-01-01

    An experimental study was performed to determine the effects of hollow cathode position, anode position, and ring cusp magnetic field configuration and strength on discharge chamber performance. The results are presented in terms of comparative plasma ion energy cost, extracted ion fraction, and beam profile data. Such comparisons are used to demonstrate whether changes in performance are caused by changes in the loss rate of primary electrons to the anode or the loss rate of ions to discharge chamber walls or cathode and anode surfaces. Results show: (1) the rate of primary electron loss to the anode decreases as the anode is moved downstream of the ring cusp toward the screen grid; (2) the loss rate of ions to hollow cathode surfaces are excessive if the cathode is located upstream of a point of peak magnetic flux density at the discharge chamber centerline; and (3) the fraction of the ions produced that are lost to discharge chamber walls and ring magnet surfaces is reduced by positioning of the magnet rings so the plasma density is uniform over the grid surface, and adjusting their strength to a level where it is sufficient to prevent excessive ion losses by Bohm diffusion.

  16. Atmospheric air diffuse array-needles dielectric barrier discharge excited by positive, negative, and bipolar nanosecond pulses in large electrode gap

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Yang, De-zheng; Wang, Wen-chun; Liu, Zhi-jie; Wang, Sen; Jiang, Peng-chao; Zhang, Shuai

    2014-09-01

    In this paper, positive, negative, and bipolar nanosecond pulses are employed to generate stable and diffuse discharge plasma using array needles-plate electrode configuration at atmospheric pressure. A comparison study of discharge images, electrical characteristics, optical emission spectra, and plasma vibrational temperature and rotational temperatures in three pulsed polarity discharges is carried on under different discharge conditions. It is found that bipolar pulse is beneficial to the excitation of diffuse dielectric barrier discharge, which can generate a room temperature plasma with more homogeneous and higher discharge intensity compared with unipolar discharges. Under the condition of 6 mm electrode gap distance, 26 kV pulse peak voltage, and 150 Hz pulse repetition rate, the emission intensity of N2 (C3?u ? B3?g) of the bipolar pulsed discharge is 4 times higher than the unipolar discharge (both positive and negative), while the plasma gas temperature is kept at 300 K, which is about 10-20 K lower than the unipolar discharge plasma.

  17. Composite Cathode for High-Power Density Solid Oxide Fuel Cells

    SciTech Connect

    Ilwon Kim; Scott Barnett; Yi Jiang; Manoj Pillai; Nikkia McDonald; Dan Gostovic; Zhongryang Zhan; Jiang Liu

    2004-01-31

    Reduction of solid oxide fuel cell (SOFC) operating temperature will play a key role in reducing the stack cost by allowing the use of low-cost metallic interconnects and new approaches to sealing, while making applications such as transportation more feasible. Reported results for anode-supported SOFCs show that cathode polarization resistance is the primary barrier to achieving high power densities at operating temperatures of 700 C and lower. This project aims to identify and develop composite cathodes that could reduce SOFC operating temperatures below 700 C. This effort focuses on study and use of (La,Sr)(Co,Fe)O{sub 3} (LSCF) based composite cathodes, which have arguably the best potential to substantially improve on the currently-used, (La,Sr)MnO{sub 3}-Yttria-stabilized Zirconia. During this Phase I, it was successfully demonstrated that high performances can be achieved with LSCF/Gadolinium-Doped Ceria composite cathodes on Ni-based anode supported cells operating at 700 C or lower. We studied electrochemical reactions at LSCF/Yttria-stabilized Zirconia (YSZ) interfaces, and observed chemical reactions between LSCF and YSZ. By using ceria electrolytes or YSZ electrolytes with ceria diffusion barrier layers, the chemical reactions between LSCF and electrolytes were prevented under cathode firing conditions necessary for the optimal adhesion of the cathodes. The protection provided by ceria layer is expected to be adequate for stable long-term cathode performances, but more testing is needed to verify this. Using ceria-based barrier layers, high performance Ni-YSZ anode supported cells have been demonstrated with maximum power densities of 0.8W/cm2 at 700 C and 1.6W/cm{sup 2} at 800 C. Ni-SDC anode supported cells with SDC electrolytes yielded >1W/cm{sup 2} at 600 C. We speculate that the power output of Ni-YSZ anode supported cell at 700 C and lower, was limited by the quality of the Ceria and Ceria YSZ interface. Improvements in the low-temperature performances are expected based on further development of barrier layer fabrication processes and optimization of cathode microstructure.

  18. Spindt cold cathode electron gun development program

    NASA Technical Reports Server (NTRS)

    Spindt, C. A.

    1983-01-01

    A thin film field emission cathode array and an electron gun based on this emitter array are summarized. Fabricating state of the art cathodes for testing at NASA and NRL, advancing the fabrication technology, developing wedge shaped emitters, and performing emission tests are covered. An anistropic dry etching process (reactive ion beam etching) developed that leads to increasing the packing density of the emitter tips to about 5 x 10 to the 6th power/square cm. Tests with small arrays of emitter tips having about 10 tips has demonstrated current densities of over 100 A/sq cm. Several times using cathodes having a packing density of 1.25 x 10 to the 6th power tips/sq cm. Indications are that the higher packing density achievable with the dry etch process may extend this capability to the 500 A/sq cm range and beyond. The wedge emitter geometry was developed and shown to produce emission. This geometry can (in principle) extend the current density capability of the cathodes beyond the 500 A/sq cm level. An emission microscope was built and tested for use with the cathodes.

  19. RHETT/EPDM Flight Hollow Cathode

    NASA Technical Reports Server (NTRS)

    Manzella, David; Patterson, Michael; Pastel, Michael

    1997-01-01

    Under the sponsorship of the BMDO Russian Hall Electric Thruster Technology program two xenon hollow cathodes, a flight unit and a flight spare were fabricated, acceptance tested and delivered to the Naval Research Laboratory for use on the Electric Propulsion Demonstration Module. These hollow cathodes, based on the International Space Station plasma contactor design, were fabricated at the NASA Lewis Research Center for use with a D-55 anode layer thruster in the first on-orbit operational application of this technology. The 2.2 Ampere nominal emission current of this device was obtained with a xenon flow rate of 0.6 mg/s. Ignition of the cathode discharge was accomplished through preheating the active electron emitter with a resistive heating element before application of a 650 volt ignition pulse between the emitter and an external starting electrode. The successful acceptance testing of the Electric Propulsion Demonstration Module utilizing these cathodes demonstrated the suitability of cathodes based on barium impregnated inserts in an enclosed keeper configuration for use with Hall thruster propulsion systems.

  20. Undervoltage breakdown between parallel plates in air

    Microsoft Academic Search

    N. Sato; S. Sakamoto

    1979-01-01

    Transient discharges in air that are started at undervoltages by supplying a large number of initial electrons at the cathode of parallel plates are investigated at gas pressures of 20 and 200 Torr. The discharge current has been measured, and factors affecting the development of the current are investigated by comparing the experimental current with a computer-simulated current. The spatiotemporal

  1. Ti Diffusion in Pyroxene

    NASA Astrophysics Data System (ADS)

    Cherniak, D.; Liang, Y.

    2008-12-01

    Diffusion of titanium has been characterized in natural enstatite and diopside under buffered conditions and in air. The sources of diffusant for the enstatite experiments were mixtures of Mg, Si and Ti oxide powders, which were combined and heated at 1300C overnight, and then thoroughly mixed with synthesized enstatite powder and heated for an additional day at 1300C. Sources for diopside experiments were prepared similarly, using Ca, Mg, Si, and Ti oxide powders combined with synthesized diopside powder, with heating of source materials at 1200C. Buffered experiments were prepared by enclosing source material and pyroxene (polished and pre-annealed under conditions comparable to those to be experienced in the experiment) in AgPd or platinum capsules, placing the metal capsule in a silica glass capsule with a solid buffer (to buffer at NNO or IW) and sealing the assembly under vacuum. Some experiments on enstatite were run in air; sample and source were placed in Pt capsules and crimped shut. Prepared capsules were then annealed in 1 atm furnaces for times ranging from 8 hours to a few months, at temperatures from 950 to 1200C. The Ti distributions in the pyroxene were profiled with Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for Ti diffusion in a natural enstatite, for diffusion normal to the (210) cleavage face (950 - 1150C, experiments run in air): DTi = 1.910-10 exp(-300 44 kJ mol-1/RT) m2 sec-1. Diffusion under NNO and IW-buffered conditions is similar to that for experiments run in air, suggesting little dependence of Ti diffusion on oxygen fugacity. There is also little evidence of anisotropy, as diffusion normal to (001) does not differ significantly from diffusion for the other orientation. Preliminary findings for Ti diffusion in diopside suggest diffusivities similar to those for enstatite. Ti diffusivities in enstatite are similar to those of the trivalent REEs (Cherniak and Liang, 2007), but more than two orders of magnitude slower than those of Fe-Mg (ter Heege et al., 2006) and Cr (Ganguly et al., 2007). These respective variations may reflect the interplay of cation size and charge, or may point to the substitution of Ti on the tetrahedral site. Measurements of diffusion under a broader range of conditions and for other high field strength elements are underway to better interpret these findings. Major and trace element zoning in pyroxenes have been observed in residual peridotites and mafic cumulates. The large differences in cation mobility among Ti, Cr, and Fe-Mg in pyroxene may allow us to distinguish the dominant process that gives rise to the chemical disequilibria. In contrast to those produced by subsolidus reequilibration during cooling, the apparent diffusive boundary layer thicknesses as measured by major and trace elements in a pyroxene grain are not sensitive to the respective cation diffusion rates if zoning is produced by magmatic processes that involves dissolution- precipitation. Examples of zoning in pyroxenes produced by magmatic and subsolidus processes will be discussed. Ganguly et al. (2007) GCA 71, 3915-3925; ter Heege et al. (2006) Eos Trans. AGU 87, Fall Mtg. Suppl. MR21A-0004; Cherniak and Liang (2007) GCA 71, 1324-1340

  2. X-ray and runaway electron generation in repetitive pulsed discharges in atmospheric pressure air with a point-to-plane gap

    NASA Astrophysics Data System (ADS)

    Shao, Tao; Tarasenko, Victor F.; Zhang, Cheng; Shut'ko, Yuliya V.; Yan, Ping

    2011-05-01

    In this paper, using two repetitive nanosecond generators, x-rays were detected in atmospheric air with a highly inhomogeneous electric field by a point-to- plane gap. The rise times of the generators were about 15 and 1 ns. The x-rays were directly measured by various dosimeters and a NaI scintillator with a photomultiplier tube. X-rays were detected in the continuous mode at pulse repetition frequency up to 1 kHz and a voltage pulse rise time of 15 ns. It is shown that the maximum x-ray intensity is attainable at different pulse repetition frequencies depending on the voltage pulse parameters and cathode design. In atmospheric pressure air the x-ray intensity is found to increase with increasing the pulse repetition frequency up to 1 kHz. It is confirmed that the maximum x-ray intensity is attained in a diffuse discharge in a point-to-plane gap.

  3. Advanced rechargeable sodium batteries with novel cathodes

    NASA Technical Reports Server (NTRS)

    Di Stefano, S.; Ratnakumar, B. V.; Bankston, C. P.

    1990-01-01

    Various high energy density rechargeable batteries are being considered for future space applications. Of these, the sodium-sulfur battery is one of the leading candidates. The primary advantage is the high energy density (760 W h/kg theoretical). Energy densities in excess of 180 W h/kg have been realized in practical batteries. More recently, cathodes other than sulfur are being evaluated. Various new cathode materials are presently being evaluated for use in high energy density sodium batteries for advanced space applications. The approach is to carry out basic electrochemical studies of these materials in a sodium cell configuration in order to understand their fundamental behaviors. Thus far, the studies have focussed on alternative metal chlorides such as CuCl2 and organic cathode materials such as TCNE.

  4. Advanced rechargeable sodium batteries with novel cathodes

    NASA Technical Reports Server (NTRS)

    Distefano, S.; Ratnakumar, B. V.; Bankston, C. P.

    1989-01-01

    Various high energy density rechargeable batteries are being considered for future space applications. Of these, the sodium sulfur battery is one of the leading candidates. The primary advantage is the high energy density (760 Wh/kg theoretical). Energy densities in excess of 180 Wh/kg have been realized in practical batteries. More recently, cathodes other than sulfur are being evaluated. Researchers at JPL are evaluating various new cathode materials for use in high energy density sodium batteries for advanced space applications. The approach is to carry out basic electrochemical studies of these materials in a sodium cell configuration in order to understand their fundamental behaviors. Thus far studies have focused on alternate metal chlorides such as CuCl2 and organic cathode materials such as tetracyanoethylene (TCNE).

  5. The cathodic behavior of titanium: Serum effect.

    PubMed

    Contu, Francesco

    2012-02-01

    The cathodic behavior of titanium was investigated in inorganic buffer solutions and in fetal bovine serum through potential sweep techniques. Under cathodic polarization, the oxygen reduction and the hydrogen evolution reactions were observed. It was found that the activity of the electrode toward the electron transfer increased with decreasing the electrode surface charge. The polarization curves recorded in serum displayed the same features as those observed in inorganic buffered solutions. However, organic molecules were likely adsorbed onto the titanium surface and the adsorption reactions were potential dependant. Additionally, it was noticed that the buffer capacity of serum could be overwhelmed by the progressive interface alkalinization during cathodic polarization. Furthermore, serum affected the corrosion current of the implant materials and the effect was pH-dependent. 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 100B: 544-552, 2011. PMID:22120993

  6. Filtered cathodic arc deposition apparatus and method

    DOEpatents

    Krauss, Alan R. (24461 W. Blvd. De John, Naperville, IL 60564)

    1999-01-01

    A filtered cathodic arc deposition method and apparatus for the production of highly dense, wear resistant coatings which are free from macro particles. The filtered cathodic arc deposition apparatus includes a cross shaped vacuum chamber which houses a cathode target having an evaporable surface comprised of the coating material, means for generating a stream of plasma, means for generating a transverse magnetic field, and a macro particle deflector. The transverse magnetic field bends the generated stream of plasma in the direction of a substrate. Macro particles are effectively filtered from the stream of plasma by traveling, unaffected by the transverse magnetic field, along the initial path of the plasma stream to a macro particle deflector. The macro particle deflector has a preformed surface which deflects macro particles away from the substrate.

  7. Field free, directly heated lanthanum boride cathode

    DOEpatents

    Leung, Ka-Ngo (Hercules, CA); Moussa, David (San Francisco, CA); Wilde, Stephen B. (Pleasant Hill, CA)

    1991-01-01

    A directly heated cylindrical lanthanum boride cathode assembly is disclosed which minimizes generation of magnetic fields which would interfere with electron emission from the cathode. The cathode assembly comprises a lanthanum boride cylinder in electrical contact at one end with a central support shaft which functions as one electrode to carry current to the lanthanum boride cylinder and in electrical contact, at its opposite end with a second electrode which is coaxially position around the central support shaft so that magnetic fields generated by heater current flowing in one direction through the central support shaft are cancelled by an opposite magnetic field generated by current flowing through the lanthanum boride cylinder and the coaxial electrode in a direction opposite to the current flow in the central shaft.

  8. Cathodic protection of reinforcement in carbonated concrete

    SciTech Connect

    Bertolini, L.; Bolzoni, F.; Pedeferri, P. [Politecnico di Milano (Italy). Dipt. di Chimica Fisica Applicata; Pastore, T. [Univ. degli Studi di Bergamo, Dalmine (Italy). Facolta di Ingegneria

    1998-12-31

    The protection mechanism of cathodic protection applied to carbonated concrete structures have been investigated, Tests were carried out on reinforced concrete specimens with alkaline concrete, carbonated concrete and carbonated concrete with 0.4% chloride by cement weight. Cathodic current densities ranging from 2 to 10 mA/m{sup 2} were applied to the reinforcement. Potential measurements and four hour depolarization tests during the first year are shown. Changes in pH in the vicinity of the steel surface have been monitored by means of activated titanium electrodes. On the basis of the experimental results, the beneficial effects of cathodic current are discussed. The importance of realkalization of concrete in contact with the reinforcement and repassivation of steel in order to achieve stable protection conditions is shown. Protection conditions are discussed to provide design parameter and protection criteria of steel in carbonated concrete.

  9. Field free, directly heated lanthanum boride cathode

    DOEpatents

    Leung, Ka-Ngo; Moussa, D.; Wilde, S.B.

    1987-02-02

    A directly heated cylindrical lanthanum boride cathode assembly is disclosed which minimizes generation of magnetic field which would interfere with electron emission from the cathode. The cathode assembly comprises a lanthanum boride cylinder in electrical contact at one end with a central support shaft which functions as one electrode to carry current to the lanthanum boride cylinder and in electrical contact, at its opposite end with a second electrode which is coaxially position around the central support shaft so that magnetic fields generated by heater current flowing in one direction through the central support shaft are cancelled by an opposite magnetic field generated by current flowing through the lanthanum boride cylinder and the coaxial electrode in a direction opposite to the current flow in the central shaft.

  10. A solid sulfur cathode for aqueous batteries.

    PubMed

    Peramunage, D; Licht, S

    1993-08-20

    Because of its high resistivity and subsequent low electroactivity, sulfur is not normally considered a room-temperature battery cathode. An elemental sulfur cathode has been made with a measured capacity of over 900 ampere.hours per kilogram, more than 90 percent of the theoretical storage capacity of solid sulfur at room temperature, accessed by means of a lightweight, highly conductive, aqueous polysulfide interface through the electrocatalyzed reaction S + H(2)O + 2e(-) --> HS(-) + OH(-). This solid sulfur cathode was first used in a battery with an aluminum anode for an overall discharge reaction 2Al + 3S + 3OH(-) + 3H(2)O --> 2Al(OH)(3) + 3HS(-), giving a cell potential of 1.3 volts. The theoretical specific energy of the aluminum-sulfur battery (based on potassium salts) is 910 watt.hours per kilogram with an experimental specific energy of up to 220 watt.hours per kilogram. PMID:17739624

  11. Characterization of carbon fiber flocked cathode materials

    SciTech Connect

    Visosky, M.M.; Advani, R.N.; Bekefi, G.; Hutchinson, I.H.; Mastovsky, I. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Research Lab. of Electronics; Ashford, V.; Knowles, T.R. [Energy Science Labs., Inc., San Diego, CA (United States)

    1996-12-31

    This paper will study the emission characteristics of new cathode materials made of carbon fiber flock that have the potential to improve electron gun performance. Relativistic electron beams with high current densities and low temperatures are a prerequisite for the successful operation of free electron lasers and other sources of coherent radiation that use electron beams. If high radiation powers are also needed, high currents, high current densities and high brightness are necessary. These requirements become more and more stringent the shorter the radiation wavelength. The authors examined three different carbon fiber flocks and measured emittance using a pepper-pot technique. The results were compared to those obtained for a standard POCO graphite cathode. The carbon fiber flocked cathodes had substantially lower turn on fields, reduced emittance, and subsequently much greater brightness.

  12. Cathodic delaminations of poly(phenyl ether ether ketone) (PEEK) coatings overlaid on zinc phosphate-deposited steels

    SciTech Connect

    Sugama, T.; Carciello, N.R. (Brookhaven National Lab., Upton, NY (United States). Dept. of Applied Science)

    1993-12-10

    The melt-crystallized poly(phenyl) ether ether ketone (PEEK) polymer was overlaid on crystalline zinc phosphate (Zn [center dot] Ph) conversion coating-deposited and nondeposited cold-rolled steels at 400 C in air or in N[sub 2] environments. The ability of these coatings systems to protect the steel against corrosion was evaluated from the rate of cathodic delamination of the coating layer from the steel. Because the cathodic reaction, H[sub 2]O + 1/20[sub 2] + 2e[sup [minus

  13. High-performance cathode-supported SOFCs prepared by a single-step co-firing process

    Microsoft Academic Search

    Mingfei Liu; Dehua Dong; Fei Zhao; Jianfeng Gao; Dong Ding; Xingqin Liu; Guangyao Meng

    2008-01-01

    Cathode-supported solid oxide fuel cells (SOFCs), comprising porous Pr0.35Nd0.35Sr0.3MnO3?? (PNSM)\\/Sm0.2Ce0.8O1.95 (SDC) cathode supports, SDC function layers, YSZ electrolyte membranes and NiO\\/SDC anode layers, were successfully fabricated via suspensions coating and single-step co-firing process. The microstructures of electrolyte membranes were observed with scanning electron microscope (SEM). The assembled single cell was electrochemically characterized with humidified hydrogen as fuel and ambient air

  14. High pressure working mode of hollow cathode arc discharges

    NASA Technical Reports Server (NTRS)

    Minoo, H.; Popovici, C.

    1985-01-01

    The behavior of high pressure cathotrons is discussed. Methods of preheating either the gas or the cathode itself are detailed together with various geometries for the hollow cathode. Three special configurations were tested, and the results are analyzed.

  15. Plotting vectors on a cathode ray oscilloscope

    E-print Network

    Foster, Kenneth William

    1950-01-01

    output s1gnal. The plate of the seoon4 tube is directly coupled to the gr14 of the next and also to the cathode of the next tubs at a lower A. -G. potential but higher D. C, level. This D. C. potential produces the bise for this tube. '1he reduced... effective pl~te voltage for this stage, which is an over-dziven amplifier stage, is obtained by means of a 60K resistor from Bt to the cathode of the next tube and 60K mors rceistanoe from there to ground. This also gives a reduoed effective plate...

  16. A cathodically protected electrical substation ground grid

    SciTech Connect

    Nelson, J.P.; Holm, W.K.

    1983-09-01

    This paper presents a discussion on the design of a cathodically protected electrical substation grounding system in which a steel ground grid and steel ground rods were used in place of the commonly used copper ground grid and copperweld ground rods. Several electrical constraints are presented which discuss common electrical utility requirements, safety considerations and economic factors. The grounding system materials which were chosen are discussed along with the means of cathodic protection. Finally, the design, construction and testing considerations are presented as an aid to others who wish to design a similar system.

  17. Cathodic protection retrofit of an offshore pipeline

    SciTech Connect

    Winters, R.H.; Holk, A.C. [Tenneco Energy, Houston, TX (United States)

    1997-09-01

    The cathodic protection anodes and corrosion coating on two 8-inch (203.2 mm) outside diameter (O.D.) offshore pipelines were damaged during deep water ({minus}380 feet, {minus}116 m) installation. In-situ methods for deep water inspection and repair of the pipelines` cathodic protection and coating systems were developed and performed. Methods are described in which underwater anode retrofits were performed and friction welding technology was used to re-attach anode leads. Standard procedures for underwater pipeline coating repair and remediation of damaged line pipe are provided.

  18. Ferroelectric Cathodes in Transverse Magnetic Fields

    SciTech Connect

    Alexander Dunaevsky; Yevgeny Raitses; Nathaniel J. Fisch

    2002-07-29

    Experimental investigations of a planar ferroelectric cathode in a transverse magnetic field up to 3 kGs are presented. It is shown that the transverse magnetic field affects differently the operation of ferroelectric plasma cathodes in ''bright'' and ''dark'' modes in vacuum. In the ''bright'' mode, when the surface plasma is formed, the application of the transverse magnetic field leads to an increase of the surface plasma density. In the ''dark'' mode, the magnetic field inhibits the development of electron avalanches along the surface, as it does similarly in other kinds of surface discharges in the pre-breakdown mode.

  19. Process For Patterning Dispenser-Cathode Surfaces

    NASA Technical Reports Server (NTRS)

    Garner, Charles E.; Deininger, William D.

    1989-01-01

    Several microfabrication techniques combined into process cutting slots 100 micrometer long and 1 to 5 micrometer wide into tungsten dispenser cathodes for traveling-wave tubes. Patterned photoresist serves as mask for etching underlying aluminum. Chemically-assisted ion-beam etching with chlorine removes exposed parts of aluminum layer. Etching with fluorine or chlorine trifluoride removes tungsten not masked by aluminum layer. Slots enable more-uniform low-work function coating dispensed to electron-emitting surface. Emission of electrons therefore becomes more uniform over cathode surface.

  20. /C Composite Cathode for Li Ion Battery

    NASA Astrophysics Data System (ADS)

    Wang, Shulan; Liu, Xuan; Li, Huiqing; Li, Li

    2014-12-01

    Li3V2(PO4)3/C composites were prepared at different temperatures and assembled as cathodes for Li ion batteries. Their structure and electrochemical properties were properly characterized. The internal and charge transfer resistance of the Li3V2(PO4)3/C cathodes were obtained by simulating the ac impedance spectra with equivalent circuits. The Li3V2(PO4)3/C composite sintered at 1123 K (850 C) exhibits excellent electrochemical performances because of its smaller internal resistance and charge transfer resistance, as well as faster Li ion inserting/extracting rates.

  1. Engineering-Scale Liquid Cadmium Cathode Experiments

    SciTech Connect

    D Vaden; B. R. Westphal; S. X. Li; T. A. Johnson; K. B. Davies; D. M. Pace

    2006-08-01

    Recovery of transuranic actinides (TRU) using electrorefining is a process being investigated as part of the Department of Energy (DOE) Advanced Fuel Cycle Initiative (AFCI). TRU recovery via electrorefining onto a solid cathode is very difficult as the thermodynamic properties of transuranics are not favourable for them to remain in the metal phase while significant quantities of uranium trichloride exist in the electrolyte. Theoretically, the concentration of transuranics in the electrolyte must be approximately 106 greater than the uranium concentration in the electrolyte to produce a transuranic deposit on a solid cathode. Using liquid cadmium as a cathode contained within a LiCl-KCl eutectic salt, the co-deposition of uranium and transuranics is feasible because the activity of the transuranics in liquid cadmium is very small. Depositing transuranics and uranium in a liquid cadmium cathode (LCC) theoretically requires the concentration of transuranics to be two to three times the uranium concentration in the electrolyte. Three LCC experiments were performed in an Engineering scale elecdtrorefiner, which is located in the argon hot cell of the Fuel Conditioning Facility at the Materials and Fuels Complex on the Idaho National Laboratory. Figure 1 contains photographs of the LCC assembly in the hot cell prior to the experiment and a cadmium ingot produced after the first LCC test. Figure 1. Liquid Cadmium Cathode (left) and Cadmium Ingot (right) The primary goal of the engineering-scale liquid cadmium cathode experiments was to electrochemically collect kilogram quantities of uranium and plutonium via a LCC. The secondary goal was to examine fission product contaminations in the materials collected by the LCC. Each LCC experiment used chopped spent nuclear fuel from the blanket region of the Experimental Breeder Reactor II loaded into steel baskets as the anode with the LCC containing 26 kg of cadmium metal. In each experiment, between one and two kilograms of heavy metal was collected in the LCC after passing an integrated current over 500 amp hours. Analysis of samples from the liquid cadmium cathode ingots showed detectable amounts of transuranics and rare-earth elements. Acknowledgements K. B. Davies and D. M. Pace for the mechanical and electrical engineering needed to prepare the equipment for the engineering-scale liquid cadmium cathode experiments.

  2. High reliability cathode heaters for ion thrusters

    NASA Technical Reports Server (NTRS)

    Mueller, L. A.

    1976-01-01

    A number of space missions were proposed which utilize 30-cm mercury bombardment ion thrusters and also require a large number of thruster restarts. A test program was carried out to determine thermal cycle life of several different cathode heater designs. Plasma/flame sprayed heaters and swaged type heaters were tested. Four of the five plasma/flame sprayed heaters tested failed in a comparatively short time. Four tantalum swaged heaters that were brazed to the tantalum cathode tube were successfully tested and met the goals that were set at the start of the test.

  3. Cathode performance improvement in calcium-thionyl chloride cells

    NASA Astrophysics Data System (ADS)

    Walker, C. W., Jr.; Wade, W. L., Jr.; Binder, M.; Gilman, S.

    1986-08-01

    Carbon cathode performance in calcium-thionyl chloride cells was markedly improved with a cathode comprised of a mixture of high and low surface area carbon blacks. Addition of sulfur dioxide gas to the electrolyte further enhanced cathode performance and electrolyte conductivity. Load potentials and cathode life were nearly equal to that of the analogous lithium based system. The advantage of the calcium based system is its potential for greater safety.

  4. High-current cathodes of high-pressure plasmatrons

    NASA Astrophysics Data System (ADS)

    Vertiprakhov, A. I.; Zakharkin, R. Ia.; Kucherov, Ia. R.; Povaliaev, O. A.; Pustogarov, A. V.

    1988-06-01

    The performance of rod-shaped tungsten cathodes in helium and nitrogen atmospheres is investigated experimentally. In a nitrogen atmosphere at pressures above 0.5 MPa, the rod cathodes fail at currents higher than 500 A. In helium, similar cathodes operate stably at a current of 1.5 kA and pressures up to 2 MPa. Zirconium cathodes with a conical insert operate stably at currents up to 2 kA and pressures up to 2 MPa.

  5. Photothermal cathode measurements at the Advanced Photon Source.

    SciTech Connect

    Sun, Y.-E.; Lewellen, J. W.; Feldman, D. W.; Univ. of Maryland

    2006-01-01

    The Advanced Photon Source (APS) ballistic bunch compression (BBC) gun in the Injector Test Stand (ITS) presently uses an M-type thermionic dispenser cathode as a photocathode. This photothermal cathode offers substantial advantages over conventional metal photocathodes, including easy replacement and easy cleaning via the cathode's built-in heater. We present the results of photoemission measurements as a function of cathode heater power, laser pulse energy, and applied rf field strength.

  6. Hydrogen diffusion and embrittlement in 7075 aluminum alloy

    Microsoft Academic Search

    N. Takano

    2008-01-01

    The effect of hydrogen on the mechanical properties of an A7075 aluminum alloy and hydrogen diffusivity are investigated using the electrochemical cathode charge method. The apparent hydrogen diffusivity in the A7075 alloy is 4.410?12m2\\/s at 318K. Hydrogen charging induces a decrease of both the tensile strength and the elongation to fracture in comparison to tests performed in atmospheric environment. In

  7. Layered charge transfer complex cathodes or solid electrolyte cells

    Microsoft Academic Search

    Louzos

    1981-01-01

    Layered charge transfer complex cathodes for use in solid electrolyte cells are described wherein one layer of the cathode contains an electronic conductor which is isolated from the cell's solid electrolyte by a second layer of the cathode that does not contain an electronic conductor.

  8. Cathodic limitations in microbial fuel cells: An overview

    Microsoft Academic Search

    Hamid Rismani-Yazdi; Sarah M. Carver; Ann D. Christy; Olli H. Tuovinen

    2008-01-01

    Microbial fuel cells (MFCs) are a promising technology for sustainable production of alternative energy and waste treatment. The performance of microbial fuel cells is severely affected by limitations based on irreversible reactions and processes in the anode and the cathode compartments. The purpose of this paper is to review the cathodic limitations MFCs and provide an overview on cathodic activation,

  9. Fabrication and performance of advanced multi-layer SOFC cathodes

    Microsoft Academic Search

    P. Holtappels; C. Bagger

    2002-01-01

    Multilayered cathodes for solid oxide fuel cells are presented. The cathodes are composed of strontium doped lanthanum manganate and yttria stabilised zirconia, the ratio of which is increased with increasing distance from a supporting zirconia electrolyte. Some cathodes additionally carry a number of layers with a graded transition from manganite to cobaltite to add an electronically highly efficient current collector.

  10. High-voltage virtual-cathode microwave simulations

    SciTech Connect

    Thode, L.; Snell, C.M.

    1991-01-01

    In contrast to a conventional microwave tube, a virtual-cathode device operates above the space-charge limit where the depth of the space-charge potential is sufficiently large to cause electron reflection. The region associated with electron reflection is referred to as a virtual cathode. Microwaves can be generated through oscillations in the position of the virtual cathode and by reflexing electrons trapped in the potential well formed between the real and virtual cathodes. A virtual-cathode device based on the first mechanism is a vircator while one based on latter mechanism is a reflex diode. A large number of low-voltage virtual-cathode microwave configurations have been investigated. Initial simulations of a high-voltage virtual-cathode device using a self-consistent particle-in-cell code indicated reasonable conversion efficiency with no frequency chirping. The nonchirping character of the high-voltage virtual-cathode device lead to the interesting possibility of locking four very-high-power microwave devices together using the four transmission lines available at Aurora. Subsequently, in support of two high-voltage experiments, simulations were used to investigate the effect of field-emission threshold and velvet position on the cathode; anode and cathode shape; anode-cathode gap spacing; output waveguide radius; diode voltage; a cathode-coaxial-cavity resonator; a high-frequency ac-voltage drive; anode foil scattering and energy loss; and ion emission on the microwave frequency and power. Microwave

  11. Ion flux from the cathode region of a vacuum arc

    Microsoft Academic Search

    J. Kutzner; H. C. Miller

    1989-01-01

    The properties of the ion flux generated in a vacuum arc are reviewed. The structure and distribution of mass erosion from individual cathode spots and the characteristics of current carriers from the cathode region at moderate arc currents are described. An appreciable ion flux (~10% of the total arc current) is emitted from the cathode of a vacuum arc. This

  12. Explosive Electron Emission From Liquid-Metal Cathodes

    Microsoft Academic Search

    Dmitry I. Proskurovsky

    2009-01-01

    Since the discovery of explosive electron emission (EEE) 40 years ago, the overwhelming majority of investigations of this phenomenon have been performed with solid-state metal cathodes. At the same time, liquid-metal (LM) pool point cathodes, by virtue of some favorable properties, allow one to perform more reliable physical experiments. The peculiarities of LM cathodes are related to the features of

  13. Transverse Forces and Motions at Cathode Spots in Vacuum Arcs

    Microsoft Academic Search

    L. P. Harris

    1983-01-01

    Consistent analyses are provided for the motion of cathode spot cells in the presence of magnetic fields parallel to the cathode surface (retrograde motion), for the spontaneous splitting of cells, and for the grouping of cathode spot cells in organized structures. The formulas for retrograde motion and cell splitting frequencies are evaluated for cells carrying 1-80 A on copper vacuum

  14. Hollow cathode and ion accelerator system for current ion sources

    Microsoft Academic Search

    Aston

    1981-01-01

    A small self-heating hollow cathode has been designed and tested which uses a novel flowing plasma starting concept to eliminate the need for cathode heating elements and low work function insert materials. In a magnetic field free ion source, this cathode has reliably and repeatedly produced arc currents, using argon, of 100 ampere (the power supply limit) at arc voltages

  15. The loss of material from the cathode of metal arcs

    NASA Technical Reports Server (NTRS)

    Seeliger, R.; Wulfhekel, H.

    1985-01-01

    A study was made of the effect of arc length, cathode thickness, current strength, gas pressure and the chemical nature of the cathode material and filling gases upon the material loss from Cu, Fe, and Ag cathodes in arcs. The results show that the analysis of the phenomenon is complex and the energy balance is difficult to formulate.

  16. DEVELOPMENTS IN PERMANENT STAINLESS STEEL CATHODES WITHIN THE COPPER INDUSTRY

    Microsoft Academic Search

    K. L. Eastwood; G. W. Whebell

    The ISA PROCESS cathode plate is characterised by its copper coated suspension bar, coupled with a blade employing austenitic stainless steel alloy 316L. The blade material has become the mainstay of the technology and has been closely copied by competing cathode designs. Improvement to the cathode plate design remains a key area for research, and ongoing developments by Xstrata Technology's

  17. Deuterization and Deuterium Reactions in the Electrolyses of D2O with the Double Structure Cathode and the Bulk Cathode

    Microsoft Academic Search

    Yoshiaki Arata; Yue-Chang Zhang

    2000-01-01

    The deuterium concentration in the bulk Pd metal used as a cathode in the electrolysis of D2O is found to be much less than that in fine Pd powders of the nano-scale in a double-structure (DS) cathode. In marked contrast to the case with the DS cathode, neither excess heat nor 4He production are observed with the bulk Pd cathode.

  18. Expansion of the cathode spot and generation of shock waves in the plasma of a volume discharge in atmospheric-pressure helium

    SciTech Connect

    Omarov, O. A.; Kurbanismailov, V. S.; Arslanbekov, M. A.; Gadzhiev, M. Kh.; Ragimkhanov, G. B.; Al-Shatravi, Ali J. G. [Dagestan State University (Russian Federation)

    2012-01-15

    The expansion of the cathode spot and the generation of shock waves during the formation and development of a pulsed volume discharge in atmospheric-pressure helium were studied by analyzing the emission spectra of the cathode plasma and the spatiotemporal behavior of the plasma glow. The transition of a diffuse volume discharge in a centimeter-long gap into a high-current diffuse mode when the gas pressure increased from 1 to 5 atm and the applied voltage rose from the statistical breakdown voltage to a 100% overvoltage was investigated. Analytical expressions for the radius of the cathode spot and its expansion velocity obtained in the framework of a spherically symmetric model agree satisfactorily with the experimental data.

  19. A model of the cathode spot glow discharge for a cathode with inclusions of low work function material

    Microsoft Academic Search

    Leonid Pekker

    1993-01-01

    A model that describes the self-maintained glow discharge for a composite cathode in which cathode spots are formed on low work function material inclusions is presented. Based on this model, expressions are obtained for the radius of the spot, the cathode voltage, and the spot current as functions of Pd (where P is the gas pressure and d is the

  20. Paschen's law for a hollow cathode discharge

    Microsoft Academic Search

    H. Eichhorn; K. H. Schoenbach; T. Tessnow

    1993-01-01

    An expression for the breakdown voltage of a one-dimensional hollow cathode discharge has been derived. The breakdown condition which corresponds to Paschens law contains, in addition to the first Townsend coefficient, and the secondary electron emission coefficient two parameters which characterize the reflecting action of the electric field and the lifetime of the electrons in the discharge. The breakdown voltage

  1. FEA cathode experiments for microwave power amplifiers

    Microsoft Academic Search

    M. Garven; M. A. Kodis

    1996-01-01

    Summary form only given, as follows. The investigation of a new class of vacuum microelectronic, microwave power amplifiers based on field emitter array (FEA) technology is currently underway at the Naval Research Laboratory. FEAs offer instant activation, higher transconductance and higher current densities than thermionic cathodes and consequently higher performance gridded microwave power tubes should be possible. FEA microwave power

  2. A cathodically protected electrical substation ground grid

    Microsoft Academic Search

    J. P. Nelson; W. K. Holm

    1983-01-01

    This paper presents a discussion on the design of a cathodically protected electrical substation grounding system in which a steel ground grid and steel ground rods were used in place of the commonly used copper ground grid and copperweld ground rods. Several electrical constraints are presented which discuss common electrical utility requirements, safety considerations and economic factors. The grounding system

  3. Solar arrays power cathodic protection stations

    Microsoft Academic Search

    1986-01-01

    Washington Natural Gas Co. has conducted tests to apply effective cathodic protection currents to coated steel pipe, in 156 ohm\\/cm soil, with photovoltaics incorporated in impressed current stations. The author describes the tests and results that give a cost-effective corrosion control system for pipe lines in extremely high resistant soil areas.

  4. Virtual cathode formation due to electromagnetic transients

    Microsoft Academic Search

    John W. Luginsland; Sarah McGee; Y. Y. Lau

    1998-01-01

    The process of virtual cathode formation in a gap is critically examined via particle simulations. It is found that the limiting current obtained from the electrostatic approximation is valid only in the deeply nonrelativistic regime. For injection energy as low as 30 keV, the transients in the injected current may produce an inductive voltage that can significantly lower the limiting

  5. Organic cathode for a secondary battery

    SciTech Connect

    Bugga, R.V.; Distefano, S.; Williams, R.M.; Bankston, C.P.

    1990-10-30

    This patent describes a battery system. It comprises: a first body of liquid meal anode comprising a Group I metal; a record body of liquid cathode comprising a combination of Group I metal salt and Group III metal salt molten at the temperature of operation of the battery containing a minor amount of an organic carbonitrile depolarizer containing at least one adjacent ethylenic bond.

  6. Cathodic protection of external tank bottoms

    Microsoft Academic Search

    K. C. Garrity; M. Urbas

    1988-01-01

    The corrosion process as it relates to buried, partially buried, and submerged metallic structures is a naturally occurring phenomenon. The principles of this process and the benefits of cathodic protection (CP) in controlling this type of corrosion have been demonstrated in many different situations. Concern has increased, at an alarming rate, over failures of ground storage tank bottoms resulting from

  7. Characterization of carbon fiber flocked cathode materials

    Microsoft Academic Search

    M. M. Visosky; R. N. Advani; G. Bekefi; I. H. Hutchinson; I. Mastovsky; V. Ashford; T. R. Knowles

    1996-01-01

    Summary form only given. The paper studies the emission characteristics of new cathode materials made of carbon fiber flock that have the potential to improve electron gun performance. Relativistic electron beams with high current densities and low temperatures are a prerequisite for the successful operation of free electron lasers and other sources or coherent radiation that use electron beams. If

  8. Cathode for molten carbonate fuel cell

    Microsoft Academic Search

    T. D. Kaun; F. C. Mrazek

    1990-01-01

    This patent describes a porous sintered cathode useful for a molten carbonate fuel cell comprising a sintered mixture and electrolyte. The sintered mixture being of a first particulate material slightly soluble in the electrolyte present in the molten carbonate fuel and a second particulate material insoluble in the electrolyte, present in the molten carbonate fuel cell. The first material forming

  9. Maximum theoretical power density of lithium-air batteries with mixed electrolyte

    NASA Astrophysics Data System (ADS)

    Mehta, M.; Bevara, V.; Andrei, P.

    2015-07-01

    An analytical model is developed for the discharge voltage of Li-air batteries with mixed organic/aqueous electrolyte and used to analyze the effects of the oxygen dissolution, solubility, pressure, and diffusivity, reaction rates, and internal resistance on the power density of Li-air batteries. By carefully identifying the model parameters using experimental data it is shown that, for discharge currents above 25 mA cm-2 the power of these batteries is mainly limited by the large internal resistance of the membrane and membrane/electrolyte interfaces (which is currently larger than 100 ? cm2), while for smaller discharge currents the power is limited by the low oxygen concentration at the reaction sites. The maximum power density can be increased by approximately 1.5 times if the internal resistance is decreased from 100 ? cm2 to 25 ? cm2. This relatively small increase in the power density is due to the low dissolution rate and solubility of the oxygen in the liquid electrolyte. Finally, when the battery is operated at maximum discharge power, the oxygen diffusion length in the aqueous electrolyte is under 1 ?m, which shows that one needs to use partly wet cathodes in order to achieve high power densities in these batteries.

  10. New Cathode Materials for Intermediate Temperature Solid Oxide Fuel Cells

    SciTech Connect

    Allan J. Jacobson

    2006-09-30

    Operation of SOFCs at intermediate temperatures (500-800 C) requires new combinations of electrolyte and electrode materials that will provide both rapid ion transport across the electrolyte and electrode-electrolyte interfaces and efficient electrocatalysis of the oxygen reduction and fuel oxidation reactions. This project concentrates on materials and issues associated with cathode performance that are known to become limiting factors as the operating temperature is reduced. The specific objectives of the proposed research are to develop cathode materials that meet the electrode performance targets of 1.0 W/cm{sup 2} at 0.7 V in combination with YSZ at 700 C and with GDC, LSGM or bismuth oxide based electrolytes at 600 C. The performance targets imply an area specific resistance of {approx}0.5 {Omega}cm{sup 2} for the total cell. The research strategy is to investigate both established classes of materials and new candidates as cathodes, to determine fundamental performance parameters such as bulk diffusion, surface reactivity and interfacial transfer, and to couple these parameters to performance in single cell tests. The initial choices for study were perovskite oxides based on substituted LaFeO{sub 3} (P1 compositions), where significant data in single cell tests exist at PNNL for example, for La{sub 0.8}Sr{sub 0.2}FeO{sub 3} cathodes on both YSZ and CSO/YSZ. The materials selection was then extended to La{sub 2}NiO{sub 4} compositions (K1 compositions), and then in a longer range task we evaluated the possibility of completely unexplored group of materials that are also perovskite related, the ABM{sub 2}O{sub 5+{delta}}. A key component of the research strategy was to evaluate for each cathode material composition, the key performance parameters, including ionic and electronic conductivity, surface exchange rates, stability with respect to the specific electrolyte choice, and thermal expansion coefficients. In the initial phase, we did this in parallel with the perovskite compositions that were being investigated at PNNL, in order to assess the relative importance of the intrinsic properties such as oxygen ion diffusion and surface exchange rates as predictors of performance in cell tests. We then used these measurements to select new materials for scaled up synthesis and performance evaluation in single cell tests. The results of the single cell tests than provided feedback to the materials synthesis and selection steps. In this summary, the following studies are reported: (1) Synthesis, characterization, and DC conductivity measurements of the P1 compositions La{sub 0.8}Sr{sub 0.2}FeO{sub 3-x} and La{sub 0.7}Sr{sub 0.3}FeO{sub 3-x} were completed. A combinational approach for preparing a range P1 (La,Sr)FeO{sub 3} compositions as thin films was investigated. Synthesis and heat treatment of amorphous SrFeO{sub 3-x} and LaFeO{sub 3-x} films prepared by pulsed laser deposition are described. (2) Oxygen transport properties of K1 compositions La{sub x}Pr{sub 2-x}NiO{sub 4+d} (x =2.0, 1.9, 1.2, 1.0 and 0) measured by electrical conductivity relaxation are presented in this report. Area specific resistances determined by ac impedance measurements for La{sub 2}NiO{sub 4+{delta}} and Pr{sub 2}NiO{sub 4+{delta}} on CGO are encouraging and suggest that further optimization of the electrode microstructure will enable the target to be reached. (3) The oxygen exchange kinetics of the oxygen deficient double perovskite LnBaCo{sub 2}O{sub 5.5+{delta}} (Ln=Pr and Nd) were determined by electrical conductivity relaxation. The high electronic conductivity and rapid diffusion and surface exchange kinetics of PBCO suggest its application as cathode material in intermediate temperature solid oxide fuel cells. The first complete cell measurements were performed on Ni/CGO/CGO/PBCO/CGO cells. (4) The oxygen exchange kinetics of highly epitaxial thin films of PrBaCo{sub 2}O{sub 5.5+{delta}} (PBCO) has been determined by electrical conductivity relaxation and isotope exchange and depth profiling and confirm the high electronic conductivit

  11. Morphologically architectured spray pyrolyzed lanthanum ferrite-based cathodes-A phenomenal enhancement in solid oxide fuel cell performance

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Jayanta; Basu, Rajendra Nath

    2014-04-01

    Nanocrystalline single phase La1-xSrxCo1-yFeyO3-? [LSCF] (0cathodes (crystallite size 30-50nm) are synthesized by two fluid spray-pyrolysis (SP) for solid oxide fuel cell (SOFC) application. The particulate sizes of the synthesized cathodes are found to be in the range of 100-200nm. Particulate morphology of highest conducting cathode (?1500Scm-1) is tailored using homomolecular seeding agent of precalcined pyrolyzed ashes. Interfacial polarizations of the such SP synthesized screen printed cathodes onto gadolinium doped ceria (CGO) based electrolyte are found to be much lower (0.032-0.16?cm2 at 800C-500C) with highest exchange current density (?722mAcm-2 at 800C) for oxygen reduction reaction. Enhanced current density of 4.0Acm-2 (0.7V, 800C) is obtained for SOFC button cells using optimized LSCF cathode with hydrogen as fuel and air as oxidant. LSCF cathodes synthesized by spray pyrolysis using homomolecular seeding exhibit interconnected mesoporosity having primary nano-particulates embedded within. Endurance test of button cells till 500h results low degradation viz. 3.8% and 8.9% 1000h-1 with electronic loads of 0.5Acm-2 and 1.0Acm-2 respectively. High performances of such cells are clinically correlated with SP processing conditions and particulate morphology of cathode powders.

  12. Development program on a Spindt cold-cathode electron gun

    NASA Technical Reports Server (NTRS)

    Spindt, C. A.

    1982-01-01

    A thin film field emission cathode (TFFEC) array and a cold cathode electron gun based on the emitter were developed. A microwave tube gun that uses the thin film field emission cathode as an electron source is produced. State-of-the-art cathodes were fabricated and tested. The tip-packing density of the arrays were increased thereby increasing the cathode's current density capability. The TFFEC is based on the well known field emission effect and was conceived to exploit the advantages of that phenomenon while minimizing the difficulties associated with conventional field emission structures, e.g. limited life and high voltage requirements. Field emission follows the Fowler-Nordheim equation.

  13. Long lifetime hollow cathodes for 30-cm mercury ion thrusters

    NASA Technical Reports Server (NTRS)

    Mirtich, M. J.; Kerslake, W. R.

    1976-01-01

    An experimental investigation of hollow cathodes for 30-cm Hg bombardment thrusters was carried out. Both main and neutralizer cathode configurations were tested with both rolled foil inserts coated with low work function material and impregnated porous tungsten inserts. Temperature measurements of an impregnated insert at various positions in the cathode were made. These, along with the cathode thermal profile are presented. A theory for rolled foil and impregnated insert operation and lifetime in hollow cathodes is developed. Several endurance tests, as long as 18000 hours at emission currents of up to 12 amps were attained with no degradation in performance.

  14. Carbon fiber paper cathodes for lithium ion batteries

    SciTech Connect

    Kercher, Andrew K [ORNL; Kiggans, Jim [ORNL; Dudney, Nancy J [ORNL

    2010-01-01

    A novel lithium ion battery cathode structure was produced which has the potential for excellent capacity retention and good thermal management. In these cathodes, the active cathode material (lithium iron phosphate) was carbon bonded to a thermally and electrically conductive carbon fiber paper (CFP) support. Electrochemical testing was performed on Swagelok cells consisting of CFP cathodes and lithium anodes. High specific energy, near-theoretical capacity, and good cycling performance were demonstrated for 0.11 mm and 0.37 mm thick CFP cathodes.

  15. Emission current control system for multiple hollow cathode devices

    NASA Technical Reports Server (NTRS)

    Beattie, John R. (Inventor); Hancock, Donald J. (Inventor)

    1988-01-01

    An emission current control system for balancing the individual emission currents from an array of hollow cathodes has current sensors for determining the current drawn by each cathode from a power supply. Each current sensor has an output signal which has a magnitude proportional to the current. The current sensor output signals are averaged, the average value so obtained being applied to a respective controller for controlling the flow of an ion source material through each cathode. Also applied to each controller are the respective sensor output signals for each cathode and a common reference signal. The flow of source material through each hollow cathode is thereby made proportional to the current drawn by that cathode, the average current drawn by all of the cathodes, and the reference signal. Thus, the emission current of each cathode is controlled such that each is made substantially equal to the emission current of each of the other cathodes. When utilized as a component of a multiple hollow cathode ion propulsion motor, the emission current control system of the invention provides for balancing the thrust of the motor about the thrust axis and also for preventing premature failure of a hollow cathode source due to operation above a maximum rated emission current.

  16. Influence of the cathode architecture in the frequency response of self-breathing proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Ferreira-Aparicio, P.; Chaparro, A. M.

    2014-12-01

    Self-breathing proton exchange membrane fuel cells are apparently simple devices, but efficient water management is critical for their performance. The cathode configuration should guarantee balanced rates between O2 accessibility from the circumventing air and H2O removal, and a good electric contact between catalyst layers and current collectors at the same time. By applying progressive modifications to the initial concept of a conventional PEMFC, the effect of the cathode architecture on cell performance has been analyzed. Frequency response analyses of the cell during steady-state potentiostatic stepping have yielded relevant information regarding limitations originated by the cathode impedance under high current load conditions. The primitive cell design has been optimized for self-breathing operation by means of this diagnostic tool. The thickness of the perforated plate in the cathode has been found to be one of the main factors contributing to limit oxygen accessibility when a high current load is demanded. Adequate cathode architecture is critical for reducing mass transport limitations in the catalytic layer and enhancing performance under self-breathing conditions.

  17. Cathode R&D for Future Light Sources

    SciTech Connect

    Dowell, D.H.; /SLAC; Bazarov, I.; Dunham, B.; /Cornell U., CLASSE; Harkay, K.; /Argonne; Hernandez-Garcia; /Jefferson Lab; Legg, R.; /Wisconsin U., SRC; Padmore, H.; /LBL, Berkeley; Rao, T.; Smedley, J.; /Brookhaven; Wan, W.; /LBL, Berkeley

    2010-05-26

    This paper reviews the requirements and current status of cathodes for accelerator applications, and proposes a research and development plan for advancing cathode technology. Accelerator cathodes need to have long operational lifetimes and produce electron beams with a very low emittance. The two principal emission processes to be considered are thermionic and photoemission with the photocathodes being further subdivided into metal and semi-conductors. Field emission cathodes are not included in this analysis. The thermal emittance is derived and the formulas used to compare the various cathode materials. To date, there is no cathode which provides all the requirements needed for the proposed future light sources. Therefore a three part research plan is described to develop cathodes for these future light source applications.

  18. Diagnostics of cathode material loss in cutting plasma torch

    NASA Astrophysics Data System (ADS)

    Gruber, J.; onsk, J.; Hlna, J.

    2014-07-01

    A cutting plasma torch was observed in several ways by a high-speed camera with a focus on the cathode area. In the first experiment, the plasma arc between the nozzle tip and anode was recorded in a series of duty cycles ranging from new unworn cathodes to cathode failure due to wear and material loss. In the second experiment, we used a specially modified nozzle to observe the inside area between the cathode and the nozzle exit through a fused silica window. Finally, using tilted view, we observed a pool of molten hafnium at the cathode tip during the plasma torch operation. The process of cathode material melting, droplet formation, their expulsion and rate of cathode material loss was examined.

  19. Cathode R&D for future light sources.

    SciTech Connect

    Dowell, D. H.; Bazarov, I.; Dunham, B.; Harkay, K.; Hernandez-Garcia, C.; Legg, R.; Padmore, H.; Rao, T.; Smedley, J.; Wan, W.; Accelerator Systems Division (APS); SLAC National Accelerator Lab.; Cornell Univ.; Thomas Jefferson Lab.; Univ. of Wisconsin; LBNL; BNL

    2010-03-18

    This paper reviews the requirements and current status of cathodes for accelerator applications, and proposes a research and development plan for advancing cathode technology. Accelerator cathodes need to have long operational lifetimes and produce electron beams with a very low emittance. The two principal emission processes to be considered are thermionic and photoemission with the photocathodes being further subdivided into metal and semi-conductors. Field emission cathodes are not included in this analysis. The thermal emittance is derived and the formulas used to compare the various cathode materials. To date, there is no cathode which provides all the requirements needed for the proposed future light sources. Therefore a three part research plan is described to develop cathodes for these future light source applications.

  20. Cathode spot motion in a vacuum arc with a long roof-shaped cathode under magnetic field

    NASA Astrophysics Data System (ADS)

    Beilis, I. I.; Sagi, B.; Zhitomirsky, V.; Boxman, R. L.

    2015-06-01

    Vacuum arc cathode spot motion was investigated on a "roof-shaped" aluminum cathode under an external magnetic field. The cathode included a flat roof-top and four sloped sides, inclined by an angle ?. A high speed camera was used to observe cathode spot motion. The spot velocity on the slopes and the distribution of cathode spots on the roof and slopes was determined. It was obtained that under a magnetic field, the spot motion on the roof was slow (<1 m/s) and mainly random, while on the slopes fast retrograde motion was observed. This velocity increased linearly with the magnetic field and decreased slightly with ?.

  1. La0.3Sr0.2Mn0.1Zn0.4 oxide-Sm0.2Ce0.8O1.9 (LSMZ-SDC) nanocomposite cathode for low temperature SOFCs.

    PubMed

    Raza, Rizwan; Abbas, Ghazanfar; Liu, Qinghua; Patel, Imran; Zhu, Bin

    2012-06-01

    Nanocomposite based cathode materials compatible for low temperature solid oxide fuel cells (LTSOFCs) are being developed. In pursuit of compatible cathode, this research aims to synthesis and investigation nanocomposite La0.3Sr0.2Mn0.1Zn0.4 oxide-Sm0.2Ce0.8O1.9 (LSMZ-SDC) based system. The material was synthesized through wet chemical method and investigated for oxide-ceria composite based electrolyte LTSOFCs. Electrical property was studied by AC electrochemical impedance spectroscopy (EIS). The microstructure, thermal properties, and elemental analysis of the samples were characterized by TGA/DSC, XRD, SEM, respectively. The AC conductivity of cathode was obtained for 2.4 Scm(-1) at 550 degrees C in air. This cathode is compatible with ceria-based composite electrolytes and has improved the stability of the material in SOFC cathode environment. PMID:22905565

  2. Double Diffusion in Enclosure Bounded by Massive and Volatilizing Walls

    E-print Network

    Liu, D.; Tang, G.; Zhao, F.

    2006-01-01

    Hazard volatilization emitted from walls enters into airflow in the room, making the indoor air quality worse. An exterior wall of some thickness is affected on its surface by the outdoor air environment. In this paper, conjugated double diffusive...

  3. Li-ion migration in Li 2FeSiO 4-related cathode materials: A DFT study

    Microsoft Academic Search

    Anti Liivat; John O. Thomas

    2011-01-01

    The orthosilicate family of materials Li2MSiO4 for M=Fe, Mn and Co are coming to be seen as potentially cheap cathode materials for large-scale Li-ion batteries, not least through the possibility for significant capacity gains if more than one Li-ion can be removed per formula unit. To gain insights into possible Li-ion migration pathways and diffusion barriers for Li-ions, model systems

  4. Review of HxPyOz-Catalyzed H + OH Recombination in Scramjet Nozzle Expansions; and Possible Phosphoric Acid Enhancement of Scramjet Flameholding, from Extinction of H3PO4 + H2 - Air Counterflow Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald

    2005-01-01

    Recent detailed articles by Twarowski indicate that small quantities of phosphorus oxides and acids in the fuel-rich combustion products of H2 + phosphine (PH3) + air should significantly catalyze H, OH and O recombination kinetics during high-speed nozzle expansions -- to reform H2O, release heat, and approach equilibrium more rapidly and closely than uncatalyzed kinetics. This paper is an initial feasibility study to determine (a) if addition of phosphoric acid vapor (H3PO4) to a H2 fuel jet -- which is much safer than using PH3 -- will allow combustion in a high-speed scramjet engine test without adverse effects on localized flameholding, and (b) if phosphorus-containing exhaust emissions are environmentally acceptable. A well-characterized axisymmetric straight-tube opposed jet burner (OJB) tool is used to evaluate H3PO4 addition effects on the air velocity extinction limit (flame strength) of a H2 versus air counterflow diffusion flame. Addition of nitric oxide (NO), also believed to promote catalytic H-atom recombination, was evaluated for comparison. Two to five mass percent H3PO4 in the H2 jet increased flame strength 4.2%, whereas airside addition decreased it 1%. Adding 5% NO to the H2 caused a 2% decrease. Products of H-atom attack on H3PO4 produced an intense green chemiluminescence near the stagnation point. The resultant exothermic production of phosphorus oxides and acids, with accelerated H-atom recombination, released sufficient heat near the stagnation point to increase flame strength. In conclusion, the addition of H3PO4 vapor (or more reactive P sources) to hydrogen in scramjet engine tests may positively affect flameholding stability in the combustor and thrust production during supersonic expansion -- a possible dual benefit with system design / performance implications. Finally, a preliminary assessment of possible environmental effects indicates that scramjet exhaust emissions should consist of phosphoric acid aerosol, with gradual conversion to phosphate aerosol. This is compared to various natural abundances and sources.

  5. Counterion Diffusion in Ionomers

    NASA Astrophysics Data System (ADS)

    Walter, Russell; Winey, Karen; Kim, Joon-Seop; Composto, Russell

    2004-03-01

    Diffusion of Cs counterions to the air/ionomer film interface is followed using Rutherford backscattering spectrometry and results compared with the "sticky reptation" model[1]. The ionomer system is poly(styrene-ran-methacrylic acid) (Cs-SMAA) neutralized at 100% by Cs. The concentration profiles exhibit a surface excess, z*, of Cs followed by a depletion of Cs. The z* and depletion layer thickness grow as t1/2, consistent with diffusion limited growth. Annealing studies at 130 C, 145 C and 208 C were used to extract the diffusion coefficient, D. In all cases, D is greater than that of the matrix chains. These results suggest that the diffusion rate is controlled by the fraction of counterions that disassociate from the acid groups and migrate through the matrix. Moreover, the "sticky reptation" model doesn't appear to predict the diffusion behavior in the Cs-SMAA system. [1] Leibler, L, Ludwick, L., Rubinstein, M., Colby, R.H., Macromolecules 24 (1991) 4701.

  6. The effect of cathode geometry on barium transport in hollow cathode plasmas

    SciTech Connect

    Polk, James E., E-mail: james.e.polk@jpl.nasa.gov; Mikellides, Ioannis G.; Katz, Ira [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109 (United States); Capece, Angela M. [California Institute of Technology, 1200 E. California Blvd., Pasadena, California 91125 (United States)

    2014-05-14

    The effect of barium transport on the operation of dispenser hollow cathodes was investigated in numerical modeling of a cathode with two different orifice sizes. Despite large differences in cathode emitter temperature, emitted electron current density, internal xenon neutral and plasma densities, and size of the plasma-surface interaction region, the barium transport in the two geometries is qualitatively very similar. Barium is produced in the insert and flows to the surface through the porous structure. A buildup of neutral Ba pressure in the plasma over the emitter surface can suppress the reactions supplying the Ba, restricting the net production rate. Neutral Ba flows into the dense Xe plasma and has a high probability of being ionized at the periphery of this zone. The steady state neutral Ba density distribution is determined by a balance between pressure gradient forces and the drag force associated with collisions between neutral Ba and neutral Xe atoms. A small fraction of the neutral Ba is lost upstream. The majority of the neutral Ba is ionized in the high temperature Xe plasma and is pushed back to the emitter surface by the electric field. The steady state Ba{sup +} ion density distribution results from a balance between electrostatic and pressure forces, neutral Xe drag and Xe{sup +} ion drag with the dominant forces dependent on location in the discharge. These results indicate that hollow cathodes are very effective at recycling Ba within the discharge and therefore maintain a high coverage of Ba on the emitter surface, which reduces the work function and sustains high electron emission current densities at moderate temperatures. Barium recycling is more effective in the cathode with the smaller orifice because the Ba is ionized in the dense Xe plasma concentrated just upstream of the orifice and pushed back into the hollow cathode. Despite a lower emitter temperature, the large orifice cathode has a higher Ba loss rate through the orifice because the Xe plasma density peaks further upstream.

  7. A comparative study of La 0.8Sr 0.2MnO 3 and La 0.8Sr 0.2Sc 0.1Mn 0.9O 3 as cathode materials of single-chamber SOFCs operating on a methaneair mixture

    Microsoft Academic Search

    Chunming Zhang; Yao Zheng; Ye Lin; Ran Ran; Zongping Shao; David Farrusseng

    2009-01-01

    As candidates of cathode materials for single-chamber solid oxide fuel cells, La0.8Sr0.2MnO3 (LSM) and La0.8Sr0.2Sc0.1Mn0.9O3 (LSSM) were synthesized by a combined EDTA-citrate complexing solgel process. The solid precursors of LSM and LSSM were calcined at 1000 and 1150C, respectively, to obtain products with similar specific surface area. LSSM was found to have higher activity for methane oxidization than LSM due

  8. Doped lanthanum ferrite cathode development for use in single-step co-fired solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zink, Peter Andrew

    A major obstacle to the commercialization of solid oxide fuel cells (SOFCs) is the high operating temperature range (800 to 1000C). Lowering the operating temperature to approximately 600C allows for cost reduction through the use of inexpensive stack housing and sealing materials, but conventional SOFC cathode materials have high charge transfer resistance at those temperatures which results in poor performance. This research focused on developing an SOFC cathode material with low charge transfer resistance at low operating temperatures and a porous microstructure that would not impede mass transfer when synthesized using the single-step co-firing process. Towards this goal, mixed ionic and electronic conducting lanthanum ferrite perovskite cathode materials were synthesized using calcium and cerium as dopants. A specific stoichiometry of calcium doped lanthanum ferrite, La0.78Ca0.16FeO3+/-delta (LCF), proved to be a superior cathode compared to state-of-the-art conventional cathode materials across a range of measures. In order to understand the LCF cathode performance, the defect model structure was determined using thermogravimetric (TGA) measurements, oxygen-ion permeability and four-probe conductivity measurements as a function of temperature and oxygen partial pressure (pO2). The results were analyzed to determine defect concentrations and mobility. The electrochemical performance of LCF was characterized using electrochemical impedance spectroscopy measurements on symmetrical cells which compared favorably to conventional lanthanum manganite cathode materials. Reactivity of LCF with yttria-stabilized zirconia (YSZ) electrolyte was confirmed and prevented using a gadolinium doped ceria (GDC) barrier layer. Microstructural analysis showed evidence of a small amount (2--5 wt%) of secondary phase that precipitated from LCF as a liquid during sintering at approximately 1220C. The secondary phase was a poor n-type oxide (Ca-Fe-O), present within both the LCF cathode and GDC barrier layer microstructures. In spite of the presence of the liquid phase, LCF symmetrical cells yielded adequate microstructures and satisfactory electrochemical performance. To understand the reasons for the superior electrochemical performance of LCF, the chemical oxygen ion diffusivity and surface exchange coefficient were determined using conductivity relaxation measurements. Both of these parameters in LCF were found to be an order of magnitude greater than conventional cathode materials.

  9. Polymeric hydrogen diffusion barrier, high-pressure storage tank so equipped, method of fabricating a storage tank and method of preventing hydrogen diffusion

    DOEpatents

    Lessing, Paul A.

    2004-09-07

    An electrochemically active hydrogen diffusion barrier which comprises an anode layer, a cathode layer, and an intermediate electrolyte layer, which is conductive to protons and substantially impermeable to hydrogen. A catalytic metal present in or adjacent to the anode layer catalyzes an electrochemical reaction that converts any hydrogen that diffuses through the electrolyte layer to protons and electrons. The protons and electrons are transported to the cathode layer and reacted to form hydrogen. The hydrogen diffusion barrier is applied to a polymeric substrate used in a storage tank to store hydrogen under high pressure. A storage tank equipped with the electrochemically active hydrogen diffusion barrier, a method of fabricating the storage tank, and a method of preventing hydrogen from diffusing out of a storage tank are also disclosed.

  10. Polymeric hydrogen diffusion barrier, high-pressure storage tank so equipped, method of fabricating a storage tank and method of preventing hydrogen diffusion

    DOEpatents

    Lessing, Paul A. (Idaho Falls, ID)

    2008-07-22

    An electrochemically active hydrogen diffusion barrier which comprises an anode layer, a cathode layer, and an intermediate electrolyte layer, which is conductive to protons and substantially impermeable to hydrogen. A catalytic metal present in or adjacent to the anode layer catalyzes an electrochemical reaction that converts any hydrogen that diffuses through the electrolyte layer to protons and electrons. The protons and electrons are transported to the cathode layer and reacted to form hydrogen. The hydrogen diffusion barrier is applied to a polymeric substrate used in a storage tank to store hydrogen under high pressure. A storage tank equipped with the electrochemically active hydrogen diffusion barrier, a method of fabricating the storage tank, and a method of preventing hydrogen from diffusing out of a storage tank are also disclosed.

  11. Fokker-Planck . . . Diffusion . . .

    E-print Network

    Fokker-Planck . . . Diffusion . . . Diffusion- . . . Application: . . . Summary and . . . First #12;Fokker-Planck . . . Diffusion . . . Diffusion- . . . Application: . . . Summary and . . . Topics: 1. Fokker-Planck transport equation 2. Diffusion approximation 3. Diffusion-convection transport

  12. Introduction Diffusion Tensor Imaging

    E-print Network

    Zhang, Shuzhong

    Introduction Diffusion Tensor Imaging Diffusion Kurtosis Imaging D-Eigenvalues and . . . Further Full Screen Close Quit Diffusion Tensor and Diffusion Kurtosis Tensor in Biomedical Engineering Diffusion Tensor Imaging Diffusion Kurtosis Imaging D-Eigenvalues and . . . Further Discussion Home Page

  13. Electrospray emitters For diffusion vacuum pumps

    E-print Network

    Diaz Gmez Maqueo, Pablo (Pablo Ly)

    2011-01-01

    Following similar principles as regular diffusion vacuum pumps, an electrospray emitter is set to produce a jet of charged particles that will drag air molecules out of a volume. To be a feasible concept, the emitted ...

  14. Relativistic diffusion

    E-print Network

    Haba, Z

    2008-01-01

    We define a relativistic diffusion equation on the phase space. We consider stochastic Ito (Langevin) differential equation on the phase space as a perturbation by noise of relativistic dynamics. The motion in an electromagnetic field is treated as an example. Transport equations and equilibrium probability distributions are investigated. A relation to diffusions appearing in heavy ion collisions is briefly discussed.

  15. Hillslope diffusion

    NSDL National Science Digital Library

    Jeni McDermott

    This lab is designed to help students apply hillslope diffusion equations (derived in class prior to the lab) to understand real-world hillslopes. The major goal is a deeper understanding of hillslope processes and the equations used to describe hillslope diffusion by observing the same factors described in the equations on real-world hillslopes.

  16. Long-term evaluation of solid oxide fuel cell candidate materials in a 3-cell generic stack test fixture, part III: Stability and microstructure of Ce-(Mn,Co)-spinel coating, AISI441 interconnect, alumina coating, cathode and anode

    NASA Astrophysics Data System (ADS)

    Chou, Yeong-Shyung; Stevenson, Jeffry W.; Choi, Jung-Pyung

    2014-07-01

    A generic solid oxide fuel cell stack test fixture was developed to evaluate candidate materials and processing under realistic conditions. Part III of the work investigated the stability of Ce-(Mn,Co) spinel coating, AISI441 metallic interconnect, alumina coating, and cell's degradation. After 6000h test, the spinel coating showed densification with some diffusion of Cr. At the metal interface, segregation of Si and Ti was observed, however, no continuous layer formed. The alumina coating for perimeter sealing areas appeared more dense and thick at the air side than the fuel side. Both the spinel and alumina coatings remained bonded. EDS analysis of Cr within the metal showed small decrease in concentration near the coating interface and would expect to cause no issue of Cr depletion. Inter-diffusion of Ni, Fe, and Cr between spot-welded Ni wire and AISI441 interconnect was observed and Cr-oxide scale formed along the circumference of the weld. The microstructure of the anode and cathode was discussed relating to degradation of the top and middle cells. Overall, the Ce-(Mn,Co) spinel coating, alumina coating, and AISI441 steel showed the desired long-term stability and the developed generic stack fixture proved to be a useful tool to validate candidate materials for SOFC.

  17. Air Cannon

    NSDL National Science Digital Library

    2012-07-09

    In this activity, learners create air cannons out of everyday materials. Learners use their air cannons to investigate air as a force and air pressure. The activity page includes a fun how-to video for learners and educators.

  18. NUMERICAL MODELING OF CATHODE CONTACT MATERIAL DENSIFICATION

    SciTech Connect

    Koeppel, Brian J.; Liu, Wenning N.; Stephens, Elizabeth V.; Khaleel, Mohammad A.

    2011-11-01

    Numerical modeling was used to simulate the constrained sintering process of the cathode contact layer during assembly of solid oxide fuel cells (SOFCs). A finite element model based on the continuum theory for sintering of porous bodies was developed and used to investigate candidate low-temperature cathode contact materials. Constitutive parameters for various contact materials under investigation were estimated from dilatometry screening tests, and the influence of processing time, processing temperature, initial grain size, and applied compressive stress on the free sintering response was predicted for selected candidate materials. The densification behavior and generated stresses within a 5-cell planar SOFC stack during sintering, high temperature operation, and room temperature shutdown were predicted. Insufficient constrained densification was observed in the stack at the proposed heat treatment, but beneficial effects of reduced grain size, compressive stack preload, and reduced thermal expansion coefficient on the contact layer densification and stresses were observed.

  19. Magnetron cathodes in plasma electrode Pockels cells

    DOEpatents

    Rhodes, M.A.

    1995-04-25

    Magnetron cathodes, which produce high current discharges, form greatly improved plasma electrodes on each side of an electro-optic crystal. The plasma electrode has a low pressure gas region on both sides of the crystal. When the gas is ionized, e.g., by a glow discharge in the low pressure gas, the plasma formed is a good conductor. The gas electrode acts as a highly uniform conducting electrode. Since the plasma is transparent to a high energy laser beam passing through the crystal, the plasma is transparent. A crystal exposed from two sides to such a plasma can be charged up uniformly to any desired voltage. A typical configuration utilizes helium at 50 millitorr operating pressure and 2 kA discharge current. The magnetron cathode produces a more uniform plasma and allows a reduced operating pressure which leads to lower plasma resistivity and a more uniform charge on the crystal. 5 figs.

  20. In situ acquisition of cathodic protection parameters

    SciTech Connect

    Baptista, W.; Costa, J.C.M. da [PETROBRAS, Rio de Janeiro (Brazil)

    1997-01-01

    Present, offshore cathodic protection (CP) design in Brazil uses parameters found in the literature and in international norms, such as: initial and average current density, coating efficiency, leaked current at the buried part of the wet Xmas tree, etc. Five data acquisition systems (DAS) were launched at the Campos Basin water in depths of 102, 290, and 975 m. The DASs were recovered after 8, 11, and 14 months, respectively. Adequate methods of data processing guaranteed the acquisition of reliable parameters for use in CP projects in seawater: initial and average current densities, anode current capacity, and polarization curves at several time intervals. The potential of {minus}800 mV{sub Ag/AgCl} is generally accepted as norm for carbon steel protection in seawater. The cathodic current density necessary to obtain this potential is extremely dependent upon environmental conditions, and the geometry and superficial condition of the submerged steel structure.

  1. International Space Station Cathode Life Testing Status

    NASA Technical Reports Server (NTRS)

    Sarver-Verhey, Timothy R.; Soulas, George C.

    1998-01-01

    To demonstrate adequate lifetime and performance capabilities of a hollow cathode for use on the International Space Station (ISS) plasma contactor system, life tests of multiple hollow cathode assemblies (HCAs) were initiated at operating conditions simulating on-orbit operation. Three HCAs are presently being tested. These HCAs are operated with a continuous 6 sccm xenon flow rate and 3 A anode current. Emission current requirements are simulated with a square waveform consisting of 50 minutes at a 2.5 A emission current and 40 minutes with no emission current. As of July 1998, these HCAs have accumulated between 1 1,700 and 14,200 hours. While there have been changes in operatin, behavior the three HCAs continue to operate stably within ISS specifications and are expected to demonstrate the required lifetime.

  2. Cathode for chlor-alkali cells

    Microsoft Academic Search

    Gray

    1981-01-01

    An improved cathode with a conductive metal core and a Raney-type catalytic surface predominantly derived from an adherent ternary aluminide intermetallic crystalline precursory outer portion of the metal core is disclosed. The precursory outer portion preferably has molybdenum and titanium added to give a precursor alloy having the formula NiXMoYTiZAL where X is within the range of from about 75

  3. Development of lanthanum ferrite SOFC cathodes

    Microsoft Academic Search

    Steve P. Simner; Jeff F. Bonnett; Nathan L. Canfield; Kerry D. Meinhardt; Jayne P. Shelton; Vince L. Sprenkle; Jeffry W. Stevenson

    2003-01-01

    A number of studies have been conducted concerning compositional\\/microstructural modifications of a Sr-doped lanthanum ferrite (LSF) cathode and protective Sm-doped ceria (SDC) layer in an anode supported solid oxide fuel cell (SOFC). Emphasis was placed on achieving enhanced low temperature (700800C) performance, and long-term cell stability. Investigations involved manipulation of the lanthanum ferrite chemistry, addition of noble metal oxygen reduction

  4. Cathode Ion Bombardment in RF Photoguns

    SciTech Connect

    Pozdeyev,E.; Kayran, D.; Litvinenko, V.

    2008-09-01

    In this paper, we use the method of rapid oscillating field to solve the equation of ion motion in an RF gun. We apply the method to the BNL 1/2-cell SRF photogun and demonstrate that a significant portion of ions produced in the gun can reach the cathode if no special precautions are taken. Also, the paper proposes a simple mitigation recipe that can reduce the rate of ion bombardment.

  5. Development of long-lifetime cold cathodes

    Microsoft Academic Search

    N. M. Bykov; V. P. Gubanov; A. V. Gunin; S. D. Korovin; O. P. Kutenkov; V. F. Landl; S. D. Polevin; V.V. Rostov; G. A. Mesyats; F. Ya. Zagulov

    1995-01-01

    The paper presents the results of an experimental study of the cold cathodes used in the Sinus-type repetitive high-current accelerators. The accelerating voltage for this accelerator is on a level of 100-1000 keV, the electron beam current is 1-10 kA, the pulse duration is 10-40 ns, and the pulse repetition rate is up to 200 pps. The emissive properties of

  6. Copper chloride cathode for a secondary battery

    NASA Technical Reports Server (NTRS)

    Bugga, Ratnakumar V. (inventor); Distefano, Salvador (inventor); Nagasubramanian, Ganesan (inventor); Bankston, Clyde P. (inventor)

    1990-01-01

    Higher energy and power densities are achieved in a secondary battery based on molten sodium and a solid, ceramic separator such as a beta alumina and a molten catholyte such as sodium tetrachloroaluminate and a copper chloride cathode. The higher cell voltage of copper chloride provides higher energy densities and the higher power density results from increased conductivity resulting from formation of copper as discharge proceeds.

  7. Fabrication of thin-film LiMn2O4 cathodes for rechargeable microbatteries

    NASA Astrophysics Data System (ADS)

    Shokoohi, F. K.; Tarascon, J. M.; Wilkens, B. J.

    1991-09-01

    Thin-film cathodes of lithiated manganese oxide (Li/x/Mn2O4, where x is 1 or less), which can reversibly intercalate nearly one Li atom per unit formula, at a steady potential of 4.1 V. This results in a theoretical energy density of about 600 Wh/kg. The polycrystalline films (thickness of 0.5-2 microns) show electrochemical performance exceeding that of bulk materials. This is attributed to the small grain size and the porosity within these Li(x)Mn2O4 three-dimensional spinel films, reducing the diffusion path length for Li(+) ions. The films are tested as the cathodes in about 70 charging/discharging cycles, in a secondary lithium cell, at current rates of of 10-100 microamperes/sq cm. No measurable self-discharge over 12 h periods is observed. These thin-film cathodes with above electrochemical properties are very promising for a new generation thin-film secondary batteries.

  8. Nanostructured ceria based thin films (?1 ?m) As cathode/electrolyte interfaces

    NASA Astrophysics Data System (ADS)

    Hierso, J.; Boy, P.; Vall, K.; Vulliet, J.; Blein, F.; Laberty-Robert, Ch.; Sanchez, C.

    2013-01-01

    Gadolinium doped cerium oxide (CGO: Ce0,9Gd0,1O2-?) films were used as an oxygen anion diffusion layer at the cathode/electrolyte interface of Solid Oxide Fuel Cells (SOFCs), between LSCF (lanthanum strontium cobalt ferrite) and YSZ (yttria-stabilized zirconia). Thin (100 nm) and thick (700 nm) mesoporous CGO layers were synthesized through a sol-gel process including organic template coupled with the dip-coating method. Structural and microstructural characterizations were performed, highlighting a well-bonded crystalline CGO nanoparticles network which delineates a 3-D inter-connected mesoporous network. Their electrical behaviors were investigated by impedance spectroscopy analysis of YSZ/mesoporous-CGO/LSCF half-cell. Anode-supported SOFCs, operating at 800 C, with either dense or mesoporous CGO dip-coated interlayers were also fabricated [NiO-YSZ anode/YSZ/CGO/LSCF cathode]. The impact of the mesoporous CGO interlayers on SOFCs performances was investigated by galvanostatic analysis and compared to the behavior of a dense CGO interlayer. The polarization curves revealed an enhancement in the electrical performance of the cell, which is assigned to a decrease of the polarization resistance at the cathode/electrolyte interface. The integrity and connectivity of the CGO nanoparticles bonded network facilitates O2- transport across the interface.

  9. ReaxFF molecular dynamics simulations on lithiated sulfur cathode materials.

    PubMed

    Islam, Md Mahbubul; Ostadhossein, Alireza; Borodin, Oleg; Yeates, A Todd; Tipton, William W; Hennig, Richard G; Kumar, Nitin; van Duin, Adri C T

    2015-02-01

    Sulfur is a very promising cathode material for rechargeable energy storage devices. However, sulfur cathodes undergo a noticeable volume variation upon cycling, which induces mechanical stress. In spite of intensive investigation of the electrochemical behavior of the lithiated sulfur compounds, their mechanical properties are not very well understood. In order to fill this gap, we developed a ReaxFF interatomic potential to describe Li-S interactions and performed molecular dynamics (MD) simulations to study the structural, mechanical, and kinetic behavior of the amorphous lithiated sulfur (a-LixS) compounds. We examined the effect of lithiation on material properties such as ultimate strength, yield strength, and Young's modulus. Our results suggest that with increasing lithium content, the strength of lithiated sulfur compounds improves, although this increment is not linear with lithiation. The diffusion coefficients of both lithium and sulfur were computed for the a-LixS system at various stages of Li-loading. A grand canonical Monte Carlo (GCMC) scheme was used to calculate the open circuit voltage profile during cell discharge. The Li-S binary phase diagram was constructed using genetic algorithm based tools. Overall, these simulation results provide insight into the behavior of sulfur based cathode materials that are needed for developing lithium-sulfur batteries. PMID:25529209

  10. Progress on diamond amplified photo-cathode

    SciTech Connect

    Wang, E.; Ben-Zvi, I.; Burrill, A.; Kewisch, J.; Chang, X.; Rao, T.; Smedley, J.; Wu, Q.; Muller, E.; Xin, T.

    2011-03-28

    Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length. The diamond-amplified photocathode, that promises to support a high average current, low emittance, and a highly stable electron beam with a long lifetime, is under development for an electron source. The diamond, functioning as a secondary emitter amplifies the primary current, with a few KeV energy, that comes from the traditional cathode. Earlier, our group recorded a maximum gain of 40 in the secondary electron emission from a diamond amplifier. In this article, we detail our optimization of the hydrogenation process for a diamond amplifier that resulted in a stable emission gain of 140. We proved that these characteristics are reproducible. We now are designing a system to test the diamond amplifier cathode using an 112MHz SRF gun to measure the limits of the emission current's density, and on the bunch charge and bunch length.

  11. Engineering-Scale Liquid Cadmium Cathode Experiments

    SciTech Connect

    D. Vaden; S. X. Li; B. R. Westphal; K. B. Davies; T. A. Johnson; D. M. Pace

    2008-05-01

    Recovery of uranium and transuranic (TRU) actinides from spent nuclear fuel by an electrorefining process was investigated as part of the U.S. Department of Energy Advanced Fuel Cycle Initiative. Experiments were performed in a shielded hot cell at the Materials and Fuels Complex at Idaho National Laboratory. The goal of these experiments was to collect, by an electrochemical process, kilogram quantities of uranium and plutonium into what is called a liquid cadmium cathode (LCC). For each experiment, a steel basket loaded with chopped spent nuclear fuel from the Experimental Breeder Reactor II acted as the anode in the electrorefiner. The cathode was a beryllium oxide crucible containing ~26 kg of cadmium metal (the LCC). In the three experiments performed to date, between 1 and 2 kg of heavy metal was collected in the LCC after passing an integrated current between 1.80 and 2.16 MC (500 and 600 A h) from the anode to the cathode. Sample analysis of the processed LCC ingots measured detectable amounts of TRUs and rare earth elements.

  12. Cathode power distribution system and method of using the same for power distribution

    DOEpatents

    Williamson, Mark A; Wiedmeyer, Stanley G; Koehl, Eugene R; Bailey, James L; Willit, James L; Barnes, Laurel A; Blaskovitz, Robert J

    2014-11-11

    Embodiments include a cathode power distribution system and/or method of using the same for power distribution. The cathode power distribution system includes a plurality of cathode assemblies. Each cathode assembly of the plurality of cathode assemblies includes a plurality of cathode rods. The system also includes a plurality of bus bars configured to distribute current to each of the plurality of cathode assemblies. The plurality of bus bars include a first bus bar configured to distribute the current to first ends of the plurality of cathode assemblies and a second bus bar configured to distribute the current to second ends of the plurality of cathode assemblies.

  13. Combustor air flow control method for fuel cell apparatus

    DOEpatents

    Clingerman, Bruce J. (Palmyra, NY); Mowery, Kenneth D. (Noblesville, IN); Ripley, Eugene V. (Russiaville, IN)

    2001-01-01

    A method for controlling the heat output of a combustor in a fuel cell apparatus to a fuel processor where the combustor has dual air inlet streams including atmospheric air and fuel cell cathode effluent containing oxygen depleted air. In all operating modes, an enthalpy balance is provided by regulating the quantity of the air flow stream to the combustor to support fuel cell processor heat requirements. A control provides a quick fast forward change in an air valve orifice cross section in response to a calculated predetermined air flow, the molar constituents of the air stream to the combustor, the pressure drop across the air valve, and a look up table of the orifice cross sectional area and valve steps. A feedback loop fine tunes any error between the measured air flow to the combustor and the predetermined air flow.

  14. Flame Velocities over a Wide Composition Range for Pentane-air, Ethylene-air, and Propyne-air Flames

    NASA Technical Reports Server (NTRS)

    Simon, Dorothy M; Wong, Edgar, L

    1951-01-01

    Fundamental flame velocities are reported for pentane air, ethylene-air, and propylene-air mixtures for the concentration range 60 to 130 percent of stoichiometric. A form of the Tanford and Pease equation, which includes a small constant velocity term independent of diffusion, will predict the observed changes in flame velocity.

  15. Rf Gun with High-Current Density Field Emission Cathode

    SciTech Connect

    Jay L. Hirshfield

    2005-12-19

    High current-density field emission from an array of carbon nanotubes, with field-emission-transistor control, and with secondary electron channel multiplication in a ceramic facing structure, have been combined in a cold cathode for rf guns and diode guns. Electrodynamic and space-charge flow simulations were conducted to specify the cathode configuration and range of emission current density from the field emission cold cathode. Design of this cathode has been made for installation and testing in an existing S-band 2-1/2 cell rf gun. With emission control and modulation, and with current density in the range of 0.1-1 kA/cm2, this cathode could provide performance and long-life not enjoyed by other currently-available cathodes

  16. Scanning optical pyrometer for measuring temperatures in hollow cathodes

    SciTech Connect

    Polk, J. E.; Marrese-Reading, C. M.; Thornber, B.; Dang, L.; Johnson, L. K.; Katz, I. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States); International Space University, 67000 Strasbourg (France); California Institute of Technology, Pasadena, California 91109 (United States); Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)

    2007-09-15

    Life-limiting processes in hollow cathodes are determined largely by the temperature of the electron emitter. To support cathode life assessment, a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe was developed. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used to determine the axial temperature profile. Thermocouples on the orifice plate provide measurements of the external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. The diagnostic method and initial measurements of the temperature distribution in a hollow cathode are discussed.

  17. Use of Auger spectroscopy in the evaluation of thermionic cathodes

    NASA Technical Reports Server (NTRS)

    Forman, R.

    1977-01-01

    Auger spectroscopy has been used to evaluate the properties of 'good' and 'poor' impregnated tungsten cathodes used in high-power microwave wave tubes. The results were interpreted to analyze failure modes in cathodes removed from TWT's because of poor emission characteristics. Most of the poor cathodes evaluated in this program were obtained from fabricated electron guns that had been employed and discarded from the 200-W TWT tubes developed for the Communication Technology Satellite program. The results of these measurements have shown there are at least two types of failure modes that one observes with poor cathodes. They are (1) chemical contamination of the cathode surface and (2) low partial layer barium coverage of the cathode surface.

  18. Microhollow Cathode Sustained Discharge with Split Third Electrodes

    NASA Astrophysics Data System (ADS)

    Sultana, Sharmin; Shin, Jichul

    2012-10-01

    The characteristics of stable, non-equilibrium, diffuse glow micro-hollow cathode sustained discharge (MCSD) with split third electrodes at moderate to atmospheric pressure in various flow rates are studied experimentally. Enlargement of sustained discharge volume in a split-electrode configuration is about eight times larger than that in a single planar third electrode case. At 100 Torr a maximum expansion of sustained glow discharge is measured as large as 10.3 mm with nine split third electrodes. Analytic estimate of average electron number density at the maximum expansion is measured to be as high as 2.99x10^10 cm-3 at 5 mA third electrode current. In the presence of 0.1 slpm gas flow, the discharge region increases to 18.8 mm with corresponding estimated density of 2.48x10^10 cm-3 at the same third electrode current. For specific pressure ranges, Faraday dark space is clearly visible near the MHCD hole. In the presence of gas flow across the gap, the sustained discharge is affected by linear momentum of the gas flow and its characteristics are altered accordingly such as current distribution over the electrodes. Feasibility of developing a flow velocimetry by using this dynamic phenomenon of MCSD with split electrodes is also studied.

  19. Nanostructured ceria based thin films ({<=}1 {mu}m) As cathode/electrolyte interfaces

    SciTech Connect

    Hierso, J. [Laboratoire de Chimie de la Matiere Condensee de Paris, Universite Paris 6-UMR 7574-College de France, 11 Place Marcelin Berthelot, 75005 Paris (France); Boy, P.; Valle, K. [CEA-Le Ripault, LSCG, BP 15, 37000 Monts (France); Vulliet, J.; Blein, F. [CEA-Le Ripault, LCCA, BP 15, 37000 Monts (France); Laberty-Robert, Ch., E-mail: christel.laberty@upmc.fr [Laboratoire de Chimie de la Matiere Condensee de Paris, Universite Paris 6-UMR 7574-College de France, 11 Place Marcelin Berthelot, 75005 Paris (France); Sanchez, C. [Laboratoire de Chimie de la Matiere Condensee de Paris, Universite Paris 6-UMR 7574-College de France, 11 Place Marcelin Berthelot, 75005 Paris (France)

    2013-01-15

    Gadolinium doped cerium oxide (CGO: Ce{sub 0,9}Gd{sub 0,1}O{sub 2-{delta}}) films were used as an oxygen anion diffusion layer at the cathode/electrolyte interface of Solid Oxide Fuel Cells (SOFCs), between LSCF (lanthanum strontium cobalt ferrite) and YSZ (yttria-stabilized zirconia). Thin ({approx}100 nm) and thick ({approx}700 nm) mesoporous CGO layers were synthesized through a sol-gel process including organic template coupled with the dip-coating method. Structural and microstructural characterizations were performed, highlighting a well-bonded crystalline CGO nanoparticles network which delineates a 3-D inter-connected mesoporous network. Their electrical behaviors were investigated by impedance spectroscopy analysis of YSZ/mesoporous-CGO/LSCF half-cell. Anode-supported SOFCs, operating at 800 Degree-Sign C, with either dense or mesoporous CGO dip-coated interlayers were also fabricated [NiO-YSZ anode/YSZ/CGO/LSCF cathode]. The impact of the mesoporous CGO interlayers on SOFCs performances was investigated by galvanostatic analysis and compared to the behavior of a dense CGO interlayer. The polarization curves revealed an enhancement in the electrical performance of the cell, which is assigned to a decrease of the polarization resistance at the cathode/electrolyte interface. The integrity and connectivity of the CGO nanoparticles bonded network facilitates O{sup 2-} transport across the interface. - Graphical abstract: Thin and thick CGO films have been prepared through a sol-gel process and their potential application as SOFC cathode/electrolyte interlayer in SOFC has been investigated. Highlights: Black-Right-Pointing-Pointer Mesoporous ceria based thin films exhibit interesting performances for Solid Oxide Fuel Cell. Black-Right-Pointing-Pointer Mesoporous films were synthesized through the sol-gel process combined with the dip-coating. Black-Right-Pointing-Pointer Integrity and connectivity of the nanoparticles facilitates O{sup 2-} transport across the interface.

  20. Solid-state synthesis and characterization of silver vanadium oxide for use as a cathode material for lithium batteries

    Microsoft Academic Search

    Randolph A. Leising; Esther Sans Takeuchi

    1994-01-01

    Silver vanadium oxide (SVO, AgV[sub 2]O[sub 5.5]) was synthesized for use as a cathode material in lithium\\/SVO batteries. The material was prepared via the solid-state thermal reaction of a silver-containing precursor and vanadium pentoxide at 500[degrees]C under an air or argon atmosphere. The silver-containing precursors examined in this study were silver nitrate, silver nitrite, silver vanadate, silver oxide, silver carbonate,