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Sample records for air diffusion cathode

  1. Nitrogen-doped carbonaceous catalysts for gas-diffusion cathodes for alkaline aluminum-air batteries

    NASA Astrophysics Data System (ADS)

    Davydova, E. S.; Atamanyuk, I. N.; Ilyukhin, A. S.; Shkolnikov, E. I.; Zhuk, A. Z.

    2016-02-01

    Cobalt tetramethoxyphenyl porphyrin and polyacrylonitrile - based catalysts for oxygen reduction reaction were synthesized and characterized by means of SEM, TEM, XPS, BET, limited evaporation method, rotating disc and rotating ring-disc electrode methods. Half-cell and Al-air cell tests were carried out to determine the characteristics of gas-diffusion cathodes. Effect of active layer thickness and its composition on the characteristics of the gas-diffusion cathodes was investigated. Power density of 300 mW cm-2 was achieved for alkaline Al-air cell with an air-breathing polyacrylonitrile-based cathode.

  2. Continuous flow membrane-less air cathode microbial fuel cell with spunbonded olefin diffusion layer.

    PubMed

    Tugtas, Adile Evren; Cavdar, Pelin; Calli, Baris

    2011-11-01

    The power production performance of a membrane-less air-cathode microbial fuel cell was evaluated for 53 days. Anode and cathode electrodes and the micro-fiber cloth separator were configured by sandwiching the separator between two electrodes. In addition, the air-facing side of the cathode was covered with a spunbonded olefin sheet instead of polytetrafluoroethylene (PTFE) coating to control oxygen diffusion and water loss. The configuration resulted in a low resistance of about 4Ω and a maximum power density of 750 mW/m2. However, as a result of a gradual decrease in the cathode potential, maximum power density decreased to 280 mW/m2. The declining power output was attributed to loss of platinum catalyst (8.26%) and biomass growth (38.44%) on the cathode. Coulombic efficiencies over 55% and no water leakage showed that the spunbonded olefin sheet covering the air-facing side of the cathode can be a cost-effective alternative to PTFE coating. PMID:21963900

  3. Development of carbon free diffusion layer for activated carbon air cathode of microbial fuel cells.

    PubMed

    Yang, Wulin; Kim, Kyoung-Yeol; Logan, Bruce E

    2015-12-01

    The fabrication of activated carbon air cathodes for larger-scale microbial fuel cells requires a diffusion layer (DL) that is highly resistant to water leakage, oxygen permeable, and made using inexpensive materials. A hydrophobic polyvinylidene fluoride (PVDF) membrane synthesized using a simple phase inversion process was examined as a low cost ($0.9/m(2)), carbon-free DL that prevented water leakage at high pressure heads compared to a polytetrafluoroethylene/carbon black DL ($11/m(2)). The power density produced with a PVDF (20%, w/v) DL membrane of 1400±7mW/m(2) was similar to that obtained using a wipe DL [cloth coated with poly(dimethylsiloxane)]. Water head tolerance reached 1.9m (∼19kPa) with no mesh supporter, and 2.1m (∼21kPa, maximum testing pressure) with a mesh supporter, compared to 0.2±0.05m for the wipe DL. The elimination of carbon black from the DL greatly simplified the fabrication procedure and further reduced overall cathode costs. PMID:26342345

  4. Air cathode structure manufacture

    DOEpatents

    Momyer, William R.; Littauer, Ernest L.

    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.

  5. 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 cm² 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.

  6. 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 1130 ± 30 mW m-2 with dry air to 980 ± 80 mW m-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 (1030 ± 130 mW m-2) and water-saturated (390 ± 190 mW m-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 (960 ± 60 mW m-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.

  7. Electro-fenton and photoelectro-fenton degradation of sulfanilic acid using a boron-doped diamond anode and an air diffusion cathode.

    PubMed

    El-Ghenymy, Abdellatif; Garrido, José Antonio; Centellas, Francesc; Arias, Conchita; Cabot, Pere Lluís; Rodríguez, Rosa María; Brillas, Enric

    2012-04-01

    The mineralization of sulfanilic acid has been studied by electro-Fenton (EF) and photoelectro-Fenton (PEF) reaction with UVA light using an undivided electrochemical cell with a boron-doped diamond (BDD) anode and an air diffusion cathode able to generate H(2)O(2). Organics were then oxidized by hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between generated H(2)O(2) and added Fe(2+). The UVA irradiation in PEF enhanced the production of hydroxyl radicals in the bulk, accelerating the removal of organics and photodecomposed intermediates like Fe(III)-carboxylate complexes. Partial decontamination of 1.39 mM sulfanilic acid solutions was achieved by EF until 100 mA cm(-2) at optimum conditions of 0.4 mM Fe(2+) and pH 3.0. The increase in current density and substrate content led to an almost total mineralization. In contrast, the PEF process was more powerful, yielding almost complete mineralization in less electrolysis time under comparable conditions. The kinetics for sulfanilic acid decay always followed a pseudo-first-order reaction. Hydroquinone and p-benzoquinone were detected as aromatic intermediates, whereas acetic, maleic, formic, oxalic, and oxamic acids were identified as generated carboxylic acids. NH(4)(+) ion was preferentially released in both treatments, along with NO(3)(-) ion in smaller proportion. PMID:22404230

  8. Oxide diffusion in innovative SOFC cathode materials.

    PubMed

    Hu, Y; Thoréton, 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)+δ 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)+δ 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

  9. Gas transport evaluation in lithium-air batteries with micro/nano-structured cathodes

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoning; Wen, Kechun; Song, Yuanqiang; Ye, Luhan; Zhang, Kelvin H. L.; Pan, Yu; Lv, Weiqiang; Liao, Yulong; He, Weidong

    2015-01-01

    Inefficient gas transport in the porous cathode is disastrous for the lithium-air battery to achieve a high electrochemical performance. Previous evaluation of the cathode diffusivity relies on indirect calculations based on multiple V-I data obtained over the intact battery system, which inevitably induces evaluation uncertainty and material waste. In this report, an electrochemical device is designed for the out-of-cell diffusivity measurement in the lithium-air battery with micro/nano-sized cathodes. With the measured diffusivity, a few electrochemical parameters including the limiting current density and the concentration polarization associated with the porous cathodes can thus be directly evaluated. The work facilitates the development of highly-efficient cathode materials in the general field of metal-air battery field.

  10. 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 (1.49 × 10-5 cm2 s-1), CE and EE of the MFC with 0.1 μm pore-size polyethersulfone membrane can reach 92.8% and 13.7%, respectively, when its average power density registers 403.5 mW m-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.

  11. 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.

  12. Multi-variable mathematical models for the air-cathode microbial fuel cell system

    NASA Astrophysics Data System (ADS)

    Ou, Shiqi; Kashima, Hiroyuki; Aaron, Douglas S.; Regan, John M.; Mench, Matthew M.

    2016-05-01

    This research adopted the version control system into the model construction for the single chamber air-cathode microbial fuel cell (MFC) system, to understand the interrelation of biological, chemical, and electrochemical reactions. The anodic steady state model was used to consider the chemical species diffusion and electric migration influence to the MFC performance. In the cathodic steady state model, the mass transport and reactions in a multi-layer, abiotic cathode and multi-bacteria cathode biofilm were simulated. Transport of hydroxide was assumed for cathodic pH change. This assumption is an alternative to the typical notion of proton consumption during oxygen reduction to explain elevated cathode pH. The cathodic steady state model provided the power density and polarization curve performance results that can be compared to an experimental MFC system. Another aspect considered was the relative contributions of platinum catalyst and microbes on the cathode to the oxygen reduction reaction (ORR). Simulation results showed that the biocatalyst in a cathode that includes a Pt/C catalyst likely plays a minor role in ORR, contributing up to 8% of the total power calculated by the models.

  13. Battery with modular air cathode and anode cage

    DOEpatents

    Niksa, Marilyn J.; Pohto, Gerald R.; Lakatos, Leslie K.; Wheeler, Douglas J.; Niksa, Andrew J.; Schue, Thomas J.; Turk, Thomas R.

    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.

  14. Battery with modular air cathode and anode cage

    DOEpatents

    Niksa, Marilyn J.; Pohto, Gerald R.; Lakatos, Leslie K.; Wheeler, Douglas J.; Niksa, Andrew J.; Schue, Thomas J.

    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.

  15. Gas transfer from air diffusers.

    PubMed

    Schierholz, Erica L; Gulliver, John S; Wilhelms, Steven C; Henneman, Heather E

    2006-03-01

    The bubble and surface volumetric mass transfer coefficients for oxygen, k(L)a(b) and k(L)a(s), are separately determined for 179 aeration tests, with diffuser depths ranging from 2.25 to 32 m, using the DeMoyer et al. 12003. Impact of bubble and free surface oxygen transfer on diffused aeration systems. Water Res 37, 1890-1904] mass transfer model. Two empirical characterization equations are developed for k(L)a(b) and k(L)a(s), correlating the coefficients to air flow, Qa, diffuser depth, hd, cross-sectional area, Acs, and volume, V. The characterization equations indicate that the bubble transfer coefficient, k(L)a(b), increases with increasing gas flow rate and depth, and decreases with increasing water volume. For fine bubble diffusers, k(L)a(b) is approximately six times greater than k(L)a(b) for coarse bubble diffusers. The surface transfer coefficient, k(L)A(s), increases with increasing gas flow rate and diffuser depth. The characterization equations make it possible to predict the gas transfer that will occur across bubble interfaces and across the free surface with a bubble plume at depths up to 32 m and with variable air discharge in deep tanks and reservoirs. PMID:16490229

  16. Effects of hydraulic pressure on the performance of single chamber air-cathode microbial fuel cells.

    PubMed

    Cheng, Shaoan; Liu, Weifeng; Guo, Jian; Sun, Dan; Pan, Bin; Ye, Yaoli; Ding, Weijun; Huang, Haobin; Li, Fujian

    2014-06-15

    Scaling up of microbial fuel cells (MFCs) without losing power density requires a thorough understanding of the effect of hydraulic pressure on MFC performance. In this work, the performance of an activated carbon air-cathode MFC was evaluated under different hydraulic pressures. The MFC under 100 mmH2O hydraulic pressure produced a maximum power density of 1260 24 mW m(-2), while the power density decreased by 24.4% and 44.7% as the hydraulic pressure increased to 500 mmH2O and 2000 mmH2O, respectively. Notably, the performance of both the anode and the cathode had decreased under high hydraulic pressures. Electrochemical impedance spectroscopy tests of the cathode indicated that both charge transfer resistance and diffusion transfer resistance increased with the increase in hydraulic pressure. Denaturing gradient gel electrophoresis of PCR-amplified partial 16S rRNA genes demonstrated that the similarity among anodic biofilm communities under different hydraulic pressures was ? 90%, and the communities of all MFCs were dominated by Geobacter sp. These results suggested that the reduction in power output of the single chamber air-cathode MFC under high hydraulic pressures can be attributed to water flooding of the cathode and suppression the metabolism of anodic exoelectrogenic bacteria. PMID:24514078

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

    SciTech Connect

    Li Zhipeng; Mori, Toshiyuki; Auchterlonie, Graeme John; Zou Jin; Drennan, John

    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.

  18. A Li-O₂/air battery using an inorganic solid-state air cathode.

    PubMed

    Wang, Xiaofei; Zhu, Ding; Song, Ming; Cai, Shengrong; Zhang, Lei; Chen, Yungui

    2014-07-23

    The "(-) lithium (Li) anode|organic anolyte + inorganic catholyte|solid-state cathode (+)" Li-O2/air battery based on an inorganic solid-state air cathode was fabricated with a simple method. The electrochemical performance and reaction products of the Li-O2/air batteries under pure O2 and ambient air were investigated, respectively. The inorganic Li-ion conductive solid-state electrolyte Li1.3Al0.3Ti1.7(PO4)3 was stable during cycling and avoided the decomposition and volatilization problems that conventional organic electrolytes faced. Moreover, the porous air cathode provided a sufficient gas-phase O2-transport channel, facilitating the achievement of a high capacity of 14192 or 7869 mA h g(-1) under pure O2 or ambient air, respectively. Our results demonstrate that the Li-O2/air battery using an inorganic porous air cathode has a great potential for practical application. PMID:24959838

  19. Influence of cathode gas diffusion media on the performance of the PEMFCs

    NASA Astrophysics Data System (ADS)

    Prasanna, M.; Ha, H. Y.; Cho, E. A.; Hong, S.-A.; Oh, I.-H.

    The influence of gas diffusion media (GDM), i.e. carbon paper, on PEMFCs was studied. The study was based on GDM thickness pore size distribution, air-permeability, electronic resistance and hydrophobicity. Cell performances were correlated with the physical properties of the GDM and reasonable agreements were made based on the oxygen-gain which was regarded as an index of mass transfer in the cathode when the reactant was changed from neat oxygen to air. The results show that gas permeability and pore size diameter of the GDM are the important factors in the performance of the cell compared to all other physical properties. When the mean pore size diameter is in the range of about 25-40 μm, thickness of the GDM and its gas permeability play crucial role in lowering oxygen-gain. GDM with larger pore size shows severe flooding in cathodes compared to GDM with smaller pore diameter. Optimized Teflon content in the GDM was found to be 20% whereas above this content gas permeability of the GDM decreased substantially due to decreased porosity.

  20. Cubic PdNP-based air-breathing cathodes integrated in glucose hybrid biofuel cells.

    PubMed

    Faggion Junior, D; Haddad, R; Giroud, F; Holzinger, M; Maduro de Campos, C E; Acuña, J J S; Domingos, J B; Cosnier, S

    2016-05-21

    Cubic Pd nanoparticles (PdNPs) were synthesized using ascorbic acid as a reducing agent and were evaluated for the catalytic oxygen reduction reaction. PdNPs were confined with multiwalled carbon nanotube (MWCNT) dispersions to form black suspensions and these inks were dropcast onto glassy carbon electrodes. Different nanoparticle sizes were synthesized and investigated upon oxygen reduction capacities (onset potential and electrocatalytic current densities) under O2 saturated conditions at varying pH values. Strong evidence of O2 diffusion limitation was demonstrated. In order to overcome oxygen concentration and diffusion limitations in solution, we used a gas diffusion layer to create a PdNP-based air-breathing cathode, which delivered -1.5 mA cm(-2) at 0.0 V with an onset potential of 0.4 V. This air-breathing cathode was combined with a specially designed phenanthrolinequinone/glucose dehydrogenase-based anode to form a complete glucose/O2 hybrid bio-fuel cell providing an open circuit voltage of 0.554 V and delivering a maximal power output of 184 ± 21 μW cm(-2) at 0.19 V and pH 7.0. PMID:27142300

  1. Diffusion of triethylene glycol (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-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) triethylene glycol; (2) air

  2. Diffusion of air (1); furfural (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-Börnstein 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) furfural

  3. Diffuse and spot mode of cathode arc attachments in an atmospheric magnetically rotating argon arc

    NASA Astrophysics Data System (ADS)

    Chen, Tang; Wang, Cheng; Liao, Meng-Ran; Xia, Wei-Dong

    2016-03-01

    A model including the cathode, near-cathode region, and arc column was constructed. Specifically, a thermal perturbation layer at the arc fringe was calculated in order to couple sheath/presheath modelling with typical arc column modelling. Comparative investigation of two modes of attachment of a dc (100, 150, 200 A) atmospheric-pressure arc in argon to a thermionic cathode made of pure tungsten was conducted. Computational data revealed that there exists two modes of arc discharge: the spot mode, which has an obvious cathode surface temperature peak in the arc attachment centre; and the diffuse mode, which has a flat cathode surface temperature distribution and a larger arc attachment area. The modelling results of the arc attachment agree with previous experimental observations for the diffuse mode. A further 3D simulation is obviously needed to investigate the non-axisymmetrical features, especially for the spot mode.

  4. Lithium-Air Battery: High Performance Cathodes for Lithium-Air Batteries

    SciTech Connect

    2010-08-01

    BEEST Project: Researchers at Missouri S&T are developing an affordable lithium-air (Li-Air) battery that could enable an EV to travel up to 350 miles on a single charge. Today’s EVs run on Li-Ion batteries, which are expensive and suffer from low energy density compared with gasoline. This new Li-Air battery could perform as well as gasoline and store 3 times more energy than current Li-Ion batteries. A Li-Air battery uses an air cathode to breathe oxygen into the battery from the surrounding air, like a human lung. The oxygen and lithium react in the battery to produce electricity. Current Li-Air batteries are limited by the rate at which they can draw oxygen from the air. The team is designing a battery using hierarchical electrode structures to enhance air breathing and effective catalysts to accelerate electricity production.

  5. 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.

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

    SciTech Connect

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

    2015-03-15

    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.

  7. Modeling of hydrogen-air diffusion flame

    NASA Technical Reports Server (NTRS)

    Isaac, K. M.

    1989-01-01

    An analytical and computational study of opposed jet diffusion flame for the purpose of understanding the effects of contaminants in the reactants and thermal diffusion of light species on extinction and reignition of diffusion flames is in progress. The methodologies that have been attempted so far are described. Results using a simple, one-step reaction for the hydrogen-air counterflow diffusion flame are presented. These results show the correct trends in the profiles of chemical species and temperature. The extinction limit can be clearly seen in the plot of temperature vs. Damkohler number.

  8. A novel carbon black graphite hybrid air-cathode for efficient hydrogen peroxide production in bioelectrochemical systems

    NASA Astrophysics Data System (ADS)

    Li, Nan; An, Jingkun; Zhou, Lean; Li, Tian; Li, Junhui; Feng, Cuijuan; Wang, Xin

    2016-02-01

    Carbon black and graphite hybrid air-cathode is proved to be effective for H2O2 production in bioelectrochemical systems. The optimal mass ratio of carbon black to graphite is 1:5 with the highest H2O2 yield of 11.9 mg L-1 h-1 cm-2 (12.3 mA cm-2). Continuous flow is found to improve the current efficiency due to the avoidance of H2O2 accumulation. In the biological system, the highest H2O2 yield reaches 3.29 mg L-1h-1 (0.079 kg m-3day-1) with a current efficiency of 72%, which is higher than the abiotic system at the same current density. H2O2 produced in this system is mainly from the oxygen diffused through this air-cathode (>66%), especially when a more negative cathode potential is applied (94% at -1.0 V). This hybrid air-cathode has advantages of high H2O2 yield, high current density and no need of aeration, which make the synthesis of H2O2 more efficient and economical.

  9. Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells

    SciTech Connect

    WANG,Z.H.; WANG,C.Y.; CHEN,KEN S.

    2000-03-20

    Two-phase flow and transport of reactants and products in the air cathode of proton exchange membrane (PEM) fuel cells is studied analytically and numerically. Four regimes of water distribution and transport are classified by defining three threshold current densities and a maximum current density. They correspond to first appearance of liquid water at the membrane/cathode interface, extension of the gas-liquid two-phase zone to the cathode/channel interface, saturated moist air exiting the gas channel, and complete consumption of oxygen by the electrochemical reaction. When the cell operates above the first threshold current density, liquid water appears and a two-phase zone forms within the porous cathode. A two-phase, multi-component mixture model in conjunction with a finite-volume-based computational fluid dynamics (CFD) technique is applied to simulate the cathode operation in this regime. The model is able to handle the situation where a single-phase region co-exists with a two-phase zone in the air cathode. For the first time, the polarization curve as well as water and oxygen concentration distributions encompassing both single- and two-phase regimes of the air cathode are presented. Capillary action is found to be the dominant mechanism for water transport inside the two-phase zone. The liquid water saturation within the cathode is predicted to reach 6.3% at 1.4 A/cm{sup 2}.

  10. Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Wang, Z. H.; Wang, C. Y.; Chen, K. S.

    Two-phase flow and transport of reactants and products in the air cathode of proton exchange membrane (PEM) fuel cells is studied analytically and numerically. Single- and two-phase regimes of water distribution and transport are classified by a threshold current density corresponding to first appearance of liquid water at the membrane/cathode interface. When the cell operates above the threshold current density, liquid water appears and a two-phase zone forms within the porous cathode. A two-phase, multicomponent mixture model in conjunction with a finite-volume-based computational fluid dynamics (CFD) technique is applied to simulate the cathode operation in this regime. The model is able to handle the situation where a single-phase region co-exists with a two-phase zone in the air cathode. For the first time, the polarization curve as well as water and oxygen concentration distributions encompassing both single- and two-phase regimes of the air cathode are presented. Capillary action is found to be the dominant mechanism for water transport inside the two-phase zone of the hydrophilic structure. The liquid water saturation within the cathode is predicted to reach 6.3% at 1.4 A cm -2 for dry inlet air.

  11. A hybrid Li-air battery with buckypaper air cathode and sulfuric acid electrolyte

    SciTech Connect

    Li, YF; Huang, K; Xing, YC

    2012-10-30

    We demonstrate a type of carbon nanotube based buckypaper cathode in a hybrid electrolyte Li-air battery (HyLAB) that showed outstanding discharging performances. The HyLAB has sulfuric acid as the catholyte and a large active electrode area (10 cm(2)). The active cathode layer was made from a buckypaper with 5 wt.% Pt supported on carbon nanotubes (Pt/CNTs) for oxygen reduction and evolution. A similar cathode was constructed with a catalyst of 5 wt.% Pt supported on carbon black (Pt/CB). It is demonstrated that sulfuric acid can achieve high discharging current densities while maintaining relatively high cell potentials. The cell with Pt/CNTs showed a much better performance than with Pt/CB at high current densities. The HyLAB with Pt/CNTs achieved a discharging capacity of 306 mAh/g and a cell voltage of 3.15 V at 0.2 mA/cm(2). The corresponding specific energy is 1067 Wh/kg based on the total weight of the sulfuric acid. Slow decrease in performance was observed, but it can be recovered by refilling the cell with new electrolyte after continuous discharging of more than 75 h. A charge-discharge experiment at 0.2 mA/cm(2) showed that the cell was rechargeable with a capacity of more than 300 mAh/g. (c) 2012 Elsevier Ltd. All rights reserved.

  12. Isotope effect of mercury diffusion in air

    PubMed Central

    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

  13. Silver electrodeposition on the activated carbon air cathode for performance improvement in microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Pu, Liangtao; Li, Kexun; Chen, Zhihao; Zhang, Peng; Zhang, Xi; Fu, Zhou

    2014-12-01

    The present work was to study silver electrodeposition on the activated carbon (AC) air cathode for performance improvement in microbial fuel cells (MFCs). The treated cathodes were proved to be effective to enhance the performance of MFCs. The maximum power density of MFC with silver electrodeposition time of 50 s (Ag-50) cathode was 1080 ± 60 mW m-2, 69% higher than the bare AC air cathode. X-ray photoelectron spectroscopy (XPS) results showed that zero-valent, monovalent and divalent silver were present to transform mutually, which illustrated that the oxygen reduction reaction (ORR) at the cathode took place through four-electron pathway. From electrochemical impedance spectroscopy (EIS) analysis, the electrodeposition method made the total resistance of the electrodes largely reduced. Meanwhile the deposited silver had no toxic effects on anode culture but inhibited the biofilm growth of the cathodes. This kind of antimicrobial efficient cathode, prepared with a simple, fast and economical method, was of good benefit to the performance improvement of MFCs.

  14. Air-cathode microbial fuel cell array: a device for identifying and characterizing electrochemically active microbes.

    PubMed

    Hou, Huijie; Li, Lei; de Figueiredo, Paul; Han, Arum

    2011-01-15

    Microbial fuel cells (MFCs) have generated excitement in environmental and bioenergy communities due to their potential for coupling wastewater treatment with energy generation and powering diverse devices. The pursuit of strategies such as improving microbial cultivation practices and optimizing MFC devices has increased power generating capacities of MFCs. However, surprisingly few microbial species with electrochemical activity in MFCs have been identified because current devices do not support parallel analyses or high throughput screening. We have recently demonstrated the feasibility of using advanced microfabrication methods to fabricate an MFC microarray. Here, we extend these studies by demonstrating a microfabricated air-cathode MFC array system. The system contains 24 individual air-cathode MFCs integrated onto a single chip. The device enables the direct and parallel comparison of different microbes loaded onto the array. Environmental samples were used to validate the utility of the air-cathode MFC array system and two previously identified isolates, 7Ca (Shewanella sp.) and 3C (Arthrobacter sp.), were shown to display enhanced electrochemical activities of 2.69 mW/m(2) and 1.86 mW/m(2), respectively. Experiments using a large scale conventional air-cathode MFC validated these findings. The parallel air-cathode MFC array system demonstrated here is expected to promote and accelerate the discovery and characterization of electrochemically active microbes. PMID:20655725

  15. 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

  16. 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.

  17. External CO2 and water supplies for enhancing electrical power generation of air-cathode microbial fuel cells.

    PubMed

    Ishizaki, So; Fujiki, Itto; Sano, Daisuke; Okabe, Satoshi

    2014-10-01

    Alkalization on the cathode electrode limits the electrical power generation of air-cathode microbial fuel cells (MFCs), and thus external proton supply to the cathode electrode is essential to enhance the electrical power generation. In this study, the effects of external CO2 and water supplies to the cathode electrode on the electrical power generation were investigated, and then the relative contributions of CO2 and water supplies to the total proton consumption were experimentally evaluated. The CO2 supply decreased the cathode pH and consequently increased the power generation. Carbonate dissolution was the main proton source under ambient air conditions, which provides about 67% of total protons consumed for the cathode reaction. It is also critical to adequately control the water content on the cathode electrode of air-cathode MFCs because the carbonate dissolution was highly dependent on water content. On the basis of these experimental results, the power density was increased by 400% (143.0 3.5 mW/m(2) to 575.0 36.0 mW/m(2)) by supplying a humid gas containing 50% CO2 to the cathode chamber. This study demonstrates that the simultaneous CO2 and water supplies to the cathode electrode were effective to increase the electrical power generation of air-cathode MFCs for the first time. PMID:25181008

  18. Mass transport in gas-diffusion electrodes: A diagnostic tool for fuel-cell cathodes

    SciTech Connect

    Perry, M.L.; Newman, J.; Cairns, E.J. |

    1998-01-01

    Two mathematical models of gas-diffusion electrodes, one for liquid electrolytes and one for ion-exchange polymer electrolytes, are presented to investigate the effects of mass-transport limitations on the polarization characteristics of a reaction obeying Tafel kinetics. The focus is on low-temperature fuel-cell cathodes, and in particular, contrasting two limiting cases that may be encountered at high current densities: control by kinetics and dissolved oxygen mass transport vs. control by kinetics and ionic mass transport. It is shown that two distinct double Tafel slopes may arise from these two limiting cases. The former is first order, and the latter is half-order with respect to oxygen concentration. How the modeling results may be applied to diagnose the performance of fuel-cell cathodes is also presented. Since the ionic-mass-transport-limited case has generally been neglected in previous gas-diffusion electrode models, specific examples of fuel-cell cathode data from the literature which display the behavior predicted by the models in this case are given and briefly discussed.

  19. A SnO2-Based Cathode Catalyst for Lithium-Air Batteries.

    PubMed

    Mei, Delong; Yuan, Xianxia; Ma, Zhong; Wei, Ping; Yu, Xuebin; Yang, Jun; Ma, Zi-Feng

    2016-05-25

    SnO2 and SnO2@C have been successfully synthesized with a simple hydrothermal procedure combined with heat treatment, and their performance as cathode catalysts of Li-air batteries has been comparatively evaluated and discussed. The results show that both SnO2 and SnO2@C are capable of catalyzing oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) at the cathode of Li-air batteries, but the battery with SnO2@C displays better performance due to its unique higher conductivity, larger surface area, complex pore distribution, and huge internal space. PMID:27152996

  20. Titanium-Aluminum Bilayer Cathode for Small-Molecular Organic Solar Cells with Prolonged Life upon Exposure to Air

    NASA Astrophysics Data System (ADS)

    Cao, Huanqi; Takezoe, Hideo; Ishikawa, Ken

    2013-04-01

    The in-air stability of unencapsulated small-molecular organic solar cells (OSCs) was improved by 3 orders of magnitude by using a Ti (inner)-Al (exposed to air) bilayer cathode, in comparison with that of Al-monolayer-cathode OSCs. The stability of the unencapsulated bilayer-cathode OSCs (AlTi-OSCs) was comparable to that of encapsulated ones. These devices were degradation-free in air for more than 3 months. Under weathering tests, the unencapsulated AlTi-OSCs recovered their performance in the idle periods. This provides us with an effective and economical approach to prevent degradation of the extensively studied aluminum-cathode OSCs.

  1. 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.

  2. Rechargeable Li-CO2 batteries with carbon nanotubes as air cathodes.

    PubMed

    Zhang, Xin; Zhang, Qiang; Zhang, Zhang; Chen, Yanan; Xie, Zhaojun; Wei, Jinping; Zhou, Zhen

    2015-10-01

    Rechargeable Li-CO2 batteries offer great promise by combining carbon capture and energy technology. However, the discharge product Li2CO3 is difficult to decompose upon recharging. In this work, carbon nanotubes (CNTs) with high electrical conductivity and porous three-dimensional networks were firstly explored as air cathodes for rechargeable Li-CO2 batteries. PMID:26290015

  3. Lithium and sodium battery cathode materials: computational insights into voltage, diffusion and nanostructural properties.

    PubMed

    Islam, M Saiful; Fisher, Craig A J

    2014-01-01

    Energy storage technologies are critical in addressing the global challenge of clean sustainable energy. Major advances in rechargeable batteries for portable electronics, electric vehicles and large-scale grid storage will depend on the discovery and exploitation of new high performance materials, which requires a greater fundamental understanding of their properties on the atomic and nanoscopic scales. This review describes some of the exciting progress being made in this area through use of computer simulation techniques, focusing primarily on positive electrode (cathode) materials for lithium-ion batteries, but also including a timely overview of the growing area of new cathode materials for sodium-ion batteries. In general, two main types of technique have been employed, namely electronic structure methods based on density functional theory, and atomistic potentials-based methods. A major theme of much computational work has been the significant synergy with experimental studies. The scope of contemporary work is highlighted by studies of a broad range of topical materials encompassing layered, spinel and polyanionic framework compounds such as LiCoO2, LiMn2O4 and LiFePO4 respectively. Fundamental features important to cathode performance are examined, including voltage trends, ion diffusion paths and dimensionalities, intrinsic defect chemistry, and surface properties of nanostructures. PMID:24202440

  4. Study of azo dye decolorization and determination of cathode microorganism profile in air-cathode microbial fuel cells.

    PubMed

    Kumru, Mert; Eren, Hilal; Catal, Tunc; Bermek, Hakan; Akarsubaşi, Alper Tunga

    2012-09-01

    Five textile azo dyes, as part of an artificial mixture, were treated in single-chamber air-cathode microbial fuel cells while simultaneously utilizing acetate for electricity production. Remazol Black, Remazol Brilliant Blue, Remazol Turquoise Blue, Reactive Yellow and Reactive Red at concentrations of 40 or 80 mg L(-1) were decolorized to a similar extent, at averages of 78, 95, 53, 93 and 74%, respectively, in 24 hours. During the process of decolorization, electricity generation from acetate oxidation continued. Power densities obtained in the presence of textile dyes ranged from 347 to 521 mW m(-2) at the current density range of 0.071 - 0.086 mA cm(-2). Microbial community analyses of cathode biofilm exhibited dynamic changes in abundant species following dye decolorization. Upon the addition of the first dye, a major change (63%) in microbial diversity was observed; however, subsequent addition of other dyes did not affect the community profile significantly. Actinobacteria, Aquamicrobium, Mesorhizobium, Ochrobactrum, Thauera, Paracoccus, Achromobacter and Chelatacoccus affiliated phylotypes were the major phylotypes detected. Our results demonstrate that microbial fuel cells could be a promising alternative for treatment of textile wastewaters and an active bacterial community can rapidly be established for simultaneous azo dye decolorization and sustainable electricity generation. PMID:23240212

  5. 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

  6. Effects of the carbon powder characteristics in the cathode gas diffusion layer on the performance of polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    Antolini, E.; Passos, R. R.; Ticianelli, E. A.

    The effects of two different carbon powders (oil-furnace carbon black and acetylene-black) as materials for carbon cloth-based cathode gas diffusion layers on the performance of polymer electrolyte fuel cell (PEFC) electrodes were investigated. The carbon powder characteristics affect the reversible potential of the cell ( E°) and both the linear and non-linear polarization components. The best fuel cell performance was obtained at an oxygen pressure of 5 atm with acetylene-black in the cathode gas diffusion layer.

  7. Diffusion of pent-1-ene (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-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) pent-1-ene; (2) air

  8. Study of Stable Cathodes and Electrolytes for High Specific Density Lithium-Air Battery

    NASA Technical Reports Server (NTRS)

    Hernandez-Lugo, Dionne M.; Wu, James; Bennett, William; Ming, Yu; Zhu, Yu

    2015-01-01

    Future NASA missions require high specific energy battery technologies, greater than 400 Wh/kg. Current NASA missions are using "state-of-the-art" (SOA) Li-ion batteries (LIB), which consist of a metal oxide cathode, a graphite anode and an organic electrolyte. NASA Glenn Research Center is currently studying the physical and electrochemical properties of the anode-electrolyte interface for ionic liquid based Li-air batteries. The voltage-time profiles for Pyr13FSI and Pyr14TFSI ionic liquids electrolytes studies on symmetric cells show low over-potentials and no dendritic lithium morphology. Cyclic voltammetry measurements indicate that these ionic liquids have a wide electrochemical window. As a continuation of this work, sp2 carbon cathode and these low flammability electrolytes were paired and the physical and electrochemical properties were studied in a Li-air battery system under an oxygen environment.

  9. 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 1041 ± 12 mW m-2 in an unbuffered medium (0.5 g L-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.

  10. 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 α-, β-, and γ-MnO2 nanowires, α-MnO2 nanospheres, and α-MnO2 nanowires on carbon ( α-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. α-MnO2 had the highest discharge capacity in the LiTFSi/TEGDME electrolyte (2500 mAh/g), whilst α-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 γ-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.

  11. Bilirubin oxidase based enzymatic air-breathing cathode: Operation under pristine and contaminated conditions.

    PubMed

    Santoro, Carlo; Babanova, Sofia; Erable, Benjamin; Schuler, Andrew; Atanassov, Plamen

    2016-04-01

    The performance of bilirubin oxidase (BOx) based air breathing cathode was constantly monitored over 45 days. The effect of electrolyte composition on the cathode oxygen reduction reaction (ORR) output was investigated. Particularly, deactivation of the electrocatalytic activity of the enzyme in phosphate buffer saline (PBS) solution and in activated sludge (AS) was evaluated. The greatest drop in current density was observed during the first 3 days of constant operation with a decrease of ~60 μA cm(-2) day(-1). The rate of decrease slowed to ~10 μA cm(-2) day(-1) (day 3 to 9) and then to ~1.5 μA cm(-2)day(-1) thereafter (day 9 to 45). Despite the constant decrease in output, the BOx cathode generated residual current after 45 days operations with an open circuit potential (OCP) of 475 mV vs. Ag/AgCl. Enzyme deactivation was also studied in AS to simulate an environment close to the real waste operation with pollutants, solid particles and bacteria. The presence of low-molecular weight soluble contaminants was identified as the main reason for an immediate enzymatic deactivation within few hours of cathode operation. The presence of solid particles and bacteria does not affect the natural degradation of the enzyme. PMID:26544631

  12. Efficient polymer light-emitting diode with air-stable aluminum cathode

    NASA Astrophysics Data System (ADS)

    Abbaszadeh, D.; Wetzelaer, G. A. H.; Doumon, N. Y.; Blom, P. W. M.

    2016-03-01

    The fast degradation of polymer light-emitting diodes (PLEDs) in ambient conditions is primarily due to the oxidation of highly reactive metals, such as barium or calcium, which are used as cathode materials. Here, we report the fabrication of PLEDs using an air-stable partially oxidized aluminum (AlOx) cathode. Usually, the high work function of aluminum (4.2 eV) imposes a high barrier for injecting electrons into the lowest unoccupied molecular orbital (LUMO) of the emissive polymer (2.9 eV below the vacuum level). By partially oxidizing aluminum, its work function is decreased, but not sufficiently low for efficient electron injection. Efficient injection is obtained by inserting an electron transport layer of poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT), which has its LUMO at 3.3 eV below vacuum, between the AlOx cathode and the emissive polymer. The intermediate F8BT layer not only serves as a hole-blocking layer but also provides an energetic staircase for electron injection from AlOx into the emissive layer. PLEDs with an AlOx cathode and F8BT interlayer exhibit a doubling of the efficiency as compared to conventional Ba/Al PLEDs, and still operate even after being kept in ambient atmosphere for one month without encapsulation.

  13. 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

  14. Dry Pressed Holey Graphene Composites for Li-air Battery Cathodes

    NASA Astrophysics Data System (ADS)

    Lacey, Steven; Lin, Yi; Hu, Liangbing

    Graphene is considered an ``omnipotent'' material due to its unique structural characteristics and chemical properties. By heating graphene powder in an open-ended tube furnace, a novel compressible carbon material, holey graphene (hG), can be created with controlled porosity and be further decorated with nanosized catalysts to increase electrocatalytic activity. All hG-based materials were characterized using various microscopic and spectroscopic techniques to obtain morphological, topographical, and chemical information as well as to identify any disordered/crystalline phases. In this work, an additive-free dry press method was employed to press the hG composite materials into high mass loading mixed, sandwich, and double-decker Li-air cathode architectures using a hydraulic press. The sandwich and double-decker (i.e. Big Mac) cathode architectures are the first of its kind and can be discharged for more than 200 hours at a current density of 0.2 mA/cm2. The scalable, binderless, and solventless dry press method and unique Li-air cathode architectures presented here greatly advance electrode fabrication possibilities and could promote future energy storage advancements. Support appreciated from the NASA Internships Fellowships Scholarships (NIFS) Program.

  15. One-dimensional manganese-cobalt oxide nanofibres as bi-functional cathode catalysts for rechargeable metal-air batteries

    NASA Astrophysics Data System (ADS)

    Jung, Kyu-Nam; Hwang, Soo Min; Park, Min-Sik; Kim, Ki Jae; Kim, Jae-Geun; Dou, Shi Xue; Kim, Jung Ho; Lee, Jong-Won

    2015-01-01

    Rechargeable metal-air batteries are considered a promising energy storage solution owing to their high theoretical energy density. The major obstacles to realising this technology include the slow kinetics of oxygen reduction and evolution on the cathode (air electrode) upon battery discharging and charging, respectively. Here, we report non-precious metal oxide catalysts based on spinel-type manganese-cobalt oxide nanofibres fabricated by an electrospinning technique. The spinel oxide nanofibres exhibit high catalytic activity towards both oxygen reduction and evolution in an alkaline electrolyte. When incorporated as cathode catalysts in Zn-air batteries, the fibrous spinel oxides considerably reduce the discharge-charge voltage gaps (improve the round-trip efficiency) in comparison to the catalyst-free cathode. Moreover, the nanofibre catalysts remain stable over the course of repeated discharge-charge cycling; however, carbon corrosion in the catalyst/carbon composite cathode degrades the cycling performance of the batteries.

  16. One-dimensional manganese-cobalt oxide nanofibres as bi-functional cathode catalysts for rechargeable metal-air batteries

    PubMed Central

    Jung, Kyu-Nam; Hwang, Soo Min; Park, Min-Sik; Kim, Ki Jae; Kim, Jae-Geun; Dou, Shi Xue; Kim, Jung Ho; Lee, Jong-Won

    2015-01-01

    Rechargeable metal-air batteries are considered a promising energy storage solution owing to their high theoretical energy density. The major obstacles to realising this technology include the slow kinetics of oxygen reduction and evolution on the cathode (air electrode) upon battery discharging and charging, respectively. Here, we report non-precious metal oxide catalysts based on spinel-type manganese-cobalt oxide nanofibres fabricated by an electrospinning technique. The spinel oxide nanofibres exhibit high catalytic activity towards both oxygen reduction and evolution in an alkaline electrolyte. When incorporated as cathode catalysts in Zn-air batteries, the fibrous spinel oxides considerably reduce the discharge-charge voltage gaps (improve the round-trip efficiency) in comparison to the catalyst-free cathode. Moreover, the nanofibre catalysts remain stable over the course of repeated discharge-charge cycling; however, carbon corrosion in the catalyst/carbon composite cathode degrades the cycling performance of the batteries. PMID:25563733

  17. Use of pyrolyzed iron ethylenediaminetetraacetic acid modified activated carbon as air-cathode catalyst in microbial fuel cells.

    PubMed

    Xia, Xue; Zhang, Fang; Zhang, Xiaoyuan; Liang, Peng; Huang, Xia; Logan, Bruce E

    2013-08-28

    Activated carbon (AC) is a cost-effective catalyst for the oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). To enhance the catalytic activity of AC cathodes, AC powders were pyrolyzed with iron ethylenediaminetetraacetic acid (FeEDTA) at a weight ratio of FeEDTA:AC = 0.2:1. MFCs with FeEDTA modified AC cathodes and a stainless steel mesh current collector produced a maximum power density of 1580 ± 80 mW/m(2), which was 10% higher than that of plain AC cathodes (1440 ± 60 mW/m(2)) and comparable to Pt cathodes (1550 ± 10 mW/m(2)). Further increases in the ratio of FeEDTA:AC resulted in a decrease in performance. The durability of AC-based cathodes was much better than Pt-catalyzed cathodes. After 4.5 months of operation, the maximum power density of Pt cathode MFCs was 50% lower than MFCs with the AC cathodes. Pyridinic nitrogen, quaternary nitrogen and iron species likely contributed to the increased activity of FeEDTA modified AC. These results show that pyrolyzing AC with FeEDTA is a cost-effective and durable way to increase the catalytic activity of AC. PMID:23902951

  18. Fatigue performance of nine bolt materials in air and in sea water with cathodic protection

    NASA Astrophysics Data System (ADS)

    Slind, Tor; Eggen, Tor Gunnar; Bardal, Einar; Haagensen, Per Jahn

    1992-07-01

    The hydrogen sensitivity of various bolt materials for subsea use was determined. The fatigue crack growth rates of eight materials were found in air and in artificial sea water 3 percent NaCl solution with Cathodic Protection (CP). SN tests of threaded bolts using a high mean stress were carried out in sea water with CP for two materials. The materials are grouped in three classes on their hydrogen susceptibility based on the crack growth results. Design curves determined from the SN test results are compared with various standard design curves.

  19. 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.

  20. Diffusion barriers in modified air brazes

    DOEpatents

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

    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.

  1. Soot Formation in Hydrocarbon/Air Laminar Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Sunderland, P. B.; Faeth, G. M.

    1994-01-01

    Soot processes within hydrocarbon/air diffusion flames are important because they affect the durability and performance of propulsion systems, the hazards of unwanted fires, the pollutant and particulate emissions from combustion processes, and the potential for developing computational combustion. Motivated by these observations, this investigation involved an experimental study of the structure and soot properties of round laminar jet diffusion flames, seeking an improved understanding of soot formation (growth and nucleation) within diffusion flames. The present study extends earlier work in this laboratory concerning laminar smoke points (l) and soot formation in acetylene/air laminar jet diffusion flames (2), emphasizing soot formation in hydrocarbon/air laminar jet diffusion flames for fuels other than acetylene. In the flame system, acetylene is the dominant gas species in the soot formation region and both nucleation and growth were successfully attributed to first-order reactions of acetylene, with nucleation exhibiting an activation energy of 32 kcal/gmol while growth involved negligible activation energy and a collision efficiency of O.53%. In addition, soot growth in the acetylene diffusion flames was comparable to new soot in premixed flame (which also has been attributed to first-order acetylene reactions). In view of this status, a major issue is the nature of soot formation processes in diffusion flame involving hydrocarbon fuels other than acetylene. In particular, information is needed about th dominant gas species in the soot formation region and the impact of gas species other than acetylene on soot nucleation and growth.

  2. Enhanced performance of an air-cathode microbial fuel cell with oxygen supply from an externally connected algal bioreactor.

    PubMed

    Kakarla, Ramesh; Kim, Jung Rae; Jeon, Byong-Hun; Min, Booki

    2015-11-01

    An algae bioreactor (ABR) was externally connected to air-cathode microbial fuel cells (MFCs) to increase power generation by supplying a high amount of oxygen to cathode electrode. The MFC with oxygen fed from ABR produced maximum cell voltage and cathode potential at a fixed loading of 459 mV and 10 mV, respectively. During polarization analysis, the MFC displayed a maximum power density of 0.63 W/m(2) (at 2.06 A/m(2)) using 39.2% O2 from ABR, which was approximately 30% higher compared with use of atmospheric air (0.44 W/m(2), 20.8% O2,). The cyclic voltammogram analysis exhibited a higher reduction current of -137 mA with 46.5% O2 compared to atmospheric air (-115 mA). Oxygen supply by algae bioreactor to air-cathode MFC could also maintain better MFC performance in long term operation by minimizing cathode potential drop over time. PMID:26188984

  3. Co3O4 nanoparticles decorated carbon nanofiber mat as binder-free air-cathode for high performance rechargeable zinc-air batteries.

    PubMed

    Li, Bing; Ge, Xiaoming; Goh, F W Thomas; Hor, T S Andy; Geng, Dongsheng; Du, Guojun; Liu, Zhaolin; Zhang, Jie; Liu, Xiaogang; Zong, Yun

    2015-02-01

    An efficient, durable and low cost air-cathode is essential for a high performance metal-air battery for practical applications. Herein, we report a composite bifunctional catalyst, Co3O4 nanoparticles-decorated carbon nanofibers (CNFs), working as an efficient air-cathode in high performance rechargeable Zn-air batteries (ZnABs). The particles-on-fibers nanohybrid materials were derived from electrospun metal-ion containing polymer fibers followed by thermal carbonization and a post annealing process in air at a moderate temperature. Electrochemical studies suggest that the nanohybrid material effectively catalyzes oxygen reduction reaction via an ideal 4-electron transfer process and outperforms Pt/C in catalyzing oxygen evolution reactions. Accordingly, the prototype ZnABs exhibit a low discharge-charge voltage gap (e.g. 0.7 V, discharge-charge at 2 mA cm(-2)) with higher stability and longer cycle life compared to their counterparts constructed using Pt/C in air-cathode. Importantly, the hybrid nanofiber mat readily serves as an integrated air-cathode without the need of any further modification. Benefitting from its efficient catalytic activities and structural advantages, particularly the 3D architecture of highly conductive CNFs and the high loading density of strongly attached Co3O4 NPs on their surfaces, the resultant ZnABs show significantly improved performance with respect to the rate capability, cycling stability and current density, promising good potential in practical applications. PMID:25522330

  4. Enhanced hydroxyl radical generation in the combined ozonation and electrolysis process using carbon nanotubes containing gas diffusion cathode.

    PubMed

    Wu, Donghai; Lu, Guanghua; Zhang, Ran; Lin, Qiuhong; Yan, Zhenhua; Liu, Jianchao; Li, Yi

    2015-10-01

    Combination of ozone together with electrolysis (ozone-electrolysis) is a promising wastewater treatment technology. This work investigated the potential use of carbon nanotube (CNT)-based gas diffusion cathode (GDC) for ozone-electrolysis process employing hydroxyl radicals (·OH) production as an indicator. Compared with conventional active carbon (AC)-polytetrafluoroethylene (PTFE) and carbon black (CB)-PTFE cathodes, the production of ·OH in the coupled process was improved using CNTs-PTFE GDC. Appropriate addition of acetylene black (AB) and pore-forming agent Na2SO4 could enhance the efficiency of CNTs-PTFE GDC. The optimum GDC composition was obtained by response surface methodology (RSM) analysis and was determined as CNTs 31.2 wt%, PTFE 60.6 wt%, AB 3.5 wt%, and Na2SO4 4.7 wt%. Moreover, the optimized CNT-based GDC exhibited much more effective than traditional Ti and graphite cathodes in Acid Orange 7 (AO7) mineralization and possessed the desirable stability without performance decay after ten times reaction. The comparison tests revealed that peroxone reaction was the main pathway of ·OH production in the present system, and cathodic reduction of ozone could significantly promote ·OH generation. These results suggested that application of CNT-based GDC offers considerable advantages in ozone-electrolysis of organic wastewater. PMID:26036588

  5. Olive mill wastewater treatment in single-chamber air-cathode microbial fuel cells.

    PubMed

    Bermek, Hakan; Catal, Tunc; Akan, S Süha; Ulutaş, Mehmet Sefa; Kumru, Mert; Özgüven, Mine; Liu, Hong; Özçelik, Beraat; Akarsubaşı, Alper Tunga

    2014-04-01

    Olive mill wastewaters create significant environmental issues in olive-processing countries. One of the most hazardous groups of pollutants in these wastewaters is phenolic compounds. Here, olive mill wastewater was used as substrate and treated in single-chamber air-cathode microbial fuel cells. Olive mill wastewater yielded a maximum voltage of 381 mV on an external resistance of 1 kΩ. Notable decreases in the contents of 3,4-dihydroxybenzoic acid, tyrosol, gallic acid and p-coumaric acid were detected. Chemical oxygen demand removal rates were 65 % while removal of total phenolics by the process was lower (49 %). Microbial community analysis during the olive mill wastewater treating MFC has shown that both exoelectrogenic and phenol-degrading microorganisms have been enriched during the operation. Brevundimonas-, Sphingomonas- and Novosphingobium-related phylotypes were enriched on the anode biofilm, while Alphaproteobacteria and Bacteriodetes dominated the cathode biofilm. As one of the novel studies, it has been demonstrated that recalcitrant olive mill wastewaters could be treated and utilized for power generation in microbial fuel cells. PMID:24165748

  6. Electron diffusion through the baffle aperture of a hollow cathode thruster

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    The use of a hollow cathode in place of an oxide cathode to increase thruster operating lifetimes requires, among other things, the addition of a baffle to restrict the flow of electrons from the hollow cathode. A theoretical model is developed which relates the baffle aperture area of a hollow-cathode thruster to the magnetic flux density and plasma properties in the aperture region, with the result that this model could be used as an aid in thruster design. Extensive Langmuir probing is undertaken to verify the validity of the model and demonstrate its capability. It is shown that the model can be used to calculate the aperture area required to effect discharge operation at a specified discharge voltage and arc current.

  7. Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells II. Role of Ni diffusion on LSM performance

    SciTech Connect

    Zhou, Xiao Dong; Simner, Steven P.; Templeton, Jared W.; Nie, Zimin; Stevenson, Jeffry W.; Gorman, B. P.

    2010-03-26

    The sintering of a standard (La0.8Sr0.2)0.98MnO3 (LSM-20) solid oxide fuel cell cathode composition (in the temperature range of 1050-1200C) on anode-supported cells utilizing a Ni-YSZ anode and thin YSZ electrolyte (<10 ?m thickness) has revealed the need for a protective ceria interlayer to prevent a detrimental interaction between the YSZ and the LSM. The interaction, however, is not the typically assumed formation of insulating La- and/or Sr-zirconate, but rather the result of Ni diffusion from the anode through the YSZ electrolyte and into the LSM resulting in coarsening and increased densification of the LSM microstructure. As an alternative to the use of a protective ceria interlayer, the presence of YSZ in the cathode material was able to suppress coarsening of LSM, thereby significantly improving the electrochemical performance.

  8. Practical method for diffusion welding of steel plate in air.

    NASA Technical Reports Server (NTRS)

    Moore, T. J.; Holko, K. H.

    1972-01-01

    Description of a simple and easily applied method of diffusion welding steel plate in air which does not require a vacuum furnace or hot press. The novel feature of the proposed welding method is that diffusion welds are made in air with deadweight loading. In addition, the use of an autogenous (self-generated) surface-cleaning principle (termed 'auto-vac cleaning') to reduce the effects of surface oxides that normally hinder diffusion welding is examined. A series of nine butt joints were diffusion welded in thick sections of AISI 1020 steel plate. Diffusion welds were attempted at three welding temperatures (1200, 1090, and 980 C) using a deadweight pressure of 34,500 N/sq m (5 psi) and a two-hour hold time at temperature. Auto-vac cleaning operations prior to welding were also studied for the same three temperatures. Results indicate that sound welds were produced at the two higher temperatures when the joints were previously fusion seal welded completely around the periphery. Also, auto-vac cleaning at 1200 C for 2-1/2 hours prior to diffusion welding was highly beneficial, particularly when subsequent welding was accomplished at 1090 C.

  9. Li Diffusion and High-Voltage Cycling Behavior of Thin-Film LiCoO2 Cathodes

    SciTech Connect

    Jang, Y.-I.

    2001-10-02

    Mass transport and thermodynamic properties of Li{sub x}CoO{sub 2} were studied by the potentiostatic intermittent titration technique (PITT) using solid-state thin-film batteries that provide a well-defined diffusion geometry. Both the chemical diffusion coefficient and the thermodynamic factor have minima at the phase boundaries of the Li/vacancy ordered phase ''Li{sub 0.5}CoO{sub 2}''. The self-diffusion coefficient of Li has a minimum at x = 0.5 associated with the Li/vacancy ordering. As the degree of ordering increases, the nonmonotonic variations become more pronounced when approaching x = 0.5 in Li{sub x}CoO{sub 2}. We also show that thin-film LiCoO{sub 2} cathodes having grains of sub-micrometer size combined with the Li upon electrolyte exhibit excellent capacity retention when charged up to 4.5 V.

  10. Mineralization of pentachlorophenol with enhanced degradation and power generation from air cathode microbial fuel cells.

    PubMed

    Huang, Liping; Gan, Linlin; Wang, Ning; Quan, Xie; Logan, Bruce E; Chen, Guohua

    2012-09-01

    The combined anaerobic-aerobic conditions in air-cathode single-chamber MFCs were used to completely mineralize pentachlorophenol (PCP; 5 mg/L), in the presence of acetate or glucose. Degradation rates of 0.140 0.011 mg/L-h (acetate) and 0.117 0.009 mg/L-h (glucose) were obtained with maximum power densities of 7.7 1.1 W/m(3) (264 39 W/m(2), acetate) and 5.1 0.1 W/m(3) (175 5 W/m(2), glucose). At a higher PCP concentration of 15 mg/L, PCP degradation rates increased to 0.171 0.01 mg/L-h (acetate) and 0.159 0.011 mg/L-h (glucose). However, power was inversely proportional to initial PCP concentration, with decreases of 0.255 W/mg PCP (acetate) and 0.184 W/mg PCP (glucose). High pH (9.0, acetate; 8.0, glucose) was beneficial to exoelectrogenic activities and power generation, whereas an acidic pH = 5.0 decreased power but increased PCP degradation rates (0.195 0.002 mg/L-h, acetate; 0.173 0.005 mg/L-h, glucose). Increasing temperature from 22 to 35C enhanced power production by 37% (glucose) to 70% (acetate), and PCP degradation rates (0.188 0.01 mg/L-h, acetate; 0.172 0.009 mg/L-h, glucose). Dominant exoelectrogens of Pseudomonas (acetate) and Klebsiella (glucose) were identified in the biofilms. These results demonstrate that PCP degradation using air-cathode single-chamber MFCs may be a promising process for remediation of water contaminated with PCP as well as for power generation. PMID:22392229

  11. Hybrid Li-air battery cathodes with sparse carbon nanotube arrays directly grown on carbon fiber papers

    SciTech Connect

    Li, YF; Huang, ZP; Huang, K; Carnahan, D; Xing, YC

    2013-11-01

    Sparsely populated, vertically aligned nitrogen doped carbon nanotube arrays (CNTAs) with dislocated-graphene stacking were grown directly on carbon fiber papers and investigated as hierarchical air cathodes in hybrid Li-air batteries with aqueous catholytes. The CNTAs were made with electrodeposited Ni nanocatalysts, followed by plasma-enhanced chemical vapor deposition. The thus obtained CNTAs can reach a population number density as low as similar to 10(7) per cm(2) on the carbon fibers, achieving an extremely high porosity of over 99% for the active layer in the cathode. The sparse CNTAs not only provide effective pathways for the reacting species, but also show a significantly high catalytic activity, which is found to be comparable to that of a supported Pt electrocatalyst. The high activity of the CNTAs is attributed to the rich graphene edges exposed on the CNT surface and nitrogen doping. Hybrid Li-air batteries with such cathodes have shown a consistent discharging capacity of 710 mA h g(-1) and a specific energy of 2057 W h kg(-1) at 0.5 mA cm(-2). Stable charge-discharge cycling at 0.5 mA cm(-2) showed an average potential difference of 1.35 V, indicative of a relatively small overpotential and high round trip efficiency (71%). Furthermore, the hybrid Li-air battery based on the hierarchical cathode can reach a power density as high as 10.4 mW cm(-2).

  12. Co3O4 nanoparticles decorated carbon nanofiber mat as binder-free air-cathode for high performance rechargeable zinc-air batteries

    NASA Astrophysics Data System (ADS)

    Li, Bing; Ge, Xiaoming; Goh, F. W. Thomas; Hor, T. S. Andy; Geng, Dongsheng; Du, Guojun; Liu, Zhaolin; Zhang, Jie; Liu, Xiaogang; Zong, Yun

    2015-01-01

    An efficient, durable and low cost air-cathode is essential for a high performance metal-air battery for practical applications. Herein, we report a composite bifunctional catalyst, Co3O4 nanoparticles-decorated carbon nanofibers (CNFs), working as an efficient air-cathode in high performance rechargeable Zn-air batteries (ZnABs). The particles-on-fibers nanohybrid materials were derived from electrospun metal-ion containing polymer fibers followed by thermal carbonization and a post annealing process in air at a moderate temperature. Electrochemical studies suggest that the nanohybrid material effectively catalyzes oxygen reduction reaction via an ideal 4-electron transfer process and outperforms Pt/C in catalyzing oxygen evolution reactions. Accordingly, the prototype ZnABs exhibit a low discharge-charge voltage gap (e.g. 0.7 V, discharge-charge at 2 mA cm-2) with higher stability and longer cycle life compared to their counterparts constructed using Pt/C in air-cathode. Importantly, the hybrid nanofiber mat readily serves as an integrated air-cathode without the need of any further modification. Benefitting from its efficient catalytic activities and structural advantages, particularly the 3D architecture of highly conductive CNFs and the high loading density of strongly attached Co3O4 NPs on their surfaces, the resultant ZnABs show significantly improved performance with respect to the rate capability, cycling stability and current density, promising good potential in practical applications.An efficient, durable and low cost air-cathode is essential for a high performance metal-air battery for practical applications. Herein, we report a composite bifunctional catalyst, Co3O4 nanoparticles-decorated carbon nanofibers (CNFs), working as an efficient air-cathode in high performance rechargeable Zn-air batteries (ZnABs). The particles-on-fibers nanohybrid materials were derived from electrospun metal-ion containing polymer fibers followed by thermal carbonization and a post annealing process in air at a moderate temperature. Electrochemical studies suggest that the nanohybrid material effectively catalyzes oxygen reduction reaction via an ideal 4-electron transfer process and outperforms Pt/C in catalyzing oxygen evolution reactions. Accordingly, the prototype ZnABs exhibit a low discharge-charge voltage gap (e.g. 0.7 V, discharge-charge at 2 mA cm-2) with higher stability and longer cycle life compared to their counterparts constructed using Pt/C in air-cathode. Importantly, the hybrid nanofiber mat readily serves as an integrated air-cathode without the need of any further modification. Benefitting from its efficient catalytic activities and structural advantages, particularly the 3D architecture of highly conductive CNFs and the high loading density of strongly attached Co3O4 NPs on their surfaces, the resultant ZnABs show significantly improved performance with respect to the rate capability, cycling stability and current density, promising good potential in practical applications. Electronic supplementary information (ESI) available: TGA curves of as electrospun Co(ii)-PAN fiber and C-CoPAN900 EDX and XPS spectra of the C-CoPAN900 photo of a home-built Zn-air cell and the preparation method of conventional catalyst electrode; polarization curves and corresponding power density plots of the battery using conventional type cathode of C-CoPN900 and commercial Pt/C catalyst; the electrocatalytic properties of hybrid CNFs obtained from varied weight ratios of PAN to cobalt acetate, e.g. 16 : 1 and 8 : 1, and their corresponding TGA curves; a comparison of the Zn-air battery performance of this work with recent literatures. See DOI: 10.1039/c4nr05988c

  13. Iron-nitrogen-activated carbon as cathode catalyst to improve the power generation of single-chamber air-cathode microbial fuel cells.

    PubMed

    Pan, Yajun; Mo, Xiaoping; Li, Kexun; Pu, Liangtao; Liu, Di; Yang, Tingting

    2016-04-01

    In order to improve the performance of microbial fuel cell (MFC), iron-nitrogen-activated carbon (Fe-N-C) as an excellent oxygen reduction reaction (ORR) catalyst was prepared here using commercial activated carbon (AC) as matrix and employed in single chamber MFC. In MFC, the maximum power density increased to 2437±55mWm(-2), which was 2 times of that with AC. The open circuit potential (OCP) of Fe-N-C cathode (0.47) was much higher than that of AC cathode (0.21V). The R0 of Fe-N-C decreased by 47% from 14.36Ω (AC) to 7.6Ω (Fe-N-C). From X-ray photoelectron spectroscopy (XPS), pyridinic nitrogen, quaternary nitrogen and iron species were present, which played an important role in the ORR performance of Fe-N-C. These results demonstrated that the as-prepared Fe-N-C material provided a potential alternative to Pt in AC air cathode MFC for relatively desirable energy generation and wastewater treatment. PMID:26898678

  14. 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

  15. Portable Cathode-Air Vapor-Feed Electrochemical Medical Oxygen Concentrator (OC)

    NASA Technical Reports Server (NTRS)

    Balasubramanian, Ashwin

    2015-01-01

    Missions on the International Space Station and future space exploration will present significant challenges to crew health care capabilities, particularly in the efficient utilization of onboard oxygen resources. Exploration vehicles will require lightweight, compact, and portable oxygen concentrators that can provide medical-grade oxygen from the ambient cabin air. Current pressure-swing adsorption OCs are heavy and bulky, require significant start-up periods, operate in narrow temperature ranges, and require a liquid water feed. Lynntech, Inc., has developed an electrochemical OC that operates with a cathode-air vapor feed, eliminating the need for a bulky onboard water supply. Lynntech's OC is smaller and lighter than conventional pressure-swing OCs, is capable of instant start-up, and operates over a temperature range of 5-80 C. Accomplished through a unique nanocomposite proton exchange membrane and catalyst technology, the unit delivers 4 standard liters per minute of humidified oxygen at 60 percent concentration. The technology enables both ambient-pressure operating devices for portable applications and pressurized (up to 3,600 psi) OC devices for stationary applications.

  16. 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 Ω 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

  17. Solid oxide fuel cell power plant having a fixed contact oxidation catalyzed section of a multi-section cathode air heat exchanger

    DOEpatents

    Saito, Kazuo; Lin, Yao

    2015-02-17

    The multi-section cathode air heat exchanger (102) includes at least a first heat exchanger section (104), and a fixed contact oxidation catalyzed section (126) secured adjacent each other in a stack association. Cool cathode inlet air flows through cool air channels (110) of the at least first (104) and oxidation catalyzed sections (126). Hot anode exhaust flows through hot air channels (124) of the oxidation catalyzed section (126) and is combusted therein. The combusted anode exhaust then flows through hot air channels (112) of the first section (104) of the cathode air heat exchanger (102). The cool and hot air channels (110, 112) are secured in direct heat exchange relationship with each other so that temperatures of the heat exchanger (102) do not exceed 800.degree. C. to minimize requirements for using expensive, high-temperature alloys.

  18. 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-δ} (LSCF) were characterized by both electrical conductivity relaxation (ECR) and oxygen isotope exchange (IE) methods. Conductivity relaxation experiments were conducted at 800°C 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.

  19. 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 892 ± 8 mW m-2 is obtained by cathodes with the mass ratio of 0.2, which is 33% higher than that of the control reactor (without PF, 671 ± 22 mW m-2). Pore analysis indicates the porosity increases by 38% and the major pore range concentrates between 0.5 μm-0.8 μm which likely facilitates to enrich the active reaction sites compared to 0.8 μm-3.0 μm 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.

  20. A diffusive sampling device for measurement of ammonia in air

    NASA Astrophysics Data System (ADS)

    Yamada, Tomomi; Uchiyama, Shigehisa; Inaba, Yohei; Kunugita, Naoki; Nakagome, Hideki; Seto, Hiroshi

    2012-07-01

    A diffusive sampling device, the DSD-NH3, has been developed for measurement of ammonia in air. The DSD-NH3 comprises silica gel impregnated with phosphoric acid as the absorbent, a porous sintered polyethylene tube that acts as a diffusive membrane, and a small polypropylene syringe that is used for the elution of analytes from the absorbent. Silica gel impregnated with phosphoric acid is used as absorbent for the DSD-NH3; basic gases in ambient air, including ammonia, are trapped in the DSD-NH3 device by their reaction with phosphoric acid in the sampler to form their corresponding phosphoric acid salts. After collection, the DSD-NH3 samplers are eluted by water. Cations in the eluate, including ammonium ions, are analyzed by ion chromatography. A side-by-side comparison was made with active samplers, demonstrating good correlation (r2 = 0.996). The sampling rate (94.5 ml min-1) was determined from comparison with an active sampling method and sampling rates. The sampling rate is also calculated from the respective molecular weights according to a rule based on Graham's law. The theoretical sampling rate with the DSD-NH3 is 95.4 ml min-1 and agrees with the experimental value (94.5 ml min-1). Little influence of wind velocity on the sampler was observed. The relative standard deviations for ammonia concentrations were 4.7% with face velocity ranging 0-5.0 m/s.

  1. Minimum interspatial electrode spacing to optimize air-cathode microbial fuel cell operation with a membrane electrode assembly.

    PubMed

    Moon, Jung Mi; Kondaveeti, Sanath; Lee, Tae Ho; Song, Young Chae; Min, Booki

    2015-12-01

    An optimum electrode spacing of less than 1cm was determined for an air cathode microbial fuel cell (MFC) with a membrane electrode assembly (MEA) system. The lag period decreased as the electrode spacing increased and the voltage generation increased. Stable power density increased from 93 mW/m(2) to 248 mW/m(2) when the electrode distance increased from 0mm to 9 mm. In the polarization test, a maximum power density (400 mW/m(2)) was obtained at a distance of 6mm. The oxygen mass transfer coefficient (KO=4.60×10(-5) cm/s) with a 0mm spacing was five times higher than that at a 9 mm spacing (0.89×10(-5) cm/s). Long-term operation of the MFC exhibited relatively stable anode potentials of -285±25 (0 mm) and -517±20 mV (3, 6, and 9 mm) and a gradual decrease in cathode potential for all distances, especially with 0-mm spacing. The performance of air cathode MFCs can be improved using minimum electrode spacing rather than no spacing. PMID:26286838

  2. Fabrication and Performance of All-Solid-State Li-Air Battery with SWCNTs/LAGP Cathode.

    PubMed

    Liu, Yijie; Li, Bojie; Kitaura, Hirokazu; Zhang, Xueping; Han, Min; He, Ping; Zhou, Haoshen

    2015-08-12

    The all-solid-state Li-air battery has been fabricated, which is constructed by a lithium foil anode, a NASICON-type solid state electrolyte Li1+xAlyGe2-y(PO4)3 (LAGP) and single-walled carbon nanotubes (SWCNTs)/LAGP nanoparticles composite as air electrode. Its electrochemical performance was investigated in air atmosphere. Particularly, this battery exhibited a larger capacity about 2800 mAh g(-1) for the first cycle, while comparatively the battery with multiwalled carbon nanotubes (MWCNTs)/LAGP as cathode had a capacity of only about 1700 mAh g(-1). Also, the battery with SWCNTs/LAGP showed improved cycling performance with a reversible capacity of 1000 mAh g(-1) at a current density of 200 mA g(-1). Our result demonstrated that the all-solid-state Li-air battery with SWCNTs/LAGP as cathode catalyst has a considerable potential for practical application. PMID:26177186

  3. Electricity generation and nutrients removal from high-strength liquid manure by air-cathode microbial fuel cells.

    PubMed

    Lin, Hongjian; Wu, Xiao; Nelson, Chad; Miller, Curtis; Zhu, Jun

    2016-01-01

    Air-cathode microbial fuel cells (MFCs) are widely tested to recover electrical energy from waste streams containing organic matter. When high-strength wastewater, such as liquid animal manure, is used as a medium, inhibition on anode and cathode catalysts potentially impairs the effectiveness of MFC performance in power generation and pollutant removal. This study evaluated possible inhibitive effects of liquid swine manure components on MFC power generation, improved liquid manure-fed MFCs performance by pretreatment (dilution and selective adsorption), and modeled the kinetics of organic matter and nutrients removal kinetics. Parameters monitored included pH, conductivity, chemical oxygen demand (COD), volatile fatty acids (VFAs), total ammoniacal nitrogen (TAN), nitrite, nitrate, and phosphate concentrations. The removals of VFA and TAN were efficient, indicated by the short half-life times of 4.99 and 7.84 d, respectively. The mechanism for phosphate decrease was principally the salt precipitation on cathode, but the removal was incomplete after 42-d operation. MFC with an external resistor of 2.2 kΩ and fed with swine wastewater generated relatively small power (28.2 μW), energy efficiency (0.37%) and Coulombic efficiency (1.5%). Dilution of swine wastewater dramatically improved the power generation as the inhibitory effect was decreased. Zeolite and granular activated carbon were effective in the selective adsorption of ammonia or organic matter in swine wastewater, and so substantially improved the power generation, energy efficiency, and Coulombic efficiency. A smaller external resistor in the circuit was also observed to promote the organic matter degradation and thus to shorten the treatment time. Overall, air-cathode MFCs are promising for generating electrical power from livestock wastewater and meanwhile reducing the level of organic matter and nutrients. PMID:26654000

  4. Using elastin protein to develop highly efficient air cathodes for lithium-O2 batteries

    NASA Astrophysics Data System (ADS)

    Guo, Guilue; Yao, Xin; Ang, Huixiang; Tan, Huiteng; Zhang, Yu; Guo, Yuanyuan; Fong, Eileen; Yan, Qingyu

    2016-01-01

    Transition metal-nitrogen/carbon (M-N/C, M = Fe, Co) catalysts are synthesized using environmentally friendly histidine-tag-rich elastin protein beads, metal sulfate and water soluble carbon nanotubes followed by post-annealing and acid leaching processes. The obtained catalysts are used as cathode materials in lithium-O2 batteries. It has been discovered that during discharge, Li2O2 nanoparticles first nucleate and grow around the bead-decorated CNT regions (M-N/C centres) and coat on the catalysts at a high degree of discharge. The Fe-N/C catalyst-based cathodes deliver a capacity of 12 441 mAh g-1 at a current density of 100 mA g-1. When they were cycled at a limited capacity of 800 mAh g-1 at current densities of 200 or 400 mA g-1, these cathodes showed stable charge voltages of ˜3.65 or 3.90 V, corresponding to energy efficiencies of ˜71.2 or 65.1%, respectively. These results are considerably superior to those of the cathodes based on bare annealed CNTs, which prove that the Fe-N/C catalysts developed here are promising for use in non-aqueous lithium-O2 battery cathodes.

  5. Integrating NiCo Alloys with Their Oxides as Efficient Bifunctional Cathode Catalysts for Rechargeable Zinc-Air Batteries.

    PubMed

    Liu, Xien; Park, Minjoon; Kim, Min Gyu; Gupta, Shiva; Wu, Gang; Cho, Jaephil

    2015-08-10

    The lack of high-efficient, low-cost, and durable bifunctional electrocatalysts that act simultaneously for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is currently one of the major obstacles to commercializing the electrical rechargeability of zinc-air batteries. A nanocomposite CoO-NiO-NiCo bifunctional electrocatalyst supported by nitrogen-doped multiwall carbon nanotubes (NCNT/CoO-NiO-NiCo) exhibits excellent activity and stability for the ORR/OER in alkaline media. More importantly, real air cathodes made from the bifunctional NCNT/CoO-NiO-NiCo catalysts further demonstrated superior performance to state-of-the-art Pt/C or Pt/C+IrO2 catalysts in primary and rechargeable zinc-air batteries. PMID:26118973

  6. Polymer coatings as separator layers for microbial fuel cell cathodes

    NASA Astrophysics Data System (ADS)

    Watson, Valerie J.; Saito, Tomonori; Hickner, Michael A.; Logan, Bruce E.

    2011-03-01

    Membrane separators reduce oxygen flux from the cathode into the anolyte in microbial fuel cells (MFCs), but water accumulation and pH gradients between the separator and cathode reduces performance. Air cathodes were spray-coated (water-facing side) with anion exchange, cation exchange, and neutral polymer coatings of different thicknesses to incorporate the separator into the cathode. The anion exchange polymer coating resulted in greater power density (1167 ± 135 mW m-2) than a cation exchange coating (439 ± 2 mW m-2). This power output was similar to that produced by a Nafion-coated cathode (1114 ± 174 mW m-2), and slightly lower than the uncoated cathode (1384 ± 82 mW m-2). Thicker coatings reduced oxygen diffusion into the electrolyte and increased coulombic efficiency (CE = 56-64%) relative to an uncoated cathode (29 ± 8%), but decreased power production (255-574 mW m-2). Electrochemical characterization of the cathodes ex situ to the MFC showed that the cathodes with the lowest charge transfer resistance and the highest oxygen reduction activity produced the most power in MFC tests. The results on hydrophilic cathode separator layers revealed a trade off between power and CE. Cathodes coated with a thin coating of anion exchange polymer show promise for controlling oxygen transfer while minimally affecting power production.

  7. Ignition time of hydrogen-air diffusion flames

    NASA Astrophysics Data System (ADS)

    Sánchez, Antonio L.; Fernández-Tarrazo, Eduardo; Boivin, Pierre; Liñán, 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.

  8. Highly Efficient and Air Stable Inverted Polymer Solar Cells Using LiF-Modified ITO Cathode and MoO3/AgAl Alloy Anode.

    PubMed

    Jia, Xiangkun; Jiang, Ziyao; Chen, Xiaohong; Zhou, Jianping; Pan, Likun; Zhu, Furong; Sun, Zhuo; Huang, Sumei

    2016-02-17

    The performance and air stability of inverted polymer solar cells (PSCs) were greatly improved using a combination of LiF-modified ITO cathode and a MoO3/AgAl alloy anode. The power conversion efficiency (PCE) of PSCs with AgAl contact reached 9.4%, which is higher than that of the cells with Ag (8.8%) and Al electrode (7.6%). The PCE of AgAl-based PSCs can further increase up to 10.3% through incorporating an ultrathin LiF-modified ITO. AgAl-based cells also exhibit a superior stability compared to the cells with Ag and Al contacts. PCE of the AgAl-based cells without encapsulation remains 78% of its original value after the cells were aged for 380 days in air. The presence of a LiF-modified ZnO interlayer between ITO and the organic active layer improves the charge collection. The improvement in PCE and stability of the AgAl-based cells is primarily attributed to the formation of AlOx at the MoO3/AgAl interface, preventing Ag diffusion and improving the built-in potential across the active layer in the cells. PMID:26790631

  9. The performance and mechanism of modified activated carbon air cathode by non-stoichiometric nano Fe3O4 in the microbial fuel cell.

    PubMed

    Fu, Zhou; Yan, Litao; Li, Kexun; Ge, Baochao; Pu, Liangtao; Zhang, Xi

    2015-12-15

    Cathodic catalyst is one of the key materials in microbial fuel cell (MFC). The addition of non-stoichiometric nano Fe3O4 in activated carbon (NSFe3O4/AC) air cathode was beneficial to boosting the charge transfer of the cathode accompanying with the enhancement of power performance in MFC. The air cathode modified by NSFe3O4 (5%, Wt%) increased the maximum power density by 83.3% from 780 mW/m(2) to 1430 mW/m(2) compared with bare air cathode. The modified cathodes showed enhanced electrochemical properties and appeared the maximum exchange current density of 18.71×10(-4) A/cm(2) for oxygen reduction reaction. The mechanism of oxygen reduction for the NSFe3O4/AC catalyst was a 4-electron pathway. The oxygen vacancy of the NSFe3O4 played a crucial role in electrochemical catalytic activity. The great catalytic performance made NSFe3O4 have a promising outlook applied in MFC. PMID:26264265

  10. 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 80°C and 400°C respectively, and then was used as catalyst layer in the air-cathode. The maximum power densities were: 1096±33mW/m(2) (SP2, AC treated at 400°C), 954±36mW/m(2) (SP1, AC treated at 80°C), which were 55%, 35% higher than the control (708±27mW/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

  11. 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.

  12. Diffusion of 4-methyl-pent-3-en-2-one (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-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) 4-methyl-pent-3-en-2-one; (2) air

  13. Ruthenium oxide modified titanium dioxide nanotube arrays as carbon and binder free lithium-air battery cathode catalyst

    NASA Astrophysics Data System (ADS)

    Zhao, Guangyu; Niu, Yanning; Zhang, Li; Sun, Kening

    2014-12-01

    RuO2 modified TiO2 nanotube arrays, growing on Ti foams, are used as carbon and binder free cathodes for Li-O2 batteries. The micrometer pores in Ti foams and nanometer pores in TiO2 nanotubes supply facilitated transport channels for oxygen diffusing into/out of the catalysts in discharge and charge processes. The RuO2 catalyst exhibits outstanding catalytic active toward oxygen evolution reaction (OER), which leads the charge voltage maintaining around 3.7 V all through the battery cycling. The stability of TiO2/Ti support, abundant oxygen transport path and favorable catalytic activity of RuO2 toward OER enable the Li-O2 batteries exhibiting 130 cycle discharge/charge.

  14. 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.

  15. Bio-electrochemical characterization of air-cathode microbial fuel cells with microporous polyethylene/silica membrane as separator.

    PubMed

    Kircheva, Nina; Outin, Jonathan; Perrier, Gérard; Ramousse, Julien; Merlin, Gérard; Lyautey, Emilie

    2015-12-01

    The aim of this work was to study the behavior over time of a separator made of a low-cost and non-selective microporous polyethylene membrane (RhinoHide®) in an air-cathode microbial fuel cell with a reticulated vitreous carbon foam bioanode. Performances of the microporous polyethylene membrane (RhinoHide®) were compared with Nafion®-117 as a cationic exchange membrane. A non-parametric test (Mann-Whitney) done on the different sets of coulombic or energy efficiency data showed no significant difference between the two types of tested membrane (p<0.05). Volumetric power densities were ranging from 30 to 90 W·m(-3) of RVC foam for both membranes. Similar amounts of biomass were observed on both sides of the polyethylene membrane illustrating bacterial permeability of this type of separator. A monospecific denitrifying population on cathodic side of RhinoHide® membrane has been identified. Electrochemical impedance spectroscopy (EIS) was used at OCV conditions to characterize electrochemical behavior of MFCs by equivalent electrical circuit fitted on both Nyquist and Bode plots. Resistances and pseudo-capacitances from EIS analyses do not differ in such a way that the nature of the membrane could be considered as responsible. PMID:26073676

  16. Water vapor exchange system using a hydrophilic microporous layer coated gas diffusion layer to enhance performance of polymer electrolyte fuel cells without cathode humidification

    NASA Astrophysics Data System (ADS)

    Kitahara, Tatsumi; Nakajima, Hironori; Morishita, Masashi

    2012-09-01

    Polymer electrolyte fuel cells (PEFCs) generally have external humidifiers to supply humidified hydrogen and oxidant gases, which prevents dehydration of the membrane. If a PEFC could be operated without humidification, then external humidifiers could be removed, which would result in a simplified PEFC system with increased total efficiency and reduced cost. A water vapor exchange system installed in the PEFC was developed to enhance the performance without cathode humidification. A gas diffusion layer (GDL) coated with a hydrophobic microporous layer (MPL) was used at the active reaction area. A GDL coated with a hydrophilic MPL consisting of polyvinyl alcohol (PVA) and carbon black was used at the cathode water vapor exchange area to promote water transport from the cathode outlet wet gas to the anode inlet dry gas. This is effective for reducing the IR overpotential, which enhances the PEFC performance. Appropriate enhancement of hydrophilicity by increasing the PVA content in the MPL to 20 mass% is effective to increase water transport from the cathode to anode. At the anode water exchange area, a GDL without the hydrophilic MPL is effective to promote water transport from the water exchange area to the active reaction area, which enhances the PEFC performance.

  17. Experimental studies on the extinction of hydrogen-air counterflow diffusion flames

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    The paper presents data on the extinction of hydrogen-air counterflow diffusion flames (CFDFs). In the experiments, five coaxial tubular opposed jet burners were used to form dish-shaped CFDFs, centered by opposing laminar jets of N2-diluted H2 and both clean and contaminated air in the argon-purged chamber at 1 atm. Air jet velocities, U(air), characterized extinction of the air-side flame (blowoff) as functions of input H2/N2 (20-100 mole pct) on the fuel side, and air contaminant (0-20 percent) steam, CO2 and O2 (16-30 percent) on the air side.

  18. Enhancement of electricity production in a mediatorless air-cathode microbial fuel cell using Klebsiella sp. IR21.

    PubMed

    Lee, Yun-Yeong; Kim, Tae Gwan; Cho, Kyung-Suk

    2016-06-01

    A novel dissimilatory iron-reducing bacteria, Klebsiella sp. IR21, was isolated from the anode biofilm of an MFC reactor. Klebsiella sp. IR21 reduced 27.8 % of ferric iron to ferrous iron demonstrating that Klebsiella sp. IR21 has electron transfer ability. Additionally, Klebsiella sp. IR21 generated electricity forming a biofilm on the anode surface. When a pure culture of Klebsiella sp. IR21 was supplied into a single chamber, air-cathode MFC fed with a mixture of glucose and acetate (500 mg L(-1) COD), 40-60 mV of voltage (17-26 mA m(-2) of current density) was produced. Klebsiella sp. IR21 was also utilized as a biocatalyst to improve the electrical performance of a conventional MFC reactor. A single chamber, air-cathode MFC was fed with reject wastewater (10,000 mg L(-1) COD) from a H2 fermentation reactor. The average voltage, current density, and power density were 142.9 ± 25.74 mV, 60.5 ± 11.61 mA m(-2), and 8.9 ± 3.65 mW m(-2), respectively, in the MFC without inoculation of Klebsiella sp. IR21. However, these electrical performances of the MFC were significantly increased to 204.7 ± 40.24 mV, 87.5 ± 17.20 mA m(-2), and 18.6 ± 7.23 mW m(-2), respectively, with inoculation of Klebsiella sp. IR21. The results indicate that Klebsiella sp. IR21 can be utilized as a biocatalyst for enhancement of electrical performance in MFC systems. PMID:26956141

  19. 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 50°C 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

  20. 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

  1. 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...

  2. Similarity laws for cathode-directed streamers in gaps with an inhomogeneous field at elevated air pressures

    SciTech Connect

    Bolotov, O. V.; Golota, V. I.; Kadolin, B. B.; Karas', V. I.; Ostroushko, V. N.; Zavada, L. M.; Shulika, A. Yu.

    2010-11-15

    Results are presented from experimental studies of cathode-directed streamers in the gap closure regime without a transition into spark breakdown. Spatiotemporal, electrodynamic, and spectroscopic characteristics of streamer discharges in air at different pressures were studied. Similarity laws for streamer discharges were formulated. These laws allow one to compare the discharge current characteristics and streamer propagation dynamics at different pressures. Substantial influence of gas photoionization on the deviations from the similarity laws was revealed. The existence of a pressure range in which the discharges develop in a similar way was demonstrated experimentally. In particular, for fixed values of the product pd and discharge voltage U, the average streamer velocity is also fixed. It is found that, although the similarity laws are violated in the interstreamer pause of the discharge, the average discharge current and the product of the pressure and the streamer repetition period remain the same at different pressures. The radiation spectra of the second positive system of nitrogen (the C{sup 3{Pi}}{sub u}-B{sup 3{Pi}}{sub g} transitions) in a wavelength range of 300-400 nm at air pressures of 1-3 atm were recorded. It is shown that, in the entire pressure range under study, the profiles of the observed radiation bands practically remain unchanged and the relative intensities of the spectral lines corresponding to the {sup 3{Pi}}{sub u}-B{sup 3{Pi}}{sub g} transitions are preserved.

  3. Effects of cathode and electrolyte properties on lithium-air battery performance: Computational study

    NASA Astrophysics Data System (ADS)

    Sergeev, Artem V.; Chertovich, Alexander V.; Itkis, Daniil M.; Goodilin, Eugene A.; Khokhlov, Alexei R.

    2015-04-01

    Li/O2 batteries draw much attention due to its outstanding theoretical specific energy, but the value of practically achievable specific energy is still under the question. In this paper we employ a numerical model of Li/O2 cell, which takes into account mass transport processes, to simulate non-uniform product precipitation at different discharge current densities in acetonitrile, dimethyl sulfoxide and 1,2-dimethoxyethane-based electrolytes. Even for 1,2-dimethoxyethane, which has the highest oxygen mobility and solubility, oxygen transport restrictions at 1 mA/cm2 lead to cell-level specific energy of about 650 Wh/kg if a pure oxygen is supplied to the cell. Finally, in order to assist the ongoing search for new cathode materials, which can be alternative to carbon, we also investigate the effect of electrode material density on cell-level specific energy and show that materials with densities up to 10 g/cm3 can be used without serious penalty to the specific energy.

  4. 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.

  5. Diffusion-Controlled Glow Discharge Pressure Extended by the Multi-Dual Microhollow Cathode Configuration for Flat Lighting

    NASA Astrophysics Data System (ADS)

    Hwang, Hyeon Seok; Park, Ki Wan; Song, Kie Moon; Jong Lee, Se; Baik, Hong Koo

    2010-05-01

    We investigated pure Xe discharge primarily as a source of vacuum ultraviolet for discharge lamps, using a multi-dual hollow cathode. One of the problems associated with the discharge properties of Xe gas is its easy constriction. We prevented the problem by using an electrode configured as a multi-dual microhollow cathode. This result originated from auxiliary charge particles generated in a lamp discharge space and less variation of electron generation rate, which reduced thermal instability and as a result sequentially suppressed the constriction of Xe discharge. Furthermore, we observed that a six-channel flat-panel lamp could be driven with a pulse power supply.

  6. 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.

  7. 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...

  8. PASSIVE/DIFFUSIVE SAMPLERS FOR PESTICIDES IN RESIDENTIAL INDOOR AIR

    EPA Science Inventory

    Pesticides applied indoors vaporize from treated surfaces (e.g., carpets and baseboards) resulting in elevated air concentrations that may persist for long periods after applications. Estimating long-term respiratory exposures to pesticide vapors in residential indoor environme...

  9. Determination of Microbial Growth by Protein Assay in an Air-Cathode Single Chamber Microbial Fuel Cell.

    PubMed

    Li, Na; Kakarla, Ramesh; Moon, Jung Mi; Min, Booki

    2015-07-01

    Microbial fuel cells (MFCs) have gathered attention as a novel bioenergy technology to simultaneously treat wastewater with less sludge production than the conventional activated sludge system. In two different operations of the MFC and aerobic process, microbial growth was determined by the protein assay method and their biomass yields using real wastewater were compared. The biomass yield on the anode electrode of the MFC was 0.02 g-COD-cell/g- COD-substrate and the anolyte planktonic biomass was 0.14 g-COD-cell/g-COD-substrate. An MFC without anode electrode resulted in the biomass yield of 0.07 ± 0.03 g-COD-cell/g-COD-substrate, suggesting that oxygen diffusion from the cathode possibly supported the microbial growth. In a comparative test, the biomass yield under aerobic environment was 0.46 ± 0.07 g-COD-cell/g-COD-substrate, which was about 3 times higher than the total biomass value in the MFC operation. PMID:25674807

  10. The addition of ortho-hexagon nano spinel Co3O4 to improve the performance of activated carbon air cathode microbial fuel cell.

    PubMed

    Ge, Baochao; Li, Kexun; Fu, Zhou; Pu, Liangtao; Zhang, Xi

    2015-11-01

    Commercial Co3O4 and ortho-hexagon spinel nano-Co3O4 (OHSNC) were doped in the AC at a different percentage (5%, 10% and 15%) to enhance the performance of microbial fuel cell (MFC). The maximum power density of MFC with 10% OHSNC doped cathode was 1500±14 mW m(-2), which was 97.36% and 41.24% higher than that with the bare AC air cathode and commercial Co3O4 respectively. The electrocatalytic behavior for their better performance was discussed in detail with the help of various structural and electrochemical techniques. The OHSNC was characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The results showed that the improved performance owed to the enhancement of both kinetics activity and the number of electron transfer in the ORR, and the internal resistance was largely reduced. Therefore, OHSNC was proved to be an excellent cathodic catalyst in AC air cathode MFC. PMID:26112347

  11. Highly ordered and ultra-long carbon nanotube arrays as air cathodes for high-energy-efficiency Li-oxygen batteries

    NASA Astrophysics Data System (ADS)

    Yu, Ruimin; Fan, Wugang; Guo, Xiangxin; Dong, Shaoming

    2016-02-01

    Carbonaceous air cathodes with rational architecture are vital for the nonaqueous Li-O2 batteries to achieve large energy density, high energy efficiency and long cycle life. In this work, we report the cathodes made of highly ordered and vertically aligned carbon nanotubes grown on permeable Ta foil substrates (VACNTs-Ta) via thermal chemical vapour deposition. The VACNTs-Ta, composed of uniform carbon nanotubes with approximately 240 μm in superficial height, has the super large surface area. Meanwhile, the oriented carbon nanotubes provide extremely outstanding passageways for Li ions and oxygen species. Electrochemistry tests of VACNTs-Ta air cathodes show enhancement in discharge capacity and cycle life compared to those made from short-range oriented and disordered carbon nanotubes. By further combining with the LiI redox mediator that is dissolved in the tetraethylene dimethyl glycol based electrolytes, the batteries exhibit more than 200 cycles at the current density of 200 mA g-1 with a cut-off discharge capacity of 1000 mAh g-1, and their energy efficiencies increase from 50% to 82%. The results here demonstrate the importance of cathode construction for high-energy-efficiency and long-life Li-O2 batteries.

  12. Density functional theory insights into the structural stability and Li diffusion properties of monoclinic and orthorhombic Li2FeSiO4 cathodes

    NASA Astrophysics Data System (ADS)

    Lu, Xia; Chiu, Hsien-Chieh; Bevan, Kirk H.; Jiang, De-Tong; Zaghib, Karim; Demopoulos, George P.

    2016-06-01

    Lithium iron orthosilicate (Li2FeSiO4) is an important alternative cathode for next generation Li-ion batteries due to its high theoretical capacity (330 mA h/g). However, its development has faced great challenges arising from significant structural complexity, including the disordered arrangement/orientation of Fe/Si tetrahedra, polytypes and its poorly understood Li storage and transport properties. In this context, ab-initio calculations are employed to investigate the phase stability and Li diffusion profiles of both monoclinic (P21) and orthorhombic (Pmn21) Li2FeSiO4 orthosilicates. The calculations demonstrate that formation of Lisbnd Fe antisites can induce a metastability competition between both phases, with neither dominating across nearly the entire discharging profile from Li2FeSiO4 through to LiFeSiO4. Furthermore, structural instability is shown to be a serious concern at discharge concentrations below LiFeSiO4 (1 Li extraction) due to the shared occupation of Li donated electrons with oxygen 2p orbitals - rather than the hypothesized transition to a tetravalent Fe4+ state. This finding is further supported by diffusion calculations that have determined a high activation energy barrier towards fast charging and rapid phase transitions. In summary, these theoretical results provide critical and timely insight into the structural dynamics of lithium iron orthosilicate, in pursuit of high energy density cathodes.

  13. Electricity generation of microbial fuel cell with waterproof breathable membrane cathode

    NASA Astrophysics Data System (ADS)

    Xing, Defeng; Tang, Yu; Mei, Xiaoxue; Liu, Bingfeng

    2015-12-01

    Simplification of fabrication and reduction of capital cost are important for scale-up and application of microbial electrochemical systems (MES). A fast and inexpensive method of making cathode was developed via assembling stainless steel mesh (SSM) with waterproof breathable membrane (WBM). Three assemble types of cathodes were fabricated; Pt@SSM/WBM (SSM as cathode skeleton, WBM as diffusion layer, platinum (Pt) catalyst applied on SSM), SSM/Pt@WBM and Pt@WBM. SSM/Pt@WBM cathode showed relatively preferable with long-term stability and favorable power output (24.7 W/m3). Compared to conventional cathode fabrication, air-cathode was made for 0.5 h. The results indicated that the novel fabrication method could remarkably reduce capital cost and simplify fabrication procedures with a comparable power output, making MFC more prospective for future application.

  14. Enrichment of anodic biofilm inoculated with anaerobic or aerobic sludge in single chambered air-cathode microbial fuel cells.

    PubMed

    Gao, Chongyang; Wang, Aijie; Wu, Wei-Min; Yin, Yalin; Zhao, Yang-Guo

    2014-09-01

    Aerobic sludge after anaerobic pretreatment and anaerobic sludge were separately used as inoculum to start up air-cathode single-chamber MFCs. Aerobic sludge-inoculated MFCs arrived at 0.27 V with a maximum power density of 5.79 W m(-3), while anaerobic sludge-inoculated MFCs reached 0.21 V with 3.66 W m(-3). Microbial analysis with DGGE profiling and high-throughput sequencing indicated that aerobic sludge contained more diverse bacterial populations than anaerobic sludge. Nitrospira species dominated in aerobic sludge, while anaerobic sludge was dominated by Desulfurella and Acidithiobacillus species. Microbial community structure and composition in anodic biofilms enriched, respectively from aerobic and anaerobic sludges tended gradually to be similar. Potentially exoelectrogenic Geobacter and Anaeromusa species, biofilm-forming Zoogloea and Acinetobacter species were abundant in both anodic biofilms. This study indicated that aerobic sludge performed better for MFCs startup, and the enrichment of anodic microbial consortium with different inocula but same substrate resulted in uniformity of functional microbial communities. PMID:24973773

  15. Direct electricity recovery from Canna indica by an air-cathode microbial fuel cell inoculated with rumen microorganisms.

    PubMed

    Zang, Guo-Long; Sheng, Guo-Ping; Tong, Zhong-Hua; Liu, Xian-Wei; Teng, Shao-Xiang; Li, Wen-Wei; Yu, Han-Qing

    2010-04-01

    Aquatic plants are widely used for phytoremediation, and effective disposal methods should be pursued for their utilization and to avoid further environmental pollution problems. This study demonstrated that, using an air-cathode microbial fuel cell (MFC) inoculated with rumen microorganisms, electricity could be directly produced with a maximum power density of 0.405 W/m(3) from Canna indica (canna), a lignocellulosic aquatic plant rich in cellulose, hemicellulose, and lignin, without pretreatment. The mechanisms of the Canna indica degradation in the MFC were elucidated through analyzing the changes of canna structure and intermediates, that is, soluble sugars and volatile fatty acids (VFAs), in the electricity generation process. The results showed that lignin was partially removed and more cellulose became exposed on the sample surface during the electricity generation in the MFC. The electron transfer in this MFC was mainly completed through electron shuttling via self-produced mediators. This work presents an attempt to understand how complex substrates like aquatic plants are decomposed in an MFC during electricity generation. It might, hopefully, provide a promising way to utilize lignocellulosic biomass for energy generation. PMID:20225844

  16. 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 μA 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 μg l(-1) cm(-2)) and a lower detection limit of only 1 μg l(-1). The biosensor dynamic range was 1-25 μg 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

  17. Catalysis kinetics and porous analysis of rolling activated carbon-PTFE air-cathode in microbial fuel cells.

    PubMed

    Dong, Heng; Yu, Hongbing; Wang, Xin

    2012-12-01

    The microbial fuel cell (MFC), being an environment-friendly technology for wastewater treatment, is limited by low efficiency and high cost. Power output based on capital cost had been greatly increased in our previous work by introducing a novel activated carbon (AC) air-cathode (ACAC). The catalysis behavior of this ACAC was studied here based on catalysis kinetics and pore analysis of both carbon powders and catalyst layers (CLs). Plain AC (AC1#), ultracapacitor AC (AC2#), and non-AC (XC-72) powders were used as catalysts. The electron transfer number (n) of oxygen reduction reaction (ORR) with CLs increased by 5-23% compared to those n values of corresponding carbon powders before being rolled to CLs with PTFE, while the n value of Pt/C decreased by 38% when it was brushed with Nafion as the CL, indicating that rolling procedure with PTFE binder substantially increased the catalytic activity of carbon catalysts. Two-four times larger in micropore area of AC powders than non-AC powder resulted in 1.3-1.9 times increase in power density of MFCs. In addition, more uniform distribution of microporosity was found in AC1# than in AC2#, which could be the reason for the 25% increase in power density of ACAC1# (1355 26 mWm(-2)) compared to 1086 8 mWm(-2) of ACAC2#. PMID:23151092

  18. The tubular MFC with carbon tube air-cathode for power generation and N,N-dimethylacetamide treatment.

    PubMed

    Liu, Jiadong; Liu, Lifen; Gao, Bo

    2016-03-01

    A continuous flow microbial fuel cell (MFC) was assembled with carbon tube air-cathode and carbon felt anode. The organic solvent N,N-dimethylacetamide (DMAC) was used as the only carbon source for power generation. After the adaptive phase, the cell potential was gradually increased from 0.15 to 0.45 V with 200 Ω of external resistor during 150 h of operation. The calculated power density of this MFC was 100 mW L(-1) when the cell potential was 0.45 V. The reversible redox peaks of carbon tube were obtained in cyclic voltammogram between -0.5 and -0.25 V under aerobic circumstance. The removal rate of DMAC was 15-50% after treatment with hydraulic retention time of 12 min. The results indicated that it is possible to realize the power extraction from DMAC wastewater in the form of electricity by the bioconversion process of MFC. PMID:26333627

  19. 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...

  20. 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.

  1. Microstructural approach towards prediction of air permeability and gas diffusivity in polar firn

    NASA Astrophysics Data System (ADS)

    Courville, Z.; Albert, M.; Horhold, M.; Hopkins, M.; Freitag, J.

    2007-12-01

    Recent investigations of the air permeability and gas diffusivity of polar firn have shown that these proporties are not solely dependent on firn density, and that prediction of these properties can be improved by considering the effect of firn microstructural geometry. Co-registered measurements of air permeability, gas diffusivity, density and microstructure were made at 10 cm resolution on cores from East Anarctica, in a megadunes area, and West Antarctica, Hercules Dome. In addition, three-dimensional imaging of the firn microstructure usng micro-CT scans of selected firn cores was done. The 3D reconstructions of firn geometry were used in lattice-Boltzmann modeling of air flow through the samples. The measurements and modeling of air flow both indicate that the firn geometry can significantly influence air permeability.

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

    SciTech Connect

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

    2014-10-15

    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 cm{sup 3}, 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.

  3. 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.

  4. Sustainable design of high-performance microsized microbial fuel cell with carbon nanotube anode and air cathode.

    PubMed

    Mink, Justine E; Hussain, Muhammad Mustafa

    2013-08-27

    Microbial fuel cells (MFCs) are a promising alternative energy source that both generates electricity and cleans water. Fueled by liquid wastes such as wastewater or industrial wastes, the microbial fuel cell converts waste into energy. Microsized MFCs are essentially miniature energy harvesters that can be used to power on-chip electronics, lab-on-a-chip devices, and/or sensors. As MFCs are a relatively new technology, microsized MFCs are also an important rapid testing platform for the comparison and introduction of new conditions or materials into macroscale MFCs, especially nanoscale materials that have high potential for enhanced power production. Here we report a 75 μL microsized MFC on silicon using CMOS-compatible processes and employ a novel nanomaterial with exceptional electrochemical properties, multiwalled carbon nanotubes (MWCNTs), as the on-chip anode. We used this device to compare the usage of the more commonly used but highly expensive anode material gold, as well as a more inexpensive substitute, nickel. This is the first anode material study done using the most sustainably designed microsized MFC to date, which utilizes ambient oxygen as the electron acceptor with an air cathode instead of the chemical ferricyanide and without a membrane. Ferricyanide is unsustainable, as the chemical must be continuously refilled, while using oxygen, naturally found in air, makes the device mobile and is a key step in commercializing this for portable technology such as lab-on-a-chip for point-of-care diagnostics. At 880 mA/m(2) and 19 mW/m(2) the MWCNT anode outperformed the others in both current and power densities with between 6 and 20 times better performance. All devices were run for over 15 days, indicating a stable and high-endurance energy harvester already capable of producing enough power for ultra-low-power electronics and able to consistently power them over time. PMID:23899322

  5. 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

  6. 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

    2015-01-01

    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 1390±76mWm(-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 1.03×10(-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 2.48Å, 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

  7. Measurement of effective air diffusion coefficients for trichloroethene in undisturbed soil cores

    NASA Astrophysics Data System (ADS)

    Bartelt-Hunt, Shannon L.; Smith, James A.

    2002-06-01

    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 cm 2/s over a range of air-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions.

  8. Measurement of effective air diffusion coefficients for trichloroethene in undisturbed soil cores.

    PubMed

    Bartelt-Hunt, Shannon L; Smith, James A

    2002-06-01

    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-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions. PMID:12102318

  9. 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.

  10. Co3O4 nanoparticle-modified MnO2 nanotube bifunctional oxygen cathode catalysts for rechargeable zinc-air batteries

    NASA Astrophysics Data System (ADS)

    Du, Guojun; Liu, Xiaogang; Zong, Yun; Hor, T. S. Andy; Yu, Aishui; Liu, Zhaolin

    2013-05-01

    We report the preparation of MnO2 nanotubes functionalized with Co3O4 nanoparticles and their use as bifunctional air cathode catalysts for oxygen reduction reaction and oxygen evolution reaction in rechargeable zinc-air batteries. These hybrid MnO2/Co3O4 nanomaterials exhibit enhanced catalytic reactivity toward oxygen evolution reaction under alkaline conditions compared with that in the presence of MnO2 nanotubes or Co3O4 nanoparticles alone.We report the preparation of MnO2 nanotubes functionalized with Co3O4 nanoparticles and their use as bifunctional air cathode catalysts for oxygen reduction reaction and oxygen evolution reaction in rechargeable zinc-air batteries. These hybrid MnO2/Co3O4 nanomaterials exhibit enhanced catalytic reactivity toward oxygen evolution reaction under alkaline conditions compared with that in the presence of MnO2 nanotubes or Co3O4 nanoparticles alone. Electronic supplementary information (ESI) available: Zinc-air cell device, XPS survey scan and power density of the cell. See DOI: 10.1039/c3nr00300k

  11. The Effects of Multiple Cooling Diffusers in an Underfloor Air Distribution System

    NASA Astrophysics Data System (ADS)

    Liu, Qing; Linden, Paul

    2004-11-01

    Previous work on an Underfloor Air Distribution (UFAD) system with a single heat source and a single cooling diffuser has been extended to study the effects of multiple cooling diffusers experimentally and theoretically. In the experiment, a plume and fountains represent a heat source and cooling vents separately. Two-layer temperature stratification forms provided that the physical characteristic of each diffuser is identical. For a fixed heat load and ventilation rate, the effect of multiple cooling diffusers is to decrease the height and the temperature of the cooler zone; and achieve displacement ventilation in the limit of a large number of diffusers per heat source. In the case of a fixed heat load and a constant underfloor plenum pressure, increasing the number of openings on the floor diminishes the two-layer stratification by cooling both layers but by different amounts.

  12. 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

  13. Oxygen vacancy diffusion across cathode/electrolyte interface in solid oxide fuel cells: An electrochemical phase-field model

    NASA Astrophysics Data System (ADS)

    Hong, Liang; Hu, Jia-Mian; Gerdes, Kirk; Chen, Long-Qing

    2015-08-01

    An electrochemical phase-field model is developed to study electronic and ionic transport across the cathode/electrolyte interface in solid oxide fuel cells. The influences of local current density and interfacial electrochemical reactions on the transport behaviors are incorporated. This model reproduces two electrochemical features. Nernst equation is satisfied through the thermodynamic equilibriums of the electron and oxygen vacancy. The distributions of charged species around the interface induce charge double layer. Moreover, we verify the nonlinear current/overpotential relationship. This model facilitates the exploration of problems in solid oxide fuel cells, which are associated with transport of species and electrochemical reactions at high operating temperature.

  14. Trioxane-Air Counterflow Diffusion Flames in Normal and Microgravity

    NASA Technical Reports Server (NTRS)

    Linteris, Gregory T.; Urban, David L.

    2001-01-01

    Trioxane, a weakly bound polymer of formaldehyde (C3H6O3, m.p. 61 C, b.p. 115 C), is a uniquely suited compound for studying material flammability. Like many of the more commonly used materials for such tests (e.g., delrin, polyethylene, acrylic sheet, wood, and paper), it displays relevant phenomena (internal heat conduction, melting, vaporization, thermal decomposition, and gas phase reaction of the decomposition products). Unlike the other materials, however, it is non-sooting and has simple and well-known chemical kinetic pathways for its combustion. Hence it should prove to be much more useful for numerical modeling of surface combustion than the complex fuels typically used. We have performed the first exploratory tests of trioxane combustion in the counterflow configuration to determine its potential as a surrogate solid fuel which allows detailed modeling. The experiments were performed in the spring and summer of 1998 at the National Institute of Standards and Technology in Gaithersburg, MD, and at NASA-GRC in Cleveland. Using counterflow flames at 1-g, we measured the fuel consumption rate and the extinction conditions with added N2 in the air; at mg conditions, we observed the ignition characteristics and flame shape from video images. We have performed numerical calculations of the flame structure, but these are not described here due to space limitations. This paper summarizes some burning characteristics of trioxane relevant to its use for studying flame spread and fire suppression.

  15. Porous nitrogen-doped carbon nanosheet on graphene as metal-free catalyst for oxygen reduction reaction in air-cathode microbial fuel cells.

    PubMed

    Wen, Qing; Wang, Shaoyun; Yan, Jun; Cong, Lijie; Chen, Ye; Xi, Hongyuan

    2014-02-01

    Porous nitrogen-doped carbon nanosheet on graphene (PNCN) was used as an alternative cathode catalyst for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). Here we report a novel, low-cost, scalable, synthetic method for preparation of PNCN via the carbonization of graphite oxide-polyaniline hybrid (GO-PANI), subsequently followed by KOH activation treatment. Due to its high concentration of nitrogen and high specific surface area, PNCN exhibited an excellent catalytic activity for ORR. As a result, the maximum power density of 1159.34mWm(-2) obtained with PNCN catalyst was higher than that of Pt/C catalyst (858.49mWm(-2)) in a MFC. Therefore, porous nitrogen-doped carbon nanosheet could be a good alternative to Pt catalyst in MFCs. PMID:24239870

  16. High pressure flame system for pollution studies with results for methane-air diffusion flames

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

    A high pressure flame system was designed and constructed for studying nitrogen oxide formation in fuel air combustion. Its advantages and limitations were demonstrated by tests with a confined laminar methane air diffusion flame over the pressure range from 1 to 50 atm. The methane issued from a 3.06 mm diameter port concentrically into a stream of air contained within a 20.5 mm diameter chimney. As the combustion pressure is increased, the flame changes in shape from wide and convex to slender and concave, and there is a marked increase in the amount of luminous carbon. The height of the flame changes only moderately with pressure.

  17. 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.

  18. Analysis of opposed-jet hydrogen-air counter flow diffusion flame

    NASA Technical Reports Server (NTRS)

    Ho, Y. H.; Isaac, K. M.; Pellett, G. L.; Northam, G. B.

    1991-01-01

    An opposed-jet counterflow diffusion-flame configuration is considered for the analysis of a nitrogen-diluted hydrogen-air diffusion flame. A boundary-layer similarity solution is employed in order to reduce the governing equations to a set of equations in one independent variable. The equation set is written in the time-dependent form and solved by the finite-volume time-marching technique. This model uses detailed chemistry and accounts for the variations of Prandtl number and Lewis number as well as the effect of thermal diffusion on the flame. It is noted that a one-step model can predict several features of the flame, while the detailed-chemistry model can be used for fine-tuning the results. The present results indicate that thermal diffusion has negligible effect on the characteristics of the flame.

  19. Novel strategy to mitigate cathode catalyst degradation during air/air startup cycling via the atmospheric resistive switching mechanism of a hydrogen anode with a platinum catalyst supported on tantalum-doped titanium dioxide

    NASA Astrophysics Data System (ADS)

    Shintani, Haruhiko; Kojima, Yuya; Kakinuma, Katsuyoshi; Watanabe, Masahiro; Uchida, Makoto

    2015-10-01

    We propose a new strategy for alleviating the reverse current phenomenon using a unique "atmospheric resistive switching mechanism" (ARSM) of a metal oxide semiconductor support, such that the electrical resistivity changes depending on the gas atmosphere. The membrane-electrode assembly (MEA) using Ta-doped TiO2-supported platinum (Pt/Ta-TiO2) as the anode catalyst showed approximately one order of magnitude greater resistance in air than in hydrogen. The overpotential of the hydrogen oxidation reaction was negligible up to at least 1.5 A cm-2. The losses of electrochemically active surface area and carbon corrosion of the cathode catalyst during air/air startup cycling were significantly suppressed by the use of the Pt/Ta-TiO2 anode. The decrease in the degradation is attributed to a reduction of the reverse current due to a low oxygen reduction reaction rate at the anode, which showed high resistivity in air. These results demonstrate the effectiveness of the ARSM in mitigating cathode catalyst degradation during air/air startup cycling.

  20. 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 4.6 V vs. Na+/Na can produce three plateaus in charge/discharge processes because of the reorganization of ions. The first discharge capacity of 111.6 mAh g-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 10-12 cm2 s-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.

  1. Novel anti-flooding poly(dimethylsiloxane) (PDMS) catalyst binder for microbial fuel cell cathodes

    NASA Astrophysics Data System (ADS)

    Zhang, Fang; Chen, Guang; Hickner, Michael A.; Logan, Bruce E.

    2012-11-01

    Poly(dimethylsiloxane) (PDMS) was investigated as an alternative to Nafion as an air cathode catalyst binder in microbial fuel cells (MFCs). Cathodes were constructed around either stainless steel (SS) mesh or copper mesh using PDMS as both catalyst binder and diffusion layer, and compared to cathodes of the same structure having a Nafion binder. With PDMS binder, copper mesh cathodes produced a maximum power of 1710 ± 1 mW m-2, while SS mesh had a slightly lower power of 1680 ± 12 mW m-2, with both values comparable to those obtained with Nafion binder. Cathodes with PDMS binder had stable power production of 1510 ± 22 mW m-2 (copper) and 1480 ± 56 mW m-2 (SS) over 15 days at cycle 15, compared to a 40% decrease in power with the Nafion binder. Cathodes with the PDMS binder had lower total cathode impedance than those with Nafion. This is due to a large decrease in diffusion resistance, because hydrophobic PDMS effectively prevented catalyst sites from filling up with water, improving oxygen mass transfer. The cost of PDMS is only 0.23% of that of Nafion. These results showed that PDMS is a very effective and low-cost alternative to Nafion binder that will be useful for large scale construction of these cathodes for MFC applications.

  2. Surface hardening of stainless steel by runaway electrons preionized diffuse discharge in air atmosphere

    NASA Astrophysics Data System (ADS)

    Erofeev, M. V.; Shulepov, M. A.; Oskomov, K. V.; Tarasenko, V. F.

    2015-11-01

    In this paper we present microhardness measurements of stainless steel surface treated by diffuse discharge in air atmosphere. The cleaning from carbon in comparison to the initial sample was observed at a depth exceeding 20 nm. The oxygen concentration was also increased in comparison to that in the initial sample at a depth of up to about 50 nm. Comparative analysis shows that after treatment the microhardness of stainless steel surface increased in 2 times due to interaction of near-surface layers with product of plasma chemical reactions produced in diffuse discharge.

  3. Dynamics of the optical emission from a high-voltage diffuse discharge in a rod-plane electrode system in atmospheric-pressure air

    SciTech Connect

    Rep'ev, A. G.; Repin, P. B.

    2006-01-15

    Results are presented from experimental investigations of the dynamics of optical emission from a nanosecond diffuse discharge in a rod-plane electrode system. A study was made of discharges in a 10-cm-long interelectrode gap in atmospheric-pressure air (the cathode being a 1-cm-diameter rod with a bullet-shaped end). The voltage across the discharge gap was 220 kV and the voltage pulse duration was 180 ns, the voltage rise time being 10 ns. In experiments, the discharges were observed to evolve through two stages: the bridging stage and the conduction stage. The bridging stage begins with intense optical emission from the cathode region, the onset of the emission being delayed with respect to the beginning of the voltage pulse. Simultaneously with the onset of optical emission, a displacement current corresponding to the motion of charged particles begins to be generated in the cathode region. The duration of this current corresponds to the time the emission front takes to bridge the gap. As the emission front reaches the anode region, the current increases abruptly, indicating the beginning of the conduction stage. It was found that the time delay of optical emission relative to the beginning of the voltage pulse largely governs the discharge parameters: as the time delay becomes longer, the emission front velocity in the bridging stage increases from 0.6 to 1.5 cm/ns, the probability of realizing a multichannel structure of the discharge becomes higher, and the discharge current and the intensity of X-ray emission from the discharge grow.

  4. Low-current electric arc in the open air between the end of the cathode and long vertical anode

    NASA Astrophysics Data System (ADS)

    Tazmeev, Kh K.; Tazmeev, B. Kh

    2015-11-01

    The electrical discharge was investigated experimentally in the open atmosphere at currents less than 1 A. The cylindrical rods and flat plates were used as anode. They were installed in front of the cathode rod vertically or obliquely. The modes in which the discharge makes regular self-oscillations were detected. Electric field intensity in the discharge column and the electron temperature were calculated.

  5. 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.

  6. Effects of test facility contaminates on supersonic hydrogen-air diffusion flames

    SciTech Connect

    Rogers, R.C.

    1986-01-01

    Results are presented from an analytical assessment of the effects of NO and H/sub 2/O in air on the ignition and reaction of hydrogen. Three flow models of the burning process were used, each including a 32 reaction chemistry mechanism. These models were a plug flow reactor to determine ignition and reaction times; a well-stirred reactor to assess flame stability or blow-off, and a parabolic Navier Stokes code to examine the diffusion flame combustion. The diffusion flame was computed for a cold supersonic H/sub 2/ jet coaxial with a supersonic air stream at a static temperature of 1100 K and a pressure of 1 atmosphere. 15 references.

  7. Partitioned airs at microscale and nanoscale: thermal diffusivity in ultrahigh porosity solids of nanocellulose

    NASA Astrophysics Data System (ADS)

    Sakai, Koh; Kobayashi, Yuri; Saito, Tsuguyuki; Isogai, Akira

    2016-02-01

    High porosity solids, such as plastic foams and aerogels, are thermally insulating. Their insulation performance strongly depends on their pore structure, which dictates the heat transfer process in the material. Understanding such a relationship is essential to realizing highly efficient thermal insulators. Herein, we compare the heat transfer properties of foams and aerogels that have very high porosities (97.3-99.7%) and an identical composition (nanocellulose). The foams feature rather closed, microscale pores formed with a thin film-like solid phase, whereas the aerogels feature nanoscale open pores formed with a nanofibrous network-like solid skeleton. Unlike the aerogel samples, the thermal diffusivity of the foam decreases considerably with a slight increase in the solid fraction. The results indicate that for suppressing the thermal diffusion of air within high porosity solids, creating microscale spaces with distinct partitions is more effective than directly blocking the free path of air molecules at the nanoscale.

  8. Partitioned airs at microscale and nanoscale: thermal diffusivity in ultrahigh porosity solids of nanocellulose.

    PubMed

    Sakai, Koh; Kobayashi, Yuri; Saito, Tsuguyuki; Isogai, Akira

    2016-01-01

    High porosity solids, such as plastic foams and aerogels, are thermally insulating. Their insulation performance strongly depends on their pore structure, which dictates the heat transfer process in the material. Understanding such a relationship is essential to realizing highly efficient thermal insulators. Herein, we compare the heat transfer properties of foams and aerogels that have very high porosities (97.3-99.7%) and an identical composition (nanocellulose). The foams feature rather closed, microscale pores formed with a thin film-like solid phase, whereas the aerogels feature nanoscale open pores formed with a nanofibrous network-like solid skeleton. Unlike the aerogel samples, the thermal diffusivity of the foam decreases considerably with a slight increase in the solid fraction. The results indicate that for suppressing the thermal diffusion of air within high porosity solids, creating microscale spaces with distinct partitions is more effective than directly blocking the free path of air molecules at the nanoscale. PMID:26830144

  9. Partitioned airs at microscale and nanoscale: thermal diffusivity in ultrahigh porosity solids of nanocellulose

    PubMed Central

    Sakai, Koh; Kobayashi, Yuri; Saito, Tsuguyuki; Isogai, Akira

    2016-01-01

    High porosity solids, such as plastic foams and aerogels, are thermally insulating. Their insulation performance strongly depends on their pore structure, which dictates the heat transfer process in the material. Understanding such a relationship is essential to realizing highly efficient thermal insulators. Herein, we compare the heat transfer properties of foams and aerogels that have very high porosities (97.3–99.7%) and an identical composition (nanocellulose). The foams feature rather closed, microscale pores formed with a thin film-like solid phase, whereas the aerogels feature nanoscale open pores formed with a nanofibrous network-like solid skeleton. Unlike the aerogel samples, the thermal diffusivity of the foam decreases considerably with a slight increase in the solid fraction. The results indicate that for suppressing the thermal diffusion of air within high porosity solids, creating microscale spaces with distinct partitions is more effective than directly blocking the free path of air molecules at the nanoscale. PMID:26830144

  10. 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.

  11. High-Rate and Cycling-Stable Nickel-Rich Cathode Materials with Enhanced Li(+) Diffusion Pathway.

    PubMed

    Tian, Jun; Su, Yuefeng; Wu, Feng; Xu, Shaoyu; Chen, Fen; Chen, Renjie; Li, Qing; Li, Jinghui; Sun, Fengchun; Chen, Shi

    2016-01-13

    The nickel-rich LiNi0.7Co0.15Mn0.15O2 material was sintered by Li source with the Ni0.7Co0.15Mn0.15(OH)2 precursor, which was prepared via hydrothermal treatment after coprecipitation. The intensity ratio of I(110)/I(108) obtained from X-ray diffraction patterns and high-resolution transmission electronmicroscopy confirm that the particles have enhanced growth of (110), (100), and (010) surface planes, which supply superior inherent Li(+) deintercalation/intercalation. The electrochemical measurement shows that the LiNi0.7Co0.15Mn0.15O2 material has high cycling stability and rate capability, along with fast charge and discharge ability. Li(+) diffusion coefficient at the oxidation peaks obtained by cyclic voltammogram measurement is as large as 10(-11) (cm(2) s(-1)) orders of magnitude, implying that the nickel-rich material has high Li(+) diffusion capability. PMID:26601895

  12. Diffusion of gases in air and its affect on oxygen deficiency hazard abatement

    SciTech Connect

    Theilacker, J.C.; White, M.J.; /Fermilab

    2005-09-01

    Density differences between air and released gases of cryogenic systems have been used to either require special oxygen deficiency hazard (ODH) control measures, or as a means of abatement. For example, it is not uncommon to assume that helium spills will quickly collect at the ceiling of a building or enclosure and will efficiently exit at the nearest vertical penetration or vent. Oxygen concentration reduction was found to be detectable during a localized helium spill throughout the entire 6.3 km Tevatron tunnel. This prompted us to perform diffusion tests in air with common gases used at Fermilab. The tests showed that gases, more readily than expected, diffused through an air column in the direction opposing buoyancy. Test results for helium and sulfur hexafluoride are presented. A system of tests were performed to better understand how easily released gases would fully mix with air and whether they remained fully mixed. The test results have been applied to a new system at Fermilab for ODH abatement.

  13. Extended reaction zone of La0.6Sr0.4Co0.2Fe0.8O3 cathode for solid oxide fuel cell

    SciTech Connect

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

    2012-01-03

    The oxygen reduction reaction at the cathode of solid oxide fuel cell (SOFC) is a complicated process which involves the interaction of oxygen molecules, electrons, and oxygen ions. Therefore, it can only proceed at locations where gas, electronic conductor, and an oxygen ion conductor meet. Although the extension of the reaction zone beyond the traditional so-called triple-phase-boundary (TPB) is widely accepted for a mixed ionically and electronically conductive cathode, work in this area has yet to reach a consensus on how far the reaction zone can be extended. In this study, anode-supported fuel cells with a variety of LSCF cathode thicknesses were fabricated and tested in two cathode environments, flowing oxygen and flowing air. In flowing oxygen, the cell performance increased with LSCF cathode thickness over the entire range investigated (from 5 to 33 m). In flowing air, the cell performance also increased with the LSCF cathode thickness from 5 to 13 m, but then remained almost constant with further increase in cathode thickness. In flowing oxygen, since there was no concentration polarization related to oxygen diffusion, the polarization resistance of oxygen reduction decreased with the LSCF cathode thickness because of the increased number of reaction sites. A linear relationship was established between the reciprocal of the polarization resistance and the cathode thickness, which was explained by a model developed for aqueous gas diffusion electrodes.

  14. Measurement of the radon diffusion through a nylon foil for different air humidities

    NASA Astrophysics Data System (ADS)

    Mamedov, Fadahat; Štekl, Ivan; Smolek, Karel

    2015-08-01

    The dependency of the radon penetration through a nylon foil on air humidity was measured. Such information is needed for the tracking part of the SuperNEMO detector, which is planned to be shielded against radon by nylon foil and in which the air humidity is not negligible. The long term measurements of radon penetration through nylon foils for different air humidities were performed with the radon diffusion setup constructed at the IEAP, CTU in Prague. The setup consists of two stainless steel hemispheres with Si detector in each of them. Both hemispheres are separated by the tested foil. While the left hemisphere contains high Rn activity, the right part contains only activity caused by the radon penetration through the tested foil. Obtained results of this study with a nylon foil with the thickness of 50 µm are presented.

  15. 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 chromium’s 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.

  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. Energy-Momentum Diffusion Effects on Energy Spectra of Relativistic Runaway Electron Avalanches in Air

    NASA Astrophysics Data System (ADS)

    Cramer, E. S.; Dwyer, J. R.; Rassoul, H.

    2014-12-01

    Simple kinetic equations for runaway electrons inside the high electric field regions of thunderstorms have been developed. These equations are useful in modeling the energy distribution of energetic electrons responsible for Terrestrial Gamma-ray Flashes (TGFs). To describe the shapes of the electron energy spectra for a wide range of electric field strengths, the diffusion term responsible for random deviation of electron energy ionization loss from the mean value is added to the kinetic equation. Previous work has shown that the runaway electron energy spectrum can be described by a power-law when the electric field strength is just above threshold. However, the runaway electron spectrum only approaches tens of MeV before being cut off by energy losses from bremsstrahlung emissions, and thus does not offer an explanation of the photon spectrum observed by the AGILE satellite [Tavani et al., 2011]. We find that the diffusion in energy space helps maintain an exponential energy spectrum for electric fields that approach the runaway electron threshold field and allows the possibility for electrons to be accelerated to energies exceeding the electrostatic potential (minus the average drag force) inside the thundercloud. Since this diffusion process depends on the applied electric field strength, we may also gain insight into the typical values that would be found inside thunderclouds. In this presentation, we first show the effects of diffusion on the relativistic runaway electron energy spectrum for several values of the electric field strength. We then demonstrate an analytical method for solving the momentum diffusion-convection transport equation for relativistic runaway electrons. Finally, we will compare the results of this method to our Monte Carlo simulation developed at Florida Institute of Technology [Dwyer, 2003, 2004, 2007]. Using these detailed simulation results, the diffusion coefficients in momentum space for relativistic runaway electron avalanches in air are found for the range of electric field strengths applicable to thunderstorm environments.

  18. Two-dimensional diffusion of amphiphiles in phospholipid monolayers at the air-water interface.

    PubMed Central

    Caruso, F; Grieser, F; Thistlethwaite, P J; Almgren, M

    1993-01-01

    Steady-state and time-resolved fluorescence spectroscopy has been used to examine lateral diffusion in dipalmitoyl-L-alpha-phosphatidylcholine (DPPC) and dimyristoyl-L-alpha-phosphatidylcholine (DMPC) monolayers at the air-water interface, by studying the fluorescence quenching of a pyrene-labeled phospholipid (pyrene-DPPE) by two amphiphilic quenchers. Steady-state fluorescence measurements revealed pyrene-DPPE to be homogeneously distributed in the DMPC lipid matrix for all measured surface pressures and only in the liquid-expanded (LE) phase of the DPPC monolayer. Time-resolved fluorescence decays for pyrene-DPPE in DMPC and DPPC (LE phase) in the absence of quencher were best described by a single-exponential function, also suggesting a homogeneous distribution of pyrene-DPPE within the monolayer films. Addition of quencher to the monolayer film produced nonexponential decay behavior, which is adequately described by the continuum theory of diffusion-controlled quenching in a two-dimensional environment. Steady-state fluorescence measurements yielded lateral diffusion coefficients significantly larger than those obtained from time-resolved data. The difference in these values was ascribed to the influence of static quenching in the case of the steady-state measurements. The lateral diffusion coefficients obtained in the DMPC monolayers were found to decrease with increasing surface pressure, reflecting a decrease in monolayer fluidity with compression. PMID:8312487

  19. A mechanistic study of Soret diffusion in hydrogen-air flames

    SciTech Connect

    Yang, F.; Law, C.K.; Sung, C.J.; Zhang, H.Q.

    2010-01-15

    The separate and combined effects of Soret diffusion of the hydrogen molecule (H{sub 2}) and radical (H) on the structure and propagation speed of the freely-propagating planar premixed flames, and the strain-induced extinction response of premixed and nonpremixed counterflow flames, were computationally studied for hydrogen-air mixtures using a detailed reaction mechanism and transport properties. Results show that, except for the conservative freely-propagating planar flame, Soret diffusion of H{sub 2} increases the fuel concentration entering the flame structure and as such modifies the mixture stoichiometry and flame temperature, which could lead to substantial increase (decrease) of the flame speed for the lean (rich) mixtures respectively. On the other hand, Soret diffusion of H actively modifies its concentration and distribution in the reaction zone, which in turn affects the individual reaction rates. In particular, the reaction rates of the symmetric, twin, counterflow premixed flames, especially at near-extinction states, can be increased for lean flames but decreased for rich flames, whose active reaction regions are respectively located at, and away from, the stagnation surface. However, such a difference is eliminated for the single counterflow flame stabilized by an opposing cold nitrogen stream, as the active reaction zone up to the state of extinction is always located away from the stagnation surface. Finally, the reaction rate is increased in general for diffusion flames because the bell-shaped temperature distribution localizes the H concentration to the reaction region which has the maximum temperature. (author)

  20. Analysis of opposed jet hydrogen-air counter flow diffusion flame

    NASA Technical Reports Server (NTRS)

    Ho, Y. H.; Isaac, K. M.

    1989-01-01

    A computational simulation of the opposed-jet diffusion flame is performed to study its structure and extinction limits. The present analysis concentrates on the nitrogen-diluted hydrogen-air diffusion flame, which provides the basic information for many vehicle designs such as the aerospace plane for which hydrogen is a candidate as the fuel. The computer program uses the time-marching technique to solve the energy and species equations coupled with the momentum equation solved by the collocation method. The procedure is implemented in two stages. In the first stage, a one-step forward overal chemical reaction is chosen with the gas phase chemical reaction rate determined by comparison with experimental data. In the second stage, a complete chemical reaction mechanism is introduced with detailed thermodynamic and transport property calculations. Comparison between experimental extinction data and theoretical predictions is discussed. The effects of thermal diffusion as well as Lewis number and Prandtl number variations on the diffusion flame are also presented.

  1. In Situ Photocatalytically Heterostructured ZnO-Ag Nanoparticle Composites as Effective Cathode-Modifying Layers for Air-Processed Polymer Solar Cells.

    PubMed

    Yuan, Kai; Chen, Lie; Chen, Yiwang

    2015-08-10

    A heterostructured semiconductor-metal ZnO-Ag nanoparticle (NP) composite was constructed through a straightforward photocatalytic strategy by using UV irradiation of ZnO NPs and an aqueous solution of Ag precursor. The ZnO-Ag NP composites serve as an effective cathode-modifying layer in polymer solar cells (PSCs) with increased short-circuit current density owing to the light-trapping effect, and improved optical and electrical conductivity properties compared with pure ZnO NPs. The Ag NPs, which are photodeposited in situ on ZnO NPs, can act as effective antennas for incident light to maximize light harvesting and minimize radiative decay or nonradiative losses, consequently resulting in the enhanced photogeneration of excitons in PSCs. Systematic photoelectron and -physical investigations confirm that heterostructured ZnO-Ag NPs can significantly improve charge separation, transport, and collection, as well as lower charge recombination at the cathode interface, leading to a 14.0 % improvement in air-processed device power conversion efficiency. In addition, this processable, cost-effective, and scalable approach is compatible with roll-to-roll manufacturing of large-scale PSCs. PMID:26135916

  2. The performance of nano urchin-like NiCo2O4 modified activated carbon as air cathode for microbial fuel cell

    NASA Astrophysics Data System (ADS)

    Ge, Baochao; Li, Kexun; Fu, Zhou; Pu, Liangtao; Zhang, Xi; Liu, Ziqi; Huang, Kan

    2016-01-01

    A nano urchin-like NiCo2O4 has been successfully synthesized via a facile and scalable hydrothermal method. A NiCo2O4 modified active carbon air cathode was designed, optimized and fabricated. The maximum power density of the microbial fuel cell with newly developed cathode is 2.28 time higher than bare active carbon and is comparable to the commercial available Pt/C, reaching 1730 ± 14 mW m-2. The modified active carbon showed remarkable improvement in activity towards the oxygen reduction reaction, which was due to the lower charger transfer, lower activation barrier, and higher exchange current density. Electrochemical evaluation showed a direct four-electron the oxygen reduction reaction on NiCo2O4 modified active carbon, compared to a two-stage process on bare active carbon. The non-precious NiCo2O4 could be considered as a promising alternative to the costly Pt.

  3. Atmospheric pressure diffuse plasma in ambient air for ITO surface cleaning

    NASA Astrophysics Data System (ADS)

    Homola, Tomáš; Matoušek, Jindřich; Medvecká, Veronika; Zahoranová, Anna; Kormunda, Martin; Kováčik, Dušan; Černák, Mirko

    2012-07-01

    Effects of atmospheric filament-free diffuse plasma in ambient air and oxygen by Diffuse Coplanar Surface Barrier Discharge (DCSBD) on surface of indium tin oxide (ITO) were studied. The DCSBD plasma treatment resulted in significant reduction of water contact angles (even for 1 s long treatment). The decrease can be explained by the chemical changes on surface. These were studied by XPS which shows considerable decrease in the carbon surface concentration. The detailed analysis of C1s peak indicates the increase of the highest binding energy component of the C1s peak that corresponds to polar bonds with oxygen, which may be also related to decrease of water contact angle. AFM measurement showed no significant effect of plasma on ITO surface morphology.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

    Zhu, Jiajian; Gao, Jinlong; Li, Zhongshan; Ehn, Andreas; Aldén, 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.

  6. Gas poisoning investigations of scandate and M-type dispenser cathodes

    NASA Astrophysics Data System (ADS)

    Shao, Wensheng; Zhang, Ke; Li, Ji; Yan, Suqiu; Chen, Qilue

    2003-06-01

    Gas poisoning tests of cathode emission were carried out with four kinds of thermal cathodes: W+Sc 2O 3 mixed matrix cathode, impregnated scandate cathode, Ir-coated cathode, Os-coated cathode. As a result, M-type cathodes are more sensitive to O 2, but can recover absolutely in a short time; scandate-type cathodes react slowly and recover partly after a long time. Compared to O 2, ambient air leaked into the vacuum chamber has a smaller influence on the cathode emission; H 2 has a little effect of activation on the four cathodes, especially on the Os-coated cathode.

  7. 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 ± 15.5 mW/m2 at a COD concentration of 400 mg/L, which was further increased to 293.33 ± 7.89 mW/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

  8. 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

  9. 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.

  10. Generating diffuse discharge via repetitive nanosecond pulses and line-line electrodes in atmospheric air.

    PubMed

    Li, Lee; Liu, Yun-Long; Ge, Ya-Feng; Bin, Yu; Huang, Jia-Jia; Lin, Fo-Chan

    2013-10-01

    Diffuse discharge in atmospheric air can generate extremely high power density and large-scale non-thermal plasma. An achievable method of generating diffuse discharge is reported in this paper. Based on the resonance theory, a compact high-voltage repetitive nanosecond pulse generator (HRNPG) has been developed as discharge excitation source. The HRNPG mainly consists of repetitive charging circuit, Tesla transformer and sharpening switch. With the voltage lower than 1.0 kV, the primary repetitive charging circuit comprises two fast thyristors as low-voltage switches. A spiral Tesla transformer is designed to provide a peak transformation ratio of more than 100. The HRNPG prototype is capable of generating a pulse with over 100 kV peak voltage and ~30 ns rise-time at the repetition frequency of 500 Hz. Using the copper line electrodes with a diameter of 0.4 mm, the gaps with highly non-uniform electric field are structured. With the suitable gap spacing and applied pulse, the glow-like diffuse discharge has been generated in line-type and ring-type electrode pairs. Some typical images are presented. PMID:24182161

  11. Diffuse plasma treatment of polyamide 66 fabric in atmospheric pressure air

    NASA Astrophysics Data System (ADS)

    Li, Lee; Peng, Ming-yang; Teng, Yun; Gao, Guozhen

    2016-01-01

    The polyamide 66 (PA66) fabrics are hard to be colored or glued in industrial production due to the poor hydrophily. Diffuse plasma is a kind of non-thermal plasma generated at atmospheric pressure in air. This paper proposes that large-scale diffuse plasma generated between wire electrodes can be employed for improving the hydrophily of PA66 fabrics. A repetitive nanosecond-pulse diffuse-discharge reactor using a cylindrical wire electrode configuration is presented, which can generate large-scale non-thermal plasmas steadily at atmospheric pressure without any barrier dielectric. Then the reactor is used to treat PA66 fabrics in different discharge conditions. The hydrophilicity property of modified PA66 is measured by wicking test method. The modified PA66 is also analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) to prove the surface changes in physical microstructure and chemical functional groups, respectively. What's more, the effects of treatment time and treatment frequency on surface modification are investigated and discussed.

  12. Generating diffuse discharge via repetitive nanosecond pulses and line-line electrodes in atmospheric air

    NASA Astrophysics Data System (ADS)

    Li, Lee; Liu, Yun-Long; Ge, Ya-Feng; Bin, Yu; Huang, Jia-Jia; Lin, Fo-Chan

    2013-10-01

    Diffuse discharge in atmospheric air can generate extremely high power density and large-scale non-thermal plasma. An achievable method of generating diffuse discharge is reported in this paper. Based on the resonance theory, a compact high-voltage repetitive nanosecond pulse generator (HRNPG) has been developed as discharge excitation source. The HRNPG mainly consists of repetitive charging circuit, Tesla transformer and sharpening switch. With the voltage lower than 1.0 kV, the primary repetitive charging circuit comprises two fast thyristors as low-voltage switches. A spiral Tesla transformer is designed to provide a peak transformation ratio of more than 100. The HRNPG prototype is capable of generating a pulse with over 100 kV peak voltage and ˜30 ns rise-time at the repetition frequency of 500 Hz. Using the copper line electrodes with a diameter of 0.4 mm, the gaps with highly non-uniform electric field are structured. With the suitable gap spacing and applied pulse, the glow-like diffuse discharge has been generated in line-type and ring-type electrode pairs. Some typical images are presented.

  13. Prevention of cathode damage from positive ion bombardment

    NASA Technical Reports Server (NTRS)

    Bennett, W. H.

    1972-01-01

    Mixed alkaline earth oxide compounds deposited into hole at cathode surface center prevent ion back bombardment damage to cathode by reducing oxide layer and by creating metallic diffusion along sides of hole for enhanced electron emission.

  14. Cathodic arcs

    SciTech Connect

    Anders, Andre

    2003-10-29

    Cathodic arc plasma deposition has become the technology of choice for hard, wear and corrosion resistant coatings for a variety of applications. The history, basic physics of cathodic arc operation, the infamous macroparticle problem and common filter solutions, and emerging high-tech applications are briefly reviewed. Cathodic arc plasmas standout due to their high degree of ionization, with important consequences for film nucleation, growth, and efficient utilization of substrate bias. Industrial processes often use cathodic arc plasma in reactive mode. In contrast, the science of arcs has focused on the case of vacuum arcs. Future research directions include closing the knowledge gap for reactive mode, large area coating, linear sources and filters, metal plasma immersion process, with application in high-tech and biomedical fields.

  15. Nonluminous diffusion flame of diluted acetylene in oxygen-enriched air

    SciTech Connect

    Sugiyama, G.

    1994-12-31

    A soot-reducing mechanism of fuel dilution and oxygen enrichment in laminar diffusion flames is suggested. Analysis using the Burke-Schumann theory for the shape of over ventilated diffusion flames has shown that there is a critical ratio of stoichiometric coefficients of the fuel and the oxidizer under which the gas flows from the fuel side to the oxidizer side throughout the flame. When this condition is satisfied, the soot growth region vanishes. A similar result is also found in a numerical simulation for diffusion flames that do not satisfy the Burke-Schumann assumption of uniform flow field. KIVA code is used for that purpose. The theoretically predicted direction of gas-flow across the flame sheet is verified in an experiment in a coaxial-flow diffusion flame. Soot cloud and velocity fields are visualized through a laser sheet method in the experiment. The fuel is a mixture of acetylene and nitrogen. The oxidizer is a mixture of oxygen and nitrogen. The compositions of the reactants are controlled so that the adiabatic flame temperature is kept constant to avoid the effect of temperature change. Experimental results show substantial reduction of scattered light intensity by fuel dilution and oxygen enrichment. When a sufficient amount of nitrogen is added to the fuel, nonluminous blue flames are obtained. At higher oxygen concentrations, blue flames are obtained at higher flame temperature region. When oxygen concentration in the oxidizer is 70 vol.%, blue flames are obtained up to 2,250 K. The critical condition of the reactants for nonluminous flames agrees with the theoretical prediction when the oxidizer is ordinary air. In oxygen-enriched conditions, the fuel must be diluted more, than theoretically predicted.

  16. Laser filamentation induced air-flow motion in a diffusion cloud chamber.

    PubMed

    Sun, Haiyi; Liu, Jiansheng; Wang, Cheng; Ju, Jingjing; Wang, Zhanxin; Wang, Wentao; Ge, Xiaochun; Li, Chuang; Chin, See Leang; Li, Ruxin; Xu, Zhizhan

    2013-04-22

    We numerically simulated the air-flow motion in a diffusion cloud chamber induced by femtosecond laser filaments for different chopping rates. A two dimensional model was employed, where the laser filaments were treated as a heat flux source. The simulated patterns of flow fields and maximum velocity of updraft compare well with the experimental results for the chopping rates of 1, 5, 15 and 150 Hz. A quantitative inconsistency appears between simulated and experimental maximum velocity of updraft for 1 kHz repetition rate although a similar pattern of flow field is obtained, and the possible reasons were analyzed. Based on the present simulated results, the experimental observation of more water condensation/snow at higher chopping rate can be explained. These results indicate that the specific way of laser filament heating plays a significant role in the laser-induced motion of air flow, and at the same time, our previous conclusion of air flow having an important effect on water condensation/snow is confirmed. PMID:23609636

  17. Surface-Tuned Co3O4 Nanoparticles Dispersed on Nitrogen-Doped Graphene as an Efficient Cathode Electrocatalyst for Mechanical Rechargeable Zinc-Air Battery Application.

    PubMed

    Singh, Santosh K; Dhavale, Vishal M; Kurungot, Sreekumar

    2015-09-30

    The most vital component of the fuel cells and metal-air batteries is the electrocatalyst, which can facilitate the oxygen reduction reaction (ORR) at a significantly reduced overpotential. The present work deals with the development of surface-tuned cobalt oxide (Co3O4) nanoparticles dispersed on nitrogen-doped graphene as a potential ORR electrocatalyst possessing some unique advantages. The thermally reduced nitrogen-doped graphene (NGr) was decorated with three different morphologies of Co3O4 nanoparticles, viz., cubic, blunt edged cubic, and spherical, by using a simple hydrothermal method. We found that the spherical Co3O4 nanoparticle supported NGr catalyst (Co3O4-SP/NGr-24h) has acquired a significant activity makeover to display the ORR activity closely matching with the state-of-the-art Pt supported carbon (PtC) catalyst in alkaline medium. Subsequently, the Co3O4-SP/NGr-24h catalyst has been utilized as the air electrode in a Zn-air battery, which was found to show comparable performance to the system derived from PtC. Co3O4-SP/NGr-24h catalyst has shown several hours of flat discharge profile at the discharge rates of 10, 20, and 50 mA/cm(2) with a specific capacity and energy density of ~590 mAh/g-Zn and ~840 Wh/kg-Zn, respectively, in the primary Zn-air battery system. In conjunction, Co3O4-SP/NGr-24h has outperformed as an air electrode in mechanical rechargeable Zn-air battery as well, which has shown consistent flat discharge profile with minimal voltage loss at a discharge rate of 50 mA/cm(2). The present results, thus demonstrate that the proper combination of the tuned morphology of Co3O4 with NGr will be a promising and inexpensive material for efficient and ecofriendly cathodes for Zn-air batteries. PMID:26376490

  18. Electrocatalysis for dioxygen reduction by a μ-oxo decavanadium complex in alkaline medium and its application to a cathode catalyst in air batteries

    NASA Astrophysics Data System (ADS)

    Dewi, Eniya Listiani; Oyaizu, Kenichi; Nishide, Hiroyuki; Tsuchida, Eishun

    The redox behavior of a decavanadium complex [(VO) 10(μ 2-O) 9(μ 3-O) 3(C 5H 7O 2) 6] ( 1) was studied using cyclic voltammetry under acidic and basic conditions. The reduction potential of V(V) was found at less positive potentials for higher pH electrolyte solutions. The oxygen reduction at complex 1 immobilized on a modified electrode was examined using cyclic voltammetry and rotating ring-disk electrode techniques in the 1 M KOH solutions. On the basis of measurements using a rotating disk electrode (RDE), the complex 1 was found to be highly active for the direct four-electron reduction of dioxygen at -0.2 V versus saturated calomel electrode (SCE). The complex 1 as a reduction catalyst of O 2 with a high selectivity was demonstrated using rotating ring-disk voltammograms in alkaline solutions. The application of complex 1 as an oxygen reduction catalyst at the cathode of zinc-air cell was also examined. The zinc-air cell with the modified electrode showed a stable discharge potential at approximately 1 V with discharge capacity of 80 mAh g -1 which was about five times larger than that obtained with the commonly used manganese dioxide catalyst.

  19. A reactive and sensitive diffusion sampler for the determination of aldehydes and ketones in ambient air

    NASA Astrophysics Data System (ADS)

    Uchiyama, Shigehisa; Hasegawa, Shuji

    We developed a diffusive sampling device (DSD-carbonyl) for organic carbonyl compounds (aldehydes and ketones) which is suitable for collection and analysis of low concentration levels. This sampling device is composed of three parts, an exposure part made of a porous polytetrafluoroethylene (PPTFE) tube, an analysis part made of polypropylene (PP) tubing and an absorbent part made of 2,4-dinitrophenylhydrazine (DNPH) coated silica gel (DNPH-silica). Aldehydes and ketones diffuse to the DSD-carbonyl through PPTFE-tube by the mechanism of molecular diffusion and react specifically with DNPH to form a stable DNPH-derivatives. Collection is controlled by moving the absorbent from the exposure part to the analysis part by changing the posture of the DSD-carbonyl. DNPH-derivatives were eluted from an analysis part of DSD-carbonyl with acetonitrile directly and analyzed by high performance liquid chromatography (HPLC). The advantages of the DSD-carbonyl are the following: (1) The DSD-carbonyl can be used in a wide range of concentration of aldehydes and ketones in atmosphere, as the DSD-carbonyl exposure part has a variable diffusion area, (2) DNPH-derivatives are eluted from DNPH-silica without contamination of air. (3) The sampler can be applied to active sampling by connecting it with a pump. The limit of detection (LOD) for concentrations of major aldehydes and ketones ranged from 0.072 to 0.13 ppb, and the limit of quantitation (LOQ) ranged from 0.24 to 0.42 ppb. The coefficient variation (CV) for concentrations of major aldehydes and ketones ranged from 2.5 to 3.0% in laboratory air. The DSD-carbonyl method and active sampling method (US EPA method IP-6A) showed a good correlation (formaldehyde, r2=0.995). The uptake rates for formaldehyde, acetaldehyde, and acetone were estimated as 0.078, 0.062 and 0.079 nmol ppb -1 h -1, respectively. It is possible to estimate atmospheric aldehydes and ketones at parts per billion (ppb), with high sensitivity and precision, by using DSD-carbonyl.

  20. Nanotubular MnO2/graphene oxide composites for the application of open air-breathing cathode microbial fuel cells.

    PubMed

    Gnana Kumar, G; Awan, Zahoor; Suk Nahm, Kee; Xavier, J Stanley

    2014-03-15

    Nanotubular shaped α-MnO2/graphene oxide nanocomposites were synthesized via a simple, cost and time efficient hydrothermal method. The growth of hollow structured MnO2 nanotubes preferentially occurred along the [001] direction as evidenced from the morphological and structural characterizations. The tunnels of α-MnO2 nanotubes easily accommodated the molecular oxygen and exhibited excellent catalytic activity towards the oxygen reduction reaction over the rod structure and was further enhanced with the effective carbon support graphene oxide. The MnO2 nanotubes/graphene oxide nanocomposite modified electrode exhibited a maximum power density of 3359 mW m(-2) which is 7.8 fold higher than that of unmodified electrode and comparable with the Pt/C modified electrode. The microbial fuel cell equipped with MnO2 nanotubes/graphene oxide nanocomposite modified cathode exhibited quick start up and excellent durability over the studied electrodes and is attributed to the high surface area and number of active sites. These findings not only provide the fundamental studies on carbon supported low-dimensional transition-metal oxides but also open up the new possibilities of their applications in green energy devices. PMID:24240107

  1. Ag-Cu nanoalloyed film as a high-performance cathode electrocatalytic material for zinc-air battery

    NASA Astrophysics Data System (ADS)

    Lei, Yimin; Chen, Fuyi; Jin, Yachao; Liu, Zongwen

    2015-04-01

    A novel Ag50Cu50 film electrocatalyst for oxygen reduction reaction (ORR) was prepared by pulsed laser deposition (PLD) method. The electrocatalyst actually is Ag-Cu alloyed nanoparticles embedded in amorphous Cu film, based on transmission electron microscopy (TEM) characterization. The rotating disk electrode (RDE) measurements provide evidence that the ORR proceed via a four-electron pathway on the electrocatalysts in alkaline solution. And it is much more efficient than pure Ag catalyst. The catalytic layer has maximum power density of 67 mW cm-2 and an acceptable cell voltage at 0.863 V when current densities increased up to 100 mA cm-2 in the Ag50Cu50-based primary zinc-air battery. The resulting rechargeable zinc-air battery exhibits low charge-discharge voltage polarization of 1.1 V at 20 mAcm-2 and high durability over 100 cycles in natural air.

  2. Magnetically Diffused Radial Electric-Arc Air Heater Employing Water-Cooled Copper Electrodes

    NASA Technical Reports Server (NTRS)

    Mayo, R. F.; Davis, D. D., Jr.

    1962-01-01

    A magnetically rotated electric-arc air heater has been developed that is novel in that an intense magnetic field of the order of 10,000 to 25,000 gauss is employed. This field is supplied by a coil that is connected in series with the arc. Experimentation with this heater has shown that the presence of an intense magnetic field transverse to the arc results in diffusion of the arc and that the arc has a positive effective resistance. With the field coil in series with the arc, highly stable arc operation is obtained from a battery power supply. External ballast is not required to stabilize the arc when it is operating at maximum power level. The electrode erosion rate is so low that the airstream contamination is no more than 0.07 percent and may be substantially less.

  3. Effect of binders on natural graphite powder-based gas diffusion electrode for Mg-air cell

    NASA Astrophysics Data System (ADS)

    Arinton, Ghenadi; Rianto, Anton; Faizal, Ferry; Hidayat, Darmawan; Hidayat, Sahrul; Panatarani, Camellia; Joni, I. Made

    2016-03-01

    This paper mainly discussed the electrical performance of gas diffusion electrode of Mg-Air Cell. The gas diffusion electrodes (GDE) use a natural graphite powder as catalyst material. The effect of additional binders to the GDE have been investigated to improve electrode performances. Several types of GDE have been developed using binder materials such as epoxy resin, natural clay, carboxymethyl cellulose (CMC) and urea-formaldehyde (UF). By using discharge performance measurement, the characteristics of the as-prepared GDEs are reported.

  4. An atmospheric air gas-liquid diffuse discharge excited by bipolar nanosecond pulse in quartz container used for water sterilization

    NASA Astrophysics Data System (ADS)

    Wang, Sen; Yang, De-Zheng; Wang, Wen-Chun; Zhang, Shuai; Liu, Zhi-Jie; Tang, Kai; Song, Ying

    2013-12-01

    In this Letter, we report that the air gas-liquid diffuse discharge plasma excited by bipolar nanosecond pulse in quartz container with different bottom structures at atmospheric pressure. Optical diagnostic measurements show that bountiful chemically and biologically active species, which are beneficial for effective sterilization in some areas, are produced. Such diffuse plasmas are then used to treat drinking water containing the common microorganisms (Candida albicans and Escherichia coli). It is found that these plasmas can sterilize the microorganisms efficiently.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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 Φ. A popular dopant ThO2 decreases Φ 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 Φ 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 Φ, 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 Φ 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.

  11. Improving design factors of air diffuser systems based on field conditions of dam reservoirs: CFD simulation approach.

    PubMed

    Shin, Sangmin; Lee, Seungjae; Lee, Sangeun; Yum, Kyungtaek; Park, Heekyung

    2012-01-01

    This study aims to improve the design factors of air diffuser systems that have been analyzed in laboratory experiments, with consideration of the field conditions of dam reservoirs. In this study, the destratification number (D(N)), destratification radius, and efficiency are considered as design factors. The computational fluid dynamics (CFD) simulation experiment is performed in diverse field conditions in order to analyze these factors. The results illustrate the wider range of D(N) values in field conditions and the relationship of the destratification radius and efficiency to D(N). The results can lead to better performance of air diffuser systems and water quality management in dam reservoir sites. PMID:22678200

  12. H2S and VOCs abatement robustness in biofilters and air diffusion bioreactors: A comparative study.

    PubMed

    Lebrero, Raquel; Rodríguez, Elisa; Martin, María; García-Encina, Pedro A; Muñoz, Raúl

    2010-07-01

    The robustness of a conventional biofilter and an air diffusion bioreactor (ADB) was comparatively evaluated in laboratory-scale plants treating a mixture of H2S, butanone, toluene and alpha-pinene at gas residence times of 50 s. Under steady state conditions, H2S, butanone and toluene were almost completely degraded, while alpha-pinene removal did not exhibit removal efficiencies (REs) higher than 11.0 +/- 2.3%. Fluctuations in temperature from 8 degrees C to 30 degrees C did not impact significantly process performance in any of the biotechnologies tested. However, while the ADB unit was able to cope with three and six fold step increases in pollutant loadings, volatile organic compounds (VOCs) REs noticeably decreased in the biofilter when subjected to a six fold step change (i.e. 90% reduction for butanone and 30% for toluene). A process shutdown of five days resulted in the temporary loss of butanone and toluene RE in the ADB system. A lack of irrigation during five days caused a slight decrease in the biofilter REs, while a failure in the pH control system drastically affected the ADB performance. Finally, process robustness was quantified. The calculated overall risks showed that both biotechnologies were reliable for H2S and VOCs treatment in wastewater treatment plants, ADB diffusion exhibiting a higher robustness towards fluctuations commonly found under routine operation. This robustness was further confirmed by the high stability of the DGGE profiles. PMID:20639014

  13. Simulation of Electron and Ion Transport in Methane-Air Counterflow Diffusion Flames

    NASA Astrophysics Data System (ADS)

    Choi, Sangkyu; Bisetti, Fabrizio; Chung, Suk Ho

    2010-11-01

    The spatial distribution of charged species in a methane-air counterflow diffusion flame is simulated with a detailed ion chemistry. The electric field induced by the distribution of charged species is calculated and compared to that obtained invoking the ambipolar diffusion assumption. The two calculations showed identical profiles for charged species and electric field. The profiles of ion mole fractions show two peaks: one near the maximum temperature and a second peak on the oxidizer side. The major ions near the maximum temperature are electron, C2H3O+ and H3O+. CHO3- and H3O+ contribute to the second peak. These profiles are quite different from those adopting a simplified three-step mechanism based solely on E-, CHO+ and H3O+, which shows only a single peak. Reaction pathway analyses showed that near the flame region, the proton is transferred by the path of CHO+ -> H3O+ -> C2H3O+ -> CHO+ in a circulating manner. In the second peak, CHO3- is produced though the pathway of E- -> O- -> OH- -> CHO3-. The sensitivity of the charged species profiles to transport properties is investigated, and it is found that the variation of charged species profiles near peak temperature is relatively small, while on the oxidizer side, it is quite sensitive to transport properties.

  14. 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 Lluís; Centellas, Francesc; Garrido, José Antonio; Rodríguez, Rosa María; 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 H₂O₂ 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 NH₄⁺ ion and in much lesser extent as NO₃⁻ ion, whereas most of its initial S was converted into SO₄²⁻ ion. PMID:23561569

  15. Soot Surface Growth in Laminar Hydrocarbon/Air Diffusion Flames. Appendix J

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    The structure and soot surface growth properties of round laminar jet diffusion flames were studied experimentally. Measurements were made along the axes of ethylene-, propylene-propane- and acetylene-benzene-fueled flames burning in coflowing air at atmospheric pressure with the reactants at normal temperature. The measurements included soot structure, soot concentrations, soot temperatures, major gas species concentrations, some radial species (H, OH and 0) concentrations, and gas velocities. These measurements yielded the local flame properties that are thought to affect soot surface growth as well as local soot surface growth rates. When present results were combined with similar earlier observations of acetylene-fueled laminar jet diffusion flames, the results suggested that soot surface growth involved decomposition of the original fuel to form acetylene and H, which were the main reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. Thus, as the distance increased along the axes of the flames, soot formation (which was dominated by soot surface growth) began near the cool core of the flow once acetylene and H appeared together and ended near the flame sheet when acetylene disappeared. Species mainly responsible for soot oxidation - OH and 02 were present throughout the soot formation region so that soot surface growth and oxidation proceeded at the same time. Present measurements of soot surface growth rates (corrected for soot surface oxidation) in laminar jet diffusion flames were consistent with earlier measurements of soot surface growth rates in laminar premixed flames and exhibited good agreement with existing Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth mechanisms in the literature with steric factors in these mechanisms having values on the order of unity, as anticipated.

  16. Soot Surface Growth in Laminar Hydrocarbon/Air Diffusion Flames. Appendix B

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    The structure and soot surface growth properties of round laminar jet diffusion flames were studied experimentally. Measurements were made along the axes of ethylene-, propylene-propane- and acetylene-benzene-fueled flames burning in coflowing air at atmospheric pressure with the reactants at normal temperature. The measurements included soot structure, soot concentrations, soot temperatures, major gas species concentrations, some radial species (H, OH and O) concentrations, and gas velocities. These measurements yielded the local flame properties that are thought to affect soot surface growth as well as local soot surface growth rates. When present results were combined with similar earlier observations of acetylene-fueled laminar jet diffusion flames, the results suggested that soot surface growth involved decomposition of the original fuel to form acetylene and H, which were the main reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. Thus, as the distance increased along the axes of the flames, soot formation (which was dominated by soot surface growth) began near the cool core of the flow once acetylene and H appeared together and ended near the flame sheet when acetylene disappeared. Species mainly responsible for soot oxidation - OH and O2 were present throughout the soot formation region so that soot surface growth and oxidation proceeded at the same time. Present measurements of soot surface growth rates (corrected for soot surface oxidation) in laminar jet diffusion flames were consistent with earlier measurements of soot surface growth rates in laminar premixed flames and exhibited good agreement with existing Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth mechanisms in the literature with steric factors in these mechanisms having values on the order of unity, as anticipated.

  17. 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.

  18. 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.

  19. 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.

  20. Cooling channels design analysis with chaotic laminar trajectory for closed cathode air-cooled PEM fuel cells using non-reacting numerical approach

    NASA Astrophysics Data System (ADS)

    N, W. Mohamed W. A.

    2015-09-01

    The thermal management of Polymer Electrolyte Membrane (PEM) fuel cells contributes directly to the overall power output of the system. For a closed cathode PEM fuel cell design, the use of air as a cooling agent is a non-conventional method due to the large heat load involved, but it offers a great advantage for minimizing the system size. Geometrical aspects of the cooling channels have been identified as the basic parameter for improved cooling performance. Numerical investigation using STAR-CCM computational fluid dynamics platform was applied for non-reacting cooling effectiveness study of various channel geometries for fuel cell application. The aspect ratio of channels and the flow trajectory are the parametric variations. A single cooling plate domain was selected with an applied heat flux of 2400 W/m2 while the cooling air are simulated at Reynolds number of 400 that corresponds to normal air flow velocities using standard 6W fans. Three channel designs of similar number of channels (20 channels) are presented here to analyze the effects of having chaotic laminar flow trajectory compared to the usual straight path trajectory. The total heat transfer between the cooling channel walls and coolant were translated into temperature distribution, maximum temperature gradient, average plate temperature and overall cooling effectiveness analyses. The numerical analysis shows that the chaotic flow promotes a 5% to 10% improvement in cooling effectiveness, depending on the single-axis or multi-axis flow paths applied. Plate temperature uniformity is also more realizable using the chaotic flow designs.

  1. Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

    NASA Astrophysics Data System (ADS)

    Nikiforov, A.; Li, L.; Britun, N.; Snyders, R.; Vanraes, P.; Leys, C.

    2014-02-01

    Treatment of samples with plasmas in biomedical applications often occurs in ambient air. Admixing air into the discharge region may severely affect the formation and destruction of the generated oxidative species. Little is known about the effects of air diffusion on the spatial distribution of OH radicals and O atoms in the afterglow of atmospheric-pressure plasma jets. In our work, these effects are investigated by performing and comparing measurements in ambient air with measurements in a controlled argon atmosphere without the admixture of air, for an argon plasma jet. The spatial distribution of OH is detected by means of laser-induced fluorescence diagnostics (LIF), whereas two-photon laser-induced fluorescence (TALIF) is used for the detection of atomic O. The spatially resolved OH LIF and O TALIF show that, due to the air admixture effects, the reactive species are only concentrated in the vicinity of the central streamline of the afterglow of the jet, with a characteristic discharge diameter of ˜1.5 mm. It is shown that air diffusion has a key role in the recombination loss mechanisms of OH radicals and atomic O especially in the far afterglow region, starting up to ˜4 mm from the nozzle outlet at a low water/oxygen concentration. Furthermore, air diffusion enhances OH and O production in the core of the plasma. The higher density of active species in the discharge in ambient air is likely due to a higher electron density and a more effective electron impact dissociation of H2O and O2 caused by the increasing electrical field, when the discharge is operated in ambient air.

  2. Chemical response of methane/air diffusion flames to unsteady strain rate

    SciTech Connect

    Im, H.G.; Chen, J.H.; Chen, J.Y.

    1998-03-01

    Effects of unsteady strain rate on the response of methane/air diffusion flames are studied. The authors use the finite-domain opposed flow configuration in which the nozzle exit velocity is imposed as a function of time. The GRI mechanism v2.11 is used for the detailed methane/air chemistry. The response of individual species to monochromatic oscillation in strain rate with various frequencies reveals that the fluctuation of slow species, such as CO and NO{sub x}, is more rapidly suppressed as the flow time scale decreases. It is also observed that the maximum CO concentration is very insensitive to the variation in the scalar dissipation rate. An extinction event due to an abrupt imposition of high strain rates is also simulated by an impulsive velocity with various frequencies. For a fast impulse, a substantial overshoot in NO{sub 2} concentration is observed after extinction. Finally, the overall fuel burning rate shows a nonmonotonic response to the variation in characteristic unsteady time scale, while the emission indices for NO{sub x} shows monotonic decay in response as frequency is increased.

  3. 24-HOUR DIFFUSIVE SAMPLING OF TOXIC VOCS IN AIR ONTO CARBOPACK X SOLID ADSORBENT FOLLOWED BY THERMAL DESORPTION/GC/MS ANALYSIS - LABORATORY STUDIES

    EPA Science Inventory

    Diffusive sampling of a mixture of 42 volatile organic compounds (VOCs) in humidified, purified air onto the solid adsorbent Carbopack X was evaluated under controlled laboratory conditions. The evaluation included variations in sample air temperature, relative humidity, and ozon...

  4. Ag-Cu nanoalloyed film as a high-performance cathode electrocatalytic material for zinc-air battery.

    PubMed

    Lei, Yimin; Chen, Fuyi; Jin, Yachao; Liu, Zongwen

    2015-01-01

    A novel Ag50Cu50 film electrocatalyst for oxygen reduction reaction (ORR) was prepared by pulsed laser deposition (PLD) method. The electrocatalyst actually is Ag-Cu alloyed nanoparticles embedded in amorphous Cu film, based on transmission electron microscopy (TEM) characterization. The rotating disk electrode (RDE) measurements provide evidence that the ORR proceed via a four-electron pathway on the electrocatalysts in alkaline solution. And it is much more efficient than pure Ag catalyst. The catalytic layer has maximum power density of 67 mW cm(-2) and an acceptable cell voltage at 0.863 V when current densities increased up to 100 mA cm(-2) in the Ag50Cu50-based primary zinc-air battery. The resulting rechargeable zinc-air battery exhibits low charge-discharge voltage polarization of 1.1 V at 20 mAcm(-2) and high durability over 100 cycles in natural air. PMID:25977668

  5. Velocity Fields of Axisymmetric Hydrogen-Air Counterflow Diffusion Flames from LDV, PIV, and Numerical Computation

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Wilson, Lloyd G.; Humphreys, William M., Jr.; Bartram, Scott M.; Gartrell, Luther R.; Isaac, K. M.

    1995-01-01

    Laminar fuel-air counterflow diffusion flames (CFDFs) were studied using axisymmetric convergent-nozzle and straight-tube opposed jet burners (OJBs). The subject diagnostics were used to probe a systematic set of H2/N2-air CFDFs over wide ranges of fuel input (22 to 100% Ha), and input axial strain rate (130 to 1700 Us) just upstream of the airside edge, for both plug-flow and parabolic input velocity profiles. Laser Doppler Velocimetry (LDV) was applied along the centerline of seeded air flows from a convergent nozzle OJB (7.2 mm i.d.), and Particle Imaging Velocimetry (PIV) was applied on the entire airside of both nozzle and tube OJBs (7 and 5 mm i.d.) to characterize global velocity structure. Data are compared to numerical results from a one-dimensional (1-D) CFDF code based on a stream function solution for a potential flow input boundary condition. Axial strain rate inputs at the airside edge of nozzle-OJB flows, using LDV and PIV, were consistent with 1-D impingement theory, and supported earlier diagnostic studies. The LDV results also characterized a heat-release hump. Radial strain rates in the flame substantially exceeded 1-D numerical predictions. Whereas the 1-D model closely predicted the max I min axial velocity ratio in the hot layer, it overpredicted its thickness. The results also support previously measured effects of plug-flow and parabolic input strain rates on CFDF extinction limits. Finally, the submillimeter-scale LDV and PIV diagnostics were tested under severe conditions, which reinforced their use with subcentimeter OJB tools to assess effects of aerodynamic strain, and fueVair composition, on laminar CFDF properties, including extinction.

  6. Effect of the cathode material on the amplitude of the ultrashort avalanche electron beam in atmospheric-pressure air

    NASA Astrophysics Data System (ADS)

    Baksht, E. Kh.; Burachenko, A. G.; Tarasenko, V. F.

    2015-11-01

    Generation of ultrashort avalanche electron beam (UAEB) during subnanosecond breakdown in atmospheric-pressure air is investigated with a picosecond time resolution. The signals of incident and reflected voltage waves measured in the transmission line of the SLEP-150M generator have made it possible to reconstruct the voltage in the electrode gap. It is found that due to an increase in the gap voltage in the case of a stainless steel conical electrode, the UAEB amplitude is larger than for identical electrodes made of copper and aluminum. It is shown that the UAEB duration and amplitude increase when the conical electrode is replaced by a tubular electrode.

  7. A search for diffuse emission of UHE gamma rays in southern sky from observation of hadronless air showers.

    NASA Astrophysics Data System (ADS)

    Ticona, R.; Inoue, N.; Imaizumi, S.; Mori, K.; Matano, T.; Tsushima, I.; Kawasumi, N.; Honda, K.; Hashimoto, K.; Martinic, N.; Aliaga, Z.; Reguerin, A.; Gironda, N.; Osco, F.

    1993-03-01

    The lateral distributions of hadrons in air showers have been determined precisely as a function of the core distance, the shower size, the zenith angle and age, and the hadronless showers as candidates of gamma-ray-initiated air showers can be discriminated with this average lateral distribution. There is no evidence of the detection of gamma rays from any diffused regions with enough significance, but the arrival directions of hadronless air showers selected under strict conditions have an anisotropy in the equatorial coordinates.

  8. Diffusion welding in air. [solid state welding of butt joint by fusion welding, surface cleaning, and heating

    NASA Technical Reports Server (NTRS)

    Moore, T. J.; Holko, K. H. (Inventor)

    1974-01-01

    Solid state welding a butt joint by fusion welding the peripheral surfaces to form a seal is described along with, autogenetically cleaning the faying or mating surfaces of the joint by heating the abutting surfaces to 1,200 C and heating to the diffusion welding temperature in air.

  9. 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...

  10. 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.

  11. 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.

  12. Opposed jet diffusion flames of nitrogen-diluted hydrogen vs air - Axial LDA and CARS surveys; fuel/air rates at extinction

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Jarrett, Olin, Jr.; Antcliff, R. R.

    1989-01-01

    An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF.

  13. Effects of gas-band radiation on soot kinetics in laminar methane/air diffusion flames

    SciTech Connect

    Sivathanu, Y.R.; Gore, J.P.

    1997-07-01

    A coupled radiation and soot kinetics calculation of laminar methane/air diffusion flame properties is described. Transport equations for mass, momentum, mixture fraction, enthalpy (sensible + chemical) including gas-band radiation, soot mass fraction, and soot number density are solved. A simplified soot kinetics model incorporating nucleation, growth, oxidation, and agglomeration processes is used. The reaction rates in the simplified kinetics model depend on the temperature and the local concentrations of C{sub 2}H{sub 2}, O{sub 2}, and OH. The major gas species and the C{sub 2}H{sub 2} and OH concentrations are obtained using state relationships. The local temperature is obtained by solving the energy equation, taking radiation loss and gain from gas species and soot particles into consideration. The radiative source/sink term in the energy equation is obtained using a multiray method in conjunction with the narrow-band algorithm RADCAL. The results of the soot kinetics model are compared with existing laser-induced incandescence (LII) measurements of soot volume fractions. Reasonable comparison can be obtained only with an arbitrary downstream shift of 20 mm in the origin of the predictions from the burner exit. This highlights the need for improved chemical kinetics, but does not affect the following conclusions: the contribution of participating gas (CO{sub 2} and H{sub 2}O) radiation dominates that of soot radiation by an order of magnitude in the present methane/air flames, and even for the present weakly radiating flames, the local radiative heat loss/gain strongly influences the soot nucleation, formation, and oxidation rates.

  14. Liftoff and blowoff of a diffusion flame between parallel streams of fuel and air

    SciTech Connect

    Fernandez-Tarrazo, Eduardo; Vera, Marcos; Linan, Amable

    2006-01-01

    A numerical analysis is presented to describe the liftoff and blowoff of a diffusion flame in the mixing layer between two parallel streams of fuel (mainly methane diluted with nitrogen) and air emerging from porous walls. The analysis, which takes into account the effects of thermal expansion, assumes a one-step overall Arrhenius reaction, where the activation energy E is allowed to vary to reproduce the variations of the planar flame propagation velocity with the equivalence ratio. First, we describe the steady flame-front structure when stabilized close to the porous wall (attached flame regime). Then, we analyze the case where the flame front is located far away from the porous wall, at a distance x{sub f}' such that, upstream of the flame front, the mixing layer has a self-similar structure (lifted flame regime). For steady lifted flames, the results, given here in the case when the fuel and air streams are injected with the same velocity, relate U{sub f}'/S{sub L}, the front velocity (relative to the upstream flow) measured with the planar stoichiometric flame velocity, with the Damkohler number D{sub m}=({delta}{sub m}/{delta}{sub L}){sup 2}, based on the thickness, {delta}{sub m}, of the nonreacting mixing layer at the flame-front position and the laminar flame thickness, {delta}{sub L}. For large values of D{sub m}, the results, presented here for a wide range of dilutions of the fuel stream, provide values of the front propagation velocity that are in good agreement with previous experimental results, yielding well-defined conditions for blowoff. The calculated flame-front velocity can also be used to describe the transient flame-front dynamics after ignition by an external energy source.

  15. Double diffusion, convection de Boussinesq et convection profonde en air atmosphérique pollué ou humide

    NASA Astrophysics Data System (ADS)

    Bois, Pierre-Antoine

    2006-11-01

    We derive the molecular diffusion equations, and we show how the determination of the molecular diffusion coefficients of passive scalars (pollutants or moisture) in the atmospheric air may be performed, in first approximation, by means of data of pressure, temperature and densities in the medium at the rest. These approximations are sufficient in order to write the equations of shallow convection (Boussinesq equations), whatever be the Brunt-Väisälä frequency of the medium (as well as in the troposphere and in the stratosphere). In the case of deep convection, which is possible in the troposphere only, the weakness of the Brunt-Väisälä frequency modifies the molecular diffusion equations, and these equations also modify the equations of convection. More accurate evaluations of the diffusion coefficients must also be made, using, for instance, static datas associated with several temperature distributions. To cite this article: P.-A. Bois, C. R. Mecanique 334 (2006).

  16. Study on electrical characteristics of barrier-free atmospheric air diffuse discharge generated by nanosecond pulses and long wire electrodes

    NASA Astrophysics Data System (ADS)

    Li, Lee; Liu, Yun-Long; Teng, Yun; Liu, Lun; Pan, Yuan

    2014-07-01

    In room-temperature atmospheric air, the large-scale diffuse plasmas can be generated via high-voltage nanosecond pulses with short rise-time and wire electrodes. Diffuse discharge with the wire electrode length up to 110.0 cm and the discharge spacing of several centimeters has been investigated in this paper. Electrical characteristics of diffuse discharge have been analyzed by their optical photographs and measuring of the voltage and current waveforms. Experimental results show the electrode spacing, and the length of wire electrodes can influence the intensity and mode transition of diffuse discharge. The characteristic of current waveforms is that there are several current oscillation peaks at the time of applied pulsed voltage peak, and at the tail of applied pulse, the conduction current component will compensate the displacement one so that the measured current is unidirectional in diffuse discharge mode. The transition from diffuse discharge to arc discharge is always with the increasing of conduction current density. As for nanosecond pulses with long tail, the long wire electrodes are help for generating non-equilibrium diffuse plasmas.

  17. Study on electrical characteristics of barrier-free atmospheric air diffuse discharge generated by nanosecond pulses and long wire electrodes

    SciTech Connect

    Li, Lee Liu, Yun-Long; Teng, Yun; Liu, Lun; Pan, Yuan

    2014-07-15

    In room-temperature atmospheric air, the large-scale diffuse plasmas can be generated via high-voltage nanosecond pulses with short rise-time and wire electrodes. Diffuse discharge with the wire electrode length up to 110.0 cm and the discharge spacing of several centimeters has been investigated in this paper. Electrical characteristics of diffuse discharge have been analyzed by their optical photographs and measuring of the voltage and current waveforms. Experimental results show the electrode spacing, and the length of wire electrodes can influence the intensity and mode transition of diffuse discharge. The characteristic of current waveforms is that there are several current oscillation peaks at the time of applied pulsed voltage peak, and at the tail of applied pulse, the conduction current component will compensate the displacement one so that the measured current is unidirectional in diffuse discharge mode. The transition from diffuse discharge to arc discharge is always with the increasing of conduction current density. As for nanosecond pulses with long tail, the long wire electrodes are help for generating non-equilibrium diffuse plasmas.

  18. Structure and Soot Properties of Nonbuoyant Ethylene/Air Laminar Jet Diffusion Flames. Appendix I

    NASA Technical Reports Server (NTRS)

    Urban, D. L.; Yuan, Z.-G.; Sunderland, P. B.; Linteris, G. T.; Voss, J. E.; Lin, K.-C.; Dai, Z.; Sun, K.; Faeth, G. M.; Ross, Howard D. (Technical Monitor)

    2000-01-01

    The structure and soot properties of round, soot-emitting, nonbuoyant, laminar jet diffusion flames are described, based on long-duration (175-230/s) experiments at microgravity carried out on orbit In the Space Shuttle Columbia. Experiments] conditions included ethylene-fueled flames burning in still air at nominal pressures of 50 and 100 kPa and an ambient temperature of 300 K with luminous Annie lengths of 49-64 mm. Measurements included luminous flame shapes using color video imaging, soot concentration (volume fraction) distributions using deconvoluted laser extinction imaging, soot temperature distributions using deconvoluted multiline emission imaging, gas temperature distributions at fuel-lean (plume) conditions using thermocouple probes, not structure distributions using thermophoretic sampling and analysis by transmission electron microscopy, and flame radiation using a radiometer. The present flames were larger, and emitted soot men readily, than comparable observed during ground-based microgravity experiments due to closer approach to steady conditions resulting from the longer test times and the reduced gravitational disturbances of the space-based experiments.

  19. Multiple Hollow Cathode Wear Testing

    NASA Technical Reports Server (NTRS)

    Soulas, George C.

    1994-01-01

    A hollow cathode-based plasma contactor has been baselined for use on the Space Station to reduce station charging. The plasma contactor provides a low impedance connection to space plasma via a plasma produced by an arc discharge. The hollow cathode of the plasma contactor is a refractory metal tube, through which xenon gas flows, which has a disk-shaped plate with a centered orifice at the downstream end of the tube. Within the cathode, arc attachment occurs primarily on a Type S low work function insert that is next to the orifice plate. This low work function insert is used to reduce cathode operating temperatures and energy requirements and, therefore, achieve increased efficiency and longevity. The operating characteristics and lifetime capabilities of this hollow cathode, however, are greatly reduced by oxygen bearing contaminants in the xenon gas. Furthermore, an optimized activation process, where the cathode is heated prior to ignition by an external heater to drive contaminants such as oxygen and moisture from the insert absorbed during exposure to ambient air, is necessary both for cathode longevity and a simplified power processor. In order to achieve the two year (approximately 17,500 hours) continuous operating lifetime requirement for the plasma contactor, a test program was initiated at NASA Lewis Research Center to demonstrate the extended lifetime capabilities of the hollow cathode. To date, xenon hollow cathodes have demonstrated extended lifetimes with one test having operated in excess of 8000 hours in an ongoing test utilizing contamination control protocols developed by Sarver-Verhey. The objectives of this study were to verify the transportability of the contamination control protocols developed by Sarver-Verhey and to evaluate cathode contamination control procedures, activation processes, and cathode-to-cathode dispersions in operating characteristics with time. These were accomplished by conducting a 2000 hour wear test of four hollow cathodes with different xenon gas purities and activation processes. The following will be presented: a description of the facility and test hardware, testing procedures and operating conditions, a discussion of test results, and conclusions.

  20. Gradient porous electrode architectures for rechargeable metal-air batteries

    DOEpatents

    Dudney, Nancy J.; Klett, James W.; Nanda, Jagjit; Narula, Chaitanya Kumar; Pannala, Sreekanth

    2016-03-22

    A cathode for a metal air battery includes a cathode structure having pores. The cathode structure has a metal side and an air side. The porosity decreases from the air side to the metal side. A metal air battery and a method of making a cathode for a metal air battery are also disclosed.

  1. Tunable diode-laser measurement of carbon monoxide concentration and temperature in a laminar methane-air diffusion flame.

    PubMed

    Houston Miller, J; Elreedy, S; Ahvazi, B; Woldu, F; Hassanzadeh, P

    1993-10-20

    The application of tunable diode lasers for in situ diagnostics in laminar hydrocarbon diffusion flames is demonstrated. By the use of both direct-absorption and wavelength-modulation (second-derivative) techniques, carbon monoxide concentrations and the local flame temperature are determined for a laminar methane-air diffusion flame supported on a Wolfhard-Parker slot burner. In both cases the results are found to be in excellent agreement with prior measurements of these quantities using bothrobe and optical techniques. PMID:20856436

  2. Validation and modelling of a novel diffusive sampler for determining concentrations of volatile organic compounds in air.

    PubMed

    Pérez Ballesta, Pascual; Grandesso, Emanuela; Field, Robert A; Cabrerizo, Ana

    2016-02-18

    A novel diffusive sampler that combines radial and axial diffusion has been developed that improves upon existing commercially available designs. The POcket Diffusive (POD) sampler has been validated under laboratory and field conditions for the measurements of VOCs in ambient air. Laboratory tests varied sampling conditions of temperature (-30-40 C), humidity (10-80%), wind velocity (0.1-4 m s(-1)), and concentration (0.5-50 μg m(-3)) for a number of specific VOCs. An overall uncertainty of circa 9% for the measurement of benzene is calculated for the validation tests, in compliance with the data quality objectives of the EU air quality directive 2008/50/EC. A semi-empirical diffusion model has been developed to estimate sampling rates for compounds that were not tested, and for conditions outside of tested ranges during validation. The diffusion model (and validation tests) shows a low influence of environmental conditions on the sampling rate for the POD sampler. Average reproducibility values of circa 3% are reported with overall sampling uncertainties ranging from 9% to 15%, for the whole range of tested conditions, depending on the compound. The adsorbent cartridge is compatible with existing thermal desorption systems in the market. The diffusive sampler can modify the sampling rate by changing the diffusive body within a range of different porosities. Field tests, conducted in parallel with independent quality controlled canister sampling, confirmed the ease of use and quality of VOC measurements with the POD sampler, for compounds that were, and were not, evaluated during laboratory tests. PMID:26826692

  3. 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.

  4. 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 μs 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.

  5. Analysis of the structure and mechanisms of extinction of a counterflow methanol-air diffusion flame

    SciTech Connect

    Seshadri, K.; Trevino, C.; Smooke, M.D.

    1989-05-01

    Numerical calculations were performed to determine the structure and to clarify the extinction mechanisms of diffusion flames stabilized between counterflowing streams of methanol and air. The calculations were performed at a value of the thermodynamic pressure equal to 1 atmosphere, with different values for the rate of strain and with two different chemical kinetic mechanisms, mechanism a and mechanism b. Mechanism a and mechanism b have the same set of elementary reactions, but the rate constants for these elementary reactions were obtained from two different references. If mechanism a is used, the authors conclude that at low rates of strain the concentration of CH/sub 2/OH and HCO are in steady state and, if partial equilibrium is assumed for certain reactions, there exist algebraic relations among the concentrations of the radicals OH, H, and O. As the rate of strain is increased, HCO is no longer in steady state and no solution was obtained for a strain rate greater than 521 s/sup -1/. However, if mechanism b is used, the concentration of HCO alone is in steady state, and there also exist algebraic relations among the concentrations of the radicals OH, H, and O. As the rate of strain is increased, no solution was obtained for a strain rate greater than 168 s/sup -1/, and the authors speculate that extinction of the flame is due to a large value of the activation energy for a reaction controlling the pyrolysis of CH/sub 2/OH to CH/sub 2/O.

  6. Effects of molecular transport on turbulence-chemistry interactions in a hydrogen-argon-air jet diffusion flame

    SciTech Connect

    Menon, S.; Calhoon, W.H. Jr.; Goldin, G.; Kerstein, A.R.

    1994-01-01

    A numerical simulation of entrainment, turbulent advection, molecular import and chemical kinetics in a turbulent diffusion flame is used to investigate effects of molecular transport on turbulence-chemistry interactions. A fun finite-rate chemical mechanism is used to represent the combustion of a hydrogen-argon mixture issuing into air. Results based on incorporation of differential diffusion and variable Lewis number are compared to cases with the former effect, or both-effects, suppressed. Significant impact on radical species production and on NO emission index (based on a reduced mechanism for thermal NO) is found. A reduced mechanism for hydrogen-air combustion, omitting both effects and incorporating other simplifications, performs comparably except that its NO predictions agree well with the case of full chemistry and molecular transport, possibly due to cancellation of errors.

  7. 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; Duan Yixiang; Research Center of Analytical Instrumentation, Sichuan University, Chengdu 610064

    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.

  8. Visualization by neutron diffraction of 2D oxygen diffusion in the Sr(0.7)Ho(0.3)CoO(3-?) cathode for solid-oxide fuel cells.

    PubMed

    Cascos, V; Martnez-Coronado, R; Alonso, J A; Fernndez-Daz, M T

    2014-06-25

    Sr0.7Ho0.3CoO3-? oxide has been recently described as an excellent cathode material (1274 mW cm(-2) at 850 C with pure H2 as fuel1) for solid oxide fuel cells (SOFCs) with LSGM as electrolyte. In this work, we describe a detailed study of its crystal structure conducted to find out the correlation between the excellent performance as a cathode and the structural features. The tetragonal crystal structure (e.g., I4/mmm) basically contains layers of octahedrally coordinated Co2O6 units alternated with layers of Co1O4 tetrahedra sharing corners. An "in situ" neutron power diffraction (NPD) experiment, between 25 and 800 C, reveals the presence of a high oxygen deficiency affecting O4 oxygen atoms, with large displacement factors that suggest a large lability and mobility. Difference Fourier maps allow the visualization at high temperatures of the 2D diffusion pathways within the tetrahedral layers, where O3 and O4 oxygens participate. The measured thermal expansion coefficient is 16.61 10(-6) K(-1) between 300 and 850 C, exhibiting an excellent chemical compatibility with the electrolyte. PMID:24873238

  9. Field-scale tests for determining mixing patterns associated with coarse-bubble air diffuser configurations, Egan Quarry, Illinois

    USGS Publications Warehouse

    Hornewer, N.J.; Johnson, G.P.; Robertson, D.M.; Hondzo, Miki

    1997-01-01

    The U.S. Geological Survey in cooperation with the U.S. Army Corps of Engineers, Chicago District did field-scale tests in August-September 1996 to determine mixing patterns associated with different configurations of coarse-bubble air diffusers. The tests were done in an approximately 13-meter deep quarry near Chicago, Ill. Three-dimensional velocity, water-temperature, dissolved oxygen concentration, and specific-conductivity profiles were collected from locations between approximately 2 to 30 meters from the diffusers for two sets of five test configurations; one set for stratified and one set for destratified conditions in the quarry. The data-collection methods and instrumentation used to characterize mixing patterns and interactions of coarse-bubble diffusers were successful. An extensive data set was collected and is available to calibrate and verify aeration and stratification models, and to characterize basic features of bubble-plume interaction.

  10. Effect of dynamic diffusion of air, nitrogen, and helium gaseous media on the microhardness of ionic crystals with juvenile surfaces

    NASA Astrophysics Data System (ADS)

    Klyavin, O. V.; Fedorov, V. Yu.; Chernov, Yu. M.; Shpeizman, V. V.

    2015-09-01

    The load dependences of the microhardness of surface layers of NaCl and LiF ionic single crystals with juvenile surfaces and surfaces exposed to air for a long time measured in the air, nitrogen, and helium gaseous media have been investigated. It has been found that there is a change in the sign of the derivative of the microhardness as a function of the load for LiF crystals indented in helium and after their aging in air, as well as a weaker effect of the nitrogen and air gaseous media on the studied dependences as compared to NaCl crystals. It has also been found that, after the aging of the surface of NaCl crystals in air, there is a change in the sign of the derivative of the microhardness in the nitrogen and air gaseous media, as well as a pronounced change in the microhardness as a function of the time of aging the samples in air as compared to the weaker effect of the gaseous medium for LiF crystals. The obtained data have been analyzed in terms of the phenomenon of dislocation-dynamic diffusion of particles from the external medium into crystalline materials during their plastic deformation along the nucleating and moving dislocations. It has been shown that this phenomenon affects the microhardness through changes in the intensity of dislocation multiplication upon the formation of indentation rosettes in different gaseous media. The performed investigation of the microhardness of the juvenile surface of NaCl and LiF crystals in different gaseous media has revealed for the first time a different character of dislocation-dynamic diffusion of these media in a "pure" form.

  11. 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

  12. Microengineered cathode interface studies

    SciTech Connect

    Kueper, T.; Doshi, R.; Krumpelt, M.

    1996-10-01

    The overpotential at the cathode/electrolyte interface has been recognized as an important limitation on the performance of solid oxide fuel cells (SOFCs). This project is an effort to gain a scientific understanding of which interface features and conditions contribute to cathode polarization in SOFCs. The paper discusses three possible rate-limiting factors in the cathode reaction. The paper studies the electronic conductivity in the electrolyte, the ionic conductivity in the cathode, cathode geometry near the interface, and cathode surface area.

  13. Air

    MedlinePlus

    ... do to protect yourself from dirty air . Indoor air pollution and outdoor air pollution Air can be polluted indoors and it can ... this chart to see what things cause indoor air pollution and what things cause outdoor air pollution! Indoor ...

  14. 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.

  15. Counterflow diffusion flames of hydrogen, and hydrogen plus methane, ethylene, propane, and silane vs. air - Strain rates at extinction

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    Five coaxial tubular opposed jet burners (OJBs) with tube diameter D(T) of 1.8-10 mm and 5 mm conical nozzles were used to form dish-shaped counterflow diffusion flames centered by opposing laminar jets of nitrogen and hydrocarbon-diluted H2 versus air in an argon-purged chamber at 1 atm. Area-averaged air jet velocities at blowoff of the central flame, U(air), characterized extinction of the airside flame as functions of input H2 concentration on the fuelside. A master plot of extensive U(air) data at blowoff versus D(T) shows that U(air) varies linearly with D(T). This and other data sets are used to find that nozzle OJB results for U(air)/diameter average 4.24 + or - 0.28 times larger than tubular OJB results for the same fuel compositions. Critical radial velocity gradients consistent with one-dimensional stagnation point boundary theory and with plug flow inputs are estimated. The results compare favorably with published numerical results based only on potential flow.

  16. 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.

  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. Synthesis cathode material LiNi0.80Co0.15Al0.05O2 with two step solid-state method under air stream

    NASA Astrophysics Data System (ADS)

    Xia, Shubiao; Zhang, Yingjie; Dong, Peng; Zhang, Yannan

    2014-01-01

    A facile generic strategy of solid-state reaction under air atmosphere is employed to prepare LiNi0.8Co0.15Al0.05O2 layer structure micro-sphere as cathodes for Li-ion batteries. The impurity phase has been eliminated wholly without changing the R-3m space group of LiNi0.8Co0.15Al0.05O2. The electrochemical performance of LiNi0.8Co0.15Al0.05O2 cathodes depend on the sintering step, temperature, particle size and uniformity. The sample pre-sintered at 540 C for 12 h and then sintered at 720 C for 28 h exhibits the best electrochemical performance, which delivers a reversible capacity of 180.4, 165.8, 154.7 and 135.6 mAhg-1 at 0.2 C, 1 C, 2 C and 5 C, respectively. The capacity retention keeps over 87% after 76 cycles at 1 C. This method is simple, cheap and mass-productive, and thus suitable to large scale production of NCA cathodes directly used for lithium ion batteries.

  19. Hollow cathodes for arcjet thrusters

    NASA Technical Reports Server (NTRS)

    Luebben, Craig R.; Wilbur, Paul J.

    1987-01-01

    In an attempt to prevent exterior spot emission, hollow cathode bodies and orifice plates were constructed from boron nitride which is an electrical insulator, but the orifice plates melted and/or eroded at high interelectrode pressures. The most suitable hollow cathodes tested included a refractory metal orifice plate in a boron nitride body, with the insert insulated electrically from the orifice plate. In addition, the hollow cathode interior was evacuated to assure a low pressure at the insert surface, thus promoting diffuse electron emission. At high interelectrode pressures, the electrons tended to flow through the orifice plate rather than through the orifice, which could result in overheating of the orifice plate. Using a carefully aligned centerline anode, electron flow through the orifice could be sustained at interelectrode pressures up to 500 torr - but the current flow path still occasionally jumped from the orifice to the orifice plate. Based on these tests, it appears that a hollow cathode would operate most effectively at pressures in the arcjet regime with a refractory, chemically stable, and electrically insulating cathode body and orifice plate.

  20. Opposed jet burner studies of effects of CO, CO2, and N2 air-contaminants on hydrogen-air diffusion flames

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    The blowoff/restore characteristics for jets of various H2/N2 mixtures opposed to jets of air contaminated by N2, CO, and CO2 have been determined using a counterflow diffusion flame formed by a tubular opposed jet burner. Both blowoff and restore limits are found to be sensitive to fuel and air composition. Empirically derived variations in the limits of the average mass flux of incoming H2 with percent contaminant, at fixed incoming fuel and H2/O2 inputs, are used to quantify the effects of oxygen dilution, flame augmentation, and flame retardation by N2, CO, and CO2 contaminants. The implications of the results are discussed.

  1. Study on Flows inside and outside an Air Diffuser for Membrane Bioreactor

    NASA Astrophysics Data System (ADS)

    Kira, Fumihiro; Furuno, Shinsuke; Hayashi, Kosuke; Sampei, Tomoyuki; Tomiyama, Akio

    Effects of the total gas flow rate on the water level in a diffuser pipe for a membrane bioreactor, the gas flow rate from each aeration hole and the bubble diameter are investigated. The diffuser has evenly positioned five aeration holes on the top and a larger hole on the bottom for introducing the liquid into the pipe. The gas flow rate from each aeration hole is measured by capturing generated bubbles. The water level and gas velocity inside the diffuser are computed by processing video images. The bubble diameter is calculated using the gas flow rate and the bubble generation frequency measured from the video images. The conclusions obtained are as follows: (1) the gas flow rate from the aeration hole depends on the water level inside the diffuser and becomes constant for all the holes as the total gas flow rate increases since the high total gas flow rate make the water level uniform, which results in a constant gas pressure in the diffuser, (2) the onset of slugging in the diffuser is well correlated in terms of the local gas velocity and the Mishima-Ishii's slugging model, (3) the increase in the total gas flow rate decreases the water level, causing suppression of the onset of slugging, (4) the diameter of aeration hole strongly affects the gas flow rate from each aeration hole and water level, and (5) the Davidson-Schuler correlation gives reasonable estimations of the bubble diameter, provided that the influence of slugging is not significant.

  2. COMPARISON OF 24H AVERAGE VOC MONITORING RESULTS FOR RESIDENTIAL INDOOR AND OUTDOOR AIR USING CARBOPACK X-FILLED DIFFUSIVE SAMPLERS AND ACTIVE SAMPLING - A PILOT STUDY

    EPA Science Inventory

    Analytical results obtained by thermal desorption GC/MS for 24h diffusive sampling of 11 volatile organic compounds (VOCs) are compared with results of time-averaged active sampling at a known constant flow rate. Air samples were collected with co-located duplicate diffusive samp...

  3. Turbulent Diffusion Combustion Model Using Chemical Equilibrium Combined with the Eddy Dissipation Concept for Reducing Detailed Chemical Mechanisms : An Application of H2-air Turbulent Diffusion Flame

    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 mechanism. 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 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 Takagi‧s experimental data and the data computed by the EDC model, which uses the complex chemical mechanisms. The mole fractions of H2, O2, H2O, temperature, and velocity obtained by using our CE-EDC model were in good agreement with these reference data without taking into account the chemical reaction rates of the O2 and H2O. Furthermore, the mole fractions of OH and H are in good agreement with the results of the EDC model at the high temperatures. On the other hand, the chemical equations involving OH and H were used for predicting the mole fractions of OH and H, which were similar to those obtained from the EDC model at low temperatures. 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.

  4. Dynamic and scalar turbulent fluctuation in a diffusion flame of an-axisymmetric methane jet into air

    NASA Astrophysics Data System (ADS)

    Hidouri, A.; Gazzah, M. H.; Tcha, H. Ben; Sassi, M.

    A study of turbulence/combustion interactions in a relatively large turbulent diffusion flame of an axisymmetric methane jet into air is presented. A first order k-? turbulence closure model is used along with two different models (equal scales and non-equal scales) for the submodel describing the scalar dissipation rate. The flamelet concept is used to model the turbulent combustion along with a joint mixture fraction/strain rate probability density function (PDF) for the prediction of the average parameters of the turbulent diffusion flame. The numerical approach is that of Patankar and Spalding, while the flamelet simulations are obtained from the RUN-1DL code of Rogg and co-workers based on a 17 species detailed reaction mechanism. The chosen configuration is that of the experimentally studied turbulent diffusion flame of Streb [1]. A comparison between these experimental results and the obtained numerical ones is thus presented. Relatively good agreements are obtained which show the usefulness of the two-scale model compared to the classical one-scale model for predicting turbulent diffusion flames. Nonetheless some discrepancies are obtained in the outer and downstream regions of the jet, especially in comparison with the experimental data. These are attributed to short coming of the considered turbulence model and soot radiation which is not accounted for.

  5. 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.

  6. 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 Liu, Lun; Liu, Yun-Long; Bin, Yu; Ge, Ya-Feng; Lin, Fo-Chang

    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.

  7. Numerical study on rectangular microhollow cathode discharge

    SciTech Connect

    He Shoujie; Ouyang Jiting; He Feng; Li Shang

    2011-03-15

    Rectangular microhollow cathode discharge in argon is investigated by using two-dimensional time-dependent self-consistent fluid model. The electric potential, electric field, particle density, and mean electron energy are calculated. The results show that hollow cathode effect can be onset in the present configuration, with strong electric field and high mean electron energy in the cathode fall while high density and quasineutral plasma in the negative glow. The potential well and electric filed reversal are formed in the negative glow region. It is suggested that the presence of large electron diffusion flux necessitates the field reversal and potential well.

  8. 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.

  9. 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.

  10. 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.

  11. Lift-off stability of n-heptane jet diffusion flames in homogeneous environments of fuel and air

    SciTech Connect

    Samuel, P.; Karim, G.A.

    1995-12-31

    The lift off of jet diffusion flames of a liquid fuel in coflowing streams of air was established experimentally for a range of jet discharge and stream velocities. The improvement in the lift off stability of the flame due to the presence of a small concentration of an auxiliary gaseous fuel in the surrounding air was established. Liquid n-heptane was the jet fuel while methane, ethylene, propane and hydrogen were employed individually as the auxiliary fuels. It is shown that the lift off distance and the corresponding ignition delay of the jet flame can be correlated for all the observations made in terms of derived dimensionless grouping of the main parameters varied.

  12. Nonlinear dynamics of hydrogen-air detonations with detailed kinetics and diffusion

    NASA Astrophysics Data System (ADS)

    Powers, Joseph; Romick, Christopher; Aslam, Tariq

    2014-11-01

    We consider the calculation of unsteady detonation in a mixture of calorically imperfect ideal gases with detailed kinetics. The use of detailed kinetics introduces multiple reaction length scales, and their interaction gives rise to complex dynamics. These are predicted using a wavelet-based adaptive mesh refinement technique and includes multi-component species, momentum, and energy diffusion, as well as DuFour and Soret effects. In the one-dimensional limit, we predict a transition from stability to unstable limit cycles as a driving piston velocity is lowered. At low overdrive, energy is partitioned into a variety of high frequency oscillatory modes. For weak low frequency instabilities, the dynamics are largely explained by a competition between advection and reaction time scales, with diffusion serving to perturb the dynamics. For higher frequency instabilities, the influence of diffusion is larger. We present new extensions to two-dimensional dynamics.

  13. 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 ...

  14. Carbon-containing cathodes for enhanced electron emission

    DOEpatents

    Cao, Renyu; Pan, Lawrence; Vergara, German; Fox, Ciaran

    2000-01-01

    A cathode has electropositive atoms directly bonded to a carbon-containing substrate. Preferably, the substrate comprises diamond or diamond-like (sp.sup.3) carbon, and the electropositive atoms are Cs. The cathode displays superior efficiency and durability. In one embodiment, the cathode has a negative electron affinity (NEA). The cathode can be used for field emission, thermionic emission, or photoemission. Upon exposure to air or oxygen, the cathode performance can be restored by annealing or other methods. Applications include detectors, electron multipliers, sensors, imaging systems, and displays, particularly flat panel displays.

  15. Experimental Study on Branch and Diffuse Type of Streamers in Leader Restrike of Long Air Gap Discharge

    NASA Astrophysics Data System (ADS)

    Chen, She; Zeng, Rong; Zhuang, Chijie; Zhou, Xuan; Ding, Yujian

    2016-03-01

    One of the main problems in the Ultra High Voltage (UHV) transmission project is to choose the external insulation distance, which requires a deep understanding of the long air gap discharge mechanism. The leader-streamer propagation is one of most important stages in long air gap discharge. In the conductor-tower lattice configuration, we have measured the voltage, the current on the high voltage side and the electric field in the gap. While the streamer in the leader-streamer system presented a conical or hyperboloid diffuse shape, the clear branch structure streamer in front of the leader was firstly observed by a high speed camera in the experiment. Besides, it is found that the leader velocity, width and injected charge for the branch type streamer are greater than those of a diffuse type. We propose that the phenomenon results from the high humidity, which was 15.5-16.5 g/m3 in our experiment. supported by the Fund of the National Priority Basic Research of China (2011CB209403) and National Natural Science Foundation of China (Nos. 51325703, 51377094, 51577098)

  16. 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.

  17. A comparison of Fick and Maxwell-Stefan diffusion formulations in PEMFC gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Lindstrom, Michael; Wetton, Brian

    2016-04-01

    This paper explores the mathematical formulations of Fick and Maxwell-Stefan diffusion in the context of polymer electrolyte membrane fuel cell cathode gas diffusion layers. The simple Fick law with a diagonal diffusion matrix is an approximation of Maxwell-Stefan. Formulations of diffusion combined with mass-averaged Darcy flow are considered for three component gases. For this application, the formulations can be compared computationally in a simple, one dimensional setting. Despite the models' seemingly different structure, it is observed that the predictions of the formulations are very similar on the cathode when air is used as oxidant. The two formulations give quite different results when the Nitrogen in the air oxidant is replaced by helium (this is often done as a diagnostic for fuel cells designs). The two formulations also give quite different results for the anode with a dilute Hydrogen stream. These results give direction to when Maxwell-Stefan diffusion, which is more complicated to implement computationally in many codes, should be used in fuel cell simulations.

  18. A review of the science and technology of cathodes from the viewpoint of spacecraft TWT applications

    NASA Astrophysics Data System (ADS)

    Stupian, G. W.

    1980-06-01

    The current state-of-the-art of cathode science and technology is summarized, with emphasis on the types of cathode now used, or with potential use, in U.S. Air Force communication satellites. The intent is that this report be a stand-alone discussion of cathode construction and of the basic physics of electron emission. Emphasis is placed on thermionic cathodes; however, one nonthermionic emitter, the field emitter, is discussed briefly. For the thermionic emitters, the barium (calcium and strontium) oxide cathode and dispenser cathodes (based on barium) are discussed, along with variant types of the oxide and dispenser cathodes. Thorium-based cathodes and lanthanum hexaboride cathodes are also described. Some of the available data on cathode failure modes and cathode lifetime are included. Electron emission from solids has been studied with varying intensity since the last century, and the present discussion, because of the scope of the subject, of course is incomplete. Extensive literature references are given.

  19. Extinguishment of a Methane Air Diffusion Flame by Using Blast Wave

    NASA Astrophysics Data System (ADS)

    Torikai, H.; Saito, S.; Ito, A.

    After the occurrence of a large-scale disaster such as the Great East Japan Earthquake, multiple simultaneous fires, consisting of diffusion flames, often break out. At the same time, infrastructure, such as water utilization for firefighting, roads and etc., is destroyed violently by the disaster impact. Therefore, it is difficult to use conventional firefighting techniques against the post-disaster fires. To mitigate and minimize the damages, the development of a new firefighting method which can extinguish each fire promptly is needed.

  20. Technology diffusion and environmental regulation: Evidence from electric power plants under the Clean Air Act

    NASA Astrophysics Data System (ADS)

    Frey, Elaine F.

    Even though environmental policy can greatly affect the path of technology diffusion, the economics literature contains limited empirical evidence of this relationship. My research will contribute to the available evidence by providing insight into the technology adoption decisions of electric generating firms. Since policies are often evaluated based on the incentives they provide to promote adoption of new technologies, it is important that policy makers understand the relationship between technological diffusion and regulation structure to make informed decisions. Lessons learned from this study can be used to guide future policies such as those directed to mitigate climate change. I first explore the diffusion of scrubbers, a sulfur dioxide (SO 2) abatement technology, in response to federal market-based regulations and state command-and-control regulations. I develop a simple theoretical model to describe the adoption decisions of scrubbers and use a survival model to empirically test the theoretical model. I find that power plants with strict command-and-control regulations have a high probability of installing a scrubber. These findings suggest that although market-based regulations have encouraged diffusion, many scrubbers have been installed because of state regulatory pressure. Although tradable permit systems are thought to give firms more flexibility in choosing abatement technologies, I show that interactions between a permit system and pre-existing command-and-control regulations can limit that flexibility. In a separate analysis, I explore the diffusion of combined cycle (CC) generating units, which are natural gas-fired generating units that are cleaner and more efficient than alternative generating units. I model the decision to consider adoption of a CC generating unit and the extent to which the technology is adopted in response to environmental regulations imposed on new sources of pollutants. To accomplish this, I use a zero-inflated Poisson model and focus on both the decision to adopt a CC unit at an existing power plant as well as the firm-level decision to adopt a CC unit in either a new or an existing power plant. Evidence from this empirical investigation shows that environmental regulation has a significant effect on both the decision to consider adoption as well as the extent of adoption.

  1. Gold Nanorods Based Air Scanning Electron Microscopy and Diffusion Reflection Imaging for Mapping Tumor Margins in Squamous Cell Carcinoma.

    PubMed

    Ankri, Rinat; Ashkenazy, Ariel; Milstein, Yonat; Brami, Yaniv; Olshinka, Asaf; Goldenberg-Cohen, Nitza; Popovtzer, Aron; Fixler, Dror; Hirshberg, Abraham

    2016-02-23

    A critical challenge arising during a surgical procedure for tumor removal is the determination of tumor margins. Gold nanorods (GNRs) conjugated to epidermal growth factor receptors (EGFR) (GNRs-EGFR) have long been used in the detection of cancerous cells as the expression of EGFR dramatically increases once the tissue becomes cancerous. Optical techniques for the identification of these GNRs-EGFR in tumor are intensively developed based on the unique scattering and absorption properties of the GNRs. In this study, we investigate the distribution of the GNRs in tissue sections presenting squamous cell carcinoma (SCC) to evaluate the SCC margins. Air scanning electron microscopy (airSEM), a novel, high resolution microscopy is used, enabling to localize and actually visualize nanoparticles on the tissue. The airSEM pictures presented a gradient of GNRs from the tumor to normal epithelium, spread in an area of 1 mm, suggesting tumor margins of 1 mm. Diffusion reflection (DR) measurements, performed in a resolution of 1 mm, of human oral SCC have shown a clear difference between the DR profiles of the healthy epithelium and the tumor itself. PMID:26759920

  2. Recent Advances in Thermionic Cathodes

    SciTech Connect

    Ives, R. Lawrence; Miram, George; Collins, George; Falce, Louis R.

    2010-11-04

    The latest advances in thermionic cathodes, including scandate and controlled porosity reservoir cathodes, are reviewed. These new cathodes provide improved performance over conventional cathodes for many applications. Advantages and disadvantages are presented.

  3. Pulsed mode cathode

    NASA Astrophysics Data System (ADS)

    Myers, Roger M.; Rawlin, Vinvent K.

    1994-10-01

    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.

  4. Cathodic protection -- Rectifier 47

    SciTech Connect

    Lane, W.M.

    1995-06-14

    This Acceptance Test Procedure (ATP) has been prepared to demonstrate that the cathodic protection system functions as required by project criteria. The cathodic protection system is for the tank farms at the Hanford Reservation. The tank farms store radioactive waste.

  5. Cathodic protection -- Rectifier 46

    SciTech Connect

    Lane, W.M.

    1995-06-14

    This Acceptance Test Procedure (ATP) has been prepared to demonstrate that the cathodic protection system functions as required by project criteria. The cathodic protection system is for the tank farms on the Hanford Reservation. The tank farms store radioactive waste.

  6. Sintered wire cathode

    DOEpatents

    Falce, Louis R.; Ives, R. Lawrence

    2009-06-09

    A porous cathode structure is fabricated from a plurality of wires which are placed in proximity to each other in elevated temperature and pressure for a sintering time. The sintering process produces the porous cathode structure which may be divided into a plurality of individual porous cathodes, one of which may be placed into a dispenser cathode support which includes a cavity for containing a work function reduction material such as BaO, CaO, and Al.sub.2O.sub.3. The work function reduction material migrates through the pores of the porous cathode from a work replenishment surface adjacent to the cavity of the dispenser cathode support to an emitting cathode surface, thereby providing a dispenser cathode which has a uniform work function and therefore a uniform electron emission.

  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. The extended Schottky cathode

    NASA Astrophysics Data System (ADS)

    Hinrichs, Clarence H.; Mackie, William A.; Pincosy, Philip A.; Poulsen, Peter

    1990-12-01

    Cathodes operating in the range of electric field strength and temperatures falling within the extended Schottky domain are discussed for applications requiring high current densities from a broad area cathode. Generally, these cathodes are operated in a pulsed high-voltage mode. Current densities of up to 300 A/sq cm have been achieved without breakdown. Cathode performance is limited by space-charge effects and excessive evaporation at the high operating temperatures required.

  9. [Diego Alcorta and diffusion of medical knowledge in Buenos Aires 1821-1842].

    PubMed

    Di Pasquale, Mariano

    2014-01-01

    The aim of this article is to analyse the medical knowledge that Dr Diego Alcorta derived from the French tradition, especially from the Idéologie movement, in the context of the University of Buenos Aires between 1821 and 1842. It analyses the circulation of these teachings alongside those of the Montpellier School, which were adapted and located at the local level, and their gradual impact on academia as an important phenomenon in the incipient formation of the medical profession in Buenos Aires. Alcorta emphasised the importance of observation as a diagnostic and therapeutic method and called for an empirical approach to medical teaching and research, which introduced a specific practical activity, i.e., hospital clinical work. This article also examines the transmission of a physiological "language" and its relevance to subsequent generations, asking what happened to these practical procedures and the dissemination of new physiological knowledge. This complex question is addressed by discussing the PhD theses developed in the Department of Medicine of the University of Buenos Aires during this period, which provide confirmation of the presence of the sensualist and physiological language derived from the teachings of Alcorta and its impact on the practice of medicine. PMID:24987784

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

    SciTech Connect

    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.

  11. 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.

  12. Effect of ferrocene on soot in a prevaporized iso-octane/air diffusion flame

    SciTech Connect

    Bonczyk, P.A. )

    1991-12-01

    This paper reports on ferrocene, or dicyclopentadienyl iron ((C{sub 5}H{sub 5}){sub 2}Fe) which is an organometallic compound of proven, considerable importance in relation to the control of soot resulting from the combustion of hydrocarbon fuels. Ferrocene as a fuel additive has been observed to suppress soot in oil-fired boilers and furnaces, jet engines, poly (vinyl chloride) combustion, acetylene pyrolysis, and laboratory-scale diffusion flames. This study of a well-defined laminar diffusion flame applies several complementary diagnostic approaches to clarify ferrocene's influence on soot particulates, their precursors, and flame temperature. Unlike most past work, the additive's intervention was evaluated with spatial precision throughout the luminous zone of the flame. To this end, light scattering measurements were made in order to determine the effect of ferrocene on particulate size, number density, and volume fraction. Sampling of the flame with a quartz microprobe was done as well to search for the perturbation of soot precursor and other gas-phase species by the additive; sample concentrations were analyzed via conventional gas chromatography.

  13. Sensitivity of Urban Airshed Model (UAM-IV) calculated air pollutant concentrations to the vertical diffusion parameterization during convective meteorological situations

    SciTech Connect

    Nowacki, P.; Samson, P.J.; Sillman, S.

    1996-10-01

    It is shown that Urban Airshed Model (UAM-IV) calculated air pollutant concentrations during photochemical smog episodes in Atlanta, Georgia, depend strongly on the numerical parameterization of the daytime vertical diffusivity. Results found suggest that vertical mixing is overestimated by the UAM-IV during unstable daytime conditions, as calculated vertical diffusivity values exceed measured and comparable literature values. Although deviations between measured and UAM-IV calculated air pollutant concentrations may only in part be due the UAM-IV diffusivity parameterization, results indicate the large error potential in vertical diffusivity parameterization. Easily implemented enhancements to UAM-IV algorithms are proposed, thus improving UAM-IV modeling performance during unstable stratification. 38 refs., 14 figs., 1 tab.

  14. Different K+-Na+ inter-diffusion kinetics between the air side and tin side of an ion-exchanged float aluminosilicate glass

    NASA Astrophysics Data System (ADS)

    Jiang, Liangbao; Guo, Xintao; Li, Xiaoyu; Li, Lei; Zhang, Guanli; Yan, Yue

    2013-01-01

    The difference between the inter-diffusion kinetics of K+-Na+ in the air and tin sides of an ion-exchanged float aluminosilicate glass was investigated as a function of the exchange temperature and time. The potassium concentration profiles of the ion-exchanged glass surface were experimentally measured by electron microprobe analysis, and the diffusion coefficient was calculated by the Boltzmann-Montano approach. On the tin side of the ion-exchanged glass, the diffusion of K+-Na+ ions is hindered by tin. The diffusion coefficient is also more sensitive to temperature and time on the tin than on the air sides. The results would be useful in guiding the strengthening process of float glass by one step ion-exchange or two step ion-exchange to obtain engineered stress profile (ESP) glasses.

  15. Spray-on polyvinyl alcohol separators and impact on power production in air-cathode microbial fuel cells with different solution conductivities.

    PubMed

    Hoskins, Daniel L; Zhang, Xiaoyuan; Hickner, Michael A; Logan, Bruce E

    2014-11-01

    Separators are used to protect cathodes from biofouling and to avoid electrode short-circuiting, but they can adversely affect microbial fuel cell (MFC) performance. A spray method was used to apply a polyvinyl alcohol (PVA) separator to the cathode. Power densities were unaffected by the PVA separator (339±29mW/m(2)), compared to a control lacking a separator in a low conductivity solution (1mS/cm) similar to wastewater. Power was reduced with separators in solutions typical of laboratory tests (7-13mS/cm), compared to separatorless controls. The PVA separator produced more power in a separator assembly (SEA) configuration (444±8mW/m(2)) in the 1mS/cm solution, but power was reduced if a PVA or wipe separator was used in higher conductivity solutions with either Pt or activated carbon catalysts. Spray and cast PVA separators performed similarly, but the spray method is preferred as it was easier to apply and use. PMID:25260178

  16. Nickel-Doped La0.8Sr0.2Mn1-xNixO3 Nanoparticles Containing Abundant Oxygen Vacancies as an Optimized Bifunctional Catalyst for Oxygen Cathode in Rechargeable Lithium-Air Batteries.

    PubMed

    Wang, Zhaodong; You, Ya; Yuan, Jing; Yin, Ya-Xia; Li, Yu-Tao; Xin, Sen; Zhang, Dawei

    2016-03-16

    In this work, Ni-doped manganite perovskite oxides (La0.8Sr0.2Mn1-xNixO3, x = 0.2 and 0.4) and undoped La0.8Sr0.2MnO3 were synthesized via a general and facile sol-gel route and used as bifunctional catalysts for oxygen cathode in rechargeable lithium-air batteries. The structural and compositional characterization results showed that the obtained La0.8Sr0.2Mn1-xNixO3 (x = 0.2 and 0.4) contained more oxygen vacancies than did the undoped La0.8Sr0.2MnO3 as well as a certain amount of Ni(3+) (eg = 1) on their surface. The Ni-doped La0.8Sr0.2Mn1-xNixO3 (x = 0.2 and 0.4) was provided with higher bifunctional catalytic activities than that of the undoped La0.8Sr0.2MnO3. In particular, the La0.8Sr0.2Mn0.6Ni0.4O3 had a lower total over potential between the oxygen evolution reaction and the oxygen reduction reaction than that of the La0.8Sr0.2MnO3, and the value is even comparable to that of the commercial Pt/C yet is provided with a much reduced cost. In the lithium-air battery, oxygen cathodes containing the La0.8Sr0.2Mn0.6Ni0.4O3 catalyst delivered the optimized electrochemical performance in terms of specific capacity and cycle life, and a reasonable reaction mechanism was given to explain the improved performance. PMID:26900959

  17. Nanoflakes-assembled three-dimensional hollow-porous v2 o5 as lithium storage cathodes with high-rate capacity.

    PubMed

    Mai, Liqiang; An, Qinyou; Wei, Qiulong; Fei, Jiayang; Zhang, Pengfei; Xu, Xu; Zhao, Yunlong; Yan, Mengyu; Wen, Wen; Xu, Lin

    2014-08-13

    Three-dimensional (3D) hollow-porous vanadium pentoxide (V2 O5 ) quasi-microspheres are synthesized by a facile solvothermal method followed by annealing at 450 °C in air. The interconnected hollow-porous networks facilitate the kinetics of lithium-ion diffusion and improve the performance of V2 O5 to achieve a high capacity and remarkable rate capability as a cathode material for lithium batteries. PMID:24711281

  18. Variation of the length of gaseous fuel diffusion flames in an accompanying air flow

    SciTech Connect

    Annushkin, Y.M.; Sverdlov, E.D.

    1984-11-01

    These authors study the effect of the relative area of the edges of the fuel nozzles or pylons on the variation of the flame length in an accompanying oxidizer flow, and seek to establish the conditions of reliable flame propagation to all the fuel jets. A diagram illustrates the experimental set-up and charts present the data gathered. Analysis of these data leads the authors to conclude: that as the relative area of the edges is increased, raising relative accompanying air velocity leads to an intensified mixing and a shorter flame; that the effect of relative area of the edges on flame length for various fuels can be represented by a single curve; and that these results are valid for both individual jets and groups of jets provided they are characterized by autonomous mixing or total fusion.

  19. Spectroscopic analysis of the excitation transfer from background air to diffusing aluminum laser produced plasma

    SciTech Connect

    Ribiere, M.; Cheron, B. G.; Karabourniotis, D.

    2009-04-15

    During the relaxation of the plasma plume generated by laser ablation of an aluminum target, a pronounced intensity enhancement is observed at the central wavelength of the 396.15 nm self-reversed resonant line. This spectral special feature is analyzed and related to the interaction of the plasma edge with the background air excited by the shockwave, prompt electrons, and extreme ultraviolet radiation produced at the earliest times of the ablation. In this article, the electron density, the aluminum ground state, and resonant level populations are determined from the fitting of the 396.15 nm calculated line profile to the experimental one at two background pressures (100 and 1000 Pa). The evolution of these densities is derived from experiments performed at delays, after the laser pulse arrival, ranging from 120 to 180 ns.

  20. Polymer electroluminescent devices with zirconium carbide cathodes

    NASA Astrophysics Data System (ADS)

    Sheats, James R.; Mackie, William A.; Anz, Samir; Xie, Tienbao

    1997-12-01

    The behavior of polymeric electroluminescent devices made using ZrC cathodes, a soluble phenylene vinylene polymer, and Au anodes is reported. ZrC is a highly air-stable metal with a work function of about 3.6 eV. Polycrystalline thin films can be formed on sapphire with electron beam evaporation and subsequent annealing at ca. 500 deg C. The devices exhibit a lower turn-on voltage than corresponding devices with Al cathodes, but very low efficiency; their lifetime is not longer than with other cathodes. The current-luminance-voltage-time characteristics suggest that the recombination zone is close to the cathode, that the metal is not exidized and efficiently quenches the excitons, and that the negative charge carriers are effectively trapped by the polymer.

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

    NASA Astrophysics Data System (ADS)

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

    1985-12-01

    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 many soluble silver salt cathodes. This paper presents the effects of temperature, current density, and cathode material on cell discharge characteristics.

  2. Spherical Ethylene/Air Diffusion Flames Subject to Concentric DC Electric Field in Microgravity

    NASA Technical Reports Server (NTRS)

    Yuan, Z. -G.; Hegde, U.; Faeth, G. M.

    2001-01-01

    It is well known that microgravity conditions, by eliminating buoyant flow, enable many combustion phenomena to be observed that are not possible to observe at normal gravity. One example is the spherical diffusion flame surrounding a porous spherical burner. The present paper demonstrates that by superimposing a spherical electrical field on such a flame, the flame remains spherical so that we can study the interaction between the electric field and flame in a one-dimensional fashion. Flames are susceptible to electric fields that are much weaker than the breakdown field of the flame gases owing to the presence of ions generated in the high temperature flame reaction zone. These ions and the electric current of the moving ions, in turn, significantly change the distribution of the electric field. Thus, to understand the interplay between the electric field and the flame is challenging. Numerous experimental studies of the effect of electric fields on flames have been reported. Unfortunately, they were all involved in complex geometries of both the flow field and the electric field, which hinders detailed study of the phenomena. In a one-dimensional domain, however, the electric field, the flow field, the thermal field and the chemical species field are all co-linear. Thus the problem is greatly simplified and becomes more tractable.

  3. Evaluation of two types of diffusive samplers and adsorbents for measuring 1,3-butadiene and benzene in air

    NASA Astrophysics Data System (ADS)

    Strandberg, Bo; Sunesson, Anna-Lena; Olsson, Katarina; Levin, Jan-Olof; Ljungqvist, Göran; Sundgren, Margit; Sällsten, Gerd; Barregard, Lars

    1,3-Butadiene and benzene are common air pollutants, the former being a suspected and the latter an established carcinogen. Road traffic and industry emissions are sources of these compounds. In order to assess the risk posed to the general population by ambient levels of these pollutants, diffusive samplers capable of monitoring them over both long timescales (weeks) and shorter periods (8-24 h) are needed. In this study, we evaluated a new diffusive sampler, the SKC-Ultra, and a partially validated sampler, the Radiello, both of which are compatible with thermal desorption. Two adsorbents, the graphitized carbon blacks Carbopack X and Carbograph 5, were also evaluated. Standard atmospheres of the target compounds were generated in order to determine uptake rates and to evaluate the effects of concentration, relative humidity, reverse-diffusion and storage of samplers. The samplers and adsorbents were also tested in a field study. Analysis and detection were performed using an automatic thermal desorber (ATD) connected to a gas chromatograph-flame ionization detector (GC/FID). Both samplers showed much higher uptake rates (ca. 25-50 fold) than those reported for the Perkin-Elmer sampler. The 24 h uptake rates for 1,3-butadiene and benzene obtained using the SKC-Ultra filled with Carbopack X were 14.9±0.8 (SD) and 16.0±1.4 (SD) mL min -1, respectively, and the corresponding figures for the Radiello were 22.0±0.9 (SD) and 30.4±1.1 (SD) mL min -1. Varying the atmospheric concentrations of the compounds had no effect on the uptake rate for the Carbopack X adsorbent and the samplers could be stored up to one month after sampling. Uptake rates of 1,3-butadiene declined over longer periods (one week). This was probably due to reverse diffusion, and the effect was less pronounced with the SKC-Ultra sampler. In summary, we consider the two samplers to be suitable both for stationary and personal monitoring of 1,3-butadiene and benzene, for the general population and for workplaces.

  4. Effects of Humidity on Solid Oxide Fuel Cell Cathodes

    SciTech Connect

    Hardy, John S.; Stevenson, Jeffry W.; Singh, Prabhakar; Mahapatra, Manoj K.; Wachsman, E. D.; Liu, Meilin; Gerdes, Kirk R.

    2015-03-17

    This report summarizes results from experimental studies performed by a team of researchers assembled on behalf of the Solid-state Energy Conversion Alliance (SECA) Core Technology Program. Team participants employed a variety of techniques to evaluate and mitigate the effects of humidity in solid oxide fuel cell (SOFC) cathode air streams on cathode chemistry, microstructure, and electrochemical performance.

  5. 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.

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

    NASA Technical Reports Server (NTRS)

    Sislian, J. P.; Glass, I. I.; Evans, J. S.

    1979-01-01

    A numerical analysis is presented of the nonequilibrium flow field resulting from the turbulent mixing and combustion of an axisymmetric hydrogen jet in a supersonic parallel ambient air stream. The effective turbulent transport properties are determined by means of a two-equation model of turbulence. The finite-rate chemistry model considers eight elementary reactions among six chemical species: H, O, H2O, OH, O2 and H2. The governing set of nonlinear partial differential equations was solved by using an implicit finite-difference procedure. Radial distributions were obtained at two downstream locations for some important variables affecting the flow development, such as the turbulent kinetic energy and its dissipation rate. The results show that these variables attain their peak values on the axis of symmetry. The computed distribution of velocity, temperature, and mass fractions of the chemical species gives a complete description of the flow field. The numerical predictions were compared with two sets of experimental data. Good qualitative agreement was obtained.

  7. DIFFUSIVE EXCHANGE OF GASEOUS POLYCYCLIC AROMATIC HYDROCARBONS AND POLYCHLORINATED BIPHENYLS ACROSS THE AIR-WATER INTERFACE OF THE CHESAPEAKE BAY. (R825245)

    EPA Science Inventory

    Dissolved and gas-phase concentrations of nine polycyclic aromatic hydrocarbons and 46 polychlorinated biphenyl congeners were measured at eight sites on the Chesapeake Bay at four different times of the year to estimate net diffusive air-water gas exchange rates. Gaseous PAHs ar...

  8. 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-δ} (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.

  9. 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.

  10. A theoretical analysis of the extinction limits of a methane-air opposed-jet diffusion flame

    NASA Technical Reports Server (NTRS)

    Olson, S. L.; T'Ien, J. S.

    1987-01-01

    A theoretical analysis is described for a methane-air diffusion flame stabilized in the forward stagnation region of a porous metal cylinder in a forced convective flow. The analysis includes effects of radiative heat loss from the porous metal surface and finite rate kinetics but neglects the effects of gravity. The theoretically predicted extinction limits compare well with experimentally observed extinction limits from the literature. After the predicted limits compared well with the experimental limits, a parametric study of the effect of fuel surface emissivity and Lewis number was conducted with the numerical model. It was found that the computed blowoff limit is independent of radiative heat loss for high fuel blowing velocities but is a strong function of Lewis number. At low fuel blowing velocities, the extinction limit varies with both radiative heat loss and Lewis number. It is discovered, however, that even if thermal losses from the fuel surface are absent, the flame can extinguish at the fuel surface independently of Lewis number due to excessive reaction zone thinning.

  11. Comparison of 24 h averaged VOC monitoring results for residential indoor and outdoor air using Carbopack X-filled diffusive samplers and active sampling--a pilot study.

    PubMed

    McClenny, William A; Jacumin, Henry H; Oliver, Karen D; Daughtrey, E Hunter; Whitaker, Donald A

    2006-02-01

    Analytical results obtained by thermal desorption GC/MS for 24 h diffusive sampling of 11 volatile organic compounds (VOCs) are compared with results of time-averaged active sampling at a known constant flow rate. Air samples were collected with co-located duplicate diffusive sampling tubes and one passivated canister. A total of eight multiple-component sampling events took place at fixed positions inside and outside three private homes. Subsequently, a known amount of sample air was transferred from the canister to an adsorbent tube for analysis by thermal desorption GC/MS. Results for the 11 most prevalent compounds--Freon 11, 1,3-butadiene, benzene, toluene, tetrachloroethene, ethylbenzene, m,p-xylene, o-xylene, 4-ethyltoluene, 1,3,5-trimethylbenzene, and p-dichlorobenzene--show that the ratio of average study values (diffusive sampling to active sampling) is 0.92 with 0.70 and 1.14 extreme ratios. Absolute percent difference for duplicate samples using diffusive sampling was <10% for the four most prevalent compounds. Agreement between the two sampling approaches indicates that the prediction of approximately constant diffusive sampling rates based on previous laboratory studies is valid under the field conditions. PMID:16470258

  12. Improved Dispenser Cathodes

    NASA Astrophysics Data System (ADS)

    Ives, R. Lawrence; Falce, Lou

    2006-01-01

    Variations in emission current from dispenser cathodes can be caused by variations in temperature and work function over the surface. This paper described research to reduce these variations using improved mechanical designs and controlled porosity cathodes made from sintered tungsten wires. The program goal is to reduce current emission variations to less than 5% over the surface of magnetron injection guns operating temperature limited.

  13. Planar-focusing cathodes.

    SciTech Connect

    Lewellen, J. W.; Noonan, J.; Accelerator Systems Division

    2005-01-01

    Conventional {pi}-mode rf photoinjectors typically use magnetic solenoids for emittance compensation. This provides independent focusing strength but can complicate rf power feed placement, introduce asymmetries (due to coil crossovers), and greatly increase the cost of the photoinjector. Cathode-region focusing can also provide for a form of emittance compensation. Typically this method strongly couples focusing strength to the field gradient on the cathode, however, and usually requires altering the longitudinal position of the cathode to change the focusing. We propose a new method for achieving cathode-region variable-strength focusing for emittance compensation. The new method reduces the coupling to the gradient on the cathode and does not require a change in the longitudinal position of the cathode. Expected performance for an S-band system is similar to conventional solenoid-based designs. This paper presents the results of rf cavity and beam dynamics simulations of the new design. We have proposed a method for performing emittance compensation using a cathode-region focusing scheme. This technique allows the focusing strength to be adjusted somewhat independently of the on-axis field strength. Beam dynamics calculations indicate performance should be comparable to presently in-use emittance compensation schemes, with a simpler configuration and fewer possibilities for emittance degradation due to the focusing optics. There are several potential difficulties with this approach, including cathode material selection, cathode heating, and peak fields in the gun. We hope to begin experimenting with a cathode of this type in the near future, and several possibilities exist for reducing the peak gradients to more acceptable levels.

  14. Cathode architectures for alkali metal / oxygen batteries

    DOEpatents

    Visco, Steven J; Nimon, Vitaliy; De Jonghe, Lutgard C; Volfkovich, Yury; Bograchev, Daniil

    2015-01-13

    Electrochemical energy storage devices, such as alkali metal-oxygen battery cells (e.g., non-aqueous lithium-air cells), have a cathode architecture with a porous structure and pore composition that is tailored to improve cell performance, especially as it pertains to one or more of the discharge/charge rate, cycle life, and delivered ampere-hour capacity. A porous cathode architecture having a pore volume that is derived from pores of varying radii wherein the pore size distribution is tailored as a function of the architecture thickness is one way to achieve one or more of the aforementioned cell performance improvements.

  15. 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.

  16. Experimental study of vortex diffusers

    SciTech Connect

    Shakerin, S.; Miller, P.L.

    1995-11-01

    This report documents experimental research performed on vortex diffusers used in ventilation and air-conditioning systems. The main objectives of the research were (1) to study the flow characteristics of isothermal jets issuing from vortex diffusers, (2) to compare the vortex diffuser`s performance with that of a conventional diffuser, and (3) to prepare a report that disseminates the results to the designers of ventilation and air-conditioning systems. The researchers considered three diffusers: a conventional round ceiling diffuser and two different styles of vortex diffusers. Overall, the vortex diffusers create slightly more induction of ambient air in comparison to the conventional diffuser.

  17. Methods and apparatus for using gas and liquid phase cathodic depolarizers

    NASA Technical Reports Server (NTRS)

    Murphy, Oliver J. (Inventor); Hitchens, G. Duncan (Inventor)

    1998-01-01

    The invention provides methods for using gas and liquid phase cathodic depolarizers in an electrochemical cell having a cation exchange membrane in intimate contact with the anode and cathode. The electrochemical conversion of cathodic depolarizers at the cathode lowers the cell potential necessary to achieve a desired electrochemical conversion, such as ozone evolution, at the anode. When gaseous cathodic depolarizers, such as oxygen, are used, a gas diffusion cathode having the cation exchange membrane bonded thereto is preferred. When liquid phase cathodic depolarizers are used, the cathode may be a flow-by electrode, flow-through electrode, packed-bed electrode or a fluidized-bed electrode in intimate contact with the cation exchange membrane.

  18. Tackling agricultural diffuse pollution: What might uptake of farmer-preferred measures deliver for emissions to water and air?

    PubMed

    Collins, A L; Zhang, Y S; Winter, M; Inman, A; Jones, J I; Johnes, P J; Cleasby, W; Vrain, E; Lovett, A; Noble, L

    2016-03-15

    Mitigation of agricultural diffuse pollution poses a significant policy challenge across Europe and particularly in the UK. Existing combined regulatory and voluntary approaches applied in the UK continue to fail to deliver the necessary environmental outcomes for a variety of reasons including failure to achieve high adoption rates. It is therefore logical to identify specific on-farm mitigation measures towards which farmers express positive attitudes for higher future uptake rates. Accordingly, a farmer attitudinal survey was undertaken during phase one of the Demonstration Test Catchment programme in England to understand those measures towards which surveyed farmers are most receptive to increasing implementation in the future. A total of 29 on-farm measures were shortlisted by this baseline farm survey. This shortlist comprised many low cost or cost-neutral measures suggesting that costs continue to represent a principal selection criterion for many farmers. The 29 measures were mapped onto relevant major farm types and input, assuming 95% uptake, to a national scale multi-pollutant modelling framework to predict the technically feasible impact on annual agricultural emissions to water and air, relative to business as usual. Simulated median emission reductions, relative to current practise, for water management catchments across England and Wales, were estimated to be in the order sediment (20%)>ammonia (16%)>total phosphorus (15%)≫nitrate/methane (11%)>nitrous oxide (7%). The corresponding median annual total cost of the modelled scenario to farmers was £3ha(-1)yr(-1), with a corresponding range of -£84ha(-1)yr(-1) (i.e. a net saving) to £33ha(-1)yr(-1). The results suggest that those mitigation measures which surveyed farmers are most inclined to implement in the future would improve the environmental performance of agriculture in England and Wales at minimum to low cost per hectare. PMID:26789365

  19. 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.

  20. Development of a method for the determination of naphthalene and phenanthrene in workplace air using diffusive sampling and thermal desorption GC-MS analysis.

    PubMed

    Lindahl, Roger; Claesson, Anna-Sara; Khan, Muhammad Akhtar; Levin, Jan-Olof

    2011-07-01

    Diffusive sampling methods have been validated for the determination of naphthalene and phenanthrene in workplace air. The diffusive sampler tested was the Perkin Elmer ATD tube, and the analysis was performed with thermal desorption, gas chromatography, and mass spectrometric detection. The sampling methods were validated in controlled test atmospheres, mainly according to the protocol proposed in the European standard EN 838. For the determination of naphthalene, the diffusive sampling rate was 0.41 ml min(-1) with a coefficient of variation (CV) of 19%. The mean sampling rate for phenanthrene was 0.49 ml min(-1) with a CV of 21%. Field tests confirmed the naphthalene results but could not be used to confirm the phenanthrene results. The method is not recommended for phenanthrene sampling unless the method has been tested in the specific environment and the results confirm the laboratory tests. PMID:21742628

  1. Oxide cathodes produced by plasma deposition

    SciTech Connect

    Scheitrum, G.; Caryotakis, G.; Pi, T.; Umstattd, R.; Brown, I.; Montiero, O.

    1997-12-31

    These are two distinct applications for high-current-density, long-life thermionic cathodes. The first application is as a substitute for explosive emission cathodes used in high-power microwave (HPM) devices being developed for Air Force programs. The second application is in SLAC`s X-band klystrons for the Next Linear Collider (NLC). SLAC, UCD, and LBL are developing a plasma deposition process that eliminates the problems with binders, carbonate reduction, peeling, and porosity. The emission layer is deposited using plasma deposition of metallic barium in vacuum with an oxygen background gas. An applied bias voltage drives the oxide plasma into the nickel surface. Since the oxide is deposited directly, it does not have problems with poisoning from a hydrocarbon binder. The density of the oxide layer is increased from the 40--50% for standard oxide cathodes to nearly 100% for plasma deposition.

  2. A Diffuse Interface Model for solid-liquid-air dissolution problems based on a porous medium theory

    NASA Astrophysics Data System (ADS)

    Luo, H.; Quintard, M.; Debenest, G.; Laouafa, F.

    2011-12-01

    The underground cavities may be dissolved by the flows of groundwater where the dissolution mainly happens at the liquid-solid interface. In many real cases, the cavities are not occupied only by the water, but also the gas phase, e.g., air, or other gases. In this case, there are solid-liquid-gas three phases. Normally, the air does not participate the dissolution. However, it may influence the dissolution as the position of the solid-liquid interface may gradually lower down with the dissolution process. Simulating the dissolution problems with multi- moving interfaces is a difficult task but rather interesting to study the evolution of the underground cavities. In this paper, we propose a diffuse interface model (DIM) to simulate the three-phase dissolution problem, based on a porous medium theory and a volume averaging theory te{Whitaker1999,Golfier2002,Quintard1994}. The interface is regarded as a continuous layer where the phase indicator (mainly for solid-liquid interface) and phase saturation (mainly for liquid-gas interface) vary rapidly but smoothly. The DIM equations enable us to simulate the moving interface under a fixed mesh system, instead of a deformed or moving mesh. Suppose we have three phases, solid, liquid and gas. The solid phase contains only species A. The gas phase contains only the air. The volume averaging theory is used to upscale the balance equations. The final DIM equations are presented below. The balance equation of solid phase can be written as {partialrho_{s}(1-\\varepsilon_{f})}/{partial t}=-K_{sl} where \\varepsilonf represents the volume fraction of the fluids (liquid+gas) and Ksl refers to the mass exchange between the solid phase and the liquid phase. Ksl cam be expressed as K_{sl}=rho_{l}alpha(omega_{eq}-Omega_{Al}). The balance equations of liquid phase can be written as {partialrho_{l}\\varepsilon_{f}S_{l}}/{partial t}+nabla\\cdot(rho_{l}{V}_{l})= K_{sl}. The balance equation of liquid phase can be written as {partialrho_{g}\\varepsilon_{f}(1-S_{l})}/{partial t}+nabla\\cdot(rho_{g}{V}_{g}) =0. The balance equations of species A can be written as rho_{l}\\varepsilon_{f}S_{l} {partialOmega_{Al}}/{partial t} +rho_{l}{V}_{l}\\cdotnablaOmega_{Al} =nabla\\cdot(rho_{l}{D}_{Al}^{*}nablaOmega_{Al})+K_{sl}. We introduce the multi-phase Darcy's Law to {V}l and {V}g, {V}_{l}=-{{K}k_{rl}}/{mu_{l}}(nabla P_{l}-rho_{l}{g}) {V}_{g}=-{K}k_{rg}}/{mu_{g}}(nabla P_{g}-rho_{g}{g}) Kozeny-Carman equation is introduced to calculate {K}, Capillary pressure theory can be used to calculate krl, krg, and the capillary pressure Pc, as a function of Sl.

  3. 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.

  4. 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.

  5. Nanostructured sulfur cathodes.

    PubMed

    Yang, Yuan; Zheng, Guangyuan; Cui, Yi

    2013-04-01

    Rechargeable Li/S batteries have attracted significant attention lately due to their high specific energy and low cost. They are promising candidates for applications, including portable electronics, electric vehicles and grid-level energy storage. However, poor cycle life and low power capability are major technical obstacles. Various nanostructured sulfur cathodes have been developed to address these issues, as they provide greater resistance to pulverization, faster reaction kinetics and better trapping of soluble polysulfides. In this review, recent developments on nanostructured sulfur cathodes and mechanisms behind their operation are presented and discussed. Moreover, progress on novel characterization of sulfur cathodes is also summarized, as it has deepened the understanding of sulfur cathodes and will guide further rational design of sulfur electrodes. PMID:23325336

  6. Cathodes - Technological review

    SciTech Connect

    Cherkouk, Charaf; Nestler, Tina

    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.

  7. 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.

  8. 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.

  9. 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.

  10. Cathode materials review

    SciTech Connect

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

    2014-06-16

    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 LiCoO{sub 2} 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.

  11. 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.

  12. Modelling cathode spots in glow discharges in the cathode boundary layer geometry

    NASA Astrophysics Data System (ADS)

    Bieniek, M. S.; Almeida, P. G. C.; Benilov, M. S.

    2016-03-01

    Self-organized patterns of cathode spots in glow discharges are computed in the cathode boundary layer geometry, which is the one employed in most of the experiments reported in the literature. The model comprises conservation and transport equations of electrons and a single ion species, written in the drift-diffusion and local-field approximations, and Poisson’s equation. Multiple solutions existing for the same value of the discharge current and describing modes with different configurations of cathode spots are computed by means of a stationary solver. The computed solutions are compared to their counterparts for plane-parallel electrodes, and experiments. All of the computed spot patterns have been observed in the experiment.

  13. Interfacial diffusion of metal atoms during air annealing of chemically deposited ZnS-CuS and PbS-CuS thin films

    SciTech Connect

    Huang, L.; Zingaro, R.A.; Meyers, E.A. . Dept. of Chemistry); Nair, P.K.; Nair, M.T.S. . Lab. de Energia Solar)

    1994-09-01

    The authors report on the interfacial diffusion of metal ions occurring during air annealing of multilayer CuS films (0.15-0.6[mu]m) deposited on thin coating of ZnS or PbS ([approximately]0.06 [mu]m) on glass substrates. All the films are deposited from chemical baths at room temperature. The interfacial diffusion on the metal atoms during the air annealing is illustrate by X-ray photoelectron spectroscopy studies. A multilayer of 0.3 [mu]m thick CuS film deposited over a thin film of ZnS upon annealing at 150 C shows atomic ratios of Zn to Cu of [approximately]0.15 and [approximately]0.48 at the surface layers of the samples annealed for 12 and 24 h, respectively. In the case of CuS on PbS film, the corresponding Pb to Cu atomic ratios at the surface layers are 0.43 and 0.83. The optical transmittance spectra and sheet resistance of these multilayer films indicate thermal stabilities superior to that of the CuS-only coatings. Application of the interfacial diffusion process in the production of thermally stable solar control coatings, solar absorber coating, or p-type films for solar cell structures is discussed.

  14. 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...

  15. Assessment of diffusion parameters of new passive samplers using optical chemical sensor for on-site measuring formaldehyde in indoor air: experimental and numerical studies.

    PubMed

    Vignau-Laulhere, Jane; Mocho, Pierre; Plaisance, Hervé; Raulin, Katarzyna; Desauziers, Valérie

    2016-03-01

    New passive samplers using a sensor consisting of a sol-gel matrix entrapping Fluoral-P as sampling media were developed for the determination of formaldehyde in indoor air. The reaction between Fluoral-P and formaldehyde produces a colored compound which is quantified on-site by means of a simple optical reading module. The advantages of this sensor are selectivity, low cost, ppb level limit of detection, and on-site direct measurement. In the development process, it is necessary to determine the sampling rate, a key parameter that cannot be directly assessed in the case of diffusive samplers using optical chemical sensor. In this study, a methodology combining experimental tests and numerical modeling is proposed and applied at five different radial diffusive samplers equipped with the same optical chemical sensor to assess the sampled material flows and sampling rates. These radial diffusive samplers differ in the internal volume of the sampler (18.97 and 6.14 cm(3)), the position of sensor inside the sampler (in front and offset of 1.2 cm above the membrane) and the width of the diffusion slot (1.4 and 5.9 mm). The influences of these three parameters (internal volume, position of sensor inside the sampler, and width of the diffusion slot) were assessed and discussed with regard to the formaldehyde sampling rate and water uptake by sensor (potential interference of measure). Numerical simulations based on Fick's laws are in agreement with the experimental results and provide to estimate the effective diffusion coefficient of formaldehyde through the membrane (3.50 × 10(-6) m(2) s(-1)). Conversion factors between the sensor response, sampled formaldehyde mass and sampling rate were also assessed. PMID:26847188

  16. 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.

  17. Cathodic protection current testing for large plant structures

    SciTech Connect

    Maynard, R.J.

    1996-07-01

    Design of cathodic protection (CP) for underground facilities in large plants is a problem. A method is described for performing data interpretation of field cathodic current requirement tests on large plant structures. It is possible to perform meaningful tests with small temporary current sources and arrive at a design where final requirements are many times larger. Examples of its use at a power plant and an air separation plant are given.

  18. 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.

  19. Filtered cathodic arc source

    DOEpatents

    Falabella, Steven (Livermore, CA); Sanders, David M. (Livermore, CA)

    1994-01-01

    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. 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.

  20. Dispenser cathode physics

    NASA Astrophysics Data System (ADS)

    Green, M. C.

    1981-07-01

    The structure and composition of the emissive layers of activated and stabilize B-type and M-type cathode surfaces at operating temperature were investigated using X-ray photoelectron spectroscopy and high spatial resolution Auger Spectroscopy. The results indicate that the activating layer consists of a monolayer or submonolayer film of barium and oxygen of stoichiometry close to Ba101. The emissive layer was found to be vertically ordered, with barium concentrated in the first monolayer above oxygen. The primary difference observed between the B-type and M-type surfaces was increased coverage of the underlying metal by the barium/oxygen layer in the M-type case. The spectra of the emissive layer, although quite different from those of 'bulk' barium oxide, were consistent with a barium-oxygen bonding interaction. A theoretical model of the bonding of barium and oxygen to each other and to the underlying metal matrix surface was proposed, consistent with the above experimental data and with the published results of other workers in the field. A calculation of the lattice stabilization energy in bulk ionic BaO indicated that the bonding in the emissive layer must be predominantly covalent. In Appendix A, a new user-oriented method of plotting cathode emission test data in the form of Miram-plots of normalized current density against temperature is described. Examples are given of the manner in which such plots clearly delineate changes in cathode performance capability with time and specific cathode failure modes. The cathode physics of a novel failure mode of a high current density cathode involving saturation of pore center emission is described.

  1. 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.

  2. NO{sub x} emissions of a jet diffusion flame which is surrounded by a shroud of combustion air

    SciTech Connect

    Tran, P.X.; White, F.P.; Mathur, M.P.; Ekmann, J.M.

    1996-08-01

    The present work reports an experimental study on the behavior of a jet flame surrounded by a shroud of combustion air. Measurements focussed on the flame length and the emissions of NO{sub x}, total unburned hydrocarbons, CO{sub 2}, and O{sub 2}. Four different fuel flow rates (40.0, 78.33, 138.33, and 166.6 cm/s), air flow rates up to 2500 cm{sup 3}/s and four different air injector diameters (0.079 cm, 0. 158 cm, 0.237 cm, and 0.316 cm) were used. The shroud of combustion air causes the flame length to decrease by a factor proportional to 1/[p{sub a}/p{sub f} + C{sub 2}({mu}{sub a}Re,a/{mu}{sub f}Re,f){sup 2}]{sup {1/2}}. A substantial shortening of the flame length occurred by increasing the air injection velocity keeping fuel rate fixed or conversely by lowering the fuel flow rate keeping air flow rate constant. NO{sub x} emissions ranging from 5 ppm to 64 ppm were observed and the emission of NO{sub x} decreased strongly with the increased air velocity. The decrease of NO{sub x} emissions was found to follow a similar scaling law as does the flame length. However, the emission of the total hydrocarbons increased with the increased air velocity or the decreased fuel flow rate. A crossover condition where both NO{sub x} and unburned- hydrocarbon emissions are low, was identified. At an air-to-fuel velocity ratio of about 1, the emissions of NO{sub x} and the total hydrocarbons were found to be under 20 ppm.

  3. Analyzing spotless mode of current transfer to cathodes of Cr, Gd, and Pb vapour arcs

    NASA Astrophysics Data System (ADS)

    Benilova, Larissa; Benilov, Mikhail

    2015-09-01

    Diffuse mode of current transfer occurs on cathodes of vacuum arcs if the average cathode surface temperature is high enough, which can be achieved by placing the (evaporating) cathode into a thermally insulated crucible. It is shown that in the case of Cr or Pb cathodes the usual mechanism of current transfer to arc cathodes cannot sustain current densities of the order of 105 -106 Am-2 observed in the experiment, the reason being that the electrical power deposited into electron gas in the near-cathode space-charge sheath is too low. It is hypothesized that the electrical power is supplied to the electron gas primarily in the bulk plasma, rather than in the sheath, and a high level of electron energy at the sheath edge is sustained by electron heat conduction from the bulk plasma. Estimates of the current of ions diffusing to the sheath edge from the quasi-neutral plasma gave values comparable to the experimental current density, which supports the above hypothesis. On the contrary, the spotless attachment of vacuum arcs to Gd cathodes may be interpreted as a manifestation of the usual arc cathode mechanism. Results given for Gd cathodes by a model of near-cathode layers in vacuum arcs conform to available experimental information. Work supported by FCT of Portugal through the projects PTDC/FIS-PLA/2708/2012 and Pest-OE/UID/FIS/50010/2013.

  4. Production of atmospheric pressure diffuse nanosecond pulsed dielectric barrier discharge using the array needles-plate electrode in air

    NASA Astrophysics Data System (ADS)

    Yang, De-zheng; Wang, Wen-chun; Jia, Li; Nie, Dong-xia; Shi, Heng-chao

    2011-04-01

    In this paper, a bidirectional high pulse voltage with 20 ns rising time is employed to generate an atmospheric pressure diffuse dielectric barrier discharge using the array needles-plate electrode configuration. Both double needle and multiple needle electrode configurations nanosecond pulsed dielectric barrier discharges are investigated. It is found that a diffuse discharge plasma with low gas temperature can be obtained, and the plasma volume increases with the increase of the pulse peak voltage, but remains almost constant with the increase of the pulse repetition rate. In addition to showing the potential application on a topographically nonuniform surface treatment of the discharge, the multiple needle-plate electrode configuration with different needle-plate electrode gaps are also employed to generate diffuse discharge plasma.

  5. Miniaturized cathodic arc plasma source

    DOEpatents

    Anders, Andre; MacGill, Robert A.

    2003-04-15

    A cathodic arc plasma source has an anode formed of a plurality of spaced baffles which extend beyond the active cathode surface of the cathode. With the open baffle structure of the anode, most macroparticles pass through the gaps between the baffles and reflect off the baffles out of the plasma stream that enters a filter. Thus the anode not only has an electrical function but serves as a prefilter. The cathode has a small diameter, e.g. a rod of about 1/4 inch (6.25 mm) diameter. Thus the plasma source output is well localized, even with cathode spot movement which is limited in area, so that it effectively couples into a miniaturized filter. With a small area cathode, the material eroded from the cathode needs to be replaced to maintain plasma production. Therefore, the source includes a cathode advancement or feed mechanism coupled to cathode rod. The cathode also requires a cooling mechanism. The movable cathode rod is housed in a cooled metal shield or tube which serves as both a current conductor, thus reducing ohmic heat produced in the cathode, and as the heat sink for heat generated at or near the cathode. Cooling of the cathode housing tube is done by contact with coolant at a place remote from the active cathode surface. The source is operated in pulsed mode at relatively high currents, about 1 kA. The high arc current can also be used to operate the magnetic filter. A cathodic arc plasma deposition system using this source can be used for the deposition of ultrathin amorphous hard carbon (a-C) films for the magnetic storage industry.

  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. Cathode material for lithium batteries

    SciTech Connect

    Park, Sang-Ho; Amine, Khalil

    2015-01-13

    A method of manufacture an article of a cathode (positive electrode) material for lithium batteries. The cathode material is a lithium molybdenum composite transition metal oxide material and is prepared by mixing in a solid state an intermediate molybdenum composite transition metal oxide and a lithium source. The mixture is thermally treated to obtain the lithium molybdenum composite transition metal oxide cathode material.

  8. Cathode material for lithium batteries

    SciTech Connect

    Park, Sang-Ho; Amine, Khalil

    2013-07-23

    A method of manufacture an article of a cathode (positive electrode) material for lithium batteries. The cathode material is a lithium molybdenum composite transition metal oxide material and is prepared by mixing in a solid state an intermediate molybdenum composite transition metal oxide and a lithium source. The mixture is thermally treated to obtain the lithium molybdenum composite transition metal oxide cathode material.

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

    SciTech Connect

    Benilov, M. S.; Cunha, M. D.

    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. 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.

  11. A numerical study on the effect of hydrogen/reformate gas addition on flame temperature and NO formation in strained methane/air diffusion flames

    SciTech Connect

    Guo, Hongsheng; Neill, W. Stuart

    2009-02-15

    This paper investigates the effects of hydrogen/reformate gas addition on flame temperature and NO formation in strained methane/air diffusion flames by numerical simulation. The results reveal that flame temperature changes due to the combined effects of adiabatic temperature, fuel Lewis number and radiation heat loss, when hydrogen/reformate gas is added to the fuel of a methane/air diffusion flame. The effect of Lewis number causes the flame temperature to increase much faster than the corresponding adiabatic equilibrium temperature when hydrogen is added, and results in a qualitatively different variation from the adiabatic equilibrium temperature as reformate gas is added. At some conditions, the addition of hydrogen results in a super-adiabatic flame temperature. The addition of hydrogen/reformate gas causes NO formation to change because of the variations in flame temperature, structure and NO formation mechanism, and the effect becomes more significant with increasing strain rate. The addition of a small amount of hydrogen or reformate gas has little effect on NO formation at low strain rates, and results in an increase in NO formation at moderate or high strain rates. However, the addition of a large amount of hydrogen increases NO formation at all strain rates, except near pure hydrogen condition. Conversely, the addition of a large amount of reformate gas results in a reduction in NO formation. (author)

  12. Morphometric partitioning of the respiratory surface area and diffusion capacity of the gills and swim bladder in juvenile Amazonian air-breathing fish, Arapaima gigas.

    PubMed

    Fernandes, Marisa Narciso; da Cruz, Andr Luis; da Costa, Oscar Tadeu Ferreira; Perry, Steven Franklin

    2012-09-01

    The gills and the respiratory swim bladders of juvenile specimens (mean body mass 100g) of the basal teleost Arapaima gigas (Cuvier 1829) were evaluated using stereological methods in vertical sections. The surface areas, harmonic mean barrier thicknesses and morphometric diffusing capacities for oxygen and carbon dioxide were estimated. The average respiratory surface area of the swim bladder (2173 cm kg?) exceeded that of the gills (780 cm kg?) by a factor of 2.79. Due to the extremely thin air-blood barrier in the swim bladder (harmonic mean 0.22 ?m) and the much thicker water-blood barrier of the gills (9.61 ?m), the morphometric diffusing capacity for oxygen and carbon dioxide was 88 times greater in the swim bladder than in the gills. These data clearly indicate the importance of the swim bladder, even in juvenile A. gigas that still engage in aquatic respiration. Because of the much greater diffusion constant of CO? than O? in water, the gills also remain important for CO? release. PMID:22512942

  13. 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.

  14. 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.

  15. 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-δ (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 Å (as determined from the integration of the first 20 hours of XRD patterns) to 3.92650 Å (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.

  16. Synopsis of Cathode #4 Activation

    SciTech Connect

    Kwan, Joe; Ekdahl, C.; Harrison, J.; Kwan, J.; Leitner, M.; McCruistian, T.; Mitchell, R.; Prichard, B.; Roy, P.

    2006-05-26

    The purpose of this report is to describe the activation of the fourth cathode installed in the DARHT-II Injector. Appendices have been used so that an extensive amount of data could be included without danger of obscuring important information contained in the body of the report. The cathode was a 612 M type cathode purchased from Spectra-Mat. Section II describes the handling and installation of the cathode. Section III is a narrative of the activation based on information located in the Control Room Log Book supplemented with time plots of pertinent operating parameters. Activation of the cathode was performed in accordance with the procedure listed in Appendix A. The following sections provide more details on the total pressure and constituent partial pressures in the vacuum vessel, cathode heater power/filament current, and cathode temperature.

  17. Hydrogen hollow cathode ion source

    NASA Technical Reports Server (NTRS)

    Mirtich, M. J., Jr.; Sovey, J. S.; Roman, R. F. (Inventor)

    1980-01-01

    A source of hydrogen ions is disclosed and includes a chamber having at one end a cathode which provides electrons and through which hydrogen gas flows into the chamber. Screen and accelerator grids are provided at the other end of the chamber. A baffle plate is disposed between the cathode and the grids and a cylindrical baffle is disposed coaxially with the cathode at the one end of the chamber. The cylindrical baffle is of greater diameter than the baffle plate to provide discharge impedance and also to protect the cathode from ion flux. An anode electrode draws the electrons away from the cathode. The hollow cathode includes a tubular insert of tungsten impregnated with a low work function material to provide ample electrons. A heater is provided around the hollow cathode to initiate electron emission from the low work function material.

  18. Evaluation of two adsorbents for diffusive sampling and thermal desorption-gas chromatographic analysis of monoterpenes in air.

    PubMed

    Sunesson, A L; Sundgren, M; Levin, J O; Eriksson, K; Carlson, R

    1999-02-01

    Tube type samplers with two different adsorbents, Chromosorb 106 and Tenax TA, were evaluated by laboratory experiments and field tests for simultaneous diffusive sampling of alpha-pinene, beta-pinene and delta 3-carene and subsequent thermal desorption-gas chromatographic analysis. No statistically significant effects of exposure time, concentrations of monoterpenes or relative humidity were found for samplers with Chromosorb 106 when running a factorial design, with the exception of the adsorption of delta 3-carene, for which some weak effects were noted. Samplers with Tenax TA were affected by the sampling time as well as the concentration for all terpenes, with a strong interaction effect between these two factors. The terpenes showed good storage stability on both adsorbents. No effect of back-diffusion was noted when using Chromosorb 106, while Tenax TA showed some back-diffusion effects. The uptake rates, in ml min-1, for the terpenes on Chromosorb 106 were 0.36 for alpha-pinene, 0.36 for beta-pinene and 0.40 for delta 3-carene. The corresponding average values on Tenax TA were 0.30 for alpha-pinene, 0.32 for beta-pinene and 0.38 for delta 3-carene. The field validation proved that diffusive sampling on Chromosorb 106 agreed well with pumped sampling on charcoal for stationary samples, while the personal samples indicated a discrepancy of 25% between Chromosorb 106 and charcoal samples. Tenax TA generally gave lower results than Chromosorb 106 in all field samples. Samplers packed with Chromosorb 106 could be used to monitor terpene levels in workplaces such as sawmills. The major advantages with this method are the sampling procedure, which is simple to perform compared to other techniques, the easily automated analysis procedure and the possibility to reuse the samplers. PMID:11529078

  19. Badge-type diffusive sampler using 3-methyl-2-benzothiazolinone hydrazone for measuring formaldehyde in indoor air.

    PubMed

    Yim, Bongbeen; Jung, Euisuk

    2006-07-01

    The evaluation of a badge-type diffusive sampler for measuring formaldehyde using 3-methyl-2-benzothiazolinone hydrazone (MBTH) was investigated. On average, the formaldehyde concentration in blanks was reduced by approximately 31% by cleaning procedures. The cleaning techniques did not significantly differ in effectiveness. The maximum sampling rate was 22.4 +/- 3.5 mL min(-1) at MBTH concentrations of 0.05%. The formaldehyde concentration in blanks did not appreciably increase over a period of about 1 month at room temperature, and was 0.36 +/- 0.03 microg, with a relative standard deviation of 8%. The diffusive sampler had good precision and accuracy for measuring formaldehyde in indoor environments. For a 24-h exposure time, the limits of detection and quantification calculated with the field blanks were 9.7 and 13.8 ppb, respectively. The minimum exposure times were calculated based on the measured and calculated limits of quantification, the sampling rate, and the atmospheric formaldehyde concentration. The capacity of the diffusive sampler with 0.5% MBTH was 3 ppm h(-1), approximately 1.5-times the capacity when the MBTH concentrations were 0.05%. PMID:16837752

  20. 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.

  1. Local ion nitriding process with hollow cathode effect computer modelling

    NASA Astrophysics Data System (ADS)

    Ramazanov, K. N.; Khusainov, Yu G.; Zolotov, I. V.

    2015-11-01

    Modelling of glow discharge plasma with hollow cathode effect (HCE) was carried out. The computer model that allows predicting the temperature distribution during local ion nitriding with HCE and depth of the diffusion zone after the treatment was developed. The influence on the HCE on the temperature distribution for the gear was studied.

  2. Plasma deposition of oxide cathodes

    NASA Astrophysics Data System (ADS)

    Umstattd, R.; Pi, T.; Luhmann, N.; Scheitrum, G.; Caryotakis, G.; Miram, G.

    1999-05-01

    Vacuum arc deposition is employed to create a barium and/or strontium plasma which is subsequently deposited/implanted onto a nickel cathode substrate. The primary motivation for this work is the critical need for a reliable, repeatable, long-lived thermionic cathode for the production of high power, microsecond duration microwave pulses; such cathodes may also have applicability for lower current density continuous wave devices. This novel approach to manufacturing an oxide cathode eliminates the binders that may subsequently (and unpredictably) poison cathode emission. Removal of the poisoning mechanisms has yielded oxide cathodes capable of emission densities in the 20 A/cm2 regime. Cathode lifetime and emission may be varied via the control over the deposition parameters such as coating thickness, implantation energy, and plasma stoichiometry. The deposition is performed by generating a cathodic arc discharge at the surface of a barium or barium-strontium alloy rod. The metal plasma thus created is then deposited on the substrate which can be negatively biased to encourage implantation during the deposition process. The deposition is performed with sufficient background oxygen present to oxidize the highly reactive metal coating. The plasma deposition is monitored via a rate thickness monitor, an optical emission spectrometer for plasma composition information, and an electrostatic Langmuir probe for the determination of the plasma density and temperature profile. Cathodes thus produced are analyzed by drawing pulsed current at a constant voltage for various values of decreasing cathode temperature in order to generate practical work function distributions which provide an indication of the quality and expected life time of the cathode. In support of analyzing these cathodes (as well as a variety of cathodes from other sources), a complete UHV cathode test and analysis system has been assembled which includes 3-D beam profiling, advanced temperature measurement, residual gas analysis, bulk cold work function measurement, and surface analysis with depth profiling.

  3. Steady-state solution of the semi-empirical diffusion equation for area sources. [air pollution studies

    NASA Technical Reports Server (NTRS)

    Lebedeff, S. A.; Hameed, S.

    1975-01-01

    The problem investigated can be solved exactly in a simple manner if the equations are written in terms of a similarity variable. The exact solution is used to explore two questions of interest in the modelling of urban air pollution, taking into account the distribution of surface concentration downwind of an area source and the distribution of concentration with height.

  4. Cathodic oxygen reduction catalyzed by bacteria in microbial fuel cells.

    PubMed

    Rabaey, Korneel; Read, Suzanne T; Clauwaert, Peter; Freguia, Stefano; Bond, Philip L; Blackall, Linda L; Keller, Jurg

    2008-05-01

    Microbial fuel cells (MFCs) have the potential to combine wastewater treatment efficiency with energetic efficiency. One of the major impediments to MFC implementation is the operation of the cathode compartment, as it employs environmentally unfriendly catalysts such as platinum. As recently shown, bacteria can facilitate sustainable and cost-effective cathode catalysis for nitrate and also oxygen. Here we describe a carbon cathode open to the air, on which attached bacteria catalyzed oxygen reduction. The bacteria present were able to reduce oxygen as the ultimate electron acceptor using electrons provided by the solid-phase cathode. Current densities of up to 2.2 A m(-2) cathode projected surface were obtained (0.303+/-0.017 W m(-2), 15 W m(-3) total reactor volume). The cathodic microbial community was dominated by Sphingobacterium, Acinetobacter and Acidovorax sp., according to 16S rRNA gene clone library analysis. Isolates of Sphingobacterium sp. and Acinetobacter sp. were obtained using H(2)/O(2) mixtures. Some of the pure culture isolates obtained from the cathode showed an increase in the power output of up to three-fold compared to a non-inoculated control, that is, from 0.015+/-0.001 to 0.049+/-0.025 W m(-2) cathode projected surface. The strong decrease in activation losses indicates that bacteria function as true catalysts for oxygen reduction. Owing to the high overpotential for non-catalyzed reduction, oxygen is only to a limited extent competitive toward the electron donor, that is, the cathode. Further research to refine the operational parameters and increase the current density by modifying the electrode surface and elucidating the bacterial metabolism is warranted. PMID:18288216

  5. 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.

  6. The cathode plasma simulation

    NASA Astrophysics Data System (ADS)

    Suksila, Thada

    Since its invention at the University of Stuttgart, Germany in the mid-1960, scientists have been trying to understand and explain the mechanism of the plasma interaction inside the magnetoplasmadynamics (MPD) thruster. Because this thruster creates a larger level of efficiency than combustion thrusters, this MPD thruster is the primary cadidate thruster for a long duration (planetary) spacecraft. However, the complexity of this thruster make it difficult to fully understand the plasma interaction in an MPD thruster while operating the device. That is, there is a great deal of physics involved: the fluid dynamics, the electromagnetics, the plasma dynamics, and the thermodynamics. All of these physics must be included when an MPD thruster operates. In recent years, a computer simulation helped scientists to simulate the experiments by programing the physics theories and comparing the simulation results with the experimental data. Many MPD thruster simulations have been conducted: E. Niewood et al.[5], C. K. J. Hulston et al.[6], K. D. Goodfellow[3], J Rossignol et al.[7]. All of these MPD computer simulations helped the scientists to see how quickly the system responds to the new design parameters. For this work, a 1D MPD thruster simulation was developed to find the voltage drop between the cathode and the plasma regions. Also, the properties such as thermal conductivity, electrical conductivity and heat capacity are temperature and pressure dependent. These two conductivity and heat capacity are usually definded as constant values in many other models. However, this 1D and 2D cylindrical symmetry MPD thruster simulations include both temperature and pressure effects to the electrical, thermal conductivities and heat capacity values interpolated from W. F. Ahtye [4]. Eventhough, the pressure effect is also significant; however, in this study the pressure at 66 Pa was set as a baseline. The 1D MPD thruster simulation includes the sheath region, which is the interface between the plasma and the cathode regions. This sheath model [3] has been fully combined in the 1D simulation. That is, the sheath model calculates the heat flux and the sheath voltage by giving the temperature and the current density. This sheath model must be included in the simulation, as the sheath region is treated differently from the main plasma region. For our 2D cylindrical symmetry simulation, the dimensions of the cathode, the anode, the total current, the pressure, the type of gases, the work function can be changed in the input process as needed for particular interested. Also, the sheath model is still included and fully integrated in this 2D cylindrical symmetry simulation at the cathode surface grids. In addition, the focus of the 2D cylindrical symmetry simulation is to connect the properties on the plasma and the cathode regions on the cathode surface until the MPD thruster reach steady state and estimate the plasma arc attachement edge, electroarc edge, on the cathode surface. Finally, we can understand more about the behavior of an MPD thruster under many different conditions of 2D cylindrical symmetry MPD thruster simulations.

  7. Preliminary results on the chemical characterisation of the cathode nickel—emissive layer interface in oxide cathodes

    NASA Astrophysics Data System (ADS)

    Jenkins, S. N.; Barber, D. K.; Whiting, M. J.; Baker, M. A.

    2003-06-01

    In cathode ray tube (CRT) thermionic oxide cathodes, the nickel-oxide interface properties are key to understanding the mechanisms of operation. At the elevated operational temperatures, free barium is formed at the interface by the reaction of reducing activators, from the nickel alloy, with barium oxide. The free barium diffuses to the outer surface of the oxide providing a low work function electron-emitting surface. However, during cathode life an interface layer grows between the nickel alloy and oxide, comprised of reaction products. The interfacial layer sets limits on the cathode performance and useful operational lifetime by inhibiting the barium reducing reaction. This paper discusses sample preparation procedures for exposure of the interface and the use of several surface and bulk analytical techniques to study interface layer formation. SEM, AES and SIMS data are presented, which provide preliminary insight into the mechanisms operating during the cathode's lifetime. There is evidence that the activator elements in the nickel alloy base, Al and Mg, are able to diffuse to the surface of the oxide during activation and ageing and that these elements are enriched at the interface after accelerated life.

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

    SciTech Connect

    Pellett, G.L.; Guerra, R.; 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 SiH/sub 4/-CH/sub 4/-N/sub 2/, SiH/sub 4/-H/sub 2/-N/sub 2/, and H/sub 2/-N/sub 2/ 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. 24 references.

  9. 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.

  10. 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.

  11. Diffusive sampling of C7-C16 hydrocarbons in workplace air: uptake rates, wall effects and use in oil mist measurements.

    PubMed

    Simpson, A T; Wright, M D

    2008-06-01

    The measurement of semi-volatile hydrocarbons in workplace air is complicated by their readiness to condense to form aerosols or adsorb on to surfaces. The diffusive sampling and analysis by thermal desorption of alkanes up to hexadecane was investigated with the aim of quantifying vapour from petroleum distillate fractions and possibly differentiating particles from vapour in oil mist measurements of light mineral oil-based metalworking fluids. Diffusive uptake rates were measured on Perkin Elmer thermal desorption tube samplers packed with Tenax TA, and the potential for deposition within the tubes was examined. Hydrocarbon vapour was found to adsorb on the oxide layer that can develop on the sampler's internal walls. General measurements of mixed hydrocarbon vapours (i.e. petroleum distillate fractions) should not be unduly affected if concentrations are greater than approximately 5 mg m(-3) and the tubes are in good condition. For the purposes of differentiating light mineral oil mist and vapour from a total hydrocarbon measurement, it is unlikely that measuring the vapour separately could be used to calculate mist concentrations <3 mg m(-3) with sufficient accuracy. PMID:18403405

  12. Defect-Tolerant Diffusion Channels for Mg2+ Ions in Ribbon-Type Borates: Structural Insights into Potential Battery Cathodes MgVBO4 and Mgx Fe2–xB2O5

    DOE PAGESBeta

    Bo, Shou-Hang; Grey, Clare P.; Khalifah, Peter G.

    2015-06-10

    The reversible room temperature intercalation of Mg2+ ions is difficult to achieve, but may offer substantial advantages in the design of next-generation batteries if this electrochemical process can be successfully realized. Two types of quadruple ribbon-type transition metal borates (MgxFe2-xB2O5 and MgVBO4) with high theoretical capacities (186 mAh/g and 360 mAh/g) have been synthesized and structurally characterized through the combined Rietveld refinement of synchrotron and time-of-flight neutron diffraction data. Neither MgVBO4 nor MgxFe2-xB2O5 can be chemically oxidized at room temperature, though Mg can be dynamically removed from the latter phase at elevated temperatures (approximately 200 - 500 °C). Findingsmore » show that Mg diffusion in the MgxFe2-xB2O5 structure is more facile for the inner two octahedral sites than for the two outer octahedral sites in the ribbons, a result supported by both the refined site occupancies after Mg removal and by bond valence sum difference map calculations of diffusion paths in the pristine material. Mg diffusion in this pyroborate MgxFe2-xB2O5 framework is also found to be tolerant to the presence of Mg/Fe disorder since Mg ions can diffuse through interstitial channels which bypass Fe-containing sites.« less

  13. Defect-Tolerant Diffusion Channels for Mg2+ Ions in Ribbon-Type Borates: Structural Insights into Potential Battery Cathodes MgVBO4 and Mgx Fe2–xB2O5

    DOE PAGESBeta

    Bo, Shou-Hang; Grey, Clare P.; Khalifah, Peter G.

    2015-06-10

    The reversible room temperature intercalation of Mg2+ ions is difficult to achieve, but may offer substantial advantages in the design of next-generation batteries if this electrochemical process can be successfully realized. Two types of quadruple ribbon-type transition metal borates (MgxFe2-xB2O5 and MgVBO4) with high theoretical capacities (186 mAh/g and 360 mAh/g) have been synthesized and structurally characterized through the combined Rietveld refinement of synchrotron and time-of-flight neutron diffraction data. Neither MgVBO4 nor MgxFe2-xB2O5 can be chemically oxidized at room temperature, though Mg can be dynamically removed from the latter phase at elevated temperatures (approximately 200 - 500 °C). Findingsmore »show that Mg diffusion in the MgxFe2-xB2O5 structure is more facile for the inner two octahedral sites than for the two outer octahedral sites in the ribbons, a result supported by both the refined site occupancies after Mg removal and by bond valence sum difference map calculations of diffusion paths in the pristine material. Mg diffusion in this pyroborate MgxFe2-xB2O5 framework is also found to be tolerant to the presence of Mg/Fe disorder since Mg ions can diffuse through interstitial channels which bypass Fe-containing sites.« less

  14. Depression cathode structure for cathode ray tubes having surface smoothness and method for producing same

    SciTech Connect

    Rychlewski, T.V.

    1984-10-23

    Depression cathode structures for cathode ray tubes are produced by dispensing liquid cathode material into the depression of a metallic supporting substrate, removing excess cathode material by passing a doctor blade across the substrate surface and over the depression, and drying the cathode layer to a substantially immobile state. The cathode layer may optionally be further shaped prior to substantially complete drying thereof.

  15. Oxygen transport resistance at gas diffusion layer - Air channel interface with film flow of water in a proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Koz, Mustafa; Kandlikar, Satish G.

    2016-01-01

    Water present as films on the gas diffusion layer-air channel interface in a proton exchange membrane fuel cell (PEMFC) alters the oxygen transport resistance, which is expressed through Sherwood number (Sh). The effect of multiple films along the flow length on Sh is investigated through 3D and stationary simulations. The effects of air Péclet number, non-dimensional film width, length, and spacing are studied. Using the simulation results, non-dimensional correlations are developed for local Sh within a mean absolute percentage error of 9%. These correlations can be used for simulating PEMFC performance over temperature and relative humidity ranges of 20-80 °C and 0-100%, respectively. Sh on the film side can be up to 31% lower than that for a dry channel, while a film may reduce the interfacial width by up to 39%. The corresponding increase in transport resistance results in lowering the voltage by 5 and 8 mV respectively at a current density of 1.5 A cm-2. However, their combined effect leads to a voltage loss of 20 mV due to this additional mass transport resistance. It is therefore important to incorporate the additional resistance introduced by the films while modeling fuel cell performance.

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

    SciTech Connect

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

    2009-07-15

    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 is the computation of approximate diffusion flames by solving the flamelet equation for the progress variable only, reading all chemical terms such as reaction rates or mass fractions from an FPI-type look-up table built from autoigniting PSR calculations using complex chemistry. These flamelets are then used to generate a turbulent look-up table where mean values are estimated by integration over presumed probability density functions. Two different versions of ADF-PCM are presented, differing by the probability density functions used to describe the evolution of the stoichiometric scalar dissipation rate: a Dirac function centered on the mean value for the basic ADF-PCM formulation, and a lognormal function for the improved formulation referenced ADF-PCM{chi}. The turbulent look-up table is read in the CFD code in the same manner as for PCM models. The developed models have been implemented into the compressible RANS CFD code IFP-C3D and applied to the simulation of the Cabra et al. experiment of a lifted methane jet flame [R. Cabra, J. Chen, R. Dibble, A. Karpetis, R. Barlow, Combust. Flame 143 (2005) 491-506]. The ADF-PCM{chi} model accurately reproduces the experimental lift-off height, while it is underpredicted by the basic ADF-PCM model. The ADF-PCM{chi} model shows a very satisfactory reproduction of the experimental mean and fluctuating values of major species mass fractions and temperature, while ADF-PCM yields noticeable deviations. Finally, a comparison of the experimental conditional probability densities of the progress variable for a given mixture fraction with model predictions is performed, showing that ADF-PCM{chi} reproduces the experimentally observed bimodal shape and its dependency on the mixture fraction, whereas ADF-PCM cannot retrieve this shape. (author)

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

    SciTech Connect

    Aaron, D; Borole, Abhijeet P; Hussey , Daniel; Jacobson, David; Yiacoumi, Sotira; Tsouris, Costas

    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.

  18. 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 Ω cm2 and 0.03 Ω 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.

  19. Optimization of a Pt-free cathode suitable for practical applications of microbial fuel cells.

    PubMed

    Lefebvre, Olivier; Ooi, Wai K; Tang, Zhe; Abdullah-Al-Mamun, Md; Chua, Daniel H C; Ng, How Y

    2009-10-01

    Microbial fuel cells (MFCs) are considered as a promising way for the direct extraction of biochemical energy from biomass into electricity. However, scaling up the process for practical applications and mainly for wastewater treatment is an issue because there is a necessity to get rid of unsustainable platinum (Pt) catalyst. In this study, we developed a low-cost cathode for a MFC making use of sputter-deposited cobalt (Co) as the catalyst and different types of cathode architecture were tested in a single-chambered air-cathode MFC. By sputtering the catalyst on the air-side of the cathode, increased contact with ambient oxygen significantly resulted in higher electricity generation. This outcome was different from previous studies using conventionally-coated Pt cathodes, which was due to the different technology used. PMID:19464880

  20. Cathodic hydrodimerization of nitroolefins

    PubMed Central

    Weßling, 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 C–C 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 ß,ß-coupling with regard to the nitro group and forms preferentially two out of six possible diastereomers as major products. PMID:26199673

  1. 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.

  2. Virtual cathode microwave devices -- Basics

    SciTech Connect

    Thode, L.E.; Snell, C.M.

    1991-01-01

    Unlike a conventional microwave tube, a virtual-cathode device operates above the space-charge limit where the depth of the space-charge potential can cause electron reflection. The region associated with this electron reflection is referred to as a virtual cathode. Microwaves can be generated through oscillations in the position of the virtual cathode and through the bunching of electrons trapped in a potential well between the real and virtual cathodes. These two mechanisms are competitive. There are three basic classes of virtual cathode devices: (1) reflex triode; (2) reditron and side-shoot vircator; and (3) reflex diode or vircator. The reflex diode is the highest power virtual-cathode device. For the reflex diode the energy exchange between the beam and electromagnetic wave occurs in both the axial and radial directions. In some designs the oscillating-virtual-cathode frequency exceeds the reflexing-electron frequency exceeds the oscillating-virtual-cathode frequency. For the flex diode a periodic disruption in magnetic insulation can modulate the high- frequency microwave power. Overall, particle-in-cell simulation predictions and axial reflex diode experiments are in good agreement. Although frequency stability and phase locking of the reflex diode have been demonstrated, little progress has been made in efficiency enhancement. 58 refs., 11 figs.

  3. 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.

  4. Anomalies accompanying the cathodic charging of some bcc metals

    SciTech Connect

    Armacanqui, M.E.; Oriani, R.A.

    1985-05-01

    That the diffusion of hydrogen can be slowed down considerably in iron alloys, in Pd-Ni, and in iron, has been known for a long time, and this is believed to be caused by interactions between the diffusing solute and pre-existing structural and chemical conditions in the lattice. This ''trapping'' phenomenon may be regarded as a type of diffusion with chemical reaction, of which internal oxidation accompanying the diffusion of oxygen, and hydride formation accompanying the diffusion of hydrogen are well-known examples. In all these cases the further inward flux of the diffusing species is decreased by its consumption by the reaction. Another less familiar case is the recombination of atomically dissolved hydrogen at internal interfaces of microvoids and cracks in iron and steel. If the hydrogen is cathodically generated at high fugacity at the input surface, the internally produced molecular hydrogen can develop pressures large enough to expand the original microvoids by plastic deformation. The voids and the dislocation structure that result effectively prevent the penetration of hydrogen beyond a shallow layer below the input surface. The single-phase bcc alloy, Ti-30 Mo, can dissolve a large concentration of hydrogen without the formation of hydride; Gerberich, et al., have measured approximately 11,000 ppm introduced by cathodic charging without observing any evidence of hydrides. Therefore, normal Fickian diffusion of dissolved hydrogen is expected. This is not observed, however, and this note is a preliminary report and tentative explanation of the very large deviation from normal behavior of the diffusion of hydrogen cathodically charged into Ti-30 Mo.

  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. Numerical analysis of reaction-diffusion effects on species mixing rates in turbulent premixed methane-air combustion

    SciTech Connect

    Richardson, E.S.; Grout, R.W.; Chen, J.H.; Sankaran, R.

    2010-03-15

    The scalar mixing time scale, a key quantity in many turbulent combustion models, is investigated for reactive scalars in premixed combustion. Direct numerical simulations (DNS) of three-dimensional, turbulent Bunsen flames with reduced methane-air chemistry have been analyzed in the thin reaction zones regime. Previous conclusions from single step chemistry DNS studies are confirmed regarding the role of dilatation and turbulence-chemistry interactions on the progress variable dissipation rate. Compared to the progress variable, the mixing rates of intermediate species is found to be several times greater. The variation of species mixing rates are explained with reference to the structure of one-dimensional premixed laminar flames. According to this analysis, mixing rates are governed by the strong gradients which are imposed by flamelet structures at high Damkoehler numbers. This suggests a modeling approach to estimate the mixing rate of individual species which can be applied, for example, in transported probability density function simulations. Flame-turbulence interactions which modify the flamelet based representation are analyzed. (author)

  7. Miniature Reservoir Cathode: An Update

    NASA Technical Reports Server (NTRS)

    Vancil, Bernard K.; Wintucky, Edwin G.

    2002-01-01

    We report on recent work to produce a small low power, low cost reservoir cathode capable of long life (more than 100,000 hours) at high loading (> 5 A/sq cm). Our objective is a highly manufacturable, commercial device costing less than $30. Small highly loaded cathodes are needed, especially for millimeter wave tubes, where focusing becomes difficult when area convergence ratios are too high. We currently have 3 models ranging from .060-inch diameter to. 125-inch diameter. Reservoir type barium dispenser cathodes have a demonstrated capability for simultaneous high emission density and long life. Seven reservoir cathodes continue to operate on the cathode life test facility at NSWC, Crane, Indiana at 2 and 4 amps/sq cm. They have accumulated nearly 100,000 hours with practically no change in emission levels or knee temperature.

  8. Linear air-fuel sensor development

    SciTech Connect

    Garzon, F.; Miller, C.

    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.

  9. Coating of porous carbon for use in lithium air batteries

    SciTech Connect

    Amine, Khalil; Lu, Jun; Du, Peng; Lei, Yu; Elam, Jeffrey W

    2015-04-14

    A cathode includes a carbon material having a surface, the surface having a first thin layer of an inert material and a first catalyst overlaying the first thin layer, the first catalyst including metal or metal oxide nanoparticles, wherein the cathode is configured for use as the cathode of a lithium-air battery.

  10. 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.

  11. Carbon velvet field-emission cathode

    NASA Astrophysics Data System (ADS)

    Shiffler, D.; Ruebush, M.; Haworth, M.; Umstattd, R.; LaCour, M.; Golby, K.; Zagar, D.; Knowles, T.

    2002-12-01

    Explosive field emission cathodes comprise an important class of cathodes for high power microwave tubes, having the advantages of light weight as well as requiring no heater for electron emission. Generally, however, this class of cathodes suffers from large amounts of outgassing, nonuniform emission, and very high emittance. This article describes a new class of carbon velvet cathodes that have been coated with a cesium iodide (CsI) salt. We discuss two manifestations of the cathode. We review the lifetime and operation of the cathodes with two different pulse durations, as well as the outgassing from the cathodes during operation. Lifetimes in excess of 980 000 pulses have been obtained, with an outgassing rate of 3.5 atoms per electron. Finally, we discuss the uniformity and emittance of tufted carbon cathodes that have been coated with CsI salt. For comparison, we relate these results to those previously obtained from other cathodes in this class. The cathodes have an emittance of 2.5? mm rad, as compared to the theoretical value, based on computation, of 2.3? mm rad. These new cathodes differ greatly from cathodes such as polymer velvet and tufted carbon fiber cathodes in that no volatiles reside on the cathode and in that a unique coating technique allows the cathodes to function. This new class of cathodes offers a potential replacement for existing thermal cathodes, in that no heater is required for superior operation with low outgassing and long lifetime.

  12. 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.

  13. Metal foams application to enhance cooling of open cathode polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Sajid Hossain, Mohammad; Shabani, Bahman

    2015-11-01

    Conventional channel flow fields of open cathode Polymer Electrolyte Membrane Fuel Cells (PEMFCs) introduce some challenges linked to humidity, temperature, pressure and oxygen concentration gradients along the conventional flow fields that reduce the cell performance. According to previous experimental reports, with conventional air flow fields, hotspot formation due to water accumulation in Gas Diffusion Layer (GDL) is common. Unlike continuous long flow passages in conventional channels, metal foams provide randomly interrupted flow passages. Re-circulation of fluid, due to randomly distributed tortuous ligaments, enhances temperature and humidity uniformity in the fluid. Moreover, the higher electrical conductivity of metal foams compared to non-metal current collectors and their very low mass density compared to solid metal materials are expected to increase the electrical performance of the cell while significantly reducing its weight. This article reviews the existing cooling systems and identifies the important parameters on the basis of reported literature in the air cooling systems of PEMFCs. This is followed by investigating metal foams as a possible option to be used within the structure of such PEMFCs as an option that can potentially address cooling and flow distribution challenges associated with using conventional flow channels, especially in air-cooled PEMFCs.

  14. Characterization of the Capillary Properties of Gas Diffusion Media

    NASA Astrophysics Data System (ADS)

    Gostick, Jeffrey T.; Ioannidis, Marios A.; Fowler, Michael W.; Pritzker, Mark D.

    The present generation of membrane materials used in polymer electrolyte membrane fuel cells (PEMFCs) requires high humidity to maintain sufficient proton conductivity. Mass transport through the porous electrodes, however, is most effective in dry conditions since the presence of liquid water in the pores reduces effective oxygen diffusivity to the catalytic sites. Management of these competing requirements is further complicated by the production of water inside the cell as a by-product of the cathode reaction. Maximizing fuel cell power density therefore requires effective water management techniques to prevent excessive liquid water from accumulating in the porous electrode components. Liquid water distribution and flow in the cathode gas diffusion media (GDM) of an operating PEMFC is critically affected by capillary forces. Perhaps the most widely employed technique for improving water management is to impregnate the fibrous GDM with a polymer, such as poly-tetra-fluoro-ethylene (PTFE), to coat the carbon fibers and thereby render the GDM more hydrophobic. It is thus important to understand the relationship between wettability and capillary properties of native (i.e., untreated) or PTFE-treated GDMs on the one hand and the relationship between GDM capillary properties and fuel cell performance on the other hand. Until recently, however, few experimental techniques were available to measure the capillary properties of GDMs. This chapter discusses the present understanding of the capillary properties of GDM-water-air systems and provides a critical analysis of reported experimental techniques that have recently contributed to this understanding.

  15. Modeling of tip evolution of point cathode for numerical calculation of electric field in electron gun

    NASA Astrophysics Data System (ADS)

    Iiyoshi, Ryo

    2011-07-01

    The numerical modeling of the tip evolution of the point cathode has been studied to obtain a more realistic shape of the cathode and to improve the numerical calculation of the electric field in the electron gun. The modeling method is based on the numerical integration of the differential equation describing the matter transport phenomena caused by surface diffusion of atoms. The tip evolution is examined for different initial shapes and for different heating conditions, considering the influence of thermal evaporation. The method provides the characteristic profile of the cathode tip. The tip radius varies depending on the heating temperature and time. The field calculation of the Schottky emission gun shows that the modeled cathode shape gives a continuous field distribution in a wide area of the tip surface. The field distribution is compared to that on the interpolated cathode shape.

  16. 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:

  17. Virtual cathode emission of an annular cold cathode

    NASA Astrophysics Data System (ADS)

    Park, S.-d.; Kim, J.-h.; Han, J.; Yoon, M.; Park, S. Y.; Choi, D. W.; Shin, J. W.; So, J. H.

    2009-11-01

    Recent measurement of voltage V and current I of the electron gun of a relativistic klystron amplifier revealed that the resulting current-voltage relationship appeared to differ from the usual Child-Langmuir law (I∝V3/2) especially during the initial period of voltage increase. This paper attempts to explain this deviation by examining the emission mechanism using particle-in-cell simulation. The emission area in the cathode increased stepwise as the applied voltage increased and within each step the current and voltage followed the Child-Langmuir law. The electron emission began when the voltage reached a threshold, and the perveance increased with the emission area. Furthermore, an apparent virtual cathode was formed which was larger than the cathode tip. This occurs because, above a certain voltage, the emission from the edge and the side of the cathode surface dominates the emission from the front-end surface.

  18. Magnetized hollow cathode activated magnetron

    NASA Astrophysics Data System (ADS)

    Baránková, H.; Bardos, L.; Bardos, A.

    2015-10-01

    Planar magnetron in which the target is coupled with a magnetized hollow cathode is presented. Detailed principles of such arrangements are explained. The hollow cathode activated magnetron produces intense and stable plasmas in a wider interval of the working gas pressures as compared to the conventional magnetrons at the same power. The developed arrangements enhance sputtering from the magnetron target by the high-density hollow cathode plasma and increase the number of sputtered/evaporated species. Results of the test experiments of these arrangements on a commercial planar magnetron with the Ti target are presented and their capabilities discussed.

  19. Metal-air electrochemical cell

    SciTech Connect

    Sarbacher, R. I.; Fechter, H. R.

    1985-01-01

    An electrochemical cell for which fuel is prepared and introduced under artificial gravity forces. The active metal is deposited through the action of the field on an anode current collecting member, effecting good compaction and reduced cell internal impedance. A microprocessor provides control of the induced gravity, flow rates, temperature, and other variables-enabling the active metal to be controlled in its thickness as well as providing a predetermined separation from the cathode. Abrasion of the cathode and the possibility of shorting are avoided by the presence of outwardly directed radial forces. These forces are induced by rotation of the electrolyte, air cathode, anode collector and the active metal. The forces promote also the passage of moisture laden air through the air cathode elements. Reaction products produced within the cell volume are circulated to an outside container for separation and possible reuse.

  20. The back-diffusion effect of air on the discharge characteristics of atmospheric-pressure radio-frequency glow discharges using bare metal electrodes

    NASA Astrophysics Data System (ADS)

    Sun, Wen-Ting; Liang, Tian-Ran; Wang, Hua-Bo; Li, He-Ping; Bao, Cheng-Yu

    2007-05-01

    Radio-frequency (RF), atmospheric-pressure glow discharge (APGD) plasmas using bare metal electrodes have promising prospects in the fields of plasma-aided etching, deposition, surface treatment, disinfection, sterilization, etc. In this paper, the discharge characteristics, including the breakdown voltage and the discharge voltage for sustaining a stable and uniform α mode discharge of the RF APGD plasmas are presented. The experiments are conducted by placing the home-made planar-type plasma generator in ambient and in a vacuum chamber, respectively, with helium as the primary plasma-forming gas. When the discharge processes occur in ambient, particularly for the lower plasma-working gas flow rates, the experimental measurements show that it is the back-diffusion effect of air in atmosphere, instead of the flow rate of the gas, that results in the obvious decrease in the breakdown voltage with increasing plasma-working gas flow rate. Further studies on the discharge characteristics, e.g. the luminous structures, the concentrations and distributions of chemically active species in plasmas, with different plasma-working gases or gas mixtures need to be conducted in future work.

  1. 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.

  2. Efficient Spectral Diffusion at the Air/Water Interface Revealed by Femtosecond Time-Resolved Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy.

    PubMed

    Inoue, Ken-Ichi; Ishiyama, Tatsuya; Nihonyanagi, Satoshi; Yamaguchi, Shoichi; Morita, Akihiro; Tahara, Tahei

    2016-05-19

    Femtosecond vibrational dynamics at the air/water interface is investigated by time-resolved heterodyne-detected vibrational sum frequency generation (TR-HD-VSFG) spectroscopy and molecular dynamics (MD) simulation. The low- and high-frequency sides of the hydrogen-bonded (HB) OH stretch band at the interface are selectively excited with special attention to the bandwidth and energy of the pump pulses. Narrow bleach is observed immediately after excitation of the high-frequency side of the HB OH band at ∼3500 cm(-1), compared to the broad bleach observed with excitation of the low-frequency side at ∼3300 cm(-1). However, the time-resolved spectra observed with the two different excitations become very similar at 0.5 ps and almost indistinguishable by 1.0 ps. This reveals that efficient spectral diffusion occurs regardless of the difference of the pump frequency. The experimental observations are well-reproduced by complementary MD simulation. There is no experimental and theoretical evidence that supports extraordinary slow dynamics in the high-frequency side of the HB OH band, which was reported before. PMID:27120559

  3. Structure and Soot Properties of Nonbuoyant Ethylene/Air Laminar Jet Diffusion Flames. Appendix E; Repr. from AIAA Journal, v. 36 p 1346-1360

    NASA Technical Reports Server (NTRS)

    Urban, D. L.; Yuan, Z.-G.; Sunderland, P. B.; Linteris, G. T.; Voss, J. E.; Lin, K.-C.; Dai, Z.; Sun, K.; Faeth, G. M.; Ross, Howard D. (Technical Monitor)

    2001-01-01

    The structure and soot properties of round, soot-emitting, nonbuoyant, laminar jet diffusion flames are described, based on long-duration (175-230-s) experiments at microgravity carried out on orbit in the Space Shuttle Columbia. Experimental conditions included ethylene-fueled flames burning in still air at nominal pressures of 50 and 100 kPa and an ambient temperature of 300 K with luminous flame lengths of 49-64 mm Measurements included luminous flame shapes using color video imaging soot concentration (volume fraction) distributions using deconvoluted laser extinction imaging, soot temperature distributions using deconvoluted multiline emission imaging, gas temperature distributions at fuel-lean (plume) conditions using thermocouple probes, soot structure distributions using thermophoretic sampling and analysis by transmission electron microscopy, and flame radiation using a radiometer.The present flames were larger, and emitted soot more readily, than comparable flames observed during ground-based microgravity experiments due to closer approach to steady conditions resulting from the longer test times and the reduced gravitational disturbances of the space-based experiments.

  4. Improved Cathode Structure for a Direct Methanol Fuel Cell

    NASA Technical Reports Server (NTRS)

    Valdez, Thomas; Narayanan, Sekharipuram

    2005-01-01

    An improved cathode structure on a membrane/electrode assembly has been developed for a direct methanol fuel cell, in a continuing effort to realize practical power systems containing such fuel cells. This cathode structure is intended particularly to afford better cell performance at a low airflow rate. A membrane/electrode assembly of the type for which the improved cathode structure was developed (see Figure 1) is fabricated in a process that includes brush painting and spray coating of catalyst layers onto a polymer-electrolyte membrane and onto gas-diffusion backings that also act as current collectors. The aforementioned layers are then dried and hot-pressed together. When completed, the membrane/electrode assembly contains (1) an anode containing a fine metal black of Pt/Ru alloy, (2) a membrane made of Nafion 117 or equivalent (a perfluorosulfonic acid-based hydrophilic, proton-conducting ion-exchange polymer), (3) a cathode structure (in the present case, the improved cathode structure described below), and (4) the electrically conductive gas-diffusion backing layers, which are made of Toray 060(TradeMark)(or equivalent) carbon paper containing between 5 and 6 weight percent of poly(tetrafluoroethylene). The need for an improved cathode structure arises for the following reasons: In the design and operation of a fuel-cell power system, the airflow rate is a critical parameter that determines the overall efficiency, cell voltage, and power density. It is desirable to operate at a low airflow rate in order to obtain thermal and water balance and to minimize the size and mass of the system. The performances of membrane/electrode assemblies of prior design are limited at low airflow rates. Methanol crossover increases the required airflow rate. Hence, one way to reduce the required airflow rate is to reduce the effect of methanol crossover. Improvement of the cathode structure - in particular, addition of hydrophobic particles to the cathode - has been demonstrated to mitigate the effects of crossover and decrease the airflow required.

  5. A Model of Barium Coverage Evolution in Thermionic Cathodes and Its Relation to Noise

    NASA Astrophysics Data System (ADS)

    Jensen, K. L.; Lau, Y. Y.; Levush, B.

    1999-11-01

    An understanding of the noise mechanisms inherent in thermionic cathodes is necessary insofar as flicker noise from the cathode (attributed to the fluctuations of the barium sites (“islands”) on the cathode surface) can degrade amplifier performance. Cathode lifetime depends upon barium atom migration to and removal from the surface of the cathode (R. Forman, JAP47, 5272 (1976); R. T. Longo, et al., IEEE-IEDM Tech Dig 318 (1984), M. C. Green, ibid 925 (1987)). An analytical model of the diffusion and removal processes (evaporation and ion sputtering) is presented which depends on material and tube environment parameters as well as simple models for the determination of important terms. It is based on a hopping model of diffusion to determine Ba concentration within the cathode and at the surface. The effective work function, current density, and desorption rates depend nontrivially on the surface coverage ratio. The analytical model and its numerical implimentation will be described. In particular, we have found that, compared with ion sputtering, thermal desorption is the dominant contribution to emission noise in a mature cathode.

  6. Air breathing direct methanol fuel cell

    DOEpatents

    Ren, Xiaoming; Gottesfeld, Shimshon

    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.

  7. 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 4×10 -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 2.4×10 -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.

  8. Hollow Cathode With Multiple Radial Orifices

    NASA Technical Reports Server (NTRS)

    Brophy, John R.

    1992-01-01

    Improved hollow cathode serving as source of electrons has multiple radial orifices instead of single axial orifice. Distributes ion current more smoothly, over larger area. Prototype of high-current cathodes for ion engines in spacecraft. On Earth, cathodes used in large-diameter ion sources for industrial processing of materials. Radial orientation of orifices in new design causes current to be dispersed radially in vicinity of cathode. Advantageous where desireable to produce plasma more nearly uniform over wider region around cathode.

  9. Magnetic-cusp, cathodic-arc source

    DOEpatents

    Falabella, Steven

    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.

  10. Cold cathode vacuum discharge tube

    DOEpatents

    Boettcher, Gordon E.

    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.

  11. Impregnant composition in dispenser cathodes

    NASA Astrophysics Data System (ADS)

    Kan, H. K. A.; Seaver, R. R.

    1985-08-01

    The compositions of impregnants inside B-type dispenser cathodes containing barium calcium aluminates were examined by means of quantitative microprobe analysis. The impregnant inside the porous tungsten structure was supported with plastic in order to prevent damage when the cathode was sectioned. The impregnant compositions were found to be consistently deficient in CaO when compared to the nominal composition. Variations and reproducibility in composition are discussed.

  12. Operation of thoriated tungsten cathodes

    SciTech Connect

    Polk, J.E. )

    1993-01-20

    The operating temperature of thoriated tungsten cathodes used in electric thrusters depends on the surface coverage of thorium, which is determined by a balance of rate processes which supply and deplete the surface layer. The fundamental processes and rates are first reviewed in detail, then a phenomenological model based on these rate processes is described. The model indicates that the thermionic emission capabilities of thoriated tungsten cathodes decay rapidly because of thorium depletion at temperatures encountered in electric thrusters.

  13. Numerical simulation of cathode plasma dynamics in magnetically insulated vacuum transmission lines

    SciTech Connect

    Thoma, C.; Genoni, T. C.; Welch, D. R.; Rose, D. V.; Clark, R. E.; Miller, C. L.; Stygar, W. A.; Kiefer, M. L.

    2015-03-15

    A novel algorithm for the simulation of cathode plasmas in particle-in-cell codes is described and applied to investigate cathode plasma evolution in magnetically insulated transmission lines (MITLs). The MITL electron sheath is modeled by a fully kinetic electron species. Electron and ion macroparticles, both modeled as fluid species, form a dense plasma which is initially localized at the cathode surface. Energetic plasma electron particles can be converted to kinetic electrons to resupply the electron flux at the plasma edge (the “effective” cathode). Using this model, we compare results for the time evolution of the cathode plasma and MITL electron flow with a simplified (isothermal) diffusion model. Simulations in 1D show a slow diffusive expansion of the plasma from the cathode surface. But in multiple dimensions, the plasma can expand much more rapidly due to anomalous diffusion caused by an instability due to the strong coupling of a transverse magnetic mode in the electron sheath with the expanding resistive plasma layer.

  14. Cold cathode vacuum gauging system

    DOEpatents

    Denny, Edward C.

    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.

  15. Performance of Stainless Steel Mesh Cathode and PVDF-graphite Cathode in Microbial Fuel Cells

    NASA Astrophysics Data System (ADS)

    Huang, Liping; Tian, Ying; Li, Mingliang; He, Gaohong; Li, Zhikao

    2010-11-01

    Inexpensive and conductive materials termed as stainless steel mesh and polyvinylidene fluoride (PVDF)-graphite were currently used as the air cathode electrodes in MFCs for the investigation of power production. By loading PTFE (poly(tetrafluoroethylene)) on the surface of stainless steel mesh, electricity production reached 3 times as high as that of the naked stainless steel. A much high catalytic activity for oxygen reduction was exhibited by Pt based and PTFE loading stainless steel mesh cathode, with an electricity generation of 1144±44 mW/m2 (31±1 W/m3) and a Coulombic efficiency (CE) of 77±2%. When Pt was replaced by an inexpensive transition metal based catalyst (cobalt tetramethylphenylporphyrin, CoTMPP), power production and CE were 845±21 mW/m2 (23±1 W/m3) and 68±1%, respectively. Accordingly, power production from PVDF-graphite (hydrophobic) MFC and PVDF-graphite (hydrophile) MFC were 286±20 mW/m2(8±1 W/m3) and 158±13 mW/m2(4±0.4 W/m3), respectively using CoTMPP as catalyst. These results give us new insight into materials like stainless steel mesh and PVDF-graphite as low cost cathode for reducing the costs of MFCs for wastewater treatment applications.

  16. Three-dimensional Batteries using a Liquid Cathode

    NASA Astrophysics Data System (ADS)

    Malati, Peter Moneir

    Three-dimensional (3D) battery architectures have emerged as a new direction for powering microelectromechanical systems and other miniature autonomous devices. Although to date there are few examples of fully functioning 3D batteries, these power sources have the potential to achieve high power density and high energy density in a small footprint. Current batteries are composed of solid state systems. In our system, the cathode and electrolyte are combined to form a liquid cathode (or catholyte). This catholyte is based on the lithium-sulfur system, which has a high theoretical gravimetric capacity of 1672 mAh/g. This dissertation focuses on creating a rechargeable 3D lithium battery using a liquid cathode. The first part of the dissertation describes the liquid cathode, which is a lithium polysulfide. The second part of the covers the formation of the 3D lithium-containing anode and its integration into the battery. Two new routes to achieve 3D lithium anodes have been developed. One approach involves the electrodeposition of lithium onto a 3D nickel current-collector array. The second method involves the electrodeposition of lithium directly onto the current collector through a polymer mold. 3D batteries fabricated using Li2S6 liquid cathodes exhibit power densities of 1.1 mW/cm2 at current densities as high as 0.5 mA/cm 2. Also included in this dissertation is a unique lithium polysulfide gel cathode which has been synthesized using sol-gel processing. Using a non-hydrolytic sol-gel route, a polysulfide-gel cathode has been integrated into a 2D battery. Similar to the liquid cathode, the polysulfide-gel battery requires no separator, i.e., is does not short with the lithium anode. The combination of high surface area (519 m2/g) and pore diameter (2.0 nm) of the silica matrix allows lithium polysulfide to diffuse to and from the current collectors. Cyclic voltammetry shows the electrochemical activity within the same potential window as that of the liquid cathode. First generation polysulfide-gel batteries exhibit areal capacities of 1 mAh/cm2 at a current density of 10 muA/cm2.

  17. Characteristics of DC and pulsed hollow cathode glow discharge

    SciTech Connect

    Atta Khedr, M.; Hefny, A.A.; Hamdy, H.; Shahen, F.; Gamal, Y.

    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.

  18. Back bombardment for dispenser and lanthanum hexaboride cathodes

    NASA Astrophysics Data System (ADS)

    Bakr, Mahmoud; Kinjo, R.; Choi, Y. W.; Omer, M.; Yoshida, K.; Ueda, S.; Takasaki, M.; Ishida, K.; Kimura, N.; Sonobe, T.; Kii, T.; Masuda, K.; Ohgaki, H.; Zen, H.

    2011-06-01

    The back bombardment (BB) effect limits wide usage of thermionic rf guns. The BB effect induces not only ramping-up of a cathode’s temperature and beam current, but also degradation of cavity voltage and beam energy during a macropulse. This paper presents a comparison of the BB effect for the case of dispenser tungsten-base (DC) and lanthanum hexaboride (LaB6) thermionic rf gun cathodes. For each, particle simulation codes are used to simulate the BB effect and electron beam dynamics in a thermionic rf gun cathode. A semiempirical equation is also used to investigate the stopping range and deposited heat power of BB electrons in the cathode material. A numerical simulation method is used to calculate the change of the cathode temperature and current density during a single macropulse. This is done by solving two differential equations for the rf gun cavity equivalent circuit and one-dimensional thermal diffusion equation. High electron emission and small beam size are required for generation of a high-brightness electron beam, and so in this work the emission properties of the cathode are taken into account. Simulations of the BB effect show that, for a pulse of 6μs duration, the DC cathode experiences a large change in the temperature compared with LaB6, and a change in current density 6 times higher. Validation of the simulation results is performed using experimental data for beam current beyond the gun exit. The experimental data is well reproduced using the simulation method.

  19. The CH4, CO2 and H2O flux at the lake-air interface based on the gradient diffusion method

    NASA Astrophysics Data System (ADS)

    Xiao, W.; Lee, X.; Liu, S.; Hu, Z.; Wang, W.; Lee, H.; Xiao, Q.

    2012-12-01

    In studies of greenhouse gases cycle and lake-atmosphere interactions, it is important to identify the fluxes of CH4, CO2 and H2O at the lake-air interface. In this study, the CH4, CO2 and H2O (latent heat) fluxes at the lake-air interface were measured simultaneously based on the gradient diffusion (GD) method employing the Cavity Ring-Down Spectroscopy (CRDS) technology with high precision and temporal resolution. The experiment was conducted over a large freshwater lake (Lake Taihu) in eastern China. Zero-gradient test supported the accuracy of the measurement. The CO2 and latent heat fluxes measured by GD method were compared with the measurements of eddy covariance (EC) system, and CH4 flux of GD was compared with the water equilibrium (WE) method. The latent heat fluxes of GD and EC agreed well with index of agreement of 0.88, RMSE of 32.1 W m-2, the median value of GD and ED were 62.6 and 60.6 W m-2 respectively. The CO2 flux measured by GD was positive according to diurnal composite analysis, while EC measurement showed negative signals in the daytime. The median values of the GD and EC measurement during the observation period were 0.012 and -0.0025 mg m-2 s-1 respectively. The CH4 flux of GD was higher than WE measurement, the median value of midday GD and WE measurement were 0.13 and 0.055 μg m-2 s-1 respectively. The difference of GD and EC in the CO2 flux measurement may contribute to the self-heating and fault signals of CO2 and H2O analyzer EC system, and the underestimation of CH4 flux of WE may due to the ignorance of ebullition. Taihu Ecosystem Research and Field Observation Station of the Chinese Academy of Sciences (31o24‧N, 120o13‧E), located in Meiliangwan (MLW) Bay, in the north part of Lake Taihu. Step changes in the CO2, CH4 and H2O mixing ratios in response to valve switching

  20. 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.

  1. Electropositive surface layer MPD thruster cathodes

    SciTech Connect

    Chamberlain, F.R.; Kelly, A.J.; Jahn, R.G.

    1989-01-01

    Lithium and barium oxide have been used to generate electropositive surface layers on tungsten cathodes in low power steady state MPD thruster experiments. The electropositive surface layer decreases the cathode work function, resulting in substantial reductions in the steady state cathode operating temperature and erosion rate. Cathode temperature is reduced by 300 degrees with a lithium surface layer and by 800 degrees with a barium oxide surface layer at a 500 ampere thruster current level. These temperature reductions substantially reduce the calculated steady state evaporative erosion rate of the cathode by factors of 20 and 10,000 respectively. Cold cathode startup erosion is also reduced dramatically. The surface melting and arc cratering that is characteristic of pure tungsten cathodes does not occur with an electropositive surface layer cathode. In addition to reducing cathode erosion, the use of these materials increases thruster efficiency. 12 refs.

  2. Application of diffuse discharges of atmospheric pressure formed by runaway electrons for modification of copper and stainless steel surface

    SciTech Connect

    Tarasenko, V. F. Shulepov, M. A.; Erofeev, M. V.

    2015-12-15

    The results of studies devoted to the influence of a runaway electron pre-ionized diffuse discharge (REP DD) formed in air and nitrogen at atmospheric pressure on the surface of copper and stainless steel are presented. Nanosecond high-voltage pulses were used to obtain REP DD in different gases at high pressures in a chamber with a flat anode and a cathode possessing a small radius of curvature. This mode of discharge was implemented owing to the generation of runaway electrons and X-rays. The conditions under which the surface of copper and stainless steel was cleaned from carbon and oxidized are described.

  3. Application of diffuse discharges of atmospheric pressure formed by runaway electrons for modification of copper and stainless steel surface

    NASA Astrophysics Data System (ADS)

    Tarasenko, V. F.; Shulepov, M. A.; Erofeev, M. V.

    2015-12-01

    The results of studies devoted to the influence of a runaway electron pre-ionized diffuse discharge (REP DD) formed in air and nitrogen at atmospheric pressure on the surface of copper and stainless steel are presented. Nanosecond high-voltage pulses were used to obtain REP DD in different gases at high pressures in a chamber with a flat anode and a cathode possessing a small radius of curvature. This mode of discharge was implemented owing to the generation of runaway electrons and X-rays. The conditions under which the surface of copper and stainless steel was cleaned from carbon and oxidized are described.

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

    SciTech Connect

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

    2012-09-15

    It is well known that LATP (Li1+x+y AlxTi2−x SiyP3−yO12) glass is a good lithium ion conductor. However, the interaction between LATP glass and H+ ions (including its diffusion and surface adsorption) needs to be well understood before the long-term application of LATP glass in an aqueous electrolyte based Li-air batteries where H+ always present. In this work, we investigate the H+ ion diffusion properties in LATP glass and their surface interactions using both experimental and modeling approaches. Our analysis indicates 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 in the glass. Furthermore, the density functional theory calculations indicate that the H+ ion diffusion energy barrier (3.21 eV) is much higher than that of Li+ ion (0.79 eV) and Na+ ion (0.79 eV) in NASICON type LiTi2(PO4)3 material. As a result, the H+ ion conductivity in LATP glass is negligible at room temperature. However, significant surface corrosion was found after the LATP glass was soaked in strong alkaline electrolyte for extended time. Therefore, appropriate electrolytes have to be developed to prevent the corrosion of LATP glass before its practical application for Li-air batteries using aqueous electrolyte.

  5. Fundamentals of cathodic protection interference

    SciTech Connect

    Lichtenstein, J.

    1999-09-01

    The primary cause of cathodic interference was initially related to operation of direct current (DC) traction systems, such as rail systems, mining carts, and the like. Nowadays the increased use of impressed current cathodic protection (ICCP) systems for pipelines and other underground and submerged metallic structures has become another major cause of cathodic interference. With the requirements of cathodic protection (CP) installations on some underground storage tanks (USTs) and the renewed interest by municipalities installing DC traction light rail systems, a higher level of cathodic interference can be expected. Although interference may be caused by stray earth currents from many different sources, this discussion only concerns interference caused by earth currents produced by the operation of ICCP systems. All forms of interference correction require considerable field work and testing by knowledgeable and experienced personnel. It can be time consuming and therefore very expensive. Much of this expense can be saved if careful planning is done in the design stage before a CP installation is made.

  6. Insights into PEMFC Performance Degradation from HCl in Air

    SciTech Connect

    O Baturina; A Epshteyn; P Northrup; K Swider-Lyons

    2011-12-31

    The performance degradation of a proton exchange membrane fuel cell (PEMFC) is studied in the presence of HCl in the air stream. The cathode employing carbon-supported platinum nanoparticles (Pt/C) was exposed to 4 ppm HCl in air while the cell voltage was held at 0.6 V. The HCl poisoning results in generation of chloride and chloroplatinate ions on the surface of Pt/C catalyst as determined by a combination of electrochemical tests and ex-situ chlorine K-edge X-Ray absorption near-edge structure (XANES) spectroscopy. The chloride ions inhibit the oxygen reduction reaction (ORR) and likely affect the wetting properties of diffusion media/catalyst layer, while the chloroplatinate ions are responsible for enhanced platinum particle growth most likely due to platinum dissolution-redeposition. The chloride ions can cause corrosion of the Pt nanoparticles in the presence of aqueous HCl in air even if no potential is applied. Although the majority of chloride ions are desorbed from the Pt surface by hydrogen treatment of the cathode, they partially remain in the system and re-adsorb on platinum at cell voltages of 0.5-0.9 V. Chloride ions are removed from the system and fuel cell performance at 0.5-0.7 V is restored by multiple exposures to low potentials.

  7. Investigation of a Mercury-Argon Hot Cathode Discharge

    NASA Astrophysics Data System (ADS)

    Wamsley, Robert Charles

    Classical absorption and laser induced fluorescence (LIF) experiments are used to investigate processes in the cathode region of a Hg-Ar hot cathode discharge. The absorption and LIF measurements are used to test the qualitative understanding and develop a quantitative model of a hot cathode discharge. The main contribution of this thesis is a model of the negative glow region that demonstrates the importance of Penning ionization to the ionization balance in the negative glow. We modeled the excited argon balance equation using a Monte Carlo simulation. In this simulation we used the trapped radiative decay rate of the resonance levels and the Penning ionization rate as the dominant loss terms in the balance equation. The simulated data is compared to and found to agree with absolute excited argon densities measured in a classical absorption experiment. We found the primary production rate per unit volume of excited Ar atoms in the simulation is sharply peaked near the cathode hot spot. We used the ion production rate from this simulation and a Green's function solution to the ambipolar diffusion equation to calculate the contribution of Penning ionization to the total ion density. We compared the results of this calculation to our experimental values of the Hg ^+ densities in the negative glow. We found that Penning ionization is an important and possibly the dominant ionization process in the negative glow.

  8. Cathode and anode plasmas in short-pulse explosive field emission cathodes

    NASA Astrophysics Data System (ADS)

    Shiffler, D.; Ruebush, M.; Zagar, D.; LaCour, M.; Sena, M.; Golby, K.; Haworth, M.; Umstattd, R.

    2002-05-01

    Explosive field emission cathodes have been a subject of research for a number of years. These cathodes offer high current densities and total current without requiring a heater for the production of electrons. Generally these cathodes consist of some structure with a series of tips or metal-dielectric regions in which a large electric field enhancement can occur. A cathode plasma is then formed from these discharge points that then supplies the electrons necessary for space charge limited emission. This article reports on a series of optical measurements in which the cathode and anode plasmas of explosive field emission cathodes are observed. Three types of cathodes are investigated. These types are a polymer velvet cathode, a metal-dielectric cathode, and a tufted carbon fiber cathode in which the fibers have been coated with a cesium iodide salt. Cesium iodide coated carbon fiber cathodes have shown a great deal of promise for various field emitter applications. From these high speed photos, the evolution of the plasmas on both cathode and anode can be qualitatively ascertained. Experimentally we find that not only does cathode plasma behavior depend on the type of cathode, but the anode plasma behavior does also. Further, we find that the best performing cathode shows the most rapid plasma formation on both anode and cathode, yet without a rapid plasma expansion across the anode-cathode gap.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Geometrical Aspects of a Hollow-cathode Magnetron (HCM)

    SciTech Connect

    Cohen, Samuel, A.; Wang, Zhehui

    1998-11-01

    A hollow-cathode magnetron (HCM), built by surrounding a planar sputtering-magnetron cathode with a hollow-cathode structure (HCS), is operable at substantially lower pressures than its planar-magnetron counterpart. We have studied the dependence of magnetron operational parameters on the inner diameter D and length L of a cylindrical HCS. Only when L is greater than L sub zero, a critical length, is the HCM operable in the new low-pressure regime. The critical length varies with HCS inner diameter D. Explanations of the lower operational pressure regime, critical length, and plasma shape are proposed and compared with a one-dimension diffusion model for energetic or primary electron transport. At pressures above 1 mTorr, an electron-impact ionization model with Bohm diffusion at a temperature equivalent to one-half the primary electron energy and with an ambipolar constraint can explain the ion-electron pair creation required to sustain the discharge. The critical length L sub zero is determined by the magnetization length of the primary electrons.

  14. Robust, Ultra-Tough Flexible Cathodes for High-Energy Li-S Batteries.

    PubMed

    Chung, Sheng-Heng; Chang, Chi-Hao; Manthiram, Arumugam

    2016-02-01

    Sulfur cathodes have become appealing for rechargeable batteries because of their high theoretical capacity (1675 mA h g(-1) ). However, the conventional cathode configuration borrowed from lithium-ion batteries may not allow the pure sulfur cathode to put its unique materials chemistry to good use. The solid(sulfur) -liquid(polysulfides) -solid(sulfides) phase transitions generate polysulfide intermediates that are soluble in the commonly used organic solvents in Li-S cells. The resulting severe polysulfide diffusion and the irreversible active-material loss have been hampering the development of Li-S batteries for years. The present study presents a robust, ultra-tough, flexible cathode with the active-material fillings encapsulated between two buckypapers (B), designated as buckypaper/sulfur/buckypaper (B/S/B) cathodes, that suppresses the irreversible polysulfide diffusion to the anode and offers excellent electrochemical reversibility with a low capacity fade rate of 0.06% per cycle after 400 cycles. Engineering enhancements demonstrate that the B/S/B cathodes represent a facile approach for the development of high-performance sulfur electrodes with a high areal capacity of 5.1 mA h cm(-2) , which increases further to approach 7 mA h cm(-2) on coupling with carbon-coated separators. PMID:26715383

  15. Characterization and optimization of cathodic conditions for H2O2 synthesis in microbial electrochemical cells.

    PubMed

    Sim, Junyoung; An, Junyeong; Elbeshbishy, Elsayed; Ryu, Hodon; Lee, Hyung-Sool

    2015-11-01

    Cathode potential and O2 supply methods were investigated to improve H2O2 synthesis in an electrochemical cell, and optimal cathode conditions were applied for microbial electrochemical cells (MECs). Using aqueous O2 for the cathode significantly improved current density, but H2O2 conversion efficiency was negligible at 0.3-12%. Current density decreased for passive O2 diffusion to the cathode, but H2O2 conversion efficiency increased by 65%. An MEC equipped with a gas diffusion cathode was operated with acetate medium and domestic wastewater, which presented relatively high H2O2 conversion efficiency from 36% to 47%, although cathode overpotential was fluctuated. Due to different current densities, the maximum H2O2 production rate was 141 mg H2O2/L-h in the MEC fed with acetate medium, but it became low at 6 mg H2O2/L-h in the MEC fed with the wastewater. Our study clearly indicates that improving anodic current density and mitigating membrane fouling would be key parameters for large-scale H2O2-MECs. PMID:26141667

  16. Structural control and impedance analysis of cathode for direct methanol fuel cell

    NASA Astrophysics Data System (ADS)

    Furukawa, Kazuyoshi; Okajima, Keiichi; Sudoh, Masao

    The effect of the Nafion content and loading method in the catalyst layer of the cathode for a Direct Methanol Fuel Cell (DMFC) was investigated. The impedance of the full cell and cathode were determined by ac impedance spectroscopy. The Nafion content of 1.0 mg cm -2 improved the current density at a cell voltage of 0.4 V up to 258 mA cm -2 versus 128 mA cm -2 at a content of 0.5 mg cm -2. The increase in the Nafion content decreased the diameter of the arc at low frequencies. For the electrode prepared by the spray method (SME), the cell performance and cathode performance using a dynamic hydrogen electrode (DHE) as the reference electrode was higher than those of the electrode prepared by the paste method (PME) by decreasing the cathode potential. From the ac impedance measurement of the cathode, the diffusion resistance of the SME electrode had the lowest interfacial resistance of the cathode electrodes. The higher cell performance was mostly dependent on the diffusion resistance. The SME with a porous structure and a catalyst layer thickness of 50 μm were characterized by SEM and BET adsorption measurements.

  17. Cathodic protection installation for underground storage tanks

    SciTech Connect

    Koszewski, L.

    1995-12-31

    The 1998 deadline is fast approaching for upgrading Underground Storage Tanks (USTs) with cathodic protection. With so many tanks requiring upgrades over the next few years, tank owners and operators will likely find a shrinking pool of quality cathodic protection installation contractors to perform the necessary upgrading. The proper installation of cathodic protection components is critical to long term effective operation of the cathodic protection system.

  18. Cathodic protection maintenance for aboveground storage tanks

    SciTech Connect

    Koszewski, L.

    1995-12-31

    Cathodic protection systems are utilized to mitigate corrosion on the external bottom surfaces of aboveground storage tanks (ASTs). Cathodic protection systems should be part of a preventative maintenance program to minimize in-service failures. A good maintenance program will permit determination of continuous adequate cathodic protection of ASTs, through sustained operation and also provide the opportunity to detect cathodic protection system malfunctions, through periodic observations and testing.

  19. Pore geometry of dispenser cathode surface vs. emission characteristics, and Ba recovery characteristics after ion bombardment

    NASA Astrophysics Data System (ADS)

    Higuchi, Toshiharu; Nakamura, Osamu; Matsumoto, Sadao; Uda, Eiichirou

    1999-05-01

    A study was conducted to investigate the emission characteristics and barium recovery characteristics after ion bombardment of two types of Ir-coated dispenser cathodes having a pore density on the surface layer of the cathodes of 4×10 4 and 1.3×10 4 pores/mm 2. Cathode current was measured under pulse operation in a range of 0.1-9% duty cycle. When the duty cycle dependence of emissions was examined, the current densities of both cathodes were the same in the case of 0.1% duty cycle, delivering about 12 A/cm 2. The work functions also showed the same value. However, evaluations of 4% duty cycle and 9% duty cycle found that the cathode with a higher pore density showed emission characteristics higher by 50% and 70%. Regarding the recovery time of barium and oxygen after argon ion bombardment with Auger electron spectroscopy (AES), the low-pore-density cathode required as long as 3 min for recovery, whereas the high-pore-density cathode recovered in 1.1 min. From the above experiments, it was clarified that emission characteristics under high duty and barium recovery characteristics after ion bombardment can be improved by increasing the pore density of the surface layer. The basic mechanisms leading to these results were also theoretically considered by solving surface diffusion equations.

  20. Heat and Mass Transfer Modeling of Dry Gases in the Cathode of PEM Fuel Cells

    NASA Astrophysics Data System (ADS)

    Kermani, M. J.; Stockie, J. M.

    2004-02-01

    The transport of three gas species, O2, H2O and N2, through the cathode of a proton exchange membrane (PEM) fuel cell is studied numerically. The diffusion of the individual species is modeled via the Maxwell-Stefan equations, coupled with appropriate conservation equations. Two mechanisms are assumed for the internal energy sources in the system: a volumetric heat source due to the electrical current flowing through the cathode; and heat flow towards the cathode at the cathode-membrane interface due to the exothermic chemical reaction at this interface, in which water is generated. The governing equations of the unsteady fluid motion are written in fully conservative form, and consist of the following: (i) three equations for the mass conservation of the species; (ii) the momentum equation for the mixture, which is approximated using Darcy's Law for flow in porous media; and (iii) an energy equation, written in a form that has enthalpy as the dependent variable.

  1. 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.

  2. Ferroelectric Emission Cathodes for Low-Power Electric Propulsion

    NASA Technical Reports Server (NTRS)

    Kovaleski, Scott D.; Burke, Tom (Technical Monitor)

    2002-01-01

    Low- or no-flow electron emitters are required for low-power electric thrusters, spacecraft plasma contactors, and electrodynamic tether systems to reduce or eliminate the need for propellant/expellant. Expellant-less neutralizers can improve the viability of very low-power colloid thrusters, field emission electric propulsion devices, ion engines, Hall thrusters, and gridded vacuum arc thrusters. The NASA Glenn Research Center (GRC) is evaluating ferroelectric emission (FEE) cathodes as zero expellant flow rate cathode sources for the applications listed above. At GRC, low voltage (100s to approx. 1500 V) operation of FEE cathodes is examined. Initial experiments, with unipolar, bipolar, and RF burst applied voltage, have produced current pulses 250 to 1000 ns in duration with peak currents of up to 2 A at voltages at or below 1500 V. In particular, FEE cathodes driven by RF burst voltages from 1400 to 2000 V peak to peak, at burst frequencies from 70 to 400 kHz, emitted average current densities from 0.1 to 0.7 A/sq cm. Pulse repeatability as a function of input voltage has been initially established. Reliable emission has been achieved in air background at pressures as high as 10(exp -6) Torr.

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

    SciTech Connect

    Borole, Abhijeet P; Hamilton, Choo Yieng; Aaron, D; Tsouris, Costas

    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.

  4. Properties and manufacture of top-layer scandate cathodes

    NASA Astrophysics Data System (ADS)

    Hasker, J.; Van Esdonk, J.; Crombeen, J. E.

    1986-08-01

    The life and/or the staying power against ion bombardment of scandate cathodes can be improved by using a top layer of W + Sc 2O 3 or W + W/ScH 2 on a tungsten matrix. The latter is impregnated with the usual 4-1-1 impregnant. Even at high voltage pulses the current densities are so high that the deviation from space charge limitation is small. The manufacture is discussed and the cathode life at the operating temperature of 1220 K is shown to be very long. Moreover, the relationship between processing parameters and emission recovery after ion bombardment is examined with the aid of combined sputter- and scanning-Auger measurements. It is shown that thin-layer coverage of tungsten by scandia is important to the high emission. This coverage is related to the impregnation process. After extended sputtering it cannot be completely recovered by reactivation. Consequently, the top layer cathodes cannot withstand sufficiently the usual processing and operation of television display tubes. On the other hand, they can improve the life and performance of electron devices with good vacuum and/or relatively low accelerating potentials. Moreover, activated top-layer scandate cathodes are relatively insensitive to exposure to (moist) air.

  5. 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.

  6. Remote control for anode-cathode adjustment

    DOEpatents

    Roose, Lars D.

    1991-01-01

    An apparatus for remotely adjusting the anode-cathode gap in a pulse power machine has an electric motor located within a hollow cathode inside the vacuum chamber of the pulse power machine. Input information for controlling the motor for adjusting the anode-cathode gap is fed into the apparatus using optical waveguides. The motor, controlled by the input information, drives a worm gear that moves a cathode tip. When the motor drives in one rotational direction, the cathode is moved toward the anode and the size of the anode-cathode gap is diminished. When the motor drives in the other direction, the cathode is moved away from the anode and the size of the anode-cathode gap is increased. The motor is powered by batteries housed in the hollow cathode. The batteries may be rechargeable, and they may be recharged by a photovoltaic cell in combination with an optical waveguide that receives recharging energy from outside the hollow cathode. Alternatively, the anode-cathode gap can be remotely adjusted by a manually-turned handle connected to mechanical linkage which is connected to a jack assembly. The jack assembly converts rotational motion of the handle and mechanical linkage to linear motion of the cathode moving toward or away from the anode.

  7. Air Pollution.

    ERIC Educational Resources Information Center

    Scorer, Richard S.

    The purpose of this book is to describe the basic mechanisms whereby pollution is transported and diffused in the atmosphere. It is designed to give practitioners an understanding of basic mechanics and physics so they may have a correct basis on which to formulate their decisions related to practical air pollution control problems. Since many…

  8. Air Pollution.

    ERIC Educational Resources Information Center

    Scorer, Richard S.

    The purpose of this book is to describe the basic mechanisms whereby pollution is transported and diffused in the atmosphere. It is designed to give practitioners an understanding of basic mechanics and physics so they may have a correct basis on which to formulate their decisions related to practical air pollution control problems. Since many

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

    SciTech Connect

    Green, M.C. . 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.

  10. Offshore platform cathodic protection retrofits

    SciTech Connect

    Turnipseed, S.P.

    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.

  11. A metal-dielectric cathode

    NASA Astrophysics Data System (ADS)

    Fan, Yu-Wei; Zhong, Hui-Huang; Li, Zhi-Qiang; Yang, Han-Wu; Shu, Ting; Zhou, Heng; Yuan, Cheng-Wei; Zhang, Jun; Luo, Ling

    2008-07-01

    In order to improve the pulse repetition rate and the maintenance-free lifetime of an improved magnetically insulated transmission line oscillator (MILO) previously developed in our laboratory, a metal-dielectric cathode is investigated experimentally. It consists of three components: a stainless steel base, bronze foils, and double-sided printed boards. The experimental results show that the shot-to-shot reproducibility of the diode voltage and current is very good and the performances of the improved MILO are steady. In addition, no observable degradation could be detected in the emissive characteristic of the metal-dielectric cathode after 350 shots. The experimental results prove that the metal-dielectric cathode is a promising cathode for repetitively pulsed MILO operation. However, the leading edge of the radiated microwave pulse is gradually delayed during the repetition rate. A likely reason is that high pressure results in gas ionization in the beam-microwave interaction region, and plasma formation delays the time that the improved MILO achieves nonlinear steady state.

  12. Cathode for molten salt batteries

    DOEpatents

    Mamantov, Gleb; Marassi, Roberto

    1977-01-01

    A molten salt electrochemical system for battery applications comprises tetravalent sulfur as the active cathode material with a molten chloroaluminate solvent comprising a mixture of AlCl.sub.3 and MCl having a molar ratio of AlCl.sub.3 /MCl from greater than 50.0/50.0 to 80/20.

  13. High-emission cold cathode

    DOEpatents

    Mancebo, L.

    1974-01-29

    A field-emission cathode having a multitude of field emission points for emitting a copious stream of electrons when subjected to a high field is described. The cathode is constructed by compressing a multitude of tungsten strips alternately arranged with molybdenum strips and copper ribbons or compressing alternately arranged copper plated tungsten and molybdenum strips, heating the arrangement to braze the tungsten and molybdenum strips together with the copper, machining and grinding the exposed strip edges of one side of the brazed arrangement to obtain a precisely planar surface, etching a portion of the molybdenum and copper to leave the edges of the tungsten strips protruding for electron emission, and subjecting the protruding edges of the tungsten strips to a high electric field to degas and roughen the surface to pnovide a large number of emitting points. The resulting structure is particularly useful as a cathode in a transversely excited gaseous laser where the cathode is mounted in a vacuum chamber for emitting electrons under the influence of a high electric field between the cathode and an extractor grid. The electrons pass through the extractor grid, a thin window in the wall of the laser chamber and into the laser chamber which is filled with a gaseous mixture of helium, nitrogen, and carbon dioxide. A second grid is mounted on the gaseous side of the window. The electrons pass into the laser chamber under the influence of a second electric field between the second grid and an anode in the laser chamber to raise selected gas atoms of the gaseous mixture to appropriately excited states so that a subsequent coherent light beam passing through the mixture transversely to the electron stream through windows in opposite ends of the laser chamber stimulates the excited atoms to amplify the beam. (Official Gazette)

  14. Testing a GaAs cathode in SRF gun

    SciTech Connect

    Wang, E.; Kewisch, J.; Ben-Zvi, I.; Burrill, A.; Rao, T.; Wu, Q.; Holmes, D.

    2011-03-28

    RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12} Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high accelerating gradient of the RF guns, potentially offering a long lived cathode with very low emittance. Testing this concept requires preparation of the cathode, transportation to the SRF gun and evaluation of the performance of the cathode and the gun at cryogenic temperatures. In our work at BNL, we successfully activated the bulk GaAs in the preparation chamber. The highest quantum efficient was 10% at 532 nm that fell to 0.5% after 100 hours. We explored three different ways to activate the GaAs. We verified that the GaAs photocathode remains stable for 30 hours in a 10{sup -11} Torr vacuum. Passing the photocathode through the low 10{sup -9} Torr transfer section in several seconds caused the QE to drop to 0.8%. The photocathode with 0.8% QE can be tested for the SRF gun. The gun and beam pipe were prepared and assembled. After baking at 200 C baking, the vacuum of the gun and beam pipe can sustain a low 10{sup -11} Torr at room temperature. The final test to extract electrons from the gun is ongoing. In this paper, we discuss our progress with this SRF gun and the results of the photocathode in preparation chamber and in magnet transfer line.

  15. Air breathing direct methanol fuel cell

    DOEpatents

    Ren, Xiaoming

    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.

  16. Cathode for aluminum producing electrolytic cell

    DOEpatents

    Brown, Craig W.

    2004-04-13

    A method of producing aluminum in an electrolytic cell comprising the steps of providing an anode in a cell, preferably a non-reactive anode, and also providing a cathode in the cell, the cathode comprised of a base material having low electrical conductivity reactive with molten aluminum to provide a highly electrically conductive layer on the base material. Electric current is passed from the anode to the cathode and alumina is reduced and aluminum is deposited at the cathode. The cathode base material is selected from boron carbide, and zirconium oxide.

  17. 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.

  18. 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.

  19. Surface structure of thermionic-emission cathodes

    NASA Astrophysics Data System (ADS)

    Norman, D.; Tuck, R. A.; Skinner, H. B.; Wadsworth, P. J.; Gardiner, T. M.; Owen, I. W.; Richardson, C. H.; Thornton, G.

    1987-02-01

    We have used surface extended x-ray absorption fine structure (SEXAFS) to study the local geometry around barium atoms on thermionic cathodes. On the surfaces of tungsten and tungsten-osmium alloy dispenser cathodes Ba is bonded to oxygen with a well-defined short-range order. The Ba-O distance is similar (2.62+/-0.04 Å) for the two cathodes, with oxygen atoms occupying hollow sites of the substrate. However, the alloy cathode has Ba bonded to two oxygen near neighbors (compared to one for the tungsten cathode), which will enhance the surface dipole, thus explaining the observed lower work function.

  20. 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.

  1. Study of Discharging Characteristics of Hollow Cathode Surge Protective Gap

    NASA Astrophysics Data System (ADS)

    Yao, Xueling; Chen, Jingliang; Xu, Xiaowei; Liu, Yong; Zhao, Yong

    2010-02-01

    A hollow cathode surge protective gap (HCSPG) was designed, and the discharge characteristics was investigated in an air and nitrogen gas environment. For both the gap spacing D and the hole diameter varphi of HCSPG of 3 mm, the voltage protective value Up of HCSPG is about 3.5 kV and its converting time tc exceeds 100 ns at an air pressure from 10 Pa to 100 Pa. The maximum converting time tc from glow to arc discharging reaches 1600 ns at an air pressure of 100 Pa, while the minimum converting time tc is 120 ns at 10 Pa. For a triggered HCSPG, Up is reduced to about 1.6 kV while the converting time is 120 ns with a semiconductor trigger device and 50 ns with a dielectric porcelain trigger device under an air pressure of 100 Pa.

  2. 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.

  3. 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 (3.21 eV) is much higher than that for Li+ ions (0.79 eV) and Na+ ions (0.79 eV) 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.

  4. 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.

  5. Surface composition and barium evaporation rate of ``pedigreed'' impregnated tungsten dispenser cathodes during accelerated life testing

    NASA Astrophysics Data System (ADS)

    Tomich, D. H.; Mescher, J. A.; Grant, J. T.

    1987-03-01

    A study has been made of the surface composition and barium evaporation rate of "pedigreed" impregnated tungsten dispenser cathodes. The effect of air exposure on coated cathodes was examined and was found to have no significant effect on barium evaporation rate although in some cases longer reactivation times were required. No changes in surface topography were apparent following air exposure and reactivation. Life testing was done at 100°C above the typical operating temperature for the cathode, where the typical operating temperature was taken to be 950°C for coated cathodes and 1050°C for uncoated cathodes. The cathodes were examined at different stages of life testing, up to 1200 h. Significant decreases in barium evaporation rates were found after as few as 500 h of life testing. After 1000 h the evaporation rate had decreased more than an order of magnitude. Changes in surface composition were also found. The effects of tungsten particle size, used in manufacture of the billet, on barium evaporation rate were also studied but no correlation was found.

  6. Doped carbon-sulfur species nanocomposite cathode for Li--S batteries

    DOEpatents

    Wang, Donghai; Xu, Tianren; Song, Jiangxuan

    2015-12-29

    We report a heteroatom-doped carbon framework that acts both as conductive network and polysulfide immobilizer for lithium-sulfur cathodes. The doped carbon forms chemical bonding with elemental sulfur and/or sulfur compound. This can significantly inhibit the diffusion of lithium polysulfides in the electrolyte, leading to high capacity retention and high coulombic efficiency.

  7. Application of hollow cathode effect for local ion nitriding of machine parts

    NASA Astrophysics Data System (ADS)

    Budilov, V. V.; Ramazanov, K. N.; Khusainov, Yu G.; Zolotov, I. V.; Babenko, N. S.

    2015-11-01

    Influence of hollow cathode effect (HCE) on local ion nitriding process of 16Kh3NVFMB-Sh steel was studied. Microstructures of nitrided layer, phase composition, microhardness profiles through the diffusion layer were obtained and investigated. Influence of ion nitriding duration on nitrided case depth and wear resistance was studied. Technology of ion nitriding with application to HCE for gear part was developed.

  8. LOW TEMPERATURE CATHODE SUPPORTED ELECTROLYTES

    SciTech Connect

    Harlan U. Anderson; Fatih Dogan; Vladimir Petrovsky

    2002-03-31

    This project has three main goals: Thin Films Studies, Preparation of Graded Porous Substrates and Basic Electrical Characterization and testing of Planar Single Cells. This period has continued to address the problem of making dense 1/2 to 5 {micro}m thick dense layers on porous substrates (the cathode LSM). Our current status is that we are making structures of 2-5 cm{sup 2} in area, which consist of either dense YSZ or CGO infiltrated into a 2-5 {micro}m thick 50% porous layer made of either nanoncrystalline CGO or YSZ powder. This composite structure coats a macroporous cathode or anode; which serves as the structural element of the bi-layer structure. These structures are being tested as SOFC elements. A number of structures have been evaluated both as symmetrical and as button cell configuration. Results of this testing indicates that the cathodes contribute the most to cell losses for temperatures below 750 C. In this investigation different cathode materials were studied using impedance spectroscopy of symmetric cells and IV characteristics of anode supported fuel cells. Cathode materials studied included La{sub 0.8}Sr{sub 0.2}Co{sub 0.2}Fe{sub 0.8}O{sub 3} (LSCF), La{sub 0.7}Sr{sub 0.2}MnO{sub 3} (LSM), Pr{sub 0.8}Sr{sub 0.2}Fe{sub 0.8}O{sub 3} (PSCF), Sm{sub 0.8}Sr{sub 0.2}Co{sub 0.2}Fe{sub 0.8}O{sub 3} (SSCF), and Yb{sub .8}Sr{sub 0.2}Co{sub 0.2}Fe{sub 0.8}O{sub 3} (SSCF). A new technique for filtering the Fourier transform of impedance data was used to increase the sensitivity of impedance analysis. By creating a filter specifically for impedance spectroscopy the resolution was increased. The filter was tailored to look for specific circuit elements like R//C, Warburg, or constant phase elements. As many as four peaks can be resolved using the filtering technique on symmetric cells. It may be possible to relate the different peaks to material parameters, like the oxygen exchange coefficient. The cathode grouped in order from lowest to highest ASR is LSCF < PSCF < SSCF < YSCF < LSM. The button cell results agree with this ordering indicating that this is an important tool for use in developing our understanding of electrode behavior in fuel cells.

  9. 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.

  10. 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.

  11. Parametric Study on Arc Behavior of Magnetically Diffused Arc

    NASA Astrophysics Data System (ADS)

    Chen, Tang; Li, Hui; Bai, Bing; Liao, Mengran; Xia, Weidong

    2016-01-01

    A model coupling the plasma with a cathode body is applied in the simulation of the diffuse state of a magnetically rotating arc. Four parametric studies are performed: on the external axial magnetic field (AMF), on the cathode shape, on the total current and on the inlet gas velocity. The numerical results show that: the cathode attachment focuses in the center of the cathode tip with zero AMF and gradually shifts off the axis with the increase of AMF; a larger cathode conical angle corresponds to a cathode arc attachment farther away off axis; the maximum values of plasma temperature increase with the total current; the plasma column in front of the cathode tip expands more severely in the axial direction, with a higher inlet speed; the cathode arc attachment shrinks towards the tip as the inlet speed increases. The various results are supposed to be explained by the joint effect of coupled cathode surface heating and plasma rotating flow. supported by National Natural Science Foundation of China (Nos. 11475174, 11035005 and 50876101)

  12. Ti- and Zr-based metal-air batteries

    NASA Astrophysics Data System (ADS)

    Van der Ven, Anton; Puchala, Brian; Nagase, Takeshi

    2013-11-01

    We propose a high-temperature, rechargeable metal-air battery that relies on Ti or Zr metal as the anode and the shuttling of oxygen anions between the cathode and the anode through a solid-oxide ion-conducting electrolyte. The cathode has much in common with solid-oxide fuel cells. Key in the proposed battery is the use of Ti or Zr as the anode as these metals are unique in their ability to dissolve oxygen up to concentrations of 33% with minimal structural and volumetric changes. First-principles statistical mechanics calculations predict open circuit voltages around 2.5 V, substantially larger than the open circuit voltage of high-temperature solid-oxide fuel cells. The calculations predict the stability of TiO and ZrO monoxides along with TiOx and ZrOx (with x as high as ½) solid solutions. These suboxide phases are all predicted to be metallic, indicating that electron transport in the anodes will not be rate limiting. The oxygen diffusion coefficients in the Ti and Zr suboxides at high temperature (˜700-800 °C) are predicted to be comparable to that of Li ions in intercalation compounds. These properties suggest theoretical capacities as high as 840 mAh g-1 and 500 mAh g-1 for Ti and Zr based metal-air batteries respectively.

  13. Filters for cathodic arc plasmas

    DOEpatents

    Anders, Andre; MacGill, Robert A.; Bilek, Marcela M. M.; Brown, Ian G.

    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.

  14. Nickel-titanium-phosphate cathodes

    DOEpatents

    Belharouak, Ilias; Amine, Khalil

    2008-12-16

    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 octahedra [TiO.sub.6] running along the C-axis. The structure is such that nearly three Li atoms are being inserted in Li.sub.xNi.sub.0.5TiOPO.sub.4. A cell in accordance with the principles of the present invention is rechargable and demonstrates a high capacity of lithium intercalation and fast kinetics.

  15. Characterization of multicapillary dielectric cathodes

    SciTech Connect

    Gleizer, J. Z.; Hadas, Y.; Yarmolich, D.; Felsteiner, J.; Krasik, Ya. E.

    2007-04-30

    Parameters of the plasma and electron beam produced by a multicapillary cathode in a diode powered by a {approx}200 kV, {approx}300 ns pulse are presented. It was found that the source of electrons is the plasma ejected from the capillaries. Inside the capillaries this plasma obtains electron density and temperature of {approx}8x10{sup 15} cm{sup -3} and {approx}5 eV, respectively. In the vicinity of the cathode, the density and temperature of the plasma electrons were found to be 2x10{sup 14} cm{sup -3} and 4.5 eV, respectively, for electron current density of {approx}40 A/cm{sup 2}. It was shown that the plasma expansion velocity is in the range of (1-2)x10{sup 6} cm/s for current density of >12 A/cm{sup 2}.

  16. Conservation in cathodic protection design

    SciTech Connect

    Sydberger, T.; Edwards, J.D.; Tiller, I.B.

    1997-02-01

    Sacrificial anode cathodic protection offers cost-effective corrosion protection of submerged marine structures. The longevity of the protection systems can be estimated with a limited degree of accuracy. Some intentional overcapacity must be included in the design. Specific parameters are defined with an intrinsic conservatism, to provide adequate reliability, thereby avoiding high overcapacity and high potential costs associated with subsea retrofitting of anodes, if the design proves to be insufficient.

  17. 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.

  18. High contrast cathode ray tube

    NASA Technical Reports Server (NTRS)

    Lisovicz, E. J.; Catlaw, T. G. (Inventor)

    1971-01-01

    A layer of material is described, which contains fine grains of phosphor material stimulated by electrons to produce visible radiation. The layer, which also contains fine grains of cobalt oxide, is deposited on the glass screen of a cathode ray tube to provide high contrast, by absorbing most of the visible radiation which is directed to the layer through the screen, while not materially affecting the visible light which the phosphor material produces in response to the electron stimulation.

  19. Electrochemical behavior of niobium triselenide cathode in lithium secondary cells

    NASA Technical Reports Server (NTRS)

    Ratnakumar, B. V.; Di Stefano, S.; Bankston, C. P.

    1988-01-01

    Niobium triselenide cathodes in Li ambient-temperature rechargeable batteries for space applications undergo a topotactic reaction, with three equivalents of Li at high positive potential furnishing high energy density. It also yields good electronic conductivity, a long life cycle, and high diffusivity for Li. An attempt is presently made to characterize the intercalation mechanism between Li and NbSe3 by means of an ac impedance study conducted at various charge stages in the process of SbSe3 reduction. An effort is also made to predict the charge state of NbSe3 nondestructively, on the basis of the impedance parameters.

  20. Theoretical study on the initial stage of a magnesium battery based on a V2O5 cathode.

    PubMed

    Zhou, Bo; Shi, Hui; Cao, Rongfang; Zhang, Xiaodong; Jiang, Zhenyi

    2014-09-14

    Several first-principles calculations based on density functional theory have been carried out looking at the key issues of a magnesium battery with a V2O5 cathode. This kind of magnesium battery was reported by D. Aurbach's group in 2013. Our theoretical studies provide explanations for the experimental findings such as higher voltage, slow ion diffusivity and the decrease of the crystallinity. The calculated open circuit voltage of a magnesium battery with a V2O5 cathode is 3.06 V, which is 0.22 V higher than a lithium battery with the same cathode. Electronic band structure calculations suggest that higher electronic conductivity must be expected in a magnesium battery. Elastic constants are obtained, which give information on the stability of the magnesiated cathode. Furthermore, we have also calculated the diffusion barriers of Li and Mg ions in the cathode using the nudged elastic band method. The hopping barrier of Mg ions is 1.26 eV, which is much higher than that of Li ions (0.35 eV). The obtained minimum energy paths show the different hopping processes in the lithium and magnesium batteries, which can explain the phenomenon of slow diffusion in experiments. The possible transition pathway between the α and δ phases is analyzed for the first time, which gives an explanation for the reversibility of Mg ions in the V2O5 cathode. PMID:25075459

  1. 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.

  2. NEXIS Reservoir Cathode 2000 Hour Life Test

    NASA Technical Reports Server (NTRS)

    Vaughn, Jason; Schneider, Todd; Polk, Jay; Goebel, Dan; Ohlinger, Wayne; Hill, D. Norm

    2004-01-01

    The current design of the Nuclear Electric Xenon Ion System (NEXIS) employs a reservoir cathode as both the discharge and neutralizer cathode to meet the 10 yr thruster design life. The main difference between a reservoir cathode and a conventional discharge cathode is the source material (barium-containing compound) is contained within a reservoir instead of in an impregnated insert in the hollow tube. However, reservoir cathodes do not have much life test history associated with them. In order to demonstrate the feasibility of using a reservoir cathode as an integral part of the NEXIS ion thruster, a 2000 hr life test was performed. Several proof-of-concept (POC) reservoir cathodes were built early in the NEXIS program to conduct performance testing as well as life tests. One of the POC cathodes was sent to Marshall Space Flight Center (MSFC) where it was tested for 2000 hrs in a vacuum chamber. The cathode was operated at the NEXIS design point of 25 A discharge current and a xenon flow rate of 5.5 sccm during the 2000 hr test. The cathode performance parameters, including discharge current, discharge voltage, keeper current; keeper voltage, and flow rate were monitored throughout test. Also, the temperature upstream of cathode heater, the temperature downstream of the cathode heater, and the temperature of the orifice plate were monitored throughout the life of the test. The results of the 2000 hr test will be described in this paper. Included in the results will be time history of discharge current, discharge voltage, and flow rate. Also, a time history of the cathode temperature will be provided.

  3. 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.

  4. 24-HOUR DIFFUSIVE SAMPLING OF 1,3-BUTADIENE IN AIR ONTO CARBONPAK X SOLID ADSORBENT WITH THEMAL DESORPTION/GC/MS ANALYSIS - FEASIBILITY STUDIES

    EPA Science Inventory

    Diffusive sampling of 1,3-butadiene for 24 hours onto the graphitic adsorbent Carbopack X contained in a stainless steel tube badge (6.3 mm OD, 5 mm ID, and 90 mm in length) with analysis by thermal desorption/GC/MS has been evaluated in controlled tests. A test matrix of 42 tr...

  5. 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...

  6. 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.

  7. Novel Composite Materials for SOFC Cathode-Interconnect Contact

    SciTech Connect

    J. H. Zhu

    2009-07-31

    This report summarized the research efforts and major conclusions of our University Coal Research Project, which focused on developing a new class of electrically-conductive, Cr-blocking, damage-tolerant Ag-perovksite composite materials for the cathode-interconnect contact of intermediate-temperature solid oxide fuel cell (SOFC) stacks. The Ag evaporation rate increased linearly with air flow rate initially and became constant for the air flow rate {ge} {approx} 1.0 cm {center_dot} s{sup -1}. An activation energy of 280 KJ.mol{sup -1} was obtained for Ag evaporation in both air and Ar+5%H{sub 2}+3%H{sub 2}O. The exposure environment had no measurable influence on the Ag evaporation rate as well as its dependence on the gas flow rate, while different surface morphological features were developed after thermal exposure in the oxidizing and reducing environments. Pure Ag is too volatile at the SOFC operating temperature and its evaporation rate needs to be reduced to facilitate its application as the cathode-interconnect contact. Based on extensive evaporation testing, it was found that none of the alloying additions reduced the evaporation rate of Ag over the long-term exposure, except the noble metals Au, Pt, and Pd; however, these noble elements are too expensive to justify their practical use in contact materials. Furthermore, the addition of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LSM) into Ag to form a composite material also did not significantly modify the Ag evaporation rate. The Ag-perovskite composites with the perovskite being either (La{sub 0.6}Sr{sub 0.4})(Co{sub 0.8}Fe{sub 0.2})O{sub 3} (LSCF) or LSM were systematically evaluated as the contact material between the ferritic interconnect alloy Crofer 22 APU and the LSM cathode. The area specific resistances (ASRs) of the test specimens were shown to be highly dependent on the volume percentage and the type of the perovskite present in the composite contact material as well as the amount of thermal cycling that the specimens were subjected to during testing. The Ag-LSCF composite contact materials proved more effective in trapping Cr within the contact material and preventing Cr migration into the cathode than the Ag-LSM composites. Ag-perovskite composite contact materials are promising candidates for use in intermediate-temperature SOFC stacks with ferritic stainless steel interconnects due to their ability to maintain acceptably low ASRs while reducing Cr migration into the cathode material.

  8. 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.

  9. Intermittent cathodic protection using solar power

    SciTech Connect

    Kessler, R.J.; Powers, R.G.; Lasa, I.R.

    1998-12-31

    An intermittent impressed current cathodic protection technique using photovoltaic energy was evaluated to determine it`s ability to protect bridge concrete piles in marine environments against corrosion. The technique uses commercially available anode systems to deliver the cathodic protection current to the concrete and onto the reinforcing steel. Cathodic protection current is only applied during the daytime hours. The magnitude of the applied current was based on sunlight availability. An evaluation was conducted on laboratory specimens as well as in the field. The laboratory work was performed on steel reinforced concrete specimens placed in simulated salt water tanks. For the field evaluation, ten prestressed concrete piles of a bridge structure with an existing rectifier powered cathodic protection system were used. In both cases, intermittent cathodic protection was provided. Polarization and depolarization of the steel reinforcement as well as the protection current delivered were monitored to evaluate the cathodic protection performance as well as the behavior of periodic polarization-depolarization.

  10. Quantitative LEIS analysis of thermionic dispenser cathodes

    NASA Astrophysics Data System (ADS)

    Cortenraad, R.; Denier van der Gon, A. W.; Brongersma, H. H.; Gärtner, G.; Manenschijn, A.

    1999-05-01

    An UHV LEIS setup has been converted into a dedicated apparatus to study the surface composition, structure and dynamics of real dispenser cathodes and cathode model systems based on W single crystals. LEIS, AES and LEED are available to investigate the surface characteristics, and the cathode emission properties are derived in situ from a close-spaced diode configuration. In this paper, the focus is on the quantitative surface composition of B-type and M-type dispenser cathodes by LEIS. A straightforward quantification is hampered by the influence of the cathode workfunction on the neutralisation of the ions. It is shown that the ion fraction decreases as the workfunction of the cathode decreases. The Ba surface density is observed to increase with decreasing workfunction. However, before an accurate quantitative surface analysis can be performed a validation of the model used to correct for the influence of the ion fraction has to be performed.

  11. 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.

  12. 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.

  13. Hollow cathode startup using a microplasma discharge

    NASA Technical Reports Server (NTRS)

    Aston, G.

    1981-01-01

    Attention is given to a microplasma discharge to initiate a hollow cathode discharge for such applications as plasma flow experiments, the electric propulsion of space vehicles, and as a replacement for filament cathodes in neutral beam injector ion sources. The technique results in a cathode that is easy to start, simple in design, and which does not require external RF exciters, inserts or heating elements. Future applications may include ion beam milling and ion implantation.

  14. A direct density modulation cathode in magnetron

    SciTech Connect

    Li, Wei; Zhang, Jun; Liu, Yong-gui; Yang, Han-wu; Shu, Ting

    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.

  15. 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.

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

    SciTech Connect

    Capece, Angela M. Shepherd, Joseph E.; Polk, James E.; Mikellides, Ioannis G.

    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.

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

    NASA Astrophysics Data System (ADS)

    Capece, Angela M.; Polk, James E.; Mikellides, Ioannis G.; Shepherd, Joseph E.

    2014-04-01

    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 O2 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 O2. The dominant ionization process for O2 is resonant charge exchange with xenon ions. Ba is effectively recycled in the plasma; however, BaO and O2 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.

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

    NASA Astrophysics Data System (ADS)

    Park, Ki Wan; Lee, Tae Il; Hwang, Hyeon Seok; Noh, Joo Hyon; Baik, Hong Koo; Song, Kie Moon

    2008-02-01

    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 200μm diameter at 9mA and the optimum value of gas velocity×diameter 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 200μm (0.31m2/s) and 500μm (0.78m2/s) air discharge at 8mA under the velocity of 156m/s. As a result, an increase of 46.7% in E /N strength of the discharge of 200μm hole was obtained compare to that of 500μm.

  19. Co-flow anode/cathode supply heat exchanger for a solid-oxide fuel cell assembly

    DOEpatents

    Haltiner, Jr., Karl J.; Kelly, Sean M.

    2005-11-22

    In a solid-oxide fuel cell assembly, a co-flow heat exchanger is provided in the flow paths of the reformate gas and the cathode air ahead of the fuel cell stack, the reformate gas being on one side of the exchanger and the cathode air being on the other. The reformate gas is at a substantially higher temperature than is desired in the stack, and the cathode gas is substantially cooler than desired. In the co-flow heat exchanger, the temperatures of the reformate and cathode streams converge to nearly the same temperature at the outlet of the exchanger. Preferably, the heat exchanger is formed within an integrated component manifold (ICM) for a solid-oxide fuel cell assembly.

  20. Apparatus for mounting a field emission cathode

    NASA Astrophysics Data System (ADS)

    Ebihara, Ben T.; Forman, Ralph

    1987-08-01

    A field emission cathode is positioned in a pair of intersecting cross grooves, in the end of a ceramic tube by a metal end cap. A spring in electrical contact with the base of the cathode provides the necessary pressure to maintain continuous circumferential electrical contact between the gate film and a raised edge on the end cap. With this structure the cathode chip is self centering and easily replaceable. Also the gate film of the cathode is not abraded or rubbed during installation, and the holder is readily degassed.

  1. 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.

  2. Emission properties of explosive field emission cathodes

    SciTech Connect

    Roy, Amitava; Patel, Ankur; Menon, Rakhee; Sharma, Archana; Chakravarthy, D. P.; Patil, D. S.

    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.

  3. Arc initiation in cathodic arc plasma sources

    DOEpatents

    Anders, Andre

    2002-01-01

    A "triggerless" arc initiation method and apparatus is based on simply switching the arc supply voltage to the electrodes (anode and cathode). Neither a mechanical trigger electrode nor a high voltage flashover from a trigger electrode is required. A conducting path between the anode and cathode is provided, which allows a hot spot to form at a location where the path connects to the cathode. While the conductive path is eroded by the cathode spot action, plasma deposition ensures the ongoing repair of the conducting path. Arc initiation is achieved by simply applying the relatively low voltage of the arc power supply, e.g. 500 V-1 kV, with the insulator between the anode and cathode coated with a conducting layer and the current at the layer-cathode interface concentrated at one or a few contact points. The local power density at these contact points is sufficient for plasma production and thus arc initiation. A conductive surface layer, such as graphite or the material being deposited, is formed on the surface of the insulator which separates the cathode from the anode. The mechanism of plasma production (and arc initiation) is based on explosive destruction of the layer-cathode interface caused by joule heating. The current flow between the thin insulator coating and cathode occurs at only a few contact points so the current density is high.

  4. Improving Best Air Conditioner Efficiency by 20-30% through a High Efficiency Fan and Diffuser Stage Coupled with an Evaporative Condenser Pre-Cooler

    SciTech Connect

    Parker, Danny S; Sherwin, John R; Raustad, Richard

    2014-04-10

    The Florida Solar Energy Center (FSEC) conducted a research project to improve the best residential air conditioner condenser technology currently available on the market by retrofitting a commercially-available unit with both a high efficiency fan system and an evaporative pre-cooler. The objective was to integrate these two concepts to achieve an ultra-efficient residential air conditioner design. The project produced a working prototype that was 30% more efficient compared to the best currently-available technologies; the peak the energy efficiency ratio (EER) was improved by 41%. Efficiency at the Air-Conditioning and Refrigeration Institute (ARI) standard B-condition which is used to estimate seasonal energy efficiency ratio (SEER), was raised from a nominal 21 Btu/Wh to 32 Btu/Wh.

  5. 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.

  6. Study of water transport phenomena on cathode of PEMFCs using Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Soontrapa, Karn

    This dissertation deals with the development of a three-dimensional computational model of water transport phenomena in the cathode catalyst layer (CCL) of PEMFCs. The catalyst layer in the numerical simulation was developed using the optimized sphere packing algorithm. The optimization technique named the adaptive random search technique (ARSET) was employed in this packing algorithm. The ARSET algorithm will generate the initial location of spheres and allow them to move in the random direction with the variable moving distance, randomly selected from the sampling range, based on the Lennard-jones potential of the current and new configuration. The solid fraction values obtained from this developed algorithm are in the range of 0.631 to 0.6384 while the actual processing time can significantly be reduced by 8% to 36% based on the number of spheres. The initial random number sampling range was investigated and the appropriate sampling range value is equal to 0.5. This numerically developed cathode catalyst layer has been used to simulate the diffusion processes of protons, in the form of hydronium, and oxygen molecules through the cathode catalyst layer. The movements of hydroniums and oxygen molecules are controlled by the random vectors and all of these moves has to obey the Lennard-Jones potential energy constrain. Chemical reaction between these two species will happen when they share the same neighborhood and result in the creation of water molecules. Like hydroniums and oxygen molecules, these newly-formed water molecules also diffuse through the cathode catalyst layer. It is important to investigate and study the distribution of hydronium oxygen molecule and water molecules during the diffusion process in order to understand the lifetime of the cathode catalyst layer. The effect of fuel flow rate on the water distribution has also been studied by varying the hydronium and oxygen molecule input. Based on the results of these simulations, the hydronium: oxygen input ratio of 3:2 has been found to be the best choice for this study. To study the effect of metal impurity and gas contamination on the cathode catalyst layer, the cathode catalyst layer structure is modified by adding the metal impurities and the gas contamination is introduced with the oxygen input. In this study, gas contamination has very little effect on the electrochemical reaction inside the cathode catalyst layer because this simulation is transient in nature and the percentage of the gas contamination is small, in the range of 0.0005% to 0.0015% for CO and 0.028% to 0.04% for CO2 . Metal impurities seem to have more effect on the performance of PEMFC because they not only change the structure of the developed cathode catalyst layer but also affect the movement of fuel and water product. Aluminum has the worst effect on the cathode catalyst layer structure because it yields the lowest amount of newly form water and the largest amount of trapped water product compared to iron of the same impurity percentage. For the iron impurity, it shows some positive effect on the life time of the cathode catalyst layer. At the 0.75 wt% of iron impurity, the amount of newly formed water is 6.59% lower than the pure carbon catalyst layer case but the amount of trapped water product is 11.64% lower than the pure catalyst layer. The lifetime of the impure cathode catalyst layer is longer than the pure one because the amount of water that is still trapped inside the pure cathode catalyst layer is higher than that of the impure one. Even though the impure cathode catalyst layer has a longer lifetime, it sacrifices the electrical power output because the electrochemical reaction occurrence inside the impure catalyst layer is lower.

  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. An experimental investigation of cathode erosion in high current magnetoplasmadynamic arc discharges

    NASA Astrophysics Data System (ADS)

    Codron, Douglas A.

    Since the early to mid 1960's, laboratory studies have demonstrated the unique ability of magnetoplasmadynamic (MPD) thrusters to deliver an exceptionally high level of specific impulse and thrust at large power processing densities. These intrinsic advantages are why MPD thrusters have been identified as a prime candidate for future long duration space missions, including piloted Mars, Mars cargo, lunar cargo, and other missions beyond low Earth orbit (LEO). The large total impulse requirements inherent of the long duration space missions demand the thruster to operate for a significant fraction of the mission burn time while requiring the cathodes to operate at 50 to 10,000 kW for 2,000 to 10,000 hours. The high current levels lead to high operational temperatures and a corresponding steady depletion of the cathode material by evaporation. This mechanism has been identified as the life-limiting component of MPD thrusters. In this research, utilizing subscale geometries, time dependent cathode axial temperature profiles under varying current levels (20 to 60 A) and argon gas mass flow rates (450 to 640 sccm) for both pure and thoriated solid tungsten cathodes were measured by means of both optical pyrometry and charged-coupled (CCD) camera imaging. Thoriated tungsten cathode axial temperature profiles were compared against those of pure tungsten to demonstrate the large temperature reducing effect lowered work function imparts by encouraging increased thermionic electron emission from the cathode surface. Also, Langmuir probing was employed to measure the electron temperature, electron density, and plasma potential near the "active zone" (the surface area of the cathode responsible for approximately 70% of the emitted current) in order to characterize the plasma environment and verify future model predictions. The time changing surface microstructure and elemental composition of the thoriated tungsten cathodes were analyzed using a scanning electron microscope (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS). Such studies have provided a qualitative understanding of the typical pathways in which thorium diffuses and how it is normally redistributed along the cathode surface. Lastly, the erosion rates of both pure and thoriated tungsten cathodes were measured after various run times by use of an analytical scale. These measurements have revealed the ability of thoriated tungsten cathodes to run as long as that of pure tungsten but with significantly less material erosion.

  9. Plasma deposition of oxide-coated cathodes

    NASA Astrophysics Data System (ADS)

    Umstattd, Ryan Jonathan

    Vacuum arc deposition is employed to create a barium and/or strontium plasma which is subsequently deposited/implanted onto a nickel cathode substrate. The primary motivation for this work is the critical need for a reliable, repeatable, long-lived thermionic cathode for the production of high power, microsecond duration microwave pulses; such cathodes may also have applicability for lower current density continuous wave devices. This novel approach to manufacturing an oxide cathode eliminates the binders that may subsequently (and unpredictably) poison cathode emission. Removal of the poisoning mechanisms has yielded oxide cathodes capable of emission densities in the 20 A/cm 2 regime. Cathode lifetime and emission may be varied via the control over the deposition parameters such as coating thickness, implantation energy, and plasma stoichiometry. The deposition is performed by generating a cathodic arc discharge at the surface of a barium or barium- strontium alloy rod. The metal plasma thus created is then deposited on the substrate which can be negatively biased to encourage implantation during the deposition process. The deposition is performed with sufficient background oxygen present to oxidize the highly reactive metal coating. The plasma deposition is monitored via a rate thickness monitor, an optical emission spectrometer for plasma composition information, and an electrostatic Langmuir probe for the determination of the plasma density and temperature profile. Cathodes thus produced are analyzed by drawing pulsed current at a constant voltage for various values of decreasing cathode temperature in order to generate practical work function distributions which provide an indication of the quality and expected life time of the cathode.

  10. Diffusion MRI

    NASA Astrophysics Data System (ADS)

    Fukuyama, Hidenao

    Recent advances of magnetic resonance imaging have been described, especially stressed on the diffusion sequences. We have recently applied the diffusion sequence to functional brain imaging, and found the appropriate results. In addition to the neurosciences fields, diffusion weighted images have improved the accuracies of clinical diagnosis depending upon magnetic resonance images in stroke as well as inflammations.

  11. 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.

  12. 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.

  13. Cathode for use with low density gases

    NASA Technical Reports Server (NTRS)

    Bennett, W. H.

    1972-01-01

    Method for preventing deterioration of mixed oxide cathodes in low density gas tubes caused by ion bombardment is discussed. Construction of cathode is described and illustration is furnished. Electron emission through space charge to neutralize ion-filled regions is basic process.

  14. Atomically mixed alloy coated cathodes specification

    NASA Astrophysics Data System (ADS)

    Haas, G. A.; Shih, A.; Marrian, C. R. K.

    1985-04-01

    The present invention pertains generally to cathodes used in thermionic electron tubes, often used in ultra high frequency and microwave radio transmitters. It is an object of this invention to produce thermionic tube cathodes which consistntly exhibit current densities higher than heretofore achieved. Another object of the present invention is to manufacture cathodes using a method that consistently results in cathodes with a large, defined, level of current density. Another object of the present invention is to produce cathodes with reduced surface work functions by means of atomic scale mixing of two selected metals in a cathode surface coating. A tungsten or tungsten-based matrix cathode impregnated with BaO is simultaneously coated with vapors of two metallic elements, in particular, tungsten and iridium, such that a binary alloy forms on the surface. A layer of BaO then spontaneously dispenses onto the surface of the binary alloy. One of the metallic elements associates with the oxygen of BaO and other with the barium. The molecular dipole of BaO thus becomes more pronounced, and the surface work function results in a greater rate of electron emission from the cathode.

  15. Preliminary Results of Field Emission Cathode Tests

    NASA Technical Reports Server (NTRS)

    Sovey, James S.; Kovaleski, Scott D.

    2001-01-01

    Preliminary screening tests of field emission cathodes such as chemical vapor deposited (CVD) diamond, textured pyrolytic graphite, and textured copper were conducted at background pressures typical of electric thruster test facilities to assess cathode performance and stability. Very low power electric thrusters which provide tens to hundreds micronewtons of thrust may need field emission neutralizers that have a capability of tens to hundreds of microamperes. From current voltage characteristics, it was found that the CVD diamond and textured metals cathodes clearly satisfied the Fowler-Nordheim emission relation. The CVD diamond and a textured copper cathode had average current densities of 270 and 380 mA/sq cm, respectively, at the beginning-of-life. After a few hours of operation the cathode emission currents degraded by 40 to 75% at background pressures in the 10(exp -5) Pa to 10(exp -4) Pa range. The textured pyrolytic graphite had a modest current density at beginning-of-life of 84 mA/sq cm, but this cathode was the most stable of all. Extended testing of the most promising cathodes is warranted to determine if current degradation is a burn-in effect or whether it is a long-term degradation process. Preliminary experiments with ferroelectric emission cathodes, which are ceramics with spontaneous electric polarization, were conducted. Peak current densities of 30 to 120 mA/sq cm were obtained for pulse durations of about 500 ns in the 10(exp -4) Pa pressure range.

  16. 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.

  17. Serrated cathode dissolution under high current density: Morphology and root cause

    NASA Astrophysics Data System (ADS)

    Yang, T. L.; Ke, J. H.; Shih, W. L.; Lai, Y. S.; Kao, C. R.

    2013-08-01

    Excessive cathode dissolution due to high current densities is investigated. Such excessive dissolution is one of the key electromigration-induced degradation processes in micro systems, and exhibits a distinctive serrated morphology. In this study, Cu cathode and Cu anode connected with Sn is stressed at a 4.5 × 104 A/cm2 current density for time as long as 1500 h. Careful sequential micro polishing is able to establish for the first time that the serrated cathode interface in fact is the expression of rod-like indentations in three-dimensional morphology. This unique morphology supports the proposition that fast Cu diffusion through Cu6Sn5 grain boundaries is the root cause for this excessive dissolution.

  18. Cathode bubbles induced by moisture electrolysis in TiO2-x -based resistive switching cells

    NASA Astrophysics Data System (ADS)

    Yin, Qiaonan; Wei, Chunyang; Xia, Yidong; Xu, Bo; Yin, Jiang; Liu, Zhiguo

    2016-03-01

    H2 production has been predicted in some metal-insulator-metal resistive switching devices and similar structures, but experimentally has not yet been reported. Here we discovered cathode bubbles in Pt/TiO2-x /Pt unipolar resistive switching cells when electroforming is implemented in a humid environment. But then these bubbles are absent when cells are operated in an anhydrous environment. The focused ion beam technique was used to observe the deformation of the cell induced by bubbles. These bubbles are deduced to be filled with H2 generated at the cathode by the reduction of protons from adsorbed water. Reduced oxides containing abundant oxygen vacancies facilitate the dissociation of adsorbed water and supply sufficient protons diffusing towards the cathode.

  19. Plasmapause diffusion

    NASA Technical Reports Server (NTRS)

    Horwitz, J. L.

    1983-01-01

    The Bohm diffusion coefficient and observed electrostatic wave scattering are used as the bases of estimates of the smoothing effect that diffusion may have on steep plasmapause density gradients. The estimate for diffusion resulting from scattering by observed electrostatic waves is found to be much lower than that of the perpendicular Bohm diffusion coefficient for characteristic plasma temperatures and magnetic fields. This diffusion rate estimate may be too small, however, if the wave amplitudes are significantly higher for steep plasmapauses. The effects are therefore negligible for most considerations of macroscopic plasmapause dynamics, but may be significant in limiting drift wave instabilities and similar phenomena driven by the steepness of the plasmapause density gradient.

  20. Cathode Effects in Cylindrical Hall Thrusters

    SciTech Connect

    Granstedt, E.M.; Raitses, Y.; Fisch, N. J.

    2008-09-12

    Stable operation of a cylindrical Hall thruster (CHT) has been achieved using a hot wire cathode, which functions as a controllable electron emission source. It is shown that as the electron emission from the cathode increases with wire heating, the discharge current increases, the plasma plume angle reduces, and the ion energy distribution function shifts toward higher energies. The observed effect of cathode electron emission on thruster parameters extends and clarifies performance improvements previously obtained for the overrun discharge current regime of the same type of thruster, but using a hollow cathode-neutralizer. Once thruster discharge current saturates with wire heating, further filament heating does not affect other discharge parameters. The saturated values of thruster discharge parameters can be further enhanced by optimal placement of the cathode wire with respect to the magnetic field.