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1

Influence of cathode opening size and wetting properties of diffusion layers on the performance of air-breathing PEMFCs  

NASA Astrophysics Data System (ADS)

Air-breathing PEMFCs consist of an open cathodic side to allow an entirely passive supply of oxygen by diffusion. Furthermore, a large fraction of the produced water is removed by evaporation from the open cathode. Gas diffusion layers (GDLs) and the opening size of the cathode have a crucial influence on the performance of an air-breathing PEMFC. In order to assure an unobstructed supply of oxygen the water has to be removed efficiently and condensation in the GDL has to be avoided. On the other hand good humidification of the membrane has to be achieved to obtain high protonic conductivity. In this paper the influence of varying cathodic opening sizes (33%, 50% and 80% opening ratios) and of GDLs with different wetting properties are analysed. GDLs with hydrophobic and hydrophilic properties are prepared by coating of untreated GDLs (Toray ® carbon paper TGP-H-120, thickness of 350 ?m). The air-breathing PEMFC test samples are realised using printed circuit board (PCB) technology. The cell samples were characterised over the entire potential range (0-0.95 V) by extensive measurements of the current density, the temperature and the cell impedance at 1 kHz. Additionally, measurements of the water balance were carried out at distinct operation points. The best cell performance was achieved with the largest opening ratio (80%) and an untreated GDL. At the maximum power point, this cell sample achieved a power density of 100 mW cm -2 at a moderate cell temperature of 43 °C. Furthermore, it could be shown that GDLs with hydrophilic or intense hydrophobic properties do not improve the performance of an air-breathing PEMFC. Based on the extensive characterisations, two design rules for air-breathing PEMFCs could be formulated. Firstly, it is crucial to maximise the cathode opening as far as an appropriate compression pressure of the cell assembly and therewith low contact resistance can be assured. Secondly, it is advantageous to use an untreated, slightly hydrophobic GDL.

Schmitz, A.; Tranitz, M.; Eccarius, S.; Weil, A.; Hebling, C.

2

Zinc/air cell cathode  

NASA Astrophysics Data System (ADS)

This invention relates to a cathode for an air depolarized cell in which the hydrophobic catalytic cathode contains or in integrally drophobi catalytic cathode contains or is integrally coated with, on the surface adjacent the cell separator, an absorbent material such as the gelling material used in the anode. The absorbent material, integrated with the cathode surface, adheres the separator to the cathode thereby preventing delamination and provides an electrolyte reservoir for the hydrophobic cathode.

McEvoy, J. J.

1986-04-01

3

Mineralization of the drug ?-blocker atenolol by electro-Fenton and photoelectro-Fenton using an air-diffusion cathode for H 2O 2 electrogeneration combined with a carbon-felt cathode for Fe 2+ regeneration  

Microsoft Academic Search

Two-electrode cells with a Pt or boron-doped diamond anode and an air-diffusion cathode for H2O2 electrogeneration, and four-electrode combined cells containing the above pair of electrodes coupled in parallel to a Pt anode and a carbon-felt cathode, have been used to degrade the pharmaceutical ?-blocker atenolol by electro-Fenton and photoelectro-Fenton methods. In these processes, organics are mainly oxidized with hydroxyl

Eloy Isarain-Chávez; Conchita Arias; Pere Lluís Cabot; Francesc Centellas; Rosa María Rodríguez; José Antonio Garrido; Enric Brillas

2010-01-01

4

Investigation of the Gas-Diffusion-Electrode Used as Lithium/Air Cathode in Non-aqueous Electrolyte and the Importance of Carbon Material Porosity  

SciTech Connect

The gas-diffusion-electrode used in a Li-air cell has been studied in a unique homemade electrochemical cell. Three major obstacles for the development of a feasible Li-air system were discussed with a focus on the development of a functional gas-diffusion-electrode in non-aqueous electrolytes and the way of avoiding the passivation of gas-diffusion-electrodes caused by the deposition of the reduction products. It is the first time that the importance of establishing the 3-phase electrochemical interface in non-aqueous electrolyte is demonstrated by creating air-diffusion paths and an air saturated portion for an air cathode. A model mechanism of electrode passivation by the reaction products was also proposed. Lithium oxides formed during O{sub 2} reduction tend to block small pores, preventing them from further utilization in the electrochemical reaction. On the other hand, lithium oxides would accumulate inside the large pores during the reduction until the density of oxides becomes high enough to choke-off the mass transfer. Carbon materials with a high surface area associated with larger pores should be selected to make the gas-diffusion-electrode for Li-air battery. For the first time, a near linear relationship between the capacity of GDE in a non-aqueous electrolyte and the average pore diameter was demonstrated, which could be used to estimate the capacity of the GDE quantitatively.

Qu, D.; Yang, X.; Tran, C.

2010-04-02

5

Nonaqueous Lithium-Air Batteries with an Advanced Cathode Structure  

Microsoft Academic Search

Lithium-air batteries consist of lithium anodes electrochemically coupled to atmospheric oxygen through an air cathode. Oxygen gas introduced into the battery through an air cathode is essentially an unlimited cathode reactant source. Theoretically with oxygen as an unlimited cathode reactant, the capacity of the battery is limited by the Li anode. The theoretical specific energy of the Li-oxygen cell is

Arthur Dobley; Joseph DiCarlo; K. M. Abraham

6

Diffusion-limited model for a lithium\\/air battery with an organic electrolyte  

Microsoft Academic Search

A diffusion-limited transient mathematical model for a lithium\\/air cell, with the air cathode pores flooded with an organic electrolyte, has been developed. During cell discharge, the cathode pore radius profile is reflective of the distribution of the lithium peroxide product in the cathode. The cathode pore radius profile has been predicted as a function of time, current density, oxygen gas

S. S. Sandhu; J. P. Fellner; G. W. Brutchen

2007-01-01

7

Bioelectricity production by air cathode microbial fuel cell  

Microsoft Academic Search

Microbial fuel cells (MFCs) are an actual biochemical system; electricity is generated via oxidation of biodegradable organic matter in the presence of active biocatalyst. The active biocatalyst or enzyme can generate electrons (e?) and protons (H+) from organic substrate. The generated electrons are transferred by anode to cathode through an external circuit. In the cathode compartment protons have to diffuse

Ali Tardast; Ghasem Najafpour; Mostafa Rahimnejad; Ali Asghar Ghoreyshi; Hossein Zare; Kasra Pirzadeh

2012-01-01

8

Hot hollow cathode diffuse arc deposition of chromium nitride films  

NASA Astrophysics Data System (ADS)

The hollow cathode in the diffuse arc regime (arc with hot thermionic cathode) was used for deposition of chromium and chromium nitride films. The chromium hollow cathode serving as a gas inlet was connected to a radio frequency (rf) generator with the rf power up to 350 W. The process of generation and performance of the hollow cathode discharge and its transition to the arc regime was examined for different gases. The comparison is also given with other target metals. The reactive process of CrN deposition was investigated. Films were deposited on unheated silicon and steel substrates. Highly oriented crystalline CrN films were deposited at rates up to 4.5 ?m/min. The effect of process parameters and their correlation to properties (microcrystalline structure, hardness, and deposition rate) of CrN is given.

Baránková, H.; Bárdoš, L.; Gustavsson, L.-E.

2005-07-01

9

Anomalous Discharge Product Distribution in Lithium-Air Cathodes: A Three Dimensional View  

SciTech Connect

Using neutron tomographic imaging we report for the first time three dimensional spatial distribution of lithium product distribution in electrochemically discharged Lithium-Air cathodes. Neutron imaging finds a non-uniform lithium product distribution across the electrode thickness; the lithium species concentration being higher near the edges of the Li-air electrode and relatively uniform in the center of the electrode. The experimental neutron images were analyzed in context of results obtained from 3D modeling of the spatial lithium product distribution using a kinetically coupled diffusion based transport model that accounts for the dynamical reaction rate dependence on the discharge product formation, porosity changes and mass transfer.

Nanda, Jagjit [ORNL; Allu, Srikanth [ORNL; Bilheux, Hassina Z [ORNL; Dudney, Nancy J [ORNL; Pannala, Sreekanth [ORNL; Veith, Gabriel M [ORNL; Voisin, Sophie [ORNL; Walker, Lakeisha MH [ORNL; Archibald, Richard K [ORNL

2012-01-01

10

The roles and electrochemical characterizations of activated carbon in zinc air battery cathodes  

Microsoft Academic Search

We prepared cathodes with various types of activated carbon and measured the cathodes’ electrochemical performance according to the kind of activated carbon. Activated carbon supplies airflow channels and reaction sites in the cathode of zinc air batteries. When we use activated carbon with a high specific surface area as the cathode's catalyst substrate, we expect high electrochemical performance because this

Seung-Wook Eom; Chang-Woo Lee; Mun-Soo Yun; Yang-Kook Sun

2006-01-01

11

The Arc Cathode Spot and Its Relation to the Diffusion of Ions within the Cathode Metal  

Microsoft Academic Search

Kesaev's recent data on the stability of vacuum arcs for a wide variety of solid and liquid cathodes furnish a greatly expanded range of criteria for determining the mechanism of the cathode spot. The large effects of phase and crystalline texture of the cathode suggest that an essential process occurs within the cathode metal itself. This is thought to be

Kenneth H. Kingdon

1965-01-01

12

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

SciTech Connect

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.

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

2011-09-15

13

A li-o2/air battery using an inorganic solid-state air cathode.  

PubMed

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

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

2014-07-23

14

New structures of thin air cathodes for zinc–air batteries  

Microsoft Academic Search

Thin composite cathodes for air reduction were manufactured using microfibre-based papermaking technology. The electrodes have a thin structural design, less than 0.15 mm in thickness. Composite cathode materials for oxygen reduction applications were fabricated by entrapping carbon particles in a sinter-locked network of 2–8 µm diameter metal fibres. The thin structure not only results in electrodes that are 30–75% thinner

W. H. Zhu; B. A. Poole; D. R. Cahela; B. J. Tatarchuk

2003-01-01

15

Assessing durability of cathodes exposed to common air impurities  

NASA Astrophysics Data System (ADS)

Data are presented to quantify how common air non-condensable impurities such as NO 2, SO 2, and H 2S show a negative effect on the performance of PEMFCs. The severity of the effects of these impurities varies depending on the impurity, concentration, and dosage but in general the impurities containing sulfur showed a stronger effect than NO 2. Complete recovery of the cell performance is obtained after applying neat air following exposure to a total NO 2 dosage of 61.8 ?mol. However, to completely recover the cathode exposed to either 118.5 ?mol SO 2 or 2160 ?mol H 2S, cyclic voltammetry is required to oxidize the sulfur adsorbed on the Pt. The sulfur species formed on the Pt cathode after exposure to these impurities appear to be the same and it appears as strongly and weakly adsorbed sulfur on the Pt. The data show that the rate of poisoning of PEMFCs by NO 2 does not strongly depend on NO 2 bulk concentration but the rate of SO 2 poisoning of the cathode appear to be strongly dependent on the concentration of SO 2 in the bulk. Relatively high concentrations of impurities were used and the data also show that the cell performance could be totally recovered from NO 2 in neat air after repetitive cycles of exposure/no exposure of 5 ppm NO 2 for 12 h for three cycles (185.4 ?mol total dosage). On the other hand, only partial recovery from 5 ppm SO 2 was observed in each cycle and the performance continued to decrease in all the five poisoning cycles (592.5 ?mol total dosage).

Mohtadi, R.; Lee, W.-k.; Van Zee, J. W.

16

Review of Cold Cathode Research at the Air Force Research Laboratory  

Microsoft Academic Search

Over the last decade, the Air Force Research Laboratory, Directed Energy Directorate (AFRL\\/DE) has engaged in a high current density field emission cathode research program. This program explored the aspects of cathode materials as well as the details of cathode geometries and emission physics. This paper summarizes the results of this ongoing research effort to date. We review the history

Don Shiffler; Michael Haworth; Keith Cartwright; Ryan Umstattd; Mitch Ruebush; Susan Heidger; Matthew Lacour; Ken Golby; Don Sullivan; Peter Duselis; John Luginsland

2008-01-01

17

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

SciTech Connect

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.

None

2010-08-01

18

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

NASA Astrophysics Data System (ADS)

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 ?m, 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.

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

19

Diffusion of propyne (1); air (2)  

NASA Astrophysics Data System (ADS)

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) propyne; (2) air

Winkelmann, J.

20

Diffusion of propionic acid (1); air (2)  

NASA Astrophysics Data System (ADS)

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) propionic acid; (2) air

Winkelmann, J.

21

Nitrogen-doped carbon nanotubes as air cathode catalysts in zinc-air battery  

Microsoft Academic Search

Nitrogen-doped carbon nanotubes (N-CNTs) derived from ethylenediamine precursor have been used as air cathode catalyst for zinc-air batteries (ZABs) in half cell and single cell. Investigation of N-CNTs employed a rotating disc electrode system revealed excellent catalytic activity towards oxygen reduction reaction (ORR) in alkaline electrolyte. The influence of alkaline electrolyte concentration on single cell performance of ZABs has also

Shaomin Zhu; Zhu Chen; Bing Li; Drew Higgins; Haijiang Wang; Hui Li; Zhongwei Chen

2011-01-01

22

Pre-acclimation of a wastewater inoculum to cellulose in an aqueous–cathode MEC improves power generation in air–cathode MFCs  

Microsoft Academic Search

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

Shaoan Cheng; Patrick Kiely; Bruce E. Logan

2011-01-01

23

Air stable hybrid organic-inorganic light emitting diodes using ZnO as the cathode  

Microsoft Academic Search

An air stable hybrid organic-inorganic light emitting device is presented. This architecture makes use of metal oxides as charge injecting materials into the light emitting polymer, avoiding the use of air sensitive cathodes commonly employed in organic light emitting diode manufacturing. We report the application of zinc oxide as a cathode in an organic light emitting device. This electroluminescent device

Henk J. Bolink; Eugenio Coronado; Diego Repetto; Michele Sessolo

2007-01-01

24

Highly durable and active non-precious air cathode catalyst for zinc air battery  

Microsoft Academic Search

The electrochemical stability of non-precious FeCo-EDA and commercial Pt\\/C cathode catalysts for zinc air battery have been compared using accelerated degradation test (ADT) in alkaline condition. Outstanding oxygen reduction reaction (ORR) stability of the FeCo-EDA catalyst was observed compared with the commercial Pt\\/C catalyst. The FeCo-EDA catalyst retained 80% of the initial mass activity for ORR whereas the commercial Pt\\/C

Zhu Chen; Ja-Yeon Choi; Haijiang Wang; Hui Li; Zhongwei Chen

2011-01-01

25

SOFC cathode\\/electrolyte interfaces. Part II: Study of NdAlO 3 diffusion barriers  

Microsoft Academic Search

The growth of La2Zr2O7 and SrZrO3 reaction layers at the cathode-electrolyte interface during the fabrication process and in operating conditions negatively affects the SOFC (solid oxide fuel cell) performance. In the present paper the effectiveness of diffusion barriers at the SOFC cathode-electrolyte interface is investigated. Thin layers of neodymium aluminate (NdAlO3) were evaporated onto yttria-stabilized zirconia (YSZ) substrates and characterized

C. Brugnoni; U. Ducati; C. Chemelli; M. Scagliotti; G. Chiodelli

1995-01-01

26

Hydrogen production in a microbial electrolysis cell with nickel-based gas diffusion cathodes  

Microsoft Academic Search

Gas diffusion cathodes with Ni alloy and Ni catalysts manufactured by chemical deposition were tested for H2 production in a microbial electrolysis cell (MEC). In a continuous flow MEC, multi-component cathodes containing Ni, Mo, Cr, and Fe, at a total catalyst load of 1mgcm?2 on carbon support demonstrated stable H2 production at rates of 2.8–3.7?L?LR?1?d?1 with only 5% methane in

M.-F. Manuel; V. Neburchilov; H. Wang; S. R. Guiot; B. Tartakovsky

2010-01-01

27

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

SciTech Connect

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}.

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

2000-03-20

28

Two-Phase Transport in Polymer Electrolyte Fuel Cells with Bilayer Cathode Gas Diffusion Media  

Microsoft Academic Search

2 framework is developed to analyze the two-phase transport in polymer electrolyte fuel cells with bilayer cathode gas diffusion media GDM, consisting of a coarse gas diffusion layer GDL with an average pore size around 10-30 m and a microporous layer MPL with an average pore size ranging from 0.1 to 1 m. Effects of the relevant properties of the

Ugur Pasaogullari; Chao-Yang Wang; Ken S. Chenb

2005-01-01

29

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

Microsoft Academic Search

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 were decolorized to a similar extent, at averages of 78, 95, 53, 93 and 74%, respectively,

Mert Kumru; Hilal Eren; Tunc Catal; Hakan Bermek; Alper Tunga Akarsuba??

2012-01-01

30

Silver nanoparticle-decorated carbon nanotubes as bifunctional gas-diffusion electrodes for zinc–air batteries  

Microsoft Academic Search

Thin, lightweight, and flexible gas-diffusion electrodes (GDEs) based on freestanding entangled networks of single-walled carbon nanotubes (SWNTs) decorated with Ag nanoparticles (AgNPs) are tested as the air-breathing cathode in a zinc–air battery. The SWNT networks provide a highly porous surface for active oxygen absorption and diffusion. The high conductivity of SWNTs coupled with the catalytic activity of AgNPs for oxygen

T. Wang; M. Kaempgen; P. Nopphawan; G. Wee; S. Mhaisalkar; M. Srinivasan

2010-01-01

31

Nanoscale mapping of ion diffusion in a lithium-ion battery cathode  

NASA Astrophysics Data System (ADS)

The movement of lithium ions into and out of electrodes is central to the operation of lithium-ion batteries. Although this process has been extensively studied at the device level, it remains insufficiently characterized at the nanoscale level of grain clusters, single grains and defects. Here, we probe the spatial variation of lithium-ion diffusion times in the battery-cathode material LiCoO2 at a resolution of ~100 nm by using an atomic force microscope to both redistribute lithium ions and measure the resulting cathode deformation. The relationship between diffusion and single grains and grain boundaries is observed, revealing that the diffusion coefficient increases for certain grain orientations and single-grain boundaries. This knowledge provides feedback to improve understanding of the nanoscale mechanisms underpinning lithium-ion battery operation.

Balke, N.; Jesse, S.; Morozovska, A. N.; Eliseev, E.; Chung, D. W.; Kim, Y.; Adamczyk, L.; García, R. E.; Dudney, N.; Kalinin, S. V.

2010-10-01

32

Isotope effect of mercury diffusion in air.  

PubMed

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

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

2014-01-01

33

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

Microsoft Academic Search

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

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

2000-01-01

34

Electrodeposition of nickel particles on a gas diffusion cathode for hydrogen production in a microbial electrolysis cell  

Microsoft Academic Search

Gas diffusion cathodes with electrodeposited nickel (Ni) particles have been developed and tested for hydrogen production in a continuous flow microbial electrolysis cell (MEC). A high catalytic activity of electrodeposited Ni particles in such a MEC was obtained without a proton exchange membrane, i.e. under direct cathode exposure to anodic liquid. Co-electrodeposition of Pt and Ni particles did not improve

S. Hrapovic; M.-F. Manuel; J. H. T. Luong; S. R. Guiot; B. Tartakovsky

2010-01-01

35

Anisotropic Heat and Water Transport in a PEFC Cathode Gas Diffusion Layer  

Microsoft Academic Search

A nonisothermal, two-phase model was developed to investigate simultaneous heat and mass transfer in the cathode gas diffusion layer GDL of a polymer electrolyte fuel cell PEFC. The model was applied in two-dimensions with the in-plane i.e., channel-to-land and through-plane i.e., catalyst layer-to-channel directions to investigate the effects of anisotropy of GDL. For the first time, the anisotropy in the

Ugur Pasaogullari; Partha P. Mukherjee; Chao-Yang Wang; Ken S. Chenc

2007-01-01

36

Optimizing Oxygen Diffusion in Cathode Materials for Solid Oxide Fuel Cells  

NASA Astrophysics Data System (ADS)

Recent investigations have revealed that the Ruddlesden-Popper series (An+1BnO3n+1) and the layered perovskite LnBaCo2O5+? (Ln = rare-earth cations) are promising as cathodes for intermediate temperature solid oxide fuel cells. For these to be economical the oxygen diffusion must be maximized. Based on atomistic simulations, we propose strategies for optimizing oxygen diffusion in these materials by modifying the oxygen stoichiometry, the composition and cation disorder. The present investigation is focused on La2CoO4+? and GdBaCo2O5+? and the results are discussed in view of recent experimental and theoretical studies.

Chroneos, A.; Parfitt, D.; Vovk, R. V.; Goulatis, I. L.

2012-12-01

37

Anomalous Discharge Product Distribution in Lithium-Air Cathodes: A Three Dimensional View  

Microsoft Academic Search

Using neutron tomographic imaging we report for the first time three dimensional spatial distribution of lithium product distribution in electrochemically discharged Lithium-Air cathodes. Neutron imaging finds a non-uniform lithium product distribution across the electrode thickness; the lithium species concentration being higher near the edges of the Li-air electrode and relatively uniform in the center of the electrode. The experimental neutron

Jagjit Nanda; Srikanth Allu; Hassina Z Bilheux; Nancy J Dudney; Sreekanth Pannala; Gabriel M Veith; Sophie Voisin; Lakeisha MH Walker; Richard K Archibald

2012-01-01

38

Portable power source based on air-hydrogen fuel cells with free-breathing cathodes  

NASA Astrophysics Data System (ADS)

Portable power source based on air-hydrogen fuel cells (FCs) operating in a free-breathing cathode regime has been developed. At a volume of 100 cm3, the source has a power capacity of 8.5 W h and generates a power of 2 W that is independent of the temperature within 5-40°C and the relative humidity of the ambient air within 40-98%. With respect to the specific energy characteristics, the proposed PTI type device exceeds other air-hydrogen FCs and in some respects is even superior to power sources based on air-methanol FCs.

Gurevich, S. A.; Terukov, E. I.; Kon'kov, O. I.; Tomasov, A. A.; Zelenina, N. K.; Kompan, M. E.; Gorokhov, M. V.; Astrova, E. V.; Andronikov, D. A.; Zabrodskii, A. G.

2011-05-01

39

Phosphorus-doped carbon derived from cellulose phosphate as efficient catalyst for air-cathode in microbial fuel cells  

NASA Astrophysics Data System (ADS)

Phosphorus-doped (P-doped) carbon was prepared via direct pyrolysis of cellulose phosphate for efficient oxygen reduction catalyst in air-cathode of microbial fuel cells (MFCs). Air-cathodes with P-doped carbon catalysts were assembled by rolling method and their performances in MFCs were studied. A maximum power density of 1312 ± 82 mW m-2 was produced by air-cathode with P-doped carbon catalyst prepared at 1000 °C. This result was higher than the air-cathode with Pt/C catalyst and three times as that with P-free carbon catalyst derived from pure cellulose. This study demonstrated that the P-doped carbon derived from cellulose phosphate was a cost-efficient and promising cathodic catalyst for scale-up MFCs.

Liu, Qin; Chen, Shuiliang; Zhou, Yan; Zheng, Suqi; Hou, Haoqing; Zhao, Feng

40

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

PubMed

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

Islam, M Saiful; Fisher, Craig A J

2014-01-01

41

Plant air systems safety study: Portsmouth Gaseous Diffusion Plant  

SciTech Connect

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

Not Available

1982-05-01

42

Carnation-like MnO2 modified activated carbon air cathode improve power generation in microbial fuel cells  

NASA Astrophysics Data System (ADS)

Highly active and low-cost electrocatalysts are of great importance for large-scale commercial applications of microbial fuel cells (MFCs). In this work, we prepared an activated carbon (AC) air cathode containing electrodeposited ?-MnO2 using a potentiostatic method. The results indicated that carnation-like MnO2 crystals were bound to the surface of the AC air cathode after a deposition time of 10 min, which greatly improved the performance of the cathode. BET analysis results demonstrated that the electrodeposition of MnO2 decreased the micropore surface area of the cathode but increased the mesopore surface area. When compared with a bare AC air cathode, the electrodeposited MnO2 cathode exhibited higher catalytic activity for oxygen reduction reaction. The maximum power density of the MFC equipped with the electrodeposited MnO2 AC air cathode was 1554 mW m-2, which is 1.5 times higher than the control cathode.

Zhang, Peng; Li, Kexun; Liu, Xianhua

2014-10-01

43

Characterization of a Microhollow Cathode Discharge Plasma in Helium or Air with Water Vapor  

NASA Astrophysics Data System (ADS)

Microhollow cathode discharge (MHCD) plasmas were generated in gas mixtures containing water vapor at pressures of up to 100 kPa of He or 20 kPa of air. The cathode diameter was 1.0 mm with a length of 2.0 mm. The electrical characteristics showed an abnormal glow mode. Spectroscopic measurements were carried out to examine the plasma and radicals. An analysis of the spectral profile of H? at 656.3 nm enabled a derivation of the electron densities, namely 2×1014 cm-3 (at 10 kPa) and 6×1014 cm-3 (at 4 kPa) for the helium and air atmospheres, respectively, in the negative glow region. By comparing the observed OH radical spectra with those calculated by the simulation code LIFBASE, the gas temperature was deduced to be 900 K for 4 kPa of He at a discharge current of 50 mA.

Fukuhara, D.; Namba, S.; Kozue, K.; Yamasaki, T.; Takiyama, K.

2013-02-01

44

Pre-acclimation of a wastewater inoculum to cellulose in an aqueous-cathode MEC improves power generation in air-cathode MFCs.  

PubMed

Cellulose has been used in two-chamber microbial fuel cells (MFCs), but power densities were low. Higher power densities can be achieved in air-cathode MFCs using an inoculum from a two-chamber, aqueous-cathode microbial electrolysis cell (MEC). Air-cathode MFCs with this inoculum produced maximum power densities of 1070 mW m(-2) (cathode surface area) in single-chamber and 880 mW m(-2) in two-chamber MFCs. Coulombic efficiencies ranged from 25% to 50%, and COD removals were 50-70% based on total cellulose removals of 60-80%. Decreasing the reactor volume from 26 to 14 mL (while maintaining constant electrode spacing) decreased power output by 66% (from 526 to 180 mW m(-2)) due to a reduction in total mass of cellulose added. These results demonstrate that air-cathode MFCs can produce high power densities with cellulose following proper acclimation of the inoculum, and that organic loading rates are important for maximizing power densities from particulate substrates. PMID:20580223

Cheng, Shaoan; Kiely, Patrick; Logan, Bruce E

2011-01-01

45

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

Microsoft Academic Search

A baffled air-cathode microbial fuel cell (BAFMFC) was designed and operated under continuous flow. With glucose fed as substrate, an average voltage of 652 mV was obtained under the external resistance of 1000 X (30 C). The maximum power density was 15.2 W\\/m 3 with the chemical oxygen demand (COD) removal rate of 88.0%. The overall resistance was 13.7 X

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

2010-01-01

46

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

Microsoft Academic Search

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

Yong Yuan; Shungui Zhou; Li Zhuang

2010-01-01

47

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

NASA Astrophysics Data System (ADS)

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

Oloniyo, Olubukun; Kumar, Senthil; Scott, Keith

2012-05-01

48

Diffusion of pent-1-ene (1); air (2)  

NASA Astrophysics Data System (ADS)

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

Winkelmann, J.

49

Diffusion of propionic acid ethyl ester (1); air (2)  

NASA Astrophysics Data System (ADS)

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) propionic acid ethyl ester; (2) air

Winkelmann, J.

50

Diffusion of propionic acid pentyl ester (1); air (2)  

NASA Astrophysics Data System (ADS)

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) propionic acid pentyl ester; (2) air

Winkelmann, J.

51

Diffusion of propionic acid methyl ester (1); air (2)  

NASA Astrophysics Data System (ADS)

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) propionic acid methyl ester; (2) air

Winkelmann, J.

52

Diffusion of propionic acid isobutyl ester (1); air (2)  

NASA Astrophysics Data System (ADS)

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) propionic acid isobutyl ester; (2) air

Winkelmann, J.

53

Diffusion of propionic acid butyl ester (1); air (2)  

NASA Astrophysics Data System (ADS)

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) propionic acid butyl ester; (2) air

Winkelmann, J.

54

Soot Formation in Hydrocarbon/Air Laminar Jet Diffusion Flames.  

National Technical Information Service (NTIS)

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 potent...

P. B. Sunderland G. M. Faeth

1994-01-01

55

The Diffusion of Air Through Monel Metal  

Microsoft Academic Search

The rate at which gases from the atmosphere diffuse through monel metal at various temperatures has been observed. An evacuated heavy-walled metal tube, a section of which was machined to a thin wall, was heated in a furnace. The rate at which the pressure inside the tube increased as a result of the diffusion of gases from the atmosphere was

H. S. Coleman; H. L. Yeagley

1943-01-01

56

Electrochemical evaluation of La 1??? x Ca x CoO 3 cathode material for zinc air batteries application  

Microsoft Academic Search

We synthesized nano-sized La1???x\\u000a Ca\\u000a x\\u000a CoO3 (x?=?0.1–0.4) cathode catalysts for zinc air secondary batteries by the citrate method, and measured electrochemical characteristics\\u000a of the cathodes according to the cathode catalyst’s calcium content. We heat treated the prepared precursor at a calcination\\u000a temperature of 700°C, and examined it by XRD analysis and electrochemical evaluation. We examined the prepared La1???x\\u000a Ca

Seung-Wook Eom; Se-Young Ahn; Ik-Jun Kim; Yang-Kook Sun; Hyun-Soo Kim

2009-01-01

57

A Single-Chamber Microbial Fuel Cell without an Air Cathode  

PubMed Central

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

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

2012-01-01

58

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

PubMed

Microbial fuel cells (MFCs) represent a novel technology for wastewater treatment with electricity production. Electricity generation with simultaneous nitrate reduction in a single-chamber MFC without air cathode was studied, using glucose (1 mM) as the carbon source and nitrate (1 mM) as the final electron acceptor employed by Bacillus subtilis under anaerobic conditions. Increasing current as a function of decreased nitrate concentration and an increase in biomass were observed with a maximum current of 0.4 mA obtained at an external resistance (R(ext)) of 1 K? without a platinum catalyst of air cathode. A decreased current with complete nitrate reduction, with further recovery of the current immediately after nitrate addition, indicated the dependence of B. subtilis on nitrate as an electron acceptor to efficiently produce electricity. A power density of 0.0019 mW/cm(2) was achieved at an R(ext) of 220 ?. Cyclic voltammograms (CV) showed direct electron transfer with the involvement of mediators in the MFC. The low coulombic efficiency (CE) of 11% was mainly attributed to glucose fermentation. These results demonstrated that electricity generation is possible from wastewater containing nitrate, and this represents an alternative technology for the cost-effective and environmentally benign treatment of wastewater. PMID:22489190

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

2012-01-01

59

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

SciTech Connect

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

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

1996-10-01

60

Soot Formation in Hydrocarbon/Air Laminar Jet Diffusion Flames  

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

61

Diffusion barriers in modified air brazes  

DOEpatents

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.

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

2013-04-23

62

The electrochemical behavior of three air cathodes for microbial electrochemical system (MES) under meter scale water pressure  

NASA Astrophysics Data System (ADS)

To produce cathodes with high water pressure tolerance for the practical application of microbial electrochemical system (MES), a 3-m test configuration is set up. Three kinds of cathodes, including Pt-CC (carbon cloth with platinum carbon), Pt-CM (carbon mesh with platinum carbon), and AC-MM (metal mesh with activated carbon), are investigated. The electrochemical performances of these cathodes are tested with linear sweep voltammetry under varied water pressures. Current densities of Pt-CC and Pt-CM increase with the rising water pressures till the maximum endurable water head, which are 100 cm for Pt-CC and 130 cm for Pt-CM. Yet electrochemical performances of AC-MM remained stable under the tested water pressure range from 0 to 30 KPa. The deformation of cathodes under varied water pressures causes the changes of cathode performances. The curvature degrees of cathodes relate to their mechanical properties. Elastic modulus of AC-MM is 4 ± 0.4 × 103 MPa, which is over 10 times larger than that of Pt-CM and over 60 times larger than that of Pt-CC. The best mechanical properties prevent AC-MM from the substantial deformation and the consequent lacerations and water flooding of diffusion layers.

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

2014-12-01

63

Modification of air standard composition by diffusive and surface processes  

Microsoft Academic Search

We present experimental evidence of modification of O2\\/N2, Ar\\/N2, 29N2\\/28N2, 34O2\\/32O2 ratios and CO2 mole fraction in dry air standards resulting from gas handling. Correlated variations among high precision measurements of multiple molecular pair ratios show diffusive fractionation to be the main modifying process. This mechanism can account for much of the previously unexplained CO2 instability commonly observed in air

R. L. Langenfelds; M. V. van der Schoot; R. J. Francey; L. P. Steele; M. Schmidt; H. Mukai

2005-01-01

64

Superior catalytic activity of nitrogen-doped graphene cathodes for high energy capacity sodium-air batteries.  

PubMed

Nitrogen-doped graphene nanosheets (N-GNSs) displayed a discharge capacity two times greater than their pristine counterpart, as well as superior electrocatalytic activity as a cathode material for sodium-air batteries. The enhanced performance of N-GNSs is attributed to the active sites introduced by nitrogen doping. PMID:24136098

Li, Yongliang; Yadegari, Hossein; Li, Xifei; Banis, Mohammad N; Li, Ruying; Sun, Xueliang

2013-12-28

65

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

PubMed

Scaling up microbial fuel cells (MFCs) requires a better understanding the importance of the different factors such as electrode surface area and reactor geometry relative to solution conditions such as conductivity and substrate concentration. It is shown here that the substrate concentration has significant effect on anode but not cathode performance, while the solution conductivity has a significant effect on the cathode but not the anode. The cathode surface area is always important for increasing power. Doubling the cathode size can increase power by 62% with domestic wastewater, but doubling the anode size increases power by 12%. Volumetric power density was shown to be a linear function of cathode specific surface area (ratio of cathode surface area to reactor volume), but the impact of cathode size on power generation depended on the substrate strength (COD) and conductivity. These results demonstrate the cathode specific surface area is the most critical factor for scaling-up MFCs to obtain high power densities. PMID:21273062

Cheng, Shaoan; Logan, Bruce E

2011-03-01

66

Measuring radon concentration in air using a diffusion cloud chamber  

NASA Astrophysics Data System (ADS)

Radon concentration in air is a major concern in lung cancer studies. A traditional technique used to measure radon abundance is the charcoal canister method. We propose a novel technique using a diffusion cloud chamber. This technique is simpler and can easily be used for physics demonstrations for high school and university students.

Cases, R.; Ros, E.; Zúñiga, J.

2011-09-01

67

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

SciTech Connect

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.

Jang, Y.-I.

2001-10-02

68

Accelerated OH(-) Transport in Activated Carbon Air Cathode by Modification of Quaternary Ammonium for Microbial Fuel Cells.  

PubMed

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

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

2014-04-01

69

MEA design for low water crossover in air-breathing DMFC  

Microsoft Academic Search

The water crossover behavior in air-breathing direct methanol fuel cell (DMFC) was studied with varying structural variables of membrane electrode assembly (MEA), such as existence of microporous layer (MPL) in cathode diffusion layer, hydrophobicity of cathode backing layer, and membrane thickness. Water crossover from anode to cathode was lowered by the introduction of MPL to cathode backing layer, the reduction

Kah-Young Song; Han-Kyu Lee; Hee-Tak Kim

2007-01-01

70

Electronic modification of Pt via Ti and Se as tolerant cathodes in air-breathing methanol microfluidic fuel cells.  

PubMed

We reported herein on the use of tolerant cathode catalysts such as carbon supported PtxTiy and/or PtxSey nanomaterials in an air-breathing methanol microfluidic fuel cell. In order to show the improvement of mixed-reactant fuel cell (MRFC) performances obtained with the developed tolerant catalysts, a classical Pt/C nanomaterial was used for comparison. Using 5 M methanol concentration in a situation where the fuel crossover is 100% (MRFC-mixed reactant fuel cell application), the maximum power density of the fuel cell with a Pt/C cathodic catalyst decreased by 80% in comparison with what is observed in the laminar flow fuel cell (LFFC) configuration. With PtxTiy/C and PtxSey/C cathode nanomaterials, the performance loss was only 55% and 20%, respectively. The evaluation of the tolerant cathode catalysts in an air-breathing microfluidic fuel cell suggests the development of a novel nanometric system that will not be size restricted. These interesting results are the consequence of the high methanol tolerance of these advanced electrocatalysts via surface electronic modification of Pt. Herein we used X-ray photoelectron and in situ FTIR spectroscopies to investigate the origin of the high methanol tolerance on modified Pt catalysts. PMID:24473103

Ma, Jiwei; Habrioux, Aurélien; Morais, Cláudia; Alonso-Vante, Nicolas

2014-07-21

71

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

PubMed

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

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

2010-01-01

72

Advances and trends in primary and small secondary batteries with zinc anodes and manganese dioxide and\\/or air cathodes  

Microsoft Academic Search

Incremental improvements continue to be made year by year in the consumer carbon-zinc and alkaline zinc-manganese dioxide cells. In addition, primary and secondary zinc-air cells many with substantial amounts of manganese dioxide in the cathode are becoming more common in consumer use. The gain in the past fifteen years in the carbon zinc cells approaches fifteen percent and that in

Brooke Schumm

2000-01-01

73

Comparison of Electrode Reduction Activities of Geobacter sulfurreducens and an Enriched Consortium in an Air-Cathode Microbial Fuel Cell  

Microsoft Academic Search

An electricity-generating bacterium, Geobacter sulfurreducens PCA, was inoculated into a single-chamber, air-cathode microbial fuel cell (MFC) in order to determine the maximum electron transfer rate from bacteria to the anode. To create anodic reaction-limiting conditions, where electron transfer from bacteria to the anode is the rate-limiting step, anodes with electrogenic biofilms were reduced in size and tests were conducted using

S. Ishii; K. Watanabe; S. Yabuki; B. E. Logan; Y. Sekiguchi

2008-01-01

74

Development of a cathode-directed streamer discharge in air at different pressures: Experiment and comparison with direct numerical simulation  

Microsoft Academic Search

The results are given of an experimental investigation of a cathode-directed streamer discharge in synthetic air in the pressure range from 760to300torr and their comparison with the results of direct numerical simulation in a 2D hydrodynamic approximation. The pattern of discharge branching upon variation of pressure is investigated experimentally. The results are given of comparison of the predicted and measured

S. Pancheshnyi; M. Nudnova; A. Starikovskii

2005-01-01

75

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

Microsoft Academic Search

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

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

2009-01-01

76

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

PubMed

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

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

2012-05-01

77

Microstructure of the current channel of an atmospheric-pressure diffuse discharge in a rod-plane air gap  

NASA Astrophysics Data System (ADS)

The multichannel structure of the current channel of an atmospheric-pressure diffuse discharge excited in a 10-cm rod-plane air gap was investigated using the imprint technique. A voltage pulse with an amplitude of 240 kV, a duration of 180 ns, and a rise time of 14 ns was applied to a 1-cm-diameter bullet-shaped cathode with a tip curvature radius of 0.2 mm; the discharge current reached 350 A. It is found that the diameter of the discharge channel in the anode plane varies in the range 2.5-9.7 mm from shot to shot. The overall imprint of the current channel is formed of 170-9500 imprints of microchannels with an average diameter of 5-20 ?m. The parameters of the observed microstructure do not correlate with variations in the main electric characteristics of the discharge and the parameters of the generated X-ray pulse. It is shown that the formation of the microstructure is related to the onset of cathode-directed plasma structures developing from the anode. It is suggested that the same mechanism is responsible for both the formation of the current channels structure and the anode microstructure of diffuse nanosecond discharges developing in atmospheric-pressure air gaps with a highly nonuniform electric field.

Rep'ev, A. G.; Repin, P. B.; Pokrovski?, V. S.

2007-01-01

78

Development of a cathode-directed streamer discharge in air at different pressures: experiment and comparison with direct numerical simulation.  

PubMed

The results are given of an experimental investigation of a cathode-directed streamer discharge in synthetic air in the pressure range from 760 to 300 torr and their comparison with the results of direct numerical simulation in a 2D hydrodynamic approximation. The pattern of discharge branching upon variation of pressure is investigated experimentally. The results are given of comparison of the predicted and measured values of anode current, streamer propagation velocity, and channel diameter. It has been demonstrated that the electric field in the streamer head is hardly affected by the pressure decrease, while the electron concentration decreases with pressure by an order of magnitude. At the same time, production of chemical species in a cathode-directed streamer discharge varies at a rate of at least the second power of inverse pressure. PMID:15697735

Pancheshnyi, S; Nudnova, M; Starikovskii, A

2005-01-01

79

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

SciTech Connect

The oxygen diffusion coefficient (D) and surface exchange coefficient (k) of a typical SOFC cathode material, La{sub 0.6}Sr{sub 0.4}Co{sub 0.2}Fe{sub 0.8}O{sub 3-?} (LSCF) were characterized by both electrical conductivity relaxation (ECR) and oxygen isotope exchange (IE) methods. Conductivity relaxation experiments were conducted at 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.

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

2013-05-05

80

Urban air pollution and atmospheric diffusion research in China  

NASA Astrophysics Data System (ADS)

Air pollution has become a serious problem in China as a result of that country's efforts in the last 30 years to become a great industrial power. The burning of coal, which currently provides over 70% of all China's energy needs, is a major source of air pollution. Because Chinese coal is high in sulfur and ash content and because most combustion devices in China have low efficiencies, SO2 and particulate emissions are a serious problem and are comparable to or exceed those found in many countries that are much more industrialized. Although most coal is burned in North China, acid precipitation is most severe in South China because of the lack of buffering loess dust found in the former region. The Chinese government has already taken major steps to mitigate air pollution, such as relocating polluting industries, supplying coal with lower sulfur content, using gas instead of coal for residential heating, and levying fines on industries that exceed pollution standards. Atmospheric environmental impact assessment (AEIA) is also required for all major new projects. This article describes three types of mathematical diffusion models and field and wind-tunnel experiments that are used in such assessments. The Chinese authorities believe that a range of technological, managerial, locational, and behavioral changes must be effected before the air of Chinese cities can be significantly improved.

Ning, Datong; Whitney, Joseph B.; Yap, David

1987-11-01

81

Momentum source model for CFD-simulation of nozzle duct air diffuser  

Microsoft Academic Search

Development of simplified models for air diffusers is essential for the applicability of CFD-modelling to room air flow simulation. The geometry of a diffuser is usually complex and, therefore, it is not possible to use an exact geometrical model in practical CFD-simulations. The model should be simple enough to enable the modelling of a room with several diffusers. In this

Hannu Koskela

2004-01-01

82

A diffusive sampling device for measurement of ammonia in air  

NASA Astrophysics Data System (ADS)

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.

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

2012-07-01

83

Degrading a mixture of three textile dyes using photo-assisted electrochemical process with BDD anode and O2-diffusion cathode.  

PubMed

In this paper, degradation of a mixture of three azo dyes was studied by the photo-assisted electrochemical process using an O2-diffusion cathode containing carbon nanotubes and boron-doped diamond (BDD) anode. The concentration of three textile dyes (C.I. Acid Orange 8 (AO8), C.I. Acid Orange 10 (AO10), and C.I. Acid Orange 12 (AO12)) was determined simultaneously despite the severe overlap of their spectra. For this purpose, partial least square (PLS), as a multivariate calibration method, was utilized based on recording UV-Vis spectra during the decolorization process. Moreover, the central composite design was used for the modeling of photo-assisted electrochemical decolorization of the aqueous solutions containing three dyes. The investigated parameters were the initial concentration of three dyes, applied current and reaction time. Analysis of variance (ANOVA) revealed that the obtained regression models match the experimental results well with R (Khataee et al. 2010, Clean-Soil Air Water 38 (1):96-103, 2010) of 0.972, 0.971, and 0.957 for AO8, AO10, and AO12, respectively. Three-dimensional surface and contour plots were applied to describe the relation between experimental conditions and the observed response. The results of TOC analysis confirmed good ability of proposed photo-assisted electrochemical process for degradation and mineralization of textile industry wastewater. PMID:24723345

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

2014-07-01

84

Characteristics and continuous operation of floating air-cathode microbial fuel cell (FA-MFC) for wastewater treatment and electricity generation  

Microsoft Academic Search

Microbial fuel cell with floating air-cathode is developed for not only wastewater treatment but also electricity generation\\u000a from the wastewater. Graphite felt and carbon cloth coated with Pt of 5 gm?2 are used as anode and cathode electrodes in this system, respectively. When organic loading rate is 15.38 kgCODm?3day?1, maximum power density is 119.7 mWm?2 with about 60% of Coulombic

Kyuseon Yoo; Young-Chae Song; Song-Keun Lee

2011-01-01

85

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

Microsoft Academic Search

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

Jian Sun; Yongyou Hu; Zhe Bi; Yunqing Cao

2009-01-01

86

Performance and microbial ecology of air-cathode microbial fuel cells with layered electrode assemblies  

Microsoft Academic Search

Microbial fuel cells (MFCs) can be built with layered electrode assemblies, where the anode, proton exchange membrane (PEM),\\u000a and cathode are pressed into a single unit. We studied the performance and microbial community structure of MFCs with layered\\u000a assemblies, addressing the effect of materials and oxygen crossover on the community structure. Four MFCs with layered assemblies\\u000a were constructed using Nafion

Caitlyn S. Butler; Robert Nerenberg

2010-01-01

87

Nitrogen-doped carbon nanotubes as cathode for lithium–air batteries  

Microsoft Academic Search

Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by a floating catalyst chemical vapor deposition (FCCVD) method. Various techniques including X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy revealed the morphology and structure of CNTs and N-CNTs as well confirmed the existence of incorporated nitrogen (10.2at.%) in N-CNTs. N-CNTs were investigated as cathode material

Yongliang Li; Jiajun Wang; Xifei Li; Jian Liu; Dongsheng Geng; Jinli Yang; Ruying Li; Xueliang Sun

2011-01-01

88

Assessment of air cathodes for metal\\/air batteries. Project 65012 final report, September--December 1978  

Microsoft Academic Search

Of the advanced battery systems currently being evaluated for electric vehicle propulsion, metal\\/air batteries are particularly attractive because the oxidant does not require storage. Many problems can be eliminated if the battery is modified to an acid electrolyte system. The air electrode is the major problem limiting the development of acid electrolyte zinc\\/air batteries. The purpose of this literature study

M. J. Powers; A. F. Sammells; K. F. Blurton

1979-01-01

89

Investigation of soot formation and temperature field in laminar diffusion flames of LPG–air mixture  

Microsoft Academic Search

Soot formation and burnout were studied at atmospheric pressure in co-flowing, axisymmetric, buoyant laminar diffusion flames and double flames of liquefied petroleum gases (LPG)–air mixtures. In diffusion flames, two different fuel flow rates were examined. In double flames, three different primary air flow rates were examined. A soot sampling probe and a thermocouple were used to measure the local soot

Haroun A. K. Shahad; Yassar K. A. Mohammed

2000-01-01

90

Diffusion of 4-methyl-pent-3-en-2-one (1); air (2)  

NASA Astrophysics Data System (ADS)

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

Winkelmann, J.

91

Comparison of Electrode Reduction Activities of Geobacter sulfurreducens and an Enriched Consortium in an Air-Cathode Microbial Fuel Cell? †  

PubMed Central

An electricity-generating bacterium, Geobacter sulfurreducens PCA, was inoculated into a single-chamber, air-cathode microbial fuel cell (MFC) in order to determine the maximum electron transfer rate from bacteria to the anode. To create anodic reaction-limiting conditions, where electron transfer from bacteria to the anode is the rate-limiting step, anodes with electrogenic biofilms were reduced in size and tests were conducted using anodes of six different sizes. The smallest anode (7 cm2, or 1.5 times larger than the cathode) achieved an anodic reaction-limiting condition as a result of a limited mass of bacteria on the electrode. Under these conditions, the limiting current density reached a maximum of 1,530 mA/m2, and power density reached a maximum of 461 mW/m2. Per-biomass efficiency of the electron transfer rate was constant at 32 fmol cell?1 day?1 (178 ?mol g of protein?1 min?1), a rate comparable to that with solid iron as the electron acceptor but lower than rates achieved with fumarate or soluble iron. In comparison, an enriched electricity-generating consortium reached 374 ?mol g of protein?1 min?1 under the same conditions, suggesting that the consortium had a much greater capacity for electrode reduction. These results demonstrate that per-biomass electrode reduction rates (calculated by current density and biomass density on the anode) can be used to help make better comparisons of electrogenic activity in MFCs.

Ishii, Shun'ichi; Watanabe, Kazuya; Yabuki, Soichi; Logan, Bruce E.; Sekiguchi, Yuji

2008-01-01

92

Effects of cathode gas diffusion layer design on polymer electrolyte membrane fuel cell water management and performance  

Microsoft Academic Search

The effects of a microporous layer (MPL) on performance and water management of polymer electrolyte fuel cells are investigated. The presence of an MPL on the cathode side is found to slightly improve performance, although the voltage gain is less significant than that obtained by wetter reactants. The effect of the MPL on water management depends on the cathode inlet-gas

Tak Cheung Yau; Massimiliano Cimenti; Xiaotao Bi; Jürgen Stumper

2011-01-01

93

Electrochemical characteriztion of the bioanode during simultaneous azo dye decolorization and bioelectricity generation in an air-cathode single chambered microbial fuel cell  

Microsoft Academic Search

To achieve high power output based on simultaneously azo dye decolorization using microbial fuel cell (MFC), the bioanode responses during decolorization of a representative azo dye, Congo red, were investigated in an air-cathode single chambered MFC using representative electrochemical techniques. It has been found that the maximum stable voltage output was delayed due to slowly developed anode potential during Congo

Jian Sun; Yong-you Hu; Bin Hou

2011-01-01

94

On the Turbulent Diffusion in the Ground Air Layer.  

National Technical Information Service (NTIS)

The Monin-Obukhov theory represented vertical diffusion in the atmospheric surface boundary layer as a two-layer problem and presented formulas for unstable and stable stratification. Monin, however, was the first to describe diffusion in stable stratific...

D. Yordanov

1969-01-01

95

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

PubMed

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. PMID:23608821

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

2013-06-01

96

The Application of Graphene as a Support for Cathode Materials of Metal--Air Batteries  

NASA Astrophysics Data System (ADS)

Graphene was compared with carbon black as a conducting and catalyst-supporting material of cathodes. A single-support electrode using carbon black and binary-support electrode using carbon black and graphene were prepared. The conductivity of the electrode using graphene was measured by the standard four-probe DC measurement. As the content of graphene in the electrode was increased, the conductivity of the electrode improved. The adoption of graphene helps in the formation of a mesopore structured electrode, and it makes the catalyst widely dispersed and increases the number of reaction sites of the catalyst. As a result of leaner sweep voltammetry (LSV), the binary-support electrode using carbon black and graphene showed improved oxygen reduction reaction (ORR) compared with the single-support electrode. We concluded that graphene affected the conductivity of the electrode and the ORR characteristics as a support material.

Moon, Eunji; Kim, Jeehoon; Nam, Sangyong; Eom, Seungwook

2012-09-01

97

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

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

98

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

SciTech Connect

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.

Bolotov, O. V.; Golota, V. I.; Kadolin, B. B.; Karas', V. I.; Ostroushko, V. N.; Zavada, L. M.; Shulika, A. Yu. [National Scientific Center Kharkov Institute of Physics and Technology (Ukraine)

2010-11-15

99

Design of Carbon Nanotube-Based Gas-Diffusion Cathode for O2 Reduction by Multicopper Oxidases (Postprint).  

National Technical Information Service (NTIS)

Multicopper oxidases, such as laccase or bilirubin oxidase, are known to reduce molecular oxygen at very high redox potentials, which makes them attractive biocatalysts for enzymatic cathodes in biological fuel cells. By designing an enzymatic gas-diffusi...

C. Lau E. R. Adkins H. R. Luckarift P. Atanassov R. P. Ramasamy

2011-01-01

100

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

PubMed

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

MacQueen, Donald; Bertoldo, Nicholas; Wegrecki, Anthony

2013-08-01

101

Correlations for predicting air permeabilities and 222Rn diffusion coefficients of soils  

Microsoft Academic Search

The rate of 222Rn gas transport through earthen materials controls 222Rn releases to the atmosphere and to indoor environments. The key soil-related parameters characterizing 222Rn transport in earthen materials are the 222Rn diffusion coefficient and the soil air permeability. Simple correlations have been developed for predicting the 222Rn diffusion coefficient and the air permeability of soils based on fraction of

V. C. Rogers; K. K. Nielson

1991-01-01

102

Study of sintered stainless steel fiber felt as gas diffusion backing in air-breathing DMFC  

Microsoft Academic Search

Adoption of a sintered stainless steel fiber felt was evaluated as gas diffusion backing in air-breathing direct methanol fuel cell (DMFC). By using a sintered stainless steel fiber felt as an anodic gas diffusion backing, the peak power density of an air-breathing DMFC is 24mWcm?2, which is better than that of common carbon paper. A 30-h-life test indicates that the

Jianguo Liu; Gongquan Sun; Fengliang Zhao; Guoxiong Wang; Gang Zhao; Likang Chen; Baolian Yi; Qin Xin

2004-01-01

103

Extinction of diffusion flames burning diluted methane and diluted propane in diluted air  

Microsoft Academic Search

A theoretical and experimental investigation of the extinction limits of counterflow diffusion flames burning methane and propane is outlined. A diffusion flame is stabilized between counterflowing streams of a fuel diluted with nitrogen and air diluted with nitrogen. Extinction limits for such flames were measured over a wide parametric range. Results for methane and propane were found to be in

I.K. Puri; K. Seshadri

1986-01-01

104

The Use of Passive Diffusion Tubes for Measuring Concentrations of Nitrogen Dioxide in Air  

Microsoft Academic Search

Passive diffusion tubes have been widely used in Europe for spatial and temporal measurement of NO2 concentrations. The method is cheap, simple, and provides concentration data in most circumstances that are sufficiently accurate for assessing exposure and compliance with air quality criteria. Tube-type diffusion samplers are prone to several sources of uncertainty, arising from the materials of construction, the absorbent

J. N. Cape

2009-01-01

105

Measurement of upwelling flow from Upper Bear Creek reservoir air diffusers  

Microsoft Academic Search

Field tests were performed to determine the upwelling flow from the air diffusers located in Upper Bear Creek reservoir. The diffusers were installed in an effort to maintain aerobic conditions throughout the water column, so that the reservoir and hence low level summer releases would not contain high concentrations of dissolved iron, manganese, and sulfide. Three tests were conducted using

R. T. Brown; J. A. Gordon

1988-01-01

106

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...

107

Advanced cathode and anode research at the Air Force Research Laboratory  

Microsoft Academic Search

High power microwave (HPM) tubes require currents and voltages generally in excess of 1 kA and 100 kV. Traditionally such systems have operated in poor vacuum (>10-6 torr) and on a single shot basis. Current work at the Air Force Research Laboratory (AFRL) has been directed toward high vacuum and high repetition rate systems, necessitating a complete revision of standard

D. Shiffler; M. Ruebush; M. LaCour; K. Golby; K. Cartwright; M. Haworth

2002-01-01

108

Emission characteristics of the cathode region of nanosecond discharge in atmospheric-pressure air  

NASA Astrophysics Data System (ADS)

The emission spectra of a nanosecond discharge between copper electrodes in atmospheric-pressure air are studied at a high discharge gap overvoltage. The discharge was ignited between two cylindrical electrodes with a small radius of curvature of the working surface. Oscillograms of radiation pulses of spectral lines of copper atoms are also studied. The electron temperature averaged over the pulse is determined from the intensity distributions of the spectral lines of copper atoms.

Shuaibov, A. K.; Laslov, G. E.; Kozak, Ya. Yu.

2014-04-01

109

Urban air pollution and atmospheric diffusion research in China  

Microsoft Academic Search

Air pollution has become a serious problem in China as a result of that country's efforts in the last 30 years to become a great industrial power. The burning of coal, which currently provides over 70% of all China's energy needs, is a major source of air pollution. Because Chinese coal is high in sulfur and ash content and because

Datong Ning; Joseph B. Whitney; David Yap

1987-01-01

110

The Dual Gravimetric Hot-Air Method for Measuring Soil Water Diffusivity  

Microsoft Academic Search

The hot-air method provides rapid measurement of a soil's unsatu- rated hydraulic diffusivity function. The original method consists of blowing hot air across one end of a soil column for a short period, and then quickly extruding, dissecting, and oven drying the soil to provide the soil water content profile, which is used to calculate the soil's un- saturated hydraulic

J. S. Tyner; L. M. Arya; W. C. Wright

2006-01-01

111

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...

112

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

PubMed

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 mW·m(-2)) compared to 1086 ± 8 mW·m(-2) of ACAC2#. PMID:23151092

Dong, Heng; Yu, Hongbing; Wang, Xin

2012-12-01

113

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

PubMed

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 0.27V with a maximum power density of 5.79Wm(-3), while anaerobic sludge-inoculated MFCs reached 0.21V with 3.66Wm(-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

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

2014-09-01

114

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

PubMed

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 3-164ppm, with a sensitivity of 0.05?AmM(-1)cm(-2) with respect to the anode total surface area. The response time was as fast as 2.8min. At saturating acetate concentrations (COD>164 ppm), the miniature SCMFC could rapidly detect the presence of cadmium in water with high sensitivity (0.2?gl(-1)cm(-2)) and a lower detection limit of only 1?gl(-1). The biosensor dynamic range was 1-25?gl(-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 12min. PMID:25005554

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

2014-12-15

115

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

NASA Astrophysics Data System (ADS)

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.

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

2010-05-01

116

Simultaneous decolorization of azo dye and bioelectricity generation using a microfiltration membrane air-cathode single-chamber microbial fuel cell  

Microsoft Academic Search

Electricity generation from readily biodegradable organic substrates accompanied by decolorization of azo dye was investigated using a microfiltration membrane air-cathode single-chamber microbial fuel cell (MFC). Batch experiment results showed that accelerated decolorization of active brilliant red X-3B (ABRX3) was achieved in the MFC as compared to traditional anaerobic technology. Biodegradation was the dominant mechanism of the dye removal, and glucose

Jian Sun; Yong-you Hu; Zhe Bi; Yun-qing Cao

2009-01-01

117

Explore various co-substrates for simultaneous electricity generation and Congo red degradation in air-cathode single-chamber microbial fuel cell  

Microsoft Academic Search

Microbial fuel cell (MFC) holds a great promise to harvest electricity directly from a wide range of ready degradable organic matters and enhance degradation of some recalcitrant contaminants. Glucose, acetate sodium and ethanol were separately examined as co-substrates for simultaneous bioelectricity generation and Congo red degradation in a proton exchange membrane (PEM) air-cathode single-chamber MFC. The batch test results showed

Yunqing Cao; Yongyou Hu; Jian Sun; Bin Hou

2010-01-01

118

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

Microsoft Academic Search

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

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

2011-01-01

119

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

NASA Technical Reports Server (NTRS)

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.

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

1979-01-01

120

Effect of chemically modified Vulcan XC-72R on the performance of air-breathing cathode in a single-chamber microbial fuel cell.  

PubMed

The catalytic activity of modified carbon powder (Vulcan XC-72R) for oxygen reduction reaction (ORR) in an air-breathing cathode of a microbial fuel cell (MFC) has been investigated. Chemical modification was carried out by using various chemicals, namely 5% nitric acid, 0.2N phosphoric acid, 0.2N potassium hydroxide and 10% hydrogen peroxide. Electrochemical study was performed for ORR of these modified carbon materials in the buffer solution pH range of 6-7.5 in the anodic compartment. Although, these treatments influenced the surface properties of the carbon material, as evident from the SEM-EDX analysis, treatment with H(2)PO(4), KOH, and H(2)O(2) did not show significant activity during the electrochemical test. The HNO(3) treated Vulcan demonstrated significant ORR activity and when used in the single-chamber MFC cathode, current densities (1115mA/m(2), at 5.6mV) greater than those for a Pt-supported un-treated carbon cathode were achieved. However, the power density for the latter was higher. Such chemically modified carbon material can be a cheaper alternative for expensive platinum catalyst used in MFC cathode construction. PMID:20171090

Duteanu, N; Erable, B; Senthil Kumar, S M; Ghangrekar, M M; Scott, K

2010-07-01

121

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

122

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

NASA Astrophysics Data System (ADS)

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.

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

2002-06-01

123

Large-eddy simulation of a turbulent piloted methane\\/air diffusion flame (Sandia flame D)  

Microsoft Academic Search

The Lagrangian Flamelet Model is formulated as a combustion model for large-eddy simulations of turbulent jet diffusion flames. The model is applied in a large-eddy simulation of a piloted partially premixed methane\\/air diffusion flame (Sandia flame D). The results of the simulation are compared to experimental data of the mean and RMS of the axial velocity and the mixture fraction

H. Pitsch; H. Steiner

2000-01-01

124

Centrifugal Compressor Surge Margin Improved With Diffuser Hub Surface Air Injection  

NASA Technical Reports Server (NTRS)

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.

Skoch, Gary J.

2002-01-01

125

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

PubMed

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

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

2014-02-01

126

Bag-type filter apparatus with combination bag support and air diffuser  

SciTech Connect

In order to achieve improved cleaning of a tubular filter bag when a reverse purge of air is directed into the filter bag, there is provided interiorly of the filter bag an elongate tube which is constructed in such a way as to serve for supporting and holding the filter bag in an open tubular configuration and for also diffusing and distributing air directed to the filter bag when a reverse purge of air is directed into the filter bag for cleaning of the filter bag. The elongate tube has peripheral portions extending outwardly beyond other portions of the tube for engaging and holding the surrounding filter bag, and the portions of the tube located inwardly therefrom have perforations located for diffusing and distributing the reverse purge of air directed into the filter bag.

Johnson, A.S.

1981-03-31

127

Laminar methane-air diffusion flame with chlorine impurities: Preliminary results  

SciTech Connect

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 of incomplete combustion during the thermal destruction of chlorinated compounds is of current interest.) The preliminary observations are concerned with soot emissions and flame temperature. The structure of the soot particles is examined under a scanning electron microscope (SEM). The SEM studies and the temperature measurements are compared to similar studies on a methane-air diffusion flame. Results indicate no change in the temperature field between the methane-air and chlorine/methane-air diffusion flames. The SEM analyzed soot indicated the absence of chlorine, although in one case the soot exhibited a porous structure, possibly due to chlorine induced attack.

Venkatesh, S.; Saito, K.; Stencel, J.M.; Lemieux, P.M.; Hall, R.E.

1990-01-01

128

Cathodic reduction of sulfur dioxide in nonaqueous electrolytes. The effect of solution composition on the diffusion coefficient of sulfur dioxide  

SciTech Connect

The authors measured the diffusion coefficients of SO/sub 2/ in electrolytes based on propylene carbonate, acetonitrile, dimethylformamide and dimethylsulfoxide in order to estimate possible diffusion limitations with respect to SO/sub 2/ and to establish the influence exerted by the solvent type on the process. The diffusion coefficients were calculated from the limiting diffusion currents of steady-state polarization curves for sulfur dioxide reduction recorded at a gold microdisk electrode which had a diameter of 2 x 10/sup -3/ cm. In lithium salt solutions the potentiodynamic curves recorded at the microelectrode do not exhibit a limiting current but are characterized by a current maximum.

Shembel, E.M.; Ksenzhek, O.S.; Lituinova, V.I.; Lobach, G.A.

1986-09-01

129

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

SciTech Connect

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

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

1997-01-01

130

Effects of Coaxial Air on Nitrogen-Diluted Hydrogen Jet Diffusion Flame Length and NOx Emission  

SciTech Connect

Turbulent nitrogen-diluted hydrogen jet diffusion flames with high velocity coaxial air flows are investigated for their NOx emission levels. This study is motivated by the DOE turbine program’s goal of achieving 2 ppm dry low NOx from turbine combustors running on nitrogen-diluted high-hydrogen fuels. In this study, effects of coaxial air velocity and momentum are varied while maintaining low overall equivalence ratios to eliminate the effects of recirculation of combustion products on flame lengths, flame temperatures, and resulting NOx emission levels. The nature of flame length and NOx emission scaling relationships are found to vary, depending on whether the combined fuel and coaxial air jet is fuel-rich or fuel-lean. In the absence of differential diffusion effects, flame lengths agree well with predicted trends, and NOx emissions levels are shown to decrease with increasing coaxial air velocity, as expected. Normalizing the NOx emission index with a flame residence time reveals some interesting trends, and indicates that a global flame strain based on the difference between the fuel and coaxial air velocities, as is traditionally used, is not a viable parameter for scaling the normalized NOx emissions of coaxial air jet diffusion flames.

Weiland, N.T.; Chen, R.-H.; Strakey, P.A.

2007-10-01

131

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

National Technical Information Service (NTIS)

Mass transport and thermodynamic properties of LixCoO2 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...

Y. I. Jang

2001-01-01

132

Nanoscale mapping of lithium-ion diffusion in a cathode within an all-solid-state lithium-ion battery by advanced scanning probe microscopy techniques.  

PubMed

High-resolution real-space mapping of Li-ion diffusion in the LiNi(1/3)Co(1/3)Mn(1/3)O? cathode within an all-solid-state thin film Li-ion battery has been conducted using advanced scanning probe microscopy techniques, namely, band excitation electrochemical strain microscopy (BE-ESM) and conductive atomic force microscopy. In addition, local variations of the electrochemical response in the LiNi(1/3)Co(1/3)Mn(1/3)O? thin film cathode at different cycling stages have been investigated. This work demonstrates the unique feature and applications of the BE-ESM technique on battery research. The results allow us to establish a direct relationship of the changes in ionic mobility as well as the electrochemical activity at the nanoscale with the numbers of charge/discharge cycles. Furthermore, various factors influencing the BE-ESM measurements, including sample mechanical properties (e.g., elastic and dissipative properties) as well as surface electrical properties, have also been studied to investigate the coupling effects on the electrochemical strain. The study on the relationships between the Li-ion redistribution and microstructure of the electrode materials within thin film Li-ion battery will provide further understanding of the electrochemical degradation mechanisms of Li-ion rechargeable batteries at the nanoscale. PMID:23336441

Zhu, Jing; Lu, Li; Zeng, Kaiyang

2013-02-26

133

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

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

134

Effect of Pressure on Structure and NOX Formation in CO-Air Diffusion Flames.  

National Technical Information Service (NTIS)

A study has been made of flame structure and nitric oxide formation in confined laminar CO-air diffusion flames over a pressure range from 1 to 50 atm. The shape of the flames changed from wide and convex at 1 atm to slender and concave at 50 atm, with th...

H. G. Maahs I. M. Miller

1979-01-01

135

Influence of a Horizontal Magnetic Field on a Co-Flow Methane\\/Air Diffusion Flame  

Microsoft Academic Search

Influence of magnetic fields on the liftoff and blow out properties of the methane\\/air co-flow diffusion flame has been investigated experimentally. The present experiments showed that magnetic gradients are able to minimize the liftoff height and increase the flow rate above which the flame blows out. This observed increase of stability of lifted flames is attributed to the magnetic force

Virginie Gilard; Pascale Gillon; Jean-Noël Blanchard; Brahim Sarh

2008-01-01

136

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

137

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

Microsoft Academic Search

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

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

1992-01-01

138

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

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

139

Study on Thermal Diffusion in Artificial Air Near the Critical Point  

NASA Astrophysics Data System (ADS)

Air is absolutely essential for our everyday life and also very important in the field of industry. The major part of it is composed of nitrogen and oxygen. We investigated the Soret effect in artificial air, which was a nitrogen-oxygen binary mixture with the composition of 0.791 mole fraction of nitrogen and 0.209 mole fraction of oxygen near the critical point. In the case of the artificial air, the estimated critical temperature and the estimated critical pressure are 132.61 K and 3.8381 MPa, respectively. We carried out the experiments by using a single stage two-chamber cell. We made a temperature difference between the two chambers, which were separated by a porous diaphragm. After an experiment had run for sufficient time to reach steady state, the concentration of oxygen in each chamber was measured by using a gas chromatograph. From the experiments, we observed that the thermal diffusion factor showed a strong drop near the critical point. The thermal diffusion ratio indicated was negative and behaved like 3He-4He mixtures. There has been no report that the thermal diffusion ratio of the nitrogen-oxygen system behaves just like the mixture of such substances. We discuss the thermal diffusion in the nitrogen-oxygen binary mixture near the critical point.

Nakano, A.; Maeda, T.

2008-03-01

140

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

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

141

Coil hollow cathode for metal vapor lasers  

Microsoft Academic Search

A metal vapor hollow cathode laser tube with a coil hollow cathode is described which facilitates diffusion of metal atoms into the discharge region. The device comprises a stainless steel cylinder with an 11 mm inner diam and 10 cm long, a cathode arranged concentrically within the anode and having a 6 mm inner diam and 10 cm length and

M. Grozeva; N. Sabotinov

1982-01-01

142

Molecular diffusion effects in LES of a piloted methane-air flame  

SciTech Connect

Molecular diffusion effects in LES of a piloted methane-air (Sandia D) flame are investigated on a series of grids with progressively increased resolution. The reacting density, temperature and chemical composition are modeled based on the mixture fraction approach combined with a steady flamelet model. With a rationale to minimize interpolation uncertainties that are routinely introduced by a flamelet table look-up, quadratic splines relationships are employed to represent thermochemical variables. The role of molecular diffusivity in effecting spatial transport is studied by drawing a comparison with the turbulent diffusivity and analyzing their statistics conditioned on temperature. Statistical results demonstrate that the molecular diffusivity in the near-field almost always exceeds the turbulent diffusivity, except at low temperatures (less than 500 K). Thus, by altering the jet near-field, molecular transport plays an important role in the further downstream jet development. Molecular diffusivity continues to dominate in the centerline region throughout the flow field. Overall, the results suggest the strong necessity to represent molecular transport accurately in LES studies of turbulent reacting flows. (author)

Kemenov, Konstantin A.; Pope, Stephen B. [Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853 (United States)

2011-02-15

143

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

SciTech Connect

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

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

2004-03-01

144

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

NASA Technical Reports Server (NTRS)

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.

Ghaderi, M.; Gupta, A. K.

2003-01-01

145

Performance of a thermally desorbable diffusion sampler for personal and indoor air monitoring  

Microsoft Academic Search

A diffusion passive sampler suitable for large-scale investigations of population exposure to volatile organic compounds (VOC) in indoor air has been developed and tested. The sampler consists of a glass tube (6Ã160 mm or 6Ã100 mm) containing an adsorbent (Tenax or Carbotrap) that collects vapours at a flow rate of 4 to 8 cm³\\/h, depending on the compound. This flow

M. De Bortoli; H. Knoeppel; E. Pecchio; H. Vissers

1989-01-01

146

Simulation and experimental investigation into diffusion absorption cooling machines for air-conditioning applications  

Microsoft Academic Search

The paper presents the development, experimental analysis and simulation of a solar heat driven ammonia\\/water (NH3\\/H2O) diffusion–absorption cooling machine (DACM). The designed cooling capacity of the machine is 2.5kW for air-conditioning applications. The indirectly heated generator with its bubble pump is the main new feature of this cooling machine and it showed good performance for all prototypes constructed. A major

U. Jakob; U. Eicker; D. Schneider; A. H. Taki; M. J. Cook

2008-01-01

147

Functional Relationships among Soil-air Permeability, Soil-gas Diffusivity, and Saturated Hydraulic Conductivity in Undisturbed Soils  

Microsoft Academic Search

Soil-pore geometric parameters including size distribution, total and air-filled porosity, pore tortuosity and connectivity strongly influence water and air flow in soils, and characterize soil-water and soil-gas transport parameters such as saturated hydraulic conductivity, soil-air permeability and soil-gas diffusivity. This study investigated functional relationships among the soil-pore dependent physical parameters in undisturbed soils and developed predictive expressions for soil-air permeability

K. Kawamoto; P. Moldrup; P. Schjønning; B. V. Iversen; T. Komatsu

2005-01-01

148

Efficiency and air-stability improvement of flexible inverted polymer solar cells using ZnO/poly(ethylene glycol) hybrids as cathode buffer layers.  

PubMed

The flexible inverted polymer solar cells composed of poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C61 butyric acid methyl ester (PC61BM) blends on the flexible poly(ethylene terephthalate) (PET) substrates were fabricated, which showed improving device performance by using solution-processed ZnO/poly(ethylene glycol) (PEG) hybrids as cathode buffer layers compared to the devices using the pristine ZnO as cathode buffer layers. It is mainly attributed to the effective passivation of the ZnO surface traps, suppression of the interfacial charge recombination, decrease of the work function and improvement of the energy-level alignment between ZnO and PC61BM. When the PEG was introduced into the ZnO, the large aggregates was dispersed and yielded large ZnO nanoclusters containing less domain boundaries. The performance of devices with ZnO/PEG6000 (with averaged molecular weight of 6000) hybrids exhibited the best power conversion efficiency (PCE) of 3.3% compared to the devices with ZnO/PEG400 (with averaged molecular weight of 400) and ZnO/PEG20000 (with averaged molecular weight of 20000). It was found that the short PEG backbone (e.g., Mw = 400) containing less oxygen could not effectively passivate ZnO surface traps, meanwhile, longer PEG backbone (e.g., Mw = 20000) could lead to the formation of the charge transport barrier because of the insulating nature of PEG. Furthermore, solar cells with the ZnO/PEG buffer also showed better air-stability. The 23% degradation was observed after 14 days, compared to the 45% degradation of devices with the pristine ZnO buffer. In addition, due to the simplicity and low-temperature process, the ZnO/PEG hybrids can be well-suitable as cathode buffer for large area roll-to-roll manufacturing of printed polymer solar cells. PMID:23738498

Hu, Ting; Li, Fan; Yuan, Kai; Chen, Yiwang

2013-06-26

149

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

150

Extinction of premixed H{sub 2}/air flames: Chemical kinetics and molecular diffusion effects  

SciTech Connect

Laminar flame speed has traditionally been used for the partial validation of flame kinetics. In most cases, however, its accurate determination requires extensive data processing and/or extrapolations, thus rendering the measurement of this fundamental flame property indirect. Additionally, the presence of flame front instabilities does not conform to the definition of laminar flame speed. This is the case for Le<1 flames, with the most notable example being ultralean H{sub 2}/air flames, which develop cellular structures at low strain rates so that determination of laminar flame speeds for such mixtures is not possible. Thus, this low-temperature regime of H{sub 2} oxidation has not been validated systematically in flames. In the present investigation, an alternative/supplemental approach is proposed that includes the experimental determination of extinction strain rates for these flames, and these rates are compared with the predictions of direct numerical simulations. This approach is meaningful for two reasons: (1) Extinction strain rates can be measured directly, as opposed to laminar flame speeds, and (2) while the unstretched lean H{sub 2}/air flames are cellular, the stretched ones are not, thus making comparisons between experiment and simulations meaningful. Such comparisons revealed serious discrepancies between experiments and simulations for ultralean H{sub 2}/air flames by using four kinetic mechanisms. Additional studies were conducted for lean and near-stoichiometric H{sub 2}/air flames diluted with various amounts of N{sub 2}. Similarly to the ultralean flames, significant discrepancies between experimental and predicted extinction strain rates were also found. To identify the possible sources of such discrepancies, the effect of uncertainties on the diffusion coefficients was assessed and an improved treatment of diffusion coefficients was advanced and implemented. Under the conditions considered in this study, the sensitivity of diffusion coefficients to the extinction response was found to be significant and, for certain species, greater than that of the kinetic rate constants.

Dong, Yufei; Holley, Adam T.; Andac, Mustafa G.; Egolfopoulos, Fokion N.; Wang, Hai [Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089-1453 (United States); Davis, Scott G. [Exponent, Natick, MA 01760 (United States); Middha, Prankul [Department of Mechanical Engineering, University of Delaware, Newark, DE 19716 (United States)

2005-09-01

151

Diffuse discharge produced by repetitive nanosecond pulses in open air, nitrogen, and helium  

NASA Astrophysics Data System (ADS)

Atmospheric-pressure gas discharge driven by high voltage pulses with fast rise-time and short duration has attracted significant attention for various plasma applications. In this paper, discharges were generated in a highly non-uniform electric field by point-plane gaps in open air by four repetitive nanosecond-pulse generators with repetition rate up to 1 kHz. The rise time of generators was 25 (generator #1), 15 (generator #2), 3 (generator #3), and 0.2 ns (generator #4) and a full width at half maximum was 40, 30-40, 5, and 1 ns, respectively. The experimental results show that there were typical discharge fashions, i.e., corona, diffuse, spark, or arc modes. The variables affecting the discharge characteristics, including the gap spacing and applied pulse parameters, were investigated. Especially, the diffuse discharges were investigated and discussed. With generator #1 at voltage 70-120 kV, characteristics of measured x-rays on the discharge modes were studied, and it indicates that counts of x-rays in a diffuse discharge are up to a peak value under the experimental conditions. With amplitude of voltage pulses in incident wave up to 18 (generator #3) and 12.5 kV (generator #4), runaway electron beam in low pressure helium, nitrogen, and air in a pulse-periodic mode of discharge with repetition rate up to 1 kHz was obtained. Electron beam was registered behind a thin foil in a pressure range from several to tens of Torr. X-ray radiation was obtained in a wide range of pressures, as well as at atmospheric pressure of helium, nitrogen, and air. Voltage pulses of positive and negative polarities were used. Generation of runaway electrons with pulses of positive polarity appeared because of reflected voltage pulses of reverse polarity.

Shao, Tao; Tarasenko, Victor F.; Zhang, Cheng; Baksht, Evgeni Kh.; Zhang, Dongdong; Erofeev, Mikhail V.; Ren, Chengyan; Shutko, Yuliya V.; Yan, Ping

2013-03-01

152

Diffuse scattering from hemispherical nanoparticles at the air-silicon interface  

NASA Astrophysics Data System (ADS)

There has been much recent interest in the application of plasmonics to improve the efficiency of silicon solar cells. In this paper we use finite difference time domain calculations to investigate the placement of hemispherical gold nanoparticles on the rear surface of a silicon solar cell. The results indicate that nanoparticles protruding into the silicon, rather than into air, have a larger scattering efficiency and diffuse scattering into the semiconductor. This finding could lead to improved light trapping within a thin silicon solar cell device.

Centeno, Anthony; Ahmed, Badar; Reehal, Haricharan; Xie, Fang

2013-10-01

153

Compact lanthanum hexaboride hollow cathode  

NASA Astrophysics Data System (ADS)

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 LaB6 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.

Goebel, Dan M.; Watkins, Ronald M.

2010-08-01

154

Compact lanthanum hexaboride hollow cathode.  

PubMed

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

Goebel, Dan M; Watkins, Ronald M

2010-08-01

155

Diffusion denuder assembly for collection and determination of gases in air  

SciTech Connect

In air pollution studies a widely used collection arrangement consists of an aerosol filter followed by a wet impinger or specially prepared filter for retention of a gaseous pollutant. However, it was shown that in many cases this method can lead to undesirable changes of the sample during collection. For example, an absorption of gaseous ammonia on the collected aerosol can result in partial neutralization of the particulate matter. It is the aim of this work to construct a system suitable for direct determination of the gaseous components and for collecting a reasonable volume of air. Also, it was decided to design an apparatus which allowed easy, quick, reproducible, and clean coating and extraction procedures and enable us to use the fairly low extraction volumes for exposed tubes. The present paper describes the construction and features of such a diffusion denuder assembly (DDA), preparation of tubes and samples, and testing of the applicability of this system for collecting ammonia and gaseous nitric acid. Knowledge of concentrations of ammonia and acidic gases in air is a prerequisite for the understanding of processes important for acidification of dry and wet deposition. The system described for collecting and treating gaseous samples can be helpful in obtaining reliable results on content of these important species in air.

Lewin, E.E.; Hansen, K.A.

1984-04-01

156

Mineralization of desmetryne by electrochemical advanced oxidation processes using a boron-doped diamond anode and an oxygen-diffusion cathode.  

PubMed

The mineralization of acidic aqueous solutions of the herbicide desmetryne has been studied by electrochemical advanced oxidation processes (EAOPs) such as anodic oxidation with electrogenerated H(2)O(2) (AO-H(2)O(2)), electro-Fenton (EF) and photoelectro-Fenton (PEF) with UVA light. Electrolyses were conducted in an open and cylindrical cell with a boron-doped diamond (BDD) anode and an O(2)-diffusion cathode for H(2)O(2) generation. The main oxidizing species are ()OH radicals formed at the BDD surface in all treatments and in the bulk from Fenton's reaction between added Fe(2+) and electrogenerated H(2)O(2) in EF and PEF. A poor mineralization was attained using AO-H(2)O(2) by the slow oxidation of persistent by-products with ()OH at the BDD surface. The synergistic action of ()OH in the bulk enhanced the degradation rate in EF, although almost total mineralization was only achieved in PEF due to the additional ()OH generation and photolysis of intermediates by UVA irradiation. The effect of current, pH and herbicide concentration on the mineralization degree and mineralization current efficiency of each EAOP was examined. Desmetryne decay always followed a pseudo first-order kinetics, being more rapidly destroyed in the sequence AO-H(2)O(2)

Borràs, Núria; Arias, Conchita; Oliver, Ramon; Brillas, Enric

2011-11-01

157

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

NASA Astrophysics Data System (ADS)

The redox behavior of a decavanadium complex [(V?O) 10(? 2-O) 9(? 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.

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

158

Laboratory determination of thermal diffusion constants for 29N 2\\/ 28N 2 in air at temperatures from ?60 to 0°C for reconstruction of magnitudes of abrupt climate changes using the ice core fossil–air paleothermometer  

Microsoft Academic Search

Rapid temperature change causes fractionation of isotopic gaseous species in air in firn (snow) by thermal diffusion, producing a signal that is preserved in trapped air bubbles as the snow forms ice. Using a model of heat penetration and gas diffusion in the firn, as well as the values of appropriate thermal diffusion constants, it is possible to reconstruct the

Alexi M Grachev; Jeffrey P Severinghaus

2003-01-01

159

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

PubMed

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

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

2013-10-01

160

Diffusion  

NSDL National Science Digital Library

Diffusion is the net movement of particles from areas of high concentration (number of particles per unit area) to low concentration. In this activity, students use a molecular dynamics model to view the behavior of diffusion in gases and liquids.

Consortium, The C.

2011-12-11

161

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

Microsoft Academic Search

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

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

1989-01-01

162

Pulsed Field Emission Cathode Studies  

NASA Astrophysics Data System (ADS)

Field emission cathodes have been a topic of research in recent years as efforts have mounted to find a cathode material that has low gas evolution with negligible impedance collapse and high current densities. In the explosive field emission cathodes utilized for high power microwave tubes, microwave pulse shortening can occur due to motion of the cathode plasma across the anode-cathode (A-K) gap. This motion is affected by the gas evolution. Ultimately, this gap closure can sufficiently change the diode impedance such that the tube can no longer operate under the desired conditions. We discuss comparisons of CsI coated carbon fiber and bare carbon fiber to velvet cathodes as potential solutions to this problem. These cathodes have demonstrated low A-K gap closure times with applied fields in the range of a few tens of kV/cm to several hundred kV/cm with currents into the several kiloampere range. We review the results of experiments on the Cathode Test Bed at the Air Force Research Laboratory and comparison with simulation.

Shiffler, Don; Umstattd, Ryan; Lacour, Matthew; Sena, Miguel; Luginsland, John; Hendricks, Kyle; Spencer, Thomas; Gibbs, Aimee; Voss, Don

1999-11-01

163

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

164

A physics-based drift-diffusion approach to model Li-air batteries with organic electrolyte  

Microsoft Academic Search

Drift diffusion models have been used extensively by the semiconductor device research community to provide a physics-based approach for the modeling and simulation of electronic devices under various bias conditions. In this article we develop a model based on the drift-diffusion equations for the simulation of Li-air batteries with organic electrolyte. The model is carefully calibrated and takes into consideration

P. Andrei; J. P. Zheng; M. Hendrickson; E. J. Plichta

2010-01-01

165

Computations of soot formation in ethylene/air counterflow diffusion flames and its interaction with radiation  

NASA Astrophysics Data System (ADS)

A methodology is presented which allows to predict soot levels produced in simple, one-dimensional laminar flames. The method is applied to the calculation of a set of well documented ethylene/air counterflow diffusion flames, using a detailed chemical mechanism (Davis et al., 1999 [1]) and a semi-empirical, two-equation soot model from Leung and Lindstedt (1991) [2]. Modifications of the original soot model are made in order to retrieve the experimental measurements of Hwang and Chung (2001) [3]. To account for radiative heat losses, a second series of fully coupled gas/soot/radiation simulations of the counterflow flames is performed. This allows to assess the effect of soot and gas radiation on soot formation and on the flame structure.

Hernández, Ignacio; Lecocq, Guillaume; Poitou, Damien; Riber, Eléonore; Cuenot, Bénédicte

2013-01-01

166

Spatially resolved laser-induced breakdown spectroscopy in methane-air diffusion flames.  

PubMed

A new setup for spatially resolved laser-induced breakdown spectroscopy (SR-LIBS) is used for the first time to analyze methane-air diffusion flames. Using this configuration, background continuum emission is reduced, signal-to-background noise ratio is increased up to eight times, and spatial resolution is enhanced. The local equivalence ratio is also quantitatively estimated and the width of the secondary combustion region at a specified height above the burner is determined for two different methane flow rates. Furthermore, the threshold energy for spark formation is measured for regions inside and outside the flame. The results show that threshold energy is larger at the secondary combustion region, near the border of the flame, than inside the flame. PMID:21211152

Majd, Abdollah Eslami; Arabanian, Atoosa Sadat; Massudi, Reza; Nazeri, Majid

2011-01-01

167

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

NASA Technical Reports Server (NTRS)

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.

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

1962-01-01

168

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

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

169

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

NASA Technical Reports Server (NTRS)

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.

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

170

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

171

Simultaneous Congo red decolorization and electricity generation in air-cathode single-chamber microbial fuel cell with different microfiltration, ultrafiltration and proton exchange membranes.  

PubMed

Different microfiltration membrane (MFM), proton exchange membrane (PEM) and ultrafiltration membranes (UFMs) with different molecular cutoff weights of 1K (UFM-1K), 5K (UFM-5K) and 10K (UFM-10K) were incorporated into air-cathode single-chamber microbial fuel cells (MFCs) which were explored for simultaneous azo dye decolorization and electricity generation to investigate the effect of membrane on the performance of the MFC. Batch test results showed that the MFC with an UFM-1K produced the highest power density of 324 mW/m(2) coupled with an enhanced coulombic efficiency compared to MFM. The MFC with UMF-10K achieved the fastest decolorization rate (4.77 mg/L h), followed by MFM (3.61 mg/L h), UFM-5K (2.38 mg/L h), UFM-1K (2.02 mg/Lh) and PEM (1.72 mg/Lh). These results demonstrated the possibility of using various membranes in the system described here, and showed that UFM-1K was the best one based on the consideration of both cost and performance. PMID:21251817

Hou, Bin; Sun, Jian; Hu, Yong-you

2011-03-01

172

Simultaneous decolorization of azo dye and bioelectricity generation using a microfiltration membrane air-cathode single-chamber microbial fuel cell.  

PubMed

Electricity generation from readily biodegradable organic substrates accompanied by decolorization of azo dye was investigated using a microfiltration membrane air-cathode single-chamber microbial fuel cell (MFC). Batch experiment results showed that accelerated decolorization of active brilliant red X-3B (ABRX3) was achieved in the MFC as compared to traditional anaerobic technology. Biodegradation was the dominant mechanism of the dye removal, and glucose was the optimal co-substrate for ABRX3 decolorization, while acetate was the worst one. Confectionery wastewater (CW) was also shown to be a good co-substrate for ABRX3 decolorization and a cheap fuel source for electricity generation in the MFC. Low resistance was more favorable for dye decolorization than high resistance. Suspended sludge (SS) should be retained in the MFC for accelerated decolorization of ABRX3. Electricity generation was not significantly affected by the ABRX3 at 300 mg/L, while higher concentrations inhibited electricity generation. However, voltage can be recovered to the original level after replacement with anodic medium not containing azo dye. PMID:19269168

Sun, Jian; Hu, Yong-You; Bi, Zhe; Cao, Yun-Qing

2009-07-01

173

Explore various co-substrates for simultaneous electricity generation and Congo red degradation in air-cathode single-chamber microbial fuel cell.  

PubMed

Microbial fuel cell (MFC) holds a great promise to harvest electricity directly from a wide range of ready degradable organic matters and enhance degradation of some recalcitrant contaminants. Glucose, acetate sodium and ethanol were separately examined as co-substrates for simultaneous bioelectricity generation and Congo red degradation in a proton exchange membrane (PEM) air-cathode single-chamber MFC. The batch test results showed that more than 98% decolorization at the dye concentration of 300 mg/L were achieved within 36 h for all tested co-substrates during electricity generation. The decolorization rate was different with the co-substrates used. The fastest decolorization rate was achieved with glucose followed by ethanol and sodium acetate. Accumulated intermediates were observed during Congo red degradation which was demonstrated by UV-Visible spectra and high performance liquid chromatography (HPLC). Electricity generation was sustained and not significantly affected by the Congo red degradation. Glucose, acetate sodium and ethanol produced maximum power densities of 103 mW/m(2), 85.9 mW/m(2) and 63.2 mW/m(2), respectively, and the maximum voltage output decreased by only 7% to 15%. Our results demonstrated the feasibility of using various co-substrates for simultaneous decolorization of Congo red and bioelectricity generation in the MFC and showed that glucose was the preferred co-substrate. PMID:20053591

Cao, Yunqing; Hu, Yongyou; Sun, Jian; Hou, Bin

2010-08-01

174

Gas diffusivity and air permeability of the firn from cold polar sites  

NASA Astrophysics Data System (ADS)

Recent field investigations of a megadunes region of East Antarctica provide evidence that differences in grain size, thermal conductivity, and permeability across a megadune are due to relative accumulation patterns in the absence of significant variations in microclimate. The differences in accumulation patterns include distinct areas of perceptible but low accumulation (less than 40 mm w.eq.a-1) and areas of accumulation hiatus within several kilometers proximity, as determined by remote sensing, surface feature classification, and GPR profiling. Near-surface firn properties are very sensitive to the amount of accumulation in low accumulation rate regions, with relatively small differences in accumulation rate (less than 40 mm w.eq.a -1) creating distinctive differences in grain size, thermal conductivity, and permeability, accompanied by variations in satellite-based microwave data from both passive and active sensors. Cores from the megadunes region exhibit variations in physical properties at depth due to temporal changes in local accumulation caused by dune migration. A new way of describing gas diffusivity and air permeability of polar firn is developed. Diffusivity-porosity and permeability-porosity power-law relationships vary from site to site with accumulation rate having the largest impact on the value of the exponent. The largest differences in firn properties occur between firn from hiatus sites compared to sites where any accumulation, from low to high values, occurs.

Courville, Zoe Renee

175

Large-Eddy Simulation of a Turbulent Piloted Methane/Air Diffusion Flame  

NASA Astrophysics Data System (ADS)

In the present study Large-Eddy Simulations for a turbulent, piloted methane/air diffusion flame have been performed and the results are compared to experimental data by Barlow et al. The Smagorinsky model is used to obtain the eddy viscosity, where the Smagorinsky constant is obtained by the Dynamic Model. The Lagrangian Flamelet Model is applied to describe turbulence-chemistry interactions. The model follows a conserved scalar approach, where the resolved mass fractions of chemical species are evaluated using a presumed pdf of the mixture fraction. The pdf is assumed to follow a ?-function, depending on the resolved mixture fraction and its subgrid-scale variance, which is also modeled using the Dynamic Procedure. In order to solve the unsteady flamelet equations, the temporal development of the scalar dissipation rate has to be specified from the solution of the turbulent flow field. In the present model, the conditional average of the scalar dissipation rate as a function of the axial distance from the nozzle is computed from the spatially filtered scalar dissipation rate, which is expressed in terms of the eddy diffusivity and the gradient of the resolved mixture fraction following the model of Girimaji et al.

Pitsch, Heinz; Steiner, Helfried

1999-11-01

176

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

NASA Technical Reports Server (NTRS)

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.

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

177

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

NASA Technical Reports Server (NTRS)

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.

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

178

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

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

179

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

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

180

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

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

181

Modified carbon-free silver electrodes for the use as cathodes in lithium-air batteries with an aqueous alkaline electrolyte  

NASA Astrophysics Data System (ADS)

Gas diffusion electrodes with silver catalysts show a high activity towards oxygen reduction reaction in alkaline media but a rather poor activity towards oxygen evolution reaction. For the use in future lithium-air batteries with an aqueous alkaline electrolyte the activity of such electrodes must be improved significantly. As Co3O4 is a promising metal oxide catalyst for oxygen evolution in alkaline media, silver electrodes were modified with Co3O4. For comparison silver electrodes were also modified with IrO2. Due to the poor stability of carbon materials at high anodic potentials these gas diffusion electrodes were prepared without carbon support to improve especially the long-term stability. Gas diffusion electrodes were electrochemically investigated in an electrochemical half-cell arrangement. In addition to cyclic voltammograms electrochemical impedance spectroscopy (EIS) was carried out. SEM and XRD were used for the physical and morphological investigations. Investigations showed that silver electrodes containing 20 wt.% Co3O4 exhibited the highest performance and highest long-term stability. For comparison, rotating - ring - disc - electrode experiments have been performed using model electrodes with thin catalyst layers, showing that the amount of hydrogen peroxide evolved is negligible.

Wittmaier, Dennis; Wagner, Norbert; Friedrich, K. Andreas; Amin, Hatem M. A.; Baltruschat, Helmut

2014-11-01

182

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

PubMed

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

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

2011-12-15

183

Carbon nanotube cathode research at AFRL  

Microsoft Academic Search

Single-wall and multi-wall nanotubes have shown some promise as field emission cathodes. Most applications have focused on small surface areas with such uses as flat panel displays. The Air Force Research Laboratory has begun to investigate the uses of these cathodes for larger areas. Several types of nanotube cathodes have been investigated. Each type is implemented in a 63 cm2

D. Shiffler; M. LaCour; K. Golby; M. Ruebush; M. Haworth; D. Zagar

2002-01-01

184

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

PubMed

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

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

2013-07-14

185

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

SciTech Connect

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. 42 refs.

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

1989-01-01

186

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)

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.

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

1989-01-01

187

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

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

188

Multiple Hollow Cathode Wear Testing  

NASA Technical Reports Server (NTRS)

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.

Soulas, George C.

1994-01-01

189

Runaway electron preionized diffuse discharges in atmospheric pressure air with a point-to-plane gap in repetitive pulsed mode  

NASA Astrophysics Data System (ADS)

This paper presents the results of the experimental studies of a pulsed discharge in atmospheric pressure air in an inhomogeneous electric field for various parameters of voltage pulses. It is shown that in a wide range of experimental conditions, including those with a positive electrode of small curvature radius, a diffuse discharge is ignited in the gap. In particular, a diffuse discharge is ignited at a pulse repetition frequency of 1 kHz and a voltage pulse amplitude of ~25 and ~40 kV across a high-resistance load. With voltage pulses of ~ 220 kV in amplitude and low repetition frequencies, an extended (~70 cm) diffuse discharge is observed in gaps of 13-40 mm. It is confirmed that the diffuse form of discharges in an inhomogeneous electric field at increased pressures is attributed to the generation of runaway electrons and x-rays.

Shao, Tao; Zhang, Cheng; Niu, Zheng; Yan, Ping; Tarasenko, Victor F.; Baksht, Evgeni Kh.; Kostyrya, Igor D.; Shutko, V.

2011-04-01

190

The influence of fuel-air swirl intensity on flame structures of syngas swirl-stabilized diffusion flame  

NASA Astrophysics Data System (ADS)

Flame structures of a syngas swirl-stabilized diffusion flame in a model combustor were measured using the OH-PLIF method under different fuel and air swirl intensity. The flame operated under atmospheric pressure with air and a typical low heating-value syngas with a composition of 28.5% CO, 22.5% H2 and 49% N2 at a thermal power of 34 kW. Results indicate that increasing the air swirl intensity with the same fuel, swirl intensity flame structures showed little difference except a small reduction of flame length; but also, with the same air swirl intensity, fuel swirl intensity showed great influence on flame shape, length and reaction zone distribution. Therefore, compared with air swirl intensity, fuel swirl intensity appeared a key effect on the flame structure for the model combustor. Instantaneous OH-PLIF images showed that three distinct typical structures with an obvious difference of reaction zone distribution were found at low swirl intensity, while a much compacter flame structure with a single, stable and uniform reaction zone distribution was found at large fuel-air swirl intensity. It means that larger swirl intensity leads to efficient, stable combustion of the syngas diffusion flame.

Shao, Weiwei; Xiong, Yan; Mu, Kejin; Zhang, Zhedian; Wang, Yue; Xiao, Yunhan

2010-06-01

191

Dual Mechanism of Gas Diffusion Through Ice Lattice Supported by Observed Temperature Dependence of Firn Air Close-off Fractionation  

NASA Astrophysics Data System (ADS)

Gas diffusion through the ice lattice is an important process, for 1) evaluating the integrity of the ice core trapped gas record of past atmospheres, 2) making corrections for fractionation that occurs as air bubbles close off at the base of the firn, 3) the possible use of that fractionation as an astronomical dating tool for ice cores (e.g. O2/N2), and 4) interpreting firn air records of atmospheric H2 over the past century. Laboratory studies of gas diffusion and permeation through ice are difficult due to the long timescales involved. An alternative approach is to sample air from the firn layer on top of polar ice sheets, and measure the in situ enrichment of small-diameter molecules such as neon, O2, and argon due to the close-off fractionation. We have measured firn air depth profiles of these gases at six polar sites spanning a wide range of temperature. Under the assumption that differential gas permeation through the ice lattice is responsible for the fractionation, and using published values for the O2 and N2 coefficients, we have inferred the neon and argon permeation coefficients. The permeation coefficients of both gases increase monotonically with site temperature, as expected, due to the Arrhenius-type temperature activation of diffusion through ice. The activation energy of argon (with a diameter of 3.54 Å) is 1.5 times that of neon (diameter 2.82 Å), consistent with the view that large diameter molecules diffuse via the breaking of hydrogen bonds in the ice lattice, which is highly temperature sensitive (Ikeda-Fukazawa et al., 2005). In contrast, small molecules diffuse primarily by the interstitial mechanism, which involves hops through the intact lattice, a process that is only weakly temperature sensitive.

Severinghaus, J. P.; Kawamura, K.; Orsi, A. J.

2013-12-01

192

Micro hollow cathode discharges  

Microsoft Academic Search

Summary form only given, as follows. Hollow cathode discharges are glow discharges with the cathode fall and negative glow confined in a cavity in the cathode. For the discharge to develop the cathode hole dimensions must be on the order of the mean free path. By reducing the cathode hole dimensions it is therefore possible to increase the pressure. Stable

K. H. Schoenbach; F. E. Peterkin; R. Verhappen

1995-01-01

193

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 ...

194

Development of a Prototype Cathode Sputtering Plant.  

National Technical Information Service (NTIS)

The coating of architectural glass with heat insulating or heat reflecting layers yields a considerable lowering of the energy consumption for room heating or air conditioning. As a method for coating the high power cathode sputtering is specifically suit...

J. Heimbach H. Hill W. Lenz B. Meyer W. D. Muenz

1983-01-01

195

Simulation of air flow in the IEA Annex 20 test room—validation of a simplified model for the nozzle diffuser in isothermal test cases  

Microsoft Academic Search

The modeling of air supply devices has been identified from the International Energy Agency (IEA) Annex 20 project as one of the most important problems in applying computational fluid dynamics (CFD) to predict air flow pattern and air distribution in buildings, and the complicated HESCO nozzle diffuser used in the IEA Annex 20 test room has been proved to be

S. Luo; J. Heikkinen; Bernard Roux

2004-01-01

196

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

SciTech Connect

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.

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

2013-01-21

197

Raman measurement of mixing and finite-rate chemistry in a supersonic hydrogen-air diffusion flame  

Microsoft Academic Search

Ultraviolet (UV) spontaneous vibrational Raman scattering and laser-induced predissociative fluorescence (LIPF) from a KrF excimer laser are combined to simultaneously measure temperature, major species concentrations (H[sub 2], O[sub 2], N[sub 2], H[sub 2]O), and OH radical concentration in a supersonic lifted co-flowing hydrogen-air diffusion flame. The axisymmetric flame is formed when a sonic jet of hydrogen mixes with a Mach

T. S. Cheng; J. A. Wehrmeyer; R. W. Pitz; O. Jr. Jarrett; G. B. Northam

1994-01-01

198

Determination of mass diffusion coefficients of oxygenated fuel additives in air using digital real-time holographic interferometry  

NASA Astrophysics Data System (ADS)

In this work, an experimental system based on digital real-time holographic interferometry for measuring the mass diffusion coefficients of fluid is introduced. The method of processing interference fringe hologram is also introduced thoroughly. By uncertainties analysis and experimental verification, the accuracy of this system is validated. The experimental uncertainties in temperature and mass diffusion coefficient are estimated to be no greater than ± 0.16 K and ± 0.2 %, respectively. On this basis, the mass diffusion coefficients of three fuel additives, diethyl 1,6-hexanedioate (diethyl adipate, DEA), dimethyl carbonate (DMC) and diethyl carbonate (DEC) in air were measured at T = (278.15 to 338.15) K under atmospheric pressure, and polynomial was fitted by the experimental data.

He, Maogang; Guo, Ying; Zhong, Qiu; Zhang, Ying

2009-02-01

199

Visualization by Neutron Diffraction of 2D Oxygen Diffusion in the Sr0.7Ho0.3CoO3-? Cathode for Solid-Oxide Fuel Cells.  

PubMed

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

Cascos, V; Martínez-Coronado, R; Alonso, J A; Fernández-Díaz, M T

2014-06-25

200

Development of a novel portable-size PEMFC short stack with electrodeposited Pt hydrogen diffusion anodes  

Microsoft Academic Search

This paper presents, for the first time, a five-cell polymer electrolyte membrane fuel cell (PEMFC) short stack with electrodeposited hydrogen diffusion anodes. The anodes were manufactured by means of galvanostatic pulse electrodeposition and the cathodes by air-brushing. Nafion® 212 was employed as a solid polymer electrolyte membrane in all cases. The short stack, whose cells had an active geometric area

Francisco Alcaide; Garbiñe Álvarez; José Alberto Blázquez; Pere L. Cabot; Oscar Miguel

2010-01-01

201

Mechanistic modelling of a cathode-supported tubular solid oxide fuel cell  

NASA Astrophysics Data System (ADS)

A two-dimensional mechanistic model of a tubular solid oxide fuel cell (SOFC) considering momentum, energy, mass and charge transport is developed. The model geometry of a single cell comprises an air-preheating tube, air channel, fuel channel, anode, cathode and electrolyte layers. The heat radiation between cell and air-preheating tube is also incorporated into the model. This allows the model to predict heat transfer between the cell and air-preheating tube accurately. The model is validated and shows good agreement with literature data. It is anticipated that this model can be used to help develop efficient fuel cell designs and set operating variables under practical conditions. The transport phenomena inside the cell, including gas flow behaviour, temperature, overpotential, current density and species concentration, are analysed and discussed in detail. Fuel and air velocities are found to vary along flow passages depending on the local temperature and species concentrations. This model demonstrates the importance of incorporating heat radiation into a tubular SOFC model. Furthermore, the model shows that the overall cell performance is limited by O 2 diffusion through the thick porous cathode and points to the development of new cathode materials and designs being important avenues to enhance cell performance.

Suwanwarangkul, R.; Croiset, E.; Pritzker, M. D.; Fowler, M. W.; Douglas, P. L.; Entchev, E.

202

Cathode Sputtering in Hollow Cathode Discharges  

Microsoft Academic Search

In order to investigate the processes responsible for a negative resistance of the hollow cathode discharge, several discharge parameters are measured with a Langmuir probe. The vapor density distributions of the sputtered cathode metal are measured by the absorption method of the resonance radiation of the metal atom. Almost all the metal atoms in the central part of the cathode

Toshimitsu Musha

1962-01-01

203

Cathodic electrode  

SciTech Connect

This patent describes a cathodic electrode suitable for use in a non-aqueous battery system comprising at least one substantially homogeneous, microporous sheet product having a void volume of from 15 to 25 volume percent and having a composition consisting essentially of from about 90-94 weight percent of particulate material consisting essentially of titanium disulfide having an average particle size of less than about 20 microns, from about 6-10 eight percent of high density polyethylene having a weight average molecular weight of from about 200,000 to 500,000 and from 0 to about 2 weight percent of an organic plasticizer for the polyethylene; and a current collector composed of a conductive material. The collector is in intimate contact with each of the least one microporous sheet product.

Anderman, M.; Lundquist, J.T. Jr.

1988-03-15

204

Cathodic electrode  

SciTech Connect

A cathodic electrode suitable for use in a non-aqueous battery system is described comprising at least one substantially homogeneous, microporous sheet product having a composition of from about 70-98 weight percent of particulate material comprising titanium disulfide having an average particle size of less than about 20 microns with the particulate material having up to about 30 weight percent of a conductive diluent having an average particle size of from 1 to 100 millimicrons, from about 2-30 weight percent of high density polyethylene having a weight average molecular weight of from about 150,000 to 5,000,000 and from 0 to about 5 weight percent of an organic plasticizer for the polyethylene; and a current collector composed of a conductive material. The collector is in intimate contact with each of at least one microporous sheet product.

Anderman, M.; Johnson, S.L.

1988-04-05

205

Electrical and optical characteristics of diffuse nanosecond pulsed discharge plasma using a needle-array electrode in atmospheric air  

NASA Astrophysics Data System (ADS)

In this paper, a stable and diffuse dielectric barrier discharge plasma excited by bipolar nanosecond pulse is obtained under a needle-array electrode at atmospheric pressure in air. The images of the diffuse discharge, electric characteristics, and the optical emission spectra emitted from the diffuse discharge are investigated under mono and multi needle electrodes configuration. The peak value of discharge current, the average power, the power density, the emission intensity of N2 (C3?u ?B3?g, 0-0), and the gas temperature of the diffuse dielectric barrier discharge plasmas are investigated under different needle electrode numbers based on the waveforms of pulse voltage-current and the optical emission spectra. Moreover, the plasma area is obviously enlarged in the transverse direction when the needle electrode number is increased from 1 to 13. An area approximately 65 × 45 mm2 diffuse discharge plasma region under 13 needle electrodes can be obtained and the discharge plasma still keeps good uniformity, which could be used for large-area surface processing in several fields spanning from biological sterilization and plasma medicine to surface modification of materials and synthesis of functional materials.

Liu, Zhi-jie; Wang, Wen-chun; Zhang, Li; Wang, Sen; Yang, De-zheng; Zhang, Shuai; Tang, Kai

2014-05-01

206

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)

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.

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

1989-01-01

207

On the air-filled effective porosity parameter of Rogers and Nielson's (1991) bulk radon diffusion coefficient in unsaturated soils.  

PubMed

The radon exhalation rate at the earth's surface from soil or rock with radium as its source is the main mechanism behind the radon activity concentrations observed in both indoor and outdoor environments. During the last two decades, many subsurface radon transport models have used Rogers and Nielson's formula for modeling the unsaturated soil bulk radon diffusion coefficient. This formula uses an "air-filled effective porosity" to account for radon adsorption and radon dissolution in the groundwater. This formula is reviewed here, and its hypotheses are examined for accuracy in dealing with subsurface radon transport problems. The author shows its limitations by comparing one dimensional steady-state analytical solutions of the two-phase (air/water) transport equation (Fick's law) with Rogers and Nielson's formula. For radon diffusion-dominated transport, the calculated Rogers and Nielson's radon exhalation rate is shown to be unrealistic as it is independent of the values of the radon adsorption and groundwater dissolution coefficients. For convective and diffusive transport, radon exhalation rates calculated using Fick's law and this formula agree only for high values of gas-phase velocity and groundwater saturation. However, these conditions are not usually met in most shallow subsurface environments where radon migration takes place under low gas phase velocities and low water saturation. PMID:24670909

Saâdi, Zakaria

2014-05-01

208

Numerical study on rectangular microhollow cathode discharge  

SciTech Connect

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.

He Shoujie [School of Science, Beijing Institute of Technology, Beijing 100081 (China); College of Physics Science and Technology, Hebei University, Baoding 071002 (China); Ouyang Jiting; He Feng; Li Shang [School of Science, Beijing Institute of Technology, Beijing 100081 (China)

2011-03-15

209

Hollow cathode apparatus  

NASA Technical Reports Server (NTRS)

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.

Aston, G. (inventor)

1984-01-01

210

Determining the coefficients of ambipolar ion diffusion by the method of laser optogalvanic spectroscopy in a luminous gas-air flame  

SciTech Connect

The coefficients of ambipolar diffusion of lithium, sodium, nickel, indium, platinum, and lead ions were measured by laser optogalvanic spectroscopy in the upper cone of a luminous gas-air flame at atmospheric pressure in the absence of an electric field in the flame. The coefficients of diffusion and mobility of the singly charged ions of these elements were calculated from the experimental data.

Novodvorskii, O.A.; Ilyukhin, A.B.; Kuzyakov, Yu.Ya.

1988-03-01

211

Determining the coefficients of ambipolar ion diffusion by the method of laser optogalvanic spectroscopy in a luminous gas-air flame  

Microsoft Academic Search

The coefficients of ambipolar diffusion of lithium, sodium, nickel, indium, platinum, and lead ions were measured by laser optogalvanic spectroscopy in the upper cone of a luminous gas-air flame at atmospheric pressure in the absence of an electric field in the flame. The coefficients of diffusion and mobility of the singly charged ions of these elements were calculated from the

O. A. Novodvorskii; A. B. Ilyukhin; Yu. Ya. Kuzyakov

1988-01-01

212

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...

213

Nitric oxide formation by inverse diffusion flames in staged-air burners  

Microsoft Academic Search

Chemiluminescent measurements of NO and NOx in the exhaust of a laboratory staged-air burner were made to investigate furnace emissions. Emissions throughout the transition from primary fuel-rich to overall fuel-lean conditions were mapped for a range of secondary-air jet parameters. This allows quantification of the NOx emissions through the rich-to-lean transition and also their sensitivity to secondary-air injection parameters. Mixing

William P. Partridge; Normand M. Laurendeau

1995-01-01

214

Nanotube cathodes.  

SciTech Connect

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.

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

2006-11-01

215

Chemical diffusion in perovskite cathodes of solid oxide fuel cells: the Sr doped LaMn 1? x M x O 3 (M?Co, Fe) systems  

Microsoft Academic Search

This paper reports the results of chemical diffusion coefficient measurements for oxygen in (La,Sr)(Mn,Co)O3 and (La,Sr)(Mn,Fe)O3 using a manometric method in the temperature range of 773 to 1023 K. It was observed that the addition of Fe or Co into (La4xSrx)1?yMnO3 results in a substantial increase of the chemical diffusion coefficient. In the range 25–100 mol% of Co or Fe

S. P. S Badwal; S. P Jiang; J Love; J Nowotny; M Rekas; E. R Vance

2001-01-01

216

On Turbulent Diffusion in the Ground Layer of Air. Part II.  

National Technical Information Service (NTIS)

The report is a continuation of a theoretical paper on vertical diffusion in the atmospheric surface boundary layer (two-layer problem) published by the author in 1965 (Bulgarian Academy of Sciences. Geophysical Institute. Trudy, no. 6, 1965). An asymptot...

D. Yordanov

1968-01-01

217

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

NASA Astrophysics Data System (ADS)

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.

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

218

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)

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.

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

1989-01-01

219

Carbon-containing cathodes for enhanced electron emission  

DOEpatents

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.

Cao, Renyu (Cupertino, CA); Pan, Lawrence (Pleasanton, CA); Vergara, German (Madrid, ES); Fox, Ciaran (Los Altos, CA)

2000-01-01

220

Pneumatosis cystoides intestinalis associated with massive free air mimicking perforated diffuse peritonitis  

PubMed Central

While pneumatosis cystoides intestinalis (PCI) is a rare disease entity associated with a wide variety of gastrointestinal and non-gastrointestinal disorders, PCI associated with massive intra- and retroperitoneal free air is extremely uncommon, and is difficult to diagnose differentially from perforated peritonitis. We present two cases of PCI associated with massive peritoneal free air and/or retroperitoneal air that mimicked perforated peritonitis. These cases highlight the clinical importance of PCI that mimics perforated peritonitis, which requires emergency surgery. Preoperative imaging modalities and diagnostic laparoscopy are useful to make an accurate diagnosis.

Sakurai, Yoichi; Hikichi, Masahiro; Isogaki, Jun; Furuta, Shinpei; Sunagawa, Risaburo; Inaba, Kazuki; Komori, Yoshiyuki; Uyama, Ichiro

2008-01-01

221

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

PubMed

The diffusion coefficients of explosives are crucial in their trace detection and lifetime estimation. We report on the experimental values of diffusion coefficients of three of the most important explosives in both military and industry: TNT, PETN, and RDX. Thermogravimetric analysis (TGA) was used to determine the sublimation rates of TNT, PETN, and RDX powders in the form of cylindrical billets. The TGA was calibrated using ferrocene as a standard material of well-characterized sublimation rates and vapor pressures to determine the vapor pressures of TNT, PETN, and RDX. The determined sublimation rates and vapor pressures were used to indirectly determine the diffusion coefficients of TNT, PETN, and RDX for the first time. A linear log-log dependence of the diffusion coefficients on temperature is observed for the three materials. The diffusion coefficients of TNT, PETN, and RDX at 273 K were determined to be 5.76×10(-6)m(2)/sec, 4.94×10(-6)m(2)/s, and 5.89×10(-6)m(2)/s, respectively. Values are in excellent agreement with the theoretical values in literature. PMID:24840410

Hikal, Walid M; Weeks, Brandon L

2014-07-01

222

A manometric method for the determination of chemical diffusion in perovskite-type cathode materials of the solid oxide fuel cell  

Microsoft Academic Search

This paper describes a manometric method for the determination of chemical diffusion coefficients from gas\\/solid equilibration kinetics for electrode materials of the type (La,Sr)(Mn,Fe,Co)O3. The equilibration kinetics was monitored by measurements of the p(O2) changes during a reaction between oxygen and the electrode material involving both oxidation and reduction experiments in the temperature range 773–1123 K. Activation energy of the

S. P. S. Badwal; S. P. Jiang; J. Love; J. Nowotny; M. Rekas; E. R. Vance

2001-01-01

223

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 ...

224

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

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

225

On the effect of carbon monoxide addition on soot formation in a laminar ethylene/air coflow diffusion flame  

SciTech Connect

The effect of carbon monoxide addition on soot formation in an ethylene/air diffusion flame is investigated by experiment and detailed numerical simulation. The paper focuses on the chemical effect of carbon monoxide addition by comparing the results of carbon monoxide and nitrogen diluted flames. Both experiment and simulation show that although overall the addition of carbon monoxide monotonically reduces the formation of soot, the chemical effect promotes the formation of soot in an ethylene/air diffusion flame. The further analysis of the details of the numerical result suggests that the chemical effect of carbon monoxide addition may be caused by the modifications to the flame temperature, soot surface growth and oxidation reactions. Flame temperature increases relative to a nitrogen diluted flame, which results in a higher surface growth rate, when carbon monoxide is added. Furthermore, the addition of carbon monoxide increases the concentration of H radical owing to the intensified forward rate of the reaction CO + OH = CO{sub 2} + H and therefore increases the surface growth reaction rates. The addition of carbon monoxide also slows the oxidation rate of soot because the same reaction CO + OH = CO{sub 2} + H results in a lower concentration of OH. (author)

Guo, Hongsheng; Thomson, Kevin A.; Smallwood, Gregory J. [Institute for Chemical Process and Environmental Technology, National Research Council of (Canada)

2009-06-15

226

Field Evaluation of a Diffusive Sampler for Monitoring Formaldehyde in Air: A Comparison of Methods  

Microsoft Academic Search

This field study was conducted to evaluate the performance of the SKC Passive Bubbler (SKC Inc., Eighty Four, Pennsylvania) in monitoring formaldehyde in a working environment. For comparison, a traditional pump and impinger method, National Institute for Occupational Safety and Health (NIOSH) Method 3500, was used as the reference method. Two approaches were used for the field evaluation of diffusive

John R. Kollman

1994-01-01

227

Recent Advances in Thermionic Cathodes  

SciTech Connect

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.

Ives, R. Lawrence; Miram, George; Collins, George [Calabazas Creek Research, Inc., 690 Port Drive, San Mateo, CA 94404 (United States); Falce, Louis R. [Consultant, 16521 W. Pueblo Lane, Surprise AZ (United States)

2010-11-04

228

Pulsed mode cathode  

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

229

Pressed boride cathodes  

NASA Technical Reports Server (NTRS)

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.

Wolski, W.

1985-01-01

230

Interactions between arrayed hollow cathodes  

NASA Astrophysics Data System (ADS)

An array of novel hollow cathode plasma sources of 4 mm diameter and driven by up to 500 W of 13.56 MHz rf power was constructed. It was investigated using spatially resolved Langmuir probe measurements in the plasma expansion region. Initial results suggest the plasma observed downstream is the combination of a diffusion from the exit orifice of the 30 mm long cylindrical source region and a uniform plasma created in the expansion region. By measuring the ion density of the plasma plumes produced by two or more active hollow cathode sources, their mutual interaction has been inferred with the aim of determining whether a much larger array of sources could be envisioned. The effectiveness of the plasma in dissociating reactive species was tested using SF6 and measuring etch rates on unbiased silicon wafers. The results have been modelled and show that it is possible to produce a uniform spread of ±5%.

Dixon, Sam; Charles, Christine; Boswell, Rod; Cox, Wes; Holland, John; Gottscho, Richard

2013-04-01

231

CO-HP2-N2/Air Diffusion Flames: Thermal Radiation and Transient Effects  

NASA Astrophysics Data System (ADS)

Flames of CO/H2/N2 fuels have been investigated for various reasons. For instance, laminar, premixed flames were investigated experimentally by van Tiggelen and coworkers to determine the rate constant of the water-gas shift reaction [12.1] and the inhibition induced by CF3BR [12.2], [12.3], and numerically by Rogg and Williams [12.4] who derived a reduced kinetic mechanism for wet CO flames. Laminar, non-premixed flames were studied, for instance, by Drake and Blint [12.5], who investigated experimentally and numerically the structure of counterflow diffusion flames in the Tsuji geometry paying special attention to NO x formation. For the latter geometry, Chen et al [12.6] derived a reduced kinetic mechanism which they used in the numerical simulation of turbulent diffusion flames. For further information on work relevant to flames of CO/H2/N2 fuels the cited papers should be consulted.

Chen, J.-Y.; Liu, Y.; Rogg, B.

232

Raman measurement of mixing and finite-rate chemistry in a supersonic hydrogen-air diffusion flame  

SciTech Connect

Ultraviolet (UV) spontaneous vibrational Raman scattering and laser-induced predissociative fluorescence (LIPF) from a KrF excimer laser are combined to simultaneously measure temperature, major species concentrations (H[sub 2], O[sub 2], N[sub 2], H[sub 2]O), and OH radical concentration in a supersonic lifted co-flowing hydrogen-air diffusion flame. The axisymmetric flame is formed when a sonic jet of hydrogen mixes with a Mach 2 annular jet of vitiated air. Mean and rms profiles of temperature, species concentrations, and mixture fraction are obtained throughout the supersonic flame. Simultaneous measurements of the chemical species and temperature are compared with frozen chemistry and equilibrium chemistry limits to assess the local state of the mixing and chemistry. Upstream of the lifted flame base, a very small amount of reaction occurs form mixing with hot vitiated air. Downstream of the lifted flame base, strong turbulent mixing leads to sub equilibrium values of temperature and OH concentration. Due to the interaction of velocity and temperature in supersonic compressible flames, the fluctuations of temperature and species concentrations are found to be higher than subsonic flames. Farther downstream, slow three-body recombination reactions result in super equilibrium OH concentrations that depress temperatures below their equilibrium values.

Cheng, T.S.; Wehrmeyer, J.A.; Pitz, R.W. (Vanderbilt Univ., Nashville, TN (United States). Dept. of Mechanical Engineering); Jarrett, O. Jr.; Northam, G.B. (NASA, Hampton, VA (United States). Langley Research Center)

1994-10-01

233

A sensitive diffusion sampler for the determination of volatile organic compounds in ambient air  

Microsoft Academic Search

We developed a diffusive sampling device (DSD-voc) for volatile organic compounds (VOCs) which is suitable for collection of low level VOCs and analysis with thermal desorption. This sampling device is composed of two parts, an exposure part made of a porous polytetrafluoroethylene (PTFE) filter, and an analysis part made of stainless-steel tubing. The DSD-voc collects VOCs through the mechanism of

Shigehisa Uchiyama; Masae Asai; Shuji Hasegawa

1999-01-01

234

The Diffusion of Market-Based Instruments: The Case of Air Pollution  

Microsoft Academic Search

This article examines adoption of a market instrument for reducing air pollution across the U.S. states. Because market instruments are viewed as reducing compliance costs, we hypothesize that market instruments should be more likely adopted in states whose electricity prices are higher than the average price in other states, especially their economic peers. Using a hazard model for a panel

Nives Dolšak; Karen Sampson

2012-01-01

235

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

SciTech Connect

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.

Nowacki, P.; Samson, P.J.; Sillman, S. [Univ. of Michigan, Ann Arbor, MI (United States)] [Univ. of Michigan, Ann Arbor, MI (United States)

1996-10-01

236

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)

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.

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

2013-01-01

237

Computational Modelling of Swirling Diffusion Flame in Air-Staged Burner  

Microsoft Academic Search

The present paper presents an application of computational fluid dynamics (CFD) to simulating an industrial-scale low NOx burner. The main aim of the performed research is to provide the experimentally validated computational prediction of turbulent, non-premixed swirling gas flame in an air-staged burner. Computations are performed using the k-?, k-? and Reynolds-stress turbulence models in order to examine the relative

P. B?lohradský; V. Kermes; P. Stehlík

238

Diffusion Coefficients of SO2 in Water and Partition Coefficients of SO2 in Water-Air Interface at Different Temperature and pH Values  

Microsoft Academic Search

Reversed flow gas chromatography was applied to measure the diffusion coefficient of SO2 in water, the partition coefficient of SO2 in air–water interface, and the rate constant, kR, for chemical reaction between SO2 and water at various temperature and pH values. A linear increment of the diffusion coefficients of SO2 in water with temperature is drawn while the partition coefficients

A. Koliadima; J. Kapolos; L. Farmakis

2009-01-01

239

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

DOEpatents

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.

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

2013-08-27

240

An improved cathode for alkaline fuel cells  

Microsoft Academic Search

The use of nickel foam as an electrode substrate in alkaline fuel cells (AFCs) has been investigated for bipolar cells incorporating an electrically conducting gas diffusion layer (GDL). Improved performance, compared to a previous design, was obtained by adding an extra active layer (AL) composed of manganese (IV) oxide (MnO2) deposited onto carbon black. This new cathode design performed significantly

F. Bidault; D. J. L. Brett; P. H. Middleton; N. Abson; N. P. Brandon

2010-01-01

241

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

NASA Astrophysics Data System (ADS)

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.

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

1985-12-01

242

Experimental method development for estimating solid-phase diffusion coefficients and material/air partition coefficients of SVOCs  

NASA Astrophysics Data System (ADS)

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 estimate parameters Dm and Kma. The SVOCs chosen for study were polychlorinated biphenyl (PCB) congeners, including PCB-52, PCB-66, PCB-101, PCB-110, and PCB-118. The test materials included polypropylene, high density polyethylene, low density polyethylene, polytetrafluoroethylene, polyether ether ketone, glass, stainless steel and concrete. Two 53-L environmental chambers were connected in series, with the relatively stable SVOCs source in the source chamber and the test materials, made as small “buttons”, in the test chamber. Prior to loading the test chamber with the test materials, the test chamber had been dosed with SVOCs for 12 days to “coat” the chamber walls. During the tests, the material buttons were removed from the test chamber at different exposure times to determine the amount of SVOC absorbed by the buttons. SVOC concentrations at the inlet and outlet of the test chamber were also monitored. The data were used to estimate the partition and diffusion coefficients by fitting a sink model to the experimental data. The parameters obtained were employed to predict the accumulation of SVOCs in the sink materials using an existing mass transfer model. The model prediction agreed reasonably well with the experimental data.

Liu, Xiaoyu; Guo, Zhishi; Roache, Nancy F.

2014-06-01

243

A sensitive diffusion sampler for the determination of volatile organic compounds in ambient air  

NASA Astrophysics Data System (ADS)

We developed a diffusive sampling device (DSD-voc) for volatile organic compounds (VOCs) which is suitable for collection of low level VOCs and analysis with thermal desorption. This sampling device is composed of two parts, an exposure part made of a porous polytetrafluoroethylene (PTFE) filter, and an analysis part made of stainless-steel tubing. The DSD-voc collects VOCs through the mechanism of molecular diffusion. Collection is controlled by moving the adsorbent from the exposure part to the analysis part by changing the posture of the DSD-voc. Adsorbates in the DSD-voc were analyzed by GC/MS with a thermal desorption cold trap injector (TCT). The TCT has the advantage of being able to accept the entire quantity of VOCs. We connected a condenser between the DSD-voc and the trap tube to prevent moisture from freezing in the trap tube when the sampler was packed with strong adsorbent. We also examined the desorption efficiency for VOCs from several types of adsorbents (Carboxen TM 1000, Carbosieve TM G, Carbosieve S III, Carbotrap TM B, and activated carbon) over a wide range of temperatures. Carboxen 1000 was suitable for the determination of VOCs with a low boiling point range, from CFC12 to hexane, while Carbotrap B was suitable for VOCs from hexane to 1,4-dichlorobenzene. The limits of detection with Carboxen 1000 and Carbotrap B were 0.036-0.046 and 0.0035-0.014 ppb, respectively, for a sampling duration of 24 h. Coefficients of variation for concentrations of major VOCs ranged from 3.8 to 14%. It is possible to estimate atmospheric VOCs at sub-parts per billion (sub-ppb), with high sensitivity, by using both adsorbents in combination.

Uchiyama, Shigehisa; Asai, Masae; Hasegawa, Shuji

244

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

SciTech Connect

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.

Ribiere, M.; Cheron, B. G. [Coria UMR 6614, CNRS, Avenue de l'Universite, 76801 Saint Etienne du Rouvray (France); Karabourniotis, D. [Department of Physics, Institute of Plasma Physics, University of Crete, 71003 Heraklion (Greece)

2009-04-15

245

Application of a Reynolds Stress turbulence model to a supersonic hydrogen-air diffusion flame  

NASA Technical Reports Server (NTRS)

A second-order differential Reynolds Stress turbulence model has been applied to the Favre-averaged Navier-Stokes equations for the study of supersonic flows undergoing hydrogen-air chemical reactions. An assumed Beta Probability Density Function is applied to account for the chemical source terms in the conservation equations. An algebraic Reynolds Flux model is used for the fluctuating density-velocity as well as the species mass fraction-velocity correlations. The variances of temperature and species fluctuations are also modelled using an algebraic flux technique. A seven-species, seven-reaction finite rate chemistry mechanism is used to simulate the combustion processes. The resulting formulation is validated by comparison with experimental data on reacting supersonic axisymmetric jets. Results obtained for specific conditions indicate that the effect of chemical reaction on the turbulence is significant.

Chandrasekhar, R.; Tiwari, S. N.

1991-01-01

246

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

NASA Astrophysics Data System (ADS)

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.

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

247

Synchrotron Investigations of SOFC Cathode Degradation  

SciTech Connect

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

Idzerda, Yves

2013-09-30

248

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...

249

Impact of salinity on cathode catalyst performance in microbial fuel cells (MFCs)  

Microsoft Academic Search

Several alternative cathode catalysts have been proposed for microbial fuel cells (MFCs), but effects of salinity (sodium chloride) on catalyst performance, separate from those of conductivity on internal resistance, have not been previously examined. Three different types of cathode materials were tested here with increasingly saline solutions using single-chamber, air-cathode MFCs. The best MFC performance was obtained using a Co

Xi Wang; Shaoan Cheng; Xiaoyuan Zhang; Xiao-yan Li; Bruce E. Logan

2011-01-01

250

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

NASA Technical Reports Server (NTRS)

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.

Sislian, J. P.

1978-01-01

251

Hollow cathode magnetron  

SciTech Connect

A new type of plasma sputtering device, named the hollow cathode magnetron (HCM), has been developed by surrounding a planar magnetron cathode with a hollow cathode structure. Operating characteristics of HCMs, current{endash}voltage (I{endash}V) curves for fixed discharge pressure and voltage{endash}pressure (V{endash}p) curves for fixed cathode current, are measured. Such characteristics are compared with their planar magnetron counterparts. New operation regimes, such as substantially lower pressures (0.3 mTorr), were discovered for HCMs. Cathode erosion profiles show marked improvement over planar magnetron in terms of material utilization. The use of HCMs for thin film deposition are discussed. {copyright} {ital 1999 American Vacuum Society.}

Wang, Z.; Cohen, S.A. [Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)] [Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)

1999-01-01

252

Novel electron beam cathode  

NASA Astrophysics Data System (ADS)

Experiments have been conducted during the past year to develop an electron beam cathode which is capable of producing a moderate perveance beam for several microsecond pulse lengths and is not susceptible to diode closure. The requirements, successfully met by this salt-based cold emission cathode, include operating in modest vacuums of 10-5 Torr, voltages less than or equal 160 kV, and the ability to generate solid or annular cross section space-charge-limited electron beams. Data on the operating performance of this salt cathode and streak photographs showing the uniformity of the emission of the electron beam are presented. Comparisons of this salt cathode will be made with other electron beam cathode materials.

Hendricks, K. J.; Voss, D. E.; Garate, E.; McWilliams, R.; Spencer, T. A.

1993-07-01

253

Coil hollow cathode for metal vapor lasers  

NASA Astrophysics Data System (ADS)

A metal vapor hollow cathode laser tube with a coil hollow cathode is described which facilitates diffusion of metal atoms into the discharge region. The device comprises a stainless steel cylinder with an 11 mm inner diam and 10 cm long, a cathode arranged concentrically within the anode and having a 6 mm inner diam and 10 cm length and made of 1 mm Mo wire. Discharges were excited by 4 ms current pulses in a repetition sequence of 12.5 Hz. Tests were conducted with different distances between the coil windings, showing a tripling of voltage in going from 0.4 to 3.2 mm, and pressure dependences are provided. Being able to increase the operating voltages is noted to allow efficient excitation of the ionic spectrum of metals.

Grozeva, M.; Sabotinov, N.

1982-03-01

254

Separation of metals at vibrating cathodes  

SciTech Connect

The authors studies of vibrating electrodes for the cathodic deposition of metals showed that diffusional difficulties in the discharge of ions can be lowered by vibration. This induced them to examine the effect of cathode vibration on the separation of Zr from Hf or of Nb from Ta which are present as impurities during refining in chloride fluoride melts. It was shown in this work that an efficient separation of metals during electrolysis first of all depends on the difference between their conventional standard potentials. A difference between the diffusion coefficients of the metal species to be separated has marked effects when the conventional standard potentials are similar or when the impurity has a more positive potential. Vibration of the cathode can have important effects.

Khramov, A.P.; Ivanovskii, L.E.; Batukhtin, V.P.

1987-10-01

255

Planar-focusing cathodes.  

SciTech Connect

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.

Lewellen, J. W.; Noonan, J.; Accelerator Systems Division (APS)

2005-01-01

256

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

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

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

2006-02-01

257

Experimental determination of the velocity and strain rate field in a laminar H2/Air counter-flow diffusion flame via LDA  

NASA Technical Reports Server (NTRS)

Measurements of the axial and radial components of velocity on the air side of stagnation in an axisymmetric H2/Air laminar counter-flow diffusion flame are reported. Results include the two-dimensional velocity field and computed velocity gradients (strain rates) along the stagnation streamline at two 'characteristic' strain rates, below the extinction limit. The measurements generally verify the modeling assumptions appropriate to the model of Kee et al. (1988). The 'traditional' potential flow model is not consistent with the measured results.

Yeo, S. H.; Dancey, C. L.

1991-01-01

258

The numerical modelling of Joule heating effects in thoriated tungsten cathodes of high-current plasma arcs  

Microsoft Academic Search

The influence of the Joule heating on the performance of thoriated tungsten cathodes working at current densities of 103-104 A cm-2 is investigated. The variation of the degree of coverage of the cathode surface by thorium atoms is considered, together with the heat conduction and the diffusion of thorium in the cathode bulk. The nonlinear system of equations governing these

E. Casado; V. Colomer

2000-01-01

259

Experimental study of vortex diffusers  

SciTech Connect

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.

Shakerin, S.; Miller, P.L. [National Renewable Energy Lab., Golden, CO (United States)

1995-11-01

260

An in-situ method to measure a soil`s undisturbed pore gas radon concentration, diffusion length for radon and air filled porosity  

Microsoft Academic Search

Previous work has shown that for soils of insignificant permeability (soils with permeability less than about 10⁻¹² m²) the important soil parameters for characterizing radon mobility in the soil`s steady-state pore gas radon concentration at depth (C{sub s}), the soil`s bulk diffusion length for radon (L) and the soil`s air filled porosity (p{sub a}). Existing methods to measure these parameters

M. S. Jarzemba; T. E. Blue

1996-01-01

261

Effect of weave tightness and structure on the in-plane and through-plane air permeability of woven carbon fibers for gas diffusion layers  

Microsoft Academic Search

In this study, woven gas diffusion layers (GDLs) with varying weave type and tightness are investigated. Plain and twill weave patterns were manufactured in-house. The in-plane and through-plane air permeability of the woven samples were tested, and mercury intrusion porosimetry (MIP) tests were performed to study the pore structure. It was found that the twill weave has a higher permeability

Terry B. Caston; Andrew R. Murphy; Tequila A. L. Harris

2011-01-01

262

Cathodes - Technological review  

NASA Astrophysics Data System (ADS)

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.

Cherkouk, Charaf; Nestler, Tina

2014-06-01

263

A model of hollow cathode plasma chemistry  

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

264

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

PubMed

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

Jaworski, Jacek; Redlarski, Grzegorz

2014-08-01

265

Cathode materials review  

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

266

Positive streamer in a weak field in air: A moving avalanche-to-streamer transition  

Microsoft Academic Search

Two-dimensional (2D) simulation of a positive streamer in air between a point anode and a plane cathode is performed within the scope of a diffusion-drift model. A fine structure of streamer head is obtained. Based on the simulation results, the head is treated as a moving region of an avalanche-to-streamer transition (AST). Using ``empirical'' relations, which follow from 2D simulations,

A. A. Kulikovsky

1998-01-01

267

Reduction of oxygen in an acidic methanol\\/oxygen (air) fuel cell: an online MS study  

Microsoft Academic Search

The reduction of oxygen was studied with online mass spectroscopy on 5% Pt\\/Norit BRX and on 20% FePP(NO2)4\\/RB PTFE-bonded gas diffusion electrodes. The performance of the catalysts was analysed under conditions of an acidic methanol\\/oxygen (air) fuel cell cathode in the presence of methanol in solution. Following the mass signalm\\/e = 32 for oxygen it can be shown that FePP(NO2)4

B. Bittins-Cattaneo; S. Wasmus; B. Lopez-Mishima; W. Vielstich

1993-01-01

268

Lanthanum hexaboride hollow cathode for dense plasma production.  

PubMed

A hollow tube cathode using lanthanum hexaboride as the electron emitter has been designed and constructed. Tests in both argon and hydrogen indicate that this cathode is capable of producing over 800 A of electron current continuously, corresponding to over 25 A/cm(2) from the LaB(6). The cathode has been operated for over 300 h and exposed to air more than 100 times with no deterioration in emission. Projected lifetime is in excess of 3500 h for the sintered LaB(6) piece tested in this configuration. Construction details, performance characteristics, and discussions of space charge limits on emission are described. PMID:18699127

Goebel, D M; Crow, J T; Forrester, A T

1978-04-01

269

Hollow-cathode arc discharge  

NASA Astrophysics Data System (ADS)

An experimental study of a high-current hollow-cathode arc is presented. It is shown that the zone of current attachment to the internal surface of the cathode is significantly narrower than the hotter zone of the cathode; the plasma current to the cathode beyond this attachment zone is equal to zero. An equation is obtained for determining the position of the attachment zone for different discharge parameters. It is shown that the flow of the plasma-forming gas through the cathode has a stabilizing effect on the plasma column between the cathode and the anode.

Cherednichenko, V. S.; Kosinov, V. A.

1980-10-01

270

Cathode Research and the Threshold Cathode Test Facility.  

National Technical Information Service (NTIS)

This technical report discusses the parameters of the Threshold Cathode Test Facility (TCTF) and the use of the TCTF to perform cathode research. Experimental and simulation results are documented, as well as references to additional, more detailed, catho...

R. J. Umstattd T. A. Spencer

2002-01-01

271

Filtered cathodic arc source  

DOEpatents

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.

Falabella, S.; Sanders, D.M.

1994-01-18

272

Three-dimensional visualization of morphology and ventilation procedure (air flow and diffusion) of a subdivision of the acinus using synchrotron radiation microtomography of the human lung specimens  

NASA Astrophysics Data System (ADS)

We have previously reported a synchrotron radiation (SR) microtomography system constructed at the bending magnet beamline at the SPring-8. This system has been applied to the lungs obtained at autopsy and inflated and fixed by Heitzman"s method. Normal lung and lung specimens with two different types of pathologic processes (fibrosis and emphysema) were included. Serial SR microtomographic images were stacked to yield the isotropic volumetric data with high-resolution (12 ?m3 in voxel size). Within the air spaces of a subdivision of the acinus, each voxel is segmented three-dimensionally using a region growing algorithm ("rolling ball algorithm"). For each voxel within the segmented air spaces, two types of voxel coding have been performed: single-seeded (SS) coding and boundary-seeded (BS) coding, in which the minimum distance from an initial point as the only seed point and all object boundary voxels as a seed set were calculated and assigned as the code values to each voxel, respectively. With these two codes, combinations of surface rendering and volume rendering techniques were applied to visualize three-dimensional morphology of a subdivision of the acinus. Furthermore, sequentially filling process of air into a subdivision of the acinus was simulated under several conditions to visualize the ventilation procedure (air flow and diffusion). A subdivision of the acinus was reconstructed three-dimensionally, demonstrating the normal architecture of the human lung. Significant differences in appearance of ventilation procedure were observed between normal and two pathologic processes due to the alteration of the lung architecture. Three-dimensional reconstruction of the microstructure of a subdivision of the acinus and visualization of the ventilation procedure (air flow and diffusion) with SR microtomography would offer a new approach to study the morphology, physiology, and pathophysiology of the human respiratory system.

Shimizu, Kenji; Ikura, Hirohiko; Ikezoe, Junpei; Nagareda, Tomofumi; Yagi, Naoto; Umetani, Keiji; Imai, Yutaka

2004-04-01

273

Comparison of membrane- and cloth-cathode assembly for scalable microbial fuel cells: Construction, performance and cost  

Microsoft Academic Search

The aim of this study is to compare the performance of different membrane cathode assembly (MCA) and cloth-cathode assembly (CCA) in air-chamber microbial fuel cells (MFCs) and provide an optimum cathode configuration for MFC scaling up. Two MCAs were prepared by hot-pressing carbon cloth containing cathodic catalyst to anion exchange membrane (AEM) and cation exchange membrane (CEM), respectively. A CCA

Li Zhuang; Chunhua Feng; Shungui Zhou; Yongtao Li; Yueqiang Wang

2010-01-01

274

Discharge with a Hollow Cathode (Selected Chapters).  

National Technical Information Service (NTIS)

Contents: Determination and classification of various types of discharge with a hollow cathode; Experimental characteristics of glow discharge with a hollow cathode; The theory of glow discharge with a hollow cathode; Gas-discharge hollow cathode lasers.

B. I. Moskalev

1973-01-01

275

Hollow Cathode Discharges: Analytical Applications.  

National Technical Information Service (NTIS)

The low pressure glow discharges considered in this paper are the hollow cathode (Paschen), and the flat cathode (Grimm). Both discharges have similar voltage--current characteristics which are responsible for their radiation stability. The analytical sam...

R. Mavrodineanu

1983-01-01

276

Soft X-Ray Spectroscopic Study of Dense Strontium-Doped Lanthanum Manganite Cathodes for Solid Oxide Fuel Cell Applications  

SciTech Connect

The modification of the Mn charge-state, chemical composition and electronic structure of La0.8Sr0.2MnO3 (LSMO) cathodes for solid oxide fuel cell (SOFC) applications remains an area of interest, due to the poorly understood enhanced catalytic activity (often referred to as the "burn-in" phenomenon) observed after many hours of operation. Using a combination of core-level X-ray photoemission spectroscopy (XPS), X-ray emission/absorption spectroscopy (XES/XAS), resonant inelastic X-ray scattering (RIXS) and resonant photoemission spectroscopy (RPES), we have monitored the evolution of these properties in LSMO at various stages of fabrication and operation. By rapidly quenching and sealing in vacuum, we were able to directly compare the pristine (as-fabricated) LSMO with both "heat-treated" (800°C in air, and no bias) and "burnt-in" (800°C in air, -1 V bias) LSMO cathodes i.e. before and after the activation observed in our electrochemical impendence spectroscopy measurements. Comparison between the O K-edge XAS/XES and Mn L3,2-edge XAS of pristine and “burnt-in” LSMO cathodes revealed a severe change in the oxygen environment along with a reduced Mn2+ presence near the surface following activation. The change in the oxygen environment is attributed to SrxMnyOz formation, along with possible passive SrO and Mn3O4 species. We present evidence from our “heat-treated” samples that SrxMnyOz regions form at elevated temperatures in air before the application of a cathodic bias. Our core-level XPS, Mn L3,2-edge RIXS and Mn L3 RPES studies of “heat-treated” and pristine LSMO determined that SOFC environments result in La-deficiency (severest near the surface) and stronger Mn4+ contribution, leading to the increased insulating character of the cathode prior to activation. The passive Mn2+ species near the surface and increased hole-doping (>0.6) of the LSMO upon exposure to the operating environment are considered responsible for the initially poor performance of the SOFC. Meanwhile, the improved oxygen reduction following the application of a cathodic bias is considered to be due to enhanced bulk oxygen-ion diffusion resulting from the migration of Mn2+ ions towards the LSMO/electrolyte interface and the SrxMnyOz regions facilitating enhanced bulk oxygen reduction reaction kinetics.

Piper, L.F.J.; Preston, Andrew R.H.; Cho, Sang Wan; DeMasi, Alexander; Chen, Bin; Laverock, J.; Smith, K. E.; Miara, Lincoln J.; Davis, Jacob N.; Basu, Soumendra; Pal, Uday B.; Gopalan, Srikanth; Saraf, Laxmikant V.; Kaspar, Tiffany C.; Matsuura, A. Y.; Glans, P.A.; Guo, Jianzhong

2010-12-02

277

Lifetime Modeling of Xenon Hollow Cathodes Used in Electric Propulsion  

NASA Astrophysics Data System (ADS)

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).

Kovaleski, Scott

2001-10-01

278

Segmented hollow cathode laser device  

Microsoft Academic Search

A laser device is described for generating multiline emissions when appropriately energized. The device consists of two major components, an anode-cathode assembly and, in a first embodiment, an adjustable brewster end section or in a second embodiment, an integral mirror end section. The anode-cathode assembly comprises one center located short cylindrical anode and two segmented cylindrical hollow cathodes located symmetrically

R. W. Hamerdinger; S. C. Wang

1981-01-01

279

Cathode material for lithium batteries  

DOEpatents

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.

Park, Sang-Ho; Amine, Khalil

2013-07-23

280

Oxidation Behavior of Nickel-Base Single-Crystal Superalloy with Rhenium-Base Diffusion Barrier Coating System at 1,423 K in Air  

Microsoft Academic Search

The oxidation behavior of the nickel-base single-crystal superalloy TMS-82+ coated with a duplex Re(W)–Cr–Ni\\/Ni(Cr)–Al layer\\u000a was investigated in air at 1,150 °C for up to 100 h. The coating layer was formed by electroplating Re(Ni) and Ni(W) films\\u000a on the alloy, followed by Cr-pack cementation at 1,300 °C, and as a result, forming a continuous Re(W)–Cr–Ni diffusion-barrier\\u000a layer. A Ni film containing fine

Toshio Narita; Fengqun Lang; Kemas Zaini Thosin; Takayuki Yoshioka; Takeshi Izumi; Hiroshi Yakuwa; Shigenari Hayashi

2007-01-01

281

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

SciTech Connect

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.

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

1996-08-01

282

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

Microsoft Academic Search

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

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

2009-01-01

283

Field evaluation of thermal and chemical desorption BTEX radial diffusive sampler radiello compared with active (pumped) samplers for ambient air measurements.  

PubMed

The performance of two types of radiello diffusive samplers, filled with a thermally desorbable adsorbent (graphitised carbon Carbograph 4) and with a solvent desorbable adsorbent (activated charcoal), respectively, have been evaluated for the monitoring of BTEX in ambient air, by comparison with active (pumped) samplers. A two year survey was carried out in Padua, a medium-sized town, in a traffic site, close to a busy crossroad. The concentrations of BTEX were measured for 15 campaigns, during which four series of radial diffusive samplers were exposed for 2 day, 7 day, 10 day and 14 day time periods, respectively. Every series of chemical desorption samplers included three replicates; thermal desorption samplers included six replicates, three of them filled with freshly conditioned cartridges and three filled with regenerated cartridges. No significant difference in the levels measured either by new or by regenerated cartridges has been found. During three campaigns (summer 2004, winter and spring 2005) two active (pumped) samplers were added for each sampling period. The diffusive uptake rates have been calculated and modelled under various conditions of concentration, temperature and exposure time. The effects of the environmental factors on the performances of both solvent and thermally desorbable samplers have been evaluated. The repeatability of the whole measurement process (sampling and analysis) was calculated for every sampling duration. The comparison of concentration levels measured by diffusive and active sampling methods shows correlation coefficients R >or= 0.98 (p<0.01) for all the compounds. The uncertainty of the diffusive sampling method under field conditions, using active sampling as the reference method, has been assessed according to the ISO 13752 requirements. On field relative expanded uncertainty for benzene has been found below 20%. PMID:19212585

Cocheo, Claudio; Boaretto, Caterina; Pagani, Diego; Quaglio, Franco; Sacco, Paolo; Zaratin, Laura; Cottica, Danilo

2009-02-01

284

A Hollow Cathode Magnetron (HCM)  

SciTech Connect

A new type of plasma sputtering device, named the hollow cathode magnetron (HCM), has been developed by surrounding a planar magnetron cathode with a hollow cathode structure (HCS). Operating characteristics of HCMs, current-voltage ( I-V ) curves for fixed discharge pressure and voltage-pressure ( V-p ) curves for fixed cathode current, are measured. Such characteristics are compared with their planar magnetron counterparts. New operation regimes, such as substantially lower pressures (0.3 mTorr), were discovered for HCMs. Cathode erosion profiles show marked improvement over planar magnetron in terms of material utilization. The use of HCMs for thin film deposition are discussed.

S.A. Cohen; Z. Wang

1998-04-01

285

DARHT 2 kA Cathode Development  

SciTech Connect

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.

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

286

Improved Rare-Earth Emitter Hollow Cathode  

NASA Technical Reports Server (NTRS)

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.

Goebel, Dan M.

2011-01-01

287

Synopsis of Cathode #4 Activation  

SciTech Connect

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.

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

2006-05-26

288

Hydrogen hollow cathode ion source  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

289

The change of pH under a paint film due to cathodic protection  

Microsoft Academic Search

The diffusion of OH?-ions and H2 formed during cathodic protection through a paint film is studied. The diffusion equation is solved for non-stationary conditions and from this the steady state is also derived. It is shown that under usual operating conditions of cathodic protection of ships the stationary state is reached in about 15 days. The danger of paint deterioration

P. J. Gellings; H. C. Ekama

1975-01-01

290

Plasma deposition of oxide cathodes  

NASA Astrophysics Data System (ADS)

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.

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

1999-05-01

291

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

PubMed

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

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

2013-03-01

292

Olivine-type cathodes  

Microsoft Academic Search

The recent progress at Sony in the design of practical olivine-type cathodes is reviewed briefly. First principle calculations revealed LiFePO4 is a semiconductor with ca. 0.3eV band gap and LiMnPO4 is an insulator with ca. 2eV band gap, which seems the major intrinsic obstacle to a smooth redox reaction at 4V in the Mn-rich phase. Attention is also focused on

Atsuo Yamada; Mamoru Hosoya; Sai-Cheong Chung; Yoshihiro Kudo; Koichiro Hinokuma; Kuang-Yu Liu; Yoshio Nishi

2003-01-01

293

Thermal sprayed titanium anode for cathodic protection of reinforced concrete bridges  

NASA Astrophysics Data System (ADS)

Stable operation of cobalt catalyzed thermal sprayed titanium anodes for cathodic protection (CP) of bridge reinforcing steel was maintained in accelerated tests for a period equivalent to 23 years service at Oregon Department of Transportation (Oregon DOT) bridge CP conditions with no evidence that operation would degrade with further aging. The cobalt catalyst dispersed into the concrete near the anodeconcrete interface with electrochemical aging to produce a more diffuse anode reaction zone. The titanium anode had a porous heterogeneous structure composed of ?-titanium containing interstitial oxygen and nitrogen, and a fee phase thought to be Ti(O,N). Splat cooling rates were 10 to 150 K/s, and microstructures were produced by equilibrium processes at the splat solidification front. Nitrogen gas atomization during thermal spraying produced a coating with more uniform composition, less cracking, and lower resistivity than using air atomization.

Cramer, S. D.; Covino, B. S.; Holcomb, G. R.; Bullard, S. J.; Collins, W. K.; Govier, R. D.; Wilson, R. D.; Laylor, H. M.

1999-03-01

294

A Review of the Science and Technology of Cathodes from the Viewpoint of Spacecraft TWT Applications.  

National Technical Information Service (NTIS)

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 ...

G. W. Stupian

1980-01-01

295

Cathodic oxygen reduction catalyzed by bacteria in microbial fuel cells.  

PubMed

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

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

2008-05-01

296

Cathode and Anode Optimization in a Virtual Cathode Oscillator  

Microsoft Academic Search

We are fabricating and testing several different types of cathodes for the same vircator driven by a single shot Marx generator and pulse forming line (300 kV, 60 ns, 30 Omega). The cathodes types, each with an emitting area of ~32 cm2, include the original velvet with a new geometry, carbon fiber, pin-array, and an array of all metal cathodes.

Y. Chen; J. Mankowski; J. Walter; M. Kristiansen; R. Gale

2007-01-01

297

A self-consistent model for the cathode fall region of an electric arc  

NASA Astrophysics Data System (ADS)

A one-dimensional model of the non-equilibrium plasma region adjacent to an electric arc cathode is developed. The collisionless space-charge zone (sheath) and the hydrodynamically described ionization zone (pre-sheath) are connected to a unified model. In the pre-sheath, ionization, diffusion and decoupling of electron and heavy-particle temperature are considered. The voltage drop in the space-charge zone is computed self-consistently including thermionic electron emission at the cathode surface. This unified model yields the overall cathode potential drop (cathode fall), the extent of the non-equilibrium region and the net energy flux towards the cathode surface. In this paper, the model is applied to an argon arc plasma at atmospheric pressure with a thoriated tungsten cathode, as is typically used for welding of stainless steel materials.

Rethfeld, B.; Wendelstorf, J.; Klein, T.; Simon, G.

1996-01-01

298

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

Microsoft Academic Search

Combustion of Hâ\\/hydrocarbon (HC) fuel mixtures may be considered in certain volume-limited supersonic airbreathing propulsion applications. Effects of HC addition to Hâ 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 (Nâ and\\/or HC)-diluted Hâ mixture opposed

G. L. Pellett; R. Guerra; L. G. Wilson; R. N. Reeves; G. B. Northam

1987-01-01

299

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

Microsoft Academic Search

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

G. L. Pellett; R. Guerra; L. G. Wilson; G. B. Northam

1986-01-01

300

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

NASA Technical Reports Server (NTRS)

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.

Lebedeff, S. A.; Hameed, S.

1975-01-01

301

A Rotatable Cold Cathode Penning ion Source  

Microsoft Academic Search

A rotatable cold cathode Penning ion source has been designed and is now operating in the Oak Ridge Isochronous Cyclotron (ORIC). Previous sources for positive heavy ions have been severely limited in life-time by cathode sputtering and buildup of sputtered cathode material. The new ion source extends the cathode lifetime by a factor of ~ 6. The source cathodes are

M. L. Mallory; E. D. Hudson

1975-01-01

302

Velocity and thermal structure, and strain-induced extinction of 14 to 100% hydrogen-air counterflow diffusion flames  

Microsoft Academic Search

Extensive results from axisymmetric convergent-nozzle and straight-tube opposed jet burners (OJBs) characterized strain-induced extinction of unanchored (free-floating), laminar Hâ\\/Nâ-air flames. Parameters included (a) plug-flow and parabolic input velocity profiles, (b) jet exit diameters ranging 2.7 to 7.2 mm for nozzles and 1.8 to 10 mm for tubes, (c) various relative jet gaps, and (d) 14 to 100% Hâ in the

G. B. Northam; W. M. Jr. Humphreys; L. R. Gartrell; K. M. Isaac; W. L. Roberts; C. L. Dancey

1998-01-01

303

Seasonality of diffusive exchange of polychlorinated biphenyls and hexachlorobenzene across the air-sea interface of Kaohsiung Harbor, Taiwan.  

PubMed

Gaseous and dissolved concentrations of polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) were measured in the ambient air and water of Kaohsiung Harbor lagoon, Taiwan, from December 2003 to January 2005. During the rainy season (April to September), gaseous PCB and HCB concentrations were low due to both scavenging by precipitation and dilution by prevailing southwesterly winds blown from the atmosphere of the South China Sea. In contrast, trace precipitation and prevailing northeasterly winds during the dry season (October to March) resulted in higher gaseous PCB and HCB concentrations. Instantaneous air-water exchange fluxes of PCB homologues and HCB were calculated from 22 pairs of air and water samples from Kaohsiung Harbor lagoon. All net fluxes of PCB homologues and HCB in this study are from water to air (net volatilization). The highest net volatile flux observed was +172 ng m(-)(2) day(-1) (dichlorobiphenyls) in December, 2003 due to the high wind speed and high dissolved concentration. The PCB homologues and HCB fluxes were significantly governed by dissolved concentrations in Kaohsiung Harbor lagoon. For low molecular weight PCBs (LMW PCBs), their fluxes were also significantly correlated with wind speed. The net PCB and HCB fluxes suggest that the annual sums of 69 PCBs and HCB measured in this study were mainly volatile (57.4 x 10(3) and 28.3 x 10(3) ng m(-2) yr(-1), respectively) and estimated yearly, 1.5 kg and 0.76 kg of PCBs and HCB were emitted from the harbor lagoon surface waters to the ambient atmosphere. The average tPCB flux in this study was about one-tenth of tPCB fluxes seen in New York Harbor and in the Delaware River, which are reported to be greatly impacted by PCBs. PMID:18977513

Fang, Meng-Der; Ko, Fung-Chi; Baker, Joel E; Lee, Chon-Lin

2008-12-15

304

A study of Eu 2 O 3 , Sc 2 O 3 co-doped tungsten matrix impregnated cathode  

NASA Astrophysics Data System (ADS)

Eu 2 O 3 and Sc 2 O 3 co-doped W matrix impregnated cathodes have been prepared by the powder metallurgy method. The constitution of active elements on activated cathode surface is analyzed by in-situ Auger electron spectroscopy. It is found that although Eu exists in the matrix, no Eu is found on the cathode surface due to the formation of a stable Eu containing compound. Sc, Ba and O diffuse to the surface of the cathode and form an active surface layer during the activation period whereas the stable Eu-compound cannot liberate free Eu, which can diffuse from the cathode to the surface. The active substance of Sc, Ba and O on the cathode surface contribute to the emission property.

Wang, Jinshu; Wang, Xi; Liu, Wei; Gao, Tao; Wang, Yiman

2011-10-01

305

Monomer-eximer dynamics in spread monolayers. Part 1. Lateral diffusion of pyrene dodecanoic acid at the air-water interface  

SciTech Connect

In this paper, a combined experimental and theoretical study of monomer-eximer dynamics in spread monolayers is presented. The system studied here is a spread monolayer of 12-(1-pyrene) dodecanoic acid (PDa) and oleic acid at the air-water interface of a neutral aqueous solution. The microscopic kinetic behavior of the PDa probe in the monolayer was monitored through the eximer-monomer, steady-state photoexcitation of the pyrene moeity. The steady-state ratio of eximer to mono intensities, 12/11, was found to depend linearly on the mole fraction of PDa in oleic acid over the concentration range studied. These data were interpreted theoretically by constructing a reaction-dynamic model to describe the lateral diffusion and subsequent interaction of the pyrene species. Using analytical results from the theory of random walks on lattices with traps, and from data from Monte Carlo simulation

Loughran, T.; Hatlee, M.D.; Patterson, L.K.; Kozak, J.J.

1980-06-01

306

An explosive emission cathode in a thermionic cathode environment  

NASA Astrophysics Data System (ADS)

Present-day high power microwave devices suffer from a lack of reliable, reproducible cathodes for generating the requisite GW-level electron beam in a vacuum. Standard explosive emission cathodes have been limited to 10's or 100's of ns due to the expansion of cathode-generated plasma and the ensuing impedance collapse that debilitates microwave output. Traditional thermionic cathodes do not suffer from this drawback of plasma generation, but have not yet been demonstrated to provide the required emission current densities. It is expected that if the plasma could be made cooler and less dense, explosive emission would be more stable. Cesium iodide (CsI) has been found to slow the impedance collapse in many explosive emission cathodes. Herein we will examine diode impedance collapse, gas production, and cathode conditioning in an effort to perform an evaluation of explosive cathode performance in a typical thermionic electron gun environment. These results will then be used to help demarcate the parameter space over which these CsI-coated carbon fiber cathodes are viable candidates for the electron beam source in next-generation high power microwave devices.

Schlise, Charles; Umstattd, Ryan

2003-10-01

307

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

NASA Astrophysics Data System (ADS)

Two types of diffusive samplers, both of which are compatible with thermal desorption, but differ in their geometry—SKC-Ultra (badge-type) and Radiello (radial symmetry-type)—were evaluated indoors and outdoors under varying temperature, humidity and wind speed conditions, using the graphitized adsorbents Carbopack X or Carbograph 5 to measure 1,3-butadiene and benzene in ambient air. The results obtained by diffusive sampling were compared with results obtained using a conventional active sampling method over both long (1 week) and shorter periods (6-24 h). Analysis and detection were performed using an automatic thermal desorber (ATD) connected to a gas chromatograph-flame ionization detector (GC/FID). Results from each sampler and adsorbent combination were examined using ordinary or multiple linear regression analysis. The overall uncertainty (OU) was also determined. In general, the results obtained with both samplers showed good agreement with those obtained by active sampling. Carbopack X appeared to be a more efficient adsorbent than Carbograph 5 for 1,3-butadiene, but the two adsorbents were equivalent for benzene. No effects of either humidity or air velocity were observed. Minor temperature effects were observed for both samplers for 1,3-butadiene. In summary, the results confirmed the accuracy of sampling rates previously determined for the two samplers and adsorbents. We consider the two samplers to be suitable for stationary and personal monitoring for the general population of 1,3-butadiene and benzene in various environments, indoors and outdoors. They are almost independent of meteorological conditions and may be suitable for monitoring industrial atmospheres.

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

308

Schlieren characterization of gas flows generated by cathodic arcs in atmospheric pressure environment  

NASA Astrophysics Data System (ADS)

Schlieren diagnostics of cathodic arc flows in air are presented. Three important processes are observed: (1) a luminous hemispherical region near the cathode with a radius of ?1 mm, identified as the cathodic metallic plasma; (2) a luminous plasma jet extending ?10 mm from the cathode, termed as the cathodic air jet (CAJ); (3) a background gas pushed to expand at subsonic velocities ?100 m/s. The gas is accelerated in the direction of the CAJ. The main collisional processes in the CAJ are identified using optical emission spectroscopy and mean free path analysis. The CAJ plasma is shown to be composed of N2+ and Cu+ ions. It is concluded that the CAJ length is determined by the dissociative recombination of N2+. With external magnetic field, the CAJ rotates according to the Lorentz force direction. Observing the CAJ motion and its affect on stationary and flowing background gas, it is concluded that the CAJ has significant directed thrust.

Kronhaus, I.; Eichler, S.; Schein, J.

2014-02-01

309

Titanium diaphragm makes excellent amplitron cathode support  

NASA Technical Reports Server (NTRS)

Cathode support structure designed around a titanium diaphragm prevents radial misalignment between the cathode and anode in amplitrons. The titanium exhibits low thermal conductivity, tolerates lateral thermal expansion of the cathode, and is a poor primary and secondary emission medium.

Teich, W. W.

1965-01-01

310

Emission from ferroelectric cathodes  

SciTech Connect

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

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

1993-05-17

311

Emission from ferroelectric cathodes  

NASA Astrophysics Data System (ADS)

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

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

1993-05-01

312

Emission from ferroelectric cathodes  

NASA Astrophysics Data System (ADS)

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

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

1994-02-01

313

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

314

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

315

[Environmental and indoor air exposure to asbestos fiber dust as a risk and causal factor of diffuse malignant pleural mesothelioma].  

PubMed

In an interdisciplinary, multicentre case control study of the causal factors of the diffuse malignant mesothelioma (DMM) standardised histories where taken from n = 324 Patients suffering from DMM, n = 315 hospital control patients (KK) and n = 182 population controls (PK). For 66 DMM, 149 KK and 107 PK a risk from asbestos fibre dust at the workplace was not detectable. For latter persons indoor and outdoor asbestos exposure outside of the workplace were investigated. The following factors were examined: neighbourhood exposure from companies using asbestos, living in big cities and nearby main traffic roads, building materials containing asbestos, electric storage heaters and household contacts. For using electric storage heaters a statistically significant increased odds ratio (OR) was observed for DMM as well in comparison with KK (OR = 2.42; 95%-CI: 1.01-5.72) and in comparison for PK (OR = 2.91; 95%-CI: 1.08-7.80). Only outside of Hamburg an increased OR compared to KK was observed for people living in the neighbourhood of asbestos factories (OR = 16.3; 95%-CI: 1.35-196.8) and also, but only in Hamburg, compared to PK living nearby main traffic roads. There is only a trend for a mesothelioma-risk for household-contacts based on a few cases. In one DMM-patient without an occupational asbestos exposure the lung dust fibre analysis yielded 2.912 FB and 1.459 x 10(3) crocydolithe fibres per gram dried lung tissue. As a child he lived in the immediate vicinity of the blue asbestos mine in Wittenoom, Australia. Therefore in special cases a para-occupational asbestos or a neighbourhood asbestos exposure can be demonstrated as a risk factor of diffuse malignant mesothelioma. PMID:9409906

Schneider, J; Rödelsperger, K; Pohlabeln, H; Woitowitz, H J

1996-11-01

316

Hot Hollow Cathode Gun Assembly.  

National Technical Information Service (NTIS)

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 th...

J. D. Zeren

1983-01-01

317

Hot hollow cathode gun assembly  

NASA Astrophysics Data System (ADS)

A hot hollow cathode deposition gun assembly is disclosed. The device 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.

Zeren, J. D.

1983-11-01

318

High Pressure Hollow Cathode Discharges  

NASA Astrophysics Data System (ADS)

The sustaining voltage of hollow cathode discharges is dependent on the product of pressure and cathode hole diameter. By reducing the dimension of the cathode hole to 0.2 mm we were able to operate micro-hollow cathode discharges at pressures up to 750 Torr in argon in a direct current mode. The current-voltage characteristics of the 0.2 mm cathode hole discharges was found to have a positive slope at currents below 0.25 mA. Up to this current level hollow cathode discharges can be operated in parallel without ballast. The negative slope observed above the threshold current seems to be due to the onset of thermionic electron emission caused by Joule heating of the cathode. This assumption is supported by the experimental observation that multi-hole operation without ballast even at currents far above the dc-threshold current was possible when the discharge was operated in a pulsed mode. The possibility of generating large arrays of ballast-free, pulsed micro-hollow cathode discharges suggests their use as flat panel light sources or electron sources.

Schoenbach, Karl H.; Tessnow, Thomas; Elhabachi, Ahmed

1996-10-01

319

Virtual cathode microwave devices -- Basics  

SciTech Connect

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.

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

1991-01-01

320

Some features of imaging of the processes occurring in an extended arc discharge in atmospheric-pressure air  

NASA Astrophysics Data System (ADS)

Processes occurring in the low-temperature plasma of extended quasi-stationary arc discharges in air between graphite electrodes are investigated. Along with the conventional (constricted) discharge geometry, other discharge modes—diffuse (distributed) and diffuse-constricted—are studied. Contraction, stratification, and shunting processes are considered. Current oscillation modes are revealed that are caused by the interaction between the cathode and anode jets and the origination of plasma jets and solid particles from the locally overheated anode surface. 1 The use of graphite electrodes with standard atmospheric pressure excludes the presence of the liquid phase in the electrode spots

German, V. O.; Glinov, A. P.; Golovin, A. P.; Kozlov, P. V.; Lyubimov, G. A.

2013-12-01

321

The base metal of the oxide-coated cathode  

NASA Astrophysics Data System (ADS)

The oxide-coated cathode has been the most widely used electron emitter in vacuum electronic devices. From one manufacturing company to another the emissive oxide is either a double—Ba, Sr—or a triple—Ba, Sr, Ca—oxide, having always the same respective compositions. Conversely, the base metal composition is very often proprietary because of its importance in the cathode emission performances. The present paper aims at explaining the operation of the base metal through a review. After a brief introduction, the notion of activator is detailed along with their diffusivities and their associated interfacial compounds. Then, the different cathode life models are described prior to few comments on the composition choice of a base metal. Finally, the specificities of the RCA/Thomson "bimetal" base metal are presented with a discussion on the optimized composition choice illustrated by a long-term life-test of five different melts.

Poret, F.; Roquais, J. M.

2005-09-01

322

Carbon velvet field-emission cathode  

NASA Astrophysics Data System (ADS)

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. Physics.

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

2002-12-01

323

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

SciTech Connect

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

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

1999-09-01

324

An experimental study of thoriated tungsten cathodes operating at different current intensities in an atmospheric-pressure plasma torch  

Microsoft Academic Search

Thoriated tungsten cathodes operating in an open-air plasma torch at current intensities between 30 and 200 A were experimentally studied. The morphology and composition of the cathode tip after arcing were investigated by scanning electron microscopy and energy-dispersive x-ray spectroscopy. Three relevant zones were found on the cathode tip (high-erosion zone, thorium-depleted zone and thorium-enriched zone), and their dimensions were

J. A. Sillero; D. Ortega; E. Muñoz-Serrano; E. Casado

2010-01-01

325

Air breathing direct methanol fuel cell  

DOEpatents

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.

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

2002-01-01

326

Hollow Cathode Ignition Studies and Model Development  

Microsoft Academic Search

The Hollow Cathode Assembly is a thermionic source of electrons critical to the operation of the L-3 ETI Xenon Ion Propulsion System (XIPS) thruster. There are two cathode subsystems on a XIPS thruster: the discharge cathode provides the current for the main discharge and the neutralizer cathode produces an electron stream to prevent the spacecraft from charging. There are two

William G. Tighe; Dan M. Goebel; Robert T. Longo

2005-01-01

327

Cathode composite for molten carbonate fuel cell  

Microsoft Academic Search

A cathode composite useful for a molten carbonate fuel cell comprised of a porous sintered cathode having a porous sintered bubble pressure barrier integrally sintered to one face thereof, said cathode composite having a porosity ranging from about 25% by volume to about 75% by volume of the total volume of said composite, said cathode having a porosity ranging from

Iacovangelo

1984-01-01

328

Cathodes for Molten-Salt Batteries.  

National Technical Information Service (NTIS)

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, me...

S. D. Argade

1993-01-01

329

Discharge with hollow cathode, selected chapters  

NASA Astrophysics Data System (ADS)

The arc discharge was utilized for dissociating a beam of deuterium. Although it had a hollow cathode, the effect of the cathode was absent. The arc began from small bright cathode spots, and was then moved rapidly over the butt end of the cylindrical thick-walled graphite cathode. The bright thin compressed cathode spot was compressed by an external magnetic field filament of discharge. Several filaments were observed simultaneously following the cathode spots, which had formed the visible positive column with a diameter approximately equal to the diameter of the cathode conductor.

Moskalev, B. I.

1983-04-01

330

Improved Cathode Structure for a Direct Methanol Fuel Cell  

NASA Technical Reports Server (NTRS)

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.

Valdez, Thomas; Narayanan, Sekharipuram

2005-01-01

331

Characterization of the Capillary Properties of Gas Diffusion Media  

NASA Astrophysics Data System (ADS)

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.

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

332

Cold cathode vacuum discharge tube  

DOEpatents

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.

Boettcher, Gordon E. (Albuquerque, NM)

1998-01-01

333

Operation of thoriated tungsten cathodes  

SciTech Connect

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.

Polk, J.E. (Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States))

1993-01-20

334

Magnetic-cusp, cathodic-arc source  

DOEpatents

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.

Falabella, Steven (Livermore, CA)

1995-01-01

335

Hollow Cathode With Multiple Radial Orifices  

NASA Technical Reports Server (NTRS)

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.

Brophy, John R.

1992-01-01

336

Cathodes for molten-salt batteries  

Microsoft Academic Search

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

Shyam D. Argade

1993-01-01

337

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

NASA Astrophysics Data System (ADS)

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.

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

2010-11-01

338

Cold cathode vacuum gauging system  

DOEpatents

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.

Denny, Edward C. (Knoxville, TN)

2004-03-09

339

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)

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 ? 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.

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

2007-05-01

340

Study of roughness-induced diffuse and specular reflectance at silver-air and silver-liquid interfaces. Final report, July 1, 1979-August 31, 1980  

SciTech Connect

Results of an extended investigation of surface plasma-wave absorption and roughness-induced optical scattering from an interface of silver and air are described. In particular, the position of the surface plasma resonance minimum in reflectivity for a stochastically roughened metal silver surface has been studied as a function of a number of distinct roughness perturbations. In the case of a transparent liquid-silver boundary the frequency red shift of the resonance minimum has been determined and the location of the surface plasmon dip for various liquids is shown to agree well with a simple roughness theory. The additional interfacial properties due to the formation of a thin inhomogeneous oxide layer occurring either spontaneously or due to application of a small interfacial electrical potential are more complex. However, the optical constants of the interlayer have been determined from differential specular reflectance measurements at the boundary. Nodule size parameters determined from scattering and absorption measurements and features of both polarized and depolarized diffuse reflectance give further information on the state of the interface. Reflectance of ordered-corrugated surfaces are also described.

Sari, S.O.

1980-07-01

341

An in-situ method to measure a soil`s undisturbed pore gas radon concentration, diffusion length for radon and air filled porosity  

SciTech Connect

Previous work has shown that for soils of insignificant permeability (soils with permeability less than about 10{sup {minus}12} m{sup 2}) the important soil parameters for characterizing radon mobility in the soil`s steady-state pore gas radon concentration at depth (C{sub s}), the soil`s bulk diffusion length for radon (L) and the soil`s air filled porosity (p{sub a}). Existing methods to measure these parameters have been based wholly or in part on measurements of soil samples taken to a laboratory for analysis. The drawbacks of this approach are twofold: (1) since soil structure can be quite heterogeneous, the sample may not have characteristics indicative of the site as a whole, and (2) since the parameters are dependent on soil structure and the soil structure of the sample may be changed in the process of acquiring the sample, one may be changing the parameters that one is trying to measure. These problems can be avoided by using a totally in-situ method to measure C{sub s}, L, and p{sub a}. This paper describes a totally in-situ method for simultaneously measuring the important soil parameters, based on measurements of the radon concentration as a function of time for the gas in a cavity in the soil. 7 refs., 3 figs., 3 tabs.

Jarzemba, M.S.; Blue, T.E. [Ohio State Univ., Columbus, OH (United States)

1996-04-01

342

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)

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.

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

1972-01-01

343

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)

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.

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

344

Direct current glow discharges in atmospheric air  

Microsoft Academic Search

A microhollow cathode discharge was used as plasma cathode to sustain a stable direct current glow discharge in atmospheric pressure air. The length of the glow discharge column was varied from 1 mm to 2 cm, with the sustaining voltage increasing linearly with length. For glow discharges with currents on the order of 10 mA, the electron density in the

Abdel-Aleam H. Mohamed; R. Block; K. H. Schoenbach

2002-01-01

345

The diffusion of electrons in a magnetic field  

Microsoft Academic Search

Experimental data concerning the anomalously high mobility of electrons across a magnetic field are discussed. It is shown that the concentration distribution of the secondary plasma of a hot-cathode discharge is almost independent of the transverse diffusion coefficient of the electrons, and so cannot be used to elucidate the mechanism of diffusion. The electron diffusion coefficient is estimated from the

A. V. Zharinov

1960-01-01

346

Insights into PEMFC Performance Degradation from HCl in Air  

SciTech Connect

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.

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

2011-12-31

347

Air cell  

NASA Astrophysics Data System (ADS)

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.

Okamura, Okiyoshi; Wakasa, Masayuki; Tamanoi, Yoshihito

1991-04-01

348

Interface chemistry in LSM–YSZ composite SOFC cathodes  

Microsoft Academic Search

(La,Sr)MnO3–3YSZ interface chemistry in air-annealed and operated SOFC cathodes has been studied by high spatial resolution TEM\\/EELS. Major changes in Mn L2,3 and O K ELNES were observed. A mixture of manganese 3+\\/4+ is found in the LSM bulk phase. In contact with LSM, zirconia forms a solid solution with dissolved lanthanum and manganese. Manganese is always divalent in this

M. Backhaus-Ricoult

2006-01-01

349

The effect of cathode geometry on stability of an atmospheric pressure arc  

SciTech Connect

Atmospheric plasma arcs are used extensively in material processing applications such as welding and metallurgy. An experimental arc furnace operating in air with graphite cathode and steel anode at 100--250 A exhibits large (approximately 10% rms) voltage and current fluctuations for certain cathode geometries, with the arc assuming a rotating helical shape persistent for many cycles. The instability occurs for cathode tip diameters of 1.5 to 3 times the cathode spot diameter, with the amplitude strongly dependent on current. A model for the instability is developed in which ordered cathode spot motion and the cathode jet give rise to the observed arc shape. Previous experiments on arc dynamics in applied AC magnetic field are used as a diagnostic for jet velocity. The model gives a good description of arc shape for low amplitudes. Possible mechanisms for spot motion on the cathode and its dependence on geometry will be proposed. Cathode shape is seen as an important means of controlling arc stability and broadening effective arc volume.

Karasik, M.; Zakharov, L.E.; Zweben, S.J.

1999-07-01

350

Cathodic corrosion. II. Properties of nanoparticles synthesized by cathodic corrosion  

NASA Astrophysics Data System (ADS)

We demonstrate how cathodic corrosion in concentrated aqueous solutions enables one to prepare nanoparticles of various metals and metal alloys. Using various characterization methods we show that the composition of nanoparticles remains that of the starting material, and the resulting size distribution remains rather narrow. For the case of platinum we show how the size and possibly even the shape of the nanoparticles can be easily controlled by the parameters of corrosion. Finally, we discuss the advantages of using the nanoparticles prepared by cathodic corrosion for applications in (electro-)catalysis.

Yanson, A. I.; Yanson, Yu. I.

2013-03-01

351

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

NASA Astrophysics Data System (ADS)

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 ?g 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

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

2012-12-01

352

Investigation of a Mercury-Argon Hot Cathode Discharge  

NASA Astrophysics Data System (ADS)

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.

Wamsley, Robert Charles

353

Pyrometric cathode temperature measurements in metal halide lamps  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

354

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

NASA Astrophysics Data System (ADS)

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.

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

2002-05-01

355

New Mechanically Rechargeable Zinc-Air Batteries.  

National Technical Information Service (NTIS)

This report describes the design, development and testing of new mechanically rechargeable zinc-air batteries. Following research and development of a low cost silver-mercury cathode catalyst, prototype battery tests were conducted. Cycle life tests at 3....

J. Giltner

1975-01-01

356

Air Pollution.  

ERIC Educational Resources Information Center

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…

Scorer, Richard S.

357

Cold cathode vacuum discharge tube  

DOEpatents

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.

Boettcher, G.E.

1998-03-10

358

Cold cathode vacuum discharge tube  

DOEpatents

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.

Boettcher, G.E.

1998-04-14

359

Geometrical Aspects of a Hollow-cathode Magnetron (HCM)  

SciTech Connect

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.

Cohen, Samuel, A.; Wang, Zhehui

1998-11-01

360

Cathodic Protection Developments for Prestressed Concrete Components.  

National Technical Information Service (NTIS)

The effects of cathodic protection on the embrittlement of high strength steel embedded in concrete were studied. The results show that cathodic protection will generate hydrogen on the steel if the potential is more negative than the thermodynamic hydrog...

J. Wagner W. Young S. Scheirer P. Fairer

1993-01-01

361

Cathode for Molten Carbonate Fuel Cell.  

National Technical Information Service (NTIS)

Disclosed are a porous sintered cathode for a molten carbonate fuel cell and method of making same. The cathode includes a skeletal structure of a first electronically conductive material slightly soluble in the electrolyte present in the molten carbonate...

T. D. Kaun F. C. Mrazek

1986-01-01

362

Air breathing direct methanol fuel cell  

DOEpatents

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.

Ren, Xiaoming (Los Alamos, NM)

2002-01-01

363

Development of High Energy Cathode (PNNL)  

Microsoft Academic Search

Lithium ion batteries with high energy densities are required to reach DOEs goal on early commercialization of electrical vehicles, including HEV, PHEV and EV. To increase the energy of cathode, voltage or\\/and capacity of cathode need to be increased. During FY10, we have investigated cathode materials with high operation voltages, for example LiMnPO4, and renewable organic cathode with high capacities.

Jiguang Zhang; Jun Liu

2011-01-01

364

Cathode materials for molten carbonate fuel cells  

SciTech Connect

It has recently been shown that cathodes in carbonate fuel cells are limited in longevity by dissolution of NiO from the cathode and precipitation as Ni in the electrolyte. Alternative cathode materials are being sought through a process of identifying the stable forms of candidate ceramics in the cathode environment, evaluating their properties, and modifying the conductivity, if necessary, through the use of dopants. 11 references, 5 figures.

Smith, J.L.; Kucera, G.H.; Minh, N.Q.; Pierce, R.D.; Ackerman, J.P.

1985-01-01

365

Air Dehydration Membranes for Nonaqueous Lithium-Air Batteries  

Microsoft Academic Search

In this paper, several types of new membranes were innovated and used as an O2-selective and H2O barrier films attached onto the cathode of non-aqueous Li-air batteries for continuous supplying of dry air into the batteries from ambient air. The membranes were prepared by depositing an O2\\/H2O selective coating layer on the exterior surface of a newly-invented thin porous Ni

Jian Zhang; Wu Xu; Xiaohong S. Li; Wei Liu

2010-01-01

366

Remote control for anode-cathode adjustment  

SciTech Connect

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.

Roose, Lars D. (Albuquerque, NM)

1991-01-01

367

Thrust production mechanisms in Hollow cathode microthrusters  

Microsoft Academic Search

Hollow cathode have recently been investigated at the University of Southampton as potential standalone microthrusters. Thrust measurements suggest that in some cases, hollow cathodes are able to generate specific impulse of over 1000s with xenon. The means by which hollow cathodes are able to generate such high levels of specific impulse is not clearly understood. This paper explores thrust production

A. N. Grubisic; S. B. Gabriel

2010-01-01

368

Variable diameter segmented hollow cathode laser device  

Microsoft Academic Search

A laser device is described for generating multiline emissions when appropriately energized. The device consists of two major components, an anode-cathode assembly and, in a first embodiment, an adjustable Brewster end section or in a second embodiment, an integral mirror end section. The anode-cathode assembly comprises one center located short cylindrical anode and two segmented cylindrical hollow cathodes located symmetrically

R. W. Hamerdinger; S. C. Wang

1981-01-01

369

Cathode Materials for Molten Carbonate Fuel Cells.  

National Technical Information Service (NTIS)

It has recently been shown that cathodes in carbonate fuel cells are limited in longevity by dissolution of NiO from the cathode and precipitation as Ni in the electrolyte. Alternative cathode materials are being sought through a process of identifying th...

J. L. Smith G. H. Kucera N. Q. Minh R. D. Pierce J. P. Ackerman

1985-01-01

370

Cathode for the electrolytic production of hydrogen  

SciTech Connect

The invention relates to a cathode for the electrolytic production of hydrogen. The cathode comprises an active surface consisting of a metal oxide obtained by the thermal decomposition of a thermally decomposable compound of a metal chosen from amongst cobalt, iron, manganese or nickel. The cathode is particularly suitable for the electrolysis of aqueous sodium chloride solutions in cells with a permeable diaphragm.

Nicolas, E.

1983-07-19

371

Cathodic protection system inspection 5  

Microsoft Academic Search

The rectifier is the heart of an impressed current cathodic protection system. As it is subject to many adverse conditions including power surges, lightning strikes, vandalism, physical damage, and deterioration from atmospheric exposure, frequent inspections of rectifiers are vital to keeping an impressed current system operating so that it can provide nearly continuous protection of the underground, or submerged structures

Jim Jenkins; Dan Polly

1994-01-01

372

Operation of thoriated tungsten cathodes  

Microsoft Academic Search

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

Jame E. Polk

1993-01-01

373

Modeling cathode boundary layer discharges  

NASA Astrophysics Data System (ADS)

A Cathode Boundary Layer Discharge or CBL (Schoenbach, et al Plasma Sources Sci. Technol. 13, 177,2004) is an electrode/dielectric/electrode sandwich with a central hole pierced through the dielectric and one of the electrodes (the anode). Thus, the cathode surface area available to the discharge is limited by the annular dielectric, and the discharge operates in an abnormal glow mode with a positive V-I characteristic at higher current. Using a two-dimensional fluid model, we have studied the electrical properties of CBLs in argon at 100 and 400 torr pressure. The spatial profiles of charged particle and metastable densities, potential, and gas temperature, as well as calculated V-I characteristics will be shown for a range of conditions for a 800 micron hole diameter. One interesting result (anticipated in the work of Belostotskiy, et al, Plasma Sources Sci. Technol 17, 045018, 2008) is that there is a sharp increase in the slope of the V-I characteristic when gas heating is taken into account. This current limiting effect is not observed when the discharge is able to expand on the outer surface of the cathode as in the case of the MicroHollow Cathode Discharge (MHCD) configuration, for example.

Munoz-Serrano, E.; Boeuf, J. P.; Pitchford, L. C.

2009-10-01

374

Prevent corrosion by cathodic protection  

Microsoft Academic Search

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

1989-01-01

375

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

NASA Technical Reports Server (NTRS)

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.

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

1979-01-01

376

Step response analysis of phosphoric acid fuel cell (PAFC) cathode through a transient model  

NASA Astrophysics Data System (ADS)

Transient state response analysis of phosphoric acid fuel cell (PAFC) cathode is important to understand various competitive processes like diffusion, reaction and product back diffusion occurring at various layers of the composite cathode. A two-dimensional unsteady state model for simulating PAFC cathode is developed as an extension of the previously developed steady-state model [S. Roy Choudhury, M.B. Deshmukh, R. Rengaswamy, A two-dimensional steady-state model for phosphoric acid fuel cells (PAFC), J. Power sources 112 (2002) 137-152]. The transient model is solved to study the impact of various parameters such as Tafel slope, diffusivity etc on the step response of the fuel cell. The effect of partial pressure variation in bulk gas for large sized PAFC cathode is also analysed. Trend analysis based on the model output is also experimentally verified using a small unit cell setup. The effect of various parameters on the settling time of the cathode, as revealed in this study, suggests possible development of a diagnostic tool employing such transient model.

Choudhury, Suman Roy; Choudhury, Suhasini Roy; Rangarajan, J.; Rengaswamy, R.

377

New Cathode Materials for Intermediate Temperature Solid Oxide Fuel Cells  

SciTech Connect

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

Allan J. Jacobson

2006-06-30

378

New Cathode Materials for Intermediate Temperature Solid Oxide Fuel Cells  

SciTech Connect

Operation of SOFCs at intermediate temperatures (500-800 C) requires new combinations of electrolyte and electrode materials that will provide both rapid ion transport across the electrolyte and electrode--electrolyte interfaces and efficient electrocatalysis of the oxygen reduction and fuel oxidation reactions. This project concentrates on materials and issues associated with cathode performance that are known to become limiting factors as the operating temperature is reduced. The specific objectives of the proposed research are to develop cathode materials that meet the electrode performance targets of 1.0 W/cm{sup 2} at 0.7 V in combination with YSZ at 700 C and with GDC, LSGM or bismuth oxide based electrolytes at 600 C. The performance targets imply an area specific resistance of {approx}0.5 {Omega}cm{sup 2} for the total cell. The research strategy is to investigate both established classes of materials and new candidates as cathodes, to determine fundamental performance parameters such as bulk diffusion, surface reactivity and interfacial transfer, and to couple these parameters to performance in single cell tests. In this report, the oxygen exchange kinetics of a P2 composition are described in detail. The oxygen exchange kinetics of the oxygen deficient double perovskite LnBaCo{sub 2}O{sub 5.5+{delta}} (Ln=Pr and Nd) have been determined by electrical conductivity relaxation. The high electronic conductivity and rapid diffusion and surface exchange kinetics of PBCO suggest its application as cathode material in intermediate temperature solid oxide fuel cells.

Allan J. Jacobson

2005-11-17

379

Testing a GaAs cathode in SRF gun  

SciTech Connect

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.

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

2011-03-28

380

Surface structure of thermionic-emission cathodes  

NASA Astrophysics Data System (ADS)

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.

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

381

Cathodes for ceria-based fuel cells  

SciTech Connect

Work is underway to develop a solid oxide fuel cell that has a ceria-based electrolyte and operates at lower temperatures (500-600{degrees}C) than conventional zirconia-based cells. At present the performance of this ceria-based solid oxide fuel cell is limited by the polarization of conventional cathode materials. The performance of alternative cathodes was measured by impedance spectroscopy and dc polarization. The performance was found to improve by using a thin dense interface layer and by using two-phase cathodes with an electrolyte and an electronic phase. The cathode performance was also found to increase with increasing ionic conductivity for single phase cathodes.

Doshi, R.; Krumpelt, M. [Argonne National Lab., IL (United States); Ricvhards, V.L. [Tri-State Univ., Angola, IN (United States). Dept. of Mech. & Aerospace Engr.

1997-08-01

382

Cathodes for molten-salt batteries  

NASA Astrophysics Data System (ADS)

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.

Argade, Shyam D.

1993-02-01

383

Considerations of the Role of the Cathodic Region in Localized Corrosion  

SciTech Connect

The ability of wetted cathodes of limited area to support localized corrosion sites on passive materials exposed to atmospheric conditions was studied computationally. The analysis pertains to conditions where metal surfaces are covered by thin layers of moisture in contrast to conditions of full immersion. The moisture may be a continuous layer or in patches with and without particulate on the surface. These conditions are of interest for the surfaces of the waste packages at the proposed Yucca Mountain Repository where waste packages are supported in air. The cathode capacity was characterized by the total net cathodic current, I{sub net}, which the surface surrounding a localized corrosion site (i.e., a pit or crevice) could supply. The cathode capacity increases with increasing cathode area, but it saturates at finite cathode sizes due to the resistance of the thin electrolyte layer. The magnitude of the capacity depends on the water layer thickness, the solution conductivity, and the electrochemical reaction kinetics. The presence of particulates is treated by considering both volume and surface coverage effects. The limited electrolyte volume under thin film conditions can lead to rapid pH changes which decrease the cathode capacity due to the slower electrochemical kinetics at elevated pH. These effects can make localized corrosion less likely to be sustained.

R.G. Kelly; A. Agarwal; F. Cui; X. Shan; U. Landau; J.H. Payer

2006-03-17

384

Thermionic cathode life-test studies  

NASA Technical Reports Server (NTRS)

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.

Forman, R.; Smith, D. H.

1979-01-01

385

Temperature Distributions in Hollow Cathode Emitters  

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

386

MPD thruster performance with cathode heating  

NASA Astrophysics Data System (ADS)

A gas-fed MPD thruster with a cathode heating system was developed which can bring the cathode to temperatures at which significant thermionic emission is present. The heat is provided by an electrical arc established between the inner surface of the cathode tip and a thoriated tungsten electrode inserted into a blind hole drilled along the cathode axis. A series of preliminary tests intended to verify the proper operation of the device and its possibility to reach temperatures beyond 2000 K at the cathode tip are described. Electrical characteristics and performance (thrust efficiency and specific impulse) obtained with cold electrodes and hot electrodes for 4g/s of Argon are shown, and a comparison between the two thermal configurations is made. The data obtained show that the electrode thermal conditions have a decisive effect on thruster electrical characteristics, instabilities and erosion phenomena. In particular, hot cathode thrust efficiency is substantially higher than cold cathode efficiency.

Andrenucci, M.; Paganucci, F.; La Motta, G.

1992-07-01

387

LOW TEMPERATURE CATHODE SUPPORTED ELECTROLYTES  

SciTech Connect

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.

Harlan U. Anderson; Fatih Dogan; Vladimir Petrovsky

2002-03-31

388

Electrochemical impedance of the cathode catalyst layer in polymer electrolyte fuel cells  

Microsoft Academic Search

A macrohomogeneous model that was studied in a previous publication under stationary conditions is used to calculate the small-signal dynamic response of the cathode catalyst layer in polymer electrolyte fuel cells. Within this approach the effects of reaction kinetics and double layer capacitance at the dispersed catalyst?electrolyte interface, proton conductivity of the electrolyte network within the layer and oxygen diffusion

M Eikerling; A. A Kornyshev

1999-01-01

389

Modelling the performance of the cathode catalyst layer of polymer electrolyte fuel cells  

Microsoft Academic Search

A known macrohomogeneous model for the cathode catalyst layer of a low temperature fuel cell, which includes the kinetics of oxygen reduction at the catalyst?electrolyte interface, proton transport through the polymer electrolyte network, and oxygen diffusion through hydrophobized voids, is considered. Analytical expressions in the relevant ranges of parameter values are obtained. These are the limits of (i) small currents,

M. Eikerling; A. A. Kornyshev

1998-01-01

390

A plasma-cathode electron source designed for industrial use  

NASA Astrophysics Data System (ADS)

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

Osipov, Igor; Rempe, Nikolai

2000-04-01

391

Oxidation of nano-multilayered CrAlBN thin films between 600 and 1000 °C in air  

Microsoft Academic Search

Thin CrAlBN films, whose composition were 41.5Cr-8.0Al-0.2B-50.3N (at.%), were deposited on steel substrates in a cathodic arc plasma deposition system. They consisted of alternating crystalline Cr2N and AlBN nanolayers. The CrAlBN film oxidized faster than the CrAlSiN film. After oxidation at 900°C for 50h in air, a thin Cr2O3 layer, containing dissolved Al and Fe ions, formed via outward diffusion

Thuan Dinh Nguyen; Sun Kyu Kim; Dong Bok Lee

2010-01-01

392

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

NASA Astrophysics Data System (ADS)

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

Martin, Boris E.

393

Nickel-titanium-phosphate cathodes  

DOEpatents

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.

Belharouak, Ilias (Westmont, IL); Amine, Khalil (Downers Grove, IL)

2008-12-16

394

Filters for cathodic arc plasmas  

DOEpatents

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.

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

2002-01-01

395

Hydrothermal synthesis of cathode materials  

Microsoft Academic Search

A number of cathodes are being considered for the next generation of lithium ion batteries to replace the expensive LiCoO2 presently used. Besides the layered oxides, such as LiNiyMnyCo1?2yO2, a leading candidate is lithium iron phosphate with the olivine structure. Although this material is inherently low cost, a manufacturing process that produces electrochemically active LiFePO4 at a low cost is

Jiajun Chen; Shijun Wang; M. Stanley Whittingham

2007-01-01

396

Barium-Dispenser Thermionic Cathode  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

397

Batteries: Overview of Battery Cathodes  

Microsoft Academic Search

The very high theoretical capacity of lithium (3829 mAh\\/g) provided a compelling rationale from the 1970's onward for development of rechargeable batteries employing the elemental metal as an anode. The realization that some transition metal compounds undergo reductive lithium intercalation reactions reversibly allowed use of these materials as cathodes in these devices, most notably, TiS. Another intercalation compound, LiCoO, was

Doeff; Marca M

2010-01-01

398

Insoluble heavy metal polysulfide cathodes  

SciTech Connect

Heavy metal polysulfides which are insoluble in non-aqueous electrolytes and having the formula M /SUB x/ /SUP m/ (S /SUB y/ ) /SUB z/ -/sup 2/ (wherein M is a heavy metal such as iron, cobalt, copper or nickel: S is sulfer; mx=2z; and y is greater than two) are utilized as very high energy density cathodes in non-aqueous electrochemical cells.

Bowden, W.L.; Barnette, L.H.; DeMuth, D.L.

1984-11-06

399

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

PubMed

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

Chung, Kyungmi; Fujiki, Itto; Okabe, Satoshi

2011-01-01

400

Electrochemical behavior of niobium triselenide cathode in lithium secondary cells  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

401

Behaviour of various cathode materials for nonaqueous lithium cells  

NASA Astrophysics Data System (ADS)

The reaction mechanisms with Li of various metal oxides, sulfides and a selenide in nonaqueous electrolyte have been studied by the galvanostatic method, X-ray diffraction analysis, and ion-microanalysis. As a result, cell reactions were classified into three types: (1) The directly reduced type: cathode materials are reduced directly to metal; CuO, etc.; (2) The 2-step reaction type: reaction proceeds through intermediate products: FeS2; and (3) The solid diffusion type, based on the so-called intercalation reaction; MnO2, TiS2, etc.

Ikeda, H.; Narukawa, S.

1983-05-01

402

NEXIS Reservoir Cathode 2000 Hour Life Test  

NASA Technical Reports Server (NTRS)

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.

Vaughn, Jason; Schneider, Todd; Polk, Jay; Goebel, Dan; Ohlinger, Wayne; Hill, D. Norm

2004-01-01

403

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

SciTech Connect

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.

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

404

Hollow cathode, quasi-steady MPD arc  

NASA Technical Reports Server (NTRS)

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.

Parmentier, N.; Jahn, R. G.

1971-01-01

405

Diffusion Flame Stabilization  

NASA Technical Reports Server (NTRS)

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.

Takahashi, Fumiaki; Katta, V. R.

2006-01-01

406

Diffusion Flame Stabilization  

NASA Technical Reports Server (NTRS)

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.

Takahashi, Fumiaki; Katta, Viswanath R.

2007-01-01

407

New Cathode Materials for Intermediate Temperature Solid Oxide Fuel Cells  

SciTech Connect

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.

Allan J. Jacobson

2004-07-23

408

Theory of the High Temperature Hollow Cathode, a Model of the Cathode Mechanism.  

National Technical Information Service (NTIS)

The hollow cathode in the discharge chamber of the electrostatic Kaufman thruster differs from the conventional hollow cathodes in allowing essentially higher operational temperatures, extremely small geometric measurements, higher discharge currents, and...

H. Bessling

1976-01-01

409

Theory of the High-Temperature, Hollow Cathode, a Model of the Cathode Mechanism.  

National Technical Information Service (NTIS)

The hollow cathode in the discharge chamber of the electrostatic Kaufman thruster differs from the conventional hollow cathodes in allowing essentially higher operational temperatures, extremely small geometric measurements, higher discharge currents, and...

H. Bessling

1977-01-01

410

Aluminum-air batteries for military applications  

Microsoft Academic Search

The authors review the basic characteristics of aluminum-air batteries, describe some of the recent advances involving aluminum anodes and air cathodes, aluminum-air batteries and demonstrate certain potential military applications. They can be transported as lightweight, collapsible batteries and can be filled with water at the site of operation. The alkaline Al\\/air battery is advantageous when a high power is desired.

B. M. L. Rao; R. Cook; W. Kobasz; G. D. Deuchars

1992-01-01

411

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

SciTech Connect

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

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

2008-02-11

412

A direct density modulation cathode in magnetron  

SciTech Connect

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.

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

2013-09-15

413

Fundamental advances for characterizing cathodic protection systems  

NASA Astrophysics Data System (ADS)

This research is developing a corrosion rate measurement to assist in (1) identifying in greater detail why corrosion occurs in pipelines that are nominally cathodically protected and (2) determining more specifically the requirements for cathodic protection. Present corrosion rate methods are limited to culmative changes such as weight loss. Under this project a new, instantaneous and nondestructive, technique has been developed to measure corrosion rate of metals under cathodic protection.

Srinivasan, R.; Zarriello, P. R.; Gopalan, P.; Murphy, J. C.

1994-03-01

414

Pyrite cathode material for a thermal battery  

NASA Astrophysics Data System (ADS)

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

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

1991-02-01

415

Compatibility of field emission cathode and electric propulsion technologies  

Microsoft Academic Search

Field emission (FE) cathodes are being considered to replace hollow cathodes in Hall and ion thrusters because they do not require propellant and operate cold, unlike hollow cathodes. In addition to higher operating efficiency these cathodes have much smaller dimensions, therefore they can be used with meso- and microscale propulsion systems. Field Emission Array (FEA) cathodes are typically used in

Colleen Marie Marrese

1999-01-01

416

Effect of gas and cathode material on the r.f. hollow cathode reactive PVD  

Microsoft Academic Search

The process of generation of the radio frequency (r.f.) hollow cathode discharge was examined for different gases and different materials of the r.f. electrode. The delivered r.f. power range used in the experiments enabled analysis of the hollow cathode discharge development together with the transition into the hollow cathode arc for selected combinations of cathode materials and gases. The results

H. Baránková; L. Bárdoš

1999-01-01

417

Physics Of The Plasma-Cathode Interface Of Glow Discharge In Oxygen With Aluminium Cathode  

Microsoft Academic Search

Glow discharge in oxygen with aluminium cathode has peculiar characteristics. It works at the product (p.Lcf) of gas pressure and the cathode space length, smaller than in other cases, e.g. even Ne\\/Al discharge. Numerical modelling of electrodynamic structure of the cathode region suggests low multiplication of electron fluxes and consequently high electron emission from the ``oxidised'' cathode surface at relatively

Z. Wronski

2008-01-01

418

Arc initiation in cathodic arc plasma sources  

DOEpatents

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.

Anders, Andre (Albany, CA)

2002-01-01

419

Development of High Energy Cathode (PNNL)  

SciTech Connect

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

Zhang, Jiguang; Liu, Jun

2011-01-01

420

Emission properties of explosive field emission cathodes  

NASA Astrophysics Data System (ADS)

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/cm2 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/?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.

Roy, Amitava; Patel, Ankur; Menon, Rakhee; Sharma, Archana; Chakravarthy, D. P.; Patil, D. S.

2011-10-01

421

Life test studies on tungsten impregnated cathodes  

NASA Technical Reports Server (NTRS)

NASA-Lewis Research Center has conducted an ongoing life test program on commercial impregnated tungsten cathodes since 1971. This brief is an update of the information as of December 1979. B-type cathodes, operated at 1100 C have been run in simulated microwave tubes at 2 A/sq cm for more than four years with about 6-percent degradation in current at a constant reference anode voltage. M-type cathodes have been operated for 30,000 h at a cathode temperature of 1010 C and 2 A/sq cm with no degradation in current as a constant reference anode voltage.

Forman, R.; Elmer, P.

1980-01-01

422

Phthalocyanine cathode materials for secondary lithium cells  

SciTech Connect

Discharge and charge characteristics of various phthalocyanine cathodes coupled with lithium metal are studied. The best capacity based only on cathode active material weight is 1440 A-hr/kg in the lithium/iron phthalocyanine system, and the cycle life of the lithium/Cu phthalocyanine system is more than 100 times at the discharge depth of 157 A-hr/kg. The cathode reaction mechanism is supposed to be lithium intercalation between phthalocyanine molecules. The results indicate that these phthalocyanines are promising cathode active materials for lithium secondary batteries. 15 refs.

Yamaki, J.; Yamaji, A.

1982-01-01

423

Phthalocyanine cathode materials for secondary lithium cells  

SciTech Connect

Discharge and charge characteristics of various phthalocyanine cathodes coupled with lithium metal are studied. The best capacity based only on cathode active material weight is 1440 A-hr/kg in the lithium/iron phthalocyanine system, and the cycle life of the lithium/Cu phthalocyanine system is more than 100 times at the discharge depth of 157 A-hr/kg. The cathode reaction mechanism is supposed to be lithium intercalation between phthalocyanine molecules. The results indicate that these phthalocyanines are promising cathode active materials for lithium secondary batteries.

Tamaki, J.; Yamaji, A.

1982-01-01

424

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

NASA Technical Reports Server (NTRS)

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.

Vaughn, Jason A.

1989-01-01

425

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

NASA Astrophysics Data System (ADS)

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.

Capece, Angela M.; Polk, James E.; Mikellides, Ioannis G.; Shepherd, Joseph E.

2014-04-01

426

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

NASA Technical Reports Server (NTRS)

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.

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

1979-01-01

427

Kinetics of intercalation of lithium into NbSe3 and TiS2 cathodes  

NASA Technical Reports Server (NTRS)

Titanium disulfide and niobium triselenide are two well-studied candidate materials for positive electrodes in rechargeable lithium cells. A comparative study of the kinetics of intercalation of lithium in both the cathodes is made here based on various electrochemical techniques, i.e., linear polarization, potentiodynamic polarization, and ac impedance under different experimental conditions such as prismatic or disk configuration of fresh, partially discharged, or cycled electrode. Further, the diffusion coefficients of lithium ions in these cathodes are estimated under these conditions using conventional techniques, i.e., ac impedance, chronocoulometry, chronoamperometry, and current pulse relaxation. Based on the values of the diffusion coefficients, the applicability of these methods for the determination of diffusion coefficients is discussed.

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

1992-01-01

428

Diffusion von Kupfer in Reinaluminiumplattierschichten: Mechanismus und Einfluss Auf das Korrosionsverhalten (Copper Diffusion in Pure Aluminum Cladding: Mechanism and Influence on Corrosion Behavior).  

National Technical Information Service (NTIS)

Copper diffusion from base material to pure aluminum cladding impairs the protective action for the following reasons. The resting potential and the local corrosion potential are shifted to positive values. Consequently the cathodic protective action of p...

U. Koch H. Dengler

1990-01-01

429

Electrochemical behaviour of mono-chloronitrobenzene as cathode material for magnesium reserve batteries  

NASA Astrophysics Data System (ADS)

Mono-chloronitrobenzene (MCNB) is investigated as a cathode material for magnesium reserve batteries that use a magnesium anode and a 2 M magnesium perchlorate aqueous electrolyte. The composition of the conducting material (acetylene black) in the cathode mix is optimized to obtain better electrochemical performance. The reduction mechanism of mono-chloronitrobenzene is examined by means of cyclic voltammetry using a glassy carbon electrode. Discharge studies at different current drains indicate that Mg-MCNB cells exhibit the highest Coulombic efficiency (86%) at a current drain of 100 mA. The reduction of MCNB to mono-chloroaniline is irreversible and diffusion-controlled.

Thirunakaran, R.; Vasudevan, S.; Sivashanmugam, A.; Gopukumar, S.

430

Generation of Larger Volume Glow Discharge in Microhollow Cathode Sustained Discharge with Split Third Electrodes  

NASA Astrophysics Data System (ADS)

Enlarged-volume diffuse glow discharge at high pressures is produced by microhollow cathode sustained discharge in a split third electrode configuration. The largest span-wise expansion of the sustained glow discharge is 12 mm at 700 Torr with seven positively biased split electrodes, while with a conventional single planar third electrode the expansion is only about 2 mm. Current--voltage characteristics reveal that the whole trilayer system behaves like a normal glow discharge at third electrode currents higher than the microhollow cathode discharge current. The current distribution over the entire electrodes exhibits moderately uniform expansion in the discharge across the electrode span.

Rahman, Mohammad Towhidur; Shin, Jichul

2011-09-01

431

Effect of cathode end caps and a cathode emissive surface on relativistic magnetron operation  

Microsoft Academic Search

Cathode plasma expansion into a vacuum gap is one of the major physical mechanisms affecting the relativistic magnetron (RM) performance and causing so-called RF pulse shortening. This paper will show how the development of new cathode technologies has led to a significant enhancement of the RM efficiency and power. We have conducted a series of experiments with various cathodes intended

Yuri M. Saveliev; Stephen N. Spark; Brian A. Kerr; Mark I. Harbour; Stephen C. Douglas; Wilson Sibbett

2000-01-01

432

Development of improved cathodes for solid oxide fuel cells  

SciTech Connect

The University of Missouri-Rolla conducted a 17 month research program focused on the development and evaluation of improved cathode materials for solid oxide fuel cells (SOFC). The objectives of this program were: (1) the development of cathode materials of improved stability in reducing environments; and (2) the development of cathode materials with improved electrical conductivity. The program was successful in identifying some potential candidate materials: Air sinterable (La,Ca)(Cr,Co)O{sub 3} compositions were developed and found to be more stable than La{sub .8}Sr{sub .2}MnO{sub 3} towards reduction. Their conductivity at 1000{degrees}C ranged between 30 to 60 S/cm. Compositions within the (Y,Ca)(Cr,Co,Mn)O{sub 3} system were developed and found to have higher electrical conductivity than La{sub .8}Sr{sub .2}MnO{sub 3} and preliminary results suggest that their stability towards reduction is superior.

Anderson, H.U.

1991-03-01

433

Performance Degradation of LSCF Cathodes  

SciTech Connect

This final report summarizes the progress made during the October 1, 2008 - September 30, 2013 period under Cooperative Agreement DE-NT0004109 for the U. S. Department of Energy/National Energy Technology Laboratory (USDOE/NETL) entitled “Performance Degradation of LSCF Cathodes”. The primary objective of this program is to develop a performance degradation mitigation path for high performing, cost-effective solid oxide fuel cells (SOFCs). Strategies to mitigate performance degradation are developed and implemented. In addition, thermal spray manufacturing of SOFCs is explored. Combined, this work establishes a basis for cost-effective SOFC cells.

Alinger, Matthew

2013-09-30

434

Lithium-Moist Air Battery.  

National Technical Information Service (NTIS)

The purpose of the first six months work in this program was to determine, insofar as possible, the feasibility of the three principle components of a lithium-moist air battery system, i.e., anode, cathode, and electrolyte. From the work done during this ...

G. D. McDonald, J. E. A. Toni, W. E. Elliott

1966-01-01

435

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...

436

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...

437

Low level plasma formation in a carbon velvet cesium iodide coated cathode  

NASA Astrophysics Data System (ADS)

Field emission cathodes have been a subject of research for many years. These cathodes hold the promise of effective electron emission in the absence of a heater. Such devices find application in the high power microwave (HPM) arena, as well as the conventional microwave industry and other areas such as flat panel displays. Over the past several years the Air Force Research Laboratory began to focus on cesium iodide cathodes as a field emission cathode of some interest. Previously reported results demonstrated a cesium iodide coated carbon velvet cathode capable of over one million pulses of operation with no degradation of emission. However, the exact emission mechanism remains somewhat unclear. This paper presents results showing that plasma formation on the cathode surface remains minimal at 1 ?s pulse lengths. While ionized cesium and iodine lines exist in the light spectrum from the diode, these lines remain quite small, with the fluorescent emission from solid cesium iodide dominating the optical spectra in the diode. Hence, we propose that the cesium iodide coated carbon velvet operates in a space charge limited regime with pure field emission alone.

Shiffler, D.; Heggemeier, J.; Lacour, M.; Golby, K.; Ruebush, M.

2004-04-01

438

Olivine-type nanosheets for lithium ion battery cathodes.  

PubMed

Olivine-type LiMPO4 (M = Fe, Mn, Co, Ni) has become of great interest as cathodes for next-generation high-power lithium-ion batteries. Nevertheless, this family of compounds suffers from poor electronic conductivities and sluggish lithium diffusion in the [010] direction. Here, we develop a liquid-phase exfoliation approach combined with a solvothermal lithiation process in high-pressure high-temperature (HPHT) supercritical fluids for the fabrication of ultrathin LiMPO4 nanosheets (thickness: 3.7-4.6 nm) with exposed (010) surface facets. Importantly, the HPHT solvothermal lithiation could produce monodisperse nanosheets while the traditional high-temperature calcination, which is necessary for cathode materials based on high-quality crystals, leads the formation of large grains and aggregation of the nanosheets. The as-synthesized nanosheets have features of high contact area with the electrolyte and fast lithium transport (time diffusion constant in at the microsecond level). The estimated diffusion time for Li(+) to diffuse over a [010]-thickness of <5 nm (L) was calculated to be less than 25, 2.5, and 250 ?s for LiFePO4, LiMnPO4, and LiCoPO4 nanosheets, respectively, via the equation of t = L(2)/D. These values are about 5 orders of magnitude lower than the corresponding bulk materials. This results in high energy densities and excellent rate capabilities (e.g., 18 kW kg(-1) and 90 Wh kg(-1) at a 80 C rate for LiFePO4 nanosheets). PMID:23713414

Rui, Xianhong; Zhao, Xiaoxu; Lu, Ziyang; Tan, Huiteng; Sim, Daohao; Hng, Huey Hoon; Yazami, Rachid; Lim, Tuti Mariana; Yan, Qingyu

2013-06-25

439

An experimental investigation of cathode erosion in high current magnetoplasmadynamic arc discharges  

NASA Astrophysics Data System (ADS)

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.

Codron, Douglas A.

440

IN SITU STUDIES ON THE CATALYTIC AND ELECTRONIC PROPERTIES OF MULTI-DIMENSIONAL CATHODE  

SciTech Connect

The overall objective of this program was to provide the fundamental background to enable SECA Industrial Team Members to select and develop oxide cathodes for the operation of solid oxide fuel cells in the intermediate temperature (500-700 C). A number of experimental techniques were used to address the specific obstacles within the program. The work expanded our existing experimental techniques to the use of in situ diffraction and spectroscopic techniques that are sensitive to the oxygen and iron structural and chemical environment. Such measurements were coupled with the evaluation and determination of the catalytic properties of potential cathode oxides. The scope of the work was to prepare carefully controlled cathode samples of various compositions and microstructure and perform fundamental measurements of their physical properties. The measurement of physical properties of the cathode materials systems were used to correlate those properties to the overall effectiveness of the material as a constituent of an SOFC cell. The measurements techniques of neutron scattering and Moessbauer are relatively unique capabilities which have significance to the LSCF cathode system. The unique ability to make thin film samples can provide special samples for surface science efforts to understand cathodic catalytic activity. The data obtained from neutron diffraction, Moessbauer Spectroscopy, electrical measurements and modeling show that the oxygen vacancy content at 500 C in air for La{sub 0.8}Sr{sub 0.2}MnO{sub 3}, La{sub 0.6}Sr{sub 0.4}FeO{sub 3} and La{sub 0.6}Sr{sub 0.4}Fe{sub 0.8}Co{sub 0.2}O{sub 3-{delta}} are 0, 1% and 5% respectively. This is a significant finding that should relate to performance as a cathode, and gives criteria for the selection of new cathode materials.

Harlan U. Anderson

2003-12-01