These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

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

PubMed

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

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

2012-04-01

2

Investigation of the gas-diffusion-electrode used as lithium\\/air cathode in non-aqueous electrolyte and the importance of carbon material porosity  

Microsoft Academic Search

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

Chris Tran; Xiao-Qing Yang; Deyang Qu

2010-01-01

3

Hot hollow cathode diffuse arc deposition of chromium nitride films  

Microsoft Academic Search

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

H. Baránková; L. Bárdos; L.-E. Gustavsson

2005-01-01

4

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

5

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

6

Thermal conditions in a hot evaporating cathode in a stationary vacuum arc with diffuse cathode emission  

SciTech Connect

A study has been made of an arc on a thermally insulated metal cathode with indirect electron-beam heating. The cathode material (gadolinium) resembles ordinary refractory metals in having a small ratio of the evaporated-atom flux to the thermionic-emission electron one. At cathode temperatures T /SUB c/ greater than or equal to 1900/sup 0/K and saturation-vapor pressures greater than or equal to Pa, one gets stationary diffuse cathode emission with a mean current density of 10-100 A/cm/sup 2/. A method has been developed from measuring the heat flux Q*c, which is the difference between the flux from the plasma to the cathode and the flux transported from the cathode by electron emission. As the heating power and correspondingly T /SUB c/ increase, Q*c decreases, and there is a continuous transition from the self-heated condition with Q*c > O to the externally heated one Q*c < O. This Q*c(Tc) dependence provides for thermal stability of the diffuse cathode emission. In the first state, the ratio of the thermionic emission current to the arc current is about1, while in the second it is >1. To explain the cathode heating at maximal values Q*c > O by the ion flux from the plasma, it has to be assumed that there are highly charged ions with energies of about200 eV.

Paranin, S.N.; Polishchuk, V.P.; Shabashov, V.I.; Sychev, P.E.; Yartsev, I.M.

1986-11-01

7

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

8

High Performance Cathodes for Li-Air Batteries  

SciTech Connect

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

Xing, Yangchuan

2013-08-22

9

Power generation by packed-bed air-cathode microbial fuel cells.  

PubMed

Catalysts and catalyst binders are significant portions of the cost of microbial fuel cell (MFC) cathodes. Many materials have been tested as aqueous cathodes, but air-cathodes are needed to avoid energy demands for water aeration. Packed-bed air-cathodes were constructed without expensive binders or diffusion layers using four inexpensive carbon-based materials. Cathodes made from activated carbon produced the largest maximum power density of 676 ± 93 mW/m(2), followed by semi-coke (376 ± 47 mW/m(2)), graphite (122 ± 14 mW/m(2)) and carbon felt (60 ± 43 mW/m(2)). Increasing the mass of activated carbon and semi-coke from 5 to ? 15 g significantly reduced power generation because of a reduction in oxygen transfer due to a thicker water layer in the cathode (?3 or ?6 cm). These results indicate that a thin packed layer of activated carbon or semi-coke can be used to make inexpensive air-cathodes for MFCs. PMID:23732924

Zhang, Xiaoyuan; Shi, Juan; Liang, Peng; Wei, Jincheng; Huang, Xia; Zhang, Chuanyi; Logan, Bruce E

2013-08-01

10

Battery with modular air cathode and anode cage  

DOEpatents

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

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

1988-01-01

11

Battery with modular air cathode and anode cage  

DOEpatents

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

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

1987-01-01

12

The characteristics of vacuum arc with stationary diffuse spot on non-thermionic cathode  

Microsoft Academic Search

The vacuum arc with stationary diffuse spot on the solid cathode from chromium has been studied. The arc current was 30-220 A, cathode temperature 1800-2100 K. The mean current density on the cathode 10-10 2 A\\/cm2. The part of thermionic current at the cathode was less than 0.1 % from arc current. Observations of cathode surface during arcing with help

V. M. Batenin; L. I. Klimovsky; V. P. Polistchook; V. A. Sinel'shchikov

2000-01-01

13

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

PubMed

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

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

2014-06-15

14

Ab initio screening of lithium diffusion rates in transition metal oxide cathodes for lithium ion batteries  

E-print Network

A screening metric for diffusion limitations in lithium ion battery cathodes is derived using transition state theory and common materials properties. The metric relies on net activation barrier for lithium diffusion. ...

Moore, Charles J. (Charles Jacob)

2012-01-01

15

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

E-print Network

Two-Phase Transport in Polymer Electrolyte Fuel Cells with Bilayer Cathode Gas Diffusion Media Ugur to analyze the two-phase transport in polymer electrolyte fuel cells with bilayer cathode gas diffusion media toward the anode by increasing the hydraulic pressure differential across the membrane, consequently

16

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

17

Microbial fuel cell cathodes with poly(dimethylsiloxane) diffusion layers constructed around stainless steel mesh current collectors.  

PubMed

A new and simplified approach for making cathodes for microbial fuel cells (MFCs) was developed by using metal mesh current collectors and inexpensive polymer/carbon diffusion layers (DLs). Rather than adding a current collector to a cathode material such as carbon cloth, we constructed the cathode around the metal mesh itself, thereby avoiding the need for the carbon cloth or other supporting material. A base layer of poly(dimethylsiloxane) (PDMS) and carbon black was applied to the air-side of a stainless steel mesh, and Pt on carbon black with Nafion binder was applied to the solution-side as catalyst for oxygen reduction. The PDMS prevented water leakage and functioned as a DL by limiting oxygen transfer through the cathode and improving coulombic efficiency. PDMS is hydrophobic, stable, and less expensive than other DL materials, such as PTFE, that are commonly applied to air cathodes. Multiple PDMS/carbon layers were applied in order to optimize the performance of the cathode. Two PDMS/carbon layers achieved the highest maximum power density of 1610 +/- 56 mW/m(2) (normalized to cathode projected surface area; 47.0 +/- 1.6 W/m(3) based on liquid volume). This power output was comparable to the best result of 1635 +/- 62 mW/m(2) obtained using carbon cloth with three PDMS/carbon layers and a Pt catalyst. The coulombic efficiency of the mesh cathodes reached more than 80%, and was much higher than the maximum of 57% obtained with carbon cloth. These findings demonstrate that cathodes can be constructed around metal mesh materials such as stainless steel, and that an inexpensive coating of PDMS can prevent water leakage and lead to improved coulombic efficiencies. PMID:20099808

Zhang, Fang; Saito, Tomonori; Cheng, Shaoan; Hickner, Michael A; Logan, Bruce E

2010-02-15

18

Increased discharge capacity of a Li-air activated carbon cathode produced by preventing carbon surface passivation  

Microsoft Academic Search

A significant discharge capacity increase (larger than 3 times) for the gas-diffusion-electrode (GDE) used in Li-air cells was demonstrated through modification of the carbon surface with long-chain hydrophobic molecules. The capacity loss of the Li-air activated carbon cathode was found to be caused by the formation of undesired surface passivation. The mechanism of such passivation was identified as the formation

Chris Tran; Janak Kafle; Xiao-Qing Yang; Deyang Qu

2011-01-01

19

Thermal conditions in a hot evaporating cathode in a stationary vacuum arc with diffuse cathode emission  

Microsoft Academic Search

A study has been made of an arc on a thermally insulated metal cathode with indirect electron-beam heating. The cathode material (gadolinium) resembles ordinary refractory metals in having a small ratio of the evaporated-atom flux to the thermionic-emission electron one. At cathode temperatures T \\/SUB c\\/ greater than or equal to 1900°K and saturation-vapor pressures greater than or equal to

S. N. Paranin; V. P. Polishchuk; V. I. Shabashov; P. E. Sychev; I. M. Yartsev

1986-01-01

20

A Stationary Vacuum Arc with a Diffuse Spot on a Nonemitting Chrome Cathode  

Microsoft Academic Search

The results are given of experimental investigations of a stationary vacuum arc with a diffuse spot on a hot cathode of solid chrome in the current range from 20 to 220 A. The characteristics of the discharge are compared to those of a similar discharge on a thermionic gadolinium cathode. It is demonstrated that, in the case of a chrome

V. M. Batenin; I. I. Klimovskii; V. P. Polishchuk; V. A. Sinel'shchikov

2003-01-01

21

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

22

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

E-print Network

Effect of nitrate on the performance of single chamber air cathode microbial fuel cells Chontisa Single chamber Air cathode Nitrate Wastewater treatment a b s t r a c t The effect of nitrate investigated. The maximum voltage output was not affected by 8.0 mM nitrate in the medium solution at higher

Tullos, Desiree

23

Prediction of Room Air Diffusion for Reduced Diffuser Flow Rates  

E-print Network

are compared against the measured data. Other important parameters such as diffuser jet inlet angle and radiation effect are also considered on the benchmark case to validate the results and to recommend the best fit parameters for room air simulations...

Gangisetti, Kavita

2011-02-22

24

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

E-print Network

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

25

Parameters of High-Temperature Diffusion and Evaporation of Alloying Elements of Thermal Emission Cathodes  

NASA Astrophysics Data System (ADS)

In a joint statement, nonlinear thermal and diffusion problems are solved by a numerical method to analyze the processes of heat and mass transfer and evaporation of activators of thermal emission cathodes for high-current plasma systems. For the two-dimensional diffusion problem, the boundary conditions are strictly formulated and nonlinear temperature dependences of the diffusion coefficients and evaporation rates of emissive and alloying elements are considered. Various mechanisms of activator diffusion are also studied together with the main regularities of heat and mass transfer and activator evaporation as functions of the system parameters.

Tsydypov, B. D.

2014-07-01

26

The transition from a filamentary dielectric barrier discharge to a diffuse barrier discharge in air at atmospheric pressure  

Microsoft Academic Search

A transparent plasma discharge reactor using air was used to investigate the transition from a filamentary dielectric barrier discharge (FDBD) operation regime into the diffuse barrier discharge regime. Recent results of other researchers indicate that the stability of diffuse barrier discharges in nitrogen may be attributed to the lack of a fully formed cathode fall layer when the discharge operates

Daniel M. Sherman

2005-01-01

27

Molecular Dynamics Study of Lithium Diffusion in Lithium-Manganese Spinel Cathode Materials  

SciTech Connect

A series of molecular dynamics computer simulations of the self-diffusion of lithium in pure and several doped lithium-manganese spinel materials has been completed. The theoretical approach is part of an effort to understand the mechanisms and rates of lithium diffusion, and to evaluate the structural control of the cathode materials upon lithium intercalation (charge-discharge) process. The molecular dynamics approach employs a fully ionic forcefield that accounts for electrostatic, repulsive, and dispersion interactions among all ions.

Cygan, R.T.; Westrich, H.R.; Dought, D.H.

1998-01-01

28

[Electrode configuration as a factor affecting electricity generation in air-cathode microbial fuel cell].  

PubMed

In air-cathode microbial fuel cell (ACMFC), oxygen diffused into the reactor from cathode without PEM can be reduced as electron acceptor via aerobic respiration by facultative microorganisms, resulting in either a decreasing of power generation or electron loss. In this study, ACMFC1 and ACMFC2 with different electrode configuration were compared to examine power density and electron recovery from glucose. The results showed that ACMFC1 generated a maximum power density of 3 070mW/m3 with internal resistance of 302.141 and anode potential of -323mV; while maximum power density of 9 800mW/m3 for ACMFC2 was obtained with internal resistance of 107.79omega and anode potential of -442mV. ACMFC2 could sustain generating electricity for nearly 220 h (ERE of 30.1%), comparing with ACMFC1 of less than 50 h (ERE of 9.78%) under batch operation. Therefore, an improved design for electrode configuration of ACMFC can be performed to generate higher power with low internal resistance, meanwhile, achieve increasing electron recovery simultaneously. PMID:17326419

You, Shi-Jie; Zhao, Qing-Liang; Jiang, Jun-Qiu

2006-11-01

29

Use of Pyrolyzed Iron Ethylenediaminetetraacetic Acid Modified Activated Carbon as Air-Cathode Catalyst in Microbial Fuel Cells  

E-print Network

Use of Pyrolyzed Iron Ethylenediaminetetraacetic Acid Modified Activated Carbon as Air activity of AC cathodes, AC powders were pyrolyzed with iron ethylenediaminetetraacetic acid (Fe MFCs was 50% lower than MFCs with the AC cathodes. Pyridinic nitrogen, quaternary nitrogen and iron

30

Microbial Fuel Cell Cathodes With Poly(dimethylsiloxane) Diffusion  

E-print Network

of poly(dimethylsiloxane) (PDMS) and carbon black was applied to the air-side of a stainless steel mesh, and Pt on carbon black with Nafion binder was applied to the solution- sideascatalystforoxygenreduction

31

Features of a near-cathode region in a gliding arc discharge in air flow  

NASA Astrophysics Data System (ADS)

This paper describes the results of the investigation of a low-current atmospheric-pressure discharge in air flow with electrode geometry typical of the so-called gliding arc. At a current of fractions of an ampere the discharge burns in a regime of normal glow rather than in an arc regime and the area of the negative glow plasma smoothly moves over the cathode surface under the effect of gas flow. At the background of the glow discharge, occasional creation of a spark cathode spot can occur. Then the discharge becomes attached to the cathode surface and the site of current attachment does not move due to the gas flow. The site of current attachment continues its smooth displacement when the cathode spot is spontaneously extinguished. The events when the cathode spot abruptly jumps to a new place of attachment downstream are also observed.

Korolev, Y. D.; Frants, O. B.; Landl, N. V.; Bolotov, A. V.; Nekhoroshev, V. O.

2014-10-01

32

Design of experiments and principal component analysis as approaches for enhancing performance of gas-diffusional air-breathing bilirubin oxidase cathode  

NASA Astrophysics Data System (ADS)

Two statistical methods, design of experiments (DOE) and principal component analysis (PCA) are employed to investigate and improve performance of air-breathing gas-diffusional enzymatic electrodes. DOE is utilized as a tool for systematic organization and evaluation of various factors affecting the performance of the composite system. Based on the results from the DOE, an improved cathode is constructed. The current density generated utilizing the improved cathode (755 ± 39 ?A cm-2 at 0.3 V vs. Ag/AgCl) is 2-5 times higher than the highest current density previously achieved. Three major factors contributing to the cathode performance are identified: the amount of enzyme, the volume of phosphate buffer used to immobilize the enzyme, and the thickness of the gas-diffusion layer (GDL). PCA is applied as an independent confirmation tool to support conclusions made by DOE and to visualize the contribution of factors in individual cathode configurations.

Babanova, Sofia; Artyushkova, Kateryna; Ulyanova, Yevgenia; Singhal, Sameer; Atanassov, Plamen

2014-01-01

33

Molecular diffusion of volatile-liquid vapors into air  

Microsoft Academic Search

Diffusion coefficients of vapors diffused into stagnant air were determined at room temperature and atmospheric pressure. Experimental data on diffusion coefficients were obtained from the steady-state open-tube evaporation method modified for this study. No fresh air is passed over the top end of a diffusion tube, and amounts of volatile liquids evaporated in the diffusion tube are measured with a

K. C. Kwon; C. M. Simmons; G. L. Tibere; T. H. Ibrahim

2003-01-01

34

Enhanced water desalination efficiency in an air-cathode stacked microbial electrodeionization cell (SMEDIC)  

E-print Network

(SMEDIC) Noura A. Shehab a , Gary L. Amy a , Bruce E. Logan b , Pascal E. Saikaly a,n a Water DesalinationEnhanced water desalination efficiency in an air-cathode stacked microbial electrodeionization cell Electrodeionization Brackish water desalination Seawater desalination a b s t r a c t A microbial desalination cell

35

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

PubMed

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

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

2012-09-01

36

The effect of preferential diffusion on soot formation in a laminar ethylene\\/air diffusion flame  

Microsoft Academic Search

The influence of preferential diffusion on soot formation in a laminar ethylene\\/air diffusion flame was investigated by numerical simulation using three different transport property calculation methods. One simulation included preferential diffusion and the other two neglected preferential diffusion. The results show that the neglect of preferential diffusion or the use of unity Lewis number for all species results in a

Hongsheng Guo; Gregory J. Smallwood

2011-01-01

37

Stability of strontium-doped lanthanum manganite cathode in humidified air  

NASA Astrophysics Data System (ADS)

The stability of strontium-doped lanthanum manganite (LSM) cathode has been studied using symmetric cells (humidified air, LSM/yttria-stabilized zirconia (YSZ)/LSM, humidified air) under a range of humidification levels (0-50%), temperatures (750-850 °C), and cathodic biases (0-0.5 V). Electrochemical impedance spectroscopy revealed an increase in non-ohmic resistance with increasing H2O/O2 ratio, temperature, and cathodic bias. Post-test surface and interface studies showed the segregation of SrO particles on the LSM surface and formation of Mn2O3 and La2Zr2O7 compounds at the cathodic LSM/YSZ interface. The increase in non-ohmic resistance is attributed to surface segregation of SrO and interfacial compound formation, whereas formation and growth of SrO at the LSM surface is attributed to water adsorption. La2Zr2O7 formation is attributed to interfacial reactions.

Hu, Boxun; Keane, Michael; Mahapatra, Manoj K.; Singh, Prabhakar

2014-02-01

38

Predicting air flow and thermal comfort in an indoor environment under different air diffusion models  

Microsoft Academic Search

Correct air diffusion and the proper quantity of conditioned air are essential for comfortable conditions in forced-ventilation systems. Three different kinds of air diffusion models are studied for summer cooling conditions. These air diffusion types include a one inlet-one outlet, a two inlet-one outlet, and a one inlet-two outlet diffuser in an indoor environment. Evaluation of thermal comfort is made

K. C. Chung; C. Y. Lee

1996-01-01

39

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

NASA Astrophysics Data System (ADS)

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

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

40

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

41

Air plasma spray processing and electrochemical characterization of SOFC composite cathodes  

Microsoft Academic Search

Air plasma spraying has been used to produce porous composite cathodes containing (La0.8Sr0.2)0.98MnO3?y (LSM) and yttria-stabilized zirconia (YSZ) for use in solid oxide fuel cells (SOFCs). Preliminary investigations focused on determining the range of plasma conditions under which each of the individual materials could be successfully deposited. A range of conditions was thereby determined that was suitable for the deposition

B. D. White; O. Kesler; Lars Rose

2008-01-01

42

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

NASA Astrophysics Data System (ADS)

The slow diffusion of hydroxyl out of the catalyst layer as well as the biofouling on the surface of cathode are two problems affecting power for membrane-less air-cathode microbial fuel cells (MFCs). In order to solve both of them simultaneously, here we simply modify activated carbon air-cathode using a bifunctional quaternary ammonium compound (QAC) by forced evaporation. The maximum power density reaches 1041 ± 12 mW m-2 in an unbuffered medium (0.5 g L-1 NaCl), which is 17% higher than the control, probably due to the accelerated anion transport in the catalyst layer. After 2 months, the protein content reduced by a factor of 26 and the power density increases by 33%, indicating that the QAC modification can effectively inhibit the growth of cathodic biofilm and improve the stability of performance. The addition of NaOH and QAC epoxy have a negative effect on power production due to the clogging of pores in catalyst layer.

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

2014-12-01

43

Diffusion of 4,5-benzopyrene (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) 4,5-benzopyrene; (2) air

Winkelmann, J.

44

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. 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

45

Effects of azide on electron transport of exoelectrogens in air-cathode microbial fuel cells.  

PubMed

The effects of azide on electron transport of exoelectrogens were investigated using air-cathode MFCs. These MFCs enriched with azide at the concentration higher than 0.5mM generated lower current and coulomb efficiency (CE) than the control reactors, but at the concentration lower than 0.2mM MFCs generated higher current and CE. Power density curves showed overshoot at higher azide concentrations, with power and current density decreasing simultaneously. Electrochemical impedance spectroscopy (EIS) showed that azide at high concentration increased the charge transfer resistance. These analyses might reflect that a part of electrons were consumed by the anode microbial population rather than transferred to the anode. Bacterial population analyses showed azide-enriched anodes were dominated by Deltaproteobacteria compared with the controls. Based on these results it is hypothesized that azide can eliminate the growth of aerobic respiratory bacteria, and at the same time is used as an electron acceptor/sink. PMID:25062537

Zhou, Xiangtong; Qu, Youpeng; Kim, Byung Hong; Choo, Pamela Yengfung; Liu, Jia; Du, Yue; He, Weihua; Chang, In Seop; Ren, Nanqi; Feng, Yujie

2014-10-01

46

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

PubMed

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

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

2012-09-01

47

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

48

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

E-print Network

Scalable air cathode microbial fuel cells using glass fiber separators, plastic mesh supporters. Logan c,** a State Key Joint Laboratory of Environment Simulation and Pollution Control, Department fiber (GF1) separators, and plastic mesh supporters were used here for the first time to create

49

Doped lanthanum nickelates with a layered perovskite structure as bifunctional cathode catalysts for rechargeable metal-air batteries.  

PubMed

Rechargeable metal-air batteries have attracted a great interest in recent years because of their high energy density. The critical challenges facing these technologies include the sluggish kinetics of the oxygen reduction-evolution reactions on a cathode (air electrode). Here, we report doped lanthanum nickelates (La2NiO4) with a layered perovskite structure that serve as efficient bifunctional electrocatalysts for oxygen reduction and evolution in an aqueous alkaline electrolyte. Rechargeable lithium-air and zinc-air batteries assembled with these catalysts exhibit remarkably reduced discharge-charge voltage gaps (improved round-trip efficiency) as well as high stability during cycling. PMID:24053465

Jung, Kyu-Nam; Jung, Jong-Hyuk; Im, Won Bin; Yoon, Sukeun; Shin, Kyung-Hee; Lee, Jong-Won

2013-10-23

50

ANALYTICAL DIFFUSION MODEL FOR LONG DISTANCE TRANSPORT OF AIR POLLUTANTS  

EPA Science Inventory

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

51

Toxic potency and effects of diffuse air pollution  

Microsoft Academic Search

Diffuse air pollution consists of an omnipresent complex mixture of pollutants that is emitted from many widely dispersed sources as traffic, industries, households, energy plants, waste incinerators, and agriculture. It can be deposited in relatively remote areas as a result of (long-range) airborne transport. It has a heterogeneous composition in time and space and consists of many known and unknown

Timo Hamers

2002-01-01

52

Field-based determination of air diffusivity using soil air and atmospheric pressure time series  

Microsoft Academic Search

Air diffusivity in two zones over a 4.6-m interval of the unsaturated zone was determined through analysis of atmospheric pressure and soil air pressure time series. Regression analysis was used to calculate the ratio of amplitudes (admittance) and phase lag between these series at diurnal and semidiurnal frequencies. The admittance for each of the monitoring zones was close to unity

Stuart Rojstaczer; John P. Tunks

1995-01-01

53

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

54

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

E-print Network

power density was shown to be a linear function of cathode specific surface area (ratio of cathode is the most critical factor for scaling-up MFCs to obtain high power densities. Ã? 2010 Elsevier Ltd. All with different types of wastewaters, including domestic, food processing, and animal wastewaters (Liu et al

55

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

56

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

E-print Network

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

Yurko, Joseph Paul

2010-01-01

57

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

NASA Astrophysics Data System (ADS)

The rolling catalyst layers in air cathode microbial fuel cells (MFCs) are prepared by introducing NH4HCO3 as pore former (PF) with four PF/activated carbon mass ratios of 0.1, 0.2, 0.3 and 1.0. The maximum power density of 892 ± 8 mW m-2 is obtained by cathodes with the mass ratio of 0.2, which is 33% higher than that of the control reactor (without PF, 671 ± 22 mW m-2). Pore analysis indicates the porosity increases by 38% and the major pore range concentrates between 0.5 ?m-0.8 ?m which likely facilitates to enrich the active reaction sites compared to 0.8 ?m-3.0 ?m in the control and other PF-cathodes. In addition, pore structure endows the cathode improved exchange current density by 2.4 times and decreased charge transfer resistance by 44%, which are the essential reasons to enhance the oxygen reduction. These results show that addition of NH4HCO3 proves an effective way to change the porosity and pore distribution of catalyst layers and then enhance the MFC performance.

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

2014-12-01

58

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

PubMed

To observe the influence of P-doped activated carbon (AC) in air-cathode microbial fuel cells (MFCs), AC was treated with H3PO4 (1M) at 80°C and 400°C respectively, and then was used as catalyst layer in the air-cathode. The maximum power densities were: 1096±33mW/m(2) (SP2, AC treated at 400°C), 954±36mW/m(2) (SP1, AC treated at 80°C), which were 55%, 35% higher than the control (708±27mW/m(2), untreated AC), respectively. The results of electrochemical impedance spectroscopy (EIS) and the Brunauer-Emmett-Teller (BET) showed that the total resistance was decreased and the pore structure was changed. The analysis of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) demonstrated that P-doped functional group was produced in SP2, which caused the 15% greater power density than SP1 by increasing O2 adsorption. What is more important, the chemically modified method is simple and economical. PMID:25151475

Chen, Zhihao; Li, Kexun; Pu, Liangtao

2014-10-01

59

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

60

Ignition time of hydrogen-air diffusion flames  

NASA Astrophysics Data System (ADS)

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

Sánchez, Antonio L.; Fernández-Tarrazo, Eduardo; Boivin, Pierre; Liñán, Amable; Williams, Forman A.

2012-11-01

61

The use of nylon and glass fiber filter separators with different pore sizes in air-cathode single-chamber microbial fuel cells  

E-print Network

in an MFC but also affect CE.5,6 Cation exchange membranes (CEMs) such as Nafion7,8 and anion exchange.22 mm) onto the water- facing side of the air cathode, and increased the maximum power density to 214 m size).12 In general, a State Key Joint Laboratory of Environment Simulation and Pollution Control

62

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

63

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.

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

2010-05-01

64

Development of Electrophoretic Process for Coating T-53 Air Diffuser, Exhaust Diffuser, and Combustion Chamber Housing with 'Sermetel W' (Trade Name).  

National Technical Information Service (NTIS)

The report covers activities accomplished to develop an electrophoretic coating method for the application of 'SERMETEL W' to all critical surfaces of the exhaust diffuser, air diffuser and combustion chamber housing of the T-53 engine. 'SERMETEL W' has b...

K. A. Gebler

1967-01-01

65

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

66

Redox mediator enhanced simultaneous decolorization of azo dye and bioelectricity generation in air-cathode microbial fuel cell.  

PubMed

Enhanced simultaneous decolorization of Congo red and bioelectricity generation with anthraquinone-2,6-disulphonic disodium salt (AQDS), riboflavin (RF) and humic acid (HA) as mediators in air-cathode microbial fuel cell (MFC) was demonstrated. Compared with mediator-free MFC, the MFC with added 0.005 mM AQDS, 0.005 mM RF or 1g/L HA showed 36%, 26% and 15% increase in maximum power density along with 394%, 450%, and 258% increases in decolorization rates of Congo red, respectively. Addition of mediators at higher concentration further increased power and Congo red decolorization but the increases were not proportional to the rise in mediator concentration. Based on decreases of anode charge transfer resistance and increases of Congo red decolorization, the mediators kinetically promote the extracellular electron transfer between bacteria, anode and Congo red. Microbial analysis showed that addition of mediators changed the composition of anodic microbial community and stimulated the growth of species belonging to Chlorobi, Endomicrobia and Firmicutes. PMID:23748088

Sun, Jian; Li, Wanjun; Li, Youming; Hu, Yongyou; Zhang, Yaping

2013-08-01

67

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 3-164 ppm, with a sensitivity of 0.05 ?A mM(-1) cm(-2) with respect to the anode total surface area. The response time was as fast as 2.8 min. At saturating acetate concentrations (COD>164 ppm), the miniature SCMFC could rapidly detect the presence of cadmium in water with high sensitivity (0.2 ?g l(-1) cm(-2)) and a lower detection limit of only 1 ?g l(-1). The biosensor dynamic range was 1-25 ?g l(-1). Within this range of concentrations, cadmium affected only temporarily the electroactive biofilm at the anode. When the SCMFCs were again fed with fresh wastewater and no pollutant, the initial steady-state current was recovered within 12 min. PMID:25005554

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

2014-12-15

68

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

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

2014-09-01

69

Reducing Indoor Air Pollution in Developing Countries through Diffusion of Clean Cookstove Technology  

Microsoft Academic Search

Indoor air pollution (IAP) produced from incomplete combustion of biomass fuel affects three billion people worldwide and results in two million premature deaths each year. Clean cookstove technology has been proposed as the most cost-effective method for reducing IAP and improving health in the developing world. Based on Rogers’ (2003) diffusion of innovation theory, a model to effectively diffuse clean

Elizabeth Hendrickson; Art Whatley

70

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

71

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

PubMed

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

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

2013-12-14

72

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

SciTech Connect

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

Ridouane, E. H.; Gawlik, K.

2011-02-01

73

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

74

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...

75

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

76

Universal Relationships in Sooting Methane-Air Diffusion Flames  

Microsoft Academic Search

The laminar flamelet concept is based on the premise that scalar properties in laminar diffusion flames are nearly universal functions of mixture fraction. It has been well-tested and proven for temperature and the major species, however, few studies have addressed its applicability for minor species especially the radical species. In this study, we present a direct numerical simulation of an

C. R. KAPLAN; G. PATNAIK; K. KAILASANATH

1998-01-01

77

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

78

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

PubMed

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

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

2011-01-01

79

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

80

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

81

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

82

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

83

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

EPA Science Inventory

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

84

Hollow cathode conditioning and discharge initiation  

NASA Astrophysics Data System (ADS)

In the framework of developing a fast-starting hollow cathode, one must understand how a cathode is conditioned for operation. The desorption of known contaminates as a function of heater power was measured to quantify cathode conditioning characteristics. In addition to conditioning, a study of hollow cathode emission characteristics under vacuum conditions was performed. Results of these two studies are described herein along with measurements of the temperature of the cathode as a function of time and heater power. The data are used to validate a transient surface diffusion model that describes the migration and surface coverage fraction of low-work-function material from the interior of the hollow cathode to the orifice barrel and to the exterior surface of the orifice plate of the cathode. A sufficiency condition is presented for our cathode geometry of vacuum emission current level and the ability to start a hollow cathode discharge once gas flow is initiated.

Rubin, Binyamin; Williams, John D.

2008-09-01

85

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

86

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

PubMed

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

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

2011-09-15

87

Development of open-air type electrolyte-as-cathode glow discharge-atomic emission spectrometry for determination of trace metals in water  

NASA Astrophysics Data System (ADS)

The open-air type electrolyte cathode atomic glow discharge (ELCAD) has been developed and studied for fundamental and analytical applications for determination of trace heavy metals in water. The normal closed-type discharge cell shows some problems such as unstable plasma due to changes in the pressure inside the cell during the discharge, and water vapor condensing onto the window. Applying approximately 1500 V to the several-millimeter gap between the electrolyte solution cathode and a Pt rod anode in atmospheric air pressure produced a stable plasma and significantly improved sensitivity. The emission spectrum of de-ionized water containing 100 mg/l Cu was measured and some emission lines were found from Cu I (324.7 nm, 327.4 nm and 510.5 nm) and Cu II (224.7 nm and 229.4 nm). The LODs of Cr, Cu, Fe, Mn, Ni, Pb, and Zn are in the ranges from 0.01 mg/l to 0.6 mg/l. The LODs of Cu, Mn, Pb and Zn improve by approximately one order of magnitude compared to the previous closed-type ELCAD.

Kim, Hyo J.; Lee, Jeong H.; Kim, Myung Y.; Cserfalvi, T.; Mezei, P.

2000-07-01

88

Evaluation of alloy anodes for aluminum-air batteries. II. Delineation of anodic and cathodic partial reactions  

Microsoft Academic Search

The design, calibration, and operation of a source\\/collector electrochemical cell for delineating anodic and cathodic partial currents for reactive metals in aqueous media is described. This cell has been used to measure the hydrogen evolution current on aluminum and aluminum alloys in 4M KOH at 25°, 50°, and 80°C over a wide range of potential. These data were then combined

S. Real; M. Urquidi-Macdonald; D. D. Macdonald

1988-01-01

89

Use of thermography to register air temperatures in cross sections of rooms and to visualize the airflow from air-supply diffusers  

NASA Astrophysics Data System (ADS)

To visualize the air flow into a room, we used a plastic screen, placed parallel to the air flow from a supply air diffuser placed at floor level. The screen takes the temperature of the air stream and registration of the screen temperature is made with an IR-camera. This gives a picture of the temperature distribution of the air stream. The information can be used to control the technical characteristics of the supply air device and to judge the impact of the air flow on human comfort.

Sundberg, Jorgen

1993-04-01

90

Development of Electrophoretic Process for Coating T-53 Air Diffuser, Exhaust Diffuser, and Combustion Chamber Housing with 'Sermetel (Trade Name) W'.  

National Technical Information Service (NTIS)

This report covers activities accomplished during Phase IV of a ten (10) month program to develop an electrophoretic coating method for the application of a corrosion-resistant coating to all critical surfaces of the exhaust diffuser, air diffuser and com...

K. A. Gebler

1968-01-01

91

Cathodic protection  

Microsoft Academic Search

Cathodic protection is the electrical solution to the corrosion problem. In this article, the history of cathodic protection (CP) is traced, and the design fundamentals are developed, including the three components of a corrosion system, the three elements of an electric circuit, and the three configurations causing potential difference. CP is the process of forcing a metal to be more

MARCUS O. DURHAM; ROBERT A. DURHAM

2005-01-01

92

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

NASA Astrophysics Data System (ADS)

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

Van Der Schijff, Hermanus P.

93

Effects of cathodic current density and temperature on morphology and microstructure of iridium coating prepared by electrodeposition in molten salt under the air atmosphere  

NASA Astrophysics Data System (ADS)

Iridium coating was prepared on a Re/C substrate (graphite substrate coated with rhenium coating by CVD) using electrodeposition in molten salt of chlorides in the air atmosphere. The effects of cathodic current density and temperature on both the morphology and microstructure of the coating were studied, respectively. The morphology and orientation of the coating were determined by scanning electron microscope and X-ray diffraction, respectively. The results showed that the cathodic current density and temperature both affected the surface morphology, roughness, grain size and compactness of the iridium coating. With increasing of current density from 5 to 50 mA/cm2, the surface roughness of the coating increased from Ra 0.98 to Ra 6.29 ?m, while the grain size decreased. With temperature increasing from 520 to 640 °C, the surface roughness of the coating decreased from Ra 4.41 to Ra 1.16 ?m, while the grain size increased. The preferred orientations of the coatings changed in the row <111>-<220>-<311> with current density increasing. With the increase of temperature, the preferred orientation of the coating changed from <1 1 1> to <2 2 0>, and again to <1 1 1>. The coating with <1 1 1> orientation was smoother and denser than that with <2 2 0> orientation regardless of the grain size.

Zhu, Li'an; Bai, Shuxin; Zhang, Hong; Ye, Yicong

2013-01-01

94

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

95

Preferential diffusion effects on the burning rate of interacting turbulent premixed hydrogen-air flames  

Microsoft Academic Search

The upstream interaction of twin premixed hydrogen-air flames in 2-D turbulence is studied using direct numerical simulations with detailed chemistry. The primary objective is to determine the effect of flame stretch on the overall burning rate during various stages of the interaction. Preferential diffusion effects are accounted for by varying the equivalence ratio from symmetric rich-rich to lean-lean interactions. The

Hong G. Im; Jacqueline H. Chen

2002-01-01

96

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

SciTech Connect

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

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

1992-05-14

97

Air-breathing laminar flow-based microfluidic fuel cell.  

PubMed

This communication reports the design and characterization of an air-breathing laminar flow-based microfluidic fuel cell (LFFC). The performance of previous LFFC designs was cathode-limited due to the poor solubility and slow transport of oxygen in aqueous media. Introduction of an air-breathing gas diffusion electrode as the cathode addresses these mass transfer issues. With this design change, the cathode is exposed to a higher oxygen concentration, and more importantly, the rate of oxygen replenishment in the depletion boundary layer on the cathode is greatly enhanced as a result of the 4 orders of magnitude higher diffusion coefficient of oxygen in air as opposed to that in aqueous media. The power densities of the present air-breathing LFFCs are 5 times higher (26 mW/cm2) than those for LFFCs operated using formic acid solutions as the fuel stream and an oxygen-saturated aqueous stream at the cathode ( approximately 5 mW/cm2). With the performance-limiting issues at the cathode mitigated, these air-breathing LFFCs can now be further developed to fully exploit their advantages of direct control over fuel crossover and the ability to individually tailor the chemical composition of the cathode and anode media to enhance electrode performance and fuel utilization, thus increasing the potential of laminar flow-based fuel cells. PMID:16316201

Jayashree, Ranga S; Gancs, Lajos; Choban, Eric R; Primak, Alex; Natarajan, Dilip; Markoski, Larry J; Kenis, Paul J A

2005-12-01

98

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

99

Cathodic arcs  

SciTech Connect

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

Anders, Andre

2003-10-29

100

Prevention of cathode damage from positive ion bombardment  

NASA Technical Reports Server (NTRS)

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

Bennett, W. H.

1972-01-01

101

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

PubMed

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

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

2008-07-01

102

Stationary vacuum arc on the hot non-thermionic cathode  

Microsoft Academic Search

A vacuum arc with a stationary diffuse spot on a solid chromium cathode has been studied. The arc current was 30-220 A, cathode temperature 1800-2100 K. The mean current density on the cathode was 10-102 A\\/cm2. The part of thermionic current at the cathode was less than 0.1% from the arc current. Observations of cathode surface during arcing with the

V. M. Batenin; I. I. Klimovsky; V. P. Polistchook; V. A. Sinel'shchikov

1998-01-01

103

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

104

CO2/oxalate Cathodes as Safe and Efficient Alternatives in High Energy Density Metal-Air Type Rechargeable Batteries  

E-print Network

We present theoretical analysis on why and how rechargeable metal-air type batteries can be made significantly safer and more practical by utilizing CO2/oxalate conversions instead of O2/peroxide or O2/hydroxide ones, in the positive electrode. Metal-air batteries, such as the Li-air one, may have very large energy densities, comparable to that of gasoline, theoretically allowing for long range all-electric vehicles. There are, however, still significant challenges, especially related to the safety of their underlying chemistries, the robustness of their recharging and the need of supplying high purity O2 from air to the battery. We point out that the CO2/oxalate reversible electrochemical conversion is a viable alternative of the O2-based ones, allowing for similarly high energy density and almost identical voltage, while being much safer through the elimination of aggressive oxidant peroxides and the use of thermally stable, non-oxidative and environmentally benign oxalates instead.

Nemeth, Karoly

2013-01-01

105

Electro-scrubbing volatile organic carbons in the air stream with a gas diffusion electrode.  

PubMed

It is demonstrated that exposing the VOC air streams to the electro-scrubbing reactor with a gas diffusion electrode leads to an efficient removal of organics. The importance order of the influence factors on the electro-scrubbing reactor performance is: conductivity, voltage and air stream flow-rate. The effective conductivity and high voltages generally are beneficial to the removal process and the air flow-rate is not a significant factor compared with the other two, indicating that the reactor might have a consistently satisfying performance within a wide range of gas volumetric load. The mass transfer of both organics and oxygen in the reactor is estimated by mathematical model, and the calculation determines the concentration boundary conditions for the 2-ethoxyethyl acetate removal: if the 2-ethoxyethyl acetate concentration in the inflow air stream holds C(G,i) ? 0.7198%, the removal in the electro-scrubbing reactor is electrochemical reaction controlled; if C(G,i)>0.7198%, the controlling step will be the oxygen mass transfer from the air to the liquid in the electro-scrubbing reactor. The Apparent Current Efficiency of the electro-scrubbing reactor was also determined using COD data, which is significantly higher than some commercial metal oxide electrodes, showing that the reactor is energy efficient and has the promise for the future scale-up. PMID:21324588

Yang, Ji; Liu, Kaichen; Jia, Jinping; Cao, Limei

2011-04-15

106

Analysis of opposed jet hydrogen-air counter flow diffusion flame  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

107

A mechanistic study of Soret diffusion in hydrogen-air flames  

SciTech Connect

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

Yang, F. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544 (United States); Department of Engineering Mechanics, Tsinghua University, Beijing (China); Law, C.K. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544 (United States); Sung, C.J. [Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269 (United States); Zhang, H.Q. [Department of Engineering Mechanics, Tsinghua University, Beijing (China)

2010-01-15

108

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

109

Interior Air Pollution in Automotive Cabins by Volatile Organic Compounds Diffusing from Interior Materials: II. Influence of Manufacturer, Specifications and Usage Status on Air Pollution, and Estimation of Air Pollution Levels in Initial Phases of Delivery as a New Car  

Microsoft Academic Search

Air pollution in the cabins of 101 Japanese cars due to organic compounds diffusing from the interior materials has been described in our previous report. In the present study, the influence of the manufacturer, specifications and usage status of these cars on the interior air pollution was evaluated by covariance analysis. Also, the levels of air pollution in the initial

Toshiaki Yoshida; Ichiro Matsunaga; Kimiko Tomioka; Shinji Kumagai

2006-01-01

110

Heat and Velocity Parameters of a Non-Isothermal Flow Generated by a Double-Chamber Air Diffuser  

NASA Astrophysics Data System (ADS)

Heat and velocity parameters of the non-isothermal flow generated by a source panel-type double-chamber air diffuser with four horizontal shelf pressure equalizers of optimal relative length at the mid-horizontal level and in the vertical axisymmetrical plane. Irregularity ratios of initial velocities and temperatures of the air flow under study have also been defined.

Klymenko, Hanna

2012-06-01

111

Efficiency of a square air diffuser with optimum angle of expansion  

E-print Network

EFFICIENCY OF A ~UAiIE AIR DIFFUSER WITH OPTIMUM ANGLE OF EXPANSION KENNETH WAYNE SMITH A Thesis Submitted to the Graduate School of the Agricultural and Mechanical College of Texas in partial fulfillment of the requirements for the degree... professor Wesley w. Smith and Mr ~ N. D. 5coates for the use of equipment necessary to conduct this experinmnt. Per theM constant sid and advice throughout the investiga- tion, the writer is grateful to Profgssor L. S. O'Bannon and professor Lee p...

Smith, Kenneth Wayne

2012-06-07

112

A large-area diffuse air discharge plasma excited by nanosecond pulse under a double hexagon needle-array electrode.  

PubMed

A large-area diffuse air discharge plasma excited by bipolar nanosecond pulse is generated under a double hexagon needle-array electrode at atmospheric pressure. The images of the diffuse discharge, electric characteristics, and the optical emission spectra emitted from the diffuse air discharge plasma are obtained. Based on the waveforms of pulse voltage and current, the power consumption, and the power density of the diffuse air discharge plasma are investigated under different pulse peak voltages. The electron density and the electron temperature of the diffuse plasma are estimated to be approximately 1.42×10(11) cm(-3) and 4.4 eV, respectively. The optical emission spectra are arranged to determine the rotational and vibrational temperatures by comparing experimental with simulated spectra. Meanwhile, the rotational and vibrational temperatures of the diffuse discharge plasma are also discussed under different pulse peak voltages and pulse repetition rates, respectively. In addition, the diffuse air discharge plasma can form an area of about 70×50 mm(2) on the surface of dielectric layer and can be scaled up to the required size. PMID:24374556

Liu, Zhi-Jie; Wang, Wen-Chun; Yang, De-Zheng; Wang, Sen; Zhang, Shuai; Tang, Kai; Jiang, Peng-Chao

2014-01-01

113

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

114

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

115

Non-precious cathode electrocatalyst for magnesium air fuel cells: Activity and durability of iron-polyphthalocyanine absorbed on carbon black  

NASA Astrophysics Data System (ADS)

A planar iron-polyphthalocyanine (PPcFe) oxygen reduction reaction (ORR) catalyst for magnesium air fuel cells (MAFC) is prepared by dispersing PPcFe on carbon black (C) and heating under argon. Thermogravimetric analysis shows PPcFe is stable below 600 °C. The X-ray diffraction and X-ray photoelectron spectroscopy results show the active site of PPcFe/C is the FeN4 in the phthalocyanine ring. The rotating disk electrode measurements in 0.5 M L-1 H2SO4 solution show the initial potential for ORR is 0.82 V vs. RHE at 20 °C and that it mainly occurs via a four-electron process. Almost no performance degradation is observed over continuous cyclic voltammetry at 10,000 cycles, linear sweep voltammetry at 200 cycles, and 60 h of the chronoamperometry test. The infrared spectrum of PPcFe, after all the durability tests, shows no changes from the initial characteristics. The polarization curves of the air electrodes with PPcFe/C, iron-phthalocyanine/C and Pt/C catalysts exhibit excellent polarization performances. The discharge performance of a MAFC single cell with PPcFe/C cathode catalyst shows an open circuit potential of 1.74 V, with a peak power density of 50.5 mW cm-2 at 20 °C. The cell voltage decreases less than 0.01 V during continuing discharge @ 20 mA cm-2 for more than 11 h.

Li, Zhongfang; Yang, Jianwei; Xu, Guofeng; Wang, Suwen

2013-11-01

116

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

PubMed

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

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

2013-05-01

117

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

118

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

NASA Technical Reports Server (NTRS)

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

Holzhauser, Curt A; Hall, Leo P

1956-01-01

119

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

120

Dynamic and scalar turbulent fluctuation in a diffusion flame ofan-axisymmetric methane jet into air  

Microsoft Academic Search

?A study of turbulence\\/combustion interactions in a relatively large\\u000d\\u000a\\u0009turbulent diffusion flame of an axisymmetric methane jet into air\\u000d\\u000a\\u0009is presented. A first order k–? turbulence closure model is used\\u000d\\u000a\\u0009along with two different models (equal scales and non-equal scales)\\u000d\\u000a\\u0009for the submodel describing the scalar dissipation rate. The flamelet\\u000d\\u000a\\u0009concept is used to model the turbulent combustion along with

A. Hidouri; M. H. Gazzah; H. Ben Tïcha; M. Sassi

2003-01-01

121

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

122

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

123

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

124

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

125

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

126

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

127

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

EPA Science Inventory

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

128

A high-performance cathode for the next generation of solid-oxide fuel cells.  

PubMed

Fuel cells directly and efficiently convert chemical energy to electrical energy. Of the various fuel cell types, solid-oxide fuel cells (SOFCs) combine the benefits of environmentally benign power generation with fuel flexibility. However, the necessity for high operating temperatures (800-1,000 degrees C) has resulted in high costs and materials compatibility challenges. As a consequence, significant effort has been devoted to the development of intermediate-temperature (500-700 degrees C) SOFCs. A key obstacle to reduced-temperature operation of SOFCs is the poor activity of traditional cathode materials for electrochemical reduction of oxygen in this temperature regime. Here we present Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-delta)(BSCF) as a new cathode material for reduced-temperature SOFC operation. BSCF, incorporated into a thin-film doped ceria fuel cell, exhibits high power densities (1,010 mW cm(-2) and 402 mW cm(-2) at 600 degrees C and 500 degrees C, respectively) when operated with humidified hydrogen as the fuel and air as the cathode gas. We further demonstrate that BSCF is ideally suited to 'single-chamber' fuel-cell operation, where anode and cathode reactions take place within the same physical chamber. The high power output of BSCF cathodes results from the high rate of oxygen diffusion through the material. By enabling operation at reduced temperatures, BSCF cathodes may result in widespread practical implementation of SOFCs. PMID:15356627

Shao, Zongping; Haile, Sossina M

2004-09-01

129

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

130

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

131

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

132

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

133

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

134

Experimental investigation of characteristics of a diffusion flame established over liquid ethanol surface under opposed air flow  

SciTech Connect

A preliminary study of the shape and the extinction characteristics of a diffusion flame established over a circular liquid fuel surface under the influence of an opposed air flow, is presented. Renewable liquid fuel such as ethanol is employed. A simple heterogeneous combustion setup, which consists of a cylindrical tube containing ethanol located at the bottom, is exposed to an opposed air flow from a coaxial circular pipe of same size located at the top at a fixed separation distance. Axial and radial extents of flame for different air flow rates are qualitatively analyzed. Burning rates of ethanol for different separation distances and air flow rates are recorded. For a fixed separation distance, at a particular air flow rate the flame extinction takes place. Extinction air flow rates and corresponding strain rates for different separation distances are presented. (author)

Sen, Anirudh; Raghavan, Vasudevan; Shet, U.S.P. [Department of Mechanical Engineering, Indian Institute of Technology Madras, 206A TDCE Lab., Chennai 600036 (India)

2009-03-15

135

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

PubMed

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

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

2005-09-01

136

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

SciTech Connect

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

Im, H.G.; Chen, J.H. [Sandia National Labs., Livermore, CA (United States); Chen, J.Y. [Univ. of California, Berkeley, CA (United States). Dept. of Mechanical Engineering

1998-03-01

137

Development of Electrophoretic Process for Coating T-53 Air Diffuser, Exhaust Diffuser, and Combustion Chamber Housing with 'Sermetel W'.  

National Technical Information Service (NTIS)

The report covers activities accomplished to develop an electrophoretic coating method for the application of 'SERMETEL W' to all critical surfaces of the exhaust diffuser, has been classified as the best coating available for corrosion protection. Its ap...

K. A. Gebler

1967-01-01

138

Effective sulfur and energy recovery from hydrogen sulfide through incorporating an air-cathode fuel cell into chelated-iron process.  

PubMed

The chelated-iron process is among the most promising techniques for the hydrogen sulfide (H2S) removal due to its double advantage of waste minimization and resource recovery. However, this technology has encountered the problem of chelate degradation which made it difficult to ensure reliable and economical operation. This work aims to develop a novel fuel-cell-assisted chelated-iron process which employs an air-cathode fuel cell for the catalyst regeneration. By using such a process, sulfur and electricity were effectively recovered from H2S and the problem of chelate degradation was well controlled. Experiment on a synthetic sulfide solution showed the fuel-cell-assisted chelated-iron process could maintain high sulfur recovery efficiencies generally above 90.0%. The EDTA was preferable to NTA as the chelating agent for electricity generation, given the Coulombic efficiencies (CEs) of 17.8 ± 0.5% to 75.1 ± 0.5% for the EDTA-chelated process versus 9.6 ± 0.8% to 51.1 ± 2.7% for the NTA-chelated process in the pH range of 4.0-10.0. The Fe (III)/S(2-) ratio exhibited notable influence on the electricity generation, with the CEs improved by more than 25% as the Fe (III)/S(2-) molar ratio increased from 2.5:1 to 3.5:1. Application of this novel process in treating a H2S-containing biogas stream achieved 99% of H2S removal efficiency, 78% of sulfur recovery efficiency, and 78.6% of energy recovery efficiency, suggesting the fuel-cell-assisted chelated-iron process was effective to remove the H2S from gas streams with favorable sulfur and energy recovery efficiencies. PMID:24220197

Sun, Min; Song, Wei; Zhai, Lin-Feng; Cui, Yu-Zhi

2013-12-15

139

Microengineered cathode interface studies  

SciTech Connect

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

Kueper, T.; Doshi, R.; Krumpelt, M. [Argonne National Lab., IL (United States). Electrochemical Technology Program

1996-10-01

140

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

E-print Network

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

Majda, Marcin

141

Diffusion  

NSDL National Science Digital Library

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

Christopher Thomas (None;)

2006-11-09

142

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

USGS Publications Warehouse

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

Vroblesky, Don A.; Pravecek, Tasha

2002-01-01

143

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

144

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

145

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

PubMed

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

146

Diffusion  

NSDL National Science Digital Library

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

147

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

PubMed

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

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

2013-07-21

148

Soot formation and temperature field structure in laminar propane-air diffusion flames at elevated pressures  

SciTech Connect

The effect of pressure on soot formation and the structure of the temperature field was studied in coflow propane-air laminar diffusion flames over the pressure range of 0.1 to 0.73 MPa in a high-pressure combustion chamber. The fuel flow rate was selected so that the soot was completely oxidized within the visible flame and the flame was stable at all pressures. Spectral soot emission was used to measure radially resolved soot volume fraction and soot temperature as a function of pressure. Additional soot volume fraction measurements were made at selected heights using line-of-sight light attenuation. Soot concentration values from these two techniques agreed to within 30% and both methods exhibited similar trends in the spatial distribution of soot concentration. Maximum line-of-sight soot concentration along the flame centerline scaled with pressure; the pressure exponent was about 1.4 for pressures between 0.2 and 0.73 MPa. Peak carbon conversion to soot, defined as the percentage of fuel carbon content converted to soot, also followed a power-law dependence on pressure, where the pressure exponent was near to unity for pressures between 0.2 and 0.73 MPa. Soot temperature measurements indicated that the overall temperatures decreased with increasing pressure; however, the temperature gradients increased with increasing pressure. (author)

Bento, Decio S.; Guelder, OEmer L. [Institute for Aerospace Studies, University of Toronto, 4925 Dufferin Street, Toronto, ON M3H 5T6 (Canada); Thomson, Kevin A. [National Research Council, ICPET Combustion Technology, 1200 Montreal Road M-9, Ontario K1A 0R6 (Canada)

2006-06-15

149

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

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

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

2000-01-01

150

Laser-induced fluorescence measurements and modeling of nitric oxide in methane-air and ethane-air counterflow diffusion flames  

SciTech Connect

Quantitative laser-induced fluorescence (LIF) measurements of nitric oxide concentrations[NO] have been obtained along the centerline in atmospheric pressure methane-air and ethane-air counterflow diffusion flames. These flames are highly diluted to avoid both soot formation and the influence of radiative heat losses on NO formation, thereby ensuring NO production mostly via the prompt mechanism. Linear LIF measurements of [NO] are corrected for variations in the electronic quenching rate coefficient by using major species profiles generated by an opposed-flow flame code and quenching cross-sections for NO available from the literature. Temperature measurements are also made in the methane-air counterflow diffusion flames by using thin SiC filament pyrometry. The excellent agreement between temperature measurements and model predictions verifies the efficacy of a new calibration method developed for thin filament pyrometry. Predictions using the GRI mechanism consistently underpredict peak [NO] in all flames. This result indicates a need for refinement of both the prompt-NO and CH kinetics, especially the rate coefficient for the prompt-NO initiation reaction. A modified rate coefficient proposed for the prompt-NO initiation reaction significantly improves agreement between modeling and measurements in both the methane-air and ethane-air counterflow diffusion flames. The remaining discrepancy in some flames can be attributed to a lack of refinement in the CH chemistry. Overall, the modified rate coefficient proposed here seems to be a good choice over a wide range of strain rates for both methane and ethane fuels.

Ravikrishna, R.V.; Laurendeau, N.M.

2000-02-01

151

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

152

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

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

153

The response of a propane-air counter-flow diffusion flame subjected to a transient flow field  

Microsoft Academic Search

OH planar laser-induced fluorescence (PLIF) and particle image velocimetry have been used to study the frequency response of laminar C3H8-air counterflow diffusion flames to assess the adequacy of the steady-flamelet models. Particle image velocimetry was used to determine the flame strain rate, while OH PLIF was used both to measure temperature at the flame front, using the two-line PLIF technique,

Eric J. Welle; William L. Roberts; Campbell D. Carter; Jeffrey M. Donbar

2003-01-01

154

Pore scale 3D modelling of heat and mass transfer in the gas diffusion layer and cathode channel of a PEM fuel cell  

Microsoft Academic Search

Flooding of the gas diffusion layer (GDL) of proton exchange membrane (PEM) fuel cells can be a bottleneck to the system’s efficiency and even durability under certain operating conditions. Due to the small scale and complex geometry of the materials involved, detailed insight into the pore scale phenomena that take place are difficult to measure or simulate. In the present

A. Kopanidis; A. Theodorakakos; M. Gavaises; D. Bouris

2011-01-01

155

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 ...

156

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

157

Using a glass fiber separator in a single-chamber air-cathode microbial fuel cell shortens start-up time and improves anode performance at ambient and mesophilic temperatures.  

PubMed

A shorter start-up time and highly negative anode potentials are needed to improve single-chamber air-cathode microbial fuel cells (MFCs). Using a glass fiber separator reduced the start-up time from 10d to 8d at 20°C, and from 4d to 2d at 30°C, and enhanced coulombic efficiency (CE) from <60% to 89% (20°C) and 87% (30°C). Separators also reduced anode potentials by 20-190mV, charge transfer resistances by 76% (20°C) and 19% (30°C), and increased CV peak currents by 24% (20°C) and 8% (30°C) and the potential range for redox activity (-0.55 to 0.10mV vs. -0.49 to -0.24mV at 20°C). Using a glass fiber separator in an air-cathode MFC, combined with inoculation at a mesophilic temperature, are excellent strategies to shorten start-up time and to enhance anode performance and CE. PMID:23334007

Zhang, Xiaoyuan; Liang, Peng; Shi, Juan; Wei, Jincheng; Huang, Xia

2013-02-01

158

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

159

Initiation of diffusion combustion in a supersonic flow of H2 air mixture by electrical-discharge-excited oxygen molecules  

NASA Astrophysics Data System (ADS)

The methodology of arranging a stable combustion in a diffusion mode in a supersonic non-premixed H2-air flow at a short distance and at a low air temperature due to excitation of O2 molecules to the a 1?g and b\\,^{1}\\!\\Sigma _g^+ states in the electrical discharge is considered. It is shown that for initiation of combustion in this case, it is sufficient to subject the oxygen molecules to an electrical discharge in a thin (with a thickness of 0.5-1 cm) layer located between hydrogen and air streams. It is shown that the mechanism of combustion enhancement is caused by accelerating the chain reactions due to the abundance of excited oxygen molecules in a shear layer and has a non-thermal character. This paper was presented at the Third International Symposium on Nonequilibrium Processes, Combustion, and Atmospheric Phenomena (Dagomys, Sochi, Russia, 25-29 June 2007).

Starik, A. M.; Titova, N. S.; Bezgin, L. V.; Kopchenov, V. I.

2008-06-01

160

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

USGS Publications Warehouse

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

Vroblesky, Don A.; Peters, Brian C.

2000-01-01

161

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

162

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

163

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

E-print Network

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

Han, Rongbin

2012-07-16

164

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...

165

Thermal analysis of air-cooled PEM fuel cells Setareh Shahsavari a  

E-print Network

. In the present study, a 3D numerical thermal model is presented to analyze the heat transfer and predict parts of a PEMFC are comprised of current collectors, anode and cathode flow channels, gas diffusion variations are found between the cool incoming air flow and the hot bipolar plates and MEA, and in contrast

Bahrami, Majid

166

Effects of an air stream on turbulent diffusion of a helium jet from a small nozzle  

Microsoft Academic Search

In a round helium jet with a small nozzle, and a Reynolds number of 2.95 × 103, with and without an air stream, mean profiles, instantaneous fluctuations, and correlations of velocity and matter are investigated using the hot-wire technique. The characteristic difference in the behavior of the jet due to the presence of an air stream is extensively studied and

Yasuhiko Aihara; Hisao Koyama; Etsuo Morishita

1974-01-01

167

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

168

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

169

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 ...

170

Numerical Modeling of Water Mist Suppression of Methane-Air Diffusion Flames  

Microsoft Academic Search

This paper describes a numerical model for studying the suppression of co-flow diffusion flames by fine water mist. A two-continuum formulation is used in which the gas phase and the water mist are both described by equations of the eulerian form. The model is used to obtain a detail understanding of the physical processes involved during the interaction of water

K. PRASAD; C. Ll; K. KAILASANATH; C. NDUBIZU; R. ANANTH; P. A. TATEM

1998-01-01

171

Dropwise condensation from flowing air–steam mixtures: Diffusion resistance assessed by controlled drainage  

Microsoft Academic Search

In this study, the initial phase of drop growth, when diffusion is not limiting, is artificially made more important. An apparatus with controlled removal of condensate droplets from the condenser plates is designed and applied. The dropwise condensation process is frequently interrupted upon which nucleation restarts upon each sweep. Condensate growth and surface temperatures are assessed by simultaneous video and

M. H. M. Grooten

2011-01-01

172

A hybrid, infrared thermography: heat diffusion equation, method for the 3D air-temperature measurement  

Microsoft Academic Search

The question of how to map the 3D indoor temperature by infrared thermography is solved by a hybrid method which is a combination of infrared thermography and the well known heat diffusion equation. The idea is to use infrared thermography to get the surface temperature of each frontier of the 3D domain of interest. A suitable procedure is devoted to

F. B. Djupkep Dizeu; X. Maldague; A. Bendada; E. Grinzato; P. Bison

2011-01-01

173

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

E-print Network

Using data from the HEGRA air shower array, taken in the period from April 1998 to March 2000, upper limits on the ratio I_gamma /I_CR of the diffuse photon flux I_gamma to the hadronic cosmic ray flux I_CR are determined for the energy region 20 TeV to 100 TeV. The analysis uses a gamma-hadron discrimination which is based on differences in the development of photon- and hadron-induced air showers after the shower maximum. A method which is sensitive only to the non-isotropic component of the diffuse photon flux yields an upper limit of I_gamma /I_CR (at 54 TeV) < 2.0*10^-3 (at the 90% confidence level) for a sky region near the inner galaxy (20 degrees < galactic longitude <60 degrees and |galactic latitude|<5 degrees). A method which is sensitive to both the isotropic and the non-isotropic component yields global upper limits of I_gamma /I_CR (at 31 TeV) <1.2*10^-2 and I_gamma /I_CR (at 53 TeV) < 1.4*10^-2 (at the 90% confidence level).

HEGRA Collaboration; F. A. Aharonian

2001-09-10

174

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

175

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

176

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

PubMed

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

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

2014-08-01

177

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

178

Flow-field effects on soot formation in normal and inverse methane–air diffusion flames  

Microsoft Academic Search

We investigate the effects of the flow-field configuration on the sooting characteristics of normal and inverse coflowing diffusion flames. The numerical model solves the time-dependent, compressible, reactive-flow, Navier-Stokes equations, coupled with submodels for soot formation and thermal radiation transfer. A benchmark calculation is conducted and compared with experimental data, and shows that computed peak temperatures and species concentrations differ from

C. R Kaplan; K Kailasanath

2001-01-01

179

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

180

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

NASA Technical Reports Server (NTRS)

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

Darabont, A.; Soiman, S.

1974-01-01

181

Microhollow cathode discharges  

NASA Astrophysics Data System (ADS)

By reducing the dimensions of hollow cathodes into the hundred micrometer range, stable, direct current, high (atmospheric) pressure glow discharges in rare gases, rare gas-halide mixtures and in air could be generated. The electron energy distribution in these microdischarges is non-Maxwellian, with a pronounced high-energy tail. The high electron energy together with the high gas density, which favors three-body collisions, is the reason for an efficient excimer generation in these microplasmas. Excimer efficiencies from 1% to 9% have been measured for argon, xenon, argon fluoride, and xenon chloride direct current excimer emitters, with a radiant excimer emittance of up to 2 W/cm2 for xenon. Adding small amounts of oxygen to argon has allowed us to generate vacuum ultraviolet line radiation at 130.5 nm with an efficiency approaching 1%. Pulsing xenon discharges with nanosecond electrical pulses has led to an increase in intensity to 15 W/cm2 and to a simultaneous increase in efficiency to more than 20%. Operating the discharges in an abnormal glow mode has allowed us to generate microdischarge arrays without individual ballast. Applications of these plasma arrays are excimer lamps and plasma reactors.

Schoenbach, K. H.; Moselhy, M.; Shi, W.; Bentley, R.

2003-07-01

182

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

183

Soft X-ray radiation due to a nanosecond diffuse discharge in atmospheric-pressure air  

Microsoft Academic Search

A source of soft X-rays with an effective photon energy of 9 keV and a subnanosecond pulse width is built around a gas diode filled with atmospheric-pressure air and a UAEB-150 generator. A collector placed behind a grounded mesh electrode detects an electron beam and a pulse with positive polarity, the latter being due to an electric field surrounding the

I. D. Kostyrya; V. F. Tarasenko

2010-01-01

184

Soft X-ray radiation due to a nanosecond diffuse discharge in atmospheric-pressure air  

Microsoft Academic Search

A source of soft X-rays with an effective photon energy of 9 keV and a subnanosecond pulse width is built around a gas diode\\u000a filled with atmospheric-pressure air and a UAEB-150 generator. A collector placed behind a grounded mesh electrode detects\\u000a an electron beam and a pulse with positive polarity, the latter being due to an electric field surrounding the

I. D. Kostyrya; V. F. Tarasenko

2010-01-01

185

Calculation of oxygen diffusion in plutonium oxide films during the high-temperature oxidation of plutonium-1 weight percent gallium in 500 torr of air  

Microsoft Academic Search

Oxygen self-diffusion in PuO\\/sub 1.995\\/ was calculated from rate constants obtained for the parabolic oxidation of the Pu-1 wt % Ga alloy in 500-torr dry air between 250 and 480\\/degree\\/C. The activation energy for oxygen vacancy diffusion in the n-type PuO\\/sub 2-x\\/ is 22.6 kcal\\/mole. Results from this investigation are compared with other reported results, and possible explanation for the

Stakebake

1988-01-01

186

Numerical and experimental study of an axisymmetric coflow laminarmethane\\/air diffusion flame at pressures between 5 and 40 atmospheres  

Microsoft Academic Search

A numerical and experimental study of an axisymmetric coflow laminar\\u000d\\u000a\\u0009methane–air diffusion flame at pressures between 5 and 40 atm was\\u000d\\u000a\\u0009conducted to investigate the effect of pressure on the flame structure\\u000d\\u000a\\u0009and soot formation characteristics. Experimental work was carried\\u000d\\u000a\\u0009out in a new high-pressure combustion chamber described in a recent\\u000d\\u000a\\u0009study [K.A. Thomson, Ö.L. Gülder, E.J. Weckman, R.A. Fraser,

Fengshan Liu; Kevin A. Thomson; Hongsheng Guo; Gregory J. Smallwood

2006-01-01

187

Comparison between experimental measurements and numerical calculations of the structure of heptane-air diffusion flames. (Reannouncement with new availability information)  

SciTech Connect

Detailed numerical calculations are performed to determine the structure of heptane-air diffusion flames. and the results are compared with experimental measurements. The configuration used is the diffusion flame stabilized in the vicinity of a stagnation plane, which is formed by directing an oxidizing gas flow onto the vaporizing surface of a pool of a heptane. Profiles of the concentration of various stable species and of the temperature have been measured by gas chromatography and by thermocouples, respectively. To evaluate the influence of strain on the structure of the flame, the measurements taken at a fixed composition of the oxidizer stream and at two values of the strain rate were chosen for comparison with the calculated results. The computations were performed using a chemical kinetic mechanism consisting of forty-two elementary reactions involving eighteen species. To simplify the chemical kinetic mechanism, it was assumed that heptane is attacked by radicals to form the heptyl radical whose decomposition to CH3, and C3H6 is represented by a one-step overall reaction. Good agreement was obtained between the results of the detailed numerical calculations and the experimental measurements. It was found that aspects of the structure of heptane-air diffusion flames relevant to asymptotic descriptions are similar to those of methane-air diffusion flames. Hence, the previously developed techniques for asymptotic analysis of the structure of methane-air flames can be used for analyzing the structure of heptane-air flames.

Bui-Pham, M.; Seshadri, K.

1991-12-31

188

Diffuse reflectance infrared spectroscopy studies of the air oxidation of coal surfaces  

SciTech Connect

Oxidation of coals is of concern to those interested in the weathering that begins as soon as the mined material is wrested from the humid, reducing, pressurized environment of the underground seam. The loss of energy content comprises an obvious economic impact to combustion processes. Floculation and coking processes are both deleteriously effected whereas systematic information regarding the structure and reaction mechanisms can be obtained. This work is directed primarily to defining the surface structures and mechanisms occurring at the air/coal interface.

Fuller, E.L. Jr.; Smyrl, N.R.

1988-01-01

189

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

190

Cathode Life Test Facility  

NASA Astrophysics Data System (ADS)

The Cathode Life Test Facility (CLTF) has been in operation for ten years and has tested ten different cathode types for a total of approximately 2.0 million hours of life test data. As part of the defense management review (DMR) process, Rome Laboratory (RL) has eliminated internal research efforts pertaining to cathode life testing. Based on this directive, the CLTF was moved to the Naval Surface Warfare Center (NSWC) at Crane, Indiana. This report summarizes the process of moving the CLTF from RL to the NSWC.

Jardieu, Ronald J.

1994-10-01

191

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

192

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

193

Factors affecting the discharge lifetime of lithium-molten nitrate thermal battery cells using soluble cathode materials  

Microsoft Academic Search

The use of soluble cathode materials in molten nitrate electrolyte thermal battery cells presents several problems related to cathode material diffusion into the anolyte. A chemical reduction of the soluble cathode material by molten lithium anodes is observed to degrade cell performance. Factors affecting cell lifetime were found to include discharge rate and temperature, cell thickness, activation into load versus

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

1986-01-01

194

Nanostructured sulfur cathodes.  

PubMed

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

Yang, Yuan; Zheng, Guangyuan; Cui, Yi

2013-04-01

195

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

USGS Publications Warehouse

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

Huffman, Raegan L.

2002-01-01

196

The interaction between soot and NO formation in a laminar axisymmetric coflow ethylene/air diffusion flame  

SciTech Connect

The interaction between soot and NO formation in a laminar axisymmetric coflow ethylene/air diffusion flame was investigated by numerical simulation. A detailed gas-phase reaction scheme and a simplified soot model were employed. The results show that the formation of NO has little effect on that of soot. However, the formation of soot in the flame significantly suppresses the formation of NO. The peak NO concentration and NO emission index are reduced by 28 and 46%, respectively, due to the formation of soot. The influence of soot on NO formation is caused by not only the radiation-induced thermal effect, but also the reaction-induced chemical effect. Relatively the thermal effect is more significant, causing 25 and 38% reduction, respectively, in peak NO concentration and NO emission index. The chemical effect is caused by the competition for acetylene (C{sub 2}H{sub 2}) between soot and NO formation. The formation of soot consumes acetylene in the flame and thus lowers the formation rate of radical CH. This reduces the reaction rate of CH + N{sub 2} = HCN + N, which is the rate-limiting step of the prompt NO formation route, the dominant route in the studied flame. (author)

Guo, Hongsheng; Smallwood, Gregory J. [Institute for Chemical Process and Environmental Technology, National Research Council Canada, 1200 Montreal Road, Ottawa, ON, K1A 0R6 (Canada)

2007-04-15

197

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

198

Calculation of oxygen diffusion in plutonium oxide films during the high-temperature oxidation of plutonium-1 weight percent gallium in 500 torr of air  

SciTech Connect

Oxygen self-diffusion in PuO/sub 1.995/ was calculated from rate constants obtained for the parabolic oxidation of the Pu-1 wt % Ga alloy in 500-torr dry air between 250 and 480/degree/C. The activation energy for oxygen vacancy diffusion in the n-type PuO/sub 2-x/ is 22.6 kcal/mole. Results from this investigation are compared with other reported results, and possible explanation for the difference in results is discussed. 21 refs., 5 figs., 1 tab.

Stakebake, J.L.

1988-05-27

199

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

200

A Study of Nonlocal Ionization Process in the Thermionic Cathode - Glow Discharge Model  

NASA Astrophysics Data System (ADS)

During high intensity discharge (HID) lamp starting, high cathode fall voltage (200-300 V) observed in the cold cathode glow discharge phase, collapses to 30-70 volts as the cathode heated up to thermionic emitting temperature. This low voltage thermionic arc phase can last up to minutes as the plasma transit to steady state arc discharge closed to local thermodynamic equilibrium. The thermionic arc phase plays an important role in the overall HID lamp starting and lumen maintenance. The hot cathode glow discharge model is being re-examined footnote Byszewski W. W., Gregor P. D., Budinger A. B., Li Y. M., "Tungsten radiation measurement during starting of metal halide lamps", J. Ill. Eng. Soc., Vol. 21, p. 85(1992) by including the nonlocal, nonequilibrium ionization process due to the thermionic emitted electrons gaining energy from the cathode fall. The cathode energy balance equation describing the hot cathode and thermionic emission will be set up. Various components of cathode heating power due to discharge ions, electrons, and neutrals will be analysis. The possible role of back diffusion of high energy plasma electron in cathode heating will be studied. Based on the numerical solution of the coupled plasma-cathode system, the current-voltage characteristics are determined and the change in cathode emission charateristics from secondary to thermionic will be explored. The effect of nonlocal ionization of thermionic emitted electrons on current-voltage characteristics of the plasma-cathode system will be presented.

Li, Yan-Ming

1998-10-01

201

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

202

Cathodic protection current testing for large plant structures  

SciTech Connect

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

Maynard, R.J. [Aurora Corrosion Control, Calgary, Alberta (Canada)

1996-07-01

203

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

204

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

USGS Publications Warehouse

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

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

2003-01-01

205

A NOVEL CFD CODE BASED ON METHOD OF LINES FOR REACTING fLOWS: VERIFICATION ON METHANE\\/AIR DIFFUSION FLAME  

Microsoft Academic Search

A novel parallel computational fluid dynamic (CFD) code based on method of lines (MOL) approach was developed for the numerical simulation of multi-component reacting flows using detailed transport and thermodynamic models. The code was applied to the prediction of a confined axi-symmetric laminar co-flowing methane-air diffusion flame for which experimental data were available in the literature. 1-, 5- and 10-step

TANIL TARHAN; NEVIN SELÇUK

2007-01-01

206

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

207

Cathode material for lithium batteries  

SciTech Connect

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

208

Synopsis of Cathode #4 Activation  

Microsoft Academic Search

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

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

2006-01-01

209

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

Microsoft Academic Search

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

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

210

Study of the Discharge Mode in Micro-Hollow Cathode  

NASA Astrophysics Data System (ADS)

In this study, micro-hollow cathode discharge (MHCD) is investigated by a fluid model with drift-diffusion approximation. The MHC device is a cathode/dielectric/anode sandwich structure with one hole of a diameter D=200 ?m. The gas is a Ne/Xe mixture at a pressure p=50~500 Torr. The evolutions of the discharge show that there are two different discharge modes. At larger pD the discharge plasma and high density excited species expand along the cathode surface and, a ringed discharge mode is formed. At smaller pD, the discharge plasma and the excited species expand along the axis of the cathode aperture to form a columnar discharge.

He, Feng; He, Shoujie; Zhao, Xiaofei; Guo, Bingang; Ouyang, Jiting

2012-12-01

211

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

212

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

SciTech Connect

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

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

2013-02-14

213

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

214

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

215

Blowout limit of a jet diffusion flame in a coflowing stream of lean gaseous fuel-air mixtures  

Microsoft Academic Search

The results of a combustor experiment investigating the blowout characteristics of a circular jet diffusion flame in the presence of fuel vapor in a surrounding coflowing stream are reported. For the pilot diffusion flame low velocity a range of jet diameters and discharge velocities were used at ambient initial temperature and pressure. The flammability limit of the premixed system of

G. A. Karim; I. Wierzba; M. Hanna

1984-01-01

216

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

217

Applications of aluminum-air batteries  

Microsoft Academic Search

Advances in aluminum-air batteries are described. These include alloys that show higher efficiencies and therefore lower hydrogen evolution, low-cost air cathodes that can be fabricated in production quantities, and methods for handling the aluminum hydroxide reaction product. Emphasis is placed on the advances in air cathodes. The application of this technology to new products and the implications for electric vehicles

R. P. Hamlen; W. H. Hoge; J. A. Hunter; W. B. O'Callaghan

1991-01-01

218

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

219

UPDATING APPLIED DIFFUSION MODELS  

EPA Science Inventory

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

220

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

SciTech Connect

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

Huang, L.; Zingaro, R.A.; Meyers, E.A. (Texas A and M Univ., College Station, TX (United States). Dept. of Chemistry); Nair, P.K.; Nair, M.T.S. (Univ. Nacional Autonoma de Mexico, Morelos (Mexico). Lab. de Energia Solar)

1994-09-01

221

Nonlinear Thermal Balance and Cathode Spot Formation in Cylindrical Thermionic Cathode  

NASA Astrophysics Data System (ADS)

It is well known that the transfer of discharge current from plasma to the thermionic cathode can occur in diffuse and spot modes. In [1], Benilov has shown that the thermal conduction problem for thermionic cathode heated by nonlinear heat flux derived from the plasma, can exhibit multiple steady state solutions under certain conditions. With simplified formulation, further analytical and numerical studies of diffuse-spot mode transition with discharge current were also made [1]. We decided to study the nonlinear thermal balance in more realistic terms, where the nonlinear heat flux applied to one end of the electrode as well as to the side cylindrical surface. Nonlinear radiative cooling is also added. The two dimensional steady state solutions are determined numerically using nonlinear finite element method. Indeed, under certain parameter range, multiple solutions do exist. Three modes are identified: spot mode with localized high temperature on axis, diffuse mode with monotonic increasing temperature towards the edge, and the third mode peaked on axis with a smaller local maximum at the edge. A general form of the nonlinear heat flux function [2], is assumed in the present computations. This function could be replaced by self-consistent heat flux function based on hot cathode-glow discharge model [3]. [1] M. S. Benilov, "Nonlinear surface heating of a plane sample and modes of current transfer to hot arc cathode", Phys. Rev. E, Vol. 58, p. 6480 (1998) [2] M. S. Benilov, "A Self-Consistent Analytical Model of Arc Spots on Electrodes", IEEE Trans. Plasma Sci., Vol. 22, No. 1, p. 73 (1994) [3] Byszewski W. W., Gregor P. D., Budinger A. B., Li Y. M., "Tungsten radiation measurement during starting of metal halide lamps", J. Ill. Eng. Soc., Vol. 21, p. 85 (1992)

Li, Yan-Ming

1999-10-01

222

Significant performance improvement in terms of reduced cathode flooding in polymer electrolyte fuel cell using a stainless-steel microcoil gas flow field  

NASA Astrophysics Data System (ADS)

Flooding at the cathode is the greatest barrier to increasing the power density of polymer electrolyte fuel cells (PEFCs) and using them at high current densities. Previous studies have shown that flooding is caused by water accumulation in the gas diffusion layer, but only a few researchers have succeeded in overcoming this issue. In the present study, microcoils are used as the gas flow channel as well as the gas diffuser directly on the microporous layer (MPL), without using a conventional carbon-fiber gas diffusion layer (GDL), to enable flood-free performance. The current-voltage curves show flooding-free performance even under low air stoichiometry. However, the high-frequency resistance (HFR) in this case is slightly higher than that in grooved flow channels and GDLs. This is due to the differences in the electron conduction path, and the in-plane electron conductivity in the MPL is the key to enhancing the microcoil fuel cell performance.

Tanaka, Shiro; Shudo, Toshio

2014-02-01

223

Electrochemical properties of ceria-based intermediate temperature solid oxide fuel cell using microwave heat-treated La0.1Sr0.9Co0.8Fe0.2O3-? as a cathode  

NASA Astrophysics Data System (ADS)

The temperature dependence of the chemical diffusion coefficient and the surface exchange coefficient of LSCF1982 is successfully determined from the D.C. conductivity relaxation in the temperature range of 500 ? T/°C ? 700 and an oxygen partial pressure of 0.21 atm. The kinetic values of chemical diffusion coefficient (D˜) and surface exchange coefficient (k) are 1.85 × 10-5 cm2 s-1 and 2.42 × 10-4 cm s-1 at 650 °C, respectively. The electrochemical properties of La0.1Sr0.9Co0.8Fe0.2O3-? (LSCF1982) as a cathode for ceria based IT-SOFC are successfully characterized by I-V performance measurement and electrochemical impedance spectroscopy (EIS) in terms of cathode microstructure effects by using microwave heat treatment. The cell with microwave heat-treated cathode shows the higher performance than conventional heat treated cathode. At 650 °C the open circuit potential (OCP) and maximum power density are respectively 0.753 V and 1.79 W cm-2 under 150 sccm of wet hydrogen and air gas flow conditions, and the ohmic and electrode area specific resistance (ASR) are 0.037 and 0.014 ? cm2, respectively.

Choi, M.-B.; Lee, K.-T.; Yoon, H.-S.; Jeon, S.-Y.; Wachsman, E. D.; Song, S.-J.

2012-12-01

224

Plasma deposition of oxide cathodes  

Microsoft Academic Search

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

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

1999-01-01

225

Revised Upper Limits of the Diffuse Tev Gamma Rays from the Galactic Planes with the Tibet II and III Air Shower Arrays  

E-print Network

The flux upper limits of the diffuse gamma rays, from the inner and outer Galactic planes, are revised by factors of 4.0$\\sim$3.7 for mode energies 3$\\sim$10 TeV, respectively, by using the simulation results of the effective area ratios for gamma-ray induced showers and cosmic-ray induced ones in the Tibet air shower array. In our previous work, (Amenomori et al., ApJ, 580, 887, 2002) the flux upper limits were deduced only from the flux ratio of air showers generated by gamma rays versus cosmic rays. The details of the simulation are given in the paper (Amenomori et al., Advances in Space Research, 37, 1932, 2006). The present result using the same data as in ApJ suggests that the spectral index of source electrons is steeper than 2.2 and 2.1 for the inner and outer Galactic planes, respectively.

Amenomori, M; Bi, X J; Chen, D; Cui, S W; Danzengluobu; Ding, L K; Ding, X H; Feng Cun Feng; Zhaoyang Feng; Feng, Z Y; Gao, X Y; Geng, Q X; Guo, H W; He, H H; He, M; Hibino, K; Hotta, N; Haibing, H; Hu, H B; Huang, J; Huang, Q; Jia, H Y; Kajino, F; Kasahara, K; Katayose, Y; Kato, C; Kawata, K; Labaciren; Le, G M; Li, A F; Li, J Y; Lou, Y Q; Lü, H; Lu, S L; Meng, X R; Mizutani, K; Mu, J; Munakata, K; Nagai, A; Nanjo, H; Nishizawa, M; Ohnishi, M; Ohta, I; Onuma, H; Ouchi, T; Ozawa, S; Ren, J R; Saitô, T; Saito, T Y; Sakata, M; Sako, T K; Sasaki, T; Shibata, M; Shiomi, A; Shirai, T; Sugimoto, H; Takita, M; Tan, Y H; Tateyama, N; Torii, S; Tsuchiya, H; Udo, S; Wang, B; Wang, H; Wang, X; Wang, Y G; Wu, H R; Xue Liang; Yamamoto, Y; Yan, C T; Yang, X C; Yasue, S; Ye, Z H; Yu, G C; Yuan, A F; Yuda, T; Zhang, H M; Zhang, J L; Zhang, N J; Zhang, X Y; Zhang, Y; Yi Zhang Zhaxisangzhu; Zhou, X X; al, et

2006-01-01

226

Revised Upper Limits of the Diffuse Tev Gamma Rays from the Galactic Planes with the Tibet II and III Air Shower Arrays  

E-print Network

The flux upper limits of the diffuse gamma rays, from the inner and outer Galactic planes, are revised by factors of 4.0$\\sim$3.7 for mode energies 3$\\sim$10 TeV, respectively, by using the simulation results of the effective area ratios for gamma-ray induced showers and cosmic-ray induced ones in the Tibet air shower array. In our previous work, (Amenomori et al., ApJ, 580, 887, 2002) the flux upper limits were deduced only from the flux ratio of air showers generated by gamma rays versus cosmic rays. The details of the simulation are given in the paper (Amenomori et al., Advances in Space Research, 37, 1932, 2006). The present result using the same data as in ApJ suggests that the spectral index of source electrons is steeper than 2.2 and 2.1 for the inner and outer Galactic planes, respectively.

The Tibet AS Gamma Collaboration; M. Amenomori

2006-11-10

227

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

SciTech Connect

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

Guo, Hongsheng; Neill, W. Stuart [Institute for Chemical Process and Environmental Technology, National Research Council Canada, 1200 Montreal Road, Ottawa, Ontario, K1A 0R6 (Canada)

2009-02-15

228

Annular diffusion denuder for simultaneous removal of gaseous organic compounds and air oxidants during sampling of carbonaceous aerosols.  

PubMed

A specially designed annular diffusion denuder for simultaneous removal of organic gaseous compounds and atmospheric oxidants in carbonaceous aerosol sampling is presented. Various kinds of denuder coatings were compared with respect to the collection efficiency of both organic gaseous compounds and NO(2) and ozone. The optimum sorbent is a mixture of activated charcoal and sulfite on molecular sieve. To ensure high collection efficiency over long-term field operation, two annular diffusion denuders are combined in series. The first half of the first denuder is filled with Na(2)SO(3) on molecular sieve (23 cm long layer) while the second half of the first denuder and the whole second denuder are filled with activated charcoal (the total length of the charcoal section is 67 cm). At a flow rate of 16.6 L min(-1), the collection efficiency of organic gaseous compounds and atmospheric oxidants in the annular diffusion denuder is better than 95%. Only small losses of aerosol particles (<3.6% in number concentration) were observed in the size range 0.12-2.26 ?m. The annular diffusion denuder is compatible with the collection of aerosols on 47-mm diameter quartz fiber filters at a flow rate of 16.6 L min(-1). The use of this denuder enables one to sample carbonaceous aerosols on filters without positive sampling artefacts from volatile organic compounds and interferences from atmospheric oxidants. The annular diffusion denuder has been applied successfully for the sampling of carbonaceous aerosols during field campaigns of typically 1 month each at urban and forested sites in Europe. PMID:22244138

Mikuška, Pavel; Ve?e?a, Zbyn?k; Bartošíková, Anna; Maenhaut, Willy

2012-02-10

229

On the mechanism of the cathode erosion in negative corona discharge  

NASA Astrophysics Data System (ADS)

Negative corona discharge was investigated in atmospheric pressure air and SF6 in Trichel pulse and glow mode in point-to-plane electrode configuration. As a cathode pointed carbon, copper and aluminum pins with tip size 0.02-1 mm were used. It is found that negative corona causes the erosion of cathode surface in form of nanometer-size craters and fissures. Observed etching may be explained in terms of microexplosive process. This process is initiated by interaction of the cathode surface with the cathode-directed ionization wave. This wave is registered as a Trichel pulse. Local electric field of the head of wave gives rise to the field emission from the cathode surface which initiates microexplosion due to Joule heating. It is assumed that a single Trichel pulse causes the ejection of an erosion fragment from the cathode surface and current on the cathode surface runs through the cross-section of elementary erosion fragment. The value of Trichel pulse action integral which depends on the cathode current density and pulse duration and serves as a criterion of micro-explosion is 10^9 A^2s/cm^4. Hence the conclusion has been made that erosion of the cathode in Trichel pulse mode of negative corona was caused by microexplosive processes. General erosion picture of the cathode surface depends on the discharge dynamics. Correlation between discharge dynamics, erosion picture and Trichel pulse parameters was found.

Petrov, Alexey; Amirov, Ravil; Samoylov, Igor

2009-10-01

230

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

231

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

Microsoft Academic Search

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

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

2011-01-01

232

Sur le coefficient de diffusion dans l'air de l'manation de l'actinium  

E-print Network

sur l'éma- nation du radium et surcelle du thorium. Les premières expériences sur la diffusion de l'émanation du radium un poids moléculaire de 85 environ. Ce nombre représentera en même temps le poids ato-- n1. Dans d'autres expériences, si. il. Makover compara la difl'usion de l'émanation du thorium à celle de l

Boyer, Edmond

233

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

PubMed

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

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

1999-02-01

234

Diffusive sampling of 25 volatile organic compounds in indoor air: Uptake rate determination and application in Flemish homes for the elderly  

NASA Astrophysics Data System (ADS)

Passive sampling of volatile organic compounds (VOCs) in air has received increasing attention in recent years. However, in order to use passive sampling as a reliable sampling technique a compound and sampler specific uptake rate is needed. Therefore, the scope of our study was threefold. First, uptake rates for 25 VOCs were determined under real indoor and outdoor conditions using axial-sampling tube-type samplers filled with Tenax TA, and active (pumped) sampling as a reference technique. Secondly, the mechanisms of passive sampling were investigated by comparing the experimentally determined uptake rates (0.13-0.46 ml min-1) to the ideal uptake rates, calculated based on Fick's first law of diffusion and sampler geometry. Sampling efficiency SE, defined as the ratio between the experimental and ideal uptake rate, was introduced as a correction factor and showed that ideal uptake rates may underestimate VOC concentrations by a factor up to 4. This compound dependent SE is explained in terms of the partitioning coefficient K, i.e. the compound's Tenax TA to air concentration equilibrium ratio. Compounds with a low K-value showed the most pronounced non-ideal sorptive behavior. Third, the experimentally determined uptake rates were used to determine VOC concentrations (between 12 and 311 ?g m-3) in 6 homes for the elderly in Antwerp (Belgium). This study provides unique data for indoor air quality at care centers in Flanders.

Walgraeve, C.; Demeestere, K.; Dewulf, J.; Van Huffel, K.; Van Langenhove, H.

2011-10-01

235

Reaction-Diffusion of Fuel with Air between Planar Solid Oxide Fuel Cells Stacked with Ceramic Felt  

Microsoft Academic Search

Solid oxide fuel cells (SOFC) hold great promise for reducing global air pollution, but the cost and fragility of current stacks is severely limiting the number of potential applications. This paper reports a new system devised to overcome these problems by stacking the zirconia plates together using a porous ceramic felt material. A sub-unit of this stack has been experimentally

R. C. Copcutt; A. C. King; K. Kendall

1996-01-01

236

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

237

Virtual cathode emission of an annular cold cathode  

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

238

Neuroinflammation, hyperphosphorylated tau, diffuse amyloid plaques, and down-regulation of the cellular prion protein in air pollution exposed children and young adults.  

PubMed

Air pollution exposures have been linked to neuroinflammation and neuropathology. Autopsy samples of the frontal cortex from control (n = 8) and pollution-exposed (n = 35) children and young adults were analyzed by RT-PCR (n = 43) and microarray analysis (n = 12) for gene expression changes in oxidative stress, DNA damage signaling, NF?B signaling, inflammation, and neurodegeneration pathways. The effect of apolipoprotein E (APOE) genotype on the presence of protein aggregates associated with Alzheimer's disease (AD) pathology was also explored. Exposed urbanites displayed differential (>2-fold) regulation of 134 genes. Forty percent exhibited tau hyperphosphorylation with pre-tangle material and 51% had amyloid-? (A?) diffuse plaques compared with 0% in controls. APOE4 carriers had greater hyperphosphorylated tau and diffuse A? plaques versus E3 carriers (Q = 7.82, p = 0.005). Upregulated gene network clusters included IL1, NF?B, TNF, IFN, and TLRs. A 15-fold frontal down-regulation of the prion-related protein (PrP(C)) was seen in highly exposed subjects. The down-regulation of the PrP(C) is critical given its important roles for neuroprotection, neurodegeneration, and mood disorder states. Elevation of indices of neuroinflammation and oxidative stress, down-regulation of the PrP(C) and AD-associated pathology are present in young megacity residents. The inducible regulation of gene expression suggests they are evolving different mechanisms in an attempt to cope with the constant state of inflammation and oxidative stress related to their environmental exposures. Together, these data support a role for air pollution in CNS damage and its impact upon the developing brain and the potential etiology of AD and mood disorders. PMID:21955814

Calderón-Garcidueñas, Lilian; Kavanaugh, Michael; Block, Michelle; D'Angiulli, Amedeo; Delgado-Chávez, Ricardo; Torres-Jardón, Ricardo; González-Maciel, Angelica; Reynoso-Robles, Rafael; Osnaya, Norma; Villarreal-Calderon, Rodolfo; Guo, Ruixin; Hua, Zhaowei; Zhu, Hongtu; Perry, George; Diaz, Philippe

2012-01-01

239

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

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

240

Air-cooled, hydrogen-air fuel cell  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

241

Discharge/charge characteristic of Li-air cells using carbon-supported LaMn0.6Fe0.4O3 as an electrocatalyst  

NASA Astrophysics Data System (ADS)

The discharge/charge performance of Li-air cell using the carbon-supported LaMn0.6Fe0.4O3 nanoparticle as a cathode catalyst was investigated in this study. The carbon-supported LaMn0.6Fe0.4O3 nanoparticle was prepared via a reverse homogeneous precipitation method, and fabricated to air electrode. Li-air cell was constructed using air electrode, Li metal foil and 1.0 M LiPF6 in propylene carbonate as a cathode, anode and electrolyte, respectively. As the result, the carbon-supported LaMn0.6Fe0.4O3 nanoparticle exhibited both the oxygen evolution activity and the oxygen reduction activity in the non-aqueous electrolyte. The investigation about the presence and absence of the catalytic layer and the gas diffusion layer revealed that each layer is indispensable for the excellent electrode performance, and that the catalytic layer and the gas diffusion layer has a important role to supply the electrolyte and the oxygen gas, respectively. The investigation about the amount of the catalytic layer and the effect of the oxygen concentration revealed that the oxygen diffusability into the air electrode strongly affects to the discharge capacity of Li-air cells.

Yuasa, Masayoshi; Matsuyoshi, Tsubasa; Kida, Tetsuya; Shimanoe, Kengo

2013-11-01

242

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

243

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

244

Diffusion Geometry Diffusion Geometry  

E-print Network

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

Hirn, Matthew

245

Linear air-fuel sensor development  

SciTech Connect

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

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

1996-12-14

246

Three-dimensional Batteries using a Liquid Cathode  

NASA Astrophysics Data System (ADS)

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

Malati, Peter Moneir

247

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

SciTech Connect

Two formulations of a turbulent combustion model based on the approximated diffusion flame presumed conditional moment (ADF-PCM) approach [J.-B. Michel, O. Colin, D. Veynante, Combust. Flame 152 (2008) 80-99] are presented. The aim is to describe autoignition and combustion in nonpremixed and partially premixed turbulent flames, while accounting for complex chemistry effects at a low computational cost. The starting point is the computation of approximate diffusion flames by solving the flamelet equation for the progress variable only, reading all chemical terms such as reaction rates or mass fractions from an FPI-type look-up table built from autoigniting PSR calculations using complex chemistry. These flamelets are then used to generate a turbulent look-up table where mean values are estimated by integration over presumed probability density functions. Two different versions of ADF-PCM are presented, differing by the probability density functions used to describe the evolution of the stoichiometric scalar dissipation rate: a Dirac function centered on the mean value for the basic ADF-PCM formulation, and a lognormal function for the improved formulation referenced ADF-PCM{chi}. The turbulent look-up table is read in the CFD code in the same manner as for PCM models. The developed models have been implemented into the compressible RANS CFD code IFP-C3D and applied to the simulation of the Cabra et al. experiment of a lifted methane jet flame [R. Cabra, J. Chen, R. Dibble, A. Karpetis, R. Barlow, Combust. Flame 143 (2005) 491-506]. The ADF-PCM{chi} model accurately reproduces the experimental lift-off height, while it is underpredicted by the basic ADF-PCM model. The ADF-PCM{chi} model shows a very satisfactory reproduction of the experimental mean and fluctuating values of major species mass fractions and temperature, while ADF-PCM yields noticeable deviations. Finally, a comparison of the experimental conditional probability densities of the progress variable for a given mixture fraction with model predictions is performed, showing that ADF-PCM{chi} reproduces the experimentally observed bimodal shape and its dependency on the mixture fraction, whereas ADF-PCM cannot retrieve this shape. (author)

Michel, Jean-Baptiste; Colin, Olivier; Angelberger, Christian [IFP, 1 et 4 avenue de Bois Preau, F92852, Rueil-Malmaison Cedex (France); Veynante, Denis [EM2C, CNRS et Ecole Centrale Paris, F92295, Chatenay-Malabry (France)

2009-07-15

248

Two-dimensional center-of-mass diffusion of lipid-tethered poly(2-methyl-2-oxazoline) at the air-water interface studied at the single molecule level.  

PubMed

The two-dimensional (2D) center-of-mass diffusion, D, of end-tethered poly(2-methyl-2-oxazoline) (PMOx) lipopolymer chains was studied in a Langmuir monolayer at the air-water interface using wide-field single molecule fluorescence microscopy. In this case, tethering and stabilization of hydrophilic PMOx chains at the air-water interface is accomplished via end-tethering to lipid molecules forming a hydrophobic anchor. To explore the influence of molecular weight, M n, and surface concentration, c s, on lateral mobility, two different PMOx chain lengths of n = 30 and 50 ( n, number of monomer units) were analyzed over a wide range of c s. Using multiparticle tracking analysis of TRITC-labeled PMOx lipopolymers, we found two regimes of lipopolymer lateral mobility. At low c s, D is independent of surface concentration but increases with decreasing n. Here diffusion properties are well described by the Rouse model. In contrast, at more elevated c s, the data do not follow Rouse scaling but are in good agreement with a free area-area model of diffusion. The current study provides for the first time experimental insight into the 2D center-of-mass diffusion of end-tethered polymers at the air-water interface. The obtained results will be of importance for the understanding of diffusion processes in polymer-tethered phospholipid bilayers mimicking biomembranes at low and high tethering concentrations. PMID:18393536

Lüdtke, Karin; Jordan, Rainer; Furr, Nathan; Garg, Sumit; Forsythe, Kelsey; Naumann, Christoph A

2008-05-20

249

The equivalence of diffusive samplers to reference methods for monitoring O3, benzene and NO2 in ambient air.  

PubMed

A study of the equivalence to the reference methods of the Radiello samplers for ozone (O(3)) and benzene as well as the membrane-closed Palmes tube (MCPT) for nitrogen dioxide (NO(2)) is presented. These samplers benefit from new model equations capable of estimating their uptake rate. For O(3), the aim here was to demonstrate the equivalence for the reference period of 8 h and 120 microg m(-3), the target value of the 3rd European Daughter Directive. For benzene, the demonstration of equivalence to the annual limit value of 5 microg m(-3) of the 2nd European Daughter Directive was examined. In the case of NO(2), the equivalence to the annual limit value of the 1st European Daughter Directive (40 microg m(-3)) was considered. Results show that the radial sampler for O(3) fails to meet the Data Quality Objective (DQO) for continuous monitoring. However, with an expanded uncertainty of less than 30%, the O(3) diffusive sampler fulfils the DQO for indicative measurements. For benzene, the Radiello sampler exposed for 7 days gave satisfying results showing the ability of the sampler to meet the DQO of the reference method. Nevertheless, the field tests should be complemented by measurements for a wider range of benzene concentrations. In the case of NO(2), all the results of the laboratory and field experiments respected the requirements necessary for the demonstration of equivalence. Overall, these findings thus show that the Radiello sampler and the MCPT are equivalent to the reference methods only for assessment of benzene and NO(2), respectively. PMID:18728897

Buzica, Daniela; Gerboles, Michel; Plaisance, Hervé

2008-09-01

250

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

251

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

252

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

253

Short communication Air humidity and water pressure effects on the performance of  

E-print Network

Short communication Air humidity and water pressure effects on the performance of air-saturated air. When the cathode was exposed to higher water pressures by placing the cathode in a horizontal salt precipitation, and therefore control of air humidity and water pressure may need to be considered

254

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

255

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

256

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

257

Characteristics of the cathodic arc discharge with a hot boron cathode  

Microsoft Academic Search

Recently, we have developed a cathodic arc plasma source with a heated boron cathode and successfully applied to the deposition of cubic boron nitride thin films. The cathode surface area under operation exhibits an extended red-hot area and it was therefore tentatively assumed that the arc operates in the distributed mode. However, high-speed photography has revealed that cathode spots exist

P. Richter; Siegfried Peter; Volodymyr B. Filippov; Gert Flemming; M. Kuhn

1999-01-01

258

Cathodic protection for prestressed concrete structures  

Microsoft Academic Search

Recently, corrosion of prestressing steel in concrete has been reported. One of the effective countermeasures to stop corrosion is cathodic protection. Cathodic protection has been applied to reinforced concrete structures so far. However, there are several uncertainties especially associated with applicability to prestressed concrete structures. The authors conducted a series of experiments using cathodic protection system on prestressed concrete structures

K Ishii; H Seki; T Fukute; K Ikawa

1998-01-01

259

Dual-Cathode Electron-Beam Source  

NASA Technical Reports Server (NTRS)

Beam from either cathode electromagnetically aligned with exit port. Electron beam from either of two cathodes deflected by magnetic and electric fields to central axis. Mechanical alignment of beam easy because cathode axes, anode apertures, and electron trajectories coplanar. Applications where uninterrupted service needed: scanning electron microscopes, transmission electron microscopes, electron-beam lithography equipment, Auger instruments, and microfocused x-ray sources.

Bradley, James G.; Conley, Joseph M.; Wittry, David B.

1988-01-01

260

System for storing cathodic protection measurement data  

Microsoft Academic Search

This paper describes a custom cathodic protection (CP) database, and discusses how this combination of data structure and software improves the ability to analyze cathodic protection. This may be a unique solution to the task of managing CP data, and may have value to others. This paper is primarily about the database design, and not about cathodic protection, per se.

Westinghouse Hanford

1996-01-01

261

Novel Cathodes Prepared by Impregnation Procedures  

SciTech Connect

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

Eduardo Paz

2006-09-30

262

Remote control for anode-cathode adjustment  

DOEpatents

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

263

Properties and manufacture of top-layer scandate cathodes  

NASA Astrophysics Data System (ADS)

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

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

1986-08-01

264

Ferroelectric Emission Cathodes for Low-Power Electric Propulsion  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

265

Microhollow Cathode Discharge Excimer Lamps  

NASA Astrophysics Data System (ADS)

character. Reducing the diameter of the cathode hole in a hollow cathode discharge geometry to values on the order of 100 ?m has allowed us to extend the pressure range of stable, direct current hollow cathode gas discharges up to atmospheric pressure. The large concentration of high-energy electrons generated in the cathode fall, in combination with the high neutral gas density favors three-body processes such as excimer formation. Excimer emission in xenon discharges peaking at 172 nm, was observed with efficiencies between 6% and 9% at pressures of several hundred Torr. Typical forward voltages are 200 V at dc currents up to 8 mA. Pulsed operation allowed us to extend the current range to 80 mA with corresponding linear increase in optical power. Spatially resolved measurements showed that the source of the excimer radiation at atmospheric pressure and currents of less than 8 mA is confined to the cathode opening. The radiative emittance at 8 mA and atmospheric pressure is approximately 20 W/cm^2. With reduced pressure and increased current, respectively, the excimer source extends into the area outside the cathode hole. Besides in xenon, excimer emission in argon at a peak wavelength of 128 nm has been recorded. In addition to operating the discharge in rare gases, we have also explored its use as rare gas-halide excimer source. In a gas mixture containing 1% ArF we were able to generate stable dc discharges in flowing gas at pressures ranging from 100 Torr to atmospheric pressure. The spectra of the high-pressure ArF discharges are dominated by excimer radiation peaking at 193 nm. The excimer emission of a single ArF discharge at 700 Torr was measured as 150 mW at an efficiency of 3%. Parallel operation of these discharges by means of a resistive anode, which has recently been demonstrated for argon discharges, offers the possibility to use microhollow cathode discharge arrays as dc-excimer lamps, with estimated power densities exceeding 10 W/cm^2. abstract. note number. be ONLY)

Schoenbach, K. H.

1999-11-01

266

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

SciTech Connect

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

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

1987-06-01

267

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

268

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

269

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

270

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. 3 figs.

Falabella, S.

1995-11-21

271

Numerical Simulation of the Interfacial Oxygen Transport Resistance for a PEMFC Cathode Incorporating Water Droplet Coverage  

E-print Network

diffusion layer interface was numerically investigated in a 3D model. This model solved for the convection of air and the diffusion of oxygen in the air in a single flow field channel. The interfacial oxygen adhered on the flow field and gas diffusion layer interface. The effects of droplet size, flow velocity

Kandlikar, Satish

272

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

273

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

274

Microhollow Cathode Discharge Excimer Lamps  

NASA Astrophysics Data System (ADS)

Reducing the diameter of the cathode hole in hollow cathode discharge geometry to values on the order of 100 ?m has allowed us to extend the pressure range of stable, direct current hollow cathode discharges up to atmospheric pressure. The large concentration of high-energy electrons in the nonthermal discharge, in combination with the high neutral gas density favors three-body processes such as rare gas excimer formation. Excimer emission in argon and xenon discharges peaking at 130 nm and 172 nm, respectively, was observed with an efficiency for xenon excimer emission between 6% and 9% in a pressure range from 250 Torr and 450 Torr. Typical forward voltages are 200 V at dc currents of up to 8 mA. Pulsed operation allowed us to extend the current range in xenon discharges to 80 mA. At pressures in the hundreds of Torr range the source of the excimer radiation extends over an area of several times the cathode opening. With increasing pressure the source is reduced in size and eventually, at pressures exceeding atmospheric becomes confined to the cathode opening. For a specific pressure the radiative power increases linearly with current at constant radiant emittance. For atmospheric pressure discharges in xenon the radiative emittance is approximately 20 W/cm^2. In addition to operating the discharge in rare gases, we have also explored its use as rare gas-halide excimer source. In a gas mixture containing 1 % ArF we were able to generate stable dc discharges in flowing gas at pressures ranging from 100 Torr to atmospheric pressure. The spectra of the high-pressure ArF discharges are dominated by excimer radiation peaking at 193 nm. The excimer emission of an ArF discharge at 700 Torr was measured as 150 mW. With a discharge voltage of 500 V, and a current of 10 mA the efficiency is 3 %. Parallel operation of the micro-discharges by means of a resistive anode offers the possibility to use microhollow cathode discharge arrays as dc-excimer lamps, with estimated power densities exceeding 10 W/cm^2. --This work is funded by the Department of Energy, Advanced Energy Division, and by the National Science Foundation. note

Schoenbach, Karl H.

1999-10-01

275

Study of Discharging Characteristics of Hollow Cathode Surge Protective Gap  

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

276

Effects of the Pt loading side and cathode-biofilm on the performance of a membrane-less and single-chamber microbial fuel cell  

Microsoft Academic Search

In order to analyze the effect of cathode’s Pt loading side on the performance of single-chamber microbial fuel cells (MFCs), power generation of a bamboo charcoal membrane-less air-cathode MFC was examined. The maximum power outputs obtained were 0.144 and 1.16mW, while the maximum voltage outputs were 0.400 and 0.500V (external resistance was 500?), respectively, when the Pt loading side facing

Shaoqiang Yang; Boyang Jia; Hong Liu

2009-01-01

277

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

NASA Astrophysics Data System (ADS)

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

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

1987-03-01

278

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

SciTech Connect

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

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

2012-09-15

279

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

280

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

E-print Network

degradation of substrate sustained by oxygen diffusion through the cathode). Ã? 2006 Elsevier B.V. All rights], ocean sediments [9], animal wastes [10], and anaerobic sewage sludge [11,12]. Electricity generation,22]. 1388-2481/$ - see front matter Ã? 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2006

281

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

282

High contrast cathode ray tube  

NASA Technical Reports Server (NTRS)

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

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

1971-01-01

283

Arc-cathode interaction study  

NASA Technical Reports Server (NTRS)

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

Zhou, X.; Heberlein, J.

1992-01-01

284

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

285

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

USGS Publications Warehouse

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

Cox, S. E.

2002-01-01

286

Cathode diameter and operating parameter effects on hafnium cathode evaporation for oxygen plasma cutting arc  

NASA Astrophysics Data System (ADS)

Evaporation of hafnium cathode in a plasma cutting arc torch was investigated numerically and experimentally to assess the effects of cathode diameter and operating parameters such as gas pressure, gas flow rate and arc current. A numerical model was developed for arc plasma with consideration of hafnium cathode evaporation. Using this model, the surface cathode temperature and the amount of cathode mass loss caused by evaporation were predicted for different operating parameters. Simulated results show that the cathode surface temperature decreases at the hafnium cathode centre with increasing gas flow rate and cathode diameter. However, an increase in gas pressure elevates the surface cathode temperature in the radial range of 0.35 mm. The total amount of mass loss of hafnium cathode evaporation was predicted to be enhanced with increasing gas flow rate, gas pressure and cathode diameter as well. Comparison of the calculated results with experimentally obtained results shows good agreement in terms of the average surface cathode temperature, with variation in gas pressure and cathode diameter.

Phi Long, Nguyen; Katada, Yusuke; Tanaka, Yasunori; Uesugi, Yoshihiko; Yamaguchi, Yoshihiro

2012-10-01

287

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.

288

Novel Composite Materials for SOFC Cathode-Interconnect Contact  

SciTech Connect

This report summarized the research efforts and major conclusions of our University Coal Research Project, which focused on developing a new class of electrically-conductive, Cr-blocking, damage-tolerant Ag-perovksite composite materials for the cathode-interconnect contact of intermediate-temperature solid oxide fuel cell (SOFC) stacks. The Ag evaporation rate increased linearly with air flow rate initially and became constant for the air flow rate {ge} {approx} 1.0 cm {center_dot} s{sup -1}. An activation energy of 280 KJ.mol{sup -1} was obtained for Ag evaporation in both air and Ar+5%H{sub 2}+3%H{sub 2}O. The exposure environment had no measurable influence on the Ag evaporation rate as well as its dependence on the gas flow rate, while different surface morphological features were developed after thermal exposure in the oxidizing and reducing environments. Pure Ag is too volatile at the SOFC operating temperature and its evaporation rate needs to be reduced to facilitate its application as the cathode-interconnect contact. Based on extensive evaporation testing, it was found that none of the alloying additions reduced the evaporation rate of Ag over the long-term exposure, except the noble metals Au, Pt, and Pd; however, these noble elements are too expensive to justify their practical use in contact materials. Furthermore, the addition of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LSM) into Ag to form a composite material also did not significantly modify the Ag evaporation rate. The Ag-perovskite composites with the perovskite being either (La{sub 0.6}Sr{sub 0.4})(Co{sub 0.8}Fe{sub 0.2})O{sub 3} (LSCF) or LSM were systematically evaluated as the contact material between the ferritic interconnect alloy Crofer 22 APU and the LSM cathode. The area specific resistances (ASRs) of the test specimens were shown to be highly dependent on the volume percentage and the type of the perovskite present in the composite contact material as well as the amount of thermal cycling that the specimens were subjected to during testing. The Ag-LSCF composite contact materials proved more effective in trapping Cr within the contact material and preventing Cr migration into the cathode than the Ag-LSM composites. Ag-perovskite composite contact materials are promising candidates for use in intermediate-temperature SOFC stacks with ferritic stainless steel interconnects due to their ability to maintain acceptably low ASRs while reducing Cr migration into the cathode material.

J. H. Zhu

2009-07-31

289

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

290

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

291

Interrelationship between marine biofouling and cathodic protection  

SciTech Connect

Microorganisms colonize and form a gelatinous biofilm on all engineering materials exposed in natural marine environments, including cathodically protected surfaces. The impact of cathodic protection (CP) potentials on the chemical/biological composition of the biofilm and the impact of the biofilms on potentials required for CP have been the subject of many recent investigations. Literature on these subjects will be reviewed with emphasis on clarifying interactions between living and nonliving deposits on cathodically protected metal surfaces.

Little, B.J.; Wagner, P.A. (Naval Research Lab., Stennis Space Center, MS (United States))

1993-09-01

292

Plasma deposition of oxide-coated cathodes  

Microsoft Academic Search

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

Ryan Jonathan Umstattd

1998-01-01

293

A analysis of the cathode coupled amplifier  

E-print Network

AN ANALySIS 0 TH CATHODE COOFL D ~iPLIPIER A Thesis by FORREST JACKS RETLING-. . R Approved as to style and content by: Chairman of Committee 'Head of Department August, 1951 AN ANALYSIS OF THE CATHODE COUPLED. AMPLIFIER by FORHEST JAMES.... The Cathode-Coupled Amplif 1er Circuit 2. The Cathode-Coupled Amplif ier Circuit shnwing a. c. components only 3. The Approximate A. C. Fquivalent, Circuit Page 17 4 ~ Aoproximate Equivalent C1rcu its f' or Calculating Output Impedances 22 5...

Hetlinger, Forrest James

2012-06-07

294

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

295

Emission properties of explosive field emission cathodes  

SciTech Connect

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

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

2011-10-15

296

Layered Manganese Oxides as Cathodes  

Microsoft Academic Search

The first commercial lithium-ion batteries used LiCo02 as the cathode active material, and this material continues to be used in most lithium-ion batteries manufactured despite\\u000a the high cost and safety hazards associated with cobalt. Apart from LiCo02, only the isostructural nickelate LiNi02, and more particularly the Co-substituted nickelate LiCo\\u000a x\\u000a Ni1?x\\u000a 02, have been considered to have sufficient energy density

B. Ammundsen

297

Ti- and Zr-based metal-air batteries  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

298

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

299

Plasma deposition of oxide-coated 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/cm 2 regime. Cathode lifetime and emission may be varied via the control over the deposition parameters such as coating thickness, implantation energy, and plasma stoichiometry. The deposition is performed by generating a cathodic arc discharge at the surface of a barium or barium- strontium alloy rod. The metal plasma thus created is then deposited on the substrate which can be negatively biased to encourage implantation during the deposition process. The deposition is performed with sufficient background oxygen present to oxidize the highly reactive metal coating. The plasma deposition is monitored via a rate thickness monitor, an optical emission spectrometer for plasma composition information, and an electrostatic Langmuir probe for the determination of the plasma density and temperature profile. Cathodes thus produced are analyzed by drawing pulsed current at a constant voltage for various values of decreasing cathode temperature in order to generate practical work function distributions which provide an indication of the quality and expected life time of the cathode.

Umstattd, Ryan Jonathan

300

Fuel Cell Electocatalysts: Anodes and Cathodes  

NASA Astrophysics Data System (ADS)

The current state-of-the-art catalyst for both the oxygen and hydrogen electrodes in a polymer electrolyte membrane (PEM) fuel cell is based on Pt. When using pure hydrogen as the fuel, essentially the same Pt catalyst is used at both electrodes, although in different amounts. Neither the hydrogen oxidation nor the oxygen reduction reaction exhibit a significant variation in kinetics with Pt(hkl) crystal face in perfluorosulfonic acid electrolytes, i.e. the reactions are structure insensitive. An electronic effect does, however, adversely influence electrode kinetics for Pt particles smaller than 2 nm. Thus, a catalyst consisting of 2-3 nm Pt particles uniformly dispersed on a high area carbon support is currently the optimum catalyst for hydrogen-air PEM fuel cells. When the fuel is impure hydrogen, containing finite (> 1 ppm) amounts of CO, then the anode must use a different catalyst, one that will not be poisoned by the CO. These catalysts are still under development. The most promising are alloys of Pt with more oxophilic metals like Ru and Mo. These catalysts function by electrochemically oxidizing CO at the same rate as the adsorption rate, thus preventing poisoning of the surface by adsorbed CO. Prospects for non-Pt cathode catalysts will be discussed.

Ross, Philip

2000-03-01

301

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

302

Electrical performance of low cost cathodes prepared by plasma sputtering deposition in microbial fuel cells.  

PubMed

Microbial fuel cells (MFCs) could potentially be utilized for a variety of applications in the future from biosensors to wastewater treatment. However, the amount of costly platinum (Pt) used as a catalyst should be minimized via innovative deposition methods such as sputtering. In addition, alternative and low-cost catalysts, such as cobalt (Co), should be sought. In this study, ultra low Pt or Co cathodes (0.1 mg cm(-2)) were manufactured by plasma sputtering deposition and scanning electron micrographs revealed nano-clusters of metal catalyst in a porous structure favorable to the three-phase heterogeneous catalytic reaction. When operated in single-chamber air-cathode MFCs, sputtered-Co cathodes generated on average the same power as sputtered-Pt cathodes (0.27 mW cell(-1)) and only 27% less than conventional Pt-ink cathodes with a catalyst load 5 times higher (0.5 mg cm(-2)). Finally, microscopy and molecular analyses showed evidence of biocatalysis activity on metal-free cathodes. PMID:22061267

Lefebvre, Olivier; Tang, Zhe; Fung, Martin P H; Chua, Daniel H C; Chang, In Seop; Ng, How Y

2012-01-15

303

Stable homogeneous microdischarge at atmospheric pressure between a flat cathode and point anode  

NASA Astrophysics Data System (ADS)

Conditions of stable operation of a homogeneous glow microdischarge in air at atmospheric pressure between a flat cathode and point anode are established and realized at interelectrode gap widths within ˜1-30 ?m and discharge currents within from ˜10-4 to 1 A.

Astaf'ev, A. M.; Kudryavtsev, A. A.

2014-09-01

304

Physical implications of an effective activation energy for arc erosion on oxidised cathodes  

Microsoft Academic Search

An effective energy of activation for arc erosion has been deduced from mass loss rates observed on oxidised copper cathode surfaces exposed to arcs of long duration rotating in atmospheric pressure air. An analysis of rate processes expected to be associated with the observed low value for the effective activation energy excludes the involvement of ion migration or the filamentation

A. E. Guile; A. H. Hitchcock; K. Dimoff; A. K. Vijh

1982-01-01

305

Enhanced Activated Carbon Cathode Performance for Microbial Fuel Cell by Blending Carbon Black  

E-print Network

is very expensive and a precious metal, and its catalytic performance can significantly decrease over time) is a useful and environmentally sustainable catalyst for oxygen reduction in air-cathode microbial fuel cells months of operation compared to a 61% decrease for the control (Pt catalyst, 570 ± 30 mW/m2 after 5

306

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

307

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

308

Multi-cathode unbalanced magnetron sputtering systems  

NASA Technical Reports Server (NTRS)

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

Sproul, William D.

1991-01-01

309

Preliminary Results of Field Emission Cathode Tests  

NASA Technical Reports Server (NTRS)

Preliminary screening tests of field emission cathodes such as chemical vapor deposited (CVD) diamond, textured pyrolytic graphite, and textured copper were conducted at background pressures typical of electric thruster test facilities to assess cathode performance and stability. Very low power electric thrusters which provide tens to hundreds micronewtons of thrust may need field emission neutralizers that have a capability of tens to hundreds of microamperes. From current voltage characteristics, it was found that the CVD diamond and textured metals cathodes clearly satisfied the Fowler-Nordheim emission relation. The CVD diamond and a textured copper cathode had average current densities of 270 and 380 mA/sq cm, respectively, at the beginning-of-life. After a few hours of operation the cathode emission currents degraded by 40 to 75% at background pressures in the 10(exp -5) Pa to 10(exp -4) Pa range. The textured pyrolytic graphite had a modest current density at beginning-of-life of 84 mA/sq cm, but this cathode was the most stable of all. Extended testing of the most promising cathodes is warranted to determine if current degradation is a burn-in effect or whether it is a long-term degradation process. Preliminary experiments with ferroelectric emission cathodes, which are ceramics with spontaneous electric polarization, were conducted. Peak current densities of 30 to 120 mA/sq cm were obtained for pulse durations of about 500 ns in the 10(exp -4) Pa pressure range.

Sovey, James S.; Kovaleski, Scott D.

2001-01-01

310

Effective cathodic protection saves energy, saves money  

Microsoft Academic Search

Ford, Bacon and Davis Construction Corp. reports that cathodic protection of underground lines reduces (1) capital expenditures by delaying replacements, (2) annual cost of capital investments by designing for optimum economic life, (3) maintenance, and (4) gas losses. Properly applied and maintained, cathodic protection will produce annual savings for a company far in excess of the annual cost of the

Minter

1976-01-01

311

Combustor air flow control method for fuel cell apparatus  

Microsoft Academic Search

A method for controlling the heat output of a combustor in a fuel cell apparatus to a fuel processor where the combustor has dual air inlet streams including atmospheric air and fuel cell cathode effluent containing oxygen depleted air. In all operating modes, an enthalpy balance is provided by regulating the quantity of the air flow stream to the combustor

Bruce J. Clingerman; Kenneth D. Mowery; Eugene V. Ripley

2001-01-01

312

Fabrication and characteristics of a composite cathode of sulfonated polyaniline and Ramsdellite-MnO 2 for a new rechargeable lithium polymer battery  

NASA Astrophysics Data System (ADS)

The ionic conductivity of a polyacrylonitrile (PAN)-based solid polymer electrolyte is 1.4×10 -3 S cm -1, which is sufficient for the electrolyte to be used in a rechargeable lithium polymer battery. The anodic stability of the solid polymer electrolyte is over 4.6 V (vs. Li/Li +). A reduced, highly sulfonated form of polyaniline (SPAn) and Ramsdellite-MnO 2 (R-MnO 2) are synthesized and used as a cathodic material for a rechargeable lithium polymer battery. Three kinds of cathodes are prepared from SPAn, R-MnO 2, and a mixture of SPAn and R-MnO 2. The electrochemical properties and diffusion coefficient of lithium ions in each cathode, and the interface between the solid polymer electrolyte and each cathode are investigated by cyclic voltammetry and impedance spectroscopy. The redox processes of the SPAn cathode are two-step reactions. The cathodic and anodic peak currents increase as the cycle number increases. In the redox processes of the R-MnO 2 cathode, the cathodic peak current on the second cycle is 62% of that on the first cycle. The Li/R-MnO 2 battery has a very high initial discharge capacity, but very poor cycleability. For the composite cathode, the cathodic peak current on the second cycle is 72% of that on the first cycle, i.e., higher than that for the R-MnO 2 cathode. The diffusion coefficient of the composite cathode during the discharge process is close to the sum of each variation in the SPAn and R-MnO 2 cathodes. The instability of the R-MnO 2 cathode at x=0.3 and x=0.2 during the charge process is not observed with the composite cathode. The discharge-charge performance of three types of battery are investigated. The initial discharge capacity of the Li/composite cathode battery is 97.0 m Ah g -1. This battery has higher discharge capacity than the Li/SPAn battery (66.8 m Ah g -1), and better cycleability than the Li/R-MnO 2 battery.

Hwang, K. S.; Lee, C. W.; Yoon, T. H.; Son, Y. S.

313

Cathode for an electrochemical cell  

DOEpatents

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

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

2001-01-01

314

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

315

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...

316

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...

317

K2CsSb Cathode Development  

SciTech Connect

K{sub 2}CsSb is an attractive photocathode for high current applications. With a quantum efficiency of >4% at 532nm and >10% at 355nm, it is the only cathode to have demonstrated an average current of 35mA in an accelerator environment We describe ongoing cathode development work. for the energy recovery linac being constructed at BNL Several cathodes have been created on both copper and stainless steel substrates, and their spatial uniformity and spectral response have been characterized. Preliminary lifetime measurements have been performed at high average current densities (>1 mA/mm{sup 2}).

Smedley,J.; Rao, T.; Wang, E.

2008-10-01

318

95 GHz gyrotron with ferroelectric cathode.  

PubMed

Ferroelectric cathodes were reported as a feasible electron source for microwave tubes. However, due to the surface plasma emission characterizing this cathode, operation of millimeter wave tubes based on it remains questionable. Nevertheless, the interest in compact high power sources of millimeter waves and specifically 95 GHz is continually growing. In this experiment, a ferroelectric cathode is used as an electron source for a gyrotron with the output frequency extended up to 95 GHz. Power above a 5 kW peak and ~0.5 ?s pulses are reported; a duty cycle of 10% is estimated to be achievable. PMID:23215293

Einat, M; Pilossof, M; Ben-Moshe, R; Hirshbein, H; Borodin, D

2012-11-01

319

Unsteady Flamelet Modeling of Differential Diffusion in Turbulent Jet Diffusion Flames  

E-print Network

Unsteady Flamelet Modeling of Differential Diffusion in Turbulent Jet Diffusion Flames HEINZ PITSCH, turbulent CH4/H2/N2­air diffusion flame. The results have been shown to be in reasonable agreement of the flow field these differential diffusion effects remain to a certain extent, even in the far downstream

Pitsch, Heinz

320

The dependence of vircator oscillation mode on cathode material  

Microsoft Academic Search

This paper presents the effects of cathode materials on the oscillation mode of a virtual cathode oscillator (vircator). In the case of the stainless steel cathode, an oscillation mode hopping appeared with two separate frequencies. Interestingly, the vircator using the carbon fiber cathode exhibited an almost unchanged microwave frequency throughout the microwave pulse. To understand this phenomenon, several parameters are

Limin Li; Lie Liu; Guoxin Cheng; Qifu Xu; Hong Wan; Lei Chang; Jianchun Wen

2009-01-01

321

Migration and escape of barium atoms in a thermionic cathode  

Microsoft Academic Search

A quantitative study of the physical processes on a thermionic cathode that are crucial to both cathode life and noise are investigated. Of particular interest are the transport of the barium atoms from the cathode interior to the cathode surface and beyond. To investigate these physical processes, a model of barium migration to the surface and its subsequent removal by

Kevin L. Jensen; Y. Y. Lau; B. Levush

2000-01-01

322

Miniature thermionic cathode assembly for high frequency linear beam devices  

Microsoft Academic Search

This paper describes a small cathode structure for a 95 GHz TWT. The prototype utilized barium oxide-coated nickel, .002 inch thick and .008 inch wide. But the technique is applicable to small tungsten impregnated cathodes, also. The cathodes were suspended via tensioned tungsten wires anchored to the back of the focus electrode. The cathode is heated by an electron beam

Bernard Vancil; James Dayton; Carol Kory; Ken Hawken

2009-01-01

323

Evaporation of thorium from carburized thoriated tungsten cathodes  

Microsoft Academic Search

The evaporation of thorium from carburized thoriated tungsten cathodes is shown experimentally to be approximately the same as that from similar uncarburized cathodes at the same temperature. The thorium in a carburized cathode is, however, produced continuously at an adequate rate at the operating temperature of 2000° K by reduction of the thoria by the tungsten carbide. The uncarburized cathode

R O Jenkins; W G Trodden

1959-01-01

324

Coated porous carbon cathodes for lithium ion batteries  

SciTech Connect

Coated porous carbon cathodes for automotive lithium batteries are being developed with the goal of overcoming the problems with capacity fade and poor thermal management in conventional polymer-bonded cathodes. The active cathode material (lithium iron phosphate nanoparticles) is carbon-bonded to the porous carbon support material. Cathodes have been developed with high specific energy and power and with good cycling behavior.

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

2008-01-01

325

Weld technology reliability analysis of cathode in vacuum tube  

Microsoft Academic Search

Influence of weld technology on reliability and life to cathode in vacuum tube was studied by requests of microwave tube. The quality of weld technology quite affects the emission capability of cathode. The mode of weld quite affects thermal efficiency of cathode in vacuum tube. Thermal efficiency of cathode can increase availably by changing the weld technology on the heat

Fang Fang Song; Xian-long Feng; Sha Jin Li; Shiji Yu

2011-01-01

326

Cathode flooding behaviour in alkaline direct ethanol fuel cells  

Microsoft Academic Search

In an alkaline fuel cell, such as a direct ethanol fuel cell (DEFC), owing to the fact that water is consumed as a reactant at the cathode and the electro-osmotic drag (EOD) moves water from the cathode to the anode, a conventional conception is that the cathode flooding is unlikely. In this work, however, it is shown experimentally that cathode

Y. S. Li; T. S. Zhao; R. Chen

2011-01-01

327

Multipoint explosive emission cathode operation in external magnetic field  

Microsoft Academic Search

For investigation of a multipoint explosive emission cathode operation in an external magnetic field an experimental electron source with a grounded cathode was developed. It allows to carry out measurements of currents through the cathode points and probe measurements of the cathode plasma parameters. The following main results were obtained. An increase of the magnetic field leads to an increase

A. D. Andreev; V. I. Engelko; G. Mueller

2001-01-01

328

The physics of non-thermionic cathodes of electric arcs  

Microsoft Academic Search

It is proposed that the process of electron emission from non-thermionic cathodes of electric arcs in inert gases is by the impact at the cathode of excited neutral states, both metastable and radiative. Electron production at the cathode by other processes such as by ionization in the cathode sheath, field emission, impact by positive ions or photoelectric emission appear to

J. J. Lowke; M. Tanaka

2008-01-01

329

Simulation of the hot core mode of arc attachment at a thoriated tungsten cathode by an emitter spot model  

NASA Astrophysics Data System (ADS)

Recently, a constricted attachment of an atmospheric pressure low-current argon arc in the centre of the flat end face of a thoriated tungsten cathode was observed and spectroscopically analysed. Its diameter of 0.6 mm and its length of the free standing part of 10 mm are the typical dimensions of electrodes for high-intensity discharge lamps. This paper gives a physical interpretation of the axially symmetric arc spot by a simulation of its properties with a cathodic sheath model which takes into account a reduction in the work function above a critical temperature of the cathode surface by a thorium ion current. At first the optical observation and spectroscopic investigations are recapitulated. Then, an overview is given on the essential elements which are needed to simulate the cathodic arc attachment on a hot electrode. A simulation of a central cathode spot with these elements gives results which are far away from the experimental findings if a constant work function φ is used. Therefore, a temperature-dependent work function φ(T) is introduced. This φ(T) transitions from 4.55 to 3 eV above temperatures of the order of 3000 K. With this emitter spot model a constricted arc attachment is obtained by simulation in the centre of the flat end face of the cathode in accordance with experiment. For currents below iarc,max ≈ 15.5 A, two spot solutions with different cathode falls are found. They form a current–voltage–characteristic consisting of two branches which extend from a turning point at iarc,max to lower currents. For iarc > iarc,max, only a diffuse mode of cathodic arc attachment is obtained. It is shown by a comparison with measured data for iarc = 7.5, 10, 12.5 and 15 A that the solution with the lower cathode fall is observed experimentally.

Bergner, A.; Scharf, F. H.; Kühn, G.; Ruhrmann, C.; Hoebing, T.; Awakowicz, P.; Mentel, J.

2014-10-01

330

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

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

331

Transient thermal response of the cathode surface of a potted heater-cathode structure  

Microsoft Academic Search

This brief presents the experimental transient thermal profiles of the cathode surface of a practical potted heater cathode structure (standard 250 Spectra-Mat heater-cathode packaging). Temperature-time history has been obtained experimentally for various input heater power levels. The experimental results have been compared with the theoretical predictions earlier reported, and it has been found that in all the cases, the theoretical

A. Sil; D. S. Venkateswarlu; A. Chatterjee; M. M. Shukla; A. J. Rani

1994-01-01

332

Advanced Measurement and Modeling Techniques for Improved SOFC Cathodes  

SciTech Connect

The goal of this project was to develop an improved understanding of factors governing performance and degradation of mixed-conducting SOFC cathodes. Two new diagnostic tools were developed to help achieve this goal: (1) microelectrode half-cells for improved isolation of cathode impedance on thin electrolytes, and (2) nonlinear electrochemical impedance spectroscopy (NLEIS), a variant of traditional impedance that allows workers to probe nonlinear rates as a function of frequency. After reporting on the development and efficacy of these tools, this document reports on the use of these and other tools to better understand performance and degradation of cathodes based on the mixed conductor La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (LSC) on gadolinia or samaria-doped ceria (GDC or SDC). We describe the use of NLEIS to measure O{sub 2} exchange on thin-film LSC electrodes, and show that O{sub 2} exchange is most likely governed by dissociative adsorption. We also describe parametric studies of porous LSC electrodes using impedance and NLEIS. Our results suggest that O{sub 2} exchange and ion transport co-limit performance under most relevant conditions, but it is O{sub 2} exchange that is most sensitive to processing, and subject to the greatest degradation and sample-to-sample variation. We recommend further work that focuses on electrodes of well-defined or characterized geometry, and probes the details of surface structure, composition, and impurities. Parallel work on primarily electronic conductors (LSM) would also be of benefit to developers, and to improved understanding of surface vs. bulk diffusion.

Stuart Adler; L. Dunyushkina; S. Huff; Y. Lu; J. Wilson

2006-12-31

333

A stable cathode for the aprotic Li-O2 battery  

NASA Astrophysics Data System (ADS)

Rechargeable lithium-air (O2) batteries are receiving intense interest because their high theoretical specific energy exceeds that of lithium-ion batteries. If the Li-O2 battery is ever to succeed, highly reversible formation/decomposition of Li2O2 must take place at the cathode on cycling. However, carbon, used ubiquitously as the basis of the cathode, decomposes during Li2O2 oxidation on charge and actively promotes electrolyte decomposition on cycling. Replacing carbon with a nanoporous gold cathode, when in contact with a dimethyl sulphoxide-based electrolyte, does seem to demonstrate better stability. However, nanoporous gold is not a suitable cathode; its high mass destroys the key advantage of Li-O2 over Li ion (specific energy), it is too expensive and too difficult to fabricate. Identifying a suitable cathode material for the Li-O2 cell is one of the greatest challenges at present. Here we show that a TiC-based cathode reduces greatly side reactions (arising from the electrolyte and electrode degradation) compared with carbon and exhibits better reversible formation/decomposition of Li2O2 even than nanoporous gold (>98% capacity retention after 100 cycles, compared with 95% for nanoporous gold); it is also four times lighter, of lower cost and easier to fabricate. The stability may originate from the presence of TiO2 (along with some TiOC) on the surface of TiC. In contrast to carbon or nanoporous gold, TiC seems to represent a more viable, stable, cathode for aprotic Li-O2 cells.

Ottakam Thotiyl, Muhammed M.; Freunberger, Stefan A.; Peng, Zhangquan; Chen, Yuhui; Liu, Zheng; Bruce, Peter G.

2013-11-01

334

A stable cathode for the aprotic Li-O2 battery.  

PubMed

Rechargeable lithium-air (O2) batteries are receiving intense interest because their high theoretical specific energy exceeds that of lithium-ion batteries. If the Li-O2 battery is ever to succeed, highly reversible formation/decomposition of Li2O2 must take place at the cathode on cycling. However, carbon, used ubiquitously as the basis of the cathode, decomposes during Li2O2 oxidation on charge and actively promotes electrolyte decomposition on cycling. Replacing carbon with a nanoporous gold cathode, when in contact with a dimethyl sulphoxide-based electrolyte, does seem to demonstrate better stability. However, nanoporous gold is not a suitable cathode; its high mass destroys the key advantage of Li-O2 over Li ion (specific energy), it is too expensive and too difficult to fabricate. Identifying a suitable cathode material for the Li-O2 cell is one of the greatest challenges at present. Here we show that a TiC-based cathode reduces greatly side reactions (arising from the electrolyte and electrode degradation) compared with carbon and exhibits better reversible formation/decomposition of Li2O2 even than nanoporous gold (>98% capacity retention after 100 cycles, compared with 95% for nanoporous gold); it is also four times lighter, of lower cost and easier to fabricate. The stability may originate from the presence of TiO2 (along with some TiOC) on the surface of TiC. In contrast to carbon or nanoporous gold, TiC seems to represent a more viable, stable, cathode for aprotic Li-O2 cells. PMID:23995325

Ottakam Thotiyl, Muhammed M; Freunberger, Stefan A; Peng, Zhangquan; Chen, Yuhui; Liu, Zheng; Bruce, Peter G

2013-11-01

335

Rapidly-refuelable 167-CM(2) aluminum-air power cell  

NASA Astrophysics Data System (ADS)

The rapidly-refuelable, 167-cm(2) aluminum-air power was tested both as a single cell and as a two cell stack. The electrolyte and is designed for rapid replacement of the anode and easy construction. A maximum power density of 4.2 kW/m(2) was measured. Cathode polarization is negligibly affected by air flow rate and air electrolyte differential pressure across the air cathode.

Homsy, R. V.

1981-11-01

336

Ion energy measurements near a dormant cathode in a multiple-cathode gridded ion thruster  

SciTech Connect

A rectangular ion thruster discharge chamber was investigated for operation with multiple discharge cathode assemblies (DCAs). The multiple cathode approach attempts to increase thruster throughput and lifetime by operating three DCAs sequentially, possibly providing a threefold increase in discharge life. Previous multiple-cathode electric propulsion devices, such as the SPT-100, have shown dormant cathode erosion to be a life-limiting phenomenon. Similar results in a multiple-cathode discharge chamber may decrease the anticipated gain in discharge lifetime. In order to assess possible dormant cathode sputtering erosion, a diagnostic canister (DC) was designed and utilized to measure bombarding ion energy at the dormant cathode locations. The DC appeared similar to the active DCA, but was outfitted with a retarding potential analyzer. Most probable ion energy measurements show ions with energy of 27-35 eV ({+-}10%) with respect to cathode common and ion energy increases with increasing magnetic field strength. These results are consistent with an ion falling from the plasma potential to cathode common. A simple sputtering erosion model shows that, if doubly charged ions are present, these energies are enough to cause sputtering erosion of the dormant units.

Rovey, Joshua L.; Gallimore, Alec D. [Starfire Industries, Champaign, Illinois 61820 (United States); University of Michigan, Ann Arbor, Michigan 48109 (United States)

2007-03-15

337

Metrology in arc plasma: a new cathode  

Microsoft Academic Search

A new cathode shape has improved the stability and reproducibility of the ultraviolet continuum emitted by the plasma of a miniature argon arc. This arc is used as a transfer standard of spectral radiance in the vacuum ultraviolet.

R Croche

1980-01-01

338

Time-shared Cathode Ray Tube  

NASA Technical Reports Server (NTRS)

Time-shared cathode tube provides high quality display at low cost display stations which utilize television moniters. It updates a cluster of graphic displays from a computer and is useful in systems not equipped for graphics time-sharing.

Herndon, E. S.

1969-01-01

339

Improved magnetron cold-cathode ion source  

NASA Technical Reports Server (NTRS)

Cold cathode ionization source generates smaller amounts of spurious gases and has a higher sensitivity than commonly used hot-filament ion sources. Photon and X-ray background noise are reduced below detectable levels.

Roehrig, J.; Torney, F.

1970-01-01

340

Brewery wastewater treatment using air-cathode microbial fuel cells.  

PubMed

Effective wastewater treatment using microbial fuel cells (MFCs) will require a better understanding of how operational parameters and solution chemistry affect treatment efficiency, but few studies have examined power generation using actual wastewaters. The efficiency of wastewater treatment of a beer brewery wastewater was examined here in terms of maximum power densities, Coulombic efficiencies (CEs), and chemical oxygen demand (COD) removal as a function of temperature and wastewater strength. Decreasing the temperature from 30 degrees C to 20 degrees C reduced the maximum power density from 205 mW/m2 (5.1 W/m3, 0.76 A/m2; 30 degrees C) to 170 mW/m2 (20 degrees C). COD removals (R COD) and CEs decreased only slightly with temperature. The buffering capacity strongly affected reactor performance. The addition of a 50-mM phosphate buffer increased power output by 136% to 438 mW/m2, and 200 mM buffer increased power by 158% to 528 mW/m2. In the absence of salts (NaCl), maximum power output varied linearly with wastewater strength (84 to 2,240 mg COD/L) from 29 to 205 mW/m2. When NaCl was added to increase conductivity, power output followed a Monod-like relationship with wastewater strength. The maximum power (P max) increased in proportion to the solution conductivity, but the half-saturation constant was relatively unaffected and showed no correlation to solution conductivity. These results show that brewery wastewater can be effectively treated using MFCs, but that achievable power densities will depend on wastewater strength, solution conductivity, and buffering capacity. PMID:18246346

Feng, Yujie; Wang, Xin; Logan, Bruce E; Lee, He

2008-04-01

341

ENVIRONMENTAL BIOTECHNOLOGY Brewery wastewater treatment using air-cathode  

E-print Network

using actual wastewaters. The efficiency of wastewater treatment of a beer brewery wastewater. Keywords Microbial fuel cell . Beer brewery wastewater. Temperature . Solution conductivity Introduction The annual wastewater production from beer breweries in China is about 0.3 billion m3 , which is 1.5% to 2

342

The plasma-cathode electron gun  

Microsoft Academic Search

The development of a new type of plasma-cathode electron gun suitable for pulsed as well as CW operation withe-beam lasers is reported. This device employs a plasma generated within a low-voltage hollow-cathode discharge rather than a thermionic emitter as the source of electrons. Electrons extracted from the plasma pass through a triode-type control grid structure and are accelerated to high

J. Bayless; R. Knechtli; G. Mercer

1974-01-01

343

Cathode materials for lithium rocking chair batteries  

Microsoft Academic Search

Cathode materials for rechargeable rocking chair or lithium-ion batteries, are reviewed. The emphasis is placed on the comparison between specific capacities and rechargeability of lithium-containing high voltage cathode materials such as manganese oxides and LiMO2 compounds, where M is Co or Ni. It is generally found that the maximum reversible capacities for the most promising materials fall in the range

R. Koksbang; J. Barker; H. Shi; M. Y. Saïdi

1996-01-01

344

A calcium aluminate electride hollow cathode  

NASA Astrophysics Data System (ADS)

The development and testing of a hollow cathode utilizing C12A7 (12CaO?Al 2O3) electride as an insert are presented. Hollow cathodes are an integral part of electric propulsion thrusters on satellites and ground-based plasma sources for materials engineering. The power efficiency and durability of these components are critical, especially when used in flight applications. A low work function material internal to the cathode supplies the electrons needed to create the cathode plasma. Current state-of-the- art insert materials are either susceptible to poisoning or need to be heated to temperatures that result in a shortened cathode lifetime. C12A7 electride is a ceramic in which electrons contained in sub-nanometer sized lattice cages act as a conductive medium. Due to its unique atomic structure and large size, C12A7 electride has a predicted work function much lower than traditional insert materials. A novel, one-step fabrication process was developed that produced an amorphous form of C12A7 electride that had a measured work function 0.76 eV. A single electride hollow cathode was operated on xenon for over 60 hours over a two-month period that included 20 restarts and 11 chamber vent pump-down sequences with no sign of degradation, and on iodine for over 20 hours with no apparent reactivity issues. The operations of cathodes with three different orifice sizes were compared, and their effects on the interior cathode plasma modeled in a zero- dimensional phenomenological model.

Rand, Lauren Paula

345

A relativistic magnetron with a thermionic cathode  

Microsoft Academic Search

A 500-kV, S-band magnetron has been designed and tested. An oxide cathode was used in an attempt to achieve 1 ?s pulse lengths by using the pre-pulse space charge to shield the cathode from vacuum dc breakdown. The magnetron was designed according to conventional, nonrelativistic scaling laws and is unstrapped, utilizing a symmetric, axial output into a circular vacuum waveguide.

W. P. Ballard; S. A. Self; F. W. Crawford

1982-01-01

346

Post-Removal Examination of GTF Cathode #2  

Microsoft Academic Search

This photo-cathode (PC), GTF Cathode No.2, was removed from the GTF in October, 2000. It was characterized in September, 1999 by G. Mulhollan and me (Report entitled ''A Brief Report on a Brief Examination of the Electropolished GTF Cathode'', LCLS-TN-99-10). The cathode conditions and results of that exam were: (1) The cathode was conventionally machined and cleaned in the SLAC

2005-01-01

347

AFM as an analysis tool for high-capacity sulfur cathodes for Li-S batteries  

PubMed Central

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

Sorgel, Seniz; Costa, Remi; Carle, Linus; Galm, Ines; Canas, Natalia; Pascucci, Brigitta; Friedrich, K Andreas

2013-01-01

348

Development of plasma cathode electron guns  

NASA Astrophysics Data System (ADS)

The status of experimental research and ongoing development of plasma cathode electron guns in recent years is reviewed, including some novel upgrades and applications to various technological fields. The attractiveness of this kind of e-gun is due to its capability of creating high current, broad or focused beams, both in pulsed and steady-state modes of operation. An important characteristic of the plasma cathode electron gun is the absence of a thermionic cathode, a feature which leads to long lifetime and reliable operation even in the presence of aggressive background gas media and at fore-vacuum gas pressure ranges such as achieved by mechanical pumps. Depending on the required beam parameters, different kinds of plasma discharge systems can be used in plasma cathode electron guns, such as vacuum arcs, constricted gaseous arcs, hollow cathode glows, and two kinds of discharges in crossed E×B fields: Penning and magnetron. At the present time, plasma cathode electron guns provide beams with transverse dimension from fractional millimeter up to about one meter, beam current from microamperes to kiloamperes, beam current density up to about 100 A/cm2, pulse duration from nanoseconds to dc, and electron energy from several keV to hundreds of keV. Applications include electron beam melting and welding, surface treatment, plasma chemistry, radiation technologies, laser pumping, microwave generation, and more.

Oks, Efim M.; Schanin, Peter M.

1999-05-01

349

Interior Air Pollution in Automotive Cabins by Volatile Organic Compounds Diffusing from Interior Materials: I. Survey of 101 Types of Japanese Domestically Produced Cars for Private Use  

Microsoft Academic Search

The types and concentrations of organic compounds in the interior air of 101 different types of Japanese domestically produced private-use cars were examined. All the vehicles had been registered in the summer season as new cars and were less than 3 years old. The airborne compounds in the cabins were collected for 24h under static condition with the engine stopped

Toshiaki Yoshida; Ichiro Matsunaga; Kimiko Tomioka; Shinji Kumagai

2006-01-01

350

Diffusive exchange of polycyclic aromatic hydrocarbons across the air-water interface of the Patapsco River, an urbanized subestuary of the Chesapeake Bay  

Microsoft Academic Search

Air-water exchange fluxes of 13 polycyclic aromatic hydrocarbons (PAHs) were determined along a transect in the Patapsco River from the Inner Harbor of Baltimore, MD, to the mainstem of the northern Chesapeake Bay. Sampling took place at six sites during three sampling intensives (June 1996, February 1997, and July 1997) and at one site every ninth day between March 1997

Holly A. Bamford; John H. Offenberg; Randolph K. Larsen; Fung-Chi Ko; Joel E. Baker

1999-01-01

351

Characteristics of Hollow Cathode Arc Plasma as a Heat Source  

NASA Astrophysics Data System (ADS)

A feasibility study has been conducted to determine whether Hollow Cathode Arc (HCA) can be used for a welding heat source in space. The HCA method enables an arc discharge to ignite and maintain under low pressure conditions, where it is extremely difficult for the conventional Gas Tungsten Arc (GTA) method to form an arc discharge. In the previous paper, it has been demonstrated that the melting process by HCA under the condition that the gas flow rate is high (1.7ml/s) is significantly dominated by the diffuse anode and is characterized by shallow penetration, and that the electron temperature is about 1200018000K in arc space. In the present paper, the volt-ampere characteristics and the plasma property of HCA under the condition that the gas flow rate is low (0.17ml/s) have been made clear, and the melting phenomenon have been discussed. The results are summarized as follows, (1) The HCA under the condition that the gas flow rate is low is characterized by high voltage and high electron temperature, and the arc column is concentrated under the cathode.(2) The electron temperature is above 60000K near the arc axis.(3) The electrons with high temperature, that is high energy, contribute to the deep/huge penetration under the condition that the gas flowrate is low.

Nishikawa, Hiroshi; Maruyama, Toshikazu; Ohji, Takayoshi

352

Air distribution effectiveness with stratified air distribution systems  

E-print Network

required amount of outdoor air, Vbz, delivered to the space (or zone) for controlling contaminant;2 outdoor airflow required at the zone (usually through the supply diffusers) is determined as Vbz (from. The parameters studied were space type, diffuser number, supply air temperature, cooling load, return location

Chen, Qingyan "Yan"

353

Difference Between IR Radiation Spectra of Ethanol in Free Diffusion Combustion Regime and Regime Influenced by an Air Flow in Modeling of a Fire Tornado  

NASA Astrophysics Data System (ADS)

Results of experimental investigations of liquid fuel combustion in the regime of a twisted jet (model of a fire tornado) are presented. Flame radiation spectra were registered. In the chosen spectral range of registration (2.2-4.8 ?m), six spectral intervals were clearly traced in which the main portion of radiated energy was concentrated. Using the ratio of the sums of spectral intensities in the vicinities of the 6th and 3rd maxima, we successfully distinguished the regimes of modeled fire tornado and free diffusion fuel combustion.

Sherstobitov, M. V.; Tsvyk, R. Sh.

2013-06-01

354

Compact Rare Earth Emitter Hollow Cathode  

NASA Technical Reports Server (NTRS)

A compact, high-current, hollow cathode utilizing a lanthanum hexaboride (LaB6) thermionic electron emitter has been developed for use with high-power Hall thrusters and ion thrusters. LaB6 cathodes are being investigated due to their long life, high current capabilities, and less stringent xenon purity and handling requirements compared to conventional barium oxide (BaO) dispenser cathodes. The new cathode features a much smaller diameter than previously developed versions that permit it to be mounted on axis of a Hall thruster ( internally mounted ), as opposed to the conventional side-mount position external to the outer magnetic circuit ("externally mounted"). The cathode has also been reconfigured to be capable of surviving vibrational loads during launch and is designed to solve the significant heater and materials compatibility problems associated with the use of this emitter material. This has been accomplished in a compact design with the capability of high-emission current (10 to 60 A). The compact, high-current design has a keeper diameter that allows the cathode to be mounted on the centerline of a 6- kW Hall thruster, inside the iron core of the inner electromagnetic coil. Although designed for electric propulsion thrusters in spacecraft station- keeping, orbit transfer, and interplanetary applications, the LaB6 cathodes are applicable to the plasma processing industry in applications such as optical coatings and semiconductor processing where reactive gases are used. Where current electrical propulsion thrusters with BaO emitters have limited life and need extremely clean propellant feed systems at a significant cost, these LaB6 cathodes can run on the crudest-grade xenon propellant available without impact. Moreover, in a laboratory environment, LaB6 cathodes reduce testing costs because they do not require extended conditioning periods under hard vacuum. Alternative rare earth emitters, such as cerium hexaboride (CeB6) can be used in this configuration with possibly an even longer emitter life. This cathode is specifically designed to integrate on the centerline of a high-power Hall thruster, thus eliminating the asymmetries in the plasma discharge common to cathodes previously mounted externally to the thruster s magnetic circuit. An alternative configuration for the cathode uses an external propellant feed. This diverts a fraction of the total cathode flow to an external feed, which can improve the cathode coupling efficiency at lower total mass flow rates. This can improve the overall thruster efficiency, thereby decreasing the required propellant loads for different missions. Depending on the particular mission, reductions in propellant loads can lead to mission enabling capabilities by allowing launch vehicle step-down, greater payload capability, or by extending the life of a spacecraft.

Watkins, Ronald; Goebel, Dan; Hofer, Richard

2010-01-01

355

COMPUTATIONAL STUDY ON THE EFFECTS OF NON-PERIODIC FLOW PERTURBATIONS ON THE EMISSIONS OF SOOT AND NOX IN A CONFINED TURBULENT METHANE\\/AIR DIFFUSION FLAME  

Microsoft Academic Search

A computational investigation on the effects of fuel inlet perturbations in a confined turbulent CH4\\/air flame has been performed. Non-periodic fluctuations were characterised at the fuel inlet via a pair of sinusoidal harmonics of incommensurate periods with identical amplitude and frequency. Harmonic amplitudes of 2.5%, 7.5%, and 12.5% with respect to the time-averaged fuel inlet velocity have been simulated and

FERNANDO LOPEZ-PARRA; ALI TURAN

2007-01-01

356

2013 Estorm - Invited Paper - Cathode Materials Review  

SciTech Connect

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 [ORNL] [ORNL; Mohanty, Debasish [ORNL] [ORNL; Li, Jianlin [ORNL] [ORNL; Wood III, David L [ORNL] [ORNL

2014-01-01

357

Neutral electrolyte aluminum air battery with open configuration  

Microsoft Academic Search

A kind of new long life aluminum air batteries with open configuration was developed, using aluminum alloy doped with Ga, In, Sn, Bi, Pb and Mn as anode, NaCl solution as electrolyte and air electrode as cathode. The polarization curves of aluminum electrode and air electrode were tested. And the cell's performance was tested to calculate the utilization of aluminum

Bin HAN; Guangchuan LIANG

2006-01-01

358

The development of aluminum-air batteries for electric vehicles  

Microsoft Academic Search

Progress made toward the development of a viable aluminum-air battery system is presented. The general aluminum\\/air reaction is discussed. Results from aluminum anode and air cathode experiments are presented. Solids separation technology, a heat exchanger unit, and cell design are also discussed. The projected specific energy and power of the battery can provide electric vehicle driving ranges comparable to those

A. S. Homa; E. J. Rudd

1989-01-01

359

Atmospheric air diffuse array-needles dielectric barrier discharge excited by positive, negative, and bipolar nanosecond pulses in large electrode gap  

NASA Astrophysics Data System (ADS)

In this paper, positive, negative, and bipolar nanosecond pulses are employed to generate stable and diffuse discharge plasma using array needles-plate electrode configuration at atmospheric pressure. A comparison study of discharge images, electrical characteristics, optical emission spectra, and plasma vibrational temperature and rotational temperatures in three pulsed polarity discharges is carried on under different discharge conditions. It is found that bipolar pulse is beneficial to the excitation of diffuse dielectric barrier discharge, which can generate a room temperature plasma with more homogeneous and higher discharge intensity compared with unipolar discharges. Under the condition of 6 mm electrode gap distance, 26 kV pulse peak voltage, and 150 Hz pulse repetition rate, the emission intensity of N2 (C3?u ? B3?g) of the bipolar pulsed discharge is 4 times higher than the unipolar discharge (both positive and negative), while the plasma gas temperature is kept at 300 K, which is about 10-20 K lower than the unipolar discharge plasma.

Zhang, Li; Yang, De-zheng; Wang, Wen-chun; Liu, Zhi-jie; Wang, Sen; Jiang, Peng-chao; Zhang, Shuai

2014-09-01

360

Self-organization in cathode boundary layer discharges  

NASA Astrophysics Data System (ADS)

Cathode boundary layer (CBL) discharge, which has been developed as a UV light source, operates in a direct current between a planar cathode and a ring-shape anode that are separated by a dielectric with an opening of the same diameter as the anode. The nonthermal CBL discharges operate in a medium pressure range down to 30 Torr, emitting excimer radiation when operated with noble gases. The radiant excimer emittance at 172 nm in xenon reaches 1.7 W/cm2, and a maximum excimer efficiency of 6% has been obtained. The high excimer radiant emittance, in addition to low cost and simple geometry compared to other UV sources, makes CBL discharges an excellent choice for deep UV lamps and a candidate for integrated flat UV panels (Moselhy et al. 2004). It has been found that CBL discharges spontaneously give rise to regularly arranged filaments, i.e., self-organization, at a low current, e.g., less than 0.2 mA at 75 Torr (Schoenbach et al. 2004). In this thesis, the self-organization of direct current xenon discharges in the CBL configuration and parallel-plate geometry have been studied for a pressure range from 30 to 140 Torr and currents from 20 muA to 1 mA. Comprehensive examinations have been performed to investigate the behavior of those filaments by the use of optical, electrical, and spectral measurements. Side-on and end-on observations of the discharges have provided information on axial structure and distance of the filaments from the cathode fall. The electrical measurement has recorded a discrete I-V characteristic associated with the change of the numbers of the filaments. The spectral measurement provides scaling information on the relative population of high-lying states (1s 4, 1s5, and 2p6) of excited xenon atoms. Moreover, temperature measurement has revealed that the thermal electron emission from the cathode surface is negligible for the formation of filaments. The reactor geometry with parallel-plate electrodes analogously gives self-organization. The gas species, the cathode material, and the reactor geometry are varied to facilitate the understanding of the CBL xenon discharges and the self-organization. When krypton is used instead of xenon, rather homogeneous plasma far from organized pattern formation is observed with decreasing current. Of the tested aluminum, copper, and tungsten cathodes, the aluminum cathode achieved higher excimer intensity at 250 Torr than that of the molybdenum cathode by a factor of two. The diameter of the plasma reactor was reduced to 300 mum, and it gave rise to a single filament, illuminating with an enhanced excimer power density of 500 mW/cm2 at 62 Torr. Three mechanisms of these self-organizations are given and discussed in this thesis. The first mechanism explains that the axial electric field can initiate instability. This instability is caused by N-shaped negative differential conductivity (NNDC) in the vicinity of negative glow, which is attributed to electron-electron collisions. Positive feedback of the current density and the electric field due to the NNDC causes fluctuation to develop. Another positive feedback effect of the gas temperature is that the first Townsend coefficient can become dominant as, the current density increases. The filaments are assumed to undergo Coulomb force from the positively charged cathode fall channels and positive space charges on the surface of the surrounding dielectric spacer. The calculations, based on these assumptions on the Coulombic interactions, showed good agreement with experimental data. The second mechanism for the pattern formation is presented as to the development of Turing instability. The discussion is based on the idea that the regular arrangement of filaments is merely a result of general phenomena such as diffusion, ionization, or drift. A reaction-diffusion process with respect to the variation of local current density j and voltage v is the physical effect in the discharge. The numerical calculation was performed and obtained was a 2-D patterned structure exhibiting resemblance to the observed pattern. The tran

Takano, Nobuhiko

361

Multiple cathodic reaction mechanisms in seawater cathodic biofilms operating in sediment microbial fuel cells.  

PubMed

In this study, multiple reaction mechanisms in cathodes of sediment microbial fuel cells (SMFCs) were characterized by using cyclic voltammetry and microelectrode measurements of dissolved oxygen and pH. The cathodes were acclimated in SMFCs with sediment and seawater from San Diego Bay. Two limiting current regions were observed with onset potentials of approximately +400?mVAg/AgCl for limiting current?I and -120?mVAg/AgCl for limiting current?II. The appearance of two catalytic waves suggests that multiple cathodic reaction mechanisms influence cathodic performance. Microscale oxygen concentration measurements showed a zero surface concentration at the electrode surface for limiting current?II but not for limiting current?I, which allowed us to distinguish limiting current?II as the conventional oxygen reduction reaction and limiting current?I as a currently unidentified cathodic reaction mechanism. Microscale pH measurements further confirmed these results. PMID:25154833

Babauta, Jerome T; Hsu, Lewis; Atci, Erhan; Kagan, Jeff; Chadwick, Bart; Beyenal, Haluk

2014-10-01

362

Mechanism for small electron current fraction in a vacuum arc cathode spot on a refractory cathode  

NASA Astrophysics Data System (ADS)

A mechanism for refractory cathode spot operation in a vacuum arc is proposed, based on the presence of a finite electric field Ep at the cathode sheath-plasma interface. The proposed model determines the relationship between the electron current and the total spot current density j and includes a system of equations solved for cathode plasma containing a mixture of ion states. The calculation shows that Ep reaches a value, ˜106 V/cm, and j is 104-108 A/cm2, when the electron current fraction s increases from 0.5 to 0.9. It is discovered that for a refractory cathode, ions with high ionicity (from 2 to 4) can be generated in the spot region for a relatively small s, 0.7-0.9, in contrast to ionization in the plasma jet, as predicted previously for copper cathodes.

Beilis, I. I.

2004-02-01

363

Investigations Of A Pulsed Cathodic Vacuum Arc  

NASA Astrophysics Data System (ADS)

Cathodic vacuum arcs are well established as a method for producing thin films for coatings and as a source of metal ions. Research into DC vacuum arcs has been going on for over ten years in the School of Physics at the University of Sydney. Recently a project was undertaken in the school to design and build a pulsed CVA for use in the investigation of plasma sheaths and plasma immersion ion implantation. Pulsed cathodic vacuum arcs generally have a higher current and plasma density and also provide a more stable and reproducible plasma density than their DC counterparts. Additionally it has been shown that if a high repetition frequency can be established the deposition rate of pulsed arcs is equal to or greater than that of DC arcs with a concomitant reduction in the rate of macro-particle formation. We present here results of our investigations into the building of a center-triggered pulsed cathodic vacuum arc. The design of the power supply and trigger mechanism and the geometry of the anode and cathode are examined. Observations of type I and II arc spots using a CCD camera, and cathode spot velocity dependence on arc current will be presented. The role of retrograde motion in a high current pulsed arc is discussed.

Oates, T. W. H.; Pigott, J.; Denniss, P.; Mckenzie, D. R.; Bilek, M. M. M.

2003-06-01

364

Diffusive exchange of polycyclic aromatic hydrocarbons across the air-water interface of the Patapsco River, an urbanized subestuary of the Chesapeake Bay  

SciTech Connect

Air-water exchange fluxes of 13 polycyclic aromatic hydrocarbons (PAHs) were determined along a transect in the Patapsco River from the Inner Harbor of Baltimore, MD, to the mainstem of the northern Chesapeake Bay. Sampling took place at six sites during three sampling intensives (June 1996, February 1997, and July 1997) and at one site every ninth day between March 1997 and March 1998 to measure spatial, daily, and annual variability in the fluxes. The direction and magnitude of the daily fluxes of individual PAHs were strongly influenced by the wind speed and direction, by the air temperature, and by the highly variable PAH concentrations in the gas and dissolved phases. Individual fluxes ranged from 14,200 ng m{sup {minus}2} day{sup {minus}1} net volatilization of fluorene during high winds to 11,400 ng m{sup {minus}2} day{sup {minus}1} net absorption of phenanthrene when prevailing winds blowing from the northwest across the city of Baltimore elevated gaseous PAH concentrations over the water. The largest PAH volatilization fluxes occurred adjacent to the stormwater discharges, driven by elevated dissolved PAH concentrations in surface waters. Estimated annual volatilization fluxes ranged from 1.1 {micro}g m{sup {minus}2} yr{sup {minus}1} for chrysene to 800 {micro}g m{sup {minus}2} yr{sup {minus}1} for fluorene.

Bamford, H.A.; Offenberg, J.H.; Larsen, R.K.; Ko, F.C.; Baker, J.E. [Univ. of Maryland, Solomons, MD (United States)] [Univ. of Maryland, Solomons, MD (United States)

1999-07-01

365

Field free, directly heated lanthanum boride cathode  

DOEpatents

A directly heated cylindrical lanthanum boride cathode assembly is disclosed which minimizes generation of magnetic fields which would interfere with electron emission from the cathode. The cathode assembly comprises a lanthanum boride cylinder in electrical contact at one end with a central support shaft which functions as one electrode to carry current to the lanthanum boride cylinder and in electrical contact, at its opposite end with a second electrode which is coaxially position around the central support shaft so that magnetic fields generated by heater current flowing in one direction through the central support shaft are cancelled by an opposite magnetic field generated by current flowing through the lanthanum boride cylinder and the coaxial electrode in a direction opposite to the current flow in the central shaft.

Leung, Ka-Ngo (Hercules, CA); Moussa, David (San Francisco, CA); Wilde, Stephen B. (Pleasant Hill, CA)

1991-01-01

366

Chromium oxides as cathodes for lithium cells  

NASA Astrophysics Data System (ADS)

The discharge behavior of organic electrolyte lithium cells with various kinds of chromium oxide cathodes was studied, as was the performance of coin-type cells. Cathodes composed of CrO2, Cr2O5, Cr3O8, Cr6O15, and Cr3O8 were examined, demonstrating the best results with Li/Cr2O5, Li/Cr6O15, and Li/Cr3O8, particularly in terms of energy density. The Li/Cr3O8 couple yielded 1210 W-h/kg. The coin-type cell with a Cr3O8 cathode displayed no significant change in the charge-discharge curves over more than 160 test cycles. Its use in combination with a solar cell as a wristwatch battery is recommended.

Takeda, Y.; Kanno, R.; Tsuji, Y.; Yamamoto, O.; Taguch, H.

1983-05-01

367

Advanced rechargeable sodium batteries with novel cathodes  

NASA Technical Reports Server (NTRS)

Various high energy density rechargeable batteries are being considered for future space applications. Of these, the sodium sulfur battery is one of the leading candidates. The primary advantage is the high energy density (760 Wh/kg theoretical). Energy densities in excess of 180 Wh/kg have been realized in practical batteries. More recently, cathodes other than sulfur are being evaluated. Researchers at JPL are evaluating various new cathode materials for use in high energy density sodium batteries for advanced space applications. The approach is to carry out basic electrochemical studies of these materials in a sodium cell configuration in order to understand their fundamental behaviors. Thus far studies have focused on alternate metal chlorides such as CuCl2 and organic cathode materials such as tetracyanoethylene (TCNE).

Distefano, S.; Ratnakumar, B. V.; Bankston, C. P.

1989-01-01

368

Advanced rechargeable sodium batteries with novel cathodes  

NASA Technical Reports Server (NTRS)

Various high energy density rechargeable batteries are being considered for future space applications. Of these, the sodium-sulfur battery is one of the leading candidates. The primary advantage is the high energy density (760 W h/kg theoretical). Energy densities in excess of 180 W h/kg have been realized in practical batteries. More recently, cathodes other than sulfur are being evaluated. Various new cathode materials are presently being evaluated for use in high energy density sodium batteries for advanced space applications. The approach is to carry out basic electrochemical studies of these materials in a sodium cell configuration in order to understand their fundamental behaviors. Thus far, the studies have focussed on alternative metal chlorides such as CuCl2 and organic cathode materials such as TCNE.

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

1990-01-01

369

Field free, directly heated lanthanum boride cathode  

DOEpatents

A directly heated cylindrical lanthanum boride cathode assembly is disclosed which minimizes generation of magnetic field which would interfere with electron emission from the cathode. The cathode assembly comprises a lanthanum boride cylinder in electrical contact at one end with a central support shaft which functions as one electrode to carry current to the lanthanum boride cylinder and in electrical contact, at its opposite end with a second electrode which is coaxially position around the central support shaft so that magnetic fields generated by heater current flowing in one direction through the central support shaft are cancelled by an opposite magnetic field generated by current flowing through the lanthanum boride cylinder and the coaxial electrode in a direction opposite to the current flow in the central shaft.

Leung, Ka-Ngo; Moussa, D.; Wilde, S.B.

1987-02-02

370

Modeling dioxygen reduction at multicopper oxidase cathodes.  

PubMed

We report a general kinetics model for catalytic dioxygen reduction on multicopper oxidase (MCO) cathodes. Our rate equation combines Butler-Volmer (BV) electrode kinetics and the Michaelis-Menten (MM) formalism for enzymatic catalysis, with the BV model accounting for interfacial electron transfer (ET) between the electrode surface and the MCO type 1 copper site. Extending the principles of MM kinetics to this system produced an analytical expression incorporating the effects of subsequent intramolecular ET and dioxygen binding to the trinuclear copper cluster into the cumulative model. We employed experimental electrochemical data on Thermus thermophilus laccase as benchmarks to validate our model, which we suggest will aid in the design of more efficient MCO cathodes. In addition, we demonstrate the model's utility in determining estimates for both the electronic coupling and average distance between the laccase type-1 active site and the cathode substrate. PMID:25188422

Agbo, Peter; Heath, James R; Gray, Harry B

2014-10-01

371

Heat treatment of cathodic arc deposited amorphous hard carbon films  

SciTech Connect

Amorphous hard carbon films of varying sp{sup 2}/sp{sup 3} fractions have been deposited on Si using filtered cathodic are deposition with pulsed biasing. The films were heat treated in air up to 550 C. Raman investigation and nanoindentation were performed to study the modification of the films caused by the heat treatment. It was found that films containing a high sp{sup 3} fraction sustain their hardness for temperatures at least up to 400 C, their structure for temperatures up to 500 C, and show a low thickness loss during heat treatment. Films containing at low sp{sup 3} fraction graphitize during the heat treatment, show changes in structure and hardness, and a considerable thickness loss.

Anders, S.; Ager, J.W. III; Brown, I.G. [and others

1997-02-01

372

Enhanced activated carbon cathode performance for microbial fuel cell by blending carbon black.  

PubMed

Activated carbon (AC) is a useful and environmentally sustainable catalyst for oxygen reduction in air-cathode microbial fuel cells (MFCs), but there is great interest in improving its performance and longevity. To enhance the performance of AC cathodes, carbon black (CB) was added into AC at CB:AC ratios of 0, 2, 5, 10, and 15 wt % to increase electrical conductivity and facilitate electron transfer. AC cathodes were then evaluated in both MFCs and electrochemical cells and compared to reactors with cathodes made with Pt. Maximum power densities of MFCs were increased by 9-16% with CB compared to the plain AC in the first week. The optimal CB:AC ratio was 10% based on both MFC polarization tests and three electrode electrochemical tests. The maximum power density of the 10% CB cathode was initially 1560 ± 40 mW/m(2) and decreased by only 7% after 5 months of operation compared to a 61% decrease for the control (Pt catalyst, 570 ± 30 mW/m(2) after 5 months). The catalytic activities of Pt and AC (plain or with 10% CB) were further examined in rotating disk electrode (RDE) tests that minimized mass transfer limitations. The RDE tests showed that the limiting current of the AC with 10% CB was improved by up to 21% primarily due to a decrease in charge transfer resistance (25%). These results show that blending CB in AC is a simple and effective strategy to enhance AC cathode performance in MFCs and that further improvement in performance could be obtained by reducing mass transfer limitations. PMID:24422458

Zhang, Xiaoyuan; Xia, Xue; Ivanov, Ivan; Huang, Xia; Logan, Bruce E

2014-02-01

373

Characterization and Comparison of Different Cathode Materials for SC-SOFC: LSM, BSCF, SSC and LSCF  

E-print Network

cathode materials for Single Chamber Solid Oxide Fuel Cell (SC-SOFC) (La0.8Sr0.2MnO3- (LSM), Ba0.5Sr0.5Co0 Chamber, Solid Oxide Fuel cell, SSC. 1 Introduction Single Chamber Solid Oxide Fuel Cells (SC-SOFC) show.1O2- (CGO) electrolyte and a Ni-CGO anode, were tested in several methane/air mixtures with each

Paris-Sud XI, Université de

374

Highly methanol-tolerant non-precious metal cathode catalysts for direct methanol fuel cell  

Microsoft Academic Search

This work reports on the oxygen reduction activity of several non-precious metal (non-PGM) catalysts for oxygen reduction reaction (ORR) at the fuel cell cathode, including pyrolyzed CoTPP, FeTPP, H2TMPP, and CoTMPP. Of the studied catalysts, pyrolyzed CoTMPP (Co-tetramethoxyphenylporphyrin) was found to perform significantly better than other materials. The catalyst underwent a thorough testing in both hydrogen–air polymer electrolyte fuel cell

Barbara Piela; Tim S. Olson; Plamen Atanassov; Piotr Zelenay

2010-01-01

375

Paired removal of color and COD from textile dyeing wastewater by simultaneous anodic and indirect cathodic oxidation.  

PubMed

The anodic and indirect cathodic removals of color and COD from real dyeing wastewater were investigated simultaneously using a stacked Pt/Ti screen anode and a graphite packed-bed cathode in a divided flow-by electrochemical reactor. The anodically generated hypochlorite and cathodically generated hydrogen peroxide were the main species used to remove color and COD in the wastewater. Various experimental operating factors that can affect the removal efficiency were investigated, including the applied current density, the amount of NaCl added, the solution pH in alkaline ranges and the temperature. The color and COD removal efficiencies in the anodic chamber were much higher than those in the cathodic chamber. The overall (anodic plus cathodic) removal efficiencies increased with the applied current density, the amount of NaCl added and the temperature. In contrast, increasing the solution pH decreased the overall removal efficiency. The anodic and cathodic current efficiencies at 20 mA/cm(2) were 63.50% and 19.57%, respectively. In this work the total treatment cost for removing 1g COD was US $0.643 when an air cylinder was used. PMID:19362772

Wang, Chih-Ta; Chou, Wei-Lung; Kuo, Yi-Ming; Chang, Fu-Lin

2009-09-30

376

Ring cusp/hollow cathode discharge chamber performance studies. [ion propulsion  

NASA Technical Reports Server (NTRS)

An experimental study was performed to determine the effects of hollow cathode position, anode position, and ring cusp magnetic field configuration and strength on discharge chamber performance. The results are presented in terms of comparative plasma ion energy cost, extracted ion fraction, and beam profile data. Such comparisons are used to demonstrate whether changes in performance are caused by changes in the loss rate of primary electrons to the anode or the loss rate of ions to discharge chamber walls or cathode and anode surfaces. Results show: (1) the rate of primary electron loss to the anode decreases as the anode is moved downstream of the ring cusp toward the screen grid; (2) the loss rate of ions to hollow cathode surfaces are excessive if the cathode is located upstream of a point of peak magnetic flux density at the discharge chamber centerline; and (3) the fraction of the ions produced that are lost to discharge chamber walls and ring magnet surfaces is reduced by positioning of the magnet rings so the plasma density is uniform over the grid surface, and adjusting their strength to a level where it is sufficient to prevent excessive ion losses by Bohm diffusion.

Vaughn, J. A.; Wilbur, Paul J.

1988-01-01

377

Effect of Gas Pressure on Polarization of SOFC Cathode Prepared by Plasma Spray  

NASA Astrophysics Data System (ADS)

A cermet-supported tubular SOFC was fabricated using thermal spray. The cell performance was investigated at temperatures from 750 to 900 °C and pressures from 0.1 to 0.5 MPa to examine the effect of operating gas pressure on the cell performance. The influence of gas pressure on the cathodic polarization was studied through the electrochemical impedance approach to examine the controlling electrochemical processes during cell operation. Results show that increasing the operating gas pressure improves the power output performance significantly. When the gas pressure is increased from 0.1 to 0.3 MPa, the maximum power density is increased by a factor of 32% at a temperature of 800 °C. The cathode polarization decreases significantly with the increase of the gas pressure. The electrochemical analysis shows that the main control processes of the cathode reaction are the oxygen species transfer at the three-phase boundary and oxygen diffusion on the surface or in the bulk of the cathode, which are enhanced with increasing gas pressure.

Li, Cheng-Xin; Wang, Zhun-Zhun; Liu, Shuai; Li, Chang-Jiu

2013-06-01

378

Investigation of anode and cathode jets influence on electric arc properties with current up to 500 kA  

Microsoft Academic Search

Summary form only given, as follows. Arcs with discharge current amplitude up to 500 kA were investigated in hydrogen and air at initial pressure from 0.1 MPa up to 40 MPa. It was found that anode and cathode jets influence both on the discharge channel properties and heat transfer between the arc and the surrounding gas: 1. High temperatures at

Ph. G. Rutberg; A. A. Bogomaz; A. V. Budin; V. A. Kolikov; E. Pinchuk; A. A. Pozubenkov

2001-01-01

379

DESCRIPTION OF ATMOSPHERIC TRANSPORT PROCESSES IN EULERIAN AIR QUALITY MODELS  

EPA Science Inventory

Key differences among many types of air quality models are the way atmospheric advection and turbulent diffusion processes are treated. Gaussian models use analytical solutions of the advection-diffusion equations. Lagrangian models use a hypothetical air parcel concept effecti...

380

Plotting vectors on a cathode ray oscilloscope  

E-print Network

and simultaneously slotted on the soreen of a cathode ray oscilloscope in the conventional foxm dispenses with all of this work for as many ourrents and/or voltages as there are provided appropx'iate input circuits and gives a complete veotor solution in a... and simultaneously slotted on the soreen of a cathode ray oscilloscope in the conventional foxm dispenses with all of this work for as many ourrents and/or voltages as there are provided appropx'iate input circuits and gives a complete veotor solution in a...

Foster, Kenneth William

2012-06-07

381

Ferroelectric Cathodes in Transverse Magnetic Fields  

SciTech Connect

Experimental investigations of a planar ferroelectric cathode in a transverse magnetic field up to 3 kGs are presented. It is shown that the transverse magnetic field affects differently the operation of ferroelectric plasma cathodes in ''bright'' and ''dark'' modes in vacuum. In the ''bright'' mode, when the surface plasma is formed, the application of the transverse magnetic field leads to an increase of the surface plasma density. In the ''dark'' mode, the magnetic field inhibits the development of electron avalanches along the surface, as it does similarly in other kinds of surface discharges in the pre-breakdown mode.

Alexander Dunaevsky; Yevgeny Raitses; Nathaniel J. Fisch

2002-07-29

382

Cathodic protection of pipelines in discontinuous permafrost  

SciTech Connect

This paper discusses the challenges in providing cathodic protection for a pipeline located in an area with discontinuous permafrost. Specific challenges included: unknown time for the permafrost to melt out, unpredictable current distribution characteristics and wet, inaccessible terrain. Based on preliminary pipe-to-soil data, it appears that cathodic protection coverage was achieved in discontinuous permafrost regions without the need of local anodes. Future work is required to verify whether this conclusion can be extended over the course of an annual freeze-thaw cycle.

Mitchell, C.J.; Wright, M.D. [NOVA Gas Transmission Ltd., Calgary, Alberta (Canada); Waslen, D.W. [Pipeline Protech Inc., Calgary, Alberta (Canada)

1997-08-01

383

Fabrication Of Metal Chloride Cathodes By Sintering  

NASA Technical Reports Server (NTRS)

Transition-metal chloride cathodes for use in high-temperature rechargeable sodium batteries prepared by sintering transition-metal powders mixed with sodium chloride. Need for difficult and dangerous chlorination process eliminated. Proportions of transition metal and sodium chloride in mixture adjusted to suit specific requirements. Cathodes integral to sodium/metal-chloride batteries, which have advantages over sodium/sulfur batteries including energy densities, increased safety, reduced material and thermal-management problems, and ease of operation and assembly. Being evaluated for supplying electrical power during peak demand and electric vehicles.

Bugga, Ratnakumar V.; Di Stefano, Salvador; Bankston, C. Perry

1992-01-01

384

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. During this time period substantial progress has been made in developing low temperature deposition techniques to produce dense, nanocrystalline yttrium-stabilized zirconia films on both dense oxide and polymer substrates. Progress has been made in the preparation and characterization of thin electrolytes and porous LSM substrates. Both of these tasks are essentially on or ahead of schedule. In our proposal, we suggested that the ZrO{sub 2}/Sc system needed to be considered as a candidate as a thin electrolyte. This was because microcrystalline ZrO{sub 2}/Sc has a significantly higher ionic conductivity than YSZ, particularly at the lower temperatures. As a result, some 0.5 micron thick film of ZrO{sub 2}/16% Sc on an alumina substrate (grain size 20nm) was prepared and the electrical conductivity measured as a function of temperature and oxygen activity. The Sc doped ZrO{sub 2} certainly has a higher conductivity that either 20nm or 2400nm YSZ, however, electronic conductivity dominates the conductivity for oxygen activities below 10{sup -15}. Whereas for YSZ, electronic conductivity is not a problem until the oxygen activity decreases below 10{sup -25}. These initial results show that the ionic conductivity of 20nm YSZ and 20nm ZrO{sub 2}/16% Sc are essentially the same and the enhanced conductivity which is observed for Sc doping in microcrystalline specimens is not observed for the same composition when it is nanocrystalline. In addition they show that the electronic conductivity of Sc doped ZrO{sub 2} is at least two orders of magnitude higher than that observed for YSZ. The conclusion one reaches is that for 0.5 to 1 micron thick nanocrystalline films, Sc doping of ZrO{sub 2} has no benefits compared to YSZ. As a result, electrolyte films of ZrO{sub 2}/Sc should not be considered as candidates. However, they have the potential of being useful as an interface on the anode side of the electrolyte. NexTech has focused much of its effort during the past few months on establishing tape casting methods for porous LSM substrates. This work, performed under a separate DOE-funded program, involved tape casting formulations comprising LSM powders with bi-modal particle size distributions and fugitive pore forming additives. Sintered LSM substrates with porosities in the 30 to 40 vol% range, and pore sizes of 10 {approx} 20 microns have been prepared. In addition, tape casting formulations involving composite mixtures of LSM and Sm-doped ceria (SDC) have been evaluated. The LSM/SDC cathode substrates are expected to provide better performance at low temperatures. Characterization of these materials is currently underway.

Harlan U. Anderson

2000-03-31

385

Electrochemical properties of aluminum anodes in gel electrolyte-based aluminum-air batteries  

Microsoft Academic Search

Various concentrations of potassium hydroxide (KOH) solution electrolytes were gelled with a hydroponics gelling agent and used in aluminum-air (Al-air) cells. An aluminum plate and a single air-cathode were used as the anode and cathode, respectively. The cells were discharged at a constant current density of 0.08, 0.80 and 1.60mA\\/cm2. The 0.6M KOH concentration gave the highest capacity and power

A. A. Mohamad

2008-01-01

386

Secondary lithium battery including a silver molybdenum cathode  

SciTech Connect

This patent describes a non-aqueous battery including a lithium anode, an electrolyte and a cathode, characterized in that the cathode comprises silver molybdenum sulfide of the formula AgMo/sub 6/S/sub 8/.

Tarascon, J.M.

1988-06-14

387

High pressure working mode of hollow cathode arc discharges  

NASA Technical Reports Server (NTRS)

The behavior of high pressure cathotrons is discussed. Methods of preheating either the gas or the cathode itself are detailed together with various geometries for the hollow cathode. Three special configurations were tested, and the results are analyzed.

Minoo, H.; Popovici, C.

1985-01-01

388

Child-Langmuir sheath structure around wedge-shaped cathodes  

Microsoft Academic Search

The steady state Child-Langmuir sheath around a wedge-shaped cathode immersed in a plasma is calculated numerically. The ions drawn from the plasma may be employed to sputter material from the cathode, or may implant into the cathode, depending upon the magnitude of the applied negative voltage. The ion impact rate onto the cathode reaches 2.2 times higher near a square

P. A. Watterson

1989-01-01

389

Hillslope diffusion  

NSDL National Science Digital Library

This lab is designed to help students apply hillslope diffusion equations (derived in class prior to the lab) to understand real-world hillslopes. The major goal is a deeper understanding of hillslope processes and the equations used to describe hillslope diffusion by observing the same factors described in the equations on real-world hillslopes.

Mcdermott, Jeni

390

Radial diffusive samplers for determination of 8-h concentration of BTEX, acetone, ethanol and ozone in ambient air during a sea breeze event  

NASA Astrophysics Data System (ADS)

The radial diffusive sampler Radiello ® filled with Carbograph 4 was evaluated for monitoring BTEX, ethanol and acetone concentrations for 8-hour exposure time. The sampling rates were first evaluated in an exposure chamber under standard conditions. Benzene and toluene showed the highest sampling rates with satisfactory standard deviations. Ethylbenzene and xylenes showed medium sampling rates but higher standard deviations that can be attributed to a low affinity of these compounds with the adsorbent medium for short sampling time. Acetone has a fair result because of the increase of its partial pressure in the vicinity of the adsorbent surface in the course of sampling. The Carbograph 4 adsorbent does not seem to be suitable for sampling ethanol, likely because of its high volatility. The influences of three environmental factors (temperature (T), relative humidity (RH) and concentration level (C)) on the sampling rates were also evaluated, following a fractional factorial design at two factor levels (low and high). Results were only investigated on benzene, toluene and acetone. Temperature and relative humidity are found to be the most important factors leading to variability of the benzene and toluene sampling rates. The applicability of the sampler for 8-hour sampling was demonstrated by the results of a measurement campaign carried out during a sea breeze event. Mapping of benzene, toluene and acetone concentrations showed the highest concentrations in the industrial zone following the wind direction coming from the North. Nevertheless, the sea breeze tends to reduce the spread of the industrial plumes. On the contrary, the ozone map presents the lowest concentrations at the same industrial area indicating a net consumption of ozone. The highest ozone concentrations were found in the southeastern zone suggesting a local ozone formation.

Roukos, Joelle; Locoge, Nadine; Sacco, Paolo; Plaisance, Hervé

2011-01-01

391

Scanning optical pyrometer for measuring temperatures in hollow cathodes  

Microsoft Academic Search

Life-limiting processes in hollow cathodes are determined largely by the temperature of the electron emitter. To support cathode life assessment, a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe was developed. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used to

J. E. Polk; C. M. Marrese-Reading; B. Thornber; L. Dang; L. K. Johnson; I. Katz

2007-01-01

392

Advanced Cathode Catalysts and Supports for PEM Fuel Cells  

E-print Network

Advanced Cathode Catalysts and Supports for PEM Fuel Cells DE-FG36-07GO17007 Mark K. Debe 3M or confidential information #12;Overview Advanced Cathode Catalysts and Supports for PEM FC's ­ 2007 DOE HFCIT (PGM) content and manufacturability], high performance cathode electrode (catalyst and support

393

Combined plasma and thermal hollow cathode insert model  

NASA Technical Reports Server (NTRS)

In this paper, we present the first results from a Hollow Cathode Thermal (HCThermal) model that uses the spatially distributed plasma fluxes calculated by the InsertRegion of an Orificed Cathode (IROrCa2D) code as the heat source to predict the hollow cathode and insert temperatures.

Katz, Ira; Polk, James E.; Mikellides, Ionnis G.; Goebel, Dan m.; Hornbeck, Sarah E.

2005-01-01

394

Cathodic protection of a buried pipeline by solar energy  

Microsoft Academic Search

Cathodic protection is employed intensively on the steel drains in oil and gas industry. It is a technique of prevention against the corrosion which transforms the structure into a cathode of a corrosion cell; Two types of cathodic protection systems are usually applied: The galvanic protection systems use the galvanic anodes, also called the sacrificial anodes, which are electrochemically more

B. Laoun; K. Niboucha; L. Serir

395

Surface Characterization of the LCLS RF Gun Cathode  

Microsoft Academic Search

The first copper cathode installed in the LCLS RF gun was used during LCLS commissioning for more than a year. However, after high charge operation (> 500 pC), the cathode showed a decline of quantum efficiency within the area of drive laser illumination. They report results of SEM, XPS and XAS studies that were carried out on this cathode after

Axel Brachmann; Franz-Josef Decker; Yuantao Ding; David Dowell; Paul Emma; Josef Frisch; Sasha Gilevich; Gregory Hays; Philippe Hering; Zhirong Huang; Richard Iverson; Henrik Loos; Alan Miahnahri; Dennis Nordlund; Heinz-Dieter Nuhn; Piero Pianetta; James Turner; James Welch; William White; Juhao Wu; Dao Xiang

2012-01-01

396

The loss of material from the cathode of metal arcs  

NASA Technical Reports Server (NTRS)

A study was made of the effect of arc length, cathode thickness, current strength, gas pressure and the chemical nature of the cathode material and filling gases upon the material loss from Cu, Fe, and Ag cathodes in arcs. The results show that the analysis of the phenomenon is complex and the energy balance is difficult to formulate.

Seeliger, R.; Wulfhekel, H.

1985-01-01

397

Functional Ion Laser Based upon a Thermionic Hollow Cathode Discharge  

Microsoft Academic Search

An ion laser based upon a thermionic hollow cathode discharge is described. The anode and the cathode are a pair of hollow metal cylinders that are spaced by a series of metal apertures along the axis of a solenoid. The laser is necessarily operated in a flowing gas mode; argon or krypton flows through the cathode tube and is pumped

D. A. Huchital; J. Dane Rigden

1968-01-01

398

Arc Cathode Emission Mechanisms at High Currents and Pressures  

Microsoft Academic Search

Cathode emission was studied at over 1 atmosphere pressure into He and A plasmas at 100- to 500-A total current. The cathode spot temperature and current density were measured by a high speed photometric method developed for this purpose. A low vacuum thermionic work function was found to be a most important criterion for long cathode life. Emission current densities

Peter W. Neurath; Thomas W. Gibbs

1963-01-01

399

Explosive Electron Emission From Liquid-Metal Cathodes  

Microsoft Academic Search

Since the discovery of explosive electron emission (EEE) 40 years ago, the overwhelming majority of investigations of this phenomenon have been performed with solid-state metal cathodes. At the same time, liquid-metal (LM) pool point cathodes, by virtue of some favorable properties, allow one to perform more reliable physical experiments. The peculiarities of LM cathodes are related to the features of

Dmitry I. Proskurovsky

2009-01-01

400

High-pressure hollow cathode discharges  

NASA Astrophysics Data System (ADS)

Reducing the diameter of the cathode hole in a plane anode - hollow cathode geometry to 0963-0252/6/4/003/img1m has allowed us to generate direct current discharges in argon at atmospheric pressure. Up to pressure times cathode hole diameter (pD) values of approximately 5 Torr cm, and at sub-mA currents, glow discharges (predischarges) are observed with a shape which is determined by the vacuum electric field. In the same pD range, but at higher currents of up to approximately 4 mA, the discharges are of the hollow cathode discharge type. At pD values exceeding 5 Torr cm the predischarges turn into surface discharges along the mica spacer between the electrodes. At currents > 4 mA filamentary, pulsed discharges are observed. Qualitative information on the electron energy distribution in the microdischarges has been obtained by studying the VUV emission from ionized argon atoms and the argon excimer radiation at 130 nm. The results of the spectral measurements indicate the presence of a relatively large concentration of electrons with energies > 15 eV over the entire pressure range. The fact that the current - voltage characteristic of the microdischarges has a positive slope over much of the current range where excimer radiation is emitted indicates the possibility of forming arrays of these discharges and using them in flat panel excimer lamps.

Schoenbach, Karl H.; El-Habachi, Ahmed; Shi, Wenhui; Ciocca, Marco

1997-11-01

401

Life test performance of thermionic cathodes  

Microsoft Academic Search

To ascertain the electron emission properties of impregnated M-type cathodes long term life tests in diodes have been performed. The evolution of the zero field current density and the emitted current during more than 100,000 h has been determined. The evolution of the emitted current in travelling wave tubes (TWT) has also been measured and compared with the results obtained

D. Dieumegard; J. C. Tonnerre; D. Brion; A. M. Shroff

1997-01-01

402

Nano-Fabrication by Cathodic Plasma Electrolysis  

Microsoft Academic Search

Cathodic plasma electrolytic (CPE) techniques are new groups of coating processes, which can be used for fabrication of nanostructured layers on surface of a wide range of metallic substrates. The most exciting visible feature of these atmospheric-based plasma techniques is continuous sparking on processed surface inside an electrolyte. Unlike the anodic part of plasma electrolysis (usually known as plasma electrolytic

M. Aliofkhazraei; A. Sabour Rouhaghdam; P. Gupta

2011-01-01

403

Electrodynamic interpretation of virtual-cathode oscillations  

SciTech Connect

Virtual-cathode oscillations and particle bunching are proved to be electrodynamic shock-induced phenomena when magnetic-field and thermal effects are small compared to those due to plasma energy and electric fields. This result is derived for general configurations. The complete solution of one-dimensional problems is reduced to quadratures.

Kadish, A.

1984-01-01

404

Analysis and simulation of virtual cathode oscillations  

SciTech Connect

A nonlinear mechanism for virtual cathode oscillations is derived from an analysis of a cold plasma fluid model. Frequency scalings and field wave shapes are predicted. These are compared with extensive numerical simulation studies of non-neutral electron beams using both one- and two-dimensional particle-in-cell codes.

Kadish, A.; Faehl, R.J.; Snell, C.M.

1986-12-01

405

HIGHLY DISPERSED ALLOY CATHODE CATALYST FOR DURABILITY  

E-print Network

HIGHLY DISPERSED ALLOY CATHODE CATALYST FOR DURABILITY T. D. Jarvi UTC Power Corporation This presentation does not contain any proprietary or confidential information #12;HIGHLY DISPERSED ALLOY CATALYSTVRHE (IR-Free) 720 A/cm2 Cost $8/kW #12;HIGHLY DISPERSED ALLOY CATALYST CurrentStateofArtcathodes (e

406

Cathodic protection of pipelines in discontinuous permafrost  

SciTech Connect

There are many unknowns and challenges in providing cathodic protection (CP) for a pipeline located in discontinuous permafrost areas. Preliminary pipe-to-soil data indicates that CP coverage was achieved in these regions without needing local anodes. Work is required to verify whether this conclusion can be extended over the course of an annual freeze-thaw cycle.

Mitchell, C.J.; Wright, M.D. [NOVA Gas Transmission Ltd., Calgary, Alberta (Canada); Waslen, D.W. [Pipeline Protech, Inc., Calgary, Alberta (Canada)

1997-10-01

407

Organic cathode for a secondary battery  

SciTech Connect

This patent describes a battery system. It comprises: a first body of liquid meal anode comprising a Group I metal; a record body of liquid cathode comprising a combination of Group I metal salt and Group III metal salt molten at the temperature of operation of the battery containing a minor amount of an organic carbonitrile depolarizer containing at least one adjacent ethylenic bond.

Bugga, R.V.; Distefano, S.; Williams, R.M.; Bankston, C.P.

1990-10-30

408

Close cathode chamber: Low material budget MWPC  

NASA Astrophysics Data System (ADS)

Performance of asymmetric-type MWPC-s are presented. In this structure, referred to as Close Cathode Chamber in an earlier study, the material budget is significantly reduced on one hand by the elimination of external support frame, on the other hand by thin detector walls. In this paper it is demonstrated that the outline is compatible with large size detectors (1 m wire length), maintaining mechanical and operation stability, with total weight of 3 kg (including support structure) for a half square meter surface. The detection efficiency and response time is shown to be sufficient for L0 triggering in the ALICE VHMPID layout. Reduced sensitivity to cathode deformations (due to internal overpressure as mechanical strain) is directly demonstrated. On small sized chambers, improvement of position resolution with analog readout is evaluated, reaching 0.09 mm RMS with 2 mm wide cathode segments. Simulation results on signal time evolutions are presented. With the above studies, comparison of classical MWPC-s and the Close Cathode Chamber design is performed in all major aspects.

Varga, Dezs?; Kiss, Gábor; Hamar, Gerg?; Bencédi, Gyula

2013-01-01

409

Bimetallic Cathode Materials for Lithium Based Batteries  

E-print Network

Bimetallic Cathode Materials for Lithium Based Batteries Frontiers in Materials Science Seminar / Chemistryg g g g g y University at Buffalo ­ The State University of New York (SUNY) Abstract Batteries/SVO batteries. A case study highlighting the rich chemistry and electrochemistry of the Li/SVO system providing

410

Development of plasma cathode electron guns  

Microsoft Academic Search

The status of experimental research and ongoing development of plasma cathode electron guns in recent years is reviewed, including some novel upgrades and applications to various technological fields. The attractiveness of this kind of e-gun is due to its capability of creating high current, broad or focused beams, both in pulsed and steady-state modes of operation. An important characteristic of

Efim M. Oks; Peter M. Schanin

1999-01-01

411

Electrorefiner Liquid Cadmium Cathode Crucible Thermal Shock  

Microsoft Academic Search

A liquid cadmium cathode is used in an electrorefiner to remove plutonium and minor actinides from spent nuclear fuel by pyroprocessing. Liquid cadmium in a beryllia crucible, originally at 35°C, is lowered into 500°C salt electrolyte to begin reprocessing. Crucible cracking from thermal stress would release cadmium into the liquid salt causing electrorefiner failure. This study's purpose was to predict

C. W. Solbrig; DeeEarl Vaden

2006-01-01

412

Anode and cathode materials characterization for a microbial fuel cell in half cell configuration.  

PubMed

Microbial fuel cells (MFCs) are novel bioelectrochemical devices for spontaneous conversion of biomass into electricity through the metabolic activity of the bacteria. Microbial production of electricity may become an important source of bioenergy in future because MFCs offer the possibility of extracting electric current from a wide range of soluble or dissolved complex organic wastes and renewable biomass. However, the materials used in these devices are still not economic and researchers use different materials as cathode and anode in MFCs. This results in variable performance which is difficult to compare. We tested several commercially available materials for their suitability as anode in an acetate fed MFC. Besides, a novel non-platinized activated carbon (AC) based, gas porous air cathode was also tested. Both the anode and cathode were tested in a half cell configuration. Carbon cloth, graphite cloth and dynamically stable anode (DSA) served as ideal anode material with carbon cloth and graphite mesh reaching the open circuit voltage (OCV) of acetate oxidation (-500 mV vs. Ag/AgCl). The effect of increasing concentration of acetate on anode OCV was also investigated and results showed that on increasing the acetate concentration from 10 mM to 40 mM has no adverse impact on the anodic activity towards electrochemical oxidation of acetate. The AC cathode showed stable current (-1.2 mA/cm2) over a period of 100 days. PMID:21977673

Pant, Deepak; Van Bogaert, Gilbert; Porto-Carrero, Christof; Diels, Ludo; Vanbroekhoven, Karolien

2011-01-01

413

Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells.  

PubMed

H(2)-air polymer-electrolyte-membrane fuel cells are electrochemical power generators with potential vehicle propulsion applications. To help reduce their cost and encourage widespread use, research has focused on replacing the expensive Pt-based electrocatalysts in polymer-electrolyte-membrane fuel cells with a lower-cost alternative. Fe-based cathode catalysts are promising contenders, but their power density has been low compared with Pt-based cathodes, largely due to poor mass-transport properties. Here we report an iron-acetate/phenanthroline/zeolitic-imidazolate-framework-derived electrocatalyst with increased volumetric activity and enhanced mass-transport properties. The zeolitic-imidazolate-framework serves as a microporous host for phenanthroline and ferrous acetate to form a catalyst precursor that is subsequently heat treated. A cathode made with the best electrocatalyst from this work, tested in H(2)-O(2,) has a power density of 0.75 W cm(-2) at 0.6 V, a meaningful voltage for polymer-electrolyte-membrane fuel cells operation, comparable with that of a commercial Pt-based cathode tested under identical conditions. PMID:21811245

Proietti, Eric; Jaouen, Frédéric; Lefèvre, Michel; Larouche, Nicholas; Tian, Juan; Herranz, Juan; Dodelet, Jean-Pol

2011-01-01

414

A pulsed DC gas flow hollow cathode  

NASA Astrophysics Data System (ADS)

A new gas flow hollow cathode discharge source (GFHC) has been developed, characterized, and applied to thin film deposition by sputtering and low-temperature PECVD. Non-reactive and reactive sputtering processes were investigated using copper and aluminum targets, respectively. For the first time, pulsed DC power was applied to a GFHC in order to avoid arcing caused by electrode surface contamination, and to stabilize the discharge in general. The electrical characteristics of the source, the parameters of the remote plasma and its optical emission, were studied and compared to those of a DC powered GFHC. We determined the electrical characteristics of the plasma, including the temporal behavior of the current and voltage under various conditions of pressure and inert gas flow through the cathode. The transition from a glow discharge mode to the hollow cathode mode was studied in an effort to determine the operating range of the GFHC. A capacitive current was discovered at the beginning of the on-time. The properties of the remote plasma were investigated using averaged and time-resolved Langmuir probe and optical emission measurements. The distribution of the remote plasma density resembles the gas flow velocity distribution through the cathode. Plasma processes during off time (decaying plasma) and on-time (plasma reestablishment) were studied and compared to those in pulsed DC magnetron and high power inductively coupled glow discharges. The dependence of the deposition rate, resistivity and thickness distribution of copper films dependence on pulse parameters, power, inert gas flow through the cathode and pressure have been studied. The thin film thickness distribution is governed by the distribution of the gas flow velocity, which can be calculated using laminar flow gas dynamics. In a pulsed DC GFHC system, the inert gas flow through the cathode prevents the penetration of the reactive gas from the chamber into the cathode. A special reactive gas delivery source placed near the substrate was used to alumina deposition. The pulsed DC GFHC discharge is a reliable technology for sputter deposition of metallic and compound films. Scale-up of this technology and its application in industrial manufacturing is under way.

Paduraru, Cristian

415

Effect of cathodic hydrogenation on the mechanical properties of AISI 304 stainless steel nitrided by ion implantation, glow discharge and plasma immersion ion implantation  

NASA Astrophysics Data System (ADS)

Hydrogen embrittlement in austenitic stainless steels is restricted to the surface due to the low hydrogen diffusion in austenitic structures. The effect of three different nitriding processes: ion implantation (II), plasma immersion ion implantation (PI3) and glow discharge (GD), on the mechanical and structural properties of cathodically hydrogenated AISI 304 stainless steel were studied in the present work. Cathodic hydrogenation was made on untreated and nitrided samples. Surface microstructure after nitriding and hydrogenation was investigated by X-ray diffraction. Mechanical properties were measured by instrumented indentation. Surface crack formation and hardness decrease was observed in non-nitrided samples after cathodic hydrogenation. Hardness of nitrided samples decreases after hydrogen degassing but still has values higher than untreated samples. Comparative analysis of nitriding processes and working conditions indicated that glow discharge plasma nitriding process at 400 °C or 450 °C is the most adequate to avoid crack formation in steel surface after cathodic hydrogenation.

Foerster, C. E.; Souza, J. F. P.; Silva, C. A.; Ueda, M.; Kuromoto, N. K.; Serbena, F. C.; Silva, S. L. R.; Lepienski, C. M.

2007-04-01

416

Graphene Modified LiFePO4 Cathode Materials for High Power Lithium ion Batteries  

SciTech Connect

Graphene-modified LiFePO{sub 4} composite has been developed as a Li-ion battery cathode material with excellent high-rate capability and cycling stability. The composite was prepared with LiFePO{sub 4} nanoparticles and graphene oxide nanosheets by spray-drying and annealing processes. The LiFePO{sub 4} primary nanoparticles embedded in micro-sized spherical secondary particles were wrapped homogeneously and loosely with a graphene 3D network. Such a special nanostructure facilitated electron migration throughout the secondary particles, while the presence of abundant voids between the LiFePO{sub 4} nanoparticles and graphene sheets was beneficial for Li{sup +} diffusion. The composite cathode material could deliver a capacity of 70 mAh g{sup -1} at 60C discharge rate and showed a capacity decay rate of <15% when cycled under 10C charging and 20C discharging for 1000 times.

Zhou, X.; Wang, F.; Zhu, Y.; Liu, Z.

2011-01-24

417

Cathode depth sensing in CZT detectors  

E-print Network

Measuring the depth of interaction in thick Cadmium-Zinc-Telluride (CZT) detectors allows improved imaging and spectroscopy for hard X-ray imaging above 100 keV. The Energetic X-ray Imaging Survey Telescope (EXIST) will employ relatively thick (5 - 10 mm) CZT detectors, which are required to perform the broad energy-band sky survey. Interaction depth information is needed to correct events to the detector "focal plane" for correct imaging and can be used to improve the energy resolution of the detector at high energies by allowing event-based corrections for incomplete charge collection. Background rejection is also improved by allowing low energy events from the rear and sides of the detector to be rejected. We present experimental results of interaction depth sensing in a 5 mm thick pixellated Au-contact IMARAD CZT detector. The depth sensing was done by making simultaneous measurements of cathode and anode signals, where the interaction depth at a given energy is proportional to the ratio of cathode/anode signals. We demonstrate how a simple empirical formula describing the event distributions in the cathode/anode signal space can dramatically improve the energy resolution. We also estimate the energy and depth resolution of the detector as a function of the energy and the interaction depth. We also show a depth-sensing prototype system currently under development for EXIST in which cathode signals from 8, 16 or 32 crystals can be read-out by a small multi-channel ASIC board that is vertically edge-mounted on the cathode electrode along every second CZT crystal boundary. This allows CZT crystals to be tiled contiguously with minimum impact on throughput of incoming photons. The robust packaging is crucial in EXIST, which will employ very large area imaging CZT detector arrays.

J. Hong; E. C. Bellm; J. E. Grindlay; T. Narita

2003-10-16

418

Cathodic delaminations of poly(phenyl ether ether ketone) (PEEK) coatings overlaid on zinc phosphate-deposited steels  

SciTech Connect

The melt-crystallized poly(phenyl) ether ether ketone (PEEK) polymer was overlaid on crystalline zinc phosphate (Zn [center dot] Ph) conversion coating-deposited and nondeposited cold-rolled steels at 400 C in air or in N[sub 2] environments. The ability of these coatings systems to protect the steel against corrosion was evaluated from the rate of cathodic delamination of the coating layer from the steel. Because the cathodic reaction, H[sub 2]O + 1/20[sub 2] + 2e[sup [minus

Sugama, T.; Carciello, N.R. (Brookhaven National Lab., Upton, NY (United States). Dept. of Applied Science)

1993-12-10

419

Fokker-Planck . . . Diffusion . . .  

E-print Network

Fokker-Planck . . . Diffusion . . . Diffusion- . . . Application: . . . Summary and . . . First #12;Fokker-Planck . . . Diffusion . . . Diffusion- . . . Application: . . . Summary and . . . Topics: 1. Fokker-Planck transport equation 2. Diffusion approximation 3. Diffusion-convection transport

420

Mesoporous ?-MnO 2\\/Pd catalyst air electrode for rechargeable lithium–air battery  

Microsoft Academic Search

Rechargeable lithium–air battery is studied using Pd\\/mesoporous ?-MnO2 air composite electrode. In the present work, we have studied the preparation and electrochemical performance of ordered mesoporous ?-MnO2 as a cathode catalyst for rechargeable Li–air batteries. ?-MnO2 was prepared by reduction of KMnO4 solution in acidic aqueous solution followed by successive proton and alkali-ion exchange method. ?-MnO2 with high surface area

Arjun Kumar Thapa; Tatsumi Ishihara

2011-01-01

421

Emission current control system for multiple hollow cathode devices  

NASA Technical Reports Server (NTRS)

An emission current control system for balancing the individual emission currents from an array of hollow cathodes has current sensors for determining the current drawn by each cathode from a power supply. Each current sensor has an output signal which has a magnitude proportional to the current. The current sensor output signals are averaged, the average value so obtained being applied to a respective controller for controlling the flow of an ion source material through each cathode. Also applied to each controller are the respective sensor output signals for each cathode and a common reference signal. The flow of source material through each hollow cathode is thereby made proportional to the current drawn by that cathode, the average current drawn by all of the cathodes, and the reference signal. Thus, the emission current of each cathode is controlled such that each is made substantially equal to the emission current of each of the other cathodes. When utilized as a component of a multiple hollow cathode ion propulsion motor, the emission current control system of the invention provides for balancing the thrust of the motor about the thrust axis and also for preventing premature failure of a hollow cathode source due to operation above a maximum rated emission current.

Beattie, John R. (Inventor); Hancock, Donald J. (Inventor)

1988-01-01

422

Heat transfer, diffusion, and evaporation  

NASA Technical Reports Server (NTRS)

Although it has long been known that the differential equations of the heat-transfer and diffusion processes are identical, application to technical problems has only recently been made. In 1916 it was shown that the speed of oxidation of the carbon in iron ore depends upon the speed with which the oxygen of the combustion air diffuses through the core of gas surrounding the carbon surface. The identity previously referred to was then used to calculate the amount of oxygen diffusing to the carbon surface on the basis of the heat transfer between the gas stream and the carbon surface. Then in 1921, H. Thoma reversed that procedure; he used diffusion experiments to determine heat-transfer coefficients. Recently Lohrisch has extended this work by experiment. A technically very important application of the identity of heat transfer and diffusion is that of the cooling tower, since in this case both processes occur simultaneously.

Nusselt, Wilhelm

1954-01-01

423

Diagnostics of cathode material loss in cutting plasma torch  

NASA Astrophysics Data System (ADS)

A cutting plasma torch was observed in several ways by a high-speed camera with a focus on the cathode area. In the first experiment, the plasma arc between the nozzle tip and anode was recorded in a series of duty cycles ranging from new unworn cathodes to cathode failure due to wear and material loss. In the second experiment, we used a specially modified nozzle to observe the inside area between the cathode and the nozzle exit through a fused silica window. Finally, using tilted view, we observed a pool of molten hafnium at the cathode tip during the plasma torch operation. The process of cathode material melting, droplet formation, their expulsion and rate of cathode material loss was examined.

Gruber, J.; Šonský, J.; Hlína, J.

2014-07-01

424

Cathode R&D for Future Light Sources  

SciTech Connect

This paper reviews the requirements and current status of cathodes for accelerator applications, and proposes a research and development plan for advancing cathode technology. Accelerator cathodes need to have long operational lifetimes and produce electron beams with a very low emittance. The two principal emission processes to be considered are thermionic and photoemission with the photocathodes being further subdivided into metal and semi-conductors. Field emission cathodes are not included in this analysis. The thermal emittance is derived and the formulas used to compare the various cathode materials. To date, there is no cathode which provides all the requirements needed for the proposed future light sources. Therefore a three part research plan is described to develop cathodes for these future light source applications.

Dowell, D.H.; /SLAC; Bazarov, I.; Dunham, B.; /Cornell U., CLASSE; Harkay, K.; /Argonne; Hernandez-Garcia; /Jefferson Lab; Legg, R.; /Wisconsin U., SRC; Padmore, H.; /LBL, Berkeley; Rao, T.; Smedley, J.; /Brookhaven; Wan, W.; /LBL, Berkeley

2010-05-26

425

Cathode R&D for future light sources  

SciTech Connect

This paper reviews the requirements and current status of cathodes for accelerator applications, and proposes a research and development plan for advancing cathode technology. Accelerator cathodes need to have long operational lifetimes and produce electron beams with a very low emittance. The two principal emission processes to be considered are thermionic and photoemission with the photocathodes being further subdivided into metal and semi-conductors. Field emission cathodes are not included in this analysis. The thermal emittance is derived and the formulas used to compare the various cathode materials. To date, there is no cathode which provides all the requirements needed for the proposed future light sources. Therefore a three part research plan is described to develop cathodes for these future light source applications.

D.H. Dowell, I. Bazarov, B. Dunham, K. Harkay, C. Hernandez-Garcia, R. Legg, H. Padmore, T. Rao, J. Smedley, W. Wan

2010-10-01

426

Virtual cathode microwave generator having annular anode slit  

DOEpatents

A microwave generator is provided for generating microwaves substantially from virtual cathode oscillation. Electrons are emitted from a cathode and accelerated to an anode which is spaced apart from the cathode. The anode has an annular slit therethrough effective to form the virtual cathode. The anode is at least one range thickness relative to electrons reflecting from the virtual cathode. A magnet is provided to produce an optimum magnetic field having the field strength effective to form an annular beam from the emitted electrons in substantial alignment with the annular anode slit. The magnetic field, however, does permit the reflected electrons to axially diverge from the annular beam. The reflected electrons are absorbed by the anode in returning to the real cathode, such that substantially no reflexing electrons occur. The resulting microwaves are produced with a single dominant mode and are substantially monochromatic relative to conventional virtual cathode microwave generators.

Kwan, Thomas J. T. (Los Alamos, NM); Snell, Charles M. (Los Alamos, NM)

1988-01-01

427

Expansion of the cathode spot and generation of shock waves in the plasma of a volume discharge in atmospheric-pressure helium  

SciTech Connect

The expansion of the cathode spot and the generation of shock waves during the formation and development of a pulsed volume discharge in atmospheric-pressure helium were studied by analyzing the emission spectra of the cathode plasma and the spatiotemporal behavior of the plasma glow. The transition of a diffuse volume discharge in a centimeter-long gap into a high-current diffuse mode when the gas pressure increased from 1 to 5 atm and the applied voltage rose from the statistical breakdown voltage to a 100% overvoltage was investigated. Analytical expressions for the radius of the cathode spot and its expansion velocity obtained in the framework of a spherically symmetric model agree satisfactorily with the experimental data.

Omarov, O. A.; Kurbanismailov, V. S.; Arslanbekov, M. A.; Gadzhiev, M. Kh.; Ragimkhanov, G. B.; Al-Shatravi, Ali J. G. [Dagestan State University (Russian Federation)

2012-01-15

428

Manganese oxide cathodes for rechargeable batteries  

NASA Astrophysics Data System (ADS)

Manganese oxides are considered as promising cathodes for rechargeable batteries due to their low cost and low toxicity as well as the abundant natural resources. In this dissertation, manganese oxides have been investigated as cathodes for both rechargeable lithium and alkaline batteries. Nanostructured lithium manganese oxides designed for rechargeable lithium cells have been synthesized by reducing lithium permanganate with methanol or hydrogen in various solvents followed by firing at moderate temperatures. The samples have been characterized by wet-chemical analyses, thermal methods, spectroscopic methods, and electron microscopy. It has been found that chemical residues in the oxides such as carboxylates and hydroxyl groups, which could be controlled by varying the reaction medium, reducing agents, and additives, make a significant influence on the electrochemical properties. The Li/Mn ratio in the material has also been found to be a critical factor in determining the rechargeability of the cathodes. The optimized samples exhibit a high capacity of close to 300 mAh/g with good cyclability and charge efficiency. The high capacity with a lower discharge voltage may make these nanostructured oxides particularly attractive for lithium polymer batteries. The research on the manganese oxide cathodes for alkaline batteries is focused on an analysis of the reaction products generated during the charge/discharge processes or by some designed chemical reactions mimicking the electrochemical processes. The factors influencing the formation of Mn3O4 in the two-electron redox process of delta-MnO2 have been studied with linear sweep voltammetry combined with X-ray diffraction. The presence of bismuth, the discharge rate, and the microstructure of the electrodes are found to affect the formation of Mn3O4, which is known to be electrochemically inactive. A faster voltage sweep and a more intimate mixing of the manganese oxide and carbon in the cathode are found to suppress the formation of Mn3O4. Bismuth has also been found to be beneficial in the one-electron process of gamma-MnO 2 when incorporated into the cathode. The results of a series of chemical reactions reveal that bismuth is blocking some reaction paths leading to the unwanted birnessite or Mn3O4. Barium is also found to play a similar role, but it is less effective than bismuth for the same amount of additive. Optimization of the additives has the potential to make the rechargeable alkaline cells based on manganese oxides to successfully compete with other rechargeable systems due to their low cost, environmental friendliness, and excellent safety features.

Im, Dongmin

429

Generation and Control of Electrolyte Cathode Atmospheric Glow Discharges using Miniature Gas Flow  

NASA Astrophysics Data System (ADS)

Stable electrolyte cathode atmospheric dc glow microdischarges were generated by using a miniature helium gas flow from a nozzle electrode in air. We developed two schemes to control the temporal evolution of the discharge and the interaction between the discharge column and the ambient air. The vaporization of electrolyte solutions takes place and affects the discharge characteristics. It takes time from the start of the discharge. Therefore the discharge was controlled by applying pulse modulated dc voltages. If the voltage was dropped down to zero before the vaporization, the gas discharge developed without the ionization of the components of solution. The helium gas discharge without air developed when the nozzle electrode was placed in a glass capillary. This was confirmed by examining the change in pH of the solution, which usually decreased owing to the generation of nitrogen oxides in the discharge in air.

Shirai, Naoki; Nakazawa, Masato; Ibuka, Shinji; Ishii, Shozo

430

Preparation of a fouling-resistant sustainable cathode for a single-chambered microbial fuel cell.  

PubMed

Two different binder materials of varying water affinity, viz. poly vinyl alcohol (PVA) and poly-tetrafluoroethylene (PTFE), and biocide vanillin were tested for cathode fouling in a single chamber air-cathode microbial fuel cell (MFC) constructed with a low-cost baked clayware cylinder and operated under fed-batch mode. PVA and PTFE loadings of 0.5 mg/cm(2) were used for MFC-1 and MFC-2, respectively as a binder; and a 1:1 mixture of PVA + PTFE was used as binder in MFC-3 with same binder loading. Vanillin was mixed with PVA and also applied at a loading of 0.5 mg/cm(2) for MFC-4. Results showed organic matter removal efficiencies around 90% for all MFCs both before and after fouling. Coulombic efficiency was, however, found to decrease 50% after fouling in the MFC-3 coated with both PVA and PTFE. After 5 weeks of operation, due to fouling 56, 40 and 69% reduction in power densities were observed in MFC-1, MFC-2 and MFC-3, respectively. In the MFC-4 having PVA and vanillin, the least fouling was observed. A consistent volumetric power of 233 mW/m(3) was observed for MFC-4, thus potentially offering a suitable solution to alleviate the problem of fouling in the making of single-chamber air-cathode MFCs. PMID:24552738

Chatterjee, Pritha; Ghangrekar, M M

2014-01-01

431

Review of HxPyOz-Catalyzed H + OH Recombination in Scramjet Nozzle Expansions; and Possible Phosphoric Acid Enhancement of Scramjet Flameholding, from Extinction of H3PO4 + H2 - Air Counterflow Diffusion Flames  

NASA Technical Reports Server (NTRS)

Recent detailed articles by Twarowski indicate that small quantities of phosphorus oxides and acids in the fuel-rich combustion products of H2 + phosphine (PH3) + air should significantly catalyze H, OH and O recombination kinetics during high-speed nozzle expansions -- to reform H2O, release heat, and approach equilibrium more rapidly and closely than uncatalyzed kinetics. This paper is an initial feasibility study to determine (a) if addition of phosphoric acid vapor (H3PO4) to a H2 fuel jet -- which is much safer than using PH3 -- will allow combustion in a high-speed scramjet engine test without adverse effects on localized flameholding, and (b) if phosphorus-containing exhaust emissions are environmentally acceptable. A well-characterized axisymmetric straight-tube opposed jet burner (OJB) tool is used to evaluate H3PO4 addition effects on the air velocity extinction limit (flame strength) of a H2 versus air counterflow diffusion flame. Addition of nitric oxide (NO), also believed to promote catalytic H-atom recombination, was evaluated for comparison. Two to five mass percent H3PO4 in the H2 jet increased flame strength 4.2%, whereas airside addition decreased it 1%. Adding 5% NO to the H2 caused a 2% decrease. Products of H-atom attack on H3PO4 produced an intense green chemiluminescence near the stagnation point. The resultant exothermic production of phosphorus oxides and acids, with accelerated H-atom recombination, released sufficient heat near the stagnation point to increase flame strength. In conclusion, the addition of H3PO4 vapor (or more reactive P sources) to hydrogen in scramjet engine tests may positively affect flameholding stability in the combustor and thrust production during supersonic expansion -- a possible dual benefit with system design / performance implications. Finally, a preliminary assessment of possible environmental effects indicates that scramjet exhaust emissions should consist of phosphoric acid aerosol, with gradual conversion to phosphate aerosol. This is compared to various natural abundances and sources.

Pellett, Gerald

2005-01-01

432

Membrane-less cloth cathode assembly (CCA) for scalable microbial fuel cells.  

PubMed

One of the main challenges for scaling up microbial fuel cell (MFC) technologies is developing low-cost cathode architectures that can generate high power output. This study developed a simple method to convert non-conductive material (canvas cloth) into an electrically conductive and catalytically active cloth cathode assembly (CCA) in one step. The membrane-less CCA was simply constructed by coating the cloth with conductive paint (nickel-based or graphite-based) and non-precious metal catalyst (MnO(2)). Under the fed-batch mode, the tubular air-chamber MFCs equipped with Ni-CCA and graphite-CCA generated the maximum power densities of 86.03 and 24.67 mW m(-2) (normalized to the projected cathode surface area), or 9.87 and 2.83 W m(-3) (normalized to the reactor liquid volume), respectively. The higher power output of Ni-CCA-MFC was associated with the lower volume resistivity of Ni-CCA (1.35 x 10(-2)Omega cm) than that of graphite-CCA (225 x 10(-2)Omega cm). At an external resistance of 100 Omega, Ni-CCA-MFC and graphite-CCA-MFC removed approximately 95% COD in brewery wastewater within 13 and 18d, and achieved coulombic efficiencies of 30.2% and 19.5%, respectively. The accumulated net water loss through the cloth by electro-osmotic drag exhibited a linear correlation (R(2)=0.999) with produced coulombs. With a comparable power production, such CCAs only cost less than 5% of the previously reported membrane cathode assembly. The new cathode configuration here is a mechanically durable, economical system for MFC scalability. PMID:19556120

Zhuang, Li; Zhou, Shungui; Wang, Yueqiang; Liu, Chengshuai; Geng, Shu

2009-08-15

433

Molecular diffusion effects in LES of a piloted methaneair flame Konstantin A. Kemenov  

E-print Network

Molecular diffusion effects in LES of a piloted methane­air flame Konstantin A. Kemenov , Stephen diffusion effects in LES of a piloted methane­air (Sandia D) flame are investigated on a series of grids diffusivity in effecting spatial transport is studied by drawing a comparison with the turbulent diffusivity

434

Morphologically architectured spray pyrolyzed lanthanum ferrite-based cathodes-A phenomenal enhancement in solid oxide fuel cell performance  

NASA Astrophysics Data System (ADS)

Nanocrystalline single phase La1-xSrxCo1-yFeyO3-? [LSCF] (0 < x ? 0.5, y = 0.2, 0.8) based cathodes (crystallite size 30-50 nm) are synthesized by two fluid spray-pyrolysis (SP) for solid oxide fuel cell (SOFC) application. The particulate sizes of the synthesized cathodes are found to be in the range of 100-200 nm. Particulate morphology of highest conducting cathode (?1500 S cm-1) is tailored using homomolecular seeding agent of precalcined pyrolyzed ashes. Interfacial polarizations of the such SP synthesized screen printed cathodes onto gadolinium doped ceria (CGO) based electrolyte are found to be much lower (0.032-0.16 ? cm2 at 800 °C-500 °C) with highest exchange current density (?722 mA cm-2 at 800 °C) for oxygen reduction reaction. Enhanced current density of 4.0 A cm-2 (0.7 V, 800 °C) is obtained for SOFC button cells using optimized LSCF cathode with hydrogen as fuel and air as oxidant. LSCF cathodes synthesized by spray pyrolysis using homomolecular seeding exhibit interconnected mesoporosity having primary nano-particulates embedded within. Endurance test of button cells till 500 h results low degradation viz. 3.8% and 8.9% 1000 h-1 with electronic loads of 0.5 A cm-2 and 1.0 A cm-2 respectively. High performances of such cells are clinically correlated with SP processing conditions and particulate morphology of cathode powders.

Mukhopadhyay, Jayanta; Basu, Rajendra Nath

2014-04-01