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Final Report: Wetted Cathodes for Low-Temperature Aluminum Smelting

Description: A low-temperature aluminum smelting process being developed differs from the Hall-Heroult process in several significant ways. The low-temperature process employs a more acidic electrolyte than cryolite, an alumina slurry, oxygen-generating metal anodes, and vertically suspended electrodes. Wetted and drained vertical cathodes are crucial to the new process. Such cathodes represent a significant portion of the capital costs projected for the new technology. Athough studies exist of wetted cathode technology with Hall-Heoult cells, the differences make such a study desirable with the new process. This project is such a study. In Phase 1, titanium diboride, zirconium diboride and composites of these with other materials were tested using a statistically useful test matrix. The materials were consolidated both by hot pressing and by a new method, plasma pressure compaction (P2C�). The materials were subject to controlled electrolysis tests under conditions of the low-temperature smelting process. Post-electrolysis characterizations included quantitative atomic analyses and electron microscopic examinations. These methods allowed evaluating the relative merits of the materials, and the mechanisms of their corrosion. Also, a few tests were performed to determine whether oxygen and carbon dioxide bathing vertically suspended cathodes exhibited different current efficiencies. In Phase 2, additional composite materials were fabricated with P2C�, electrolysis tested, and subsequently characterized. The statistical test matrix was not used in this Phase. However, the materials were tested with electrolysis lasting both five and twenty hours. The project demonstrated that good current efficiencies are obtained with the new process at this scale. All of the materials tested except for aluminum infiltrated aluminum nitride wetted well and gave comparable electrolysis voltages. Both hot pressing and P2C� produce grain structures in the consolidated materials. Grain loss to the product metal is the dominant corrosion mechanism of these materials as cathodes. Grain loss is more of a problem with the composites ...
Date: September 30, 2002
Creator: Brown, Craig W.
Partner: UNT Libraries Government Documents Department

Characterization of SEI layers on LiMn2O4 cathodes with in-situ spectroscopic ellipsometry

Description: In situ spectroscopic ellipsometry was employed to study the initial stage of SEI layer formation on thin-film LiMn{sub 2}O{sub 4} electrodes. It was found that the SEI layer formed immediately upon exposure of the electrode to EC/DMC (1:1 by vol) 1.0 M LiPF{sub 6} electrolyte. The SEI layer thickness then increased in proportion to a logarithmic function of elapsed time. In comparison, the SEI layer thickness on a cycled electrode increased in proportion to a linear function of the number of cycles.
Date: August 30, 2004
Creator: Lei, Jinglei; Li, Lingjie; Kostecki, Robert; Muller, Rolf & McLarnon, Frank
Partner: UNT Libraries Government Documents Department

Approaches to rid cathodic arc plasmas of macro- andnanoparticles: A review

Description: A major obstacle for the broad application of cathodic arc plasma deposition is the presence of micro- and nanoparticles in the plasma, also often referred to as 'macroparticles'. This paper reviews the formation of macroparticles at cathode spots, their interaction with the arc plasma and substrate, and macroparticle separation and removal from the plasma by various filtering methods. Nineteen variants of filters are discussed, including Aksenov's classic 90{sup o}-duct filter, filters of open architecture, and the concept of stroboscopic filtering.
Date: June 1, 1999
Creator: Anders, Andre
Partner: UNT Libraries Government Documents Department

Simulating Nonuniform Properties in Polymer-Electrolyte FuelCells

Description: In this transaction, results from mathematical, pseudo 2-D simulations are shown for four different thickness distributions of both the membrane and cathode catalyst layer. The results and subsequent analysis clearly demonstrate that the position along the gas channel is more important than the local thickness variations, especially for the membrane.
Date: July 1, 2006
Creator: Weber, A.Z. & Newman, J.
Partner: UNT Libraries Government Documents Department

Particle-In-Cell/Monte Carlo Simulation of Ion Back Bombardment in Photoinjectors

Description: In this paper, we report on studies of ion back bombardment in high average current dc and rf photoinjectors using a particle-in-cell/Monte Carlo method. Using H{sub 2} ion as an example, we observed that the ion density and energy deposition on the photocathode in rf guns are order of magnitude lower than that in a dc gun. A higher rf frequency helps mitigate the ion back bombardment of the cathode in rf guns.
Date: March 2, 2009
Creator: Qiang, Ji; Corlett, John & Staples, John
Partner: UNT Libraries Government Documents Department

Operational characteristics and analysis of the immersed-Bz diode on RITS-3.

Description: The immersed-B{sub z} diode is being developed as a high-brightness, flash x-ray radiography source. This diode is a foil-less electron-beam diode with a long, thin, needle-like cathode inserted into the bore of a solenoid. The solenoidal magnetic field guides the electron beam emitted from the cathode to the anode while maintaining a small beam radius. The electron beam strikes a thin, high-atomic-number anode and produces bremsstrahlung. We report on an extensive series of experiments where an immersed-B{sub z} diode was fielded on the RITS-3 pulsed power accelerator, a 3-cell inductive voltage generator that produced peak voltages between 4 and 5 MV, {approx}140 kA of total current, and power pulse widths of {approx}50 ns. The diode is a high impedance device that, for these parameters, nominally conducts {approx}30 kA of electron beam current. Diode operating characteristics are presented and two broadly characterized operating regimes are identified: a nominal operating regime where the total diode current is characterized as classically bipolar and an anomalous impedance collapse regime where the total diode current is in excess of the bipolar limit and up to the full accelerator current. The operating regimes are approximately separated by cathode diameters greater than {approx}3 mm for the nominal regime and less than {approx} 3 mm for the anomalous impedance collapse regime. This report represents a compilation of data taken on RITS-3. Results from key parameter variations are presented in the main body of the report and include cathode diameter, anode-cathode gap, and anode material. Results from supporting parameter variations are presented in the appendices and include magnetic field strength, prepulse, pressure and accelerator variations.
Date: February 1, 2006
Creator: Bruner, Nichelle "Nicki"; Oliver, Bryan Velten; Portillo, Salvador; Puetz, Elizabeth A.; Johnston, Mark D.; Welch, Dale Robert et al.
Partner: UNT Libraries Government Documents Department

Pencil-like mm-size electron beams produced with linear inductive voltage adders (LIVA)

Description: This paper presents design, analysis, and first results of the high brightness electron beam experiments currently under investigation at Sandia. Anticipated beam parameters are: energy 12 MeV, current 35-40 kA, rms radius 0.5 mm, pulse duration 40 ns FWHM. The accelerator is SABRE, a pulsed LIVA modified to higher impedance, and the electron source is a magnetically immersed foilless electron diode. 20 to 30 Tesla solenoidal magnets are required to insulate the diode and contain the beam to its extremely small sized (1 mm) envelope. These experiments are designed to push the technology to produce the highest possible electron current in a submillimeter radius beam. Design, numercial simulations, and first experimental results are presented.
Date: September 1, 1996
Creator: Mazarakis, M.G.; Poukey, J.W. & Rovang, D.C.
Partner: UNT Libraries Government Documents Department

Lithium-oxide-stabilized alpha manganese dioxide for rechargeable lithium batteries

Description: Objective was to increase the reversible cycling capacity of anhydrous {alpha}-MnO{sub 2} by stabilizing its structure. We have synthesized various {alpha}-MnO{sub 2} materials and modified their structures via lithia doping in order to determine what properties are important for controlling cycling performance. A set of new stabilized {alpha}-[xLi{sub 2}O]{center_dot}MnO{sub 2} (x<0.2) cathode materials was synthesized, structurally characterized, and electrochemically evaluated.
Date: June 1996
Creator: Johnson, C. S.; Dees, D. W.; Mansuetto, M. F.; Thackeray, M. M.; Vissers, D. R.; Argyriou, D. et al.
Partner: UNT Libraries Government Documents Department

Field-emission cathode micro-electro-mechanical system technology for sensors, diagnostics, and microelectronics

Description: We have investigated field-emission devices for applications in sensors, diagnostics, and micro-electronics. Field-emission devices micromachined from silicon and molybdenum have been fabricated and tested. Experimental results have shown that the presence of nitrogen gas molecules for pressures up to 1 mtorr has only a moderate impact on device emission performance, and has no long term effect on device operation. These results demonstrate that field-emission cathodes can potentially be used in sensors applications where gas ionization by election impact is desirable, or other applications in which the field-emission device is exposed to less than ideal vacuum conditions.
Date: March 30, 1998
Creator: Morse, J.D.; Koo, J.C.; Graff, R.T.; Jankowski, A.F. & Hayes, J.P.
Partner: UNT Libraries Government Documents Department

IGT Stack No. 6 (SDG{ampersand}E-1) Test Plan and Component Specification Document: Topical report, March 1996

Description: The purpose of Stack-6 (SDG{ampersand}E-1) is to scale up and demonstrate the long term performance and endurance characteristics of the IMHEX stack design and the Generation No. 2 cell components (improved pore matching electrodes) in a 20 cell subscale stack test.
Date: December 31, 1997
Partner: UNT Libraries Government Documents Department


Description: Nickel hydroxides have been used as the active material in the positive electrodes of several alkaline batteries for over a century. These materials continue to attract a lot of attention because of the commercial importance of nickel-cadmium and nickel-metal hydride batteries. This review gives a brief overview of the structure of nickel hydroxide battery electrodes and a more detailed review of the solid state chemistry and electrochemistry of the electrode materials. Emphasis is on work done since 1989.
Date: November 1997
Creator: McBreen, J.
Partner: UNT Libraries Government Documents Department

Flash X-Ray Injector Study

Description: The study described in this report1 models the FXR injector from the cathode to the exit of the injector. The calculations are compared to actual experimental measurements, table 1. In these measurements the anode voltage was varied by changing the Marks-Bank charging voltage. The anode-cathode spacing was varied by adjusting the location of the cathode in hopes of finding an island of minimum emittance (none found). The bucking coil current was set for zero field on the cathode. In these measurements, a pepper-pot mask was inserted into FXR at beam bug 135 and viewed downstream via a wiggle probe diagnostic at cell gap J21, figure 1. The observed expansion of the beamlets passing through the mask of known geometric layout and hole size allow a calculation of the phase space beam properties.
Date: March 26, 2004
Creator: Paul, A C
Partner: UNT Libraries Government Documents Department

Effects of Membrane- and Catalyst-layer-thickness Nonuniformitiesin Polymer-electrolyte Fuel Cells

Description: In this paper, results from mathematical, pseudo 2-D simulations are shown for four different along-the-channel thickness distributions of both the membrane and cathode catalyst layer. The results and subsequent analysis clearly demonstrate that for the membrane thickness distributions, cell performance is affected a few percent under low relative-humidity conditions and that the position along the gas channel is more important than the local thickness variations. However, for the catalyst-layer thickness distributions, global performance is not impacted, although for saturated conditions there is a large variability in the local temperature and performance depending on the thickness.
Date: September 1, 2006
Creator: Weber, Adam Z. & Newman, John
Partner: UNT Libraries Government Documents Department

Material and time dependence of the voltage noise generated bycathodic vacuum arcs

Description: The high frequency fluctuations of the burning voltage of cathodic vacuum arcs have been investigated in order to extract information on cathode processes. Eight cathode materials (W, Ta, Hf, Ti, Ni, Au, Sn, Bi) were selected covering a wide range of cohesive energy. The voltage noise was recorded using both a broad-band voltage divider and an attenuator connected to a fast oscilloscope (limits 1 GHz analog and 5 GS/s digital). Fast Fourier transform revealed a power spectrum that is linear in log-log presentation, with a slope of 1/f{sup 2}, where f is the frequency (brown noise). The amplitude of the spectral power of the voltage noise was found to scale with the cohesive energy, in agreement with earlier measurements at lower resolution. These basic results do not depend on the time after arc initiation. However, lower arc current in the beginning of the pulse shows greater voltage noise, suggesting an inverse relation between the noise amplitude and number of emission sites (cathode spot fragments).
Date: July 15, 2005
Creator: Rosen, Johanna & Anders, Andre
Partner: UNT Libraries Government Documents Department


Description: Thermal emittance is a very important characteristic of cathodes. A carefully designed method of measuring the thermal emittance of secondary emission from diamond is presented. Comparison of possible schemes is carried out by simulation, and the most accessible and accurate method and values are chosen. Systematic errors can be controlled and maintained at small values, and are carefully evaluated. Aberration and limitations of all equipment are taken into account.
Date: June 25, 2007
Creator: WU,Q.; BEN-ZVI, I.; BURRILL, A.; CHANG, X.; KAYRAN, D.; RAO, T. et al.
Partner: UNT Libraries Government Documents Department

Synopsis of Cathode #4 Activation

Description: The purpose of this report is to describe the activation of the fourth cathode installed in the DARHT-II Injector. Appendices have been used so that an extensive amount of data could be included without danger of obscuring important information contained in the body of the report. The cathode was a 612 M type cathode purchased from Spectra-Mat. Section II describes the handling and installation of the cathode. Section III is a narrative of the activation based on information located in the Control Room Log Book supplemented with time plots of pertinent operating parameters. Activation of the cathode was performed in accordance with the procedure listed in Appendix A. The following sections provide more details on the total pressure and constituent partial pressures in the vacuum vessel, cathode heater power/filament current, and cathode temperature.
Date: May 26, 2006
Creator: Kwan, Joe; Ekdahl, C.; Harrison, J.; Kwan, J.; Leitner, M.; McCruistian, T. et al.
Partner: UNT Libraries Government Documents Department