Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session RR3: Discharges in Liquids II |
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Chair: David Staack, Texas A&M University Room: 2b |
Thursday, October 13, 2016 11:00AM - 11:15AM |
RR3.00001: Discharge processes in a laser ablation-induced cavitation bubble K. Sasaki, Y. Takahashi The cavitation bubble is not a static bubble but has the dynamics of expansion, shrinkage, and collapse. In this work, we tried to produce electrical discharge in a cavitation bubble which was induced by laser ablation of a titanium target in water. We placed a needle electrode at a distance of 0.5 mm from the gas-liquid boundary of the cavitation bubble at the maximum size. The electrode was connected to a high-voltage pulsed power supply. The temporal variation of the bubble size was measured by shadowgraph imaging using a high-speed camera. The high-speed camera also captured the optical emission image from the discharge. At 50 $\mu$s after applying a pulsed high voltage, we observed the formation of a swelling from the cavitation bubble. The swelling was lengthened toward the needle electrode. We observed the electrical discharge between the needle electrode and the target when they are connected by the cavitation bubble and its swelling. It is noted that both the directions of the swelling lengthening and the discharge channel are perpendicular to the gas-liquid boundary of the cavitation bubble, suggesting that the electric field is perpendicular to the gas-liquid boundary because of the existence of movable electrical charges. [Preview Abstract] |
Thursday, October 13, 2016 11:15AM - 11:30AM |
RR3.00002: Preparation of silver-carbon nanotubes composites with plasma electrochemistry Oliver Hoefft, Lara Lohmann, Mark Olschewski, Frank Endres Plasma electrochemistry is a powerful tool to generate free nanoparticles in aqueous solutions and especially in ionic liquids (ILs) [1,2]. Due to their very low vapour pressure, ionic liquids can be employed under vacuum conditions as fluid substrates or solvents. Thus, ionic liquids are well suitable electrolytes for plasma electrochemical processes delivering stable and homogeneous plasmas. We have shown that free copper and germanium nanoparticles can be obtained in ILs by applying a plasma as a mechanically contact-free electrode [2]. Here we present our results using an argon plasma for the electrochemical synthesis of silver on pure and pre-treated multiwall carbon nanotubes (MWCNTs) in 1-ethyl-3-methylimidazolium dicyanamide. For the pre-treatment of the MWCNTS we have used a dielectric barrier discharge plasma (DBD) at atmospheric pressure. For the untreated MWCNTs we have found a formation of free silver nanoparticles between, on and in the vicinity of the carbon nanotubes. In case of the plasma treated MWCNTs a silver-carbon nanotubes composite is formed. Thus, the treatment of the MWCNTs obviously has a great influence on the deposit. Therefore we additionally have investigated the influence of the DBD on the chemical composition of the MWCNTs surface with X-Ray Photoelectron Spectroscopy. [1] R. Akolkar and R. M. Sankaran, J. Vac. Sci. Technol. A 2013, 31, 050811 [2] N. Spitczok v. Brisinski, O. H\"{o}fft and Frank Endres, J. Mol. Liquids 2014, 192, 59 [Preview Abstract] |
Thursday, October 13, 2016 11:30AM - 11:45AM |
RR3.00003: Underwater electrical discharge in plate to plate configuration Vitaliy Stelmashuk Two main configurations of high voltage electrodes submersed in water have been used for an electrical discharge generation: pin to pin and pin to plate. An electrical breakdown between plate electrodes is generally difficult to reproduce, because there is a uniform and weak electric field. One major advantage of using plate electrodes is their greater ``wear hardness'' to high-energy discharges. The plate electrodes can withstand extremely high energy deposition at which the pin electrode is quickly destroyed. The electrical discharge between plate electrodes can be initiated by creating an inhomogeneity in the electrical field. Two methods of discharge initiation between plate electrodes are proposed for this aim: 1) focusing of a shock wave in the interelectrode region; 2) a bubble injection into the electrode gap. The shock wave creates favourable conditions for the electrical breakdown between the two plate electrodes: it causes that numerous microbubbles of dissolved air start to grow and serve as locations for streamer initiation. In the second method the gas bubble is injected from the one of the electrodes, which has a gas inlet hole on the lateral face for this purpose. A ``volcano'' like morphology of positive streamers are observed in the experiments with weak electric field. [Preview Abstract] |
Thursday, October 13, 2016 11:45AM - 12:00PM |
RR3.00004: Development and Applications of discharges generated in liquids with short high voltage pulses Juergen Kolb, Camelia Miron, Angela Kruth, Michal Balcerak, Michal Bonislawski, Marcin Holub Discharges that are generated within a liquid have been of scientific interest for more than a century. The possibility for a breakdown development that is not mediated by an initial gaseous phase is still disputed. In this respect are especially discharges that are instigated with short high voltage pulses calling for attention. Associated with this specific excitation scheme is a change in plasma development, plasma parameters and reaction mechanisms in the liquid. We have compared discharges in a point-to-plane geometry that were generated with 50-us or 10-ns high voltage pulses. Time-resolved shadowgraphy and spectroscopy were performed to evaluate discharge structures, plasma parameter and reactive species that were formed in distilled water or ethanol. Different propagation modes, with velocities of 6.7 km/s for tree-like streamers and only 50 m/s for bush-like streamers, were observed. Optical emission spectroscopy has shown the formation of molecular bands of nitrogen, as well as strongly broadened atomic hydrogen and oxygen, which are likely to be responsible for the observed surface modifications of polymers. With nanosecond high voltage pulses we found an increase of unsaturated bondings for polyimide surfaces that were exposed in the discharge volume. [Preview Abstract] |
Thursday, October 13, 2016 12:00PM - 12:15PM |
RR3.00005: Computational investigations of streamers in a single bubble suspended in distilled water under atmospheric pressure conditions Ashish Sharma, Dmitry Levko, Laxminarayan Raja We present a computational model of nanosecond streamers generated in helium bubbles immersed in distilled water at the atmospheric pressure conditions. The model is based on the self-consistent, multispecies and the continuum description of plasma and takes into account the presence of water vapor in the gas bubble for a more accurate description of the kinetics of the discharge. We find that the dynamic characteristics of the streamer discharge are completely different at low and high over voltages. We observe that the polarity of the trigger voltage has a substantial effect on initiation, transition and evolution stages of streamers with the volumetric distribution of species in the streamer channel much more uniform for negative trigger voltages due to the presence of multiple streamers. We also find that the presence of water vapor significantly influences the distribution of the dominant species in the streamer trail and has a profound effect on the flux of the dominant species to the bubble wall. [Preview Abstract] |
Thursday, October 13, 2016 12:15PM - 12:30PM |
RR3.00006: Oxygen reduction reaction on highly-durable Pt/nanographene fuel cell catalyst synthesized employing in-liquid plasma Tomoki Amano, Hiroki Kondo, Keigo Takeda, Kenji Ishikawa, Hiroyuki Kano, Mineo Hiramatsu, Makoto Sekine, Masaru Hori We recently have established ultrahigh-speed synthesis method of nanographene materials employing in-liquid plasma, and reported high durability of Pt/nanographene composites as a fuel cell catalyst. Crystallinity and domain size of nanographene materials were essential to their durability. However, their mechanism is not clarified yet. In this study, we investigated the oxygen reduction reaction using three-types of nanographene materials with different crystallinity and domain sizes, which were synthesized using ethanol, 1-propanol and 1-butanol, respectively. According to our previous studies, the nanographene material synthesized using the lower molecular weight alcohol has the higher crystallinity and larger domain size. Pt nanoparticles were supported on the nanographene surfaces by reducing 8 wt{\%} H$_{\mathrm{2}}$PtCl$_{\mathrm{6}}$ diluted with H$_{\mathrm{2}}$O. Oxygen reduction current densities at a potential of 0.2 V vs. RHE were 5.43, 5.19 and 3.69 mA/cm2 for the samples synthesized using ethanol, 1-propanol and 1-butanol, respectively. This means that the higher crystallinity nanographene showed the larger oxygen reduction current density. The controls of crystallinity and domain size of nanographene materials are essential to not only their durability but also highly efficiency as catalyst electrodes. [Preview Abstract] |
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