Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session ET1: Atmospheric Pressure Plasma Chemistry |
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Chair: Anne Bourdon, CNRS-Ecole Centrale, Paris Room: 162 |
Tuesday, October 5, 2010 4:00PM - 4:30PM |
ET1.00001: Experimental and computational characterization of He+H$_2$O plasmas at atmospheric pressure Invited Speaker: Atmospheric pressure plasmas have received growing attention in recent years for their economic and scientific potential. In many of the envisioned applications (e.g. sterilization, surface modification, biomedical applications, air pollution, water treatments, etc.), water plays an important role on determining the discharge characteristics. In this contribution, I present the results of experimental and computational studies aimed at unravelling the chemistry and dynamics of low-temperature He+H$_2$O atmospheric pressure plasmas envisioned for biomedical applications. In these discharges helium is used as a buffer gas and helps keeping the discharge temperature low. While in many atmospheric pressure systems water is present as an impurity, here water is deliberately introduced in the discharge and used as a precursor of reactive species of biomedical relevance. By means of a comprehensive global model (46 species and 576 reactions), optical spectroscopy, and mass spectrometry, the discharge is characterized as a function of the water concentration and main species/reactions are identified. Finally, the chemistry of He+H$_2$O plasmas is compared with that of He+O$_2$ plasmas commonly used in the growing field of plasma medicine. [Preview Abstract] |
Tuesday, October 5, 2010 4:30PM - 4:45PM |
ET1.00002: Characterisation of a He/O$_2$/HMDSO microplasma jet by molecular beam mass spectrometry Dirk Ellerweg, Ruediger Reuter, Jan Benedikt, Achim von Keudell A microscale atmospheric pressure plasma jet with parallel-plate rf-driven electrodes at 1mm separation is used to deposit thin organic SiO$_x$C$_y$ and anorganic SiO$_x$ films on silicon substrates. This is done by admixing a small amount ($<$0.01\%) of hexamethyldisiloxane (HMDSO) or HMDSO/O$_2$ to the He flow (5slm) of the microplasma jet. However, the HMDSO plasma chemistry at atmospheric pressure is not well-understood. Therefore a molecular beam mass spectrometer (MBMS) is used to get an insight into the HMDSO and HMDSO/O$_2$ plasma chemistry, respectively. An HMDSO depletion up to 6\% can be measured without O$_2$ addition and several stable reaction products are identified. This condition leads to organic films. The resulting film quality improves when O$_2$ is added to the He/HMDSO flow. The MBMS measurements revealed that thereby the HMDSO depletion doubles and the densities of the main reaction products increase significantly, too. Additionally, polymerisation products larger than HMDSO appear. These MBMS measurements help to understand the HMDSO plasma chemistry at atmospheric pressure and can help to determine the reaction mechanism leading to anorganic SiO$_2$ film growth. [Preview Abstract] |
Tuesday, October 5, 2010 4:45PM - 5:00PM |
ET1.00003: Ignition Delay Time and OH Concentration Measurements in Nanosecond Repetitively Pulsed Hydrogen-Air Plasmas Igor Adamovich, Zhiyao Yin, Inchul Choi, Walter Lempert Ignition delay time and OH concentrations are measured in a spatially uniform, repetitive nanosecond pulse discharge in premixed hydrogen-air flows. Ignition delay is measured in hydrogen-air flows preheated in a tube furnace, at initial temperatures of T=100-200 C (significantly below autoignition temperature), in a wide range of pressures (40-150 torr), equivalence ratios (0.5-1.2), and discharge pulse repetition rates (10-40 kHz). The results show that the plasma remains uniform in the entire range of experimental conditions, and that uniform ignition occurs in the entire plasma volume. The number of discharge pulses necessary for ignition decreases considerably as the pressure and the initial temperature are increased. Ignition delay time remains nearly independent of the equivalence ratio. Time-resolved, absolute OH concentrations in hydrogen-air mixtures, initially at room temperature, excited by the nanosecond pulse discharge are measured by Laser Induced Fluorescence, using adiabatic Hencken burner flame for calibration. OH concentrations are measured both in single-pulse and in repetitively pulsed discharges. The results demonstrate OH accumulation in the repetitively pulsed plasma until ignition occurs due to plasma chemical reactions. [Preview Abstract] |
Tuesday, October 5, 2010 5:00PM - 5:15PM |
ET1.00004: Generation and Control of Atmospheric-pressure Glow Microdischarges along Miniature Water Flow Makoto Kanemaru, Nao Tatsumura, Shinji Ibuka, Shozo Ishii To increase the effective area for surface interaction between liquid and plasma, we developed a radio-frequency glow microdischarge along a miniature water flow that was surrounded by a coaxial helium gas flow in a quartz tube under atmospheric pressure. The de-ionized water was supplied through a nozzle electrode that had a counter needle electrode. The discharge developed at the edge of nozzle electrode, the triple point including gas, water, and metal. The stable microdischarges were obtained without the formation of water droplets. Glow to spark transition appeared at high input rf power. Thanks to the quartz tube, the discharges were not affected by ambient air including nitrogen and oxygen molecules. Optical emission spectroscopy was conducted to examine the effect of water flow on the discharges. OH and HeI lines with significant intensities were observed. The microplasma structure enhances the surface interaction between the glow discharge and the water flow, which assists physical and chemical reactions. This was verified by observing the emission of intense OH lines. [Preview Abstract] |
Tuesday, October 5, 2010 5:15PM - 5:30PM |
ET1.00005: The role of negative ions in the formation of filamentary efficient plasma in air at atmospheric pressure Emmanuel Marode Pollution control by removal of hazardous species in flue gas exhaust, sterilization for medical purposes, triggering fuel combustion in vehicle motors, etc{\ldots} all these applications require that the electrical discharge create electron swarms with electron energies able to trigger sets of collision reactions into the gas to meet the needs of the specific application. For such a purpose, non-thermal plasmas are now widely used. During the streamer-to-spark transition in air, in positive non-uniform gaps, at atmospheric pressure, various discharge regions appear characterized by different values of the electron energy $\varepsilon $. Within the small front of ionization wave, called streamer (some tens of micrometer), $\varepsilon $ may reach tens of eV. But within the filamentary plasma track left by the streamer, $\varepsilon $ goes down since, the mean electrical field is very low. But, in spite of the low mean field, a high field region is created named ``secondary streamer'', where plasma chemistry may take place. Attachment and detachment of electrons within this filamentary plasma seams to have a key role in the properties of that region. Such filamentary plasma state may be controlled by external means, and offer a basis to chemical plasma reactors. [Preview Abstract] |
Tuesday, October 5, 2010 5:30PM - 5:45PM |
ET1.00006: Non-thermal plasma synthesis of H$_{2}$O$_{2}$: investigation of DBD and surface-DBD performances Frederic Thevenet, Julien Couble, Markus Brandhorst, Jean-Luc Dubois, Daniel Bianchi Authors focused on H$_{2}$O$_{2}$ non-thermal plasma synthesis. A H$_{2}$/ O$_{2}$ mixture is used as reactant gas flow. If the reaction is performed into a simple glass discharge tube selectivities regarding H$_{2}$O and H$_{2}$O$_{2}$ are respectively 98.5 and 1.5{\%}. In order to improve performances, materials were associated to the discharge. This aimed at using material surface properties to drive recombination of dissociated species toward targeted products. Four materials were tested: SiO$_{2}$ coating, TiO$_{2}$ coating, SiO$_{2}$ fibres, TiO$_{2}$ fibres. Regardless to their chemical nature, coatings do not induce any improvement. On the contrary, fibres multiplied by 20 the selectivity toward H$_{2}$O$_{2}$. The yield of H$_{2}$O$_{2}$ is multiplied by 35 with SiO$_{2}$ fibres and by 50 with TiO$_{2}$ fibres. Investigations have been performed in order to understand the interaction between the discharge and inorganic fibres. Authors propose a reaction scheme in order to summarize gaseous and adsorbed reactions. [Preview Abstract] |
Tuesday, October 5, 2010 5:45PM - 6:00PM |
ET1.00007: Chemical kinetics in a helium humid air atmospheric pressure plasma Tomoyuki Murakami, Timo Gans, Deborah O'Connell, W.G. Graham The results of a zero-dimensional, time-dependent numerical simulation of the chemical kinetics in an atmospheric pressure helium-air mixture plasma are reported. The system is driven with ionization pulses every 100 kHz. 58 species and 461 reactions are included in the simulation. Dry air and air with various molecular fractions of H2O are compared. Positive ions are the dominant ion species, with NO+ and H3O+.H2O being most pronounced. Some of the positively charged ions are strongly modulated at the driving frequency. The density of electrons and the total density of negative ion species are comparable. The main negative ion species are O2-, and O2-.H2O. The negative ions are only weakly modulated at the driving frequency. The main radical species, OH, H, O and O3, are also only weakly modulated. The effect of changes in the input parameters, particularly water humidity will be discussed [Preview Abstract] |
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