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Aramid is widely recognized for its effectiveness as a matrix in high-performance composite materials. However, the inert nature of its surface necessitates plasma pretreatment for proper resin immersion. With a particular focus on interactions involving O radicals, this study employs Vacuum Ultra-Violet Photolysis Reactive-species Supply to investigate the interaction mechanisms between aramid and plasma reactive species. The water contact angle serves as an indicator of the degree of surface reactions, demonstrating a clear correlation between its reduction and the concentration of O radicals. Analysis using ATR-FTIR and XPS revealed the depletion of amide groups and the formation of hydroxyl groups during the treatment process. Through reactive molecular dynamics simulations, we identified the specific reaction sites of the amide groups on aramid and quantified the variations in typical reaction products. We also summarized the reaction pathways and confirmed the generation of polar structures, such as N-OH. This study offers valuable theoretical insights for the surface modification of inert polymers and contributes to advancements in industrial plasma technology. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of various O 2 concentrations, from 20% to 90%, in nitrogen–oxygen ( N 2 / O 2 ) mixtures on the characteristics of secondary streamers. As oxygen molecules have different molecular characteristics from nitrogen molecules in terms of ionisation threshold and electron attachment property, streamer discharges generated under various nitrogen–oxygen ratios may exhibit differing characteristics such as electron density, electric field, and radical formation. We focused on the changes in these parameters in secondary streamers using simulations. Simulations were first performed under the same conditions as those in previous experiments to compare the results of the ozone production, discharge current, and discharge emission characteristics. To compare the ozone production characteristics, simulated O radicals–the precursor of ozone–were used in the simulation for simplicity. This comparison showed that, although the absolute values of each parameter were different, the simulation exhibited a similar trend in the case of the experimentally obtained oxygen concentration dependence. After the validity of the simulation was verified to some extent via a comparison with the experiment, the results obtained from the simulation were analysed in detail. The results showed that, although the electric field strength in the secondary streamer did not change much as the oxygen concentration increased, the decrease rate of the electron density was greatly accelerated by the electron attachment reaction of oxygen. As a result, many of the electrons had already dissipate during the development of the primary streamer, and few electrons remained when the secondary streamer was formed. This effect suggests that the ratio of the amount of O radicals produced in the primary streamer to that produced in the secondary streamer changes as the oxygen concentration changes. [ABSTRACT FROM AUTHOR]

This study evaluates the individual effects of electron‐impact ionization, attachment, and photoionization on streamer propagation to provide a deeper understanding of the streamer propagation mechanism and useful knowledge to obtain the best set of input data for verification and validation studies. The results show that streamers with higher electron‐impact ionization rates have higher propagation velocities and lower electric fields, while those with higher attachment rates have slower propagation velocities and higher electric fields. Streamers with higher photoionization rates have lower electric fields at the head, but the velocity remains largely unaffected. The effects of different rates of ionization, attachment, and photoionization have been analyzed using an analytical solution called the diameter‐speed relation. [ABSTRACT FROM AUTHOR]

In this paper, we measured the electrical potential distribution of surface dielectric barrier discharges (SDBD) caused by alternating voltage in synthetic air and nitrogen using the Pockels effect. It was shown that different potential distributions of filament thickness and length are generated in synthetic air and nitrogen. A filament analysis based on mathematical morphology was performed to quantify the geometric characteristics of the filaments produced in each gas atmosphere. The results show that the discharge filament thickness and the entropy in the filament direction depend on the oxygen ratio and the magnitude of the applied voltage. [ABSTRACT FROM AUTHOR]

Limited research has been conducted on the formation mechanism of chemically active species in streamer discharges with respect to the oxygen concentration, which is critical to various applications such as ozone generation, air purification, and plasma-assisted combustion, among others. Herein, the oxygen concentration in an N2/O2 gas atmosphere is varied from 1% to 99% under atmospheric pressure and room temperature to investigate changes in the characteristics of streamer discharge propagation and generation of chemically active species. As the oxygen concentration increases from 10% to 90%, the decay rate of the discharge current, propagation velocity of the primary streamer, and ozone production efficiency increase. These phenomena are qualitatively explained by the electron attachment reaction to oxygen molecules and changes in the electron energy distribution function caused by the change in the oxygen concentration. However, the amount of discharge emission from N2(C) cannot be explained by changes in the fraction of electron energy lost in excitation of N2(C) and its quantum yield, implying that changes in the production of N2(C) in the primary and secondary streamers must be considered in a spatiotemporal manner. This study demonstrates that the ozone and N2(C) production characteristics in streamer discharges vary nonlinearly with respect to the oxygen concentration. [ABSTRACT FROM AUTHOR]

The electric field induced second harmonic generation (E-FISH) technique has been widely utilized for the electric field measurement of atmospheric-pressure nonthermal plasmas. However, the measurement accuracy has not been quantified. Further, the E-FISH signal generation that is necessary to the evaluation of the measurement accuracy has been formulated only for the probe laser beam focused by a spherical lens and not for the cylindrical lens. Here, the E-FISH method utilizing the focusing cylindrical lens was studied for accurate one-dimensional (1D) electric field measurement of the primary-to-secondary transition phase of a single-filament positive streamer discharge generated in atmospheric-pressure air. A combination of numerical analysis and the E-FISH signal measurement was used to establish the radial distribution of the electric field vectors and the accompanying measurement accuracy. The E-FISH methodology captured a distinct evolution in the 1D electric field varying over timescales of ∼ 1  ns and length scales of 100  µ m. At the instant when the primary streamer arrived at the cathode, the electric field at 3 mm above the cathode surface was found to be as high as 225 Td, while the field at 10 mm above the cathode surface was as low as 5 Td. At the final stage of the primary-to-secondary transition phase completed in 3 ns from the primary streamer arrival at the cathode, the electric field at 3 mm above the cathode was found to be lower than that observed at 10 mm from the cathode; this finding is consistent with predictions made based on a previous model describing the initiation of the secondary streamer discharge and previously published electron density measurement. [ABSTRACT FROM AUTHOR]

In order to improve the energy efficiency in the dilute trichloroethylene (TCE) removal by the nonthermal plasma process, the barrier discharge reactor was studied experimentally. It is investigated by combining it with catalyst of manganese dioxide at the downstream of the barrier discharge reactor. Decomposition efficiency by the barrier discharge reactor was about 83% at the gas flow rate 2 L/min, where the dilute TCE concentration is 250 ppm. Decomposition efficiency with passing through manganese dioxide was improved about 99% at the specific energy of 40 J/L. However, other by-products including ozone and oxidation by-products such as DCAC and TCAA were detected by the gas chromatograph mass spectrometry or the Fourier transform infrared spectroscope measurement. DCAC is generated at the plasma reactor, but TCAA is generated at catalyst during ozone decomposition. C[O.sub.x] yield increased about twice with passing through catalyst in the Direct Process. Nitric oxides such as NO, N[O.sub.2], and [N.sub.2]O did not generate so much in this barrier discharge process. The dielectric barrier discharge process combined with manganese dioxide is considered as a very desirable way to improve the energy efficiency. Index Terms--Barrier discharge, manganese dioxide (Mn[O.sub.2]), trichloroethylene (TCE).

Negatively corona-charged 50-[micro]m-thick polypropylene (PP) film is measured using laser-induced pressure pulse (LIPP) and thermally stimulated current (TSC) in order to study the charge storage mechanism in the PP film. The LIPP can reveal the space-charge distribution in the depth direction of the PP films and the TSC can be used to measure the energetic depth of the charge trap. The LIPP shows that negative charge is deposited on the charged surface of the sample. Almost all surface charges are removed by soaking the sample in ethanol. However, about 5% of the surface charge is injected into the sample up to a depth of about 7 [micro]m from the surface. The injected charge is not removed by the dip-in-ethanol method because the ethanol does not penetrate into the sample. The injection of the surface charge increases with corona-charging temperature. Besides the negative charge injection, the injection of positive charge from the opposite surface is also observed when the sample is charged at higher than 60 [degrees]C. In addition, negative bulk charge is formed when the sample is charged at higher than 80 [degrees]C. The LIPP profile is compared with the TSC spectrum. It is shown that the space charge observed using LIPP disappears when the temperature of the sample exceeds 80 [degrees]C. However, TSC is observed at even higher than 80 [degrees]C. This indicates that the TSC is observed even after the disappearance of the space charge measured using LIPP. Index Terms--Corona charging, laser-induced pressure pulse (LIPP), polypropylene (PP) film, thermally stimulated current (TSC).

Sputtering enables uniform and clean deposition over a large area, which is an issue with exfoliation and chemical vapor deposition methods. On the other hand, the process of physical vapor deposition (PVD) film formation has not yet been clarified. We prepared several samples from the sub-monolayer region, and performed Raman spectroscopy, X-ray photon spectroscopy and high-angle annular dark-field scanning transmission electron microscopy. From these results, the internal stresses inherent to PVD films, the bonding states specific to sub-monolayers, and the unique film structure and the grain formation process of PVD films were discussed from the perspective of sub-monolayers. As a conclusion, we found that it is important to suppress the formation of sub-monolayers on the substrate to completely form the first layer. [ABSTRACT FROM AUTHOR]

Nitrogen is a very common element, comprising approximately 78% of Earth’s atmosphere, and is an important component of various electronic devices while also being essential for life. However, it is challenging to directly utilize dinitrogen because of the highly stable triple bond in this molecule. The present review examines the use of non-equilibrium plasmas to generate controlled electron impacts as a means of generating reactive nitrogen species (RNS) with high internal energy values and extremely short lifetimes. These species include ground state nitrogen atoms, excited nitrogen atoms, etc. RNS can subsequently react with oxygen and/or hydrogen to generate new highly reactive compounds and can also be used to control various cell functions and create new functional materials. Herein, plasma-processing methods intended to provide RNS serving as short-lived precursors for a range of applications are examined in detail. [ABSTRACT FROM AUTHOR]

ABSTRACT To examine the surface modification of polypropylene (PP) by O atoms, PP surfaces are treated using a vacuum ultraviolet (VUV) photodissociation reactive species supply method. The O‐atom treatment initially reduces the water contact angle (WCA) on the PP surface; however, prolonged treatment leads to an increase in the WCA. This increase is likely due to the evaporation of low‐molecular‐weight oxidized materials generated by PP chain scission. The relationship between O‐atom density and the observed reduction and subsequent increase in WCA is analyzed in detail. The results are compared with findings from previous studies on PP plasma treatment to elucidate the specific role of O atoms in plasma‐based surface treatments. [ABSTRACT FROM AUTHOR]

This study investigates the effects of voltage rise rates from 0.1 kV ns−1 to 100 kV ns−1 on streamer discharge in air at atmospheric pressure using numerical simulation. The curvature of the needle electrode is also used as an input parameter to change the streamer inception voltage and the average voltage, Vave, during streamer propagation. The results show that the streamer propagation velocity, vpri, the electric field strength at the streamer head, Eh, the diameter of the streamer channel, and the O radical production characteristics during the primary streamer propagation are dependent on Vave. vpri and Eh exhibit different effects on Vave/d, where d is the gap distance of the electrode, which indicates that the streamer remains in the transient state from the filament-type discharge to the diffuse-type discharge. The comparison between the simulation and experimental results shows that the simulated vpri characteristics are in good agreement with the experimental results, regardless of the voltage waveform and electrode configuration, which indicates that Vave/d has a strong correlation with the primary streamer characteristics. [ABSTRACT FROM AUTHOR]

OH density and rotational temperature were measured in a saturated water vapor slot-excited microwave plasma using spatio-temporally resolved laser-induced fluorescence. The microwave power was 20–100 W under continuous wave mode, whereas 40–200 W peak under pulse-modulated mode (30% duty cycle, 100 Hz). The water vapor pressure was 2.3 kPa. An approximately 2 mm thick flat-shaped plasma was generated on the surface of a slot antenna. The OH density and rotational temperature in the plasma ranged from 1 × 1014 cm−3 to 1 × 1015 cm−3 and from 1100 K to 3000 K, respectively. OH was produced via various routes originating from electron collisions (e + H2O) and was primarily lost through recombination (OH+OH → H2O+O) and diffusion. The production rate (kp) of OH per H2O molecule, which was calculated based on a simplified reaction model using the measured OH density and temperature, showed a relation of , where P represents the microwave power. This relationship implies a two-step production process of OH via the vibrational excitation of H2O. Although the OH density increased with increasing microwave power, the density became saturated at high power values. [ABSTRACT FROM AUTHOR]

Vibrationally excited N2(v=1, 2) in an atmospheric-pressure air pulsed corona discharge was measured using coherent anti-Stokes Raman scattering (CARS). In a dry air discharge, the vibrational temperature determined from the ratio N2(v=2)/N2(v=0), Tv2, was approximately 500K higher than that determined from N2(v=1)/N2(v=0), Tv1, immediately after the discharge pulse. Both vibrational temperatures reached equilibrium within 100 μs after the discharge pulse by the vibration-to-vibration (V-V) process of N2-N2. The translational temperature was also measured using CARS. The rise in the translational temperature due to vibration-to-translation (V-T) energy transfer was not observed for a postdischarge time of 5 μs-1 ms in the dry-air discharge. However, when the air was humidified, a significant V-T energy transfer was observed. It was due to an extremely rapid V-T process of H2O-H2O following the V-V process of N2-H2O. Measurements showed that the humidification of the ambient air accelerated the decrease in the N2 vibrational temperature and increased the translational temperature. N2(v) was generated mostly in the secondary streamer, not in the primary one, according to estimation from the measured N2(v) density. [ABSTRACT FROM AUTHOR]

In this study, the effect of oxygen (O2) concentration in the range of 0.000 1% (= 1 ppm) to 20% on the decay of hydroxyl (OH) density after pulsed streamer discharge is examined in a humid nitrogen-oxygen mixture under atmospheric pressure. The decay of OH density was measured using laser-induced fluorescence and compared with one-dimensional postdischarge simulations. The simulation results are consistent with the measured decay of OH density for all O2 concentrations. Essentially, the OH decay was double exponential, consisting of initial rapid decay for t < 0.1 ms and subsequent slow decay for t > 1 ms, where t represents the postdischarge time. In the slow decay phase, O2 change in the order of 10 ppm markedly affected the OH decay rate when O2 < 100 ppm. The sensitive effect of the small amount of O2 can be attributed to the reaction, , which converts H atoms to HO2, and the subsequent OH production via H+HO2→ OH+OH. Other production and loss processes of OH in the postdischarge phase were also examined. [ABSTRACT FROM AUTHOR]

OH and O radicals are considered to be the most important reactive species in polymer surface treatment using plasma. However, the treatment effect of OH and O radicals has not been measured quantitatively due to the difficulty in separating the effects of OH and O from those of many other reactive species produced in plasma. In this study, the effect of OH radicals on the surface treatment of polypropylene (PP) is quantitatively measured using specially designed equipment that was developed in our previous research. The equipment produces OH radicals using vacuum ultraviolet photolysis of water vapor and supplies them to the PP surface while limiting the supply of other reactive species. The water contact angle on the PP surface is decreased by 1° per OH supply of [OH]τ = 7.1 × 1012 s/cm3, where τ is the treatment time. [ABSTRACT FROM AUTHOR]

The axial distribution and time evolution of OH density from upstream to downstream in a He/H2O(10–6000 ppm) atmospheric-pressure plasma jet was measured using laser-induced fluorescence (LIF). The plasma was generated with repetitive positive pulses (7–10 kV, 800 ns, and 1 kHz). We investigated (i) the dependence of OH density on various discharge parameters, (ii) the production and loss processes of OH radicals, and (iii) the effect of O2 admixture on OH density with the help of simulations. The simulations included only postdischarge reactions. To simulate the discharge pulse, the increase in the OH density in a discharge pulse measured using LIF was used as an input parameter. The results suggested that the OH density at any position in the plasma was approximately proportional to regardless of the H2O concentration, where εd is the discharge energy density at the position and f is the pulse repetition frequency. The results also suggested that OH was mainly produced by rather than , where was produced by Penning ionization, and its main loss processes were and. [ABSTRACT FROM AUTHOR]

To study the production mechanism of atomic nitrogen, the temporal profile and spatial distribution of atomic nitrogen are measured in atmospheric pressure pulsed positive corona discharge using two-photon absorption laser-induced fluorescence. The absolute atomic nitrogen density in the streamer filaments is estimated from decay rate of atomic nitrogen in N2 discharge. The results indicate that the absolute atomic nitrogen density is approximately constant against discharge energy. When the discharge voltage is 21.5 kV, production yield of atomic nitrogen produced by an N2 discharge pulse is estimated to be 2.9 - 9.8 × 1013 atoms and the energy efficiency of atomic nitrogen production is estimated to be about 1.8 - 6.1 × 1016 atoms/J. The energy efficiency of atomic nitrogen production in N2 discharge is constant against the discharge energy, while that in N2/O2 discharge increases with discharge energy. In the N2/O2 discharge, two-step process of N2 dissociation plays significant role for atomic nitrogen production. [ABSTRACT FROM AUTHOR]

Plasma application for environmental improvement is desirable, and it is worthwhile to clarify the behavior of OH radicals in nonthermal plasma. Under atmospheric-pressure humid air, the time evolutions and spatial distribution of relative density and rotational temperature of OH radicals are measured in pulsed positive corona discharge using laser-induced fluorescence with a tunable optical parametric oscillator laser. The density of OH radicals generated by discharge when 28 kV is applied is estimated to be about 1×1015cm-3 at 3 μs after discharge. The OH density increases with humidity. The rotational temperature rises after discharge. The rate of temperature rise increases with humidity. This phenomenon arises from fast vibration-to-translation energy relaxation of H2O. The spatial distributions of OH rotational temperature indicate that the temperature rises in the secondary streamer channel. [ABSTRACT FROM AUTHOR]

Atomic oxygen is measured in the afterglow of pulsed positive corona discharge using time-resolved two-photon absorption laser-induced fluorescence. The discharge occurs in a 14 mm point-to-plane gap in dry air. After the discharge pulse, the atomic oxygen density decreases at a rate of 5×104 s-1. Simultaneously, ozone density increases at almost the same rate, where the ozone density is measured using laser absorption method. This agreement between the increasing rate of atomic oxygen and decreasing rate of ozone proves that ozone is mainly produced by the well-known three-body reaction, O+O2+M→O3+M. No other process for ozone production such as O2(v)+O2→O3+O is observed. The spatial distribution of atomic oxygen density is in agreement with that of the secondary streamer luminous intensity. This agreement indicates that atomic oxygen is mainly produced in the secondary streamer channels, not in the primary streamer channels. [ABSTRACT FROM AUTHOR]

Capacitance spark discharge has been widely used for studying the ignition of flammable gas caused by electrostatic discharge. In the present study, the gas temperature of capacitance spark discharge is measured. The gas temperature is an important factor in understanding the electrostatic ignition process because it influences the reaction rate of ignition. Spark discharge is generated in air with a pulse duration shorter than 100 ns. The discharge energy is set to 0.03–1 mJ. The rotational and vibrational temperatures of the N2 molecule are measured using the emission spectrum of the N2 second positive system. The rotational and vibrational temperatures are estimated to be 500 and 5000 K, respectively, which are independent of the discharge energy. This result indicates that most of the electron energy is consumed in the excitation of vibrational levels of molecules rather than the heating of the gas. The gas temperature after discharge is also measured by laser-induced fluorescence of OH radicals. It is shown that the gas temperature increases after discharge and reaches approximately 1000 K at 3 μs after discharge. Then the temperature decreases at a rate in the range of 8–35 K/μs depending on the discharge energy. [ABSTRACT FROM AUTHOR]

Nitrogen oxide γ-band emissions (A2 Σ+→X2 Π) from primary and secondary streamers are observed in O2/N2 and NO/N2 pulsed positive corona discharges with the aim of investigating the production of NO molecules and N2(A3 Σu+) metastables in these primary and secondary streamers. The spatial distribution of the NO-γ emission shows that the NO-γ emission is mostly observed in the secondary streamer propagation area of the O2/N2 discharge. That is, NO molecules are mainly produced in the secondary streamer in the O2/N2 discharge. On the other hand, in the NO/N2 discharge, the NO-γ emission is observed in the primary streamer propagation area. This result indicates that N2(A3 Σu+) metastables are mostly produced in the primary streamer because the NO-γ emission is observed following the process NO(X2 Π)+N2(A3 Σu+)→NO(A2 Σ+)+N2(X2 Σg), where NO(X2 Π) is distributed uniformly in the background gas in the NO/N2 discharge. [ABSTRACT FROM AUTHOR]

The dynamics of ozone and OH radicals are studied in pulsed corona discharge plasma in a humid-air environment. Ozone density is measured by the laser absorption method, and OH density is measured by the laser-induced fluorescence (LIF) method. A 100-ns pulsed corona discharge occurs between a series of 25 needle electrodes and a plate electrode. After the pulsed discharge, the time evolutions of ozone and OH densities are measured in humid air or a humid nitrogen-oxygen mixture. Results show that the addition of 2.4% water vapor to dry air reduces ozone production by a factor of about 6, and shortens the ozone formation time constant from 30 to 6 ms. Water vapor may reduce atomic oxygen levels leading to the decreased production of ozone by O+O[SUB2] reaction. The LIF measurement for OH radicals shows that OH density is approximately constant for 10 ms after the pulsed discharge, then decays by recombination reaction and reactions with the discharge products of oxygen, such as ozone or atomic oxygen. Absolute OH density is estimated; it is about 3×10[SUP15] cm[SUP-3]in streamers at 10 ms after discharge in the H[SUB2]O(2.4%)/N[SUB2] mixture. [ABSTRACT FROM AUTHOR]

Gas heating in an atmospheric-pressure streamer discharge was analysed by a two-dimensional streamer discharge simulation model describing internal molecular energy transfer. Our two-dimensional streamer simulation model incorporates concepts from the fast gas heating mechanism proposed by Popov (2011 J. Phys. D: Appl. Phys.44 285201) and our self-developed state-to-state vibrational kinetics. In dry air, gas heating occurs mainly from electron-impact dissociation reactions of O2 molecules and from quenching processes of electronically excited N2(B3Πg, C3Πu) molecules and O(1D) atoms. In humid air, rapid vibration-to-translation transitions of H2O and the exothermicity of the OH formation reactions additionally increase the gas temperature. It is shown that gas heating during the discharge pulse increases with humidity. [ABSTRACT FROM AUTHOR]

Plasma application for environment improvement is desirable. In order to improve the efficiency of toxic gas decomposition by plasma, it is worthwhile to clarify the behavior of radicals in nonthermal plasma. Although previous studies have revealed the behavior of radical densities and temperatures in atmospheric discharge, they are not yet connected to apprehension or simulation of practical toxic gas decomposition by atmospheric plasma. In this study, the coaxial dielectric barrier discharge cylinder reactor is prepared, where the radical behavior and the toxic gas decomposition efficiency can be measured altogether. The density of OH radical is directly measured by laser-induced fluorescence, and trichloroethylene (TCE) decomposition efficiency is also investigated in the same reactor. TCE decomposition efficiency is suppressed as background humidity increases. On another front, OH density measurement in ac barrier discharge indicates that OH density is about 2–4 \times 10^11\ \cm^-3 in time and spatial average and saturated with increasing humidity. From the saturation pattern, the initial OH density is estimated to be about the order of 10^14\ \cm^-3 in streamer site. In addition, TCE addition in background reduces OH density, which indicates that OH reacts with TCE. The reason for the suppression of decomposition efficiency with increasing humidity is estimated as a consequence of O radical reduction by water-originated particles. [ABSTRACT FROM AUTHOR]

The effect of pulse rise rate on a streamer discharge is investigated through both experiments and simulations. Pulsed voltages with a pulse rise rate of 0.11–0.52 kV ns−1 are applied to point-to-plane electrode configurations, and the effects are observed from ICCD photographs. The streamer emission of light is simulated by a previously developed two-dimensional streamer simulation model, and the simulation results are compared with experimental results. The results show that as the pulse rise rate is decreased, there is a decrease in the discharge current, velocity of the primary streamer, diameter of the streamer channel and emission length of the secondary streamer. The simulated reduced electric field of the primary streamer head remains constant and does not depend on the pulse rise rate. The simulated temporal variations of O and OH radical production show that almost the same number of the radicals are produced in the primary streamer, regardless of the pulse rise rate. However, the radical production in the secondary streamer decreases as the pulse rise rate decreases. Therefore, the pulse rise rate affects the ratio of radical production in the primary streamer to that in the secondary streamer. [ABSTRACT FROM AUTHOR]

In order to improve the energy efficiency in the dilute trichloroethylene (TCE) removal by the nonthermal plasma process, the barrier discharge reactor was studied experimentally. It is investigated by combining it with catalyst of manganese dioxide at the downstream of the barrier discharge reactor. Decomposition efficiency by the barrier discharge reactor was about 83% at the gas flow rate 2 L/min, where the dilute TCE concentration is 250 ppm. Decomposition efficiency with passing through manganese dioxide was improved about 99% at the specific energy of 40 J/L. However, other by-products including ozone and oxidation by-products such as DCAC and TCAA were detected by the gas chromatograph mass spectrometry or the Fourier transform infrared spectroscope measurement. DCAC is generated at the plasma reactor, but TCAA is generated at catalyst during ozone decomposition. COx, yield increased about twice with passing through catalyst in the Direct Process. Nitric oxides such as NO, NO2, and N2O did not generate so much in this barrier discharge process. The dielectric barrier discharge process combined with manganese dioxide is considered as a very desirable way to improve the energy efficiency. [ABSTRACT FROM AUTHOR]

The spatial distribution of ozone density is measured in pulsed corona discharges with a 40 µm spatial resolution using a two-dimensional laser absorption method. Discharge occurs in a 13 mm point-to-plane gap in dry air with a pulse duration of 100 ns. The result shows that the ozone density increases for about 100 µs after the discharge pulse. The rate coefficient of the ozone-producing reaction, O + O2 + M → O3 + M, is estimated to be 3.5 × 10-34 cm6 s-1. It is observed that ozone is mostly distributed in the secondary-streamer channel. This suggests that most of the ozone is produced by the secondary streamer, not the primary streamer. After the discharge pulse, ozone diffuses into the background from the secondary-streamer channel. The diffusion coefficient of ozone is estimated to be approximately 0.1 to 0.2 cm2 s-1. [ABSTRACT FROM AUTHOR]

Primary and secondary streamers of positive pulsed corona discharge are observed in a point-to-plane gap using a short-gated intensified CCD camera in an air-like environment. The influences of oxygen concentration and applied voltage on the properties of both streamers are presented. It is shown that the propagation velocity, the diameter, and the shape of the streamers are strongly influenced by the oxygen concentration. In pure nitrogen, the primary streamer shows branching with a diameter of about 0.2–0.4 mm, while in air, the branching disappears almost completely and the shape of the primary streamer becomes quite smooth with a diameter of more than 1 mm. After the arrival of the primary streamer at the cathode, a secondary streamer develops from the anode toward the cathode as far as the middle of the gap. The propagation length of the secondary streamer increases approximately linearly with the applied voltage. It is shown that the ratio of the energy consumed by the secondary streamer to the whole energy consumed by the discharge increases with the applied voltage. [ABSTRACT FROM AUTHOR]

Describes the measurement of hydroxyl (OH) radicals in a pulsed arc discharge plasma under atmospheric conditions. OH excitation spectra in humid air; Two-dimensional distribution of OH; Channels for OH formation in an atmospheric pulsed arc discharge; Calculation of OH density.

Deals with a study which measured hydroxyl radicals in an atmospheric pressure discharge plasma by laser-induced fluorescence. Significance of nonthermal discharge plasma in removing pollutant gases at atmospheric pressure; Experiments; Results and discussion; Conclusion.