Application Of Atmospheric Pressure Plasma Research Articles

Mass analysis of an atmospheric pressure plasma needle discharge

Mass spectrometric measurements of a plasma needle (an example of atmospheric pressure non-equilibrium plasma source) were made for neutrals and ions. The measurements were performed for the same geometry as the standard plasma needles albeit for a somewhat increased gas flow. We discuss some of the problems of performing mass analysis at atmospheric pressures.The yields of N, O and NO radicals from the plasma needle were determined for different powers of the RF source and different flow rates of working gas. Positive ions generated by the plasma needle itself were measured for the first time. Significant conversion of feed gases (nitrogen and oxygen) into radicals and ions of N and O, and NO was observed as well as depletion of atomic radicals N and O which in chemical reactions form more complex molecules. Biomedical and nanotechnology applications of atmospheric pressure plasmas require a detailed understanding of the source, and mass analysis is perhaps the best technique to focus on chemical kinetics and in many ways interaction with surfaces.

Intracellular electric fields produced by dielectric barrier discharge treatment of skin

The application of atmospheric pressure plasmas to human tissue has been shown to have therapeutic effects for wound healing and in treatment of skin diseases. These effects are attributed to both production of beneficial radicals which intersect with biological reaction chains and to the surface and intracellular generation of electric fields. In this paper, we report on computational studies of the intersection of plasma streamers in atmospheric pressure dielectric barrier discharges (DBDs) sustained in air with human skin tissue, with emphasis on the intracellular generation of electric fields. Intracellular structures and their electrical properties were incorporated into the computational mesh in order to self-consistently couple gas phase plasma transport with the charging of the surface of the skin and the intracellular production of electrical currents. The short duration of a single plasma filament in DBDs and its intersection with skin enables the intracellular penetration of electric fields. The magnitude of these electric fields can reach 100 kV cm−1 which may exceed the threshold for electroporation.

Effects of pH on Bacterial Inactivation in Aqueous Solutions due to Low‐Temperature Atmospheric Pressure Plasma Application

AbstractLow‐temperature atmospheric pressure plasmas applied to the surface of an aqueous solution have been shown to be efficient bactericides for bacteria suspended in the solution, if the solution is sufficiently acidic. Especially of interest is the finding that there is a critical pH value of about 4.7 for the bactericidal effects, below which the bacteria are efficiently inactivated and above which the bacteria are hardly affected by the plasma application. It has been also found that the presence of superoxide anion radicals O• in the solution is essential for bacterial inactivation by the plasma application. Therefore, the critical pH value may arise from the pKa of the equilibrium reaction between O• and hydroperoxy radicals HOO•, which is known to be approximately 4.8. The present experiments, where plasmas are not directly applied to bacterium surfaces and it has been confirmed that neither UV light nor heat from the plasma is the cause of bacterial inactivation, suggest the importance of highly reactive species generated in the solution via plasma–liquid interaction for the bactericidal effects. magnified image

Charging of aerosol and nucleation in atmospheric pressure electrical discharges

The paper focuses on applications of atmospheric pressure plasmas (dc corona, streamer, spark and ac dielectric barrier discharges (DBDs)) in aerosol processes for materials and environment.Since aerosol kinematics depends mainly on electric forces acting on charged particles, the two mechanisms of aerosol charging by the collection of ions are presented in corona, post-corona and DBDs. In such defined charging conditions, field and diffusion charging laws are depicted, with respect to applications of controlled kinematics of charged aerosol.Then key parameters controlling the formation by nucleation and the growth by coagulation of particles in plasmas are presented. Sources of vapor leading to nucleated nanoparticles are depicted in atmospheric pressure electrical discharges: (i) when filamentary dc streamer and spark as well as ac-DBDs interact with metal or dielectric surfaces and (ii) when discharges induce reactions with gaseous precursors in volume. In both cases, condensable gaseous species are produced, leading to nano-sized particles by physical and chemical routes of nucleation. The composition, size and structure of primary nanoparticles as well as the final size of agglomerates are related to plasma parameters (energy, number per unit surface and time and thermal gradients around each filament as well as the transit time).

Application of Atmospheric Pressure Plasma in the Ultrasmooth Polishing of SiC Optics

This paper presents a novel, rapid and damage-free method to polish the ultra-smooth surface of the SiC optics. First, the basic philosophy of this method is introduced, which uses the active radicals got from CF4 in the atmospheric pressure plasma zone to react with the SiC material at the optics surface to generate the vaporization of SiF4. Then, the design of the atmospheric pressure plasma jet and the corresponding prototyping polishing facility are introduced. The theoretical analysis on the necessary conditions to generate the excited radicals is also presented in this part. To verify the effectiveness of this novel polishing method, experiments on the generation of atmospheric pressure plasma and the SiC optics polishing are carried out with our prototyping facility. The experiment results show that plasma discharge is stable at the atmospheric pressure and sub-nanometer roughness of the polished SiC surface can be obtained.

Ultraprecision Machining Utilizing Numerically Controlled Scanning of Localized Atmospheric Pressure Plasma

By the application of atmospheric pressure plasma, we have developed a new ultraprecision machining method named plasma chemical vaporization machining (CVM). In this method, several types of rotary or pipe electrodes are prepared for optimizing the required machining. In particular, by rotating the electrode in a high-pressure environment, both the supply of reactive species to the machining point and the exhaust of reaction products are effectively performed. In the case of fabricating a grazing-incidence total-reflection X-ray mirror, figuring accuracies of 3 nm (p–v) or less were achieved and a nearly diffraction-limited focusing performance was realized. As a result of the correction of the thickness distribution of the AT cut quartz crystal wafer, thickness uniformity was improved to a 10 nm level, and resonance property was also markedly improved without degradation by high-energy ion bombardment.

Control of radio-frequency atmospheric pressure argon plasma characteristics by helium gas mixing

The control of plasma characteristics is one of the important issues in many atmospheric pressure plasma applications. In order to accomplish this control, a feasibility study was performed by investigating the role of helium gas in an argon glow plasma that were produced in ambient air by 13.56MHz radio-frequency power. Optical emission spectroscopy was used to measure rotational temperature and emission spectra acquired between 300 and 840nm. Based on electrical and optical measurements, parameters such as gas temperature, breakdown voltage, power coupling efficiency, spatial uniformity of rotational temperature, and the sum of the emission intensity were controlled by varying the argon and helium gas mixing ratio. The addition of helium gas (from 0to10ℓpm) to the argon flow (of 10ℓpm) lowered the breakdown voltage (from 430to300Vpk) and the rotational temperature (from 465to360K). However, an excessive addition of helium resulted in a reduction of the spatial uniformity and efficiency of power coupling. When the ratio of helium to argon flow was between 0.3 and 0.5, a high spatial uniformity with a relatively low gas temperature and breakdown voltage was achieved. This suggests that mixing of the supply gas is a useful way of controlling the plasma characteristics that may be utilized for applications with specific required discharge conditions.

Experimental study and sterilizing application of atmospheric pressure plasmas

The atmospheric pressure surface barrier discharge (APSBD) in air has been used in killing Escherichia coli. We have developed two similar dielectric barrier discharge (DBD) structure types of nonthermal plasma jets (PJ) driven by 5–20 kHz audio-frequency power at atmospheric pressure. At a flow rate of 200 L/h (argon), a stable, arc-free discharge was produced. At 1.5 cm from the nozzle, the gas temperature was kept at 47 °C for PJ-1 source and 38 °C for PJ-2 source. Some research on sterilization has been carried out and results show that such a plasma jet source as PJ-2 is very effective in the disruption of E. coli.

Decomposition of toluene using an atmospheric pressure plasma/TiO 2 catalytic system

Application of atmospheric pressure plasma as an alternative technology for the destruction of toluene is demonstrated in this study. Used TiO 2 colloidal solution was obtained by an improved sol–gel method, and coated on glass beads to prepare decomposition of toluene. The physical property of synthesized TiO 2 catalyst film was analyzed by XRD and SEM spectroscopy. From these results, it was identified that the catalyst film exhibited anatase structure with particle size of about 50–100 nm after calcination at 500 °C for 1 h. The decomposition of toluene in TiO 2/O 2 plasma system was investigated. Amounts of the catalyst and toluene concentration were fixed as 3 wt.% and 1000 ppm, respectively. The analyses for performance of toluene decomposition and intermediates in reaction were done by the in situ method using the mass spectroscopy and gas chromatography. The toluene of 40% was decomposed at pulse voltage of 13 kV in the only O 2 plasma condition without TiO 2 catalyst. Furthermore, the conversion enhanced remarkably in the TiO 2/O 2 plasma system, and it reached 70% at pulse voltage of 13 kV after 120 min. This result was very notable compared with that in photocatalytic system, with below 40% after 120 min reaction.