Plasma Chemistry and Plasma Processing

The spatial distributions of electron temperature and density in a dc glow discharge that is created by a pair of planar electrodes were obtained by using double Langmuir probes. The contribution of double Langmuir probes measurement is to provide a relatively quantitative tool to identify the electron distribution behavior. Electrons gain energy from the imposed electric field, and electron temperature (Te) rises very sharply from the cathode to the leading edge of the negative glow where Te reaches the maximum. In this region, the number of electrons (Ne) is relatively small and does not increase much. The accelerated electrons lose energy by ionizing gas atoms, and Te decreases rapidly from the trailing edge of the negative glow and extends to the anode. Ne was observed to increase from the cathode to the anode, which is due to the electron impact ionization and electron movement. The electron density was observed to increase with increasing discharge voltage while the electron temperature remained approximately. At 800 V and 50 mTorr argon glow discharge, Te ranged from 15 to 52 eV and Ne ranged from 6.3×106/cm3 to 3.1×108/cm3 in the DC glow discharge, and Te and Ne were dependent on the axial position.

Allowing water/hydrogen or water/hydrogen/He gas mixture to flow through micro- hollow type of electrodes and applying 60 Hz AC power between the electrodes made it possible to sustain large area and atmospheric pressure discharge. The electrode assembly was constructed by sandwiching a dielectric spacer with two thin metal sheets and boring an array of micro holes through them. Another variation of the assembly was prepared by stacking thin metallic sheets so that the stack functions as an electrode through which the gas mixture flows for generating dielectric barrier discharge. A large volume of the gas mixture, while producing plasma, underwent instantaneous hydrogen isotope exchange reactions between H2O and D2O or between D2O and H2 gas molecules. The efficiency of the atmospheric pressure discharge was assessed by measuring the extent of the exchange reactions at a given flow rate of the gas mixture.

High quality amorphous arsenic selenide chalcogenide films of different structure and stoichiometry were synthesized via plasma-enhanced chemical vapor deposition (PECVD). The low-temperature non-equilibrium RF (13.56 MHz) argon inductively-coupled plasma at low pressure (0.1 Torr) was implemented for the process. Commercial high-pure elemental arsenic and selenium were utilized as the starting materials. The chemical content and the structure of the samples were altered via change of parameters of the plasma process. The in situ optical emission spectroscopy of the chemically active plasma was employed to pinpoint the ways of initiation of plasma-chemical interactions between precursors. The obtained characteristics of the arsenic selenide PECVD films have been compared with ones for CVD. The behavior of impurities of the carbon nature in the processes of PECVD and CVD deposition was also studied.

The decomposition of methylene blue (MB) in aqueous solution was investigated using a pulsed corona discharge. The discharge was ignited in the gas bubbled in the solution through several needle electrodes. The influence of treatment time, volume of the treated solution and initial concentration of the dye in solution on MB degradation was studied. The effect of the nature of the gas introduced was also investigated. For the same energy input, MB conversion increased in the order air < argon < oxygen. When using oxygen, the decomposition of MB exceeded 95% after ~20 min plasma treatment. Higher efficiency was obtained for higher treated volume and higher initial concentration. At 90% conversion the yield obtained with oxygen was ~5 g/kWh for an initial concentration of 150 mg/l and a treated volume of solution of 100 ml.

This study focuses on metal/polymer nanocomposite thin films made by atmospheric pressure Plasma-Enhanced Chemical Vapor Deposition. The aerosol of isopropanol-dissolved tetrachloroauric acid (HAuCl4:3H2O gold salt) is injected in a dielectric barrier discharge to synthesize plasmonic nanocomposite thin films. Argon is used as carrier gas with or without 133 ppm addition of ammonia (NH3) to respectively get or not a Penning mixture. Results show that NH3 largely influences the salt reduction and thin film properties. According to the aerosol characterization, the size distribution at the plasma entrance supports that isopropanol mainly evaporates before injection in the plasma. The salt initially dissolved in each droplet precipitates during evaporation before injection as solid nanoparticles of about 30 nm diameter with eventual traces of solvent. Then, the nanocomposite thins film are studied. Optical properties, as plasmonic resonance, are characterized by UV–visible absorption spectroscopy. The chemical composition is analyzed using X-ray photoelectron spectroscopy and Raman spectroscopy, complemented by X-ray diffraction analysis as well as chemical mapping obtained by Energy dispersive spectroscopy coupled to scanning electron microscopy (SEM) operating in Scanning Transmission Electron Microscopy mode. Additionally, the morphology of the deposits is investigated by atomic force microscopy and SEM, highlighting the influence of NH3 gas on the film nature and therefore its role in the overall deposition process. Finally, optical emission spectroscopy of the plasma gives clue to better understand the effect of NH3. The overall results show that the salt nanoparticles are reduced in the plasma phase leading to non-aggregated metal Au NPs embedded in a carbon-based matrix formed by isopropanol polymerization. The presence of NH3 in the plasma unambiguously decreases the salt reduction and affects the thin film properties, consequently changing their plasmonic response related to the size, concentration, and composition of the embedded NPs.

Biomass gasification for synthesis gas production represents a promising source of energy based on plasma treatment of renewable fuel resources. Gasification/pyrolysis of crushed wood as a model substance of biomass has been experimentally carried out in the plasma-chemical reactor equipped with gas–water stabilized torch which offer advantage of low plasma mass-flow, high enthalpy and temperature making it possible to attain an optimal conversion ratio with respect to synthesis gas production in comparison with other types of plasma torches. To investigate this process of gasification in detail with possible impact on performance, a numerical model has been created using ANSYS FLUENT program package. The aim of the work presented is to create a parametric study of biomass gasification based on various diameters of wooden particles. Results for molar fractions of CO for three different particles diameters obtained by the modeling (0.55, 0.52 and 0.48) at the exit are relatively good approximation to the corresponding experimental value (0.60). The numerical results reveal that the efficiency of gasification and syngas production slightly decreases with increasing diameter of the particles. Computed temperature inhomogeneities in the volume of the reactor are strongest for the largest particle diameter and decrease with decreasing size of the particles.

Cold atmospheric pressure ambient air plasma generated by Diffuse Coplanar Surface Barrier Discharge (DCSBD) was investigated for inhibition of native microbiota and potentially dangerous pathogens (Aspergillus flavus, Alternaria alternata and Fusarium culmorum) on the maize surface. Moreover, the improvement of germination and growth parameters of maize seeds was evaluated. Maize (Zea mays L.; cv. Ronaldinio), one of the most important cultivated crops worldwide, was selected as the research material. Electrical measurements confirmed the high volume power density (80 W cm−3) of DCSBD plasma. Non-equilibrium plasma state evaluated using optical emission spectroscopy showed values of vibrational and rotational temperature (2700 ± 300) K and (370 ± 75) K, respectively. Changes on the plasma treated seeds surface were studied by water contact angle measurement, scanning electron microscope analysis and Fourier transform infrared spectroscopy. A complete devitalisation of native microbiota on the surface of seeds was observed after a short treatment time of 60 s (bacteria) and 180 s (filamentous fungi). The plasma treatment efficiency of artificially contaminated maize seeds was estimated as a reduction of 3.79 log (CFU/g) in F. culmorum after a 60-s plasma treatment, 4.21 log (CFU/g) in A. flavus and 3.22 log (CFU/g) in A. alternata after a 300-s plasma treatment. Moreover, the obtained results show an increase in wettability, resulting in a better water uptake and in an enhancement of growth parameters. The investigated DCSBD plasma source provides significant technical advantages and application potential for seed surface finishing without the use of hazardous chemicals.

In this study, multiple colors and deluster polyethylene terephthalate (PET) fabrics at one-time printing were obtained by different plasma treating times. Radio frequency (13.56 MHz) plasma was employed to selectively etch on deluster polyethylene terephthalate-titanium dioxide (PET-TiO2) fabrics, which improved the surface roughness and introduced active groups. TiO2 nanoparticles were exposed on the surface of the PET fabrics. The treated PET fabrics exhibited superhydrophilicity, as evidenced by the reduction of the water contact angle to zero degree (0°). A magnetic screen-printing machine was utilized to apply a paste printing consisting of blue pigment, binder, and synthetic thickener. After plasma selective etching, the delusted PET fabric with exposed TiO2 improved the printability. Moreover, this work provided a simple and eco-friendly method for different surface, physical, and chemical properties of the PET fabrics. The method also enhanced the color strength rate, washing, and rubbing fastness of the PET fabrics. Thus, the printing of organic component PET fabrics could be one step toward improving print qualities after plasma etching treatment.

Reliable high-altitude relight is a key combustor requirement for the aero-engine. In general, low pressure and low temperature at high altitude will result in difficult ignition after extinction. In the present work, a simulated high-altitude test facility was designed to establish the capability of high-altitude relight testing. A multi-channel plasma igniter (MCPI) was proposed and designed to obtain reliable altitude ignition. Furthermore, the ignition performance of the MCPI and the traditional spark igniter was compared under varying high-altitude conditions. The separation of the breakdown stage from the discharge was confirmed by observing a time-phased breakdown process between multi-couple electrodes during MCPI discharge. Moreover, the discharge efficiency of the power source is increased from 17 to 36% by MCPI. A plasma kernel with high energy and strong penetration was generated within microsecond scale, while a flame kernel with high energy and large initial volume was formed on millisecond scale. In addition, the stable flame was obtained rapidly owing to the preheating evaporation area expansion, the improving mixture and the increasing heat release. MCPI extends the ignition limit FAR by 39%, 30% and 10% at ground level, 4 km and 8 km, respectively. The advantage of initial flame kernel from MCPI is that it resists heat loss at low temperature, while it does not perform well at extremely low pressure due to the spark-to-glow transition.

Experiments indicate that the temperature in chemical vapor deposition (CVD) of TiN can be decreased from about 1000°C in conventional CVD to about 500°C by the application of a D.C. nonequilibrium plasma. The hardness of the TiN film is greater than 2000 kg/mm2 (Vickers). The effect of pressure, ratio of gas mixture, and discharge parameters on the film deposition rate, its hardness, and microstructures has been studied.