Plasma Chemistry and Plasma Processing (v.29, #3)

Oxidation of Acetylene in Atmospheric Pressure Pulsed Corona Discharge Cell Working in the Nanosecond Regime by M. Redolfi; N. Aggadi; X. Duten; S. Touchard; S. Pasquiers; K. Hassouni (173-195).
Combined experimental and modeling studies of acetylene oxidation in pulsed corona discharges working in the nanosecond regime are presented. The corona cell was characterized in term of power deposition to provide input data for the model. The concentrations of ozone, CO, CO2 and residual acetylene were systematically measured for model validation purposes. The model used allows describing the detailed chemistry in the discharge and the mass transfer between the microdischarges and the discharge free regions in the corona cell. Results showed that the model allows a satisfactory prediction of the acetylene residual fraction, CO and CO2 yields and O3 concentration for a wide range of conditions. They enabled a precise identification of the product distribution and confirmed the central role of O-atom in the oxidation process. They also revealed that ketene, H2CCO, plays an important role in the oxidation mechanism and allowed drawing some conclusions on the optimization of the oxidation process.
Keywords: Corona discharge; Acetylene; Kinetic; Oxygen atom; Ozone

Plasma Grooving System Using Atmospheric Pressure Surface Discharge Plasma by Toshiyuki Hamada; Tatsuya Sakoda; Masahisa Otsubo (197-204).
To fabricate narrow front contact grooves on a single crystalline silicon solar cell, we carried out etching of a silicon nitride film on a silicon substrate using the surface discharge plasma operated at atmospheric pressure. The control of groove width by changing the discharge voltage (V d) and the length of a back electrode (l) used for formation of the surface discharge was examined. It was found that narrower electrode grooves could be obtained when l was short. For the case of l = 2 mm, the narrowest groove of 116 μm was obtained at V d = 3.5 kV and the processing time (t e) of 10 s.
Keywords: Surface discharge plasma; Silicon nitride film; Front contact; Electrode groove; Back electrode length

NO Conversion by Dielectric Barrier Discharge and TiO2 Catalyst: Effect of Oxygen by I. Jõgi; V. Bichevin; M. Laan; A. Haljaste; H. Käämbre (205-215).
Present study was carried out to investigate the conversion of NO by simultaneous action of the dielectric barrier discharge (DBD) and TiO2 catalyst. NO conversion was recorded as a function of the input energy density by varying the percentage of NO and O2. NO conversion efficiency increased at higher content of O2. The presence of a TiO2 coating inside the reactor resulted in initially enhanced NO conversion but in few minutes the positive effect of TiO2 diminished. The increased conversion of NO in initial stage of the process was more pronounced at higher densities of input energy (higher than 100 J/l) and at lower O2 concentrations, but without O2 the TiO2 coating had no effect on the conversion of NO. The results indicate that the conversion of NO during first few minutes is related to the surface reactions with adsorbed atomic oxygen.
Keywords: NO conversion; Dielectric barrier discharge; Catalysis

Investigation of Dry Reforming of Methane in a Dielectric Barrier Discharge Reactor by Qi Wang; Bin-Hang Yan; Yong Jin; Yi Cheng (217-228).
Low temperature conversion of CH4 and CO2 was investigated in a coaxial dielectric barrier discharge reactor at ambient pressure. Main parameters, including the input power, the residence time, the discharge gap, the molar ratio of the feed gases and the multi-stage ionization design were evaluated to understand the ways to improve the conversion of greenhouse gases and reduce the output of by-products. At certain input power, the conversion of CH4 and CO2 can reach 0.797 and 0.527, respectively, when the molar ratio of CH4/CO2 is one. When this ratio was low to 1:5, the conversion of CH4 was promoted to 0.843 and the selectivity to CO and H2 was almost 100%. The multi-stage ionization favored the conversion of CO2, which would also be an efficient design to promote the selectivity to the main products such as CO and H2 and suppress the selectivity to the by-products.
Keywords: Dry reforming; Methane; CO2 ; Cold plasma; Dielectric barrier discharge

The distribution of active species in remote oxygen and nitrogen plasma and the germicidal effect (GE) of Staphylococcus aureus on the surface of medical poly(tetrafluoroethylene), polyvinyl chloride and polyethylene terephthalate films, which had been widely used in medical devices, were studied. The results showed that the concentration of electrons and ions decreased rapidly with increasing the distance from the center of induction coil, which approximated to 0 at 40 cm, whereas the concentration of both oxygen and nitrogen radicals reduced slowly, which decreased 20% within 40 cm. Fast etching action on cell membrane by electrons, ions and radicals are primary reasons of oxygen and nitrogen plasma inactivation, which leads to the cellular contents effuse and engender bacteria death, however, the GE of UV radiation in remote plasma is feebleness comparatively. The GE also depends on the oxidation of gas for discharge and the surface characters of material.
Keywords: Remote plasma; Inactivation; Staphylococcus aureus ; SEM

In the present study, formation of hydrogen peroxide (H2O2) and degradation of 4-chlorophenol (4-CP) induced by DC diaphragm glow discharge (DGD) in a sodium sulfate solution were investigated. The discharge was generated in a small hole on a quarts plate interposed between two submersed graphite electrodes. Experimental results showed that 750 V was the optimum voltage for H2O2 formation and 4-CP degradation. Both the H2O2 formation and the 4-CP degradation proceeded faster in cathodic compartment than in anodic compartment. Lowering the solution pH was favorable for 4-CP degradation but showed no appreciable effect on H2O2 formation. Addition of hydroxyl radical scavenger (methanol) to the solution decreased the H2O2 formation and the 4-CP degradation. Iron species especially ferric ions enhanced the 4-CP degradation markedly. Based on the analyzes of Current–Voltage characteristics and chemical effects, it was deduced that the mechanism of DGD was similar to that of contact glow discharge electrolysis.
Keywords: CGDE; Diaphragm discharge; Hydrogen peroxide; p-Chlorophenol