Plasma Chemistry and Plasma Processing (v.32, #1)

We have employed 800 nm 150 fs laser pulses to carry out photoionization (PI) time-of-flight mass spectrometric detection of intermediates following corona discharges on aromatic molecules (alkylbenzenes and pyridine) in He, stabilized by subsequent supersonic gas expansions. Observed product peaks appear to be at least roughly in proportion to actual number densities; PI induced fragmentation of parent ions appears not to be excessive. Consequently, 800 nm fs PI should be useful for general product analysis applications in plasma chemistry. For most alkylbenzenes subjected to corona discharges in rare gas, the overall trends in product chemistry are similar in many respects to observed flame and pyrolysis chemistry in rare gases for the same species. Following discharge, as in those other cases, H deficient carbon radical fragments initially produced react in turn to form larger aromatic species. However, compared with flame/pyrolysis, discharge produced a larger number of fragment species, which can lead to a wider and somewhat different range of higher mass aromatic products. Co-addition of even a small component of O2 to the discharge mixes has a potent effect in inhibiting formation of higher mass aromatic products in alkylbenzenes.
Keywords: Toluene; Volatile organic compounds; Non-thermal plasma; Time-of-flight mass spectrometry; Photoionization

We investigated the effect of a polyethylene terephthalate (PET) forming process on radiofrequency ammonia plasma surface-treated PET flat films and fibres obtained by melt blowing. Ammonia plasma treatment allowed for the incorporation of amino functionalities on both the film and fibre surfaces, with higher values observed at very short treatment times. This plasma treatment also induced polymer chain scissions which were observed as the formation of hydrophilic nodules that coalesced together and were loosely bound to the underlying polymeric materials. These plasma-induced surface damages were notably more important on the melt-blown PET fibres. Consequently, maximisation of the surface amino groups with minimal polymer chain breaking was achieved using very short plasma treatment times (typically 1 s). We also demonstrated that the polymer forming process must be taken into account when plasma modifications are to be performed on PET, as it may already lead to polymer chain breakings subsequently added to those induced in the plasma environment.
Keywords: Fragmentation; Plasma modification; Polyethylene terephtalate; Stability; Surface morphology

Polyfluorene Thin Films Synthesized by a Novel Plasma Polymerization Method by Hilal Goktas; Dogan Mansuroglu; Betul Atalay; Sinan Bilikmen; Ismet Kaya (35-44).
The synthesis of polyfluorene (PF) thin films by simultaneously superposing a continuous and pulsed discharge and the characterizations of these samples are presented. The double discharge plasma system is constructed by superposing two discharges; namely, a low pressure dc glow one and a high current pulsed one. The fluorene monomer in powder form was vaporized in the system at argon plasma without any modification, at 0.5 mbar operating pressure. The structure of the thin films was investigated via XPS, UV–visible, FTIR, XRD and SEM. The FTIR and the UV–visible results revealed that the fluorene structure was retained at the produced samples. Semi-conducting behavior was established, and upon the iodine doping, the optical energy band gap (E g ) dropped down from 3.7 to 2.4 eV. The morphology of the synthesized PF thin films was amorphous, with granular structures of different sizes depending on the location of the substrate.
Keywords: Double discharge; Filamentary discharge; Plasma polymerization; Polyfluorene; Thin films

Torch Design Modification Using Micro-jets to Suppress Fluid Dynamic Instabilities in Plasma Arc Cutting by Sungje Kim; Joachim Heberlein; Jon Lindsay; John Peters (45-63).
Highly constricted plasma arcs are widely used for metal cutting. One important characteristic of the cutting process is the consistency of the cut edge around the perimeter of the workpiece. Cut edge properties, including surface roughness, edge shape and dross formation, are presumed to depend on the local temperature and chemical composition of the cutting arc adjacent to the cut edge. Fluid dynamic instabilities in the arc boundary leading to entrainment of the low temperature ambient gas can have a strong effect on cutting performance. This paper describes the use of micro-jets to suppress fluid dynamic instabilities in the boundary layer of a plasma cutting arc. Previously developed optical diagnostics and analysis methods are used to characterize the arc boundary layer. Multiple nozzle designs have been investigated to quantify the effects of utilizing micro-jet flow around the arc column, and some relationships between nozzle design and cut quality are presented.
Keywords: Plasma arc cutting; Fluid dynamic instability; Symmetry; Micro-jets; Cut quality

Direct current (dc) plasma torch with inter-electrode inserts has the merits of fixed arc length, relative high enthalpy and may show advantages in future plasma processes where stability and controllability are must-have. Energy fluctuations in the plasma may result from power supply ripple, arc length variation, and/or acoustic oscillation. Using an improved power supply with a flat waveform, the characteristics of an argon plasma energy instabilities under reduced pressure were studied by means of simultaneously monitoring the arc voltage and arc current spectrum. Dependence of the arc fluctuation behavior on the plasma generating parameters, such as the current intensity, the plasma gas flow rates and the vacuum chamber pressure were investigated and discussed. Results show that the plasma torch has a typical U-shaped voltage-ampere characteristic (VAC). The correlation between the VAC and the probability of energy distributions was studied. Through pressure measurements at the cathode cavity and the vacuum chamber, the existence of sonic flow in the inter-electrode insert channel was confirmed.
Keywords: dc plasma; Inter-electrode insert; Fluctuation; Stability

This paper is devoted to the calculation of the chemical equilibrium composition and thermodynamic properties of reacting mixtures of carbon and water at high temperature. Equilibrium particle concentrations and thermodynamic properties including mass density, molar weight, entropy, enthalpy and specific heat at constant pressure, sonic velocity, and heat capacity ratio are determined by the method of Gibbs free energy minimization, using species data from standard thermodynamic tables. The calculations, which assume local thermodynamic equilibrium, are performed in the temperature range from 400 to 30,000 K for pressures of 0.10, 1.0, 3.0, 5.0 and 10.0 atm. The properties of the reacting mixture are affected by the possible occurrence of solid carbon formation at low temperature, and therefore attention is paid to the influence of the carbon phase transition by comparing the results obtained with and without considering solid carbon formation. The results presented here clarify some basic chemical process and are reliable reference data for use in the simulation of plasmas in reacting carbon and water mixtures together with the need of transport coefficients computation.
Keywords: Carbon; Water; Thermal plasmas; Equilibrium composition; Thermodynamic properties; Phase transition

The decomposition kinetics of sulfonol (surfactant) in water solutions as well as the formation kinetics of decomposition products under the action of an oxygen dielectric barrier discharge (DBD) at atmospheric pressure in the presence or absence of TiO2, NiO and Ag2O catalysts in the plasma zone was studied. The DBD discharge was shown to have high decomposition efficiency (phenol-up to 98%, sulfonol-up to 80%). In a plasma-catalytic hybrid process, the efficiency of organic substances decomposition was higher than efficiency for the DBD treatment without catalyst. The catalysts application resulted in a change in the ratio and yield of decomposition products.
Keywords: Oxygen surface barrier discharge; Surfactant; Phenol; Decomposition; Catalysts

Wastewater containing pentachlorophenol (PCP) was treated by granular activated carbon (GAC) adsorption and double-dielectric barrier discharge (D-DBD) plasma. A packed bed D-DBD reactor was applied for removal of PCP on GAC and GAC regeneration, where the discharge gap was filled with GAC. PCP degradation efficiency of 65% and GAC regeneration efficiency (RE) of 87% were achieved. Effects of discharge power, treatment time and O2 flow rate on PCP degradation and GAC regeneration were investigated. Increasing discharge power, treatment time and O2 flow rate were favorable for PCP degradation, and also contributed to GAC RE. C–Cl bonds in PCP were cleaved by D-DBD plasma. Effect of D-DBD plasma on physical and chemical properties of GAC during GAC regeneration process was characterized by N2 adsorption and Boehm titration. This study is expected to demonstrate the feasibility of applying D-DBD plasma for efficient organic wastewater treatment by coupling with GAC adsorption.
Keywords: Double-dielectric barrier discharge plasma; Activated carbon adsorption; Wastewater treatment; Degradation; Activated carbon regeneration

Role of CH, CH3, and OH Radicals in Organic Compound Decomposition by Water Plasmas by Takayuki Watanabe; Narengerile; Hiroshi Nishioka (123-140).
Decomposition of acetone, methanol, ethanol, and glycerine by water plasmas at atmospheric pressure has been investigated using a direct current discharge. At torch powers of 910–1,050 W and organic compound concentrations of 1–10 mol%, the decomposition rate of methanol and glycerine was over 99%, while those of acetone and ethanol was 95.4–99%. The concentrations of H2 obtained were 60–80% in the effluent gas for any compounds by pyrolysis. Based on the experimental results, the decomposition mechanism of organic compounds in water plasmas was proposed and the roles of intermediate species such as CH, CH3, and OH have been investigated; CH radical generated from organic compounds decomposition was easily oxidized to form CO; incomplete oxidation of CH3 leads to C2H2 generation as well as soot formation; and negligible amount of soot observed from glycerine decomposition even at high concentration indicated that oxidation of CH×(×:1–3) was enhanced by OH radical.
Keywords: Water plasma; Decomposition of organic compounds; CH, CH3, and OH radicals

A strong ionization dielectric barrier discharge was used to produce a high concentration of reactive oxygen species that were then injected into a simulated flue gas in a duct to remove SO2 by oxidation. Sulfuric acid (H2SO4) was produced through the following two reactions: (1) O3 oxidation of SO2–SO3, which then reacted with H2O to produce H2SO4; and (2) reaction of O2 + with H2O to produce ·OH radicals, which then rapidly and non-selectively oxidized SO2–H2SO4. When the molar ratio of reactive oxygen species to SO2 was 4:1, the SO2 removal efficiency was 94.6%, the energy consumption per cubic meter of flue gas was 13.3 Wh/m3, the concentration of recovered H2SO4 was 4.53 g/l, and the H2SO4 recovery efficiency was 28.8%. The H2O volume fraction in the simulated flue gas affected the SO2 removal efficiency, whereas the O2 and CO2 volume fractions did not. These results prove that oxidation by reactive oxygen species is a feasible method for flue gas desulfurization.
Keywords: Reactive oxygen species; ·OH radicals; Removal SO2 ; SO2 removal efficiency; H2SO4

Characteristics of the Decomposition of CO2 in a Dielectric Packed-Bed Plasma Reactor by Qinqin Yu; Meng Kong; Tong Liu; Jinhua Fei; Xiaoming Zheng (153-163).
The decomposition of CO2 in a dielectric packed-bed plasma reactor has been studied. It was found that the dielectric properties and morphology of packing dielectric pellets play important roles in the reaction due to their influence on the electron energy distribution in the plasma. The acid–base properties of the packing materials also affect the reaction through the chemisorption of CO2 on basic sites of the materials. Heterogeneous reactions on the solid surfaces of the dielectric materials also play a role in the reaction, which was also confirmed through the investigation of the influence of the discharge length on the reaction. The reverse reaction of CO2 decomposition, the oxidation of CO, was also investigated to further understand the role of dielectric materials in the plasma and their effect on plasma reactions. Both the decomposition of CO2 and the oxidation of CO in non-packed or dielectric packed reactors are first-ordered.
Keywords: Packed-bed plasma reactor; CO2 ; Non-thermal plasma; Dielectric materials

Effect of Dielectric Barrier Discharge Treatment of Blood Plasma to Improve Rheological Properties of Blood by Jin M. Jung; Yong Yang; Dong H. Lee; Greg Fridman; Alexander Fridman; Young I. Cho (165-176).
The whole blood viscosity (WBV) is one of the major independent indicators for the risk of cardiovascular disease, stroke, and peripheral arterial diseases. Furthermore, oxidized LDL molecules are known to cause atherosclerotic plaques in arteries, and it is one of the key components that increase WBV. The present study attempted to reduce WBV by coagulating plasma proteins and lipid molecules from blood plasma using non-thermal dielectric barrier discharge (DBD) and removing them through filtration. The DBD treatment was found to produce coagulated particles in blood plasma. After filtration of the coagulated particles, WBV decreased by 9.1 and 17.7% for both systolic and diastolic blood viscosities, respectively. The present results suggest that the removal of excess plasma proteins and lipid molecules might be feasible using DBD treatment.
Keywords: Dielectric barrier discharge (DBD); Blood viscosity; Filtration; Fibrinogen; LDL