Plasma Chemistry and Plasma Processing (v.28, #6)

Abatement of Trichloromethane by Using Nonthermal Plasma Reactors by Y. S. Mok; S.-B. Lee; J.-H. Oh; K.-S. Ra; B.-H. Sung (663-676).
This work investigated the destruction of a halogenated carbon (trichloromethane) using different types of nonthermal plasma reactors. Three reactors, i.e., a surface discharge reactor, a dielectric-packed bed reactor and a barrier discharge reactor with a perforated dielectric tube, were compared with respected to the trichloromethane destruction efficiency. The effect of oxygen content and input power on the trichloromethane destruction was examined, and the byproducts were analyzed to elucidate the destruction pathways. The dielectric-packed bed reactor was found to show better performance in the trichloromethane destruction than the other two reactors. The increase in the oxygen content decreased the destruction efficiency, and the highest destruction efficiency was obtained at oxygen content 0.5%. The calculations for electron-molecule collisions indicated that the most abundant reactive species initiating the destruction of trichloromethane are metastable nitrogen molecules. The major byproducts were CO and Cl2, and the formations of NO2 and N2O were also significant.
Keywords: Nonthermal plasma; Halogenated carbon; Trichloromethane; Destruction; Byproducts

Decomposition of Methylene Blue in Water by Corona Discharges by Monica Magureanu; Daniela Piroi; Florin Gherendi; Nicolae Bogdan Mandache; Vasile Parvulescu (677-688).
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.
Keywords: Corona discharges; Degradation; Methylene blue; Plasma treatment

Microbial pollution commonly causes serious pipe corrosion in oil field injection water system. This paper reports on the application of non-thermal plasma to inactivate bacteria in oil filed injection water. As an efficient inactivation technology, pulsed streamer discharge plasma method injects energy into solution through a plasma channel formed by discharge between electrodes and produces various active species in solution with physical effects (electric field, UV etc.) occurring. Saprophytic bacteria, iron bacteria and sulfate reducing bacteria are used as target. The effects of various gases bubbling (oxygen, nitrogen and air) as well as aeration intensity are investigated. Experimental results show that the inactivation efficiency is greatly enhanced by gas bubbling. After 150 s discharge with oxygen bubbling (667 m3 (m3 h)−1), the inactivation efficiencies of saprophytic bacteria, iron bacteria and sulfate reducing bacteria achieve 1.85, 4.51 and 5.70 log reduction, respectively. The possible mechanism of bacteria inactivation is also discussed.
Keywords: Plasma discharge; Inactivation; Biocorrosion inhibition; Mechanism

Application of Low-Pressure Plasma Pretreatment in Silk Fabric Degumming Process by Jia-Jie Long; Hong-Wei Wang; Tong-Qing Lu; Ren-Cheng Tang; Ya-wei Zhu (701-713).
A novel and effective method was developed for raw silk fabric degumming with the application of low-pressure argon plasma in pretreatment combining a subsequent one-step mild wet-chemical process. The plasma parameters, such as argon pressure, discharge power and exposure time, were optimized according to degumming loss and the properties of fabric such as capillary rise, tensile strength, bending rigidity, etc. An optimized plasma pretreatment for raw silk fabric degumming was at 80 Pa of argon gas and 60 W glow discharge power for 5–10 min. The raw silk fabric and fibers pretreated by argon plasma were characterized by scanning electronic microscopy and X-ray powder diffraction. In comparison with a conventional degumming process, the proposed method achieved comparable degumming efficiency and properties of silk fabric, and it was more environmentally friendly by shortening the conventional wet-chemical treatment process, saving the dosage of degumming agents, water and energy.
Keywords: Low pressure discharge; Etching; Degumming; Sericin; Silk fabric

Surface Modification of Silicone Rubber by CF4 Radio Frequency Plasma Immersion by Song-Hua Gao; Ke-Sheng Zhou; Ming-Kai Lei; Li-Shi Wen (715-728).
Silicone rubber samples were treated by CF4 capacitively coupled plasma at radio frequency (RF) power of 60, 100 and 200 W for a treatment time up to 20 min under CF4 flow rate of 20 sccm, respectively. Static contact angle, ATR-FTIR and XPS, and AFM were employed to characterize the changes of surface on hydrophobicity, functional groups, and topography. The results indicate the static contact angle is improved from 100.7 to 150.2°, and the super-hydrophobic surface, which corresponds to a static contact angle of 150.2°, appears at RF power of 200 W for a 5 min treatment time. It is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of surface roughness created by the ablation reaction of CF4 plasma and the formation of [–SiF x (CH3)2−x –O–] n (x = 1, 2) structure produced by the direct attachment of F atoms to Si.
Keywords: Silicone rubber; Surface modification; CF4 plasma; Hydrophobicity; XPS

Effects of Nozzle Length and Process Parameters on Highly Constricted Oxygen Plasma Cutting Arc by Qianhong Zhou; Hui Li; Feng Liu; Shaofeng Guo; Wenkang Guo; Ping Xu (729-747).
The influence of nozzle length and two process parameters (arc current, mass flow rate) on the plasma cutting arc is investigated. Modeling results show that nozzle length and these two process parameters have essential effects on plasma arc characteristics. Long nozzle torch can provide high velocity plasma jet with high heat flux. Both arc voltage and chamber pressure increase with the nozzle length. High arc current increases plasma velocity and temperature, enhances heat flux and augments chamber pressure and thus, the shock wave. Strong mass flow has pinch effect on plasma arc inside the torch, enhances the arc voltage and power, therefore increases plasma velocity, temperature and heat flux.
Keywords: Nozzle length; Arc current; Mass flow rate; Plasma cutting arc; Numerical simulation