Plasma Chemistry and Plasma Processing (v.33, #3)

A comparison is made for the helium and argon dielectric barrier discharge, in symmetrical electrode configuration, and on the plasma-induced effects, under He and Ar gaseous environment, on polypropylene and poly methyl methacrylate films, selected as polymers bearing distinct structure, functionality, polarity, degree of oxidation and crystallinity, thus allowing an analysis on the role of plasma active species created in inert gas environment in the surface mechanisms and assessment on the discharge efficiency in surface treatment. It is shown that He allows more fine tuning of the discharge parameters and control over the discharge energy, offering overall a larger range of variation both for plasma conditions and surface properties. The effects of the two discharges are similar at the material surface, whereas He-DBD induces a higher level of modification within the depth of the material. Although the amount of activated oxidizing species is lower in Ar-DBD, it conducts to comparable surface modification, under, indeed, much limited plasma parameters, which points to the role of oxygen due to residual air. The nature of the polymer, mainly the presence of intrinsic oxidized functionalities in its structure, limits only the overall level of modification, whereas the discharge controls the timescale and the mechanisms. Helium offers indeed some obvious advantages to produce and stabilize the discharge at atmospheric pressure, due to particular discharge physics. Nonetheless, the discharge parameters and the surface properties for Ar-DBD treated samples show a good balance, supporting the substitution of He with Ar for surface processing applications.
Keywords: Dielectric barrier discharge; Inert gas; Helium metastables; Polymer; Functionalization

Removal of Carbon Disulfide from Gas Streams Using Dielectric Barrier Discharge Plasma Coupled with MnO2 Catalysis System by Chengzhu Zhu; Jun Lu; Xiaohui Wang; Qin Huang; Li Huang; Jiaquan Wang (569-579).
The removal of gaseous carbon disulfide (CS2) via dielectric barrier discharge (DBD) combined with MnO2 catalysis has been investigated. CS2 removal and energy yield (EY) had been examined as a function of catalyzer position in DBD reactor, initial CS2 concentration, input power, and gas residence time. The results showed that DBD combined with MnO2 catalyst can improve the CS2 energy and removal efficiency, and MnO2 catalyst placed in afterglow area can enhance the CS2 removal efficiency by about 10 % as compared with DBD treatment only. When increasing initial CS2 concentration and flow rate, a higher EY is obtained. The possible CS2 removal pathways by DBD combined with MnO2 were proposed based on the product identification by FT-IR.
Keywords: Dielectric barrier discharge (DBD); MnO2 ; CS2 ; Removal efficiency; CS2 removal energy yield

Plasmas in saline solution driven by a repetitive bipolar pulsed power source are studied. We use a negative pulse to generate electrolytic gas with a controllable amount, followed by a positive pulse to ignite the plasma. With an increase in the negative voltage pulse amplitude from 0 to −80 V, we observed an increase in the amount of electrolytic gas (hydrogen) formation, resulting in a reduced time delay, from 65 to 6 μs, required to ignite the plasma upon the onset of the positive pulse. A decrease, from 1.75 to 1.0 A, in the peak currents within the positive voltage pulse is also observed. Optical emission spectroscopy shows that the intensity ratio of the Hα (656 nm) to Na (588 nm) emission lines increases from zero to 0.0035. These observations can be well explained by the increase in the gas coverage on the electrode surface and the change in the gas composition within which the plasma is ignited with the application of the negative pulse.
Keywords: Plasmas in solution; Bipolar power source; Gas composition

Measurement of Temperature in the Steam Arcjet During Plasma Arc Cutting by A. Mašláni; V. Sember; T. Stehrer; H. Pauser (593-604).
Spectroscopic measurements were performed by observing the plasma inside the kerf during cutting of stainless steel using direct current electric arc. Experiments were carried out on the plasma torch operated with the plasma gas composed of the vaporized mixture of water and ethanol; arc current was 60 A and cutting speed 30 cm/min. Emission spectral lines of neutral iron were used to experimental evaluation of the temperature of plasma in the kerf and close under the cut plate. Complicated nature of the plasma inside the kerf, including presence of metallic vapours and departures from equilibrium, was taken into account. Hence relatively reliable results were obtained, from which it was possible to get insight into the energy balance and cutting performance of the torch. Temperature of the plasma in the kerf was substantially lower than at the nozzle exit of the torch; however the temperature drop along the kerf was small.
Keywords: Plasma arc cutting; Optical emission spectroscopy; Plasma temperature; Steam torch

Tungsten Carbide and Vanadium Carbide Nanopowders Synthesis in DC Plasma Reactor by A. V. Samokhin; N. V. Alekseev; S. A. Kornev; M. A. Sinaiskii; Yu. V. Blagoveschenskiy; A. V. Kolesnikov (605-616).
Air–methane and nitrogen–hydrogen DC thermal plasma confined flows were used to synthesize tungsten carbide and vanadium carbide nanopowders. The influence of input process parameters such as C/W and C/V molar ratio, plasma jet chemical composition, plasma jet enthalpy, and reactants flow rates on the average nanoparticle size, chemical and crystallographic phase compositions were investigated. During post heat treatment, the synthesized MeC1−x nanopowders were fully carburized to monocarbides WC and VC with particles size less than 80 and 40 nm correspondently.
Keywords: High-temperature alloys; Chemical vapour condensation; Plasmachemical synthesis

Ammonia Decomposition Using Electron Beam by Youn-Suk Son; Ki-Hyung Kim; Ki-Joon Kim; Jo-Chun Kim (617-629).
This study was carried out to determine the decomposition characteristics of ammonia using an electron beam (EB). Factors influencing these decomposition characteristics such as background gases (air, N2, O2, and He), initial ammonia concentration (50–150 ppm), relative humidity (0 or 90 %), and absorbed dose (1–15 kGy) were investigated. In the results of removal characteristics by different background gases, the decomposition efficiency of ammonia was lower (approximately 45 % at 5 kGy) when He was used as a background gas compared to the efficiencies when other background gases were selected. Ammonia removal efficiencies, when initial concentrations were 50 and 150 ppm, were 95 and 75 %, respectively, at 15 kGy. Ozone generation by EB irradiation increased from 2.5 kGy and reached a maximum of 45 ppm when 5 kGy of the absorbed dose was irradiated. However, ozone generation started to decrease when the absorbed dose exceeded 5 kGy and decreased to 0.27 ppm at 15 kGy.
Keywords: Ammonia; Electron beam; Radical; Decomposition; By-product