Plasma Chemistry and Plasma Processing (v.28, #5)

Submerged Arc Breakdown of Sulfadimethoxine (SDM) in Aqueous Solutions by Naum Parkansky; Boris A. Alterkop; Raymond L. Boxman; Hadas Mamane; Dror Avisar (583-592).
Low voltage, low energy submerged pulsed arcs were used to break-down Sulfadimethoxine (SDM) contamination in aqueous solutions. The SDM concentration decreased exponentially with rate constants of 0.13–1.9 min−1 during processing by pulsed arcs with a pulse repetition rate of 100 Hz, energies of 2.6–192 mJ and durations of 20, 50 and 100 μs. The electrical energy consumption was minimized with short duration pulses––1.5 kW-hr/m3 with 7.5 mJ, 20 μs pulses for 90% SDM removal.
Keywords: Submerged pulsed arc; Electro-hydraulic discharge; Water treatment; Antibiotic; Plasma

Plasma-Induced Synthesis of Organic Compounds From Graphite and Aqueous Solution by Xiangqin Wang; Huaibin Shi; Zengliang Yu (593-599).
Discharge experiments were performed to explore the synthesis between graphite and aqueous solution. It was found that atomic carbon was transferred from anode into the solution by arc-discharge experiments and various kinds of organic compounds were generated by synthetic reactions from graphite and water or ammonia water. Carboxylic acids and amino acids were identified in the products by GC-MS and HPLC analyses. It is well known that graphite can hardly combine with other substances under common conditions. So the reaction not only provided an interesting attempt for the chemical transformation from graphite to organic compounds but also served as a useful reference for the formation of organic compounds from atomic carbon under primitive earth conditions.
Keywords: Plasma-induced; Synthesis; Graphite; Aqueous solution; Organic compounds; Discharge

Microcapillary Supersonic Free-jet Injection: Plasma Diagnostics by Ruina Gu; Tito Garza-Lopez; R. Bruce Doak (601-615).
Supersonic injection of a neutral, ground state gas through a microcapillary nozzle into a low density, weakly ionized, flowing plasma is employed to obtain information on the plasma characteristics. The “zone of silence” of the injected free-jet constitutes a pristine pocket of injected gas, adjustable in size by varying nozzle pressure and diameter of the injector. The shock waves bounding this region exclude massive particles yet transmit electrons, which excite the injected gas to yield radiative emission on lines specific to the gas. Other possible uses of microcapillary injection are discussed.
Keywords: Plasma diagnostics; Supersonic free-jet; Microcapillary nozzle; Microjet; Gas injection

Cold Plasma Processing and Plasma Chemistry of Metallic Cobalt Surface by Sang Hwan Jeon; Yong Soo Kim; Chong Hun Jung (617-628).
Plasma processing of metallic cobalt was experimentally investigated with three fluorine-containing gases, CF4–O2, SF6–O2, and NF3 to determine the surface decontamination rate and to examine the reaction mechanism. Results show that the maximum etching rate reaches 17.12 μm/min with NF3 gas at 420°C, while the rates are 2.56 μm/min and 1.14 μm/min with CF4–O2 and SF6–O2 gas, respectively, at the same temperature. AES analysis identified the constituent elements of the reaction products to be oxygen, fluorine, and cobalt, and XPS analysis reveals that the reaction product with all three plasma gases is very likely to be CoF2.
Keywords: Cold plasma; Metallic surface decontamination; Cobalt; Cobalt fluoride; Auger electron spectroscopy; X-ray photoelectron spectroscopy

Ethylene oxide (EO), a valuable chemical feedstock in producing many industrial chemicals, which is industrially produced by the partial oxidation of ethylene, so-called ethylene epoxidation, has been of great interest in many global research studies. In this work, the epoxidation of ethylene under a low-temperature dielectric barrier discharge (DBD) was feasibly investigated to find the best operating conditions. It was experimentally found that the EO yield decreased with increasing O2/C2H4 feed molar ratio, feed flow rate, input frequency, and electrode gap distance, while it increased with increasing applied voltage up to 19 kV. The highest EO yield of 5.6% was obtained when an input frequency of 500 Hz and an applied voltage of 19 kV were used, with an O2/C2H4 feed molar ratio of 1:1, a feed flow rate of 50 cm3/min, and an electrode gap distance of 10 mm. Under these best conditions, the power consumption was found to be as low as 6.07 × 10−16 Ws/molecule of EO produced.
Keywords: Epoxidation; Ethylene oxide; Dielectric barrier discharge

Ethylene Epoxidation over Alumina-Supported Silver Catalysts in Low-Temperature AC Corona Discharge by Sumaeth Chavadej; Anothai Tansuwan; Thammanoon Sreethawong (643-662).
In this paper, the epoxidation of ethylene over different catalysts—namely Ag/(low-surface-area, LSA)α-Al2O3, Ag/(high-surface-area, HSA)γ-Al2O3, and Au–Ag/(HSA)γ-Al2O3—in a low-temperature corona discharge system was investigated. In a comparison among the studied catalysts, the Ag/(LSA)α-Al2O3 catalyst was found to offer the highest selectivity for ethylene oxide, as well as the lowest selectivity for carbon dioxide and carbon monoxide. The selectivity for ethylene oxide increased with increasing applied voltage, while the selectivity for ethylene oxide remained unchanged when the frequency was varied in the range of 300–500 Hz. Nevertheless, the selectivity for ethylene oxide decreased with increasing frequency beyond 500 Hz. The optimum Ag loading on (LSA)α-Al2O3 was found to be 12.5 wt.%, at which a maximum ethylene oxide selectivity of 12.9% was obtained at the optimum applied voltage and input frequency of 15 kV and 500 Hz, respectively. Under these optimum conditions, the power consumption was found to be 12.6 × 10−16 W s/molecule of ethylene oxide produced. In addition, a low oxygen-to-ethylene molar ratio and a low feed flow rate were also experimentally found to be beneficial for the ethylene epoxidation.
Keywords: Ethylene epoxidation; Ethylene oxide; Corona discharge; Silver; Alumina