Plasma Chemistry and Plasma Processing (v.30, #3)

DC-Pulsed Plasma for Dry Reforming of Methane to Synthesis Gas by Naser Seyed-Matin; Amir Hossein Jalili; Masih Hosseini Jenab; Seyed Majid Zekordi; Ali Afzali; Chapar Rasouli; Akbar Zamaniyan (333-347).
The carbon dioxide reforming of methane to synthesis gas under DC-pulsed plasma was investigated. The effects of specific input energy and feed ratio on the product distribution and also feed conversion was studied. At the input energy of about 11 eV/molecule per methane and/or carbon dioxide the feed conversion of 38% for CH4 and 28% for CO2 and product selectivity of 74% has been attained for H2 and CO at feed flow rate of 90 ml/min. The energy consumption in this work displays potential to further study and optimization of the process. The importance of the electron impact reactions in the process was discussed. The results show that by prudent tuning of system variables, the process be able to run in the way of synthesis gas, instead of hydrocarbon production.
Keywords: Methane; Pulsed plasma; Synthesis gas; Dry reforming; Carbon dioxide reforming

Determinations of Intermediate Neutral Species in Hydrocarbon Discharge Plasma by J. H. Liu; L. P. Wang; Q. M. Xiao; Z. Yao; H. Ding (349-361).
This work reports laser ionization combined with Time-Of-Flight (TOF) mass spectrometry investigation on intermediate species in the hydrocarbon plasma of atmospheric-pressure fast-flow pulsed dc-discharge. All neutral intermediate species including transient radicals from benzene/Ar discharge have been characterized by a molecular beam sampling combined with TOF mass spectrometry. This shows that with a hydrocarbon gas mixture of 0.3% C6H6 in Ar discharge the intermediate species consist of simple radicals (such as C2, C5H5, C7H7) and polycyclic organic molecules (C10H8, C13H10, C14H10). Theoretical studies on total energies and ionization potentials of the intermediate species have been carried out using the hybrid density functional theory. Effect of the ionization potential on mass spectral intensity has been discussed. Based on the observed data, the possible major neutral reaction channels of the plasma chemistry have been discussed. The developed experimental method has implications in volatile organic compounds removing and impurities diagnosis in Tokamak edge-plasma.
Keywords: Pulsed benzene-discharge; F2-laser-ionization; Molecular beam; TOF mass spectrometer; Intermediate species

Downstream Characterization of an Atmospheric Pressure Pulsed Arc Jet by Yao-wen Hsu; Yao-jhen Yang; Cheng-yi Wu; Cheng-che Hsu (363-372).
An atmospheric pressure nitrogen plasma jet sustained by a repetitive pulsed DC power source is studied. The afterglow characteristics of this plasma jet are studied by an optical emission spectrometer and thermocouples. The effects of the process parameters, namely the applied voltage and the gas flow rate, on the plasma characteristics are investigated. It is shown that the plasma reactivity is controlled by the power deposition to the plasma as well as the decay process of the reactive species upon formation. The reactivity increases with the increase in the applied voltage and with the decrease in the gas flow rate. The jet temperature is primarily controlled by the power density, and it increases with the increase in the applied voltage and with the decrease in the gas flow rate. These observations suggest that the plasma reactivity and the jet temperature of this plasma jet can be nearly independently controlled.
Keywords: Downstream characterization; Atmospheric pressure plasma jet

This work reports on the results of investigations conducted with three layered polypropylene (PP) membranes which were exposed to a N2 flowing microwave (100 W) post discharge, at several flow rates (0.03–1 Slm) and at gas pressure from 0.3 to 40 Torr. The N atoms transmission through the membrane was measured from the intensity variation of the N2, 580 nm afterglow which is related to N atom density, before and after the membranes. The results obtained showed that N-atoms penetrate and cross the membranes with a transmission factor (T N) varying from 20 to 70% during the exposure time (15 min), depending on flow rate and gas pressure. A maximum value T N = 0.7 (±0.05) is found for sufficient low flow rate (less than 0.1 Slm), that is for low flow gas velocity (about 2 × 102 cm s−1).
Keywords: Membranes; Atom transmission; Post-discharge plasma

Decontamination of VX Surrogate Malathion by Atmospheric Pressure Radio-frequency Plasma Jet by Wen-Chao Zhu; Bai-Rong Wang; Hai-Ling Xi; Yi-Kang Pu (381-389).
Decontamination of the VX surrogate (malathion) by the atmospheric pressure radio-frequency plasma jet (APPJ) was investigated. Optical emission spectroscopy was used to identify the active species and measure the neutral gas temperature. The effects of RF input power and exposing time on the decontamination efficiency and neutral gas temperature were investigated. The thermal effect and volatilization could be ignored from the APPJ decontamination mechanism in our processing conditions. The degradation products were identified by gas chromatograph coupled with mass spectrometers (GC–MS). Besides the trace amount of the oxidation product (malaxon), the main degradation products were formed by breaking the S–C bond of malathion. In the end, the main degradation mechanism was drawn out.
Keywords: Radio frequency plasma jet; Dry decontamination; VX surrogate; Malathion

Experimental Study of Capacitive RF c-C4F8 Discharge with Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry by Zhongyue Zhou; Mingfeng Xie; Tang Tang; Yijun Zhang; Tao Yuan; Fei Qi; Tom Ni; Xueyu Qian (391-400).
Capacitive radio frequency (RF) discharge of c-C4F8 (octafluorocyclobutane) has been studied with synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry (PIMS) at 4 Torr and 33.33 kHz. Various free radicals and reactive intermediates have been identified through measurement of photoionization mass spectra and photoionization efficiency (PIE) spectra. CF2=CF2 is main product in the plasma, indicating that the dissociation of c-C4F8 into CF2=CF2 is one of prominent reactions in the present experimental conditions. The observation of large species including C5F8, C5F10 and C6F10 is presented in our work. Besides, the dependences of the signals of neutral species in the discharge of c-C4F8 on RF power are presented in this paper.
Keywords: c-C4F8 ; Capacitive discharge; Photoionization; Mass spectrometry

The deposition of amorphous hydrogenated carbon thin films by inductively coupled radio frequency (IC RF) pure methane plasma and its subsequent removal by IC RF pure oxygen plasma have been studied within a cylindrical glass tube. Both processes were simultaneously monitored by optical emission spectroscopy, light transmission through thin film deposits, temperature of the discharge tube and total gas pressure measurements. Comparing the time evolution of all parameters, various stages of oxygen plasma cleaning process were established. The transitions between E-mode and H-mode of plasma induced by the presence of cleaning products impurities were observed and discussed.
Keywords: Methane plasma; Optical emission spectroscopy; Amorphous hydrogenated carbon; Oxygen plasma cleaning; Plasma sterilization

In this paper, pre-reduced ilmenite concentrate of Indian region was processed successfully by thermal plasma routes to produce high titania slag. Effects of various parameters like time, yield and energy consumption, on TiO2 and FeO content in the slag were studied. One of the main drawbacks of thermal plasma process is higher specific electrical power consumption, especially where power is costlier. So, the main focus is to reduce the energy consumption with better yield in various thermal plasma reactors. It is found that energy consumption decreases in respect to in-flight static bed plasma reactor. If the melting time kept within 2 min, the TiO2 content and iron recovery increased, whereas melting time exceeds 2 min, low yield has been observed. At optimum conditions, TiO2 content in the slag and the iron recovery are 84.5 and 80%, respectively. The phases before and after reduction, the sample were analyzed using X-ray diffraction.
Keywords: Thermal plasma processing; Titania slag; Ilmenite reduction; Titanium dioxide; Plasma rectors

Influence of Solution Conductivity on Contact Glow Discharge Electrolysis by Xing-Long Jin; Xiao-Yan Wang; Hong-Mei Zhang; Qing Xia; Dong-Bin Wei; Jun-Jie Yue (429-436).
Using a thin platinum anode in contact with an electrolytic solution, normal electrolysis develops spontaneously to contact glow discharge electrolysis (CGDE) at sufficiently high voltage. During this transition, midpoint voltage (VD) is an important critical value. From VD on, plasma is sustained by direct current glow discharge between the electrode and the electrolyte surface. And H2O2 is the main non-faradaic yield. In this study, effects of conductivity on VD and the concentration of H2O2 have been investigated in Na2SO4 and NaCl solution. The results indicate that VD decreases with the increasing conductivity. And the value of VD and the concentration of H2O2 in NaCl solution are less than those in Na2SO4 solution. The concentration of H2O2 increases steadily and then decreases to maintain a stationary value.
Keywords: Contact glow discharge electrolysis; Conductivity; Midpoint voltage; Hydrogen peroxide