Study of the Anode Region of a DC Glow Discharge by a Spatially One-Dimensional Hybrid Method

The anode region of a dc glow discharge at low pressure and current is studied by a new self-consistent, spatially one-dimensional hybrid method. The method consists of the coupled solution of the steady-state fluid equations of electrons, ions, and excited atoms and the Poisson equation using the electron transport properties as well as the excitation and ionization frequencies from a strict solution of the non-uniform kinetic equation of the electrons. Results such as the electric potential, the electron velocity distribution function, and the densities of the charge carriers and excited atoms are reported for the anode region of neon glow discharges. Physical properties of the plasma in the anode region known from experiments have been confirmed by the model such as the occurrence of the anode fall, a formation of plateau-like areas of the potential profile in front of the anode, the anode dark space, and the anode glow.     

Steel surface processing by a continuous optical discharge plasma

The influence of a continuous optical discharge (COD) plasma generated in flowing argon and argon-nitrogen mixture on alloy and carbon steel surfaces has been investigated. Changes in the structure, element composition, and microhardness of steel surface layers under the action of a COD plasma and laser beam were observed. In the presence of a COD plasma the microhardness distribution in hardened zone reaches its maximum at the metal surface and is different from that measured for samples processed by laser beam only.     

Spectroscopic characterization of a microplasma used as ionization source for ion mobility spectrometry

We report a miniaturized excitation source for soft ionization of molecules based on a dielectric barrier discharge. An atmospheric plasma is established at the end of a 500 μm diameter capillary using He as buffer gas. The plasma jet which comes out of the capillary is dependent on the gas flow rate. The mechanism of the production of N₂⁺ outside the capillary, which is relevant for the protonation of molecules and sustains the production of primary ions, is investigated by spatially resolved spectroscopic measurements throughout the plasma. Possible application of such miniaturized plasmas is the ionization of gaseous compounds under atmospheric pressure as an alternative to traditional APCI (atmospheric pressure chemical ionization). The miniaturized plasma was applied as ionization source for ion mobility spectrometry where the common sources are radioactive, thus limiting the place of installation. First measurements of gaseous compounds with such a plasma ion mobility spectrometer with promising results showed detection limits comparable or even better than those obtained using common radioactive ionization sources.     

Methane Conversion Using Dielectric Barrier Discharge：Comparison with Thermal Process and Catalyst Effects

The direct conversion of methane using a dielectric barrier discharge has been experimentally studied. Experiments with different values of flow rates and discharge voltages have been performed to investigate the effects on the conversion and reaction products both qualitatively and quantitatively. Experimental results indicate that the maximum conversion of methane has been 80% at an input flow rate of 5 ml/min and a discharge voltage of 4 kV. Experimental results also show that the optimum condition has occurred at a high discharge voltage and higher input flow rate. In terms of product distribution, a higher flow rate or shorter residence time can increase the selectivity for higher hydrocarbons. No hydrocarbon product was detected using the thermal method, except hydrogen and carbon. Increasing selectivity for ethane was found when Pt and Ru catalysts presented in the plasma reaction. Hydrogenation of acetylene in the catalyst surface could have been the reason for this phenomenon as the selectivity for acetylene in the products was decreasing.     

Impact of Electron–Electron Collisions on the Spatial Electron Relaxation in Non-Isothermal Plasmas

The impact of electron–electron collisions on the spatial relaxation of electrons in the column-anode plasma of a glow discharge, acted upon by a space-independent electric field and initiated by a constant influx at the cathode side of the plasma, is investigated in inert gas plasmas. The investigations are based on a new method for numerically solving the one-dimensional inhomogeneous Boltzmann equation of the electrons including electron–electron interaction in weakly ionized, collision-dominated plasmas. A detailed analysis of the spatial behaviour of the velocity distribution function and relevant macroscopic properties of the electrons is given for various degrees of ionization and electric field strengths. A significant impact of the electron–electron collisions on the relaxation structure and the resultant relaxation length already at relatively low ionization degrees has been found for low to medium electric fields.     

Novel AC and DC Non-Thermal Plasma Sources for Cold Surface Treatment of Polymer Films and Fabrics at Atmospheric Pressure

Novel types of non-thermal plasma sources at atmospheric pressure based on multi-pin DC (direct current) diffusive glow discharge and AC (alternative current) streamer barrier corona have been elaborated and tested successfully for cold surface treatment of polymer films [polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET),] and polyester fabric. Results on physical properties ofdischarges mentioned and output energy characteristics of new plasma sources as well as data on after-treatment changes in wettability of films and fabrics are presented. The main goal of this study was to find out the experimental conditions for gas discharge and surface processing to achieve a remarkable wettability change for a short treatment time.     

常压辉光放电等离子体转化CH4制C2烃的研究

采用新型的旋转电极辉光放电反应器, 在常温常压下对辉光等离子体作用下的甲烷转化制C₂烃进行了研究. 在氢气共存条件下, 考察了反应器电极的结构、材料, 输入电场峰值电压和反应物流率等参数对甲烷转化率和C₂烃单程收率及其选择性的影响规律, 同时比较了不同反应器的能量效率. 结果表明: 在本实验条件下, 金属铜材料好于不锈钢, 螺旋形结构优于三排圆盘结构. CH₄转化率和C₂烃选择性和收率均随输入电场峰值电压的升高而增大, 随反应物流量的增加而减小. 从CH₄转化率、C₂烃的收率和选择性的指标来评价这些反应器, 采用旋转螺旋状铜电极反应器时最好, 当反应物流量为60 mL/min时, 甲烷最高转化率为77.31%, 对应的C₂烃收率和选择性分别为75.66%和97.88%; 当能量密度为800 kJ/mol时, 能效最高为13.5%.     

Grafting of acrylamide onto cellulosic fibers via dielectric-barrier discharge

Fully bleached kraft pulp (BKP) and thermomechanical pulp (TMP) fibers were grafted with acrylamide via dielectric-barrier discharge treatment at various treatment dosages. The results indicate that increased dielectric-barrier discharge treatment leads to the increased polymerization and incorporation of acrylamide onto fiber surfaces. Greater incorporation of poly(acrylamide) occurs on the BKP fibers than the TMP at the same treatment conditions. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy (SEM) indicate that dielectric-barrier discharge initiated modifications to fiber surface topo-chemistry occur across the fiber such that the sheet is randomly peppered with modified areas; however, it occurs in patches on individual fibers as opposed to occurring as an evenly distributed thin film. SEM and elemental analysis also showed that the incorporation of acrylamide onto the fiber surface increases with increased treatment dosages.     

Electric discharge-induced oxidation of hydrogen cyanide

The AC high-voltage discharge-induced decomposition chemistry of trace levels of hydrogen cyanide in helium has been studied. In the absence of oxygen only low levels of molecular nitrogen were evolved. With oxygen added, the principal products were CO, CO₂, and N₂. No significant concentrations of NO or N₂O were observed. The response of a commercial NO_x analyzer to HCN and C₂N₂, in the NO_x mode, was determined to be linear through three decades in concentration. The oxidation chemistry of HCN and C₂N₂ in the stainless steel converter of the analyzer was studied as a function of the amount of added oxygen.NRL/NRC Postdoctoral Fellow (1983–1985).     

Kinetics and mechanism of the decomposition of CS2, OCS,and SCl2 in a radiofrequency pulse discharge

The identification of transient species in r.f. discharges and measurement of rate coefficients for their reactions contributes to the understanding of the complex mechanisms in r.f. plasma chemistry. Using kinetic spectroscopy in conjunction with a short-duration r.f. pulse to investigate the decomposition of CS₂, OCS, and SCl₂ at low pressure, it has been shown that the predominant primary dissociation steps are CS₂CS+S, OCSCO+S(¹D), and SCl₂S+Cl+Cl. With OCS the most important subsequent steps involved the formation and removal of S₂: S(¹D)+OCSCO+S₂(a¹), S₂(a¹)+MS₂(X³)+M, (13), and 2S₂+MS₄+M(15). Taking the previously published value of k₁₂, computer simulation gave the rate coefficient values k₁₃=6.4±2.4×10⁸ mol^–1 dm³ s^–1 and k₁₅=1.8±0.5×10¹³ mol^–2 dm⁶ s^–1 at 295±3 K.