Plasma Chemistry and Plasma Processing (v.31, #4)

In this work, a mini-gliding arc discharge reactor was employed for the reforming of methane under ambient temperature and pressure operation. Acetylene and hydrogen were produced dominantly with high selectivities of ~70–90 and ~75%, respectively. The results showed that both methane conversion and product selectivities depended strongly on various operating parameters, including feed methane concentration, feed flow rate, electrode gap distance, residence time, and the presence of a reforming catalyst (as a function of catalyst distance). The Ni catalyst-loaded porous alumina-silica plate was used to study the catalytic effect on the process performance at various residence times. A considerable enhancement of methane conversion and product yields was achieved in the combined plasma-catalytic system, particularly at a longer residence time. The catalyst distance, or packing position of catalyst plate, was also found to be an important factor affecting the process performance of the combined plasma-catalytic methane reforming. The closer catalyst distance led to the greater methane conversion because of the greater possibility of adsorption–desorption interactions of excited gaseous species on the catalyst surface to enhance subsequent reactions.
Keywords: Gliding arc discharge reactor; Methane conversion; Combined plasma-catalysis

Ultra-Shallow Chemical Characterization of Organic Thin Films Deposited by Plasma and Vacuum-Ultraviolet, Using Angle- and Excitation Energy-Resolved XPS by Pierre-Luc Girard-Lauriault; Juan-Carlos Ruiz; Thomas Gross; Michael R. Wertheimer; Wolfgang E. S. Unger (535-550).
Nitrogen (N)-rich organic thin films were deposited using both low-pressure plasma- and vacuum-ultraviolet-based techniques, from mixtures of ammonia (NH3) and ethylene (C2H4). These films were investigated using angle-resolved and excitation energy resolved X-ray photoelectron spectroscopy (ARXPS and ERXPS, respectively) in order to determine their sub-surface chemical profiles. These two techniques enable one to tune the “XPS 95%” information depth, z 95%, by varying either the angle or the excitation energy. Using a combination of both techniques, z 95% can be varied continuously from 0.7 to 11 nm. The surface-near chemistry is investigated using both high-resolution C 1s spectra and elemental concentrations derived from elemental peak intensities. Results show that while laboratory XPS, and even ARXPS, suggest homogenous surface chemistries, the novel combination of ARXPS and ERXPS points to the existence of a compositional profile in the extreme outer surface layer. Our conclusions are supported by simulations using SESSA software.
Keywords: Plasma polymers; Vacuum ultraviolet photopolymers; Synchrotron XPS; Depth profile

Significance of Hydrogen–Deuterium Exchange at Polyolefin Surfaces on Exposure to Ammonia Low-Pressure Plasma by S. Wettmarshausen; H. Min; W. Unger; C. Jäger; G. Hidde; J. Friedrich (551-572).
Since more than 40 years ammonia plasma exposure of polyolefins is used for introduction of primary amino groups. The selectivity of this reaction and the yield in primary amino groups was found to be low. Here, a prominent side-reactions of this process was investigated, the hydrogenation by NH3 plasma. For identification of hydrogenation ammonia (NH3) and deuterated ammonia (ND3) were exposed to polyethylene (h-PE) and fully deuterated polyethylene (d-PE) as well as hexatriacontane (h-HTC) and fully deuterated hexatriacontane (d-HTC) as low-molecular weight model for PE. H–D exchange was assumed and detected by Time-of-Flight Secondary Ion Mass Spectrometry (ToF–SIMS), X-ray Photoelectron Spectroscopy (XPS), Attenuated Total Reflectance (ATR-FTIR) and 1H and 2H Nuclear magnetic Resonance. Results show a significant H–D exchange within the sampling depth of ATR (2.5 μm). However, N- and NH2 introduction was limited to the topmost surface as shown by SIMS and XPS (a few nanometers).
Keywords: Deuterated ammonia; Ammonia plasma; Deuterated polyolefins; Hexatriacontane; H–D exchange

Application of Dielectric Barrier Discharge for Waste Water Purification by V. I. Grinevich; E. Y. Kvitkova; N. A. Plastinina; V. V. Rybkin (573-583).
This study considers treatment of real city rain sewage under the action of an oxygen dielectric barrier discharge (DBD) at atmospheric pressure in the presence or absence of TiO2 catalyst in the plasma zone. The DBD discharge has been shown to have high decomposition efficiency (up to 98%) for oil hydrocarbons, phenols and synthetic surfactants. The discharge action resulted in the decrease of heavy metal (Pb, Cd, Fe, Mn) content as well. In a plasma-catalytic hybrid process, the efficiency of organic substances decomposition was higher than efficiency for the DBD treatment without catalyst.
Keywords: Oxygen surface barrier discharge; Real city rain sewage; Oil hydrocarbons; Phenols; Synthetic surfactants; Decomposition; Catalysts

Removal of C3F8 Via the Combination of Non-Thermal Plasma, Adsorption and Catalysis by Bor Yuan Lin; Moo Been Chang; Hsin Liang Chen; How Ming Lee; Sheng Jen Yu; Shou Nan Li (585-594).
The feasibility of C3F8 abatement via combining nonthermal plasma with adsorption and/or catalysis is investigated in this study. In terms of the simultaneous combination of plasma, adsorption and catalysis (CPAC), three different configurations including A/C layer (adsorbent layer prior to catalyst layer), C/A layer (catalyst layer prior to adsorbent layer) and A/C mixture (adsorbent and catalyst are mechanically mixed) are adopted. For all the experimental tests conducted in this study, the gas stream consists of 500 ppm C3F8, 2% O2, and balanced N2. The experimental results indicate that C3F8 removal efficiencies depend on what kind of packing material is adopted (adsorbent, catalyst or both) and how the material is packed within the plasma reactor. The removal efficiencies obtained with different reactors are in the order as: CPAC (A/C layer; AC mixture) > CPA (plasma with adsorbent alone) > CPC (plasma with catalyst alone) > CPAC (C/A layer). The indentified products after treatment include CO2, CO, N2O and CF4. The formation of C2F6 is not observed in this study, which is encouraging since the global warming potential of C2F6 is actually higher than that of C3F8.
Keywords: Global warming; Greenhouse gases (GHGs); Perfluorocompounds (PFCs); Plasma catalysis; Adsorbent

In the present work, the plasma nitriding behavior of a nickel based dental alloy was investigated. Plasma nitriding experiments carried out under constant gas mixture (15% H2–85% N2) for different process parameters including time (4, 6, 10, and 20 h) and temperature (400, 450, 500, and 550 °C). Depending on nitriding parameters, it was found that triple or double layers formed on the surface of the samples. Increasing of treatment time and temperature has resulted in a double layer. γN1 layer was in formed all nitrided samples. However, γN2 layer is formed only at low temperatures and in short times. Layer growth of nickel based alloys increases until a critical time or a critical temperature reached. Above these critical values, it is observed that the layer thickness decreases. It was also found that plasma nitriding not only increases the surface hardness but also improves the wear resistance of nickel based dental alloy. The maximum wear resistance was observed at 400 °C for 10 h due to the high hardness and thickness of the nitride layers.
Keywords: Nitriding; Wear; Nickel based alloy; Dental alloy

In recent years, cyclodextrin applications have been expanding to include textile finishing, providing new and unique functionalities to the fabric substrates. In this work the grafting of Per-(2,3,6-O-allyl)-β cyclodextrin by plasma and conventional thermofixation methods is described. The fabric substrate was cotton and activated by the surface modification of the fibers by the synthesis of iododeoxycellulose, cellulose peroxide, and a cellulose diazonium salt. Several plasma machines and conventional thermal techniques for fixation were studied. Iododeoxycellulose gave the best results by thermofixation and the in situ mode of the APJeT atmospheric plasma machine. Linoleic, ricinoleic, oleic acids were included in the grafted cyclodextrin fabrics as possible wound healing agents. The cyto-compatibility of the treated samples either included or un-included with fatty acids shows promising results.
Keywords: Atmospheric plasma; Cyclodextrin; Cotton; Oleic acid; Linoleic acid; Ricinoleic acid

Pectinase enzyme treatment subsequent to atmospheric air- or argon-plasma surface modification was applied in linen fabric preparation. Wettability by water drop test, wickability by thin layer wicking experiment, residual pectin content and colour of the fabrics were characterized. Results clearly proved that the efficiency of pectinase in improving linen water absorbency can be significantly enhanced by plasma pretreatment. Argon-plasma pretreatment followed by a Beisol PRO enzyme treatment reduced the wetting time considerably and resulted in a fabric surface that has been characterized by the lowest water contact angle (86.6°). All the applied treatments increased the energy of the fibre surface. The alkaline scoured, the argon-plasma treated and the argon-plasma-pectinase treated samples have been characterized by the highest $$ gamma_{S}^{total} $$ values. Plasma treatment significantly decreased the whiteness and increased the yellowness of the raw fabrics. However, the enzyme treatment applied after the plasma treatment has overcome the colour differences.
Keywords: Linen; Air-plasma; Argon-plasma; Pectinase enzyme; Hydrophilicity; Surface energy; Change is colour; Bioscouring