Plasma Chemistry and Plasma Processing (v.27, #6)

Magnetically Enhanced 15 kHz Glow Discharge of Methane by L. Ledernez; F. Olcaytug; G. A. Urban; H. K. Yasuda (659-667).
This work deals with the luminous chemical vapour deposition (plasma polymerization) of hydrocarbon polymeric thin films in a magnetic field enhanced discharge of methane. The films were deposited on 4″ <111> single crystal silicon substrates. We investigated the influence of the different glow discharge parameters (e.g. pressure, flow rate, power input, etc.) on the deposition rate of methane and the refractive index of the resulting polymeric films, as well as the distribution of these parameters across the wafer. We used a Shinko Seiki Plasma Polymerization equipment with a bell jar reactor comprising two electrodes connected to a symmetric AC power supply of 15 kHz. Two magnetrons were formed by placing two circular shaped concentric magnetic poles behind each electrode. The substrates were attached on both sides of a rotating wheel held at a floating potential in the middle of the two electrodes. This equipment allowed us to vary a single parameter and keep the other parameters constant over the whole process. We measured the thickness and the refractive index and their distribution over the wafer. The effect of the system pressure, decoupled from the effect of flow rate, is explained by the characteristic nature of luminous gas phase and by the polymerization/deposition mechanism of luminous chemical vapour deposition.
Keywords: AF magnetron glow discharge; Methane; Deposition kinetic; Refractive index

Atmospheric Pressure Dielectric Barrier Discharge (APDBD) initiated decomposition of CO2 and C6–C9 alkanes (in Ar carrier) with uncoated and TiO2/ZnO coated glass surfaces, and under molecular sieve 10 X packing are presented in this study. Alkanes employed include 2-methylpentane, cyclohexane, n-hexane, n-heptane, n-octane, n-nonane and their decomposition products studied include C1–C3 hydrocarbons viz. CH4, C2H4, C2H6 and C3H8. Generally the yields of all these C1–C3 products increased with discharge energy, however to a major extent the parent alkane structure controlled the relative concentration profiles of the individual products. Typically the slopes of the increase in various products yield varied from 0.025 to 0.25 ppm (v/v) mm V−1. However, in the case of cyclohexane the total yield of methane, ethane and propane were only ∼20% of ethylene yield. Use of TiO2 as well as TiO2/ZnO coated central glass electrode in the APDBD apparatus showed ∼11% enhancement in $$ hbox{CO}_{2} ightarrow hbox{CO} $$ degradation efficiency. However, while overall 2-methylpentane decomposition reduced significantly to ∼30%, in case of n-octane its decomposition to the C1–C3 products remained unaffected. On the other hand under molecular sieve 10X packing, yield of CH4 and C2H4 increased significantly in both cases.
Keywords: Atmospheric pressure dielectric barrier discharge; Carbon dioxide; Carbon monoxide; Hydrocarbon

Chlorinated Organic Compounds Decomposition in a Dielectric Barrier Discharge by M. Magureanu; N. B. Mandache; V. I. Parvulescu (679-690).
The decomposition of chlorinated volatile organic compounds by non-thermal plasma generated in a dielectric barrier discharge was investigated. As model compounds trichloroethylene (TCE) and 1,2-dichloroethane (DCE) were chosen. It was found that TCE removal exceeds 95% for input energy densities above 0.2 eV/molecule, regardless of the initial concentration of TCE, in the range 100–750 ppm. On the other hand, DCE was more difficult to decompose, the removal rate reached a maximum of 60% at the highest input energy used. For both investigated compounds the selectivity towards carbon dioxide was significantly influenced by their initial concentration, increasing when low concentrations were used. The gas flow rate had also an effect on CO2 selectivity, which is higher at low flow rate, due to the higher residence time of the gas in the plasma. The best values obtained in these experiments were around 80%.
Keywords: Non-equilibrium plasma; Dielectric barrier discharge; Chlorinated volatile organic compounds; Trichloroethylene; 1,2-Dichloroethane

The Dependence of Gliding Arc Gas Discharge Characteristics on Reactor Geometrical Configuration by Zheng Bo; Jian Hua Yan; Xiao Dong Li; Yong Chi; Bruno Chéron; Ke Fa Cen (691-700).
The dependence of gliding arc gas discharge characteristics, including gas flow field, arc column motion and volatile organic compounds (VOCs) decomposition performance, on reactor configuration parameters was investigated based on numerical simulation and laboratory experimental findings. For a given supply voltage (10 kV) and a certain nozzle outlet diameter (1.5 mm), increasing the electrodes gap (1–4 mm) or decreasing vertical distance between electrode throat and nozzle outlet (25–10 mm) will increase the gas flow rate through the electrode throat, the gas velocity in the plasma region, the arc column velocity, the maximum attainable position of the arc column and the electrical power consumption, also, higher VOCs decomposition rate and lower specific energy requirement are observed according to the n-butane and toluene decomposition experiments.
Keywords: Gliding arc discharge; Characteristics; Reactor geometrical configuration; Volatile organic compounds; Non-thermal plasma

This paper investigates the influence of particle injection angle on particle in-flight behaviors and characteristics at different primary and carrier gas flow rates through an integrated modeling and experimental approach. Particle in-flight status such as temperature, velocity, size and their distribution are analyzed to examine particle’s melting status before impact. Results from the experiments and numerical simulations both show that, when carrier gas flow rate is fixed, a small injection angle favors the particle melting and flattening. This behavior is independent of primary and secondary gas flow rates, spray distance and carrier gas flow rate. When both carrier gas flow and injection angle vary, a high carrier gas flow rate and a small injection angle are recommended for high particle temperature and velocity.
Keywords: Air plasma spray; Particle in-flight characteristics; Injection angle; Optimization

Toward the Achievement of Substrate Melting and Controlled Solidification in Thermal Spraying by W. Zhang; G. H. Wei; H. Zhang; L. L. Zheng; D. O. Welch; S. Sampath (717-736).
The substrate is usually kept at a distant location in traditional thermal spraying, and substrate melting, which can improve splat adhesion usually does not happen. By moving the substrate close to the plasma flame and attaching a temperature control device to the backside of the substrate, as well as by additional heating from the molten droplets, substrate melting may occur and directional splat solidification becomes possible. In this proposed design, the substrate temperature is controlled by spray distance, flame temperature and initial substrate temperature. The variations of particle in-flight characteristics and contact interface temperature on spray distance are investigated. Optimal operating conditions are determined.
Keywords: Air plasma spray; Plasma particle interaction; Substrate melting; Crystal growth; Splat solidification

A new reactor and a novel in-situ sampling technique were developed for the study of the synthesis of CeO2 powders produced from dissolved cerium nitrate salts. The conical reactor minimized particle recirculation and provided a highly symmetrical and undisturbed plasma flow suitable for the analysis of the phenomena affecting the formation of CeO2 powders. Both a calorimetric study of the reactor and a thermodynamic analysis of CeO2 formation were conducted. The sampling probe is described and near-isokinetic sampling was achieved. The sampled particles were collected using a miniature wet collection system, i.e. a mist atomizer and a custom-made spray chamber. A numerical simulation of the velocity and temperature fields of the plasma gas in the reactor was done using Fluent. A comprehensive droplet-to-particle formation mechanism presented elsewhere is revisited and expanded based on calorimetry, thermodynamics of CeO2 formation, numerical simulations and collected particles. No traces of other oxidation states other than CeO2 were found.
Keywords: Radio-frequency inductively coupled plasma; CeO2 particles; Sampling probe; Iso-kinetic sampling; Solution plasma synthesis of particles; Particle size distribution; Calorimetry

A novel reactor design, sampling probe and wet collection system were used to investigate the combined effects of plasma operating parameters and particle collection mechanisms on the synthesis of CeO2 particles from liquid precursors. The sampling of particles in-flight and the collection of particles at several reactor regions were used to provide experimental evidence of particle size at different reactor locations at various plasma operating conditions, i.e., power and plasma gas flow rates. This information provided a picture of how CeO2 particles were formed and how these particles were collected in various locations. The effect of adding water-soluble fuels (alanine and glycine) to the original cerium nitrate solutions was also investigated. Fuel addition decreased the temperature of CeO2 formation by acting as a local heat source as a result of fuel auto-ignition. Photographs of the particles in-flight were taken using a fast speed CCD camera.
Keywords: Radio-frequency inductively coupled plasma; CeO2 particles; Sampling probe; Solution plasma synthesis of particles; Particle size distribution; CCD camera; Image analysis

W–C Electrode Erosion in a Pulsed Arc Submerged in Liquid by N. Parkansky; L. Glikman; I. I. Beilis; B. Alterkop; R. L. Boxman; D. Gindin (789-797).
Electrode erosion was studied in pulsed arcs ignited between two electrodes comprised of 99.99% C (graphite) and 99.5% W submerged in deionized water or analytical (99.8%) ethanol. In the both cases the erosion rate increased proportionally to the pulse energy, and the total electrode erosion per unit energy was inversely proportional to the discharge pulse duration. Fifteen and sixty-μF discharge capacitors were used for formation of the pulses in water. It was obtained that, respectively (a) erosion of the tungsten anode (Wa) was by factors of 5–6 and ∼10 greater than that of the carbon (Cc) cathode; (b) erosion of the carbon anode (Ca) was by a factor of 1.34 greater and by a factor of 2.65 less than that of the tungsten cathode (Wc); (c) the total erosion rate of both electrodes (anode and cathode) per unit pulse energy for the Wa–Cc pair was greater by factors of 11 and 12.5 than that for the Wc–Ca pair.
Keywords: Pulsed arc; Erosion; Liquid; Electrode

Surface Modification of Fine Particles with a SnO2 Film by Using a Polyhedral-Barrel Sputtering System by Takayuki Abe; Shingo Higashide; Mitsuhiro Inoue; Satoshi Akamaru (799-811).
Fine particles were modified with a thin film of SnO2 by using a barrel sputtering system that is a dry process. The conditions for the preparation of SnO2 were studied by reactive sputtering onto a glass plate substrate. The optimal conditions for the preparation of tetragonal SnO2 were identified as 60% partial oxygen pressure and 1.0 Pa total gas pressure with the substrate at room temperature. Under the optimized conditions, the surfaces of Al flake particles were modified with a thin film of SnO2. XRD and SEM/EDS analysis of the prepared samples showed that the Al particle surfaces were uniformly modified by a thin film of SnO2 in all cases. The film thicknesses were 80, 130, and 180 nm at RF outputs of 195, 350, and 490 W. These measured thicknesses coincided with the values estimated from the interference colors of the samples.
Keywords: Sputtering; Coatings; Oxides; Optical reflectivity; Powder processing