Plasma Chemistry and Plasma Processing (v.29, #4)

Study of Internal Linear Inductively Coupled Plasma Source for Ultra Large-Scale Flat Panel Display Processing by Jong Hyeuk Lim; Kyong Nam Kim; Gwang Ho Gweon; Jae Beom Park; Geun Young Yeom (251-259).
An internal-type linear inductive antenna, which is referred to as “double comb-type antenna”, was used as a large-area inductively coupled plasma (ICP) source with a substrate area of 2,300 mm × 2,000 mm. The characteristics of the ICP source were investigated for potential applications to flat panel display (FPD) processing. The source showed higher power transfer efficiency at higher RF power and higher operating pressures. The power transfer efficiency was approximately 88.1% at 9 kW of RF power and a pressure of 20 mTorr Ar. This source showed increasing plasma density and improved plasma uniformity with increasing RF power at a given operating pressure. A plasma density >1.5 × 1011/cm3 and a plasma uniformity of approximately 11% was obtained at 9 kW of RF power and 15 mTor Ar using this internal ICP source, which is applicable to FPD processing.
Keywords: Large area; Inductive antenna; Flat panel display; Impedance; Uniformity

Aqueous solutions polluted by contaminants different from those generally studied (phenol and chlorophenols) were treated in a falling film gas–liquid dielectric barrier discharge reactor. The lower was the Henry’s law constant of a molecule, the better was its removal percentage, regardless of its other chemical properties. In the case of saturated molecules, the removal mechanism is the transfer of pollutants from the liquid phase to the gas phase where they react with the active species of the discharge. For phenol, the reaction with ozone in the liquid phase was estimated to be responsible of about 30% of the removal. A computational fluid dynamic modelling provided a better understanding of the phenomena, indicating that mass transfer of pollutants from liquid to gas is accelerated due to (1) the intense mixing in the liquid film and (2) the reaction of the pollutant with the active species in the gaseous phase.
Keywords: Advanced oxidation processes; Electrical discharge; Non-thermal plasma; Phenol

Plasma Chemical Reactor with Exploding Water Jet by Vladimir M. Shmelev; Alexei V. Saveliev; Lawrence A. Kennedy (275-290).
Exploding water jet discharge simultaneously generating powerful UV radiation, non-thermal plasma, and aerosol of fine water droplets has potential applications for removal of chemical and biological pollutants from air and water streams. A model plasma chemical reactor based on the exploding water jet discharge is considered. The radiation properties of the discharge, reactions of nitrogen oxide and hydrogen peroxide formation, and reactions of carbon dioxide and hydrogen sulfide decomposition are studied experimentally.
Keywords: Pulsed discharges; Surface discharges; UV sources

Degradation of Azo Dye Acid Red 88 by Gas Phase Dielectric Barrier Discharges by Qiong Tang; Wenju Jiang; Yi Zhang; Wenyun Wei; T. M. Lim (291-305).
The degradation of an azo dye, acid red 88 (AR88) in aqueous solutions by a gas-phase dielectric barrier discharge (DBD) system was investigated. The reactive species generated from the DBD system such as OH radical, ozone and hydrogen peroxide were measured. The effects of various parameters such as gas flow rate, initial pH, input power, initial concentration of AR88 and the gas source on the degradation of AR88 were studied. The results show that OH radical was the major reactive species generated when 100% relative humidity (RH) air was used. An aqueous solution of 25 mg L−1 AR88 was 96.3% degraded in 5 min treatment, and 68% of the initial total organic carbon was removed in 90 min treatment with 100% RH air at 60 W input power and 7 L min−1 gas flow rate. The degradation kinetics of AR88 followed a pseudo-first-order reaction and was dependent on the input power, gas flow rate, initial AR88 concentration and initial pH.
Keywords: Advanced oxidation processes; Oxidation degradation; Azo dyes; Dielectric barrier discharge; Degradation kinetics

Nanopowders of metals and metal oxides have been produced using an arc operated between a refractory rod anode and a hollow cathode (J. Haidar in A method and apparatus for production of material vapour, Australian Patent No. 756273, 1999). the arc attachment to the anode is through a small region of molten metal located at the tip of the rod anode. Heat from the arc evaporates the molten metal and the vapour is passed through the arc plasma before condensing into sub-micron particles downstream of the cathode. A precursor metal is continuously fed onto the tip of the anode to maintain the molten metal region and compensate for losses of materials due to evaporation. The particle size of the produced powder depends on the pressure in the arc chamber and for production of nanoparticles in the range below 100 nm we use a pressure of 100 torr. Aluminium has been used as a precursor material, leading to production of aluminium metal nanopowders when the arc is operated in argon and to aluminium oxide nanopowders for operation in air. For operation in air, the products are made of γ-Al2O3.
Keywords: Plasma; Arc; Nanopowder; Aluminium; Gamma-Al2O3

A computer model is used to study the volatility of some radioelements (Cerium, Plutonium and Strontium) during radioactive wastes treatment by thermal plasma technology. This model is based on the calculation of system composition using the free enthalpy minimization method, coupled with the equation of mass transfer at the reactional interface. The model enables the determination of the effects of various parameters (e.g., temperature, plasma current, and presence of oxygen in the carrier gas) on the radioelement volatility. The obtained results indicate that any increase in molten bath temperature causes an increase in the radioelement volatility. It is also found that the oxygen flux in the carrier gas strengthens the radioelement incorporation in the containment matrix. For electrolyses effects, an increase in the plasma current increases both the vaporization speed and the vaporized quantities of 239Pu, 144Ce, and 90Sr.
Keywords: Radioactive wastes; Volatility; Arc plasma; Modeling; Thermodynamics