Han Sup Uhm

Microplasma jet at atmospheric pressure

A nitrogen microplasma jet operated at atmospheric pressure was developed for treating thermally sensitive materials. For example, the plasma sources in treatment of vulnerable biological materials must operate near the room temperature at the atmospheric pressure, without any risk of arcing or electrical shock. The microplasma jet device operated by an electrical power less than 10W exhibited a long plasma jet of about 6.5cm with temperature near 300K, not causing any harm to human skin. Optical emission measured at the wide range of 280–800nm indicated various reactive species produced by the plasma jet.

Superhydrophobicity of a material made from multiwalled carbon nanotubes

Superhydrophobic carbon nanotubes (CNTs) were prepared by low-pressure CF4 glow plasma to provide roughness and fluorination in CNTs. The water droplet falling freely on the superhydrophobic CNT powders bounced dynamically. The superhydrophobicity resulted from the combined effects of the chemical modification and surface roughness. Using the contact angles obtained from the capillary rise method based on the Washburn equation, the total surface free energy of CNT powder treated by CF4 plasma for 20min was calculated to be drastically decreased from 27.04to4.06×10−7mJ∕m2.

Electron plasma wave propagation in external-electrode fluorescent lamps

The optical propagation observed along the positive column of external electrode fluorescent lamps is shown to be an electron plasma wave propagating with the electron thermal speed of (kTe∕m)1∕2. When the luminance of the lamp is 10000–20000cd∕m2, the electron plasma temperature and the plasma density in the positive column are determined to be kTe∼1.26–2.12eV and no∼(1.28–1.69)×1017m−3, respectively.

Propagation of a Light-Emitting Wave-Front in a Fine Tube Positive Column Discharge

The propagation velocity of a light-emitting wave-front is observed to be up~2×10+5 m/s before Townsend breakdown and up~5×10+6 m/s after Townsend breakdown along a discharge tube of inner diameter ro~1.2 mm and length of 900 mm relevant to liquid crystal display television backlighting. Before Townsend breakdown, the origin of this wave is the ambipolar diffusion of plasma flux with the propagation speed up∝Da/ro for the plasma bounded by the radius ro with the diffusion coefficient Da along the positive column. After Townsend breakdown, the light-emitting wave-front propagates with the electron plasma wave generated by the pulses of driving voltage. The electron plasma wave propagates such a long distance along the tube without damping due to the effect of localized plasma generation by electron impact ionization collisions. The propagation velocity is described by up~2ue2/ud, which is larger than the electron thermal velocity ue as well as the electron drift velocity ud.

Plasma Diffusion Along a Fine Tube Positive Column

The propagation velocity of light emission is observed to be u_p ~0.92 times10⁺⁵ m/s along a tube of an inner diameter r_o ~1.5 times10^-3 m with an external electrode fluorescent lamp filled with 97% Ne and 3% Ar at a total pressure of 30 torr, a mercury-free lamp without phosphor coating the inside glass wall. The origin of this propagation is shown to be ambipolar diffusion with a plasma diffusion speed of u_p ~ (4.8/r_o)D_a for diffusion coefficient D_a along the positive column. When a high voltage magnitude is applied at the external electrode, a high-density plasma is generated inside the hollow electrode, and the plasma diffuses along the positive column toward the ground electrode.

Plasma Flame Sustained by Microwaves and Burning Hydrocarbon Fuel: Its Applications

Thermal plasma torches have been developed for various industrial applications. Industries require them to be high power, contaminant-free, low-maintenance, low-cost, and largevolume. Principally, the plasma torch is a device to produce an arc plasma column between two electrodes. There are several kinds of plasma torches, including dc arc torch, induction torch, and high-frequency capacitive torch. The dc arc torch is operated by the dc electric field between two electrodes at a severe environment of high arc current in the range from several tens to thousands of amperes. Therefore, their electrodes are replaced often due to their limited lifetime, in particular an oxidative environment. Almost all radio frequency torches are inductively coupled discharges. Their typical thermal efficiencies (% of power effectively dissipated in the plasma forming gas) are in the range of 40-50% (Fauchais & Vardelle, 1997). These conventional torches also have a small volume of plasma, high operational cost and require many expensive additional systems for operation. Although the conventional plasma torches are used in many industrial applications, the wide acceptance of these processes is limited by economic, competitive, reliability, and other concerns. From the reason above-mentioned, they may not be useful in environmental applications. In order to overcome problems related with the conventional plasma torch, an electrodeless microwave plasma torch at atmospheric pressure was developed (Hong et al., 2003; Kim et al., 2003). Microwave plasmas operated at the atmospheric pressure, especially waveguidebased plasma, have been subject of increased attention during the last decade (Margot, 2001; Moisan et al., 2001). Such an interest comes from their potential and actual use in various applications, including excitation sources for elemental analysis, lighting, and purification or remediation of gas effluents detrimental to the environment (Hartz et al., 1998; Woskov & Haddi, 1999). The microwave plasma torch can easily be made by modifying typical household microwave ovens as inexpensive method (Kim et al., 2003). Therefore, the microwave plasma torch is simple, compact and economical. Furthermore, in previous works, the microwave plasma torch has been investigated in various applications such as the abatement of CF4, NF3 and SF6, the elimination of chemical and biological warfare agents, and synthesis of carbon nanotube, titanium dioxide, titanium nitride, and zinc oxide (Hong et al., 2004; Kim et al., 2007). Although the microwave plasma torch in air discharge 10