Yusuke Kudo

DC corona discharge from a wire particle floated with a microgap in parallel plate electrodes

A conductive particles existing in a high electric field could deteriorate the performance of insulating system due to electric discharge via the particles. In the case when the particles are around of the high voltage electrode, the position of the particle affects the aspect of the electric discharge. Corona onset and breakdown voltage from a metallic wire particle were investigated under the condition of the wire particle with a length of ranging from 6 to 12 mm and a diameter of 0.25 mm inserted a parallel plate electrode with a spacing of 20 mm or 30 mm. When the particle was close to the negative electrode, corona discharge occurred stably and the corona onset voltage was increased with the gap length bellow 0.8 mm. In contrast, when the particle was close to the positive electrode, breakdown always occurred without stable corona discharge. At the middle region between the electrodes, the corona onset voltage kept almost constant.

Oxygen-Plasma Treatment of Indium–Tin Oxide in a Triode Glow Discharge

An indium–tin oxide (ITO) surface was treated with oxygen (O2) plasma in a triode glow discharge system. The processing time and the radio frequency (rf) voltage applied to the substrate electrode were changed. The contact angle, X-ray photoelectron spectroscopy (XPS) spectra and scanning electron microscopy (SEM) image of the O2-plasma-treated ITO surface, and the characteristics of organic electroluminescence (EL) devices fabricated on O2-plasma-treated ITO were investigated. By applying an rf voltage of 200 V, contact angle decreased from 35 to 11°, the concentration ratio of C 1s/In 3d decreased, that of O 1s/In 3d increased, and the operating voltage of the EL devices decreased.

Experimental study of the visible-light photocatalytic activity of oxygen-deficient TiO2 prepared with Ar/H2 plasma surface treatment

Oxygen-deficient TiO2 (TiO2−x) has been proposed as a visible-light-responsive photocatalyst. TiO2−x thin films were prepared by Ar/H2 plasma surface treatment, applying varying levels of microwave input power and processing times. The highest visible light photocatalytic activity was observed when using an input power of 200 W, a plasma processing time of 10 min, and a ratio, conditions that generate an electron temperature of 5.7(±1.0) eV and an electron density of 8.5 × 1010 cm−3. The maximum formaldehyde (HCHO) removal rate of the TiO2−x film was 2.6 times higher than that obtained from a TiO2−xNx film under the same test conditions.

Visible-light-responsive photocatalyst prepared by sintering a TiO2/Cu plate

A visible-light-responsive photocatalyst has been prepared simply by sintering a TiO2-coated Cu plate. The new photocatalyst was able to reduce the concentration of formaldehyde by 8–12% at ca. 296 K with an air flow rate of ca. 0.5 L/min (ca. 1 ppm formaldehyde included), a photocatalyst cross section of 50 × 100 mm2, ca. 50% humidity, and light intensity of 30 W/m2 (white LED light). The reduction rate was approximately two times higher than that for N-doped TiO2 (TiO2−xNx) under almost the same test conditions.

Dependence of Plasma Density on Air Gap Length of Resonant Cavity with Bottom Plate Replaced by High-Density Plasma

To excite selectively transverse magnetic (TM) waves and to maximize E-field of a microwave oriented parallel to the plasma density gradient at a plasma surface, a resonant cavity was formed using an air gap between an upper conduction plate with a slot antenna (part of a waveguide) and a dielectric window of a microwave plasma source, in which a high-density plasma has been shown to act as the bottom plate of the cavity. The local maxima of plasma density have been observed experimentally when changing the air gap length. Finite-difference time-domain (FDTD) simulations and analytical studies show that two of these maxima may be due to the formation of TM111 and TM112 wave resonant cavities.

Anomalous thermally stimulated currents in polypropylene films

Thermally stimulated current (TSC) spectra were observed in open-circuit condition for corona-charged polypropylene films from room temperature to about 160°C. In these TSC spectra, two kinds of reversal currents I₁ and I₂ were found: I₁ appeared at room temperature and rapidly decreased with increasing temperature, whereas I₂ increased with temperature to form a TSC band. These anomalous currents practically appeared only for the positively charged samples because of their strong charging-polarity dependence. After I₁ decayed, the same sample was exposed to the humid ambient air for less than 100 s, and then I₁ revived again. Whereas, I₂ was not observed in the sample, which was quickly cooled in, the ambient air just after I₂ was once observed, and reheated again from room temperature. To explain these anomalous behaviors of I₁ and I₂, a simple model was made and three discriminants were also derived from the model for determining hetero-charges contribution to I₁ and I₂. From these discriminants, most of I₁ and I₂ were concluded to be due to direct charge flow from the charged surface of the sample to the current-measuring electrode placed above the sample. A tentative explanation for the source of the reversal currents was also made.

Influence of Ratio of NO/NO2 on NOx Removal using DBD with Urea Solution

Air pollution due to the exhaust gas from motorcars causes serious environmental problems, so it is necessary to remove NO x from the exhaust gas. In this study, NO x removal by dielectric barrier discharge (DBD) with an urea solution without any catalyst at room temperature has been investigated. The NO x removal rate and NO x removal efficiency has been measured with and without adding an urea solution. Furthermore, the influence of the ratio of NO and NO2 on the amount of removed NO x by DBD with the urea solution in actual apparatus has been measured experimentally. The ratio of NO and NO2 of an initial mimic exhaust gas was adjusted by DBD treatment. From the results of measurement, it has been found that NO x removal by DBD with an urea solution is effective and the optimum concentration of the urea solution is 23% in the present study. And it was estimated that the optimum ratio of NO and NO2 is about 6 to 1 for NO x removal with an urea solution

Anomalous thermally stimulated currents in high molecular weight polypropylene

In this note, we report anomalous currents the type of which is different to that of Giacometti et al. or Coelho et al. for corona-charged film samples of polypropylene (PP) with higher molecular weight in comparison with the usual film-use PP.