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SUMMARY Acetic acid simulating a persistent organic compound in water was decomposed by a discharge on water using a thin blade electrode. The thin blade electrode facilitates the generation of wide-ranging discharges on water. The effect of differences in the species of the supply gas and the discharge power on the decomposition of acetic acid was investigated. Compared with argon, when helium was used, a larger amount of acetic acid was decomposed. Experiments also confirmed that the decomposition rate of acetic acid rose with the discharge power. It was also found that the decomposition efficiency was improved when the discharge power was reduced. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 1–10, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22318

A new method for water treatment utilizing radicals produced by a discharge on the surface of a bubble in water is proposed and this method is applied to the de-color of indigo solution whose original color is blue. The discharge of this method begins at the crossing points of mesh electrode, acrylic resin spacer, and bubbling gas (i.e., called a triple junction where there is a weak point for the electrical breakdown in the electrical power devices). This weak point for the electrical breakdown is used very actively for the surface discharge. The discharge process on the surface of the bubble in water is also observed using a wire-to-plane electrode system to fix the observation region of discharge (type-A reactor). The streamer length estimated by photographs increased linearly with the applied voltage. The energy consumption of discharge for type-B reactor with a mesh-to-plane electrode in oxygen is about 0.09 J when the applied voltage is 20 kV. Production efficiency of the H 2 O 2 concentration of about 27 mg . L - 1 in oxygen (46 mg . L - 1 in helium) has been obtained when the repetition rate of discharge operated by a pulsed-power generator, the peak value of applied voltage, and the discharge period are 100 pps (pulsed power generator), 25 kV and 60 min, respectively.

Solid oxide fuel cell (SOFC) having a thin yttria-stabilized zirconia (YSZ) electrolyte was prepared on the anode electrode of a porous Ni-YSZ cermet substrate using the RF ion plating method. The constitutional YSZ electrolyte films were characterized based on dependence on the electron beam current and annealing treatment. A thin YSZ electrolyte film evaporated at higher electron emission current indicated a columnar structure with longitudinal pinholes in the film. By annealing temperature above 1300°C, YSZ film was improved as a denser film having a bulk electrolyte structure. Furthermore, the conductivity of thin YSZ film was increased with increasing the annealing temperature, although its conductivity became smaller by about three figures than the theoretical value of the bulk electrolyte.

A new method for a water treatment utilizing radicals produced by a discharge inside bubbles in water is proposed. Radicals with short lifetime (atomic oxygen and OH radical) are used effectively for the water purification because those are generated by discharge inside bubbles in water. OH radical production was confirmed by a light emission of the discharge using the spectroscopic technique. Dissolved ozone concentration of about 0.3 mg/l was obtained when oxygen was used as a bubbling gas. Decolorization process of indigo solution by a discharge inside bubbles in water was investigated.

In the present research, a new method for a water treatment utilizing the discharge of bubbles in water is proposed. The radicals with short lifetime can be effective for water purification because the discharge is expected to occur inside the bubbles in water. Magnetic-pulse-compression pulsed-power generator was used as a repetitive power supply. The bubbles generated by a bubbling tube were passed through a discharge region between the electrodes. In this phase of the experiment, argon was used as a bubbling gas. The experimental results showed that a discharge was generated inside the bubbles in water by the mentioned pulsed-power generator. Simultaneously, measurements of the excited OH radical emission were carried out using a spectroscopic technique. The repetition rate of pulsed-power generator, the peak value of applied voltage and the gap length were 100 pps (pulse per second), 20 kV and 7.5 mm, respectively.

The performance of a single solid oxide fuel cell (SOFC) was studied using a thin yttria-stabilized zirconia (YSZ) electrolyte film grown by RF magnetron sputtering in mixtures of argon and oxygen. It is found that crystal system of YSZ electrolyte film controlled by plasma sputtering added oxygen to argon. The density of YSZ electrolyte film was improved with an increase of (111) cubic system by adding 14% oxygen. Maximum current density of a single SOFC having YSZ electrolyte film prepared by adding 14% oxygen obtained 147.5 mA at terminal voltage of 239 mV at the operating temperature of 1000°C. Moreover the resistance of the cell reduced from 9.1 Ω to 4.9 Ω.

The final goal of this research is to realize the efficient utilization of radicals such as atomic oxygen, OH radical, and ozone for water purification. The radicals were generated by a discharge occurring inside the bubbles produced by a bubbling tube immersed in water. The Blumlein line, a repetitive pulsed power generator, was used as the power source. In the experiments, a maximum ozone concentration of approximately 300 ppm was obtained when the repetition rate of pulsed power generator, the peak value of applied voltage and the gap length were 15 pps, approximately 30 kV, and 7.5 mm, respectively. Oxygen was used as the bubbling gas. The time duration of voltage pulse was approximately 200 ns.