Tatsuya Misawa

Observation of Transverse Dust Lattice Wave Excited by Unstable Vertical Oscillations of Dust Particles in an Ion Sheath with Low Gas Pressure.

A self-excited transverse wave propagating along a one-dimensional dust chain, which is levitated around the plasma-sheath boundary, has been clearly observed in the plasma with a low gas pressure using a high-speed intensified charge-coupled device (ICCD) camera. The vertically polarized transverse wave was found to be excited due to the positional dust instability. The frequency and wavelength obtained from the experimental observations have been found to satisfy the dispersion relationship theoretically predicted for the transverse dust lattice wave.

INFLUENCE OF INTERNAL PULSED CURRENT ON THE SINTERING BEHAVIOR OF PULSED CURRENT SINTERING PROCESS

To clarify the influence of internal pulsed current upon the sintering behavior of powder materials during spark plasma sintering processing, simultaneous measurement of internal current using magnetic probe was carried out. Magnetic probe is installed to the side of the sintering ZnO powder material through the carbon graphite sintering die, and detects the magnetic field generated by internal current which flow through the specimen. By magnetic probe measurement, the internal current that flows through the specimen during SPS process was several hundred ampere, and the ratio of the internal current to the total current was found to be dependent on the electrical conductivity, diameter of powder material and the progress of SPS process. The measurement and estimation of an internal pulsed current using a magnetic probe in the specimen is very useful for in situ observation of the sintering behavior during the SPS process.

Low-Pressure Plasma Application for the Inactivation of the Seed-borne Pathogen Xanthomonas campestris

The aim of this study was to investigate the effect of low-pressure plasma treatment on seed disinfection and the possible mechanisms underlying this effect. Seed-borne disease refers to plant diseases that are transmitted by seeds; seed disinfection is an important technique for prevention of such diseases. In this study, the effectiveness of low-pressure plasma treatment in the inactivation of the seed-borne plant pathogenic bacterium, Xanthomonas campestris, inoculated on cruciferous seeds, was evaluated. The highest inactivation effect was observed when the treatment voltage and argon gas flow rate were 5.5 kV and 0.5 L/min, respectively. The viable cell number of X. campestris was 6.6 log cfu/seed before plasma treatment, and decreased by 3.9 log after 5 min of treatment and by 6.6 log after 40 min. Ethidium monoazide treatment and quantitative real-time PCR results indicated that both the cell membrane and target DNA region were damaged following 5 min of plasma treatment. Although both heat and ozone were generated during the plasma treatment, the contribution of both factors to the inactivation of X. campestris was small by itself in our low-pressure plasma system. Overall, we have shown that our low-pressure plasma system has great applicability to controlling plant pathogenic bacterium contamination of seeds.

In situ observations of sintering process during pulsed current sintering of Al2O3, ZnO and WC alloy

Pulsed Current Sintering (PCS) process possesses some problems that need to be resolved. We, therefore aims at understanding phenomena of PCS process by presenting some basic data on in situ sintering behavior of PCS. In order to observe in situ sintering behavior of PCS, a special graphite mold equipped with thermo couple and electrodes were designed to measure the temperature, electric current and voltage inside the powder during PCS process. We apply three types of raw materials, especially for ZnO (thermoelectric material) as semiconductor, Al2O3 as non-conductor and WC (Tungsten Carbide) as good conductor. The observation succeeded and some valuable data were obtained. The results showed that the temperature in the Al2O3 powder is 100 K higher than the graphite mold at the temperature of 1473K and ZnO powder is 150 K higher than the graphite mold at the temperature of 1373K. The electric current and voltage were measured for each powder during PCS process. In addition, their electric resistance properties were calculated. The electric resistance showed different behavior.

Influence of Ultraviolet Light on the Coulomb Coupling between Dust Particles

The influence of ultraviolet light on the Coulomb coupling between dust particles was experimentally investigated in Radio‐Frequency (RF, 13.56MHz) inductively coupled plasma. Flask shape dust cloud and the filamentary structure of dust particles were observed by adopting two turn ring far from the RF antenna. The ultraviolet radiation seemed to be not easy to pick up the polarization of the dust particles in the laboratory.

Influence of Substrate Biasing on (Ba,Sr)TiO3 Films Prepared by Electron Cyclotron Resonance Plasma Sputtering

(Ba,Sr)TiO3 (BST) films were deposited by electron cyclotron resonance (ECR) plasma sputtering with mirror confinement. DC bias voltage was applied to Pt/Ti/SiO2/Si substrates during deposition to vary the intensity of bombardment of energetic ions and to modify film properties. BST films deposited on the substrates at floating potential (approximately +20 V) were found to be amorphous, while films deposited on +40 V-biased substrates were crystalline in spite of a low substrate temperature below 648 K. In addition, atomic diffusion, which causes deterioration in the electrical properties of the films, was hardly observed in the crystallized films deposited with +40 V bias perhaps due to the low substrate temperature. Plasma diagnoses revealed that application of a positive bias to the substrate reduced the energy of ion bombardment and increased the density of excited neutral particles, which was assumed to result in the promotion of chemical reactions during deposition and the crystallization of BST films at a low temperature.

Microstructure and Thermoelectric Properties of Al-Doped ZnO Sintered Body

ZnO is heat-resistant and inexpensive, and the raw material of which is abundant, it is considered to be a good candidate thermoelectric material. Usually, a low-resistance n-type ZnO sintered body is obtained by doping 0.5-5 mol% Al2O3 followed by burning at a high temperature of approximately 1673K. However, this high-temperature burning has drawbacks, such as high power consumption and an increase in thermal conductivity with grain growth. Under these circumstances, we attempted to address these disadvantages. When ZnO was burned with Al as a dopant in an electric furnace at a temperature as low as approximately 1473K, ZnO with relatively good thermoelectric properties was obtained. In addition, the Al-doped sample showed lower electric resistance (332 K: 6.85×10-4Ωcm) than the Al2O3-doped sample, as determined on the basis of the resistance temperature characteristics of these samples. The causes of this low resistance may be as follows: 1) the metal-Al-mediated sample was densified by burning at a low temperature of approximately 1473K and 2) the Al distribution to the entire region of the ZnO bulk, resulting in the spread of Al solid-solution regions in the ZnO. We also found that the thermal conductivity decreased (973 K: 3.66 Wm-1K-1) in the Al-doped sample.

Microstructure and Sintering Behavior of ZnO Thermoelectric Materials Prepared by the Pulse-Current-Sintering Method

Thermoelectric elements using environment-friendly materials with high thermoelectric conversion efficiency and of these thermoelectric elements can be increased by using a structure combining n-type and p-type semiconductors. From the above point of view, attention was directed at ZnO as a candidate n-type semiconductor material and investigations were made. As the result, a dimensionless figure of merit ZT close to 0.28 (1073K) was obtained for specimens produced by the PCS (Pulse Current Sintering) method with addition of specified quantities of TiO2, CoO, and Al2O3 to ZnO. It was found that the interstitial TiO2 in the ZnO restrains the grain growth and CoO acts onto the bond between grains.