Shigeo Yatsu

Controlled formation of metallic nanoballs during plasma electrolysis

Formation of spherical nanoparticles (hereafter “nanoballs”) in a gas/liquid mixed dual phase system during plasma electrolysis is reported. A gas/vapor sheath is formed at the electrode/electrolyte interface when the applied voltage is high enough to induce discharge plasma. Through this nonequilibrium process, the authors have produced Ni, Ti, Ag, and Au metallic nanoballs from the cathode mother materials with a certain size controllability. The electrode surface is partially melted by the local current concentration induced by electrothermal instability followed by an immediate cooldown, yielding nanoballs without contamination from electrolyte.

In situ observation of self-organizing nanodot formation under nanosecond-pulsed laser irradiation on Si surface

An in situ observation of the formation of a laser-irradiation-induced nanodot array on a Si surface was performed using a pulsed-laser-equipped high-voltage electron microscope (laser-HVEM). Under multiple nanosecond (ns) pulsed laser irradiation shots, atomic clusters were first formed and distributed on the surface in order to grow them epitaxially into protruded dots with diameters of ten nanometers or less. This is followed by their diffusion induced by successive laser shots to cannibalize and merge them into a ripple line with aligned, larger dots. We conclude that the present subwavelength two-dimensionally-ordered nanodot array is formed by self-organization under pulsed laser irradiation.

Size-Controlled Ni Nanoparticles Formation by Solution Glow Discharge

We report the size control of Ni nanoparticles generated via solution glow discharge and focus on the effect of electrolyte concentration on Ni nanoparticles. In our experiments, voltage was applied to generate a plasma in NaOH electrolytes with concentrations ranging from 1.0 to 0.001 kmol m -3 . The applied voltage strongly depended on the electrolyte concentration, and interestingly, product size decreased with electrolyte concentration; for example, (mean diameter, applied voltage, electrolyte concentration) = (148 nm, 90 V, 0.5 kmol m -3 ), and (70 nm, 590 V, 0.001 kmol m -3 ). These results suggested the possibility of using plasma electrolysis for synthesizing size-controlled nanoparticles by changing only electrolyte concentration.

Synthesis of stainless steel nanoballs via submerged glow-discharge plasma and its photocatalytic performance in methylene blue decomposition

Stainless steel nanoparticles or ‘nanoballs’ have been synthesised using submerged glow-discharge plasma. Transmission electron microscopy showed that the nanoballs are uniformly spherical and size distribution estimation showed that their diameters are below 200 nm. The decomposition of methylene blue solution under ultraviolet light with the wavelength of 354 nm was observed in the presence of stainless steel nanoballs. A mixture of stainless steel nanoballs and 0.1% methylene blue dye was irradiated with ultraviolet light. The concentration of methylene blue was reduced to baseline level in 72 hours. This shows that the stainless steel nanoballs have photocatalytic ability. In stainless steel nanoballs, methylene blue showed two different decomposition pathways; showing fast and slow reactions. Also, methylene blue was oxidised into sulphoxide before reducing into lighter by-products. X-ray diffraction analysis has shown that the nanoballs consist of Fe2O3 and Cr2O3, which are photocatalytically active species.

A pathway of nanocrystallite fabrication by photo-assisted growth in pure water

We report a new production pathway for a variety of metal oxide nanocrystallites via submerged illumination in water: submerged photosynthesis of crystallites (SPSC). Similar to the growth of green plants by photosynthesis, nanocrystallites shaped as nanoflowers and nanorods are hereby shown to grow at the protruded surfaces via illumination in pure, neutral water. The process is photocatalytic, accompanied with hydroxyl radical generation via water splitting; hydrogen gas is generated in some cases, which indicates potential for application in green technologies. Together with the aid of ab initio calculation, it turns out that the nanobumped surface, as well as aqueous ambience and illumination are essential for the SPSC method. Therefore, SPSC is a surfactant-free, low-temperature technique for metal oxide nanocrystallites fabrication.

High-temperature coal-syngas plasma characteristics for advanced MHD power generation

Properties of magnetohydrodynamic (MHD) plasma based on syngas (CO, H/sub 2/) combustion products were investigated experimentally with shock tube facility. The experiments were carried out under various MHD generator load and shock tube operation conditions. Important characteristics of syngas plasma such as temperature, electric field, conductivity, and total output power were directly measured and evaluated. Special attention was paid to the influence of syngas composition (CO:H/sub 2/:O/sub 2/ ratio). The results show that syngas combustion can provide high plasma ionization and attainable plasma electrical conductivity has an order of 60-80 S/m at gas temperature 3100-3300 K.

Effects of ion and nanosecond-pulsed laser co-irradiation on the surface nanostructure of Au thin films on SiO2 glass substrates

Ion irradiation and short-pulsed laser irradiation can be used to form nanostructures on the surfaces of substrates. This work investigates the synergistic effects of ion and nanosecond-pulsed laser co-irradiation on surface nanostructuring of Au thin films deposited under vacuum on SiO2 glass substrates. Gold nanoparticles are randomly formed on the surface of the substrate after nanosecond-pulsed laser irradiation under vacuum at a wavelength of 532 nm with a repetition rate of 10 Hz and laser energy density of 0.124 kJ/m2. Gold nanoparticles are also randomly formed on the substrate after 100-keV Ar+ ion irradiation at doses of up to 3.8 × 1015 ions/cm2, and nearly all of these nanoparticles are fully embedded in the substrate. With increasing ion irradiation dose (number of incident laser pulses), the mean diameter of the Au nanoparticles decreases (increases). However, Au nanoparticles are only formed in a periodic surface arrangement after co-irradiation with 6000 laser pulses and 3.8 × 1015 ions/cm...

Time-Resolved Two-Dimensional Temperature Measurement From Acetylene-Oxygen Flame Using Chemical Seeding Spectrocamera

EVWUDFW The electrical conductivity, Seebeck coefficient, and the thermal conductivity of Fe -doped B4C ceramics with several Fe compositions were investigated experimentally. The ceramics specimens were made by SPS apparatus. The figure of merit for the each specimen were calculated using the above experimental results It was found that the values of the dimensionless figure of merit for the specimens with low concentrations of Fe (less than 15wt%) is much larger compared with one of pure B4C . It was not succeeded to obtain the B4C with higher Fe density(more than 15wt%),by SPS method, because the large part of Fe was precipitated as metal Fe during the sintering process.

3D Analysis of Coal Synthesized Gas Combustion MHD Generator

Precise knowledge on temperature and its fluctuation in combustion systems are among the important energy issues in almost all industrial sectors, energy conversion and power fields. In this study, a spectroscopic technique is used to measure the time-resolved temperature distribution by a comparatively simple optical system that involved two band-pass filters (BPF), and a charge-coupled device with image intensifier (ICCD) video camera. The system was assembled and applied to an acetylene-oxygen premixed flame that are widely used for welding purposes because of very high temperature in such flames. The temperature distribution and its fluctuation directly impact the quality of soldering. The results provided direct visualization of temperature and its fluctuation in the flames that are conjectured to emanate from thermal and hydrodynamic phenomena from chemical reactions in the flame and interaction with surrounding air.