Papers by Author: Yamato Hayashi

Abstract: Ti-doped SrLaAlO₄ green-emitting phosphor was synthesized via solid-state reactions in air and N₂ atmosphere. Sample heated in air showed no emission, however, sample heated in N₂ showed broad green emission around 492 nm and broad near-infrared emission around 950 nm by 321 nm near-ultraviolet excitation. XPS measurement and UV-Vis diffuse reflectance spectra suggest that Ti in the sample was reduced to Ti³⁺ state when the sample was heated in N₂. Possible emission mechanism of the sample can be explained as O^2-–Ti³⁺ charge-transfer transition.

Abstract: Mn⁴⁺-doped magnetoplumbite-type BaMg₆Ti₆O₁₉ and spinel-type Mg₂TiO₄ red phosphors were synthesized by a solid-state reaction. BaMg₆Ti₆O₁₉:Mn⁴⁺ and Mg₂TiO₄:Mn⁴⁺ were formed as main phase above 1200 oC. Although the emission peak of BaMg₆Ti₆O₁₉:Mn⁴⁺ and Mg₂TiO₄:Mn⁴⁺ were almost the same, the excitation peak of BaMg₆Ti₆O₁₉:Mn⁴⁺ and Mg₂TiO₄:Mn⁴⁺ were different. The ⁴A₂→⁴T₁ transition peak of Mg₂TiO₄:Mn⁴⁺ shifted to a shorter wavelength side than that of BaMg₆Ti₆O₁₉:Mn⁴⁺ and ⁴A₂→⁴T₂ shifted to a longer wavelength side. The crystal field splitting energy of Mg₂TiO₄:Mn⁴⁺ was lower than that of BaMg₆Ti₆O₁₉:Mn⁴⁺. By the additional of R block, the racah parameter B increased and C decreased. Although the increase of B causes a blue-shift of the emission wavelength and the decrease of C causes a red-shift of the emission wavelength, PL emission wavelength was little different due to the influence of both racah parameter. Thus, it was suggested that the existence of R block results in a difference of photoluminescence properties.

Abstract: We developed new synthetic method of silver nanowire by reducing silver acetate precursor. Silver acetate could be easily synthesized by ultrasound irradiation to the mixture of non-toxic starting materials, only ethanol and silver (I) oxide. All of reaction was performed in relatively low temperature and it does not need any protective agents. The precursors had high aspect ratio needle-shaped morphology. They decomposed easily by heating up to 300 °C and then produce only silver without any residues. This process is expected to be new synthetic method of silver nanowire that doesn’t require any protective agents and emit much waste.

Abstract: In this study, Graphite Oxide (GO) and Ag/Graphene nanocomposites were synthesized by solid-liquid sonochemical reactions easily and briefly. GO was synthesized by means of Hummers method using sonication or stirring. From XRD patterns and FT-IR spectra, chemical and physical effects of ultrasound promoted the oxidation of Graphite. Ag/graphene nanocomposites were synthesized from GO and silver oxide by sonication. UV-vis spectra showed the peaks of Graphene oxide and Ag nanoparticle plasmon resonance absorption. EDX images and electron diffraction patterns confirmed Ag nanoparticles were decorated on Graphene sheets by ultrasound. Using sonication, GO and Ag/Graphene nanocomposites could be synthesized easily in short time.

Abstract: Eco (Ecology & Economy)-fabrication is important in the future manufacturing. There are some elements to achieve this synthesis. When synthesizing, neither waste nor the air pollutant are not generated, and it is safe material is preferable with cheap fabrication device. We developed a new metal nanoparticle related materials synthesis method that achieved in these viewpoints. This new synthesis method is with microwave as non-equilibrium reactor and the metal oxide and alcohol based solvent are used for the raw material. Moreover, the oxide and alcohol generally are cheap without toxicity. We synthesized metal nanoparticle related materials by microwave in liquid-solid (alcohol - metal oxide) slurry and controlled morphology of products. Microwave irradiation in liquid-solid process can be expected as chemical non-equilibrium and nonlinear reactors for metal nanoparticle related materials synthesis. The alcohol based solvent and the metal oxide powder are put in the beaker and only irradiated by ultrasound or microwave. The metal oxide simply was reduced into metal and morphology of metal nanoparticles was changed by various conditions. Various metal nanoparticle related materials were fabricated by microwave irradiation as non-equilibrium reaction field.

Abstract: Various (ZnO)₅In₂O₃ ceramics were fabricated by microwave heating. Density, XRD pattern and microstructure were examined and those of Al-doped (ZnO)₅In₂O₃ were almost the same as Al-free one. Highly textured (ZnO)₅In₂O₃ ceramic was also fabricated by reactive templated grain growth (RTGG) method. The electrical conductivity was not improved by Al-doping; however it was improved slightly by microwave heating compared with conventional heating and especially improved by texturing using RTGG method. On the other hand, the absolute Seebeck coefficient in microwave heating was improved about 25% by Al-doped. Maximum electric power factor of textured specimen fabricated by RTGG method along ab-plane showed 5.76×10^-4 WK^-2m^-1 (at 873K), which was attributed to high electrical conductivity.

Abstract: Applications of various noble metal nanoparticles were investigated for newly, ecology and economy home electric appliances (microwave, ultrasonic) used system. Noble metal oxides have merit in metal particles fabrication, as one of these example example, there are decomposed by only heating in air. That is, noble metal oxide don't use strong reduction atmosphere. This reduction is ecologically clean, because many noble metal oxides are not toxic and during decomposition O2 is evolved. We have reduced noble metal oxides by microwave and ultrasound, and tried to fabricate noble metal nanoparticles, and investigated various processing. These energy are widely used by home electric appliances. By choosing suitable process and conditions, it is reasonable to expect that home electric appliances ecology and economy fabrications can be extended to obtain simply various noble metal nanoparticles related materials.

Abstract: In2O3(ZnO)3 layered compound was synthesized by 2.45 GHz microwave heating in a solid state reaction. Microwave-processed samples were obtained at low temperature by the enhancement of solid state diffusion and sublimation of the powder bed. Plate-like grain microstructures formed on the bottom part of the pellet, and vicinity of the surface was dense. The plate-like grain was oriented in the ab-plane direction. Compared with a conventional heated sample, the electrical conductivity increased and the band gap energy decreased. In the case of deposition on a silica substrate by microwave heating, the plate-like grain film was synthesized.

Abstract: The commercial nano-sized TiO2 powder (P25) coated with PtO2 powder by a sonochemistry method was immobilized on the foamed waste-glass substrates by using plasma spray coating technology. The immobilized TiO2-Pt coatings were applied to treat both green tide and red tide under illumination of an UV light. Their photocatalytic characterizations were evaluated as functions of the number of residual algae, transmission as well as pH value with illumination time. It’s found that the plasma sprayed Pt-doped TiO2 nanostructured coatings on foamed waste-glass showed higher photocatalytic activity, which was effective to treat the green tide and red tide.

Abstract: Nano-sized metal particles have recently attracted considerable interest owing to their application potential. Such particles can be synthesized using physical and chemical methods. In this study, nano-sized noble metals were synthesized through the reaction of metal oxides by ultrasonic. This means that the chemical reactions which take place under conventional conditions can be accelerated by ultrasonic cavitations. In general, the chemical effects of ultrasonic irradiation fall into three areas: homogeneous sonochemical efffects of liquids, heterogeneous sonochemical effects of liquid-liquid or liquid-solid systems, and sonocatalytic effects. It has been proposed that liquid-liquid systems are used for the fabrication of nano-metal particles in the past. In this study, the fabrication of nano-metal particles and supported composites was investigated for the liquid-solid system from a viewpoint of economy and ecology. By choosing suitable conditions, it is reasonable to expect that these simple ultrasonic processes can be extended to obtain nano-sized metal particles. Thus applications by using these reactions were investigated to prepare the nano-sized metal particle supported materials, and mechanisms were investigated.