Takafumi Kusunose

Synthesis, atomic structures and properties of carbon and boron nitride fullerene materials

Carbon (C) and boron nitride (BN) fullerene materials (clusters, onions, intercalation, nanopolyhedra, nanotubes and nanocapsules) were synthesized by polymer pyrolysis, chemical reaction, arc-melting and electron-beam irradiation. Atomic structure and formation mechanism were investigated by high-resolution electron microscopy, energy dispersive spectroscopy and electron energy-loss spectroscopy. Fullerene clusters and atomic clouds (atom hopping) were formed on the surface of the C and BN fullerene materials. They provided angular and spherical nanocage structures which consist of four-, five-, six-, and seven-membered ring bonding. Detection possibility of doping atoms in metallofullerene was discussed. Included clusters showed some crystallographic relationship with {001} layers of C and BN fullerene materials, and a structure model was proposed. Photoluminescence and magnetic properties of C and BN nanocapsules were measured, which showed higher energy shift of luminescence and superparamagnetism. The present work indicates that the new C and BN fullerene materials with various atomic structure and properties can be produced by various synthesis methods, and a guideline for designing the C and BN fullerene materials is summarized.

Chemical synthesis of silver nanoparticles encapsulated in boron nitride nanocages

Silver nanoparticles encapsulated within boron nitride nanocages were produced from mixtures of boric acid, urea and silver nitrate upon reduction at 700°C in hydrogen; this is a useful fabrication method for the mass production of boron nitride nanocapsules at low temperatures compared to the ordinary arc discharge method.

Preparation and Electrical Properties of Carbon Nanotubes Dispersed Zirconia Nanocomposites

Multi Wall Carbon Nanotubes (MWCNTs) with a diameter of 20-30 nm were used as a conductive phase to add electric conductivity to yttria stabilized tetragonal zirconia (3Y-TZP). Almost fully dense 3Y-TZP/MWCNTs nanocomposite was obtained by pressureless sintering under inert atmosphere and Hot Isostatic Pressing (HIP) treatment. The conductivity of the nanocomposites increased with increasing content of MWCNTs. Moreover, the fracture toughness increment of the composite was confirmed at 0.5 wt% addition. Scanning electron microscopy and transmission electron microscopy observation of the microstructures showed that MWCNTs were fairly homogeneously dispersed in the 3Y-TZP matrix.

Formation and structure of Ag, Ge and SiC nanoparticles encapsulated in boron nitride and carbon nanocapsules

Abstract Boron nitride nanocapsules with silver nanoparticles and carbon nanocage structures with Ge and SiC nanoparticles were produced by the new chemical solution process and hybrid arc-discharge method. High-resolution electron microscopy, energy dispersive spectroscopy and X-ray diffraction showed the formation of silver and silver oxide nanoparticles encapsulated in boron nitride nanocages, which were synthesized from mixtures of boric acid, urea and silver nitrate by reduction at 300–700°C in hydrogen gas. Ge and SiC nanoparticles and nanowires encapsulated in carbon nanocapsules and nanotubes were also produced by direct current and radio frequency hybrid arc-discharge of C, Ge and Si elements. The present work indicates that the various boron nitride and carbon nanocage structures with electronic conductors, superhard materials, semiconductor nanoparticles and nanowires can be synthesized by the new chemical process and hybrid arc-discharge method, and the chemical synthesis of the boron nitride nanocapsules from the organic solution materials is a useful fabrication method for the mass production of low-dimensional nanocage structures at low temperatures compared to the ordinary arc-discharge method.

Synthesis and Properties of Titania Nanotube Doped with Small Amount of Cations

We have investigated a synthesis of metal (Nb, V, Cr, Mn, Co) -doped titania nanotubes using a solution chemical processing in order to control optical and electrical properties. Titania nanotubes doped with a small amount of cations up to 1 wt% exhibited similar morphology and XRD pattern as the pure titania nanotubes, however, color of nanotubes was changed depending on the dopants. It was found that Cr, Mn and Co doped titania nanotubes formed new absorption bands in UV spectra. On the other hand, electrical resistivity of doped titania nanotubes was lower than that of pure titania nanotubes.

Synthesis of gold/magnetic iron oxide composite nanoparticles for biomedical applications with good dispersibility

Composite nanoparticles consisting of gold and magnetic iron oxide were synthesized in an aqueous solution system by sonochemical and radiochemical processes. Small Au nanoparticles were immobilized on the surface of the iron oxide nanoparticles. Removal of the excess polymers in the solution leads to the good dispersibility of the composite nanoparticles. The composite nanoparticles are expected as a type of nanocarrier for biomedical applications.Composite nanoparticles consisting of gold and magnetic iron oxide were synthesized in an aqueous solution system by sonochemical and radiochemical processes. Small Au nanoparticles were immobilized on the surface of the iron oxide nanoparticles. Removal of the excess polymers in the solution leads to the good dispersibility of the composite nanoparticles. The composite nanoparticles are expected as a type of nanocarrier for biomedical applications.

Phase stability and electrical property of NiO-doped yttria-stabilized zirconia

Abstract The effects of NiO solid solution into yttria fully stabilized cubic zirconia (YSZ) on the phase stability and electrical properties of YSZ were investigated. Time-dependent conductivity change of NiO-doped YSZ at 1000 °C was also investigated. Raman spectra showed that weak tetragonal peaks in the YSZ monolith disappeared when NiO was added. In addition, the time-dependent conductivity of YSZ monolith sharply decreased after the first 30 h of annealing at 1000 °C, whereas NiO-doped YSZ did not show such decline. Therefore, the solid solution of NiO enhanced YSZ stability and produced time-dependent conductivity change with moderate time.

Mechanical and magnetic properties of nickel-dispersed tetragonal zirconia nanocomposites.

Effects of Ni dispersions on microstructure and mechanical properties have been studied for Y2O3-stabilized tetragonal zirconia (Y-TZP)/Ni nanocomposites with Ni dispersion up to 10 vol%. Composites were successfully fabricated by reducing and hot-pressing Y-TZP/NiO powder mixtures. Fracture strength was significantly improved from 1.5 GPa for monolithic Y-TZP to 1.9 GPa for nanocomposites with a small addition of Ni (1-2 vol%). Magnetic properties of Y-TZP/Ni nanocomposites were also investigated. Magnetization curves of Y-TZP/Ni nanocomposites showed typical hysteresis loops of soft magnetic materials, whereas coercivity was much larger than that of pure Ni metal. A new function arising from magnetomechanical effects of metallic Ni is also discussed for the present nanocomposites.

Measurement of microscopic stress distribution of multilayered composite by X-ray stress analysis

Abstract In order to evaluate the effect of nano-sized dispersoid to microscopic stress distribution of multilayered composite, two kinds of multilayered composites, Al 2 O 3 /3 mol% Y 2 O 3 -stabilized ZrO 2 (3Y-TZP) and Al 2 O 3 /3Y-TZP(SiC), were fabricated. The latter composite contained nano-sized SiC dispersion within 3Y-TZP layers. The micro-residual stress measurement by X-ray diffraction (XRD) analysis for the monolithic 3Y-TZP and 3Y-TZP(SiC) nanocomposite layers within each composite revealed the existence of tensile and compressive stresses perpendicular and parallel directions to the layers, respectively. The tensile stress of approximately 200–300 MPa was observed to distribute across the zirconia layers in both composites. On the other hand, much higher compressive stress (i.e., 500–700 MPa) existed with a steep distribution across the layer especially for the monolithic Al 2 O 3 /3Y-TZP multilayered composite. However, both tensile and compressive stress distributions were found to be flattened when nano-sized SiC was incorporated into 3Y-TZP layer.

Specific heat and thermal conductivity of HoN and ErN at cryogenic temperatures

The rare earth nitrides, HoN and ErN, were synthesized by the hot isostatic pressing method. Their specific heat CH(T) and the thermal conductivity κ were measured at cryogenic temperatures. In zero field, the peak values of the C0(T) of HoN and ErN are larger than those of the magnetic regenerators such as Er3Ni. The peak values of the adiabatic temperature change ΔT(T) of HoN and ErN showed similar or larger values compared with those of the candidate materials for the magnetic refrigerants such as ErAl2. The thermal conductivity of HoN and ErN are comparable to those of the magnetic regenerators such as Er3Ni. The present results indicate that HoN and ErN are promising materials as the magnetic refrigerant and regenerator for the cryogenic refrigeration system.