Hisato Tokoro

Microstructures and magnetic properties of boron nitride- and carbon-coated iron nanoparticles synthesized by a solid phase reaction

A promising technique to synthesize iron nanoparticles with boron nitride (BN) and carbon (C) nanocoatings was developed. Mixtures of α-Fe2O3 and boron or carbon powders were employed as starting materials and were annealed at temperatures above 1273 K in a nitrogen atmosphere. Products were mainly composed of α-Fe and hexagonal BN or graphite carbon without hematite, which was confirmed by X-ray diffraction. High-resolution transmission electron microscope observation revealed that BN and C nanocapsules with iron nanoparticles of ca. 300 nm in diameter were formed, and they exhibited soft magnetic properties from magnetization measurements. In addition, multi-walled BN and C nanotubes with diameters of a few hundred nanometers were produced by the present method.

High energy product Nd-Fe-B sintered magnets produced by wet compacting process

High energy product ((BH)/sub max/) Nd-Fe-B sintered magnets can be produced by the wet compacting process. In the wet process, the milled powders are mixed in a mineral oil to the slurry and the slurry was compacted in the magnetic field. In order to improve the alignment of powders, some lubricants were added to the slurry for the reduction of friction between grains and/or the dispersion of grains. At first, a surface-active agent of nonion type was examined, with the result that the residual magnetization (Br) was increased by 0.02 T with the improvement of the grain alignment, while the coercivity (N/sub cJ/) decreased by 0.1 MA/m. The chemical structures of lubricants were studied to reduce the decrease of H/sub cJ/ and the requirements for suitable lubricants were found out. By the addition of the methyl oleate, the high performance magnets with (BH)/sub max/=409 kJ/m/sup 3/ (51.4 MGOe), Br=1.46 T (14.6 kG), H/sub cJ/=1.20 MA/m (15.1 kOe) were obtained in mass-production.

Iron nanoparticles coated with boron nitride nanolayers synthesized by a solid phase reaction

In this paper, we have developed a new technique which uses Fe/sub 2/O/sub 3/ and B powders as a raw material, and synthesized Fe nanoparticles of around 200nm in diameter coated with BN nanolayers of 5nm in thickness under a solid phase reaction. Saturation magnetization showed that Fe/sub 2/O/sub 3/ were reduced to Fe almost completely.

Fe–Co and Fe–Ni magnetic fine particles encapsulated by graphite carbon

Magnetic fine particles of Fe–Co and Fe–Ni alloys encapsulated by graphitic carbon (C) were synthesized by annealing Fe2O3,Co3O4, and NiO with carbon powders at 1273 K in nitrogen atmosphere. Saturation magnetizations of the Fe–Co and Fe–Ni particles were 122–150 and 7.8–105Am2∕kg, respectively. X-ray diffraction measurement showed that the Fe–Co was composed of two phases with face-centered-cubic (fcc) and body-centered-cubic phases, while the Fe–Ni was only a fcc phase. Lattice constants of both particles depended on their composition, which suggested that they were alloys. This was confirmed by Mossbauer spectroscopy. Electron microscope images and electron energy loss spectroscope spectra revealed that these particles with diameters of 100–200 nm were encapsulated by C layers with a thickness of several tens of nanometers.

Magnetic Beads With High Saturation Magnetization

Magnetic beads with the core-shell structure of an iron core encapsulated by titanium oxide and silica shell layers were prepared. The beads, HMM-beads, exhibited soft magnetic properties with high magnetization of 105 Amiddotm2/kg and low coercitivity of ~4 kA/m. HMM-beads with a diameter of 3 mum showed DNA isolation performance comparable to that of conventional beads composed of iron oxides. HMM-beads with a diameter of 1 mum coupled with biotinylated anti-EpCAM antibody through Streptavidin linkers also exhibited comparable yields to conventional beads of the same diameter in respect to capturing tumor cells. The response time of the HMM-beads to a magnetic field at magnetic separation was less than one third that of conventional beads in both cases.

57Fe Mössbauer Spectroscopic Study of Fe—B Compounds

57Fe Mossbauer measurements of Fe doped β-rhombohedral boron (β-B) were performed in the temperature range between 300 K and 4.5 K. The spectra of Fe doped β-B consist of three paramagnetic doublets at room temperature and show a magnetic ordered state below 11.8 K, the temperature of which was determined by the 57Fe Mossbauer thermal scanning method at zero Doppler-velocity. The magnitude of the hyperfine magnetic field of Fe atoms in β-B at 4.5 K is about 30 T or more according to hyperfine distribution analysis.

Synthesis of boron nitride nanolayers encapsulating iron fine particles and boron nitride nanotubes

Boron nitride (BN) nanolayers encapsulating iron (Fe) fine particles have been synthesized by annealing mixtures of hematite (α-Fe 2 O 3 ) and boron powders at 1373 K for 2 hours in nitrogen atmosphere. The Fe particles had an average diameter of ∼300 nm with BN nanolayers coating of ∼10 nm. The α-Fe 2 O 3 was transformed into Fe and then Fe-B on a process of annealing. The Fe-B was decomposed into Fe and BN, and consequently Fe particles coated with BN nanolayers were synthesized. They showed soft magnetic properties with coercivity of 1.5 kA/m. The BN nanolayers encapsulation was effective on improving oxidation resistance. BN nanotubes with diameter of ∼100 nm were also synthesized as a resultant product by this method.