Papers by Author: Kiyoshi Itatani

Abstract: Preparation conditions of titanium oxide (TiO₂) powders were examined by the hydrolysis of titanium potassium oxalate (K₂TiO(C₂O₄)₂), through the homogeneous precipitation method (80oC for 24 h) and hydrothermal treatment (160 or 170oC for 1 h). According to the Rietveld analysis, almost a single phase of anatase TiO₂ could be obtained by the hydrothermal treatment at 160oC for 1 h, followed by the heating at 900oC for 10 min in air. The molar ratio of anatase to rutile TiO₂ was found to be controlled by optimizing the hydrothermal conditions in the solution and the heating conditions in air for the photocatalytic activity.

Abstract: The novel hemostatic film for the surgery of bone diseases was fabricated using TEMPO(2,2,6,6-tetramethylpiperidine-1-oxyl)-oxidized cellulose nanofibers (TOCNs), and phosphoryl oligosaccharides of calcium (POs-Ca) or sugar-containing hydroxyapatite (s-Ca₁₀(PO₄)₆(OH)₂; s-HAp). Three kinds of the hydrophilic and transparent films with the thicknesses of 10 to 20 μm were fabricated, i.e., TOCN, POs-Ca-added TOCN and s-HAp-added TOCN films. Among these films, the uptake amount of the simulated body fluid by s-HAp-added TOCN film was as high as 5,543%, which was expected to quickly stop bleeding of larger amount of blood for the hemostasis.

Abstract: The luminescence properties of Eu²⁺-doped barium calcium silicon oxynitrides (general formula: Ba_4-xCa_xSi₆ON₁₀: Eu²⁺ (x = 1.8 ~ 2.2)) were examined, together with the preparation conditions for the solid state reaction. Firstly, the stoichiometric amounts of Ba, Ca₃N₂, SiO₂ and Si₃N₄ were mixed with Eu₂O₃ (activator; the molar ratios of Eu to (Ca + Ba + Eu) (= m; 0.05 to 1.0)) for the preparation of Ba_1.8Ca_2.2Si₆ON₁₀: Eu²⁺, Ba_2.0Ca_2.0Si₆ON₁₀: Eu²⁺ and Ba_2.2Ca_1.8Si₆ON₁₀: Eu²⁺, and then the mixtures were heated at a temperature between 1300 and 1550°C for 10 h in N₂ atmosphere. The single phase compounds, which were prepared by the heating at and above 1350°C, emitted the red color light whose wavelength could be changed from 638 to 653 nm with increasing m value from 0.05 to 1.00, due to the excitation at the wavelength of 528 nm.

Abstract: The fabrication conditions of dense silicon carbide (SiC) composites containing chopped Tyranno Si-Al-C (SA) fiber were examined in this work; SiC compacts containing SA fiber (mean lengths: 214, 394 and 706 m) were hot-pressed at 1800°C for 30 min under a pressure of 31 MPa in Ar atmosphere. The fracture toughness of SiC composites with 40 mass% of SA fiber addition (sintering aid: 5 mol% Al4C3) increased from 2.8 up to 4.7 MPa•m1/2 as the fiber length increased from 214 to 706 m. The enhanced fracture toughness of the SiC composites was attributed to the lowering of fiber orientation angle (i.e., the angle between the fiber length and direction perpendicular to the hot-pressing direction) to 5° with increasing fiber length. The fracture toughness of SiC composites could be further enhanced through the incorporation of SA fibers with a carbon interface (thickness: 100 nm) into the SiC matrix. The fracture toughness of SiC composite containing 40 mass% of these fibers attained 6.0 MPa•m1/2. The thermal conductivity of SiC composites increased with fiber length from 30.5 W•m-1•K-1 to 45.5 W•m-1•K-1; with no significant influence being noted for the case of fibers with a carbon interface.

Abstract: The phosphoryl oligosaccharides of calcium (POC), extracted from potato starch, are composed of phosphorus oligosaccharides and calcium ions. Ultrafine calcium phosphate particles, whose main phase was hydroxyapatite (Ca10(PO4)6(OH)2: HAp), could be prepared through the hydrothermal treatment of POC solution at a temperature between 110 and 130°C; X-ray diffraction indicated the crystallinity of HAp in the resulting powder to be poor and similar to that of living bone. The present HAp powder was regarded to be calcium deficient carbonate apatite with the OH- group being partly substituted by a carbonate (CO3 2-) group. The solubility of the resulting powder in dilute hydrochloric acid was higher compared to that of commercially available HAp, suggesting excellent bioabsorbability for the present powder.