Hirotaka Fujimori

Hydrothermal preparation of fibrous apatite and apatite sheet

Abstract Hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 :HA) with highly designed microstructures is required for bone filling materials and tissue engineering of cultured bones. This study deals with the shape control of HA particles and preparation of HA sheet from fibrous HA. Fibrous particles of HA with the aspect ratio of about 60 were prepared hydrothermally at 150 °C from the mixed solution of calcium acetate and phosphoric acid. The aspect ratio of the fibrous particles depended on the concentration and the value of Ca/P ratio of the mixed solution. The HA sheet must be a biostable material according to the soaking test with simulated body fluid.

Cubic-tetragonal phase change of yttria-doped hafnia solid solution : high-resolution X-ray diffraction and Raman scattering

Abstract High-resolution synchrotron X-ray powder diffraction and Raman scattering have demonstrated the existence of tetragonal yttria-doped hafnia solid solution with an axial ratio, c f / a f , of unity, but having displacements along the c f -axis from the ideal fluorite position in the oxygen sublattice. The values of c f / a f ratio in HfO 2 – X mol%YO 1.5 samples ( X =13, 14, and 16) are estimated to be unity with the precision of ±0.00003 from the estimated standard deviation of the peak position and less than ±0.001 from the full-width at the half-maximum of the 400 f reflection peak. However, the Raman spectra of the samples of X =13, 14, and 16 clearly demonstrate the tetragonal phase.

β-cubic phase transition of scandia-doped zirconia solid solution: Calorimetry, x-ray diffraction, and Raman scattering

Differential scanning calorimetry and Raman spectroscopy measurements have been performed to investigate the β-cubic (c) phase transition of the compositionally homogeneous ZrO2-22 mol % ScO1.5 solid solution. The enthalpy of transition (1.11 kJ/mol of cation) and thermal hysteresis between β- and c-phases were smaller than those between monoclinic (m) and tetragonal (t) phases of ZrO2, reflecting the structural information that the cell volume ratio of β- to c-phases is smaller than that of m- to t-phases. Raman spectroscopy allowed us to observe the β-c phase transition, and we could obtain Raman spectra of the c-phase in the ZrO2–ScO1.5 system. This result was strongly supported by the observation of x-ray diffraction patterns at high temperatures.

In situ observation of defects in hydroxyapatite up to 1200°C by ultraviolet Raman spectroscopy

Abstract Raman spectra of hydroxyapatite have been successfully obtained at temperatures up to 1200°C for the first time by using a new system of ultraviolet (UV) Raman spectroscopy. With increasing temperature, the intensity of a band ascribed to the stretching vibration of the OH ion continuously decreased. The total intensity of bands in the wavenumber range of 3300–3800 cm−1 did not change significantly up to about 800°C, whereas they decreased at temperatures higher than about 800°C. This result is interpreted as producing oxy-hydroxyapatite due to dehydration of hydroxyapatite over 800°C. The withdrawal of water is accompanied by the creation of defects. This consideration is strongly supported by results of thermodynamic calculations and the line width of the Raman band.

Ultraviolet 363.8-nm Raman Spectroscopic System for in Situ Measurements at High Temperatures

A new ultraviolet (UV) Raman spectroscopic system to measure the Raman scattering from materials at high temperatures up to 1500 °C has been designed. This system is based on a CW (continuous-wave) ultraviolet argon-ion laser (363.8 nm), a spatial filter, a single monochromator coupled to a double-grating rejection filter, and a two-dimensional charge-coupled device (CCD) detector. The plasma lines from the laser are almost completely rejected by a Pellin—Broca prism combined with apertures. In situ Raman measurements for a zirconia (ZrO2) specimen at various high temperatures have been performed by using the UV excitation as well as the conventional visible 488.0-nm excitation for comparison. In the case of visible excitation, thermal emission obstructs the observation of the Raman scattering from zirconia even at 900 °C; it becomes rapidly pronounced between 900 and 1100 °C, and finally it is impossible to observe Raman spectra at temperatures higher than 1200 °C. In sharp contrast to the visible excitation, the UV excitation provides good-quality Raman spectra with practically flat backgrounds for the Raman signal of tetragonal zirconia in the spectral region of 20–1100 cm−1 even at 1500 °C, and it enables clear observation of the monoclinic-tetragonal phase transformation of zirconia occurring between 1100 and 1200 °C.

Advantage of anti-Stokes Raman scattering for high-temperature measurements

We present the results of experiments that assess the viability of anti-Stokes scattering to investigate in situ materials at high temperatures. Both anti-Stokes and Stokes Raman measurements have been performed at various high temperatures using hafnia as a test material. As compared with Stokes Raman spectra, anti-Stokes spectra were observed with lower thermal emission backgrounds in accordance with Planck’s equation. The intensity ratio of anti-Stokes to Stokes scattering approaches 1 as the temperature increases at high temperatures satisfying the Boltzmann distribution law. These results clearly demonstrate the advantage and feasibility of anti-Stokes Raman scattering for the elimination of the thermal emission in comparison with Stokes scattering.

Hydrothermal Preparation of Granular Hydroxyapatite with Controlled Surface

Microstructure designed hydroxyapatite granules from about 50 μm to 1 mm in size were prepared by hydrothermal vapor exposure method at temperatures from 105 oC to 250 oC under the saturated vapor pressure of pure water. As starting materials, powder of α-tricalcium phosphate, gelatin and a vegetable oil were used. The size of granules, the shape of particles in the granules, and the microporosity of about 0.1 μm in size of the granules were controlled. The granular hydroxyapatite prepared at 200 oC under the saturated vapor pressure of pure water for 20 h was composed of rod-shaped crystals of about 40 μm in length with mean aspect ratio of 50. Rod-shaped hydroxyapatite crystals were locked together to make micropores of about 0.1 μm in size. It was non-stoichiometric hydroxyapatite with calcium deficient composition. This granular hydroxyapatite should have the advantage of adsorptive activity, because it has large specific crystal surface and micropores. Introduction Hydroxyapatite (Ca10(PO)4(OH)2; HA) is known as the major component of human bones. Sintered HA with random crystal surface has already been used as a bone-repairing material which can directly bond to natural bones in bony defect. It has been known to be biocompatible and osteoconductive [1]. If materials of HA could have the tailored specific crystal surface, the HA materials should have the advantage of adsorptive activity. The authors reported various kinds of HA materials prepared by the unique hydrothermal methods [2-11]. In the present study, HA granules with tailored crystal surface were prepared by the hydrothermal vapor exposure method [7,8,10]. The granules must be suitable as scaffold for cultured bone, for bone graft material and for drug delivery system (DDS). Experimental Commercial powders of α-tricalcium phosphate (α-Ca3(PO4)2: α-TCP, Taihei Chemical Industrial Co., Ltd., Japan) were used as the starting material. After the addition of 10 mass% gelatin (Wako Chemical Co., Japan) aqueous solution, the obtained slurry was dispersed in the vegetable oil at 70 oC, and then stirred at the rate of 0-600 r.p.m. In order to control granules size. The samples were filtered off to recover, washed with ethanol, and dried at 105 oC in air. After heating at 1200 oC for 1 h in air, the samples were set in a 105 cm autoclave with 30 cm of pure water, and then they were exposed to vapor of the pure water at the temperatures from 30 oC to 250 oC under saturated vapor pressure for 20 h (Fig. 1). Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 19-22 doi:10.4028/www.scientific.net/KEM.254-256.19

Complex susceptibilities of Co-substituted YBa2Cu3O7−d synthesized by the polymerized complex method

Abstract Practically impurity-free ceramic samples of YBa 2 Cu 3− x Co x O 7− d with x = 0−0.5 and Y 0.8 Ca 0.2 Ba 2 Cu 2.8 Co 0.2 O 7− d were synthesized by the polymerized complex method through two different routes, starting either from metal nitrates (route P) or from metal carbonates (route Q). Better compositional homogeneity was achieved in the latter route, where neither colloids nor precipitates were formed during the polymerization procedure. The magnetic response of the samples was measured in terms of AC magnetic susceptibilities and variation of the onset temperature T c (onset) of the superconducting transition was precisely determined as a function of Co content. The T c (onset) were almost unaffected for 0 ⩽ x ⩽ 0.5, decreased linearly with ΔT c / Δx ∼ −220 K for 0.07 ⩽ x ⩽ 0.3, and the superconductivity vanished for x ⩾ 0.4. The depression of T c was interpreted in terms of the localization of holes in the Cu(1)O y planes. The replacement of 20% of Y with Ca in YBa 2 Cu 2.8 Co 0.2 O 7− d enhanced T c from the initial value of 57.1 K up to 88.6 K. It was suggested that the rise in T c induced by Ca doping was connected with the delocalization effect of holes in which the hole charge transfer from the Cu(1)O y planes to the Cu(2)O 2 conduction sheets played a crucial role.

Fabrication of ultrathin Ni-Zn ferrite films using electron cyclotron resonance sputtering method

Well-crystallized Ni–Zn ferrite (Ni0.4Zn0.6Fe2O4) highly oriented ultrathin films were obtained at a substrate temperature of 200 °C by a reactive sputtering method utilizing electron cyclotron resonance microwave plasma, which is very effective to crystallize oxide or nitride materials without heat treatment. Thin films of Ni–Zn ferrite deposited on a MgO (100) underlayer showed an intense X-ray-diffraction peak of (400) from the Ni–Zn ferrite as compared to similar films deposited directly onto thermally oxidized Si substrates. A 1.5-nm-thick Ni–Zn ferrite film, which corresponds to twice the lattice constant for bulk Ni–Zn ferrite, crystallized on a MgO (100) underlayer.

Fabrication of circulator with coplanar wave guide structure

A circulator with a coplanar wave-guide structure, whose external form is rectangular, was designed and analyzed by using a three-dimensional finite-element method. In this analysis, the nonreciprocal transmission characteristics with an insertion loss of 1.0 dB and an isolation of 33 dB appeared at around 7 GHz. The bandwidth defined as the band with isolation of over 20 dB was 50 MHz. A circulator was fabricated based on the design, and the transmission characteristic of the circulator was measured. The fabricated circulator showed an insertion loss of 4.9 dB and an isolation of 28 dB at around 8 GHz. The bandwidth at isolation over 20 dB was 70 MHz.