Papers by Author: Takashi Goto

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Authors: Xin Yan Yue, Rong Tu, Takashi Goto
Abstract: b-axis oriented SrO substituted BaTi2O5 (Ba1-xSrxTi2O5) was prepared by arc-melting. The effect of SrO substitution on the dielectric properties of BaTi2O5 (BT2) was investigated by A.C. impedance spectroscopy. The Cole-Cole plot of Ba1-xSrxTi2O5 showed a distorted semi-circle which was deconvoluted into two semicircles corresponding to the bulk BT2 and a second phase. The complex impedance, modulus and capacitances from the ferroelectric bulk matrix and the paraelectric second phase of Ba1-xSrxTi2O5 were simulated by a Maxwell-Wagner model.
Authors: Dong Yun Guo, Akihiko Ito, Rong Tu, Takashi Goto
Abstract: Ba2TiO4 and Ba4Ti13O30 Thick Films Were Prepared by Laser Chemical Vapor Deposition Using Ba- and Ti-Dipivaloylmethanate Precursors. Single-Phase Ba2TiO4 Thick Films Were Obtained at 845–946 K and Ba/Ti Source Molar Ratio 2.4. Single-Phase Ba4Ti13O30 Films Were Obtained at 944–1011 K and Ba/Ti Source Molar Ratio 0.38. Ba2TiO4 Thick Films Consisted of Truncated Grains, while Ba4ti13o30 Thick Films Had Shellfish-Like Grains. Ba2TiO4 and Ba4Ti13O30 Thick Films Showed a Columnar Growth and their Deposition Rates Were 72 and 132 μm h−1, Respectively.
Authors: Kyosuke Ueda, Takayuki Narushima, Takashi Goto, T. Katsube, Hironobu Nakagawa, Hiroshi Kawamura, M. Taira
Abstract: Calcium phosphate coating films were fabricated on Ti-6Al-4V plates and screw-type implants with a blast-treated surface using radiofrequency (RF) magnetron sputtering and were evaluated in vitro and in vivo. Amorphous calcium phosphate (ACP) and oxyapatite (OAp) films obtained in this study could cover the blast-treated substrate very efficiently, maintaining the surface roughness. For the in vitro evaluations of the calcium phosphate coating films, bonding strength and alkaline phosphatase (ALP) activity were examined. The bonding strength of the coating films to a blast-treated substrate exceeded 60 MPa, independent of film phases except for the film after post-heat-treatment in silica ampoule. When compared with an uncoated substrate, the increase in the ALP activity of osteoblastic SaOS-2 cells on a calcium phosphate coated substrate was confirmed by a cell culture test. The removal torque of screw-type Ti-6Al-4V implants with a blast-treated surface from the femur of Japanese white rabbit increased with the duration of implantation and it was statistically improved by coating an ACP film 2 weeks after implantation. The in vitro and in vivo studies suggested that the application of the sputtered ACP film as a coating on titanium implants was effective in improving their biocompatibility with bones.
Authors: Takayuki Narushima, Kyosuke Ueda, Takashi Goto, Jun Kurihara, Hiroshi Kawamura
Abstract: Oxyapatite, amorphous calcium phosphate, and double-layered calcium phosphate coating films were fabricated on mirror-polished commercially pure titanium (CP Ti) and blasted Ti-6Al-4V alloy substrates by radiofrequency (RF) magnetron sputtering; the properties of these films were evaluated in vivo and in vitro. The bonding strength between the calcium phosphate films and the Ti substrates was higher than 50 MPa. This value is higher than the bonding strength reported in the case of plasma-sprayed calcium phosphate coating films fabricated on Ti substrates. The removal torque of screw-type blasted Ti-6Al-4V alloy implants in the femurs of Japanese white rabbits increased with the duration of implantation, and the removal torque values of the coated implants was observed to be higher than those of the non-coated implants. In vitro and in vivo studies indicate that coating Ti implants with calcium phosphate films using RF magnetron sputtering is effective in improving the bone compatibility of Ti implants. Finally, the factors that should be considered in fabricating biomedical coating films were discussed.
Authors: Takayuki Narushima, Kyosuke Ueda, Takashi Goto, Tomoyuki Katsube, Hiroshi Kawamura, Chiaki Ouchi, Yasutaka Iguchi
Abstract: Calcium phosphate films were coated on commercially pure titanium substrates by radiofrequency magnetron sputtering using β-tricalcium phosphate targets. The films consisted of amorphous calcium phosphate and oxyapatite phases. Immersion tests of the films were carried out in Hanks’ solution and PBS(-), and apatite formation and calcium ion elution from the films were investigated. The titanium cylinders coated with calcium phosphate films were implanted into the mandibles of beagle dogs. These results suggest that coating with calcium phosphate improves the biocompatibility of titanium implants with bone tissue.
Authors: Mettaya Kitiwan, Akihiko Ito, Takashi Goto
Abstract: Sintering Behavior of Monolithic TiN and TiB2 Was Investigated Using Spark Plasma Sintering (SPS) at Temperatures between 1673 and 2573 K. Relative Density of TiN Was Increased from 82.3 to 96.7% while that of TiB2 Increased from 70.1 to 92.8% with Increasing Temperature. At Temperatures between 1673 and 2273 K, TiB2 Was More Difficult to Consolidate Compare to TiN. At 2473 K, TiB2 Densified Rapidly to 92.8%.
Authors: Xin Yan Yue, Rong Tu, Takashi Goto
Abstract: Poly- and single-crystalline BaTi2O5 co-substituted with SrO and ZrO2, Ba0.99Sr0.01(Ti1-xZrx)2O5 (BT2SZ) were prepared by arc-melting and floating-zone (FZ) melting, respectively. The specimens showed a significant (020) orientation. The highest permittivity of poly-crystalline BT2SZ was 3880 at x = 0.005 and that of single-crystal was 27000 at x = 0.005. The Curie temperature (Tc) of poly-crystals decreased from 750 to 640 K with increasing x from 0 to 0.026 and that of single-crystals decreased from 750 to 710 K with increasing x from 0 to 0.008. The highest remnant polarization of single crystalline BT2SZ was 7.8×10-2 Cm-2 at x = 0.008, higher than that of the poly-crystal.
Authors: Yusuke Orii, Hiroshi Masumoto, Takashi Goto, Yoshitomo Honda, Takahisa Anada, Keiichi Sasaki, Osamu Suzuki
Abstract: The surface oxide films were prepared by Electron Cyclotron Resonance (ECR) plasma oxidation on Ti substrates. Octacalcium phosphate (OCP) and dicalcium phosphate dihydrate (DCPD) peaks were formed after calcification by supersaturated calcium and phosphate solutions. Calcification ability was enhanced with increasing the oxidation time and the total pressure of ECR plasma treatment during oxidation. The results demonstrated that the calcium phosphate nucleation and the deposition can be controlled by various ECR plasma conditions.
Authors: Nittaya Keawprak, Rong Tu, Takashi Goto
Abstract: Ca-Ru-O compounds were prepared by spark plasma sintering (SPS) using CaCO3 and RuO2 powders at various molar ratio of Ru to Ca (RRu/Ca). CaRuO3 in a single phase was obtained at RRu/Ca = 1.0. A non-stoichiometric solid solution range of CaRuO3 was identified at RRu/Ca = 0.7 to 1.0. The electrical conductivity (σ) showed metallic conduction behavior and increased with increasing RRu/Ca. The electrical conductivity at RRu/Ca = 0.8 to 1.0 increased with decreasing oxygen partial pressure (PO2) and the PO2 dependence of σ became significant with increasing temperature.
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