Papers by Author: Takashi Goto

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.

Abstract: Functionally graded Ca-Ti-O/Ca-P-O films were prepared by MOCVD. The phases, composition and morphology of Ca-Ti-O and Ca-P-O films changed depending on the molar ratio of each precursors, total pressure (Ptot) and substrate temperature (Tsub). CaTiO3 films in a single phase were obtained at Tsub = 973 and 1073 K. CaTiO3 films prepared at 873 K had a dense and smooth surface, whereas that prepared at Tsub = 1073 K had complicated rough surface with a cauliflower-like texture. The graded texture of CaTiO3 films from columnar to fine grains was advantageous to good adherence for metal substrates. -TCP and HAp films in a single phase were obtained at Tsub = 973 and 1073 K. Both -TCP and HAp films had a dense and smooth surface. The maximum deposition rate of Ca-Ti-O and Ca-P-O films were 44 and 20 m/h, respectively, and several 10 times grater than that of sputtering method. Apatite formation rate strongly depended on the surface morphology of film. Apatite formed after 3 days on the CaTiO3 film, 14 days on the -TCP film and 6 hours on the HAp film in a Hanks’ solution.

Abstract: SiAlON-cubic boron nitride (cBN) composite was prepared by spark plasma sintering (SPS) using -SiAlON and cBN powders as starting materials, and the effect of holding time on densification, phase transformation and hardness of the composite was investigated. The SiAlON-cBN composite containing 20 vol% cBN sintered at 1650oC for 60s was densified to >97% of theoretical density. cBN phase transformed to hexagonal boron nitride (hBN) in the SiAlON-cBN composite with increasing holding time at 1650oC. Vickers hardness of the SiAlON-20vol%cBN composite sintered at 1650oC for 60-300s was 17.7GPa, and the hardness decreased with increasing holding time.

Abstract: ZrB2-SiC composites were prepared by arc melting using ZrB2 and -SiC powders as raw materials and their oxidation behavior were investigated. The eutectic composition of the ZrB2-SiC system was ZrB2-58.5mol%SiC and the melting point temperature was about 2570 K. At 1673 K mass gain was observed in the oxidation of ZrB2-SiC eutectic composition and the mass gain rate increased with decreasing Ptot. The oxide scale consisted of an amorphous SiO2 layer, a ZrO2-SiO2 eutectic-like layer and a Si-deficient layer.

Abstract: AlN–SiC solid solutions with p-type electrical conduction were fabricated with the addition of small amounts of Al and C. Powder mixtures of AlN and SiC with small amounts of Al and C (below 10 mol%) were consolidated by spark plasma sintering (SPS) at 2000°C for 10 min under 1 atm Ar, and then heat-treated at 2200°C for 3 h in an Ar flow to afford 2H AlN–SiC solid solutions. The relative densities of the 50AlN-50SiC-Al4C3 (A50-1AC) and 50AlN-50SiC-3Al4C3 (A50-3AC) samples were about 95%, whereas that of the 75AlN-25SiC-Al4C3 (A75-1AC) sample was about 86%. X-ray diffractometry (XRD) analysis showed that the samples comprised only the 2H phase, and except in the case of the A50-3AC sample, no diffraction peaks of Al and C were observed. Although the samples without the additives (Al and C) were electrical insulators, addition of Al and C introduced p-type semiconduction. The electrical conductivities at 300°C of the A50-1AC and A50-3AC samples were about 30 and 100 S/m, respectively, whereas that of the A75-1AC sample was about 10–1 S/m. It was found that addition of Al and C brought about electrical conduction in AlN–SiC solid solutions.

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.

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.

Abstract: Surface titanium oxide (TiO2) films were fabricated on implant titanium (Ti) at low temperatures by electron-cyclotron-resonance (ECR) plasma oxidation. The relationship among the oxidization conditions, crystal structure, morphology and osteoconductive property were investigated. Although crystallized TiO2 film was not prepared by thermal oxidation at 300°C, crystallized rutile-type TiO2 film was formed by ECR plasma oxidation at 300°C. Rough morphology was observed in the substrate surface oxidized by ECR plasma. Mixtures of octacalcium phosphate (OCP) and dicalcium phosphate dihydrate (DCPD) were observed after calcification. The XRD peak intensities of the OCP and DCPD formed on the ECR plasma oxidized Ti were larger than those of calcified on the thermal oxidized Ti. ECR plasma oxidation at low temperature would induce osteoconductive calcium phosphate on implant Ti.

Abstract: C-Ru-RuO2 nano-composite films were prepared by plasma-enhanced chemical vapor deposition and their microstructure and electrode properties were investigated. Ru-C nano-composite films consisted of Ru nano-particles of 3 nm in diameter and an amorphous C matrix. With increasing oxygen gas flow rate (FRO2), the volume fraction of C decreased from 0.91 to 0 and Ru nano-particle size increased from 2.5 to 4.5 nm. At high FRO2, the film consisted on the fibrous RuO2 and Ru-C nano-composite layer. Ru-C nano-composite containing 91 vol% C showed the highest interfacial electrical conductivity below 673 K, and Ru-C/RuO2 composite containing 0 – 5 vol% C showed the highest interfacial electrical conductivity at 873 K. Electro-motive-force (EMF) values of an oxygen concentration cell constructed from a YSZ electrolyte and Ru-C or Ru-C/RuO2 composite electrodes responded to the change of oxygen gas partial pressure at more than 473 K. The response time of the concentration cell with Ru-C nano-composite electrodes at 573 K was less than 10 s, and that with Ru-C/RuO2 composite electrodes was about 300 s.

Abstract: BaTi2O5 film was prepared on MgO (100) substrate by laser ablation, and the structure and electric property of the film were investigated. The film was b-axis oriented and epitaxially grown on the substrate along two in-plane directions with the a-axes ([100]-orientation) perpendicular to each other. The b-axis oriented BaTi2O5 film exhibited a sharp permittivity maximum (~ 2000) and had a high Curie temperature (750 K). The electrical conductivity increased with temperature and showed the Arrhenius relationship having an activation energy of 1.25 eV.