Hirokazu Katsui

Enhancement of adhesive strength of hydroxyapatite films on Ti–29Nb–13Ta–4.6Zr by surface morphology control

Hydroxyapatite (HAp) films were deposited on a β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), by metal organic chemical vapor deposition (MOCVD) in order to improve its hard-tissue compatibility. The surface morphologies of TNTZ substrates were changed by acid treatments and mechanical polishing prior to the HAp film deposition. The adhesive strength of the HAp films formed on TNTZ substrates treated with an HF solution increased to twice that of the HAp film deposited on a TNTZ substrate with a mirror-like finish. Complex microstructures with deeply etched grain boundaries, formed on the TNTZ substrates after immersion in the HF solution, were responsible for the increase in the adhesive strength of the HAp film caused by an interlocking effect. The HAp films on TNTZ substrates treated with a H(2)SO(4) solution exhibited lower adhesive strength than HAp films on TNTZ substrates treated with HF solution, regardless of the surface roughness of the substrates. Additionally, acid treatments using HNO(3) and H(2)O(2) solutions did not change the surface morphologies of the TNTZ substrates. The complex microstructures with deeply etched grain boundaries and nanosized asperities formed on the TNTZ substrates are important factors in the improvement of the adhesive strengths of HAp films deposited on TNTZ substrates.

Complex impedance and ionic conduction of single-crystalline BaTiO3

ABSTRACT Dielectric properties of single-crystalline BaTiO3 in the direction to <001> were investigated by impedance spectroscopy. The complex plane plots showed high- and low-frequency semicircles and an inclined spike at 548–648 K. The spectroscopic plots of M″ comprised a single relaxation peak at 102–104 Hz, whereas those of Z″ exhibited a peak at high frequencies (102–104 Hz), a low-frequency peak, and dispersion. The high-frequency relaxation was attributed to the ferroelectric bulk. The low-frequency peak and dispersion were associated with the charge transfer and the Warburg impedance, respectively. The low-frequency impedance response implied the ionic conduction of BaTiO3.

Silicon Carbide Coating on Diamond Powder by Rotary Chemical Vapor Deposition

Silicon Carbide (SiC) Layers Were Prepared on Diamond Powders by Rotary Chemical Vapor Deposition (RCVD) Using C6H18Si2 as a Precursor. Diamond Particles with Cleavable and Sharp Configurations Were Covered with Smooth Layers by RCVD. Infrared Absorption Bands at around 800 and 1000 cm-1 Attributed to Si-C Bonding Were Observed in FTIR Spectrum on the Diamond Powders. The Pellet Sample Sintered by Spark Plasma Sintering Using the Diamond Powders Suggested that β-SiC Was Deposited on the Diamond Particles.

Study on Compatibility Between Silicon Carbide and Solid Breeding Materials Under Neutron Irradiation

Abstract Compatibility of monolithic silicon carbide (SiC) with ternary lithium ceramics (Li1-xAlO2-y, Li2-xTiO3-y, Li2-xZrO3-y and Li4-xSiO4-y) under irradiation of neutrons at high temperatures was studied. Disk samples of SiC in contact with sintered ternary lithium ceramics were irradiated in High Flux Isotope Reactor (HFIR) at 800 °C to 5.9 displacements per atom (dpa). Chemical reactions of SiC as determined by appearance of the surface were relatively less significant for the systems of SiC/Li1-xAlO2-y and SiC/Li2-xTiO3-y, whereas some bonding likely due to chemical reaction between SiC and the lithium ceramics and broken samples were observed in the systems of SiC/Li2-xZrO3-y and SiC/Li4-xSiO4-y. The effect of lithium burnup due to the (n, α) nuclear reaction was also examined by using samples of lithium ceramics whose lithium ratio was hypo-stoichiometric in the fabrication process. More reaction products were observed on the surface of β-SiC in contact with Li1-xAlO2-y having the lower lithium ratio (Li/Al). It was considered that the formation of LiAl5O8 phase due to lithium loss could deteriorate the compatibility of the SiC - Li1-xAlO2-y system.

Consolidation of Titanium Carbide with Zirconium Carbide by Spark Plasma Sintering

Titanium carbide (TiC) was consolidated with 20 mol% zirconium carbide (ZrC) by spark plasma sintering in the temperature range of 1773–2473 K, and the phase formation, microstructure, relative density and mechanical properties were investigated. The composite consisted of Ti-rich (Ti, Zr)C and Zr-rich (Zr, Ti)C solid solutions at 1773–2373 K, and was single-phase (Ti, Zr)C at 2473 K. The relative density of the composite was over 98% above 2073 K. The composite prepared at 2273 K exhibited the maximum HV of 29.7 GPa with the KIC of 3.76 MPa m1/2.

Surface Modification of Silicon Carbide Powder with Silica Coating by Rotary Chemical Vapor Deposition

The surface of silicon carbide (SiC) powder was modified by coating with amorphous silica (SiO2) using (C2H5O4)Si (tetraethyl orthosilicate: TEOS) as a precursor by rotary chemical vapor deposition (RCVD). With increasing deposition time from 0.9 to 14.4 ks, the mass content of SiO2 coating increased from 1 to 35 mass%. The SiO2 mass content had a linear relationship with deposition time from 2.7 to 7.2 ks. The effects of O2 gas flow, deposition temperature (Tdep), total pressure (Ptot) and precursor vaporization temperature (Tvap) on the SiO2 yield by RCVD were investigated. At O2 gas flow of 4.2 × 10-7 m3 s-1, Tdep of 948 K, Ptot of 400 Pa and deposition time of 7.2 ks, the maximum SiO2 yield of 1.82 × 10-7 kg/s with SiC powder of 4.5 × 10-3 kg by RCVD was obtained.

Spark plasma sintering of cBN(core)/SiO2(shell) powder prepared by rotary chemical vapor deposition

Abstract SiO2 nanolayer coated cubic boron nitride (cBN), cBN(core)/SiO2(shell) powder, was prepared by rotary chemical vapor deposition. The cBN/SiO2 powder was densified by spark plasma sintering at 1873 K for 0.3 ks. The hexagonal boron nitride (hBN) phase was not observed in the cBN–SiO2 composites, indicating that the SiO2 nanolayer depressed the phase transformation from cBN to hBN. The relative density of cBN–SiO2 increased with increasing SiO2 content (). The highest hardness of the cBN–SiO2 composite was 17.5 GPa at and a load of 0.98 N.

Consolidation of SiC Powder Coated with SiO2 Nanolayer by Spark Plasma Sintering

Silica (SiO2) nanolayer was coated on silicon carbide (SiC) powder by rotary chemical vapor deposition (RCVD). The SiC/SiO2 composite were consolidated by spark plasma sintering (SPS) at 1923 K using the SiO2 coated SiC powder. The relative density and hardness of the SiC/SiO2 composites increased with increasing SiO2 content, and were 97% and 17 GPa, respectively, at SiO2 content of 22 mass%. The relative density and hardness of a composite consolidated using the mixture powders of SiC and SiO2 (22 mass%) at 1923 K were 81% and 8 GPa, respectively.

Orientation and Morphology of LiCoO2 Prepared by Chemical Vapor Deposition on Al2O3 Single Crystal

Lithium Cobaltate (LiCoO2) Films Were Prepared on the (001), (110), (110) and (112) Planes of Al2O3 Single Crystals Substrates by Metal Organic Chemical Vapor Deposition, and the Phases, Orientated Textures and Surface Morphologies Were Examined. (001)-Oriented LiCoO2 Films Were Obtained on (001) and (110) Al2O3 Substrates, while (018)- and (104)-Oriented LiCoO2 Films Were Grown on (110) and (112) Al2O3 Substrate. Triangular and Elongated Rectangular Faceted Structures Were Directionally Aligned, and (001)- and (018)-Oriented Grains Were Epitaxially Grown on (001) and (110) Al2O3 Substrates. Randomly Arranged Polygonal Faceted Structures Were Observed in the (001)-Oriented Licoo2 Film on (110) Al2O3 Substrate, while Locally Inhomogeneous Grains Were Observed in the (104)-Oriented LiCoO2 Film on (1_,12) Al2O3 Substrate.

Ball milling effects for induced carriers and reduced grain size on thermoelectric properties in Bi1-x Srx CuSeO(x = 0,0.1)

We have investigated the ball milling effects for thermoelectric Bi1− x Sr x CuSeO materials. The characteristic rotation speed R for the ball milling exists, at which the crystallite size of the starting powder suddenly decreased. The grain size in the bulks sintered using ball-milled powders also decreased and thermoelectric properties were enhanced mainly by the induced carriers, rather than by the reduction in thermal conductivity. The ball milling effects of carrier doping on thermoelectricity are discussed.