Papers by Author: Hirokazu Katsui

Abstract: TiB₂-TiC, TiB₂-TiN and TiB₂-TiC_xN_1-x composites were prepared by arc-melting mixtures of TiB₂, TiC and TiN powders. 28TiB₂-72TiC (mol%) composite showed a lamellar eutectic structure, while 55TiB₂-45TiN (mol%) composite with a lamellar structure consisted of TiB₂, TiN and TiB. 36TiB₂-44TiC-20TiN (mol%) was a quasi-binary eutectic composite having a rod-like structure.

Abstract: 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.

Abstract: 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 (T_dep), total pressure (P_tot) and precursor vaporization temperature (T_vap) on the SiO₂ yield by RCVD were investigated. At O₂ gas flow of 4.2 × 10^-7 m³ s^-1, T_dep of 948 K, P_tot 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.

Abstract: α-LiAl₅O₈, γ-LiAlO₂, α-Al₂O₃ and those composite films were prepared on AlN polycrystalline substrates by laser chemical vapor deposition (LCVD), and the effects of total pressure (P_tot) and the molar ratio of Li to Al (R_Li/Al) on the morphology and deposition rates were investigated. The typical morphology of single-phase γ-LiAlO₂ films prepared at R_Li/Al > 1.0 and P_tot > 400 Pa was granular, whereas γ-LiAlO₂ films prepared at P_tot < 200 Pa and γ-LiAlO₂-α-LiAl₅O₈ composite films had pyramidal grains. Single-phase α-LiAl₅O₈ films showed polygonally faceted morphologies. Composite films of α-LiAl₅O₈ and α-Al₂O₃ consisted of carifllower-like and faceted grains. A single-phase γ-LiAlO₂ film deposited at 200 Pa showed the maximum deposition rate of 48 μm h^-1.

Abstract: Highly pure transparent single-crystalline BaTi₂O₅, 6 mm in diameter and 15 mm in length, was prepared by a floating zone (FZ) method using high purity BaCO₃ as a source material. The as-prepared crystal was partially dark blue and became transparent by annealing at 773 K in air. The maximum value of permittivity (ε_max) was 36000 at the frequency of 100 kHz and the Curie temperature (T_C) was 757 K.

Abstract: (004)-oriented γ-LiAlO₂ films were prepared on poly-crystalline AlN substrates by laser chemical vapor deposition at deposition temperature (T_dep) of 1100–1250 K, molar ratio of Li/Al (R_Li/Al) of 1.0–10 and low total pressure (P_tot) of 100–200 Pa. The (004)-oriented γ-LiAlO₂ films consisted of pyramidal grains with a columnar structure. The deposition rate of (004)-oriented γ-LiAlO₂ films reached to 65–72 μm h^-1.

Abstract: 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 H_V of 29.7 GPa with the K_IC of 3.76 MPa m^1/2.

Abstract: 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.

Abstract: 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.