Seiichi Suenaga

Interfacial reactions between titanium film and single crystal α-Al2O3

Titanium is commonly used to join metals and ceramics by active metal brazing methods. In this work, titanium was sputter deposited on to single-crystal α-Al2O3 substrates and the interfacial reactions between the titanium film and the Al2O3 substrate were studied. Al2O3 was reduced by titanium when samples were annealed at 973 and 1173 K for 300 s in an argon gas flow. Metallic aluminium was produced at the interface, and this diffused from the interface into the titanium film. At 1173 K, the intermetallic compound Ti3Al and the intermediate titanium oxides, such as Ti2O and TiO, were formed. The Al0 diffusion is important in stimulating interfacial reactions.

Fabrication of nanocomposite using self-forming core/shell nanoparticles and its magnetic properties at up to gigahertz bands for high-frequency applications

A nanocomposite with a magnetic loss factor (tan δ=μ″/μ′) of less than 1% at up to 1 GHz was synthesized using self-forming core/shell nanoparticles of metal/oxide; these were concentrated to achieve a relative permeability (μ′) of more than three. The self-forming core/shell nanoparticles were synthesized by oxidation of a portion of FeCoAl nanoparticles in thermal plasma. An FeCoAl complex oxide shell of approximately 2 nm in thickness was formed on the surface of FeCo nanoparticle, which had approximately 20 nm in diameter. The core/shell nanoparticles were mixed with resin to form bulk material of millimeter-order thickness.

Solid-state reactions of the Ag-Cu-Ti thin film-Al2O3 substrate system

A new interpretation of the reaction mechanism between active metal thin-film filler and ceramic substrate is proposed. The authors predict the possibility of prebonding reactions, prior to melting of the filler, at the interface of the system described above. To prove this, solid-state reactions of Ag–Cu–Ti thin films on sapphire substrates have been studied with Auger electron spectroscopy (AES) and x-ray diffraction (XRD). Reaction process and products have been clarified at the temperature just below the melting point of the filler. It is evident that Cu 3 Ti 3 O (diamond structure of Fd 3 m ) is formed by the reaction between Cu 3 Ti and O which results from the reduction of sapphire. It seems that Cu 3 Ti 3 O contributes to bonding between metals and sapphire as an intermediate phase.

Relationship between microstructure of plasma-sprayed 8YZ coatings and thermal fatigue life of thermal barrier coatings

Microstructure of plasma-sprayed yttria-stabilized zirconia coatings (8YZ) was characterized by the measurement of surface roughness, hardness, and pore size distribution and was correlated with thermal fatigue life. It was confirmed that the coatings which had greater roughness tended to show both lower hardness and higher porosity. Furthermore, such coatings were found to have a longer thermal fatigue life. We propose that measurement of the roughness of 8YZ coatings is useful as a non-destructive evaluation method for predicting thermal fatigue life.

Bulk nanocomposite using self-forming core/shell nanoparticles and its magnetic properties for high-frequency applications

A bulk nanocomposite composed of tightly packed self-forming core/shell nanoparticles of metal/oxide was fabricated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition were controlled in the nanocomposite, and their effects on the magnetic properties were investigated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition strongly influenced the magnetic anisotropy field, magnetic coercivity, relative permeability, and loss factor at GHz bands. High permeability with a low loss factor of less than 1.5% at up to 1 GHz was obtained in the nanocomposite in which the nanoparticles with a crystalline grain size of approximately 15 nm were tightly packed.

High-frequency magnetic properties of (FeCoNbB)-(SiO2) nanocolumnar films

(FeCo)-(SiO2) nanogranular films in which magnetic metal particles form nanosized columns, nanocolumnar, were studied. The nanostructure was formed by controlling the composition ratio of magnetic metal and insulating oxide. Inducing uniaxial anisotropy in the film plane resulted in high permeability in the GHz band and a high ferromagnetic resonance frequency. To improve the permeability loss factor, crystallinity of FeCo was controlled by adding B and Nb. As a result, an amorphous nanocolumnar film with ferromagnetic resonance frequency of greater than 5 GHz, high relative permeability of 44.9, and low loss factors of less than 1% up to 1 GHz was achieved.

Vapor-grown carbon nanofibers synthesized from a Fe2O3–Al2O3 composite catalyst

Vapor-grown carbon nanofibers (CNFs) were synthesized from a Fe 2 O 3 -Al 2 O 3 composite ceramic catalyst. It was revealed that the CNF constructions and structures depended on the catalyst phase. Fe 2 O 3 solid solution and FeAlO 3 catalysts synthesized fine CNFs with diameter of 10-15 nm. These CNF structures were similar to those of MW-CNTs. Notably, the FeAlO 3 catalyst could synthesize aligned CNF structures. The secondary phase precipitated from FeAlO 3 in the specific crystal direction and this precipitation induced the cleavage fracture of FeAlO 3 grain during CNF synthesis. As a result, CNFs grew on the specific plane and aligned in one direction.

Solid-State Reactions of a 3D-Transition Metal-Ti/Al 2 O 3 System

An interfacial mechanism for reactions between a Me-Ti thin film (Me=3d transition metals; Cu,Ni) and an A1 2 O 3 substrate is newly proposed. It has been clarified that Me 3 Ti 3 O (diamond cubic of Fd3m), which is formed as an intermediate phase in both the Cu-Ti/Al 2 O 3 and Ni-Ti/Al 2 O 3 systems, is responsible for the bonding between Me and A1 2 O 3 . The solid-state reactions of the Me-Ti bilayer film/Al 2 O 3 system were studied with Auger electron spectroscopy (AES) and X-ray diffraction (XRD) to clarify the interfacial reaction between Me-Ti and the A1 2 O 3 substrate. Me 3 Ti 3 O was observed at the interface between A1 2 O 3 and Me after annealing. Me 3 Ti 3 O was formed by oxidation of the Me-Ti compounds. The oxygen which reacted with the Me-Ti compounds has been found to be generated from the reduction of the A1 2 O 3 substrate.