This paper reviews the investigations carried out in the author’s laboratory for developing of new-type binderless cemented carbides. WC-WB, WC-SiC, and WC-MoC composites were prepared by using resistance-heated hot-pressing (called spark-plasma sintering), and the sinterability, microstructure, and mechanical properties and carbide addition effects on them were mainly examined for application as binderless cemented carbides. WC-SiC had the best sinterability, but the SiC addition induced hardness decrease due to the abnormal growth of WC grains. The abnormal grain growth was prohibited by the addition of small amounts of Cr₃C₂ and/or V₈C₇. WC-MoC composites were prepared by reaction sintering of WC, C, and Mo₂C powder mixtures accompanied by the solid-state reaction (1 − x)WC + x/2Mo₂C + x/2WC → W_1−xMo_xC during sintering. This reaction was accelerated by SiC addition. Carbon addition to WC greatly influenced the grain growth of WC. Carbon nonstoichiometry generated by carbide addition is discussed on the basis of the phase diagram of the added carbide-WC system.

Powder injection molding is a combined technique of traditional powder metallurgy and plastic injection molding. Since injection molding step in the process enables to produce complex shapes, powder injection molding technique has high design flexibility and provides a chance to overcome limitations in the current manufacturing process. In this paper, the optimization of powder injection molding process was discussed. The process was roughly divided into 5 steps from solids loading determination to sintering, and the optimization approaches for each step was detailed. Thereafter, the industrial application of powder injection molding process was described with hydrophobic surgical forceps, soft magnet components, PZT array for ultrasound probe and PDP glass components. The process optimization was conducted for each product, and sound products were obtained with the process.

New production method of nano-crystals was proposed. Over the past few decades, with improvements in nanotechnology, production of nano-materials had been paid interest markedly. There are some production methods of nano-materials, such as inert gas evaporation method, hydrothermal synthesis method, mechanical grinding method and etc. In recently, solution plasma method was developed, in that method nano-crystals were produced by microwave induced plasma in liquid. The authors have found new nano-crystal production method. In the new method, nano-crystals were produced by application of relatively low voltage DC current in aqueous electrolyte solution. The various combinations of electrodes (Au, Cu, W, Si, etc.) and aqueous electrolyte solution (Na₂SiO₃, Na₂CO₃, Na₂SO₄, etc.) were tested to produce nano-crystals. After few tens minutes of current application, precipitated materials were gathered and identified by X-ray diffraction analysis and TEM observation. From XRD analysis and TEM observation, it was found that the collected materials were nano-crystals of around few tens nm of the same material as the electrode. From measurement of mass change of electrode before and after DC current application, it turned out that nano-crystals were generated from the electrode to which the positive voltage was applied.

The effect of nitrogen distribution on the magnetic properties for the NdFe₁₁TiN_x powder was investigated. In case of the heat treatment under a constant pressure of nitrogen gas, the nitrogen distribution in the powder showed the gradient from the surface to the core, so that the saturation magnetization was relatively low (137-146 emu/g). In order to solve the gradient of nitrogen distribution, switching of the atmosphere from nitrogen to argon gas during the heat treatment was adopted. The nitrogen distribution was improved to be averaged in the powder. As a result, the saturation magnetization of the newly processed powder increased to about 155 emu/g (1.48 T). This process would be effective for the homogenization of the nitrogen distribution in the NdFe₁₁TiN_x powder.

We investigated the synthesis of Sr₃SiO₅:Eu²⁺(SSE) yellow-orange phosphors by three different gelation methods using Propylene Glycol-Modified Silane (①Gelation with Sr, Eu nitrate solution, ②Gelation with Sr, Eu citrate solution, ③Gelation with SrCO₃ and Eu₂O₃ slurry) and the effects of the synthetic methods on the main phase (Sr₃SiO₅) purity and quantum efficiency of SSE phosphors. SSE phosphor synthesized by the nitrate solution method exhibited relatively low main phase purity and quantum efficiency due to segregation of Sr and Eu that occurred during a drying process of the synthesis. SSE phosphor with higher quantum efficiency was obtained by the citrate solution method, but decomposition of a large amount of citric acid was a problem. Obtaining a pasty white gel by adding PGMS to the slurry of SrCO₃ and Eu₂O₃ without adding citric acid was the best way to obtain SSE phosphor having the highest phase purity and quantum efficiency with constituent elements evenly distributed. The slurry method was also effective from the viewpoint of not requiring decomposition of a large amount of organic components.

The pressurized sintering behaviors of 3 mol% Y₂O₃ partially stabilized tetragonal ZrO₂ polycrystals (3Y-TZP) powder compacts by microwave irradiation (28-GHz) were investigated. The 3Y-TZP powder compacts were densified in a cylindrical closed α-Al₂O₃ die at constant external compression pressures (σ_ex) of 50–100 MPa and a temperature of 1273 K. To obtain adequate microwave permeability and block microwave irradiation, a die with thicknesses of 10 and 15 mm was used, respectively. The relative density (ρ_re) increased while the densification rate (ρ̇) decreased with increasing sintering times. Increasing σ_ex led to an increase in ρ_re and ρ̇. A stress exponent (n) was estimated from ρ̇ and the effective stress acting on the compact. Regardless of the die thickness, n values of 2 and 1 were respectively obtained in a low-stress region (i.e., densification rate was dependent on vacancy generation/annihilation) and a high-stress region (i.e., densification rate was dependent on vacancy flow). Thus, there was no difference in the densification rate-controlling mechanism by microwave irradiation. Regarding ρ̇ obtained by using the thin 10 mm die (microwave penetrating) and the thick 15 mm die (microwave blocking), both show similar ρ̇ values in the low-stress region, but the former shows a higher ρ̇ value than the latter in the high-stress region. These results indicate that microwave irradiation does not influence the rate of vacancy generation/annihilation, but promote vacancy flow.

The microstructure of WC/Co interface at 1623 K was investigated using the WC-Co diffusion couples with small amount of tungsten or carbon addition to the couple halves, and from the microstructure, the diffusion path at the interface was inferred. The microstructure and diffusion path depend on the W and C additives. The η phase formation was observed at the interface in the ((WC)₉₈ + C₂)-Co and WC-(Co₉₈ + C₂) diffusion couples. In the case of ((WC)₉₈ + W₂)-Co and WC-Co diffusion couples, both η and η’ phase were formed. The η, η’, W₂C and W phases were seen in the (WC)-(Co₉₈ + W₂) diffusion couple. Three diffusion paths were inferred from these microstructures. In the case of ((WC)₉₈ + W₂)-Co and WC-Co diffusion couples, the diffusion path of Co⇔η’⇔η⇔WC regions was inferred on the isothermal section of C-Co-W ternary phase diagram at 1623 K (path 1). The path 2 (observed in ((WC)₉₈ + C₂)-Co and WC-(Co₉₈ + C₂) diffusion couples) was through the Co⇔η⇔WC phase regions. The WC-(Co₉₈ + W₂) diffusion couple showed the path through the Co⇔η’⇔η⇔WC regions with crossing the (η + W) and (η + W₂C) two phase regions (path 3).

This study deals with the preparation of CeO₂ nanoparticles (NPs) catalyst supported by YTZ ball ceramics, and investigations of its morphology and hydrogen oxidation property. A CeO₂ NP layer was prepared by a simple dipping process. As the results, the CeO₂ NPs maintained the high dispersion state even after heat treatment at 1000°C. According to H₂-TPR measurement, it was also found that a CeO₂ NPs-modified YTZ sample has better catalytic property than CeO₂ powder. Thus, the catalytic functionalized YTZ ball-type ceramic was provided by simple processing with the modification of CeO₂ NPs as a novel catalytic material.

Titanomagnetite solid solution Fe_3−xTi_xO₄ films have been prepared on α-Al₂O₃(0001) substrates by a reactive sputtering method. Nearly single phase of Fe_3−xTi_xO₄ with (111)-orientation was epitaxially formed on the substrate. The epitaxial relationship of Fe_3−xTi_xO₄ [11̄0] (111) || α-Al₂O₃ [11̄00] (0001) was confirmed. All films with x < 0.6 exhibited ferrimagnetic property at room temperature. The saturation magnetization of the films showed systematic changes depending on the Ti concentration x. The Ti⁴⁺ ions in Fe_3−xTi_xO₄ can be expected to substitute for the octahedral Fe³⁺ ions by following the Néel-Chevallier model. The films had thermally activated semiconductor behavior and the electrical resistivity with exponentially increasing of the Ti concentration. In-direct optical band gap observed from an absorption spectroscopy also shows monotonical increase with the increasing of Ti concentration.

W-type ferrite magnets haven’t been industrialization yet because they have low coercive force and difficulty of preparation to be caused by instability of Fe²⁺. We have challenged to control of the oxygen concentration profile during semi-sintering. In this research, the influence of oxygen concentration at high temperature of semi-sintering on crystal structure are discussed. Furthermore, the effect of excessive amount of Sr on crystal structure are discussed, too. At a result, it was found that preparation of W-type phase are affected from the oxygen concentration at start of semi-sintering and maximum oxygen concentration at 1300°C. In this experiment, the optimum conditions to prepare W-type single phase are as follows; oxygen concentration at start of semi-sintering is under 1%, maximum oxygen concentration at 1300°C is under 2%, excessive amount of Sr is 0.1 mol at most.

Synthesis and characteristics of magnetic gold nanoshells are investigated and discussed from the viewpoint of photothermal therapy (PTT). Morphological properties of thickness, roughness, surface coverage of the shell, the pore size and so on influence their optical properties and the magnetic properties controlling the conditions of synthesis and thermal treatment. NIR light-absorbing gold nanoshells are successfully fabricated on silica/Fe-Pt core-shell nanoparticles via the two-step seed-mediated growth method using a polymer layer of polyethylenimine (PEI) as an interlayer. The cationic polyelectrolyte PEI with high amine content binds to the negatively charged Fe-Pt nanoshell through electrostatic self-assembly to form a stabilizing polyelectrolyte layer, which is necessary to not only the deposition of Au nanoparticles but also the growth of the uniform gold shell. The surface modification using PEI polymers with lower molecular weight of the Fe-Pt nanoshell leads to the formation of a high-quality gold shell with a smooth and thin morphology being responsible to the appearance of a strong NIR absorption. The photothermal properties are obtained by NIR laser irradiation without any deformation of the nanoshells.