The effects of heat-treatments with various conditions such as temperature, atmosphere on photoluminescence properties of (Ba, Sr)₂SiO₄:Eu²⁺ phosphors were investigated in detail. The change of Photoluminescence and XRD pattern of (Ba, Sr)₂SiO₄:Eu²⁺ phosphors heat-treated at various temperatures revealed that the reduction from Eu³⁺ to Eu²⁺ in the precursor powder was effectively promoted at the temperatures higher than melting temperature of fluxing agent. We also found that photoluminescence properties and particle shape of (Ba, Sr)₂SiO₄:Eu²⁺ phosphors were deeply affected by the incomplete reduction of Eu (Eu³⁺→Eu²⁺) and fluxing effect of BaCl₂, and they were caused by a very small quantity of oxygen gas under reduced atmosphere.

The preparation of a stable suspension dispersing carbon nanotube (CNT) in aqueous media using polystyrene maleic acid (PSMA)-based polymer as surfactant was attempted to be subsequently used in the fabrication of high-performance ceramic matrix composites. Settling velocity under centrifugation analysis was experimentally evaluated as one of the stability criteria of the dispersion and pulsed nuclear magnetic resonance was used to evaluate the amount of adsorbed molecules. The settling velocity decreased considerably with the PSMA concentration up to the saturation at around 7 mass%, then further decreased gradually with PSMA. The former was thought to be based on the dissociation of CNT agglomerate and the latter would be attributed to the surfactant-induced network structure formed in the aqueous media.

Leptothrix species, one of the Fe/Mn-oxidizing bacteria, are ubiquitous in aqueous environments, especially at sites characterized by outwelling groundwater with a nearly neutral pH, an oxygen gradient and a source of Fe(II) and/or Mn(II). The genus Leptothrix forms lined-cell chains by repeating cell division and then forms uniquely shaped microtubular sheaths surrounding the cell chains through the precipitation of copious amounts of iron or manganese oxides which were accumulated from groundwater. The sheath is an ingenious hybrid of organic and inorganic materials produced through the interaction of bacterial exopolymer fibrils with aqueous-phase inorganics. Intriguingly, Leptothrix sheaths, that we call biogenous iron oxides (BIOXs), have a variety of unexpected functions that are suitable for industrial applications such as lithium-ion battery anode, a catalyst support, a starting material of bright red pigment among others. This review focuses on the structural and chemical properties of BIOXs produced by Leptothrix and their noteworthy functions that show promise for variety of industrial applications.

The microstructures of Ca-La-Co M-type sintered ferrite magnets were analyzed by Spherical Aberration Corrected Scanning Transmission Electron Microscopy (Cs-STEM) to devise guidelines for improving performance. It was confirmed that there were Ca-Si-based oxides, which consists of Si, Ca, La and Fe, at multiple-junction phases of the sintered body, after adding only SiO₂ instead of both CaCO₃ and SiO₂, which are sintering aids for ferrite magnets. It was also confirmed that the ratio of Si, Ca, La and Fe at multiple-junction phases was 30:60:2:5. Moreover, we found that a step-terrace structure of Ca-Si-based oxides formed at the boundary of the M-type ferrite grain, and that the maximum width of the intergranular grain boundary was about half (1.15 nm) the edge length of the c-axis of the M phase. This suggested that ferrite grains were magnetically isolated by the presence of Ca-Si-based oxide phases at the intergranular grain boundary, whereby improving coercivity.

Although immunochromatograph using nanoparticles has some merits such as an ease of use and a quick response, it has some issues such as a poor sensitivity and a lack of quantitativity. To overcome the issues, we investigate a new immunoassay method using a magneto-optical (MO) effect based on nanoparticle technologies. Bismuth-substituted yttrium-iron garnet (Bi-YIG) is one of the candidates, which exhibits a large Faraday effect. To enhance the Faraday effect for highly sensitive MO immunoassay, surface plasmon resonance (SPR) effect is employed in the preset study. Au nanoparticles have an absorption peak based on the SPR effect in the wavelength range of 500-600 nm by optimizing their size and interparticle distance. We fabricate MO and plasmonic particles composed of a Bi-YIG particle as a core and Au nanoparticles deposited on the core. The clear SPR absorption and the MO enhancement are obtained in the composites with a larger amount of Au nanoparticles deposited on Bi-YIG particles. The enhancement of the Faraday rotation is observed in the range of 500-700 nm, corresponding to the wavelength range where the clear SPR absorption was observed. The Faraday rotation increases by 50% in maximum at around 550 nm of wavelength.

Ti-8.4 vol% M-47.4 vol% TiC (M: Cr, Mo, W) alloys were prepared through P/M technology and their microstructures and mechanical properties were investigated. It was noted that TiC grain size of W alloy was much smaller than that of both Cr alloy and Mo alloy. Smaller diffusion coefficient of M in β-Ti phase and smaller absolute value of Helmholtz standard free energy of formation of MC were thought to suppress TiC grain growth. It was found that hardness and transverse-rupture strength of W alloy were much higher than those of both Cr alloy and Mo alloy.

The occurrence of numerous shallow cracks on the rubbing surface of cemented carbide was studied by using an apparatus simulated mechanical seal. If the Vickers indentation tests were conducted on the rubbing surface where the crack spacing was large, indentation cracks with almost the same length as the neighboring pre-cracks could be formed by the tensile residual surface stress. Thermal and elastic-plastic analyses shows that thermo-cracking mechanism cannot explain why cracks run perpendicular to the direction of sliding and that the dynamical action of a high contact stress together with a high tangential force plays a very important role in the occurrence of cracks.

WC-based cemented carbides are widely used as cutting tool materials. Tungsten, a main component of the cemented carbides, is one of the rare metals and its production is concentrated in certain countries. Therefore, a development of cutting tool materials containing less tungsten is highly desired today. Although Ti(C,N)-based cermets have higher hardness and provide higher machined surface quality as compared to cemented carbides, their applications have been limited due to their low fracture toughness and thermal conductivity.

Mechanical properties of Ti(C,N)-based cermets using Ti(C,N) solid solution powders prepared by dissolving various transition carbide powders as the starting materials were studied. The cermet using the Ti(C,N) solid solution powder containing Ta and Nb had the highest hardness and fracture toughness in the all prepared samples. In addition, it was found that the Ti(C,N)-based cermet with an optimized WC content prepared by controlling the sintering condition and the texture had both high fracture toughness and thermal conductivity. Cutting tools of our developed cermet exhibited a comparable cutting performance with those of WC-based cemented carbides (ISO P30).

A higher efficiency and a higher stability in machining processes are always required for cutting tools. Improvements of mechanical properties of hard materials, especially a plastic deformation resistance and a fracture resistance at high temperature, are desired for achieving such requirements. Our studies for understanding fundamental phenomenon of the hard materials have played important roles to enhance their mechanical properties for cutting tools.

Our previous work about a forming mechanism of open pore on sintered surface of Ti(C,N) based cermet figured out the origin and the growth mechanism of the open pore by microstructure observation and elemental analysis of the hard material samples sintered under various sintering conditions. Another work about mechanical properties and forming mechanism of plate-like triangular prismatic WC cemented carbide revealed that the triangular prismatic WC grains were preferably oriented along the pressing direction when tungsten (W) and carbon (C) powders were used as the starting materials. The cemented carbide exhibited higher plastic deformation resistance and fracture toughness at high temperature as compared to conventional cemented carbides prepared using a tungsten carbide (WC) powder as the starting material did.

TiC-SiC ceramics were sintered at 1600–1800 °C using a resistance-heated hot pressing machine. No phase except TiC and α-SiC was detected after sintering. Dense ceramics were obtained in the range of 0–70 mol% SiC at a sintering temperature of 1800 °C. The Young’s moduli for dense TiC-SiC ceramics ranged from 426–457 GPa, regardless of the SiC additive amount. The addition of SiC above 10 mol% increased Vickers hardness by 2–3 GPa. The addition of SiC above 10 mol% inhibited the grain growth of TiC, and brought fine equiaxed granular structure to sintered bodies. The addition of SiC increased fracture toughness in the conditions 0–50 mol% SiC at 1800 °C, 0–20 mol% SiC at 1700 °C, and 0–10 mol% SiC at 1600 °C. The highest fracture toughness value 6.5 MPa m^1/2 was obtained for the TiC-50 mol% SiC ceramic sintered at 1800 °C. The addition of SiC greatly increased thermal conductivity from 27 W m⁻¹ K⁻¹ for pure TiC to 98 W m⁻¹ K⁻¹ at 70 mol% SiC.

Titanium carbonitrides containing transition metal ((Ti, Me)(C, N), Me: transition metal) have been studied for applying them to cutting tools and wear- resistant tools. Thermal shock resistance is an important property of tool materials used in severer thermal environment. Therefore, the thermal conductivity of such materials is important to improve the thermal shock resistance of tool materials. The present work is aimed to clarify the effects of the composition of carbonitrides on thermal conductivity and electrical conductivity of carbonitrides. The experimental results showed that the thermal conductivity and electrical conductivity of carbonitrides decreased with increasing solid solution of transition metal.