To understand the mechanism of antibacterial activity of bulk Cu, N₂-atomized Cu powder has been used instead. It was heated from 425 to 673 K in air for 4.2 • 10² s and measured by XRD and Chemi-luminescence (CL) to determine the contents of Cu₂O and CuO, and reactive oxygen species (ROS), respectively; ROS being much affected by Cu₂O and CuO can play a role to kill bacteria. Cu₂O increased from 3.3 mass% (R.T.) to around 20% (673 K), however, CuO was almost constant (1.2~3.5%). High CL intensity was observed for Cu powders heated at 598~673 K. Then, a small amount of anatase TiO₂ (a-TiO₂) was added and heated at 673 K for 4.2 • 10² s in air, 1% O₂-99% N₂, and N₂. The powder heated under 1% O₂ showed the high CL intensity summation (∑CL), especially, 8.0 mol% a-TiO₂ added and heated sample (“8.0Ti powder”) gave the about 4.7 times higher ∑CL than the starting material. ESR results using the spin-trap method showed that they contained hydroxyl radical •OH and its intensity increased from starting material to “8.0Ti powder”. However, bio-test proved that these samples revealed the same antibiotic activity. Formation mechanism of ROS (•OH and super oxide radical •O₂^-) on the surfaces of Cu/Cu₂O/CuO has been proposed.

Dense alumina and Ni-Zn-Cu ferrites, and porous hydroxyapatite (HAP) have been fabricated using a fused deposition modeling (FDM) type 3D printer, so-called “Additive Manufacturing (AM)”. Green bodies of the former two were consisted of the laminated layer filaments from ceramics/resin = 60/40 vol% kneaded bodies to obtain dense ceramics. On the other hand, the latter was composed of 50/50 or 55/45 vol% filaments for porous scaffold. Binder-out process was performed in air with the selected temperature range/heating rate and final 673~723 K for 1.08~18.0 • 10⁵ s, corresponding to each material. Hot Isostatic Pressed fine grained alumina after microwave sintering with an apparent relative density of 94%, substantially more than 98% by looking at the microstructure, revealed a bending strength of 562 MPa. Permeability µ of dense Ni-Zn-Cu ferrite sintered in air was nearly the same as that of conventional one; at low frequencies µ of “AM” ferrite surpassed the latter. Porous two kinds of HAP ceramics were fabricated from the different calcining temperatures 1223 and 1248 K, and biotested in terms of the cell culture at 310 K for 8.64 and 25.9 • 10⁴ s. The cells on HAP produced from 1223 K calcined grew twofold in comparison with those of control glass.

This report investigated the spark plasma sintering (SPS) of Shuri castle breakage roof tile powder for the effective utilization of the Shuri castle breakage roof tiles. First, we examined the fundamental characteristics of Shuri castle breakage roof tiles. The chemical composition of broken roof tiles mainly comprises SiO₂. Scanning electron microscopy analysis revealed the dispersion of quartz lumps in the inner structure. Additionally, the density of the broken roof tile was 2.43 g/cm³, and the open porosity was 17.9%, the Vickers hardness (HV) was 87.5 at the matrix side and 1200 at the quartz lump, and the flexural strength was 15.7 MPa. Meanwhile, the fundamental characteristics of the SPS compact formed using breakage roof tile powder comprised a density of 2.68 g/cm³, an open porosity of approximately 0%, an HV of 259, a flexural strength of 105 MPa, and a flexural modulus of 83.1 GPa at a sintering temperature of 1323 K. The formation of magnetite was confirmed via X-ray diffraction patterns of the sintered products; however, the crystalline phases were almost identical to those of the broken roof tile powders.

It was a great honour for us to receive the 59th technical achievement award of Japan Society of Powder and Powder metallurgy (JSPM). We presented an overview of the metal injection moulding (MIM) technology development over 25 years of experience and future trends through our originally developed μ-MIM technology in the annual spring meeting of JSPM 2022, which are summarised in this paper.

The μ-MIM technology is developed for especially small size metal parts with strict dimensional tolerances. We have focused only on a small complex designed metal part production in a net shaping, thus, the trend related to MIM parts larger than 50 mm in size is not covered. We have also joined the Micro Manufacturing Association in Japan since its establishment in 2018, which promotes micro parts manufacturing technology to the world. The demand increment of micro parts in various industries is never slowdown thus our μ-MIM technology overview might be instructive for both powder metallurgy and micro parts manufacturing interests.

In recent years, metal injection molding (MIM) has been adopted as a manufacturing method for solenoid valves which are parts of electronic fuel injectors, and PB permalloy parts have been commercialized. However, Ni, a constituent element of PB permalloy, is an expensive material, making it difficult to produce fuel injector parts at low cost. To solve this problem, the use of inexpensive Fe-Cr alloys has been considered. However, its properties are insufficient as a material for solenoid valves, which require improved magnetic properties, reduced core loss, and improved corrosion resistance, and these requirements have been increasing year by year. As a solution to this problem, we studied magnetic and material properties of Fe-Cr-Si and Fe-Cr-Si-Mo alloys produced by MIM process. These results revealed that magnetic properties were improved by reducing the amount of Cr, and that corrosion resistance was improved by adding Mo even if the amount of Cr was reduced. In this review, we describe the magnetic and material properties of Fe-Cr-Si and Fe-Cr-Si-Mo alloys produced by MIM process.

Metal Injection Molding (MIM) process is suitable for fabricating small and complex shaped metal parts with high production volume. In this study, in order to improve the MIM process, cellulose nanofibers (CNF) were focused. There are problems such as deformation during debinding and sintering due to the addition of a large amount of binder. On the other hand, the strength of the green compact decreased with decreasing binder contents. In this study, cellulose nanofibers were added with a binder during mixing in order to improve the handling of green compacts, and decrease the deformation during debinding and sintering. The effects of CNF contents on the mechanical properties were investigated. It was clarified that CNF is effective in improving the handleability of the debound compacts and suppressing deformation during sintering.