In recent years, significant attention has been given to the physical properties of low-dimensional materials. Carbon nanotubes (CNTs), a prime example of such materials, are emerging as a promising next-generation candidate material for sensor components, including yoctogram (10⁻²⁴ g) measurement devices and antennas capable of handling large-scale digital data. CNTs exhibit a variety of atomic arrangements due to their chirality. However, even 30 years after their discovery, controlling the chirality of CNTs remains challenging, and the specifics of their physical properties still require clarification. Understanding the vibration characteristics of carbon nanotubes (CNTs) is crucial for designing nanoscale structures and devices. In this study, we analyzed the effects of tube diameter, push ratio, and length of CNTs on vibration using molecular dynamics simulation. This method allows for the modeling of ideal geometric structures at the atomic level and the tracking of their behavior. The findings are as follows: For armchair carbon nanotubes, the resonance frequency decreased with an increase in the length of the CNTs. It was observed that the thermal energy generated during vibration tends to decrease with an increase in tube diameter. The full width at half maximum increases with an increase in the push ratio.

Synchrotron radiation small-angle scattering measurements and transmission electron microscopy observations have been carried out on the microstructure formation process of Mg_83.8Co_6.7Y_9.5 alloys. In the MgCoY alloy, Y clusters, which are different from the Y and Zn clusters precipitated in the initial stage in the MgZnY alloy, were precipitated from the amorphous state with increasing temperature. Subsequently, the Y clusters transformed into β′′, β′ and β phase with increasing temperature, while a stacking structure was also observed to coexist.

Rocks containing clay minerals exhibit diminished strength and undergo physical and chemical deterioration of their texture due to the presence of these clay minerals. Specifically, rocks containing swelling clay minerals experience a significant decrease in strength when subjected to repeated drying and wetting compared to rocks with non-swelling clay minerals. This study conducted a comprehensive series of experiments (physical, uniaxial compressive, and swelling pressure tests) using artificial soft rock mixed with clay minerals. The primary objective was to elucidate the impact of the types of clay minerals present on the physical properties of rock materials under repeated drying and wetting. The clay minerals investigated in this study included Na-type and Ca-type smectites (swelling clay minerals) and mica (non-swelling clay minerals). The smectite-mixed specimen demonstrated higher swelling pressure than the mica-clay-mineral-mixed specimen. Moreover, the uniaxial compressive strength and P-wave velocity of the specimens were remarkably reduced due to repeated drying and wetting process. Hence, the difference in clay mineral content and type in the clay mineral-bearing rock material specimens directly influences the physical and mechanical properties of rock materials when subjected to dry and wet cycles. Furthermore, the outcomes suggest a close association between the reduction in rock material strength, inclusive of clay minerals, and the swelling pressure observed in the specimen.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 73 (2024) 198–204.

Cesium-tin-bromide perovskite (CsSnBr₃) has focused on as a candidate material for all-inorganic perovskite solar cell and thermoelectric energy converter because of its optical, electrical, and thermal properties. On the other hand, the electrical properties have not been clarified yet because of several inconsistent reports. In this paper, we produced CsSnBr₃ bulk from a melt using the precursor powder prepared by a mechanochemical process. From powder X-ray diffraction analysis, main phase of the precursor was CsSnBr₃ perovskite, and minor impurities were Cs₂SnBr₄ and CsSn₂Br₅. Although main phase of the bulk produced from a melt was CsSnBr₃, small amount impurity, CsSn₂Br₅ was confirmed. From the electrical conductivity (σ_t) measurement, irreversible temperature dependence of σ_t was observed at first time increasing temperature. The conductivity measured from room temperature to 443 K at the first time showed metallic behavior. On the other hand, the temperature dependence is changed into opposite with decreasing temperature. At this operation, σ_t decrease with decreasing temperature. This semiconductor like behavior was found to be reversible after first increasing temperature operation. These results indicate that post anneal as well as production process of CsSnBr₃ would be important to control its electric property.

This Paper was Originally Published in Japanese in J. Japan Soc. Powder Powder Metallurgy 70 (2023) 427–431.

Aging behavior, cluster formation including near grain boundaries, and mechanical properties of Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) alloy were investigated. The effect of Ag as a microalloying element was also clarified. The Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) alloy showed higher aging hardening ability and shorter time to peak aging than the Al-5%Zn-2%Mg (-0.3%Ag) alloy from the early aging stage. The effect was greater with the addition of Ag, showing that the effects of solute content and micro-alloying elements on age hardening were recognized. 3DAP analysis revealed that Ag contributed significantly to the initial stage of cluster formation even when the solute elements were high. It was also found that clustering occurred in the vicinity of the grain boundary at a high density and fineness from the early stage of aging. By increasing the solute content of Zn and Mg to 11% and 3% respectively, the tensile strength of the alloy was over 800 MPa, and the addition of Ag further increased the strength.

This Paper was Originally Published in Japanese in J. JILM 73 (2023) 604–610.

For powder magnetic cores, a spinel ferrite insulating layer offers the advantages of high magnetic flux density and low iron loss. However, FeO is generated in the insulting layer after annealing at 873 K, which causes a decrease in electrical resistivity. To overcome this problem, we focused on fayalite (Fe₂SiO₄), which exhibits a high electrical resistivity and is stable even at temperatures above 1273 K. Fe₂SiO₄ can be formed by a reaction between FeO and SiO₂. Therefore, if Fe powder particles mixed with both spinel ferrite and SiO₂ are heated at a temperature that is sufficiently high to form FeO, Fe₂SiO₄ is expected to be produced, and the resulting particles are likely to exhibit high electrical and thermal resistance. To examine this possibility, a mixture of Fe₃O₄ of spinel-type ferrite, SiO₂, and Fe powder was heated at 1023 K, and the structure and composition of the resulting material were investigated. Analyses using X-ray diffraction and Fourier-transform infrared spectroscopy confirmed the formation of Fe₂SiO₄, which showed a high electrical resistivity. These results indicate that Fe₂SiO₄ can be used as an insulating layer for powder magnetic cores.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 47–50.

An all-solid-state battery featuring a Ga–30Sn anode, Na silicate electrolyte, and graphite cathode was fabricated. This study investigated the effects of operating temperatures and discharge currents on the charge–discharge cycle performance of the battery. Specifically, the optimal cathode materials were determined to be graphite. The battery had considerable charge–discharge cycling performance at an operating temperature of 55°C. At a high operating temperature of 85°C, the battery reached its maximum capacity with a small number of cycles; however, prolonged exposure to this temperature compromised the stability of the solid electrolyte, thus affecting the battery’s capacity. High-discharge currents promoted ion participation in electrochemical reactions and thereby enhanced the battery’s capacity. Nevertheless, excessive ion accumulated on the electrode surface during the charge–discharge cycles and adversely affected ion insertion and extraction processes. Both Ga and Na ions served as cation carriers in the Ga–30Sn/Na silicate/graphite battery, which exhibited acceptable capacity. Thus, this all-solid-state battery is non-toxic, safe, and robust when applied in high-temperature environments.

To reduce the cost of solution heat treatment process Ni-base single crystal superalloy TMS-238 containing Re and Ru, quantitative analysis of dendrite-interdendrite segregation of alloying elements under various solution heat treatment conditions were conducted, and influence on high-temperature creep strength were investigated. In this study, we defined the solution rate R_sol (= (1 − V_f,e) × 100%, where V_f,e is volume fraction of eutectic γ′ that precipitates in the final solidification zone during casting) as a parameter to reveal the microstructure homogeneity. The R_sol values were 71%, 97%, 99%, 100% for solutioning at 1250°C/20 h, 1320°C/5 h, 1320°C/20 h and 1335°C/20 h, respectively. Furthermore, it was confirmed that Re and W segregated in the dendrite core area and γ′ formers whereas Ta and Al segregated in the interdendrite. The magnitude of these segregations decreased as the solution temperature and time increased, and eventually the structure became almost homogeneous for solutioning at 1335°C for 20 hours. Additionally, creep test results indicate that Larson-Miller parameter (LMP) at 800°C–735 MPa, 900°C–392 MPa and 1000°C–245 MPa creep conditions show the same values for R_sol ≥ 97%. On the other hand, under 1100°C–137 MPa creep condition, LMP decreased as the R_sol decreased. A factor analysis of creep rupture properties suggested that the degradation of LMP under 1100°C–137 MPa was caused by the decrease of Re content and γ/γ′ lattice misfit in the interdendritic region.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 288–297.

Carbon nanomaterials are a class of low-dimensional materials that have aroused a great deal of interest for decades. Carbon nano-onions (CNOs) are carbon nanomaterials with a wide range of applications. In this study, we report a novel process for synthesizing CNOs from SiC—the only inorganic carbon source—through one-pot sonication in pure water at room temperature. This synthesis process is more facile and can be performed under gentler conditions and lower temperatures than previous methods. The as-synthesized samples were characterized using transmission electron microscopy (TEM), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and scanning transmission electron microscopy–electron energy loss spectroscopy (STEM-EELS). The TEM results revealed CNOs with diameters of approximately 20–30 nm, and the FTIR and STEM-EELS results indicated the presence of oxygen-containing functional groups on the CNOs and the growth of carbon from a SiC single crystal. The proposed method for obtaining CNOs from an inorganic carbon source via sonication provides novel insights into the CNO generation mechanism and its functionalization.

Microscopic hydrogen visualization has long been required to clarify the hydrogen embrittlement mechanism of metallic materials. In this study, hydrogen diffusion depending on microstructure in polycrystalline pure nickel film was successfully visualized using an Ir complex, whose color changes with hydrogen. The hydrogen flux in nickel was found to be large at random grain boundaries and small inside grains and at coincidence site lattice grain boundaries.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 73 (2024) 194–199.