Up to the present, many studies on calcium leaching have focused on ultra-long-term durability. On the other hand, it has been pointed out that aqueous solutions of chlorides such as anti-freezing agents that are sprayed on road structures in cold regions promote calcium leaching, and the author has confirmed this fact experimentally. NaCl, CaCl₂, etc. are sprayed on roads as anti-freezing agents, and their usage has been increasing rapidly since the 1990s. Therefore, it is important to investigate the effect of calcium leaching on the mechanical properties of concrete. In this study, the Young's modulus of hardened cement paste specimens with calcium leaching was determined by bending tests. After the bending test, the calcium concentration distribution on the cross section of the specimen was investigated by EPMA. Based on these results, the relationship between the decrease in calcium concentration and Young's modulus in hardened cement paste was formulated as a power function.

Binders affect both the mechanical properties and electrochemical performance of electrode materials for lithium-ion batteries. This study has developed and applied a mechanical model of electrode materials on negative electrodes made of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR) based binders. A series of tensile tests was performed on carbon-based negative electrodes with several concentration ratios of the binders, and the stress, strain and dissipated strain energy of the binders inside the electrodes were estimated using the mechanical model. The results were summarized as follows. (1) Both the PVDF-based and SBR-based specimens fractured microscopically due to the rupture of the binder inside the specimen. This indicates that the structure of the negative electrode is supported by the binder. (2) The mechanical model was valid for the PVDF-based specimen in that the constituent of the PVDF-based binder formed inside the specimen did not change with respect to the binder concentration. (3) The tensile strength and permanent strain of the SBR-based specimen showed the same tendency as those of the PVDF-based specimen, and the mechanical model was valid for the SBR-based specimen as well. The dissipated strain energy showed a bipolarized tendency between the low and middle binder concentrations. This tendency would be caused by the adhesion mechanism between carbon particles, SBR and CMC, and the dispersibility of carbon particles.

Silicon carbonitride (SiCN) thin films were deposited on Si(100) substrates using plasma-enhanced chemical vapor deposition (PECVD) at a substrate temperature of 500℃. The films were synthesized using a gas mixture of SiH₄, CH₄, and N₂ with flow rates of 1, 16, and 83 sccm, respectively. The effect of RF power (50-150 W) on the film properties was systematically investigated. The deposition rate increased from 14.5 nm/min at 50 W to 43.3 nm/min at 150 W, with a reduced growth rate acceleration above 100 W. X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS) and hydrogen forward scattering (HFS) analyses revealed that the films contained Si (35-39 at.%), C (24-27 at.%), N (33 at.%), and H (23 at.%). X-ray diffraction (XRD) measurements indicated an amorphous structure of the deposited films. The optical properties showed that the band gap decreased from 3.2 to 2.3 eV and the refractive index decreased from 2.1 to 2.0 with increasing RF power. Nanoindentation measurements demonstrated that the maximum hardness of 30 GPa was achieved at 75 W RF power, which is attributed to the optimum balance between Si-N and Si-C bonds. The obtained a-SiCN:H films exhibited properties suitable for applications in semiconductor devices as insulating and protective layers, as well as for optical coatings and hard protective coatings for tools.

This investigation examines the utilization of amorphous gallium oxide (a-Ga₂O₃) thin films, deposited via mist CVD, as deep-ultraviolet (UV-C) photodetectors, and assesses the influence of annealing treatment on their structural, optical, and UV photoresponse characteristics. Initially, a-Ga₂O₃ thin films were deposited on c-plane sapphire substrates at 260°C, followed by annealing at various temperatures in dry air. The crystal structure, surface morphology, and optical properties of these films were analyzed. Furthermore, Ni/Au electrodes were deposited to fabricate metal-semiconductor-metal (MSM) type photodetectors, and their responses to UV-A, UV-B, and UV-C light were evaluated. The findings indicated that annealing at temperatures exceeding 600°C induced the crystallization of Ga₂O₃, transitioning from a mixed phase of α, β, and κ phases to a predominantly β-phase structure. Annealing at temperatures above 800°C increased the optical bandgap, which is hypothesized to be due to the diffusion of Al atoms from the sapphire substrate. The a-Ga₂O₃ photodetectors exhibited responsiveness to UV-A, UV-B, and UV-C light, demonstrating persistent photoconductivity (PPC) after deactivation of the light source. On the other hand, annealing enhanced the selective response to UV-C light and eliminated the PPC phenomenon. This study suggests that annealing treatment of Mist-CVD grown a-Ga₂O₃ thin films is effective in enhancing the response performance of UV-C photodetectors.

Gallium oxide (Ga₂O₃) is known to be an ultrawide-gap semiconductor material and is expected to have applications in power semiconductor devices and optical devices for deep ultraviolet (UV) light. In this study, as a continuation of our paper published in this journal in FY2024, we report experimental results of Ga₂O₃ thin films grown by mist chemical vapor deposition (CVD) method on quartz substrates whose surfaces are made hydrophilic by UV irradiation. For the equipment used in this study, the optimum UV irradiation time for the quartz substrate was 60 minutes. Amorphous Ga₂O₃ thin films were grown on the quartz substrates at substrate temperatures of 450°C and 500°C, while a mixture of β-Ga₂O₃ and amorphous Ga₂O₃ thin film was obtained when grown at 550°C. The surface roughness of the amorphous Ga₂O₃ thin films were low, but the surface roughness deteriorated when β-Ga₂O₃ was intermixed. The optical absorption properties showed high transmittance of more than 85% for all samples in visible region. The optical absorption edges were like that of β-Ga₂O₃ at growth temperatures of 450°C and 500°C, but became shorter at 550°C. It was found that amorphous Ga₂O₃ was deposited without hydrophilization, but the surface roughness deteriorated compared to that with hydrophilization. In the previous report, hydrophilization was performed with hydrofluoric acid, but the method using UV irradiation was found to provide better crystal growth with less variation in results, especially at a growth temperature of 500°C.

New technique for fabricating TiNiCu ternary shape memory alloy foils was proposed. These alloy foils were obtained by using diffusion heat-treatment of laminated pure Ti, Ni, and Cu foils in vacuum. The alloy foils were subjected to a series of the heat-treatments at 1123K for varying holding times and compressive forces. These alloy foils were then examined using scanning electron microscopy and energy dispersive X-ray spectroscopy. The alloy foil heat-treated for 777.4ks with 405kPa compression formed significantly fewer voids than the alloy foil heat-treated for 777.4ks with 180kPa compression. The composition distributions of the alloy foil, which was heat-treated for 777.4ks with 405kPa compression, were found to be devoid of any discernible bias. The alloy foil, which was solution treated at 1273K for 0.9ks in argon atmosphere, was measured with differential scanning calorimetry (DSC), and then their shape recovery motions were observed during the heating and cooling processes. The endothermic and exothermic peaks were clearly obtained on the DSC curves of the alloy foil at heating and cooling process, respectively. Furthermore, the DSC curves showed typical characteristics of thermoelastic martensitic transformation. The alloy foil, which was curled at room temperature, demonstrated a recovery to its original flat shape after the heating process.

High strength metallic materials have been developed based on various material designs, and investigations of their mechanical properties at high strain rates have been required. Previous studies have shown that the athermal component of flow stress would be the primary cause of increased stress in many high strength metallic materials. As a result, the thermal component of flow stress, which is affected by the strain rate, is relatively small. Therefore, it is difficult to evaluate the thermal component of flow stress with high accuracy in impact deformation test. In this study, a preloading split Hopkinson bar (SHB) method is proposed to establish an impact tensile test method that can evaluate thermal component of flow stress with high accuracy. The preloading applied using a hydraulic jack. Stress, strain, and strain rate were calculated based on the principle of the usual SHB method under preloading effect. The amount of plastic strain to fracture evaluated from the stress-strain relationship was almost identical to the elongation of the specimen optically measured after the test. Therefore, it would be concluded that a highly accurate preloading SHB tensile test apparatus was successfully developed.

The adhesion strength and wettability at the interfaces between a polyetheretherketone (PEEK) resin and aluminum oxide (Al₂O₃), which have become more and more important for direct joining of PEEK resin and aluminum (Al), is investigated by using molecular simulations. Especially, the dependence of the adhesion strength and wettability on crystal orientations of sapphire Al₂O₃ were focused on to realize strong joint between the PEEK resin and Al₂O₃. By placing a PEEK-resin sphere on a sapphire Al₂O₃ surface and by heating the system to 650 K, the contact angles at the interfaces were calculated to evaluate the wettability. After the system is cooled to 300 K from 650 K, the adhesive fracture energy is calculated to evaluate the adhesion strength. The results of the contact angles showed that PEEK resin on the Al₂O₃ (10-10) and that on the Al₂O₃ (11-20) surface have low wettability with large contact angles. On the other hand, PEEK resin on the Al₂O₃ (0001) surface has high wettability with a small contact angle. The results of the adhesive fracture energies showed that the adhesion at the PEEK-resin/ Al₂O₃ (10-10) and PEEK-resin/ Al₂O₃ (11-20) interfaces are weak. On the other hand, the adhesion at the PEEK-resin/ Al₂O₃ (0001) interface is extraordinarily strong. To clarify the reason that the higher wettability and higher adhesion strength are obtained at the PEEK/Al₂O₃ (0001) interface, atomic configurations were visualized. The atomic configuration showed that the lattice-matched coherent interface and high surface atomic density is realized only at the PEEK/Al₂O₃ (0001) interface. Therefore, the lattice matching and the high surface atomic density at the PEEK/ Al₂O₃ (0001) interface are considered to be dominant factors in the high wettability and strong adhesion. The experimental results show that the wettability and critical load of scratch tests increase in the order: PEEK/Al₂O₃(10-10)< PEEK/Al₂O₃(11-20)<< PEEK/Al₂O₃ (0001).