Rice husks are a by-product of rice production. When rice husks are burned in an appropriate manner, rice husk ash, which is mainly composed of amorphous silica, is produced. Currently, rice husk ash is expected to be a biomass resource. In this study, we aimed to synthesize water glass using rice husk ash in a low-process and low-cost manner. A porous geopolymer was fabricated by mixing water glass and metakaolin and adding additives such as Si powder. In addition, we evaluated the thermal conductivity and other physical properties of porous materials with different alkali concentrations at room and high temperatures, assuming their use as heat insulating materials. It was found that water glass could be synthesized by simply mixing rice husk ash with a potassium hydroxide solution and allowing the mixture to stand at room temperature. When the porous geopolymer was fired at 800°C, shrinkage occurred, and the rate of shrinkage was greater for samples with higher alkali concentrations. Furthermore, it was found that the heat conduction at high temperatures was suppressed in the sample with a smaller alkali concentration.

Yttria-stabilized zirconia (YSZ) nanoparticles were synthesized using a flow-type supercritical hydrothermal method using different alkaline reagents. The obtained YSZ nanoparticles had a tetragonal phase and a primary particle size of 4–6 nm. The synthesized nanoparticles were characterized using optical microscopy, elemental composition analysis, X-ray diffraction, transmission electron microscopy, and surface area measurements. The choice of alkaline reagent significantly played a crucial role in influencing the particle size and impurity contents of YSZ nanoparticles. Each sample contained several impurities, which were derived from alkaline reagents, and tubing elements that were corroded under subcritical and supercritical conditions. However, titanium was not detected in the YSZ nanoparticles synthesized using titanium-lined reaction tubes. The findings highlight the importance of alkaline reagents and tube materials in controlling the quality of synthesized nanoparticles. Moreover, this study provides valuable insights for the synthesis of YSZ nanoparticles using the supercritical hydrothermal method to control contamination by impurities.

The effect of the addition of SnO₂ on the crystallization behavior was investigated for ZnO-Al₂O₃-SiO₂ glass, which can be used to produce transparent crystallized glass. Addition of SnO₂ promoted nucleation, and nucleation proceeded most actively at 775°C after the heat treatment of 24 hours. During crystallization, ZnAl₂O₄ and Al₆Si₂O₁₃ precipitated, but Al₆Si₂O₁₃ changed to ZnAl₂O₄ at temperatures above 1000℃. SnO₂ is dissolved in ZnAl₂O₄ as a solid solution, but SnO₂ in the solid solution is metastable and precipitated as stable SnO₂ at high temperatures.

Zinc oxide, ZnO, was synthesized using layered zinc hydroxide chloride, ZHC, and acetate, ZHA, as precursors. In the first experiment, ZHC and ZHA were hydrothermally synthesized in deionized water. Due to the different precursors, rod-like ZnO particles of 1 μm in length were synthesized by aging ZHC, while rod-like zinc oxide particles of 4 μm in length were synthesized by aging ZHA. In the second experiment, a two-step aging was performed. ZHC and ZHA were aged in a zinc acetate aqueous solution before being aged in deionized water. After the first aging, a mixture of ZHA and ZnO was obtained in both samples. Because of the acetate ions in the solution, coin-shaped ZnO particles with diameters of 1 μm for the ZHC sample and hexagonal plate-like ZnO particles with diameters of 4 μm for the ZHA sample were obtained. Acetate ions form zinc complexes and inhibit the growth of ZnO in the c-axis direction for rod-like growth. Therefore, coin shaped ZnO was obtained. After the second aging, ZnOs with the same shape as in the first aging were obtained in a single phase. From these results, we conclude that the particle size of ZnO can be controlled by the choice of precursor and the particle shape of ZnO can be controlled by the choice of aqueous solution.

Cerium oxide nanoparticles were synthesized by using the Forced Thin-Film Type Reactor (FTFR). A reaction region which promotes forced diffusion is formed in FTFR. Aqueous solutions of cerium (III) nitrate and a diammonium cerium (IV) nitrate were prepared as raw materials. The mixing ratio of trivalent and tetravalent cerium ions in the solutions were 100:0, 50:50 and 0:100. A sodium hydroxide aqueous solution was added to the cerium solutions to precipitate cerium oxide. The nanoparticles which have an average diameter of 3 nm and 15 nm were synthesized in a tetravalent cerium ion solution and a trivalent cerium ion solution, respectively. The different solubility of cerium (III) and cerium (IV) hydroxide which acted as a crystal nucleus was assumed to be the cause of the different size of the nanoparticles. The measurement results of average particle size determined by TEM observation and crystallite size determined by XRD were suggested that the synthesized cubic cerium oxide nanoparticles were single crystals.

The authors have investigated the possibility of reusing gypsum board, a type of construction waste, as a phosphorus removal material by carbonating in an aqueous sodium carbonate solution to precipitate calcium carbonate on the surface after coating with a mixed solution of silica sol and binder. It became possible to prepare a phosphorus removal material with high phosphorus removal ability, but there were problems such as peeling of the calcium carbonate layer on the surface of the sample. In addition, the process of carbonation treatment after coating treatment was complicated and required a long time to prepare the sample. Therefore, in this study, by adding calcium carbonate powder to a mixed solution of silica sol and binder, calcium carbonate, which acts as a crystallization site for calcium phosphate, was supported on gypsum board without carbonation treatment using an aqueous sodium carbonate solution. The process used in this study significantly shortened sample preparation time. The phosphorus removal ratio increased with increasing the amount of calcium carbonate added to the coating solution, and by stirring during the coating process, the amount of calcium carbonate that could be supported on the gypsum board surface increased, further increasing the phosphorus removal ratio.

The authors have developed a water purification material that can remove phosphorus and organic matter by supporting yeast bacteria, lactic acid bacteria, and natto bacteria on gypsum consolidated bodies containing calcium carbonate. However, the effects of each type of bacteria on water purification properties have been still unclear. In this study, we focused on natto bacteria among these bacterias and investigated its effects on phosphorus and organic matter removal properties. Carrying natto bacteria alone does not contribute to organic matter removal, but coexistence with yeast bacteria or lactic acid bacteria was confirmed to be effective in promoting organic matter removal. When these bacterias were supported on a phosphorus removal material, the phosphorus removal ability generally decreased, but for natto bacteria, the decrease in phosphorus removal ability was small. Furthermore, when natto bacteria and yeast bacteria coexisted, an effect of suppressing the decrease in phosphorus removal ability by yeast bacteria was observed, but this effect was not observed with lactic acid bacteria.

We studied the influence of the surface and crystal lattice about both H₂-oxidation reaction and electronic properties of CeO₂ nanoparticles (NPs). The oxygen evolution phenomena in CeO₂ NPs were observed in reducing (hydrogen or vacuum) atmosphere. In the catalytic hydrogen temperature-programmed reduction experiments (H₂-TPR) of CeO₂, nonstoichiometric CeO₂ produces active oxygen species which react with H₂ to form H₂O. The CeO₂ NPs showed the main TPR temperature of the lattice oxygen at around 700 °C (slow reaction). A low temperature peak appeared at around 500 °C, which is originated from the surface of CeO₂ (fast reaction). The active oxygen formation was characterized by different activation energies which were newly determined as 77±18 kJmol^-1 (on surface) and 131±16 kJmol^-1 (in lattice) for NPs, respectively. Regarding with the electric current response of CeO₂ NP, we found the relatively fast peak-out peak and then the gradual increase at 300 °C under the low oxygen pressure of 5×10^-3 Pa (vacuum). These were both related to the fast and slow release of oxygen on the surface and then in the lattice of CeO₂ NPs. The comparative TPR and electric current observations revealed the common reduction behavior on surface and in bulk region of CeO₂ NPs.

In order to improve the performance of lithium-ion batteries, nano-sized zeolite was added to the batteries and its supression deterioration effect was confirmed. The nano-sized zeolite was shown to suppress SEI growth on the anode surface by SEM and TEM observations, and to suppress the increase in internal resistance by AC impedance measurements. The nano-sized zeolite not only absorbs water and gases generated by the decomposition of the electrolyte, but also suppresses the swelling of the cell, thus contributing significantly to the safety of the cell.

We developed a small punch (SP) test system enables SP testing in a hydrogen atmosphere at elevated temperatures in order to utilize the SP testing for the remaining-life assessment of mechanical components used in advanced high-temperature hydrogen technologies, such as SOFC and SOEC. Type 304 stainless steel was subjected to the SP and SP creep tests with a small disk-type specimen. A small disk specimen with a diameter of 8 mm and thickness of 0.5 mm was tested in hydrogen and argon gases. The absolute gas pressure and temperature at which the SP test was carried out were 0.12 MPa and 600℃, respectively. The experimental results showed that the 0.2% proof stress and tensile strength in hydrogen and argon gases, which were predicted based on the SP test results, were consistent with those obtained from the tensile tests. The SP creep rupture time tended to be shorter in hydrogen gas than argon gas, and the equivalent fracture strain (rupture ductility) was slightly higher in hydrogen gas. The results obtained in the SP creep test were also qualitatively in agreement with those in the standard uniaxial creep test.

Cavitation damage, so called pitting damage, is one of crucial issues to predict the structural endurability of the mercury targets for highly intensive pulsed neutron sources. Experiments to systematically investigate the cavitation damage evolution on the surface in contact with the mercury have been carried out by using specially developed electroMagnetic IMpact Testing Machine (MIMTM) and then pit depth and equivalent diameter distributions in a certain damaged area of the specimen were measured in detail using a laser microscope. Pits with a maximum depth of less than 0.5 μm and an equivalent diameter of less than 5 μm were mainly observed. Based on the comparison with numerical simulation on the pit shape, the cavitation bubble collapsing was assumed to be resulted in the micro jet with the impact velocity of 160-200 m/s, imposing then impact pressure of 3-4 GPa at the input power simulating the operation condition in the mercury targets. As results, it was statistically understandable that cavitation damage evolution was proportional to 4^th power of the input power approximately, as taking the aggressivity of cavitation bubbles and the distribution of the maximum diameter of grown bubbles and the space of distribution of bubbles in the mercury into account.

Conventional Casting (CC) and Directional Solidified Casting (DS) Ni-based superalloy Rene80 are being widely used for high temperature components such as gas turbine blades due to their superior high temperature strength and corrosion resistance. Creep damage gradually proceeds especially at stress concentration portion under multiaxial stress with stress gradient in high temperature components. Therefore, it is important to clarify creep damage extension process and to develop a creep rupture time prediction method for maintaining reliable operation. In this study, smooth and two kinds of circular notch specimens were machined from both CC and DS Rene80, and creep tests using these specimens were performed at 900℃. Creep deformation until steady state creep regime of both CC and DS smooth specimens are similar, while transition to acceleration creep of the CC specimens is much shorter period than that of the DS specimens resulting in lower rupture ductility and shorter rupture time in the CC specimens. Creep rupture times of notch specimens of both CC and DS are longer than those of smooth specimens indicating notch strengthen effect. Although creep voids and grew on grain boundaries causing intergranular failure in CC specimens, no void was observed in DS specimens. From finite element creep analysis, multiaxial stress states occurred across notch root section in notch specimens causing lower axial strain rate than smooth specimens. It was demonstrated that creep rupture times of both CC and DS notch specimens were accurately predicted based on the area average creep damage concept.

With an intention to clarify creep-fatigue behavior of welded joint of Ni-based alloy HR6W (23Cr-45Ni-6W), creep-fatigue tests at 700℃ were carried out for both uniaxial cross-weld and stub weld subjected to cyclic displacement. The location of crack at creep-fatigue life N_f was at a base metal near a Heat Affected Zone (HAZ) for uniaxial cross-weld; and at a toe of weld for stub-weld specimen. Elastic-plastic-creep FEM analysis using cyclic stress-strain behavior at N_f/2 was performed for the two types of welded joint to clarify a strain-concentration behavior and to predict a creep-fatigue life using a local strain. FEM results considering material behaviors depending on hardness distribution in welded joints, revealed that creep-fatigue life for the two types welded joint could be predicted by a factor of about two.