Tsuchi-kabe (called as soil wall or mud wall in English) utilized in Japanese traditional buildings is well known to have the characteristics of humidity conditioning. However, the characteristics have not been well examined. For preparing tsuchi-kabe material, soil, sand and rice straw are well mixed with water and then kept from a few weeks to months to promote fermentation. This aging process that is called as “Nekashi” gives plasticity to the material and is very important to construct tsuchi-kabe. In the present study, effect of “Nekashi” on the characteristics of humidity conditioning was examined. Long period of “Nekashi” enhanced the characteristics in nakanuri-kabe with a smaller amount of clay component.
Eu, Dy -codoped Sr4Al14O25 phosphors were prepared with B2O3 additives as flux at the temperature of 1300 to 1400°C for 3h in flowing hydrogen gas. These products were characterized by XRD analysis, ESR, UV-Vis spectroscopy and SEM. XRD analysis showed that single phase Sr4Al14O25 was synthesized at the samples added with small amount of B2O3 (B/Sr = 0.2), but the impurity phase was also observed at the samples added with large amount of B2O3 (B/Sr = 0.7). The emission wavelength of the sample added with large amount of B2O3 shifted to shorter wavelength than that of the sample added with small amount of B2O3. The afterglow characteristics of both samples were comparable level. The intensity of emission spectra decreased and afterglow characteristics degraded in the samples cooled in argon gas in behalf of hydrogen. ESR measurement indicated that the change in optical properties of the sample cooled in argon gas due to the oxidation of Eu2+ in the phosphor by trace of oxygen in argon gas.
The development of low melting temperature coating materials for brazing diamonds was attempted for diamonds wire saw for slicing single crystal silicon.The diamonds wire saw was made by brazing diamonds on SUS-304 wire with high strength for the sawing equipments. Since the degradation of SUS-304 wire was generally generated at higher temperature over 600°C, the high performance coating materials, composed of 47.5 wt.%Ag-25.5 wt.%Cu-27.0 wt.%Sn based materials, was developed by addition of Ni into them to improve the brittleness for SUS-304 wire. These results suggested that the coating material of (47.5 wt.%Ag-25.5 wt.%Cu-27.0 wt.%Sn)-1 wt.%Ni was the suitable brazing of the diamonds SUS-304 wire for sawing equipments.
It has been reported that a sub-wavelength structure can be formed at the surface of glass, into which silver ions are incorporated through ion-exchange, by means of imprint molding at a lower temperature than softening temperature of the glass. In order to apply this technique to practical glass systems used in mold processing, we investigated ion-exchange behaviors, variation in softening temperature and optical transmission spectra after the ion-exchange and post-heat-treatment for various kinds of glasses. The results were discussed from the viewpoint of the glass composition and structure. The investigated glasses were soda-lime silicate, aluminosilicate, borosilicate, aluminoborosilicate, and fluoroaluminoborosilicate glasses. The amount of incorporated silver at the same ion-exchange condition was the highest for the aluminosilicate glass, and decreased in the order of aluminoborosilicate, soda-lime silicate, borosilicate, and fluoroaluminoborosilicate glasses. The lowering rate of softening temperature had a good correlation with the ion-exchange rate, i.e., molar fraction of Ag to total monovalent ions at the glass surface. For aluminosilicate and aluminoborosilicate glasses having no or little non-bridging oxygen, no coloration was occurred after the ion-exchange and post-heat-treatment although the absorption edge at the short wavelength side shifted to the near ultra violet region. Whereas the fluoride ions in fluoroaluminoborosilicate glass hindered the ion-exchange, they suppressed the reduction of Ag+ ions and the red-shift of the absorption edge.
The effects of TiO2 on the crystallization behaviors of ZnO-Al2O3-SiO2 glasses were investigated for the preparation of transparent glass ceramics containing ZnAl2O4 nano-crystal. Nucleation in 20ZnO·20Al2O3·60SiO2 glass proceeded vigorously at the temperature range between 660°C and 780°C, which decreased with the increase of TiO2 content. The nucleated samples with TiO2 more than 4mol% were transparent after crystallization. Acceleration of the nucleation by the addition of TiO2 was confirmed by the fact that the addition of TiO2 made the crystal size smaller.
Large-scale deformation processes and mechanisms of the model aggregates comprising close-packed spherical particles are examined by the use of a discrete element method (DEM). It is demonstrated that the movement of grain groups, i.e., the cooperative grain-boundary sliding (CGBS), is essential in the large-scale elongation of polycrystalline materials. The strain energy of grain aggregates during CGBS is also estimated as a function of true strain, yielding a good agreement with the theoretical prediction of CGBS process. The discrete element analysis used in this study is an efficient technique in examining the large-scale deformation mechanism such as the superplastic deformation of polycrystalline materials.
The authors reported reduction of fretting fatigue strength in hydrogen gas using several kinds of materials such as low alloy steel, heat resistant steel, aluminum alloy, austenitic stainless steels, etc. In this study, mechanism of the reduction was discussed thorough detailed observations of small fretting fatigue cracks and two-step test in which the environment was changed during a test. The material was 30% pre-strained austenitic stainless steel SUS304. Hydrogen gas pressure was 0.12MPa in absolute pressure. Whereas oxidation process was important to develop fretting damage in air, adhesion was dominant in the fretting in hydrogen gas. In hydrogen gas, small cracks were emanated at both ends of the adhered parts. Since the major crack was propagated from one of the small cracks emanating adhered part, the adhesion and formation of small cracks were important determinants of the reduction of fretting fatigue strength in hydrogen gas. In the fretting fatigue test in hydrogen gas following fretting fatigue test in air, no fracture occurred even if the stress amplitude was higher than the fretting fatigue limit in hydrogen gas. The reason was that the oxidized wear film, which was produced in the first air environment, prevented the adhesion and the formation of small cracks. Another two-step test was that small cracks were formed in hydrogen gas and the test environment was then changed to air. As the result, there was no fracture of the specimen even the test was performed at stress amplitude that the fracture of specimen occurred in the single hydrogen gas environment. The result suggested that the stress field in the vicinity of small cracks were severer in hydrogen gas than in air.
In order to confirm the validity of the model for creep damage mechanism constructed from a series of experiments on reheat pipe elbow of mod. 9Cr-1Mo steel with a practical size, microstructural observation and uniaxial creep rupture tests were carried out using the welded joint of the hot reheat pipe elbows (No. 5 and No. 25) taken from a practical plant after long-term service. The obtained results are as follows : (1) Nucleation and growth of creep voids were observed in the fine-grained HAZ region of the inside-elbow region, where the triaxiality factor of stress was high compared to the other regions in the HAZ. The phenomenon of creep damage in the long-term used elbows was consistent with that in the practical sized experimental elbow used for the model construction. (2) The degree of creep damage observed for No. 5 and No. 25 elbows corresponded to the early stage of creep damage. But the creep damage of No. 5 elbow was more serious than that of No. 25 elbow due to the difference in degree of circularity between the two elbows. (3) Considering that the long-term used elbows underwent creep damage to some extent, the creep rupture strength except for the repair-welded specimen exhibited high enough to exceed the demand strength estimated from the life assessment curve for the welded joint of high chromium ferritic steels presented by Nuclear and Industrial Safety Agency.
Damages in thermal barrier coatings (TBCs) exposured under high temperature are accumulated by various factors, and ultimately the spallation of top coats in TBCs is occurred. One of the damages is formation of thermally grown oxide (TGO). In the present study, measurements of crystallinity, microstructures and residual stresses in TGO layers grown under various thermal exposure conditions were conducted by using Raman microspectroscopy with sub-micro spatial resolution. In TGO layers, Raman spectrum of Alumina was obtained. Its crystallinity was varied with thermal exposure time. In crystallographic orientations, TGO layers had Alumina c-axis direction perpendicular to bond coat surface. It means that TGO layer grew in the direction perpendicular to interface between top and bond coat. TGO layer had high compressive residual stress, 1.0GPa at maximum value in TBCs exposured for 300h at 900°C and 1.2GPa for 500h at 900°C. On the other hand, in top coat, Raman peak shift of α-Chromia (Cr2O3) was obtained. Especially, isolated islands of α-Chromia were formed in top coat near TGO layers, and some micro cracks were observed near the region of Cr2O3. Therefore it was considered that Cr2O3 formation significantly affected micro crack initiation in top coat.
Although micro-Raman spectroscopy is a useful method as a strain probe with high spatial resolution, this method can not be applied to certain isotropic materials, such as less oriented polymers. To overcome the limitation diacetylene-containing copolymers, which were shown to have Raman band shift with tensile strain, were coated on substrates as an optical strain gage. In this study, diacetylene-containing copolyurethanes were prepared from new compositions by employing polycaprolactone instead of poly(propylene glycol). A solution of the copolymer was coated onto a single filament of an aramid fiber and cross-polymerized by heat treatment. And then, Raman spectra from the coating and the fiber substrate at the same point were measured simultaneously during a tensile test. The Raman frequency of the carbon triple bond (C = C) in the cross-polymerized polymer coated on the fiber was found to follow closely the local strain of the fiber substrate. The Raman frequency of the coated polymer shifted with strain at a rate of -6.6cm-1/% and held an approximate linear relationship up to 2% strain. Both of the shifting rate and the linear range were improved by replacing ether bonds with ester bonds in the copolyurethanes used as matrices.
It is the worldwide problem to improve the earthquake-proof and the durability of concrete structure; therefore, the many researches concerned have been carried out and good results already have been obtained. However, the enormous time and labor are spent in the event of evaluating the freezing and thawing deterioration. The practical evaluation method has been developed newly on the basis of the phenomenal fact of the durability deterioration. Thus, the surface deterioration index being able to be applied to the existing concrete structure has been obtained as the surface defect ratio due to the popping-out instead of the usual relative dynamic modulus of elasticity and the mass variation. Furthermore, the present paper deals with the relationships between the surface defect ratio, the compressive strength and the relative dynamic modulus of elasticity and also that the boundary relative dynamic modulus of elasticity βb = 60% corresponds to the boundary surface defect ratio αb=8.0% for the first time. Such an index indicates that the surface defect ratio is highly structure-sensitive in comparison with the mass variation. In addition, the overdesign factor of structural concrete strength has been clarified considering the durability deterioration.