Nano-porous NaNbO3 was successfully synthesized from Na-Nb ethoxide by sol-crystal method. Structural characterization of specimens annealed at various temperatures was performed by a transmission electron microscope (TEM) and X-ray diffractometory. The single crystal of Na-Nb ethoxid was decomposed to an amorphous matrix below 473K. Small crystals were grown by heating above 573K, and the crystal sizes became larger with increasing temperature. At 673K, well crystallized NaNbO3 grain with an orthorhombic structure (S.G. Pbcm) was observed. The three-dimensional image constructed by a tomography system showed that the grain had many inner-pores with a few ten nano-meter sizes. Thermal behavior of the inner-pore could be observed in-situ with a TEM using a heating stage during the crystallization process.
Superplastic deformation and creep resistance of Si3N4/Si3N4-SiC hybrid composites that formed belt-like network structure by Si3N4-SiC composite domain (the second domain) were investigated with tensile tests at 1873K and with bending tests at 1473K, respectively. The supserplastic elongation of Si3N4/Si3N4-SiC hybrid composites was dramatically improved with decreasing in SiC contents of the second domain from 20wt% to 10wt%. As the results, the Si3N4/Si3N4-SiC hybrid composites exhibited superplastic elongation more than 200% at 1873K. Furthermore, the hybrid composites exhibited the high-performance in both of the superplasitc deformation and the creep resistance.
An instrumented indentation microscope is developed for determining the in-situ contact area during indentation loading/unloading, and then applied to examining the Meyer hardness and the elastic modulus of several engineering materials ranging from ductile metals to brittle ceramics. Since it is capable of making the in-situ optical observation of indentation contact impression and the determination of contact area that is synchronized to the hysteresis curve of indentation load-penetration depth relation, the mechanical properties determined on the indentation microscope are precise and reliable without any undesirable approximations and assumptions required for estimating the contact area in the conventional test systems. It is also demonstrated that the instrumented indentation microscope is very efficient for determining in a quantitative manner the in-situ contact profiles of impression (sink-in/pile-up profiles). Through the present studies for the experimental determinations of the Meyer hardness HM, elastic modulus E', and the consideration on the sink-in/pile-up profiles of contact impressions, it is emphasized that the direct measurement of contact area Ac by the use of the indentation microscope is very essential in examining the mechanical properties of materials in micro-scales. The present work suggests that the instrumented indentation microscope will be a powerful tool in the science and engineering of indentation contact mechanics.
The effect of addition to the gypsum was investigated on phosphorous removal properties of wollastonite-type adsorbent. Typical calcium silicate powder, wollastonite, was mechano-chemically activated in air for 24h with a vibration ball-mill. The cakes of the vibration ball-milled wollastonite added with a fair amount of water and gypsum were carbonated at 80°C in 0.33MPa CO2 for 3h. The removal efficiencies of phosphorus for the carbonated specimens were investigated by immersing them in Na3PO4 aqueous solution containing 5ppm phosphorus. After immersing the specimens for prescribed duration in the test solution, the remaining amount of phosphorus in a supernatant liquid was measured by a molybdenum blue method. Ca ion concentrations dissolved from specimens were measured with a selective electrode instruction. In addition, various consolidated bodies were investigated by immersing them in Na3PO4 aqueous solution containing various amounts phosphorus. The obtained results are the following: (1) The addition of gypsum increase released Ca ion amounts compared with consolidated bodies without gypsum, so, the removal efficiencies of phosphorous for the specimens markedly improve, and we can produce specimens available for Na3PO4 aqueous solution containing various amounts phosphorus by addition of gyrpsum. (2) Released Ca ion amounts more affect the removal efficiencies of phosphorous than wollastonite amounts.
In automotive three-way catalyst, cerium dioxide and alumina are used as sub-catalyst and support, respectively. The composite particles of them are important for better catalytic performance. In the preparation of catalysts, the rheological properties of slurry are important. The dispersibility of particles is an indicator of the properties, and the surface charge of particles is an important factor for the dispersibility. In this paper, the surface charge of cerium dioxide-alumina composite particles was examined using ultrasonic vibration potential (UVP) method for the colloidal solutions. We synthesized cerium dioxide-alumina composite particles by impregnation method. We determined the UVP, zeta potential (ζ) and iep (isoelectric point) of them in water by using measured voltage value under ultrasonic irradiation. The iep depended on the composition of these particles. The iep was 7.6-7.9 for the composite particles, 8.3 for alumina and 6.8 for cerium dioxide. The surface compositions of Ce on particles were estimated by XPS. The result indicated that particle size of cerium dioxide increased with Ce-content. The surface charge of the composite particles was affected by both the surface composition and the size of cerium dioxide particles.
The sol-gel method was applied to create Al2O3-Cr2O3 ceramics using aluminum ethylacetoacetate diisopropylate and chromium (III) chloride hexahydrate as starting materials. In the calcination at 600-1200°C it was found that the grains of Cr2O3-rich solid solution grew when they were exposed to the surrounding Al2O3-rich amorphous particles. The composition of the powders obtained by the sol-gel process changed with calcining temperature. Cr2O3-rich solid solutions firstly crystallize at low temperature and the composition of the crystallites changes as the crystals grow and react with the surrounding Al2O3-rich phases. The final sintered bodies fired under an Ar atmosphere showed higher relative densities as compared with those fired in air. A dense sintered body was not obtained when abnormal grains grew when calcining occurred.
The yield strength and electrical conductivity of precipitation-hardenable Cu-2.05mass%Ni-0.35mass%Be and Cu-1.27mass%Ni-0.22mass%Be alloys aged at 360 to 560°C after cold rolling have been investigated. The former alloy exhibits a higher strength and a lower electrical conductivity in the under-aging and peak-aging stages, but a lower strength and a higher electrical conductivity in the over-aging stage than the latter alloy. Both alloys are hardened by plate-shaped coherent precipitates of γ" phase, which is body-centered tetragonal with a = b = 0.24nm and c = 0.28nm. In the peak-aging stage, the yield strength of both alloys is controlled by the precipitate shearing mechanism. Both alloys recrystallize in the over-aging stage at the coarse γ precipitates which are residual even after solutionizing. A higher number density of the coarse γ precipitates in the Cu-2.05%Ni-0.35%Be alloy gives rise to a larger volume fraction of recrystallization, resulting in a greater decrease in strength. The growth of incoherent precipitates in recrystallized grains is faster than that of coherent γ" precipitates in unrecrystallized grains. This causes a higher electrical conductivity of the Cu-2.05%Ni-0.35%Be alloy in the over-aging stage.
In this paper, fatigue behaviour of friction stir spot welded joints in Al-Mg-Si aluminium alloy was investigated. Fatigue tests were conducted using lap-shear specimens at a stress ratio R = 0.1. It was found that fatigue fracture morphology was dependent on load level. When high load was applied, debonding and opening deformation took place along the boundary between the upper and lower sheets around the weld nugget. The opening deformation caused stress concentration, which resulted in fatigue crack initiation at the edge of the nugget followed by crack growth through the mixed zone (MZ) until final fracture. When low load was applied, fatigue crack initiated at the edge of the nugget and propagated through the sheet thickness and grew to the width direction. Based on experimental observation of the weld zone, fatigue fracture mechanism of friction stir spot welded joint was discussed.
Using the reliability approach such as an advanced first order second moment method (AFOSM), FTS Committee organized in the Japan Welding Engineering Society (JWES) has discussed the defect assessment methodology which employs the partial safety factors for characterized defect size, applied strain and fracture toughness to warrant the reliability of the welded structures with respect to brittle fracture. This paper describes the procedure of introducing reliability approach to the JWES2805 standard and the partial safety factors are evaluated to secure the expected reliability. This methodology is to be adopted in the revised JWES standard 2805 “Method of assessment for flaws in fusion welded joints with respect to brittle fracture and fatigue crack growth”.
A cold spraying process has been developed for dense and clean and tightly bonded coatings in contract with other established thermal spraying processes. The cold sprayed aluminum is particularly well suited for metallic coatings, such as electric conductor and corrosion resistance. However, the mechanical properties of aluminum coatings formed by the cold spraying have not always been clarified. Two kinds of free-standing aluminum specimens, which were formed by the cold spraying process and an atmospheric plasma spraying process, were machined from the thick coatings and were used for measuring the Young's modulus, Poisson's ratio and bending strength etc. in comparison with a rolled aluminum plate. The experimental results suggested that the crack length and crack density in aluminum coatings had an important effect on the mechanical properties. Namely, high bending strength and high Young's modulus of aluminum coatings could be obtained from the cold spraying process, because of the short crack length and the low crack density.