Development of Mo(Si,Al)<Subscript>2</Subscript>-base oxidation-resistant coating on Nb-base structural materials

Mo(Si,Al)₂-base oxidation-resistant coatings for Nb-base structural materials have been studied. The coating is composed of a Mo(Si,Al)₂-base Al reservoir and Al₂O₃ interlayer to suppress interface reactions between the Al reservoir and the substrate. To develop a suitable Al-reservoir material, some Mo(Si_0.6,Al_0.4)₂-HfB₂ composites were prepared. Their oxidation resistance and coefficients of thermal expansion were investigated, in addition to their chemical reactivity with the Nb substrate at high temperatures. As a result, Mo(Si_0.6,Al_0.4)₂-20 vol pct HfB₂ was selected as one of the satisfactory Al reservoirs. The introduction of a stable Al₂O₃ interlayer was attempted using a novel powder metallurgical process to overlay the Nb substrates with the Al reservoir, where the Nb substrates were subjected to a slight surface oxidation prior to the coating process. The Nb specimens, which are thoroughly coated with the Al reservoir and Al₂O₃ interlayer, can be successfully fabricated by this method. The coated Nb specimens are not damaged at all after prolonged exposure in flowing Ar-20 pct O₂ at 1673 K for 120 hours. Furthermore, the Al₂O₃ interlayer is very effective and no reactions occur at the interface. Thus, this Mo(Si,Al)₂-base oxidation-resistant coating is applicable to Nb. The utility of the coating system is also confirmed for a Nb_SS/Nb₅Si₃ composite. This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory Metals Committee.     

Why Spatial Planning Often Fails to Control the Spreading Locations of Large Scale Commercial Facilities？

The purpose of this paper is to clarify the mechanism of planning failure on land use control in case of sprawl developments of large scale commercial facilities, which is often seen in many countries. The author demonstrates actual three cases in Japan： a huge commercial development established in the middle of rice field between the two local cities, two huge commercial accumulations established at the opposite fringes of urban area, and many large commercial developments established one by one within the small municipalities surrounding a central city. And by examining the statistical sales amount, the author describes that these huge suburban commercial developments apparently deprived the sales of the downtown. Through analyzing these cases, the author empirically stated that for the motorized local cites, the optimum location of commercial accumulation is no longer the central area of the city but about 15 min away from the center with the smooth accessible arterial road. At last, the author mentions that the ＂planning failure＂ could be occurred if the territory of planning authority and the scale of the development are inconsistent, such as the authority of small municipal government and the large scale commercial facility which impacts beyond the municipal boundary.     

Investigation of nitrate salts for solar latent heat storage

Solar thermal applications require some means of thermal energy storage. Amongst several storage concepts, latent heat storage is quite suitable because of its high storage density and almost constant temperature during charging and discharging. The temperature range between 200 and 300°C is considered to be important for solar total energy systems. In this temperature range, sodium nitrate and its mixed salts with other nitrates including eutectic and off-eutectic salts are candidates.

The present paper deals with heat transfer in a latent heat storage unit utilizing these salts. A method of rough estimation of the thermal conductivity of the storage materials is described, and the temperature history of the storage material experimentally obtained is compared with numerical solutions and found to be in reasonably good agreement.

It is seen that the temperature of the heat transfer surface quickly drops soon after the appearance of a solid phase due to low thermal conductivity of these salts. Ways to avoid this temperature drop are discussed.     

Perspective on full reusable SSTO aerospace plane research and development in Japan

For the promotion of extended and diversified space activities in Japan, it is required to build immediately the technology bases capable of supporting such space activities and thereby to expand positively international cooperation as one of Japan's roles towards the world's prosperity of the 21st century. Especially, development of the manned space transportation system to and from lower earth orbit is the key issue, requiring an unprecedented approach. The Single Stage to Orbit(SSTO) Aerospace Plane is the unique answer to this issue. This paper will discuss the perspective on the research and development of the Space Plane in Japan. The topics will cover a long range R&D scenario and current activities of the related organizations in Japan.     

Cardiac Arrival Time Analyzer

The sequence of excitation of cardiac muscles is greatly affected by any abnormality in the conduction system of the heart. Epicardial mapping for the measurement of activation time at different points is helpful for the diagnosis of such abnormalities. For the measurement of activation time at different points of the epicardial surface, a number of sophisticated instruments, including microcomputer-based ones, have been reported. However, the need for a reliable, low-cost, and easy to operate instrument cannot be denied. In this note, such a cardiac arrival time analyzer is described.     

9H-xanthene-2,7-diols as antioxidants for autoxidation of linoleic acid

The antioxidant activities of 9H-xanthene-2,7-diols and α-tocopherol were studied during the oxidation of linoleic acid in a homogeneous solution and in an aqueous micelle dispersion. The antioxidant activities of 9H-xanthene-2,7-diols for both systems were 1.0–2.4 times greater relative to α-tocopherol. In addition, the 1,3,4,5,6,8-hexamethylxanthene-2,7-diol showed less cytotoxicity toward human fibroblasts than did 2,6-di-t-butyl-4-methylphenol.     

Scanning-laser-beam semiconductor pH-imaging sensor

We have constructed a two-dimensional (2-D) pH-imaging sensor that enables us to observe th H⁺ distribution produced by living cells. The pH-sensing principle is similar to that of thelight-addressable potentiometric sensor. The electrolyte-insulator-semiconductor (EIS) structure (electrolyte---Si₃N₄---SiO₂---Si) is illuminated by a focused (1 μm) and modulated (1–10 kHz) He—Ne laser bean from the backside of the semiconductor, and the a.c. photocurrent flowing through the EIS structure is measured. By scanning the laser beam, 2-D pH images can be obtained. By using this sensor, pH distributions of colonies of yeast (Saccharomyces cerevisiae) have been observed. The spatial resolution of this sensor could be improved by thinning the Si wafer.     

Low-temperature growth of highly crystallized transparent conductive fluorine-doped tin oxide films by intermittent spray pyrolysis deposition

Following the procedure by Sawada et al. (Thin Solid Films 409 (2002) 46), high-quality SnO₂:F films were grown on glass substrates at relatively low temperatures of 325–340°C by intermittent spray pyrolysis deposition using a perfume atomizer for cosmetics use. Even though the substrate temperature is low, as-deposited films show a high optical transmittance of 92% in the visible range, a low electric resistivity of 5.8×10⁻⁴ Ω cm and a high Hall mobility of 28 cm²/V s. The F/Sn atomic ratio (0.0074) in the films is low in comparison with the value (0.5) in the sprayed solution. The carrier density in the film is approximately equal to the F-ion density, suggesting that most of the F-ions effectively function as active dopants. Films’ transmittance and resistivity show little change after a 450°C 60 min heat treatment in the atmosphere, evidencing a high heat resistance. The SnO₂:F films obtained in this work remove the difficulty to improve the figure of merit at low synthesis temperatures.     

Air permeability of the artificially synthesized Zn-Al-Mg alloy rusts

The rust particles of Zn-Al-Mg alloys were synthesized from aqueous solutions dissolving ZnCl₂, AlCl₃, and MgCl₂ at different atomic ratios of the metal ions. The crystal phase and particle morphology of the products depended on the composition of the starting solutions. The compactness of the layers of the products was estimated by measuring their air permeability. The layer of mixed metal hydroxide chloride formed at Zn:Al:Mg = 1:1:1 showed a highest compactness, that was ascribed to the preferred orientation of the fine plate particles. The addition of Mg(II) made plate particles smaller to give more compact layers.