Pd-SiO2复合膜的氢气选择渗透特性

Palladium membranes were prepared on an a-alumina support by metal-organic compound chemical vapor deposition (MOCVD) method from palladium(Ⅲ) acetate precursor. Permeation properties of hydrogen and helium gas were studied as a function of the number of times of deposition of palladium on the peeling off phenomenon of palladium, which is common in electroless plated membrane, was observed. Silica was introduced into the pores to prevent the palladium grain from peeling off. The palladium-silica conjugated membrane does not show the peeling off phenomenon and can withstand the high temperature up to 800℃ which is the upper limit of our apparatus.The separation factor for hydrogen gas over carbon dioxide gas was improved with the increase of number of times of silica coating by sacrificing the H2 permeation and finally increased to four times. The improvement on the separation of hydrogen gas over carbon dioxide for pulladium-silica conjugated membrane was evaluated and a model of permeation pattern (palladium and silica) was proposed. This model suggests that the separation factor for hydrogen over carbon dioxide could be improved by introducing silica layer because the silica layer fills the pores and reduces the gas permeation without sacrificing the hydrogen permeation through the palladium region. These results indicate that the introduction of silica into the palladium grain is a promising means to improve the hydrogen separation performance of palladium based composite membranes.     

Corrosion behavior of rapidly solidified Mg-Zn-rare earth element alloys in NaCl solution

Rapidly solidified flaky powder metallurgy (RS FP/M) processing was applied for preparation of corrosion-resistant bulk Mg alloys with Zn and rare earth elements. The corrosion behavior of the melt spun Mg-Zn-La and Mg-Zn-Yb alloy ribbons in 1% NaCl solution was investigated in order to determine optimum composition of corrosion-resistant Mg alloys. The effect of heat-treatment on the corrosion behavior of RS Mg-Zn-La and Mg-Zn-Yb alloys also was studied. In the Mg-Zn-La alloys, as-quenched alloys showed good corrosion resistance in the NaCl solution, but heat-treatment led to degradation due to microstructure change, that is, reduction in dispersion of the Mg₁₇La₂-type intermetallic compound. In the Mg-Zn-Yb alloys, both as-quenched and heat-treated Mg_97.5Zn_0.5Yb₂ alloys exhibited low corrosion rates because fine distribution of Mg₂Yb-type intermetallic compound in α-Mg matrix was not largely changed by heat treatment.     

Formation of 14H long period stacking ordered structure and profuse stacking faults in Mg–Zn–Gd alloys during isothermal aging at high temperature

This paper proposes a time–temperature-transformation diagram of an Mg–Zn–Gd alloy. An Mg₉₇Zn₁Gd₂ (at.%) alloy shows different precipitation sequences at low, medium and high temperatures. Low-temperature aging at <523 K brings about coherent β′-phase precipitation to a -Mg solid solution, resulting in increase in strength of the alloys. However, aging at medium and high temperatures >623 K led to strengthening of the Mg–Zn–Gd alloy, owing to the formation of profuse stacking faults and 14H long period stacking ordered structure from the supersaturated -Mg matrix, respectively.     

Grwoth rate versus temperature relations characteristic of environmental stress cracks in low-density polyethylenes and the underlying thermodynamic mechanism

Growth rate versus temperature relations of environmental stress cracks (ESC) in low-density polyethylenes (PE) are investigated. In the experiments, bent PE specimens are immersed in dimethylsiloxanes (DMS) of various molecular sizes. The growth rates are increased from 10^?9 to 10^?4 m s^?1 by a few tens of degrees increase in temperature. The relations behave in apparently complicated manners depending on DMS molecular size, PE molecular weight and amount of bending deformation. Their Arrhenius type plots, however, fall into either of the two characteristic shapes as in PE ESC induced by several non-ionic surfactants and n-propanol. They are consistently interpreted in terms of the authors' thermodynamic theory. The active liquids, though incompatible with a stress-free polymer, migrate into its matrices in a restricted region at the crack tip. The change in the paths of the state shifts leading to failure in the relevant thermodynamic potential diagrams is essential to the ESC kinetics.     

Microwave Dielectric Study on Water Structure and Physical Properties of Aqueous Systems Using Time Domain Reflectometry with Flat-End Cells

Microwave dielectric measurements were performed in the frequency range from 1 mHz up to 30 GHz using a time domain reflectometry (TDR) method for emulsions and gels. Flat-end sample cells have been used in the TDR measurement to contact a small spot of the surface of those viscoelastic and solid samples without any destruction. Relaxation processes due to various water structures were observed for these aqueous systems. Relaxation parameters thus obtained offer information about these water structures and amounts. The relaxation strength obtained from the high frequency process due to free water can be an adequate measure of water content in spite of some ambiguities for different water structures in some materials. Comparisons of actual water contents in emulsion with those estimated from the relaxation strength indicate that water structure is affected by the interaction between water and micelle. Unfreezable water observed in DNA gel under the freezing point consists of bound water and a fraction of free water. Bound water molecules are still unfreezable to keep the double helical structure of DNA, when the fraction of free water is frozen at lower temperatures. These water structures determine physical properties of moist materials. TDR measuring technique with the flat-end cell is effective to investigate water structures in viscoelastic moist materials and to evaluate physical properties and structures of complex molecular systems.     

Isolation of Endotoxin Eliminating Lactic Acid Bacteria and a Property of Endotoxin Eliminating Protein

Recently, many scholars have reported lactic acid bacteria (LAB) functions, such as anticancer activity and anti‐inflammatory activity for intestines. To decrease inflammatory substances such as endotoxins, LAB consumed safely with meals were isolated from food and food ingredients. First, LAB were isolated as 168 strains of bacillus LAB (49 strain) and coccus LAB (119 strains) from food ingredients and fermented foods such as rice, rice bran, malt, grains, miso soy paste, and some pickles. Their LAB (168 strains) were cultivated in medium containing endotoxin from Escherichia coli O18 LPS at 15 and 30 °C for 64 h to identify endotoxin‐eliminating LAB. Consequently, the AK‐23 strain was screened as an endotoxin‐eliminating LAB strain. The strain decreased endotoxin in YP medium without sugar at 30 °C for 64 h until 9% of endotoxin. The strain was identified as Pediococcus pentosaceus according to morphological characteristics such as its cell shape, physiological characteristics related to its fermentation type, assimilation of sugars, pH tolerance, optimum growth temperature, and molecular biological characteristics as its homology to 16S rRNA. To investigate the location of the endotoxin‐eliminating substance, 4 fractions were separated from AK‐23 cells as extracellular, cell wall digestion, cytoplasm, and cell membrane fractions. The endotoxin‐decreasing substance, located on a cell wall, was identified as a 217 kDa protein.     

Grinding Forces and Elastic Recovery in Ceramic Materials

Understanding grinding technology using a diamond grinding wheel is very important to achieve the dimensional accuracy of the final product in structural application of ceramics. Because Si₃N₄ is very difficult to grind, its grindability, which is estimated from the grinding force, is examined with regard to some of its physical properties. The difficult-to-grind nature of Si₃N₄ depends on its high elastic recovery energy.     

Plasma-initiated graft polymerization of water-soluble vinyl monomers onto hydrophobic films and its application to metal ion adsorbing films

Plasma-initiated graft polymerization of water-soluble vinyl monomers such as acrylic acid, 2-hydroxyethyl methacrylate and acrylamide was carried out onto polyethylene, polypropylene and poly(ethylene terephthalate) films. It was found that these monomers could be graft polymerized quite easily to 0.5%–670% of the mass of the dry films by exposing the films to a plasma for 90s, with subsequent post-polymerization at room temperature. Thus, polyethylene films capable of adsorbing and desorbing metal ions reversibly could be prepared by grafting the monomers described.     

In Situ measurement of effective gas diffusivity through hematite pellets during stepwise reductions

The Wicke-Kallenbach (W-K) method for effective gas diffusivity measurements could only be used in the vicinity of ambient temperatures. However, in the present study, this technique has been extended to temperatures of about 1273 K through use of a high-temperature cement. This newly developed high-temperature W-K method was applied toin situ measurements of the diffusive and viscous fluxes through hematite pellets during stepwise reductions. When the sam-ple (acid and basic pellets) is reduced, it swells significantly. However, a gas-tight seal between the holder and specimen was successfully maintained by use of a high-temperature cement. This cement, composed mainly of Na₂O (20 mass pct) and SiO₂, separates into a solid and liquid phase at elevated temperatures. Thus, it can move in the same direction as the expansion of sample and thereby maintain the gas-tight seal. With this new technique, the structural param-eters of gases based on the “dusty gas model” for D’Arcy’s flow, Knudsen diffusion, and mo-lecular diffusion were obtained. These parameters were compared with those estimated through pore structure models.