Structure of polyphenylsilsesquioxane particles prepared by two-step acid-base catalyzed sol-gel process and formation of hollow particles

Spherical polyphenylsilsesquioxane (PhSiO(3/2)) particles, one of the inorganic-organic hybrid materials, were synthesized by a two-step acid-base catalyzed sol-gel process, and hollow particles were successfully prepared by washing the as-prepared particles with organic solvents. It was found that the inside and outside parts of the as-prepared particles were composed of PhSi03/2 species with relatively low and high molecular weight, respectively, i.e., the PhSiO(3/2) particles had a kind of "core-shell" structure. Because the core portion in the as-prepared particles was soluble in ethanol and tetrahydrofuran, hollow particles were obtained through washing the as-prepared PhSiO(3/2) particles with ethanol or tetrahydrofuran. Furthermore, the molecular weight of the as-prepared particles was varied by the concentration of phenyltriethoxysilane used as a starting alkoxide. As a result of the variation of the molecular weight, the hollow PhSiO(3/2) particles with different stabilities against organic solvents were formed.     

Effects of divalent cations on Halobacterium salinarum cell aggregation

Ca(2+) was found to be essential for initiating Halobacterium salinarum CCM 2090 cell aggregation. The floc formed from such aggregation could easily be dissociated without cellular lysis by sodium citrate. Cr(2+), Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), and Zn(2+) could replace Ca(2+). However, Mg(2+), Sr(2+), Mo(2+), Cd(2+), Sn(2+), Hg(2+), and Pb(2+) induced no flocculation of cells of this halophilic archaeon. Mg(2+) acted antagonistically against Ca(2+)-induced aggregation. Such aggregation might be directly caused by the interaction of Ca(2+) and aggregation factors from 55 degrees C-treated cell extract.     

Effects of Nano Metal Coatings on Growth Kinetics of α-Al2O3 Formed on Ni-50Al Alloy

The effects of pure metal coatings, including Ni, Fe and Cr, on long-term oxidation kinetics, surface morphology and structure were studied. Ni-50Al alloy and Ni-coated, Fe-coated and Cr-coated samples were pre-oxidized at 900 °C in air. They were then oxidized isothermally at 1,000 °C in air. The bare Ni-50Al alloy oxidized rapidly during the initial stage of oxidation due to the formation of θ-Al₂O₃, but the oxidation rate decreased after α-Al₂O₃ had developed. Oxidation of the Ni-coated sample was slow from the beginning of oxidation even though the θ-Al₂O₃ was predominated for a longer oxidation time. No θ-Al₂O₃ developed on the Cr and Fe-coated samples, but the oxidation rates of these samples were much faster than those of bare and Ni-coated samples. Cross-sectional images revealed that the grain size of α-Al₂O₃, which formed on Cr and Fe-coated samples, was smaller than those of bare and Ni-coated samples. These metal coatings affected the microstructure of α-Al₂O₃ and they showed a strong effect on the growth rate of α-Al₂O₃ in the steady-state oxidation stage.     

Laser roll welding of dissimilar metal joint of titanium to aluminium alloy

Recently, the demand for dissimilar metal joints of titanium to aluminium alloy has arisen in industry, especially in the transportation vehicle industry. However, it is well known that fusion welding of titanium to aluminium alloy is difficult because of generating the brittle intermetallic compound at the joint interface. Therefore, new welding processes with high reliability and productivity for these dissimilar materials are demanded. In the present work, Laser roll welding of titanium to aluminium alloy using a 2 kW fibre laser was tried to investigate the effects of the process parameters on the formation of the interlayer and the mechanical properties of the joint. As a result, the cross-section of the joint shows partial melting of the aluminium sheet and spreading of molten aluminium alloy on the titanium sheet occurs during the welding thermal cycle. Various types of intermetallic compound were confirmed at the interlayer of the welded joint. The specimen with a bonding width of 2.8 mm failed in the base metal of titanium in the tensile shear test. In Erichsen cupping tests, the Erichsen value was 5.7 mm. This value was 89% of the base metal of aluminium sheet.     

MICROSOLIDIFICATION PROCESS IN MULTICOMPONENT SYSTEM

In conventional solidification of multicomponent mixtures, a mushy zone appears between the pure solid and liquid regions and promotes stable solidification by accepting the rejected solute regionally. From the standpoint that the fineness of inhomogeneity influences the mechanical properties in material processing, the linking of macro heat transfer and microsolidification in the mushy zone was studied. First, the crystal growth and its accompanying concentration field near the advancing front of the mushy zone were observed precisely by using the light absorption method. It was clarified that the mushy zone consisted of the leading front in which the frame structure formed with an accompanying concentration boundary layer and a growing region where the solidification proceeds by fattening of the crystals. Second, the mechanism of side-branch evolution was studied in conjunction with interfacial instability due to constitutional supercooling and curvature supercooling around the primary arm surface. Summarizing these results, the microsolidification process is discussed quantitatively in relation to macro heat transfer.     

DNA adsorption characteristics of hollow spherule allophane nano-particles

To understand the propensity of natural allophane to adsorb the DNA molecules, the adsorption characteristics were assessed against natural allophane (AK70), using single-stranded DNA (ss-DNA) and adenosine 5′-monophosphate (5′-AMP) as a reference molecule. The adsorption capacity of ss-DNA on AK70 exhibited one order of magnitude lower value as compared with that of 5′-AMP. The adsorption capacity of ss-DNA decreased with increasing pH due to the interaction generated between phosphate groups of ss-DNA and functional Al–OH groups on the wall perforations through deprotonating, associated with higher energy barrier for the adsorption of ss-DNA. The adsorption morphologies consisting of the individual ss-DNA with mono-layer coverage of the clustered allophane particle were observed successfully through transmission electron microscopy analysis.     

西式发酵火腿粗肽的制备及抗氧化活性和氨基酸组成分析

采用磷酸盐缓冲液和盐酸溶液提取西式发酵火腿的粗肽,测定并比较2种溶液提取的粗肽1,1-二苯基-2-三硝基苯肼(1,1-diphenyl-2-picrylhydrazyl,DPPH)自由基、羟自由基清除能力、Fe2+螯合能力及总抗氧化能力,同时对氨基酸组成进行分析.结果表明:磷酸盐法提取得到的粗肽粉A的质量和肽含量显著高...     

Enhanced electrical conductivities of N-doped carbon nanotubes by controlled heat treatment

The thermal stability of nitrogen (N) functionalities on the sidewalls of N-doped multi-walled carbon nanotubes was investigated at temperatures ranging between 1000 °C and 2000 °C. The structural stability of the doped tubes was then correlated with the electrical conductivity both at the bulk and at the individual tube levels. When as-grown tubes were thermally treated at 1000 °C, we observed a very significant decrease in the electrical resistance of the individual nanotubes, from 54 kΩ to 0.5 kΩ, which is attributed to a low N doping level (e.g. 0.78 at% N). We noted that pyridine-type N was first decomposed whereas the substitutional N was stable up to 1500 °C. For nanotubes heat treated to 1800 °C and 2000 °C, the tubes exhibited an improved degree of crystallinity which was confirmed by both the low R value (I(D)/I(G)) in the Raman spectra and the presence of straight graphitic planes observed in TEM images. However, N atoms were not detected in these tubes and caused an increase in their electrical resistivity and resistance. These partially annealed doped tubes with enhanced electrical conductivities could be used in the fabrication of robust and electrically conducting composites, and these results could be extrapolated to N-doped graphene and other nanocarbons.