Gasoline permeation resistance of the as‐blow‐molded and annealed polyethylene,polyethylene/polyamide,and polyethylene/modified polyamide bottles

An investigation of the gasoline permeation resistance of the as‐blow‐molded and annealed polyethylene, polyethylene (PE)/polyamide (PA), and polyethylene/modified polyamide (MPA) bottles is reported. The gasoline permeation resistance improves dramatically after blending PA and MPA barrier resins in PE matrices during blow‐molding, and the order of barrier improvement corresponds to the order of barrier improvement of the barrier resins added in PE. Somewhat unexpectedly, the gasoline permeation rates of the annealed PE and/or PE/PA bottles annealed at 90°C or higher temperatures increase significantly with the annealing temperature and time. On the contrary, the gasoline permeation resistance of the annealed PE/MPA bottles increase significantly as the annealing temperature and/or time increase. For instance, the gasoline permeation rate of the PE/MPA bottle annealed at 120°C for 32 h is about 190 times slower than that of the as‐blow‐molded PE bottle. Further investigations found that, after blending the MPA and PA barrier resins in PE matrices, the relatively nonpolar hydrocarbon components present in the gasoline fuels were significantly blocked, without permeation during the permeation tests, in which the as‐blow‐molded PE/MPA bottle inhibited the permeation of hydrocarbon components more successfully than did the as‐blow‐molded PE/PA bottle. In contrast, the amounts of polar components that permeated through the as‐blow‐molded PE/PA and PE/MPA bottles were very small and about the same as the amount that permeated through the as‐blow‐molded PE bottle. Possible mechanisms accounting for these interesting behaviors are proposed in this study. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2827–2837, 2001     

Fabrication of the KSTAR vacuum vessel and ports

The construction of the steady-state-capable superconducting KSTAR tokamak is in close proximity to the finalization. As one of the main components of the KSTAR device, the vacuum vessel is designed and manufactured during the construction period. The KSTAR vacuum vessel is composed of two large sectors forming the 337.5° of a full torus, and the remaining 22.5° section consisting of 24 small pieces. The large two sectors were welded at the site, and the 22.5° space was used for toroidal field coil assembly. The remaining 22.5° section of the vacuum vessel was assembled after 16 toroidal field coils assembly. The total 72 penetration ports were used to connect the vacuum vessel body and the cryostat. The major fabrication activity started in January 2003 after the finalization of fabrication design. The final components and structures were warehoused in June 2004 and site assembly is finished in 2007. Details of analysis, shop fabrication, and inspection results of the vacuum vessel including ports are summarized in the present work.     

Preparation of kanamycin powder by an optimized spray freeze-drying method

The physical and antibiotic properties of kanamycin powders obtained by spray freeze drying (SFD) were compared with those of raw kanamycin. The SFD procedures were optimized to prepare kanamycin for use as an inhaled drug. Scanning electron microscopy (SEM) and a laser particle size analyzer were applied to estimate physical structure and properties of the particle. In addition, the disk diffusion method was used to compare the antibiotic activity of raw kanamycin and that produced by SFD. According to SEM, the kanamycin particles had various sizes and shapes with porous structures at different SFD conditions. The diameters of the kanamycin powders were between 13.5 μm and 21.8 μm, and their aerodynamic particle sizes were between 3.58 μm and 6.39 μm. The antibiotic activities of the raw and spray freeze-dried kanamycin samples were not significantly different (P > 0.05). The optimized conditions for annealing temperature, annealing time, kanamycin concentration, pressure, and nozzle tip lift were ? 15 °C, 5 h, 10% kanamycin, 100 kPa, and, 1 mm, respectively.     

High-flexibility piezoelectric ribbon fiber fabrication through multi-material thermal drawing

In this study, an amorphous poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer with a high yield strain (approximately 18 %) is proposed as a cladding material for highly flexible and reliable piezoelectric ribbon fibers. Macro preforms are fabricated for thermal drawing (TD) processes, in which a poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) film is sandwiched between two electrically conductive composite sheets (carbon black (CB)/polypropylene (PP)). The piezoelectric device is cladded with the P(VDF-HFP) copolymer. The preform geometries and TD parameters are optimized to overcome the incompatibility of flow characteristics among P(VDF-HFP), P(VDF-TrFE), and CB/PP composite at the drawing temperature, yielding fibers of length more than 80 m through TD. After annealing and poling, the fiber produces approximately 5 V (peak-to-peak) under 2.5 % tensile strain and 0.5 V (peak-to-peak) under bending deformation, with a 5-mm radius of curvature. Furthermore, the piezoelectric fiber shows no severe degradation in the output voltage after 10000 cycles of bending deformation with 1-mm radius of curvature. The piezoelectric ribbon fiber developed herein has potential as a flexible tensile, pressure, or bending sensor fiber for wearable applications.

     

High-Field Magnetization of the Distorted Spin Frustration System Ni5(TeO3)4Br2

We performed high-field magnetization measurements, M(H), on the Ni₅(TeO₃)₄Br₂ by using a pulse magnet. The Ni²⁺ ions (S = 1) of this compound form a two dimensional distorted spin frustrated system (distorted kagome lattice), and undergo a Neel transition at T _N ～29 K, due to the anisotropy. Below T _N , a complex spin arrangement which contains ten spin sub-lattices was suggested by neutron scattering and electron spin resonance studies. We observed a step-like transition at H _c ～11 T when T<T _N . By contrast, at T>T _N , the field-dependent magnetization curves behaved like a straight line. The H _c is close to those obtained by previous spin resonance studies of Ni₅(TeO₃)₄Br₂ and Ni₅(TeO₃)₄Cl₂ in which a spin-flop-like transition was proposed to explain the field-dependent resonance spectra. Interestingly, the observed change in magnetization (ΔM) at H _c corresponds to nearly one-half of the magnetic moment of Ni²⁺ ion, suggesting that the observed step-like behavior possibly corresponds to a spin-flip-like transition (i.e. from antiferromagnetic state to ferrimagnetic state). In addition, in the high-field region (H>H _c ), the M(H) curves did not show plateau behavior, but exhibited the straight lines having finite slopes without any sign of saturation up to 55 T.     

Stepped-impedance directional coupler with enhanced isolation using interdigital capacitance compensation

A novel and successful stepped-impedance coupler with enhanced isolation is presented. By incorporating the distributed interdigital capacitance at the ends of the coupled section in the planar structure, the even- and odd-mode phase velocities can be equalised so as to enhance the isolation. Measured results show an enhanced isolation of 47.5 dB at the centre frequency 2.4 GHz and a size reduction of 30% when compared with the conventional parallel-line coupler. It is also shown that the coupling frequency flatness is as broadband as 3.1 GHz.     

On the bonding of porcelain on titanium

The interface structure and bond strength between Ti and porcelain were studied using various firing times and vacuum levels. During firing an interfacial oxide layer was formed between Ti and porcelain. Fracture occurred between this oxide layer and Ti. A correlation was observed between the thickness of the interfacial layer and the bond strength: the thicker the layer, the weaker was bonding. An improved vacuum was found to increase the bond strength. Oxygen was observed by ESCA to dissolve into Ti, causing brittleness in the uppermost Ti layer with prolonged firing time.     

Interface-controlled fatigue cracking of SCS-6/Ti-22Al-23Nb “orthorhombic” titanium aluminide composite

The effect of aging at elevated temperature on interfacial stability and fatigue behavior of a SCS-6/Ti-22Al-23Nb “orthorhombic” (O) titanium aluminide composite is investigated. The composite was heat treated in vacuum at 900 °C for up to 250 hours to change the microstructural characteristics. The stability of the matrix alloy and interfacial reaction zone after extended thermal exposure was analyzed. The effect of interface on fatigue behavior, including stiffness degradation, evolution of fatigue damage, and crack growth rates, was characterized. Finally, a modified shear-lag model was used to predict the saturated matrix crack spacing in the composite under fatigue loading. The results demonstrate that aging at elevated temperature affects the stability of the interfacial reaction zone, which, in turn, degrades the fatigue properties of the composite. However, fatigue crack will not develop from the ruptured interfacial reaction layer until the thickness of the reaction zone or the maximum applied stress exceeds a critical value.