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Crystallization and wetting of ZnO-AlO-BO-SiO glass-ceramic for sealing
to Kovar alloy
WU Mao, HE Xin-bo, SHEN Zhuo-shen, QU Xuan-hui
Front. Mater. Sci.. 2008, 2 (4): 345-350.
https://doi.org/10.1007/s11706-008-0067-8
A new type of ZnO-Al2O3-B2O3-SiO2 glass-ceramics seals to Kovar in electronic packaging was developed, whose coefficient of thermal expansion (CTE) and electrical resistance were 5.2 × 10-6/°C and over 1 × 1013 ?·cm, respectively. The major crystalline phases in the glass-ceramics seals were ZnAl2O4, ZnB2O4 and NaSiAl2O4. The dielectric resistance of the glass-ceramic could be remarkably enhanced through the control of the alkali metal ions into the crystal lattices. It was found that the crystallization happened first on the surface of the sample, leaving the amorphous phase in the inner parts, which makes the glass suitable for sealing. The glass-ceramic showed better wetting on the Kovar surface, and sealing atmosphere and temperature showed great effect on the wetting angle. Strong interfacial bonding was obtained, which was mainly attributed to the interfacial reaction between SiO2 and FeO or Fe3O4.
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Study on Al-Cu-Si braze containing small amount
of rare earth erbium
SHI Yao-wu, YU Yang, XIA Zhi-dong, LEI Yong-ping, LI Xiao-yan, GUO Fu, LIU Jian-ping
Front. Mater. Sci.. 2008, 2 (4): 351-356.
https://doi.org/10.1007/s11706-008-0061-1
In the present work, the effect of a small amount of rare earth Er addition on the microstructure of Al-Cu-Si brazing alloy has been investigated. In the study, the Al-20Cu-7Si brazing alloys with various Er contents were prepared. 3003 aluminum alloy was chosen as a substrate. The microstructure of the brazed alloys was carefully observed. In addition, melting temperature, wettability and hardness of the brazing alloys were measured. The results indicate that the constituent of the microstructure of Al-20Cu-7Si-Er brazed alloy is similar to the Al-20Cu-7Si, which is mainly comprised of solid solutions of aluminum, silicon and the intermetallic compounds CuAl2. When the Er content increases, the size of Al phases is decreased, and the filament-like or needle-like Si phase is thickened. The Si phases dominating in the shape of a filament or needle are transformed to those in the shape of a block when Er content is increased. Moreover, adding a small amount of Er can improve the wettability and hardness of the Al-20Cu-7Si brazing alloy. However, the melting temperature of the Al-20Cu-7Si alloy is almost unchanged when a small amount of Er is added.
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Electrochemical characteristics of pipeline-steel
with planar-defect epoxy-coating in simulated solutions of Ku'erle
soil
DU Cui-wei, LI Xiao-gang, WANG Wei, SONG Yi-quan
Front. Mater. Sci.. 2008, 2 (4): 357-364.
https://doi.org/10.1007/s11706-008-0072-y
An X70 pipeline steel and a low-carbon steel with different types of coating defects were studied using corrosion tests in Ku’erle simulated soil solution containing 0.6000 mol/L Cl-. Electrochemical characteristics of the X70 pipeline steel with planar-defect epoxy-coating in simulated solutions of Ku’erle soil were tested. The results show that in 0.6000 mol/L Cl- simulated solution, for low-carbon steel with coating defects (the area ratio is 4.91%), at free corrosion potential and with immersion time, the corrosion with disbond was more severe than that with a break or with break and disbond. In Ku’erle soil simulated solution, when the coating defect area ratio was increased gradually (0.39% → 1.57% → 6.28%), the corrosion of the X70 steel under coating with break was promoted gradually, and the influence of immersion time on the corrosion decreased. The influence of the immersion time on the corrosion was weakened when the defect area ratio increased to a certain degree.
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Microstructural study of oxidation of carbon-rich
amorphous boron carbide coating
ZENG Bin, FENG Zu-de, LI Si-wei, LIU Yong-sheng
Front. Mater. Sci.. 2008, 2 (4): 375-380.
https://doi.org/10.1007/s11706-008-0074-9
Carbon-rich amorphous boron carbide (BxC) coatings were annealed at 400°C, 700°C, 1000°C and 1200°C for 2 h in air atmosphere. The microstructure and composition of the as-deposited and annealed coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-Raman spectroscopy and energy dispersive X-ray spectroscopy (EDS). All of the post-anneal characterizations demonstrated the ability of carbon-rich BxC coatings to protect the graphite substrate against oxidation. Different oxidation modes of the coatings were found at low temperature (400°C), moderate temperature (700°C) and high temperature (1000°C and 1200°C). Finally, the feasibility of the application of carbon-rich BxC instead of pyrolytic carbon (PyC) as a fiber/matrix interlayer in ceramics-matrix composites (CMCs) is discussed here.
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Effect of micro-characterization on thrombus
formation ability of TiO film
JIANG Xiao-song, CHEN Jun-ying, HUANG Nan
Front. Mater. Sci.. 2008, 2 (4): 386-391.
https://doi.org/10.1007/s11706-008-0058-9
The thrombus formation ability of a biomedical microcoil for hemangioma treatment is one of the basic requirements in clinical intervention application. Surface modification of a biomedical microcoil can improve its thrombus formation ability. In this work, TiO2 films were deposited using the unbalanced magnetron sputtering method. The structures, components and micro-morphologies of the films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and scanning electron microscope (SEM). The thrombus formation ability of the films was studied by in vitro platelet adhesion test. The results indicated that a certain characteristic TiO2 film has the ability to increase thrombus formation. Furthermore, the biological behavior of cultured human umbilical vein endothelial cells (HUVECs) onto different films was investigated by an in vitro HUVECs cultured experiment. The results showed that endothelial cells on certain TiO2 film surfaces have good adherence, growth and proliferation. Additionally, the relationship between the micro-characterization and biological properties of TiO2 films is discussed.
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Effect of particle size distribution on green
properties during high velocity compaction
WANG Jian-zhong, QU Xuan-hui, YIN Hai-qing, YI Ming-jun, YUAN Xian-jie
Front. Mater. Sci.. 2008, 2 (4): 392-396.
https://doi.org/10.1007/s11706-008-0070-0
Iron powders with two different particle size distributions were compacted by high velocity compaction. The influences of particle size distribution and impact velocity on green properties, including green density, springback, tensile strength and bending strength etc., were studied with scanning electron microscopy (SEM) and a computer controlled universal testing machine. The results show that the particle size distribution and the impact velocity strongly affect its properties. Wider size distribution results in green compact with higher density and better strength. Furthermore, springback of compacts is lower produced by the powder with wider size distribution, especially for radial springback. As impact velocity increases, its green density and green strength gradually increases, but the increasing rate of density decreases gradually. No special relation is found between springback and impact velocity. In addition, the axial springback and the bending strength are higher than the radial springback and the tensile strength, respectively.
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Synthesis, characterization and fluorescence
quenching of poly(fluorene-alt-enylenevinylene)s
XIAO Jian-hua, LIU Feng, CHEN Hai-li, HU Jun, LIU Hong-lai
Front. Mater. Sci.. 2008, 2 (4): 409-416.
https://doi.org/10.1007/s11706-008-0069-6
Two poly(fluorine-alt-phenylenevinylene)s fluorescent conjugated polymers, poly(9,9-dioctylfluorene-alt-phenylenevinylene) (PFO/PPV1) and poly(fluorene-alt-2,5-dioctoxyphenylenevinylene) (PFO/PPV2), were obtained through a Heck polycondensation. The structures of the obtained polymers were characterized by FT-IR, 1H-NMR and GPC. The thermal stabilities of the polymers were evaluated by TGA. The photophysical properties were studied by UV and photoluminescence (PL) spectroscopy both in solution and film. Their applications in the detection of nitro compounds were researched, and the results show high fluorescence quenching sensitivity of PFO/PPV1 towards nitro compounds such as 2,4-dinitrotoluene (DNT) and 4-nitrotoluene (p-NT) in solution and thin film.
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Electron beam irradiated HDPE/EVA/Mg(OH) composites for flame-retardant electric cables
LIU Hui, ALKADASI Nabil A. Noman, ZHU Yan, TONG Li-fang, FANG Zheng-ping, WANG Yong-chang
Front. Mater. Sci.. 2008, 2 (4): 426-429.
https://doi.org/10.1007/s11706-008-0064-y
The mechanical properties and flammability of high-density polyethylene (HDPE)/ethylene vinyl acetate (EVA) mixed with various amounts of magnesium hydroxide (Mg(OH)2) as the filler in composites, irradiated with electron beam at an irradiation dose of 150 kGy, have been studied. It is found that high-energy electron beam irradiation has significant effects on the mechanical properties of the HDPE/EVA/Mg(OH)2 composites. The tensile strength and elastic modulus increased greater than in the unirradiated ones. Meanwhile, with increasing the content of Mg(OH)2 in the composites, the limiting oxygen index (LOI) value increased sharply. The microstructure of the caves of the unirradiated HDPE/EVA/Mg(OH)2 composites show poor interface of composites compared with the irradiated ones, as observed in SEM micrographs.
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17 articles
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