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61.
采用激光共聚焦拉曼技术获得聚丙烯腈基碳纤维的拉曼光谱,分析了碳纤维拉曼特征峰在不同的激发功率下的变化。通过Gaussian-Lorentz混合函数拟合得到了不同激发功率下碳纤维拉曼特征峰的拉曼位移、半高宽和R值。研究发现,随着激发功率的增大,碳纤维的拉曼特征峰向低波数方向移动。激发功率在3.8 mW以内,对碳纤维的拉曼位移和半高宽影响较小;激发功率不超过3.2 mW,R值基本保持不变。研究还发现,在较高的激发功率下,碳纤维表面发生了无定形态向结晶态的转变,石墨微晶尺寸有所增大,碳纤维局部表面结构遭到破坏。 相似文献
62.
联苯四羧酸二酐(BPDA)与4,4′-二氨基二苯醚(ODA)及自制的2,6-二(对氨基苯)苯并[1,2-d;5,4-d']二噁唑(DAPBBO)在二甲基乙酰胺中共聚,然后进行铺膜和热酰亚胺化,得到了含有双苯并噁唑的共聚酰亚胺薄膜,对其结构、热性能、力学性能及光学性能进行了表征。结果表明:杂环单体的引入提高了聚酰亚胺的力学性能,增加了聚酰亚胺的玻璃化转变温度,并且使聚酰亚胺薄膜具有良好的紫外吸收能力。 相似文献
63.
WC-doped ZrB2–ZrSi2 ceramic composites were fabricated by hot pressing at temperatures ranging from 1450 °C to 1550 °C. The influence of ZrSi2 content on the mechanical properties of the composites was investigated by means of three point bending test and single edge notched-beam test, respectively. The microstructure and phase composition were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. The results revealed that: (i) the highest relative density was 99.5% for the composite fabricated at 1550 °C; (ii) the doping of WC refined the grain size and led to an anisotropic grain growth which was evidenced by the occurrence of elongated grains; (iii) the highest strength and fracture toughness were 585 MPa and 6.87 MPa m1/2, respectively; (iv) the main toughening mechanism was considered as the pull out of elongated grains and the deflection of cracks. 相似文献
64.
《Ceramics International》2016,42(10):12115-12118
Mono-dispersed crystalline Zinc selenide nanoparticles (ZnSe-NPs) have been synthesized at ambient temperature conditions via a “green” chemistry method. The nanoparticles were characterized by Transmission electron microscopy (TEM) and UV–vis spectrophotometry. In vitro cytotoxicity studies on Neuro2A and HeLa cell lines illustrated a dose dependent toxicity with non-toxic effect of ZnSe-NPs up to a concentration of 3.9 and 7.8 µg/mL, respectively. The influencing reaction time was also investigated, and the possible formation mechanism was also proposed. The suggested method is facile, green, easy, and it can be employed to large-scale fabrication. 相似文献
65.
CeO2 nanoparticles (NPs) were synthesized by coprecipitation using cerium(III) nitrate hexahydrate as the precursor and ethanol as the solvent. Different concentration of cobalt-doped cerium oxide NPs (3mol % and 6 mol %) were prepared by adding various concentrations of cobalt chloride to cerium nitrate. The as-synthesized NPs were characterized through X-ray diffraction (XRD) measurements, ultraviolet (UV)–visible spectroscopy, Photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). XRD results reveal that the as-prepared CeO2 NPs had a face-centered cubic structure with crystallite size in the range of 5–8 nm. TEM analyses showed that the CeO2 NPs and Co-doped CeO2 NPs had a homogenous size distribution (sizes were within 5–12 nm). Band-edge absorption of CeO2 NPs redshifted upon increasing the Co concentration as compared to undoped CeO2 NPs. PL spectra reveal a peak shift of CeO2 emission upon cobalt doping, which were due to an increase in oxygen defects localized between the Ce4f and O2p energy levels (i.e., via formation of Ce3+ states). Photocatalytic degradation of methylene blue in aqueous solution under UV and visible (sunlight) irradiation in the presence of pure CeO2 NPs and of Co-doped CeO2 NPs was investigated. The efficiency of photocatalytic degradation of CeO2 NPs increased with the Co concentration both under UV irradiation and under visible light. Co-doped CeO2 NPs (6 mol%) showed degradation efficiencies of 98% and 89% at 420 min of exposure to UV irradiation and to visible light, respectively. 相似文献
66.
Jianhua Jiang Jiangwei Ren Aidang Shan Junliang Liu Hongwei Song 《Materials Science and Engineering: A》2009,520(1-2):80-89
The mechanical property and microstructure evolutions of Ni3Al intermetallic compound subjected to surface mechanical attrition treatment (SMAT) were investigated in relation to surface nanocrystalization. Grain size in topmost surface of SMATed Ni3Al alloy was refined to a minimum size of about 10 nm, and then increased with the enhancement of the depth from surface to matrix. The original ordered L12 phase transformed to Ni (Al) solid solution with a disordered face-centered cubic structure. The maximum nanohardness of the deformed Ni3Al alloy was near 12 GPa. The microstructure evolution including the variation of defects during the SMAT as well as post-annealing processes showed that the surface nanocrystallization of Ni3Al intermetallic compound was predominantly controlled by dislocations which divided the coarse grains. The different microstructures at each sublayer illustrated that the nanocrystallization process was decided by the accumulated energy resulted from plastic strain. 相似文献
67.
《Carbon》2013
A set of resistance-type strain sensors has been fabricated from metal-coated carbon nanofiller (CNF)/epoxy composites. Two nanofillers, i.e., multi-walled carbon nanotubes and vapor growth carbon fibers (VGCFs) with nickel, copper and silver coatings were used. The ultrahigh strain sensitivity was observed in these novel sensors as compared to the sensors made from the CNFs without metal-coating, and conventional strain gauges. In terms of gauge factor, the sensor made of VGCFs with silver coating is estimated to be 155, which is around 80 times higher than that in a metal-foil strain gauge. The possible mechanism responsible for the high sensitivity and its dependence with the networks of the CNFs with and without metal-coating and the geometries of the CNFs were thoroughly investigated. 相似文献
68.
综述了高温金相显微镜的组成和工作原理,高温金相技术在高温相变原位观察,金属材料的高温显微组织、晶粒长大和力学性能研究等方面的应用以及高温金相技术的发展趋势。 相似文献
69.
You Zhou Yu-ichi Yoshizawa Kiyoshi Hirao Zoltán Lenčéš Pavol Šajgalík 《Journal of the European Ceramic Society》2011,31(1-2):151-157
LaSi3N5:Eu2+ phosphor powders were prepared by a highly efficient combustion synthesis method. It was found that the compositions of the raw powder mixtures had great influences on the phase compositions and particle morphologies of the synthesized powders. By selecting appropriate starting compositions and combustion parameters, single phase LaSi3N5:Eu2+ phosphors could be synthesized. When excited by a UV light, the LaSi3N5:Eu2+ phosphors emitted green light. The wavelength and intensity of the emission spectra were affected by the amount of Eu2+ dopant. With increasing amount of Eu2+ dopant, concentration quenching could occur and emission spectra shifted to longer wavelengths. 相似文献
70.