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991.
The effectiveness of carbon nanotubes as reinforcements in the next generation of composites is designated by their mechanical behavior as standalone units. One of the most commonly present topological defects, whose effect on the mechanical behavior of carbon nanotubes needs to be clarified, is the Stone–Wales (SW) defect. In this paper, the effect of SW defect on the tensile behavior and fracture of armchair, zigzag and chiral single-walled carbon nanotubes (SWCNTs) was studied using an atomistic-based progressive fracture model. The model uses the finite element method for analyzing the structure of SWCNTs and the modified Morse interatomic potential for describing the nonlinear force-field of the C–C bonds. In all cases examined, the SW defect serves as nucleation site for fracture. Its effect on the tensile behavior of the SWCNTs depends solely on nanotube chirality. In armchair SWCNTs, contrary to zigzag ones, a significant reduction in failure stress and failure strain was predicted; ranging from 18% to 25% and from 30% to 41%, respectively. In chiral SWCNTs, the effect of the defect is between those of the armchair and zigzag SWCNTs, depending on chiral angle. The stiffness of the nanotubes was not affected. The nanotube size was found to play a minimal role in the tensile behavior of SW-defected SWCNTs; only in cases of very small nanotube diameters, where the fraction of defect area to the nanotube area is high, was a larger decrease in the failure stress predicted. 相似文献
992.
993.
分别采用扫描电镜(SEM)、广角X-ray衍射(WAXD)和小角X-ray散射(SAXS)研究分析了经含硫酸和尿素催化剂催化处理的Lyocell纤维在热解过程中结构、性能的变化。发现在低温热解前阶段(<200℃)随着处理温度的升高其密度增大,高于200℃后密度有所下降。纤维强度则表现出先下降后升高的变化规律,并在150℃~200℃温度区存在一个“零强度点”。在此过程中纤维聚合度也发生了类似强度的变化。同时,纤维结晶结构由纤维素II型向炭纤维的二维乱层石墨结构转化。 相似文献
994.
壳状碳纳米颗粒的制备和分散 总被引:1,自引:0,他引:1
利用高功率CO2连续激光照射C2H2,使之热解,成功制备了中空壳状碳纳米颗粒(CNSs),为增强其分散性,用王水对所制备的CNSs进行表面处理。利用TEM、XRD、FTIR以及Zeta电位测量等技术对CNSs和经化学处理后的碳纳米颗粒(T-CNSs)进行了对比分析。结果表明:CNSs壳层内碳原子呈石墨状规则排列;T-CNSs表面带有含氧的亲水官能团,使其很容易分散;化学处理没有改变CNSs的结构。 相似文献
995.
采用流动反应器研究了丙烯热解和在铁黄颗粒表面生成热解炭的化学热力学以及化学气相沉积(CVD)过程。发现在600oC之前丙烯热解发生的化学气相沉积基本为表面反应过程;在热解炭沉积过程中铁黄颗粒的比表面积迅速减少,同时由于脱去水分而发生失重;随着温度的升高,Fe2O3逐渐被还原为Fe3O4和FeO,在800℃以上Fe2O3完全被还原为Fe3C。在化学气相沉积过程中,500℃以前铁黄可以保持大长径比形貌,在600℃~700℃之间则生成长径比较小的哑铃型颗粒。非球形氧化铁颗粒在氢气还原过程中能够保持原有形状,同时被还原成为单质铁。上述化学气相沉积和气化过程可以用于制备热解炭包覆的或者纯净的非球形铁颗粒材料。 相似文献
996.
997.
负载铂纳米粒子大孔炭材料的无模板制备 总被引:2,自引:0,他引:2
研究了负载铂纳米粒子大孔炭材料的可控制备。淀粉和氯铂酸分别被用作碳源和铂源,采用两种不同的方法将铂注入基于淀粉凝胶的大孔炭。方法A:将淀粉凝胶块材浸入氯铂酸水溶液中,然后用硼氢化钠还原。方法B:在形成淀粉凝胶块材之前将氯铂酸加入前驱体中。研究发现:大孔炭的孔径和壁厚可以通过改变淀粉含量进行调节,产炭率从负载前的24%分别提高到37%(方法A)和44%(方法B),凝胶在炭化过程中的体积膨胀也得到有效抑制。方法A得到的铂纳米粒子(平均粒径为3.5nm,粒径平均偏差为0.9nm)比方法B制备的(平均粒径为5.5nm,粒径平均偏差为1.8nm)粒径更小、粒径分布更窄。 相似文献
998.
Mahdi Pourfath Hans Kosina Siegfried Selberherr 《Journal of Computational Electronics》2007,6(1-3):243-246
Based on the non-equilibrium Green’s function formalism we numerically studied gate-controlled tunneling carbon nanotube field-effect
transistors. The effect of doping concentration on the performance of the device has been investigated. We show that an asymmetric
doping profile can improve the I
on/I
off ratio of the device improves. 相似文献
999.
Theera Anukunprasert Chintana Saiwan Elisabetta Di Bartolomeo Enrico Traversa 《Journal of Electroceramics》2007,18(3-4):295-303
Nanostructured powders of Nb-doped TiO2 (TN) and SnO2 mixed with Nb-doped TiO2 in two different atomic ratios—10 to 1 (TSN 101) and 1 to 1 (TSN 11)—were synthesized using the reverse micelle microemulsion
of a nonionic surfactant (brine solution/1-hexanol/Triton X-100/cyclohexane). The powders were characterized by transmission
electron microscopy (TEM) and X-ray diffraction (XRD). Thick films were fabricated for gas sensors and characterized by XRD
analysis and field emission scanning electron microscopy (FE-SEM). The effects of the film morphology and firing temperature
in the range 650–850 °C on CO sensitivity were studied. The best gas response, expressed as the ratio between the resistance
in air and the resistance under gas exposure (R
air/R
gas), was measured for TSN 11 at 11 for 1,000 ppm CO exposure. All types of sensors showed good thermal stability. The electrochemical
impedance spectroscopy (EIS) measurements were performed in different gas atmospheres (air, O2, CO and NO2) to better understand the electrical properties of the nanostructured mixed metal oxides. 相似文献
1000.
Kexin LI Zhexun YU Yanhong LUO Dongmei LI Qingbo MENG 《材料科学技术学报》2007,23(5):577-582
Dye-sensitized solar cell (DSC) consists a combination of several different materials: photoanodes with nanoparticulated semiconductors, sensitizers, electrolytes and counter electrodes (CEs). Each materials performs specific task for the conversion of solar energy into electricity. The main function of CE is to transfer electrons to the redox electrolyte and regenerate iodide ion. The work of CE is mainly focused on the studies of the kinetic performance and stability of the traditional CEs to improve the overall efficiency of DSC, seeking novel design concepts or new materials. In this review, the development and research progress of different CE materials and their electrochemical performance, and the problems are discussed. 相似文献