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351.
《Ceramics International》2020,46(3):3183-3189
Bi2O3: Yb3+/Tm3+ nanoparticles with varied phase structures and morphologies were synthesized via the co-precipitation method assisted with a subsequent high-temperature calcination process. The influences of experimental parameters including dosage of urea, dopant concentration, reaction temperature and time on the crystal phase structures and morphologies of the as-prepared nanoparticles were investigated. Results revealed that the morphology, the crystal phase and the up-conversion emission of Bi2O3: Yb3+/Tm3+ could be simultaneously controlled by varying Yb3+ doping concentration. With increasing Yb3+ doping concentration (0-40%), the dramatic morphological evolution (nano-sheet to nano-flower to nano-sphere) and phase transition (monoclinic to tetragonal to cubic phase) were observed. Under the excitation of CW and pulse 980 nm lasers, Bi2O3: Yb3+/Tm3+ samples exhibited red (693 nm) and NIR (795 nm) double-band up-conversion emissions, where the increase of Yb3+ concentration leaded to the decreased emission intensity ratio of NIR to red (I795/I693) and the suppressed pulse-width-dependent up-conversion output. 相似文献
352.
《Journal of Microcomputer Applications》1990,13(4):347-360
A magnetic arc oscillation system has been developed to control the fusion characteristic of arc welding. A single-pole electromagnet generates a transverse magnetic field parallel to the weld line. The weave pattern of the magnetic field, hence the bead geometry, is controlled by a custom-built computer. The applied magnetic field has a marked influence on the bead width, but less on the bead depth. Experiments also show that bead appearance is improved by magnetically oscillating the arc. 相似文献
353.
354.
《Applied Superconductivity》1999,6(1):19-29
Thermal peeling stress between a thin film and the substrate is caused by the mismatch of thermal expansion coefficients while the film and substrate undergo a temperature change. The thermal peeling stress resulting from the temperature decrease from ambient to operating conditions (cryogenic temperatures) between a thin-film high-temperature superconductor and its substrate is calculated using finite element analysis (FEA). The superconductor thin film is idealized as a long bridge on a large substrate. A two-dimensional FEA model is applied to calculate the tensile (peeling) stress at the thin film/substrate interface. Results are obtained for different geometries and temperature conditions, and these results are compared with analytical predictions. A stress singularity is found at the very edge of the thin film which is not predicted by the analytical prediction. The peeling stress can be very high due to this stress singularity, even if the temperature change is not large. The stress singularity area depends on the local geometry of the edge, suggesting that refining the geometry of the thin-film HTS device is important. 相似文献
355.
《Diamond and Related Materials》2001,10(9-10):1709-1713
Both diamond and carbon nanotubes are efficient field emitters. Both materials can emit electrons at very low electric fields (3–7 V/μm for a current density of 10 mA/cm2). Moreover, nanotube emitters are capable of delivering very high emission currents densities, with current density routinely exceeding 1 A/cm2. Improvements of emission uniformity are critical in realizing the potential of these carbon materials in enabling practically useful cold cathode devices. 相似文献
356.
《Diamond and Related Materials》2001,10(9-10):1810-1813
A new method for carbon nanotube (CNT) growth by rapid thermal processing (RTP) of amorphous carbon film is reported. This is a two-step method, involving an ion-beam sputtering process followed by an RTP treatment. Amorphous carbon film containing iron was first deposited by ion-beam sputtering. The as-deposited films were then annealed by RTP under an inert environment. High-density multi-wall carbon nanotubes with a length of 1 μm and a diameter of approximately 30 nm were observed on the surface of amorphous carbon film after RTP at 1200°C for 30 s in nitrogen (N2). Detailed morphology and structure analyses of carbon nanotubes thus obtained using SEM and HR-TEM indicated that the number density and growth rate of the CNT were dependent on the process temperature and ambient gas. The use of RTP provides a straightforward, convenient and cost-effective method to grow carbon nanotubes with controllable length and density. 相似文献
357.
A comparison of the mechanical properties of fibers spun from different carbon nanotubes 总被引:2,自引:0,他引:2
Jingjing Jia Jingna Zhao Geng Xu Jiangtao Di Zhenzhong Yong Yuyu Tao Chao Fang Zuoguang Zhang Xiaohua Zhang Lianxi Zheng Qingwen Li 《Carbon》2011,(4):1333-1339
Spinnable carbon nanotube (CNT) arrays with different CNT structures have been synthesized using different growth methods and carbon sources, and long and stable fibers have been produced. Parameters of the nanotubes such as tube diameter, wall thickness, tube length and level of defects were found to play a more important role in the mechanical properties of the fibers than did the initial tube arrangement. To improve the fiber strength, as well as the modulus, the tubes must be long and have a small diameter and thin walls. The strongest fiber from double- and triple-walled CNTs is 1.23 GPa in strength, and 32% and 221% higher than those from CNTs with ∼6 and ∼15 walls (932 and 383 MPa), respectively. The fiber strength can be improved by 25%, up to 1.54 GPa, after poly(vinyl alcohol) infiltration with volume fraction of ∼20%. Our study also shows that C2H4 is superior to C2H2 as the carbon source for the growth of mainly double- and triple-walled CNTs, and therefore the spinning of high-strength fibers. 相似文献
358.
359.
360.
《International Journal of Hydrogen Energy》2020,45(43):22808-22816
Developing highly efficient electrocatalysts for oxygen evolution reaction (OER) is of significant importance for the application of many energy conversion and storage technologies. Perovskite oxides have attracted great attention as potential OER electro-catalysts. Their performance, however, are strongly limited by large particle size, owing to the high synthesis temperature. Herein, we report a facile top-down strategy for fabricating perovskite oxide nanostructures with large surface area and strongly improved intrinsic OER activity. SrNb0.1Co0.7Fe0.2O3-δ (SNCF) particles with micro size are treated by (NH4)2Fe(SO4)2 saturated solution for different time length at room temperature. The obtained catalysts exhibit significantly increased surface area with nanosheet structure in the outer layer. Furthermore, cobalt on the surface are reduced from Co3+ to Co2+, suggesting oxygen vacancy formation on the surface. The defective SNCF nanostructure exhibits significantly improved OER activity and good stability. The facile methodology reported in this work can be generally applied to other oxide electrocatalysts for energy applications. 相似文献