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861.
Ziming Ye Yi Zeng Xiang Xiong Tianxiao Qian Huilin Lun Yalei Wang Wei Sun Zhaoke Chen Lijun Zhang Ping Xiao 《Journal of the American Ceramic Society》2020,103(12):6978-6990
Early transition metal carbides are considered to be superior candidate materials for oxidizing environments at temperatures exceeding 2000°C. Generally, the remarkable oxidation resistance is largely attributed to a carbonaceous oxide interlayer (eg, Hf–O–C, Zr–O–C, and Ta–O–C), located at the interface between the external oxide layer and internal carbide (eg, HfC, ZrC, and TaC), acting as the primary oxygen barrier. However, the oxygen barrier mechanism of the carbonaceous oxide interlayer remains unclear. Herein, through studying the oxidation behavior of a novel multicomponent carbide Hf0.5Zr0.3Ti0.2C in oxidizing environments up to 2500°C, the oxygen barrier mechanism of the carbonaceous oxide was recently revealed. We found that the oxygen barrier resulted from the slow oxygen diffusion through the inner grains of Hf-Zr–Ti–O due to the presence of carbon formed at the grain boundaries because of the existence of compact external oxide layer, beneath which the Hf–Zr–Ti–O–C interlayer possesses much lower oxygen activity and temperature that allow carbon to exist stably. This as-formed carbon strongly retarded the fast diffusion of oxygen along the grain boundaries of oxides. Additionally, desirable synergisms of the designed multicomponent system, particularly, the outward short-circuit diffusion of Ti, lead to the self-healing of the external oxide layer, evidently enhancing integral protection performance against oxidizing environments. 相似文献
862.
Phosphaphenanthrene derivative tri-(3-DOPO-2-hydroxypropan-1-yl)-1,3,5-triazine-2,4,6-trione (TGD) and organo-modified montmorillonite (OMMT) were jointly introduced into the diglycidyl ether of bisphenol A cured by 4,4-diamino-diphenylmethane (EP) to investigate their flame retardant behaviors. With only addition of 0.5%OMMT and 2.5%TGD, epoxy thermoset achieved a limiting oxygen index value of 33.7% and passed UL 94 V-0 rating test. Compared with the combustion behaviors of 3%OMMT/EP and 3%TGD/EP, an obvious synergistic flame retardant effect between OMMT and TGD can be concluded in OMMT/TGD/EP. Meanwhile, the FTIR spectra of gas-phase and condensed-phase products further proved this synergistic effect working in a physical way. On one hand, the co-existence of hydroxyl-containing TGD enabled montmorillonite (MMT) particles to filtrate and adhere more smoke fragments. On the other hand, the co-action of MMT help the polar phosphorus-containing fragments from TGD better strengthened char layer, enhancing the barrier and protective effect of residue. The synergistic flame retardant effect from OMMT/TGD system endowed themselves with higher flame retardant efficiency, and epoxy thermoset with better flame retardant performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47500. 相似文献
863.
864.
865.
介绍了光传输网(OTN)线型保护的体系结构及匹配要求、常用命令,详细分析了OTN线型保护的APS协议,并举例分析了APS协议的传输过程. 相似文献
866.
Charge recombination in reaction center (RC) of photosystem II(PS II) is regarded as the location of 685 nm delayed fluorescence
(DF). The mechanism of 730 nm component appearing in the DF spectrum for chloroplast was studied by various spectral analysis
methods. Experimental results of the DF spectrum at different chloroplast concentration show that the intensity of peaks at
685nm and 730 nm ascends with the chloroplast concentration increasing when the concentration is relatively low. When the
concentration increases to the level of 7.8μg/ml, a maximum intensity of the peak at 685 nm appears but the intensity of 730
nm peak still increases. The peak at 730 nm finally reaches a maximum intensity at the chloroplast concentration of 31.2 μg/ml
while the intensity of the 685 nm peak has apparently fallen down. The results of absorption spectrum show that the ratios
of A685 to A730 keep almost constant with the increasing of chloroplast concentration. Furthermore, the excitation spectrum
for 730 nm fluorescence shows that the 685nm light has high excitation efficiency. These results indicate that the 730 nm
component of DF spectrum is the fluorescence of chlorophyll in PS I RC excited by 685 nm DF. Meanwhile, this can be further
verified by the invariability of DF spectrum at different delay time (1 second∼9 seconds).
This research is supported by the National Natural Science Foundation of China (60378043), and supported by the Opening Foundation
of the Key Laboratory of Opto-Electronic Technology and Intelligent Control (Lanzhou Jiaotong University), Ministry of Education
(K04108) 相似文献
867.
868.
Iron-based anodes for lithium-ion batteries(LIBs) with higher theoretical capacity,natural abundance and cheapness have received considerable attention,but they still suffer from the fast capacity fading.To address this issue,we report a facile synthesis of plate-like carbonsupported Fe3 C nanoparticles through chemical blowing/carbonization under calcination.The ultrafine Fe3 C nanoparticles are prone to be oxidized when exposing in air;thus,Fe3 C/C with mild oxidization and the fully oxidized product of Fe_2 O_3/C are successfully prepared by controlling the oxidization condition.When applied as an anode material in LIB,the Fe3 C/C electrode demonstrates excellent cycle stability(826 mAh·g~(-1) after 120 cycles under 500 mA·g~(-1)) and rate performance(410.6 mAh·g~(-1)under 2 A·g~(-1)),compared with the Fe_2 O_3/C counterpart.The enhanced electrochemical performance can be ascribed to the synergetic effect of the Fe3 C with mild oxidation and the unique hierarchical structure of plate-like carbon decorated with Fe_3 C catalyst.More importantly,this work may offer new approaches to synthesize other transition metal(e.g.,Co,Ni)-based anode material by replacing the precursor ingredient. 相似文献
869.
主题追踪系统的研究与实现 总被引:3,自引:0,他引:3
主题追踪系统是Web挖掘的重要研究方向,它是指在给定的主题下,根据文本的内容自动判别文本归属主题的过程,该文对主题追踪系统中所涉及的关键技术,包括训练算法、追踪算法和阈值确定方法,进行了研究和探讨,并且提出了主题追踪系统的结构,给出了评估实验结果。 相似文献
870.
提出了一种基于窗口的快速聚类算法——F-CABDET(Fast Clustering Algorithm based on Building a DEnsity-Tree)。该算法采用基于窗口的计算方法将全局计算转化为局域计算,大幅度提高了计算效率,降低了程序的执行时间,并取得了满意的聚类质量。同时F-CABDET仅需要一个输入参数,在聚类过程中采用动态邻域半径不仅可以发现任意形状的簇,而且具有处理噪音数据的能力。实验结果表明了F-CABDET算法的有效性。 相似文献