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991.
S Cui H Pu EC Mattson G Lu S Mao M Weinert CJ Hirschmugl M Gajdardziska-Josifovska J Chen 《Nanoscale》2012,4(19):5887-5894
We have investigated the room-temperature sensing enhancement of Ag nanoparticles (NPs) for multiwalled carbon nanotube (MWCNT)-based gas sensors using electrical measurements, in situ infrared (IR) microspectroscopy, and density functional theory (DFT) calculations. Multiple hybrid nanosensors with structures of MWCNTs/SnO(2)/Ag and MWCNTs/Ag have been synthesized using a process that combines a simple mini-arc plasma with electrostatic force directed assembly, and characterized by electron microscopy techniques. Ag NPs were found to enhance the sensing behavior through the "electronic sensitization" mechanism. In contrast to sensors based on bare MWCNTs and MWCNTs/SnO(2), sensors with Ag NPs show not only higher sensitivity and faster response to NO(2) but also significantly enhanced sensitivity to NH(3). Our DFT calculations indicate that the increased sensitivity to NO(2) is attributed to the formation of a NO(3) complex with oxygen on the Ag surface accompanying a charge rearrangement and a net electron transfer from the hybrid to NO(2). The significant response to NH(3) is predicted to arise because NH(3) is attracted to hollow sites on the oxidized Ag surface with the H atoms pointing towards Ag atoms and electron donation from H to the hybrid sensor. 相似文献
992.
聚羧酸减水剂的分子结构对水泥水化过程的影响 总被引:6,自引:0,他引:6
在水溶液体系下合成了一系列不同分子结构的聚羧酸减水剂,利用凝胶渗透色谱对其分子结构进行表征,探讨了分子结构对聚羧酸减水剂的分散性及其分散保持性的影响,并采用"水化热法"和"电阻率法"分析了聚羧酸减水剂的分子结构对水泥水化过程的影响。结果表明:聚氧化乙烯(polyethylene oxide,PEO)侧链较短时,聚羧酸减水剂表现出较高的分散保持性;PEO侧链接枝密度为1:3时,聚羧酸减水剂同时表现出较高的分散性及分散保持性,同时与减水剂的分子量分布密切相关;聚羧酸减水剂使水泥水化的诱导前期缩短,但诱导期延长,表现出一定的缓凝作用;PEO侧链较短、PEO侧链接枝密度适中的聚羧酸减水剂表现出较强的缓凝作用,与其在水泥颗粒表面的吸附行为有关;随分子量减小,这种缓凝作用略有加强;聚羧酸减水剂使电阻率曲线上对应的离子溶解平衡期延长,当PEO侧链较短、PEO侧链接枝密度适中时,聚羧酸减水剂对溶解平衡期的延长作用更明显,这与分子结构对水化热曲线上诱导期的延长规律类似。 相似文献
993.
994.
Thermal stability and electric‐field‐induced strain behaviors for PIN‐PSN‐PT piezoelectric ceramics 下载免费PDF全文
Pb (In1/2Nb1/2) O3‐Pb (Sc1/2Nb1/2) O3‐PbTiO3 (PIN‐PSN‐PT) ternary ceramics with compositions near morphotropic phase boundary (MPB) were fabricated by solid‐state‐sintering process. Dielectric and piezoelectric properties of xPIN‐yPSN‐zPT (x = 0.19, 0.23 and z = 0.365, 0.385) ceramics were investigated as a function of temperature, showing high Tr‐t and Tc on the order of 160 ~ 200°C and 280 ~ 290°C, respectively. The xPIN‐yPSN‐0.365PT (x = 0.19 and 0.23) ceramics do not depolarize at the temperature up to 200°C, showing a better thermal stability when compared to the state‐of‐the‐art relaxor‐PbTiO3 systems. A slight variation (<9%) of kp, kt, and k33 was observed in the temperature range of 25°C‐160°C for xPIN‐yPSN‐0.385PT (x = 0.19 and 0.23) ceramics. Rayleigh analysis was employed to quantify the contribution of domain wall motion to piezoelectric response, where the domain wall contribution was found to increase with composition approaching MPB for PIN‐PSN‐PT system. 相似文献
995.
工业无线通信技术是继现场总线之后,工业控制领域的又一热点技术,是降低工业测控系统成本、扩展工业测控系统应用范围、推动自动化发展的关键技术。 相似文献
996.
文中对一次二阶矩概率设计法的理论基础作了剖析,分析了人防工程设计特点,认为在相对运算意义上,采用可靠指标β度量人防工程诸构件的可靠性虽然有嫌粗糙,但作为设计方法仍然是一种进步,并进而提出了具体运算步骤及简化办法,可供修订人防工程设计规范参考. 相似文献
997.
本文在相对正交曲线座标系中建立了两类相对流面(S_1流面和S_2流面)上边界层微分方程组。所给方程不仅描述了静、动叶流道内边界层流动的一般特性,而且可用于叶片表面和内外端壁附近由于二次流动引起流面翘曲时的计算,特别适用于与S1、S_2流面的势流方程相互迭代,求解高R_e值下叶栅流道内的三元粘性流场。 相似文献
998.
添加剂对秸秆成型燃料燃烧特性的影响 总被引:1,自引:0,他引:1
生物质成型燃料作为生物质能源的主要利用方式,优化其燃烧性能具有重要意义。在秸秆成型燃料中添加CaO、Ca(OH)2、SiO2、Al2O3、尿素、粉煤灰等常见添加剂,研究了其对SO2、NOx释放规律的影响。研究表明:提高钙硫比且降低含水量,能够降低SO2、NOx释放量。Al2O3的催化助燃作用增加了SO2、NOx的释放,粉煤灰与秸秆熔融烧结增强了异相脱硝。添加SiO2的成型燃料促进了钙硅酸盐复合物的生成,从而减少SO2的释放。通过分析不同SiO2添加量时的燃烧情况发现,添加量5%时,脱硫脱硝效果最好。在成型燃料燃烧15 s后添加尿素,尿素高温热解产生的还原性气体能够与SO2、NOx反应从而减少硫、氮氧化物的释放。温度升高促进熔融反应和异相脱硝反应,阻碍了焦炭中N的燃烧使NOx释放量大幅降低。 相似文献
999.
Yusuke Kashihara Shun Okada Yoshiaki Urahama Shigeki Hikasa Satoshi Makuta Kazuko Fujiwara Syuji Fujii Yoshinobu Nakamura 《应用聚合物科学杂志》2019,136(13):47272
The effects of the tensile test rate on the properties of a pressure-sensitive adhesive (PSA) and of vulcanized rubber were ascertained and compared, using a poly(n-butyl acrylate-acrylic acid) random copolymer with varying degrees of crosslinking as the PSA. The 100% modulus of the PSA was found to increase along with the crosslinking degree and with faster tensile test rates. In contrast, the 100% modulus of the vulcanized rubber did not exhibit any test rate dependence. To assess this effect, the molecular weights between chemical and physical crosslinking points were determined via equilibrium swelling, dynamic mechanical analysis, and tensile tests. The proportion of physical crosslinking points was found to be far larger in the crosslinked PSA. Because these entanglement points can readily disentangle in response to slow deformation, variations in the test rate only affected the PSA. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47272. 相似文献
1000.
Shun J. Wu Lutgard C. De Jonghe Mohamed N. Rahaman 《Journal of the American Ceramic Society》1996,79(8):2207-2211
The sintering of ultrafine γ-Al2 O3 powder (particle size ∼10–20 nm) prepared by an inert gas condensation technique was investigated in air at a constant heating rate of 10°C/min. Qualitatively, the kinetics followed those of transition aluminas prepared by other methods. Measurable shrinkage commenced at ∼ 1000°C and showed a region of rapid sintering between ∼1125° and 1175°C followed by a transition to a much reduced sintering rate at higher temperatures. Starting from an initial density of ∼0.60 relative to the theoretical value, the powder compact reached a relative density of 0.82 after sintering to 1350°C. Compared to compacts prepared from the as-received powder, dispersion of the powder in water prior to compaction produced a drastic change in the microstructural evolution and a significant reduction in the densification rate during sintering. The incorporation of a step involving the rapid heating of the loose powder to ∼1300°C prior to compaction (which resulted in the transformation to α-Al2 O3 ) provided a method for significantly increasing the density during sintering. 相似文献