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排序方式: 共有3147条查询结果,搜索用时 15 毫秒
31.
Fanqin Meng Steven F. Dec Don Williamson Phat Pham Michael A. Yandrasits Andrew M. Herring 《Electrochimica acta》2007,53(3):1372-1378
A perfluorosulfonic acid (PFSA) polymer with pendant side chain -O(CF2)4SO3H was doped with the heteropoly acids (HPAs), H3PW12O40 and H4SiW12O40. Infrared spectroscopy revealed a strong interaction between the HPA and the PFSA ionomer. Modes associated with the peripheral bonds of the HPA were shifted to lower wave numbers when doped into PFSA membranes. Small-angle X-ray scattering (SAXS) measurements showed the presence of large crystallites of HPA in the membrane with d spacings of ca. 10 Å, close to the lattice spacing observed in bulk HPA crystals. Under wet conditions the HPA was more dispersed and constrained the size of the sulfonic acid clusters to 20 Å at a 5 wt% HPA doping level, the same as in the vacuum treated ionomer samples. Under conditions of minimum hydration the HPA decreased the Ea for the self-diffusion of water from 27 to 15 kJ mol−1. The reverse trend was seen under 100% RH conditions. Proton conductivity measurements showed improved proton conductivity of the HPA doped PFSAs at a constant dew point of 80 °C for all temperatures up to 120 °C and at all relative hummidities up to 80%. The activation energy for proton conduction generally was lower than for the undoped materials at RH ≤80%. Significantly the Ea was 1/2 that of the undoped material at RHs of 40 and 60%. A practical proton conductivity of 113 mS cm−1 was observed at 100 °C and 80% RH. 相似文献
32.
The catalytic activities of WCI6Ph4Sn, MoCl5Ph4Sn and tetrabenzyltitanium were examined in the polymerization of acetylene. The structure, morphology and electrical conductivity of the doped and non doped polyacetylene were also studied. 相似文献
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The time dependences of electrical conduction and self‐heating behaviors in high‐density polyethylene filled with acetylene carbon black of 0.082 in volume fraction are studied in relation to voltage and ambient temperature. The characteristic decay current constant τi, and the exponential growth time constant for self‐heating τg are determined for the samples under voltages U above the critical value Uc for the onset of self‐heating. The influences of voltage and ambient temperature on τi and τg as well as the amplitude of the low‐resistance to high‐resistance switching are discussed on the basis of the random resistor network (RRN) model and the relationship between Uc and the intrinsic resistivity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1124–1131, 2006 相似文献
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转化乳剂的离子电导和光电导研究 总被引:1,自引:0,他引:1
本文研究了AgBrCl转化乳剂的离子电导和光电导。随着乳剂中溴含量的增高,其离子电导也随之升高,而光电子寿命则降低。AgBrCl乳剂的离子电导主要取决于其组成;AgBrCl转化乳剂的光电子寿命主要受隙间银子浓度的影响,隙间银离子浓度越大,光电子寿命越短。 相似文献
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采用超声氧化剥离法制备氧化石墨烯(GO),通过浸轧法将GO溶液整理到棉织物上,经过烘干、还原得到还原氧化石墨烯(RGO)整理棉织物。探讨了GO浓度,GO溶液pH、还原条件、浸轧-还原次数等因素对RGO整理棉织物导电性能的影响,采用SEM和Raman光谱对整理棉织物进行表征。研究结果表明,当GO溶液pH=6,质量浓度2.5 g/L,采用质量浓度5 g/L的保险粉于90 ℃对浸轧GO烘干后的棉织物还原30 min,整理棉织物的表面电阻值降低至2220 Ω,经过4次和8次浸轧-还原后棉织物表面电阻值可降低至270 Ω和130 Ω。通过SEM发现RGO能在棉纤维表面形成薄膜并包覆纤维,且随着浸轧-还原次数的增加,棉织物表面沉积的RGO逐渐增多。Raman光谱较好地证实了GO在棉织物表面的沉积,且GO较充分地还原成RGO。通过对整理棉织物的耐洗性能测试发现整理织物的导电耐久性较好。 相似文献
40.
Combustion characteristics and flame stability at the microscale: a CFD study of premixed methane/air mixtures 总被引:1,自引:0,他引:1
D.G. Norton 《Chemical engineering science》2003,58(21):4871-4882
A two-dimensional elliptic, computational fluid dynamics (CFD) model of a microburner is solved to study the effects of microburner dimensions, conductivity and thickness of wall materials, external heat losses, and operating conditions on combustion characteristics and flame stability. We have found that the wall conductivity and thickness are very important as they determine the upstream heat transfer, which is necessary for flame ignition and stability, and the material's integrity by controlling the existence of hot spots. Two modes of flame extinction occur: a spatially global type for large wall thermal conductivities and/or low flow velocities and blowout. It is shown that there exists a narrow range of flow velocities that permit sustained combustion within a microburner. Large transverse and axial gradients are observed even at these small scales under certain conditions. Periodic oscillations are observed near extinction in cases of high heat loss. Engineering maps that delineate flame stability, extinction, and blowout are constructed. Design recommendations are finally made. 相似文献