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11.
《Ceramics International》2016,42(14):15876-15880
The influence of ZnO nanoseeds on the formation of ZnO nanorods from ε-Zn(OH)2 in NaOH solution at 80 °C was investigated, using ZnO nanoparticles with a diameter of 4–10 nm as the seeds. The experimental results indicated that the presence of ZnO nanoseeds promoted the rapid heterogeneous formation of ultrathin ZnO nanorods. Compared with the ZnO submicron rods with a diameter of 0.5–1.0 µm, the ultrathin ZnO nanorods with a diameter of 10–15 nm were found to be more sensitive for detecting NO2 at room temperature owing to their higher variation of channel conduction to the diameter. 相似文献
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Power semiconductors in the wind turbine power converter system suffer from two-scale thermal loadings, the fundamental frequency thermal cycling caused by the output frequency of converter and the low frequency thermal cycling due to the variation of long-term wind speed. These two-scale thermal loadings introduce different consumed lifetimes. Accurate lifetime estimation in the wind power application is desired for reliability prediction and health management. This paper adopts the Bayerer lifetime model to evaluate the consumed lifetime of power semiconductors in wind power converter systems based on a numerical junction temperature calculation method. Lifetime estimation can be improved by taking into account the ambient temperature. Studies show that fluctuations of the ambient temperature increase the consumed lifetime due to the low frequency thermal cycling, but have little effect on the consumed lifetime due to the fundamental frequency thermal cycling. Our results also show that the consumed lifetime due to fundamental frequency thermal cycling mainly falls on the high wind speed area, whereas the consumed lifetime due to low frequency thermal cycling is clustered in the area due to large low frequency junction temperature fluctuations. The resulting distribution characteristics can be used in the thermal management for reliability improvement. 相似文献
13.
Two polymeric hosts PCzTPP and PCzTPPO with twisted geometrical configurations for blue phosphorescent polymer light-emitting diodes (PhPLEDs) were designed and synthesized by incorporating electron-accepting carbazole units with electron-donating TPP/TPPO groups. This molecular design endows PCzTPP and PCzTPPO with high glass transition temperatures of 204 °C and 215 °C, high triplet energies of 2.72 eV and bipolar features. In addition, the HOMO and LUMO of these polymers matched well with the HOMO of the hole-transport layer and the Fermi level of cathode compared with PVK, which facilitated the injection of holes and electrons. PCzTPP- and PCzTPPO-based single-emissive-layer blue PhPLEDs were fabricated with simplified device configuration by solution process using FIrpic as a dopant. These devices exhibited lower turn on voltages (<8 V) than PVK-based devices (12 V). The maximum luminances of PCzTPP- and PCzTPPO-based devices were twofold and threefold that of PVK-based devices, and the maximum current efficiencies were nearly threefold and ninefold, respectively. Moreover, PCzTPPO-based solution processed blue PhPLEDs with improved configuration showed maximum current efficiency and external quantum efficiency of 14.5 cd/A and 6.6%, respectively. 相似文献
14.
Nanoparticle reinforced lead-free solder has previously been studied by several investigators, but few studies have evaluated its reliability. In this study, resistor chip (RC) micro joints were soldered using nano-Al2O3 particle reinforced Sn–Ag–Cu solder paste. The microstructure and reliability of RC micro joints having different nano-Al2O3 contents (0, 0.25, 0.5 and 1.0 wt%) were investigated in detail. More than 40 solder joints for each condition were made and examined in order to achieve reliable data. The results indicated that nano-Al2O3 particles refined the β-Sn grain size and enlarged the eutectic area of the micro solder joints. Those nanoparticles also reduced the IMC thickness of the Ni-solder and Cu-solder interfaces. Those effects can be attributed to the poor-wetting behavior of nano-Al2O3 particles. The nano-Al2O3 reinforcement mainly enhanced the reliability of the micro solder joints, but did not affect the strength of as-soldered joints obviously. The improvement of reliability was proportional to the nano-Al2O3 content. The microstructure and fracture analysis indicated that the reinforcement and stability of Ni-IMC and Cu-IMC interfaces accounted for better reliability. 相似文献
15.
This article is focused on both macro and microvoids in soldered joints and the use of additional flux to reduce their frequency and minimize their negative effect on the soldered joint reliability. In total five fluxes were used, three were gel based (NC559, MTV-125R, TSF-6516) and two of them were liquid based (Topnik G-5, JBC FL-15). They were used within two solder pastes, both lead and lead-free. The reflow process was identical for all of the combinations and was within the range of manufacturer recommended profiles. The amount of voids was evaluated using X-ray analysis. It was found that the use of increased amount of proper flux, specifically flux with higher activity, in the solder paste may significantly lower the void occurrence. 相似文献
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