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1.
针对孔径(100~200)μm高深宽比微细孔电解加工中,电极侧壁绝缘层在电解液冲击和气泡撕裂中易损伤/脱落等问题,提出一种基于丙烯酸环氧树脂双极性电泳法的微细中空电极侧壁绝缘制备工艺。通过工艺参数优化后,利用所制备的侧壁绝缘电极,开展加工对比实验,结果表明双极性电泳法所制备的侧壁绝缘层,具有较高的致密性、均匀性、耐久性和一致性,其性能符合微细电解加工对电极侧壁绝缘层的特殊要求。最后,在500μm厚304钢片上加工出入口约168.4μm、出口约165.8μm、锥度约为0.15°的高深宽比微细孔,其锥度降低了约60%以上,基本为直孔,可满足实际需求,进而验证了本方法的应用可行性。  相似文献   
2.
Hydrogen produced from renewable resources is one of the cleanest fuels and could be used to store intermittent solar, wind and other energies. The main concern about using hydrogen is its hazards, such as high storage pressure, wide-range flammability, low mass density, and high diffusion. This study investigated the hazards of compressed hydrogen storage by developing a CFD model to understand the gas dispersion behaviour. The model was validated using the past experimental data and showed a good agreement, which could demonstrate the diffusion characteristics and gas stratification of a buoyant gas. A case study of an accidental release of compressed hydrogen from a storage tank was investigated to evaluate the risk of a hydrogen plant. A mathematical model of the jet spill was used to account for the choking effect from a high-pressure release to ensure the input velocity in CFD simulation is suitable for modelling gas dispersion using verified spatial and temporal scales, then the simulation results were used as inputs of vapour cloud explosions (VCEs) to investigate the potential overpressure effect. It was found the CFD model could predict a more reasonable flammable gas amount in cloud than using the bulk hydrogen release rate. The safety distance based on the overpressure prediction was reduced by 35%. The method proposed in this study can provide more validity for the consequence analysis as part of risk assessment.  相似文献   
3.
《Ceramics International》2022,48(2):1889-1897
SiC fiber reinforced ceramic matrix composites (SiCf-CMCs) are considered to be one of the most promising materials in the electromagnetic (EM) stealth of aero-engines, which is expected to achieve strong absorption and broad-band performance. Multiscale structural design was applied to SiCf/Si3N4–SiOC composites by construction of micro/nanoscale heterogeneous interfaces and macro double-layer impedance matching structure. SiCf/Si3N4–SiOC composites were fabricated by using SiC fibers with different conductivities and SiOC–Si3N4 matrices with gradient impedance structures to improve impedance matching effectively. Owing to its unique structure, SiCf/Si3N4–SiOC composites (A3-composites) achieved excellent EM wave absorption performance with a minimum reflection coefficient (RCmin) of ?25.1 dB at 2.45 mm and an effective absorption bandwidth (EAB) of 4.0 GHz at 2.85 mm in X-band. Moreover, double-layer SiCf/Si3N4–SiOC with an improved impedance matching structure obtained an RCmin of ?56.9 dB and an EAB of 4.2 GHz at 3.00 mm, which means it can absorb more than 90% of the EM waves in the whole X-band. The RC is less than ?8 dB at 2.6–2.8 mm from RT to 600 °C in the whole X-band, displaying excellent high-temperature absorption performance. The results provide a new design opinion for broad-band EM absorbing SiCf-CMCs at high temperatures.  相似文献   
4.
The influences of the SiC infiltration and coating on the compressive mechanical behaviours of 2D C/SiC composites were determined up to 1600 °C at 0.001 and 1000/s strain rates in argon and air. In addition, the failure mechanisms responsible for the compressive mechanical behaviours were elucidated through in-situ observation and micro-analysis-based methods. The 2D C/SiC composite compressive strength was highly sensitive to temperature, loading rate, and oxidation, and was enhanced by the change in the thermal residual stress and decreased by oxidation. In argon, because of the extra infiltrated SiC matrix, SiC treated 2D C/SiC specimens exhibited higher compressive strengths and lower strain rate sensitivity factors than SiC untreated 2D C/SiC specimens. The SiC coating effectively improved the oxidation resistance of the 2D C/SiC composites in air, regardless of the temperature, strain rate, and oxidative damage-which depends on SiC coating, strain rate, and temperature.  相似文献   
5.
Customizing catalysts from the electronic structure, such as spin state, is an effective but challenging strategy for oxygen evolution reaction (OER). Herein, an ultrafine Co–Fe material highly dispersed on nitrogen carbide matrix is fabricated by coordination polymer and self-templating method to scrutinize the impact of spin state of Co on OER through Fe doping. The optimized catalyst shows boosted OER performance, which only requires overpotential of 333 mV at 10 mA cm?2, outperforming other control samples and commercial RuO2. The elevated local spin states of Co by Fe doping lead to charge transfer acceleration and fast generation of oxygenated intermediates, which is proved to account for the OER elevation. In addition, the long-term stability of Co–Fe material is guaranteed by the strong coordination of Co/Fe to the melamine-formaldehyde resin, which is used to adsorb metal ions, contributing to the high dispersion of active sites during the OER process.  相似文献   
6.
基于深度学习的图像超分辨率算法通常采用递归的方式或参数共享的策略来减少网络参数,这将增加网络的深度,使得运行网络花费大量的时间,从而很难将模型部署到现实生活中。为了解决上述问题,本文设计一种轻量级超分辨率网络,对中间特征的关联性及重要性进行学习,且在重建部分结合高分辨率图像的特征信息。首先,引入层间注意力模块,通过考虑层与层之间的相关性,自适应地分配重要层次特征的权重。其次,使用增强重建模块提取高分辨率图像中更精细的特征信息,以此得到更加清晰的重建图片。通过大量的对比实验表明,本文设计的网络与其他轻量级模型相比,有更小的网络参数量,并且在重建精度和视觉效果上都有一定的提升。  相似文献   
7.
High-quality p-type semiconducting Co3O4 with mixed morphology of nanoparticles/nanorods are synthesized using a hydrothermal route for high response and selective hydrogen sulphide (H2S) sensor application. XRD and Raman studies revealed the crystal structure and molecular bonding for obtained Co3O4, respectively. The nanoparticles/nanorods-like structures were confirmed for Co3O4 using FESEM and TEM analysis. The EDS and XPS spectra analysis were carried out for elemental composition and chemical atomic states of Co3O4. The Co3O4 sensor is investigated for gas sensing properties in dynamic conditions. The sensor exhibited the highest selectivity towards H2S among various hydrogen-contained gases at 225 °C. The sensor revealed a high response of 357% and 44% for 100 and 10 ppm H2S gas concentrations, respectively. The Co3O4 sensor exhibited a systematic dynamic resistance response for 100–10 ppm range H2S gas. The excellent dynamic resistance repeatability of the sensor was shown towards 25 ppm H2S gas. The response of Co3O4 sensor was investigated at different operating temperatures and H2S concentrations. The sensor stability and H2S sensing mechanism for the Co3O4 sensor have been reported. Highly uniform and mixed nanostructures of Co3O4 can be the potential sensor material for real-time high-performance H2S sensor application.  相似文献   
8.
Water electrolysis technologies aim to provide a significant increase in green hydrogen production efficiency. In this work, a framework was developed to explore the use of supercritical water for alkaline electrolysis. This framework was used to perform Arrhenius analysis as a function of potential, and to explore activation energies for sub- and supercritical water electrolysis. An analysis of the conductivity of solution unveiled a discontinuity in the trends between sub- and supercritical potassium hydroxide solution conductivity. Unlike prior work on supercritical water electrolysis, this work investigates trends in electrochemical parameters, the sources of these trends, and how they change between the sub- and supercritical regimes.  相似文献   
9.
建立了高效液相色谱法测定N-甲基-对硝基苯胺含量不确定度评定的数学模型,全面考虑样品在测量过程中的不确定度来源。结果表明,称样量较小时,样品、标样在称量过程中引入的不确定度较大;稀释定容过程中,使用量程较大的移液管和容量较大的容量瓶会降低稀释定容过程中引入的不确定度;提高分析工作者的业务技能也可以降低样品测定的不确定度。当取样量为0.0141g时,测定样品中含有MNA的质量为(7.0±0.5)mg, k=2。  相似文献   
10.
《Ceramics International》2022,48(20):29959-29966
High-purity SiC ceramic devices are applied in semiconductor industry owing to their outstanding properties. Nevertheless, it is difficult to densify SiC ceramics without any sintering additive even by HP sintering. In this work, high-purity and dense SiC ceramics were fabricated by HP sintering with very low amounts of sintering aids. Residual B content was only 556 ppm and relative density was more than 99.5%. Furthermore, thermal conductivity of as-prepared SiC ceramics was improved from 155 W m?1 K?1 to 167 W m?1 K?1 by increasing holding time and their plasma corrosion resistance was promoted in the meantime. The as-prepared high-purity SiC ceramics have broad application prospects in the field of semiconductor industry.  相似文献   
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