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排序方式: 共有1013条查询结果,搜索用时 15 毫秒
1.
《Journal of the European Ceramic Society》2019,39(2-3):340-345
The Ca(1+2y)Sn(1-x)Si(1+y)O(5-2x+4y) low-permittivity microwave dielectric ceramics were prepared through solid-state reaction at 1350–1450 °C for 5 h. The relations between microwave dielectric properties and phase compositions for non-stoichiometric Ca(1+2y)Sn(1-x)Si(1+y)O(5-2x+4y) ceramics have been investigated. A single CaSnSiO5 phase with abnormally positive temperature coefficient of resonant frequency (τf = + 62.5 ppm/°C) was synthesised at 1450 °C. This composition was an effective τf compensator of CaSiO3 and Ca3SnSi2O9 phases with typically negative τf value. The CaSiO3 second phase was related to the Sn deficiency in the CaSn(1-x)SiO(5-2x) (0 < x < 1.0) composition, whereas the Ca3SnSi2O9 second phase was obtained by controlling the Ca:Sn:Si ratios on the basis of the Ca(1+2y)SnSi(1+y)O(5+4y) (0 < y < 1.0) composition. A promising low-permittivity millimetre-wave ceramic with most excellent microwave dielectric properties (εr = 10.2, Q×f = 81,000 GHz and τf = −4.8 ppm/°C) was produced from the Ca(1+2y)SnSi(1+y)O(5+4y) (y = 0.4) ceramic. 相似文献
2.
《Journal of power sources》2006,153(2):413-418
Three types of electrically conducting polymers (ECPs), i.e. polyaniline (PANI), polypyrrole (PPy) and poly-(3,4-ethylenedioxythiophene) (PEDOT) have been tested as supercapacitor electrode materials in the form of composites with multiwalled carbon nanotubes (CNTs). The energy storage in such a type of composite combines an electrostatic attraction as well as quick faradaic processes called pseudo-capacitance. It has been shown that carbon nanotubes play the role of a perfect backbone for a homogenous distribution of ECP in the composite. It is well known that pure conducting polymers are mechanically weak, hence, the carbon nanotubes preserve the ECP active material from mechanical changes (shrinkage and breaking) during long cycling. Apart of excellent conducting and mechanical properties, the presence of nanotubes improves also the charge transfer that enables a high charge/discharge rate. For an optimal use of ECPs in electrochemical capacitors, a special electrode composition with ca. 20 wt.% of CNTs and a careful selection of the potential range is necessary. The capacitance values ranging from 100 to 330 F g−1 could be reached for different asymmetric configurations with a capacitor voltage from 0.6 to 1.8 V. It is also noteworthy that such a type of ECP/CNTs composite does not need any binding substance that is an important practical advantage. 相似文献
3.
Sun Zijun He Xiong Liu Jinghua Liu Baosheng Li Hongda Jia Xiaobo Yu Zhiqiang Chang Haixin 《Catalysis Letters》2021,151(11):3135-3144
Catalysis Letters - Hematite (α-Fe2O3) is a potential photoanode material for photoelectrochemical (PEC) water splitting, but its short hole diffusion length and low water oxidation kinetics... 相似文献
4.
综述:板材零件冲锻成形研究进展
王新云,金俊松,邓磊
创新点说明:
1) 按照工艺组合方式,将板冲锻成形分为复合成形方法与板锻成形方法两大类,并将每大类进行细分;
2)基于对板冲锻工艺的发展现状综述,指出高强度模具材料、新型的润滑技术、功能更丰富的智能冲锻设备以及适用于高强钢板冲锻方法是板冲锻工艺未来的发展方向。研究目的:
通过对冲锻工艺进行分类归纳和总结,为从事该领域的研究人员、工程师提供应用参考,指引未来发展方向。
研究方法:
首先按照工艺组合方式的不同,将冲锻工艺进行分类,然后对每一类工艺列举典型的成形方法并进行讨论,包括其工艺特点,优缺点、适用范围、存在的问题等。基于全部的工艺进行归纳总结,指出冲锻工艺领域未来发展方向。
结果:
1) 板冲锻适合制造具有结构单元的板型零件;
2) 相对于传统的锻造或冲压工艺,板冲锻成形中模具压力非常高;
3) 相对于传统的锻造或冲压工艺,摩擦对金属流动影响显著;
4) 相对于传统的锻造或冲压工艺,模具或者设备动作相对复杂;
5)目前,针对高强度材料冲锻成形工艺较少。
结论:
1)冲锻成形工艺是制造具有功能单元板型件的有效方法,按照工艺组合方式的不同可以分为复合成形和板锻成形两大类;
2)板冲锻中,模具承受压力非常大,需要开发更高强度的模具材料来满足工艺的需要;
3) 板冲锻中,摩擦对金属流动影响显著,需要新的润滑技术和材料流动控制技术;
4)板冲锻中,模具动作相对复杂,因此需要能实现更多动作的新型智能设备;
5)随着轻量化的需求,高强度材料应用越来越广,需要开发出适合于高强度材料成形的冲锻工艺。
关键词:
钣金;冲压;锻造;冲锻工艺 相似文献5.
《Journal of the European Ceramic Society》2021,41(14):7375-7379
New generation wireless communication systems require characterisations of dielectric permittivity and loss tangent at microwave and terahertz bands. La2Ti2O7 is a candidate material for microwave application. However, all the reported microwave dielectric data are average value from different directions of a single crystal, which could not reflect its anisotropic nature due to the layered crystal structure. Its dielectric properties at the microwave and terahertz bands in a single crystallographic direction have rarely been reported. In this work, a single crystal ferroelectric La2Ti2O7 was prepared by floating zone method and its dielectric properties were characterized from 1 kHz to 1 THz along one single direction. The decrease in dielectric permittivity with increasing frequency is related to dielectric relaxation from radio frequency to microwave then to terahertz band. The capability of characterizing anisotropic dielectric properties of a single crystal in this work opens the feasibility for its microwave and terahertz applications. 相似文献
6.
Akhtar Farid GUO Shi-ju 《中国有色金属学会会刊》2006,16(3):629-632
Pressureless infiltration process to synthesize Si3N4/Al composite was investigated. Al-2%Mg alloy was infiltrated into Si3N4 and Si3N4 containing 10% Al2O3 preforms in the atmosphere of nitrogen. It is possible to infiltrate Al-2%Mg alloy in Si3N4 and Si3N4 containing 10% Al2O3 preforms. The growth of the dense composite of useful thickness was facilitated by the presence of magnesium powder at the interface and by flowing nitrogen. During infiltration Si3N4 reacted with aluminium to form Si and AIN, the growth of composite was found to proceed in two ways, depending on the Al2O3 content in the initial preform. Firstly, preform without Al2O3 content gives rise to AIN, Al3.27Si0.47 and Al type phases after infiltration. Secondly, perform with 10% Al2O3 content gives rise to AIN-Al2O3 solid solution phase (AION), MgAl2O4, Al and Si type phases. AlON phase was only present in composite, containing 10% Al2O3 in the Si3N4 preforms before infiltration. 相似文献
7.
Bolun Peng Quanqian Lyu Miaomiao Li Shuo Du Jintao Zhu Lianbin Zhang 《Advanced functional materials》2023,33(18):2214045
Solar steam generation (SSG) through hydrogel-based evaporators has shown great promise for freshwater production. However, developing hydrogel-based evaporators with stable SSG performance in high-salinity brines remains challenging. Herein, phase-separated polyzwitterionic hydrogel-based evaporators are presented with sponge-like structures comprising interconnected pores for stable SSG performance, which are fabricated by photopolymerization of sulfobetaine methacrylate (SBMA) in water-dimethyl sulfoxide (DMSO) mixed solvents. It is shown that driven by competitive adsorption, the structures of the resulting poly(sulfobetaine methacrylate) (PSBMA) hydrogels can be readily tuned by the volume ratio of DMSO to achieve phase separation. The optimized phase-separated PSBMA hydrogels, combining the unique anti-polyelectrolyte effects of polyzwitterionic hydrogels, demonstrate a rapid water transport capability in brines. After introducing photothermal polypyrrole particles on the surface of the phase-separated PSBMA hydrogel evaporators, a stable water evaporation rate of ≈2.024 kg m−2 h−1 and high solar-to-vapor efficiency of ≈97.5% in a 3.5 wt.% brine are obtained under simulated solar light irradiation (1.0 kW m−2). Surprisingly, the evaporation rates remain stable even under high-intensity solar irradiation (2.0 kW m−2). It is anticipated that the polyzwitterionic hydrogel evaporators with sponge-like porous structures will contribute to developing SSG technology for high-salinity seawater applications. 相似文献
8.
Potential safety hazards (PSHs) along the track needs to be inspected and evaluated regularly to ensure a safe environment for high-speed railroad operations. Other than track inspection, evaluating potential safety hazards in the nearby areas often requires inspectors to patrol along the track and visually identify potential threads to the train operation. The current visual inspection approach is very time-consuming and may raise safety concerns for the inspectors, especially in remote areas. Using the unmanned aerial vehicle (UAV) has great potential to complement the visual inspection by providing a better view from the top and ease the safety concerns in many cases. This study develops an automatic PSH detection framework named YOLARC (You Only Look at Railroad Coefficients) using UAV imagery for high-speed railroad monitoring. First, YOLARC is equipped with a new backbone having multiple available receptive fields to strengthen the multi-scale representation capability at a granular level and enrich the semantic information in the feature space. Then, the system integrates the abundant semantic features at different high-level layers by a light weighted feature pyramid network (FPN) with multi-scale pyramidal architecture and a Protonet with residual structure to precisely predict the track areas and PSHs. A hazard level evaluation (HLE) method, which calculates the distance between identified PSH and the track, is also developed and integrated for quantifying the hazard level. Experiments conducted on the UAV imagery of high-speed railroad dataset show the proposed system can quickly and effectively turn UAV images into useful information with a high detection rate and processing speed. 相似文献
9.
This study focuses on ways to systematically evaluate stakeholder requirements when developing a smart industrial service ecosystem (SISE) in a complex industrial context. The SISE development requires considering the service requirement from both the complex industrial context and service ecosystem manners. This study proposes a systematic framework for stakeholder requirement evaluation in SISE. The first part of the framework is the industrial context-viable system model with ecological thinking (IC-VESM) to elicit the service requirements for the SISE, which facilitates a systematic analysis of the service value proposition and service requirement elicitation in the operational lifecycle of an entire industrial context. This second part of the framework proposes a method for evaluating service requirements that is both feasible and systematic. This is achieved by combining the Fuzzy Kano and AHP methods in a Pythagorean fuzzy (PF) environment. The PF Kano computes the categories and determines the weights of service requirements from a consumer perspective, while the PF AHP hierarchically analyzes the service requirements and provides pairwise comparison paths for design experts. Finally, an illustrative case study in a renewable energy context was used to demonstrate the feasibility and effectiveness of the methodology. The proposed theoretical model provides more reliable and systematic outcomes than traditional methods when eliciting service requirements and evaluating complex smart industrial service solutions. The study has practical implications by providing useful insights for companies to recognize key smart service requirements in complex industrial contexts and to improve sustainable development. 相似文献
10.
The conventional autonomous cruise and tracking system cannot transition and change its motion mode according to the underwater environment during operation, so it is of great significance to study the multi-mode switching of cruise control for Autonomous Underwater Vehicles (AUVs). In this paper, a Multi-Mode Adaptive Switching (MMAS) strategy for the Spherical Underwater Robot with Hybrid Thruster (HPSUR) was proposed, which provided the possibility for the robot to choose optimal control mode according to the unpredictable operating environment. Then, the dynamic and force of the hybrid thruster are analyzed to improve the accuracy of multi-mode switching, and the MMAS strategy is developed linking the attitude adjustment and switching problems. Furthermore, a series of multi-mode switching experiments were conducted using water-jet mode, propeller mode and hybrid mode. Finally, the experimental result was discussed, which verified the effectiveness and accuracy of the proposed MMAS strategy. The proposed control strategy has a certain reference value for the multi-mode switching of propulsion devices. 相似文献