Core–Shell Structure and Interaction Mechanism of γ‐MnO2 Coated Sulfur for Improved Lithium‐Sulfur Batteries

Lithium‐sulfur batteries have attracted worldwide interest due to their high theoretical capacity of 1672 mAh g^?1 and low cost. However, the practical applications are hampered by capacity decay, mainly attributed to the polysulfide shuttle. Here, the authors have fabricated a solid core–shell γ‐MnO₂‐coated sulfur nanocomposite through the redox reaction between KMnO₄ and MnSO₄. The multifunctional MnO₂ shell facilitates electron and Li⁺ transport as well as efficiently prevents polysulfide dissolution via physical confinement and chemical interaction. Moreover, the γ‐MnO₂ crystallographic form also provides one‐dimensional (1D) tunnels for the Li⁺ incorporation to alleviate insoluble Li₂S₂/Li₂S deposition at high discharge rate. More importantly, the MnO₂ phase transformation to Mn₃O₄ occurs during the redox reaction between polysulfides and γ‐MnO₂ is first thoroughly investigated. The S@γ‐MnO₂ composite exhibits a good capacity retention of 82% after 300 cycles (0.5 C) and a fade rate of 0.07% per cycle over 600 cycles (1 C). The degradation mechanism can probably be elucidated that the decomposition of the surface Mn₃O₄ phase is the cause of polysulfide dissolution. The recent work thus sheds new light on the hitherto unknown surface interaction mechanism and the degradation mechanism of Li‐S cells.     

连续混炼过程比能耗分析

将连续混炼过程的有效比能耗分为升温、混炼、脱挥和建压比能耗,并提出了计算各项的一种方法。用该方法对不同机型、不同规格、不同加工对象的连续混炼机的比能耗进行了分析。结果表明,在多数连续混炼过程中,升温比能耗在总有效比能耗中所占比例都较大,建压比能耗所占比例都很小;原料热物性是影响有效比能耗及其构成的根本因素;当原料和混炼产物质量确定时,连续混炼机的螺杆与机筒结构、螺杆直径、产量、混炼工艺等都会影响有效比能耗及其构成。     

Hybrid Perovskite Light‐Emitting Diodes Based on Perovskite Nanocrystals with Organic–Inorganic Mixed Cations

Organic–inorganic hybrid perovskite materials with mixed cations have demonstrated tremendous advances in photovoltaics recently, by showing a significant enhancement of power conversion efficiency and improved perovskite stability. Inspired by this development, this study presents the facile synthesis of mixed‐cation perovskite nanocrystals based on FA_{(1?x )}Cs_x PbBr₃ (FA = CH(NH₂)₂). By detailed characterization of their morphological, optical, and physicochemical properties, it is found that the emission property of the perovskite, FA_{(1?x )}Cs_x PbBr₃, is significantly dependent on the substitution content of the Cs cations in the perovskite composition. These mixed‐cation perovskites are employed as light emitters in light‐emitting diodes (LEDs). With an optimized composition of FA_0.8Cs_0.2PbBr₃, the LEDs exhibit encouraging performance with a highest reported luminance of 55 005 cd m^?2 and a current efficiency of 10.09 cd A^?1. This work provides important instructions on the future compositional optimization of mixed‐cation perovskite for obtaining high‐performance LEDs. The authors believe this work is a new milestone in the development of bright and efficient perovskite LEDs.     

Chemical-assisted bonding of thermoplastics/elastomer for fabricating microfluidic valves

Thermoplastics such as cyclic olefin copolymer (COC) and polymethylmethacrylate (PMMA) have been increasingly used in fabricating microfluidic devices. However, the state-of-the-art microvalve technology is a polydimethylsiloxane (PDMS)-based three-layer structure. In order to integrate such a valve with a thermoplastics-based microfluidic device, a bonding method for thermoplastics/PDMS must be developed. We report here a method to bond COC with PDMS through surface activation by corona discharge, surface modification using 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), and thermal annealing. The method is also applicable to PMMA. The bonding strength between thermoplastics and PDMS was represented by the peeling force, which was measured using a method established by the International Organization for Standardization (ISO). The bonding strength measurement offered an objective and quantitative indicator for protocol optimization, as well as comparison with other PDMS-associated bonding methods. Using optimized bonding conditions, two valve arrays were fabricated in a COC/PDMS/COC device and cyclic operations of valve closing/opening were successfully demonstrated. The valve-containing devices withstood 100 psi (～689 KPa) without delamination. Further, we integrated such valve arrays in a device for protein separation and demonstrated isoelectric focusing in the presence of valves.     

Dislocation-Induced Precipitation and Its Strengthening of Al–Cu–Li–Mg Alloys with High Mg

Generally, the good combination of pre-deformation and aging can improve the mechanical strength of the Al–Cu–Li–Mg alloys. However, the effects of pre-deformation on competitive precipitation relationship and precipitation strengthening have not been clarified in detail in Al–Cu–Li–Mg alloys with high Mg. In the present study, the effects of pre-deformation level on the microstructure and mechanical properties of an Al–2.95 Cu–1.55 Li–0.57 Mg–0.18 Zr alloy have been investigated. It is found that the introduction of dislocation by 5% pre-deformation can facilitate the precipitation of new successive composite precipitates and T _1 precipitates along the sub-grain boundaries or dislocations and inhibit the precipitation of dispersive GPB zones which is the main precipitates of the alloys without pre-deformation. The introduction of 5% pre-deformation can enhance the mechanical properties considerably. When the pre-deformation level increases from 5 to 15%, the number density of the successive composite precipitates and T _1 precipitates increases, and the aspect ratio of T _1 precipitates decreases. The decrease in T _1 precipitate aspect ratio and the increment of the successive composite precipitates result in the reduction in precipitation strengthening. Therefore, the increase in pre-deformation level from 5 to 15% does not further improve the mechanical properties of the alloys, although the dislocation strengthening increases continuously.     

空调用贮氢合金对的循环效率

制备汽车空调用贮氢合金并研究了操作温度、合金的坪区平直性和滞后程度对合金对循环效率COP值的影响,结果表明:随着高温操作温度的升高COP值先增大后减小,高温操作温度存在最佳工作范围;低温操作温度升高,坪区的平直性系数φ和滞后系数β减小,均有利于得到更高的COP值。     

稀土元素对W型钡铁氧体微波吸收特性的作用

采用化学共沉淀法制备W型钡铁氧体,研究稀土元素Dy、Nd、Pr掺杂对铁氧体微波特性的作用.发现:稀土元素的掺入能有效调整铁氧体的微波电磁参数,使自然共振频率向高频移动,并明显提高试样的高频弛豫特征,同时减小复介电常数,以利于阻抗匹配.在一定范围内增大Dy的掺杂量x,有利于进一步获得低介电损耗和高磁损耗,用数值计算模拟方法得到x=0.05时匹配厚度下铁氧体在2～18GHz范围的反射率曲线:吸收峰值达-52.34dB,吸收率小于-10dB的带宽7.9GHz,结果表明稀土Dy掺杂有利于制备轻、薄铁氧体吸波材料.     

双臂机器人协作空间的解算

双臂机器人能极大的拓展机器人的活动能力,在空间科学领域中得到了越来越多的应用.双臂机器人工作空间的形状边界的精确计算在它的优化设计和应用中非常重要.本文针对一种双臂空间机器人的二维地面实验系统,给出了双臂的运动学模型.依据从关节空间到工作空间的运动学映射,采用蒙特卡洛方法分别建立每只操作臂的工作空间.在此基础上针对机器人双臂工作空间的公共区域即协作空间,采用计算机图形学理论中的射线相交方法加以分析计算,得到了协作空间的几何形状.     

优化催化裂化装置吸收稳定系统回收干气中的丙烯

通过对中国石油化工股份有限公司、中国石油天然气股份有限公司两大公司的70余套催化裂化装置生产数据的分析,发现多数催化裂化装置存在于气中C3 组分含量较高的问题,并提出了解决这一问题的措施.认为通过对催化裂化装置吸收稳定系统的整体优化,采用溴化锂吸收制冷技术,即降低吸收塔操作温度、调整吸收塔操作压力、增加吸收塔和解吸塔的塔盘数等措施,可以有效地降低催化裂化干气中的C3 组分含量,从而增加液化石油气、丙烯的产率.从对中国石油化工股份有限公司的40套催化裂化装置的统计分析看,若采用整体优化措施后,该40套装置总共可以增产98 kt液化石油气和49 kt丙烯,经济效益超过3.5 x108 RMB$.