Mechanical activation-assisted electro-thermal explosion synthesis of the Ti2AlC phase

This study deals with the synthesis of the Ti₂AlC phase using the Electro-Thermal Explosion under Pressure with Confinement (ETEPC) technique. The effects of the ETEPC technique and the milling process parameters on the TiC_x phase content and the formation mechanism of the Ti₂AlC phase were investigated. The latter is mainly affected by the morphology of the powder mixture and aluminum melted amount. The optimization of the above parameters allowed the achievement of the desired reaction, leading to the formation of the Ti₂AlC phase with a purity of about 97?wt%. The results clearly demonstrate that the ETEPC process enables one to control both time and material synthesis temperature.     

Dynamic response of Kevlar®29/epoxy laminates under projectile impact-experimental investigation

This authors of this article investigated the dynamic response of woven Kevlar®29/epoxy laminates subjected to the impact loading. The cylindrical aluminum foam projectile and steel projectile were used to exert the impulse on the laminates. Deformation/failure modes, deflections, strain histories, and failure mechanisms were obtained and discussed. The results showed that with the high toughness of Kevlar fiber, the deformation modes of the laminates exhibited some characteristics similar to the metal panel, such as large global deformation. The failure mechanisms like matrix failure, fiber splitting, and fibrillation were observed. These micron failures led to the macroscopic delamination and fracture of the laminates.     

A Novel and Facile Route to Synthesize Atomic‐Layered MoS2 Film for Large‐Area Electronics

High‐quality and large‐area molybdenum disulfide (MoS₂) thin film is highly desirable for applications in large‐area electronics. However, there remains a challenge in attaining MoS₂ film of reasonable crystallinity due to the absence of appropriate choice and control of precursors, as well as choice of suitable growth substrates. Herein, a novel and facile route is reported for synthesizing few‐layered MoS₂ film with new precursors via chemical vapor deposition. Prior to growth, an aqueous solution of sodium molybdate as the molybdenum precursor is spun onto the growth substrate and dimethyl disulfide as the liquid sulfur precursor is supplied with a bubbling system during growth. To supplement the limiting effect of Mo (sodium molybdate), a supplementary Mo is supplied by dissolving molybdenum hexacarbonyl (Mo(CO)₆) in the liquid sulfur precursor delivered by the bubbler. By precisely controlling the amounts of precursors and hydrogen flow, full coverage of MoS₂ film is readily achievable in 20 min. Large‐area MoS₂ field effect transistors (FETs) fabricated with a conventional photolithography have a carrier mobility as high as 18.9 cm² V^?1 s^?1, which is the highest reported for bottom‐gated MoS₂‐FETs fabricated via photolithography with an on/off ratio of ≈10⁵ at room temperature.     

Advanced Nanostructured Anode Materials for Sodium‐Ion Batteries

Sodium–ion batteries (NIBs), due to the advantages of low cost and relatively high safety, have attracted widespread attention all over the world, making them a promising candidate for large‐scale energy storage systems. However, the inherent lower energy density to lithium–ion batteries is the issue that should be further investigated and optimized. Toward the grid‐level energy storage applications, designing and discovering appropriate anode materials for NIBs are of great concern. Although many efforts on the improvements and innovations are achieved, several challenges still limit the current requirements of the large‐scale application, including low energy/power densities, moderate cycle performance, and the low initial Coulombic efficiency. Advanced nanostructured strategies for anode materials can significantly improve ion or electron transport kinetic performance enhancing the electrochemical properties of battery systems. Herein, this Review intends to provide a comprehensive summary on the progress of nanostructured anode materials for NIBs, where representative examples and corresponding storage mechanisms are discussed. Meanwhile, the potential directions to obtain high‐performance anode materials of NIBs are also proposed, which provide references for the further development of advanced anode materials for NIBs.     

Revolving Vernier Mechanism Controls Size of Linear Homomultimer

A new kind of the Vernier mechanism that is able to control the size of linear assembly of DNA origami nanostructures is proposed. The mechanism is realized by mechanical design of DNA origami, which consists of a hollow cylinder and a rotatable shaft in it connected through the same scaffold. This nanostructure stacks with each other by the shape complementarity at its top and bottom surfaces of the cylinder, while the number of stacking is limited by twisting angle of the shaft. Experiments have shown that the size distribution of multimeric assembly of the origami depends on the twisting angle of the shaft; the average lengths of the multimer are decamer, hexamer, and tetramer for 0°, 10°, and 20° twist, respectively. In summary, it is possible to affect the number of polymerization by adjusting the precise shape and movability of a molecular structure.     

Fatigue Crack Growth and Fracture of 30 wt% B4C/6061Al Composites

This paper focuses on studying the fatigue crack growth (FCG) characteristics and fracture behaviours of 30 wt% B₄C/6061Al composites fabricated by using powder metallurgy and hot extrusion method. Compact tension (CT) specimens having incisions parallel to the extrusion direction (T‐D) and perpendicular to the extrusion direction (E‐D) were investigated through FCG tests. Results show that, at low/medium stress‐intensity factor range levels (ΔK ≤ 9), crack propagation rate in E‐D specimens is lower than that in T‐D specimens because the elongated B₄C particles parallel to the extrusion direction in E‐D specimens can deflect the crack. The scanning electron microscope micrographs of the fractured surface illustrate that crack mainly propagates in the matrix alloy at the initial stage of its propagation and propagates more remarkably near the particle‐matrix interface with the increase of ΔK value. B₄C particles are also found to be easy to fracture during the rapid crack propagation. Based on fracture analyses, considering the impacts of factors like crack deviation, plastic zone size at the crack tip, and crack driving force, a 2‐D crack propagation model was developed to study the fatigue crack propagation mechanism in the 30 wt% B₄C/6061Al composite.     

接触触发式探头结构优化设计

设计了一种适用于微纳米三坐标测量机的高灵敏度接触触发式探头。介绍了该探头的结构和原理,建立了探头的灵敏度模型和刚度模型,依据三维方向等灵敏度和等刚度的原则,利用最优化方法得出了探头结构参数的最优解。对探头的刚度进行了仿真验证;分别对探头的刚度、分辨率以及稳定性进行了实验测试。实验结果表明:该探头在三维方向上的刚度均小于1 mN/μm,且近似相等;分辨率高于50 nm;当环境温度的波动范围小于±0.025℃时,探头在1.3 h内的漂移量为20nm。     

聚丙烯发泡珠粒的结晶熔融行为与发泡特性

以CO_2为发泡剂,用高压釜式法制备了发泡聚丙烯(EPP)珠粒。采用差示扫描量热仪和扫描电子显微镜探讨了发泡温度(T_f)和发泡压力(p_f)对EPP结晶熔融行为和发泡特性的影响。结果表明,分别提高发泡温度或压力,EPP的熔融双峰均向高温方向移动,低温晶体与高温晶体的结晶度之比增大,而且温度对双峰的影响比压力更敏感。p_f在2~4 MPa内,EPP的发泡倍率和泡孔密度随p_f增大而增大;T_f在133.6~140℃间,发泡倍率和泡孔尺寸随T_f升高而变大,泡孔密度随T_f升高而变小。在T_f为133.6℃,pf为4 MPa时,EPP的熔融双峰结构比例合适,发泡倍率较大,泡孔密度最大且尺寸分布均匀、表面光滑。     

含磷腈环氧树脂阻燃和热解动力学

采用热重(TG)和微商热重(DTG)实验分析技术,分别对自制的六-对氨基苯氧基环三磷腈(PNH)和4,4’-二氨基二苯甲烷(DMA)为E51型环氧树脂的固化剂,研究了在氮气和空气氛围中2种环氧树脂的阻燃特性和热解动力学;运用Achar法和Coats-Redfern法建立了二者的热裂解动力学模型,得到了2种体系的动力学表观活化能和指前因子。研究表明,与不含磷环氧树脂相比,磷腈固化的环氧树脂更易发生热裂解,而在高温阶段却明显具有阻燃特性;磷腈固化的环氧树脂裂解后期残炭量较高,其活化能与其阻燃机理有关:即表观活化能越大阻燃性越强。     

新型自润滑YBa_2Cu_3O_7/Cu复合材料的制备及性能

采用草酸盐共沉淀法制备了YBa2Cu3O7(YBCO)粉体,利用真空热压烧结法制备了不同质量分数的YBCO/Cu复合材料,测定了YBCO/Cu复合材料的密度、硬度和电导率,利用MMU-5GA磨损试验机对YBCO/Cu复合材料进行了摩擦磨损试验。采用XRD、SEM和TEM对YBCO粉体及YBCO/Cu复合材料的微观结构、磨损表面形貌及物相组成进行了表征。研究了YBCO质量分数对YBCO/Cu复合材料组织及性能的影响。结果表明:所制备的YBCO粉体物相为Y123相,其层状结构明显,粉体纯度高、杂质少,粒度达到纳米级;纳米YBCO可显著细化YBCO/Cu复合材料的基体组织,提高复合材料的摩擦学性能。随着YBCO质量分数增加,基体组织中纳米YBCO颗粒分布均匀度降低,逐渐出现团聚;YBCO/Cu复合材料的电导率和密度降低,硬度先升高后降低,摩擦系数逐渐减小。3%YBCO/Cu复合材料的摩擦磨损性能最好。YBCO/Cu复合材料强化机制为Orowan强化、热错配强化和细晶强化;其磨损机制主要为塑变磨损、磨粒磨损和疲劳剥落。