Porous nitrogen-enriched hollow carbon nanofibers as freestanding electrode for enhanced lithium storage

One-dimensional porous carbons bearing high surface areas and sufficient heteroatom doped functional-ities are essential for advanced electrochemical energy storage devices, especially for developing free-standing film electrodes. Here we develop a porous, nitrogen-enriched, freestanding hollow carbon nanofiber (PN-FHCF) electrode material via filtration of polypyrrole (PPy) hollow nanofibers formed by in situ self-degraded template-assisted strategy, followed by NH3-assisted carbonization. The PN-FHCF retains the freestanding film morphology that is composed of three-dimensional networks from the entanglement of 1D nanofiber and delivers 3.7-fold increase in specific surface area (592 m2·g-1) com-pared to the carbon without NH3 treatment (FHCF). In spite of the enhanced specific surface area, PN-FHCF still exhibits comparable high content of surface N functionalities (8.8％, atom fraction) to FHCF. Such developed hierarchical porous structure without sacrificing N doping functionalities together enables the achievement of high capacity, high-rate property and good cycling stability when applied as self-supporting anode in lithium-ion batteries, superior to those of FHCF without NH3 treatment.     

Comb-shaped diblock copolystyrene for anion exchange membranes

To improve the properties of diblock copolystyrene-based anion exchange membranes (AEMs), a series of AEMs with comb-shaped quaternary ammonium (QA) architecture (QA-PS_m-b-PDVPPA_n-xC where x denotes the number of carbon atoms in different alkyl tail chains and has values of 1, 4, 8, and 10 and C denotes carbon) were designed and synthesized via subsequent quaternization reactions with three different alkyl halogens (methyl iodide and N-alkane bromines (CH₃[CH₂] _x-1Br where x = 4, 8, and 10). Compared with triblock analogues quaternized with methyl iodide in our previous research, QA-PS_m-b-PDVPPA_n-xC (x = 4, 8, and 10) AEMs are more flexible with the introduction of a long alkyl tail chain; this probably impedes crystallization of the rigid polystyrene-based main chain and induces sterically adjustable ionic association. An increase in the pendant alkyl tail chain length generally led to enhanced microphase separation of the obtained AEMs, and this was confirmed using small-angle X-ray scattering and atomic force microscopy. The highest conductivity (25.5 mS cm⁻¹) was observed for QA-PS₁₂₀-b-PDVPPA₈₀-10C (IEC = 1.94 meq g^–1) at 20 °C. Furthermore, the water uptake (<30%) and swelling ratio (<13.1%) of QA-PS_m-b-PDVPPA_n-xC AEMs are less than half of these corresponding values for their triblock counterparts. The QA-PS₁₂₀-b-PDVPPA₈₀-10C membrane retained a maximum stability that was as high as 86.8% of its initial conductivity after a 40-day test (10 M NaOH, 80 °C), and this was probably because of the steric shielding of the cationic domains that were surrounded by the longest alkyl tail chains. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47370.     

Damage growth-based constitutive model of satin weave composites under different temperatures and strain rates

In this study, a constitutive model, which took into account the temperature and strain rate dependences of progressive damage behavior, was developed to describe the compressive behavior of satin weave carbon/epoxy composites over the temperature range of 298–448 K and strain rate range of 0.001–1100 s⁻¹. To further understand the mechanical behavior of satin weave carbon/epoxy composites, systematic experiments were first conducted using electronic universal testing machine and enhanced split Hopkinson pressure bar (SHPB) system. In addition, the progressive damage mechanism was observed with scanning electron microscope (SEM) and digital image correlation (DIC) technique. Results showed that the modulus and damage growth of composites are temperature and strain rate sensitive. Under quasi-static compression, failure mode changed from shear fracture to kink-band formation with increasing temperature. Samples failed predominantly by delamination under dynamic compression. It is shown that the mechanical behavior of satin weave composites obtained by the constitutive model agrees well with the experimental data over a wide range of temperature and strain rate. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47575.     

Adsorbed O2 on the Graphite‐Induced Growth of Ultra‐Long Single‐Crystalline 6H–SiC Nanowires

Large‐scale ultra‐long 6H–SiC nanowires were in situ synthesized on the as‐prepared SiC–Si ceramic substrate using graphite as the carbon source and substrate as the silicon source via improving the adsorbed O₂ content on the graphite precursors using milling technology. The as‐grown nanowires were typical single crystal of hexagonal 6H–SiC with diameters of 50–100 nm and lengths of up to several millimeters (or even centimeters). Vapor‐solid mechanism was proposed for the growth mode of the as‐grown ultra‐long 6H–SiC nanowires. This study not only provided new insight into the growth mode for in situ synthesizing 6H–SiC nanowires on silicon‐based ceramics, but also suggested a new design methodology for synthesizing ultra‐long nanowires.     

聚己二酸丁二醇酯-共对苯二甲酸酯基可降解塑料改性研究进展

随着人们环保意识的提高,可生物降解塑料逐步取代部分不可降解塑料,将成为一个趋势。目前,聚己二酸丁二醇酯-共对苯二甲酸酯（PBAT）,作为最具商业潜力的可生物降解塑料,具有与低密度聚乙烯相当的延展性和柔韧性,被普遍认为是当代绿色材料制造中最有前途和最受欢迎的可持续材料之一。但PBAT在力学性能、热性能、阻隔性能及生产成本等方面存在不足,其应用范围受到限制。本文旨在系统性地简述近年来PBAT基复合材料的制备方法、回顾国内外研究人员在PBAT力学性能和阻隔性能等提升方面所做的工作、并详细介绍和讨论PBAT的降解原理和降解所带来的环境风险。开发低成本综合性能优异,兼顾良好降解性、抑菌性和耐久性能的PBAT基复合材料,应当予以重视和进一步研究。     

合金化元素Ti对Laves相Cr_2Nb力学性能及耐蚀性的影响

采用真空非自耗电弧熔炼工艺制备了Cr2Nb-XTi(X=5,10,15,at%)合金,利用光学显微镜(OM),X射线衍射(XRD)仪,扫描电镜(SEM)对电弧熔炼态铸锭的组织进行了研究,探讨了合金化元素Ti的含量对Laves相Cr2Nb力学性能及耐蚀性的影响。结果表明:3种成分的电弧熔炼态合金凝固组织主要由C15-Cr2(Nb,Ti)相和六方的β-(Ti,Nb)以及体心立方结构的β-(Nb,Ti)相组成。在5Ti和10Ti合金冷速较小的铸锭上部凝固组织中出现了亚稳相C14-Cr2(Nb,Ti)。通过对合金力学性能研究表明,随合金化元素Ti含量的增加,Laves相Cr2Nb合金的显微硬度逐渐降低,断裂韧性增大,当Ti含量达到15at%时,合金的断裂韧性达到了3.1 MPa·m1/2,比单相Laves相Cr2Nb提高1倍。另外,对腐蚀性能的测试表明,Ti含量增加材料腐蚀性能下降,但15Ti合金仍表现出良好的耐蚀性。     

MEMS谐振器刚度非线性特性及其表征

为了准确表征微电子机械系统(MEMS)谐振器在大振幅运动时的行为特性,建立了刚度非线性MEMS谐振器集总参数模型,并创建了一整套MEMS谐振器非线性特性的表征方法和测试系统。搭建了基于锁相环和自动增益控制的MEMS谐振器闭环工作电路,分析了不同驱动振幅下,MEMS谐振器的工作状态。推导建立了工作振幅、工作频率与MEMS谐振器刚度非线性之间的数量关系。最后,基于衰减模式和稳定振荡模式两种工作形态,实际测量了MEMS谐振器的无阻尼自然谐振频率和刚度非线性。结果显示:无阻尼自然谐振频率和刚度非线性系数的测量重复性分别为18.6×10-6和1.50%。针对实测的MEMS谐振器无激励振幅自衰减曲线,分别用理想二阶系统谐振器模型和刚度非线性谐振器模型进行残差分析。结果显示后者的残差要比前者的残差小9.5%,表明刚度非线性MEMS谐振器模型更接近真实情况,也验证了该刚度非线性特性表征方法的准确性。基于该方法,测量了MEMS谐振器刚度非线性系数和无阻尼自然谐振频率的温度特性,得到的无阻尼自然谐振频率的温度系数为-0.487Hz/℃,线性拟合度达99.964%。     

空水共用涡轮机气动设计与数值仿真

跨介质航行器是一种具备远程快速打击、重复出入水以及高效突防能力的新概念航行器,而其中涡轮发动机在跨介质航行器不同航行阶段的工作参数差别很大。为解决水下、空中及起飞工况下的空水共用涡轮机的气动设计,结合损失模型的方法提出一种空水共用涡轮机设计方法,通过数值仿真方法验证气动设计方法的合理性以及起飞工况的可行性。研究结果表明：在不同工况下,数值仿真结果与一维气动设计结果的相对误差均在2%以内;使用数值损失分解方法进一步分析了涡轮机的各部分损失,发现叶型损失为空水共用涡轮机的主要损失;水下工况时流场内存在激波和分离涡,部分进气度很小,损失较大;空中工况则流动更为均匀,损失较小;起飞工况时涡轮机工作在非设计点,此时主要依靠水下喷管做功,空中喷管则会产生负功率。该方法可为空水共用涡轮机的优化设计和试验提供参考。     

一款应用于多通道CZT探测器的12-bit 1MS/s SAR-ADC芯片

本文提出了一种应用于多通道CZT探测器低功耗、小面积、抗辐照12位1MS/s逐次逼近模数转换器芯片。为了提高SAR-ADC的精度,提出了一种新型比较器,该比较器能够实现失调电压自校准功能。同时为了减少电荷分配DAC中电容失配的问题,提出了分散式电容阵列。通过电路级和版图级技术加固,提高该SAR-ADC芯片的抗辐照能力。原型芯片采用TSMC 0.35um 2P4M CMOS工艺。电源电压为3.3V和5V,采样率是1MS/s。该SAR-ADC芯片能够实现高达67.64dB的信纳比SINAD,然而仅消耗10mWz功耗。该芯片核心面积为1180um×1080um。