金属纳米线中凸凹微结构对初始形变的影响

构建了具有代表性的系列凸纳米线和凹纳米线,利用分子动力学模拟研究了2种微结构对拉伸形变的影响.结果表明,微凸纳米线与单晶纳米线表现出类似的行为,其能量和应力应变曲线等均无显著差异.改变不同的凸起高度未发现显著差别.沿z轴的应力分布分析表明凸微结构使局域应力降低,不能诱导产生初始位错滑移;微凹纳米线表现更明显的塑性形变特征,小应变时能量上升的幅度低于单晶和凸纳米线,但大应变条件下能量上升更高,微凹纳米线的第一屈服点早于单晶和凸纳米线,且其屈服应力不是最大应力,沿z轴的应力分布表明凹陷处产生增加的局域应力,凹陷附近可以诱导产生初始位错滑移.原子排布位图从微观上进一步阐述了上述形变特征.     

利用傅立叶变换研究铜双晶纳米线的断裂行为

利用超大规模分子动力学模拟程序研究了[111]||[110]双晶铜纳米线的拉伸断裂行为. 针对样品的周期性结构, 开发了离散傅立叶变换进行晶体特征分析的技术. 通过转换实空间的原子密度分布函数, 得到振幅-频率图和归一化的长轴原子密度分布图. 这两种处理方法提供了晶体取向和结晶状态的信息, 其中振幅-频率图适合描述大范围的晶体特征, 而归一化长轴的原子密度分布则反映了局部的细节. 利用该方法, 考察了不同拉伸时刻[111]||[110]双晶铜材料的晶体取向和结晶状态. 在拉伸过程中, 从振幅-频率图可以观察到4.78 nm-1处的[111]特征峰和7.81 nm-1处的[110]特征峰发生了低频移动和峰形变宽的现象; 同时在断裂时刻观察到了5.50 nm-1处的[100]特征峰. 证明[111]||[110]铜双晶纳米线在拉伸形变过程中发生了界面融合, 同时界面层原子向[100]晶向的转变, 最终导致了双晶纳米线在[111]晶向一侧断裂. 傅立叶变换晶体分析技术在纳米材料和器件的研究中可以发挥积极的作用.     

不同孪晶界密度银纳米线拉伸形变行为的分子动力学模拟

采用分子动力学方法模拟了不同孪晶界密度银纳米线的拉伸形变行为, 分析了孪晶界密度对多晶银纳米线屈服强度、弹性模量和塑性变形机理的影响. 在弹性形变区域, 孪晶界的存在对杨氏模量变化的作用不明显. 在塑性形变阶段, 首先从表面边缘开始产生位错成核, 然后延伸并受阻于孪晶界. 在进一步拉伸载荷作用下, 孪晶界将作为位错源产生新的位错. 模拟结果表明, 银纳米线的强度与孪晶界和晶粒的尺寸有关. 孪晶界密度较小(即晶粒的长径比大于1)时, 此纳米线的屈服应力比单晶纳米线还要小, 只有当孪晶界密度较大时(即晶粒的长径比小于1), 孪晶界使得纳米线得到强化. 综合分析了孪晶界和晶粒尺寸对银纳米线的影响, 为构建高强度金属纳米线打下基础. 最后讨论了温度和拉伸速度对孪晶纳米线屈服应力所产生的影响, 随着温度的升高, 孪晶纳米线与单晶纳米线的屈服应力差先升高后趋于稳定; 当拉伸速度逐渐增大, 孪晶纳米线与单晶纳米线的屈服应力差先稳定后增大.     

不同孪晶界密度银纳米线拉伸形变行为的分子动力学模拟

采用分子动力学方法模拟了不同孪晶界密度银纳米线的拉伸形变行为,分析了孪晶界密度对多晶银纳米线屈服强度、弹性模量和塑性变形机理的影响.在弹性形变区域,孪晶界的存在对杨氏模量变化的作用不明显.在塑性形变阶段,首先从表面边缘开始产生位错成核,然后延伸并受阻于孪晶界.在进一步拉伸载荷作用下,孪晶界将作为位错源产生新的位错.模拟结果表明,银纳米线的强度与孪晶界和晶粒的尺寸有关.孪晶界密度较小(即晶粒的长径比大于1)时,此纳米线的屈服应力比单晶纳米线还要小,只有当孪晶界密度较大时(即晶粒的长径比小于1),孪晶界使得纳米线得到强化.综合分析了孪晶界和晶粒尺寸对银纳米线的影响,为构建高强度金属纳米线打下基础.最后讨论了温度和拉伸速度对孪晶纳米线屈服应力所产生的影响,随着温度的升高,孪晶纳米线与单晶纳米线的屈服应力差先升高后趋于稳定;当拉伸速度逐渐增大,孪晶纳米线与单晶纳米线的屈服应力差先稳定后增大.     

DFT法研究离子液中EMIM~ 催化丁烯双键异构反应机理(II)

用密度泛函理论(DFT)在B3LYP/6鄄31G(d,p)的计算水平上研究了离子液中1鄄乙基鄄3鄄甲基咪唑阳离子(EMIM )的4鄄H和5鄄H原子催化丁烯双键异构反应的可能途径,优化了反应体系的平衡态和过渡态的几何构型,分析了反应过程中键参数的变化,通过振动分析对平衡态和过渡态进行了验证.计算结果表明,离子液中的EMIM 首先通过4鄄H和5鄄H原子吸附丁烯,进而催化丁烯的双键异构反应,EMIM 的4鄄H和5鄄H催化1鄄丁烯异构为2鄄丁烯的正反应活化能分别为204.2和207.3kJ·mol-1,逆反应活化能约为220.9和223.8kJ·mol-1,反应为基元反应.     

银负载量对网状TiO_2柔性薄膜电极储锂性能的影响

采用水热法结合银镜反应制备出一系列不同Ag负载量(2.2%、4.0%、6.4%,w/w)改性的3D纳米网状结构Ag@Ti O2薄膜电极。利用电感耦合等离子体技术(ICP)、X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和X射线能谱(EDX)等表征手段测试所合成材料的形貌及成分,实验结果表明Ag纳米颗粒可以成功沉积在Ti O2纳米线表面。电化学测试数据则表明,4.0%(w/w)负载量的Ag@Ti O2相比于未改性和其他负载量的Ti O2纳米线具有更好的倍率性能和更稳定的可逆容量。在50,100,200,400,800和1 200 m A·g~(-1)的电流密度条件下,该改性电极的放电容量可分别达到261.4,253.7,239.5,216.5,193.1和185.1 m Ah·g~(-1),在200 m A·g~(-1)下循环80次后容量保持率仍能达到99.8%。     

CdSe纳米线阵列的制备及其表征(英)

通过在含有SeSO₃^2-和Cd²⁺的室温水溶液中，用模板-电沉积法在纳米孔阵列阳极氧化铝膜(AAM)模板中制备了高有序性的CdSe纳米线阵列，并对其形貌、结构和组分进行了表征。扫描电子显微镜(SEM)和透射电子显微镜(TEM)结果表明，纳米线阵列中的CdSe纳米线具有相同的长度和直径，分别对应于使用的AAM模板的厚度和孔径；X-射线衍射(XRD)和X-射线能谱(EDAX)结果表明，CdSe纳米线中Cd和Se的化学组成非常接近于1∶1，其结构为立方CdSe。另外，对模板-电沉积法制备CdSe纳米线的机理进行了讨论。     

W(100)c(2×2)表面的STM图像

用基于第一性原理的密度泛函理论研究了W(100)c(2×2)再构表面的表面弛豫以及扫描隧道显微镜(STM)图像和衬底偏压的关系.计算所得到的表面原子沿[110]方向的畸变位移δ为0.027nm,畸变能△E为80.6meV·atom-1,表面原子的弛豫分别为-7.6%(△d12/d0)和 0.8%(△d23/d0),功函数Φ为4.55eV.STM图像模拟表明,由于表面原子沿[110]方向的位移,会导致出现平行于[110]方向的亮暗带状条纹.STM图像中突起所对应的并不是表面或次表面的钨原子,而是zig-zag型W原子链中线位置;而STM暗区对应于原子位置畸变形成的相邻zig-zag型W原子链中间区域.当衬底负偏压时,STM针尖典型起伏高度大约在0.008-0.013nm之间;而当衬底正偏压时,针尖起伏高度在0.019-0.024nm之间变化.     

碳化硼纳米线的制备和结构

以碳纳米管为模板，通过加热碳纳米管与硼粉的混合物，获得了笔直的硼碳纳米线.对纳米线的结构和成分进行研究，结果表明纳米线主要为B4C纳米线.在部分B4C纳米线的端部存在Ni颗粒，这些端部具有Ni颗粒的纳米线构成了纳米磁针.讨论了B4C纳米线的生长机制，B4C纳米线的生长主要为硼原子在碳纳米管中扩散并发生化学反应，使得碳纳米管晶格结构发生重组，形成B4C纳米线.反应后，硼原子部分取代了碳纳米管中碳原子，修补了碳纳米管中的晶格缺陷，获得了形态笔直的B4C纳米线.     

基于宏观金属辅助化学刻蚀制备硅纳米线的研究

分别利用镀银的硅衬底和铂丝电极作为原电池反应中的阴极和阳极,基于金属辅助化学刻蚀采用宏观原电池的方法制备硅纳米线,深入研究了该法制备硅纳米线阵列的机理。通过改变电连接、镀银、刻蚀参数、硅衬底和光照等实验条件,系统地研究了所得硅纳米线形貌与其对应短路电流的关系,实验发现短路电流与硅纳米线长度有一定的对应关系。文章中所提出的模型旨在从根本上解决金属辅助化学刻蚀制备硅纳米线的机理。最后对这种方法所具有的潜在应用价值进行了展望和讨论。     

Preparation of [18F]fluoromisonidazole by nucleophilic substitution on THP-protected precursor: Yield dependence on reaction parameters

The dependence of the radiochemical yield of [¹⁸F]fluoromisonidazole (1) on different reaction parameters such as reaction time, temperature and amount of precursor was investigated for the nucleophilic substitution of tosylate by [¹⁸F]fluoride and subsequent hydrolysis of the protecting group on 1-(2′-nitro-1′-imidazolyl)-2-O-tetrahydropyranyl-3-O-toluenesulfonylpropanediol as the precursor molecule (2). Highest yields (86%±6%) were obtained using 10 mg (2) at 100°C for 10 minutes, whereas both at 80 and 120°C the yields were lower (46%±11% and 29%±14%, respectively). A rapid decrease of the yield was observed when the reaction time exceeded 15 minutes, i.e., at 100°C using 5 mg (2) the radiochemical yield decreased from 61%±8% at 15 minutes to 18%±10% at 60 minutes.     

Experimental investigation and modeling of the mechanical behavior of PC/ABS during monotonic and cyclic loading

The purpose of this work is to characterize the mechanical behavior of blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) during monotonic and cyclic loading. Compression experiments were performed using a SHIMADZU universal testing machine (10⁻⁴ to 10⁻² s⁻¹) and a split Hopkinson pressure bar (1600–5000 s⁻¹), with, the test temperatures ranging from 293 to 353 K. The influence of the rate and temperature on the deformation of PC/ABS is discussed in detail. Based on the investigation of numerous constitutive models, a phenomenological model called DSGZ was chosen to describe the compression behavior of PC/ABS. This model could not accurately reproduce the deformation of polymers at high strain rates when utilizing the same material coefficients for the low and high strain–rate deformations. In addition, this model was unable to capture the deformation features during unloading and subsequent reloading when adopting the original stress–strain updating algorithm. Hence, some improvements to the model have been implemented to better predict the deformation. Finally, the model predictions are shown to be consistent with the experimental results.     

高铝沸石的钙离子交换动力学研究

由于含磷洗涤剂的使用所带来的环境危害日益严重，高铝沸石作为洗涤剂助剂三聚磷酸钠的替代品已获得广泛的应用。作为洗涤剂助剂，沸石的Ca２＋、Mg２＋离子交换性能是影响其助洗效果的主要因素之一犤１，２犦。但目前对沸石的离子交换性质的研究多集中在离子交换平衡等温线的研究犤３～６犦，涉及沸石离子交换动力学的研究却鲜有报道。作为硬水的软化剂，洗涤剂用沸石对Ca２＋、Mg２＋离子的交换速率大小对洗涤效果的意义更为重要犤１犦。沸石的离子交换过程包括离子由溶液中扩散到沸石表面，再由沸石表面扩散到沸石孔道中的离子位等步骤…     

Cultivating <Emphasis Type="BoldItalic">Chlorella</Emphasis> sp. in a Pilot-Scale Photobioreactor Using Centrate Wastewater for Microalgae Biomass Production and Wastewater Nutrient Removal

This study is concerned with a novel mass microalgae production system which, for the first time, uses “centrate”, a concentrated wastewater stream, to produce microalgal biomass for energy production. Centrate contains a high level of nutrients that support algal growth. The objective of this study was to investigate the growth characteristics of a locally isolated microalgae strain Chlorella sp. in centrate and its ability to remove nutrients from centrate. A pilot-scale photobioreactor (PBR) was constructed at a local wastewater treatment plant. The system was tested under different harvesting rates and exogenous CO₂ levels with the local strain of Chlorella sp. Under low light conditions (25 μmol·m^-2s^-1) the system can produce 34.6 and 17.7 g·m^-2day^-1 biomass in terms of total suspended solids and volatile suspended solids, respectively. At a one fourth harvesting rate, reduction of chemical oxygen demand, total Kjeldahl nitrogen, and soluble total phosphorus were 70%, 61%, and 61%, respectively. The addition of CO₂ to the system did not exhibit a positive effect on biomass productivity or nutrient removal in centrate which is an organic carbon rich medium. The unique PBR system is highly scalable and provides a great opportunity for biomass production coupled with wastewater treatment.     

基于生物质的高度有序的管状碳材料及其在锂硫电池中的应用

将棕榈纤维经过炭化和氢氧化钾活化制备高度有序的管状碳材料(OCT),并且将其应用于锂硫电池。所制备的OCT具备高的比表面积和大的孔体积,可以有效地储存硫,合成方法简单且成本较低。同时,所制备的S@OCT复合物呈现出优异的电化学性能。载硫量为65%(w/w)的S@OCT复合材料在0.2C(1C=1 672 mA·g-1)的倍率下库伦效率接近于100%,其首圈容量高达1 255.2 mAh·g-1(1.8 mAh·cm-2),并且100圈后容量保持在756.9 mAh·g-1(1.09 mAh·cm-2)。使用5C的大电流测试时,其首圈容量达到了649.1 mAh·g-1(0.93 mAh·cm-2),且在100圈后容量保持在504.2 mAh·g-1(0.72 mAh·cm-2)。     

Inter- and Intramolecular Hetero Diels-Alder Reactions, 49[1] Kinetics and Selectivity of the Intramolecular Hetero Diels-Alder Reaction of 1-Oxa-1,3-butadienes using a Benzylidenebarbituric Acid Derivative Effect of Pressure,Temperature, and Solvent

The intramolecular hetero Diels-Alder reaction of the benzy-lidenebarbituric acid derivative 1 to give the ortho and meta products 2 and 3 is studied under high pressure up to 6 kbar in various solvents. The kinetics is measured by on-line FT-IR spectroscopy up to 3 kbar. The cycloaddition shows a pressure-dependent increase in regioselectivity in favour of the ortho adduct 2. The activation volumes, ΔV, are determined to be -(33.1· 1.2) and -(34.2· 1.5) cm³· mol⁻¹ for the reactions in dichloromethane and tetrahydrofuran at 100°C, respectively. For the cycloaddition in toluene and acetonitrile the activation volumes are found to be -(13.4· 1.5) and -(17.0· 4.1) cm³· mol⁻¹, respectively. Contrary to the large solvent effect on the activation volume, only a minor effect on the activation volume differences, ΔΔV, is observed. Measurement of the molar volumes of 1 and the cycloadducts 2 and 3 show a strong solvent dependency.     

Experimental investigation and constitutive modeling of the deformation behavior of Poly-Ether-Ether-Ketone at elevated temperatures

The present study investigates the deformation behavior of Poly-Ether-Ether-Ketone (PEEK) at elevated temperatures and low strain rates through a combination of experiments and simulations. Uniaxial tension tests at elevated temperatures (293–543 K) and strain rates (8.3 × 10⁻³ to 3.3 × 10⁻¹ s⁻¹) were performed, and the temperature- and rate-dependencies of the deformation behavior and mechanism of PEEK were discussed in detail. The Erichsen test was performed at temperatures varying from 473 to 533 K and a fixed speed of 1 mm/s. Based on an investigation of numerous constitutive models, a phenomenological model called DSGZ was employed in ABAQUS/Explicit to characterize the deformation behavior of PEEK at elevated temperatures, and the deviation between experimental and simulation data was less than 10% at large deformations. Moreover, the simulation results accurately predicted the necking and cold drawing phenomena in the tension test as well as the deformation in the Erichsen test.     

Insight into the Excellent Tribological Performance of Highly Oriented Poly(phenylene sulfide)

Achieving low friction and wear of poly(phenylene sulfide)(PPS) without using fillers or blending is a challenging task, but one of considerable practical importance. Here we describe how neat PPS with high tribological performance is achieved by manipulating processing parameters(pressure, flow and temperature). The key to achieving high tribological performance is comparatively high molecular chain orientation, realized in neat PPS, at high shear rates and low pressure. The friction coefficient and wear rate are as low as ~0.3 and~10^-6 mm³·N^-1·m^-1, respectively, which break the record for neat PPS. These values are even better than those for PPS-based blends and comparable to PPS composites. Further studies show, for the first time, that wear rate decreases exponentially with increasing molecular chain orientation, prompting us to revise the classical Archard's law by including the effect of molecular chain orientation. These findings open the possibility of using neat PPS in highly demanding tribological applications.     

石墨烯/硫酸铅复合材料的制备及其在铅酸电池中的电化学性能

利用简单的浸渍法制备了石墨烯/硫酸铅复合材料,使得硫酸铅可以直接用作铅酸电池负极材料。该复合材料分别以100 mA.g-1、200 mA.g-1和300 mA.g-1电流密度放电时,平均放电比容量分别可达到110、94和69 mAh.g-1,而硫酸铅仅为49、5和0.5 mAh.g-1,显示出复合材料在高倍率充放电下更好的比容量和再接受充电能力。循环伏安测试表明石墨烯的电容效应随扫描速率增大而增强,同时析氢也变得严重,使得复合材料在充放电过程中充电效率比纯硫酸铅低20%。在充放电过程中,石墨烯能够提高硫酸铅1倍以上的放电容量,并将充电电压提高0.1 V。XRD和SEM结果显示硫酸铅均匀分布在石墨烯片层上,没有出现团聚现象。     

简易电沉积法制备CoFe-P催化剂用于高效析氧反应

开发低成本、高活性且稳定的非贵金属催化剂是实现大规模电解水制氢的关键所在。在此,我们通过简便、合理的电沉积法在泡沫镍(NF)上构建了一种具备超薄二维纳米片形貌的高度非晶相Co1Fe1-P薄膜用于高效催化析氧反应（OER）。在1.0mol·L^-1 KOH溶液中,所制备的Co1Fe1-P/NF催化剂在电流密度为10和100 mA·cm^-2处的过电位分别为274.4和329.5 mV,Tafel斜率仅为45.3 mV·dec^-1,可以媲美商业RuO₂催化剂。此外,Co1Fe1-P/NF催化剂在10 mA·cm^-2的100 h计时电压法测试和1 000次循环伏安法测试中均表现出卓越的催化稳定性。Co1Fe1-P/NF催化剂优秀的催化活性归因于其独特的形貌、高度非晶相结构提供的低能垒、优化的电子结构以及钴磷化物和铁磷化物的强协同效应。