金属Nb级联碰撞的分子动力学模拟

运用分子动力学方法研究了bcc结构Nb在辐照损伤初期因辐照诱发位移损伤形成和演化的微观过程以及原子机制。选取初级离位原子(primary knock-on atom,PKA)能量5～50 keV,模拟温度300 K,研究了Nb中级联碰撞产生的缺陷数量及其分布随模拟时间的演化,PKA能量对稳定Frenkel缺陷数目的影响,缺陷团簇的分布等。研究结果显示,级联碰撞会在体系中产生辐照缺陷,Frenkel缺陷对数目和不同的PKA能量区间(5～30 keV和30～50 keV)之间满足不同的幂函数关系,所形成的缺陷大多数以点缺陷的形式存在,空位团簇成团率17%～35%,间隙原子团簇成团率23%～40%,PKA能量越高,空位越容易形成较大的团簇;级联碰撞产生的间隙原子形成了大量的沿110方向的哑铃型结构;当PKA能量高于30 keV时,级联碰撞将产生1/2111间隙型位错环和100空位型位错环。     

模拟热峰冲击下UO2微观结构的变化

利用分子动力学方法,通过热峰模型模拟了高能辐照下UO2的损伤过程.通过在单次热峰模拟中设定不同入射温度、不同入射半径的热峰,观察到基体中心区域原子获得了能量.在热激活的作用下以压力波的形式向外层快速传递,在原子大量离位的同时也有大量回复在进行.随入射能量的不同,最终形成了非晶态、半非晶、晶态3种微观结构.模拟结果可以较好地重现热峰辐照的物理过程,能够对在实验上无法观测的微小尺度的变化给予直观的描述.     

真空电子束焊时的X射线防护

真空电子束焊接时的X射线,主要能引起眼睛晶体损伤及皮肤潜在的危害,如在较高能量的X射线条件下,受到长期超剂量的照射,可能引起慢性幅射损伤。因此,本文就X射线的防护问题进行如下探讨。 X射线的来源和性质真空电子束焊机的真空室(包括电子枪和焊接真空室)很像一个X射线球管,它以高速电子轰击金属靶,使1％左右的能量转换为X射线。真空电子束焊时除了由电子束直接轰击焊件所产生的X射线外,还可能由于电子束聚焦不全,散射电子轰击金属的真空室壁而产生X射线。     

超声辐照对碳纳米管增强环氧树脂黏度和力学性能的影响

采用超声辐照处理多壁碳纳米管增强环氧树脂复合材料,分析了超声辐照条件对复合材料的黏度、力学性能及拉伸断口显微形貌的影响。结果表明:温度一定时,多壁碳纳米管增强环氧树脂体系的黏度随超声辐照时间的延长而逐渐降低;超声辐照时间为5min时,环氧树脂的拉伸强度、弯曲强度、拉伸剪切强度达到最大值,较处理前分别提高了37%,167%和86%;经超声辐照后,拉伸断口形貌显示出更多的韧性断裂特征。     

强流脉冲电子束表面处理

以T8钢、D2模具钢和AZ91HP镁合金为试验材料,利用强流脉冲电子束(加速电压为27 keV,脉冲持续时间约为1 μs,能量密度约为2.2 J/cm2)在试样表面进行辐照处理,研究了处理试样的表层组织、相结构及性能变化规律.另外,结合电子束能量沉积过程中瞬时温度和应力的作用特点,详细讨论了表面熔坑及深层硬化现象的形成机理.     

Fe-Cr-Mn钢时效析出碳化物的辐照损伤行为

采用电子束辐照及电子束-氦离子束（He^＋）复合辐照方式,研究低活性Fe-Cr-Mn奥氏体钢时效析出碳化物的辐照损伤行为．结果表明：空洞可以在碳化物内部及边界处形成,而边界是优先形成位置;溶质元素在碳化物边界产生偏析;碳化物与γ相界面可以发生移动．从点缺陷与溶质元素相互作用和He的协同相助效应,讨论了时效碳化物辐照损伤的原因,提出相界面的局部移动也是辐照损伤的一种表现形式．     

0.29V-0.09Ta RAFM钢辐照条件下空洞演化的实验和理论研究

为研究辐照条件下空洞的演化,分别在200 °C, 350 °C和550 °C对低活化铁素体/马氏体钢(RAFM)进行He离子辐照。实验结果显示辐照损伤沿深度呈钟型分布,空洞的尺寸和密度均与空位产生率正相关。随着辐照温度升高,空洞的尺寸增大,密度降低,高温下可以观察到空洞在晶界的聚集和无空洞区(VDZs),在550 °C可以观察到方形空洞。使用相场模型模拟空洞的演化机制,模拟结果显示辐照条件下空洞演化可以分为孕育、形核和生长三个阶段,空洞界面能的各项异性是空洞形状的可能原因。     

纳米带

正美国佐治亚理工学院的三位中国科学家2001年初利用高温气体固相法,首次合成了半导体化合物纳米带状结构。是继发现多壁碳纳米管和合成单壁纳米管以来,一维纳米材料合成领域的又一大突破。它的横截面是窄矩形结构,带宽为30~300mm,厚度为5~10 nm,长度可达几毫米,是迄今为止合成的惟一具有结构可控且无缺陷的宽带半导体准一维带状结构。目前已     

纳米带

美国佐治亚理工学院的三位中国科学家2001年初利用高温气体固相法,首次合成了半导体化合物纳米带状结构。是继发现多壁碳纳米管和合成单壁纳米管以来,一维纳米材料合成领域的又一大突破。它的横截面是窄矩形结构,带宽为30～300mm,厚度为5—10nm,长度可达几毫米,是迄今为止合成的惟一具有结构可控且无缺陷的宽带半导体准一维带状结构。     

强流脉冲离子束辐照对316L不锈钢表面改性的实验研究

利用离子能量为300 keV、束流密度为200 A/cm2、脉冲宽度为75 ns的混合离子束(70%H 30%C )组成的强流脉冲离子束(HIPIB)对316L不锈钢进行了表面辐照处理,辐照次数分别为1,5,10次.采用SEM,XRD,TEM和EPMA分析辐照后试样表面形貌、表面层相组成和微观结构及元素分布的变化.结果表明,HIPIB辐照使试样表面光滑化,表面层晶粒细化、产生择优取向,杂质元素选择性烧蚀,电化学腐蚀性能明显提高.由于HIPIB辐照引起的大应力和冲击波的影响,辐照后在深度达100μm表层内显微硬度提高,表面摩擦系数降低,表面抗磨损性能显著改善.随着辐照次数的增加,316L疲劳极限和蠕变断裂寿命延长,稳态蠕变速率降低.     

微波合成WCx/MWCNTs及其电催化性能研究

目的制备多壁碳纳米管负载碳化钨的纳米复合材料(WC_x/MWCNTs),探索微波加热温度对WC_x/MWCNTs合成的影响规律。方法利用分子自组装技术与微波加热技术相结合,以钨酸钠为W源,制备了WC_x/MWCNTs纳米复合材料。采用X射线衍射(XRD)和透射电子显微镜技术(TEM)对不同条件下制得样品的物相组成、结构及微观形貌进行了表征;采用循环伏安法在酸性环境下测试了WC_x/MWCNTs对氢和CH3OH的电催化性能。结果当微波加热温度为1000℃时,制备的WC_x/MWCNTs纳米复合材料由WC、WC2和C组成,碳纳米管的多壁结构保留较好,碳化钨颗粒均匀地分布在碳纳米管外表面,粒径为20~50 nm。循环伏安测试结果表明,制备的WC_x/MWCNTs在酸性环境下对氢具有一定的催化作用,但对甲醇没有明显的电催化作用。结论通过控制合理的微波加热温度,可制备出碳化钨粒径小、分布均匀、碳纳米管多壁结构完好的WC_x/MWCNTs纳米复合材料。制备的WC_x/MWCNTs在酸性环境下对氢具有一定的催化作用,可作为催化剂载体来负载其他金属制备复合催化剂。     

RuO2/carbon nanotubes composites synthesized by microwave-assisted method for electrochemical supercapacitor

A simple and efficient way has been developed to decorate multiwalled carbon nanotubes (MWCNTs) with RuO₂ nanoparticles for use of electrochemical supercapacitor. In this method, RuO₂ nanoparticles was directly synthesized and attached onto MWCNTs in the mixture with RuCl₃ solution by microwave-assisted irradiation. Energy dispersive X-rays analysis (EDXA) elucidated the presence of ruthenium oxide in the as-prepared composites. Transmission electron microscopy (TEM) results showed that RuO₂ nanoparticles had the narrow size distribution and were attached on MWCNTs. Cyclic voltammetry results demonstrated that RuO₂/MWCNTs had significantly greater specific capacitance than that of the pristine MWCNTs in the same medium.     

激光熔铸多壁纳米碳管增强铝基复合材料

利用激光熔铸技术制备多壁纳米碳管增强铝基复合材料,并使用SEM、XRD对其熔铸成形性以及纳米碳管与基体金属界面结合行为进行观察和分析.结果表明,在单位面积激光能量为800×105J/m2时,纳米碳管增强铝基复合材料能够熔合而不破坏纳米碳管结构;在该复合材料中适量添加表面张力较低的金属Mg,可降低基体铝的表面张力,进而降低铝-纳米碳管的液固界面能,改善铝合金和纳米碳管的润湿性;当纳米碳管含量为5%(质量分数)时,并添加3%(质量分数)合金化元素Mg,激光熔铸的复合材料熔合性较好,铸块致密,在复合铸块的断口上能观察到增强体纳米碳管.     

Drilling delamination and thermal damage of carbon nanotube/carbon fiber reinforced epoxy composites processed by microwave curing

The drilling-induced delamination and thermal damage of carbon fiber reinforced epoxy composite materials are serious problems especially for high value components of the aviation industry. To suppress the delamination and drilling ablation, an innovative approach was employed in this study. The multiwalled carbon nanotubes (MWCNTs) were introduced to the matrix resin to improve the interlaminar strength and thermal conductivity. The as-prepared composite was processed by microwave curing to enhance the interface strength between carbon fiber and the carbon nanotubes modified matrix. During the drilling processes, optical fiber Bragg grating sensors were utilized to precisely measure the drilling temperature. Experimental results indicated that the interlaminar fracture toughness was increased by more than 66% compared to that of the traditional thermal cured samples without MWCNTs. And the delamination factor was decreased by 16% according to the computerized tomography scanning results. The maximum drilling temperature of the MWCNTs reinforced composite was below the glass transition temperature of the matrix resin and declined by 23 °C compared to traditional composites. With this novel method of carbon nanotube modification and microwave curing, we provide the capability of reducing the drilling delamination and thermal damage of carbon fiber composites simultaneously, and explored the possibility of manufacturing and machining integration.     

超声法制备纳米Pt/MWCNT催化剂及其在CO2传感器上的应用

采用超声合成法制备了纳米铂/多壁碳纳米管复合催化剂(Pt/MWCNT),通过场发射扫描电镜(FE-SEM)、X-射线衍射(XRD)及电化学技术表征了该催化剂的性质.结果表明:纳米Pt均匀地镶嵌在MWCNTs表面,粒径为40±20 nm.该催化剂对CO2的还原呈现良好的催化作用,可用作制备CO2电化学传感器,CO2在纳米铂/多壁碳纳米碳管修饰玻碳电极上的还原电流响应(Pt/MWCNTs/GCE),分别在1～10 ppm和10～100 ppm两个浓度范围内呈良好的线性关系,检测限为1 ppm.     

Fabrication and mechanical properties of MWCNTs-reinforced aluminum composites by hot extrusion

Over the past decade,the interest in aluminum composites reinforced with carbon nanotubes has grown significantly.Studies have been carried out to overcome problems with uniform dispersion,interfacial bonding,void formation and carbide formation of the composites.In the present work,multi-wall carbon nanotubes(MWCNTs)aluminum composites were produced.High-energy ball milling with the aim at developing well-dispersed MWCNTs Al composites was followed by cold compaction,sintering,and hot extrusion at 500 ℃.Different amounts of stearic acid as processing control agent(PCA)is used in order to minimize cold welding of the Al particles,and to produce finer particles.Differential scanning calorimetry(DSC),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and X-ray diffraction(XRD)were employed to analyze the MWCNTs,the aluminum powder,and the composites' microstructural behavior.The hardness and tensile properties of the composites are also evaluated.The results showed 500％ increase in yield stress after the addition of 1 wt％ MWCNTs in Al-MWCNTs based composite.The ball-milling time of 4 h is found to be sufficient as excessive milling time destroys a vast number of MWCNTs.     

多壁碳纳米管/氧化铕复合材料的制备

利用混合酸对催化裂解法制备的多壁碳纳米管进行纯化,然后先后用氨水和柠檬酸对纯化后的多壁碳纳米管进行修饰,最后利用共沉淀法和热处理制各了碳纳米管氧化铕复合材料,并使用红外光谱、X-衍射仪(XRD)、扫描电镜(SEM)研究了碳纳米管及氧化铕复合材料的结构和形貌.光谱结果表明:经过混合酸纯化后,碳纳米管表面拥有丰富的羟基和羧基等官能团,而且能够在纯化后的多壁碳纳米管表面引入氨基和柠檬酸分子.电子显微图像显示,在450℃下热处理,获得了多壁碳纳米管/氧化铕纳米线复合材料;在750℃下热处理,获得了多壁碳纳米管/纳米氧化铕复合材料.     

Aligned multi-walled carbon nanotubes on different substrates by floating catalyst chemical vapor deposition: Critical effects of buffer layer

Aligned multi-walled carbon nanotubes (MWCNTs) were synthesized by floating catalyst chemical vapor deposition on two types of substrates, with emphasis on the effects of an aluminum buffer layer. It has been revealed that the presence of the aluminum buffer layer on insulating/semiconducting silicon oxide/silicon wafer resulted in a higher growth rate, narrower diameter distribution, neater morphology and improved crystalline quality of MWCNTs. When an aluminum buffer layer is deposited on electrically conductive carbon paper, high yield CNTs can be achieved while no CNTs can be observed without this buffer layer. Morphology, structure and chemical states of the products were examined by field-emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The generation of alumina from the aluminum buffer layer is thought to play an important role in promoting the nanotube growth. Detailed growth mechanism of MWCNTs was also discussed.     

Surface functionalization of multi-walled carbon nanotubes via electron reduction of benzophenone by potassium metal

The covalent sidewall functionalization of multi-walled carbon nanotubes (MWCNTs) via the electron reduction of benzophenone by potassium metal is reported. Fourier transform infrared spectroscopy (FTIR) results show that diphenylcarbinol (DPC) groups were successfully grafted to the MWCNTs sidewalls after 10 days of reaction time. Raman and UV–vis spectroscopies reveal the presence of covalent sidewall functionalization. The percentage of residues for DPC-MWCNTs was found to be lower than that for pristine MWCNTs, which indicates the existence of functional groups on the sidewalls of DPC-MWCNTs. It is shown that the sidewall of the DPC-MWCNTs was covered by non-uniform layer of DPC, as observed by transmission electron microscopy (TEM). Results from Raman spectroscopy, FTIR, TGA, UV–vis spectroscopy and TEM confirm that the functionalization of the covalent sidewalls of MWCNTs was successfully performed by this method.     

Microwave-assisted synthesis and magnetic properties of size-controlled CoNi/MWCNT nanocomposites

Size-controlled CoNi alloy nanoparticles with average diameters in the range of 15-48 nm attached on the multi-walled carbon nanotubes (MWCNTs) were prepared to form CoNi/MWCNT nanocomposites by microwave-assisted method. The size of CoNi alloy nanoparticles can be controlled through adjusting the atomic ratios of metals to carbon nanotubes in the mixed acetate solution. The as-prepared nanocomposites have been characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-disperse X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). The results show that CoNi alloy nanoparticles are face-centered cubic structure, quasi-spherical and disperse uniformly on the surface of MWCNTs. Magnetic measurement shows that both the coercivity and the saturation magnetization of the samples increase with the increase of the particle size from 15 to 37 nm, and decrease from 37 to 48 nm.