第一性原理研究hcp-C3碳体环材料的力学性质

为探索新型高强度材料, 使用第一性原理方法研究了hcp-C3碳体环材料的晶体结构、电子性质与力学性质. 结构计算与电子性质分析表明, 基于特殊的分子结构, 碳体环结构中出现了变形的sp³杂化形式. 这使得hcp-C3碳体环结构中力学特性具有明显的方向依赖性. 力学性质计算表明, 沿着[0001]晶向, 碳体环结构的弹性模量达到1033 GPa, 抗拉强度达到124.17 GPa, 抗压强度达到381.83 GPa, 沿[2110]晶向的抗压强度达到了458.34 GPa, 从而显示了hcp-C3碳体环材料优秀的力学性质. hcp-C3碳体环材料可作为新型的高强度材料而使用.     

新型金刚石科学与技术国际学术会议在东京召开

1988年10月24-26日在日本东京举行了第一届新型会刚石科学与技术国际学术会议.这次会议是日本新型金刚石论坛(JNDF)举办的.出席会议的有20多个国家的360多位有关人员,会议论文共105篇. 听谓新型金刚石是指先作为功能材料应用的金刚石、硬质碳膜和立方氮化硼.其应用范围包括切削刀具,耐磨和润滑部件,散热片,半导体材料,以及光学、声学、医学应用等. 大会的议题分为:(1)气相沉积;(2)电学和热学性质及其功能应用;(3)高压合成;(4)机械加工和力学性质;(5)物理化学性质和地球科学. 尽管会议有以上几个方面的内容,但化学气相沉积(CVD)生长金刚石…     

物理学与新型(功能)材料专题系列介绍(Ⅰ) 金刚石薄膜能成为新一代半导体材料吗?

自从８０年代金刚石薄膜的低压化学汽相淀积获得成功以来，人们对用金刚石薄膜制作高温、高速和大功率器件产生了浓厚的兴趣，因为金刚石的禁带宽，载流子迁移率高，同时具有优异的热学、光学和力学性质．本文对金刚石的电子学特征和金刚石器件的研制现伏作了评述，对发展金刚石器件的若干问题特别是金刚石薄膜的ｎ型掺杂、金刚石膜的异质外延和降低缺陷浓度等作了分析和讨论．金刚石薄膜是一种潜在的新型半导体材料，但要实现器件应用尚需作大量的材料研究．     

多晶金刚石与硬质合金的复合材料的制备方法

多晶金刚石与硬质合金的复合材料由0.5—1mm厚的多晶金刚石层和3—4mm厚的硬质合金基底构成.这种材料既具有金刚石的硬度、耐磨性、高导热等性质,又具有硬质合金的强度,因此是一种很好的工具材料.它被广泛地用于制造石油、地质、煤炭等工业部们用的钻进钻头,用来制造加工有色金属及其合金,非金属材料等的车削工具,如车刀、铣刀、镗刀等.还可以用作其他耐磨部件. 使用多晶金刚石复合材料制作的工具可以提高工效,减轻劳动强度,提高产品质量,节省能源,因而可以大大降低生产成本.例如,据石油部门的专家估计,用多晶金刚石复合片钻头代替三牙轮钻…     

几种新型超硬薄膜的研究进展

超硬材料主要由Ⅲ,Ⅳ,Ⅴ族共价键化合物（碳化物,氮化物）和单质（金刚石）组成,硬度高于40GPa,有单晶,多晶,非晶等多种,除金刚石外,这些材料都是人工合成的,没有天然对应物,除超硬性质以外,这些材料大都具有宽带隙,高温稳定性,化学惰性等优良的物理化学性质,新型超硬薄膜材料研究从金刚石开始,目前主要的研究对象有金刚石,类金刚石碳（DLC）,立方氮化硼（cBN),氮化碳（C3N4,CNx),硼碳氮（BCN）等,是近二十年来材料研究的热门方向之一,文章结合作者近年来的工作,介绍这几种超硬薄膜的研究进展和展望。     

科学家通过激光脉冲照射获得碳元素第3种固体相态Q-碳

正美国科学家最近合成出一种不同于石墨和金刚石的固态碳元素新相态,并称其为Q-碳。他们还开发出一种技术,能在常温常压下利用Q-碳造出多种金刚石结构。一堆从0.02到0.04克拉的单粒钻石,总重5.36克拉(示意图)。Q-碳具有很不寻常的性质,比如它有铁磁性,而其他固态碳没有;它比金刚石还硬;在能量较低时就能燃烧。此外,它还能用于制造多种单晶金刚石材料。相态是同一元素的不同形式,如石墨和金刚石是碳的两种固体形式。论文第一作者、北卡罗莱纳州立大学材料科学与工程教授杰伊·纳拉扬说:"现在我们造出了碳的第3种固体相     

金刚石-碳化硅超硬复合材料的冲击强度

不同于延性介质,脆性介质的失效破坏严重制约着材料的强度.本文采用一种定量描述脆性介质力学性质的格点-弹簧模型,研究了金刚石-碳化硅超硬复合材料的冲击强度及其细观损伤机理,有助于避免灾变破坏、提高冲击强度.在模型中,通过构建不同体积分数比的金刚石和碳化硅两相复合材料,模拟获得了经受冲击波压缩形变后的宏观波剖面,显示出随着金刚石颗粒含量增加,冲击强度逐渐增大,而后减小;对应于这种变化,损伤演化分析揭示出存在三种细观损伤模式,当金刚石颗粒含量在10%—50%范围内增加时,长距离扩展滑移带占主导;当金刚石颗粒含量为70%时,滑移带已由长距离扩展演化为短细滑移带,损伤主要来自于碳化硅基体,多数金刚石颗粒未发生损伤;当金刚石颗粒含量超过70%的临界值后,短细滑移带也将被强烈限制,应力集中致使金刚石颗粒被严重损伤,冲击强度下降.研究结果为优化设计金刚石-碳化硅超硬复合材料以及制备新型抗冲击材料提供了物理认知.     

金刚石氮空位色心耦合机械振子和腔场系统中方差压缩研究

研究了金刚石氮空位中心(NV色心)同时耦合腔场和机械振子系统中声子场的方差压缩动力学特性,分析了金刚石NV色心初态和NV色心与机械振子耦合强度对声子场方差压缩影响.结果发现:可以制备压缩时间长、压缩幅度大的声子场压缩态,其物理原因是机械振子具有最大相干性,并且通过调控NV色心初态以及磁场梯度可以实现对机械振子方差压缩非经典特性的操控,从而在理论上提供了一种调控声子场方差压缩的方式.     

人造金刚石生长速率的探讨

《在有金属或合金参与下人造金刚石形成机理的探讨》[1]一文中,阐述了非金刚石型碳转变成金刚石的历程──在有金属或合金作用下金刚石成核和长大的本质.本文着重探讨人造金刚石晶体的生长速率问题.所用碳素材料为石墨. 人造金刚石成核后的长大过程是一个复杂的过程,可以视为在各向异性的基体上在最有利的条件下所发生的个别过程的总和. 我们在用Ni-MnB合金作催溶剂的试验研究中,测量了合成条件下金刚石晶体的尺寸,通过图解,计算出了在这一条件下石墨转变成金刚石的活化能和活化体积,并且确定了金刚石生长速率与压力、温度的关系. 试验分…     

合成人造金刚石的几个问题

金刚石系目前自然界已知物质中硬度最高的一种物质,它是一种重要工业材料,在国民经济中有着重大的意义.在工业中广泛地使用金刚石和金刚石制品,可以大大地提高劳动生产率和产品质量.天然金刚石的资源有限,开采困难,远不能满足工业日益增长的需要.人造金刚石的出现,为工业的发展创造了有利的条件.要求生产大量高质量、大颗粒、新品种的人造金刚石,是目前人造金刚石生产者和研究者面临的课题.一、合成金刚石用的超高压、高温装置 目前,各国超高压高温工作者,正在大力提高超高压水平,由十几万巴、二十万巴水平提高到六十万巴左右(静压),并开始…     

Families of superhard crystalline carbon allotropes constructed via cold compression of graphite and nanotubes

We report a general scheme to systematically construct two classes of structural families of superhard sp(3) carbon allotropes of cold-compressed graphite through the topological analysis of odd 5+7 or even 4+8 membered carbon rings stemmed from the stacking of zigzag and armchair chains. Our results show that the previously proposed M, bct-C(4), W and Z allotropes belong to our currently proposed families and that depending on the topological arrangement of the native carbon rings numerous other members are found that can help us understand the structural phase transformation of cold-compressed graphite and carbon nanotubes (CNTs). In particular, we predict the existence of two simple allotropes, R and P carbon, which match well the experimental x-ray diffraction patterns of cold-compressed graphite and CNTs, respectively, display a transparent wide-gap insulator ground state and possess a large Vickers hardness comparable to diamond.     

Novel superhard carbon: C-centered orthorhombic C8

A novel carbon allotrope of C-centered orthorhombic C(8) (Cco-C(8)) is predicted by using a recently developed particle-swarm optimization method on structural search. Cco-C(8) adopts a sp(3) three-dimensional bonding network that can be viewed as interconnected (2,2) carbon nanotubes through 4- and 6-member rings and is energetically more favorable than earlier proposed carbon polymorphs (e.g., M carbon, bct-C(4), W carbon, and chiral C(6)) over a wide range of pressures studied (0-100 GPa). The simulated x-ray diffraction pattern, density, and bulk modulus of Cco-C(8) are in good accordance with the experimental data on structurally undetermined superhard carbon recovered from cold compression of carbon nanotube bundles. The simulated hardness of Cco-C(8) can reach a remarkably high value of 95.1 GPa, such that it is capable of cracking diamond.     

Compressive characteristics of single walled carbon nanotube with water interactions investigated by using molecular dynamics simulation

The elastic properties of single walled carbon nanotube (SWCNT) with surrounding water interactions are studied using molecular dynamics simulation technique. The compressive loading characteristic of carbon nanotubes (CNTs) in a fluidic medium such as water is critical for its role in determining the lifetime and stability of CNT based nano-fluidic devices. In this paper, we conducted a comprehensive analysis on the effect of geometry, chirality and density of encapsulated water on the elastic properties of SWCNT. Our studies show that defect density and distribution can strongly impact the compressive resistance of SWCNTs in water. Further studies were conducted on capped SWCNTs with varying densities of encapsulated water, which is necessary to understand the strength of CNT as a potential drug carrier. The results obtained from this paper will help determining the potential applications of CNTs in the field of nano-electromechanical systems (NEMS) such as nano-biological and nano-fluidic devices.     

Estimation of mechanical properties of nanomaterials using artificial intelligence methods

Computational modeling tools such as molecular dynamics (MD), ab initio, finite element modeling or continuum mechanics models have been extensively applied to study the properties of carbon nanotubes (CNTs) based on given input variables such as temperature, geometry and defects. Artificial intelligence techniques can be used to further complement the application of numerical methods in characterizing the properties of CNTs. In this paper, we have introduced the application of multi-gene genetic programming (MGGP) and support vector regression to formulate the mathematical relationship between the compressive strength of CNTs and input variables such as temperature and diameter. The predictions of compressive strength of CNTs made by these models are compared to those generated using MD simulations. The results indicate that MGGP method can be deployed as a powerful method for predicting the compressive strength of the carbon nanotubes.     

Investigation of the radial compression of carbon nanotubes with a scanning probe microscope

Efforts have been made to characterize the mechanical properties of carbon nanotubes. Previous work has concentrated on the tubes' longitudinal properties, and studies of their radial properties have lagged behind. We have used a scanning probe microscope with an indentation/scratch function to investigate the radial compression of multiwalled carbon nanotubes under an asymmetric stress. In particular, we have determined the radial compressive elastic modulus at different compression levels and have estimated the compressive strength to be well beyond 5.3 GPa.     

温度、应变率和空位缺陷对氮化硼纳米管压缩性能的影响

采用分子动力学方法,分别模拟了完好的和含有缺陷的氮化硼纳米管的轴向压缩过程。原子间的相互作用采用Tersoff多体势函数来描述。结果表明,同尺寸的锯齿型氮化硼纳米管的临界轴向压缩强度高于扶手型氮化硼纳米管,这与碳纳米管的研究结果一致。发现纳米管的压缩强度,如临界轴向内力在低温下受温度影响明显,并且和应变率的大小有关。然而,应变率对纳米管的弹性变形没有影响。另外,还发现空位缺陷降低了纳米管的力学性能。与完好的纳米管相比,含有缺陷的纳米管轴向压缩强度对于温度的影响并不敏感。     

Relation between interfacial shear strength and compressive strength of carbon fiber/epoxy resin composite strands

The mechanism with which the fiber-matrix interfacial strength exerts its influence on the compressive strength of fiber reinforced composites has been studied by measuring the axial compressive strength of carbon fiber/epoxy resin unidirectional composite strands having different levels of interfacial shear strength. The composite strands are used for experiments in order to investigate the compressive strength which is not affected by the delamination taking place at a weak interlayer of the laminated composites. The interfacial strength is varied by applying various degrees of liquid-phase surface treatment to the fibers. The efficiency of the compressive strength of the fibers utilized in the strength of the composite strands is estimated by measuring the compressive strength of the single carbon filaments with a micro-compression test. The compressive strength of the composite strands does not increase monotonically with increasing interfacial shear strength but showes lower values at higher interfacial shear strengths. With increasing interfacial shear strength, the suppression of the interfacial failure in the misaligned fiber region increases the compressive strength, while at higher interfacial shear strengths, the enhancement of the crack sensitivity decreases the compressive strength.     

Molecular dynamic investigation of mechanical properties of armchair and zigzag double-walled carbon nanotubes under various loading conditions

Using molecular dynamic simulation (MDS), effects of chirality and Van der Waals interaction on Young's modulus, elastic compressive modulus, bending, tensile, and compressive stiffness, and critical axial force of double-walled carbon nanotube (DWCNT) and its inner and outer tubes are considered. Achieving the highest safety factor, mechanical properties have been investigated under applied load on both inner and outer tubes simultaneously and on each one of them separately. Results indicate that as a compressive element, DWCNT is more beneficial than single-walled carbon nanotube (SWCNT) since it carries two times higher compression before buckling. Except critical axial pressure and tensile stiffness, in other parameters zigzag DWCNT shows higher amounts than armchair type. Outer tube has lower strength than inner tube; therefore, most reliable design of nanostructures can be attained if the mechanical properties of outer tube taken as the properties of DWCNT.     

陶瓷纤维对普通硅酸盐混凝土的强韧化效应

 采用液压试验机和Φ100 mm分离式霍普金森压杆实验装置,研究了体积分数为0.1%、0.2%和0.3%的陶瓷纤维混凝土的准静态和动态力学性能,分析了陶瓷纤维的增强机理,并将其与相同纤维体积分数的碳纤维混凝土进行对比。结果表明：陶瓷纤维改善了普通硅酸盐混凝土的准静态力学性能;纤维体积分数为0.3%时,抗压强度提高15.0%,劈裂抗拉强度提高8.5%,抗折强度提高12.7%。冲击荷载作用下,陶瓷纤维混凝土的动态抗压强度和比能量吸收随平均应变率的增加近似线性增长;体积分数为0.2%时,陶瓷纤维的增强、增韧效果最佳。陶瓷纤维对普通硅酸盐混凝土的增强、增韧效果总体上优于碳纤维。