Physical Review B
The van der Waals (vdW) interactions between carbon nanotubes (CNTs) were studied based on the continuum Lennard-Jones model. It was found that all the vdW potentials between two arbitrary CNTs fall on the same curve when plotted in terms of certain reduced parameters, the well depth, and the equilibrium vdW gap. Based on this observation, an approximate approach is developed to obtain the vdW potential between two CNTs without time-consuming computations. The vdW potential estimated by this approach is close to that obtained from complex integrations. Therefore, the developed approach can greatly simplify the calculation of vdW interactions between CNTs.
关键词:
molecules;clusters;bundles;growth;phase;c-60
Chemical Physics Letters
The potential energies of van der Waals (VDW) interactions between two parallel, infinitely long and perfect SWNTs with identical, and different sizes were studied based on the continuum Lennard-Jones model. The conclusion of Girifalco's work on (n, n) SWNTs that the potentials of SWNT-SWNT fell on a single curve, is also applicable to SWNTs with different sizes. We further obtained the corresponding constants of the well depth \phi(0)\ and equilibrium VDW gap g(0) for SWNTs with a radius from 2 to 25 Angstrom. (C) 2005 Elsevier B.V. All rights reserved.
关键词:
carbon nanotubes;graphite;bundles;c-60;moduli;ropes
方平安
,
顾辉
,
Vleugels Jef
,
Van der Biest Omer
无机材料学报
doi:10.3321/j.issn:1000-324X.2004.05.007
采用XRD、SEM、 TEM等分析手段对由液相包覆工艺制备的Ce-TZP陶瓷的微结构进行了研究, 并和共沉淀粉体制备的Ce-TZP陶瓷进行了对比分析.力学性能表明, 同共沉淀粉体制备的Ce-TZP陶瓷相比, 由液相包覆工艺制备的Ce-TZP陶瓷虽硬度下降, 但断裂韧性改善; 液相添加少量 Al2O3硬度随之增加、断裂韧性显著提高.电镜分析表明, 液相包覆工艺制备的Ce-TZP陶瓷晶粒尺寸分布宽化, 一部分晶粒尺寸较大但CeO2含量低、易发生马氏体相转变晶粒的存在是断裂韧性改善的主要原因.陶瓷体中单斜相大晶粒与四方相之间的残余应力、添加少量 Al2O3在晶界上易形成薄的非晶包裹层, 是增加可相变四方相数量, 提高断裂韧性的其它机制.
关键词:
Ce-TZP陶瓷
,
包覆
,
力学性能
,
相变
Journal of Physical Chemistry B
The potential energies of van der Waals interactions between two multiwalled carbon nanotubes (MWNTs) as well as two carbon nanoparticles (CNPs) were calculated and compared on the basis of the continuum Lennard-Jones model. The well depth of the potential is 1 order of magnitude higher for MWNTs than for CNPs, indicating that MWNTs and CNPs can be separated from each other through polymer-induced steric stabilization. On the basis of this prediction, a novel method for the purification of MWNTs was proposed. The method involves a high-temperature annealing ( 2600 degrees C, 1 h) followed by an extraction treatment with a selected dispersing agent. While the annealing process evaporates the metal particles, the extraction treatment removes CNPs. The quality of the nanotubes obtained after purification was examined by laser Raman, thermogravimetric analysis, and electron microscopy observations.
关键词:
decomposition;hydrocarbons;temperature;nanofibers;pyrolysis;monoxide;bundles;purity;gas
Y. Q. Jia1)
,
J. G. Li1)
,
Y. M. Wang2)
,
L. X. Ding2)
,
X. M . Qin1) and X. D. Sun1)1) School of Materials and Metallurgy
,
Northeastern University
,
Shenyang 110006
,
China2) Department of Materials
,
School of Mechanical Engineering
,
Shenyang University
,
Shenyang 110044
,
China
金属学报(英文版)
Using yttriu m nitrate as the m other salt , synthesis of ultrafine yttria po w der through w et che mical route w as investigated . Choice of precipitant has dra m atic effects on co m position ,particle size distribution and particle m orphology of the precipitates . When a m m onia solutionw as used as the precipitant , the precursor precipitate w as m ainly Y2( O H) 5 14( N O3) 0 86· H2 O with co m paratively large particle size , broad size distribution and co m plex particleshapes . When sodiu m hydroxide solution w as used , roughly spherical α Y( O H)3·3 H2 Opre cipitate w ith sm all particle size and narro w size distribution w as obtained . The transfor m a tion sequence of dry α Y( O H)3 ·3 H2 O gel during calcination w as determ ined to be α Y( O H) 3·3 H2 O→ Y O O H→ Y2 O3 . After calcining at 600 ℃ for 1 hour , both Y2( O H) 5 14( N O3) 0 86· H2 O and α Y( O H) 3·3 H2 O transfor m to well crystallized Y2 O3 pow ders ,w ith particle sizes of 50 ～3000 n m and 20 n m , respectively .
关键词:
KEYW ORDS yttria
,
null
,
null
,
null
张霞
,
苏希玉
,
侯芹英
,
侯艳丽
低温物理学报
doi:10.3969/j.issn.1000-3258.2008.03.011
考虑态密度的Van Hove奇异性和非电声作用,我们在BCS理论框架内研究了HgBa2Cun-1CunO2n+2+δ(n=1,2,3)系统的超导转变温度和同位素效应.结果表明,当同时考虑Van Hove奇异性和非电声作用时,可以更好地解释HgBa2Cun-1CunO2n+2+δ(n=1,2,3)系统的超导性质.
关键词:
Van Hove奇异性
,
非电声作用
,
超导转变温度
,
同位素效应
Science in China Series B-Chemistry
The equation of the state of the hydrogen bonding fluid system of A(a)D(d) type is studied by the principle of statistical mechanics. The influences of hydrogen bonds on the equation of state of the system are obtained based on the change in volume due to hydrogen bonds. Moreover, the number density fluctuations of both molecules and hydrogen bonds as well as their spatial correlation property are investigated. Furthermore, an equation describing relation between the number density correlation function of "molecules-hydrogen bonds" and that of molecules and hydrogen bonds is derived. As application, taking the van der Waals hydrogen bonding fluid as an example, we considered the effect of hydrogen bonds on its relevant statistical properties.
关键词:
hydrogen bonding fluid;equation of state;fluctuation;correlation;effect;liquid methanol;temperature;water;dependence
Transactions of Nonferrous Metals Society of China
The method for preparing a new solid lubrication system of nano S-W-S was presented. The microstructure of the S-W-S nano cluster was investigated using TEM and XRD. The system is a mixture clusters of both monocrystal and polycrystal of layered hexagonal structure with one tungsten atom linking with two sulphur atoms, and the week Van der Waals' force bonding together the different layers. The changes of electronic structure were studied with XPS. The hybridization of different electronic shelf orbitals of the sulphur atom in the nano cluster is regarded as the quantum size effect. The clusters are found to be of a closed spherical,structure without any dangling bond.
关键词:
solid lubrication system;nanometer cluster;quantum size effect;powders
