oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
COMPUTER SIMULATION STUDY ON PRESSURE EFFECT IN AMORPHOUS IRON
非晶铁结构的加压模拟

HONG JING-XIN,SHEN ZHONG-YI,YIN XIU-JUN,ZHANG YUN,HE SHOU-AN,
洪景新
,沈中毅,殷岫君,张云,何寿安

物理学报 , 1987,
Abstract: By computer simulation, the pressure induced variation in the behavior of amorphous metals is investigated. We used the Lennard-Jones potential, which is fitted with the equation of state of iron, to relax the amorphous model constructed by sequentially stacking the hard sphere together with energy minimization consideration, so as to yield an amorphous iron model containing 1067 atoms with periodic boundary. The variation of RDF of this amorphous iron model under the application of high pressure is also examined. From the obscuring tendency of two splitted sub-peaks in the second maximum of the RDF of the pressurized model, we suggest that the local ordered correlation in the amorphous alloys might be destroyed during compression. The P-V relation of amorphous iron has also been estimated by comparing with the crystalline state.
Modelling of amorphous polymer surfaces in computer simulation  [PDF]
Thorsten Hapke,Andreas Linke,Gerald Paetzold,Dieter W. Heermann
Physics , 1996, DOI: 10.1016/S0039-6028(96)01148-X
Abstract: We study surface effects in amorphous polymer systems by means of computer simulation. In the framework of molecular dynamics, we present two different methods to prepare such surfaces. {\em Free} surfaces are stabilized solely by van--der--Waals interactions whereas {\em confined} surfaces emerge in the presence of repelling plates. The two models are compared in various computer simulations. For free surfaces, we analyze the migration of end--monomers to the surface. The buildup of density and pressure profiles from zero to their bulk values depends on the surface preparation method. In the case of confined surfaces, we find density and pressure oszillations next to the repelling plates. We investigate the influence of surfaces on the coordination number, on the orientation of single bonds, and on polymer end--to--end vectors. Furthermore, different statistical methods to determine location and width of the surface region for systems of various chain lengths are discussed and applied. We introduce a ``height function'' and show that this method allows to determine average surface profiles only by scanning the outermost layer of monomers.
Structure and diffusion in amorphous aluminium silicate: A molecular dynamics computer simulation  [PDF]
Anke Winkler,Jurgen Horbach,Walter Kob,Kurt Binder
Physics , 2003, DOI: 10.1063/1.1630562
Abstract: The amorphous aluminium silicate (Al2O3)2(SiO2) [AS2] is investigated by means of large scale molecular dynamics computer simulations. We consider fully equilibrated melts in the temperature range 6100K >= T >= 2300K as well as glass configurations that were obtained from cooling runs from T=2300K to 300K with a cooling rate of about 10^12K/s. Already at temperatures as high as 4000K, most of the Al and Si atoms are four-fold coordinated by oxygen atoms. Thus, the structure of AS2 is that of a disordered tetrahedral network. The packing of AlO4 tetrahedra is very different from that of SiO4 tetrahedra in that Al is involved with a relatively high probability in small-membered rings and in triclusters in which an O atom is surrounded by four cations. We find as typical configurations two-membered rings with two Al atoms in which the shared O atoms form a tricluster. On larger length scales, the system shows a microphase separation in which the Al-rich network structure percolates through the SiO2 network. The latter structure gives rise to a prepeak in the static structure factor at a wavenumber q=0.5\AA^{-1}. The comparison of experimental X-ray data with the results from the simulation shows a good agreement for the structure function. The diffusion dynamics in AS2 is found to be much faster than in SiO2. We show that the self-diffusion constants for O and Al are very similar and that they are by a factor of 2-3 larger than the one for Si.
Thermophysical Properties of Undercooled Alloys: An Overview of the Molecular Simulation Approaches  [PDF]
Yong J. Lv,Min Chen
International Journal of Molecular Sciences , 2011, DOI: 10.3390/ijms12010278
Abstract: We review the studies on the thermophysical properties of undercooled metals and alloys by molecular simulations in recent years. The simulation methods of melting temperature, enthalpy, specific heat, surface tension, diffusion coefficient and viscosity are introduced and the simulated results are summarized. By comparing the experimental results and various theoretical models, the temperature and the composition dependences of the thermophysical properties in undercooled regime are discussed.
Molecular dynamics computer simulation of amorphous silica under high pressure  [PDF]
Juergen Horbach
Physics , 2008, DOI: 10.1088/0953-8984/20/24/244118
Abstract: The structural and dynamic properties of silica melts under high pressure are studied using molecular dynamics (MD) computer simulation. The interactions between the ions are modeled by a pairwise-additive potential, the so-called CHIK potential, that has been recently proposed by Carre et al. The experimental equation of state is well-reproduced by the CHIK model. With increasing pressure (density), the structure changes from a tetrahedral network to a network containing a high number of five- and six-fold Si-O coordination. In the partial static structure factors, this change of the structure with increasing density is reflected by a shift of the first sharp diffraction peak towards higher wavenumbers q, eventually merging with the main peak at densities around 4.2 g/cm^3. The self-diffusion constants as a function of pressure show the experimentally-known maximum, occurring around a pressure of about 20 GPa.
Computer simulation of low-energy excitations in amorphous silicon with voids  [PDF]
Serge M. Nakhmanson,D. A. Drabold
Physics , 1999, DOI: 10.1016/S0022-3093(99)00795-4
Abstract: We use empirical molecular dynamics technique to study the low-energy vibrations in a large 4096 atom model for pure amorphous silicon and a set of models with voids of different size based on it. Numerical vibrational eigenvalues and eigenvectors for our models are obtained by exact diagonalization of their dynamical matrices. Our calculations show that localized low-energy vibrational excitations of rather complex structure are present in amorphous silicon models with voids. According to their spatial localization patterns we make an attempt to classify these excitations as modes associated with the void and "mixed" modes associated with the interaction of the void with strained regions of silicon network.
Cooling rate effects in amorphous Silica: A Computer Simulation Study  [PDF]
Katharina Vollmayr,Walter Kob,Kurt Binder
Physics , 1996, DOI: 10.1103/PhysRevB.54.15808
Abstract: Using molecular dynamics computer simulations we investigate how in silica the glass transition and the properties of the resulting glass depend on the cooling rate with which the sample is cooled. By coupling the system to a heat bath with temperature $T_b(t)$, we cool the system linearly in time, $T(t)=T_i-\gamma t$, where $\gamma$ is the cooling rate. We find that the glass transition temperature $T_g$ is in accordance with a logarithmic dependence on the cooling rate. In qualitative accordance with experiments, the density shows a local maximum, which becomes more pronounced with decreasing cooling rate. The enthalpy, density and the thermal expansion coefficient for the glass at zero temperature decrease with decreasing $\gamma$. We show that also microscopic quantities, such as the radial distribution function, the bond-bond angle distribution function, the coordination numbers and the distribution function for the size of the rings depend significantly on $\gamma$. We demonstrate that the cooling rate dependence of these microscopic quantities is significantly more pronounced than the one of macroscopic properties. Furthermore we show that these microscopic quantities, as determined from our simulation, are in good agreement with the ones measured in real experiments, thus demonstrating that the used potential is a good model for silica glass. The vibrational spectrum of the system also shows a significant dependence on the cooling rate and is in qualitative accordance with the one found in experiments. Finally we investigate the properties of the system at finite temperatures in order to understand the microscopic mechanism for the density anomaly. We show that the anomaly is related to a densification and subsequent opening of the tetrahedral network when the temperature is decreased, whereas
Computer simulation of the microstructure and rheology of semi-solid alloys under shear  [PDF]
M. Perez,J-C. Barbe,Z. Neda,Y. Brechet,L. Salvo
Physics , 2000,
Abstract: The rheological behavior of metallic alloys containing both solid and liquid phases is investigated in the low solid fraction range (<50%). This behavior depends on both the solid fraction and the shear rate. The concept of Effective Volume Fraction (EVF) is used to decorrelate the influence of these two parameters. At high shear rate the slurry behaves like a suspension of hard spheres, whereas at lower shear rate, particles tend to aggregate in clusters, entrapping liquid and thus, increasing the EVF and the viscosity. A lattice model is introduced to simulate the aggregation / break-up processes within a slurry under shear. When the steady state is reached, the entrapped liquid fraction is calculated, leading to a viscosity estimation. Simulation results for the viscosity and 3D cluster structure are in good agreement with experimental results.
Structure and transport properties of amorphous aluminium silicates: computer simulation studies  [PDF]
Patrick Pfleiderer,Juergen Horbach,Kurt Binder
Physics , 2005,
Abstract: The structure and transport properties of SiO2-Al2O3 melts containing 13 mol% and 47 mol% Al2O3 are investigated by means of large scale molecular dynamics computer simulations. The interactions between the atoms are modelled by a pair potential which is a modified version of the one proposed by Kramer et al. [J. Am. Chem. Soc. 64, 6435 (1991)]. Fully equilibrated melts in the temperature range 6000 K >= T > 2000 K are considered as well as glass configurations, that were obtained by a rapid quench from the lowest melt temperatures. Each system is simulated at two different densities in order to study the effect of pressure on structural and dynamic properties. We find that the Al atoms are, like the Si atoms, mainly four-fold coordinated by oxygen. However, the packing of the AlO4 tetrahedra is very different from that of the SiO4 tetrahedra, which is reflected by the presence of triclusters (O atoms surrounded by three cations) and edge--sharing AlO4 tetrahedra. On larger length scales, a micro-segregation occurs, resulting in an Al-rich network percolating through the Si-O network. This is reflected in a prepeak of concentration-concentration structure factors around 0.5 A^-1 (both in the system with 47 mol% and 13 mol% Al2O3!). We also address the interplay between structure and mass transport. To this end, the behavior of the selfdiffusion constants for the different compositions and densities is studied.
Study of the influence mechanism of additional elements on the corrosion behavior of bulk Cu-based amorphous alloys
铜基大块非晶合金添加微量元素对腐蚀行为的影响机理研究

Zhang Hui,Wu Di,Zhang Guo-Ying,Xiao Ming-Zhu,
张辉
,吴迪,张国英,肖明珠

物理学报 , 2010,
Abstract: The liquid state Cu-Al alloy system was simulated by using the molecular dynamics method, then Cu-Al amorphous alloy is obtained by cooling process simulation. This article firstly sets up crystalline Cu-Al alloy liquid by using the molecular dynamics. The models of Cu-Al-M bulk amorphous alloys, their clean surfaces and their surfaces with O adsorption are set up by computer programming. The influence mechanism of additional elements Zr, Nb, Ta, V, Y and Sc on the corrosion behavior of bulk Cu-based amorphous alloys are investigated by using real-place recursive method. Results show that the alloying elements do not aggregate on the clean surface of bulk Cu-based amorphous alloys, but tend to aggregate on the surface with O adsorption with the exception of Y, which indicates that the segregation of the bulk Cu-based amorphous alloy surface with O adsorption is reversed. Calculations of the total bond order integral show that additional element can interact with oxygen easily to form oxide film on the surface of Cu-based amorphous alloys, which can improve the corrosion resistance of bulk Cu-based amorphous alloys. The improvement in corrosion resistance of Cu-based metallic glass with Y addition may be due to the aggregation of Y to the interface between alloy and oxide film, which improves the adhesion.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.