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1.
基于Flory-Huggins理论,我们建立理论模型,研究在共非溶剂(CNS)中,高分子凝胶(PG)体积相变中的共非溶性作用.理论模型考虑PG中CNS的桥接作用、各种分子的混溶效应.研究发现,当CNS与高分子单体间的吸引强度较小时,CNS与高分子单体间桥接作用的减弱,会导致PG体积相变.当CNS与高分子单体间的吸引作用强度较大时,随着CNS与高分子单体间桥接作用的减弱,PG的体积分数呈现两次台阶式的转变,表明PG体系出现两次体积相变.这是由于桥接作用的减弱,虽然会有部分CNS分子被排挤出PG,但是并未完全消除CNS与高分子单体间的桥接吸引作用.所得理论结果符合实验观测,由此表明了共非溶性作用会在很大程度上调控PG的相变行为. 相似文献
2.
J. W. Shaner 《高压研究》2013,33(1-6):469-471
Abstract The recent discovery of a solid-solid phase change in shock-compressed Mo and the theoretical interpretation suggest valence d-electron density as a major influence on structural stability. The relationship of this experimental result to the transition metal structures and alloy phase diagrams will be discussed. Specific predictions will be presented for the locations and slopes of transition metal and transition metal alloy phase boundaries. 相似文献
3.
采用分子动力学方法对液态金属In的快速凝固过程进行计算机模拟跟踪研究.运用HA键型指 数法和原子成团类型指数法分析了金属原子In的成键类型和形成的原子团簇结构.发现:与通常的液态金属(如Al)相反,随着温度的降低,二十面体及与二十面体相关的1 551 键越来越少;与四方体,六角密堆积相关的1421,1422和1431键数目总和变化很小;而与菱 面体相关的132l,1311,1301和1201的数目却随着温度的降低而显著增加,逐渐占据优势 .最后形成一种新型的以菱面体结构为主、夹杂着立方体(fcc,bcc)
关键词:
液态金属In
微结构转变
团簇结构
分子动力学
计算机模拟 相似文献
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5.
O. Donzelli M. Bassani F. Spizzo D. Palmeri 《Journal of magnetism and magnetic materials》2008,320(14):e261-e263
We have grown, by sputtering, Co films on (1 1 1) Si substrate, with the aim to find the critical thickness of the reorientational transition of the magnetization from the plane to out of the plane as the hcp axis is oriented perpendicular to the film. Stripe Domains (SD) by Magnetic Force Microscopy, characteristic signature of Perpendicular Magnetic Anisotropy, have been found only in samples grown in some series while samples grown with the same growth parameters do not show stripe domains, indicating an in-plane orientation of the magnetization. These apparently controversial results will be explained in terms of the system fundamental parameters, magnetization, exchange stiffness constant and perpendicular magnetic anisotropy of the sample, which play a crucial role especially in Co films. 相似文献
6.
Spatial variation behaviors of argon inductively coupled plasma during discharge mode transition
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A Langmuir probe and an ICCD are employed to study the discharge mode transition in Ar inductively coupled plasma. Electron density and plasma emission intensity are measured during the E (capacitive discharge) to H (inductive discharge) mode transitions at different pressures. It is found that plasma exists with a low electron density and a weak emission intensity in the E mode, while it has a high electron density and a strong emission intensity in the H mode. Meanwhile, the plasma emission intensity spatial (2D image) profile is symmetrical in the H mode, but the 2D image is an asymmetric profile in the E mode. Moreover, the electron density and emission intensity jump up discontinuously at high pressure, but increase almost continuously at the E to H mode transition under low pressure. 相似文献
7.
The structural transitions of Ti during two different quenching processes (Q1: 7.5×1011 K/s, Q2: 2.0×1014 K/s) were studied using molecular dynamics simulations. The calculated pair-correlation function agrees acceptably with available experimental data. This work gives the structural properties, including the variations with temperature of pair-correlation function, bond-angle distribution function, bond pairs and Voronoi indices, in both rapid quenching processes. Our results indicated that the liquid Ti transformed to hcp phase at the temperature about of 400 K under the quenching condition Q1 while the liquid Ti was frozen into a glass state at the temperature about of 800 K under the quenching condition Q2. 相似文献
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VO2是一种热致相变金属氧化物. 在341 K附近, VO2发生由低温绝缘体相到高温金属相的可逆转变, 同时伴随着光学、电学和磁学等性质的可逆突变, 这种独特的性质使得VO2在光电开关材料、智能玻璃、存储介质材料等领域有着广阔的应用前景. 因此, VO2金属-绝缘体可逆相变一直是人们的研究热点, 但其相变机理至今未有定论. 首先, 简要概述了VO2相变时晶体结构和能带结构的变化情况: 从晶体结构来讲, 相变前后VO2从低温时的单斜相VO2(M)转变为高温稳定的金红石相VO2(R), 在一定条件下此过程也可能伴随着亚稳态单斜相VO2(B)与四方相VO2(A)的产生; 从能带结构来看, VO2处于低温单斜相时, 其d//能带和π*能带之间存在一个禁带, 带宽约为0.7 eV, 费米能级恰好落在禁带之间, 表现出绝缘性, 而在高温金红石相时, 其费米能级落在π*能带与d//能带之间的重叠部分, 因此表现出金属导电性. 其次, 着重总结了VO2相变物理机理的研究现状. 主要包括: 电子关联驱动相变、结构驱动相变以及电子关联和结构共同驱动相变的3种理论体系以及支撑这些理论体系的实验结果. 文献报道争论的焦点在于, VO2是否是Mott绝缘体以及结构相变与MIT相变是否精确同时发生. 最后, 展望了VO2材料研究的发展方向. 相似文献
10.
利用溶质扩散控制模型对TiAl合金柱状晶/等轴晶转变过程进行了数值模拟,结果表明,等轴晶在柱状晶前沿形核及生长过程中,当两个扩散场相遇时,观察到成分冲击波,它可能是导致柱状晶停止生长的一个主要原因.利用该模型,对小铸件柱状晶/等轴晶转变过程进行了预测,在模拟过程中发现柱状晶界面前沿液相温度梯度,成分过冷度可联合对柱状晶/等轴晶转变产生影响,模拟与实验观察符合较好.
关键词:
TiAl合金
成分冲击波
柱状晶/等轴晶转变 相似文献
11.
The structural properties and pressure-induced phase transitions of CrO2 have been investigated using the pseudopotential plane-wave method based on the density functional theory (DFT). The rutile-type (P42/mnm), CaCl2-type (Pnnm), pyrite-type (Pā3), and CaF2-type (Fm-3m) phases of CrO2 have been considered. The structural properties such as lattice parameters, bulk moduli and its pressure derivative are consistent with the available experimental data. The second-order phase-transition pressure of CrO2 from the rutile phase to CaCl2 phase is 10.9?GPa, which is in good agreement with the experimental result. The sequence of these phases is rutile-type?→?CaCl2-type?→?pyrite-type?→?CaF2-type with the phase-transition pressures 10.9, 23.9, and 144.5?GPa, respectively. The equation of state of different phases has also been presented. It is more difficult to compress with the increase of pressure for different phases of CrO2. 相似文献
12.
TiO2 powders were synthesized by two types of mixed explosives in a sealed reaction kettle. The phase and morphology of TiO2 powders were obtained by X-ray diffractometry and transmission electron microscopy. Results indicate that powders obtained from metatitanic acid contained mixed explosive are mixed crystal of anatase and rutile. The phase transition rate of anatase increases from 22.9% to 93.3% with the rise of mass ratio of hexogen, and the grain size also enlarges gradually. The powder obtained from anatase contained mixed explosive is rutile, and the phase transition rate of anatase is 100%. Compared with that before detonation, the grain size of anatase after detonation significantly changes, from nanoscale to micronscale. Based on the calculation of detonation parameters, the phase transition process and grain growth during the synthesis of TiO2 by means of detonation method are analyzed, and the nucleating collision–growth model is proposed. 相似文献
13.
A.T. Asvini meenaatci R. RajeswarapalanichamyK. Iyakutti 《Physica B: Condensed Matter》2011,406(13):2610-2615
First principles calculation was performed using tight-binding LMTO method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of chromium nitride. The equilibrium geometries, the magnetic moment, the electronic band structure, the total and partial DOS are obtained under various pressures and are analyzed in comparison with the available experimental data. The most stable structure of CrN is NaCl structure in the FM state. A pressure-induced second order magnetic phase transition from ferromagnetic (FM) to non-magnetic (NM) at very high pressure of 0.5549 Mbar is predicted. Our results indicate that CrN can be used as a hydrogen storage material. 相似文献
14.
Archana Singh Mahendra Aynyas Sankar P. Sanyal 《Central European Journal of Physics》2009,7(1):102-107
We have predicted the phase transition pressure (P
T
)and high pressure behavior of Zirconium and Niobium carbide (ZrC, NbC). The high pressure structural phase transitions in
ZrC and NbC has been studied by using a two body inter-ionic potential model, which includes the Coulomb screening effect,
due to the semi-metallic nature of these compounds. These transition metal carbides have been found to undergo NaCl (B1) to CsCl (B2)-type structural phase transition, at high pressure like other binary systems. We predict such structural transformation
in ZrC and NbC at a pressure of 98GPa and 85GPa respectively. We have also predicted second order elastic constant and bulk
modulus. The present theoretical work has been compared with the corresponding experimental data and prediction of LAPW and
GGA and LDA theories.
相似文献
15.
In the framework of the virtual crystal approximation, the temperature dependences of frequencies and integral intensities of infrared absorption spectral lines are established for an adsorbate monolayer near the point of the order-to-disorder orientational phase transition. The results obtained are consistent with the experimentally observed temperature dependences of the vibrational spectra for the 2 × 1 monolayer CO/NaCl (100). For this system, the Davydov splitting does not vanish on the phase transition due to a nonzero value of the average dipole moment (unlike molecular crystals and orientationally planar monolayers in which the average dipole moment becomes zero at the phase transition temperature). 相似文献
16.
Wei Li 《Physics letters. A》2010,374(29):2957-1991
The strong Coulomb interaction between massless Dirac fermions can drive a semimetal-insulator transition in single-layer graphene by dynamically generating an excitonic fermion gap. There is a critical interaction strength λc that separates the semimetal phase from the insulator phase. We calculate the specific heat and susceptibility of the system and show that they exhibit distinct behaviors in the semimetal and insulator phases. 相似文献
17.
采用分子动力学方法对液态金属Ga的快速凝固过程进行计算机模拟跟踪研究,运用HA键型指数法和原子团类型指数法分析了金属原子Ga的成键类型和形成的基本原子团结构.发现:与通常的液态金属(如Al)相反,随着温度的降低,二十面体及与二十面体相关的1551, 1541键型数目明显下降;与立方体(fcc,bcc),六角密集结构相关的1421,1422键型数目明显增加;而与菱面体相关的1321,1311键型的数目却显著增加,逐渐占据优势.最后形成一种新型的以菱面体结构为主、夹杂着立方体(fcc,bcc)、六角密集(hcp)等团簇结构所组成的非晶态结构.这正是非晶态金属Ga的g(r)曲线分裂的第二峰的顺序为前低后高,而与非晶态金属Al的g(r)曲线(其分裂的第二峰的顺序为前高后低)明显不同的微观结构上的物理根源. 相似文献
18.
The high pressure phase transition and elastic behavior of rare earth monoselenides (CeSe, EuSe and LaSe) which crystallize
in a NaCl-structure have been investigated using the three body interaction potential (TBIP) approach. These interactions
arise due to the electronshell deformation of the overlapping ions in crystals. The TBP model consists of a long range Coulomb,
three body interactions and the short range overlap repulsive forces operative up to the second neighboring ions. The authors
of this paper estimated the values of the phase transition pressure and the associated volume collapse to be closer than other
calculations. Thus, the TBIP approach also promises to predict the phase transition pressure and pressure variations of elastic
constants of lanthanide compounds.
相似文献
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Ross Graham 《Journal of statistical physics》1984,35(5-6):473-488
Progress in the area of the Ising model roughening transition has previously been limited by the lack of a good definition for the interface separating the pure phases. In the present work, a graphical definition is introduced and it is shown that roughening occurs precisely when this interface fluctuates to infinity. 相似文献