共查询到19条相似文献,搜索用时 203 毫秒
1.
用分子动力学模拟方法研究了五种不同冷却速率对Lennard-Jones体系凝固过程中结构与动力学性质的影响。采用两种不同的方法来确定玻璃转变温度Tg,并且对结晶温度Tc、径向分布函数g(r)、均方位移函数MSD与扩散系数D、平均配位数进行比较分析。结果表明:冷却速率影响Lennard-Jones体系凝固过程中的结构。当使用足够高的冷却速率冷却时,体系发生玻璃化转变,而且冷却速率越快,玻璃转变温度越高;当冷却速率较小时,体系形成晶体,而且冷却速率越慢,结晶温度越高,结晶程度也越高。同时发现,冷却速率对扩散系数和平均配位数也有很大影响,二者在体系发生玻璃转变时都有一个缓变的过程,表明了过冷液相区的存在。 相似文献
2.
《原子与分子物理学报》2015,(4)
用分子动力学模拟方法研究了五种不同冷却速率对Lennard-Jones体系凝固过程中结构与动力学性质的影响.采用两种不同的方法来确定玻璃转变温度Tg,并且对结晶温度Tc、径向分布函数g(r)、均方位移函数MSD与扩散系数D、平均配位数进行比较分析.结果表明:冷却速率影响Lennard-Jones体系凝固过程中的结构.当使用足够高的冷却速率冷却时,体系发生玻璃化转变,而且冷却速率越快,玻璃转变温度越高;当冷却速率较小时,体系形成晶体,而且冷却速率越慢,结晶温度越高,结晶程度也越高.同时发现,冷却速率对扩散系数和平均配位数也有很大影响,二者在体系发生玻璃转变时都有一个缓变的过程,表明了过冷液相区的存在. 相似文献
3.
4.
5.
采用F S多体势对液态合金Al3Ni和Ni3Al在不同冷却速度下的微观结构及其转变机制进行了分子动力学模拟 ,得到了不同冷速下各温度的双体分布函数 ;采用HA键型指数法对其结构进行了分析 ,结果表明 :Al3Ni在两种冷速下均以非晶的形式出现 ,只是慢冷时体系的有序度略有升高 ;而Ni3Al的结构及能量转变受冷速影响较大 ,快冷时形成非晶 ,而慢冷时出现明显结晶 ;同样冷速下Al含量较少的Ni3Al体系的有序度高 ,更易形成晶体 ,晶体的形成过程中有能量突变 . 相似文献
6.
单个地利用非晶物质对X射线、中子和电子的相干散射,可以计算其原子、电子或分子密度全径向分布函数(RDF),也可以同时利用这三种射线的干涉函数求解偏径向分布函数(P-RDF),以获得更精细的结构信息. 作者已报道了一个根据广角度X射线数据计算全径向分布函数的通用计算机程序[1](此程序已修改移置到通用的IBM-PC微机上).阚香兰等人[2]介绍了一个用 BASIC 语言编写的根据电子衍射数据计算非晶高聚物径向分布函数(RDF)的程序.本文简要介绍我们在IBM-PC 微机上用FORTRAN 语言(绘图程序用BASIC 语言)编写的根据中子散射数据计算各… 相似文献
7.
采用分子动力学方法计算得到DHI-乙烯醇聚合体系统的结构和径向分布函数。讨论了系统结构和径向分布函数与温度和压力之间的关系。结果表明粘合系统的空间分布一般地随着温度和压力的增加而收窄,对增加聚氨酯系统的粘合性具有积极的意义。 相似文献
8.
采用分子动力学方法计算得到DHI-乙烯醇聚合体系统的结构和径向分布函数.讨论了系统结构和径向分布函数与温度和压力之间的关系.结果表明粘合系统的空间分布一般地随着温度和压力的增加而收窄,对增加聚氨酯系统的粘合性具有积极的意义. 相似文献
9.
对液态Al在不同冷速下的微观结构及其转变机制进行了分子动力学模拟,模拟采用紧束缚势,得到了不同温度、不同冷速下,Al的双体分布函数;采用HA键型指数法统计了各种小原子团在不同温度下所占比例,得到原子组态变化的重要信息.结果表明,在冷却速率较慢时,液态金属Al最终形成晶态,当冷却速率较快时,液态Al最终形成非晶态;液态金属中的键对是液态Al的基本构成单元,液态Al在形成晶体时,1421,1422键对起非常重要的作用;而1551,1541键对对非晶的形成有重要的影响
关键词: 相似文献
10.
11.
Cooling rate effects on structure and thermodynamics of amorphous nanoparticles were studied in a spherical model using Molecular Dynamics (MD) method. The good equilibrium melts are cooling down by three different cooling rates in order to observe the cooling rate effects. We find that cooling rate effects on thermodynamic quantities such as potential energy and surface energy are more pronounced than those for static quantities. Microstructure of amorphous nanoparticles is analyzed via radial distribution function (RDF) and coordination number distributions. Relatively weak cooling rate effects on such quantities are found. Microstructure of surface and core of amorphous nanoparticles are analyzed. 相似文献
12.
Cooling-rate effects in simple monatomic amorphous nanoparticles were studied in a spherical model containing 2469 atoms using a molecular dynamics (MD) method under non-periodic boundary conditions. We used the pair double-well interaction potential developed by Engel and Trebin [Phys. Rev. Lett. 98 225505 (2007)]. To observe the cooling-rate effects, the initial, well-relaxed models at a high temperature (i.e. in liquid state) were cooled to zero temperature at three different cooling rates. Cooling-rate effects on thermodynamic quantities, such as potential and surface energy, were more pronounced than those for static quantities. The potential and surface energy of the nanoparticles decreased with decreasing cooling rate, indicating the formation of more stable configurations with lower cooling rates. The microstructure of amorphous nanoparticles was analyzed via radial distribution function (RDF), coordination number and bond-angle distributions. Relatively weak cooling-rate effects on such quantities were found. Honeycutt–Andersen analysis for different bond pairs was used and discussed. The microstructure of the surface and core of amorphous nanoparticles were analyzed and the evolution of nanoparticle structures upon cooling from the melt discussed. Cooling-rate effects in a short-range interaction system are discussed and compared with those in long-range systems. 相似文献
13.
利用差示扫描量热仪研究了5种高浓度丙三醇水溶液(60%、70%、80%、90%、100%)的玻璃化转变行为,以考察水分含量和升降温速率对其玻璃化转变行为和结构松弛参数的影响.采用4种线性升降温速率(10、15、20、25K/min)获得玻璃化转变的相关参数.利用GordonTaylor方程对玻璃化转变温度的分析结果表明,水对丙三醇增塑常数的计算结果与升降温速率和玻璃化转变温度的读取方法有很大关系.玻璃化转变过程的比热容变化不仅随水分含量的增加而增加,而且与升降温速率也有一定的依赖关系.结构松弛活化能的计算结果表明,随体系水分含量的增加,体系的结构松弛活化能和动力学脆度都逐渐降低.随水分含量的变化,热力学脆度和动力学脆度表现出相反的变化趋势. 相似文献
14.
15.
16.
用分子动力学结合嵌入原子势研究了含有531个原子的Co531, Cu531和Ni531团簇从不同初始温度以不同冷却速率凝固到200 K时的凝固行为. 结果表明初始温度和冷却速率对团簇的凝固点有很大影响. 初始温度越高, 冷却速率越小, 团簇的凝固点越高. 凝固条件的改变会对三种团簇的凝固结构产生不同的影响. Cu531和Ni531团簇尽管在不同条件下的凝固点不同, 但凝固结构都是二十面体. 而Co
关键词:
金属团簇
凝固
分子动力学模拟 相似文献
17.
18.
The present study investigated the relative contributions of water content and non-equilibrium cooling and warming rates to the survival of cryopreserved axes of recalcitrant P. trifoliata seeds. Reducing water contents from 1.7 and 0.26 g water per g dry mass is believed to increase cytoplasmic viscosity. Cooling to -196 degree C was done at rates averaging between 0.17 and 1300 degree C per second, and warming at 600 or 1.35 degree C per second. Survival was assessed after 4 weeks in vitro. Rapid warming resulted in higher survival and normal development of axes at all water contents. The effects of cooling rate were dependent on the water content of axes. Cooling rates resulting in >70 percent normal development ranged between 0.17 and about 1300 degree C per second for axes at a water content of 0.26 g water per g dry mass narrowing with increasing hydration to an apparent optimum at about 686 degree C per second in axes at 0.8 g water per g dry mass At 1.7 g water per g dry mass, axes cooled at 0.17 degree C per second yielded nearly 40 percent normal development, whereas faster cooling was deleterious. Results are interpreted in the context of the effect of water content on cytoplasmic viscosity and the rate of intracellular ice formation. At low water contents, the high intracellular viscosity slows ice crystallization making survival independent of cooling rate. At higher water contents, the reduced viscosity requires faster cooling to prevent ice crystal damage. The ability to cool rapidly with increasing hydration is balanced with an increasing limitation to dissipate heat fast enough to prevent severe damage. 相似文献
19.
应用商业软件CFX 计算了液态锂流速、热通量、冷却水的速度和温度对自由流动液态锂在热负荷作用下液态锂温度和水冷效率的影响。结果表明:液态锂温度随液态锂流速的增大而降低。热通量小于2MW·m-2 时,水冷能够满足对液态锂温度控制的要求;在更大热通量作用下,水冷却显现出冷却能力不足。增大冷却水流速是降低液态锂温度、提高冷却效率的有效途径;冷却水温度对液态锂温度和冷却效率的影响较小。 相似文献