不安分的运动

A. Sutton
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引用次数: 0

摘要

固体中的原子处于不断的随机运动中。它们的动能是热。与局部区域相关的热量可能会波动。波动的大小随区域大小的减小而增大。这种波动使热活化过程得以发生。在平衡状态下,间隙和空位在固体中随机游走,从而引起晶体中的扩散和聚合物中的重复。活化能是这些缺陷在位点之间跳跃所必须克服的自由能垒。扩散受到由化学势梯度引起的驱动力的偏倚。迁移率将缺陷的漂移速度与驱动缺陷的作用力联系起来。爱因斯坦关系将迁移率与扩散率联系起来。这是涨落耗散定理的一个例子。原子运动使扩散成为可能,但限制了流动性。热膨胀也是原子运动的结果,这是由所有原子间力的基本不对称造成的。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Restless motion
Atoms in solids are in constant random motion. Their kinetic energy is heat. Heat associated with local regions may fluctuate. The size of the fluctuations increases with decreasing size of the region. Such fluctuations enable thermally activated processes to occur. At equilibrium interstitials and vacancies undergo random walks in solids, which gives rise to diffusion in crystals and reptation in polymers. The activation energy is the free energy barrier these defects have to overcome to jump between sites. Diffusion is biased by driving forces resulting from gradients of chemical potential. The mobility relates the drift velocity of defects to the driving force on them. The Einstein relation relates the mobility to the diffusivity. It is an example of the fluctuation-dissipation theorem. Atomic motion enables diffusion and limits mobility. Thermal expansion is also a consequence of atomic motion, resulting from a fundamental asymmetry in all interatomic forces.
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