Ostwald Ripening of Two-Phase Mixtures
Ostwald Ripening of Two-Phase Mixtures
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DOI：
10.1146/annurev.ms.22.080192.001213
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
P. Voorhees
中科院分区：
文献类型：
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作者：
P. Voorhees
相分离过程经常产生两相的多分散混合物，其组成和体积分数接近平衡。这种混合物也可以通过照射材料来制造空洞，或者像在液相烧结过程中那样，通过混合不同成分的粉末来人工制造。尽管两相体系接近平衡状态，但混合物并没有处于最低能量状态。这是由于混合物本身的多分散性质和非零界面能的存在。因此，在没有弹性应力的情况下，为了使系统达到热力学平衡，系统的总界面面积必须随时间减少。系统有许多方法可以减少这种多余的界面面积。这里感兴趣的过程是当界面面积通过扩散传质过程从高界面曲率区域减少到低界面曲率区域时。这种界面面积减少的过程通常被称为粗化，或奥斯特瓦尔德成熟，以物理化学家W.奥斯特瓦尔德命名，他首先描述了这一过程(1)。这种界面能驱动的传质过程可以显著改变两相混合物的形貌。一般来说，混合物的平均尺寸必须随着时间的推移而增加，而第二相域或粒子的数量必须随着时间的推移而减少。图1显示了一个Ostwald成熟过程的示例。上图显示了等温铅锡共晶液体中富锡固体颗粒随时间的变化。明显
Phase-separation processes frequently result in a polydisperse mixture of two phases of nearly equilibrium compositions and volume fractions. Such mixtures can also be created artificially by irradiating materials to create voids or, as is done in liquid phase sintering processes, by mixing together powders of different composition. Despite the nearly equilibrium state of the two-phase system, the mixture is not in its lowest energy state. This is because of the polydisperse nature of the mixture itself and the presence of a nonzero interfacial energy. Thus in the absence of elastic stress, the total interfacial area of the system must decrease with time in order for the system to reach thermodynamic equilibrium. There are many ways the system can reduce this excess interfacial area. The process of interest here is when the interfacial area is reduced via a diffusional mass transfer process from regions of high interfacial curvature to regions of low interfacial curvature. This interfacial area reduction process is commonly called coarsening, or Ostwald ripening, after the physical chemist W. Ostwald, who first described the process (I). This interfacial energy driven mass transfer process can significantly alter the morphology of the two-phase mixture. In general, the average size-scale of the mixture must increase with time and the number of second phase domains, or particles, must decrease with time. An example of an Ostwald ripening process is shown in Figure 1. The upper row of micro graphs shows the evolution of Sn-rich solid particles in an isothermal Pb Sn eutectic liquid as a function of time at constant magnification. Evident