Influence of Externally Imposed and Internally Generated Electrical Fields on Grain Growth, Diffusional Creep, Sintering and Related Phenomena in Ceramics
Influence of Externally Imposed and Internally Generated Electrical Fields on Grain Growth, Diffusional Creep, Sintering and Related Phenomena in Ceramics
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DOI：
10.1111/j.1551-2916.2011.04652.x
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发表时间：
2011-07-01
影响因子：
3.9
通讯作者：
Francis, John S. C.
中科院分区：
文献类型：
--
作者：
Raj, Rishi;Cologna, Marco;Francis, John S. C.
微波和放电等离子烧结 (SPS) 增强了可烧结性。通过一对电极施加到裸露样品上的简单电场已被证明可以加速超塑性变形的速率，减少烧结的时间和温度，并延缓晶粒生长的速率。由此推断，电场和电磁场对晶界能量学和动力学的影响是明确无误的。通常，在陶瓷中，晶界本身具有空间电荷，可以与外部施加的场耦合。讨论了从零频率到微波频率范围内的这种耦合的频率依赖性。模拟晶粒生长、蠕变和烧结的经典方法考虑热力学驱动力下的化学扩散（自扩散），并以物理机制为基础，以再现现象学观察的方式可视化质量传输流。在所有情况下，最终的分析结果都可以分为三个函数的乘积：第一个是晶粒尺寸，第二个与热力学驱动力有关，第三个与质量传递动力学有关。讨论了电场对这些功能中每一个功能的影响。这些电相互作用的基本机制通过以下方式讨论：（i）晶体和晶界处的介电损耗和焦耳热，（ii）机械应力和带电物质的电化学势之间的耦合，（iii）施加的电场和空间电荷层内存在的本征场之间的相互作用，（iv）以及成核缺陷的可能性 电场作用下的雪崩。我们将自己限制在至少具有一定程度离子特性的陶瓷上。在这些实验中，电场范围从每厘米几伏到几百伏，焦耳热的功率耗散约为每立方厘米样品几瓦。不考虑金属，在相对低的施加电场下获得非常高的电流密度，导致诸如电迁移的现象。
Microwaves and spark plasma sintering (SPS) enhance sinterability. Simple electrical fields, applied by means of a pair of electrodes to bare specimens, have been shown to accelerate the rate of superplastic deformation, reduce the time and temperature for sintering, and to retard the rate of grain growth. By inference, the influence of electrical and electromagnetic fields on grain boundary energetics and kinetics is unmistakable. Often, in ceramics, grain boundaries are themselves endowed with space charge that can couple with externally applied fields. The frequency dependence of this coupling ranging from zero frequency to microwave frequencies is discussed. The classical approach for modeling grain growth, creep, and sintering, considers chemical diffusion (self-diffusion) under a thermodynamic driving force, underpinned by a physical mechanism that visualizes the flow of mass transport in a way that reproduces the phenomenological observations. In all instances, the final analytical result can be separated into a product of three functions: one of the grain size, the second related to the thermodynamic driving force, and the third to the kinetics of mass transport. The influence of an electrical field on each of these functions is addressed. The fundamental mechanisms of these electrical interactions are discussed in the following ways: (i) dielectric loss and Joule heating in the crystal and at the grain boundary, (ii) the coupling between mechanical stress and the electrochemical potential of charged species, (iii) the interaction between applied electrical fields and the intrinsic fields that exist within the space charge layers, (iv) and the possibility of nucleating defect avalanches under electrical fields. We limit ourselves to ceramics that have at least some degree of ionic character. In these experiments the electrical fields range from several volts to several hundred volts per centimeter, and the power dissipation from Joule heating is of the order of several watts per cubic centimeter of the specimen. Metals, where very high current densities are obtained at relatively low applied electric fields, leading to phenomenon such as electromigration, are not considered.