Surface features and energy considerations related to the erosion processes of Cu and Ni electrodes in a spark discharge nanoparticle generator
Surface features and energy considerations related to the erosion processes of Cu and Ni electrodes in a spark discharge nanoparticle generator
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DOI：
10.1016/j.jaerosci.2018.02.005
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发表时间：
2018-05-01
影响因子：
4.5
通讯作者：
Galbacs, G.
中科院分区：
文献类型：
--
作者：
Kohut, A.;Wagner, M.;Galbacs, G.
在本研究中，研究了在火花放电纳米粒子发生器中暴露于少量（1-3）火花的抛光镍和铜电极表面（平均粗糙度约为4.5 nm）的侵蚀，目的是更好地了解泵入电极的能量的利用以及导致气溶胶纳米粒子产生的过程。结果表明，即使是单次振荡放电也会在电极表面产生复杂的形态变化。通过光学、共聚焦激光扫描和原子力显微镜，确定了三个主要的侵蚀特征（称为陨石坑、波浪形区域和树枝状区域）。并讨论了它们的形成机制。通过估算熔化电极材料所需的总能量，这些能量与单独识别的凹坑的体积相对应，并与放电的前半个周期相关联，结果表明，以焦耳加热的形式泵入电极的电能主要被电极材料的熔化消耗，然后再凝固。因此，只有一小部分电极材料实际上蒸发到周围的气体中。这解释了在常用的琼斯模型中，能源效率的值非常低的原因。我们的结果表明，只有一部分离开电极表面的材料实际上转化为气溶胶。气溶胶形成的输入是由陨石坑喷出的蒸汽或熔融物质。喷射出的熔融物质会形成微米大小的气溶胶颗粒（“飞溅颗粒”）。一些金属蒸汽沉积在陨石坑附近的表面，形成树枝状区域，而只有一小部分金属蒸汽被周围的气体带走，并可能形成气溶胶纳米颗粒。该研究清楚地表明，火花放电纳米颗粒发生器的侵蚀过程非常复杂，不能用简化的侵蚀模型来合理地描述。
In the present study, the erosion of polished nickel and copper electrode surfaces (with an average roughness of ca. 4.5 nm) exposed to a low number (1-3) of sparks in a spark discharge nanoparticle generator were investigated with the purpose of better understanding the utilization of the energy pumped into the electrodes as well as the processes leading to the generation of aerosol nanoparticles. It was shown that even a single oscillatory discharge creates complex morphological changes on the electrode surfaces. Three main erosion features were identified (referred to as craters, undulated areas and dendritic areas) and characterized by optical, confocal laser scanning and atomic force microscopy. Their potential formation mechanisms are also discussed. By estimating the total energy needed to melt the electrode material corresponding to the volume of the craters individually identified and associated with the first half-cycle of the discharge, it was shown that the electric energy pumped into the electrodes in the form of Joule heating is mostly consumed by the melting of the electrode material, which is followed by re-solidification. Hence, only a small fraction of the electrode material is actually evaporated into the ambient gas. This explains the very low value of the energy-efficiency in the commonly used Jones model.Our results indicate that only a part of the material that leaves the electrode surface is actually converted into an aerosol. The input to the aerosol formation is either vapor or molten material ejected from craters. Ejected molten material can lead to the formation of micrometer-sized aerosol particles ("splashing particles"). Some of the metal vapor is deposited on the surface in the vicinity of craters forming dendritic areas, whereas only a fraction of the metal vapor is carried away by the ambient gas and may form aerosol nanoparticles. This study clearly indicates that erosion processes in spark discharge nanoparticle generators are very complex and can not be reasonably described by simplified erosion models.