Study on intelligent properties of arc cathode spot and their applications to surface cleaning of metals

真空电弧的阴极点优选地产生在金属氧化物上。它们通过蒸发选择性地去除氧化物，并清洁金属表面。在这项工作中，研究人员研究了阴极斑的特征特征，并了解了其独特性质的物理背景。主要研究结果如下：(1)开尔文探针对金属氧化物表面的分析表明，与纯金属相比，金属氧化物表面形成较好的阴极斑是由于氧化物的功函数较低所致。(2)金属氧化物上存在两种不同的阴极斑产生方式。一种比另一种具有更高的能量密度。具有较高能量密度的阴极斑有助于提高氧化物的脱除率。经高能阴极斑处理的表面比经低能阴极斑处理的表面更加光滑。(3)同一表面可同时出现两种不同的模式。高能斑点与低能斑点的比例取决于表面条件。在金属阴极表面加入氢氧化钠或氢氧化钾后，其除氧率增大，即除氧化率增加。聚乙二醇的加入也有助于去除效率的提高。(4)由于去除氧化物时形成的薄熔层迅速凝固，阴极斑处理后的表面硬度增加。(5)减小阳极和阴极之间的间隙宽度，提高了去除氧化物的能量效率。当间隙宽度小于临界值时，阳极电位降消失。在这种情况下，输入能量的大部分被消耗在阴极上的氧化物的去除上。

Cathode spots of a vacuum arc are preferably produced on the metallic oxide. They remove the oxide selectively by evaporation and clean the metal surface. In this work investigators have studied the characteristic features of the cathode spots and understand physical background of the unique properties. Main results are summarized below.(1)The analysis of surface using a Kelvin probe reveals that the preferable formation of cathode spots on the metallic oxide results from the lower work function of the oxide compared with pure metal.(2)There exist two different modes of cathode spots produced on the metallic oxide. One has higher energy density than the other. The cathode spots with higher energy density contribute the high rate of oxide removal. The surface treated by high energy cathode spots becomes smoother than that by low energy cathode spots.(3)Two different modes can appear on the same surface at the same time. The ratio of high energy spots to low energy ones depends on the surface condition. The application of NaOH or KOH to the cathode surface of the metal results in the increase of the ratio, which means the increase of the rate oxide removal. The addition of polyethylene glycol also contributes the increase of the removal rate.(4)The hardness of the surface treated by the cathode spots increases because of the rapid solidification of the thin molten layer formed during the removal of oxide.(5)Reduction of gap width between an anode and a cathode results in the increase of the energy efficiency of the oxide removal. The anode potential drop disappears in a gap width shorter than a critical value. In such condition, a major part of the input energy is consumed for the removal of oxide on the cathode.