低圧雰囲気におけるアーク現象(第2報)

黒鉛陰極の消耗特性と陰極形態

抄録

As stated in the previous paper, there found two kinds of the cathode modes, i.e. the cold and hot cathode modes, in a low pressure arc generated between the graphite electrodes. Consumption of a graphite cathode was quite different in each cathode mode. For example, a carbon vapour stream and spattering from the cathode root were ovserved in the cold cathode mode, while no vapour stream nor spattering was seen in the hot one.
The consumption characteristics of a graphite cathode and the corelation to the cathode mode were investigated to clarify the cathode mechanism. Experiments were conducted on an arc with a graphite cathode and a water cooled copper anode under the condition of the current range being 10-120 Amp and of the pressure 10-100 Torr of hydrogen and 10-60 Torr of helium and argon.
Results obtained in this study are as follows.
(1) In addition to the cold and hot cathode modes, anew mode which was termed the plasma cathode mode was distinguished in a C(-)-Cu(+) arc at low pressure, regardless of the kinds of gas. This mode which was featured by a bright sphere in front of the cathode tip (cathode plasma ball) appeared as an intermediate stage of the cold and hot cathode modes. The existence of the plasma cathode mode was clearly recognized in the consumption characteristics of a graphite cathode but hardly detected in the electric characteristics of an arc.
(2) A cathode plasma ball expaoded its size with the increase of current or the reduction of pressure. In the plasma cathode mode, it was clearly separated from the arc column by a dark space. When the dark space became undetectable, the hot cathode mode emerged.
(3) Under the condition of this experiment, specific consumption rate m_G/I (mg/A min) of a graphite cathode ith the cold cathode mode was as hifih as five times or compared with so the one in the hot cathode. Meanwhile, in the plasma cathode mode, m_G/I was a little higher than that in the hot one. In the cold cathode mode, more than 90% of the consumption was the sublimation of carbon at the cathode root, and the spattering loss was less than 10%.
(4) In the cold cathode mode, carbon rather than the ambient gas might be preferentially ionized in the cathode fall region.
(5) The transition of the cathode mode was determined by the systematic study of the consumption characteristics of a graphite cathode. In this study, three governing factors of the cathode mode(p, I & V_i), which were mentioned in the previous paper, were clearly proved.