抄録
The light emitting elements around a tungsten electrode during tungsten inert gas welding were identified using an optical emission spectroscopy. A white and blue umbrella-shaped light emitting bilayer region was observed above the tip of the tungsten electrode containing the lanthanum oxide during the welding on a water-cooled copper plate. On the other hand, the umbrella-shaped light emitting region was not clearly observed when the pure tungsten electrode was used. The optical emission spectroscopy revealed that the umbrella-shaped light emitting region was the emission from lanthanum vapor. The white region in the upper layer mainly consisted of the emission from lanthanum atoms, and the blue region in the lower layer mainly consisted of the emission from lanthanum ions. The lanthanum atoms emitted strong light at 5800 K, and the lanthanum ions emitted strong light at 10800 K. Therefore, it was considered that the bilayer regions appeared like the umbrella depending on the temperature field and the shape of the arc plasma around the electrodes. The temperature range in which the tungsten vapor emitted strong light was almost the same as that of the lanthanum vapor. Nevertheless, the spectrum of tungsten vapor was not measured. This was because the electrode surface during this welding was covered with the molten lanthanum, and the amount of tungsten vapor was smaller than that of lanthanum vapor. The temperature range in which the cerium and thorium vapors emitted strong light was almost the same as that of the lanthanum vapor. It was suggested that the umbrella-shaped light emitting region appeared around the electrode during welding when the tungsten electrode containing the cerium oxide or the thorium oxide was used as well.
