1995 年 13 巻 4 号 p. 524-531
Waste treatment by thermal plasma is an attractive technology from the viewpoint of environmen-tal problems. For this application, the short lifetime of plasma generator (torch) is the most serious problem. It is essentially governed by the durability of electrode, which is used in the severe condition of a rather high current for a long time.
In this study, the consumption of tungsten electrode under a high current condition was studied. The consumption test was carried out under the following conditions. For 2.4 mmφ electrode a 350 A, Ar arc was applied for an hour and also for 3.2 mmφ electrode a 500 A, Ar arc was applied. After the test, the weight change was measured, and the morphology was observed by SEM and analyzed by EDX. Tip shape effect was also discussed from the viewpoint of current density.
At high current conditions, the tungsten electrode activated by 2% rare-earth-metal oxide (La2O3, Y203, Ce2O3) showed severe consumption. In those cases, rare-earth-metal oxide disappeared near the tip and sometimes vacant holes were formed at the area.
The effects of grain morphology on the cosumption were studied. The electrode of longitudinalgrain micro-structure showed better property than that of granular one. This may indicate that migration of oxide is important factor to the consumption of electrode.