____ has the poorest heat resistance and electron emission characteristic of all the tungsten electrodes.

• A. Lanthanum tungsten
• B. Zirconium tungsten
• C. Pure tungsten
• D. Thoriated tungsten

Answer: (C)

In GTAW, how well the electrode emits electrons and stands up to the arc heat is greatly affected by its composition. Pure tungsten has no dopants that lower the work function or boost high-temperature stability, so its electron emission is poorer and it erodes more readily under heat. That combination means it performs worse for both starting and sustaining the arc than the alloyed/tungsten oxide–doped varieties. Dopants like thorium, lanthanum, or zirconium oxide enhance emission and heat resistance, making those electrodes better suited for welding. So the electrode with the poorest heat resistance and electron emission among common tungsten types is the pure tungsten.