What does thorium oxide addition do for the tungsten electrode?

• A. Up to 0.6% improves current carrying capacity.
• B. Also provide a much easier arc starting characteristic than pure or zirconiated tungsten.
• C. They work well with DCEN and maintain a sharpened point well. Do not use with AC.
• D. 1-2% improves electron emission allowing approximately 20% more current, and reduces electrode tip temperature, reducing erosion.

Answer: (C)

Thorium oxide in tungsten lowers the work function and boosts electron emission, which helps start and sustain the arc more easily. In DC TIG, you want a concentrated current at the tip and a stable, easy-to-start arc, and thoriated tungsten is known for holding a sharp point while emitting electrons efficiently. This makes it a reliable choice for DCEN and DCEP welding. However, the rapid polarity changes and oxide cycling in AC welding tend to erode thoriated tips faster, so this type is not preferred for AC. So, the idea that thoriated electrodes perform well with DCEN and keep a sharpened tip, with caution about AC use, is the best description.