What is the effect of thorium oxide addition at 1-2% on erosion?

• A. It has no effect on erosion.
• B. It increases erosion.
• C. It reduces electrode tip temperature and erosion.
• D. It eliminates tungsten erosion completely.

Answer: (C)

Thorium oxide at about 1–2% improves how easily the tungsten tip emits electrons. With easier electron emission, the arc can be sustained with less heat concentrating at the tip, so the electrode tip stays cooler. That cooler tip means less melting and wear, i.e., reduced erosion. It also helps arc stability, which further protects the tip from rapid wear. It doesn’t completely prevent erosion, nor does it increase erosion, and it certainly doesn’t eliminate it entirely, but it does lower both the tip temperature and the erosion rate.