Which tungsten electrode type has the poorest heat resistance and electron emission characteristics?

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

Answer: (C)

In GTAW, electrode performance hinges on two things: how easily it emits electrons to start and sustain the arc, and how well it withstands the heat of the welding arc. Pure tungsten has no dopants, so its electron emission is relatively poor compared with doped varieties. That means it requires higher starting voltage, can struggle to maintain a stable arc at higher currents, and wears away faster under heat. The doped tungsten types—lanthanum-tungsten, zirconium-tungsten, and thoriated tungsten—add oxides that boost thermionic emission and improve heat resistance, giving better arc stability and longer electrode life. So pure tungsten ends up with the poorest heat resistance and electron emission characteristics among the options.