welding electrodes usually contain small quantities of
metallic oxides which can offer the following benefits:
Facilitate arc starting
Increase arc stability
carrying capacity of the electrode
the risk of weld contamination
Oxides used are
primarily zirconium, thorium, lanthanum or cerium.
Additions are usually 1% - 4%. These oxides greatly
improve arc initiation, especially when direct current
(DC) welding is employed. Thorium oxide (thoria) has
been used for many years, having been found effective in
terms of long life and thermal efficiency. Zirconium
oxide (zirconia) has been commonly used for alternating
(AC) TIG welding, normally for welding aluminum.