What percentage of Lanthana is added to produce a black color in welding electrodes?

In the context of welding electrodes, specifically those used in Gas Tungsten Arc Welding (GTAW), the addition of lanthanum oxide serves to enhance the electrode's performance and longevity. When lanthanum oxide is included at a concentration of 1%, it produces a black color, which is significant in identifying the type of electrode and its intended use.

Lanthana is used in welding electrodes for its properties that improve arc stability and reduce the formation of weld defects. The black coloration is distinctive and helps welders easily identify the electrode type in a mixed environment. This trait is essential for ensuring that the correct electrode is used for specific welding applications, ultimately impacting the quality and aesthetics of the weld.

The other options present higher percentages or none at all, which do not accurately represent the concentration needed to achieve the characteristic black color in the electrodes. Therefore, the accurate addition of 1% lanthanum leads to the desired outcome in electrode appearance and function.