Roles and Behaviors of Rare Earth Metal Oxides During the Operation of Tungsten Doped Electrodes

A comparative study has been made on the metallurgical characteristics of several tungsten electrode types. The work was carried out with tungsten electrodes activated with a small quantity of single and combined additions of the rare earth metal oxides. Metallographic studies of the electrodes indicate that the superiority of operating characteristics strongly depends on the behavior of the rare earth metal oxides during arc burning. It is observed that the rare earth metal oxides form tungstate or oxytungstate during arc burning. Those newly formed compounds have low melting points and migrate from the low temperature zones to the high temperature zones throughout the electrode tip, while ThO_2 reacts with a tungsten forming pure Th. Also the investigation demonstrates good stability of La_2O_3 during arc burning comparing with the other oxides in the case of single additions. However, the electrode activated with three combined additions shows superior stability and durability for long time operation.