Why Adding Rare Earth Oxides to Tungsten Electrodes

Metal tungsten has the characteristics of high melting point, strong electron emission ability and low vapor pressure, making it the preferred thermionic emission material. However, the higher electron work function, electrode tip temperature and grain growth are prone to cause the instability of the pure tungsten electrode arc beam, difficulty in starting the arc, and short service life, and it can only be used for AC welding. In order to overcome the above-mentioned shortcomings, manufacturers often add rare earth oxides with low electron work functions such as lanthanum oxide, cerium oxide, yttrium oxide, etc. to pure tungsten materials, which can increase the recrystallization temperature of the product and activate the electrons. emission.

Studies have shown that the nature of rare earth oxides during combustion is the most important factor affecting electrode performance, electrode temperature, work function and thermal stability.

Under normal circumstances, rare earth metal oxides react with tungsten to form tungstate or tungstate oxide. The melting point of these salts is lower than the melting point of the reactants, so they melt first during the arcing process and migrate from the low temperature zone to the high temperature zone along the axial boundary. The reaction behavior of different rare earth oxides and the melting point of the tungstate or tungstate oxide produced by them are also different.

Taking cerium oxide, lanthanum oxide, and yttrium oxide as examples, cerium tungstate has the lowest melting point, and cerium oxide has the highest mobility; the higher melting point of lanthanum tungstate is related to its stability, and its migration compensates for evaporation. Stable; the melting point of yttrium tungstate is relatively high, and it takes a long time for yttrium oxide to migrate along the grain boundary to the end and the surface.

In general, in order to improve the thermal stability, service life, emission capability of electrode materials, and improve its arc performance, adding a small amount of rare earth oxide to tungsten is an effective way.