Comparison of electrode materials of plasma spray nozzle

      Thorium tungsten electrode is used to be the earliest rare earth tungsten electrode, and it is also a type of tungsten electrode with excellent welding performance. Therefore, thorium tungsten electrode has the highest market share in the world. However, due to radioactive contamination of thorium tungsten electrode in the time of powder metallurgy and calender grinding, the production of this kind of electrode is restricted to European and American countries. For example, the use of thorium tungsten electrode is no longer allowed in Switzerland and other countries. Since June 2014, Plansee has only produced environmentally friendly plasma spraying electrode made of tungsten-lanthanum. However, most countries have no restrictions on its use because of excellent welding performance. Owing to the radioactive contamination in production and use, it is an inevitable trend that thorium tungsten electrodes will be withdrawn from the market. Cerium tungsten and lanthanum tungsten are both popular alternatives.

      Cerium tungsten electrode is not radioactive pollution and belongs to green environmental protection products. Moreover, the arc can be easily started with a very small current. Cerium tungsten electrode is very prevalent at low dc current. However, it is not as resistant to burn as thorium tungsten and the consumption is faster, leading to large input and high cost. Lanthanum tungsten electrode equipped with similar properties to thorium tungsten electrode. Furthermore, the arc performance and fire resistance are better than thorium tungsten electrode when using small and medium current. Lanthanum tungsten electrode is not radioactive with high durable current and low burn rate. The tungsten-lanthanum (WL10) and thorium (WT20) electrodes were tested at the Institute of Physical Metallurgy and Materials Testing at Leauburn University. The experiment shows that lanthanum tungsten electrode has the advantages of good ignition performance, higher deposition efficiency, slower arc voltage drop speed as well as less wear, and can produce continuous high-quality coating. Therefore, lanthanum tungsten electrode is considered to be the most suitable high-performance material to replace thorium tungsten electrode.

Reference：Plansee Official Website