Molybdenum Erosion in an Hollow Cathode-like Iodine Plasma Enviroment

The maturation of electric propulsion technology has led to an increased interest in replacing Xenon as the propellant of choice. Iodine is an attractive alternative to Xenon, due to its similar performance characteristics, improved storage capabilities, and dramatically lower price.  However due to its nature as a halogen, iodine is very reactive and presents serious challenges for the lifespan of plasma facing materials. The most critical component of a typical electric propulsion system is the hollow cathode due to the high plasma densities and wall temperature required for operation. 

In this work, we investigate the impact that a hollow cathode-like iodine plasma environment has on molybdenum. An RF inductively coupled plasma source is used to approximate the plasma environment of a hollow cathode. Molybdenum material samples were exposed to three different conditions: iodine plasma, iodine vapor, and argon plasma. In each case, the molybdenum samples were exposed to multiple different high temperatures ranging from 1500K to 2000K. The plasma cases were additionally performed for several different plasma densities.

Molybdenum is expected to perform well under iodine vapor conditions due to being relatively chemically resistant. The material samples underwent a dramatic change in surface grain structure during the tests due to the high temperatures used. Molybdenum does not experience a significant change in material color before and after iodine testing.