Rare Earth Compounds for Extreme Aerospace and Space Environments

Rare earth compounds (REs) have a variety of unique properties that can be exploited for use in extreme aerospace and space environments. This includes extreme temperature, heat flux, and space radiation. In the case of high temperatures and heat fluxes, ultra-high temperature ceramics (UHTCs) are of interest for high melting temperatures (3000C+) but suffer from limited oxidation resistance. The addition of REs acts to improve oxidation resistance through 1) formation of more favorable oxidation phases (i.e., stabilized zirconia (ZrO₂) in the case of zirconium diboride (ZrB₂)) and 2) increasing the surface emissivity. For the latter, the increase in surface emissivity acts to lower the effective surface temperature for a given heat flux which can limit the detrimental oxidation and improve survivability. First principal calculations that were used to down select REs based on emissivity in the wavelengths of interest will be presented. Experimental data includes pellet pressing and oxidation results of ZrB₂ with samarium and dysprosium compounds.
For the case of space environments, radiation damage can be a major issue. This is especially true in the medium earth orbit where trapped high energy protons in the Van Allen radiation belt range from ~1 MeV upwards of 10s of GeVs. Traditional solutions including aluminum slabs can be limited in terms of resistance and weight. Here we present exploration of RE dopants in ZrO₂ as a radiation shielding material to provide enhanced radiation shielding. Experimental data including microstructure and density of pressed and sintered pellets will be presented along with initial screening of relevant radiation environment species. Monte Carlo simulations of the high energy environments were further explored to determine the viability of these materials for radiation shielding within relevant space environment conditions.