Simulated Van Allen Belt Exposure of Zirconium Diboride by Electron Irradiation

Abstract

Due to their innately robust thermal and mechanical qualities, ultra-high temperature ceramics (UHTCs) such as zirconium diboride (ZrB2) have been investigated as viable materials to be used in reusable thermal protection systems (TPS). TPSs are vital to a spacecraft’s heat balance in atmospheric reentry and in space. Here, the thermal and optical properties are especially critical in determining the heat balance. However, radiation exposure in space can degrade such material properties, especially over a prolonged mission duration. The interaction of electron radiation-which can be found in the outer Van Allen belt with ZrB2 has not been studied previously and was, therefore, the main scope of this study. The response of thermo-optical properties of ZrB2 to increasing electron radiation doses simulating 5,10, and 50 years of outer Van Allen belt radiation exposure was investigated. ZrB2 samples were made through spark plasma sintering and exposed to 3 MeV electron irradiation. The ZrB2 samples were characterized by their microstructure, thermal conductivity, coefficient of thermal expansion (CTE), emittance, absorptivity, and surface roughness. It was found that ZrB2’s thermo-optical properties showed high radiation resistance at these dosages, and no apparent microstructural change was observed after irradiation. However, the irradiated samples had, on average, a 29 % lower surface roughness than the unirradiated samples, possibly originating from electron sputtering. Moreover, ZrB2 samples produced at various sintering temperatures did not display a different radiation resistance.