Evaluation of changes in physical properties of low thermal expansion ceramics and glass induced by radiation

Cordierite ceramics have excellent physical properties such as a high elastic modulus, low bulk density, high thermal conductivity and low coefficient of thermal expansion (CTE). These features make cordierite ceramics attractive materials for ultra-lightweight and thermally-stable components used in changing thermal environments. Thus, cordierite ceramics have been widely used in ground-based precision systems, but have not yet been applied to space missions. Their resistance against the space environment must first be demonstrated in order to apply these materials to space missions. One of the main issues in the space environment is the deterioration of materials induced by space radiation. The electrons and protons trapped around Earth and having energies of several MeV to tens of MeV cause ionization inside materials. Long-term radiation exposure may induce changes in physical properties, leading to degraded performance. This study evaluated two cordierite ceramics and a SiAlON ceramic for the changes in key physical properties (i.e. Young's modulus, CTE) induced by radiation as compared with traditional low CTE glass materials. The irradiation test conditions of 10 MeV energy and 2.5×10¹⁶ /cm² total fluence were set by assuming the worst-case condition for operation on geostationary orbit (GEO) over a 20-year period. The total fluence was irradiated in several divided doses, and the changes in physical properties were evaluated relative to increases in irradiation dose. As a characteristic result, the cordierite ceramics showed virtually no changes in terms of Young's modulus and CTE, while all the compared glass materials gradually showed an increase in CTE in line with increases in irradiation dose. This result indicates that the cordierite ceramics have superior radiation resistance in terms of the stability of physical properties as compared to the low CTE glass materials.