H2 Blister formation on metallic surfaces - a candidate for fegradation processes in space

Kurzfassung

H2-blisters are metal bubbles filled with hydrogen molecular gas resulting from recombination processes of protons in metal lattice. Bubble formation depends on many physical parameters, for instance: proton energy, proton flux, or the temperature of an exposed sample. Up to now no metallic sample that has been exposed to conditions prevalent in the interplanetary medium has been returned to Earth. Therefore, a direct evidence that blistering appears in space is missing. However, blistering is certainly a candidate of degradation processes which may occur in space. It could play an important role in the solar sail technology, where the performance of the sail is significantly affected by both the sail geometry but especially by optical properties of sail materials. Thus, both theoretical and laboratory studies of the blistering process have to be performed. The here presented model simulates the growth of molecular hydrogen bubbles on metallic surfaces. Additionally, it calculates the decrease of reflectivity of the by blistering degraded foils. First theoretical results show that the reflectivity of an Aluminum foil decreases by about 27% for a bubble surface density of 1500 cm-2 and an average bubble radius of 100 μm. Therefore, if blistering occurs, the propulsion performance of any sail-craft will be decreased by a significant factor.