Degradation of metallic surfaces under space conditions, with particular emphasis on Hydrogen recombination processes

Abstract

The widespread use of metallic structures in space technology brings risk of degradation which occurs under space conditions. New types of materials dedicated for space applications, that have been developed in the last decade, are in majority not well tested for different space mission scenarios. Very little is known how material degradation may affect the stability and functionality of space vehicles and devices during long term space missions.Our aim is to predict how the solar wind and electromagnetic radiation degrade metallic structures. Therefore both experimental and theoretical studies of material degradation under space conditions have been performed. The studies are accomplished at German Aerospace Center (DLR) in Bremen (Germany) and University of Zielona Góra (Poland).The paper presents the results of the theoretical part of those studies. It is proposed that metal bubbles filled with Hydrogen molecular gas, resulting from recombination of the metal free electrons and the solar protons, are formed on the irradiated surfaces. A thermodynamic model of bubble formation has been developed. We study the creation process of H 2 -bubbles as function of, inter alia, the metal temperature, proton dose and energy. Our model has been verified by irradiation experiments completed at the DLR facility in Bremen.Consequences of the bubble formation are changes of the physical and thermo-optical properties of such degraded metals. We show that a high surface density of bubbles (up to 10 8 cm −2 ) with a typical bubble diameter of ∼ 0.4µm will cause a significant increase of the metallic surface roughness. This may have serious consequences to any space mission.Changes in the thermo-optical properties of metallic foils are especially important for the solar sail propulsion technology because its efficiency depends on the effective momentum transfer from the solar photons onto the sail structure. This transfer is proportional to the reflectivity of a sail. Therefore, the propulsion abilities of sail material will be affected by the growing population of the molecular Hydrogen bubbles on metallic foil surfaces.

Hydrogen blistering under extreme radiation conditions

“…As a consequence, the propulsion abilities of the sail are reduced by the growing population of the blisters. 2 In irradiation tests, the proton flux magnitude can be set freely from low to high values. The selected value is determined by the requirement to shorten laboratory time as much as possible to reach the number of incident protons which corresponds to the physical situation under study.…”

“…1 A similar situation appears if metallic surfaces react with solar wind ions in the interplanetary medium. 2 For the here presented results, the examined metals were exposed to protons at elevated temperature.…”

Membrane Deployment Technology Development at DLR for Solar Sails and Large-Scale Photovoltaics

“…The blisters of approx. 0.4 µm diameter were produced by exposure of the VDA to a flux of low energy protons at only 2.5 keV [39]. The hydrogen gas results from recombination processes of the incident protons and the metal's electrons.…”

Энергия растворения водорода в ГЦК-гидридах неупорядоченных сплавов Ti-V-Cr по данным теории функционала плотности

“…[1][2][3][4][5]. Энергия растворения водорода в металлах, E sol , одна из фундаментальных характеристик TM−H системы, поскольку определяет диффузию водорода в металле, его водородоемкость, энтальпию формирования гидрида и другие свойства, важные для практических приложений.…”