Showing papers by "Ulrich Geppert published in 2018"
23 Jan 2018
TL;DR: In this article, the effect of the proton flux magnitude on the degradation of native metal oxide layers and its consequences for hydrogen blisters was examined, and it was found that intense proton irradiation increases the permeability of aluminium oxide layers for hydrogen atoms, thereby counteracting hydrogen blister formation.
Abstract: Metallic surfaces, exposed to a proton flux, start to degradate by molecular hydrogen blisters. These are created by recombination of protons with metal electrons. Continued irradiation progresses blistering, which is undesired for many technical applications. In this work, the effect of the proton flux magnitude onto the degradation of native metal oxide layers and its consequences for blister formation has been examined. To study this phenomenon, we performed proton irradiation experiments of aluminium surfaces. The proton kinetic energy was chosen so that all recombined hydrogen is trapped within the metal structure. As a result, we discovered that intense proton irradiation increases the permeability of aluminium oxide layers for hydrogen atoms, thereby counteracting blister formation. These findings may improve the understanding of the hydrogen blistering process, are valid for all metals kept under terrestrial ambient conditions, and important for the design of proton irradiation tests.
21 citations
01 Jan 2018
TL;DR: In this paper, degradation studies of thin metallized foil with an oxide layer were carried out and the irradiation tests were performed by use of a linear proton accelerator at DLR-Bremen for three different proton flux magnitudes.
Abstract: Materials need to undergo qualification testing before being applied to any space mission. Testing includes radiation hardness. It is the aging response of materials to corpuscular and/or electromagnetic radiation. The type of radiation and its amplitude depend on the space environment under study. To perform tests within reasonable times, radiation amplitude must exceed that present in space. Hence, accelerated irradiation tests must be performed.
Our main objective is to emphasise potential risks, which may occur upon performing irradiation tests of satellite components with an acceleration factor higher than one.
Degradation studies of thin metallized foil with an oxide layer were carried out. The irradiation tests were performed by use of a linear proton accelerator at DLR-Bremen for three different proton flux magnitudes.
During the irradiation, the sample surfaces were populated with blisters filled with molecular hydrogen gas. It turns out that the size and the number of blisters depends strongly on the proton flux magnitude. More importantly, we have proven that there exists a threshold of the flux magnitude above which the blistering process is being decelerated. It has direct correlation with the metal oxide layer and its aging condition.
The here presented results are important for planning of proton irradiation tests. Too high proton fluxes lead to an acceleration of material degradation that does not reflect the true nature of aging processes as take place in the environment under study. In our case, the presence of the outer aluminium oxide layer has a decisive role in the aluminium degradation process.