Impact of hyperthermal oxygen on alumina surfaces investigated by molecular dynamics simulations

Abstract Atomic oxygen (AO) impinging on satellite surfaces in very low Earth orbit (VLEO) transfers momentum and energy, leading to material degradation and drag forces. To be able to counteract these effects, we investigate the impact mechanisms of AO on both crystalline and amorphous alumina (Al $$_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> O $$_3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>3</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> ) surfaces, which occur as oxidized surface layers of bulk aluminum, commonly used in satellite design. Al $$_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> O $$_3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>3</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> also serves as a protective coating for solar panels, often covering extensive satellite surfaces. Using Molecular Dynamics (MD) simulations with classical and machine-learned (ML) force fields, we gain insights into material stability, angular distributions of reflected particles, and adsorption rates. Our findings indicate that bare Al $$_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> O $$_3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>3</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> does not degrade under AO impacts but accumulates oxygen due to high adsorption rates. The angular distribution of reflected particles is highly dependent on the surface structure and the angle of incidence, with a higher ratio of specular reflection observed on smoother surfaces and at larger incidence angles measured to the surface normal.