# Carbon Nanocomposites in Aerospace Technology: A Way to Protect Low-Orbit Satellites
## 3 Importance of Carbon Nanomaterials for the Corrosion Mitigation
### Carbon Nanotubes  
Carbon nanotubes are among the most extensively studied carbon-based nanomaterial for space applications since their discovery in 1991 [78]. [PERSON] et al. conducted an in situ study by simulating the influence of proton, electron and gamma irradiation on CNTs and reported no significant structural changes [79]. [PERSON] et al. conducted a thermal and \(AO\) study on CNT yarns and compared the results with highly oriented pyrolytic graphite. Despite the fact that the tenacity of the CNT yarns decreased with the addition of more yarns, it showed better space durability compared to pyrolytic graphite and graphite composites. However, 7% carbon depletion was observed with 18% electrical conductivity loss, indicating the effect of physically damaged CNT not only affect the mechanical properties but also negatively impacting the continuous electrical conducting pathways which carry electricity [80]. Reactive molecular dynamics simulation conducted by [PERSON] et al. on CNT and graphene showed the relationship between nanotube orientation and the extent of \(AO\) damage. Randomly oriented CNT or graphene nanoparticles demonstrated better results in terms of lower mass loss, erosion yield, surface damage and penetration depth [81].  
The feasibility of employing CNT as a filler material in polybenzimidazole (PBI)-based epoxy composites were investigated by [PERSON] et al. It was demonstrated that a 2 wt% addition of CNT composite improved shielding performance by 50.13%. Further mechanical interlocking of the coating material and resistance to thermal cycles was also improved [82]. The self-healing property of silane with \(AO\) was employed by [PERSON] et al. to prepare an \(AO\)-resistant MWCNT composite. Silicone reacted with \(AO\) and formed a SiO\({}_{2}\) layer which protected the nano carbon. Furthermore, siloxane bond strengths (\(\sim\)8 eV) were much higher than the average energy of \(AO\) (\(\sim\)5 eV), which prevented the \(AO\)-induced bond from breaking [83]. [PERSON] et al. developed a nano composite based on CNT and polyhedral oligomeric silsesquioxane (POSS) for the protection of polyimide films. The resulting film reduced the \(AO\) erosion by roughly one order of magnitude [84]. Figure 9 shows the erosion yields and sheet resistivity of these nanocomposites as a function of atomic oxygen fluence.  
Figure 9: \(AO\) resistance mechanism of multiwalled carbon nanotubes. (**a**) Scheme of the test in space environment; (**b**) pristine hydrogen-rich benzoxazine; (**c**) small amount of multiwalled carbon nanotubes/hydrogen-rich benzoxazine, and (**d**) large amount of multiwalled carbon nanotubes/hydrogen-rich benzoxazine. Reprinted with permission from [PERSON] et al., 2022 [85] © 2022 Elsevier.  
A multifunctional nanocomposite with radiation shielding properties was synthesized by [PERSON] et al. by incorporating amine-modified MWCNT with benzoxazine. The hydrogen atoms of benzoxazine acted as the radiation shield material while MWCNT provided the mechanical strength. The composite demonstrated a 25% decrease in the total mass loss, 20% increase in tensile strength, 36% increase in tensile modulus, and it improved glass transition temperatures. This resulted in a 5.9-6.4% reduction in shielding mass comparative to the epoxy resin [75]. Figure 10 illustrates the possible \(AO\) resistance mechanism of multiwalled carbon nanotubes.