Plasma-Sprayed Graphene Nanosheets/ZnO/Al₂O₃ Coatings with Highly Efficient Microwave Absorption Properties

Graphene nanosheets (GNSs)/ZnO/Al₂O₃ composite coatings with different GNSs content were prepared by air plasma spraying technique. The scanning electron microscope results show that the GNSs were homogeneously dispersed in the powders and coatings. The influence of different GNSs content on complex permittivity and microwave absorption properties have been systematically investigated at the frequency range from 8.2 to 12.4 GHz. The complex permittivity of the coating was improved with the increase in GNS content, due to the high conductivity and polarization loss of GNS. The GNSs/ZnO/Al₂O₃ coating with 15 wt.% GNSs in the thickness of 1.82 mm presented the most prominent microwave absorption properties, which exhibited strong absorption (minimum reflection loss of −45 dB) and the reflection loss ≤ −10 dB bandwidth at the frequency range of 11.2-12.0 GHz. Meanwhile, the hardness of the coating increased from 914.2 HV_0.2 to 1057.3 HV_0.2 with the introduced 15 wt.% GNSs. These results suggest that GNS can be a promising nanofiller to simultaneously improve the microwave absorption properties and mechanical properties of absorbing coatings.